Advanced glycation end products evoke inflammatory reactions in proximal tubular cells via autocrine production of dipeptidyl peptidase-4

We have previously shown that albuminuria and renal levels of advanced glycation end products (AGEs), receptor for AGEs (RAGE), and oxidative stress are suppressed in dipeptidyl peptidase-4 (DPP-4)-deficient diabetic rats, thus suggesting the crosstalk between AGE-RAGE axis and DPP-4 in experimental diabetic nephropathy. Therefore, we examined here the role of DPP-4 in AGE-evoked inflammatory reactions in human proximal tubular cells. Proteins were extracted from proximal tubular cells, and conditioned medium was collected, both of which were subjected to western blot analysis using anti-DPP-4 antibody. RAGE-aptamer was prepared using a systemic evolution of ligands by exponential enrichment. NF-κB p65 and monocyte chemoattractant protein-1 (MCP-1) gene expression was analyzed by reverse transcription-polymerase chain reaction. AGEs significantly increased DPP-4 expression and soluble DPP-4 production by tubular cells, the latter of which was attenuated by RAGE-aptamer or an anti-oxidant, N-acetylcysteine. AGEs or DPP-4 up-regulated NF-κB p65 or MCP-1 mRNA levels in tubular cells, which were suppressed by linagliptin, an inhibitor of DPP-4. AGEs stimulated NF-κB p65 gene expression in tubular cells isolated from control rats, but not from DPP-4-deficient rats. Our present results suggest that the AGE-RAGE-mediated oxidative stress could evoke inflammatory reactions in proximal tubular cells via autocrine production of DPP-4.