Raulin, Ana‐Caroline

Aging and neurodegenerative disorders like Alzheimer’s Disease (AD) are associated with progressive dysfunction of the blood-brain barrier (BBB) and neurovascular unit (NVU), contributing to impaired vascular integrity and neuronal vulnerability. Apolipoprotein E (APOE) is a key regulator of neurovascular function, and the rare APOE3-R136S “Christchurch” variant ( APOE3Ch ) confers protection against AD. Mesenchymal stromal cells (MSCs) represent a promising cell-based therapy for the treatment of neurodegenerative diseases due to their paracrine effect exerted on vascular and neural cells. To investigate how APOE3Ch influences MSC-mediated neurovascular support, we used isogenic iPSC-derived MSCs (iMSCs) with homozygous APOE3Ch or APOE3 . We found that APOE3Ch iMSCs have stronger immunosuppressive effect on LPS-induced NFκB activation of THP1 cells. APOE3Ch iMSCs also enhanced endothelial barrier resistance and angiogenic capacity compared to APOE3 iMSCs when directly co-cultured with endothelial cells. In addition, conditioned medium from APOE3Ch iMSCs promoted neurite outgrowth more efficiently than that from APOE3 iMSCs. Metabolic profiling revealed differences between APOE3Ch and APOE3 iMSCs, suggesting altered metabolic resilience. Together, these findings demonstrate that iMSCs support vascular and neuronal function through paracrine mechanisms and suggest that APOE3Ch variant improves specific aspects of MSC-mediated neurovascular support. This work highlights the potential of combining MSC-based therapies with protective APOE variants to target BBB and NVU dysfunction in aging and neurodegeneration.

Abstract Background The rare APOE3 ‐Christchurch ( APOE3Ch ) variant is associated with remarkable protective effects, delaying the age at onset of PSEN1 ‐E280A driven autosomal dominant Alzheimer's disease (AD). While much of the research on APOE3C h has focused on its role in AD, little is known about how this variant impacts APOE biology under non‐disease conditions. Using cortical organoids as a model system, we aim to investigate the fundamental mechanisms by which APOE3Ch alters APOE biology, including its effects on metabolism and cellular interactions, to better understand its unique properties and potential implications for broader applications. Method Cortical organoids were derived from the isogenic neurodegeneration iPSC line series, with either the APOE3 or APOE3Ch genotype. Single‐cell RNA sequencing (scRNA‐seq) was performed on three independent batches of 6‐month‐old cerebral organoids to identify pathways differentially regulated by APOE3Ch. To further investigate APOE lipidation and its effects on lipid metabolism, lipidomics analysis was conducted on 8‐month‐old cerebral organoids, offering additional insights into APOE3Ch ‐specific biological mechanisms. Validation was also carried out using iPSC‐derived astrocytes and neurons to confirm key findings. Result ScRNA‐seq revealed differences in cell populations and astrocyte subtypes between APOE3 and APOE3Ch organoids, with mitochondrial‐related pathways differentially regulated in APOE3Ch cerebral organoids. These findings were validated in iPSC‐derived astrocytes. APOE3Ch iPSC‐derived astrocytes exhibited increased APOE secretion compared to APOE3 . They also demonstrated enhanced mitochondrial function, as evidenced by increased spare respiratory capacity measured by Seahorse stress assays. Furthermore, APOE3Ch astrocytes showed reduced lipid droplet formation following oleic acid treatment. Lipidomics analysis of APOE3Ch cerebral organoids revealed decreased cholesterol ester levels, suggesting alterations in lipid metabolism. Conclusion Our findings provide novel insights into how the APOE3Ch variant alters APOE biology, revealing differences in mitochondrial function and lipid metabolism. The differential regulation of mitochondrial pathways in APOE3Ch cerebral organoids, along with the enhanced mitochondrial capacity and altered lipid metabolism observed in APOE3Ch astrocytes, highlights the unique properties of this variant. These results offer valuable mechanistic understanding that may inform future therapeutic strategies targeting APOE biology, particularly in the context of AD.

ABSTRACT Most brain organoids derived from human induced pluripotent stem cells (iPSCs) lack microglia and thus immune function. Microglia‐like cells (MGCs) can be differentiated from iPSCs, while the characteristics of isogenic MGC‐containing brain organoids in modeling neurodegeneration and cell‐cell communications have not been well investigated. In this study, iPSC‐derived MGCs are co‐cultured with isogenic forebrain cortical organoids (iFCo), which are stimulated with extracellular vesicles (EVs) of brain organoids differentiated from Alzheimer's disease (AD) patient‐derived iPSCs ( APOE ε4/ε4 and presenilin 1). The AD EV‐stimulated co‐culture organoids are treated with EVs from healthy MGCs or co‐culture. Differential responses of the co‐cultured organoids and the MGCs to AD EVs are demonstrated. The co‐cultured organoids mitigated pro‐inflammatory gene expressions. EVs from healthy MGCs or co‐culture reduced the expression of IL‐12β , iNOS , TREM2 , and CASS4 , which are associated with neural inflammation and degeneration, as well as showed regulation on genes involved in microglial activation and carbon metabolism. AD EV cargo analysis by proteomics and microRNA‐sequencing revealed APOE and APP proteins and microRNAs regulated pathways such as mitophagy. This study paves the way for understanding the role of microglia and brain organoids in modeling neural degeneration and the development of EV‐based cell‐free therapeutics for AD treatment.

Abstract Parkinson’s disease (PD) is a neurodegenerative disorder characterized by the progressive loss of dopaminergic neurons and the accumulation of Lewy bodies, leading to motor and nonmotor symptoms. While both genetic and environmental factors contribute to PD, recent studies highlight the crucial role of lipid metabolism disturbances in disease progression. Altered lipid homeostasis promotes protein aggregation and oxidative stress, with significant changes in lipid classes such as sphingolipids and glycerolipids observed in patients with PD. These disturbances are involved in key pathological processes, such as α-synuclein aggregation, organelle dysfunction, lipid-mediated neuroinflammation, and impaired lipid homeostasis. This review examines the relationship between lipid species and PD progression, focusing on the physiological roles of lipids in the central nervous system. It explores the mechanistic links between lipid metabolism and PD pathology, along with lipid-related genetic risk factors. Furthermore, this review discusses lipid-targeting therapeutic strategies to mitigate PD progression, emphasizing the potential of lipid modulation for effective treatment development.

Abstract INTRODUCTION Loss‐of‐function variants of the ABCA7 gene are associated with an increased risk of Alzheimer's disease (AD). How neuronal ABCA7 contributes to AD pathogenesis is unknown. METHODS Using neuron‐specific Abca7 KO mice (n Abca7 −/− ) with or without 5×FAD amyloid model background and post mortem AD brains, we investigated AD‐related phenotypes through comprehensive approaches including transcriptomics and lipidomics. RESULTS Lipidomics analysis detected altered lipid profiles in the brains and synaptosomes of 5×FAD; n Abca7 −/− mice compared to controls. Transcriptomics profiling revealed that neuronal ABCA7 deficiency altered the expression of genes and pathways related to mitochondrial homeostasis and apoptosis, particularly in excitatory neurons. Consistently, synaptosomes isolated from 5×FAD; n Abca7 −/− mice showed diminished mitochondria respiration and reduced synaptic protein levels, which is further supported by results from human AD brains. DISCUSSION Our findings reveal that neuronal ABCA7 plays a critical role in mitochondrial homeostasis important for neuronal function and survival in the presence of AD pathology. Highlights Neuronal ABCA7 deficiency exacerbates Aβ pathology and neuronal damage in 5×FAD mice. Neuronal ABCA7 deficiency alters brain transcriptomes and lipidomes of 5×FAD mice. Neuronal ABCA7 deficiency disturbs mitochondria functions in synaptosomes from 5×FAD mice. Neuronal ABCA7 expression associates with genes and pathways related to mitochondrial homeostasis in AD brains.

AbstractBackgroundHomozygosity for the rare APOE3‐Christchurch (APOE3Ch) variant, encoding for apoE3‐R136S (apoE3‐Ch), was linked to resistance against an aggressive form of familial Alzheimer’s disease (AD). Carrying two copies of APOE3Ch was sufficient to delay autosomal AD onset by 30 years. This remarkable protective effect makes it a strong candidate for uncovering new therapies against AD. Thus, we aim to explore the protective mechanisms of APOE3Ch against AD onset, to inform therapy.MethodsWe used both amyloid mouse models and human induced‐pluripotent stem cells (iPSC) models to address this aim. We examined whether astrocytic expression of apoE3‐Ch through an AAV‐mediated approach can mitigate AD‐related pathology and toxicity in early (3.5 months old) and late (8 months old) amyloid pathology in 5xFAD mice. We also used isogenic iPSC lines carrying the APOE3Ch variant that were generated from APOE3 parental lines using CRISPR/Cas9 technology. Biochemical and biophysical properties of both recombinant and native apoE3‐Ch lipoprotein particles secreted by iPSC‐derived astrocytes have been investigated using different techniques including heparin affinity chromatography and size‐exclusion chromatography.ResultsWe investigated the impact of astrocytic apoE3‐Ch on amyloid pathology and toxicity in 3.5‐month‐old and 8‐month‐old 5xFAD mice. We confirmed successful AAV‐mediated overexpression of apoE3 and apoE3‐Ch in astrocytes. We found apoE3‐Ch specific changes in protein levels and solubility. Astrocytic expression of apoE3‐Ch reduced soluble Aβ oligomer levels and ameliorated ER stress response compared to apoE3 in the 8‐month‐old 5xFAD mice. Furthermore, our findings showed altered biochemical properties of HEK cell‐derived apoE3‐Ch protein, including decreased heparin binding, altered receptor binding, and enhanced lipid accepting capacity. We also characterized APOE3Ch iPSC‐derived cell models, including iPSC‐derived astrocytes, neurons, and cerebral organoids, and found differences between APOE3 and APOE3Ch at the functional level in these iPSC models.ConclusionsThe proposed work and the developed methods to study apoE3‐Ch promises to provide new insights into the possible roles of this rare, mutated protein in protecting against AD, offering new therapeutic avenues for AD treatment.

AbstractINTRODUCTIONThe 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.METHODSIn 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.RESULTSThis manuscript presents highlights from the conference and provides an overview of opportunities for further research in the field.DISCUSSIONUnderstanding 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.

Importance Numerous studies have established the association of the common APOE ε2 and APOE ε4 alleles with Alzheimer disease (AD) risk across ancestries. Studies of the interaction of these alleles with other amino acid changes on APOE in non-European ancestries are lacking and may improve ancestry-specific risk prediction. Objective To determine whether APOE amino acid changes specific to individuals of African ancestry modulate AD risk. Design, Setting, and Participants Case-control study including 31 929 participants and using a sequenced discovery sample (Alzheimer Disease Sequencing Project; stage 1) followed by 2 microarray imputed data sets derived from the Alzheimer Disease Genetic Consortium (stage 2, internal replication) and the Million Veteran Program (stage 3, external validation). This study combined case-control, family-based, population-based, and longitudinal AD cohorts, which recruited participants (1991-2022) in primarily US-based studies with 1 US/Nigerian study. Across all stages, individuals included in this study were of African ancestry. Exposures Two APOE missense variants (R145C and R150H) were assessed, stratified by APOE genotype. Main Outcomes and Measures The primary outcome was AD case-control status, and secondary outcomes included age at AD onset. Results Stage 1 included 2888 cases (median age, 77 [IQR, 71-83] years; 31.3% male) and 4957 controls (median age, 77 [IQR, 71-83] years; 28.0% male). In stage 2, across multiple cohorts, 1201 cases (median age, 75 [IQR, 69-81] years; 30.8% male) and 2744 controls (median age, 80 [IQR, 75-84] years; 31.4% male) were included. In stage 3, 733 cases (median age, 79.4 [IQR, 73.8-86.5] years; 97.0% male) and 19 406 controls (median age, 71.9 [IQR, 68.4-75.8] years; 94.5% male) were included. In ε3/ε4-stratified analyses of stage 1, R145C was present in 52 individuals with AD (4.8%) and 19 controls (1.5%); R145C was associated with an increased risk of AD (odds ratio [OR], 3.01; 95% CI, 1.87-4.85; P = 6.0 × 10 −6 ) and was associated with a reported younger age at AD onset (β, −5.87 years; 95% CI, −8.35 to −3.4 years; P = 3.4 × 10 −6 ). Association with increased AD risk was replicated in stage 2 (R145C was present in 23 individuals with AD [4.7%] and 21 controls [2.7%]; OR, 2.20; 95% CI, 1.04-4.65; P = .04) and was concordant in stage 3 (R145C was present in 11 individuals with AD [3.8%] and 149 controls [2.7%]; OR, 1.90; 95% CI, 0.99-3.64; P = .051). Association with earlier AD onset was replicated in stage 2 (β, −5.23 years; 95% CI, −9.58 to −0.87 years; P = .02) and stage 3 (β, −10.15 years; 95% CI, −15.66 to −4.64 years; P = 4.0 × 10 −4 ). No significant associations were observed in other APOE strata for R145C or in any APOE strata for R150H. Conclusions and Relevance In this exploratory analysis, the APOE ε3[R145C] missense variant was associated with an increased risk of AD among individuals of African ancestry with the ε3/ε4 genotype. With additional external validation, these findings may inform AD genetic risk assessment in individuals of African ancestry.

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.

A rare APOE variant APOE3 -Jac reduces self-aggregation and promotes healthy brain aging.