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Published on: March 30, 2018
Macrophage-colony stimulating factor as an inducer of microglial proliferation in axotomized rat facial nucleus
Shinichi Yamamoto1, Kazuyuki Nakajima, Shinichi Kohsaka
1Department of Bioinformatics, Faculty of Engineering, Soka University, Tokyo, Japan.
Abstract:
We analyzed the mechanism of microglial proliferation in rat axotomized facial nucleus (axotFN). In immunoblotting analysis for possible mitogens, we noticed that the amounts of macrophage-colony stimulating factor (M-CSF) increased in the axotFN for 3-7 days after transection. In contrast, the amounts of granulocyte macrophage-CSF and interleukin-3 did not significantly increase. A potential source for M-CSF was immunohistochemically verified to be microglia. Immunoblotting showed that the amounts of receptor for M-CSF (cFms) increased in the axotFN for 3-14 days after injury, and immunohistochemical staining showed that cFms is expressed in microglia. Proliferating cell nuclear antigen as a marker of proliferation was immunohistochemically identified in microglia in axotFN, and the level was found to peak 3 days after transection in immunoblotting. Hypothesizing that up-regulated M-CSF triggers the above phenomena, we investigated the effects of M-CSF on cFms and proliferating cell nuclear antigen levels in primary microglia. The biochemical experiments revealed that M-CSF induces cFms and drives the cell cycle in microglia. The neutralization of M-CSF in microglia derived from axotFN significantly reduced the proliferation. These results demonstrate that up-regulated M-CSF triggers the induction of cFms in microglia and causes the microglia to proliferate in the axotFN.
Insights
Macrophage-colony stimulating factor (M-CSF) drives microglial proliferation after nerve injury. This study shows M-CSF upregulates its receptor (cFms) on microglia, stimulating cell division in the axotomized facial nucleus.
Area of Science:
- Neuroscience
- Immunology
- Cell Biology
Background:
- Microglial proliferation is a key response to neuronal injury.
- The specific molecular mechanisms driving microglial proliferation in the axotomized facial nucleus (axotFN) remain incompletely understood.
Purpose of the Study:
- To elucidate the mechanism of microglial proliferation in the rat axotFN following axotomy.
- To investigate the role of macrophage-colony stimulating factor (M-CSF) in this process.
Main Methods:
- Immunoblotting to quantify protein levels of M-CSF, its receptor (cFms), and proliferating cell nuclear antigen (PCNA).
- Immunohistochemistry to identify the cellular source of M-CSF and the localization of cFms and PCNA in microglia within the axotFN.
- In vitro experiments using primary microglia to assess the effects of M-CSF on cFms expression and cell proliferation.
- In vivo M-CSF neutralization experiments in the axotFN.
Main Results:
- M-CSF levels significantly increased in the axotFN between 3-7 days post-transection, while other factors like granulocyte macrophage-CSF and interleukin-3 did not.
- Microglia were identified as the source of M-CSF.
- M-CSF receptor (cFms) expression increased in microglia within the axotFN from 3-14 days post-injury.
- PCNA, a proliferation marker, was elevated in microglia, peaking at 3 days post-transection.
- In vitro, M-CSF treatment induced cFms expression and promoted cell cycle progression in primary microglia.
- Neutralization of M-CSF in vivo significantly reduced microglial proliferation in the axotFN.
Conclusions:
- Up-regulated M-CSF in the axotFN triggers the induction of its receptor, cFms, in microglia.
- This M-CSF/cFms signaling pathway is a critical mechanism driving microglial proliferation after nerve injury.
- Targeting the M-CSF pathway may offer therapeutic potential for modulating microglial responses in neurological conditions.
