Short-term exposure of human minor salivary gland stem cells to hypergravity enhances stemness

Abstract: Radiation therapy for head and neck cancer damages local stem cells and epithelial cells in salivary glands (SG), leading to irreversible SG dysfunction. Biological understanding of the responses of tissue-resident stem cells to gravity is required to develop therapeutic strategies for damaged tissue regeneration. In this study, we successfully isolated human minor salivary gland stem cells (huMSGSCs), which have high proliferation rates, express multiple stem markers, and can be differentiated into mesenchymal cell types. Cell proliferation, sphere-forming ability, stemness marker expressions, and epithelial differentiation potentials were checked after exposing huMSGSCs short-term to hypergravity (HyperG) or microgravity (MicroG). Proliferation after exposure to HyperG (40 G ) was greater than exposure to 1G, but no difference was observed between MicroG (10^− 3 G) and 1G. Numbers of large spheres were significantly higher post-HyperG and lower post-MicroG than at 1G, whereas numbers of small spheres were significantly lower post-HyperG and higher post-MicroG. The expressions of stemness markers (CD90, LGR5, CD29, and CD24) and junction markers (ZO-1 and ZO-2) were increased post-HyperG. Furthermore, increases in PAS staining and the gene expressions of albumin and CK19 confirmed that HyperG enhances the epithelial differentiation potential of huMSGSCs. This study shows that cultivating huMSGSCs under HyperG conditions enhances stemness and that a gravity control system could be applied to modulate huMSGSC functions.