The role of Rab GTPases in osteoclasts

Bisphosphonates are the most widely prescribed anti-resorptive agents and work by preventing the post-translational modification (prenylation) of small GTPases in osteoclasts, subsequently leading to cell death by apoptosis. Phosphonocarboxylate analogues of bisphosphonates also have anti-resorptive activity and work by inhibiting the enzyme Rab GGTase, thereby preventing the prenylation of Rab GTPases specifically. Rab GTPases comprise a large family of related proteins that coordinate vesicular trafficking, which involves the processing, transportation and delivery of cellular cargo in a strict temporal and spatial manner. In osteoclasts, vesicular trafficking is vital for the formation of the ruffled border (the resorptive organelle of the cell), the delivery of lytic enzymes and acid into the resorption space, and the uptake and disposal of bone degradation products. However, the role that specific Rabs play in this functionally unique cell type remains poorly defined, and the Rab expression profile in osteoclasts is incomplete. The work presented here aimed to increase our understanding of the role that Rabs play in osteoclasts. Results indicate that the 70% reduction of Rab GGTase activity observed in gunmetal mice is detrimental to the activity of osteoclasts and osteoblasts in vitro, therefore highlighting the importance of Rabs for bone resorption and deposition. Furthermore, this study is the first to determine the Rab expression profile of human osteoclasts, following a proteomic approach, and describes the transfection methods devised to characterise these candidate Rabs in osteoclasts. Finally, this study details the characterisation of Rab18 in human osteoclasts, following its discovery during proteomic analysis.EThOS - Electronic Theses Online ServiceGBUnited Kingdo