Author(s): SUN, W., YE, X., XINMENG, Y., MENGQI, X., YARAN, G., HONGJIAN, X., JIAO, L., YUAN, Z., Institution: NANJING SPORT INSTITUTE, Country: CHINA, Abstract-ID: 800

INTRODUCTION:
Nonalcoholic fatty liver disease（NAFLD）is primarily characterized by excessive triglyceride accumulation in lipid droplets within liver cells.Lipophagy is one of selective autophagy that specifically acts on degrading the lipid droplets.In this study, we investigated the changes in hepatic lipophagy levels during energy crisis produced by fasting and acute exercise in diet-induced NAFLD and provided theoretical bases for prevention of NAFLD.
METHODS:
A total of 36 male C57/black mice were maintained on high-fat, high-fructose and high-cholesterol（HC）diet for 12 weeks.The mice were then divided into HC (n=12),HF(HC diet with 24h fasting,n=12),and HE(HC diet with acute exercise,n=12)groups.At the end of the experiment, serum was used to measure lipid levels, liver tissues were collected to observe lipid deposition or to extract primary hepatocytes and lipid droplet layer for detecting hepatic lipophagy level.Immunoblotting was performed to measure the expression level of lipid droplet metabolism-related proteins.
RESULTS:
1)Mice in HC group exhibited higher body weight, increased liver index and dyslipidemia,24h fasting significantly decreased the body weight(30.87±2.81g),liver index(4.73±0.41g/100g),and the levels of serum CHOL(4.23±0.43mmol/L),HDL-C(2.16±0.17mmol/L),LDL-C(0.41±0.05mmol/L),but markedly increased the serum TG content(0.66±0.12mmol/L).Acute exercise significantly reduced the body weight(32.94±2.73g) and liver index(4.86±0.34g/100g),and has not effect on serum lipid levels.
2)Compared to HC group,the number and area of lipid droplets were markedly increased by 826 and 12.01% respectively in HF group,however,the lipid droplet size was significantly decreased in HF (0.02±0.01%) and HE (0.02±0.01%) groups（p<0.05）.
3)The positive area of lipid droplet overlapping with lysosome was significantly greater in HF(0.57±0.19) and HE(0.61±0.21)group compared to HC group(0.22±0.16)(P<0.05).The same results described above were also shown in primary hepatocytes in HF(0.20±0.13)group,but not in HE group(P<0.05).In addition, WB results showed enhanced LC3 expression in HF mice (0.46±0.33vs1.13±0.74) and reduced p62 protein levels in HF(0.58±0.34)and HE(0.54±0.40) groups, compared to HC(1.08±0.44)group (P<0.05).
CONCLUSION:
1)Mice with a 12-week HC diet exhibited significant dyslipidemia and suppressed hepatic lipophagy activity,which resulted in lipid deposition in the liver.
2)24h fasting resulted in the accumulation of numerous small lipid droplets within the cytoplasm accompanied by increased lysosomes via improving the level of hepatic lipophagy.
3)Acute exercise significantly decreased HC diet-induced lipid droplet size, but showed non-significant effect on lipophagy, probably due to the stimulation intensity generated by a single exercise is relatively low.