Melatonin attenuates cardiac dysfunction and inflammation in dilated cardiomyopathy via M2 macrophage polarization.

Melatonin is a neuroendocrine hormone that exerts protective effects on the heart. Increasing evidence suggests that macrophage M2-type polarization improves myocardial regeneration and repair. Therefore, this study investigated whether melatonin ameliorates dilated cardiomyopathy (DCM) by modulating M2-type polarization. DCM mice were established by induction with doxorubicin and then treated with melatonin. Cardiac dysfunction was determined by measuring left ventricular ejection fraction (LVEF) and left ventricular internal dimensions at end-diastole and end-systole. Heart injury and fibrosis were determined by hematoxylin and eosin staining and Sirius Red staining, respectively. Serum concentrations of melatonin, tumor necrosis factor-alpha (TNF-α), interleukin-1 beta (IL-1β), and interleukin-6 (IL-6) were measured through enzyme-linked immunosorbent assays. M2-type macrophages were analyzed by flow cytometry. Relative mRNA and protein levels were determined by reverse transcription quantitative polymerase chain reaction and western blotting, respectively. Circulating melatonin levels were significantly decreased in DCM mice and were associated with LVEF. Treatment with melatonin markedly ameliorated cardiac dysfunction, improved survival, and alleviated pathological changes and collagen deposition in DCM mice. Furthermore, melatonin-treated DCM mice displayed lower serum and cardiac levels of IL-1β, IL-6, and TNF-α, as well as higher numbers of M2-type macrophages in cardiac tissue, indicating that melatonin treatment could decrease inflammatory responses and facilitate M2 macrophage polarization in DCM mice. Thus, melatonin treatment alleviated cardiac dysfunction and inflammatory responses by promoting M2 macrophage polarization in the DCM mouse model.