E-Poster Presentation ESA-SRB-ANZBMS 2021

Lymphocytes are not required for the development of neurogenic heterotopic ossification after spinal cord injury (#46)

Kylie A Alexander 1 , Hsu-Wen Tseng 1 , Irina Kulina 1 , Whitney Fleming 1 , Cedryck Vaquette 2 , Francois Genet 3 4 , Marc Ruitenberg 5 , Jean-Pierre Levesque 1
  1. Mater Research, The University of Queensland, Brisbane, Queensland, Australia
  2. School of Dentrisy, The University of Queensland, Herston, Queensland, Australia
  3. Department of Physical Medicine and Rehabilitation, Raymond Poincaré Hospital, APHP, CIC 1429, Garches, France
  4. END:ICAP U1179 INSERM, UFR Simone Veil-Santé, University of Versailles Saint Quentin en Yvelines, Montigny le Bretonneux, France
  5. School of Biomedical Sciences, Faculty of Medicine, The University of Queensland, Saint Lucia, Queensland, Australia

Neurogenic heterotopic ossifications (NHO) are incapacitating complications of traumatic brain and spinal cord injuries (SCI) which manifest as abnormal heterotopic bones in periarticular muscles.  NHOs are debilitating, causing pain, joint ankylosis, as well as vascular and nerve compression. The mechanisms leading to NHO are unknown and the only effective treatment remains surgical resection. To elucidate NHO pathophysiology we developed the first model of NHO following SCI in genetically unmodified mice. Using this model, we established that the innate immune system plays multiple roles in NHO pathogenesis. We demonstrated that macrophage / monocyte release of oncostatin M and subsequent JAK/STAT3 signalling in injured muscles promoted NHO development and treatment with the JAK1/2 tyrosine kinase inhibitor ruxolitinib significantly attenuated NHO1,2,3. Both clinical and experimental studies have previously established that SCI results in depressed adaptive immune responses and reduced lymphocyte frequency, however, the contribution of adaptive immune cells to NHO pathogenesis remains largely unexplored. We established that T cell subsets are present in muscles after SCI (at T12-T13 vertebrae level), or muscle damage, but there was no significant changes in T cell frequency between surgical groups when compared to naïve mice. In contrast, B cells were significantly increased in muscles developing NHO. We also noted a reduction in B cell frequency in blood and splenic B cell frequency was reduced after SCI compared to muscle injury alone. Interestingly, mice that underwent splenectomy prior to SCI and muscle damage developed NHO volumes similar to Sham operated mice. Finally, to determine if adaptive immune cells play a direct role in NHO pathogenesis, Rag1-/- mice (defective for mature T and B lymphocytes), developed NHO with volumes similar to wild type mice. Overall, these findings suggest that functional T and B cells have minimal influence or at most make redundant contributions to NHO development following SCI.