Mechanisms of calcium-induced arrhythmias in arrhythmogenic right ventricular cardiomyopathy

PROJECT SUMMARY / ABSTRACT
Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a complex inherited disorder of the heart produced
by mutation in proteins of the desmosome, such as plakophilin-2 (PKP2). Cardiac arrhythmias, and potentially
sudden death, often occur in ARVC patients during the early stages of the disease, a “concealed phase” that
presents before the onset of structural cardiomyopathy. The molecular and cellular mechanisms of these
arrhythmic events remain unclear, hindering the search for effective strategies to treat patients. My long-term
goal is to delineate the mechanisms of arrhythmia in ARVC and to identify potential drug targets to prevent
sudden cardiac death. Mice with tamoxifen (TAM)-induced ablation of PKP2 (PKP2cKO) develop a phenotype
evocative of human ARVC: a concealed stage with high incidence of arrhythmia but without structural remodeling
at 14 days, cardiomyopathy of right ventricle dominance at 21 days, and biventricular cardiomyopathy, heart
failure and death at ~42 days post-TAM. We reported that PKP2cKO hearts show significant dysregulation of
Ca2+ handling at different stages of disease progression but, most remarkably, during the concealed stage of the
disease. This proposal aims to elucidate the mechanisms underlying cardiac arrhythmia in PKP2-deficient hearts
focusing on the microdomain where Ca2+ regulation takes place. I hypothesize that dysfunction of the cardiac
ryanodine receptor (RyR2), a major intracellular Ca2+ release channel, and the ensuing Ca2+ mishandling are
critical triggers of cardiac arrhythmia in the PKP2cKO mouse and, hence, in ARVC. These aims will test my
hypothesis: 1) Determine the role of protein kinase C (PKC) phosphorylation in the regulation of RyR2 channel
function and calcium homeostasis. Preliminary data suggest that RyR2 is undergoing phosphorylation in
PKP2cKO hearts at Thr2810. This previously uncharacterized site is a predicted PKC substrate. I hypothesize
that PKC phosphorylation of RyR2 at Thr2810 regulates channel function and contributes to arrhythmogenic
Ca2+ release in the diseased heart. 2) Define the contribution of RyR2 dysfunction in the onset and progression
of heart disease in PKP2cKO mice. Preliminary data suggest that RyR2 phosphorylation at Thr2810 and Ser2030
is increased in ARVC. I hypothesize that inhibition of RyR2 phosphorylation at these sites prevents arrhythmia
and sudden death in PKP2cKO mice. 3) Test the efficacy of RyR2 modulators for the prevention of arrhythmia
in PKP2-deficient hearts. I hypothesize that pharmacological modulation of RyR2 is beneficial to prevent
arrhythmia in PKP2cKO mice and hearts. The completion of these aims will provide significant insight into the
regulation of RyR2 function in a model of PKP2cKO deficiency and hence shed light on the mechanisms
underlying ARVC. I anticipate these results will advance the status of RyR2 as a potential therapeutic target to
reduce the risk of arrhythmias and increase life-expectancy of patients with ARVC.

Grant Number: 5R01HL161070-05
NIH Institute/Center: NIH
Principal Investigator: Francisco Alvarado