Abstract: Objective To examine whether calcineurin/NFAT signaling pathway mediates endothelin-1 (ET-1)-induced
proliferation of pulmonary artery smooth muscle cells (PASMCs) by regulating phosphodiesterase-5 (PDE5) and the effect of
the selective calcineurin inhibitor cyclosporine A and PDE5 inhibitor sildenafil on ET-1-induced PASMC proliferation.
Methods PASMCs were treated with ET-1 to stimulate their proliferation with or without prior treatment of the cells with CsA
or sildenafil. Calcineurin activity in the cells was measured using a calcineurin activity assay kit, PDE5 expression examined
using immunoblotting, and cGMP level detected using a cGMP direct immunoassay kit. PASMC proliferation following the
treatments was determined using [3H]thymidine incorporation assay. Results ET-1 caused a 2.05-fold increase in the cellular
calcineurin activity, a 1.80-fold increase in PDE5 expression, and a 3.20-fold increase in the DNA synthesis rate, and reduced
the cGMP level by 67% . Pretreatment of the cells with Cycloporine blocked the effects of ET-1, and PDE5 inhibition by
sildenafil pretreatment also abolished ET-1-induced reduction of cGMP level in the cells. Both Cycloporine and sildenafil
suppressed ET-1-stimulated PASMC proliferation. Conclusion Activation of calcineurin/NFAT signaling pathway mediates
ET-1-induced PASMC proliferation by stimulating PDE5 expression, which further degrades cGMP. Both Cycloporine and
sildenafil can suppress ET-1-stimulated PASMC proliferation in vitro.