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Title: Oxygen and pH-sensitivity of articular chondrocytes
Author: Collins, John
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2014
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Articular chondrocytes reside in a unique and challenging avascular environment in cartilage. During joint disease, O2 and pH levels are further reduced, and may be involved in chondrocyte dysfunction and cartilage matrix breakdown. How fluctuations in these environmental parameters affect factors such as redox balance and mitochondrial function in articular chondrocytes is largely unknown but may provide a link between the extracellular environment to cell signalling pathways that may alter cellular and hence cartilage integrity. Additionally, ROS-regulatory compounds may offer scope for therapeutic intervention in joint disease. In this project, the effects of different O2 levels (<1%, 2%, 5% or 21% O2), pH (pH 7.2 or pH 6.2) and exposure to the pro-inflammatory cytokine, interleukin-1β (10ng/ml) on cell viability and glycosaminoglycan (GAG) release, redox balance (ROS production, GSH:GSSG ratio, NO release, SOD expression) and mitochondrial function (mitochondrial membrane potential (ΔΨm)) in articular chondrocytes cultured in 3-D alginate beads were analysed. The ability of the ROS regulatory compounds N-acetylcysteine (NAC) (2mM) and resveratrol (10μM) to alter these variables was also assessed. This study demonstrates the distinct and interactive effect of O2 tension and pH to influence articular chondrocyte redox balance and mitochondrial function. Cellular ROS levels, ΔΨm and SOD expression all displayed O2 sensitivity, being reduced by hypoxia/anoxia. Articular chondrocytes also displayed pH sensitivity with acidosis modulating ROS levels, ΔΨm and GSH content. Combined conditions (hypoxia/anoxia and acidosis) accentuated responses and further compromised chondrocyte integrity (survival, GAG release, phenotype expression). Treatment with NAC and resveratrol altered these variables through distinct mechanisms and conferred protection against O2 and acid-mediated oxidative stress. Both NAC and resveratrol abolished anoxic-induced inhibition of SOD levels. NAC significantly abrogated anoxic and acidosis-induced GSH inhibition, whereas resveratrol modulated ROS levels and restored O2 and pH mediated mitochondrial depolarisation. This thesis details the powerful effect of the cellular environment to modulate chondrocyte function. Manipulation of this environment or targeting related molecular pathways may hold promise for alleviation of disease-associated oxidative stress and are discussed.
Supervisor: Milner, Peter; Clegg, P. D.; Moots, Robert Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QP Physiology