Mechanical loading is an important regulatory factor in bone homeostasis, and plays an essential role in maintaining the structure and mass of bone throughout a lifetime. Although the exact mechanism is unknown the data presented in this thesis supports the concept that substrate signals influence MSC growth and differentiation. A better understanding of the cellular and molecular responses of bone cells to mechanical stimuli is the key to further improvements to therapeutic approaches in orthopaedics, orthodontics, periodontics, bone repair, bone regeneration, implantology and tissue engineering. However, the mechanisms by which cells transduce mechanical signals are poorly understood. There has also been an increased awareness of the need for improvement and development of 3-D in vitro models of mechanotransduction to mimic the 3-D environment, as found in intact bone tissue and to validate 2-D in vitro results. The aims of the project were (i) to optimize a model system by which bone cells can survive in 3-D static culture and their responses to mechanical stimuli can be examined in vitro, (ii) to test the effects of intermittent mechanical compressive loading on cell growth, matrix maturation and mineralization by osteoblastic cells, (iii) to examine the role of the primary cilia, (iv) to assess the effect of dynamic compressive loading on human mesenchymal stem cells in the 3-D environment. The optimized model system has the potential to be used in in vitro studies of bone in 3-D environments including a better understanding of the mechanically controlled tissue differentiation process and matrix maturation in the engineered bone constructs. It has less complicated equipment and techniques compared to dynamic seeding and culture systems making it easy to use in the laboratory. In addition, cells are not pre stimulated by any mechanical stimuli during seeding and culture which enables the researcher to study selected mechanical stimuli and mechanotransduction in bone tissue constructs. The model can mimic the bone environment providing a better physiological model than cells cultured in 2-D monolayer. Using our 3-D system, several loading regimens were compared and it was shown that intermittent short periods of compressive loading can improve cell growth and/or matrix production by MLO-A5 osteoblastic cells during 3-D static culture. This VI suggests that the cells are responding to the mechanical compression stimulus either by directly sensing the substrate strain or the fluid shear stress induced by flow through the porous scaffold. We also demonstrated that our mechanical loading system has the potential to induce osteogenic differentiation and bone matrix production by human MSCs in the same way as treatment with dexamethasone. Although the exact mechanism is unknown the data presented supports the concept that the dynamic compressive loading influence MSC growth, differentiation and production. In further experiments, we used the optimized 3-D model system to study the effects of mechanical loading on primary cilia, which have recently been shown to be potential mechanosensors in bone. We demonstrated that mature cells lacking a cilium were less responsive, less able to upregulate matrix protein gene expression and did not increase matrix production in response to mechanical stimulation suggesting that the primary cilia are sensors for mechanical forces such as fluid flow and/or strain induced shear stress.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:512001 |
| Date | January 2010 |
| Creators | Sittichokechaiwut, Anuphan |
| Publisher | University of Sheffield |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://etheses.whiterose.ac.uk/14959/ |
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