Epigenetic Modifications in the Biology of Nonalcoholic Fatty Liver Disease: The Role of DNA-Hydroxymethylation and TET Proteins

CARLOS J. PIROLA; ROMINA SCIAN; TOMAS FERNANDEZ GIANOTTI; DOPAZO HERNAN; ROHR C; MARTINO JS; GUSTAVO O. CASTANO; SILVIA SOOKOIAN

MEDICINE

LIPPINCOTT WILLIAMS & WILKINS

Lugar: Philadelphia,; Año: 2015 vol. 94 p. 1480 - 1490

0025-7974

Purpose and Methods: 5-hydroxymethylcytosine (5-hmC) is an epigenetic modification whose role in the pathogenesis of metabolic-related complex diseases remains unexplored; 5-hmC appears to be prevalent in the mitochondrial genome. The Ten-Eleven-Translocation (TET) family of proteins is responsible for catalyzing the conversion of 5-methylcytosine to 5-hmC. We hypothesized that epigenetic editing by 5-hmC might be a novel mechanism through which nonalcoholic fatty liver disease (NAFLD)-associated molecular traits could be explained.Hence, we performed an observational study to explore global levels of 5-hmC in fresh liver samples of patients with NAFLD and controls (n = 90) using an ELISA assay and immunohistochemistry. We also screened for genetic variation in TET 1-3 loci by next generation sequencing to explore its contribution to the disease biology. The study was conducted in two stages (discovery and replication) and included 476 participants. Results: We observed that the amount of 5-hmc in the liver of both NAFLD patients and controls was relatively low (up to 0.1%); a significant association was found with liver mtDNA copy number (R= 0.50, p = 0.000382) and PPARGC1A-mRNA levels (R= -0.57, p = 0.04). We did not observe any significant difference in the 5-hmC nuclear immunostaining score between NAFLD patients and controls; nevertheless, we found that patients with NAFLD (0.4±0.5) had significantly lower non-nuclear-5hmc staining compared with controls (1.8±0.8), means ±, p = 0.028. The missense p.Ile1123Met variant (TET1-rs3998860) was significantly associated with serum levels of CK-18-cell death biomarker in the discovery and replication stage, and the disease severity (OR: 1.47, 95% CI: 1.10-1.97 p = 0.005). The p.Ile1762Val substitution (TET2-rs2454206) was associated with liver PPARGC1A- methylation and transcriptional levels, and Type 2 diabetes. Conclusion: Our results suggest that 5-hmc might be involved in the pathogenesis of NAFLD by regulating liver mitochondrial biogenesis and PPARGC1A expression. Genetic diversity at TET loci suggests an ?epigenetic? regulation of programmed liver-cell death and a TET-mediated fine-tuning of the liver PPARGC1A- transcriptional program.