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Analysis of Microglia and Monocyte-derived Macrophages from the Central Nervous System by Flow Cytometry
Published on: June 22, 2017
Circulating monocytic cells infiltrate layers of anterograde axonal degeneration where they transform into microglia
Ingo Bechmann1, Jana Goldmann, Adam D Kovac
1Institute of Cell Biology and Neurobiology, Charité University Hospital, Berlin, Germany. ingo.bechmann@charite.de
Abstract:
In this study, we demonstrate the infiltration of blood-derived monocytic cells and their morphologic transformation into microglia in zones of acute, anterograde (Wallerian) axonal degeneration induced by entorhinal cortex lesion (ECL). ECL was performed in mice which had received green fluorescent protein (GFP)-transduced bone marrow grafts allowing identification of blood-derived elements within the brain. While in the unlesioned hemisphere GFP+ cells were restricted to perivascular and leptomeningeal sites, many round fluorescent cells appeared in hippocampal zones of axonal degeneration at 24 h post lesion (hpl). Within 72 hpl, these GFP+ cells acquired ramified, microglia-like morphologies, which persisted for at least 7 days post ECL. Differentiation of GFP+ cells into glial fibrillary acidic protein (GFAP)+ astrocytes was never observed. To exclude that this recruitment is an artifact of irradiation or bone marrow transplantation, the fluorescent cell tracker 6-carboxylfluorescein diacetate (CFDA) was injected into spleens of normal mice 1 day before ECL. Again, fluorescent cells appeared at the lesion site and along the layers of axonal degeneration at 48 hpl and CFDA+/MAC-1+, cells exhibited amoeboid and ramified morphologies. Thus, blood-derived cells infiltrate not only the site of mechanical lesion, but also the layers of anterograde axonal degeneration, where they readily transform into microglia-like elements. A role for infiltrating leukocytes in facilitating or modulating postlesional plasticity, e.g., by phagocytosis of growth-inhibiting myelin should now be considered. Moreover, monocytic cells may serve as vehicles to transport therapeutic substances such as neurotrophic factors or caspase inhibitors to zones of axonal degeneration.
Insights
Blood monocytes infiltrate brain lesions and transform into microglia, aiding axonal degeneration repair. These cells may deliver therapeutic agents to damaged neural tissues, offering new treatment avenues.
Area of Science:
- Neuroscience
- Immunology
- Cell Biology
Background:
- Acute axonal degeneration, such as Wallerian degeneration, occurs after brain injury.
- The origin and role of microglia in response to brain lesions are not fully understood.
- Blood-derived cells' contribution to neuroinflammation and repair requires further investigation.
Purpose of the Study:
- To investigate the infiltration and transformation of blood-derived monocytic cells into microglia in response to entorhinal cortex lesion (ECL).
- To determine if these infiltrating cells contribute to the cellular response at sites of acute axonal degeneration.
- To explore the potential therapeutic implications of these findings.
Main Methods:
- Utilized green fluorescent protein (GFP)-transduced bone marrow transplantation in mice to track blood-derived cells.
- Induced entorhinal cortex lesion (ECL) to create a model of acute axonal degeneration.
- Employed the fluorescent cell tracker 6-carboxylfluorescein diacetate (CFDA) to confirm findings in non-transplanted mice.
Main Results:
- GFP-positive cells infiltrated hippocampal zones of axonal degeneration within 24 hours post-lesion (hpl).
- These cells acquired ramified, microglia-like morphologies by 72 hpl and persisted for at least 7 days.
- CFDA-labeled cells also appeared at lesion sites, exhibiting amoeboid and ramified morphologies, confirming blood cell infiltration and transformation.
- No differentiation into glial fibrillary acidic protein (GFAP)-positive astrocytes was observed.
Conclusions:
- Blood-derived monocytic cells infiltrate brain injury sites and transform into microglia-like cells during acute axonal degeneration.
- These findings suggest a significant role for infiltrating leukocytes in post-lesional plasticity and repair mechanisms.
- Monocytic cells represent potential vehicles for targeted delivery of therapeutics to damaged neural areas.
