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Reconstruction of the Human Blood-Brain Barrier in vitro reveals a Pathogenic Mechanism of APOE4 in Pericytes

ABSTRACT: The majority of Alzheimer’s disease patients and 20–40% of non-demented elderly experience amyloid deposits along their cerebral vasculature, a condition known as cerebral amyloid angiopathy (CAA). CAA impairs the function of the blood-brain barrier (BBB) leading to ischemia, hemorrhages, and accelerated cognitive dysfunction. The APOE4 allele is the strongest known genetic risk factor for CAA and sporadic AD, however the pathogenic mechanisms underlying this predisposition are unknown. Here, we recreate the human BBB in vitro by co-culturing the three cellular components of the BBB, endothelial cells, pericytes, and astrocytes in 3D scaffolding to construct a tractable model that recapitulates key anatomical and physiological properties of the BBB. Similar to the in vivo BBB, we find amyloid accumulates on our in vitro BBB (iBBB) and both APOE4 homozygous and heterozygous iBBBs exhibit significantly more amyloid accumulation than APOE3/3 iBBBs. Combinatorial experiments revealed that pericytes have a causal role in the development of CAA. We found that APOE expression is markedly up-regulated in APOE4 pericytes, but not in astrocytes or endothelial cells. Transcriptional profiling revealed that calcineurin/NFAT signaling is dysregulated in APOE4 pericytes. Pharmacologically inhibiting calcineurin led to downregulation of APOE and subsequently reduced amyloid deposition on the iBBB. These results demonstrate an unexpected role of pericytes in cerebral amyloid deposition and advocate for inhibiting calcineurin/NFAT-signaling as a therapeutic strategy to mitigate APOE4 predisposition to CAA and potentially AD.

ORGANISM(S): Homo sapiens

PROVIDER: GSE125869 | GEO | 2019/07/31

REPOSITORIES: GEO

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Project description:Human APOE genotype is intricately involved in the homeostasis of the central nervous system, which is particularly evident from its association with neurodegenerative disease. Compared to APOE3, APOE4 is associated with greater cognitive decline in aging, poorer outcomes following stroke and traumatic brain injury, and is a major genetic risk factor for Alzheimer’s disease. Human APOE genotypes can differentially modulate neuronal function via both direct and indirect pathways. Of the indirect pathways, increasing evidence supports that APOE4-associated neurovascular dysfunction plays a significant role in neurodegeneration. For example, deficits in cerebral blood flow, neuronal-vascular coupling and blood-brain barrier integrity are observed with APOE4 both during aging and in Alzheimer’s disease patients; data that has been recapitulated in mouse models. Therefore, the identification of cellular mechanistic pathways that contribute to APOE-modulated vascular function is important for fundamental and disease-focused research. Highly specialized brain endothelial cells (BECs) are essential for virtually all neurovascular functions and, therefore, the influence of apoE on the cerebrovasculature likely involves alterations in brain endothelial cells function, directly or via supporting cells. ApoE synthesis has been demonstrated in multiple cell types in both the brain (e.g. astrocytes, pericytes and neurons) and periphery (e.g. hepatocytes and macrophages). Current research has largely focused on the effects of apoE produced by supporting cell types, particularly astrocytes and pericytes, on BEC function. However, less explored is whether BECs produce apoE to modulate their function. Data from limited studies on apoE production by BECs and APOE genotype-specific functional differences are conflicting. Evaluation of whether the APOE genotype of BECs modulates their function is important, as this could represent a novel mechanisms that contributes to altered cerebrovascular function in aging and AD. The goal of this study was to evaluate the role of human APOE genotype in modulating the phenotype and/or function of brain endothelial cells in vitro. To this end, we utilized primary brain endothelial cells isolated from APOE-targeted replacement mice that express human APOE3 or APOE4 under the endogenous mouse APOE promoter. BECs are highly specialized and functionally complex to maintain homeostasis of the central nervous system and APOE genotype could theoretically alter levels of any number of molecules and associated functions. Thus, without a priori knowledge we initially evaluated the extent that APOE modulated the transcriptomic profile of brain endothelial cells.

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Reconstruction of the Human Blood-Brain Barrier in vitro reveals a Pathogenic Mechanism of APOE4 in Pericytes

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