The Role of the KCa3.1 Channel in Aortic Stenosis

Introduction: Aortic stenosis (AS) is the most common heart valve lesion requiring surgery. It is characterised by progressive fibrosis and calcification of the aortic valve (AV) leaflets. Despite its prevalence, no medical therapies have been proven to ameliorate disease progression. Myofibroblasts are key effector cells driving AV fibrosis owing to their exaggerated extracellular matrix production and contractile activity. KCa3.1 channels are expressed by myofibroblasts and promote pro-fibrotic activity in rodent hearts and several human organs by regulating myofibroblast secretion, proliferation, and contraction. However, the role of KCa3.1 in AS has not been explored.Methods: AVs were collected from patients with severe tricuspid AS undergoing surgical AV replacement. AV myofibroblasts were isolated from the AV tissue and cultured. KCa3.1 mRNA and protein expression were assessed in AS valve tissue, isolated myofibroblast cells and human ventricular fibroblasts using qRT-PCR and immunofluorescence. Patch clamp electrophysiology was used to confirm the presence of functional KCa3.1 channels in the plasma membrane. The effects of transforming growth factor β1 (TGFβ1, 10 ng/ml), and the selective KCa3.1 blocker senicapoc (100 nM) were evaluated on fibrotic mRNA expression, stress fibre formation, contractility, proliferation and wound healing. An ex vivo AS valve culture model was also developed and optimised for future anti-fibrotic drug testing.Results: KCa3.1 mRNA and protein expression were detected in all AS valves tested and in all isolated myofibroblasts (n=7 valves and n=8 myofibroblast cultures). Cultured AV myofibroblasts expressed functional KCa3.1 currents (n=5 myofibroblast cultures, n=13 cells measured), with currents elicited by the KCa3.1 opener 1-EBIO, and inhibited by senicapoc. Stimulation of myofibroblasts with TGFβ1 significantly increased KCa3.1 and α-smooth muscle actin (αSMA) mRNA expression. The TGFβ1-dependent upregulation of αSMA mRNA expression was significantly decreased by senicapoc. TGFβ1-dependent αSMA stress fibre formation and TGFβ1-dependent myofibroblast contraction in collagen gels were also significantly reduced by senicapoc.Conclusions: This is the first study to demonstrate KCa3.1 expression and function in human AS valve tissue and myofibroblasts. The findings identify KCa3.1 as a novel modulator of TGFβ1-dependent AV myofibroblast activation and contractility. Targeting KCa3.1 may represent a novel anti-fibrotic strategy in AS. Moreover, as senicapoc was well tolerated for 12 months in a phase 3 clinical trial for sickle cell disease, there is the potential for the rapid translation of these findings to the clinic.