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Loss of exosomes in progranulin-associated frontotemporal dementia
... Since pathogenic proteins are released within exosomes, these vesicles have been suggested as "Trojan horses" of neurodegeneration (Ghidoni et al., 2008a). Conversely a loss of exosomes, might enhance neurodegeneration (Ghidoni et al., 2011;Benussi et al., 2016). ...
... In line with this observation, cutting edge molecular research suggests that progranulin is essential for proper lysosomal function and, as a consequence, a loss of progranulin might cause lysosomal dysfunction. Researchers demonstrated that (i) progranulin loss leads to progressive up-regulation of genes that control lysosomal functions and the innate immunity response and to profound microglia lysosomal defects that facilitate more efficient processing via the endolysosomal pathway (Lui et al., 2016); (ii) progranulin regulates lysosomal function and biogenesis through acidification of lysosomes (Tanaka et al., 2017); (iii) progranulin facilitates neuronal uptake and lysosomal delivery of prosaposin, the precursor of saposin peptides that are essential for lysosomal glycosphingolipids degradation (Zhou et al., 2017a); (iv) progranulin is a co-chaperone of HSP70 and plays an important role in beta-Glucocerebrosidase lysosomal localization (Jian et al., 2016): thus, loss of progranulin may directly affect the HSP70-based disaggregases leading to defects in the clearance of proteins associated with neurodegenerative diseases or indirectly affect the function of lysosomes resulting from the impairment of beta-Glucocerebrosidase lysosomal localization; (v) progranulin loss leads to an accumulation of polyunsaturated triacylglycerides, as well as a reduction of diacylglycerides and phosphatidylserines in fibroblast and enriched lysosome lipidomes (Evers et al., 2017); (vi) progranulin seems to promote TMEM106B degradation to maintain in the aged brain the physiological level of TMEM106B on lysosomal membranes; thus, shortage of progranulin results in accumulation of TMEM106B protein, which is accompanied by lysosomal abnormalities and lipofuscin accumulation (Zhou et al., 2017b); remarkably, TMEM106B deletion in GRN-/-mice normalizes lysosomal protein levels and rescues FTD-related behavioral abnormalities (Klein et al., 2017); (vii) in human primary fibroblasts from patients, progranulin loss alters exosome release and composition with an enrichment of the lysosomal marker Lamp1 (Benussi et al., 2016). ...
... Frontiers in Neuroscience | www.frontiersin.org Progranulin, a multifunctional growth factor, is secreted by the classical ER and/or Golgi secretory pathway (Ryan et al., 2009), it is incorporated into exosomes in a highly glycosylated form (Benussi et al., 2016) and it also ends up in lysosomes. Thus, progranulin seems to carry out both extracellular and endo-lysosomal functions. ...
Recent clinical, genetic and biochemical experimental evidences highlight the existence of common molecular pathways underlying neurodegenerative diseases. In this review, we will explore a key common pathological mechanism, i.e. the loss of neuroprotective factors, across the three major neurodegenerative diseases leading to dementia: Alzheimer’s disease (AD), Frontotemporal dementia (FTD) and Lewy body dementia (LBD). We will report evidences that the Brain Derived Neurotrophic Factor (BDNF), the most investigated and characterized brain neurotrophin, progranulin, a multi-functional adipokine with trophic and growth factor properties, and cystatin C, a neuroprotective growth factor, are reduced in AD, FTD and LBD. Moreover, we will review the molecular mechanism underlying the loss of neuroprotective factors in neurodegenerative diseases leading to dementia, with a special focus on endo-lysosomal pathway and intercellular communication mediated by extracellular vesicles. Exploring the shared commonality of disease mechanisms is of pivotal importance to identify novel potential therapeutic targets and to develop treatments to delay, slow or block disease progression.
... R. Soc. B 379: 20220387 in FTD pathogenesis can be secreted by exosomes [72,96,97]. Consolidating these findings, other investigations using neural stem cells, autopsy brains and plasma from genetic FTD patients all reported alterations of the endo-lysosomal system and, more specifically, changes in level, size, and content of EVs/exosomes compared to control individuals [97][98][99][100][101]. ...
... B 379: 20220387 in FTD pathogenesis can be secreted by exosomes [72,96,97]. Consolidating these findings, other investigations using neural stem cells, autopsy brains and plasma from genetic FTD patients all reported alterations of the endo-lysosomal system and, more specifically, changes in level, size, and content of EVs/exosomes compared to control individuals [97][98][99][100][101]. These recent discoveries open new opportunities to investigate FTD-specific exosomal biomarkers with diagnostic and prognostic potential. ...
Over the past two decades, increased research has highlighted the connection between endosomal trafficking defects and neurodegeneration. The endo-lysosomal network is an important, complex cellular system specialized in the transport of proteins, lipids, and other metabolites, essential for cell homeostasis. Disruption of this pathway is linked to a wide range of neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, Huntington's disease and frontotemporal dementia. Furthermore, there is strong evidence that defects in this pathway create opportunities for diagnostic and therapeutic intervention. In this Opinion piece, we concisely address the role of endo-lysosomal dysfunction in five neurodegenerative diseases and discuss how future research can investigate this intracellular pathway, including extracellular vesicles with a specific focus on exosomes for the identification of novel disease biomarkers.
This article is part of a discussion meeting issue ‘Understanding the endo-lysosomal network in neurodegeneration’.
... In patient-derived fibroblasts and induced pluripotent stem-cell-derived motor neurons, C9orf72 hexanucleotide repeat expansion led to haploinsufficiency and consequent defective intracellular and extracellular vesicle trafficking and a dysfunctional trans-Golgi network phenotype, strengthening the connection between lysosomal imbalance and FTLD [33]. In a previous study of ours, we demonstrated that a null mutation in GRN reduces release and alters the exosome composition in primary human fibroblasts [34]. Furthermore, we reported a lower EV concentration and an increased EV size in human plasma samples from patients with Alzheimer's disease (AD) and related dementias [35]. ...
... We previously demonstrated, in human primary fibroblasts from patients, that the loss of GRN results in reduced exosome secretion and altered exosome composition [34]. Herein, we demonstrated that these alterations are also detectable in the blood; furthermore, they are common to either the C9orf72 or Sporadic FTLD. ...
Cutting-edge research suggests endosomal/immune dysregulation in GRN/C9orf72-associated frontotemporal lobar degeneration (FTLD). In this retrospective study, we investigated plasma small extracellular vesicles (sEVs) and complement proteins in 172 subjects (40 Sporadic FTLD, 40 Intermediate/Pathological C9orf72 expansion carriers, and 49 Heterozygous/Homozygous GRN mutation carriers, 43 controls). Plasma sEVs (concentration, size) were analyzed by nanoparticle tracking analysis; plasma and sEVs C1q, C4, C3 proteins were quantified by multiplex assay. We demonstrated that genetic/sporadic FTLD share lower sEV concentrations and higher sEV sizes. The diagnostic performance of the two most predictive variables (sEV concentration/size ratio) was high (AUC = 0.91, sensitivity 85.3%, specificity 81.4%). C1q, C4, and C3 cargo per sEV is increased in genetic and sporadic FTLD. C4 (cargo per sEV, total sEV concentration) is increased in Sporadic FTLD and reduced in GRN+ Homozygous, suggesting its specific unbalance compared with Heterozygous cases. C3 plasma level was increased in genetic vs. sporadic FTLD. Looking at complement protein compartmentalization, in control subjects, the C3 and C4 sEV concentrations were roughly half that in respect to those measured in plasma; interestingly, this compartmentalization was altered in different ways in patients. These results suggest sEVs and complement proteins as potential therapeutic targets to mitigate neurodegeneration in FTLD.
... Homozygous Pgrn mutations lead to neuronal ceroid lipofuscinosis, a lysosomal storage disease, which further supports lysosomal regulation by PGRN (Smith et al. 2012). Moreover, PGRN has also been implicated in the release of exosomes, as PGRN silencing was shown to lead to a reduction in the number of released exosomes (Benussi et al. 2016). Overall, these suggest PGRN implicates in the regulation of membrane trafficking machinery. ...
... Hence, H 2 O 2 -and PGRN-dependent Alix induction may not only regulate neurite outgrowth, but also other cellular processes dependent on the vesicular transport system. Consistent with this, PGRN appears to be involved in the control of exosome release (Benussi et al. 2016) and lysosomal functions, as reported previously (Hu et al. 2010;Zhou et al. 2015;Tanaka et al. 2017). Overall, it can be hypothesized that PGRN regulates Figure 6. ...
Progranulin (PGRN) is a multifunctional growth factor expressed in central nervous system. Although PGRN expression is regulated by various stressors, its precise role(s) and regulatory mechanism(s) remain elusive. In this study, we used HT22 cells to investigate the physiological implications of oxidative stress-induced PGRN expression and the regulation of PGRN expression by oxidative stress. We observed that p38 MAP kinase was activated upon the addition of H2O2, and a selective p38 MAP kinase inhibitor, attenuated PGRN induction by H2O2. To explore the physiological role(s) of the PGRN induction, we first confirmed H2O2-dependent responses of HT22 cells and found that the length and number of neurites were increased by H2O2. Pgrn knockdown experiments suggested these changes were mediated by H2O2-induced PGRN expression, at least in part. Overall, the results suggested that an increase in oxidative stress in HT22 cells induced PGRN expression via p38 MAP kinase pathway, thereby controlling neurite outgrowth.
... Fibroblasts from GRN mutation carriers secreted fewer EVs than controls, but knockdown of progranulin in SH-SY5Y cells appeared to increase EV secretion. 37 There is increasing evidence that EV secretion in the brain plays a role in progression of neurodegenerative disease, 30,33,35,38,39 so we were particularly interested in how progranulin insufficiency affects EV secretion in the brain. Given the lysosomal abnormalities in the brain of both progranulin-insufficient mice and FTD-GRN patients, we hypothesized that progranulin insufficiency would increase brain exosome secretion, resulting in an increase in total EV levels in the brain. ...
... This is consistent with a report that fibroblasts from GRN mutation carriers secrete fewer EV than controls. 37 Instead, the increase in EV levels in brains of 12-month-old Grn -/mice and FTD-GRN patients is likely downstream of other changes associated with the symptomatic stages of disease in humans or the onset of pathology and behavioral deficits in mice. These changes might include buildup of lysosomal storage material and worsening of lysosomal dysfunction, or gliosis and inflammation. ...
Objective
The goal of this study was to investigate the effect of progranulin insufficiency on extracellular vesicles (EVs), a heterogeneous population of vesicles that may contribute to progression of neurodegenerative disease. Loss‐of‐function mutations in progranulin (GRN) are a major cause of frontotemporal dementia (FTD), and brains from GRN carriers with FTD (FTD‐GRN) exhibit signs of lysosomal dysfunction. Lysosomal dysfunction may induce compensatory increases in secretion of exosomes, EVs secreted from the endolysosomal system, so we hypothesized that progranulin insufficiency would increase EV levels in the brain.
Methods
We analyzed levels and protein contents of brain EVs from Grn–/– mice, which model the lysosomal abnormalities of FTD‐GRN patients. We then measured brain EVs in FTD‐GRN patients. To assess the relationship of EVs with symptomatic disease, we measured plasma EVs in presymptomatic and symptomatic GRN mutation carriers.
Results
Grn–/– mice had elevated brain EV levels and altered EV protein contents relative to wild‐type mice. These changes were age‐dependent, occurring only after the emergence of pathology in Grn–/– mice. FTD‐GRN patients (n = 13) had elevated brain EV levels relative to controls (n = 5). Symptomatic (n = 12), but not presymptomatic (n = 7), GRN carriers had elevated plasma EV levels relative to controls (n = 8).
Interpretation
These data show that symptomatic FTD‐GRN patients have elevated levels of brain and plasma EVs, and that this effect is modeled in the brain of Grn–/– mice after the onset of pathology. This increase in EVs could influence FTD disease progression, and provides further support for EVs as potential FTD biomarkers.
... • (Arampatzis et al., 2017;Banyai et al., 2010;Barber and Lieth, 1997;Bentzinger et al., 2005;Berzin et al., Rimer, 1998;Romi et al., 2008;Rudolf et al., 2014;Ruegg and Bixby, 1998;Sanes et al., 1998a, b;Sanes and Lichtman, 2001;Serpinskaya et al., 1999;Sole et al., 2004;Steinbeck et al., 2015;Stephan et al., 2008;Stetefeld et al., 2004;Steubl et al., 2013Steubl et al., , 2016Stout et al., 2015;Tatrai et al., 2006;Terrado et al., 2001;Trautmann and Vivier, 2001;Ueta and Yamanashi, 2018;VanSaun et al., 2003;VanSaun and Werle, 2000;Verbeek et al., 1999;Wei et al., 1997;Williams et al., 2008;Xi et al., 2017;Xiao et al., 2018;Yan et al., 2018;Yang et al., 2001;Yard et al., 2001;Yu et al., 2017b;Zhang et al., 2008) Progranulin Alquezar et al., 2015;Benussi et al., 2016;Chang et al., 2017b;Fardo et al., 2017;Holler et al., 2016;Kawase et al., 2013;Korolczuk and Beltowski, 2017;Kwack and Lee, 2017;Ma et al., 2017;Nicholson et al., 2014;Vercellino et al., 2011;Wang et al., 2016b;Xu et al., 2017a;Yamamoto et al., 2014b;Zhao et al., 2015;Zhou et al., 2015a) C3/C1q ...
... Progranulin is mostly associated with the secretory pathway and can be found in plasma and cerebrospinal fluid and also in secreted exosomes. In fact, loss of progranulin leads to a reduction in the number of exosomes and alters exosome composition (Benussi et al., 2016). Progranulin is cleaved by extracellular proteases into eight different granulin domains, which present distinct and sometimes contrary roles to progranulin. ...
Objective:
Use of the frailty index to measure an accumulation of deficits has been proven a valuable method for identifying elderly people at risk for increased vulnerability, disease, injury, and mortality. However, complementary molecular frailty biomarkers or ideally biomarker panels have not yet been identified. We conducted a systematic search to identify biomarker candidates for a frailty biomarker panel.
Methods:
Gene expression databases were searched (http://genomics.senescence.info/genes including GenAge, AnAge, LongevityMap, CellAge, DrugAge, Digital Aging Atlas) to identify genes regulated in aging, longevity, and age-related diseases with a focus on secreted factors or molecules detectable in body fluids as potential frailty biomarkers. Factors broadly expressed, related to several "hallmark of aging" pathways as well as used or predicted as biomarkers in other disease settings, particularly age-related pathologies, were identified. This set of biomarkers was further expanded according to the expertise and experience of the authors. In the next step, biomarkers were assigned to six "hallmark of aging" pathways, namely (1) inflammation, (2) mitochondria and apoptosis, (3) calcium homeostasis, (4) fibrosis, (5) NMJ (neuromuscular junction) and neurons, (6) cytoskeleton and hormones, or (7) other principles and an extensive literature search was performed for each candidate to explore their potential and priority as frailty biomarkers.
Results:
A total of 44 markers were evaluated in the seven categories listed above, and 19 were awarded a high priority score, 22 identified as medium priority and three were low priority. In each category high and medium priority markers were identified.
Conclusion:
Biomarker panels for frailty would be of high value and better than single markers. Based on our search we would propose a core panel of frailty biomarkers consisting of (1) CXCL10 (C-X-C motif chemokine ligand 10), IL-6 (interleukin 6), CX3CL1 (C-X3-C motif chemokine ligand 1), (2) GDF15 (growth differentiation factor 15), FNDC5 (fibronectin type III domain containing 5), vimentin (VIM), (3) regucalcin (RGN/SMP30), calreticulin, (4) PLAU (plasminogen activator, urokinase), AGT (angiotensinogen), (5) BDNF (brain derived neurotrophic factor), progranulin (PGRN), (6) α-klotho (KL), FGF23 (fibroblast growth factor 23), FGF21, leptin (LEP), (7) miRNA (micro Ribonucleic acid) panel (to be further defined), AHCY (adenosylhomocysteinase) and KRT18 (keratin 18). An expanded panel would also include (1) pentraxin (PTX3), sVCAM/ICAM (soluble vascular cell adhesion molecule 1/Intercellular adhesion molecule 1), defensin α, (2) APP (amyloid beta precursor protein), LDH (lactate dehydrogenase), (3) S100B (S100 calcium binding protein B), (4) TGFβ (transforming growth factor beta), PAI-1 (plasminogen activator inhibitor 1), TGM2 (transglutaminase 2), (5) sRAGE (soluble receptor for advanced glycosylation end products), HMGB1 (high mobility group box 1), C3/C1Q (complement factor 3/1Q), ST2 (Interleukin 1 receptor like 1), agrin (AGRN), (6) IGF-1 (insulin-like growth factor 1), resistin (RETN), adiponectin (ADIPOQ), ghrelin (GHRL), growth hormone (GH), (7) microparticle panel (to be further defined), GpnmB (glycoprotein nonmetastatic melanoma protein B) and lactoferrin (LTF). We believe that these predicted panels need to be experimentally explored in animal models and frail cohorts in order to ascertain their diagnostic, prognostic and therapeutic potential.
... Recent analyses of exosomes from neurodegenerative cells have documented disease-associated cargoes in the exosomes. For further details see references (Bellingham et al., 2012a,b;Taylor and Shah, 2015;Benussi et al., 2016;Willms et al., 2016). therapy. ...
... Mutations in the progranulin gene (GRN), leading to a loss of functional progranulin proteins associated with exosomes, are a leading cause of FTLD (Baker et al., 2006;Cruts et al., 2006). Null mutations in GRN are shown to significantly reduce the quantity of exosomes released, and the resulting reduction of progranulin in the brain is thought to underlie the neurodegeneration characterizing FTLD cases associated with GRN mutations (Benussi et al., 2016). This GRN-associated alteration of cell-to-cell communication through exosomes offers a therapeutic target in addressing one aspect of the multifaceted underlying causes of dementia. ...
Exosomes, small lipid bilayer vesicles, are part of the transportable cell secretome that can be taken up by nearby recipient cells or can travel through the bloodstream to cells in distant organs. Selected cellular cytoplasm containing proteins, RNAs, and other macromolecules is packaged into secreted exosomes. This cargo has the potential to affect cellular function in either healthy or pathological ways. Exosomal content has been increasingly shown to assist in promoting pathways of neurodegeneration such as β-amyloid peptide (Aβ) accumulation forming amyloid plaques in the brains of patients with Alzheimer's disease, and pathological aggregates of proteins containing α-synuclein in Parkinson's disease transferred to the central nervous system via exosomes. In attempting to address such debilitating neuropathologies, one promising utility of exosomes lies in the development of methodology to use exosomes as natural delivery vehicles for therapeutics. Because exosomes are capable of penetrating the blood-brain barrier, they can be strategically engineered to carry drugs or other treatments, and possess a suitable half-life and stability for this purpose. Overall, analyses of the roles that exosomes play between diverse cellular sites will refine our understanding of how cells communicate. This mini-review introduces the origin and biogenesis of exosomes, their roles in neurodegenerative processes in the central nervous system, and their potential utility to deliver therapeutic drugs to cellular sites.
... Frontotemporal lobular degeneration (FTLD) primarily affects patients younger than 65 years where loss of function is in the frontal and anterior temporal brain lobes [48]. Upwards of 50% of patients have a family history and genetic factors are considered the primary cause of FTLD. ...
... Granulin mutations (GRN) are associated with FTLD that cause haploinsufficiency or loss of progranulin protein in these patients. Benussi and colleagues [48] cultured fibroblasts from 16 FTLD patients with GRN mutations and appropriate cell controls. They found progranulin associated with exosomes from culture medium in its N-glycosylated form and the quantity of GRN was reduced in exosomes from the FTLD fibroblast cultures. ...
... Progranulin is secreted by regulated exocytosis (Figure 1) as a highly glycosylated protein of around 70-80 kDa [24], as soluble protein or in exosomes [25]. Progranulin N-glycosylation can occur on five different N-glycosylation sites with a prevalent addition of fucosylated oligosaccharides [26]. ...
Progranulin is a pleiotropic growth factor with important physiological roles in embryogenesis and maintenance of adult tissue homeostasis. While-progranulin deficiency is associated with a broad range of pathological conditions affecting the brain, such as frontotemporal dementia and neuronal ceroid lipofuscinosis, progranulin upregulation characterizes many tumors, including brain tumors, multiple myeloma, leiomyosarcoma, mesothelioma and epithelial cancers such as ovarian, liver, breast, bladder, adrenal, prostate and kidney carcinomas. The increase of progranulin levels in tumors might have diagnostic and prognostic significance. In cancer, progranulin has a pro-tumorigenic role by promoting cancer cell proliferation, migration, invasiveness, anchorage-independent growth and resistance to chemotherapy. In addition, progranulin regulates the tumor microenvironment, affects the function of cancer-associated fibroblasts, and modulates tumor immune surveillance. However, the molecular mechanisms of progranulin oncogenic function are not fully elucidated. In bladder cancer, progranulin action relies on the activation of its functional signaling receptor EphA2. Notably, more recent data suggest that progranulin can also modulate a functional crosstalk between multiple receptor-tyrosine kinases, demonstrating a more complex and context-dependent role of progranulin in cancer. Here, we will review what is currently known about the function of progranulin in tumors, with a focus on its molecular mechanisms of action and regulation.
... It has been documented that many proteins involved in FTD pathogenesis are secreted by cells in association with exosomes. Furthermore, mutations in GRN result in the reduction of exosomes and the alteration of their composition [97]. Neurofilament light chain has been considered as a biomarker for axonal injury and is reportedly increased in sera of FTD patients [98,99]. ...
Neurodegenerative diseases are a set of progressive and currently incurable diseases that are primarily caused by neuron degeneration. Neurodegenerative diseases often lead to cognitive impairment and dyskinesias. It is now well recognized that molecular events precede the onset of clinical symptoms by years. Over the past decade, intensive research attempts have been aimed at the early diagnosis of these diseases. Recently, exosomes have been shown to play a pivotal role in the occurrence and progression of many diseases including cancer and neurodegenerative diseases. Additionally, because exosomes can cross the blood-brain barrier, they may serve as a diagnostic tool for neural dysfunction. In this review, we detail the mechanisms and current challenges of these diseases, briefly review the role of exosomes in the progression of neurodegenerative diseases, and propose a novel strategy based on sali-vary neuronal exosomes and nanoparticle tracking analysis that could be employed for screening the early onset of neurodegenerative diseases.
... As for EVs, while in plasma and in human primary fibroblasts from GRN patients, a significant concentration decrease of EVs was described [37,38], in our EVs from GRNmutated LCLs only a trend towards concentration decrease was observed, not reaching statistical significance. In EVs, the level of FL p-TDP-43 did not show significant difference among genotypes, but the level of 25 kDa CTFs p-TDP-43 confirmed the situation of the respective LCLs: CTFs p-TDP-43 were absent in WT EVs, very abundant in GRN heterozygous EVs and also present, at lower levels, in GRN homozygous EVs. ...
Frontotemporal lobar degeneration (FTLD) is a complex disease, characterized by progressive degeneration of frontal and temporal lobes. Mutations in progranulin (GRN) gene have been found in up to 50% of patients with familial FTLD. Abnormal deposits of post-translationally-modified TAR DNA-binding protein of 43 kDa (TDP-43) represent one of the main hallmarks of the brain pathology. To investigate in peripheral cells the presence of the different TDP-43 forms, especially the toxic 25 kDa fragments, we analyzed lymphoblastoid cell lines (LCLs) and the derived extracellular vesicles (EVs) from patients carrying a GRN mutation, together with wild-type (WT) healthy controls. After characterizing EV sizes and concentrations by nanoparticle tracking analysis, we investigated the levels of different forms of the TDP-43 protein in LCLs and respective EVs by Western blot. Our results showed a trend of concentration decreasing in EVs derived from GRN-mutated LCLs, although not reaching statistical significance. A general increase in p-TDP-43 levels in GRN-mutated LCLs and EVs was observed. In particular, the toxic 25 kDa fragments of p-TDP-43 were only present in GRN-mutated LCLs and were absent in the WT controls. Furthermore, these fragments appeared to be more concentrated in EVs than in LCLs, suggesting a relevant role of EVs in spreading pathological molecules between cells.
... Dementia caused by damage in the neurons of the frontal and temporal lobes of the brain is termed frontotemporal dementia (FTD). The nerve cell death in these regions results in shrinking or atrophy of the frontal and temporal lobes which gradually cause a decline of the functions regulated by these regions like behavior and thinking abilities [21]. After AD and Lewy bodies, FTD is considered as a third prime cause of dementia, contributes around 5%-15% of total cases. ...
Dementia is a collective term for various physiological conditions related to abnormal functions of the brain like a deficit of memory, thinking, behavior, and cognitive ability, and difficulty in performing routine activities. Severity in the pathophysiological factors leads to various neurodegenerative diseases (comes under the umbrella term “dementia”) including Alzheimer’s disease, vascular dementia, Lewy body associated dementia, frontotemporal dementia, Parkinson’s disease, viral infection associated neurological manifestation, and mixed dementia. With more than 50 million patients worldwide, dementia is considered one of the most widespread neurological disorders with no potential therapy. Very limited drugs are available for the treatment of different types of dementia which only exerts symptomatic effects. The complex anatomy of the brain and the presence of various protective mechanisms create major constraints in dementia therapy. Thus, various novel carrier systems have been explored to target the bioactives to the brain across blood–brain barrier (BBB). Liposome is one of the most promising novel delivery systems for brain targeting therapeutics. The phospholipid bilayer allows better permeation across the BBB and amphiphilic nature supported the encapsulation of both lipophilic and hydrophilic moieties. Alongside, it is also found suitable for the brain targeting of large molecules like protein and peptides that have wide application in dementia therapy. This review chapter highlighted different types of dementia, application of stealth liposome, surface-modified liposomes, and direct nose-to-brain delivery of liposome along with its application for delivery of protein/peptide and gene therapy.
... About one-third of FTD patients have an autosomal dominant family history (Rohrer et al., 2009), typified by mutations in three genes: granulin (GRN; Baker et al., 2006;Cruts et al., 2006), chromosome 9 open reading frame 72 (C9orf72) (DeJesus-Hernandez et al., 2011;Renton et al., 2011) and microtubule-associated protein tau (MAPT; Hutton et al., 1998). It has been demonstrated that several proteins involved in FTD pathogenesis can be secreted by cells in association with exosomes (Ghidoni et al., 2011;Benussi et al., 2016). Furthermore, mutations in GRN strongly reduce the number of released exosomes also altering their composition . ...
Differential diagnosis of neurological disorders and their subtype classification are challenging without specific biomarkers. Genetic forms of these disorders, typified by an autosomal dominant family history, could offer a window to identify potential biomarkers by exploring the presymptomatic stages of the disease. Frontotemporal dementia (FTD) is the second cause of dementia with an age of onset < 65, and its most common mutations are in GRN , C9orf72 , and MAPT genes. Several studies have demonstrated that the main proteins involved in FTD pathogenesis can be secreted in exosomes, a specific subtype of extracellular vesicles able to transfer biomolecules between cells avoiding cell-to-cell contact. Neurofilament light chain (NfL) levels in central nervous system have been advocated as biomarkers of axonal injury. NfL concentrations have been found increased in FTD and have been related to disease severity and prognosis. Little information on the relationship between NfL and exosomes in FTD has been collected, deriving mainly from traumatic brain injury. Current review deals with this matter in the attempt to provide an updated discussion of the role of NfL and exosomes as biomarkers of genetic forms of FTD.
... Specifically, a progranulin deficiency due to the presence of GRN pathogenic null mutations, one of the most common genetic causes of FTLD, leads to an upregulation of lysosomal genes as well as profound lysosomal defects [13]. Moreover, GRN null mutations cause a strong alteration of the release and composition of exosomes [14]. Of note, homozygous GRN null mutations cause adult-onset neuronal ceroid lipofuscinosis (NCL), a lysosomal storage disorder [15]. ...
Dysfunctions in the endo-lysosomal system have been hypothesized to underlie neurodegeneration in major neurocognitive disorders due to Alzheimer’s disease (AD), Frontotemporal Lobar Degeneration (FTLD), and Lewy body disease (DLB). The aim of this study is to investigate whether these diseases share genetic variability in the endo-lysosomal pathway. In AD, DLB, and FTLD patients and in controls (948 subjects), we performed a targeted sequencing of the top 50 genes belonging to the endo-lysosomal pathway. Genetic analyses revealed (i) four previously reported disease-associated variants in the SORL1 (p.N1246K, p.N371T, p.D2065V) and DNAJC6 genes (p.M133L) in AD, FTLD, and DLB, extending the previous knowledge attesting SORL1 and DNAJC6 as AD- and PD-related genes, respectively; (ii) three predicted null variants in AD patients in the SORL1 (p.R985X in early onset familial AD, p.R1207X) and PPT1 (p.R48X in early onset familial AD) genes, where loss of function is a known disease mechanism. A single variant and gene burden analysis revealed some nominally significant results of potential interest for SORL1 and DNAJC6 genes. Our data highlight that genes controlling key endo-lysosomal processes (i.e., protein sorting/transport, clathrin-coated vesicle uncoating, lysosomal enzymatic activity regulation) might be involved in AD, FTLD and DLB pathogenesis, thus suggesting an etiological link behind these diseases.
... The presence of an amino-terminal secretion signal directs mature GRN through the trans-golgi network into secretory vesicles, in which it undergoes regulated exocytosis (Petoukhov et al., 2013). GRN can be secreted as a soluble protein or associated with exosomes (Benussi et al., 2016). Alternatively, by binding sortilin or through an interaction with prosaposin, GRN can be diverted from the secretory pathway to the endolysosomal system Zhou X. et al., 2015). ...
Frontotemporal dementia (FTD) is a neurodegenerative disease, leading to behavioral changes and language difficulties. Heterozygous loss-of-function mutations in progranulin (GRN) induce haploinsufficiency of the protein and are associated with up to one-third of all genetic FTD cases worldwide. While the loss of GRN is primarily associated with neurodegeneration, the biological functions of the secreted growth factor-like protein are more diverse, ranging from wound healing, inflammation, vasculogenesis, and metabolic regulation to tumor cell growth and metastasis. To date, no disease-modifying treatments exist for FTD, but different therapeutic approaches to boost GRN levels in the central nervous system are currently being developed (including AAV-mediated GRN gene delivery as well as anti-SORT1 antibody therapy). In this review, we provide an overview of the multifaceted regulation of GRN levels and the corresponding therapeutic avenues. We discuss the opportunities, advantages, and potential drawbacks of the diverse approaches. Additionally, we highlight the therapeutic potential of elevating GRN levels beyond patients with loss-of-function mutations in GRN.
... The cells showed signs of reduced lysosomes and accumulation of endosomes (162). Null mutation of the gene progranulin in frontotemporal dementia also reduced EV secretion and cargo by altering the secretion pathway in cells (163). ...
Extracellular vesicles (EVs) including exosomes are emerging as important carriers of signals in normal and patho- physiology. As EVs are a long-range communication or signaling modality – just like hormones are, the field of endocrinology is uniquely poised to offer insight into their functional biology and regulation. EVs are membrane bound particles secreted by many different cell types and can have local or systemic effects, being transported in body fluids. They express trans-membrane proteins, some of which are shared between EVs and some being specific to the tissue of origin, that can interact with target cells directly (much like hormones can). They also contain cargo within them that includes DNA, RNA, miRNA and various metabolites. They can fuse with target cells to empty their cargo and alter their target cell physiology in this way too. Similar to the endocrine system, the EV system is likely to be under homeostatic control, making the regulation of their biogenesis and secretion important aspects to study. In this review, we briefly highlight select examples of how EVs are implicated in normal physiology and disease states. We also discuss what is known about their biogenesis and regulation of secretion. We hope that this paper inspires the endocrinology field to use our collective expertise to explore these new multi-modal ‘hormones’.
... In addition, we demonstrated that CysC, a trophic protein targeted to the classical secretory pathway, is secreted by mouse primary neurons in association with exosomes and the overexpression of familial AD-associated presenilin 2 mutations (PS2 M239I and PS2 T122R) resulted in a loss of exosomal CysC and of Aβ precursor protein (APP) metabolites within exosomes (Ghidoni et al., 2011). FTD-causing progranulin null mutations cause a loss of progranulin (PGRN), a neurotrophic factor (Ghidoni et al., 2008b); we demonstrated that also PGRN, a protein targeted to the classical secretory pathway, is secreted in association with exosomes by human primary fibroblasts and that null mutations in the GRN gene strongly reduce the number of released exosomes and alter their composition (Benussi et al., 2016). Brain-derived neurotrophic factor (BDNF), a key regulator of neuronal survival, was suggested to play an important role in the pathophysiology of neurodegenerative diseases including AD, FTD, and DLB (Ventriglia et al., 2013;Mitre et al., 2017). ...
Alzheimer’s disease (AD), frontotemporal dementia (FTD), and dementia with Lewy bodies (DLB) are the three major neurodegenerative dementias. In this study, we provide evidence that an alteration in extracellular vesicles (EVs) release is common across the three most common neurodegenerative dementias, AD, DLB, and FTD. Specifically, we analyzed plasma EVs in three groups of patients affected by AD, DLB, and FTD, and we found a significant reduction in EVs concentration and larger EVs size in all patient groups. We then investigated whether the loss of neurotrophic factors is also a common pathogenic mechanism among FTD, DLB, and AD, and if levels of neurotrophic factors might affect EVs release. Plasma levels of progranulin and cystatin C (CysC) were partially altered; however, taking together all variables significantly associated with the diagnostic groups only EVs size and concentration were able to distinguish patients from controls. The diagnostic performance of these two EVs parameters together (ratio) was high, with a sensitivity of 83.3% and a specificity of 86.7%, able to distinguish patients from controls but not to differentiate the different forms of dementias. Among the candidate neurotrophic factors, only CysC levels were associated with EVs concentration. Our study suggests that an alteration in the intercellular communication mediated by EVs might be a common molecular pathway underlying neurodegenerative dementias. The identification of shared disease mechanisms is of pivotal importance to develop treatments to delay disease progression. To this aim, further studies investigating plasma EVs size and concentration as early biomarkers of dementia are required.
... The overall exosome ELISA kit is an active, twofold sandwich protein-connected immunoassay for subjective quantitative evaluation of exosomes from a limited quantity of cell media ( Fig. 21.3) (Higginbotham et al., 2011). The overall exosome ELISA kit comprises 96-well regular ELISA plates that are pre-covered with restrictive skillet exosome antibodies empowered to catch exosomes from the culture supernatant explicitly (Logozzi et al., 2009;Benussi et al., 2016). The measurement and portrayal of exosomal proteins are based on utilizing conventional or cell/tissue-explicit exosomes suitable for recognition of antibodies against exosome-related antigens. ...
The release of a division of extracellular entities with 40–100 nm dimension from both tumor and varied mesenchymal stem cells during pathologic conditions is termed as exosomes that are shown to actively participate in chemical signaling events occurring in multicellular organisms’ infection. Exosomes act as a vehicle for shifting amino acids, lipids, and genetic components that are readily engulfed by far-flanging cells (or adjacent cells) at the site of release for remolding the receptor cell functions once the biological contents get activated. Furthermore, pathogens too display the dispense of exosomes to temper the host’s immune response and trigger the infection rate, making them apt investigation markers for diseases. Additionally, aiding in antigen presentation and immune response stimulation, exosomes are significant in showing contrasting role as initiating anticarcinogenic responses and involving in promoting tumorigenesis as they are released from tumor cells. Due to their site specificity, cell lineage property, and encapsulation of specific constituents, exosomes can be potentially utilized as a precious investigatory and prognostic tool along with a possible carrier of drugs and gene shipment for curative goal. Since exosome groundwork is at the infancy stage, deeper insight is required to know its composition, formation, and targeting mechanism along with its significant role in disease diagnosis and treatment. This states, as mentioned previously, we have tried to focus solely on the functional and clinical implications of exosomes in-depth in this review.
... SOD1 and TPD-43, which are thought to contribute to ALS pathogenesis by adopting abnormal conformation are also contained in exosomes. In turn, null mutations in GRN gene, associated with certain cases of frontotemporal dementia, lead to significant reduction in exosome release and consequently to a decrease in progranulin levels, implicated in the pathogenesis of FTD [150]. The role of exosomes in wound healing is also worth elaborating, as it is already known that the exosome, an important paracrine factor in intercellular communication, modulates the molecular activity of recipient cells [151]. ...
Exosomes belong to structures called extracellular vesicles (EVs). These spherical units, secreted by most eukaryotic cells, attracted significant interest among researchers in recent years. Exosomes undergo secretion from almost all types of mammalian cells, including dendritic cells, B cells, epithelial cells, mastocytes, reticulocytes, platelets, T cells, mesenchymal stem cells, adipocytes, bone marrow-derived stem cells, embryonic stem cells, fibroblasts, cardiac myocytes, endothelial cells, oligodendrocytes, astrocytes, microglia, neurons, neural stem cells, hepatocytes, lung spheroid cells, as well as tumor cells. Exosomes have several features that enable many methods of their isolation from biological material. Furthermore, physicochemical properties such as size, mass, density, or the ability to interact with specific proteins allowed for the development and advance of several effective methods. Work on exosomes’ recovery and purity made it possible to most effectively determine their isolation methods’ efficiency and accuracy. A common ground for the researchers’ interest in exosomal analyses is the role of exosomes as carriers of disease biomarkers. It has been suggested that exosomes can be used in vaccine development and other immunological-related purposes, as one of their characteristics is the ability to present antigens. Moreover, exosomes have a long half-life. As the human body does not perceive them as foreign bodies, they can penetrate cell membranes and target specific cells, making them even better candidates for the applications mentioned above. Therefore, the following review deals with the nature of exosomes, as well as various methods of their isolation and use in medicine.
Running title : Current application of exosomes in medicine
... In fact, it has been found that several NDs-related proteins are secreted in double membrane spherical particles known as extracellular vesicles. This is the case for the amyloid-beta peptide and tau/phosphorylated tau for Alzheimer's disease (Pérez et al., 2019), alpha-synuclein for Parkinson's disease (Longoni et al., 2019), misfolded/mutant SOD1, TDP-43 and its pathologicalrelated C-terminal fragments (of 35 kDa and 25 kDa) and FUS for ALS (Basso and Bonetto, 2016;Iguchi et al., 2016;Hanspal et al., 2017;Sproviero et al., 2018), and progranulin, TDP-43, and C9orf72 DPRs for FTD and ALS-FTD (Benussi et al., 2016;Iguchi et al., 2016;Westergard et al., 2016). The extracellular vesicles are heterogeneous in size and are mainly classified into three different types: exosomes, microvesicles, and apoptotic bodies. ...
Motor neuron diseases (MNDs) are fatal diseases characterized by loss of motor neurons in the brain cortex, in the bulbar region, and/or in the anterior horns of the spinal cord. While generally sporadic, inherited forms linked to mutant genes encoding altered RNA/protein products have also been described. Several different mechanisms have been found altered or dysfunctional in MNDs, like the protein quality control (PQC) system. In this review, we will discuss how the PQC system is affected in two MNDs-spinal and bulbar muscular atrophy (SBMA) and amyotrophic lateral sclerosis (ALS)-and how this affects the clearance of aberrantly folded proteins, which accumulate in motor neurons, inducing dysfunctions and their death. In addition, we will discuss how the PQC system can be targeted to restore proper cell function, enhancing the survival of affected cells in MNDs.
... In 2015, Goetzl et al. found out that increased level of cathepsin D, lysosomal-associated membrane protein 1 (LAMP1) and ubiquitinylated proteins, as well as lowered content of HSP70 in exosomes is related to pre-clinical phase of AD [104]. Multiple sclerosis, frontotemporal dementia, amyotrophic lateral sclerosis, Huntington's disease and prion protein-associated diseases are all neurodegenerative illnesses in which exosomes and their content may serve as effective, pre-clinical diagnosis [105][106][107][108][109][110]. Acquired brain injuries could also be diagnosed based upon exosomes. ...
Exosomes are a heterogenous subpopulation of extracellular vesicles 30–150 nm in range and of endosome-derived origin. We explored the exosome formation through different systems, including the endosomal sorting complex required for transport (ESCRT) and ESCRT-independent system, looking at the mechanisms of release. Different isolation techniques and specificities of exosomes from different tissues and cells are also discussed. Despite more than 30 years of research that followed their definition and indicated their important role in cellular physiology, the exosome biology is still in its infancy with rapidly growing interest. The reasons for the rapid increase in interest with respect to exosome biology is because they provide means of intercellular communication and transmission of macromolecules between cells, with a potential role in the development of diseases. Moreover, they have been investigated as prognostic biomarkers, with a potential for further development as diagnostic tools for neurodegenerative diseases and cancer. The interest grows further with the fact that exosomes were reported as useful vectors for drugs.
... Thus, the release of EV-associated CysC may lead to a positive-feedback loop further amplifying the protective effects of CysC within the brain. The exosome association of CysC and other neurotrophic proteins such progranulin, which is also both secreted and localized to the endosomal pathway (Benussi et al., 2016), likely prolongs the extracellular survival of these proteins, extending their ability to exert beneficial effects. We have shown that EVs secreted by CysC-deficient cells, subsequently loaded with exogenous CysC, significantly protected primary neurons from nutrients-deprivation-induced death , revealing the potential for the loading of EVs with CysC and other neuroprotective proteins for clinical purposes. ...
Dysfunction of the endosomal–lysosomal system is a prominent pathogenic factor in Alzheimer’s disease (AD) and other neurodevelopmental and neurodegenerative disorders. We and others have extensively characterized the neuronal endosomal pathway pathology that results from either triplication of the amyloid-β precursor protein (APP) gene in Down syndrome (DS) or from expression of the apolipoprotein E ε4 allele (APOE4), the greatest genetic risk factor for late-onset AD. More recently brain exosomes, extracellular vesicles that are generated within and released from endosomal compartments, have been shown to be altered in DS and by APOE4 expression. In this review, we discuss the emerging data arguing for an interdependence between exosome production and endosomal pathway integrity in the brain. In vitro and in vivo studies indicate that altered trafficking through the endosomal pathway or compromised cargo turnover within lysosomes can affect the production, secretion, and content of exosomes. Conversely, exosome biogenesis can affect the endosomal–lysosomal system. Indeed, we propose that efficient exosome release helps to modulate flux through the neuronal endosomal pathway by decompressing potential “traffic jams.” Exosome secretion may have the added benefit of unburdening the neuron’s lysosomal system by delivering endosomal–lysosomal material into the extracellular space, where other cell types may contribute to the degradation of neuronal debris. Thus, maintaining robust neuronal exosome production may prevent or mitigate endosomal and lysosomal abnormalities linked to aging and neurodegenerative diseases. While the current evidence suggests that the exosomal system in the brain can be modulated both by membrane lipid composition and the expression of key proteins that contribute to the formation and secretion of exosomes, how exosomal pathway-regulatory elements sense and respond to perturbations in the endosomal pathway is not well understood. Based upon findings from the extensively studied DS and APOE4 models, we propose that enhanced neuronal exosome secretion can be a protective response, reducing pathological disruption of the endosomal–lysosomal system in disease-vulnerable neurons. Developing therapeutic approaches that help to maintain or enhance neuronal exosome biogenesis and release may be beneficial in a range of disorders of the central nervous system.
... Lastly, Benussi et al. (2016) studied human primary fibroblasts without GRN null mutations. They conclude that the glycosylated form of PGRN was released with exosomes and in the presence of mutation, the secretion of exosomes was extremely reduced and their composition changed enriching in Lamp1 protein. ...
Aging is consistently reported as the most important independent risk factor for neurodegenerative diseases. As life expectancy has significantly increased during the last decades, neurodegenerative diseases became one of the most critical public health problem in our society. The most investigated neurodegenerative diseases during aging are Alzheimer disease (AD), Frontotemporal Dementia (FTD) and Parkinson disease (PD). The search for biomarkers has been focused so far on cerebrospinal fluid (CSF) and blood. Recently, exosomes emerged as novel biological source with increasing interest for age-related neurodegenerative disease biomarkers. Exosomes are tiny Extracellular vesicles (EVs; 30–100 nm in size) released by all cell types which originate from the endosomal compartment. They constitute important vesicles for the release and transfer of multiple (signaling, toxic, and regulatory) molecules among cells. Initially considered with merely waste disposal function, instead exosomes have been recently recognized as fundamental mediators of intercellular communication. They can move from the site of release by diffusion and be retrieved in several body fluids, where they may dynamically reflect pathological changes of cells present in inaccessible sites such as the brain. Multiple evidence has implicated exosomes in age-associated neurodegenerative processes, which lead to cognitive impairment in later life. Critically, consolidated evidence indicates that pathological protein aggregates, including Aβ, tau, and α-synuclein are released from brain cells in association with exosomes. Importantly, exosomes act as vehicles between cells not only of proteins but also of nucleic acids [DNA, mRNA transcripts, miRNA, and non-coding RNAs (ncRNAs)] thus potentially influencing gene expression in target cells. In this framework, exosomes could contribute to elucidate the molecular mechanisms underneath neurodegenerative diseases and could represent a promising source of biomarkers. Despite the involvement of exosomes in age-associated neurodegeneration, the study of exosomes and their genetic cargo in physiological aging and in neurodegenerative diseases is still in its infancy. Here, we review, the current knowledge on protein and ncRNAs cargo of exosomes in normal aging and in age-related neurodegenerative diseases.
... Another recent work demonstrated that exosomes released by human primary fibroblasts contain progranulin mainly in its glycosylated form [87]. Moreover, by analyzing the fibroblasts of FTDP-17 patients carrying GRN null mutations and control subjects, they observed a strong reduction of progranulin in exosomes released by GRN mutant cells. ...
The abnormal deposition of proteins in brain tissue is a common feature of neurodegenerative diseases (NDs) often accompanied by the spread of mutated proteins, causing neuronal toxicity. Exosomes play a fundamental role on their releasing in extracellular space after endosomal pathway activation, allowing to remove protein aggregates by lysosomal degradation or their inclusion into multivesicular bodies (MVBs), besides promoting cellular cross-talk. The emerging evidence of pathogenic mutations associated to ND susceptibility, leading to impairment of exosome production and secretion, opens a new perspective on the mechanisms involved in neurodegeneration. Recent findings suggest to investigate the genetic mechanisms regulating the different exosome functions in central nervous system (CNS), to understand their role in the pathogenesis of NDs, addressing the identification of diagnostic and pharmacological targets. This review aims to summarize the mechanisms underlying exosome biogenesis, their molecular composition and functions in CNS, with a specific focus on the recent findings invoking a defective exosome biogenesis as a common biological feature of the major NDs, caused by genetic alterations. Further definition of the consequences of specific genetic mutations on exosome biogenesis and release will improve diagnostic and pharmacological studies in NDs.
... In addition to cognitive decline, alterations in executive functions and language processing were observed in patients carrying this genetic alteration [40,41]. Alterations in the lysosomal pathways have been widely described in sporadic and genetic FTD [42][43][44][45]. Similarly, it is interesting to note that null mutations in GRN can cause a lysosomal storage disorder and alterations in lysosomal homeostasis [46][47][48]. ...
Frontotemporal dementia (FTD) is a common form of dementia among early-onset cases. Several genetic factors for FTD have been revealed, but a large proportion of FTD cases still have an unidentified genetic origin. Recent studies highlighted common pathobiological mechanisms among neurodegenerative diseases. In the present study, we investigated a panel of candidate genes, previously described to be associated with FTD and/or other neurodegenerative diseases by targeted next generation sequencing (NGS). We focused our study on sporadic FTD (sFTD), devoid of disease-causing mutations in GRN, MAPT and C9orf72. Since genetic factors have a substantially higher pathogenetic contribution in early onset patients than in late onset dementia, we selected patients with early onset (<65 years). Our study revealed that, in 50% of patients, rare missense potentially pathogenetic variants in genes previously associated with Alzheimer’s disease, Parkinson disease, amyotrophic lateral sclerosis and Lewy body dementia (GBA, ABCA7, PARK7, FUS, SORL1, LRRK2, ALS2), confirming genetic pleiotropy in neurodegeneration. In parallel, a synergic genetic effect on FTD is suggested by the presence of variants in five different genes in one single patient. Further studies employing genome-wide approaches might highlight pathogenic variants in novel genes that explain the still missing heritability of FTD.
... Similar to the protective role of CysC-loaded EVs shown here, we have demonstrated in granulin-associated frontotemporal dementia that exosome release and composition is strongly impaired. Along with shortage of the circulating progranulin, a neurotrophic factor, a decrease in EV release contributes to progranulin deficiency 59 . We propose that high levels of CysC expression, as observed in neuronal population vulnerable to AD-related pathology 11,12 , serve to increase EV release. ...
Cystatin C (CysC) is implicated in neuroprotection and repair in the nervous system in response to diverse neurotoxic conditions. In addition to being secreted from cells in a soluble form, CysC is released by cells in association with extracellular vesicles (EVs), including exosomes. We demonstrate that EVs containing CysC protect cultured cells from starvation-induced death. Moreover, while EVs secreted by CysC-deficient cells were not protective, EVs secreted by CysC-deficient cells treated with exogenous human CysC significantly enhanced the survival of the cells. CysC also plays a role in modulating the secretion of EVs, enhancing secretion of EVs by primary cortical neurons and primary cortical smooth muscle cells. Confirming these in vitro findings, higher EV levels were observed in the brain extracellular space of transgenic mice expressing human CysC as compared to littermate controls. Regulation of cell-secreted EV levels and content in the brain is likely to be essential to maintaining normal brain function. We propose that enhanced EV release could rescue the deleterious effects of dysfunction of the endosomal-lysosomal system in neurodegenerative disorders. Moreover, a higher level of CysC-loaded EVs released from cells in the central nervous system has important protective functions, representing a potential therapeutic tool for disorders of the central nervous system.
... N-glycosylated PGRN can be secreted in exosomes by human primary skin fibroblast cells and neuronal cells. Significantly reduced numbers of exosomes were produced from SH-SY5Y cells following GRN silencing or from fibroblast cells derived from FTLD cases with PGRN mutations [52]. ...
Neurodegenerative diseases such as Alzheimer’s disease have proven resistant to new treatments. The complexity of neurodegenerative disease mechanisms can be highlighted by accumulating evidence for a role for a growth factor, progranulin (PGRN). PGRN is a glycoprotein encoded by the GRN/Grn gene with multiple cellular functions, including neurotrophic, anti-inflammatory and lysosome regulatory properties. Mutations in the GRN gene can lead to frontotemporal lobar degeneration (FTLD), a cause of dementia, and neuronal ceroid lipofuscinosis (NCL), a lysosomal storage disease. Both diseases are associated with loss of PGRN function resulting, amongst other features, in enhanced microglial neuroinflammation and lysosomal dysfunction. PGRN has also been implicated in Alzheimer’s disease (AD). Unlike FTLD, increased expression of PGRN occurs in brains of human AD cases and AD model mice, particularly in activated microglia. How microglial PGRN might be involved in AD and other neurodegenerative diseases will be discussed. A unifying feature of PGRN in diseases might be its modulation of lysosomal function in neurons and microglia. Many experimental models have focused on consequences of PGRN gene deletion: however, possible outcomes of increasing PGRN on microglial inflammation and neurodegeneration will be discussed. We will also suggest directions for future studies on PGRN and microglia in relation to neurodegenerative diseases.
... Furthermore, in neuronal stem cells derived from these patients, the accumulation of endosomes and EXs was observed (Wren et al., 2015). Accordingly, a decrease of EX release in progranulin-associated FTD using human fibroblasts was reported (Benussi et al., 2016). ...
Increased life expectancy impacts directly on the number of older people worldwide with the associated increase in neurodegenerative diseases. Besides their social implications, the different forms of dementia, including Alzheimer's disease, Parkinson's disease, dementia with Lewy bodies or frontotemporal dementia, show clinical and pathological overlaps; this hinders their specific and differential diagnosis. To date, biomarkers for each of these types of dementia have been investigated in the cerebrospinal fluid or blood. More recently, the field of biomarker search found a new opportunity to improve diagnosis in extracellular vesicles (EVs). EVs are released by cells including those of the central nervous system and these can be isolated from cerebrospinal fluid and blood. This review summarizes the current knowledge related to the search for dementia biomarkers in the field of EVs including studies of specific EV content, mainly proteins such as α-synuclein or tau and RNA species.
https://www.sciencedirect.com/science/article/pii/S0197458018303701?dgcid=author
... Exosomes have been studied in preclinical models of acute TBI and other neurocritical care disorders (e.g. stroke; spinal cord injury) (20,23,28,(35)(36)(37)(38)(39)(40)(41), but there remains a critical gap in the knowledge surrounding the role of exosomes and blood-based proteins as biomarkers in remote mild TBI (mTBI) and their relationship to chronic TBI-like symptoms and outcomes. ...
Objective: The objective of the study is to measure plasma and exosomal levels of tau, phosphorylated tau (p-tau), and amyloid beta (Aβ) in Veterans with historical mild traumatic brain injury (mTBI) and chronic neuropsychological symptoms.
Methods: Tau, p-tau, Aβ40, and Aβ42 were measured by ultrasensitive immunoassay in plasma and exosomes from 195 Veterans enrolled in the Chronic Effects of Neurotrauma Consortium Multicenter Observational Study. Protein biomarkers were compared among groups with and without mTBI with loss of consciousness (LOC) or post-traumatic amnesia (PTA), and also in those with and without repetitive (≥3) mTBI (rTBI) compared to those with 0 (TBI-neg) and 1–2 mTBI.
Results: There were no differences in measures of plasma and exosomal protein levels among mTBI with LOC or PTA, mTBI with alteration of consciousness only or TBI-neg. Exosomal tau and exosomal p-tau were elevated in rTBI compared to those with 2 or fewer mTBIs and TBI-neg (p < 0.05). Elevations of exosomal tau and p-tau significantly correlated with post-traumatic and post-concussive symptoms, with exosomal tau also relating specifically to cognitive, affective, and somatic post-concussive symptoms (p < 0.05).
Conclusion: rTBI is associated with elevations of exosomal p-tau and exosomal tau, suggesting that blood-based exosomes may provide a peripheral source of informative, centrally derived biomarkers in remote mTBI and that rTBI may contribute to chronic neuropsychological symptoms.
... Thus, diagnostic or therapeutic approaches addressing neurodegenerative pathologies may be of benefit for TBI, SCI, and stroke patients. For example, exosomes have shown promise in the contexts of AD/dementia [55][56][57], Parkinson's disease [58][59][60], amyotrophic lateral sclerosis [61][62][63], and Huntington's disease [64][65][66]. Not only does building evidence related to exosomes in TBI, SCI, and stroke adds to the evidence gleaned using traditional biomarkers (e.g., DNA, RNA, protein), it also offers some advantages over these more well-studied alternatives. ...
Exosomes are endogenous nanovesicles that play critical roles in intercellular signaling by conveying functional genetic information and proteins between cells. Exosomes readily cross the blood-brain barrier and have promise as therapeutic delivery vehicles that have the potential to specifically deliver molecules to the central nervous system (CNS). This unique feature also makes exosomes attractive as biomarkers in diagnostics, prognostics, and therapeutics in the context of multiple significant public health conditions, including acquired neurological disorders. The purpose of this review is to summarize the state of the science surrounding the relevance of extracellular vesicles (EVs), particularly exosomes, to acquire neurological disorders, specifically traumatic brain injury (TBI), spinal cord injury (SCI), and ischemic stroke. In total, ten research articles were identified that examined exosomes in the context of TBI, SCI, or stroke; these manuscripts were reviewed and synthesized to further understand the current role of exosomes in the context of acquired neurological disorders. Of the ten published studies, four focused exclusively on TBI, one on both TBI and SCI, and five on ischemic stroke; notably, eight of the ten studies were limited to pre-clinical samples. The present review is the first to discuss the current body of knowledge surrounding the role of exosomes in the pathophysiology, diagnosis, and prognosis, as well as promising therapeutic strategies in TBI, SCI, and stroke research.
... EVs were isolated from conditioned medium of cells by differential centrifugation as described. 24,25 Nanoparticle tracking analysis by tunable resistive pulse sensing was performed using qNano (Izon) to examine microparticle size and distribution. In some cases, cells were stimulated by recombinant TGF-b1 (10 ng/ml) to simulate conditions of fibrogenesis in vitro. ...
Increased export of transglutaminase-2 (TG2) by tubular epithelial cells (TECs) into the surrounding interstitium modifies the extracellular homeostatic balance, leading to fibrotic membrane expansion. Although silencing of extracellular TG2 ameliorates progressive kidney scarring in animal models of CKD, the pathway through which TG2 is secreted from TECs and contributes to disease progression has not been elucidated. In this study, we developed a global proteomic approach to identify binding partners of TG2 responsible for TG2 externalization in kidneys subjected to unilateral ureteric obstruction (UUO) using TG2 knockout kidneys as negative controls. We report a robust and unbiased analysis of the membrane interactome of TG2 in fibrotic kidneys relative to the entire proteome after UUO, detected by SWATH mass spectrometry. The data have been deposited to the ProteomeXchange with identifier PXD008173. Clusters of exosomal proteins in the TG2 interactome supported the hypothesis that TG2 is secreted by extracellular membrane vesicles during fibrosis progression. In established TEC lines, we found TG2 in vesicles of both endosomal (exosomes) and plasma membrane origin (microvesicles/ectosomes), and TGF-β1 stimulated TG2 secretion. Knockout of syndecan-4 (SDC4) greatly impaired TG2 exosomal secretion. TG2 coprecipitated with SDC4 from exosome lysate but not ectosome lysate. Ex vivo, EGFP-tagged TG2 accumulated in globular elements (blebs) protruding/retracting from the plasma membrane of primary cortical TECs, and SDC4 knockout impaired bleb formation, affecting TG2 release. Through this combined in vivo and in vitro approach, we have dissected the pathway through which TG2 is secreted from TECs in CKD.
... Exosomes, which are secreted vesicles that are derived from endosomes, mediate important aspects of cell-cell communication. Not only is progranulin part of the cargo in human fibroblast exosomes but also, when progranulin content is depleted due to GRN mutation, the pattern of global exosome protein secretion was markedly altered (Benussi et al., 2016) supporting a role for progranulin in regulating exosome formation or secretion. Transcription factor EB (TFEB) has a central role in controlling lysosome biogenesis and when it is overexpressed in HeLa cells results in increased transcription of GRN mRNA (Belcastro et al., 2011). ...
Progranulin, a secreted glycoprotein, is encoded in humans by the single GRN gene. Progranulin consists of seven and a half, tandemly repeated, non-identical copies of the 12 cysteine granulin motif. Many cellular processes and diseases are associated with this unique pleiotropic factor that include, but are not limited to, embryogenesis, tumorigenesis, inflammation, wound repair, neurodegeneration and lysosome function. Haploinsufficiency caused by autosomal dominant mutations within the GRN gene leads to frontotemporal lobar degeneration, a progressive neuronal atrophy that presents in patients as frontotemporal dementia. Frontotemporal dementia is an early onset form of dementia, distinct from Alzheimer's disease. The GRN-related form of frontotemporal lobar dementia is a proteinopathy characterized by the appearance of neuronal inclusions containing ubiquitinated and fragmented TDP-43 (encoded by TARDBP). The neurotrophic and neuro-immunomodulatory properties of progranulin have recently been reported but are still not well understood. Gene delivery of GRN in experimental models of Alzheimer's- and Parkinson's-like diseases inhibits phenotype progression. Here we review what is currently known concerning the molecular function and mechanism of action of progranulin in normal physiological and pathophysiological conditions in both in vitro and in vivo models. The potential therapeutic applications of progranulin in treating neurodegenerative diseases are highlighted.
... PGRN has been also implicated in the regulation of motor neuron development as well as neurite outgrowth and branching ( Chitramuthu et al., 2010;Laird et al., 2010) while gene silencing of PGRN in primary hippocampal neurons affects neuronal connectivity ( Tapia et al., 2011). In line with these evidences, we demonstrated ( Benussi et al., 2016) that the presence of GRN null mutations strongly reduces the number of released exosomes, microvesicles serving as intercellular communication tools that can be released by neurons following synaptic activation ( Laulagnier et al., 2017). Collectively, these evidences support that PGRN deficiency can affect neuronal structural plasticity. ...
Loss-of-function mutations in the progranulin (PGRN) gene are a common cause of familial frontotemporal lobar degeneration (FTLD). This an age-related neurodegenerative disorder characterized by brain atrophy in the frontal and temporal lobes and with typical symptoms such as cognitive and memory impairment, profound behavioral abnormalities and personality changes, that are thought to be related to connectome dysfunctions. Recently, PGRN reduction has been found to induce a behavioural phenotype reminiscent of FTLD symptoms in mice by affecting neuron spine density and morphology, suggesting that the protein can influence neuronal structural plasticity. Here, we evaluated whether a partial haploinsufficiency-like PGRN depletion, achieved by using RNA interference in primary mouse cortical neurons, could modulate GluN2B-containing N-methyl-D-aspartate (NMDA) receptors and tau phosphorylation, that are crucially involved in the regulation of the structural plasticity of these cells. In addition, we studied the effect of PGRN decrease on neuronal cell arborization both in the presence and absence of GluN2B-containing NMDA receptor stimulation.We found that PGRN decline diminished GluN2B-containing NMDA receptor levels and density as well as NMDA-dependent tau phosphorylation. These alterations were accompanied by a marked drop of neuronal arborization, that was prevented by an acute GluN2B-containing NMDA receptor stimulation. Our findings support that PGRN decrease, resulting from pathogenic mutations, might compromise the trophism of cortical neurons by affecting GluN2B-contaning NMDA receptors. These mechanisms might be implicated in the pathogenesis of FTLD.
... Intracerebrally injected exosomes result in reduction of Aβ pathology (Yuyama et al., 2014(Yuyama et al., , 2015. Secretion of exosomes is decreased in progranulin-associated frontotemporal dementia (Benussi et al., 2016). However, Dinkins et al. (2014) show that exosomes interfere with the uptake of Aβ by primary cultured astrocytes and microglia in vitro. ...
Exosomes, a type of extracellular vesicle, have been shown to be involved in many disorders, including Alzheimer’s disease (AD). Exosomes may contribute to the spread of misfolded proteins such as amyloid-β (Aβ) and α-synuclein. However, the specific diffusion process of exosomes and their final destination in brain are still unclear. In the present study, we isolated exosomes from peripheral plasma and injected them into the hippocampus of an AD mouse model, and investigated exosome diffusion. We found that injected exosomes can spread from the dentate gyrus (DG) to other regions of hippocampus and to the cortex. Exosomes targeted microglia preferentially; this phenomenon is stable and is not affected by age. In AD mice, microglia take up lower levels of exosomes. More interestingly, plasma exosomes cluster around the Aβ plaques and are engulfed by activated microglia nearby. Our data indicate that exosomes can diffuse throughout the brain and may play a role in the dynamics of amyloid deposition in AD through microglia.
... Importantly, our aged PGRN-deficient mice showed marked accumulation of lipofuscin, an end-product of lysosomal digestion in the thalamus, and microglia were round or amoeboid with vacuole-like structures (18,30,31). Moreover, null mutations in GRN greatly reduce the number of released exosomes and alter their composition (32). These findings indicate that PGRN deficiency suppresses digestion in and efflux from lysosomes. ...
Progranulin (PGRN) haploinsufficiency resulting from loss-of-function mutations in the PGRN gene causes frontotemporal lobar degeneration accompanied by TDP-43 accumulation, and patients with homozygous mutations in the PGRN gene present with neuronal ceroid lipofuscinosis. Although it remains unknown why PGRN deficiency causes neurodegenerative diseases, there is increasing evidence that PGRN is implicated in lysosomal functions. Here, we show PGRN is a secretory lysosomal protein that regulates lysosomal function and biogenesis by controlling the acidification of lysosomes. PGRN gene expression and protein levels increased concomitantly with increase of lysosomal biogenesis induced by lysosome alkalizers or serum starvation. Down-regulation or insufficiency of PGRN led to increased lysosomal gene expression and protein levels, while PGRN overexpression led to decreased lysosomal gene expression and protein levels. In particular, the level of mature cathepsin D (CTSDmat) dramatically changed depending upon PGRN levels. The acidification of lysosomes was facilitated in cells transfected with PGRN. Then, this caused degradation of CTSDmat by cathepsin B. Secreted PGRN is incorporated into cells via sortilin or cation-independent mannose 6-phosphate receptor, and facilitated the acidification of lysosomes and degradation of CTSDmat. Moreover, change of PGRN levels led to a cell-type-specific increase of insoluble TDP-43. In the brain tissue of FTLD-TDP patients with PGRN deficiency, CTSD and phosphorylated TDP-43 accumulated in neurons. Our study provides new insights into the physiological function of PGRN and the role of PGRN insufficiency in the pathogenesis of neurodegenerative diseases.
... In particular, EVs are considered valuable for liquid biopsies in cancer diagnosis since they carry molecular and proteomic cargo from their tumour cell of origin 10 . In human CSF, EVs are rich reservoirs of biomarkers for neurological disorders and there is increasing evidence that deregulation of EVs secretion play a pathological role in neurodegenerative diseases such as Alzheimer's disease (AD) and Frontotemporal dementia (FTD) [11][12][13][14][15] . ...
Exosomes, which are membranous nanovesicles, are actively released by cells and have been attributed to roles in cell-cell communication, cancer metastasis, and early disease diagnostics. The small size (30–100 nm) along with low refractive index contrast of exosomes makes direct characterization and phenotypical classification very difficult. In this work we present a method based on Single Particle Interferometric Reflectance Imaging Sensor (SP-IRIS) that allows multiplexed phenotyping and digital counting of various populations of individual exosomes (>50 nm) captured on a microarray-based solid phase chip. We demonstrate these characterization concepts using purified exosomes from a HEK 293 cell culture. As a demonstration of clinical utility, we characterize exosomes directly from human cerebrospinal fluid (hCSF). Our interferometric imaging method could capture, from a very small hCSF volume (20 uL), nanoparticles that have a size compatible with exosomes, using antibodies directed against tetraspanins. With this unprecedented capability, we foresee revolutionary implications in the clinical field with improvements in diagnosis and stratification of patients affected by different disorders.
... k Quantification of secreted PGRN immunoreactivity from Western blots of conditioned media in j (n = 3 independent experiments). In all graphs, the bars represent the mean ± SEM. *Differs from control, P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001 using one-way ANOVA followed by Dunnett's comparison post-hoc test and may reflect a defect in exosome secretion [37]. Treatment of GRN fibroblasts with trehalose significantly increased intracellular and secreted PGRN compared to vehicle treated GRN fibroblasts (Fig. 5a-c). ...
Background
Progranulin (PGRN) is a secreted growth factor important for neuronal survival and may do so, in part, by regulating lysosome homeostasis. Mutations in the PGRN gene (GRN) are a common cause of frontotemporal lobar degeneration (FTLD) and lead to disease through PGRN haploinsufficiency. Additionally, complete loss of PGRN in humans leads to neuronal ceroid lipofuscinosis (NCL), a lysosomal storage disease. Importantly, Grn−/− mouse models recapitulate pathogenic lysosomal features of NCL. Further, GRN variants that decrease PGRN expression increase the risk of developing Alzheimer’s disease (AD) and Parkinson’s disease (PD). Together these findings demonstrate that insufficient PGRN predisposes neurons to degeneration. Therefore, compounds that increase PGRN levels are potential therapeutics for multiple neurodegenerative diseases.
Results
Here, we performed a cell-based screen of a library of known autophagy-lysosome modulators and identified multiple novel activators of a human GRN promoter reporter including several common mTOR inhibitors and an mTOR-independent activator of autophagy, trehalose. Secondary cellular screens identified trehalose, a natural disaccharide, as the most promising lead compound because it increased endogenous PGRN in all cell lines tested and has multiple reported neuroprotective properties. Trehalose dose-dependently increased GRN mRNA as well as intracellular and secreted PGRN in both mouse and human cell lines and this effect was independent of the transcription factor EB (TFEB). Moreover, trehalose rescued PGRN deficiency in human fibroblasts and neurons derived from induced pluripotent stem cells (iPSCs) generated from GRN mutation carriers. Finally, oral administration of trehalose to Grn haploinsufficient mice significantly increased PGRN expression in the brain.
Conclusions
This work reports several novel autophagy-lysosome modulators that enhance PGRN expression and identifies trehalose as a promising therapeutic for raising PGRN levels to treat multiple neurodegenerative diseases.
Electronic supplementary material
The online version of this article (doi:10.1186/s13024-016-0114-3) contains supplementary material, which is available to authorized users.
... Then, we have further characterized the produced exosomes for the content of the FTLD-related protein PRGN, that has been demonstrated to be transported in these vesicles in SH-SY5Y cells as well as in fibroblasts from patients affected by genetic forms of FTLD (Benussi et al., 2016). We have performed an electron microscopy analysis on isolated exosomes to assess whether cells retain their capability to secrete PRGN in exosomes. ...
Frontotemporal lobar degeneration (FTLD) is a severe neurodegenerative disorder that is diagnosed with increasing frequency in clinical setting. Currently, no therapy is available and in addition the molecular basis of the disease are far from being elucidated. Consequently, it is of pivotal importance to develop reliable and cost-effective in vitro models for basic research purposes and drug screening. To this respect, recent results in the field of Alzheimer’s disease have suggested that a tridimensional (3D) environment is an added value to better model key pathologic features of the disease. Here, we have tried to add complexity to the 3D cell culturing concept by using a microfluidic bioreactor, where cells are cultured under a continuous flow of medium, thus mimicking the interstitial fluid movement that actually perfuses the body tissues, including the brain. We have implemented this model using a neuronal-like cell line (SH-SY5Y), a widely exploited cell model for neurodegenerative disorders that shows some basic features relevant for FTLD modeling, such as the release of the FTLD-related protein progranulin (PRGN) in specific vesicles (exosomes). We have efficiently seeded the cells on 3D scaffolds, optimized a disease-relevant oxidative stress experiment (by targeting mitochondrial function that is one of the possible FTLD-involved pathological mechanisms) and evaluated cell metabolic activity in dynamic culture in comparison to static conditions, finding that SH-SY5Y cells cultured in 3D scaffold are susceptible to the oxidative damage triggered by a mitochondrial-targeting toxin (6-OHDA) and that the same cells cultured in dynamic conditions kept their basic capacity to secrete PRGN in specific vesicles (exosomes) once recovered from the bioreactor and plated in standard 2D conditions. We think that a further improvement of our microfluidic system may help in providing a full device where assessing basic FTLD-related features (including PRGN dynamic secretion) that may be useful for monitoring disease progression over time or evaluating therapeutic interventions.
Neurodegenerative diseases, such as Alzheimer’s disease (AD), Parkinson’s disease (PD), amyotrophic lateral sclerosis (ALS), Huntington’s disease (HD), stroke, and aneurysms, are characterized by the abnormal accumulation and aggregation of disease-causing proteins in the brain and spinal cord. Recent research suggests that proteins linked to these conditions can be secreted and transferred among cells using exosomes. The transmission of abnormal protein buildup and the gradual degeneration in the brains of impacted individuals might be supported by these exosomes. Furthermore, it has been reported that neuroprotective functions can also be attributed to exosomes in neurodegenerative diseases. The potential neuroprotective functions may play a role in preventing the formation of aggregates and abnormal accumulation of proteins associated with the disease. The present review summarizes the roles of exosomes in neurodegenerative diseases as well as elucidating their therapeutic potential in AD, PD, ALS, HD, stroke, and aneurysms. By elucidating these two aspects of exosomes, valuable insights into potential therapeutic targets for treating neurodegenerative diseases may be provided.
Ceroid lipofuscinosis neuronal (CLN) genes encode 13 proteins that localize throughout the endomembrane system to regulate a variety of cellular processes. In humans, mutations in CLN genes cause a devastating form of neurodegeneration called neuronal ceroid lipofuscinosis (NCL), commonly known as Batten disease. Each CLN gene is associated with a specific subtype of the disease that differ from each other in severity and age of onset. The NCLs affect all ages and ethnicities worldwide but primarily affect children. The pathology underlying the NCLs is poorly understood, which has prevented the development of a cure or effective therapy for most subtypes of the disease. A growing body of literature supports the networking of CLN genes and proteins within cells, which aligns with the broadly similar cellular and clinical manifestations among the different subtypes of NCL. Here, all relevant literature is reviewed to provide a comprehensive overview of our current understanding of how CLN genes and proteins are networked in mammalian cells with an aim towards revealing new molecular targets for therapy development. Intriguingly, CLN gene and protein networking extends beyond the NCLs as recent work has linked several CLN genes and proteins to other forms of neurodegeneration such as Alzheimer's disease and Parkinson's disease. Thus, a deeper understanding of the pathways and cellular processes impacted by mutations in CLN genes will not only strengthen our knowledge of the pathological mechanisms underlying the NCLs but may also provide new insight into related forms of neurodegeneration.
An extracellular network of molecular chaperones protects a diverse array of proteins that reside in or pass-through extracellular spaces. Proteins in the extracellular milieu face numerous challenges that can lead to protein misfolding and aggregation. As a checkpoint for proteins that move between cells, extracellular chaperone networks are of growing clinical relevance. J-domain proteins (JDPs) are ubiquitous molecular chaperones that are known for their essential roles in a wide array of fundamental cellular processes through their regulation of Hsp70s. As the largest molecular chaperone family, JDPs have long been recognized for their diverse functions within cells. Some JDPs are elegantly selective for their ‘client proteins’, some do not discriminate among substrates and others act co-operatively on the same target. The realization that JDPs are exported through both classical and unconventional secretory pathways has fueled investigation into the roles that JDPs play in protein quality control and intercellular communication. The proposed functions of exported JDPs are diverse. Studies suggest that export of DnaJB11 enhances extracellular proteostasis, that intercellular movement of DnaJB1 or DnaJB6 enhances the proteostasis capacity in recipient cells, while the import of DnaJB8 increases resistance to chemotherapy in recipient cancer cells. In addition, the export of DnaJC5 and concurrent DnaJC5-dependent ejection of dysfunctional and aggregation-prone proteins are implicated in the prevention of neurodegeneration. This review provides a brief overview of the current understanding of the extracellular chaperone networks and outlines the first wave of studies describing the cellular export of JDPs.
Alzheimer’s disease (AD), dementia with Lewy bodies (DLB) and frontotemporal dementia (FTD) represent the three major neurodegenerative dementias characterized by abnormal brain protein accumulation. In this study, we investigated extracellular vesicles (EVs) and neurotrophic factors in the cerebrospinal fluid (CSF) of 120 subjects: 36 with AD, 30 with DLB, 34 with FTD and 20 controls. Specifically, CSF EVs were analyzed by Nanoparticle Tracking Analysis and neurotrophic factors were measured with ELISA. We found higher EV concentration and lower EV size in AD and DLB groups compared to the controls. Classification tree analysis demonstrated EV size as the best parameter able to discriminate the patients from the controls (96.7% vs. 3.3%, respectively). The diagnostic performance of the EV concentration/size ratio resulted in a fair discrimination level with an area under the curve of 0.74. Moreover, the EV concentration/size ratio was associated with the p-Tau181/Aβ42 ratio in AD patients. In addition, we described altered levels of cystatin C and progranulin in the DLB and AD groups. We did not find any correlation between neurotrophic factors and EV parameters. In conclusion, the results of this study suggest a common involvement of the endosomal pathway in neurodegenerative dementias, giving important insight into the molecular mechanisms underlying these pathologies.
Long‐term or severe lack of protective factors is important in the pathogenesis of neurodegenerative dementia. Progranulin (PGRN), a neurotrophic factor expressed mainly in neurons and microglia, has various neuroprotective effects such as anti‐inflammatory effects, promoting neuron survival and neurite growth, and participating in normal lysosomal function. Mutations in the PGRN gene ( GRN ) have been found in several neurodegenerative dementias, including frontotemporal lobar degeneration (FTLD) and Alzheimer's disease (AD). Herein, PGRN deficiency and PGRN hydrolytic products (GRNs) in the pathological changes related to dementia, including aggregation of tau and TAR DNA‐binding protein 43 (TDP‐43), amyloid‐β (Aβ) overproduction, neuroinflammation, lysosomal dysfunction, neuronal death, and synaptic deficit have been summarized. Furthermore, as some therapeutic strategies targeting PGRN have been developed in various models, we highlighted PGRN as a potential anti‐neurodegeneration target in dementia.
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Progranulin (PGRN) haploinsufficiency resulting from the loss-of-function mutations of GRN gene causes frontotemporal lober degeneration characteristic of TDP-43-positive inclusion (FTLD-TDP). The patients with homozygous mutations in the GRN gene present with adult onset neuronal ceroid lipofuscinosis. While the functional role of PGRN regulating neurodegenerative diseases is still controversial, evidences that PGRN regulates lysosomal function and biogenesis are accumulating. We previously demonstrated that PGRN is localized to lysosomes and the expression increases in lysosomal biogenesis. Furthermore, PGRN suppresses exacerbated lysosomal biogenesis especially in activated microglia after traumatic brain injury and with aging in mice, indicating that PGRN composes of negative feedback loop of lysosomal biogenesis. Interestingly, secreted PGRN is incorporated and transported into lysosomes through sortilin or cation-independent mannose 6-phosphate receptor, and facilitated acidification of lysosomes. These findings indicate that PGRN is a secretory lysosomal protein that regulates lysosomal function and biogenesis through acidification of lysosomes. On the other hand, other groups recently reported that granulin peptides stabilize Cathepsin D and work as a chaperone for beta-glucocerebrosidase. These investigations about PGRN function involved in lysosomes have spotlighted on the pathogenic mechanisms of neurodegenerative diseases especially in FTLD-TDP. The understanding of PGRN trafficking into lysosomes and its regulation of lysosomes could provide a clue of the remedy for currently incurable neurodegenerative diseases.
The finding of an effective cure or treatment for neurodegenerative diseases is one of the biggest challenges for this century. Although these diseases show different clinical manifestations, the presence of toxic protein aggregates in the brain of patients is a common feature to all of them, suggesting a loss of protein homeostasis. Aging, the primary risk factor for the majority of neurodegenerative disorders, is linked to the impairment of degradative compartments such as lysosomes and autophagosomes. Besides, many genetic factors for Alzheimer's disease, Parkinson's disease, or frontotemporal dementia, as examples of frequent neurodegenerative diseases, are causative of endo‐lysosomal and autophagosomal dysfunctions. There is scientific evidence suggesting that neurons can counteract the accumulation of undegraded cellular material by the secretion of extracellular vesicles (EVs), which are vesicles with a size ranging from 50 to 100 nm generated in a type of endosomal compartment named multivesicular body. EVs play a crucial role in removing cellular waste, promoting protein aggregation, and spreading toxic protein aggregates in the brain of patients. In this review, the interplay between the impairment of degradative compartments, the secretion of EVs, and their pathological/beneficial role in neurodegeneration is described.
Although the traditional strategy of developing general medical treatments for heterogeneous patient populations has a well-established track record, the acknowledgment that one-size-does-not-fit-all is pushing health-care to enter a new era of tailored interventions. The advent of precision medicine is fueled by the high-throughput analysis of individual DNA variants and mRNA expression profiles. However, due to the role of proteins in providing a more direct view of disease states than genomics alone, the ability to comprehensively analyze protein alterations and post translational modifications (PTMs) is a necessary step to unravel disease mechanisms, develop novel biomarkers and targeted therapies. Protein and peptide microarrays can play a major role in this frame, due to high-throughput, low sample consumption and wide applicability. Here, their current role and potentialities are discussed through the review of some promising applications in the fields of PTMs analysis, enzyme screening, high-content immune-profiling and the phenotyping of extracellular vesicles.
Exosomes are vesicles of endocytic origin released by many cells. These vesicles can mediate communication between cells, facilitating processes such as antigen presentation. Here, we show that exosomes from a mouse and a human mast cell line (MC/9 and HMC-1, respectively), as well as primary bone marrow-derived mouse mast cells, contain RNA. Microarray assessments revealed the presence of mRNA from approximately 1300 genes, many of which are not present in the cytoplasm of the donor cell. In vitro translation proved that the exosome mRNAs were functional. Quality control RNA analysis of total RNA derived from exosomes also revealed presence of small RNAs, including microRNAs. The RNA from mast cell exosomes is transferable to other mouse and human mast cells. After transfer of mouse exosomal RNA to human mast cells, new mouse proteins were found in the recipient cells, indicating that transferred exosomal mRNA can be translated after entering another cell. In summary, we show that exosomes contain both mRNA and microRNA, which can be delivered to another cell, and can be functional in this new location. We propose that this RNA is called " exosomal shuttle RNA " (esRNA). Exosomes are small (50–90 nm) membrane vesicles of endocytic origin that are released into the extracellular environment on fusion of multivesicular bodies (MVB) with the plasma membrane 1. Many cells have the capacity to release exosomes, including reticulo-cytes 2 , dendritic cells 3 , B cells 4 , T cells 5 , mast cells 6 , epithelial cells 7 and tumour cells 8. The functions of exosomes are not completely understood, although it has been shown that exosomes can participate in the signalling events contributing to antigen presentation to T cells 4 and the development of tolerance 9. Several mechanisms have been hypothesized describing the interactions of exosomes and recipient cells. Exosomes can bind to cells through recep-tor–ligand interactions, similar to cell–cell communication mediating , for example, antigen presentation 4. Alternatively, exosomes could putatively attach or fuse with the target-cell membrane, delivering exosomal surface proteins and perhaps cytoplasm to the recipient cell 10,11. Finally, exosomes may also be internalized by the recipient cells by mechanisms such as endocytosis 12. Exosomes were isolated from a mast-cell line (MC/9), primary bone marrow-derived mast cells (BMMC) and a human mast-cell line (HMC-1) through a series of microfiltration and ultracentrifugation steps modified from what has been previously described 4. To confirm that the structures studied indeed are exosomes, they were examined by electron microscopy (Fig. 1a), flow cytometric analysis (FACS; Fig. 1b), and proteomic analysis (see Supplementary Information, Table S1). The electron micrographs of the exosomes revealed rounded structures with a size of approximately 50–80 nm, similar to previously described exo-somes 4,13–15. The identity of the studied vesicles was further confirmed as exosomes by FACS analysis (Fig. 1b), which show the presence of the surface protein CD63 — a commonly used marker of exosomes. Finally, extensive protein analysis of the MC/9 exosomes was performed on multiple samples using LC-MS/MS technology. A total of 271 proteins were identified (see Supplementary Information, Table S1) from three preparations of the isolated vesicles, of which 47 proteins were present in all three samples. More importantly, a large number of the proteins found in the preparations were the same as proteins previously identified in exosomes produced by other cells (that is, exosomes derived from intestinal epithelial cells, urine, dendritic cells, microglia, melanoma, T-cells and B-cells). In particular, 60% of the 47 proteins found in all samples of mast-cell exosomes have been previously found in other types of exosomes. Moreover, 39% of the 271 total proteins found in the analysed exosome samples have also been previously found in other types of exosomes. Thus, the electron microscopy, the FACS, and the detailed protein analyses each provided significant evidence in favour of the identification of the isolated vesicles as exosomes. The presence of nucleic acids was examined in exosomes derived from MC/9, BMMC and HMC-1 cells to define a potential mechanism by which exosomes may mediate cell–cell communication. These assessments showed that isolated exosomes contain no DNA (see Supplementary Information, Fig. S1). However, substantial amounts of RNA were detected by agarose gel electrophoresis, spectrophotometry
Mutations in the progranulin (PGRN) gene have been linked to two distinct neurodegenerative diseases, frontotemporal lobar degeneration (FTLD) and neuronal ceroid lipofuscinosis (NCL). Accumulating evidence suggests a critical role of PGRN in lysosomes. However, how PGRN is trafficked to lysosomes is still not clear. Here we report a novel pathway for lysosomal delivery of PGRN. We found that prosaposin (PSAP) interacts with PGRN and facilitates its lysosomal targeting in both biosynthetic and endocytic pathways via the cation-independent mannose 6-phosphate receptor and low density lipoprotein receptor-related protein 1. PSAP deficiency in mice leads to severe PGRN trafficking defects and a drastic increase in serum PGRN levels. We further showed that this PSAP pathway is independent of, but complementary to, the previously identified PGRN lysosomal trafficking mediated by sortilin. Collectively, our results provide new understanding on PGRN trafficking and shed light on the molecular mechanisms behind FTLD and NCL caused by PGRN mutations.
The intercellular transfer of amyloid-β (Aβ) and tau proteins has received increasing attention in Alzheimer's disease (AD). Among other transfer modes, Aβ and tau dissemination has been suggested to occur through release of Extracellular Vesicles (EVs), which may facilitate delivery of pathogenic proteins over large distances. Recent evidence indicates that EVs carry on their surface, specific molecules which bind to extracellular Aβ, opening the possibility that EVs may also influence Aβ assembly and synaptotoxicity. In this review we focus on studies which investigated the impact of EVs in Aβ-mediated neurodegeneration and showed either detrimental or protective role for EVs in the pathology.
Background:
Frontotemporal dementia is a highly heritable neurodegenerative disorder. In about a third of patients, the disease is caused by autosomal dominant genetic mutations usually in one of three genes: progranulin (GRN), microtubule-associated protein tau (MAPT), or chromosome 9 open reading frame 72 (C9orf72). Findings from studies of other genetic dementias have shown neuroimaging and cognitive changes before symptoms onset, and we aimed to identify whether such changes could be shown in frontotemporal dementia.
Methods:
We recruited participants to this multicentre study who either were known carriers of a pathogenic mutation in GRN, MAPT, or C9orf72, or were at risk of carrying a mutation because a first-degree relative was a known symptomatic carrier. We calculated time to expected onset as the difference between age at assessment and mean age at onset within the family. Participants underwent a standardised clinical assessment and neuropsychological battery. We did MRI and generated cortical and subcortical volumes using a parcellation of the volumetric T1-weighted scan. We used linear mixed-effects models to examine whether the association of neuropsychology and imaging measures with time to expected onset of symptoms differed between mutation carriers and non-carriers.
Findings:
Between Jan 30, 2012, and Sept 15, 2013, we recruited participants from 11 research sites in the UK, Italy, the Netherlands, Sweden, and Canada. We analysed data from 220 participants: 118 mutation carriers (40 symptomatic and 78 asymptomatic) and 102 non-carriers. For neuropsychology measures, we noted the earliest significant differences between mutation carriers and non-carriers 5 years before expected onset, when differences were significant for all measures except for tests of immediate recall and verbal fluency. We noted the largest Z score differences between carriers and non-carriers 5 years before expected onset in tests of naming (Boston Naming Test -0·7; SE 0·3) and executive function (Trail Making Test Part B, Digit Span backwards, and Digit Symbol Task, all -0·5, SE 0·2). For imaging measures, we noted differences earliest for the insula (at 10 years before expected symptom onset, mean volume as a percentage of total intracranial volume was 0·80% in mutation carriers and 0·84% in non-carriers; difference -0·04, SE 0·02) followed by the temporal lobe (at 10 years before expected symptom onset, mean volume as a percentage of total intracranial volume 8·1% in mutation carriers and 8·3% in non-carriers; difference -0·2, SE 0·1).
Interpretation:
Structural imaging and cognitive changes can be identified 5-10 years before expected onset of symptoms in asymptomatic adults at risk of genetic frontotemporal dementia. These findings could help to define biomarkers that can stage presymptomatic disease and track disease progression, which will be important for future therapeutic trials.
Funding:
Centres of Excellence in Neurodegeneration.
Information exchange executed by extracellular vesicles, including exosomes, is a newly described form of intercellular communication important in the development and physiology of neural systems. These vesicles can be released from cells, are packed with information including signaling proteins and both coding and regulatory RNAs, and can be taken up by target cells, thereby facilitating the transfer of multilevel information. Recent studies demonstrate their critical role in physiological processes, including nerve regeneration, synaptic function, and behavior. These vesicles also have a sinister role in the propagation of toxic amyloid proteins in neurodegenerative conditions, including prion diseases and Alzheimer's and Parkinson's diseases, in inducing neuroinflammation by exchange of information between the neurons and glia, as well as in aiding tumor progression in the brain by subversion of normal cells. This article provides a summary of topics covered in a symposium and is not meant to be a comprehensive review of the subject.
Two major types of intercellular communication are found in the central nervous system (CNS), namely wiring transmission (WT; point-to-point communication via private channels, e.g. synaptic transmission) and volume transmission (VT; communication in the extracellular fluid and in the cerebrospinal fluid). Volume and synaptic transmission become integrated because their chemical signals activate different types of interacting receptors in heteroreceptor complexes located synaptically and extrasynaptically in the plasma membrane. In VT, we focus on the role of the extracellular-vesicle type of VT, and in WT, on the potential role of the tunnelling-nanotube (TNT) type of WT. The so-called exosomes appear to be the major vesicular carrier for intercellular communication but the larger microvesicles also participate. Extracellular vesicles are released from cultured cortical neurons and different types of glial cells and modulate the signalling of the neuronal-glial networks of the CNS. This type of VT has pathological relevance, and epigenetic mechanisms may participate in the modulation of extracellular-vesicle-mediated VT. Gerdes and co-workers proposed the existence of a novel type of WT based on TNTs, which are straight transcellular channels leading to the formation in vitro of syncytial cellular networks found also in neuronal and glial cultures.
Heterozygous loss-of-function mutations in the progranulin (GRN) gene and the resulting reduction of GRN levels is a common genetic cause for frontotemporal lobar degeneration (FTLD) with accumulation of TAR DNA-binding protein (TDP)-43. Recently, it has been shown that a complete GRN deficiency due to a homozygous GRN loss-of-function mutation causes neuronal ceroid lipofuscinosis (NCL), a lysosomal storage disorder. These findings suggest that lysosomal dysfunction may also contribute to some extent to FTLD. Indeed, Grn(-/-) mice recapitulate not only pathobiochemical features of GRN-associated FTLD-TDP (FTLD-TDP/GRN), but also those which are characteristic for NCL and lysosomal impairment. In Grn(-/-) mice the lysosomal proteins cathepsin D (CTSD), LAMP (lysosomal-associated membrane protein) 1 and the NCL storage components saposin D and subunit c of mitochondrial ATP synthase (SCMAS) were all found to be elevated. Moreover, these mice display increased levels of transmembrane protein (TMEM) 106B, a lysosomal protein known as a risk factor for FTLD-TDP pathology. In line with a potential pathological overlap of FTLD and NCL, Ctsd(-/-) mice, a model for NCL, show elevated levels of the FTLD-associated proteins GRN and TMEM106B. In addition, pathologically phosphorylated TDP-43 occurs in Ctsd(-/-) mice to a similar extent as in Grn(-/-) mice. Consistent with these findings, some NCL patients accumulate pathologically phosphorylated TDP-43 within their brains. Based on these observations, we searched for pathological marker proteins, which are characteristic for NCL or lysosomal impairment in brains of FTLD-TDP/GRN patients. Strikingly, saposin D, SCMAS as well as the lysosomal proteins CTSD and LAMP1/2 are all elevated in patients with FTLD-TDP/GRN. Thus, our findings suggest that lysosomal storage disorders and GRN-associated FTLD may share common features.
The term frontotemporal lobar degeneration (FTLD) refers to a group of progressive brain diseases, which preferentially involve the frontal and temporal lobes. Depending on the primary site of atrophy, the clinical manifestation is dominated by behavior alterations or impairment of language. The onset of symptoms usually occurs before the age of 60 years, and the mean survival from diagnosis varies between 3 and 10 years. The prevalence is estimated at 15 per 100,000 in the population aged between 45 and 65 years, which is similar to the prevalence of Alzheimer's disease in this age group. There are two major clinical subtypes, behavioral-variant frontotemporal dementia and primary progressive aphasia. The neuropathology underlying the clinical syndromes is also heterogeneous. A common feature is the accumulation of certain neuronal proteins. Of these, the microtubule-associated protein tau (MAPT), the transactive response DNA-binding protein, and the fused in sarcoma protein are most important. Approximately 10% to 30% of FTLD shows an autosomal dominant pattern of inheritance, with mutations in the genes for MAPT, progranulin (GRN), and in the chromosome 9 open reading frame 72 (C9orf72) accounting for more than 80% of familial cases. Although significant advances have been made in recent years regarding diagnostic criteria, clinical assessment instruments, neuropsychological tests, cerebrospinal fluid biomarkers, and brain imaging techniques, the clinical diagnosis remains a challenge. To date, there is no specific pharmacological treatment for FTLD. Some evidence has been provided for serotonin reuptake inhibitors to reduce behavioral disturbances. No large-scale or high-quality studies have been conducted to determine the efficacy of non-pharmacological treatment approaches in FTLD. In view of the limited treatment options, caregiver education and support is currently the most important component of the clinical management.
Genetic research in frontotemporal lobar degeneration (FTLD) is gaining momentum. Following the discovery of a repeat expansion in the gene C9 open reading frame 72 (C9orf72), three major genes and associated disease mechanisms and inclusion body pathologies have emerged, paving the way for personalized medicine in FTLD.
In the nervous system, glia cells maintain homeostasis, synthesize myelin, provide metabolic support, and participate in immune defense. The communication between glia and neurons is essential to synchronize these diverse functions with brain activity. Evidence is accumulating that secreted extracellular vesicles (EVs), such as exosomes and shedding microvesicles, are key players in intercellular signaling. The cells of the nervous system secrete EVs, which potentially carry protein and RNA cargo from one cell to another. After delivery, the cargo has the ability to modify the target cell phenotype. Here, we review the recent advances in understanding the role of EV secretion by astrocytes, microglia, and oligodendrocytes in the central nervous system. Current work has demonstrated that oligodendrocytes transfer exosomes to neurons as a result of neurotransmitter signaling suggesting that these vesicles may mediate glial support of neurons.
Progranulin (GRN) mutations causing haploinsufficiency are a major cause of frontotemporal lobar degeneration (FTLD-TDP). Recent discoveries demonstrating sortilin (SORT1) is a neuronal receptor for PGRN endocytosis and a determinant of plasma PGRN levels portend the development of enhancers targeting the SORT1/PGRN axis. We demonstrate the preclinical efficacy of several approaches through which impairing PGRN's interaction with SORT1 restores extracellular PGRN levels. Our report is the first to demonstrate the efficacy of enhancing PGRN levels in iPSC-neurons derived from FTD patients with PGRN deficiency. We validate a small molecule preferentially increases extracellular PGRN by reducing SORT1 levels in various mammalian cell lines and patient-derived iPSC-neurons and lymphocytes. We further demonstrate that SORT1 antagonists and a small molecule binder of PGRN588-593, residues critical for PGRN-SORT1 binding, inhibit SORT1-mediated PGRN endocytosis. Collectively, our data demonstrate that the SORT1/PGRN axis is a viable target for PGRN-based therapy, particularly in FTD-GRN patients.
Cells release into the extracellular environment diverse types of membrane vesicles of endosomal and plasma membrane origin called exosomes and microvesicles, respectively. These extracellular vesicles (EVs) represent an important mode of intercellular communication by serving as vehicles for transfer between cells of membrane and cytosolic proteins, lipids, and RNA. Deficiencies in our knowledge of the molecular mechanisms for EV formation and lack of methods to interfere with the packaging of cargo or with vesicle release, however, still hamper identification of their physiological relevance in vivo. In this review, we focus on the characterization of EVs and on currently proposed mechanisms for their formation, targeting, and function.
In vitro studies have shown that neuronal cell cultures secrete exosomes containing amyloid β precursor protein (APP) and the APP processing products, carboxyl-terminal fragments (APP-CTFs) and amyloid β (Aβ). We investigated the secretion of full-length APP (flAPP) and APP-CTFs via the exosome secretory pathway in vivo. To this end, we developed a novel protocol designed to isolate exosomes secreted into mouse brain extracellular space. Exosomes with typical morphology were isolated from freshly removed mouse brains and from frozen mouse and human brain tissues, demonstrating that exosomes can be isolated from postmortem tissue frozen for long periods of time. flAPP, APP-CTFs, and enzymes that cleave both flAPP and APP-CTFs were identified in brain exosomes. While higher levels of both flAPP and APP-CTFs were observed in exosomes isolated from the brain of transgenic mice overexpressing human APP (Tg2576) compared to wild type control mice, there was no difference in the number of secreted brain exosomes. These data indicate that the levels of flAPP and APP-CTFs associated with exosomes mirror the cellular levels of flAPP and APP-CTFs. Interestingly, exosomes isolated from brains of both Tg2576 and wild type mice are enriched with APP-CTFs relative to flAPP. Thus, we hypothesize that the exosome-secretory pathway plays a pleiotropic role in the brain; exosome secretion is beneficial to the cell acting as a specific releasing system of the neurotoxic APP-CTFs and Aβ but the secretion of exosomes enriched with the APP-CTFs, neurotoxic proteins that are also a source of secreted Aβ, is harmful to the brain.
The pathogenic mechanisms of frontotemporal dementia (FTD) remain poorly understood. Here we generated multiple induced pluripotent stem cell lines from a control subject, a patient with sporadic FTD, and an FTD patient with a novel heterozygous GRN mutation (progranulin [PGRN] S116X). In neurons and microglia differentiated from PGRN S116X induced pluripotent stem cells, the levels of intracellular and secreted PGRN were reduced, establishing patient-specific cellular models of PGRN haploinsufficiency. Through a systematic screen of inducers of cellular stress, we found that PGRN S116X neurons, but not sporadic FTD neurons, exhibited increased sensitivity to staurosporine and other kinase inhibitors. Moreover, the serine/threonine kinase S6K2, a component of the phosphatidylinositol 3-kinase and mitogen-activated protein kinase pathways, was specifically downregulated in PGRN S116X neurons. Both increased sensitivity to kinase inhibitors and reduced S6K2 were rescued by PGRN expression. Our findings identify cell-autonomous, reversible defects in patient neurons with PGRN deficiency, and provide a compelling model for studying PGRN-dependent pathogenic mechanisms and testing potential therapies.
Frontotemporal lobar degeneration (FTLD) is a heterogeneous group of disorders characterized by disturbances of behavior and personality and different types of language impairment with or without concomitant features of motor neuron disease or parkinsonism. FTLD is characterized by atrophy of the frontal and anterior temporal brain lobes. Detailed neuropathological studies have elicited proteinopathies defined by inclusions of hyperphosphorylated microtubule-associated protein tau, TAR DNA-binding protein TDP-43, fused-in-sarcoma or yet unidentified proteins in affected brain regions. Rather than the type of proteinopathy, the site of neurodegeneration correlates relatively well with the clinical presentation of FTLD. Molecular genetic studies identified five disease genes, of which the gene encoding the tau protein (MAPT), the growth factor precursor gene granulin (GRN), and C9orf72 with unknown function are most frequently mutated. Rare mutations were also identified in the genes encoding valosin-containing protein (VCP) and charged multivesicular body protein 2B (CHMP2B). These genes are good markers to distinguish underlying neuropathological phenotypes. Due to the complex landscape of FTLD diseases, combined characterization of clinical, imaging, biological and genetic biomarkers is essential to establish a detailed diagnosis. Although major progress has been made in FTLD research in recent years, further studies are needed to completely map out and correlate the clinical, pathological and genetic entities, and to understand the underlying disease mechanisms. In this review, we summarize the current state of the rapidly progressing field of genetic, neuropathological and clinical research of this intriguing condition.
Frontotemporal dementia (FTD) is a clinical syndrome with a heterogeneous molecular basis. Until recently, the underlying cause was known in only a minority of cases that were associated with abnormalities of the tau protein or gene. In 2006, however, mutations in the progranulin gene were discovered as another important cause of familial FTD. That same year, TAR DNA-binding protein 43 (TDP-43) was identified as the pathological protein in the most common subtypes of FTD and amyotrophic lateral sclerosis (ALS). Since then, substantial efforts have been made to understand the functions and regulation of progranulin and TDP-43, as well as their roles in neurodegeneration. More recently, other DNA/RNA binding proteins (FET family proteins) have been identified as the pathological proteins in most of the remaining cases of FTD. In 2011, abnormal expansion of a hexanucleotide repeat in the gene C9orf72 was found to be the most common genetic cause of both FTD and ALS. All common FTD-causing genes have seemingly now been discovered and the main pathological proteins identified. In this Review, we highlight recent advances in understanding the molecular aspects of FTD, which will provide the basis for improved patient care through the development of more-targeted diagnostic tests and therapies.
Objective
Familial autosomal dominant frontotemporal dementia with ubiquitin-positive, tau-negative inclusions in the brain linked to 17q21-22 recently has been reported to carry null mutations in the progranulin gene (PGRN). Hereditary dysphasic disinhibition dementia (HDDD) is a frontotemporal dementia with prominent changes in behavior and language deficits. A previous study found significant linkage to chromosome 17 in a HDDD family (HDDD2), but no mutation in the MAPT gene. Longitudinal follow-up has enabled us to identify new cases and to further characterize the dementia in this family. The goals of this study were to develop research criteria to classify the different clinical expressions of dementia observed in this large kindred, to identify the causal mutation in affected individuals and correlate this with phenotypic characteristics in this pedigree, and to assess the neuropathological characteristics using immunohistochemical techniques.Methods
In this study we describe a detailed clinical, pathological and mutation analysis of the HDDD2 kindred.ResultsNeuropathologically, HDDD2 represents a familial frontotemporal lobar degeneration with ubiquitin-positive, tau-negative inclusions (FTLD-U). We developed research classification criteria and identified three distinct diagnostic thresholds, which helped localize the disease locus. The chromosomal region with the strongest evidence of linkage lies within the minimum critical region for FTLD-U. Sequencing of each exon of the PGRN gene led to the identification of a novel missense mutation, Ala-9 Asp, within the signal peptide.InterpretationHDDD2 is an FTLD-U caused by a missense mutation in the PGRN gene that cosegregates with the disease and with the disease haplotype in at-risk individuals. This mutation is the first reported pathogenic missense mutation in the signal peptide of the PGRN gene causing FTLD-U. In light of the previous reports of null mutations and its position in the gene, two possible pathological mechanisms are proposed: (1) the protein may accumulate within the endoplasmic reticulum due to inefficient secretion; and (2) mutant RNA may have a lower expression because of degradation via nonsense-mediated decay. Ann Neurol 2006;60:314–322
We performed hypothesis-free linkage analysis and exome sequencing in a family with two siblings who had neuronal ceroid lipofuscinosis (NCL). Two linkage peaks with maximum LOD scores of 3.07 and 2.97 were found on chromosomes 7 and 17, respectively. Unexpectedly, we found these siblings to be homozygous for a c.813_816del (p.Thr272Serfs∗10) mutation in the progranulin gene (GRN, granulin precursor) in the latter peak. Heterozygous mutations in GRN are a major cause of frontotemporal lobar degeneration with TDP-43 inclusions (FTLD-TDP), the second most common early-onset dementia. Reexamination of progranulin-deficient mice revealed rectilinear profiles typical of NCL. The age-at-onset and neuropathology of FTLD-TDP and NCL are markedly different. Our findings reveal an unanticipated link between a rare and a common neurological disorder and illustrate pleiotropic effects of a mutation in the heterozygous or homozygous states.
We collected a massive and heterogeneous dataset of 20 255 gene expression profiles (GEPs) from a variety of human samples and experimental conditions, as well as 8895 GEPs from mouse samples. We developed a mutual information (MI) reverse-engineering approach to quantify the extent to which the mRNA levels of two genes are related to each other across the dataset. The resulting networks consist of 4 817 629 connections among 20 255 transcripts in human and 14 461 095 connections among 45 101 transcripts in mouse, with a inter-species conservation of 12%. The inferred connections were compared against known interactions to assess their biological significance. We experimentally validated a subset of not previously described protein-protein interactions. We discovered co-expressed modules within the networks, consisting of genes strongly connected to each other, which carry out specific biological functions, and tend to be in physical proximity at the chromatin level in the nucleus. We show that the network can be used to predict the biological function and subcellular localization of a protein, and to elucidate the function of a disease gene. We experimentally verified that granulin precursor (GRN) gene, whose mutations cause frontotemporal lobar degeneration, is involved in lysosome function. We have developed an online tool to explore the human and mouse gene networks.
To assess the relative frequency of unique mutations and their associated characteristics in 97 individuals with mutations in progranulin (GRN), an important cause of frontotemporal lobar degeneration (FTLD).
A 46-site International Frontotemporal Lobar Degeneration Collaboration was formed to collect cases of FTLD with TAR DNA-binding protein of 43-kDa (TDP-43)-positive inclusions (FTLD-TDP). We identified 97 individuals with FTLD-TDP with pathogenic GRN mutations (GRN+ FTLD-TDP), assessed their genetic and clinical characteristics, and compared them with 453 patients with FTLD-TDP in which GRN mutations were excluded (GRN- FTLD-TDP). No patients were known to be related. Neuropathologic characteristics were confirmed as FTLD-TDP in 79 of the 97 GRN+ FTLD-TDP cases and all of the GRN- FTLD-TDP cases.
Age at onset of FTLD was younger in patients with GRN+ FTLD-TDP vs GRN- FTLD-TDP (median, 58.0 vs 61.0 years; P < .001), as was age at death (median, 65.5 vs 69.0 years; P < .001). Concomitant motor neuron disease was much less common in GRN+ FTLD-TDP vs GRN- FTLD-TDP (5.4% vs 26.3%; P < .001). Fifty different GRN mutations were observed, including 2 novel mutations: c.139delG (p.D47TfsX7) and c.378C>A (p.C126X). The 2 most common GRN mutations were c.1477C>T (p.R493X, found in 18 patients, representing 18.6% of GRN cases) and c.26C>A (p.A9D, found in 6 patients, representing 6.2% of cases). Patients with the c.1477C>T mutation shared a haplotype on chromosome 17; clinically, they resembled patients with other GRN mutations. Patients with the c.26C>A mutation appeared to have a younger age at onset of FTLD and at death and more parkinsonian features than those with other GRN mutations.
GRN+ FTLD-TDP differs in key features from GRN- FTLD-TDP.
Progranulin (GRN) haploinsufficiency is a frequent cause of familial frontotemporal dementia, a currently untreatable progressive neurodegenerative disease. By chemical library screening, we identified suberoylanilide hydroxamic acid (SAHA), a Food and Drug Administration-approved histone deacetylase inhibitor, as an enhancer of GRN expression. SAHA dose-dependently increased GRN mRNA and protein levels in cultured cells and restored near-normal GRN expression in haploinsufficient cells from human subjects. Although elevation of secreted progranulin levels through a post-transcriptional mechanism has recently been reported, this is, to the best of our knowledge, the first report of a small molecule enhancer of progranulin transcription. SAHA has demonstrated therapeutic potential in other neurodegenerative diseases and thus holds promise as a first generation drug for the prevention and treatment of frontotemporal dementia.
Numerous loss-of-function mutations in the progranulin (GRN) gene cause frontotemporal lobar degeneration with ubiquitin and TAR-DNA binding protein 43-positive inclusions by reduced production and secretion of GRN. Consistent with the observation that GRN has neurotrophic properties, pharmacological stimulation of GRN production is a promising approach to rescue GRN haploinsufficiency and prevent disease progression. We therefore searched for compounds capable of selectively increasing GRN levels. Here, we demonstrate that four independent and highly selective inhibitors of vacuolar ATPase (bafilomycin A1, concanamycin A, archazolid B, and apicularen A) significantly elevate intracellular and secreted GRN. Furthermore, clinically used alkalizing drugs, including chloroquine, bepridil, and amiodarone, similarly stimulate GRN production. Elevation of GRN levels occurs via a translational mechanism independent of lysosomal degradation, autophagy, or endocytosis. Importantly, alkalizing reagents rescue GRN deficiency in organotypic cortical slice cultures from a mouse model for GRN deficiency and in primary cells derived from human patients with GRN loss-of-function mutations. Thus, alkalizing reagents, specifically those already used in humans for other applications, and vacuolar ATPase inhibitors may be therapeutically used to prevent GRN-dependent neurodegeneration.
alpha-Synuclein is central in Parkinson's disease pathogenesis. Although initially alpha-synuclein was considered a purely intracellular protein, recent data suggest that it can be detected in the plasma and CSF of humans and in the culture media of neuronal cells. To address a role of secreted alpha-synuclein in neuronal homeostasis, we have generated wild-type alpha-synuclein and beta-galactosidase inducible SH-SY5Y cells. Soluble oligomeric and monomeric species of alpha-synuclein are readily detected in the conditioned media (CM) of these cells at concentrations similar to those observed in human CSF. We have found that, in this model, alpha-synuclein is secreted by externalized vesicles in a calcium-dependent manner. Electron microscopy and liquid chromatography-mass spectrometry proteomic analysis demonstrate that these vesicles have the characteristic hallmarks of exosomes, secreted intraluminar vesicles of multivesicular bodies. Application of CM containing secreted alpha-synuclein causes cell death of recipient neuronal cells, which can be reversed after alpha-synuclein immunodepletion from the CM. High- and low-molecular-weight alpha-synuclein species, isolated from this CM, significantly decrease cell viability. Importantly, treatment of the CM with oligomer-interfering compounds before application rescues the recipient neuronal cells from the observed toxicity. Our results show for the first time that cell-produced alpha-synuclein is secreted via an exosomal, calcium-dependent mechanism and suggest that alpha-synuclein secretion serves to amplify and propagate Parkinson's disease-related pathology.
Mutation in the progranulin gene (GRN) can cause frontotemporal dementia (FTD). However, it is unclear whether some rare FTD-related GRN variants are pathogenic and whether neurodegenerative disorders other than FTD can also be caused by GRN mutations.
To delineate the range of clinical presentations associated with GRN mutations and to define pathogenic candidacy of rare GRN variants.
Case-control study.
Clinical and neuropathology dementia research studies at 8 academic centers.
Four hundred thirty-four patients with FTD, including primary progressive aphasia, semantic dementia, FTD/amyotrophic lateral sclerosis (ALS), FTD/motor neuron disease, corticobasal syndrome/corticobasal degeneration, progressive supranuclear palsy, Pick disease, dementia lacking distinctive histopathology, and pathologically confirmed cases of frontotemporal lobar degeneration with ubiquitin-positive inclusions (FTLD-U); and 111 non-FTD cases (controls) in which TDP-43 deposits were a prominent neuropathological feature, including subjects with ALS, Guam ALS and/or parkinsonism dementia complex, Guam dementia, Alzheimer disease, multiple system atrophy, and argyrophilic grain disease.
Variants detected on sequencing of all 13 GRN exons and at least 80 base pairs of flanking introns, and their pathogenic candidacy determined by in silico and ex vivo splicing assays.
We identified 58 genetic variants that included 26 previously unknown changes. Twenty-four variants appeared to be pathogenic, including 8 novel mutations. The frequency of GRN mutations was 6.9% (30 of 434) of all FTD-spectrum cases, 21.4% (9 of 42) of cases with a pathological diagnosis of FTLD-U, 16.0% (28 of 175) of FTD-spectrum cases with a family history of a similar neurodegenerative disease, and 56.2% (9 of 16) of cases of FTLD-U with a family history.
Pathogenic mutations were found only in FTD-spectrum cases and not in other related neurodegenerative diseases. Haploinsufficiency of GRN is the predominant mechanism leading to FTD.
Progranulin is a secreted high molecular weight growth factor bearing seven and one half copies of the cysteine-rich granulin-epithelin motif. While inappropriate over-expression of the progranulin gene has been associated with many cancers, haploinsufficiency leads to atrophy of the frontotemporal lobes and development of a form of dementia (frontotemporal lobar degeneration with ubiquitin positive inclusions, FTLD-U) associated with the formation of ubiquitinated inclusions. Recent reports indicate that progranulin has neurotrophic effects, which, if confirmed would make progranulin the only neuroprotective growth factor that has been associated genetically with a neurological disease in humans. Preliminary studies indicated high progranulin gene expression in spinal cord motor neurons. However, it is uncertain what the role of Progranulin is in normal or diseased motor neuron function. We have investigated progranulin gene expression and subcellular localization in cultured mouse embryonic motor neurons and examined the effect of progranulin over-expression and knockdown in the NSC-34 immortalized motor neuron cell line upon proliferation and survival.
In situ hybridisation and immunohistochemical techniques revealed that the progranulin gene is highly expressed by motor neurons within the mouse spinal cord and in primary cultures of dissociated mouse embryonic spinal cord-dorsal root ganglia. Confocal microscopy coupled to immunocytochemistry together with the use of a progranulin-green fluorescent protein fusion construct revealed progranulin to be located within compartments of the secretory pathway including the Golgi apparatus. Stable transfection of the human progranulin gene into the NSC-34 motor neuron cell line stimulates the appearance of dendritic structures and provides sufficient trophic stimulus to survive serum deprivation for long periods (up to two months). This is mediated at least in part through an anti-apoptotic mechanism. Control cells, while expressing basal levels of progranulin do not survive in serum free conditions. Knockdown of progranulin expression using shRNA technology further reduced cell survival.
Neurons are among the most long-lived cells in the body and are subject to low levels of toxic challenges throughout life. We have demonstrated that progranulin is abundantly expressed in motor neurons and is cytoprotective over prolonged periods when over-expressed in a neuronal cell line. This work highlights the importance of progranulin as neuroprotective growth factor and may represent a therapeutic target for neurodegenerative diseases including motor neuron disease.
Mutations of the progranulin gene lead to progranulin haploinsufficiency and to frontotemporal lobar degeneration (FTD) with TDP-43 positive inclusions. It is assumed that unknown genetic, epigenetic and environmental factors are responsible for the observed marked degree of phenotypic variability among mutation carriers. This is the first published series of German FTD cases screened for progranulin mutations. Mean age at onset was 62 years, 19 patients (24%) had a positive family history of dementia, and 11 patients (14%) had a positive family history for probable FTD. Data on FTD subtypes are presented. Two mutations were identified (3%), one of which has been described previously. Clinically, both patients showed the frontal-behavioural variant type of FTD. Remarkably, a sibling of one case presented with progressive nonfluent aphasia, clinically distinct from the brother. We also performed quantitative PCR analyses to detect potential whole progranulin gene and exon deletions. Here, results were negative.
Mutations in the progranulin gene (GRN) are an important cause of frontotemporal lobar degeneration (FTLD) with ubiquitin and TAR DNA-binding protein 43 (TDP43)-positive pathology. The clinical presentation associated with GRN mutations is heterogeneous and may include clinical probable Alzheimer's disease. All GRN mutations identified thus far cause disease through a uniform disease mechanism, i.e. the loss of functional GRN or haploinsufficiency. To determine if expression of GRN in plasma could predict GRN mutation status and could be used as a biological marker, we optimized a GRN ELISA and studied plasma samples of a consecutive clinical FTLD series of 219 patients, 70 control individuals, 72 early-onset probable Alzheimer's disease patients and nine symptomatic and 18 asymptomatic relatives of GRN mutation families. All FTLD patients with GRN loss-of-function mutations showed significantly reduced levels of GRN in plasma to about one third of the levels observed in non-GRN carriers and control individuals (P < 0.001). No overlap in distributions of GRN levels was observed between the eight GRN loss-of-function mutation carriers (range: 53-94 ng/ml) and 191 non-GRN mutation carriers (range: 115-386 ng/ml). Similar low levels of GRN were identified in asymptomatic GRN mutation carriers. Importantly, ELISA analyses also identified one probable Alzheimer's disease patient (1.4%) carrying a loss-of-function mutation in GRN. Biochemical analyses further showed that the GRN ELISA only detects full-length GRN, no intermediate granulin fragments. This study demonstrates that using a GRN ELISA in plasma, pathogenic GRN mutations can be accurately detected in symptomatic and asymptomatic carriers. The approximately 75% reduction in full-length GRN, suggests an unbalanced GRN metabolism in loss-of-function mutation carriers whereby more GRN is processed into granulins. We propose that plasma GRN levels could be used as a reliable and inexpensive tool to identify all GRN mutation carriers in early-onset dementia populations and asymptomatic at-risk individuals.
The growth factor progranulin is as an important regulator of transformation in several cellular systems. We have previously demonstrated that progranulin acts as an autocrine growth factor and stimulates motility, proliferation and anchorage-independent growth of castration-resistant prostate cancer cells supporting the hypothesis that progranulin may play a critical role in prostate cancer progression. However, the mechanisms regulating progranulin action in castration-resistant prostate cancer cells have not been characterized. Sortilin, a single-pass type I transmembrane protein of the Vps10 family, binds progranulin in neurons and negatively regulates progranulin signaling by mediating progranulin targeting for lysosomal degradation. However, whether sortilin is expressed in prostate cancer cells and plays any role in regulating progranulin action has not been established. Here we show that sortilin is expressed at very low levels in castration-resistant PC3 and DU145 cells. Significantly, enhancing sortilin expression in PC3 and DU145 cells severely diminishes progranulin levels, and inhibits motility, invasion, proliferation and anchorage-independent growth. In addition, sortilin overexpression negatively modulates Akt stability. These results are recapitulated by depleting endogenous progranulin in PC3 and DU145 cells. On the contrary, targeting sortilin by shRNA approaches enhances progranulin levels and promotes motility, invasion and anchorage-independent growth. We dissected the mechanisms of sortilin action and demonstrated that sortilin promotes progranulin endocytosis through a clathrin-dependent pathway, sorting into early endosomes and subsequent lysosomal degradation. Collectively, these results point out a critical role for sortilin in regulating progranulin action in castration-resistant prostate cancer cells suggesting that sortilin loss may contribute to prostate cancer progression.
To investigate the patterns of brain atrophy, white matter (WM) tract changes, and functional connectivity (FC) abnormalities in asymptomatic granulin (GRN) mutation carriers.
Ten cognitively normal subjects (five mutation carriers, GRN+; years to estimated disease onset: 12 ± 7; five mutation noncarriers, GRN-) underwent a clinical and imaging (structural, diffusion tensor, and resting-state functional magnetic resonance imaging) assessment. Brain atrophy was measured with cortical thickness analysis, WM abnormalities with tract-based spatial statistics, and FC with independent component analysis.
GRN+ showed smaller cortical thickness than GRN- in the right orbitofrontal and precentral gyrus and left rostral middle frontal gyrus. WM tracts abnormalities were limited to increased axial diffusivity in the right cingulum, superior longitudinal fasciculus, and corticospinal tract. There were no differences in FC of resting-state networks.
Brain atrophy and WM tract abnormalities in frontal-parietal circuits can be detected at least a decade before the estimated symptom onset in asymptomatic mutation carriers.
An abnormal expansion of a GGGGCC hexanucleotide repeat in a non-coding region of the chromosome 9 open reading frame 72 gene (C9ORF72) is the most common genetic abnormality in familial and sporadic FTLD and ALS and the cause in most families where both, FTLD and ALS, are inherited. Pathologically, C9ORF72 expansion cases show a combination of FTLD-TDP and classical ALS with abnormal accumulation of TDP-43 into neuronal and oligodendroglial inclusions consistently seen in the frontal and temporal cortex, hippocampus and pyramidal motor system. In addition, a highly specific feature in C9ORF72 expansion cases is the presence of ubiquitin and p62 positive, but TDP-43 negative neuronal cytoplasmic and intranuclear inclusions. These TDP-43 negative inclusions contain dipeptide-repeat (DPR) proteins generated by unconventional repeat-associated translation of C9ORF72 transcripts with the expanded repeats and are most abundant in the cerebellum, hippocampus and all neocortex regions. Another consistent pathological feature associated with the production of C9ORF72 transcripts with expanded repeats is the formation of nuclear RNA foci that are frequently observed in the frontal cortex, hippocampus and cerebellum. Here, we summarize the complexity and heterogeneity of the neuropathology associated with the C9ORF72 expansion. We discuss implications of the data to the current classification of FTLD and critically review current insights from clinico-pathological correlative studies regarding the fundamental questions as to what processes are required and sufficient to trigger neurodegeneration in C9ORF72 disease pathogenesis.
Within the past decade, extracellular vesicles have emerged as important mediators of intercellular communication, being involved in the transmission of biological signals between cells in both prokaryotes and higher eukaryotes to regulate a diverse range of biological processes. In addition, pathophysiological roles for extracellular vesicles are beginning to be recognized in diseases including cancer, infectious diseases and neurodegenerative disorders, highlighting potential novel targets for therapeutic intervention. Moreover, both unmodified and engineered extracellular vesicles are likely to have applications in macromolecular drug delivery. Here, we review recent progress in understanding extracellular vesicle biology and the role of extracellular vesicles in disease, discuss emerging therapeutic opportunities and consider the associated challenges.
Objective
Mutations that lead to a loss of progranulin (PGRN) explain a considerable portion of the occurrence of frontotemporal lobar degeneration. We tested a biomarker allowing rapid detection of a loss of PGRN.Methods
We used an enzyme-linked immunosorbent assay to measure in serum the PGRN protein levels of six affected and eight unaffected carriers from within an extended Belgian founder family segregating the null mutation IVS1+5G>C. Further, we measured serum PGRN levels in 2 patients with another null mutation (a Met1 and a frameshift mutation), in 4 patients carrying a predicted pathogenic missense mutation and in 5 patients carrying a benign missense polymorphism, in 9 unaffected noncarrier relatives, and in 22 community controls.ResultsSerum PGRN levels were reduced in both affected and unaffected null mutation carriers compared with noncarrier relatives (pexact < 0.0001), and allowed perfect discrimination between carriers and noncarriers (sensitivity: 1.0; 1 − specificity: 0.0). Serum PGRN levels in Cys139Arg and Arg564Cys mutation carriers were significantly lower than in controls, but greater than in null mutation carriers, fitting the hypothesis of partial loss of function caused by these missense mutations. As expected, levels for carriers of benign missense polymorphisms were not significantly different from controls.InterpretationOur results indicate that the serum PGRN level is a reliable biomarker for diagnosing and early detection of frontotemporal lobar degeneration caused by PGRN null mutations, and provided the first in vivo evidence that at least some missense mutations in PGRN may lead to a (partial) loss of PGRN. Ann Neurol 2009
Cells continuously secrete a large number of microvesicles, macromolecular complexes, and small molecules into the extracellular space. Of the secreted microvesicles, the nanoparticles called exosomes are currently undergoing intense scrutiny. These are small vesicles (30-120 nm) containing nucleic acid and protein, perceived to be carriers of this cargo between diverse locations in the body. They are distinguished in their genesis by being budded into endosomes to form multivesicular bodies (MVBs) in the cytoplasm. The exosomes are released to extracellular fluids by fusion of these multivesicular bodies with the cell surface, resulting in secretion in bursts. Exosomes are secreted by all types of cells in culture, and also found in abundance in body fluids including blood, saliva, urine, and breast milk.
In this review, we summarize strategies for exosome isolation, our understanding to date of exosome composition, functions, and pathways, and discuss their potential for diagnostic and therapeutic applications.
Currently, the control of exosome formation, the makeup of the "cargo", biological pathways and resulting functions are incompletely understood. One of their most intriguing roles is intercellular communication--exosomes are thought to function as the messengers, delivering various effectors or signaling macromolecules between supposedly very specific cells.
Both seasoned and newer investigators of nanovesicles have presented various viewpoints on what exosomes are, with some differences but a large common area. It would be useful to develop a codified definition of exosomes in both descriptive and practical terms. We hope this in turns leads to a consistent set of practices for their isolation, characterization and manipulation.
It is well known that progranulin protein is involved in wound repair, inflammation, and tumor formation. The wedding between progranulin and brain was celebrated in 2006 with the involvement of progranulin gene (GRN) in Frontotemporal lobar degeneration (FTLD), the most common form of early-onset dementia: up to date, 75 mutations have been detected in FTLD patients as well as in patients with widely variable clinical phenotypes. All pathogenic GRN mutations identified thus far cause the disease through a uniform mechanism, i.e. loss of functional progranulin or haploinsufficiency. Studies on GRN knockout mice suggest that progranulin-related neurodegenerative diseases may result from lifetime depletion of neurotrophic support together with cumulative damage in association with dysregulated inflammation, thus highlighting possible new molecular targets for GRN-related FTLD treatment. Recently, the dosage of plasma progranulin has been proposed as a useful tool for a quick and inexpensive large-scale screening of affected and unaffected carriers of GRN mutations. Before it is systematically translated into clinical practice and, more importantly, included into diagnostic criteria for dementias, further standardization of plasma progranulin test and harmonization of its use are required. Once a specific treatment becomes available for these pathologies, this test - being applicable on large scale - will represent an important step towards personalized healthcare. This article is part of a Special Issue entitled: Brain Integration.
Recently, attention was drawn to a role for progranulin in the central nervous system with the identification of mutations in the progranulin gene (GRN) as an important cause of frontotemporal lobar degeneration. GRN mutations are associated with a strong reduction of circulating progranulin and widely variable clinical phenotypes: thus, the dosage of plasma progranulin is a useful tool for a quick and inexpensive large-scale screening of carriers of GRN mutations.
To establish the best cutoff threshold for normal versus abnormal levels of plasma progranulin.
309 cognitively healthy controls (25-87 years of age), 72 affected and unaffected GRN+ null mutation carriers (24-86 years of age), 3 affected GRN missense mutation carriers, 342 patients with neurodegenerative diseases and 293 subjects with mild cognitive impairment were enrolled at the Memory Clinic, IRCCS S. Giovanni di Dio-Fatebenefratelli, Brescia, Italy, and at the Alzheimer Unit, Ospedale Maggiore Policlinico and IRCCS Istituto Neurologico C. Besta, Milan, Italy. Plasma progranulin levels were measured using an ELISA kit (AdipoGen Inc., Seoul, Korea).
Plasma progranulin did not correlate with age, gender or body mass index. We established a new plasma progranulin protein cutoff level of 61.55 ng/ml that identifies, with a specificity of 99.6% and a sensitivity of 95.8%, null mutation carriers among subjects attending to a memory clinic. Affected and unaffected GRN null mutation carriers did not differ in terms of circulating progranulin protein (p = 0.686). A significant disease anticipation was observed in GRN+ subjects with the lowest progranulin levels.
We propose a new plasma progranulin protein cutoff level useful for clinical practice.
Recently, mutations in the progranulin gene (GRN) were reported to account for the vast majority of Frontotemporal lobar Degeneration (FTLD) and a growing number of reports describe the implication of this gene in the development of the FTLD pathology with a significant variation in clinical features. To better clarify the contribution of GRN mutations to Italian FTLD, we screened 381 subjects: 171 cases and 210 healthy subjects, all from Central Italy, particularly of Tuscan origins.
GRN gene was analyzed using High Resolution Melting Analysis and automated Genetic Analyzer. Human Progranulin ELISA Kit was employed to determine the plasma progranulin levels. The screening showed a total of six genetic variants in the GRN gene: 3 pathogenic and 3 non pathogenic in 13 out of 171 patients. The rare intronic variant IVS2 +7 G > A was found in one patient. The pathogenetic mutation, p.T272SfsX10, is confirmed as the most common GRN mutation in Italian FTLD patients with a frequency in our study of 2.32%. Moreover, we identified the first Italian patient with the p.R493X mutation, to date described in 43 families worldwide. Our data report, for the first time, the occurrence of GRN mutations in Tuscany, Central Italy, confirming that genetic variations in this gene could be a considerable genetic cause of FTLD and that genetic screening might be useful both in familial and sporadic FTLD patients.
Exosomes are microvesicles released into the extracellular medium upon fusion to the plasma membrane of endosomal intermediates called multivesicular bodies. They represent ways for discarding proteins and metabolites and also for intercellular transfer of proteins and RNAs. In the nervous system, it has been hypothesized that exosomes might be involved in the normal physiology of the synapse and possibly allow the trans-synaptic propagation of pathogenic proteins throughout the tissue. As a first step to validate this concept, we used biochemical and morphological approaches to demonstrate that mature cortical neurons in culture do indeed secrete exosomes. Using electron microscopy, we observed exosomes being released from somato-dendritic compartments. The endosomal origin of exosomes was demonstrated by showing that the C-terminal domain of tetanus toxin specifically endocytosed by neurons and accumulating inside multivesicular bodies, is released in the extracellular medium in association with exosomes. Finally, we found that exosomal release is modulated by glutamatergic synaptic activity, suggesting that this process might be part of normal synaptic physiology. Thus, our study paves the way towards the demonstration that exosomes take part in the physiology of the normal and pathological nervous system.
Oligomannosidic glycans play important roles in nervous system development and function. By performing a phage display screening with oligomannose-specific antibodies, we identified an oligomannose-mimicking peptide that was functionally active in modulating neurite outgrowth and neuron-astrocyte adhesion. Using the oligomannose-mimicking peptide in crosslinking experiments, synapsin I was identified as a novel oligomannose-binding protein in mouse brain. Further analyses not only verified that synapsin I is an oligomannose-binding lectin, but also indicated that it is a glycoprotein carrying oligomannose and Lewis(x). We also found that synapsin I is expressed in glia-enriched cultures and is released from glial cells via exosomes. Incubation of glial-derived exosomes in the presence of high KCl concentrations or subjecting glial cell cultures to either oxygen/glucose deprivation or hydrogen peroxide resulted in release of synapsin I from exosomes. Application of synapsin I promoted neurite outgrowth from hippocampal neurons and increased survival of cortical neurons upon hydrogen peroxide treatment or oxygen/glucose deprivation. Coculture experiments using wild-type hippocampal neurons and wild-type or synapsin-deficient glial cells showed enhanced neurite outgrowth when synapsin was expressed by glial cells. Synapsin-induced neurite outgrowth was dependent on oligomannose on synapsin I and the neural cell adhesion molecule NCAM at the neuronal cell surface. The data indicate that, under conditions of high neuronal activity and/or oxidative stress, synapsin can be released from glial-derived exosomes and promotes neurite outgrowth and neuronal survival by modulating the interactions between glia and neurons.
A new silicon chip for protein microarray development, fabrication and validation is proposed. The chip is made of two areas with oxide layers of different thicknesses: an area with a 500nm SiO(2) layer dedicated to interferometric label-free detection and quantification of proteins and an area with 100nm SiO(2) providing enhanced fluorescence. The chip allows, within a single experiment performed on the same surface, label-free imaging of arrayed protein probes coupled with high sensitivity fluorescence detection of the molecular interaction counterparts. Such a combined chip is of high practical utility during assay development process to image arrays, check consistency and quality of the protein array, quantify the amount of immobilized probes and finally detect fluorescence of bioassays.
Video abstract:
The most common inherited form of Frontotemporal Lobar Degeneration (FTLD) known stems from Progranulin (GRN) mutation and exhibits TDP-43 plus ubiquitin aggregates. Despite the causative role of GRN haploinsufficiency in FTLD-TDP, the neurobiology of this secreted glycoprotein is unclear. Here, we examined PGRN binding to the cell surface. PGRN binds to cortical neurons via its C terminus, and unbiased expression cloning identifies Sortilin (Sort1) as a binding site. Sort1⁻/⁻ neurons exhibit reduced PGRN binding. In the CNS, Sortilin is expressed by neurons and PGRN is most strongly expressed by activated microglial cells after injury. Sortilin rapidly endocytoses and delivers PGRN to lysosomes. Mice lacking Sortilin have elevations in brain and serum PGRN levels of 2.5- to 5-fold. The 50% PGRN decrease causative in FTLD-TDP cases is mimicked in GRN+/⁻ mice, and is fully normalized by Sort1 ablation. Sortilin-mediated PGRN endocytosis is likely to play a central role in FTLD-TDP pathophysiology.
Accumulating evidence shows that several cell types have the capacity to secrete membrane proteins by incorporating them into exosomes, which are small lipid vesicles derived from the intralumenal membranes of multivesicular bodies (MVBs) of the endocytic pathway. Exosomes are expelled in the extracellular space upon fusion of the MVB with the plasma membrane. Exosomal release is a way of secreting membrane proteins meant to be discarded, or to be passed on to other cells. Here, we demonstrate, using primary cortical cultures, that neurones and astrocytes can secrete exosomes. We find that exosomes released by cortical neurones contain the L1 cell adhesion molecule, the GPI-anchored prion protein, and the GluR2/3 but not the NR1 subunits of glutamate receptors. We also show that exosomal release is regulated by depolarisation. Our observation suggests that exosomes may have a regulatory function at synapses and could also allow intercellular exchange of membrane proteins within the brain.
It has recently become clear that proteins associated with neurodegenerative disorders can be selectively incorporated into intraluminal vesicles of multivesicular bodies and subsequently released within exosomes. Multiple lines of research support a neuroprotective role for cystatin C in Alzheimer's disease (AD). Herein we demonstrate that cystatin C, a protein targeted to the classical secretory pathway by its signal peptide sequence, is also secreted by mouse primary neurons in association with exosomes. Immunoproteomic analysis using SELDI-TOF MS revealed the presence in exosomes of at least 9 different cystatin C glycoforms. Moreover, the over-expression of familial AD-associated presenilin 2 mutations (PS2 M239I and PS2 T122R) resulted in reduced levels of all cystatin C forms (native and glycosylated) and of amyloid-β precursor protein (APP) metabolites within exosomes. A better understanding of the mechanisms involved in exosomal processing and release may have important implications for the fight against AD and other neurodegenerative diseases.
Mutations that lead to a loss of progranulin (PGRN) explain a considerable portion of the occurrence of frontotemporal lobar degeneration. We tested a biomarker allowing rapid detection of a loss of PGRN.
We used an enzyme-linked immunosorbent assay to measure in serum the PGRN protein levels of six affected and eight unaffected carriers from within an extended Belgian founder family segregating the null mutation IVS1+5G>C. Further, we measured serum PGRN levels in 2 patients with another null mutation (a Met1 and a frameshift mutation), in 4 patients carrying a predicted pathogenic missense mutation and in 5 patients carrying a benign missense polymorphism, in 9 unaffected noncarrier relatives, and in 22 community controls.
Serum PGRN levels were reduced in both affected and unaffected null mutation carriers compared with noncarrier relatives (p(exact) < 0.0001), and allowed perfect discrimination between carriers and noncarriers (sensitivity: 1.0; 1 - specificity: 0.0). Serum PGRN levels in Cys139Arg and Arg564Cys mutation carriers were significantly lower than in controls, but greater than in null mutation carriers, fitting the hypothesis of partial loss of function caused by these missense mutations. As expected, levels for carriers of benign missense polymorphisms were not significantly different from controls.
Our results indicate that the serum PGRN level is a reliable biomarker for diagnosing and early detection of frontotemporal lobar degeneration caused by PGRN null mutations, and provided the first in vivo evidence that at least some missense mutations in PGRN may lead to a (partial) loss of PGRN.
Mutations in the progranulin gene (PGRN) are a major cause of frontotemporal lobar degeneration (FTLD). Herein we estimated the contribution of the PGRN Leu271LeufsX10 mutation to FTLD and related disorders in the Brescia cohort. The PGRN Leu271LeufsX10 mutation was found in 31% of corticobasal syndrome (CBS), 29% of frontotemporal dementia with motorneuron disease (FTD-MND), 15% of behavioral variant frontotemporal dementia (FTD), 9.5% of primary progressive aphasia (PPA), 2% dementia with Lewy bodies and 0% of progressive supranuclear palsy and multiple system atrophy cases. The prevalence strongly increased in familial forms (75% CBS, 50% FTD-MND, 27% FTD, 18% PPA): in our cohort this mutation is a major disease determinant for FTLD-related disorders with a prominent motor component. MAPT haplotype was demonstrated to be a disease modifier in PGRN Leu271LeufsX10 carriers: in H1H2 subjects the disease onset was earlier than in H2H2 individuals. Sequencing of the whole PGRN gene disclosed a previously described mutation (c.2T>C, Met1X) and three novel ones (c.709-3; c.1011delG, His340ThrfsX21; c.1021C>T, Gln341X) in single families. In the Brescia cohort, while MAPT mutations have low prevalence, mutations in PGRN were shown in 28% of familial FTLD and 75% of familial CBS cases. The PGRN Leu271LeufsX10 mutation becomes one of the most common mutations worldwide, since it was identified in 38 patients belonging to 27 unrelated families.
Mutations in the progranulin gene (PGRN) were identified as the causal mechanism underlying frontotemporal lobar degeneration (FTLD). Most of these mutations are predicted to create null alleles leading to a 50% loss of progranulin transcript.
Patients underwent clinical and neurologic examination at the Memory Clinic of the IRCCS S. Giovanni di Dio-Fatebenefratelli, Brescia, Italy. We enrolled affected (n = 6) and unaffected at risk members (n = 73) of families carrying the FTLD associated progranulin Leu271LeufsX10 mutation; additionally, we included subjects affected by sporadic/familial FTLD (n = 65), controls (n = 75), and a family carrying the tau P301L mutation. The presence of mutations in PGRN and MAPT genes was investigated by direct sequencing of exonic and flanking intronic regions. Progranulin plasma and CSF levels were measured using ELISA.
We demonstrated that progranulin protein is strongly reduced (up to 3.93-fold) both in plasma and CSF of affected and unaffected subjects carrying mutations in progranulin gene (PGRN Leu271LeufsX10 and Q341X). We established a plasma progranulin protein cutoff level of 74.4 ng/mL that identifies, with specificity and sensitivity of 100%, mutation carriers among unaffected subjects. In FTLD, values <or=110.9 ng/mL give a specificity of 92.8% and a sensitivity of 100% for PGRN mutations.
We propose the dosage of plasma progranulin as a useful tool for a quick and inexpensive large-scale screening of carriers of progranulin mutations and for monitoring future treatments that might boost the level of this protein.
To improve clinical recognition and provide research diagnostic criteria for three clinical syndromes associated with frontotemporal lobar degeneration.
Consensus criteria for the three prototypic syndromes-frontotemporal dementia, progressive nonfluent aphasia, and semantic dementia-were developed by members of an international workshop on frontotemporal lobar degeneration. These criteria build on earlier published clinical diagnostic guidelines for frontotemporal dementia produced by some of the workshop members.
The consensus criteria specify core and supportive features for each of the three prototypic clinical syndromes and provide broad inclusion and exclusion criteria for the generic entity of frontotemporal lobar degeneration. The criteria are presented in lists, and operational definitions for features are provided in the text.
The criteria ought to provide the foundation for research work into the neuropsychology, neuropathology, genetics, molecular biology, and epidemiology of these important clinical disorders that account for a substantial proportion of cases of primary degenerative dementia occurring before the age of 65 years.