Arrhythmogenic cardiomyopathy with reduction of connexin40 and altered ion channel expression due to an inactivation of cyclase-associated protein 2

Abstract

Purpose: The inactivation of Cyclase Associated Protein 2 (CAP2) by a gene trap approach (gt) in the mouse leads to a cardiomyopathy with morphological predominance of the right ventricle resulting in an increased mortality. The purpose of our investigation was to identify potential arrhythmogenic reasons leading to this premature cardiac death. Methods: We performed in vivo electrophysiological studies in CAP2gt/+, CAP2gt/gt and corresponding Wild Type (WT) mice to determine surface and intracardiac ECG parameters and to test the inducibility of Ventricular Tachycardias (VTs). Long-term-ECG recordings were used to detect spontaneous arrhythmias. mRNA expression analysis of Cardiac Connexins (Cx) and ion channels were carried out as well as quantitative cardiac fibrosis determination. Immunofluorescence of Cx40 and Cx43 was performed to visualise their distribution pattern. Results: In comparison to WT, CAP2gt/gt showed marked conduction delays on atrial and ventricular level (reduced heart rate, prolonged PQ, QRS and QT time). AV-time prolongation was due to an infra Hisian conduction delay. Functional testing revealed a trend towards a prolonged ventricular refractory period. The inducibility of VTs was significantly higher in the mutant mice. Long-term-ECG recordings showed polymorphic premature ventricular contractions and spontaneous VTs in the CAP2 deficient mice. Compared to WT, the ventricles of CAP2gt/gt mice presented enhanced myocardial fibrosis (9.1±6.7% vs. 5.6±3.3%; p=0.01) that was found predominantly in the left ventricle. CAP2gt/gt resulted in a significant reduction of Cx40 expression (septum area) and elevated ventricular expression of Cx43, desmin and the calcium channel Cav 1.2. Conclusions: Loss of CAP2 results in marked electrophysiological disturbances leading to malignant ventricular arrhythmias. Impaired sinus node function, conduction delays, and susceptibility to arrhythmias are in accordance with a reduction of Cx40 and alterations in Cx43 and calcium channel expression. Cases of right ventricular cardiomyopathy may be due to dysfunction of CAP2, so further evaluation of its influence on cardiomyopathy and arrhythmogenesis should ensue to fully understand its functioning.