Study Of The Molecular Mechanisms Of Mesenchymal Stem Cells (MSCs) In Reducing Ischemia-induced Cerebral Edema By Inhibiting Aquqporin4(AQP4) Up-regulation

Purpose: Cerebral ischemia can induce up-regulation of aquaporin4(AQP4) and breakdown of blood brain barrier (BBB), leading tobrain edema. Mesenchymal Stem Cells (MSCs) are widely reportedas an inflammatory cytokine repressor and show a great potentialin the treatment of brain ischemia. However, the effects of MSCs onBBB permeability are unclear. In present study, we tested whetherMSCs treatment had benefits on BBB integrity and further exploredthe molecular mechanism of AQP4on BBB integrity.Methods: Adult CD1male mice subjected to90min transientmiddle cerebral artery occlusion (tMCAO) were received striataltransplantation of MSCs within20min after reperfusion.Neurological severity scores, BBB permeability and edemaformation were evaluated at day1and day3following tMCAO. Wethen investigated the apoptotic astrocytes, AQP4and inflammatorycytokines IL-1, IL-6and TNF-expression in vivo and in vitro. Weused conditioned medium from LPS-activated microglia to stimulate cultured astrocytes and determined the expression of AQP4invitro.Moreover, the regulatory mechanism of AQP4referring to p38,JNK and ERK1/2MAPK signaling pathway were further explored.Results: The modified Neurological Severity Score (mNSS) wasgreatly ameliorated and ischemia-induced brain edema, IgG proteinand Evans Blue leakage were reduced in MSCs treated micecompared to the control mice after tMCAO (p<0.05). Lessdiscontinuous tight junction protein Occludin and ZO-1were alsoobserved in MSCs treated mice (p<0.05). MSCs efficiently inhibitedischemia-induced AQP4overexpression and decreased theapoptotic astrocytes (p<0.05). In vitro studies, conditioned mediumfrom LPS-activated microglia effectively enhanced AQP4expression, p38, JNK phosphorylation and apoptosis in culturedastrocytes (p<0.05). MSCs treatment resulted in less inflammatorycytokines expression in LPS-activated microglia, which therebyinduced milder up-regulation of AQP4in cultured astrocytes andless apoptosis. Knockdown of AQP4in cultured astrocytes couldalso reduce apoptosis (p<0.05).Treatment with p38and JNKinhibitors demonstrated that p38but not JNK MAPK signalingpathway took responsibility for the AQP4overexpression (p<0.05).Conclusion: We conclude that MSCs protect BBB integrity viareducing the apoptotic astrocytes, which is due to attenuated inflammatory response and down-regulated AQP4expressionduring ischemic attack. Moreover, our data also demonstrate thatinflammatory cytokines are responsible for the up-regulation ofAQP4through activating p38MAPK signaling pathway.