Figure 3.

Exuberant osteoclast (OC) activity is associated with increased circulating levels of osteoprotegerin (OPG), interleukin-6 (IL-6), and fibrinogen and with accumulation of fibrin(ogen) in bone. Triangles represent plasminogen-deficient (PLG^−/−) mice; squares represent control mice. A–D, Plasma levels of tartrate-resistant acid phosphatase 5b (TRAP-5b) (A), soluble RANKL (sRANKL) (B), and OPG (C) and the resulting sRANKL:OPG ratios (D) were determined by enzyme-linked immunosorbent assay (ELISA). Increased osteoclast activity was observed without a change in RANKL:OPG ratio. E and F, Plasma IL-6 levels determined by flow cytometry (E) and fibrinogen levels determined by ELISA (F) indicate a progressive increase in inflammation and acute-phase reactants at ages 5, 10, and 20 weeks (measurements for all data were collected from separate mice at the time that they were killed; Student’s t-test was performed at each time point). Bars show the mean ±SD (n=4 at each time point). *=P<0.05; ** = P<0.01 versus control mice. G, Immunolocalization of fibrinogen demonstrates abundant fibrin within the L5 vertebrae of 20-week-old PLG^−/− mice (red signal), but not in control mice. Bars =100 μm. H, Left, The number of osteoclasts per unit bone surface in L5 vertebrae at age 8 weeks (time point of maximal TRAP-5b concentration) was determined by TRAP staining. Representative images from each group are shown. Insets are higher-magnification views of boxed areas. Original magnification ×200; ×400 in insets. Bars =500 μm. Right, Quantification of osteoclasts/bone surface area illustrates increased numbers of osteoclasts in PLG^−/− mice (n=4) compared to control mice (n = 4) at age 8 weeks. Bars show the mean ±SD. *=P<0.01 versus control mice.