Evaluation of hypothalamic murine and human melanocortin 3 receptor transcript structure

Prevalence of Deleterious Variants in MC3R in Patients With Constitutional Delay of Growth and Puberty

CONTEXT

The melanocortin 3 receptor (MC3R) has recently emerged as a critical regulator of pubertal timing, linear growth, and the acquisition of lean mass in humans and mice. In population-based studies, heterozygous carriers of deleterious variants in MC3R report a later onset of puberty than noncarriers. However, the frequency of such variants in patients who present with clinical disorders of pubertal development is currently unknown.

OBJECTIVE

This work aimed to determine whether deleterious MC3R variants are more frequently found in patients clinically presenting with constitutional delay of growth and puberty (CDGP) or normosmic idiopathic hypogonadotropic hypogonadism (nIHH).

METHODS

We examined the sequence of MC3R in 362 adolescents with a clinical diagnosis of CDGP and 657 patients with nIHH, experimentally characterized the signaling properties of all nonsynonymous variants found and compared their frequency to that in 5774 controls from a population-based cohort. Additionally, we established the relative frequency of predicted deleterious variants in individuals with self-reported delayed vs normally timed menarche/voice-breaking in the UK Biobank cohort.

RESULTS

MC3R loss-of-function variants were infrequent but overrepresented in patients with CDGP (8/362 [2.2%]; OR = 4.17; P = .001). There was no strong evidence of overrepresentation in patients with nIHH (4/657 [0.6%]; OR = 1.15; P = .779). In 246 328 women from the UK Biobank, predicted deleterious variants were more frequently found in those self-reporting delayed (aged ≥16 years) vs normal age at menarche (OR = 1.66; P = 3.90E-07).

CONCLUSION

We have found evidence that functionally damaging variants in MC3R are overrepresented in individuals with CDGP but are not a common cause of this phenotype.

Molecular characteristics of rhesus macaque interleukin-22: cloning, in vitro expression and biological activities

Interleukin-22 (IL-22) is a potential therapeutic agent for diseases driven by epithelial injury. To characterize the IL-22 expressed by rhesus macaques, animals that are irreplaceable for human disease research, rhesus macaque IL-22 (rhIL-22) was cloned and expressed, and its biological activity and in vivo distribution were examined. It was found that the rhIL-22 gene consists of five introns and six exons, including a short non-coding exon starting 22 bp downstream of a putative TATA box. The amino acid sequence of rhIL-22 showed 95·5% identity to that of humans, and it shared two conserved disulphide bonds, three N-glycosylation sites and all the critical residues for binding to IL-22R1. High levels of IL-22 mRNA were observed in the liver, pancreas, lymphoid tissues and especially in the outer-body barriers such as the intestinal tract of rhesus macaques. Functionally, purified rhIL-22 has a similar but a little earlier effect on signal transducer and activator of transcription 3 phosphorylation at Tyr705 compared with that of commercial human IL-22. The expression of the antibacterial proteins β-defensin-2, S100A8, S100A9, RegIIIα and Muc1 by HT-29 cells was largely upregulated after stimulation with rhIL-22. Recombinant rhIL-22 could also significantly promote the proliferation of human intestinal epithelial cells without affecting cell apoptosis. These data indicate that rhesus macaque IL-22 is highly similar to that of humans in both structure and function, and tests of therapeutic effects of human IL-22 on human diseases in rhesus macaques are warranted.

Polymorphisms and mutations in the melanocortin-3 receptor and their relation to human obesity

Inactivating mutations in the melanocortin 3 receptor (Mc3r) have been described as causing obesity in mice, but the physiologic effects of MC3R mutations in humans have been less clear. Here we review the MC3R polymorphisms and mutations identified in humans, and the in vitro, murine, and human cohort studies examining their putative effects. Some, but not all, studies suggest that the common human MC3R variant T6K+V81I, as well as several other rare, function-altering mutations, are associated with greater adiposity and hyperleptinemia with altered energy partitioning. In vitro, the T6K+V81I variant appears to decrease MC3R expression and therefore cAMP generation in response to ligand binding. Knockin mouse studies confirm that the T6K+V81I variant increases feeding efficiency and the avidity with which adipocytes derived from bone or adipose tissue stem cells store triglycerides. Other MC3R mutations occur too infrequently in the human population to make definitive conclusions regarding their clinical effects. This article is part of a Special Issue entitled: Melanocortin Receptors - edited by Ya-Xiong Tao.

In silico approach to identify non-synonymous SNPs in human obesity related gene, MC3R (melanocortin-3-receptor)

The melanocortin-3-receptor (MC3R) is a novel gene candidate for human obesity, which involved in controlling the energy homeostasis and food intake behavior. The main aim behind this work is to investigate the potentially deleterious non-synonymous single nucleotide polymorphisms (nsSNPs) in obesity related gene MC3R by using six computational tools viz., PolyPhen, I-Mutant, PROVEAN, SIFT, PANTHER and PhD-SNP. In our study, we predicted eight nsSNPs i.e., rs74315393 (Ile146Asn), rs368205448 (Asp121Tyr), rs143321797 (Phe45Ser), rs17847261 (Cys274Ser), rs144166442 (Pro257His), rs370533946 (Leu224Pro), rs371354428 (Pro72Leu) and rs373708098 (Gly249Ser) found to be potentially deleterious. The functional impact of three nsSNPs i.e., rs74315393, rs368205448 and rs143321797 have already been validated experimentally in the context of human obesity. Moreover, Homology modeling and structural analysis were carried out for already experimentally validated nsSNPs i.e., rs74315393, rs368205448 and rs143321797 to check the stability of predicted models. The mutant models showed higher energy and RMSD (Root mean square deviation) values. In addition, FTSite server predicted one nsSNP i.e., rs368205448 (Asp121Tyr) out of eight identified nsSNPs found in the MC3R protein binding site. Thus, the present computational study may suggest that predicted nsSNPs possibly be a better drug target and contribute to the treatment and better understanding of human obesity.