Dnmt3a as an epigenetic mediator of insulin resistance

胰岛素抵抗（IR）是2型糖尿病和肥胖的病理生理学标志。尽管已经提出了几种生物学途径是IR的背后，但关于细胞和生物体变得胰岛素抵抗的机制仍然存在很大的不确定性。 IR的病因学涉及基因和环境之间复杂的相互作用，这些相互作用由表观遗传机制介导。DNA甲基化是由DNA甲基转移酶（Dnmts）进行的主要表观遗传修饰。DNA甲基化模式的改变与各种代谢紊乱有关，但因果关系仍然知之甚少。 我们最近的研究表明，IR与表观遗传修饰中的许多位点特异性变化相关。当我们寻找差异表达的表观遗传修饰剂时，我们发现在IR小鼠模型中脂肪中Dnmts的表达升高，并且这种表达的增加在很大程度上被胰岛素增敏剂罗格列酮逆转。我们已经表明，Dnmt3a，特别是在Dmnt家族中，是必要的和足够的，以介导培养的脂肪细胞中的IR。与我们的体外结果一致，我们的主要体内研究发现，脂肪特异性Dnmt3a敲除小鼠具有改善的全身胰岛素敏感性和葡萄糖耐量。此外，我们的基因谱研究确定Fgf21作为Dnmt3a抑制的关键靶基因，其启动子处的DNA甲基化发生一致变化。基于这些发现，我们假设脂肪Dnmt3a通过改变关键顺式调控区的位点特异性DNA甲基化来调节关键代谢基因，从而介导IR。 为了检验我们的中心假设，我们将追求以下目标。目的1探讨Dnmt 3a在细胞自主性IR中的作用及其与PPARγ的上位性关系。目的2是研究脂肪特异性Dnmt3a耗竭对全身代谢的全面影响，并阐明改善胰岛素敏感性的潜在机制，目的3是阐明Dnmt3a介导IR的潜在分子和表观遗传基础。总的来说，这项研究将建立脂肪Dnmt3a在IR的病理生理学中的作用，并阐明潜在的分子和表观遗传机制。它还可以提供新的IR生物标志物并揭示IR的治疗靶点。

Insulin resistance (IR) is the pathophysiological hallmark of type 2 diabetes and obesity. Although several biological pathways have been proposed to be behind IR, there is still a great deal of uncertainty about the mechanisms by which cells and organisms become insulin resistant. The etiology of IR involves intricate interactions between genes and the environment, interactions mediated by epigenetic mechanisms. DNA methylation is a major epigenetic modification that is performed by DNA methyltransferases (Dnmts). Altered patterns of DNA methylation associate with a variety of metabolic perturbations, yet the cause-and-effect relationship remains poorly understood. Our recent studies have demonstrated that IR associates with many locus-specific changes in epigenetic modification. While we were searching for differentially expressed epigenetic modifiers, we discovered that adipose expression of Dnmts was elevated in mouse models of IR and that the increased expression was largely reversed by the insulin sensitizer Rosiglitazone. We have shown that Dnmt3a, in particular among the Dmnt family, is both necessary and sufficient to mediate IR in cultured adipocytes. Consistent with our in vitro results, our primary in vivo studies found that adipose-specific Dnmt3a-knockout mice had improved whole-body insulin sensitivity and glucose tolerance. Furthermore, our gene profiling studies identified Fgf21 as a key target gene repressed by Dnmt3a, with concordant changes in DNA methylation at its promoter. Based on these findings, we hypothesize that adipose Dnmt3a mediates IR by regulating key metabolic genes through altering site-specific DNA methylation at critical cis-regulatory regions. To test our central hypothesis, we will pursue the following aims. Aim 1 is to ascertain the role of Dnmt3a in cell-autonomous IR and to delineate the epistatic relationship of Dnmt3a and PPARγ. Aim 2 is to investigate the full impact of adipose-specific Dnmt3a depletion on whole-body metabolism and to elucidate the underlying mechanisms of the improved insulin sensitivity, and Aim 3 is to elucidate the underlying molecular and epigenetic basis through which Dnmt3a mediates IR using both focused and unbiased approaches. Overall, this research will establish the role of adipose Dnmt3a in the pathophysiology of IR and elucidate the underlying molecular and epigenetic mechanisms. It may also provide novel biomarkers of IR and reveal therapeutic target(s) for IR.