Epigenetic Mechanisms of Human Hypothalamic Body Weight Regulation

肥胖症是世界范围内工业化国家以及低收入和中等收入国家（LMICS）的主要卫生保健问题之一，每年造成约200万人死亡。虽然双胞胎研究指出遗传背景高达70%，但单基因形式的肥胖症是罕见的，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。这一观察结果的一个潜在解释，被称为“缺失遗传性”，可能与表观遗传修饰有关。我们将注意力集中在阿黑皮素原（POMC）基因的DNA甲基化上，POMC基因在瘦素-黑皮质素信号级联中起着关键作用，瘦素-黑皮质素信号级联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体风险因素的作用。有证据表明，分析的POMC区域满足亚稳态表观等位基因的标准，在早期胚胎发育过程中设置，并受到父亲的影响和在受孕期间母亲的C1代谢物状态的变化。由于啮齿动物和人类样本之间的POMC甲基化差异，目前没有合适的动物模型，因此我们的结论是基于不同队列中的几个可重复观察结果。为了进一步了解该机制，我们在第一个资助期内开始建立一个基于幼稚多能干细胞的模型，在该模型中，我们现在能够分析POMC超甲基化的功能后果（工作包1）。此外，我们想扩大我们的视野，并分析几百万个CpG位点的激光显微解剖的人，死后MSH和NPY神经元分别肥胖和非肥胖的个人，使用后亚硫酸氢盐适配器标记（PBAT）技术（工作包2）。因此，我们将能够识别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。这两个工作包的目的是实现这项拨款申请的主要目标，并获得进一步的见解，如何在个人表观遗传签名的差异影响体重调节和修改个人的风险，成为肥胖在一生中。

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.