Articular cartilage is a connective tissue with a very limited self-repair capacity and -once degraded- it is extremely susceptible to structural damage, making it difficult to restore. Osteoarthritis is the most common form of chronic arthritis, may involve different joints and is characterised by a progressive cartilage degradation which is difficult to reverse. Its clinical management is initially based on conservative therapies, the efficacy of which is a matter of debate. Novel strategies with promising results -as Extracorporeal Shock Wave Therapy (ESWT), Hyaluronic Acid (HA) and Platelets-Rich Plasma (PRP)- were proposed for such musculoskeletal disorders. Nevertheless, the scientific rationale for those treatments remains partially uncertain. A possible involvement of several microenvironmental mediators -such as growth factors and cytokines- able to affect the cartilage-specific cells, called chondrocytes, has been suggested. Considering our previous experience in establishing an in vitro model of human tendon derived cells, we propose here to set up primary cultures of human chondrocytes derived from cartilage explants. The biological properties of the cells -subjected to ESWT, HA and/or PRP stimulations- will be then evaluated at a phenotypical and molecular level, in order to investigate the possible mechanisms responsible for the clinical benefits encountered after those treatments. Our preliminary data seem to suggest that the association of HA and PRP treatments induces a significant increase in the proliferation index of primary cultured human chondrocytes derived from femoral head articular cartilage. The analysis of different mediators produced in the supernatants of culture will be crucial to provide an efficient strategy for maintaining chondrocyte integrity and eventually regenerating the degraded cartilage.
Osteoarthritis is traditionally classified into different stages of the disease. During the acute inflammation, anabolic molecules, including some Growth Factors and Cytokines (e.g. TGF-ß ligand signalling pathway), should protect cartilage against progressive loss, actively stimulating chondrocyte-mediated cartilage repair. In fact, in this stage, mechanical stimulation of articular cartilage may be more efficient in inducing chondrocyte synthetic activity. On the contrary, advanced osteoarthritis is characterised by a chronic inflammation that -through a panel of catabolic mediators (e.g. Inflammatory Cytokines and Proteases)- participate in progressive cartilage matrix degradation and unable to reverse cartilage damage (Brittberg NEnglJMed 1994; Zhang BoneRes 2016; Duan AmJTranslRes 2015). Therefore, chondrocytes are directly involved in the production of cartilage ECM, but -similarly to other cell cultures (e.g. tenocytic lineage)- their expansion in vitro is unluckily associated to a natural tendency to dedifferentiate toward a fibroblast-like phenotype, which is unsuitable for cartilage production. Also for this reason, previous attempts to maintain the chondrocyte phenotype, to develop an optimal approach for autologous cell implantation in patients affected by severe osteoarthritis, have been only partially successful (Zhang, BoneRes 2016; Cook, AmJSport Med 2016). To date, several types of research did not definitively clarify the complex molecular mechanisms underlying chondrocyte differentiation, even though it is well accepted that it is influenced by a large panel of microenvironmental mediators.
The innovative goal of this project is to provide novel strategies to better investigate the chondrocyte differentiation under mechanical and/or biological stimuli, in order to explain the clinical benefits induced by those therapies.
In particular, this work may contribute to the ambitious aim to optimise the cell culture conditions, finalised to autologous chondrocyte implantation in patients affected by advanced osteoarthritis, with very limited repair capabilities. In fact, novel approaches are diffusely required to counteract the previously described chondrocyte¿ dedifferentiation for ameliorating the efficiency of cell-based cartilage therapy. Emerging data seem to suggest a central role of several mediators of cartilage damage and repair, which can drive chondrocyte differentiation and then significantly influence the mechanisms of cartilage remodelling. In particular, during OA, quiescent chondrocytes with limited matrix turnover undergo phenotypic modulation by both inflammatory and anabolic cytokines (Goldring EurCellMater 2011).
Nevertheless, a better knowledge of the biological mechanisms triggered by ESWT, HA and/or PRP approaches may implement their use -particularly but not exclusively- in the early stages of OA. Exploring the molecular mechanisms underlying ESWT and PRP may contribute to elucidate which cocktail mediators may be administered in vivo to regenerate the degraded cartilage. Finally, as we recently published (Leone, Oncotarget 2015), human stem cell are now considered a promising tool for the management of several musculoskeletal disorders, albeit the modalities of their effective contribution to tissue regeneration in vivo are still unclear. Considering the complexity of the intracellular signalling pathways involved in cell differentiation, our work could allow new information for using satisfactory autologous stem cell therapies, especially in OA patient refractory to other treatments.