Identity of tendon stem cells – how much do we know?

Pauline Po Yee Lui

doi:10.1111/jcmm.12007

Abstract

Tendon stem cells are multi-potent adult stem cells with broad differentiation plasticity that render them of great importance in cell-based therapies for the repair of tendons. We called them tendon-derived stem cells (TDSCs) to indicate the tissue origin from which the stem cells were isolated in vitro. Based on the work of other sources of MSCs and specific work on TDSCs, some properties of TDSCs have been characterized / implicated in vitro. Despite these findings, tendon stem cells remained controversial cells. This was because MSCs residing in different organs, although very similar, were not identical cells. There is evidence of differences in stem cell-related properties and functions related to tissue origins. Similar to other stem cells, tendon stem cells were identified and characterized in vitro. Their in vivo identities, niche (both anatomical locations and regulators) and roles in tendons were less understood. This review aims to summarize the current evidence of the possible anatomical locations and niche signals regulating the functions of tendon stem cells in vivo. The possible roles of tendon stem cells in tendon healing and non-healing are presented. Finally, the potential strategies for understanding the in vivo identity of tendon stem cells are discussed.

Highlights

Mesenchymal stem cells (MSCs) are multi-potent cells that have the capacity to develop into different mature mesenchymal cell types
Our results showed that more iododeoxyuridine (IdU) label-retaining cells (LRC) were observed in the peritenon compared with the tendon proper, and some, but not all, LRC, were observed at the perivascular regions in the peritenon in rat patellar tendons [41]
We found that LRC in tendons was a heterogeneous cell population as none of the individual MSC markers tested labelled all the LRC and there were non-LRC that were positive for MSC markers

Summary

Introduction

Mesenchymal stem cells (MSCs) are multi-potent cells that have the capacity to develop into different mature mesenchymal cell types. Better understanding of the interaction between tendon stem cells and tenocytes in vivo may provide information for maintaining the plasticity of TDSCs during in vitro culture and for developing new strategies for the promotion of tendon repair. Using a double nucleoside analogue cell-labelling system (IdU/CldU), Kurth et al [45] reported the identification of a population of quiescent, slowcycling, non-hematopoietic, non-endothelial, MSC-like stromal cells, present in both the lining layer and sublining tissue of synovium of knee joint in vivo This method is not specific for stem cells and might label cells that have stopped proliferating because of various reasons (e.g. differentiation) and might be subjected to false-positive errors.

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Conclusion