Renal CCAAT/enhancer-binding proteins in experimental diabetes mellitus

There is evidence that mediators of inflammation including components of the cytokine system are present in human and experimental diabetic kidney disease. CCAAT/enhancer-binding proteins (C/EBPs) represent a family of cytokine-inducible transcription factors. C/EBPs themselves regulate cytokine expression and also the expression of acute-phase reactants and connective tissue proteins. At least three C/EBP isoforms (alpha, beta, delta) are known. Upon stimulation with cytokines or bacterial lipopolysaccharide, the expression of the alpha isoform typically decreases, and the expression of the beta and/or delta isoforms increases. In view of the fact that components of the inflammatory response are present in diabetic kidney disease, there is a potential that the expression and activity of renal C/EBPs are altered in the diabetic state. In this study we sought to examine the status of C/EBP proteins in kidneys of rats with streptozotocin-induced diabetes mellitus. Diabetes was induced in 5 male Sprague-Dawley rats. Eight weight-matched non-diabetic rats were used as controls. Animals were sacrificed after 4 weeks, and the whole kidney nuclear protein was extracted. An electrophoretic mobility shift assay showed that DNA-binding activity was present in all five kidney nuclear extracts of the diabetic animals, but in only 2 out of 8 control samples (p < 0.05). A supershift assay showed that the DNA-bound protein complex consisted mainly of the C/EBPbeta isoform. Western analysis showed an increase of the C/EBPbeta protein in renal nuclear extracts of the diabetic animals compared to controls (p < 0.05). There was a decrease of the C/EBPalpha protein in the kidney nuclear extracts of the diabetic animals compared to controls (p < 0.05). We conclude that renal C/EBP dynamics are altered in experimental diabetes mellitus and that the patterns of C/EBP changes resemble those observed after cytokine or lipopolysaccharide stimulation.