TNF-α and IL-1β–mediated regulation of MMP-9 and TIMP-1 in renal proximal tubular cells.
Background
Tubulointerstitial fibrosis is a morphologic hallmark of chronic kidney disease and is a key factor in the prediction of progression to end-stage renal failure. Disruption of tubular basement membrane and interstitial extracellular matrix (ECM) via cytokine-induced alterations in matrix metalloproteinases (MMPs), and tissue inhibitors of metalloproteinases (TIMPs) may be an important mechanism in this process. The presence of the proinflammatory cytokines tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) and their effects on proximal tubular cells may be critical in this process.
Methods
Human proximal tubular cells were cultured in hormonally defined medium. Cells at 80% confluency were exposed to TNF-α (0.1 to 100 ng/mL) or IL-1β (0.1 to 100 ng/mL) or a combination of both for 48 hours. Activity and expression of MMP-9 was examined by gelatin zymography and Western blot analysis. TIMP-1 expression was analyzed by Western blotting. Signaling through cytokine receptors, protein kinase C (PKC) and mitogen-activated protein kinase (MAPK) pathways was investigated.
Results
TNF-α but not IL-1β resulted in a dose-dependent increase in the latent form of MMP-9. TIMP-1 was decreased by treatment with either TNF-α or IL-1β. Cotreatment with IL-1β abolished the induction of MMP-9 but augmented the inhibition of TIMP-1 in the presence of TNF-α. Inhibition of PKC provided evidence of the importance of this pathway in mediating the cytokine-induced suppression of TIMP-1 in human kidney (HK-2) cells. Activation of the extracellular signal-regulated protein kinase (ERK1/2) MAPK mediated the up-regulation of MMP-9 by TNF-α whereas p38 was found to be involved in the IL-1β–mediated inhibition of TNF-α–stimulated MMP-9.
Conclusion
The differential effects of TNF-α and IL-1β on proximal tubular MMP-9 and TIMP-1 expression are mediated through the TNF-RI, the IL-1-RI and the different signaling pathways of PKC, ERK1/2, and p38 MAPK. These findings may provide new insights into the role of proinflammatory cytokines TNF-α and IL-1β in the development and possible therapeutic intervention in tubulointerstitial fibrosis.
