Plenary Poster 30th Australian and New Zealand Bone and Mineral Society Annual Scientific Meeting 2020

Neutrophils are dispensable for neurogenic heterotopic ossification development following spinal cord injury (#24)

Hsu-Wen HWT Tseng 1 , Irina IK Kulina 1 , Marjorie MS Salga 1 2 , Whitney WF Fleming 1 , Cedryck CV Vaquette 3 4 , François FG Genêt 2 5 , Jean-Pierre JPL Levesque 1 , Kylie KA Alexander 1
  1. Mater Research Institute-The University of Queensland, Brisbane, Queensland, Australia
  2. Unité Péri Opératoire du Handicap (UPOH), PMR department, Hôpital Raymond-Poincaré, Assistance Publique – Hôpitaux de Paris (AP-HP), Raymond Poincaré Hospital, APHP, CIC 1429, Garches, France
  3. Regenerative Medicine, Institute of Health and Biomedical Innovation, Queensland University of Technology, Brisbane, Queensland, Australia
  4. The University of Queensland, School of Dentistry, Herston, Brisbane, Queensland, Australia
  5. INSERM UMRS-MD 1197, Université de Paris-Saclay, Université de Paris-Saclay, Palaiseau, France

Neurogenic heterotopic ossifications (NHO) are a frequent complications after spinal cord injuries (SCI), which manifest as abnormal ossification in soft tissues. NHO leads to pain, joint deformation, ankylosis and vascular and nerve compression that largely compromises life quality of patients. NHO pathogenesis is poorly understood and the only treatment remains surgical resection. Our team developed the first mouse model of NHO following SCI, which mimics most clinical features of NHO to investigate the pathogenesis. Using this model, we have demonstrated that 1) monocytes/macrophages are necessary for NHO development, 2) SCI exacerbates macrophage infiltration into injured muscles and 3) that oncostatin M (OSM), a pro-inflammatory cytokine produced by macrophages, is an important driver of NHO formation in both mouse model and patients. Indeed, inhibition of OSM downstream signalling with the JAK1/2 inhibitor ruxolitinib significantly attenuated NHO development in mice. We have now investigated the potential role of neutrophils, another major source of OSM in injured muscles. We find that granulocyte stimulating factor (G-CSF) is significantly upregulated by either SCI or muscle injury. However, mice defective for the G-CSF receptor gene Csf3r, which are neutropenic, have unaltered NHO development following SCI. As the administration of recombinant human G-CSF (rhG-CSF) has been trialed after SCI to increase neuroprotection and neuronal regeneration, we then investigated the impact of rhG-CSF treatment after SCI and muscle injury, on NHO development. Treatment with rhG-CSF significantly increased neutrophils in the blood, bone marrow and injured muscles however micro-computed tomography confirmed no change in NHO bone volumes compared to saline treated controls after 7 days of treatment post-surgery. Overall, our results establish that unlike macrophages, neutrophils are dispensable for NHO development and rhG-CSF treatment post-injuries does not impact NHO development. Therefore, G-CSF treatment to promote neuro-regeneration is unlikely to adversely promote NHO development in SCI patients.