Concepedia

Mineralocorticoid versus Glucocorticoid Receptor Occupancy Mediating Aldosterone-Stimulated Sodium Transport in a Novel Renal Cell Line

H. P. Gaeggeler, Elena González Rodríguez, Nicole Fowler Jaeger, Dominique Loffing‐Cueni, Rikke Nørregaard, Johannes Loffing, Jean‐Daniel Horisberger, Bernard C. Rossier

Journal of the American Society of Nephrology · 2005 · 217 citations · 31 references

DOI

TL;DR

Aldosterone regulates sodium balance by activating ENaC in the aldosterone‑sensitive distal nephron, with mineralocorticoid specificity ensured by 11β‑hydroxysteroid dehydrogenase type 2, yet the fractional occupancy of MR and GR by aldosterone cannot be studied in vivo. The authors addressed this gap by employing a novel mouse cortical collecting duct cell line (mCCD(cl1)) that expresses significant levels of MR and GR and exhibits a robust aldosterone‑stimulated sodium transport response. In mCCD(cl1) cells, aldosterone produced a biphasic sodium transport response—low doses induced a transient early peak, while high doses produced a larger, sustained response—corticosterone required much higher concentrations and its effect was reversed by 11β‑HSD2 inhibition; dexamethasone only elicited a sustained response at high doses, and binding assays showed that aldosterone and corticosterone share a high‑affinity, low‑capacity site whereas dexamethasone binds a single site, indicating that within physiological aldosterone ranges sodium transport is governed by MR occupancy during circadian cycles and by both MR and GR during salt restriction or acute stress.

Abstract

Aldosterone controls sodium balance by regulating an epithelial sodium channel (ENaC)-mediated sodium transport along the aldosterone-sensitive distal nephron, which expresses both mineralocorticoid (MR) and glucocorticoid receptors (GR). Mineralocorticoid specificity is ensured by 11beta-hydroxysteroid dehydrogenase type 2, which metabolizes cortisol or corticosterone into inactive metabolites that are unable to bind MR and/or GR. The fractional occupancy of MR and GR by aldosterone mediating the sodium transport response in the aldosterone-sensitive distal nephron cannot be studied in vivo. For answering this question, a novel mouse cortical collecting duct cell line (mCCD(cl1)), which expresses significant levels of MR and GR and a robust aldosterone sodium transport response, was used. Aldosterone elicited a biphasic response: Low doses (K(1/2) = approximately 0.5 nM) induced a transient and early increase of sodium transport (peaking at 3 h), whereas high doses (K(1/2) = approximately 90 nM) entailed an approximately threefold larger, long-lasting response. At 3 h, the corticosterone dose-response curve was shifted to the right compared with that of aldosterone by more than two log concentrations, an effect that was fully reverted in the presence of the 11beta-hydroxysteroid dehydrogenase type 2 inhibitor carbenoxolone. Low doses of dexamethasone (0.1 to 1 nM) failed to induce an early response, but high doses elicited a long-lasting response (K(1/2) = approximately 8 nM), similar to that observed for high aldosterone concentrations. Equilibrium binding assays showed that both aldosterone and corticosterone bind to a high-affinity, low-capacity site, whereas dexamethasone binds to one site. Within the physiologic range of aldosterone concentrations, sodium transport is predicted to be controlled by MR occupancy during circadian cycles and by MR and GR occupancy during salt restriction or acute stress.