Effect of macrophages on podocytes apoptosis in diabetic nephropathy

Abstract

Objective To investigate the effect of macrophages on podocytes apoptosis in diabetic nephropathy. Methods Differentiated mouse macrophages (RAW264.7) were exposed to normal glucose, high glucose, then the conditioned media (CM) was collected and considered as NC-CM or HG-CM, respectively. Western blotting and immunofluorescent staining were used to detect the specific markers for M1 macrophages (iNOS) and M2 macrophages (MR). ELISA was used to detect the concentration of TNF-α in the CM. Then normal PRMI 1640 media (control), NC-CM or HG-CM was added to podocytes. In some experiments, ROS inhibitors (Tempo), p38 MAPK inhibitor (SB203580), anti-TNF-α neutralizing antibody, and IgG1 isotype control were respectively added to cells with HG-CM. Besides, recombinant mouse TNF-α alone was applied to incubate podocytes. Podocytes apoptosis was accessed by Annexin V-FITC/PI and Hoechst33342 staining. DCFH-DA staining was used to analyse ROS level. Western blotting was used to detect cleaved casepase-3, p38MAPK, and p-p38MAPK protein. Results Macrophages were activated when exposed to high glucose, displaying pro-inflammatory M1 polarization with higher iNOS and lower MR expression. HG-CM but not NC-CM trigged podocytes apoptosis, up-regulated ROS, cleaved casepase-3 and p-p38MAPK. However, the podocytes apoptosis trigged by HG-CM was abolished by either a ROS inhibitor (Tempo) or a p38 MAPK inhibitor (SB203580). Additionally, TNF-α was increased in the HG-CM. TNF-α protein in macrophage was aslo increased when exposed to high glucose. Anti-TNF-α neutralizing antibody blunted the apoptotic response, excess ROS generation and p-p38 MPAK expression in podocytes induced by HG-CM. Moreover, addition of recombinant TNF-α similarly led to podocytes apoptosis, increased ROS and p38 MPAK expression. Conclusion M1 macrophages activated by high glucose released TNF-α to promote podocytes apoptosis via ROS-p38 MAPK pathway. (Chin J Endocrinol Metab, 2017, 33: 680-686) Key words: Macrophage; Podocytes; Apoptosis; Diabetic nephropathy