Lithium Enhances Osteogenic Responses to Fluid Shear Stress

Bone is a dynamic tissue that is continuously remodelling itself in response to the mechanical loading that it is placed under. The cells within the bone sense the mechanical loads and respond in an appropriate manner. This can be through increasing bone resorption or increasing bone deposition in response to decreased or increased loading respectively. Cells themselves have a number of mechanisms thought to be involved in sensing mechanical loads and transforming them into biochemical signals in a process known as mechanotransduction. One such mechanism thought to be involved is the primary cilium. The primary cilium is a hair-like organelle that protrudes from the surface of the majority of cells during interphase. It is theorised that the bending of this organelle in response to fluid shear stress (FSS) results in the activation of downstream signalling pathways. Primary cilia have been shown to regulate their mechanosensitivity through altering their length, becoming shorter and less sensitive in response to continuous loads. Lithium chloride has been shown to elongate primary cilia and could therefore have the potential to increase osteogenic responses to FSS. The aim of this thesis was to examine the effect of lithium chloride on mechanoinduced osteogenesis. An in vitro FSS stimulus was optimised to stimulate osteogenic responses in hES-MP and MLO-A5 cells. The effects of LiCl on primary cilia length and osteogenesis was than evaluated at a range of concentrations and durations. Continuous 1 mM LiCl was found to increase osteogenesis in both cell lines. Intermittent treatment with 1 mM LiCl was found to increase cilia length without affecting cilia prevalence or osteogenesis. Cells treated with LiCl were then stimulated, where they showed increased osteogenic responses to FSS in both monolayer culture and 3D culture. LiCl was also found to decrease cAMP but increase Ca2+ responses to FSS. These results demonstrate that LiCl increases mechanically induced osteogenic responses in vitro.