Transgenic mouse model of ventricular preexcitation and atrioventricular reentrant tachycardia induced by an AMP-activated protein kinase loss-of-function mutation responsible for Wolff-Parkinson-White syndrome

Abstract

Background: We identified a gene (PRKAG2) that encodes the gamma-2 regulatory subunit of AMP-activated protein kinase (AMPK) with a mutation (Arg302Gln) responsible for familial Wolff-Parkinson-White (WPW) syndrome. The human phenotype consists of ventricular preexcitation, conduction abnormalities, and cardiac hypertrophy.

Methods and results: To elucidate the molecular basis for the phenotype, transgenic mice were generated by cardiac-restricted expression of the wild-type (TG(WT)) and mutant(TG(R302Q)) PRKAG2 gene with the cardiac-specific promoter alpha-myosin heavy chain. ECG recordings and intracardiac electrophysiology studies demonstrated the TG(R302Q) mice to have ventricular preexcitation (PR interval 10+/-2 versus 33+/-5 ms in TG(WT), P<0.05) and a prolonged QRS (20+/-5 versus 10+/-1 ms in TG(WT), P<0.05). A distinct AV accessory pathway was confirmed by electrical and pharmacological stimulation and substantiated by induction of orthodromic AV reentrant tachycardia. Enzymatic activity of AMPK in the mutant heart was significantly reduced (0.009+/-0.003 versus 0.025+/-0.001 nmol x min(-1) x g(-1) in nontransgenic mice), presumably owing to the mutation disrupting the AMP binding site. Excessive cardiac glycogen was observed. Hypertrophy was confirmed by increases in heart weight (296 versus 140 mg in TG(WT)) and ventricular wall thickness.

Conclusions: We have developed a genetic animal model of WPW that expresses a mutation responsible for a familial form of WPW syndrome with a phenotype identical to that of the human, including induction of supraventricular arrhythmia. The defect is due to loss of function of AMPK. Elucidation of the molecular basis should provide insight into development of the cardiac conduction system and accessory pathways.

Figure 1

Northern blot analysis of PKRAG2 for cardiac expression. Expression was evident in transgenic, wild-type (lane 2), and mutant (lane 3) mice with absence of expression in non-transgenic mouse heart (lane 1).

Figure 2

A, Enzymatic activity of AMPK in myocardial tissue is shown for transgenic wild type (WT), mutant, and nontransgenic mice (non-TG). B, Total myocardial enzymatic activity of AMPK as detected by pan antibody to β-2 subunit is shown for transgenic wild-type (WT), mutant, and nontransgenic (non-TG) mice. Activity as detected by γ-2 antibody is expressed as mean±SD. Specific activity expressed as nmol · min⁻¹ · g⁻¹ wet weight is shown on ordinate, and 3 groups indicated on abscissa are wild-type (WT), mutant, and nontransgenic (non-TG) mice. IP indicates immunoprecipitate.

Figure 3

Mutant, transgenic heart stained with PAS shows thickened wall with abundance of vacuoles. Vacuoles primarily contain PAS-positive material, which indicates increased deposition of glycogen.

Figure 4

Higher magnification of heart shown in Figure 3.

Figure 5

Left, ECG of TG_WT mouse with normal PR and QRS intervals. Right, Tracings of TG_R302Q mouse with ventricular preexcitation evidenced by short PR interval and wide QRS duration.

Figure 6

Age distribution of TG_R302Q mice. Solid bars indicate number of mice exhibiting preexcitation on 3-lead surface ECG.

Figure 7

Simultaneous ECG and intracardiac electrograms during atrial stimulation in TG_R302Q mouse with ventricular preexcitation. AV conduction propagated through accessory pathway during stimulation drive train (S1) delivered at cycle length of 100 ms. PR interval and QRS duration and morphology during S1 were similar to intrinsic rhythm. Premature extrastimulus (S2) delivered during accessory pathway refractoriness (70 ms after S1) caused AV conduction to proceed only through AV node, as evidenced by prolonged PR interval and narrowed QRS. LRA indicates low right atrial electrogram; HRA, high right atrial electrogram.

Figure 8

Simultaneous ECG and intracardiac electrograms during orthodromic AV reentrant tachycardia induced by atrial stimulation in TG_R302Q mouse with ventricular preexcitation. After stimulation drive train (S1) at cycle length of 100 ms, 2 progressively premature extrastimuli were delivered at S1-S2 of 80 ms and S2-S3 of 50 ms. Conduction due to S3 was blocked at accessory pathway, with antegrade conduction only through AV node (long AV interval). After accessory pathway recovery from refractoriness, VA conduction was retrograde through accessory pathway (short VA interval), which completed the reentry loop. Reentrant tachycardia continued for a few beats until it self-terminated. LRA indicates low right atrial electrogram; HRA, high right atrial electrogram.

Figure 9

Simultaneous ECG and intracardiac electrograms during procainamide administration in TG_R302Q mouse with ventricular pre-excitation. Procainamide resulted in sudden block of accessory pathway 3 to 5 minutes after intravenous infusion, as evidenced by spontaneous PR interval prolongation and QRS narrowing. RVA indicates right ventricular apical electrogram; RVB, right ventricular basal electrogram; LRA, low right atrial electrogram; and HRA, high right atrial electrogram.