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Adenosine A(2A) receptor mediates microglial process retraction.

Orr AG, Orr AL, Li XJ, Gross RE, Traynelis SF - Nat. Neurosci. (2009)

Bottom Line: Thus, A(2A) 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia, USA. anna.orr@gladstone.ucsf.edu

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 A(2A) adenosine receptor coincident with P2Y(12) downregulation. Thus, A(2A) 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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Adenosine A2A receptor upregulation mediates process retraction and reverses chemotaxis in activated microglia(a) A2A receptor mRNA is upregulated upon microglial activation with LPS (n = 4), LTA (n = 3), TNF-α (n = 3), CpG (n = 2), or amyloid-β (Aβ, n = 3, 1 µM), while P2Y12 is downregulated. (b) A2A agonist triggered retraction in LPS-treated microglia (CGS: 20 µM, n = 6, p < 0.01 compared to baseline), but not in untreated cells (Con: n = 3). (c) The A2A antagonist SCH-58261 (SCH: 5 µM) and adenosine deaminase (ADA: 5 U/ml) inhibited ATP-induced retraction in LPS-activated microglia (ATP: n = 5; ATP + SCH: n = 7, p < 0.05; ATP + ADA: n = 5, p < 0.05 compared to responses in ATP-treated cells). All graphs show mean + s.e.m.
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Figure 5: Adenosine A2A receptor upregulation mediates process retraction and reverses chemotaxis in activated microglia(a) A2A receptor mRNA is upregulated upon microglial activation with LPS (n = 4), LTA (n = 3), TNF-α (n = 3), CpG (n = 2), or amyloid-β (Aβ, n = 3, 1 µM), while P2Y12 is downregulated. (b) A2A agonist triggered retraction in LPS-treated microglia (CGS: 20 µM, n = 6, p < 0.01 compared to baseline), but not in untreated cells (Con: n = 3). (c) The A2A antagonist SCH-58261 (SCH: 5 µM) and adenosine deaminase (ADA: 5 U/ml) inhibited ATP-induced retraction in LPS-activated microglia (ATP: n = 5; ATP + SCH: n = 7, p < 0.05; ATP + ADA: n = 5, p < 0.05 compared to responses in ATP-treated cells). All graphs show mean + s.e.m.

Mentions: Together, our data implicate a Gs-coupled receptor in the chemorepulsion of activated microglia by ATP. However, there is no known Gs-coupled mouse P2Y receptor. Therefore, we considered other receptor classes. Upon release in the brain, ATP is rapidly broken down to adenosine by extracellular and membrane-bound nucleotidases, including CD39 and CD7318. Thus, we investigated the role of adenosine receptors, two of which (A2A and A2B) are Gs-coupled19. Reverse transcription-polymerase chain reaction (RT-PCR) revealed that, while P2Y12 is lost, the high-affinity adenosine receptor A2A is selectively upregulated upon microglial activation with toll-like receptor agonists or with TNF-α (Fig. 5a). Indeed, A2A mRNA upregulation has been observed previously in microglia treated with LPS, but not functionally studied20. Notably, aggregated amyloid-β (Aβ), a main component of extracellular amyloid plaques in Alzheimer’s disease, also triggered microglial A2A upregulation and P2Y12 downregulation (Fig. 5a).


Adenosine A(2A) receptor mediates microglial process retraction.

Orr AG, Orr AL, Li XJ, Gross RE, Traynelis SF - Nat. Neurosci. (2009)

Adenosine A2A receptor upregulation mediates process retraction and reverses chemotaxis in activated microglia(a) A2A receptor mRNA is upregulated upon microglial activation with LPS (n = 4), LTA (n = 3), TNF-α (n = 3), CpG (n = 2), or amyloid-β (Aβ, n = 3, 1 µM), while P2Y12 is downregulated. (b) A2A agonist triggered retraction in LPS-treated microglia (CGS: 20 µM, n = 6, p < 0.01 compared to baseline), but not in untreated cells (Con: n = 3). (c) The A2A antagonist SCH-58261 (SCH: 5 µM) and adenosine deaminase (ADA: 5 U/ml) inhibited ATP-induced retraction in LPS-activated microglia (ATP: n = 5; ATP + SCH: n = 7, p < 0.05; ATP + ADA: n = 5, p < 0.05 compared to responses in ATP-treated cells). All graphs show mean + s.e.m.
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Figure 5: Adenosine A2A receptor upregulation mediates process retraction and reverses chemotaxis in activated microglia(a) A2A receptor mRNA is upregulated upon microglial activation with LPS (n = 4), LTA (n = 3), TNF-α (n = 3), CpG (n = 2), or amyloid-β (Aβ, n = 3, 1 µM), while P2Y12 is downregulated. (b) A2A agonist triggered retraction in LPS-treated microglia (CGS: 20 µM, n = 6, p < 0.01 compared to baseline), but not in untreated cells (Con: n = 3). (c) The A2A antagonist SCH-58261 (SCH: 5 µM) and adenosine deaminase (ADA: 5 U/ml) inhibited ATP-induced retraction in LPS-activated microglia (ATP: n = 5; ATP + SCH: n = 7, p < 0.05; ATP + ADA: n = 5, p < 0.05 compared to responses in ATP-treated cells). All graphs show mean + s.e.m.
Mentions: Together, our data implicate a Gs-coupled receptor in the chemorepulsion of activated microglia by ATP. However, there is no known Gs-coupled mouse P2Y receptor. Therefore, we considered other receptor classes. Upon release in the brain, ATP is rapidly broken down to adenosine by extracellular and membrane-bound nucleotidases, including CD39 and CD7318. Thus, we investigated the role of adenosine receptors, two of which (A2A and A2B) are Gs-coupled19. Reverse transcription-polymerase chain reaction (RT-PCR) revealed that, while P2Y12 is lost, the high-affinity adenosine receptor A2A is selectively upregulated upon microglial activation with toll-like receptor agonists or with TNF-α (Fig. 5a). Indeed, A2A mRNA upregulation has been observed previously in microglia treated with LPS, but not functionally studied20. Notably, aggregated amyloid-β (Aβ), a main component of extracellular amyloid plaques in Alzheimer’s disease, also triggered microglial A2A upregulation and P2Y12 downregulation (Fig. 5a).

Bottom Line: Thus, A(2A) 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia, USA. anna.orr@gladstone.ucsf.edu

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 A(2A) adenosine receptor coincident with P2Y(12) downregulation. Thus, A(2A) 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.

Show MeSH
Related in: MedlinePlus