Moderate Treadmill Exercise Alleviates NAFLD by Regulating the Biogenesis and Autophagy of Lipid Droplet.

ABSTRACT

Lipid droplet is a dynamic organelle that undergoes periods of biogenesis and degradation under environmental stimuli. The excessive accumulation of lipid droplets is the major characteristic of non-alcoholic fatty liver disease (NAFLD). Moderate aerobic exercise is a powerful intervention protecting against the progress of NAFLD. However, its impact on lipid droplet dynamics remains ambiguous. Mice were fed with 15 weeks of high-fat diet in order to induce NAFLD. Meanwhile, the mice performed 15 weeks of treadmill exercise. Our results showed that 15 weeks of regular moderate treadmill exercise alleviated obesity, insulin intolerance, hyperlipidemia, and hyperglycemia induced by HFD. Importantly, exercise improved histological phenotypes of NAFLD, including hepatic steatosis, inflammation, and locular ballooning, as well as prevented liver fat deposition and liver injury induced by HFD. Exercise reduced hepatic lipid droplet size, and moreover, it reduced PLIN2 protein level and increased PLIN3 protein level in the liver of HFD mice. Interestingly, our results showed that exercise did not significantly affect the gene expressions of DGAT1, DGAT2, or SEIPIN, which were involved in TG synthesis. However, it did reduce the expressions of FITM2, CIDEA, and FSP27, which were major involved in lipid droplet growth and budding, and lipid droplet expansion. In addition, exercise reduced ATGL protein level in HFD mice, and regulated lipophagy-related markers, including increasing ATG5, LAMP1, LAMP2, LAL, and CTSD, decreasing LC3II/I and p62, and promoting colocalization of LAMP1 with LDs. In summary, our data suggested that 15 weeks of moderate treadmill exercise was beneficial for regulating liver lipid droplet dynamics in HFD mice by inhibiting abnormal lipid droplets expansion and enhancing clearance of lipid droplets by lysosomes during the lipophagic process, which might provide highly flexible turnover for lipid mobilization and metabolism. Abbreviations ß-actin actin beta; ATG5 autophagy related 5; LAMP2 lysosomal-associated membrane protein 2; LAMP1 lysosomal-associated membrane protein 1; SQSTM1/p62 sequestosome 1; GAPDH glyceraldehyde-3-phosphate dehydrogenase; MAP1LC3/LC3 microtubule associated protein 1 light chain 3; ATGL adipose triglyceride lipase; CSTD cathepsin D; LAL lysosomal acid lipase; DGAT1 diacylglycerol-o-acyltransferase 1; DGAT2 diacylglycerol-o-acyltransferase 2; CIDEA cell death inducing dffa-like effector a; CIDEC/FSP27 cell death inducing dffa-like effector c; FITM2 fat storage-inducing transmembrane protein 2; PLIN2 adipose differentiation related protein; PLN3 tail-interacting protein 47; HSP90 heat shock protein 90; SREBP1c sterol regulatory element binding protein-1c; chREBP carbohydrate response element binding protein.