Past Research Projects
The chondrocyte primary cilium – a purinergic mechanoreceptor?
Wellcome Trust Project Grant. Prof Martin Knight (PI), Dr Sue McGlashan, Prof Tony Poole and Prof Cynthia Jensen
The aim of this research project was to test the hypothesis that the primary cilium acts as a fundamental mechanoreceptor in articular chondrocytes triggering mechanosensitive intracellular calcium signalling via a purinergic pathway that involves the release of ATP. We aimed to elucidate the underlying physiological mechanisms involved in ATP release and how this pathway is modulated by loading conditions. We also aimed to investigate the effect of pathway activation on subsequent downstream anabolic and catabolic responses and the presence of signalling elements in diseased cartilage.
At the start of this grant the function of the primary cilium in articular chondrocytes was largely unknown, indeed some scientists were even sceptical of its existence. This study has shown, for the first, time that primary cilia are essential for chondrocyte mechanotransduction. We have elucidated the signalling pathway which involves release of ATP via connexin hemichannels and activation of purine receptors leading to intracellular calcium signalling. We have demonstrated that primary cilia are involved not in the initial mechanosensitive release of ATP but that they are necessary for the downstream signalling response. This represents a totally novel primary cilia mechanotransduction pathway different to that seen in other tissues.
The grant also paved the way for subsequent studies looking at the role of primary cilia in osteoarthritis and the potential therapeutic intervention using reagents that modulate primary cilia structure:function.
Changes in primary cilia length and function modulate the pathogenesis of osteoarthritis in response to lithium
AO Foundation Project Grant. Prof Martin Knight (PI), Prof Tony Poole
Osteoarthritis has recently been shown to involve aberrant up-regulation of hedgehog signaling leading to increased expression of ADAMTS5 resulting in degradation of the articular cartilage (Lin, Seeto et al. 2010). Hedgehog signaling requires the presence of a primary cilium. The widely used psychiatric drug, lithium, is known to cause cilia elongation in a wide variety of cell types although the functional consequences are unclear.
The aim of this study was to test the hypothesis that lithium treatment influences chondrocyte primary cilia structure and associated hedgehog signaling leading to alterations in ADAMTS5 expression and cartilage degradation. Studies examined the composition and structure of articular cartilage from the knee joints of rats given a lithium enriched diet at clinically relevant concentrations. We used confocal microscopy to examine changes in primary cilia structure and length both in vivo within the rat articular cartilage and using isolated chondrocytes in 2D culture. This allowed us to determine the precise dose response characteristics and the mechanism responsible for cilia elongation in chondrocytes. Quantitative PCR was used to measure lithium induced changes in hedgehog signaling and ADAMTS5 expression and to identify whether these are triggered by changes in cilia structure. Finally we used a cartilage explant model to investigate whether lithium causes cartilage degradation through changes in cilia structure.
These studies enable further understanding of the role of the primary cilium in osteoarthritis and the specific effects of lithium on articular cartilage. Such studies may lead to the development of novel strategies for the treatment of osteoarthritis through manipulation of primary cilia structure and function.
Past PhD Studentship Projects:
Interaction between primary cilia length and hedgehog signalling in response to mechanical and thermal stress.
BBSRC PhD Studentship (2010 - 2013) Clare Thompson. Supervisors: Prof Martin Knight and Prof Paul Chapple.
The effect of pharmaceutical modulation of hedgehog signalling on cartilage degradation
Intercallated BSc in Biomedical Engineering Research Project: Riana Patel. Supervisor: Prof Martin Knight
The hedgehog signalling pathway, first discovered in Drosophila, triggers an intracellular cascade resulting in gene transcription in response to the binding of one of its three ligands: Sonic hedgehog (Shh), Indian hedgehog (Ihh), and Desert hedgehog (Dhh). Many of the components of this pathway have been localized to the primary cilium, where their activation or inhibition is responsible for the degree of pathway activation. Recent studies have suggested that an upregulation of hedgehog signalling occurs in the early development of osteoarthritis (OA). This research project, linked to the above ARUK project grant, is focused on defining the interaction between hedgehog pathway components and OA. Specifically, we are using a cytokine-induced model of OA in order to examine how targeting certain components of the hedgehog pathway affects IL1B induced cartilage degradation. A better understanding of the role hedgehog signalling plays in OA may potentially provide us with exciting new therapeutic options.