Epigenetic Mechanisms of Human Hypothalamic Body Weight Regulation

肥胖是世界范围内的主要卫生保健问题之一，在工业国家以及低收入和中等收入国家(LMIC)每年造成约200万人死亡。尽管双胞胎研究指出了高达70%的遗传背景，但单基因形式的肥胖症很少见，包括全基因组分析在内的大型全基因组关联研究的结果解释了不到25%的个体内体重变异性。对这一被称为“缺失遗传性”的观察结果的一种可能解释可能与表观遗传修饰有关。我们将注意力集中在前阿片黑素皮质素(POMC)基因的DNA甲基化上，该基因在瘦素-黑素皮质素信号级联中发挥关键作用，瘦素-黑素皮质素信号通路是调节下丘脑内饱腹感和能量消耗的主要途径之一。第一个资助期的结果强调了POMC DNA超甲基化作为肥胖发展的个人风险因素的作用。有证据表明，所分析的POMC区域符合亚稳定表型的标准，该表型是在胚胎早期发育时设定的，并受到父亲的影响和母亲受孕期间C1代谢物状态的变化的影响。由于啮齿类动物和人类样本之间POMC甲基化的差异，目前还没有合适的动物模型，因此我们的结论是基于在不同队列中的几个可重复的观察。为了进一步了解这一机制，我们已经开始在第一个资助期建立一个基于幼稚多能干细胞的模型，在该模型中，我们现在将能够在体外分析POMC超甲基化的功能后果(工作包1)。此外，我们希望拓宽我们的视野，并使用后亚硫酸盐适配器标记(PBAT)技术(工作包2)，分别分析肥胖和非肥胖者的激光显微解剖的人死后MSH和NPY神经元中的数百万个CpG位点。因此，我们将能够确定个体内和个体间的差异甲基化区域，这可能在表观遗传体重调节中发挥作用。这两个工作包都旨在实现这一赠款申请的主要目标，并进一步深入了解个人表观遗传特征的差异如何影响体重调节，并改变个人在一生中变得肥胖的风险。

Obesity is one of the major health care problems worldwide in industrial as well as in in low and middle-income countries (LMICS) being responsible for approximately 2 millions death per year. Although twin studies point towards a genetic background up to 70%, monogenic forms of obesity are rare and results of large genome-wide association studies including genome-wide analysis explain less than 25 % of intra-individual body weight variability. One potential explanation for this observation, which has been termed “missing heritability” might be related to epigenetic modifications. We have focused our attention on the DNA methylation of the pro-opiomelanocortin (POMC) gene, which plays a pivotal role in the leptin-melanocortin signaling cascade, one of the main pathways regulating satiety and energy expenditure within the hypothalamus. The results of the first funding period have underlined the role for a POMC DNA hypermethylation as an individual risk factor for the development of obesity. There are evidences that the analyzed POMC region fulfills the criteria for a metastable epiallele, being set during early embryonic development and being influenced by a paternal influence and changes in C1 metabolite status of the mother during conception. Due to POMC methylation differences between rodent and human samples, no appropriate animal model is available at the moment and for this reason our conclusions are based on several reproducible observation in different cohorts. To gain further insights into the mechanism we have started to establish during the first funding period a naïve-pluripotent stem cell based model, in which we will now be able to analyze the functional consequences of POMC hypermethylation in-vitro (work package 1). Additionally we want to broaden our view and analyze a few million CpG sites in laser-microdissected human, postmortem MSH and NPY neurons separately of obese and non-obese individuals, using a post-bisulfite adapter tagging (PBAT) technique (work-package 2). Thereby we will be able to identify intra-and inter-individual differentially methylated regions, which might play a role in epigenetic body weight regulation. Both work packages are designed to achieve the major goal of this grant application and to gain further insights how differences within the individual epigenetic signature are affecting body weight regulation and modifying the individual risk to become obese during lifetime.