Abstract 191: Paracrine Impact of Cardiac Progenitor Cells on Macrophage Phenotypes and Human Ipsc-derived Cardiomyocyte Survival

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The clinical progression of myocardial infarction, the foremost cause of death globally, to heart failure is proportionally higher with increasing infarct size. Thus, preventing cardiomyocyte loss at time of injury and stimulating self-repair are fruitful approaches to counteract the severity of cardiac damage. We previously found that intramyocardial injection of cardiac progenitor cells (CPCs) at time of ischemia improves cardiac function 12 weeks later. Given poor long-term engraftment in our studies and many others’, the consensus is that early paracrine effects are the probable cause of the benefits observed, including direct effects on cardiomyocytes but also macrophages as key players in the response to injury. Here, using transwell and conditioned medium experiments, we show that CPCs suppress the death of cardiomyocytes after oxidative stress. In this highly tractable model system, CPCs protect not only mouse cardiomyocytes, but also human iPSC-derived cardiomyocytes. Moreover, we show that CPC-conditioned medium affects macrophage differentiation and polarization. Cardioprotective CPCs disrupt the pro-inflammatory (“M1”) programme induced by GM-CSF/LPS/IFNγ, and promote instead the formation of anti-inflammatory (“M2”) macrophages as shown by single cell qRT-PCR. To identify the effectors of the cardioprotective paracrine cocktail, we performed RNA-Seq on unfractionated Sca1 + cardiac stromal cells, identified wound healing and immune response enriched GeneOntologies, then mapped noteworthy hits by single-cell qPCR to the PDGFRα + CPC subpopulation. By a combination of single-cell gene expression profiling in protective versus non-protective cells, plus highly multiplexed immunoassays (LEGENDplex, O-Link), we identified 6-8 candidates as potential mediators of cardiomyocyte protection and M2 macrophage induction. In summary, our data: (1) Define a consistent single-cell paracrine gene signature in adult CPCs; (2) Resolve specific benefits conferred by CPCs in the M1 versus M2 macrophage phenotypes; (3) Demonstrate the utility of iPSC-derived cardiomyocytes as a human platform for paracrine protection studies.