Superoxide dismutase type 1 in monocytes of chronic kidney disease patients

Abstract

We analyzed proteomic profiles in monocytes of chronic kidney disease (CKD) patients and healthy control subjects. Two-dimensional electrophoresis (2-DE) and silver staining indicated differences in protein pattern. Among the analyzed proteins, superoxide dismutase type 1 (SOD1), which was identified both by MS/MS mass-spectrometry and immunoblotting, was reduced in kidney disease. We characterized SOD1 protein amount, using quantitative in-cell Western assay and immunostaining of 2-DE gel blots, and SOD1 gene expression, using quantitative real-time polymerase chain reaction (PCR), in 98 chronic hemodialysis (HD) and 211 CKD patients, and 34 control subjects. Furthermore, we showed that different SOD1 protein species exist in human monocytes. SOD1 protein amount was significantly lower in HD (normalized SOD1 protein, 27.2±2.8) compared to CKD patients (34.3±2.8), or control subjects (48.0±8.6; mean±SEM; P<0.05). Analysis of SOD1 immunostaining showed significantly more SOD1 protein in control subjects compared to patients with CKD or HD (P<0.0001, analysis of main immunoreactive protein spot). SOD1 gene expression was significantly higher in HD (normalized SOD1 gene expression, 17.8±2.3) compared to CKD patients (9.0±0.7), or control subjects (5.5±1.0; P<0.0001). An increased SOD1 gene expression may indicate increased protein degradation in patients with CKD and compensatory increase of SOD1 gene expression. Taken together, we show reduced SOD1 protein amount in monocytes of CKD, most pronounced in HD patients, accompanied by increased SOD1 gene expression.