RESUMO
Bradykinin (BK) promotes insulin sensitivity and glucose uptake in adipocytes and other cell types. We demonstrated that in rat adipocytes BK enhances insulin-stimulated glucose transport via endothelial nitric oxide synthase, nitric oxide (NO) generation, and decreased activity of the mitogen-activated protein kinase (MAPK) JNK (c-Jun NH2-terminal kinase). In endothelial cells, NO increases soluble guanylate cyclase (sGC) activity, which, in turn, activates protein kinase G (PKG) by increasing cGMP levels. In this study, we investigated whether BK acts via the sGC-cGMP-PKG pathway to inhibit the negative effects of JNK on insulin signaling and glucose uptake in rat adipocytes. BK augmented cGMP concentrations. The BK-induced enhancement of insulin-stimulated glucose uptake was mimicked by the sGC activator YC-1 and a cell-permeable cGMP analog, CPT-cGMP, and inhibited by the sGC inhibitor ODQ and the PKG inhibitor KT 5823. Transfection of dominant-negative PKG reduced the BK augmentation of insulin-induced Akt phosphorylation. The activation of JNK and ERK1/2 by insulin was attenuated by BK, which was mediated by the sGC-cGMP-PKG pathway. Whereas insulin-stimulated phosphorylation of upstream activators of JNK and ERK, i.e., MKK4 and MEK1/2, was unaffected, BK augmented insulin-mediated induction of MKP-5 mRNA and protein levels. Furthermore, zaprinast, a phosphodiesterase inhibitor, enhanced cGMP and MKP-5 and prolonged the action of BK. These data indicate that BK enhances insulin action by inhibition of negative feedback by JNK and ERK via upregulation of MKP-5, mediated by the sGC-cGMP-PKG signaling pathway.
Assuntos
Adipócitos/efeitos dos fármacos , Bradicinina/farmacologia , Proteínas Quinases Dependentes de GMP Cíclico/efeitos dos fármacos , Fosfatases de Especificidade Dupla/efeitos dos fármacos , Resistência à Insulina , Proteínas Quinases JNK Ativadas por Mitógeno/antagonistas & inibidores , Fosfatases da Proteína Quinase Ativada por Mitógeno/efeitos dos fármacos , RNA Mensageiro/efeitos dos fármacos , Adipócitos/metabolismo , Animais , Western Blotting , GMP Cíclico/metabolismo , Proteínas Quinases Dependentes de GMP Cíclico/metabolismo , Fosfatases de Especificidade Dupla/genética , Fosfatases de Especificidade Dupla/metabolismo , Glucose/metabolismo , Guanilato Ciclase/efeitos dos fármacos , Guanilato Ciclase/metabolismo , Imunoprecipitação , Proteínas Quinases JNK Ativadas por Mitógeno/efeitos dos fármacos , Masculino , Fosfatases da Proteína Quinase Ativada por Mitógeno/metabolismo , Óxido Nítrico/metabolismo , Óxido Nítrico Sintase Tipo III/efeitos dos fármacos , Óxido Nítrico Sintase Tipo III/metabolismo , Inibidores de Fosfodiesterase/farmacologia , Proteínas Proto-Oncogênicas c-akt/efeitos dos fármacos , Purinonas/farmacologia , RNA Mensageiro/metabolismo , Ratos , Ratos Sprague-Dawley , Reação em Cadeia da Polimerase em Tempo Real , Transdução de Sinais/efeitos dos fármacosRESUMO
BACKGROUND: Rheumatoid arthritis (RA) represents a challenge for therapeutic interventions due to complex inflammatory signalling pathways underlying its pathogenesis. The MAPK signalling network, a major effector limb of the inflammatory lesion, is an attractive therapeutic target. MAPK phosphatases (MKPs), endogenous negative regulators of MAPK signalling, have received increasing recognition as modulators of inflammatory and immune responses, and hence as a potential therapeutic avenue for RA. OBJECTIVE: To present the rationale for therapeutically targeting MAPK signalling and explore the case for addressing MKP1 as a novel therapeutic strategy for RA. METHODS: We summarise literature describing the importance of MAPK signalling in RA and review reports describing the roles of MKPs in modulating innate and adaptive immune responses. Finally we expand on the role of MKP1 in RA pathogenesis and explore data defining MKP1 as a mediator of glucocorticoid action. CONCLUSION: MKP1 constitutes an exciting, novel potential therapeutic target for RA.
