AMPA receptor desensitization is the determinant of AMPA receptor mediated excitotoxicity in purified retinal ganglion cells

作者：Park Yong H; Mueller Brett H II; McGrady Nolan R; Ma Hai Ying; Yorio Thomas^*

来源：Experimental Eye Research, 2015, 132: 136-150.

DOI：10.1016/j.exer.2015.01.026

• Primary retinal ganglion cells
• AMPA receptor
• Excitotoxicity
• Desensitization
• cAMP response element-binding protein

The ionotropic glutamate receptors (iGLuR) have been hypothesized to play a role in neuronal pathogenesis by mediating excitotoxic death. Previous studies on iGluR in the retina have focused on two broad classes of receptors: NMDA and non-NMDA receptors including the cc-amino-3-hydroxy-5-methyl-4-isoxazolepropionic receptor (AMPAR) and kainate receptor. In this study, we examined the role of receptor desensitization on the specific excitotoxic effects of AMPAR activation on primary retina] ganglion cells (RGCs). Purified rat RGCs were isolated from postnatal day 4-7 Sprague Dawley rats. Calcium imaging was used to identify the functionality of the AMPARs and selectivity of the s-AMPA agonist. Phosphorylated CREB and ERK1/2 expression were performed following s-AMPA treatment. s-AMPA excitotoxicity was determined by JC-1 mitochondrial membrane depolarization assay, caspase 3/7 luciferase activity assay, immunoblot analysis for cc-fodrin, and Live (calcein AM)/Dead (ethidium homodimer-1) assay. RGC cultures of 98% purity, lacking lba1 and GFAP expression were used for the present studies. Isolated prenatal RGCs expressed calcium permeable AMPAR and s-AMPA (100 liM) treatment of cultured RGCs significantly increased phosphorylation of CREB but not that of ERK1/2. A prolonged (6 h) AMPAR activation in purified RGCs using s-AMPA (100 mu M) did not depolarize the RGC mitochondria] membrane potential. In addition, treatment of cultured RGCs with s-AMPA, both in the presence and absence of trophic factors (BDNF and CNTF), did not increase caspase 3/7 activities or the cleavage of cc-fodrin (neuronal apoptosis marker), as compared to untreated controls. Lastly, a significant increase in cell survival of RGCs was observed after s-AMPA treatment as compared to control untreated RGCs. However, preventing the desensitization of AMPAR with the treatment with either kainic acid (100 mu M) or the combination of s-AMPA and cyclothiazide (50 mu M) significantly reduced cell survivability. Activation of the AMPAR in RGCs does not appear to activate a signaling cascade to apoptosis, suggesting that RGCs in vitro are not susceptible to AMPA excitotoxicity as previously hypothesized. Conversely, preventing AMPAR desensitization through differential agonist activation caused AMPAR mediated excitotoxicity. Activation of the AMPAR in increasing CREB phosphorylation was dependent on the presence of calcium, which may help explain this action in increasing RGC survival.

• 出版日期2015-3