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Use of Mesenchymal Stem Cells in Bone Repair
Equine bone fractures are often catastrophic, potentially fatal, and costly to repair. Traditional methods of healing fractures have limited success, long recovery periods, and a high rate of re-injury. Current research in the equine industry has demonstrated that stem cell therapy is a promising novel therapy to improve fracture healing and reduce the incidence of re-injury; however reports of success in horses have been variable and limited. Stem cells can be derived from embryonic, fetal and adult tissue. However, based on the ease of collection, opportunity for autologous cells, and proven success in other models, adipose or bone marrow derived mesenchymal stem cells (MSC) are often used in equine therapies. Methods for isolation, proliferation, and differentiation of MSC are well established in rodent and human models but are not well characterized in horses. There is recent evidence that equine bone marrow MSC are able to proliferate in culture for several passages in the presence of autologous and fetal bovine serum which is important for expansion of cells. Mesenchymal stem cells are able to differentiate into osteoblasts, the bone forming cells, and this complex process is regulated by a number of transcription factors including, runt-related transcription factor 2 (Runx2) and osterix (Osx). However, it has not been well established if equine MSC are regulated in a similar manner. In the presence of L-ascorbic acid-2-phosphate, glycerol-2-phosphate, and dexamethasone, equine bone marrow MSC are able to differentiate into osteoblasts in culture as demonstrated by increased alkaline phosphatase activity and mineralization (P < 0.05). In addition, similar to rodent and human models, in equine bone marrow MSC, Runx2 expression increased 3-fold (P < 0.001) during early differentiation and Osx expression increased 9-fold (P < 0.05) during late differentiation. Further, expression of a novel transcription factor, T-box3, which is required for proliferation of mouse osteoblast cells and inhibits differentiation of osteoblasts, was reduced 4-fold (P< 0.01) during differentiation of equine bone marrow MSC. These data demonstrate that equine bone marrow MSC may be regulated similar to rodent and human cells during osteoblast differentiation. Stem cell therapy is promising in equine bone repair, however additional research is need to identify optimal methods for reintroduction and potential manipulations to improve their ability to form new bone.
Keywords: bone, equine, mesenchymal stem cells