Inhibition of overactive TGF-β attenuates progression of heterotopic ossification in mice

Abstract

Acquired heterotopic ossification (HO) is a painful and debilitating disease characterized by extraskeletal bone formation after injury. The exact pathogenesis of HO remains unknown. Here we show that TGF-β initiates and promotes HO in mice. We find that calcified cartilage and newly formed bone resorb osteoclasts after onset of HO, which leads to high levels of active TGF-β that recruit mesenchymal stromal/progenitor cells (MSPCs) in the HO microenvironment. Transgenic expression of active TGF-β in tendon induces spontaneous HO, whereas systemic injection of a TGF-β neutralizing antibody attenuates ectopic bone formation in traumatic and BMP-induced mouse HO models, and in a fibrodysplasia ossificans progressive mouse model. Moreover, inducible knockout of the TGF-β type II receptor in MSPCs inhibits HO progression in HO mouse models. Our study points toward elevated levels of active TGF-β as inducers and promoters of ectopic bone formation, and suggest that TGF-β might be a therapeutic target in HO.

NF-κB/MAPK activation underlies ACVR1-mediated inflammation in human heterotopic ossification

“…In addition, VEGF is essential for bone vascularization, fracture repair, and chondro-and osteogenic precursor function. Finally, the increased production of TGF-β found in our study correlates with recent findings where TGF-β levels are elevated in human heterotopic ossification and can trigger heterotopic ossification (25). Further investigation of whether local tissue-resident macrophages are affected by the ACVR1 R206H mutation, and whether communication with other immune cell lineages occurs, remain important challenges to overcome.…”

“…We found a trend toward elevated levels of TGF-β1 in stimulated FOP macrophages, but it was not statistically significant, likely due to biological variability. These results suggest that M2 macrophages may contribute to the fibrosis (70, 71) seen in developing heterotopic ossification lesions (25). Phagocytic abilities of FOP macrophages showed no major differences from control macrophages (Supplemental Figure 6).…”

“…Mouse models of heterotopic ossification also show that macrophages and TGF-β are important regulators of heterotopic ossification (24,25). Trauma-induced heterotopic ossification from hind limb Achilles' tenotomy and dorsal burns in mice cause increased levels of TNF-α and IL-1β within 48 hours after injury, with persistent MCP1 and VEGF elevations detectable in saliva 1 week after injury (26).…”

“…Our supernatant analysis showed evidence of functional differences between FOP and control macrophages. Macrophages can produce TGF-β, a secreted protein implicated in fibrosis and heterotopic ossification (25,70). TGFB expression was significantly increased in FOP antiinflammatory M2 macrophages upon LPS stimulation ( Figure 8A).…”

“…MIP1-β, eotaxin, and GROα are upregulated during the acute phase of fracture healing (90). PDGFBB + cells and PDGFBB in serum are increased during heterotopic ossification progression (25). PDGFs, which can be produce by macrophages (91), are chemoattractant for osteoprogenitors (92) and may recruit mesenchymal cells and osteoprogenitors to form heterotopic ossification.…”