Cytoreductive treatment differentially affects platelet size and cytoskeletal megakaryocyte organization during thrombopoiesis in myeloproliferative neoplasms.

Overview

abstract

Cytoreductive treatment is a main strategy to reduce thrombotic complications and ameliorate symptoms in Phi-negative myeloproliferative neoplasms (MPNs) comprising essential thrombocythemia, polycythemia vera, and primary myelofibrosis. Based on the observation of differences in platelet size during microscopic analysis of blood smears from MPN patients, in this work we studied whether these differences could be dependent on the type of cytoreductive drug used for patients' treatment and whether changes in platelet size could be induced by the effect of these drugs on thrombopoiesis. Maximum platelet diameter (MPD) was measured in 120 patients with MPN. The effect of drugs on thrombopoiesis was evaluated in normal megakaryocytes (MKs) obtained from cord blood-derived CD34+ hematopoietic progenitors. Anagrelide (ANA), α-interferon (IFN), and ruxolitinib (Ruxo) increased, whereas hydroxyurea (HU) decreased platelet size. MK incubation with these drugs revealed that ANA and IFN induced abnormal proplatelet (PP) architecture and affected microtubular structure, but only ANA altered actin organization, whereas neither Ruxo nor HU modified MK cytoskeleton. By bioinformatic analysis, RANTES downregulation was identified as a candidate responsible for ANA-induced abnormalities. RANTES downregulation was confirmed in MK incubated with ANA but not with IFN. Addition of recombinant RANTES reverted ANA-induced cytoskeletal abnormalities. Evaluation of RANTES plasmatic levels and platelet RNA expression in patients with MPN showed RANTES decrease in both samples during ANA treatment, suggesting that in vitro findings could reflect ANA action in vivo. In conclusion, this study demonstrates the influence of cytoreductive drugs on platelet size and reveals their differential mechanisms of action during platelet production.