Involvement of the spinal NALP1 inflammasome in neuropathic pain and aspirin-triggered-15-epi-lipoxin A4 induced analgesia
Introduction
Chronic neuropathic pain presents as a common disease severely disrupting the patients’ quality of life (McCarberg and Billington, 2006). Although it is a complicated condition, neuroinflammation, including glial activation and the production of proinflammatory cytokines, has been widely regarded as one important mechanism of neuropathic pain (Myers et al., 2006). The proinflammatory cytokine interleukin-1β (IL-1β) has been shown to actively participate in the pathogenesis of neuropathic pain and to induce a secondary injury cascade during the course of disease (Thacker et al., 2007). Clinically, elevated IL-1β was observed in the cerebrospinal fluid (CSF) of patients with complex regional pain syndrome (Alexander et al., 2005), and the same pathology was observed in the spinal cord of rats with neuropathic pain (Amin et al., 2012). Previous studies had demonstrated that exogenous administration of IL-1β in the CNS induced obvious pain behaviors (Sung et al., 2012). Further, blockade of IL-1 signaling has been shown to relieve nerve-injury-induced neuropathic pain (Kleibeuker et al., 2008). All these reports support a crucial role for IL-1β in the development of neuropathic pain, but the mechanisms underlying IL-1β production had not been clearly recognized, particularly in the CNS.
IL-1β is synthesized as an inactive cytoplasmic precursor and cleaved into the biologically active form by certain cysteine proteases in response to proinflammatory stimuli (Thornberry et al., 1992). The inflammasome caspase-1 platform is one of the primary pathways regulating the maturation of IL-1β (Martinon et al., 2002). Inflammasomes are groups of protein complexes that recognize diverse sets of inflammation-inducing stimuli such as pathogenic infection or tissue damage (Strowig et al., 2012). Recently, a newly discovered inflammasome family, the NAcht leucine-rich-repeat protein (NALP) inflammasome, composed of the NALP protein, caspase-1 and the adaptor protein apoptosis-associated speck-like protein containing a caspase-activating recruitment domain (CARD) (ASC) was first found in humans and then implicated in multiple neuroinflammation-related disorders (Tschopp et al., 2003). Notably, studies have demonstrated that the NALP1 inflammasome was activated in spinal motor neurons after spinal cord injury (de Rivero Vaccari et al., 2008). In the peripheral mechanisms of complex regional pain syndrome, the NALP1 inflammasome also participated in the process of peripheral sensitization (Shi et al., 2011). However, whether the NALP1 inflammasome is activated in the spinal cord of neuropathic pain in rat has not been previously described.
Lipoxin and its exogenous analog aspirin-triggered carbon-15 epimer aspirin-triggered-15-epi-lipoxin A4 (ATL) belong to a class of eicosanoids that exhibit powerful anti-inflammatory effects and act as endogenous ‘brake signals’ in inflammation reactions (Serhan, 2005, Serhan et al., 2008). In the rat model of neuropathic pain and cancer-induced bone pain, intrathecal administration of lipoxin reduced the elevated mRNA level of IL-1β, and pain behaviors were significantly relieved (Svensson et al., 2007, Hu et al., 2012). According to our previous research, ATL showed the longest and most potent analgesic effect compared to the two structural isomers of lipoxins, lipoxin A4 and lipoxin B4 (Hu et al., 2012). In this study, we aimed to investigate whether intrathecal administration of ATL would inhibit NALP inflammasome activation and the subsequent IL-1β maturation in the spinal cords of rats with chronic constriction injury (CCI)-induced neuropathic pain.
The present study found that the spinal inflammasome-caspase-1 pathway was activated in the development of CCI neuropathic pain and inhibiting the product of activated inflammasome significantly attenuated the CCI pain behaviors. Moreover, the activated NALP1 inflammasome was found in both dorsal astrocytes and neurons, especially in the superficial laminae of the spinal dorsal horn. Finally, intrathecal administration of ATL relieved CCI-induced thermal pain behaviors and inhibited the activation of the NALP1 inflammasome, providing a new therapeutic target for neuropathic pain.
Section snippets
Animals
Experiments were performed on adult (180–200 g) male Sprague–Dawley rats. Animals were obtained from the Experimental Animal Center, Shanghai Institutes for Biological Science, Chinese Academy of Sciences. They were housed under a 12/12-h light/dark cycle at a room temperature of 23 ± 1 °C with food and water ad libitum. All experiments were conducted in accordance with the National Institutes of Health Guide for the Care and Use of Laboratory Animals and the Ethical Issues of the International
CCI induced pain-like behavior in rats
In the Hargreaves test, CCI on rats’ right hind limbs provoked a significant decrease in the PWL of the ipsilateral hind paws from day 3 after the sciatic nerve injury that was stably sustained for 1 month (Fig. 1A, B). It also induced a profound decrease in the mechanical threshold over the same timeframe (Fig. 1C, D). However, there were no significant differences in the above pain behaviors between normal and sham surgery rats. Collectively, these data suggest that rats subjected to the CCI
Discussion
In our study, we observed for the first time that the NALP1 inflammasome system participated in the development of neuropathic pain. CCI initiated the activation of the NALP1 inflammasome, leading to the cleavage of pro-caspase-1, upregulation of the adaptor protein ASC and the maturation of IL-1β. The components of the NALP1 inflammasome complex were visible in the astrocytes and neurons of the spinal cord dorsal horn. Repeated intrathecal administration of ATL to the CCI rats significantly
Author contributions
Qian Li carried out the major part of the study. Qian Li and Zhi-Fu Wang performed the animal surgery and the behavioral tests. Qian Li and Yu Tian carried out the immunoprecipitation study. Qian Li drafted the manuscript. Shen-Bin Liu, Wen-Li Mi and Hong-Jian Ma carried out part of the immunofluorescence study. Gen-Cheng Wu, Jun Wang and Jin Yu revised the manuscript. Yan-Qing Wang conceived and designed the study. All authors read and approved the final manuscript.
Acknowledgements
This work was supported by the National Key Basic Research program of China (2013CB531906), the National Natural Science Fund of China (30970975, 31000495, 81171045, 81072875, 81371247 and 31121061), the Excellent Doctoral Graduate Research Program of Fudan University and the Doctoral Fund of the Ministry of Education of China (Nos. 20100071120046, 20100071120042).
References (42)
- et al.
Changes in cerebrospinal fluid levels of pro-inflammatory cytokines in CRPS
Pain
(2005) - et al.
Antinociceptive evaluation of ceftriaxone and minocycline alone and in combination in a neuropathic pain model in rat
Neuroscience
(2012) - et al.
A peripheral mononeuropathy in rat that produces disorders of pain sensation like those seen in man
Pain
(1988) - et al.
A new and sensitive method for measuring thermal nociception in cutaneous hyperalgesia
Pain
(1988) - et al.
IL-1 beta signaling is required for mechanical allodynia induced by nerve injury and for the ensuing reduction in spinal cord neuronal GRK2
Brain Behav Immun
(2008) - et al.
Lipoxin A4 attenuates brain damage and downregulates the production of pro-inflammatory cytokines and phosphorylated mitogen-activated protein kinases in a mouse model of traumatic brain injury
Brain Res
(2013) - et al.
The inflammasome: a molecular platform triggering activation of inflammatory caspases and processing of proIL-beta
Mol Cell
(2002) - et al.
The role of neuroinflammation in neuropathic pain: mechanisms and therapeutic targets
Drug Discov Today
(2006) - et al.
Sensing pathogens and danger signals by the inflammasome
Curr Opin Immunol
(2009) Lipoxins and aspirin-triggered 15-epi-lipoxins are the first lipid mediators of endogenous anti-inflammation and resolution
Prostaglandins Leukot Essent Fatty Acids
(2005)
The pannexin 1 channel activates the inflammasome in neurons and astrocytes
J Biol Chem
Ethical guidelines for investigations of experimental pain in conscious animals
Pain
Nalp1b controls mouse macrophage susceptibility to anthrax lethal toxin
Nat Genet
The lipoxin receptor ALX: potent ligand-specific and stereoselective actions in vivo
Pharmacol Rev
Caspase-1 is involved in the genesis of inflammatory hypernociception by contributing to peripheral IL-1beta maturation
Mol Pain
A molecular platform in neurons regulates inflammation after spinal cord injury
J Neurosci
Therapeutic neutralization of the NLRP1 inflammasome reduces the innate immune response and improves histopathology after traumatic brain injury
J Cereb Blood Flow Metab
Immunological and inflammatory functions of the interleukin-1 family
Annu Rev Immunol
Efficient analysis of experimental observations
Annu Rev Pharmacol Toxicol
Lipoxins and aspirin-triggered lipoxin alleviate bone cancer pain in association with suppressing expression of spinal proinflammatory cytokines
J Neuroinflammation
Glia as a link between neuroinflammation and neuropathic pain
Immune Netw
Cited by (52)
Curcumin: an inflammasome silencer
2020, Pharmacological ResearchCitation Excerpt :Previous studies have indicated that decreased intracellular K+ levels promotes IL-1β maturation through activation of caspase-1 in cultured astrocytes and neurons (Fig. 1) [95]. Moreover, increasing evidence suggested that NLRC4 and NALP1 inflammasomes also participate in the cleavage of caspase-1, and thus maturation of IL-1β and exert a significant effect on neuropathic pain [96,97]. IL-1β is remarkably expressed in astrocyte cells in the spinal cord [98].
Specialized pro-resolving lipid mediators: A new class of non-immunosuppressive and non-opioid analgesic drugs
2020, Pharmacological ResearchAnti-nociceptive effects of caloric restriction on neuropathic pain in rats involves silent information regulator 1
2018, British Journal of Anaesthesia