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Updated: Jun 3, 2026
In vitro Quantitative Imaging Assay for Phagocytosis of Dead Neuroblastoma Cells by iPSC-Macrophages
Published on: February 14, 2021
Inhibition of microglial phagocytosis is sufficient to prevent inflammatory neuronal death
Jonas J Neher1, Urte Neniskyte, Jing-Wei Zhao
1Department of Biochemistry, University of Cambridge, Cambridge CB2 1QW, United Kingdom. jjn24@cam.ac.uk
Abstract:
It is well-known that dead and dying neurons are quickly removed through phagocytosis by the brain's macrophages, the microglia. Therefore, neuronal loss during brain inflammation has always been assumed to be due to phagocytosis of neurons subsequent to their apoptotic or necrotic death. However, we report in this article that under inflammatory conditions in primary rat cultures of neurons and glia, phagocytosis actively induces neuronal death. Specifically, two inflammatory bacterial ligands, lipoteichoic acid or LPS (agonists of glial TLR2 and TLR4, respectively), stimulated microglial proliferation, phagocytic activity, and engulfment of ∼30% of neurons within 3 d. Phagocytosis of neurons was dependent on the microglial release of soluble mediators (and peroxynitrite in particular), which induced neuronal exposure of the eat-me signal phosphatidylserine (PS). Surprisingly, however, eat-me signaling was reversible, so that blocking any step in a phagocytic pathway consisting of PS exposure, the PS-binding protein milk fat globule epidermal growth factor-8, and its microglial vitronectin receptor was sufficient to rescue up to 90% of neurons without reducing inflammation. Hence, our data indicate a novel form of inflammatory neurodegeneration, where inflammation can cause eat-me signal exposure by otherwise viable neurons, leading to their death through phagocytosis. Thus, blocking phagocytosis may prevent some forms of inflammatory neurodegeneration, and therefore might be beneficial during brain infection, trauma, ischemia, neurodegeneration, and aging.
Insights
Inflammation can cause microglia to engulf and kill healthy neurons by exposing "eat-me" signals. Blocking this phagocytic pathway rescues neurons, suggesting a new target for treating neurodegenerative diseases.
Area of Science:
- Neuroscience
- Immunology
Background:
- Microglia, the brain's immune cells, typically clear dead neurons via phagocytosis.
- Neuronal loss in brain inflammation was assumed to result from phagocytosis of already dead neurons.
Purpose of the Study:
- To investigate the role of phagocytosis in neuronal death during inflammation.
- To identify mechanisms by which inflammation induces neuronal death and explore potential therapeutic targets.
Main Methods:
- Primary rat cultures of neurons and glia were exposed to inflammatory bacterial ligands (lipoteichoic acid and LPS).
- Microglial activity, neuronal engulfment, and the "eat-me" signal phosphatidylserine (PS) exposure were monitored.
- Pharmacological inhibition of the phagocytic pathway (PS exposure, MFG-E8, vitronectin receptor) was employed.
Main Results:
- Inflammatory stimuli (LPS, lipoteichoic acid) activated microglia, leading to the engulfment of approximately 30% of viable neurons within 3 days.
- Neuronal phagocytosis was dependent on microglial release of soluble mediators, particularly peroxynitrite, which induced PS exposure on neurons.
- Blocking the phagocytic pathway, including PS signaling, rescued up to 90% of neurons without reducing overall inflammation.
Conclusions:
- Phagocytosis actively induces neuronal death under inflammatory conditions, representing a novel mechanism of inflammatory neurodegeneration.
- Inflammation can trigger "eat-me" signals on viable neurons, leading to their phagocytic clearance.
- Inhibiting microglial phagocytosis offers a potential therapeutic strategy for neurodegenerative conditions associated with inflammation.
