Variant Plasminogen Research Articles

Mechanisms involved in hereditary angioedema with normal C1-inhibitor activity.

Patients with the inherited disorder hereditary angioedema (HAE) suffer from episodes of soft tissue swelling due to excessive bradykinin production. In most cases, dysregulation of the plasma kallikrein-kinin system due to deficiency of plasma C1 inhibitor is the underlying cause. However, at least 10% of HAE patients have normal plasma C1 inhibitor activity levels, indicating their syndrome is the result of other causes. Two mutations in plasma protease zymogens that appear causative for HAE with normal C1 inhibitor activity have been identified in multiple families. Both appear to alter protease activity in a gain-of-function manner. Lysine or arginine substitutions for threonine 309 in factor XII introduces a new protease cleavage site that results in formation of a truncated factor XII protein (Δ-factor XII) that accelerates kallikrein-kinin system activity. A glutamic acid substitution for lysine 311 in the fibrinolytic protein plasminogen creates a consensus binding site for lysine/arginine side chains. The plasmin form of the variant plasminogen cleaves plasma kininogens to release bradykinin directly, bypassing the kallikrein-kinin system. Here we review work on the mechanisms of action of the FXII-Lys/Arg309 and Plasminogen-Glu311 variants, and discuss the clinical implications of these mechanisms.

Effects of Disruption of The Plasminogen Gene on Thrombosis, Growth, and Health in Mice

Circumstantial evidence suggests that the plasminogen/plasmin system plays a role in many biological processes, including hemostasis, cell migration, and development. The in vivo function of the plasminogen/plasmin system was studied by generation of plasminogen-deficient (Plg-/-) mice. Inactivation of the murine plasminogen-gene (Plg) was achieved by replacing, via homologous recombination in embryonic stem cells, genomic sequences encoding the exons containing the catalytic site amino acids His605 and Asp648 with a neomycin phosphotransferase expression cassette. Germline transmission of the mutated allele, as determined by Southern blot hybridization and polymerase chain reaction, was obtained via blastocyst injection. Mendelian inheritance of the inactivated plasminogen allele was observed, and homozygous-deficient mice (Plg-/-) displayed normal viability but retarded growth up to at least 12 weeks of age. At 8 weeks of age, body weight was 21.8 +/- 1.2 g (n = 10) for wild-type (Plg+/+) mice, 21.0 +/- 1.1 g (n = 16) for heterozygous-deficient (Plg+/-) mice, and 17.4 +/- 1.3 g (n = 12) for Plg-/- mice; P < .05 versus Plg+/+ or Plg+/-. None of 36 Plg+/+ or 65 Plg+/- mice but 7 of 37 Plg-/- mice (19%) developed rectal prolapse at 7.4 +/- 0.6 weeks of age (P = .03 versus Plg+/+ and P = .003 versus Plg+/-); 4 of 37 Plg-/- mice (11%) became runted and apathic at 5.3 +/- 0.3 weeks of age (P = .041 versus Plg+/-); and 6 of 37 Plg-/- mice (16%) died prematurely at 8.8 +/- 1.7 weeks of age (P = .057 versus Plg+/+ and P = .029 versus Plg+/-). Although male and female Plg-/- mice were able to sire offspring, the fertility of Plg-/- female mice was reduced, possibly owing to their impaired health. Levels of plasminogen-related antigen in plasma, measured by ELISA, were 84 +/- 8 micrograms/mL (n = 4) in Plg+/+, 35 +/- 2 micrograms/mL (n = 3) in Plg+/-, and 0.076 +/- 0.032 microgram/mL (n = 6) in Plg-/- mice (P < .001 versus Plg+/- and Plg+/+). Plasmin activity generated by urokinase activation was unmeasurable in Plg-/- mice (< 5% of Plg+/+ mice). Plasminogen-specific immunoreactivity was observed in hepatocytes from Plg+/+ mice but not from Plg-/- mice (< 10% of Plg+/+ mice). Neither native nor variant plasminogen mRNA nor translation products could be identified by Northern or Western blot of liver extracts from Plg-/- mice. Spontaneous lysis within 24 hours of a 125I-fibrin-labeled pulmonary plasma clot was 85 +/- 5% (n = 5) in Plg+/+ mice, 62 +/- 7% (n = 3) in Plg+/- mice, and -2 +/- 1% (n = 3) in Plg-/- mice (P < .001 versus Plg+/- and Plg+/+). Delayed clot lysis within 72 hours was 33 +/- 1% (n = 3) in tPA-/- mice and 26 +/- 2% (n = 3) in Plg-/- mice (P = .054). Histological examination of several organs revealed fibrin deposition in the liver; lung; and in the stomach, associated with gastric ulcers, in 6- to 12-week-old Plg-/- mice but not in Plg+/+ or Plg+/- littermates. Plasminogen-deficient mice survive embryonic development but develop spontaneous fibrin deposition due to impaired thrombolysis and suffer retarded growth and reduced fertility and survival. The Plg-/- phenotype is reminiscent of the combined tPA-/-:uPA-/- phenotype, which suggests that there is no significant additional pathway for physiological plasminogen activation in mice.

Thrombolytic therapy with tissue-type plasminogen activator: new modes and novel variant plasminogen activators.

Tissue-type plasminogen activator produced by recombinant DNA technology, has been established as an important thrombolytic agent in the treatment of acute myocardial infarction. New approaches to increase the effectiveness of this agent, including rapid high dose administration are being investigated. Several novel protein engineered variant forms of plasminogen activators have been produced that have increased thrombolytic potency in animal models and offer the potential of a more effective lower dose agent than can be administered clinically as a single bolus intravenous injection.

Abnormal Plasminogen Maywood I

Maywood I is a dysfunctional plasminogen. It is described in a patient (W.Y.) with a reduced plasma functional activity and with a low normal antigen level. Plasminogen was isolated from the patients plasma by affinity chromatography with L-lysine-substituted Sepharose. The protein yield was 86 mg/l, which was 88% of the plasma Plg antigen level; the specific activity was 24.4 IU/mg protein compared to 28.5 IU/mg protein for the native molecule. The protein was the Glu-form determined by SDS-PAGE and by isoelectric focusing. Six major isoelectric forms were found with isoelectric points between pH's 6.40 and 5.45. Titration of the equimolar plasminogen.streptokinase complex with p-nitrophenyl-p-guanidinobenzoate gave 85% active-sites indicating a homogenous population of molecules; therefore, the propositus is a homozygote. Four different plasminogen activators: a) streptokinase, b) urokinase c) the plasmin-derived light (B) chain-streptokinase complex, and d) tissue plasminogen activator (with soluble fibrin/CNBr-fibrinogen fragments) generated little plasmin from the variant plasminogen (4.5 to 45 nM), 5% or less than that generated from normal plasminogen. At 45 nM plasminogen, the molar ratio of plasminogen:activator was 3.0 for streptokinase, 3.9 for urokinase, 7.1 for the light (B) chain-streptokinase complex, and 155 for tissue plasminogen activator. In the equimolar variant plasminogen.streptokinase complex, the active-site was slowly developed, to a maximum of 85% in 40 min; in the normal complex, 100% active-sites were developed in 15 min. The variant plasminogen forms two equimolar complexes with streptokinase (I and II), with different mobilities in PAGE, in about equal amounts.(ABSTRACT TRUNCATED AT 250 WORDS)

The plasminogen polymorphism in South African Negro populations: genetics and anthropogenetics.

Genetic polymorphism of human plasminogen (PLG) was investigated in 1252 unrelated individuals from eight South African Bantu-speaking Negro tribes. PLG phenotypes were determined by isoelectric focusing (pH 3.5-9.5 and 5-8 gradients) of neuraminidase-treated samples and subsequent detection by caseinolytic overlay or immunoblotting with specific antibody. No significant difference in the distribution of PLG alleles among the eight ethnic groups was observed. The combined allele frequencies of the common alleles in South African Negroes were 0.6977 for PLG*A, 0.2736 for PLG*B. In addition, six rare alleles were seen: PLG*A3, *A1, *M2, *B1, *B2, *B3. The rare variant PLG*B2 was proven to segregate by autosomal Mendelian inheritance in a family. The combined frequency for the rare alleles was 0.0287. The distribution of phenotypes in the total population sample was found to be in Hardy-Weinberg equilibrium. A striking difference in PLG allele distribution between Negroes from South Africa and published Negroid frequencies from North America could be observed. This difference was also seen in comparison with Mongoloid populations; in contrast, PLG frequencies for South African Negroes were similar or almost identical to known Caucasoid distributions.