Role of myeloid cells in heterotopic ossification (HO) in a burn and incision-induced mouse model

Despite the high frequency of musculoskeletal extremity trauma, little is known about the dynamics of the initial inflammatory response that can result in pathologic healing. Here, we assess the circulatory monocyte/macrophage recruitment to sites of pathologic extremity wound healing as seen with heterotopic ossification (HO). Using single cell transcriptome analyses at key time points, we identify distinct monocyte/macrophage subpopulations that are recruited to the site of HO formation and contribute to ectopic bone development through varied transforming growth factor-1 (Tgfb1) expression. Monocyte/macrophage specific deletion of Tgfb1 leads to altered function of macrophages and reduced HO. We further identify CD47 as a novel target for Tgfb1 regulation on monocytes/macrophages as CD47 activation leads to decreased expression of Tgfb1 in macrophages and systemic treatment with CD47 activating peptide results in attenuation of canonical TGFB1 signaling and HO. These findings elucidate the critical role of monocytes/macrophage subpopulations in aberrant wound healing and provide a novel therapeutic avenue. We have used 10x Genomics to perform single cell sequencing on HO cells