BNIP3 induced by hypoxia supports the survival of mesenchymal stromal cells (MSCs) after intravenous cell transplantation.

Introduction: Mesenchymal stromal cells (MSCs) are widely recognized as a valuable cell source for transplantation therapy due to their anti-inflammatory and tissue-regenerative properties in various inflammatory disorders. However, numerous studies have reported that transplanted MSCs frequently undergo cell death shortly after transplantation, leading to a limited number of surviving cells in recipient tissues. Methods: We found that culturing both mouse and human MSCs under 5 % oxygen conditions enhances the short-term survival rate after cell transplantation in the bleomycin treated model mice. Based on this finding, we performed transcriptomic analysis to identify the responsible genes, allogeneic and xenogeneic transplantation in mice following siRNA treatment, and measured reactive oxygen species (ROS) levels with assessment of mitophagy activity. Results: We identified Bnip3 as a gene that is consistently upregulated in both human and mouse MSCs under hypoxic culture conditions. Suppression of Bnip3 reduced the survival rate of MSCs cultured under hypoxic conditions, which should normally show high survival rates after transplantation. Bnip3 involved regulation of mitophagy, and we also found that preconditioning cells with hypoxic culture prior to transplantation upregulates Bnip3, conferring resistance to the transient ROS surge that occurs post-transplantation. Conclusion: This suggests that cell culture under hypoxia facilitates accumulation of Bnip3, a key regulator of mitophagy and confers stress tolerance to the MSCs. The findings indicate that pre-treating MSCs in hypoxic environment prior to transplantation could be a simple and effective strategy to improve cell viability in cell transplantation therapy.