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Overexpression of macrophage colony-stimulating factor receptor on microglial cells induces an inflammatory response
O M Mitrasinovic1, G V Perez, F Zhao
1Department of Psychiatry and Behavioral Sciences, Stanford University School of Medicine, Stanford, California 94305, USA.
Abstract:
Microglia are important in the inflammatory response in Alzheimer's disease (AD). We showed previously that macrophage colony-stimulating factor receptor (M-CSFR), encoded by the c-fms protooncogene, is overexpressed on microglia surrounding amyloid beta (Abeta) deposits in the APP(V717F) mouse model for AD. The M-CSFR is also increased on microglia after experimental brain injury and in AD. To determine the relevance of these findings, we transiently expressed M-CSFR on murine BV-2 and human SV-A3 microglial cell lines using an SV40-promoted c-fms construct. M-CSFR overexpression resulted in microglial proliferation and increased expression of inducible nitric-oxide synthase, the proinflammatory cytokines interleukin-1alpha, macrophage inflammatory protein 1-alpha, and interleukin-6 and of macrophage colony-stimulating factor (M-CSF) itself. Antibody neutralization of M-CSF showed that the M-CSFR-induced proinflammatory response was dependent on M-CSF in the culture media. By using a co-culture of c-fms-transfected murine microglia and rat organotypic hippocampal slices and a species-specific real time reverse transcriptase-polymerase chain reaction assay and enzyme-linked immunosorbent assay, we showed that M-CSFR overexpression on exogenous microglia induced expression of interleukin-1alpha by the organotypic culture. These results show that increased M-CSFR expression induces microglial proliferation, cytokine expression, and a paracrine inflammatory response, suggesting that in APP(V717F) mice increased M-CSFR on microglia could be an important factor in Abeta-induced inflammatory response.
Insights
Increased macrophage colony-stimulating factor receptor (M-CSFR) on microglia drives inflammation in Alzheimer's disease models. This receptor overexpression promotes microglial proliferation and cytokine release, contributing to neuroinflammation.
Area of Science:
- Neuroscience
- Immunology
- Cell Biology
Background:
- Microglia play a key role in the neuroinflammatory response observed in Alzheimer's disease (AD).
- Macrophage colony-stimulating factor receptor (M-CSFR) is upregulated on microglia in AD and following experimental brain injury.
- Previous work indicated M-CSFR overexpression on microglia near amyloid beta (Abeta) deposits in an AD mouse model.
Purpose of the Study:
- To investigate the functional consequences of M-CSFR overexpression on microglial cells.
- To determine the role of M-CSFR in mediating microglial proliferation and inflammatory responses.
- To assess the contribution of M-CSFR to Abeta-induced inflammation in an AD context.
Main Methods:
- Transient expression of M-CSFR in murine BV-2 and human SV-A3 microglial cell lines.
- Analysis of microglial proliferation and expression of inflammatory mediators (iNOS, IL-1α, MIP-1α, IL-6, M-CSF).
- In vitro co-culture system with transfected microglia and rat organotypic hippocampal slices, employing RT-PCR and ELISA to assess inflammatory responses.
Main Results:
- M-CSFR overexpression led to increased microglial proliferation and expression of pro-inflammatory cytokines and iNOS.
- The M-CSFR-induced inflammatory response was dependent on M-CSF in the culture medium.
- Exogenous microglia overexpressing M-CSFR induced IL-1α expression in hippocampal slices, indicating a paracrine inflammatory effect.
Conclusions:
- Increased M-CSFR expression on microglia stimulates proliferation and cytokine production.
- M-CSFR signaling contributes to a paracrine inflammatory response in the brain.
- Upregulated M-CSFR on microglia may be a significant factor in Abeta-induced inflammation in Alzheimer's disease.