Characterization of Epigenetic Changes in Adult OPCs Identifies TET2 as a Key Regulator of Their Epitranscriptome

Author

Ipek Selcen, CUNY Graduate CenterFollow

Date of Degree

9-2025

Document Type

Doctoral Dissertation

Degree Name

Doctor of Philosophy

Program

Biochemistry

Advisor

Patrizia Casaccia

Committee Members

Pinar Ayata

Kevin Gardner

Mark Emerson

Ian Maze

Subject Categories

Biochemistry | Molecular and Cellular Neuroscience | Molecular Biology | Molecular Genetics

Keywords

oligodendrocytes, brain, alternative splicing, epigenetics, rna biology, hydroxymethylation

Abstract

Oligodendrocyte progenitor cells (OPCs) are the most abundant proliferative cell population in the adult brain. During development, they serve as precursor of oligodendrocytes, the myelinating cells of the central nervous system (CNS). A subset of these developmentally derived neonatal OPCs persists into adulthood, where they form 8% of the total brain cells. These adult OPCs are widely distributed throughout the brain; they receive synaptic contacts from neurons and retain the capacity to proliferate, migrate, and differentiate in response to injury or physiological cues, such as metabolic changes and social or learning experiences, thereby contributing to adaptive myelination and neural circuit refinement.

Previous work from our laboratory and others demonstrated that the progression of OPCs to myelinating oligodendrocytes during development and repair of demyelinating lesions is regulated by transcriptional and epigenetic mechanisms, including post-translational modifications of aminoacids on histone tails. While developmental myelination was governed by deacetylation and repressive methylation of lysine and arginine residues on histone H3, we found that the persistence of adult OPCs was regulated by histone H4 lysine acetylation and methylation. However, the functional significance of these H4 histone changes remained undefined. In Chapter 3 of this thesis, I addressed the transcriptional and functional role of the previously identified histone H4 acetylation (H4K8ac) and methylation (H4K20me3), as a distinctive chromatin signature enriched in adult OPCs. My results suggest a role for H4 acetylation in driving the expression of cell cycle genes responsible for proliferation, while the role of H4 methylation remains to be further investigated.

Previous work also showed that DNA methylation and hydroxymethylation (catalyzed by the TET enzymes) is important for developmental myelination and myelin repair. The TET1 and TET2 enzymes were reported to be both expressed in the oligodendrocyte lineage, but only TET1 levels declined with aging and were critical for remyelination, leaving the open question on TET2 function in this lineage. In Chapter 4, I identified the highest levels of TET2 in adult OPCs, with both a cytosolic and nuclear localization, thereby suggesting a role for TET2 also in RNA hydroxymethylation, which was further investigated. Loss of Tet2 in these cells resulted in global reduction in 5-hydroxymethylcytosine (hm⁵C) with compensatory increases in N⁶-methyladenosine (m⁶A) RNA, identified by mass-spectrometry. Using hydroxymethylation RNA profiling and bulk RNA sequencing, I detected disrupted hydroxymethylation, splicing and expression levels of transcripts regulating chromatin and cell-cycle. In addition, I detected increased levels of myelin genes. At a functional level, this epitranscriptomic imbalance was characterized by decreased proliferation and increased OPC differentiation. Experiments conducted in Tet2-null immortalized OPCs, using CRISPR technology, further validated these conclusions. Together, these findings suggest that TET2-mediated hm⁵C maintains proliferative competence in adult OPCs and prevents their differentiation, representing a novel epitranscriptomic regulatory axis in these cells.

In addition, in Chapter 5, I have tested the ability of mice with oligodendrocyte lineage-specific ablation of Tet2 to learn a new motor task. The data reveal a deficit in the behavioral task, thereby reinforcing the interpretation that TET2 acts as a rheostat for the regulation of OPC population and maturation.

Overall, this dissertation offers new molecular insights that may prove relevant to future remyelination-based therapies for demyelinating diseases such as multiple sclerosis and age-related white-matter decline.

Recommended Citation

Selcen, Ipek, "Characterization of Epigenetic Changes in Adult OPCs Identifies TET2 as a Key Regulator of Their Epitranscriptome" (2025). CUNY Academic Works.
https://academicworks.cuny.edu/gc_etds/6412