Macrophage TGF-beta signaling is critical for wound healing with heterotopic ossification after trauma

Transforming growth factor-beta 1 (TGF-beta 1) plays a central role in normal and aberrant wound healing, but the precise mechanism in the local environment remains elusive. Here, using a mouse model of aberrant wound healing resulting in heterotopic ossification (HO) after traumatic injury, we find autocrine TGF-beta 1 signaling in macrophages, and not mesenchymal stem/progenitor cells, is critical in HO formation. In-depth single-cell transcriptomic and epigenomic analyses in combination with immunostaining of cells from the injury site demonstrated increased TGF-beta 1 signaling in early infiltrating macrophages, with open chromatin regions in TGF-beta 1-stimulated genes at binding sites specific for transcription factors of activated TGF-beta 1 (SMAD2/3). Genetic deletion of TGF-beta 1 receptor type 1 (Tgfbr1; Alk5), in macrophages, resulted in increased HO, with a trend toward decreased tendinous HO. To bypass the effect seen by altering the receptor, we administered a systemic treatment with TGF-beta 1/3 ligand trap TGF-beta RII-Fc, which resulted in decreased HO formation and a delay in macrophage infiltration to the injury site. Overall, our data support the role of the TGF-beta 1/ ALK5 signaling pathway in HO.