Abstract
BackgroundMicroglia are multifunctional cells that are primarily neuroprotective and a deficit in their functional integrity is likely to be a contributory factor in the deteriorating neuronal function that occurs with age and neurodegeneration. One aspect of microglial dysfunction is reduced phagocytosis, and this is believed to contribute to the accumulation of amyloid-β (Aβ) in Alzheimer’s disease (AD). Therefore, improving phagocytosis should be beneficial in limiting the amyloidosis that characterises AD.MethodsHere, we investigated whether an antibody that targets toll-like receptor (TLR)2 might attenuate the inflammatory and metabolic changes induced by lipopolysaccharide (LPS) and amyloid-β. The impact on phagocytosis was assessed by immunohistochemistry. We evaluated the metabolic changes with the SeaHorse Extracellular Flux Analyser and studied the expression of key enzymes driving glycolysis by western blotting. For all experiments, statistical significance was determined by unpaired Student’s t test and two-way analysis of variance (ANOVA).ResultsWe have reported that, when exposed to an inflammatory stimulus, microglia switch their metabolism towards the metabolically- inefficient glycolysis; this potentially impacts on metabolically demanding functions like phagocytosis. Anti-TLR2 antibody increased phagocytosis of Aβ in LPS + Aβ-stimulated microglia and this was linked with the ability of the antibody to attenuate the LPS + Aβ-triggered inflammasome activation. LPS + Aβ increased glycolysis in microglia and increased the expression of 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase (PFKFB)3, an enzyme that plays a key role in driving glycolysis; these effects were inhibited when cells were incubated with the anti-TLR2 antibody. The data also show that antibody treatment increased oxidative metabolism.ConclusionsThus, microglia with an inflammatory phenotype, specifically cells in which the inflammasome is activated, are glycolytic; this may compromise the metabolic efficiency of microglia and thereby provide an explanation for the reduced phagocytic function of the cells. We propose that, by restoring oxidative metabolism and reducing inflammasome activation in microglia, phagocytic function is also restored.
Highlights
Microglia are multifunctional cells that are primarily neuroprotective and a deficit in their functional integrity is likely to be a contributory factor in the deteriorating neuronal function that occurs with age and neurodegeneration
Isolated mixed glia from cortical tissue of neonatal mice were cultured in T25 cm2 flasks in Dulbecco’s modified Eagle’s medium containing foetal bovine serum (FBS), penicillin and streptomycin (100 U/ml) supplemented with macrophage colony stimulating factor (M-CSF; 100 ng/ml; R&D Systems, UK) and granulocyte macrophage colony stimulating factor (GM-CSF; 100 ng/mL; R&D Systems, UK) for 10–12 days, after which time non-adherent microglia were seeded in 24-well plates (1 × 105cells/well) and cultured for a further 2 days
We assessed phagocytosis of Aβ in microglia treated with LPS in the presence/absence of anti-Toll-like receptor 2 (TLR2) antibody and show that cells incubated with LPS + Aβ and anti-TLR2 antibody exhibited an increase in Aβ engulfment compared with cells incubated with LPS + Aβ (**p < 0.01; Student’s t test for independent means; Fig. 1a, b)
Summary
Microglia are multifunctional cells that are primarily neuroprotective and a deficit in their functional integrity is likely to be a contributory factor in the deteriorating neuronal function that occurs with age and neurodegeneration. Hexokinase 1, which catalyses the first step in glycolysis, and PKM2, can both lead to activation of the inflammasome and interleukin (IL)-1β production [6, 7] Recent evidence from this laboratory has revealed that microglia, like macrophages, adopt a glycolytic phenotype when challenged with an inflammatory stimulus. Interferon-γ (IFNγ) triggered activation of primary cultured microglia, increased production of inflammatory cytokines and shifted the cells towards glycolysis [8]. It has been shown in BV2 cells that stimulation with lipopolysaccharide (LPS) + IFNγ increased glucose consumption, hexokinase activity and lactate production which are indicative of glycolysis [9], while LPS alone increased glycolysis and decreased mitochondrial metabolism in BV2 cells [10]. We have demonstrated that microglia prepared from transgenic mice that overexpress human amyloid precursor protein (APP) and presenilin 1 (PS1; APP/PS1 mice) had both an inflammatory and glycolytic phenotype [8] while amyloid-β (Aβ) stimulates inflammatory cytokine production in LPS-primed microglia [11]
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
