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Int J Biol Sci 2017; 13(10):1287-1296. doi:10.7150/ijbs.18890

Research Paper

Exosomal miR-7 Mediates Bystander Autophagy in Lung after Focal Brain Irradiation in Mice

Shang Cai1, 2*, Geng-Sheng Shi3*, Hui-Ying Cheng2, 4, Ya-Nan Zeng2, 4, Gen Li2, 4, Meng Zhang2, 4, Man Song2, 4, Ping-Kun Zhou2, Ye Tian1, 2, Feng-Mei Cui2, 4✉, Qiu Chen2, 4✉

1. Department of Radiotherapy and Oncology, The Second Affiliated Hospital of Soochow University, Suzhou 215004, P R China;
2. Collaborative Innovation Center of Radiation Medicine of Jiangsu Higher Education Institutions, Suzhou 215123, P R China;
3. Shandong Academy of Occupational Health and Occupational Medicine, Shandong Academy of Medical Sciences, Jinan 250062, P R China;
4. Department of Radiation Medicine, School of Radiation Medicine and Protection, Medical College of Soochow University, Suzhou 215123, P R China.
* These authors have contributed equally to this work.

Abstract

This study investigated whether exosomal microRNA-7 (miR-7) mediates lung bystander autophagy after focal brain irradiation in mice. After 10 Gy or sham irradiation of mice brains, lung tissues were extracted for the detection of autophagy markers by immunohistochemistry, western blotting, and quantitative real-time reverse transcription PCR (qRT-PCR), meanwhile the brains were dissociated, the neuron/astrocyte/microglia/oligodendrocyte were isolated, and the miR-7 expression in each population were detected, respectively. A dual-luciferase reporter assay was developed to identify whether Bcl-2 is a target gene of miR-7. After 10 Gy or sham irradiation of astrocytes, exosomes were extracted, stained with Dil (1,1'-Dioctadecyl-3,3,3',3'-Tetramethylindocarbocyanine Perchlorate), and added into non-irradiated astrocytes. Meanwhile, Dil-stained exosomes released from 10 Gy or sham irradiated astrocytes were injected into LC3B-GFP mice via the tail vein. Lung tissues were then extracted for western blotting and qRT-PCR. Irradiation of mouse brains increased the LC3B-II/I ratio, Beclin-1 and miR-7 levels, while decreased the Bcl-2 level in non-irradiated lung tissue. Interestingly, brain irradiation remarkably increased the miR-7 expression in astrocyte and oligodendrocyte. MiR-7 significantly inhibited the luciferase activity of the wild-type Bcl-2-3′-untranslated regions (UTR) reporter vector, but not that of the Bcl-2-3′-UTR mutant vector, indicating that Bcl-2 is directly targeted by miR-7. In in vitro study, the addition of irradiated astrocyte-secreted exosomes increased the LC3B-II/I ratio, Beclin-1 and miR-7 levels, while decreased the Bcl-2 level in non-irradiated astrocytes. Further, the injection of irradiated astrocyte-secreted exosomes through the tail vein increased the lung LC3B-II/I ratio, Beclin-1 and miR-7 level, but decreased the Bcl-2 level in vivo. We concluded that exosomal miR-7 targets Bcl-2 to mediate distant bystander autophagy in the lungs after brain irradiation.

Keywords: exosome, miR-7, radiation, radiation induced bystander effect (RIBE), autophagy.

This is an open access article distributed under the terms of the Creative Commons Attribution (CC BY-NC) license (https://creativecommons.org/licenses/by-nc/4.0/). See http://ivyspring.com/terms for full terms and conditions.
How to cite this article:
Cai S, Shi GS, Cheng HY, Zeng YN, Li G, Zhang M, Song M, Zhou PK, Tian Y, Cui FM, Chen Q. Exosomal miR-7 Mediates Bystander Autophagy in Lung after Focal Brain Irradiation in Mice. Int J Biol Sci 2017; 13(10):1287-1296. doi:10.7150/ijbs.18890. Available from http://www.ijbs.com/v13p1287.htm