Hedgehog signaling mediates woven bone formation and vascularization during stress XXXX healing.

@entity10196 @entity56950 @entity9248 @entity174 @entity9249 @entity34726 @entity72170 @entity30933 @entity60739 @entity13827 @entity16705 @entity2752 @entity22601 @entity35 @entity28254
UNASSIGNED: Hedgehog (Hh) signaling is critical in developmental osteogenesis, and recent studies suggest it may also play a role in regulating osteogenic gene expression in the post-natal setting. However, there is a void of studies directly assessing the effect of Hh inhibition on post-natal osteogenesis. This study utilized a cyclic loading-induced ulnar stress @entity174 model to evaluate the hypothesis that Hh signaling contributes to osteogenesis and angiogenesis during stress @entity174 healing. Immediately prior to loading, adult @entity35 were given @entity2752 ( @entity2752 - a selective Hh pathway inhibitor; 50mg/kg orally twice daily), or vehicle. Hh signaling was upregulated in response to stress @entity174 at 3days ( @entity56950 , @entity10196 expression), and was markedly inhibited by @entity2752 at 1day and 3days in the loaded and non-loaded ulnae. @entity2752 did not affect Hh ligand expression ( @entity13827 , Ihh, @entity72170 ) at 1day, but decreased @entity13827 expression by 37% at 3days. @entity2752 decreased woven bone volume (-37%) and mineral density (-17%) at 7days. Dynamic histomorphometry revealed that the 7day callus was composed predominantly of woven bone in both groups. The observed reduction in woven bone occurred concomitantly with decreased expression of @entity60739 and @entity28254 , but was not associated with differences in early cellular proliferation (as determined by callus PCNA staining at 3days), osteoblastic differentiation (Osx expression at 1day and 3days), chondrogenic gene expression ( @entity34726 , @entity30933 , and @entity22601 expression at 1day and 3days), or bone resorption metrics (callus TRAP staining at 3days, @entity9248 and @entity9249 expression at 1day and 3days). To evaluate angiogenesis, vWF immunohistochemistry showed that @entity2752 reduced @entity174 callus blood vessel density by 55% at 3days, which was associated with increased @entity16705 gene expression (+30%). Dynamic histomorphometric analysis demonstrated that @entity2752 also inhibited lamellar bone formation. Lamellar bone analysis of the loaded limb (directly adjacent to the woven bone callus) showed that @entity2752 significantly decreased mineral apposition rate (MAR) and bone formation rate (BFR/BS) (-17% and -20%, respectively). Lamellar BFR/BS in the non-loaded ulna was also significantly decreased (-37%), indicating that Hh signaling was required for normal bone modeling. In conclusion, Hh signaling plays an important role in post-natal osteogenesis in the setting of stress @entity174 healing, mediating its effects directly through regulation of bone formation and angiogenesis.
