skip to content

Department of Pharmacology



The main interests of the Harper lab are to understand how vascular responses to injury can lead to haemostasis, thrombosis or vascular inflammation.


Procoagulant platelets in thrombosis and haemostasis

Platelets play a major role in pathological arterial thrombosis on ruptured atherosclerotic plaques. Platelets bind to exposed matrix proteins and become activated, resulting in platelet aggregation. Importantly, phosphatidylserine exposure on the outer leaflet of the plasma membrane in a subpopulation of strongly-activated platelets is essential to the development of arterial thrombosis. Phosphatidylserine is the archetypical ‘eat-me’ signal on dying cells. In platelets, phosphatidylserine exposure has a pathologically important addition role as an efficient surface for assembly of coagulation complexes, generating a burst of thrombin that is responsible for producing an occlusive thrombus. phosphatidylserine exposure in this context is driven by a high, sustained intracellular calcium signals, mitochondrial calcium handling and ROS production. We aim to understand how phosphatidylserine exposure is controlled during platelet activation and how it can be inhibited to reduce thrombosis.

In addition to supporting coagulation, procoagulant platelets show features similar to a cell dying by necrosis. Although the role of phosphatidylserine-exposing platelets in coagulation and thrombosis has been well established, little is known about the biochemical mechanisms that underlie this regulated death pathway, nor about relevance of platelet ‘necrosis’ beyond phosphatidylserine exposure, and is currently being investigated in the lab.


Platelet death

The balance between cell death and cell survival is essential to organism homeostasis and both must be tightly regulated. For many years, apoptosis was seen as the only regulated cell death pathway, whereas necrosis was seen as largely seen as an ‘accidental’ result of physical or chemical injury. It is now clear, however, that cells can undergo several distinct cell death programs that show features of necrosis, yet can be inhibited by pharmacological or genetic interventions. These pathways of regulated necrosis are biochemically distinct from apoptosis and are controlled by intracellular signalling cascades. The cell death pathways found in nucleated cells are conserved in anucleate blood platelets. This makes them an excellent model, uncomplicated by the distinct processes of nuclear death, in which to study these critical processes that are central to many diseases.


Our research on platelet death therefore focuses on the role and regulation of different cell death pathways in platelets:

  • What triggers regulated cell death in platelets?
  • How are different death pathways controlled by intracellular signalling?
  • What are the physiological and pathological consequences of platelet death?

Platelets are an essential element in the primary haemostatic system that prevents bleeding. Platelet count is a delicate balance between platelet production and platelet death. Circulating platelets survive for about ten days in humans, and approximately 1011 platelets are made and destroyed every day. Decreased platelet production or increased platelet death and clearance can lead to a severe reduction in platelet count in the circulation (thrombocytopenia) and risk of serious bleeding.  Thrombocytopenia is a major side-effect of many anti-cancer chemotherapy drugs. The mechanism is often assumed to be reduced platelet production, but there is increasing evidence that some drugs can rapidly trigger platelet death. We are interested in how chemotherapy drugs might trigger platelet death as an off-tumour side effect of treatment.


Vascular injury models

We aim to develop new models of arterial, venous and microvascular thrombosis. These models incorporate microfluidics with thrombogenic substrates, endothelial cells or ex vivo vessel perfusion. Physiological variables such as flow and oxygenation are modelled on in vivo conditions as far as possible, since these are likely to significantly affect the translational relevance of the models.