Abstract
Purpose:
Previous studies have linked nonselective inhibition of all histone deacetylases using Trichostatin A or Sodium Butyrate to a complete blockage of rod photoreceptor development. These studies, however, fail to narrow down the specific HDACs important in retinal development. Here we investigate two HDAC classes possibly involved in rod photoreceptor growth in neonatal mice retinas. Our hypothesis is that histone deacetylation is essential for proper retina development and that inhibition of one specific HDAC will block rod photoreceptor differentiation.
Methods:
Animal use was in accordance to ARVO/IACUC guidelines. Postnatal day 1 mice retinas were dissected from C57Bl6 mice and cultured for 96 hours with or without treatments of HDAC inhibitors Sodium Butyrate, MC1568, entinostat, apicidin and CAS 193551-00-7. They were then fixed in 4% paraformaldehyde, equilibrated in 20% sucrose, embedded and cryosectioned. Immunohistochemical staining was performed using antibodies for rhodopsin, H3K9ac, H4K12ac, PCNA and recoverin proteins. Image quantifications were done using Image J.
Results:
Select inhibition of Class IIa HDACs using MC1568 at differing concentrations resulted in little to no change of rhodopsin expression or the level of H3K9ac. On the other hand, inhibition of Class I HDACs, HDAC1 and HDAC3, using entinostat resulted in a loss of retina structure comparable to that of nonspecific HDAC inhibition. A significant increase in H3K9ac and H4K12ac levels and a decrease in rhodopsin expression were observed. The selective inhibitors CAS 193551-00-7 (HDAC1) and apicidin (HDAC3) were then used to investigate which HDAC, 1 or 3 or both, have a role in rod development. No statistically significant change in rhodopsin expression and acetylation levels were found in retinas treated with apicidin. However, when retinas were treated with CAS 193551-00-7 a statistically significant decrease in rhodopsin expression accompanied with a statistically significant increase in histone acetylation levels were observed.
Conclusions:
These findings suggest that the Class I HDAC1 is essential in regulating the expression of critical genes required for neonatal rod photoreceptor development.