B-008 Unveiling Molecular Mechanisms and Biomarkers of Eosinophilic Myocarditis: Insights from a Mouse Model and Single-Cell RNA Sequencing

Background Hypereosinophilic syndromes (HES) are rare disorders characterized by unexplained, persistent eosinophilia (>1,500 eosinophils/mm³) and evidence of eosinophil-mediated end-organ damage. Among the most severe complications is eosinophilic myocarditis (EM), which contributes to significant morbidity and mortality in approximately 60% of HES patients. Diagnosing EM remains challenging as patients often present without cardiac symptoms, and traditional diagnostic tools, including electrocardiography and echocardiography, frequently yield unremarkable results. While advanced imaging modalities such as cardiac magnetic resonance imaging and endomyocardial biopsy can aid diagnosis, they are effective primarily in advanced disease stages. Despite these clinical challenges, the molecular drivers of EM and early diagnostic biomarkers remain largely unexplored. This study aims to develop and characterize models of EM, explore its intricacies, and identify early diagnostic markers and therapeutic targets. Methods We developed and characterized a mouse model of eosinophilic experimental autoimmune myocarditis (eoEAM) using hypereosinophilic (CD2-IL5 transgenic) mice immunized with cardiac myosin peptide. This model replicates key features of human EM. Disease progression was assessed using heart histology, flow cytometry, complete blood counts, RT-PCR, and circulating biomarkers including cell-free DNA (cfDNA) and cardiac troponin. Single-cell RNA sequencing (RNA-Seq) was also performed to map inflammatory and resident cardiac cell populations, identifying gene signatures and enriched pathways associated with disease. Results After three weeks, the eoEAM model exhibited eosinophil-predominant cardiac inflammation. Peripheral blood analysis revealed elevated cardiac troponin and cfDNA, indicating systemic markers of myocardial damage and cell death. However, these markers lacked specificity for EM. scRNAseq of the heart uncovered distinct populations of inflammatory cells, including eosinophils, and resident cardiac cells driving the disease process. Novel gene signatures and enriched pathways critical to the pathogenesis of EM were identified, offering potential avenues for biomarker discovery and therapeutic intervention. Conclusion We successfully established a reproducible mouse model of eoEAM that mimics human eosinophilic myocarditis. While serum troponin and cfDNA serve as systemic markers of cardiac injury, they are nonspecific. In contrast, single-cell transcriptomics revealed unique gene signatures and pathways that provide a foundation for developing noninvasive and disease-specific biomarkers. This study highlights the potential of advanced molecular approaches in elucidating the pathophysiology of EM and improving diagnostic accuracy. This work emphasizes the integration of molecular diagnostics into clinical practice, advancing precision medicine for eosinophilic myocarditis and related diseases.