Doxorubicin induces bone marrow B-cell dysmaturation via Ebf1/Pax5 suppression to drive peripheral B-cell reduction in cardiotoxicity

Introduction Cardiotoxicity of doxorubicin (DOX) represents a major contributor to cancer therapy-related cardiac dysfunction (CTRCD), severely limiting the clinical utility of this first-line chemotherapeutic agent. Its pathological mechanisms involve not only direct cardiomyocyte injury but also systemic immune dysregulation. Previous studies implicate splenic B cell dysfunction in DOX-induced cardiotoxicity, yet fail to explain the primary mechanism underlying persistent peripheral B cell reducion in CTRCD patients. As the primary site of B cell ontogeny, the bone marrow's regulatory role in B cell lineage differentiation under DOX exposure remains largely unexplored. Methods This study employed a combined clinical-animal validation strategy. For the clinical cohort, peripheral B cell counts were quantified in CTRCD patients post-DOX chemotherapy. For the animal experiment, a murine model of DOX-induced cardiotoxicity was established，cardiac function was assessed via echocardiography. B cells and its subsets were analyzed via flow cytometry. Furthermore, scRNA-seq was utilized to analyze the transcriptomic profiles, developmental trajectories, and expression of key regulatory molecules in bone marrow B cells, thus identifying the molecular mechanisms by which DOX impairs bone marrow B-cell maturation. Results Clinical analysis revealed that CTRCD patients exhibited significant peripheral lymphocytopenia, predominantly characterized by B cell reduction (Fig. 1A-C). Animal experiments confirmed that DOX administration impaired cardiac function, elevated myocardial injury biomarkers, and aggravated cardiac atrophy and fibrosis (Figs. 1D–1H). Consistent with clinical observations, DOX-treated mice showed a significant reduction in blood B cells accompanied by a mild compensatory increase in total bone marrow B cells (Figs. 1I–1J). Notably, a negative correlation was identified between blood B cells and cardiac function in these mice (Figs. 1K). Flow cytometric analysis of bone marrow B-cell subsets showed an accumulation of pro-B and pre-B cells, whereas the frequencies of mature naïve B and follicular B cells were significantly decreased in DOX-treated mice (Figs. 1L–1P). Bone marrow single-cell RNA sequencing confirmed a significant reduction in B cells following DOX treatment (Figs. 1Q). Pseudotime trajectory analysis further revealed a block in B-cell maturation (Figures 1L–1M), accompanied by marked downregulation of the key B-cell developmental transcription factors Ebf1 and Pax5 (Figures 1R–1S). Collectively, these findings indicate that DOX impairs the developmental maturation of bone marrow B cells. Conclusions This study identifies DOX-mediated downregulation of Ebf1/Pax5 as a potential mechanism impairing bone marrow B cell development, which contributes to peripheral B cell reduction in CTRCD patients.