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 alphaENaC 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 alphaENaC 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 alphaENaC gene expression.


METHODS
Mouse CCD cells (mpkCCDcl(4)) were cultured with AGE to determine the effects of AGE on alphaENaC 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 alphaENaC 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 alphaENaC 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 alphaENaC promoter-driven luciferase activity by AGEs in mpkCCDcl(4) cells.


CONCLUSIONS
Experimental results indicate that AGEs induced alphaENaC expression and increased sodium uptake in renal CCD cells. The mechanism through which AGEs activate alphaENaC expression may be via activation of Sgk1 in mpkCCDcl(4) cells.
Chang
Chiz-Tzung
CT
Kidney Research Institute and Department of Nephrology, Chang Gung Memorial Hospital, 5, Fu-Shing St., Kueishan, Taoyuan 333, Taiwan.
Wu
Mai-Szu
MS
Tian
Ya-Chung
YC
Chen
Kuan-Hsing
KH
Yu
Chun-Chen
CC
Liao
Chang-Hui
CH
Hung
Cheng-Chieh
CC
Yang
Chih-Wei
CW
D000818:Animals; D015153:Blotting, Western; D002478:Cells, Cultured; D003513:Cycloheximide / Q000494:pharmacology; D003609:Dactinomycin / Q000494:pharmacology; D003928:Diabetic Nephropathies / Q000235:genetics* / Q000378:metabolism / Q000517:prevention & control; D004195:Disease Models, Animal; D053503:Epithelial Sodium Channels / Q000096:biosynthesis / Q000187:drug effects / Q000235:genetics*; D017127:Glycation End Products, Advanced / Q000494:pharmacology*; D017874:Immediate-Early Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D007685:Kidney Tubules, Collecting / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D019384:Nucleic Acid Synthesis Inhibitors / Q000494:pharmacology; D010770:Phosphotransferases / Q000378:metabolism; D010957:Plasmids; D011401:Promoter Regions, Genetic / Q000187:drug effects; D017346:Protein Serine-Threonine Kinases / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D012333:RNA, Messenger / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects; D014162:Transfection; D015854:Up-Regulation / Q000187:drug effects*; D019459:Urothelium / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D000099184:Serum-Glucocorticoid Regulated Kinases
D003513:Cycloheximide; D003609:Dactinomycin; D053503:Epithelial Sodium Channels; D017127:Glycation End Products, Advanced; D017874:Immediate-Early Proteins; D019384:Nucleic Acid Synthesis Inhibitors; D010770:Phosphotransferases; D017346:Protein Serine-Threonine Kinases; D011500:Protein Synthesis Inhibitors; D012333:RNA, Messenger; D000099184:Serum-Glucocorticoid Regulated Kinases