Unexpected timely fracture union in matrix metalloproteinase 9 deficient mice.

Yuasa M, Saito M, Molina C, Moore-Lotridge SN, Benvenuti MA, Mignemi NA, Okawa A, Yoshii T, Schwartz HS, Nyman JS, Schoenecker JG
PLoS One. 2018 13 (5): e0198088

PMID: 29851987 · PMCID: PMC5978876 · DOI:10.1371/journal.pone.0198088

Immediately following a fracture, a fibrin laden hematoma is formed to prevent bleeding and infection. Subsequently, the organized removal of fibrin, via the protease plasmin, is essential to permit fracture repair through angiogenesis and ossification. Yet, when plasmin activity is lost, the depletion of fibrin alone is insufficient to fully restore fracture repair, suggesting the existence of additional plasmin targets important for fracture repair. Previously, activated matrix metalloproteinase 9 (MMP-9) was demonstrated to function in fracture repair by promoting angiogenesis. Given that MMP-9 is a defined plasmin target, it was hypothesized that pro-MMP-9, following plasmin activation, promotes fracture repair. This hypothesis was tested in a fixed murine femur fracture model with serial assessment of fracture healing. Contrary to previous findings, a complete loss of MMP-9 failed to affect fracture healing and union through 28 days post injury. Therefore, these results demonstrated that MMP-9 is dispensable for timely fracture union and cartilage transition to bone in fixed femur fractures. Pro-MMP-9 is therefore not a significant target of plasmin in fracture repair and future studies assessing additional plasmin targets associated with angiogenesis are warranted.

MeSH Terms (7)

Animals Femoral Fractures Fracture Fixation, Internal Fracture Healing Matrix Metalloproteinase 9 Mice Mice, Inbred C57BL

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