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Project 1: Studies on the role of CLEC-2 and Syk in lymphatic development and response to radiation & Project 2: A role for atrial natiuretic peptide in platelet inhibition and evidence for compartmentation of cGMP signalling.

Lowe, Kate (2011)
M.Res. thesis, University of Birmingham.

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Project 1: The platelet C type lectin-like type II (CLEC-2) transmembrane receptor has been shown to interact with its endogenous ligand, podoplanin, on lymphatic endothelium and mediate separation from blood vessels. Here, conditional deletion of CLEC-2 or a mutation in signalling molecule Syk, specifically in the megakaryocyte/platelet lineage, was seen to cause a severe blood-lymphatic mixing phenotype. As constitutive loss of CLEC-2 in mice is lethal at birth, radiation chimeras have been pivotal to investigating the role of CLEC-2 in platelet function. This pilot study was conducted to investigate the role of platelets in the recovery from radiation injury. Mice were subjected to irradiation and reconstituted with CLEC-2+/+ or CLEC-2-/- foetal liver cells. Immunofluorescence in the intestinal mesentery at 9 days showed disrupted vasculature in CLEC-2-/- mice. The only visible difference between the two sets of chimeras was blood in the intestine of CLEC-2-/- mice at 28 days. Terminal deoxynucleotidyl end labeling (TUNEL) showed no difference in the percentage of apoptotic cells in the livers of CLEC-2+/+ and CLEC-2-/- mice but an increase in the spleen. These results support the idea of a progressive intestinal phenotype and support a role for CLEC-2 and Syk in the separation and organization of blood and lymphatic vessels.

Project 2: Nitric oxide (NO) has long been accepted as a potent and powerful inhibitor of platelet function acting through soluble guanylyl cyclase (sGC) to elevate levels of cyclic guanosine 3’,5’-monophosphate (cGMP). In cells such as cardiac myocytes, cGMP levels are also influenced by natriuretic peptides (NP) which bind to a particulate GC (pGC). Despite a number of studies indicating binding sites for atrial NP (ANP) on platelets, their influence on platelet function is unclear. Here it is demonstrated that NO and ANP mediate concentration-dependant inhibition of platelet aggregation to thrombin which is not overcome by high concentrations of the protease. ANP also stimulated weak phosphorylation of vasodilator stimulated phosphoprotein (VASP) in contrast to the robust response to NO and which was highly variable between donors. Further, sildenafil, a selective PDE5 inhibitor, was shown to enhance NO but not ANP mediated platelet inhibition and VASP phosphorylation indicating soluble and particulate cGMP pools are compartmentalised in platelets. Together these findings indicate a role for ANP in inhibiting platelet function which is distinct from that of NO.

Type of Work:M.Res. thesis.
Supervisor(s):Watson, Steve P. and Finney, Brenda and Madhani, Melanie
School/Faculty:Colleges (2008 onwards) > College of Medical & Dental Sciences
Department:Centre for Cardiovascular Sciences, Institute of Biomedical Research, College of Medical and Dental Services
Subjects:QD Chemistry
QH301 Biology
QH426 Genetics
RC Internal medicine
Institution:University of Birmingham
Library Catalogue:Check for printed version of this thesis
ID Code:3209
This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder.
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