Effects Of Methionine Restriction On Energy Metabolism And Protein Metabolism In High-fat Diet-fed Mice

Objectives: Thyroid hormones are highly significant in the regulation of energy metabolism,glycolipid metabolism and protein metabolism.Thyroid hypofunction may cause many diseases,including obesity and cardiovascular disease.In previous studies,it has been confirmed that high fat diet with methionine restriction could promote food intake,engery expenditure and lipolysis,decrease blood glucose level,thus promoting engery supply.These might be relative to the promotion of thyroid hormones.Protein synthesis is a process of high energy consumption,and need methionine as a substrate for protein synthesis.Nevertheless,even methionine had be restricted to 80%,animals still maintained normal physiological function,and did not decrease a lot of protein synthesis.Therefore,the protein synthesis of methionine restricted animals might be promoted by enough energy supply through enhancing food intake,lipolysis and glycolysis,which maintained protein metabolism.This study was aimed to investigate the effect of methionine restriction on energy and protein metabolism in skeletal muscle,and its potential influence of thyroid hormones regulation.Methods: In this study,a total of 60 male C57BL/6J mice were divided into three groups: a control group(CON: methionine content 0.86%,lard 4%),a high-fat diet group(HFD: methionine content 0.86%,lard 20%)and a methionine-restricted group(MR: methionine content 0.17%,lard 20%).Before sacrificing,fecal samples of each group were collected for detecting fat apparent digestibility at 11-week and 22-week respectively.At 21-week,CLAMS was utilized to monitor the energy metabolism of 4 mice each group,while CT scanner was employed to measure the body fat ratio and leg muscle fat ratio of another 6 mice each group.After sacrificing,thyroid hormone levels,lipid levels and redox state of the plasma were measured.Meanwhile,thyroid hormones related gene expression in mRNA level and thyroid histology was detected in thyroid.Furthermore,the gastrocnemius mass and soleus mass,protein content,muscular glycogen,NEFA,MMP,ATP content,mitochondrial DNA copy number,redox state related indicators were determined in skeletal muscle respectivly.Moreover,m RNA level expression of thyroid hormones,mitochondrial biogenesis and protein metabolism related genes,protein level expression of DIO2 and TR?1 were detected in skeletal muscle.Results: After a 3-week's feeding,HF group showed a significant increase in body weight than CON group,and methionine restriction decreased the body weight to CON group level.Compared with HF group,the food intake,energy expenditure and night locomotor activity were significantly decreased in MR group,meanwhile,MR did not change the RER value.In the 11-week,MR group had a significant increase in expression of TR?1 at mRNA and protein level,and had no significant effect on plasma TSH,T4,T3,thyroid follicle area and mRNA level expression of thyroid hormones related genes(TPO and TGB),when Compared with HF group.In the 22-week,MR group had a significant increase in plasma T4,T3,thyroid follicle area,and mRNA level expression of thyroid hormones related genes(TPO,NIS,TGB and TSHR),and had a significant decrease in TSH,when compared with HF group.In the 11-week and 22-week,MR group significantly decreased skeletal muscle ATP content,mitochondrial DNA copy number and mRNA level expression of genes(Tfam and ATP6),while MMP level and PGC-1? mRNA level only had a significant increase in the 22-week,when Compared with HF group.In the 11-week and 22-week,Compared with HF group,body fat ratio,leg muscle fat ratio,plasma TG,TC,LDL-C and NEFA level,NEFA level of skeletal muscle were all significantly reduced.Furthermore,Compared with HF group,methionine restriction significantly increased skeletal muscle protein content,muscular glycogen level,protein synthesis related genes(PI3K and Akt)mRNA level,meanwhile significantly decreased protein degradation related genes(FOXO3a?MAFbx and MuRF1)mRNA level.The mTORC1 and S6K1 mRNA level in MR group only had an significant decrease in the11-week,but had no statistically significant difference in the 22-week.Moreover,in MR group,blood and skeletal muscle redox indicators ROS,T-AOC,GPx and GSH/GSSG were all significantly increased,while MDA and AOPP level were all significantly decreased,when compared with HF group in the 11-week and 22-week.Conclusions: Methionine restriction increased skeletal muscle T3 level by promoting thyroid function and expression of DIO2,meanwhile improved the effective utilization of T3 by promoting expression of TR?1 in skeletal muscle.Therefore,mitochondrial content were improved,which promoted lipolysis and energy supply.Furthermore,protein synthesis rate was ameliorated by enough engery supply and ultimately protein content was maintained in skeletal muscle by methionine restriction.