KCa3.1 mediates activation of fibroblasts in diabetic renal interstitial fibrosis

Background. Fibroblast activation plays a critical role in diabetic nephropathy (DN). The Ca2+-activated K+ channel KCa3.1 mediates cellular proliferation of many cell types including fibroblasts. KCa3.1 has been reported to be a potential molecular target for pharmacological intervention in a diverse array of clinical conditions. However, the role of KCa3.1 in the activation of myofibroblasts in DN is unknown. These studies assessed the effect of KCa3.1 blockade on renal injury in experimental diabetes. Methods. As TGF-beta 1 plays a central role in the activation of fibroblasts to myofibroblasts in renal interstitial fibrosis, human primary renal interstitial fibroblasts were incubated with TGF-beta 1 +/- the selective inhibitor of KCa3.1, TRAM34, for 48 h. Two streptozotocin-induced diabetic mouse models were used in this study: wild-type KCa3.1+/+ and KCa3.1-/- mice, and secondly eNOS-/- mice treated with or without a selective inhibitor of KCa3.1 (TRAM34). Then, markers of fibroblast activation and fibrosis were determined. Results. Blockade of KCa3.1 inhibited the upregulation of type I collagen, fibronectin, alpha-smooth muscle actin, vimentin and fibroblast-specific protein-1 in renal fibroblasts exposed to TGF-beta 1 and in kidneys from diabetic mice. TRAM34 reduced TGF-beta 1-induced phosphorylation of Smad2/3 and ERK1/2 but not P38 and JNK MAPK in interstitial fibroblasts. Conclusions. These results suggest that blockade of KCa3.1 attenuates diabetic renal interstitial fibrogenesis through inhibiting activation of fibroblasts and phosphorylation of Smad2/3 and ERK1/2. Therefore, therapeutic interventions to prevent or ameliorate DN through targeted inhibition of KCa3.1 deserve further consideration.