Exosomes: A Novel Strategy for Treatment and Prevention of Diseases

Exosomes are vesicles of endocytic origin released by many cells. These vesicles can mediate communication between cells, facilitating processes such as antigen presentation. Here, we show that exosomes from a mouse and a human mast cell line (MC/9 and HMC-1, respectively), as well as primary bone marrow-derived mouse mast cells, contain RNA. Microarray assessments revealed the presence of mRNA from approximately 1300 genes, many of which are not present in the cytoplasm of the donor cell. In vitro translation proved that the exosome mRNAs were functional. Quality control RNA analysis of total RNA derived from exosomes also revealed presence of small RNAs, including microRNAs. The RNA from mast cell exosomes is transferable to other mouse and human mast cells. After transfer of mouse exosomal RNA to human mast cells, new mouse proteins were found in the recipient cells, indicating that transferred exosomal mRNA can be translated after entering another cell. In summary, we show that exosomes contain both mRNA and microRNA, which can be delivered to another cell, and can be functional in this new location. We propose that this RNA is called "exosomal shuttle RNA" (esRNA).

Normal and malignant cells shed from their surface membranes as well as secrete from the endosomal membrane compartment circular membrane fragments called microvesicles (MV). MV that are released from viable cells are usually smaller in size compared to the apoptotic bodies derived from damaged cells and unlike them do not contain fragmented DNA. Growing experimental evidence indicates that MV are an underappreciated component of the cell environment and play an important pleiotropic role in many biological processes. Generally, MV are enriched in various bioactive molecules and may (i) directly stimulate cells as a kind of 'signaling complex', (ii) transfer membrane receptors, proteins, mRNA and organelles (e.g., mitochondria) between cells and finally (iii) deliver infectious agents into cells (e.g., human immuno deficiency virus, prions). In this review, we discuss the pleiotropic effects of MV that are important for communication between cells, as well as the role of MV in carcinogenesis, coagulation, immune responses and modulation of susceptibility/infectability of cells to retroviruses or prions.

Using ferritin-labeled protein A and colloidal gold-labeled anti-rabbit IgG, the fate of the sheep transferrin receptor has been followed microscopically during reticulocyte maturation in vitro. After a few minutes of incubation at 37 degrees C, the receptor is found on the cell surface or in simple vesicles of 100-200 nm, in which the receptor appears to line the limiting membrane of the vesicles. With time (60 min or longer), large multivesicular elements (MVEs) appear whose diameter may reach 1-1.5 micron. Inside these large MVEs are round bodies of approximately 50-nm diam that bear the receptor at their external surfaces. The limiting membrane of the large MVEs is relatively free from receptor. When the large MVEs fuse with the plasma membrane, their contents, the 50-nm bodies, are released into the medium. The 50-nm bodies appear to arise by budding from the limiting membrane of the intracellular vesicles. Removal of surface receptor with pronase does not prevent exocytosis of internalized receptor. It is proposed that the exocytosis of the approximately 50-nm bodies represents the mechanism by which the transferrin receptor is shed during reticulocyte maturation.