Delayed administration of rapamycin inhibits glial scar formation through upregulating matrilin-3 in an autophagy-dependent manner in ischemic stroke.

Glial scar formation is one of the major pathological mechanisms following ischemic stroke. Rapamycin is a potent specific mTOR inhibitor and an autophagy activator. Although it has neuroprotective effects against acute ischemic stroke, it is unknown whether delayed administration of rapamycin can reduce ischemic stroke-induced pathogenesis such as glial scar formation, independent on its effects of acute administration. We recently reported that matrilin-3, an extracellular matrix component, provides neuroprotection in ischemic stroke by suppressing astrocyte-mediated neuroinflammation and glial scar formation. Here, in rat models of middle cerebral artery occlusion and reperfusion (I/R), rapamycin was administered for consecutive 7 or 14 days starting at day 1 post-reperfusion; and in an oxygen-glucose deprivation and reoxygenation (OGD/Re)-induced primary astrocyte or human astrocyte injury model, rapamycin was given upon reoxygenation. We found that rapamycin improved I/R-mediated rats' neurological dysfunction, accompanied by reduced glial scar formation and neuronal loss. To our surprise, rapamycin increased the levels of matrilin-3 in the peri-infarct region of rats and in OGD/Re-treated astrocytes associating with restoring autophagic flux. In contrast, the autophagy inhibitors wortmannin and bafilomycin A1 blocked autophagic flux, decreased the levels of matrilin-3 and enhanced glial scar formation, respectively. Overexpression of matrilin-3 significantly reduced the glial scar formation. Mechanistically, rapamycin could decrease the ADAMTS-4 and ADAMTS-5 levels, two hydrolases responsible for the breakdown of matrilin-3, thus upregulating the matrilin-3 levels. Our results reveal that delayed administration of rapamycin suppresses the glial scar formation by upregulating the astrocytic matrilin-3 related to restoring autophagic flux in ischemic stroke.