Knocking Down HMGB1 Using Dendrimer-Delivered siRNA Unveils Its Key Role in NMDA-Induced Autophagy in Rat Cortical Neurons

To explore the role of the High Mobility Group Box 1 (HMGB1) protein in NMDA-mediated excitotoxicity in rat cortical neurons. We knocked down HMGB1 using small-interfering RNA (siRNA) delivered into neurons by means of a dendrimer. We determined autophagy activation by measuring the ratio of light chain 3 protein isoforms (LC3B-I)/LC3B-II and by determining autophagolysosome labeling using the specific marker monodansyl cadaverine. Neuronal toxicity was induced by exposing the neurons to N-methyl-D-aspartate (NMDA) and it was determined by measuring Lactate dehydrogenase and MTT reduction. We found that NMDA receptor stimulation induced both neuronal death and autophagy in rat cortical neurons. In addition, NMDA also caused HMGB1 translocation from the neuronal nucleus to the cytoplasm where it formed a complex with Beclin1. HMGB1 was efficiently knocked down using a specific siRNA causing a blockade of NMDA-induced autophagy and potentiating NMDA-induced neuronal death. Our study demonstrates that HMGB1 plays a relevant role in neuronal autophagy regulation and suggest a protective role of autophagy during excitotoxicity. In addition, the dendrimer that we have used here is a good vector for siRNA delivery to neurons allowing lack-of-function studies.