Partial endothelial-to-mesenchymal transition mediated by HIF-induced CD45 in neointima formation upon carotid artery ligation

Aims Endothelial-to-mesenchymal transition (EndMT) is a fundamental process in vascular remodelling. However, the precise regulatory mechanism of vascular remodelling during neointima formation and the source of neointima cells are not entirely understood. Methods and results To investigate the origin of neointima cells and their relevance to vascular wall remodelling, we used an endothelial cell (EC)-specific lineage tracing system [VE-Cadherin (Cdh5)-BAC-Cre(ERT2) mice] and carotid artery ligation model and showed evidence that resident ECs transdifferentiate into neointima cells with the expression of CD45. During the early stages of neointima formation, ECs transiently expressed CD45, a haematopoietic marker, accompanied by a host of EndMT markers, and CD31 and alpha SMA were prominently expressed in developing neointima. In vitro, CD45-positive EndMT was induced by stabilization of HIF1 alpha with cobalt chloride or with a VHL inhibitor in human primary ECs, which mimicked the hypoxic condition of the ligated artery, and promoted the formation of an integrin alpha 11-shank-associated RH domain-interacting protein (SHARPIN) complex. Notably, a CD45 phosphatase inhibitor disrupted this integrin alpha 11-SHARPIN complex, thereby destabilizing cell-cell junctions. Deletion of Hif1 alpha in ECs suppressed expression of CD45 and EndMT markers and ameliorated neointima formation. Conclusion These results suggest that the HIF-induced CD45 expression is normally required for the retention of an EC fate and cell-cell junctions, CD45-positive EndMT (termed as 'partial EndMT') contributes to neointima formation and vascular wall remodelling.