Roles Of An Autophagy/lysosomal Pathway In Excitotoxicity Mediated By NMDA Receptor

Aim: To study the role of an autophagy/lysosomal pathway in excitotoxicity mediated by NMDA receptors.Methods: Excitotoxic rat model was produced with stereotaxic administration of quinolinic acid into unilateral striatum. Autophagosomes were observed with electron microscopy. Protein levels of Lamp-1, cathepsin B, cathepsin D, Bc1-2 and caspase-3 were determined with immunohistochemistry and Western blot analysis. The neuroprotective effects of the autophagy inhibitor 3-MA and the lysosomal cathepsin B inhibitor were accessed with internucleosomal DNA fragmentation and Cresyl violet staining.Results: Electron microscopy revealed that the formation of autophagosomes in the rat striatum started 0.5 hours and reached maxiamum 4 hours after injection of QA. Immunohistochemistry demonstrated the increase in Lamp-1 and cathepsin B protein levels in a time-dependent fashion. Western blot analysis revealed the increase in cathepsin B and cathepsin D activation, and the decrease in pro-caspase-3 protein levels. Bcl-2 protein levels increased 8 hours and decreased 12 hours after QA injection. Pretreated with 3-MA and cathepsin B inhibitor attenuated QA-induced internucleosomal DNA fragmentation and significantly reduced the striatal neuronal loss (P<0.01).Conclusions: The increase in autophagosomes and the activation of lysosomes may be involved in the excitotoxicity mediated by NMDA receptors. Autophagy inhibitors and lysosome inhibitors have neuroprotective actions in against QA-induced apoptotic death of rat stritatal neurons.