The Role of 12-Lipoxygenase in the Regulation of Platelet Function
Yeung, Jennifer
2018
Abstract
Platelets are small, anucleated cellular fragments derived from the megakaryocytes of the bone marrow. These small cellular fragments have a specialized role in maintaining hemostasis, a process that prevents blood loss, through the initiation of blood coagulation. However, excessive platelet reactivity can lead to a pathophysiological condition known as thrombosis. Platelet-mediated thrombosis is the primary underlying mechanism leading to cardiovascular life-threatening clinical events, such as myocardial infarction and stroke. Regulating excessive platelet reactivity is an essential aspect of antithrombotic therapy. A number of anti-platelet drugs have been developed to target specific signaling pathways or endpoints involved in platelet activation. Despite the effectiveness of current anti-platelet therapies, uncontrolled thrombosis or bleeding complications still persist. Therefore, elucidating the mechanisms involved in platelet activation is crucial for identifying the development of novel or alternative anti-thrombotic strategies. Platelet 12-lipoxygenase (12-LOX), an oxygenase principally found to convert freed polyunsaturated fatty acids (PUFA) substrates from the membrane phospholipids following cellular stimulation, was identified to be a potential target for regulating platelet reactivity. Thus, the studies described in this thesis seek to assess whether 12-LOX activity modulated platelet responses or reactivity by using newly developed selective 12-LOX inhibitors, NCTT-956 and ML355. Although both NCTT-956 and ML355 blocked 12-LOX activity in platelets, ML355 was shown to be much more potent in inhibiting platelet activation. In support of the pharmacological ex vivo studies, mice lacking 12-LOX (12-LOX-/-) in platelets were protected from platelet-induced activation as well as thrombosis in vivo. Additionally, the role of 12-LOX in immune-mediated platelet activation was also investigated in this thesis work. One form of immune-mediated platelet activation or thrombosis is heparin-induced thrombocytopenia and thrombosis (HITT), a life-threatening cardiovascular disorder. A key component of this disorder is the activation of FcRIIa, a transmembrane receptor, by immune-complexes. I had shown that 12-LOX potentiated immune-mediated platelet activation and 12-LOX activity regulated early signaling effectors in the immune signaling pathways of platelet activation. 12-LOX predominantly generates 12(S)-HETE, an oxylipin or metabolite, from arachidonic acid (AA), since this is the most abundant -6 PUFA found in the lipid bilayer of cells. Dietary supplementation of plant- or fish-based oils can alter and enrich the contents of the lipid bilayer by which they shift 12-LOX substrate from AA to other PUFAs. Consumption of borage or primrose oil, which is enriched in -6 PUFA dihomo--linolenic acid (DGLA), has been shown to be cardioprotective; however, its mechanism of action was unclear. In this thesis, I had also sought to elucidate the underlying mechanism by which DGLA could provide cardioprotection via the prevention of thrombosis. I had demonstrated that the oxylipin of DGLA generated by 12-LOX, 12(S)-HETrE, inhibited platelet activation and thrombosis in vivo in a G-signaling dependent manner. Altogether, my thesis work highlighted the importance of targeting 12-LOX in platelets or using its endogenous mechanism to generate oxylipins that have anti-platelet effects as potential therapeutic avenues for preventing unwanted platelet activation.Subjects
Platelet biology 12-Lipoxygenase Immune-mediated thrombocytopenia and thrombosis
Types
Thesis
Metadata
Show full item recordCollections
Remediation of Harmful Language
The University of Michigan Library aims to describe library materials in a way that respects the people and communities who create, use, and are represented in our collections. Report harmful or offensive language in catalog records, finding aids, or elsewhere in our collections anonymously through our metadata feedback form. More information at Remediation of Harmful Language.
Accessibility
If you are unable to use this file in its current format, please select the Contact Us link and we can modify it to make it more accessible to you.