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The Journal of Clinical Investigation Jan 2024Melanocortin 4 receptor (MC4R) mutations are the most common cause of human monogenic obesity and are associated with hyperphagia and increased linear growth. While MC4R...
Melanocortin 4 receptor (MC4R) mutations are the most common cause of human monogenic obesity and are associated with hyperphagia and increased linear growth. While MC4R is known to activate Gsα/cAMP signaling, a substantial proportion of obesity-associated MC4R mutations do not affect MC4R/Gsα signaling. To further explore the role of specific MC4R signaling pathways in the regulation of energy balance, we examined the signaling properties of one such mutant, MC4R (F51L), as well as the metabolic consequences of MC4RF51L mutation in mice. The MC4RF51L mutation produced a specific defect in MC4R/Gq/11α signaling and led to obesity, hyperphagia, and increased linear growth in mice. The ability of a melanocortin agonist to acutely inhibit food intake when delivered to the paraventricular nucleus (PVN) was lost in MC4RF51L mice, as well as in WT mice in which a specific Gq/11α inhibitor was delivered to the PVN; this provided evidence that a Gsα-independent signaling pathway, namely Gq/11α, significantly contributes to the actions of MC4R on food intake and linear growth. These results suggest that a biased MC4R agonist that primarily activates Gq/11α may be a potential agent to treat obesity with limited untoward cardiovascular and other side effects.
Topics: Humans; Mice; Animals; Receptor, Melanocortin, Type 4; Hyperphagia; Obesity; Signal Transduction; Mutation
PubMed: 38175730
DOI: 10.1172/JCI165418 -
Frontiers in Genetics 2023Monogenic diabetes (MD) accounts for 3%-6% of all cases of diabetes. This prevalence is underestimated due to its overlapping clinical features with type 1 and type 2...
Monogenic diabetes (MD) accounts for 3%-6% of all cases of diabetes. This prevalence is underestimated due to its overlapping clinical features with type 1 and type 2 diabetes. Hence, genetic testing is the most appropriate tool for obtaining an accurate diagnosis. In Tunisia, few cohorts of MD have been investigated until now. The aim of this study is to search for pathogenic variants among 11 patients suspected of having MD in Tunisia using whole-exome sequencing (WES). WES was performed in 11 diabetic patients recruited from a collaborating medical center. The pathogenicity of genetic variation was assessed using combined filtering and bioinformatics prediction tools. The online ORVAL tool was used to predict the likelihood of combinations of pathogenic variations. Then, Sanger sequencing was carried out to confirm likely pathogenic predicted variants among patients and to check for familial segregation. Finally, for some variants, we performed structural modeling to study their impact on protein function. We identified novel variants related to MD in Tunisia. Pathogenic variants are located in several MODY and non-MODY genes. We highlighted the presence of syndromic forms of diabetes, including the Bardet-Biedl syndrome, Alström syndrome, and severe insulin resistance, as well as the presence of isolated diabetes with significantly reduced penetrance for Wolfram syndrome-related features. Idiopathic type 1 diabetes was also identified in one patient. In this study, we emphasized the importance of genetic screening for MD in patients with a familial history of diabetes, mainly among admixed and under-represented populations living in low- and middle-income countries. An accurate diagnosis with molecular investigation of MD may improve the therapeutic choice for better management of patients and their families. Additional research and rigorous investigations are required to better understand the physiopathological mechanisms of MD and implement efficient therapies that take into account genomic context and other related factors.
PubMed: 38162681
DOI: 10.3389/fgene.2023.1224284 -
Molecular Metabolism Jan 2024The consequences of mutations in genes associated with monogenic forms of diabetes on human pancreas development cannot be studied in a time-resolved fashion in vivo....
OBJECTIVE
The consequences of mutations in genes associated with monogenic forms of diabetes on human pancreas development cannot be studied in a time-resolved fashion in vivo. More specifically, if recessive mutations in the insulin gene influence human pancreatic endocrine lineage formation is still an unresolved question.
METHODS
To model the extremely reduced insulin levels in patients with recessive insulin gene mutations, we generated a novel knock-in H2B-Cherry reporter human induced pluripotent stem cell (iPSC) line expressing no insulin upon differentiation to stem cell-derived (SC-) β cells in vitro. Differentiation of iPSCs into the pancreatic and endocrine lineage, combined with immunostaining, Western blotting and proteomics analysis phenotypically characterized the insulin gene deficiency in SC-islets. Furthermore, we leveraged FACS analysis and confocal microscopy to explore the impact of insulin shortage on human endocrine cell induction, composition, differentiation and proliferation.
RESULTS
Interestingly, insulin-deficient SC-islets exhibited low insulin receptor (IR) signaling when stimulated with glucose but displayed increased IR sensitivity upon treatment with exogenous insulin. Furthermore, insulin shortage did not alter neurogenin-3 (NGN3)-mediated endocrine lineage induction. Nevertheless, lack of insulin skewed the SC-islet cell composition with an increased number in SC-β cell formation at the expense of SC-α cells. Finally, insulin deficiency reduced the rate of SC-β cell proliferation but had no impact on the expansion of SC-α cells.
CONCLUSIONS
Using iPSC disease modelling, we provide first evidence of insulin function in human pancreatic endocrine lineage formation. These findings help to better understand the phenotypic impact of recessive insulin gene mutations during pancreas development and shed light on insulin gene function beside its physiological role in blood glucose regulation.
Topics: Humans; Insulin; Induced Pluripotent Stem Cells; Cell Differentiation; Pancreas; Insulin, Regular, Human; Endocrine Cells
PubMed: 38103636
DOI: 10.1016/j.molmet.2023.101853 -
Diabetes, Metabolic Syndrome and... 2023Type 2 diabetes mellitus (T2DM) is one of the most widespread diseases in Western countries, and its incidence is constantly increasing. Epidemiological studies have... (Review)
Review
Type 2 diabetes mellitus (T2DM) is one of the most widespread diseases in Western countries, and its incidence is constantly increasing. Epidemiological studies have shown that in the next 20 years. The number of subjects affected by T2DM will double. In recent years, owing to the development and improvement in methods for studying the genome, several authors have evaluated the association between monogenic or polygenic genetic alterations and the development of metabolic diseases and complications. In addition, sedentary lifestyle and socio-economic and pandemic factors have a great impact on the habits of the population and have significantly contributed to the increase in the incidence of metabolic disorders, obesity, T2DM, metabolic syndrome, and liver steatosis. Moreover, patients with type 2 diabetes appear to respond to antihyperglycemic drugs. Only a minority of patients could be considered true non-responders. Thus, it appears clear that the main aim of precision medicine in T2DM is to identify patients who can benefit most from a specific drug class more than from the others. Precision medicine is a discipline that evaluates the applicability of genetic, lifestyle, and environmental factors to disease development. In particular, it evaluated whether these factors could affect the development of diseases and their complications, response to diet, lifestyle, and use of drugs. Thus, the objective is to find prevention models aimed at reducing the incidence of pathology and mortality and therapeutic personalized approaches, to obtain a greater probability of response and efficacy. This review aims to evaluate the applicability of precision medicine for T2DM, a healthcare burden in many countries.
PubMed: 38028995
DOI: 10.2147/DMSO.S390752 -
Frontiers in Endocrinology 2023Pediatric obesity has steadily increased in recent decades. Large-scale genome-wide association studies (GWAS) conducted primarily in Eurocentric adult populations have...
INTRODUCTION
Pediatric obesity has steadily increased in recent decades. Large-scale genome-wide association studies (GWAS) conducted primarily in Eurocentric adult populations have identified approximately 100 loci that predispose to obesity and type II diabetes. GWAS in children and individuals of non-European descent, both disproportionately affected by obesity, are fewer. Rare syndromic and monogenic obesities account for only a small portion of childhood obesity, so understanding the role of other genetic variants and their combinations in heritable obesities is key to developing targeted and personalized therapies. Tight and responsive regulation of the cAMP-dependent protein kinase (PKA) signaling pathway is crucial to maintaining healthy energy metabolism, and mutations in PKA-linked genes represent the most common cause of monogenic obesity.
METHODS
For this study, we performed targeted exome sequencing of 53 PKA signaling-related genes to identify variants in genomic DNA from a large, ethnically diverse cohort of obese or metabolically challenged youth.
RESULTS
We confirmed 49 high-frequency variants, including a novel variant in the PDE11A gene (c.152C>T). Several other variants were associated with metabolic characteristics within ethnic groups.
DISCUSSION
We conclude that a PKA pathway-specific variant search led to the identification of several new genetic associations with obesity in an ethnically diverse population.
Topics: Adult; Adolescent; Humans; Child; Pediatric Obesity; Genome-Wide Association Study; Diabetes Mellitus, Type 2; Mutation
PubMed: 38027204
DOI: 10.3389/fendo.2023.1272939 -
Endocrine Reviews May 2024Since hypothalamic obesity (HyOb) was first described over 120 years ago by Joseph Babinski and Alfred Fröhlich, advances in molecular genetic laboratory techniques... (Review)
Review
Since hypothalamic obesity (HyOb) was first described over 120 years ago by Joseph Babinski and Alfred Fröhlich, advances in molecular genetic laboratory techniques have allowed us to elucidate various components of the intricate neurocircuitry governing appetite and weight regulation connecting the hypothalamus, pituitary gland, brainstem, adipose tissue, pancreas, and gastrointestinal tract. On a background of an increasing prevalence of population-level common obesity, the number of survivors of congenital (eg, septo-optic dysplasia, Prader-Willi syndrome) and acquired (eg, central nervous system tumors) hypothalamic disorders is increasing, thanks to earlier diagnosis and management as well as better oncological therapies. Although to date the discovery of several appetite-regulating peptides has led to the development of a range of targeted molecular therapies for monogenic obesity syndromes, outside of these disorders these discoveries have not translated into the development of efficacious treatments for other forms of HyOb. This review aims to summarize our current understanding of the neuroendocrine physiology of appetite and weight regulation, and explore our current understanding of the pathophysiology of HyOb.
Topics: Humans; Obesity; Hypothalamic Diseases; Appetite; Neurosecretory Systems; Animals; Hypothalamus; Body Weight
PubMed: 38019584
DOI: 10.1210/endrev/bnad033 -
International Journal of Molecular... Nov 2023The leptin-melanocortin pathway is pivotal in appetite and energy homeostasis. Pathogenic variants in genes involved in this pathway lead to severe early-onset monogenic...
The leptin-melanocortin pathway is pivotal in appetite and energy homeostasis. Pathogenic variants in genes involved in this pathway lead to severe early-onset monogenic obesity (MO). The gene plays a central role in leptin-melanocortin signaling, and heterozygous variants in this gene are the most common cause of MO. A targeted gene panel consisting of 52 obesity-related genes was used to screen for variants associated with obesity. Variants were analyzed and filtered to identify potential disease-causing activity and validated using Sanger sequencing. We identified two novel heterozygous variants, c.253A>G p.Ser85Gly and c.802T>C p.Tyr268His, in the gene in two unrelated patients with morbid obesity and evaluated the functional impact of these variants. The impact of the variants on the gene was assessed using in silico prediction tools and molecular dynamics simulation. To further study the pathogenicity of the identified variants, GT1-7 cells were transfected with plasmid DNA encoding either wild-type or mutant variants. The effects of allelic variations in the gene on cAMP synthesis, protein level, and activation of PKA, ERB, and CREB signaling pathways in both stimulated and unstimulated ɑ-MSH paradigms were determined for their functional implications. In silico analysis suggested that the variants destabilized the structure and affected the overall dynamics of the protein, possibly leading to intracellular receptor retention. In vitro analysis of the functional impact of these variants showed a significant reduction in cell surface receptor expression and impaired extracellular ligand binding activity, leading to reduced cAMP production. Our analysis shows that the variants do not affect total protein expression; however, they are predicted to affect the post-translational localization of the protein to the cell surface and impair downstream signaling cascades such as PKA, ERK, and CREB signaling pathways. This finding might help our patients to benefit from the novel therapeutic advances for monogenic forms of obesity.
Topics: Humans; Leptin; Obesity, Morbid; Qatar; Alleles; alpha-MSH; Receptor, Melanocortin, Type 4; Mutation
PubMed: 38003551
DOI: 10.3390/ijms242216361 -
A diagnostic conundrum in Bardet-Biedl syndrome: when genetic diagnosis precedes clinical diagnosis.Endocrinology, Diabetes & Metabolism... Oct 2023Bardet-Biedl syndrome (BBS) is a rare, autosomal recessive, multisystem non-motile ciliopathy of progressive onset. It is primarily characterised by rod-cone dystrophy,...
SUMMARY
Bardet-Biedl syndrome (BBS) is a rare, autosomal recessive, multisystem non-motile ciliopathy of progressive onset. It is primarily characterised by rod-cone dystrophy, early-onset obesity and related complications, postaxial polydactyly, renal and genitourinary abnormalities, learning disabilities, and hypogonadism. The diagnosis is based on Beales' modified diagnostic criteria. We present a case of two monozygotic female twins, 17 years of age at presentation, referred for obesity since childhood. The initial hormonal work-up was negative and no dysmorphic features were noted. They were diagnosed with exogenous obesity. However, after ophthalmologic problems became apparent, rod-cone dystrophy was observed and genetic testing was performed. A mutation in the BBS2 gene led to the diagnosis of BBS, although the full diagnostic criteria were not met. This case not only highlights the need to raise awareness for BBS but also exposes two limitations of the current diagnostic standard. The first limitation is the low sensitivity of the clinical diagnostic model, due to the progressive onset and the high variability of the syndrome. The second limitation is the unclear role of genetic testing. As genetic testing becomes more widely available, genetic diagnosis preceding clinical diagnosis will become more common, leading to a diagnostic conundrum. We propose an update of the diagnostic model. A less strict application in the presence of confirmed genetic mutations should be applied, as this could facilitate earlier diagnosis and intervention. This is important because therapeutic agents are being developed that could have a significant impact on quality of life and prognosis.
LEARNING POINTS
Due to the low prevalence, the significant inter-and intrafamilial variation, and the slowly evolving phenotype, monogenic forms of obesity such as Bardet-Biedl syndrome are difficult to diagnose. Despite advances in the understanding of the presentation, pathophysiology and access to accurate genetic characterisation, a substantial number of diagnoses are still made by ophthalmology, as recognition of BBS in other departments of medicine, remains limited. Clinical diagnosis of BBS is based on Beales' modified diagnostic criteria which require the presence of four primary features or three primary features plus two secondary features. This model has its limitations. Due to the progressive onset of clinical symptoms, patients generally do not meet the diagnostic criteria early in life, leading to a delay in diagnosis. In addition, the role of genetic testing remains controversial. However, as it becomes more widely available, genetic diagnosis may precede a full clinical diagnosis. BBS has an impact on the quality of life and prognosis of both the patient and the family. Obesity management strategies are an important part of the multidisciplinary approach, as there is no cure available. Setmelanotide has shown promising results in a phase 3 trial, but its effect in clinical practice remains unproven.
PubMed: 37997784
DOI: 10.1530/EDM-23-0055 -
JCI Insight Dec 2023HNF1A haploinsufficiency underlies the most common form of human monogenic diabetes (HNF1A-maturity onset diabetes of the young [HNF1A-MODY]), and hypomorphic HNF1A...
HNF1A haploinsufficiency underlies the most common form of human monogenic diabetes (HNF1A-maturity onset diabetes of the young [HNF1A-MODY]), and hypomorphic HNF1A variants confer type 2 diabetes risk. But a lack of experimental systems for interrogating mature human islets has limited our understanding of how the transcription factor HNF1α regulates adult islet function. Here, we combined conditional genetic targeting in human islet cells, RNA-Seq, chromatin mapping with cleavage under targets and release using nuclease (CUT&RUN), and transplantation-based assays to determine HNF1α-regulated mechanisms in adult human pancreatic α and β cells. Short hairpin RNA-mediated (shRNA-mediated) suppression of HNF1A in primary human pseudoislets led to blunted insulin output and dysregulated glucagon secretion after transplantation in mice, recapitulating phenotypes observed in patients with diabetes. These deficits corresponded with altered expression of genes encoding factors critical for hormone secretion, including calcium channel subunits, ATPase transporters, and extracellular matrix constituents. Additionally, HNF1A loss led to upregulation of transcriptional repressors, providing evidence for a mechanism of transcriptional derepression through HNF1α. CUT&RUN mapping of HNF1α DNA binding sites in primary human islets imputed a subset of HNF1α-regulated genes as direct targets. These data elucidate mechanistic links between HNF1A loss and diabetic phenotypes in mature human α and β cells.
Topics: Animals; Humans; Mice; Diabetes Mellitus, Type 2; Gene Expression Regulation; Insulin; Insulin-Secreting Cells; Pancreas
PubMed: 37943614
DOI: 10.1172/jci.insight.170884 -
European Journal of Endocrinology Oct 2023Mutations in genes encoding proteins located in the leptin/melanocortin pathway have been identified in the rare cases of genetic obesities. Heterozygous variants of...
Mutations in genes encoding proteins located in the leptin/melanocortin pathway have been identified in the rare cases of genetic obesities. Heterozygous variants of MRAP2, encoding a G coupled-protein receptor accessory protein implicated in energy control notably via the melanocortin-4 receptor, have been recently identified. A 24-year-old patient with early-onset severe obesity (body mass index [BMI]: 64 kg/m2) associated with hypertension, respiratory complications, nonalcoholic fatty liver disease, and type 2 diabetes was referred to our department. Sleeve gastrectomy was successful. A new heterozygous variant in MRAP2 (NM_138409.4: c.154G>C/p.G52R) variant was identified in the patient DNA. Functional assessment confirmed that this new variant was pathogenic. We report a new pathogenic loss-of-function mutation in MRAP2 in a patient suffering from a severe multicomplicated obesity. This confirms the metabolic phenotype in patients with this monogenic form of obesity. Longer follow-up will be necessary. Our finding will allow a personalized medicine.
Topics: Humans; Young Adult; Adaptor Proteins, Signal Transducing; Bariatric Surgery; Carrier Proteins; Diabetes Mellitus, Type 2; Obesity; Receptor, Melanocortin, Type 4
PubMed: 37888144
DOI: 10.1093/ejendo/lvad132