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Abram Akopian, Tamas Atlasz, Stewart A Bloomfield; Excitotoxic and Ischemic Conditions Change the Expression of Gap Junction Connexins in the Inner Retina. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2390.
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© ARVO (1962-2015); The Authors (2016-present)
Secondary cell death via gap junctions plays a critical role in the cell loss associated with neurodegenerative diseases (Belousov and Fontes 2013). In the retina we reported that secondary cell death accounts for most cell loss that occurs under excitotoxic and ischemic conditions (ARVO, 2011). Secondary cell death in CNS may be connexin specific and connexins may be up- or down-regulated under different pathological conditions (Rouach et al., 2002). Here we examined whether secondary cell death of retinal ganglion cells (RGCs) under excitotoxic and ischemic conditions is connexin-specific and whether the expression of Cx36 and Cx45 in inner retina is differentially effected.
Excitotoxicity was induced in vitro by incubation of mouse retinas in NMDA. Transient retinal ischemia was induced in vivo by elevation of IOP. Levels of cell death were assayed histologically and antibodies against Cx36 and Cx45 were used to assess their levels in the IPL.
Consistent with our earlier work, we found that excitotoxic and ischemic conditions produced a significant loss of RGCs. Ablation of Cx36 in the Cx36 knockout (KO) mouse retina resulted in an ~70% decrease in RGC loss under excitotoxic conditions, whereas RGC loss in the Cx45 KO retina was not statistically different than that seen in WT mice. In contrast, RGC loss with ischemia was significantly reduced in Cx45 KO retinas, whereas the loss in Cx36 KO retinas was similar to that in the WT. In WT retinas the expression of Cx36 and Cx45 in the IPL followed a punctuate pattern typical for gap junctions. Under excitotoxic conditions the expression of Cx45 was down-regulated, whereas there were no detectable changes in Cx36 expression. In contrast, induction of ischemic conditions produced a dramatic change in Cx36 expression, which appeared as dense clusters around nuclei rather than as puncta. We found no change in the control punctate labeling pattern of Cx45 expression in ischemic retinas.
Secondary cell death of RGCs is connexin specific where Cx36 gap junctions play a role under excitotoxic conditions and Cx45 gap junctions play a role during ischemia. These results are consistent with changes in connexin expression seen under these two conditions. These results suggest that targeting of specific connexins can be a novel therapeutic strategy for reducing RGC loss under different pathological conditions.
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