title: The role of excitotoxic programmed necrosis in acute brain injury.
abstract: Excitotoxicity involves the excessive release of glutamate from presynaptic nerve terminals and from reversal of astrocytic glutamate uptake, when there is excessive neuronal depolarization. N-methyl-d-aspartate (NMDA) receptors, a subtype of glutamate receptor, are activated in postsynaptic neurons, opening their receptor-operated cation channels to allow Ca(2 +) influx. The Ca(2 +) influx activates two enzymes, calpain I and neuronal nitric oxide synthase (nNOS). Calpain I activation produces mitochondrial release of cytochrome c (cyt c), truncated apoptosis-inducing factor (tAIF) and endonuclease G (endoG), the lysosomal release of cathepsins B and D and DNase II, and inactivation of the plasma membrane Na(+)-Ca(2 +) exchanger, which add to the buildup of intracellular Ca(2 +). tAIF is involved in large-scale DNA cleavage and cyt c may be involved in chromatin condensation; endoG produces internucleosomal DNA cleavage. The nuclear actions of the other proteins have not been determined. nNOS forms nitric oxide (NO), which reacts with superoxide (O2 (-)) to form peroxynitrite (ONOO(-)). These free radicals damage cellular membranes, intracellular proteins and DNA. DNA damage activates poly(ADP-ribose) polymerase-1 (PARP-1), which produces poly(ADP-ribose) (PAR) polymers that exit nuclei and translocate to mitochondrial membranes, also releasing AIF. Poly(ADP-ribose) glycohydrolase hydrolyzes PAR polymers into ADP-ribose molecules, which translocate to plasma membranes, activating melastatin-like transient receptor potential 2 (TRPM-2) channels, which open, allowing Ca(2 +) influx into neurons. NADPH oxidase (NOX1) transfers electrons across cellular membranes, producing O2 (-). The result of these processes is neuronal necrosis, which is a programmed cell death that is the basis of all acute neuronal injury in the adult brain.
authors.affiliation: David Geffen School of Medicine, University of California at Los Angeles, VA Greater Los Angeles Healthcare System, United States.
authors.forename: Denson G
authors.initials: DG
authors.lastname: Fujikawa
keywords: Excitotoxicity; NMDA receptor; Necrosis; Programmed cell death