LEFTYA Activates the Epithelial Na+ Channel (ENaC) in Endometrial Cells via Serum and Glucocorticoid Inducible Kinase SGK1

Abstract

Background: Serum & glucocorticoid inducible kinase (SGK1) regulates several ion channels, including amiloride sensitive epithelial Na⁺ channel (ENaC). SGK1 and ENaC in the luminal endometrium epithelium, are critically involved in embryo implantation, although little is known about their regulation. The present study explored whether SGK1 and ENaC are modulated by LEFTYA, a negative regulator of uterine receptivity. Methods: Expression levels were determined by qRT-PCR and Western blotting, ENaC channel activity by whole cell patch clamp and transepithelial current by Ussing chamber experiments. Results: Treatment of Ishikawa cells, an endometrial adenocarcinoma model cell line of endometrial epithelial cells, with LEFTYA rapidly up-regulated SGK1 and ENaC transcript and protein levels. Induction of ENaC in response to LEFTYA was blunted upon co-treatment with the SGK1 inhibitor EMD638683. ENaC levels also significantly upregulated upon expression of a constitutively active, but not a kinase dead, SGK1 mutant in Ishikawa cells. LEFTYA increased amiloride sensitive Na⁺-currents in Ishikawa cells and amiloride sensitive transepithelial current across the murine endometrium. Furthermore, LEFTYA induced the expression of ENaC in the endometrium of wild-type but not of Sgk1-deficient mice. Conclusions: LEFTYA regulates the expression and activity of ENaC in endometrial epithelial cells via SGK1. Aberrant regulation of SGK1 and ENaC by LEFTYA could contribute to the pathogenesis of unexplained infertility.