ABSTRACT: Recent evidence suggests that hypoxia caused by acute myocardial infarction (AMI) can induce evident cardiomyocyte apoptosis. Exosomes, as paracrine signaling mediators by delivering cytosolic components (including miRNA, mRNA, protein), play crucial roles in intercellular communication. However, the systemic regulation of exosome-mediated miRNA delivery and subsequent regulation effect underlying AMI are not well-understood to date. Here, using small RNA-seq, we investigated the miRNAome of H9C2 cells and corresponding paracrine exosmes after hypoxia stress, and identified total of 92 and 62 differentially expressed (DE) miRNAs in cells and exosomes from hypoxia vs. normoxia condition. We found that hypoxia strongly induced the expression of hypoxamiRs in H9C2 cells and altered cardiomyocyte-derived exosomal miRNAome. Functional enrichment analysis revealed extensive roles of DE exosomal miRNAs in HIF-1 signaling pathway and cell apoptosis process, such as TNF signaling pathway, MAPK signaling pathway, mTOR signaling pathway. Furthermore, the gain- and loss-of-function analysis demonstrated the anti-apoptotic effects of hypoxia-induced exosomal miRNAs, i.e. miR-21-5p, miR-378-3p, miR-152-3p, let-7i-5p, and then the luciferase reporter assay confirmed that miR-152-3p and let-7i-5p implemented their anti-apoptotic function by directly targeting Atg12 and Faslg, respectively. In short, this study revealed that hypoxia-exosomes derived from cardiomyocyte, loaded abundant cardio-protective miRNAs, mediate crosstalk among cardiomyocytes and prevent cardiomyocytes apoptosis after hypoxia. Methods: we established the anoxia model using H9C2 cells, an immortal cardiac muscle cell line, to imitate hypoxia condition caused by AMI in vitro, and then small RNA-seq were employed to investigate the miRNA transcriptome of H9C2 cells and its exosomes collected from hypoxia and normoxia culture medium. Results: we identified the miRNAome of H9C2 cells and its exosmes under both hypoxia and normoxia, including 331, 338, 144, 74 unique mature miRNAs from hypoxia-cells, normoxia-cells, hypoxia-exosomes, normoxia-exosomes, respectively. Total of 92 and 62 DE miRNAs were identified from cells and exosomes. Among of which, the DE exosomal miRNAs were mainly involved in HIF-1 signaling pathway and cell apoptosis process, such as TNF signaling pathway, MAPK signaling pathway, mTOR signaling pathway. Interestingly, we found that some DE exosomal miRNAs, including miR-21-5p, miR-378-3p, miR-152-3p, let-7i-5p, have an anti-apoptotic and pro-viability effects in H9C2 cells under hypoxic stress. In addition, Atg12 and Faslg to be respective target of miR-152-3p and let-7i-5p were partly elucidated the anti-apoptosis mechanism of hypoxia-exosomes. Conclusions:In brief, this study illustrated a potential mechanism that, under hypoxic stress, hypoxia pre-perceived cardiomyocytes can spontaneously secrete the hypoxamiRs enriched exosomes, loaded a large amount of cardio-protective miRNA, which mediate crosstalk among cardiomyocytes and prevent apoptosis to heighten the hypoxia adaptability of cardiomyocytes. In more detail, we first discovered that miR-152-3p and let-7i-5p, enriched in hypoxia-exosomes derived by cardiomyocytes, played an anti-apoptosis role via mitochondrial pathway(intrinsic pathway) and death receptor pathway (extrinsic pathway), respectively.
