Histone modifications influence the insulin-signaling genes and are related to insulin resistance in human adipocytes.

Insulin resistance (IR) is a state when the physiological amount of insulin is not sufficient to evoke proper action, that is, glucose uptake. Numerous conditions lead to IR, including epigenetic components. Epigenetic modifications, associated with obesity and IR are one of the main mechanisms leading to IR pathogenesis. The adipose tissue samples (subcutaneous (SAT) and visceral (VAT)) were collected during abdominal surgery from 40 patients of a wide range of BMI, age, and insulin resistance ratios (F = 9, M = 31). IR was induced in 3T3-L1 adipocytes and human adipocytes collected from SAT and VAT of healthy subjects. Global and site-specific histone modifications (H3K4me3 and H3K9/14ac) were determined. We found lower histone modifications in adipose tissue of IR patients. Furthermore, numerous genes regulating insulin action (PPARG, SLC2A4, ADIPOQ) were differently marked by histone methylation and acetylation. Moreover, we noticed that epigenetic changes appear as soon as 72 h following IR induction. The epigenetic changes appeared to be mediated through the SIRT family. Based on obtained results, the histone marks related to insulin resistance mostly concerned PPARG and SLC2A4 genes. Furthermore, our results proved a vital role of the SIRT family in insulin action and IR pathogenesis.

Obesity-induced insulin resistance via changes in the DNA methylation profile of insulin pathway genes.

BACKGROUND: Obesity has been shown to play a key role in the development of insulin resistance (IR). Abundant data implicate obesity in DNA hypermethylation at global and site-specific levels, including genes regulating insulin sensitivity. Deregulation of epigenetic marks implicates gene expression and changes in cell metabolism. OBJECTIVES: Our previous reports demonstrated that the strongest risk factor in the development of IR is BMI; accordingly, the objective of this study was to investigate the effect of obesity on DNA methylation and insulin sensitivity. MATERIAL AND METHODS: A study was carried out on lymphocytes (N-34) and visceral adipose tissue (VAT; N-35) of insulin-resistant subjects and healthy controls. Genetic material (DNA and RNA) was extracted from cells. Global and site-specific DNA methylation was analyzed with the use of restriction enzymes followed by real-time polymerase chain reaction (PCR). Gene expression was analyzed as relative mRNA level normalized to a housekeeping gene. RESULTS: Global DNA methylation increased in both types of tissue in obese and insulin-resistant individuals and correlated positively with IR. Two of the 3 investigated promoters of insulin pathway genes were hypermethylated, which correlated negatively with gene expression and positively with IR. The DNMT3a gene was upregulated in obese insulin-resistant individuals in both types of tissues and correlated positively with global DNA methylation. CONCLUSIONS: DNA methylation profile changed depending on body mass index (BMI) and influenced glucose metabolism and insulin sensitivity in VAT.