The work we proposed here is centered on the specific hypothesis that somatic stem cells responsible for tissue regeneration may require the mechanical stimulation of gravity to proliferate and differentiate, and to regenerate tissues at normal rates, and that therefore, exposure to microgravity may slow down tissue regenerative processes based on adult stem cell progenitors. Our results from spaceflight experiments with amphibian (newt) tail regeneration during the Foton M2 and Foton M3 missions, suggests that spaceflight significantly retards tissue regeneration by interfering with newt tail blastema stem cell progenitor proliferation and differentiation. These findings suggest that normal long-term homeostatic tissue regenerative processes in mammals may also be sensitive to the absence of gravity-generated forces in space, and that this may cause tissue degeneration. In this study we sought to gather further evidence about the role of gravity-generated forces in promoting tissue regeneration and the molecular mechanisms by which gravity in stem cells is translated into proliferation and differentiation.
The Cell Culture Module (CCM) hardware was used to differentiate mouse embryonic stem cells in spaceflight and in ground controls, using an experimental model based on the formation of embryoid bodies containing various differentiated tissue lineages and cell types. Three bioreactors were recovered with cells fixed during spaceflight for mRNA /gene expression analysis, and three maintained live cells for cell biology assays conducted post-flight.
Experimental analysis showed that spaceflight cell cultures fixed in space did not express tissue lineage markers characteristic of differentiation and retained elevated stem cell markers, versus ground control cultures that expressed tissue markers indicative of normally differentiated embryoid bodies, and lacked stem cell markers. In ground controls a variety of gene markers of tissue differentiation quantified using real time qPCR, appeared normally as differentiated embryoid bodies. These markers included specific genes for endoderm, mesoderm, ectoderm, and specific cell types within these tissues. Additionally, we observed the disappearance of stem cell markers in these controls. However in spaceflight samples, nearly of 80% of the tissue lineage markers characteristic of embryoid body differentiation were not detected, and stem cell markers remained elevated. Measurements of cell number, DNA content, and glucose consumption also revealed a slight decrease in initial cell proliferation in space, but no changes in cell viability or apoptosis. Finally, live cells recovered in adhesion outgrowth assays from post-flight embryoid bodies in spaceflight bioreactors, when cultured, showed greater potential for de novo differentiation of contractile cardiomyocyte colonies, suggesting greater numbers of undifferentiated progenitors were present. The results suggest that spaceflight inhibited normal stem cell differentiation and maintained the stem cell potential of the differentiating cultures, and support the hypothesis that the tissue regenerative potential of stem cells may be decreased during spaceflight. Further gene expression analysis and cell biology studies are currently underway.
No data submitted. Summarized and analyzed data may be available through publications.
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