Evaluation of a melanocortin-4 receptor (MC4R) agonist (Setmelanotide) in MC4R deficiency.
TL;DR: It is shown that Setmelanotide is significantly more potent at MC4R than the endogenous ligand alpha-melanocyte stimulating hormone and can disproportionally rescue signaling by a subset of severely impairedMC4R mutants.
Abstract: Objective
Pro-opiomelanocortin (POMC)-derived peptides act on neurons expressing the Melanocortin 4 receptor (MC4R) to reduce body weight. Setmelanotide is a highly potent MC4R agonist that leads to weight loss in diet-induced obese animals and in obese individuals with complete POMC deficiency. While POMC deficiency is very rare, 1–5% of severely obese individuals harbor heterozygous mutations in MC4R. We sought to assess the efficacy of Setmelanotide in human MC4R deficiency.
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TL;DR: This Review comprehensively assess the benefits and limitations of GWAS in human populations and discusses the relevance of performing more GWAS, with a focus on the cardiometabolic field.
Abstract: Genome-wide association studies (GWAS) involve testing genetic variants across the genomes of many individuals to identify genotype–phenotype associations. GWAS have revolutionized the field of complex disease genetics over the past decade, providing numerous compelling associations for human complex traits and diseases. Despite clear successes in identifying novel disease susceptibility genes and biological pathways and in translating these findings into clinical care, GWAS have not been without controversy. Prominent criticisms include concerns that GWAS will eventually implicate the entire genome in disease predisposition and that most association signals reflect variants and genes with no direct biological relevance to disease. In this Review, we comprehensively assess the benefits and limitations of GWAS in human populations and discuss the relevance of performing more GWAS. Despite the success of human genome-wide association studies (GWAS) in associating genetic variants and complex diseases or traits, criticisms of the usefulness of this study design remain. This Review assesses the pros and cons of GWAS, with a focus on the cardiometabolic field.
1,002 citations
TL;DR: Metabolically healthy obesity represents a model to study mechanisms linking obesity to cardiometabolic complications and should not be considered a safe condition, which does not require obesity treatment, but may guide decision-making for a personalized and risk-stratified obesity treatment.
Abstract: Obesity contributes to reduced life expectancy, impaired quality of life, and disabilities, mainly in those individuals who develop cardiovascular diseases, type 2 diabetes, osteoarthritis, and cancer. However, there is a large variation in the individual risk to developing obesity-associated comorbid diseases that cannot simply be explained by the extent of adiposity. Observations that a proportion of individuals with obesity have a significantly lower risk for cardiometabolic abnormalities led to the concept of metabolically healthy obesity (MHO). Although there is no clear definition, normal glucose and lipid metabolism parameters-in addition to the absence of hypertension-usually serve as criteria to diagnose MHO. Biological mechanisms underlying MHO lower amounts of ectopic fat (visceral and liver), and higher leg fat deposition, expandability of subcutaneous adipose tissue, preserved insulin sensitivity, and beta-cell function as well as better cardiorespiratory fitness compared to unhealthy obesity. Whereas the absence of metabolic abnormalities may reduce the risk of type 2 diabetes and cardiovascular diseases in metabolically healthy individuals compared to unhealthy individuals with obesity, it is still higher in comparison with healthy lean individuals. In addition, MHO seems to be a transient phenotype further justifying therapeutic weight loss attempts-even in this subgroup-which might not benefit from reducing body weight to the same extent as patients with unhealthy obesity. Metabolically healthy obesity represents a model to study mechanisms linking obesity to cardiometabolic complications. Metabolically healthy obesity should not be considered a safe condition, which does not require obesity treatment, but may guide decision-making for a personalized and risk-stratified obesity treatment.
343 citations
TL;DR: Loos and Yeo as mentioned in this paper summarized the current understanding of the genetic underpinnings of monogenic and polygenic obesity and highlighted the commonalities revealed by recent studies and discuss the implications for treatment and prediction of obesity risk.
Abstract: The prevalence of obesity has tripled over the past four decades, imposing an enormous burden on people’s health. Polygenic (or common) obesity and rare, severe, early-onset monogenic obesity are often polarized as distinct diseases. However, gene discovery studies for both forms of obesity show that they have shared genetic and biological underpinnings, pointing to a key role for the brain in the control of body weight. Genome-wide association studies (GWAS) with increasing sample sizes and advances in sequencing technology are the main drivers behind a recent flurry of new discoveries. However, it is the post-GWAS, cross-disciplinary collaborations, which combine new omics technologies and analytical approaches, that have started to facilitate translation of genetic loci into meaningful biology and new avenues for treatment. In this Review, Loos and Yeo summarize our current understanding of the genetic underpinnings of monogenic and polygenic obesity. They highlight the commonalities revealed by recent studies and discuss the implications for treatment and prediction of obesity risk.
231 citations
TL;DR: By delivering this system into the mouse hypothalamus using adeno-associated virus, they rescued the obesity phenotype caused by haploinsufficiency of either of two genes known to promote obesity when mutated in mice and humans, highlighting the translational potential of the CRISPR activation system to treat haplo Insufficient disease.
Abstract: INTRODUCTION Loss-of-function mutations in one gene copy can lead to reduced amounts of protein and, consequently, human disease, a condition termed haploinsufficiency. It is currently estimated that more than 660 genes cause human disease as a result of haploinsufficiency. The delivery of extra copies of the gene by way of gene therapy is a promising therapeutic strategy to increase gene dosage in such conditions. Recombinant adeno-associated virus (rAAV) provides a promising tool for delivery of transgenes in an efficient and safe way for gene therapy. However, it has some limitations, including an optimal DNA packaging constraint of 4700 base pairs and ectopic expression. RATIONALE Increasing the expression levels of the normal gene copy by directly targeting the endogenous gene regulatory elements that control it could potentially correct haploinsufficiency. CRISPR-mediated activation (CRISPRa), whereby a nuclease-deficient Cas9 (dCas9) is used to target a transcriptional activator to the gene’s regulatory element (promoter or enhancer), could be used for this purpose. Such an approach could overcome the ectopic expression and DNA packaging limitations of rAAV. Using obesity as a model, we tested in mice whether CRISPR-mediated activation of the existing normal copy of two different genes, Sim1 or Mc4r, where loss-of-function mutations that lead to haploinsufficiency are a major cause of human obesity, can rescue their obesity phenotype. RESULTS We first generated a transgenic CRISPRa system using dCas9 fused to a transcriptional activator, VP64, to test whether it can rescue the obesity phenotype in a Sim1 haploinsufficient mouse model. CRISPRa targeting of the Sim1 promoter or its hypothalamus-specific enhancer, which is 270 kilobases away from the gene, in Sim1 haploinsufficient mice increased the expression of the normal copy of Sim1. This up-regulation was sufficient to rescue the obesity phenotype of Sim1 heterozygous mice and led to significantly reduced food intake and body fat content in these mice. We assessed the off-targeting effects of CRISPRa using both RNA sequencing (RNA-seq) and Cas9 chromatin immunoprecipitation sequencing (ChIP-seq) analyses. We found CRISPRa targeting to be highly specific and without any overt changes in the expression of other genes. We also observed that Sim1 up-regulation occurred only in tissues where the regulatory element (promoter or enhancer) that was being targeted was active. Although promoter-CRISPRa–targeted mice up-regulated Sim1 in all the tissues where it is expressed, the enhancer-CRISPRa–targeted mice showed Sim1 up-regulation only in the hypothalamus. We then delivered CRISPRa packaged into rAAV targeting the Sim1 promoter or its hypothalamus-specific enhancer using either Streptococcus pyogenes or the shorter Staphylococcus aureus CRISPRa system. We show that postnatal injection of CRISPRa-rAAV into the hypothalamus can up-regulate Sim1 expression and rescue the obesity phenotype in Sim1 haploinsufficient mice in a long-lasting manner. To further highlight the therapeutic potential of this approach to rescue other haploinsufficient genes, we targeted Mc4r, where haploinsufficiency leads to severe obesity in mice and humans. CRISPRa-rAAV targeting of the Mc4r promoter rescued the obesity phenotype of Mc4r heterozygous mice. CONCLUSION These findings show that the CRISPRa system can rescue a haploinsufficient phenotypein vivo. This CRISPR-mediated activation strategy is different from a conventional gene therapy strategy, as it uses the endogenous regulatory elements to up-regulate the existing functional gene copy. As such, it can overcome the problem of ectopic gene expression. In addition, it could be used for genes that are not amenable to conventional gene therapy because their coding sequences are longer than the rAAV packaging limit. Our results provide a framework to further develop CRISPRa as a potential tool to treat gene dosage–sensitive diseases.
218 citations
Cites background from "Evaluation of a melanocortin-4 rece..."
...MC4R is a promising drug target for anti-obesity drugs, and several agonists have been developed to target this receptor (44, 45)....
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TL;DR: It is found that obesity results in profound perturbation of the metabolome; nearly a third of the assayed metabolites associated with changes in BMI are associated withChanges in BMI.
211 citations
Cites background from "Evaluation of a melanocortin-4 rece..."
...The BMI data in the participants supported a pathogenic role for at least five of the variants (Met292fs, Arg236Cys, Ser180Pro, Ala175T, and Thr11Ala), but did not corroborate a role of Ile170V, which is defined in HGMD, ClinVar, and the literature as pathogenic (Clément et al., 2018; Collet et al., 2017; Landrum et al., 2018; Stenson et al., 2003)....
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...Studies of rare variants in obesity have identified melanocortin 4 receptor (MC4R) mutations as having effects large and clear enough to be appropriate for study in our dataset (Collet et al., 2017; Turcot et al., 2018)....
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References
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TL;DR: The data identify a novel signaling pathway in the mouse for body weight regulation and support a model in which the primary mechanism by which agouti induces obesity is chronic antagonism of the MC4-R.
2,979 citations
"Evaluation of a melanocortin-4 rece..." refers background in this paper
...MC4R knockout mice are severely obese while loss of one MC4R allele results in an intermediate obesity phenotype demonstrating that weight regulation is sensitive to quantitative variation in MC4R expression [5]....
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TL;DR: This new information provides a biological context within which to consider the global obesity epidemic and identifies numerous potential avenues for therapeutic intervention and future research.
Abstract: The capacity to adjust food intake in response to changing energy requirements is essential for survival. Recent progress has provided an insight into the molecular, cellular and behavioural mechanisms that link changes of body fat stores to adaptive adjustments of feeding behaviour. The physiological importance of this homeostatic control system is highlighted by the severe obesity that results from dysfunction of any of several of its key components. This new information provides a biological context within which to consider the global obesity epidemic and identifies numerous potential avenues for therapeutic intervention and future research.
2,263 citations
TL;DR: In this paper, the nucleotide sequence of the MC4R gene in 500 children with severe childhood obesity was determined, and the results were correlated with the signaling properties of mutant receptors.
Abstract: Background Melanocortin 4 receptor (MC4R) deficiency is the commonest monogenic form of obesity. However, the clinical spectrum and mode of inheritance have not been defined, pathophysiological mechanisms leading to obesity are poorly understood, and there is little information regarding genotype–phenotype correlations. Methods We determined the nucleotide sequence of the MC4R gene in 500 probands with severe childhood obesity. Family studies were undertaken to examine cosegregation of identified mutations with obesity. Subjects with MC4R deficiency underwent metabolic and endocrine evaluation; the results were correlated with the signaling properties of mutant receptors. Results Twenty-nine probands (5.8 percent) had mutations in MC4R; 23 were heterozygous, and 6 were homozygous. Mutation carriers had severe obesity, increased lean mass, increased linear growth, hyperphagia, and severe hyperinsulinemia; homozygotes were more severely affected than heterozygotes. Subjects with mutations retaining residual...
1,518 citations
"Evaluation of a melanocortin-4 rece..." refers background in this paper
...(G) Ad libitum food intake adjusted for lean mass in 35 children age < 10 years (Hom cLOF (n 1⁄4 5); Hom pLOF (n 1⁄4 2); Het cLOF (n 1⁄4 17); Het pLOF (n 1⁄4 11)) (data on obese children have been reported previously [10]....
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...Heterozygous loss of function (LOF) mutations in MC4R are found more frequently with prevalence estimates ranging from 1 to 5% in children or adults with severe obesity [9,10,24]....
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TL;DR: Given that the central melanocortin system is an active target for development of drugs for the treatment of obesity, diabetes and cachexia, it is important to understand the system in its full complexity, including the likelihood that the system also regulates the cardiovascular and reproductive systems.
Abstract: The central melanocortin system is perhaps the best-characterized neuronal pathway involved in the regulation of energy homeostasis. This collection of circuits is unique in having the capability of sensing signals from a staggering array of hormones, nutrients and afferent neural inputs. It is likely to be involved in integrating long-term adipostatic signals from leptin and insulin, primarily received by the hypothalamus, with acute signals regulating hunger and satiety, primarily received by the brainstem. The system is also unique from a regulatory point of view in that it is composed of fibers expressing both agonists and antagonists of melanocortin receptors. Given that the central melanocortin system is an active target for development of drugs for the treatment of obesity, diabetes and cachexia, it is important to understand the system in its full complexity, including the likelihood that the system also regulates the cardiovascular and reproductive systems.
1,453 citations
Additional excerpts
...com melanocortin-4 receptor (MC4R) [3,4]....
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TL;DR: A cohort of severely obese children in whom no evidence for a recognized clinical syndrome or a structural hypothalamic cause for their obesity has been found is identified, and one subject who was heterozygous for a 4-bp deletion at codon 211 is likely to result in a non-functional receptor.
Abstract: T he melanocortin-4 receptor (MC4R) is a G-protein coupled, seven-trans-membrane receptor which is highly expressed in the hypothalamus, a region of the brain intimately involved in appetite regulation 1. It is a high-affinity receptor for αMSH, a product of the pro-opiomelanocortin (POMC) gene, which inhibits feeding when administered to rodents 2. Hypothalamic POMC neurons are stimulated by leptin, an adipocyte-specific hormone which regulates appetite and energy expenditure, and constitute a link between leptin and the melanocortin system. Mc4r-deficient mice are hyper-phagic, severely obese, hyperinsulinaemic and show increased linear growth 3. Mice heterozygous for a null Mc4r allele exhibit weight gain intermediate to that seen in wild-type and homozygous mutant litter-mates. Additionally, ectopic expression in the brain of agouti 4 and agouti-related transcript 5 , natural antagonists of the MC4R ligand, αMSH, results in obesity in rodents. In humans, obesity syndromes associated with abnormalities in POMC (ref. 6) and prohormone processing defects involving POMC (ref. 7) have also been described. We have identified a cohort of severely obese children in whom no evidence for a recognized clinical syndrome or a structural hypothalamic cause for their obesity has been found. All are severely obese (mean body mass index (weight/height 2) is 34 kg/m 2) from an early age (<10 years). Sixty-three of these subjects were screened for mutations in MC4R by direct nucleotide sequencing. We identified one subject who was heterozygous for a 4-bp deletion at codon 211 (Fig. 1b). This results in a frameshift that introduces five aberrant amino acids culminating in a stop codon in the region encoding the fifth transmembrane domain, resulting in a truncated protein. As residues at the base of the fifth and sixth transmembrane domains are needed for G-protein binding and activation 8 , this mutation is likely to result in a non-functional receptor. No mutations were found in the 62 other subjects studied. The index patient II.1 (Fig. 1a) is four years old and is the only child from a non-consanguinous union. His weight is 32 kg (>99th centile), height 107 cm (91st cen-tile) and body mass index (BMI) is 28 kg/m 2 (>99th centile). His birthweight was 3.8 kg (50th centile), and progressive weight gain was noted from the age of four months (Fig. 2a). There is no clinical or biochemical evidence of adrenal or thyroid disease, the subject has a normal karyotype and intellectual development is normal. There is a history of hyperphagia …
1,083 citations