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Lipoxins and aspirin-triggered lipoxin inhibit inflammatory pain processing.

Svensson CI, Zattoni M, Serhan CN - J. Exp. Med. (2007)

Bottom Line: Furthermore, activation of extracellular signal-regulated kinase and c-Jun N-terminal kinase in astrocytes, which has been indicated to play an important role in spinal pain processing, was attenuated in the presence of lipoxins.This linkage opens the possibility that lipoxins regulate spinal nociceptive processing though their actions upon astrocytic activation.Targeting mechanisms that counterregulate the spinal consequences of persistent peripheral inflammation provide a novel endogenous mechanism by which chronic pain may be controlled.

View Article: PubMed Central - PubMed

Affiliation: Department of Anesthesiology, University of California, San Diego, La Jolla, CA 92093, USA. csvensson@ucsd.edu

ABSTRACT
Inflammatory conditions can lead to debilitating and persistent pain. This hyperalgesia reflects sensitization of peripheral terminals and facilitation of pain signaling at the spinal level. Studies of peripheral systems show that tissue injury triggers not only inflammation but also a well-orchestrated series of events that leads to reversal of the inflammatory state. In this regard, lipoxins represent a unique class of lipid mediators that promote resolution of inflammation. The antiinflammatory role of peripheral lipoxins raises the hypothesis that similar neuraxial systems may also down-regulate injury-induced spinal facilitation of pain processing. We report that the lipoxin A(4) receptor is expressed on spinal astrocytes both in vivo and in vitro and that spinal delivery of lipoxin A(4), as well as stable analogues, attenuates inflammation-induced pain. Furthermore, activation of extracellular signal-regulated kinase and c-Jun N-terminal kinase in astrocytes, which has been indicated to play an important role in spinal pain processing, was attenuated in the presence of lipoxins. This linkage opens the possibility that lipoxins regulate spinal nociceptive processing though their actions upon astrocytic activation. Targeting mechanisms that counterregulate the spinal consequences of persistent peripheral inflammation provide a novel endogenous mechanism by which chronic pain may be controlled.

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ATLa prevents ATP-evoked ERK and JNK phosphorylation in primary astrocyte cultures. (A) Representative images demonstrating that ALXR colocalizes with the astrocyte marker GFAP in cultured primary astrocytes. Bar, 50 μm. (B) Western blots probed for phosphorylated ERK and JNK in samples from primary astrocytes stimulated with ATP, SP, IL-1β, and TNF-α for 15 min. Incubation with 10 nM ATLa, starting 30 min before TNF-α stimulation, had no effect on JNK phosphorylation (C), whereas ATLa prevented both ERK and JNK phosphorylation evoked by ATP (D and E). Each bar represents the mean ± SEM (n = 4–5). *, P < 0.05 as compared with control; #, P < 0.05 as compared with PBS + ATP.
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fig4: ATLa prevents ATP-evoked ERK and JNK phosphorylation in primary astrocyte cultures. (A) Representative images demonstrating that ALXR colocalizes with the astrocyte marker GFAP in cultured primary astrocytes. Bar, 50 μm. (B) Western blots probed for phosphorylated ERK and JNK in samples from primary astrocytes stimulated with ATP, SP, IL-1β, and TNF-α for 15 min. Incubation with 10 nM ATLa, starting 30 min before TNF-α stimulation, had no effect on JNK phosphorylation (C), whereas ATLa prevented both ERK and JNK phosphorylation evoked by ATP (D and E). Each bar represents the mean ± SEM (n = 4–5). *, P < 0.05 as compared with control; #, P < 0.05 as compared with PBS + ATP.

Mentions: The finding that spinal astrocytes express ALXR is intriguing, as the number of reports indicating that spinal nonneuronal cells play an important role in spinal facilitation of pain processing is rapidly increasing. It has been shown that both nerve injury and peripheral inflammation lead to activation of spinal dorsal horn astrocytes and microglia (12). Spinal delivery of inhibitors or modulators of astrocyte function block initiation and maintenance of persistent pain states (13–16), supporting an important role for these cells in spinal sensitization. Astrocytes respond to changes in their environment by releasing, for example, cytokines, chemokines, and nitric oxide. Thus, it is possible that lipoxins, by acting on astrocyte ALXR, dampen this response by counterregulating the production of proinflammatory factors. Based on reports demonstrating that ERK and c-Jun N-terminal kinase (JNK) mitogen-activated protein kinase (MAPK) are activated (phosphorylated) in spinal astrocytes in models of persistent pain (14, 17), we sought to examine the effect of lipoxins on ERK and JNK phosphorylation in astrocytes. For this purpose, primary cultures of astrocytes (>95% astrocytes) were established from postnatal rat spinal cord, and ALXR expression was verified (Fig. 4 A). The astrocyte cultures were subjected to 250 μM of stable ATP, 50 ng/ml TNF-α, 10 ng/ml IL-1β, and 10 μM substance P (SP), factors indicated to act on glia and play a role in spinal pain processing, for 15 min. This study showed that ATP drives activation of both ERK and JNK, whereas TNF-α stimulation activated only JNK. SP and IL-1β did not evoke phosphorylation of these MAPKs at the chosen concentration and time point. Strikingly, ATP-evoked ERK and JNK phosphorylation, but not TNF-α–evoked JNK phosphorylation, was reduced in the presence of 10 nM ATLa (30-min pretreatment). This observation is in line with studies in fibroblasts and T cells where it has been shown that ERK activation is attenuated in the presence of lipoxins (for review see reference 2). Of importance, ERK activity in spinal astrocytes is thought to be important for the maintenance of chronic pain, and inhibition of spinal ERK, at the time point when it is activated in astrocytes, attenuates neuropathic pain (17). In addition to ERK, this work has identified the JNK family as an intracellular mechanism through which lipoxins may exert their antiinflammatory and antihyperalgesic actions in spinal tissues. Importantly, it has been reported that persistent activation of JNK in spinal astrocytes appears critical for the maintenance of neuropathic pain (14). In the current study, increased JNK activation was observed in spinal astrocytes after peripheral inflammation, and the carrageenan-evoked JNK phosphorylation was reduced in the presence of i.t. LXA4 (Fig. S2, available at http://www.jem.org/cgi/content/full/jem.20061826/DC1). The antihyperalgesic effects observed after i.t. injection of lipoxins in our model of inflammatory pain, in conjunction with the prevention of JNK activation in vivo and JNK and ERK phosphorylation in primary astrocytes, suggest that ALXR activation mediates antinociception through prevention of intracellular MAPK signaling in spinal astrocytes. This is a striking finding, as it provides support for the existence of a mechanism through which spinal nonneuronal cells can participate in the regulation of sensory neuronal activity, not only through sensitization, but also by normalization, of pain signaling.


Lipoxins and aspirin-triggered lipoxin inhibit inflammatory pain processing.

Svensson CI, Zattoni M, Serhan CN - J. Exp. Med. (2007)

ATLa prevents ATP-evoked ERK and JNK phosphorylation in primary astrocyte cultures. (A) Representative images demonstrating that ALXR colocalizes with the astrocyte marker GFAP in cultured primary astrocytes. Bar, 50 μm. (B) Western blots probed for phosphorylated ERK and JNK in samples from primary astrocytes stimulated with ATP, SP, IL-1β, and TNF-α for 15 min. Incubation with 10 nM ATLa, starting 30 min before TNF-α stimulation, had no effect on JNK phosphorylation (C), whereas ATLa prevented both ERK and JNK phosphorylation evoked by ATP (D and E). Each bar represents the mean ± SEM (n = 4–5). *, P < 0.05 as compared with control; #, P < 0.05 as compared with PBS + ATP.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2118737&req=5

fig4: ATLa prevents ATP-evoked ERK and JNK phosphorylation in primary astrocyte cultures. (A) Representative images demonstrating that ALXR colocalizes with the astrocyte marker GFAP in cultured primary astrocytes. Bar, 50 μm. (B) Western blots probed for phosphorylated ERK and JNK in samples from primary astrocytes stimulated with ATP, SP, IL-1β, and TNF-α for 15 min. Incubation with 10 nM ATLa, starting 30 min before TNF-α stimulation, had no effect on JNK phosphorylation (C), whereas ATLa prevented both ERK and JNK phosphorylation evoked by ATP (D and E). Each bar represents the mean ± SEM (n = 4–5). *, P < 0.05 as compared with control; #, P < 0.05 as compared with PBS + ATP.
Mentions: The finding that spinal astrocytes express ALXR is intriguing, as the number of reports indicating that spinal nonneuronal cells play an important role in spinal facilitation of pain processing is rapidly increasing. It has been shown that both nerve injury and peripheral inflammation lead to activation of spinal dorsal horn astrocytes and microglia (12). Spinal delivery of inhibitors or modulators of astrocyte function block initiation and maintenance of persistent pain states (13–16), supporting an important role for these cells in spinal sensitization. Astrocytes respond to changes in their environment by releasing, for example, cytokines, chemokines, and nitric oxide. Thus, it is possible that lipoxins, by acting on astrocyte ALXR, dampen this response by counterregulating the production of proinflammatory factors. Based on reports demonstrating that ERK and c-Jun N-terminal kinase (JNK) mitogen-activated protein kinase (MAPK) are activated (phosphorylated) in spinal astrocytes in models of persistent pain (14, 17), we sought to examine the effect of lipoxins on ERK and JNK phosphorylation in astrocytes. For this purpose, primary cultures of astrocytes (>95% astrocytes) were established from postnatal rat spinal cord, and ALXR expression was verified (Fig. 4 A). The astrocyte cultures were subjected to 250 μM of stable ATP, 50 ng/ml TNF-α, 10 ng/ml IL-1β, and 10 μM substance P (SP), factors indicated to act on glia and play a role in spinal pain processing, for 15 min. This study showed that ATP drives activation of both ERK and JNK, whereas TNF-α stimulation activated only JNK. SP and IL-1β did not evoke phosphorylation of these MAPKs at the chosen concentration and time point. Strikingly, ATP-evoked ERK and JNK phosphorylation, but not TNF-α–evoked JNK phosphorylation, was reduced in the presence of 10 nM ATLa (30-min pretreatment). This observation is in line with studies in fibroblasts and T cells where it has been shown that ERK activation is attenuated in the presence of lipoxins (for review see reference 2). Of importance, ERK activity in spinal astrocytes is thought to be important for the maintenance of chronic pain, and inhibition of spinal ERK, at the time point when it is activated in astrocytes, attenuates neuropathic pain (17). In addition to ERK, this work has identified the JNK family as an intracellular mechanism through which lipoxins may exert their antiinflammatory and antihyperalgesic actions in spinal tissues. Importantly, it has been reported that persistent activation of JNK in spinal astrocytes appears critical for the maintenance of neuropathic pain (14). In the current study, increased JNK activation was observed in spinal astrocytes after peripheral inflammation, and the carrageenan-evoked JNK phosphorylation was reduced in the presence of i.t. LXA4 (Fig. S2, available at http://www.jem.org/cgi/content/full/jem.20061826/DC1). The antihyperalgesic effects observed after i.t. injection of lipoxins in our model of inflammatory pain, in conjunction with the prevention of JNK activation in vivo and JNK and ERK phosphorylation in primary astrocytes, suggest that ALXR activation mediates antinociception through prevention of intracellular MAPK signaling in spinal astrocytes. This is a striking finding, as it provides support for the existence of a mechanism through which spinal nonneuronal cells can participate in the regulation of sensory neuronal activity, not only through sensitization, but also by normalization, of pain signaling.

Bottom Line: Furthermore, activation of extracellular signal-regulated kinase and c-Jun N-terminal kinase in astrocytes, which has been indicated to play an important role in spinal pain processing, was attenuated in the presence of lipoxins.This linkage opens the possibility that lipoxins regulate spinal nociceptive processing though their actions upon astrocytic activation.Targeting mechanisms that counterregulate the spinal consequences of persistent peripheral inflammation provide a novel endogenous mechanism by which chronic pain may be controlled.

View Article: PubMed Central - PubMed

Affiliation: Department of Anesthesiology, University of California, San Diego, La Jolla, CA 92093, USA. csvensson@ucsd.edu

ABSTRACT
Inflammatory conditions can lead to debilitating and persistent pain. This hyperalgesia reflects sensitization of peripheral terminals and facilitation of pain signaling at the spinal level. Studies of peripheral systems show that tissue injury triggers not only inflammation but also a well-orchestrated series of events that leads to reversal of the inflammatory state. In this regard, lipoxins represent a unique class of lipid mediators that promote resolution of inflammation. The antiinflammatory role of peripheral lipoxins raises the hypothesis that similar neuraxial systems may also down-regulate injury-induced spinal facilitation of pain processing. We report that the lipoxin A(4) receptor is expressed on spinal astrocytes both in vivo and in vitro and that spinal delivery of lipoxin A(4), as well as stable analogues, attenuates inflammation-induced pain. Furthermore, activation of extracellular signal-regulated kinase and c-Jun N-terminal kinase in astrocytes, which has been indicated to play an important role in spinal pain processing, was attenuated in the presence of lipoxins. This linkage opens the possibility that lipoxins regulate spinal nociceptive processing though their actions upon astrocytic activation. Targeting mechanisms that counterregulate the spinal consequences of persistent peripheral inflammation provide a novel endogenous mechanism by which chronic pain may be controlled.

Show MeSH
Related in: MedlinePlus