Role of Pro-opiomelanocortin mutations in human obesity

描述（由申请人提供）：我们的长期目标是确定导致人类肥胖的基因突变并了解其致病作用。我们之前已经证明，黑色素皮质素-4受体（MC4-R）的突变导致人类常见的肥胖。MC4-R是下丘脑表达的一种基因，与食物摄入的中枢调节有关。本研究拟重点研究促opiomelanocortin （POMC）基因。该基因在下丘脑弓状核中表达，并编码MC4R的生理激动剂配体。POMC基因的纯合零突变导致一种罕见的肥胖，与肾上腺功能不全和头发色素沉着改变有关。最近的文献结果以及我们的初步发现表明，杂合的POMC突变可导致常见的肥胖。我们的假设是，大量常见的严重肥胖病例是由于POMC基因的这种杂合突变引起的。为了研究这一假设，我们提出以下具体目标：目的1)确定罕见POMC基因变异在严重和/或早发性人类肥胖中的患病率及其相关性。我们将通过系统筛选POMC编码序列突变的严重肥胖儿童和成人队列，评估罕见POMC突变在严重肥胖中的流行程度。我们将在非肥胖对照中验证这种突变的缺失。我们将分析先证者家族中肥胖与突变的分离。我们将寻找将肥胖POMC突变携带者与其他肥胖患者区分开来的特定表型。目的2)确定肥胖相关POMC突变的体外效应。从已知的与肥胖相关的POMC基因杂合突变开始，我们将系统地评估所有与肥胖相关的POMC突变的影响。具体来说，我们将：2.1-检查人类肥胖相关的POMC突变对POMC加工的影响。2.2-研究突变的人类肥胖相关POMC衍生肽对MC4R和MC3R激活的影响。2.3-测试人类肥胖相关的POMC突变对神经元原代培养物的毒性作用。目的3)确定肥胖相关POMC突变在体内的影响。为了进一步确认人类肥胖相关POMC突变的致病性，我们将：3.1-评估突变的人类肥胖相关POMC衍生肽对大鼠食物摄入的短期影响。3.2-在小鼠中评估转基因过表达人类肥胖相关的POMC突变的长期影响。这项工作将是人类肥胖遗传分类的又一步，并将有助于开发基于患者潜在遗传缺陷的有针对性的预防和治疗干预措施。

DESCRIPTION (provided by applicant): Our long term objectives are to identify gene mutations that cause obesity in humans and to understand their pathogenic effects. We have previously demonstrated that mutations in the Melanocortin-4 receptor (MC4-R), a hypothalamus expressed gene implicated in the central regulation of food intake, cause a common form of obesity in humans. This research proposal focuses on the pro-opiomelanocortin (POMC) gene. This gene is expressed in the arcuate nucleus of the hypothalamus and encodes the physiologic agonist ligands of the MC4R. Homozygous null mutations in the POMC gene result in a rare form of obesity associated with adrenal insufficiency and alterations in hair pigmentation. Recent results in the literature as well as our preliminary findings suggest that heterozygous POMC mutations can predispose to common obesity. Our hypothesis is that a significant number of common severe obesity cases are due to such heterozygous mutations in the POMC gene. To investigate this hypothesis we propose the following specific aims: Aim 1) To determine the prevalence and association of rare POMC gene variants in severe and or early onset human obesity. We will evaluate the prevalence of rare POMC mutations in severe obesity by systematically screening cohorts of severely obese children and adults for mutations in the POMC coding sequence. We will verify the absence of such mutations in non-obese controls. We will analyze the segregation of obesity with the mutations in the families of the probands. We will search for specific phenotypes distinguishing obese POMC mutation carriers from other obese patients. Aim 2) To determine the in vitro effects of obesity associated POMC mutations. Starting with the known obesity-associated heterozygous mutations in the POMC gene, we will systematically evaluate the effects of all the obesity-associated POMC mutations. Specifically we will: 2.1- Examine the effects of human obesity associated POMC mutations on the processing of POMC. 2.2- Examine the effects of mutated human obesity associated POMC derived peptides on MC4R and MC3R activation. 2.3- Test for a toxic effect of human obesity associated POMC mutations on primary cultures of neurons. Aim 3) To determine the effects of obesity associated POMC mutations in vivo. To further confirm the pathogenicity of human obesity associated POMC mutations we will: 3.1- Evaluate the short term effects of mutated human obesity associated POMC derived peptides on food intake in rats. 3.2- Evaluate the long-term effects of transgenic over-expression of human obesity associated POMC mutations in mice. This work will be an additional step towards the genetic classification of obesity in humans and will contribute to the development of targeted preventive and therapeutic interventions based on the underlying genetic defects in the patients.