Early life alcohol exposure primes hypothalamic microglia to later-life hypersensitivity to immune stress: possible epigenetic mechanism

Abstract

Growing evidence has shown that developmental alcohol exposure induces central nervous system inflammation and microglia activation, which may contribute to long-term health conditions, such as fetal alcohol spectrum disorders. These studies sought to investigate whether neonatal alcohol exposure during postnatal days (PND) 2–6 in rats (third trimester human equivalent) leads to long-term disruption of the neuroimmune response by microglia. Exposure to neonatal alcohol resulted in acute increases in activation and inflammatory gene expression in hypothalamic microglia including tumor necrosis factor alpha (TNF-α) and interleukin 6 (IL-6). Adults with neonatal alcohol pre-exposure (alcohol fed; AF) animals showed an exaggerated peripheral stress hormonal response to an immune challenge (lipopolysaccharides; LPS). In addition, there were significantly more microglia present in the hypothalamus of adult AF animals, and their hypothalamic microglia showed more cluster of differentiation molecule 11b (Cd11b) activation, TNF-α expression, and IL-6 expression in response to LPS. Interestingly, blocking microglia activation with minocycline treatment during PND 2–6 alcohol exposure ameliorated the hormonal and microglial hypersensitivity to LPS in AF adult animals. Investigation of possible epigenetic programming mechanisms by alcohol revealed neonatal alcohol decreased several repressive regulators of transcription in hypothalamic microglia, while concomitantly increasing histone H3 acetyl lysine 9 (H3K9ac) enrichment at TNF-α and IL-6 promoter regions. Importantly, adult hypothalamic microglia from AF animals showed enduring increases in H3K9ac enrichment of TNF-α and IL-6 promoters both at baseline and after LPS exposure, suggesting a possible epigenetic mechanism for the long-term immune disruption due to hypothalamic microglial priming.