Reproductive Technology

Leptin Promotes Meiotic Progression and Developmental Capacity of Bovine Oocytes via Cumulus Cell-Independent and -Dependent Mechanisms

Abstract
Leptin has been shown to exert positive effects during maturation of bovine oocytes influencing blastocyst development, apoptosis and transcript levels of developmentally important genes. The present study was conducted to further characterize the mechanisms of leptin action on oocytes and the role of cumulus cells (CCs) in this context. In the first series of experiments, cumulus-oocyte complexes (COCs) were matured in serum-free medium containing 0, 1 or 10 ng/ml leptin or in medium supplemented with 10% (v/v) estrous cow serum (ECS). Leptin concentrations of 1 and 10 ng/ml stimulated meiotic progression of oocytes. Moreover, TUNEL-staining demonstrated that these leptin doses reduced the proportion of apoptotic CCs. In the second series of experiments, COCs or denuded oocytes (DOs) were matured in the presence of 0 or 10 ng/ml leptin. The percentage of COCs and DOs with extruded polar body was increased by leptin. In contrast, positive effects of leptin on fertilization rate and blastocyst development were only observed after treatment of COCs but not of DOs. Leptin treatment of COCs consistently enhanced blastocyst development even after parthenogenetic activation of oocytes or after the removal of CCs before fertilization. The proportion of polyspermic oocytes was not affected by leptin treatment or oocyte denudation. In the last experiment COCs were matured in the presence of 0, 1 or 10 ng/ml leptin. Transcript levels of specific genes were determined by reverse transcriptase-quantitative PCR (RT-qPCR) analysis of cumulus cells and single oocytes. Leptin treatment increased FAS, FASLG and STAT3 transcript levels in oocytes, but did not affect LEPR, BAX, and BIRC4 mRNA concentrations. In cumulus cells, leptin treatment increased mRNA levels for LEPR, STAT3, BAX, BIRC4 and FAS, but did not alter FASLG mRNA abundance. In conclusion, leptin differentially regulated gene expression in oocytes and cumulus cells. Moreover, leptin enhanced oocyte maturation and developmental capacity via cumulus cell-independent and -dependent mechanisms.

Key words: Apoptosis • Cumulus cells • Leptin • Leptin receptor • Oocyte development

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