Ventricular remodeling after injury by growth differentiation factor 11 secreted by endogenously cycling cardiomyocytes - myocardial infarction (MI) has an estimated 30% one-year mortality rate,…

Ventricular remodeling after injury by growth differentiation factor 11 secreted by endogenously cycling cardiomyocytes - myocardial infarction (MI) has an estimated 30% one-year mortality rate, affecting over 9 million americans annually. A characteristic feature of this pathology is the chronic loss of ventricular cardiomyocytes (CMS) due to low proliferation rates - contributing to the progression to heart failure. Chronic CM necrosis is associated with well-characterized immune infiltration, inducing excessive matrix deposition and leading to infarct scar formation. Inflammatory cells and cytokines orchestrate the immune response after MI which is mediated by cytokines. One cytokine of interest in this proposal is growth differentiation factor 11 (GDF11), which is implicated in macrophage polarization and fibrosis. Preliminary studies from our lab in murine models show that knockout of GDF11 in all CMS worsens infarct scar after heart attack. Knockout of GDF11 from only cycling CMS recapitulates this effect. Furthermore, ablation of GDF11 from only cycling cells causes a significant increase in macrophage density in the infarct zone 3 days after MI. This correlates with in vitro elisa and qpcr assays demonstrating GDF11'S anti-inflammatory capacity. Interestingly, the loss of GDF11 from cycling CMS increases CM cycling in the tissue, suggesting a novel role of GDF11 in cell cycle regulation in CMS after injury. IT is unclear as to 1) how GDF11 from the small population of cycling CMS modulates the immune response and 2) the regulatory role of GDF11 in cycling after injury. We hypothesize that cycling CMS are a source of GDF11, driving macrophage polarization, decreasing fibrosis, and preventing cytokinesis in CMS after heart attack. To address these hypotheses rigorously, experiments were designed to incorporate murine models integrated with cellular biology. In vivo, the spatial and temporal modulation of the immune system as a result of GDF11 ablation from cycling cells will be determined through flow cytometry, scrna-SEQ of the CD45+ cardiac population, and histology. Bone-marrow- derived macrophages will be cultured EX vivo to rigorously determine the effect of GDF11 on macrophage polarization through molecular biology tools, such as qpcr and elisa. Additionally, murine models will evaluate the temporal change in cycling cells after MI due to cycling CM-specific GDF11 ablation to address the second aim. In vitro, GDF11'S capacity to inhibit cell cycle entry in model culture systems such as H9C2 and neonatal RAT ventricular myocytes will be determined. Conclusions from these experiments will elucidate previously undefined mechanisms in heart failure that can contribute to eventual therapies, benefiting millions of americans.