Differentiation of CD45−/CD31+ lung side population cells into endothelial and smooth muscle cells in vitro

摘要

Side population (SP) cells are a small subpopulation of cells found in many mammalian tissues and organs, identified by their capacity to efflux Hoechst 33342 dye. They are enriched for stem/progenitor cell activity. SP cells isolated from the adult mouse lung can be separated into a CD45⁺ subset (bone marrow-derived) and a CD45⁻ subset that can be subdivided into CD31⁻ and CD31⁺ subpopulations. CD45⁻/CD31⁻ lung SP (LSP) cells are known to be mesenchymal stem cells. However, CD45⁻/CD31⁺ LSP cells are not fully characterized. In the present study, it was found that CD45⁻/CD31⁺ LSP cells were able to form colonies. Based on the expression of vascular endothelial growth factor receptor 2 (VEGFR2), these cells were separated into VEGFR2⁻ and VEGFR2⁺ cells. The CD45⁻/CD31⁺/VEGFR2⁻ LSP cells expressed genes characteristic of smooth muscle and endothelial progenitors, and were able to differentiate into smooth muscle and endothelial cells in vitro. The CD45⁻/CD31⁺/VEGFR2⁺ LSP cells expressed genes characteristic of endothelial progenitors and gave rise to endothelial cells, although not smooth muscle, in vitro. The data demonstrate that CD45⁻/CD31⁺/VEGFR2⁻ LSP cells differentiated into CD45⁻/CD31⁺/VEGFR2⁺ LSP cells and then endothelial cells, indicating that CD45⁻/CD31⁺/VEGFR2⁺ LSP cells are likely to be derived from CD45⁻/CD31⁺/VEGFR2⁻ LSP cells. Taken together, the results suggest that CD45⁻/CD31⁺ LSP cells can be separated into CD45⁻/CD31⁺/VEGFR2⁻ LSP cells, which may be progenitors of endothelial and smooth muscle, whereas CD45⁻/CD31⁺/VEGFR2⁺ LSP cells may serve as late commitment endothelial progenitors in the adult mouse lung.