Effect of leptin during in vitro maturation of prepubertal calf oocytes: Embryonic development and relative mRNA abundances of genes involved in apoptosis and oocyte competence

Abstract

During the in vitro maturation of adult bovine oocytes, leptin has beneficial effects on blastocyst development, apoptosis and transcription levels of developmentally important genes. The present study analyzes the differential effects of leptin on prepubertal bovine oocytes and cumulus cells. Effects were determined of leptin treatment during oocyte maturation on their developmental capacity after fertilization (Exp. 1), incidence of apoptosis in cumulus oocyte complexes (COCs) (Exp. 2) or on relative mRNA abundances of genes in cumulus cells and oocytes (Exp. 3). COCs were matured in serum-free medium containing 1 mg/mL polyvinyl alcohol and 0, 10, 100, or 1000 ng/mL leptin (L0, L10, L100, and L1000, respectively), or in medium supplemented with 10% fetal calf serum (FCS) as a positive control. Addition of leptin during oocyte maturation had no effect on cleavage rates after fertilization (FCS, 68.6%; L0, 62.9%; L10, 66.9%; L100, 63.4%; L1000, 60.9%). Similarly, no significant differences in blastocyst rates were observed when oocytes were matured in the presence of L0 (8.4%), L10 (9.3%), L100 (6.7%), L1000 (8.2%), compared to control FCS (9.4%). In Experiment 2, maturation in the presence of 1000 ng/mL of leptin increased the proportion of TUNEL-positive cumulus cell (6.9%) with respect to those matured in the presence of FCS (4.96%), but not at the lower leptin doses. When relative mRNA abundances were examined for seven genes by qRT-PCR, five (TP53, BAX, DNMT3A, PGTS2 and LEPR) showed differences among groups. LEPR expression was significantly higher in the oocytes matured with FCS compared with the other groups and in those matured with PVA (L0) without leptin compared with the three groups of oocytes matured in the presence of leptin. In conclusion, the addition of leptin to the in vitro maturation medium used for prepubertal bovine oocytes does not increase the development potential of the oocytes or reduce the percentage of apoptosis in cumulus cells. Leptin blocks transcription of the leptin receptor (LEPR) probably reflecting selective, differential degradation by doses of leptin.