Abstract
Purpose :
Cone cell death in inherited retinal degeneration leads to devastating loss of color perception and visual acuity. We have previously shown that a pharmacological inhibition of aberrant histone deacetylase activity (HDACs) prevents cone loss in the cpfl1 mouse (Trifunovic et al., Hum Mol Genet. 5(20):4462-4472, 2016). However, the mechanisms of cone neuroprotection by the HDAC inhibitor, Trichostatin A (TSA), remain unknown. In the present study, we investigated the effect of intravitreally (IV) injected TSA on histone H3 lysine methylation (H3Kme) by analyzing the epigenetic chromatin marks H3K27me3 and H3K9me3 in response to TSA.
Methods :
We performed immunostaining against H3K27me3 and H3K9me3 in untreated cpfl1 and wt animals and in cpfl1 animals IV-treated with 10nM TSA. Co-labeling with cone arrestin was used to identify cone-specific H3K-methylation patterns. The neuroprotective property of the Jumonji H3K27me3/me2 demethylase inhibitor GSKJ4, was tested on cpfl1 retinal explants. Cpfl1 retinas were explanted at the onset of degeneration at postnatal day 14 (P14) and the effects of GSK-J4 were by quantified by cone counting in the treated vs. control explants at P24, the peak of degeneration.
Results :
In wt retinas H3K27me3 and H3K9me3 staining was observed in various cells in the INL and the GCL layer, while in the ONL only cones were prominently stained. In the cpfl1 retinas as well as in the sham-treated retinas at P24 the cone-specific H3Kme staining was undetectable. In contrast, a single IV treatment of TSA at P14 restored the cone-specific H3K methylations. To confirm that the increased H3K27 methylation is associated with increased cone survival we treated cpfl1 retinal explants with 10μM GSK-J4, an inhibitor of the H3K27 histone demethylases JMJD3 and UTX, from P14 to P24. GSK-J4 treatment increased cone survival for 30% at P24 compared to sham-treated controls (13.89 ± 0.69 SEM vs. 9.61 ± 0.91 SEM cones/100 μm, p=0.019, respectively).
Conclusions :
We show that primary cone photoreceptor degeneration is also associated with the loss of cone-specific H3K27 and H3K9 methylation. Pharmacological inhibition of Jumonji H3K27me3/me2 demethylase can significantly attenuate hereditary cone photoreceptor degeneration, opening new venues for targeted cone neuroprotection and highlighting the importance of epigenetic modifications in inherited cone dystrophies.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.