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Adenosine A2A receptor mediates microglial process retraction

Nature Neuroscience volume 12, pages 872–878 (2009)Cite this article

Abstract

Cell motility drives many biological processes, including immune responses and embryonic development. In the brain, microglia are immune cells that survey and scavenge brain tissue using elaborate and motile cell processes. The motility of these processes is guided by the local release of chemoattractants. However, most microglial processes retract during prolonged brain injury or disease. This hallmark of brain inflammation remains unexplained. We identified a molecular pathway in mouse and human microglia that converted ATP-driven process extension into process retraction during inflammation. This chemotactic reversal was driven by upregulation of the A2A adenosine receptor coincident with P2Y12 downregulation. Thus, A2A receptor stimulation by adenosine, a breakdown product of extracellular ATP, caused activated microglia to assume their characteristic amoeboid morphology during brain inflammation. Our results indicate that purine nucleotides provide an opportunity for context-dependent shifts in receptor signaling. Thus, we reveal an unexpected chemotactic switch that generates a hallmark feature of CNS inflammation.

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Figure 1: Microglial activation in vitro.
Figure 2: ATP induces migratory repulsion in activated microglia.
Figure 3: ATP induces process retraction and slowed motility in activated microglia.
Figure 4: Gs-coupled signaling mediates microglial repulsion from ATP.
Figure 5: Adenosine A2A receptor upregulation mediates process retraction in activated microglia.
Figure 6: Human microglia show a similar shift in purinergic receptor expression and chemotactic response to ATP.
Figure 7: A2A receptor upregulation and involvement in microglial retraction in vivo.
Figure 8: A2A stimulation inhibits uptake by LPS-treated microglia.

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Acknowledgements

We thank B.D. Shur, R. Dingledine and J.M. Boss for discussions on the manuscript, J. Olson for assistance in the studies of human microglia, and E.R. Weeks and D. Semwogerere in the Emory University Department of Physics for useful discussions of image analysis techniques. We are also grateful to K.M. Vellano, A.G. Almonte and J.B. Revennaugh for excellent technical assistance with cell cultures, imaging equipment and animal maintenance. This work was supported by a US National Institutes of Health National Research Service Award fellowship to A.G.O., a pilot grant from the US National Institutes of Health (P01 ES016731), the National Parkinson's Foundation (S.F.T.) and US National Institutes of Health funding for S.F.T.

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Authors and Affiliations

  1. Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia, USA

    Anna G Orr & Stephen F Traynelis

  2. Department of Human Genetics, Emory University School of Medicine, Atlanta, Georgia, USA

    Adam L Orr & Xiao-Jiang Li

  3. Department of Neurosurgery, Emory University School of Medicine, Atlanta, Georgia, USA

    Robert E Gross

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Contributions

A.G.O. designed and carried out the study, collected and analyzed data, and wrote the paper. A.L.O. helped carry out in vivo experiments, brain tissue processing and manuscript revisions. X.-J.L. provided surgical equipment and immunohistochemical reagents, R.E.G. provided human tissue samples and helped with experimental design and interpretation, and S.F.T. was involved in study design, interpretation of data and revision of the manuscript and figures.

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Correspondence to Anna G Orr or Stephen F Traynelis.

Supplementary information

Supplementary Text and Figures

Supplementary Figures 1–6 (PDF 675 kb)

Supplementary Video 1

ATP repels LPS-treated microglia. Time-lapse three-dimensional reconstruction of a cultured LPS-activated mouse microglia migrating away from an ATP-filled micropipette positioned just beyond right edge of screen (pipette not shown). (MOV 1378 kb)

Supplementary Video 2

ATP induces process extension in untreated microglia. Time-lapse three-dimensional reconstruction of a mouse microglia exhibiting process extension toward the periphery of field during bath application of ATP. (MOV 1448 kb)

Supplementary Video 3

ATP induces process retraction in LPS-treated microglia. Time-lapse three-dimensional reconstruction of an LPS-activated mouse microglia exhibiting process retraction during bath application of ATP. (MOV 1371 kb)

Supplementary Video 4

ATP inhibits microglial process motion. Three-dimensional tracking (red traces) of cell processes of an LPS-activated mouse microglia. Bath application of ATP inhibited process motility. (MOV 1037 kb)

Supplementary Video 5

ATP attracts untreated human microglia. Cultured human microglia migrated toward and engulfed an ATP-filled micropipette at right. (MOV 5096 kb)

Supplementary Video 6

ATP repels LPS-treated human microglia. Cultured LPS-activated human microglia migrated away from an ATP-filled micropipette at right (pipette chases cell across field). (MOV 5700 kb)

Supplementary Video 7

Acute injury attracts untreated microglia in vitro. Untreated GFP-positive mouse microglia extended their processes toward acutely injured astrocytes. Mechanical injury (right edge) was induced with a micropipette at approximately 9 min (n = 3). (MOV 1323 kb)

Supplementary Video 8

Acute injury repels LPS-treated microglia in vitro. LPS-activated GFP-positive mouse microglia retracted its processes following astrocyte injury. Mechanical injury (right edge) was induced with a micropipette at approximately 8 min (n = 6). (MOV 1139 kb)

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Orr, A., Orr, A., Li, XJ. et al. Adenosine A2A receptor mediates microglial process retraction. Nat Neurosci 12, 872–878 (2009). https://doi.org/10.1038/nn.2341

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