Objective To explore the effect of Numb on tubular epithelial-to-mesenchymal transition (EMT) in rat proximal epithelial cells. Methods NRK52E cells were treated with different concentrations of recombinant human transforming growth factor-β1 (TGF-β1) (0, 1, 5, 10, 15, 20 μg/L) for 48 h or 10 μg/L TGF-β1 for different times (0, 24, 48, 72 h) in vitro. The expressions of E-cadherin, a-smooth muscle actin(α-SMA) and Numb in NRK 52E cells were detected by RT-PCR, Western blot and immunofluorescence staining. Meanwhile Numb siRNA oligo was transfected into NRK 52E cells with lipofectamine before TGF-β1 treatment, then Western blot was applied to detect the protein expression of E-cadherin, α-SMA and Numb in NRK52E cells. Results TGF-β1 could induce EMT in NRK52E cells in dose- and time-dependent manner. During the progress of TGF-β1-induced EMT, the protein expression of Numb in 5, 10, 15, 20 μg/L group was 1.33 folds (P=0.024), 1.39 folds (P=0.035), 1.45 folds (P=0.025), 1.51 folds (P=0.000) respectively as compared to 0 μg/L group. Likewise, the protein and mRNA expression of Numb in 24 h, 48 h, 72 h group was 1.48 folds (P=0.046) and 1.56 folds (P=0.012), 1.54 folds (P=0.011) and 1.82 folds (P=0.008), 1.79 folds (P=0.028) and 1.82 folds (P=0.002) respectively as compared to 0 h group. Moreover, large amount of Numb was accumulated in the cytoplasm. Down-regulation of Numb expression by siRNA transfection did not influence the basal expression of E-cadherin and α-SMA in NRK 52E cells, but attenuated the progression of EMT in NRK52E cells induced by TGF-β1. The up-regulation of α-SMA protein was reduced to 18.1% (P=0.004) while the down-regulation of E-cadherin protein was reversed to 2.19 folds (P=0.004). Conclusion Numb can promote EMT in rat proximal epithelial cells.

Objective To investigate the role of Notch signaling in the progression of peritoneal fibrosis in a rat model induced by high glucose dialysate. Methods Male Sprague Dawley rats were subjected to daily peritoneal dialysis (PD) with a lactate-buffered solution containing 4.25% glucose. They were sacrificed at 2 and 4 weeks after PD. The parietal thickness was measured with Masson staining. The expression of TGF-β1, E-cadherin, α-SMA and collagen Ⅰ was examined by immunoblotting. The expression of Notch ligand Jagged-1 and the negative Notch signaling regulato--Numb was analyzed by both immunoblotting and RT-PCR. The expression of a Notch nuclear target gene Hcs-1 was examined by RT-PCR. Results Both HE and Masson trichrome staining revealed an increase in peritoneal thickness with a loss of mesothelial cells and a rich of collagen matrix deposition in the submesothelial zone was evident at 4 weeks after PD. Meanwhile, compared to healthy rats, the expression of TGF-β1, ct-SMA and collagen Ⅰ was significantly increased, but the expression of E-cadherin was decreased in peritoneum after PD treatment. It was difficult to detect the Jagged-1 and Hes-1 expression in normal peritoneum, but their expression was graduaUy increased after PD. In contrast, the expression level of Numb, a negative regulator of Notch signaling, was dramatically decreased after PD. Conclusions Notch signaling is activated during the process of PD-induced peritoneal fibrosis and the activation of Notch signaling is associated with the loss of negative regulation of Notch signaling via decreased expression of Numb. Inhibition of Notch signaling via overexpression of its negative regulators such as Numb may be a novel therapeutic approach for peritoneal fibrosis in PD patients.