The TGFβ-ERK pathway contributes to Notch3 upregulation in the renal tubular epithelial cells of patients with obstructive nephropathy

Renal interstitial fibrosis is a common renal injury resulted from a variety of chronic kidney conditions and an array of factors. We report here that Notch3 is a potential contributor. In comparison to 6 healthy individuals, a robust elevation of Notch3 expression was observed in the renal tubular epithelial cells of 18 patients with obstructive nephropathy. In a rat unilateral ureteral obstruction (UUO) model which mimics the human disease, Notch3 upregulation closely followed the course of renal injury, renal fibrosis, TGF beta expression, and alpha-smooth muscle actin (alpha-SMA) expression, suggesting a role of Notch3 in promoting tubulointerstitial fibrosis. This possibility was supported by the observation that TGF beta, the major renal fibrogenic cytokine, stimulated Notch3 expression in human proximal tubule epithelial HK-2 cells. TGF beta enhanced the activation of ERK, p38, but not JNK MAP kinases in HK-2 cells. While inhibition of p38 activation using SB203580 did not affect TGF beta-induced Notch3 expression, inhibition of ERK activation with a MEK1 inhibitor PD98059 dramatically reduced the event. Furthermore, enforced ERK activation through overexpression of the constitutively active MEK1 mutant MEK1Q56P upregulated Notch3 expression in HK-2 cells, and PD98059 reduced ERK activation and Notch3 expression in HK-2 cells expressing MEK1Q56P. Collectively, we provide the first clinical evidence for Notch3 upregulation in patients with obstructive nephropathy; the upregulation is likely mediated through the TGF beta-ERK pathway. This study suggests that Notch3 upregulation contributes to renal injury caused by obstructive nephropathy, which could be prevented or delayed through ERK inhibition.