Endothelial Cell Reprogramming in Familial Intracranial Aneurysm

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ABSTRACT Saccular intracranial aneurysms (IA) represent a significant health issue in the US and worldwide. IA rupture leads to intracranial hemorrhage, with devastating outcomes: 30% of patients die within a month of the initial event, and 50% of survivors are left with severe neurological deficits requiring long-term care. IA is a multi- factorial disorder underlain by genetic and environmental risk factors. In a series of genome-wide association studies we identified multiple common variants that contribute to IA risk. To discover rare coding variants with large-effect size, we conducted whole exome sequencing analysis of a cohort of >250 patients from 58 families, each with at least 3 members diagnosed with IA. This analysis identified heterozygous rare and deleterious mutations in two novel genes, WBP11 and PPIL4, which collectively explain more than 10% of familial IA cases in our cohort. In preliminary experiments, we demonstrated that loss- of-function ppil4 and wbp11 zebrafish and mouse models display dramatic and similar changes in cerebrovascular morphology and cerebral hemorrhage, suggesting convergent action, and uncovered a specific requirement for both genes in endothelial cells (ECs). We also determined that depletion of WBP11 or PPIL4 in human ECs induces a pathological transcriptional reprogramming towards a senescent cellular state. Collectively, these findings led to the hypotheses that a) PPIL4 and WBP11 are critical components of a network that regulates cerebrovascular morphology and EC homeostasis; b) pathological EC reprogramming is the underlying mechanism in IA associated PPIL4 and WBP11 variants; and c) PPIL4 and WBP11 convergent action to the Wnt signaling pathway is mediated through binding partners and disrupted by IA-associated mutations. In this proposal we apply experimental and functional genomics approaches to test these hypotheses, aiming to establish the converging role of WBP11 and PPIL4 in cerebrovascular ECs, following the discovery of rare- deleterious coding mutations associated with familial IA. The expected outcome of this work is to define and integrate multiple facets that underpin the function of WBP11 and PPIL4: 1) the morphologic and histologic consequences of global and EC-specific deficiency of WBP11 and PPIL4 for structural integrity of the cerebral vessels in model organisms; 2) the impact of WBP11 and PPIL4 depletion and IA-associated variants on EC function at the cellular and molecular level; and 3) the convergence of WBP11 and PPIL4 in ECs via activation of Wnt signaling. These outcomes will inform a framework implicating pathological EC reprogramming as an overlooked contributing factor in IA etiology, while providing a novel conceptual framework for IA pathophysiology, with the long-term goal to develop precision medicine strategies to improve diagnosis and molecularly informed therapeutic interventions for IA patients.