Neuroprotective effect of AIP on N-methyl- d-aspartate-induced cell death in retinal neurons

Abstract

Excessive activation of glutamate receptors mediates neuronal death, but the intracellular signaling pathways that mediate this type of neuronal death are only partly understood. Previously, we have demonstrated that calcium/calmodulin-dependent protein kinase II-α B (CaMKII-α B) containing a nuclear localizing signal but not CaMKII-α is altered in retinal neurons exposed to N-methyl- d-aspartate (NMDA). The present study describes a prospective function of CaMKII-α B in signal transduction leading to apoptosis. The terminal deoxyribonucleotidyl transferase (TdT)-mediated biotin-16-dUTP nick-end labelling (TUNEL) method was used to detect fragmented DNA in fixed tissue sections of rat retina. The TUNEL assay confirmed that cell death occurs in the inner nuclear and ganglion cell layers following injection of 4 mM NMDA. A specific AIP (myristoylated autocamtide-2-related inhibitory peptide) with proven cell permeability inhibits CaMKII activity in vivo. Neuroprotection achieved by 500 μM AIP was complete when administered 2 h before and coincident with the NMDA application. Additionally, 100 μM of AIP protects only partially against the NMDA-induced excitotoxicity. The conformationally active fragment of caspase-3 (17 kDa), known to be involved in neuronal apoptosis was apparent within 30 min and at 2 h postinjection with NMDA. This activation was inhibited by 500 μM AIP when administered 2 h before and coincident with the NMDA application. The results suggest that CaMKII-α B isoform plays a role in excitotoxicity-induced neuronal apoptosis.