The Effect Of SS31 On The In Vitro Maturation Of Immature Oocytes In Aged Mice

Objective:To observe the effect of SS31(D-Arg-2,6-dimethyltyrosine-Lys-Phe-NH2)on the in vitro maturation(IVM)of immature oocytes of aged mice and evaluate the influence of SS31 to the occytes quality and potential after IVM of immature oocytes of aged mice.Methods:48-52-week-old mice were selected as the study subjects.In vitro culture,in vitro fertilization,cell morphology evaluation and confocal microscopy were used to compare the effect of ovulation induction treated by Urinary gonadotropin and Pregnant Mare Serum Gonadotropin(PMSG)and to analyze the effects of different concentrations(0μmol/L,0.5μmol/L,1μmol/L,and 2μmol/L)of SS31 added into the culture medium on the maturation rate and maturation time of immature oocytes and to calculate the optimal culture time for each concentration group.All the oocytes collected were treated by in vitro fertilization and embryo culture after being cultured to the optimal maturation time.The fertilization rate,cleavage rate,high-quality embryos rate and blastocyst formation rate were compared between groups,the size and distribution of the oocytes membrane potential were also compared.Results: The acquisition rate of GV oocytes treated by Urinary gonadotropin was distinctly higher than that of PMSG and control(91.22% vs 79.17%、63.77%)(P<0.05).There were significant differences in the oocytes maturation rate after in vitro culture by adding SS31 to the culture medium between the groups of different concentration of SS31.The oocytes maturation rate of the group of 1μmol/L SS31 was much higher than those of 0μmol/L group,0.5μmol/L group and 2μmol/L group(87.69%vs70.49%,72.91%,73.73%)(P<0.05).The oocytes fertilization rate and the high-quality embryos rate of the group treated with 1μmol/L SS31 were significantly higher than those of 0μmol/L group,0.5μmol/L group and 2μmol/L group(68.47%vs54.90%,54.37%,57.02%;22.37% vs 8.93%,10.71%,8.70%)(P<0.05).There was also significant difference in the high-quality embryos rate between the mature group and IVM group(37.33% vs 22.37%)(P<0.05).The oocytes mitochondria membranepotential and distribution rate of the group treated without SS31 in the culture medium was significantly lower than that of 1μmol/L SS31 group and in vivo mature group(0.199 vs 0.732,0.821;17.65% vs 56.36%,58.00%)(P<0.05).Conclusions : Urinary gonadotropin is superior to Pregnant Mare Serum Gonadotropin(PMSG)in the ovulation-promoting protocol for senior mice.The addition of SS31 in the culture medium can significantly increase the in vitro maturation rate of oocytes of aged mice.The best maturation time for SS31 is 18 h and the optimum SS31 concentration is 1μmol/L.The fertilization rate and blastocyst formation rate of in vitro maturation of aged mice oocytes could be increased by adding SS31 to culture medium.It is thought that the role of SS31 in oocyte maturation may be to raise the oocyte quality by improving oocyte mitochondrial function.The results of this study will provide experimental evidence for the IVM of oocytes of elder female in clinic.