Identification Of Bone-chondro-stromal Progenitor Cell Populations Within Trauma-induced Heterotopic Ossification
Shawn Loder, BS, Shailesh Agarwal, MD, Joshua Peterson, BS, John Li, MD, David Cholok, BS, James Drake, BS, Christopher Breuler, BS, Stewart Wang, MD, PhD, Benjamin Levi, MD.
University of Michigan, Ann Arbor, MI, USA.
PURPOSE: Recently, Longaker et al have identified a bone-chondro-stromal progenitor (BCSP) cell in developing bone and fracture sites, which contribute to normal bone formation. Here we investigate whether pathologic extra-skeletal bone is composed of the cellular components of normal bone with attention to BCSPs.
METHODS: C57BL/6 mice underwent 30% TBSA partial-thickness burn with Achilles’ tenotomy. Mice were euthanized three weeks post-injury and tenotomy site harvested and digested for FACS to quantify BCSPs (AlphaV+/CD105+/Tie2-/CD45-/Thy1-/6C3-). Immunostaining was performed to localize BCSPs in trauma sites. Subsequently, BCSPs were isolated from neonatal mice with ubiquitous tdTomato expression using FACS, and transplanted into burn/tenotomy recipients at the tenotomy site to identify the phases of HO to which these cells contribute.
RESULTS: BCSPs were noted on flow cytometry in sites of developing HO (A,B). No enrichment of BCSPs was noted in the uninjured hindlimb after injury. Immunostaining confirmed the presence of BCSPs within developing HO at the tenotomy site (C). When transplanted into the burn/tenotomy site, these cells integrate into the cartilage and osseous phases of HO (D).
DISCUSSION: Our study confirms that a previously identified population of bone-chondro-stromal progenitors contribute to pathologic, ectopic bone. These findings suggest that HO exhibits qualities similar to normal, developing or healing bone. Studies are underway to determine whether the presence of these cells can serve as an early marker for HO formation.
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