PCP4 Is a Key Regulator of Cardiac Purkinje Cell Calcium Homeostasis and Suppresses Arrhythmogenic Calcium Waves

Abstract

Background Triggered activity in cardiac Purkinje cells (PCs) has been implicated in the genesis of inherited and acquired ventricular arrhythmias. PC arrhythmogenicity is attributed, at least in part, to dysregulation of intracellular calcium homeostasis; however, the molecular basis for differential calcium handling in PCs vs ventricular myocytes (VMs) is incompletely characterized. The goal of this study was to identify and characterize novel molecular mechanisms responsible for altered calcium handling in PCs. Methods and Results Compound transgenic mice harboring both a Cntn2-eGFP BAC reporter and an α-MHC-Cre/floxed tdTomato reporter were used to isolate cardiac PCs (eGFP + /tomato + ) from VMs (eGFP – /tomato + ) by FACS. Gene profiling was performed on total RNA extracted from each cell population. The transcript encoding Purkinje cell protein 4 ( PCP4 ), a modulator of calmodulin-dependent signaling, was significantly enriched in PCs. Restricted expression of PCP4 protein in PCs was confirmed by immunohistochemistry. PCP4 knockout mice were obtained and crossed with the Cntn2-eGFP reporter mouse, and isolated VMs and PCs from wild-type (WT) and mutant hearts were distinguished by epifluorescence and intracellular Ca 2+ dynamics recorded by microfluorometry. PCP4 –/– PCs displayed significantly slower kinetics of relaxation [τ(decay)] than that observed in wild-type PCs (328.9 ± 24.9 ms vs 235.8 ± 20.7 ms, P PCP4 –/– ) PCs were also more likely to develop rate dependent early aftertransients [63.6% (21/33) vs 8.3% (3/36) at 0.5 Hz, P P PCP4 –/– ) mice elicited PVCs (4/5, P Conclusions PCP4 is preferentially expressed in the murine ventricular conduction system, where it modulates intracellular calcium homeostasis. Loss of function of PCP4 results in an increased propensity for the development of early and delayed aftertransients and triggered arrhythmias.