(Pro)renin receptor contributes to regulation of renal epithelial sodium channel

Abstract

Background: Recent studies reported increased (Pro)renin receptor (PRR) expression during low-salt intake. We hypothesized that PRR plays a role in regulation of renal epithelial sodium channel (ENaC) through serum and glucocorticoid-inducible kinase isoform 1 (SGK-1)-neural precursor cell expressed, developmentally downregulated 4-2 (Nedd4-2) signaling pathway.

Method: Male Sprague-Dawley rats on normal-sodium diet and mouse renal inner medullary collecting duct cells treated with NaCl at 130 mmol/l (normal salt), or 63 mmol/l (low salt) were studied. PRR and α-ENaC expressions were evaluated 1 week after right uninephrectomy and left renal interstitial administration of 5% dextrose, scramble shRNA, or PRR shRNA (n = 6 each treatment).

Results: In-vivo PRR shRNA significantly reduced expressions of PRR throughout the kidney and α-ENaC subunits in the renal medulla. In inner medullary collecting duct cells, low salt or angiotensin II (Ang II) augmented the mRNA and protein expressions of PRR (P < 0.05), SGK-1 (P < 0.05), and α-ENaC (P < 0.05). Low salt or Ang II increased the phosphorylation of Nedd4-2. In cells treated with low salt or Ang II, PRR siRNA significantly downregulated the mRNA and protein expressions of PRR (P < 0.05), SGK-1 (P < 0.05), and α-ENaC expression (P < 0.05).

Conclusion: We conclude that PRR contributes to the regulation of α-ENaC via SGK-1-Nedd4-2 signaling pathway.

FIGURE 1

Expression of (Pro)renin receptor (PRR) in the kidney. PRR mRNA (a) and protein expression (b) in response to different doses of PRR shRNA. PRR mRNA and protein expression in total kidney tissue (c and d), renal medulla (e and f), and renal medulla α-ENaC mRNA and protein expression (f and g), respectively, at the end of the study in rats treated with vehicle (open bars), scramble shRNA (solid bars), or PRR shRNA (diamond bars). mRNA and protein levels were normalized to β-actin. ^*P < 0.05 compared with vehicle or scramble shRNA.

FIGURE 2

mRNA and protein expression of (Pro)renin receptor in heart (a and b), prorenin and renin mRNA (c), and protein expression (d and e) in total kidney at the end of the study in the rats given vehicle (open bars), scramble shRNA (solid bars), (Pro)renin receptor shRNA (diamond bars). mRNA and protein levels were normalized to β-actin.

FIGURE 3

Representative images of (Pro)renin receptor (b and c) and α-epithelial sodium channel (d and e) immunostaining in renal medulla. Left column represents scramble shRNA and right column represents (Pro)renin receptor shRNA.

FIGURE 4

Expression of PRR, serum and glucocorticoid-inducible kinase isoform 1, p-neural precursor cell expressed, developmentally downregulated 4–2, and α-epithelial sodium channel in mIMCD and effect of PRR siRNA. PRR mRNA and protein expression (a and b), serum and glucocorticoid-inducible kinase isoform 1 mRNA and protein expression (c and d), phosphorylation of neural precursor cell expressed, developmentally downregulated 4–2 (e), α-epithelial sodium channel mRNA and (f and g) protein expression in response to normal salt and low salt. mRNA and protein levels were normalized to β-actin. PRR, (Pro)renin receptor.^*P < 0.05 compared to normal salt and ⁺P < 0.05 compared to low salt.

FIGURE 5

Expression of PRR, serum and glucocorticoid-inducible kinase isoform 1, p-neural precursor cell expressed, developmentally downregulated 4–2 and α-epithelial sodium channel in mIMCD treated with Ang II and effect of PRR siRNA. PRR mRNA and protein expression (a and b), serum and glucocorticoid-inducible kinase isoform 1 mRNA, and protein expression (c and d), Phosphorylation of neural precursor cell expressed, developmentally downregulated 4–2 (e), α-epithelial sodium channel mRNA and (f and g) protein expression in response to normal salt and Angiotensin II. mRNA and protein levels were normalized to β-actin. PRR, (Pro)renin receptor. ^*P < 0.05 compared to normal salt and ⁺P < 0.05 compared to Ang II.