Renal Ca2+ handling in sgk1 knockout mice.

Area of Science:

• Nephrology
• Molecular Biology
• Calcium Homeostasis

Background:

• Serum- and glucocorticoid-inducible kinase 1 (SGK1) is known to stimulate the renal epithelial calcium channel TRPV5 in vitro.
• SGK1 enhances TRPV5 protein abundance in the plasma membrane, a process involving Na+/H+ exchanger regulating factor 2 (NHERF2).

Purpose of the Study:

• To investigate the in vivo role of SGK1 in regulating renal calcium handling.
• To analyze the impact of SGK1 deficiency on TRPV5 and calbindin D-28K abundance and renal calcium excretion in mice.

Main Methods:

• Gene-targeted mice lacking functional SGK1 (sgk1-/-) and wild-type littermates (sgk1+/+) were studied.
• Immunohistochemistry was used to assess TRPV5 and calbindin D-28K protein levels.
• Renal calcium excretion and fractional calcium excretion were measured under control and calcium-deficient diets, with and without furosemide administration.

Main Results:

• sgk1-/- mice exhibited lower abundance of TRPV5 and calbindin D-28K proteins compared to sgk1+/+ mice on a control diet.
• A calcium-deficient diet increased TRPV5 abundance in both genotypes, and renal calcium excretion decreased similarly in both groups.
• Furosemide administration increased fractional calcium excretion and eliminated the difference between sgk1-/- and sgk1+/+ mice.

Conclusions:

• SGK1 deficiency leads to reduced TRPV5 abundance in the connecting tubules but does not abolish TRPV5 regulation.
• Compensatory calcium reabsorption in upstream nephron segments, potentially due to altered sodium handling, may occur in SGK1-deficient mice.
• These findings highlight SGK1's role in maintaining renal calcium homeostasis, with evidence of adaptive mechanisms in its absence.