Bone Abstracts

Objectives: Osteogenesis imperfecta (OI) displays a heterozygous phenotype even amongst similar genotypes. It has therefore been difficult to establish a mouse model which represents clinical OI in children. By engrafting human OI bone into mice we have developed a hybrid model enabling us to investigate the efficacy of new treatments for this phenotypically diverse condition.

Methods: Bone chips, that would otherwise be discarded, were collected from children with (3) and without (2) OI, undergoing orthopaedic surgery. 10 to 14 bone chips were collected from each participant, each measuring 5mm3. These were grafted subcutaneously onto immune deficient NOD SCID mice. Two bone chips were implanted into each mouse. After 4 weeks, the mice were sacrificed, and the bone chips removed. One bone chip was fixed and sectioned for histomorphology/immunohistochemistry. The other bone chip was homogenised and RNA extracted. Genetic expression of target pathways were investigated from bone pre and post xenograft to test for genetic stability of bone in the hybrid model.

Results: Human OI and control bone remained alive and metabolically active for the 4-week time period tested. Osteoclasts remained active, as defined by the uptake of TRAP staining and the surrounding lytic areas were visible on histological sections. Osteoblasts were identified on H&E stain. Good quality and quantity RNA was extracted- identified on nanodrop spectrophotometers, 260/280 ratio 1.93 and 260/230 ratio 1.93, count >350 ng/μL. We are currently using microfluidic cards to analyse expression of genes associated with the TGFB pathway in OI and control bone before and after xenotransplantation.

Conclusion: We have generated a human-mouse hybrid model of OI that contains metabolically active human bone, that remains architecturally identical to the original patient sample. The presence of the osteoclasts after 4 weeks suggests successful engraftment of haemopoietic precursors, as well as the presence of osteoblasts expressing RANK- ligand, a necessary factor for osteoclastogenesis. This model may provide a novel method of identifying changes to gene expression, bone microarchitecture and mechanical properties following therapeutic intervention across multiple different patients, allowing for review of heterogeneity to response.

Disclosure: Nick Bishop consults for Alexion, Mereo, UCB and Amgen, and receives grant support for clinical studies from Alexion and Amgen.