Secondary cone degeneration is prevented by HDAC inhibition

Abstract

Purpose : Mutation-independent secondary cone degeneration, as it happens in Retinitis Pigmentosa (RP), is a main contributor to inherited blindness in the working age population. Current knowledge on the mechanisms of secondary cone degeneration is scarce and therapeutic options to prevent or delay cone loss is practically non-existing. Our previous work showed that a pharmacological inhibition of aberrant histone deacetylase activity (HDACs) prevents both primary cone and rod loss. Here we investigated whether HDAC inhibition also harbors a potential for the treatment of secondary cone degeneration.

Methods : The neuroprotective properties of the HDAC inhibitor, Trichostatin A (TSA) on secondary cone death was evaluated on rd1^TN-XL retinal explants. rd1^TN-XL transgenic mice are homozygous for the rd1 allele and express fluorescent TN-XL biosensor exclusively in cones (Kulkarni et al., 2016). The retinas were explanted at PN19 and PN21, when almost all rods have already fully degenerated and were cultured with or without 10nM TSA for one week. Cone survival was assessed by quantifying the number of cones/100 µm. Whole transcriptome analysis was performed on flow sorted-treated and -untreated TN-XL-labeled cones.

Results : Independent on the number of cones at the start of the treatment, HDAC inhibition resulted in an up to 30% increase in the cone survival in the rd1^TN-XL explants. More specifically, HDAC inhibition significantly increased cone survival at both stages PN19 (9.15 ± 0.8 SEM in the TSA-treated vs. 6.35 ± 0.6 cones in control retinas, p=0.019, n=7) and PN21 (5 ± 0.7 cones surviving in treated vs. 2.62 ± 0.6 cones in control retinas p=0.015, n=5). RNA-seq analysis from PN19 treated or untreated flow-sorted cones identified 813 differentially expressed genes (FC1.5, p≤0.05) in the TSA-treated cones. Top molecular pathways associated with cone survival included metabolic pathways, MAPK and PI3k-Akt signaling pathways, endoplasmic reticulum stress and autophagy.

Conclusions : Our results strongly suggest that HDAC inhibition can prevent secondary cone degeneration, ex vivo in the rd1 mouse model for RP, even at late stages of degeneration when all rods have fully degenerated. Together with our previous findings these data suggest a unique possibility for targeted neuroprotection of both primary degenerating rods and mutation-free secondary dying cones and creates hope to maintain vision in RP patients independent of the disease stage.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.