Cells under pressure - the relationship between hydrostatic pressure and mesenchymal stem cell chondrogenesis.

Early osteoarthritis (OA), characterised by cartilage defects, is a degenerative disease that greatly affects the adult population. Cell-based tissue engineering methods are being explored as a solution for the treatment of these chondral defects. Chondrocytes are already in clinical use but other cell types with chondrogenic properties, such as mesenchymal stem cells (MSCs), are being researched. However, present methods for differentiating these cells into stable articular-cartilage chondrocytes that contribute to joint regeneration are not effective, despite extensive investigation. Environmental stimuli, such as mechanical forces, influence chondrogenic response and are beneficial with respect to matrix formation. In vivo, the cartilage is subjected to multiaxial loading involving compressive, tensile, shear and fluid flow and cellular response. Tissue formation mechanobiology is being intensively studied in the cartilage tissue-engineering research field. The study of the effects of hydrostatic pressure on cartilage formation belongs to the large area of mechanobiology. During cartilage loading, interstitial fluid is pressurised and the surrounding matrix delays pressure loss by reducing fluid flow rate from pressurised regions. This fluid pressurisation is known as hydrostatic pressure, where a uniform stress around the cell occurs without cellular deformation. In vitro studies, examining chondrocytes under hydrostatic pressure, have described its anabolic effect and similar studies have evaluated the effect of hydrostatic pressure on MSC chondrogenesis. The present review summarises the results of these studies and discusses the mechanisms through which hydrostatic pressure exerts its effects.

Bone block augmentation from the iliac crest for treatment of deep osteochondral defects of the knee resembles biomechanical properties of the subchondral bone.

PURPOSE: Bone block augmentation from the iliac crest can be used for reconstruction of the osteochondral unit to restore the underlying subchondral bone upon restoration of the cartilaginous layer via matrix-induced chondrocyte transplantation. To critically understand the successful restoration of the defect, biomechanical and histological analysis of the implanted bone blocks is required. The aim of the study was to analyse the ability of the bone block technique to restore huge bone defects by mimicking the physiological subchondral zone. METHODS: The experiments were performed using lateral femoral condyles and iliac crest bone grafts from the same cadavers (n = 6) preserved using the Thiel method. CT scans were made to evaluate bone pathology. Bone mineral density of all specimens was evaluated in the femoral head prior to testing. A series of tests were conducted for each pair of specimens. A static compression test was performed using an electro dynamic testing machine with maximal strength and failure behavior analyzed. Biomechanical tests were performed in the medial-lateral direction for iliac crest and for femoral condyles with and without removal of the cartilage layer. Histological analysis was performed on decalcified specimens for comparison of the condyle at lesion site and the graft. RESULTS: No significant difference in failure load could be found for iliac crest (53.3-180.5 N) and femoral condyle samples upon cartilage removal (38.5-175.1 N) (n.s.). The femoral condyles with an intact cartilage layer showed significantly higher loads (118.3-260.4N) compared to the other groups indicating that native or regenerated cartilage can further increase the failure load (p < 0.05). Bone mineral density significantly influenced failure load in all study groups (p < 0.05). Histological similarity of the cancellous bone in the femoral condyle and in the iliac crest was observed. However, within the subchondral zone, there was a higher density of sponge like organized trabeculae in the bone samples from the iliac crest. Tide mark was only detected at the osteochondral interface in femoral condyles. CONCLUSION: This study demonstrated that, bone blocks derived from the iliac crest allow a biomechanical appropriate and stable restoration of huge bony defects by resembling the subchondral zone of the femoral condyle. Therefore, bone augmentation from the iliac crest combined with matrix-induced autologous chondrocyte transplantation seems to be a reasonable method to treat these challenging injuries.

CCL5/RANTES is a key chemoattractant released by degenerative intervertebral discs in organ culture.

Release of chemotactic factors in response to tissue damage has been described for different musculoskeletal tissues, including the intervertebral disc (IVD). This study investigated the chemoattractants that are released by induced degenerative IVDs and may be involved in recruiting mesenchymal stem cells (MSCs). Bovine caudal discs were cultured within a bioreactor and loaded under conditions that mimicked physiological or degenerative settings. Between days 4-6, medium was replaced by PBS, which was subsequently used for proteomic, ELISA and immunoprecipitation analyses of secreted chemokines and cytokines. A Boyden chamber assay was used to observe human MSC migration towards native and chemokine depleted media. Gene expression levels of chemokine receptors in human MSCs were analysed, and CCL5 was localised in bovine and human IVD by immunohistochemistry. Proteomic analysis revealed the presence of CCL5 and CXCL6 within conditioned media. Higher concentrations of CCL5 were found in the degenerative media, and a relationship was found between interleukin-1ß and CCL5 concentration. Chemokine immunoprecipitation showed that MSCs had a significantly reduced chemotactic migration towards CCL5-immunoprecipitated and CCL5/CXCL6 co-immunoprecipitated media, whilst CXCL6 depletion did not change MSC chemotaxis. MSCs showed a significant increase in mRNA expression of the CCL5 receptors, CCR1 and CCR4, upon culture in degenerative media. Furthermore, CCL5 was identified in bovine and human disc tissue by immunohistochemistry. Hence, CCL5 may be a key chemoattractant that is produced and released by the intervertebral disc cells. Therefore, these factors could be used to enhance stem/progenitor cell mobilisation in regenerative therapies for early stages of disc degeneration.