[alpha Klotho and inorganic phosphate metabolism]

Area of Science:

• Nephrology
• Endocrinology
• Molecular Biology

Background:

• Klotho protein is crucial for calcium and phosphate homeostasis.
• Klotho and FGF receptor 1 form the FGF23 receptor complex.
• Dysregulation of phosphate transport is implicated in various kidney diseases.

Purpose of the Study:

• To investigate the relationship between hyperphosphatemia and phosphate (Pi) transport in klotho mutant mice (kl/kl).
• To determine the impact of klotho deficiency on renal and intestinal Pi cotransporter expression and activity.
• To explore the role of FGF23 and transporter trafficking in klotho-associated hyperphosphatemia.

Main Methods:

• Comparative analysis of kl/kl mice and wild-type littermates.
• Measurement of plasma phosphate, 1,25(OH)2D3, and FGF23 levels.
• Assessment of renal and intestinal sodium-dependent Pi cotransporter activity and protein/mRNA expression.
• Dietary manipulation (low-Pi diet) and pharmacological intervention (colchicine treatment).

Main Results:

• Kl/kl mice exhibited hyperphosphatemia, elevated 1,25(OH)2D3, and increased renal/intestinal Pi cotransporter activity.
• Type IIa, IIb, and IIc transporter protein levels were increased, but type IIa/IIc mRNA levels were decreased in kl/kl mice.
• Plasma FGF23 levels were significantly higher in kl/kl mice.
• Low-Pi diet normalized klotho expression and reduced FGF23, while colchicine revealed abnormal type IIa transporter membrane trafficking.

Conclusions:

• Hyperphosphatemia in klotho-deficient mice stems from dysregulated expression and trafficking of renal type IIa/IIc phosphate transporters.
• Intestinal phosphate uptake is not the primary cause of hyperphosphatemia in this model.
• These findings highlight klotho's critical role in regulating phosphate balance through renal transporter modulation.