Primitive Macrophages Enhance The Function Of Bioengineered Human Cardiac Microtissues

Human cardiac bioengineering has traditionally focused on cardiomyocyte differentiation and maturation. Unlike normal cardiac growth in the native human heart, human pluripotent stem cell (hPSC)- derived cardiomyocytes are typically grown in the absence of key supportive populations, which may negatively impact function due to a failure to recreate complex multicellular environments. In vivo murine studies have demonstrated that embryonic-derived resident cardiac macrophages promote neonatal cardiac regeneration, yet macrophages have not been incorporated in cardiac bioengineering approaches. We hypothesized that inclusion of human embryonic stem cell derived primitive macrophages (hESC-macrophages) into bioengineered human cardiac microtissues (“Biowires”) would improve cardiomyocyte functional properties. We found that addition of hESC-macrophages into Biowires led to enhanced contractile force, improved relaxation, reduced excitation threshold, increased maximum capture rate, and increased conduction velocity that mechanistically was correlated with improved calcium cycling, indicating hESC-macrophages improve a broad range of electromechanical properties. Moreover, hESC-macrophages enhanced microtissue function across cardiomyocyte cell sources and bioengineering platforms (Experimental N=6 independent cellular differentiations across 2 different platforms). These changes occurred in the absence of significant transcriptional shifts in cardiomyocytes. Rather, Biowires with hESC-macrophages had reduced mitochondrial DNA release, oxidative stress and cytotoxicity in the very early phases of tissue formation, thereby promoting a favorable environment for cardiac microtissue development. In conclusion, these data reveal a previously unappreciated, yet major beneficial role for macrophages specifically in human cardiac tissue engineering. In general, bioengineering human tissue continues to be a major research focus, and our data argue that inclusion of yolk sac-derived macrophages may improve early microtissue formation and modeling in vitro , and could enhance cell delivery approaches in vivo .