Methods for the reliable induction of heterotopic ossification in the conditional Alk2(Q207D) mouse

OBJECTIVE: Conditional ALK2(Q207D-floxed) (caALK2(fl)) mice have previously been used as a model of heterotopic ossification (HO). However, HO formation in this model can be highly variable, and it is unclear which methods reliably induce HO. Hence, these studies report validated methods for reproducibly inducing HO in caALK2(fl) mice. METHODS: Varying doses of Adex-cre and cardiotoxin (CTX) were injected into the calf muscles of 9, 14, or 28-day-old caALK2(fl/-) or caALK2(fl/fl) mice. HO was measured by planar radiography or microCT at 14-28 days post-injury. RESULTS: In 9-day-old caALK2(fl/-) or caALK2(fl/fl) mice, single injections of 10(9) PFU Adex-cre and 0.3 µg of CTX were sufficient to induce extensive HO within 14 days post-injury. In 28-day-old mice, the doses were increased to 5 x 10(9) PFU Adex-cre and 3.0 µg of CTX to achieve similar consistency, but at a slower rate versus younger mice. Using a crush injury, instead of CTX, also provided consistent induction of HO. Finally, the Type 1 BMPR inhibitor, DMH1, significantly reduced HO formation in 28-day-old caALK2(fl/fl) mice. CONCLUSIONS: These data illustrate multiple methods for reliable induction of localized HO in the caALK2(fl) mouse that can serve as a starting point for new laboratories utilizing this model.