Abstract Body (Do not enter title and authors here): BACKGROUND
Hypertrophic cardiomyopathy (HCM), affecting approximately 1 in 500 individuals globally, is a leading cause of sudden cardiac death in young adults. Current treatments are largely symptomatic and fail to alter disease progression. This study addresses the critical need for disease-modifying interventions by elucidating molecular mechanisms underlying HCM and identifying therapeutic candidates through a drug repurposing strategy.

METHODS
We employed a systems biology framework, integrating transcriptomic profiles from human HCM cardiac tissue with drug-response signatures from the Connectivity Map (CMAP) database to predict compounds capable of reversing disease-associated gene expression patterns. Atovaquone emerged as a top candidate. Its therapeutic efficacy was evaluated using in vitro and in vivo models, including established genetic HCM mouse models and cardiomyocyte hypertrophy assays. Target deconvolution and mechanistic analyses were conducted to define the molecular basis of its action.

RESULTS
Atovaquone markedly ameliorated pathological features in HCM models, including reduced left ventricular wall thickness, heart weight-to-body weight ratios, myocardial fibrosis, cardiomyocyte size, and expression of hypertrophy markers (Nppa/Nppb). CETSA-based thermal proteome profiling identified the membrane-associated E3 ubiquitin ligase MARCH3 as a direct target of Atovaquone. This interaction was supported by molecular docking and validated by CETSA and DARTS assays. Functional studies demonstrated that MARCH3 knockdown abrogated Atovaquone’s anti-hypertrophic effects in phenylephrine-stimulated neonatal rat ventricular myocytes, evidenced by increased hypertrophic gene expression and cell size. Mechanistically, Atovaquone enhanced MARCH3-mediated polyubiquitination of GP130, facilitating its lysosomal degradation and suppressing STAT3 phosphorylation at Y705 and S727. The use of leupeptin, but not MG132, reversed GP130 downregulation, confirming lysosomal pathway specificity.

CONCLUSION
This study identifies Atovaquone as a repurposed, disease-modifying candidate for HCM therapy. By targeting MARCH3 and inducing lysosomal degradation of GP130, it disrupts pathological STAT3 signaling. These findings provide both mechanistic insight and translational potential for a novel therapeutic approach in HCM.