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Title: Effects of mechanical simulation on the organisation and expression of cytoskeletal elements and extracellular matrix metabolism in bovine intervertebral disc cells
Author: Li, Siyuan
ISNI:       0000 0004 2748 0411
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2009
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Introduction: Disc degeneration is the primary cause of low hack pain. Due to the main function of the spine, mechanical stimuli play a pivotal role in the development of disc degeneration. Previous studies have shown that cytoskeletal elements are involved in the mechanotransduction pathways between the extracellular matrix (ECM) and cell nucleus. However, the precise mechanism of this mechano-induced signalling is not clear in the intervertebral disc (IVD). Therefore, the effects of tensile strain and compression on the organisation and expression of cytoskeletal elements in bovine disc cells and on ECM metabolism molecules were investigated using confocal microscopy, real-time PCR, Western blotting, gelatin zymography and reverse gelatin zymography. Results: (i) In situ: F-actin filaments were punctate and distributed beneath the cell membrane in both nucleuspulposus (NP) and outer annulus fibrosus (OAF). There was higher p-actin expression in the OAF than NP. p-tubulin filaments formed a meshwork distributed throughout the cytoplasm with more p-tubulin gene and protein expression in the NP. Vimentin filaments formed a meshwork distributed throughout the cytoplasm with lower vimentin protein content in the OAF. There was less vimentin protein, but an increase in partially degraded vimentin in OAF with maturity, (ii) Cyclic tensile strain (CTS): CTS promoted the reorganisation of F-actin and P-tubulin networks and increased both their mRNA and protein expression, whilst reducing vimentin levels. CTS differentially-regidated mRNA expression levels of MMPs and TIMPs suggesting accelerated ECM remodelling processes in IVD cells. OAF cells are more responsive to tensile strain than NP cells. Stretch-induced mechano-respouses in IVD cells are age and strain-dependent. Age delayed the cell's response to tensile force. Low (5%) and medium (10%) strains induced anabolic effects but high strain (15%) induced more catabolic responses. (Hi) Compressive loading: Compressive loading (10%, 1Hz) altered the architecture of F-actin, P-tubulin and vimentin filaments, along with an increase in P-tubulin mRNA and a decrease in vimentin and vinculin gene expression. Compressive loading increased transcription of matrix molecules and decreased mRNA levels of catabolic enzymes in I D cells, suggesting an overall anabolic effect of physiological compression on I T> cell metabolism. Ageing delayed or reversed these mechano-responses in mature IVD cells. Conclusion: Cytoskeletal elements including P-actin, P-tubulin and vimentin are involved in strain-induced and compression-induced mechanotransduction in IVD cells. NP and OAF cells respond differently to the type of mechanical stimulus applied. However physiological loads induce matrix synthesis in NP and OAF cells, whilst non-physiological strains promote a catabolic phenotype. Ageing can delay the cell's response to mechanical load which may induce "abnormal" ECM remodelling events, and increase the potential risk of a loss of tissue homeostasis and the likelihood of disc degeneration.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available