Fibrinolysis is essential for fracture repair and prevention of heterotopic ossification
Masato Yuasa, … , Justin M.M. Cates, Jonathan G. Schoenecker
Masato Yuasa, … , Justin M.M. Cates, Jonathan G. Schoenecker
Published July 27, 2015
Citation Information: J Clin Invest. 2015;125(8):3117-3131. https://doi.org/10.1172/JCI80313.
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Research Article Bone biology Hematology Hepatology Nephrology Pulmonology

Fibrinolysis is essential for fracture repair and prevention of heterotopic ossification

Abstract

Bone formation during fracture repair inevitably initiates within or around extravascular deposits of a fibrin-rich matrix. In addition to a central role in hemostasis, fibrin is thought to enhance bone repair by supporting inflammatory and mesenchymal progenitor egress into the zone of injury. However, given that a failure of efficient fibrin clearance can impede normal wound repair, the precise contribution of fibrin to bone fracture repair, whether supportive or detrimental, is unknown. Here, we employed mice with genetically and pharmacologically imposed deficits in the fibrin precursor fibrinogen and fibrin-degrading plasminogen to explore the hypothesis that fibrin is vital to the initiation of fracture repair, but impaired fibrin clearance results in derangements in bone fracture repair. In contrast to our hypothesis, fibrin was entirely dispensable for long-bone fracture repair, as healing fractures in fibrinogen-deficient mice were indistinguishable from those in control animals. However, failure to clear fibrin from the fracture site in plasminogen-deficient mice severely impaired fracture vascularization, precluded bone union, and resulted in robust heterotopic ossification. Pharmacological fibrinogen depletion in plasminogen-deficient animals restored a normal pattern of fracture repair and substantially limited heterotopic ossification. Fibrin is therefore not essential for fracture repair, but inefficient fibrinolysis decreases endochondral angiogenesis and ossification, thereby inhibiting fracture repair.

Authors

Masato Yuasa, Nicholas A. Mignemi, Jeffry S. Nyman, Craig L. Duvall, Herbert S. Schwartz, Atsushi Okawa, Toshitaka Yoshii, Gourab Bhattacharjee, Chenguang Zhao, Jesse E. Bible, William T. Obremskey, Matthew J. Flick, Jay L. Degen, Joey V. Barnett, Justin M.M. Cates, Jonathan G. Schoenecker

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Figure 5

Heterotopic ossification in plasminogen-deficient mice.

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Heterotopic ossification in plasminogen-deficient mice. (A) 2D μCT sagit...
(A) 2D μCT sagittal slices of WT and Plg–/– mice at 14 and 42 DPF. 14 DPF images show hard-tissue callus formation in both WT and Plg–/– mice (yellow arrowheads). In addition, separate foci of mineralization in soft tissue away from the fracture callus seen only in Plg–/– mice are suggestive of heterotopic ossification (red arrowheads). By 42 DPF, the hard-tissue fracture callus has largely remodeled in WT mice. In contrast, the fracture callus in Plg–/– mice is not only persistent, but also hypertrophic and disorganized, with an irregular pattern of mineralization. Scale bars: 1 mm. n ≥ 13 for each genotype. (B) 2D μCT axial images of fractured femurs at 14 and 42 DPF in Plg–/– mice show that the areas of soft-tissue mineralization (red arrowheads) are distinct from the femoral fracture callus (yellow arrowheads), consistent with heterotopic ossification. Scale bars: 1 mm. n ≥ 13 for each genotype. (C) Macroscopic photograph of lateral aspect of a fractured femur of a Plg–/– mouse at 42 DPF (macro, yellow bracket denotes fracture callus). Nondemineralized tissue sections from the fracture callus of Plg–/– mice were stained with von Kossa and van Gieson solution to identify regions of hard-tissue callus formation (box i) and heterotopic ossification (box ii). Red boxes denote regions shown at higher power magnification. Foci of heterotopic ossification are denoted by white asterisks. Scale bars: 1 mm (top and second row); 200 μm (third row); 20 μm (bottom row). AC, avascular cartilage; M, muscle.