Expression and localization of 11β-hydroxysteroid dehydrogenase (11βHSD) in the rat endolymphatic sac

Abstract

Conclusions: 11β-Hydroxysteroid dehydrogenase type 2 (11βHSD-2) enables aldosterone to bind to mineralocorticoid receptors (MRs) selectively by converting cortisol (corticosterone) into inactive metabolites. Its expression in the endolymphatic sac (ES) suggests that aldosterone may selectively act on the ES through its binding to MRs by the action of 11βHSD-2, and supports the notion that ES is an aldosterone target organ. We propose that 11βHSD-2 is a dominant isoform of 11βHSDs in the ES, and the ES (especially the intermediate portion of the ES) may be the main aldosterone target in the inner ear. Objective: The purpose of this study was to examine 11βHSD isoform expression in the rat inner ear, mainly 11βHSD-2 in the ES. Materials and methods: In the ES and whole cochlea, 11βHSDs were examined by RT-PCR using highly specific ES RNA by laser capture microdissection. In addition, 11βHSD-2 localization in the rat ES was determined by immunohistochemistry. Results: RT-PCR demonstrated 11βHSD-2 expressed in the rat ES. In addition, its localization was observed mainly in the intermediate portion and a faint immune positive signal was observed in other parts of the ES. In contrast, 11βHSD-1 was undetectable in the ES by RT-PCR. Both types of 11βHSDs were expressed in rat cochlea.

Keywords::

• Aldosterone
• inner ear
• endolymph homeostasis
• laser capture microdissection
• steroid

Acknowledgements

This work was supported in part by Grants-in-Aid for Scientific Research (#13671783 and #16591711 to N.M., and #16791003 and #19791208 to T.M.).

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.