Epigenetic Regulation of Insulin Resistance in Nonalcoholic ... : Hepatology (original) (raw)

Steatohepatitis/Metabolic Liver Disease

Impact of Liver Methylation of the Peroxisome Proliferator–Activated Receptor γ Coactivator 1_α_ Promoter

Sookoian, Silvia1,3,4; Rosselli, Maria Soledad1; Gemma, Carolina2; Burguen˜o, Adriana L.2; Ferna´ndez Gianotti, Tomas2; Castan˜o, Gustavo O.3,4; Pirola, Carlos J.2

1From the Departments of Clinical and Molecular Hepatology

2Molecular Genetics and Biology of the Complex Diseases, Institute of Medical Research A Lanari-IDIM, University of Buenos Aires National Council of Scientiﬁc and Technological Research, Buenos Aires, Argentina

3Liver Unit, Medicine and Surgery Department, Hospital Abel Zubizarreta, Buenos Aires, Argentina

4Research Council in Health, Buenos Aires, Argentina

Abbreviations: HOMA-IR, homeostasis model assessment of insulin resistance; IR, insulin resistance; mRNA, messenger RNA; MS, metabolic syndrome; mtDNA, mitochondrial DNA; NAFLD, nonalcoholic fatty liver disease; NASH, nonalcoholic steatohepatitis; nDNA, nuclear DNA; PCR, polymerase chain reaction; PPARGC1A, peroxisome proliferator–activated receptor c coactivator 1a; RT-PCR, real-time polymerase chain reaction; Tfam, mitochondrial transcription factor A; TSS, transcriptional start site.

Received July 7, 2010; accepted August 11, 2010.

Supported in part by Grants UBACYT M055 (University of Buenos Aires), PICT 2006-124 (National Agency for Scientiﬁc and Technological Promotion) and Research Council in Health, Government of the City of Buenos Aires. S. S., M. S. R., T. F. G., A. L. B., and C. J. P. belong to National Council of Scientiﬁc and Technological Research (CONICET). S. S. and G. C. belong to Research Council in Health, Government of the City of Buenos Aires.

Online date: October 1, 2010

Abstract

Insulin resistance (IR) and mitochondrial dysfunction play a central role in the patho-physiology of nonalcoholic fatty liver disease (NAFLD). We hypothesized that genetic fac-tors and epigenetic modiﬁcations occurring in the liver contribute to the IR phenotype. We speciﬁcally examined whether fatty liver and IR are modiﬁed by hepatic DNA methyla-tion of the peroxisome proliferator–activated receptor c coactivator 1_a_ (PPARGC1A) and mitochondrial transcription factor A (TFAM) promoters, and also evaluated whether liver mitochondrial DNA (mtDNA) content is associated with NAFLD and IR. We studied liver biopsies obtained from NAFLD patients in a case–control design. After bisulﬁte treatment of DNA, we used methylation-speciﬁc polymerase chain reaction (PCR) to assess the puta-tive methylation of three CpG in the PPARGC1A and TFAM promoters. Liver mtDNA quantiﬁcation using nuclear DNA (nDNA) as a reference was evaluated by way of real-time PCR. Liver PPARGC1A methylated DNA/unmethylated DNA ratio correlated with plasma fasting insulin levels and homeostasis model assessment of insulin resistance (HOMA-IR); TFAM methylated DNA/unmethylated DNA ratio was inversely correlated with insulin levels. PPARGC1A promoter methylation was inversely correlated with the abundance of liver PPARGC1A messenger RNA. The liver mtDNA/nDNA ratio was signif-icantly higher in control livers compared with NAFLD livers. mtDNA/nDNA ratio was inversely correlated with HOMA-IR, fasting glucose, and insulin and was inversely corre-lated with PPARGC1A promoter methylation. Conclusion: Our data suggest that the IR phenotype and the liver transcriptional activity of PPARGC1A show a tight interaction, probably through epigenetic modiﬁcations. Decreased liver mtDNA content concomi-tantly contributes to peripheral IR. (HEPATOLOGY 2010;52:1992-2000)