| BACKGROUND:Non-alcoholic fatty liver disease(NAFLD)refers to the clinical pathology syndrome without alcohol and other clear liver damage factors,characterized by diffuse hepatic steatosis.The pathogenesis of NAFLD is still not very clear,however,most theories are based on the ’two-hit hypothesis’.Interestingly,some studies have shown that hypoxia is closely related to hepatic lipid metabolism,and the prevalence of NAFLD was found to be higher in both obese and Obstructive Sleep Apnea(OSA)patients.OBJECTIVE:To clarify the relationship between high-fat diet(HFD)and NAFLD,to explore the relationship between high-fat diet and hypoxia,as well as to investigate the role of hypoxia in the pathogenesis of fatty liver disease.MATERIALS AND METHODS:1.HFD model:Mice were fed with 60%high fat diet,and lipid accumulation in hepatocytes was induced by 0.4 mM palmitic acid.2.Hypoxia model:In order to create an animal model that simulates hypoxia,7-days-old neonatal mice were placed in high oxygen environment(75%)for 5 days,followed by placing them in hypoxic environment.At the same time,cell hypoxia models were constructed using 1%O2 and 0.4 mM CoCl2,respectively.3.In vivo,mice were intraperitoneally injected with hypoxia reagent(100 mg/Kg mice,hydroxyprobe),and 1 hour later liver tissue was extracted to detect hypoxia.In vitro,cells were treated with hypoxia reagent(100 mM,hydroxyprobe)for 2 hours before cells were analyzed to detect hypoxia.Finally,we used siRNA to silence HIF-la and HIF-2a in order to determine the role of Hypoxia-Inducible Factor(HIF)in lipid accumulation that was induced by hyperlipidemia and hypoxia.The expression of hypoxia probe and lipid metabolism related protein was detected by Western blot.RESULT:1.In mice fed with HFD,the amount of lipid in the liver were more than control group,and the amount of Triglyceride(TG)was also increased in the cytoplasm of hepatocytes under the action of palmitic acid.2.HFD for 7 days induced liver hypoxia in mice and the hypoxic condition persisted for 2 months as mice were fed with HFD.Moreover,hepatocytes that were treated with palmitic acid for 2 hours,also showed hypoxia that continued for 24 hours.3.In hypoxic environment,the amount of TG increased in both neonatal mice liver were more than control group as well as in hepatocyte.And also,hepatocytes that were treated with palmitic acid or hypoxia condition showed Triglyceride(TG)increased in the cytoplasm of hepatocytes.4.HIF-1α and HIF-2a could not ameliorate lipid accumulation which was induced by hyperlipidemia and hypoxia.5.Hypoxia inhibits lipid degradation while promoting lipid synthesis.Conclusion:The research demonstrate HFD can induce liver lipid accumulation and also induced liver hypoxia.However,the amount of TG increased under hypoxia condition.Blocking the HIF-la and HIF-2a signaling pathways cannot improve the lipid accumulation in liver caused by high fat and hypoxia,whereas hypoxia can promote lipid synthesis while suppressing lipid degeneration and then causing lipid accumulation.These results suggest that we hypoxia plays an important role in the process of NAFLD caused by high fat diet. |
