title: Fetuin A promotes lipotoxicity in β cells through the TLR4 signaling pathway and the role of pioglitazone in anti-lipotoxicity.
abstract: OBJECTIVE
  Fetuin A (FetA), a secreted glycoprotein, is known to affect inflammation and insulin resistance (IR) in obese humans and animals. Lipotoxicity from chronic hyperlipidemia damages pancreatic β cells, hastening the onset of diabetes. We sought to determine whether FetA promotes lipotoxicity through modulation of the toll-like receptor 4 (TLR4) inflammatory signaling pathway as well as the protective effect of pioglitazone(PIO) on lipotoxicity.
  
  
  METHODS
  βTC6, a glucose-sensitive mouse pancreatic β cell line, and Sprague-Dawley rats with diet-induced obesity, were used to investigate FetA-mediated lipotoxicity. Protein expression/activation were measured by Western blotting. Small interfering (si)RNAs for TLR4 were used. Cell apoptosis was quantified by TUNEL analysis or flow cytometry, respectively. Insulin release was assessed with an insulin ELISA.
  
  
  RESULTS
  FetA dose-dependently aggravated palmitic acid (PA)-induced βTC6 cell apoptosis, insulin secretion impairment, and inhibition of the expression of G-protein-coupled receptor 40 (GPR40) and pancreatic duodenal homeobox-1(PDX-1). Combined FetA + PA induced TLR4 expression, and subsequent inhibition of TLR4 signaling or expression was shown to prevent the strengthening effect of FetA on PA-induced lipotoxicity in βTC6 cells. FetA + PA induced p-JNK and nuclear factor-κB (NF-κB) subunit P65 expression, and inhibition of this activity reduced PA+ FetA lipotoxicity in βTC6 cells. PIO could ameliorate PA+ FetA-induced damage to βTC6 cells. Similarly, PIO improved insulin secretion disorder, reduced apoptosis, decreased FetA, TLR4, p-JNK, NF-κB subunit P65 and cleaved caspase 3 expression, and increased GPR40 and PDX-1 expression in islet β cells of diet-induced obese rats. The correlative bivariate analysis showed that increases in Fetuin A were directly proportional to the development of β cell injury.
  
  
  CONCLUSIONS
  FetA can promote lipotoxicity in β cells through the TLR4-JNK-NF-κB signaling pathway. The protective effects of PIO on lipotoxicity in β cells may involve the inhibition of the activation of the FetA and TLR4 signaling pathway.
authors.affiliation: Endocrinology Department, the First Affiliated Hospital of Fujian Medical University, Fuzhou 350005, Fujian, China.
authors.forename: Ximei
authors.initials: X
authors.lastname: Shen
authors.affiliation: Endocrinology Department, the First Affiliated Hospital of Fujian Medical University, Fuzhou 350005, Fujian, China. Electronic address: liyongy@yahoo.com.
authors.forename: Liyong
authors.initials: L
authors.lastname: Yang
authors.affiliation: Endocrinology Department, the First Affiliated Hospital of Fujian Medical University, Fuzhou 350005, Fujian, China.
authors.forename: Sunjie
authors.initials: S
authors.lastname: Yan
authors.affiliation: Endocrinology Department, the First Affiliated Hospital of Fujian Medical University, Fuzhou 350005, Fujian, China.
authors.forename: Huanhuan
authors.initials: H
authors.lastname: Zheng
authors.affiliation: Endocrinology Department, the First Affiliated Hospital of Fujian Medical University, Fuzhou 350005, Fujian, China.
authors.forename: Liyu
authors.initials: L
authors.lastname: Liang
authors.affiliation: Endocrinology Department, the First Affiliated Hospital of Fujian Medical University, Fuzhou 350005, Fujian, China.
authors.forename: Xiuhui
authors.initials: X
authors.lastname: Cai
authors.affiliation: Endocrinology Department, the First Affiliated Hospital of Fujian Medical University, Fuzhou 350005, Fujian, China.
authors.forename: Meng
authors.initials: M
authors.lastname: Liao
mesh_terms: D000818:Animals; D017209:Apoptosis; D002460:Cell Line; D059305:Diet, High-Fat / Q000009:adverse effects; D004353:Drug Evaluation, Preclinical; D018398:Homeodomain Proteins / Q000378:metabolism; D007328:Insulin / Q000378:metabolism; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D050356:Lipid Metabolism; D008070:Lipopolysaccharides / Q000494:pharmacology; D008297:Male; D009363:Neoplasm Proteins / Q000378:metabolism; D029543:Nucleocytoplasmic Transport Proteins / Q000378:metabolism; D009765:Obesity / Q000209:etiology / Q000378:metabolism / Q000473:pathology; D047495:PPAR gamma / Q000819:agonists; D019308:Palmitic Acid / Q000494:pharmacology; D000077205:Pioglitazone; D017207:Rats, Sprague-Dawley; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism; D015398:Signal Transduction; D045162:Thiazolidinediones / Q000494:pharmacology*; D051197:Toll-Like Receptor 4 / Q000378:metabolism*; D015534:Trans-Activators / Q000378:metabolism; D060749:alpha-2-HS-Glycoprotein / Q000502:physiology*
chemical_list: C473035:G-protein-coupled receptor 40, rat; D018398:Homeodomain Proteins; D007328:Insulin; D008070:Lipopolysaccharides; D009363:Neoplasm Proteins; D029543:Nucleocytoplasmic Transport Proteins; D047495:PPAR gamma; D043562:Receptors, G-Protein-Coupled; D045162:Thiazolidinediones; C495347:Tlr4 protein, rat; D051197:Toll-Like Receptor 4; D015534:Trans-Activators; D060749:alpha-2-HS-Glycoprotein; C063447:p65 oncofetal mRNA transport protein, rat; C084010:pancreatic and duodenal homeobox 1 protein; D019308:Palmitic Acid; D000077205:Pioglitazone
keywords: Apoptosis; Fetuin A; G-protein-coupled receptor 40; JNK; Palmitic acid; Toll-like receptor 4