Marrow Mesenchymal Stem Cell-Derived Exosomes Upregulate Astrocytic Glutamate Transporter-1 Expression via miR-124/mTOR Pathway against Oxygen-Glucose Deprivation/Reperfusion Injury

Background: Experimental investigations have reported the efficacy of marrow mesenchymal stem cell-derived exosomes (MSC-Exos) for the treatment of ischemic stroke. The therapeutic mechanism, however, is still unknown. The purpose of the study is to show whether MSC-Exos increases astrocytic glutamate transporter-1 (GLT-1) expression in response to ischemic stroke and to investigate further mechanisms.

Methods and results: An in vitro ischemia model (oxygen-glucose deprivation/reperfusion, OGD/R) was used. MSC-Exos was identified by Western blot (WB) and transmission electron microscopy (TEM). To further investigate the mechanism, MSC-Exos, miR-124 inhibitor, and mimics, and a mTOR pathway inhibitor (rapamycin, Rap) were used. The interaction between GLT-1 and miR-124 was analyzed by luciferase reporter assay. The GLT-1 RNA expression and miR-124 was assessed by quantitative real-time polymerase chain reaction (qRTPCR). The protein expressions of GLT-1, S6, and pS6 were detected by WB. Results demonstrated that MSC-Exos successfully inhibited the decrease of GLT-1 and miR-124 expression and the increase of pS6 expression in astrocytes after OGD/R. miR-124 inhibitor suppressed the effect of MSC-Exos on GLT-1 upregulation after OGD/R. Rapamycin notably decreased pS6 expression with significantly higher GLT-1 expression in astrocytes injured by OGD/R. Luciferase activity of the reporter harboring the wild-type or mutant GLT-1 3'UTR was not inhibited by miR-124 mimics. Further results showed that the inhibiting effect of MSC-Exos on pS6 expression and promoting effect of MSC-Exos on GLT-1 expression could be reversed by miR-124 inhibitor after OGD/R; meanwhile, the above conditions could be reversed again by rapamycin.

Conclusions: Results show that miR-124 and the mTOR pathway are involved in regulation of MSC-Exos on GLT-1 expression in astrocytes injured by OGD/R. miR-124 does not directly target GLT-1. MSC-Exos upregulates GLT-1 expression via the miR-124/mTOR pathway in astrocytes injured by OGD/R.