Expression and induction by IL-6 of the normal and variant genes for human plasminogen

Fibrinogen and clot-related phenotypes determined by fibrinogen polymorphisms: Independent and IL-6-interactive associations

Interleukin-6 (IL-6) induces the expression of fibrinogen, and polymorphic variation within the fibrinogen genes is believed to alter the magnitude of this expression. The identification of the functional relevance of individual fibrinogen single nucleotide polymorphisms (SNPs) has been hindered by the high linkage disequilibrium (LD) reported in the European fibrinogen gene locus. This study investigated two novel and 12 known fibrinogen SNPs of potential functional relevance, in 2010 Tswana individuals known to have low LD. We aimed to identify functional polymorphisms that contribute to clot-related phenotypes and total and γ’ fibrinogen concentrations independently and through their interaction with IL-6, by taking advantage of the high fibrinogen and IL-6 concentrations and the low LD reported in black South Africans. Fibrinogen was significantly associated with IL-6, thereby mediating associations of IL-6 with clot formation and structure, although attenuating the association of IL-6 with clot lysis time. None of the common European fibrinogen haplotypes was present in this study population. Putative functional fibrinogen SNPs FGB–rs7439150, rs1800789 (–1420_G/A) and rs1800787 (–148_C/T) were significantly associated with fibrinogen concentration and altered clot properties, with several associations significantly influenced by IL-6 concentrations. The impact of harbouring several minor fibrinogen SNP alleles on the association of IL-6 and fibrinogen concentration was cumulative, with possession of each additional minor allele showing a stronger relationship of IL-6 with fibrinogen. This was also reflected in differences in clot properties, suggesting potential clinical relevance. Therefore, when investigating the effect of fibrinogen genetics on fibrinogen concentrations and CVD outcome, the possible interactions with modulating factors and the fact that SNP effects seem to be additive should be taken into account.

Circulating levels of plasminogen and oxidized phospholipids bound to plasminogen distinguish between atherothrombotic and non-atherothrombotic myocardial infarction

Oxidized phospholipids (OxPL) are abundant in atherosclerotic plaques. They are also bound to circulating plasminogen after myocardial infarction (MI), and their binding to plasminogen may accentuate fibrinolysis. We sought to assess whether circulating levels of plasminogen and OxPL bound to plasminogen (OxPL-PLG) increase following acute MI and whether this increase differs between atherothrombotic (Type 1) and non-atherothrombotic (Type 2) MI. We measured circulating levels of plasminogen and OxPL-PLG at 0, 6, 24, 48 h, and >3 months (stable state) following acute MI and following an angiogram for stable coronary artery disease (CAD). Forty-nine subjects met the criteria for acute MI, of whom 34 had clearly defined atherothrombotic (n = 22) or non-atherothrombotic (n = 12) MI; 15 patients met the criteria for stable CAD. Mean baseline levels of plasminogen and OxPL-PLG were lower in the acute MI group than in the stable CAD group (9.75 vs 20.2, p < 0.0001 for plasminogen and 165.5 vs 275.1, p = 0.0002 for OxPL-PLG) and did not change over time or between time points, including the 3-month follow-up. Mean baseline levels of plasminogen and OxPL-PLG were also lower in atherothrombotic (Type 1) than in non-atherothrombotic (Type 2) MI subjects (8.65 vs 12.1, p < 0.03 for plasminogen and 164.5 vs 245.7, p = 0.02 for OxPL-PLG), and this relationship did not change over time or between time points. Plasminogen and OxPL-PLG were lower in patients presenting with an acute MI than in those with stable CAD and also in those with atherothrombotic MI (Type 1) vs. those with non-atherothrombotic MI (Type 2). These findings persisted at a median follow-up of 3 months post-MI. The association of plasminogen and OxPL-PLG with acute MI, particularly atherothrombotic MI (Type 1), could reflect a reduced fibrinolytic capacity, associated with an increased risk of atherothrombotic events differentiating stable CAD from unstable CAD and atherothrombotic MI (Type 1) from non-atherothrombotic MI (Type 2). Additional study with a larger sample size is warranted.

A kringle-containing protease with plasminogen-like activity in the basal chordate Branchiostoma belcheri

Plg (plasminogen), a member of the serine protease superfamily, is a key component constituting the fibrinolytic system, and its evolutionary origin remains unknown during the course of animal evolution. In the present study, we isolated a cDNA, designated BbPlgl, encoding a kringle-containing protease with plasminogen-like activity from the basal chordate Branchiostoma belcheri. The deduced protein, BbPlgl, consisted of 430 amino acids, which is structurally characterized by the presence of an N-terminal signal peptide of 16 amino acids, 2 kringle domains with a Lys-binding site structure, a serine protease domain with the putative tPA (tissue plasminogen activator)-cleavage site (between Arg297 and Val298), the catalytic triad His237-Asp288-Ser379 expected for protease function, and a potential N-linked glycosylation site, all characteristic of Plgs. Besides, the recombinant refolded BbPlgl was readily activated by human uPA (urokinase plasminogen activator), and exhibited Plg-like activity. BbPlgl was also able to auto-activate at neutral and alkaline pH at 4°C without the addition of uPA, and the activation was accelerated by addition of human uPA. These results demonstrate that BbPlgl is a novel member of the Plg family, with a domain structure of K-K-SP (kringle-kringle-serine protease) lacking the PAN domain, pushing the evolutionary origin of Plg to the protochordate. In addition, BbPlgl displays a tissue-specific expression pattern in B. belcheri, with the most abundant expression in the hepatic caecum and hind-gut, agreeing with the notion that the hepatic caecum of amphioxus is the precursor of the vertebrate liver.

Imbalanced Plasminogen System in Lymphangioleiomyomatosis

Pulmonary lymphangioleiomyomatosis (LAM) is characterized by abnormal smooth muscle-like cell (LAM cell) proliferation leading to tissue destruction. We previously demonstrated that serum response factor (SRF), a critical smooth muscle transcription factor, is highly expressed in LAM cells. Here we show that a high SRF level alters the plasminogen (Plg) system. Specifically, overexpression of SRF in human lung fibroblasts upregulated urokinase-type plasminogen activator (uPA) and its substrate Plg, whereas it downregulated plasminogen activator inhibitor (PAI)-1. Because uPA cleaves Plg into plasmin, which activates matrix metalloproteinases (MMP), the end result was an increase in MMP activity. To determine whether uPA, Plg, and PAI-1 were abnormally expressed in LAM in vivo, we immunostained 12 LAM cases. In all cases, the LAM lesions showed stronger immunoreaction for uPA and Plg than the surrounding normal lung parenchyma. On the contrary, PAI-1 was absent in LAM lesions, whereas it was ubiquitous in normal lung parenchyma. Microdissection-based reverse transcriptase/polymerase chain reaction further confirmed upregulation of uPA and Plg and downregulation of PAI-1 message in LAM. Altogether, our findings suggest that the high SRF level seen in LAM contributes to extracellular matrix degradation and progressive LAM cell infiltration of the lung.

Cellular density regulation of plasminogen gene expression in mouse hepatocytes

The liver produces a variety of proteins including plasminogen. Plasminogen is pro-enzyme that is converted into plasmin by plasminogen activator. Plasmin has a broad substrate spectrum and participates in several biological processes, such as fibrinolysis, tissue remodeling, cell migration, angiogenesis and embryogenesis. In the present study, the regulation of plasminogen expression in mouse hepatocytes was investigated in the primary culture system. Expression level of plasminogen mRNA in the culture at the low cell density condition (0.2 x 10(5) cells / cm(2)) was compared with that at the high cell density condition (1.0 x 10 (5) cells / cm(2)). In the low cell density culture, the expression level of plasminogen mRNA decreased by a time-dependent manner. However, mRNAs for albumin and alpha(2)-antiplasmin were not influenced by the low cell density culture. On the other hand, in the high cell density culture, plasminongen mRNA expressed constantly as well as albumin and alpha(2)-antiplasmin mRNAs. Thus, the decrease in plasminogen mRNA expression could specifically occur when the density of hepatocytes was low. The down-regulation of plasminogen mRNA in the low cell density culture is not observed in the presence of cycloheximide, suggesting that the de novo protein synthesis is required for the regulatory mechanism. These findings indicate that the expression of plasminogen mRNA from hepatocyte is dependent on the cell density and the stimulation by cell-cell contact may be an important factor for the constitutive expression of plasminogen gene in hepatocytes.

Hemostatic factors as predictors of coronary events and total mortality: The FINRISK '92 Hemostasis Study

The role of hemostatic factors as predictors of coronary heart disease (CHD) and total mortality is poorly understood. Therefore, we carried out a prospective cohort study in Finland. In 1992, a random population sample of 2378 men and women aged 45 to 64 years was investigated and then followed up until December 31, 1998. During the follow-up, 133 CHD events were observed; 73 were among participants free of CHD at baseline. The total number of deaths was 124. After adjustment for traditional risk factors and prevalent CHD at baseline and correction for regression dilution bias, a 1-SD increase in plasminogen was associated with a 1.41-fold (95% CI 1.09 to 1.81) increase in CHD risk. The predictive power of plasminogen depended significantly on the level of total cholesterol being stronger for persons with high cholesterol. A 1-SD increase in fibrinogen was associated with a 1.23-fold (95% CI 1.05 to 1.44) increase in all-cause mortality, but its association with CHD events did not reach statistical significance. Factor VII antigen or coagulant activity or lipoprotein(a) were not independent predictors of CHD risk. These findings support the role of plasminogen as a risk factor for CHD events.

Prospective study of fibrinolytic factors and incident coronary heart disease: the Atherosclerosis Risk in Communities (ARIC) Study

The fibrinolytic system may play a role in the pathogenesis of coronary heart disease (CHD), but existing prospective studies have not consistently shown an independent association between fibrinolytic factors and CHD. None has reported an association between plasminogen and CHD incidence. In the prospective Atherosclerosis Risk in Communities (ARIC) Study of middle-aged adults, we examined the association of incident CHD with several fibrinolytic factors: tissue plasminogen activator antigen, plasminogen activator inhibitor-1, plasminogen, and fibrin fragment D-dimer as well as a marker of coagulation activation (prothrombin fragment F1.2). We measured these in stored baseline plasma samples of 326 subjects who developed CHD and, for comparison, a stratified random sample of the entire cohort (n=720). Tissue plasminogen activator and plasminogen activator inhibitor-1 antigen levels were associated positively with CHD incidence in analyses adjusted for age, race, and sex but were not associated with CHD after adjustment for other risk factors. Plasminogen and D-dimer levels were associated positively and independently with CHD incidence; the multivariable-adjusted relative risks (95% CIs) for the highest versus lowest quintiles were 2.20 (1.2 to 4.2) for plasminogen and 4.21 (1.9 to 9.6) for D-dimer. F1.2 was not associated with CHD incidence. Our findings lend support for a link between fibrinolytic factors and CHD incidence. A positive association between plasminogen and CHD is seemingly opposite the direction expected but may reflect a compensatory response to impaired plasminogen activation in subjects prone to CHD.

Induction of plasminogen in rat hippocampal pyramidal neurons by kainic acid

Tissue plasminogen activator (tPA) is used to treat acute stroke, but tPA- and plasminogen-gene-deficient mice exhibit resistance to neurodegeneration. Thus, it is unclear whether the tPA-plasminogen system, an extracellular proteolytic cascade plays a helpful or harmful role, and whether plasminogen is induced by neurodegeneration. In the CA3, kainic acid (KA)-injection caused neuronal damage after 6 h, and almost all of the neurons were lost after 7 days. Plasminogen mRNA was strongly induced 6 h after injection, then gradually decreased, and was very weak at 2 days after injection. Plasminogen protein was expressed after 6 h and localized in abnormally shaped neurons. The in vivo expression of plasminogen was synchronous with morphological changes in neurons. These results suggest that the expression of plasminogen induced by KA-injection may disrupt of neuron-extracellular matrix interaction and thereby contribute to cell death in neurons in the hippocampus.