Diabetologia. 2014 Jan;57(1):236-45. doi: 10.1007/s00125-013-3072-0.
AIMS/HYPOTHESIS: Pro-opiomelanocortin (POMC) neurons in the arcuate nucleus (ARC) regulate energy homeostasis by secreting α-melanocyte-stimulating hormone (α-MSH), derived from POMC precursor, in response to leptin signalling. Expression of Pomc is subject to multiple modes of regulation, including epigenetic regulation. Methyl-CpG-binding protein 2 (MeCP2), a nuclear protein essential for neuronal function, interacts with promoters to influence gene expression. We aim to address whether MeCP2 regulates hypothalamic Pomc expression and to investigate the role of epigenetics, particularly DNA methylation, in this process.
We generated a mouse line with MeCP2 specifically deleted in POMC neurons (Mecp2 flox/y /Pomc-Cre [PKO]) and characterised its metabolic phenotypes. We examined the DNA methylation pattern of the Pomc promoter and its impact on hypothalamic gene expression. We also studied the requirement of MeCP2 for, and the effects of, DNA methylation on Pomc promoter activity using luciferase assays.
PKO mice are overweight, with increased fat mass resulting from increased food intake and respiratory exchange ratio. PKO mice also exhibit elevated plasma leptin. Deletion of MeCP2 in POMC neurons leads to increased DNA methylation of the hypothalamic Pomc promoter and reduced Pomc expression. Furthermore, in vitro studies show that hypermethylation of the Pomc promoter reduces its transcriptional activity and reveal a functional synergy between MeCP2 and cAMP responsive element binding protein 1 (CREB1) in positively regulating the Pomc promoter.
CONCLUSIONS/INTERPRETATION: Our results demonstrate that MeCP2 positively regulates Pomc expression in the hypothalamus. Absence of MeCP2 in POMC neurons leads to increased DNA methylation of the Pomc promoter, which, in turn, downregulates Pomc expression, leading to obesity in mice with an accentuating degree of leptin resistance.
目的/假设：弓状核（ARC）中的前阿黑皮素原（POMC）神经元通过分泌α-促黑素细胞激素（α-MSH）来调节能量稳态，α-MSH 来源于 POMC 前体，对瘦素信号作出反应。Pomc 的表达受到多种调控模式的调节，包括表观遗传调控。甲基化CpG 结合蛋白 2（MeCP2）是一种对神经元功能至关重要的核蛋白，它与启动子相互作用以影响基因表达。我们旨在探讨 MeCP2 是否调节下丘脑 Pomc 的表达，并研究表观遗传，特别是 DNA 甲基化，在这一过程中的作用。
我们生成了一种 MeCP2 特异性缺失于 POMC 神经元的小鼠品系（Mecp2 flox/y /Pomc-Cre [PKO]），并对其代谢表型进行了描述。我们检查了 Pomc 启动子的 DNA 甲基化模式及其对下丘脑基因表达的影响。我们还使用荧光素酶测定法研究了 MeCP2 对 Pomc 启动子活性的必需性和 DNA 甲基化的影响。
PKO 小鼠超重，其脂肪量增加是由于食物摄入量和呼吸交换率增加所致。PKO 小鼠的血浆瘦素水平也升高。POMC 神经元中 MeCP2 的缺失导致下丘脑 Pomc 启动子的 DNA 甲基化增加和 Pomc 表达减少。此外，体外研究表明，Pomc 启动子的过度甲基化降低了其转录活性，并揭示了 MeCP2 和环磷酸腺苷反应元件结合蛋白 1（CREB1）在正向调节 Pomc 启动子方面的功能协同作用。
结论/解释：我们的结果表明，MeCP2 正向调节下丘脑 Pomc 的表达。POMC 神经元中 MeCP2 的缺失导致 Pomc 启动子的 DNA 甲基化增加，进而下调 Pomc 表达，导致小鼠肥胖，并伴有肥胖抵抗程度加重的瘦素抵抗。
