Targeting Fibro-fatty Replacement In Arrhythmogenic Cardiomyopathy

Arrhythmogenic cardiomyopathy (ACM) is a genetic cardiac disease, generally inherited as an autosomal dominant trait, and clinically characterised by syncope, arrhythmias, and sudden cardiac death especially among young individuals and athletes. The main histopathological features of ACM are the death of cardiomyocytes and the progressive loss of normal myocardial tissue, followed by replacement with fibro-fatty tissue. Nearly 50% of ACM cases are associated with genetic causes, even though the disease manifests intrafamilial variable expressivity and incomplete penetrance. Many causative pathogenic variants are identifiable in one or more genes coding for junctional proteins of intercalated discs (IDs), ensuring electromechanical coupling among cardiomyocytes. A detailed knowledge of the molecular mechanisms involved in the pathogenesis of ACM is still missing, making the identification of suitable targets for the development of therapeutic compounds more complex. The overall aim of this PhD project was to address the fibro-fatty replacement characteristic of the disease by directly targeting the cell types responsible for the fibro-adipogenic deposition, such as cardiac fibro-adipogenic progenitors (cFAPs), which represent a key cellular source of this pathological process. Initially, we characterized a newly generated knock-in murine model (DSG2_KI), carrying in heterozygosity the c.313G>C Dsg2 mutation (corresponding to the human c.298G>C mutation). Baseline analyses of these animals revealed altered junctional structures, cardiac inflammation, and dysregulation of pathways implicated in ACM pathogenesis. To directly modulate fibro-fatty remodeling in this model, we targeted the differentiation of cFAPs. Cells isolated from the hearts of DSG2_KI and wild-type (WT) mice were employed as an in vitro platform to assess the efficacy of Givinostat, a pan-histone deacetylase (HDAC) inhibitor previously shown to exert anti-fibrogenic and anti-adipogenic effects in the context of Duchenne muscular dystrophy (DMD). In the ACM setting, Givinostat effectively reduced the propensity of cFAPs to differentiate into both adipocytes and fibroblasts. We then extended this approach to a human model. Specifically, we evaluated the effects of Givinostat and additional, more selective HDAC inhibitors in vitro using cardiac fibroblasts derived from patient-specific hiPSCs carrying the c.2013delC PKP2 mutation. In this system as well, Givinostat inhibited both pro-fibrogenic and pro-adipogenic induction. Moreover, the identification of other specific HDAC inhibitors with comparable mechanisms of action and efficacy to Givinostat underscores their potential as novel therapeutic strategies for ACM.