Rescue of the mineralocorticoid receptor knock-out mouse

Area of Science:

• Physiology
• Endocrinology
• Nephrology

Background:

• The mineralocorticoid receptor (MR) is crucial for sodium and water balance.
• MR knockout (MR-/-) mice exhibit pseudohypoaldosteronism and die neonatally due to circulatory failure.
• Understanding MR's role in kidney and colon function is vital for treating related disorders.

Purpose of the Study:

• To investigate the functional defects in the kidney and colon of MR knockout mice.
• To determine if neonatal MR knockout mice can be rescued through sodium chloride (NaCl) substitution.
• To analyze the long-term physiological adaptations and persistent defects in rescued MR knockout mice.

Main Methods:

• Comparative analysis of amiloride-sensitive currents in the colon of MR-/- and control mice.
• In vitro perfusion of collecting ducts to assess basolateral membrane potential and urinary Na+ excretion.
• Subcutaneous NaCl injections and oral NaCl supplementation for rescue attempts in neonatal MR-/- mice.
• Monitoring growth, salt/water intake, and renal function in rescued adult MR-/- mice.

Main Results:

• Neonatal MR-/- mice showed reduced colonic current and increased urinary Na+ excretion.
• NaCl substitution therapy enabled survival of MR-/- mice past the critical neonatal period.
• Rescued MR-/- mice exhibited delayed growth initially but normalized later, retaining a persistent Na+-losing defect.
• Elevated plasma renin and aldosterone levels were observed in MR-/- mice, with hypertrophic/hyperplastic renin-producing cells.

Conclusions:

• Timely and matched NaCl substitution is effective in rescuing MR knockout mice from neonatal lethality.
• Rescued MR-/- mice adapt their oral salt and water intake to compensate for persistent renal salt-losing defects.
• This study highlights the critical role of MR in early life and the potential for therapeutic intervention in related conditions.