RESUMO
Progressive renal diseases are characterized by an increased synthesis of extracellular matrix (ECM) components. The mechanisms involved in the development of these alterations are not completely known, but a crucial role for TGF-beta 1 has been suggested. Moreover, the ability of the ECM to modulate the phenotypic expression of different cell types has been widely described. In experiments presented here, human mesangial cells (HMC) were grown on collagen type I (COL I) or IV (COL IV). ECM protein and TGF-beta 1 mRNA expression were evaluated by Northern blot analysis, and TGF-beta 1 secretion was evaluated by ELISA. The involvement of tyrosine kinase and serine-threonine kinase pathways was studied by Western blot analysis, immunofluorescence, and in vitro kinase assays. HMC cultured on COL I showed an increased mRNA expression of COL I and COL IV, fibronectin, and TGF-beta 1. Both tyrosine phosphorylation and integrin-linked kinase (ILK) activity increased when HMC were cultured on COL I, and blockade of these pathways inhibited the increased secretion of TGF-beta 1. In conclusion, the present results support a role for extracellular COL I in the regulation of TGF-beta 1 synthesis during progressive renal sclerosis and fibrosis and the subsequent increase in newly synthesized ECM proteins. In addition, ILK, along with the tyrosine kinases, participates in the genesis of this effect.
Assuntos
Colágeno Tipo I/metabolismo , Matriz Extracelular/genética , Fibroblastos/metabolismo , Mesângio Glomerular/metabolismo , Fator de Crescimento Transformador beta/metabolismo , Células Cultivadas , Colágeno Tipo I/farmacologia , Colágeno Tipo IV/metabolismo , Colágeno Tipo IV/farmacologia , Proteínas da Matriz Extracelular/biossíntese , Proteínas da Matriz Extracelular/genética , Fibroblastos/efeitos dos fármacos , Mesângio Glomerular/citologia , Mesângio Glomerular/efeitos dos fármacos , Humanos , Fosforilação/efeitos dos fármacos , Proteínas Serina-Treonina Quinases/metabolismo , Proteínas Tirosina Quinases/metabolismo , RNA Mensageiro/efeitos dos fármacos , RNA Mensageiro/metabolismo , Fator de Crescimento Transformador beta/biossíntese , Fator de Crescimento Transformador beta/genética , Fator de Crescimento Transformador beta1 , Tirosina/metabolismo , Regulação para Cima/efeitos dos fármacos , Regulação para Cima/genéticaRESUMO
Extracellular matrix (ECM) components, through specific peptide motifs such as Arg-Gly-Asp (RGD), interact with integrins and can modify the behavior of cells. Transforming growth factor-beta1 (TGF-beta1) is the main cytokine involved in the synthesis of ECM proteins. We analyzed the effect of a RGD-containing peptide, as Arg-Gly-Asp-Ser (RGDS), on the regulation of TGF-beta1 secretion in cultured human mesangial cells. We found that RGDS increased mRNA expression and secretion of TGF-beta1 by stimulating the TGF-beta1 gene promoter. This effect was dependent on the interaction of RGDS with integrins. We evaluated the signaling pathways implicated in TGF-beta1 production by analyzing the effect of RGDS on kinase-related integrins. RGDS stimulated tyrosine phosphorylation as well as integrin-linked kinase (ILK) activity. However, tyrosine kinase inhibitors did not prevent the RGDS effect. In contrast, the inhibition of ILK by cell transfection with a kinase dead-ILK completely abolished the increased TGF-beta1 secretion and promoter activity in the presence of RGDS. Thus RGDS modulates the secretion of TGF-beta1, probably through increased synthesis by interacting with integrins and activating ILK. This supports a role for ECM components in the regulation of their own secretion.
Assuntos
Integrinas/metabolismo , Oligopeptídeos/farmacologia , Fator de Crescimento Transformador beta/biossíntese , Células Cultivadas , Mesângio Glomerular/citologia , Mesângio Glomerular/metabolismo , Humanos , Modelos Biológicos , Fosforilação , Proteínas Serina-Treonina Quinases/metabolismo , RNA Mensageiro/biossíntese , Ativação Transcricional , Fator de Crescimento Transformador beta/genética , Fator de Crescimento Transformador beta/metabolismo , Fator de Crescimento Transformador beta1 , Tirosina/metabolismoRESUMO
BACKGROUND: Reactive oxygen species (ROS) are excessively produced in pathologic states, including many renal diseases. Transforming growth factor-beta (TGF-beta) may mediate renal fibrotic injury, and ROS may act through the TGF-beta pathway to exert a profibrotic effect. METHODS: The expression of TGF-beta1 and extracellular matrix (ECM) components were assessed in cultured human mesangial cells (HMCs) incubated with glucose oxidase (GO), an enzyme that continuously generates hydrogen peroxide from glucose. A neutralizing anti-TGF-beta antibody was added to test the hypothesis that hydrogen peroxide acts through activation of the TGF-beta pathway to stimulate ECM expression. RESULTS: Northern blot analysis revealed significantly increased steady-state levels of TGF-beta1 and ECM proteins (collagen types I, III, and IV, and fibronectin) by approximately twofold. While no significant effect on mRNA stability after treatment with GO was observed, other studies employing promoter-reporter assays, competitive-quantitative reverse transcription-polymerase chain reaction, mink lung epithelial cell proliferation assay, and TGF-beta1 enzyme-linked immunosorbent assay all demonstrated significant stimulation by GO (>1.5-fold) of TGF-beta1 promoter activity, mRNA level, bioactivity, and protein production, respectively. Catalase pretreatment prevented the GO-induced stimulation of TGF-beta1 mRNA. When incubations were performed with a panselective neutralizing anti-TGF-beta antibody, the GO-stimulated expression of ECM molecules was prevented. CONCLUSIONS: GO-induced hydrogen peroxide production induces TGF-beta1 synthesis and thereby increases ECM gene expression in cultured HMCs. These cellular responses may underlie the development and progression of renal diseases characterized by oxidative stress.
