Neurogenic Heterotopic Ossifications Develop Independently of Granulocyte Colony-Stimulating Factor and Neutrophils

Abstract

Neurogenic heterotopic ossifications (NHOs) are incapacitating heterotopic bones in periarticular muscles that frequently develop following traumatic brain or spinal cord injuries (SCI). Using our unique model of SCI-induced NHO, we have previously established that mononucleated phagocytes infiltrating injured muscles are required to trigger NHO via the persistent release of the proinflammatory cytokine oncostatin M (OSM). Because neutrophils are also a major source of OSM, we investigated whether neutrophils also play a role in NHO development after SCI. We now show that surgery transiently increased granulocyte colony-stimulating factor (G-CSF) levels in blood of operated mice, and that G-CSF receptor mRNA is expressed in the hamstrings of mice developing NHO. However, mice defective for the G-CSF receptor gene Csf3r, which are neutropenic, have unaltered NHO development after SCI compared to C57BL/6 control mice. Because the administration of recombinant human G-CSF (rhG-CSF) has been trialed after SCI to increase neuroprotection and neuronal regeneration and has been shown to suppress osteoblast function at the endosteum of skeletal bones in human and mice, we investigated the impact of a 7-day rhG-CSF treatment on NHO development. rhG-CSF treatment significantly increased neutrophils in the blood, bone marrow, and injured muscles. However, there was no change in NHO development compared to saline-treated controls. Overall, our results establish that unlike monocytes/macrophages, neutrophils are dispensable for NHO development following SCI, and rhG-CSF treatment post-SCI does not impact NHO development. Therefore, G-CSF treatment to promote neuroregeneration is unlikely to adversely promote or affect NHO development in SCI patients.

Mapping the immune microenvironment for mandibular alveolar bone homeostasis at single-cell resolution

“…Osm is a cytokine secreted by monocytes/macrophages, and has important regulatory role on bone homeostasis. [37][38][39][40] Osm receptor knockout mice exhibit decreased bone remodeling activity. 34 In a tibial defect model, Osm knockout led to a decrease in osteoblasts number and delayed bone healing.…”

Neurological heterotopic ossification: novel mechanisms, prognostic biomarkers and prophylactic therapies

“…A number of factors released by macrophages are also released by neutrophils, therefore to determine the role of neutrophils in SCI-induced NHO, Tseng et al recently examined NHO formation in neutropenic mice. 77 Neutrophil depletion had no effect on NHO volumes. 77 Nor did treatment with rhG-CSF which significantly increased the number of neutrophils in the blood, bone marrow and injured muscles.…”

“…77 Nor did treatment with rhG-CSF which significantly increased the number of neutrophils in the blood, bone marrow and injured muscles. 77 These findings suggest that macrophage related factors in combination with CNS injury drive NHO.…”

Current Understanding of Osteoimmunology in Certain Osteoimmune Diseases

“…indispensable for NHO development (Genêt et al, 2015;Tseng et al, 2020). While the investigation of the relationship between osteoimmunology and neurogenic regulation has not been thoroughly understood, it seems that few attention is paid to neurogenic bone abnormalities, which is worth further investigation and clarification in the future.…”