Basolateral brain endothelial cilia and its role in promoting vascular stability

PROJECT SUMMARY Endothelial cilia are normally considered to be present on the apical side of the vessel wall. Our data shows that endothelial cilia are also found on the basolateral side of the vasculature. The significance of this cilia location is not known. We hypothesize that endothelial cilia on the basolateral side is critical for cell-cell communication with cells of the neurovascular unit such as pericytes to promote vascular stability. In this proposal, we propose that vascular stability is governed by interaction between endothelial cell (EC)-cilia and pericytes through an interaction with basement membrane that interfaces between them. Molecules at the interface namely heparan sulfate proteoglycans (HSPGs) and the modifications associated with them are responsible for binding ligands secreted by ECs such as platelet derived growth factor-BB (PDGF-BB) to promote interaction with pdgfr-β+ pericytes. Signals emerging from ciliogenesis such as ARL13b and vascular stability promoting molecules such as PAK2 are responsible for PDGF-BB secretion and promote metabolic homeostasis in ECs. We investigate the hypothesis PDGF-BB induced PAK2-ARL13B autocrine EC signal promotes PDGF-BB secretion in brain ECs, facilitates metabolic homeostasis to influence endothelial HS sulfation, ensuring basolateral retention of PDGF-BB to facilitate recruitment of pericytes and promote vascular stability. We will investigate this hypothesis in three aims. In aim 1, we evaluate the PDGF-BB localization in vivo in the context of matrix and basolateral EC-cilia. In aim 2, we investigate basolateral EC-cilia role in pericyte recruitment. In aim 3, we determine whether the EC-cilia:HS interface promotes brain vascular stability. We use a combination of zebrafish, mice and primary human brain microvascular ECs model along with approaches of genetic mutant, loss- and gain-of function strategies, and microfluidic based co-culture systems to investigate these questions. The significance of this proposal is that understanding the basolateral EC-cilia communication with pericytes, and the underlying mechanisms associated with it, will offer avenues for intervention in conditions where vascular stability is compromised. The innovation is conceptual in nature, and merges three fields of EC-cilia, PDGF-BB and HSPG biology to address the vascular stability question. The impact of this work is the potential use of PDGF-BB as a repurposing candidate molecule for brain vascular stability.