Space microgravity increases expression of genes associated with proliferation and differentiation in human cardiac spheres

Previously, we reported upregulation of cardiac proliferation in cardiac progenitors derived from human induced pluripotent stem cells (hiPSC-CPCs) that were exposed to space microgravity for 3 days. The overall objective of this investigation was to understand how long-term exposure to microgravity affects the expansion and differentiation of hiPSC-CPCs. Cryopreserved cardiomyocytes derived from human-induced pluripotent stem cells (hiPSC-CMs) were exposed to space microgravity for 3 weeks in the International Space Station (ISS) and retrieved for transcriptomic profiling. RNA-seq analysis and gene ontology analysis revealed upregulation of cardiac tissue function and morphological terms while downregulating inflammation and ECM regulation terms. Upregulation of genes associated with cell cycle regulation and proliferation were notable as well. Combined with previous work, these results suggest that space microgravity improved cardiac differentiation and structure formation and potentially, proliferation. On the ISS, the astronauts thawed the cryopreserved cardiac progenitor spheres, and cultured the cells using the MVP system from Techshot, Inc.33 The MVP system allows loading of multiple samples under both ISS µG and ISS 1G conditions (the 1G condition on the ISS was achieved by centrifugation). Each condition was run in triplicates.The cells were cultured at 37°C in the MVP system for 22 days on the ISS with medium exchange every other day. At the end of the mission, live cultures were returned to ground via warm storage after having been cultured aboard the ISS. Upon arrival at Emory University, cardiac spheres were transferred immediately into an incubator and let recover overnight. The following day cardiac spheres were transferred from the collection bags into low adhesion dishes. Medium was changed from CO2-independent medium to standard cardiomyocyte culture medium (RPMI 1640 with 2% B27 supplement), and cardiac spheres were then maintained overnight, followed by RNA isolation.