Exosomes are nanoscale membrane vesicles secreted from many types of cells. Carrying functional molecules, exosomes transfer information between cells and mediate many physiological and pathological processes. In this report, utilizing selective inhibitors, molecular tools, and specific endocytosis markers, the cellular uptake of PC12 cell-derived exosomes was imaged by high-throughput microscopy and statistically analyzed. It was found that the uptake was through clathrin-mediated endocytosis and macropinocytosis. Furthermore, PC12 cell-derived exosomes can enter and deliver microRNAs (miRNAs) into bone marrow-derived mesenchymal stromal cells (BMSCs), and decrease the expression level of transforming growth factor β receptor II (TGFβRII) and tropomyosin-1 (TPM1) through miR-21. These results show the pathway of exosome internalization and demonstrate that tumor cell-derived exosomes regulate target gene expression in normal cells.

Background: 5-Fluorouracil (5-FU) has been commonly prescribed for patients with colorectal cancer (CRC), but resistance to 5-FU is one of the main reasons for failure in CRC. Recently, microRNAs (miRNAs) have been established as a means of reversing the dilemma by regulating signaling pathways involved in initiation and progression of CRC. However, how to safely and effectively deliver miRNA to target cells becomes a main challenge. Results: In this study, Engineered exosomes were exploited to simultaneously deliver an anticancer drug 5-FU and miR-21 inhibitor oligonucleotide (miR-21i) to Her2 expressing cancer cells. Purified engineered exosomes from the donor cells loaded with 5-FU and miR-21i via electroporation to introduce into 5-FU-resistant colorectal cancer cell line HCT-116^5FR. Furthermore, systematic administration of 5-FU and miR-21i loaded exosomes in tumor bearing mice indicated a significantly anti-tumor effect. The results showed that the engineered exosome-based 5-FU and miR-21i co-delivery system could efficiently facilitate cellular uptake and significantly down-regulate miR-21 expression in 5-FU resistant HCT-116^5FR cell lines. Consequently, the down-regulation of miR-21 induced cell cycle arrest, reduced tumor proliferation, increased apoptosis and rescued PTEN and hMSH2 expressions, regulatory targets of miR-21. Of particular importance was the significant reduction in tumor growth in a mouse model of colon cancer with systematic administration of the targeting miR-21i. More excitedly, the combinational delivery of miR-21i and 5-FU with the engineered exosomes effectively reverse drug resistance and significantly enhanced the cytotoxicity in 5-FU-resistant colon cancer cells, compared with the single treatment with either miR-21i or 5-FU. Conclusion: The strategy for co-delivering the functional small RNA and anticancer drug by exosomes foreshadows a potential approach to reverse the drug resistance in CRC and thus to enhance the efficacy of the cancer treatment.

Mesenchymal stromal/stem cells (MSCs) exist in almost all tissues, possessing the potential to differentiate into specialized cell types and exert immunomodulatory functions. Thus, they have attracted much attention as a promising therapeutic candidate. Recent studies have demonstrated that paracrine signaling is mainly responsible for the involvement of MSCs in the modulation of immune responses and the progression of diseases. Through release of secretome consisting of a diverse range of cytokines, chemokines, and extracellular vesicles (EVs), MSCs convey regulatory messages to recipient immune cells in the microenvironment. In this review, we focus on the recent advances in how MSCs contribute to immunomodulation through the secretion of paracrine factors. The further improved understanding of the molecular mechanism underlying the interactions between MSCs and immune cells highlights the paracrine biology of MSCs in the modulation of the immune microenvironment and promotes the clinical application of MSCs in regenerative medicine and immune diseases.

MicroRNAs (miRNAs), a class of small RNAs, are important molecules that influence several developmental processes and regulate RNA interference (RNAi), and are abundant in animals, plants, and plant tissues that are traditionally consumed in the diet. The survival of plant small RNAs from the diet in animals, however, remains unclear, and the persistence of miRNAs from dietary plants in the animal gastrointestinal (GI) tract is still under debate. In this study, ICR mice were fed plant total RNAs in quantities of 10–50 μg, extracted from Brassica oleracea. Serum, feces, and various tissues were collected from the mice after RNA consumption and analyzed for several miRNAs. Exogenous plant miRNAs were present in the sera, feces, and tissues of animals and these exogenous plant miRNAs were primarily acquired orally. MiR‐172, the most highly enriched exogenous plant miRNA in B. oleracea, was found in the stomach, intestine, serum, and feces of mice that were fed plant RNA extracts including miR‐172. The amount of miR‐172 that survived passage through the GI tract varied among individuals, with a maximum of 4.5% recovered at the stomach of one individual, and had a range of 0.05–4.5% in different organs. Furthermore, miR‐172 was detected in the blood, spleen, liver, and kidney of mice.