No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Protein Folding and Misfolding, Endoplasmic Reticulum Stress in Neurodegenerative Diseases: in Trace of Novel Drug Targets
Abstract
Alzheimer's disease (AD) is characterized by severe cognitive impairment and memory loss. AD is classified both into the "protein conformational" and the "endoplasmic reticulum-mitochondria stress" disorders. AD is a very complex, multifactorial disease of heterogeneous genetic and environmental background. The amyloid hypothesis of AD cannot fully explain the various clinical forms of the disease. Protein folding and misfolding in the endoplasmic reticulum (ER), and accumulation of several misfolded proteins (β-amyloid, Tau, alpha-synuclein, etc.) in ER and mitochondria (MT) may play a key role in the development of AD. Functional degradation of the synapse and the synapse holding neurites represents the first step in the pathogenesis of neurodegeneration. MT and ER are tightly coupled both physically and functionally with a special lipid raft called mitochondria-associated ER-membrane (MAM). MAM is crucial for Ca2+ signalling and metabolic regulation of the cell. In turn, the impairment of ER-MT interplay is a common mechanism of different neurodegenerative diseases. In this review, we discuss recent findings focusing on the protein conformational and metabolic dysfunction, and the role of MAM and ER-MT crosstalk in neurodegeneration.
... ROS-mediated insults to proteins may lead to cell death (Karbowski and Neutzner, 2012). Recently, it has been demonstrated that dysfunction of mitochondria-assisted ER membrane, as well as ER-mitochondria crosstalk, may contribute to a toxic cellular milieu (Penke et al., 2016). Calcium-induced protein misfolding is initiated by pathological conditions leading to excess glutamate in the synaptic cleft, resulting in overstimulation of NMDA receptors, which leads to intracellular calcium influx. ...
... Recently, a series of experiments have been conducted with old and novel drugs that can act on UPR and modulate the ER-MT Ca 2+ transfer. Studies have also demonstrated that a new chaperone co-inducer shows neuroprotective and precognitive effects and may serve as a novel AD drug candidate (Penke et al., 2016). ...
Protein folding is a complex, multisystem process characterized by heavy molecular and cellular footprints. Chaperone machinery enables proper protein folding and stable conformation. Other pathways concomitant with the protein folding process include transcription, translation, post-translational modifications, degradation through the ubiquitin-proteasome system, and autophagy. As such, the folding process can go awry in several different ways. The pathogenic basis behind most neurodegenerative diseases is that the disruption of protein homeostasis (i.e. proteostasis) at any level will eventually lead to protein misfolding. Misfolded proteins often aggregate and accumulate to trigger neurotoxicity through cellular stress pathways and consequently cause neurodegenerative diseases. The manifestation of a disease is usually dependent on the specific brain region that the neurotoxicity affects. Neurodegenerative diseases are age-associated, and their incidence is expected to rise as humans continue to live longer and pursue a greater life expectancy. We presently review the sequelae of protein misfolding and aggregation, as well as the role of these phenomena in several neurodegenerative diseases including Alzheimer’s disease, Huntington’s disease, amyotrophic lateral sclerosis, Parkinson’s disease, transmissible spongiform encephalopathies, and spinocerebellar ataxia. Strategies for treatment and therapy are also conferred with respect to impairing, inhibiting, or reversing protein misfolding.
... A rash of intracellular abnormalities are found in all the NDs: endoplasmic reticular, lysosomal and mitochondrial dysfunctions, diminished energy substrates like ATP, accumulation of reactive oxygen species and other toxic by-products, lowering of cellular pH, and defects in processes responsible for protein folding as well as the degradation and elimination of misfolded proteins [386][387][388][389][390][391][392][393][394][395]. The laundry list of cellular abnormalities in the NDs once again implicates a global energy deficit. ...
In this paper we examine 20th century conceptual developments regarding dementia and the NDs, from the first recognition of their clinical and pathological characteristics, through recognition of their molecular and cellular attributes and, ultimately, to recognition of their dynamic and vascular origins. We introduce a new energy based causal model of these disabling neurologic conditions that provides vital insights into their origins and necessary treatment. The term 'causal' implies that future treatment of these conditions necessarily entails recognition and correction of underlying energy deficits.
... Furthermore, most organisms are unable to regenerate neurons due to the terminally differentiated nature of these cells. To this end, neurons typically adopt robust responses to stressors evoked by accumulated misfolded proteins, particularly, in the setting of pathological conditions such as neurodegenerative diseases [6]. Damaged, misfolded, and unfolded proteins contribute to the storage and conformational anomalies within the ER [7,8], triggering the onset of ER stress, a process commonly seen in various neurodegenerative disorders including Alzheimer's disease (AD) and Parkinson's disease (PD) [9,10]. ...
Alzheimer’s disease (AD) is a devastating neurodegenerative disorder characterized by gradual loss of memory and cognitive function, which constitutes a heavy burden on the healthcare system globally. Current therapeutics to interfere with the underlying disease process in AD is still under development. Although many efforts have centered on the toxic forms of Aβ to effectively tackle AD, considering the unsatisfactory results so far it is vital to examine other targets and therapeutic approaches as well. The endoplasmic reticulum (ER) stress refers to the build-up of unfolded or misfolded proteins within the ER, thus, perturbing the ER and cellular homeostasis. Emerging evidence indicates that ER stress contributes to the onset and development of AD. A thorough elucidation of ER stress machinery in AD pathology may help to open up new therapeutic avenues in the management of this devastating condition to relieve the cognitive dementia symptoms. Herein, we aim at deciphering the unique role of ER stress in AD pathogenesis, reviewing key findings, and existing controversy in an attempt to summarize plausible therapeutic interventions in the management of AD pathophysiology.
... There is increasing evidence that the generation and untimely clearance of large amounts of misfolded proteins play an important role in the pathogenesis of AD [38]. The ubiquitin-proteasome system (UPS) and autophagy pathways are the main degradation mechanisms of intracellular proteins. ...
Alzheimer’s disease (AD) is the most prevalent neurodegenerative disease in the world. However, there is no effective drug to cure it. Caesalmin C is a cassane-type diterpenoid abundant in Caesalpinia bonduc (Linn.) Roxb. In this study, we investigated the effect of caesalmin C on Aβ-induced toxicity and possible mechanisms in the transgenic Caenorhabditis elegans AD model. Our results showed that caesalmin C significantly alleviated the Aβ-induced paralysis phenotype in transgenic CL4176 strain C. elegans. Caesalmin C dramatically reduced the content of Aβ monomers, oligomers, and deposited spots in AD C. elegans. In addition, mRNA levels of sod-3, gst-4, and rpt-3 were up-regulated, and mRNA levels of ace-1 were down-regulated in nematodes treated with caesalmin C. The results of the RNAi assay showed that the inhibitory effect of caesalmin C on the nematode paralysis phenotype required the DAF-16 signaling pathway, but not SKN-1 and HSF-1. Further evidence suggested that caesalmin C may also have the effect of inhibiting acetylcholinesterase (AchE) and upregulating proteasome activity. These findings suggest that caesalmin C delays the progression of AD in C. elegans via the DAF-16 signaling pathway and that it could be developed into a promising medication to treat AD.
... ER and oxidative stress have been implicated as important contributors to chronic inflammatory diseases, including inflammatory bowel disease (IBD). 7,[12][13][14][15][16][17][18][19][20] Multiple experimental mouse models have reproduced the ER stress, oxidative stress, and decreased mucin production observed in patients, which demonstrate a causative role for ER stress in intestinal inflammation. 4,[21][22][23][24][25][26][27][28][29][30][31][32] Compounds commonly used in animal models of colitis, including 2,4,6-Trinitrobenzenesulfonic acid (TNBS) and dextran-sodium-sulfate (DSS), activate ER stress. ...
Endoplasmic reticulum (ER) stress compromises the secretion of MUC2 from goblet cells and has been linked with inflammatory bowel disease (IBD). Although Bifidobacterium can beneficially modulate mucin production, little work has been done investigating the effects of Bifidobacterium on goblet cell ER stress. We hypothesized that secreted factors from Bifidobacterium dentium downregulate ER stress genes and modulates the unfolded protein response (UPR) to promote MUC2 secretion. We identified by mass spectrometry that B. dentium secretes the antioxidant γ-glutamylcysteine, which we speculate dampens ER stress-mediated ROS and minimizes ER stress phenotypes. B. dentium cell-free supernatant and γ-glutamylcysteine were taken up by human colonic T84 cells, increased glutathione levels, and reduced ROS generated by the ER-stressors thapsigargin and tunicamycin. Moreover, B. dentium supernatant and γ-glutamylcysteine were able to suppress NF-kB activation and IL-8 secretion. We found that B. dentium supernatant, γ-glutamylcysteine, and the positive control IL-10 attenuated the induction of UPR genes GRP78, CHOP, and sXBP1. To examine ER stress in vivo, we first examined mono-association of B. dentium in germ-free mice which increased MUC2 and IL-10 levels compared to germ-free controls. However, no changes were observed in ER stress-related genes, indicating that B. dentium can promote mucus secretion without inducing ER stress. In a TNBS-mediated ER stress model, we observed increased levels of UPR genes and pro-inflammatory cytokines in TNBS treated mice, which were reduced with addition of live B. dentium or γ-glutamylcysteine. We also observed increased colonic and serum levels of IL-10 in B. dentium- and γ-glutamylcysteine-treated mice compared to vehicle control. Immunostaining revealed retention of goblet cells and mucus secretion in both B. dentium- and γ-glutamylcysteine-treated animals. Collectively, these data demonstrate positive modulation of the UPR and MUC2 production by B. dentium-secreted compounds.
... Endoplasmic reticulum (ER) stress is thought to drive the pathology of multiple chronic neurological disorder due to its potential to promote neuronal dysfunction [45,46]. For decades, ER stress has also been proved to disturb neuronal function in the central nervous system and contribute to cognitive impairment [47]. Recently, the contribution of ER stress to DACD has also been reported [48]. ...
Diabetes-associated cognitive dysfunction (DACD) characterized by hippocampal injury increases the risk of major cerebrovascular events and death. Endoplasmic reticulum (ER) stress and synaptic dysfunction play vital roles in the pathological process. At present, no specific treatment exists for the prevention and/or the therapy of DACD. We have recently reported that hydrogen sulfide (H2S) exhibits therapeutic potential for DACD, but the underlying mechanism has not been fully elucidated. Silent information regulator 1 (SIRT1) has been shown to play a role in regulating the progression of diabetes and is also indispensable for memory formation and cognitive performance. Hence, the present study was performed to explore whether SIRT1 mediates the protective effect of H2S on streptozotocin (STZ)-induced cognitive deficits, an in vivo rat model of DACD, via inhibiting hippocampal ER stress and synaptic dysfunction. The results showed that administration of NaHS (an exogenous H2S donor) increased the expression of SIRT1 in the hippocampus of STZ-induced diabetic rats. Then, results proved that sirtinol, a special blocker of SIRT1, abrogated the inhibition of NaHS on STZ-induced cognitive deficits, as appraised by Morris water maze test, Y-maze test, and Novel object recognition behavioral test. In addition, administration of NaHS eliminated STZ-induced ER stress as evidenced by the decreases in the expressions of ER stress-related proteins including glucose-regulated protein 78, C/EBP homologous protein, and cleaved caspase-12 in the hippocampus, while these effects of NaHS were also reverted by sirtinol. Furthermore, the NaHS-induced up-regulation of hippocampal synapse-related protein (synapsin-1, SYN1) expression in STZ-induced diabetic rats was also abolished by sirtinol. Taken together, these results demonstrated that SIRT1 mediates the protection of H2S against cognitive dysfunction in STZ-diabetic rats partly via inhibiting hippocampal ER stress and synaptic dysfunction.
Graphic Abstract
... As the dopaminergic neurons die, patients with PD progressively exhibit motor symptoms-resting tremor, muscular rigidity, bradykinesia, sympathetic instability, and the like-which severely degrade their quality of life [5]. Despite the rapid advancement in elemental research on the molecular mechanisms of PD pathogenesis over the past decades, systemic and effective treatment strategies for treating this disease are yet to be found [6,7]. Recent studies have identified the presence of many dying neurons that exhibit chromatin condensation, DNA fragmentation, morphological changes, and engulfment of apoptotic bodies, in the dopaminergic neurons of autoptic brains of PD patients [8]. ...
Parkinson’s disease (PD) is an incurable progressive disorder resulting from neurodegeneration, and apoptosis is considered a dominant mechanism underlying the process of neurodegeneration. MicroRNAs (miRNAs), which are small and noncoding RNAs involved in many a biological process like apoptosis and regulation of gene expressions, have been found in postmortem brain samples of patients with PD, as well as in vitro and in vivo models of PD. To explore the impact of miR-15b-5p and Akt3 on apoptosis in the progression of PD, the method of quantitative reverse transcription polymerase chain reaction (qRT-PCR) was employed, and the analysis result showed upregulated expression of miR-15b-5p and downregulated expression of Akt3 in the serum of PD patients, MPP+-induced SH-SY5Y cells, and the brain tissues of MPTP-induced mice. Meanwhile, the dual-luciferase reporter assay was used to demonstrate the regulator-target interaction between miR-15b-5p and Akt3; flow cytometry and spectrophotometry revealed that transfection of miR-15b-5p mimic and si-Akt3 increased the rate of apoptosis and caspase-3 activity, whereas transfecting the miR-15b-5p inhibitor and Akt3-overexpression plasmid repressed the rate of apoptosis and caspase-3 activity in the MPP+-induced SH-SY5Y cell model and the MPTP-induced mouse model. Additionally, analysis of western blotting (WB) assays in vivo and in vitro revealed that proapoptosis proteins (Bax, caspase-3, GSK-3β, and β-catenin) showed markedly upregulated expression in the miR-15b-5p inhibitor and si-Akt3-overexpression groups, while the expression of an antiapoptosis gene (i.e., Bcl2) was downregulated. These analysis results indicate that downregulation of miR-15b-5p by targeting the Akt3-mediated GSK-3β/β-catenin signaling pathway would repress cell apoptosis in PD in vivo and in vitro. It is expected that the research findings would help find new therapeutic targets for treatment of PD.
... Las enfermedades neurodegenerativas pueden ser definidas como alteraciones consistentes en la pérdida selectiva de neuronas, acompañada de una implicación distintiva de sistemas funcionales que define la presentación clínica. (12,13) Numerosas evidencias experimentales recientes han demostrado que un número significativo de enfermedades neurodegenerativas se debe al mal plegamiento, agregación y acumulación de proteínas dentro de las neuronas o en el parénquima cerebral. (2,14) Estas enfermedades se agrupan bajo el concepto de proteinopatías del sistema nervioso. ...
Introducción:
Varias proteinopatías del sistema nervioso están asociadas a la ocurrencia de alteraciones en componentes del eje hipotálamo-hipófisis-gonadal.
Objetivo:
Reflejar la relevancia de componentes del eje hipotálamo-hipófisis-gonadal en la fisiopatología de proteinopatías del sistema nervioso.
Material y Métodos:
Se realizó una revisión bibliográfica durante los meses de enero de 2018 a diciembre de 2018. Fueron consultadas bases de datos de referencia, con el uso de descriptores y operadores booleanos. La estrategia de búsqueda avanzada para la selección de los artículos fue empleada, teniendo en cuenta la calidad metodológica o validez de los estudios.
Desarrollo:
Fueron identificaron alteraciones del funcionamiento normal del eje hipotálamo-hipófisis-gonadal en varias proteinopatías del sistema nervioso. Las alteraciones más frecuentemente reportadas fueron el incremento en los niveles de gonadotropinas, principalmente de la hormona luteinizante, en la enfermedad de Alzheimer, y la disminución de los niveles de testosterona en las enfermedades de Alzheimer, Parkinson, Huntington y Esclerosis Lateral Amiotrófica, con el consiguiente agravamiento del fenotipo clínico. Se obtuvieron evidencias de naturaleza preliminar, que fundamentan la posible ocurrencia de disfunción hipotalámica en pacientes con ataxias espinocerebelosas.
Conclusiones:
Aun cuando existen evidencias que demuestran la existencia de un vínculo entre la fisiopatología de proteinopatías del sistema nervioso y alteraciones en componentes del eje hipotálamo-hipófisis-gonadal, se requerirán estudios más extensos e integrales para confirmar estas asociaciones y para caracterizar los mecanismos moleculares implicados.
... Tal como se mencionó anteriormente, la creación de nuevas proteínas es el resultado de la combinación de aminoácidos encadenados que se pliegan de forma regular hasta un estado tridimensional final que les permita ser funcionales, este proceso de plegamiento no está exento de fallas, durante el plegamiento se producen aberraciones que evitan que una proteína llegue a su estadio final, lo que desemboca en la producción de una proteína no terminada que será disfuncional a sus propósitos. Estas fallas de ser constantes conllevan a resultados biológicos desastrosos en los seres vivientes, tales como el Alzheimer [4], la enfermedad de Huntington [5], inmunodeficiencias, parkinson, fibrosis quística entre muchas otras. ...
INTRODUCCIÓN: Las proteínas son una de las moléculas orgánicas que cumplen funciones vitales en la mantención de la vida y reproducción celular, su fabricación es un proceso complejo gobernado por una secuencia de plegamientos aún desconocida. En el contexto del Covid19, la iniciativa Folding@home llevó a cabo un proyecto de computación distribuida que permite la simulación del proceso de plegamiento de la proteína Spike del Covid19, cuya función es acoplarse al receptor ACE2 de las células animales y así penetrar a la célula y utilizar su maquinaria para reproducirse. OBJETIVO: Probar que el tiempo computacional ocioso disponible en los laboratorios de informática educacionales, puede ser usado para la simulación del plegamiento de proteínas. MÉTODO: Esta fue una investigación descriptiva donde se instaló un software cliente en computadores de gama baja que continuamente enviaron unidades de trabajo de plegamiento proteico a un servidor central. RESULTADOS: Tras 90 días de trabajo, un clúster de 27 PCs finalizaron 1993 unidades de trabajo de simulación de la proteína Spike. DISCUSIÓN Y CONCLUSIONES: A pesar de que el piloteo fue un éxito, se advierte que el software cliente debe ser optimizado para sacar el máximo de provecho a los diferentes procesadores y sistemas operativos con los cuales es compatible el software de computación distribuida proveído por Folding@home.
... In this respect, recent findings show a link between protein conformational anomalies and metabolic dysfunction, and the role of MAM and ER-mitochondria c rosstalk in neurodegeneration. (147) . ...
Metabolic syndrome (MetS) consists of a constellation of metabolic abnormalities such as central obesity, impaired fasting glucose, hypertriglyceridemia, low HDL cholesterol and hypertension. Cardiovascular diseases are the primary clinical outcome of MetS whereas endothelial dysfunction represents a primary disturbance in cardiovascular events. Recently, it has been shown that microparticles (MPs), small membrane vesicles released from the plasma membrane of activated and/or apoptotic cells, are involved in the pathogenesis of MetS by inducing endothelial dysfunction through the decrease of nitric oxide (NO) production. Also, MPs from apoptotic T cells induce endothelial dysfunction by decreasing NO production. However, the mechanism through which this endothelial dysfunction takes place is not completely elucidated. Thus, the objective of this study is to study the mechanisms through which human MPs induce endothelial dysfunction.
... ER stress occurs in different pathological conditions, including ischemia, hypoxia, altered glycosylation, nutrient deprivation, oxidative stress and Ca 2+ depletion of ER stores; and consequently activates ER membrane-associated proteins and complex downstream signaling pathways to regulate targeted gene expression [3]. Studies have demonstrated that chronic ER stress performs a role in the pathogenesis of diseases including atherosclerosis [4], hypertension [5], diabetes mellitus and obesity, as well as the associated vascular dysfunctions [6], neurological disorders [7] and cancer [8]. Moreover, several drugs and natural compounds have been identified to reduce ER stress and thereby show protective effects against ER stressassociated pathologies. ...
... In this regard, the modulation of the ER -related quality control mechanisms via activation of protective and adaptive UPR responses, and/or the inhibition of the apoptotic pathways emerge as significant strategies. 58 Drawing on chemical chaperones such as 4-phenylbutyric acid (PBA), tauroursodeoxycholic acid (TUDCA) or trimethylamine oxide (TMAO) may be beneficial as these compounds improve ER folding capacity and stabilize protein conformation. 59 In an AD mouse model, PBA was shown to enhance ER functioning, thwart A accumulation, and avoid the loss of dendritic spines and memory. ...
The Endoplasmic reticulum (ER), an indispensable sub-cellular component of the eukaryotic cell carries out essential functions, is critical to the survival of the organism.
The chaperone proteins and the folding enzymes which are multi-domain ER effectors
carry out 3-dimensional conformation of nascent polypeptides and check misfolded protein aggregation, easing the exit of functional proteins from the ER. Diverse conditions,
for instance redox imbalance, alterations in ionic calcium levels, and inflammatory signaling can perturb the functioning of the ER, leading to a build-up of unfolded or misfolded proteins in the lumen. This results in ER stress, and aiming to reinstate protein
homeostasis, a well conserved reaction called the unfolded protein response (UPR) is
elicited. Equally, in protracted cellular stress or inadequate compensatory reaction,
UPR pathway leads to cell loss. Dysfunctional ER mechanisms are responsible for neuronal degeneration in numerous human diseases, for instance Alzheimer’s, Parkinson’s
and Huntington’s diseases. In addition, mounting proof indicates that ER stress is incriminated in psychiatric diseases like major depressive disorder, bipolar disorder, and
schizophrenia. Accumulating evidence suggests that pharmacological agents regulating the working of ER may have a role in diminishing advancing neuronal dysfunction
in neuropsychiatric disorders. Here, new findings are examined which link the foremost mechanisms connecting ER stress and cell homeostasis. Furthermore, a supposed
new pathogenic model of major neuropsychiatry disorders is provided, with ER stress
proposed as the pivotal step in disease development.
... Alzheimer's disease (AD) is a common neurodegenerative disease affecting the aged populations, and it is classified under protein misfolding disorders (PMDs), where amyloid -β and tau proteins accumulate and aggregate in the brain, leading to altered synaptic function and neuronal death (Penke et al. 2016). Various environmental toxins including aluminum (Al) are considered as the potent risk factor that contributes to the development of Alzheimer's disease (AD) (Platt 2006). ...
The neuroprotective role of tannoid principles of Emblica officinalis (EoT), an Indian and Chinese traditional medicinal plant against memory loss in aluminum chloride-induced in vivo model of Alzheimer’s disease through attenuating AChE activity, oxidative stress, amyloid and tau toxicity, and apoptosis, was recently reported in our lab. However, to further elucidate the mechanism of neuroprotective effect of EoT, the current study was designed to evaluate endoplasmic reticulum stress-suppressing and anti-inflammatory role of EoT in PC 12 and SH-SY 5Y cells. These cells were divided into four groups: control (aluminum maltolate (Al(mal)3), EoT + Al(mal)3, and EoT alone based on 3-(4, 5-dimethyl 2-yl)-2, and 5-diphenyltetrazolium bromide (MTT) assay. EoT significantly reduced Al(mal)3-induced cell death and attenuated ROS, mitochondrial membrane dysfunction, and apoptosis (protein expressions of Bax; Bcl-2; cleaved caspases 3, 6, 9, 12; and cytochrome c) by regulating endoplasmic reticulum stress (PKR-like ER kinase (PERK), α subunit of eukaryotic initiation factor 2 (EIF2-α), C/EBP-homologous protein (CHOP), and high-mobility group box 1 protein (HMGB1)). Moreover, inflammatory response (NF-κB, IL-1β, IL-6, and TNF-α) and Aβ toxicity (Aβ1–42) triggered by Al(mal)3 was significantly normalized by EoT. Our results suggested that EoT could be a possible/promising and novel therapeutic lead against Al-induced neurotoxicity. However, further extensive research is needed to prove its efficacy in clinical studies.
... Recently, they wrote another review, which describes "common or generic features of fibrils, from a physicochemical, biochemical, genetic, and biological angle, with particular emphasis on the observations and principles that emerge from the study of multiple protein and disease systems" [3]. There and many recent review articles which describe the structure, mechanism of formation and functions of amyloid fibril [15][16][17][18]. ...
Arranging into well-organized fibrillar aggregate, commonly known as amyloid fibril is an inherent property of any polypeptide chain. Amyloid fibrils are associated with a number of severe human pathologies like the Alzheimer's disease, Parkinson's disease, type2 diabetes and many more. Recent studies suggest that most of the fibrils are inert and extremely stable, thus could be used for the bio-nanotechnological applications. As the native state is protected by evolution from aggregation under physiological condition, understanding the structure of aggregation precursor state (APS) will be of extreme importance to decode mechanism of its formation and prevention. This review article includes the recent studies of identification and characterization of possible conformations of proteins which can act as APS. The literature regarding the research in this field revealed that any conformation ranging from native-like state to completely unfolded state could be an APS. The structural characteristics of the APS depend on the protein and on its surrounding environment. From this review of literatures, we conclude that exposure of aggregation-prone segments is the requirement for amyloid fibril formation and the amyloid state seems to be the most stable known physical state of the proteins. This means all conformations of proteins with exposed aggregation-prone segments can promote intermolecular interactions and channel to amyloid fibril pathway to acquire their minimum energy state.
... CCAATenhancer-binding protein homologous protein (CHOP) is a downstream effector of the PERK pathway that functions as a pro-apoptotic factor (Jiang et al., 2012). Previous studies have shown that ER stress activates caspase-12 to induce cell apoptosis (Kim et al., 2010;Penke et al., 2016). However, and it is not known whether ER stress and apoptosis contribute to ICHinduced SBI. ...
The protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK) signaling pathway was reported to exert an important role in neuronal apoptosis. The present study was designed to investigate the roles of the PERK signaling pathway in the secondary brain injury (SBI) induced by intracerebral hemorrhage (ICH) and its potential mechanisms. Sprague–Dawley rats were used to establish ICH models by injecting autologous blood (100 μl), and cultured primary rat cortical neurons were exposed to oxyhemoglobin (10 μM) to mimic ICH in vitro. The PERK antagonist, GSK2606414, and inhibitor of eukaryotic translation initiation factor 2 subunit α (eIF2α) dephosphorylation, salubrinal, were used to study the roles of PERK signaling pathway in ICH-induced SBI. Our results showed that the protein levels of p-eIF2α and ATF4 were upregulated following ICH, peaking at 48 h. Application of GSK2606414 reversed this increase in vivo and in vitro, thereby preventing ICH-induced neuronal apoptosis. On the contrary, salubrinal inhibited the dephosphorylation of eIF2α, resulting in the elevation of p-eIF2α, which could activate downstream of PERK signaling and induce neuronal apoptosis and necrosis following ICH in vitro and in vivo. Thus, PERK signaling pathway plays an important role in ICH-induced apoptosis and blocking its activation has neuroprotective effects that alleviates SBI, suggesting that targeting this pathway could be a promising therapeutic strategy for improving patient outcome after ICH.
... Alzheimer's disease (AD) and the other protein conformational diseases are caused by misfolding and aggregation of proteins and by the accumulation of intracellular and extracellular deposits [1]. Formation of toxic β-amyloid (Aβ) oligomers plays a pivotal role in AD pathogenesis [2]. ...
Intracellular β-amyloid (Aβ) accumulation is an early event in Alzheimer's disease (AD) progression. Recently, it has been uncovered that presenilins (PSs), the key components of the amyloid precursor protein (APP) processing and the β-amyloid producing γ-secretase complex, are highly enriched in a special sub-compartment of the endoplasmic reticulum (ER) functionally connected to mitochondria, called mitochondria-associated ER membrane (MAM). A current hypothesis of pathogenesis of Alzheimer's diseases (AD) suggests that MAM is involved in the initial phase of AD. Since MAM supplies mitochondria with essential proteins, the increasing level of PSs and β-amyloid could lead to metabolic dysfunction because of the impairment of ER-mitochondrion crosstalk. To reveal the early molecular changes of this subcellular compartment in AD development MAM fraction was isolated from the cerebral cortex of 3 months old APP/PS1 mouse model of AD and age-matched C57BL/6 control mice, then mass spectrometry-based quantitative proteome analysis was performed. The enrichment and purity of MAM preparations were validated with EM, LC-MS/MS and protein enrichment analysis. Label-free LC-MS/MS was used to reveal the differences between the proteome of the transgenic and control mice. We obtained 77 increased and 49 decreased protein level changes in the range of - 6.365 to + 2.988, which have mitochondrial, ER or ribosomal localization according to Gene Ontology database. The highest degree of difference between the two groups was shown by the ATP-binding cassette G1 (Abcg1) which plays a crucial role in cholesterol metabolism and suppresses Aβ accumulation. Most of the other protein changes were associated with increased protein synthesis, endoplasmic-reticulum-associated protein degradation (ERAD), oxidative stress response, decreased mitochondrial protein transport and ATP production. The interaction network analysis revealed a strong relationship between the detected MAM protein changes and AD. Moreover, it explored several MAM proteins with hub position suggesting their importance in Aβ induced early MAM dysregulation. Our identified MAM protein changes precede the onset of dementia-like symptoms in the APP/PS1 model, suggesting their importance in the development of AD.
... Our data show that in young (5-month-old) animals, pharmacological as well as genetic Segev et al., 2013Segev et al., , 2015Segev et al., , 2016Wang et al., 2013b). Recent publications have 495 highlighted PERK as a potential therapeutic target for several neurodegenerative diseases such as 496 prion disease, AD, and fronto-temporal dementia ( Moreno et al., 2012;Ma et al., 2013;Devi and 497 Ohno, 2014;Radford et al., 2015;Penke et al., 2016). One possible mechanism through which 498 PERK is thought to mediate brain diseases in aging is via its role in the regulation of the Ma et al., 2013;Moreno et al., 2013). ...
Abstract
Protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK) is one of four known kinases that respond to cellular stress by deactivating the eukaryotic initiation factor 2 alpha (eIF2α) or other signal transduction cascades. Recently, both eIF2α and its kinases were found to play a role in normal and pathological brain function. Here, we show that reduction of either the amount or the activity of PERK, specifically in the CA1 region of the hippocampus in young adult male mice, enhances neuronal excitability and improves cognitive function. In addition, this manipulation rescues the age-dependent cellular phenotype of reduced excitability and memory decline. Specifically, the reduction of PERK expression in the CA1 region of the hippocampus of middle-aged male mice using a viral vector rejuvenates hippocampal function and improves hippocampal-dependent learning. These results delineate a mechanism for behavior and neuronal aging and position PERK as a promising therapeutic target for age-dependent brain malfunction.
Significance Statement
We found that (1) local reduced PERK expression or activity in the hippocampus enhances neuronal excitability and cognitive function in young normal mice, (2) old CA1 pyramidal cells have reduced excitability and an increased PERK expression, which can be rescued by reducing PERK expression in the hippocampus, and (3) reducing PERK expression in the hippocampus of middle-aged mice enhances hippocampal-dependent learning and memory and restores it to normal performance levels of young mice. These findings uncover an entirely new biological link among PERK, neuronal intrinsic properties, aging, and cognitive function. Moreover, our findings propose a new way to fight mild cognitive impairment and aging-related cognitive deterioration.
... Aggregation of specific proteins into protein inclusions and plaques is characteristic for many neurodegenerative diseases (NDDs), including AD, Parkinson's (PD), Huntington's disease (HD) and amyotrophic lateral sclerosis (ALS). Table 1 summarizes the short list of some NDDs and their corresponding misfolded proteins [3]. ...
Protein dyshomeostasis is the common mechanism of neurodegenerative diseases such as Alzheimer’s disease (AD). Aging is the key risk factor, as the capacity of the proteostasis network declines during aging. Different cellular stress conditions result in the up-regulation of the neurotrophic, neuroprotective amyloid precursor protein (APP). Enzymatic processing of APP may result in formation of toxic Aβ aggregates (β-amyloids). Protein folding is the basis of life and death. Intracellular Aβ affects the function of subcellular organelles by disturbing the endoplasmic reticulum-mitochondria cross-talk and causing severe Ca2+-dysregulation and lipid dyshomeostasis. The extensive and complex network of proteostasis declines during aging and is not able to maintain the balance between production and disposal of proteins. The effectivity of cellular pathways that safeguard cells against proteotoxic stress (molecular chaperones, aggresomes, the ubiquitin-proteasome system, autophagy) declines with age. Chronic cerebral hypoperfusion causes dysfunction of the blood-brain barrier (BBB), and thus the Aβ-clearance from brain-to-blood decreases. Microglia-mediated clearance of Aβ also declines, Aβ accumulates in the brain and causes neuroinflammation. Recognition of the above mentioned complex pathogenesis pathway resulted in novel drug targets in AD research.
... Caspase-12 knockout mice are resistant to ERS-induced apoptosis . ERS also induces mitochondrial dysfunction, caspase activation, and apoptosis via organelle crosstalk between the endoplasmic reticulum and mitochondria (Penke et al. 2016). Ample empirical evidence suggests that mitochondria dysfunction evoked by genetic and environmental factors that are associated with PD plays key roles in dopaminergic neuronal loss (reviewed by Camilleri and Vassallo 2014). ...
Endoplasmic reticulum stress (ERS) and mitochondrial dysfunctions are thought to be involved in the dopaminergic neuronal death in Parkinson's disease (PD). In this study, we found that isorhynchophylline (IRN) significantly attenuated 1-methyl-4-phenylpyridinium (MPP(+))-induced apoptotic cell death and oxidative stress in PC12 cells. IRN markedly reduced MPP(+)-induced-ERS responses, indicative of inositol-requiring enzyme 1 (IRE1) phosphorylation and caspase-12 activation. Furthermore, IRN inhibits MPP(+)-triggered apoptosis signal-regulating kinase 1 (ASK1)/c-Jun N-terminal Kinase (JNK) signaling-mediated mitochondria-dependent apoptosis pathway. IRN-mediated attenuation of endoplasmic reticulum modulator caspase-12 activation was abolished by diphenyleneiodonium (DPI) or IRE-1α shRNA, but not by SP600125 or pifithrin-α in MPP(+)-treated PC12 cells. Inhibitions of MPP(+)-induced both cytochrome c release and caspase-9 activation by IRN were blocked by pre-treatment with DPI or pifithrin-α, but not by IRE-1α shRNA. IRN blocks the generation of reactive oxygen species upstream of both ASK1/JNK pathway and IRE1/caspase-12 pathway. Altogether, our in vitro findings suggest that IRN possesses potent neuroprotective activity and may be a potential candidate for the treatment of PD.
... In this context, MAM play a fundamental role in ERmitochondria crosstalk, and mitochondria along with the UPR transducers and ER-localized Ca 2+ receptors could represent a potential target for AD treatment (Volgyi et al., 2015;Penke et al., 2016). ...
In eukaryotic cells, the endoplasmic reticulum (ER) is the cell compartment involved in secretory protein translocation and quality control of secretory protein folding. Different conditions can alter ER function, resulting in the accumulation of unfolded or misfolded proteins within the ER lumen. Such a condition, known as ER stress, elicits an integrated adaptive response known as the unfolded protein response (UPR) that aims to restore proteostasis within the secretory pathway. Conversely, in prolonged cell stress or insufficient adaptive response, UPR signaling causes cell death. ER dysfunctions are involved and contribute to neuronal degeneration in several human diseases, including Alzheimer, Parkinson and Huntington disease and amyotrophic lateral sclerosis. The correlations between ER stress and its signal transduction pathway known as the UPR with neuropathological changes are well established. In addition, much evidence suggests that genetic or pharmacological modulation of UPR could represent an effective strategy for minimizing the progressive neuronal loss in neurodegenerative diseases. Here, we review recent results describing the main cellular mechanisms linking ER stress and UPR to neurodegeneration. Furthermore, we provide an up-to-date panoramic view of the currently pursued strategies for ameliorating the toxic effects of protein unfolding in disease by targeting the ER UPR pathway.
... In these cells, the ER may experience accumulation of partially folded proteins that require chaperone assistance. Impaired protein folding, as exemplified by increased mal-folded protein accumulation, is associated with neurodegenerative disorders such as Alzheimer's and Parkinson's disease, as well as prion protein diseases [42][43][44][45]. Furthermore, induction of GRP78 in multiple types of solid tumors is attributed to glucose starvation resulting from poor perfusion within tumors as well as hyper-metabolic characteristics of cancer cells that require much higher glucose utilization rates [18]. ...
The endoplasmic reticulum (ER), comprises 60% of the total cell membrane and interacts directly or indirectly with several cell organelles i.e., Golgi bodies, mitochondria and proteasomes. The ER is usually associated with large numbers of attached ribosomes. During evolution, ER developed as the specific cellular site of synthesis, folding, modification and trafficking of secretory and cell-surface proteins. The ER is also the major intracellular calcium storage compartment that maintains cellular calcium homeostasis. During the production of functionally effective proteins, several ER-specific molecular steps sense quantity and quality of synthesized proteins as well as proper folding into their native structures. During this process, excess accumulation of unfolded/misfolded proteins in the ER lumen results in ER stress, the homeostatic coping mechanism that activates an ER-specific adaptation program, (the unfolded protein response; UPR) to increase ER-associated degradation of structurally and/or functionally defective proteins, thus sustaining ER homeostasis. Impaired ER homeostasis results in aberrant cellular responses, contributing to the pathogenesis of various diseases. Both female and male reproductive tissues undergo highly dynamic cellular, molecular and genetic changes such as oogenesis and spermatogenesis starting in prenatal life, mainly controlled by sex-steroids but also cytokines and growth factors throughout reproductive life. These reproductive changes require ER to provide extensive protein synthesis, folding, maturation and then their trafficking to appropriate cellular location as well as destroying unfolded/misfolded proteins via activating ER-associated degradation mediated proteasomes. Many studies have now shown roles for ER stress/UPR signaling cascades in the endometrial menstrual cycle, ovarian folliculogenesis and oocyte maturation, spermatogenesis, fertilization, pre-implantation embryo development and pregnancy and parturition. Conversely, the contribution of impaired ER homeostasis by severe/prolong ER stress-mediated UPR signaling pathways to several reproductive tissue pathologies including endometriosis, cancers, recurrent pregnancy loss and pregnancy complications associated with pre-term birth have been reported. This review focuses on ER stress and UPR signaling mechanisms, and their potential roles in female and male reproductive physiopathology involving in menstrual cycle changes, gametogenesis, preimplantation embryo development, implantation and placentation, labor, endometriosis, pregnancy complications and preterm birth as well as reproductive system tumorigenesis.
... Recent studies have suggested that the ER stress induced UPR pathway is involved in neurodegenerative diseases, and that ER stress is a potential therapeutic target for preventing these diseases [89][90][91][92]. In addition to being involved in the pathology of neurological diseases, the UPR also plays vital roles in neural differentiation during brain development [53, [93][94][95]. ...
The unfolded protein response (UPR) is an evolutionarily conserved adaptive mechanism to increase cell survival under endoplasmic reticulum (ER) stress conditions. The UPR is critical for maintaining cell homeostasis under physiological and pathological conditions. The vital functions of the UPR in development, metabolism and immunity have been demonstrated in several cell types. UPR dysfunction activates a variety of pathologies, including cancer, inflammation, neurodegenerative disease, metabolic disease and immune disease. Stem cells with the special ability to self-renew and differentiate into various somatic cells have been demonstrated to be present in multiple tissues. These cells are involved in development, tissue renewal and certain disease processes. Although the role and regulation of the UPR in somatic cells has been widely reported, the function of the UPR in stem cells is not fully known, and the roles and functions of the UPR are dependent on the stem cell type. Therefore, in this article, the potential significances of the UPR in stem cells, including embryonic stem cells, tissue stem cells, cancer stem cells and induced pluripotent cells, are comprehensively reviewed. This review aims to provide novel insights regarding the mechanisms associated with stem cell differentiation and cancer pathology.
... It is inherent consequence of neuronal cell loss that the dimensions for promotional recruitment for further subsets of neurons progress as evidenced by the downhill clinical course of neurodegenerative states. Both endoplasmic reticulummitochondria stress and protein conformational disorders interplay as a common mechanism in various neurodegenerative conditions [44]. ...
Dimensions of inclusion within the overall concept of neurodegeneration would appear to arise as inherent consequences of the high metabolic rates of neuronal patho-physiology that dimensionally characterizes the subset neuronal populations. It is valid to consider the essential neurodegenerative state as a highly inclusive pathobiologic state of response to neuronal injury that elicits multiple pathways of apoptosis. It is within the spectral manifestations for further heightened susceptibility that disorders such as Alzheimer's, Parkinson's, Huntington's and also other disorders of the CNS would include also specific manifestations within the further contrasting specificities of disease states such as amyotrophic lateral sclerosis. Hence, it is beyond specificity issues that the neurodegenerative state projects the overall dimensions of a generic cell injury within the strict confines of highly selective sub-type neuronal pathobiology in terms of the essential progressive manifestations of cell loss.
Viruses have evolved sophisticated mechanisms to manipulate host cell processes and utilize intracellular organelles to facilitate their replication. These complex interactions between viruses and cellular organelles allow them to hijack the cellular machinery and impair homeostasis. Moreover, viral infection alters the cell membrane’s structure and composition and induces vesicle formation to facilitate intracellular trafficking of viral components. However, the research focus has predominantly been on the immune response elicited by viruses, often overlooking the significant alterations that viruses induce in cellular organelles. Gaining a deeper understanding of these virus-induced cellular changes is crucial for elucidating the full life cycle of viruses and developing potent antiviral therapies. Exploring virus-induced cellular changes could substantially improve our understanding of viral infection mechanisms.
Inflammatory bowel disease (IBD) is a chronic inflammatory disease involving the digestive tract, characterized by abdominal pain, diarrhea, rectal bleeding, and so on, which can make patients physically weakened and live difficult. Although IBD has been recognized for many years, the pathogenesis of IBD has not yet been established and damages to intestinal barrier is thought to be closely associated with IBD. Intestinal barrier is an innate barrier that maintains the homeostasis of the intestinal environment and impedes pathogenic bacteria and toxins, and the endoplasmic reticulum (ER) has recently been found to be involved in maintaining the integrity of intestinal barrier. Endoplasmic reticulum stress (ERS) is a status of endoplasmic reticulum damaged when unfolded or misfolded proteins accumulate in excess of the degradation systematic clearance limit of the misfolded proteins. The regulation of ERS on protein folding synthesis and maintenance of cellular homeostasis is an important factor in influencing the integrity of the intestinal barrier. This paper mainly discusses the relationship between ERS and the intestinal barrier, aiming to understand the regulatory role of ERS on the intestinal barrier and the mechanism and to improve new solutions and notions for the treatment or prevention of IBD.
Purpose
Studies argue in favor of hydrogen sulfide (H2S) as the next potent therapeutic agent for neurodegenerative diseases. In present study, we investigated the effect of long term treatment with NaHS (as donor of H2S) on induction and progress of the 6-hydroxydopamine (6-OHDA) -induced Parkinsonism in rat.
Methods
The 6-OHDA was injected into medial forebrain bundle of right hemisphere by stereotaxic surgery. Behavioral tests and treatments were carried out to eight weeks after the toxin. Immunohistochemistry and western blotting were carried out to evaluate the survival of tyrosine hydroxylase (TH) -positive neurons in substantia nigra (SN) and also expression of glucose-regulated protein 78 (GRP78) and C/EBP homologous protein (CHOP), the markers of endoplasmic reticulum (ER) stress, in striatum and SN.
Results
Eight weeks assessment of the behavioral symptoms showed that NaHS especially at dose of 100 μmol/kg attenuates remarkably induction of the Parkinsonism and prevents its progress. NaHS also increased the survival of TH- positive neurons and suppressed 6-OHDA- induced overexpression of GRP78 and CHOP. Blockade of ATP-sensitive potassium (K-ATP) channels with glibenclamide (Glib) prevented markedly the effect of NaHS on both the induction phase and survival of TH- positive neurons. But Glib did not affect the preventing effect of NaHS on the progress phase and its suppressing effect on the overexpression of ER stress markers.
Conclusion
H2S attenuates induction of the 6-OHDA- induced Parkinsonism and also increases the survival of dopaminergic neurons through activation of K-ATP channels. H2S also prevents progress of the Parkinsonism probably through suppression of ER stress.
Tauopathies are a heterogeneous group of neurodegenerative dementias involving perturbations in the levels, phosphorylation or mutations of the neuronal microtubule-binding protein Tau. Tauopathies are characterized by accumulation of hyperphosphorylated Tau leading to formation of a range of aggregates including macromolecular ensembles such as Paired Helical filaments and Neurofibrilary Tangles whose morphology characterizes and differentiates these disease states. Why nonphysiological Tau proteins elude the surveillance normal proteostatic mechanisms and eventually form these macromolecular assemblies is a central mostly unresolved question of cardinal importance for diagnoses and potential therapeutic interventions. We discuss the response of the Ubiquitin–Proteasome system, autophagy and the Endoplasmic Reticulum-Unfolded Protein response in Tauopathy models and patients, revealing interactions of components of these systems with Tau, but also of the effects of pathological Tau on these systems which eventually lead to Tau aggregation and accumulation. These interactions point to potential disease biomarkers and future potential therapeutic targets.
The global burden of Alzheimer's disease (AD) is growing. Valiant efforts to develop clinical candidates for treatment have continuously met with failure. Currently available palliative treatments are temporary and there is a constant need to search for reliable disease pathways, biomarkers and drug targets for developing diagnostic and therapeutic tools to address the unmet medical needs of AD. Challenges in drug‐discovery efforts raise further questions about the strategies of current conventional diagnosis; drug design; and understanding of disease pathways, biomarkers and targets. In this context, post‐translational modifications (PTMs) regulate protein trafficking, function and degradation, and their in‐depth study plays a significant role in the identification of novel biomarkers and drug targets. Aberrant PTMs of disease‐relevant proteins could trigger pathological pathways, leading to disease progression. Advancements in proteomics enable the generation of patterns or signatures of such modifications, and thus, provide a versatile platform to develop biomarkers based on PTMs. In addition, understanding and targeting the aberrant PTMs of various proteins provide viable avenues for addressing AD drug‐discovery challenges. This review highlights numerous PTMs of proteins relevant to AD and provides an overview of their adverse effects on the protein structure, function and aggregation propensity that contribute to the disease pathology. A critical discussion offers suggestions of methods to develop PTM signatures and interfere with aberrant PTMs to develop viable diagnostic and therapeutic interventions in AD.
Our previous data indicated that tanshinone IIA (tan IIA) improves learning and memory in a mouse model of Alzheimer's disease (AD) induced by streptozotocin via restoring cholinergic function, attenuating oxidative stress and blocking p38 MAPK signal pathway activation. This study aims to estimate whether tan IIA inhibits endoplasmic reticulum (ER) stress-induced apoptosis to prevent cognitive decline in APP/PS1 transgenic mice. Tan IIA (10 mg/kg and 30 mg/kg) was intraperitoneally administered to the six-month-old APP/PS1 mice for 30 consecutive days. β-amyloid (Aβ) plaques were measured by immunohistochemisty and Thioflavin S staining, apoptotic cells were observed by TUNEL, ER stress markers and apoptosis signaling proteins were investigated by western blotting and RT-PCR. Our results showed that tan IIA significantly ameliorates cognitive deficits and improves spatial learning ability of APP/PS1 mice in the nest-building test, novel object recognition test and Morris water maze test. Furthermore, tan IIA significantly reduced the deposition of Aβ plaques and neuronal apoptosis, and markedly prevented abnormal expression of glucose regulated protein 78 (GRP78), initiation factor 2α (eIF2α), inositol-requiring enzyme 1α (IRE1α), activating transcription factor 6 (ATF6), as well as suppressed the activation of C/EBP homologous protein (CHOP) and c-Jun N-terminal kinase (JNK) pathways in the parietal cortex and hippocampus. Moreover, tan IIA induced an up-regulation of the Bcl-2/Bax ratio and down-regulation of caspase-3 protein activity. Taken together, the above findings indicated that tan IIA improves learning and memory through attenuating Aβ plaques deposition and inhibiting ER stress-induced apoptosis. These results suggested that tan IIA might become a promising therapeutic candidate drug against AD.
Endoplasmic reticulum (ER) stress and the resulting neuronal cell damage have been implicated in the development and progression of Alzheimer's disease. Tunicamycin (TM) induces ER stress in vitro, and the protective effects of the carotenoid zeaxanthin against the effects of TM have recently been studied. Zeaxanthin has been shown to hold several beneficial health properties in human studies. The protective role of zeaxanthin against the toxic effects of TM has recently been studied for the first time. The present study investigated whether zeaxanthin protects SH-SY5Y cells against TM-induced cell damage in vitro. Both pretreatment and post-treatment with zeaxanthin increased cell viability and suppressed lactate dehydrogenase release compared to levels in controls. Further, we found that zeaxanthin considerably ameliorated TM-induced cell damage by protecting the integrity of the mitochondrial membrane decreasing caspase-3 activity, and by reducing the apoptosis rate as well as the expression of the ER stress biomarker GRP78. Modulation of GRP78 may be one of the mechanisms by which zeaxanthin affects cell viability. Our results indicate a potential application of zeaxanthin in the development of new therapeutic drugs for the treatment of Alzheimer's disease.
Okadaic acid (OA)-induced neurotoxicity may be considered a novel tool used to study Alzheimer's disease (AD) pathology, and may be helpful in the development of a novel therapeutic approach. It has been reported that galangin inhibits β-site amyloid precursor protein-cleaving enzyme 1 expression, which is a key enzyme for amyloid β (Aβ) generation and is a potential drug candidate for AD therapy. However, further studies are required to confirm its neuroprotective effects in other AD models. The present study aimed to explore the neuroprotective effects of galangin on OA-induced neurotoxicity in PC12 cells. The cells were divided into the following groups: Control group, model group (175 nM OA for 48 h) and galangin groups (0.25, 0.5 and 1 µg/ml). Beclin-1, phosphorylated (p)-protein kinase B (Akt), p-glycogen synthase kinase (GSK)3β and p-mechanistic target of rapamycin (mTOR) expression was also measured in the following PC12 cell groups: Control group, model group, 3-methyladenine group (5 nM), rapamycin group (100 nM) and galangin group (1 µg/ml). The levels of β-secretase, Aβ 42 and p-tau were detected by ELISA, Beclin-1 expression was examined by immunohistochemistry and the protein expression levels of p-Akt, p-mTOR p-GSK3β, and Beclin-1 were detected by western blotting. Galangin treatment enhanced cell viability in cells treated with OA, and decreased β-secretase, Aβ 42 and p-tau levels. In addition, it suppressed Beclin-1 and p-GSK3β expression, but promoted p-Akt and p-mTOR expression by regulating the Akt/GSK3β/mTOR pathway. These results indicated that galangin protected PC12 cells from OA-induced cytotoxicity and inhibited autophagy via the Akt/GSK3β/mTOR pathway, thus suggesting that it may be considered a potential therapeutic agent for AD.
Parkinson's disease (PD) is a highly prevalent neurodegenerative disorder, often associated with oxidative stress-induced transcriptional changes in dopaminergic neurons. Phenolic antioxidants, oleuropein (OLE) and rutin (RUT) have attracted a great interest due to their potential to counteract oxidative protein aggregation and toxicity. This study aimed at examining the effects of OLE and RUT against 6-OHDA-induced stress response in rat pheochromocytoma cells. When differentiated PC12 cells were exposed to oxidative stress composer 6-OHDA (100 μM, 8 h), a decreased mitochondrial membrane potential (ΔΨm) was observed along with a significant loss of cell viability and apoptotic nuclear changes. Exposure to 6-OHDA resulted in unfolded protein response (UPR) in differentiated PC12 cells as evidenced by an increased level of endoplasmic reticulum (ER)-localized transmembrane signal transducer IRE1α, adaptive response proteins ATF-4 and proapoptotic transcription factor CHOP. OLE or RUT pretreatment (24 h) at low doses (1-50 μM) protected the differentiated PC12 cells from 6-OHDA-induced cytotoxicity as assessed by increased viability, improved ΔΨm and inhibited apoptosis, whereas relatively high doses of OLE or RUT (>50 μM) inhibited cell growth and proliferation, indicating a typical hormetic effect. In hormetic doses, OLE and RUT up-regulated 6-OHDA-induced increase in IRE1α, ATF-4 and inhibited CHOP, PERK, BIP and PDI. 6-OHDA-activated XBP1 splicing was also inhibited by OLE or RUT. The presented results suggest that neuroprotection against 6-OHDA-induced oxidative toxicity may be attributable to neurohormetic effects of OLE or RUT at low doses through regulating mitochondrial functions, controlling persistent protein misfolding, activating and/or amplificating the adaptive response-related signaling pathways, leading to UPR prosurvival output.
Endoplasmic reticulum stress (ERS)-induced intracellular calcium (Ca²⁺) overload and ROS burst plays a critical role in apoptosis. Protein kinase C epsilon (PKCε) is involved in regulating the homeostasis of Ca²⁺ and ROS production. isorhamnetin (Iso), as an ROS scavenger, effectively inhibit apoptosis, but the mechanism is still unclear. This study was to investigate whether Iso can inhibit ERS-induced apoptosis in N2a cells, and the protective effects are involved in PKCε-mediated Ca²⁺ homeostasis and inhibition of ROS. The effects of Iso against ERS injury in N2a cells were detected by cell viability, the levels of Ca²⁺, apoptosis and reactive oxygen species (ROS). The protein GRP78 expression levels were measured by western blot assay. The results showed that Iso can reduce ERS-induced injury by inhibiting Ca²⁺ overload, reducing the generation of ROS and decreasing apoptosis. In addition, Iso can promote PKCε phosphorylation, and εV1-2 (a PKCε inhibitor) drastically attenuated the protective effects of Iso against ERS injury in N2a cells. In conclusion, we firstly demonstrated that Iso can elicit protective effects against ERS injury in N2a cells and these effects are mediated at least in part via PKCε pathway.
Alzheimer’s disease (AD) is the most common neurodegenerative disorder leading to dementia in the elderly population. AD is associated with the buildup of β-amyloid and tau, which aggregate into extracellular plaques and neurofibrillary tangles. Although the exact mechanism of pathological process of AD is unclear, the dysfunction of protein degradation mechanisms has been proposed to play an important role in AD. The cellular degradation of abnormal or misfolded proteins consists of three different mechanisms: the ubiquitin proteasomal system (UPS), autophagy-lysosomal pathway (ALP), and interaction of molecular chaperones with UPS or ALP. Any disturbance to these systems causes proteins to accumulate, resulting in pathological process of AD. In this review, we summarize the knowledge of protein degradation pathways in the pathogenesis of AD in light of the current literature. In the future, the regulation UPS or ALP machineries could be the cornerstones of the treatment of AD.
Alzheimer's disease (AD) is a dementia disease with neuronal loss and synaptic impairment. This impairment is caused, at least partly, by the generation of two main AD hallmarks, namely the hyperphosphorylated tau protein comprising neurofibrillary tangles and senile plaques containing amyloid-β (Aβ) peptides. The amyloid-β protein precursor (AβPP) and glycogen synthase kinase-3β (GSK3β) are two main proteins associated with AD and are closely correlated with these hallmarks. Recently, both of the proteins were reported to be modulated by endoplasmic reticulum stress (ERS) and are involved in the pathogenesis of AD. The mechanism of ERS plus the modulation of AβPP processing and GSK3β activity by ERS in AD are summarized and explored in this review.
Brain aging is a balance between homeostatic processes and harmful interactions with the environment. Each individual has a unique aging path. Healthy neurological aging requires maintenance of normal brain functioning and prevention of neuronal damage. Diet is a cornerstone of disease prevention and health promotion. B group vitamins (BGVs) and choline are micronutrients that share a key role in multiple metabolic pathways related to the nervous system’s structural and functional integrity. Almost all BGVs show clinically relevant neurological manifestations in case of insufficient dietary intake. BGVs and choline seem to have a role in optimizing brain energy metabolism, containing oxidative stress and inflammation, maintaining deoxyribonucleic acid stability and regulation of gene expression, modulating neurotransmission, and preventing vascular damage. A possible role in neurodegenerative disease prevention has been hypothesized. BGV deficiency-related disturbances in homocysteine metabolism result in hyperhomocysteinemia, a plausible contributor in many of these processes.
Amyloid-β protein (Aβ) accumulates in the neurons of Alzheimer’s disease (AD) patients at an early stage of
the disease. Recently, we found that Aβ with a toxic turn at positions 22 and 23 accumulates in neurons in AD brain.
Here, we studied the accumulation of Aβ, toxic turn Aβ and high-molecular-weight Aβ oligomers in presenilin 1 (PS1)
gene-transfected SH-SY5Y cells as well as in the brains of 3xTg-AD mice and AD patients. Immunostaining revealed that
accumulation of toxic turn Aβ was promoted in G384A- and I143T-mutant PS1-transfected cells and further enhanced by
co-transfection of cells with the Aβ-precursor protein (AβPP) gene. In contrast, accumulation of high-molecular-weight
Aβ oligomers was promoted in mutant PS1 cells but attenuated by co-transfection of cells with the AβPP gene. Toxic turn
Aβ was detected in the neurons of 3xTg-AD mice aged 2 months, when the mice were cognitively unimpaired. In contrast,
high-molecular-weight Aβ oligomers were detected in the neurons of 7-month-old mice, when memory dysfunction
is apparent. Furthermore, immunostaining and western blotting for Rab4, Rab6 and GRP78 revealed increased levels of
these proteins in mutant PS1 cells and their accumulation in the neurons of 3xTg-AD mice. Remarkably, GRP78 immunoreactivity
was increased at 2 months of age. Double-label immunostaining of AD brain revealed an apparent association
between toxic turn Aβ and GRP78, an endoplasmic reticulum (ER) stress marker. Intraneuronal accumulation of toxic
turn Aβ may be associated with ER stress in the brains of AD model mice and AD patients at an early stage.
Background:
Alzheimer's disease (AD) is characterized by cerebral deposition of β-amyloid peptide (Aβ). Aβ is produced by sequential cleavage of the Amyloid Precursor Protein (APP) by β- and γ-secretases. Many studies have demonstrated that the internalization of APP from the cell surface can regulate Aβ production, although the exact organelle in which Aβ is produced remains contentious. A number of recent studies suggest that intracellular trafficking also plays a role in regulating Aβ production, but these pathways are relatively under-studied. The goal of this study was to elucidate the intracellular trafficking of APP, and to examine the site of intracellular APP processing.
Results:
We have tagged APP on its C-terminal cytoplasmic tail with photoactivatable Green Fluorescent Protein (paGFP). By photoactivating APP-paGFP in the Golgi, using the Golgi marker Galactosyltranferase fused to Cyan Fluorescent Protein (GalT-CFP) as a target, we are able to follow a population of nascent APP molecules from the Golgi to downstream compartments identified with compartment markers tagged with red fluorescent protein (mRFP or mCherry); including rab5 (early endosomes) rab9 (late endosomes) and LAMP1 (lysosomes). Because γ-cleavage of APP releases the cytoplasmic tail of APP including the photoactivated GFP, resulting in loss of fluorescence, we are able to visualize the cleavage of APP in these compartments. Using APP-paGFP, we show that APP is rapidly trafficked from the Golgi apparatus to the lysosome; where it is rapidly cleared. Chloroquine and the highly selective γ-secretase inhibitor, L685, 458, cause the accumulation of APP in lysosomes implying that APP is being cleaved by secretases in the lysosome. The Swedish mutation dramatically increases the rate of lysosomal APP processing, which is also inhibited by chloroquine and L685, 458. By knocking down adaptor protein 3 (AP-3; a heterotetrameric protein complex required for trafficking many proteins to the lysosome) using siRNA, we are able to reduce this lysosomal transport. Blocking lysosomal transport of APP reduces Aβ production by more than a third.
Conclusion:
These data suggests that AP-3 mediates rapid delivery of APP to lysosomes, and that the lysosome is a likely site of Aβ production.
Alzheimer's disease (AD) is the most common form of dementia caused by neurodegenerative process and is tightly related to amyloid β (Aβ) and neurofibrillary tangles. The lack of early diagnostic biomarker and therapeutic remedy hinders the prevention of increasing population of AD patients every year. In spite of accumulated scientific information, numerous clinical trials for candidate drug targets have failed to be preceded into therapeutic development, therefore, AD-related sufferers including patients and caregivers, are desperate to seek the solution. Also, effective AD intervention is desperately needed to reduce AD-related societal threats to public health. In this review, we summarize various drug targets and strategies in recent preclinical studies and clinical trials for AD therapy: Allopathic treatment, immunotherapy, Aβ production/aggregation modulator, tau-targeting therapy and metabolic targeting. Some has already failed in their clinical trials and the others are still in various stages of investigations, both of which give us valuable information for future research in AD therapeutic development.
Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by progressive loss of upper and lower motor neurons. Although the etiology remains unclear, disturbances in calcium homoeostasis and protein folding are essential features of neurodegeneration in this disorder. Here, we review recent research findings on the interaction between endoplasmic reticulum (ER) and mitochondria, and its effect on calcium signaling and oxidative stress. We further provide insights into studies, providing evidence that structures of the ER mitochondria calcium cycle serve as a promising targets for therapeutic approaches for treatment of ALS.
A recently studied endoplasmic reticulum (ER) stress regulator, Bax inhibitor-1 (BI-1) plays a regulatory role in mitochondrial Ca(2+) levels. In this study, we identified ER-resident and mitochondria-associated ER membrane (MAM)-resident populations of BI-1. ER stress increased mitochondrial Ca(2+) to a lesser extent in BI-1-overexpressing cells (HT1080/BI-1) than in control cells, most likely as a result of impaired mitochondrial Ca(2+) intake ability and lower basal levels of intra-ER Ca(2+). Moreover, opening of the Ca(2+)-induced mitochondrial permeability transition pore (PTP) and cytochrome c release were regulated by BI-1. In HT1080/BI-1, the basal mitochondrial membrane potential was low and also resistant to Ca(2+) compared with control cells. The activity of the mitochondrial membrane potential-dependent mitochondrial Ca(2+) intake pore, the Ca(2+) uniporter, was reduced in the presence of BI-1. This study also showed that instead of Ca(2+), other cations including K(+) enter the mitochondria of HT1080/BI-1 through mitochondrial Ca(2+)-dependent ion channels, providing a possible mechanism by which mitochondrial Ca(2+) intake is reduced, leading to cell protection. We propose a model in which BI-1-mediated sequential regulation of the mitochondrial Ca(2+) uniporter and Ca(2+)-dependent K(+) channel opening inhibits mitochondrial Ca(2+) intake, thereby inhibiting PTP function and leading to cell protection.
Mitochondria and the endoplasmic reticulum (ER) form tight structural associations and these facilitate a number of cellular functions. However, the mechanisms by which regions of the ER become tethered to mitochondria are not properly known. Understanding these mechanisms is not just important for comprehending fundamental physiological processes but also for understanding pathogenic processes in some disease states. In particular, disruption to ER-mitochondria associations is linked to some neurodegenerative diseases. Here we show that the ER-resident protein VAPB interacts with the mitochondrial protein tyrosine phosphatase-interacting protein-51 (PTPIP51) to regulate ER-mitochondria associations. Moreover, we demonstrate that TDP-43, a protein pathologically linked to amyotrophic lateral sclerosis and fronto-temporal dementia perturbs ER-mitochondria interactions and that this is associated with disruption to the VAPB-PTPIP51 interaction and cellular Ca(2+) homeostasis. Finally, we show that overexpression of TDP-43 leads to activation of glycogen synthase kinase-3β (GSK-3β) and that GSK-3β regulates the VAPB-PTPIP51 interaction. Our results describe a new pathogenic mechanism for TDP-43.
The endoplasmic reticulum (ER) is the principal organelle responsible for the proper folding/processing of nascent proteins and perturbed ER function leads to a state known as ER stress. Mammalian cells try to overcome ER stress through a set of protein signalling pathways and transcription factors termed the unfolded protein response (UPR). However, under unresolvable ER stress conditions, the UPR is hyperactivated inducing cell dysfunction and death. The accumulation of misfolded proteins in the brain of Alzheimer's disease (AD) patients suggests that alterations in ER homeostasis might be implicated in the neurodegenerative events that characterize this disorder. This review discusses the involvement of ER stress in the pathogenesis of AD, focusing the processing and trafficking of the AD-related amyloid precursor protein (APP) during disease development. The potential role of ER as a therapeutic target in AD will also be debated.
This review is an update of an article published four years ago (Uversky V.N. (2009) Intrinsically disordered proteins in neurodegenerative diseases: another illustration of the D² concept. Frontiers in Bioscience 14, 5188-5238). The major goal of this review is to show the interconnections between intrinsically disordered proteins (IDPs) and human neurodegeneration. This brings to existence a new D³ concept: protein intrinsic Disorder in neuroDegenerative Diseases. An important aspect of the D³ concept is that it deals with three D³'s, emphasizing that intrinsically Disordered proteins are abundantly found in various neuroDegenerative Diseases (the first D³), that these IDPs provoke neuroDegeneration due to their Dysfunctionality (the second D³), and that neuroDegeneration-related IDPs are often controlled by other Disordered proteins (the third D³).
Pathogenic mechanisms of Alzheimer's disease (AD) are intensely investigated as it is the most common form of dementia and burdens society by its costs and social demands. While key molecules such as A-beta peptides and tau have been identified decades ago, it is still enigmatic what drives the disease in its sporadic manifestation. Synthesis of A-beta peptides as well as phosphorylation of tau proteins comprise normal cellular functions and occur in principle in the healthy as well as in dementia-affected persons. Dyshomeostasis of Amyloid Precursor Protein (APP) cleavage, energy metabolism or kinase/phosphatase activity due to stressors has been suggested as a trigger of the disease. One way for cells to escape stress based on dysfunction of ER is the unfolded protein response - the UPR. This pathway is composed out of three different routes that differ in proteins involved, targets and consequences for cell fate: activation of transmembrane ER resident kinases IRE1-alpha and PERK or monomerization of membrane-anchored activating transcription factor 6 (ATF6) induce activation of versatile transcription factors (XBP-1, eIF2-alpha/ATF4 and ATF6 P50). These bind to specific DNA sequences on target gene promoters and on one hand attenuate general ER-prone protein synthesis and on the other equip the cell with tools to de-stress. If cells fail in stress compensation, this signaling also is able to evoke apoptosis. In this review we summarized knowledge on how APP processing and phosphorylation of tau might be influenced by ER-stress signaling. In addition, we depicted the effects UPR itself seems to have on molecules closely related to AD and describe what is known about UPR in AD animal models as well as in human patients.
Under physiological conditions, the endoplasmic reticulum (ER) is a central subcellular compartment for protein quality control in the secretory pathway that prevents protein misfolding and aggregation. Instrumental in protein quality control in the ER is the unfolded protein response (UPR), which is activated upon ER stress to reestablish homeostasis through a sophisticated transcriptionally and translationally regulated signaling network. However, this response can lead to apoptosis if the stress cannot be alleviated. The presence of abnormal protein aggregates containing specific misfolded proteins is recognized as the basis of numerous human conformational disorders, including neurodegenerative diseases. Here, I will highlight the overwhelming evidence that the presence of specific aberrant proteins in Alzheimer’s disease (AD), Parkinson’s disease (PD), Huntington’s disease (HD), prion diseases, and Amyotrophic Lateral Sclerosis (ALS) is intimately associated with perturbations in the ER protein quality control machinery that become incompetent to restore protein homeostasis and shift adaptive programs toward the induction of apoptotic signaling to eliminate irreversibly damaged neurons. Increasing our understanding about the deadly crosstalk between ER dysfunction and protein misfolding in these neurodegenerative diseases may stimulate the development of novel therapeutic strategies able to support neuronal survival and ameliorate disease progression.
During prion disease, an increase in misfolded prion protein (PrP) generated by prion replication leads to sustained overactivation of the branch of the unfolded protein response (UPR) that controls the initiation of protein synthesis. This results in persistent repression of translation, resulting in the loss of critical proteins that leads to synaptic failure and neuronal death. We have previously reported that localized genetic manipulation of this pathway rescues shutdown of translation and prevents neurodegeneration in a mouse model of prion disease, suggesting that pharmacological inhibition of this pathway might be of therapeutic benefit. We show that oral treatment with a specific inhibitor of the kinase PERK (protein kinase RNA–like endoplasmic reticulum kinase), a key mediator of this UPR pathway, prevented UPR-mediated translational repression and abrogated development of clinical prion disease in mice, with neuroprotection observed throughout the mouse brain. This was the case for animals treated both at the preclinical stage and also later in disease when behavioral signs had emerged. Critically, the compound acts downstream and independently of the primary pathogenic process of prion replication and is effective despite continuing accumulation of misfolded PrP. These data suggest that PERK, and other members of this pathway, may be new therapeutic targets for developing drugs against prion disease or other neurodegenerative diseases where the UPR has been implicated.
Ten years ago we first proposed the Alzheimer's disease (AD) mitochondrial cascade hypothesis. This hypothesis maintains gene inheritance defines an individual's baseline mitochondrial function; inherited and environmental factors determine rates at which mitochondrial function changes over time; and baseline mitochondrial function and mitochondrial change rates influence AD chronology. Our hypothesis unequivocally states in sporadic, late-onset AD, mitochondrial function affects amyloid precursor protein (APP) expression, APP processing, or beta amyloid (Aβ) accumulation and argues if an amyloid cascade truly exists, mitochondrial function triggers it. We now review the state of the mitochondrial cascade hypothesis, and discuss it in the context of recent AD biomarker studies, diagnostic criteria, and clinical trials. Our hypothesis predicts biomarker changes reflect brain aging, new AD definitions clinically stage brain aging, and removing brain Aβ at any point will marginally impact cognitive trajectories. Our hypothesis, therefore, offers unique perspective into what sporadic, late-onset AD is and how to best treat it. This article is part of a Special Issue entitled: Misfolded Proteins, Mitochondrial Dysfunction and Neurodegenerative Diseases.
Neurodegenerative diseases such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), and the rarer prion diseases, share a number of key similarities, including aggregation of disease-specific proteins in the brain and neuronal loss. The focus of research in these disorders has centred on pathogenesis caused by individual proteins and their build up in their specific diseases, but there are also likely to be more generic pathways that are active in neurodegeneration across the spectrum of these disorders. The unfolded protein response (UPR) has recently emerged as one such pathway. The UPR is normally a protective cellular response that protects against endoplasmic reticulum (ER) stress, which occurs with the build up of misfolded proteins. Recent evidence indicates that in neurodegenerative disease this pathway becomes constitutively activated, preventing protein translation. UPR activation is found in post mortem brains in a variety of diseases, including AD, PD and prion diseases, and has also been found to be activated in mouse models of neurodegeneration and in various in vitro models. We propose that modulation of the UPR in neurodegeneration is therefore a promising target for future therapeutic treatments. This article is part of a Special Issue entitled 'Neurodegenerative Disorders'.
The unfolded protein response (UPR) allows cells to cope with endoplasmic reticulum (ER) stress by adjusting the capacity of the ER to the load of ER-associated tasks. The UPR is important for maintaining ER homeostasis under extreme ER stress. UPR genes are important under normal growth conditions as well, but what they are required for under these conditions is less clear. Using C. elegans, we show that the ire-1/xbp-1 arm of the UPR plays a crucial role in maintaining ER plasticity and function also in the absence of external ER stress. We find that during unstressed growth conditions, loss of ire-1 or xbp-1 compromises basic ER functions required for the metabolism of secreted proteins, including translation, folding and secretion. Notably, by compromising ER-associated degradation (ERAD) and phagocytosis, loss of ire-1 abrogates the clearance of misfolded proteins from the ER as well as the clearance of proteins that were secreted into the pseudocoleom. Whereas the basal activity of the UPR is beneficial under normal conditions, it accelerates the pathology caused by toxic Aß protein in a C. elegans model of Alzheimer's disease. Taken together, our findings indicate that UPR genes are critical for maintaining secretory protein metabolism under normal growth conditions.
The ability to ensure proteostasis is critical for maintaining proper cell function and organismal viability but is mitigated by aging. We analyzed the role of the endoplasmic reticulum unfolded protein response (UPR(ER)) in aging of C. elegans and found that age-onset loss of ER proteostasis could be reversed by expression of a constitutively active form of XBP-1, XBP-1s. Neuronally derived XBP-1s was sufficient to rescue stress resistance, increase longevity, and activate the UPR(ER) in distal, non-neuronal cell types through a cell-nonautonomous mechanism. Loss of UPR(ER) signaling components in distal cells blocked cell-nonautonomous signaling from the nervous system, thereby blocking increased longevity of the entire animal. Reduction of small clear vesicle (SCV) release blocked nonautonomous signaling downstream of xbp-1s, suggesting that the release of neurotransmitters is required for this intertissue signaling event. Our findings point toward a secreted ER stress signal (SERSS) that promotes ER stress resistance and longevity. PAPERFLICK:
It is well-established that subcompartments of endoplasmic reticulum (ER) are in physical contact with the mitochondria. These lipid raft-like regions of ER are referred to as mitochondria-associated ER membranes (MAMs), and they play an important role in, for example, lipid synthesis, calcium homeostasis, and apoptotic signaling. Perturbation of MAM function has previously been suggested in Alzheimer's disease (AD) as shown in fibroblasts from AD patients and a neuroblastoma cell line containing familial presenilin-2 AD mutation. The effect of AD pathogenesis on the ER-mitochondria interplay in the brain has so far remained unknown. Here, we studied ER-mitochondria contacts in human AD brain and related AD mouse and neuronal cell models. We found uniform distribution of MAM in neurons. Phosphofurin acidic cluster sorting protein-2 and σ1 receptor, two MAM-associated proteins, were shown to be essential for neuronal survival, because siRNA knockdown resulted in degeneration. Up-regulated MAM-associated proteins were found in the AD brain and amyloid precursor protein (APP)Swe/Lon mouse model, in which up-regulation was observed before the appearance of plaques. By studying an ER-mitochondria bridging complex, inositol-1,4,5-triphosphate receptor-voltage-dependent anion channel, we revealed that nanomolar concentrations of amyloid β-peptide increased inositol-1,4,5-triphosphate receptor and voltage-dependent anion channel protein expression and elevated the number of ER-mitochondria contact points and mitochondrial calcium concentrations. Our data suggest an important role of ER-mitochondria contacts and cross-talk in AD pathology.
The endoplasmic reticulum (ER) is a dynamic intracellular organelle with multiple functions essential for cellular homeostasis, development, and stress responsiveness. In response to cellular stress, a well-established signaling cascade, the unfolded protein response (UPR), is activated. This intricate mechanism is an important means of re-establishing cellular homeostasis and alleviating the inciting stress. Now, emerging evidence has demonstrated that the UPR influences cellular metabolism through diverse mechanisms, including calcium and lipid transfer, raising the prospect of involvement of these processes in the pathogenesis of disease, including neurodegeneration, cancer, diabetes mellitus and cardiovascular disease. Here, we review the distinct functions of the ER and UPR from a metabolic point of view, highlighting their association with prevalent pathologies.
The endoplasmic reticulum (ER) and mitochondria communicate via contact sites known as mitochondria-associated ER membranes or MAM. The region has emerged as the primary area of Ca(2+) traffic between the two organelles, and as such, has been implicated in the regulation of protein folding, oxidative phosphorylation, and Ca(2+)-mediated apoptosis. In order to better understand biological processes and molecular functions at the MAM, we report a global mass spectrometry-based proteomic evaluation of the MAM obtained from mouse brain samples. Gel-assisted sample preparation in conjunction with our two-dimensional chromatography approach allowed for the identification of 1,212 high confidence proteins. Bioinformatic interrogation of this protein catalogue using Ingenuity Pathway Analysis revealed new potential connections between our list of MAM proteins and neurodegenerative diseases in addition to anticipated biological processes. Based on our results, we postulate that proteins of the MAM may play essential roles in dysfunctions responsible for several neurological disorders in addition to facilitating key cellular survival processes.
Alzheimer disease (AD) is associated with the accumulation in the brain of extracellular neuritic plaques composed mainly of β-amyloid (Aβ) and of intracellular neurofibrillary tangles composed of hyperphosphorylated forms of the microtubule-associated protein tau. It is also associated with other features that have received less attention, including aberrant phospholipid, cholesterol, and calcium metabolism, and altered mitochondrial function and dynamics. The underlying mechanism(s) that might explain these observations are currently unknown. We recently showed that presenilin-1 (PS1), presenilin-2 (PS2), and γ-secretase activity, which processes the amyloid precursor protein (APP) to generate Aβ, are located predominantly in a specialized subcompartment of the endoplasmic reticulum (ER) that is physically and biochemically connected to mitochondria, called mitochondria-associated ER membranes (MAM). MAM is an intracellular lipid raft-like structure intimately involved in cholesterol and phospholipid lipid metabolism, in calcium homeostasis, and in mitochondrial function and dynamics. The coincidence of the functions associated with MAM with the symptomatology of AD led us to speculate that presenilins play a role in maintaining MAM function. We found that, consistent with this supposition, both MAM function and ER-mitochondrial connectivity are increased significantly in AD, which may help explain many of the biochemical and morphological features of the disease. Based on these findings, we propose that AD is fundamentally a disorder of ER-mitochondrial communication (the "MAM hypothesis"). This article is part of a Special Issue entitled: Mitochondrial Function and Dysfunction in Neurodegeneration.
Alzheimer disease (AD) is associated with aberrant processing of the amyloid precursor protein (APP) by γ-secretase, via an unknown mechanism. We recently showed that presenilin-1 and -2, the catalytic components of γ-secretase, and γ-secretase activity itself, are highly enriched in a subcompartment of the endoplasmic reticulum (ER) that is physically and biochemically connected to mitochondria, called mitochondria-associated ER membranes (MAMs). We now show that MAM function and ER-mitochondrial communication-as measured by cholesteryl ester and phospholipid synthesis, respectively-are increased significantly in presenilin-mutant cells and in fibroblasts from patients with both the familial and sporadic forms of AD. We also show that MAM is an intracellular detergent-resistant lipid raft (LR)-like domain, consistent with the known presence of presenilins and γ-secretase activity in rafts. These findings may help explain not only the aberrant APP processing but also a number of other biochemical features of AD, including altered lipid metabolism and calcium homeostasis. We propose that upregulated MAM function at the ER-mitochondrial interface, and increased cross-talk between these two organelles, may play a hitherto unrecognized role in the pathogenesis of AD.
Alzheimer's disease (AD) is the major cause of dementia. During the development of AD, neurofibrillary tangles progress in a fixed pattern, starting in the transentorhinal cortex followed by the hippocampus and cortical areas. In contrast, the deposition of β-amyloid (Aβ) plaques, which are the other histological hallmark of AD, does not follow the same strict spatiotemporal pattern, and it correlates poorly with cognitive decline. Instead, soluble Aβ oligomers have received increasing attention as probable inducers of pathogenesis. In this study, we use microinjections into electrophysiologically defined primary hippocampal rat neurons to demonstrate the direct neuron-to-neuron transfer of soluble oligomeric Aβ. Additional studies conducted in a human donor-acceptor cell model show that this Aβ transfer depends on direct cellular connections. As the transferred oligomers accumulate, acceptor cells gradually show beading of tubulin, a sign of neurite damage, and gradual endosomal leakage, a sign of cytotoxicity. These observations support that intracellular Aβ oligomers play a role in neurodegeneration, and they explain the manner in which Aβ can drive disease progression, even if the extracellular plaque load is poorly correlated with the degree of cognitive decline. Understanding this phenomenon sheds light on the pathophysiological mechanism of AD progression. Additional elucidation will help uncover the detailed mechanisms responsible for the manner in which AD progresses via anatomical connections and will facilitate the development of new strategies for stopping the progression of this incapacitating disease.
Prion science has been on a rollercoaster for two decades. In the mid 1990s, the specter of mad cow disease (bovine spongiform encephalopathy, BSE) provoked an unprecedented public scare that was first precipitated by the realization that this animal prion disease could be transmitted to humans and then rekindled by the evidence that BSE-infected humans could pass on the infection through blood transfusions. Along with the gradual disappearance of BSE, the interest in prions has waned with the general public, funding agencies and prospective PhD students. In the past few years, however, a bewildering variety of diseases have been found to share features with prion infections, including cell-to-cell transmission. Here we review these developments and summarize those open questions that we currently deem most interesting in prion biology: how do prions damage their hosts, and how do hosts attempt to neutralize invading prions?
The aggregation and deposition of amyloid-β (Aβ) peptides are believed to be central events in the pathogenesis of Alzheimer's disease (AD). Inoculation of brain homogenates containing Aβ aggregates into susceptible transgenic mice accelerated Aβ deposition, suggesting that Aβ aggregates are capable of self-propagation and hence might be prions. Recently, we demonstrated that Aβ deposition can be monitored in live mice using bioluminescence imaging (BLI). Here, we use BLI to probe the ability of Aβ aggregates to self-propagate following inoculation into bigenic mice. We report compelling evidence that Aβ aggregates are prions by demonstrating widespread cerebral β-amyloidosis induced by inoculation of either purified Aβ aggregates derived from brain or aggregates composed of synthetic Aβ. Although synthetic Aβ aggregates were sufficient to induce Aβ deposition in vivo, they exhibited lower specific biological activity compared with brain-derived Aβ aggregates. Our results create an experimental paradigm that should lead to identification of self-propagating Aβ conformations, which could represent novel targets for interrupting the spread of Aβ deposition in AD patients.
Depending on endoplasmic reticulum (ER) stress levels, the ER transmembrane multidomain protein IRE1a promotes either adaptation or apoptosis. Unfolded ER proteins cause IRE1a lumenal domain homo-oligomerization, inducing trans autophosphor-ylation that further drives homo-oligomerization of its cytosolic kinase/endoribonuclease (RNase) domains to activate mRNA splicing of adaptive XBP1 transcrip-tion factor. However, under high/chronic ER stress, IRE1a surpasses an oligomerization threshold that expands RNase substrate repertoire to many ER-localized mRNAs, leading to apoptosis. To modulate these effects, we developed ATP-competitive IRE1a Kinase-Inhibiting RNase Attenuators—KIRAs—that allosterically inhibit IRE1a's RNase by breaking oligo-mers. One optimized KIRA, KIRA6, inhibits IRE1a in vivo and promotes cell survival under ER stress. In-travitreally, KIRA6 preserves photoreceptor functional viability in rat models of ER stress-induced retinal degeneration. Systemically, KIRA6 preserves pancre-atic b cells, increases insulin, and reduces hypergly-cemia in Akita diabetic mice. Thus, IRE1a powerfully controls cell fate but can itself be controlled with small molecules to reduce cell degeneration. INTRODUCTION
Imbalance in protein homeostasis in specific subcellular organelles is alleviated through organelle-specific stress response pathways. As a canonical example of stress activated pathway, accumulation of misfolded proteins in Endoplasmic Reticulum (ER) activate unfolded protein response (UPR) in almost all eukaryotic organisms. However, very little is known about the involvement of proteins of other organelles that help to maintain the cellular protein homeostasis during ER stress. In this study, using iTRAQ based LC-MS approach, we identified organelle enriched proteins that are differentially expressed in yeast (Saccharomyces cerevisiae) during ER stress in the absence of UPR sensor IRE1. We have identified about 750 proteins from enriched organelle fraction in three independent iTRAQ experiments. Induction of ER stress resulted in the differentialexpression of 93 proteins in wild type strains, 40 of which were found to be dependent on IRE1. Our study reveals a cross-talk between ER- and mitochondrial proteostasis exemplified by an Ire1-dependent induction of Hsp60p, a mitochondrial chaperone. Thus, in this study we show changes in protein levels in various organelles in response to ER stress. A large fraction of these changes were dependent on canonical UPR signalling through Ire1, highlighting the importance of inter- organellar cross talk during stress..This article is protected by copyright. All rights reserved
Proteins are the major component of the living cell. They play crucial roles in the maintenance of life, and their dysfunctions are known to cause different pathologies. Simple amino acid propensities reflect some basic physical or sequence features. Such propensity-based predictors rely on simple statistics of amino acid propensity, on the physical/chemical features of amino acids, or on a preliminary concept on the physical background of disorder. Regions of missing electron density in the PDB are generally short, as long regions prevent crystallization. As such, short disorder is overrepresented in the database of disordered regions, and hence these predictors tend to perform better in predicting short disorder than long disorder. Predictors can also be classified based on the binary nature of the prediction. Examples of binary predictors are the CH plot and the cumulative distribution function (CDF) analysis.
The endoplasmic reticulum (ER) serves many crucial cellular functions. However, when misfolded or unfolded proteins accumulated in the ER, the stress of ER will be induced. Meanwhile, the intracellular signaling network, which is called unfolded protein response, will also be activated to cope with. Those unfolded proteins can be recognized by three kinds of stress sensors which are IRE1, PERK, and ATF6. Based on lots of medical reports, ER stress in postmortem brains from Alzheimer's disease (AD) patients, animals, and vitro models have indicated that ER dysfunction might work as an important part in causing AD. In this review, we demonstrated that the effect of ER stress contributed to the pathogenesis of AD. ER stress associates almost the whole brain pathology processes which can be observed in AD, such as gene mutation of presenilin1, the abnormal clipped mRNA of presenilin2, β-amyloid production, tau phosphorylation, and cell death. The status of ER stress and unfolded protein response in the pathogenesis of AD also suggests they can be used as potential therapeutic agents.
The unfolded protein response (UPR) is a homeostatic mechanism by which cells regulate levels of misfolded proteins in the endoplasmic reticulum (ER). Although it is well characterized in non-neuronal cells, a proliferation of papers over the past few years has revealed a key role for the UPR in normal neuronal function and as an important driver of neurodegenerative diseases. A complex scenario is emerging in which distinct UPR signalling modules have specific and even opposite effects on neurodegeneration depending on the disease context. Here, we provide an overview of the most recent findings addressing the biological relevance of ER stress in the nervous system.
Intraneuronal amyloid-β (iAβ) accumulation has been demonstrated in Alzheimer disease (AD). Although extracellular amyloid plaques composed primarily of aggregated amyloid-β are one of the main pathological features of AD, functional characterization of iAβ is still lacking. In this study, we identified the normal distribution of iAβ through an analysis of hippocampal sections from a series of over 90 subjects with diverse antemortem clinical findings. In addition to AD cases, iAβ in pyramidal neurons was readily and reproducibly demonstrated in the majority of control cases. Similar findings for controls were made across all ages, spanning from infants to the elderly. There was no correlation of iAβ between gender, postmortem interval, or age. While the possible pathophysiological significance of iAβ accumulation in AD remains to be elucidated, careful examination of iAβ found in the normal brain may be informative for determining the biological role of iAβ and how this function changes during disease. Current findings support a physiological role for iAβ in neuronal function over the entire lifespan.
Anesthetic treatment has been associated with widespread apoptotic neurodegeneration in the neonatal rodent brain. It has recently been suggested that propofol, a short-acting intravenous anesthetic agent, may have a potential as a neuroprotective agent. An apoptotic pathway mediated through endoplasmic reticulum (ER) stress has been attracting attention. ER stress is associated with accumulation of unfolded or misfolded proteins in ER, and ER stress-induced apoptosis is implicated in a wide range of diseases, including ischemia/reperfusion injury, neurodegeneration, and diabetes. We investigated whether thapsigargin-induced ER stress is prevented by propofol in human neuroblastoma SH-SY5Y cells. SH-SY5Y cells were pretreated with various concentrations of propofol (1-10 μM) for 3h before co-treatment with 0.5 μM thapsigargin and propofol for 20h. Levels of ssDNA, specific evidence of apoptosis, and biomarkers of ER stress (mRNA expression of Chop and sXbp-1) were determined. We also assayed calpain and caspase-4 activities and intracellular Ca(2+) ([Ca(2+)]i) levels. Thapsigargin-induced increases in ssDNA levels, expressions of ER stress biomarkers, activities of caspase-4 and calpain, and level of [Ca(2+)]i were suppressed by co-incubation with propofol. Our data indicate the possibility that propofol inhibits the Ca(2+) release from ER at clinically employed dose levels. These results demonstrate that propofol suppresses the ER stress-induced apoptosis in this cell system, and may have the neuroprotective potency. It may also be a promising agent for preventing damage from cerebral ischemia or edema.
Despite the importance of the aberrant polymerization of A in the early pathogenic cascade of Alzheimer's disease, little is known about the induction of A aggregation in vivo. Here we show that induction of cerebral -amyloidosis can be achieved in many different brain areas of APP23 transgenic mice through the injection of dilute A-containing brain extracts. Once the amyloidogenic process has been exogenously induced, the nature of the induced A-deposition is determined by the brain region of the host. Because these observa-tions are reminiscent of a prion-like mechanism, we then investigated whether cerebral -amyloidosis also can be induced by peripheral and systemic inoculations or by the intracerebral implantation of stainless steel wires previously coated with minute amounts of A-containing brain extract. Results reveal that oral, intravenous, intraocular, and intranasal inoculations yielded no detectable induction of cerebral -amyloidosis in APP23 transgenic mice. In contrast, transmission of cerebral -amyloidosis through the A-contaminated steel wires was demonstrated. Notably, plasma sterilization, but not boiling of the wires before implantation, prevented the induction of -amyloidosis. Our results suggest that minute amounts of A-containing brain material in direct contact with the CNS can induce cerebral -amyloidosis, but that systemic cellular mechanisms of prion uptake and transport to the CNS may not apply to A. Alzheimer's disease amyloid prion sterilization transmission
Endoplasmic reticulum (ER) stress is a common feature of several physiological and pathological conditions affecting the function of the secretory pathway. To restore ER homeostasis, an orchestrated signaling pathway is engaged that is known as the unfolded protein response (UPR). The UPR has a primary function in stress adaptation and cell survival; however under irreversible ER stress a switch to pro-apoptotic signaling events induces apoptosis of damaged cells. The mechanisms that initiate ER stress-dependent apoptosis are not fully understood. Several pathways have been described where we highlight the participation of the BCL-2 family of proteins and ER calcium release. In addition, recent findings also suggest that microRNAs and oxidative stress are relevant players on the transition from adaptive to cell death programs. Here we provide a global and integrated overview of the signaling networks that may determine the elimination of cell under chronic ER stress. This article is part of a Special Issue entitled:Cell Death Pathways.
Oligomeric forms of amyloid-β peptide (Aβ) are thought to play a pivotal role in the pathogenesis of Alzheimers disease (AD), but the mechanism involved is still unclear. Here, we generated induced pluripotent stem cells (iPSCs) from familial and sporadic AD patients and differentiated them into neural cells. Aβ oligomers accumulated in iPSC-derived neurons and astrocytes in cells from patients with a familial amyloid precursor protein (APP)-E693 mutation and sporadic AD, leading to endoplasmic reticulum (ER) and oxidative stress. The accumulated Aβ oligomers were not proteolytically resistant, and docosahexaenoic acid (DHA) treatment alleviated the stress responses in the AD neural cells. Differential manifestation of ER stress and DHA responsiveness may help explain variable clinical results obtained with the use of DHA treatment and suggests that DHA may in fact be effective for a subset of patients. It also illustrates how patient-specific iPSCs can be useful for analyzing AD pathogenesis and evaluating drugs.
Alzheimer's disease (AD) is an age-related, progressive degenerative disorder that is characterized by synapse and neuron loss in the brain and the accumulation of protein-containing deposits (referred to as 'senile plaques') and neurofibrillary tangles. Insoluble amyloid beta-peptide (Abeta) fibrillar aggregates found in extracellular plaques have long been thought to cause the neurodegenerative cascades of AD. However, accumulating evidence suggests that prefibrillar soluble Abeta oligomers induce AD-related synaptic dysfunction. The size of Abeta oligomers is distributed over a wide molecular weight range (from < 10 kDa to > 100 kDa), with structural polymorphism in Abeta oligomers of similar sizes. Recent studies have demonstrated that Abeta can accumulate in living cells, as well as in extracellular spaces. This review summarizes current research on Abeta oligomers, focusing on their structures and toxicity mechanism. We also discuss possible formation mechanisms of intracellular and extracellular Abeta oligomers.
Progressive memory loss and cognitive dysfunction are the hallmark clinical features of Alzheimer's disease (AD). Identifying the molecular triggers for the onset of AD-related cognitive decline presently requires the use of suitable animal models, such as the 3xTg-AD mice, which develop both amyloid and tangle pathology. Here, we characterize the onset of learning and memory deficits in this model. We report that 2-month-old, prepathologic mice are cognitively unimpaired. The earliest cognitive impairment manifests at 4 months as a deficit in long-term retention and correlates with the accumulation of intraneuronal Abeta in the hippocampus and amygdala. Plaque or tangle pathology is not apparent at this age, suggesting that they contribute to cognitive dysfunction at later time points. Clearance of the intraneuronal Abeta pathology by immunotherapy rescues the early cognitive deficits on a hippocampal-dependent task. Reemergence of the Abeta pathology again leads to cognitive deficits. This study strongly implicates intraneuronal Abeta in the onset of cognitive dysfunction.
Protein misfolding in the endoplasmic reticulum (ER) leads to cell death through PERK-mediated phosphorylation of eIF2α, although the mechanism is not understood. ChIP-seq and mRNA-seq of activating transcription factor 4 (ATF4) and C/EBP homologous protein (CHOP), key transcription factors downstream of p-eIF2α, demonstrated that they interact to directly induce genes encoding protein synthesis and the unfolded protein response, but not apoptosis. Forced expression of ATF4 and CHOP increased protein synthesis and caused ATP depletion, oxidative stress and cell death. The increased protein synthesis and oxidative stress were necessary signals for cell death. We show that eIF2α-phosphorylation-attenuated protein synthesis, and not Atf4 mRNA translation, promotes cell survival. These results show that transcriptional induction through ATF4 and CHOP increases protein synthesis leading to oxidative stress and cell death. The findings suggest that limiting protein synthesis will be therapeutic for diseases caused by protein misfolding in the ER.
The endoplasmic reticulum is a major compartment of protein biogenesis in the cell, dedicated to production of secretory, membrane and organelle proteins. The secretome has distinct structural and post-translational characteristics, since folding in the ER occurs in an environment that is distinct in terms of its ionic composition, dynamics and requirements for quality control. The folding machinery in the ER therefore includes chaperones and folding enzymes that introduce, monitor and react to disulfide bonds, glycans, and fluctuations of luminal calcium. We describe the major chaperone networks in the lumen and discuss how they have distinct modes of operation that enable cells to accomplish highly efficient production of the secretome. This article is part of a Special Issue entitled:Functional and structural diversity of endoplasmic reticulum.
Neurotoxic effects of amyloid β peptides are mediated through deregulation of intracellular Ca2+ homeostasis and signaling, but relatively little is known about amyloid β modulation of Ca2+ homeostasis and its pathological influence on glia. Here, we found that amyloid β oligomers caused a cytoplasmic Ca2+ increase in cultured astrocytes, which was reduced by inhibitors of PLC and ER Ca2+ release. Furthermore, amyloid β peptides triggered increased expression of glial fibrillary acidic protein (GFAP), as well as oxidative and ER stress, as indicated by eIF2α phosphorylation and overexpression of chaperone GRP78. These effects were decreased by ryanodine and 2APB, inhibitors of ryanodine receptors and InsP3 receptors, respectively, in both primary cultured astrocytes and organotypic cultures of hippocampus and entorhinal cortex. Importantly, intracerebroventricular injection of amyloid β oligomers triggered overexpression of GFAP and GRP78 in astrocytes of the hippocampal dentate gyrus. These data were validated in a triple-transgenic mouse model of Alzheimer's disease (AD). Overexpression of GFAP and GRP78 in the hippocampal astrocytes correlated with the amyloid β oligomer load in 12-month-old mice, suggesting that this parameter drives astrocytic ER stress and astrogliosis in vivo. Together, these results provide evidence that amyloid β oligomers disrupt ER Ca2+ homeostasis, which induces ER stress that leads to astrogliosis; this mechanism may be relevant to AD pathophysiology.
The angiotensin-converting enzyme (ACE) insertion/deletion (I/D) genotype and its protein activity have been widely implicated to be associated with Alzheimer's disease (AD). However, whether the insertion sequence, Alu element, in intron 16 of the human ACE gene plays a functional role remains uncertain. To investigate the influence of the I/D polymorphism on ACE promoter, we recombined the I and D form fragments with the human ACE promoter sequence before the reporter gene in pSEAP-Basic2 vector. The effect of the Alu element on regulating the transcriptional activity of ACE promoter was examined using transient transfection in SH-SY5Y cells. We found that the I form fragment upregulated the transcriptional activity of ACE promoter by approximately 70% but that the D form fragment did not. Our study first reveals that Alu sequence in human ACE gene possesses a regulatory function on the ACE promoter activity in neuron. This novel finding bridges the gap between the association of ACE I/D genotype with AD, and suggests that Alu sequence is not merely a "junk" DNA in human ACE gene.
Endoplasmic reticulum (ER) dysfunction might have an important part to play in a range of neurological disorders, including cerebral ischaemia, sleep apnoea, Alzheimer's disease, multiple sclerosis, amyotrophic lateral sclerosis, the prion diseases, and familial encephalopathy with neuroserpin inclusion bodies. Protein misfolding in the ER initiates the well studied unfolded protein response in energy-starved neurons during stroke, which is relevant to the toxic effects of reperfusion. The toxic peptide amyloid β induces ER stress in Alzheimer's disease, which leads to activation of similar pathways, whereas the accumulation of polymeric neuroserpin in the neuronal ER triggers a poorly understood ER-overload response. In other neurological disorders, such as Parkinson's and Huntington's diseases, ER dysfunction is well recognised but the mechanisms by which it contributes to pathogenesis remain unclear. By targeting components of these signalling responses, amelioration of their toxic effects and so the treatment of a range of neurodegenerative disorders might become possible.
The manner in which a newly synthesized chain of amino acids transforms itself into a perfectly folded protein depends both on the intrinsic properties of the amino-acid sequence and on multiple contributing influences from the crowded cellular milieu. Folding and unfolding are crucial ways of regulating biological activity and targeting proteins to different cellular locations. Aggregation of misfolded proteins that escape the cellular quality-control mechanisms is a common feature of a wide range of highly debilitating and increasingly prevalent diseases.
Although Aβ peptides are causative agents in Alzheimer's disease (AD), the underlying mechanisms are still elusive. We report that Aβ42 induces a translational block by activating AMPK, thereby inhibiting the mTOR pathway. This translational block leads to widespread ER stress, which activates JNK3. JNK3 in turn phosphorylates APP at T668, thereby facilitating its endocytosis and subsequent processing. In support, pharmacologically blocking translation results in a significant increase in Aβ42 in a JNK3-dependent manner. Thus, JNK3 activation, which is increased in human AD cases and a familial AD (FAD) mouse model, is integral to perpetuating Aβ42 production. Concomitantly, deletion of JNK3 from FAD mice results in a dramatic reduction in Aβ42 levels and overall plaque loads and increased neuronal number and improved cognition. This reveals AD as a metabolic disease that is under tight control by JNK3.
The prevalence of dementia in the Western world in people over the age of 60 has been estimated to be greater than 5%, about two-thirds of which are due to Alzheimer's disease. The age-specific prevalence of Alzheimer's disease nearly doubles every 5 years after age 65, leading to a prevalence of greater than 25% in those over the age of 90 (ref. 3). Here, to search for low-frequency variants in the amyloid-β precursor protein (APP) gene with a significant effect on the risk of Alzheimer's disease, we studied coding variants in APP in a set of whole-genome sequence data from 1,795 Icelanders. We found a coding mutation (A673T) in the APP gene that protects against Alzheimer's disease and cognitive decline in the elderly without Alzheimer's disease. This substitution is adjacent to the aspartyl protease β-site in APP, and results in an approximately 40% reduction in the formation of amyloidogenic peptides in vitro. The strong protective effect of the A673T substitution against Alzheimer's disease provides proof of principle for the hypothesis that reducing the β-cleavage of APP may protect against the disease. Furthermore, as the A673T allele also protects against cognitive decline in the elderly without Alzheimer's disease, the two may be mediated through the same or similar mechanisms.
Amyloid precursor protein (APP) is processed sequentially by the β-site APP cleaving enzyme and γ-secretase to generate amyloid β (Aβ) peptides, one of the hallmarks of Alzheimer's disease. The intracellular location of Aβ production-endosomes or the trans-Golgi network (TGN)-remains uncertain. We investigated the role of different postendocytic trafficking events in Aβ(40) production using an RNAi approach. Depletion of Hrs and Tsg101, acting early in the multivesicular body pathway, retained APP in early endosomes and reduced Aβ(40) production. Conversely, depletion of CHMP6 and VPS4, acting late in the pathway, rerouted endosomal APP to the TGN for enhanced APP processing. We found that VPS35 (retromer)-mediated APP recycling to the TGN was required for efficient Aβ(40) production. An interruption of the bidirectional trafficking of APP between the TGN and endosomes, particularly retromer-mediated retrieval of APP from early endosomes to the TGN, resulted in the accumulation of endocytosed APP in early endosomes with reduced APP processing. These data suggest that Aβ(40) is generated predominantly in the TGN, relying on an endocytosed pool of APP recycled from early endosomes to the TGN.