Validation of a stem cell derived cartilage model for osteoarthritis research and drug screening

Osteoarthritis (OA) is a chronic, progressive joint disorder affecting 8.5 million people in the UK alone. Despite overwhelming need, little progress has been made towards understanding disease progression, to improve early diagnosis and disease treatments. Experimental studies have relied heavily on animal models, which are inefficient, often producing drugs failing in phase I/II clinical trials due to off-target side effects or failure to predict human disease. This project aims to address this challenge by developing a scalable in vitro human organotypic tissue model. Previous work has shown that a stratified 3D-tissue akin to articular cartilage can be generated from primary human chondrocyte progenitor cells over a 35-day long tissue engineering approach. This project focused on further optimisation of the 3D culture system, to explore its validity for OA research. Alternative cell lines at different stages of chondrogenic commitment were tested as cell source for the model, to avoid the need for less available primary cells. Cell commitment to chondrogenic lineage was found to be a pre-requisite for induction of appropriate appositional growth and stratification of cartilage. Fully differentiated chondrocytes failed to produce a zonated cartilage-like matrix, while mesenchymal stem cells (MSCs) and chondrocyte progenitor cells showed similar performance, with engineered tissue mimicking native cartilage, both in structural organisation and biochemical composition. MSCs were found to induce higher extents of tissue contraction, similar to the intrinsic mesenchymal condensation observed during cartilage development in vivo. hTERT immortalised chondroprogenitor clonal cell lines were generated and revealed the existence of variability in chondrogenic potential of chondrocyte progenitor cell populations when isolated from native cartilage. Identified changes might reveal a possible biomarker or (biomarker ‘fingerprint’) with strong discriminatory potential to identify chondrocyte progenitor cells with increased potential for chondrogenic differentiation and cartilage formation. The generation of cartilage tissue at scale in a highly controlled way was demonstrated, with possibility to consider developmental positional information or genetics within the model. Applicability to explore the 3D spatial organisation of ECM using SHG and Raman microscopy was proven. In homeostasis, the model was found to mimic native collagen fibre organisation and chemical composition changes associated with tissue zonation. This thesis therefore demonstrates the validity of the proposed model for cartilage research and as a platform to seek biomarkers for early OA diagnosis or screen potential drugs for treatment