High salt intake increases uroguanylin expression in mouse kidney.

Area of Science:

• Nephrology
• Endocrinology
• Molecular Biology

Background:

• Intestinal peptides guanylin and uroguanylin are implicated in endocrine control of renal function.
• Both peptides and their receptor, guanylyl cyclase C (GC-C), are present in the kidney, suggesting local roles.
• Physiological regulation of these peptides within the kidney remains unstudied.

Purpose of the Study:

• To investigate the distribution of uroguanylin and guanylin messenger RNA (mRNA) in the mouse nephron.
• To determine how dietary salt and water intake regulate renal expression of these peptides.
• To explore the relationship between receptor presence and ligand expression.

Main Methods:

• RT-PCR, Northern blotting, and immunocytochemistry were used to analyze gene and protein expression.
• Studies were conducted in wild-type mice, GC-A-/- mice, GC-C-/- mice, and cultured M-1 renal epithelial cells.
• Dietary salt loading (1% NaCl) and hypertonic media were employed to assess regulatory effects.

Main Results:

• Uroguanylin mRNA expression was higher than guanylin and localized primarily to proximal tubules, while guanylin was found in collecting ducts.
• Uroguanylin expression was significantly lower in GC-C-/- mice, indicating receptor-mediated down-regulation of ligand.
• Salt-loading increased uroguanylin mRNA expression by over 1.8-fold, with no effect on guanylin.
• Uroguanylin transcripts, but not guanylin, were detected in M-1 cells and increased with hypertonic conditions.

Conclusions:

• High-salt intake up-regulates uroguanylin expression in the mouse kidney.
• Guanylin expression is not significantly affected by high-salt intake.
• Tubular epithelial synthesis of uroguanylin may contribute to local renal function control and salt adaptation.