Abstract Fri102: Ryanodine receptor 2 Dysfunction Triggers Cardiac Muscle Loss and Fibrofatty Infiltrations Consistent with Arrhythmogenic Cardiomyopathy in a Rabbit Model

Background: Ryanodine receptor 2 (RyR2) dysfunction occurs early in Arrhythmogenic Cardiomyopathy (ACM), contributing to ventricular arrhythmia, but its role in subsequent structural remodeling remains unclear. While RyR2 mutations have been linked to ACM, this association has been disputed due to conflicting clinical data and the lack of appropriate animal models. Here, we present a RyR2-V2475F rabbit model that exhibits hallmark ACM features. Methods: RyR2-V2475F New Zealand white rabbits were generated via CRISPR-Cas9. Cardiac function and structure changes were assessed in vivo and in vitro using histology, telemetry, echocardiography, Ca 2+ imaging, and single-nucleus RNA sequencing (snRNA-seq). Results: Sudden death (SD) occurred in 33% (28/84) of homozygous (Homo) rabbits, whereas no wild-type or heterozygotes littermates were affected. Hearts from SD rabbits exhibited right ventricular (RV)-dominant muscle loss and fibrofatty infiltration , initiating epicardially and progressing transmurally, closely resembling ACM. Ventricular tachycardia and SD occurred even before structural remodeling was evident. Echocardiography revealed early biventricular dilation, followed by RV specific contractile dysfunction. Isolated Homo cardiomyocytes (CMs) exhibited increased Ca 2+ leak, reduced Ca 2+ transient amplitude, and prolonged time to peak and decay. snRNA-seq identified early CM metabolic defects, including increased fatty acid uptake and impaired mitochondrial function, shifting toward inflammation and advanced disease stages. Fibroblasts (FBs) were initially proliferative but later transitioned to a fibrosis-producing phenotype, particularly in the RV, contributing to increased fibrosis. Conclusion: The RyR2-V2475F rabbit is the first animal model of RyR2-induced ACM with RV-dominant muscle loss, fibrofatty infiltration, and lethal arrhythmias. RyR2 dysfunction and Ca 2+ mishandling drive not only early arrhythmias but also progressive structural remodeling. Metabolic defects in CMs and RV-specific FB activation contribute to disease progression, providing mechanistic insights that may guide therapeutic strategies.