The Serological Characteristics And Mechanisms Of Selenoprotein P In Nonalcoholic Fatty Liver Disease

Background and aimWith the development of economy and changes of lifestyle,nonalcoholic fatty liver disease(NAFLD)has become one of the most prevalent chronic liver diseases in the world.At present,the prevalence of NAFLD is approximately 15-20%in China.Following viral hepatitis and alcoholic liver disease,NAFLD is now one of the major causes of liver cirrhosis and malignancy.Additionally,NAFLD can aggravate the natural process of type 2 diabetes and cardiovascular diseases by interfering with glucose and lipid metabolism.Recently,the relationship between hepatokines and metabolic diseases is gaining increasing attention worldwide.Selenoprotein P(SeP),a member of hepatokines and selenium-binding proteins,has been reported to be elevated in serum of patients with type 2 diabetes and obesity,and is implicated in the development of insulin resistance.However,the relationship between SeP and NAFLD remains unclear.In the present study,we analyzed the serological characteristics of SeP in Chinese NAFLD patients and investigated the effect of SeP on the steatosis of hepatocytes in order to provide a novel diagnostic strategy and therapeutic target for NAFLD.MethodsIn this case-control study,subjects were selected from those who received physical examinations from March 2016 to October 2016 in the First Affiliated Hospital of Zhejiang University,School of medicine.After profiling of general information and medical history,serum samples of these subjects were collected.In addition to biochemistry parameter assays,enzyme linked immunosorbent assay was conducted to measure the serum concentration of SeP.Diagnosis of liver steatosis was based on abdominal ultrasonography.Classical NAFLD animal and cellular model were constructed respectively by the administration of high fat diet to C57BL/6 mice and palmitate acid treatment to HepG2 cell line.Protein and mRNA levels of SeP were analyzed in both the animal and cellular models.SeP expression levels were altered using siRNA knockdown or transient overexpression plasmid transfection.Purified recombinant SeP protein was added in the medium of the cell line.Finally,the intracellular triglyceride content and cellular signaling transduction of HepG2 were analyzed after the expression profiles of SeP were changed.ResultsIn this case-control study,158 subjects were enrolled with 79 fitting the criteria of NAFLD and the other 79 being allocated to the control group.There was no significant difference in age and gender between two groups.Serum level of SeP was significantly higher in patients with NAFLD than that of the control group(13.4±7.0 vs.11.1±7.1?g/mL,p<0.05).Also,NAFLD detection rate was positively correlated with an increase of SeP level.NAFLD detection rate in the middle tertile of SeP was much higher than that in the first tertile(58%vs.38%,p<0.05).Furthermore,SeP was found to be elevated as NAFLD exacerbated,where the SeP concentration in the moderate NAFLD tertile(13.1 ±5.7 ?g/mL)and severe tertile(15.6±8.1 ?g/mL)were significantly higher than that in the control group(11.1±7.1 ?g/mL)with p<0.05 and p<0.01,respectively.At last,serum SeP level was positively correlated with risk factors of NAFLD including body mass index(r=0.287,p<0.05),alanine aminotransferase(r=0.275,p<0.001),aspartate aminotransferase(r=0.199,p<0.05),?-glutamyl transferase(r=0.231,p<0.0 1)and serum uric acid(r=0.208,p<0.01).SeP protein level was elevated significantly in both NAFLD animal model and cellular model,while its mRNA level was decreased.Knocking down SeP expression by small interfering RNA attenuated fat accumulation in HepG2 cells and increased the phosphorylation of adenosine monophosphate activated protein(AMPK)and acetyl-CoA carboxylase(ACC).On the contrary,after up-regulating SeP expression by plasmid transfection,fat accumulation was exacerbated and the phosphorylation of AMPK and ACC were reduced in HepG2 cells.Besides,HepG2 cells treated with purified recombinant SeP protein in vitro showed significantly elevated fat accumulation.ConclusionsSerum SeP level is elevated in NAFLD patients and is associated with NAFLD prevalence and disease severity.Also,SeP is positively correlated with risk factors of NAFLD.Altered expressions of SeP can directly impact fat accumulation in the hepatocytes.We propose that SeP may interfere with intra-liver energy metabolism and fat accumulation by regulating AMPK-ACC signaling pathway.The present study indicate that SeP may be a novel diagnostic marker and therapeutic target of NAFLD.