Cited by 1,044Neuroinflammation and Neurodegeneration MechanismsRedox biology and oxidative stressNeurological Disease Mechanisms and Treatments

The DOI matches its Crossref record; 194 of the 198 references it cites were found in a registry or an index; 6 of the 222 sources its claims cite were checked for support.

ROS Generation in Microglia: Understanding Oxidative Stress and Inflammation in Neurodegenerative Disease

Open access

Abstract

Neurodegenerative disorders, such as Alzheimer’s disease, are a global public health burden with poorly understood aetiology. Neuroinflammation and oxidative stress (OS) are undoubtedly hallmarks of neurodegeneration, contributing to disease progression. Protein aggregation and neuronal damage result in the activation of disease-associated microglia (DAM) via damage-associated molecular patterns (DAMPs). DAM facilitate persistent inflammation and reactive oxygen species (ROS) generation. However, the molecular mechanisms linking DAM activation and OS have not been well-defined; thus targeting these cells for clinical benefit has not been possible. In microglia, ROS are generated primarily by NADPH oxidase 2 (NOX2) and activation of NOX2 in DAM is associated with DAMP signalling, inflammation and amyloid plaque deposition, especially in the cerebrovasculature. Additionally, ROS originating from both NOX and the mitochondria may act as second messengers to propagate immune activation; thus intracellular ROS signalling may underlie excessive inflammation and OS. Targeting key kinases in the inflammatory response could cease inflammation and promote tissue repair. Expression of antioxidant proteins in microglia, such as NADPH dehydrogenase 1 (NQO1), is promoted by transcription factor Nrf2, which functions to control inflammation and limit OS. Lipid droplet accumulating microglia (LDAM) may also represent a double-edged sword in neurodegenerative disease by sequestering peroxidised lipids in non-pathological ageing but becoming dysregulated and pro-inflammatory in disease. We suggest that future studies should focus on targeted manipulation of NOX in the microglia to understand the molecular mechanisms driving inflammatory-related NOX activation. Finally, we discuss recent evidence that therapeutic target identification should be unbiased and founded on relevant pathophysiological assays to facilitate the discovery of translatable antioxidant and anti-inflammatory therapeutics.

Overview

AI snapshot

Written from the paper’s full text.

TL;DR

This review argues that microglial reactive oxygen species (ROS), generated mainly by NOX2 and NOX4, link neuroinflammation and oxidative stress in neurodegenerative disease, with ROS also acting as second messengers and lipid droplet-accumulating microglia contributing to pathology. It proposes targeting microglial NOX, Nrf2-driven antioxidant pathways, and unbiased disease-relevant drug discovery.

Key findings

  • NOX2 (CYBB) is the most highly expressed NOX isotype transcript in human and mouse brain microglia, with NOX4 second-highest at a much lower level; NOX2 activation in disease-associated microglia is associated with DAMP signalling, inflammation, and amyloid plaque deposition, especially in the cerebrovasculature.
  • ROS from both NOX and mitochondria may act as second messengers to propagate immune activation: H₂O₂ can activate NFκB, and suppressing mitochondrial ROS with mitoTEMPO reduced MAPK/NFκB activation and pro-inflammatory factors (TNFα, IL1β, IL6, iNOS, Cox-2) in LPS-stimulated microglia.
  • Nrf2 controls antioxidant genes such as NQO1 and GSTs in microglia; Nrf2 deficiency promotes inflammatory markers (IL6, Cox2, iNOS) and inhibits anti-inflammatory markers, while sulforaphane enhances Nrf2, limits pro-inflammatory microglial markers, and confers neuroprotection.
  • Lipid droplet-accumulating microglia (LDAM) may be a double-edged sword: ROS/JNK drive lipid droplet formation in flies, antioxidant treatment or SOD1 expression reduces it, and GRN−/− mice show ROS-generating, pro-inflammatory LDAM defective in phagocytosis; ToxSeq identified a ROS-positive microglial signature rescued by acivin in EAE.

Methods

  • Narrative review; no primary data, experimental sample, or statistical analysis are reported.
  • The paper synthesizes literature on microglial NOX/ROS biology, oxidative stress, neuroinflammation, lipid droplet-accumulating microglia, antioxidant regulation, and therapeutic strategies.
  • It discusses evidence from human post-mortem tissue, rodent models, cell lines, single-cell RNA-seq, and drug-screening studies, and proposes future directions including cell-specific NOX manipulation.

Limitations

  • The paper does not state limitations of its own review; it repeatedly notes limitations in the underlying literature, including lack of stringent controls and specific antibodies for NOX expression studies, possible artefactual NOX1 expression in Cx3cr1-EGFP reporter mice, and a human microglial cell line lacking NOX2.
  • It also notes that apocynin specificity for NOX4 has been questioned, mitoTEMPO selectivity is questioned especially at higher concentrations, and a causal relationship between ROS and NFκB activation in microglia remains undetermined.
  • Evident from the text: as a narrative review, no systematic search or formal quality assessment is described, and many conclusions rely on preclinical models or immortalized cells, with calls for validation in primary and iPSC-derived microglia.

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Integrity signals

Registry

Crossref · 10.3390/antiox9080743

Cites

194 of 194 references verified0 citation errors · 0 not checkable

Statistics

Nothing to recompute.

Figures

Figure 1 NADPH oxidase 2 (NOX2) is activated by translocation of cytosolic subunits to the membrane. gp91phox and p22phox are membrane-bound components of NOX2 that together form the flavocytochrome b558. Upon activation signalling by pro-inflammatory stimuli, e.g., interferon-γ, protein kinases activate the cytosolic regulatory subunits: p40phox, p47phox and p67phox. Phosphorylation of p47phox by p21-activated kinase is thought to be the rate-limiting step in NOX2 activation [62]. The small GTPase Rac1/2 is also activated and translocated to the flavocytochrome. Upon activation, NOX2 catalyses the production of the superoxide radical (O2•–) from molecular oxygen (O2) by oxidation of nicotinamide adenine dinucleotide phosphate (NADPH) to form NADP+ and H+.
Figure 1 NADPH oxidase 2 (NOX2) is activated by translocation of cytosolic subunits to the membrane. gp91phox and p22phox are membrane-bound components of NOX2 that together form the flavocytochrome b558. Upon activation signalling by pro-inflammatory stimuli, e.g., interferon-γ, protein kinases activate the cytosolic regulatory subunits: p40phox, p47phox and p67phox. Phosphorylation of p47phox by p21-activated kinase is thought to be the rate-limiting step in NOX2 activation [62]. The small GTPase Rac1/2 is also activated and translocated to the flavocytochrome. Upon activation, NOX2 catalyses the production of the superoxide radical (O2•–) from molecular oxygen (O2) by oxidation of nicotinamide adenine dinucleotide phosphate (NADPH) to form NADP+ and H+.CC BY · PubMed Central
Figure 2 Damage-associated molecular patterns (DAMPs) contribute to neuroinflammation and oxidative stress. DAMPs originate from damaged or dying cells in response to acute injury and neuroinflammation. DAMPs, such as amyloid-β, fibrinogen, high mobility group box 1 (HMGB1), mitochondrial transcription factor A (TFAM) and cytochrome c may contribute to inflammatory-driven phagocytic activation of microglia by signalling on pattern recognition receptors (PRRs), such as complement receptor 3 (CD11b, CD18) and toll-like receptor 4 (TLR4). These signals are transduced in microglia by nuclear factor κB (NFκB) and mitogen-activated protein kinases (MAPKs), such as p38 and extracellular signal-regulated kinase (ERK). Phagocyte activation causes translocation of NADPH oxidase (NOX) subunits to the plasma membrane to activate NOX and drive reactive oxygen species generation, contributing to oxidative stress.
Figure 2 Damage-associated molecular patterns (DAMPs) contribute to neuroinflammation and oxidative stress. DAMPs originate from damaged or dying cells in response to acute injury and neuroinflammation. DAMPs, such as amyloid-β, fibrinogen, high mobility group box 1 (HMGB1), mitochondrial transcription factor A (TFAM) and cytochrome c may contribute to inflammatory-driven phagocytic activation of microglia by signalling on pattern recognition receptors (PRRs), such as complement receptor 3 (CD11b, CD18) and toll-like receptor 4 (TLR4). These signals are transduced in microglia by nuclear factor κB (NFκB) and mitogen-activated protein kinases (MAPKs), such as p38 and extracellular signal-regulated kinase (ERK). Phagocyte activation causes translocation of NADPH oxidase (NOX) subunits to the plasma membrane to activate NOX and drive reactive oxygen species generation, contributing to oxidative stress.CC BY · PubMed Central
Figure 3 Control of microglial activation by NFκB and MAPKs. Proinflammatory stimulation of microglia is mediated by damage-associated molecular patterns (DAMPs), lipopolysaccharide (LPS) and interferon-gamma at pattern recognition receptors (PRRs), toll-like receptor 4 (TLR4) and interferon-γ receptor, respectively. Signal transduction by nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB) and mitogen-activated protein kinases (MAPKs) results in the upregulation of cytokines, such as interleukin (IL) 1β, IL6 and tumour necrosis factor α (TNFα) which contribute to chronic inflammation and oxidative stress in the CNS.
Figure 3 Control of microglial activation by NFκB and MAPKs. Proinflammatory stimulation of microglia is mediated by damage-associated molecular patterns (DAMPs), lipopolysaccharide (LPS) and interferon-gamma at pattern recognition receptors (PRRs), toll-like receptor 4 (TLR4) and interferon-γ receptor, respectively. Signal transduction by nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB) and mitogen-activated protein kinases (MAPKs) results in the upregulation of cytokines, such as interleukin (IL) 1β, IL6 and tumour necrosis factor α (TNFα) which contribute to chronic inflammation and oxidative stress in the CNS.CC BY · PubMed Central

Verification

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Citations

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  1. 2018, Epidemiology of Alzheimer’s disease and other dementias, Rev. Neurol., 66, 377

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Metadata

Authors
Simpson, D. S. A., & Oliver, P. L.
Affiliations
University of Oxford (GB)
Corresponding author
Oliver, Peter L.
Venue
Antioxidants
Publisher
MDPI AG
Published
2020-08-13
Volume
9
Issue
8
Pages
743
ISSN
2076-3921 (ISSN-L)
OpenAlex
W3048426432
Cited by
1,044
References
198
Citations by year
2026: 156 · 2025: 249 · 2024: 201 · 2023: 183 · 2022: 133 · 2021: 113 · 2020: 9
FWCI
10.90
Type
journal article
Language
en
Open access
Locations
  • Antioxidants (publishedVersion, cc-by)
  • PubMed Central (publishedVersion, cc-by)
  • PubMed (publishedVersion)
  • DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
Funders
Medical Research Council (MR/P502005/1)
Topics
  • Life Sciences › Neuroscience › Neurology › Neuroinflammation and Neurodegeneration Mechanisms
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Redox biology and oxidative stress
  • Life Sciences › Neuroscience › Neurology › Neurological Disease Mechanisms and Treatments
Keywords
reactive oxygen species, microglia, neuroinflammation, oxidative stress, neurodegenerative diseases, Alzheimer's disease, NADPH oxidase 2, NOX2, damage-associated molecular patterns, disease-associated microglia, mitochondrial reactive oxygen species, NQO1, Nrf2, amyloid plaques, antioxidant therapeutics, anti-inflammatory agents

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