Prior Hypoxia Exposure Enhances Murine Microglial Inflammatory Gene Expression in vitro Without Concomitant H3K4me3 Enrichment

Abstract

Hypoxia (Hx) is a component of multiple disorders, including stroke and sleep-disordered breathing, which often precede or are comorbid with neurodegenerative diseases. However, little is known about how hypoxia affects the ability of microglia, resident CNS macrophages, to respond to subsequent inflammatory challenges that are often present during neurodegenerative processes. We, therefore, tested the hypothesis that hypoxia would enhance or “prime” microglial pro-inflammatory gene expression in response to a later inflammatory challenge without programmatically increasing basal levels of pro-inflammatory cytokine expression. To test this, we pre-exposed immortalized N9 and primary microglia to hypoxia (1% O 2 ) for 16 h and then challenged them with pro-inflammatory lipopolysaccharide (LPS) either immediately or 3–6 days following hypoxic exposure. We used RNA sequencing coupled with chromatin immunoprecipitation sequencing to analyze primed microglial inflammatory gene expression and modifications to histone H3 lysine 4 trimethylation (H3K4me3) at the promoters of primed genes. We found that microglia exhibited enhanced responses to LPS 3 days and 6 days post-hypoxia. Surprisingly, however, the majority of primed genes were not enriched for H3K4me3 acutely following hypoxia exposure. Using the bioinformatics tool MAGICTRICKS and reversible pharmacological inhibition, we found that primed genes required the transcriptional activities of NF-κB. These findings provide evidence that hypoxia pre-exposure could lead to persistent and aberrant inflammatory responses in the context of CNS disorders.

Dapagliflozin Ameliorates Diabetic Kidney Disease via Upregulating Crry and Alleviating Complement Over-activation in db/db Mice

“…One speculation is that transcriptional downregulation may occur through epigenetic modifications. Hypoxia targets Jumonji AT-rich interactive domain 1A (JARID1A) activity, which in turn increases Histone H3 lysine 4 (H3K4) trimethylation (H3K4me3), leading to the altered programs of gene expression including CD55 (Zhou et al, 2010;Kiernan et al, 2020). The current study found that dapagliflozin reduced HIF-1α accumulation, upregulated Crry and ameliorated complement over-activation; with the accumulation of HIF-1α stabilized by DMOG, the expression of Crry was decreased.…”

Cyclooxygenase‑2 contributes to the hypoxia‑induced aggravation of the neuroinflammation response stimulated by lipopolysaccharide in microglia

“…Zhang et al also revealed that acute hypoxia induces an imbalanced M1/M2 activation of microglia through the NF-κB signaling pathway ( 21 ). Furthermore, even preexposure to hypoxia for 3-6 days can lead to persistent and aberrant inflammatory responses ( 22 ). The present study revealed that compared with 3% O 2 , 1% O 2 increased the expression of proinflammatory cytokines, including IL-6, TNF-α and IL-β.…”