RESUMO
Alzheimer's disease (AD) is characterized by the deposition in the brain of senile plaques composed of amyloid-ß peptides (Aßs) that increase inflammation. An endogenous peptide derived from the insulin-like growth factor (IGF)-I, glycine-proline-glutamate (GPE), has IGF-I-sensitizing and neuroprotective actions. Here, we examined the effects of GPE on Aß levels and hippocampal inflammation generated by the intracerebroventricular infusion of Aß25-35 for 2 weeks (300 pmol/day) in ovariectomized rats and the signaling-related pathways and levels of Aß-degrading enzymes associated with these GPE-related effects. GPE prevented the Aß-induced increase in the phosphorylation of p38 mitogen-activated protein kinase and the reduction in activation of signal transducer and activator of transcription 3, insulin receptor substrate-1, and Akt, as well as on interleukin (IL)-2 and IL-13 levels in the hippocampus. The functionality of somatostatin, measured as the percentage of inhibition of adenylate cyclase activity and the levels of insulin-degrading enzyme, was also preserved by GPE co-treatment. These findings indicate that GPE co-administration may protect from Aß insult by changing hippocampal cytokine content and somatostatin functionality through regulation of leptin- and IGF-I-signaling pathways that could influence the reduction in Aß levels through modulation of levels and/or activity of Aß proteases.
Assuntos
Peptídeos beta-Amiloides , Hipocampo , Fator de Crescimento Insulin-Like I , Oligopeptídeos , Transdução de Sinais , Animais , Peptídeos beta-Amiloides/metabolismo , Hipocampo/metabolismo , Hipocampo/efeitos dos fármacos , Ratos , Fator de Crescimento Insulin-Like I/metabolismo , Transdução de Sinais/efeitos dos fármacos , Feminino , Oligopeptídeos/farmacologia , Inflamação/metabolismo , Inflamação/tratamento farmacológico , Fragmentos de Peptídeos/metabolismo , Ratos Wistar , Doença de Alzheimer/metabolismo , Doença de Alzheimer/tratamento farmacológico , Proteínas Quinases p38 Ativadas por Mitógeno/metabolismo , Proteínas Proto-Oncogênicas c-akt/metabolismo , Peptídeos Semelhantes à InsulinaRESUMO
Excess body weight is frequently associated with low-grade inflammation. Evidence indicates a relationship between obesity and cancer, as well as with other diseases, such as diabetes and non-alcoholic fatty liver disease, in which inflammation and the actions of various adipokines play a role in the pathological mechanisms involved in these disorders. Leptin is mainly produced by adipose tissue in proportion to fat stores, but it is also synthesized in other organs, where leptin receptors are expressed. This hormone performs numerous actions in the brain, mainly related to the control of energy homeostasis. It is also involved in neurogenesis and neuroprotection, and central leptin resistance is related to some neurological disorders, e.g., Parkinson's and Alzheimer's diseases. In peripheral tissues, leptin is implicated in the regulation of metabolism, as well as of bone density and muscle mass. All these actions can be affected by changes in leptin levels and the mechanisms associated with resistance to this hormone. This review will present recent advances in the molecular mechanisms of leptin action and their underlying roles in pathological situations, which may be of interest for revealing new approaches for the treatment of diseases where the actions of this adipokine might be compromised.
Assuntos
Leptina , Obesidade , Humanos , Leptina/metabolismo , Obesidade/metabolismo , Adipocinas/metabolismo , Tecido Adiposo/metabolismo , Inflamação/metabolismoRESUMO
Leptin is involved in the modulation of insulin signaling in peripheral tissues, being closely associated with changes in lipid metabolism. This adipokine modifies inflammatory pathways that can interact with insulin targets in peripheral organs; however, the mechanisms remain unclear. Inflammatory and insulin signaling targets, cytokines, adiponectin, irisin and non-esterified fatty acid (NEFA) levels and enzymes of fatty acid anabolism were studied in the gastrocnemius of chronic centrally infused leptin (L), pair-fed and control rats. The phosphorylation of signal transducer and activator of transcription 3 (STAT3) and c-Jun N-terminal kinase (JNK) was reduced in L rats (59% and 58%, respectively). The phosphorylation of the insulin receptor and Akt and adiponectin and irisin content was increased in L rats (154%, 157%, 308% and 329%, respectively). The levels of glucose-6-phosphate dehydrogenase, the mRNA content of acetyl Co-A carboxylase and NEFA concentrations were diminished in the muscles of L rats (59%, 50% and 61%, respectively). The activation of JNK correlated positively with STAT3 phosphorylation, tumoral necrosis factor-α and NEFA and negatively with irisin and Akt phosphorylation. These data suggest that the activation of insulin signaling targets and a decrease in NEFA content are associated with a reduction in muscle inflammation parameters, suggesting that leptin may integrate these pathways.
RESUMO
The growth hormone (GH)/insulin-like growth factor I (IGF-I) axis is involved in metabolic control. Malnutrition reduces IGF-I and modifies the thermogenic capacity of brown adipose tissue (BAT). Leptin has effects on the GH/IGF-I axis and the function of BAT, but its interaction with IGF-I and the mechanisms involved in the regulation of thermogenesis remains unknown. We studied the GH/IGF-I axis and activation of IGF-I-related signaling and metabolism related to BAT thermogenesis in chronic central leptin infused (L), pair-fed (PF), and control rats. Hypothalamic somatostatin mRNA levels were increased in PF and decreased in L, while pituitary GH mRNA was reduced in PF. Serum GH and IGF-I concentrations were decreased only in PF. In BAT, the association between suppressor of cytokine signaling 3 and the IGF-I receptor was reduced, and phosphorylation of the IGF-I receptor increased in the L group. Phosphorylation of Akt and cyclic AMP response element binding protein and glucose transporter 4 mRNA levels were increased in L and mRNA levels of uncoupling protein-1 (UCP-1) and enzymes involved in lipid anabolism reduced in PF. These results suggest that modifications in UCP-1 in BAT and changes in the GH/IGF-I axis induced by negative energy balance are dependent upon leptin levels.
Assuntos
Tecido Adiposo Marrom/efeitos dos fármacos , Metabolismo Energético/efeitos dos fármacos , Hormônio do Crescimento/genética , Fator de Crescimento Insulin-Like I/genética , Leptina/farmacologia , Termogênese/efeitos dos fármacos , Tecido Adiposo Marrom/metabolismo , Animais , Proteína de Ligação ao Elemento de Resposta ao AMP Cíclico/genética , Proteína de Ligação ao Elemento de Resposta ao AMP Cíclico/metabolismo , Metabolismo Energético/genética , Transportador de Glucose Tipo 4/genética , Transportador de Glucose Tipo 4/metabolismo , Hormônio do Crescimento/metabolismo , Hipotálamo/efeitos dos fármacos , Hipotálamo/metabolismo , Injeções Intraventriculares , Fator de Crescimento Insulin-Like I/metabolismo , Masculino , Fosforilação/efeitos dos fármacos , Hipófise/efeitos dos fármacos , Hipófise/metabolismo , Proteínas Proto-Oncogênicas c-akt/genética , Proteínas Proto-Oncogênicas c-akt/metabolismo , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Ratos , Ratos Wistar , Receptor IGF Tipo 1/genética , Receptor IGF Tipo 1/metabolismo , Somatostatina/genética , Somatostatina/metabolismo , Proteína 3 Supressora da Sinalização de Citocinas/genética , Proteína 3 Supressora da Sinalização de Citocinas/metabolismo , Termogênese/genética , Proteína Desacopladora 1/genética , Proteína Desacopladora 1/metabolismoRESUMO
Obesity is one of the most important health problems facing developed countries because being overweight is associated with a higher incidence of type 2 diabetes, cardiovascular disease and cancer, as well as other comorbidities. Although increased weight gain results from a combination of poor dietary habits and decreased energy expenditure, not all individuals have equal propensities to gain weight or to develop secondary complications of obesity. This is partially a result not only of genetics, including sex, but also the time during which an individual is exposed to an obesogenic environment. In the present study, we have compared the response of male and female mice to short-term exposure to a high-fat diet (HFD) or a low-fat diet during the peripubertal period (starting at 42 days of age) because this is a stage of dramatic hormonal and metabolic modifications. After 1 week on a HFD, there was no significant increase in body weight, although females significantly increased their energy intake. Serum leptin levels increased in both sexes, even though no change in fat mass was detected. Glyceamia and homeostasis model assessment increased in males, suggesting a rapid change in glucose metabolism. Hypothalamic pro-opiomelanocortin mRNA levels were significantly higher in females on a HFD compared to all other groups, which may be an attempt to reduce their increased energy intake. Hypothalamic inflammation and gliosis have been implicated in the development of secondary complications of obesity; however, no indication of activation of inflammatory processes or gliosis was found in response to 1 week of HFD in the hypothalamus, hippocampus or cerebellum of these young mice. These results indicate that there are both sex and age effects in the response to poor dietary intake because peripubertal male and female mice respond differently to short-term dietary changes and this response is different from that reported in adult rodents.
Assuntos
Glicemia/metabolismo , Peso Corporal/fisiologia , Dieta Hiperlipídica , Hipotálamo/metabolismo , Maturidade Sexual/fisiologia , Adiposidade/fisiologia , Animais , Ingestão de Energia/fisiologia , Feminino , Insulina/sangue , Leptina/sangue , Masculino , Camundongos , Pró-Opiomelanocortina/genética , Pró-Opiomelanocortina/metabolismo , Fatores SexuaisRESUMO
Somatostatin (SRIF), a neuropeptide highly distributed in the hippocampus and involved in learning and memory, is markedly reduced in the brain of Alzheimer's disease patients. The effects of insulin-like growth factor-I (IGF-I) against ß amyloid (Aß)-induced neuronal death and associated cognitive disorders have been extensively reported in experimental models of this disease. Here, we examined the effect of IGF-I on the hippocampal somatostatinergic system in Aß-treated rats and the molecular mechanisms associated with changes in this peptidergic system. Intracerebroventricular Aß25-35 administration during 14â¯days (300â¯pmol/day) to male rats increased Aß25-35 levels and cell death and markedly reduced SRIF and SRIF receptor 2 levels in the hippocampus. These deleterious effects were associated with reduced Akt and cAMP response element-binding protein (CREB) phosphorylation and activation of c-Jun N-terminal kinase (JNK). Subcutaneous IGF-I co-administration (50⯵g/kg/day) reduced hippocampal Aß25-35 levels, cell death and JNK activation. In addition, IGF-I prevented the reduction in the components of the somatostatinergic system affected by Aß infusion. Its co-administration also augmented protein kinase A (PKA) activity, as well as Akt and CREB phosphorylation. These results suggest that IGF-I co-administration may have protective effects on the hippocampal somatostatinergic system against Aß insult through up-regulation of PKA activity and Akt and CREB phosphorylation.
Assuntos
Doença de Alzheimer/tratamento farmacológico , Hipocampo/efeitos dos fármacos , Fator de Crescimento Insulin-Like I/farmacologia , Fármacos Neuroprotetores/farmacologia , Somatostatina/metabolismo , Doença de Alzheimer/metabolismo , Doença de Alzheimer/patologia , Peptídeos beta-Amiloides , Animais , Morte Celular/efeitos dos fármacos , Morte Celular/fisiologia , Proteína de Ligação ao Elemento de Resposta ao AMP Cíclico/metabolismo , Proteínas Quinases Dependentes de AMP Cíclico/metabolismo , Modelos Animais de Doenças , Regulação para Baixo/efeitos dos fármacos , Hipocampo/metabolismo , Hipocampo/patologia , Proteínas Quinases JNK Ativadas por Mitógeno/metabolismo , Masculino , Fragmentos de Peptídeos , Fosforilação/efeitos dos fármacos , Proteínas Proto-Oncogênicas c-akt/metabolismo , Ratos Wistar , Receptores de Somatostatina/metabolismo , Transdução de Sinais/efeitos dos fármacosRESUMO
Insulin receptor substrate-2-deficient (IRS2(-/-)) mice are considered a good model to study the development of diabetes because IRS proteins mediate the pleiotropic effects of insulin-like growth factor-I (IGF-I) and insulin on metabolism, mitogenesis and cell survival. The hypothalamus might play a key role in the early onset of diabetes, owing to its involvement in the control of glucose homeostasis and energy balance. Because some inflammatory markers are elevated in the hypothalamus of diabetic IRS2(-/-) mice, our aim was to analyze whether the diabetes associated with the absence of IRS2 results in hypothalamic injury and to analyze the intracellular mechanisms involved. Only diabetic IRS2(-/-) mice showed increased cell death and activation of caspase-8 and -3 in the hypothalamus. Regulators of apoptosis such as FADD, Bcl-2, Bcl-xL and p53 were also increased, whereas p-IκB and c-FLIPL were decreased. This was accompanied by increased levels of Nox-4 and catalase, enzymes involved in oxidative stress. In summary, the hypothalamus of diabetic IRS2(-/-) mice showed an increase in oxidative stress and inflammatory markers that finally resulted in cell death via substantial activation of the extrinsic apoptotic pathway. Conversely, non-diabetic IRS2(-/-) mice did not show cell death in the hypothalamus, possibly owing to an increase in the levels of circulating IGF-I and in the enhanced hypothalamic IGF-IR phosphorylation that would lead to the stimulation of survival pathways. In conclusion, diabetes in IRS2-deficient male mice is associated with increased oxidative stress and apoptosis in the hypothalamus.
Assuntos
Apoptose , Diabetes Mellitus Experimental/patologia , Hipotálamo/patologia , Proteínas Substratos do Receptor de Insulina/deficiência , Estresse Oxidativo , Animais , Biomarcadores/metabolismo , Caspases/metabolismo , Citocinas/metabolismo , Inflamação/patologia , Proteínas Substratos do Receptor de Insulina/metabolismo , Fator de Crescimento Insulin-Like I/metabolismo , Masculino , Camundongos Endogâmicos C57BL , Camundongos Knockout , Proteínas Proto-Oncogênicas c-bcl-2/metabolismo , Receptor IGF Tipo 1/metabolismoRESUMO
Several studies indicate that 17ß-estradiol (E2) protects against amyloid ß-peptide (Aß)-induced cell death and activates factors associated with learning and memory, a function involving the hippocampal somatostatinergic system. As alterations in somatostatin have been demonstrated in Alzheimer's disease, we examined whether E2 prevents changes in the hippocampal somatostatinergic system induced by Aß25-35 and cell death, as well as the possible involvement of leptin and insulin-like growth factor (IGF)-I signaling. We also measured the levels of Aß proteases neprilysin and insulin-degrading-enzyme. Co-administration of E2 with Aß25-35 reduced both its levels and cell death, in addition to preventing the Aß-induced depletion of some somatostatinergic parameters. Activation of leptin and IGF-I pathways increased after E2 co-administration, and this correlated with changes in the somatostatinergic system. Changes in some components of this system were inversely related with Aß levels and cell death. Moreover, neprilysin levels were increased only in Aß plus E2-treated rats and E2 prevented the Aß-induced insulin-degrading-enzyme reduction. Our results suggest that the E2-induced reduction in cell death is related to lower Aß levels, probably because of IGF-I and somatostatin modulation of Aß proteases. We asked how 17ß-estradiol (E2) protects against ß-amyloid (Aß)-induced cell death. E2 co-administration prevents Aß-produced depletion of hippocampal somatostatin (SRIF) by an IGF-I-mediated mechanism, being related this protective effect with an increase in Aß proteases. Our results suggest that the E2-induced reduction in cell death is related to lower Aß levels, probably because of SRIF modulation of Aß proteases. CREB, cAMP response element-binding protein; IGF-I, insulin-like growth factor-I; STAT3, signal transducer and activator of transcription-3.
Assuntos
Peptídeos beta-Amiloides/metabolismo , Estradiol/farmacologia , Hipocampo/efeitos dos fármacos , Fator de Crescimento Insulin-Like I/metabolismo , Receptores de Somatostatina/metabolismo , Transdução de Sinais/efeitos dos fármacos , Doença de Alzheimer/metabolismo , Animais , Morte Celular/efeitos dos fármacos , Feminino , Hipocampo/metabolismo , Ratos Wistar , Somatostatina/metabolismoRESUMO
GH is important in metabolic control, and mice with disruption of the gene encoding the GH receptor (GHR) and GH binding protein (GHR-/- mice) are dwarf with low serum IGF-1 and insulin levels, high GH levels, and increased longevity, despite their obesity and altered lipid and metabolic profiles. Secondary complications of high-fat diet (HFD)-induced obesity are reported to be associated with hypothalamic inflammation and gliosis. Because GH and IGF-1 can modulate inflammatory processes, our objective was to evaluate the effect of HFD on hypothalamic inflammation/gliosis in the absence of GH signaling and determine how this correlates with changes in systemic metabolism. On normal chow, GHR-/- mice had a higher percentage of fat mass and increased circulating nonesterified free fatty acids levels compared with wild type (WT), and this was associated with increased hypothalamic TNF-α and phospho-JNK levels. After 7 weeks on a HFD, both WT and GHR-/- mice had increased weight gain, with GHR-/- mice having a greater rise in their percentage of body fat. In WT mice, HFD-induced weight gain was associated with increased hypothalamic levels of phospho-JNK and the microglial marker Iba-1 (ionized calcium-binding adapter molecule 1) but decreased cytokine production. Moreover, in GHR-/- mice, the HFD decreased hypothalamic inflammatory markers to WT levels with no indication of gliosis. Thus, the GH/IGF-1 axis is important in determining not only adipose tissue accrual but also the inflammatory response to HFD. However, how hypothalamic inflammation/gliosis is defined will determine whether it can be considered a common feature of HFD-induced obesity.
Assuntos
Dieta Hiperlipídica/efeitos adversos , Gliose/etiologia , Hormônio do Crescimento/deficiência , Doenças Hipotalâmicas/etiologia , Inflamação/etiologia , Animais , Glicemia , Composição Corporal , Tamanho Corporal , Citocinas/sangue , Doenças Hipotalâmicas/sangue , Hipotálamo/metabolismo , Inflamação/sangue , Insulina/sangue , Fator de Crescimento Insulin-Like I/metabolismo , Lipídeos/sangue , Masculino , Camundongos Endogâmicos C57BL , Camundongos Knockout , Neuropeptídeos/sangueRESUMO
Ghrelin is an endogenous hormone that stimulates appetite and adipose tissue accrual. Both the acylated (AG) and non-acylated (DAG) isoforms of this hormone are also reported to exert anti-inflammatory and protective effects systemically and in the central nervous system. As inflammatory processes have been implicated in obesity-associated secondary complications, we hypothesized that this natural appetite stimulator may protect against negative consequences resulting from excessive food intake. Adult male Wistar rats were treated icv (5 µg/day) with AG, DAG, the ghrelin mimetic GH-releasing peptide (GHRP)-6, AG, and pair-fed with controls (AG-pf) or saline for 14 days. Regardless of food intake AG increased visceral adipose tissue (VAT) and decreased circulating cytokine levels. However, AG reduced cytokine production in VAT only in rats fed ad libitum. Hypothalamic cytokine production was increased in AG-treated rats fed ad libitum and by DAG, but intracellular inflammatory signaling pathways associated with insulin and leptin resistance were unaffected. Gliosis was not observed in response to any treatment as glial markers were either reduced or unaffected. AG, DAG, and GHRP-6 stimulated production of hypothalamic insulin like-growth factor I that is involved in cell protective mechanisms. In hypothalamic astrocyte cell cultures AG decreased tumor necrosis factorα and DAG decreased interleukin-1ß mRNA levels, suggesting direct anti-inflammatory effects on astrocytes. Thus, whereas ghrelin stimulates food intake and weight gain, it may also induce mechanisms of cell protection that help to detour or delay systemic inflammatory responses and hypothalamic gliosis due to excess weight gain, as well as its associated pathologies.
Assuntos
Ingestão de Alimentos/fisiologia , Grelina/fisiologia , Hipotálamo/metabolismo , Mediadores da Inflamação/metabolismo , Aumento de Peso/fisiologia , Acilação , Adiposidade , Animais , Citocinas/metabolismo , Hipotálamo/patologia , Fator de Crescimento Insulin-Like I/metabolismo , Masculino , Ratos , Ratos WistarRESUMO
GH and GH secretagogues (GHSs) are involved in many cellular activities such as stimulation of mitosis, proliferation and differentiation. As astrocytes are involved in developmental and protective functions, our aim was to analyse the effects of GH and GH-releasing hexapeptide on astrocyte proliferation and differentiation in the hypothalamus and hippocampus. Treatment of adult male Wistar rats with GH (i.v., 100âµg/day) for 1 week increased the levels of glial fibrillary acidic protein (GFAP) and decreased the levels of vimentin in the hypothalamus and hippocampus. These changes were not accompanied by increased proliferation. By contrast, GH-releasing hexapeptide (i.v., 150âµg/day) did not affect GFAP levels but increased proliferation in the areas studied. To further study the intracellular mechanisms involved in these effects, we treated C6 astrocytoma cells with GH or GH-releasing hexapeptide and the phosphatidylinositol 3'-kinase (PI3K) inhibitor, LY294002, and observed that the presence of this inhibitor reverted the increase in GFAP levels induced by GH and the proliferation induced by GH-releasing hexapeptide. We conclude that although GH-releasing hexapeptide is a GHS, it may exert GH-independent effects centrally on astrocytes when administered i.v., although the effects of both substances appear to be mediated by the PI3K/Akt pathway.
Assuntos
Astrócitos/metabolismo , Hormônio do Crescimento/metabolismo , Oligopeptídeos/metabolismo , Animais , Astrócitos/citologia , Linhagem Celular , Proliferação de Células , Proteína Glial Fibrilar Ácida/metabolismo , Hipocampo/metabolismo , Hipotálamo/metabolismo , Masculino , Ratos , Ratos Wistar , Vimentina/metabolismoRESUMO
Subchronic gestational stress leads to permanent modifications in the hippocampus-hypothalamus-pituitary-adrenal axis of offspring probably due to the increase in circulating glucocorticoids known to affect prenatal programming. The aim of this study was to investigate whether cell turnover is affected in the hippocampus-hypothalamus-pituitary axis by subchronic prenatal stress and the intracellular mechanisms involved. Restraint stress was performed in pregnant rats during the last week of gestation (45 minutes; 3 times/day). Only male offspring were used for this study and were sacrificed at 6 months of age. In prenatally stressed adults a decrease in markers of cell death and proliferation was observed in the hippocampus, hypothalamus and pituitary. This was associated with an increase in insulin-like growth factor-I mRNA levels, phosphorylation of CREB and calpastatin levels and inhibition of calpain -2 and caspase -8 activation. Levels of the anti-apoptotic protein Bcl-2 were increased and levels of the pro-apoptotic factor p53 were reduced. In conclusion, prenatal restraint stress induces a long-term decrease in cell turnover in the hippocampus-hypothalamus-pituitary axis that might be at least partly mediated by an autocrine-paracrine IGF-I effect. These changes could condition the response of this axis to future physiological and pathophysiological situations.
Assuntos
Sistema Hipotálamo-Hipofisário/metabolismo , Sistema Hipófise-Suprarrenal/metabolismo , Estresse Fisiológico/fisiologia , Animais , Proteínas de Ligação ao Cálcio/metabolismo , Calpaína/metabolismo , Caspase 8/metabolismo , Proteína de Ligação ao Elemento de Resposta ao AMP Cíclico/metabolismo , Feminino , Fator de Crescimento Insulin-Like I/metabolismo , Masculino , Fosforilação , Gravidez , Efeitos Tardios da Exposição Pré-Natal , Proteínas Proto-Oncogênicas c-bcl-2/metabolismo , RNA Mensageiro/genética , Ratos , Tempo , Proteína Supressora de Tumor p53/metabolismoRESUMO
Poorly controlled type1 diabetes is associated with hormonal imbalances and increased cell death in different tissues, including the pituitary, hypothalamus and cerebellum. In the pituitary, lactotrophs are the cell population with the greatest increase in cell death, whereas in the hypothalamus and cerebellum astrocytes are most highly affected. Insulin treatment can delay, but does not prevent, diabetic complications. As ghrelin and growth hormone (GH) secretagogues are reported to prevent apoptosis in different tissues, and to modulate glucose homeostasis, a combined hormonal treatment may be beneficial. Hence, we analyzed the effect of insulin and GH-releasing peptide 6 (GHRP-6) on diabetes-induced apoptosis in the pituitary, hypothalamus and cerebellum of diabetic rats. Adult male Wistar rats were made diabetic by streptozotocin injection (65 mg/kg ip) and divided into four groups from diabetes onset: those receiving a daily sc injection of saline (1 ml/kg/day), GHRP-6 (150 µg/kg/day), insulin (1-8U/day) or insulin plus GHRP-6 for 8 weeks. Control non-diabetic rats received saline (1 ml/kg/day). Diabetes increased cell death in the pituitary, hypothalamus and cerebellum (P<0.05). In the pituitary, insulin treatment prevented diabetes-induced apoptosis (P<0.01), as well as the decline in prolactin and GH mRNA levels (P<0.05). In the hypothalamus, neither insulin nor GHRP-6 decreased diabetes-induced cell death. However, the combined treatment of insulin+GHRP-6 prevented the diabetes induced-decrease in glial fibrillary acidic protein (GFAP) levels (P<0.05). In the cerebellum, although insulin treatment increased GFAP levels (P<0.01), only the combined treatment of insulin+ GHRP-6 decreased diabetes-induced apoptosis (P<0.05). In conclusion, insulin and GHRP-6 exert tissue specific effects in STZ-diabetic rats and act synergistically on some processes. Indeed, insulin treatment does not seem to be effective on preventing some of the diabetes-induced alterations in the central nervous system.
Assuntos
Morte Celular/efeitos dos fármacos , Cerebelo/patologia , Diabetes Mellitus Experimental/patologia , Hipotálamo/patologia , Insulina/farmacologia , Oligopeptídeos/farmacologia , Hipófise/patologia , Animais , Caspases/metabolismo , Cerebelo/metabolismo , Diabetes Mellitus Experimental/induzido quimicamente , Diabetes Mellitus Experimental/metabolismo , Proteína Glial Fibrilar Ácida/metabolismo , Proteínas de Choque Térmico HSP72/metabolismo , Hipotálamo/metabolismo , Fator de Crescimento Insulin-Like I/genética , Fator de Crescimento Insulin-Like I/metabolismo , Masculino , Hipófise/metabolismo , Hormônios Hipofisários/genética , Hormônios Hipofisários/metabolismo , Antígeno Nuclear de Célula em Proliferação/metabolismo , Proteínas Proto-Oncogênicas c-bcl-2/metabolismo , Ratos , Ratos Wistar , Receptor de Insulina/genética , Receptor de Insulina/metabolismo , Receptores de Grelina/genética , Receptores de Grelina/metabolismo , Estreptozocina , Transcrição Gênica/efeitos dos fármacos , Fator de Necrose Tumoral alfa/metabolismo , Aumento de Peso/efeitos dos fármacos , Proteínas Inibidoras de Apoptose Ligadas ao Cromossomo X/metabolismoRESUMO
Cell death is increased in the anterior pituitary of poorly controlled diabetic rats, but anti-apoptotic mechanisms are also activated. We hypothesized that specific cell types are selectively protected against diabetes-induced cell death. To determine when anti-apoptotic mechanisms are activated, streptozotocin-induced diabetic rats were killed after 1, 4, 6 and 8 weeks of evolution. Anterior pituitaries were processed for western blot analysis to determine changes in the intrinsic cell death pathway and upstream kinases involved in cell protection mechanisms. An increase in cell death was detected by ELISA at 4 weeks of diabetes. TUNEL labelling demonstrated that this corresponded to death of primarily lactotrophs, a few somatotrophs, and no thyrotrophs, corticotrophs or gonadotrophs. Levels of phosphorylated (p) Akt were increased at 1 week of diabetes, while pERK1/2 levels increased at 4 weeks and pJNK at 6 weeks. Activation of caspase 3 decreased and anti-apoptotic members of the Bcl-2 protein family increased as early as 1 week after diabetes onset. These changes were coincident with increased IGF-I receptor levels. Levels of X-linked inhibitor of apoptosis protein (XIAP) increased significantly after 6 weeks of diabetes, as did activation of nuclear factor (NF)kappaB. Double immunohistochemistry indicated that XIAP was expressed in less than 1% of lactotrophs and gonadotrophs, approximately 50% of somatotrophs and more than 90% of corticotrophs and thyrotrophs. These results suggest that some cell survival mechanisms are rapidly activated in the anterior pituitary, even before increased cell death can be detected, while others are more delayed. Furthermore, both pituitary cell death and expression of protective mechanisms such as XIAP are cell-type specific.
Assuntos
Diabetes Mellitus Experimental/metabolismo , Adeno-Hipófise/metabolismo , Proteínas Inibidoras de Apoptose Ligadas ao Cromossomo X/metabolismo , Animais , Apoptose , Glicemia/análise , Caspases/análise , Caspases/metabolismo , Corticotrofos/metabolismo , Corticotrofos/patologia , Diabetes Mellitus Experimental/patologia , Ensaio de Imunoadsorção Enzimática/métodos , MAP Quinases Reguladas por Sinal Extracelular/análise , MAP Quinases Reguladas por Sinal Extracelular/metabolismo , Gonadotrofos/metabolismo , Gonadotrofos/patologia , Immunoblotting/métodos , Imuno-Histoquímica/métodos , Marcação In Situ das Extremidades Cortadas , Insulina/sangue , Lactotrofos/metabolismo , Lactotrofos/patologia , Masculino , Proteínas Proto-Oncogênicas c-akt/análise , Proteínas Proto-Oncogênicas c-akt/metabolismo , Proteínas Proto-Oncogênicas c-bcl-2/análise , Proteínas Proto-Oncogênicas c-bcl-2/metabolismo , Ratos , Ratos Wistar , Somatotrofos/metabolismo , Somatotrofos/patologia , Tireotrofos/metabolismo , Tireotrofos/patologia , Fatores de Tempo , Proteínas Inibidoras de Apoptose Ligadas ao Cromossomo X/análiseRESUMO
Estradiol prevents amyloid-beta peptide (Abeta)-induced cell death through estrogen receptors (ERs) and modulates somatostatin (SRIF) responsiveness in the rat brain. As intracerebroventricular (ICV) Abeta25-35 administration reduces SRIFergic tone in the temporal cortex of ovariectomized (Ovx) rats, we asked whether 17beta-estradiol (E2) treatment can restore the Abeta25-35 induced changes in SRIF content, SRIF receptor density and adenylyl cyclase (AC) activity, as well as if these effects are mediated by ERs. E2 treatment did not change Abeta25-35 levels in the temporal cortex, but partially restored the SRIFergic parameters affected by Abeta insult and decreased cell death, which was correlated with Akt activation. The ER antagonist ICI 182,780 prevented the protective effect of E2 on sst2 levels, but did not modify SRIF levels. Furthermore, ICI 182,780 treatment further decreased sst2 protein and mRNA levels when administered alone to Abeta25-35-treated rats, suggesting that it may block the effects of endogenous estrogens. These findings indicate that E2 protects the temporal cortical SRIFergic system from Abeta-induced depletion independently of Abeta accumulation.
Assuntos
Peptídeos beta-Amiloides/administração & dosagem , Estradiol/farmacologia , Fragmentos de Peptídeos/administração & dosagem , Somatostatina/metabolismo , Lobo Temporal/efeitos dos fármacos , Adenilil Ciclases/metabolismo , Análise de Variância , Animais , Fator Neurotrófico Derivado do Encéfalo/genética , Fator Neurotrófico Derivado do Encéfalo/metabolismo , Morte Celular/efeitos dos fármacos , Estradiol/análogos & derivados , Estradiol/sangue , Antagonistas de Estrogênios/farmacologia , Feminino , Fulvestranto , Marcação In Situ das Extremidades Cortadas , Ovariectomia/métodos , Ligação Proteica/efeitos dos fármacos , RNA Mensageiro/biossíntese , Radioimunoensaio/métodos , Ratos , Ratos Wistar , Receptores de Somatostatina/metabolismo , Reação em Cadeia da Polimerase Via Transcriptase Reversa/métodos , Transdução de Sinais/efeitos dos fármacosRESUMO
Chronic systemic treatment given to adult male rats with growth hormone releasing peptide-6, an agonist of the ghrelin receptor, increases insulin-like growth factor I levels in various brain regions, including the hypothalamus and cerebellum. Furthermore, intracellular signalling cascades normally associated with anti-apoptotic actions are activated in the same areas and are coincident with decreased basal cell death. Because abnormally high concentrations of glutamate can lead to overexcitation of neurones leading to cell damage and/or death, we investigated whether administration of growth hormone releasing peptide-6 attenuates monosodium glutamate-induced apoptosis in the rat hypothalamus and cerebellum. Glutamate increased activation of caspase 9 followed by cleavage of caspase 7, which in turn fragmented poly(ADP-ribose) polymerase, terminating in cell death in both the hypothalamus and cerebellum. Growth hormone releasing peptide-6 reversed glutamate-induced cell death by decreasing activation of caspases 9 and 7 and poly(ADP-ribose) polymerase fragmentation. These results provide a better understanding of the neuroprotective role of growth hormone secretagogues and the mechanisms involved.
Assuntos
Ácido Glutâmico/toxicidade , Hormônio Liberador de Hormônio do Crescimento/farmacologia , Neurotoxinas/antagonistas & inibidores , Neurotoxinas/toxicidade , Oligopeptídeos/farmacologia , Animais , Apoptose/efeitos dos fármacos , Western Blotting , Caspase 7/metabolismo , Morte Celular/efeitos dos fármacos , Cerebelo/efeitos dos fármacos , Cerebelo/metabolismo , Proteína de Ligação ao Elemento de Resposta ao AMP Cíclico/metabolismo , Fragmentação do DNA/efeitos dos fármacos , Ativação Enzimática/efeitos dos fármacos , Ensaio de Imunoadsorção Enzimática , Fluoresceínas , Corantes Fluorescentes , Hipotálamo/efeitos dos fármacos , Hipotálamo/metabolismo , Técnicas Imunoenzimáticas , Imuno-Histoquímica , Fator de Crescimento Insulin-Like I/metabolismo , Masculino , Neurônios/efeitos dos fármacos , Compostos Orgânicos , Ratos , Ratos Wistar , Transdução de Sinais/efeitos dos fármacosRESUMO
Poorly controlled diabetes mellitus can result in decreased prolactin production and thus problems with lactation, reproduction, and other physiological processes. This may be due to a loss of lactotrophs, as we have previously shown that long-term (8 weeks) poorly controlled streptozotocin-induced diabetes results in increased death of lactotrophs and that this most likely occurs through the activation of caspase-8 and the extrinsic cell death cascade. However, cell proliferation is also increased in the anterior pituitary at this time, although the cell type undergoing this proliferation and whether it is a response to the increased cell death remains unknown. In order to determine the time-course of increased cell death and proliferation in the anterior pituitary and if this is related to changes in tumor necrosis factor (TNF)-alpha, a cytokine involved in the activation of the extrinsic cell death pathway, rats were killed at 1, 4, 6, and 8 weeks after the induction of diabetes. Cell death was significantly increased after 4 weeks, as was caspase-8 activation, although circulating levels of TNF-alpha were increased as early as 1 week. Pituitary levels of TNF-alpha did not change significantly until 8 weeks after diabetes onset. Similarly, Western-blot analysis of proliferating cell nuclear antigen showed that anterior pituitary cell proliferation increased significantly 8 weeks after diabetes onset, with the majority of proliferating cells, as detected by BrdU incorporation, corresponding to lactotrophs. These results suggest that the increased death of lactotrophs in poorly controlled diabetic rats is followed by increased proliferation of this cell type, even when no treatment is given.
Assuntos
Apoptose , Diabetes Mellitus Experimental/patologia , Lactotrofos/patologia , Animais , Biomarcadores/análise , Bromodesoxiuridina/análise , Caspase 8/metabolismo , Proliferação de Células , Diabetes Mellitus Experimental/metabolismo , Ativação Enzimática , Ensaio de Imunoadsorção Enzimática/métodos , Immunoblotting/métodos , Lactotrofos/metabolismo , Masculino , Adeno-Hipófise/química , Adeno-Hipófise/metabolismo , Adeno-Hipófise/patologia , Antígeno Nuclear de Célula em Proliferação/análise , Ratos , Ratos Wistar , Fatores de Tempo , Fator de Necrose Tumoral alfa/análiseRESUMO
Lactotroph cell death is increased in streptozotocin-induced diabetic rats. To determine the mechanism involved, cell death proteins were accessed in pituitaries of diabetic (streptozotocin at 65 mg/kg, 2 months evolution) and control male rats by Western blot analysis and double immunohistochemistry. The intact and cleaved forms of caspase 9 were increased in diabetic rat pituitaries compared with controls. Although the proforms of caspases 3, 6, and 7 were increased in diabetic rat pituitaries, their activated forms were either unchanged or decreased. Activation of these effector caspases may be blocked by the increased expression of X-chromosome-linked inhibitor of apoptosis protein (XIAP) in diabetic rat pituitaries. However, in diabetic rats, XIAP expression in lactotrophs was decreased, suggesting that this cell type is not protected. Caspase 8, p53, and nuclear factor kappaB were more highly activated in diabetic rat pituitaries, with caspase 8 colocalization in lactotrophs being increased. These results suggest that, in the pituitaries of diabetic rats, the cascades of normal cell turnover are partially inhibited, possibly via XIAP, and this may be cell specific. Furthermore, activation of the extrinsic cell-death pathway, including activation of caspase 8, may underlie the diabetes-associated increase in lactotroph death.
Assuntos
Caspases/metabolismo , Diabetes Mellitus Experimental/enzimologia , Hipófise/enzimologia , Animais , Apoptose , Caspase 8 , Morte Celular , Ativação Enzimática , Histonas/análise , Hormônios Hipotalâmicos/fisiologia , Imuno-Histoquímica , Hipófise/patologia , Proteínas Proto-Oncogênicas c-bcl-2/análise , RatosRESUMO
Gonadal sex steroids modulate GH synthesis and secretion with effects on both the hypothalamus and anterior pituitary. In the post-pubertal animal, androgens and oestrogens modulate hypothalamic somatostatin (SS) and GHRH synthesis respectively. These effects may be direct as SS neurons express the androgen receptor and many GHRH neurons are oestrogen receptor positive. The neonatal steroid environment modulates the number of GHRH neurons in the adult hypothalamus, as well as their responsivity to post-pubertal steroids. Furthermore, both neonatal and post-pubertal steroids modulate hypothalamic synaptic organisation affecting the number of synaptic inputs and the morphology of glial cells. This in turn has important effects on the ability of the hypothalamus to drive the secretory pulsatility of anterior pituitary hormone release. At the level of the somatotroph, androgens and oestrogens have been reported to stimulate, inhibit or have no effect on GH synthesis. In primary cultures, we found no effect of either androgens or oestrogens on GH mRNA levels. However, the sex steroid environment significantly modified the response of somatotrophs to SS. Furthermore, males have more somatotrophs compared with female rats and this partially depends on the neonatal sex steroid environment. In conclusion, sex steroids have both organisational and activational effects on the GH axis. These effects range from modulating the number of hypothalamic neurons controlling GH secretion, their responsiveness to later steroids, and the synaptic connectivity and neuropeptide production, to modulation of somatotroph numbers in the anterior pituitary and their responsiveness to inputs controlling GH synthesis and secretion.
Assuntos
Hormônios Esteroides Gonadais/fisiologia , Hormônio do Crescimento/metabolismo , Adolescente , Adulto , Animais , Estrogênios/fisiologia , Feminino , Hormônios Esteroides Gonadais/farmacologia , Hormônio Liberador de Hormônio do Crescimento , Humanos , Hipotálamo/metabolismo , Recém-Nascido , Fator de Crescimento Insulin-Like I/fisiologia , Masculino , Adeno-Hipófise/metabolismo , Ratos , Somatostatina/metabolismoRESUMO
Nerve growth factor induces cell death in organotypic cultures of otic vesicle explants. This cell death has a restricted pattern that reproduces the in vivo pattern of apoptosis occurring during inner ear development. In this study, we show that binding of nerve growth factor to its low affinity p75 neurotrophin receptor is essential to achieve the apoptotic response. Blockage of binding to p75 receptor neutralized nerve-growth-factor-induced cell death, as measured by immunoassays detecting the presence of cytosolic oligonucleosomes and by TUNEL assay to visualize DNA fragmentation. Nerve growth factor also induced a number of cell-death-related intracellular events including ceramide generation, caspase activation and poly-(ADP ribose) polymerase cleavage. Again, p75 receptor blockade completely abolished all of these effects. Concerning the intracellular pathway, ceramide increase depended on initiator caspases, whereas its actions depended on both initiator and effector caspases, as shown by using site-specific caspase inhibitors. Conversely, insulin-like growth factor I, which promotes cell growth and survival in the inner ear, abolished apoptosis induced by nerve growth factor. Insulin-like growth factor cytoprotective actions were accomplished, at least in part, by decreasing endogenous ceramide levels and activating Akt. Taken together, these results strongly suggest that regulation of nerve-growth-factor-induced apoptosis in the otocysts occurs via p75 receptor binding and is strictly controlled by the interaction with survival signalling pathways.