Maturation rates of oocytes and levels of FSHR, LHR and GnRHR of COCs response to FSH concentrations in IVM media for sheep

Abstract

This study investigated the FSH influence on maturation rates of oocytes in vitro maturation (IVM), and expression levels of the follicle-stimulating hormone receptor (FSHR), luteinizing hormone receptor (LHR) and gonadotropin releasing hormone receptor (GnRHR) of cumulus-oocyte complexes (COCs) response to FSH treatment. 1686 COCs were harvested from 1063 ovaries of sheep. COCs were cultured 26h at 38.5°C and 5.0% CO2 in IVM media supplemented with 0, 5, 10, 20 and 30 IU/ml FSH. They were allocated in to FSH-1 (basal line), FSH-2, FSH-3, FSH-4 and FSH-5 groups. The apoptosis of COCs was assessed by Tunel assay. Expression levels of mRNA and protein for FSHR, LHR and GnRHR in sheep COCs were detected using real time RT-PCR and Western blotting respectively. The results showed that the maturation rates of oocytes were improved gradually when FSH supplement increased from 0 to 10μg/ml. FSH-3 group showed the highest maturation rate. Apoptosis rates of FSH-treated groups were less than that of FSH-1 group with a minimum of FSH-3 group. Expression levels of FSHR and LHR mRNAs in FSH-3 and FSH-4 were significantly higher than in FSH-1. Expression level of GnRHR mRNA in FSH-3 was higher than in FSH-1 (P<0.05). Expression levels of FSHR proteins in FSH-3 and FSH-4 groups were higher than that of FSH-1 group. Expression levels of GnRHR proteins increased gradually with a maximal increment of FSH-5. Maturation rates of COCs had significant positive correlations with mRNA and protein levels of FSHR, LHR and GnRHR. In conclusion, FSH could accelerate the maturation rate of sheep oocytes and reduce their apoptosis rate, also increase the expression levels of FSHR, LHR and GnRHR mRNAs, and strengthen expressions of FSHR and GnRHR proteins. 10 IU/ml FSH additions were the optimal dose for IVM of sheep oocytes.