RESUMEN
Glucagon hypersecretion from pancreatic islet α-cells exacerbates hyperglycemia in type 1 diabetes (T1D) and type 2 diabetes. Still, the underlying mechanistic pathways that regulate glucagon secretion remain controversial. Among the three complementary main mechanisms (intrinsic, paracrine, and juxtacrine) proposed to regulate glucagon release from α-cells, juxtacrine interactions are the least studied. It is known that tonic stimulation of α-cell EphA receptors by ephrin-A ligands (EphA forward signaling) inhibits glucagon secretion in mouse and human islets and restores glucose inhibition of glucagon secretion in sorted mouse α-cells, and these effects correlate with increased F-actin density. Here, we elucidate the downstream target of EphA signaling in α-cells. We demonstrate that RhoA, a Rho family GTPase, plays a key role in this pathway. Pharmacological inhibition of RhoA disrupts glucose inhibition of glucagon secretion in islets and decreases cortical F-actin density in dispersed α-cells and α-cells in intact islets. Quantitative FRET biosensor imaging shows that increased RhoA activity follows directly from EphA stimulation. We show that in addition to modulating F-actin density, EphA forward signaling and RhoA activity affect α-cell Ca2+ activity in a novel mechanistic pathway. Finally, we show that stimulating EphA forward signaling restores glucose inhibition of glucagon secretion from human T1D donor islets.
Asunto(s)
Células Secretoras de Glucagón , Glucagón , Proteína de Unión al GTP rhoA , Animales , Humanos , Ratones , Actinas/metabolismo , Calcio/metabolismo , Diabetes Mellitus Tipo 1/metabolismo , Diabetes Mellitus Tipo 2/metabolismo , Efrinas/metabolismo , Glucagón/metabolismo , Células Secretoras de Glucagón/metabolismo , Glucosa/metabolismo , Insulina/metabolismo , Islotes Pancreáticos/metabolismo , Ligandos , Receptores de la Familia Eph/metabolismo , Proteína de Unión al GTP rhoA/metabolismoRESUMEN
Type 2 Diabetes Mellitus (T2DM) is one of the most prevalent chronic metabolic disorders, and insulin has been placed at the epicentre of its pathophysiological basis. However, the involvement of impaired alpha (α) cell function has been recognized as playing an essential role in several diseases, since hyperglucagonemia has been evidenced in both Type 1 and T2DM. This phenomenon has been attributed to intra-islet defects, like modifications in pancreatic α cell mass or dysfunction in glucagon's secretion. Emerging evidence has shown that chronic hyperglycaemia provokes changes in the Langerhans' islets cytoarchitecture, including α cell hyperplasia, pancreatic beta (ß) cell dedifferentiation into glucagon-positive producing cells, and loss of paracrine and endocrine regulation due to ß cell mass loss. Other abnormalities like α cell insulin resistance, sensor machinery dysfunction, or paradoxical ATP-sensitive potassium channels (KATP) opening have also been linked to glucagon hypersecretion. Recent clinical trials in phases 1 or 2 have shown new molecules with glucagon-antagonist properties with considerable effectiveness and acceptable safety profiles. Glucagon-like peptide-1 (GLP-1) agonists and Dipeptidyl Peptidase-4 inhibitors (DPP-4 inhibitors) have been shown to decrease glucagon secretion in T2DM, and their possible therapeutic role in T1DM means they are attractive as an insulin-adjuvant therapy.
Asunto(s)
Comunicación Autocrina , Diabetes Mellitus Tipo 1/metabolismo , Diabetes Mellitus Tipo 2/metabolismo , Células Secretoras de Glucagón/metabolismo , Células Secretoras de Insulina/metabolismo , Comunicación Paracrina , Animales , Diabetes Mellitus Tipo 1/tratamiento farmacológico , Diabetes Mellitus Tipo 1/patología , Diabetes Mellitus Tipo 2/tratamiento farmacológico , Diabetes Mellitus Tipo 2/patología , Inhibidores de la Dipeptidil-Peptidasa IV/uso terapéutico , Glucagón/metabolismo , Péptido 1 Similar al Glucagón/antagonistas & inhibidores , Péptido 1 Similar al Glucagón/metabolismo , Células Secretoras de Glucagón/patología , Humanos , Hipoglucemiantes/uso terapéutico , Células Secretoras de Insulina/patologíaRESUMEN
Patients with type 2 diabetes (T2D) often exhibit hyperglucagonemia despite hyperglycemia, implicating defective α-cell function. Although endoplasmic reticulum (ER) stress has been suggested to underlie ß-cell dysfunction in T2D, its role in α-cell biology remains unclear. X-box binding protein 1 (XBP1) is a transcription factor that plays a crucial role in the unfolded protein response (UPR), and its deficiency in ß-cells has been reported to impair insulin secretion, leading to glucose intolerance. To evaluate the role of XBP1 in α-cells, we created complementary in vivo (α-cell-specific XBP1 knockout [αXBPKO] mice) and in vitro (stable XBP1 knockdown α-cell line [αXBPKD]) models. The αXBPKO mice exhibited glucose intolerance, mild insulin resistance, and an inability to suppress glucagon secretion after glucose stimulation. αXBPKD cells exhibited activation of inositol-requiring enzyme 1, an upstream activator of XBP1, leading to phosphorylation of Jun NH2-terminal kinase. Interestingly, insulin treatment of αXBPKD cells reduced tyrosine phosphorylation of insulin receptor substrate 1 (IRS1) (pY(896)) and phosphorylation of Akt while enhancing serine phosphorylation (pS(307)) of IRS1. Consequently, the αXBPKD cells exhibited blunted suppression of glucagon secretion after insulin treatment in the presence of high glucose. Together, these data indicate that XBP1 deficiency in pancreatic α-cells induces altered insulin signaling and dysfunctional glucagon secretion.
Asunto(s)
Proteínas de Unión al ADN/metabolismo , Células Secretoras de Glucagón/metabolismo , Glucagón/metabolismo , Intolerancia a la Glucosa/metabolismo , Resistencia a la Insulina/genética , Insulina/metabolismo , Factores de Transcripción/metabolismo , Animales , Proteínas de Unión al ADN/genética , Glucagón/genética , Células Secretoras de Glucagón/efectos de los fármacos , Intolerancia a la Glucosa/genética , Insulina/farmacología , Proteínas Sustrato del Receptor de Insulina/metabolismo , Proteínas Quinasas JNK Activadas por Mitógenos/genética , Proteínas Quinasas JNK Activadas por Mitógenos/metabolismo , Masculino , Ratones , Ratones Noqueados , Fosforilación/efectos de los fármacos , Proteínas Proto-Oncogénicas c-akt/genética , Proteínas Proto-Oncogénicas c-akt/metabolismo , Factores de Transcripción del Factor Regulador X , Transducción de Señal/efectos de los fármacos , Transducción de Señal/genética , Factores de Transcripción/genética , Proteína 1 de Unión a la X-BoxRESUMEN
Neuronostatin, derived from the somatostatin preprohormone, is a recently described peptide that is produced by several tissues involved in cardiovascular regulation and metabolism, including the hypothalamus. Injection of neuronostatin into the lateral cerebroventricle led to a dose-related increase in mean arterial pressure (MAP) in rats. Any attempt to inhibit the production of neuronostatin would alter somatostatin production as well, making determination of the physiological relevance of the peptide's pharmacologic effects by compromise of production approaches impossible. Therefore, we employed an alternative approach to identify and compromise the production of the neuronostatin receptor. Because neuronostatin was shown to signal via a PKA-dependent mechanism, we hypothesized that the neuronostatin receptor was a G protein-coupled receptor (GPCR), in particular, one of the orphan GPCRs for which the ligand is unknown. Therefore, we screened neuronostatin-responsive tissues, including hypothalamus, heart, pancreatic α-cells, and the gastric tumor cell line KATOIII, for expression of orphan GPCRs. Four orphan GPCRs were expressed by all cell types, including GPR56 and GPR107. Knockdown of GPR107, but not GPR56 or GPR146, led to a loss of responsiveness to neuronostatin by KATOIII cells. Rats injected with siRNA directed against GPR107 (2 µg/day for 2 days) into the lateral cerebroventricle did not exhibit an increase in MAP in response to neuronostatin treatment. Rats with compromised GPR107 expression also displayed blunted reactivity in a baroreflex sensitivity test, indicating that GPR107 and neuronostatin may be important regulators of cardiovascular function. Thus, GPR107 is a promising candidate receptor for neuronostatin, and neuronostatin, interacting with GPR107, may play an important role in the central control of cardiovascular function.
Asunto(s)
Fragmentos de Péptidos/metabolismo , Hormonas Peptídicas/metabolismo , Receptores Acoplados a Proteínas G/metabolismo , Somatostatina/metabolismo , Animales , Presión Sanguínea/efectos de los fármacos , Presión Sanguínea/fisiología , Fenómenos Fisiológicos Cardiovasculares , Línea Celular , Línea Celular Tumoral , Células Cultivadas , Células Secretoras de Glucagón/metabolismo , Células Secretoras de Glucagón/patología , Humanos , Hipotálamo/metabolismo , Hipotálamo/patología , Masculino , Ratones , Miocardio/metabolismo , Miocardio/patología , ARN Interferente Pequeño/farmacología , Ratas , Neoplasias Gástricas/metabolismo , Neoplasias Gástricas/patologíaRESUMEN
Nutrient availability is critical for the physiological functions of all tissues. By contrast, an excess of nutrients such as carbohydrate and fats impair health and shorten life due by stimulating chronic diseases, including diabetes, cancer and neurodegeneration. The control of circulating glucose and lipid levels involve mitochondria in both central and peripheral mechanisms of metabolism regulation. Mitochondrial uncoupling protein 2 (UCP2) has been implicated in physiological and pathological processes related to glucose and lipid metabolism, and in this review we discuss the latest data on the relationships between UCP2 and glucose and lipid sensing from the perspective of specific hypothalamic neuronal circuits and peripheral tissue functions. The goal is to provide a framework for discussion of future therapeutic strategies for metabolism-related chronic diseases.
Asunto(s)
Glucosa/metabolismo , Canales Iónicos/metabolismo , Metabolismo de los Lípidos/fisiología , Proteínas Mitocondriales/metabolismo , Proteína Relacionada con Agouti/metabolismo , Animales , Células Secretoras de Glucagón/metabolismo , Humanos , Hipotálamo/metabolismo , Células Secretoras de Insulina/metabolismo , Mitocondrias/metabolismo , Neuronas/metabolismo , Obesidad/metabolismo , Proopiomelanocortina/metabolismo , Especies Reactivas de Oxígeno/metabolismo , Transducción de Señal , Proteína Desacopladora 2RESUMEN
Glucagon is a hormone secreted from the alpha cells of the pancreatic islets. Through its effect on hepatic glucose production (HGP), glucagon plays a central role in the regulation of glucose homeostasis. In patients with type 2 diabetes mellitus (T2DM), abnormal regulation of glucagon secretion has been implicated in the development of fasting and postprandial hyperglycaemia. Therefore, new therapeutic agents based on antagonizing glucagon action, and hence blockade of glucagon-induced HGP, could be effective in lowering both fasting and postprandial hyperglycaemia in patients with T2DM. This review focuses on the mechanism of action, safety and efficacy of glucagon antagonists in the treatment of T2DM and discusses the challenges associated with this new potential antidiabetic treatment modality.
Asunto(s)
Diabetes Mellitus Tipo 2/tratamiento farmacológico , Células Secretoras de Glucagón/metabolismo , Glucagón/antagonistas & inhibidores , Hiperglucemia/tratamiento farmacológico , Hipoglucemiantes/farmacología , Hígado/metabolismo , Receptores de Glucagón/antagonistas & inhibidores , Compuestos de Bifenilo/administración & dosificación , Compuestos de Bifenilo/farmacología , Diabetes Mellitus Tipo 2/metabolismo , Ayuno , Glucagón/biosíntesis , Glucagón/metabolismo , Células Secretoras de Glucagón/efectos de los fármacos , Humanos , Hiperglucemia/metabolismo , Hipoglucemiantes/uso terapéutico , Hígado/efectos de los fármacos , Transducción de Señal/efectos de los fármacosRESUMEN
High-content screening for small-molecule inducers of insulin expression identified the compound BRD7389, which caused alpha-cells to adopt several morphological and gene expression features of a beta-cell state. Assay-performance profile analysis suggests kinase inhibition as a mechanism of action, and we show that biochemical and cellular inhibition of the RSK kinase family by BRD7389 is likely related to its ability induce a beta-cell-like state. BRD7389 also increases the endocrine cell content and function of donor human pancreatic islets in culture.
Asunto(s)
Células Secretoras de Glucagón/efectos de los fármacos , Células Secretoras de Glucagón/metabolismo , Insulina/biosíntesis , Inhibidores de Proteínas Quinasas/farmacología , Quinolonas/farmacología , Animales , Diferenciación Celular/efectos de los fármacos , Línea Celular , Evaluación Preclínica de Medicamentos , Expresión Génica/efectos de los fármacos , Células Secretoras de Glucagón/citología , Humanos , Células Secretoras de Insulina/citología , Células Secretoras de Insulina/efectos de los fármacos , Células Secretoras de Insulina/metabolismo , Islotes Pancreáticos/efectos de los fármacos , Islotes Pancreáticos/metabolismo , Ratones , Estructura Molecular , Inhibidores de Proteínas Quinasas/química , Quinolonas/química , Interferencia de ARN , Proteínas Quinasas S6 Ribosómicas/antagonistas & inhibidores , Proteínas Quinasas S6 Ribosómicas/genética , Técnicas de Cultivo de TejidosRESUMEN
Insulin and glucagon secretion from the islets of Langerhans is highly regulated. Although an increased plasma glucose level is the major stimulus for insulin exocytosis, roles for glutamine and glutamate have been suggested. Interestingly, the islet cells display elements associated with synaptic transmission. In the central nervous system (CNS), glutamine transport by SN1 and SAT2 sustain the generation of neurotransmitter glutamate. We hypothesized that the same transporters are essential for glutamine transport into the islet cells and for subsequent formation of glutamate acting as an intracellular signaling molecule. We demonstrate that islet cells express several transporters which can mediate glutamine transport. In particular, we show pronounced expression of SN1 and SAT2 in B-cells and A-cells, respectively. The cell-specific expression of these transporters together with their functional characteristics suggest an important role for glutamine in the regulation of insulin secretion.