HMGB1 Enhances the AGE-Induced Expression of CTGF and TGF-β via RAGE-Dependent Signaling in Renal Tubular Epithelial Cells

Background/Aims: Advanced glycation end products (AGEs) induce epithelial mesenchymal transition (EMT) in renal proximal tubular epithelial cells (PTECs) by promoting the two EMT regulators, transforming growth factor beta (TGF-β) and connective tissue growth factor (CTGF). However, the exact signaling mechanism remains largely unclear. Methods: We investigated the promotion to high mobility group box 1 (HMGB1) in renal tubular epithelial HK-2 cells by AGE-BSA with quantitative PCR and western blot assay, and then determined the regulatory role of HMGB1 in the AGE-BSA-induced CTGF and TGF-β. In addition, the dependence of the receptor of advanced glycation end products (RAGE) was also examined in the CTGF and TGF-β promotion by AGEs and HMGB1 in HK-2 cells using the RNAi method. Results: It was demonstrated that AGEs induced translocation and release of HMGB1 from tubular epithelial HK-2 cells, and the released HMGB1 enhanced the promotion to CTGF and TGF-β by AGEs in HK-2 cells. On the other side, the HMGB1 knockdown by siRNA attenuated the AGE-BSA-induced expression of TGF-β. Moreover, the CTGF and TGF-β promotion in HK-2 cells by AGEs and HMGB1 was RAGE-dependent. Conclusion: Our results indicated that AGEs induced HMGB-1 and promoted the CTGF and TGF-β in renal epithelial HK-2 cells RAGE-dependently. And there was a synergism between AGEs and HMGB1 in the RAGE signaling activation. The in vitro data suggested that the AGE-RAGE and HMGB-1-RAGE signaling might play an important role in the promotion of CTGF and TGF-β in the renal fibrosis process of diabetic nephropathy.