Article

APOE immunotherapy reduces cerebral amyloid angiopathy and amyloid plaques while improving cerebrovascular function

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Abstract

The ε4 allele of the apolipoprotein E ( APOE ) gene is the strongest genetic risk factor for late-onset Alzheimer’s disease (AD) and greatly influences the development of amyloid-β (Aβ) pathology. Our current study investigated the potential therapeutic effects of the anti-human APOE antibody HAE-4, which selectively recognizes human APOE that is co-deposited with Aβ in cerebral amyloid angiopathy (CAA) and parenchymal amyloid pathology. In addition, we tested whether HAE-4 provoked brain hemorrhages, a component of amyloid-related imaging abnormalities (ARIA). ARIA is an adverse effect secondary to treatment with anti–Aβ antibodies that can occur in blood vessels with CAA. We used 5XFAD mice expressing human APOE4 +/+ (5XE4) that have prominent CAA and parenchymal plaque pathology to assess the efficacy of HAE-4 compared to an Aβ antibody that removes parenchymal Aβ but increases ARIA in humans. In chronically treated 5XE4 mice, HAE-4 reduced Aβ deposition including CAA compared to a control antibody, whereas the anti–Aβ antibody had no effect on CAA. Furthermore, the anti–Aβ antibody exacerbated microhemorrhage severity, which highly correlated with reactive astrocytes surrounding CAA. In contrast, HAE-4 did not stimulate microhemorrhages and instead rescued CAA-induced cerebrovascular dysfunction in leptomeningeal arteries in vivo. HAE-4 not only reduced amyloid but also dampened reactive microglial, astrocytic, and proinflammatory-associated genes in the cortex. These results suggest that targeting APOE in the core of both CAA and plaques could ameliorate amyloid pathology while protecting cerebrovascular integrity and function.

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... One possibility is that apoE4 promotes more aggregation of Aβ than the other isoforms by interacting directly with Aβ when the two meet in the extracellular space. The discovery of codeposited apoE in AD amyloid plaques provided early circumstantial evidence for this idea 15,22,23 , but biophysical studies are equivocal: apoE can either speed up or slow down Aβ aggregation in vitro, depending on the conditions 24 . Targeting non-lipidated apoE in amyloid plaques with an antibody can signi cantly reduce Aβ pathology in transgenic mouse models 15,22 as well as reduce Aβ-induced tau seeding and spreading 25 . ...
... The discovery of codeposited apoE in AD amyloid plaques provided early circumstantial evidence for this idea 15,22,23 , but biophysical studies are equivocal: apoE can either speed up or slow down Aβ aggregation in vitro, depending on the conditions 24 . Targeting non-lipidated apoE in amyloid plaques with an antibody can signi cantly reduce Aβ pathology in transgenic mouse models 15,22 as well as reduce Aβ-induced tau seeding and spreading 25 . However, studies disagree on whether soluble forms of apoE and Aβ associate signi cantly in brain tissue 17,26 . ...
... Having established that non-lipidated apoE-Aβ co-aggregates were especially in ammatory and toxic, we wondered whether their selective removal might rescue Aβ-induced dysfunction. To test this hypothesis, we immunoprecipitated non-lipidated apoE4-Aβ co-aggregates from a 1:1 mixture of lipidated and nonlipidated co-aggregates using HAE-4, an antibody speci c for non-lipidated apoE4 15,22,25 , and an isotype control ( Fig. 6A-B). Cellular uptake and neuroin ammation assays on the mixture and supernatant showed that removing non-lipidated co-aggregates does indeed enhance Aβ clearance and reduces Aβassociated in ammation in both microglia ( Fig. 6C-D) and astrocytes ( Fig. 6E-F). ...
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Which isoforms of apolipoprotein E (apoE) we inherit determine our risk of developing late-onset Alzheimer’s Disease (AD), but the mechanism underlying this link is poorly understood. In particular, the relevance of direct interactions between apoE and amyloid-β (Aβ) remains controversial. Here, single-molecule imaging shows that all isoforms of apoE associate with Aβ in the early stages of aggregation and then fall away as fibrillation happens. ApoE-Aβ co-aggregates account for ~ 50% of the mass of soluble Aβ aggregates detected in the frontal cortices of homozygotes with the higher-risk APOE4 gene. Our results connect inherited APOE genotype with the risk of developing AD by demonstrating how, in an isoform- and lipidation-specific way, apoE modulates the aggregation, clearance and toxicity of Aβ. Selectively removing non-lipidated apoE4-Aβ co-aggregates enhances clearance of toxic Aβ by glial cells, and reduces inflammation and membrane damage, demonstrating a clear path to AD therapeutics.
... These results indicate that CAA-related brain changes obviously not only accompany AD, but causally promote the disease themselves. Accordingly, in the ApoE-ε4 genotype, the strongest and most prevalent genetic risk factor for late-onset AD, the encoded lipidtransporting ε4 variant of ApoE is deposited together with Aß [78]. This deposition is associated with an increased severity of CAA and parenchymal Aß load [78], as well as with a reduction in glia-mediated Aß clearance [30]. ...
... Accordingly, in the ApoE-ε4 genotype, the strongest and most prevalent genetic risk factor for late-onset AD, the encoded lipidtransporting ε4 variant of ApoE is deposited together with Aß [78]. This deposition is associated with an increased severity of CAA and parenchymal Aß load [78], as well as with a reduction in glia-mediated Aß clearance [30]. Treatment with the anti-human ApoE antibody HAE-4 in an AD mouse model decreased CAA and parenchymal amyloid plaques and improved cerebrovascular function [78]. ...
... This deposition is associated with an increased severity of CAA and parenchymal Aß load [78], as well as with a reduction in glia-mediated Aß clearance [30]. Treatment with the anti-human ApoE antibody HAE-4 in an AD mouse model decreased CAA and parenchymal amyloid plaques and improved cerebrovascular function [78]. According to a recent imaging study in mouse brain, ApoE shuttles astrocyte-derived cholesterol to neuronal membranes, where cholesterol intensifies Aß production by increasing AßPP precursor interaction with ß-and γ-secretase [79]. ...
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Article
Although preclinical research and observer studies on patients with atrial fibrillation concluded that direct oral anticoagulants (DOACs) can protect against dementia like Alzheimer’s disease (AD), clinical investigation towards therapeutical approval is still pending. DOACs target pathological thrombin, which is, like toxic tau and amyloid-ß proteins (Aß), an early hallmark of AD. Especially in hippocampal and neocortical areas, the release of parenchymal Aß into the blood induces thrombin and proinflammatory bradykinin synthesis by activating factor XII of the contact system. Thrombin promotes platelet aggregation and catalyzes conversion of fibrinogen to fibrin, leading to degradation-resistant, Aß-containing fibrin clots. Together with oligomeric Aß, these clots trigger vessel constriction and cerebral amyloid angiopathy (CAA) with vessel occlusion and hemorrhages, leading to vascular and blood–brain barrier (BBB) dysfunction. As consequences, brain blood flow, perfusion, and supply with oxygen (hypoxia) and nutrients decrease. In parenchymal tissue, hypoxia stimulates Aß synthesis, leading to Aß accumulation, which is further enhanced by BBB-impaired perivascular Aß clearance. Aß triggers neuronal damage and promotes tau pathologies. BBB dysfunction enables thrombin and fibrin(ogen) to migrate into parenchymal tissue and to activate glial cells. Inflammation and continued Aß production are the results. Synapses and neurons die, and cognitive abilities are lost. DOACs block thrombin by inhibiting its activity (dabigatran) or production (FXa-inhibitors, e.g., apixaban, rivaroxaban). Therefore, DOAC use could preserve vascular integrity and brain perfusion and, thereby, could counteract vascular-driven neuronal and cognitive decline in AD. A conception for clinical investigation is presented, focused on DOAC treatment of patients with diagnosed AD in early-stage and low risk of major bleeding.
... Furthermore, the binding of aducanumab with C1q (a complement protein subcomponent) and the interaction of C1q with Aβ may trigger microgliosis and astrogliosis, leading to chronic inflammation and neurodegeneration [11][12][13]. In this line, Xiong et al. proposed that aducanumab, via C1q-mediated astrogliosis, might disrupt the blood-brain barrier, thereby contributing to chronic cerebrovascular inflammation and ARIA [14]. ...
... Even though VITT is rare, it is associated with devastating morbidity and mortality. It is possible that the platelet activation -a pivotal event in the VITT pathology -could trigger an inflammatory reaction and lead to aggravation of microvascular injury and brain hemorrhage caused by aducanumab [14,19]. In addition, the stimulation of Iba-1-positive microglia directly by aducanumab and indirectly by COVID-19 vaccines via platelet activation may increase the risk and severity of brain hemorrhage when compared to the risk of these treatments alone [4,11,14]. ...
... It is possible that the platelet activation -a pivotal event in the VITT pathology -could trigger an inflammatory reaction and lead to aggravation of microvascular injury and brain hemorrhage caused by aducanumab [14,19]. In addition, the stimulation of Iba-1-positive microglia directly by aducanumab and indirectly by COVID-19 vaccines via platelet activation may increase the risk and severity of brain hemorrhage when compared to the risk of these treatments alone [4,11,14]. Considering the odds of exacerbated cerebrovascular adverse reactions and consequent brain hemorrhage due to combined effects of COVID-19 vaccine (i.e. VITT) and aducanumab (i.e. ...
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The abstract was removed and reincorporated into the main body of the text. (Since Editorial articles within the expert collection journals no longer include abstracts.).
... We hypothesized that modification of meningeal lymphatic drainage would affect the ability of monoclonal antibodies to clear Aβ aggregates. To test this hypothesis, we used mAducanumab 16 and mAb158 9 , the mouse chimeric analogues of Aducanumab 3 and BAN2401 2,17 , respectively. We induced meningeal lymphatic dysfunction using a previously described method of Visudyne injection into the CSF and transcranial photoconversion 4,12 that results in the loss of lymphatic vasculature lining the transverse sinus (in the dorsal meninges) (Extended Data Fig. 3a, b). ...
... The protein sequences for mouse chimeric Aducanumab (mAducanumab) variable heavy chain and light chain (WO 2016/087944) were codon-optimized, generated as double-stranded DNA fragments (Integrated DNA Technologies), and cloned into expression vectors with mouse IgG2ab and mouse Kappa constant regions, respectively. Recombinant antibody was produced by transient co-transfection of heavy and light chain vectors in Expi293 cells (Thermo Fisher) followed by purification by Protein G chromatography 16 . The generation of the control mouse IgG2ab (mIgG), recognizing human PLD3 sequences not found in mice, was performed as previously described 16 . ...
... Recombinant antibody was produced by transient co-transfection of heavy and light chain vectors in Expi293 cells (Thermo Fisher) followed by purification by Protein G chromatography 16 . The generation of the control mouse IgG2ab (mIgG), recognizing human PLD3 sequences not found in mice, was performed as previously described 16 . The mAducanumab and respective control mIgG antibodies were produced by the Holtzman laboratory and can be obtained by academic investigators with a Material Transfer Agreement from the Washington University in St. Louis. ...
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Article
Alzheimer’s disease (AD) is the most prevalent cause of dementia¹. Although there is no effective treatment for AD, passive immunotherapy with monoclonal antibodies against amyloid beta (Aβ) is a promising therapeutic strategy2,3. Meningeal lymphatic drainage has an important role in the accumulation of Aβ in the brain⁴, but it is not known whether modulation of meningeal lymphatic function can influence the outcome of immunotherapy in AD. Here we show that ablation of meningeal lymphatic vessels in 5xFAD mice (a mouse model of amyloid deposition that expresses five mutations found in familial AD) worsened the outcome of mice treated with anti-Aβ passive immunotherapy by exacerbating the deposition of Aβ, microgliosis, neurovascular dysfunction, and behavioural deficits. By contrast, therapeutic delivery of vascular endothelial growth factor C improved clearance of Aβ by monoclonal antibodies. Notably, there was a substantial overlap between the gene signature of microglia from 5xFAD mice with impaired meningeal lymphatic function and the transcriptional profile of activated microglia from the brains of individuals with AD. Overall, our data demonstrate that impaired meningeal lymphatic drainage exacerbates the microglial inflammatory response in AD and that enhancement of meningeal lymphatic function combined with immunotherapies could lead to better clinical outcomes.
... Immunotherapy against AD opens another attractive therapeutic alternative, the use of anti-apoE antibodies. To date, studies in animal models have shown that the use of anti-apoE monoclonal antibodies such as HJ6-3 and HAE-4 reduces Aβ and apoE levels in the brain, along with an improvement in cognitive performance [640][641][642][643]. Specifically, the use of the HAE-4 antibody that identifies low-lipidated apoE reduced both parenchymal Aβ plaques and Aβ in the cerebral vasculature without vascular complications associated with Aβ antibodies [643]. ...
... Immunotherapy against AD opens another attractive therapeutic alternative, the use of anti-apoE antibodies. To date, studies in animal models have shown that the use of anti-apoE monoclonal antibodies such as HJ6-3 and HAE-4 reduces Aβ and apoE levels in the brain, along with an improvement in cognitive performance [640][641][642][643]. Specifically, the use of the HAE-4 antibody that identifies low-lipidated apoE reduced both parenchymal Aβ plaques and Aβ in the cerebral vasculature without vascular complications associated with Aβ antibodies [643]. These studies evidence the potential interest of this strategy, which could be interesting to test in clinical trials in the coming years. ...
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Article
ApoE is the major lipid and cholesterol carrier in the CNS. There are three major human polymorphisms, apoE2, apoE3, and apoE4, and the genetic expression of APOE4 is one of the most influential risk factors for the development of late-onset Alzheimer's disease (AD). Neuroinflammation has become the third hallmark of AD, together with Amyloid-β plaques and neurofibrillary tangles of hyperphosphorylated aggregated tau protein. This review aims to broadly and extensively describe the differential aspects concerning apoE. Starting from the evolution of apoE to how APOE's single-nucleotide polymorphisms affect its structure, function, and involvement during health and disease. This review reflects on how APOE's polymorphisms impact critical aspects of AD pathology, such as the neuroinflammatory response, particularly the effect of APOE on astrocytic and microglial function and microglial dynamics, synaptic function, amyloid-β load, tau pathology, autophagy, and cell–cell communication. We discuss influential factors affecting AD pathology combined with the APOE genotype, such as sex, age, diet, physical exercise, current therapies and clinical trials in the AD field. The impact of the APOE genotype in other neurodegenerative diseases characterized by overt inflammation, e.g., alpha- synucleinopathies and Parkinson's disease, traumatic brain injury, stroke, amyotrophic lateral sclerosis, and multiple sclerosis, is also addressed. Therefore, this review gathers the most relevant findings related to the APOE genotype up to date and its implications on AD and CNS pathologies to provide a deeper understanding of the knowledge in the APOE field.
... Predicted cognitive impairment in asymptomatic individuals [196] ↓ Association with cross-sectional impairment of delayed recall memory Significantly associated with a 7 to 10-fold increase in the risk of AD [191] Compared with AD (CDR = 1) patients and controls [190] ↑ Higher level predicted hippocampal volume loss and cognitive impairment [11][12][13][14][15][16][17][18][19][20] and severe (MMSE 0-10) AD patients [147] ↑ CSF Not specified Compared to iNPH patients [186] GlcCer ↑ Serum Not specified Correlation between Aβ 1-42 levels in CSF [194] LacCer ↑ Elderly women without dementia (MMSE score ≥ 24) ...
... Mild (MMSE 23-29), moderate (MMSE [11][12][13][14][15][16][17][18][19][20] and severe (MMSE 0-10) AD patients [147] ↑ CSF Prodromal AD (MMSE [24][25][26][27][28][29] Compared to cognitively normal controls [185] ↓ CSF nanoparticle and supernatant fraction Probable AD [184] ↑ Plasma Elderly men Increased risk of AD ↑ Elderly women Association with lower risk of AD. Greater association among APOEε4 carriers [192] ↑ Serum Elderly women without dementia MMSE score ≥ 24 ...
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Article
Alzheimer’s disease (AD) is considered the most prevalent neurodegenerative disease and the leading cause of dementia worldwide. Sphingolipids, such as ceramide or sphingosine 1-phosphate, are bioactive molecules implicated in structural and signaling functions. Metabolic dysfunction in the highly conserved pathways to produce sphingolipids may lead to or be a consequence of an underlying disease. Recent studies on transcriptomics and sphingolipidomics have observed alterations in sphingolipid metabolism of both enzymes and metabolites involved in their synthesis in several neurodegenerative diseases, including AD. In this review, we highlight the most relevant findings related to ceramide and neurodegeneration, with a special focus on AD.
... Apolipoprotein E (APOE) haplotype variants such as APOE4 have been associated with increased risk of sporadic Alzheimer's disease [35]. APOE's possible role in Alzheimer's pathophysiology include cellular mechanisms involving neuronal and glial functions [34,35], together with direct effects in amyloid-β (Aβ) aggregation and deposition [37]. We previously reported a PSEN1 E280A mutation carrier from the world's largest known autosomal dominant Alzheimer's disease (ADAD) kindred who was spared from Alzheimer's symptoms until her seventies, nearly three decades after the typical age of clinical onset among mutation carriers in this kindred [1]. ...
... It is known that ApoE has a relevant role in AD pathophysiology in astrocytes and immune response to the disease [35,36]. Depletion of astrocytic APOE4 reduces tau levels [35], while ApoE specific immunotherapy against human ApoE reduces CAA [37], both findings obtained in murine models. ApoE also functions as an activator of microglia response against Aβ plaque deposition [34]. ...
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Article
We describe in vivo follow-up PET imaging and postmortem findings from an autosomal dominant Alzheimer’s disease (ADAD) PSEN1 E280A carrier who was also homozygous for the APOE3 Christchurch (APOE3ch) variant and was protected against Alzheimer’s symptoms for almost three decades beyond the expected age of onset. We identified a distinct anatomical pattern of tau pathology with atypical accumulation in vivo and unusual postmortem regional distribution characterized by sparing in the frontal cortex and severe pathology in the occipital cortex. The frontal cortex and the hippocampus, less affected than the occipital cortex by tau pathology, contained Related Orphan Receptor B (RORB) positive neurons, homeostatic astrocytes and higher APOE expression. The occipital cortex, the only cortical region showing cerebral amyloid angiopathy (CAA), exhibited a distinctive chronic inflammatory microglial profile and lower APOE expression. Thus, the Christchurch variant may impact the distribution of tau pathology, modulate age at onset, severity, progression, and clinical presentation of ADAD, suggesting possible therapeutic strategies.
... This microgliainduced A1 astrocytic subtype is characterized by increased expression of complement component 3 (C3) and has been identified in human patients and mouse models of Alzheimer's disease (AD), Huntington's disease, amyotrophic lateral sclerosis, multiple sclerosis, Parkinson's disease, prion disease and frontotemporal dementia 6,[8][9][10] . We and others have recently reported that reactive C3 + astrocytes are highly abundant and cluster around vascular amyloid deposits without major microglial reactivity in three different mouse models of Cerebral Amyloid Angiopathy (CAA) [11][12][13] . The lack of microglial reactivity suggests that proinflammatory signaling from another source may be responsible and sufficient for the induction of reactive astrocytes associated with vascular amyloid deposits. ...
... The aggregation and accumulation of vascular amyloid has long been recognized as a major contributor to neuroinflammation, playing a fundamental role in the pathogenesis of CAA and AD 25 . We and others have reported severe astrogliosis with a C3 + astrocytic phenotype without reactive microgliosis in CAA, suggesting that other cell types may be responsible for C3 + astrocytic induction associated with vascular amyloid deposits, independent of microglia activation [11][12][13] . Interestingly, in CAA, endothelial cells are well preserved. ...
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Article
Reactive astrogliosis is a universal response of astrocytes to abnormal events and injuries. Studies have shown that proinflammatory microglia can polarize astrocytes (designated A1 astrocytes) toward a neurotoxic phenotype characterized by increased Complement Component 3 (C3) expression. It is still unclear if inflammatory stimuli from other cell types may also be capable of inducing a subset of C3 + neurotoxic astrocytes. Here, we show that a subtype of C3 + neurotoxic astrocytes is induced by activated endothelial cells that is distinct from astrocytes activated by microglia. Furthermore, we show that endothelial-induced astrocytes have upregulated expression of A1 astrocytic genes and exhibit a distinctive extracellular matrix remodeling profile. Finally, we demonstrate that endothelial-induced astrocytes are Decorin-positive and are associated with vascular amyloid deposits but not parenchymal amyloid plaques in mouse models and AD/CAA patients. These findings demonstrate the existence of potentially extensive and subtle functional diversity of C3 +-reactive astrocytes.
... During therapy, in a mice model, bleeding and swelling of the brain were observed, which consequently causes headaches, confusion, or convulsions. For comparison, Xiong et al. [134] in 2021 did not notice these adverse effects after therapy with a new antibody targeting APOE. This antibody is determined as HAE-4. ...
... In studies in mice treated with HAE-4, amyloid plaques were removed from brain tissue and blood vessels without increasing the risk of bleeding into the brain. What is more, the researchers pointed out that the brain's blood vessels showed a greater ability to expand and narrow on demand, and inflammation within the brain was significantly reduced [134]. A monoclonal antibody targeting amyloid is also a candidate for treatment-it is BAN240, developed by Eisai and Biogen [135]. ...
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Article
The accumulation of amyloid plaques, or misfolded fragments of proteins, leads to the development of a condition known as amyloidosis, which is clinically recognized as a systemic disease. Amyloidosis plays a special role in the pathogenesis of neurodegenerative diseases such as Alzheimer's disease (AD), Parkinson's disease, and rheumatoid arthritis (RA). The occurrence of amyloidosis correlates with the aging process of the organism, and since nowadays, old age is determined by the comfort of functioning and the elimination of unpleasant disease symptoms in the elderly, exposure to this subject is justified. In Alzheimer's disease, amyloid plaques negatively affect glutaminergic and cholinergic transmission and loss of sympathetic protein, while in RA, amyloids stimulated by the activity of the immune system affect the degradation of the osteoarticular bond. The following monograph draws attention to the over-reactivity of the immune system in AD and RA, describes the functionality of the blood-brain barrier as an intermediary medium between RA and AD, and indicates the direction of research to date, focusing on determining the relationship and the cause-effect link between these disorders. The paper presents possible directions for the treatment of amyloidosis, with particular emphasis on innovative therapies.
... 9 ARIA-like findings have also been identified in other disease states such as cerebral amyloid angiopathy and cerebral amyloid angiopathyrelated inflammation and can also occur spontaneously. 10,11 Anti-Aβtreatment-induced ARIA is a commonality of mAbs targeting fibrillar amyloid; it is mostly clinically asymptomatic, and as such has typically been identified through routine MRI scans during clinical trials; therefore, routine monitoring for ARIA in patients receiving anti-Aβ therapies is recommended. 7,9 ARIA-E is best visualized via a T2fluid-attenuated inversion recovery (T2-FLAIR) sequence. ...
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Article
Introduction: Amyloid-related imaging abnormalities-edema (ARIA-E) is associated with anti-amyloid beta monoclonal antibody treatment. ARIA-E severity may be assessed using the Barkhof Grand Total Scale (BGTS) or the 3- or 5-point Severity Scales of ARIA-E (SSAE-3/SSAE-5). We assessed inter- and intra-reader correlations between SSAE-3/5 and BGTS. Methods: Magnetic resonance imaging scans were collected from 75 participants in the SCarlet RoAD and Marguerite RoAD studies. Three neuroradiologists reviewed scans at baseline and at follow-up. Concordance in dichotomized ARIA-E ratings was assessed for a range of BGTS thresholds. Results: SSAE-3/5 scores correlated with BGTS scores, with high inter-reader intraclass correlation coefficients across all scales. There was high agreement in dichotomized ratings for SSAE-3 > 1 versus BGTS > 3 for all readers (accuracy 0.85-0.93) and between pairs of readers. Discussion: SSAE-3/5 showed high degrees of correlation with BGTS, potentially allowing seamless transition from the BGTS to SSAE-3/5 for ARIA-E management.
... Moreover, transgenic mice (P301S tau/Aldh1l1-Cre/apoE3) with deletion of APOE-ε4 showed a reduction in astrocyte activation, decreased phosphorylated tau accumulation, attenuation of brain atrophy and reduction in microglial synaptic pruning [66]. Likewise, anti-human APOE antibody (HAE-4) in 5xFAD mice model reduced Aβ deposition, amyloid angiopathy and also dampened reactive microglial, astrocytic, and proinflammatory-associated genes in the cortex [260]. Interaction between APOE-ε4 and Aβ is related to less amyloid clearance due to unstable complexes formation. ...
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Article
Alzheimer’s disease (AD) is a frequent and disabling neurodegenerative disorder, in which astrocytes participate in several pathophysiological processes including neuroinflammation, excitotoxicity, oxidative stress and lipid metabolism (along with a critical role in apolipoprotein E function). Current evidence shows that astrocytes have both neuroprotective and neurotoxic effects depending on the disease stage and microenvironmental factors. Furthermore, astrocytes appear to be affected by the presence of amyloid-beta (Aβ), with alterations in calcium levels, gliotransmission and proinflammatory activity via RAGE-NF-κB pathway. In addition, astrocytes play an important role in the metabolism of tau and clearance of Aβ through the glymphatic system. In this review, we will discuss novel pharmacological and non-pharmacological treatments focused on astrocytes as therapeutic targets for AD. These interventions include effects on anti-inflammatory/antioxidant systems, glutamate activity, lipid metabolism, neurovascular coupling and glymphatic system, calcium dysregulation, and in the release of peptides which affects glial and neuronal function. According to the AD stage, these therapies may be of benefit in either preventing or delaying the progression of the disease.
... Direct icv application of mAb 9D11 prevented accumulation of Aβ in hippocampal neurons and Tau hyperphosphorylation and was associated with reversal of the cognitive impairments [216]. Another Anti-ApoE mAb HAE-4 cleared plaque from a mouse model and also cleared amyloid deposits from blood vessel walls [217]. Notably, HAE-4 did all this without causing microhemorrhages, hinting that this approach might be safer than using anti-Aβ mAbs. ...
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Article
Since 1906, when Dr. Alois Alzheimer first described in a patient “a peculiar severe disease process of the cerebral cortex”, people suffering from this pathology have been waiting for a breakthrough therapy. Alzheimer’s disease (AD) is an irreversible, progressive neurodegenerative brain disorder and the most common form of dementia in the elderly with a long presymptomatic phase. Worldwide, approximately 50 million people are living with dementia, with AD comprising 60–70% of cases. Pathologically, AD is characterized by the deposition of amyloid β-peptide (Aβ) in the neuropil (neuritic plaques) and blood vessels (amyloid angiopathy), and by the accumulation of hyperphosphorylated tau in neurons (neurofibrillary tangles) in the brain, with associated loss of synapses and neurons, together with glial activation, and neuroinflammation, resulting in cognitive deficits and eventually dementia. The current competitive landscape in AD consists of symptomatic treatments, of which there are currently six approved medications: three AChEIs (donepezil, rivastigmine, and galantamine), one NMDA-R antagonist (memantine), one combination therapy (memantine/donepezil), and GV-971 (sodium oligomannate, a mixture of oligosaccharides derived from algae) only approved in China. Improvements to the approved therapies, such as easier routes of administration and reduced dosing frequencies, along with the developments of new strategies and combined treatments are expected to occur within the next decade and will positively impact the way the disease is managed. Recently, Aducanumab, the first disease-modifying therapy (DMT) has been approved for AD, and several DMTs are in advanced stages of clinical development or regulatory review. Small molecules, mAbs, or multimodal strategies showing promise in animal studies have not confirmed that promise in the clinic (where small to moderate changes in clinical efficacy have been observed), and therefore, there is a significant unmet need for a better understanding of the AD pathogenesis and the exploration of alternative etiologies and therapeutic effective disease-modifying therapies strategies for AD. Therefore, a critical review of the disease-modifying therapy pipeline for Alzheimer’s disease is needed.
... Monoclonal antibodies against Aβ have been found to increase the incidence of intracerebral hemorrhage (ARIA-H) due to their bindings to Aβ deposited in the cerebral vasculature 10,11 . To determine how CAA and its related microhemorrhage can be affected by αAβ-Gas6 treatment, we first induced CAA in 9-m-old APP/ PS1 and 5xFAD mice by injecting brain homogenate obtained from 20-m-old APP/PS1 mice into their ventricles (Fig. 3g) 36 . ...
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Article
Clearing amyloid-β (Aβ) through immunotherapy is one of the most promising therapeutic approaches to Alzheimer’s disease (AD). Although several monoclonal antibodies against Aβ have been shown to substantially reduce Aβ burden in patients with AD, their effects on improving cognitive function remain marginal. In addition, a significant portion of patients treated with Aβ-targeting antibodies experience brain edema and microhemorrhage associated with antibody-mediated Fc receptor activation in the brain. Here, we develop a phagocytosis inducer for Aβ consisting of a single-chain variable fragment of an Aβ-targeting monoclonal antibody fused with a truncated receptor binding domain of growth arrest-specific 6 (Gas6), a bridging molecule for the clearance of dead cells via TAM (TYRO3, AXL, and MERTK) receptors. This chimeric fusion protein (αAβ–Gas6) selectively eliminates Aβ plaques through TAM receptor-dependent phagocytosis without inducing NF-kB-mediated inflammatory responses or reactive gliosis. Furthermore, αAβ–Gas6 can induce synergistic clearance of Aβ by activating both microglial and astrocytic phagocytosis, resulting in better behavioral outcomes with substantially reduced synapse elimination and microhemorrhage in AD and cerebral amyloid angiopathy model mice compared with Aβ antibody treatment. Our results suggest that αAβ–Gas6 could be a novel immunotherapeutic agent for AD that overcomes the side effects of conventional antibody therapy.
... ApoE-targeted therapeutics for AD have focused predominantly on modulating the overall levels of apoE or the degree of its lipidation. ApoE depletion in AD mouse models has been accomplished using antisense oligonucleotides, immunotherapies, or tamoxifen-inducible APOE repression, each of which was found to reduce amyloid pathology [27][28][29]. However, given that apoE is expressed throughout the body where it carries out many critical functions, a reduction in total apoE levels is expected to have many undesirable side effects [30]. ...
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Article
Background The apolipoprotein E (APOE) ε4 allele confers the strongest risk for late-onset Alzheimer’s disease (AD) besides age itself, but the mechanisms underlying this risk are debated. One hypothesis supported by evidence from multiple labs is that apoE4 binds to the amyloid-β (Aβ) peptide and catalyzes its polymerization into neurotoxic oligomers and fibrils. Inhibiting this early step in the amyloid cascade may thereby reduce or prevent neurodegeneration and AD. Methods Using a design of experiments (DOE) approach, we developed a high-throughput assay to identify inhibitors of apoE4-catalyzed polymerization of Aβ into oligomers and fibrils. We used it to screen the NIH Clinical Collection of small molecule drugs tested previously in human clinical trials. We then evaluated the efficacy and cytotoxicity of the hit compounds in primary neuron models of apoE4-induced Aβ and phosphorylated tau aggregation. Finally, we performed retrospective analyses of the National Alzheimer’s Coordinating Center (NACC) clinical dataset, using Cox regression and Cox proportional hazards models to determine if the use of two FDA-approved hit compounds was associated with better cognitive scores (Mini-Mental State Exam), or improved AD clinical diagnosis, when compared with other medications of the same clinical indication. Results Our high-throughput screen identified eight blood-brain barrier (BBB)-permeable hit compounds that reduced apoE4-catalyzed Aβ oligomer and fibril formation in a dose-dependent manner. Five hit compounds were non-toxic toward cultured neurons and also reduced apoE4-promoted Aβ and tau neuropathology in a dose-dependent manner. Three of the five compounds were determined to be specific inhibitors of apoE4, whereas the other two compounds were Aβ or tau aggregation inhibitors. When prescribed to AD patients for their normal clinical indications, two of the apoE4 inhibitors, imipramine and olanzapine, but not other (non-hit) antipsychotic or antidepressant medications, were associated with improvements in cognition and clinical diagnosis, especially among APOE4 carriers. Conclusions The critical test of any proposed AD mechanism is whether it leads to effective treatments. Our high-throughput screen identified two promising FDA-approved drugs, imipramine and olanzapine, which have no structural, functional, or clinical similarities other than their shared ability to inhibit apoE4-catalyzed Aβ polymerization, thus identifying this mechanism as an essential contribution of apoE4 to AD.
... Targeting APOE ε4 through pharmacological interventions has resulted in both beneficial and damaging outcomes meaning therapies targeting APOE-dependent pathways will likely need to be tailored to specific mechanisms. [13][14][15][16] While pharmacological interventions are still being investigated, others have turned to non-pharmacological interventions to reduce risk for ADRDs, such as exercise. 13,17 Studies in mice show benefits of exercise to peripheral health, as well as improvements to cognitive function. ...
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Introduction: Apolipoprotein E (APOE) ε4 is the strongest genetic risk factor for Alzheimer's disease and related dementias (ADRDs), affecting many different pathways that lead to cognitive decline. Exercise is one of the most widely proposed prevention and intervention strategies to mitigate risk and symptomology of ADRDs. Importantly, exercise and APOE ε4 affect similar processes in the body and brain. While both APOE ε4 and exercise have been studied extensively, their interactive effects are not well understood. Methods: To address this, male and female APOE ε3/ε3, APOE ε3/ε4, and APOE ε4/ε4 mice ran voluntarily from wean (1 month) to midlife (12 months). Longitudinal and cross-sectional phenotyping were performed on the periphery and the brain, assessing markers of risk for dementia such as weight, body composition, circulating cholesterol composition, murine daily activities, energy expenditure, and cortical and hippocampal transcriptional profiling. Results: Data revealed chronic running decreased age-dependent weight gain, lean and fat mass, and serum low-density lipoprotein concentration dependent on APOE genotype. Additionally, murine daily activities and energy expenditure were significantly influenced by an interaction between APOE genotype and running in both sexes. Transcriptional profiling of the cortex and hippocampus predicted that APOE genotype and running interact to affect numerous biological processes including vascular integrity, synaptic/neuronal health, cell motility, and mitochondrial metabolism, in a sex-specific manner. Discussion: These data in humanized mouse models provide compelling evidence that APOE genotype should be considered for population-based strategies that incorporate exercise to prevent ADRDs and other APOE-relevant diseases.
... However, the two groups were significantly different in age, hypertension, LAD and LVEF, suggesting that elderly people with hypertension, larger LAD, and lower ants of the protein and adjusts lipid metabolism through various ways, thus playing a crucial role in tissue repair, inhibition of platelet aggregation and immune regulation, and it is correlated with diseases including atherosclerosis and high lipoproteinemia [16,17]. ApoE impacts the secretion of inflammatory mediators and resists oxidative stress, but the ApoE ε4 allele can activate the nuclear transcription factor NF-κB which is pro-inflammatory, giving rise to TNF-α, TGF-β1, MCP-1, hs-CRP, IL-1, IL-6, and the expression of inflammatory mediators [18][19][20], resulting in myocardial electrical remodelling [21], structural remodelling, and atrial arrhythmia. As a crucial factor in fibrosis, ApoE gives rise to TGF-β1 expression and thus induces myocardial fibrosis. ...
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Objective: To determine the correlation of Apolipoprotein E (ApoE) gene polymorphism with acute myocardial infarction (AMI) and aspirin (APC) resistance after percutaneous coronary intervention (PCI). Methods: In this randomized controlled trial (The Second People's Hospital of Lianyungang Ethics Committee No.L1719), a total of 120 AMI patients admitted to the Second People's Hospital of Lianyungang from January 2019 to June 2020 were enrolled into the research group (Res group) and 120 healthy individuals during the same time period into the control group (Con group). ApoE gene polymorphism was detected by gene microarray and analyzed statistically. The occurrence of APC resistance after PCI was recorded, and the relationship between ApoE gene polymorphism and APC resistance was analyzed. Results: The Res group showed a significantly lower level of ε3/ε3 gene and significantly higher levels of ε3/ε4 and ε4/ε4 genes than the Con group (all P<0.05), but no notable difference was found in the distribution of ApoE ε2 between the two groups (P>0.05). ApoE ε3 carriers were the main carriers in both groups. However, the Res group showed a lower frequency of ApoE ε3 and a higher frequency of ApoE ε4 compared to the Con group (both P<0.05), and patients with more severe AMI had a significantly higher frequency of ApoE ε4 genotype (P<0.05). According to logistic regression analysis, carrying ApoE ε4 allele (ε3/ε4, ε4/ε4) was a risk factor for AMI (P<0.05). Additionally, patients with APC resistance had a significantly higher frequency of ApoE ε4 allele than those without it (P<0.05). A higher frequency of ApoE ε4 allele was also a risk factor of APC resistance in AMI patients after PCI, and its adjusted risk ratio (OR) was 2.26 times (P<0.05). Moreover, no significant difference was observed among patients with different ApoE genotypes in the incidence of adverse events (P>0.05). Conclusion: ApoE gene polymorphism is correlated with AMI and APC resistance after PCI, and ApoE ε4 genotype is probably the risk allele for AMI.
... Brain tissue staining was performed at room temperature and on a shaker as previously described [34]. Briefly, tissue sections were rinsed 3 times for 5 min each with Tris-buffered saline (TBS) and then blocked for nonspecific binding with 3% milk in TBS containing 0.25% Triton-X100 (TBS-X) for 30 min. ...
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Background: The role of viral infection in Alzheimer Disease (AD) pathogenesis is an area of great interest in recent years. Several studies have suggested an association between the human roseoloviruses, HHV-6 and HHV-7, and AD. Amyloid-β (Aβ) plaques are a hallmark neuropathological finding of AD and were recently proposed to have an antimicrobial function in response to infection. Identifying a causative and mechanistic role of human roseoloviruses in AD has been confounded by limitations in performing in vivo studies. Recent -omics based approaches have demonstrated conflicting associations between human roseoloviruses and AD. Murine roseolovirus (MRV) is a natural murine pathogen that is highly-related to the human roseoloviruses, providing an opportunity to perform well-controlled studies of the impact of roseolovirus on Aβ deposition. Methods: We utilized the 5XFAD mouse model to test whether MRV induces Aβ deposition in vivo. We also evaluated viral load and neuropathogenesis of MRV infection. To evaluate Aβ interaction with MRV, we performed electron microscopy. RNA-sequencing of a cohort of AD brains compared to control was used to investigate the association between human roseolovirus and AD. Results: We found that 5XFAD mice were susceptible to MRV infection and developed neuroinflammation. Moreover, we demonstrated that Aβ interacts with viral particles in vitro and, subsequent to this interaction, can disrupt infection. Despite this, neither peripheral nor brain infection with MRV increased or accelerated Aβ plaque formation. Moreover, -omics based approaches have demonstrated conflicting associations between human roseoloviruses and AD. Our RNA-sequencing analysis of a cohort of AD brains compared to controls did not show an association between roseolovirus infection and AD. Conclusion: Although MRV does infect the brain and cause transient neuroinflammation, our data do not support a role for murine or human roseoloviruses in the development of Aβ plaque formation and AD.
... Research into drugs that target APOE and APOE-related mechanisms should be greatly expanded, and initiatives aiming to repurpose drugs with a potentially APOE-mediated mechanism should be encouraged. A recent report encouragingly showed that APOE immunotherapy reduces amyloid-related pathology while improving cerebrovascular function in mice 206 . As APOE ε4-unrelated sporadic AD pathophysiology is driven largely by non-APOE factors, and analogous to the treatment of risk factors for vascular diseases, therapeutic interventions in APOE ε4 non-carriers should prioritize combined preventive interventions (drugs acting on multiple molecular targets, multiple lifestyle interventions, or combined drug and lifestyle interventions). ...
Article
The current conceptualization of Alzheimer disease (AD) is driven by the amyloid hypothesis, in which a deterministic chain of events leads from amyloid deposition and then tau deposition to neurodegeneration and progressive cognitive impairment. This model fits autosomal dominant AD but is less applicable to sporadic AD. Owing to emerging information regarding the complex biology of AD and the challenges of developing amyloid-targeting drugs, the amyloid hypothesis needs to be reconsidered. Here we propose a probabilistic model of AD in which three variants of AD (autosomal dominant AD, APOE ε4-related sporadic AD and APOE ε4-unrelated sporadic AD) feature decreasing penetrance and decreasing weight of the amyloid pathophysiological cascade, and increasing weight of stochastic factors (environmental exposures and lower-risk genes). Together, these variants account for a large share of the neuropathological and clinical variability observed in people with AD. The implementation of this model in research might lead to a better understanding of disease pathophysiology, a revision of the current clinical taxonomy and accelerated development of strategies to prevent and treat AD. The amyloid hypothesis has been the dominant model for the pathogenesis of Alzheimer disease for several decades. In this Perspective, Giovanni Frisoni and colleagues examine evidence for and against this hypothesis before outlining an alternative model, the probabilistic model of Alzheimer disease.
... For example, apoE4 catalyzes the formation of neurotoxic Aβ oligomers and fibrils (Ma et al., 1994(Ma et al., , 1996Sanan et al., 1994;Wisniewski et al., 1994;Castano et al., 1995;Golabek et al., 1996;Soto et al., 1996;Manelli et al., 2007;Cerf et al., 2011;Hashimoto et al., 2012;Koffie et al., 2012;Liu et al., 2017). Fortunately, this mechanistic pathway lends itself to therapeutic approaches targeting apoE using antibodies, antisense oligonucleotides, or structural correctors (Brodbeck et al., 2011;Chen et al., 2012;Liao et al., 2014;Huynh et al., 2017;Wang et al., 2018;Xiong et al., 2021), or by targeting the interaction between apoE and Aβ using peptide blockers or small molecule drugs (Ma et al., 1996;Sadowski et al., 2004;Pankiewicz et al., 2014;Johnson et al., 2021a). Recently, high-throughput screens from our lab have identified several Food and Drug Administration (FDA)-approved drugs, including the anti-depressant drug imipramine and the anti-psychotic drug olanzapine, that inhibit the apoE-Aβ interaction and appear to improve cognition in AD patients, and especially in APOE4 carriers, in our retrospective analyses of human clinical data (Johnson et al., 2021a). ...
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Innate immune system activation and inflammation are associated with and may contribute to clinical outcomes in people with Down syndrome (DS), neurodegenerative diseases such as Alzheimer’s disease (AD), and normal aging. In addition to serving as potential diagnostic biomarkers, innate immune system activation and inflammation may play a contributing or causal role in these conditions, leading to the hypothesis that effective therapies should seek to dampen their effects. However, recent intervention studies with the innate immune system activator granulocyte-macrophage colony-stimulating factor (GM-CSF) in animal models of DS, AD, and normal aging, and in an AD clinical trial suggest that activating the innate immune system and inflammation may instead be therapeutic. We consider evidence that DS, AD, and normal aging are accompanied by innate immune system activation and inflammation and discuss whether and when during the disease process it may be therapeutically beneficial to suppress or promote such activation.
... Of interest, Aducanumab (Biogen, Cambridge, MA, USA), which has a high affinity for neurotoxic oligomeric species, has been partly authorized by the FDA, although its efficacy remains disputable [66]. Recently, the HAE-4 antibody targeting APOE4 did not display the aforementioned side effects in mice and seems effective at reducing amyloid in parenchyma and blood vessels [67]. ...
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Multiple sclerosis and Alzheimer’s disease are two complex neurodegenerative diseases involving the immune system. So far, available treatments provide at best mild improvements to patients’ conditions. For decades now, a new set of molecules have been used to modulate and regulate the innate immunity in these pathologies. Most studies have been carried out in rodents and some of them have reported tremendous beneficial effects on the disease course. The modulation of innate immune cells is of great interest since it provides new hope for patients. In this review, we will briefly overview the therapeutic potential of some molecules and receptors in multiple sclerosis and Alzheimer’s disease and how they could be used to exploit new therapeutic avenues.
... Immunotherapy against ApoE improves amyloid-associated phenotypes rather than Aβ (Xiong et al., 2021), suggesting elucidation of the regulatory mechanisms of APP expression can provide effective therapeutic strategies to interrupt the development or further progression of AD. Moreover, recent advances in high-throughput sequencing technologies have facilitated the reconstruction of the entire transcriptional landscape and RNA-RBP networks in human diseases. ...
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Alzheimer’s disease (AD) is an age-associated neurodegenerative disorder characterized by progressive impairment of memory, thinking, behavior, and dementia. Based on ample evidence showing neurotoxicity of amyloid-β (Aβ) aggregates in AD, proteolytically derived from amyloid precursor protein (APP), it has been assumed that misfolding of Aβ plays a crucial role in the AD pathogenesis. Additionally, extra copies of the APP gene caused by chromosomal duplication in patients with Down syndrome can promote AD pathogenesis, indicating the pathological involvement of the APP gene dose in AD. Furthermore, increased APP expression due to locus duplication and promoter mutation of APP has been found in familial AD. Given this background, we aimed to summarize the mechanism underlying the upregulation of APP expression levels from a cutting-edge perspective. We first reviewed the literature relevant to this issue, specifically focusing on the transcriptional regulation of APP by transcription factors that bind to the promoter/enhancer regions. APP expression is also regulated by growth factors, cytokines, and hormone, such as androgen. We further evaluated the possible involvement of post-transcriptional regulators of APP in AD pathogenesis, such as RNA splicing factors. Indeed, alternative splicing isoforms of APP are proposed to be involved in the increased production of Aβ. Moreover, non-coding RNAs, including microRNAs, post-transcriptionally regulate the APP expression. Collectively, elucidation of the novel mechanisms underlying the upregulation of APP would lead to the development of clinical diagnosis and treatment of AD.
... Such further studies may also help to further characterize the therapeutic potential of targeting ApoE signaling at various cell types. Recent studies have highlighted the therapeutic potential of targeting ApoE4, with one such study finding that ApoE immunotherapy was able to ameliorate amyloid-related pathology and protect cerebrovascular function in a mouse model of AD [44]. ...
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Mutations to the cholesterol transport protein apolipoprotein E (ApoE) have been identified as a major risk factor for the development of sporadic or late-onset Alzheimer’s disease (AD), with the e4 allele representing an increased risk and the rare e2 allele having a reduced risk compared to the primary e3 form. The reasons behind the change in risk are not entirely understood, though ApoE4 has been connected to inflammation and toxicity in both the brain and the periphery. The goal of this study was to better understand how the ApoE isoforms (ApoE2/3/4) confer differential AD-related risk by assessing cell-specific ApoE-related neuroinflammatory and neurotoxic effects. We compared the effects of ApoE isoforms in vitro on human astrocytes, a human immortalized microglia cell line (HMC3), and the human neuroblastoma cell line SH-SY5Y. Cells were treated for 24 h with or without recombinant ApoE2, ApoE3, or ApoE4 (20 nM) and inflammation and toxicity markers assessed. Our results indicated the expression of inflammatory cytokines IL-1β, TNFα, and IL-6 in human astrocytes was increased in response to all ApoE isoforms, with ApoE4 evoking the highest level of cytokine expression. In response to ApoE2 or ApoE3, microglial cells showed reduced levels of microglial activation markers TREM2 and Clec7a, while ApoE4 induced increased levels of both markers. ApoE2 promoted neuron survival through increased BDNF release from astrocytes. In addition, ApoE2 promoted, while ApoE4 reduced, neuronal viability. Overall, these results suggest that ApoE4 acts on cells in the brain to promote inflammation and neuronal injury and that the deleterious effects of ApoE4 on these cells may, in part, contribute to its role as a risk factor for AD.
... Investigational dementia therapies include targeting APOE directly, such as reducing APOE4 expression, with antibodies (Xiong et al., 2021), anti-sense oligonucleotides (Huynh et al., 2017), gene therapy, and gene editing (Liu et al., 2013;Yamazaki et al., 2016). In fact, an individual harboring a frameshift mutation ablating APOE expression had relatively normal cognition (Mak et al., 2014), possibly indicating treatment safety in altering APOE expression. ...
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Vascular contributions to cognitive impairment and dementia (VCID) are a common cause of cognitive decline, yet limited therapies exist. This cerebrovascular disease results in neurodegeneration via acute, chronic, local, and systemic mechanisms. The etiology of VCID is complex, with a significant impact from atherosclerosis. Risk factors including hypercholesterolemia and hypertension promote intracranial atherosclerotic disease and carotid artery stenosis (CAS), which disrupt cerebral blood flow and trigger ischemic strokes and VCID. Apolipoprotein E (APOE) is a cholesterol and phospholipid carrier present in plasma and various tissues. APOE is implicated in dyslipidemia and Alzheimer disease (AD); however, its connection with VCID is less understood. Few experimental models for VCID exist, so much of the present information has been drawn from clinical studies. Here, we review the literature with a focus on the clinical aspects of atherosclerotic cerebrovascular disease and build a working model for the pathogenesis of VCID. We describe potential intermediate steps in this model, linking cholesterol, atherosclerosis, and APOE with VCID. APOE4 is a minor isoform of APOE that promotes lipid dyshomeostasis in astrocytes and microglia, leading to chronic neuroinflammation. APOE4 disturbs lipid homeostasis in macrophages and smooth muscle cells, thus exacerbating systemic inflammation and promoting atherosclerotic plaque formation. Additionally, APOE4 may contribute to stromal activation of endothelial cells and pericytes that disturb the blood-brain barrier (BBB). These and other risk factors together lead to chronic inflammation, atherosclerosis, VCID, and neurodegeneration. Finally, we discuss potential cholesterol metabolism based approaches for future VCID treatment.
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For decades, the amyloid cascade hypothesis has been the leading hypothesis in studying Alzheimer’s disease (AD) pathology and drug development. However, a growing body of evidence indicates that simply removing amyloid plaques may not significantly affect AD progression. Alternatively, it has been proposed that AD progression is driven by increased neuronal excitability. Consistent with this alternative hypothesis, recent studies showed that pharmacologically limiting ryanodine receptor 2 (RyR2) open time with the R-carvedilol enantiomer prevented and reversed neuronal hyperactivity, memory impairment, and neuron loss in AD mouse models without affecting the accumulation of ß-amyloid (Aβ). These data indicate that R-carvedilol could be a potential new therapy for AD.
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Alzheimer’s disease (AD) is the most common cause of dementia worldwide, and its prevalence is rapidly increasing due to extended lifespans. Among the increasing number of genetic risk factors identified, the apolipoprotein E ( APOE ) gene remains the strongest and most prevalent, impacting more than half of all AD cases. While the ε4 allele of the APOE gene significantly increases AD risk, the ε2 allele is protective relative to the common ε3 allele. These gene alleles encode three apoE protein isoforms that differ at two amino acid positions. The primary physiological function of apoE is to mediate lipid transport in the brain and periphery; however, additional functions of apoE in diverse biological functions have been recognized. Pathogenically, apoE seeds amyloid-β (Aβ) plaques in the brain with apoE4 driving earlier and more abundant amyloids. ApoE isoforms also have differential effects on multiple Aβ-related or Aβ-independent pathways. The complexity of apoE biology and pathobiology presents challenges to designing effective apoE-targeted therapeutic strategies. This review examines the key pathobiological pathways of apoE and related targeting strategies with a specific focus on the latest technological advances and tools.
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Genetic studies have highlighted microglia as pivotal in orchestrating Alzheimer's disease (AD). Microglia that adhere to Aβ plaques acquire a transcriptional signature, "disease-associated microglia" (DAM), which largely emanates from the TREM2-DAP12 receptor complex that transmits intracellular signals through the protein tyrosine kinase SYK. The human TREM2R47H variant associated with high AD risk fails to activate microglia via SYK. We found that SYK-deficient microglia cannot encase Aβ plaques, accelerating brain pathology and behavioral deficits. SYK deficiency impaired the PI3K-AKT-GSK-3β-mTOR pathway, incapacitating anabolic support required for attaining the DAM profile. However, SYK-deficient microglia proliferated and advanced to an Apoe-expressing prodromal stage of DAM; this pathway relied on the adapter DAP10, which also binds TREM2. Thus, microglial responses to Aβ involve non-redundant SYK- and DAP10-pathways. Systemic administration of an antibody against CLEC7A, a receptor that directly activates SYK, rescued microglia activation in mice expressing the TREM2R47H allele, unveiling new options for AD immunotherapy.
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Human apolipoprotein E (apoE) is a 299‐amino acid secreted glycoprotein binding cholesterol and phospholipids, and with three common isoforms (APOE ε2, APOE ε3, and APOE ε4). The exact mechanism by which APOE gene variants increase/decrease Alzheimer's disease (AD) risk is not fully understood, but APOE isoforms differently affect brain homeostasis and neuroinflammation, blood–brain barrier (BBB) permeability, glial function, synaptogenesis, oral/gut microbiota, neural networks, amyloid beta (Aβ) deposition, and tau‐mediated neurodegeneration. In this perspective, we propose a comprehensive interpretation of APOE‐mediated effects within AD pathophysiology, describing some specific cellular, biochemical, and epigenetic mechanisms and updating the different APOE‐targeting approaches being developed as potential AD therapies. Intracisternal adeno‐associated viral‐mediated delivery of APOE ε2 is being tested in AD APOE ε4/ε4 carriers, while APOE mimetics are being used in subjects with perioperative neurocognitive disorders. Other approaches including APOE ε4 antisense oligonucleotides, anti‐APOE ε4 monoclonal antibodies, APOE ε4 structure correctors, and APOE–Aβ interaction inhibitors produced positive results in transgenic AD mouse models.
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Accumulating data suggest that cerebrovascular disease contributes to Alzheimer’s disease pathophysiology and progression toward dementia. Cerebral amyloid angiopathy is a form of cerebrovascular pathology that results from the build-up of β-amyloid in the vessel walls. Cerebral amyloid angiopathy commonly co-occurs with Alzheimer’s disease pathology in the ageing brain and increases the risk of Alzheimer’s disease dementia. In the present study, we examined whether cerebral amyloid angiopathy influences tau deposition and cognitive decline independently or synergistically with parenchymal β-amyloid burden. Secondly, we examined whether tau burden mediates the association between cerebral amyloid angiopathy and cognitive decline. We included data from autopsied subjects recruited from one of three longitudinal clinical–pathological cohort studies: the Rush Memory and Aging Project, the Religious Orders Study and the Minority Aging Research Study. Participants completed annual clinical and cognitive evaluations and underwent brain autopsy. Cerebral amyloid angiopathy pathology was rated as none, mild, moderate or severe. Bielschowsky silver stain was used to visualize neuritic β-amyloid plaques and neurofibrillary tangles. We used linear regression and linear mixed models to test independent versus interactive associations of cerebral amyloid angiopathy and neuritic plaque burden with tau burden and longitudinal cognitive decline, respectively. We used causal mediation models to examine whether tau mediates the association between cerebral amyloid angiopathy and cognitive decline. The study sample included 1722 autopsied subjects (age at baseline = 80.2 ± 7.1 years; age at death = 89.5 ± 6.7 years; 68% females). Cerebral amyloid angiopathy interacted with neuritic plaques to accelerate tau burden and cognitive decline. Specifically, those with more severe cerebral amyloid angiopathy pathology and higher levels of neuritic plaque burden had greater tau burden and faster cognitive decline. We also found that tau mediated the association between cerebral amyloid angiopathy and cognitive decline among participants with higher neuritic plaque burden. In summary, more severe levels of cerebral amyloid angiopathy and higher parenchymal β-amyloid burden interacted to promote cognitive decline indirectly via tau deposition. These results highlight the dynamic interplay between cerebral amyloid angiopathy and Alzheimer’s disease pathology in accelerating progression toward dementia. These findings have implications for Alzheimer’s disease clinical trials and therapeutic development.
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Peptide vaccines and immunotherapies against aggregating proteins involved in the pathogenesis and progression of Alzheimer's disease (AD)—the β‐amyloid peptide (Aβ) and tau—are promising therapeutic avenues against AD. Two decades of effort has led to the controversial United States Food and Drug Administration (FDA) approval of the monoclonal antibody Aducanumab (Aduhelm), which has subsequentially sparked the revival and expedited review of promising monoclonal antibody immunotherapies that target Aβ. In this review, we explore the development of Aβ and tau peptide vaccines and immunotherapies with monoclonal antibodies in clinical trials against AD.
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Emerging evidence indicates that acute exercise improves executive function, but its effects on higher-order executive functioning skills among people with a risk of Alzheimer’s disease are not well understood. This study addressed the effects of acute exercise on the planning dimension of executive function among late middle-age adults who carried Apolipoprotein (APOE)-ɛ4. Exercise volume was kept constant, but exercise intensity and duration were manipulated. Eighteen adults in the age range 55–70 years who carried APOE-ɛ4 were recruited for a laboratory-based study set in a within-subjects, counterbalanced design. There was a reading control condition along with three exercise conditions: Acute cycle exercise at a moderate intensity for 30 min (MI-30); higher intensity exercise of a shorter duration (16 min); and lower intensity exercise of a longer duration (40 min). Exercise volume was set with reference to energy expenditure in MI-30. The Tower of London Test was administered at the end of each condition. Acute aerobic exercise improved cognitive performance in regard to move-related scores and time-related scores, but not violation-related scores, when compared to the control condition. There was no difference in terms of the facilitation effect among the three exercise conditions. The present findings indicate that acute aerobic exercise, regardless of intensity/duration manipulation, facilitates higher-order executive function in late middle-aged APOE-ɛ4 carriers. Practitioners should, accordingly, consider exercise as a suitable intervention for those at risk of Alzheimer’s disease.
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Purpose of review: Alzheimer disease (AD) is the most common cause of dementia in adults (mid to late life), highlighting the importance of understanding the risk factors, clinical manifestations, and recent developments in diagnostic testing and therapeutics. Recent findings: Advances in fluid (CSF and blood-based) and imaging biomarkers are allowing for a more precise and earlier diagnosis of AD (relative to non-AD dementias) across the disease spectrum and in patients with atypical clinical features. Specifically, tau- and amyloid-related AD pathologic changes can now be measured by CSF, plasma, and positron emission tomography (PET) with good precision. Additionally, a better understanding of risk factors for AD has highlighted the need for clinicians to address comorbidities to maximize prevention of cognitive decline in those at risk or to slow decline in patients who are symptomatic. Recent clinical trials of amyloid-lowering drugs have provided not only some optimism that amyloid reduction or prevention may be beneficial but also a recognition that addressing additional targets will be necessary for significant disease modification. Summary: Recent developments in fluid and imaging biomarkers have led to the improved understanding of AD as a chronic condition with a protracted presymptomatic phase followed by the clinical stage traditionally recognized by neurologists. As clinical trials of potential disease-modifying therapies continue, important developments in the understanding of the disease will improve clinical care now and lead to more effective therapies in the near future.
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Intracerebral hemorrhage (ICH) is a devastating form of stroke with high morbidity and mortality. This review article focuses on the epidemiology, cause, mechanisms of injury, current treatment strategies, and future research directions of ICH. Incidence of hemorrhagic stroke has increased worldwide over the past 40 years, with shifts in the cause over time as hypertension management has improved and anticoagulant use has increased. Preclinical and clinical trials have elucidated the underlying ICH cause and mechanisms of injury from ICH including the complex interaction between edema, inflammation, iron-induced injury, and oxidative stress. Several trials have investigated optimal medical and surgical management of ICH without clear improvement in survival and functional outcomes. Ongoing research into novel approaches for ICH management provide hope for reducing the devastating effect of this disease in the future. Areas of promise in ICH therapy include prognostic biomarkers and primary prevention based on disease pathobiology, ultra-early hemostatic therapy, minimally invasive surgery, and perihematomal protection against inflammatory brain injury.
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APOE4 is the first identified genetic risk factor and remains as the strongest predictor for late-onset Alzheimer's disease (AD). Studies of AD patients, AD patient-specific induced pluripotent stem cell-derived neurons and cerebral organoids, and human apoE4-expressing and apoE-deficient mouse models clearly demonstrate that apoE4 provokes neuroinflammation, impairs cerebrovasculature, and exacerbates amyloid and tau pathologies. ApoE expression is greatly up-regulated in disease-associated microglia in mouse models of amyloidosis and in human microglia from AD brains. Importantly, genetic knock-down or depletion of apoE in mice greatly attenuates neuroinflammation and alleviates amyloid and tau pathologies. Similar beneficial effects can be achieved when apoE reduction is induced by the overexpression of apoE metabolic receptor LDLR. Towards therapeutic implications, administration of apoE antisense oligonucleotides or apoE siRNAs leads to significant pharmacological effects, i.e., significant alleviation of AD pathologies in mouse models. Therefore, apoE reduction represents a promising therapeutic strategy for the treatment of AD patients carrying the APOE ε4 allele. In this review, we summarize evidence and rationale on why and how we target apoE4 reduction for AD therapy.
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The brain, as one of the most lipid-rich organs, heavily relies on lipid transport and distribution to maintain homeostasis and neuronal function. Lipid transport mediated by lipoprotein particles, which are complex structures composed of apolipoproteins and lipids, has been thoroughly characterized in the periphery. Although lipoproteins in the central nervous system (CNS) were reported over half a century ago, the identification of APOE4 as the strongest genetic risk factor for Alzheimer's disease has accelerated investigation of the biology and pathobiology of lipoproteins in the CNS. This review provides an overview of the different components of lipoprotein particles, in particular apolipoproteins, and their involvements in both physiological functions and pathological mechanisms in the CNS. Expected final online publication date for the Annual Review of Biochemistry, Volume 91 is June 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
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Human apolipoprotein E (ApoE) is a 299-amino acid secreted glycoprotein that binds cholesterol and phospholipids. ApoE exists as three common isoforms (ApoE2, ApoE3, and ApoE4) and heterozygous carriers of the ε4 allele of the gene encoding ApoE ( APOE) have a fourfold greater risk of developing Alzheimer’s disease (AD). The enzymes thrombin, cathepsin D, α-chymotrypsin-like serine protease, and high-temperature requirement serine protease A1 are responsible for ApoE proteolytic processing resulting in bioactive C-terminal-truncated fragments that vary depending on ApoE isoforms, brain region, aging, and neural injury. The objectives of the present narrative review were to describe ApoE processing, discussing current hypotheses about the potential role of various ApoE fragments in AD pathophysiology, and reviewing the current development status of different anti-ApoE drugs. The exact mechanism by which APOE gene variants increase/decrease AD risk and the role of ApoE fragments in the deposition are not fully understood, but APOE is known to directly affect tau-mediated neurodegeneration. ApoE fragments co-localize with neurofibrillary tangles and amyloid β (Aβ) plaques, and may cause neurodegeneration. Among anti-ApoE approaches, a fascinating strategy may be to therapeutically overexpress ApoE2 in APOE ε4/ε4 carriers through vector administration or liposomal delivery systems. Another approach involves reducing ApoE4 expression by intracerebroventricular antisense oligonucleotides that significantly decreased Aβ pathology in transgenic mice. Differences in the proteolytic processing of distinct ApoE isoforms and the use of ApoE fragments as mimetic peptides in AD treatment are also under investigation. Treatment with peptides that mimic the structural and biological properties of native ApoE may reduce Aβ deposition, tau hyperphosphorylation, and glial activation in mouse models of Aβ pathology. Alternative strategies involve the use of ApoE4 structure correctors, passive immunization to target a certain form of ApoE, conversion of the ApoE4 aminoacid sequence into that of ApoE3 or ApoE2, and inhibition of the ApoE-Aβ interaction.
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The ε4 allele of the apolipoprotein E gene (APOE4) is a strong genetic risk factor for Alzheimer’s disease (AD) and several other neurodegenerative conditions, including Lewy body dementia (LBD). The three APOE alleles encode protein isoforms that differ from one another only at amino acid positions 112 and 158: apoE2 (C112, C158), apoE3 (C112, R158), and apoE4 (R112, R158). Despite progress, it remains unclear how these small amino acid differences in apoE sequence among the three isoforms lead to profound effects on aging and disease-related pathways. Here, we propose a novel “ApoE Cascade Hypothesis” in AD and age-related cognitive decline, which states that the biochemical and biophysical properties of apoE impact a cascade of events at the cellular and systems levels, ultimately impacting aging-related pathogenic conditions including AD. As such, apoE-targeted therapeutic interventions are predicted to be more effective by addressing the biochemical phase of the cascade.
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APOE is the strongest genetic factor for late‐onset Alzheimer's disease (AD). A specific conformation of the ApoE protein is present in amyloid‐β (Aβ) containing plaques. Immunotherapy targeting ApoE in plaques reduces brain Aβ deposits in mice. Here, we evaluated the effects of the anti‐human APOE antibody HAE‐4 on amyloid plaques, Aβ‐mediated tau seeding and spreading, and neuritic dystrophy in the 5XFAD amyloid mice expressing human ApoE4. HAE‐4 reduced Aβ plaques as well as Aβ‐driven tau seeding/spreading and neuritic dystrophy. These results demonstrate that HAE‐4 may provide therapeutic effects on amyloid removal and Aβ driven downstream consequences such as tauopathy. This article is protected by copyright. All rights reserved.
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Neuroinflammation is a central mechanism involved in neurodegeneration as observed in Alzheimer’s disease (AD), the most prevalent form of neurodegenerative disease. Apolipoprotein E4 (APOE4), the strongest genetic risk factor for AD, directly influences disease onset and progression by interacting with the major pathological hallmarks of AD including amyloid-β plaques, neurofibrillary tau tangles, as well as neuroinflammation. Microglia and astrocytes, the two major immune cells in the brain, exist in an immune-vigilant state providing immunological defense as well as housekeeping functions that promote neuronal well-being. It is becoming increasingly evident that under disease conditions, these immune cells become progressively dysfunctional in regulating metabolic and immunoregulatory pathways, thereby promoting chronic inflammation-induced neurodegeneration. Here, we review and discuss how APOE and specifically APOE4 directly influences amyloid-β and tau pathology, and disrupts microglial as well as astroglial immunomodulating functions leading to chronic inflammation that contributes to neurodegeneration in AD.
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The prognosis of patients with microvascular lesions remains poor because vascular remodeling eventually obliterates the lumen. Here we have focused our efforts on vessel dysfunction in two different organs, the lung and brain. Despite tremendous progress in understanding the importance of blood vessel integrity, gaps remain in our knowledge of the underlying molecular factors contributing to vessel injury, including microvascular lesions. Most of the ongoing research on these lesions have focused on oxidative stress but have not found major molecular targets for the discovery of new treatment or early diagnosis. Herein, we have focused on elucidating the molecular mechanism(s) based on two new emerging molecules NRF1 and ID3, and how they may contribute to microvascular lesions in the lung and brain. Redox sensitive transcriptional activation of target genes depends on not only NRF1, but the recruitment of co-activators such as ID3 to the target gene promoter. Our review highlights the fact that targeting NRF1 and ID3 could be a promising therapeutic approach as they are major players in influencing cell growth, cell repair, senescence, and apoptotic cell death which contribute to vascular lesions. Knowledge about the molecular biology of these processes will be relevant for future therapeutic approaches to not only PAH but cerebral angiopathy and other vascular disorders. Therapies targeting transcription regulators NRF1 or ID3 have the potential for vascular disease-modification because they will address the root causes such as genomic instability and epigenetic changes in vascular lesions. We hope that our findings will serve as a stimulus for further research towards an effective treatment of microvascular lesions.
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Recent drug development efforts targeting Alzheimer’s disease (AD) have failed to produce effective disease-modifying agents for many reasons, including the substantial presymptomatic neuronal damage that is caused by the accumulation of the amyloid β (Aβ) peptide and tau protein abnormalities, deleterious adverse effects of drug candidates, and inadequate design of clinical trials. New molecular targets, biomarkers, and diagnostic techniques, as well as alternative nonpharmacological approaches, are sorely needed to detect and treat early pathological events. This article analyzes the successes and debacles of pharmaceutical endeavors to date, and highlights new technologies that may lead to the more effective diagnosis and treatment of the pathologies that underlie AD. The use of focused ultrasound, deep brain stimulation, stem cell therapy, and gene therapy, in parallel with pharmaceuticals and judicious lifestyle adjustments, holds promise for the deceleration, prevention, or cure of AD and other neurodegenerative disorders.
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Alzheimer disease (AD) is the first progressive neurodegenerative disease worldwide, and the disease is characterized by an accumulation of amyloid in the brain and neurovasculature that triggers cognitive decline and neuroinflammation. The innate immune system has a preponderant role in AD. The last decade, scientists focused their efforts on therapies aiming to modulate innate immunity. The latter is of great interest, since they participate to the inflammation and phagocytose the amyloid in the brain and blood vessels. We and others have developed pharmacological approaches to stimulate these cells using various ligands. These include toll-like receptor 4, macrophage colony stimulating factor, and more recently nucleotide-binding oligomerization domain-containing 2 receptors. This review will discuss the great potential to take advantage of the innate immune system to fight naturally against amyloid β accumulation and prevent its detrimental consequence on brain functions and its vascular system. SIGNIFICANCE STATEMENT: The focus on amyloid β removal from the perivascular space rather than targeting CNS plaque formation and clearance represents a new direction with a great potential. Small molecules able to act at the level of peripheral immunity would constitute a novel approach for tackling aberrant central nervous system biology, one of which we believe would have the potential of generating a lot of interest.
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It has been indicated that amyloid β (Aβ) plaques can be accumulated within the basement membranes of cerebrovascular smooth muscle cells (CVSMCs) and stimulate the induction of cerebral amyloid angiopathy (CAA). However, the exact mechanism(s) of which small molecules including callistephin mitigate the formation of Aβ aggregation and associated CAA is not well-understood. Therefore, in the present study, Aβ1–42 samples in the aggregation buffer were co-incubated for 36 h without or with of callistephin and the protein aggregation features along with the associated cytotoxicity against CVSMCs as the core components of cerebral arterial wall were explored by different biochemical and cellular methods. Fluorescence (ThT, Nile red) and CD techniques indicated the inhibition of Aβ1–42 fibrillization in the presence of callistephin. Cellular assays indicated that cytotoxicity of Aβ1–42 samples aged in the aggregation buffer with callistephin was much less against CVSMCs than Aβ1–42 amyloid alone through regulation of membrane leakage and downregulation of TNF-α and IL-6 at protein level. In conclusion, these data may provide useful information about the possible mechanisms by which callistephin can show its protective effect against CAA.
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Aptamer-based proteomics revealed differentially abundant proteins in Alzheimer's disease (AD) brains in the Baltimore Longitudinal Study of Aging and Religious Orders Study (mean age, 89 ± 9 years). A subset of these proteins was also differentially abundant in the brains of young APOE ε4 carriers relative to noncarriers (mean age, 39 ± 6 years). Several of these proteins represent targets of approved and experimental drugs for other indications and were validated using orthogonal methods in independent human brain tissue samples as well as in transgenic AD models. Using cell culture-based phenotypic assays, we showed that drugs targeting the cytokine transducer STAT3 and the Src family tyrosine kinases, YES1 and FYN, rescued molecular phenotypes relevant to AD pathogenesis. Our findings may accelerate the development of effective interventions targeting the earliest molecular triggers of AD.
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Alzheimer’s disease (AD) is the most common neurodegenerative disorder where the accumulation of amyloid plaques and the formation of tau tangles are the prominent pathological hallmarks. Increasing preclinical and clinical studies have revealed that different components of the immune system may act as important contributors to AD etiology and pathogenesis. The recognition of misfolded Aβ and tau by immune cells can trigger a series of complex immune responses in AD, and then lead to neuroinflammation and neurodegeneration. In parallel, genome-wide association studies have also identified several immune related loci associated with increased the risk of AD by interfering with the function of immune cells. Other immune related factors, such as impaired immunometabolism, defective meningeal lymphatic vessels and autoimmunity might also be involved in the pathogenesis of AD. Here, we review the data showing the alterations of immune cells in the AD trajectory and seek to demonstrate the crosstalk between the immune cell dysfunction and AD pathology. We then discuss the most relevant research findings in regards to the influences of gene susceptibility of immune cells for AD. We also consider impaired meningeal lymphatics, immunometabolism and autoimmune mechanisms in AD. In addition, immune related biomarkers and immunotherapies for AD are also mentioned in order to offer novel insights for future research.
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Down syndrome (DS) is the largest genetically determined form of early-onset Alzheimer disease (AD). Adults with DS develop AD pathology by 40 years of age mainly because of overexpression of the APP gene on chromosome 21 that results in the early accumulation of amyloid-β (Aβ) plaques and cerebral amyloid angiopathy followed by tau pathology, neuroinflammation, and brain atrophy.¹ The age at which people with DS convert to AD-related cognitive impairment varies from younger than 50 years to older than 70 years.² However, little is known regarding biomarkers that may help to identify the age at onset of cognitive decline during this preclinical phase of AD in DS.
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Background: Cerebral amyloid angiopathy (CAA) is typified by the cerebrovascular deposition of amyloid. The mechanisms underlying the contribution of CAA to neurodegeneration are not currently understood. Although CAA is highly associated with the accumulation of amyloid beta (Aβ), other amyloids are known to associate with the vasculature. Alzheimer's disease (AD) is characterized by parenchymal Aβ deposition, intracellular accumulation of tau, and significant neuroinflammation. CAA increases with age and is present in 85-95% of individuals with AD. A substantial amount of research has focused on understanding the connection between parenchymal amyloid and glial activation and neuroinflammation, while associations between vascular amyloid pathology and glial reactivity remain understudied. Methods: Here, we dissect the glial and immune responses associated with early-stage CAA with histological, biochemical, and gene expression analyses in a mouse model of familial Danish dementia (FDD), a neurodegenerative disease characterized by the vascular accumulation of Danish amyloid (ADan). Findings observed in this CAA mouse model were complemented with primary culture assays. Results: We demonstrate that early-stage CAA is associated with dysregulation in immune response networks and lipid processing, severe astrogliosis with an A1 astrocytic phenotype, and decreased levels of TREM2 with no reactive microgliosis. Our results also indicate how cholesterol accumulation and ApoE are associated with vascular amyloid deposits at the early stages of pathology. We also demonstrate A1 astrocytic mediation of TREM2 and microglia homeostasis. Conclusion: The initial glial response associated with early-stage CAA is characterized by the upregulation of A1 astrocytes without significant microglial reactivity. Gene expression analysis revealed that several AD risk factors involved in immune response and lipid processing may also play a preponderant role in CAA. This study contributes to the increasing evidence that brain cholesterol metabolism, ApoE, and TREM2 signaling are major players in the pathogenesis of AD-related dementias, including CAA. Understanding the basis for possible differential effects of glial response, ApoE, and TREM2 signaling on parenchymal plaques versus vascular amyloid deposits provides important insight for developing future therapeutic interventions.
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Background: The apolipoprotein E (APOE) gene is the strongest genetic risk factor for late-onset Alzheimer disease (AD). ApoE is produced by both astrocytes and microglia in the brain, whereas hepatocytes produce the majority of apoE found in the periphery. Studies using APOE knock-in and transgenic mice have demonstrated a strong isoform-dependent effect of apoE on the accumulation of amyloid-β (Aβ) deposition in the brain in the form of both Aβ-containing amyloid plaques and cerebral amyloid angiopathy. However, the specific contributions of different apoE pools to AD pathogenesis remain unknown. Methods: We have begun to address these questions by generating new lines of APOE knock-in (APOE-KI) mice (ε2/ε2, ε3/ε3, and ε4/ε4) where the exons in the coding region of APOE are flanked by loxP sites, allowing for cell type-specific manipulation of gene expression. We assessed these mice both alone and after crossing them with mice with amyloid deposition in the brain. Using biochemical and histological methods. We also investigated how removal of APOE expression from hepatocytes affected cerebral amyloid deposition. Results: As in other APOE knock-in mice, apoE protein was present predominantly in astrocytes in the brain under basal conditions and was also detected in reactive microglia surrounding amyloid plaques. Primary cultured astrocytes and microglia from the APOE-KI mice secreted apoE in lipoprotein particles of distinct size distribution upon native gel analysis with microglial particles being substantially smaller than the HDL-like particles secreted by astrocytes. Crossing of APP/PS1 transgenic mice to the different APOE-KI mice recapitulated the previously described isoform-specific effect (ε4 > ε3) on amyloid plaque and Aβ accumulation. Deletion of APOE in hepatocytes did not alter brain apoE levels but did lead to a marked decrease in plasma apoE levels and changes in plasma lipid profile. Despite these changes in peripheral apoE and on plasma lipids, cerebral accumulation of amyloid plaques in APP/PS1 mice was not affected. Conclusions: Altogether, these new knock-in strains offer a novel and dynamic tool to study the role of APOE in AD pathogenesis in a spatially and temporally controlled manner.
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Chronic activation of brain innate immunity is a prominent feature of Alzheimer's disease (AD) and primary tauopathies. However, to what degree innate immunity contributes to neurodegeneration as compared with pathological protein-induced neurotoxicity, and the requirement of a particular glial cell type in neurodegeneration, are still unclear. Here we demonstrate that microglia-mediated damage, rather than pathological tau-induced direct neurotoxicity, is the leading force driving neurodegeneration in a tauopathy mouse model. Importantly, the progression of ptau pathology is also driven by microglia. In addition, we found that APOE, the strongest genetic risk factor for AD, regulates neurodegeneration predominantly by modulating microglial activation, although a minor role of apoE in regulating ptau and insoluble tau formation independent of its immunomodulatory function was also identified. Our results suggest that therapeutic strategies targeting microglia may represent an effective approach to prevent disease progression in the setting of tauopathy.
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Objective Cerebral amyloid angiopathy (CAA) is caused by cerebrovascular deposition of β‐amyloid fragments leading to cerebrovascular dysfunction and other brain injuries. This phase 2, randomized, double–blind trial in patients with probable CAA assessed the efficacy and safety of ponezumab, a novel monoclonal antibody against Aβ1–40. Methods Thirty‐six participants aged 55–80 years with probable CAA received intravenous placebo (n = 12) or ponezumab (n = 24). The change from baseline to Days 2 and 90 in cerebrovascular reactivity (CVR) was measured in the visual cortex as the natural log of the rising slope of the BOLD fMRI response to a visual stimulus. Safety and tolerability were also assessed. Results The mean change from baseline to Day 90 was 0.817 (ponezumab) and 0.958 (placebo): a mean ratio of 0.852 (90% CI 0.735–0.989) representing a trend towards reduced CVR in the ponezumab group. This trend was not present at Day 2. There was one asymptomatic occurrence of amyloid–related imaging abnormality–edema in the ponezumab group. The total number of new cerebral microbleeds from baseline to day 90 did not differ between groups. The ponezumab group had a participant with nonfatal new cerebral hemorrhage with aphasia and a participant with subdural hemorrhage that site investigators deemed to be nondrug related. In the placebo group one participant had a fatal intracerebral hemorrhage and one participant had migraine with aura. Interpretation Ponezumab was safe and well‐tolerated. The ponezumab group showed a trend towards treatment effect at Day 90 that was opposite to the hypothesized direction. The prespecified efficacy criteria were thus not met.
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Introduction: We investigated the proteomic profiles of amyloid plaques (APs) from Alzheimer's disease (AD) and age-matched non-AD brains and APP/PS1 transgenic model mice. Methods: APs and adjacent control regions were collected from fresh-frozen brain sections using laser capture dissection. Proteins were quantitated using tag-labeling coupled high-throughput mass spectra. Results: Over 4000 proteins were accurately quantified, and more than 40 were identified as highly enriched in both AD and non-AD APs, including apoE, midkine, VGFR1, and complement C4. Intriguingly, proteins including synaptic structural proteins and complement C1r, C5, and C9 were found to be upregulated in AD APs but not non-AD APs. Moreover, the proteomic pattern of AD APs was distinct from APP/PS1 APs and exhibited correlation with aging hippocampus. Discussion: Our results provide new insight into AP composition. We demonstrate unexpected differences between AD, non-AD, and APP/PS1 mouse APs, which may relate to different pathological processes.
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Background: Gantenerumab is a fully human monoclonal antibody that binds aggregated amyloid-β (Aβ) and removes Aβ plaques by Fc receptor-mediated phagocytosis. In the SCarlet RoAD trial, we assessed the efficacy and safety of gantenerumab in prodromal Alzheimer's disease (AD). Methods: In this randomized, double-blind, placebo-controlled phase III study, we investigated gantenerumab over 2 years. Patients were randomized to gantenerumab 105 mg or 225 mg or placebo every 4 weeks by subcutaneous injection. The primary endpoint was the change from baseline to week 104 in Clinical Dementia Rating Sum of Boxes (CDR-SB) score. We evaluated treatment effects on cerebrospinal fluid biomarkers (all patients) and amyloid positron emission tomography (substudy). A futility analysis was performed once 50% of patients completed 2 years of treatment. Safety was assessed in patients who received at least one dose. Results: Of the 3089 patients screened, 797 were randomized. The study was halted early for futility; dosing was discontinued; and the study was unblinded. No differences between groups in the primary (least squares mean [95% CI] CDR-SB change from baseline 1.60 [1.28, 1.91], 1.69 [1.37, 2.01], and 1.73 [1.42, 2.04] for placebo, gantenerumab 105 mg, and gantenerumab 225 mg, respectively) or secondary clinical endpoints were observed. The incidence of generally asymptomatic amyloid-related imaging abnormalities increased in a dose- and APOE ε4 genotype-dependent manner. Exploratory analyses suggested a dose-dependent drug effect on clinical and biomarker endpoints. Conclusions: The study was stopped early for futility, but dose-dependent effects observed in exploratory analyses on select clinical and biomarker endpoints suggest that higher dosing with gantenerumab may be necessary to achieve clinical efficacy. Trial registration: ClinicalTrials.gov, NCT01224106 . Registered on October 14, 2010.
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APOE4 is the strongest genetic risk factor for late-onset Alzheimer disease. ApoE4 increases brain amyloid-β pathology relative to other ApoE isoforms¹. However, whether APOE independently influences tau pathology, the other major proteinopathy of Alzheimer disease and other tauopathies, or tau-mediated neurodegeneration, is not clear. By generating P301S tau transgenic mice on either a human ApoE knock-in (KI) or ApoE knockout (KO) background, here we show that P301S/E4 mice have significantly higher tau levels in the brain and a greater extent of somatodendritic tau redistribution by three months of age compared with P301S/E2, P301S/E3, and P301S/EKO mice. By nine months of age, P301S mice with different ApoE genotypes display distinct phosphorylated tau protein (p-tau) staining patterns. P301S/E4 mice develop markedly more brain atrophy and neuroinflammation than P301S/E2 and P301S/E3 mice, whereas P301S/EKO mice are largely protected from these changes. In vitro, E4-expressing microglia exhibit higher innate immune reactivity after lipopolysaccharide treatment. Co-culturing P301S tau-expressing neurons with E4-expressing mixed glia results in a significantly higher level of tumour-necrosis factor-α (TNF-α) secretion and markedly reduced neuronal viability compared with neuron/E2 and neuron/E3 co-cultures. Neurons co-cultured with EKO glia showed the greatest viability with the lowest level of secreted TNF-α. Treatment of P301S neurons with recombinant ApoE (E2, E3, E4) also leads to some neuronal damage and death compared with the absence of ApoE, with ApoE4 exacerbating the effect. In individuals with a sporadic primary tauopathy, the presence of an ε4 allele is associated with more severe regional neurodegeneration. In individuals who are positive for amyloid-β pathology with symptomatic Alzheimer disease who usually have tau pathology, ε4-carriers demonstrate greater rates of disease progression. Our results demonstrate that ApoE affects tau pathogenesis, neuroinflammation, and tau-mediated neurodegeneration independently of amyloid-β pathology. ApoE4 exerts a ‘toxic’ gain of function whereas the absence of ApoE is protective.
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Purpose of review APOE4 genotype is the strongest genetic risk factor for Alzheimer's disease. Prevailing evidence suggests that amyloid β plays a critical role in Alzheimer's disease. The objective of this article is to review the recent findings about the metabolism of apolipoprotein E (ApoE) and amyloid β and other possible mechanisms by which ApoE contributes to the pathogenesis of Alzheimer's disease. Recent findings ApoE isoforms have differential effects on amyloid β metabolism. Recent studies demonstrated that ApoE-interacting proteins, such as ATP-binding cassette A1 (ABCA1) and LDL receptor, may be promising therapeutic targets for Alzheimer's disease treatment. Activation of liver X receptor and retinoid X receptor pathway induces ABCA1 and other genes, leading to amyloid β clearance. Inhibition of the negative regulators of ABCA1, such as microRNA-33, also induces ABCA1 and decreases the levels of ApoE and amyloid β. In addition, genetic inactivation of an E3 ubiquitin ligase, myosin regulatory light chain interacting protein, increases LDL receptor levels and inhibits amyloid accumulation. Although amyloid β-dependent pathways have been extensively investigated, there have been several recent studies linking ApoE with vascular function, neuroinflammation, metabolism, synaptic plasticity, and transcriptional regulation. For example, ApoE was identified as a ligand for a microglial receptor, TREM2, and studies suggested that ApoE may affect the TREM2-mediated microglial phagocytosis. Summary Emerging data suggest that ApoE affects several amyloid β-independent pathways. These underexplored pathways may provide new insights into Alzheimer's disease pathogenesis. However, it will be important to determine to what extent each mechanism contributes to the pathogenesis of Alzheimer's disease.
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Introduction: Amyloid β (Aβ) accumulates in the extracellular space as diffuse and neuritic plaques in Alzheimer's disease (AD). Aβ also deposits on the walls of arterioles as cerebral amyloid angiopathy (CAA) in most cases of AD and sometimes independently of AD. Apolipoprotein E (apoE) ɛ4 is associated with increases in both Aβ plaques and CAA in humans. Studies in mouse models that develop Aβ deposition have shown that murine apoE and human apoE4 have different abilities to facilitate plaque or CAA formation when studied independently. To better understand and compare the effects of murine apoE and human apoE4, we bred 5XFAD (line 7031) transgenic mice so that they expressed one copy of murine apoE and one copy of human apoE4 under the control of the normal murine apoE regulatory elements (5XFAD/apoE(m/4)). Results: The 5XFAD/apoE(m/4) mice contained levels of parenchymal CAA that were intermediate between 5XFAD/apoE(m/m) and 5XFAD/apoE(4/4) mice. In 5XFAD/apoE(m/4) mice, we found that Aβ parenchymal plaques co-localized with much more apoE than did parenchymal CAA, suggesting differential co-aggregation of apoE with Aβ in plaques versus CAA. More importantly, within the brain parenchyma of the 5XFAD/apoE(m/4) mice, plaques contained more murine apoE, which on its own results in more pronounced and earlier plaque formation, while CAA contained more human apoE4 which on its own results in more pronounced CAA formation. We further confirmed the co-aggregation of mouse apoE with Aβ in plaques by showing a strong correlation between insoluble mouse apoE and insoluble Aβ in PS1APP-21/apoE(m/4) mice which develop plaques without CAA. Conclusions: These studies suggest that both murine apoE and human apoE4 facilitate differential opposing effects in influencing Aβ plaques versus CAA via different co-aggregation with these two amyloid lesions and set the stage for understanding these effects at a molecular level.
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Prominent cerebral amyloid angiopathy is often observed in the brains of elderly individuals and is almost universally found in patients with Alzheimer's disease. Cerebral amyloid angiopathy is characterized by accumulation of the shorter amyloid-β isoform(s) (predominantly amyloid-β40) in the walls of leptomeningeal and cortical arterioles and is likely a contributory factor to vascular dysfunction leading to stroke and dementia in the elderly. We used transgenic mice with prominent cerebral amyloid angiopathy to investigate the ability of ponezumab, an anti-amyloid-β40 selective antibody, to attenuate amyloid-β accrual in cerebral vessels and to acutely restore vascular reactivity. Chronic administration of ponezumab to transgenic mice led to a significant reduction in amyloid and amyloid-β accumulation both in leptomeningeal and brain vessels when measured by intravital multiphoton imaging and immunohistochemistry. By enriching for cerebral vascular elements, we also measured a significant reduction in the levels of soluble amyloid-β biochemically. We hypothesized that the reduction in vascular amyloid-β40 after ponezumab administration may reflect the ability of ponezumab to mobilize an interstitial fluid pool of amyloid-β40 in brain. Acutely, ponezumab triggered a significant and transient increase in interstitial fluid amyloid-β40 levels in old plaque-bearing transgenic mice but not in young animals. We also measured a beneficial effect on vascular reactivity following acute administration of ponezumab, even in vessels where there was a severe cerebral amyloid angiopathy burden. Taken together, the beneficial effects ponezumab administration has on reducing the rate of cerebral amyloid angiopathy deposition and restoring cerebral vascular health favours a mechanism that involves rapid removal and/or neutralization of amyloid-β species that may otherwise be detrimental to normal vessel function.
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EXPEDITION and EXPEDITION2 were identically designed placebo-controlled phase 3 studies assessing effects of solanezumab, an antiamyloid monoclonal antibody binding soluble amyloid-β peptide, on cognitive and functional decline over 80 weeks in patients with mild-to-moderate Alzheimer's disease (AD). Primary findings for both studies have been published. Secondary analyses of efficacy, biomarker, and safety endpoints in the pooled (EXPEDTION + EXPEDITION2) mild AD population were performed. In the mild AD population, less cognitive and functional decline was observed with solanezumab (n = 659) versus placebo (n = 663), measured by Alzheimer's Disease Assessment Scale Cognitive subscale, Mini-Mental State Examination, and Alzheimer's Disease Cooperative Study-Activities of Daily Living functional scale Instrumental ADLs. Baseline-to-endpoint changes did not differ between treatment groups for Alzheimer's Disease Cooperative Study-Activities of Daily Living functional scale, basic items of the ADCS-ADL, and Clinical Dementia Rating Sum of Boxes. Plasma/cerebrospinal fluid biomarker findings indicated target engagement by solanezumab. Solanezumab demonstrated acceptable safety. Efficacy findings for the moderate AD population are also provided. These findings describe solanezumab effects on efficacy/safety measures in a mild AD population. Another phase 3 study, EXPEDITION3, will investigate solanezumab's effects in a mild AD population. Copyright © 2015 Eli Lilly and Company, Indianapolis, IN. Published by Elsevier Inc. All rights reserved.
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Significance One of the hallmarks of Alzheimer’s disease (AD) is cerebral amyloid angiopathy (CAA), which is a strong and independent risk factor for cerebral hemorrhage, ischemic stroke, and dementia. However, the mechanisms by which CAA contributes to these conditions are poorly understood. Results from the present study provide strong evidence that vascular oxidative stress plays a causal role in CAA-induced cerebrovascular dysfunction, CAA-induced cerebral hemorrhage, and CAA formation, itself. They also suggest that NADPH oxidase is the source of this oxidative stress and that strategies to inhibit NADPH oxidase may have therapeutic potential in patients with AD and CAA.
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Apolipoprotein E (apoE) is the strongest known genetic risk factor for late onset Alzheimer's disease (AD). It influences amyloid-β (Aβ) clearance and aggregation, which likely contributes in large part to its role in AD pathogenesis. We recently found that HJ6.3, a monoclonal antibody against apoE, significantly reduced Aβ plaque load when given to APPswe/PS1ΔE9 (APP/PS1) mice starting before the onset of plaque deposition. To determine whether the anti-apoE antibody HJ6.3 affects Aβ plaques, neuronal network function, and behavior in APP/PS1 mice after plaque onset, we administered HJ6.3 (10 mg/kg/week) or PBS intraperitoneally to 7-month-old APP/PS1 mice for 21 weeks. HJ6.3 mildly improved spatial learning performance in the water maze, restored resting-state functional connectivity, and modestly reduced brain Aβ plaque load. There was no effect of HJ6.3 on total plasma cholesterol or cerebral amyloid angiopathy. To investigate the underlying mechanisms of anti-apoE immunotherapy, HJ6.3 was applied to the brain cortical surface and amyloid deposition was followed over 2 weeks using in vivo imaging. Acute exposure to HJ6.3 affected the course of amyloid deposition in that it prevented the formation of new amyloid deposits, limited their growth, and was associated with occasional clearance of plaques, a process likely associated with direct binding to amyloid aggregates. Topical application of HJ6.3 for only 14 d also decreased the density of amyloid plaques assessed postmortem. Collectively, these studies suggest that anti-apoE antibodies have therapeutic potential when given before or after the onset of Aβ pathology.
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Bapineuzumab, a humanized anti-amyloid-beta monoclonal antibody, is in clinical development for the treatment of Alzheimer's disease. We conducted two double-blind, randomized, placebo-controlled, phase 3 trials involving patients with mild-to-moderate Alzheimer's disease--one involving 1121 carriers of the apolipoprotein E (APOE) ε4 allele and the other involving 1331 noncarriers. Bapineuzumab or placebo, with doses varying by study, was administered by intravenous infusion every 13 weeks for 78 weeks. The primary outcome measures were scores on the 11-item cognitive subscale of the Alzheimer's Disease Assessment Scale (ADAS-cog11, with scores ranging from 0 to 70 and higher scores indicating greater impairment) and the Disability Assessment for Dementia (DAD, with scores ranging from 0 to 100 and higher scores indicating less impairment). A total of 1090 carriers and 1114 noncarriers were included in the efficacy analysis. Secondary outcome measures included findings on positron-emission tomographic amyloid imaging with the use of Pittsburgh compound B (PIB-PET) and cerebrospinal fluid phosphorylated tau (phospho-tau) concentrations. There were no significant between-group differences in the primary outcomes. At week 78, the between-group differences in the change from baseline in the ADAS-cog11 and DAD scores (bapineuzumab group minus placebo group) were -0.2 (P=0.80) and -1.2 (P=0.34), respectively, in the carrier study; the corresponding differences in the noncarrier study were -0.3 (P=0.64) and 2.8 (P=0.07) with the 0.5-mg-per-kilogram dose of bapineuzumab and 0.4 (P=0.62) and 0.9 (P=0.55) with the 1.0-mg-per-kilogram dose. The major safety finding was amyloid-related imaging abnormalities with edema among patients receiving bapineuzumab, which increased with bapineuzumab dose and APOE ε4 allele number and which led to discontinuation of the 2.0-mg-per-kilogram dose. Between-group differences were observed with respect to PIB-PET and cerebrospinal fluid phospho-tau concentrations in APOE ε4 allele carriers but not in noncarriers. Bapineuzumab did not improve clinical outcomes in patients with Alzheimer's disease, despite treatment differences in biomarkers observed in APOE ε4 carriers. (Funded by Janssen Alzheimer Immunotherapy and Pfizer; Bapineuzumab 301 and 302 ClinicalTrials.gov numbers, NCT00575055 and NCT00574132, and EudraCT number, 2009-012748-17.).
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The contributing effect of cerebrovascular pathology in Alzheimer's disease (AD) has become increasingly appreciated. Recent evidence suggests that amyloid-beta peptide (Abeta), the same peptide found in neuritic plaques of AD, may play a role via its vasoactive properties. Several studies have examined young Tg2576 mice expressing mutant amyloid precursor protein (APP) and having elevated levels of soluble Abeta but no cerebral amyloid angiopathy (CAA). These studies suggest but do not prove that soluble Abeta can significantly impair the cerebral circulation. Other studies examining older Tg2576 mice having extensive CAA found even greater cerebrovascular dysfunction, suggesting that CAA is likely to further impair vascular function. Herein, we examined vasodilatory responses in young and older Tg2576 mice to further assess the roles of soluble and insoluble Abeta on vessel function. We found that (1) vascular impairment was present in both young and older Tg2576 mice; (2) a strong correlation between CAA severity and vessel reactivity exists; (3) a surprisingly small amount of CAA led to marked reduction or complete loss of vessel function; 4) CAA-induced vasomotor impairment resulted from dysfunction rather than loss or disruption of vascular smooth muscle cells; and 5) acute depletion of Abeta improved vessel function in young and to a lesser degree older Tg2576 mice. These results strongly suggest that both soluble and insoluble Abeta cause cerebrovascular dysfunction, that mechanisms other than Abeta-induced alteration in vessel integrity are responsible, and that anti-Abeta therapy may have beneficial vascular effects in addition to positive effects on parenchymal amyloid.
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Importance: Sporadic Alzheimer disease (AD) is caused in part by decreased clearance of the β-amyloid (Aβ) peptide breakdown products. Lipid-depleted (LD) apolipoproteins are less effective at binding and clearing Aβ, and LD Aβ peptides are more toxic to neurons. However, not much is known about the lipid states of these proteins in human cerebrospinal fluid. Objective: To characterize the lipidation states of Aβ peptides and apolipoprotein E in the cerebrospinal fluid in adults with respect to cognitive diagnosis and APOE ε4 allele carrier status and after a dietary intervention. Design: Randomized clinical trial. Setting: Veterans Affairs Medical Center clinical research unit. Participants: Twenty older adults with normal cognition (mean [SD] age, 69 [7] years) and 27 with amnestic mild cognitive impairment (67 [6] years). Interventions: Randomization to a diet high in saturated fat content and with a high glycemic index (High diet; 45% of energy from fat [>25% saturated fat], 35%-40% from carbohydrates with a mean glycemic index >70, and 15%-20% from protein) or a diet low in saturated fat content and with a low glycemic index (Low diet; 25% of energy from fat [<7% saturated fat], 55%-60% from carbohydrates with a mean glycemic index <55, and 15%-20% from protein). Main outcomes and measures: Lipid-depleted Aβ42 and Aβ40 and apolipoprotein E in cerebrospinal fluid. Results: Baseline levels of LD Aβ were greater for adults with mild cognitive impairment compared with adults with normal cognition (LD Aβ42, P = .05; LD Aβ40, P = .01). These findings were magnified in adults with mild cognitive impairment and the ε4 allele, who had higher LD apolipoprotein E levels irrespective of cognitive diagnosis (P < .001). The Low diet tended to decrease LD Aβ levels, whereas the High diet increased these fractions (LD Aβ42, P = .01; LD Aβ40, P = .15). Changes in LD Aβ levels with the Low diet negatively correlated with changes in cerebrospinal fluid levels of insulin (LD Aβ42 and insulin, r = -0.68 [P = .01]; LD Aβ40 and insulin, r = -0.78 [P = .002]). Conclusions and relevance: The lipidation states of apolipoproteins and Aβ peptides in the brain differ depending on APOE genotype and cognitive diagnosis. Concentrations can be modulated by diet. These findings may provide insight into the mechanisms through which apolipoprotein E4 and unhealthy diets impart risk for developing AD.
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Apolipoprotein E (Apo-E) is a major cholesterol carrier that supports lipid transport and injury repair in the brain. APOE polymorphic alleles are the main genetic determinants of Alzheimer disease (AD) risk: individuals carrying the ε4 allele are at increased risk of AD compared with those carrying the more common ε3 allele, whereas the ε2 allele decreases risk. Presence of the APOE ε4 allele is also associated with increased risk of cerebral amyloid angiopathy and age-related cognitive decline during normal ageing. Apo-E-lipoproteins bind to several cell-surface receptors to deliver lipids, and also to hydrophobic amyloid-β (Aβ) peptide, which is thought to initiate toxic events that lead to synaptic dysfunction and neurodegeneration in AD. Apo-E isoforms differentially regulate Aβ aggregation and clearance in the brain, and have distinct functions in regulating brain lipid transport, glucose metabolism, neuronal signalling, neuroinflammation, and mitochondrial function. In this Review, we describe current knowledge on Apo-E in the CNS, with a particular emphasis on the clinical and pathological features associated with carriers of different Apo-E isoforms. We also discuss Aβ-dependent and Aβ-independent mechanisms that link Apo-E4 status with AD risk, and consider how to design effective strategies for AD therapy by targeting Apo-E.
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The apolipoprotein E (APOE) ε4 allele is the strongest genetic risk factor for late-onset, sporadic Alzheimer's disease (AD). The APOE ε4 allele markedly increases AD risk and decreases age of onset, likely through its strong effect on the accumulation of amyloid-β (Aβ) peptide. In contrast, the APOE ε2 allele appears to decrease AD risk. Most rare, early-onset forms of familial AD are caused by autosomal dominant mutations that often lead to overproduction of Aβ(42) peptide. However, the mechanism by which APOE alleles differentially modulate Aβ accumulation in sporadic, late-onset AD is less clear. In a cohort of cognitively normal individuals, we report that reliable molecular and neuroimaging biomarkers of cerebral Aβ deposition vary in an apoE isoform-dependent manner. We hypothesized that human apoE isoforms differentially affect Aβ clearance or synthesis in vivo, resulting in an apoE isoform-dependent pattern of Aβ accumulation later in life. Performing in vivo microdialysis in a mouse model of Aβ-amyloidosis expressing human apoE isoforms (PDAPP/TRE), we find that the concentration and clearance of soluble Aβ in the brain interstitial fluid depends on the isoform of apoE expressed. This pattern parallels the extent of Aβ deposition observed in aged PDAPP/TRE mice. ApoE isoform-dependent differences in soluble Aβ metabolism are observed not only in aged but also in young PDAPP/TRE mice well before the onset of Aβ deposition in amyloid plaques in the brain. Additionally, amyloidogenic processing of amyloid precursor protein and Aβ synthesis, as assessed by in vivo stable isotopic labeling kinetics, do not vary according to apoE isoform in young PDAPP/TRE mice. Our results suggest that APOE alleles contribute to AD risk by differentially regulating clearance of Aβ from the brain, suggesting that Aβ clearance pathways may be useful therapeutic targets for AD prevention.
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There is increasing evidence that cerebrovascular dysfunction plays a role not only in vascular causes of cognitive impairment but also in Alzheimer's disease (AD). Vascular risk factors and AD impair the structure and function of cerebral blood vessels and associated cells (neurovascular unit), effects mediated by vascular oxidative stress and inflammation. Injury to the neurovascular unit alters cerebral blood flow regulation, depletes vascular reserves, disrupts the blood-brain barrier, and reduces the brain's repair potential, effects that amplify the brain dysfunction and damage exerted by incident ischemia and coexisting neurodegeneration. Clinical-pathological studies support the notion that vascular lesions aggravate the deleterious effects of AD pathology by reducing the threshold for cognitive impairment and accelerating the pace of the dementia. In the absence of mechanism-based approaches to counteract cognitive dysfunction, targeting vascular risk factors and improving cerebrovascular health offers the opportunity to mitigate the impact of one of the most disabling human afflictions.
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Background Anti-Aβ immunotherapy in transgenic mice reduces both diffuse and compact amyloid deposits, improves memory function and clears early-stage phospho-tau aggregates. As most Alzheimer disease cases occur well past midlife, the current study examined adoptive transfer of anti-Aβ antibodies to 19- and 23-month old APP-transgenic mice. Methods We investigated the effects of weekly anti-Aβ antibody treatment on radial-arm water-maze performance, parenchymal and vascular amyloid loads, and the presence of microhemorrhage in the brain. 19-month-old mice were treated for 1, 2 or 3 months while 23-month-old mice were treated for 5 months. Only the 23-month-old mice were subject to radial-arm water-maze testing. Results After 3 months of weekly injections, this passive immunization protocol completely reversed learning and memory deficits in these mice, a benefit that was undiminished after 5 months of treatment. Dramatic reductions of diffuse Aβ immunostaining and parenchymal Congophilic amyloid deposits were observed after five months, indicating that even well-established amyloid deposits are susceptible to immunotherapy. However, cerebral amyloid angiopathy increased substantially with immunotherapy, and some deposits were associated with microhemorrhage. Reanalysis of results collected from an earlier time-course study demonstrated that these increases in vascular deposits were dependent on the duration of immunotherapy. Conclusions The cognitive benefits of passive immunotherapy persist in spite of the presence of vascular amyloid and small hemorrhages. These data suggest that clinical trials evaluating such treatments will require precautions to minimize potential adverse events associated with microhemorrhage.
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Passive immunization with an antibody directed against the N terminus of amyloid beta (Abeta) has recently been reported to exacerbate cerebral amyloid angiopathy (CAA)-related microhemorrhage in a transgenic animal model. Although the mechanism responsible for the deleterious interaction is unclear, a direct binding event may be required. We characterized the binding properties of several monoclonal anti-Abeta antibodies to deposited Abeta in brain parenchyma and CAA. Biochemical analyses demonstrated that the 3D6 and 10D5, two N-terminally directed antibodies, bound with high affinity to deposited forms of Abeta, whereas 266, a central domain antibody, lacked affinity for deposited Abeta. To determine whether 266 or 3D6 would exacerbate CAA-associated microhemorrhage, we treated aged PDAPP mice with either antibody for 6 weeks. We observed an increase in both the incidence and severity of CAA-associated microhemorrhage when PDAPP transgenic mice were treated with the N-terminally directed 3D6 antibody, whereas mice treated with 266 were unaffected. These results may have important implications for future immune-based therapeutic strategies for Alzheimer's disease.
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Mutations in the genes for amyloid precursor protein (APP) and presenilins (PS1, PS2) increase production of beta-amyloid 42 (Abeta42) and cause familial Alzheimer's disease (FAD). Transgenic mice that express FAD mutant APP and PS1 overproduce Abeta42 and exhibit amyloid plaque pathology similar to that found in AD, but most transgenic models develop plaques slowly. To accelerate plaque development and investigate the effects of very high cerebral Abeta42 levels, we generated APP/PS1 double transgenic mice that coexpress five FAD mutations (5XFAD mice) and additively increase Abeta42 production. 5XFAD mice generate Abeta42 almost exclusively and rapidly accumulate massive cerebral Abeta42 levels. Amyloid deposition (and gliosis) begins at 2 months and reaches a very large burden, especially in subiculum and deep cortical layers. Intraneuronal Abeta42 accumulates in 5XFAD brain starting at 1.5 months of age (before plaques form), is aggregated (as determined by thioflavin S staining), and occurs within neuron soma and neurites. Some amyloid deposits originate within morphologically abnormal neuron soma that contain intraneuronal Abeta. Synaptic markers synaptophysin, syntaxin, and postsynaptic density-95 decrease with age in 5XFAD brain, and large pyramidal neurons in cortical layer 5 and subiculum are lost. In addition, levels of the activation subunit of cyclin-dependent kinase 5, p25, are elevated significantly at 9 months in 5XFAD brain, although an upward trend is observed by 3 months of age, before significant neurodegeneration or neuron loss. Finally, 5XFAD mice have impaired memory in the Y-maze. Thus, 5XFAD mice rapidly recapitulate major features of AD amyloid pathology and may be useful models of intraneuronal Abeta42-induced neurodegeneration and amyloid plaque formation.
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Aducanumab is a human monoclonal antibody that selectively targets aggregated forms of Aβ, including soluble oligomers and insoluble fibrils. EMERGE and ENGAGE are two 18‐month, randomized, double‐blind, placebo‐controlled, global Phase 3 studies with identical design that evaluated the efficacy and safety of aducanumab in patients aged 50–85 years with early Alzheimer’s disease (MCI due to AD or mild AD dementia). Key inclusion criteria included positive amyloid PET, MMSE score of 24–30, CDR Global score of 0.5, and an RBANS‐DMI score ≤85. During the 18‐month placebo‐controlled period, patients were randomized 1:1:1 to low‐dose aducanumab, high‐dose aducanumab, or placebo, administered via IV infusion every 4 weeks. The primary endpoint for EMERGE and ENGAGE was change from baseline at Week 78 on the CDR‐SB. Secondary endpoints included change from baseline on MMSE, ADAS‐Cog13, and ADCS‐ADL‐MCI. Following pre‐planned futility analysis, analysis of the data from the final database lock showed that EMERGE met its primary endpoint, based on the pre‐specified statistical analysis plan. Patients treated with high dose aducanumab showed a significant reduction of clinical decline from baseline in CDR‐SB scores at 78 weeks (22% versus placebo, P = 0.01). ENGAGE did not meet its primary endpoint. However, data from patients in ENGAGE who achieved sufficient exposure to high dose aducanumab supported the findings of EMERGE. EMERGE met its primary endpoint, based on the pre‐specified statistical analysis plan. Data from a subset of patients in ENGAGE support the results of EMERGE. The safety and tolerability profile of aducanumab in EMERGE and ENGAGE was consistent with previous studies of aducanumab.
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The shared role of amyloid-β (Aβ) deposition in cerebral amyloid angiopathy (CAA) and Alzheimer disease (AD) is arguably the clearest instance of crosstalk between neurodegenerative and cerebrovascular processes. The pathogenic pathways of CAA and AD intersect at the levels of Aβ generation, its circulation within the interstitial fluid and perivascular drainage pathways and its brain clearance, but diverge in their mechanisms of brain injury and disease presentation. Here, we review the evidence for and the pathogenic implications of interactions between CAA and AD. Both pathologies seem to be driven by impaired Aβ clearance, creating conditions for a self-reinforcing cycle of increased vascular Aβ, reduced perivascular clearance and further CAA and AD progression. Despite the close relationship between vascular and plaque Aβ deposition, several factors favour one or the other, such as the carboxy-terminal site of the peptide and specific co-deposited proteins. Amyloid-related imaging abnormalities that have been seen in trials of anti-Aβ immunotherapy are another probable intersection between CAA and AD, representing overload of perivascular clearance pathways and the effects of removing Aβ from CAA-positive vessels. The intersections between CAA and AD point to a crucial role for improving vascular function in the treatment of both diseases and indicate the next steps necessary for identifying therapies.