The Effect Of Different Proportions Of Methionine And Cystine On The Reproductive Performance In Low-protein Diet

As the development of low-protein diets in many countries including China,more researches of amino acid nutrition(AA)have been carried out.But the ideal AA pattern,especially the reasonable proportion of amino acids,are not yet clear,such as the desired methionine/cystine ratios.Meanwhile,the abnormality rate of sperm increased as the ratio of methionine and cystine increased.Methionine is the only sulfur-containing amino acid in essential amino acids,and it is also a methyl donor which is involved in the transfer of methyl in animals,the synthesis of proteins,cysteine,adrenaline,choline and creatine.In this study,the experiments of low-protein diet with varying ratios of methionine:cystine(low ratio of 1:3,medium ratio of 1:1,and high ratio of 3:1)were conducted to investigate the effect on mice growth,reproductive performance,methionine cycle and nutritional epigenetic regulation.The object of this study is to investigate the effects of different methionine/cystine ratios on the growth performance and reproductive performance of mice and the mechanism of effects and provide experimental basis for the precise nutrition utilization of two amino acids.The results are shown as follows:(1)Different ratio of methionine/cystine had no significant effect on food intake and body weight of mice.(2)Lower Met:Cys ratio improves reproductive performance in male mice.We observed that the litter size was increased 23.53% in low rate group(P < 0.05),and the medium rate group was increased 12.07%(P = 0.056)compared with the high rate group.Meanwhile,the abnormality rate of sperm increased as the ratio of methionine and cystine increased.Although the serum testosterone level and the m RNA levels of AR was significantly decrease in low rate group(P < 0.05),there was no significant difference in the protein levels of androgen receptors between three groups.(3)Different methionine/cystine ratios had no significant effect on spermatogenesis related genes Prm2,Pgk2 and apoptosis-related Ba K1 and Bcl-2 in mice testis,but the protein abundance of Bax increased with the increase of methionine/cystine ratio(P < 0.05).This was consistent with the sperm abnormality rate and phenotypic.(4)Different ratio of methionine/cystine can regulate the methionine cycle.The result of ELISA showed that the concentration of SAM and Hcy in low rate group serum was significantly higher than in the high rate group(P < 0.05).Quantitative analysis showed that m RNA expression levels of MAT2 B,GNMT,AHCY and BHMT were significantly upregulated in low rate group,compared with the high rate group.This was consistent with the result of ELISA.(5)Determine of serum antioxidant related indicators show that: the serum GSH-PX activity was significantly increased in the low rate group(P < 0.05),the concentration of MDA was decreased compare with other two groups.(6)Detection of DNA methyltransferase found that: Different methionine/cystine ratios will not affect the expression of DNMT3 a,but will affect the expression of DNMT1.In other words that the methyl donor changes affect DNA methylation which is DNA maintenance methylation,not the DNA De novo synthesis methylation causes by different methionine/cystine ratios.Overall,the present study showed that a dietary lower methionine/cystine ratio in a low-protein diet had a positive influence on the reproductive performance of male animal through obviously improving sperm quality and antioxidant capacity,and inhibiting apoptosis.