RESUMO
BACKGROUND: Prominent activation of microglial immune/inflammatory processes is a characteristic feature of brains of patients with tauopathies including Alzheimer's disease (AD), suggesting that neuroinflammation may be a critical factor in their pathogenesis. Strategies aimed at developing new therapeutics for tauopathies based on anti-inflammation or immunomodulation are likely to be promising avenues of research. We previously developed JM4-a 19'mer cyclic peptide derived from the first loop of human erythropoietin. This peptide possesses beneficial immune modulatory and tissue protective effects while lacking the undesirable side effects of full-length erythropoietin. In this preclinical study, we investigated the effect of chronic JM4 treatment on the PS19 mouse that carries the P301S mutant human tau gene, linked to a form of frontotemporal dementia. This transgenic mouse has been widely used as a model of tauopathies including AD and related dementias. METHODS: Daily subcutaneous treatment of female PS19 mice with JM4 was initiated before disease onset and continued on for the animals' lifespan. The progression of neurological deficit and the lifespan of these mice were assessed. To evaluate the effect of JM4 treatment on cognition of these animals, the PS19 mice underwent Barnes maze test and elevated plus maze test. In addition, neuronal loss, phosphorylated tau aggregation, and microglial activation were assessed using immunohistochemistry of PS19 mouse brain sections. RESULTS: JM4 treatment of PS19 mice initiated before disease onset reduced neurological deficit, prolonged lifespan, and rescued memory impairment. The beneficial effects of JM4 were accompanied by reductions in neuronal loss, phosphorylated tau aggregation, and microglial activation in the PS19 mouse brain. LIMITATIONS: Use of a single dose of JM4 and female mice only. CONCLUSION: JM4 is a potential novel therapeutic agent for the treatment of tauopathies including AD and related dementias.
Assuntos
Eritropoetina , Tauopatias , Animais , Encéfalo/metabolismo , Modelos Animais de Doenças , Feminino , Humanos , Camundongos , Camundongos Transgênicos , Tauopatias/tratamento farmacológico , Proteínas tau/genética , Proteínas tau/metabolismoRESUMO
Many studies of tauopathy use transgenic mice that overexpress the P301S mutant form of tau. Neuronal damage in these mice is associated with astrogliosis and induction of glial fibrillary acidic protein (GFAP) expression. GFAP-luc transgenic mice express firefly luciferase under the GFAP promoter, allowing bioluminescence to be measured non-invasively as a surrogate biomarker for astrogliosis. We bred double transgenic mice possessing both P301S and GFAP-luc cassettes and compared them to control mice bearing only the GFAP-luc transgene. We used serial bioluminescent images to define the onset and the time course of astrogliosis in these mice and this was correlated with the development of clinical deficit. Mice containing both GFAP-luc and P301S transgenes showed increased luminescence indicative of astroglial activation in the brain and spinal cord. Starting at 5 months old, the onset of clinical deterioration in these mice corresponded closely to the initial rise in the luminescent signal. Post mortem analysis showed the elevated luminescence was correlated with hyperphosphorylated tau deposition in the hippocampus of double transgenic mice. We used this method to determine the therapeutic effect of JM4 peptide [a small peptide immunomodulatory agent derived from human erythropoietin (EPO)] on double transgenic mice. JM4 treatment significantly decreased the intensity of luminescence, neurological deficit and hyperphosphorylated tau in mice with both the P301S and GFAP-luc transgenes. These findings indicate that bioluminescence imaging (BLI) is a powerful tool for quantifying GFAP expression in living P301S mice and can be used as a noninvasive biomarker of tau-induced neurodegeneration in preclinical therapeutic trials.
RESUMO
Amylin phosphorylates ERK (p-ERK) in the area postrema to reduce eating and synergizes with leptin to phosphorylate STAT3 in the arcuate (ARC) and ventromedial (VMN) hypothalamic nuclei to reduce food intake and body weight. The current studies assessed potential amylin and amylin-leptin ARC/VMN interactions on ERK signaling and their roles in postnatal hypothalamic pathway development. In amylin knockout mice, the density of agouti-related protein (AgRP)-immunoreactive (IR) fibers in the hypothalamic paraventricular nucleus (PVN) was increased, while the density of α-melanocyte-stimulating hormone (αMSH) fibers was decreased. In mice deficient of the amylin receptor components RAMP1/3, both AgRP and αMSH-IR fiber densities were decreased, while only αMSH-IR fiber density was decreased in rats injected neonatally in the ARC/VMN with an adeno-associated virus short hairpin RNA against the amylin core receptor. Amylin induced p-ERK in ARC neurons, 60% of which was present in POMC-expressing neurons, with none in NPY neurons. An amylin-leptin interaction was shown by an additive effect on ARC ERK signaling in neonatal rats and a 44% decrease in amylin-induced p-ERK in the ARC of leptin receptor-deficient and of ob/ob mice. Together, these results suggest that amylin directly acts, through a p-ERK-mediated process, on POMC neurons to enhance ARC-PVN αMSH pathway development.
Assuntos
Núcleo Arqueado do Hipotálamo/metabolismo , Polipeptídeo Amiloide das Ilhotas Pancreáticas/metabolismo , Leptina/metabolismo , Sistema de Sinalização das MAP Quinases , Neurônios/metabolismo , Núcleo Hipotalâmico Paraventricular/metabolismo , Pró-Opiomelanocortina/metabolismo , Proteína Relacionada com Agouti/metabolismo , Animais , Animais Recém-Nascidos , Comportamento Alimentar , Feminino , Polipeptídeo Amiloide das Ilhotas Pancreáticas/genética , Masculino , Camundongos , Camundongos Knockout , Camundongos Obesos , Neuropeptídeo Y/metabolismo , Ratos Sprague-Dawley , Proteína 1 Modificadora da Atividade de Receptores/genética , Proteína 1 Modificadora da Atividade de Receptores/metabolismo , Proteína 3 Modificadora da Atividade de Receptores/genética , Proteína 3 Modificadora da Atividade de Receptores/metabolismo , Núcleo Hipotalâmico Ventromedial/metabolismo , alfa-MSH/metabolismoRESUMO
Selectively bred diet-induced obese (DIO) rats become obese on a high-fat diet and are leptin resistant before becoming obese. Compared with diet-resistant (DR) neonates, DIO neonates have impaired leptin-dependent arcuate (ARC) neuropeptide Y/agouti-related peptide (NPY/AgRP) and α-melanocyte-stimulating hormone (α-MSH; from proopiomelanocortin (POMC) neurons) axon outgrowth to the paraventricular nucleus (PVN). Using phosphorylation of STAT3 (pSTAT3) as a surrogate, we show that reduced DIO ARC leptin signaling develops by postnatal day 7 (P7) and is reduced within POMC but not NPY/AgRP neurons. Since amylin increases leptin signaling in adult rats, we treated DIO neonates with amylin during postnatal hypothalamic development and assessed leptin signaling, leptin-dependent ARC-PVN pathway development, and metabolic changes. DIO neonates treated with amylin from P0-6 and from P0-16 increased ARC leptin signaling and both AgRP and α-MSH ARC-PVN pathway development, but increased only POMC neuron number. Despite ARC-PVN pathway correction, P0-16 amylin-induced reductions in body weight did not persist beyond treatment cessation. Since amylin enhances adult DIO ARC signaling via an IL-6-dependent mechanism, we assessed ARC-PVN pathway competency in IL-6 knockout mice and found that the AgRP, but not the α-MSH, ARC-PVN pathway was reduced. These results suggest that both leptin and amylin are important neurotrophic factors for the postnatal development of the ARC-PVN pathway. Amylin might act as a direct neurotrophic factor in DIO rats to enhance both the number of POMC neurons and their α-MSH ARC-PVN pathway development. This suggests important and selective roles for amylin during ARC hypothalamic development.
Assuntos
Hipotálamo/fisiopatologia , Polipeptídeo Amiloide das Ilhotas Pancreáticas/administração & dosagem , Leptina/metabolismo , Obesidade/tratamento farmacológico , Obesidade/fisiopatologia , Animais , Núcleo Arqueado do Hipotálamo/efeitos dos fármacos , Núcleo Arqueado do Hipotálamo/patologia , Núcleo Arqueado do Hipotálamo/fisiopatologia , Peso Corporal/efeitos dos fármacos , Dieta Hiperlipídica , Gorduras na Dieta , Feminino , Hipotálamo/efeitos dos fármacos , Hipotálamo/patologia , Polipeptídeo Amiloide das Ilhotas Pancreáticas/farmacologia , Masculino , Neurogênese/efeitos dos fármacos , Núcleo Hipotalâmico Paraventricular/efeitos dos fármacos , Núcleo Hipotalâmico Paraventricular/patologia , Núcleo Hipotalâmico Paraventricular/fisiopatologia , Cuidado Pós-Natal , Ratos , Resultado do TratamentoRESUMO
Rats selectively bred to develop diet-induced obesity (DIO) have an early onset reduction in the sensitivity of their ventromedial hypothalamic nucleus (VMN) neurons to leptin compared with diet-resistant (DR) rats. This reduced sensitivity includes decreased leptin receptor (Lepr-b) mRNA expression, leptin receptor binding, leptin-induced phosphorylation of STAT3 (pSTAT3), and impaired leptin excitation (LepE) of VMN neurons. When administered exogenously, the pancreatic peptide, amylin, acts synergistically to reduce food intake and body weight in obese, leptin-resistant DIO rats by increasing VMN leptin signaling, likely by stimulation of microglia IL-6, which acts on its receptor to increase leptin-induced pSTAT3. Here, we demonstrate that incubation of cultured VMN neurons of outbred rats with IL-6 increases their leptin sensitivity. Control, dissociated DIO VMN neurons express 66% less Lepr-b and 75% less Bardet Biedl Syndrome-6 (BBS6) mRNA and have reduced leptin-induced activation of LepE neurons compared with DR neurons. Incubation for 4 days with IL-6 increased DIO neuron Lepr-b expression by 77% and BBS6 by 290% and corrected their defective leptin activation of LepE neurons to DR levels. Since BBS6 enhances trafficking of Lepr-b to the cell membrane, the increases in Lepr-b and BBS6 expression appear to account for correction of the reduced leptin excitation of DIO LepE neurons to that of control DR rats. These data support prior findings suggesting that IL-6 mediates the leptin-sensitizing effects of amylin on VMN neurons and that the inherent leptin resistance of DIO rats can be effectively reversed at a cellular level by IL-6.
Assuntos
Interleucina-6/imunologia , Leptina/imunologia , Neurônios/metabolismo , Obesidade/imunologia , Receptores para Leptina/metabolismo , Núcleo Hipotalâmico Ventromedial/imunologia , Animais , Células Cultivadas , Gorduras na Dieta , Masculino , Obesidade/induzido quimicamente , Ratos , Ratos Sprague-DawleyRESUMO
Amylin enhances arcuate (ARC) and ventromedial (VMN) hypothalamic nuclei leptin signaling and synergistically reduces food intake and body weight in selectively bred diet-induced obese (DIO) rats. Since DIO (125)I-amylin dorsomedial nucleus-dorsomedial VMN binding was reduced, we postulated that this contributed to DIO ventromedial hypothalamus (VMH) leptin resistance, and that impairing VMH (ARC + VMN) calcitonin receptor (CTR)-mediated signaling by injecting adeno-associated virus (AAV) expressing a short hairpin portion of the CTR mRNA would predispose diet-resistant (DR) rats to obesity on high-fat (45%) diet (HFD). Depleting VMH CTR by 80-90% in 4-wk-old male DR rats reduced their ARC and VMN (125)I-labeled leptin binding by 57 and 51%, respectively, and VMN leptin-induced phospho-signal transducer and activator of transcription 3-positive neurons by 59% vs. AAV control rats. After 6 wk on chow, VMH CTR-depleted DR rats ate and gained the equivalent amount of food and weight but had 18% heavier fat pads (relative to carcass weight), 144% higher leptin levels, and were insulin resistant compared with control AAV DR rats. After 6 wk more on HFD, VMH CTR-depleted DR rats ate the same amount but gained 28% more weight, had 60% more carcass fat, 254% higher leptin levels, and 132% higher insulin areas under the curve during an oral glucose tolerance test than control DR rats. Therefore, impairing endogenous VMH CTR-mediated signaling reduced leptin signaling and caused DR rats to become more obese and insulin resistant, both on chow and HFD. These results suggest that endogenous VMH amylin signaling is required for full leptin signaling and protection from HFD-induced obesity.
Assuntos
Polipeptídeo Amiloide das Ilhotas Pancreáticas/metabolismo , Leptina/metabolismo , Obesidade/fisiopatologia , Núcleo Hipotalâmico Ventromedial/metabolismo , Animais , Núcleo Arqueado do Hipotálamo/metabolismo , Dieta Hiperlipídica , Ingestão de Alimentos , Intolerância à Glucose/genética , Resistência à Insulina/genética , Radioisótopos do Iodo , Polipeptídeo Amiloide das Ilhotas Pancreáticas/genética , Leptina/genética , Masculino , Obesidade/genética , RNA Interferente Pequeno/genética , Cintilografia , Ratos , Receptores da Calcitonina/genética , Receptores da Calcitonina/metabolismo , Fator de Transcrição STAT3/genética , Núcleo Hipotalâmico Ventromedial/diagnóstico por imagem , Aumento de PesoRESUMO
While the neural control of glucoregulatory responses to insulin-induced hypoglycemia is beginning to be elucidated, brain sites responsible for behavioral responses to hypoglycemia are relatively poorly understood. To help elucidate central control mechanisms associated with hypoglycemia unawareness, we first evaluated the effect of recurrent hypoglycemia on a simple behavioral measure, the robust feeding response to hypoglycemia, in rats. First, food intake was significantly, and similarly, increased above baseline saline-induced intake (1.1 ± 0.2 g; n = 8) in rats experiencing a first (4.4 ± 0.3; n = 8) or third daily episode of recurrent insulin-induced hypoglycemia (IIH, 3.7 ± 0.3 g; n = 9; P < 0.05). Because food intake was not impaired as a result of prior IIH, we next developed an alternative animal model of hypoglycemia-induced behavioral arousal using a conditioned place preference (CPP) model. We found that hypoglycemia severely blunted previously acquired CPP in rats and that recurrent hypoglycemia prevented this blunting. Pretreatment with a brain penetrant, selective orexin receptor-1 antagonist, SB-334867A, blocked hypoglycemia-induced blunting of CPP. Recurrently hypoglycemic rats also showed decreased preproorexin expression in the perifornical hypothalamus (50%) but not in the adjacent lateral hypothalamus. Pretreatment with sertraline, previously shown to prevent hypoglycemia-associated glucoregulatory failure, did not prevent blunting of hypoglycemia-induced CPP prevention by recurrent hypoglycemia. This work describes the first behavioral model of hypoglycemia unawareness and suggests a role for orexin neurons in mediating behavioral responses to hypoglycemia.
Assuntos
Comportamento Animal , Glicemia/metabolismo , Encéfalo/metabolismo , Condicionamento Psicológico , Comportamento Alimentar , Hipoglicemia/metabolismo , Orexinas/metabolismo , Transdução de Sinais , Animais , Nível de Alerta , Comportamento Animal/efeitos dos fármacos , Benzoxazóis/farmacologia , Encéfalo/efeitos dos fármacos , Encéfalo/fisiopatologia , Condicionamento Psicológico/efeitos dos fármacos , Modelos Animais de Doenças , Comportamento Alimentar/efeitos dos fármacos , Hipoglicemia/fisiopatologia , Hipoglicemia/psicologia , Masculino , Naftiridinas , Antagonistas dos Receptores de Orexina/farmacologia , Receptores de Orexina/efeitos dos fármacos , Receptores de Orexina/metabolismo , Ratos Sprague-Dawley , Recompensa , Sertralina/farmacologia , Transdução de Sinais/efeitos dos fármacos , Fatores de Tempo , Ureia/análogos & derivados , Ureia/farmacologiaRESUMO
The objective of this study was to determine the potential role of astrocyte-derived ketone bodies in regulating the early changes in caloric intake of diet induced-obese (DIO) versus diet-resistant (DR) rats fed a 31.5% fat high-energy (HE) diet. After 3 days on chow or HE diet, DR and DIO rats were assessed for their ventromedial hypothalamic (VMH) ketone bodies levels and neuronal ventromedial hypothalamic nucleus (VMN) sensing using microdialysis coupled to continuous food intake monitoring and calcium imaging in dissociated neurons, respectively. DIO rats ate more than DR rats over 3 days of HE diet intake. On day 3 of HE diet intake, DR rats reduced their caloric intake while DIO rats remained hyperphagic. Local VMH astrocyte ketone bodies production was similar between DR and DIO rats during the first 6 h after dark onset feeding but inhibiting VMH ketone body production in DR rats on day 3 transiently returned their intake of HE diet to the level of DIO rats consuming HE diet. In addition, dissociated VMN neurons from DIO and DR rats were equally sensitive to the largely excitatory effects of ß-hydroxybutyrate. Thus while DR rats respond to increased VMH ketone levels by decreasing their intake after 3 days of HE diet, this is not the case of DIO rats. These data suggest that DIO inherent leptin resistance prevents ketone bodies inhibitory action on food intake.
Assuntos
Ingestão de Energia/fisiologia , Corpos Cetônicos/metabolismo , Neurônios/metabolismo , Obesidade/metabolismo , Núcleo Hipotalâmico Ventromedial/metabolismo , Ácido 3-Hidroxibutírico/farmacologia , Animais , Cálcio/metabolismo , Dieta Hiperlipídica , Glucose/farmacologia , Masculino , Neurônios/efeitos dos fármacos , Obesidade/etiologia , Ácido Oleico/farmacologia , Ratos , Ratos Sprague-Dawley , Núcleo Hipotalâmico Ventromedial/efeitos dos fármacosRESUMO
Amylin acts acutely via the area postrema to reduce food intake and body weight, but it also interacts with leptin over longer periods of time, possibly via the ventromedial hypothalamus (VMH), to increase leptin signaling and phosphorylation of STAT3. We postulated that amylin enhances VMH leptin signaling by inducing interleukin (IL)-6, which then interacts with its gp130 receptor to activate STAT3 signaling and gene transcription downstream of the leptin receptor. We found that components of the amylin receptor (RAMPs1-3, CTR1a,b) are expressed in cultured VMH astrocytes, neurons, and microglia, as well as in micropunches of arcuate and ventromedial hypothalamic nuclei (VMN). Amylin exposure for 5 days increased IL-6 mRNA expression in VMH explants and microglia by two- to threefold, respectively, as well as protein abundance in culture supernatants by five- and twofold, respectively. Amylin had no similar effects on cultured astrocytes or neurons. In rats, 5 days of amylin treatment decreased body weight gain and/or food intake and increased IL-6 mRNA expression in the VMN. Similar 5-day amylin treatment increased VMN leptin-induced phosphorylation of STAT3 expression in wild-type mice and rats infused with lateral ventricular IgG but not in IL-6 knockout mice or rats infused with ventricular IL-6 antibody. Lateral ventricular infusion of IL-6 antibody also prevented the amylin-induced decrease of body weight gain. These results show that amylin-induced VMH microglial IL-6 production is the likely mechanism by which amylin treatment interacts with VMH leptin signaling to increase its effect on weight loss.
Assuntos
Interleucina-6/metabolismo , Polipeptídeo Amiloide das Ilhotas Pancreáticas/farmacologia , Leptina/metabolismo , Transdução de Sinais/fisiologia , Núcleo Hipotalâmico Ventromedial/metabolismo , Animais , Astrócitos/metabolismo , Regulação da Expressão Gênica/efeitos dos fármacos , Regulação da Expressão Gênica/fisiologia , Interleucina-6/genética , Leptina/genética , Masculino , Camundongos , Camundongos Knockout , Microglia/metabolismo , Neurônios/metabolismo , RNA Mensageiro , Ratos , Ratos Sprague-Dawley , Fator de Transcrição STAT3/genética , Fator de Transcrição STAT3/metabolismo , Núcleo Hipotalâmico Ventromedial/citologiaRESUMO
Hypothalamic fatty acid (FA) sensing neurons alter their activity utilizing the FA translocator/receptor, FAT/CD36. Depletion of ventromedial hypothalamus (VMH) CD36 with adeno-associated viral vector expressing CD36 shRNA (AAV CD36 shRNA) leads to redistribution of adipose stores and insulin resistance in outbred rats. This study assessed the requirement of VMH CD36-mediated FA sensing for the regulation of energy and glucose homeostasis in postnatal day 5 (P5) and P21 selectively bred diet-induced obese (DIO) and diet-resistant (DR) rats using VMH AAV CD36 shRNA injections. P5 CD36 depletion altered VMH neuronal FA sensing predominantly in DIO rats. After 10 wk on a 45% fat diet, DIO rats injected with VMH AAV CD36 shRNA at P21 ate more and gained more weight than DIO AAV controls, while DR AAV CD36 shRNA-injected rats gained less weight than DR AAV controls. VMH CD36 depletion increased inguinal fat pad weights and leptin levels in DIO and DR rats. Although DR AAV CD36 shRNA-injected rats became as obese as DIO AAV controls, only DIO control and CD36 depleted rats became insulin-resistant on a 45% fat diet. VMH CD36 depletion stunted linear growth in DIO and DR rats. DIO rats injected with AAV CD36 shRNA at P5 had increased fat mass, mostly due to a 45% increase in subcutaneous fat. They were also insulin-resistant with an associated 71% increase of liver triglycerides. These results demonstrate that VMH CD36-mediated FA sensing is a critical factor in the regulation of energy and glucose homeostasis and fat deposition in DIO and DR rats.
Assuntos
Glicemia , Antígenos CD36/metabolismo , Ingestão de Energia/fisiologia , Ácidos Graxos/metabolismo , Homeostase/fisiologia , Obesidade/metabolismo , Tecido Adiposo/metabolismo , Ração Animal , Animais , Glicemia/metabolismo , Peso Corporal/fisiologia , Modelos Animais de Doenças , Insulina/metabolismo , Leptina , Masculino , RatosRESUMO
Metabolic sensing neurons in the ventromedial hypothalamus (VMH) alter their activity when ambient levels of metabolic substrates, such as glucose and fatty acids (FA), change. To assess the relationship between a high-fat diet (HFD; 60%) intake on feeding and serum and VMH FA levels, rats were trained to eat a low-fat diet (LFD; 13.5%) or an HFD in 3 h/day and were monitored with VMH FA microdialysis. Despite having higher serum levels, HFD rats had lower VMH FA levels but ate less from 3 to 6 h of refeeding than did LFD rats. However, VMH ß-hydroxybutyrate (ß-OHB) and VMH-to-serum ß-OHB ratio levels were higher in HFD rats during the first 1 h of refeeding, suggesting that VMH astrocyte ketone production mediated their reduced intake. In fact, using calcium imaging in dissociated VMH neurons showed that ketone bodies overrode normal FA sensing, primarily by exciting neurons that were activated or inhibited by oleic acid. Importantly, bilateral inhibition of VMH ketone production with a 3-hydroxy-3-methylglutaryl-CoA synthase inhibitor reversed the 3- to 6-h HFD-induced inhibition of intake but had no effect in LFD-fed rats. These data suggest that a restricted HFD intake regimen inhibits caloric intake as a consequence of FA-induced VMH ketone body production by astrocytes.
Assuntos
Ingestão de Alimentos/efeitos dos fármacos , Ácidos Graxos/farmacologia , Hipotálamo/fisiologia , Corpos Cetônicos/farmacologia , Neurônios/fisiologia , Ácido 3-Hidroxibutírico/sangue , Animais , Hipotálamo/efeitos dos fármacos , Masculino , Neurônios/efeitos dos fármacos , RatosRESUMO
The delivery of blood-borne molecules conveying metabolic information to neural networks that regulate energy homeostasis is restricted by brain barriers. The fenestrated endothelium of median eminence microvessels and tight junctions between tanycytes together compose one of these. Here, we show that the decrease in blood glucose levels during fasting alters the structural organization of this blood-hypothalamus barrier, resulting in the improved access of metabolic substrates to the arcuate nucleus. These changes are mimicked by 2-deoxyglucose-induced glucoprivation and reversed by raising blood glucose levels after fasting. Furthermore, we show that VEGF-A expression in tanycytes modulates these barrier properties. The neutralization of VEGF signaling blocks fasting-induced barrier remodeling and significantly impairs the physiological response to refeeding. These results implicate glucose in the control of blood-hypothalamus exchanges through a VEGF-dependent mechanism and demonstrate a hitherto unappreciated role for tanycytes and the permeable microvessels associated with them in the adaptive metabolic response to fasting.
Assuntos
Núcleo Arqueado do Hipotálamo/metabolismo , Barreira Hematoencefálica/metabolismo , Epêndima/metabolismo , Fator A de Crescimento do Endotélio Vascular/metabolismo , Animais , Barreira Hematoencefálica/efeitos dos fármacos , Desoxiglucose/farmacologia , Epêndima/citologia , Jejum , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Transdução de Sinais , Junções Íntimas/metabolismo , Fator A de Crescimento do Endotélio Vascular/genéticaRESUMO
Hypothalamic "metabolic-sensing" neurons sense glucose and fatty acids (FAs) and play an integral role in the regulation of glucose, energy homeostasis, and the development of obesity and diabetes. Using pharmacologic agents, we previously found that ~50% of these neurons responded to oleic acid (OA) by using the FA translocator/receptor FAT/CD36 (CD36). For further elucidation of the role of CD36 in neuronal FA sensing, ventromedial hypothalamus (VMH) CD36 was depleted using adeno-associated viral (AAV) vector expressing CD36 short hairpin RNA (shRNA) in rats. Whereas their neuronal glucosensing was unaffected by CD36 depletion, the percent of neurons that responded to OA was decreased specifically in glucosensing neurons. A similar effect was seen in total-body CD36-knockout mice. Next, weanling rats were injected in the VMH with CD36 AAV shRNA. Despite significant VMH CD36 depletion, there was no effect on food intake, body weight gain, or total carcass adiposity on chow or 45% fat diets. However, VMH CD36-depleted rats did have increased plasma leptin and subcutaneous fat deposition and markedly abnormal glucose tolerance. These results demonstrate that CD36 is a critical factor in both VMH neuronal FA sensing and the regulation of energy and glucose homeostasis.
Assuntos
Antígenos CD36/metabolismo , Ácidos Graxos/metabolismo , Homeostase/fisiologia , Neurônios/metabolismo , Núcleo Hipotalâmico Ventromedial/metabolismo , Animais , Glicemia , Peso Corporal/efeitos dos fármacos , Peso Corporal/fisiologia , Antígenos CD36/genética , Ingestão de Alimentos/efeitos dos fármacos , Ingestão de Alimentos/fisiologia , Metabolismo Energético/efeitos dos fármacos , Metabolismo Energético/fisiologia , Ácidos Graxos/sangue , Homeostase/efeitos dos fármacos , Insulina/sangue , Leptina/sangue , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Neurônios/efeitos dos fármacos , Ácido Oleico/farmacologia , Ratos , Ratos Sprague-Dawley , Núcleo Hipotalâmico Ventromedial/efeitos dos fármacosRESUMO
A major side effect of insulin treatment of diabetes is weight gain, which limits patient compliance and may pose additional health risks. Although the mechanisms responsible for this weight gain are poorly understood, it has been suggested that there may be a link to the incidence of recurrent episodes of hypoglycemia. Here we present a rodent model of marked weight gain associated with weekly insulin-induced hypoglycemic episodes in the absence of diabetes. Insulin treatment caused a significant increase in both body weight and fat mass, accompanied by reduced motor activity, lowered thermogenesis in response to a cold challenge, and reduced brown fat uncoupling protein mRNA. However, there was no effect of insulin treatment on total food intake nor on hypothalamic neuropeptide Y or proopiomelanocortin mRNA expression, and insulin-treated animals did not become insulin-resistant. Our results suggest that repeated iatrogenic hypoglycemia leads to weight gain, and that such weight gain is associated with a multifaceted deficit in metabolic regulation rather than to a chronic increase in caloric intake.
Assuntos
Hipoglicemia/induzido quimicamente , Hipoglicemia/complicações , Insulina/efeitos adversos , Obesidade/etiologia , Aumento de Peso/efeitos dos fármacos , Animais , Modelos Animais de Doenças , Relação Dose-Resposta a Droga , Esquema de Medicação , Hiperfagia/complicações , Hipoglicemiantes/administração & dosagem , Hipoglicemiantes/efeitos adversos , Insulina/administração & dosagem , Resistência à Insulina/fisiologia , Masculino , Obesidade/induzido quimicamente , Obesidade/patologia , Periodicidade , Ratos , Ratos Sprague-Dawley , Índice de Gravidade de Doença , Fatores de TempoRESUMO
To discover hypothalamic genes that might play a role in regulating energy balance, we carried out a microarray screen for genes induced by a 48-h fast in male C57Bl/6J mouse hypothalamus. One such gene was Fkbp51 (FK506 binding protein 5; Locus NP_034350). The product of this gene is of interest because it blocks glucocorticoid action, suggesting that fasting-induced elevation of this gene in the hypothalamus may reduce glucocorticoid negative feedback, leading to elevated glucocorticoid levels, thus promoting obese phenotypes. Subsequent analysis demonstrated that a 48-h fast induces Fkbp51 in ventromedial, paraventricular, and arcuate hypothalamic nuclei of mice and rats. To assess if hypothalamic Fkbp51 promotes obesity, the gene was transferred to the hypothalamus via an adeno-associated virus vector. Within 2 wk following Fkbp51 overexpression, mice on a high-fat diet exhibited elevated body weight, without hyperphagia, relative to mice receiving the control mCherry vector. Body weight remained elevated for more than 8 wk and was associated with elevated corticosterone and impaired glucose tolerance. These studies suggest that elevated hypothalamic Fkbp51 promotes obese phenotypes.
Assuntos
Jejum/metabolismo , Hipotálamo/metabolismo , Obesidade/metabolismo , Proteínas de Ligação a Tacrolimo/metabolismo , Regulação para Cima , Animais , Núcleo Arqueado do Hipotálamo/metabolismo , Corticosterona/sangue , Ingestão de Energia , Perfilação da Expressão Gênica , Intolerância à Glucose/sangue , Intolerância à Glucose/metabolismo , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Obesidade/sangue , Análise de Sequência com Séries de Oligonucleotídeos , Núcleo Hipotalâmico Paraventricular/metabolismo , RNA Mensageiro/metabolismo , Ratos , Ratos Sprague-Dawley , Proteínas de Ligação a Tacrolimo/antagonistas & inibidores , Proteínas de Ligação a Tacrolimo/genética , Núcleo Hipotalâmico Ventromedial/metabolismo , Aumento de PesoRESUMO
Unique subpopulations of specialized metabolic sensing neurons reside in a distributed network throughout the brain and respond to alterations in ambient levels of various metabolic substrates by altering their activity. Variations in local brain substrate levels reflect their transport across the blood- and cerebrospinal-brain barriers as well as local production by astrocytes. There are a number of mechanisms by which such metabolic sensing neurons alter their activity in response to changes in substrate levels, but it is clear that these neurons cannot be considered in isolation. They are heavily dependent on astrocyte and probably tanycyte metabolism and function but also respond to hormones (e.g. leptin and insulin) and cytokines that cross the blood-brain barrier from the periphery as well as hard-wired neural inputs from metabolic sensors in peripheral sites such as the hepatic portal vein, gastrointestinal tract, and carotid body. Thus, these specialized neurons are capable of monitoring and integrating multiple signals from the periphery as a means of regulating peripheral energy homeostasis.
Assuntos
Encéfalo/fisiologia , Metabolismo Energético , Homeostase , Células Receptoras Sensoriais/fisiologia , Animais , Astrócitos/fisiologia , Humanos , Eminência Mediana/fisiologiaRESUMO
Because rearing rats in large litters (LLs) protects them from becoming obese, we postulated that LL rearing would protect rats selectively bred to develop diet-induced obesity (DIO) from becoming obese by overcoming their inborn central leptin resistance. Male and female DIO rats were raised in normal litters (NLs; 10 pups/dam) or LLs (16 pups/dam) and assessed for anatomical, biochemical, and functional aspects of leptin sensitivity at various ages when fed low-fat chow or a 31% fat high-energy (HE) diet. LL rearing reduced plasma leptin levels by postnatal day 2 (P2) and body weight gain by P8. At P16, LL DIO neonates had increased arcuate nucleus (ARC) binding of leptin to its extracellular receptors and at P28 an associated increase of their agouti-related peptide and alpha-MSH axonal projections to the paraventricular nucleus. Reduced body weight persisted and was associated with increased ARC leptin receptor binding and sensitivity to the anorectic effects of leptin, reduced adiposity, and enhanced insulin sensitivity in LL DIO rats fed chow until 10 wk of age. The enhanced ARC leptin receptor binding and reduced adiposity of LL DIO rats persisted after an additional 5 wk on the HE diet. Female LL DIO rats had similar reductions in weight gain on both chow and HE diet vs. normal litter DIO rats. We postulate that LL rearing enhances DIO leptin sensitivity by lowering plasma leptin levels and thereby increasing leptin receptor availability and that this both enhances the ARC-paraventricular nucleus pathway development and protects them from becoming obese.
Assuntos
Dieta , Leptina/sangue , Tamanho da Ninhada de Vivíparos/fisiologia , Obesidade/fisiopatologia , Adiposidade/fisiologia , Proteína Relacionada com Agouti/metabolismo , Animais , Animais Recém-Nascidos , Núcleo Arqueado do Hipotálamo/metabolismo , Peso Corporal/fisiologia , Cruzamento , Ingestão de Alimentos/fisiologia , Feminino , Idade Gestacional , Imuno-Histoquímica , Lactação/fisiologia , Leptina/metabolismo , Masculino , Obesidade/sangue , Obesidade/etiologia , Núcleo Hipotalâmico Paraventricular/metabolismo , Ligação Proteica , Ratos , Receptores para Leptina/metabolismo , Fatores de Tempo , Desmame , Aumento de Peso/fisiologia , alfa-MSH/metabolismoRESUMO
The present studies aimed to identify mechanisms contributing to amylin/leptin synergy in reducing body weight and adiposity. We reasoned that if amylin/leptin harnessed complementary neuronal pathways, then in the leptin-sensitive state, amylin should augment leptin signaling/binding and that in the absence of endogenous amylin, leptin signaling should be diminished. Amylin (50 microg/kg, ip) amplified low-dose leptin-stimulated (15 microg/kg, ip) phosphorylated signal transducer and activator of transcription-3 signaling within the arcuate nucleus (ARC) in lean rats. Amylin (50 microg/kg x d) or leptin (125 microg/kg x d) infusion to lean rats decreased 28-d food intake (14 and 10%, respectively), body weight (amylin by 4.3%, leptin by 4.9%), and epididymal fat (amylin by 19%, leptin by 37%). Amylin/leptin co-infusion additively decreased food intake (by 26%) and reduced body weight (by 15%) and epididymal fat (by 78%; all P < 0.05 vs. all groups) in a greater than mathematically additive manner, consistent with synergy. Amylin increased leptin binding within the ventromedial hypothalamus (VMN) by 35% and dorsomedial hypothalamus by 47% (both P < 0.05 vs. vehicle). Amylin/leptin similarly increased leptin binding in the VMN by 40% and ARC by 70% (P < 0.05 vs. vehicle). In amylin-deficient mice, hypothalamic leptin receptor mRNA expression was reduced by 50%, leptin-stimulated phosphorylated signal transducer and activator of transcription-3 within ARC and VMN was reduced by 40%, and responsiveness to leptin's (1 mg/kg x d for 28 d) weight-reducing effects was attenuated (all P < 0.05 vs. wild-type controls). We suggest that amylin/leptin's marked weight- and fat-reducing effects are due to activation of intrinsic synergistic neuronal signaling pathways and further point to the integrated neurohormonal therapeutic potential of amylin/leptin agonism in obesity.
Assuntos
Amiloide/fisiologia , Sinergismo Farmacológico , Leptina/fisiologia , Modelos Animais , Roedores , Amiloide/genética , Amiloide/metabolismo , Amiloide/farmacologia , Animais , Núcleo Arqueado do Hipotálamo/efeitos dos fármacos , Núcleo Arqueado do Hipotálamo/metabolismo , Área Postrema/efeitos dos fármacos , Área Postrema/metabolismo , Feminino , Polipeptídeo Amiloide das Ilhotas Pancreáticas , Leptina/genética , Leptina/metabolismo , Leptina/farmacologia , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Proteínas Proto-Oncogênicas c-fos/metabolismo , Ratos , Ratos Sprague-Dawley , Roedores/genética , Roedores/metabolismo , Fator de Transcrição STAT3/genética , Fator de Transcrição STAT3/metabolismo , Transdução de Sinais/efeitos dos fármacos , Transdução de Sinais/genéticaRESUMO
Maternal obesity accentuates offspring obesity in dams bred to develop diet-induced obesity (DIO) on a 31% fat, high-sucrose, high-energy (HE) diet but has no effect on offspring of diet-resistant (DR) dams. Also, only DIO dams become obese when they and DR dams are fed HE diet throughout gestation and lactation. We assessed glucose and oleic acid (OA) sensitivity of dissociated ventromedial hypothalamic nucleus (VMN) neurons from 3- to 4-wk old offspring of DIO and DR dams fed chow or HE diet using fura-2 calcium imaging to monitor intracellular calcium fluctuations as an index of neuronal activity. Offspring of DIO dams fed chow had approximately 2-fold more glucose-inhibited (GI) neurons than did DR offspring. This difference was eliminated in offspring of DIO dams fed HE diet. At 2.5 mM glucose, offspring of chow-fed DIO dams had more GI neurons that were either excited or inhibited by OA than did DR offspring. Maternal HE diet intake generally increased the percentage of neurons that were excited and decreased the percentage that were inhibited by OA in both DIO and DR offspring. However, this effect was more pronounced in DIO offspring. These data, as well as concentration-dependent differences in OA sensitivity, suggest that genotype, maternal obesity, and dietary content can all affect the sensitivity of offspring VMN neurons to glucose and long-chain fatty acids. Such altered sensitivities may underlie the propensity of DIO offspring to become obese when fed high-fat, high-sucrose diets.
Assuntos
Glicemia/metabolismo , Gorduras na Dieta/farmacologia , Sacarose Alimentar/farmacologia , Ácidos Graxos/metabolismo , Neurônios/efeitos dos fármacos , Efeitos Tardios da Exposição Pré-Natal/metabolismo , Núcleo Hipotalâmico Ventromedial/metabolismo , Animais , Animais Recém-Nascidos/metabolismo , Peso Corporal/fisiologia , Cálcio/metabolismo , Modelos Animais de Doenças , Feminino , Genótipo , Insulina/sangue , Leptina/sangue , Masculino , Obesidade/metabolismo , Ácido Oleico/farmacologia , Gravidez , Prenhez/metabolismo , Efeitos Tardios da Exposição Pré-Natal/genética , Ratos , Ratos Endogâmicos , Núcleo Hipotalâmico Ventromedial/efeitos dos fármacosRESUMO
Both genetic and environmental factors contribute to individual differences in body weight regulation. The present study examined a possible role for the dendritic arbor of hypothalamic ventromedial nucleus (VMH) neurons in a model of diet-induced obesity (DIO) in male rats. Rats were screened and selectively bred for being either susceptible, i.e., exhibiting DIO, or diet resistant (DR) when exposed to a 31% fat diet. A 2x2 experimental design was used, based on these two strains of rats and exposure to rat chow versus the 31% fat diet for seven weeks. Golgi-impregnated neurons were measured for soma size and dendrite parameters, including number, length, and direction. As previously observed, each VMH neuron had a single long primary dendrite. Genetic background and diet did not affect soma size or the number of dendrites of VMH neurons. However, genetic background exerted a main effect on the length of the long primary dendrites. In particular, the long primary dendrites were approximately 12.5% shorter on the VMH neurons in the DIO rats compared with DR rats regardless of diet. This effect was isolated to the long primary dendrites extending in the dorsolateral direction, with these long primary dendrites 19% shorter for the DIO group compared with the DR group. This finding implicates the connectivity of the long primary dendrites on VMH neurons in the control of energy balance. The functional significance of these shortened dendrites and their afferents warrants further study.