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ADP and AMP induce interleukin-1beta release from microglial cells through activation of ATP-primed P2X7 receptor
Yassar Chakfe1, Rosanne Seguin, Jack P Antel
1Cell Biology of Excitable Tissue Group and Neuroimmunology Unit, Montreal Neurological Institute, Montreal, Quebec, Canada.
Abstract:
P2X(7) is a subtype of ATP-gated channels that is highly expressed in astrocytes, microglia, and other immune cells. Activation of P2X(7) purinoceptors by ATP or 3'-O-(4-benzoyl)-benzoyl ATP (BzATP) induces the formation of cytolytic pores and provokes release of interleukin-1beta from immune cells. We investigated the actions of other endogenous nucleotides on recombinant and microglial P2X(7) receptors using electrophysiology, fluorescence imaging, and interleukin-1beta release measurement. We found that initial application of ADP or AMP to Xenopus oocytes expressing P2X(7) receptors was ineffective. However, when ADP and AMP, but not UTP or adenosine, were applied after a brief exposure to ATP or BzATP, they activated P2X(7) receptors in a dose-dependent manner. Moreover, responses to ADP and AMP were also elicited after exposure to low concentrations of ATP and were recorded several minutes after removal of ATP from the extracellular medium. Whole-cell recordings from mouse microglial cells showed that significant responses to ADP and AMP were elicited only after ATP application. YO-PRO-1 dye uptake imaging revealed that, unlike ATP, prolonged application of ADP or AMP did not cause an opening of large cytolytic pores in mouse microglial cells. Finally, ADP and AMP stimulated the release of interleukin-1beta from ATP-primed mouse and human microglial cells. We conclude that selective sensitization of P2X(7) receptors to ADP and AMP requires priming with ATP. This novel property of P2X(7) leads to activation by ATP metabolites and proinflammatory cytokine release from microglia without cytotoxicity.
Insights
Priming P2X(7) receptors with ATP enables subsequent activation by ADP and AMP. This process stimulates interleukin-1beta release from microglia without causing cell death, revealing a novel mechanism for immune cell activation.
Area of Science:
- Neuroscience
- Immunology
- Cell Biology
Background:
- P2X(7) receptors are ATP-gated ion channels crucial in immune cell function.
- ATP binding to P2X(7) receptors can induce pore formation and cytokine release.
Purpose of the Study:
- To investigate the effects of endogenous nucleotides on P2X(7) receptors.
- To understand the role of ATP metabolites in P2X(7) receptor activation and microglial function.
Main Methods:
- Electrophysiology
- Fluorescence imaging (YO-PRO-1 dye uptake)
- Interleukin-1beta release assays
- Recombinant and primary microglial cell models (mouse and human)
Main Results:
- ADP and AMP alone do not activate P2X(7) receptors, but sensitize them after ATP priming.
- ATP-primed P2X(7) receptors respond to ADP and AMP, with sustained signaling after ATP removal.
- ADP and AMP activate ATP-primed microglia to release interleukin-1beta without inducing cytotoxicity.
Conclusions:
- P2X(7) receptor activation by ATP metabolites (ADP, AMP) requires prior ATP exposure (priming).
- This priming mechanism allows for controlled microglial activation and pro-inflammatory cytokine release.
- P2X(7) receptor sensitization offers a pathway for immune modulation without direct cytotoxicity.