Effect of leptin supplementation during in vitro oocyte maturation and embryo culture on bovine embryo development and gene expression patterns.

Leptin is a metabolic hormone related to body condition and nutritional status that influences fertility in assisted reproductive technologies modulating oocyte and embryo quality. The aim of the present study was to establish the effect of various leptin concentrations (0, 10, 100 ng/mL) during in vitro oocyte maturation (IVM) and in vitro embryo culture (IVC) on bovine embryo development and quality in terms of gene expression. The relative mRNA abundance of the genes encoding solute carrier family 2 (facilitated glucose transporter) member 1 (SLC2A1), Bcl-2-associated X protein (BAX), placenta-specific 8 (PLAC8), aldo-keto reductase family 1 member B1 (AKR1B1) and leptin receptor (LEPR) were determined on Day 7 blastocysts by qRT-PCR. Cleavage rate (P < 0.005) and blastocyst yield (P = 0.05) was significantly lower when cumulus-oocyte complexes (COCs) were matured with 100 ng/mL leptin compared to 0 or 10 ng/mL leptin. No significant effect of different concentrations of leptin added during IVC on blastocyst yield was observed. The presence of 100 ng/mL leptin in both IVM and IVC further decreased cleavage rate (P < 0.005) and blastocyst yield compared to the control group without leptin (P = 0.05) and those supplemented with 10 ng/mL leptin or FCS (P < 0.005). There was no evidence of any leptin-induced difference in the relative transcript abundance of SLC2A1, BAX and PLAC8 genes in Day 7 blastocysts. Expression of AKR1B1 was significantly lower in blastocysts from COCs matured with 100 ng/mL leptin compared to those matured with 0 or 10 ng/mL leptin (P < 0.005). LEPR expression was up regulated when leptin concentration was increased from 0 ng/mL during IVM to 10 ng/mL during IVC, but it was down-regulated in the opposite situation (P < 0.005). In conclusion, high leptin concentrations possibly related to obesity seem to be more detrimental rather than the absence of this hormone for preimplantation embryo survival; this effect is independent of LEPR gene expression and it does not influence expression of SLC2A1, BAX and PLAC8 genes in Day 7 blastocysts.