Enhancement of epithelial sodium channel expression in renal cortical collecting ducts cells by advanced glycation end products

Background. The epithelial sodium channel (ENaC) is a complex, and the alpha ENaC subunit has a crucial role in sodium uptake induced by aldosterone in the distal nephron. Although experimental animal models of diabetes have demonstrated up-regulation of alpha ENaC expression in renal cortical collecting duct (CCD) cells, the molecular mechanism remains unclear. Advanced glycation end products (AGEs) are by-products of long-term hyperglycaemia and comprise a significant pathogenic factor in diabetic nephropathy. We hypothesize that AGEs play a role in regulating alpha ENaC gene expression. Methods. Mouse CCD cells (mpkCCDcl(4)) were cultured with AGE to determine the effects of AGE on alpha ENaC expression and sodium uptake. Gene expressions of ENaC were measured by real-time PCR and sodium uptake was measured with fluorescent dye as a sodium indicator (SBFI-AM). This study analysed mitogen-activated protein kinases signalling pathways by western blotting. Cells co-transfected with plasmids of the alpha ENaC promoter carrying a luciferase reporter and plasmids expressing wild-type or mutant serum- and glucocorticoid-induced kinase 1 (Sgk1) mRNA were stimulated with AGE to identify the signalling pathway. Results. The AGEs, stimulated in a time- and dose-dependent manner, enhanced alpha ENaC mRNA expression and sodium uptake in mpkCCDcl(4) cells. The AGEs also significantly stimulated Sgk1 mRNA and Sgk1 activity in a time- and dose-dependent manner. Co-transfected with plasmid expressing mutant Sgk1 significantly limited stimulated alpha ENaC promoter-driven luciferase activity by AGEs in mpkCCDcl(4) cells. Conclusion. Experimental results indicate that AGEs induced alpha ENaC expression and increased sodium uptake in renal CCD cells. The mechanism through which AGEs activate alpha ENaC expression may be via activation of Sgk1 in mpkCCDcl(4) cells.