Melatonin improves the ability of spermatozoa to bind with oocytes in the mouse

Melatonin is a powerful antioxidant regulating various biological functions, including alleviating male reproductive damage under pathological conditions. Here, we aim to analyse the effect of melatonin on normal male reproduction in mice.Male mice received an intraperitoneal injection of melatonin (10mg/kg body weight) for 35 consecutive days. The testis and epididymis morphology, and epididymal sperm parameters were examined. PCNA, HSPA2, SYCP3, ZO-1 and CYP11A1 expressions in epididymis or testis were detected by immunohistochemistry or Western blotting. Male fertility was determined by in vivo and in vitro fertilisation (IVF) experiments. The differentially expressed sperm proteins were identified by proteomics.No visible structural changes and oxidative damage in the testis and epididymis, and no significant side effects on testis weight, testosterone levels, sperm motility, and sperm morphology were observed in the melatonin-treatment group compared with the control group. Spermatogenesis-related molecules of PCNA, SYCP3, ZO-1, and CYP11A1 showed no significant differences in melatonin-treated testis. However, PCNA and HSPA2 increased their expressions in the epididymal initial segments in the melatonin-treatment group. Normal sperm fertilisation, two-cell and blastocyst development were observed in the melatonin-treated group, but melatonin significantly enhanced the sperm binding ability characterised as more sperm binding to one oocyte (control 7.2±1.3 versus melatonin 11.8±1.5). Sperm proteomics demonstrated that melatonin treatment enhanced the biological process of cell adhesion in sperm.This study suggests that melatonin can promote sperm maturation and sperm function, providing important information for further research on the physiological function and protective effect of melatonin in male reproduction.