Akkermansia muciniphila promotes type H vessels formation and bone fracture healing by reducing gut permeability and inflammation

Improving revascularization is one of the major measures in fracture treatment. Moderate local inflammation triggers angiogenesis, whereas systemic inflammation hampers angiogenesis. Previous studies showed that Akkermansia muciniphila (A. muc), a gut probiotic, ameliorates systemic inflammation by tightening intestinal barrier. In this study, fractured mice intragastrically administrated with A. muc were found to display better fracture healing than mice treated with vehicle. Notably, more preosteclasts positive for platelet-derived growth factor-BB (PDGF-BB) were induced by A. muc at 2 weeks post fracture, coinciding with increased formation of type H vessels, a specific vessel subtype that couples angiogenesis and osteogenesis and can be stimulated by PDGF-BB. Moreover, A. muc treatment significantly reduced gut permeability and inflammation at early stage. Dextran Sulfate Sodium (DSS) was used to disrupt the gut barrier to determine the role of gut barrier in fracture healing and whether A. muc still can stimulate bone fracture healing. As expected, A. muc evidently improved gut barrier, reduced inflammation, and restored the impaired bone healing and angiogenesis in DSS-treated mice. Our results suggest that A. muc reduces intestinal permeability and alleviates inflammation, which probably induces more PDGF-BB positive preosteoclasts and type H vessel formation in callus, thereby promoting fracture healing. This study provides the evidences about the involvement of type H vessels in fracture healing and suggests the potential of A. muc as a promising strategy for bone healing.