TDAG8 deficiency reduces satellite glial number and pro-inflammatory macrophage number to relieve rheumatoid arthritis disease severity and chronic pain

Immunomodulation of Proton-activated G Protein-coupled Receptors in Inflammation

Proton-activated G protein-coupled receptors (GPCRs), initially discovered by Ludwig in 2003, are widely distributed in various tissues. These receptors have been found to modulate the immune system in several inflammatory diseases, including inflammatory bowel disease, atopic dermatitis, and asthma. Proton-activated GPCRs belong to the G protein-coupled receptor family and can detect alternations in extracellular pH. This detection triggers downstream signaling pathways within the cells, ultimately influencing the function of immune cells. In this review, we specifically focused on investigating the immune response of proton-activated GPCRs under inflammatory conditions.

Recent advances in acid sensing by G protein coupled receptors

Changes in extracellular proton concentrations occur in a variety of tissues over a range of timescales under physiological conditions and also accompany virtually all pathologies, notably cancers, stroke, inflammation and trauma. Proton-activated, G protein coupled receptors are already partially active at physiological extracellular proton concentrations and their activity increases with rising proton concentrations. Their ability to monitor and report changes in extracellular proton concentrations and hence extracellular pH appears to be involved in a variety of processes, and it is likely to mirror and in some cases promote disease progression. Unsurprisingly, therefore, these pH-sensing receptors (pHR) receive increasing attention from researchers working in an expanding range of research areas, from cellular neurophysiology to systemic inflammatory processes. This review is looking at progress made in the field of pHRs over the past few years and also highlights outstanding issues.

Acidosis-related pain and its receptors as targets for chronic pain

Sensing acidosis is an important somatosensory function in responses to ischemia, inflammation, and metabolic alteration. Accumulating evidence has shown that acidosis is an effective factor for pain induction and that many intractable chronic pain diseases are associated with acidosis signaling. Various receptors have been known to detect extracellular acidosis and all express in the somatosensory neurons, such as acid sensing ion channels (ASIC), transient receptor potential (TRP) channels and proton-sensing G-protein coupled receptors. In addition to sense noxious acidic stimulation, these proton-sensing receptors also play a vital role in pain processing. For example, ASICs and TRPs are involved in not only nociceptive activation but also anti-nociceptive effects as well as some other non-nociceptive pathways. Herein, we review recent progress in probing the roles of proton-sensing receptors in preclinical pain research and their clinical relevance. We also propose a new concept of sngception to address the specific somatosensory function of acid sensation. This review aims to connect these acid-sensing receptors with basic pain research and clinical pain diseases, thus helping with better understanding the acid-related pain pathogenesis and their potential therapeutic roles via the mechanism of acid-mediated antinociception.

Central role of purinergic receptors with inflammation in neuropathic pain-related macrophage-SGC-neuron triad

Adenosine triphosphate (ATP) acts on P2 purinergic receptors as an extracellular signaling molecule. P2 purinergic receptors include P2X ionotropic receptors and P2Y metabotropic receptors. Satellite glial cells (SGCs) and macrophages express P2X and P2Y receptors. Inflammatory cytokines and pro-nociceptive mediators are released by activated macrophages and SGCs, which can act on neurons to promote excitability and firing. In the primary sensory ganglia, in response to signals of injury, SGCs and macrophages accumulate around primary sensory neurons, forming a macrophage-SGC-neuron triad. In addition to affecting the pathological alterations of inflammation-related neuropathic pain, inflammatory cytokines and pro-nociceptive mediators are released by the action of ATP on P2X and P2Y receptors in macrophages and SGCs. Macrophages and SGCs work together to enhance and prolong neuropathic pain. The macrophage-SGC-neuron triad communicates with each other through ATP and other inflammatory mediators and maintains and promotes the initiation and development of inflammation related-neuropathic pain. This article is part of the Special Issue on "Purinergic Signaling: 50 years".

Sinomenine regulates immune cell subsets: Potential neuro-immune intervene for precise treatment of chronic pain

Chronic pain is a disease of long-lasting pain with unpleasant feelings mediated by central and (or) peripheral sensitization, its duration usually lasts more than 3 months or longer than the expected recovery time. The patients with chronic pain are manifested with enhanced sensitivity to noxious and non-noxious stimuli. Due to an incomplete understanding of the mechanisms, patients are commonly insensitive to the treatment of first line analgesic medicine in clinic. Thus, the exploration of non-opioid-dependent analgesia are needed. Recent studies have shown that "sinomenine," the main active ingredient in the natural plant "sinomenium acutum (Thunb.) Rehd. Et Wils," has a powerful inhibitory effect on chronic pain, but its underlying mechanism still needs to be further elucidated. A growing number of studies have shown that various immune cells such as T cells, B cells, macrophages, astrocytes and microglia, accompanied with the relative inflammatory factors and neuropeptides, are involved in the pathogenesis of chronic pain. Notably, the interaction of the immune system and sensory neurons is essential for the development of central and (or) peripheral sensitization, as well as the progression and maintenance of chronic pain. Based on the effects of sinomenine on immune cells and their subsets, this review mainly focused on describing the potential analgesic effects of sinomenine, with rationality of regulating the neuroimmune interaction.

The Novel Small Molecule BTB Inhibits Pro-Fibrotic Fibroblast Behavior though Inhibition of RhoA Activity

Idiopathic pulmonary fibrosis (IPF) is a progressive, chronic, interstitial lung disease with a poor prognosis. Although specific anti-fibrotic medications are now available, the median survival time following diagnosis remains very low, and new therapies are urgently needed. To uncover novel therapeutic targets, we examined how biochemical properties of the fibrotic lung are different from the healthy lung. Previous work identified lactate as a metabolite that is upregulated in IPF lung tissue. Importantly, inhibition of the enzyme responsible for lactate production prevents fibrosis in vivo. Further studies revealed that fibrotic lesions of the lung experience a significant decline in tissue pH, likely due to the overproduction of lactate. It is not entirely clear how cells in the lung respond to changes in extracellular pH, but a family of proton sensing G-protein coupled receptors has been shown to be activated by reductions in extracellular pH. This work examines the expression profiles of proton sensing GPCRs in non-fibrotic and IPF-derived primary human lung fibroblasts. We identify TDAG8 as a proton sensing GPCR that is upregulated in IPF fibroblasts and that knockdown of TDAG8 dampens myofibroblast differentiation. To our surprise, BTB, a proposed positive allosteric modulator of TDAG8, inhibits myofibroblast differentiation. Our data suggest that BTB does not require TDAG8 to inhibit myofibroblast differentiation, but rather inhibits myofibroblast differentiation through suppression of RhoA mediated signaling. Our work highlights the therapeutic potential of BTB as an anti-fibrotic treatment and expands upon the importance of RhoA-mediated signaling pathways in the context of myofibroblast differentiation. Furthermore, this works also suggests that TDAG8 inhibition may have therapeutic relevance in the treatment of IPF.

Role of proton-activated G protein-coupled receptors in pathophysiology

Local acidification is a common feature of many disease processes such as inflammation, infarction, or solid tumor growth. Acidic pH is not merely a sequelae of disease but contributes to recruitment and regulation of immune cells, modifies metabolism of parenchymal, immune and tumor cells, modulates fibrosis, vascular permeability, oxygen availability and consumption, invasiveness of tumor cells, and impacts on cell survival. Thus, multiple pH-sensing mechanisms must exist in cells involved in these processes. These pH-sensors play important roles in normal physiology and pathophysiology, and hence might be attractive targets for pharmacological interventions. Among the pH-sensing mechanisms, OGR1 (GPR68), GPR4 (GPR4), and TDAG8 (GPR65) have emerged as important molecules. These G protein-coupled receptors are widely expressed, are upregulated in inflammation and tumors, sense changes in extracellular pH in the range between pH 8 and 6, and are involved in modulating key processes in inflammation, tumor biology, and fibrosis. This review discusses key features of these receptors and highlights important disease states and pathways affected by their activity.

Osteoporosis in patients with rheumatoid arthritis is associated with serum immune regulatory cellular factors

OBJECTIVE

Osteoporosis (OP) is a comorbidity of rheumatoid arthritis (RA) that largely causes disability. This study discussed the expression patterns of serum immunoregulatory factors and their clinical significance in RA patients complicated with OP.

METHODS

A total of 116 RA patients were enrolled. Bone mineral density (BMD) was measured using dual energy X-ray absorptiometry to allocate patients to OP group (N = 62) and non-OP group (N = 54). CRP, rheumatoid factor, IgG, IgA, and IgM were detected using rate nephelometry. Erythrocyte sedimentation rate (ESR) and bone metabolic indexes were detected using Microsed automatic ESR analyzer and Cobas e601 automated immunoassay systems and reagents. IL-17, IL-6, TNF-α, IL-10, and IL-4 levels were determined using ELISA kit and their prediction values on OP were analyzed using the ROC curve. Influencing factors of OP incidence were analyzed using logistic regression model.

RESULTS

RA patients with OP showed increased age, disease course, tender and swollen joints, ESR, CRP, DAS28 scores, β-CTX, IL-17, IL-6, and TNF-α, and decreased 25(OH)D3, IL-10, and IL-4. DAS28 was positively correlated with IL-17, IL-6, and TNF-α, and negatively correlated with IL-10 and IL-4. DAS28, IL-17, IL-10, and IL-4 were independently correlated with OP in RA patients. The combination of DAS28, IL-17, IL-10, and IL-4 can better predict the incidence of OP complication in RA patients.

CONCLUSION

IL-17, IL-6, TNF-α, IL-10, and IL-4 were associated with disease activity of RA patients complicated with OP. A combination of DAS28, IL-17, IL-10, and IL-4 might predict OP incidence in RA patients.

The analgesic properties of Yu-Xue-Bi tablets in the inflammatory pain mice: By the inhibition of CCL3-mediated macrophage transmigration into the spinal cord

ETHNOPHARMACOLOGICAL RELEVANCE

Until now, inflammatory pain, especially ones with central sensitization in the spinal cord, is far from effectively treated. Yu-Xue-Bi Tablets (YXB) is a patented medicine, which has been widely applied for inflammatory pain. However, its therapeutic characteristics and mechanism remain unknown.

AIM OF THE STUDY

This study is designed to evaluate the analgesic characteristics and explore the underlying mechanism of YXB in the inflammatory pain model induced by Complete Freund's Adjuvant (CFA).

MATERIALS AND METHODS

The analgesic effects were measured by Von Frey test. The expression of calcitonin gene-related peptide (CGRP) was quantified by immunofluorescence. The expression of immune factors was analyzed via Luminex assay. The further quantifications of C-C Motif chemokine ligand 3 (CCL3) were verified by Enzyme-linked immunosorbent assay (ELISA). The transmigration of macrophage and activation of microglia were evaluated by immunofluorescence. Spinal injections of purified CCL3, CCR1 antagonist (J113863) and CCR5 antagonist (Maraviroc) were used to clarify roles of CCL3 assumed in the pharmacological mechanism of YXB.

RESULTS

In CFA mice, YXB ameliorated the mechanical allodynia in dose and time dependent way, suppressed the central sensitization in dose dependent way. In the L5 spinal cord, YXB downregulated the expression of macrophage M1 pro-inflammatory factors TNFRI and CCL3, inhibited the transmigration of circulating macrophage and the activation of microglia. Purified CCL3 led to the transmigration of macrophage, activation of microglia, central sensitization, and mechanical allodynia in the Sham mice. Inhibitors of CCR1 and CCR5 attenuated above symptoms in CFA mice. Purified CCL3 blocked YXB mediated down regulation of CCL3, inhibition of macrophage transmigration, but not activation of microglia.

CONCLUSION

YXB exerts the analgesic effects by inhibiting CCL3-mediated peripheral macrophage transmigrate into spinal cord. This study provided a novel approach for inflammatory pain treatment and new insight into the pharmacological action of YXB.

Identification and Validation of Prognostic Biomarkers Specifically Expressed in Macrophage in IgA Nephropathy Patients Based on Integrated Bioinformatics Analyses

Background: Immunoglobulin A nephropathy (IgAN) is the most common type of primary glomerulonephritis worldwide and a frequent cause of end-stage renal disease. The inflammation cascade due to the infiltration and activation of immune cells in glomeruli plays an essential role in the progression of IgAN. In this study, we aimed to identify hub genes involved in immune infiltration and explore potential prognostic biomarkers and therapeutic targets in IgAN.

Methods: We combined the single-cell and bulk transcriptome profiles of IgAN patients and controls with clinical data. Through single-cell analysis and weighted gene co-expression network analysis (WGCNA), Gene Ontology (GO) enrichment analysis, and differentially expressed gene (DEG) analysis in the bulk profile, we identified cell-type-specific potential hub genes in IgAN. Real hub genes were extracted via validation analysis and clinical significance analysis of the correlation between the expression levels of genes and the estimated glomerular filtration rate (eGFR) in the external dataset. Gene set enrichment analysis was performed to predict the probable roles of the real hub genes in IgAN.

Results: A total of eleven cell clusters were classified via single-cell analysis, among which macrophages showed a variable proportion between the IgAN and normal control samples. We recognized six functional co-expression gene modules through WGCNA, among which the black module was deemed an IgAN-related and immune-involving module via GO enrichment analysis. DEG analysis identified 45 potential hub genes from genes enriched in GO terms. A total of twenty-three potential hub genes were specifically expressed in macrophages. Furthermore, we validated the differential expression of the 23 potential hub genes in the external dataset and identified nine genes with prognostic significance as real hub genes, viz., CSF1R, CYBB, FPR3, GPR65, HCLS1, IL10RA, PLA2G7, TYROBP, and VSIG4. The real hub gens are thought to contribute to immune cell regulation, immunoreaction, and regulation of oxidative stress, cell proliferation, and material metabolism.

Conclusion: In this study, we demonstrated that macrophages infiltrated the glomeruli and contributed to the inflammatory response in IgAN. Based on integrated bioinformatics analyses of single-cell and bulk transcriptome data, we highlighted nine genes as novel prognostic biomarkers, which may enable the development of innovative prognostic and therapeutic strategies for IgAN.

Gut Mucosal Microbiome Is Perturbed in Rheumatoid Arthritis Mice and Partly Restored after TDAG8 Deficiency or Suppression by Salicylanilide Derivative

Rheumatoid arthritis (RA), an autoimmune disease, is characterized by chronic joint inflammation and pain. We previously found that the deletion of T-cell death-associated gene 8 (TDAG8) significantly reduces disease severity and pain in RA mice. Whether it is by modulating gut microbiota remains unclear. In this study, 64 intestinal samples of feces, cecal content, and cecal mucus from the complete Freund’s adjuvant-induced arthritis mouse models were compared. The α- and β-diversity indices of the microbiome were significantly lower in RA mice. Cecal mucus showed a higher ratio of Firmicutes to Bacteroidetes in RA than healthy mice, suggesting the ratio could serve as an RA indicator. Four core genera, Eubacterium_Ventriosum, Alloprevotella, Rikenella, and Treponema, were reduced in content in both feces and mucus RA samples, and could serve microbial markers representing RA progression. TDAG8 deficiency decreased the abundance of proinflammation-related Eubacterium_Xylanophilum, Clostridia, Ruminococcus, Paraprevotella, and Rikenellaceae, which reduced local mucosal inflammation to relieve RA disease severity and pain. The pharmacological block of the TDAG8 function by a salicylanilide derivative partly restored the RA microbiome to a healthy composition. These findings provide a further understanding of specific bacteria interactions with host gut mucus in the RA model. The modulation by TDAG8 on particular bacteria can facilitate microbiota-based therapy.

A Novel Progress: Glial Cells and Inflammatory Pain

Inflammatory pain is the perception of noxious stimuli that occurs during inflammation or an immune response. Glial cells are widespread in the central and peripheral nervous systems, supporting and guiding the migration of neurons, participating in the immune response, forming the myelin sheath and blood-brain barrier, and maintaining the concentration of potassium ions outside nerve cells. Recent studies have shown that glial cells have a significant connection with the production and development of inflammatory pain. This article reviews the relationship, mechanisms, therapeutic targets between five types of glial cells and inflammatory pain, and the medicine composition that can effectively inhibit inflammatory pain. It expands the study on the mechanism of glial cells regulating pain and provides new ideas for the therapy of inflammatory pain.

LCC-09, a Novel Salicylanilide Derivative, Exerts Anti-Inflammatory Effect in Vascular Endothelial Cells

OBJECTIVE

Endothelial cell (EC) activation facilitates leukocyte adhesion to vascular walls, which is implicated in a variety of cardiovascular diseases and is a target for prevention and treatment. Despite the development of anti-inflammatory medications, cost-effective therapies with significant anti-inflammatory effects and lower organ toxicity remain elusive. The goal of this study is to identify novel synthetic compounds that inhibit EC inflammatory response with minimal organ toxicity.

METHODS AND RESULTS

In this study, we discovered LCC-09, a salicylanilide derivative consisting of the functional fragment of magnolol, 2,4-difluorophenyl, and paeonol moiety of salicylate, as a novel anti-inflammatory compound in cultured ECs and zebrafish model. LCC-09 was shown to inhibit pro-inflammatory cytokine tumor necrosis factor-α (TNFα)-induced expression of adhesion molecules and inflammatory cytokines, leading to reduced leukocyte adhesion to ECs. Mechanistically, LCC-09 inhibits the phosphorylation of signal transducer and activator of transcription 1 (STAT1), TNFα-induced degradation of NF-κ-B Inhibitor-α (IκBα) and phosphorylation of NFκB p65, resulting in reduced NFκB transactivation activity and binding to E-selectin promoter. Additionally, LCC-09 attenuated TNFα-induced generation of reactive oxygen species in ECs. Molecular docking models suggest the binding of LCC-09 to NFκB essential modulator (NEMO) and Janus tyrosine kinase (JAK) may lead to dual inhibition of NFκB and STAT1. Furthermore, the anti-inflammatory effect of LCC-09 was validated in the lipopolysaccharides (LPS)-induced inflammation model in zebrafish. Our results demonstrated that LCC-09 significantly reduced the LPS-induced leukocyte recruitment and mortality of zebrafish embryos. Finally, LCC-09 was administered to cultured ECs and zebrafish embryos and showed minimal toxicities.

CONCLUSION

Our results support that LCC-09 inhibits EC inflammatory response but does not elicit significant toxicity.

Uncovering the interplay between pH receptors and immune cells: Potential drug targets (Review)

Extracellular acidosis is associated with various immunopathological states. The microenvironment of numerous solid tumours and inflammatory responses during acute or chronic infection are all related to a pH range of 5.5‑7.0. The relationship between inflammation and immune escape, cancer metabolism, and immunologic suppression drives researchers to focus on the effects of low pH on diverse components of disease immune monitoring. The potential effect of low extracellular pH on the immune function reveals the importance of pH in inflammatory and immunoreactive processes. In this review, the mechanism of how pH receptors, including monocarboxylate transporters (MCTs), Na⁺/H⁺ exchanger 1, carbonic anhydrases (CAs), vacuolar‑ATPase, and proton‑sensing G‑protein coupled receptors (GPCRs), modulate the immune system in disease, especially in cancer, were studied. Their role in immunocyte growth and signal transduction as part of the immune response, as well as cytokine production, have been documented in great detail. Currently, immunotherapy strategies have positive therapeutic effects for patients. However, the acidic microenvironment may block the effect of immunotherapy through compensatory feedback mechanisms, leading to drug resistance. Therefore, we highlight promising therapeutic developments regarding pH manipulation and provide a framework for future research.

Mast cell stabilizer ketotifen fumarate reverses inflammatory but not neuropathic-induced mechanical pain in mice

Supplemental Digital Content is Available in the Text.

Our preclinical findings indicate that ketotifen fumarate's analgesic effects are MC-dependent, and the case series report presented supports its use for the treatment of chronic pain.

Introduction:

Mast cell (MC) activation could establish a positive feedback loop that perpetuates inflammation and maintains pain. Stabilizing MCs with ketotifen fumarate (KF) may disrupt this loop and relieve pain.

Objective:

We aimed to test the effect of treatment with KF in pain assays in mice and in a case series of patients with chronic widespread pain.

Methods:

The analgesic effect of KF was tested in CD-1 mice injected with formalin, complete Freund's adjuvant, or subjected to spared nerve injury. In addition, wild-type (C57BL/6) and MC-deficient (C57BL/6-Kit^W-sh/W-sh) mice were injected with formalin or complete Freund's adjuvant and treated with KF. Patients with chronic widespread pain (n = 5; age: 13–16 years) who failed to respond to standard of care participated in a 16-week treatment trial with KF (6 mg/d). Ketotifen fumarate's therapeutic effect was evaluated using the patient global impression of change.

Results:

In the mouse experiments, KF produced dose- and MC-dependent analgesic effects against mechanical allodynia in the acute and chronic inflammatory pain but not neuropathic pain assays. In the patient case series, 4 patients reported that activity limitations, symptoms, emotions, and overall quality of life related to their pain condition were “better” or “a great deal better” since beginning treatment with KF. This was accompanied by improvements in pain comorbid symptoms.

Conclusion:

Treatment with KF is capable of reducing established inflammatory-induced mechanical nociception in an MC-dependent manner in mice, and it may be beneficial for the treatment of chronic pain conditions.