Roles of the Hypoximir microRNA-424/322 on Acute Hypoxia and Hypoxia-Induced Pulmonary Vascular Leakage

Background: Acute mountain sickness (AMS) occurs in up to 25% of unacclimatized persons who ascend to 3000 m and can result in highaltitude pulmonary edema (HAPE) or cerebral edema (HACE). MicroRNAs (miRs) can regulate gene expression on the post-transcriptional level via translational repression of the target mRNA. Hypoxia selectively disrupts brain microvascular endothelial tight junction complexes through a HIF1α-dependent mechanism. While increased HIF-1α expression is associated with adaptation and protection from the development of AMS in the early stage of hypoxia, the downstream effector of HIF-1α, VEGF, can induce overzealous endothelial barrier dysfunction, increase vascular permeability and hence result in HAPE and HACE. We hypothesized that the fine-tuning of downstream effectors, such as VEGF, by hypoximirs is paramount for the preservation of endothelial barrier integrity and prevention of vascular leakage. Materials and Methods: RNA sequencing was performed, and miR-424 was selected as the target miR. Human pulmonary microvascular endothelial cells and human umbilical endothelial cells were used in the in vitro experiments. miR-424 mimics and inhibitors were used to test their effects on the putative target molecules, cell senescence and apoptosis. miR-322 (mouse analog of miR-424)-deficient mice and their littermates were also studied. Results: Several hypoximirs, including miR-210, miR-92a, miR-199, miR-193, miR-424 and miR-221, were elevated in healthy volunteers who were subjected to high-altitude conditions. Hypoxia-induced miR-424 overexpression is HIF-1α dependent. miR-424 could stabilize HIF-1α and decrease VEGF as well as induce the phosphorylation of VE-cadherin. miR424 could also attenuate hypoxia-induced endothelial cell (EC) senescence and apoptosis. As expected, miR-322 KO mice were susceptible to hypoxia- induced pulmonary vascular leakage. Finally, miR-322 mimics could attenuate hypoxia-induced pulmonary vascular leakage in vivo. Conclusions: Several hypoximirs were upregulated in healthy adult volunteers subjected to hypobaric hypoxemia. miR-424/322 could modulate the HIF-1α-VEGF axis and prevent hypoxia-induced pulmonary vascular leakage under hypoxic conditions. Funding Statement: This study was supported by a grant from the Tri-Service General Hospital of the National Defense Medical Center in Taipei, Taiwan (TSGH-C105-056, TSGH-C107-047), and the Ministry of Science and Technology (MOST 106-2314-B-016-031 and MOST 106-2314-B-016-008-MY3). Declaration of Interests: The authors declare that they have received no financial support and have no conflicts of interest. Ethics Approval Statement: The study was approved by the Institutional Research Board of the Tri-Service General Hospital in Taipei, Taiwan and was conducted in accordance with the Declaration of Helsinki and relevant guidelines. Written informed consent was obtained from each participant.