Fibroblast growth factor 23 stimulates cardiac fibroblast activity through phospholipase c‐mediated calcium signaling

Fibroblast growth factor (FGF)‐23 induces hypertrophy and calcium (Ca2+) dysregulation in cardiomyocytes, leading to cardiac arrhythmia and heart failure. However, knowledge regarding the effects of FGF‐23 on cardiac fibrogenesis remains limited. This study investigated whether FGF‐23 modulates cardiac fibroblast activity and explored its underlying mechanisms. We performed MTS analysis, 5‐ethynyl‐2’‐deoxyuridine assay, and wound‐healing assay in cultured human atrial fibroblasts without and with FGF‐23 (1, 5 and 25 ng/mL for 48 h) to analyze cell proliferation and migration. We found that FGF‐23 (25 ng/mL, but not 1 or 5 ng/mL) increased proliferative and migratory abilities of human atrial fibroblasts. Compared to control cells, FGF‐23 (25 ng/mL)‐treated fibroblasts had a significantly higher Ca2+ entry and intracellular inositol 1,4,5‐trisphosphate (IP3) level (assessed by fura‐2 ratiometric Ca2+ imaging and enzyme‐linked immunosorbent assay). Western blot analysis showed that FGF‐23 (25 ng/mL)‐ treated cardiac fibroblasts had higher expression levels of calcium release‐activated calcium channel protein 1 (Orai1) and transient receptor potential canonical (TRPC) 1 channel, but similar expression levels of α‐smooth muscle actin, collagen type IA1, collagen type Ⅲ, stromal interaction molecule 1, TRPC 3, TRPC6 and phosphorylated‐calcium/calmodulin‐dependent protein kinase II when compared with control fibroblasts. In the presence of ethylene glycol tetra‐acetic acid (a free Ca2+ chelator, 1 mM) or U73122 (an inhibitor of phospholipase C, 1 µM), control and FGF‐23‐treated fibroblasts exhibited similar proliferative and migratory abilities. Moreover, polymerase chain reaction analysis revealed that atrial fibroblasts abundantly expressed FGF receptor 1 but lacked expressions of FGF receptors 2‐4. FGF‐23 significantly increased the phosphorylation of FGF receptor 1. Treatment with PD166866 (an antagonist of FGF receptor 1, 1 µM) attenuated the effects of FGF‐23 on cardiac fibroblast activity. In conclusion, FGF‐23 may activate FGF receptor 1 and subsequently phospholipase C/IP3 signaling pathway, leading to an upregulation of Orai1 and/or TRPC1‐mediated Ca2+ entry and thus enhancing human atrial fibroblast activity.