Embryonic stem (ES) cells have the inherent potential to replace or repair almost every tissue in the body. One key to this prowess is the ability to migrate, without which ES cells could not travel to the sites where they are needed. While their wanderlust may be good for health, it is problematic for researchers, who have difficulty tracking therapeutic stem cells after having implanted them into a damaged tissue or organ.
In this week's PNAS early online edition, researchers from Christian Buehrle's lab at the Max Planck Institute for Neurological Research, Cologne, Germany, describe a noninvasive method for monitoring transplanted stem cells in live rats. First author Mathias Hoehn and colleagues used a magnetic resonance imaging (MRI) technique to track stem cells implanted in the brain. The authors used cells that had been transfected with an MRI contrast agent consisting of tiny super-paramagnetic iron-oxide particles (see related news story), which allow the stem cells to be starkly visualized against the background of the host tissue.
This enhanced MRI allowed the researchers to follow the migratory patterns of cells that were transplanted into rats that had suffered stroke. ES cells that were placed into the side of the brain opposite the stroke damage were seen, after a few days, to migrate along the corpus callosum and to populate the hemisphere where the ischemia had occurred. Within two weeks, these cells spread into the lateral cortex of the damaged hemisphere while, by contrast, no migration of cells was apparent after implantation into healthy animals.
Not only does this work show that stem cells can be tracked in vivo, but as the authors point out, it also demonstrates that cerebral ischemia must trigger some signaling mechanism which, though intended for endogenous cells, can entice implanted stem cells into the damaged region.—Tom Fagan
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- Hoehn M, Küstermann E, Blunk J, Wiedermann D, Trapp T, Wecker S, Föcking M, Arnold H, Hescheler J, Fleischmann BK, Schwindt W, Bührle C. Monitoring of implanted stem cell migration in vivo: a highly resolved in vivo magnetic resonance imaging investigation of experimental stroke in rat. Proc Natl Acad Sci U S A. 2002 Dec 10;99(25):16267-72. PubMed.