Abstract 19324: Effects of Simulated Microgravity on Ckit+ Cardiac Progenitor Cells

Abstract

Introduction: Space flight has profound negative impacts on cardiac health. Whereas microgravity appears to benefit cardiomyogenesis, long-duration space flight results in increased risk for cardiomyopathy. Here, we focused on cKit+ cardiac progenitor cells (CPCs) to elucidate the effects of microgravity in the heart. Hypothesis: Microgravity inhibits migration, proliferation and differentiation of CPCs. Methods: Adult heart tissue or induced pluripotent stem cells (iPSCs) from cKitCreErt2;IRG mice were grown for up to 24- (n=5) or 21-days (n=6), respectively, in static (SC) or a rotary cell-culture system (RCCS, simulated microgravity) in the presence of 4-OH tamoxifen to irreversibly label CPCs with EGFP. Expression of EGFP was quantified at selected time points in heart explants and iPSC-derived beating embryoid bodies (EBs). In addition, microarray analysis was performed on EBs at selected time points (n=11). Results: We found that, although explants in SC consistently produced EGFP+ CPCs with full capacity to proliferate and migrate, expression of EGFP was abolished in RCCS (p<0.05). Similarly, when day-4 EBs (formed via the hanging-drop method) were transferred to RCCS, they generated significantly fewer spontaneously beating EBs compared to EBs grown in SC (p=0.0005), whereas expression of EGFP in beating EBs was downregulated ~10-fold (p=0.01). Microarray analysis of EBs illustrated that the effect of CPs was accompanied by downregulation of genes related to migration, differentiation and development of the cardiac neural crest cell (CNC) lineage (i.e. Pax3, semaphorins, endothelin) without affecting the expression of cardiac mesoderm-related genes (i.e. GATA4, NKX2-5, MEF2C). Intriguingly, the effect of RCCS in CNC-related genes could be partly rescued upon transfer of EBs from RCCS to SC. Conclusions: cKit expression and CNC pathways are inhibited under simulated microgravity but can be reversed by returning to normal gravity. Our findings provide novel insights into the role of gravity in cardiomyogenesis and suggest that CPCs should be targeted therapeutically for the prevention and treatment of microgravity-induced cardiomyopathy.