RESUMEN
Resistin is a recently described novel adipokine that has been suggested to play an important role in the development of insulin resistance and type 2 diabetes by inhibiting insulin receptor signaling in myocytes and adipocytes. In the present study, we evaluated the direct effect of resistin on insulin secretion in pancreatic beta-cells. After treatment with recombinant resistin for 30 min, changes in glucose uptake, intracellular ATP and calcium levels, and insulin secretion were measured in glucose-stimulated INS-1 cells. The number of insulin granules morphologically docked to the plasma membrane was measured using a total internal reflection fluorescence microscope. Resistin significantly inhibited glucose-stimulated insulin secretion in INS-1 cells. Although resistin had no effects on intracellular glucose uptake, ATP and calcium levels, it caused a significant decrease in the number of docked insulin granules. In addition, the expression of rab3A was decreased after treatment with resistin. These results suggest that resistin can inhibit insulin secretion through inhibition of insulin granule docking via downregulation of rab3A in pancreatic beta-cells. The present finding may also be an important mechanism of resistin for the development of type 2 diabetes.
Asunto(s)
Adenosina Trifosfato , Adipocitos , Adipoquinas , Calcio , Membrana Celular , Regulación hacia Abajo , Fluorescencia , Glucosa , Resistencia a la Insulina , Insulina , Células Musculares , Obesidad , Receptor de Insulina , ResistinaRESUMEN
Low molecular weight GTP-binding proteins are molecular switches that are believed to play pivotal roles in cell growth, differentiation, cytoskeletal organization, and vesicular trafficking. Rab proteins are key players in the regulation of vesicular transport, while Rho family members control actin-dependent cell functions, i.e. the regulation of cytoskeletal organization in response to extracelluar growth factors and in dendritic neuron development. In this study, we have examined the regulation of small GTP-binding proteins that are implicated in neurosecretion and differentiation of neuron during ageing processes. Comparison of small GTP-binding proteins from the synaptosome and crude synaptic vesicles (LP2 membranes) of 2 months and 20 months old rat brain respectively showed no difference in the level of Rab family proteins (Rab3A and Rab5A). However, Rho family proteins such as RhoA and Cdc42 were elevated in LP2 membranes of the aged brain. The dissociation of Rab3A by Ca2+/calmodulin (CaM) from SV membranes was not changed during aging. Ca2+/CaM stimulated phosphorylation of the 22 and 55-kDa proteins in SV membranes from the aged rat brain, and inhibited phosporylation of 30-kDa proteins. GTPgammaS inhibited phosphorylation of the 100-kDa proteins and stimulated phosphorylation of the 70 kDa in LP2 membranes from both the young and aged rat brains, whereas GDPbetaS caused just the opposite reaction. These results suggest that protein phosphorylation and regulation of Rho family GTPases in rat brain appears to be altered during ageing processes.
Asunto(s)
Bovinos , Ratas , Envejecimiento , Animales , Encéfalo/metabolismo , Calcio/farmacología , Estudio Comparativo , Proteínas de Unión al GTP/metabolismo , Guanosina 5'-O-(3-Tiotrifosfato)/metabolismo , Peso Molecular , Fosforilación/efectos de los fármacos , Ratas Sprague-Dawley , Membranas Sinápticas/metabolismo , Sinaptosomas/metabolismo , Proteína de Unión al GTP cdc42/biosíntesis , Proteína de Unión al GTP rab3A/metabolismo , Proteínas de Unión al GTP rab5/metabolismo , Proteína de Unión al GTP rhoA/biosíntesisRESUMEN
Low molecular weight GTP-binding proteins are molecular switches that are believed to play pivotal roles in cell growth, differentiation, cytoskeletal organization, and vesicular trafficking. Rab proteins are key players in the regulation of vesicular transport, while Rho family members control actin-dependent cell functions, i.e. the regulation of cytoskeletal organization in response to extracelluar growth factors and in dendritic neuron development. In this study, we have examined the regulation of small GTP-binding proteins that are implicated in neurosecretion and differentiation of neuron during ageing processes. Comparison of small GTP-binding proteins from the synaptosome and crude synaptic vesicles (LP2 membranes) of 2 months and 20 months old rat brain respectively showed no difference in the level of Rab family proteins (Rab3A and Rab5A). However, Rho family proteins such as RhoA and Cdc42 were elevated in LP2 membranes of the aged brain. The dissociation of Rab3A by Ca2+/calmodulin (CaM) from SV membranes was not changed during aging. Ca2+/CaM stimulated phosphorylation of the 22 and 55-kDa proteins in SV membranes from the aged rat brain, and inhibited phosporylation of 30-kDa proteins. GTPgammaS inhibited phosphorylation of the 100-kDa proteins and stimulated phosphorylation of the 70 kDa in LP2 membranes from both the young and aged rat brains, whereas GDPbetaS caused just the opposite reaction. These results suggest that protein phosphorylation and regulation of Rho family GTPases in rat brain appears to be altered during ageing processes.