Cx43 hemichannels and panx1 channels contribute to ethanol-induced astrocyte dysfunction and damage

BACKGROUND

Alcohol, a widely abused drug, significantly diminishes life quality, causing chronic diseases and psychiatric issues, with severe health, societal, and economic repercussions. Previously, we demonstrated that non-voluntary alcohol consumption increases the opening of Cx43 hemichannels and Panx1 channels in astrocytes from adolescent rats. However, whether ethanol directly affects astroglial hemichannels and, if so, how this impacts the function and survival of astrocytes remains to be elucidated.

RESULTS

Clinically relevant concentrations of ethanol boost the opening of Cx43 hemichannels and Panx1 channels in mouse cortical astrocytes, resulting in the release of ATP and glutamate. The activation of these large-pore channels is dependent on Toll-like receptor 4, P2X7 receptors, IL-1β and TNF-α signaling, p38 mitogen-activated protein kinase, and inducible nitric oxide (NO) synthase. Notably, the ethanol-induced opening of Cx43 hemichannels and Panx1 channels leads to alterations in cytokine secretion, NO production, gliotransmitter release, and astrocyte reactivity, ultimately impacting survival.

CONCLUSION

Our study reveals a new mechanism by which ethanol impairs astrocyte function, involving the sequential stimulation of inflammatory pathways that further increase the opening of Cx43 hemichannels and Panx1 channels. We hypothesize that targeting astroglial hemichannels could be a promising pharmacological approach to preserve astrocyte function and synaptic plasticity during the progression of various alcohol use disorders.

TRPA1/M8 agonists upregulate ciliary beating through the pannexin-1 channel in the human nasal mucosa

BACKGROUND

Nasal breathing is important for maintaining physiological respiration. However, airflow in the nasal cavity has an inherent cooling effect and may suppress ciliary beating, an essential frontline defense in the airway. Nasal airflow is thought to be perceived by thermoreceptors for cool temperatures. We herein investigated the effect of the activation of thermosensitive transient receptor potentials (TRPs) for cool/cold temperatures on ciliary beating to search for a compensatory mechanism.

METHODS

Inferior turbinates were collected from patients with chronic hypertrophic rhinitis. Ex vivo ciliary beat frequency (CBF) and ATP release were measured using a high-speed digital video camera and by luciferin-luciferase assay, respectively. Intracellular Ca²⁺ ([Ca²⁺]_i) imaging of isolated ciliated cells was performed using Fluo-8. The nasal mucosae were also subjected to fluorescence immunohistochemistry and real-time RT-PCR for TRPA1/TRPM8.

RESULTS

CBF was significantly increased by adding either cinnamaldehyde (TRPA1 agonist) or l-menthol (TRPM8 agonist). This increase was inhibited by pannexin-1 blockers, carbenoxolone and probenecid. Cinnamaldehyde and l-menthol also increased the ATP release from the nasal mucosa and [Ca²⁺]_i of isolated ciliated cells. Immunohistochemistry detected TRPA1 and TRPM8 on the epithelial surface including the cilia and in the submucosal nasal glands. Existence of these receptors were confirmed at the transcriptional level by real-time RT-PCR.

CONCLUSIONS

These results indicate the stimulatory effect of the activation of TRPA1/TRPM8 on ciliary beating in the nasal mucosa, which would be advantageous to maintain airway mucosal defense against the fall of temperature under normal nasal breathing. This stimulatory effect is likely to be mediated by pannexin-1.

Increased serum pannexin-1 concentrations reflect illness severity and predict a poor prognosis after acute supratentorial intracerebral hemorrhage: A prospective longitudinal cohort study

BACKGROUND

Pannexin-1 is a nonselective, large pore and voltage gated channel protein, whose activation may aggravate acute brain injury. We ascertained the clinical significance of serum pannexin-1 as a prognostic biomarker of acute intracerebral hemorrhage (ICH).

METHODS

In this prospective, observational study of 124 acute supratentorial ICH patients and 124 healthy controls, serum pannexin-1 concentrations were determined. Admission National Institutes of Health Stroke Scale (NIHSS) score and hematoma volume were used for assessment of hemorrhagic severity, post-stroke 6-month modified Rankin scale (mRS) score was registered to reflect clinical outcome and early neurologic deterioration (END) and 6-month poor outcome (mRS score of 3-6) were regarded as the 2 prognostic parameters. Their associations with serum pannexin-1 concentrations were investigated using multivariate analysis. The predictive performance was evaluated in terms of area under receiver operating characteristic curve (AUC).

RESULTS

In comparison to controls, significantly increased serum pannexin-1 concentrations after ICH (median, 6.8 vs. 2.7 mg/ml) were independently correlative with NIHSS score (β, 0.193; 95% CI: 0.086-0.300), hematoma volume (β, 0.641; 95% CI: 0.423-0.859) and mRS score (β, 0.199; 95% CI: 0.065-0.174), were independently predictive of END (OR, 1.176; 95% CI: 1.081-1.280) and poor outcome (odds ratio, 1.218; 95% CI: 1.059-1.400), as well as were efficiently discriminative of END (AUC, 0.764; 95% CI: 0.663-0.864) and poor 6-month outcome (AUC, 0.790; 95% CI: 0.711-0.870). Serum pannexin-1 combined with NIHSS score and hematoma volume (AUC, 0.908; 95% CI: 0.857-0.960) displayed significantly higher predictive ability for poor 6-month outcome than NIHSS score and hematoma volume alone (both P < 0.05).

CONCLUSION

Rising serum pannexin-1 concentrations following ICH, in strong correlation with hemorrhagic severity, independently distinguish the risk of END and 90-day poor outcome. Assumably, serum pannexin-1 may represent a valuable prognostic biomarker of ICH.

Purinergic signaling is essential for full Psickle activation by hypoxia and by normoxic acid pH in mature human sickle red cells and in vitro-differentiated cultured human sickle reticulocytes

Paracrine ATP release by erythrocytes has been shown to regulate endothelial cell function via purinergic signaling, and this erythoid-endothelial signaling network is pathologically dysregulated in sickle cell disease. We tested the role of extracellular ATP-mediated purinergic signaling in the activation of Psickle, the mechanosensitive Ca²⁺-permeable cation channel of human sickle erythrocytes (SS RBC). Psickle activation increases intracellular [Ca²⁺] to stimulate activity of the RBC Gardos channel, KCNN4/KCa3.1, leading to cell shrinkage and accelerated deoxygenation-activated sickling.We found that hypoxic activation of Psickle recorded by cell-attached patch clamp in SS RBC is inhibited by extracellular apyrase, which hydrolyzes extracellular ATP. Hypoxic activation of Psickle was also inhibited by the pannexin-1 inhibitor, probenecid, and by the P2 antagonist, suramin. A Psickle-like activity was also activated in normoxic SS RBC (but not in control red cells) by bath pH 6.0. Acid-activated Psickle-like activity was similarly blocked by apyrase, probenecid, and suramin, as well as by the Psickle inhibitor, Grammastola spatulata mechanotoxin-4 (GsMTx-4).In vitro-differentiated cultured human sickle reticulocytes (SS cRBC), but not control cultured reticulocytes, also exhibited hypoxia-activated Psickle activity that was abrogated by GsMTx-4. Psickle-like activity in SS cRBC was similarly elicited by normoxic exposure to acid pH, and this acid-stimulated activity was nearly completely blocked by apyrase, probenecid, and suramin, as well as by GsMTx-4.Thus, hypoxia-activated and normoxic acid-activated cation channel activities are expressed in both SS RBC and SS cRBC, and both types of activation appear to be mediated or greatly amplified by autocrine or paracrine purinergic signaling.

Pannexin-1 Channels as Mediators of Neuroinflammation

Neuroinflammation is a major component of central nervous system (CNS) injuries and neurological diseases, including Alzheimer’s disease, multiple sclerosis, neuropathic pain, and brain trauma. The activation of innate immune cells at the damage site causes the release of pro-inflammatory cytokines and chemokines, which alter the functionality of nearby tissues and might mediate the recruitment of leukocytes to the injury site. If this process persists or is exacerbated, it prevents the adequate resolution of the inflammation, and ultimately enhances secondary damage. Adenosine 5′ triphosphate (ATP) is among the molecules released that trigger an inflammatory response, and it serves as a chemotactic and endogenous danger signal. Extracellular ATP activates multiple purinergic receptors (P2X and P2Y) that have been shown to promote neuroinflammation in a variety of CNS diseases. Recent studies have shown that Pannexin-1 (Panx1) channels are the principal conduits of ATP release from dying cells and innate immune cells in the brain. Herein, we review the emerging evidence that directly implicates Panx-1 channels in the neuroinflammatory response in the CNS.

The interplay between α7 nicotinic acetylcholine receptors, pannexin-1 channels and P2X7 receptors elicit exocytosis in chromaffin cells

Pannexin-1 (Panx1) forms plasma membrane channels that allow the exchange of small molecules between the intracellular and extracellular compartments, and are involved in diverse physiological and pathological responses in the nervous system. However, the signaling mechanisms that induce their opening still remain elusive. Here, we propose a new mechanism for Panx1 channel activation through a functional crosstalk with the highly Ca²⁺ permeable α7 nicotinic acetylcholine receptor (nAChR). Consistent with this hypothesis, we found that activation of α7 nAChRs induces Panx1-mediated dye uptake and ATP release in the neuroblastoma cell line SH-SY5Y-α7. Using membrane permeant Ca²⁺ chelators, total internal reflection fluorescence microscopy in SH-SY5Y-α7 cells expressing a membrane-tethered GCAMP3, and Src kinase inhibitors, we further demonstrated that Panx1 channel opening depends on Ca²⁺ signals localized in submembrane areas, as well as on Src kinases. In turn, Panx1 channels amplify cytosolic Ca²⁺ signals induced by the activation of α7 nAChRs, by a mechanism that seems to involve ATP release and P2X7 receptor activation, as hydrolysis of extracellular ATP with apyrase or blockage of P2X7 receptors with oxidized ATP significantly reduces the α7 nAChR-Ca²⁺ signal. The physiological relevance of this crosstalk was also demonstrated in neuroendocrine chromaffin cells, wherein Panx1 channels and P2X7 receptors contribute to the exocytotic release of catecholamines triggered by α7 nAChRs, as measured by amperometry. Together these findings point to a functional coupling between α7 nAChRs, Panx1 channels and P2X7 receptors with physiological relevance in neurosecretion.

Pannexin-1 channel "fuels" by releasing ATP from bone marrow cells a state of sterile inflammation required for optimal mobilization and homing of hematopoietic stem cells

An efficient harvest of hematopoietic stem/progenitor cells (HSPCs) after pharmacological mobilization from the bone marrow (BM) into peripheral blood (PB) and subsequent proper homing and engraftment of these cells are crucial for clinical outcomes from hematopoietic transplants. Since extracellular adenosine triphosphate (eATP) plays an important role in both processes as an activator of sterile inflammation in the bone marrow microenvironment, we focused on the role of Pannexin-1 channel in the secretion of ATP to trigger both egress of HSPCs out of BM into PB as well as in reverse process that is their homing to BM niches after transplantation into myeloablated recipient. We employed a specific blocking peptide against Pannexin-1 channel and noticed decreased mobilization efficiency of HSPCs as well as other types of BM-residing stem cells including mesenchymal stroma cells (MSCs), endothelial progenitors (EPCs), and very small embryonic-like stem cells (VSELs). To explain better a role of Pannexin-1, we report that eATP activated Nlrp3 inflammasome in Gr-1+ and CD11b+ cells enriched for granulocytes and monocytes. This led to release of danger-associated molecular pattern molecules (DAMPs) and mitochondrial DNA (miDNA) that activate complement cascade (ComC) required for optimal egress of HSPCs from BM. On the other hand, Pannexin-1 channel blockage in transplant recipient mice leads to a defect in homing and engraftment of HSPCs. Based on this, Pannexin-1 channel as a source of eATP plays an important role in HSPCs trafficking.

Pannexin-1 promotes NLRP3 activation during apoptosis but is dispensable for canonical or noncanonical inflammasome activation

Inflammasomes are multimeric protein complex that assemble in the cytosol upon microbial infection or cellular stress. Upon activation, inflammasomes drive the maturation of proinflammatory cytokines, IL-1β and IL-18, and also activate the pore-forming protein, gasdermin D to initiate a form of lytic cell death known as "pyroptosis". Pannexin-1 is channel-forming glycoprotein that promotes membrane permeability and ATP release during apoptosis; and was implicated in canonical NLRP3 or noncanonical inflammasome activation. Here, by utilizing three different pannexin-1 channel inhibitors and two lines of Panx1^-/- macrophages, we provide genetic and pharmacological evidence that pannexin-1 is dispensable for canonical or noncanonical inflammasome activation. In contrast, we demonstrate that pannexin-1 cleavage and resulting channel activity during apoptosis promotes NLRP3 inflammasome activation.

Pannexin-1 limits the production of proinflammatory cytokines during necroptosis

The activation of mixed lineage kinase-like (MLKL) by receptor-interacting protein kinase-3 (RIPK3) controls the execution of necroptosis, a regulated form of necrosis that occurs in apoptosis-deficient conditions. Active oligomerized MLKL triggers the exposure of phosphatidylserine residues on the cell surface and disrupts the plasma membrane integrity by forming lytic pores. MLKL also governs endosomal trafficking and biogenesis of small extracellular vesicles as well as the production of proinflammatory cytokines during the early steps of necroptosis; however, the molecular basis continues to be elucidated. Here, we find that MLKL oligomers activate Pannexin-1 (PANX1) channels, concomitantly to the loss of phosphatidylserine asymmetry. This plasma membrane "leakiness" requires the small GTPase RAB27A and RAB27B isoforms, which regulate intracellular vesicle trafficking, docking, and fusion with the plasma membrane. Although cells in which PANX1 is silenced or inhibited normally undergo necroptotic death, they display enhanced production of cytokines such as interleukin-8, indicating that PANX1 may tamper with inflammation. These data identify a novel signaling nexus between MLKL, RAB27, and PANX1 and propose ways to interfere with inflammation associated with necroptosis.

Evaluation of serum pannexin-1 as a prognostic biomarker for traumatic brain injury

BACKGROUND

Pannexin-1 is a type of hexameric plasma membrane channel-forming proteins, and plays a significant role in brain injury. We investigated the potential prognostic value of pannexin-1 in traumatic brain injury.

METHODS

A single peripheral blood sample in 112 patients with severe traumatic brain injury and 112 controls was prospectively collected for subsequent measurement of serum pannexin-1. Clinical follow-up was performed at 6 months. An unfavorable outcome was defined as Glasgow Outcome Scale score of 1-3.

RESULTS

The patients showed markedly higher serum pannexin-1 concentrations than the controls. Among the patients, pannexin-1 concentrations were significantly and negatively correlated with Glasgow coma scale scores. On receiver operating characteristic curve analysis, the predictive value in terms of area under the curve was substantially high for serum pannexin-1 as a predictor for both 6-month mortality and unfavorable outcome. Regression analyses confirmed that there was an increased risk of either 6-month mortality, overall survival or unfavorable outcome associated with serum pannexin-1 concentrations after adjusting for possible confounders.

CONCLUSIONS

Serum pannexin-1 may represent a potential prognostic biomarker for head trauma.

Synchronized roles of pannexin and connexin in nasal mucosal epithelia

BACKGROUND

Nasal mucosal epithelial cells express connexins, the prototypical gap junction proteins, and pannexins, a new family of channel proteins homologous to the invertebrate gap junction proteins. The physiological and pathophysiological roles of these transmembrane proteins in nasal mucosa are largely still unknown.

PURPOSE

Pannexins participate in ATP release into the extracellular space in various tissues, and ATP plays important roles in mucociliary clearance, especially by regulating ciliary beat activity. Therefore, we focused on the functional relationship between connexins, pannexin-1, ATP release, and mucociliary clearance in nasal epithelia.

RESULTS AND CONCLUSIONS

Connexins participate in the generation of intercellular calcium waves, in which calcium-mediated signaling responses spread to contiguous cells through the gap junction formed by connexins to transmit calcium signaling throughout the airway epithelium. Pannexins in the nasal mucosa may contribute to not only ciliary beat modulation via ATP release, but also regulation of mucus blanket components via H₂O efflux. The synchronized roles of pannexin and connexin may provide a new insight into effective mucociliary clearance systems in nasal mucosa.

Pannexin-1 channel dysfunction in the medial prefrontal cortex mediates depressive-like behaviors induced by chronic social defeat stress and administration of mefloquine in mice

Mefloquine (MFQ) is widely used for the treatment of malaria clinically. Apart from antimalarial effect, psychiatric side effects such as depression and anxiety of MFQ have been reported. Interestingly, MFQ is also known as a broad-spectrum pannexin-1 (Panx1) inhibitor. Panx1 is a new gap junction channel in the brain which mediates efflux of adenosine triphosphate (ATP). Although exogenous ATP has been known to produce a potential antidepressant-like effect, little is known about the role of Panx1 in pathophysiology of depression, especially the depression induced by administration of MFQ. Here, we used the chronic social defeat stress (CSDS) model and found a decrease in the expression and function of Panx1 in the medial prefrontal cortex (mPFC) of susceptible mice. Furthermore, pharmacological blockade of Panx1 in the mPFC with carbenoxolone (CBX) (100 mM) or ¹⁰Panx (100 μM) was sufficient to induce depressive-like behaviors and increase vulnerability to stress in mice, which were prevented by preconditioning with ATP (25 μM). Finally, systemic and intral-mPFC injection of MFQ both inhibited the activity of Panx1 and induced depressive-like and anxiety behaviors in mice with sub-threshold social defeat stress. Indeed, the behavioral abnormalities induced by MFQ were prevented by preconditioning with ATP in the mPFC. In conclusion, our study demonstrates a role of the Panx1 channel in chronic stress and MFQ-induced depressive-like and anxiety behaviors, which may provide a novel molecular mechanism for psychiatric side effects of MFQ.

Parental vitamin D deficiency during pregnancy is associated with increased blood pressure in offspring via Panx1 hypermethylation

Vitamin D deficiency is one of the most common nutritional deficiencies worldwide. Maternal vitamin D deficiency is associated with increased susceptibility to hypertension in offspring, but the reasons for this remain unknown. The aim of this study was to determine if parental vitamin D deficiency leads to altered DNA methylation in offspring that may relate to hypertension. Male and female Sprague-Dawley rats were fed a standard or vitamin D-depleted diet. After 10 wk, nonsibling rats were mated. The conceived pups received standard chow. We observed an increased systolic and diastolic blood pressure in the offspring from depleted parents (F1-depl). Genome-wide methylation analyses in offspring identified hypermethylation of the promoter region of the Pannexin-1 (Panx1) gene in F1-depl rats. Panx1 encodes a hemichannel known to be involved in endothelial-dependent relaxation, and we demonstrated that in F1-depl rats the increase in blood pressure was associated with impaired endothelial relaxation of the large vessels, suggesting an underlying biological mechanism of increased blood pressure in children from parents with vitamin deficiency. Parental vitamin D deficiency is associated with epigenetic changes and increased blood pressure levels in offspring.

Acetylcholine-induced ex vivo ATP release from the human nasal mucosa

OBJECTIVE

The present study aimed at investigating ATP release in response to acetylcholine (Ach) and pharmacologically elucidating the intracellular signal transduction pathway of this reaction in an ex vivo experiment.

METHODS

The inferior turbinate mucosa was collected from 21 patients with chronic hypertrophic rhinitis who underwent endoscopic turbinectomy. The mucosa was shaped into a filmy round piece, and incubated with chemical(s) in Hank's balanced salt solution for 10min. After incubation, the ATP concentration was measured by a luciferin-luciferase assay.

RESULTS

The baseline release of ATP without stimulus was 57.2±10.3fM. The ATP release was significantly increased by stimulation with 100μM Ach. The Ach-induced ATP release was completely inhibited by removing extracellular Ca²⁺. Significant inhibition of the Ach-induced ATP release was also observed by the addition of 1μM atropine, 40μM 2-APB, 10μM CBX, and 100μM PPADS, whereas 30nM bafilomycin A1 did not affect the ATP release.

CONCLUSION

These results indicate that the Ach-induced ATP release from the human nasal mucosa is dependent on the pannexin-1 channel and purinergic P2X7 receptor, suggesting that these two molecules constitute a local autocrine/paracrine signaling system in the human nasal epithelium.

Effect of pannexin-1 on the release of glutamate and cytokines in astrocytes

We investigated the effect of pannexin-1 (PANX-1) on the release of glutamate and cytokines in U87 human malignant glioma (U87-MG) cells using small interfering RNA (siRNA) transfection and adenosine triphosphate/lipopolysaccharide treatment. PANX-1 is a new family member of the gap junction proteins, and is permeable to ions, metabolic molecules, second messengers, and neurotransmitters, among other factors. PANX-1 plays an important role in the regulation of cell inflammation. However, the relationship between PANX-1 and the secretion of glutamate, interleukin (IL)-6 and IL-8 in astrocytes is still poorly understood. We found that the levels of IL-6, IL-8 and glutamate were lower in PANX-1 siRNA transfected cells, while the levels of IL-6, IL-8 and glutamate were unaltered in cells without changes in the expression of PANX-1 protein. This provides further support for the hypothesis that PANX-1 plays an important role in the release of IL-6, IL-8 and glutamate in U87-MG cells.

Pannexin-1 channels and their emerging functions in cardiovascular diseases

Pannexin-1, Pannexin-2, and Pannexin-3 are three members of the Pannexin family of channel-forming glycoprotein. Their primary function is defined by their ability to form single-membrane channels. Pannexin-1 ubiquitously exists in many cells and organs throughout the body and is specially distributed in the circulatory system, while the expressions of Pannexin-2 and Pannexin-3 are mostly restricted to organs and tissues. Pannexin-1 oligomers have been shown to be functional single membrane channels that connect intracellular and extracellular compartments and are not intercellular channels in appositional membranes. The physiological functions of Pannexin-1 are to link to the adenosine triphosphate efflux that acts as a paracrine signal, and regulate cellular inflammasomes in a variety of cell types under physiological and pathophysiological conditions. However, there are still many functions to be explored. This review summarizes recent reports and discusses the role of Pannexin-1 in cardiovascular diseases, including ischemia, arrhythmia, cardiac fibrosis, and hypertension. Pannexin-1 has been suggested as an exciting, clinically relevant target in cardiovascular diseases.

Pannexin-1-mediated ATP release from area CA3 drives mGlu5-dependent neuronal oscillations

The activation of Group I metabotropic glutamate receptors (GI mGluRs) in the hippocampus results in the appearance of persistent bursts of synchronised neuronal activity. In response to other stimuli, such activity is known to cause the release of the purines ATP and its neuroactive metabolite, adenosine. We have thus investigated the potential release and role of the purines during GI mGluR-induced oscillations in rat hippocampal areas CA3 and CA1 using pharmacological techniques and microelectrode biosensors for ATP and adenosine. The GI mGluR agonist DHPG induced both persistent oscillations in neuronal activity and the release of adenosine in areas CA1 and CA3. In contrast, the DHPG-induced release of ATP was only observed in area CA3. Whilst adenosine acting at adenosine A1 receptors suppressed DHPG-induced burst activity, the activation of mGlu5 and P2Y1 ATP receptors were necessary for the induction of DHPG-induced oscillations. Selective inhibition of pannexin-1 hemichannels with a low concentration of carbenoxolone (10 μM) or probenecid (1 mM) did not affect adenosine release in area CA3, but prevented both ATP release in area CA3 and DHPG-induced bursting. These data reveal key aspects of GI mGluR-dependent neuronal activity that are subject to bidirectional regulation by ATP and adenosine in the initiation and pacing of burst firing, respectively, and which have implications for the role of GI mGluRs in seizure activity and neurodevelopmental disorders.

Activation of P2RY11 and ATP release by lipoxin A4 restores the airway surface liquid layer and epithelial repair in cystic fibrosis

In cystic fibrosis (CF), the airway surface liquid (ASL) height is reduced as a result of impaired ion transport, which favors bacterial colonization and inflammation of the airway and leads to progressive lung destruction. Lipoxin (LX)A4, which promotes resolution of inflammation, is inadequately produced in the airways of patients with CF. We previously demonstrated that LXA4 stimulates an ASL height increase and epithelial repair. Here we report the molecular mechanisms involved in these processes. We found that LXA4 (1 nM) induced an apical ATP release from non-CF (NuLi-1) and CF (CuFi-1) airway epithelial cell lines and CF primary cultures. The ATP release induced by LXA4 was completely inhibited by antagonists of the ALX/FPR2 receptor and Pannexin-1 channels. LXA4 induced an increase in intracellular cAMP and calcium, which were abolished by the selective inhibition of the P2RY11 purinoreceptor. Pannexin-1 and ATP hydrolysis inhibition and P2RY11 purinoreceptor knockdown all abolished the increase of ASL height induced by LXA4. Inhibition of the A2b adenosine receptor did not affect the ASL height increase induced by LXA4, whereas the PKA inhibitor partially inhibited this response. The stimulation of NuLi-1 and CuFi-1 cell proliferation, migration, and wound repair by LXA4 was inhibited by the antagonists of Pannexin-1 channel and P2RY11 purinoreceptor. Taken together, our results provide evidence for a novel role of LXA4 in stimulating apical ATP secretion via Pannexin-1 channels and P2RY11 purinoreceptors activation leading to an ASL height increase and epithelial repair.

Probenecid reduces infection and inflammation in acute Pseudomonas aeruginosa pneumonia

The activation of inflammasome signaling mediates pathology of acute Pseudomonas aeruginosa pneumonia. This suggests that the inflammasome might represent a target to limit the pathological consequences of acute P. aeruginosa lung infection. Pannexin-1 (Px1) channels mediate the activation of caspase-1 and release of IL-1β induced by P2X7 receptor activation. The approved drug probenecid is an inhibitor of Px1 and ATP release. In this study, we demonstrate that probenecid reduces infection and inflammation in acute P. aeruginosa pneumonia. Treatment of mice prior to infection with P. aeruginosa resulted in an enhanced clearance of P. aeruginosa and reduced levels of inflammatory mediators, such as IL-1β. In addition, probenecid inhibited the release of inflammatory mediators in murine alveolar macrophages and human U937 cell-derived macrophages upon bacterial infection but not in human bronchial epithelial cells. Thus, Px1 blockade via probenecid treatment may be a therapeutic option in P. aeruginosa pneumonia by improving bacterial clearance and reducing negative consequences of inflammation.

CR1-mediated ATP release by human red blood cells promotes CR1 clustering and modulates the immune transfer process

Humans and other higher primates are unique among mammals in using complement receptor 1 (CR1, CD35) on red blood cells (RBC) to ligate complement-tagged inflammatory particles (immune complexes, apoptotic/necrotic debris, and microbes) in the circulation for quiet transport to the sinusoids of spleen and liver where resident macrophages remove the particles, but allow the RBC to return unharmed to the circulation. This process is called immune-adherence clearance. In this study we found using luminometric- and fluorescence-based methods that ligation of CR1 on human RBC promotes ATP release. Our data show that CR1-mediated ATP release does not depend on Ca(2+) or enzymes previously shown to mediate an increase in membrane deformability promoted by CR1 ligation. Furthermore, ATP release following CR1 ligation increases the mobility of the lipid fraction of RBC membranes, which in turn facilitates CR1 clustering, and thereby enhances the binding avidity of complement-opsonized particles to the RBC CR1. Finally, we have found that RBC-derived ATP has a stimulatory effect on phagocytosis of immune-adherent immune complexes.