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MTOR-dependent translation amplifies microglia priming in ageing

ABSTRACT: Microglia maintain homeostasis in the brain. However, with age, they become primed and respond more strongly to inflammatory stimuli. We show here that microglia from aged mice upregulated mammalian target of rapamycin (mTOR) complex 1 signaling regulating translation, as well as cytokine protein levels. Genetic ablation of mTOR signaling showed a dual, yet contrasting effect on microglia priming: it caused an NF-kB-dependent upregulation of priming genes at mRNA level; however, mice displayed reduced cytokine protein levels, diminished microglia activation and milder sickness behavior. The effect on translation was dependent on reduced phosphorylation of 4EBP1 and increased 4EBP1 expression, resulting in decreased binding of EIF4E to EIF4G. Similar changes were present in aged human microglia and in damage-associated microglia, indicating upregulation of mTOR-dependent translation is an essential step licensing microglia priming in ageing and neurodegeneration.

ORGANISM(S): Mus musculus

PROVIDER: GSE156762 | GEO | 2021/07/30

REPOSITORIES: GEO

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Project description:Acute cognitive impairment (i.e., delirium) is common in elderly emergency department patients and frequently results from infections that are unrelated to the central nervous system. Since activation of the peripheral innate immune system induces brain microglia to produce inflammatory cytokines that are responsible for behavioral deficits, we investigated if aging exacerbated neuroinflammation and sickness behavior after peripheral injection of lipopolysaccharide (LPS). Microarray analysis revealed a transcriptional profile indicating the presence of primed or activated microglia and increased inflammation in the aged brain. Furthermore, aged mice had a unique gene expression profile in the brain after an intraperitoneal injection of LPS, and the LPS-induced elevation in the brain inflammatory cytokines and oxidative stress was both exaggerated and prolonged compared with adults. Aged mice were anorectic longer and lost more weight than adults after peripheral LPS administration. Moreover, reductions in both locomotor and social behavior remained 24 h later in aged mice, when adults had fully recovered, and the exaggerated neuroinflammatory response in aged mice was not reliably paralleled by increased circulating cytokines in the periphery. Taken together these data establish that activation of the peripheral innate immune system leads to exacerbated neuroinflammation in the aged as compared with adult mice. This dysregulated link between the peripheral and central innate immune system is likely to be involved in the severe behavioral deficits that frequently occur in older adults with systemic infections. Experiment Overall Design: In this study, adult and aged mice were injected intraperitoneal with sterile saline or Escherichia coli LPS (0.33 mg/kg, ~10 µg/mouse; serotype 0127:B8, Sigma). This dosage of LPS was used because it induces a mild transient sickness behavior in young adults. Mice were killed 4 h after saline or LPS injection by CO2 asphyxiation. Blood samples were collected and brains were removed, separated in half at the longitudinal fissure, frozen in liquid nitrogen, and stored (-80°C) until assaying. Total RNA was later isolated from some brain samples for microarray analysis (n=3).

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MTOR-dependent translation amplifies microglia priming in ageing

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