Differentiation of Adult Stem Cells towards Microglial Cells

Introduction: During aging, the role of microglia in the brain changes from 'friend to foe' - in young organisms microglia are actively participating in the clearing of protein debris from the brain. Microglia are replenished by adult stem cells (ASC) that migrate into the brain and by proliferation of local cells. In aged and old organisms however, microglial replenishment is impaired. The brain is burdened with 'old' microglia that remain in chronic activation and thus cause inflammation and damage in the brain. We therefore wanted to study to in vitro differentiation of adult stem cells from the bone marrow towards microglial cells. Methods: Adult stem cells were in vitro differentiated using media, including astrocyte conditioned medium, Flt3, TGF-b, FGF and other substances. Cells were then tested for their surface antigen profile using flow cytometry (CD11b, F4/80, CD45, CD45/ B220). Phagocytotic activity and oxidative burst were tested using phorbol ester phorbol 12-myristate 13-acetate (1 mu M PMA) activation. Incorporation, survival and migration of the in vitro derived microglia-like cells was tested in organotypic brain slices. Conclusion: We found changes in the expression profile of the cells, showing increased expression of macrophage/microglial marker and haematopoietic markers, including CD45, F4/80 and CD45/B220. In vitro differentiated microglia-like cells show phagocytotic activity and oxidative burst after stimulation with PMA. Invasion into the brain slice was observed starting at around day 3 and showed only very few apoptotic cells.