RESUMO
Expression of the STAT3 transcription factor in the heart is cardioprotective and decreases the levels of reactive oxygen species. Recent studies indicate that a pool of STAT3 resides in the mitochondria where it is necessary for the maximal activity of complexes I and II of the electron transport chain. However, it has not been explored whether mitochondrial STAT3 modulates cardiac function under conditions of stress. Transgenic mice with cardiomyocyte-specific overexpression of mitochondria-targeted STAT3 with a mutation in the DNA-binding domain (MLS-STAT3E) were generated. We evaluated the role of mitochondrial STAT3 in the preservation of mitochondrial function during ischemia. Under conditions of ischemia heart mitochondria expressing MLS-STAT3E exhibited modest decreases in basal activities of complexes I and II of the electron transport chain. In contrast to WT hearts, complex I-dependent respiratory rates were protected against ischemic damage in MLS-STAT3E hearts. MLS-STAT3E prevented the release of cytochrome c into the cytosol during ischemia. In contrast to WT mitochondria, ischemia did not augment reactive oxygen species production in MLS-STAT3E mitochondria likely due to an MLS-STAT3E-mediated partial blockade of electron transport through complex I. Given the caveat of STAT3 overexpression, these results suggest a novel protective mechanism mediated by mitochondrial STAT3 that is independent of its canonical activity as a nuclear transcription factor.
Assuntos
Complexo II de Transporte de Elétrons/metabolismo , Complexo I de Transporte de Elétrons/metabolismo , Mitocôndrias Cardíacas/metabolismo , Isquemia Miocárdica/metabolismo , Espécies Reativas de Oxigênio/metabolismo , Fator de Transcrição STAT3/metabolismo , Animais , Citocromos c/genética , Citocromos c/metabolismo , Complexo I de Transporte de Elétrons/genética , Complexo II de Transporte de Elétrons/genética , Humanos , Masculino , Camundongos , Camundongos Transgênicos , Mitocôndrias Cardíacas/genética , Mitocôndrias Cardíacas/patologia , Mutação , Isquemia Miocárdica/genética , Isquemia Miocárdica/patologia , Consumo de Oxigênio/genética , Estrutura Terciária de Proteína , Fator de Transcrição STAT3/genéticaRESUMO
BACKGROUND: Skin injury leads to the release of heme, a potent prooxidant which is degraded by heme oxygenase-1 (HO-1) to carbon monoxide, iron, and biliverdin, subsequently reduced to bilirubin. Recently the involvement of HO-1 in angiogenesis has been shown; however, the role of heme and HO-1 in wound healing angiogenesis has not been yet investigated. RESULTS: Treatment of HaCaT keratinocytes with hemin (heme chloride) induced HO-1 expression and activity. The effect of heme on vascular endothelial growth factor (VEGF) synthesis is variable: induction is significant after a short, 6 h treatment with heme, while longer stimulation may attenuate its production. The involvement of HO-1 in VEGF synthesis was confirmed by inhibition of VEGF expression by SnPPIX, a blocker of HO activity and by attenuation of HO-1 mRNA expression with specific siRNA. Importantly, induction of HO-1 by hemin was able to overcome the inhibitory effect of high glucose on VEGF synthesis. Moreover, HO-1 expression was also induced in keratinocytes cultured in hypoxia, with concomitant augmentation of VEGF production, which was further potentiated by hemin stimulation. Accordingly, conditioned media from keratinocytes overexpressing HO-1 enhanced endothelial cell proliferation and augmented formation of capillaries in angiogenic assay in vitro. CONCLUSIONS: HO-1 is involved in hemin-induced VEGF expression in HaCaT and may play a role in hypoxic regulation of this protein. HO-1 overexpression may be beneficial in restoring the proper synthesis of VEGF disturbed in diabetic conditions.
Assuntos
Heme Oxigenase-1/farmacologia , Hemina/farmacologia , Queratinócitos/metabolismo , Neovascularização Fisiológica/fisiologia , Fator A de Crescimento do Endotélio Vascular/biossíntese , Proliferação de Células/efeitos dos fármacos , Células Cultivadas , Meios de Cultivo Condicionados/farmacologia , Endotélio Vascular/citologia , Radicais Livres/metabolismo , Glucose/farmacologia , Humanos , Hipóxia/metabolismo , Regiões Promotoras Genéticas/efeitos dos fármacos , RNA Interferente Pequeno/farmacologia , Cicatrização/fisiologiaRESUMO
Cytokines such as interleukin-6 induce tyrosine and serine phosphorylation of Stat3 that results in activation of Stat3-responsive genes. We provide evidence that Stat3 is present in the mitochondria of cultured cells and primary tissues, including the liver and heart. In Stat3(-/-) cells, the activities of complexes I and II of the electron transport chain (ETC) were significantly decreased. We identified Stat3 mutants that selectively restored the protein's function as a transcription factor or its functions within the ETC. In mice that do not express Stat3 in the heart, there were also selective defects in the activities of complexes I and II of the ETC. These data indicate that Stat3 is required for optimal function of the ETC, which may allow it to orchestrate responses to cellular homeostasis.