Histone lysine demethylase inhibition is a disease-modifying therapy for hypertrophic cardiomyopathy

Rationale: Hypertrophic cardiomyopathy (HCM) is a common inherited cardiac disorder characterized by cardiac hypertrophy, fibrosis, arrhythmias, and sudden cardiac death (SCD). Although current therapies primarily target sarcomere dysfunction, the contribution of epigenetic dysregulation to HCM pathogenesis and its therapeutic potential remain poorly understood. Objective: To determine whether pharmacological inhibition of histone lysine demethylases (KDMs) with JIB-04 can prevent or reverse HCM progression and to identify the underlying epigenetic mechanisms. Methods and Results: mice carrying the murine equivalent of the pathogenic human MYH7 R403Q mutation. JIB-04 prevented disease progression, reduced cardiac hypertrophy and fibrosis, preserved cardiac function, and completely prevented SCD in cyclosporin A- accelerated HCM. JIB-04 also reversed established disease, produced sustained therapeutic benefits after drug withdrawal, and improved cardiac function in aged mice with spontaneous HCM. Bulk RNA sequencing and ATAC-seq demonstrated partial restoration of disease-associated transcriptional programs and chromatin accessibility. Proteomic analyses identified PHF2 (KDM7C) as a candidate target of JIB-04 in both mouse and human HCM hearts. PHF2 knockdown suppressed hypertrophic, inflammatory, and fibrotic gene expression in cardiomyocytes, macrophages, and fibroblasts, respectively. Human HCM hearts exhibited increased expression of multiple JIB-04-sensitive KDMs, including PHF2. In MYH7 R403Q induced pluripotent stem cell- derived cardiomyocytes, JIB-04 normalized disease-associated gene expression, restored connexin-43 membrane localization, and improved mitochondrial respiration. Although prolonged treatment induced reversible hepatomegaly with hepatic lipid accumulation, co-administration of the antioxidant N-acetylcysteine mitigated liver toxicity while preserving the therapeutic efficacy of JIB-04. Conclusions: Pharmacological KDM inhibition prevents and reverses HCM through epigenetic remodeling of disease-associated transcriptional and chromatin programs. These findings identify KDM inhibition as a promising therapeutic strategy for HCM, establish PHF2 as a candidate mediator of disease pathogenesis, and support further development of KDM-targeted therapies.