Effects of leptin on in vitro maturation, fertilization and embryonic cleavage after ICSI and early developmental expression of leptin (Ob) and leptin receptor (ObR) proteins in the horse

Compact and expanded-cumulus horse oocytes were matured in medium containing different concentrations (1, 10, 100, 1000 ng/ml) of recombinant human leptin and the effects on maturation, fertilization and embryo cleavage were evaluated. Furthermore, early developmental expression of Ob and leptin receptor (Ob-R) was investigated by immunocytochemical staining.In expanded-cumulus oocytes, the addition of leptin in IVM medium improved maturation (74% vs 44%, for 100 ng/ml leptin-treated and control groups, respectively; P < 0.05) and fertilization after ICSI (56% vs 23% for 10 ng/ml leptin-treated and control groups, respectively; P < 0.05). However, the developmental rate and quality of 8-cell stage embryos derived from leptin-treated oocytes (100 ng/ml) was significantly reduced, in contrast to previous data in other species where leptin increased embryo cleavage. Ob and Ob-R proteins were detected up to the 8-cell stage with cortical and cytoplasmic granule-like distribution pattern in each blastomere.Leptin plays a cumulus cell-mediated role in the regulation of oocyte maturation in the mare. Species-specific differences may exist in oocyte sensitivity to leptin.Leptin, the product of the obesity (Ob) gene [1], predominantly synthesized by adipocytes, has been shown to be involved in the regulation of the reproductive function [2] and recent studies have been performed, by exploiting the potential role of this hormone in animal models, such as mouse, swine and bovine, to evaluate the possibility of improving in vitro oocyte maturation and embryo culture procedures. In the mouse, Kawamura et al. [3,4] demonstrated that leptin supplementation in the culture medium (10, 100 and 1000 ng/ml) promoted embryo development and increased the cell numbers of cultured blastocysts and the effect was preferentially observed in the trophoectoderm. These findings raised the possibility that leptin might regulate mouse preimplantation embryo development through a paracrine pathway.