| dc.description.abstract | Bone Research Society Abstracts Late Breaking Abstracts LB1 Multiple tissue targets revealed in a transgenic mouse model for inducible and specific osteocyte ablation A. Aljazzar1*, C. Scudamore2, M. Boyd1, A. Boyde3, C. Farquharson4, B. Javaheri1, M. Prideaux5 and A.A. Pitsillides1 1. Comparative Biomedical Science, Royal Veterinary Collge, London, UK 2. Mary Lyon Centre, MRC, Harwell, UK 3. Centre for Oral Growth & Development, Queen Mary’s School of Medicine & Dentistry, London E1 4NS, UK 4. Division of Developmental Biology, The Roslin Institute, R(D)SVS, University of Edinburgh, Edinburgh, UK 5. Discipline of Orthopaedics and Trauma, University of Adelaide, Adelaide, Australia Many approaches highlight a potential for osteocyte-mediated control of bone remodelling. Direct in vivo support for this pivotal role stems mostly from osteocyte-selective ablation achieved following diphtheria toxin (DT) injection in mice, harbouring a DMP1 promoter-regulated human diphtheria toxin receptor (hDTR) transgene. These DTR-DMP1 mice have been used to support multiple osteocyte roles: in mechanical unloading responses and in regulating primary lymphoid organs, fat metabolism, and hematopoietic stem cell mobilisation. To explore osteocyte roles fully, we sought to confirm the selectivity of DT effects and DMP1-driven hDTR expression in bone. A total of fifty-three 8–50 week-old WT and DTR-DMP1 mice were DT-injected (50 ng/g), calcein double-labelled, and sacrifi ced within 8 days. human diphtheria toxin receptor,, DMP1, and endogenous murine-DTR mRNA levels were assessed in multiple tissues by standard- and qRT–PCR. Tibia/femur were processed for histomorphometric analysis, and samples collected for histology and assessment of EF-2 activity (DTR activation target). Health status was evaluated daily for signs of modifi ed welfare. The hDTR (and DMP1) mRNA was detected in muscle, spleen, marrow, heart, liver, brain, lung, kidney, and bone in DTR-DMP1, but not WT mice, and levels correlated with histopathology (mDTR did not). Histopathological changes included liver vacuolation, acute kidney necrosis, and splenic/thymic atrophy in DTR-DMP1 only after DT treatment within 3 days. Marked DT-induced distension and congestion of bone marrow sinusoids was also evident in DTR-DMP1. Histomorphometry revealed significantly reduced bone formation rate on endosteal, not periosteal, surfaces in DTR-DMP1 mice (not WT) after DT treatment. This was not, however, linked with expected widespread osteocyte ablation (<20% in DTR-DMP1 mice 6 days after single DT (WT, <6%) and only 50% after fi ve daily DT doses). Although DT-treated WT showed little ill-health, surprisingly marked deterioration was observed (condition score, weight loss, low temperature, rough coat, staggered gait, and signs of pain) in all DTR-DMP1 mice after DT treatment. Our data question the utility of DTR-DMP1 mouse model for inducible and specifi c osteocyte ablation. We find hDTR expression in multiple tissues and ill-health in response to DT treatment, suggesting that conclusions regarding osteocyte function, based solely on this model, are premature. Conflict of Interest: None declared. page 126 ISBN: 978-2-88919-300-4 doi: 10.3389/978-2-88919-300-4 | en_US |
