Effect of electroacupuncture on hepatic autophagy in obese mice based on the AMPK/mTOR/ULK1 pathway

ObjectiveTo investigate the effect of electroacupuncture （EA） on hepatic autophagy in obese mice by regulating the adenosine monophosphate-activated protein kinase （AMPK）/mammalian target of rapamycin （mTOR）/unc-51 like autophagy activating kinase 1 （ULK1） signaling pathway.MethodsC57BL/6J mice were randomly divided into normal group， model group and EA group， with 8 mice in each group. The obese mice model was established by feeding high-fat diet. Mice in the EA group received EA at bilateral “Zusanli”（ST36） and “Tianshu”（ST25） for 30 min， 5 times a week for 4 consecutive weeks. The Lee’s index and body mass of mice in each group were observed before and after treatment； fasting serum glucose was measured； the insulin tolerance test （ITT） was performed， and the area under the curve （AUC） was calculated； the levels of fasting insulin， serum low-density lipoprotein cholesterol （LDL-C）， high-density lipoprotein cholesterol （HDL-C）， total cholesterol （TC）， and triacylglycerol （TG） were detected by ELISA， and the insulin resistance index was calculated； the mass of mesenteric white adipose tissue （mWAT） and liver tissue was weighed； the morphological changes of mWAT and liver tissue were observed by HE staining； the lipid deposition in the liver tissue was observed by Oil Red O staining； the ultrastructure of liver tissue was observed by transmission electron microscopy； the protein expressions of p-AMPK/AMPK， p-mTOR/mTOR， ULK1， microtubule-associated protein 1 light chain 3 type Ⅱ （LC3-Ⅱ）， autophagy-related 5 （Atg5）， autophagy-related 7 （Atg7）， and sequestosome 1 （SQSTM1/p62） in liver tissue were detected by Western blot； the mRNA expression of AMPK， mTOR， ULK1， LC3-Ⅱ， Atg5， Atg7， and p62 in liver tissue were detected by quantitative real-time PCR.ResultsCompared with the normal group， the model group showed significant increases in Lee’s index， body mass， fasting blood glucose， fasting insulin， insulin resistance index， and ITT-AUC （P<0.01）； increased serum TG， TC， and LDL-C levels （P<0.01）； decreased serum HDL-C level （P<0.01）； increased mWAT and liver mass （P<0.01）； enlarged adipocytes with reduced cell number per unit area in mWAT； swollen and disorganized hepatocytes with numerous lipid droplets and vacuoles； extensive orange-red lipid deposition； mitochondrial shrinkage and reduced autophagic vacuoles； decreased AMPK mRNA and p-AMPK/AMPK protein expression （P<0.01）； increased mTOR mRNA and p-mTOR/mTOR protein expressions （P<0.01）； decreased mRNA and protein expressions of ULK1， LC3-Ⅱ， Atg5， and Atg7 （P<0.01）； and increased mRNA and protein expression of p62 （P<0.01）. Compared with the model group， the EA group showed significant reductions in Lee’s index， body mass， fasting blood glucose， fasting insulin， insulin resistance index， and ITT-AUC （P<0.01）； decreased serum TG， TC， and LDL-C levels （P<0.01）； increased serum HDL-C level （P<0.01）； reduced mWAT and liver mass （P<0.01， P<0.05）； decreased adipocyte diameter and increased cell number per unit area in mWAT； no obvious lipid droplets or vacuoles in hepatocytes； reduced orange-red lipid deposition； normal mitochondrial structure， increased autophagic vacuoles， and occasional autophagosomes and autolysosomes； increased AMPK mRNA and p-AMPK/AMPK protein expressions （P<0.01）； decreased mTOR mRNA and p-mTOR/mTOR protein expressions （P<0.01）； increased mRNA and protein expressions of ULK1， LC3-Ⅱ， Atg5， and Atg7 （P<0.01）； and decreased mRNA and protein expressions of p62 （P<0.01）.ConclusionEA at ST36 and ST25 can promote hepatic autophagy， and its mechanism may be related to the regulation of the AMPK/mTOR/ULK1 signaling pathway.