Platelet glycoprotein Ibalpha Kozak polymorphism is associated with an increased risk of ischemic stroke

Sex Differences in Thrombin Generation in Patients with Acute Ischemic Stroke

Sex differences in stroke exist, including variation in stroke risk and outcome. Differences in thrombin generation may contribute to this variation between females and males. To examine this, we assessed sex differences in thrombin generation between females and males with acute ischemic stroke and the relationship to blood cell gene expression. In 97 patients with acute ischemic stroke, thrombin generation was measured by thrombin generation assay. Blood cell gene expression was measured by microarray. Differences in thrombin generation between sexes were identified and the relationship to blood cell gene expression examined. Genes associated with sex differences in thrombin generation were analyzed by functional pathway analysis. Females and males had similar overall capacity to generate thrombin. The peak thrombin generated in females was 468.8 nM (SD 91.6), comparable to males (479.3nM;SD 90.8; p = 0.58). Lag time, time to peak thrombin, and endogenous thrombin potential were also similar between females and males. While overall thrombin generation was comparable between females and males with stroke, differences in genes that promote this thrombin generation exist. Females with high peak thrombin had an increase in genes that promote thrombosis, and platelet activation. In contrast, males with high peak thrombin had a decrease in genes involved in thrombus degradation. Females and males with acute ischemic stroke have similar capacity to generate thrombin, however, differences may exist in how this thrombin generation is achieved, with females having increased thrombin signaling, and platelet activation, and males having decreased thrombus degradation. This suggests regulatory differences in thrombosis may exist between females and males that may contribute to sex differences in stroke.

Precise genome editing of the Kozak sequence enables bidirectional and quantitative modulation of protein translation to anticipated levels without affecting transcription

None of the existing approaches for regulating gene expression can bidirectionally and quantitatively fine-tune gene expression to desired levels. Here, on the basis of precise manipulations of the Kozak sequence, which has a remarkable influence on translation initiation, we proposed and validated a novel strategy to directly modify the upstream nucleotides of the translation initiation codon of a given gene to flexibly alter the gene translation level by using base editors and prime editors. When the three nucleotides upstream of the translation initiation codon (named KZ3, part of the Kozak sequence), which exhibits the most significant base preference of the Kozak sequence, were selected as the editing region to alter the translation levels of proteins, we confirmed that each of the 64 KZ3 variants had a different translation efficiency, but all had similar transcription levels. Using the ranked KZ3 variants with different translation efficiencies as predictors, base editor- and prime editor-mediated mutations of KZ3 in the local genome could bidirectionally and quantitatively fine-tune gene translation to the anticipated levels without affecting transcription in vitro and in vivo. Notably, this strategy can be extended to the whole Kozak sequence and applied to all protein-coding genes in all eukaryotes.

Reprogramming translation for gene therapy

Translational control plays a fundamental role in the regulation of gene expression in eukaryotes. Modulating translational efficiency allows the cell to fine-tune the expression of genes, spatially control protein localization, and trigger fast responses to environmental stresses. Translational regulation involves mechanisms acting on multiple steps of the protein synthesis pathway: initiation, elongation, and termination. Many cis-acting elements present in the 5' UTR of transcripts can influence translation at the initiation step. Among them, the Kozak sequence impacts translational efficiency by regulating the recognition of the start codon; upstream open reading frames (uORFs) are associated with inhibition of translation of the downstream protein; internal ribosomal entry sites (IRESs) can promote cap-independent translation. CRISPR-Cas technology is a revolutionary gene-editing tool that has also been applied to the regulation of gene expression. In this chapter, we focus on the genome editing approaches developed to modulate the translational efficiency with the aim to find novel therapeutic approaches, in particular acting on the cis-elements, that regulate the initiation of protein synthesis.

Platelet Glycoprotein Ib α-Chain as a Putative Therapeutic Target for Juvenile Idiopathic Arthritis: A Mendelian Randomization Study

Objective

To ascertain the role of platelet glycoprotein Ib α‐chain (GPIbα) plasma protein levels in cardiovascular, autoimmune, and autoinflammatory diseases and whether its effects are mediated by platelet count.

Methods

We performed a two‐sample Mendelian randomization (MR) study, using both a cis‐acting protein quantitative trait locus (cis‐pQTL) and trans‐pQTL near the GP1BA and BRAP genes as instruments. To assess if platelet count mediated the effect, we then performed a two‐step MR study. Putative associations (GPIbα/platelet count/disease) detected by MR analyses were subsequently assessed using multiple‐trait colocalization analyses.

Results

After correction for multiple testing (Bonferroni‐corrected threshold P ≤ 2 × 10⁻³), GPIbα, instrumented by either cis‐pQTL or trans‐pQTL, was causally implicated with an increased risk of oligoarticular and rheumatoid factor (RF)–negative polyarticular juvenile idiopathic arthritis (JIA). These effects of GPIbα appeared to be mediated by platelet count and were supported by strong evidence of colocalization (probability of all 3 traits sharing a common causal variant ≥0.80). GPIbα instrumented by cis‐pQTL did not appear to affect cardiovascular risk, although the GPIbα trans‐pQTL was associated with an increased risk of cardiovascular diseases and autoimmune diseases but a decreased risk of autoinflammatory diseases, suggesting that this trans‐acting instrument operates through other pathways.

Conclusion

The role of platelets in thrombosis is well‐established; however, our findings provide some novel genetic evidence that platelets may be causally implicated in the development of oligoarticular and RF‐negative polyarticular JIA, and indicate that GPIbα may serve as a putative therapeutic target for these JIA subtypes.

von Willebrand Factor and Platelet Glycoprotein Ib: A Thromboinflammatory Axis in Stroke

von Willebrand factor (VWF) and platelets are key mediators of normal hemostasis. At sites of vascular injury, VWF recruits platelets via binding to the platelet receptor glycoprotein Ibα (GPIbα). Over the past decades, it has become clear that many hemostatic factors, including VWF and platelets, are also involved in inflammatory processes, forming intriguing links between hemostasis, thrombosis, and inflammation. The so-called “thrombo-inflammatory” nature of the VWF-platelet axis becomes increasingly recognized in different cardiovascular pathologies, making it a potential therapeutic target to interfere with both thrombosis and inflammation. In this review, we discuss the current evidence for the thrombo-inflammatory activity of VWF with a focus on the VWF-GPIbα axis and discuss its implications in the setting of ischemic stroke.

CD69 Plays a Beneficial Role in Ischemic Stroke by Dampening Endothelial Activation

RATIONALE

CD69 is an immunomodulatory molecule induced during lymphocyte activation. Following stroke, T-lymphocytes upregulate CD69 but its function is unknown.

OBJECTIVE

We investigated whether CD69 was involved in brain damage following an ischemic stroke.

METHODS AND RESULTS

We used adult male mice on the C57BL/6 or BALB/c backgrounds, including wild-type mice and CD69^-/- mice, and CD69^+/+ and CD69^-/- lymphocyte-deficient Rag2^-/- mice, and generated chimeric mice. We induced ischemia by transient or permanent middle cerebral artery occlusion. We measured infarct volume, assessed neurological function, and studied CD69 expression, as well as platelet function, fibrin(ogen) deposition, and VWF (von Willebrand factor) expression in brain vessels and VWF content and activity in plasma, and performed the tail-vein bleeding test and the carotid artery ferric chloride-induced thrombosis model. We also performed primary glial cell cultures and sorted brain CD45^-CD11b^-CD31⁺ endothelial cells for mRNA expression studies. We blocked VWF by intravenous administration of anti-VWF antibodies. CD69^-/- mice showed larger infarct volumes and worse neurological deficits than the wild-type mice after ischemia. This worsening effect was not attributable to lymphocytes or other hematopoietic cells. CD69 deficiency lowered the time to thrombosis in the carotid artery despite platelet function not being affected. Ischemia upregulated Cd69 mRNA expression in brain endothelial cells. CD69-deficiency increased fibrin(ogen) accumulation in the ischemic tissue, and plasma VWF content and activity, and VWF expression in brain vessels. Blocking VWF reduced infarct volume and reverted the detrimental effect of CD69^-/- deficiency.

CONCLUSIONS

CD69 deficiency promotes a prothrombotic phenotype characterized by increased VWF and worse brain damage after ischemic stroke. The results suggest that CD69 acts as a downregulator of endothelial activation.

[The association of hemostasis system genes with the development of ischemic stroke in patients under the age of 50 years]

AIM

To study an influence of polymorphic variants of hemostasis system genes on the risk of ischemic stroke (IS) in patients of the Slavic population under the age of 50 years.

MATERIAL AND METHODS

Ninety-two patients (19 women and 73 men), aged 18-50 years, were examined. The diagnosis of stroke was confirmed by neuroimaging (CT or MRI) in all patients. Polymorphic alleles of GP1BA, F2, F5 were studied by a real-time polymerase chain reaction using the TaqMan technology.

RESULTS AND CONCLUSION

An analysis of the GP1BA -5T/C polymorphism showed that it was associated with IS in young men, lacunar stroke and stroke due to thrombosis of the brachiocephalic arteries. This association was not found in young women. The F5 G1691A polymorphism was associated with lacunar stroke. The F2 G20210A polymorphism was associated with stroke due to thrombosis of the brachiocephalic arteries.

Platelet glycoprotein gene Ia C807T, HPA-3, and Ibα VNTR polymorphisms are associated with increased ischemic stroke risk: Evidence from a comprehensive meta-analysis

Background/aims

Platelet glycoproteins play a crucial role in the initial stage of thrombus formation and may contribute to the pathophysiology of atherosclerosis. Polymorphisms in glycoprotein genes alter the function of the protein, possibly leading to increased risk of ischemic stroke. However, previous genetic association studies that examined the relationship between glycoprotein genes polymorphisms and ischemic stroke have yielded inconsistent results. This study aimed to evaluate the association between glycoprotein genes and ischemic stroke by the application of meta-analysis.

Methods

Relevant studies were identified by an extensive search through databases. The quality of included studies was assessed independently using the Newcastle–Ottawa Scale. Allele and genotype frequencies for each included study were extracted. The odds ratio (OR) with 95% confidence interval (95%CI) was calculated using a random-effects or fixed-effects model. Q statistic was used to evaluate homogeneity, and a meta-regression model was used to explore the study-level variables and to describe the heterogeneity in included studies. Egger’s test and funnel plot were used to assess publication bias.

Results

A total of 60 studies (9 polymorphisms) were included and identified in the current meta-analysis. The Newcastle–Ottawa Scale scores ranged from 7 to 9 except for two studies with Newcastle–Ottawa Scale scores of 6. The T allele or TT genotype of the glycoprotein Ia C807T polymorphism were associated with an increased susceptibility to ischemic stroke in combined population (807T allele: OR, 95%CI: 1.24, 1.03–1.50, p = 0.02) or Asian populations (807T allele: OR, 95%CI: 1.31, 1.10–1.54, p = 0.002 and 807TT genotype: OR, 95%CI: 1.53, 1.13–2.08, p = 0.006, respectively), and the Ser allele of HPA-3 was associated with increased risk of ischemic stroke in combined population or in Asians (OR, 95%CI: 1.21, 1.04–1.40, p = 0.01 or 1.54, 1.18–2.01, p = 0.001). Of note, the Ser/Ser genotype was more common in Asians (OR, 95%CI: 2.09, 1.40–3.13, p < 0.001). For glycoprotein Ibα variable number tandem repeat, only B allele showed a mild significant association with ischemic stroke risk in combined population or in Caucasians (OR, 95%CI: 2.17, 1.04–4.55, p = 0.04 or 1.79, 1.02–3.13, p = 0.04). There was no significant association between HPA-1, HPA-2, HPA-4, HPA-5, glycoprotein Ibα-5 T/C as well as Ia G873A polymorphisms and increased risk of ischemic stroke.

Conclusions

We found that glycoprotein Ia C807T T allele or the TT genotype, the Ser-allele of HPA-3 and B allele of glycoprotein Ibα variable number tandem repeat polymorphisms were associated with increased risk for ischemic stroke. Future studies with larger sample sizes will be necessary to confirm the results. In addition, analyses of ischemic stroke subtypes and gene–gene and gene–environment interactions are warranted.

Common genetic variants in platelet surface receptors and its association with ischemic stroke

Ischemic stroke has been named one of the leading causes of death worldwide. Whereas numerous biological mechanisms and molecules were found to be associated with stroke, platelets are particularly contributive to its pathogenesis. Recent data indicate considerable variability in platelet phenotype which accounts for differences in platelet surface receptor function, count and reactivity. These features collectively influence both the events leading to a disease and effectiveness of antiplatelet therapies. Consequently, genetic variants predisposing to cerebrovascular diseases can be sequenced using a wide array of techniques and become a useful tool in clinical setting. In this review, we provide an outline of common platelet polymorphisms that impose risk on ischemic stroke development and should be evaluated as targets to improve treatment. As study results are often inconsistent, partly due to differences in demographic characteristics between study populations and the fact that the functional impact of these variants has been relatively small, we conclude that both rare, low-frequency and common variants might account for genetic contribution on abnormal platelet response to antiplatelet drugs.

[The molecular mechanisms of platelets activation in patients with cerebrovascular disease]

Cerebrovascular disease is a main cause of mortality and one of the big medical problems. After the vascular wall's damage the endothelial cells secrete the von Willebrand factor which then connects with its platelet's receptor GP Ib-V-IX. There are two polymorphisms Thr145Met and T(-5)C of the GP Iba gene associated with arterial thrombosis development. Also the difference in platelets' genes expressions was shown in patients with various clinical course of ischemic heart disease. The aim of this study was to investigate the role of platelet's receptor for von Willebrand factor in platelets' activation in patients with cerebrovascular disease. 123 patients with cerebrovascular disease and 97 healthy donors were included into the study. We analyzed the level of receptor for von Willebrand factor on platelet's membrane by flow cytometry, Thr145Met and T(-5)C GP Iba polymorphiams by PCR-RFLP, the GP Iba gene expression by RT-PCR and ADP-induced platelet aggregation by Born method. We have shown: 1) the 145Met GP Iba allele prevalence in patients with atherotrombotic stroke development due to macroangiopathy; 2) the pre-mRNA transform into the mature mRNA in activated platelets and this process may be stopped by the antiplatelet therapy by acetylsalicylic acid.

A novel snake venom-derived GPIb antagonist, anfibatide, protects mice from acute experimental ischaemic stroke and reperfusion injury

BACKGROUND AND PURPOSE

Ischaemic stroke is a serious disease with limited therapy options. Glycoprotein (GP)Ib binding to von Willebrand factor (vWF) exposed at vascular injury initiates platelet adhesion and contributes to platelet aggregation. GPIb has been suggested as an effective target for antithrombotic therapy in stroke. Anfibatide is a GPIb antagonist derived from snake venom and we investigated its protective effect on experimental brain ischaemia in mice.

EXPERIMENTAL APPROACH

Focal cerebral ischaemia was induced by 90 min of transient middle cerebral artery occlusion (MCAO). These mice were then treated with anfibatide (4, 2, 1 μg·kg(-1) ), injected i.v., after 90 min of MCAO, followed by 1 h of reperfusion. Tirofiban, a GPIIb/IIIα antagonist, was used as a positive control.

KEY RESULTS

Twenty-four hours after MCAO, anfibatide-treated mice showed significantly improved ischaemic lesions in a dose-dependent manner. The mice had smaller infarct volumes, less severe neurological deficits and histopathology of cerebrum tissues compared with the untreated MCAO mice. Moreover, anfibatide decreased the amount of GPIbα, vWF and accumulation of fibrin(ogen) in the vasculature of the ischaemic hemisphere. Tirofiban had similar effects on infarct size and fibrin(ogen) deposition compared with the MCAO group. Importantly, the anfibatide-treated mice showed a lower incidence of intracerebral haemorrhage and shorter tail bleeding time compared with the tirofiban-treated mice.

CONCLUSIONS AND IMPLICATIONS

Our data indicate anfibatide is a safe GPIb antagonist that exerts a protective effect on cerebral ischaemia and reperfusion injury. Anfibatide is a promising candidate that could be beneficial for the treatment of ischaemic stroke.

Case-control study of platelet glycoprotein receptor Ib and IIb/IIIa expression in patients with acute and chronic cerebrovascular disease

Background

Animal models have been instrumental in defining thrombus formation, including the role of platelet surface glycoprotein (GP) receptors, in acute ischemic stroke (AIS). However, the involvement of GP receptors in human ischemic stroke pathophysiology and their utility as biomarkers for ischemic stroke risk and severity requires elucidation.

Aims

To determine whether platelet GPIb and GPIIb/IIIa receptors are differentially expressed in patients with AIS and chronic cerebrovascular disease (CCD) compared with healthy volunteers (HV) and to identify predictors of GPIb and GPIIb/IIIa expression.

Methods

This was a case—control study of 116 patients with AIS or transient ischemic attack (TIA), 117 patients with CCD, and 104 HV who were enrolled at our University hospital from 2010 to 2013. Blood sampling was performed once in the CCD and HV groups, and at several time points in patients with AIS or TIA. Linear regression and analysis of variance were used to analyze correlations between platelet GPIb and GPIIb/IIIa receptor numbers and demographic and clinical parameters.

Results

GPIb and GPIIb/IIIa receptor numbers did not significantly differ between the AIS, CCD, and HV groups. GPIb receptor expression level correlated significantly with the magnitude of GPIIb/IIIa receptor expression and the neutrophil count. In contrast, GPIIb/IIIa receptor numbers were not associated with peripheral immune-cell sub-population counts. C-reactive protein was an independent predictor of GPIIb/IIIa (not GPIb) receptor numbers.

Conclusions

Platelet GPIb and GPIIb/IIIa receptor numbers did not distinguish between patient or control groups in this study, negating their potential use as a biomarker for predicting stroke risk.

Impact of platelet phenotype on myocardial infarction

In acute myocardial infarction patients the injured vascular wall triggers thrombus formation in the damage site. Fibrin fibers and blood cellular elements are the major components of thrombus formed in acute occlusion of coronary arteries. It has been established that the initial thrombus is primarily composed of activated platelets rapidly stabilized by fibrin fibers. This review highlights the role of platelet membrane phenotype in pathophysiology of myocardial infarction. Here, we regard platelet phenotype as quantitative and qualitative parameters of the plasma membrane outer surface, which are crucial for platelet participation in blood coagulation, development of local inflammation and tissue repair.

Platelet Reactivity in Patients With Stroke and Hyperlipidemia, GPIbα Assessment

The aim of this study was to assess platelet reactivity in patients after ischemic stroke and to investigate the influence of hyperlipidemia (HL) on platelet activity markers. A total of 41 patients after ischemic stroke were divided into the following 2 groups: patients with HL and patients with normolipidemia. Expression of CD42b on resting, thrombin-activated blood platelets, and fibrinogen level was assessed. The CD42b-positive platelets were analyzed using the flow cytometer, anti-CD61, and anti-CD42b monoclonal antibodies. The results confirmed increased platelet reactivity to thrombin in all patients after ischemic stroke manifested by significantly lower CD42b expression and percentage of CD42b(+) platelets after activation by thrombin. The influence of HL on the expression of CD42b on resting and thrombin-activated platelets was not found. However, increased level of fibrinogen but no influence of HL on fibrinogen concentration was observed in patients after ischemic stroke. Increased susceptibility to platelet agonists was found in patients after ischemic stroke in the convalescent phase.

Genetic dissection of platelet function in health and disease using systems biology

Technological advances in protein and genetic analysis have altered the means by which platelet disorders can be characterized and studied in health and disease. When integrated into a single analytical framework, these collective technologies are referred to as systems biology, a unified approach that links platelet function with genomic/proteomic studies to provide insight into the role of platelets in broad human disorders such as cardiovascular and cerebrovascular disease. This article reviews the historical progression of these applied technologies to analyze platelet function, and demonstrates how these approaches can be systematically developed to provide new insights into platelet biomarker discovery.

Platelet systems biology using integrated genetic and proteomic platforms

Platelets retain megakaryocyte-derived mRNA, an abundant and diverse array of miRNAs, and have evolved unique adaptive signals for maintenance of genetic and protein diversity. Quiescent platelets generally display minimal translational activity, although maximally-activated platelets retain the capacity for protein synthesis. Progressive data using multiple platelet activation models clearly demonstrate that platelet responses to the majority (if not all) agonists are highly variable within the population, demonstrating considerable heritability in siblings, twins, and families with premature coronary artery disease. Research from our laboratory has adapted global profiling strategies to close the knowledge gap currently existing between genetic variability and platelet phenotypic responsiveness. We have applied iterative algorithms for genetic biomarker discovery and class prediction models of platelet phenotypes, with the goal of systematically analyzing integrated mRNA/miRNA/proteomic datasets for identification of regulatory networks that define phenotypic variability in platelet responses. This approach has the potential to define platelet genetic biomarkers predictive of thrombohemorrhagic outcomes in both normal and widely disparate clinical conditions.

Next-generation antithrombotics in ischemic stroke: preclinical perspective on 'bleeding-free antithrombosis'

The present antithrombotic drugs used to treat or prevent ischemic stroke have significant limitations: either they show only moderate efficacy (platelet inhibitors), or they significantly increase the risk for hemorrhages (thrombolytics, anticoagulants). Although most strokes are caused by thrombotic or embolic vessel occlusions, the pathophysiological role of platelets and coagulation is largely unclear. The introduction of novel transgenic mouse models and specific coagulation inhibitors facilitated a detailed analysis of molecular pathways mediating thrombus formation in models of acute ischemic stroke. Prevention of early platelet adhesion to the damaged vessel wall by blocking platelet surface receptors glycoprotein Ib alpha (GPIbα) or glycoprotein VI (GPVI) protects from stroke without provoking bleeding complications. In addition, downstream signaling of GPIbα and GPVI has a key role in platelet calcium homeostasis and activation. Finally, the intrinsic coagulation cascade, activated by coagulation factor XII (FXII), has only recently been identified as another important mediator of thrombosis in cerebrovascular disease, thereby disproving established concepts. This review summarizes the latest insights into the pathophysiology of thrombus formation in the ischemic brain. Potential clinical merits of novel platelet inhibitors and anticoagulants as powerful and safe tools to combat ischemic stroke are discussed.

Glycoprotein Ib-alpha Kozak polymorphism in ischemic stroke

BACKGROUND

Recently, a T/C polymorphism in the Kozak sequence of glycoprotein Ib-alpha (GPIb-alpha) gene at position -5 from the initiator ATG codons, has been identified. The presence of -5C allele increases the surface expression of GPIb-IX-V complex in a gene dosage-dependent manner. It has been suggested that higher receptor levels might increase the adhesiveness of the platelets and confer risk for thrombosis. In this study, we aimed to investigate the association between GPIb-alpha Kozak polymorphism and ischemic stroke.

METHODS

We prospectively and consecutively recruited 231 patients (118 women and 113 men; mean age: 65 ± 14.2 years) with first ever ischemic stroke admitted to Istanbul Faculty of Medicine Edip Aktin Stroke Unit between April 2007 and June 2009. Demographic features, risk factors, clinical, and etiological subtypes were analyzed. As the control group, 220 unrelated healthy subjects were included.

RESULTS

We found that 156 patients had TT, 70 patients had TC, and 5 patients had CC genotype. At least one copy of C allele carriers were overrepresented in the ischemic stroke group (32.5%) compared with controls (23%) [odds ratio (OR): 0.61; 95% confidence interval (CI): 0.40-0.93; P = 0.03]. Among etiologic subtypes, the distribution of C allele carriers was the highest in patients with undetermined etiology (45%) and it was significantly higher than controls (OR: 0.36; 95% CI: 0.20-0.65; P = 0.0008). In other subtypes, there was no association with Kozak -5C allele.

CONCLUSION

In conclusion, these encouraging preliminary results show that GPIb-alpha T/C polymorphism might increase the risk of ischemic stroke, especially in those with undetermined etiology.

Platelet receptor gain-of-function single nucleotide polymorphisms in carotid and vertebral stenosis patients

The role of platelet receptor gain-of-function single nucleotide polymorphisms (SNP) in cardiovascular disease is controversial. We hypothesised that certain SNPs may accelerate the development of carotid artery stenosis. The intronic PAR-1 receptor intervening sequence-14 A/T (IVSn-14 A/T) polymorphism and three additional platelet receptor polymorphisms, i.e. GPIa (807C/T), GPIbα (5T/C) and HPA-1a/HPA-1b (Pl (A1/A2)) of GPIIIa were studied. The interaction of SNPs with conventional risk factors including male gender, hypertension, high cholesterol, diabetes, advanced age and smoking were investigated. The hypothesis was tested in 114 well-characterised patients with symptomatic carotid or vertebral stenosis from the British CAVATAS population and compared the results with 97 unrelated controls. The allele frequency of the platelet gain-of-function SNP was not significantly different in the CAVATAS population as compared to controls (PAR-1A/T (P = 0.13), GPIa C/T (P = 0.25), GPIIIa HPA-1a/HPA-1b (PlA1/A2) (P = 0.66) and GPIb T/C (P = 0.20)). In the subgroup of smokers, however, the prothrombotic GPIbα C mutated allele was found in a significantly higher frequency in the patient as compared to the control group (P = 0.04). Contrary to the primary hypothesis, the PAR-1A/T SNP as well as the other SNPs tested were not over- or underrepresented in the CAVATAS population. However, a significantly increased prevalence of GPIb-α (5C/T) was found in the subgroup of smokers and may represent an important cofactor in this patient group of our hypothesis-generating study.

Platelet glycoprotein Ibα is an important mediator of ischemic stroke in mice

BACKGROUND

Platelets play an important role in ischemic stroke. GPIbα is a major platelet receptor that is critical for platelet adhesion to exposed subendothelial matrix components at sites of vascular damage.

METHODS

In this study, we used transgenic mice in which the extracellular part of GPIbα is replaced by human interleukin 4-receptor (GPIbα/IL4Rα). We observed normal brain vasculature in these mice. We compared infarct size in GPIbα/IL4Rα and wild-type (WT) mice 23 hours after 1-hour transient middle cerebral artery occlusion (tMCAO). In addition, the functional outcome was evaluated using a modified Bederson score.

RESULTS

We found a significantly smaller infarct size in GPIbα/IL4Rα mice compared to WT mice (38.0 ± 6.5 mm3 vs. 74.2 ± 8.6 mm3, p < 0.001). The decrease in infarct size was functionally relevant as indicated by a significantly better functional Bederson score in GPIbα/IL4Rα mice compared to WT animals (1.3 ± 0.4 vs. 2.7 ± 0.3, p < 0.05).

CONCLUSIONS

Our data illustrate and further confirm the important role of platelet GPIbα in ischemic stroke, suggesting that targeted inhibition of this receptor may open new avenues in stroke treatment.

Genetic regulation of platelet receptor expression and function: application in clinical practice and drug development

Understanding genetic contributions to platelet function could have profound clinical ramifications for personalizing platelet-directed pharmacotherapy, by providing insight into the risks and possible benefits associated with specific genotypes. This article represents an integrated summary of presentations related to genetic regulation of platelet receptor expression and function given at the Fifth Annual Platelet Colloquium in January 2010. It is supplemented with additional highlights from the literature covering (1) approaches to determining and evidence for the associations of genetic variants with platelet hypo- and hyperresponsive phenotypes, (2) the ramifications of these polymorphisms with regard to clinical responses to antiplatelet therapies, and (3) the role of platelet function/genetic testing in guiding antiplatelet therapy.

Impact of COX-2 rs5275 and rs20417 and GPIIIa rs5918 polymorphisms on 90-day ischemic stroke functional outcome: a novel finding

We hypothesized that polymorphisms in 5 genes related to thrombolytic and inflammation pathways will independently influence occurrence, severity, and 3-month functional outcome in patients with ischemic stroke. This was a case-control design with ischemic stroke patients recruited from 4 public hospitals (n = 640) and community controls (n = 627). Baseline clinical data were collected, and follow-up telephone interviews were conducted with 520 patients at 90 days postevent to determine stroke outcome using the Barthel Index (BI), Modified Rankin Scale (mRS) and Glasgow Outcome Scale (GOS). Blood samples were collected and genotyped for polymorphisms in platelet glycoprotein Ibα (GPIbα) rs224309 and rs6065, glycoprotein IIIa (GPIIIa) rs5918, tissue plasminogen activator (tPA) rs63020761, plasminogen activating inhibitor (PAI-1) rs72578597, and cyclooxygenase-2 (COX-2) rs5275 and rs20417. COX-2 polymorphism rs5275 demonstrated a significant association with poststroke mRS, with a dominant genetic model demonstrating the best fit (CC + TC) (adjusted odds ratio [aOR] = 1.61; P = .026). The COX-2 rs20417 C allele showed an association with GOS (aOR = 1.95; P = .012), and again a dominant genetic model demonstrated the best fit (CC + GC). GPIIIa rs5918 (A1A2) was associated with poststroke BI, with a dominant model demonstrating the best fit (A1A2 + A2A2) (aOR = 0.56; P = .014). There was a significant association between stroke severity and tPA rs63020761 TT allele (aOR = 1.96; 95% CI = 1.03-3.72; P = .040). This is the first study to demonstrate associations between stroke functional outcome and 2 COX-2 variants (rs20417 and rs5275) and a GPIIIa variant (rs5918).

Class prediction models of thrombocytosis using genetic biomarkers

Criteria for distinguishing among etiologies of thrombocytosis are limited in their capacity to delineate clonal (essential thrombocythemia [ET]) from nonclonal (reactive thrombocytosis [RT]) etiologies. We studied platelet transcript profiles of 126 subjects (48 controls, 38 RT, 40 ET [24 contained the JAK2V(617)F mutation]) to identify transcript subsets that segregated phenotypes. Cross-platform consistency was validated using quantitative real-time polymerase chain reaction (RT-PCR). Class prediction algorithms were developed to assign phenotypic class between the thrombocytosis cohorts, and by JAK2 genotype. Sex differences were rare in normal and ET cohorts (< 1% of genes) but were male-skewed for approximately 3% of RT genes. An 11-biomarker gene subset using the microarray data discriminated among the 3 cohorts with 86.3% accuracy, with 93.6% accuracy in 2-way class prediction (ET vs RT). Subsequent quantitative RT-PCR analysis established that these biomarkers were 87.1% accurate in prospective classification of a new cohort. A 4-biomarker gene subset predicted JAK2 wild-type ET in more than 85% patient samples using either microarray or RT-PCR profiling, with lower predictive capacity in JAK2V(617)F mutant ET patients. These results establish that distinct genetic biomarker subsets can predict thrombocytosis class using routine phlebotomy.

Human platelet alloantigens (HPA) 1, HPA2, HPA3, HPA4, and HPA5 polymorphisms in sickle cell anemia patients with vaso-occlusive crisis

OBJECTIVES

Vaso-occlusive crisis (VOC) is a significant cause of morbidity and mortality in sickle cell anemia (SCA) patients. Insofar as polymorphism in human platelet alloantigen (HPA) exhibit a prothrombotic nature, we hypothesized that specific HPA polymorphic variants are associated with VOC. We investigated the distribution of HPA1, HPA2, HPA3, HPA4, and HPA5 alleles genotypes among VOC and non-VOC control SCA patients.

PATIENTS/METHODS

This was a case-control study. Study subjects comprised SCA patients with (VOC group; n = 127) or without (Steady-state group; n = 130) VOC events. HPA genotyping was done by PCR-SSP.

RESULTS

Significantly higher frequencies of HPA-2b, HPA-3b, and HPA-5b alleles, and marked enrichment of HPA-3b/3b, HPA-5a/5b, and HPA-5b/5b genotypes, were seen in VOC than in control SCA patients. Taking homozygous wild-type genotypes as reference, univariate analysis identified HPA-3a/3b, HPA-3b/3b, and HPA-5b/5b to be associated with VOC. Multivariate analysis confirmed the independent association of only HPA-3a/3b and HPA-3b/3b genotypes with VOC. HPA-3 genotypes were significantly correlated with VOC frequency, type, and medication, and requirement for hospitalization. While both HPA 3a/3b (P = 0.002; OR = 2.94; 95% CI = 1.49-5.77) and 3b/3b (P = 0.006; OR = 3.16; 95% CI = 1.40-7.17) genotypes were associated with need for hospitalization, only HPA-3b/3b was associated with VOC frequency, type (localized vs. generalized), and medication (narcotics vs. NSAIDs).

CONCLUSION

This confirms the association of HPA polymorphisms with SCA VOC, of which HPA-3 appears to be independent genetic risk factors for SCA VOC.

Deficiency of von Willebrand factor protects mice from ischemic stroke

We recently demonstrated that blockade of the platelet adhesion receptor glycoprotein (GP) Ibalpha protects mice from ischemic stroke. Although von Willebrand factor (VWF) is the major ligand for GPIbalpha, GPIbalpha can engage other counterreceptors on endothelial cells, platelets, and leukocytes (eg, Mac-1 or P-selectin) potentially involved in stroke outcome. To further analyze whether VWF is of particular relevance for stroke development, VWF(-/-) mice underwent 60 minutes of middle cerebral artery occlusion. After 24 hours, VWF(-/-) mice had significantly smaller infarctions (P< .05) and less severe neurologic deficits (P< .01) compared with controls. This effect was sustained after 1 week, and intracranial bleeding was absent in VWF(-/-) mice as revealed by serial magnetic resonance imaging. Hydrodynamic injection of a VWF-encoding plasmid restored the susceptibility for stroke in VWF(-/-) mice. This study indicates that VWF is critically involved in cerebral ischemia. Hence, targeted inhibition of the GPIbalpha-VWF pathway might become a promising therapeutic option.

Polymorphisms of the human platelet alloantigens HPA-1, HPA-2, HPA-3, and HPA-4 in ischemic stroke

Polymorphism in human platelet antigen (HPA)-1 and HPA-3 (GPIIb/IIIa), HPA-2 (GPIb/IX), HPA-4 (GPIIIa), and HPA-5 (GPIa/IIa) was investigated in 329 stroke patients and 444 matched control subjects. HPA genotyping was done by PCR-SSP method. Lower HPA-1a (P < 0.001) and higher HPA-1b (P < 0.001) allele frequencies were seen in patients than control subjects, and homozygosity for HPA-1b (P < 0.001) alleles was more prevalent in stroke cases than in controls. The allele and genotype distributions of the other HPA polymorphic variants were similar between cases and controls. Select HPA combined genotypes comprising the 2121 (Pc = 0.008) and 2221 (Pc = 0.018) genotypes, which were positively associated, and the 1111 (Pc < 0.001), which was negatively associated with stroke, thereby conferred a disease susceptibility and protective nature to these genotype combinations. Multivariate analysis confirmed the negative association of the 1111 (P < 0.001) and the positive association of the 2121 (P = 0.017) combined genotypes with stroke, after adjustment for a number of covariates. This is the first evidence demonstrating differential association of the common 4 HPA gene variants and specific HPA genotype combinations with stroke.

Polymorphisms in platelet glycoprotein 1balpha and factor VII and risk of ischemic stroke: a meta-analysis

BACKGROUND AND PURPOSE

Platelets and components of the coagulation cascade are known to be instrumental in the pathogenesis of arterial occlusive disorders. The aim of this meta-analysis is to test the hypothesis that genetic variation in the platelet glycoprotein 1balpha and Factor VII genes influence the occurrence of ischemic stroke. All genetic association studies that examined the R353Q (rs6046) polymorphism of the Factor VII gene and 2 polymorphisms of the platelet glycoprotein (1balpha) gene (Thr/Met rs6065 and Kozak sequence -5 C/T rs2243093) in relation to ischemic stroke were examined.

METHODS

Electronic databases Embase, Medline, and HuGEnet were searched for all years up until June 2006 for all studies that evaluated any of these candidate genes and stroke.

RESULTS

Pooled ORs were calculated with 95% CIs using both fixed and random effects models. Meta-analysis for Factor VII (R353Q) did not detect any effect on ischemic stroke risk. Further estimation resulted in pooled OR(1) QQ versus RR=0.9 (95% CI: 0.4 to 1.9) and pooled OR(2) for RQ versus RR=0.9 (95% CI: 0.6 to 1.4). These results were robust and homogeneous. Pooling ORs for the platelet glycoprotein 1balpha Kozak variant -5 T/C polymorphism showed extreme heterogeneity with differing effect directions across studies. Fisher's method of pooling was therefore used to calculate a combined probability value, which was highly significant (P<0.001). The pooled OR for platelet glycoprotein 1balpha Met/Met v Thr/Thr was 1.0 to 2.0, depending on the sensitivity analyses, and for Thr/Met versus Thr/Thr, the pooled OR was between 1.3 and 1.4. These results were consistent, reasonably robust, and implied a dominant genetic effect.

CONCLUSIONS

This analysis provides strong evidence that the Factor VII R353Q gene polymorphism is not associated with ischemic stroke, that the Thr/Met polymorphism of GP1balpha is associated with ischemic stroke in a dominant genetic model, and that the Kozak sequence polymorphism of GP1balpha may be close to another causative locus that is associated with ischemic stroke.

Platelet glycoprotein Ibalpha gene polymorphism and massive or submassive pulmonary embolism

OBJECTIVE

The -5T/C polymorphism in the Kozak sequence of glycoprotein Ibalpha, a component of the platelet glycoprotein Ib-IX-V receptor complex, is associated with an increase in this receptor density on the surface of the platelet. This study was designed to investigate the effect of platelet glycoprotein Ibalpha Kozak polymorphism on the clinical presentation of the patients with acute pulmonary embolism.

METHODS

Forty-two patients with pulmonary embolism were genotyped for Kozak polymorphism of the glycoprotein Ibalpha by polymerase chain reaction/restriction fragment length polymorphism.

RESULTS

Carriers of the -5T/C polymorphism of glycoprotein Ibalpha were significantly over-represented in the patient group with clinically massive or submassive pulmonary embolism (odds ratio 5.5, 95% confidence interval 1.4 to 22.2, P = 0.023). Also the association between this polymorphism and massive or submassive pulmonary embolism still existed even after being adjusted for conventional risk factors.

CONCLUSION

The -5T/C polymorphism in the Kozak sequence of glycoprotein Ibalpha may present as a risk factor for clinical manifestation of pulmonary embolism in which clot burden plays an important role.

Prognostic modelling in ischaemic stroke study, additional value of genetic characteristics. Rationale and design

BACKGROUND AND AIM

The prediction of prognosis after cerebral infarction might be improved by genetic information. The aim of the Prognostic Modelling in Ischaemic Stroke study is to develop 2 different prognostic models on the basis of traditional vascular risk factors and genetic information in patients who have suffered from cerebral ischaemia of arterial origin, 1 concerning new ischaemic and the other new haemorrhagic events.

METHODS

Polymorphisms and haplotypes describing the haemostatic system and those that influence antithrombotic drug activity will be identified in a cohort of 1,200 patients with cerebral ischaemia of arterial origin who will be followed up for a mean of 6.5 years. In total, 312 ischaemic and 78 haemorrhagic events are anticipated. With a prevalence of a genetic characteristic of 10% a relative risk of 1.4 (95% confidence interval = 1.1-1.8) for ischaemic events and of 1.8 (95% confidence interval = 1.0-3.2) for haemorrhagic events can be estimated with sufficient precision. To determine the additional prognostic value of genetic characteristics the area under the ROC curves of 2 separate models will be compared: 1 based on non-genetic risk factors only, the other also including genetic data.

Platelet glycoprotein VI-related clinical defects

Human patients with defects associated with the platelet collagen receptor, glycoprotein (GP)VI, are rare and usually described as having a mild bleeding disorder. However, here we review clinical profiles of patients with familial or acquired GPVI defects, revealing the bleeding defect is often severe and associated with immune dysfunction. GPVI is a member of the immunoreceptor family, and co-expressed on platelets with Fc receptor gamma-chain (FcRgamma). Ligand binding to GPVI leads to activation of platelet integrins, in particular alpha(IIb)beta(3) that mediates platelet aggregation; and activation of endogenous platelet metalloproteinases resulting in ectodomain shedding and release of a soluble GPVI fragment. Increasing evidence supports the functional importance of GPVI/FcRgamma in thrombus formation at arterial shear rates, and expression levels of platelet GPVI may be a marker of thrombotic risk. Over the past 20 years, patients have been reported with GPVI-related defects involving: (i) an acquired deficiency, resulting from (a) anti-GPVI autoantibodies or (b) other causes; or (ii) a congenital deficiency, where (c) GPVI is not expressed or (d) is expressed in a dysfunctional form with defective signalling to alpha(IIb)beta(3). Clinical consequences of GPVI-related defects may be uniquely informative about the role of platelet GPVI in health and disease.

Platelet genomics and the risk of atherothrombosis

Platelets play a pivotal role in atherothrombosis after coronary artery plaque rupture. The extent of response of platelets to such an event varies between individuals. This variation is for a large extent genetically controlled. A comprehensive study of sequence variation that modifies the platelet response to agonists is, however, lacking. We set out to discover the regulatory nodes of platelet function by an integrated systems biology approach. The high density genotyping of 110 genes in a cohort of more than 500 individuals, in whom the platelet response to ADP and collagen-related peptide was determined, allowed the robust definition of the first set of regulatory nodes. Microarray and proteomics studies on platelets from individuals with a so-called 'extreme end' response phenotype provided further insight into key regulators of platelet function. In addition, the completion of the HapMap project allows the comprehensive surveying of the genome for sequence variation by the testing of a limited number of single nucleotide polymorphisms (SNPs). With the advent of high density (i.e. 500,000 SNPs) genotyping arrays large number of case and control samples can be tested at an affordable cost. The recently completed Wellcome Trust Case Control Consortium (WTCCC) study has allowed us to address the question of whether common sequence variation confers risk for seven common diseases, one being myocardial infarction. The results of the WTCCC genome-wide association study and issues of case-control study design, particularly the selection of suitable controls, will be reviewed. In conclusion the integration of the results from the platelet systems biology study with those of the WTCCC project enhances our understanding of the mechanisms underlying common conditions such as atherothrombosis and provides pointers to novel cellular mechanisms and pathways.

The BC genotype of the VNTR polymorphism of platelet glycoprotein Ibalpha is overrepresented in patients with recurrent stroke regardless of aspirin therapy

BACKGROUND

The contribution of genetic factors to aspirin treatment failure (ATF) for secondary prevention is not settled in patients with ischemic stroke.

METHODS

We assessed the polymorphisms VNTR (A, B, C, D) of glycoprotein (GP) Ibalpha, 807C/T of GP Ia/IIa, and Pl(A1/A2) of GP IIb/IIIa, and the 5-year incidence of major recurrent events in 82 stroke patients with no major sources of cardioembolism (mean age 70, SD 9.0 years; female gender 23%). Using a structured interview, all participants confirmed good compliance with aspirin (100-300 mg/day) for secondary prevention. Demographics and atherothrombotic risk factors assessed included diabetes, hypertension, dyslipemia, smoking, and coronary heart disease.

RESULTS

Thirty-one stroke patients had one recurrent stroke or myocardial infarction within 33 (7-48) months of aspirin onset, while 51 patients demonstrated an uneventful clinical course. Female gender (p < 0.05), diabetes (p < 0.05), dyslipemia (p < 0.05), and the BC genotype of VNTR (25.8 vs. 7.8%, p < 0.05) were more prevalent in patients in whom aspirin failed to prevent clinical events than in those in whom it did not. The BC genotype of VNTR was the only factor that remained associated with ATF in an age-, sex-, and risk factor-adjusted logistic regression analysis (OR 9.6, 95% CI 1.5-61.0).

CONCLUSION

The BC genotype of the VNTR polymorphism of GP Ibalpha is an independent predictor of recurrent events in stroke patients treated with aspirin. This finding suggests that high shear-induced platelet activation mediated by GP Ibalpha and von Willebrand factor is an important contributor to ATF in the stroke population.

Targeting Platelets in Acute Experimental Stroke

Background— Ischemic stroke is a frequent and serious disease with limited treatment options. Platelets can adhere to hypoxic cerebral endothelial cells by binding of their glycoprotein (GP) Ib receptor to von Willebrand factor. Exposure of subendothelial matrix proteins further facilitates firm attachment of platelets to the vessel wall by binding of collagen to their GPVI receptor. In the present study, we addressed the pathogenic role of GPIb, GPVI, and the aggregation receptor GPIIb/IIIa in experimental stroke in mice.

Methods and Results— Complete blockade of GPIbα was achieved by intravenous injection of 100 μg Fab fragments of the monoclonal antibody p0p/B to mice undergoing 1 hour of transient middle cerebral artery occlusion. At 24 hours after transient middle cerebral artery occlusion, cerebral infarct volumes were assessed by 2,3,5-triphenyltetrazolium chloride staining. In mice treated with anti-GPIbα Fab 1 hour before middle cerebral artery occlusion, ischemic lesions were reduced to ≈40% compared with controls (28.5±12.7 versus 73.9±17.4 mm 3 , respectively; P <0.001). Application of anti-GPIbα Fab 1 hour after middle cerebral artery occlusion likewise reduced brain infarct volumes (24.5±7.7 mm 3 ; P <0.001) and improved the neurological status. Similarly, depletion of GPVI significantly diminished the infarct volume but to a lesser extent (49.4±19.1 mm 3 ; P <0.05). Importantly, the disruption of early steps of platelet activation was not accompanied by an increase in bleeding complications as revealed by serial magnetic resonance imaging. In contrast, blockade of the final common pathway of platelet aggregation with anti-GPIIb/IIIa F(ab) 2 fragments had no positive effect on stroke size and functional outcome but increased the incidence of intracerebral hemorrhage and mortality after transient middle cerebral artery occlusion in a dose-dependent manner.

Conclusions— Our data indicate that the selective blockade of key signaling pathways of platelet adhesion and aggregation has a different impact on stroke outcome and bleeding complications. Inhibition of early steps of platelet adhesion to the ischemic endothelium and the subendothelial matrix may offer a novel and safe treatment strategy in acute stroke.

Association between platelet glycoprotein Ib-alpha and myocardial infarction: results of a pilot study performed in male and female patients from Sicily

Myocardial infarction (AMI) is a complex multifactorial disorder. Platelet adhesion and thrombosis are pivotal events in the development of atherosclerotic lesions. Occlusive thrombus is almost exclusively initiated by plaque rupture and adhesion of platelets to subendothelial von Willebrand factor (vWf) by its specific platelet receptor, the alpha-chain of glycoprotein (GP) Ib-IX-V complex of the human platelet-specific antigens (HPA). Two polymorphisms have been reported in the sequence of GPIb-alpha. The first, a C/T transition at nucleotide 1018 results in an amino acid dimorphism (Thr/Met) at residue 145 of GPIb-alpha, which is located within the vWF-binding domain of the receptor. The second is a T/C polymorphism in the Kozak sequence at position -5 from the initiator ATG. This affects the receptor density on the platelet surface. We assessed 1018 C/T and -5 T/C Kozak polymorphisms to see whether they are associated with AMI in homogeneous populations of Sicilian patients with AMI. To this end, we have analyzed the distribution of 1018 C/T and -5 T/C Kozak polymorphisms in 105 young Sicilian patients (<46 years) and 110 healthy age-related controls, by PCR-SSP and PCR-RFLP. Our results demonstrate no significant differences in the frequency of 1018 C/T and -5 T/C Kozak polymorphism between patients with AMI and controls. Stratifying by gender, there is no difference between male and female patients and control data. Thus, our results indicate that the HPA-2 polymorphisms are not associated with an increased risk for AMI at early onset (< 46 years) both in men and in women.

Platelet functional implications of glycoprotein Ibalpha polymorphisms in African Americans

The platelet glycoprotein Ibalpha is crucial in the binding of platelets to Von Willebrand Factor within areas of high stress. A single nucleotide polymorphism of GP Ibalpha gives rise to the Ko(a) (HPA-2b) and the -5C Kozak polymorphism. The presence of these polymorphisms has been associated with an increased risk for atherothrombotic disease. The Ko(a) polymorphism has been shown to have a higher prevalence in African Americans compared to American Caucasians. However, very little is known regarding any functional consequences of these platelet polymorphisms in African Americans. We assessed the prevalence of the Ko and -5C Kozak polymorphisms in a population of both African American and American Caucasian patients with and without CAD and determined whether there were platelet functional consequences in both groups. We studied 99 patients of which 22 were African American and 77 were American Caucasian. Aggregations were performed and shear induced platelet plug formation was tested using a platelet function analyzer. The HPA-2b allele was significantly higher in African Americans when compared to Caucasians (P = 0.001). Genotype frequencies of the -5C Kozak polymorphism were not significantly different between the two groups. We found no differences in platelet aggregation in African Americans who were either heterozygous or homozygous for the HPA-2b allele or the -5C Kozak allele when compared to American Caucasians of the same category. We found no significant differences in PFA-100 testing. We conclude from our study that these polymorphisms do not lead to altered platelet function in African Americans.