Influence of miR-155 on Cell Apoptosis in Rats with Ischemic Stroke: Role of the Ras Homolog Enriched in Brain (Rheb)/mTOR Pathway
Guoping Xing, Zengxiang Luo, Chi Zhong, Xudong Pan, Xiaowei Xu
Department of Neurology, The Affiliated Hospital of Qingdao University, Qingdao, Shandong, China (mainland)
Med Sci Monit 2016; 22:5141-5153
DOI: 10.12659/MSM.898980
Available online:
Published: 2016-12-27

BACKGROUND:
We designed and carried out this study to examine the role of miR-155 and the Rheb/mTOR pathway in ischemic stroke. We also investigated how these two elements interact with each other and contribute to injuries resulting from ischemic stroke.
MATERIAL AND METHODS:
We used both a middle cerebral artery occlusion rat model in vivo and an oxygen-glucose deprivation cell model in vitro to simulate the onset of ischemic stroke. miR-155 mimics, miR-155 inhibitors, and Rheb siRNA were transfected to alter the expression of miR-155 and Rheb. Infarct sizes were measured using magnetic resonance imaging (MRI) and triphenyltetrazolium chloride (TTC) staining; cell apoptosis rates were calculated using Annexin V-FITC/PI staining and flow cytometry. Levels of miR-155, Rheb, mTOR, and S6K were examined by RT-PCR, immunofluorescence, and western blot. We performed a luciferase activity assay so that the association between miR-155 and Rheb could be fully assessed.
RESULTS:
We demonstrated that miR-155 bound the 3’-UTR of Rheb and suppressed Rheb expression. As suggested by animal models, significant cerebral infarct volumes and cell apoptosis were induced by increased expression of miR-155 and decreased expression of Rheb, mTOR, and p-S6K (P<0.05). miR-155 inhibitors exhibited protective effects on ischemic stroke, including down-regulation of infarction size in cerebral tissues in vivo and reduced apoptosis of BV2 cells in vitro with increased expression of Rheb, mTOR and p-S6K (P<0.05). These protective effects could be substantially antagonized by the transfection of Rheb siRNA (P<0.05).
CONCLUSIONS:
Inhibition of miR-155 may play protective roles in ischemic stroke by phosphorylating S6K through the Rheb/mTOR pathway.
Keywords: Infarction, Middle Cerebral Artery, Stroke, TOR Serine-Threonine Kinases