Regulation of mesenchymal stem cell function by TGFβ-1 on mast cell extracellular vesicles — role of endosomal retention

Extracellular vesicles (EVs) convey biological messages between cells, either by surface-to-surface interaction, or by shuttling of bioactive molecules to a recipient cell cytoplasm. Here we show that EVs released by human primary mast cells or transformed human mast cells (HMC1), carry TGFβ-1 on their surface. EV-associated TGFβ-1 enhance the migratory activity of human mesenchymal stem cells (MSCs) compared to free TGFβ-1, as both knockdown of TGFB1, or a TGFβ-antibody, attenuate the effect. The MSCs respond by increasing matrix metalloproteinase-2 and -9 (MMP) activity. Further, EVs given to MSCs are retained in the endosomal compartments at a time of biological function, prolonging EV-associated TGFβ-1 signaling vs free TGFβ-1. When exposed to EVs, MSCs home more toward allergen-exposed lung in a mouse allergen model, resulting in attenuated allergic inflammation. Our results show that mast cell-EVs are decorated with TGFβ-1, are retained in endosomes, which influences both MSC phenotype and function.