Renal function of gene-targeted mice lacking both SGK1 and SGK3

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Abstract
Serum- and glucocorticoid-inducible kinase (SGK) 1 and SGK3 share the ability to upregulate several ion channels, including the epithelial Na+ channel. Whereas SGK1 is under genomic control of mineralocorticoids and glucocorticoids, SGK3 is constitutively expressed. The SKG1-knockout (sgk1−/−) mouse is seemingly normal when it is fed a standard diet, but its ability to retain NaCl is impaired when it is fed a salt-deficient diet. In the SGK3-knockout (sgk3−/−) mouse fed standard and salt-deficient diets, hair growth is strikingly delayed but NaCl excretion is normal. Thus the possibility was considered that SGK1 and SGK3 could mutually replace each other, thus preventing severe NaCl loss in sgk1−/− and sgk3−/− mice. We crossed SGK1- and SGK3-knockout mice and compared renal electrolyte excretion of the double mutants (sgk1−/−/sgk3−/−) with that of their wild-type littermates (sgk1+/+/sgk3+/+). Similar to sgk3−/− mice, the sgk1−/−/sgk3−/− mice display delayed hair growth. Blood pressure was slightly, but significantly (P < 0.03), lower in sgk1−/−/sgk3−/− (102 ± 4 mmHg) than in sgk1+/+/sgk3+/+ (114 ± 3 mmHg) mice, a difference that was maintained in mice fed low- and high-salt diets. Plasma aldosterone concentrations were significantly (P < 0.01) higher in sgk1−/−/sgk3−/− than in sgk1+/+sgk3+/+ mice fed control (511 ± 143 vs. 143 ± 32 pg/ml) and low-salt (1,325 ± 199 vs. 362 ± 145 pg/ml) diets. During salt depletion, absolute and fractional excretions of Na+ were significantly (P < 0.01) higher in sgk1−/−/sgk3−/− (1.2 ± 0.2 μmol/24 h g body wt, 0.12 ± 0.03%) than in sgk1+/+/sgk3+/+ (0.4 ± 0.1 μmol/24 h g body wt, 0.04 ± 0.01%) mice. The sgk1−/−/sgk3−/− mice share the delayed hair growth with sgk3−/− mice and the modestly impaired renal salt retention with sgk1−/− mice. Additional lack of the isoform kinase does not substantially compound the phenotype for either property.