The effects of intrinsic pathway protease deficiencies on plasminogen-deficient mice

Abstract

Plasminogen (Plg)-deficient mice experience wasting and have decreased longevity due to disseminated fibrin deposition. We generated mice with combined deficiencies of Plg and coagulation factor IX (fIX) or XI (fXI) to determine the effects on the Plg null phenotype. Mice lacking Plg and fIX (Plg(-/-)/fIX-/-) have lower mortality at age 6 months than Plg(-/-)/fIX+/+ mice (15% and 67%, respectively) and less severe wasting, consistent with the importance of fIX in fibrin formation. In contrast, combined Plg and fXI deficiency (Plg(-/-)/fXI-/-) reduces life span (more than 90% mortality at 6 months) and is associated with leukocyte infiltration of the lungs and pulmonary fibrosis. These abnormalities are not seen in Plg-/- or Plg(-/-)/fIX-/- animals. Activated fXI is thought to function primarily as a fIX activator; however, our observation suggests that fXI may have functions in regulation of inflammation or tissue repair distinct from its role in coagulation.

Figure 1.

Effects of fIX or fXI deficiency on growth and longevity in Plg^–/– mice. (A) Plg null allele and weight. Shown are average weights for 9 Plg^+/+ (□), 19 Plg^+/– (▵), and 14 Plg^–/– (○) mice followed from birth to age 6 months. Error bars are not shown because of space limitations in the figure. (B) Plg null allele and survival. Shown is survival for Plg^+/+ (solid line), Plg^+/– (dotted line), and Plg^–/– (dashed line) mice in panel A. (C) Effect of fIX or fXI deficiency on weight in Plg^–/– mice. Shown are average weights for 19 wild-type (□) and 14 Plg^–/– (○) mice (as in panel A) and 21 Plg^+/+/fIX^–/– (▴), 24 Plg^+/+/fXI^–/– (♦), 24 Plg^–/–/fIX^–/– (♦), and 25 Plg^–/–/fXI^–/– (▴) mice followed from birth to age 6 months. (D) Effect of fIX or fXI deficiency on survival in Plg^–/– mice. Survival is shown for wild-type, Plg^+/+/fIX^–/–, and Plg^+/+/fXI^–/– mice (all represented by solid line) and Plg^–/– (long-dashed line), Plg^–/–/fIX^–/– (short-dashed line), and Plg^–/–/fXI^–/– (dotted line) mice. Average weights in panels A and C are for surviving animals at each time point. Animals with the most significant weight loss die early and are not counted at subsequent time points. Lung fibrosis induced by 0.04 units (E) or 0.08 units (F) of intratracheal bleomycin. Lung fibrosis scores ± SEM were obtained 3 weeks after administration of bleomycin for wild-type (n = 6) and fXI^–/– (n = 5) mice, as described in “Study design.” Results for Plg^–/– mice (n = 6) are shown for comparison in the 0.04 unit experiment.

Figure 2.

Photomicrographs of murine lung from wild-type, Plg^–/–, and Plg^–/–/fXI^–/– mice. Shown are sections of lung from 6-week-old mice at × 40 magnification. Panels A, D, and G are from wild-type mice; B, E, and H from Plg^–/–/fXI^+/+ mice; and C, F, and I from Plg^–/–/fXI^–/– mice. (A-C) Hematoxylin and eosin. (D-F) Immunostaining with a polyclonal anti–murine fibrinogen/fibrin antibody. (G-I) Masson trichrome stain for collagen. The fields in panels B, E, and H were chosen to show a typical lung lesion in Plg^–/– mice. These lesions are patchy, and most pulmonary architecture appears normal. In contrast, the leukocyte infiltration shown in panels C, F, and I for Plg^–/–/fXI^–/– is typically diffuse by age 6 weeks. Images were taken with an Olympus BX41 microscope (Olympus, Tokyo, Japan) fitted with a DP70 digital camera, using a 40 ×/1.7 NA UPlanF1 objective and Olympus DP controller software (version 1.2.1.108).