Effect Of L-carnitine On Aging Oocytes And Early Embryo Development Of Bovine

Aging occurs in oocytes both in vivo or in vitro.Aging also leads to oxidative stress,the accumulation of reactive oxygen species(ROS),which may have harmful effects on cells or embryos.This experiment aims to explore the role of L-carnitine on bovine aging oocytes and the early embryos in vitro culture,which is divided into two parts:Experiment 1:Effect of LC on aged bovine oocytesL-carnitine(LC)is well known for its antioxidant activity.In this study,we explored the effects of LC supplementation on aged bovine oocytes in vitro.We showed that in-vitro maturation could enhance the subsequent developmental capacity of aging oocytes,when supplemented with LC.After in vitro fertilization,the blastocyst formation rate in the aged oocytes post-LC treatment significantly increased compared to that in untreated aged oocytes(P<0.05).Furthermore,after LC treatment,the level of intracellular reactive oxygen species in aged oocytes significantly decreased,and glutathione(GSH)levels significantly increased,compared to those in untreated aged oocytes(P<0.05).Mitochondrial membrane potential,the percentage of early apoptotic oocytes,and Caspase-3 activity were significantly reduced in LC-treated aged oocytes compared to those in untreated aged oocytes(P<0.05).Furthermore,during in vitro aging,the mRNA levels of the anti-apoptotic genes,Bcl-xl and survivin in LC-treated aged oocytes were significantly higher than those in untreated aged oocytes(P<0.05).Overall,these results indicate that LC can prevent the aging of bovine oocytes and improve the developmental capacity of bovine embryo.Experiment 2:Effect of LC on the early embryonic development in bovineAging oocytes undergo various molecular,cellular,and biochemical changes.Aging of oocytes results in reduced embryo developmental capacity and blastocyst quality,which is thought to be caused partly by the accumulation of reactive oxygen species.This study aimed to determine the effect of LC on the development of embryos formed from aged oocytes in vitro.The results showed that after the addition of LC in vitro culture(IVC),there was no significant difference in the cleavage rate between the LC-treated group and the aged group(P>0.05),but the blastocyst rate of the LC-treated group was significantly higher than that of the aged group(P<0.05).In addition,after LC treatment,the level of intracellular ROS in aged group significantly decreased,and GSH levels significantly increased compared with those in the untreated aged group(P<0.05).There was no significant difference in the mitochondrial membrane potential among the three groups(P>0.05).Moreover,ROS could induce autophagy and LC3 antibody was widely used as a marker for detecting autophagy.The fluorescence intensity of LC3 in the aged group was significantly higher than that of LC3 in the LC-treated group(P<0.05).Furthermore,Real-time reverse transcriptase-polymerase chain reaction showed that the mRNA levels of antioxidation genes GPX4 and SOD1 were significantly higher in embryos from LC-treated group than in those from the untreated aged group(P<0.05).In summary,our results indicated that LC can improve the developmental capacity of embryos from aging oocytes in vitro by reducing oxidative stress.