Latvian Biomedical Research and Study Centre, Ratsupites Str. 1, 1067, Riga, Latvia.
Mol Biol Rep. 2014 Mar;41(3):1491-500. doi: 10.1007/s11033-013-2994-4. Epub 2014 Jan 3.
Melanocortin 4 receptor (MC4R) is an important regulator of food intake and number of studies report genetic variations influencing the risk of obesity. Here we explored the role of common genetic variation from MC4R locus comparing with SNPs from gene FTO locus, as well as the frequency and functionality of rare MC4R mutations in cohort of 380 severely obese individuals (BMI > 39 kg/m(2)) and 380 lean subjects from the Genome Database of Latvian Population (LGDB). We found correlation for two SNPs--rs11642015 and rs62048402 in the fat mass and obesity-associated protein (FTO) with obesity but no association was detected for rs17782313 located in the MC4R locus in these severely obese individuals. We sequenced the whole gene MC4R coding region in all study subjects and found five previously known heterozygous non-synonymous substitutions V103I, I121T, S127L, V166I and I251L. Expression in mammalian cells showed that the S127L, V166I and double V103I/S127L mutant receptors had significantly decreased quantity at the cell surface compared to the wild type MC4R. We carried out detailed functional analysis of V166I that demonstrated that, despite low abundance in plasma membrane, the V166I variant has lower EC50 value upon αMSH activation than the wild type receptor, while the level of AGRP inhibition was decreased, implying that V166I cause hyperactive satiety signalling. Overall, this study suggest that S127L may be the most frequent functional MC4R mutation leading to the severe obesity in general population and provides new insight into the functionality of population based variants of the MC4R.
黑皮质素 4 受体（MC4R）是调节食物摄入的重要因子，有许多研究报道称，遗传变异会影响肥胖风险。在这里，我们比较了 MC4R 基因座上的常见遗传变异与 FTO 基因座上的 SNP，以及在 380 名严重肥胖个体（BMI>39kg/m²）和 380 名来自拉脱维亚人群基因组数据库（LGDB）的瘦个体中 MC4R 罕见突变的频率和功能，探索了 MC4R 基因座常见遗传变异的作用。我们发现，与肥胖相关的脂肪量和肥胖基因（FTO）上的两个 SNP--rs11642015 和 rs62048402 与肥胖相关，但在这些严重肥胖个体中，位于 MC4R 基因座的 rs17782313 没有关联。我们对所有研究对象的 MC4R 编码区进行了全基因测序，发现了五个先前已知的杂合性非同义取代 V103I、I121T、S127L、V166I 和 I251L。在哺乳动物细胞中的表达表明，与野生型 MC4R 相比，S127L、V166I 和双 V103I/S127L 突变受体的细胞表面数量明显减少。我们对 V166I 进行了详细的功能分析，结果表明，尽管在质膜中的丰度较低，但 V166I 变体在 αMSH 激活时的 EC50 值低于野生型受体，而 AGRP 抑制水平降低，这表明 V166I 导致饱食信号过度活跃。总的来说，这项研究表明，S127L 可能是导致一般人群严重肥胖的最常见功能性 MC4R 突变，并为 MC4R 人群变异的功能提供了新的见解。
