| The heart and its cellular components are profoundly altered by missions to space and injury on Earth. Increasing evidence has identified that one such alteration induced by spaceflight is the promotion of the efficacious use of stem cells in therapies on Earth. For this reason, neonatal and adult human cardiovascular progenitor cells (CPCs) were cultured aboard the International Space Station (ISS). Subsequently, we assessed the effects of mechanical unloading on developmental properties and signaling. Spaceflight induced the expression of genes that are typically associated with an earlier state of cardiovascular development. In particular, in neonatal CPCs, we measured increased expression of pre-cardiac and developmental regulatory (Bmp and Tbx) genes; decreased expression of mesodermal derivative markers, including endothelial tube formation; and enhanced proliferative potential, as indicated by cell growth and cell cycle analysis. Interestingly, these changes were not observed in adult CPCs. To understand the mechanism by which such changes occurred in neonatal CPCs, we assessed the expression of mechanosensitive small RhoGTPases. Given the effect of these molecules on intracellular calcium levels, we evaluated changes in non-canonical Wnt/calcium signaling. ISS-cultured CPCs exhibited elevated levels of calcium handling and signaling genes, which corresponded to activation of protein kinase C alpha (PKCalpha), a calcium-dependent protein kinase, and Akt, a regulator of stem cell self-renewal, after 30 days. To explore the effect of calcium induction in neonatal CPCs, we activated PKCalpha using hWnt5a treatment on Earth, which resulted in an induction of early cardiovascular developmental marker expression. Interestingly, markers of the sinoatrial node, which may represent embryonic myocardium maintained in its primitive state, were induced by culture of neonatal CPCs aboard the ISS, which was modeled on Earth, at least in part, using the calcium signaling activators angiotensin II and hWnt5a. To test whether such signaling could induce sinoatrial nodal gene development on Earth, we treated neonatal CPCs with angiotensin II and observed the reliable induction of a sinoatrial nodal phenotype. We found that, in neonatal CPCs, spaceflight induces PKC? and Akt signaling, promotes the induction of an earlier developmental state, and highlights signaling events that may underpin biological pacemaker development on Earth. |
