GSDMD-N Accelerates The Progression Of High-fat Diet-induced Nonalcoholic Fatty Liver Disease

With the development of living standards and the change of dietary structure,the prevalence of NAFLD has increased with years,and there has been a young trend of its development,which has become liver disease with highest prevalence in China.NAFLD gradually progress to non-alcoholic steatohepatitis,liver cirrhosis,liver cancer,etc.,and eventually lead 30%-40%of patients to death.In addition,NAFLD is an important part of the metabolic syndrome,interwovens and coordinates with diabetes and cardiovascular disease.It seems that NAFLD has now become one of the most fatal diseases that threaten human health,causing a heavy burden on public health.The major symptoms of NAFLD are hepatic steatosis and excessive lipid accumulation.Epidemiological studies have confirmed the link between NAFLD and various inflammatory factors,for instance,the polymorphism at the position 238 of TNF-? gene is significantly associated with the susceptibility of NAFLD.Clinical studies also revealed that when ROS increased,the degree of lipid peroxidation increased significantly in the liver of patients with NAFLD.Combined with the wellknown"two-hits" hypothesis of NAFLD,inflammation and oxidative stress are related to and affect each other,and plays a very important role in the progression of NAFLD.Inflammatory necrosis(pyroptosis)is a new form of programmed cell death that has been discovered and confirmed recently.Pyroptosis is innate immune defense response which is initiated due to detecting infection of pathogenic microorganisms and plays important role in antagonizing and eliminating pathogenic infections and endogenic danger signals.Pyroptosis mainly depends on the inflammasome-mediated caspase-1 and caspase-11/4/5 activation.In recent years,researchers have discovered an unknown protein-GSDMD,through genome-wide genetic screening,and demonstrated that GSDMD is a common substrate of all inflammatory caspases.The cleavage of this protein triggers the activation of inflammatory caspase-dependent pyroptosis.Various studies have revealed that pyroptosis had a close relationship with a variety of diseases including infectious diseases,cardiovascular diseases,and diabetes.Our preliminary data suggested that in hepatocytes of NAFLD mice,pyroptosis and gasdermin-N domain of executor protein GSDMD were dramatically elevated.Therefore,we hypothesize that there may be an inextricable link between pyroptosis and NAFLD,and it may be a new direction for the treatment of NAFLD.In this study,we found that overexpression and knock down of GSDMD aggravated and released intracellular lipid accumulation in vitro,respectively.Furthermore,interleukin regulatory factor 7(IRF7)forms a protein complexe with GSDMD in mouse livers,and may serves as a adapter which links GSDMD as a cytoplasmic protein with the transcriptional regulation of lipid metabolism genes.In the liver of high-fat diet induced NAFLD mice,the binding of GSDMD to IRF7 was significantly lower than that of normal diet(ND)mice.Additionly,we also explored an anti-pyroptosis drug dimethyl fumarate(DMF)to improving the excessive lipid accumulation in the hepatocytes in vitro for the first time,thereby expanding the use of anti-inflammatory drugs such as DMF in the perspective of "new drugs".Collectively,our results suggested that pyroptosis and its executive factor GSDMD,play a vital role in the pathological process of NAFLD,and regulating pyroptosis and GSDMD will provide a new perspective for the novel therapeutic drugs development of NAFLD.