A new SGK1 knockout mouse

Serum and Glucocorticoid Regulated Kinase 1 in Sodium Homeostasis

The ubiquitously expressed serum and glucocorticoid regulated kinase 1 (SGK1) is tightly regulated by osmotic and hormonal signals, including glucocorticoids and mineralocorticoids. Recently, SGK1 has been implicated as a signal hub for the regulation of sodium transport. SGK1 modulates the activities of multiple ion channels and carriers, such as epithelial sodium channel (ENaC), voltage-gated sodium channel (Nav1.5), sodium hydrogen exchangers 1 and 3 (NHE1 and NHE3), sodium-chloride symporter (NCC), and sodium-potassium-chloride cotransporter 2 (NKCC2); as well as the sodium-potassium adenosine triphosphatase (Na⁺/K⁺-ATPase) and type A natriuretic peptide receptor (NPR-A). Accordingly, SGK1 is implicated in the physiology and pathophysiology of Na⁺ homeostasis. Here, we focus particularly on recent findings of SGK1’s involvement in Na⁺ transport in renal sodium reabsorption, hormone-stimulated salt appetite and fluid balance and discuss the abnormal SGK1-mediated Na⁺ reabsorption in hypertension, heart disease, edema with diabetes, and embryo implantation failure.

The circadian clock protein Period 1 regulates expression of the renal epithelial sodium channel in mice

The mineralocorticoid aldosterone is a major regulator of sodium transport in target epithelia and contributes to the control of blood pressure and cardiac function. It specifically functions to increase renal absorption of sodium from tubular fluid via regulation of the alpha subunit of the epithelial sodium channel (alphaENaC). We previously used microarray technology to identify the immediate transcriptional targets of aldosterone in a mouse inner medullary collecting duct cell line and found that the transcript induced to the greatest extent was the circadian clock gene Period 1. Here, we investigated the role of Period 1 in mediating the downstream effects of aldosterone in renal cells. Aldosterone treatment stimulated expression of Period 1 (Per1) mRNA in renal collecting duct cell lines and in the rodent kidney. RNA silencing of Period 1 dramatically decreased expression of mRNA encoding alphaENaC in the presence or absence of aldosterone. Furthermore, expression of alphaENaC-encoding mRNA was attenuated in the renal medulla of mice with disruption of the Per1 gene, and these mice exhibited increased urinary sodium excretion. Renal alphaENaC-encoding mRNA was expressed in an apparent circadian pattern, and this pattern was dramatically altered in mice lacking functional Period genes. These results suggest a role for Period 1 in the regulation of the renal epithelial sodium channel and more broadly implicate the circadian clock in control of sodium balance.