Department of Medicine - DIMED, University of Padua, Padua, Italy.
Department of Reproduction and Growth, University Hospital of Ferrara, Ferrara, Italy.
J Clin Endocrinol Metab. 2021 Mar 8;106(3):736-749. doi: 10.1210/clinem/dgaa885.
Melanocortin receptor-4 (MC4R) gene mutations are associated with early-onset severe obesity, and the identification of potential pathological variants is crucial for the clinical management of patients with obesity.
To explore whether and how a novel heterozygous MC4R variant (MC4R-F313Sfs*29), identified in a young boy (body mass index [BMI] 38.8 kg/m2) during a mutation analysis conducted in a cohort of patients with obesity, plays a determinant pathophysiological role in the obesity development.
The genetic screening was carried out in a total of 209 unrelated patients with obesity (BMI ≥ 35 kg/m2). Structural and functional characterization of the F313Sfs*29-mutated MC4R was performed using computational approaches and in vitro, using HEK293 cells transfected with genetically encoded biosensors for cAMP and Ca2+.
The F313Sfs29 was the only variant identified. In vitro experiments showed that HEK293 cells transfected with the mutated form of MC4R did not increase intracellular cAMP or Ca2+ levels after stimulation with a specific agonist in comparison with HEK293 cells transfected with the wild type form of MC4R (∆R/R0 = -90% ± 8%; P < 0.001). In silico modeling showed that the F313Sfs29 mutation causes a major reorganization in the cytosolic domain of MC4R, thus reducing the affinity of the putative GalphaS binding site.
The newly discovered F313Sfs*29 variant of MC4R may be involved in the impairment of α-MSH-induced cAMP and Ca2+ signaling, blunting intracellular G protein-mediated signal transduction. This alteration might have led to the dysregulation of satiety signaling, resulting in hyperphagia and early onset of obesity.
黑素皮质素受体-4（MC4R）基因突变与早发性严重肥胖有关，鉴定潜在的病理性变异对于肥胖患者的临床管理至关重要。
探索在肥胖患者队列中进行突变分析时发现的一种新型杂合 MC4R 变体（MC4R-F313Sfs*29）是否以及如何在肥胖发展中起决定性的病理生理作用，该变体在一个年轻男孩（体重指数 [BMI] 38.8 kg/m2）中被鉴定出来。
设计、设置和患者：共对 209 名肥胖患者（BMI≥35 kg/m2）进行了基因筛查。使用计算方法和体外方法，使用转染了用于 cAMP 和 Ca2+的基因编码生物传感器的 HEK293 细胞，对 F313Sfs*29 突变的 MC4R 进行了结构和功能特征分析。
仅鉴定出 F313Sfs29 变体。与转染野生型 MC4R 的 HEK293 细胞相比，转染突变型 MC4R 的细胞在用特定激动剂刺激后细胞内 cAMP 或 Ca2+水平没有增加（∆R/R0=-90%±8%；P<0.001）。计算机建模显示，F313Sfs29 突变导致 MC4R 胞质域的重大重组，从而降低了假定的 GalphaS 结合位点的亲和力。
新发现的 MC4R F313Sfs*29 变体可能参与了 α-MSH 诱导的 cAMP 和 Ca2+信号的损害，从而削弱了细胞内 G 蛋白介导的信号转导。这种改变可能导致饱食信号的失调，导致食欲过盛和肥胖的早期发生。
