Real microgravity condition promoted regeneration capacity of induced pluripotent stem cells during the TZ-1 space mission.

Induced pluripotent stem cells (iPSCs) are reprogrammed somatic cells that gained self-renewal and differentiation capacity similar to embryonic stem cells. Taking the precious opportunity of the TianZhou-1 spacecraft mission, we studied the effect of space microgravity (µg) on the self-renewal capacity of iPSCs. Murine iPSCs carrying pluripotency reporter Oct4-GFP were used. The Oct4-EGFP-iPSCs clones were loaded into the bioreactor and exposed to μg in outer space for 14 days. The control experiment was performed in identical device but on the ground in earth gravity (1 g). iPSCs clones were compact and highly expressed Oct4 before launch. In μg condition, cells in iPSC clones spread out more rapidly than those in ground 1 g condition during the first 3 days after launch. However, in 1 g condition, as the cell density increases, the Oct4-GFP signal dropped significantly during the following 3 days. Interestingly, in μg condition, iPSCs originated from the spread-out clones during the first 3 days appeared to cluster together and reform colonies that activated strong Oct4 expression. On the other hand, iPSC clones in 1 g condition were not able to recover Oct4 expression after overgrown. Our study for the first time performed real-time imaging on the proliferation process of iPSCs in space and found that in μg condition, cell behaviour appeared to be more dynamic than on the ground.