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Review: microglia of the aged brain: primed to be activated and resistant to regulation

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Norden, D. M., Godbout, J. P.·2013·Neuropathology and Applied Neurobiology

Abstract

Innate immunity within the central nervous system ( CNS ) is primarily provided by resident microglia. Microglia are pivotal in immune surveillance and also facilitate the co‐ordinated responses between the immune system and the brain. For example, microglia interpret and propagate inflammatory signals that are initiated in the periphery. This transient microglial activation helps mount the appropriate physiological and behavioural response following peripheral infection. With normal ageing, however, microglia develop a more inflammatory phenotype. For instance, in several models of ageing there are increased pro‐inflammatory cytokines in the brain and increased expression of inflammatory receptors on microglia. This increased inflammatory status of microglia with ageing is referred to as primed, reactive or sensitized. A modest increase in the inflammatory profile of the CNS and altered microglial function in ageing has behavioural and cognitive consequences. Nonetheless, there are major differences in microglial biology between young and old age when the immune system is challenged and microglia are activated. In this context, microglial activation is amplified and prolonged in the aged brain compared with adults. The cause of this amplified microglial activation may be related to impairments in several key regulatory systems with age that make it more difficult to resolve microglial activation. The consequences of impaired regulation and microglial hyper‐activation following immune challenge are exaggerated neuroinflammation, sickness behaviour, depressive‐like behaviour and cognitive deficits. Therefore the purpose of this review is to discuss the current understanding of age‐associated microglial priming, consequences of priming and reactivity, and the impairments in regulatory systems that may underlie these age‐related deficits.

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Crossref · 10.1111/j.1365-2990.2012.01306.x

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  • Astrocytes and microglia become hyper-activated with age.

    “Astrocytes and microglia, mediators of the innate immune response of the central nervous system, become hyper-activated with age (Baruch et al., 2014; Norden and Godbout, 2013).”

    From Loss of epigenetic information as a cause of mammalian aging (2023) · cites this paper as Norden and Godbout, 2013

    The section “Astrocytes also have a more inflammatory profile with age” reports age-related changes resembling an activated astrocytic profile. The Abstract and “Innate immune challenge leads to prolonged and exaggerated neuroinflammation” describe aged microglia as primed, with hyper-activation occurring following immune challenge. The claim omits that condition and overstates what the review says about activation with age alone. (LLM, conf=0.86)

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  • Astrocytes demonstrate similar age-related changes, including elevated GFAP expression and hypertrophic morphology, suggesting a transition toward a proinflammatory state.

    “Astrocytes also demonstrate similar age-related changes, including elevated glial fibrillary acidic protein (GFAP) expression and hypertrophic morphology (160), both of which suggest a transition toward a proinflammatory state.”

    From Connecting aging biology and inflammation in the omics era (2022) · cites this paper as [160]

  • The primed state is thought to make aged microglia disproportionately reactive to immunological challenges, leading to prolonged neuroinflammation and cognitive deficits associated with age.

    “This state of ‘priming’ is thought to make aged microglia disproportionately reactive to immunological challenges, leading to prolonged neuroinflammation and the cognitive deficits associated with age [65,66].”
  • This morphological profile of the aged microglia first reported in rats has also been confirmed in mice, gerbils, and dogs.

    “This morphological profile of the aged microglia first reported in rats has also been confirmed in mice, gerbils, and dogs (Hwang et al, 2008;Korhonen et al, 1997;Norden and Godbout, 2013;Streit and Xue, 2010).”

    From Microglia Priming with Aging and Stress (2017) · cites this paper as Norden and Godbout, 2013

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Authors
Norden, D. M., & Godbout, J. P.
Affiliations
The Ohio State University (US)
Corresponding author
Godbout, J. P.
Venue
Neuropathology and Applied Neurobiology
Publisher
Wiley
Published
2013-01-22
Volume
39
Issue
1
Pages
19-34
ISSN
  • 0305-1846 (ISSN-L)
  • 1365-2990
OpenAlex
W1622777525
Cited by
792
References
153
Citations by year
2026: 55 · 2025: 42 · 2024: 63 · 2023: 55 · 2022: 73 · 2021: 89 · 2020: 74 · 2019: 55 · 2018: 64 · 2017: 61 · 2016: 44 · 2015: 49 · 2014: 43 · 2013: 22 · 2012: 2
FWCI
3.45
Type
journal article
Language
en
Open access
Locations
  • Neuropathology and Applied Neurobiology (publishedVersion)
  • PubMed (publishedVersion)
  • Europe PMC (PubMed Central) (acceptedVersion)
  • PubMed Central (acceptedVersion)
Funders
  • National Institutes of Health
  • National Institute on Aging (R01AG033028)
Topics
  • Life Sciences › Neuroscience › Neurology › Neuroinflammation and Neurodegeneration Mechanisms
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Inflammasome and immune disorders
  • Life Sciences › Neuroscience › Biological Psychiatry › Tryptophan and brain disorders
Keywords
microglia, brain aging, microglial priming, microglial activation, neuroinflammation, innate immunity, inflammatory cytokines, sickness behavior, depression-like behavior, cognitive impairment
MeSH terms
Aging, Animals, Brain, Humans, Immunity, Innate, Inflammation, Microglia

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