Abstract
Administration of sclerostin-neutralizing antibody (Scl-Ab) treatment has been shown to elicit an anabolic bone response in growing and adult mice. Prior work characterized the response of individual mouse strains but did not establish whether the impact of Scl-Ab on whole bone strength would vary across different inbred mouse strains. Herein, we tested the hypothesis that two inbred mouse strains (A/J and C57BL/6J (B6)) will show different whole bone strength outcomes following sclerostin-neutralizing antibody (Scl-Ab) treatment during growth (4.5–8.5 weeks of age). Treated B6 femurs showed a significantly greater stiffness (S) (68.8% vs. 46.0%) and maximum load (ML) (84.7% vs. 44.8%) compared to A/J. Although treated A/J and B6 femurs showed greater cortical area (Ct.Ar) similarly relative to their controls (37.7% in A/J and 41.1% in B6), the location of new bone deposition responsible for the greater mass differed between strains and may explain the greater whole bone strength observed in treated B6 mice. A/J femurs showed periosteal expansion and endocortical infilling, while B6 femurs showed periosteal expansion. Post-yield displacement (PYD) was smaller in treated A/J femurs (-61.2%, p < 0.001) resulting in greater brittleness compared to controls; an effect not present in B6 mice. Inter-strain differences in S, ML, and PYD led to divergent changes in work-to-fracture (Work). Work was 27.2% (p = 0.366) lower in treated A/J mice and 66.2% (p < 0.001) greater in treated B6 mice relative to controls. Our data confirmed the anabolic response to Scl-Ab shown by others, and provided evidence suggesting the mechanical benefits of Scl-Ab administration may be modulated by genetic background, with intrinsic growth patterns of these mice guiding the location of new bone deposition. Whether these differential outcomes will persist in adult and elderly mice remains to be determined.
Highlights
The protein sclerostin, which is a negative regulator of bone formation, inhibits osteoblast differentiation by preventing the binding of Wnt ligand to the LRP5/6 receptor [1,2,3,4]
Our results supported the hypothesis that treatment with sclerostin-neutralizing antibody (Scl-Ab) is associated with a significantly greater whole bone stiffness and strength for the wide bones of B6 mice compared to the narrow bones of A/J mice
The greater strength benefit of Scl-Ab treatment was reflected in Work to failure for only the B6 femurs
Summary
The protein sclerostin, which is a negative regulator of bone formation, inhibits osteoblast differentiation by preventing the binding of Wnt ligand to the LRP5/6 receptor [1,2,3,4]. We tested the hypothesis that whole bone strength following administration of Scl-Ab would differ between inbred mouse strains that differ in the external size of their femoral diaphysis and vertebral body We tested this hypothesis by evaluating the effects of a 4-week treatment of sclerostin-neutralizing antibody on the whole bone strength of long bones and vertebrae of A/J and C57BL/6J (B6) mice. The emergent outcome of this coordination is that A/J and B6 long bones show different growth patterns yet achieve similar whole bone mechanical strength at musculoskeletal maturity [14] Given these differences in external bone size, we tested the hypothesis that the wider B6 long bones would be associated with a greater whole bone strength following administration of Scl-Ab compared to that of the narrow A/J long bones
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