Silencing matrix metalloproteinase 9 exerts a protective effect on astrocytes after oxygen-glucose deprivation and is correlated with suppression of aquaporin-4

Abstract

Cerebral ischemia, followed by brain edema, can be life-threatening. It has been widely reported that matrix metalloproteinase-9 (MMP-9) and aquaporin-4 (AQP4) have prominent roles in the development of brain edema. However, the exact mechanisms by which MMP-9 and AQP4 influence brain edema are not fully understood.In this study, astrocytes were subjected to oxygen-glucose deprivation (OGD) /reperfusion (OGD/R) injury, an in vitro model of Ischemia/reperfusion (I/R). Cell viability was evaluated through the measurement of LDH release. The expression of MMP-9 and AQP4 also were measured by qPCR and western blot. Subsequently, we knocked out the MMP-9 gene using MMP-9 siRNA. AQP4 and its gene expression, and the LDH release rate were measured using ELISA, Western blotting, and RT-PCR. We also assessed cAMP-dependent protein kinase (PKA), cGMP-dependent protein kinase (PKG), protein kinase C (PKC), and Ca2+/calmodulin-dependent protein kinase II (CaMK II) in MMP-9 knockout astrocytes. All measurements were performed with or without an OGD/R challenge.OGD/reperfusion enhanced LDH release levels, and also increased MMP-9 and AQP4 expression in astrocytes. Silencing the MMP-9 gene decreased LDH release levels, and also was associated with decreased AQP4 expression. The expression of PKC, but not PKA, PKG, or CaMK II, was decreased. This study revealed that OGD/reperfusion could cause cell damage in vitro. MMP-9 silencing protected astrocytes from hypoxic insult, and the protective effect may be enhanced by the downregulation of AQP4 expression. In conclusion, downregulating MMP-9 expression may be useful for the prevention and treatment of brain ischemia.