Background and Purpose— Bone marrow mononuclear cells (BM-MNCs) are a rich source of hematopoietic stem cells and have been widely used in experimental therapies for patients with ischemic diseases. Activation of angiogenesis is believed to be one of major BM-MNC mode of actions, but the essential mechanism by which BM-MNCs activate angiogenesis have hitherto been elusive. The objective of this study is to reveal the mechanism how BM-MNCs activate angiogenesis. Methods— We have evaluated the effect of direct cell-cell interaction between BM-MNC and endothelial cell on uptake of VEGF (vascular endothelial growth factor) into endothelial cells in vitro. Cerebral ischemia model was used to evaluate the effects of direct cell-cell interaction with transplanted BM-MNC on endothelial cell at ischemic tissue. Results— The uptake of VEGF into endothelial cells was increased by BM-MNC, while being inhibited by blockading the gap junction. Low-molecular-weight substance was transferred from BM-MNC into endothelial cells via gap junctions in vivo, followed by increased expression of hypoxia-inducible factor-1α and suppression of autophagy in endothelial cells. The concentration of glucose in BM-MNC cytoplasm was significantly higher than in endothelial cells, and transfer of glucose homologue from BM-MNC to endothelial cells was observed. Conclusions— Our findings demonstrated cell-cell interaction via gap junction is the prominent pathway for activation of angiogenesis at endothelial cells after ischemia and provided novel paradigm that energy source supply by stem cell to injured cell is one of the therapeutic mechanisms of cell-based therapy. Visual Overview— An online visual overview is available for this article.

f Development of the metanephric kidney begins with the induction of a single ureteric bud (UB) on the caudal Wolffian duct (WD) in response to GDNF (glial cell line-derived neurotrophic factor) produced by the adjacent metanephric mesenchyme (MM). Mutual interaction between the UB and MM maintains expression of GDNF in the MM, thereby supporting further outgrowth and branching morphogenesis of the UB, while the MM also grows and aggregates around the branched tips of the UB. Ror2, a member of the Ror family of receptor tyrosine kinases, has been shown to act as a receptor for Wnt5a to mediate noncanonical Wnt signaling. We show that Ror2 is predominantly expressed in the MM during UB induction and that Ror2-and Wnt5a-deficient mice exhibit duplicated ureters and kidneys due to ectopic UB induction. During initial UB formation, these mutant embryos show dysregulated positioning of the MM, resulting in spatiotemporally aberrant interaction between the MM and WD, which provides the WD with inappropriate GDNF signaling. Furthermore, the numbers of proliferating cells in the mutant MM are markedly reduced compared to the wild-type MM. These results indicate an important role of Wnt5a-Ror2 signaling in morphogenesis of the MM to ensure proper epithelial tubular formation of the UB required for kidney development.

We have shown previously that transplanted bone marrow mononuclear cells (BM-MNC), which are a cell fraction rich in hematopoietic stem cells, can activate cerebral endothelial cells via gap junction-mediated cell-cell interaction. In the present study, we investigated such cell-cell interaction between mesenchymal stem cells (MSC) and cerebral endothelial cells. In contrast to BM-MNC, for MSC we observed suppression of vascular endothelial growth factor uptake into endothelial cells and transfer of glucose from endothelial cells to MSC in vitro. The transfer of such a small molecule from MSC to vascular endothelium was subsequently confirmed in vivo and was followed by suppressed activation of macrophage/microglia in stroke mice. The suppressive effect was absent by blockade of gap junction at MSC. Furthermore, gap junction-mediated cell-cell interaction was observed between circulating white blood cells and MSC. Our findings indicate that gap junction-mediated cell-cell interaction is one of the major pathways for MSC-mediated suppression of inflammation in the brain following stroke and provides a novel strategy to maintain the blood-brain barrier in injured brain. Furthermore, our current results have the potential to provide a novel insight for other ongoing clinical trials that make use of MSC transplantation aiming to suppress excess inflammation, as well as other diseases such as COVID-19 (coronavirus disease 2019).

We recently reported that intravenous bone marrow mononuclear cell (BM-MNC) transplantation in stroke improves neurological function through improvement of cerebral metabolism. Cerebral metabolism is known to diminish with aging, and the reduction of metabolism is one of the presumed causes of neurological decline in the elderly. We report herein that transcription of glucose transporters, monocarboxylate transporters, and Na + /K +-ATPase is downregulated in the hippocampus of aged mice with impaired neurological functions. Intravenous BM-MNC transplantation in aged mice stimulated the transcription of glucose transporter 1 and Na + /K +-ATPase α1 followed by restoration of neurological function. As glucose transporters and Na + /K +-ATPases are closely related to cerebral metabolism and neurological function, our data indicate that BM-MNC transplantation in aged mice has the potential to restore neurological function by activating transcription of glucose transporter and Na + /K +-ATPase. Furthermore, our data indicate that changes in transcription of glucose transporter and Na + /K +-ATPase could be surrogate biomarkers for age-related neurological impairment as well as quantifying the efficacy of therapies.

Circulating white blood cells (WBC) contribute toward maintenance of cerebral metabolism and brain function. Recently, we showed that during aging, transcription of metabolism related genes, including energy source transports, in the brain significantly decreased at the hippocampus resulting in impaired neurological functions. In this article, we investigated the changes in RNA transcription of metabolism related genes (glucose transporter 1 [Glut1], Glut3, monocarboxylate transporter 4 [MCT4], hypoxia inducible factor 1-α [Hif1-α], prolyl hydroxylase 3 [PHD3] and pyruvate dehydrogenase kinase 1 [PDK1]) in circulating WBC and correlated these with brain function in mice. Contrary to our expectations, most of these metabolism related genes in circulating WBC significantly increased in aged mice, and correlation between their increased RNA transcription and impaired neurological functions was observed. Bone marrow mononuclear transplantation into aged mice decreased metabolism related genes in WBC with accelerated neurogenesis in the hippocampus. In vitro analysis revealed that cell-cell interaction between WBC and endothelial cells via gap junction is impaired with aging, and blockade of the interaction increased their transcription in WBC. Our findings indicate that gross analysis of RNA transcription of metabolism related genes in circulating WBC has the potential to provide significant information relating to impaired cell-cell interaction between WBC and endothelial cells of aged mice. Additionally, this can serve as a tool to evaluate the change of the cell-cell interaction caused by various treatments or diseases.