CD226 deletion improves post-infarction healing via modulating macrophage polarization in mice

Macrophages are essential for wound repair after myocardial infarction (MI). CD226, a member of immunoglobulin superfamily, is expressed on inflammatory monocytes, however, the role of CD226 in infarct healing and the effect of CD226 on macrophage remain unknown. Methods: Wild type and CD226 knockout (CD226 KO) mice were subjected to permanent coronary ligation. CD226 expression, cardiac function and ventricular remodeling were evaluated. Profile of macrophages, myofibroblasts, angiogenesis and monocytes mobilization were determined. Results: CD226 expression increased in the infarcted heart, with a peak on day 7 after MI. CD226 KO attenuated infarct expansion and improved infarct healing after MI. CD226 deletion resulted in increased F4/80⁺ CD206⁺ M2 macrophages and diminished Mac-3⁺ iNOS⁺ M1 macrophages accumulation in the infarcted heart, as well as enrichment of α-smooth muscle actin positive myofibroblasts and Ki67⁺ CD31⁺ endothelial cells, leading to increased reparative collagen deposition and angiogenesis. Furthermore, CD226 deletion restrained inflammatory monocytes mobilization, as revealed by enhanced retention of Ly6C^hi monocytes in the spleen associated with a decrease of Ly6C^hi monocytes in the peripheral blood, whereas local proliferation of macrophage in the ischemic heart was not affected by CD226 deficiency. In vitro studies using bone marrow-derived macrophages showed that CD226 deletion potentiated M2 polarization and suppressed M1 polarization. Conclusion: CD226 expression is dramatically increased in the infarcted heart, and CD226 deletion improves post-infarction healing and cardiac function by favoring macrophage polarization towards reparative phenotype. Thus, inhibition of CD226 may represent a novel therapeutic approach to improve wound healing and cardiac function after MI.