Proteomic Analysis of Bradykinin Signaling in Podocytes

Diabetic kidney disease is the major cause of end-stage kidney failure worldwide. Podocyte damage is one of the hallmarks of diabetic nephropathy, where the loss of the podocyte filtration barrier leads to proteinuria and progressive renal damage. Bradykinin (BK) is a vasoactive peptide that was shown to play an important role in the progression of renal damage. In this study, we aim to evaluate the changes in protein expression profiles of rat podocytes upon the treatment with BK by an advanced proteomics platform in conjunction with bioinformatics and pathway enrichment analysis. This analysis will help in discovering core effectors whose upstream and downstream protein profile can elucidate signaling mechanisms underlying BK’s modulation of the podocyte biology. Cultured immortalized rat podocytes were treated with BK at 10-7 M for 3 and 6 hours. Proteome profile was evaluated by LC-MS/MS analysis, and pathway enrichment analysis was performed on the resulting differential proteomic data. Proteomic analysis of podocytes treated by BK revealed 61 proteins that were differentially altered (up or downregulated) in response to BK treatment compared to unstimulated control podocytes. Pathway enrichment analysis suggested an inhibition of the cell death pathway and the involvement of elements of the cytoskeletal activity as well as activation of the inflammatory pathways. Of interest, one of the inflammatory proteins that were identified to be induced by BK treatment is Prostaglandin H Synthase-2 (PTGS-2, also known as COX-2). The upregulation of COX-2 by BK treatment was validated by western blot analysis. In addition, treatment of podocytes with BK significantly induced the production and release of PGE2 and this effect was inhibited by both COX-2 and MAPK inhibitors, demonstrating that the production of PGE2 by BK is mediated via a COX-2 and MAPK-dependent mechanisms. The findings of the present study provide a global understanding of the effector modulated proteome in response to BK treatment, and also reveal BK as an important modulator in the arachidonic acid metabolism pathway and a potential player in the progression of diabetic nephropathy.