ADP and AMP Induce Interleukin-1β Release from Microglial Cells through Activation of ATP-Primed P2X₇ Receptor Channels

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.

Distribution of purinergic P2X receptors in the equine digit, cervical spinal cord and dorsal root ganglia

“…In the dorsal root ganglia, P2X 7 receptor subunit expression was similarly localised to supporting cells, such as, Schwann cells, and this finding is supported by published data in other species [32,33]. Neuronal expression of P2X 1- Fig.…”

Neuroprotective roles of the P2Y2 receptor

“…Although the endogenous expression of P2Y 2 Rs has been reported in mouse microglia [67,214], it seems likely that increased levels of proinflammatory cytokines should further increase P2Y 2 R expression in glial cells in vivo. Our recent in vitro data show that treatment of mouse primary oligomeric/oligomeric Aβ 1-42 upregulates P2Y 2 R expression [145] via a pathway likely involving P2X7R-mediated IL-1β release [16,75,105,[154][155][156]. It also has been determined that P2X7R activation increases P2Y 2 R expression in rat astrocytes [215].…”

“…Indeed, it has been shown that the P2Y 2 R promoter contains a NF-κB binding sequence that is required for inflammation-induced P2Y 2 R upregulation, a pathway that can be blocked by Bay-11-7085, a specific inhibitor of the phosphorylation of IκB-α, the endogenous regulator of NF-κB activity [104]. Thus, it seems likely that the co-release of IL-1β and nucleotides mediated by ATP-induced P2X7R activation in microglia [16,75,105] provides an in vivo mechanism for both the upregulation and activation of P2Y 2 Rs in neurons and other cell types. ATP release also occurs from activated microglia and astrocytes under oxidative stress [15] and following neuronal excitation [17,106] via volume-activated anion channels [106], P2X7Rs [107], and pannexin hemichannels [37,108] or upon exposure to fibrillar or oligomeric Aβ [14,75,109].…”

“…P2Y 2 R expression in mouse primary cortical neurons can be upregulated in response to the proinflammatory cytokine IL-1β [16,48], the levels of which are elevated in the AD brain [153]. Activation of the P2X7R in microglia promotes the release of IL-1β, TNF-α, and ATP [16,75,105,[154][155][156], suggesting a mechanism whereby the P2X7R regulates functional P2Y 2 R expression in neurons and other cells. The finding that P2Y 2 R expression under proinflammatory conditions is regulated by NF-κB binding to the P2Y 2 R promoter [104] is consistent with the established role of NF-κB activation in the induction of inflammation [157].…”

Extracellular nucleotide metabolism and signaling in the pathophysiology of articular cartilage

“…However, rat growth plate chondrocytes express P2X 2 and P2X 5 receptors (154), raising the possibility that articular chondrocytes express a subset of P2X receptors. Another P2X receptor, P2X 7 , is required for IL-1 maturation and release from macrophages (155), microglia (156), and endothelial cells (157). Chondrocytes release IL-1␤ and may therefore express P2X 7 .…”