Interleukin-1 Is Overexpressed in Injured Muscles Following Spinal Cord Injury and Promotes Neurogenic Heterotopic Ossification

Neurogenic heterotopic ossifications (NHOs) form in periarticular muscles after severe spinal cord (SCI) and traumatic brain injuries. The pathogenesis of NHO is poorly understood with no effective preventive treatment. The only curative treatment remains surgical resection of pathological NHOs. In a mouse model of SCI-induced NHO that involves a transection of the spinal cord combined with a muscle injury, a differential gene expression analysis revealed that genes involved in inflammation such as interleukin-1 beta (IL-1 beta) were overexpressed in muscles developing NHO. Using mice knocked-out for the gene encoding IL-1 receptor (IL1R1) and neutralizing antibodies for IL-1 alpha and IL-1 beta, we show that IL-1 signaling contributes to NHO development after SCI in mice. Interestingly, other proteins involved in inflammation that were also overexpressed in muscles developing NHO, such as colony-stimulating factor-1, tumor necrosis factor, or C-C chemokine ligand-2, did not promote NHO development. Finally, using NHO biopsies from SCI and TBI patients, we show that IL-1 beta is expressed by CD68(+) macrophages. IL-1 alpha and IL-1 beta produced by activated human monocytes promote calcium mineralization and RUNX2 expression in fibro-adipogenic progenitors isolated from muscles surrounding NHOs. Altogether, these data suggest that interleukin-1 promotes NHO development in both humans and mice. (c) 2021 American Society for Bone and Mineral Research (ASBMR).

Automated summary

Neurogenic heterotopic ossifications (NHO) occur in periarticular muscles following severe spinal cord and traumatic brain injuries, with the pathogenesis poorly understood. Research suggests that IL-1 signaling contributes to NHO development after SCI in mice, while other inflammation-related proteins were not found to promote NHO development. Biopsies from NHO patients indicate that IL-1 beta is expressed by macrophages, and IL-1 promotes NHO development by enhancing calcium mineralization and RUNX2 expression in fibro-adipogenic progenitors.