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Oday Alsarraf, Jie Fan, C. James Chou, Craig Crosson; Localization and Activity of Histone Deacetylases in the Retina. Invest. Ophthalmol. Vis. Sci. 2013;54(15):3698.
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© ARVO (1962-2015); The Authors (2016-present)
The increase in histone deacetylase (HDAC) activity and resulting dysregulation of protein acetylation is an integral event in retinal degenerations associated with ischemia and ocular hypertension. The purpose of the current study is to determine activity profiles and distribution of individual HDACs in the retina, and if the selective modulation of individual isoforms can limit retinal injury.
Isolated mouse retinas were evaluated for class-I and II HDAC activity using a class-specific fluorometric enzymatic assay. The activities of individual HDAC isoforms were determined by the addition of selective isoform inhibitors and gene deletion. Retinal localization and relative abundance of individual HDAC isoforms was determined by immunohistochemistry and Western blotting. In selected knockout and wild type mice, electroretinogram (ERG) analysis was used to evaluate responses to 45-minutes of ischemic retinal injury at 7 days post-injury as compared to baseline values.
Although class-II HDACs were detected by Western blot analysis in retinas from control mice, class-I HDACs accounted for all the measureable activity. Analysis of individual class-I isoforms demonstrated that HDAC1 and 2 accounted for 34 ± 3.5% of total activity, and HDAC3 for the remaining 66 ± 5.0% activity. Immunolocalization demonstrated that HDAC1, 2 and 3 were primarily located in the cell bodies of inner nuclear and retinal ganglion cell layers. However, HDAC1 and 2 also exhibited limited expression in the outer nuclear layer. In wild-type mice, ERG a- and b-wave amplitudes from ischemic eyes were significantly reduced by 53.3 ± 6.3% and 59.8 ± 6.9%, respectively, as compared to pre-ischemia baseline values. In HDAC2 heterozygote knockout mice, baseline ERGs were not altered; however, ERG a- and b-wave amplitudes from ischemic eyes were significantly greater by 66.4 ± 4.8% and 60.0 ± 7.6%, respectively, as compared to waveforms from ischemic eyes in wild-type mice.
Although HDACs are detected in most retinal cell bodies, these studies provide evidence that HDAC1, 2 and 3 isoforms account for almost all activity and are predominantly expressed in inner retinal layers. The selective reduction in HDAC2 expression is sufficient to significantly reduce ischemic retinal injury. These data support the idea that isoform selective HDAC inhibitors may provide an efficacious strategy to protect the retina from injury.
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