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, TGFβ expression, and alpha-smooth muscle actin (α-SMA) expression, suggesting a role of Notch3 in promoting tubulointerstitial fibrosis. This possibility was supported by the observation that TGFβ, the major renal fibrogenic cytokine, stimulated Notch3 expression in human proximal tubule epithelial HK-2 cells. TGFβ 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 TGFβ-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 TGFβ-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.

肾间质纤维化是由多种慢性肾脏疾病和一系列因素导致的常见肾脏损伤。我们在这里报告Notch3是潜在的贡献者。与6名健康个体相比，在18例梗阻性肾病患者的肾小管上皮细胞中观察到Notch3表达的强烈升高。在模仿人类疾病的大鼠单侧输尿管阻塞（UUO）模型中，Notch3的上调紧随肾脏损伤，肾纤维化，TGFβ表达和α-平滑肌肌动蛋白（α-SMA）表达的过程，提示Notch3的作用促进肾小管间质纤维化。TGFβ是主要的肾纤维化细胞因子，可刺激人近端肾小管上皮HK-2细胞中Notch3表达，从而证实了这种可能性。TGFβ增强HK-2细胞中ERK，p38的激活，但不增强JNK MAP激酶的激活。尽管使用SB203580抑制p38激活不会影响TGFβ诱导的Notch3表达，但用MEK1抑制剂PD98059抑制ERK激活可显着降低事件发生率。此外，通过过表达组成型活性MEK1突变体MEK1Q56P来增强ERK激活，从而上调了HK-2细胞中的Notch3表达，而PD98059降低了表达MEK1Q56P的HK-2细胞中的ERK激活和Notch3表达。我们共同为阻塞性肾病患者的Notch3上调提供了首个临床证据。上调可能是通过TGFβ-ERK途径介导的。这项研究表明，Notch3的上调有助于阻塞性肾病引起的肾脏损伤，