OXIDANTS INDUCE TRANSCRIPTIONAL ACTIVATION OF MANGANESE SUPEROXIDE-DISMUTASE IN GLOMERULAR CELLS

Cultured rat glomerular mesangial acid epithelial cells and bovine glomerular endothelial cells were exposed to various concentrations of hydrogen peroxide (H2O2). Mesangial cells treated with 10 to 100 mu M H2O2 for 24 hours showed a two- to ninefold increase in Mn-SOD mRNA expression associated with significantly (P < 0.005) increased Mn-SOD activity (22.2 +/- 1.2 and 12.2 +/- 0.7 mu/mg protein for H2O2 100 mu M treated and untreated cells, respectively). In contrast, expression of Cu-Zn SOD and beta-actin mRNA was not affected by H2O2. Induction of Mn-SOD mRNA by H2O2 was inhibited by actinomycin-D (4 mu M) treatment. Glomerular endothelial cells also showed an increase in Mn-SOD mRNA expression following 100 mu M H2O2 treatment, as did glomerular epithelial cells following treatment with 500 and 1000 mu M H2O2 but not with 100 mu M. Transcriptional activity of the Mn-SOD gene was assessed with a fusion reporter gene consisting of a luciferase gene (pGL2P) and a 1.2 kb fragment from the rat Mn-SOD genomic DNA (-806 to +408 bp of the transcription initiation site, -806:+408). The construct was transfected into rat glomerular mesangial and epithelial cells. Mesangial and epithelial cells transfected with pCL2P (-806: +408) and treated with H2O2 (100 mu M and 1 mM for mesangial and epithelial cells, respectively) demonstrated some threefold increase in luciferase activity, whereas cells transfected with pGL2P lacking the Mn-SOD fragment did not show changes in luciferase activity following H2O2 treatment. Other oxidants, namely alpha- and beta-naphthoflavone (50 mu M to mesangial cells) and puromycin aminonucleoside (25 to 50 mu g/ml to epithelial cells), also induced transcriptional activation (2- to 5-fold increase) in these cells. Thus, Mn-SOD levels in glomerular cells are enhanced when they are exposed to oxidant stress, and this up-regulation involves transcriptional activation. Further, the Mn-SOD gene contains enhancer element(s) which respond to diverse oxidant stress. The inducibility by oxidants of local Mn-SOD demonstrates that glomerular SOD may play a decisive role in the pathogenesis of glomerular injuries in which the balance between oxidants and antioxidants is critical.