Negative Effect Of Resistin On SIRT1Function In Hepatocytes

Resistin is a mammalian hormone of which expression is responsive to nutritional availability. Its expression is up-regulated after feeding while down-regulated during fasting. Resistin was firstly discovered and cloned from mouse adipocytes in2001, and it was thought that resistin is a bridge that links obesity and type2diabetes. Following researches indicated that resistin can induce insulin resistance in human insulin target cells such as hepatocytes, and resistin is involved in kinds of human inflammatory diseases.Sir2(Silent information regulator2) was discovered as a calorie restriction responsive factor which mediates lifespan extension during calorie restriction in yeasts. When sir2is overexpressed, the yeasts lifespan are significantly extended even without calorie restriction. There are seven homologous of sir2genes in mammals named SIRT1-SIRT7, and SIRT1is the most investigated one among them. Similar to sir2in yeasts, SIRT1is also a nutrition responsive factor. It is up-regulated during calorie restriction or fasting and down-regulated in response to high fat diet or feeding. SIRT1agonist SRT1720can significantly extend the lifespan of obese mouse induced by high fat diet, indicating the crucial effect of SIRT1on protecting age associated diseases.In the light of resistin and SIRT1display the opposite expression profile in response to different nutritional availability as well as their opposite effect on insulin sensitivity, this present study investigated the effect of resistin on SIRT1expression and function in hepatocytes by using quantitative real time PCR, western blot, co-immunoprecipitation, proximity ligation assay, chromatin immunoprecipitation, ELISA and senescence associated β-galactosidase staining. Obtained results are listed as follows:In human HepG2cells, resistin decreases SIRT1mRNA and protein expression in a dosage dependent manner and decreases Nampt expression that is important to SIRT1activity. PGC-la and PPARa, which are two interacting protein of SIRT1, are also down-regulated by resistin treatment. Resistin decreases the interaction between SIRT1and PGC-la as well as PPARa, and FGF21and CPT-1α mRNA which are positively regulated by PPARa-SIRT1-PGC-la complex are decreased in response to resistin treatment.In mouse primary hepatocytes, resistin significantly decreases SIRT1mRNA and protein level and up-regulates SIRT1target genes, Farp2and Pisd, mRNA level in a SIRT1dependent manner. Resistin treatment also weakens the existed interaction between SIRT1and its target DNA Major satellite repeat sequences. Resistin mRNA of white adipose tissue and resistin protein serum concentration are up-regulated in60weeks old mice compared to10weeks old mice.72h resistin treatment significantly increased SA-β-gal activity of mouse primary hepatocytes, and this increased activity could be eliminated by SIRT1agonists resveratrol (RSV) and nicotinamide mononucleotide (NMN).In mouse macrophages cell line Ana-1, high glucose and palmitic acid (PA) significantly increase resistin mRNA while conditioned media from macrophages exposed to high glucose or palmitic acid in turn decreased the expression level of SIRT1in NIH-3T3, mouse primary hepatocytes and HepG2cell lines.In conclusion, resistin decreases SIRT1mRNA and protein level and weakens the interactions between SIRT1and its interacting proteins as well as its target genomic DNA, then alters SIRT1target genes expression.