Exercise-induced dysregulation of the adrenergic response in a mouse model of PKP2-arrhythmogenic cardiomyopathy.

BACKGROUND

Plakophilin-2 (PKP2) is a component of the desmosome. Pathogenic variants can lead to arrhythmogenic cardiomyopathy (PKP2-ACM). In patients with PKP2-ACM, exercise and catecholamine surges negatively impact arrhythmia incidence and severity.

OBJECTIVE

The study aimed to characterize remodeling of the sympathetic input and adrenergic response in hearts of PKP2-deficient mice (PKP2cKO) subjected to endurance exercise.

METHODS

We used expansion microscopy and structured illumination to characterize the abundance of beta 1-adrenergic receptors (β1-ARs) in the sarcolemma in PKP2cKO-myocytes, sedentary or trained, and Cre-negative controls. We prevented endogenous catecholamine import by short hairpin RNA (shRNA)-mediated knockdown of its transporter [organic cation transporter 3 (OCT3)] and characterized differential effects of isoproterenol (membrane permeable) vs norepinephrine (non-membrane permeable) on Ca2+ transient dynamics. Separately, we evaluated the distribution of sympathetic terminals in PKP2cKO-trained hearts vs controls.

RESULTS

Exercise led to "increased" abundance of sarcolemma β1-ARs in control, and "decreased" abundance in PKP2cKO-myocytes. OCT3 knockdown drastically reduced the response of trained PKP2cKO-myocytes to norepinephrine but not isoproterenol, indicating preserved response to native catecholamines by intracellular (dyad-associated) receptors in the setting of a reduced sarcolemma pool. In tissue, we observed reduced abundance of sympathetic terminals and heterogeneous distribution across the myocardium.

CONCLUSION

Endurance exercise in PKP2-deficient myocytes leads to a reduced pool of functional β1-ARs in the sarcolemma and yet availability of intracellular receptors, which can activate selected (and heterogeneous) routes of intracellular signaling cascades. We speculate that remodeling of nerve terminals affects sympathetic input distribution and hence, regional modulation of excitability and conduction. These changes can facilitate cell-generated triggered activity and heterogeneity of the underlying substrate, setting the stage for life-threatening arrhythmias.