Effects And Mechanism Of Perilipin5 On Lipid Metabolism And Metabolic Associated Fatty Liver Disease

Background and ObjectivesMetabolic associated fatty liver disease(MAFLD)is the primary liver disease that affects about a quarter of the world’s population.The standard for diagnosis of MAFLD is based on the evidence of liver steatosis,which is often associated with metabolic syndromes such as overweight/obesity,type 2 diabetes,dyslipidemia,and cardiovascular disease.In the liver,triglycerides are mainly stored in the lipid droplets(LDs)of hepatocytes.The metabolic regulation of LDs is mediated by LD-related proteins.Perilipin family proteins are the main LD-related proteins,which exist on the surface of lipid droplets.Perilipin5(Plin5)is a vital member of the perilipin family,which is specifically expressed in tissues with high oxidative capacity,such as liver,skeletal muscle,heart,brown adipose tissue(BAT).Plin5 can coordinate the action of lipases on the surface of lipid droplets and regulate lipid contents.Previous studies have found that Plin5 alleviates hepatic oxidative stress,protects heart from oxidative burden and improves lipotoxicity in liver and pancreas,indicating its protective influence.However,the effects of Plin5 on MAFLD and its underlying mechanism remain unclear.This study aims to induce MAFLD by a high-fat diet and compare the differences between Plin5 knockout(Plin5-/-)mice model and wild-type mice to clarify the effects of Plin5 on lipid metabolism and MAFLD induced by high fat diet and its potential mechanism.MethodsPlin5 knockout mice(Plin5-/-)and wild-type mice(C57BL/6J)were fed with a high-fat diet(HFD)and a normal diet(ND)for 20 weeks,respectively,the high-fat diet was used to induce MAFLD model.During the feeding process,we observed the state of the mice and measured their body weight regularly.After the experiment,we measured their liver weight and fat weight,we also used the serum to measure the blood lipid level.The histopathological changes of liver were observed by HE staining,Sirius red and Masson trichrome staining.Quantitative real-time PCR was used to detect the expression of genes related to lipid absorption,synthesis,oxidation,lipolysis,and oxidative stress in liver.The expression of total AMP-activated protein kinase(AMPK)and phosphorylated AMP-activated protein kinase(p-AMPK)expression,SREBP1 and its downstream lipid synthases,acetyl coenzyme A-carboxylase(ACC),fatty acid synthetase(FAS)expression were detected by western blotting.The metabolic differences between different groups were analyzed by metabolomics.Results1.Changes of indictors associated with obesity: The body weight,liver weight and subcutaneous fat tissue weight of mice fed with high-fat diet were significantly increased compared with mice fed with normal diet.Compared with HFD-C57BL/6J mice,these indicators of HFD-Plin5-/-mice were significantly reduced(P<0.05).2.Changes in blood lipids of mice: The serum TC and LDL levels of mice in high-fat diet groups were significantly higher than those in normal diet group(P<0.01);compared with mice in the HFD-C57BL/6J group,the serum TC and LDL levels of HFD-Plin5-/-mice were significantly reduced(P<0.05).3.Liver pathological changes: The liver of HFD-C57BL/6J mice showed fatty liver-like changes.HE staining under microscope showed a large number of lipid droplets in hepatocytes,and Masson and Sirius red staining showed a large amount of collagen deposition;the fatty liver changes were significantly reduced in HFD-Plin5-/-mice,fewer and smaller lipid droplets were observed in the HE staining,and the Masson and Sirius red staining showed a significant reduction in collagen deposition.4.The expression of liver lipid metabolism and oxidative stress associated genes:Compared with HFD-C57BL/6J group mice,the m RNA expression of hepatic lipid absorption genes FATP2 and FATP5 was significantly increased in HFD-Plin5-/-group mice(P<0.05),m RNA expression of L-FABP/FABP1 was significantly reduced(P<0.001);Plin5-/-mice also decreased the m RNA expression of genes closely related to lipogenesis(HMG-Co A and SREBP-1c)(P<0.05);additionally,Plin5 deficiency down-regulated the expression of PPAR-α,the vital participant in fatty acids β-oxidation(P<0.05).Compared with mice in HFD-C57BL/6J group,there was no significant difference in the expression of LDLR,LPL,CGI-58,MAPK and NF-κB(P>0.05).5.The expression of AMPK and SREBP1 pathway in mice: Compared with the HFD-C57BL/6J group,the expression of total AMPK and phosphorylated AMPK(p-AMPK)in the HFD-Plin5-/-group was significantly increased.The m RNA and protein expression of SREBP1 and its key downstream molecules,fatty acid synthase(FAS),acetyl-Co A-carboxylate(ACC)were significantly reduced.6.Metabolomics analysis of liver found that there were 32 different compounds between HFD groups.Analysis of the pathways of the different compounds showed that the different compounds were mainly enriched in the fatty acid synthesis pathway.ConclusionsPlin5 deficiency reduces liver lipid accumulation and improves metabolic associated fatty liver disease by regulating lipid metabolism,especially by inhibiting lipogenesis via activating AMPK and inhibiting SREBP1 and its downstream lipid synthases.