P2Y6 receptor-mediated proinflammatory signaling in human bronchial epithelia

SARS-CoV-2 spike protein receptor binding domain promotes IL-6 and IL-8 release via ATP/P2Y2 and ERK1/2 signaling pathways in human bronchial epithelia

The spike protein of SARS-CoV-2 as well as its receptor binding domain (RBD) has been demonstrated to be capable of activating the release of pro-inflammatory mediators in endothelial cells and immune cells such as monocytes. However, the effects of spike protein or its RBD on airway epithelial cells and mechanisms underlying these effects have not been adequately characterized. Here, we show that the RBD of spike protein alone can induce bronchial epithelial inflammation in a manner of ATP/P2Y2 dependence. Incubation of human bronchial epithelia with RBD induced IL-6 and IL-8 release, which could be inhibited by antibody. The incubation of RBD also up-regulated the expression of inflammatory indicators such as ho-1 and mkp-1. Furthermore, ATP secretion was observed after RBD treatment, P2Y2 receptor knock down by siRNA significantly suppressed the IL-6 and IL-8 release evoked by RBD. Additionally, S-RBD elevated the phosphorylation level of ERK1/2, and the effect that PD98059 can inhibit the pro-inflammatory cytokine release suggested the participation of ERK1/2. These novel findings provide new evidence of SARS-CoV-2 on airway inflammation and introduce purinergic signaling as promising treatment target.

Ligand-dependent intracellular trafficking of the G protein-coupled P2Y6 receptor

Endosomal trafficking is intricately linked to G protein-coupled receptors (GPCR) fate and signaling. Extracellular uridine diphosphate (UDP) acts as a signaling molecule by selectively activating the GPCR P2Y₆. Despite the recent interest for this receptor in pathologies, such as gastrointestinal and neurological diseases, there is sparse information on the endosomal trafficking of P2Y₆ receptors in response to its endogenous agonist UDP and synthetic selective agonist 5-iodo-UDP (MRS2693). Confocal microscopy and cell surface ELISA revealed delayed internalization kinetics in response to MRS2693 vs. UDP stimulation in AD293 and HCT116 cells expressing human P2Y₆. Interestingly, UDP induced clathrin-dependent P2Y₆ internalization, whereas receptor stimulation by MRS2693 endocytosis appeared to be associated with a caveolin-dependent mechanism. Internalized P2Y₆ was associated with Rab4, 5, and 7 positive vesicles independent of the agonist. We have measured a higher frequency of receptor expression co-occurrence with Rab11-vesicles, the trans-Golgi network, and lysosomes in response to MRS2693. Interestingly, a higher agonist concentration reversed the delayed P2Y₆ internalization and recycling kinetics in the presence of MRS2693 stimulation without changing its caveolin-dependent internalization. This work showed a ligand-dependent effect affecting the P2Y₆ receptor internalization and endosomal trafficking. These findings could guide the development of bias ligands that could influence P2Y₆ signaling.

Inhibition of P2Y6 receptor expression in Kupffer cells alleviates alcoholic steatohepatitis in mice

Inflammation plays an important role in the progression of alcohol-related liver disease (ALD). UDP-P2Y₆ signaling is involved in many human diseases. The purinergic P2Y₆ receptor, an important regulator of inflammation and phagocytosis, has attracted attention, but its role in alcoholic steatohepatitis remains unclear. Here, we found that P2Y₆ levels were significantly elevated in Kupffer cells in the livers of mice with alcoholic steatohepatitis and ethanol (EtOH)-induced RAW264.7 cells. In this study, mice with alcoholic steatohepatitis were intraperitoneally injected with MRS2578, a specific inhibitor of the P2Y₆ receptor, and P2Y₆ was silenced in EtOH-induced RAW264.7 cells. We found a marked improvement in steatosis and inflammation in the livers of mice with alcoholic steatohepatitis and EtOH-induced RAW264.7 cells. However, P2Y₆ activation in vivo and overexpression in vitro showed contrasting results. In addition, the expression of phospho-p38 mitogen-activated protein kinase (p-p38 MAPK), a phosphorylated protein in the p38 MAPK signaling pathway, was significantly altered after P2Y₆ silencing or overexpression in vitro. P2Y₆ can induce the activation of the p38 MAPK signaling pathway by mediating the calcium influx, whereas inhibition of the expression of P2Y₆ can block the inflammatory process to some extent and thus improve the inflammatory response. The results of this study suggested that targeting P2Y₆ signaling may be a potentially effective strategy for the treatment of alcoholic steatohepatitis.

Neutrophils Dominate the Cervical Immune Cell Population in Pregnancy and Their Transcriptome Correlates With the Microbial Vaginal Environment

The cervicovaginal environment in pregnancy is proposed to influence risk of spontaneous preterm birth. The environment is shaped both by the resident microbiota and local inflammation driven by the host response (epithelia, immune cells and mucous). The contributions of the microbiota, metabolome and host defence peptides have been investigated, but less is known about the immune cell populations and how they may respond to the vaginal environment. Here we investigated the maternal immune cell populations at the cervicovaginal interface in early to mid-pregnancy (10–24 weeks of gestation, samples from N = 46 women), we confirmed neutrophils as the predominant cell type and characterised associations between the cervical neutrophil transcriptome and the cervicovaginal metagenome (N = 9 women). In this exploratory study, the neutrophil cell proportion was affected by gestation at sampling but not by birth outcome or ethnicity. Following RNA sequencing (RNA-seq) of a subset of neutrophil enriched cells, principal component analysis of the transcriptome profiles indicated that cells from seven women clustered closely together these women had a less diverse cervicovaginal microbiota than the remaining three women. Expression of genes involved in neutrophil mediated immunity, activation, degranulation, and other immune functions correlated negatively with Gardnerella vaginalis abundance and positively with Lactobacillus iners abundance; microbes previously associated with birth outcome. The finding that neutrophils are the dominant immune cell type in the cervix during pregnancy and that the cervical neutrophil transcriptome of pregnant women may be modified in response to the microbial cervicovaginal environment, or vice versa, establishes the rationale for investigating associations between the innate immune response, cervical shortening and spontaneous preterm birth and the underlying mechanisms.

β2-Adrenoceptor Activation Stimulates IL-6 Production via PKA, ERK1/2, Src, and Beta-Arrestin2 Signaling Pathways in Human Bronchial Epithelia

Objective

β₂-Adrenoceptor agonists are widely used to treat asthma because of their bronchial-dilation effects. We previously reported that isoprenaline, via the apical and basolateral β₂-adrenoceptor, induced Cl⁻ secretion by activating cyclic AMP (cAMP)-dependent pathways in human bronchial epithelia. Despite these results, whether and how the β₂-adrenoceptor-mediated cAMP-dependent pathway contributes to pro-inflammatory cytokine release in human bronchial epithelia remains poorly understood.

Methods

We investigated β₂-adrenoceptor-mediated signaling pathways involved in the production of two pro-inflammatory cytokines, interleukin (IL)-6 and IL-8, in 16HBE14o- human bronchial epithelia. The effects of isoprenaline or formoterol were assessed in the presence of protein kinase A (PKA), exchange protein directly activated by cAMP (EPAC), Src, and extracellular signal-regulated protein kinase (ERK)1/2 inhibitors. The involvement of β-arrestin2 was examined using siRNA knockdown.

Results

Isoprenaline and formoterol (both β₂ agonists) induced IL-6, but not IL-8, release, which could be inhibited by ICI 118,551 (β₂ antagonist). The PKA-specific inhibitor, H89, partially inhibited IL-6 release. Another intracellular cAMP receptor, EPAC, was not involved in IL-6 release. Isoprenaline-mediated IL-6 secretion was attenuated by dasatinib, a Src inhibitor, and PD98059, an ERK1/2 inhibitor. Isoprenaline treatment also led to ERK1/2 phosphorylation. In addition, knockdown of β-arrestin2 by siRNA specifically suppressed cytokine release when a high concentration of isoprenaline (1 mM) was used.

Conclusion

Our results suggest that activation of the β₂-adrenoceptor in 16HBE14o- cells stimulated the PKA/Src/ERK1/2 and/or β-arrestin2 signaling pathways, leading to IL-6 release. Therefore, our data reveal that β₂-adrenoceptor signaling plays a role in the immune regulation of human airway epithelia.

Methylglyoxal augments uridine diphosphate-induced contraction via activation of p38 mitogen-activated protein kinase in rat carotid artery

The methylglyoxal elicits diverse adverse effects on the body. Uridine diphosphate, an extracellular nucleotide, plays an important role as a signaling molecule controlling vascular tone. This study aimed to evaluate the relationship between methylglyoxal and uridine diphosphate-induced carotid arterial contraction in rats. Additionally, we examined whether p38 mitogen-activated protein kinase (MAPK) would involve such responses. Organ baths were conducted to determine vascular reactivity in isolated carotid arterial rings, and western blotting was used for protein analysis. Treatment with methylglyoxal to carotid arterial rings showed concentration-dependent augmentation to uridine diphosphate-induced contraction in the absence and presence of NG-nitro-L-arginine, which is a nitric oxide synthase inhibitor, whereas, methylglyoxal did not affect serotonin- or isotonic high K+-induced contraction in the presence of a nitric oxide synthase inhibitor. Under nitric oxide synthase inhibition, SB203580, which is a selective p38 MAPK inhibitor, suppressed uridine diphosphate-induced contraction in both the control and methylglyoxal-treated groups, and the difference in uridine diphosphate-induced contraction was abolished by SB203580 treatment. The levels of phosphorylated p38 MAPK were increased by methylglyoxal in carotid arteries, not only under the basal condition but also under uridine diphosphate stimulation. The suppression of uridine diphosphate-induced contraction by a highly selective cell-permeable protein kinase C inhibitor bisindolylmaleimide I was observed in the methylglyoxal-treated group but not in the controls. Moreover, methylglyoxal-induced augmentation of uridine diphosphate-induced contraction was prevented by N-acetyl-L-cysteine. These results suggest that methylglyoxal could enhance uridine diphosphate-induced contraction in rat carotid arteries and may be caused by activation of p38 MAPK and protein kinase C and increased oxidative stress.

Purinergic Receptors of the Central Nervous System: Biology, PET Ligands, and Their Applications

Purinergic receptors play important roles in central nervous system (CNS). These receptors are involved in cellular neuroinflammatory responses that regulate functions of neurons, microglial and astrocytes. Based on their endogenous ligands, purinergic receptors are classified into P1 or adenosine, P2X and P2Y receptors. During brain injury or under pathological conditions, rapid diffusion of extracellular adenosine triphosphate (ATP) or uridine triphosphate (UTP) from the damaged cells, promote microglial activation that result in the changes in expression of several of these receptors in the brain. Imaging of the purinergic receptors with selective Positron Emission Tomography (PET) radioligands has advanced our understanding of the functional roles of some of these receptors in healthy and diseased brains. In this review, we have accumulated a list of currently available PET radioligands of the purinergic receptors that are used to elucidate the receptor functions and participations in CNS disorders. We have also reviewed receptors lacking radiotracer, laying the foundation for future discoveries of novel PET radioligands to reveal these receptors roles in CNS disorders.

P2 purinergic receptor signaling and interleukin-1 synergistically induce interleukin-6 production in a human oral squamous carcinoma cell line

OBJECTIVES

The aim of this study was to investigate the inflammatory roles of P2 purinergic receptor (P2R) signaling in oral squamous cell carcinoma (OSCC).

METHODS

Human OSCC cell lines HSC-2, Ca9-22, and HO-1-u-1 were stimulated with P2R agonists. The concentration of interleukin (IL)-6 in culture supernatants was measured using an enzyme-linked immune sorbent assay. Expression levels of messenger RNAs (mRNAs) were analyzed using reverse transcription polymerase chain reaction. Phosphorylation of intracellular signaling molecules was analyzed using western blotting.

RESULTS

HSC-2 cells expressed the mRNAs for P2X4-6 and all P2YRs. ATP or ADP induced significantly greater production of IL-6 by HSC-2 cells. Ca9-22 cells expressed mRNAs for P2X4-6 and all P2YRs except P2Y4. ATP or ADP induced the production of IL-6 by Ca9-22 cells, but the IL-6 concentration was much lower than that in HSC-2 cells. Although HO-1-u-1 cells expressed the mRNAs for P2X4-6 and all P2YRs, ATP or ADP did not induce IL-6 production. The production of IL-6 by HSC-2 cells stimulated with adenine nucleotides was significantly inhibited by P2R antagonists and a p38 mitogen-activated protein kinase inhibitor, but not by extracellular signal-related kinase or c-Jun N-terminal kinase inhibitors. The proinflammatory cytokine IL-1 significantly augmented P2R-induced IL-6 production by HSC-2 cells via the nuclear factor-κB signaling pathway.

CONCLUSIONS

The present study suggests that P2Rs signaling and IL-1 synergistically induce chronic inflammation in OSCC. Because chronic inflammation is a well-known driving force of tumor progression, these results support therapeutic strategies that target P2Rs signaling in OSCC.

Targeting Streptococcus pneumoniae UDP-glucose pyrophosphorylase (UGPase): in vitro validation of a putative inhibitor

Background:

Genome plasticity of Streptococcus pneumoniae is responsible for the reduced efficacy of various antibiotics and capsular polysaccharide-based vaccines. Therefore, targets independent of capsular types are sought to control the pneumococcal pathogenicity. UDP-glucose pyrophosphorylase (UGPase) is one such desired candidate being responsible for the synthesis of UDP-glucose, a sugar precursor in capsular biosynthesis and metabolic Leloir pathway. Being crucial to pneumococcal pathobiology, the effect of UGPase inhibition on virulence was evaluated in vitro.

Methods:

A putative inhibitor, uridine diphosphate (UDP), was evaluated for effective inhibitory concentration in S. pneumoniae and A549 cells, its efficacy and toxicity. The effect of UDP on adherence and phagocytosis was measured in human respiratory epithelial (A549 and HEp-2) and macrophage (THP1 and J774.A.1) cell lines respectively.

Results:

A differential effective inhibitory concentration of UDP for UGPase inhibition was observed in S. pneumoniae and A549 cells, that is, 5 and 100 µM respectively. UDP treatments lowered percent cytotoxicity in pneumococcal-infected monolayers and didn’t exert adverse effects on viabilities. S. pneumoniae adherence to host cells decreased significantly with UDP treatments. UDP induced the secretion of interleukin (IL)-1β, tumor necrosis factor (TNF)-α, IL-6, and IL-8 and increased pneumococcal phagocytosis.

Conclusion:

Our study shows UDP-mediated decrease in the virulence of S. pneumoniae and demonstrates UDP as an effective inhibitor of pneumococcal UGPase.

Potential Therapeutic Applications of P2 Receptor Antagonists: From Bench to Clinical Trials

BACKGROUND

Extracellular purines and pyrimidines have important physiological functions in mammals. Purines and pyrimidines act on P1 and P2 purinergic receptors, which are widely expressed in the plasma membrane in various cell types. P2 receptors act as important therapeutic targets and are associated with several disorders, such as pain, neurodegeneration, cancer, inflammation, and thrombosis. However, the use of antagonists for P2 receptors in clinical therapy, with the exception of P2Y12, is a great challenge. Currently, many research groups and pharmaceutical companies are working on the development of specific antagonist molecules for each receptor subtype that could be used as new medicines to treat their respective disorders.

OBJECTIVE

The present review compiles some interesting findings on the application of P2 receptor antagonists in different in vitro and in vivo experimental models as well as the progress of advanced clinical trials with these compounds.

CONCLUSION

Despite all of the exciting results obtained on the bench, few antagonists of P2 receptors advanced to the clinical trials, and once they reach this stage, the effectiveness of the therapy is not guaranteed, as in the example of P2X7 antagonists. Despite this, P2Y12 receptor antagonists have a history of success and have been used in therapy for at least two decades to prevent thrombosis in patients at risk for myocardial infarctions. This breakthrough is the motivation for scientists to develop new drugs with antagonistic activity for the other P2 receptors; thus, in a matter of years, we will have an evolution in the field of purinergic therapy.

IL-33/IL1RL1 axis regulates cell survival through the p38 MAPK pathway in acute myeloid leukemia

Acute myeloid leukemia (AML) is often characterized by the presence of specific and recurrent chromosomal abnormalities. Current treatments have greatly increased remission rate, but relapse still occurs. Therefore, novel therapeutic approaches are required. Previously, using a conditional Cbfb-MYH11 knockin mouse model, we showed that Cbfb-MYH11 induces the expression of a cytokine receptor, IL1RL1. Treatment with IL-33, the only known ligand of IL1RL1, promotes leukemia cell survival in vitro. We further found that IL1RL1⁺ cells survive better with chemotherapy than IL1RL1^- population. However, the mechanism is not clear. Here, we show that IL-33 treatment decreased drug sensitivity in the human inv(16) AML cell line ME-1. By RT-PCR, we found that IL-33 increased the expression of IL-4 and IL-6 and led to the activation of both p38 MAPK and NF-κB. We also showed that IL-33 decreased apoptosis with increased phosphorylation of p38 MAPK. Moreover, pre-treatment with MAPK inhibitor attenuated the phosphorylation of p38 enhanced by IL-33 and reversed the anti-apoptotic effect by IL-33. Taken together, our findings give news insights into the potential mechanism of the anti-apoptotic effect by IL-33/IL1RL1 axis in AML which will help in future drug development.

Signaling Through Purinergic Receptor P2Y2 Enhances Macrophage IL-1β Production

The release of nucleotides during necrosis or apoptosis has been described to have both proinflammatory and anti-inflammatory effect on the surrounding cells. Here we describe how low concentrations of UTP and ATP applied during macrophage priming enhance IL-1β production when subsequently the NLRP3 inflammasome is activated in murine resident peritoneal macrophages. Deficiency or pharmacological inhibition of the purinergic receptor P2Y₂ reverted the increase of IL-1β release induced by nucleotides. IL-1β increase was found dependent on the expression of Il1b gene and probably involving JNK activity. On the contrary, nucleotides decreased the production of a different proinflammatory cytokines such as TNF-α. These results suggest that nucleotides could shape the response of macrophages to obtain a unique proinflammatory signature that might be relevant in unrevealing specific inflammatory conditions.

The role of ATP in cough hypersensitivity syndrome: new targets for treatment

Clinically, chronic cough can be effectively controlled in most patients by etiological treatment; however, there remain a small number of patients whose cough has unidentifiable etiology or where treatment efficacy is poor following etiology identification, whose condition is described as unexplained chronic cough or refractory chronic cough. Patients with refractory chronic or unexplained chronic cough commonly have increased cough reflex sensitivity, which has been described as cough hypersensitivity syndrome. The adenosine triphosphate (ATP)-gated P2X₃ receptor may be a key link in the activation of sensory neurons that regulate cough reflexes and has recently draw attention as a potential target for the treatment of refractory chronic cough, with a number of clinical studies validating the therapeutic effects of P2X₃ receptor antagonists in patients with this condition. As the energy source for various cells in vivo, ATP localizes within cells under normal physiological conditions, and has physiological functions, including in metabolism; however, under some pathological circumstances, ATP can act as a neuromodulator and is released into the extracellular space in large quantities as a signal transduction molecule. In addition, ATP is involved in regulation of airway inflammation and the cough reflex. Here, we review the generation, release, and regulation of ATP during airway inflammation and its role in the etiology of cough hypersensitivity syndrome, including the potential underlying mechanism.

β2 adrenoceptor signaling regulates ion transport in 16HBE14o- human airway epithelial cells

We investigated the regulation of Cl^- secretion by adrenoceptors in polarized 16HBE14o- human bronchial epithelial cells. Treatment with the nonselective β adrenoceptor agonist isoprenaline stimulated an increase in short-circuit current (I_SC ), which was inhibited by the β adrenoceptor blocker propranolol. Treatment with procaterol, an agonist specific for the β₂ adrenoceptor subtype, stimulated a similar increase in I_SC , which was inhibited by the β₂ adrenoceptor antagonist ICI 118551. Inhibitors of cystic fibrosis transmembrane conductance regulator (CFTR) and calcium-activated Cl^- channel (CaCC), but not K⁺ channel blockers, were able to inhibit the increase in I_SC . "Trimultaneous" recording of I_SC and intracellular cyclic adenosine monophosphate (cAMP) and Ca²⁺ levels in 16HBE14o- epithelia confirmed that the I_SC induced by isoprenaline or procaterol involved both cAMP and Ca²⁺ signaling. Our results demonstrate that β₂ adrenoceptors regulate Cl^- secretion in the human airway epithelium by activating apical CFTRs and CaCCs via cAMP-dependent and intracellular Ca²⁺ -dependent mechanisms, respectively.

P2Y6 Receptor-Mediated Spinal Microglial Activation in Neuropathic Pain

Objective

To explore the role of purine family member P2Y6 receptors in regulating neuropathic pain (NP) via neuroinflammation in the spinal cord.

Methods

Chronic constriction injury of the sciatic nerve (CCI) of NP was classic in setting up models on Sprague-Dawley (SD) rats. Experiments were performed on rats with sham surgery, CCI, CCI + MRS2578 (a P2Y6 receptor antagonist), and UDP (a P2Y6 receptor agonist). The hyperalgesia intensity was mirrored by paw withdrawal threshold (PWT) and thermal withdrawal latency (TWL). Immunofluorescence staining and western blot were used to evaluate activated microglial marker Iba-1. Enzyme-linked immunosorbent assay (ELISA) was used to access levels of IL-6. Conventional reverse transcription polymerase chain reaction (RT-PCR) and western blot analysis were used to detect the expression of P2Y6 mRNA and activation of JAK/STAT signaling.

Results

Among all groups, CCI caused decreased PWT and TWL compared to sham surgery, meaning a successful establishment of the NP model. These decreased values of PWT and TWL tests could be prevented by intraperitoneally injected MRS2578 and enhanced by UDP administration. Similarly, CCI induced increase of Iba-1 protein, P2Y6 mRNA expression, and circulating IL-6 secretion, as well as increased JAK2/STAT3 mRNA expression and phosphorylating modification in spinal cord tissues could also be diminished by MRS2578 treatment and exacerbated by UDP.

Conclusions

These findings indicated the crucial role of the P2Y6 receptor in modulating the microglial and inflammatory responses in the process of NP in vivo. Results from this study would provide insights into targeting the P2Y6 receptor to treat NP in the near future.

Adenosine diphosphate-sensitive P2Y11 receptor inhibits endothelial cell proliferation by induction of cell cycle arrest in the S phase and induces the expression of inflammatory mediators

Extracellular adenosine diphosphate (ADP) mediates a wide range of physiological effects as an extracellular signaling molecule, including platelet aggregation, vascular tone, cell proliferation, and apoptosis by interacting with plasma membrane P2 receptors. However, the effect of ADP on cell proliferation was contradictory. In this study, we found that ADP significantly inhibited cell proliferation of human umbilical vein endothelial cells at high concentrations (50 to 100 µM). Treatment with ADP did not induce cell apoptosis but instead induced cell cycle arrest in the S phase, which may be partly due to the downregulation of cyclin B1. The inhibition of cell proliferation was blocked by suramin, a nonspecific antagonist of the P2 receptors, and high concentrations of ADP significantly upregulated the messenger RNA (mRNA) and protein expression of P2Y11 in endothelial cells. Moreover, the downregulation of P2Y11 by RNA interference reversed the inhibition of cell proliferation. In addition, ADP (100 µM) can induce the formation of cytosolic autophagy in endothelial cells and a rapid phosphorylation of extracellular signal regulated kinase (ERK) 1/2, which is a canonical signal molecule downstream of P2Y receptors, accompanied by a mRNA expression of proinflammatory cytokines such as intercellular adhesion molecule 1 and vascular cell adhesion molecule 1. Taken together, our study excludes a mechanism for extracellular ADP impairing endothelial cells proliferation via P2Y11 receptor by downregulating cyclin B1 and arresting cell cycle at the S phase, besides, ADP induces cell autophagy and mRNA expression of inflammatory cytokines, whether it is mediated by Erk signaling pathways needs further studies to confirm.

A purinergic P2Y6 receptor agonist prodrug modulates airway inflammation, remodeling, and hyperreactivity in a mouse model of asthma

Background

Purinergic receptors control cell proliferation, apoptosis, migration, inflammation, and cytokine secretion. Increased expression of specific purinergic receptors is reported in asthma. The role of purinergic P2Y6 receptors (P2Y6R) in asthma is controversial.

Hypothesis

P2Y6R activation in asthma improves pulmonary function and reduces inflammation and smooth muscle amount.

Methods

Female mice (C57/BL6, age 30 days) were randomly assigned to receive intranasal house dust mite (HDM) antigen (40 or 80 µg) or saline, 5 days/week, for 6 weeks. Randomly selected subgroups received intraperitoneal P2Y6R agonist prodrug (GC021109; 10 or 100 µg/kg weight/dose) simultaneously with HDM. After 6 weeks, lung function was measured. Lung lavage fluid (LLF) was used to measure total cell count, total protein, and cytokines. Immunohistochemistry for alpha smooth muscle actin (α-SMA) was done. Airway wall thickness was measured on micro-computed tomography (micro-CT) images.

Results

Pulmonary function testing revealed a HDM dose-dependent airway hyperresponsiveness. Airway resistance was increased 2-fold while compliance was decreased by 50% at the higher HDM dose (P<0.05). GC021109 prevented these changes. HDM-exposed mice had elevated inflammatory cell and total protein levels in LLF which were prevented by GC021109 (P<0.05). HDM mice also had elevated LLF levels of interleukin (IL)-4, IL-5, IL-12, granulocyte colony stimulating factor, chemokine (C-X-C) motif ligand 1, and leukemia inhibitory factor that were reduced by GC021109 with a dose-dependent pattern. HDM mice had increased peribronchial and perivascular inflammatory cell infiltration and increased α-SMA; these changes were absent with GC021109. Airway wall thickness measured on micro-CT images was increased after HDM exposure and significantly reduced by GC021109 treatment.

Conclusion

The P2Y6R prodrug GC021109 inhibited allergen-induced changes in pulmonary function, inflammatory responses, and airway and vascular smooth muscle mass. P2Y6R activation may be an effective therapeutic maintenance strategy in asthma.

P2Y6 receptor activation is involved in the development of neuropathic pain induced by chronic constriction injury of the sciatic nerve in rats

Purinergic signaling in spinal cord microglia plays an important role in the pathogenesis of neuropathic pain. Among all P2 receptors, P2Y₆ receptor is expressed in rat dorsal spinal cord. However, it's not clear that the role of P2Y₆ receptor in the chronic constriction injury (CCI) model of neuropathic pain rats. We evaluated the effect of repeated intrathecal administration of MRS2578 (selective P2Y₆ receptor antagonist) on CCI-induced nociceptive behaviors in rats. After CCI, MRS2578 (10^-11-10^-4 M) was administration. The thermal withdrawal latency (TWL) and mechanical withdrawal threshold (MWT) were assessed. The expression of P2Y₆ receptor and Iba-1 at rat dorsal spinal cord was observed by using RT-PCR. We found that intrathecal injection of MRS2578 suppressed CCI-induced mechanical allodynia and thermal hyperalgesia with a dose-dependent manner. The CCI rats presented increased expression of P2Y₆ receptor and Iba-1 at the mRNA level in the ipsilateral dorsal spinal cord than that in sham group. Treatment with either minocycline or SB203580 effectively inhibited P2Y₆ receptor expression compared to CCI rats. Intrathecal injection of UDP enhanced mechanical and thermal allodynia than that in CCI group. To the further study, intrathecal injection of UDP causes mechanical allodynia and thermal hyperalgesia in naive rats. The increased expression of P2Y₆ receptor and Iba-1 were observed in UDP-treated rats. Intrathecal injection of MRS2578 alleviates pain response in UDP-treated rats. These observations suggested that P2Y₆ receptor in dorsal spinal cord contribute to mechanical allodynia and thermal hyperalgesia in CCI-induced neuropathic pain.

Poly-L-Arginine Induces Apoptosis of NCI-H292 Cells via ERK1/2 Signaling Pathway

Cationic protein is a cytotoxic protein secreted by eosinophils and takes part in the damage of airway epithelium in asthma. Poly-L-arginine (PLA), a synthetic cationic protein, is widely used to mimic the biological function of the natural cationic protein in vitro. Previous studies demonstrated the damage of the airway epithelial cells by cationic protein, but the molecular mechanism is unclear. The purpose of this study aimed at exploring whether PLA could induce apoptosis of human airway epithelial cells (NCI-H292) and the underlying mechanism. Methods. The morphology of apoptotic cells was observed by transmission electron microscopy. The rate of apoptosis was analyzed by flow cytometry (FCM). The expressions of the phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2), Bcl-2/Bax, and cleaved caspase-3 were assessed by western blot. Results. PLA can induce apoptosis in NCI-H292 cells in a concentration-dependent manner. Moreover, the phosphorylation of the ERK1/2 and the unbalance of Bcl2/Bax, as well as the activation of caspase-3, were involved in the PLA-induced apoptosis. Conclusions. PLA can induce the apoptosis in NCI-H292 cells, and this process at least involved the ERK1/2 and mitochondrial pathway. The results could have some indications in revealing the apoptotic damage of the airway epithelial cells. Besides, inhibition of cationic protein-induced apoptotic death in airway epithelial cells could be considered as a potential target of anti-injury or antiremodeling in asthmatics.

Tools and drugs for uracil nucleotide-activated P2Y receptors

P2Y receptors (P2YRs) are a family of G protein-coupled receptors activated by extracellular nucleotides. Physiological P2YR agonists include purine and pyrimidine nucleoside di- and triphosphates, such as ATP, ADP, UTP, UDP, nucleotide sugars, and dinucleotides. Eight subtypes exist, P2Y₁, P2Y₂, P2Y₄, P2Y₆, P2Y₁₁, P2Y₁₂, P2Y₁₃, and P2Y₁₄, which represent current or potential future drug targets. Here we provide a comprehensive overview of ligands for the subgroup of the P2YR family that is activated by uracil nucleotides: P2Y₂ (UTP, also ATP and dinucleotides), P2Y₄ (UTP), P2Y₆ (UDP), and P2Y₁₄ (UDP, UDP-glucose, UDP-galactose). The physiological agonists are metabolically unstable due to their fast hydrolysis by ectonucleotidases. A number of agonists with increased potency, subtype-selectivity and/or enzymatic stability have been developed in recent years. Useful P2Y₂R agonists include MRS2698 (6-01, highly selective) and PSB-1114 (6-05, increased metabolic stability). A potent and selective P2Y₂R antagonist is AR-C118925 (10-01). For studies of the P2Y₄R, MRS4062 (3-15) may be used as a selective agonist, while PSB-16133 (10-06) is a selective antagonist. Several potent P2Y₆R agonists have been developed including 5-methoxyuridine 5'-O-((R_p)α-boranodiphosphate) (6-12), PSB-0474 (3-11), and MRS2693 (3-26). The isocyanate MRS2578 (10-08) is used as a selective P2Y₆R antagonist, although its reactivity and low water-solubility are limiting. With MRS2905 (6-08), a potent and metabolically stable P2Y₁₄R agonist is available, while PPTN (10-14) represents a potent and selective P2Y₁₄R antagonist. The radioligand [³H]UDP can be used to label P2Y₁₄Rs. In addition, several fluorescent probes have been developed. Uracil nucleotide-activated P2YRs show great potential as drug targets, especially in inflammation, cancer, cardiovascular and neurodegenerative diseases.

P2Y6 Receptors Regulate CXCL10 Expression and Secretion in Mouse Intestinal Epithelial Cells

In this study, we investigated the role of extracellular nucleotides in chemokine (KC, MIP-2, MCP-1, and CXCL10) expression and secretion by murine primary intestinal epithelial cells (IECs) with a focus on P2Y₆ receptors. qRT-PCR experiments showed that P2Y₆ was the dominant nucleotide receptor expressed in mouse IEC. In addition, the P2Y₆ ligand UDP induced expression and secretion of CXCL10. For the other studies, we took advantage of mice deficient in P2Y₆ (P2ry6^-/-). Similar expression levels of P2Y₁, P2Y₂, P2X2, P2X4, and A_2A were detected in P2ry6^-/- and WT IEC. Agonists of TLR3 (poly(I:C)), TLR4 (LPS), P2Y₁, and P2Y₂ increased the expression and secretion of CXCL10 more prominently in P2ry6^-/- IEC than in WT IEC. CXCL10 expression and secretion induced by poly(I:C) in both P2ry6^-/- and WT IEC were inhibited by general P2 antagonists (suramin and Reactive-Blue-2), by apyrase, and by specific antagonists of P2Y₁, P2Y₂, P2Y₆ (only in WT), and P2X4. Neither adenosine nor an A_2A antagonist had an effect on CXCL10 expression and secretion. Macrophage chemotaxis was induced by the supernatant of poly(I:C)-treated IEC which was consistent with the level of CXCL10 secreted. Finally, the non-nucleotide agonist FGF2 induced MMP9 mRNA expression also at a higher level in P2ry6^-/- IEC than in WT IEC. In conclusion, extracellular nucleotides regulate CXCL10 expression and secretion by IEC. In the absence of P2Y₆, these effects are modulated by other P2 receptors also present on IEC. These data suggest that the presence of P2Y₆ regulates chemokine secretion and may also regulate IEC homeostasis.

Purinergic Signalling: Therapeutic Developments

Purinergic signalling, i.e., the role of nucleotides as extracellular signalling molecules, was proposed in 1972. However, this concept was not well accepted until the early 1990's when receptor subtypes for purines and pyrimidines were cloned and characterised, which includes four subtypes of the P1 (adenosine) receptor, seven subtypes of P2X ion channel receptors and 8 subtypes of the P2Y G protein-coupled receptor. Early studies were largely concerned with the physiology, pharmacology and biochemistry of purinergic signalling. More recently, the focus has been on the pathophysiology and therapeutic potential. There was early recognition of the use of P1 receptor agonists for the treatment of supraventricular tachycardia and A2A receptor antagonists are promising for the treatment of Parkinson's disease. Clopidogrel, a P2Y12 antagonist, is widely used for the treatment of thrombosis and stroke, blocking P2Y12 receptor-mediated platelet aggregation. Diquafosol, a long acting P2Y2 receptor agonist, is being used for the treatment of dry eye. P2X3 receptor antagonists have been developed that are orally bioavailable and stable in vivo and are currently in clinical trials for the treatment of chronic cough, bladder incontinence, visceral pain and hypertension. Antagonists to P2X7 receptors are being investigated for the treatment of inflammatory disorders, including neurodegenerative diseases. Other investigations are in progress for the use of purinergic agents for the treatment of osteoporosis, myocardial infarction, irritable bowel syndrome, epilepsy, atherosclerosis, depression, autism, diabetes, and cancer.

P2Y6 regulates cytoskeleton reorganization and cell migration of C2C12 myoblasts via ROCK pathway

Migration of skeletal muscle precursor cells is required for limb muscle development and skeletal muscle repair. This study aimed to examine the role of P2Y6 receptor in C2C12 myoblasts migration. C2C12 myoblasts were treated with P2Y6 agonist UDP, P2Y6 antagonist MRS2578, Ca²⁺ channel blocker BTP2, or ROCK inhibitor GSK269962 or Y27632, and the migration ability of C2C12 cells was assessed by wound healing assay. The cellular Ca²⁺ content was analyzed with fluo-4 probe and the activation of ROCK (phosphorlyation of LIMK and cofilin) was assayed by western blot. The cytoskeleton was labeled with Actin-Tracker Green and Tubulin-Tracker-Red. Silencing P2Y6 expression in C2C12 myoblasts reduced intracellular Ca²⁺ content and cell motility. Whereas UDP increased cellular Ca²⁺ content, actin filaments, and cell migration, MRS2578 had the opposite effects. The effects of UDP were abrogated by BTP2 and GSK269962 (and Y27632). Disruption of P2Y6 signaling pathway caused C2C12 myoblasts to have an elongated morphology. These results demonstrated that P2Y6 signaled through Ca²⁺ influx and RhoA/ROCK to reorganize cytoskeleton and promote migration in myoblasts.

P2Y6 receptors are involved in mediating the effect of inactivated avian influenza virus H5N1 on IL-6 & CXCL8 mRNA expression in respiratory epithelium

One of the key pathophysiologies of H5N1 infection is excessive proinflammatory cytokine response (cytokine storm) characterized by increases in IFN-β, TNF-α, IL-6, CXCL10, CCL4, CCL2 and CCL5 in the respiratory tract. H5N1-induced cytokine release can occur via an infection-independent mechanism, however, detail of the cellular signaling involved is poorly understood. To elucidate this mechanism, the effect of inactivated (β-propiolactone-treated) H5N1 on the cytokine and chemokine mRNA expression in 16HBE14o- human respiratory epithelial cells was investigated. We found that the inactivated-H5N1 increased mRNA for IL-6 and CXCL8 but not TNF-α, CCL5 or CXCL10. This effect of the inactivated-H5N1 was inhibited by sialic acid receptor inhibitor (α-2,3 sialidase), adenosine diphosphatase (apyrase), P2Y receptor (P2YR) inhibitor (suramin), P2Y6R antagonist (MRS2578), phospholipase C inhibitor (U73122), protein kinase C inhibitors (BIM and Gö6976) and cell-permeant Ca2+ chelator (BAPTA-AM). Inhibitors of MAPK signaling, including of ERK1/2 (PD98059), p38 MAPK (SB203580) and JNK (SP600125) significantly suppressed the inactivated-H5N1-induced mRNA expression of CXCL8. On the other hand, the inactivated-H5N1-induced mRNA expression of IL-6 was inhibited by SB203580, but not PD98059 or SP600125, whereas SN-50, an inhibitor of NF-κB, inhibited the effect of virus on mRNA expression of both of IL-6 and CXCL8. Taken together, our data suggest that, without infection, inactivated-H5N1 induces mRNA expression of IL-6 and CXCL8 by a mechanism, or mechanisms, requiring interaction between viral hemagglutinin and α-2,3 sialic acid receptors at the cell membrane of host cells, and involves activation of P2Y6 purinergic receptors.

Extracellular ATP is involved in dsRNA-induced MUC5AC production via P2Y2R in human airway epithelium

BACKGROUND

In response to tissue damage or inflammation, adenosine-5'-triphosphate (ATP) is released into the extracellular compartment and has been demonstrated to augment inflammation via purinergic P2 receptors (P2Rs). Recently, ATP has been shown to be increased in the airways of COPD patients. In the present study, we examined the possible involvement of extracellular ATP in airway mucus hypersecretion during viral-induced COPD exacerbations.

METHODS

The involvement of extracellular ATP in the release of a major airway mucin, MUC5AC, and its signal pathway was examined after stimulation with polyinosine-polycytidylic acid [poly(I:C)], a synthetic analog of dsRNA to mimic viral infection, and rhinovirus (RV) infection in NCI-H292 cells and differentiated airway epithelial cells from COPD patients.

RESULTS

Treatment with poly(I:C) significantly increased the amount of extracellular ATP and induced MUC5AC release in NCI-H292 cells. Pre-treatment with a pannexin channel inhibitor, carbenoxolone (CBX), reduced the amount of extracellular ATP and suppressed MUC5AC release from poly(I:C)-treated cells. Pre-treatment with the P2R antagonist suramin significantly reduced the expression and release of MUC5AC. The inhibitory effects of CBX and suramin on the release of ATP and/or MUC5AC were replicated with RV infection. Pre-treatment with suramin also significantly reduced the expression and amount of extracellular EGFR ligands and the phosphorylation of EGFR and ERK in poly(I:C)-treated cells. In addition, pre-treatment with a P2Y2 receptor siRNA significantly suppressed the poly(I:C)-potentiated EGFR ligands and MUC5AC release. After poly(I:C) stimulation, the expression of MUC5AC in the differentiated cells from COPD patients was significantly higher than those from healthy subjects and the values of MUC5AC expression were inversely related with forced expiratory volume in 1 s (FEV1) % predicted. The inhibitory effects of CBX and suramin on poly(I:C)-potentiated MUC5AC expression were confirmed in differentiated airway epithelium from COPD patients.

CONCLUSIONS

These results demonstrate that dsRNA induces the release of ATP via pannexin channel and that the extracellular ATP is involved in the expression and release of MUC5AC, mainly via P2Y2R, in an autocrine manner. Modulation of this pathway could be a therapeutic target for viral-induced mucus hypersecretion in COPD exacerbations.

G protein-coupled estrogen receptor inhibits the P2Y receptor-mediated Ca(2+) signaling pathway in human airway epithelia

P2Y receptor activation causes the release of inflammatory cytokines in the bronchial epithelium, whereas G protein-coupled estrogen receptor (GPER), a novel estrogen (E₂) receptor, may play an anti-inflammatory role in this process. We investigated the cellular mechanisms underlying the inhibitory effect of GPER activation on the P2Y receptor-mediated Ca²⁺ signaling pathway and cytokine production in airway epithelia. Expression of GPER in primary human bronchial epithelial (HBE) or 16HBE14o- cells was confirmed on both the mRNA and protein levels. Stimulation of HBE or 16HBE14o- cells with E₂ or G1, a specific agonist of GPER, attenuated the nucleotide-evoked increases in [Ca²⁺]_i, whereas this effect was reversed by G15, a GPER-specific antagonist. G1 inhibited the secretion of two proinflammatory cytokines, interleukin (IL)-6 and IL-8, in cells stimulated by adenosine 5′-(γ-thio)triphosphate (ATPγS). G1 stimulated a real-time increase in cAMP levels in 16HBE14o- cells, which could be inhibited by adenylyl cyclase inhibitors. The inhibitory effects of E₂ or G1 on P2Y receptor-induced increases in Ca²⁺ were reversed by treating the cells with a protein kinase A (PKA) inhibitor. These results demonstrated that the inhibitory effects of G1 or E₂ on P2Y receptor-mediated Ca²⁺ mobilization and cytokine secretion were due to GPER-mediated activation of a cAMP-dependent PKA pathway. This study has reported, for the first time, the expression and function of GPER as an anti-inflammatory component in human bronchial epithelia, which may mediate through its opposing effects on the pro‐inflammatory pathway activated by the P2Y receptors in inflamed airway epithelia.