| The innate immune system is particularly important for protecting the body against dangerous external substances.cGAS-STING is an important innate immune signaling pathway that plays an important role in the field of immune inflammation.Moderate activation of this signaling pathway can alleviate excessive inflammatory responses and improve metabolic disorders,while excessive activation or impairment of the signaling pathway can exacerbate inflammatory responses and lead to metabolic disorders.In addition,chronic inflammation has been found to be an important causal factor in many metabolic diseases such as type II diabetes and obesity.Therefore,the cGAS-STING signaling pathway may play an important role in the pathogenesis of metabolic disorders,in improving the inflammatory response,and in alleviating metabolic diseases.Exercise is an important intervention to improve metabolic abnormalities and promote health,but there are few studies on the cGAS-STING signaling pathway in skeletal muscle during exercise,and it is not known whether different exercise intensities can alleviate the abnormal metabolic phenotype through cGAS-STING.In this study,we investigated the effects of different exercise intensities on the cGAS-STING signaling pathway in skeletal muscle of mice fed a high-fat diet and its effect on the abnormal metabolic phenotype,and then investigated the mechanisms of regulation of skeletal muscle innate immunity in a model of metabolic disease.Objective:This study was conducted in high-fat diet-fed C57BL/6 mice and combined two different intensity exercise interventions,moderate intensity exercise and high intensity intermittent exercise,and then investigated the effects of different exercise intensities on the cGAS-STING signaling pathway in skeletal muscle of high-fat diet mice,and further revealed the relationship between exercise,immune inflammation,and abnormal lipid metabolism,as well as the specific regulatory mechanisms.Methods:Twenty-nine 6-8 week old C57BL/6 male mice were purchased from Shanghai Slac Laboratory Animal Research Institute.All mice were housed in an SPF-grade animal feeding room with a room temperature of 25±2℃,air humidity of50±10%,and a 12-h day/night cycle.After 2 weeks of adaptive feeding,all mice were randomly divided into 4 groups as follows:（1）Group C:normal control group CON（n=7）;（2）Group D:high-fat diet quiet group HFD（n=7）;（3）Group M:MICT+HFD（n=7）;（4）Group H:HIIT+HFD（n=8）.The mice in groups C and D did not exercise.Mice in groups M and H first underwent 2 weeks of pre-adaptation training on a running platform at a speed of 10 m/min for 20 min each time,once a day.After the acclimatization training,groups M and H started the 8-week formal training on the running platform.Group M was trained with a continuous running platform of 14m/min,60 min/time,1 time/day,5 times/week,for 8 weeks.Group H was trained with22 m/min（85%of the maximum speed of the exercise capacity test）for 2 min alternating with 8.8 m/min（40%of the initial weekly speed）for 2 min for 12 cycles,1time/day,5 times/week,in the first week.The running speed was increased by 1 m/min from the previous week for a total of 8 weeks.A 5-minute warm-up and relaxation activity was performed before and after the exercise at a speed of 8m/min.During the complete exercise intervention,body weight was measured and recorded in mice regularly every week.Glucose tolerance test was performed 1 week before the end of the exercise intervention,and insulin tolerance test was performed two days before the end of the exercise intervention;in terms of serum indexes,total cholesterol,triglyceride and glucose levels in serum were detected;oil red staining technique was used to observe the changes of lipid droplets in gastrocnemius muscle of each group of mice;Enzyme-linked immunosorbent assay was used to detect the changes of serum IL-6 and IFN-βin each group of mice.The Wes TM fully automated protein expression analysis system was used to detect the protein expression levels of cGAS-STING signaling pathway in skeletal muscle,including the protein levels of cGAS,STING,IFN-β,Phospho-IRF3（Ser396）,Phospho-TBK1（Ser172）,IRF3,and TBK1.Results:（1）During the first two weeks of preconditioning,there was no significant difference in body weight among each group.The body weight of mice in group D increased steadily over time after 1 week of high-fat diet feeding.At week 3,the body weight of mice in group D increased significantly（p<0.05）compared with that of mice in group C.At week 4,the body weight of mice in group H decreased significantly（p<0.05）compared with that of mice in group D,the body weight of mice in group M decreased significantly（p<0.01）compared with that of mice in group D,the body weight of mice in group D increased significantly（p<0.01）compared with that of mice in group C.From week 5 onwards,the body weight of mice in groups M and H decreased significantly（p<0.01）compared with that of mice in group D,the body weight of mice in group D increased significantly（p<0.0001）compared with group C.（2）Compared with group C,the lean body mass of mice in group D was significantly lower（p<0.05）;compared with group D,the lean body mass of mice in group M was significantly higher（p<0.05）,and there was no significant difference between the lean body mass of mice in group H and group D.Compared with group C,the fat content of mice in group D was significantly higher（p<0.0001）;compared with group D,the fat content of mice in groups M and H were both significantly lower（p<0.0001）.（3）Compared with group D,the glucose level of mice in group M was significantly lower（p<0.05）,while that of mice in group H was not significantly different from that of group D.Compared with group C,the AUC of GTT of mice in group D was significantly higher（p<0.01）;compared with group D,the AUC of GTT of mice in group M was significantly lower（p<0.05）,and the AUC of GTT of mice in group H was not significantly different from that of group D.The AUC of ITT of mice in group D was highly significant higher compared to group C（p<0.01）;the AUC of ITT of mice in groups M and H was significantly lower compared to group D（p<0.05）.（4）Compared with group C,the level of total cholesterol in mice in group D was significantly increased（p<0.01）;compared with group D,the levels of triglyceride and total cholesterol in mice in group M were significantly decreased（p<0.01）,the levels of triglyceride and total cholesterol in group H were significantly lower than those in group D（p<0.05）;compared with group M,the total cholesterol level of group H was significantly increased（p<0.01）.（5）Mice in group D had more lipid droplets in the area of skeletal muscle fibres,with a large number of red-stained fat droplets surrounding the nucleus in the visual field;mice in group M had fewer lipid droplets in the area of skeletal muscle fibres,with a scattered distribution;mice in group H had fewer lipid droplets in the area of skeletal muscle fibres,with only a small distribution.Compared with group D,the fat deposition in the area of skeletal muscle fibers was significantly reduced in group M and group H mice.（6）Compared with group C,the serum levels of IL-6 and IFN-βin mice in group D were both increased significantly（p<0.01）;compared with group D,the serum levels of IL-6 and IFN-βin mice in groups M and H were both decreased significantly（p<0.01）.（7）Compared with group C,the level of cGAS-STING signaling pathway-related proteins in gastrocnemius muscle tissues of mice in group D showed a downward trend,but the difference was not statistically significant.Compared with group D,the protein expression levels of STING,p-TBK1 and p-IRF3 in gastrocnemius muscle tissues of mice in group H were significantly increased（p<0.05）.Compared with group D,the protein expression levels of STING in gastrocnemius muscle tissues of mice in group M were significantly higher（p<0.05）,but the expression of other proteins were not significantly different.Conclusions:（1）Long-term high-fat diets can lead to a range of metabolic disorders such as obesity,hyperglycaemia,hyperlipidaemia,insulin resistance,abnormal lipid metabolism,and severe inflammatory response.（2）There was no significant difference between MICT and HIIT in weight loss and fat loss and improvement of severe inflammatory response;MICT was better than HIIT in increasing lean body mass,lowering blood glucose,improving glucose tolerance,improving insulin sensitivity and improving blood lipid metabolism.These results suggest that different exercise intensities have different effects on the improvement of metabolic disorders induced by high-fat diet.（3）HIIT may improve the severe inflammatory response through the cGAS-STING signaling pathway,thereby alleviating the metabolic disorder phenotype.Whereas the improvement of the metabolic disorder phenotype by MICT did not involve the cGAS-STING signaling pathway,and the exact mechanism of its effect needs to be further investigated. |
PDF Full Text Request