Interleukin-lβ induces human proximal tubule cell injury, α-smooth muscle actin expression and fibronectin production

Abstract

Background. Tubulointerstitial lesions, characterized by tubular injury, interstitial fibrosis and the appearance of myofibroblasts, are the strongest predictors of the degree and progression of chronic renal failure. These lesions are typically preceded by macrophage infiltration of the tubulointerstitium, raising the possibility that these inflammatory cells promote progressive renal disease through fibrogenic actions on resident tubulointerstitial cells. The aim of the present study, therefore, was to investigate the potentially fibrogenic mechanisms of interleukin-1β (IL-1β), a macrophage-derived pro-inflammatory cytokine, on human proximal tubule cells (PTC). Methods. Confluent, quiescent, passage 2 PTC were established in primary culture from histologically normal segments of human renal cortex (N = 11) and then incubated in serum- and hormone-free media supplemented with either IL-1β (0 to 4 ng/mL) or vehicle (control). Results. IL-1β significantly enhanced fibronectin secretion by up to fourfold in a time- and concentration-dependent fashion. This was accompanied by significant (2.5- to 6-fold) increases in α-smooth muscle actin (α-SMA) expression, transforming growth factor beta (TGF-β1 secretion, nitric oxide (NO) production, NO synthase 2 (NOS2) mRNA and lactate dehydrogenase (LDH) release. Cell proliferation was dose-dependently suppressed by IL-1β. NG-methyl-L-arginine (L-NMMA; 1 mmol/L), a specific inhibitor of NOS, blocked NO production but did not alter basal or IL-1β-stimulated fibronectin secretion. In contrast, a pan-specific TGF-β neutralizing antibody significantly blocked the effects of IL-1β on PTC fibronectin secretion (IL-1β, 268.1 ± 30.6 vs. IL-1β + αLTGF-β 157.9 ± 14.4%, of control values, P < 0.001) and DNA synthesis (IL-1β 81.0 ± 6.7% vs. IL-1β + αTGF-β 93.4 ± 2.1%, of control values, P < 0.01). Conclusion. IL-1β acts on human PTC to suppress cell proliferation, enhance fibronectin production and promote α-smooth muscle actin expression. These actions appear to be mediated by a TGF-β1 dependent mechanism and are independent of nitric oxide release.