TRKB AND OB-R · Functional characterization of TrkB and Ob-R mutations identified in severely obese children
FP6 — Marie Curie Actions (Human Resources and Mobility)
- Duration
- 2007-12-01 → 2009-06-30
- EU contribution
- €160,180
- Participants
- 1
- Scheme
- IIF
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Results in brief
Final Activity Report Summary - TRKB AND OB-R (Functional characterization of TrkB and Ob-R mutations identified in severely obese children)
Genome wide association studies have recently revealed the importance of fat mass and obesity associated gene (FTO) as an obesity-susceptibility gene. Based on in silico structural and sequence analysis, we have suggested that FTO is part of the family of Fe(II) 2-oxoglutarate (2-OG) oxygenases. Murine Fto can demethylate 3-methylthymine in vitro, in a 2-OG-dependent manner, suggesting a possible role in DNA repair. Fto is highly expressed in the hypothalamus of mice, including in the arcuate nucleus, where it is nutritionally regulated. However, nothing is known about its role in the regulation of energy balance. A key objective was to further investigate the role of FTO in humans, we asked whether there is a difference in the number of functionnaly significant mutations in FTO in lean and obese individuals. As a result we sequenced FTO coding exons and intron-exon boundaries in 1433 lean and 1433 severely obese individuals. Results: We identified 33 heterozygous non-synonymous variants in lean (2.3%) and 35 in obese (2.4%) individuals, with 8 mutations unique to the obese and 11 unique to the lean. Three mutations replace absolutely conserved residues; R316Q and R322Q in the catalytic domain, and R96H in the predicted substrate recognition lid of the protein. R316Q and R322Q were unable to catalyse the conversion of 2-OG to succinate in the presence or absence of 3-methylthymidine. R96H retained some basal activity, which was not enhanced by 3-methylthymidine. However, these mutations were found in both lean and obese individuals. The other missense mutations did not significantly alter FTO function. While these studies were on-going, we ascertained a large consanguineous multiplex family in which nine individuals presented with a previously unreported polymalformative syndrome including intra-uterine and post-natal growth retardation, severe psychomotor delay, structural and functional brain malformations, cardiac defects, genital anomalies, cleft palate and characteristic facial dysmorphism. All affected children died before the age of 3 years. Genetic screening revealed that all affected individuals were homozygous for R316Q, one of the mutations that ablate FTO function. While body composition has not yet been investigated, it is worth noting that an obese phenotype was NOT reported in the homozygous affected individuals or heterozygous carrier relatives. Thus, we have reported the first case of FTO deficiency in humans and found that FTO is absolutely necessary for normal development of the central nervous and cardiovascular systems. We can also conclude from our genetics studies that heterozygosity for a severely dysfunctional FTO allele is compatible with being either lean or obese in humans.
Data: CORDIS, © European Union
Project objective
The obesity epidemic is a pressing problem, resulting in diverse metabolic and psychological disorders.Identification of genes whose disruption causes obesity in rodents has led to rapid progress in understanding the signalling pathways responsible for the regulation of body weight in mammals, and an increasing number of severely obese humans have been found to carry mutations in those same genes.The fat-derived hormone leptin and the neurotrophin brain-derived neurotrophic factor (BDNF) are key players in the brain circuitry regulating energy homeostasis, and genetic disruption of their receptors, the leptin receptor (Ob-R) and the neurotrophin receptor Tropomyosin-related kinase (TrkB), causes hyperphagia and obesity in rodents and humans.Only one pathogenic mutation has been described to date in human for both TrkB and Ob-R and the data strongly indicate causality. Recently, the host laboratory has identified several novel mutations in TrkB and Ob-R in severely obese children.To determine whether these mutations result in non-functional receptors and thus are the causes of obesity in the affected individuals, we propose to make constructs of the mutant receptors and transfect them in appropriate cell lines.We will use state-of-the art methodologies for immunohistochemistry, confocal microscopy, Western blotting and receptor ligand binding assays to characterize the functionality of the presumed pathogenic variants.This proposal is part of a multidisciplinary project that will combine human genetics, human pathophysiology and functional genomics to explore the contribution of TrkB and Ob-R mutations to the development of severe childhood onset obesity.Moreover, the results of these experiments will provide new knowledge on the role of these signalling pathways in the regulation of body weight, and possibly lead to identification of new targets for the treatment of obesity.
Original text from CORDIS.
Participants
- University of Cambridge · CambridgeCoordinatorUnited Kingdom
Links
Data: CORDIS, © European Union