Fibroblast growth factor-23 promotes rhythm alterations and contractile dysfunction in adult ventricular cardiomyocytes

Background Cardiac dysfunction and arrhythmia are common and onerous cardiovascular events in end-stage renal disease (ESRD) patients, especially those on dialysis. Fibroblast growth factor (FGF)-23 is a phosphate-regulating hormone whose levels dramatically increase as renal function declines. Beyond its role in phosphorus homeostasis, FGF-23 may elicit a direct effect on the heart. Whether FGF-23 modulates ventricular cardiac rhythm is unknown, prompting us to study its role on excitation-contraction (EC) coupling. Methods We examined FGF-23 in vitro actions on EC coupling in adult rat native ventricular cardiomyocytes using patch clamp and confocal microscopy and in vivo actions on cardiac rhythm using electrocardiogram. Results Compared with vehicle treatment, FGF-23 induced a significant decrease in rat cardiomyocyte contraction, L-type Ca2+ current, systolic Ca2+ transients and sarcoplasmic reticulum (SR) load and SR Ca2+-adenosine triphosphatase 2a pump activity. FGF-23 induced pro-arrhythmogenic activity in vitro and in vivo as automatic cardiomyocyte extracontractions and premature ventricular contractions. Diastolic spontaneous Ca2+ leak (sparks and waves) was significantly increased by FGF-23 via the calmodulin kinase type II (CaMKII)-dependent pathway related to hyperphosphorylation of ryanodine receptors at the CaMKII site Ser(2814). Both contraction dysfunction and spontaneous pro-arrhythmic Ca2+ events induced by FGF-23 were blocked by soluble Klotho (sKlotho). Conclusions Our results show that FGF-23 reduces contractility and enhances arrhythmogenicity through intracellular Ca2+ mishandling. Blocking its actions on the heart by improving sKlotho bioavailability may enhance cardiac function and reduce arrhythmic events frequently observed in ESRD.