The development of culture conditions to promote the differentiation of hyaline chondrocytes from mesenchymal stem cells

Osteoarthritis (OA) is a degenerative joint disease caused by loss of hyaline articular cartilage. Given the spread of OA in elderly patients and the desirability of avoiding extensive surgery, there is strong interest in developing minimally-invasive cell-based therapies to replace damaged articular cartilage. It is well-recognised that bone marrow-derived mesenchymal stem cells (MSC) can readily differentiate to chondrocytes in vitro, and are thus a promising source for OA cell therapy. However, there are two major challenges facing MSC-based therapies: firstly, it is difficult to direct MSC to differentiate to hyaline cartilage, and secondly, future therapies would require the development of a biocompatible material scaffold capable of maintaining the phenotype of MSC-derived chondrocytes following transplantation. Differentiation of hyaline chondrocytes: MSC chondrogenesis in vitro is poorly controllable, with the resulting chondrocytes resembling the transient hypertrophic chondrocytes that serve as a template for bone formation, rather than the permanent hyaline chondrocytes required for the normal functioning of joints. The laboratory of the lead academic supervisor (PM) has recently shown that novel biomimetic material substrates containing specific fibronectin-based motifs can induce the differentiation of bone marrow-derived MSC to nascent chondrocytes, without the need for additional growth factors (see above, PM research experience). The chondrocytes that form under these conditions express markers of early differentiating chondrocytes, such as N-cadherin, Sox9 and collagen II, which are expressed in the progenitors of both hypertrophic and hyaline chondrocytes. Recently, much progress has been made towards elucidating the mechanisms that regulate the differentiation of these two chondrocytic cell types in vivo. Interestingly, the formation of hyaline cartilage is not only dependent on factors with chondrogenic activity, such as the TGF-b family member, Gdf5, but is also dependent on the activity of anti-chondrogenic factors, such as Wnt9a. Biomaterials for chondrocyte transplantation: Although some progress has been made towards the development of biomaterial scaffolds for transplantation of primary hyaline chondrocytes, a major problem is that over time, the transplanted chondrocytes fail to maintain their phenotype and tend to form fibrocartilage. A likely reason for this is that following transplantation, the chondrocytes are no longer exposed to the culture medium components that help maintain their phenotype in vitro. Various approaches have been taken to improve the performance of biomaterial scaffolds, many of which involve incorporating signalling molecules or peptidic motifs into the scaffold matrix. However, it has proved difficult to achieve the correct density of ligands/motifs needed to elicit the required cellular response. The group of the academic co-supervisor (OM) has developed a novel self-assembling protein co-polymer (termed ZT) with proven bottom-up functionalization capabilities that holds high promise to overcome many of these problems (see above, OM research experience). Project Aims: [1] To establish culture conditions capable of directing the differentiation of nascent chondrocytes derived from MSC to hyaline, rather than hypertrophic cartilage. [2] To test if the growth factors identified in 1 can be replaced by small molecular weight mimetics or peptidic motifs. [3] To fabricate molecularly engineered variants of the ZT biomaterial scaffold to incorporate the key motifs/peptide motifs identified in 2. [4] To determine if the molecularly engineered biomaterials fabricated in 3 are able to maintain the phenotype of MSC-derived hyaline chondrocytes in vitro. [5] To implement a commercialisation strategy for culture conditions, media compositions and engineered biomaterials derived from this work that are capable of maintaining the phenotype of hyaline chondrocytes.