Plasminogen with type-I mutation is polymorphic in the Japanese population

Plasminogen missense variants and their involvement in cardiovascular and inflammatory disease

Human plasminogen (PLG), the zymogen of the fibrinolytic protease, plasmin, is a polymorphic protein with two widely distributed codominant alleles, PLG/Asp453 and PLG/Asn453. About 15 other missense or non-synonymous single nucleotide polymorphisms (nsSNPs) of PLG show major, yet different, relative abundances in world populations. Although the existence of these relatively abundant allelic variants is generally acknowledged, they are often overlooked or assumed to be non-pathogenic. In fact, at least half of those major variants are classified as having conflicting pathogenicity, and it is unclear if they contribute to different molecular phenotypes. From those, PLG/K19E and PLG/A601T are examples of two relatively abundant PLG variants that have been associated with PLG deficiencies (PD), but their pathogenic mechanisms are unclear. On the other hand, approximately 50 rare and ultra-rare PLG missense variants have been reported to cause PD as homozygous or compound heterozygous variants, often leading to a debilitating disease known as ligneous conjunctivitis. The true abundance of PD-associated nsSNPs is unknown since they can remain undetected in heterozygous carriers. However, PD variants may also contribute to other diseases. Recently, the ultra-rare autosomal dominant PLG/K311E has been found to be causative of hereditary angioedema (HAE) with normal C1 inhibitor. Two other rare pathogenic PLG missense variants, PLG/R153G and PLG/V709E, appear to affect platelet function and lead to HAE, respectively. Herein, PLG missense variants that are abundant and/or clinically relevant due to association with disease are examined along with their world distribution. Proposed molecular mechanisms are discussed when known or can be reasonably assumed.

Proteolytic Cleavages in the VEGF Family: Generating Diversity among Angiogenic VEGFs, Essential for the Activation of Lymphangiogenic VEGFs

Specific proteolytic cleavages turn on, modify, or turn off the activity of vascular endothelial growth factors (VEGFs). Proteolysis is most prominent among the lymph-angiogenic VEGF-C and VEGF-D, which are synthesized as precursors that need to undergo enzymatic removal of their C- and N-terminal propeptides before they can activate their receptors. At least five different proteases mediate the activating cleavage of VEGF-C: plasmin, ADAMTS3, prostate-specific antigen, cathepsin D, and thrombin. All of these proteases except for ADAMTS3 can also activate VEGF-D. Processing by different proteases results in distinct forms of the "mature" growth factors, which differ in affinity and receptor activation potential. The "default" VEGF-C-activating enzyme ADAMTS3 does not activate VEGF-D, and therefore, VEGF-C and VEGF-D do function in different contexts. VEGF-C itself is also regulated in different contexts by distinct proteases. During embryonic development, ADAMTS3 activates VEGF-C. The other activating proteases are likely important for non-developmental lymphangiogenesis during, e.g., tissue regeneration, inflammation, immune response, and pathological tumor-associated lymphangiogenesis. The better we understand these events at the molecular level, the greater our chances of developing successful therapies targeting VEGF-C and VEGF-D for diseases involving the lymphatics such as lymphedema or cancer.

Plasminogen deficiency

Plasminogen (plg) deficiency has been classified as (i) hypoplasminogenemia or 'true' type I plg deficiency, and (ii) dysplasminogenemia, also called type II plg deficiency. Both forms, severe hypoplasminogenemia and dysplasminogenemia, are not causally linked to venous thrombosis. Dysplasminogenemia does not lead to a specific clinical manifestation and probably represents only a polymorphic variation in the general population, mainly in Asian countries. Severe hypoplasminogenemia is associated with compromised extracellular fibrin clearance during wound healing, leading to pseudomembraneous (ligneous) lesions on affected mucous membranes (eye, middle ear, mouth, pharynx, duodenum, upper and lower respiratory tract and female genital tract). Ligneous conjunctivitis is by far the most common clinical manifestation. More than 12% of patients with severe hypoplasminogenemia exhibit congenital occlusive hydrocephalus. In milder cases of ligneous conjunctivitis, topical application of plg-containing eye drops, fresh frozen plasma, heparin, corticosteroids or certain immunosuppressive agents (such as azathioprine) may be more or less effective. Oral treatment with sex hormones was successful in two female patients with ligneous conjunctivitis. In severe cases with possibly life-threatening multi-organ involvement, true therapeutic options are not available at present. The plg-knockout mouse is a useful tool to study the many different properties of plg in a variety of settings, such as wound healing, tissue repair and tissue remodeling, virulence and invasiveness of certain bacteria in the human host, tumor growth and dissemination, as well as arteriosclerosis.

Population-based distribution of plasminogen activity and estimated prevalence and relevance to thrombotic diseases of plasminogen deficiency in the Japanese: the Suita Study

Reduced plasminogen activity with a normal level of antigen is commonly observed in Japanese individuals. The first reported patient with plasminogen deficiency was accompanied with deep vein thrombosis. The present study examines whether heterozygous or homozygous deficiency of plasminogen is a risk factor for thrombotic disease. This study measures the plasminogen activity of 4517 individuals in the general population, determines the cut-off to define plasminogen deficiency, and identifies plasminogen deficiencies in the control groups and thrombotic disease groups. In another study, we examined the phenotypes of consecutive patients with homozygous plasminogen deficiency detected in our hospital. We found 173 and two of 4517 individuals to have heterozygous and homozygous deficiency with normal plasminogen antigen level, respectively, and 19 to have heterozygous deficiency with reduced antigen levels. The incidence of plasminogen deficiency in an age- and sex-matched control group (13/324, 4.01% for deep vein thrombosis or 13/330, 3.94% for stroke) selected from the 4517 individuals was not significantly different from those in patients with deep vein thrombosis (3/108, 2.78%) or cardioembolic stroke (6/110, 5.55%). Among 19 patients with homozygous plasminogen deficiency showing about 10% plasminogen activity, none had deep vein thrombosis. These findings indicate that neither heterozygous nor homozygous plasminogen deficiency constitutes a significant risk factor for thrombotic disease.

A K19E missense mutation in the plasminogen gene is a common cause of familial hypoplasminogenaemia

The prevalence of familial plasminogen deficiency in Scotland has recently been calculated at 2.9/1000. However, little is known of the molecular genetic background and the frequency of plasminogen gene mutations in most cases of inherited plasminogen deficiency. Having previously identified 28 unrelated subjects with familial plasminogen deficiency from a cohort of 9611 blood donors, we have now reviewed 19 of these 28 subjects and screened the plasminogen gene in 15 subjects with hypoplasminogenaemia (plus five relatives) and four subjects with dysplasminogenaemia for mutations and polymorphisms. A missense mutation K19E in the plasminogen gene was found in 13 of the 15 propositi with hypoplasminogenaemia, in one of these in a homozygous manner. In two subjects with hypoplasminogenaemia, two new mutations (P353A and R471X) were identified. These three different mutations, if inherited in a homozygous or compound-heterozygous manner, may be associated with the development of ligneous conjunctivitis. In four subjects with dysplasminogenaemia, three heterozygous mutations (C548G, n = 1; A601T, n = 1; G693R, n = 2) were found. None of the propositi with plasminogen deficiency developed venous thrombosis at any time. In conclusion, the K19E mutation in the plasminogen gene is a common cause of hypoplasminogenaemia in Scotland, with an estimated prevalence of around 0.14%.

Compound-Heterozygous Mutations in the Plasminogen Gene Predispose to the Development of Ligneous Conjunctivitis

Homozygous type I plasminogen deficiency has been identified as a cause of ligneous conjunctivitis. In this study, 5 additional patients with ligneous conjunctivitis are examined. Three unrelated patients (1 boy, 1 elderly woman, and 1 man) had plasminogen antigen levels of less than 0.4, less than 0.4, and 2.4 mg/dL, respectively, but had plasminogen functional residual activity of 17%, 18%, and 17%, respectively. These subjects were compound-heterozygotes for different missense mutations in the plasminogen gene: Lys19 → Glu/Arg513 → His, Lys19 → Glu/Arg216 → His, and Lys19 → Glu/Leu128 → Pro, respectively. The other 2 patients, a 14-year-old boy and his 19-year-old sister, who both presented with a severe course of the disease, exhibited plasminogen antigen and functional activity levels below the detection limit (<0.4 mg/dL and <5%, respectively). These subjects were compound-heterozygotes for a deletion mutation (del Lys212) and a splice site mutation in intron Q (Ex17 + 1del-g) in the plasminogen gene. These findings show that certain compound-heterozygous mutations in the plasminogen gene may be associated with ligneous conjunctivitis. Our findings also suggest that the severity of clinical symptoms of ligneous conjunctivitis and its associated complications may depend on the amount of plasminogen functional residual activity.

Homozygous Mutations in the Plasminogen Gene of Two Unrelated Girls With Ligneous Conjunctivitis

Ligneous conjunctivitis is a rare and unusual form of chronic pseudomembranous conjunctivitis that usually starts in early infancy. The disease may be associated with pseudomembranous lesions of other mucous membranes in the mouth, nasopharynx, trachea, and female genital tract. We examined two unrelated Turkish girls both suffering from ligneous conjunctivitis and occlusive hydrocephalus. Both children exhibited a severe plasminogen deficiency. Genomic DNA from both patients as well as from clinically healthy family members were screened for mutations in the plasminogen gene by polymerase chain reaction, single-strand conformation polymorphism (SSCP) analysis, and DNA sequencing. In the first girl with ligneous conjunctivitis a homozygous G → A point mutation was identified in plasminogen exon 7 at position 780 leading to an amino acid exchange (Arg216 → His). Her healthy sister and her healthy parents were heterozygous for this mutation. The second patient revealed a homozygous G → A point mutation in plasminogen exon 15 at position 1924 which leads to a stopcodon (Trp597 → Stop). The healthy parents were shown to be heterozygous for this mutation. In addition, the father's second allele revealed another mutation in the same codon (Trp597 → Cys) (compound heterozygosity). In conclusion, certain homozygous mutations in the plasminogen gene may cause ligneous conjunctivitis.

Homozygous Mutations in the Plasminogen Gene of Two Unrelated Girls With Ligneous Conjunctivitis

Ligneous conjunctivitis is a rare and unusual form of chronic pseudomembranous conjunctivitis that usually starts in early infancy. The disease may be associated with pseudomembranous lesions of other mucous membranes in the mouth, nasopharynx, trachea, and female genital tract. We examined two unrelated Turkish girls both suffering from ligneous conjunctivitis and occlusive hydrocephalus. Both children exhibited a severe plasminogen deficiency. Genomic DNA from both patients as well as from clinically healthy family members were screened for mutations in the plasminogen gene by polymerase chain reaction, single-strand conformation polymorphism (SSCP) analysis, and DNA sequencing. In the first girl with ligneous conjunctivitis a homozygous G → A point mutation was identified in plasminogen exon 7 at position 780 leading to an amino acid exchange (Arg216 → His). Her healthy sister and her healthy parents were heterozygous for this mutation. The second patient revealed a homozygous G → A point mutation in plasminogen exon 15 at position 1924 which leads to a stopcodon (Trp597 → Stop). The healthy parents were shown to be heterozygous for this mutation. In addition, the father's second allele revealed another mutation in the same codon (Trp597 → Cys) (compound heterozygosity). In conclusion, certain homozygous mutations in the plasminogen gene may cause ligneous conjunctivitis.

Plasminogen with type-I mutation in the Chinese Han population

A functionally inactive plasminogen (PLG) variant, PLG M5, is polymorphic in the Japanese population and has a codon 601 mis-sense mutation (GCT for Ala to ACT for Thr), designated type-I mutation. The present study aimed to reveal whether the plasminogen with type-I mutation is present in the Chinese Han population. Among 104 healthy Chinese students, phenotype PLG AM5 was found in three subjects (2.9%), while 100 subjects were phenotype A and one was phenotype AA3. In the three subjects with PLG AM5, plasma concentrations of immunoreactive PLG were normal but PLG activities were decreased. Analysis using PCR and dot-blot hybridization with allele-specific oligonucleotide probes revealed the presence of the type-I mutation in the PLG gene of all three subjects with PLG AM5. The data indicate that PLG with type-I mutation is present in the Chinese Han population, possibly at a polymorphic frequency.