AimsThis study aimed to investigate the roles of DNA methylation and miR-34a in the regulation of peroxisome proliferator-activated receptor gamma (PPARγ) in patients with type 2 diabetes (T2D). MethodsWe investigated the methylation status of four regions of the PPARγ promoter and PPARγ expression in a panel of 84 T2D patients using methylation-specific PCR (MSP) and RT-qPCR, respectively. Moreover, we quantified DNA methyltransferases (DNMTs) expression and global DNA methylation levels by RT-qPCR and ELISA, respectively. We measured the expression levels of miR-34a and protein expression of PPARγ by stem-loop RT-qPCR and ELISA, respectively. ResultsWe found significant DNA hypermethylation in the R2 and R3 regions of the PPARγ promoter in people with diabetes. Functionally, this was associated with a significant reduction in PPARγ expression. In addition, we observed a significant increase in 5-methylcytosine levels in people with diabetes. A marked increase in circulating miR-34a in the early stages of T2D (up to 10 years) and a significant decrease in circulating miR-34a with increasing diabetes duration from 10 years after the onset of diabetes. Interestingly, upregulation of DNA methyltransferases 1 (DNMT1), DNMT3A, and DNMT3B was observed in people with diabetes, and the average expression of DNMTs was negatively correlated with circulating miR-34a levels. In contrast, the serum protein level of PPARγ, a direct target of miR-34a, increased considerably with diabetes duration and showed a negative correlation with circulating miR-34a, cholesterol, triglyceride, and low-density lipoprotein. ConclusionPPARγ promoter hypermethylation and miR-34a upregulation are associated with T2D pathogenesis through PPARγ dysregulation.
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