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Exosomes (Exo) secreted from hypoxia-conditioned bone marrow mesenchymal stem cells (BM-MSCs) were found to be protective for ischemic disease. However, the role of exosomal miRNA in the protective effect of hypoxia-conditioned BM-MSCs-derived Exo (Hypo-Exo) remains largely uncharacterized and the poor specificity of tissue targeting of Exo limits their clinical applications. Therefore, the objective of this study was to examine the effect of miRNA in Hypo-Exo on the repair of ischemic myocardium and its underlying mechanisms. We further developed modified Hypo-Exo with high specificity to the myocardium and evaluate its therapeutic effects.Methods: Murine BM-MSCs were subjected to hypoxia or normoxia culture and Exo were subsequently collected. Hypo-Exo or normoxia-conditioned BM-MSC-derived Exo (Nor-Exo) were administered to mice with permanent condition of myocardial infarction (MI). After 28 days, to evaluate the therapeutic effects of Hypo-Exo, infarction area and cardio output in Hypo-Exo and Nor-Exo treated MI mice were compared through Masson's trichrome staining and echocardiography respectively. We utilized the miRNA array to identify the significantly differentially expressed miRNAs between Nor-Exo and Hypo-Exo. One of the most enriched miRNA in Hypo-Exo was knockdown by applying antimiR in Hypoxia-conditioned BM-MSCs. Then we performed intramyocardial injection of candidate miRNA-knockdown-Hypo-Exo in a murine MI model, changes in the candidate miRNA's targets expression of cardiomyocytes and the cardiac function were characterized. We conjugated Hypo-Exo with an ischemic myocardium-targeted (IMT) peptide by bio-orthogonal chemistry, and tested its targeting specificity and therapeutic efficiency via systemic administration in the MI mice.Results: The miRNA array revealed significant enrichment of miR-125b-5p in Hypo-Exo compared with Nor-Exo. Administration of miR-125b knockdown Hypo-Exo significantly increased the infarction area and suppressed cardiomyocyte survival post-MI. Mechanistically, miR-125b knockdown Hypo-Exo lost the capability to suppress the expression of the proapoptotic genes p53 and BAK1 in cardiomyocytes. Intravenous administration of IMT-conjugated Hypo-Exo (IMT-Exo) showed specific targeting to the ischemic lesions in the injured heart and exerted a marked cardioprotective function post-MI.Conclusion: Our results illustrate a new mechanism by which Hypo-Exo-derived miR125b-5p facilitates ischemic cardiac repair by ameliorating cardiomyocyte apoptosis. Furthermore, our IMT- Exo may serve as a novel drug carrier that enhances the specificity of drug delivery for ischemic disease.

Exosomes, as novel noninvasive biomarkers for disease prediction and diagnosis, have shown fascinating prospects in monitoring cancer-linked public health issues. Herein, a unique Cy3 labeled CD63 aptamer (Cy3-CD63 aptamer)/Ti 3 C 2 MXenes nanocomplex was constructed as a self-standard ratiometric fluorescence resonance energy transfer (FRET) nanoprobe for quantitative detection of exosomes. The Cy3-CD63 aptamer can be selectively adsorbed onto the Ti 3 C 2 MXene nanosheets by hydrogen bond and metal chelate interaction between the aptamer and MXenes, and the fluorescence signal from Cy3-CD63 aptamer was quenched quickly owing to the FRET between the Cy3 and MXenes. The fluorescence of Cy3 greatly recovered after the addition of the exosomes which can specifically combine with the aptamer and release from the surface of Ti 3 C 2 MXenes due to the high affinity between the aptamer and CD63 protein on exosome surface. Meanwhile, the self-fluorescence signal of MXenes in the whole process showed little change, which can be used as a standard reference. Based on the self-standard turn-on FRET biosensing platform the detection limit of exosome was determined as 1.4 × 10 3 particles mL −1 , which was over 1000× lower than that of conventional ELISA method. This fluorescence sensor can also be used for the identification of multiple biomarkers on the exosome surface and different kinds of exosomes, combining with the fluorescent confocal scanning microscope image. The proposed strategy not only provides a universal nanoplatform for exosomes, but also can be extensively expanded to multiple biomarkers detection, which may promise the prospect of MXenes as robust candidates in biological fields.

Background Accumulating evidence shows that microRNA-210 (miR-210) holds great promise to improve angiogenesis for brain tissue repair after cerebral ischemia. However, safe and efficient delivery of miR-210 via intravenous administration is still a challenge. In the past decade, exosomes have emerged as a novel endogenous delivery system. Here, c(RGDyK) peptide is conjugated to exosomes, and they are loaded with cholesterol-modified miR-210 (RGD-exo:miR-210). Results In a transient middle cerebral artery occlusion (MCAO) mouse model, the RGD-exo:miR-210 targets the lesion region of the ischemic brain after intravenous administration, resulting in an increase in miR-210 at the site. Furthermore, RGD-exo:miR-210 are administered once every other day for 14 days, and the expressions of integrin β 3 , vascular endothelial growth factor (VEGF) and CD34 are significantly upregulated. The animal survival rate is also enhanced. Conclusions These results suggest a strategy for the targeted delivery of miR-210 to ischemic brain and provide an angiogenic agent for the treatment of ischemic stroke. Electronic supplementary material The online version of this article (10.1186/s12951-019-0461-7) contains supplementary material, which is available to authorized users.

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