Melatonin, as a downstream molecule of follicle-stimulating hormone, improves nutrient accumulation and mitochondrial function in mammalian oocytes.
Background: Melatonin (MLT) supplementation has been shown to improve the quality of oocytes and embryos in vitro through its antioxidant mechanism. However, it is unclear whether endogenous MLT plays a role in oocyte quality control, casting doubt on the rationality of oral MLT in improving oocyte quality or fecundity. Methods:we measured the effects of PMSG on MLT synthesis in follicles, evaluated the effects of MLT on oocyte growth and quality in mice and goat, used RNA-seq to explore the mechanism underlying MLT's effects on oocyte growth and quality, and generated SNAT-knockout mice to assess the effects of endogenous MLT on oocyte growth and quality. Lastly, we investigated the feasibility of short-term MLT intake to improve the fertility of older mice. Result: we revealed that the follicle-stimulating hormone induces the expression of intra-ovarian SNAT, resulting in increased levels of intra-ovarian MLT in mice. Administering MLT during the gonadotropin-dependent phase improved the oocyte size and quality in both mice and goat by enhancing nutrient accumulation and mitochondrial function. Deficiency of MLT in mice reduced oocyte size and weakened mitochondrial function. Furthermore, our findings demonstrate that short-term MLT intake during the gonadotropin phase improves the litter size of older mice. Conclusion: This study reveals that endogenous MLT is involved in determining oocyte quality as a target molecule of follicle-stimulating hormone, shedding light on its potential utilization in improving oocyte quality or rejuvenating aged mammalian oocytes. Overall design: Follicular mRNA  profiles of  gonadotropin-induced ovaries in mice.There are 8 samples represented two treatments, Control (n=4) and Melatonin (n=4).