The role of SGK-1 in angiotensin II-mediated sodium reabsorption in human proximal tubular cells.
BACKGROUND
The role of angiotensin II (Ang II) in mediating excessive sodium reabsorption in diabetic nephropathy is recognized. Serine-glucocorticoid kinase-1 (SGK-1) increases sodium-hydrogen exchanger-3 (NHE3) expression and is known to be upregulated in in vitro and in vivo models of diabetic nephropathy. However, a link between Ang II and SGK-1 in diabetic nephropathy has not been established.


METHODS
Ang II production in cultured human proximal tubular cells was measured under normal (5 mM) and high (25 mM) glucose conditions. The Ang II type 1 receptor was identified by RT-PCR. SGK-1 and NHE3 mRNA and protein expression was measured in proximal tubule cells (PTCs) exposed to Ang II. EIPA inhibitable changes in cell sodium uptake were undertaken to confirm that alterations in NHE3 mRNA and protein were reflected in transport activity. SGK-1 was silenced in the PTCs using small interfering RNA to determine the role of SGK-1 in mediating Ang II-induced increases in NHE3-mediated sodium uptake.


RESULTS
Ang II production by PTCs was significantly increased by exposure to high glucose (P < 0.02). Ang II increased NHE3 and SGK-1 mRNA expression to 275 +/- 30% (P < 0.02) and 130 +/- 10% (P < 0.05) respectively. Silencing of SGK-1 reduced Ang II-stimulated NHE3 protein expression to 49.8 +/- 6.1% (P < 0.05) of control levels. SGK-1 silencing abolished increases in (22)Na(+) uptake seen in Ang II-treated cells to 86.7 +/- 1.6% of control values.


CONCLUSIONS
These data suggest that increased sodium reabsorption in renal proximal tubular cells considered to be due to Ang II in diabetes mellitus is mediated through SGK-1 expression.
Stevens
Veronica A
VA
Department of Medicine, University of Sydney, Renal Research Group, Kolling Institute, Royal North Shore Hospital, St Leonards, NSW 2065, Australia .
Saad
Sonia
S
Poronnik
Philip
P
Fenton-Lee
Carol A
CA
Polhill
Tania S
TS
Pollock
Carol A
CA
D000704:Analysis of Variance; D000804:Angiotensin II / Q000378:metabolism / Q000494:pharmacology*; D015153:Blotting, Western; D002478:Cells, Cultured; D003928:Diabetic Nephropathies / Q000503:physiopathology; D004797:Enzyme-Linked Immunosorbent Assay; D005947:Glucose / Q000494:pharmacology*; D006801:Humans; D007687:Kidney Tubules, Proximal / Q000166:cytology* / Q000502:physiology; D011336:Probability; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis; D044140:Receptor, Angiotensin, Type 1 / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012680:Sensitivity and Specificity; D012964:Sodium / Q000378:metabolism; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism*; D015854:Up-Regulation
D012333:RNA, Messenger; D044140:Receptor, Angiotensin, Type 1; C000613385:SLC9A3 protein, human; D000074083:Sodium-Hydrogen Exchanger 3; D017923:Sodium-Hydrogen Exchangers; D000804:Angiotensin II; D012964:Sodium; D017346:Protein Serine-Threonine Kinases; D005947:Glucose