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Abram Akopian, Tamas Atlasz, Jacqueline Romero, Sze Wong, Yi Zhang, David Paul, Bela Volgyi, Stewart Bloomfield; Propagation of Cell Death by Gap Junctions in Retina is Connexin-Specific. Invest. Ophthalmol. Vis. Sci. 2012;53(14):2453.
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© ARVO (1962-2015); The Authors (2016-present)
Neuronal loss through cell death is a hallmark of many pathological conditions in the nervous system. In addition to the intrinsic mechanisms underlying primary cell death, intercellular communication through gap junctions (gjs) appears to play a major, but presently unclear, role in secondary or bystander cell death. Like at other CNS loci, secondary cell death via gjs has been implicated in a number of neurodegenerative diseases, including ischemic neuropathy, retinitus pigmentosa, glaucoma, and stroke. Here, we conducted the first comprehensive study of the role of gjs in secondary cell death in retina associated with excitotoxic and ischemic conditions.
Experiments were performed on retinas of wild type (WT), connexin knockout (KO) and heterozygous (Het) littermate mouse strains. Excitotoxicity was induced in vitro by incubation in NMDA (300 µM). To induce retinal ischemia, we employed both in vitro (oxygen/glucose depivation) and in vivo (elevated IOP) methods. Apoptotic and necrotic cell death was assessed by a number of different assays, including propidium iodide (PI), Live/Dead viability assay, TUNEL, or activated caspase-3 immunocytochemistry.
We found that excitotoxic and ischemic conditions produced a significant increase in the cell death of amacrine and ganglion cells in both the INL and GCL of WT and Het mice. However, in comparison to Het mouse retinas, we found that cell death was reduced by ~60% in Cx36 KO retinas exposed to excitotoxic conditions. Further, we found no statistical difference between excitotoxic cell death found in Cx45 KO mouse retinas and their Het littermates. Measurements of cell death in Cx36/45 dKO mice were no different than those made in Cx36 KOs. In contrast, we found that cell death induced by ischemia was reduced by ~80% in Cx45 KO mouse retinas, but differences between WT and Cx36 KO mice were negligable.
Our results indicate that secondary cell death via gjs results in the vast majority of cell loss under different pathological conditions. Moreover, our findings indicate that depending on the type of initial insult, different gjs, as indicated by the connexins they express, underlie the associated secondary cell death. Gap junction connexins may thus be novel targets for therapeutic interventions aimed at increasing cell survival under a variety of neurodegenerative conditions in retina.
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