The Mechanism Of Chromium Via PPARα Improving Glycolipid Metabolism And Inflammation Of Skeletal Muscle In Broilers Under Heat Stress

This study focused on the problem that heat stress induces glycolipid metabolism disorders and inflammation of skeletal muscle,resulting in slowing growth and declining quality in broilers,through the regulation of Peroxisome proliferators-activated receptors α(PPARα)in skeletal muscle glycolipid metabolism and inflammation of broilers under heat stress,by establishing the heat stress model of broilers,using metabolomics technology and making the tests of activating PPARα in vivo,inhibiting PPARα in vivo,and glucose load in broilers to study the mechanism of chromium via PPARα improving glycolipid metabolism and inflammation of skeletal muscle in broilers under heat stress.And carried out the following four experiments:Experiment 1: Effects of chromium picolinate on glycolipid metabolism,inflammation and breast muscle metabolomics in broilers under heat stressTotal of 22-day-old Arbor Acres male broilers(AA)240 were randomly divided into normal control group(21℃),heat stress group(31℃),heat stress(31℃)supplemented with chromium400μg/kg group(as Cr,in the form of chromium picolinate)and the heat stress(31°C)chromium supplementation 800μg/kg(as Cr,in the form of chromium picolinate)group,with 6 replicates per group and 10 chickens per replicate.The broilers were adapted to the experimental chamber for 7 days,the experiment started at the age of 29 days,the trial continued for 14 days.The results showed that: 1)Heat stress reduced the broilers’ daily weight gain and feed intake,increased the feed/weight;reduced the rate of breast muscle,destroyed the tissue morphology of breast muscle;caused insulin resistance,glycolipid metabolism disorders and inflammation in broilers.2)Supplementation with chromium picolinate 400μg/kg increased the broilers’ daily weight gain and feed intake,reduced the feed/weight ratio;increased breast muscle rate,improved breast muscle tissue damage;reduced insulin resistance and inflammation.There was no significant difference between the chromium picolinate 400μg/kg and800μg/kg.3)The results of breast muscle metabolomics and gene expression in breast muscle and liver preliminarily suggest that the mechanism of chromium picolinate working in vivo may be related to PPARα.Experiment 2: Regulatory effects of chromium picolinate and activating PPARα in vivo on glycolipid metabolism disorders and inflammation of skeletal muscle in broilers under heat stressA total of 240 22-day-old male broiler were selected and randomly divided into 4 groups: normal temperature control group(21°C),heat stress group(31°C),heat stress(31°C)supplemented with400μg/kg chromium group(as Cr,in the form of chromium picolinate)and heat stress supplemented with the PPARα activator fenofibrate group with 6 replicates of 10 chickens per replicate.The broilers were adapted to the experimental chamber for 7 days,the experiment started at the age of 29 days,the experiment period lasted for 14 days.The results showed that: 1)Heat stress led to insulin resistance,decreased immune organ index,decreased glycogen synthesis,decreased fatty acid β-oxidation,affected the regulation of glycolipid metabolism,increased breast muscle fat content,increased oxidative stress and inflammation,and destroyed the tissue morphology of breast muscle,reducing the muscle fibers’ diameter and density and reducing the breast muscle rate in broilers;2)Supplementation of chromium picolinate 400 μg/kg and supplementation of PPARα activator under heat stress can reduce insulin resistance,increase immune organ index,up-regulate PPARα gene expression in skeletal muscle,and reduce pectoral muscle.fat deposition in breast muscle,improve the oxidative inflammatory response,improve breast muscle rate,and promote broiler production performance.3)The results of supplementing chromium picolinate and exogenous PPARα activator under heat stress were similar,indicating that chromium picolinate,similar to exogenous PPARα activator,up-regulates PPARα in skeletal muscle of broilers under heat stress,and affects the related glycolipid metabolism genes,thereby affecting glycolipid utilization and inflammation.Experiment 3: Regulatory effects of chromium picolinate and activating PPARα in vivo on glycolipid metabolism disorders and inflammation of skeletal muscle in broilers under heat stress after glucose loadOn the basis of experiment 2,on the 14 th day,42-day-old broilers were fed glucose(2g/kg)for glucose load trial.The results showed that: 1)Glucose administration aggravated the insulin resistance of the heat stress group,reached a peak at 0.5h,and then gradually decreased with time.The insulin resistance of the chromium supplement group and the supplement activator group was significantly lower than that of the heat stress group.2)Chromium supplementation and activator supplementation under heat stress at 2 h after glucose load can reduce the contents of free fatty acid(FFA)and triglyceride(TG)in the body,increase liver glycogen and muscle glycogen,decrease the content of proinflammatory factors,Malondialdehyde(MDA)concentration and nuclear factor kappa-B(NF-κB)m RNA in breast muscle expression,reducing oxidative stress and inflammation in broilers.3)Chromium supplementation and activator supplementation under heat stress significantly increased the expression of PPARα protein in breast muscle,increased the m RNA expression of genes related to glucose and lipid metabolism such as PPARα and carnitine acyl-transferase(CPT-1),and improved the body’s glucose and lipid metabolism after 2 h of glucose load.4)The glucose load test further clarified that the activation of PPARα by chromium picolinate improved insulin resistance,skeletal muscle glucose and lipid metabolism disorders and inflammation in broilers under heat stress.Experiment 4: Inhibiting PPARα in vivo to study the regulatory effect of chromium picolinate on skeletal muscle glucose and lipid metabolism disorders and inflammatory responses in broilers under heat stressA total of 192 22-day-old male broilers were selected and randomly divided into 4 groups: heat stress + PPARα inhibitor group,heat stress control group,heat stress chromium supplementation(400μg/kg(as Cr,in the form of chromium picolinate))control group and heat stress chromium supplementation + PPARα inhibitor group,adapted to the experimental chamber for 7 days,6repetitions per group,8 chickens per repetition.The experiment started at the age of 29 days,the experimental period was 14 days.On the 14 th day of the experiment,all chickens in the heat stress group and the heat stress chromium supplement group were injected with PPARα inhibitor.The results showed: 1)The heat stress chromium supplementation injection PPARα inhibitor group significantly increased blood glucose,insulin and insulin resistance index,significantly increased serum FFA and TG in liver and chest muscle,and significantly decreased liver glycogen and muscle glycogen content,the changes in the heat stress injection PPARα inhibitor group were more significant than those in the heat stress chromium supplementation injection PPARα inhibitor group;2)Compared with the control group,the heat stress chromium supplementation injection PPARα inhibitor group were significantly increased the serum and breast muscle interleukin(IL)-6,IL-1β and tumor necrosis factor(TNF)α levels,increased the content of MDA and the expression of inflammatory gene NF-κB in breast muscle,and increased oxidative stress and inflammation;3)The heat stress chromium supplementation injection PPARα inhibitor group significantly decreased the PPARα protein expression,significantly decreased the expression of glucose and lipid metabolism genes related to the PPARα and increased the expression of gluconeogenesis genes,resulting in disorder of glucose and lipid metabolism.In conclusion,this study shows that: Heat stress leads to insulin resistance,glycolipid metabolism disorders,skeletal muscle growth retardation and tissue inflammatory damage in broilers by inhibiting the expression of PPARα protein;chromium picolinate improves insulin resistance,glycolipid metabolism disorders in broilers under heat stress by increasing the expression of PPARα protein,and alleviates the skeletal muscle growth retardation and tissue inflammatory damage.