APOE4 disrupts intracellular lipid homeostasis in human iPSC-derived glia

Deciphering the role of APOE in cerebral amyloid angiopathy: from genetic insights to therapeutic horizons

Cerebral amyloid angiopathy (CAA), characterized by the deposition of amyloid-β (Aβ) peptides in the walls of medium and small vessels of the brain and leptomeninges, is a major cause of lobar hemorrhage in elderly individuals. Among the genetic risk factors for CAA that continue to be recognized, the apolipoprotein E (APOE) gene is the most significant and prevalent, as its variants have been implicated in more than half of all patients with CAA. While the presence of the APOE ε4 allele markedly increases the risk of CAA, the ε2 allele confers a protective effect relative to the common ε3 allele. These allelic variants encode three APOE isoforms that differ at two amino acid positions. The primary physiological role of APOE is to mediate lipid transport in the brain and periphery; however, it has also been shown to be involved in a wide array of biological functions, particularly those involving Aβ, in which it plays a known role in processing, production, aggregation, and clearance. The challenges posed by the reliance on postmortem histological analyses and the current absence of an effective intervention underscore the urgency for innovative APOE-targeted strategies for diagnosing CAA. This review not only deepens our understanding of the impact of APOE on the pathogenesis of CAA but can also help guide the exploration of targeted therapies, inspiring further research into the therapeutic potential of APOE.

Conformational features of guinea pig apolipoprotein E offer insights into functioning of human apolipoprotein E

Apolipoprotein (apo) E is a major cholesterol transport protein in the plasma and brain of humans, with the APOE ε4 allele (coding for R112) associated with a higher risk for cardiovascular and Alzheimer's diseases (CVD and AD, respectively) compared to APOE ε3 (coding for C112). The molecular basis underlying the link between APOE ε4 and CVD/AD is poorly understood. Here apoE from Cavia porcellus (guinea pig, GP), which is 72 % identical to human apoE4 but lacking residues 193-197 and 246-252, a feature noted in all hystricomorph apoE, was used as a model to understand the role of apoE4. Western blot with anti-human apoE antibody revealed cross reactivity with bacterially expressed recombinant GP apoE. GP apoE solubilized phospholipids far more efficiently than apoE3/E4 but promoted macrophage cholesterol efflux to a similar extent. The overall secondary structure and tetrameric organization of GP apoE were broadly similar to those of apoE3/E4. Guanidine HCl-induced denaturation revealed a biphasic unfolding pattern indicative of a two-domain architecture for GP apoE. Hydrogen-deuterium exchange coupled to mass spectrometry of GP apoE revealed mixed EX1/EX2 kinetics similar to that noted for apoE4, with peak broadening indicative of the presence of partially folded intermediate states. Limited proteolysis reveals more resistance to cleavage compared to apoE3/E4. Taken together, the findings suggest that the CT domain modulates the lipid-binding ability of apoE and attenuates the overall dynamics of the protein, which bears direct relevance in regulation of lipoprotein metabolism with implications in amyloid-related neurodegeneration.

Longitudinal associations between lipid panel and cognitive decline modified by APOE 4 carrier status in biracial community-dwelling older adults: Findings from the Chicago health and aging project

BACKGROUND

There have been contradictory findings on the associations between lipids and cognitive decline (CD), which may be attributed to the heterogeneity in the APOE4 carrier status, given APOE's lipid transportation roles. However, extant studies rarely examined the modifying effects of APOE4 carrier status on the associations between lipids and CD.

METHODS

We analyzed the Chicago Health and Aging Project, a 20-year cohort study comprising older adults with lipid panel assayed, i.e., total cholesterol (TC), triglycerides (TG), high-density lipoprotein (HDL), and low-density lipoprotein (LDL), and longitudinal cognitive tests. We ran adjusted linear mixed-effects models, regressing cognitive test composite on each of the four lipids independently, first with the total sample and subsequently using interaction and stratified subgroup analyses, examining the modifying effects of APOE4 carrier status on the associations.

RESULTS

3,496 biracial community-dwelling older adults were recruited from the South side of Chicago (58% African American & 64% women; mean follow-up = 4.6 years). In the total sample, there was a borderline association between TG and CD, estimate (SD, p-value) = 0.0001 (0.0000,0.0565). No associations were detected with other lipids. In the interaction and subgroup analyses, only in ε4 carriers that higher TC levels were significantly associated with accelerated CD, -0.020 (0.009,0.035), whereas higher TG levels were significantly associated with decelerated CD, 0.001 (0.001,0.045). No modifying effects of ε4 carrier status were detected with other lipids.

DISCUSSION

Specific lipids, i.e., TC and TG, were associated with CD only in the ε4 carriers, highlighting the potential importance of measuring APOE4 status to better inform risk prediction and treatment.

Function and application of brain‑derived neurotrophic factor precursors (Review)

Brain‑derived neurotrophic factor precursor (proBDNF) plays a critical role in the pathogenesis and progression of various human diseases. Through its interaction with p75NTR and sortilin receptors, proBDNF promotes apoptosis, impairs synaptic plasticity, and contributes to the regulation of immune system function, inflammatory responses and cellular metabolic processes. proBDNF is widely distributed throughout the body, and as such, extensive research has demonstrated that proBDNF is significantly associated with the pathophysiological mechanisms underlying several diseases. In the present review, the mechanisms by which proBDNF contributes to different diseases are summarized to highlight its potential therapeutic and diagnostic implications. Specifically, the role of proBDNF in cognitive disorders, focusing on its effects on synaptic function and neural network dynamics, while analyzing the cascade reactions involving proBDNF and downstream effector molecules in inflammatory diseases, to elucidate its bidirectional regulatory effects in tumor initiation and progression. Furthermore, the function of proBDNF in neurogenesis, the mechanism by which it regulates the memory of fear, and enhances individual behavioral flexibility is discussed. Finally, the potential of proBDNF as a biomarker for disease diagnosis and the therapeutic prospects of targeting it using monoclonal antibodies are highlighted while also proposing future research directions. The present review can serve as a reference for translational medical research on proBDNF and its receptors.

Contributions of Genetic Variation in Astrocytes to Cell and Molecular Mechanisms of Risk and Resilience to Late-Onset Alzheimer's Disease

Reactive astrocytes are associated with Alzheimer's disease (AD), and several AD genetic risk variants are associated with genes highly expressed in astrocytes. However, the contribution of genetic risk within astrocytes to cellular processes relevant to the pathogenesis of AD remains ill-defined. Here, we present a resource for studying AD genetic risk in astrocytes using a large collection of induced pluripotent stem cell (iPSC) lines from deeply phenotyped individuals with a range of neuropathological and cognitive outcomes. IPSC lines from 44 individuals were differentiated into astrocytes followed by unbiased molecular profiling using RNA sequencing and tandem mass tag-mass spectrometry. We demonstrate the utility of this resource in examining gene- and pathway-level associations with clinical and neuropathological traits, as well as in analyzing genetic risk and resilience factors through parallel analyses of iPSC-astrocytes and brain tissue from the same individuals. Our analyses reveal that genes and pathways altered in iPSC-derived astrocytes from individuals with AD are concordantly dysregulated in AD brain tissue. This includes increased levels of prefoldin proteins, extracellular matrix factors, COPI-mediated trafficking components and reduced levels of proteins involved in cellular respiration and fatty acid oxidation. Additionally, iPSC-derived astrocytes from individuals resilient to high AD neuropathology show elevated basal levels of interferon response proteins and increased secretion of interferon gamma. Correspondingly, higher polygenic risk scores for AD are associated with lower levels of interferon response proteins in astrocytes. This study establishes an experimental system that integrates genetic information with a matched iPSC lines and brain tissue data from a large cohort of individuals to identify genetic contributions to molecular pathways affecting AD risk and resilience.

ApoE4 requires lipidation enhancement to resolve cellular lipid and protein abnormalities following NPC1 inhibition

Apolipoprotein E (ApoE) variants are central to Alzheimer's disease (AD), Lewy body dementia (LBD) and Niemann-Pick disease type C (NPC). The ApoE4 variant elevates AD risk by 3-15-fold. ApoE's normal function in lipid transport is known. The question remains how different ApoE isoforms cause cellular pathogenesis. We determined the effects of ApoE isoforms on lipid accumulation induced by inhibiting the endo-lysosomal cholesterol transporter NPC1. In human fibroblasts and astrocytes, NPC1 inhibition caused a 4-fold cholesterol accumulation and mis-localization with altered cholesterol sensing and increased synthesis of cholesterol and triglycerides. Total APP, APP C-terminal fragments (CTF) and BACE1 levels increased 3-fold. Remarkably, the intracellular neutral lipids co-localized with APP and APP C-terminal fragments. ApoE2 and ApoE3, but not ApoE4, reduced intracellular cholesterol levels by 67% and 62%, respectively, normalized APP, BACE, CTF, and improved cell survival. ApoE4 combined with a synthetic lipopeptide, which increased the proportion of large lipidated ApoE4 particles, corrected these abnormalities. This highlights ApoE in lipid pathogenesis and targeting ApoE4 lipidation to restore ApoE4 function.

Astrocytic lipid droplets contain MHCII and may act as cogs in the antigen presentation machinery

Lipid droplets (LDs) are crucial for energy homeostasis, but are also involved in a wide spectrum of other cellular processes. Accumulating data identifies LDs as an important player in inflammation. However, the underlying mechanisms and the impact of LDs on neuroinflammation remain unclear. Here, we describe a novel function of LDs in human astrocytes, in the context of Alzheimer's disease (AD). Although, the overall lipid profile was unchanged in astrocytes with AD pathology, our data show a clear effect on LD metabolism and specific fatty acids involved in neuroinflammation. Importantly, we found astrocytes to be in close contact with infiltrating CD4 + T cells in the AD brain. Moreover, PLIN3 + LDs in astrocytes co-localize with major histocompatibility complex II (MHCII), indicating a role of LDs in adaptive immunity. Comprehensive analysis of human induced pluripotent stem cell (hiPSC)-derived astrocytes revealed that MHCII is in fact loaded within PLIN3 + LDs and forwarded to neighboring cells via tunneling nanotubes and secretion. Notably, the MHCII molecules are cleaved into its active form prior to packing, indicating an alternative route of MHCII shuttling through LDs, transporting functional immune complexes between cells. Quantification of PLIN3 + LDs in astrocytic cultures, human brain tissue and cerebral organoids indicates that AD pathology initially stimulates PLIN3 + LD formation, but in the long-run results in PLIN3 + LD consumption, which may have consequences on the astrocytes' MHCII distribution capacity. Taken together, our findings present a novel function of PLIN3 + LDs that can be of relevance for AD and other inflammatory conditions.

SOAT1 dysregulation in astrocytes drives Blood-Brain barrier dysfunction and neuroinflammation in Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder that leads to memory loss and cognitive decline, in which blood-brain barrier (BBB) and astrocyte dysfunction are significantly involved. Recent evidence suggests that dysregulation of lipid metabolism in astrocytes contributes to BBB disruption and neuroinflammation in AD. Sterol O-acyltransferase 1 (SOAT1), an enzyme involved in cholesterol esterification, has been implicated in BBB disruption and neuroinflammation, but its specific role in AD remains unclear. This study aimed to investigate the impact of SOAT1 on lipid metabolism, BBB integrity, and neuroinflammation in AD. Using Oil Red O staining of human autopsy brain tissue and reanalysis of publicly available single-nucleus RNA sequencing (snRNA-seq) data, we identified a significant increase in lipid droplet accumulation and lipid metabolism gene expression, particularly in astrocytes, in the brains of AD patients. Furthermore, in vitro BBB models and the 5 × FAD mouse model were used to explore how SOAT1 expression influences BBB function. Our results demonstrated that elevated SOAT1 expression in astrocytes was positively correlated with increased lipid droplet accumulation and compromised BBB integrity. Knockdown of SOAT1 using siRNA or treatment with the SOAT1 inhibitor K604 restored BBB function, reduced neuroinflammation, and improved cognitive function in 5 × FAD mice. These findings suggest that SOAT1 plays a critical role in astrocytic lipid metabolism and BBB dysfunction in AD. Targeting SOAT1 may be a promising therapeutic approach to alleviate neuroinflammation and restore cognitive function in AD patients.

APOE4 impairs macrophage lipophagy and promotes demyelination of spiral ganglion neurons in mouse cochleae

The ApoE-ε4 gene is a well-established genetic risk factor for neurodegenerative diseases, such as Alzheimer's disease and multiple sclerosis, which are characterized by axonal demyelination in the central nervous system. Recent studies have implicated ApoE-ε4 in age-related hearing loss (ARHL), suggesting a potential role of APOE4 isoform in peripheral nervous system degeneration. However, the role of APOE4 in ARHL are still unclear. In this study, we explored the potential role of APOE4 in axonal demyelination of spiral ganglion neurons (SGNs). ApoE-ε4/ε4 (APOE4) and ApoE-ε3/ε3 (APOE3) mice were used to characterize SGNs. The effect of APOE4 on phagocytosis and autophagy as well as intracellular cholesterol level was evaluated in resident cochlear macrophages (RCMs) and mouse bone marrow-derived macrophages (BMDMs). The results showed that significant axonal demyelination was observed in SGNs of 10-month-old APOE4 mice, accompanied by the presence of myelin debris engulfed by RCMs. Meanwhile, inhibited phagocytosis of myelin debris and impaired lipophagy were detected in APOE4 RCMs and APOE4 BMDMs with an aberrant accumulation of lipid droplets (LDs), which could be reversed by trehalose treatment. This study provided a deep insight into the pathogenesis of APOE4-induced axonal demyelination of SGNs associated with the impaired lipophagy in RCMs, which helped to elucidate the underlying mechanism of ApoE-ε4 in ARHL.

Current Development of iPSC-Based Modeling in Neurodegenerative Diseases

Over the past two decades, significant advancements have been made in the induced pluripotent stem cell (iPSC) technology. These developments have enabled the broader application of iPSCs in neuroscience, improved our understanding of disease pathogenesis, and advanced the investigation of therapeutic targets and methods. Specifically, optimizations in reprogramming protocols, coupled with improved neuronal differentiation and maturation techniques, have greatly facilitated the generation of iPSC-derived neural cells. The integration of the cerebral organoid technology and CRISPR/Cas9 genome editing has further propelled the application of iPSCs in neurodegenerative diseases to a new stage. Patient-derived or CRISPR-edited cerebral neurons and organoids now serve as ideal disease models, contributing to our understanding of disease pathophysiology and identifying novel therapeutic targets and candidates. In this review, we examine the development of iPSC-based models in neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, and Huntington's disease.

Metabolic Alteration in Oxylipins and Endocannabinoids Point to an Important Role for Soluble Epoxide Hydrolase and Inflammation in Alzheimer's Disease - Finding from Alzheimer's Disease Neuroimaging Initiative

Mounting evidence implicates inflammation as a key factor in Alzheimer's disease (AD) development. We previously identified pro-inflammatory soluble epoxide hydrolase (sEH) metabolites to be elevated in plasma and CSF of AD patients and to be associated with lower cognition in non-AD subjects. Soluble epoxide hydrolase is a key enzyme converting anti-inflammatory epoxy fatty acids to pro-inflammatory diols, reported to be elevated in multiple cardiometabolic disorders. Here we analyzed over 700 fasting plasma samples from the baseline of Alzheimer's Disease Neuroimaging Initiative (ADNI) 2/GO study. We applied targeted mass spectrometry method to provide absolute quantifications of over 150 metabolites from oxylipin and endocannabinoids pathway, interrogating the role for inflammation/immune dysregulation and the key enzyme soluble epoxide hydrolase in AD. We provide further insights into the regulation of this pathway in different disease stages, APOE genotypes and between sexes. Additionally, we investigated in mild cognitive impaired (MCI) patients, metabolic signatures that inform about resilience to progression and conversion to AD. Key findings include I) confirmed disruption in this key central pathway of inflammation and pointed to dysregulation of sEH in AD with sex and disease stage differences; II) identified markers of disease progression and cognitive resilience using sex and ApoE genotype stratified analysis highlighting an important role for bile acids, lipid peroxidation and stress response hormone cortisol. In conclusion, we provide molecular insights into a central pathway of inflammation and links to cognitive dysfunction, suggesting novel therapeutic approaches that are based on targeting inflammation tailored for subgroups of individuals based on their sex, APOE genotype and their metabolic profile.

Lipid metabolism, remodelling and intercellular transfer in the CNS

Lipid metabolism encompasses the catabolism and anabolism of lipids, and is fundamental for the maintenance of cellular homeostasis, particularly within the lipid-rich CNS. Increasing evidence further underscores the importance of lipid remodelling and transfer within and between glial cells and neurons as key orchestrators of CNS lipid homeostasis. In this Review, we summarize and discuss the complex landscape of processes involved in lipid metabolism, remodelling and intercellular transfer in the CNS. Highlighted are key pathways, including those mediating lipid (and lipid droplet) biogenesis and breakdown, lipid oxidation and phospholipid metabolism, as well as cell-cell lipid transfer mediated via lipoproteins, extracellular vesicles and tunnelling nanotubes. We further explore how the dysregulation of these pathways contributes to the onset and progression of neurodegenerative diseases, and examine the homeostatic and pathogenic impacts of environment, diet and lifestyle on CNS lipid metabolism.

Human induced pluripotent stem cell models for Alzheimer's disease research: a bibliometric analysis

Introduction

Alzheimer's disease (AD), the leading cause of dementia, remains without adequate treatment. Current models do not fully replicate human physiology and pathology. The advent of human induced pluripotent stem cell (hiPSC) technology offers a novel approach to studying AD.

Methods

Our study conducted a bibliometric analysis to assess the application and development of hiPSC technology in AD research. We retrieved 531 articles on hiPSC models of AD from the Web of Science Core Collection, published between January 2010 and June 2024. CiteSpace and VOSviewer were used to analyze authorship, geographic contributions, journal influence, and citation patterns.

Results

Our findings reveal a steady increase in publications over 14 years, with the United States leading in contributions, followed by China. Li-Huei Tsai from the Massachusetts Institute of Technology is a prominent researcher. PLoS One emerges as the most influential journal. Research trends have focused on inflammation, astrocytes, microglia, apolipoprotein E (ApoE), and tau.

Discussion

Bibliometric analysis is crucial in identifying research gaps and trends and guiding future studies to address unmet needs in understanding and modeling human physiology and pathology. Leveraging hiPSC models to investigate the molecular mechanisms of familial and sporadic AD is expected to provide a crucial foundation for developing future treatment strategies.

Conclusion

In summary, the bibliometric findings from this study provide a comprehensive overview of the current research landscape in hiPSC models for AD. It also highlights emerging trends and research gaps, crucial for guiding future research efforts, particularly in exploring novel therapeutic targets and improving understanding of disease mechanisms.

Changes in iPSC-astrocyte morphology reflect Alzheimer's disease patient clinical markers

Human induced pluripotent stem cells (iPSCs) provide powerful cellular models of Alzheimer's disease (AD) and offer many advantages over non-human models, including the potential to reflect variation in individual-specific pathophysiology and clinical symptoms. Previous studies have demonstrated that iPSC-neurons from individuals with Alzheimer's disease (AD) reflect clinical markers, including β-amyloid (Aβ) levels and synaptic vulnerability. However, despite neuronal loss being a key hallmark of AD pathology, many risk genes are predominantly expressed in glia, highlighting them as potential therapeutic targets. In this work iPSC-derived astrocytes were generated from a cohort of individuals with high versus low levels of the inflammatory marker YKL-40, in their cerebrospinal fluid (CSF). iPSC-derived astrocytes were treated with exogenous Aβ oligomers and high content imaging demonstrated a correlation between astrocytes that underwent the greatest morphology change from patients with low levels of CSF-YKL-40 and more protective APOE genotypes. This finding was subsequently verified using similarity learning as an unbiased approach. This study shows that iPSC-derived astrocytes from AD patients reflect key aspects of the pathophysiological phenotype of those same patients, thereby offering a novel means of modelling AD, stratifying AD patients and conducting therapeutic screens.

Dysregulated glycerophospholipid metabolism in amygdala may mediate favipiravir-induced anxiety-like behaviors in mice

Favipiravir, the first RNA polymerase inhibitor approved to treat resistant influenza, has been reported to be associated with central nervous system (CNS) side effects, particularly anxiety-like behavior; nevertheless, the underlying mechanism remains largely unknown. In this study, we investigated the effect of favipiravir on the neurobehavior of mice, and combined lipidomics and transcriptomics analysis to explore the mechanism underlying this effect. In behavioral tests, the mice displayed anxiety-like behaviors after oral favipiravir administration (200 mg/kg) for 7 days continuously. By lipidomics analysis, we observed that favipiravir induced a dysregulation of glycerophospholipid metabolism in the amygdala. Moreover, favipiravir significantly reduced the mRNA level of glycerol-3-phosphate acyltransferase 2 (Gpat2), the rate-limiting enzyme of glycerophospholipid synthesis. Notably, favipiravir markedly reduced the levels of docosahexaenoic acid-enriched phosphatidylethanolamine or phosphatidylcholine (DHA-PE/PC) and arachidonic acid-enriched phosphatidylethanolamine or phosphatidylcholine (AA-PE/PC), two components of glycerophospholipids, in the amygdala. The increased expression of phospholipase A2 (Pla2) may attribute to the enhanced release of arachidonic acid (AA) from AA-PE/PC. Furthermore, favipiravir altered neurite morphology and reduced neurophysiological activity in amygdala neurons in vitro. Collectively, dysregulated glycerophospholipid metabolism in the amygdala may contribute to the adverse effect of favipiravir.

Beyond plaques and tangles: The role of immune cell dysfunction in Alzheimer's disease

The interplay between immune cell dysfunction and associated neuroinflammation plays a critical role in the pathogenesis of Alzheimer's disease. Neuroinflammation, orchestrated by microglia and peripheral immune cells, exacerbates synaptic dysfunction and neurodegeneration in AD. Emerging evidence suggests a systemic immune response in AD, challenging traditional views of neurocentric pathology. Therapeutic strategies targeting neuroinflammation hold promise, yet translating preclinical findings into clinical success remains elusive. This article presents recent advances in AD scientific studies, highlighting the pivotal role of immune cell dysfunction and signaling pathways in disease progression. We also discussed therapeutic studies targeting immune cell dysregulation, as treatment methods. This advocates for a paradigm shift towards holistic approaches that integrate peripheral and central immune responses, fostering a comprehensive understanding of AD pathophysiology and paving the way for transformative interventions.

The Glutamate/GABA-Glutamine Cycle: Insights, Updates, and Advances

Synaptic homeostasis of the principal neurotransmitters glutamate and GABA is tightly regulated by an intricate metabolic coupling between neurons and astrocytes known as the glutamate/GABA-glutamine cycle. In this cycle, astrocytes take up glutamate and GABA from the synapse and convert these neurotransmitters into glutamine. Astrocytic glutamine is subsequently transferred to neurons, serving as the principal precursor for neuronal glutamate and GABA synthesis. The glutamate/GABA-glutamine cycle integrates multiple cellular processes, including neurotransmitter release, uptake, synthesis, and metabolism. All of these processes are deeply interdependent and closely coupled to cellular energy metabolism. Astrocytes display highly active mitochondrial oxidative metabolism and several unique metabolic features, including glycogen storage and pyruvate carboxylation, which are essential to sustain continuous glutamine release. However, new roles of oligodendrocytes and microglia in neurotransmitter recycling are emerging. Malfunction of the glutamate/GABA-glutamine cycle can lead to severe synaptic disruptions and may be implicated in several brain diseases. Here, I review central aspects and recent advances of the glutamate/GABA-glutamine cycle to highlight how the cycle is functionally connected to critical brain functions and metabolism. First, an overview of glutamate, GABA, and glutamine transport is provided in relation to neurotransmitter recycling. Then, central metabolic aspects of the glutamate/GABA-glutamine cycle are reviewed, with a special emphasis on the critical metabolic roles of glial cells. Finally, I discuss how aberrant neurotransmitter recycling is linked to neurodegeneration and disease, focusing on astrocyte metabolic dysfunction and brain lipid homeostasis as emerging pathological mechanisms. Instead of viewing the glutamate/GABA-glutamine cycle as individual biochemical processes, a more holistic and integrative approach is needed to advance our understanding of how neurotransmitter recycling modulates brain function in both health and disease.

Multi Layered Omics Approaches Reveal Glia Specific Alterations in Alzheimer's Disease: A Systematic Review and Future Prospects

Alzheimer's disease (AD) is the most common neurodegenerative dementia with multi-layered complexity in its molecular etiology. Multiple omics-based approaches, such as genomics, epigenomics, transcriptomics, proteomics, metabolomics, and lipidomics are enabling researchers to dissect this molecular complexity, and to uncover a plethora of alterations yielding insights into the pathophysiology of this disease. These approaches reveal multi-omics alterations essentially in all cell types of the brain, including glia. In this systematic review, we screen the literature for human studies implementing any omics approach within the last 10 years, to discover AD-associated molecular perturbations in brain glial cells. The findings from over 200 AD-related studies are reviewed under four different glial cell categories: microglia, oligodendrocytes, astrocytes and brain vascular cells. Under each category, we summarize the shared and unique molecular alterations identified in glial cells through complementary omics approaches. We discuss the implications of these findings for the development, progression and ultimately treatment of this complex disease as well as directions for future omics studies in glia cells.

Microfluidics in neural extracellular vesicles characterization for early Alzheimer's disease diagnosis

Dementia is a general term for conditions impairing cognitive abilities including perception, reasoning, attention, judgment, memory, and daily brain function. Early diagnosis of Alzheimer's disease (AD), the most common form of dementia, using neural extracellular vesicles (nEVs) is the focus of the current study. These nEVs carry AD biomarkers including β-amyloid proteins and phosphorylated tau proteins. The novelty of this review lies in developing a microfluidic perspective by introducing the techniques using a microfluidic platform for early diagnosis of AD. A microfluidic device can detect small sample sizes with significantly low concentrations. These devices combine nEV isolation, enrichment, and detection, which makes them ideal candidates for early AD diagnosis.

Inherited Dyslipidemic Splenomegaly: A Genetic Macrophage Storage Disorder Caused by Disruptive Apolipoprotein E (APOE) Variants

BACKGROUND

Persistent splenomegaly, often an incidental finding, can originate from a number of inherited metabolic disorders (IMDs). Variants of APOE are primarily known as risk factors in terms of cardiovascular disease; however, severe dysfunction of APOE can result in a disease phenotype with considerable overlap with lysosomal storage disorders (LSDs), including splenomegaly and gross elevation of N-palmitoyl-O-phosphocholine-serine (PPCS).

METHODS

A case study (deep phenotyping, genetic and FACS analysis) and literature study was conducted.

RESULTS

The index patient, with a family history of early-onset cardiovascular disease, presented with splenic infarctions in a grossly enlarged spleen. The identified genetic cause was homozygosity for two APOE variants (c.604C>T, p.(Arg202Cys) and c.512G>A, p.(Gly171Asp); ε1/ε1), resulting in a macrophage storage phenotype resembling an LSD that was also present in the brother of the index patient. A FACS analysis of the circulating monocytes showed increased lipid content and the expression of activation markers (CD11b, CCR2, CD36). This activated state enhances lipoprotein intake, which eventually converts these monocytes/macrophages into foam cells, accumulating in tissues (e.g., spleen and vascular wall). A literature search identified seven individuals with splenomegaly caused by APOE variants (deletion of leucine at position 167). The combined data from all patients identified male gender, splenectomy and obesity as potential modifiers determining the severity of the phenotype (i.e., degree of triglyceride increase in plasma and/or spleen size). Symptoms are (partially) reversible by lipid-lowering medication and energy restricted diets and splenectomy is contra-indicated.

CONCLUSIONS

Inherited dyslipidemic splenomegaly caused by disruptive APOE variants should be included in the differential diagnoses of unexplained splenomegaly with abnormal lipid profiles. A plasma lipid profile consistent with dysbetalipoproteinemia is a diagnostic biomarker for this IMD.

Imaging lipid rafts reveals the principle of ApoE4-induced Aβ upregulation in human neurons

Lipid rafts in plasma membranes are thought to provide a platform for regulating signaling pathways by increasing the expression or proximity of proteins in the same pathway. Despite this understanding, the absence of direct, simultaneous observations of lipid rafts and their affiliated proteins has hindered a comprehensive assessment of their roles across various biological contexts. Amyloid-β (Aβ), a hallmark of Alzheimer's disease (AD), is generated from the sequential cleavage of amyloid precursor proteins (APPs) by β- and γ-secretases, primarily within endosomes after APP endocytosis by canonical clathrin-mediated endocytosis in neurons. In this study, we developed a protocol for imaging APP on lipid rafts using time-of-flight secondary ion mass spectrometry (ToF-SIMS) and found that astrocyte ApoE4 contributes to an increase in APP localization on lipid rafts, subsequently elevating Aβ42 synthesis in a clathrin-independent manner in neurons.

Cell type transcriptomics reveal shared genetic mechanisms in Alzheimer's and Parkinson's disease

Historically, Alzheimer's disease (AD) and Parkinson's disease (PD) have been investigated as two distinct disorders of the brain. However, a few similarities in neuropathology and clinical symptoms have been documented over the years. Traditional single gene-centric genetic studies, including GWAS and differential gene expression analyses, have struggled to unravel the molecular links between AD and PD. To address this, we tailor a pattern-learning framework to analyze synchronous gene co-expression at sub-cell-type resolution. Utilizing recently published single-nucleus AD (70,634 nuclei) and PD (340,902 nuclei) datasets from postmortem human brains, we systematically extract and juxtapose disease-critical gene modules. Our findings reveal extensive molecular similarities between AD and PD gene cliques. In neurons, disrupted cytoskeletal dynamics and mitochondrial stress highlight convergence in key processes; glial modules share roles in T-cell activation, myelin synthesis, and synapse pruning. This multi-module sub-cell-type approach offers insights into the molecular basis of shared neuropathology in AD and PD.

Electrophysiological insights into Alzheimer's disease: A review of human and animal studies

This review highlights the crucial role of neuroelectrophysiology in illuminating the mechanisms underlying Alzheimer's disease (AD) pathogenesis and progression, emphasizing its potential to inform the development of effective treatments. Electrophysiological techniques provide unparalleled precision in exploring the intricate networks affected by AD, offering insights into the synaptic dysfunction, network alterations, and oscillatory abnormalities that characterize the disease. We discuss a range of electrophysiological methods, from non-invasive clinical techniques like electroencephalography and magnetoencephalography to invasive recordings in animal models. By drawing on findings from these studies, we demonstrate how electrophysiological research has deepened our understanding of AD-related network disruptions, paving the way for targeted therapeutic interventions. Moreover, we underscore the potential of electrophysiological modalities to play a pivotal role in evaluating treatment efficacy. Integrating electrophysiological data with clinical neuroimaging and longitudinal studies holds promise for a more comprehensive understanding of AD, enabling early detection and the development of personalized treatment strategies. This expanded research landscape offers new avenues for unraveling the complexities of AD and advancing therapeutic approaches.

Intermittent Fasting Ameliorates β-Amyloid Deposition and Cognitive Impairment Accompanied by Decreased Lipid Droplet Aggregation Within Microglia in an Alzheimer's Disease Model

SCOPE

Alzheimer's disease (AD) is the most prevalent form of dementia, lack of effective therapeutic interventions. In this study, we investigate the impact of intermittent fasting (IF), an alternative strategy of calorie restriction, on cognitive functions and AD-like pathology in a transgenic mouse model of AD.

METHODS AND RESULTS

APP/PS1 mice at 6 months were randomly allocated to two dietary groups: one receiving ad libitum (AL) feeding and the other undergoing IF for 1 month. Y maze, Barnes maze, western blotting, and immunofluorescence were employed. Behavioral assessments revealed that the APP/PS1-IF group demonstrated notable improvements in cognitive function compared to the AL group. Further analysis showed that microglia in the APP/PS1-IF mice exhibited enhanced phagocytic activity, characterized by prominent enlargement of soma and reduced complexity of their processes. Importantly, IF significantly decreased the accumulation of lipid droplets (LDs) within microglia. These microglia with less LDs may contribute to enhanced β-amyloid (Aβ) phagocytosis, thereby ameliorating Aβ deposition in the brains of APP/PS1-IF mice.

CONCLUSION

Our findings demonstrate that IF ameliorates amyloid deposition and cognitive deficits in the AD model mice, which is associated with the reduction of LDs within microglia, providing support for the use of the dietary intervention against AD pathology.

The glial UDP-glycosyltransferase Ugt35b regulates longevity by maintaining lipid homeostasis in Drosophila

Lipid droplets (LDs) are dynamic organelles essential for lipid storage and organismal survival. Studies have highlighted the importance of glial function in brain LD formation during aging; however, the genes and mechanisms involved remain elusive. Here, we found that Ugt35b, a member of the uridine diphosphate (UDP)-glycosyltransferases that catalyze the transfer of glycosyl groups to acceptors, is highly expressed in glia and crucial for Drosophila lifespan. By integrating multiomics data, we demonstrated that glial Ugt35b plays key roles in regulating glycerolipid and glycerophospholipid metabolism in the brain. Notably, we found that Ugt35b and Lsd-2 are co-expressed in glia and confirmed their protein interaction in vivo. Knockdown of Ugt35b significantly reduced LD formation by downregulating Lsd-2 expression, while overexpression of Lsd-2 partially rescued the shortened lifespan in glial Ugt35b RNAi flies. Our findings reveal the crucial role of glial Ugt35b in regulating LD formation to maintain brain lipid homeostasis and support Drosophila lifespan.

Lipids shape brain function through ion channel and receptor modulations: physiological mechanisms and clinical perspectives

Lipids represent the most abundant molecular type in the brain, with a fat content of ∼60% of the dry brain weight in humans. Despite this fact, little attention has been paid to circumscribe the dynamic role of lipids in brain function and disease. Membrane lipids such as cholesterol, phosphoinositide, sphingolipids, arachidonic acid, and endocannabinoids finely regulate both synaptic receptors and ion channels that ensure critical neural functions. After a brief introduction on brain lipids and their respective properties, we review here their role in regulating synaptic function and ion channel activity, action potential propagation, neuronal development, and functional plasticity and their contribution in the development of neurological and neuropsychiatric diseases. We also provide possible directions for future research on lipid function in brain plasticity and diseases.

Altered lipid profile and reduced neuronal support in human induced pluripotent stem cell-derived astrocytes from adrenoleukodystrophy patients

X-linked adrenoleukodystrophy (ALD) is a peroxisomal disorder resulting from pathogenic variants in the ABCD1 gene that primarily affects the nervous system and is characterized by progressive axonal degeneration in the spinal cord and peripheral nerves and leukodystrophy. Dysfunction of peroxisomal very long-chain fatty acid (VLCFA) degradation has been implicated in ALD pathology, but the impact on astrocytes, which critically support neuronal function, remains poorly understood. Fibroblasts from four ALD patients were reprogrammed to generate human-induced pluripotent stem cells (hiPSC). hiPSC-derived astrocytes were generated to study the impact of ALD on astrocytic fatty acid homeostasis. Our study reveals significant changes in the lipidome of ALD hiPSC-derived astrocytes, characterized by an enrichment of VLCFAs across multiple lipid classes, including triacylglycerols, cholesteryl esters, and phosphatidylcholines. Importantly, ALD hiPSC-derived astrocytes not only exhibit intrinsic lipid dysregulation but also affect the dendritic tree complexity of neurons in co-culture systems. These findings highlight the cell-autonomous effects of pathogenic variants in the ABCD1 protein on astrocytes and their microenvironment, shed light on potential mechanisms underlying ALD neuropathology, and underscore the critical role of astrocytes in neuronal health.

The Promise of Epigenetic Editing for Treating Brain Disorders

Brain disorders, especially neurodegenerative diseases, affect millions of people worldwide. There is no causal treatment available; therefore, there is an unmet clinical need for finding therapeutic options for these diseases. Epigenetic research has resulted in identification of various genomic loci with differential disease-specific epigenetic modifications, mainly DNA methylation. These biomarkers, although not yet translated into clinically approved options, offer therapeutic targets as epigenetic modifications are reversible. Indeed, clinical trials are designed to inhibit epigenetic writers, erasers, or readers using epigenetic drugs to interfere with epigenetic dysregulation in brain disorders. However, since such drugs elicit genome-wide effects and potentially cause toxicity, the recent developments in the field of epigenetic editing are gaining widespread attention. In this review, we provide examples of epigenetic biomarkers and epi-drugs, while describing efforts in the field of epigenetic editing, to eventually make a difference for the currently incurable brain disorders.

Lipid trajectories improve risk models for Alzheimer's disease and mild cognitive impairment

In this retrospective, case-control study, we tested the hypothesis that blood-lipid concentrations during the decade prior to cognitive symptom onset can inform risk prediction for Alzheimer's disease (AD) and stable mild cognitive impairment (MCI). Clinically well-characterized cases were diagnosed using Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) criteria; MCI cases had been stable for ≥5 years; and controls were propensity matched to cases at symptom onset (MCI: 116 cases, 435 controls; AD: 215 cases, 483 controls). Participants were grouped based on (i) longitudinal trajectories and (ii) quintile of variability independent of the mean (VIM) for total cholesterol, HDL-C, low-density lipoprotein cholesterol, non-HDL-C, and ln(triglycerides). Risk models evaluated the contributions of lipid trajectory and VIM groups relative to APOE genotype or polygenic risk scores (PRSs) for AD and lipid levels and major lipoprotein confounders: age, lipid-lowering medications, comorbidities, and other longitudinal correlates of blood-lipid concentrations. In models with AD-PRS, higher MCI-risk was associated with the two lower HDL-C trajectories [odds ratios: 3.8(1.3-11.3; P = 0.014), 3.2(1.1-9.3; P = 0.038), relative to the high trajectory], and the lowest VIM quintile of non-HDL-C [odds ratio: 2.2 (1.3-3.8: P = 0.004), relative to quintiles 2-5]. Higher AD-risk was associated with the two lower HDL-C trajectories [odds ratios: 2.8(1.5-5.1; P = 0.001), 3.7 (2.0-7.0; P < 0.001)], and the lowest VIM quintile of total cholesterol [odds ratio: 2.5(1.5-4.0: P < 0.001)]. Inclusion of lipid-trajectory and VIM groups improved risk-model predictive performance independent of APOE and AD or lipid-level PRSs, providing important real-world perspectives on how longitudinal levels and variation of blood-lipid concentrations contribute to risk of cognitive decline.

The Effect of APOE ε4 on Alzheimer's Disease Fluid Biomarkers: A Cross-Sectional Study Based on the COAST

AIMS

To analyze the effect of APOE ε4 on fluid biomarkers and the correlations between blood molecules and CSF biomarkers in AD patients.

METHODS

This study enrolled 575 AD patients, 131 patients with non-AD dementia, and 112 cognitively normal (CN) participants, and AD patients were divided into APOE ε4 carriers and non-carriers. Cerebrospinal fluid (CSF) biomarkers and blood-derived biomolecules were compared between AD and CN groups, between non-AD dementia and CN groups, as well as within APOE ε4 subgroups of AD patients. Utilizing Spearman's correlation analysis and quantile regression analysis, the relationships between blood-derived biomolecules and CSF biomarkers were analyzed in APOE ε4 carriers and non-carriers.

RESULTS

The levels of CSF biomarkers and blood molecules exhibited significant differences between the AD and CN groups, including Aβ42, t-tau, p-tau 181, high-density lipoprotein, low-density lipoprotein (LDL), and uric acid. In AD patients, APOE ε4 carriers had increased levels of CSF t-tau, p-tau 181, and plasma LDL. In the correlation and regression analyses, the negative relationships between plasma TG and t-tau, between plasma TG and p-tau 181 levels, as well as the positive relationship between serum IgA and CSF Aβ42, were observed significantly in APOE ε4+ AD groups, but not in APOE ε4- AD group.

CONCLUSION

APOE ε4 is associated with accelerated progression of AD pathology. The blood-derived biomolecules correlated with CSF biomarkers in APOE ε4 carriers are related to neuroinflammation and lipid metabolism, which may indicate the role of APOE ε4 in AD pathophysiology and offer insights for diagnostic and therapeutic strategies for AD.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT03653156.

Unraveling APOE4's Role in Alzheimer's Disease: Pathologies and Therapeutic Strategies

Alzheimer's disease (AD), the most common kind of dementia worldwide, is characterized by elevated levels of the amyloid-β (Aβ) peptide and hyperphosphorylated tau protein in the neurons. The complexity of AD makes the development of treatments infamously challenging. Apolipoprotein E (APOE) genes's ε4 allele is one of the main genetic risk factors for AD. While the APOE gene's ε4 allele considerably increases the chance of developing AD, the ε2 allele is protective compared to the prevalent ε3 variant. It is fiercely discussed how APOE affects the development and course of disease since it has a variety of activities that influence both neuronal and non-neuronal cells. ApoE4 contributes to the formation of tau tangles, deposition of Aβ, neuroinflammation, and other processes. Four decades of research have provided a significant understanding of the structure of APOE and how this may affect the neuropathology and pathogenesis of AD. APOE is a crucial lipid transporter essential for the growth of the central nervous system (CNS), upkeep, and repair. The mechanisms by which APOE contributes to the pathophysiology of AD are still up for discussion, though. Evidence suggests that APOE affects the brain's clearance and deposition of Aβ. Additionally, APOE has Aβ-independent pathways in AD, which has led to the identification of new functions for APOE, including mitochondrial dysfunction. This study summarizes important studies that describe how APOE4 affects well-known AD pathologies, including tau pathology, Aβ, neuroinflammation, and dysfunction of neural networks. This study also envisions some of the therapeutic approaches being used to target APOE4 in the hopes of preventing or treating AD.

Neuroglia in neurodegeneration: Alzheimer, Parkinson, and Huntington disease

The conspicuous rise of chronic neurodegenerative diseases, including Alzheimer (AD), Parkinson (PD), and Huntington (HD) diseases, is currently without disease-modifying therapies and accompanied by an excessive rate of unsuccessful clinical trials. This reflects a profound lack of understanding of the pathogenesis of these diseases, indicating that the current paradigms guiding disease modeling and drug development are in need of reconsideration. The role of neuroglia, namely astrocytes, microglial cells, and oligodendrocytes, in the pathogenesis of neurodegenerative diseases emerged during the last decades. This chapter provides the state-of-the-art update on the changes of astrocytes, microglial cells, and oligodendrocytes in AD, PD, and HD. A growing body of evidence suggests that homeostatic and defensive functions of glial cells are compromised at different disease stages, leading to increased susceptibility of neurons to noxious stimuli, eventually resulting in their malfunction and degeneration. Investments are needed in the generation of novel preclinical models suitable for studying glial pathology, in "humanizing" research, and in-depth investigation of glial cell alterations to slow down and, possibly, halt and prevent the rise of neurodegenerative disease. Targeting glial cells opens new therapeutic avenues to treat AD, PD, and HD.

The Aβ42:Aβ40 ratio modulates aggregation in beta-amyloid oligomers and drives metabolic changes and cellular dysfunction

The pathophysiological role of Aβ42 oligomers in the onset of Alzheimer's disease (AD) is heavily disputed, pivoting research toward investigating mixed oligomers composed of Aβ42 and Aβ40, which is more abundant but less aggregation-prone. This study investigates Aβ42:Aβ40 oligomers in different ratios, examining their adverse effects on endothelial cells, neurons, astroglia, and microglia, as well as in a human blood-brain barrier (BBB) model. Combining label-free Raman microscopy with complementary imaging techniques and biochemical assays, we show the prominent impact of Aβ40 on Aβ42 fibrillation, suggesting an inhibitory effect on aggregation. Mixed oligomers, especially with low proportions of Aβ42, were equally detrimental as pure Aβ42 oligomers regarding cell viability, functionality, and metabolism. They also differentially affected lipid droplet metabolism in BBB-associated microglia, indicating distinct pathophysiological responses. Our findings demonstrate the overarching significance of the Aβ42:Aβ40 ratio in Aβ oligomers, challenging the traditional focus on Aβ42 in AD research.

Sex differences in interacting genetic and functional connectivity biomarkers in Alzheimer's disease

As of 2023, it is estimated that 6.7 million individuals in the United States live with Alzheimer's disease (AD). Prior research indicates that AD disproportionality affects females; females have a greater incidence rate, perform worse on a variety of neuropsychological tasks, and have greater total brain atrophy. Recent research shows that hippocampal functional connectivity differs by sex and may be related to the observed sex differences in AD, and apolipoprotein E (ApoE) ε4 carriers have reduced hippocampal functional connectivity. The purpose of this study was to determine if the ApoE genotype plays a role in the observed sex differences in hippocampal functional connectivity in Alzheimer's disease. The resting state fMRI and T2 MRI of individuals with AD (n = 30, female = 15) and cognitively normal individuals (n = 30, female = 15) from the Alzheimer's Disease Neuroimaging Initiative (ADNI) were analyzed using the functional connectivity toolbox (CONN). Our results demonstrated intrahippocampal functional connectivity differed between those without an ε4 allele and those with at least one ε4 allele in each group. Additionally, intrahippocampal functional connectivity differed only by sex when Alzheimer's participants had at least one ε4 allele. These results improve our current understanding of the role of the interacting relationship between sex, ApoE genotype, and hippocampal function in AD. Understanding these biomarkers may aid in the development of sex-specific interventions for improved AD treatment.

Should We Consider Neurodegeneration by Itself or in a Triangulation with Neuroinflammation and Demyelination? The Example of Multiple Sclerosis and Beyond

Neurodegeneration is preeminent in many neurological diseases, and still a major burden we fail to manage in patient's care. Its pathogenesis is complicated, intricate, and far from being completely understood. Taking multiple sclerosis as an example, we propose that neurodegeneration is neither a cause nor a consequence by itself. Mitochondrial dysfunction, leading to energy deficiency and ion imbalance, plays a key role in neurodegeneration, and is partly caused by the oxidative stress generated by microglia and astrocytes. Nodal and paranodal disruption, with or without myelin alteration, is further involved. Myelin loss exposes the axons directly to the inflammatory and oxidative environment. Moreover, oligodendrocytes provide a singular metabolic and trophic support to axons, but do not emerge unscathed from the pathological events, by primary myelin defects and cell apoptosis or secondary to neuroinflammation or axonal damage. Hereby, trophic failure might be an overlooked contributor to neurodegeneration. Thus, a complex interplay between neuroinflammation, demyelination, and neurodegeneration, wherein each is primarily and secondarily involved, might offer a more comprehensive understanding of the pathogenesis and help establishing novel therapeutic strategies for many neurological diseases and beyond.

The association between activities and cognitive health: Stratified analysis by APOE ε4 status

Background

Despite the growing evidence on the modifiable and genetic factors associated with cognitive health, little is known about the role of the apolipoprotein E (APOE) gene ε4 allele in the associations between productive or leisure activities and cognitive health.

Objective

This study fills a gap of knowledge by examining the associations among employment, civic engagement, and leisure activities and cognitive health by the presence of APOE ε4 allele, an established risk factor of Alzheimer's disease (AD).

Methods

Using pooled data from the Health and Retirement Study (HRS) Psychosocial and Lifestyle Questionnaires (2010-2016) and the HRS data on APOE ε4 alleles, linear regression models with a lagged dependent variable were performed to examine associations between productive or leisure activities and cognitive functioning at the follow-up time point, as well as the role of APOE ε4 in these associations.

Results

Among all participants, employment, low or high-intensity volunteering, and cognitive/social leisure activities were associated with higher levels of cognitive functioning. The presence of at least one ε4 allele was related to poorer cognitive functioning at the follow-up time point. Among people without the APOE ε4 allele, employment, high-intensity volunteering, and cognitive/social leisure activities were significantly associated with cognitive functioning. Among people with at least one APOE ε4 allele, low-intensity volunteering and cognitive/physical leisure activities were significantly associated with better cognitive functioning.

Conclusions

We found that employment, civic engagement, and leisure activities all contribute to cognitive health, although the benefits may be restricted to low-intensity volunteering and cognitive/physical leisure activities among individuals with at least one APOE ε4 allele, who are known to be inherently at a greater risk of AD, highlighting an avenue to a relatively easily implementable strategy to promote cognitive health in this subpopulation.

Isoform- and cell-state-specific APOE homeostasis and function

Apolipoprotein E is the major lipid transporter in the brain and an important player in neuron-astrocyte metabolic coupling. It ensures the survival of neurons under stressful conditions and hyperactivity by nourishing and detoxifying them. Apolipoprotein E polymorphism, combined with environmental stresses and/or age-related alterations, influences the risk of developing late-onset Alzheimer's disease. In this review, we discuss our current knowledge of how apolipoprotein E homeostasis, i.e. its synthesis, secretion, degradation, and lipidation, is affected in Alzheimer's disease.

Circulating apoE4 protein levels from dried blood spots predict cognitive function in a large population-based survey setting

INTRODUCTION

The apolipoprotein E (APOE) ε4 allele carries risk for cognitive impairment, but whether the level of circulating apoE4 protein in carriers affects cognition is unclear, as is how health and lifestyle impact circulating apoE4 levels.

METHODS

We assayed apoE4 protein levels in dried blood spots of 12,532 adults aged 50+. Regression analyses tested the likelihood of cognitive impairment between groups and within those with detected apoE4 protein. Predictors of circulating apoE4 were assessed.

RESULTS

We detected protein binding that indicates the presence of an APOE ε4 allele in 28.4% of this group. This group was more likely to have cognitive impairment, and this risk increases with age. However, higher apoE4 levels were associated with less likelihood of cognitive impairment within this group. Antihypertensive medication predicted apoE4 protein levels.

DISCUSSION

The apoE4 isoform is associated with a deficient protein and worse cognition. This association is modulated by the level of circulating apoE4 protein in ε4 carriers.

HIGHLIGHTS

An assay to quantify apoE4 levels from dried blood spot samples was applied. The apoE4 protein was detected as specific binding at ≥30,000 pg/mL in 28.4% of samples. Having the apoE4 protein was associated with worse cognitive performance. Higher apoE4 protein levels in those who have it were associated with better cognition. Cardiovascular factors influenced levels of apoE4 protein.

TRPV1 alleviates APOE4-dependent microglial antigen presentation and T cell infiltration in Alzheimer's disease

BACKGROUND

Persistent innate and adaptive immune responses in the brain contribute to the progression of Alzheimer's disease (AD). APOE4, the most important genetic risk factor for sporadic AD, encodes apolipoprotein E4, which by itself is a potent modulator of immune response. However, little is known about the immune hub that governs the crosstalk between the nervous and the adaptive immune systems. Transient receptor potential vanilloid type 1 (TRPV1) channel is a ligand-gated, nonselective cation channel with Ca2+ permeability, which has been proposed as a neuroprotective target in AD.

METHODS

Using Ca2+-sensitive dyes, dynamic changes of Ca2+ in microglia were measured, including exogenous Ca2+ uptake and endoplasmic reticulum Ca2+ release. The mRFP-GFP-tagged LC3 plasmid was expressed in microglia to characterize the role of TRPV1 in the autophagic flux. Transcriptomic analyses and flow cytometry were performed to investigate the effects of APOE4 on brain microglia and T cells from APOE-targeted replacement mice with microglia-specific TRPV1 gene deficiency.

RESULTS

Both APOE4 microglia derived from induced pluripotent stem cells of AD patients and APOE4-related tauopathy mouse model showed significantly increased cholesterol biosynthesis and accumulation compared to their APOE3 counterparts. Further, cholesterol dysregulation was associated with persistent activation of microglia and elevation of major histocompatibility complex II-dependent antigen presentation in microglia, subsequently accompanied by T cell infiltration. In addition, TRPV1-mediated transient Ca2+ influx mitigated cholesterol biosynthesis in microglia by suppressing the transcriptional activation of sterol regulatory element-binding protein 2, promoted autophagic activity and reduced lysosomal cholesterol accumulation, which were sufficient to resolve excessive immune response and neurodegeneration in APOE4-related tauopathy mouse model. Moreover, microglia-specific deficiency of TRPV1 gene accelerated glial inflammation, T cell response and associated neurodegeneration in an APOE4-related tauopathy mouse model.

CONCLUSIONS

The findings provide new perspectives for the treatment of APOE4-dependent neurodegeneration including AD.

TOMM40-APOE chimera linking Alzheimer's highest risk genes: a new pathway for mitochondria regulation and APOE4 pathogenesis

The patho-mechanism of apolipoprotein variant, APOE4, the strongest genetic risk for late-onset Alzheimer's disease (AD) and longevity, remains unclear. APOE's neighboring gene, TOMM40 (mitochondria protein transport channel), is associated with brain trauma outcome and aging-related cognitive decline, however its role in AD APOE4-independently is controversial. We report that TOMM40 is prone to transcription readthrough into APOE that can generate spliced TOMM40-APOE mRNA chimera (termed T9A2) detected in human neurons and other cells and tissues. T9A2 translation tethers APOE (normal APOE3 or APOE4) to near-full-length TOM40 that is targeted to mitochondria. Importantly, T9A2-APOE3 boosts mitochondrial bioenergetic capacity and decreases oxidative stress significantly more than T9A2-APOE4 and APOE3, and lacking in APOE4. We describe detailed interactomes of these actors that may inform about the activities and roles in pathogenesis. T9A2 uncovers a new candidate pathway for mitochondria regulation and oxidative stress-protection that are impaired in APOE4 genotypes and could initiate neurodegeneration.

Role of lipid droplets in neurodegenerative diseases: From pathogenesis to therapeutics

Neurodegenerative diseases (NDDs) are a series of disorders characterized by the progressive loss of specific neurons, leading to cognitive and locomotor impairment. NDDs affect millions of patients worldwide but lack effective treatments. Dysregulation of lipids, particularly the accumulation of lipid droplets (LDs), is strongly implicated in the pathogenesis of NDDs. How LDs contribute to the occurrence and development of NDDs, and their potential as therapeutic targets remain to be addressed. In present review, we first introduce the processes of LDs formation, transportation and degradation. We then highlight how the accumulation of LDs contributes to the pathogenesis of NDDs in a cell type-specific manner. Moreover, we discuss currently available methods for detecting LDs and elaborate on LDs-based therapeutic strategies for NDDs. Lastly, we identify gaps that need to be filled to better leverage LD-based theranostics in NDDs and other diseases. We hope this review could shed light on the role of LDs in NDDs and facilitate the development of novel therapeutic strategies for NDDs.

New insights into innate immunity in Alzheimer's disease: from APOE protective variants to therapies

Recent discoveries of rare variants of human APOE may shed light on novel therapeutic strategies for Alzheimer's disease (AD). Here, we highlight the newly identified protective variant [APOE3 Christchurch (APOE3ch, R136S)] as an example. We summarize human AD and mouse amyloidosis and tauopathy studies from the past 5 years that have been associated with this R136S variant. We also propose a potential mechanism for how this point mutation might lead to protection against AD pathology, from the molecular level, to cells, to mouse models, and potentially, to humans. Lastly, we extend our discussion of the recent insights gained regarding different APOE variants to putative therapeutic approaches in AD.

Diverse signaling mechanisms and heterogeneity of astrocyte reactivity in Alzheimer's disease

Alzheimer's disease (AD) affects various brain cell types, including astrocytes, which are the most abundant cell types in the central nervous system (CNS). Astrocytes not only provide homeostatic support to neurons but also actively regulate synaptic signaling and functions and become reactive in response to CNS insults through diverse signaling pathways including the JAK/STAT, NF-κB, and GPCR-elicited pathways. The advent of new technology for transcriptomic profiling at the single-cell level has led to increasing recognition of the highly versatile nature of reactive astrocytes and the context-dependent specificity of astrocyte reactivity. In AD, reactive astrocytes have long been observed in senile plaques and have recently been suggested to play a role in AD pathogenesis and progression. However, the precise contributions of reactive astrocytes to AD remain elusive, and targeting this complex cell population for AD treatment poses significant challenges. In this review, we summarize the current understanding of astrocyte reactivity and its role in AD, with a particular focus on the signaling pathways that promote astrocyte reactivity and the heterogeneity of reactive astrocytes. Furthermore, we explore potential implications for the development of therapeutics for AD. Our objective is to shed light on the complex involvement of astrocytes in AD and offer insights into potential therapeutic targets and strategies for treating and managing this devastating neurodegenerative disorder.

Lipid Trajectories Improve Risk Models for Alzheimer's Disease and Mild Cognitive Impairment

To assess the relationship between lipids and cognitive dysfunction, we retrospectively analyzed blood-lipid levels in clinically well-characterized individuals with stable mild cognitive impairment (MCI) or Alzheimer's disease (AD) over the decade prior to first cognitive symptoms. In this case/control cohort study, AD and MCI cases were diagnosed using DSM-IV criteria; MCI cases had not progressed to dementia for ≥5 years; and controls were propensity matched to cases at age of symptom onset (MCI: 116 cases, 435 controls; AD: 215 cases, 483 controls). Participants were grouped based on longitudinal trajectories and quintile of variability independent of the mean (VIM) for total cholesterol, HDL-C, LDL-C, non-HDL-C and ln(triglycerides). Models for the risk of cognitive dysfunction evaluated trajectory and VIM groups, APOE genotype, polygenic risk scores (PRS) for AD and lipid levels, age, comorbidities, and longitudinal correlates of blood-lipid concentrations. Lower HDL-C trajectories (OR = 3.8, 95% CI = 1.3-11.3) and the lowest VIM quintile of non-HDL-C (OR = 2.2, 95% CI = 1.3-3.0) were associated with higher MCI risk. Lower HDL-C trajectories (OR = 3.0, 95% CI = 1.6-5.7) and the lowest VIM quintile of total cholesterol (OR = 2.4, 95% CI = 1.5-3.9) were associated with higher AD risk. The inclusion of lipid-trajectory and VIM groups improved risk-model predictive performance independent of APOE genotype or PRS for AD and lipid levels. These results provide an important real-world perspective on the influence of lipid metabolism and blood-lipid levels on the development of stable MCI and AD.

Advancements in APOE and dementia research: Highlights from the 2023 AAIC Advancements: APOE conference

INTRODUCTION

The apolipoprotein E gene (APOE) is an established central player in the pathogenesis of Alzheimer's disease (AD), with distinct apoE isoforms exerting diverse effects. apoE influences not only amyloid-beta and tau pathologies but also lipid and energy metabolism, neuroinflammation, cerebral vascular health, and sex-dependent disease manifestations. Furthermore, ancestral background may significantly impact the link between APOE and AD, underscoring the need for more inclusive research.

METHODS

In 2023, the Alzheimer's Association convened multidisciplinary researchers at the "AAIC Advancements: APOE" conference to discuss various topics, including apoE isoforms and their roles in AD pathogenesis, progress in apoE-targeted therapeutic strategies, updates on disease models and interventions that modulate apoE expression and function.

RESULTS

This manuscript presents highlights from the conference and provides an overview of opportunities for further research in the field.

DISCUSSION

Understanding apoE's multifaceted roles in AD pathogenesis will help develop targeted interventions for AD and advance the field of AD precision medicine.

HIGHLIGHTS

APOE is a central player in the pathogenesis of Alzheimer's disease. APOE exerts a numerous effects throughout the brain on amyloid-beta, tau, and other pathways. The AAIC Advancements: APOE conference encouraged discussions and collaborations on understanding the role of APOE.

Development and validation of the eMCI-CHD tool: A multivariable prediction model for the risk of mild cognitive impairment in patients with coronary heart disease

OBJECTIVE

This study aimed to develop and validate an eMCI-CHD tool based on clinical data to predict mild cognitive impairment (MCI) risk in patients with coronary heart disease (CHD).

METHODS

This cross-sectional study prospectively collected data from 400 patients with coronary heart disease (aged 55-90 years, 62% men) from July 2022 to September 2023 and randomized (7:3 ratio) them into training and validation sets. After determining the modeling variables through least absolute shrinkage and selection operator regression analysis, four ML classifiers were developed: logistic regression, extreme gradient boosting (XGBoost), support vector machine, and random forest. The performance of the models was evaluated using area under the ROC curve, accuracy, sensitivity, specificity, and F1 score. Decision curve analysis was used to assess the clinical performance of the established models. The SHapley Additive exPlanations (SHAP) method was applied to determine the significance of the features, the predictive model was visualized with a nomogram, and an online web-based calculator for predicting CHD-MCI risk scores was developed.

RESULTS

Of 400 CHD patients (average age 70.86 ± 8.74 years), 220 (55%) had MCI. The XGBoost model demonstrated superior performance (AUC: 0.86, accuracy: 78.57%, sensitivity: 0.74, specificity: 0.84, F1: 0.79) and underwent validation. An online tool (https://mr.cscps.com.cn/mci/index.html) with seven predictive variables (APOE gene typing, age, education, TyG index, NT-proBNP, C-reactive protein, and occupation) assessed MCI risk in CHD patients.

CONCLUSION

This study highlights the potential for predicting MCI risk among CHD patients using an ML model-driven nomogram and risk scoring tool based on clinical data.

APOE ε4-associated downregulation of the IL-7/IL-7R pathway in effector memory T cells: Implications for Alzheimer's disease

INTRODUCTION

The apolipoprotein E (APOE) ε4 allele exerts a significant influence on peripheral inflammation and neuroinflammation, yet the underlying mechanisms remain elusive.

METHODS

The present study enrolled 54 patients diagnosed with late-onset Alzheimer's disease (AD; including 28 APOE ε4 carriers and 26 non-carriers). Plasma inflammatory cytokine concentration was assessed, alongside bulk RNA sequencing (RNA-seq) and single-cell RNA sequencing (scRNA-seq) analysis of peripheral blood mononuclear cells (PBMCs).

RESULTS

Plasma tumor necrosis factor α, interferon γ, and interleukin (IL)-33 levels increased in the APOE ε4 carriers but IL-7 expression notably decreased. A negative correlation was observed between plasma IL-7 level and the hippocampal atrophy degree. Additionally, the expression of IL-7R and CD28 also decreased in PBMCs of APOE ε4 carriers. ScRNA-seq data results indicated that the changes were mainly related to the CD4+ Tem (effector memory) and CD8+ Tem T cells.

DISCUSSION

These findings shed light on the role of the downregulated IL-7/IL-7R pathway associated with the APOE ε4 allele in modulating neuroinflammation and hippocampal atrophy.

HIGHLIGHTS

The apolipoprotein E (APOE) ε4 allele decreases plasma interleukin (IL)-7 and aggravates hippocampal atrophy in Alzheimer's disease. Plasma IL-7 level is negatively associated with the degree of hippocampal atrophy. The expression of IL-7R signaling decreased in peripheral blood mononuclear cells of APOE ε4 carriers Dysregulation of the IL-7/IL-7R signal pathways enriches T cells.

Autism-associated CHD8 controls reactive gliosis and neuroinflammation via remodeling chromatin in astrocytes

Reactive changes of glial cells during neuroinflammation impact brain disorders and disease progression. Elucidating the mechanisms that control reactive gliosis may help us to understand brain pathophysiology and improve outcomes. Here, we report that adult ablation of autism spectrum disorder (ASD)-associated CHD8 in astrocytes attenuates reactive gliosis via remodeling chromatin accessibility, changing gene expression. Conditional Chd8 deletion in astrocytes, but not microglia, suppresses reactive gliosis by impeding astrocyte proliferation and morphological elaboration. Astrocyte Chd8 ablation alleviates lipopolysaccharide-induced neuroinflammation and septic-associated hypothermia in mice. Astrocytic CHD8 plays an important role in neuroinflammation by altering the chromatin landscape, regulating metabolic and lipid-associated pathways, and astrocyte-microglia crosstalk. Moreover, we show that reactive gliosis can be directly mitigated in vivo using an adeno-associated virus (AAV)-mediated Chd8 gene editing strategy. These findings uncover a role of ASD-associated CHD8 in the adult brain, which may warrant future exploration of targeting chromatin remodelers in reactive gliosis and neuroinflammation in injury and neurological diseases.

Metabolic Reprogramming of Astrocytes in Pathological Conditions: Implications for Neurodegenerative Diseases

Astrocytes play a pivotal role in maintaining brain energy homeostasis, supporting neuronal function through glycolysis and lipid metabolism. This review explores the metabolic intricacies of astrocytes in both physiological and pathological conditions, highlighting their adaptive plasticity and diverse functions. Under normal conditions, astrocytes modulate synaptic activity, recycle neurotransmitters, and maintain the blood-brain barrier, ensuring a balanced energy supply and protection against oxidative stress. However, in response to central nervous system pathologies such as neurotrauma, stroke, infections, and neurodegenerative diseases like Alzheimer's and Huntington's disease, astrocytes undergo significant morphological, molecular, and metabolic changes. Reactive astrocytes upregulate glycolysis and fatty acid oxidation to meet increased energy demands, which can be protective in acute settings but may exacerbate chronic inflammation and disease progression. This review emphasizes the need for advanced molecular, genetic, and physiological tools to further understand astrocyte heterogeneity and their metabolic reprogramming in disease states.

Multifaceted roles of APOE in Alzheimer disease

For the past three decades, apolipoprotein E (APOE) has been known as the single greatest genetic modulator of sporadic Alzheimer disease (AD) risk, influencing both the average age of onset and the lifetime risk of developing AD. The APOEε4 allele significantly increases AD risk, whereas the ε2 allele is protective relative to the most common ε3 allele. However, large differences in effect size exist across ethnoracial groups that are likely to depend on both global genetic ancestry and local genetic ancestry, as well as gene-environment interactions. Although early studies linked APOE to amyloid-β - one of the two culprit aggregation-prone proteins that define AD - in the past decade, mounting work has associated APOE with other neurodegenerative proteinopathies and broader ageing-related brain changes, such as neuroinflammation, energy metabolism failure, loss of myelin integrity and increased blood-brain barrier permeability, with potential implications for longevity and resilience to pathological protein aggregates. Novel mouse models and other technological advances have also enabled a number of therapeutic approaches aimed at either attenuating the APOEε4-linked increased AD risk or enhancing the APOEε2-linked AD protection. This Review summarizes this progress and highlights areas for future research towards the development of APOE-directed therapeutics.