Enhanced Activation of Canonical Wnt Signaling Confers Mesoderm-Derived Parietal Bone with Similar Osteogenic and Skeletal Healing Capacity to Neural Crest-Derived Frontal Bone

Bone formation and skeletal repair are dynamic processes involving a fine-tuned balance between osteoblast proliferation and differentiation orchestrated by multiple signaling pathways. Canonical Wnt (cWnt) signaling is known to playing a key role in these processes. In the current study, using a transgenic mouse model with targeted disruption of axin2, a negative regulator of cWnt signaling, we investigated the impact of enhanced activation of cWnt signaling on the osteogenic capacity and skeletal repair. Specifically, we looked at two calvarial bones of different embryonic tissue origin: the neural crest-derived frontal bone and the mesoderm-derived parietal bone, and we investigated the proliferation and apoptotic activity of frontal and parietal bones and derived osteoblasts. We found dramatic differences in cell proliferation and apoptotic activity between Axin2-/- and wild type calvarial bones, with Axin2-/- showing increased proliferative activity and reduced levels of apoptosis. Furthermore, we compared osteoblast differentiation and bone regeneration in Axin2-/- and wild type neural crest-derived frontal and mesoderm-derived parietal bones, respectively. Our results demonstrate a significant increase either in osteoblast differentiation or bone regeneration in Axin2-/- mice as compared to wild type, with Axin2-/- parietal bone and derived osteoblasts displaying a "neural crest-derived frontal bone-like" profile, which is typically characterized by higher osteogenic capacity and skeletal repair than parietal bone. Taken together, our results strongly suggest that enhanced activation of cWnt signaling increases the skeletal potential of a calvarial bone of mesoderm origin, such as the parietial bone to a degree similar to that of a neural crest origin bone, like the frontal bone. Thus, providing further evidence for the central role played by the cWnt signaling in osteogenesis and skeletal-bone regeneration.