Bone marrow-derived extracellular vesicles carry the TGF-β signal transducer Smad2 to preserve hematopoietic stem cells in mice

Abstract

Abstract Extracellular vesicles (EVs) released by cells in the BM are important to regulate proliferation, differentiation and other properties of hematopoietic stem cell (HSC). While the TGF-β signaling is now well known since a long time to be involved in HSC’s quiescence and maintenance, the TGF-β pathway related to EVs is still largely unknown in the hematopoietic system. We discovered that EVs inhibitor Calpeptin, intravenously injected in mice, particularly affected the in vivo production of EVs, carrying phosphorylated Smad2 (p-Smad2) in mouse BM. This was accompanied with an alteration in the quiescence and maintenance of murine HSC in vivo. Murine stromal MS-5 cells also expressed p-Smad2 as a cargo. To prove that the signal transducer p-Smad2 was required for HSC maintenance, we treated murine mesenchymal stromal cells (MSC) with the TGF-β inhibitor SB431542, in order to produce EVs without the expression of p-Smad2 and discovered that this mediator was required for maintenance of HSC ex vivo. In conclusion, we discovered a new mechanism, which involved EVs, produced in the mouse BM that, as a cargo, transport bioactive phosphorylated Smad2 to enhance the TGF-β signaling-mediated quiescence and maintenance of HSC.