Pro-osteogenic Effects of WNT in a Mouse Model of Bone Formation Around Femoral Implants.

Calcified tissue international (2020-09-30)
Zhijun Li, Xue Yuan, Masaki Arioka, Daniel Bahat, Qiang Sun, Jinlong Chen, Jill A Helms

Wnt signaling maintains homeostasis in the bone marrow cavity: if Wnt signaling is inhibited then bone volume and density would decline. In this study, we identified a population of Wnt-responsive cells as osteoprogenitor in the intact trabecular bone region, which were responsible for bone development and turnover. If an implant was placed into the long bone, this Wnt-responsive population and their progeny contributed to osseointegration. We employed Axin2CreCreERT2/+;R26mTmG/+ transgenic mouse strain in which Axin2-positive, Wnt-responsive cells, and their progeny are permanently labeled by GFP upon exposure to tamoxifen. Each mouse received femoral implants placed into a site prepared solely by drilling, and a single-dose liposomal WNT3A protein was used in the treatment group. A lineage tracing strategy design allowed us to identify cells actively expressing Axin2 in response to Wnt signaling pathway. These tools demonstrated that Wnt-responsive cells and their progeny comprise a quiescent population residing in the trabecular region. In response to an implant placed, this population becomes mitotically active: cells migrated into the peri-implant region, up-regulated the expression of osteogenic proteins. Ultimately, those cells gave rise to osteoblasts that produced significantly more new bone in the peri-implant region. Wnt-responsive cells directly contributed to implant osseointegration. Using a liposomal WNT3A protein therapeutic, we showed that a single application at the time of implant placed was sufficient to accelerate osseointegration. The Wnt-responsive cell population in trabecular bone, activated by injury, ultimately contributes to implant osseointegration. Liposomal WNT3A protein therapeutic accelerates implant osseointegration in the long bone.

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Hydrochloric acid, ACS reagent, 37%
Iron(III) chloride, reagent grade, 97%
Phosphotungstic acid hydrate, reagent grade
Alcian Blue 8GX, powder
Acid Fuchsin, used in tissue staining
Ser-Phe-Leu-Leu-Arg-Asn-Pro-Asn-Asp-Lys-Tyr-Glu-Pro-Phe, ≥97% (HPLC)