Articular cartilage is an extraordinary tissue, allowing frictionless movements of articulated joints, and acting as a load-bearing cushion to protect joints from damage. Breakdown of articular cartilage may result in crippling diseases such as osteoarthritis (OA) and, since articular cartilage has a limited repair capacity, a greater understanding of the mechanisms of joint homeostasis and its response to injury are of great clinical need. In this project the hypothesis that endogenous mesenchymal stem cells (MSCs) may contribute to the healing process of a full-thickness articular cartilage defect was investigated by combining a mouse model of joint surface injury and repair with a nucleoside analogue labelling scheme in DBA/1 mice. Following injury, proliferative responses of nucleoside analogue-retaining cells were detected between 4 and 12 days post injury (dpi) in both the bone marrow and the synovial membrane of the knee joint. Phenotypic analysis of these label-retaining cells using immunofluorescence staining revealed an MSC-compatible phenotype (CD44+, CD105+, CD146+, PDGFRα+ and p75NGFR+), with differences observed between the two tissues in expression of CD105 and CD146. The response of the label-retaining cells to the injury was associated with early activation of Notch signalling (4 dpi), followed by BMP signalling at 8 dpi and TGF-β at 12 dpi. Conversely, canonical Wnt signalling, which was active in uninjured knee joints and in injured knee joints up to 8 dpi, was attenuated at 12 dpi. The contribution of nerve growth factor (NGF), known as a pain mediator in OA, to the repair process was then investigated in vitro. NGF was released by both cartilage explants and femoral head cultures following injury. Using a Transwell-based cell migration assay, NGF was revealed to have a chemotactic effect on human bone marrow derived MSCs, but not synovial membrane derived MSCs. High-density micromass cultures also revealed NGF had a potent stimulatory effect on the chondrogenic differentiation of mesenchymal cells. The data presented here demonstrate a contribution of endogenous MSCs to the repair of articular cartilage in vivo and suggest a possible new therapeutic strategy: stimulation of in vivo recruitment of MSCs by modulating signalling pathways activated during the healing process. Furthermore, a novel role for NGF as a factor involved in migration and the chondrogenic differentiation of MSCs is suggested.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:680963 |
| Date | January 2015 |
| Creators | Armiento, Angela Rita |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=228555 |
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