Diverse activation of microglia by chemokine (C-C motif) ligand 2 overexpression in brain

Maj Linda B. Selenica, Jennifer A. Alvarez, Kevin R. Nash, Daniel C. Lee, Chuanhai Cao, Xiaoyang Lin, Patrick Reid, Peter R. Mouton, Dave Morgan, Marcia N. Gordon

Research output: Contribution to journalArticlepeer-review

73 Scopus citations


Background: The chemokine (C-C motif) ligand 2 (CCL2) is a monocyte chemoattractant protein that mediates macrophage recruitment and migration during peripheral and central nervous system (CNS) inflammation.Methods: To determine the impact of CCL2 in inflammation in vivo and to elucidate the CCL2-induced polarization of activated brain microglia, we delivered CCL2 into the brains of wild-type mice via recombinant adeno-associated virus serotype 9 (rAAV-9) driven by the chicken β-actin promoter. We measured microglial activation using histological and chemical measurement and recruitment of monocytes using histology and flow cytometry.Results: The overexpression of CCL2 in the CNS induced significant activation of brain resident microglia. CD45 and major histocompatibility complex class II immunoreactivity significantly increased at the sites of CCL2 administration. Histological characterization of the microglial phenotype revealed the elevation of " classically activated" microglial markers, such as calgranulin B and IL-1β, as well as markers associated with " alternative activation" of microglia, including YM1 and arginase 1. The protein expression profile in the hippocampus demonstrated markedly increased levels of IL-6, GM-CSF and eotaxin (CCL-11) in response to CCL2, but no changes in the levels of other cytokines, including TNF-α and IFN-γ. Moreover, real-time PCR analysis confirmed increases in mRNA levels of gene transcripts associated with neuroinflammation following CCL2 overexpression. Finally, we investigated the chemotactic properties of CCL2 in vivo by performing adoptive transfer of bone marrow-derived cells (BMDCs) isolated from donor mice that ubiquitously expressed green fluorescent protein. Flow cytometry and histological analyses indicated that BMDCs extravasated into brain parenchyma and colabeled with microglial markers.Conclusion: Taken together, our results suggest that CCL2 strongly activates resident microglia in the brain. Both pro- and anti-inflammatory activation of microglia were prominent, with no bias toward the M1 or M2 phenotype in the activated cells. As expected, CCL2 overexpression actively recruited circulating monocytes into the CNS. Thus, CCL2 expression in mouse brain induces microglial activation and represents an efficient method for recruitment of peripheral macrophages.

Original languageEnglish
Article number856
JournalJournal of Neuroinflammation
StatePublished - Jul 17 2013

Bibliographical note

Funding Information:
This work is supported by grants from the National Institutes of Health (AG 15490 and AG25711). We thank the staff of the Division of Comparative Medicine, especially Margaret Baldwin for her assistance with the intracardiac puncture injections. We also thank Dr Karoly Szekeres for his assistance in performing the flow cytometry of the brain tissue. We would like to thank Dr. Sidney Morris Jr. at University of Pittsburgh for his generosity in providing the Arg-1 antibody. The authors appreciate the editorial assistance of Dr. Jane Carver of the Clinical and Translational Science Institute at the University of South Florida.


  • BMDC
  • CCL2
  • Infiltration
  • Inflammation
  • Macrophage
  • Microglial activation
  • rAAV9

ASJC Scopus subject areas

  • General Neuroscience
  • Immunology
  • Neurology
  • Cellular and Molecular Neuroscience


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