Regenerative biology of tendon: mechanisms for renewal and repair.

Understanding the molecular and cellular mechanisms underlying tissue turnover and repair are essential towards addressing pathologies in aging, injury and disease. Each tissue has distinct means of maintaining homeostasis and healing after injury. For some, resident stem cell populations mediate both of these processes. These stem cells, by definition, are self renewing and give rise to all the differentiated cells of that tissue. However, not all organs fit with this traditional stem cell model of regeneration, and some do not appear to harbor somatic stem or progenitor cells capable of multilineage in vivo reconstitution. Despite recent progress in tendon progenitor cell research, our current knowledge of the mechanisms regulating tendon cell homeostasis and injury response is limited. Understanding the role of resident tendon cell populations is of great importance for regenerative medicine based approaches to tendon injuries and disease. The goal of this review is to bring to light our current knowledge regarding tendon progenitor cells and their role in tissue maintenance and repair. We will focus on pressing questions in the field and the new tools, including model systems, available to address them.