Cuts, bruises, lacerations, abrasions, of the skin are some of the most common injuries. Deeper wounds that extend into the dermis are more susceptible to chronic inflammation and suffer greatly if they are bumped, knocked, or run into. Such wounds are also more difficult to heal, since a full-thickness cutaneous wound usually damages many different structures and cell lineages. Fortunately, the healing of these structures begins directly after production of the wound. Regeneration is largely orchestrated by growth factors such as Vascular Endothelial Growth Factor and Transforming Growth Factor-β. Since mesenchymal stem cells (MSCs) are a good source of these growth factors, they might be promising candidates for treating full-thickness wounds.
Yan Jin and his colleagues at the Research and Development Center for Tissue Engineering in Shaanxi, China have tested the ability of bone marrow-derived mesenchymal stem cells (BMMSCs) to accelerate the healing of deep skin wounds.
Jin and his colleagues, Yulin An, Wei Wei, Huan Jing, Leigo Ming, and Shiyu Lui used bone marrow from mice that had been genetically engineered to express Green Fluorescent Protein (GFP) in their bone marrow. After isolating mesenchymal stem cells from the bone marrow of these mice, they applied the cells to rats that had suffered full-layer skin cutaneous wounds. However, they tested several different ways of applying these cells to the wound.
In one group of rats, GFP+BMMSCs were grown in cell culture that used a growth medium that contained a steroid drug called dexamethasone and ascorbic acid phosphate. These chemicals caused the BMMSCs to grow in the form of clusters of cells called “cell aggregates” that could be scraped off mechanically and readily transplanted onto the wounds without the need for any scaffold. These cell aggregates grow as sheets of cells that can act as a kind of patch made from healing MSCs that can be easily and readily applied to a wound or other lesion. In a second group of rats, the same number of GFP+BMMSCs was topically administered around the wound. In the third group of rats, the BMMSCs were given intravenously through tail vein. All three groups of rats received the same number of BMMSCs. Samples from the bed of the wounds were taken at different time points, and the morphological, histological and molecular characteristics of the wounds were analyzed and compared.
According to the results, the BMMSCs administered in cell-aggregates produced the highest expression of pro-healing genes than the other methods. Also animals treated with the BMMSC cell aggregates also showed better vascularization and more regular dermal collagen deposition than the other two groups of rats.
Detection of inflammatory cells as ascertained by immunofluorescence staining of inflammatory cells also revealed that the duration of inflammation in the cell-aggregate-treated group was significantly shorter than the other two groups. These results were corroborated by RT-PCR experiments that measured the expression of pro-inflammatory genes in the wound tissue.
In situ immunofluorescence staining also demonstrated higher rates of GFP+-cell engraftment in the rats treated with BMMSC cell-aggregates than the other groups.
These data show that not only are BMMSC cell aggregates safe, but they might also stimulate greater cutaneous regeneration for full layer cutaneous wounds than BMMSCs administered by other means. These successful studies will hopefully be followed by large animal studies to confirm the expandability and efficacy of this technology in larger animals.