RESUMO
More than one-half billion people are obese, and despite progress in genetic research, much of the heritability of obesity remains enigmatic. Here, we identify a Trim28-dependent network capable of triggering obesity in a non-Mendelian, "on/off" manner. Trim28(+/D9) mutant mice exhibit a bi-modal body-weight distribution, with isogenic animals randomly emerging as either normal or obese and few intermediates. We find that the obese-"on" state is characterized by reduced expression of an imprinted gene network including Nnat, Peg3, Cdkn1c, and Plagl1 and that independent targeting of these alleles recapitulates the stochastic bi-stable disease phenotype. Adipose tissue transcriptome analyses in children indicate that humans too cluster into distinct sub-populations, stratifying according to Trim28 expression, transcriptome organization, and obesity-associated imprinted gene dysregulation. These data provide evidence of discrete polyphenism in mouse and man and thus carry important implications for complex trait genetics, evolution, and medicine.
Assuntos
Epigênese Genética , Haploinsuficiência , Proteínas Nucleares/genética , Obesidade/genética , Proteínas Repressoras/genética , Magreza/genética , Adolescente , Animais , Índice de Massa Corporal , Criança , Pré-Escolar , Humanos , Camundongos , Inquéritos Nutricionais , Polimorfismo Genético , Proteína 28 com Motivo TripartidoRESUMO
Metformin, the world's most prescribed anti-diabetic drug, is also effective in preventing type 2 diabetes in people at high risk1,2. More than 60% of this effect is attributable to the ability of metformin to lower body weight in a sustained manner3. The molecular mechanisms by which metformin lowers body weight are unknown. Here we show-in two independent randomized controlled clinical trials-that metformin increases circulating levels of the peptide hormone growth/differentiation factor 15 (GDF15), which has been shown to reduce food intake and lower body weight through a brain-stem-restricted receptor. In wild-type mice, oral metformin increased circulating GDF15, with GDF15 expression increasing predominantly in the distal intestine and the kidney. Metformin prevented weight gain in response to a high-fat diet in wild-type mice but not in mice lacking GDF15 or its receptor GDNF family receptor α-like (GFRAL). In obese mice on a high-fat diet, the effects of metformin to reduce body weight were reversed by a GFRAL-antagonist antibody. Metformin had effects on both energy intake and energy expenditure that were dependent on GDF15, but retained its ability to lower circulating glucose levels in the absence of GDF15 activity. In summary, metformin elevates circulating levels of GDF15, which is necessary to obtain its beneficial effects on energy balance and body weight, major contributors to its action as a chemopreventive agent.
Assuntos
Peso Corporal/efeitos dos fármacos , Metabolismo Energético/efeitos dos fármacos , Fator 15 de Diferenciação de Crescimento/metabolismo , Metformina/farmacologia , Administração Oral , Adulto , Idoso , Animais , Glicemia/análise , Glicemia/metabolismo , Dieta Hiperlipídica , Método Duplo-Cego , Ingestão de Energia/efeitos dos fármacos , Enterócitos/citologia , Enterócitos/efeitos dos fármacos , Feminino , Receptores de Fator Neurotrófico Derivado de Linhagem de Célula Glial/antagonistas & inibidores , Receptores de Fator Neurotrófico Derivado de Linhagem de Célula Glial/deficiência , Receptores de Fator Neurotrófico Derivado de Linhagem de Célula Glial/genética , Fator 15 de Diferenciação de Crescimento/sangue , Fator 15 de Diferenciação de Crescimento/deficiência , Fator 15 de Diferenciação de Crescimento/genética , Homeostase/efeitos dos fármacos , Humanos , Intestinos/citologia , Intestinos/efeitos dos fármacos , Masculino , Metformina/administração & dosagem , Camundongos , Camundongos Obesos , Pessoa de Meia-Idade , Redução de Peso/efeitos dos fármacosRESUMO
An Amendment to this paper has been published and can be accessed via a link at the top of the paper.
RESUMO
An acute increase in the circulating concentration of glucocorticoid hormones is essential for the survival of severe somatic stresses. Circulating concentrations of GDF15, a hormone that acts in the brain to reduce food intake, are frequently elevated in stressful states. We now report that GDF15 potently activates the hypothalamic-pituitary-adrenal (HPA) axis in mice and rats. A blocking antibody to the GDNF-family receptor α-like receptor completely prevented the corticosterone response to GDF15 administration. In wild-type mice exposed to a range of stressful stimuli, circulating levels of both corticosterone and GDF15 rose acutely. In the case of Escherichia coli or lipopolysaccharide injections, the vigorous proinflammatory cytokine response elicited was sufficient to produce a near-maximal HPA response, regardless of the presence or absence of GDF15. In contrast, the activation of the HPA axis seen in wild-type mice in response to the administration of genotoxic or endoplasmic reticulum toxins, which do not provoke a marked rise in cytokines, was absent in Gdf15-/- mice. In conclusion, consistent with its proposed role as a sentinel hormone, endogenous GDF15 is required for the activation of the protective HPA response to toxins that do not induce a substantial cytokine response. In the context of efforts to develop GDF15 as an antiobesity therapeutic, these findings identify a biomarker of target engagement and a previously unrecognized pharmacodynamic effect, which will require monitoring in human studies.
Assuntos
Fator 15 de Diferenciação de Crescimento/metabolismo , Sistema Hipotálamo-Hipofisário/metabolismo , Sistema Hipófise-Suprarrenal/metabolismo , Animais , Cisplatino/administração & dosagem , Cisplatino/farmacologia , Estresse do Retículo Endoplasmático/efeitos dos fármacos , Receptores de Fator Neurotrófico Derivado de Linhagem de Célula Glial/metabolismo , Glucocorticoides/metabolismo , Fator 15 de Diferenciação de Crescimento/administração & dosagem , Humanos , Lipopolissacarídeos , Camundongos , Ratos , Tunicamicina/farmacologiaRESUMO
An intergenic region of human chromosome 2 (2p25.3) harbors genetic variants which are among those most strongly and reproducibly associated with obesity. The gene closest to these variants is TMEM18, although the molecular mechanisms mediating these effects remain entirely unknown. Tmem18 expression in the murine hypothalamic paraventricular nucleus (PVN) was altered by changes in nutritional state. Germline loss of Tmem18 in mice resulted in increased body weight, which was exacerbated by high fat diet and driven by increased food intake. Selective overexpression of Tmem18 in the PVN of wild-type mice reduced food intake and also increased energy expenditure. We provide evidence that TMEM18 has four, not three, transmembrane domains and that it physically interacts with key components of the nuclear pore complex. Our data support the hypothesis that TMEM18 itself, acting within the central nervous system, is a plausible mediator of the impact of adjacent genetic variation on human adiposity.
Assuntos
Apetite/genética , Peso Corporal/genética , Proteínas de Membrana/metabolismo , Obesidade/genética , Animais , Masculino , Proteínas de Membrana/genética , Camundongos , Camundongos Knockout , Núcleo Hipotalâmico Paraventricular/metabolismo , Proteínas de Transporte VesicularRESUMO
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.
Assuntos
Composição Corporal/genética , Ingestão de Alimentos/genética , Metabolismo Energético/genética , Oxigenases de Função Mista/genética , Obesidade , Oxo-Ácido-Liases/genética , Dioxigenase FTO Dependente de alfa-Cetoglutarato , Animais , Peso Corporal/genética , Desenvolvimento Embrionário/genética , Regulação da Expressão Gênica no Desenvolvimento , Células Germinativas/metabolismo , Homeostase , Humanos , Masculino , Camundongos , Obesidade/genética , Obesidade/metabolismoRESUMO
Tre-2, BUB2, CDC16, 1 domain family member 4 (TBC1D4) (AS160) is a Rab-GTPase activating protein implicated in insulin-stimulated glucose transporter 4 (GLUT4) translocation in adipocytes and myotubes. To determine whether loss-of-function mutations in TBC1D4 might impair GLUT4 translocation and cause insulin resistance in humans, we screened the coding regions of this gene in 156 severely insulin-resistant patients. A female presenting at age 11 years with acanthosis nigricans and extreme postprandial hyperinsulinemia was heterozygous for a premature stop mutation (R363X) in TBC1D4. After demonstrating reduced expression of wild-type TBC1D4 protein and expression of the truncated protein in lymphocytes from the proband, we further characterized the biological effects of the truncated protein in 3T3L1 adipocytes. Prematurely truncated TBC1D4 protein tended to increase basal cell membrane GLUT4 levels (P = 0.053) and significantly reduced insulin-stimulated GLUT4 cell membrane translocation (P < 0.05). When coexpressed with wild-type TBC1D4, the truncated protein dimerized with full-length TBC1D4, suggesting that the heterozygous truncated variant might interfere with its wild-type counterpart in a dominant negative fashion. Two overweight family members with the mutation also manifested normal fasting glucose and insulin levels but disproportionately elevated insulin levels following an oral glucose challenge. This family provides unique genetic evidence of TBC1D4 involvement in human insulin action.
Assuntos
Acantose Nigricans/genética , Proteínas Ativadoras de GTPase/genética , Hiperinsulinismo/genética , Códon sem Sentido , Feminino , Transportador de Glucose Tipo 4/genética , Humanos , Masculino , Linhagem , Mutação PuntualRESUMO
Neuronatin (Nnat) has previously been reported to be part of a network of imprinted genes downstream of the chromatin regulator Trim28. Disruption of Trim28 or of members of this network, including neuronatin, results in an unusual phenotype of a bimodal body weight. To better characterise this variability, we examined the key contributors to energy balance in Nnat+/-p mice that carry a paternal null allele and do not express Nnat. Consistent with our previous studies, Nnat deficient mice on chow diet displayed a bimodal body weight phenotype with more than 30% of Nnat+/-p mice developing obesity. In response to both a 45% high fat diet and exposure to thermoneutrality (30 °C) Nnat deficient mice maintained the hypervariable body weight phenotype. Within a calorimetry system, food intake in Nnat+/-p mice was hypervariable, with some mice consuming more than twice the intake seen in wild type littermates. A hyperphagic response was also seen in Nnat+/-p mice in a second, non-home cage environment. An expected correlation between body weight and energy expenditure was seen, but corrections for the effects of positive energy balance and body weight greatly diminished the effect of neuronatin deficiency on energy expenditure. Male and female Nnat+/-p mice displayed subtle distinctions in the degree of variance body weight phenotype and food intake and further sexual dimorphism was reflected in different patterns of hypothalamic gene expression in Nnat+/-p mice. Loss of the imprinted gene Nnat is associated with a highly variable food intake, with the impact of this phenotype varying between genetically identical individuals.
Assuntos
Ingestão de Alimentos/fisiologia , Proteínas de Membrana/metabolismo , Proteínas do Tecido Nervoso/metabolismo , Obesidade/metabolismo , Animais , Biomarcadores/metabolismo , Peso Corporal , Dieta Hiperlipídica , Metabolismo Energético , Feminino , Perfilação da Expressão Gênica , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Obesidade/etiologia , Obesidade/patologiaRESUMO
In a recent issue of Cell, Orthofer et al. (2020) present a body of data from mice, flies, and humans that suggest (1) a physiological role for Alk in the normal control of energy balance across several species and (2) a possible contribution of genetic variants in or near ALK to the variability of adiposity in humans, more specifically at its lower end.
Assuntos
Obesidade , Magreza , Animais , Metabolismo Energético , Camundongos , Receptores Proteína Tirosina QuinasesRESUMO
The metabolic effects of leptin may involve both centrally and peripherally mediated actions with a component of the central actions potentially independent of alterations in food intake. Ob/ob mice have significant abnormalities in lipid metabolism, correctable by leptin administration. We used ob/ob mice to study the relative importance of the subtypes of actions of leptin (central vs. peripheral; food intake dependent vs. independent) on lipid metabolism. Mice were treated for 3 d with leptin, either centrally [intracerebroventricular (icv)] or peripherally (ip), and compared with mice pair-fed to the leptin-treated mice (PF) and with ad libitum-fed controls (C). All treatment groups (icv, ip, PF) showed indistinguishable changes in liver weight; hepatic steatosis; hepatic lipidemic profile; and circulating free fatty acids, triglycerides, and cholesterol lipoprotein profile. Changes in the expression of genes involved in lipogenesis and fatty acid oxidation in liver, muscle, and white fat were broadly similar in ip, icv, and PF groups. Leptin (both icv and ip) stimulated expression of both mitochondrial and peroxisomal acyl-coenzyme A oxidase (liver) and peroxisomal proliferator-activated receptor-alpha (skeletal muscle) to an extent not replicated by pair feeding. Leptin had profound effects on peripheral lipid metabolism, but the majority were explained by its effects on food intake. Leptin had additional centrally mediated effects to increase the expression of a limited number of genes concerned with fatty acid oxidation. Whereas we cannot exclude direct peripheral effects of leptin on certain aspects of lipid metabolism, we were unable to detect any such effects on the parameters measured in this study.
Assuntos
Encéfalo/efeitos dos fármacos , Ingestão de Alimentos/efeitos dos fármacos , Leptina/farmacologia , Metabolismo dos Lipídeos/efeitos dos fármacos , Adipócitos/efeitos dos fármacos , Adipócitos/metabolismo , Animais , Ácidos Graxos/sangue , Regulação da Expressão Gênica/efeitos dos fármacos , Injeções Intraperitoneais , Injeções Intraventriculares , Leptina/administração & dosagem , Metabolismo dos Lipídeos/genética , Fígado/efeitos dos fármacos , Fígado/metabolismo , Camundongos , Camundongos Obesos , Proteínas Musculares/genética , Músculo Esquelético/efeitos dos fármacos , Músculo Esquelético/metabolismo , Triglicerídeos/sangue , Redução de Peso/efeitos dos fármacos , Redução de Peso/genéticaRESUMO
Complete proopiomelanocortin (POMC) deficiency causes a human syndrome of hypoadrenalism, altered skin and hair pigmentation, and severe hyperphagic obesity. Heterozygote carriers of nonsense mutations are strongly predisposed to obesity. Pomc(+/-) mice have normal body weight on a chow diet but increase food intake and become more obese than wild-type littermates when placed on a high-fat diet. To further explore the mechanisms whereby dietary fat interacts with Pomc genotype to produce obesity, we examined Pomc-null, Pomc(+/-), and wild-type mice for changes in the components of energy balance in response to provision of a high-fat diet and macronutrient preference when presented with a selection of dietary choices. In contrast to wild-type mice, Pomc null mice did not increase their resting energy expenditure or their spontaneous physical activity when given a high-fat diet. Pomc(+/-) mice increased resting energy expenditure similarly to wild types, but their increase in physical activity was significantly less than that seen in wild-type mice. In two independent experimental tests of macronutrient preference, Pomc genotype was a strong predictor of dietary fat preference with Pomc null animals choosing to eat approximately twice as much fat, but similar amounts of carbohydrate and protein, as wild-type animals. Pomc(+/-) mice showed an intermediate response. In summary, POMC-derived peptides have influences on multiple aspects of the organism's response to the presentation of high-fat diet. This includes a major influence, readily discernible even in heterozygote animals, on the dietary preference for fat.
Assuntos
Dieta Aterogênica , Gorduras na Dieta/farmacologia , Preferências Alimentares/efeitos dos fármacos , Atividade Motora/genética , Pró-Opiomelanocortina/fisiologia , Termogênese/genética , Animais , Gorduras na Dieta/administração & dosagem , Metabolismo Energético/efeitos dos fármacos , Metabolismo Energético/genética , Masculino , Camundongos , Camundongos Knockout , Atividade Motora/efeitos dos fármacos , Pró-Opiomelanocortina/genética , Termogênese/efeitos dos fármacosRESUMO
The neurotrophin brain-derived neurotrophic factor (BDNF) inhibits food intake, and rodent models of BDNF disruption all exhibit increased food intake and obesity, as well as hyperactivity. We report an 8-year-old girl with hyperphagia and severe obesity, impaired cognitive function, and hyperactivity who harbored a de novo chromosomal inversion, 46,XX,inv(11)(p13p15.3), a region encompassing the BDNF gene. We have identified the proximal inversion breakpoint that lies 850 kb telomeric of the 5' end of the BDNF gene. The patient's genomic DNA was heterozygous for a common coding polymorphism in BDNF, but monoallelic expression was seen in peripheral lymphocytes. Serum concentration of BDNF protein was reduced compared with age- and BMI-matched subjects. Haploinsufficiency for BDNF was associated with increased ad libitum food intake, severe early-onset obesity, hyperactivity, and cognitive impairment. These findings provide direct evidence for the role of the neurotrophin BDNF in human energy homeostasis, as well as in cognitive function, memory, and behavior.
Assuntos
Fator Neurotrófico Derivado do Encéfalo/genética , Aberrações Cromossômicas , Inversão Cromossômica/genética , Transtornos Cognitivos/genética , Hipercinese/genética , Hiperfagia/genética , Mutação , Obesidade/genética , Adulto , Fator Neurotrófico Derivado do Encéfalo/sangue , Cromossomos Artificiais Bacterianos , DNA/genética , DNA/isolamento & purificação , Feminino , HumanosRESUMO
Thyroid hormones (THs) act in the brain to modulate energy balance. We show that central triiodothyronine (T3) regulates de novo lipogenesis in liver and lipid oxidation in brown adipose tissue (BAT) through the parasympathetic (PSNS) and sympathetic nervous system (SNS), respectively. Central T3 promotes hepatic lipogenesis with parallel stimulation of the thermogenic program in BAT. The action of T3 depends on AMP-activated protein kinase (AMPK)-induced regulation of two signaling pathways in the ventromedial nucleus of the hypothalamus (VMH): decreased ceramide-induced endoplasmic reticulum (ER) stress, which promotes BAT thermogenesis, and increased c-Jun N-terminal kinase (JNK) activation, which controls hepatic lipid metabolism. Of note, ablation of AMPKα1 in steroidogenic factor 1 (SF1) neurons of the VMH fully recapitulated the effect of central T3, pointing to this population in mediating the effect of central THs on metabolism. Overall, these findings uncover the underlying pathways through which central T3 modulates peripheral metabolism.
Assuntos
Metabolismo Energético , Hipotálamo/metabolismo , Proteína Quinase 8 Ativada por Mitógeno/metabolismo , Transdução de Sinais , Hormônios Tireóideos/metabolismo , Tecido Adiposo Marrom/metabolismo , Animais , Metabolismo dos Lipídeos , Fígado/metabolismo , Masculino , Camundongos Endogâmicos C57BL , Ratos , Ratos Sprague-Dawley , Termogênese , Tri-Iodotironina/metabolismoRESUMO
Functional disruption of either MC3R or MC4R results in obesity, implicating both in the control of energy homeostasis. The ligands for these receptors are derived from the prohormone proopiomelancortin (POMC), which is posttranslationally processed to produce a set of melanocortin peptides with a range of activities at the MC3R and MC4R. The relative importance of each of these peptides alpha-MSH, gamma3-MSH, gamma2-MSH, gamma-lipotropin (gamma-LPH) and, in man but not in rodents, beta-MSH] in the maintenance of energy homeostasis is, as yet, unclear. To investigate this further, equimolar amounts (2 nmol) of each peptide were centrally administered to freely feeding, corticosterone-supplemented, Pomc null (Pomc-/-) mice. After a single dose at the onset of the dark cycle, alpha-MSH had the most potent anorexigenic effect, reducing food intake to 35% of sham-treated animals. beta-MSH, gamma-LPH, and gamma3- and gamma2-MSH all reduced food intake but to a lesser degree. The effects of peptide administration over 3 d were also assessed. Only alpha-MSH significantly reduced body weight, affecting both fat and lean mass. Other peptides had no significant effect on body weight. Pair-feeding of sham-treated mice to those treated with alpha-MSH resulted in identical changes in total weight, fat and lean mass indicating that the effects of alpha-MSH were primarily due to reduced food intake rather than increased energy expenditure. Although other melanocortins can reduce food intake in the short-term, only alpha-MSH can reduce the excess fat and lean mass found in Pomc-/- mice, mediated largely through an effect on food intake.
Assuntos
Peso Corporal/efeitos dos fármacos , Sistema Nervoso Central/efeitos dos fármacos , Ingestão de Alimentos/efeitos dos fármacos , Melanocortinas/farmacologia , Pró-Opiomelanocortina/genética , Animais , Regulação do Apetite/efeitos dos fármacos , Regulação do Apetite/fisiologia , Vias de Administração de Medicamentos , Masculino , Melanocortinas/administração & dosagem , Camundongos , Camundongos Knockout , Placebos , Pró-Opiomelanocortina/química , Redução de Peso/efeitos dos fármacos , alfa-MSH/farmacologia , alfa-MSH/fisiologiaRESUMO
Pro-opiomelanocortin (POMC) is a polypeptide precursor that undergoes extensive processing to yield a range of peptides with biologically diverse functions. POMC-derived ACTH is vital for normal adrenal function and the melanocortin alpha-MSH plays a key role in appetite control and energy homeostasis. However, the roles of peptide fragments derived from the highly conserved N-terminal region of POMC are less well characterized. We have used mice with a null mutation in the Pomc gene (Pomc(-/-)) to determine the in vivo effects of synthetic N-terminal 1-28 POMC, which has been shown previously to possess adrenal mitogenic activity. 1-28 POMC (20 mug) given s.c. for 10 days had no effect on the adrenal cortex of Pomc(-/-) mice, with resultant cortical morphology and plasma corticosterone levels being indistinguishable from sham treatment. Concurrent administration of 1-28 POMC and 1-24 ACTH (30 mug/day) resulted in changes identical to 1-24 ACTH treatment alone, which consisted of upregulation of steroidogenic enzymes, elevation of corticosterone levels, hypertrophy of the zona fasciculate, and regression of the X-zone. However, treatment of corticosterone-depleted Pomc(-/-) mice with 1-28 POMC reduced cumulative food intake and total body weight. These anorexigenic effects were ameliorated when the peptide was administered to Pomc(-/-) mice with circulating corticosterone restored either to a low physiological level by corticosterone-supplemented drinking water (CORT) or to a supraphysiological level by concurrent 1-24 ACTH administration. Further, i.c.v. administration of 1-28 POMC to CORT-treated Pomc(-/-) mice had no effect on food intake or body weight. In wild-type mice, the effects of 1-28 POMC upon food intake and body weight were identical to sham treatment, but 1-28 POMC was able to ameliorate the hyperphagia induced by concurrent 1-24 ACTH treatment. In a mouse model which lacks all endogenous POMC peptides, s.c. treatment with synthetic 1-28 POMC alone can reduce food intake and body weight, but has no impact upon adrenal growth or steroidogenesis.
Assuntos
Glândulas Suprarrenais/efeitos dos fármacos , Hormônio Adrenocorticotrópico/farmacologia , Peso Corporal/efeitos dos fármacos , Ingestão de Alimentos/efeitos dos fármacos , Fragmentos de Peptídeos/administração & dosagem , Pró-Opiomelanocortina/administração & dosagem , Glândulas Suprarrenais/crescimento & desenvolvimento , Hormônio Adrenocorticotrópico/análise , Hormônio Adrenocorticotrópico/metabolismo , Animais , Contagem de Células , Proliferação de Células , Feminino , Immunoblotting/métodos , Camundongos , Camundongos Knockout , Pró-Opiomelanocortina/genética , Pró-Opiomelanocortina/metabolismoRESUMO
OBJECTIVE: Loss of function FTO mutations significantly impact body composition in humans and mice, with Fto-deficient mice reported to resist the development of obesity in response to a high-fat diet (HFD). We aimed to further explore the interactions between FTO and HFD and determine if FTO can influence the adverse metabolic consequence of HFD. METHODS: We studied mice deficient in FTO in two well validated models of leptin resistance (HFD feeding and central palmitate injection) to determine how Fto genotype may influence the action of leptin. Using transcriptomic analysis of hypothalamic tissue to identify relevant pathways affected by the loss of Fto, we combined data from co-immunoprecipitation, yeast 2-hybrid and luciferase reporter assays to identify mechanisms through which FTO can influence the development of leptin resistant states. RESULTS: Mice deficient in Fto significantly increased their fat mass in response to HFD. Fto (+/-) and Fto (-/-) mice remained sensitive to the anorexigenic effects of leptin, both after exposure to a HFD or after acute central application of palmitate. Genes encoding components of the NFкB signalling pathway were down-regulated in the hypothalami of Fto-deficient mice following a HFD. When this pathway was reactivated in Fto-deficient mice with a single low central dose of TNFα, the mice became less sensitive to the effect of leptin. We identified a transcriptional coactivator of NFкB, TRIP4, as a binding partner of FTO and a molecule that is required for TRIP4 dependent transactivation of NFкB. CONCLUSIONS: Our study demonstrates that, independent of body weight, Fto influences the metabolic outcomes of a HFD through alteration of hypothalamic NFкB signalling. This supports the notion that pharmacological modulation of FTO activity might have the potential for therapeutic benefit in improving leptin sensitivity, in a manner that is influenced by the nutritional environment.
RESUMO
The fat mass and obesity-associated (FTO) gene was placed center stage when common intronic variants within the gene were robustly associated with human obesity. Murine models of perturbed Fto expression have shown effects on body weight and composition. However, a clear understanding of the link between FTO intronic variants and FTO activity has remained elusive. Two recent reports now indicate that obesity-associated SNPs appear functionally connected not with FTO but with two neighboring genes: IRX3 and RPGRIP1L. Here, we review these new findings and consider the implications for future analysis of GWAS hits.
Assuntos
Loci Gênicos , Oxigenases de Função Mista/genética , Obesidade/genética , Animais , Dopamina/metabolismo , Estudo de Associação Genômica Ampla , Humanos , Polimorfismo de Nucleotídeo Único/genéticaRESUMO
An understanding of the mechanisms underlying body-weight regulation is crucial to tackle the growing problem of obesity. Recent technological advances in the analysis of genetic variation have given novel insights into the molecular basis of common disease. In particular, genomic variants in the fat mass and obesity-associated (FTO) gene have been consistently associated with human adiposity and metabolic disorders. Studies of the product of this previously mysterious gene have formed a vanguard in the quest to turn statistical association into hard biology. In this review, we examine data from human genetic and murine studies that explore the potential role of FTO, a member of the Fe(II)- and 2-oxoglutarate-dependent oxygenase superfamily, in the regulation of energy homeostasis and metabolism.
Assuntos
Obesidade/genética , Proteínas/genética , Dioxigenase FTO Dependente de alfa-Cetoglutarato , Animais , Índice de Massa Corporal , Metilação de DNA , Ingestão de Energia , Metabolismo Energético/genética , Predisposição Genética para Doença , Homeostase/genética , Humanos , Camundongos , Mutação , Fenótipo , Polimorfismo de Nucleotídeo Único/genética , Proteínas/química , Proteínas/fisiologiaRESUMO
OBJECTIVE: Genetic defects in human pericentrin (PCNT), encoding the centrosomal protein pericentrin, cause a form of osteodysplastic primordial dwarfism that is sometimes reported to be associated with diabetes. We thus set out to determine the prevalence of diabetes and insulin resistance among patients with PCNT defects and examined the effects of pericentrin depletion on insulin action using 3T3-L1 adipocytes as a model system. RESEARCH DESIGN AND METHODS: A cross-sectional metabolic assessment of 21 patients with PCNT mutations was undertaken. Pericentrin expression in human tissues was profiled using quantitative real-time PCR. The effect of pericentrin knockdown on insulin action and adipogenesis in 3T3-L1 adipocytes was determined using Oil red O staining, gene-expression analysis, immunoblotting, and glucose uptake assays. Pericentrin expression and localization also was determined in skeletal muscle. RESULTS: Of 21 patients with genetic defects in PCNT, 18 had insulin resistance, which was severe in the majority of subjects. Ten subjects had confirmed diabetes (mean age of onset 15 years [range 5-28]), and 13 had metabolic dyslipidemia. All patients without insulin resistance were younger than 4 years old. Knockdown of pericentrin in adipocytes had no effect on proximal insulin signaling but produced a twofold impairment in insulin-stimulated glucose uptake, approximately commensurate with an associated defect in cell proliferation and adipogenesis. Pericentrin was highly expressed in human skeletal muscle, where it showed a perinuclear distribution. CONCLUSIONS: Severe insulin resistance and premature diabetes are common features of PCNT deficiency but are not congenital. Partial failure of adipocyte differentiation may contribute to this, but pericentrin deficiency does not impair proximal insulin action in adipocytes.