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Updated: Jun 4, 2025
Metabolic Characterization of Polarized M1 and M2 Bone Marrow-derived Macrophages Using Real-time Extracellular Flux Analysis
Published on: November 28, 2015
Pro-inflammatory macrophage activation does not require inhibition of oxidative phosphorylation
Andréa B Ball1, Anthony E Jones1, Kaitlyn B Nguyễn1
1Department of Molecular and Medical Pharmacology, University of California, Los Angeles, Los Angeles, CA, USA.
Abstract:
Pro-inflammatory macrophage activation is a hallmark example of how mitochondria serve as signaling organelles. Oxidative phosphorylation sharply decreases upon classical macrophage activation, as mitochondria are thought to shift from ATP production towards accumulating signals that amplify effector function. However, evidence is conflicting regarding whether this collapse in respiration is essential or dispensable. Here we systematically examine this question and show that reduced oxidative phosphorylation is not required for pro-inflammatory macrophage activation. Different pro-inflammatory stimuli elicit varying effects on bioenergetic parameters, and pharmacologic and genetic models of electron transport chain inhibition show no causative link between respiration and macrophage activation. Furthermore, the signaling metabolites succinate and itaconate can accumulate independently of characteristic breaks in the TCA cycle in mouse and human macrophages, and peritoneal macrophages can be activated in vivo without inhibition of oxidative phosphorylation. The results indicate there is plasticity in the metabolic phenotypes that can support pro-inflammatory macrophage activation.
Insights
Reduced mitochondrial oxidative phosphorylation is not essential for pro-inflammatory macrophage activation. Macrophage metabolic flexibility allows for activation independent of respiration inhibition, challenging previous assumptions.
Area of Science:
- Immunology
- Cell Biology
- Metabolic Signaling
Background:
- Mitochondria are recognized as key signaling organelles in cellular processes.
- Pro-inflammatory macrophage activation is linked to decreased oxidative phosphorylation, with mitochondria potentially shifting from ATP production to signaling.
- Conflicting evidence exists on whether this respiratory collapse is a prerequisite for macrophage activation.
Purpose of the Study:
- To systematically investigate the necessity of reduced oxidative phosphorylation for pro-inflammatory macrophage activation.
- To determine the relationship between mitochondrial respiration and macrophage effector functions.
- To explore the metabolic plasticity supporting macrophage activation.
Main Methods:
- Systematic examination of bioenergetic parameters in macrophages.
- Pharmacologic and genetic inhibition of the electron transport chain.
- Analysis of signaling metabolites (succinate, itaconate) and TCA cycle integrity.
- In vivo activation of peritoneal macrophages.
Main Results:
- Reduced oxidative phosphorylation is not required for pro-inflammatory macrophage activation.
- Different pro-inflammatory stimuli induce varied bioenergetic changes.
- Inhibition of electron transport chain components does not causally link to macrophage activation.
- Signaling metabolites accumulate independently of TCA cycle disruptions.
- Macrophages can be activated in vivo without suppressed oxidative phosphorylation.
Conclusions:
- Pro-inflammatory macrophage activation exhibits metabolic plasticity.
- The collapse of oxidative phosphorylation is dispensable for this immune response.
- Mitochondrial function in macrophages is more adaptable than previously thought.
