Epigenetic regulation of insulin resistance in nonalcoholic fatty liver disease: impact of liver methylation of the peroxisome proliferator-activated receptor γ coactivator 1α promoter.
Insulin resistance (IR) and mitochondrial dysfunction play a central role in the pathophysiology of nonalcoholic fatty liver disease (NAFLD). We hypothesized that genetic factors 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 methylation of the peroxisome proliferator-activated receptor γ coactivator 1α (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 putative 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 significantly higher in control livers compared with NAFLD livers. mtDNA/nDNA ratio was inversely correlated with HOMA-IR, fasting glucose, and insulin and was inversely correlated with PPARGC1A promoter methylation.


CONCLUSIONS
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 concomitantly contributes to peripheral IR.
Sookoian
Silvia
S
Department of Clinical and Molecular Hepatology, Institute of Medical Research A Lanari-IDIM, University of Buenos Aires National Council of Scientific and Technological Research, Buenos Aires, Argentina. ssookoian@lanari.fmed.uba.ar
Rosselli
Maria Soledad
MS
Gemma
Carolina
C
Burgueño
Adriana L
AL
Fernández Gianotti
Tomas
T
Castaño
Gustavo O
GO
Pirola
Carlos J
CJ
D000328:Adult; D016022:Case-Control Studies; D018899:CpG Islands / Q000235:genetics; D019175:DNA Methylation; D004272:DNA, Mitochondrial / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics; D044127:Epigenesis, Genetic / Q000502:physiology*; D005234:Fatty Liver / Q000235:genetics*; D005260:Female; D006360:Heat-Shock Proteins / Q000235:genetics*; D006801:Humans; D007333:Insulin Resistance / Q000235:genetics*; D008297:Male; D008875:Middle Aged; D008930:Mitochondria, Liver / Q000502:physiology; D024101:Mitochondrial Proteins / Q000235:genetics; D047495:PPAR gamma / Q000235:genetics*; D000071248:Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; D011401:Promoter Regions, Genetic / Q000235:genetics*; D012333:RNA, Messenger / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics*
D004272:DNA, Mitochondrial; D004268:DNA-Binding Proteins; D006360:Heat-Shock Proteins; D024101:Mitochondrial Proteins; D047495:PPAR gamma; C486497:PPARGC1A protein, human; D000071248:Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; D012333:RNA, Messenger; C499631:TFAM protein, human; D014157:Transcription Factors