Bifunctional effect of the inflammatory cytokine tumor necrosis factor α on megakaryopoiesis and platelet production.

BACKGROUND AND OBJECTIVES: Platelets are affected by many factors, such as infectious or aseptic inflammation, and different inflammatory states may induce either thrombocytopenia or thrombocytosis. Tumor necrosis factor α (TNFα) is an important inflammatory cytokine that has been shown to affect the activity of hematopoietic stem cells. However, its role in megakaryocyte (MK) development and platelet production remains largely unknown. This study aimed to investigate the effects of TNFα on MK and platelet generation. METHODS AND RESULTS: The ex vivo study with human CD34+ cells demonstrated that TNFα differentially modulated commitment toward the MK lineage. Specifically, a low concentration of 0.5 ng/ml TNFα promoted MK maturation, proplatelet formation, and platelet production, whereas a high concentration of 10 ng/ml or more TNFα exhibited a substantial inhibitory effect on MK and platelet production. The distinct effect of TNFα on MKs was mainly dependent on TNFα receptor 1. TNFα differentially regulated the MAPK-ERK1/2 signaling pathway and the cytoskeletal proteins cofilin and MLC2. The in vivo study with Balb/c mice indicated that low-dose or high-dose TNFα administration differentially affected short-term platelet recovery after bone marrow transplantation. CONCLUSIONS: Our study revealed distinct roles for TNFα in megakaryopoiesis and thrombopoiesis and may provide new insights regarding the treatment for platelet disorders.