Effects Of Corticosterone On Protein And Energy Metabolism In Breast Muscle Of Broilers Showing Different Ti Phenotype And On Cholesterol Metabolism Of Broilers

Tonic immobility(TI),which can be divided into short(STI)or long(LTI)duration,is a character related to stress response.Hypothalamic-pituitary-adrenal(HPA)axis controls stress hormones synthesis and secretion,which has been proved to have profound effects on TI duration,and here's a majority of stress could influence the chickens' behavior,reproductive performance,as well as animal welfare.Different TI phenotype broiler chickens showed different growth and welfare in normal condition or stress condition,and STI chickens showed better performonce than LTI chickens.Our previous study has demonstrated LTI phenotype and chronic corticosterone(CORT)administration retarded growth of breast muscle in broiler chickens,and their mechanisms which retarded muscle growth are different.Chronic CORT maily increased muscle oxidative stress injury,but TI may affect glucose metabolism in muscle.Protein is the major structure of muscle,so in this experiment,we detected protein and energy metabolism to realize the potential reason that LTI phenotype and chronic CORT administration retarded growth of breast muscle.Moreover,we explored the reason of cholesterol accumulation in broiler breast muscle under chronic CORT treatment,which will be helpful for estimating chickens' well-being and meat quality.1 Effect of CORT on protein metabolism of broiler chickens showing long or short TIBased on the duration of TI response,broiler chickens were divided into STI and LTI group.And chickens were free to drinking water without CORT or with 5 mg/L CORT from 27 d to 42 d.Our previous study demonstrated that CORT and LTI decreased body weight and muscle/body weight.In order to investigate the mechanism behind the negative effects of LTI and CORT on growth,the level of mRNA transcription of several key genes linked to protein metabolism were measured in muscle.Neither TI nor CORT altered genes expression in Akt/mTOR/p70s6k cascade pathway and protein degradation related genes:Atrogin-1 and MuRF1 in muscle(p>0.05).However,western blot results showed that LTI chickens exhibited higher protein content of total Akt(p = 0.05)and phosphorylated Akt(p=0.06)than STI.CORT treatment decreased the total protein content of Akt(p = 0.09)and p70s6k(p = 0.08).These results suggest that the retardation of muscle growth by LTI and chronic CORT administration might not be mediated through mTOR-dependent signaling pathways.Moreover,we didn't detected the translation level of genes Atrogin-1 and MuRF1,thus protein degradation in muscle growth needs further study.2 Effect of CORT on mitochondria metabolism of broiler chickens showing long or short TIGlycolytic pathway provides energy for muscle contraction and growth in birds,and our previous study demonstrated that LTI and CORT treatment decreased glycolysis efficiency.So we hypothesise energy status and metabolism changed in LTI phenotype and chronic CORT group in chicken breast muscle.Thus,we detected the glycogen content in breast muscle and liver of chickens,and ATP content in breast muscle to determine the effect of CORT and TI on energy statures in chicken breast muscle.The results showed that LTI broilers showed lower levels of ATP,energy charge(EC)(p<0.01),and lower muscle glycogen content(p<0.05)but higher level of ADP(p = 0.08)than STI birds.CORT treatment reduced liver glycogen content(p<0.05)and elevated EC level(p<0.05).Real-time PCR results showed that STI chickens had higher mRNA expression of PPAR a(p = 0.06)and AMPK ?(p = 0.09)than LTI.CORT significantly down-regulated a-enolase mRNA expression in breast muscle compared to control(p<0.05).These results suggest that the retardation of muscle growth by LTI and chronic CORT administration parallels a strong alternation in energy status.Mitochondrial oxidative phosphorylation(OXPHOS)is vital in regulating energy homeostasis.So we determined some indicators in mitochondia metabolism.In this study,STI broilers showed higher mtDNA copy number and cytochrome c oxidase(COX)enzyme activity compared to LTI types(p<0.05).MtDNA-encoded OXPHOS genes were analyzed,mRNA expression of COX subunit 1,2,NADH dehydrogenase subunits 1,3 and 6,were also increased in STI broilers compared to LTI broilers(p<0.05),but methylation of mitochondria control region was not different between TI phenotype or under CORT treatment(p>0.05).PGC-la plays an important role in mitochondria synthesis,protein content was higher in STI broilers(p<0.05),but avUCP,a mitochondrial inner membrane protein and regulates proton transportation,was not different between TI phenotype.In our study,chronic CORT administration did not induce mitochondrial metabolism change.These results suggest that mitochondrial function in breast muscle of STI broilers was better than LTI broilers and mitochondria were not sensitive to CORT.3 Effect of CORT on cholesterol metabolism in breast muscle and liver of broilers chickensChronic endogenous glucocorticoid(GC)excess in mammals is associated with metabolic dysfunction and dyslipidemia that is characterized by increased plasma triglyceride and total cholesterol(Tch)levels.However,the effects of chronic GC administration on muscle cholesterol metabolism are unknown.Chronic CORT treatment significantly increased Tch levels in pectoralis major muscle(PMC)(p<0.001).leg muscle(p<0.01),as well as liver(p<0.05)and enhanced triglyceride levels in the PMC(p<0.001)and liver(p = 0.06).Real-time PCR results showed that CORT administration up-regulated HMGCR(p<0.05)mRNA expression and have a tendancy to decreased 11?-HSD1 gene transription(p = 0.08)in PMC,but have no effcts on gene expression of GR?11?-HSD2?CYP7A1?CYP27A1?ApoB and LDLR(p>0.05).Moreover,chronic CORT treatment only slightly induced liver CYP7A1(p = 0.07)and ABCA1(p = 0.06)gene expression.Western blot results showed that CORT administration increased muscle nuclear GR?HMGCR and LDLR protein(p<0.05),and have a tendency to increased total GR(p = 0.08).ApoA1(p = 0.06)and 11?-HSD2(p =0.07)protein expression in PMC.CORT administration significantly increased liver GR?11?-HSD2 and LDLR protein expression(p<0.05),but slightly decreased HMGCR protein content(p = 0.06).These results indicate that chronic CORT administration causes cholesterol accumulation in PMC tissues of broiler chickens by increasing cholesterol synthesis and uptake.And the cholesterol accumulation in liver upon Chronic CORT administration maybe relate to increasing cholesterol uptake and reducing efflux.