Background: Different extracellular vesicles (EVs) can be secreted by almost any type of MSCs and are found to be high levels in biological fluids. According to the size of these vesicles are divided into three subtypes: exosomes (30–130 nm), microvesicles (100–1000 nm), and apoptotic bodies (50– 4000 nm). Exosomes, membrane-bound vesicles of 40–100 nm in diameter, are present in almost all biological fluids. They are released from most cell types into the extracellular space after fusion with the plasma membrane. Exosomes can be separated from MSCs culture media and they are called MSCs derived exosomes (MSCs-EXO) by ultracentrifugation, density gradient separation, immunoaffinity capture, size exclusion chromatography, and ExoQuick Precipitation (System Biosciences, USA). The useage of different exosome purification strategies could slightly affect exosomal contents, including proteins and miRNAs. Exosomal microRNAs are a class of small (17–24 nucleotides), noncoding RNAs carried in MSCs-EXO, which mediate post transcriptional gene silencing by binding to the 3 untranslated region (UTR) or open reading frame (ORF) region of target mRNAs

Exosomes and Exosomal miRNA