SphK1 Suppresses Human Dental Pulp Stem Cell Apoptosis by Promoting Glycolysis Under Simulated Microgravity

Glycolysis supports mesenchymal stem cell (MSC) proliferation and sustains their undifferentiated state by maintaining energy supply and limiting apoptosis. The rapid advancement of space life sciences has spurred considerable interest in the effects of microgravity on stem cells. However, the contribution of glycolytic metabolism to apoptotic regulation under simulated microgravity (SMG) remains unclear. This study examined the influence of SMG on glycolytic activity and apoptosis in human dental pulp stem cells (hDPSCs). Lactic acid and glucose measurements were used to evaluate glycolytic flux, while transcript levels of HK2, PKM2, and LDHA were quantified by qPCR, HK2 and PKM2 protein expression was assessed by Western blotting, and annexin V-FITC/PI staining combined with immunoblotting of apoptosis-related proteins (BAX, BCL-2, and cleaved caspase-3) was performed to assess cell death. SMG markedly increased glycolytic capacity and attenuated apoptosis in hDPSCs. SphK1 expression was also elevated, indicating a role in cell survival. Pharmacological inhibition of SphK1 with PF-543 reduced both glycolysis and the antiapoptotic effect, implicating SphK1 as a critical regulator of these processes. Inhibition of glycolysis by 2-DG further increased apoptosis, confirming the protective role of glycolytic metabolism under SMG. These findings demonstrate that SMG enhances glycolysis and limits apoptosis in hDPSCs via SphK1 upregulation, suggesting that microgravity conditions may augment stem cell survival and function.