(23c) A 3D Bicellular Biomimetic Model of Vasculitis Reveals New Insights into Vascular Barrier Function

The integrity of the endothelial barrier between circulating blood and tissue is important for blood vessel function and ultimately, for organ homeostasis. Here, we present a 3D bi-cellular model to mimic the barrier function and study the role of pericyte cells in vascular inflammation. In particular, we developed a human vessel-on-a-chip with perfused endothelialized channels lined with human bone marrow cells, which adopt a pericyte-like cell phenotype that recapitulates barrier function of the vasculature. Our in vitro platform captures the essential features of the 3D vascular environment, the polarized endothelium, and the matrix for pericytes to build cell-cell or cell-matrix interactions. These attractive features make our platform suitable for modeling vasculitis and for better understanding the behavior of perivascular cells in pathophysiological contexts such as inflammation, thus offering a powerful complement to animal models for preclinical drug evaluations. In particular, we used the 3D biomimetic vascular platform to examine pericytes behavior under inflammation. We modeled vascular inflammation by introducing different pro-inflammatory stimuli into the chip, such as Lipopolysaccharides (LPS), Thrombin and TNFα, which have been shown to affect vascular integrity and endothelial blood barrier function. Interestingly, we observed a rapid physical withdrawal of pericyte-like cells from the endothelium that was accompanied by an inhibition of endogenous Rac1 activity and increase in RhoA activity in the pericyte-like cells themselves upon inflammation. Using a system to chemically induce activity in exogenously expressed Rac1 or RhoA within minutes of stimulation, we demonstrated RhoA activation induced loss of pericyte-like cell coverage on the endothelium and reduced endothelial barrier function, and this effect was abrogated when Rac1 was simultaneously activated. We further showed that N-cadherin expression in pericyte-like cells plays a key role in barrier function and controlling the heterocellular interaction of pericyte-endothelial cells. Specifically, CRISPR-mediated knockout of N-cadherin in the pericyte-like cells led to loss of barrier function and overexpression of N-cadherin promoted barrier function. In summary, this bi-cellular model demonstrates the continuous and rapid modulation of interactions between perivascular cells and endothelial cells and its impact on vascular barrier function, and highlights a new in vitro platform to study the biology of perivascular-endothelial interactions.