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Published on: April 13, 2017
Microglia as hunters or gatherers of brain synapses
Marta Pereira-Iglesias1,2, Joel Maldonado-Teixido1,3, Alejandro Melero1
1Achucarro Basque Center for Neuroscience, Leioa, Spain.
Abstract:
Over a decade ago, it was discovered that microglia, the brain's immune cells, engulf synaptic material in a process named microglial pruning. This term suggests that microglia actively sculpt brain circuits by tagging and phagocytosing unwanted synapses. However, live imaging studies have yet to demonstrate how microglial synapse elimination occurs. To address this issue, we propose a new conceptual framework distinguishing between two potential mechanisms of synapse elimination, culling and scavenging. During culling, microglia may use a contractile ring to sever the neuronal plasma membrane, removing the unwanted synapse. During scavenging, synapse elimination is neuronal-driven, and the neuronal plasma membrane fission machinery sheds off synapses that are later phagocytosed by microglia. We will discuss the current limitations of studying microglial synapse elimination and evaluate evidence supporting either culling or scavenging. Discerning between these mechanisms is essential for determining the therapeutic value of phagocytosis modulators in diseases with altered brain connectivity.
Insights
Microglia prune synapses through two proposed mechanisms: culling, where microglia actively sever synapses, or scavenging, where neurons shed synapses for microglial uptake. Understanding these processes is key for brain connectivity disorders.
Area of Science:
- Neuroscience
- Immunology
- Cell Biology
Background:
- Microglia, the brain's immune cells, were found to engulf synaptic material via microglial pruning.
- Microglial pruning suggests active sculpting of neural circuits through synapse elimination.
- Live imaging has not yet demonstrated the precise mechanisms of microglial synapse elimination.
Purpose of the Study:
- To propose a new conceptual framework for microglial synapse elimination.
- To distinguish between two potential mechanisms: culling and scavenging.
- To evaluate current evidence and limitations in studying these processes.
Main Methods:
- Conceptual framework development.
- Literature review and evidence evaluation.
- Discussion of live imaging limitations.
Main Results:
- Proposed two distinct mechanisms for microglial synapse elimination: culling and scavenging.
- Culling involves microglia using a contractile ring to sever synapses.
- Scavenging involves neuronal-driven synapse shedding followed by microglial phagocytosis.
Conclusions:
- Distinguishing between culling and scavenging is crucial for understanding brain circuit development.
- Identifying the correct mechanism is essential for developing therapies targeting phagocytosis modulators.
- This framework aids in understanding altered brain connectivity in disease states.
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