COL8A1 regulates endothelial phenotype in inflammatory endothelial-to-mesenchymal transition.

Endothelial-to-mesenchymal transition (EndMT) has been implicated in inflammatory vascular pathologies such as atherosclerosis. The nonfibrillar collagen type VIII functions as a pivotal player in atherogenesis, but its role in EndMT is not well understood. We assessed the role of the α 1 chain of collagen type VIII (COL8A1) in inflammatory EndMT. Single-cell RNA-seq analysis of murine and human endothelial cells exposed to atherogenic stimuli in vivo revealed increased COL8A1 expression. Immunofluorescent analyses showed that COL8A1 expression was increased in murine atherosclerotic lesions, coinciding with the decreased expression of the endothelial marker platelet endothelial cell adhesion molecule-1. Treatment of human aortic endothelial cells (HAECs) with tumor necrosis factor-α (TNF-α) induced inflammatory EndMT. Interestingly, TNF-α treatment had a biphasic effect on COL8A1 expression in HAECs, with an initial downregulation followed by upregulation at 5 days of treatment. HAECs were then subjected to either exogenous recombinant COL8A1 (rcol8a1) exposure, lentiviral COL8A1 overexpression, or COL8A1 siRNA inhibition. Functionally, COL8A1 knockdown in HAECs suppressed endothelial gene programs, impaired tube formation, and enhanced NF-κB/Snail activation. Conversely, recombinant COL8A1 or lentiviral overexpression preserved endothelial morphology and markers and attenuated TNF-α-induced EndMT. Our findings suggest that COL8A1 is a key regulator of endothelial stability during inflammatory stress. Its transient inhibition facilitates early EndMT via NF-kB/Snail signaling, whereas its later induction in advanced disease reflects endothelial remodeling within atherosclerotic lesions. These findings identify COL8A1 as both a biomarker and a potential therapeutic target in vascular disease.