Simulated Microgravity Culture Enhances the Neuroprotective Effects of Human Cranial Bone-Derived Mesenchymal Stem Cells in Traumatic Brain Injury

Fundamental cures of central nervous system (CNS) diseases are rarely achieved due to the low regenerative ability of the CNS. Recently, cell-based therapy using mesenchymal stem cells (MSCs) has been explored as an effective treatment for CNS diseases. Among the various tissue-derived MSCs, we have isolated human cranial bone-derived MSCs (cMSCs) in our laboratory. In addition, we have focused on simulated microgravity (MG) as a valuable culture environment of MSCs. However, detailed mechanisms underlying functional recovery from transplantation of MSCs cultured under MG conditions remain unclear. In this study, we investigated the therapeutic mechanisms of transplantation of cMSCs cultured under MG conditions in traumatic brain injury (TBI) model mice. Human cMSCs were cultured under 1G and MG conditions, and cMSCs cultured under MG conditions expressed significantly higher messenger RNA (mRNA) levels of hepatocyte growth factor ( HGF ) and transforming growth factor beta ( TGF-β ). In TBI model mice, the transplantation of cMSCs cultured under MG conditions (group MG) showed greater motor functional improvement compared with only phosphate-buffered saline administration (group PBS). Moreover, the protein expression levels of tumor necrosis factor alpha (TNF-α) and the Bcl-2-associated X protein (Bax)/b cell leukemia/lymphoma 2 protein (Bcl-2) ratio were significantly lower at brain injury sites in mice of group MG than those of group PBS. In addition, an in vitro study showed that the conditioned medium of cMSCs cultured under MG conditions significantly suppressed the cell death of NG108-15 cells exposed to oxidative or inflammatory stress through anti-inflammatory and antiapoptosis effects. These findings demonstrate that culturing cMSCs under simulated MG increases the neuroprotective effects, suggesting that simulated MG cultures may be a useful method for cell-based therapy strategies for CNS diseases.