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Thyroid hormone-mediated histone modificaiton protects primary mouse cortical neurons from the toxic effects of hypoxic injury.

ABSTRACT: Epigenetic and genetic regulation mediates the response to stress at the cellular level and allows cells for adaptation and survival. Thyroid hormone has been shown to have a protective role in neuronal injury, although the mechanisms are not established. We hypothesized that the neuroprotective role of thyroid hormone was associated with epigenetic modifications of histone proteins. We used hypoxic neurons as a model system for hypoxia-induced brain injury. Mouse primary cortical neurons were exposed to 0.2% oxygen for 7 hours with or without treatment with 10 nM Triiodotyroxine (T3). We analyzed the mRNA expression of histone modifying enzymes by RNA-seq and the posttranslationally modified histone 3 proteins by ELISA assay and Western blot. We found that methylation of H3K27, associated with inactive promoters, was highly induced in hypoxic neurons, and this methylation was reduced by T3 treatment. H3K4 methylation is the hallmark of active promoters. Three (Set1db, Kmta2c and Kmt2e) out of six H3K4 methyltransferases were downregulated by hypoxia and restored by T3 treatment. H3K4me3 protein, by ELISA assay, was increased 76% in T3-treated hypoxic neurons, compared to without T3 treatment. H3K56ac, plays a critical role in transcription initiation, was markedly increased in T3-treaed hypoxic neurons, compared to those without T3 treatment, indicating that T3 treatment stimulated gene transcription. Additionally, T3 treatment restored hypoxia-induced downregulation of histone acetyltransferase, Kat6a, Kat6b and Crebbp, which function as transcription factors. These findings indicate that T3 treatment mitigates hypoxia-induced alteration of the histone modifications and protects neurons from hypoxia-induced injury.

ORGANISM(S): Mus musculus

PROVIDER: GSE205801 | GEO | 2022/07/27

REPOSITORIES: GEO

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Project description:Hypoxia in stem cell niches and inner core of solid tumors contributes to cellular senescence and differentiation inhibition. It directly increases histone methylationby inhibiting the activities of O2-and α-ketoglutarate (α-KG)-dependent histone lysine demethylases. This study is the first to demonstrate how the hypoxic increment of methylated histones cross-talks with other epigenetic changes, such as histone clipping and heterochromatin redistribution, named senescence-associated heterochromatin foci (SAHF), which are found during oncogene-induced senescence (OIS). This study showed that Raf activation in primary human fibroblasts IMR90 increases mature cathepsin L (CTSL)-mediated cleavage of H3, H2B, and H4. Hypoxia prevented H3 cleavage not by inhibiting CTSL but by increasing H3K18me3 and H3K23me3 nearby cleaved site of H3. Forced expression of cleaved H3 in IMR90 cells induced senescence even under hypoxia, suggesting that hypoxia breaks this positive feedback senescence driving circle by increasing methylated histones. The decrease in methylated histones is necessary for OIS to trigger histone clipping and SAHFs, but hypoxia maintains methylated histones to prevent both. Forced reduction of methylated histones in hypoxic cells using inhibitors of methyl-transferases makes hypoxic conditions unable to prevent OIS from inducing both histone clipping and SAHFs. Reversely forced enhancement of methylated histones in normoxic cells using inhibitors of histone demethylases protected histones from clipping during OIS but failed to block SAHFs. Altogether, the maintenance of methylated histones, especially H3K23me3 and H3K18me3, is sufficient to protect histones from clipping during OIS, but not for inhibiting SAHFs, suggesting that besides inhibiting KDMs, hypoxia adopts other methods to inhibit SAHFs. These findings provide a novel mechanism by which hypoxia affects cell fate by increasing methylated histones that protect histones and chromatin from dramatic epigenetic changes.

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Thyroid hormone-mediated histone modificaiton protects primary mouse cortical neurons from the toxic effects of hypoxic injury.

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