The low-frequency allele of the platelet collagen signaling receptor glycoprotein VI is associated with reduced functional responses and expression

Department of Haematology, University of Cambridge, United Kingdom.
Blood (Impact Factor: 10.45). 06/2003; 101(11):4372-9. DOI: 10.1182/blood-2002-08-2591
Source: PubMed


Interaction of platelets with collagen under conditions of blood flow is a multi-step process with tethering via glycoprotein IbIXV (GPIbIXV) over von Willebrand factor, adhesion by direct interaction with the integrin GPIaIIa, and signaling via GPVI. GPVI can be specifically agonized by cross-linked collagen-related peptide (CRP-XL), which results in a signaling cascade very similar to that evoked by native collagen. The GPVI gene has 2 common alleles that differ by 3 replacements in the glycosylated stem and 2 in the cytoplasmic domain. We used CRP-XL to elucidate the variation in responses observed in platelet function in different individuals. We observed a 3-fold difference in the response to CRP-XL in platelet aggregation when comparing platelets from 10 high-frequency allele homozygotes with 8 low-frequency ones (2-way analysis of variance [ANOVA], P <.0001). The difference in functional responses was reflected in fibrinogen binding and in downstream signaling events as measured by tyrosine phosphorylation, the expression of P-selectin, and the binding of annexin V and the generation of thrombin on the platelet surface (2-way ANOVA, P <.001). Platelets homozygous for the low-frequency allele tended to be less able to form a thrombus on a collagen surface in flowing whole blood or in the platelet function analyzer-100 (t test, P =.065 and P =.061, respectively). The functional difference was correlated to a difference in total and membrane-expressed GPVI measured by monoclonal and polyclonal antibodies. This study demonstrates for the first time that platelet function may be altered by allelic differences in GPVI.

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    • "Low frequency allele homozygotes of GP VI, such as the CC genotype of T > C rs 1613662, are associated with reduced activation and platelet responses to collagen when compared with high frequency allele homozygotes. [27] In this study, the rare C-allele of GP VI offered some protection of renal function, but did not correlate with the platelet count or other variables of disease severity. A lower platelet count nadir was associated with the low frequency C-allele of GP Ia (HPA-5), the other major platelet receptor for collagen. "
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    ABSTRACT: Puumala virus (PUUV) infection is a viral hemorrhagic fever with renal syndrome (HFRS) characterized by thrombocytopenia and acute impairment of renal function. We aimed to assess whether genetic polymorphisms of platelet antigens together with those of von Willebrand factor (VWF) and plasminogen activator inhibitor (PAI-1) correlate with disease severity. Patients and methods 172 consecutive hospital-treated patients with serologically confirmed acute PUUV infection were included. Platelet glycoprotein (GP) IIIa T>C (rs5918), GP Ia T>C (rs1126643), GP Ib C>T (rs6065), GP VI T>C (rs1613662), VWF A>G (rs1063856) and PAI-1 A>G (rs2227631) were genotyped. The associations of the rarer alleles with variables reflecting the severity of the disease were analyzed. PAI-1G-carriers had higher maximum creatinine level compared with the non-carriers (median 213 μmol/l, range 60-1499 μmol/l vs. median 122 μmol/l, range 51-1156 μmol/l, p = 0.01). The GG-genotypes had higher creatinine levels than GA- and AA-genotypes (medians 249 μmol/l, 204 μmol/l and 122 μmol/l, respectively, p = 0.03). Polymorphisms of GP VI and VWF associated with lower creatinine levels during PUUV infection. The minor C-allele of GP Ia associated with lower platelet counts (median 44 × 10(9)/l, range 20-90 × 10(9)/l vs median 64 × 10(9)/l, range 3-238 × 10(9)/l; p = 0.02). Polymorphism of PAI-1, a major regulator of fibrinolysis, has an adverse impact on the outcome of kidney function in PUUV-HFRS. Platelet collagen receptor GP Ia polymorphism associates with lower platelet count.
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    ABSTRACT: Abstract Background Both platelet function and heart disease show strong genetic components, many of which remain to be elucidated. Materials and methods The roles of candidate polymorphisms in ten platelet-associated genes were compared between 1,237 Acute Coronary Syndrome (ACS) cases (withmyocardial infarction and unstable angina) and 386 controls, from an Irish Caucasian population. Additionally, 361 stable angina patients were investigated. Two genes of interest were followed up in a separate Irish study of 1,484 individuals (577 with IHD and 907 unaffected). Results The GALNT4 (N-acetyl galactosaminyl transferase 4) 506I allele was significantly underrepresented inACS (OR =0.66, CI = 0.52–0.84; P = 0.001; P = 0.01 after correction for multiple testing), while the SULT1A1 (Sulphotransferase 1A1) 213H allele was associated with risk of ACS (OR = 1.37, CI = 1.08–1.74; P = 0.01; P = 0.1 after correction for multiple testing). Subsequent genotyping of further SNPs in GALNT4 in the family-based (IHD) group revealed that the 506I allele showed the same trend towards protecting against ACS but the haplotypic test over the four commonest haplotypes was not significant (P = 0.55). In contrast, the SULT1A1/SULT1A2 gene complex showed suggestive haplotypic association in the family-based study (P = 0.07), with the greatest increase in risk conferred by the SULT1A2 235T allele (P = 0.025). Conclusion We have identified two risk genes for cardiovascular disease, one of whose (GALNT4) effects may be on either platelet or endothelial function through modifications of PSGL1 or other important glycosylated proteins. The role of sulphotransferases (SULT1A1/2) in cardiovascular disease requires further exploration. Further validation of cardiovascular risks conferred by both genes in other populations (including gene copy number variation) is warranted.
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