BackgroundAdipogenesis is the process of adipocytes formation from unspecialized progenitor cells called mesenchymal stromal cells. Numerous mechanisms including epigenetic regulation modulate the correct progress of this process. Dietary exposures occurring over a specific period of time might cause long-lasting and even permanent changes in gene expression regulated by epigenetic mechanisms. For that reason, we investigated the adipogenesis of 3 T3-L1 cells with the excess of saturated and monounsaturated fatty acids and their influence on global and site-specific DNA methylation in these cells.Materials and methods3T3-L1 cells were cultured in vitro to obtain 100% of confluence, then the adipogenesis was induced by a differentiation cocktail with the addition of the excess of 0.25 mM and 0.5 mM of palmitic (16:0), stearic (18:0) and oleic (18:1n-9) acids. DNA and RNA were extracted at five-time points to assess the adipogenesis process. The phenotype of mature adipocytes (insulin sensitivity, adipokines secretion, fat content) was estimated in fully mature adipocytes. DNA methylation was investigated both during adipogenesis and in mature adipocytes.ResultsOleic acids stimulated expression of C/ebpα and Pparγ, which was correlated with lower methylation levels at promoters sites. Furthermore, cells cultured with an excess of oleic acid were characterized by higher lipid accumulation rate, higher leptin, and lower adiponectin secretion. Moreover, in all experimental cells, insulin signaling and glucose utilization were impaired.ConclusionOleic acid affected the methylation of Pparγ and C/ebpα promoters, what correlated with higher expression. Furthermore, examined free fatty acids influenced the phenotype of mature adipocytes, especially insulin signaling pathway and adipokine secretion.

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

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Obesity is a major health problem in highly industrialized countries. High-fat diet (HFD) is one of the most common causes of obesity and obesity-related disorders. There are considerable differences between fat depots and the corresponding risks of metabolic disorders. We investigated the various effects of an excess of fatty acids (palmitic 16:0, stearic 18:0, and oleic acids 18:1n−9) on adipogenesis of subcutaneous- and visceral-derived mesenchymal stem cells (MSCs) and phenotypes of mature adipocytes. MSCs of white adipose tissue were acquired from adipose tissue biopsies obtained from subcutaneous and visceral fat depots from patients undergoing abdominal surgery. The MSCs were extracted and differentiated in vitro with the addition of fatty acids. Oleic acid stimulated adipogenesis, resulting in higher lipid content and larger adipocytes. Furthermore, oleic acid stimulated adipogenesis by increasing the expression of CCAAT enhancer binding protein β (CEBPB) and peroxisome proliferator activated receptor γ (PPARG). All of the examined fatty acids attenuated the insulin-signaling pathway and radically reduced glucose uptake following insulin stimulation. Visceral adipose tissue was shown to be more prone to generate inflammatory stages. The subcutaneous adipose tissue secreted a greater quantity of adipokines. To summarize, oleic acid showed the strongest effect on adipogenesis. Furthermore, all of the examined fatty acids attenuated insulin signaling and secretion of cytokines and adipokines.

Insulin acts by binding with a specific receptor called an insulin receptor (INSR), ending up with glucose transporter activation and glucose uptake. Insulin resistance (IR) is a state when the physiological amount of insulin is not sufficient to evoke proper action, i.e., glucose uptake. Epigenetic modifications associated with obesity and IR are some of the main mechanisms leading to IR pathogenesis. The mesenchymal stem cells of adipose tissue (subcutaneous (SAT) and visceral (VAT)) were collected during abdominal surgery. IR was induced ex vivo by palmitic acid. DNA methylation was determined at a global and site-specific level. We found higher global DNA methylation in IR adipocytes after 72 h following IR induction. Furthermore, numerous genes regulating insulin action (PPARG, SLC2A4, ADIPOQ) were hypermethylated in IR adipocytes; the earliest changes in site-specific DNA methylation have been detected for PPARG. Epigenetic changes appear to be mediated through DNMT1. DNA methylation is an important component of IR pathogenesis; the PPARG and its epigenetic modification appear to be the very first epigenetic modification in newly onset IR and are probably of the greatest importance.