The role of TFEB activated by aerobic exercise on insulin resistance in skeletal muscle of high fat diet mice
Objective To explore the role of transcription factor EB(TFEB)induced by aerobic exer-cise in improving insulin resistance(IR)of skeletal muscles in high-fat diet mice.Method Eighteen male SPF C57BL/6 mice aged 6 weeks were randomly divided into a common diet group(CON),a high-fat diet group(HFD),and a high-fat diet exercise group(HFDE),each of 6.Both high-fat groups were on high-fat diet for 12 weeks.Then the HFDE group underwent daily 60-minute tread-mill exercise with the slope of 0°,at a speed of 12 m/min,5 times per week for 12 weeks.Finally,the glucose tolerance and insulin sensitivity were detected using the intraperitoneal injection glucose tol-erance test(IPGTT)and intraperitoneal injection insulin tolerance test(IPITT).The fasting blood glu-cose and insulin contents were measured by biochemical method,and the IR level was calculated by using the homeostatic model assessment of insulin resistance(HOMA-IR).Moreover,Western blotting was employed to detect the expression of phosphorylated transcription factor EB(pTFEB)and TFEB in skeletal muscle,glucose transporter 4(GLUT4)in cytoplasm and membrane,phosphorylated insulin re-ceptor substrates1(pIRS1),phosphorylated protein kinase B(pAKT),phosphoinositide 3-kinase(PI3K),and phosphorylated akt substrate of 160 kD(pTBC1D4)in skeletal muscle.The correlation of pTFEB and TFEB to insulin signaling pathway-related proteins was analyzed.Results(1)Compared with the CON group,there was a significant increase in the average body weight,IPGTT,blood glucose at each time point of IPGTT,area under curve(AUC),serum insulin,HOMA-IR,protein expressions of pTFEB,total-TFEB and GLUT4 in cytoplasm of the HFD group(P<0.01),but a significant decrease in the average protein expressions of pIRS1,pAKT,PI3K,pTBC1D4 and GLUT4 in cell membrane of skeletal muscles(P<0.01).However,no significant differences were found between the two groups in the average expression of pTFEB and T-TFEB proteins.(2)Compared to the HFD group,a signifi-cant increase was found in the average body weight,blood glucose at each time point of IPGTT,blood glucose of IPITT at 0 min,30 min and 60 min and AUC,serum insulin,HOMA-IR,expres-sions of pTFEB,T-TFEB and GLUT4 in cytoplasm of HFDE group(P<0.05 or P<0.01),with a signifi-cant decrease in the average protein expressions of pIRS1,pAKT,PI3K,pTBC1D4 and GLUT4 in cell membrane and T-TFEB in nucleus(P<0.01).(3)TFEB was negatively correlated with the expres-sion of pIRS1,PI3K,pAKT,and pTBC1D4 proteins(r=-0.8642,r=-0.7789,r=-0.8946,r=-0.8040)but positively correlated with cytoplasmic GLUT4(r=0.8532,P<0.01).Moreover,TFEB in the nucleus was of positive correlation with GLUT4 in the cell membrane(r=0.7744,P<0.01).Conclusions High-fat diet can decrease the expression of insulin signaling pathway related proteins in skeletal mus-cles of mice and weaken their insulin action,leading to the disorder of glucose and lipid metabolism.However,aerobic exercise can significantly increase the expression of such proteins to promote insulin function and sensitivity,and relieve disorders in glucose and lipid metabolism.This effect may be achieved through the promotion of skeletal muscle TFEB nuclear translocation,which activates IRS1/PI3K/AKT/TBC1D4/GLUT4 signaling pathway and facilitates GLUT4 membrane translocation,ultimately enhancing glucose uptake in skeletal muscle cells.The authors speculate that the TFEB-mediated insu-lin signaling pathway may be an important molecular pathway for aerobic exercise to improve insulin re-sistance.
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