The role of leptin in mammalian oocyte developmental competence and pre-implantation embryo development

Leptin is primarily involved in energy homeostasis and has been implicated in fertility. Leptin- and leptin receptor-deficient mouse models have demonstrated that expression of leptin signalling in the central nervous system is essential for ovulation. However, evidence from ruminants and other species gathered from models with physiological leptin signalling suggests that modulation of leptin may not play a major role in the attainment of ovulation in post-pubertal individuals, despite influencing ovarian steroidogenesis and folliculogenesis. In vitro studies indicate that leptin concentrations between 10 and 100 ng/ml may inconsistently enhance oocyte maturation across several species. However, most livestock studies report positive effects only at concentrations higher than those found in follicular fluid, raising questions about the physiological relevance of these findings. Similarly, in humans, leptin levels in follicular fluid show inconsistent correlations with oocyte maturation, further questioning the role of leptin in the completion of meiosis. In null mutant models of leptin or its receptor, leptin expression is required for pre-implantation development but does not appear to be essential for implantation. Furthermore, contradictory in vitro data on leptin-mediated effects during oocyte maturation and pre-implantation development across various species do not support an essential role of leptin in the ability of oocytes to form a blastocyst or in the progression of early embryos to the blastocyst stage. Overall, while the presence of leptin is crucial for ovulation and pre-implantation development, its modulation under physiological leptin signalling appears to have a minimal impact on blastocyst formation, suggesting a dispensable role in mammalian reproduction.