Megakaryocytes and platelets in vascular disease.

Platelets are anucleate cells with no DNA. They are derived from their precursor, the megakaryocyte (MK), whose differentiation is characterized by nuclear polyploidization through a process called endomitosis. Changes in the MK-platelet-haemostasis axis may precede acute thrombotic events. Changes in MK ploidy distribution may be associated with the production of large platelets. Mean platelet volume (MPV) is an important biological variable as it is a determinant of platelet reactivity. Large platelets are denser and more active haemostatically. MPV is increased in patients after myocardial infarction (MI) and is a predictor of a further ischaemic event and death when measured after MI. It has been suggested that changes not only in platelets but also in the parental MK are associated with chronic and acute vascular events. The regulation of megakaryocytopoiesis depends on several haematopoietic factors such as thrombopoietin. An understanding of the signalling system that controls platelet number and size might give insight into a role of platelet production in thrombogenesis and atherogenesis.