The Role And Mechanism Of Granulocyte Colony Stimulating Factor In Nonalcoholic Fatty Liver Disease

Backgrounds and Aims:Nonalcoholic fatty liver disease(NAFLD),characterized by pathologic accumulation of lipids in hepatocytes,is one of the most common causes of chronic liver disease.However,its pathogenesis remains not fully understood and treatment strategies are still to be improved.Granulocyte colony stimulating factor(GCSF)is an immunomodulatory cytokine that promotes the production and maturation of granulocyte lineages,especially neutrophils.Combination to granulocyte colony stimulating factor receptor(GCSFR)is essential for the biological effects of GCSF.GCSFR has been found to exist outside the hematopoietic system including in the liver,suggesting that the GCSF/GCSFR system may participate in liver diseases not only by regulating the infiltration of immune cells but also by directly targeting on hepatocytes.Nevertheless,whether GCSF plays a role in NAFLD and the potential mechanism is unclear.This study aimed to explore the effect of GCSF on NAFLD with its molecular mechanism.Materials and Methods:Laboratory data of patients were collected at baseline and after injection with GCSF.Primary hepatocytes isolated from mice were treated with palmitic acid(PA)for 24 hours to construct NAFLD cell model.GCSF wild-type mice(GCSF+/+)and GCSF knockout mice(GCSF-/-)were fed a high fat diet(HFD)for 13 weeks to establish NAFLD mouse model.Steatosis was evaluated by hematoxylin-eosin(H&E)staining,oil red O staining and triglyceride(TG)measurement.Enzyme linked immunosorbent assay(ELISA)was used to detect serum GCSF levels in mice.Western blot(WB)and coimmunoprecipitation(Co-IP)were used to detect the expression of NAFLD related proteins and to study the GCSF-related pathways and molecular mechanisms.Immunohistochemistry(IHC)and flow cytometry were used to analyze the changes in liver neutrophils and macrophages.Results:In this study,we observed an elevation in the serum TG level of patients after GCSF treatment.NAFLD modeling induced the increase of serum GCSF level in mice and the expression of GCSFR in primary hepatocytes.GCSF-/-mice exhibited alleviated HFDinduced obesity,insulin resistance and hepatic steatosis.GCSF-/-mice had lower liver TG content,decreased liver lipid synthesis and increased lipid oxidation.Extra administration of GCSF significantly aggravated PA-induced lipid accumulation and insulin resistance in primary hepatocytes.GCSF significantly increased TG content,promoted lipid synthesis and downregulated lipid oxidation in primary hepatocytes.Regarding mechanisms,GCSF acted directly on hepatocytes,activation of GCSFR by GCSF induced the expression of cytokine signaling pathway inhibitor 3(SOCS3),GCSFR directly interacted with SOCS3 to regulate hepatocyte lipid metabolism and insulin resistance through the SOCS3-Janus kinase-signal transduction factor and transcriptional activator 3(SOCS3-JAK-STAT3)pathway.GCSF also enhanced hepatic infiltration of neutrophils and macrophages,thereby modulating NAFLD.Conclusions:GCSF participates in NAFLD directly by acting on hepatocytes through the GCSFRSOCS3-JAK-STAT3 pathway,and indirectly by regulating liver immune cells infiltration.GCSF may provide a new strategy for the treatment of NAFLD.