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ATP mediates rapid microglial response to local brain injury in vivo


Parenchymal microglia are the principal immune cells of the brain. Time-lapse two-photon imaging of GFP-labeled microglia demonstrates that the fine termini of microglial processes are highly dynamic in the intact mouse cortex. Upon traumatic brain injury, microglial processes rapidly and autonomously converge on the site of injury without cell body movement, establishing a potential barrier between the healthy and injured tissue. This rapid chemotactic response can be mimicked by local injection of ATP and can be inhibited by the ATP-hydrolyzing enzyme apyrase or by blockers of G protein–coupled purinergic receptors and connexin channels, which are highly expressed in astrocytes. The baseline motility of microglial processes is also reduced significantly in the presence of apyrase and connexin channel inhibitors. Thus, extracellular ATP regulates microglial branch dynamics in the intact brain, and its release from the damaged tissue and surrounding astrocytes mediates a rapid microglial response towards injury.

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Figure 1: Transcranial two-photon imaging shows rapid dynamics of fine microglial processes.
Figure 2: Microglial processes move rapidly towards the site of injury induced either by the two-photon laser, or mechanically with a glass electrode.
Figure 3: Extracellular ATP and activation of purinergic G protein–coupled receptors are necessary for rapid chemotactic microglial response.
Figure 4: ATP-induced ATP release is essential for rapid microglial response.
Figure 5: The microglial response towards the laser ablation is inhibited after blocking connexin hemichannels, the conduits of ATP.


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We thank H. Suk-Woo, G. Shakhar, Y-C. Chen and R. Uglesich for offering useful comments and help with experiments. This work is supported by grants from the National Institute of Health and the Dana Foundation to M. L. D and W-B. G.

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Correspondence to Wen-Biao Gan.

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Supplementary information

Supplementary Video 1

Baseline dynamics of fine microglial processes. Microglia in the cerebral cortex display a highly branched morphology with each cell soma decorated by long processes with fine termini. Timelapse imaging of microglia in the intact mouse brain reveals rapid extension, retraction, shape and volume changes of fine processes over intervals of seconds to minutes, while microglial cell bodies and main branches remain morphologically stable over hours. (MOV 147 kb)

Supplementary Video 2

Rapid microglial response after laser-induced ablation. This movie shows the dynamics of microglial processes before and immediately after a small laser ablation is induced ~40 µm from the pial surface. Within the first minutes post-ablation, the tips of the processes of the cells immediately surrounding the ablation appear bulbous and slightly enlarged. In the next few minutes, these cells extend their processes toward the damaged site where they appear to fuse together and form a spherical containment around it. During this period, the same cells also retract those processes that previously lied in directions opposite to the site of injury. Most of the cellular content of each of the immediate neighbors is directed towards the damaged site within the first 1-3 hours, whereas the cell bodies remain at approximately the same location for at least 10 hours. Cells located further away also respond in a directional way, sending their processes towards the ablation but without ever reaching the already contained injury site. (MOV 1031 kb)

Supplementary Video 3

Rapid microglial response after dual laser ablation. Immediately after the first ablation, the surrounding cells begin extending their processes toward the injury site, and retracting those on opposite sides. When the second ablation occurs 20 minutes after the first one, the previously retracting processes of the cell lying in between the two ablations started to extend toward the second site of damage. Although the cell had committed a number of its processes to respond to the first ablation, the same cell was still able to detect the second ablation and immediately assign its remaining processes on the opposite side to the new ablation. (MOV 537 kb)

Supplementary Video 4

Rapid microglial response after a small-scale mechanical injury, induced with a glass electrode through a small craniotomy. Using a micromanipulator, we inserted the glass electrode inside the brain and performed lateral movements around an area of 50 µm in diameter. We observed that similar to the laser-induced response, microglial processes assumed the bulbous morphology at their termini and rapidly moved into the damaged tissue. (MOV 143 kb)

Supplementary Video 5

Local injection of 10 mM ATP in an ACSF solution containing 3% rhodamine-dextran (to make the electrode visible) induces rapid microglial response toward the tip of the glass electrode in a way strikingly similar to that towards the laser-induced injury. (MOV 413 kb)

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Davalos, D., Grutzendler, J., Yang, G. et al. ATP mediates rapid microglial response to local brain injury in vivo. Nat Neurosci 8, 752–758 (2005).

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