CaMKIIαB mediates a survival response in retinal ganglion cells subjected to a glutamate stimulus

PURPOSE. During N-methyl-D-aspartate-induced cell death in the neural retina, levels of the nuclear isoform of CaMKII alpha, CaMKII alpha B, previously reported to be detected only in the midbrain and diencephalon, become elevated. The purpose of this study was to investigate whether CaMKII alpha B is present specifically in retinal ganglion cells (RGCs) and to determine whether it can be implicated in the cell death or cell survival of signal transduction pathways. METHODS. Pan-purified RGCs were obtained from the retinas of postnatal day (P) 6 to P8 Sprague-Dawley rats. The expression level of CaMKII alpha B was investigated in RGCs with the aid of RT-PCR and immunostaining under normal and glutamate-stressed conditions. siRNA targeted to CaMKII alpha B was used to knock down the level of endogenous mRNA in RGCs, and cell viability was tested. The putative role of CaMKII alpha B in the downstream expression of survival genes such as BDNF was evaluated in CaMKII alpha B knocked-down RGCs with the aid of RT-PCR, real-time PCR, and immunofluorescence microscopy. RESULTS. Basal levels of CaMKII alpha B were expressed in RGCs. Expression levels became increased in response to glutamate treatment and were translocated to the nuclei after a glutamate stimulus. In pan-purified RGCs with knocked down levels of CaMKII alpha B, a glutamate stimulus led to an increase in cell death. When CaMKII alpha B was knocked down in RGCs, a corresponding decrease occurred in the level of BDNF expression. CONCLUSIONS. These data indicate that the presence of basal levels of CaMKII alpha B in RGCs may afford them some ongoing protection from a stressful environment. In response to the glutamate stimulus, the expression of survival genes such as BDNF may be enhanced through elevation of this particular isoform of the CaMKII alpha gene.