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标志。虽然已经提出了几种生物学途径来支持胰岛素抵抗，但细胞和生物体成为胰岛素抵抗的机制仍然存在很大的不确定性。IR的病因涉及基因和环境之间错综复杂的相互作用，这种相互作用是由表观遗传机制介导的。DNA甲基化是一种主要的表观遗传修饰，由DNA甲基转移酶(DNMT)执行。DNA甲基化模式的改变与多种代谢紊乱有关，然而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有关。当我们寻找差异表达的表观遗传修饰物时，我们发现在IR的小鼠模型中，DNMTS的脂肪表达增加，并且这种增加的表达在很大程度上被胰岛素增敏剂罗格列酮逆转。我们已经证明，DNMT3A，特别是在DMNT家族中，对于介导培养的脂肪细胞的IR是必要和充分的。与我们的体外结果一致，我们的初步体内研究发现，脂肪特异性DNMT3A基因敲除小鼠改善了全身胰岛素敏感性和葡萄糖耐量。此外，我们的基因图谱研究发现，FGF21是一个受DNMT3A抑制的关键靶基因，其启动子DNA甲基化发生了相应的变化。基于这些发现，我们假设脂肪DNMT3A通过改变关键顺式调控区域的位点特异性DNA甲基化来调节关键代谢基因，从而介导IR。为了验证我们的中心假设，我们将追求以下目标。目的1确定DNMT3A在细胞自主性IR中的作用，阐明DNMT3A与PPARγ的上位关系。目的2是研究脂肪特异性DNMT3A缺失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是通过聚焦和无偏倚两种方法阐明DNMT3A介导IR的潜在分子和表观遗传学基础。总之，本研究将确定脂肪DNMT3A在IR的病理生理学中的作用，并阐明其潜在的分子和表观遗传学机制。也可能为胰岛素抵抗提供新的生物标志物，揭示胰岛素抵抗的治疗靶点(S)。

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.