In Alzheimer's disease (AD), amyloid deposits along the brain vasculature leading to a condition known as cerebral amyloid angiopathy (CAA), which impairs blood-brain barrier (BBB) function and accelerates cognitive degeneration. APOE4 is the strongest risk factor for CAA, yet the mechanisms underlying this genetic susceptibility are unknown. Here, we developed an iPSCbased 3D model that recapitulates anatomical and physiological properties of the human BBB in vitro. Similar to CAA, our in vitro BBB displayed significantly more amyloid accumulation in APOE4 compared to APOE3. Combinatorial experiments revealed that dysregulation of Calcineurin/NFAT-signaling and APOE in pericyte-like mural cells induces APOE4-associated CAA pathology. In the human brain, we identify APOE and NFAT are selectively dysregulated in pericytes of APOE4-carriers, and that inhibiting calcineurin/NFAT-signaling reduces APOE4associated CAA pathology in vitro and in vivo. Our study reveals the role of pericytes in APOE4mediated CAA and highlights calcineurin/NFAT-signaling as a therapeutic target in CAA and AD.The BBB is critical for proper neuronal function, protecting the brain from pathogens and tightly regulating the composition of brain fluids. Neuronal health is directly coupled to the *

No abstract

The E4 allele of the apolipoprotein E gene (APOE) has been established as a genetic risk factor for many diseases including cardiovascular diseases and Alzheimer’s disease (AD), yet its mechanism of action remains poorly understood. APOE is a lipid transport protein, and the dysregulation of lipids has recently emerged as a key feature of several neurodegenerative diseases including AD. However, it is unclear how APOE4 perturbs the intracellular lipid state. Here, we report that APOE4, but not APOE3, disrupted the cellular lipidomes of human induced pluripotent stem cell (iPSC)–derived astrocytes generated from fibroblasts of APOE4 or APOE3 carriers, and of yeast expressing human APOE isoforms. We combined lipidomics and unbiased genome-wide screens in yeast with functional and genetic characterization to demonstrate that human APOE4 induced altered lipid homeostasis. These changes resulted in increased unsaturation of fatty acids and accumulation of intracellular lipid droplets both in yeast and in APOE4-expressing human iPSC-derived astrocytes. We then identified genetic and chemical modulators of this lipid disruption. We showed that supplementation of the culture medium with choline (a soluble phospholipid precursor) restored the cellular lipidome to its basal state in APOE4-expressing human iPSC-derived astrocytes and in yeast expressing human APOE4. Our study illuminates key molecular disruptions in lipid metabolism that may contribute to the disease risk linked to the APOE4 genotype. Our study suggests that manipulating lipid metabolism could be a therapeutic approach to help alleviate the consequences of carrying the APOE4 allele.