Phenotypic approaches to gene mapping in platelet function disorders Identification of new variant of P2Y12, TxA2 and GPVI receptors

Centre for Cardiovascular Sciences, Institute for Biomedical Research, College of Medical and Dental Sciences, University of Birmingham, UK.
Hamostaseologie (Impact Factor: 1.6). 02/2010; 30(1):29-38.
Source: PubMed


Platelet number or function disorders cause a range of bleeding symptoms from mild to severe. Patients with platelet dysfunction but normal platelet number are the most prevalent and typically have mild bleeding symptoms. The study of this group of patients is particularly difficult because of the lack of a gold-standard test of platelet function and the variable penetrance of the bleeding phenotype among affected individuals. The purpose of this short review is to discuss the way in which this group of patients can be investigated through platelet phenotyping in combination with targeted gene sequencing. This approach has been used recently to identify patients with mutations in key platelet activation receptors, namely those for ADP, collagen and thromboxane A2 (TxA2). One interesting finding from this work is that for some patients, mild bleeding is associated with heterozygous mutations in platelet proteins that are co-inherited with other genetic disorders of haemostasis such as type 1 von Willebrand's disease. Thus, the phenotype of mild bleeding may be multifactorial in some patients and may be considered to be a complex trait.

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    • "DNA-based diagnosis of MYH9- related renal disease therefore allows identification of susceptible individuals and early intervention to reduce disease progression. Similar approaches have identified the genes underlying a large number of inherited platelet disorders (Watson et al, 2010). "
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    ABSTRACT: Inherited platelet function disorders (PFDs), associated with normal or reduced platelet counts, account for a significant proportion of bleeding diatheses. Identification of the underlying genetic defects is difficult in the majority of cases due to the variable clinical expression of the bleeding symptoms and the redundancy of platelet receptor and signalling pathways, which add to the complexity of diagnosis. The gold standard method for phenotyping platelets, light transmission aggregometry (LTA), has allowed classification of functional defects in the majority of patients referred for investigation of suspected PFDs, while DNA-based analysis has primarily played a confirmatory role and been restricted mainly to analysis of candidate genes. Recent advances in next generation sequencing have facilitated the identification of gene defects in patients with PFDs where the underlying genetic defect was previously unknown, especially when combined with genome-wide linkage analysis. These studies have provided new insights into the mechanisms controlling platelet formation and function, and it is likely that, as understanding of the relationships between platelet phenotype and genotype increases and pipelines for the interpretation of genetic variations identified in patients are developed, DNA-based analysis will play an increasingly important role in the first-line investigation of patients with PFDs.
    British Journal of Haematology 01/2014; 165(2). DOI:10.1111/bjh.12751 · 4.71 Impact Factor
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    • "Eicosanoids, such as prostaglandins (PGs) and thromboxanes, play an important role in the development of various diseases, as well as APAP hepatotoxicity [22-25]. North et al. [21] and Cavar et al. [26] demonstrated that PGE2 has a protective role in APAP-induced liver injury in zebrafish and mice, respectively. "
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    ABSTRACT: Background Overdosed acetaminophen (paracetamol, N-acetyl-p-aminophenol; APAP) causes severe liver injury. We examined the effects of ozagrel, a selective thromboxane A2 (TXA2) synthase inhibitor, on liver injury induced by APAP overdose in mice. Methods Hepatotoxicity was induced to ICR male mice by an intraperitoneal injection with APAP (330 mg/kg). The effects of ozagrel (200 mg/kg) treatment 30 min after the APAP injection were evaluated with mortality, serum alanine aminotransferase (ALT) levels and hepatic changes, including histopathology, DNA fragmentation, mRNA expression and total glutathione contents. The impact of ozagrel (0.001-1 mg/mL) on cytochrome P450 2E1 (CYP2E1) activity in mouse hepatic microsome was examined. RLC-16 cells, a rat hepatocytes cell line, were exposed to 0.25 mM N-acetyl-p-benzoquinone imine (NAPQI), a hepatotoxic metabolite of APAP. In this model, the cytoprotective effects of ozagrel (1–100 muM) were evaluated by the WST-1 cell viability assay. Results Ozagel treatment significantly attenuated higher mortality, elevated serum alanine aminotransferase levels, excessive hepatic centrilobular necrosis, hemorrhaging and DNA fragmentation, as well as increase in plasma 2,3-dinor thromboxane B2 levels induced by APAP injection. Ozagrel also inhibited the hepatic expression of cell death-related mRNAs induced by APAP, such as jun oncogene, FBJ osteosarcoma oncogene (fos) and C/EBP homologous protein (chop), but did not suppress B-cell lymphoma 2-like protein11 (bim) expression and hepatic total glutathione depletion. These results show ozagrel can inhibit not all hepatic changes but can reduce the hepatic necrosis. Ozagrel had little impact on CYP2E1 activity involving the NAPQI production. In addition, ozagrel significantly attenuated cell injury induced by NAPQI in RLC-16. Conclusions We demonstrate that the TXA2 synthase inhibitor, ozagrel, dramatically alleviates liver injury induced by APAP in mice, and suggest that it is a promising therapeutic candidate for the treatment of APAP-induced liver injury.
    BMC Gastroenterology 01/2013; 13(1):21. DOI:10.1186/1471-230X-13-21 · 2.37 Impact Factor
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    ABSTRACT: The P2Y receptors are a widely expressed group of eight nucleotide-activated G protein-coupled receptors (GPCRs). The P2Y(1)(ADP), P2Y(2)(ATP/UTP), P2Y(4)(UTP), P2Y(6)(UDP), and P2Y(11)(ATP) receptors activate G(q) and therefore robustly promote inositol lipid signaling responses. The P2Y(12)(ADP), P2Y(13)(ADP), and P2Y(14)(UDP/UDP-glucose) receptors activate G(i) leading to inhibition of adenylyl cyclase and to Gβγ-mediated activation of a range of effector proteins including phosphoinositide 3-kinase-γ, inward rectifying K(+) (GIRK) channels, phospholipase C-β2 and -β3, and G protein-receptor kinases 2 and 3. A broad range of physiological responses occur downstream of activation of these receptors ranging from Cl(-) secretion by epithelia to aggregation of platelets to neurotransmission. Useful structural models of the P2Y receptors have evolved from extensive genetic analyses coupled with molecular modeling based on three-dimensional structures obtained for rhodopsin and several other GPCRs. Selective ligands have been synthesized for most of the P2Y receptors with the most prominent successes attained with highly selective agonist and antagonist molecules for the ADP-activated P2Y(1) and P2Y(12) receptors. The widely prescribed drug, clopidogrel, which results in irreversible blockade of the platelet P2Y(12) receptor, is the most important therapeutic agent that targets a P2Y receptor.
    Advances in pharmacology (San Diego, Calif.) 01/2011; 61:373-415. DOI:10.1016/B978-0-12-385526-8.00012-6
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