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Age-dependent decline of TET1-mediated DNA hydroxy-methylation impairs myelin regeneration after injury

ABSTRACT: Adult myelination is recognized as essential for brain function and response to injury and yet, its molecular understanding is mostly inferred from developmental studies. In this study, we identify DNA hydroxy-methylation, an epigenetic mark catalyzed by Ten-Eleven translocation (TET) enzymes, as necessary for adult, but not for developmental, myelin formation. While hydroxy-methylation and high levels of TET1 were detected in young adult mice during myelin regeneration after lysolecithin-induced demyelination, this process was defective in older mice. Lineage specific ablation of the enzyme Tet1 (but not of Tet2) recapitulated the age-related decline of TET1 and inefficient remyelination, without impacting developmental myelination. Genome-wide DNA hydroxy-methylation profiling of adult progenitors and mature oligodendrocytes, identified solute carriers regulating neuronal-glial communication as gene targets, whose expression was dramatically decreased in mutants and in older mice. We conclude that TET1-mediated hydroxy-methylation is critical for adult myelination in response to injury.

ORGANISM(S): Mus musculus

PROVIDER: GSE122446 | GEO | 2020/03/14

REPOSITORIES: GEO

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Project description:DNA methylation is a key epigenetic regulator of mammalian embryogenesis and somatic cell differentiation. Using high-resolution genome-scale maps of methylation patterns, we show that the formation of myelin in the peripheral nervous system, proceeds with progressive DNA demethylation, which coincides with an upregulation of critical genes of the myelination process. More importantly, we found that, in addition to expression of DNA methyltransferases and demethylases, the levels of S-adenosylmethionine (SAMe), the principal biological methyl donor, could also play a critical role in regulating DNA methylation during myelination and in the pathogenesis of diabetic neuropathy. In summary, this study provides compelling evidence that SAMe levels need to be tightly controlled to prevent aberrant DNA methylation patterns, and together with recently published studies on the influence of SAMe on histone methylation in cancer and embryonic stem cell differentiation show that in diverse biological processes, the methylome, and consequently gene expression patterns, are critically dependent on levels of SAMe. Axonal myelination by Schwann cells in the peripheral nervous system is essential for rapid saltatory impulse conduction, and malformation or destruction of myelin sheaths can lead to severe motor and sensory disabilities (peripheral neuropathies). Using high-resolution genome-scale methylome maps, we found that DNA methylation could play a critical role in the generation of myelinated Schwann cells. This process was accompanied by a global DNA demethylation at most genomic elements. Notably, demethylation at gene-regulatory regions was associated with activation of critical myelination-specific genes. Furthermore, we found an aberrant DNA methylation pattern in a mouse model of diabetic neuropathy, which could be involved in the pathogenesis of the disease. Importantly, we found that these methylation patterns in both situations could be regulated by levels of S-adenosylmethionine (SAMe), the principal biological methyl donor. Together with recent studies on the influence of SAMe on histone methylation in diverse biological processes, we conclude that the methylation landscape of cells could be critically dependent on levels of SAMe. These provide a mechanistic link between metabolism and gene regulatory networks in normal and pathological situations. Sciatic nerves from C57Bl6J mice of either sex, were dissected and pooled together at different developmental stages, 3 replicates per sample group.

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Age-dependent decline of TET1-mediated DNA hydroxy-methylation impairs myelin regeneration after injury

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