Trpv4 Regulates Topography-Mediated Bone Formation Via Macrophage-Osteoclast Axis

Osteoinductive biomaterial hold great potentials in repairing segmental jaw bone defects. However, the mechanism behind remains unknown. This study investigated the molecular mechanism by which surface topography differences between osteoinductive TCP-S and non-osteoinductive TCP-B regulate osteoclast formation and bone regeneration through mechanically-sensitive cation channel TRPV4. Using wo tricalcium phosphate (TCP) ceramics (osteoinductive TCP-S and non-osteoinductive TCP-B) fabricated with identical chemistry and microporosity but different surface topography (TCP-S with sub-micro topography while TCP-B with micro topography), we performed in vitro material-cell coculture and in vivo intramuscular implantation model. Calcium flux was measured using Fluo-4 AM, while immunofluorescence and TRAP staining were employed to analyze cytoskeletal differences, macrophage polarization, and osteoclastogenesis. Compared to non-osteoinductive TCP-B, macrophages cultured on osteoinductive TCP-S showed elongated morphology, increased TRPV4 expression, significantly higher intracellular calcium level, greater M2 macrophage and osteoclast formation. Moreover, the in vivo and in vitro results demonstrated activation of TRPV4 promoted M2 macrophage and osteoclast formation whereas inhibition suppressed it. The surface topography of osteoinductive TCP-S activated mechanically-sensitive cation channel TRPV4 through cytoskeletal tension, inducing calcium influx that driven M2 polarization, osteoclast formation and bone formation. The current study revealed the mechanism of osteoinductive biomaterial-induced bone formation from the innovative perspective of mechanotransduction, and provided the theoretical basis for optimizing the design of bioactive biomaterials.