A variety of experiments, clinical trials, and strategies have attempted to exploit stem cells as therapeutic agents in regenerative medicine. However, once stem cells are removed from their niches within the body and grown in artificial culture systems their properties can change. Such culture-acquired changes can often compromise the therapeutic potential of some stem cells. For this reason, the development of relatively simple but effective stem cell isolation and manipulation techniques represents someone of the prominent technical hurdles to the clinical use of stem cells.
Several laboratories have used exogenous factors to direct the differentiation of tissue-resident stem cells, but these exogenous factors can often cause unwanted side effects. For this reason, simpler manipulation techniques are always a welcome addition to the armamentarium of stem cell scientists.
To that end, Ashok B. Kulkarni from the National Institute of Dental and Craniofacial Research in Bethesda, MD and David J. Mooney from the Harvard School of Engineering and their colleagues and co-workers have used non-ionizing, low-power laser (LPL) treatments to activate host stem cells and promote tissue regeneration. This is a minimally invasive treatment that directs stem cells already present in tissues to heal damaged tissues.
LPL treatment was used to activate human dental stem cells in a laboratory culture system. Upon LPL treatment, the dental stem cells began to synthesize a powerful growth factor called transforming growth factor–β1 (TGF-β1). The endogenous synthesis of TGF-β1 and its receptor drove the dental stem cells to form dentin tubes.
When Kulkami and Mooney used an assay in animals called a “pulp capping model,” they discovered that LPL-activated dental stem cells were able to regenerate dentin after laser activation. To further demonstrate that these regenerative effects were the result of TGF-β1, Kalkami and Mooney and others made cells that did not have a functional TGF-β receptor II. This mutation completely abrogated the effects of LPL treatments. Also, if the dental stem cells were incubated with a TGF-βRI inhibitor, the effects of LPL on the dental stem cells was attenuated.
Thus, there is a simple and non-invasive way to activate a resident stem cell population in our bodies. Furthermore, the mechanisms by which LPL activates these stem cells has been defined as TGF-β mediated. These experiments also outlines the mechanism by which resident stem cells might be harnessed by means of light-activated endogenous cues for clinical regenerative applications. Exciting, huh?