Activation of the microglial P2X7R/NLRP3 inflammasome mediates central sensitization in a mouse model of medication overuse headache

Hypercapnia promotes NLRP3 inflammasome activation in microglia by activating P2X7R after lipopolysaccharide-induced activation of the TLR4/NF-κB signaling pathway

BACKGROUND

Sepsis is an uncontrolled inflammatory response to infection and is closely associated with the occurrence of acute respiratory distress syndrome (ARDS). Low tidal volume lung ventilation and permissive hypercapnia is a recognized therapy for ARDS. However, whether permissive hypercapnia aggravates sepsis-associated encephalopathy (SAE) remains unclear. The present study investigated whether hypercapnia contributed to the development of SAE through the purinergic 2X7 receptor (P2X7R) by activating the Nod-like receptor protein 3 (NLRP3) inflammasome in sepsis.

METHODS

The SAE model was established by intracranial injection of lipopolysaccharide (LPS) (1 μg/ml, 5 μl) in C57BL/6 mice. Hypercapnia was induced by mechanical ventilation with a high concentration of CO2 (5 % CO2, 21 % O2 and 74 % N2) in vivo. Toll-like receptor 4 (TLR4) and P2X7R knockout (KO) mice were employed in the study, while in vitro, BV2 microglial cells were treated with LPS or a high concentration of CO2 (15 % CO2 + 20 % O2). Immunofluorescence and western blot analysis were used to assess the expression levels of TLR4, NF-κB, phosphorylated (p)-NF-κB, P2X7R, pro-caspase-1, caspase-1, pro-IL-1β, IL-1β, pro-IL-18 and IL-18. ATP levels in the cell culture medium were detected by fluorometric assay.

RESULT

The results revealed that, compared with the sham group, the expression levels of TLR4, p-NF-κB, pro-IL-1β, pro-IL-18 and NLRP3 were significantly upregulated in the LPS and LPS + hypercapnia groups, but not in the hypercapnia group. Although the expression levels of caspase-1, IL-1β and IL-18 were increased slightly in the LPS group, their upregulation was more pronounced in the LPS + hypercapnia group, and it was suppressed when TLR4 was knocked out. Furthermore, P2X7R expression and ATP levels in the cell culture medium remained unchanged in the LPS group compared with the sham group but were remarkably increased both in the hypercapnia and LPS + hypercapnia groups. Additionally, P2X7R KO restrained the caspase-1, IL-1β and IL-18 increased induced by LPS injected intracranially and hypercapnia.

CONCLUSIONS

In conclusion, LPS induced the priming step of NLRP3 inflammasome activation, but had little effect on the activation step, while hypercapnia played an important role in the activation step through P2X7R, depending on the priming step stimulated by LPS.

Regulation of the Nur77-P2X7r Signaling Pathway by Nodakenin: A Potential Protective Function against Alcoholic Liver Disease

Alcoholic liver disease (ALD) is the main factor that induces liver-related death worldwide and represents a common chronic hepatopathy resulting from binge or chronic alcohol consumption. This work focused on revealing the role and molecular mechanism of nodakenin (NK) in ALD associated with hepatic inflammation and lipid metabolism through the regulation of Nur77-P2X7r signaling. In this study, an ALD model was constructed through chronic feeding of Lieber-DeCarli control solution with or without NK treatment. Ethanol (EtOH) or NK was administered to AML-12 cells, after which Nur77 was silenced. HepG2 cells were exposed to ethanol (EtOH) and subsequently treated with recombinant Nur77 (rNur77). Mouse peritoneal macrophages (MPMs) were treated with lipopolysaccharide/adenosine triphosphate (LPS/ATP) and NK, resulting in the generation of conditioned media. In vivo, histopathological alterations were markedly alleviated by NK, accompanied by reductions in serum triglyceride (TG), aspartate aminotransferase (AST), and alanine aminotransferase (ALT) levels and the modulation of Lipin-1, SREBP1, and Nur77 levels in comparison to the EtOH-exposed group (p < 0.001). Additionally, NK reduced the production of P2X7r and NLRP3. NK markedly upregulated Nur77, inhibited P2X7r and Lipin-1, and promoted the function of Cytosporone B, a Nur77 agonist (p < 0.001). Moreover, Nur77 deficiency weakened the regulatory effect of NK on P2X7r and Lipin-1 inhibition (p < 0.001). In NK-exposed MPMs, cleaved caspase-1 and mature IL-1β expression decreased following LPS/ATP treatment (p < 0.001). NK also decreased inflammatory-factor production in primary hepatocytes stimulated with MPM supernatant. NK ameliorated ETOH-induced ALD through a reduction in inflammation and lipogenesis factors, which was likely related to Nur77 activation. Hence, NK is a potential therapeutic approach to ALD.

Involvement of microglial P2X7 receptor in pain modulation

BACKGROUND

Pain is a rapid response mechanism that compels organisms to retreat from the harmful stimuli and triggers a repair response. Nonetheless, when pain persists for extended periods, it can lead to adverse changes into in the individual's brain, negatively impacting their emotional state and overall quality of life. Microglia, the resident immune cells in the central nervous system (CNS), play a pivotal role in regulating a variety of pain-related disorders. Specifically, recent studies have shed light on the central role that microglial purinergic ligand-gated ion channel 7 receptor (P2X7R) plays in regulating pain. In this respect, the P2X7R on microglial membranes represents a potential therapeutic target.

AIMS

To expound on the intricate link between microglial P2X7R and pain, offering insights into potential avenues for future research.

METHODS

We reviewed 140 literature and summarized the important role of microglial P2X7R in regulating pain, including the structure and function of P2X7R, the relationship between P2X7R and microglial polarization, P2X7R-related signaling pathways, and the effects of P2X7R antagonists on pain regulation.

RESULTS

P2X7R activation is related to M1 polarization of microglia, while suppressing P2X7R can transfer microglia from M1 into M2 phenotype. And targeting the P2X7R-mediated signaling pathways helps to explore new therapy for pain alleviation. P2X7R antagonists also hold potential for translational and clinical applications in pain management.

CONCLUSIONS

Microglial P2X7R holds promise as a potential novel pharmacological target for clinical treatments due to its distinctive structure, function, and the development of antagonists.

Medication overuse headache is associated with elevated lipopolysaccharide binding protein and pro-inflammatory molecules in the bloodstream

OBJECTIVE

Medication overuse headache (MOH) is a secondary headache that accompanies chronic migraine. Nonsteroidal anti-inflammatory drugs (NSAIDs) are the most frequently used analgesics worldwide and they are known to induce leaky gut. In this study, we aimed to investigate whether NSAID induced MOH is associated with altered circulating lipopolysaccharide binding protein (LBP) levels and inflammatory molecules.

MATERIALS AND METHODS

Piroxicam (10 mg/kg/day, po) for 5 weeks was used to induce MOH in female Sprague Dawley rats. Pain behavior was evaluated by periorbital withdrawal thresholds, head-face grooming, freezing, and head shake behavior. Serum samples and brain tissues were collected to measure circulating LBP, tight junction protein occludin, adherens junction protein vascular endothelial (VE)-cadherin, calcitonin gene-related peptide (CGRP), IL-6 levels and brain high mobility group box-1 (HMGB1) and IL-17 levels.

RESULTS

Chronic piroxicam exposure resulted in decreased periorbital mechanical withdrawal thresholds, increased head-face grooming, freezing, and head shake behavior compared to vehicle administration. Serum LBP, CGRP, IL-6, IL-17, occludin, VE-cadherin levels and brain IL-17 and HMGB1 levels were significantly higher in piroxicam group compared to controls. Serum LBP was positively correlated with occludin (r = 0.611), VE-cadherin (r = 0.588), CGRP (r = 0.706), HMGB1 (r = 0.618) and head shakes (r = 0.921), and negatively correlated with periorbital mechanical withdrawal thresholds (r = -0.740).

CONCLUSION

Elevated serum LBP, VE-cadherin and occludin levels indicating disrupted intestinal barrier function and leakage of LPS into the systemic circulation were shown in female rats with MOH. LPS induced low-grade inflammation and elevated nociceptive and/or pro-inflammatory molecules such as HMGB1, IL-6, IL-17 and CGRP may play a role in the development and maintenance of MOH. Interference with leaky gut and pro-inflammatory nociceptive molecules could also be a target for sustained management of MOH.