The importance of mechanical loading in maintaining bone quality is well illustrated by the drastic effects of its absence in, for example, microgravity, cast immobilisation or paraplegia. The mechanisms underlying adaptation of bone to mechanical loading occur on the cellular level. However, it remains unclear how a mechanical stimulus is detected by an osteoblast or an osteocyte to subsequently influence the signalling pathways that would lead to important signalling responses such as nitric oxide (NO) or prostaglandin E₂ (PGE₂) release.

The aim of this thesis is to devise both computational and experimental methods that will yield new insights into the mechanisms of mechanotransduction in bone cells. It is hypothesised that mechanically-induced osteoblast and osteocyte NO and PGE₂ response is dependent on the physical consequences of a mechanical stimulus on the cellular level, and that this mechanotransduction mechanism is mediated by the cytoskeleton.

A computational cell model was developed to serve as a mechanobiological tool to both probe the structural characteristics of cells, and to investigate the physical effects of various magnitudes of fluid flow or strain stimuli on cells. Experimental methods were devised to determine the involvement of actin and microtubule components in mechanotransduction o f NO and PGE₂ in both monolayers of bone cells and in single cells.

By extending the results of the cell model to interpreting past in vitro experiments, it was concluded that NO and PGE₂ signalling response is dependent not only on the magnitude but also on the nature of cell deformation caused by the stimulus. Experimental results indicate that the cytoskeleton is involved in the mechanotransduction of NO and PGE₂, but differently in osteoblasts and osteocytes. The dynamics and locations of mechanically-induced synthesis and diffusion of NO response occurring in a single osteoblast when stimulated with an indenting force were also determined. Combining these results with what has been reported in literature suggests that mechanotransduction of NO occurs via actin filament regulation of eNOS localised to both caveolae and Golgi membranes. The actin cytoskeleton modulates the PGE₂ pathway in osteocytes via stretch-activated ion channels, whereas in osteoblast PGE₂ response focal adhesions may be the primary mechanosensors.

This information will strengthen the fundamental knowledge required for understanding bone diseases such as osteoporosis, for in vitro engineering of bone tissue and for the design of orthopaedic devices that maintain bone health in ‘disuse’ conditions such as microgravity.