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H. R. Pelzel, C. L. Schlamp, R. W. Nickells; The Role of Histone Acetylation/Deacetylation on Early Changes in Gene Expression in Retinal Ganglion Cells Following Optic Nerve Crush. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4953.
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© ARVO (1962-2015); The Authors (2016-present)
The loss of retinal ganglion cells during glaucoma occurs by apoptosis. Both decreases and increases in gene expression are early events in the apoptotic pathway. We examined what role promoter histone acetylation levels play in these gene expression changes.
Histone deacetylase (HDAC) activity assays were performed on nuclear protein extracts from retinas harvested from mice 1, 3, 5, and 7 days after optic nerve crush (ONC). Western blots (WB) and immunofluorescence (IF) were used to determine the presence and localization of HDACs in the mouse retina. Chromatin immunoprecipitations (ChIP) with antibodies against acetylated H4 histones and quantitative mRNA analyses were performed on samples from retinas following ONC to compare patterns in promoter histone acetylation and expression of select genes - Thy1, BclX, Brn3b, Fem1c, Bim, and GFAP.
HDAC activity assays showed a significant increase in HDAC activity at 5 day (P=0.07) and 7 days (P=0.021) post-ONC. WB analysis showed that HDACs 2 and 3 were the predominant isoforms in the murine retina. Preliminary results from WB and IF experiments demonstrated HDAC 3 localization changed from cytosolic to nuclear following ONC. IF experiments also showed a concomitant decrease in histone H4 acetylation in the ganglion cell layer, but not the inner nuclear layer. ChIP and mRNA analysis revealed a correlation between changes in histone acetylation and transcript levels after ONC. Genes that become down-regulated, such as Thy1, show a decrease in histone acetylation, while genes that become up-regulated, such as Bim, show an increase.
The data illustrate that early changes in gene expression may be regulated by promoter histone acetylation status. The role of histone acetylation/deacetylation in the ganglion cell apoptotic program is being studied further using inhibitors of HDAC activity.
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