Extracellular ATP Triggers Tumor Necrosis Factor‐α Release from Rat Microglia

Abstract

Brain microglia are a major source of inflammatory cytokines, such as tumor necrosis factor-␣ (TNF-␣), which have been implicated in the progression of neurodegenerative diseases. Recently, microglia were revealed to be highly responsive to ATP, which is released from nerve terminals, activated immune cells, or damaged cells. It is not clear, however, whether released ATP can regulate TNF-␣ secretion from microglia. Here we demonstrate that ATP potently stimulates TNF-␣ release, resulting from TNF-␣ mRNA expression in rat cultured brain microglia. The TNF-␣ release was maximally elicited by 1 mM ATP and also induced by a P2X 7 receptorselective agonist, 2Ј-and 3Ј-O-(4-benzoylbenzoyl)adenosine 5Ј-triphosphate, suggesting the involvement of P2X 7 receptor. ATP-induced TNF-␣ release was Ca 2ϩ -dependent, and a sustained Ca 2ϩ influx correlated with the TNF-␣ release in ATP-stimulated microglia. ATP-induced TNF-␣ release was inhibited by PD 098059, an inhibitor of extracellular signal-regulated protein kinase (ERK) kinase 1 (MEK1), which activates ERK, and also by SB 203580, an inhibitor of p38 mitogen-activated protein kinase. ATP rapidly activated both ERK and p38 even in the absence of extracellular Ca 2ϩ . These results indicate that extracellular ATP triggers TNF-␣ release in rat microglia via a P2 receptor, likely to be the P2X 7 subtype, by a mechanism that is dependent on both the sustained Ca 2ϩ influx and ERK/p38 cascade, regulated independently of Ca 2ϩ influx. Key Words: Microglia-Tumor necrosis factor-␣-ATP-P2X 7 receptor-Ca 2ϩ -Mitogenactivated protein kinase. J. Neurochem. 75, 965-972 (2000).

Spinal Glia and Proinflammatory Cytokines Mediate Mirror-Image Neuropathic Pain in Rats

“…Indeed, astrocytes in spinal cord, but not astrocytes isolated from various brain regions, release prostaglandins in response to substance P (Marriott et al, 1991), suggesting that spinal glia are uniquely responsive to neurotransmitters in dorsal horn. Extracellular ATP and ATP metabolites also stimulate astrocytes to release prostaglandins (Marriott et al, 1991) and microglia to release TNF (Hide et al, 2000), IL1 (Chakfe et al, 2002), and IL6 (ShigemotoMogami et al, 2001). CGRP and glutamate stimulate IL6 release as well (Kiriyama et al, 1997;Wu et al, 1997).…”

Biochemical Regulation of Sleep and Sleep Biomarkers

“…ATP binds to purine type 2X7 receptors (P2X7R) on nearby cells to trigger the processing and release of IL1 and TNF from glia. [53][54][55][56] Intracerebroventricular administration of an ATP agonist or ATP antagonists increases or decrease sleep, respectively. 57 P2X7R knockout animals have reduced time spent in NREMS and EEG slow wave activity after sleep deprivation.…”

Hypoxia induced amoeboid microglial cell activation in postnatal rat brain is mediated by ATP receptor P2X4

“…We have shown previously that ATP is involved in hypoxia induced microglial activation [9]. It has been reported that on exposure to ATP, microglia exhibited changes in its electrophysiological properties [10] and increased expression of cytokines in BV2 microglial cell line as well as the primary cultured microglial cells [9,11,12]. Microglial cells are known to express P2X receptors [13].…”

“…Microglial cells are known to express P2X receptors [13]. ATP would then induce various effects through its receptors [8,11,12]. As a group of membrane cation-selective receptor channels, P2X receptors interact with extracellular ATP [13].…”