Figure 9. Fibrinogen knockdown rescues impaired callus formation and revascularization.

(A) Representative histological sections of femoral fracture sites from Plg^–/– mice treated with ASO as a control and Plg^–/– mice (Plg^–/– control; n = 5) treated with an ASO against fibrinogen (Plg^–/– Fbg^lo; n = 10) at 14 DPF. Sections were stained with safranin O and assessed by immunofluorescence for fibrin and by immunohistochemistry for CD31. Whereas the fracture callus of Plg^–/– mice is somewhat disorganized, with multiple foci of chondroid soft-tissue callus (safranin O, yellow asterisks), the callus in Plg^–/– Fbg^lo mice is more organized, with a central soft-tissue callus bordered proximally and distally by hard-tissue callus. There is markedly reduced fibrin deposition in the fracture callus of Plg^–/– Fbg^lo mice compared with Plg^–/– control mice (yellow arrows; white box denotes area shown for CD31 staining). CD31 highlights numerous CD31-positive cells lining blood vessels in the hard-tissue callus of Plg^–/– Fbg^lo mice (red arrowheads), with fewer vessels in Plg^–/– mice (black asterisks denote areas of soft-tissue callus in fracture gap). Scale bars: 1 mm. Statistical comparison (Student’s t test) of (B) fibrin deposition at fracture site, (C) number of CD31-positive vessels in the callus (left), and total area of CD31-positive vessels (right). n ≥ 5 for each group. Four sections in each sample were averaged to constitute a single replicate (1 n). **P < 0.01. Error bars represent SEM.