Calcineurin Inhibition Affects Na(K)Cl Cotransporter Activity in Kidney Distal Nephron

Abstract

The calcineurin inhibitors (CNI) tacrolimus and cyclosporine A (CsA) are widely used for immunosuppression. However, side effects such as hypertension and electrolyte disorders commonly occur. Our previous data suggest that tacrolimus exerts local effects in kidney distal convoluted tubule (DCT), leading to activation of the Na+, Cl- cotransporter (NCC), salt retention and hypertension. This study aims to provide the molecular basis for the renal action of CsA. Calcineurin Aa and Ab isoforms were ubiquitously detected along mouse isolated nephron segments by immunoblotting and qPCR. Calcineurin Aa was preferentially colocalized with NCC in DCT subapical region, whereas calcineurin Ab was enriched together with Na+, K+, Cl- cotransporter (NKCC2) in the thick ascending limb (TAL). Immunophilins, mediating the inhibitory effects of CsA, were detected in both TAL and DCT of mice and rats using immunofluorescence and in situ hybridization. Acute as well as chronic administration of CsA in rats induced strong increases of NKCC2 and NCC phosphorylation without changes in their abundance, suggesting that activation of both cotransporters occurred at the posttranslational level. Analysis of the WNK-SPAK/OSR1 kinase cascade, controlling phosphorylation of the transporters, suggested enhanced activity in both distal segments. In sum, our data identify local components of calcineurin signalling in TAL and DCT which are likely involved in the activation of NKCC2 and NCC upon CNI. These results may have implications for antihypertensive therapy during immune suppression.