Increased Tolerance to Ischemic Neuronal Damage by Knockdown of Na+Ca2+ Exchanger Isoform 1
We hypothesize that stimulation of Na+K+Cl+ cotransporter (NKCC1) causes Na+ overload that may lead to reversal of Na+Ca2+ exchanger isoform 1 (NCX1) and ischemic neuronal damage. NCX1 protein expression and Ca2+ influx via reversal of NCX were decreased by ?70% in NCX1+/? neurons. Compared to NCX1+/+ neurons, NCX1+/? neurons exhibited significantly less cell death (?30%) after 3 h oxygen and glucose deprivation (OGD) and 21 h reoxygenation. Additional neuroprotection was found in NCX1+/? neurons treated with NCX inhibitor KB-R7943. Moreover, expression of NCX1 protein was ?40% lower in NCX1+/? brains than in NCX1+/+ brains. However, there was no significant reduction in cerebral infarction in NCX1+/? mice following middle cerebral artery occlusion (MCAO). These data suggest that moderate reduction of NCX1 protein may be not enough to exert protection. We used small RNA-interference (siRNA) approach to further elucidate the role of NCX1 in ischemic cell damage. Efficacy of anti-NCX1 siRNA was tested in astrocytes and ?50% knockdown of NCX1 protein expression was achieved after 2472 h transfection. Reduction in NCX1 protein expression was also found in brains of NCX1+/? mice after the siRNA injection. NCX1+/? mice treated with siRNA showed ?20% less MCAO-induced infarction, compared to NCX1+/? mice. Approximately 50% neuroprotection was detected in NKCC1+/?/NCX1+/? mice following MCAO. In conclusion, these data suggest that NCX1 plays an important role in ischemia/reperfusion-induced neuronal injury
reversal of ncx infarction ca2+ overload neuronal death focal ischemia