Different effects of Wnt/β-catenin activation and parathyroid hormone on diaphyseal and metaphyseal in the early phase of femur bone healing of mice

Wnt/β-catenin signalling promotes more effective fracture healing in aged mice than in adult mice by inducing angiogenesis and cell differentiation

To investigate whether activating the Wnt/β-catenin signalling pathway differentially promotes fracture healing in aged and adult individuals. CatnbTM2Kem, Catnblox(ex3) and wild-type adult and aged mice were used in this study. The femur was electroporated through a hole with a diameter of 0.6 mm. On the 7th, 14th and 21st days after fracture establishment, repair of the femoral diaphyseal bone was examined using X-ray and CT, the levels of mRNAs related to Wnt/β-catenin signalling were detected using real-time polymerase chain reaction (RT-PCR), and angiogenesis and cell differentiation were observed using immunohistochemistry. The numbers of osteoclasts were determined by TRAP staining. Wnt/β-catenin activation accelerated fracture healing in adult mice, with more pronounced effects on aged mice. Compared with wild-type mice at the corresponding ages, Wnt/β-catenin signalling activation induced higher levels of angiogenesis and cell differentiation in aged mice than in adult mice and promoted fracture healing. The administration of medications targeting Wnt/β-catenin signalling to aged patients may accelerate fracture healing to a greater extent.

Unleashing β-catenin with a new anti-Alzheimer drug for bone tissue regeneration

The Wnt/β-catenin signaling pathway is critical for bone differentiation and regeneration. Tideglusib, a selective FDA approved glycogen synthase kinase-3β (GSK-3β) inhibitor, has been shown to promote dentine formation, but its effect on bone has not been examined. Our objective was to study the effect of localized Tideglusib administration on bone repair. Bone healing between Tideglusib treated and control mice was analysed at 7, 14 and 28 days postoperative (PO) with microCT, dynamic histomorphometry and immunohistology. There was a local downregulation of GSK-3β in Tideglusib animals, resulting in a significant increase in the amount of new bone formation with both enhanced cortical bone bridging and medullary bone deposition. The bone formation in the Tideglusib group was characterized by early osteoblast differentiation with down-regulation of GSK-3β at day 7 and 14, and higher accumulation of active β-catenin at day 14. Here, for the first time, we show a positive effect of Tideglusib on bone formation through the inactivation of GSK-3β. Furthermore, the findings suggest that Tideglusib does not interfere with precursor cell recruitment and commitment, contrary to other GSK-3β antagonists such as lithium chloride. Taken together, the results indicate that Tideglusib could be used directly at a fracture site during the initial intraoperative internal fixation without the need for further surgery, injection or drug delivery system. This FDA-approved drug may be useful in the future for the prevention of non-union in patients presenting with a high risk for fracture-healing.

A novel mouse model to study fracture healing of the proximal femur

The majority of fractures, especially in elderly and osteoporotic patients, occurs in metaphyseal bone. However, only a few experimental models exist to study metaphyseal bone healing in mice. Currently used mouse models of metaphyseal fracture healing are either based on drill hole defects, lacking adequate biomechanical stimulation at the site of fracture and therefore endochondral ossification in the fracture callus, or are introduced into the distal part of the mouse femur stabilized by a locking plate, which is challenging due to the small specimen size. Therefore, the aim of the current study was to develop a new mouse model to study metaphyseal fracture healing of the proximal femur. We chose a combination between an open osteotomy and a closed intramedullary stabilization. A 24 G needle was inserted into the femur in a closed manner, then an osteotomy was made with a 0.4-mm Gigli wire saw between the third and the lesser trochanter of the femur using an open approach. Fractured femurs were analyzed using microcomputed tomography and histology at days 14 and 21 after surgery. No animals were lost due to surgery or anesthesia. All animals displayed normal limb loading and a physiological gait pattern within the first three days after fracture. We found robust endochondral ossification during the fracture healing process with high expression of late chondrocyte and early osteogenic markers at day 14 (d14). By day 21 (d21), all fractures had a bony bridging score of 3 or more, indicating successful healing. Callus volume significantly decreased from d14 to d21, whereas high numbers of osteoclasts appeared at the fracture callus until d21, indicating that callus remodeling had already started at d21. In conclusion, we successfully developed a novel mouse model to study endochondral fracture healing of the proximal femur. This model might be useful for future studies using transgenic animals to unravel molecular mechanisms of osteoporotic metaphyseal fracture healing.

Wnt modulation in bone healing

Genetic studies have been instrumental in the field of orthopaedics for finding tools to improve the standard management of fractures and delayed unions. The Wnt signaling pathway that is crucial for development and maintenance of many organs also has a very promising pathway for enhancement of bone regeneration. The Wnt pathway has been shown to have a direct effect on stem cells during bone regeneration, making Wnt a potential target to stimulate bone repair after trauma. A more complete view of how Wnt influences animal bone regeneration has slowly come to light. This review article provides an overview of studies done investigating the modulation of the canonical Wnt pathway in animal bone regeneration models. This not only includes a summary of the recent work done elucidating the roles of Wnt and β-catenin in fracture healing, but also the results of thirty transgenic studies, and thirty-eight pharmacological studies. Finally, we discuss the discontinuation of sclerostin clinical trials, ongoing clinical trials with lithium, the results of Dkk antibody clinical trials, the shift into combination therapies and the future opportunities to enhance bone repair and regeneration through the modulation of the Wnt signaling pathway.

Different effects of Wnt/β-catenin activation and parathyroid hormone on diaphyseal and metaphyseal in the early phase of femur bone healing of mice

Parathyroid hormone (PTH) and agents related to the manipulation of Wnt/β-catenin signalling are two promising anabolic anti-osteoporotic therapies that have been shown to promote the healing of bone fractures. Now, it is widely accepted that cortical bone and trabecular bone are two different compartments, and should be treated as separate compartments in pathological processes, such as fracture healing. It is currently unknown whether PTH and the activation of β-catenin signalling would demonstrate different effects on cortical bone and trabecular bone healing. In the current study, single 0.6-mm cortex holes were made in the femur metaphysis and diaphysis of mice, and then, PTH application and β-catenin activation were used to observe the promoting effect on bone healing. The effects of β-catenin and PTH signalling on fracture healing were observed by X-ray and CT at 3, 6, and 14 days after fracture, and the levels of β-catenin were detected by RT-PCR assay, and the number of specific antigen-positive cells of BRDU, OCN, RUNX2 was counted by immunohistochemical staining. While β-catenin activation and PTH were found to demonstrate similar effects on accelerating metaphyseal bone healing, activation of β-catenin showed a more striking effect than PTH on promoting diaphyseal bone healing. These findings might be helpful for selecting proper medication to accelerate fracture healing of different bone compartments.