Histone Acetylation and Deacetylation in rd1 Mouse Photoreceptors

Abstract

Purpose: : Nucleosomes are the smallest structural subunit in chromatin, formed by 146 base-pairs of DNA wrapped on to a histone protein octamer. Histones may be modified, by different posttranslational modification mechanisms, such as methylation, phosphorylation or acetylation leading to changes in chromatin, and in transcription. Acetylation is regulated by two enzymes: Histone acetyl transferases (HATs), in charge of adding acetyl groups to the lysine residues, and histone deacetylases (HDACs), which will remove them. Hyperacetylation may enhance expression of pro-apoptotic transcription factors (apaf, caspase-3), as well as other factors critical for rod differentiation (Otx2, Nrl, Crx, Neurod1). The aim of this study was to investigate the relevance of histone acetylation or deacetylation in rd1 mouse photoreceptor degeneration.

Methods: : Retinae from rd1 and wild-type (wt) animals were cultured in an organotypic explant system and treated with specific inhibitors and activators of HDACs. Cell death and oxidative DNA damage was assessed using TUNEL assay and avidin staining respectively. A newly adapted in situ activity assay was performed to study activity of different classes of HDACs in rd1 and wt retinae.

Results: : The HDAC activity assay allowed to efficiently resolve activation of HDACs both at the tissue and cellular level, showing an enhanced positive signal in rd1 outer nuclear layer, when compared with wt. The application of HDAC class III (a.k.a. sirtuins) inhibitor (nicotinamide) and activator (resveratrol) did not significantly affect viability of degenerating photoreceptor cells. Oxidatively damaged DNA was numerically reduced with the treatment with Resveratrol, but further experiments are needed to established statistic significance.

Conclusions: : HDACs may be involved in the development and progression of the photoreceptor degeneration in the rd1 mouse. Further research is needed to investigate the role of these enzymes in the degeneration process and to evaluate potential rescue effects on rd1 photoreceptors by experimentally induced modifications.

Keywords: retina • photoreceptors • retinal culture