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Background A homozygous loss-of-function mutation p.(Arg316Gln) in the fat mass and obesity-associated ( FTO ) gene, which encodes for an iron and 2-oxoglutarate-dependent oxygenase, was previously identified in a large family in which nine affected individuals present with a lethal syndrome characterised by growth retardation and multiple malformations. To date, no other pathogenic mutation in FTO has been identified as a cause of multiple congenital malformations. Methods We investigated a 21-month-old girl who presented distinctive facial features, failure to thrive, global developmental delay, left ventricular cardiac hypertrophy, reduced vision and bilateral hearing loss. We performed targeted next-generation sequencing of 4813 clinically relevant genes in the patient and her parents. Results We identified a novel FTO homozygous missense mutation (c.956C>T; p.(Ser319Phe)) in the affected individual. This mutation affects a highly conserved residue located in the same functional domain as the previously characterised mutation p.(Arg316Gln). Biochemical studies reveal that p.(Ser319Phe) FTO has reduced 2-oxoglutarate turnover and N -methyl-nucleoside demethylase activity. Conclusion Our findings are consistent with previous reports that homozygous mutations in FTO can lead to rare growth retardation and developmental delay syndrome, and further support the proposal that FTO plays an important role in early development of human central nervous and cardiovascular systems.

Lymphangioleiomyomatosis (LAM) is a progressive destructive neoplasm of the lung associated with inactivating mutations in the TSC1 or TSC2 tumor suppressor genes. Cell or animal models that accurately reflect the pathology of LAM have been challenging to develop. Here we generated a robust human cell model of LAM by reprogramming TSC2 mutation-bearing fibroblasts from a patient with both Tuberous Sclerosis Complex (TSC) and LAM (TSC-LAM) into induced pluripotent stem cells (iPSCs), followed by selection of cells that resemble those found in LAM tumors by unbiased in vivo differentiation. We established expandable cell lines under smooth muscle cell (SMC) growth conditions that retained a patient-specific genomic TSC2+/− mutation and recapitulated the molecular and functional characteristics of pulmonary LAM cells. These include multiple indicators of hyperactive mTORC1 signaling, presence of specific neural crest and SMC markers, expression of VEGF-D and female sex hormone receptors, reduced autophagy, and metabolic reprogramming. Intriguingly, the LAM-like features of these cells suggest that haploinsufficiency at the TSC2 locus contributed to LAM pathology, and demonstrated that iPSC reprogramming and SMC lineage differentiation of somatic patient cells with germline mutations was a viable approach to generate LAM-like cells. The patient-derived SMC lines we have developed thus represent a novel cellular model of LAM which can advance our understanding of disease pathogenesis and develop therapeutic strategies against LAM.

High levels of reactive oxygen species (ROS) are intricately linked to obesity and associated pathologies, notably insulin resistance and type 2 diabetes. However, ROS are also thought to be important in intracellular signaling, which may paradoxically be required for insulin sensitivity. Many theories have been developed to explain this apparent paradox, which have broadened our understanding of these important small molecules. While many sites for intracellular ROS production have been described, mitochondrial generated ROS remain a major contributor in most cell types. Mitochondrial ROS generation is controlled by a number of factors described in this review. Moreover, these studies have established both a demand for novel sensitive approaches to measure ROS, as well as a need to standardize and review their suitability for different applications.To properly assess levels of ROS and mitochondrial ROS in the development of obesity and its complications, a growing number of tools have been developed. This paper reviews many of the common methods for the investigation of ROS in mitochondria, cell, animal, and human models.Available approaches can be generally divided into those that measure ROS-induced damage (e.g., DNA, lipid, and protein damage); those that measure antioxidant levels and redox ratios; and those that use novel biosensors and probes for a more direct measure of different forms of ROS (e.g., 2',7'-di-chlorofluorescein (DCF), dihydroethidium (DHE) and its mitochondrial targeted form (MitoSOX), Amplex Red, roGFP, HyPer, mt-cpYFP, ratiometric HAdvances in these techniques will undoubtedly advance the understanding of ROS in obesity and may help resolve unanswered questions in the field.

Type 2 diabetes prevalence is increasing worldwide. Treatments are available, but glycaemic control is not always effective in many patients. Better models are needed to create new and improved therapies and to expand our understanding of how type 2 diabetes begins and progresses. Translational research involves the transformation of knowledge from basic scientific discoveries to impacting on public health. This can allow identification of novel molecular mechanisms underlying the disease which can lead to preventative measures, biomarkers for diagnosis, or future therapies. Generation of genetically modified mice has allowed us to investigate the function of genes and develop reproducible models in which the phenotype of the animal can be tested. Mouse models have already given us insight into glucose metabolism and insulin secretion, identified novel pathways, and have been used to confirm genome-wide association studies. In this review we discuss the use of the mouse to clarify human genome-wide association study loci, understand genes and pathways involved in type 2 diabetes, and uncover novel targets for drug discovery.

Skeletal muscle mitochondrial dysfunction has been documented in patients with type 2 diabetes mellitus; however, specific respiratory defects and their mechanisms are poorly understood. The aim of the current study was to examine oxidative phosphorylation and electron transport chain (ETC) supercomplex assembly in rectus abdominis muscles of 10 obese diabetic and 10 obese non-diabetic individuals.Twenty obese women undergoing Roux-en-Y gastric bypass surgery were recruited for this study. Muscle samples were obtained intraoperatively and subdivided for multiple analyses, including high-resolution respirometry and assessment of supercomplex assembly. Clinical data obtained from referring physicians were correlated with laboratory findings.Participants in both groups were of a similar age, weight and BMI. Mitochondrial respiration rates were markedly reduced in diabetic vs non-diabetic patients. This defect was observed during maximal ADP-stimulated respiration in the presence of complex I-linked substrates and complex I- and II-linked substrates, and during maximal uncoupled respiration. There were no differences in fatty acid (octanoyl carnitine) supported respiration, leak respiration or isolated activity of cytochrome c oxidase. Intriguingly, significant correlations were found between glycated haemoglobin (HbA1c) levels and maximal respiration or respiration supported by complex I, complex I and II or fatty acid. In the muscle of diabetic patients, blue native gel electrophoresis revealed a striking decrease in complex I, III and IV containing ETC supercomplexes.These findings support the hypothesis that ETC supercomplex assembly may be an important underlying mechanism of muscle mitochondrial dysfunction in type 2 diabetes mellitus.

ENU (N-ethyl-N-nitrosourea) is a chemical mutagen that randomly induces point mutations in DNA. Since the 1990s ENU has been successfully used as a means to obtain mouse mutants using both gene-driven (reverse genetics) and phenotype-driven (forward genetics) approaches. A high-efficiency ENU approach results in approx. 25 functional mutations per genome; most of these will result in hypomorphic alleles. Our group has recently begun using ENU mutagenesis as a tool for understanding lung development and disease. In collaboration with other groups at MRC Harwell, we have undertaken a screen for recessive mutations affecting mouse lung development. We are currently pursuing two lines identified from this screen, Hel (head, eye and lung) and RecBA17. Both these lines exhibit lung defects and we believe that by studying the phenotypes and identifying the causative mutations, we may also shed light on lung disease pathogenesis. In collaboration with Bill Cookson and Miriam Moffatt, we are also taking a gene-driven approach for understanding asthma. Using the Harwell ENU sperm archive, we have recovered mouse lines harbouring mutations in the asthma-susceptibility genes Phf11 (PHD finger protein 11) and Dpp10 (dipeptidylpeptidase 10). Functional analyses of these alleles are currently under way.

© 2014 Osborn et al. Common intronic variants in the Human fat mass and obesity-associated gene (FTO) are found to be associated with an increased risk of obesity. Overexpression of FTO correlates with increased food intake and obesity, whilst loss-of-function results in lethality and severe developmental defects. Despite intense scientific discussions around the role of FTO in energy metabolism, the function of FTO during development remains undefined. Here, we show that loss of Fto leads to developmental defects such as growth retardation, craniofacial dysmorphism and aberrant neural crest cells migration in Zebrafish. We find that the important developmental pathway, Wnt, is compromised in the absence of FTO, both in vivo (zebrafish) and in vitro (Fto−/− MEFs and HEK293T). Canonical Wnt signalling is down regulated by abrogated β-Catenin translocation to the nucleus whilst non-canonical Wnt/Ca2+ pathway is activated via its key signal mediators CaMKII and PKCδ. Moreover, we demonstrate that loss of Fto results in short, absent or disorganised cilia leading to situs inversus, renal cystogenesis, neural crest cell defects and microcephaly in Zebrafish. Congruently, Fto knockout mice display aberrant tissue specific cilia. These data identify FTO as a protein-regulator of the balanced activation between canonical and non-canonical branches of the Wnt pathway. Furthermore, we present the first evidence that FTO plays a role in development and cilia formation/function.

The strongest BMI–associated GWAS locus in humans is the FTO gene. Rodent studies demonstrate a role for FTO in energy homeostasis and body composition. The phenotypes observed in loss of expression studies are complex with perinatal lethality, stunted growth from weaning, and significant alterations in body composition. Thus understanding how and where Fto regulates food intake, energy expenditure, and body composition is a challenge. To address this we generated a series of mice with distinct temporal and spatial loss of Fto expression. Global germline loss of Fto resulted in high perinatal lethality and a reduction in body length, fat mass, and lean mass. When ratio corrected for lean mass, mice had a significant increase in energy expenditure, but more appropriate multiple linear regression normalisation showed no difference in energy expenditure. Global deletion of Fto after the in utero and perinatal period, at 6 weeks of age, removed the high lethality of germline loss. However, there was a reduction in weight by 9 weeks, primarily as loss of lean mass. Over the subsequent 10 weeks, weight converged, driven by an increase in fat mass. There was a switch to a lower RER with no overall change in food intake or energy expenditure. To test if the phenotype can be explained by loss of Fto in the mediobasal hypothalamus, we sterotactically injected adeno-associated viral vectors encoding Cre recombinase to cause regional deletion. We observed a small reduction in food intake and weight gain with no effect on energy expenditure or body composition. Thus, although hypothalamic Fto can impact feeding, the effect of loss of Fto on body composition is brought about by its actions at sites elsewhere. Our data suggest that Fto may have a critical role in the control of lean mass, independent of its effect on food intake., Author Summary The fat mass and obesity (FTO) gene has one of the strongest links with body mass index (BMI) in the human population. One in six people have the “risk” alteration and weigh 3 kg more than those with the unaltered gene, but it is not understood how this gene influences BMI and obesity. We set out to understand how and where in the body FTO affects food intake, energy expenditure, and body composition using a mouse model that can be manipulated to lack FTO at particular times and/or places. Removing FTO everywhere from conception had a dramatic effect on body composition and resulted in stunted growth and some lethality. Removing FTO everywhere but only in adult animals resulted in better viability and normal growth but, surprisingly, reduced lean mass and increased fat mass with a change in the type of metabolic fuel being used. Finally, we removed FTO from the hypothalamus of adult animals, an important brain region involved in energy metabolism. These animals showed a mild reduction in food intake and weight gain. Our experiments show that FTO has an important role in body composition and that other brain areas outside of the hypothalamus are also important in determining its effects.

The genomes of many species have now been completely sequenced including human and mouse. Great progress has been made in understanding the complex genetics that underlie diabetes and obesity in human populations. One of the current challenges is the functional identification and characterization of the genes within loci that are being mapped. There are many approaches to this problem and this review outlines the valuable role that the mouse can play. We outline the mouse resources that are available to the research community, including knockouts with conditional potential for every gene, and the efforts of the International Mouse Phenotyping Consortium to attach phenotype information to these genes. We also briefly consider the potential of TALEN technology to tailor-make new mouse models of specific mutations discovered in humans. Finally, we consider the recent progress in characterizing the GWAS genes FTO, TCF7L2, CDKAL1, and SLC30A8 in engineered mouse models.