Blood Platelets as an Important but Underrated Circulating Source of TGF beta

When treating diseases related primarily to tissue remodeling and fibrosis, it is desirable to regulate TGF beta concentration and modulate its biological effects. The highest cellular concentrations of TGF beta are found in platelets, with about 40% of all TGF beta found in peripheral blood plasma being secreted by them. Therefore, an understanding of the mechanisms of TGF beta secretion from platelets may be of key importance for medicine. Unfortunately, despite the finding that platelets are an important regulator of TGF beta levels, little research has been carried out into the development of platelet-directed therapies that might modulate the TGF beta-dependent processes. Nevertheless, there are some very encouraging reports suggesting that platelet TGF beta may be specifically involved in cardiovascular diseases, liver fibrosis, tumour metastasis, cerebral malaria and in the regulation of inflammatory cell functions. The purpose of this review is to briefly summarize these few, extremely encouraging reports to indicate the state of current knowledge in this topic. It also attempts to better characterize the influence of TGF beta on platelet activation and reactivity, and its shaping of the roles of blood platelets in haemostasis and thrombosis.