Oxidized ATP (oATP) attenuates proinflammatory signaling via P2 receptor‐independent mechanisms

Abstract

1 Periodate-oxidized ATP (oATP), which covalently modifies nucleotide-binding proteins, can significantly attenuate proinflammatory signaling. Although the P2X 7 nucleotide receptor (P2X 7 R) is irreversibly antagonized by oATP, it is unclear whether anti-inflammatory actions of oATP are predominantly mediated via its actions on P2X 7 R. Here, we describe inhibitory effects of oATP on proinflammatory responses in three human cell types that lack expression of P2X 7 R: human umbilical vein endothelial cells (HUVEC), HEK293 cells, and 1321N1 astrocytes. 2 oATP decreased by 40 -70% the secretion of interleukin (IL)-8 stimulated by tumor necrosis factor-a (TNF-a) in all three cell types, by IL-1b in HUVEC and 1321N1 cells, and by endotoxin in HUVEC. Attenuation of TNF-a-stimulated IL-8 secretion by oATP was similar in wild-type HEK cells or HEK cells stably expressing recombinant P2X 7 R. 3 oATP also attenuated cytokine-stimulated expression of nuclear factor-kB-luciferase reporter genes expressed in HEK or 1321N1 cells, but did not affect the rapid downregulation of IkB. 4 oATP had no effect on uridine triphosphate-induced activation of native P2Y 2 receptors in HEK cells, but reduced the potency and efficacy of ADP as an agonist of native P2Y 1 receptors. However, inhibition of P2Y 1 receptors with the specific antagonist MRS2216 did not mimic the effects of oATP on TNF-a-stimulated IL-8 secretion. 5 Although 1321N1 astrocytes lack expression of any known P2 receptor subtypes, oATP markedly inhibited ecto-ATPase activity in these cells, resulting in a significant accumulation of extracellular ATP. 6 In summary, oATP can attenuate proinflammatory signaling by mechanisms independent of the expression or activation of known P2 receptor subtypes.

Autocrine activation of P2Y1 receptors couples Ca2+ influx to Ca2+ release in human pancreatic beta cells

“…**p<0.01 and ***p<0.001 compared with 1 mmol/l glucose or as indicated agreement with the findings of a recent study [12], our findings vary from those of another study suggesting a dominant role for P2X 3 [11]. However, the latter study employed pyridoxalphosphate-6-azophenyl-2′,5′-disulfonic acid (iso-PPADS) and oxidised ATP at concentrations that also strongly inhibit P2Y 1 [21,22]. The more selective P2X (1/3) blocker TNP-ATP [23] does not affect [Ca 2+ ] i (Fig.…”

Expression, signaling, and function of P2X7 receptors in bone

“…These responses were inhibited by oxidized ATP and attributed to activation of P2X7 receptors. However, oxidized ATP is not a specific antagonist of P2X7 receptors [66,67]. Moreover, in rabbit osteoclasts, the initial transient elevation of [Ca 2+ ] i in response to BzATP is caused by P2Y receptor-mediated release of Ca 2+ from intracellular stores [57].…”

Physiological and pathological functions of P2X7 receptor in the spinal cord

“…oATP, an antagonist considered specific of P2X7Rs, affects pro-inflammatory responses independently from the activation of P2X7 receptors because HUVEC, HEK293 and 1321N1 cells all secrete less IL-8 without expressing P2X7Rs [78]. P2X7R knock-out studies in autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis, have also shown a significant reduction in the protein levels of IL-1 and IL-6 with a concomitant decrease in lymphocytic apoptosis which, in turn, exacerbates the susceptibility to the disorder [79].…”