RESUMO
This review critically reappraises recent scientific evidence concerning central leptin insufficiency versus leptin resistance formulations to explain metabolic and neural disorders resulting from subnormal or defective leptin signaling in various sites in the brain. Research at various fronts to unravel the complexities of the neurobiology of leptin is surveyed to provide a comprehensive account of the neural and metabolic effects of environmentally imposed fluctuations in leptin availability at brain sites and the outcome of newer technology to restore leptin signaling in a site-specific manner. The cumulative new knowledge favors a unified central leptin insufficiency syndrome over the, in vogue, central resistance hypothesis to explain the global adverse impact of deficient leptin signaling in the brain. Furthermore, the leptin insufficiency syndrome delineates a novel role of leptin in the hypothalamus in restraining rhythmic pancreatic insulin secretion while concomitantly enhancing glucose metabolism and non-shivering thermogenic energy expenditure, sequelae that would otherwise promote fat accrual to store excess energy resulting from consumption of energy-enriched diets. A concerted effort should now focus on development of newer technologies for delivery of leptin or leptin mimetics to specifically target neural pathways for remediation of diverse ailments encompassing the central leptin insufficiency syndrome.
Assuntos
Leptina/deficiência , Leptina/metabolismo , Doenças Metabólicas , Doenças do Sistema Nervoso , Obesidade , Animais , Humanos , Doenças Metabólicas/etiologia , Doenças Metabólicas/metabolismo , Doenças Metabólicas/terapia , Doenças do Sistema Nervoso/etiologia , Doenças do Sistema Nervoso/metabolismo , Doenças do Sistema Nervoso/terapia , Obesidade/etiologia , Obesidade/metabolismo , Obesidade/terapia , SíndromeRESUMO
Low-grade systemic inflammation, as indicated by increased circulating levels of inflammatory markers CRP and IL-6, is linked to increased risks for cardiovascular diseases (CVD) and diabetes mellitus in obese subjects. Whereas hyperleptinemia in obesity are associated with increased CRP and IL-6 release, the hypothalamic versus peripheral site of leptin action has not been ascertained. The effects of increased leptin supply selectively in the hypothalamus by gene therapy on pro-inflammatory CRP and IL-6 levels and on markers of diabetes in the circulation of ob/ob mice displaying either age-related or dietary obesity were assessed. A recombinant adeno-associated viral vector encoding either green-fluorescent protein (control) or leptin gene was injected intracerebroventricularly. Five weeks later, one-half of each of the vector groups was switched to high-fat diet consumption and the other half continued to consume regular low-fat chow diet. Body weight and visceral white adipose tissue were drastically reduced and hyperinsulinemia and hyperglycemia were abrogated by leptin gene therapy, independent of the dietary fat content. The elevated plasma CRP and IL-6 levels seen in obese ob/ob mice receiving the control vector, regardless of the fat content of the diet, were markedly suppressed by increased hypothalamic leptin in both groups. The results show for the first time that leptin deficiency elevates and reinstatement of leptin selectively in the hypothalamus suppresses the release of pro-inflammatory biomarkers, a response likely to alleviate CVD associated with obesity.
Assuntos
Proteína C-Reativa/análise , Complicações do Diabetes/imunologia , Hipotálamo/metabolismo , Interleucina-6/sangue , Leptina/genética , Obesidade/complicações , Animais , Biomarcadores/sangue , Peso Corporal , Vetores Genéticos/administração & dosagem , Leptina/metabolismo , Masculino , Camundongos , Camundongos Obesos , Camundongos TransgênicosRESUMO
Multidisciplinary research from my and my colleagues' laboratory has shown that disruption at various levels of leptin signaling to the interactive hypothalamic network of neuropeptide Y (NPY) and cohorts contributes to the antecedent pathophysiologic sequelae of the disease cluster of the metabolic syndrome. Disruptions in NPY signaling due to high or low abundance of NPY and cognate receptors dysregulate the homeostatic milieu to promote hyperinsulinemia, hyperglycemia, fat accrual, and overt diabetes. Hyperleptinemia induced by consumption of energy-rich diets inhibits leptin transport across the blood-brain barrier and thereby produces leptin insufficiency in the hypothalamus. Sustained leptin insufficiency results in loss of hypothalamic restraint on pancreatic insulin secretion and diminished glucose metabolism and energy expenditure. This chain of events culminates in hyperinsulinemia, hyperglycemia, and diabetes. Our recent studies have shown that increasing the supply of leptin centrally by gene therapy reinstates the restraint on hypothalamic NPY signaling and ameliorates diabetes and the attendant disease cluster of the metabolic syndrome. Thus, newer therapies that would enhance leptin transport across the blood-brain barrier in a timely manner or reinstate leptin restraint on NPY signaling through central leptin gene therapy or pharmacologically with leptin mimetics are likely to curtail the pathophysiologic sequelae of diabetes and related ailments of the metabolic syndrome.
Assuntos
Diabetes Mellitus/metabolismo , Diabetes Mellitus/terapia , Leptina/metabolismo , Síndrome Metabólica/metabolismo , Síndrome Metabólica/terapia , Neuropeptídeo Y/metabolismo , Animais , Hipotálamo/fisiopatologia , Camundongos , RatosRESUMO
The interactive network of neuropeptide Y (NPY) and cohorts is necessary for integrating the hypothalamic regulation of appetite and energy expenditure with the endocrine and neuroendocrine systems on a daily basis. Genetic and environmental factors that produce an insufficiency of leptin restraint on NPY and cognate receptors deregulate the homeostasis to engender various life-threatening risk factors. Recent studies from our laboratory show that neurotherapy consisting of a single central administration of recombinant adeno-associated virus vector encoding the leptin gene can repress the hypothalamic NPY system for the lifetime of rodents. A major benefit of this stable tonic restraint is deceleration of pathophysiologic sequalae that shorten life span. These include suppression of weight gain, fat accumulation, circulating adipokines, amelioration of major symptoms of metabolic syndrome, improved reproduction and bone health. Thus, sustained repression of NPY signaling in the hypothalamus by leptin transgene expression can improve the quality of life and extend longevity.
Assuntos
Hipotálamo/fisiologia , Neuropeptídeo Y/fisiologia , Qualidade de Vida , Apetite , Terapia Genética , Humanos , Leptina/genética , Neuropeptídeo Y/antagonistas & inibidoresRESUMO
States of increased metabolic demand are associated with up-regulation of NPY and hyperphagia. However, we present some instances of hyperphagia in which NPY is not up-regulated. Ablation or functional disruption of specific sites in the hypothalamus, such as the ventromedial or paraventricular nuclei, or transection of inputs to the hypothalamus from the hindbrain results in hyperphagia and excess body weight gain. However, NPY expression and concentration in these experimental models is either decreased or unchanged. While there is no up-regulation of NPY in these models, there is increased sensitivity to the orexigenic effects of NPY. This enhanced responsiveness to NPY may more than compensate for the reduced levels of NPY and result in hyperphagia and excess body weight gain. The hyper-responsiveness may be due either to an increase in NPY receptors or to other changes in target cells and response pathways that may result from the treatments used in these models.
Assuntos
Hiperfagia/metabolismo , Hipotálamo/metabolismo , Neuropeptídeo Y/metabolismo , Obesidade/metabolismo , HumanosRESUMO
Skeletal growth is tightly coupled to energy balance via complex and incompletely understood mechanisms. Leptin-deficient ob/ob mice are obese and develop multiple pathologies associated with the metabolic syndrome. Additionally, ob/ob mice have skeletal abnormalities. The objective of this study was to evaluate the effects of leptin deficiency and long duration selective central leptin repletion via recombinant adeno-associated virus-leptin (rAAV-lep) gene therapy on bone in growing ob/ob mice. The ob/ob mice were injected in the hypothalamus with either rAAV-lep or rAAV-GFP (control vector). Treated ob/ob and untreated wild-type (WT) mice were then maintained on a normal diet for 15 weeks. In a second experiment, similarly treated mice along with a group of pair-fed mice were maintained for 30 weeks. Leptin was not detected in blood of either rAAV-lep- or rAAV-GFP-treated mice although rAAV-lep-treated mice displayed leptin transgene expression in the hypothalamus. As expected, rAAV-lep normalized body weight and food intake. Compared to WT mice, rAAV-GFP-treated ob/ob mice had decreased femoral length (by 1.6 mm or 10%, P<0.001), decreased total femur bone volume (by 3.3 mm(3) or 19%, P<0.001), but increased cancellous bone volume in the distal femur (by 0.04 mm(3) or 60%, P<0.09) and lumbar vertebrae (by 0.26 mm(3) or 118%, P<0.001). Treatment with rAAV-lep rescued the ob/ob skeletal phenotype by increasing femoral length and total bone volume, and decreasing femoral and vertebral cancellous bone volume, so that at 15 weeks post-rAAV-lep injection the ob/ob mice no longer differed from WT mice. No further skeletal changes in either the femur or lumbar vertebra were observed at 30 weeks post-rAAV-lep administration. The results suggest that hypothalamic leptin functions as an essential permissive factor for normal bone growth.
Assuntos
Doenças Ósseas Metabólicas/terapia , Terapia Genética/métodos , Leptina/fisiologia , Animais , Peso Corporal , Osso e Ossos/anormalidades , Osso e Ossos/metabolismo , Dependovirus/genética , Fêmur/anormalidades , Fêmur/metabolismo , Vetores Genéticos/genética , Hipotálamo/metabolismo , Leptina/deficiência , Leptina/genética , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Camundongos Obesos , Resultado do TratamentoRESUMO
Leptin insufficiency at crucial target sites in the hypothalamic circuitries that integrate energy intake and expenditure underlies abnormal rates of fat accumulation. The payload of this "fat burden" is metabolic syndrome, a cluster of life-threatening metabolic afflictions, and a shorter lifespan. Currently available therapies employed to combat obesity have disadvantages such as poor compliance for lifestyle modification or transient effectiveness and undesirable side-effects of pharmacological interventions. Recent studies suggest that neurotherapy comprising a single central administration of recombinant adeno-associated virus vector encoding the leptin gene severely depletes fat and ameliorates the major symptoms of metabolic syndrome for extended periods in rodents. These persistent benefits avert the deleterious impact of the "fat burden" and extend life expectancy. Thus, the novel approach of central gene-transfer technology has distinct advantages over current therapies and has the potential to correct or slow the progression of inherited or acquired hypothalamic diseases.
Assuntos
Terapia Genética/métodos , Leptina/genética , Expectativa de Vida , Doenças Metabólicas/terapia , Obesidade/terapia , Adenoviridae/genética , Animais , Vetores Genéticos , Humanos , Leptina/biossíntese , Expectativa de Vida/tendências , Doenças Metabólicas/genética , Doenças Metabólicas/metabolismo , Obesidade/genética , Obesidade/metabolismoRESUMO
An interactive network comprised of neuropeptide Y (NPY) and cohorts is obligatory in the hypothalamic integration of appetite and energy expenditure on a minute-to-minute basis. High or low abundance of NPY and cognate receptors dysregulates the homeostatic milieu engendering hyperphagia, decreased energy expenditure, obesity and attendant metabolic syndrome cluster of dyslipidemia, glucose intolerance, insulin resistance and hyperinsulinemia, risk factors for type II diabetes and cardiovascular diseases. Increasing the supply of the endogenous repressor hormone leptin locally in the hypothalamus with the aid of leptin gene therapy, blocked age-related and dietary obesities, and the sequential development of dyslipidemia, hyperglycemia, and insulin resistance. Thus, sustained repression of NPY signaling with increased leptin selectively in the hypothalamus can avert environmental obesity and the risks of metabolic diseases.
Assuntos
Dislipidemias/terapia , Terapia Genética/métodos , Hipotálamo/metabolismo , Resistência à Insulina/fisiologia , Leptina/genética , Neuropeptídeo Y/antagonistas & inibidores , Obesidade/terapia , Animais , Dislipidemias/metabolismo , Humanos , Resistência à Insulina/genética , Leptina/metabolismo , Síndrome Metabólica/metabolismo , Síndrome Metabólica/terapia , Neuropeptídeo Y/fisiologia , Obesidade/genéticaRESUMO
Bilateral electrolytic lesions of the paraventricular nucleus of the hypothalamus (PVN) produce hyperphagia with excess weight gain. The orexigenic neuropeptide Y (NPY) system and the anorexigenic melanocortin system act in the PVN to regulate food intake, and participate in mediating the anorexic effects of leptin. We hypothesized that changes in the responsiveness of these systems may contribute to the hyperphagia observed in PVN-lesioned rats. Adult female Sprague-Dawley rats received either sham or electrolytic lesions in the PVN immediately followed by implantation of a guide cannula into the third cerebroventricle. Twenty-five days following surgery groups of sham and hyperphagic PVN-lesioned rats were injected intracerebroventricularly (i.c.v.) with either 118 pmole or 470 pmole of NPY and food intake was measured for 3 h. Food intake in response to NPY was nearly three-fold higher in PVN-lesioned rats as compared to sham rats. However, the response to 5 microg leptin i.c.v. was not different in lesioned versus sham rats. The effect of the melanocortin agonist MTII on food intake was tested in additional rats beginning either 7-14 days or 30-40 days following surgery. Doses of 0.1 nmole or 1.0 nmole of MTII were injected immediately before lights-off and food intake was measured at 2 h, 24 h and 48 h post-injection. Suppression of food intake in PVN-lesioned rats was not different from that in sham-lesioned rats. These data suggest that hyper-responsiveness to NPY may account in part for the hyperphagia observed in PVN-lesioned rats. Furthermore, based on the similarities of responses of PVN-lesioned and sham control rats to the anorexigenic agents MTII and leptin and the hypersensitivity of lesioned rats to NPY, we conclude that the PVN is not essential for NPY stimulation of food intake or for melanocortin suppression of food intake and that NPY and melanocortin receptors outside of the PVN are sufficient to produce these effects.
Assuntos
Ingestão de Alimentos/efeitos dos fármacos , Neuropeptídeo Y/farmacologia , Núcleo Hipotalâmico Paraventricular/fisiologia , alfa-MSH/análogos & derivados , Animais , Peso Corporal/efeitos dos fármacos , Feminino , Leptina/administração & dosagem , Leptina/farmacologia , Núcleo Hipotalâmico Paraventricular/citologia , Núcleo Hipotalâmico Paraventricular/efeitos dos fármacos , Ratos , Ratos Sprague-Dawley , Receptor Tipo 3 de Melanocortina/agonistas , Receptor Tipo 3 de Melanocortina/metabolismo , Fatores de Tempo , alfa-MSH/farmacologiaRESUMO
We have tested the hypothesis that sustained leptin action in the hypothalamus alone can engender and maintain euglycemia in wild type mice and in two monogenic diabetic models, the insulin-deficient nonobese Akita mice and the hyperinsulinemic leptin-deficient obese, ob/ob mice. A single intracerebroventricular injection of recombinant adeno-associated virus vector encoding leptin (rAAV-lep) enhanced leptin transgene expression in the hypothalamus without any evidence of leptin leakage to the peripheral circulation, and promptly reinstated euglycemia that persisted along with severe insulinopenia in all three genotypes through the 7-week period of observation. A comparative evaluation of known etiologic factors of hyperglycemia showed that this long-term benefit on glucose homeostasis was not due to diminished energy consumption, weight and adiposity, but was conferred by at least two mechanisms operating simultaneously, enhanced glucose metabolism to meet the demand for the rAAV-lep induced increased non-shivering thermogenesis mediated by brown adipose tissue and insulin hypersensitivity. These findings endorse the hypothesis that increased leptin action locally in the hypothalamus can impose euglycemia independent of pancreatic insulin, and central leptin reinforcement may serve as a newer adjunct therapy to treat type 1 and type 2 diabetes.
Assuntos
Glicemia/análise , Diabetes Mellitus/metabolismo , Hipotálamo/metabolismo , Insulina/sangue , Leptina/genética , Adenoviridae/genética , Animais , Peso Corporal/genética , Peso Corporal/fisiologia , Diabetes Mellitus/sangue , Diabetes Mellitus/genética , Ingestão de Alimentos/genética , Ingestão de Alimentos/fisiologia , Vetores Genéticos/administração & dosagem , Técnica Clamp de Glucose , Teste de Tolerância a Glucose , Hipotálamo/citologia , Insulina/genética , Canais Iônicos/genética , Canais Iônicos/metabolismo , Leptina/metabolismo , Masculino , Camundongos , Camundongos Obesos , Camundongos Transgênicos , Proteínas Mitocondriais/genética , Proteínas Mitocondriais/metabolismo , Fatores de Tempo , Transgenes , Proteína Desacopladora 1RESUMO
The effects of sustained leptin action locally in the hypothalamus on the functional link between fat accrual and insulin secretion after chronic high fat diet (HFD) consumption in leptin-deficient ob/ob mice, and on the post-prandial insulin response in rats consuming regular chow diet (RCD), was examined in this study. A single intracerebroventricular (icv) injection of recombinant adeno-associated virus vector encoding leptin gene (rAAV-lep) enhanced hypothalamic leptin-transgene expression in ob/ob mice consuming RCD and suppressed the time-related weight gain and fat accumulation concomitant with abrogation of hyperinsulinemia and enhanced glucose tolerance. This increased hypothalamic leptin-transgene expression continued to impose insulinopenia and increased glucose tolerance but was ineffective in suppressing weight gain and fat accumulation after these mice were switched to chronic HFD consumption. A similar icv rAAV-lep pretreatment in rats consuming RCD markedly attenuated the post-prandial rise in insulin release concomitant with suppressed weight and fat depots. These results show for the first time that a sustained hypothalamic leptin action can stably clamp pancreatic insulin secretion independent of the status of fat accrual engendered by diets of varying caloric enrichment. Thus, the efficacy of increased leptin afferent signaling in the hypothalamus to persistently restrain pancreatic insulin release and insulin resistance can be explored as an adjunct therapeutic modality to alleviate pathophysiological derrangements that confer type 2 diabetes.
Assuntos
Hipotálamo/fisiologia , Insulina/metabolismo , Leptina/biossíntese , Leptina/genética , Animais , Feminino , Técnicas de Transferência de Genes , Secreção de Insulina , Leptina/metabolismo , Masculino , Camundongos , Camundongos Transgênicos , Ratos , Ratos Sprague-DawleyRESUMO
Low bone mass is often associated with elevated bone marrow adiposity. Since osteoblasts and adipocytes are derived from the same mesenchymal stem cell (MSC) progenitor, adipocyte formation may increase at the expense of osteoblast formation. Leptin is an adipocyte-derived hormone known to regulate energy and bone metabolism. Leptin deficiency and high-fat diet-induced obesity are associated with increased marrow adipose tissue (MAT) and reduced bone formation. Short-duration studies suggest that leptin treatment reduces MAT and increases bone formation in leptin-deficient ob/ob mice fed a regular diet. Here, we determined the long-duration impact of increased hypothalamic leptin on marrow adipocytes and osteoblasts in ob/ob mice following recombinant adeno-associated virus (rAAV) gene therapy. Eight- to 10-week-old male ob/ob mice were randomized into four groups: (1) untreated, (2) rAAV-Lep, (3) rAAV-green fluorescent protein (rAAV-GFP), or (4) pair-fed to rAAV-Lep. For vector administration, mice were injected intracerebroventricularly with either rAAV-leptin gene therapy (rAAV-Lep) or rAAV-GFP (9 × 10(7) particles) and maintained for 30 weeks. In a second study, the impact of increased hypothalamic leptin levels on MAT was determined in mice fed high-fat diets; ob/ob mice were randomized into two groups and treated with either rAAV-Lep or rAAV-GFP. At 7 weeks post-vector administration, half the mice in each group were switched to a high-fat diet for 8 weeks. Wild-type (WT) controls included age-matched mice fed regular or high-fat diet. High-fat diet resulted in a threefold increase in MAT in WT mice, whereas MAT was increased by leptin deficiency up to 50-fold. Hypothalamic leptin gene therapy increased osteoblast perimeter and osteoclast perimeter with minor change in cancellous bone architecture. The gene therapy decreased MAT levels in ob/ob mice fed regular or high-fat diet to values similar to WT mice fed regular diet. These findings suggest that leptin plays an important role in regulating the differentiation of MSCs to adipocytes and osteoblasts, a process that may be dysregulated by high-fat diet. However, the results also illustrate that reducing MAT by increasing leptin levels does not necessarily result in increased bone mass.
RESUMO
Recombinant adeno-associated virus (rAAV), encoding either rat leptin (rAAV-lep) or green fluorescent protein (rAAV-GFP, control), was injected intracerebroventricularly in rats consuming a high-fat diet (HFD; 45 kcal%). Caloric consumption and body weight were monitored weekly until the rats were killed at 9 weeks. Untreated control rats consuming regular rat diet (RCD; 11 kcal%) were monitored in parallel. Body weight gain was accelerated in rAAV-GFP + HFD control rats relative to those consuming RCD, despite equivalent kcal consumption. At 9 weeks, serum leptin, free fatty acids, triglycerides, and insulin were elevated in HFD control rats. In contrast, rAAV-lep treatment reduced intake and blocked the HFD-induced increase in weight, adiposity, and metabolic variables. Blood glucose was slightly reduced but within the normal range, and serum ghrelin levels were significantly elevated in rAAV-lep + HFD rats. Uncoupling protein-1 (UCP1) mRNA in brown adipose tissue (BAT), an index of energy expenditure through nonshivering thermogenesis, was decreased in rats consuming HFD. Treatment with rAAV-lep significantly augmented BAT UCP1 mRNA expression, indicating increased thermogenic energy expenditure. These findings demonstrate that central leptin gene therapy efficiently prevents weight gain, increased adiposity, and hyperinsulinemia in rats consuming an HFD by decreasing energy intake and increasing thermogenic energy expenditure.
Assuntos
Gorduras na Dieta/administração & dosagem , Terapia Genética , Hiperinsulinismo/prevenção & controle , Leptina/genética , Hormônios Peptídicos , Peptídeos/sangue , Aumento de Peso , Tecido Adiposo , Tecido Adiposo Marrom/química , Animais , Composição Corporal , Proteínas de Transporte/genética , Dependovirus/genética , Ingestão de Energia , Metabolismo Energético , Ácidos Graxos não Esterificados/sangue , Técnicas de Transferência de Genes , Vetores Genéticos , Grelina , Proteínas de Fluorescência Verde , Canais Iônicos , Leptina/sangue , Proteínas Luminescentes/genética , Masculino , Proteínas de Membrana/genética , Proteínas Mitocondriais , Obesidade/prevenção & controle , RNA Mensageiro/análise , Ratos , Ratos Sprague-Dawley , Termogênese , Triglicerídeos/sangue , Proteína Desacopladora 1RESUMO
Leptin is a hormone secreted primarily by white adipocytes that regulates energy homeostasis and reproduction via CNS receptors. Koletsky (f/f) rats with a leptin receptor (OB-Rb) gene mutation are obese, diabetic and infertile. We employed recombinant adeno-associated viral (rAAV) vectors to transfer the human OB-Rb gene into the brains of female Koletsky rats to identify sites of leptin action in the brain. rAAV-OB-Rb was microinjected into the medial preoptic area (MPOA), the paraventricular nucleus (PVN), the ventromedial hypothalamus, the arcuate nucleus (ARC), or the dorsal vagal complex in the brainstem. Food intake and body weight were monitored bi-weekly for 55 days. Vaginal cytology was examined daily to assess estrous cyclicity. After sacrifice, uncoupling protein-1 (UCP-1) mRNA in brown adipose tissue and serum concentrations of leptin, insulin, glucose, estradiol and progesterone were measured. Expression of OB-Rb was documented by RT-PCR and site specificity of microinjection was verified by immunohistochemical detection of green fluorescent protein following a control microinjection of rAAV-GFP. OB-Rb installation in the ARC reduced food intake, however, energy expenditure, assessed by UCP-1 mRNA expression, was increased by OB-Rb installation in all sites except the PVN. When injected into the MPOA and ARC, rAAV-OB-Rb stimulated the reproductive axis as evidenced by normalization of estrous cycle length and increased luteinizing hormone releasing hormone concentrations in the hypothalamus. These studies show that long-term installation of a functional leptin receptor in the CNS is achievable using rAAV vectors and further show that leptin acts on specific sites in the brain to produce differential effects on food intake, energy expenditure and reproduction.
Assuntos
Dependovirus , Metabolismo Energético , Terapia Genética , Infertilidade Feminina/metabolismo , Obesidade/metabolismo , Receptores de Superfície Celular/metabolismo , Animais , Ciclo Estral/genética , Ciclo Estral/metabolismo , Feminino , Técnicas de Transferência de Genes , Hipotálamo Médio/metabolismo , Infertilidade Feminina/terapia , Mutação , Obesidade/genética , Obesidade/terapia , Ratos , Ratos Mutantes , Receptores de Superfície Celular/genética , Receptores para LeptinaRESUMO
The efficacy of central leptin therapy on weight homeostasis through various phases of reproduction, pregnancy outcome and postnatal, prepubertal and pubertal growth of offspring was assessed. Enhanced leptin transgene expression after a single intracerebroventricular injection of recombinant adeno-associated virus vector encoding the leptin gene (rAAV-lep) decreased calorie intake and weight in adult nulliparous female rats. rAAV-lep treated rats conceived normally, displayed unremarkable pregnancy rate, parturition and delivered normal sized litters. Significantly lower weight was maintained through gestation, lactation, and post-lactation periods. The maintenance of a modest weight reduction was accompanied by voluntarily reduced calorie intake, increased thermogenic energy expenditure, decreased adiposity as reflected by drastically reduced leptin levels, and suppressed insulin and insulin-like growth factor 1 levels through lactation and post-lactation in rAAV-lep treated dams. The offspring at birth weighed significantly less than those of controls and this lower weight range was sustained during postnatal, prepubertal, pubertal and adult (3 months old) periods, contemporaneous with metabolic circulating hormones in the normal range. For the first time we show the persistent efficacy of central leptin gene therapy to suppress weight gain through all phases of reproduction, lactation and post-lactation in dams and reveal the potential imprinting link to producing lower weight in the F1 generation.
Assuntos
Regulação do Apetite , Terapia Genética , Leptina/genética , Obesidade/prevenção & controle , Aumento de Peso , Tecido Adiposo/metabolismo , Animais , Peso Corporal/genética , Ingestão de Alimentos/genética , Feminino , Expressão Gênica , Hipotálamo/metabolismo , Insulina/sangue , Insulina/metabolismo , Fator de Crescimento Insulin-Like I/metabolismo , Lactação/genética , Leptina/sangue , Masculino , Obesidade/genética , Gravidez , RNA Mensageiro/análise , RNA Mensageiro/metabolismo , Ratos , Ratos Sprague-DawleyRESUMO
We tested the hypothesis that leptin acts centrally to differentially modulate the ultradian communication of leptin, insulin and ghrelin with the hypothalamus. The ultradian fluctuation of these hormones in plasma after central leptin gene therapy was analyzed. Increased leptin transgene expression in the hypothalamus significantly decreased energy intake and body weight concomitant with severe hypoleptinemia and hypoinsulinemia resulting from drastically suppressed peak heights with unchanged frequency discharge of these hormones. Ghrelin secretion was, however, increased solely due to increased pulse amplitude. In pair-fed control rats leptin and ghrelin secretion was unchanged. In conclusion, independent of restraint on caloric intake and weight, leptin acting centrally modulates only the pulse amplitude of ultradian rhythmicity of the three afferent signals involved in the hypothalamic integration of energy balance. Since rhythmic discharge patterns dictate target response of hormones, these findings reveal a novel hypothalamic action of leptin in the pathophysiology of the obesity-dependent metabolic syndrome.
Assuntos
Adenoviridae , Peso Corporal , Ingestão de Alimentos , Insulina/sangue , Leptina , Hormônios Peptídicos/sangue , Animais , Metabolismo Energético , Feminino , Técnicas de Transferência de Genes , Terapia Genética/métodos , Grelina , Hipotálamo/metabolismo , Leptina/genética , Doenças Metabólicas/sangue , Doenças Metabólicas/complicações , Obesidade/sangue , Obesidade/complicações , Ratos , Ratos Sprague-Dawley , TransgenesRESUMO
Unexpended energy is stored as fat in the body and increased rate of fat accretion culminates in obesity. Obesity increases the risks of many diseases several folds and shortens life span. A progressive deficit in the central feedback effects of leptin, a peptide produced by fat cells and hypothalamus, results in increased weight gain and obesity. This article summarizes our experimental findings to show that a stable increase in leptin availability in the hypothalamus alone with the aid of leptin gene therapy suppresses fat accretion and metabolic hormones for nearly the lifetime of laboratory rodents. Consequently, central leptin gene therapy is a novel modality that offers a viable therapeutic option to reduce fat depots and attendant metabolic sequelae implicated in obesity-related illnesses.
Assuntos
Gorduras/metabolismo , Terapia Genética/métodos , Leptina/genética , Obesidade/prevenção & controle , Animais , Peso Corporal/efeitos dos fármacos , Ingestão de Energia/genética , Retroalimentação Fisiológica/genética , Feminino , Leptina/deficiência , Leptina/farmacologia , Obesidade/metabolismo , Ratos , Ratos Sprague-Dawley , Fatores de Tempo , Resultado do TratamentoRESUMO
Excessive weight gain in adults is associated with a variety of negative health outcomes. Unfortunately, dieting, exercise, and pharmacological interventions have had limited long-term success in weight control and can result in detrimental side effects, including accelerating age-related cancellous bone loss. We investigated the efficacy of using hypothalamic leptin gene therapy as an alternative method for reducing weight in skeletally-mature (9 months old) female rats and determined the impact of leptin-induced weight loss on bone mass, density, and microarchitecture, and serum biomarkers of bone turnover (CTx and osteocalcin). Rats were implanted with cannulae in the 3rd ventricle of the hypothalamus and injected with either recombinant adeno-associated virus encoding the gene for rat leptin (rAAV-Leptin, n=7) or a control vector encoding green fluorescent protein (rAAV-GFP, n=10) and sacrificed 18 weeks later. A baseline control group (n=7) was sacrificed at vector administration. rAAV-Leptin-treated rats lost weight (-4±2%) while rAAV-GFP-treated rats gained weight (14±2%) during the study. At study termination, rAAV-Leptin-treated rats weighed 17% less than rAAV-GFP-treated rats and had lower abdominal white adipose tissue weight (-80%), serum leptin (-77%), and serum IGF1 (-34%). Cancellous bone volume fraction in distal femur metaphysis and epiphysis, and in lumbar vertebra tended to be lower (P<0.1) in rAAV-GFP-treated rats (13.5 months old) compared to baseline control rats (9 months old). Significant differences in cancellous bone or biomarkers of bone turnover were not detected between rAAV-Leptin and rAAV-GFP rats. In summary, rAAV-Leptin-treated rats maintained a lower body weight compared to baseline and rAAV-GFP-treated rats with minimal effects on bone mass, density, microarchitecture, or biochemical markers of bone turnover.
Assuntos
Peso Corporal/efeitos dos fármacos , Densidade Óssea/efeitos dos fármacos , Terapia Genética/métodos , Hipotálamo/efeitos dos fármacos , Leptina/uso terapêutico , Animais , Feminino , Fator de Crescimento Insulin-Like I/metabolismo , Leptina/sangue , Leptina/farmacologia , Obesidade/tratamento farmacológico , Obesidade/genética , Obesidade/terapia , Ratos , Ratos Sprague-Dawley , Redução de Peso/efeitos dos fármacosRESUMO
Ghrelin stimulates and leptin inhibits appetite by modulating neuropeptide Y (NPY) signaling in the hypothalamus. Analysis of plasma ghrelin and leptin by sensitive radioimmunoassays showed that the two peripheral hormones are secreted in pulsatile fashion in rats consuming ad libitum rat chow. Fasting augmented all parameters of ghrelin pulsatile secretion and diminished leptin secretion by selectively attenuating the pulse amplitude; concomitantly it produced synchrony in ghrelin and leptin pulse discharge. These studies imply that a synchronous leptin restraint and ghrelin stimulus on NPYergic signaling may underlie robust appetitive drive.
Assuntos
Jejum/metabolismo , Leptina/fisiologia , Neuropeptídeo Y/fisiologia , Hormônios Peptídicos , Peptídeos/fisiologia , Animais , Peso Corporal/fisiologia , Feminino , Grelina , Hipotálamo/fisiologia , Cinética , Leptina/metabolismo , Radioimunoensaio , Ratos , Ratos Sprague-DawleyRESUMO
We tested the hypothesis that leptin acts centrally and peripherally by different mechanisms to control peripheral hormones that normally regulate weight homeostasis. The paradigm of selectively increasing leptin transgene expression with a single intracerebroventricular injection of adeno-associated viral vectors encoding leptin (rAAV-lep) or green fluorescent protein (control) in the hypothalamus of mutant leptin-deficient ob/ob and wild-type (wt) mice was employed in these experiments. rAAV-lep injection increased hypothalamic leptin expression in the complete absence of peripheral leptin in ob/ob mice; suppressed body weight and adiposity; voluntarily decreased dark-phase food intake; suppressed plasma levels of adiponectin, TNFalpha, free fatty acids and insulin, concomitant with normoglycemia; and elevated ghrelin levels for extended period. Body weight and plasma levels of leptin and metabolic variables were suppressed to a lesser extent in rAAV-lep wt mice without decreasing food intake. The sustained high leptin transgene expression decreased only the dark-phase phagia in both genotypes, but wt mice escaped from leptin restraint during the lights-on phase, resulting in normal overall food intake. Leptin administration rapidly decreased plasma gastric ghrelin and adipocyte adiponectin but not TNFalpha levels, thereby demonstrating a peripheral restraining action of leptin on the secretion of hormones of varied origins. Whereas ghrelin administration readily stimulated feeding in controls, it was completely ineffective in rAAV-lep-treated wt mice. Thus, leptin expressed locally in the hypothalamus counteracted the central orexigenic effects of peripheral ghrelin. Cumulatively, these results identify newer central and peripheral modulatory influences of leptin on hormonal signals of disparate origin implicated in weight homeostasis and metabolic disorders.