Purinergic receptor regulation of LPS-induced signaling and pathophysiology

Abstract

Macrophages express several lipopolysaccharide (LPS) binding proteins and are potently activated by LPS to produce inflammatory mediators. Recent studies have shown that receptors for exogenous nucleotides (P2X and P2Y purinergic receptors) can modulate macrophage production of TNF-alpha, IL-1beta and nitric oxide (NO) following LPS exposure. Macrophages and LPS-stimulated monocytes express elevated levels of P2Y1, P2Y2 and P2X7 mRNA, suggesting that both P2Y and P2X receptors can contribute to LPS-induced pathophysiology. In addition, oxidized-ATP treatment (which inhibits P2X7) of macrophages blocks LPS-induced NO production, NF-kappaB and ERK-1/2 activation. Also, an LPS-binding domain located in the P2X7 C-terminus appears important for receptor trafficking/function. Moreover, the purinergic receptor ligand 2-MeS-ATP attenuates LPS-induced cytokine and NO production in vivo and ex vivo. These data suggest that P2X7 and certain P2Ys are linked to LPS effects, although their relative contribution in vivo is unclear. Accordingly, we tested the capacity of several adenine nucleotides to modulate LPS-induced mortality in mice. We found that the P2X7-directed ligand BzATP was unable to prevent LPS-induced death, whereas 2-MeS-ATP and 2-Cl-ATP, which bind to multiple P2X and P2Y receptors were able to protect mice from LPS-induced death. These data suggest that the co-ordinate action of P2Y and P2X7 receptors are critical for controlling LPS responses in vivo and that agents directed against both receptor classes may provide the greatest therapeutic advantage.

Mastoparan, a G Protein Agonist Peptide, Differentially Modulates TLR4- and TLR2-Mediated Signaling in Human Endothelial Cells and Murine Macrophages

“…A role for G proteins in LPS signaling was further bolstered by the observations that many LPS-inducible events (e.g., MAPK activation, NF-B activation, and others) are mimicked by G protein activation and that LPS increased GTPase activity in macrophages (reviewed in Ref. 60). Since the original observations of Jakway and DeFranco, there have been a number of papers that have confirmed and extended these findings in human and murine monocytes and macrophages, .…”

Cell signaling via the P2X7 nucleotide receptor: linkage to ROS production, gene transcription, and receptor trafficking

“…Past studies have shown that P2X 7 agonists are able to modulate macrophage activation in response to LPS, resulting in increased pro-inflammatory mediator production [17,18,23,56,[67][68][69][70][71][72][73][74][75][76]. Because LPS is known to activate ROS production in leukocytes [77,78], and because P2X 7 activation is able to augment several LPSinduced signaling events, we tested the hypothesis that P2X 7 -stimulated ROS production is enhanced in LPSprimed macrophages.…”

“…When properly regulated, ROS maintain an integral role in host defense, regulation of apoptosis, and modulation of cell signaling. The generation of ROS has also been implicated in several human disorders, including hypertension, atherosclerosis, ischemia/reperfusion injury, neurodegenerative disease, chronic granulomatous disease, and the deleterious effects of aging [18,56]. The use of ROS by leukocytes in the defense against pathogens is well recognized, but the role of ROS as second messengers is sill emerging, e.g., ROS generation has been linked to the activation of transcription factors, including apurinic/apyrimidinic endonuclease 1 (APE1)/Ref1, nuclear factor κB (NFκB), and AP-1, as well as the signaling kinases p90 ribosomal S6 kinase (p90RSK) and various MAPKs [21,[57][58][59][60][61][62][63][64][65].…”

“…Specifically, we will provide evidence that P2X 7 stimulation in macrophages promotes ROS production via the extracellular-regulated kinases-1 and 2 (ERK1/2) and the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase complex, and that ligand binding to P2X 7 results in activation of the transcription factor cyclic-AMP response element-binding protein (CREB) and the expression of key components of the transcription factor activating protein-1 (AP-1) complex. Because receptor trafficking appears critical for controlling cell responsiveness to extracellular ATP [7][8][9]18, 30], we will also discuss the mechanisms by which P2X 7 activity/trafficking may be regulated by specific residues in its C-terminus. As an overview, we will first discuss the general properties of P2X 7 as well as human genetic and animal studies that have revealed several of the biological roles of this receptor.…”

“…Interestingly, P2X 7 ligation by extracellular ATP can also modulate lipopolysaccharide (LPS)-mediated macrophage activation, and P2X 7 stimulation is known to potentiate the release of several LPS-induced pro-inflammatory mediators, including interleukin-1β (IL-1β), tumor necrosis factor-α, and nitric oxide [17][18][19][20][21][22]. However, although there is a growing literature regarding several cell signaling and cytokine processing events that are initiated upon P2X 7 activation, relatively little is known about the regulation of receptor trafficking and the mechanisms by which P2X 7 activation can impact on long-term cellular processes such as the regulation of gene transcription.…”