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Published on: April 13, 2017
Heterogeneity of Microglia Phenotypes: Developmental, Functional and Some Therapeutic Considerations
Yun Yuan1, Chunyun Wu1, Eng-Ang Ling2
1Department of Anatomy and Histology/Embryology, Kunming Medical University, 1168 West Chunrong Road, Kunming, China.
Background:
Microglia play a pivotal role in maintaining homeostasis in complex brain environment. They first exist as amoeboid microglial cells (AMCs) in the developing brain, but with brain maturation, they transform into ramified microglial cells (RMCs). In pathological conditions, microglia are activated and have been classified into M1 and M2 phenotypes. The roles of AMCs, RMCs and M1/M2 microglia phenotypes especially in pathological conditions have been the focus of many recent studies.
Methods:
Here, we review the early development of the AMCs and RMCs and discuss their specific functions with reference to their anatomic locations, immunochemical coding etc. M1 and M2 microglia phenotypes in different neuropathological conditions are also reviewed.
Results:
Activated microglia are engaged in phagocytosis, production of proinflammatory mediators, trophic factors and synaptogenesis etc. Prolonged microglia activation, however, can cause damage to neurons and oligodendrocytes. The M1 and M2 phenotypes featured prominently in pathological conditions are discussed in depth. Experimental evidence suggests that microglia phenotype is being modulated by multiple factors including external and internal stimuli, local demands, epigenetic regulation, and herbal compounds.
Conclusion:
Prevailing views converge that M2 polarization is neuroprotective. Thus, proper therapeutic designs including the use of anti-inflammatory drugs, herbal agents may be beneficial in suppression of microglial activation, especially M1 phenotype, for amelioration of neuroinflammation in different neuropathological conditions. Finally, recent development of radioligands targeting 18 kDa translocator protein (TSPO) in activated microglia may hold great promises clinically for early detection of brain lesion with the positron emission tomography.
Insights
Microglia, including amoeboid (AMCs) and ramified (RMCs) forms, shift to M1/M2 phenotypes during brain pathology. Targeting M2 polarization offers neuroprotection, while TSPO radioligands aid early brain lesion detection.
Area of Science:
- Neuroscience
- Immunology
- Cell Biology
Background:
- Microglia are crucial for brain homeostasis, transitioning from amoeboid microglial cells (AMCs) in development to ramified microglial cells (RMCs) in mature brains.
- In neuropathological conditions, microglia activate into M1 and M2 phenotypes, with their roles being a significant area of research.
Purpose of the Study:
- To review the developmental stages of AMCs and RMCs.
- To discuss the functions of different microglial phenotypes (M1/M2) in neuropathological contexts.
- To explore therapeutic strategies targeting microglial activation.
Main Methods:
- Literature review focusing on microglial development, function, and phenotypes (M1/M2).
- Analysis of experimental evidence regarding factors modulating microglial phenotype.
- Examination of emerging diagnostic tools like TSPO radioligands.
Main Results:
- Microglia perform functions such as phagocytosis, cytokine production, and synaptogenesis, but prolonged activation can be detrimental.
- M1 and M2 phenotypes play distinct roles in various neuropathologies.
- Microglial phenotype is influenced by stimuli, local environment, epigenetics, and compounds like herbal agents.
Conclusions:
- M2 microglial polarization is generally considered neuroprotective.
- Therapeutic strategies aimed at suppressing M1 activation, potentially using anti-inflammatory or herbal agents, may alleviate neuroinflammation.
- 18 kDa translocator protein (TSPO) radioligands show promise for early detection of brain lesions via positron emission tomography.
