Beta-casomorphin-7 prevents epithelial-mesenchymal transdifferentiation of NRK-52E cells at high glucose level: Involvement of AngII-TGF-β1 pathway

Background: Hyperglycemia is the most important risk factor in the progression of renal fibrosis in diabetic kidney. Based on previous studies, beta-casomorphin-7 may exert anti-fibrotic activities in diabetic rats. However, the role of beta-casomorphin-7 in the pathogenesis of renal tubulointerstitial fibrosis remains unclear. Thus, this study was designed to investigate the protective effect of beta-casomorphin-7 on epithelial-mesenchymal transition (EMT) of NRK-52E cells treated under hyperglycemic condition and to explore the possible mechanism. Research design and methods: NRK-52E cells were cultured in high glucose (30 mM) for 3 days. Different concentrations of beta-casomorphin-7, naloxone (antagonist of opioid receptor) and losartan (antagonist of angiotensin II type I receptor) were added in the culture. Expression of alpha-smooth muscle actin (alpha-SMA), E-cadherin, vimentin and cytokeratin19 mRNA were determined by real-time PCR. Protein levels of E-cadherin and alpha-SMA were analyzed by Western blotting. The concentrations of angiotensin (Ang) II and transforming growth factor beta 1 (TGF-beta 1) in the culture medium were determined. Results: High glucose-induced up-regulation of vimentin mRNA and alpha-SMA mRNA and protein were significantly inhibited by beta-casomorphin-7. On the contrary, high glucose-induced down-regulation of cytokeratin19 mRNA and E-cad mRNA and protein was significantly reversed by beta-casomorphin-7. beta-casomorphin-7 significantly alleviate high glucose induced increase of AngII and TGF-beta 1 in the culture. Moreover, losartan significantly attenuated the expression of TGF-beta 1 and EMT of NRK-52E cells treated under hyperglycemic condition. But naloxone did not affect the EMT of NRK-52E cells treated by high glucose and beta-casomorphin-7. Conclusion: We demonstrate that beta-casomorphin-7 has the potential to inhibit high glucose-induced renal proximal tubular EMT partly by modulating AngII-TGF-beta 1 pathway, but not by opioid receptor. (C) 2015 Elsevier Inc. All rights reserved.