Oct4 Methylation-Mediated Silencing As an Epigenetic Barrier Preventing Müller Glia Dedifferentiation in a Murine Model of Retinal Injury

Abstract

Müller glia (MG) is the most abundant glial type in the vertebrate retina. Among its many functions, it is capable of responding to injury by dedifferentiating, proliferating, and differentiating into every cell types lost to damage. This regenerative ability is notoriously absent in mammals. We have previously reported that cultured mammalian MG undergoes a partial dedifferentiation, but fails to fully acquire a progenitor phenotype and differentiate into neurons. This might be explained by a mnemonic mechanism comprised by epigenetic traits, such as DNA methylation. To achieve a better understanding of this epigenetic memory, we studied the expression of pluripotency-associated genes, such as Oct4, Nanog, and Lin28, which have been reported as necessary for regeneration in fish, at early times after NMDA-induced retinal injury in a mouse experimental model. We found that although Oct4 is expressed rapidly after damage (4 hpi), it is silenced at 24 hpi. This correlates with a significant decrease in the DNA methyltransferase Dnmt3b expression, which returns to basal levels at 24 hpi. By MS-PCR, we observed a decrease in Oct4 methylation levels at 4 and 12 hpi, before returning to a fully methylated state at 24 hpi. To demonstrate that these changes are restricted to MG, we separated these cells using a GLAST antibody coupled with magnetic beads. Finally, intravitreous administration of the DNA-methyltransferase inhibitor SGI-1027 induced Oct4 expression at 24 hpi in MG. Our results suggest that mammalian MG injury-induced dedifferentiation could be restricted by DNA methylation, which rapidly silences Oct4 expression, preventing multipotency acquisition.

Activating the regenerative potential of Müller glia cells in a regeneration-deficient retina

“…We speculate that this upregulation is due to epigenetic modifications of the sox2 locus. A recent study in the mouse retina showed that the expression of oct4 is upregulated shortly after injury and then downregulated at 24 hpi ( Reyes-Aguirre and Lamas, 2016 ). This correlates with a decrease in the expression of DNA methyltransferase 3b and its subsequent upregulation at 24 hpi, triggering a decrease in methylation and subsequent re-methylation of oct4 .…”

A journey into the retina: Müller glia commanding survival and death

“…It has been proposed that mammalian retinas become enriched with quiescent MGCs, so they fail to renew neurons. In this sense, studies in zebrafish have proved extremely useful for determining the master regulators of this complex process; therefore, further investigations are now being focused on the modulation of these proteins in mammalian or avian retinas to stimulate MGC reprogramming (Beach, Wang, & Otteson, ; Reyes‐Aguirre & Lamas, ). Thus, inducing changes in the expression of certain proteins or epigenetic modifications is considered to be a possible therapy for restoring the pool of neurons in the retina.…”

Histone Deacetylase-Mediated Müller Glia Reprogramming through Her4.1-Lin28a Axis Is Essential for Retina Regeneration in Zebrafish

“…Hdac1 being part of multi-protein nuclear complexes that are important for causing transcriptional repression and epigenetic landscaping to inhibit the expression of neuronal-specific genes in rest of the tissues ( Huang et al., 1999 ) made us explore the global gene regulations that occur in MGPCs mediated through Hdacs with a particular focus on Hdac1. Furthermore, MG reprogramming leading to induction of MGPCs, with little neuronal characteristics, during retina regeneration is associated with essential expression of pluripotency-inducing factors ( Gorsuch et al., 2017 , Ramachandran et al., 2010a , Reyes-Aguirre and Lamas, 2016 ), which could also be targets of epigenome modifiers like Hdacs.…”