Abstract
Introduction
Tendon is prone to degeneration through ageing and injury and current therapies are largely ineffective. The recent identification of a cell population within tendon with stem cell-like characteristics holds potential for regeneration of tendon. The local stem cell environment (niche) is important for stem cell maintenance and function. This study aims to characterize extracellular matrix (ECM) components of the stem cell niche in equine tendon, which is prone to age-related degeneration and rupture.
Materials and Methods
Putative tendon stem cells (TSCs) were isolated from equine superficial digital flexor tendon by low-density plating and differential adhesion to fibronectin. Cells were analysed by flow cytometry using antibodies to mesenchymal stem cell markers, as well as qRT-PCR for stem cell and tenogenic markers. The multipotency of cells was assessed using tri-lineage differentiation assays. ECM components of the tenocyte and TSC niche were analysed using radio-isotope labelling, immunohistochemistry and histology.
Results
Putative TSCs were able to form colonies, and both tenocytes and TSCs expressed CD90, CD105 and CD73 as determined by flow cytometry. However, TSCs did not exhibit increased expression of stem cell marker genes when compared with tenocytes. TSCs and tenocytes both displayed osteogenic and chondrogenic differentiation, however not adipogenic differentiation. Tenocytes and TSCs labelled with 14C-labelled amino acids both displayed similar labelling profiles. Histological analysis of tendon tissue highlighted the varied structure and composition of tendon, with tenascin C expression confined to the interfascicular matrix.
Discussion
TSCs do not highly express stem cell markers when compared with tenocytes, indicating that these cells may not be true stem cells. In addition the similar labelling profiles of the two cell types indicates that a stem cell population has not been differentially isolated, however the tri-lineage differentiation assays suggest the cells may possess some stem cell-like properties. It is possible that the equine tendon cell population consists of a heterogeneous mixture of cells at different stages of differentiation.
