p38α in macrophages aggravates arterial endothelium injury by releasing IL-6 through phosphorylating megakaryocytic leukemia 1

BACKGROUND: Macrophages regulate the inflammatory response and affect re-endothelialization. Inflammation and macrophages play important roles in promoting tissue repair, but p38α mitogen-activated protein kinase's role in re-endothelialization is unknown. METHODS AND RESULTS: Wire injuries of carotid arteries and Evans blue staining were performed in macrophage-specific p38α-knockout (p38α(fl/fl)LysMCre(+/-)) mice and control mice (p38α(fl/fl)). Re-endothelialization of the carotid arteries at 3, 5 and 7 days was significantly promoted in p38α(fl/fl)LysMCre(+/-) mice. In vitro experiments indicated that both the proliferation and migration of endothelial cells were enhanced in conditioned medium from peritoneal macrophages of p38α(fl/fl)LysMCre(+/-) mice. Interleukin-6 (IL-6) level was decreased significantly in macrophages of p38α(fl/fl)LysMCre(+/-) mice and an IL-6-neutralizing antibody promoted endothelial cell migration in vitro and re-endothelialization in p38α(fl/fl) mice in vivo. Phosphoproteomics revealed that the phosphorylation level of S544/T545/S549 sites in megakaryocytic leukemia 1 (MKL1) was decreased in p38α(fl/fl)LysMCre(+/-) mice. The mutation of either S544/S549 or T545/S549 sites could reduce the expression of IL-6 and the inhibition of MKL1 reduced the expression of IL-6 in vitro and promoted re-endothelialization in vivo. CONCLUSION: p38α in macrophages aggravates injury of arteries by phosphorylating MKL1, and increasing IL-6 expression after vascular injury.