Novel Role of Endothelial CD45 in Regulating Endothelial-to-Mesenchymal Transition in Atherosclerosis

BackgroundThe protein tyrosine phosphatase CD45 is expressed in all nucleated cells of the hematopoietic system and in mitral valve endothelial cells (ECs) undergoing endothelial-to-mesenchymal transition (EndoMT). Our recent work indicated that activation of endogenous CD45 in human endothelial colony-forming cells (ECFCs) induced expression of multiple EndoMT marker genes. We hypothesized that CD45 may contribute to atherosclerosis; however, detailed molecular mechanisms underlying how CD45 may contribute to EndoMT and the impact of therapeutic manipulation of CD45 expression in atherosclerosis are unknown. MethodsWe generated a tamoxifen-inducible EC-specific CD45-deficient mouse strain (EC-iCD45KO) on an ApoE-deficient (WT/ApoE-/-) background and fed them a Western diet (WD) to produce atherosclerosis. We enriched mouse aortic ECs with anti-CD31 beads to perform single-cell RNA sequencing. Cellular, biochemical and molecular approaches were used to investigate the effect of endothelial CD45-specific deletion on EndoMT and lesion development in an ApoE-/- mouse model of atherosclerosis. ResultsEC-iCD45KO mice showed reductions in lesion development, plaque macrophage infiltration, and expression of cell adhesion molecules when compared to WT/ApoE-/- controls. Single-cell RNA sequencing revealed that loss of endothelial CD45 decreases EndoMT marker expression and TGF-{beta} signaling in atherosclerotic mice, which is associated with reduction of lesions. Mechanistically, CD45 loss increases Fibroblast Growth Factor Receptor 2 (FGFR2) expression in mouse aortic ECs and Kruppel-like Factor 2 (KLF2) expression in the aortic root. Endothelial CD45-deficiency also inhibits EndoMT and TGF{beta} signaling in atherosclerosis. ConclusionsOur findings demonstrate that genetic depletion of endothelial CD45 protects against EndoMT-driven atherosclerosis by promoting FGFR2 and KLF2 expression while inhibiting Transforming Growth Factor beta (TGF{beta}) signaling and EndoMT. Consequently, targeting endothelial CD45 may represent a novel therapeutic strategy to reduce EndoMT in atherosclerosis.