Melatonin regulates neuroinflammation ischemic stroke damage through interactions with microglia in reperfusion phase

Even today, ischemic stroke is a major cause of death and disabilities because of its high incidence, limited treatments and poor understanding of the pathophysiology of ischemia/reperfusion, neuroinflammation and secondary injuries following ischemic stroke. The function of microglia as a part of the immune system of the brain following ischemic stroke can be destructive or protective. Recent surveys indicate that melatonin, a strong antioxidant agent, has receptors on microglial cells and can regulate them to protective form; yet, more findings are required for better understanding of this mechanism, particularly in the reperfusion phase. In this study, we initially aimed to evaluate the therapeutic efficacy of melatonin intra-arterially and to clarify the underlying mechanisms. After that by using an in vitro approach, we evaluated the protective effects of melatonin on microglial cells following the hypoxia condition. Our results proved that a single dose of melatonin at the beginning of reperfusion phase improved structural and behavioral outcomes. Melatonin increased NeuN and decreased GFAP, Iba1 and active caspase-3 at protein level. Furthermore, melatonin elevated BDNF, MAP2, HSPA1A and reduced VEGF at mRNA level. We also showed that melatonin receptor 1B highly expressed in microglial cells after 3 h hypoxia. Besides, melatonin increased the ratio of TREM2/iNOS as a marker of the most protective form of microglia (M2). In summary, our data suggest that melatonin has the possibility to serve as targeting microglial action for preventing secondary injury of reperfusion phase after ischemic stroke.