Tendon-derived stem cells (TDSCs): from basic science to potential roles in tendon pathology and tissue engineering applications.

Traditionally, tendons are considered to only contain tenocytes that are responsible for the maintenance, repair and remodeling of tendons. Stem cells, which are termed tendon-derived stem cells (TDSCs), have recently been identified in tendons. This review aims to summarize the current information about the in vitro characteristics of TDSCs, including issues related to TDSC isolation and culture, their cell morphology, immunophenotypes, proliferation and differentiation characteristics and senescence during in vitro passaging. The challenges in studying the functions of these cells are also discussed. The niche where TDSCs resided essentially provides signals that are conducive to the maintenance of definitive stem cell properties of TDSCs. Yet the niche may also induce pathologies by imposing an aberrant function on TDSCs or other targets. The possible niche factors of TDSCs are herein discussed. We presented current evidences supporting the potential pathogenic role of TDSCs in the development of tendinopathy with reference to the recent findings on the altered biological responses of these cells in response to their potential niche factors. The use of resident stem cells may promote engraftment and differentiation of transplanted cells in tendon and tendon-bone junction repair because the tendon milieu is an ideal and familiar environment to the transplanted cells. Evidences are presented to show the potential advantages and results of using TDSCs as a new cell source for tendon and tendon-bone junction repair. Issues pertaining to the use of TDSCs for tissue repair are also discussed.