Oral Presentation Annual Meetings of the Endocrine Society of Australia and Society for Reproductive Biology and Australia and New Zealand Bone and Mineral Society 2016

Real-time intravital longitudinal imaging of osteoclast formation, function and fate within the bone marrow microenvironment (#18)

Michelle M McDonald 1 2 , Danyal Butt 2 , Rachael L Terry 1 2 , Julian Quinn 1 2 , Jessica A Pettitt 2 , Paul Baldock 1 2 , Mike Rogers 1 2 , Robert Brink 1 2 , Tri Phan 1 2 , Peter Croucher 1 2
  1. St Vincents School Faculty of Medicine, UNSW, Sydney, NSW, Australia
  2. Garvan Institute of Medical Research, Darlinghurst, NSW, Australia

Alterations in osteoclast formation and function underlie multiple metabolic bone diseases. Furthermore, osteoclast activity has been implicated in the mobilisation of haematopoietic stem cells (HSC’s) and the activation of dormant metastatic tumour cells. The interactions which occur between osteoclasts and other cells within bone marrow have typically been examined in a static state using histological techniques. Although in vitro imaging has revealed the dynamic nature of osteoclast fusion, resorption and apoptosis in real time, it does not capture the complexities of the cellular interactions between osteoclasts and their local bone microenvironment. To directly document, for the first time, the complex cellular interactions between osteoclasts and neighbouring bone marrow cells in real time, we developed a novel in vivo method to image deep into the bone marrow cavity of long bones. Using intravital two-photon microscopy, combined with lineage reporters and fluorescent probes to capture cell activity, we have visualised, in real time, the behaviour of osteoclasts engaging in normal bone remodelling. We have demonstrated intricate networks of connecting cellular processes between osteoclasts, suggesting direct cell communication. We have also visualised interactions between osteoclasts and other cell lineages within bone. Following injection of recombinant RANKL, we documented alterations in osteoclast morphology and captured cell fusion events in vivo. Interestingly, we have visualised a novel mechanism of osteoclast fate, suggesting an alternative to apoptosis. Our novel intravital imaging technique reveals previously unappreciated dynamics in osteoclast biology, providing new insight into the intercellular interactions within bone marrow, and highlights the potential for manipulating osteoclasts to alter cellular dynamics in normal bone remodelling, metabolic bone disease and skeletal metastases.