primary-microglia-isolation-from-postnatal-mouse-brains

Primary Microglia Isolation from Postnatal Mouse Brains

Microglia are the mononuclear phagocytes in the central nervous system (CNS), which play key roles in maintaining homeostasis and regulating the ...

Shanghai Jiao Tong University School of Medicine

It has been suggested that inflammation is involved in the pathophysiology of depression. As tissue-specific macrophages in the central nervous system (CNS), microglia play an important role in neuroinflammation. Resident microglia become activated towards the pro-inflammatory (M1) phenotype or the anti-inflammatory (M2) phenotype during neuroinflammation. In the CNS, neurons report to microglia regarding their statuses and can regulate microglial activation, while microglia also modulate neuronal activities, including neuroplasticity. The molecular mechanisms underlying the communication between microglia and neurons, which include intracellular and extracellular signalling pathways, might be complex and of great importance for new research on the pathogenesis of depression. The present review aims to discuss the common cellular and molecular mechanisms for microglial activation and aberrant neuroplasticity in depression and the role of these processes in the pathogenesis of depression.

Common cellular and molecular mechanisms and interactions between microglial activation and aberrant neuroplasticity in depression.

Newborn microglia rapidly replenish the whole brain after selective elimination of most microglia (>99%) in adult mice. Previous studies reported that repopulated microglia were largely derived from microglial progenitor cells expressing nestin in the brain. However, the origin of these repopulated microglia has been hotly debated. In this study, we investigated the origin of repopulated microglia by a series of fate-mapping approaches. We first excluded the blood origin of repopulated microglia via parabiosis. With different transgenic mouse lines, we then demonstrated that all repopulated microglia were derived from the proliferation of the few surviving microglia (<1%). Despite a transient pattern of nestin expression in newly forming microglia, none of repopulated microglia were derived from nestin-positive non-microglial cells. In summary, we conclude that repopulated microglia are solely derived from residual microglia rather than de novo progenitors, suggesting the absence of microglial progenitor cells in the adult brain.

Repopulated microglia are solely derived from the proliferation of residual microglia after acute depletion.

Elucidating the origin of microglia is crucial for understanding their functions and homeostasis. Previous study has indicated that Nestin-positive progenitor cells differentiate into microglia and replenish the brain after depleting most brain microglia. Microglia have also shown the capacity to repopulate the retina after eliminating all retinal microglia. However, the origin(s) of repopulated retinal microglia is/are unknown. In this study, we aim to investigate the origins of repopulated microglia in the retina. Interestingly, we find that repopulated retinal microglia are not derived from Nestin-positive progenitor cells. Instead, they have two origins: the center-emerging microglia are derived from residual microglia in the optic nerve and the periphery-emerging microglia are derived from macrophages in the ciliary body/iris. Therefore, we have for the first time identified the extra-retinal origins of microglia in the adult mammalian retina by using a model of microglial repopulation, which may shed light on the target exploration of therapeutic interventions for retinal degenerative disorders.

Dual extra-retinal origins of microglia in the model of retinal microglia repopulation.

Microglia are important immune cells in the central nervous system (CNS). Dysfunctions of gene-deficient microglia contribute to the development and progression of multiple CNS diseases. Microglia replacement by nonself cells has been proposed to treat microglia-associated disorders. However, some attempts have failed due to low replacement efficiency, such as with the traditional bone marrow transplantation approach. In this study, we develop three efficient strategies for microglia replacement: microglia replacement by bone marrow transplantation (mrBMT), microglia replacement by peripheral blood (mrPB), and microglia replacement by microglia transplantation (mrMT). mrBMT and mrPB allow microglia-like cells to efficiently replace resident microglia in the whole CNS. On the other hand, mrMT achieves microglia replacement in brain regions of interest. In summary, the present study offers effective tactics for microglia replacement with diverse application scenarios, which potentially opens up a window on treating microglia-associated CNS disorders.

Article	Year
Common cellular and molecular mechanisms and interactions between microglial activation and aberrant neuroplasticity in depression. Neuropharmacology\| PubMed ID: 32980387	2020
Repopulated microglia are solely derived from the proliferation of residual microglia after acute depletion. Nature neuroscience\| PubMed ID: 29472620	2018
Dual extra-retinal origins of microglia in the model of retinal microglia repopulation. Cell discovery\| PubMed ID: 29507754	2018
Efficient Strategies for Microglia Replacement in the Central Nervous System. Cell reports\| PubMed ID: 32783928	2020
Author Correction: Repopulated microglia are solely derived from the proliferation of residual microglia after acute depletion. Nature neuroscience\| PubMed ID: 33219354	2021

Yanxia Rao

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