Vascular endothelial growth factor enhances profibrotic activities through modulation of calcium homeostasis in human atrial fibroblasts

Vascular endothelial growth factor increases the profibrotic activity of atrial fibroblasts by activating the currents through transient receptor potential channels and intermediate-conductance calcium-activated K+ (K(Ca)3.1) channels and by enhancing Ca2+ entry-induced phosphorylated Ca2+/calmodulin-dependent protein kinase II (CaMKII) signaling. These findings suggest a novel strategy targeting atrial myopathy and arrhythmofibrosis. Vascular endothelial growth factor (VEGF), a pivotal activator of angiogenesis and calcium (Ca2+) signaling in endothelial cells, was shown to increase collagen production in atrial fibroblasts. In this study, we evaluated whether VEGF may regulate Ca2+ homeostasis in atrial fibroblasts and contribute to its profibrogenesis. Migration, and proliferation analyses, patch-clamp assay, Ca2+ fluorescence imaging, and western blotting were performed using VEGF-treated (300 pg/mL or 1000 pg/mL) human atrial fibroblasts with or without coadministration of Ethylene glycol tetra-acetic acid (EGTA, 1 mmol/L), or KN93 (a Ca2+/calmodulin-dependent protein kinase II [CaMKII] inhibitor, 10 mu mol/L). VEGF (1000 pg/mL) increased migration, myofibroblast differentiation, pro-collagen type I, pro-collagen type III production, and phosphorylated VEGF receptor 1 expression of fibroblasts. VEGF (1000 pg/mL) increased the nonselective cation current (I-NSC) of transient receptor potential (TRP) channels and potassium current of intermediate-conductance Ca2+-activated K+ (K(Ca)3.1) channels thereby upregulating Ca2+ entry. VEGF upregulated phosphorylated ERK expression. An ERK inhibitor (PD98059, 50 mu mol/L) attenuated VEGF-activated I-NSC of TRP channels. The presence of EGTA attenuated the profibrotic effects of VEGF on pro-collagen type I, pro-collagen type III production, myofibroblast differentiation, and migratory capabilities of fibroblasts. VEGF upregulated the expression of phosphorylated CaMKII in fibroblasts, which was attenuated by EGTA. In addition, KN93 reduced VEGF-increased pro-collagen type I, pro-collagen type III production, myofibroblast differentiation, and the migratory capabilities of fibroblasts. In conclusion, we found that VEGF increases atrial fibroblast activity through CaMKII signaling by enhancing Ca2+ entry. Our findings provide benchside evidence leading to a potential novel strategy targeting atrial myopathy and arrhythmofibrosis.