X-irradiated umbilical cord blood cells retain their regenerative effect in experimental stroke.

Although regenerative therapy with stem cells is believed to be affected by their proliferation and differentiation potential, there is insufficient evidence regarding the molecular and cellular mechanisms underlying this regenerative effect. We recently found that gap junction-mediated cell-cell transfer of small metabolites occurred very rapidly after stem cell treatment in a mouse model of experimental stroke. This study aimed to investigate whether the tissue repair ability of umbilical cord blood cells is affected by X-irradiation at 15 Gy or more, which suppresses their proliferative ability. In this study, X-irradiated mononuclear (XR) cells were prepared from umbilical cord blood. Even though hematopoietic stem/progenitor cell activity was diminished in the XR cells, the regenerative activity was surprisingly conserved and promoted recovery from experimental stroke in mice. Thus, our study provides evidence regarding the possible therapeutic mechanism by which damaged cerebrovascular endothelial cells or perivascular astrocytes may be rescued by low-molecular-weight metabolites supplied by injected XR cells in 10 min as energy sources, resulting in improved blood flow and neurogenesis in the infarction area. Thus, XR cells may exert their tissue repair capabilities by triggering neo-neuro-angiogenesis, rather than via cell-autonomous effects.