Abstract
Purpose :
To determine if epigenetic changes play critical roles in retinal ganglion cells (RGCs) neuroprotection during glaucoma pathology.
Methods :
Intraocular pressure (IOP) was raised in Brown Norway rats by injecting 2M hypertonic saline into the limbal veins. Rats were treated with δ-opioid receptor agonist (SNC-121, 1 mg/kg; i.p), or DNA methylation inhibitor (Decitabine; 1.5 mg/kg, i.p injections) daily for 7 days. Changes in IOP, pattern ERGs, histone acetylation, histone deacetylases (HDACs), and DNA methylation were measured at the end of the experiments.
Results :
Pattern-ERGs (a measure of RGC function) were reduced in ocular hypertensive (OH) animals, which were significantly (p<0.05) improved by SNC-121 and Decitabine treatment in OH animals, at day 42, post injury. Protein acetylation was reduced while the enzyme activities of HDACs, DNA methyltransferases (DNMTs), and DNA methylation (as measured by changes in the 5-methylcytosine) were significantly increased in OH animals. Interestingly, SNC-121 treatment increases protein acetylation and reduces histone deacetylases and DNA methyltransferases activities in OH animals. We also investigated downstream signaling targets and find out a significant decrease in histone H3 acetylation and CREB binding selectively at promotor regions II and VI of brain-derived nerve growth factor (BDNF) in the retina of OH animals. The reduction in acetylation at promoter regions II and VI was significantly increased in SNC-121 treated OH animals. Our RNA Seq data further confirms the differential expression of key genes (e.g., Class I & II HDACs, DNMTs, and transcriptional factors) in OH animals. Overall, our data provide clues that both HDACs and DNMTs were overexpressed in response to elevated IOP, and they were significantly suppressed by SNC-121 treatment.
Conclusions :
Our data shown that elevated levels of HDACs and DNA methylation are detrimental for RGCs. Delta-opioid receptor activation can maintain the homeostasis of protein acetylation and DNA methylation and subsequently can provide RGC neuroprotection. Our data also suggest that acetylation of promoter regions of BDNF is reduced and subsequently CREB binding is also reduced, which results in the reduced production of BDNF in glaucoma. Therefore, maintaining the homeostasis of acetylation could be a potential avenue to regulate the supplies of neurotrophic factors and eventually RGC neuroprotection in glaucoma.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.