Swimming Exercise Alleviates Liver Injury Of Type Ⅱ Diabetic Rats By Inhibiting The P38 MAPK Signaling Pathway

Aim:Type 2 diabetes mellitus（T2DM）is an age-and lifestyle-related metabolic disease caused by the combination of pancreaticβ-cell dysfunction and peripheral organ insulin resistance,affecting multiple organs and tissues in the body.Physical activity has long been recognized as having significant health benefits for people with chronic diseases such as diabetes.At the same time,the activation of p38 mitogen-activated protein kinase（p38 MAPK）signaling pathway is also associated with the pathogenesis of obesity,diabetes and other metabolic diseases.Therefore,we explored whether exercise in diabetes can exert therapeutic effects by inhibiting p38 MAPK-related pathways.Methods:After two weeks of adaptive feeding,48 healthy SD（Sprague Dawley,SD）rats were randomly divided into groups,12 were fed basal diet and 36 were fed high-sugar and high-fat diet.Rats fed with high-sugar and high-fat diet for eight weeks were fasted overnight and injected intraperitoneally with 1%streptozotocin STZ solution（30 mg/kg）.L means that the model was successfully established,and they were randomly divided into four groups:diabetic control group（DM）,diabetic rat group（DY）with intraperitoneal injection of p38 inhibitor SB203580,diabetic rat group with swimming intervention（DE）,drug injection and swimming Intervention rat group（DYE）.In addition,basal diet-fed rats were randomly divided into normal control group（NC）and p38 inhibitor SB203580 injection group（NY）.The exercise program is non-weight-bearing swimming training for a total of 8 weeks,five times a week,90minutes each time.The injection dose of p38 inhibitor was 2 mg/kg body weight,and the corresponding control group was injected with an equal volume of normal saline.During the intervention period,the blood glucose and body weight of the rats were monitored in real time.After the eight-week intervention,the rats were anesthetized and sacrificed,and fresh liver tissues were taken for photographing and weighing.The activity of superoxide dismutase（SOD）and malondialdehyde（MDA）in tissue homogenates were detected to evaluate liver cells.Antioxidant system status;detection of alanine aminotransferase and aspartate aminotransferase activities in tissues to assess the degree of hepatocyte damage;fresh tissue paraffin sections for Hematoxylin-Eosin（HE）staining and TUNEL（Td T-mediated d UTP Nick-End Labeling）The morphology and apoptosis of rat liver cells were observed by staining,respectively;total RNA and total protein were extracted from the tissue for quantitative Real-time PCR（q RT-PCR）and Western blotting（WB）to detect specific gene expression and protein expression.Results:Compared with the normal control rats,the diabetic rats were lethargic,lazy,sleepy,slow in growth,significantly decreased in body weight（p<0.001）,significantly increased in blood sugar（p<0.001）,and increased in liver index（p<0.001）;HE staining showed that the hepatic lobules of the diabetic rats were disordered and irregularly arranged,fat vacuoles appear in the cytoplasm.TUNEL staining showed apoptosis in diabetic liver cells.Biochemical tests performed after liver tissue homogenization showed that the level of Superoxide Dismutase（SOD）in the liver antioxidant system was decreased（p<0.01）,and the Malondialdehyde（MDA）was significantly increased（p<0.001）.The Alanine aminotransferase（ALT）and Aspartate aminotransferase（AST）were further increased（p<0.01,p<0.001）.Swimming intervention can stably reduce blood glucose in rats（p<0.01）.Two interventions can respectively improve the microstructure of hepatocytes and decrease the proportion of apoptosis,reduce the levels of ALT and MDA in the liver tissue（p<0.05,p<0.01）,and exercise can also enhance the SOD activity in the liver tissue（p<0.05）.However,injection of the p38 inhibitor SB203580 and the combined intervention group both reduced fasting blood glucose in diabetic rats to a certain extent,but without statistical significance.The cell state was improved as comparing with that in the diabetes model group.TUNEL fluorescence staining showed that the apoptosis rate was reduced compared with the diabetes model group.Compared with the model group,the ALT/AST/SOD level had no significant difference,but it effectively decreased the MDA level（p<0.01,p<0.51）.qRT-PCR detection of p38-related genes（P38/Atf2）,inflammation-related genes（Il-6/P65）and insulin-related genes（Irs1/Pi3k/Akt2/Glut2）in liver cells of rats in each group,and WB detection of p-p38^{Thr180/Tyr182} and total p38 protein,p-Akt^Thr473 and total Akt protein,apoptosis pathways（Bcl-2,Bax,BNIP3,cleaved caspase3,caspase3）and autophagy-related proteins（Atg7,Beclin1,p62,LC3-II）Quantitative findings:Injection of the inhibitor almost completely inhibited the phosphorylation level of p38αin the liver of diabetic rats,but had no significant effect on the transcription level of p38 m RNA;swimming exercise also prevented part of the phosphorylation of p38αat the protein level;combined intervention may trigger a feedback mechanism leading to p38αPhosphorylation was not significantly altered.Subsequently,we found that exercise can activate autophagy and insulin signaling pathways in a p38-dependent manner through the expression of p38 MAPK-related signaling pathway genes and proteins,and simultaneously inhibit apoptosis and excessive inflammatory responses.Conclusion:The p38 MAPK pathway was shown to be over-activated in the livers of successfully constructed type II diabetic rats,and injection of the p38 inhibitor SB203580 and swimming exercise effectively reduced the activation of the p38 MAPK pathway.Swimming exercise was more effective in improving liver homeostasis in diabetic rats compared to p38inhibitor injection alone and combined intervention.Finally,we demonstrated that swimming restored hepatocyte autophagy and insulin sensitivity and significantly inhibited apoptosis and inflammatory responses to promote hepatocyte survival by inhibiting the p38 MAPK signaling pathway.