Low-dose paclitaxel ameliorates renal fibrosis by suppressing transforming growth factor-β1-induced plasminogen activator inhibitor-1 signaling

Abstract

Background and objectives: Plasminogen activator inhibitor-1 (PAI-1), a major downstream target of transforming growth factor-β1 (TGF-β1), plays an important role in the pathogenesis of renal fibrosis. Smad and non-Smad-mediated signaling pathways including mitogen-activated protein kinases (MAPKs) are both required for PAI-1 induction by TGF-β1. Previous reports have indicated that microtubule networks can modulate these signaling pathways. The aim of this study was to investigate the effect of low-dose paclitaxel, which is a microbutule stabilizer, on renal fibrosis, focusing on the TGF-β1-induced PAI-1 signaling cascade. Methods: Forty-eight male Sprague-Dawley rats were randomly assigned to four groups (n = 12 per group): sham/vehicle, sham/paclitaxel, unilateral ureteral obstruction (UUO)/vehicle and UUO/paclitaxel. Rats were treated with a 0.3 mg/kg intraperitoneal dose of paclitaxel or vehicle twice per week for 14 days. Half of the rats in each group were sacrificed respectively at days 7 and 14 after operation. Inner medullary collecting duct (IMCD) cells stimulated with TGF-β1 were incubated with 0, 1 and 2 nM paclitaxel for 24 and 72 hours. Histological changes were assessed using periodic acid-Schiff, Massons trichrome and immunohistochemistry staining. The TGF-β1-induced PAI-1 signaling and status of extracellular matrix proteins in the renal cortex were evaluated by western blot analysis. Results: Renal interstitial collagen deposition and the protein expression of collagen I, fibronectin and α-smooth muscle actin (α-SMA) were increased over time after UUO. Semiquantitative analysis of Masson's trichrome staining showed that paclitaxel resulted in an approximately 50% reduction in the fibrotic areas caused by UUO. In the UUO kidneys, paclitaxel significantly attenuated the expression of collagen I, fibronectin and α-SMA as well as TGF-β1 and PAI-1. Paclitaxel also inhibited the UUO-induced activation of Smad2/3 and c-Jun N-terminal kinase (JNK). However, paclitaxel treatment did not inhibit extracellular signal-regulated kinase 1/2 (ERK1/2) or p38 MAPK expression. In TGF-β1-treated IMCD cells, treatment with 1 and 2 nM paclitaxel for 72 h reduced fibronectin, α-SMA and PAI-1 protein expression. Moreover, a 2 nM dose of paclitaxel for 24 h significantly inhibited the TGF-β1-stimulated activation of Smad2/3, JNK and ERK1/2 in IMCD cells. Conclusion: Paclitaxel at low non-cytotoxic doses attenuates PAI-1 expression through inhibiting activation of TGF-β1, Smad2/3 and JNK, thereby ameliorating renal fibrosis.