Study of the role of secreted platelet thiol isomerases in the regulation of platelet function, haemostasis & thrombosis

Platelets are tiny blood cells whose role is to trigger the blood to clot when blood vessels become ruptured during injury. While this is clearly essential to prevent excessive and life-threatening bleeding, abnormal stimulation of blood clotting can be catastrophic, particularly if this leads to the clotting of blood within an artery or vein. This is a condition known as thrombosis, and when this happens in arteries that supply the heart muscle with blood it can cause a heart attack. Thrombosis also commonly occurs in the blood vessels that supply the brain with blood, and in this case it causes strokes. Both of these conditions are very common in the UK and are frequently fatal. The cause of thrombosis in these situations is often underlying diseases such as the formation of fatty lesions in the wall of blood vessels that are liable to rupture, but platelets are ultimately responsible for triggering a dangerous clot to form. The use of drugs to dampen down the responses of platelets has been successful in many 'at risk' patients in the prevention of thrombosis, although many patients gain no benefit and may even suffer side effects such as bleeding. In order to develop better drugs that target platelets to prevent thrombosis, scientists need to know more about how platelets recognise injury, and then stimulate the blood to clot. In this research project we will investigate some proteins known as thiol isomerases that we have found to be released by platelets when they encounter tissue injury. We know that once released some of these molecules attach themselves to the platelet surface and somehow enhance the platelet clotting activity. The purpose of this study is to work out which of the proteins that are released are important to control the functions of platelets in their normal responses and to determine the impact of this on thrombosis. To study thrombosis we will use a newly developed type of microscopy that enables us to visualise thrombosis as it forms within the circulation of mice. Through neutralisation of the function of individual proteins, we will be able to assess their contributions to thrombosis.
To begin to work out how to convert these new discoveries into new medicines to prevent thrombosis, it will be important that we understand how these new proteins function on the surface of platelets. Using a range of techniques, and unique reagents that we have developed to study the molecules, we will begin to unravel the biochemical processes that they control and the molecules on the platelet surface that they target.
It is anticipated that this project will equip us with a new understanding of how platelets regulate their functions and the identification of the molecules involved. This knowledge may lead, in future studies, to the development of more effective drugs to successfully prevent thrombosis.

Platelets perform a vital role in haemostasis, although inappropriate platelet activation causes arterial thrombosis leading to heart attacks and strokes. Understanding the mechanisms that regulate platelet function is important for the development of more effective strategies to prevent thrombosis.
We have reported that during platelet activation and thrombus formation platelets release ERp5, a member of the thiol isomerase family of enzymes. This protein interacts with the beta3 integrin subunit on the platelet surface, whereupon its enzymatic activity enhances platelet function. Protein disulphide isomerase (PDI) is also known to be secreted from platelets and influence their reactivity. Increasing evidence supports the role of thiol isomerases in haemostasis, and recent data implicate PDI in thrombosis in the mouse. Extracellular PDI has also been implicated in the regulation of tissue factor, which triggers coagulation following exposure and de-encryption at sites of injury.
We have recently demonstrated that platelets contain a range of additional thiol isomerases, some of which are also secreted and bind to the cell surface during activation. The aims of this study are to systematically characterise catalytically-competent thiol iomerases that are released from platelets during activation, to establish their roles in the regulation of platelet function in vitro, and to determine the potential contribution of each to the regulation of pathological thrombus formation using intravital microscopy models of thrombosis in the mouse. Using reagents that selectively inhibit thiol isomerase family members, we aim to establish the identities of thiol isomerase substrates on the platelet surface, and begin to understand the means by which they modulate platelet reactivity.
Understanding of this paradigm for the regulation of thrombus formation may lead to the identification of new targets for the effective pharmacological suppression of platelet function.

This research will impact on the establishment of new therapeutic strategies and medicines for more effective and safer prevention and treatment of thrombotic disease. As the principal cause of mortality and morbidity in the UK, Europe, and North America, and an increasing burden in rapidly developing nations such as India and China, this would have substantial implications for health and quality of life, and as such have both economic and societal impact.

Key beneficiaries in this respect will be the pharmaceutical and biotechnology sectors. The UK holds as strong pharmaceutical research base, with cardiovascular drug development integrated within this in a multi-national manner. Research in this area will support the generation of economic impact through the identification of possible drug targets, and could result in further inward investment to the UK in this area. In addition, cardiovascular disease is estimated to cost the UK economy around £31B annually. Given the scale of cardiovascular disease in the UK, this research holds the potential for healthcare savings, wealth creation and increased economical prosperity.

The development of more effective anti-thrombotic drugs will have substantial societal impact, and reductions in mortality and morbidity will result in increased quality of life for the UK's aging population.

Understanding of this research and its implications for normal and pathological blood clotting may form a component of increasing public understanding of cardiovascular disease prevention and treatment, and understanding of science and medicine generally. This will be relevant in the contexts of schools and the general public, and may involve key third sector organisations such as charities and societies (e.g. BHF, HRUK, Royal Institution) engaged in increasing national health and well-being, and scientific understanding.

Finally, this project will deliver highly skilled researchers that are able to integrate disciplines from biochemistry and cell biology through to in vivo models of disease, skills that are deficient in the UK graduate workforce and are recognised as essential in both the private sector and Universities to enable the UK to remain competitive in the pharmaceutical arena.