Thrombopoietin emerges as a new haematopoietic cytokine that confers cardioprotection against acute myocardial infarction

Colony stimulating factors (CSFs), also called haematopoietic growth factors, are circulating cytokines that regulate the bone marrow production of red cells, white cells, and platelets. CSFs have also been reported to act on stem cells to regulate lineage-specific differentiation.1 Erythropoietin (EPO) controls red cell production and has been utilized in recombinant form for the treatment of anaemia in patients with end-stage renal disease since 1988. Granulocyte CSF (G-CSF) acts on haematopoietic stem cells to regulate neutrophil progenitor proliferation and differentiation. G-CSF is routinely used to mobilize stem cells in normal patients for transplantation of cells into patients with haematological malignancies, or in the patients themselves. Several recent reports have suggested that these cytokines possess properties that extend beyond their haematopoietic properties, such as the ability to protect the heart against injury caused by ischaemia and reperfusion (I/R).2,3 Baker et al. 4 now demonstrate for the first time in this issue of Cardiovascular Research that a third haematopoietic growth factor, thrombopoietin (TPO), is able to provide cardioprotection against myocardial I/R injury in a rat model by mechanisms independent of its haematopoietic properties.TPO affects nearly all aspects of platelet production, from self-renewal and expansion of haematopoietic stem cells, through stimulation of the proliferation of megakaryocyte progenitor cells, to support the maturation of these cells into platelet-producing cells.5 Since its purification in 1994, TPO has been used to treat thrombocytopenia caused by many conventional chemotherapy regimens.6 … *Corresponding author. Tel: +1 718 430 2645; fax: +1 718 430 8989. E-mail address : dlefer{at}aecom.yu.edu