CaSR signaling down‐regulates AQP2 expressionviaa novel microRNA pathway in pendrin and NaCl cotransporter knockout mice

Abstract

High concentrations of urinary calcium counteract vasopressin action via the activation of the calcium-sensing receptor (CaSR) that is expressed in the luminal membrane of collecting duct cells, which impairs the trafficking of aquaporin-2 (AQP2). Pendrin/NaCl cotransporter double-knockout (dKO) mice display significant calcium wasting and develop severe volume depletion, despite increased circulating vasopressin levels. We hypothesized that the CaSR-mediated impairment of AQP2 expression/trafficking underlies vasopressin resistance in dKO mice. Compared with wild-type mice, in renal inner medulla, dKO mice had reduced total AQP2 sensitive to proteasome inhibitors, higher levels of AQP2-pS261, ubiquitinated AQP2, and p38-MAPK, an enzyme that is activated by CaSR signaling and known to phosphorylate AQP2 at Ser261. CaSR inhibition with the calcilytic NPS2143 reversed these effects, which indicates that CaSR mediates the up-regulation of AQP2-pS261, ubiquitination, and degradation. Of note, dKO mice demonstrated significantly higher AQP2-targeting miRNA-137 that was reduced upon CaSR inhibition, supporting a critical role for CaSR in the down-regulation of AQP2 expression. Our data indicate that CaSR signaling reduces AQP2 abundance both via AQP2-targeting miRNA-137 and the p38-MAPK/AQP2-pS261/ubiquitination/proteasomal axis. These effects may contribute to the reduced renal concentrating ability that has been observed in dKO mice and underscore a physiologic mechanism of the CaSR-dependent regulation of AQP2 abundance via a novel microRNA pathway.-Ranieri, M., Zahedi, K., Tamma, G., Centrone, M., Di Mise, A., Soleimani, M., Valenti, G. CaSR signaling down-regulates AQP2 expression via a novel microRNA pathway in pendrin and NaCl cotransporter knockout mice.

Vasopressin–aquaporin-2 pathway: recent advances in understanding water balance disorders

“…Novel AQP-targeting therapies through modulation of microRNA (miRNA) function have recently been suggested (reviewed in 122). The possibility of using miRNA alone or in combination with other drugs to modulate the vasopressin–AQP2 pathway specifically provides new hints for AQP-based therapeutics 27, 123 . In this respect, the recent identification of miR-132 as a first miRNA target which blocks vasopressin gene expression has opened new avenues for drug development 124 .…”

New insights into the transcriptional regulation of aquaporin-2 and the treatment of X-linked hereditary nephrogenic diabetes insipidus

“…The abundance of AQP2 protein is regulated by transcription of the Aqp2 gene and translation, and post-translational modification of products, including ubiquitination and subsequent proteasomal and/or lysosomal degradation, which involve the actions of E3 ubiquitin-protein ligases (e.g., NEDD4 and CHIP) [43,46–52]. In addition, microR-NAs (miRNA; e.g., miR-32 and miR-137) are important post-transcriptional modulators that regulate AQP2 protein abundance [53,54]. A recent study showed that miR-132 regulates hypothalamic AVP mRNA expression [55].…”

Renal Ca2+ and Water Handling in Response to Calcium Sensing Receptor Signaling: Physiopathological Aspects and Role of CaSR-Regulated microRNAs

“…This theory that elevated concentration of calcium in urine counteract vasopressin action via the activation of CaSR expressed at luminal membrane of principal cells has been further validated in a mouse model double-knockout (dKO) for Pendrin/NaCl Cotransporter (NCC) [66], which display significant calcium wasting and severe volume depletion, despite high circulating vasopressin levels [67].…”

“…Moreover, inhibition of p38-MAPK caused a drastic decrease in AQP2-pS261, along with a nearly five-fold increase in total AQP2. Furthermore, in dKO mice, p38-MAPK inhibition results in a drastic reduction in ubiquitinated AQP2 that is paralleled by a strong increase in total AQP2 [66].…”