ATP release through pannexon channels

ATP-release pannexin channels are gated by lysophospholipids

In addition to its role as cellular energy currency, adenosine triphosphate (ATP) serves as an extracellular messenger that mediates diverse cell-to-cell communication. Compelling evidence supports that ATP is released from cells through pannexins, a family of membrane proteins that form heptameric large-pore channels. However, the activation mechanisms that trigger ATP release by pannexins remain poorly understood. Here, we discover lysophospholipids as endogenous pannexin activators, using activity-guided fractionation of mouse tissue extracts combined with untargeted metabolomics and electrophysiology. We show that lysophospholipids directly and reversibly activate pannexins in the absence of other proteins. Secretomics experiments reveal that lysophospholipid-activated pannexin 1 leads to the release of not only ATP but also other signaling metabolites, such as 5'-methylthioadenosine, which is important for immunomodulation. We also demonstrate that lysophospholipids activate endogenous pannexin 1 in human monocytes, leading to the release of IL-1β through inflammasome activation. Our results provide a connection between lipid metabolism and purinergic signaling, both of which play major roles in immune responses.

Pathophysiological role of connexin and pannexin hemichannels in neuromuscular disorders

A growing body of research has provided evidence that de novo expression of connexin hemichannels and upregulation of pannexin hemichannels (Cx HCs and Panx HCs, respectively) in the cytoplasmic membrane of skeletal muscle (sarcolemma) are critical steps in the pathogenesis of muscle dysfunction of many genetic and acquired muscle diseases. This review provides an overview of the current understanding of the molecular mechanisms regulating the expression of Cx and Panx HCs in skeletal muscle, as well as their roles in both muscle physiology and pathologies. Additionally, it addresses existing gaps in knowledge and outlines future challenges in the field.

Pannexin1 Mediates Early-Life Seizure-Induced Social Behavior Deficits

There is a high co-morbidity between childhood epilepsy and autism spectrum disorder (ASD), with age of seizure onset being a critical determinant of behavioral outcomes. The interplay between these comorbidities has been investigated in animal models with results showing that the induction of seizures at early post-natal ages leads to learning and memory deficits and to autistic-like behavior in adulthood. Modifications of the excitation/inhibition (glutamate/GABA, ATP/adenosine) balance that follows early-life seizures (ELS) are thought to be the physiological events that underlie neuropsychiatric and neurodevelopmental disorders. Although alterations in purinergic/adenosinergic signaling have been implicated in seizures and ASD, it is unknown whether the ATP release channels, Pannexin1 (Panx1), contribute to ELS-induced behavior changes. To tackle this question, we used the ELS-kainic acid model in transgenic mice with global and cell type specific deletion of Panx1 to evaluate whether these channels were involved in behavioral deficits that occur later in life. Our studies show that ELS results in Panx1 dependent social behavior deficits and also in poor performance in a spatial memory test that does not involve Panx1. These findings provide support for a link between ELS and adult behavioral deficits. Moreover, we identify neuronal and not astrocyte Panx1 as a potential target to specifically limit astrogliosis and social behavioral deficits resultant from early-life seizures.

Three-Dimensional Ultrastructure of Flower-Spray Nerve Endings in the Rat Carotid Sinus

The flower-spray nerve endings are afferent nerve terminals in the carotid sinus that arise from carotid sinus nerve of glossopharyngeal nerve. However, the three-dimensional ultrastructural characteristics of flower-spray nerve endings and spatial relationships between the terminal parts and other cellular elements have not been fully understood. To elucidate their detailed relationship, backscattered electron imaging of serial sections was performed with a scanning electron microscope to produce a three-dimensional reconstruction of the flower-spray endings. The terminal parts of flower-spray endings were distributed horizontally approximately 5 µm outside the external elastic membrane in the tunica adventitia of the internal carotid artery. The three-dimensional reconstruction showed that the terminal parts of flower-spray endings were flat with irregular contours and were partially covered by the thin cytoplasmic processes of Schwann cells. The complex consisting of the nerve terminals and associated Schwann cells was surrounded by a multilayered basement membrane. The terminal parts of the endings were also surrounded by fibroblasts with elastic fibers and collagen fibrils. Secretory vesicles without an electron-dense core were observed in the terminal parts of the endings. The accumulation of vesicles just below the axonal membrane was observed in terminal parts not covered by Schwann cell cytoplasmic processes on both the luminal and basal sides. Swollen mitochondria, concentric membranous structures, and glycogen granule-like electron-dense materials were often noted in some of the terminal parts of the endings and the parent axon. Collectively, the present results suggest that flower-spray endings are baroreceptors because their morphology was similar to other mechanoreceptors. Furthermore, flower-spray endings may be affected by glutamate secreted in an autocrine manner.

PANX1-mediated ATP release confers FAM3A's suppression effects on hepatic gluconeogenesis and lipogenesis

BACKGROUND

Extracellular adenosine triphosphate (ATP) is an important signal molecule. In previous studies, intensive research had revealed the crucial roles of family with sequence similarity 3 member A (FAM3A) in controlling hepatic glucolipid metabolism, islet β cell function, adipocyte differentiation, blood pressure, and other biological and pathophysiological processes. Although mitochondrial protein FAM3A plays crucial roles in the regulation of glucolipid metabolism via stimulating ATP release to activate P2 receptor pathways, its mechanism in promoting ATP release in hepatocytes remains unrevealed.

METHODS

db/db, high-fat diet (HFD)-fed, and global pannexin 1 (PANX1) knockout mice, as well as liver sections of individuals, were used in this study. Adenoviruses and adeno-associated viruses were utilized for in vivo gene overexpression or inhibition. To evaluate the metabolic status in mice, oral glucose tolerance test (OGTT), pyruvate tolerance test (PTT), insulin tolerance test (ITT), and magnetic resonance imaging (MRI) were conducted. Protein-protein interactions were determined by coimmunoprecipitation with mass spectrometry (MS) assays.

RESULTS

In livers of individuals and mice with steatosis, the expression of ATP-permeable channel PANX1 was increased (P < 0.01). Hepatic PANX1 overexpression ameliorated the dysregulated glucolipid metabolism in obese mice. Mice with hepatic PANX1 knockdown or global PANX1 knockout exhibited disturbed glucolipid metabolism. Restoration of hepatic PANX1 rescued the metabolic disorders of PANX1-deficient mice (P < 0.05). Mechanistically, ATP release is mediated by the PANX1-activated protein kinase B-forkhead box protein O1 (Akt-FOXO1) pathway to inhibit gluconeogenesis via P2Y receptors in hepatocytes. PANX1-mediated ATP release also activated calmodulin (CaM) (P < 0.01), which interacted with c-Jun N-terminal kinase (JNK) to inhibit its activity, thereby deactivating the transcription factor activator protein-1 (AP1) and repressing fatty acid synthase (FAS) expression and lipid synthesis (P < 0.05). FAM3A stimulated the expression of PANX1 via heat shock factor 1 (HSF1) in hepatocytes (P < 0.05). Notably, FAM3A overexpression failed to promote ATP release, inhibit the expression of gluconeogenic and lipogenic genes, and suppress gluconeogenesis and lipid deposition in PANX1-deficient hepatocytes and livers.

CONCLUSIONS

PANX1-mediated release of ATP plays a crucial role in maintaining hepatic glucolipid homeostasis, and it confers FAM3A's suppressive effects on hepatic gluconeogenesis and lipogenesis.

P2X7 receptors and pannexin1 hemichannels shape presynaptic transmission

Over the last decades, since the discovery of ATP as a transmitter, accumulating evidence has been reported about the role of this nucleotide and purinergic receptors, in particular P2X7 receptors, in the modulation of synaptic strength and plasticity. Purinergic signaling has emerged as a crucial player in orchestrating the molecular interaction between the components of the tripartite synapse, and much progress has been made in how this neuron-glia interaction impacts neuronal physiology under basal and pathological conditions. On the other hand, pannexin1 hemichannels, which are functionally linked to P2X7 receptors, have appeared more recently as important modulators of excitatory synaptic function and plasticity under diverse contexts. In this review, we will discuss the contribution of ATP, P2X7 receptors, and pannexin hemichannels to the modulation of presynaptic strength and its impact on motor function, sensory processing, synaptic plasticity, and neuroglial communication, with special focus on the P2X7 receptor/pannexin hemichannel interplay. We also address major hypotheses about the role of this interaction in physiological and pathological circumstances.

Activation of Pannexin-1 channels causes cell dysfunction and damage in mesangial cells derived from angiotensin II-exposed mice

Chronic kidney disease (CKD) is a prevalent health concern associated with various pathological conditions, including hypertensive nephropathy. Mesangial cells are crucial in maintaining glomerular function, yet their involvement in CKD pathogenesis remains poorly understood. Recent evidence indicates that overactivation of Pannexin-1 (Panx1) channels could contribute to the pathogenesis and progression of various diseases. Although Panx1 is expressed in the kidney, its contribution to the dysfunction of renal cells during pathological conditions remains to be elucidated. This study aimed to investigate the impact of Panx1 channels on mesangial cell function in the context of hypertensive nephropathy. Using an Ang II-infused mouse model and primary mesangial cell cultures, we demonstrated that in vivo exposure to Ang II sensitizes cultured mesangial cells to show increased alterations when they are subjected to subsequent in vitro exposure to Ang II. Particularly, mesangial cell cultures treated with Ang II showed elevated activity of Panx1 channels and increased release of ATP. The latter was associated with enhanced basal intracellular Ca2+ ([Ca2+]i) and increased ATP-mediated [Ca2+]i responses. These effects were accompanied by increased lipid peroxidation and reduced cell viability. Crucially, all the adverse impacts evoked by Ang II were prevented by the blockade of Panx1 channels, underscoring their critical role in mediating cellular dysfunction in mesangial cells. By elucidating the mechanisms by which Ang II negatively impacts mesangial cell function, this study provides valuable insights into the pathogenesis of renal damage in hypertensive nephropathy.

A metastasis-associated Pannexin1 mutant (Panx1 1-89 ) forms a minimalist ATP release channel

A truncated form of the ATP release channel pannexin 1 (Panx1), Panx1 1-89 , is enriched in metastatic breast cancer cells and has been proposed to mediate metastatic cell survival by increasing ATP release through mechanosensitive Panx1 channels. However, whether Panx1 1-89 on its own (without the presence of wtPanx1) mediates ATP release has not been tested. Here, we show that Panx1 1-89 by itself can form a constitutively active membrane channel, capable of releasing ATP even in the absence of wild type Panx1. Our biophysical characterization reveals that most basic structure-function features of the channel pore are conserved in the truncated Panx1 1-89 peptide. Thus, augmenting extracellular potassium ion concentrations enhances Panx1 1-89 -mediated conductance. Moreover, despite the severe truncation, Panx1 1-89 retains the sensitivity to most of wtPanx1 channel inhibitors and can thus be targeted. Therefore, Panx1 blockers have the potential to be of therapeutic value to combat metastatic cell survival. Our study not only elucidates a mechanism for ATP release from cancer cells, but it also supports that the Panx1 1-89 mutant should facilitate structure-function analysis of Panx1 channels.

The Mechanism of Pyroptosis and Its Application Prospect in Diabetic Wound Healing

Pyroptosis defines a form of pro-inflammatory-dependent programmed cell death triggered by gasdermin proteins, which creates cytoplasmic pores and promotes the activation and accumulation of immune cells by releasing several pro-inflammatory mediators and immunogenic substances upon cell rupture. Pyroptosis comprises canonical (mediated by Caspase-1) and non-canonical (mediated by Caspase-4/5/11) molecular signaling pathways. Numerous studies have explored the contributory roles of inflammasome and pyroptosis in the progression of multiple pathological conditions such as tumors, nerve injury, inflammatory diseases and metabolic disorders. Accumulating evidence indicates that the activation of the NOD-like receptor thermal protein domain associated protein 3 (NLRP3) inflammasome results in the activation of pyroptosis and inflammation. Current evidence suggests that pyroptosis-dependent cell death plays a progressive role in the development of diabetic complications including diabetic wound healing (DWH) and diabetic foot ulcers (DFUs). This review presents a brief overview of the molecular mechanisms underlying pyroptosis and addresses the current research on pyroptosis-dependent signaling pathways in the context of DWH. In this review, we also present some prospective therapeutic compounds/agents that can target pyroptotic signaling pathways, which may serve as new strategies for the effective treatment and management of diabetic wounds.

Involvement of microglial P2X7 receptor in pain modulation

BACKGROUND

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

AIMS

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Purinergic Signaling and its Role in the Stem Cell Differentiation

Purinergic signaling is a mechanism in which extracellular purines and pyrimidines interact with specialized cell surface receptors known as purinergic receptors. These receptors are divided into two families of P1 and P2 receptors, each responding to different nucleosides and nucleotides. P1 receptors are activated by adenosine, while P2 receptors are activated by pyrimidine and purines. P2X receptors are ligand-gated ion channels, including seven subunits (P2X1-7). However, P2Y receptors are the G-protein coupled receptors comprising eight subtypes (P2Y1/2/4/6/11/12/13/14). The disorder in purinergic signaling leads to various health-related issues and diseases. In various aspects, it influences the activity of non-neuronal cells and neurons. The molecular mechanism of purinergic signaling provides insight into treating various human diseases. On the contrary, stem cells have been investigated for therapeutic applications. Purinergic signaling has shown promising effect in stem cell engraftment. The immune system promotes the autocrine and paracrine mechanisms and releases the significant factors essential for successful stem cell therapy. Each subtype of purinergic receptor exerts a beneficial effect on the damaged tissue. The most common effect caused by purinergic signaling is the proliferation and differentiation that treat different health-related conditions.

P2Y1 and P2Y2 receptors differ in their role in the regulation of signaling pathways during unloading-induced rat soleus muscle atrophy

The current study aimed to investigate the hypothesis that purinergic receptors P2Y1 and P2Y2 play a regulatory role in gene expression in unloaded muscle. ATP is released from cells through pannexin channels, and it interacts with P2Y1 and P2Y2 receptors, leading to the activation of markers of protein catabolism and a reduction in protein synthesis. To test this hypothesis thirty-two rats were randomly divided into four groups (8 per group): a non-treated control group (C), a group subjected to three days of hindlimb unloading with a placebo (HS), a group subjected to three days of hindlimb unloading treated with a P2Y1 receptor inhibitor, MRS2179 (HSM), and a group subjected to three days of hindlimb unloading treated with a P2Y2 receptor inhibitor, AR-C 118925XX (HSA). This study revealed several key findings following three days of soleus muscle unloading: 1: Inhibition of P2Y1 or P2Y2 receptors prevented the accumulation of ATP, the increase in IP3 receptor content, and the decrease in the phosphorylation of GSK-3beta. This inhibition also mitigated the reduction in the rate of protein synthesis. However, it had no significant effect on the markers of mTORC1-dependent signaling. 2: Blocking P2Y1 receptors prevented the unloading-induced upregulation of phosphorylated p38MAPK and partially reduced the increase in MuRF1mRNA expression. 3: Blocking P2Y2 receptors prevented muscle atrophy during unloading, partially maintained the levels of phosphorylated ERK1/2, reduced the increase in mRNA expression of MAFbx, ubiquitin, and IL-6 receptor, prevented the decrease in phosphorylated AMPK, and attenuated the increase in phosphorylated p70S6K. Taken together, these results suggest that the prevention of muscle atrophy during unloading, as achieved by the P2Y2 receptor inhibitor, is likely mediated through a reduction in catabolic processes and maintenance of energy homeostasis. In contrast, the P2Y1 receptor appears to play a relatively minor role in muscle atrophy during unloading.

Differential activation of mouse and human Panx1 channel variants

Pannexins are ubiquitously expressed in human and mouse tissues. Pannexin 1 (Panx1), the most thoroughly characterized member of this family, forms plasmalemmal membrane channels permeable to relatively large molecules, such as ATP. Although human and mouse Panx1 amino acid sequences are conserved in the presently known regulatory sites involved in trafficking and modulation of the channel, differences are reported in the N- and C-termini of the protein, and the mechanisms of channel activation by different stimuli remain controversial. Here we used a neuroblastoma cell line to study the activation properties of endogenous mPanx1 and exogenously expressed hPanx1. Dye uptake and electrophysiological recordings revealed that in contrast to mouse Panx1, the human ortholog is insensitive to stimulation with high extracellular [K+] but responds similarly to activation of the purinergic P2X7 receptor. The two most frequent Panx1 polymorphisms found in the human population, Q5H (rs1138800) and E390D (rs74549886), exogenously expressed in Panx1-null N2a cells revealed that regarding P2X7 receptor mediated Panx1 activation, the Q5H mutant is a gain of function whereas the E390D mutant is a loss of function variant. Collectively, we demonstrate differences in the activation between human and mouse Panx1 orthologs and suggest that these differences may have translational implications for studies where Panx1 has been shown to have significant impact.

ShlA toxin of Serratia induces P2Y2- and α5β1-dependent autophagy and bacterial clearance from host cells

Serratia marcescens is an opportunistic human pathogen involved in antibiotic-resistant hospital acquired infections. Upon contact with the host epithelial cell and prior to internalization, Serratia induces an early autophagic response that is entirely dependent on the ShlA toxin. Once Serratia invades the eukaryotic cell and multiples inside an intracellular vacuole, ShlA expression also promotes an exocytic event that allows bacterial egress from the host cell without compromising its integrity. Several toxins, including ShlA, were shown to induce ATP efflux from eukaryotic cells. Here, we demonstrate that ShlA triggered a nonlytic release of ATP from Chinese hamster ovary (CHO) cells. Enzymatic removal of accumulated extracellular ATP (eATP) or pharmacological blockage of the eATP-P2Y2 purinergic receptor inhibited the ShlA-promoted autophagic response in CHO cells. Despite the intrinsic ecto-ATPase activity of CHO cells, the effective concentration and kinetic profile of eATP was consistent with the established affinity of the P2Y2 receptor and the known kinetics of autophagy induction. Moreover, eATP removal or P2Y2 receptor inhibition also suppressed the ShlA-induced exocytic expulsion of the bacteria from the host cell. Blocking α5β1 integrin highly inhibited ShlA-dependent autophagy, a result consistent with α5β1 transactivation by the P2Y2 receptor. In sum, eATP operates as the key signaling molecule that allows the eukaryotic cell to detect the challenge imposed by the contact with the ShlA toxin. Stimulation of P2Y2-dependent pathways evokes the activation of a defensive response to counteract cell damage and promotes the nonlytic clearance of the pathogen from the infected cell.

The neuroinflammatory astrocytic P2X7 receptor: Alzheimer's disease, ischemic brain injury, and epileptic state

INTRODUCTION

Astrocytes have previously been considered as cells supporting neuronal functions, but they are now recognized as active players in maintaining central nervous system (CNS) homeostasis. Astrocytes can communicate with other CNS cells, i.e. through the gliotransmitter ATP and P2X7 receptors (Rs).

AREAS COVERED

In this review, we will discuss how the P2X7R initiates the release of gliotransmitters and proinflammatory cytokines/chemokines, thereby establishing a dialog between astrocytes and neurons and, in addition, causing neuroinflammation. In astrocytes, dysregulation of P2X7Rs has been associated with neurodegenerative illnesses such as Alzheimer's disease (AD), as well as the consequences of cerebral ischemic injury and status epilepticus (SE).

EXPERT OPINION

Although all CNS cells are possible sources of ATP release, the targets of this ATP are primarily at microglial cells. However, astrocytes also contain ATP-sensitive P2X7Rs and have in addition the peculiar property over microglia to continuously interact with neurons via not only inflammatory mediators but also gliotransmitters, such as adenosine 5'-triphosphate (ATP), glutamate, γ-amino butyric acid (GABA), and D-serine. Cellular damage arising during AD, cerebral ischemia, and SE via P2X7R activation is superimposed upon the original disease, and their prevention by blood-brain barrier permeable pharmacological antagonists is a valid therapeutic option.

A scoping review: What are the cellular mechanisms that drive the allergic inflammatory response to fungal allergens in the lung epithelium?

Allergic airway disease (AAD) is a collective term for respiratory disorders that can be exacerbated upon exposure to airborne allergens. The contribution of fungal allergens to AAD has become well established over recent years. We conducted a comprehensive review of the literature using Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines to better understand the mechanisms involved in the allergic response to fungi in airway epithelia, identify knowledge gaps and make recommendations for future research. The search resulted in 61 studies for final analysis. Despite heterogeneity in the models and methods used, we identified major pathways involved in fungal allergy. These included the activation of protease-activated receptor 2, the EGFR pathway, adenosine triphosphate and purinergic receptor-dependent release of IL33, and oxidative stress, which drove mucin expression and goblet cell metaplasia, Th2 cytokine production, reduced barrier integrity, eosinophil recruitment, and airway hyperresponsiveness. However, there were several knowledge gaps and therefore we recommend future research should focus on the use of more physiologically relevant methods to directly compare key allergenic fungal species, clarify specific mechanisms of fungal allergy, and assess the fungal allergy in disease models. This will inform disease management and future interventions, ultimately reducing the burden of disease.

Probenecid affects muscle Ca2+ homeostasis and contraction independently from pannexin channel block

Tight control of skeletal muscle contractile activation is secured by the excitation-contraction (EC) coupling protein complex, a molecular machinery allowing the plasma membrane voltage to control the activity of the ryanodine receptor Ca2+ release channel in the sarcoplasmic reticulum (SR) membrane. This machinery has been shown to be intimately linked to the plasma membrane protein pannexin-1 (Panx1). We investigated whether the prescription drug probenecid, a widely used Panx1 blocker, affects Ca2+ signaling, EC coupling, and muscle force. The effect of probenecid was tested on membrane current, resting Ca2+, and SR Ca2+ release in isolated mouse muscle fibers, using a combination of whole-cell voltage-clamp and Ca2+ imaging, and on electrically triggered contraction of isolated muscles. Probenecid (1 mM) induces SR Ca2+ leak at rest and reduces peak voltage-activated SR Ca2+ release and contractile force by 40%. Carbenoxolone, another Panx1 blocker, also reduces Ca2+ release, but neither a Panx1 channel inhibitory peptide nor a purinergic antagonist affected Ca2+ release, suggesting that probenecid and carbenoxolone do not act through inhibition of Panx1-mediated ATP release and consequently altered purinergic signaling. Probenecid may act by altering Panx1 interaction with the EC coupling machinery, yet the implication of another molecular target cannot be excluded. Since probenecid has been used both in the clinic and as a masking agent for doping in sports, these results should encourage evaluation of possible effects on muscle function in treated individuals. In addition, they also raise the question of whether probenecid-induced altered Ca2+ homeostasis may be shared by other tissues.

The P2X7 Receptor as a Mechanistic Biomarker for Epilepsy

Epilepsy, characterized by recurrent spontaneous seizures, is a heterogeneous group of brain diseases affecting over 70 million people worldwide. Major challenges in the management of epilepsy include its diagnosis and treatment. To date, video electroencephalogram (EEG) monitoring is the gold-standard diagnostic method, with no molecular biomarker in routine clinical use. Moreover, treatment based on anti-seizure medications (ASMs) remains ineffective in 30% of patients, and, even if seizure-suppressive, lacks disease-modifying potential. Current epilepsy research is, therefore, mainly focussed on the identification of new drugs with a different mechanism of action effective in patients not responding to current ASMs. The vast heterogeneity of epilepsy syndromes, including differences in underlying pathology, comorbidities and disease progression, represents, however, a particular challenge in drug discovery. Optimal treatment most likely requires the identification of new drug targets combined with diagnostic methods to identify patients in need of a specific treatment. Purinergic signalling via extracellularly released ATP is increasingly recognized to contribute to brain hyperexcitability and, consequently, drugs targeting this signalling system have been proposed as a new therapeutic strategy for epilepsy. Among the purinergic ATP receptors, the P2X7 receptor (P2X7R) has attracted particular attention as a novel target for epilepsy treatment, with P2X7Rs contributing to unresponsiveness to ASMs and drugs targeting the P2X7R modulating acute seizure severity and suppressing seizures during epilepsy. In addition, P2X7R expression has been reported to be altered in the brain and circulation in experimental models of epilepsy and patients, making it both a potential therapeutic and diagnostic target. The present review provides an update on the newest findings regarding P2X7R-based treatments for epilepsy and discusses the potential of P2X7R as a mechanistic biomarker.

Activation of immune signals during organ transplantation

The activation of host's innate and adaptive immune systems can lead to acute and chronic graft rejection, which seriously impacts graft survival. Thus, it is particularly significant to clarify the immune signals, which are critical to the initiation and maintenance of rejection generated after transplantation. The initiation of response to graft is dependent on sensing of danger and stranger molecules. The ischemia and reperfusion of grafts lead to cell stress or death, followed by releasing a variety of damage-associated molecular patterns (DAMPs), which are recognized by pattern recognition receptors (PRRs) of host immune cells to activate intracellular immune signals and induce sterile inflammation. In addition to DAMPs, the graft exposed to 'non-self' antigens (stranger molecules) are recognized by the host immune system, stimulating a more intense immune response and further aggravating the graft damage. The polymorphism of MHC genes between different individuals is the key for host or donor immune cells to identify heterologous 'non-self' components in allogeneic and xenogeneic organ transplantation. The recognition of 'non-self' antigen by immune cells mediates the activation of immune signals between donor and host, resulting in adaptive memory immunity and innate trained immunity to the graft, which poses a challenge to the long-term survival of the graft. This review focuses on innate and adaptive immune cells receptor recognition of damage-associated molecular patterns, alloantigens and xenoantigens, which is described as danger model and stranger model. In this review, we also discuss the innate trained immunity in organ transplantation.

An emerging master inducer and regulator for epithelial-mesenchymal transition and tumor metastasis: extracellular and intracellular ATP and its molecular functions and therapeutic potential

Despite the rapid development of therapeutic strategies in cancer treatment, metastasis remains the major cause of cancer-related death and scientific challenge. Epithelial-Mesenchymal Transition (EMT) plays a crucial role in cancer invasion and progression, a process by which tumor cells lose cell-cell adhesion and acquire increased invasiveness and metastatic activity. Recent work has uncovered some crucial roles of extracellular adenosine 5'- triphosphate (eATP), a major component of the tumor microenvironment (TME), in promoting tumor growth and metastasis. Intratumoral extracellular ATP (eATP), at levels of 100-700 µM, is 10³-10⁴ times higher than in normal tissues. In the current literature, eATP's function in promoting metastasis has been relatively poorly understood as compared with intracellular ATP (iATP). Recent evidence has shown that cancer cells internalize eATP via macropinocytosis in vitro and in vivo, promoting cell growth and survival, drug resistance, and metastasis. Furthermore, ATP acts as a messenger molecule that activates P2 purinergic receptors expressed on both tumor and host cells, stimulating downstream signaling pathways to enhance the invasive and metastatic properties of tumor cells. Here, we review recent progress in understanding eATP's role in each step of the metastatic cascade, including initiating invasion, inducing EMT, overcoming anoikis, facilitating intravasation, circulation, and extravasation, and eventually establishing metastatic colonization. Collectively, these studies reveal eATP's important functions in many steps of metastasis and identify new opportunities for developing more effective therapeutic strategies to target ATP-associated processes in cancer.

Purinergic Signalling in the Cochlea

The mammalian cochlea is the sensory organ of hearing with a delicate, highly organised structure that supports unique operating mechanisms. ATP release from the secretory tissues of the cochlear lateral wall (stria vascularis) triggers numerous physiological responses by activating P2 receptors in sensory, supporting and neural tissues. Two families of P2 receptors, ATP-gated ion channels (P2X receptors) and G protein-coupled P2Y receptors, activate intracellular signalling pathways that regulate cochlear development, homeostasis, sensory transduction, auditory neurotransmission and response to stress. Of particular interest is a purinergic hearing adaptation, which reflects the critical role of the P2X₂ receptor in adaptive cochlear response to elevated sound levels. Other P2 receptors are involved in the maturation of neural processes and frequency selectivity refinement in the developing cochlea. Extracellular ATP signalling is regulated by a family of surface-located enzymes collectively known as "ectonucleotidases" that hydrolyse ATP to adenosine. Adenosine is a constitutive cell metabolite with an established role in tissue protection and regeneration. The differential activation of A₁ and A_2A adenosine receptors defines the cochlear response to injury caused by oxidative stress, inflammation, and activation of apoptotic pathways. A₁ receptor agonism, A_2A receptor antagonism, and increasing adenosine levels in cochlear fluids all represent promising therapeutic tools for cochlear rescue from injury and prevention of hearing loss.

Connexins and Pannexins: Important Players in Neurodevelopment, Neurological Diseases, and Potential Therapeutics

Cell-to-cell communication is essential for proper embryonic development and its dysfunction may lead to disease. Recent research has drawn attention to a new group of molecules called connexins (Cxs) and pannexins (Panxs). Cxs have been described for more than forty years as pivotal regulators of embryogenesis; however, the exact mechanism by which they provide this regulation has not been clearly elucidated. Consequently, Cxs and Panxs have been linked to congenital neurodegenerative diseases such as Charcot-Marie-Tooth disease and, more recently, chronic hemichannel opening has been associated with adult neurodegenerative diseases (e.g., Alzheimer's disease). Cell-to-cell communication via gap junctions formed by hexameric assemblies of Cxs, known as connexons, is believed to be a crucial component in developmental regulation. As for Panxs, despite being topologically similar to Cxs, they predominantly seem to form channels connecting the cytoplasm to the extracellular space and, despite recent research into Panx1 (Pannexin 1) expression in different regions of the brain during the embryonic phase, it has been studied to a lesser degree. When it comes to the nervous system, Cxs and Panxs play an important role in early stages of neuronal development with a wide span of action ranging from cellular migration during early stages to neuronal differentiation and system circuitry formation. In this review, we describe the most recent available evidence regarding the molecular and structural aspects of Cx and Panx channels, their role in neurodevelopment, congenital and adult neurological diseases, and finally propose how pharmacological modulation of these channels could modify the pathogenesis of some diseases.

ATP indirectly stimulates hippocampal CA1 and CA3 pyramidal neurons via the activation of neighboring P2X7 receptor-bearing astrocytes and NG2 glial cells, respectively

There is ongoing dispute on the question whether CNS neurons possess ATP-sensitive P2X7 receptors (Rs) or whether only non-neuronal cells bear this receptor-type and indirectly signal to the neighboring neurons. We genetically deleted P2X7Rs specifically in astrocytes, oligodendrocytes and microglia, and then recorded current responses in neurons to the prototypic agonist of this receptor, dibenzoyl-ATP (Bz-ATP). These experiments were made in brain slice preparations taken from the indicated variants of the P2X7R KO animals. In hippocampal CA3, but not CA1 pyramidal neurons, the deletion of oligodendrocytic (NG2 glial) P2X7Rs abolished the Bz-ATP-induced current responses. In contrast to the Bz-ATP-induced currents in CA3 pyramidal neurons, current amplitudes evoked by the ionotropic glutamate/GABA_AR agonists AMPA/muscimol were not inhibited at all. Whereas in the CA3 area NG2 glia appeared to mediate the P2X7R-mediated stimulation of pyramidal neurons, in the CA1 area, astrocytic P2X7Rs had a somewhat similar effect. This was shown by recording the frequencies and amplitudes of spontaneous excitatory currents (sPSCs) in brain slice preparations. Bz-ATP increased the sPSC frequency in CA1, but not CA3 pyramidal neurons without altering the amplitude, indicating a P2X7R-mediated increase of the neuronal input. Micro-injection of the selective astrocytic toxin L-α-aminoadipate into both hippocampi, or the in vitro application of the GABA_AR antagonistic gabazine, completely blocked the frequency increases of sPSCs. Hence, CA1 and CA3 pyramidal neurons of the mouse did not possess P2X7Rs, but were indirectly modulated by astrocytic and oligodendrocytic P2X7Rs, respectively.

High PANX1 Expression Leads to Neutrophil Recruitment and the Formation of a High Adenosine Immunosuppressive Tumor Microenvironment in Basal-like Breast Cancer

Background: A high adenosine level is an important characteristic of the tumor microenvironment (TME) in breast cancer. Pannexin 1 (PANX1) can release intracellular ATP to the extracellular space and elevate extracellular ATP (exATP) levels under physiological conditions. Methods: We performed public database bioinformatics analysis, surgical specimen histological validation, RNA sequencing, and exATP/extracellular adenosine (exADO) assays to reveal the role of PANX1 in regulating the immune microenvironment of basal-like breast cancer. Results: Our results revealed that PANX1 acted as a poor prognostic factor for breast cancer and had high expression in basal-like breast cancer. PANX1 expression was positively correlated with exATP and exADO levels in basal-like breast cancer TME. PANX1 expression was also positively correlated with tumor-associated neutrophil (TAN) infiltration in breast cancer TME and TANs highly expressed ENTPD1 (CD39)/NT5E (CD73). Conclusions: This study suggests that high PANX1 expression is associated with high TAN infiltration and adenosine production to induce local immunosuppression in basal-like breast cancer TME.

Connexin and Pannexin Large-Pore Channels in Microcirculation and Neurovascular Coupling Function

Microcirculation homeostasis depends on several channels permeable to ions and/or small molecules that facilitate the regulation of the vasomotor tone, hyperpermeability, the blood–brain barrier, and the neurovascular coupling function. Connexin (Cxs) and Pannexin (Panxs) large-pore channel proteins are implicated in several aspects of vascular physiology. The permeation of ions (i.e., Ca²⁺) and key metabolites (ATP, prostaglandins, D-serine, etc.) through Cxs (i.e., gap junction channels or hemichannels) and Panxs proteins plays a vital role in intercellular communication and maintaining vascular homeostasis. Therefore, dysregulation or genetic pathologies associated with these channels promote deleterious tissue consequences. This review provides an overview of current knowledge concerning the physiological role of these large-pore molecule channels in microcirculation (arterioles, capillaries, venules) and in the neurovascular coupling function.

Roles of ATP and SERCA in the Regulation of Calcium Turnover in Unloaded Skeletal Muscles: Current View and Future Directions

A decrease in skeletal muscle contractile activity or its complete cessation (muscle unloading or disuse) leads to muscle fibers’ atrophy and to alterations in muscle performance. These changes negatively affect the quality of life of people who, for one reason or another, are forced to face a limitation of physical activity. One of the key regulatory events leading to the muscle disuse-induced changes is an impairment of calcium homeostasis, which leads to the excessive accumulation of calcium ions in the sarcoplasm. This review aimed to analyze the triggering mechanisms of calcium homeostasis impairment (including those associated with the accumulation of high-energy phosphates) under various types of muscle unloading. Here we proposed a hypothesis about the regulatory mechanisms of SERCA and IP3 receptors activity during muscle unloading, and about the contribution of these mechanisms to the excessive calcium ion myoplasmic accumulation and gene transcription regulation via excitation–transcription coupling.

ATP, an attractive target for the treatment of refractory chronic cough

Chronic cough is the most common complaint in respiratory clinics. Most of them have identifiable causes and some may respond to common disease-modifying therapies. However, there are many patients whose cough lacks effective aetiologically targeted treatments or remains unexplained after thorough assessments, which have been described as refractory chronic cough. Current treatments for refractory chronic cough are limited and often accompanied by intolerable side effects such as sedation. In recent years, various in-depth researches into the pathogenesis of chronic cough have led to an explosion in the development of drugs for the treatment of refractory chronic cough. There has been considerable progress in the underlying mechanisms of chronic cough targeting ATP, and ongoing or completed clinical studies have confirmed the promising antitussive efficacy of P2X3 antagonists for refractory cough. Herein, we review the foundation on which ATP target was developed as potential antitussive medications and provide an update on current clinical progresses.

ATP Secretion and Metabolism in Regulating Pancreatic Beta Cell Functions and Hepatic Glycolipid Metabolism

Diabetes (DM), especially type 2 diabetes (T2DM) has become one of the major diseases severely threatening public health worldwide. Islet beta cell dysfunctions and peripheral insulin resistance including liver and muscle metabolic disorder play decisive roles in the pathogenesis of T2DM. Particularly, increased hepatic gluconeogenesis due to insulin deficiency or resistance is the central event in the development of fasting hyperglycemia. To maintain or restore the functions of islet beta cells and suppress hepatic gluconeogenesis is crucial for delaying or even stopping the progression of T2DM and diabetic complications. As the key energy outcome of mitochondrial oxidative phosphorylation, adenosine triphosphate (ATP) plays vital roles in the process of almost all the biological activities including metabolic regulation. Cellular adenosine triphosphate participates intracellular energy transfer in all forms of life. Recently, it had also been revealed that ATP can be released by islet beta cells and hepatocytes, and the released ATP and its degraded products including ADP, AMP and adenosine act as important signaling molecules to regulate islet beta cell functions and hepatic glycolipid metabolism via the activation of P2 receptors (ATP receptors). In this review, the latest findings regarding the roles and mechanisms of intracellular and extracellular ATP in regulating islet functions and hepatic glycolipid metabolism would be briefly summarized and discussed.

Active role of glia-like supporting cells in the organ of Corti: Membrane proteins and their roles in hearing

The organ of Corti, located in the cochlea in the inner ear, is one of the major sensory organs involved in hearing. The organ of Corti consists of hair cells, glia-like supporting cells, and the cochlear nerve, which work in harmony to receive sound from the outer ear and transmit auditory signals to the cochlear nucleus in the auditory ascending pathway. In this process, maintenance of the endocochlear potential, with a high potassium gradient and clearance of electrolytes and biochemicals in the inner ear, is critical for normal sound transduction. There is an emerging need for a thorough understanding of each cell type involved in this process to understand the sophisticated mechanisms of the organ of Corti. Hair cells have long been thought to be active, playing a primary role in the cochlea in actively detecting and transmitting signals. In contrast, supporting cells are thought to be silent and function to support hair cells. However, growing lines of evidence regarding the membrane proteins that mediate ionic movement in supporting cells have demonstrated that supporting cells are not silent, but actively play important roles in normal signal transduction. In this review, we summarize studies that characterize diverse membrane proteins according to the supporting cell subtypes involved in cochlear physiology and hearing. This review contributes to a better understanding of supporting cell functions and facilitates the development of potential therapeutic tools for hearing loss.

Protective Effect of Purinergic P2X7 Receptor Inhibition on Acrolein-Induced Urothelial Cell Damage

Patients undergoing chemotherapy with cyclophosphamide experience cystitis due to excretion of a toxic metabolite, acrolein. Cystitis, an inflammation of the bladder, is associated with damage to the integrity of the urothelial barrier. The purinergic P2X7 receptor (P2X7R) is increasingly recognized for its role in inflammation and cell death. P2X7R is expressed abundantly on the bladder urothelium. The aim of this study was to investigate the role of P2X7R in acrolein-induced inflammatory damage in primary cultured porcine bladder urothelial cells. Confluent urothelial cells in culture were treated with acrolein to induce damage; also, with the P2X7R selective antagonist, A804598. Cell viability assay, immunocytochemistry, and trans-epithelial electrical resistance (TEER) studies were carried out to investigate the effect of treatments on urothelial cell function. Acrolein induced a significant reduction in urothelial cell viability, which was protected by the presence of A804598 (10 µM). The urothelial barrier function, indicated by TEER values, was also significantly reduced by acrolein, whereas pre-incubation with P2X7R antagonist significantly protected the urothelial cell barrier from acrolein-induced TEER reduction. The structure of urothelial cell tight junctions was similarly impacted by acrolein treatment, showing the fragmentation of zona occludens-1 (ZO-1) immunoreactivity. Pre-treatment of cells with A804598 countered against the actions of acrolein and maintained ZO-1 expression level and cell structure. The damaging effect of acrolein on urothelial cells integrity could be impaired by inhibition of P2X7R, therefore P2X7R blockade may be a possible therapy in patients with bladder cystitis caused by cyclophosphamide treatment.

Propidium uptake and ATP release in A549 cells share similar transport mechanisms

The lipid bilayer of eukaryotic cells' plasma membrane is almost impermeable to small ions and large polar molecules, but its miniscule basal permeability in intact cells is poorly characterized. This report describes the intrinsic membrane permeability of A549 cells toward the charged molecules propidium (Pr²⁺) and ATP^4-. Under isotonic conditions, we detected with quantitative fluorescence microscopy, a continuous low-rate uptake of Pr (∼150 × 10^-21 moles (zmol)/h/cell, [Pr]_o = 150 μM, 32°C). It was stimulated transiently but strongly by 66% hypotonic cell swelling reaching an influx amplitude of ∼1500 (zmol/h)/cell. The progressive Pr uptake with increasing [Pr]_o (30, 150, and 750 μM) suggested a permeation mechanism by simple diffusion. We quantified separately ATP release with custom wide-field-of-view chemiluminescence imaging. The strong proportionality between ATP efflux and Pr²⁺ influx during hypotonic challenge, and the absence of stimulation of transmembrane transport following 300% hypertonic shock, indicated that ATP and Pr travel the same conductive pathway. The fluorescence images revealed a homogeneously distributed intracellular uptake of Pr not consistent with high-conductance channels expressed at low density on the plasma membrane. We hypothesized that the pathway consists of transiently formed water pores evenly spread across the plasma membrane. The abolition of cell swelling-induced Pr uptake with 500 μM gadolinium, a known modulator of membrane fluidity, supported the involvement of water pores whose formation depends on the membrane fluidity. Our study suggests an alternative model of a direct permeation of ATP (and other molecules) through the phospholipid bilayer, which may have important physiological implications.

Pairing cells of different sizes in a microfluidic device for immunological synapse monitoring

Analyzing cell-cell interaction is essential to investigate how immune cells function. Elegant designs have been demonstrated to study lymphocytes and their interaction partners. However, these devices have been targeting cells of similar dimensions. T lymphocytes are smaller, more deformable, and more sensitive to pressure than many cells. This work aims to fill the gap of a method for pairing cells with different dimensions. The developed method uses hydrodynamic flow focusing in the z-direction for on-site modulation of effective channel height to capture smaller cells as single cells. Due to immune cells' sensitivity to pressure, the proposed method provides a stable system without any change in flow conditions at the analysis area throughout experiments. Paired live cells have their activities analyzed with calcium imaging at the immunological synapse formed under a controlled environment. The method is demonstrated with primary human T lymphocytes, acute myeloid leukemia (AML) cell lines, and primary AML blasts.

High, in Contrast to Low Levels of Acute Stress Induce Depressive-like Behavior by Involving Astrocytic, in Addition to Microglial P2X7 Receptors in the Rodent Hippocampus

Extracellular adenosine 5'-triphosphate (ATP) in the brain is suggested to be an etiological factor of major depressive disorder (MDD). It has been assumed that stress-released ATP stimulates P2X7 receptors (Rs) at the microglia, thereby causing neuroinflammation; however, other central nervous system (CNS) cell types such as astrocytes also possess P2X7Rs. In order to elucidate the possible involvement of the MDD-relevant hippocampal astrocytes in the development of a depressive-like state, we used various behavioral tests (tail suspension test [TST], forced swim test [FST], restraint stress, inescapable foot shock, unpredictable chronic mild stress [UCMS]), as well as fluorescence immunohistochemistry, and patch-clamp electrophysiology in wild-type (WT) and genetically manipulated rodents. The TST and FST resulted in learned helplessness manifested as a prolongation of the immobility time, while inescapable foot shock caused lower sucrose consumption as a sign of anhedonia. We confirmed the participation of P2X7Rs in the development of the depressive-like behaviors in all forms of acute (TST, FST, foot shock) and chronic stress (UCMS) in the rodent models used. Further, pharmacological agonists and antagonists acted in a different manner in rats and mice due to their diverse potencies at the respective receptor orthologs. In hippocampal slices of mice and rats, only foot shock increased the current responses to locally applied dibenzoyl-ATP (Bz-ATP) in CA1 astrocytes; in contrast, TST and restraint depressed these responses. Following stressful stimuli, immunohistochemistry demonstrated an increased co-localization of P2X7Rs with a microglial marker, but no change in co-localization with an astroglial marker. Pharmacological damage to the microglia and astroglia has proven the significance of the microglia for mediating all types of depression-like behavioral reactions, while the astroglia participated only in reactions induced by strong stressors, such as foot shock. Because, in addition to acute stressors, their chronic counterparts induce a depressive-like state in rodents via P2X7R activation, we suggest that our data may have relevance for the etiology of MDD in humans.

Piezo1-Pannexin1 complex couples force detection to ATP secretion in cholangiocytes

Cholangiocytes actively contribute to the final composition of secreted bile. These cells are exposed to abnormal mechanical stimuli during obstructive cholestasis, which has a deep impact on their function. However, the effects of mechanical insults on cholangiocyte function are not understood. Combining gene silencing and pharmacological assays with live calcium imaging, we probed molecular candidates essential for coupling mechanical force to ATP secretion in mouse cholangiocytes. We show that Piezo1 and Pannexin1 are necessary for eliciting the downstream effects of mechanical stress. By mediating a rise in intracellular Ca²⁺, Piezo1 acts as a mechanosensor responsible for translating cell swelling into activation of Panx1, which triggers ATP release and subsequent signal amplification through P2X4R. Co-immunoprecipitation and pull-down assays indicated physical interaction between Piezo1 and Panx1, which leads to stable plasma membrane complexes. Piezo1–Panx1–P2X4R ATP release pathway could be reconstituted in HEK Piezo1 KO cells. Thus, our data suggest that Piezo1 and Panx1 can form a functional signaling complex that controls force-induced ATP secretion in cholangiocytes. These findings may foster the development of novel therapeutic strategies for biliary diseases.

Mechanisms of ATP release in pain: role of pannexin and connexin channels

Pain is a physiological response to bodily damage and serves as a warning of potential threat. Pain can also transform from an acute response to noxious stimuli to a chronic condition with notable emotional and psychological components that requires treatment. Indeed, the management of chronic pain is currently an important unmet societal need. Several reports have implicated the release of the neurotransmitter adenosine triphosphate (ATP) and subsequent activation of purinergic receptors in distinct pain etiologies. Purinergic receptors are broadly expressed in peripheral neurons and the spinal cord; thus, purinergic signaling in sensory neurons or in spinal circuits may be critical for pain processing. Nevertheless, an outstanding question remains: what are the mechanisms of ATP release that initiate nociceptive signaling? Connexin and pannexin channels are established conduits of ATP release and have been suggested to play important roles in a variety of pathologies, including several models of pain. As such, these large-pore channels represent a new and exciting putative pharmacological target for pain treatment. Herein, we will review the current evidence for a role of connexin and pannexin channels in ATP release during nociceptive signaling, such as neuropathic and inflammatory pain. Collectively, these studies provide compelling evidence for an important role of connexins and pannexins in pain processing.

PANX1 is a potential prognostic biomarker associated with immune infiltration in pancreatic adenocarcinoma: A pan-cancer analysis

Pannexin 1 (PANX1) channel is a critical ATP-releasing pathway that modulates tumor immunity, progression, and prognosis. However, the roles of PANX1 in different cancers remain unclear. We analyzed the expression of PANX1 in human pan-cancer in the Oncomine and GEPIA2.0 databases. The prognostic value of PANX1 expression was determined using Kaplan-Meier plotter and OncoLnc tools. The correlation between PANX1 and tumor-infiltrating immune cells was investigated using the TIMER 2.0. In addition, the relationship between PANX1 and immunomodulators was explored using TISIDB. Finally, gene set enrichment analysis (GSEA) was performed utilizing LinkedOmics. The results indicated that PANX1 was overexpressed in most cancers compared to normal tissues. The high expression of PANX1 was associated with poor prognosis in multiple tumors, especially in pancreatic adenocarcinoma (PAAD). In addition, PANX1 was correlated with a variety of immunomodulators, such as CD274, IL10, CD276, IL2RA, TAP1, and TAP2. PANX1 expression level was significantly related to infiltration of multiple immune cells in many cancers, including cancer associated fibroblast, macrophage, and neutrophil cells. Further analysis revealed that PANX1 was significantly associated with T cells CD8+ (rho = 0.524, P = 1.94e-13) and Myeloid dendritic cell (rho = 0.564, P = 9.45e-16). GSEA results showed that PANX1 was closely associated with leukocyte cell-cell adhesion, endoplasmic reticulum lumen, ECM-receptor interaction, and Focal adhesion pathways in PAAD. PANX1 expression was higher in pan-cancer samples than in normal tissues. The high expression of PANX1 was associated with poor outcome and immune infiltration in multiple cancers, especially in PAAD.

Panx1b Modulates the Luminance Response and Direction of Locomotion in the Zebrafish

Pannexin1 (Panx1) can form ATP-permeable channels that play roles in the physiology of the visual system. In the zebrafish two ohnologs of Panx1, Panx1a and Panx1b, have unique and shared channel properties and tissue expression patterns. Panx1a channels are located in horizontal cells of the outer retina and modulate light decrement detection through an ATP/pH-dependent mechanisms and adenosine/dopamine signaling. Here, we decipher how the strategic localization of Panx1b channels in the inner retina and ganglion cell layer modulates visually evoked motor behavior. We describe a panx1b knockout model generated by TALEN technology. The RNA-seq analysis of 6 days post-fertilization larvae is confirmed by real-time PCR and paired with testing of locomotion behaviors by visual motor and optomotor response tests. We show that the loss of Panx1b channels disrupts the retinal response to an abrupt loss of illumination and it decreases the larval ability to follow leftward direction of locomotion in low light conditions. We concluded that the loss of Panx1b channels compromises the final output of luminance as well as motion detection. The Panx1b protein also emerges as a modulator of the circadian clock system. The disruption of the circadian clock system in mutants suggests that Panx1b could participate in non-image forming processes in the inner retina.

Role of Pannexin 1 ATP-Permeable Channels in the Regulation of Signaling Pathways during Skeletal Muscle Unloading

Skeletal muscle unloading results in atrophy. We hypothesized that pannexin 1 ATP-permeable channel (PANX1) is involved in the response of muscle to unloading. We tested this hypothesis by blocking PANX1, which regulates efflux of ATP from the cytoplasm. Rats were divided into six groups (eight rats each): non-treated control for 1 and 3 days of the experiments (1C and 3C, respectively), 1 and 3 days of hindlimb suspension (HS) with placebo (1H and 3H, respectively), and 1 and 3 days of HS with PANX1 inhibitor probenecid (PRB; 1HP and 3HP, respectively). When compared with 3C group there was a significant increase in ATP in soleus muscle of 3H and 3HP groups (32 and 51%, respectively, p < 0.05). When compared with 3H group, 3HP group had: (1) lower mRNA expression of E3 ligases MuRF1 and MAFbx (by 50 and 38% respectively, p < 0.05) and MYOG (by 34%, p < 0.05); (2) higher phosphorylation of p70S6k and p90RSK (by 51 and 35% respectively, p < 0.05); (3) lower levels of phosphorylated eEF2 (by 157%, p < 0.05); (4) higher level of phosphorylated GSK3β (by 189%, p < 0.05). In conclusion, PANX1 ATP-permeable channels are involved in the regulation of muscle atrophic processes by modulating expression of E3 ligases, and protein translation and elongation processes during unloading.

Targeting purinergic receptors to suppress the cytokine storm induced by SARS-CoV-2 infection in pulmonary tissue

The etiological agent of coronavirus disease (COVID-19) is the new member of the Coronaviridae family, a severe acute respiratory syndrome coronavirus 2 virus (SARS-CoV-2), responsible for the pandemic that is plaguing the world. The single-stranded RNA virus is capable of infecting the respiratory tract, by binding the spike (S) protein on its viral surface to receptors for the angiotensin II-converting enzyme (ACE2), highly expressed in the pulmonary tissue, enabling the interaction of the virus with alveolar epithelial cells promoting endocytosis and replication of viral material. The infection triggers the activation of the immune system, increased purinergic signaling, and the release of cytokines as a defense mechanism, but the response can become exaggerated and prompt the so-called “cytokine storm”, developing cases such as severe acute respiratory syndrome (SARS). This is characterized by fever, cough, and difficulty breathing, which can progress to pneumonia, failure of different organs and death. Thus, the present review aims to compile and correlate the mechanisms involved between the immune and purinergic systems with COVID-19, since the modulation of purinergic receptors, such as A2A, A2B, and P2X7 expressed by immune cells, seems to be effective as a promising therapy, to reduce the severity of the disease, as well as aid in the treatment of acute lung diseases and other cases of generalized inflammation.

The role of Pannexin-1 channels and extracellular ATP in the pathogenesis of the human immunodeficiency virus

Only recently, the role of large ionic channels such as Pannexin-1 channels and Connexin hemichannels has been implicated in several physiological and pathological conditions, including HIV infection and associated comorbidities. These channels are in a closed stage in healthy conditions, but in pathological conditions including HIV, Pannexin-1 channels and Connexin hemichannels become open. Our data demonstrate that acute and chronic HIV infection induces channel opening (Pannexin and Connexin channels), ATP release into the extracellular space, and subsequent activation of purinergic receptors in immune and non-immune cells. We demonstrated that Pannexin and Connexin channels contribute to HIV infection and replication, the long-term survival of viral reservoirs, and comorbidities such as NeuroHIV. Here, we discuss the available data to support the participation of these channels in the HIV life cycle and the potential therapeutic approach to prevent HIV-associated comorbidities.

On the molecular nature of large-pore channels

Membrane transport is a fundamental means to control basic cellular processes such as apoptosis, inflammation, and neurodegeneration and is mediated by a number of transporters, pumps, and channels. Accumulating evidence over the last half century has shown that a type of so-called "large-pore channel" exists in various tissues and organs in gap-junctional and non-gap-junctional forms in order to flow not only ions but also metabolites such as ATP. They are formed by a number of protein families with little or no evolutionary linkages including connexin, innexin, pannexin, leucine-rich repeat-containing 8 (LRRC8), and calcium homeostasis modulator (CALHM). This review summarizes the history and concept of large-pore channels starting from connexin gap junction channels to the more recent developments in innexin, pannexin, LRRC8, and CALHM. We describe structural and functional features of large-pore channels that are crucial for their diverse functions on the basis of available structures.

Human digital merkel cells display pannexin1 immunoreactivity

Pannexins are channel proteins displaying functional similarities to gap junctions in vertebrates and are regarded as transmembrane ATP-releasing channels. A member of this family, denominate pannexin1, has been detected in the epidermis and cutaneous adnexal structures. Here we used immunohistochemistry to investigate whether human digital Merkel cells express this protein since ATP is postulated as a neurotransmitter in the Merkel cell-axon complexes low-threshold mecahoreceptors. Pannexin1 immunoreactivity was found in cytokeratine 20-, chromogranin A- and synaptophysin-positive cells placed at the basal layer of the epidermis. Cell displaying pannexin1 immunoreactivities were thus identified as Merkel cells and showed close contact with nerve profiles. Light pannexin1 immunoreactivity in dermal blood vessels was also verified. Present results demonstrate for the first time the expression of pannexin1 in human digital Merkel cells supporting the idea that ATP can be involved directly or indirectly in the mechanotransductional process at Merkel-axon complexes.

The Cough Reflex: The Janus of Respiratory Medicine

In clinical practice, we commonly face adversity when encountering dysfunction of the cough reflex. Similar to ancient Roman deity Janus, it often presents with one of two opposing "faces". Continual aberrant activation of the cough reflex, also known as chronic cough, can cause great detriment to quality of life and many of these patients are left misdiagnosed and undertreated. In contrast, loss of normal functioning of the cough reflex is the cause of a significant proportion of mortality in the elderly, primarily through the development of aspiration pneumonia. In this review we discuss both hyper- and hypo-activation of the cough reflex and how airway reflux and chronic aspiration may be involved in the aetiology and sequalae of both disease states. We detail the physiological and pharmacological mechanisms involved in cough, and how the recent development of P2X3 receptor antagonists may lead to the first pharmaceutical agent licensed for chronic cough. The treatment and prevention of loss of the cough reflex, which has been largely neglected, is also discussed as novel low-cost interventions could help prevent a number of hospital and domiciliary deaths from both acute and chronic aspiration.

Altered Expression of Ion Channels in White Matter Lesions of Progressive Multiple Sclerosis: What Do We Know About Their Function?

Despite significant advances in our understanding of the pathophysiology of multiple sclerosis (MS), knowledge about contribution of individual ion channels to axonal impairment and remyelination failure in progressive MS remains incomplete. Ion channel families play a fundamental role in maintaining white matter (WM) integrity and in regulating WM activities in axons, interstitial neurons, glia, and vascular cells. Recently, transcriptomic studies have considerably increased insight into the gene expression changes that occur in diverse WM lesions and the gene expression fingerprint of specific WM cells associated with secondary progressive MS. Here, we review the ion channel genes encoding K⁺, Ca²⁺, Na⁺, and Cl^- channels; ryanodine receptors; TRP channels; and others that are significantly and uniquely dysregulated in active, chronic active, inactive, remyelinating WM lesions, and normal-appearing WM of secondary progressive MS brain, based on recently published bulk and single-nuclei RNA-sequencing datasets. We discuss the current state of knowledge about the corresponding ion channels and their implication in the MS brain or in experimental models of MS. This comprehensive review suggests that the intense upregulation of voltage-gated Na⁺ channel genes in WM lesions with ongoing tissue damage may reflect the imbalance of Na⁺ homeostasis that is observed in progressive MS brain, while the upregulation of a large number of voltage-gated K⁺ channel genes may be linked to a protective response to limit neuronal excitability. In addition, the altered chloride homeostasis, revealed by the significant downregulation of voltage-gated Cl^- channels in MS lesions, may contribute to an altered inhibitory neurotransmission and increased excitability.

Purinergic signaling: a new front-line determinant of resistance and susceptibility in leishmaniasis

Leishmaniasis is a neglected tropical disease that causes several clinical manifestations. Parasites of the genus Leishmania cause this disease. Spread across five continents, leishmaniasis is a particular public health problem in developing countries. Leishmania infects phagocytic cells such as macrophages, where it induces adenosine triphosphate (ATP) release at the time of infection. ATP activates purinergic receptors in the cell membranes of infected cells and promotes parasite control by inducing leukotriene B4 release and NLRP3 inflammasome activation. Moreover, uridine triphosphate induces ATP release, exacerbating the immune response. However, ATP may also undergo catalysis by ectonucleotidases present in the parasite membrane, generating adenosine, which activates P1 receptors and induces the production of anti-inflammatory molecules such as prostaglandin E2 and IL-10. These mechanisms culminate in Leishmania's survival. Thus, how Leishmania handles extracellular nucleotides and the activation of purinergic receptors determines the control or the dissemination of the disease.

ATP and cancer immunosurveillance

While intracellular adenosine triphosphate (ATP) occupies a key position in the bioenergetic metabolism of all the cellular compartments that form the tumor microenvironment (TME), extracellular ATP operates as a potent signal transducer. The net effects of purinergic signaling on the biology of the TME depend not only on the specific receptors and cell types involved, but also on the activation status of cis- and trans-regulatory circuitries. As an additional layer of complexity, extracellular ATP is rapidly catabolized by ectonucleotidases, culminating in the accumulation of metabolites that mediate distinct biological effects. Here, we discuss the molecular and cellular mechanisms through which ATP and its degradation products influence cancer immunosurveillance, with a focus on therapeutically targetable circuitries.