Mitochondrial Transfer Improves Fertilization Capability Of Aging Mouse Oocyte And Developmental Potential Of Subsequent Preimplantation Embryo

Objective:To investigate the effect of mitochondrial transfer(MIT) on the fertilization capability of aging mouse oocyte,and developmental potential of cryopreserved subsequent preimplantation embryo.Methods:Six to eight weeks old female KM BAI mice were superovulated,and the oocytes retrieved were treated by intracytoplasmic sperm injection(ICSI) and medium blank injection(BI).The subsequent embryos were distributed in group A. Twelve months old female KM BAI mice were superovulated and the oocytes obtained were divided into two subsets.One was treated by ICSI and medium blank injection and the subsequent embryos were included in group B,the other was treated by ICSI and MIT and the subsequent embryos were included in group C.Comparisons were made among three groups on survival rates,fertilization rates and cleavage rates after ICSI and MIT or BI,as well as survival rates and blastulation rates after cryopreservation of the subsequent embryos. The mitochondrial membrane potential(ΔΨm) were detected by using JC-1,a fluorochrome and comparisons were also performed onΔΨm among three groups during the preimplantation stages and on the alterations ofΔΨm across the preimplantation stages of each group. Result:(1) The survival rate of oocytes from group A was significantly higher than those from both group B and group C(P＜0.01),however there was no significant difference between the latter two groups (P＞0.05).The fertilization rate in group B was significantly lower than that in either group A or group C(P＜0.05),while there was no significant difference between the latter two groups(P＞0.05). Differences of cleavage rates among the three groups were not significant(P＞0.05).On the other hand,both the survival rate and the blastulation rate of the subsequent embryos after cryopreservation from group C were significantly higher than those from group B(P＜0.05), but significant difference was not found in either of the two items between groups A and C(P＞0.05).(2) At 2-cell stage and morula stage,ΔΨm of embryos from groups A and C was extremely significantly higher than that from group B(P＜0.01),while at 4-cell stage,8-cell stage and blastocyst stage,ΔΨm of embryos from groups A and C was significantly higher than that from group B(P＜0.05).In any of the three groups,ΔΨm of embryos at either morula stage or blastocyst stage was significantly higher than that at any cleavage stage(P＜0.05), while there was no significant difference between morula stage and blastocyst stage and also no significant differences among the cleavage stages.Conclusion:MIT can significantly improve the fertilization capability of aging mouse oocyte and the developmental potential of cryopreserved subsequent embryo by elevating the mitochondrial activity in oocyte and blastomeres.