Effects Of Protein Intake On Skeletal Muscle Composition In Overweight/Obese Rats With Low Energy Intake

Objective:To investigate the effects of low,normal and high protein intake on skeletal muscle composition and its mechanism in overweight/obese rats with low energy intake.Methods:72 healthy SD rats were fed with normal maintenance diet for one week.According to their body weight,72 healthy SD rats were randomly divided into normal control group(n-12)and model group(n=60).After 9 weeks of high-fat diet,the successful rats were randomly divided into model control group(MC),low energy low protein group(LP),low energy normal protein group(NP)and low energy high protein group(HP).The body weight and food intake of rats were weighed every weekend,and blood samples were taken from abdominal aorta after 8 weeks of intervention:(1)Serum was taken to detect the content of blood glucose and blood lipid,quadriceps femoris and gastrocnemius muscle were weighed respectively,and their protein and fat contents were measured.Part of skeletal muscle was stained with HE and the distribution of muscle tissue and fat was observed.(2)To detect the indexes related to skeletal muscle protein synthesis and decomposition:the contents of insulin(INS),estradiol(E2),testosterone(T),nitric oxide synthase(NOS),insulin-like growth factor-1(IGF-1)and growth hormone(GH),which promote skeletal muscle protein synthesis were measured.The contents of insulin-like growth factor(IGF-1),phosphatidylinositol 3 kinase(PI3K),protein kinase B(PKB),rapamycin target protein(mTOR)and ribosomal protein S6 kinase 1(S6K1)were measured.And the contents of cortisol(Cortisol),muscle atrophy F-box(MAFbx)and muscle ring finger 1(MuRF-1),which promote skeletal muscle protein degradation,were measured.(3)The contents of indexes related to the synthesis and decomposition of skeletal muscle fat were detected:glucagon(GC),the hormone that promotes oxidative decomposition of skeletal muscle fat,signal factor peroxisome proliferator-activated receptor ?(PPAR?),peroxisome proliferator-activated receptor ?(PPAR?),and adenosine monophosphate activated protein kinase(AMPK).Insulin(INS),the hormone that promotes fat synthesis in skeletal muscle,signal factors sterol regulatory element binding protein-1c(SREBP-1c),fatty acid synthetase(FAS),acetyl-CoA carboxylase(ACC),stearyl CoA desaturase-1(SCD-1)and Lipin1(Lipin1)were measured,and the relative expression of SREBP-1c gene was detected by real-time fluorescence quantitative PCR.Results:1.Energy,nutrient intake and body weight of rats:(1)The daily food intake,energy and fat intake of the three intervention groups were significantly lower than those of the MC group.The protein intake of male rats in LP group was significantly lower than that in MC group,while that in HP group was significantly higher than that in MC group,and the carbohydrate intake in HP group was significantly lower than that in MC group.The protein intake of female rats in NP group and HP group was significantly higher than that in MC group,and the carbohydrate intake in LP group was significantly higher than that in MC group,while that in HP group was significantly lower than that in MC group.(2)After the establishment of the model,the body weight of male and female rats in MC group was significantly higher than that in NC group,and the body weight in three intervention groups was significantly lower than that in NC group and MC group(P<0.05).2.Effects of protein intake on blood glucose,blood lipid and skeletal muscle components in overweight/obese rats with low energy intake:(1)After intervention,the blood glucose(GLU)of male rats was significantly lower than that of MC group(P<0.05),but the effect on female rats was not significant.For male rats,the insulin(INS)content of male rats in LP group was significantly lower than that in MC group,while the content of INS in NP group and HP group was significantly higher than that in MC group(P<0.05).For female rats,the content of INS in NP group and HP group was significantly higher than that in MC group(P<0.05).The content of glucagon(GC)in three intervention groups of male rats was significantly lower than that in MC group(P<0.05),but there was no significant difference between intervention groups,while the GC content in female rats in LP group and NP group was significantly lower than that in MC group(P<0.05).There was no significant difference between),HP group and MC group(2)The Triglycerides(TG)of male rats in the intervention group was significantly lower than that in the MC group(P<0.05).The levels of Total cholesterol(TC),High-density lipoprotein cholesterol(HDL-C),Low-density lipoprotein cholesterol(LDL-C)and Very low-density lipoprotein cholesterol(VLDL-C)in the intervention group were significantly higher than those in the MC group(P<0.05),but there was no significant difference among the three groups.TG in the female intervention group was significantly lower than that in the MC group(P<0.05).Contents of TC,HDL-C,LDL-C and VLDL-C in NP group were significantly higher than that in MC group(P<0.05).The other groups were not significantly different(3)The weight of quadriceps femoris and gastrocnemius muscles in the 3 intervention groups were significantly lower than that in the MC group(P<0.05).The protein content,protein weight,fat content and fat weight of quadriceps femoris and gastrocnemius muscle in the intervention group were significantly lower than those in the MC group.The protein content and protein weight of the quadriceps femoris muscle decreased with the increase of protein intake.The protein content and protein weight,fat content and fat weight of the gastrocnemius muscle in the NP group were the best.HE staining section showed that the tissue of quadriceps femoris in MC group was disordered and the adipose tissue was dense.After intervention,the adipose tissue decreased gradually,and the fat content of quadriceps femoris was significantly lower than that of gastrocnemius muscle in NP group.The variation trend of female rats was consistent with that of male rats3.Effects of protein intake on skeletal muscle protein metabolism of overweight/obese rats with low energy intake:(1)The contents of insulin(INS)?estradiol(E2),testosterone(T),nitric oxide synthase(NOS),insulin-like growth factor-1(IGF-1),growth hormone(GH)and cortisol(Cortisol)in male and female MC group were significantly lower than those in NC group(P<0.05).The contents of all hormones in),NP group and HP group were significantly higher than those in MC group(P<0.05).(2)Signal factors promoting skeletal muscle protein synthesis:the contents of IGF-1,PI3K,PKB,mTOR and S6K1 in the quadriceps femoris intervention group were significantly lower than those in the MC group,and significantly higher than those in the NC group.With the increase of protein intake,the content of signal factors decreased,but there was no statistical difference.While the gastrocnemius muscle of male rats increased with the increase of egg ? white matter intake,the content of signal factors in NP group was the most,and the other changes were the same as those of quadriceps femoris.The variation trend of female rats was consistent with that of male rats.(3)For the signal factors promoting skeletal muscle protein degradation:the contents of MAFbx and MuRF-1 in the quadriceps femoris intervention group were significantly lower than those in the MC group(P<0.05),and significantly higher than those in the NC group(P<0.05).With the increase of protein intake,the signal factors increased,but there was no significant difference between the intervention groups.With the increase of protein intake in gastrocnemius muscle of male rats,the content of degradation factor in NP group was the least,and the other changes were the same as those of quadriceps femoris.The variation trend of female rats was consistent with that of male rats.4.Effects of protein intake on skeletal muscle fat metabolism of overweight/obese rats with low energy intake:(1)Signaling factors that promote skeletal muscle fat synthesis:The contents of SREBP-1c-FAS,ACC,SCD-1 and Lipin1 in quadriceps femoris and gastrocnemius muscle intervention group were significantly lower than those in NC group and MC group(P<0.05).The content of signal factors in NC group was significantly lower than that in MC group(P<0.05).The signal factor content of NP group was lower than any other groups.The variation trend of female rats was consistent with that of male rats.(2)Signal factors promoting lipid oxidation and decomposition of skeletal muscle:the contents of AMPK,PPAR?,and PPARy in quadriceps femoris in male intervention group were significantly higher than those in MC group and NC group(P<0.05).The content of signal factor in MC group was significantly higher than that in NC group(P<0.05).The content of signal factor in NP group was significantly higher than that in LP group,but there was no statistical difference.With the increase of protein intake,the signal factor content of gastrocnemius muscle in NP group was the highest,but there was no significant difference between intervention groups,and the other changes were the same as those of quadriceps femoris.The variation trend of female rats was consistent with that of male rats.Conclusions:Energy restriction could significantly reduce the protein and fat content of quadriceps femoris and gastrocnemius muscle of overweight/obese rats,while appropriately increase the protein energy supply ratio of energy-limited diet(so that the protein intake of energy-limited diet was consistent with that of normal diet).it can promote the expression of signal factors related to protein synthesis and fat decomposition in gastrocnemius muscle,and reduce the expression of signal factors related to protein decomposition and fat synthesis.At the same time,it can promote the expression of signal factors related to fat decomposition and reduce the expression of signal factors related to fat synthesis in quadriceps femoris.As a result,the loss of protein in gastrocnemius muscle was reduced,and the loss of fat in quadriceps femoris and gastrocnemius muscle was increased,and there was no gender difference in this effect.