Abstract 118: Interleukin 4 And 13 Signaling In Macrophages Regulates Neonatal Cardiac Regeneration

Introduction: Heart failure (HF) is a prevalent disease, projected to affect over 8 million Americans by 2030. Current therapy partially decreases progression; however, mortality and disease burden continue to be high. Therefore, there is an unmet need to develop new strategies that target HF progression. Our lab employs the neonatal mouse model of cardiac regeneration to identify pro-reparative pathways that can be applied to treating HF in humans. Previously we demonstrated that the anti-inflammatory cytokine, Interleukin 13 (IL13), promotes cardiac regeneration, however, the cell types mediating this response remain unknown. IL13 and the related cytokine, IL4, share a common receptor (IL4Rα) and both cytokines polarize macrophages into a reparative phenotype. Here, we hypothesize that IL4/13 signaling to macrophages promotes heart regeneration after cardiac injury and we explore the cell source of these cytokines during neonatal development and cardiac regeneration. Methods and Results: We generated a genetic model whereby IL4Rα is depleted in macrophages by crossing IL4Rα floxed (IL4Rα fl/fl ) mice with transgenic mice CX3Cr1 driven-Cre recombinase (CX3CR1 Cre ). Flow cytometry analysis confirmed depletion of IL4Rα in cardiac macrophages. We performed myocardial infarction (MI) on postnatal day 1 (P1) mice and assessed cardiac regeneration by ultrasonography 21 days post-injury (dpi). We found that IL4Rα fl/fl CX3CR1 Cre mice had lower ejection fraction compared to IL4Rα fl/fl littermate controls. Preliminary results suggest there is a reduced capillary density in peri-ischemic myocardium. In addition, we used fluorescent reporter mouse lines; IL4-enhanced green fluorescent protein (IL4-GFP) and IL13-yellow fluorescent protein (IL13-YFP), to assess the cellular source of IL4 and IL13 expression in the hearts of neonatal mice. In unoperated mice, we found no detectable expression of IL13 by any cell type in the heart, whereas IL4 was expressed in innate lymphoid cells (ILCs) and T cells. 4 days after MI in P1 mice IL13 was upregulated in ILCs and T cells and IL4 was expressed by ILCs and T cells and upregulated in myeloid cells. Conclusions and Discussion: We found that IL13 and IL4 are primarily expressed in ILCs and T cells following neonatal injury, suggesting a novel role for ILCs and T cells in the production of IL4 and 13 during the neonatal regeneration process. In addition, we found that lack of IL4/13 signaling in macrophages via depletion IL4Rα impairs cardiac regeneration after MI in neonatal mice, and results in reduced capillary density in peri-ischemic myocardium. We hypothesize that IL4Rα depletion in macrophages impairs reparative macrophage polarization after MI and promotes an inflammatory polarization. Future studies will be aimed to assess macrophage phenotypes in response to IL13/IL4 signaling by transcriptional profiling and flow cytometry.