Transforming growth factor beta3 promotes tendon differentiation of equine embryo-derived stem cells.

Tendon injuries occur frequently in horses and have a poor capacity to regenerate, which leads to high re-injury rates. Equine embryo-derived stem cells (ESCs) survive in high numbers in the injured horse tendon and we hypothesized that they differentiate into tenocytes in vivo. Immunocytochemistry revealed that in the injured horse tendon ESCs express the tendon progenitor marker scleraxis and that there is a local upregulation of the transforming growth factor-β (TGF-β) at the injury site. The aim of this study was to determine if TGF-β signaling was able to drive tenocyte differentiation by ESCs. Exposure of differentiating ESCs to TGF-β in vitro produced an upregulation of scleraxis at the gene and protein level with the greatest effect being produced in the presence of TGF-β3. TGF-β3 treatment of differentiating ESCs also promotes a significant upregulation of other tendon-associated genes and proteins suggesting it can promote ESC differentiation into tenocytes. Our results demonstrate that equine ESCs can differentiate into a therapeutically relevant cell type and that TGF-β driven differentiation of ESCs may provide a model to study tendon development and better understand the transcriptional networks that are involved in equine tendon cell differentiation from the early embryonic stages.