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Establishing a Diaphyseal Femur Fracture Model in Mice
Published on: December 9, 2022
Does Sclerostin Depletion Stimulate Fracture Healing in a Mouse Model?
Mohammad M Alzahrani1,2,3,4, Frank Rauch5, Reggie C Hamdy5,6
1Shriners Hospital for Children, Montreal Children's Hospital, Montreal, QC, Canada. mohammad.alzahrani2@mail.mcgill.ca.
Background:
Sclerostin is a secreted glycoprotein that inhibits the intracellular Wnt signaling pathway, which, when inactivated, stimulates bone formation. This has been seen in fracture studies, which have shown larger and stronger calluses with accelerated fracture healing in sclerostin knockout and sclerostin antibody injection models. However, the effects of these two mechanisms have not been compared in the context of fracture healing.
Questions/Purposes:
We sought to determine the degree to which sclerostin inhibition (Scl-Ab injection) and complete sclerostin depletion inhibit fracture healing in a mouse model as evaluated by (1) morphometric trabecular bone measures at the fracture site, and (2) fracture site structural strength.
Methods:
Ten-week-old male sclerostin knockout (n = 20) and wild type (n = 40) mice underwent insertion of a tibial intramedullary pin after which a midshaft tibial osteotomy was performed. The mice were divided in three groups: sclerostin knockout (n = 20), wild type with sclerostin antibody injection (intravenous dose of 100 mg/kg weekly) (n = 20), and wild type with saline injection (n = 20). The mice for each group where subdivided and euthanized at 14, 21, 28, and 35 days after surgery, at which time the fractured tibias were assessed with microCT (to assess morphometric trabecular bone measures: bone volume to total volume (BV/TV), trabecular thickness, trabecular number, and structural model index at the fracture site. Biomechanical testing in the form of three-point bending also was done to assess fracture site structural strength. A difference greater than 3.7% in our primary outcome (BV/TV) would be required to detect a difference between groups with a power of 80%, as per our power analysis.
Results:
The wild type with sclerostin antibody and the sclerostin knockout groups showed increased trabecular BV/TV at the fracture site compared with the wild type group with saline at all times, however no difference was seen between the treatment groups with the numbers available, except at 28 days postoperatively when the sclerostin knockout group showed greater BV/TV than the wild type sclerostin antibody group (47.0 ± 3.5 vs 40.1 ± 2.1; p < 0.05). On biomechanical testing the wild type sclerostin antibody showed increased stiffness at Days 14 and 28 compared with the wild type with saline group (70.9 ± 6.4 vs 14.8 ± 8.1; p = 0.001), (106.8 ± 24.3 vs 74.9 ± 16.0; p = 0.004); respectively. However, with the numbers available, no differences were detected between the wild type with sclerostin antibody and the sclerostin knockout groups in terms of whole-bone structural strength.
Conclusions:
Sclerostin antibody injections showed promising results, which were not different with the numbers available, from results achieved with complete depletion of sclerostin, especially at earlier stages of the healing process, and therefore completed the healing process at an earlier time.
Clinical Relevance:
Sclerostin antibody injections appear to enhance fracture healing to a degree that is not different than complete sclerostin depletion, but larger animal studies are required to assess the accurate dosage and timing of administration in the fracture healing process to further evaluate its potential clinical utility to enhance fracture healing.
Insights
Sclerostin antibody injections and complete sclerostin depletion similarly enhance fracture healing in mice. This suggests antibody therapy may be a viable option for accelerating bone repair, though further studies are needed.
Area of Science:
- Orthopedics
- Regenerative Medicine
- Biochemistry
Background:
- Sclerostin inhibits the Wnt signaling pathway, crucial for bone formation.
- Inhibiting sclerostin or depleting it accelerates fracture healing in preclinical models.
- Direct comparison of sclerostin inhibition versus depletion in fracture healing is lacking.
Purpose of the Study:
- To compare the efficacy of sclerostin antibody (Scl-Ab) injection versus genetic depletion on fracture healing.
- To evaluate fracture healing using microCT for bone measures and biomechanical testing for structural strength.
Main Methods:
- Tibial osteotomy and intramedullary pinning in mice.
- Groups included sclerostin knockout, Scl-Ab treated wild-type, and saline-treated wild-type mice.
- MicroCT and three-point bending biomechanical tests were performed at multiple time points.
Main Results:
- Both Scl-Ab and knockout groups showed increased bone volume (BV/TV) compared to controls.
- Sclerostin knockout mice had higher BV/TV than Scl-Ab treated mice at 28 days.
- Scl-Ab treatment increased fracture stiffness at 14 and 28 days; no significant difference in overall strength between Scl-Ab and knockout groups.
Conclusions:
- Sclerostin antibody injections show comparable fracture healing enhancement to complete sclerostin depletion.
- Sclerostin inhibition may accelerate the early stages of fracture healing.
- Further research is needed to optimize Scl-Ab dosage and timing for clinical application.
