싸이클로스포린 신독성에서 클로라이드션트 기전에 작용하는 밀착결합단백의 발현 변화

Abstract

Cyclosporine A (CsA) may cause tubular dysfunction, for which an increased permeability for chloride in the distal cortical nephron (chloride shunt) is responsible. Two representative examples of Cl– shunt disorder are pseudohypoaldosteronism type II (PHAII) and cyclosporine nephrotoxicity. In PHAII, both the transcellular pathway mediated by the thiazide-sensitive Na-Cl cotransporter (NCC) in the distal convoluted tubule and the paracellular pathway mediated by the tight junction in the cortical collecting duct. Cyclosporine was subcutaneously administered to Sprague-Dawley rats for six (7.5 mg/kg BW) and two (25 mg/kg BW) weeks, and tight epithelial MDCK I (Madin-Darby canine kidney I) cells were treated with cyclosporine for 72 hours. The transepithelial electrical resistance (TER) was measured to evaluate the degree of sealing of the tight junction. Immunoblot analysis revealed that cyclosporine treatment induced a decrease of NCC in rat renal cortex. Consistent with downregulation of NCC, WNK4 protein was increased in both rat kidneys and MDCK I cells. Occludin, a tight junction protein colocalizing with WNK4, was also increased in rat kidneys and MDCK I cells exposed to 100 ng/mL cyclosporine. These results were confirmed by immunohistochemistry for NCC, WNK4 and occludin in rat kidney. In contrast, cyclosporine treatment induced a decrease of ZO-1 protein and no changes of claudin-1 and claudin-4 in both rat kidneys and MDCK I cells. As a measure of the barrier to small ions, TER of MDCK monolayers was decreased by cyclosporine 100 ng/mL, but increased by cyclosporine 500 ng/mL. We demonstrate that in cyclosporine nephrotoxicity, upregulation of WNK4 is associated with downregulation of NCC. Changes in tight junction protein assembly induced by altered expression of WNK4, occludin, and ZO-1 may affect paracellular permeability to produce Cl– shunt.