circFUT8 promotes proplatelet formation by interacting with IGF2BP2 and stabilizing TNS1 mRNA in megakaryocytes

ABSTRACT: During thrombopoiesis, megakaryocytes (MKs) transform their cytoplasm into proplatelets through complex cytoskeletal rearrangements. The shear force of blood flow releases newly formed platelets from the proplatelets into the bloodstream. Defects at any phase of this process can impair platelet production. Although various noncoding RNAs have been identified as regulators of platelet production, the regulatory mechanisms of thrombopoiesis remain to be further investigated. Despite the high abundance of circular RNAs (circRNAs) in platelets, their role in platelet production is unclear. In this study, using RNA sequencing and bioinformatics analysis, we identified a circular RNA from the FUT8 gene (circFUT8) as a novel circRNA that increases as hematopoietic stem cells from human umbilical cord blood differentiate into mature MKs, showing high expression in these mature cells. Knockdown of circFUT8 led to diminished proplatelet formation (PPF) and abnormal demarcation membrane system formation in human cultured MKs. In addition, inhibition of circFut8 in vivo decreased murine platelet counts. circFut8 deficiency reduced the number of MKs in contact with sinusoids. Mechanistically, we revealed that circFUT8 interacts with insulin-like growth factor 2 messenger RNA (mRNA)-binding protein 2 to stabilize tensin-1 (TNS1) mRNA in an m6A-dependent manner. In human cultured MKs, TNS1 knockdown resulted in defective filamentous actin polymerization and assembly, impaired spreading on extracellular matrix proteins, and decreased PPF. Taken together, our research reveals the crucial functions of circRNAs in platelet production and has significant implications for the development of therapeutic strategies for thrombocytopenia and bleeding disorders.