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Synaptic Pruning by Microglia: Lessons from Genetic Studies in Mice
Junia Lara de Deus1, Oluwaseun Samuel Faborode1, Sayan Nandi1
1Department of Anatomy, Howard University College of Medicine, Washington, DC, USA.
Background:
Neural circuits are subjected to refinement throughout life. The dynamic addition and elimination (pruning) of synapses are necessary for maturation of neural circuits and synaptic plasticity. Due to their phagocytic nature, microglia have been considered as the primary mediators of synaptic pruning. Synaptic pruning can strengthen an active synapse by removing excess weaker synapses during development. Inappropriate synaptic pruning can often influence a disease outcome or an injury response.
Summary:
This review offers a focused discussion on microglial roles in synaptic pruning, based on the evidence gathered from genetic manipulations in mice. Genetically labeled microglia and synapses often allow assessment of their interactions in real time. Further manipulations involving synaptically localized molecules, neuronally or glial-derived diffusible factors, and their respective cognate receptors in microglia provide critical evidence in support of a direct role of microglia in synaptic pruning.
Key Message:
We discuss microglial contact-dependent "eat-me," "don't-eat-me," and "find-me" signals, as well as recently identified noncontact pruning, under the contexts of neural circuit, brain region, developmental window, and an injury or a disease state.
Insights
Microglia, the brain's immune cells, actively prune synapses, refining neural circuits throughout life. This process is crucial for brain development and plasticity, with implications for neurological health and disease.
Area of Science:
- Neuroscience
- Cell Biology
- Immunology
Background:
- Neural circuits undergo lifelong refinement through synapse addition and elimination (pruning).
- Microglia, with their phagocytic capabilities, are key players in mediating synaptic pruning.
- Dysfunctional synaptic pruning is linked to neurological diseases and injury responses.
Purpose of the Study:
- To review the critical roles of microglia in synaptic pruning.
- To explore the molecular mechanisms and signaling pathways involved in microglial-mediated pruning.
- To discuss the context-dependent nature of microglial pruning in different brain regions and conditions.
Main Methods:
- Analysis of genetic manipulation studies in mice.
- Real-time assessment of microglia-synapse interactions using genetically labeled cells.
- Investigation of synaptically localized molecules and glial-derived factors.
Main Results:
- Evidence supports a direct role for microglia in eliminating weaker synapses, strengthening active ones.
- Microglial pruning involves contact-dependent signals like "eat-me," "don't-eat-me," and "find-me."
- Noncontact-dependent pruning mechanisms mediated by microglia have also been identified.
Conclusions:
- Microglia actively sculpt neural circuits via synaptic pruning, essential for maturation and plasticity.
- Understanding microglial pruning mechanisms offers insights into brain development, injury, and disease.
- Further research on microglial signaling pathways can reveal therapeutic targets for neurological disorders.
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