Mechanisms of APOE4-Driven Alzheimer’s Disease Pathogenesis and Related Therapeutic Approaches

Apolipoprotein E4 (APOE4) is the strongest known genetic risk factor for late-onset Alzheimer’s disease (AD), however, its pathogenic mechanisms remain unclear. We performed in-depth studies on two intriguing, yet understudied, features of APOE4 pathogenesis to better understand their roles in promoting AD. First, APOE can be produced in a variety of cell types and may exert different pathological effects depending on its cellular source. We report a rigorous characterization of neuronal APOE4 effects on prominent AD-related pathologies by selectively removing APOE4 from neurons in an APOE4-expressing tauopathy mouse model. We found that removal of neuronal APOE4 led to a drastic reduction in Tau pathology, gliosis, neurodegeneration, neurodysfunction, and myelin deficits and eliminated disease-associated subpopulations of neurons, oligodendrocytes, astrocytes, and microglia that were enriched in APOE4-expressing tauopathy mice. Thus, neuronal APOE4 plays a central role in promoting the development of major AD pathologies. Second, APOE4 has been shown to be an important driver of Tau pathology, gliosis and degeneration in AD but the mechanisms underlying these APOE4-driven pathological effects remain elusive. We demonstrated in a tauopathy mouse model that APOE4 promotes significantly more nucleo-cytoplasmic translocation and release of high mobility group box 1 (HMGB1) from hippocampal neurons than APOE3. Treatment of APOE4-expressing tauopathy mice with HMGB1 inhibitors effectively blocked the nucleo-cytoplasmic translocation of HMGB1 and ameliorated the development of prominent APOE4-driven AD pathologies. Notably, treatment of APOE3-expressing tauopathy mice with HMGB1 inhibitors did not show significant beneficial effects on these pathological parameters. Thus, APOE4 drives Tau-mediated gliosis and degeneration by promoting neuronal HMGB1 release, and HMGB1 inhibitors represent a promising approach for treating APOE4-related AD and other tauopathies

Temperature and moisture variability in the eastern Mediterranean region during Marine Isotope Stages 11-10 based on biomarker analysis of the Tenaghi Philippon peat deposit

The Mediterranean region is highly sensitive to climate change, particularly with regard to warming and increasing aridity. Understanding its past climate history during periods similar to the Holocene is key to understand the long-term dynamics that accompany anthropogenic climate change. Marine Isotope Stage (MIS) 11 (ca. 424-367 ka BP) is considered one of the best Holocene analogues. Despite detailed insight from Atlantic marine records and European continental records, MIS 11 temperature and rainfall evolution in the Mediterranean remains poorly understood.We present a detailed record of MIS 11-10 climate change at Tenaghi Philippon, a telmatic peatland in NE Greece. We use microbial membrane lipids (brGDGTs), the delta D of n-C-29 (delta D-wax) and distribution of n-alkanes derived from plant leaf waxes, and levoglucosan concentrations to reconstruct changes in temperature, rainfall sources and vegetation burning. Glacial-interglacial temperature patterns indicate strong Atlantic influence in the Eastern Mediterranean region.Low delta D-wax values and high temperatures indicate a predominance of Atlantic-sourced winter precipitation during MIS 11, and vice versa during MIS 10. The latter is attributed to a suppression of the Mediterranean storm track, probably due to a persistent high-pressure cell over most of the European continent, mainly in response to an extended ice cover during the glacial. The levoglucosan record is consistent with rapid change to drier conditions and increased vegetation burning from MIS 11 to 10. Millennial-scale oscillations allow to characterise cooling episodes previously recorded at other sites, with conditions of decreased winter precipitation, while suggesting increased seasonality during the interglacial optimum. (C) 2019 Elsevier Ltd. All rights reserved

In Vivo Chimeric Alzheimer’s Disease Modeling of Apolipoprotein E4 Toxicity in Human Neurons

Despite its clear impact on Alzheimer's disease (AD) risk, apolipoprotein (apo) E4's contributions to AD etiology remain poorly understood. Progress in answering this and other questions in AD research has been limited by an inability to model human-specific phenotypes in an in vivo environment. Here we transplant human induced pluripotent stem cell (hiPSC)-derived neurons carrying normal apoE3 or pathogenic apoE4 into human apoE3 or apoE4 knockin mouse hippocampi, enabling us to disentangle the effects of apoE4 produced in human neurons and in the brain environment. Using single-nucleus RNA sequencing (snRNA-seq), we identify key transcriptional changes specific to human neuron subtypes in response to endogenous or exogenous apoE4. We also find that Aβ from transplanted human neurons forms plaque-like aggregates, with differences in localization and interaction with microglia depending on the transplant and host apoE genotype. These findings highlight the power of in vivo chimeric disease modeling for studying AD

Neuronal APOE4 removal protects against tau-mediated gliosis, neurodegeneration and myelin deficits

Apolipoprotein E4 (APOE4) is the strongest known genetic risk factor for late-onset Alzheimer's disease (AD). Conditions of stress or injury induce APOE expression within neurons, but the role of neuronal APOE4 in AD pathogenesis is still unclear. Here we report the characterization of neuronal APOE4 effects on AD-related pathologies in an APOE4-expressing tauopathy mouse model. The selective genetic removal of APOE4 from neurons led to a significant reduction in tau pathology, gliosis, neurodegeneration, neuronal hyperexcitability and myelin deficits. Single-nucleus RNA-sequencing revealed that the removal of neuronal APOE4 greatly diminished neurodegenerative disease-associated subpopulations of neurons, oligodendrocytes, astrocytes and microglia whose accumulation correlated to the severity of tau pathology, neurodegeneration and myelin deficits. Thus, neuronal APOE4 plays a central role in promoting the development of major AD pathologies and its removal can mitigate the progressive cellular and tissue alterations occurring in this model of APOE4-driven tauopathy

Dentate gyrus and CA3 GABAergic interneurons bidirectionally modulate signatures of internal and external drive to CA1

Specific classes of GABAergic neurons play specific roles in regulating information processing in the brain. In the hippocampus, two major classes, parvalbumin-expressing (PV+) and somatostatin-expressing (SST+), differentially regulate endogenous firing patterns and target subcellular compartments of principal cells. How these classes regulate the flow of information throughout the hippocampus is poorly understood. We hypothesize that PV+ and SST+ interneurons in the dentate gyrus (DG) and CA3 differentially modulate CA3 patterns of output, thereby altering the influence of CA3 on CA1. We find that while suppressing either interneuron class increases DG and CA3 output, the effects on CA1 were very different. Suppressing PV+ interneurons increases local field potential signatures of coupling from CA3 to CA1 and decreases signatures of coupling from entorhinal cortex to CA1; suppressing SST+ interneurons has the opposite effect. Thus, DG and CA3 PV+ and SST+ interneurons bidirectionally modulate the flow of information through the hippocampal circuit

Neuronal ApoE upregulates MHC-I expression to drive selective neurodegeneration in Alzheimer’s disease

Selective neurodegeneration is a critical causal factor in Alzheimer's disease (AD); however, the mechanisms that lead some neurons to perish, whereas others remain resilient, are unknown. We sought potential drivers of this selective vulnerability using single-nucleus RNA sequencing and discovered that ApoE expression level is a substantial driver of neuronal variability. Strikingly, neuronal expression of ApoE-which has a robust genetic linkage to AD-correlated strongly, on a cell-by-cell basis, with immune response pathways in neurons in the brains of wild-type mice, human ApoE knock-in mice and humans with or without AD. Elimination or over-expression of neuronal ApoE revealed a causal relationship among ApoE expression, neuronal MHC-I expression, tau pathology and neurodegeneration. Functional reduction of MHC-I ameliorated tau pathology in ApoE4-expressing primary neurons and in mouse hippocampi expressing pathological tau. These findings suggest a mechanism linking neuronal ApoE expression to MHC-I expression and, subsequently, to tau pathology and selective neurodegeneration

The APOE-R136S mutation protects against APOE4-driven Tau pathology, neurodegeneration and neuroinflammation.

Apolipoprotein E4 (APOE4) is the strongest genetic risk factor for late-onset Alzheimers disease (LOAD), leading to earlier age of clinical onset and exacerbating pathologies. There is a critical need to identify protective targets. Recently, a rare APOE variant, APOE3-R136S (Christchurch), was found to protect against early-onset AD in a PSEN1-E280A carrier. In this study, we sought to determine if the R136S mutation also protects against APOE4-driven effects in LOAD. We generated tauopathy mouse and human iPSC-derived neuron models carrying human APOE4 with the homozygous or heterozygous R136S mutation. We found that the homozygous R136S mutation rescued APOE4-driven Tau pathology, neurodegeneration and neuroinflammation. The heterozygous R136S mutation partially protected against APOE4-driven neurodegeneration and neuroinflammation but not Tau pathology. Single-nucleus RNA sequencing revealed that the APOE4-R136S mutation increased disease-protective and diminished disease-associated cell populations in a gene dose-dependent manner. Thus, the APOE-R136S mutation protects against APOE4-driven AD pathologies, providing a target for therapeutic development against AD

APOE4/4 is linked to damaging lipid droplets in Alzheimers disease microglia.

Several genetic risk factors for Alzheimers disease implicate genes involved in lipid metabolism and many of these lipid genes are highly expressed in glial cells1. However, the relationship between lipid metabolism in glia and Alzheimers disease pathology remains poorly understood. Through single-nucleus RNA sequencing of brain tissue in Alzheimers disease, we have identified a microglial state defined by the expression of the lipid droplet-associated enzyme ACSL1 with ACSL1-positive microglia being most abundant in patients with Alzheimers disease having the APOE4/4 genotype. In human induced pluripotent stem cell-derived microglia, fibrillar Aβ induces ACSL1 expression, triglyceride synthesis and lipid droplet accumulation in an APOE-dependent manner. Additionally, conditioned media from lipid droplet-containing microglia lead to Tau phosphorylation and neurotoxicity in an APOE-dependent manner. Our findings suggest a link between genetic risk factors for Alzheimers disease with microglial lipid droplet accumulation and neurotoxic microglia-derived factors, potentially providing therapeutic strategies for Alzheimers disease

Experimental and real-world evidence supporting the computational repurposing of bumetanide for APOE4-related Alzheimer’s disease

The evident genetic, pathological and clinical heterogeneity of Alzheimer’s disease (AD) poses challenges for traditional drug development. We conducted a computational drug-repurposing screen for drugs to treat apolipoprotein E4 (APOE4)-related AD. We first established APOE genotype-dependent transcriptomic signatures of AD by analyzing publicly available human brain databases. We then queried these signatures against the Connectivity Map database, which contains transcriptomic perturbations of more than 1,300 drugs, to identify those that best reverse APOE genotype-specific AD signatures. Bumetanide was identified as a top drug for APOE4-related AD. Treatment of APOE4-knock-in mice without or with amyloid β (Aβ) accumulation using bumetanide rescued electrophysiological, pathological or cognitive deficits. Single-nucleus RNA sequencing revealed transcriptomic reversal of AD signatures in specific cell types in these mice, a finding confirmed in APOE4 induced pluripotent stem cell (iPSC)-derived neurons. In humans, bumetanide exposure was associated with a significantly lower AD prevalence in individuals over the age of 65 years in two electronic health record databases, suggesting the effectiveness of bumetanide in preventing AD.National Institutes of HealthDepto. de Estadística y Ciencia de los DatosFac. de Estudios EstadísticosTRUEpu