Table 1.

Epigenetic Studies in Optic Nerve Tissues.

Cell Type	Epigenetic Player	Experimental Model	Effect	References
RGCs (Retinal ganglion cells)	TET1-dependent deletion of PTEN	Optic nerve crush model	Optic nerve regeneration	[94]
	Class I HDACs and HDAC 2 & 3 upregulation and HDAC3 nuclear localization in RGCs	Optic nerve crush model	Optic nerve degeneration/RGC apoptosis	[64]
	Increased G9a expression and H3K9Me2 activity in the retina (RGC) and optic nerve	Traumatic brain injury (TBI) model	TBI causes apoptosis and oxidative stress in the retina (RGC) and optic nerve	[80]
	Inhibition of retinal HDAC activity (post valproic acid treatment)	-RGCs purified from new-born (postnatal day P0–P2) rat retinas -HeLa cells	Neuroprotection and histone hyperacetylation	[73,74]
	Inhibition of HDAC3 activity (RGFP966 activity)	Optic nerve crush model	RGC survival and repression of the apoptotic gene in RGCs post optic nerve injury	[24,64]
	Double knock out of HDAC1&2	Optic nerve axotomy	Anti-apoptosis and neuroprotection effect	[68]
	3-deazaneplanocin (DZNep) inhibits Ezh2 inhibition using 3-deazaneplanocin (DZNep) -reduces the trimethylation of histone 3 lysine 27 (H3K27me3) or activity	Retinal/RGC damage caused by intravitreal injection of N-methyl-D-aspartate (NMDA)	Prevent cell death and inner nuclear layer thinning induced by NMDA and improved visual function	[84]
	Increased Histone H3K9 acetylation using Trichostatin A (TSA)	Lead-induced neurotoxicity	Promotes neurite outgrowth and branching, neuroprotection, neuronal differentiation, and neurite branching	[95]
	Intravitreal JQ1 (BET inhibitor) administration	RGC damage induced by NMDA excitotoxicity	Sustained RGC number and gene expression and decreased TUNEL-positive cells in the ganglion cell layer	[48]
	Promotion of p38 MAPKc activity and intravitreal administration of tranylcypromine (lysine-specific demethylase 1 (LSD1) inhibitor)	NMDA-induced excitotoxicity	Enhanced RGC survival	[85]
	OSK-mediated vision restoration is TET1/2 dependent ectopic expression of Oct4 (also known as Pou5f1), Sox2, and Klf4 genes (OSK) in RGC	Optic nerve crush model	Axon regeneration	[12]
OPCs (Oligodendrocyte progenitor cells)	Increased levels of H3K27me3 from NSCs (neural stem cells) to immature OL and significantly decreased levels of histone acetylation (i.e., H3K9ac) at the early stages of OPC differentiation associated with increasing levels of H3K9me3 during OPC maturation	Human pluripotent stem cell culture	Differentiation of OPCs into OLs	[96]
	DNMT1 downregulation in oligodendrocytes	-Conditional mutation in the mouse DNMT1 gene in embryonic stem (ES) cells. -T24, a human bladder transitional carcinoma-derived cell line; A549, a human non-small-cell lung carcinoma cell line, and NIH 3T3, a mouse fibroblast cell line	-Inhibition of OPC growth -Cell apoptosis -Mild impact on myelin reparation process	[38,39]
Myelin	Downregulation of TET1	-TET1 KO mice model	-inefficient myelin repair and axo-myelinic swellings	[32]
			-alters astrocyte morphology and impairs neuronal function	[97]

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