Abstract
Microglia are the principal immune cells of the brain. In Alzheimer disease, these brain mononuclear phagocytes are recruited from the blood and accumulate in senile plaques. However, the role of microglia in Alzheimer disease has not been resolved. Microglia may be neuroprotective by phagocytosing amyloid-β (Aβ), but their activation and the secretion of neurotoxins may also cause neurodegeneration. Ccr2 is a chemokine receptor expressed on microglia, which mediates the accumulation of mononuclear phagocytes at sites of inflammation. Here we show that Ccr2 deficiency accelerates early disease progression and markedly impairs microglial accumulation in a transgenic mouse model of Alzheimer disease (Tg2576). Alzheimer disease mice deficient in Ccr2 accumulated Aβ earlier and died prematurely, in a manner that correlated with Ccr2 gene dosage, indicating that absence of early microglial accumulation leads to decreased Aβ clearance and increased mortality. Thus, Ccr2-dependent microglial accumulation plays a protective role in the early stages of Alzheimer disease by promoting Aβ clearance.
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Acknowledgements
We thank D. Selkoe for discussing the data and for suggestions, K. Hsiao-Ashe for permission to use the APP mice, I. Charo (Gladstone Institute of Cardiovascular Disease) for providing the Ccr2−/− mice, the Harvard Center for Neurodegeneration and Repair for funding J.E.K. and C.G., the American Health Assistance Foundation and the Dana Foundation for funding J.E.K. and the US National Institutes of Health for funding J.E.K. and A.D.L.
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J.E.K. designed the experiments, analyzed the data, wrote the manuscript, performed the chemotaxis experiments and directly supervised M.T. in breeding the mice and in performing the immunostaining and the ELISA experiments. S.E.H. isolated brain cells and macrophages and performed the Aβ binding experiments, and the laser capture microdissection experiments. T.K.M. performed the Q-PCR. S.E.H. and T.K.M. were also involved in detailed discussions of the data and manuscript. K.T. and C.G. designed and performed the stereotaxic microinjection experiments. A.D.L. participated in designing experiments, evaluating data and writing the manuscript.
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Supplementary information
Supplementary Fig. 1
Florid Aβ deposition and senile plaque formation in aged APP mice. (PDF 72 kb)
Supplementary Fig. 2
Ccl2 is produced in Cd11b-positive cells in APP mice but not in Gfap-positive cells. (PDF 766 kb)
Supplementary Fig. 3
Expression of Ccr2 correlates with Cd11b expression in brain cells. (PDF 331 kb)
Supplementary Fig. 4
Absence of microglial accumulation in 65-day old Ccr2 deficient APP mice. (PDF 73 kb)
Supplementary Fig. 5
Migration of resident peritoneal macrophages from Ccr2+/−, Ccr2−/−, and WT mice to Ccl2 and Ccl3. (PDF 75 kb)
Supplementary Table 1
Sequences of primers used for Q-PCR. (PDF 51 kb)
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El Khoury, J., Toft, M., Hickman, S. et al. Ccr2 deficiency impairs microglial accumulation and accelerates progression of Alzheimer-like disease. Nat Med 13, 432–438 (2007). https://doi.org/10.1038/nm1555
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DOI: https://doi.org/10.1038/nm1555
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