P2X7 receptor: A potential therapeutic target for autoimmune diseases

P2X7 Variants in Pathophysiology

P2X7 receptor activation by extracellular adenosine triphosphate (eATP) modulates different intracellular pathways, including pro-inflammatory and tumor-promoting cascades. ATP is released by cells and necrotic tissues during stressful conditions and accumulates mainly in the inflammatory and tumoral microenvironments. As a consequence, both the P2X7 blockade and agonism have been proposed as therapeutic strategies in phlogosis and cancer. Nevertheless, most studies have been carried out on the WT fully functional receptor variant. In recent years, the discovery of P2X7 variants derived by alternative splicing mechanisms or single-nucleotide substitutions gave rise to the investigation of these new P2X7 variants' roles in different processes and diseases. Here, we provide an overview of the literature covering the function of human P2X7 splice variants and polymorphisms in diverse pathophysiological contexts, paying particular attention to their role in oncological and neuroinflammatory conditions.

NLRP3 inflammasome and its role in autoimmune diseases: A promising therapeutic target

The NOD-like receptor protein 3 (NLRP3) inflammasome is a protein complex that regulates innate immune responses by activating caspase-1 and the inflammatory cytokines IL-1β and IL-18. Numerous studies have highlighted its crucial role in the pathogenesis and development of inflammatory bowel disease, rheumatoid arthritis, systemic lupus erythematosus, autoimmune thyroid diseases, and other autoimmune diseases. Therefore, investigating the underlying mechanisms of NLRP3 in disease and targeted drug therapies holds clinical significance. This review summarizes the structure, assembly, and activation mechanisms of the NLRP3 inflammasome, focusing on its role and involvement in various autoimmune diseases. This review also identifies studies where the involvement of the NLRP3 inflammasome in the disease mechanism within the same disease appears contradictory, as well as differences in NLRP3-related gene polymorphisms among different ethnic groups. Additionally, the latest therapeutic advances in targeting the NLRP3 inflammasome for autoimmune diseases are outlined, and novel clinical perspectives are discussed. Conclusively, this review provides a consolidated source of information on the NLRP3 inflammasome and may guide future research efforts that have the potential to positively impact patient outcomes.

The bumpy road of purinergic inhibitors to clinical application in immune-mediated diseases

ABSTRACT

Purinergic signaling plays important roles throughout the body in the regulation of organ functions during and following the disruption of homeostasis. This is also reflected by the widespread expression of two families of purinergic receptors (P1 and P2) with numerous subtypes. In the last few decades, there has been increasing evidence that purinergic signaling plays an important role in the regulation of immune functions. Mainly, signals mediated by P2 receptors have been shown to contribute to immune system-mediated pathologies. Thus, interference with P2 receptors may be a promising strategy for the modulation of immune responses. Although only a few clinical studies have been conducted in isolated entities with limited success, preclinical work suggests that the use of P2 receptor inhibitors may bear some promise in various autoimmune diseases. Despite the association of P2 receptors with several disorders from this field, the use of P2 receptor antagonists in clinical therapy is still very scarce. In this narrative review, we briefly review the involvement of the purinergic system in immunological responses and clinical studies on the effect of purinergic inhibition on autoimmune processes. We then open the aperture a bit and show some preclinical studies demonstrating a potential effect of purinergic blockade on autoimmune events. Using suramin, a non-specific purinergic inhibitor, as an example, we further show that off-target effects could be responsible for observed effects in immunological settings, which may have interesting implications. Overall, we believe that it is worthwhile to further investigate this hitherto underexplored area.

A patent review of P2X7 receptor antagonists to treat inflammatory diseases (2018-present)

INTRODUCTION

The purinergic P2X7 receptor (P2X7R) is expressed on the surface of many different types of cells, including immune cells. Targeting P2X7R with antagonists has been studied for its potential therapeutic effects in a variety of inflammatory illnesses.

AREA COVERED

Many chemical substances, including carboxamides, benzamides and nitrogen containing heterocyclic derivatives have demonstrated promising inhibitory potential for P2X7 receptor. The chemistry and clinical applications of P2X7R antagonists patented from 2018- present are discussed in this review.

EXPERT OPINION

Purinergic receptor inhibitor discovery and application has demonstrated the potential for therapeutic intervention, as demonstrated by pharmacological research. Few chemical modalities have been authorized for use in clinical settings, despite the fact that breakthroughs in crystallography and chemical biology have increased the knowledge of purinergic signaling and its consequences in disease. The many research projects and pharmaceutical movements that sustain dynamic P2X receptor programs over decades are evidence of the therapeutic values and academic persistence in purinergic study. P2X7R is an intriguing therapeutic target and possible biomarker for inflammation. Although several companies like Merck and AstraZeneca have published patents on P2X3 antagonists, the search for P2X7R antagonists has not stopped. Numerous pharmaceutical companies have disclosed different scaffolds, and some molecules are presently being studied in clinical studies.

P2X7 Receptor in Dendritic Cells and Macrophages: Implications in Antigen Presentation and T Lymphocyte Activation

The P2X7 receptor, a member of the P2X purinergic receptor family, is a non-selective ion channel. Over the years, it has been associated with various biological functions, from modulating to regulating inflammation. However, its emerging role in antigen presentation has captured the scientific community's attention. This function is essential for the immune system to identify and respond to external threats, such as pathogens and tumor cells, through T lymphocytes. New studies show that the P2X7 receptor is crucial for controlling how antigens are presented and how T cells are activated. These studies focus on antigen-presenting cells, like dendritic cells and macrophages. This review examines how the P2X7 receptor interferes with effective antigen presentation and activates T cells and discusses the fundamental mechanisms that can affect the immune response. Understanding these P2X7-mediated processes in great detail opens up exciting opportunities to create new immunological therapies.

How is the P2X7 receptor signaling pathway involved in epileptogenesis?

Epilepsy, a condition characterized by spontaneous recurrent epileptic seizures, is among the most prevalent neurological disorders. This disorder is estimated to affect approximately 70 million people worldwide. Although antiseizure medications are considered the first-line treatments for epilepsy, most of the available antiepileptic drugs are not effective in nearly one-third of patients. This calls for the development of more effective drugs. Evidence from animal models and epilepsy patients suggests that strategies that interfere with the P2X7 receptor by binding to adenosine triphosphate (ATP) are potential treatments for this patient population. This review describes the role of the P2X7 receptor signaling pathways in epileptogenesis. We highlight the genes, purinergic signaling, Pannexin1, glutamatergic signaling, adenosine kinase, calcium signaling, and inflammatory response factors involved in the process, and conclude with a synopsis of these key connections. By unraveling the intricate interplay between P2X7 receptors and epileptogenesis, this review provides ideas for designing potent clinical therapies that will revolutionize both prevention and treatment for epileptic patients.

Exploring potential causal associations between autoimmune diseases and colorectal cancer using bidirectional Mendelian randomization

Several observational studies have revealed an association between autoimmune diseases (AIDs) and colorectal cancer (CRC), although their causal association remained controversial. Therefore, our study used a two-sample Mendelian randomization (MR) analysis to verify the causal association between AIDs and CRC. We employed three common MR approaches, including inverse variance weighted (IVW), weighted median, and MR-Egger methods, to assess the causal association between type 1 diabetes (T1D), systemic lupus erythematosus, rheumatoid arthritis, psoriasis, multiple sclerosis, juvenile idiopathic arthritis, celiac disease, and primary sclerosing cholangitis (PSC) and CRC. The reverse MR analysis was performed to assess the possibility of reverse causation. To evaluate the validity of the analysis, we also performed sensitivity analysis, such as the heterogeneity test, the horizontal pleiotropy test, and the leave-one-out sensitivity analysis, and validated the results in the validation cohort. Our results showed that genetically predicted T1D was nominally associated with a lower risk of CRC (IVW OR = 0.965, 95% CI = 0.939-0.992, P = 0.012). However, genetic susceptibility to psoriasis nominally increased the risk of CRC (IVW OR = 1.026, 95% CI = 1.002-1.050, P = 0.037). Genetically predicted PSC had a significant causal effect on the increasing risk of CRC (IVW OR = 1.038, 95% CI = 1.016-1.060, P = 5.85 × 10-4). Furthermore, the MR analysis between PSC and the CRC validation cohort indicated consistent results. We found no causal association between genetically predicted other five AIDs and CRC (P > 0.05). The results of reverse MR analysis showed that genetically predicted CRC had no causal effect on T1D, psoriasis, and PSC (P > 0.05). The sensitivity analysis demonstrated that the results of the MR analysis were reliable. Our findings help to understand the causal association between AIDs and CRC, which deserves further investigation.

Extracellular ATP (eATP) inhibits the progression of endometriosis and enhances the immune function of macrophages

BACKGROUND

Extracellular adenosine triphosphate (eATP) is an important inflammatory mediator that can boost the antitumour immune response, but its role in endometriosis remains unknown. We hypothesized that eATP could inhibit endometriosis cell function both directly and indirectly through macrophages.

METHODS

Peritoneal and cyst fluid from endometriosis patients and non-endometriosis controls was collected to measure eATP levels. The addition of eATP was performed to explore its effects on endometriotic cell and macrophage functions, including cell proliferation, apoptosis, pyroptosis, mitochondrial membrane potential, phagocytosis, and the production of inflammatory cytokines and reactive oxygen species. A coculture of endometriotic epithelial cells and U937 macrophages was established, followed by P2X7 antagonist and eATP treatment. Endometriosis model eATP-treated rats were used to evaluate in situ cell death and macrophage marker expression.

RESULTS

The pelvic microenvironment of endometriosis patients shows high eATP levels, which could induce endometriotic epithelial cell apoptosis and pyroptosis and significantly inhibit cell growth via the MAPK/JNK/Akt pathway. eATP treatment ameliorated endometriosis-related macrophage dysfunction and promoted macrophage recruitment. eATP treatment in the presence of macrophages exerted a stronger cytotoxic effect on endometriotic epithelial cells by regulating P2X7. eATP treatment effectively induced cell death in an endometriosis rat model and prominently increased the macrophage number without affecting the eutopic endometrium.

CONCLUSION

eATP induces endometriotic epithelial cell death and enhances the immune function of macrophages to inhibit the progression of endometriosis, while eutopic endometrium is not affected. eATP treatment may serve as a nonhormonal therapeutic strategy for endometriosis.

Sinomenine ameliorates collagen-induced arthritis in mice by targeting GBP5 and regulating the P2X7 receptor to suppress NLRP3-related signaling pathways

Sinomenine (SIN) is an isoquinoline alkaloid isolated from Sinomenii Caulis, a traditional Chinese medicine used to treat rheumatoid arthritis (RA). Clinical trials have shown that SIN has comparable efficacy to methotrexate in treating patients with RA but with fewer adverse effects. In this study, we explored the anti-inflammatory effects and therapeutic targets of SIN in LPS-induced RAW264.7 cells and in collagen-induced arthritis (CIA) mice. LPS-induced RAW264.7 cells were pretreated with SIN (160, 320, 640 µM); and CIA mice were administered SIN (25, 50 and 100 mg·kg-1·d-1, i.p.) for 30 days. We first conducted a solvent-induced protein precipitation (SIP) assay in LPS-stimulated RAW264.7 cells and found positive evidence for the direct binding of SIN to guanylate-binding protein 5 (GBP5), which was supported by molecular simulation docking, proteomics, and binding affinity assays (KD = 3.486 µM). More importantly, SIN treatment markedly decreased the expression levels of proteins involved in the GBP5/P2X7R-NLRP3 pathways in both LPS-induced RAW264.7 cells and the paw tissue of CIA mice. Moreover, the levels of IL-1β, IL-18, IL-6, and TNF-α in both the supernatant of inflammatory cells and the serum of CIA mice were significantly reduced. This study illustrates a novel anti-inflammatory mechanism of SIN; SIN suppresses the activity of NLRP3-related pathways by competitively binding GBP5 and downregulating P2X7R protein expression, which ultimately contributes to the reduction of IL-1β and IL-18 production. The binding specificity of SIN to GBP5 and its inhibitory effect on GBP5 activity suggest that SIN has great potential as a specific GBP5 antagonist.

P2X7 receptor promotes migration and invasion of non-small cell lung cancer A549 cells through the PI3K/Akt pathways

It has been demonstrated that the ATP-gated ion channel P2X7 receptor is involved in tumor progression and plays an important role in regulating tumor cell growth, invasion, migration and angiogenesis. However, P2X7 receptors have been relatively poorly studied in non-small cell lung cancer (NSCLC) cells. Therefore, the aim of this study was to investigate the effects of P2X7 receptor on A549 cells (NSCLC cell line) migration and invasion and to reveal the molecular mechanisms mediated by it. We detected the expression and function of P2X7 receptor in A549 cells. The effects and mechanisms of P2X7 receptor on A549 cells migration, invasion, and epithelial-mesenchymal transition were detected in vitro and in vivo. The results showed P2X7 receptor expressed by A549 cells had ion channel and macropore formation function. In addition, activation of P2X7 receptor by adenosine triphosphate (ATP) or 2'(3')-O-(4-Benzoylbenzoyl)-adenosine-5'-triphosphate (BzATP) promoted Epithelial-mesenchymal transition (EMT), migration and invasion of A549 cells, which was attenuated by treatment of cells with P2X7 receptor antagonist A438079 and Oxidized ATP. Furthermore, activation of P2X7 receptor increased phosphorylated protein kinase B (p-Akt) levels, and the phosphatidylinositol-tris-phosphate kinase 3 (PI3K)/protein kinase B (Akt) inhibitor LY294002 blocked migration and invasion of A549 cells induced by ATP or BzATP. At the same time, in vivo results showed that P2X7 receptor could also promote EMT and PI3K/Akt expression in transplanted tumors. Our study indicated that P2X7 receptor promotes A549 cells migration and invasion through the PI3K/Akt signaling pathway, suggesting that P2X7 receptor may be a potential therapeutic target for NSCLC.

Age-standardized incidence, prevalence, and mortality rates of autoimmune diseases in women of childbearing age from 1990 to 2019

AIM

To estimate the age-standardized incidence, prevalence, and mortality rates of autoimmune diseases including rheumatoid arthritis (RA), inflammatory bowel disease (IBD), multiple sclerosis (MS), type 1 diabetes mellitus (T1DM), asthma, and psoriasis in women of childbearing age from 1990 to 2019, and to further analyze their changing trends, at global, regional, and national levels.

METHODS

Women of childbearing age was defined as 15-49 years old. The estimates and 95% uncertainty intervals (UIs) for case number of RA, IBD, MS, T1DM, asthma and psoriasis in seven age groups (15-19, 20-24, 25-29, 30-34, 35-39, 40-44, 45-49 years) were extracted from the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2019. Age standardization by direct method was adopted to estimate the age-standardized incidence, prevalence, and mortality rates of these autoimmune diseases in women of childbearing age. Joinpoint regression analysis was utilized to analyze the changing trends of estimated age-standardized incidence, prevalence, and mortality rates from 1990 to 2019 by calculating the average annual percentage change (AAPC) and its 95% confidence intervals (CIs).

RESULTS

In 2019, the estimated global age-standardized incidence, prevalence, and mortality rates of RA in women of childbearing age was 17.13 (95% UI: 12.39 to 22.60), 215.86 (95% UI: 179.04 to 259.70), and 0.06 (95% UI: 0.04 to 0.08); of IBD was 5.85 (95% UI: 4.72 to 7.12), 63.54 (95% UI: 53.50 to 74.37), and 0.11 (95% UI: 0.08 to 0.13); of MS was 1.63 (95% UI: 1.05 to 2.28), 28.74 (95% UI: 23.80 to 34.46), and 0.17 (95% UI: 0.14 to 0.27); of T1DM was 6.22 (95% UI: 2.75 to 11.50), 290.51 (95% UI: 221.39 to 370.19), and 0.63 (95% UI: 0.48 to 0.78); of asthma was 291.14 (95% UI: 157.06 to 468.78), 2796.25 (95%UI: 1987.07 to 3842.97), and 1.42 (95% UI: 1.12 to 1.75), respectively. The estimated global age-standardized incidence and prevalence rates of psoriasis in women of childbearing age was 58.68 (95% UI: 51.04 to 66.85) and 477.20 (95% UI: 440.30 to 515.76). Highest disease burden generally exists in Region of the Americas and European Region. From 1990 to 2019, the estimated global age-standardized incidence and prevalence rates of RA (AAPC: 0.18, 95% CI: 0.11 to 0.24; AAPC: 0.24, 95% CI: 0.18 to 0.30) and T1DM (AAPC: 1.47, 95% CI: 1.40 to 1.54; AAPC: 0.83, 95% CI: 0.79 to 0.88) in women of childbearing age showed significantly increasing trends whereas those of IBD (AAPC: -0.76, 95% CI: -0.80 to -0.73; AAPC: -0.65, 95% CI: -0.70 to -0.60), MS (AAPC: -0.20, 95% CI: -0.23 to -0.16; AAPC: -0.25, 95% CI: -0.26 to -0.23), asthma (AAPC: -0.53, 95% CI: -0.60 to -0.47; AAPC: -0.74, 95% CI: -0.81 to -0.68), and psoriasis (AAPC: -0.83, 95% CI: -0.85 to -0.82; AAPC: -0.99, 95% CI: -1.02 to -0.96) showed significantly decreasing trends. Favorably, the estimated global age-standardized mortality rate of RA (AAPC: -1.32, 95% CI: -1.63 to -1.01), IBD (AAPC: -0.95, 95% CI: -1.06 to -0.84), MS (AAPC: -0.96, 95% CI: -1.12 to -0.80), T1DM (AAPC: -1.05, 95% CI: -1.21 to -0.89), and asthma (AAPC: -2.27, 95% CI: -2.34 to -2.19) in women of childbearing age all declined. The changing trends of estimated age-standardized incidence, prevalence, and mortality rates varied significantly across 204 countries and territories.

CONCLUSIONS

Our study provides an accurate estimation on the age-standardization of disease indicators of autoimmune diseases in women of childbearing age. There are remarkable disparities in the incidence, prevalence, and mortality burden related to autoimmune diseases in women of childbearing age, as well as their changing trends across the world, suggesting that each individual government should establish flexible health policies and make reasonable source allocation to address different needs for autoimmune diseases in this population.

A global assessment of incidence trends of autoimmune diseases from 1990 to 2019 and predicted changes to 2040

AIM

To analyze the global incidence trends for four autoimmune diseases (ADs) including rheumatoid arthritis (RA), inflammatory bowel disease (IBD), multiple sclerosis (MS) and psoriasis from 1990 to 2019, and further predict their changes to 2040 at global, regional, and national levels.

METHODS

The estimates and 95% uncertainty intervals (UIs) for case number and agestandardized incidence rate (ASIR) of RA, IBD, MS and psoriasis were derived from the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2019. Estimated annual percentage change (EAPC) was utilized to quantify the global incidence trends for RA, IBD, MS and psoriasis from 1990 to 2019. Furthermore, a log-linear age-period-cohort model was adopted to predict the new case number and incidence rates for these four ADs through 2040.

RESULTS

From 1990 to 2019, the global ASIR rose significantly for RA (EAPC = 0.30%, 95% CI: 0.26 to 0.34) whereas declined significantly for IBD (EAPC = -0.60%, 95% CI: -0.72 to - 0.48), MS (EAPC = -0.19%, 95% CI: -0.24 to -0.13) and psoriasis (EAPC = -0.77%, 95% CI: -0.78 to -0.76). From 2020 to 2040, the global ASIR of RA, IBD, and psoriasis was predicted to decrease whereas the global ASIR of MS was predicted to increase, with continuous increasing case number of all these diseases. Furthermore, the predicted incidence trends of these four ADs varied significantly across 195 countries and territories, with a prominent higher burden in high-income North America and Western Europe.

CONCLUSIONS

There are strong heterogeneities in the global incidence trends (1990-2019) and predicted changes (2020-2040) of ADs across the world, highlighting prominent challenges in the control of ADs, including both growing case number and distributive disparities of these diseases worldwide, which may be instructive for better public health policy establishment and healthcare resource allocation.

The P2X7 Receptor in Autoimmunity

The P2X7 receptor (P2X7R) is an ATP-gated nonselective cationic channel that, upon intense stimulation, can progress to the opening of a pore permeable to molecules up to 900 Da. Apart from its broad expression in cells of the innate and adaptive immune systems, it is expressed in multiple cell types in different tissues. The dual gating property of P2X7R is instrumental in determining cellular responses, which depend on the expression level of the receptor, timing of stimulation, and microenvironmental cues, thus often complicating the interpretation of experimental data in comprehensive settings. Here we review the existing literature on P2X7R activity in autoimmunity, pinpointing the different functions in cells involved in the immunopathological processes that can make it difficult to model as a druggable target.

Leveraging the ATP-P2X7 receptor signalling axis to alleviate traumatic CNS damage and related complications

The P2X7 receptor is an exceptional member of the P2X purinergic receptor family, with its activation requiring high concentrations of extracellular adenosine 5'-triphosphate (ATP) that are often associated with tissue damage and inflammation. In the central nervous system (CNS), it is highly expressed in glial cells, particularly in microglia. In this review, we discuss the role and mechanisms of the P2X7 receptor in mediating neuroinflammation and other pathogenic events in a variety of traumatic CNS damage conditions, which lead to loss of neurological and cognitive functions. We raise the perspective on the steady progress in developing CNS-penetrant P2X7 receptor-specific antagonists that leverage the ATP-P2X7 receptor signaling axis as a potential therapeutic strategy to alleviate traumatic CNS damage and related complications.

P2X7 Receptor Regulates Collagen Expression in Human Intestinal Fibroblasts: Relevance in Intestinal Fibrosis

Intestinal fibrosis is a common complication that affects more than 50% of Crohn´s Disease (CD) patients. There is no pharmacological treatment against this complication, with surgery being the only option. Due to the unknown role of P2X7 in intestinal fibrosis, we aim to analyze the relevance of this receptor in CD complications. Surgical resections from CD and non-Inflammatory Bowel Disease (IBD) patients were obtained. Intestinal fibrosis was induced with two different murine models: heterotopic transplant model and chronic-DSS colitis in wild-type and P2X7-/- mice. Human small intestine fibroblasts (HSIFs) were transfected with an siRNA against P2X7 and treated with TGF-β. A gene and protein expression of P2X7 receptor was significantly increased in CD compared to non-IBD patients. The lack of P2X7 in mice provoked an enhanced collagen deposition and increased expression of several profibrotic markers in both murine models of intestinal fibrosis. Furthermore, P2X7-/- mice exhibited a higher expression of proinflammatory cytokines and a lower expression of M2 macrophage markers. Moreover, the transient silencing of the P2X7 receptor in HSIFs significantly induced the expression of Col1a1 and potentiated the expression of Col4 and Col5a1 after TGF-β treatment. P2X7 regulates collagen expression in human intestinal fibroblasts, while the lack of this receptor aggravates intestinal fibrosis.

Temporal trends in the prevalence of autoimmune diseases from 1990 to 2019

AIM

To describe current situation and analyze temporal trends of prevalence for four autoimmune diseases including rheumatoid arthritis (RA), inflammatory bowel disease (IBD), multiple sclerosis (MS) and psoriasis, at the global, continental, and national levels.

METHODS

The estimates and 95% uncertainty interval (UI) for age-standardized prevalence rate (ASPR) of RA, IBD, MS and psoriasis were obtained from the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2019. ASPR of RA, IBD, MS and psoriasis in 2019 was illustrated at the global, continental, and national levels. Joinpoint regression analysis was adopted to analyze the 1990-2019 temporal trends by calculating the annual percentage change (APC) and average APC (AAPC), as well as their 95% confidence interval (CI).

RESULTS

In 2019, the global ASPR of RA, IBD, MS and psoriasis was 224.25 (95% UI: 204.94 to 245.99), 59.25 (95% UI: 52.78 to 66.47), 21.25 (95% UI: 18.52 to 23.91) and 503.62 (95% UI: 486.92 to 519.22), respectively, with ASPRs generally higher in Europe and America than in Africa and Asia. From 1990 to 2019, the global ASPR increased significantly for RA (AAPC = 0.27%, 95% CI: 0.24 to 0.30; P < 0.001) and decreased significantly for IBD (AAPC = -0.73%, 95% CI: -0.76 to -0.70; P < 0.001), MS (AAPC = -0.22%, 95% CI: -0.25 to -0.18; P < 0.001) and psoriasis (AAPC = -0.93%, 95% CI: -0.95 to -0.91; P < 0.001), with the most substantial changes occurring at different continents and periods. The trends of ASPR of these four autoimmune diseases varied significantly across 204 countries and territories.

CONCLUSIONS

There is a strong heterogeneity in prevalence (2019), as well as their temporal trends (1990-2019) of autoimmune diseases across the world, highlighting the strong distributive inequities of autoimmune diseases worldwide, which may be instructive for better understanding the epidemiology of these diseases, appropriately allocating the medical resources, as well as making relevant health policies.

Global burden and cross-country inequalities in autoimmune diseases from 1990 to 2019

AIM

To describe burden, and to explore cross-country inequalities across sociodemographic development levels for four autoimmune diseases (ADs) including rheumatoid arthritis (RA), inflammatory bowel disease (IBD), multiple sclerosis (MS) and psoriasis (PS).

METHODS

The estimates and their 95% uncertainty interval (UI) for disability-adjusted life-years (DALYs) of RA, IBD, MS and PS were extracted from the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2019. Age-standardized DALYs rate (ASDR) across 204 countries, as well as age and sex distribution of global DALYs rate of these four ADs were illustrated. Slope index of inequality and concentration index, which are two standard metrics of absolute and relative gradient inequality recommended by World Health Organization (WHO), were utilized to quantify the distributive inequalities in the burden of ADs.

RESULTS

In 2019, the ASDR of RA, IBD, MS and PS varied remarkably across 204 countries, with different age and sex distribution of global DALYs rate. The slope index of inequality changed from 26.7 (95% CI: 20.7 to 32.8) in 1990 to 40.3 (95% CI: 31.9 to 48.7) in 2019 for RA, from 17.1 (95% CI: 12.4 to 21.7) in 1990 to 25.2 (95% CI: 20.1 to 30.2) in 2019 for IBD, from 19.3 (95% CI: 15.2 to 23.4) in 1990 to 28.9 (95% CI: 24.2 to 33.5) in 2019 for MS, from 42.3 (95% CI: 33.1 to 51.6) in 1990 to 40.2 (95% CI: 32.5 to 48.0) in 2019 for PS. Moreover, the concentration index showed 20.4 (95% CI: 18.9 to 22.0) in 1990 and 18.2 (95% CI: 16.7 to 19.6) in 2019 for RA, 25.0 (95% CI: 23.0 to 27.1) in 1990 and 33.5 (95% CI: 31.6 to 35.5) in 2019 for IBD, 46.7 (95% CI: 44.0 to 49.3) in 1990 and 41.8 (95% CI: 39.6 to 44.1) in 2019 for MS, 31.7 (95% CI: 29.0 to 34.4) in 1990 and 32.6 (95% CI: 29.9 to 35.2) in 2019 for PS.

CONCLUSIONS

There is a strong heterogeneity in ASDR across all countries, as well as in age and sex distribution of global DALYs rate for four ADs including RA, IBD, MS and PS. Countries with higher sociodemographic development levels shouldered disproportionately higher burden of ADs, and the magnitude of this sociodemographic development level-related inequalities increased over time.

Origin, distribution, and function of three frequent coding polymorphisms in the gene for the human P2X7 ion channel

P2X7, an ion channel gated by extracellular ATP, is widely expressed on the plasma membrane of immune cells and plays important roles in inflammation and apoptosis. Several single nucleotide polymorphisms have been identified in the human P2RX7 gene. In contrast to other members of the P2X family, non-synonymous polymorphisms in P2X7 are common. Three of these occur at overall frequencies of more than 25% and affect residues in the extracellular “head”-domain of P2X7 (155 Y/H), its “lower body” (270 R/H), and its “tail” in the second transmembrane domain (348 T/A). Comparison of the P2X7 orthologues of human and other great apes indicates that the ancestral allele is Y—R—T (at 155–270–348). Interestingly, each single amino acid variant displays lower ATP-sensitivity than the ancestral allele. The originally published reference sequence of human P2X7, often referred to as “wildtype,” differs from the ancestral allele at all three positions, i.e. H—H—A. The 1,000 Genome Project determined the sequences of both alleles of 2,500 human individuals, including roughly 500 persons from each of the five major continental regions. This rich resource shows that the ancestral alleles Y155, R270, and T348 occur in all analyzed human populations, albeit at strikingly different frequencies in various subpopulations (e.g., 25%–59% for Y155, 59%–77% for R270, and 13%–47% for T348). BLAST analyses of ancient human genome sequences uncovered several homozygous carriers of variant P2X7 alleles, possibly reflecting a high degree of inbreeding, e.g., H—R—T for a 50.000 year old Neanderthal, H—R—A for a 24.000 year old Siberian, and Y—R—A for a 7,000 year old mesolithic European. In contrast, most present-day individuals co-express two copies of P2X7 that differ in one or more amino acids at positions 155, 270, and 348. Our results improve the understanding of how P2X7 structure affects its function and suggest the importance of considering P2X7 variants of participants when designing clinical trials targeting P2X7.

Cathepsin L-containing exosomes from α-synuclein-activated microglia induce neurotoxicity through the P2X7 receptor

Uncontrolled microglial activation is pivotal to the pathogenesis of Parkinson's disease (PD), which can secrete Cathepsin L (CTSL) to affect the survival of neurons in the PD patients; however, the precise mechanism has yet to be determined. We demonstrated for the first time that CTSL was mostly released by exosomes derived from α-Syn-activated microglia, resulting in neuronal damage and death. The elevation of CTSL activity was blocked by GW4869, suggesting a critical role for exosomes in mediating CTSL release. Furthermore, the P2X7R/PI3K/AKT signalling pathway was identified as the underlying molecular mechanism since specific antagonists of this signalling pathway, P2X7R knockdown and exosome release inhibitors significantly reduced the injury to cultured mouse cortical neurons. Our study suggests that increased extracellular release of CTSL from α-Syn-activated microglia through exosomes amplifies and aggravates of the neurotoxic effect of microglia, implying that CTSL may be involved in a fresh mechanism of PD pathogenesis, and serve as a potential biomarker and a target for PD drug development.

Calcium-Permeable Channels Cooperation for Rheumatoid Arthritis: Therapeutic Opportunities

Rheumatoid arthritis is a common autoimmune disease that results from the deposition of antibodies–autoantigens in the joints, leading to long-lasting inflammation. The main features of RA include cartilage damage, synovial invasion and flare-ups of intra-articular inflammation, and these pathological processes significantly reduce patients’ quality of life. To date, there is still no drug target that can act in rheumatoid arthritis. Therefore, the search for novel drug targets has become urgent. Due to their unique physicochemical properties, calcium ions play an important role in all cellular activities and the body has evolved a rigorous calcium signaling system. Calcium-permeable channels, as the main operators of calcium signaling, are widely distributed in cell membranes, endoplasmic reticulum membranes and mitochondrial membranes, and mediate the efflux and entry of Ca2+. Over the last century, more and more calcium-permeable channels have been identified in human cells, and the role of this large family of calcium-permeable channels in rheumatoid arthritis has gradually become clear. In this review, we briefly introduce the major calcium-permeable channels involved in the pathogenesis of RA (e.g., acid-sensitive ion channel (ASIC), transient receptor potential (TRP) channel and P2X receptor) and explain the specific roles and mechanisms of these calcium-permeable channels in the pathogenesis of RA, providing more comprehensive ideas and targets for the treatment of RA.

P2X7R-NEK7-NLRP3 Inflammasome Activation: A Novel Therapeutic Pathway of Qishen Granule in the Treatment of Acute Myocardial Ischemia

Background

Acute myocardial ischemia (AMI) is a common heart disease with increasing morbidity and mortality year by year. Persistent and sterile inflammatory infiltration of myocardial tissue is an important factor triggering of acute myocardial ischemia secondary to acute myocardial infarction, and NLRP3 inflammasome activation is an important part of sterile inflammatory response after acute myocardial ischemia. Previous studies have shown that Qishen granule (QSG) can significantly inhibit the inflammatory injury of myocardial tissue caused by ischemia, but its effect and specific mechanism of inhibiting the activation of NLRP3 inflammasome have not been reported. This study was to investigate the specific mechanism of QSG inhibiting inflammation after AMI, and to validate the possible targets.

Methods

The myocardial ischemia model in mice was established by ligation of the left anterior descending coronary artery. Echocardiography was used to evaluate the cardiac function of the mice. Plasma CK-MB and cTnl were detected by ELISA to evaluate the degree of myocardial injury. The extent of myocardial tissue inflammation in mice was assessed by HE staining and immunohistochemistry of IL-18, IL-1β. The expressions of NLRP3, ASC, Caspase-1, and CD86 were detected by immunofluorescence; detection of key pathway proteins P2X7R, NEK7, NLRP3, ASC, Caspase-1, and effector proteins IL-18, IL-1β by Western blot. In vitro experiments, ATP+LPS was used to construct a RAW264.7 macrophage NLRP3 inflammasome activation model. Immunofluorescence and Western blot analysis were performed to detect the expression of NLRP3 pathway activator and effector proteins. Plasmid-transfected P2X7R overexpression and immunoprecipitation assays were used to evaluate the QSG-regulated NLRP3 inflammasome activation pathway.

Results

QSG rescued cardiac function and further reduced inflammatory effects in mice by inhibiting NLRP3 inflammasome activation. In vitro, QSG inhibited LPS combined with ATP-induced NLRP3 inflammasome activation in RAW264.7 macrophages by downregulating the expression of NLRP3 inflammasome key pathway proteins. In addition, inhibition or overexpression of P2X7R in RAW264.7 macrophages and immunoprecipitated protein interactions further confirmed that QSG reduces macrophages inflammasome activation via the P2X7R-NEK7-NLRP3 pathway.

Conclusion

P2X7R-NEK7-NLRP3 inflammasome activation is a novel therapeutic mechanism of QSG in the treatment of acute myocardial ischemia.

Decoding the Mechanism of CheReCunJin Formula in Treating Sjögren’s Syndrome Based on Network Pharmacology and Molecular Docking

Background

Sjögren's syndrome (SS) is a chronic autoimmune disease characterized by progressive oral and ocular dryness that correlates poorly with autoimmune damage to the glands. CheReCunJin (CRCJ) formula is a prescription formulated according to the Chinese medicine theory for SS treatment.

Objective

This study aimed to explore the underlying mechanisms of CRCJ against SS.

Methods

The databases, including Traditional Chinese Medicine System Pharmacology, Encyclopedia of Traditional Chinese Medicine, Bioinformatics Analysis Tool for the molecular mechanism of Traditional Chinese Medicine, and Traditional Chinese Medicine Integrated Databases, obtained the active ingredients and predicted targets of CRCJ. Then, DrugBank, Therapeutic Target Database, Genecards, Comparative Toxicogenomics Database, and DisGeNET disease databases were used to screen the predicted targets of SS. Intersected targets of CRCJ and SS were visualized by using Venn diagrams. The overlapping targets were uploaded to the protein–protein interaction network analysis search tool. Cytoscape 3.8.2 software constructed a “compound-targets-disease” network. Gene Ontology and the Kyoto Encyclopedia of Genes and Genomes analyses characterized potential targets' biological functions and pathways. AutoDock Vina 1.1.2 software was used to research and verify chemical effective drug components and critical targets.

Results

From the database, we identified 878 active components and 2578 targets of CRCJ, and 827 SS-related targets. 246 SS-related genes in CRCJ were identified by intersection analysis, and then ten hub genes were identified as crucial potential targets from PPI, including ALB, IL-6, TNF, INS, AKT1, IL1B, VEGFA, TP53, JUN, and TLR4. The process of CRCJ action against SS was mainly involved in human cytomegalovirus infection and Th17 cell differentiation, as well as the toll-like receptor signaling and p53 signaling pathways. Molecular docking showed that the bioactive compounds of CRCJ had a good binding affinity with hub targets.

Conclusions

The results showed that CRCJ could activate multiple pathways and treat SS through multiple compounds and targets. This study lays a foundation for better elucidation of the molecular mechanism of CRCJ in the treatment of SS, and also provides basic guidance for future research on Chinese herbal compounds.

Adenosine signaling: Optimal target for gastric cancer immunotherapy

Gastric cancer (GC) is one of the most common malignancy and leading cause of cancer-related deaths worldwide. Due to asymptomatic or only nonspecific early symptoms, GC patients are usually in the advanced stage at first diagnosis and miss the best opportunity of treatment. Immunotherapies, especially immune checkpoint inhibitors (ICIs), have dramatically changed the landscape of available treatment options for advanced-stage cancer patients. However, with regards to existing ICIs, the clinical benefit of monotherapy for advanced gastric cancer (AGC) is quite limited. Therefore, it is urgent to explore an optimal target for the treatment of GC. In this review, we summarize the expression profiles and prognostic value of 20 common immune checkpoint-related genes in GC from Gene Expression Profiling Interactive Analysis (GEPIA) database, and then find that the adenosinergic pathway plays an indispensable role in the occurrence and development of GC. Moreover, we discuss the pathophysiological function of adenosinergic pathway in cancers. The accumulation of extracellular adenosine inhibits the normal function of immune effector cells and facilitate the effect of immunosuppressive cells to foster GC cells proliferation and migration. Finally, we provide insights into potential clinical application of adenosinergic-targeting therapies for GC patients.

P2RY13 Exacerbates Intestinal Inflammation by Damaging the Intestinal Mucosal Barrier via Activating IL-6/STAT3 Pathway

The pathogenesis of ulcerative colitis (UC) is unclear, while genetic factors have been confirmed to play an important role in its development. P2RY13 is a G protein-coupled receptor (GPCRs), which are involved in the pathogenesis of inflammation and immune disorders. According to GEO database analysis, we first observed that the expression of P2Y13 was increased in UC patients. Therefore, we sought to determine the role of P2Y13 in the development of colitis. Our data showed that P2RY13 was highly expressed in the inflamed intestinal tissues of UC patients. In mice, pharmacological antagonism of P2Y13 can significantly attenuate the intestinal mucosal barrier disruption. In LPS-induced NCM460 cell, knockdown or pharmacological inhibition of P2RY13 increased the expression of intestinal tight junction protein and reduced apoptosis. In addition, we found that the effect of P2Y13 on colitis is related to the activation of the IL-6/STAT3 pathway. Activation of P2Y13 increases IL-6 expression and promotes STAT3 phosphorylation and nuclear transport. Deletion of the STAT3 gene in the intestinal epithelial cells of mice significantly mitigated the exacerbation of colitis due to P2Y13 activation. Thus, P2Y13 can aggravate intestinal mucosal barrier destruction by activating the IL-6/STAT3 pathway. P2Y13 might be a potential drug target for UC.

P2X7 receptor in inflammation and pain

Different studies have confirmed P2X7 receptor-mediated inflammatory mediators play a key role in the development of pain. P2X7 receptor activation can induce the development of pain by mediating the release of inflammatory mediators. In view of the fact that P2X7 receptor is expressed in the nervous system and immune system, it is closely related to the stability and maintenance of the nervous system function. ATP activates P2X7 receptor, opens non-selective cation channels, activates multiple intracellular signaling, releases multiple inflammatory cytokines, and induces pain. At present, the role of P2X7 receptor in inflammatory response and pain has been widely recognized and affirmed. Therefore, in this paper, we discussed the pathological mechanism of P2X7 receptor-mediated inflammation and pain, focused on the internal relationship between P2X7 receptor and pain. Moreover, we also described the effects of some antagonists on pain relief by inhibiting the activities of P2X7 receptor. Thus, targeting to inhibit activation of P2X7 receptor is expected to become another potential target for the relief of pain.

P2 Receptors: Novel Disease Markers and Metabolic Checkpoints in Immune Cells

Extracellular ATP (eATP) and P2 receptors are novel emerging regulators of T-lymphocyte responses. Cellular ATP is released via multiple pathways and accumulates at sites of tissue damage and inflammation. P2 receptor expression and function are affected by numerous single nucleotide polymorphisms (SNPs) associated with diverse disease conditions. Stimulation by released nucleotides (purinergic signalling) modulates several T-lymphocyte functions, among which energy metabolism. Energy metabolism, whether oxidative or glycolytic, in turn deeply affects T-cell activation, differentiation and effector responses. Specific P2R subtypes, among which the P2X7 receptor (P2X7R), are either up- or down-regulated during T-cell activation and differentiation; thus, they can be considered indexes of activation/quiescence, reporters of T-cell metabolic status and, in principle, markers of immune-mediated disease conditions.

Relevance of NLRP3 Inflammasome-Related Pathways in the Pathology of Diabetic Wound Healing and Possible Therapeutic Targets

Wound healing is a major secondary complication in type 2 diabetes, which results in significant disability and mortality, imposing a significant clinical and social burden. Sustained activation of the Nod-like receptor protein (NLRP) inflammasome in wounds is responsible for excessive inflammatory responses and aggravates wound damage. The activation of the NLRP3 inflammasome is regulated by a two-step process: the priming/licensing (signal 1) step involved in transcription and posttranslation and the protein complex assembly (signal 2) step triggered by danger molecules. This review focuses on the advances made in understanding the pathophysiological mechanisms underlying wound healing in the diabetic microenvironment. Simultaneously, this review summarizes the molecular mechanisms of the main regulatory pathways associated with signal 1 and signal 2, which trigger the NLRP3 inflammasome complex assembly in the development of diabetic wounds (DW). Activation of the NLRP3 inflammasome-related pathway, involving the disturbance in Nrf2 and the NF-κB/NLRP3 inflammasome, TLR receptor-mediated activation of the NF-κB/NLRP3 inflammasome, and various stimuli inducing NLRP3 inflammasome assembly play a pivotal role in DW healing. Furthermore, therapeutics targeting the NLRP3 inflammasome-related pathways may promote angiogenesis, reprogram immune cells, and improve DW healing.

Pyroptosis and Its Role in Autoimmune Disease: A Potential Therapeutic Target

Autoimmune diseases are a group of heterogeneous diseases with diverse clinical manifestations that can be divided into systemic and organ-specific. The common etiology of autoimmune diseases is the destruction of immune tolerance and the production of autoantibodies, which attack specific tissues and/or organs in the body. The pathogenesis of autoimmune diseases is complicated, and genetic, environmental, infectious, and even psychological factors work together to cause aberrant innate and adaptive immune responses. Although the exact mechanisms are unclear, recently, excessive exacerbation of pyroptosis, as a bond between innate and adaptive immunity, has been proven to play a crucial role in the development of autoimmune disease. Pyroptosis is characterized by pore formation on cell membranes, as well as cell rupture and the excretion of intracellular contents and pro-inflammatory cytokines, such as IL-1β and IL-18. This overactive inflammatory programmed cell death disrupts immune system homeostasis and promotes autoimmunity. This review examines the molecular structure of classical inflammasomes, including NLRP3, AIM2, and P2X7-NLRP3, as the switches of pyroptosis, and their molecular regulation mechanisms. The sophisticated pyroptosis pathways, including the canonical caspase-1-mediated pathway, the noncanonical caspase-4/5/11-mediated pathway, the emerging caspase-3-mediated pathway, and the caspase-independent pathway, are also described. We highlight the recent advances in pyroptosis in autoimmune diseases, such as systemic lupus erythematosus, rheumatoid arthritis, inflammatory bowel disease, Sjögren's syndrome and dermatomyositis, and attempt to identify its potential advantages as a therapeutic target or prognostic marker in these diseases.

TIGIT as a Promising Therapeutic Target in Autoimmune Diseases

Co-inhibitory receptors (IRs) are molecules that protect host against autoimmune reactions and maintain peripheral self-tolerance, playing an essential role in maintaining immune homeostasis. In view of the substantial clinical progresses of negative immune checkpoint blockade in cancer treatment, the role of IRs in autoimmune diseases is also obvious. Several advances highlighted the substantial impacts of T cell immunoglobulin and ITIM domain (TIGIT), a novel IR, in autoimmunity. Blockade of TIGIT pathway exacerbates multiple autoimmune diseases, whereas enhancement of TIGIT function has been shown to alleviate autoimmune settings in mice. These data suggested that TIGIT pathway can be manipulated to achieve durable tolerance to treat autoimmune disorders. In this review, we provide an overview of characteristics of TIGIT and its role in autoimmunity. We then discuss recent approaches and future directions to leverage our knowledge of TIGIT as therapeutic target in autoimmune diseases.

Inhibition of the P2X7/NLRP3 Inflammasome Signaling Pathway by Deacetylgedunin from Toona sinensis

Limonoids are considered the effective part in Meliaceae plants that exert anti-inflammatory effects. Gedunin-type limonoids specifically have anti-inflammatory effects. However, the role of gedunin-type limonoids in the inflammatory diseases mediated by NLRP3 inflammasome remains to be explored. We found that deacetylgudunin (DAG), a gedunin-type limonoid from Toona sinensis, had similar anti-inflammatory effects and lower toxicity than gedunin. Further studies showed that DAG down-regulated the NF-κB pathway, inhibited K⁺ efflux and ROS release, inhibited ASC oligomerization, and significantly weakened the interaction of NLRP3 with ASC and NEK7. Furthermore, DAG could not further inhibit IL-1β secretion and K⁺ efflux when combined with the P2X7 inhibitor A438079. In conclusion, our research revealed that DAG exerted an anti-inflammatory effect by inhibiting the P2X7/NLRP3 signaling pathway and enriched the application of gedunin-type limonoids in inflammatory diseases driven by the NLRP3 inflammasome.

P2X7 Receptor Triggers Lysosomal Leakage Through Calcium Mobilization in a Mechanism Dependent on Pannexin-1 Hemichannels

The P2X7 receptor is a critical purinergic receptor in immune cells. Its activation was associated with cathepsin release into macrophage cytosol, suggesting its involvement in lysosomal membrane permeabilization (LMP) and leakage. Nevertheless, the mechanisms by which P2X7 receptor activation induces LMP and leakage are unclear. This study investigated cellular mechanisms associated with endosomal and lysosomal leakage triggered by P2X7 receptor activation. We found that ATP at 500 μM and 5 mM (but not 50 μM) induced LMP in non-stimulated peritoneal macrophages. This effect was not observed in P2X7-deficient or A740003-pretreated macrophages. We found that the P2X7 receptor and pannexin-1 channels mediate calcium influx that might be important for activating specific ion channels (TRPM2 and two-pore channels) on the membranes of late endosomes and lysosomes leading to LMP leakage and consequent cathepsin release. These findings suggest the critical role of the P2X7 receptor in inflammatory and infectious diseases via lysosomal dysfunction.

P2X7 Receptor Expression and Signaling on Dendritic Cells and CD4+ T Cells is Not Required but Can Enhance Th17 Differentiation

The purinergic receptor P2X7 (P2X7R) is important in inflammasome activation and generally considered to favor proinflammatory immune responses. However, there is still a limited understanding of the role of P2X7R signaling in Th cell differentiation, particularly, Th17 differentiation. Herein, the impact of P2X7R signaling on primary Th17 and Th1 cell responses was examined when P2X7R was expressed specifically on dendritic cells (DCs) and CD4+ T cells. Surprisingly, global genetic ablation and pharmacological inhibition of the P2X7R did not affect the generation of Th17 and Th1 development in response to immunization with Complete Freund's Adjuvant and the model antigens, keyhole limpet hemocyanin or OVA. However, in-depth in vitro and in vivo investigations revealed differences in the balance of Th1/Th17 differentiation when P2X7R blockade was restricted to either DCs or CD4+ T cells. In this regard, in vitro DCs treated with a P2X7R agonist released more IL-6 and IL-1β and induced a more robust Th17 response in mixed leukocyte reactions when compared to controls. To test the hypothesis that P2X7R signaling specifically in DCs enhances Th17 responses in vivo, DC-specific P2X7R deficient chimeras were immunized with CFA and OVA. In this model, the P2X7R expression on DCs decreased the Th1 response without impacting Th17 responses. Following an assessment of CD4+ T cell P2X7R signaling, it was determined that in vitro P2X7R sufficient T cells develop an increased Th17 and suppressed Th1 differentiation profile. In vivo, P2X7R expression on CD4+ T cells had no effect on Th17 differentiation but likewise significantly suppressed the Th1 response, thereby skewing the immune balance. Interestingly, it appears that WT OT-II Th1 cells are more sensitive to P2X7R-induced cell death as evidence by a decrease in cell number and an increase in T cell death. Overall, these studies indicate that in vitro P2X7R signaling does enhances Th17 responses, which suggests that compensatory Th17 differentiation mechanisms are utilized in vivo in the absence of P2X7R signaling.

N6-methyladenosine modification of TGM2 mRNA contributes to the inhibitory activity of sarsasapogenin in rheumatoid arthritis fibroblast-like synoviocytes

BACKGROUND

Developing alternative targets and drugs for rheumatoid arthritis (RA) treatment is currently an urgent issue. The relationship between TGM2 and the abnormal immune microenvironment in synovium tissues, as well as the specific role of TGM2 in RA are yet to be elucidated. Sarsasapogenin (Sar) is a sapogenin extracted from the Chinese medical herb Anemarrhena asphodeloides Bunge. and served as a representative anti-inflammatory drug capable of ameliorating inflammatory responses in several human diseases. However, the therapeutic effect of Sar on RA remains unknown.

PURPOSE

This investigation aims to elucidate the role of TGM2 in RA and investigate whether Sar is a candidate drug to target TGM2 of fibroblast-like synoviocytes (FLS).

METHODS

Bioinformatics analyses were applied for elucidating the role of N(6)-methyladenine (m6A) RNA methylation in RA and identifying the specific target regulated by m6A methylation in RA-FLS. Methylated RNA immunoprecipitation, CCK8 assay, Edu assay, flow cytometry, RT-qPCR and Western blot were utilized to investigate the function of Sar and TGM2 in RA-FLS.

RESULTS

Bioinformatics analyses emphasized the importance of m6A RNA methylation in RA and identified an m6A methylation-mediated gene TGM2. Interestingly, both m6A RNA methylation and TGM2 expression in RA synovium tissues correlated with activated immuno-inflammatory phenotype and associated with clinical characteristics and therapy response of RA patients. TGM2 served as a promoter of RA-FLS proliferation by inducing DNA replication and cell cycle transition and inhibiting apoptosis through activating NF-κB signaling. Intriguingly, Sar could impair m6A methylation of TGM2 mRNA and downregulate TGM2 expression. Downregulated TGM2 contributed to the suppressive role of Sar in DNA replication and the stimulatory role of Sar in cell cycle arrest and apoptosis of RA-FLS. Mechanically, Sar inhibited the expression of key regulators in DNA replication, cell cycle, and apoptosis by impairing NF-κB signaling, thus abolishing FLS proliferation to ameliorate RA progression.

CONCLUSIONS

This cross-validated work based on three independent datasets is detailedly delineated using cell lines and clinical samples, recognizing that TGM2 can be an attractive target and Sar might be a novel anti-RA drug.

P2X7 receptor is essential for cross-dressing of bone marrow-derived dendritic cells

T cell activation requires the processing and presentation of antigenic peptides in the context of a major histocompatibility complex (MHC complex). Cross-dressing is a non-conventional antigen presentation mechanism, involving the transfer of preformed peptide/MHC complexes from whole cells, such as apoptotic cells (ACs) to the cell membrane of professional antigen-presenting cells (APCs), such as dendritic cells (DCs). This is an essential mechanism for the induction of immune response against viral antigens, tumors, and graft rejection, which until now has not been clarified. Here we show for first time that the P2X7 receptor (P2X7R) is crucial to induce cross-dressing between ACs and Bone-Marrow DCs (BMDCs). In controlled ex vivo assays, we found that the P2X7R in both ACs and BMDCs is required to induce membrane and fully functional peptide/MHC complex transfer to BMDCs. These findings show that acquisition of ACs-derived preformed antigen/MHC-I complexes by BMDCs requires P2X7R expression.

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Cross-dressing of antigens to Dendritic Cells (DCs) is dependent of P2X7 receptor

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The P2X7 receptor must be present in both Dendritic Cells and antigen source

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The transfer of antigen/MHC-I complexes to DCs is functional and activates T CD8 cells

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The P2X7 receptor allows Cross-Dressing possibly through a membrane fusion process

Enteric nervous system and inflammatory bowel diseases: Correlated impacts and therapeutic approaches through the P2X7 receptor

The enteric nervous system (ENS) consists of thousands of small ganglia arranged in the submucosal and myenteric plexuses, which can be negatively affected by Crohn's disease and ulcerative colitis - inflammatory bowel diseases (IBDs). IBDs are complex and multifactorial disorders characterized by chronic and recurrent inflammation of the intestine, and the symptoms of IBDs may include abdominal pain, diarrhea, rectal bleeding, and weight loss. The P2X7 receptor has become a promising therapeutic target for IBDs, especially owing to its wide expression and, in the case of other purinergic receptors, in both human and model animal enteric cells. However, little is known about the actual involvement between the activation of the P2X7 receptor and the cascade of subsequent events and how all these activities associated with chemical signals interfere with the functionality of the affected or treated intestine. In this review, an integrated view is provided, correlating the structural organization of the ENS and the effects of IBDs, focusing on cellular constituents and how therapeutic approaches through the P2X7 receptor can assist in both protection from damage and tissue preservation.

The role of P2X7 receptor in infection and metabolism: Based on inflammation and immunity

The P2X7 receptor (P2X7R) is a ligand-gated receptor belonging to the P2 receptor family. It is distributed in various tissues of the human body and is involved in regulating the physiological functions of tissues and cells to affect the occurrence and development of diseases. Unlike all other P2 receptors, the P2X7 receptor is mainly expressed in immune cells and can be activated not only by extracellular nucleotides but also by non-nucleotide substances which act as positive allosteric modulators. In this review, we comprehensively describe the role of the P2X7 receptor in infection and metabolism based on its role as an important regulator of inflammation and immunity, and briefly introduce the structure and general function of the P2X7 receptor. These provide a clear knowledge framework for the study of the P2X7 receptor in human health. Targeting the P2X7 receptor may be an effective method for the treatment of inflammatory and immune diseases. And its role in microbial infection and metabolism may be the main direction for in-depth research on the P2X7 receptor in the future.

Blockage of P2X7R suppresses Th1/Th17-mediated immune responses and corneal allograft rejection via inhibiting NLRP3 inflammasome activation

P2X7R is a vital modifier of various inflammatory and immune-related diseases. However, the immunomodulatory effects of P2X7R on corneal allograft rejection remains unknown. Here we showed that P2X7R expression was significantly upregulated in corneal grafts of allogeneic transplant mice. Pharmacological blockage of P2X7R remarkably prolonged graft survival time, and reduced inflammatory cell infiltration in corneal grafts, in particular Th1/Th17 cells. Meanwhile, the frequencies of Th1/Th17 cells in draining lymph nodes were significantly decreased in P2X7R blocked allogeneic mice. Further results showed that the effect of P2X7R on promoting Th1/Th17 mediated immune responses in corneal allograft rejection relied heavily on its activation on the NLRP3/caspase-1/IL-1β axis, while P2X7R blockage could mitigate such activation. Nevertheless, the addition of IL-1β in vivo abrogated the protective effect of P2X7R blockage on promoting corneal graft survival. These findings demonstrate that blockage of P2X7R can substantially alleviate corneal allograft rejection and promote grafts survival, highlighting it as a promising target for preventing or treating corneal allograft rejection.

Tyrosine 288 in the extracellular domain of the human P2X7 receptor is critical for receptor function revealed by structural modeling and site-directed mutagenesis

The P2X7 receptor (P2X7R) is a calcium-permeable cation channel activated by high concentrations of extracellular ATP. It plays a role in vital physiological processes, particularly in innate immunity, and is dysregulated in pathological conditions such as inflammatory diseases, neurodegenerative diseases, mood disorders, and cancers. Structural modeling of the human P2X7R (hP2X7R) based on the recently available structures of the rat P2X7 receptor (rP2XR) in conjunction with molecular docking predicts the orientation of tyrosine at position 288 (Y288) in the extracellular domain to face ATP. In this short communication, we combined site-directed mutagenesis and whole-cell patch-clamp recording to investigate the role of this residue in the hP2X7R function. Mutation of this extracellular residue to amino acids with different properties massively impaired current responses to both ATP and BzATP, suggesting that Y288 is important for normal receptor function. Such a finding facilitates development of an in-depth understanding of the molecular basis of hP2X7R structure-function relationships.

Immunomodulatory functions of TRPM7 and its implications in autoimmune diseases

An autoimmune disease is an inappropriate response to one's tissues due to a break in immune tolerance and exposure to self-antigens. It often leads to structural and functional damage to organs and systemic disorders. To date, there are no effective interventions to prevent the progression of autoimmune diseases. Hence, there is an urgent need for new treatment targets. TRPM7 is an enzyme-coupled, transient receptor ion channel of the subfamily M that plays a vital role in pathologic and physiologic conditions. While TRPM7 is constitutively activated under certain conditions, it can regulate cell migration, polarization, proliferation and cytokine secretion. However, a growing body of evidence highlights the critical role of TRPM7 in autoimmune diseases, including rheumatoid arthritis, multiple sclerosis and diabetes. Herein, we present (a) a review of the channel kinase properties of TRPM7 and its pharmacological properties, (b) discuss the role of TRPM7 in immune cells (neutrophils, macrophages, lymphocytes and mast cells) and its upstream immunoreactive substances, and (c) highlight TRPM7 as a potential therapeutic target for autoimmune diseases.

Autoimmunity in 2019

Based on the PubMed data, we have been performing a yearly evaluation of the publications related to autoimmune diseases and immunology to ascertain the relative weight of the former in the scientific literature. It is particularly intriguing to observe that despite the numerous new avenues of immune-related mechanisms, such as cancer immunotherapy, the proportion of immunology manuscripts related to autoimmunity continues to increase and has been approaching 20% in 2019. As in the previous 13 years, we performed an arbitrary selection of the peer-reviewed articles published by the major dedicated Journals and discussed the common themes which continue to outnumber peculiarites in autoimmune diseases. The investigated areas included systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), psoriatic arthritis (PsA), autoantibodies (autoAbs), and common therapeutic avenues and novel pathogenic mechanisms for autoimmune conditions. Some examples include new pathogenetic evidence which is well represented by IL21 or P2X7 receptor (P2X7R) in SLE or the application of single-cell RNA sequencing (scRNA-seq), mass cytometry, bulk RNA sequencing (RNA-seq), and flow cytometry for the analysis of different cellular populations in RA. Cumulatively and of interest to the clinicians, a large number of findings continue to underline the importance of a strict relationship between basic and clinical science to define new pathogenetic and therapeutic developments. The therapeutic pipeline in autoimmunity continues to grow and maintain a constant flow of new molecules, as well illustrated in RA and PsA, and this is most certainly derived from the new basic evidence and the high-throughput tools applied to autoimmune diseases.

Potential Implications of Quercetin in Autoimmune Diseases

Autoimmune diseases are a worldwide health problem with growing rates of morbidity, and are characterized by breakdown and dysregulation of the immune system. Although their etiology and pathogenesis remain unclear, the application of dietary supplements is gradually increasing in patients with autoimmune diseases, mainly due to their positive effects, relatively safety, and low cost. Quercetin is a natural flavonoid that is widely present in fruits, herbs, and vegetables. It has been shown to have a wide range of beneficial effects and biological activities, including anti-inflammation, anti-oxidation, and neuroprotection. In several recent studies quercetin has reportedly attenuated rheumatoid arthritis, inflammatory bowel disease, multiple sclerosis, and systemic lupus erythematosus in humans or animal models. This review summarizes the evidence for the pharmacological application of quercetin for autoimmune diseases, which supports the view that quercetin may be useful for their prevention and treatment.

Role of P2X7 Receptors in Immune Responses During Neurodegeneration

P2X7 receptors are ion-gated channels activated by ATP. Under pathological conditions, the extensive release of ATP induces sustained P2X7 receptor activation, culminating in induction of proinflammatory pathways with inflammasome assembly and cytokine release. These inflammatory conditions, whether occurring peripherally or in the central nervous system (CNS), increase blood-brain-barrier (BBB) permeability. Besides its well-known involvement in neurodegeneration and neuroinflammation, the P2X7 receptor may induce BBB disruption and chemotaxis of peripheral immune cells to the CNS, resulting in brain parenchyma infiltration. For instance, despite common effects on cytokine release, P2X7 receptor signaling is also associated with metalloproteinase secretion and activation, as well as migration and differentiation of T lymphocytes, monocytes and dendritic cells. Here we highlight that peripheral immune cells mediate the pathogenesis of Multiple Sclerosis and Parkinson's and Alzheimer's disease, mainly through T lymphocyte, neutrophil and monocyte infiltration. We propose that P2X7 receptor activation contributes to neurodegenerative disease progression beyond its known effects on the CNS. This review discusses how P2X7 receptor activation mediates responses of peripheral immune cells within the inflamed CNS, as occurring in the aforementioned diseases.

Structural basis for the functional properties of the P2X7 receptor for extracellular ATP

The P2X7 receptor, originally known as the P2Z receptor due to its distinctive functional properties, has a structure characteristic of the ATP-gated ion channel P2X receptor family. The P2X7 receptor is an important mediator of ATP-induced purinergic signalling and is involved the pathogenesis of numerous conditions as well as in the regulation of diverse physiological functions. Functional characterisations, in conjunction with site-directed mutagenesis, molecular modelling, and, recently, structural determination, have provided significant insights into the structure–function relationships of the P2X7 receptor. This review discusses the current understanding of the structural basis for the functional properties of the P2X7 receptor.

Therapeutic implications of inflammasome in inflammatory bowel disease

Inflammatory bowel disease (IBD) remains a persistent health problem with a global burden surging over 6.8 million cases currently. Clinical pathology of IBD is complicated; however, hyperactive inflammatory and immune responses in the gut is shown to be one of the persistent causes of the disease. Human gut inflammasome, the activator of innate immune system is believed to be a primary underlying cause for the pathology and is largely associated with the progression of IBD. To manage IBD, there is a need to fully understand the role of inflammasome activation in IBD. Since inflammasome potentially play a significant role in IBD, systemic modulation of inflammasome may provide an effective therapeutic and clinical approach to control IBD symptoms. In this review, we have focused on this association between IBD and gut inflammasome, and recent advances in the research and therapeutic strategies for IBD. We have discussed inflammasomes and their components, outcomes from the experimental animals and human studies, inflammasome inhibitors, and developments in the inflammasome-targeted therapies for IBD.

Mitochondria as Key Players in the Pathogenesis and Treatment of Rheumatoid Arthritis

Mitochondria are major energy-producing organelles that have central roles in cellular metabolism. They also act as important signalling hubs, and their dynamic regulation in response to stress signals helps to dictate the stress response of the cell. Rheumatoid arthritis is an inflammatory and autoimmune disease with high prevalence and complex aetiology. Mitochondrial activity affects differentiation, activation and survival of immune and non-immune cells that contribute to the pathogenesis of this disease. This review outlines what is known about the role of mitochondria in rheumatoid arthritis pathogenesis, and how current and future therapeutic strategies can function through modulation of mitochondrial activity. We also highlight areas of this topic that warrant further study. As producers of energy and of metabolites such as succinate and citrate, mitochondria help to shape the inflammatory phenotype of leukocytes during disease. Mitochondrial components can directly stimulate immune receptors by acting as damage-associated molecular patterns, which could represent an initiating factor for the development of sterile inflammation. Mitochondria are also an important source of intracellular reactive oxygen species, and facilitate the activation of the NLRP3 inflammasome, which produces cytokines linked to disease symptoms in rheumatoid arthritis. The fact that mitochondria contain their own genetic material renders them susceptible to mutation, which can propagate their dysfunction and immunostimulatory potential. Several drugs currently used for the treatment of rheumatoid arthritis regulate mitochondrial function either directly or indirectly. These actions contribute to their immunomodulatory functions, but can also lead to adverse effects. Metabolic and mitochondrial pathways are attractive targets for future anti-rheumatic drugs, however many questions still remain about the precise role of mitochondrial activity in different cell types in rheumatoid arthritis.

An update on the regulatory mechanisms of NLRP3 inflammasome activation

The NOD-, LRR-, and pyrin domain-containing protein 3 (NLRP3) inflammasome is a multiprotein complex involved in the release of mature interleukin-1β and triggering of pyroptosis, which is of paramount importance in a variety of physiological and pathological conditions. Over the past decade, considerable advances have been made in elucidating the molecular mechanisms underlying the priming/licensing (Signal 1) and assembly (Signal 2) involved in NLRP3 inflammasome activation. Recently, a number of studies have indicated that the priming/licensing step is regulated by complicated mechanisms at both the transcriptional and posttranslational levels. In this review, we discuss the current understanding of the mechanistic details of NLRP3 inflammasome activation with a particular emphasis on protein-protein interactions, posttranslational modifications, and spatiotemporal regulation of the NLRP3 inflammasome machinery. We also present a detailed summary of multiple positive and/or negative regulatory pathways providing upstream signals that culminate in NLRP3 inflammasome complex assembly. A better understanding of the molecular mechanisms underlying NLRP3 inflammasome activation will provide opportunities for the development of methods for the prevention and treatment of NLRP3 inflammasome-related diseases.

Phosphoinositides: Roles in the Development of Microglial-Mediated Neuroinflammation and Neurodegeneration

Microglia are increasingly recognized as vital players in the pathology of a variety of neurodegenerative conditions including Alzheimer’s (AD) and Parkinson’s (PD) disease. While microglia have a protective role in the brain, their dysfunction can lead to neuroinflammation and contributes to disease progression. Also, a growing body of literature highlights the seven phosphoinositides, or PIPs, as key players in the regulation of microglial-mediated neuroinflammation. These small signaling lipids are phosphorylated derivates of phosphatidylinositol, are enriched in the brain, and have well-established roles in both homeostasis and disease.Disrupted PIP levels and signaling has been detected in a variety of dementias. Moreover, many known AD disease modifiers identified via genetic studies are expressed in microglia and are involved in phospholipid metabolism. One of these, the enzyme PLCγ2 that hydrolyzes the PIP species PI(4,5)P₂, displays altered expression in AD and PD and is currently being investigated as a potential therapeutic target.Perhaps unsurprisingly, neurodegenerative conditions exhibiting PIP dyshomeostasis also tend to show alterations in aspects of microglial function regulated by these lipids. In particular, phosphoinositides regulate the activities of proteins and enzymes required for endocytosis, toll-like receptor signaling, purinergic signaling, chemotaxis, and migration, all of which are affected in a variety of neurodegenerative conditions. These functions are crucial to allow microglia to adequately survey the brain and respond appropriately to invading pathogens and other abnormalities, including misfolded proteins. AD and PD therapies are being developed to target many of the above pathways, and although not yet investigated, simultaneous PIP manipulation might enhance the beneficial effects observed. Currently, only limited therapeutics are available for dementia, and although these show some benefits for symptom severity and progression, they are far from curative. Given the importance of microglia and PIPs in dementia development, this review summarizes current research and asks whether we can exploit this information to design more targeted, or perhaps combined, dementia therapeutics. More work is needed to fully characterize the pathways discussed in this review, but given the strength of the current literature, insights in this area could be invaluable for the future of neurodegenerative disease research.

The role of innate immunity in myasthenia gravis

Myasthenia gravis (MG) is a T cell-driven, B cell-mediated and autoantibody-dependent autoimmune disorder against neuromuscular junctions (NMJ). Accumulated evidence has emerged regarding the role of innate immunity in the pathogenesis of MG. In this review, we proposed two hypothesis underlying the pathological mechanism. In the context of gene predisposition, on the one hand, Toll-like receptors (TLRs) pathways were initiated by viral infection in the thymus with MG to generate chemokines and pro-inflammatory cytokines such as Type I interferon (IFN), which facilitate the thymus to function as a tertiary lymphoid organ (TLO). On the another hand, the antibodies against acetylcholine receptors (AChR) generated by thymus then activated the classical pathways on thymus and neuromuscular junction (NMJ). Futher, we also highlight the role of innate immune cells in the pathogenic response. Finally, we provide some future perspectives in developing new therapeutic approaches particularly targeting the innate immunity for MG.

Danegaptide Prevents TGFβ1-Induced Damage in Human Proximal Tubule Epithelial Cells of the Kidney

Chronic kidney disease (CKD) is a global health problem associated with a number of comorbidities. Recent evidence implicates increased hemichannel-mediated release of adenosine triphosphate (ATP) in the progression of tubulointerstitial fibrosis, the main underlying pathology of CKD. Here, we evaluate the effect of danegaptide on blocking hemichannel-mediated changes in the expression and function of proteins associated with disease progression in tubular epithelial kidney cells. Primary human proximal tubule epithelial cells (hPTECs) were treated with the beta1 isoform of the pro-fibrotic cytokine transforming growth factor (TGFβ1) ± danegaptide. qRT-PCR and immunoblotting confirmed mRNA and protein expression, whilst a cytokine antibody array assessed the expression/secretion of proinflammatory and profibrotic cytokines. Carboxyfluorescein dye uptake and ATP biosensing measured hemichannel activity and ATP release, whilst transepithelial electrical resistance was used to assess paracellular permeability. Danegaptide negated carboxyfluorescein dye uptake and ATP release and protected against protein changes associated with tubular injury. Blocking Cx43-mediated ATP release was paralleled by partial restoration of the expression of cell cycle inhibitors, adherens and tight junction proteins and decreased paracellular permeability. Furthermore, danegaptide inhibited TGFβ1-induced changes in the expression and secretion of key adipokines, cytokines, chemokines, growth factors and interleukins. The data suggest that as a gap junction modulator and hemichannel blocker, danegaptide has potential in the future treatment of CKD.

The role of lysosomal ion channels in lysosome dysfunction

Lysosomes offer a unique arrangement of degradative, exocytic, and signaling capabilities that make their continued function critical to cellular homeostasis. Lysosomes owe their function to the activity of lysosomal ion channels and transporters, which maintain concentration gradients of H⁺, K⁺, Ca²⁺, Na⁺, and Cl^- across the lysosomal membrane. This review examines the contributions of lysosomal ion channels to lysosome function, showing how ion channel function is integral to degradation and autophagy, maintaining lysosomal membrane potential, controlling Ca²⁺ signaling, and facilitating exocytosis. Evidence of lysosome dysfunction in a variety of disease pathologies creates a need to understand how lysosomal ion channels contribute to lysosome dysfunction. For example, the loss of function of the TRPML1 Ca²⁺ lysosome channel in multiple lysosome storage diseases leads to lysosome dysfunction and disease pathogenesis while neurodegenerative diseases are marked by lysosome dysfunction caused by changes in ion channel activity through the TRPML1, TPC, and TMEM175 ion channels. Autoimmune disease is marked by dysregulated autophagy, which is dependent on the function of multiple lysosomal ion channels. Understanding the role of lysosomal ion channel activity in lysosome membrane permeability and NLRP3 inflammasome activation could provide valuable mechanistic insight into NLRP3 inflammasome-mediated diseases. Finally, this review seeks to show that understanding the role of lysosomal ion channels in lysosome dysfunction could give mechanistic insight into the efficacy of certain drug classes, specifically those that target the lysosome, such as cationic amphiphilic drugs.