Abstract 111: COL8A1 Modulates Endothelial Phenotype During Inflammatory Endothelial-to-Mesenchymal Transition

Abstract

Background: Endothelial-to-mesenchymal transition (EndMT), the dynamic process whereby endothelial cells (ECs) gradually lose endothelial identity while acquiring mesenchymal characteristics, plays significant roles in inflammatory cardiovascular pathologies such as atherosclerosis. The mechanisms of EC phenotypic modulation during EndMT remain widely unexplored. Understanding the factors driving the endothelial changes during EndMT may allow for the development of novel therapeutic targets to modulate this transition. Methods/Results: Inflammatory EndMT was induced in human aortic ECs (HAECs) by treatment with tumor necrosis factor-α (TNF-α), which showed a partial EndMT as evidenced by morphological changes, downregulation of endothelial markers, decreased angiogenic capacity, upregulation of mesenchymal markers, and increased cellular invasion. Results indicated that TNF-α treatment resulted in the loss of endothelial markers after short-term (24h) treatment. Interestingly, the expression of COL8A1 , which encodes for one of the two alpha chains of the non-fibrillar type VIII collagen, was selectively downregulated among collagens by TNF-a treatment at early time-points. In HAECs, overexpression of COL8A1 , as well as exposure to exogenous recombinant COL8A1, led to increased endothelial marker expression. COL8A1 knockdown potentiates TNF-α induced endothelial phenotype loss (reduced endothelial markers and decreased angiogenic capacity), while COL8A1 overexpression partially rescues TNF-α induced endothelial phenotype loss. RNA sequencing revealed that COL8A1 knockdown resulted in the decreased expression of genes related to endothelial function (e.g., focal adhesion, cell-cell connections). Gene Set Enrichment Analysis (GSEA) showed significant enrichment of the TNF-α/NFKB signaling geneset and cardiac epithelial-mesenchymal transition geneset following COL8A1 knockdown. Conclusion: Our findings suggest that COL8A1 mediates the EC transition during inflammatory EndMT by serving to maintain normal endothelial function, whereby TNF-α decreases COL8A1 expression to facilitate the loss of the EC phenotype.