Chemokines in mesenchymal stem cell therapy for bone repair: a novel concept of recruiting mesenchymal stem cells and the possible cell sources

Skeletal injury is one of the most prevalent clinical problems that jeopardize the activities of daily life, especially in our aging society. Mesenchymal stem cells (MSCs) play pivotal roles in regenerating bones after bone injury. MSCs come from the surrounding tissues and/or circulation. Cell sources may be the bone marrow, periosteum, vessel walls, muscle, circulation, and elsewhere, and the migration of MSCs is necessary for bone healing. The mechanism(s) of recruitment and crucial molecules for cell migration are still unclear, but chemokines and their receptors seem to play critical roles. The induction of MSC recruitment from surrounding tissues or from the circulation can be a helpful modality to induce or to support cell-based therapy for bone regeneration.