Inducible renal principal cell-specific mineralocorticoid receptor gene inactivation in mice

Abstract

To investigate the role of the mineralocorticoid receptor (MR) in renal ENaC-mediated sodium reabsorption, we have previously used the Cre-loxP system to generate mice with principal-cell specific MR ablation (MRAQP2Cre mice). To restrict Cre expression to principal cells, we have used the regulatory elements of the mouse aquaporin-2 (AQP2) gene to drive Cre expression. Since AQP2 is already expressed during renal development, MR ablation took place long before the analysis performed at the adult stage. To investigate whether the early onset of MR ablation affected the adult renal sodium handling, we developed a transgene expressing the CreERT2 fusion protein under control of the regulatory elements of the AQP2 gene (AQP2CreERT2). Immunofluorescence revealed MR loss in the collecting duct (CD) and late connecting tubule after induction of MR ablation by tamoxifen in MRAQP2CreERT2 mice that equals the MR loss in MRAQP2Cre mice. Surprisingly, tamoxifen-independent MR loss is observed in CDs of noninduced mutants without affecting circulating aldosterone levels. Under a low-salt diet, the induced ablation of MR at the adult stage recapitulates the renal sodium wasting observed in mice with constitutive early-onset MR ablation. The AQP2CreERT2 transgene is a new tool for investigating in vivo the function of genes downstream of MR in renal ENaC-mediated sodium reabsorption by inducible somatic gene inactivation.

Direct and Indirect Mineralocorticoid Effects Determine Distal Salt Transport

“…Genetic deletion of MR throughout the body largely recapitulates this phenotype, 13 but deletion of MR along the CNT and CD causes only mild salt wasting. 15,18 The present results show that MRs along the DCT2 and proximal CNT account for this difference, because deletion of MR along the entire nephron recapitulates the effects of rescued total body knockout.…”

Adult nephron-specific MR-deficient mice develop a severe renal PHA-1 phenotype

“…Again, only under a low-salt diet and at adult stage, the induced ablation of MR recapitulates the renal sodium wasting observed in mice with constitutive early-onset MR ablation, but not hyperkalemia and/or increased mortality [24]. This was explained by compensatory mechanisms either by upregulation of sodium transporters upstream of the CNT i.e.…”

Regulation of ion transport by microRNAs

“…It is therefore impossible to study the impact of miR depletion from the collecting duct on ion transport. This problem could be overcome by using the recently described transgenic mouse line expressing an inducible Cre recombinase under the control of the Aqp2 promoter, which permits timely controlled expression of the recombinase in principal cells of the distal nephron [47]. The characterization of the role of miRs in intercalated cells could then be performed by using mice expressing the Cre recombinase under the control of the promoter of the B1 subunit of the H þ -ATPase [48].…”