Purine and purinergic receptors

P2Y1 receptor in Alzheimer's disease

Alzheimer's disease is the most frequent form of dementia characterized by the deposition of amyloid-beta plaques and neurofibrillary tangles consisting of hyperphosphorylated tau. Targeting amyloid-beta plaques has been a primary direction for developing Alzheimer's disease treatments in the last decades. However, existing drugs targeting amyloid-beta plaques have not fully yielded the expected results in the clinic, necessitating the exploration of alternative therapeutic strategies. Increasing evidence unravels that astrocyte morphology and function alter in the brain of Alzheimer's disease patients, with dysregulated astrocytic purinergic receptors, particularly the P2Y1 receptor, all of which constitute the pathophysiology of Alzheimer's disease. These receptors are not only crucial for maintaining normal astrocyte function but are also highly implicated in neuroinflammation in Alzheimer's disease. This review delves into recent insights into the association between P2Y1 receptor and Alzheimer's disease to underscore the potential neuroprotective role of P2Y1 receptor in Alzheimer's disease by mitigating neuroinflammation, thus offering promising avenues for developing drugs for Alzheimer's disease and potentially contributing to the development of more effective treatments.

Microglial P2Y6 calcium signaling promotes phagocytosis and shapes neuroimmune responses in epileptogenesis

Microglial calcium signaling is rare in a baseline state but strongly engaged during early epilepsy development. The mechanism(s) governing microglial calcium signaling are not known. By developing an in vivo uridine diphosphate (UDP) fluorescent sensor, GRABUDP1.0, we discovered that UDP release is a conserved response to seizures and excitotoxicity across brain regions. UDP can signal through the microglial-enriched P2Y6 receptor to increase calcium activity during epileptogenesis. P2Y6 calcium activity is associated with lysosome biogenesis and enhanced production of NF-κB-related cytokines. In the hippocampus, knockout of the P2Y6 receptor prevents microglia from fully engulfing neurons. Attenuating microglial calcium signaling through calcium extruder ("CalEx") expression recapitulates multiple features of P2Y6 knockout, including reduced lysosome biogenesis and phagocytic interactions. Ultimately, P2Y6 knockout mice retain more CA3 neurons and better cognitive task performance during epileptogenesis. Our results demonstrate that P2Y6 signaling impacts multiple aspects of myeloid cell immune function during epileptogenesis.

Ablation of the dystrophin Dp71f alternative C-terminal variant increases sarcoma tumour cell aggressiveness

Alterations in Dp71 expression, the most ubiquitous dystrophin isoform, have been associated with patient survival across tumours. Intriguingly, in certain malignancies, Dp71 acts as a tumour suppressor, while manifesting oncogenic properties in others. This diversity could be explained by the expression of two Dp71 splice variants encoding proteins with distinct C-termini, each with specific properties. Expression of these variants has impeded the exploration of their unique roles. Using CRISPR/Cas9, we ablated the Dp71f variant with the alternative C-terminus in a sarcoma cell line not expressing the canonical C-terminal variant, and conducted molecular (RNAseq) and functional characterisation of the knockout cells. Dp71f ablation induced major transcriptomic alterations, particularly affecting the expression of genes involved in calcium signalling and ECM-receptor interaction pathways. The genome-scale metabolic analysis identified significant downregulation of glucose transport via membrane vesicle reaction (GLCter) and downregulated glycolysis/gluconeogenesis pathway. Functionally, these molecular changes corresponded with, increased calcium responses, cell adhesion, proliferation, survival under serum starvation and chemotherapeutic resistance. Knockout cells showed reduced GLUT1 protein expression, survival without attachment and their migration and invasion in vitro and in vivo were unaltered, despite increased matrix metalloproteinases release. Our findings emphasise the importance of alternative splicing of dystrophin transcripts and underscore the role of the Dp71f variant, which appears to govern distinct cellular processes frequently dysregulated in tumour cells. The loss of this regulatory mechanism promotes sarcoma cell survival and treatment resistance. Thus, Dp71f is a target for future investigations exploring the intricate functions of specific DMD transcripts in physiology and across malignancies.

ERNEST COST action overview on the (patho)physiology of GPCRs and orphan GPCRs in the nervous system

G protein-coupled receptors (GPCRs) are a large family of cell surface receptors that play a critical role in nervous system function by transmitting signals between cells and their environment. They are involved in many, if not all, nervous system processes, and their dysfunction has been linked to various neurological disorders representing important drug targets. This overview emphasises the GPCRs of the nervous system, which are the research focus of the members of ERNEST COST action (CA18133) working group 'Biological roles of signal transduction'. First, the (patho)physiological role of the nervous system GPCRs in the modulation of synapse function is discussed. We then debate the (patho)physiology and pharmacology of opioid, acetylcholine, chemokine, melatonin and adhesion GPCRs in the nervous system. Finally, we address the orphan GPCRs, their implication in the nervous system function and disease, and the challenges that need to be addressed to deorphanize them.

Role of microglia in stroke

Microglia play key roles in the post-ischemic inflammatory response and damaged tissue removal reacting rapidly to the disturbances caused by ischemia and working to restore the lost homeostasis. However, the modified environment, encompassing ionic imbalances, disruption of crucial neuron-microglia interactions, spreading depolarization, and generation of danger signals from necrotic neurons, induce morphological and phenotypic shifts in microglia. This leads them to adopt a proinflammatory profile and heighten their phagocytic activity. From day three post-ischemia, macrophages infiltrate the necrotic core while microglia amass at the periphery. Further, inflammation prompts a metabolic shift favoring glycolysis, the pentose-phosphate shunt, and lipid synthesis. These shifts, combined with phagocytic lipid intake, drive lipid droplet biogenesis, fuel anabolism, and enable microglia proliferation. Proliferating microglia release trophic factors contributing to protection and repair. However, some microglia accumulate lipids persistently and transform into dysfunctional and potentially harmful foam cells. Studies also showed microglia that either display impaired apoptotic cell clearance, or eliminate synapses, viable neurons, or endothelial cells. Yet, it will be essential to elucidate the viability of engulfed cells, the features of the local environment, the extent of tissue damage, and the temporal sequence. Ischemia provides a rich variety of region- and injury-dependent stimuli for microglia, evolving with time and generating distinct microglia phenotypes including those exhibiting proinflammatory or dysfunctional traits and others showing pro-repair features. Accurate profiling of microglia phenotypes, alongside with a more precise understanding of the associated post-ischemic tissue conditions, is a necessary step to serve as the potential foundation for focused interventions in human stroke.

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

ABSTRACT

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

A Prospective Study Investigating Immune Checkpoint Molecule and CD39 Expression on Peripheral Blood Cells for the Prognostication of COVID-19 Severity and Mortality

In patients with COVID-19, broad panels of immune checkpoint molecules (ICPMs) and the purinergic signaling have not been studied in parallel. We aimed to perform in-depth immunophenotyping of major cell subsets present in human peripheral blood of COVID-19 patients and controls using PD1, TIM3, LAG3, TIGIT, and CD200R, as well as CD39, as markers for the purinergic signaling pathway. We studied 76 COVID-19 patients and 12 healthy controls using peripheral blood mononuclear cells on flow cytometry. Univariable and multivariable statistics were performed. All ICPMs studied were significantly overexpressed on different cell subsets of COVID-19 patients when compared with healthy controls. Elevated lactate dehydrogenase; C-reactive protein; age; and high expression of CD45+, CD39+CD45+, TIM3+CD39+CD4+CD45+, and TIM3+CD39+CD8+CD3+CD4+ cells were significantly associated with severe COVID-19. On multivariable analysis, however, only high expression of CD39+CD45+ (OR 51.4, 95% CI 1.5 to 1763) and TIM3+CD39+CD4+CD3+CD45+ (OR 22.6, 95% CI 1.8 to 277) cells was an independent predictor for severe COVID-19. In conclusion, numerous ICPMs are overexpressed in COVID-19 patients when compared with healthy controls, suggesting a pathophysiological role of these molecules in SARS-CoV-2 infection. However, only TIM3 in co-expression with CD39 remained as a significant independent prognostic ICPM on multivariable analysis. The flow cytometric evaluation of TIM3+CD39+CD4+CD3+CD45+, as well as CD39+CD45+, is a powerful tool for the prognostication of COVID-19 patients on hospital admission.

Cytokine storm in human monkeypox: A possible involvement of purinergic signaling

Some evidence has indicated that monkeypox can induce a cytokine storm. Purinergic signaling is a cell pathway related to the cytokine storm. However, the precise mechanisms that lead to cytokine storms in monkeypox infections and the possible involvement of purinergic signaling in the immune response to this virus remain unknown. In this review article, we aimed to highlight a body of scientific evidence that consolidates the role of the cytokine storm in monkeypox infection and proposes a new hypothesis regarding the roles of purinergic signaling in this immune-mediated mechanism. We further suggested some purinergic signaling modulators to mitigate the deleterious and aggravating effects of immune dysregulation in human monkeypox virus infection by inhibiting P2X3, P2X7, P2Y2, and P2Y12, reducing inflammation, and activating A1 and A2A receptors to promote an anti-inflammatory response.

P2X7 receptor knockout does not alter renal function or prevent angiotensin II-induced kidney injury in F344 rats

P2X7 receptors mediate immune and endothelial cell responses to extracellular ATP. Acute pharmacological blockade increases renal blood flow and filtration rate, suggesting that receptor activation promotes tonic vasoconstriction. P2X7 expression is increased in kidney disease and blockade/knockout is renoprotective. We generated a P2X7 knockout rat on F344 background, hypothesising enhanced renal blood flow and protection from angiotensin-II-induced renal injury. CRISPR/Cas9 introduced an early stop codon into exon 2 of P2rx7, abolishing P2X7 protein in kidney and reducing P2rx7 mRNA abundance by ~ 60% in bone-marrow derived macrophages. The M1 polarisation response to lipopolysaccharide was unaffected but P2X7 receptor knockout suppressed ATP-induced IL-1β release. In male knockout rats, acetylcholine-induced dilation of the renal artery ex vivo was diminished but not the response to nitroprusside. Renal function in male and female knockout rats was not different from wild-type. Finally, in male rats infused with angiotensin-II for 6 weeks, P2X7 knockout did not reduce albuminuria, tubular injury, renal macrophage accrual, and renal perivascular fibrosis. Contrary to our hypothesis, global P2X7 knockout had no impact on in vivo renal hemodynamics. Our study does not indicate a major role for P2X7 receptor activation in renal vascular injury.

Testosterone Enhances KV Currents and Airway Smooth Muscle Relaxation Induced by ATP and UTP through P2Y4 Receptors and Adenylyl Cyclase Pathway

Numerous studies suggest the involvement of adenosine-5'-triphosphate (ATP) and similar nucleotides in the pathophysiology of asthma. Androgens, such as testosterone (TES), are proposed to alleviate asthma symptoms in young men. ATP and uridine-5'-triphosphate (UTP) relax the airway smooth muscle (ASM) via purinergic P2Y2 and P2Y4 receptors and K+ channel opening. We previously demonstrated that TES increased the expression of voltage-dependent K+ (KV) channels in ASM. This study investigates how TES may potentiate ASM relaxation induced by ATP and UTP. Tracheal tissues treated with or without TES (control group) from young male guinea pigs were used. In organ baths, tracheas exposed to TES (40 nM for 48 h) showed enhanced ATP- and UTP-evoked relaxation. Tetraethylammonium, a K+ channel blocker, annulled this effect. Patch-clamp experiments in tracheal myocytes showed that TES also increased ATP- and UTP-induced K+ currents, and this effect was abolished with flutamide (an androgen receptor antagonist). KV channels were involved in this phenomenon, which was demonstrated by inhibition with 4-aminopyridine. RB2 (an antagonist of almost all P2Y receptors except for P2Y2), as well as N-ethylmaleimide and SQ 22,536 (inhibitors of G proteins and adenylyl cyclase, respectively), attenuated the enhancement of the K+ currents induced by TES. Immunofluorescence and immunohistochemistry studies revealed that TES did not modify the expression of P2Y4 receptors or COX-1 and COX-2, while we have demonstrated that this androgen augmented the expression of KV1.2 and KV1.5 channels in ASM. Thus, TES leads to the upregulation of P2Y4 signaling and KV channels in guinea pig ASM, enhancing ATP and UTP relaxation responses, which likely limits the severity of bronchospasm in young males.

P2X7 regulates ependymo-radial glial cell proliferation in adult Danio rerio following spinal cord injury

In contrast to mammals, zebrafish undergo successful neural regeneration following spinal cord injury. Spinal cord ependymo-radial glia (ERG) undergo injury-induced proliferation and neuronal differentiation to replace damaged cells and restore motor function. However, the molecular cues driving these processes remain elusive. Here, we demonstrate that the evolutionarily conserved P2X7 receptors are widely distributed on neurons and ERG within the zebrafish spinal cord. At the protein level, the P2X7 receptor expressed in zebrafish is a truncated splice variant of the full-length variant found in mammals. The protein expression of this 50 kDa isoform was significantly downregulated at 7 days post-injury (dpi) but returned to basal levels at 14 dpi when compared to naïve controls. Pharmacological activation of P2X7 following SCI resulted in a greater number of proliferating cells around the central canal by 7 dpi but did not affect neuronal differentiation at 14 dpi. Our findings suggest that unlike in mammals, P2X7 signaling may not play a maladaptive role following SCI in adult zebrafish and may also work to curb the proliferative response of ERG following injury.

P2X7 receptor-dependent increase in endocannabinoid 2-arachidonoyl glycerol production by neuronal cells in culture: Dynamics and mechanism

BACKGROUND AND PURPOSE

Neurotransmission and neuroinflammation are controlled by local increases in both extracellular ATP and the endocannabinoid 2-arachidonoyl glycerol (2-AG). While it is known that extracellular ATP stimulates 2-AG production in cells in culture, the dynamics and molecular mechanisms that underlie this response remain poorly understood. Detection of real-time changes in eCB levels with the genetically encoded sensor, GRABeCB2.0, can address this shortfall.

EXPERIMENTAL APPROACH

2-AG and arachidonoylethanolamide (AEA) levels in Neuro2a (N2a) cells were measured by LC-MS, and GRABeCB2.0 fluorescence changes were detected using live-cell confocal microscopy and a 96-well fluorescence plate reader.

KEY RESULTS

2-AG and AEA increased GRABeCB2.0 fluorescence in N2a cells with EC50 values of 81 and 58 nM, respectively; both responses were reduced by the cannabinoid receptor type 1 (CB1R) antagonist SR141617 and absent in cells expressing the mutant-GRABeCB2.0. ATP increased only 2-AG levels in N2a cells, as measured by LC-MS, and induced a transient increase in the GRABeCB2.0 signal within minutes primarily via activation of P2X7 receptors (P2X7R). This response was dependent on diacylglycerol lipase β activity, partially dependent on extracellular calcium and phospholipase C activity, but not controlled by the 2-AG hydrolysing enzyme, α/β-hydrolase domain containing 6 (ABHD6).

CONCLUSIONS AND IMPLICATIONS

Considering that P2X7R activation increases 2-AG levels within minutes, our results show how these molecular components are mechanistically linked. The specific molecular components in these signalling systems represent potential therapeutic targets for the treatment of neurological diseases, such as chronic pain, that involve dysregulated neurotransmission and neuroinflammation.

Is there a biochemical basis for purinergic P2X3 and P2X4 receptor antagonists to be considered as anti-seizure medications?

Patients with epilepsy require improved medications. Purinergic receptors were identified as late as 1976 and are slowly emerging as potential drug targets for the discovery of antiseizure medications. While compounds interacting with these receptors have been approved for use as medicines (e.g., gefapixant for cough) and continue to be explored for a number of diseases (e.g., pain, cancer), there have been no purinergic receptor antagonists that have been advanced for epilepsy. There are very few studies on the channel conducting receptors, P2X3 and P2X4, that suggest their possible role in seizure generation or control. However, the limited data available provides some compelling reasons to believe that they could be valuable antiseizure medication drug targets. The data implicating P2X3 and P2X4 receptors in epilepsy includes the role played by ATP in neuronal excitability and seizures, receptor localization, increased receptor expression in epileptic brain, the involvement of these receptors in seizure-associated inflammation, crosstalk between these purinergic receptors and neuronal processes involved in seizures (GABAergic and glutamatergic neurotransmission), and the significant attenuation of seizures and seizure-like activity with P2X receptor blockade. The discovery of new and selective antagonists for P2X3 and P2X4 receptors is ongoing, armed with new structural data to guide rational design. The availability of safe, brain-penetrant compounds will likely encourage the clinical exploration of epilepsy as a disease entity.

Purinergic ligands induce extracellular acidification and increased ATP turnover in HepG2 cells

Nucleosides and nucleotides at μM concentrations stimulated a 300% increase in acid secretion in HepG2 cells, which was quantitatively accounted for as increased export of lactate generated by glycogenolysis. Agonist selectivity encompassed nucleosides and nucleotides for all 5 natural nucleobases and, along with antagonist profiles, was inconsistent with a role for purinergic receptors in mediating this activity. Agonist catabolism did not contribute significantly to either low selectivity or lactate production. Lactate production was driven by an increase in ATP turnover of as much as 56%. For some agonists, especially adenosine, ATP turnover decreased precipitously at mM concentrations, correlating with known adenosine-stimulated apoptosis. We propose that nucleoside/nucleotide agonists induce a futile energy cycle via a novel mechanism, which results in increased ATP turnover and initiates a continuum of events that for some agonists culminates in apoptosis.

G protein-coupled receptor-mediated autophagy in health and disease

G protein-coupled receptors (GPCRs) constitute the largest and most diverse superfamily of mammalian transmembrane proteins. These receptors are involved in a wide range of physiological functions and are targets for more than a third of available drugs in the market. Autophagy is a cellular process involved in degrading damaged proteins and organelles and in recycling cellular components. Deficiencies in autophagy are involved in a variety of pathological conditions. Both GPCRs and autophagy are essential in preserving homeostasis and cell survival. There is emerging evidence suggesting that GPCRs are direct regulators of autophagy. Additionally, autophagic machinery is involved in the regulation of GPCR signalling. The interplay between GPCR and autophagic signalling mechanisms significantly impacts on health and disease; however, there is still an incomplete understanding of the underlying mechanisms and therapeutic implications in different tissues and disease contexts. This review aims to discuss the interactions between GPCR and autophagy signalling. Studies on muscarinic receptors, beta-adrenoceptors, taste receptors, purinergic receptors and adhesion GPCRs are summarized, in relation to autophagy.

Implications of COVID-19 in Parkinson's disease: the purinergic system in a therapeutic-target perspective to diminish neurodegeneration

The pathophysiology of Parkinson's disease (PD) is marked by degeneration of dopaminergic neurons in the substantia nigra. With advent of COVID-19, which is closely associated with generalized inflammation and multiple organ dysfunctions, the PD patients may develop severe conditions of disease leading to exacerbated degeneration. This condition is caused by the excessive release of pro-inflammatory markers, called cytokine storm, that is capable of triggering neurodegenerative conditions by affecting the blood-brain barrier (BBB). A possible SARS-CoV-2 infection, in serious cases, may compromise the immune system by triggering a hyperstimulation of the neuroimmune response, similar to the pathological processes found in PD. From this perspective, the inflammatory scenario triggers oxidative stress and, consequently, cellular dysfunction in the nervous tissue. The P2X7R seems to be the key mediator of the neuroinflammatory process, as it acts by increasing the concentration of ATP, allowing the influx of Ca2+ and the occurrence of mutations in the α-synuclein protein, causing activation of this receptor. Thus, modulation of the purinergic system may have therapeutic potential on the effects of PD, as well as on the damage caused by inflammation of the BBB, which may be able to mitigate the neurodegeneration caused by diseases. Considering all the processes of neuroinflammation, oxidative stress, and mitochondrial dysfunction that PD propose, we can conclude that the P2X7 antagonist acts in the prevention of viral diseases, and it also controls purinergic receptors formed by multi-target compounds directed to self-amplification circuits and, therefore, may be a viable strategy to obtain the desired disease-modifying effect. Thus, purinergic system receptor modulations have a high therapeutic potential for neurodegenerative diseases such as PD.

Extracellular adenosine triphosphate regulates inflammatory responses of periodontal ligament cells

BACKGROUND

Various stimuli, that is, mechanical stresses or inflammation, induce the release of adenosine triphosphate (ATP) by human periodontal ligament cells (HPDLCs). Extracellular adenosine triphosphate (eATP) affects HPDLCs' functions such as immunosuppressive action and inflammatory responses. Lipopolysaccharide (LPS) is the key factor involved in periodontal inflammation. However, the possible correlation and detailed mechanism of inflammation-mediated eATP by LPS and inflammatory cascade formation in HPDLCs is unclarified. This study aims to examine the role of eATP on the HPDLCs' responses concerning inflammatory actions after LPS treatment.

METHODS

HPDLCs were stimulated with Porphyromonas gingivalis LPS and polyinosinic:polycytidylic acid (poly I:C). The amount of ATP release was measured at different time points using a bioluminescence assay. HPDLCs were treated with eATP. The expression of pro-inflammatory and anti-inflammatory genes was determined. Specific P2X purinoreceptor 7 (P2X7) inhibitors (brilliant blue G [BBG] and KN62), a specific P2Y purinoreceptor 1 (P2Y1) inhibitors (MRS2179), calcium chelator (EGTA), protein kinase C (PKC) inhibitors, nuclear factor kappa-light-chain-enhancer of activated B cells (NF𝜅B) activation inhibitors, and cyclic adenosine monophosphate (cAMP)-dependent protein kinase A (PKA) inhibitors (H89 dihydrochloride) and activators (forskolin) were used to dissect the mechanism of eATP-induced HPDLCs' inflammatory responses.

RESULTS

LPS and poly I:C induced ATP release. A low concentration of eATP (50 µM) increased pro-inflammatory genes (COX2, IL1B, IL6, IL8, IL12, and TNFA), while a high concentration (500 µM) enhanced anti-inflammatory genes (IL4 and IL10). BBG, KN62, and NF𝜅B activation inhibitors impeded eATP-induced pro-inflammatory genes. MRS2179 and H89 markedly suppressed eATP-induced anti-inflammatory genes. Forskolin induced IL4 and IL10.

CONCLUSION

HPDLCs respond to LPS by releasing ATP. eATP has dose-dependent dual functions on HPDLCs' inflammatory responses via different pathways. As regulation of inflammation is important in regeneration, eATP may help to limit inflammation and trigger periodontal regeneration.

Therapeutic Effects of AF219 on Interstitial Cystitis/Bladder Pain Syndrome Induced by Cyclophosphamide or Water Avoidance Stress in Rats

INTRODUCTION AND HYPOTHESIS

To evaluate the effect of AF219, a P2X3 receptor antagonist, in animal models of interstitial cystitis/bladder pain syndrome (IC/BPS) induced by cyclophosphamide (CYP) or water avoidance stress (WAS).

METHODS

Thirty-two adult female Wistar albino rats were used in each IC/BPS model. Assessment of nociception and anxiety and severity of inflammation in the bladder were assessed by behavioral experiments and histopathological examinations respectively. The contraction responses of the bladder were evaluated in vitro and protein levels of P2X3, P2X7, Trk-A, TRPV1, and TRPA1 were analyzed by Western blot.

RESULTS

The IC/BPS groups had shorter response times to noxious stimuli, exhibited more anxiety-like behavior, had higher inflammation-based histological scores, and showed greater increased contraction responses to carbachol, adenosine triphosphate, and electrical field stimulation in in vitro bladder strips than controls for both models (p < 0.05). The improvements in behavioral and bladder contraction responses and inflammation scores in the IC/BPS + AF219 groups were similar to control findings (p > 0.05). Exposure to WAS or CYP increased P2X3 expression in the bladder compared with the controls (p < 0.05). Apart from TRPA1, the levels of P2X7, Trk-A, and TRPV1 were also higher in the IC/BPS groups than in the controls (p < 0.05). No significant differences were observed between IC/BPS + AF219 and controls regarding P2X3, P2X7, Trk-A, and TRPV1 in the WAS model (p > 0.05). Moreover, P2X3 and P2X7 levels were significantly lower in IC/BPS + AF219 than in the AF219-untreated WAS model (p < 0.05).

CONCLUSIONS

These findings suggest that P2X3 receptors play a significant role in bladder functional responses, nociception, and also the pathogenesis of IC/BPS. AF219 may be a promising therapeutic strategy for IC/BPS. Comparing AF219 with current IC/BPS treatment agents in future studies may yield valuable insights into its efficacy.

Comorbidity Genes of Alzheimer's Disease and Type 2 Diabetes Associated with Memory and Cognitive Function

Alzheimer's disease (AD) and type 2 diabetes mellitus (T2DM) are comorbidities that result from the sharing of common genes. The molecular background of comorbidities can provide clues for the development of treatment and management strategies. Here, the common genes involved in the development of the two diseases and in memory and cognitive function are reviewed. Network clustering based on protein-protein interaction network identified tightly connected gene clusters that have an impact on memory and cognition among the comorbidity genes of AD and T2DM. Genes with functional implications were intensively reviewed and relevant evidence summarized. Gene information will be useful in the discovery of biomarkers and the identification of tentative therapeutic targets for AD and T2DM.

Fetal bovine serum contains biologically available ATP

ATP is a ubiquitous extracellular messenger released in a wide number of pathophysiological conditions. ATP is known to be present in minute amounts in the extracellular space in healthy tissues and in the blood, and to modulate a multiplicity of cell responses. Cell culture systems are widely used to explore purinergic signaling. We show here that currently used fetal bovine sera contain ATP in the 300-1300 pmol/L range. Serum ATP is associated with albumin as well as with microparticle/microvesicle fraction. Serum microparticles/microvesicles affect in vitro cell responses due to their content of miRNAs, growth factors, and other bioactive molecules. ATP is likely to be one of these bioactive factors found in a variable amount in sera of different commercial sources. ATP in serum supports ATP-dependent biochemical reactions such as the hexokinase-dependent phosphorylation of glucose to glucose 6-phosphate, and affects purinergic signaling. These findings show that cells growing in vitro in serum-supplemented media are exposed to varying levels of extracellular ATP, and thus to varying degrees of purinergic stimulation.

Extracellular nucleotides in smooth muscle contraction

Extracellular nucleotides and nucleosides are crucial signalling molecules, eliciting diverse biological responses in almost all organs and tissues. These molecules exert their effects by activating specific nucleotide receptors, which are finely regulated by ectonucleotidases that break down their ligands. In this comprehensive review, we aim to elucidate the relevance of extracellular nucleotides as signalling molecules in the context of smooth muscle contraction, considering the modulatory influence of ectonucleotidases on this intricate process. Specifically, we provide a detailed examination of the involvement of extracellular nucleotides in the contraction of non-vascular smooth muscles, including those found in the urinary bladder, the airways, the reproductive system, and the gastrointestinal tract. Furthermore, we present a broader overview of the role of extracellular nucleotides in vascular smooth muscle contraction.

The potential value of the Purinergic pathway in the prognostic assessment and clinical application of kidney renal clear cell carcinoma

The Purinergic pathway is involved in a variety of important physiological processes in living organisms, and previous studies have shown that aberrant expression of the Purinergic pathway may contribute to the development of a variety of cancers, including kidney renal clear cell carcinoma (KIRC). The aim of this study was to delve into the Purinergic pathway in KIRC and to investigate its potential significance in prognostic assessment and clinical treatment. 33 genes associated with the Purinergic pathway were selected for pan-cancer analysis. Cluster analysis, targeted drug sensitivity analysis and immune cell infiltration analysis were applied to explore the mechanism of Purinergic pathway in KIRC. Using the machine learning process, we found that combining the Lasso+survivalSVM algorithm worked well for predicting survival accuracy in KIRC. We used LASSO regression to pinpoint nine Purinergic genes closely linked to KIRC, using them to create a survival model for KIRC. ROC survival curve was analyzed, and this survival model could effectively predict the survival rate of KIRC patients in the next 5, 7 and 10 years. Further univariate and multivariate Cox regression analyses revealed that age, grading, staging, and risk scores of KIRC patients were significantly associated with their prognostic survival and were identified as independent risk factors for prognosis. The nomogram tool developed through this study can help physicians accurately assess patient prognosis and provide guidance for developing treatment plans. The results of this study may bring new ideas for optimizing the prognostic assessment and therapeutic approaches for KIRC patients.

Molecular mechanisms of cholinergic neurotransmission in visceral smooth muscles with a focus on receptor-operated TRPC4 channel and impairment of gastrointestinal motility by general anaesthetics and anxiolytics

Acetylcholine is the primary excitatory neurotransmitter in visceral smooth muscles, wherein it binds to and activates two muscarinic receptors subtypes, M2 and M3, thus causing smooth muscle excitation and contraction. The first part of this review focuses on the types of cells involved in cholinergic neurotransmission and on the molecular mechanisms underlying acetylcholine-induced membrane depolarisation, which is the central event of excitation-contraction coupling causing Ca2+ entry via L-type Ca2+ channels and smooth muscle contraction. Studies of the muscarinic cation current in intestinal myocytes (mICAT) revealed its main molecular counterpart, receptor-operated TRPC4 channel, which is activated in synergy by both M2 and M3 receptors. M3 receptors activation is of permissive nature, while activation of M2 receptors via Gi/o proteins that are coupled to them plays a direct role in TRPC4 opening. Our understanding of signalling pathways underlying mICAT generation has vastly expanded in recent years through studies of TRPC4 gating in native cells and its regulation in heterologous cells. Recent studies using muscarinic receptor knockout have established that at low agonist concentration activation of both M2 receptor and the M2/M3 receptor complex elicits smooth muscle contraction, while at high agonist concentration M3 receptor function becomes dominant. Based on this knowledge, in the second part of this review we discuss the cellular and molecular mechanisms underlying the numerous anticholinergic effects on neuroactive drugs, in particular general anaesthetics and anxiolytics, which can significantly impair gastrointestinal motility. This article is part of the Special Issue on "Ukrainian Neuroscience".

Inosine: novel activator of brown adipose tissue and energy homeostasis

Extracellular purinergic molecules act as signaling molecules that bind to cellular receptors and regulate signaling pathways. Growing evidence suggests that purines regulate adipocyte function and whole-body metabolism. Here, we focus on one specific purine: inosine. Brown adipocytes, which are important regulators of whole-body energy expenditure (EE), release inosine when they are stressed or become apoptotic. Unexpectedly, inosine activates EE in neighboring brown adipocytes and enhances differentiation of brown preadipocytes. Increasing extracellular inosine, either directly by increasing inosine intake or indirectly via pharmacological inhibition of cellular inosine transporters, increases whole-body EE and counteracts obesity. Thus, inosine and other closely related purines might be a novel approach to tackle obesity and associated metabolic disorders by enhancing EE.

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.

Computational prediction and in vitro analysis of the potential ligand binding site within the extracellular ATP receptor, P2K2

The plant extracellular ATP (eATP) receptor, P2K2, binds eATP with strong ligand affinity through its extracellular lectin domain. Ligand binding activates the intracellular kinase domain of P2K2 resulting in a variety of intracellular responses and, ultimately, increased plant immunity to invading fungal and bacterial pathogens. Here, using a computational prediction approach, we developed a tertiary structure model of the P2K2 extracellular lectin domain. In silico target docking of ATP to the P2K2-binding site predicted interaction with several residues through hydrophobic interactions and hydrogen bonding. Our confirmation of the modeling was obtained by showing that H99, R144, and S256 are key residues essential for in vitro binding of ATP by P2K2.

Aberrations in Cell Signaling Quantified in Diabetic Murine Globes after Injury

The corneal epithelium is an avascular structure that has a unique wound healing mechanism, which allows for rapid wound closure without compromising vision. This wound healing mechanism is attenuated in diabetic patients, resulting in poor clinical outcomes and recurrent non-healing erosion. We investigated changes in cellular calcium signaling activity during the wound response in murine diabetic tissue using live cell imaging from both ex vivo and in vitro models. The calcium signaling propagation in diabetic cells was significantly decreased and displayed altered patterns compared to non-diabetic controls. Diabetic cells and tissue display distinct expression of the purinergic receptor, P2X7, which mediates the wound healing response. We speculate that alterations in P2X7 expression, interactions with other proteins, and calcium signaling activity significantly impact the wound healing response. This may explain aberrations in the diabetic wound response.

Co-exposure to cadmium and microplastics promotes liver fibrosis through the hemichannels -ATP-P2X7 pathway

Microplastics (MPs) and cadmium (Cd) are important environmental pollutants, that damage the liver. However, the effect and mechanism of combined Cd and MPs exposure on liver fibrosis are still largely unknown. In this study investigated, Cd + MPs exposure increased superoxide anion production and promoted extracellular ATP release compared with exposure to Cd or MPs individually. Cd + MPs increased inflammatory cell infiltration, activated the P2X7-NLRP3 signaling pathway, and promoted inflammatory factor release. Cd + MPs aggravated Cd- or MPs-induced liver fibrosis and induced liver inflammation. In AML12/HSC-T6 cell in vitro poisoning model, exposure of AML12 cells to Cd + MPs increased the opening of connexin hemichannels and promoted extracellular ATP release. Treatment of HSC-T6 cells with the supernatant of AML12 cells exposed to Cd + MPs significantly promoted HSC-T6 cell activation. Treatment of HSC-T6 cells with different concentrations of ATP produced similar results. TAT-Gap19TFA, an inhibitor of connexin hemichannels, significantly inhibited the ATP release and activation of Cd + MPs-treated HSC-T6 cells. Finally, the expression of the ATP receptor P2X7 was silenced in HSC-T6 cells, which significantly inhibited their activation. In conclusion, exposure to Cd + MPs promoted liver fibrosis through the ATP-P2X7 pathway and synergistically affected liver inflammation and fibrosis.

ATP breakdown in plasma of children limits the antimicrobial effectiveness of their neutrophils

Neutrophils (PMNs) require extracellular ATP and adenosine (ADO) to fight bacterial infections, which often have life-threatening consequences in pediatric patients. We wondered whether the ATP and ADO levels in the plasma of children change with age and if these changes influence the antimicrobial efficacy of the PMNs of these children. We measured plasma concentrations of ATP and ADO and the activities of the enzymes responsible for the breakdown of these mediators in plasma samples from healthy children and adolescents (n = 45) ranging in age from 0.2 to 15 years. In addition, using blood samples of these individuals, we compared how effective their PMNs were in the phagocytosis of bacteria. In an experimental sepsis model with young (10 days) and adolescent mice (10 weeks), we studied how age influenced the resilience of these animals to bacterial infections and whether addition of ATP could improve the antimicrobial capacity of their PMNs. We found that plasma ATP levels correlated with age and were significantly lower in infants (< 1 year) than in adolescents (12-15 years). In addition, we observed significantly higher plasma ATPase and adenosine deaminase activities in children (< 12 years) when compared to the adolescent population. The activities of these ATP and ADO breakdown processes correlated inversely with age and with the ability of PMNs to phagocytize bacteria. Similar to their human counterparts, young mice also had significantly lower plasma ATP levels when compared to adolescent animals. In addition, we found that mortality of young mice after bacterial infection was significantly higher than that of adolescent mice. Moreover, bacterial phagocytosis by PMNs of young mice was weaker when compared to that of older mice. Finally, we found that ATP supplementation could recover bacterial phagocytosis of young mice to levels similar to those of adolescent mice. Our findings suggest that rapid ATP hydrolysis in the plasma of young children lowers the antimicrobial functions of their PMNs and that this may contribute to the vulnerability of pediatric patients to bacterial infections.

Purinergic signaling: decoding its role in COVID-19 pathogenesis and promising treatment strategies

The pathogenesis of coronavirus disease (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS‑CoV‑2), is complex and involves dysregulated immune responses, inflammation, and coagulopathy. Purinergic signaling, mediated by extracellular nucleotides and nucleosides, has emerged as a significant player in the pathogenesis of COVID-19. Extracellular adenosine triphosphate (ATP), released from damaged or infected cells, is a danger signal triggering immune responses. It activates immune cells, releasing pro-inflammatory cytokines, contributing to the cytokine storm observed in severe COVID-19 cases. ATP also promotes platelet activation and thrombus formation, contributing to the hypercoagulability seen in COVID-19 patients. On the other hand, adenosine, an immunosuppressive nucleoside, can impair anti-viral immune responses and promote tissue damage through its anti-inflammatory effects. Modulating purinergic receptors represents a promising therapeutic strategy for COVID-19. Understanding the role of purinergic signaling in COVID-19 pathogenesis and developing targeted therapeutic approaches can potentially improve patient outcomes. This review focuses on the part of purinergic signaling in COVID-19 pathogenesis and highlights potential therapeutic approaches targeting purinergic receptors.

The role of Pannexin-1 channels, ATP, and purinergic receptors in the pathogenesis of HIV and SARS-CoV-2

Infectious agents such as human immune deficiency virus-1 (HIV) and severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) use host proteins to infect, replicate, and induce inflammation within the host. A critical component of these diseases is the axis between pannexin-1 channels, extracellular ATP, and purinergic receptors. Here, we describe the potential therapeutic role of Pannexin-1/purinergic approaches to prevent or reduce the devastating consequences of these pathogens.

Extracellular ATP Neurotransmission and Nicotine Sex-Specifically Modulate Habenular Neuronal Activity in Adolescence

The recent increase in the use of nicotine products by teenagers has revealed an urgent need to better understand the impact of nicotine on the adolescent brain. Here, we sought to examine the actions of extracellular ATP as a neurotransmitter and to investigate whether ATP and nicotinic signaling interact during adolescence. With the GRABATP (G-protein-coupled receptor activation-based ATP sensor), we first demonstrated that nicotine induces extracellular ATP release in the medial habenula, a brain region involved in nicotine aversion and withdrawal. Using patch-clamp electrophysiology, we then demonstrated that activation of the ATP receptors P2X or P2Y1 increases the neuronal firing of cholinergic neurons. Surprisingly, contrasting interactive effects were observed with nicotine exposure. For the P2X receptor, activation had no observable effect on acute nicotine-mediated activity, but during abstinence after 10 d of nicotine exposure, coexposure to nicotine and the P2X agonist potentiated neuronal activity in female, but not male, neurons. For P2Y1 signaling, a potentiated effect of the agonist and nicotine was observed with acute exposure, but not following extended nicotine exposure. These data reveal a complex interactive effect between nicotinic and ATP signaling in the adolescent brain and provide mechanistic insights into extracellular ATP signaling with sex-specific alterations of neuronal responses based on prior drug exposure.SIGNIFICANCE STATEMENT In these studies, it was discovered that nicotine induces extracellular ATP release in the medial habenula and subsequent activation of the ATP purinergic receptors increases habenular cholinergic neuronal firing in the adolescent brain. Interestingly, following extended nicotine exposure, nicotine was found to alter the interplay between purinergic and nicotinic signaling in a sex-specific manner. Together, these studies provide a novel understanding for the role of extracellular ATP in mediating habenular activity and reveal how nicotine exposure during adolescence alters these signaling mechanisms, which has important implications given the high incidence of e-cigarette/vape use by youth.

Energy Regulation in Inflammatory Sarcopenia by the Purinergic System

The purinergic system has a dual role: the maintenance of energy balance and signaling within cells. Adenosine and adenosine triphosphate (ATP) are essential for maintaining these functions. Sarcopenia is characterized by alterations in the control of energy and signaling in favor of catabolic pathways. This review details the association between the purinergic system and muscle and adipose tissue homeostasis, discussing recent findings in the involvement of purinergic receptors in muscle wasting and advances in the use of the purinergic system as a novel therapeutic target in the management of sarcopenia.

The Plasma Membrane Purinoreceptor P2K1/DORN1 Is Essential in Stomatal Closure Evoked by Extracellular Diadenosine Tetraphosphate (Ap4A) in Arabidopsis thaliana

Dinucleoside polyphosphates (NpnNs) are considered novel signalling molecules involved in the induction of plant defence mechanisms. However, NpnN signal recognition and transduction are still enigmatic. Therefore, the aim of our research was the identification of the NpnN receptor and signal transduction pathways evoked by these nucleotides. Earlier, we proved that purine and pyrimidine NpnNs differentially affect the phenylpropanoid pathway in Vitis vinifera suspension-cultured cells. Here, we report, for the first time, that both diadenosine tetraphosphate (Ap4A) and dicytidine tetraphosphate (Cp4C)-induced stomatal closure in Arabidopsis thaliana. Moreover, we showed that plasma membrane purinoreceptor P2K1/DORN1 (does not respond to nucleotide 1) is essential for Ap4A-induced stomata movements but not for Cp4C. Wild-type Col-0 and the dorn1-3 A. thaliana knockout mutant were used. Examination of the leaf epidermis dorn1-3 mutant provided evidence that P2K1/DORN1 is a part of the signal transduction pathway in stomatal closure evoked by extracellular Ap4A but not by Cp4C. Reactive oxygen species (ROS) are involved in signal transduction caused by Ap4A and Cp4C, leading to stomatal closure. Ap4A induced and Cp4C suppressed the transcriptional response in wild-type plants. Moreover, in dorn1-3 leaves, the effect of Ap4A on gene expression was impaired. The interaction between P2K1/DORN1 and Ap4A leads to changes in the transcription of signalling hubs in signal transduction pathways.

Modulation of Thalamocingulate Nociceptive Transmission and Glutamate Secretion by Targeting P2×7 Receptor

The complexity and diversity of pain signaling have led to obstacles for prominent treatments due to mechanisms that are not yet fully understood. Among adenosine triphosphate (ATP) receptors, P2×7 differs in many respects from P2×1-6, it plays a significant role in various inflammatory pain, but whether it plays a role in noninflammatory pain has not been widely discussed. In this study, we utilized major neuropharmacological methods to record the effects of manipulating P2×7 during nociceptive signal transmission in the thalamocingulate circuits. Our results show that regardless of the specific cell type distribution of P2×7 in the central nervous system (CNS), it participates directly in the generated nociceptive transmission, which indicates its apparent functional existence in the major pain transmission path, the thalamocingulate circuits. Activation of P2×7 may facilitate transmission velocity along the thalamocingulate projection as well as neuron firings and synaptic vesicle release in anterior cingulate cortical neurons. Targeting thalamic P2×7 affects glutamate and ATP secretion during nociceptive signal transmission. PERSPECTIVE: The observations in this study provide evidence that the ATP receptor P2×7 presents in the central ascending pain path and plays a modulatory role during nociceptive transmission, which could contribute new insights for many antinociceptive applications.

Aging is associated with impaired triggering of TRPV3-mediated cutaneous vasodilation: a crucial process for local heat exposure

Sensing temperature is vitally important to adapt our body to environmental changes. Local warm detection is required to initiate regulation of cutaneous blood flow, which is part of the peripheral thermoregulatory mechanisms, and thus avoid damage to surrounding tissues. The mechanisms mediating cutaneous vasodilation during local heat stress are impaired with aging. However, the impact of aging on the ability of the skin to detect subtle thermal changes is unknown. Among heat-activated cation channels, transient receptor potential vanilloid 3 (TRPV3) is a thermo-sensor predominantly expressed on keratinocytes and involved in local vascular thermoregulatory mechanisms of the skin in young mice. In the present study, using a murine in vivo model of local heat exposure of the skin, we showed that heat-induced vasodilation was reduced in old mice associated with reduced expression of TRPV3 channels. We also found a decrease in expression and activity of TRPV3 channel, as well as reduced TRPV3-dependent adenosine tri-phosphate release in human primary keratinocytes from old donors. This study shows that aging alters the epidermal TRPV3 channels, which might delay the detection of changes in skin temperature, thereby limiting the mechanisms triggered for local vascular thermoregulation in the old skin.

Adenosine A2A receptors in the rostral ventrolateral medulla participate in blood pressure decrease with electroacupuncture in hypertensive rats

Acupuncture is increasingly used to manage high blood pressure (BP) as a complementary therapy. However, the mechanisms underlying its hypotensive effects remain unclear. Our previous studies have shown that electroacupuncture (EA) at the ST36-37 acupoints, overlying the deep peroneal nerve, attenuates pressor responses through adenosine A2A receptors (A2AR) in the rostral ventrolateral medulla (rVLM). However, it is uncertain whether rVLM A2AR contributes to EA's BP-lowering effect in sustained hypertension. We hypothesized that a course of EA treatment lowers BP, in part, through the activation of adenosine A2AR in the rVLM in hypertensive rats. To mimic essential hypertension in the clinic, we performed EA in conscious Dahl salt-sensitive hypertensive rats (DSHRs). EA (0.1-0.4 mA, 2 Hz) was applied at ST36-37 for 30 min twice weekly for four weeks, while sham-EA was conducted in a similar manner but without electrical input. In hypertensive rats, BP was reduced by EA (n = 14) but neither by sham-EA (n = 14) nor in the absence of needling (n = 8). Following four weeks of eight treatments and then under anesthesia, EA's modulatory effect on elevated BP was reversed by unilateral rVLM microinjection of SCH 58261 (1 mM in 50 nl; an A2AR antagonist; n = 7; P < 0.05) but not the vehicle (n = 5) in EA-treated DSHRs. Activation of rVLM A2AR in DSHRs treated with sham-EA by an A2AR agonist, CGS-21680 (0.4 mM in 50 nl; n = 8), decreased BP. Unilateral administration of SCH 58261 or CGS-21680 into the rVLM did not alter basal BP in Dahl salt-sensitive rats fed a regular diet with normal BP. The A2AR level in the rVLM after EA was increased compared to the sham-EA and untreated DSHRs (n = 5 in each group; all P < 0.05). These data suggest that a 4-week twice weekly EA treatment reduced BP in salt-sensitive hypertensive rats likely through adenosine-mediated A2AR in the rVLM.

Synthetic molecules as P2X7 receptor antagonists: A medicinal chemistry update focusing the therapy of inflammatory diseases

Stimulation of the P2X7 receptor by extracellular adenosine 5'-triphosphate induces a series of responses in the organism, exceptionally protein cascades related to the proinflammatory process. This has made P2X7 a target for research on inflammatory diseases such as rheumatoid arthritis. Thus, the incessant search for new prototypes that aim to antagonize the action of P2X7 has been remarkable in recent decades, a factor that has already led to numerous clinical studies in humans. In this review, we present the key molecules developed over the years with potential inhibition of P2X7 and inflammation. In addition, an update with newly developed chemical classes with promising activity and results in clinical studies for human pathologies focusing on P2X7 inhibition.

Ion Channels and Ionotropic Receptors in Astrocytes: Physiological Functions and Alterations in Alzheimer's Disease and Glioblastoma

The human brain is composed of nearly one hundred billion neurons and an equal number of glial cells, including macroglia, i.e., astrocytes and oligodendrocytes, and microglia, the resident immune cells of the brain. In the last few decades, compelling evidence has revealed that glial cells are far more active and complex than previously thought. In particular, astrocytes, the most abundant glial cell population, not only take part in brain development, metabolism, and defense against pathogens and insults, but they also affect sensory, motor, and cognitive functions by constantly modulating synaptic activity. Not surprisingly, astrocytes are actively involved in neurodegenerative diseases (NDs) and other neurological disorders like brain tumors, in which they rapidly become reactive and mediate neuroinflammation. Reactive astrocytes acquire or lose specific functions that differently modulate disease progression and symptoms, including cognitive impairments. Astrocytes express several types of ion channels, including K+, Na+, and Ca2+ channels, transient receptor potential channels (TRP), aquaporins, mechanoreceptors, and anion channels, whose properties and functions are only partially understood, particularly in small processes that contact synapses. In addition, astrocytes express ionotropic receptors for several neurotransmitters. Here, we provide an extensive and up-to-date review of the roles of ion channels and ionotropic receptors in astrocyte physiology and pathology. As examples of two different brain pathologies, we focus on Alzheimer's disease (AD), one of the most diffuse neurodegenerative disorders, and glioblastoma (GBM), the most common brain tumor. Understanding how ion channels and ionotropic receptors in astrocytes participate in NDs and tumors is necessary for developing new therapeutic tools for these increasingly common neurological conditions.

Strategies for Drug Delivery into the Brain: A Review on Adenosine Receptors Modulation for Central Nervous System Diseases Therapy

The blood-brain barrier (BBB) is a biological barrier that protects the central nervous system (CNS) by ensuring an appropriate microenvironment. Brain microvascular endothelial cells (ECs) control the passage of molecules from blood to brain tissue and regulate their concentration-versus-time profiles to guarantee proper neuronal activity, angiogenesis and neurogenesis, as well as to prevent the entry of immune cells into the brain. However, the BBB also restricts the penetration of drugs, thus presenting a challenge in the development of therapeutics for CNS diseases. On the other hand, adenosine, an endogenous purine-based nucleoside that is expressed in most body tissues, regulates different body functions by acting through its G-protein-coupled receptors (A1, A2A, A2B and A3). Adenosine receptors (ARs) are thus considered potential drug targets for treating different metabolic, inflammatory and neurological diseases. In the CNS, A1 and A2A are expressed by astrocytes, oligodendrocytes, neurons, immune cells and ECs. Moreover, adenosine, by acting locally through its receptors A1 and/or A2A, may modulate BBB permeability, and this effect is potentiated when both receptors are simultaneously activated. This review showcases in vivo and in vitro evidence supporting AR signaling as a candidate for modifying endothelial barrier permeability in the treatment of CNS disorders.

Endothelial Effects of Simultaneous Expression of Human HO-1, E5NT, and ENTPD1 in a Mouse

The vascular endothelium is key target for immune and thrombotic responses that has to be controlled in successful xenotransplantation. Several genes were identified that, if induced or overexpressed, help to regulate the inflammatory response and preserve the transplanted organ function and metabolism. However, few studies addressed combined expression of such genes. The aim of this work was to evaluate in vivo the effects of the simultaneous expression of three human genes in a mouse generated using the multi-cistronic F2A technology. Male 3-month-old mice that express human heme oxygenase 1 (hHO-1), ecto-5'-nucleotidase (hE5NT), and ecto-nucleoside triphosphate diphosphohydrolase 1 (hENTPD1) (Transgenic) were compared to wild-type FVB mice (Control). Background analysis include extracellular nucleotide catabolism enzymes profile on the aortic surface, blood nucleotide concentration, and serum L-arginine metabolites. Furthermore, inflammatory stress induced by LPS in transgenic and control mice was used to characterize interleukin 6 (IL-6) and adhesion molecules endothelium permeability responses. Transgenic mice had significantly higher rates of extracellular adenosine triphosphate and adenosine monophosphate hydrolysis on the aortic surface in comparison to control. Increased levels of blood AMP and adenosine were also noticed in transgenics. Moreover, transgenic animals demonstrated the decrease in serum monomethyl-L-arginine level and a higher L-arginine/monomethyl-L-arginine ratio. Importantly, significantly decreased serum IL-6, and adhesion molecule levels were observed in transgenic mice in comparison to control after LPS treatment. Furthermore, reduced endothelial permeability in the LPS-treated transgenic mice was noted as compared to LPS-treated control. The human enzymes (hHO-1, hE5NT, hENTPD1) simultaneously encoded in transgenic mice demonstrated benefits in several biochemical and functional aspects of endothelium. This is consistent in use of this approach in the context of xenotransplantation.

Purine and purinergic receptors in health and disease

Purines and purinergic receptors are widely distributed throughout the human body. Purine molecules within cells play crucial roles in regulating energy metabolism and other cellular processes, while extracellular purines transmit signals through specific purinergic receptors. The ubiquitous purinergic signaling maintains normal neural excitability, digestion and absorption, respiratory movement, and other complex physiological activities, and participates in cell proliferation, differentiation, migration, and death. Pathological dysregulation of purinergic signaling can result in the development of various diseases, including neurodegeneration, inflammatory reactions, and malignant tumors. The dysregulation or dysfunction of purines and purinergic receptors has been demonstrated to be closely associated with tumor progression. Compared with other subtypes of purinergic receptors, the P2X7 receptor (P2X7R) exhibits distinct characteristics (i.e., a low affinity for ATP, dual functionality upon activation, the mediation of ion channels, and nonselective pores formation) and is considered a promising target for antitumor therapy, particularly in patients with poor response to immunotherapy This review summarizes the physiological and pathological significance of purinergic signaling and purinergic receptors, analyzes their complex relationship with tumors, and proposes potential antitumor immunotherapy strategies from tumor P2X7R inhibition, tumor P2X7R overactivation, and host P2X7R activation. This review provides a reference for clinical immunotherapy and mechanism investigation.

A liquid chromatography-tandem mass spectrometry based method for the quantification of adenosine nucleotides and NAD precursors and products in various biological samples

Adenine nucleotides (AN) are ubiquitous metabolites that regulate cellular energy metabolism and modulate cell communication and inflammation. To understand how disturbances in AN balance arise and affect cellular function, robust quantification techniques for these metabolites are crucial. However, due to their hydrophilicity, simultaneous quantification of AN across various biological samples has been challenging. Here we present a hydrophilic interaction high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) based method for the quantification of 26 adenosine nucleotides and precursors as well as metabolic products of nicotinamide adenine dinucleotide (NAD) in plasma, liver, and adipose tissue samples as well as cell culture supernatants and cells. Method validation was performed with regard to linearity, accuracy, precision, matrix effects, and carryover. Finally, analysis of cell culture supernatants derived from intestinal organoids and RAW 264.7 cells illustrates that the here described method is a reliable and easy-to-use tool to quantify AN and opens up new avenues to understand the role of AN generation and breakdown for cellular functions.

Pharmacology of Adenosine Receptors: Recent Advancements

Adenosine receptors (ARs) are widely acknowledged pharmacological targets yet are still underutilized in clinical practice. Their ubiquitous distribution in almost all cells and tissues of the body makes them, on the one hand, excellent candidates for numerous diseases, and on the other hand, intrinsically challenging to exploit selectively and in a site-specific manner. This review endeavors to comprehensively depict the substantial advancements witnessed in recent years concerning the development of drugs that modulate ARs. Through preclinical and clinical research, it has become evident that the modulation of ARs holds promise for the treatment of numerous diseases, including central nervous system disorders, cardiovascular and metabolic conditions, inflammatory and autoimmune diseases, and cancer. The latest studies discussed herein shed light on novel mechanisms through which ARs exert control over pathophysiological states. They also introduce new ligands and innovative strategies for receptor activation, presenting compelling evidence of efficacy along with the implicated signaling pathways. Collectively, these emerging insights underscore a promising trajectory toward harnessing the therapeutic potential of these multifaceted targets.

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.

Drugs targeting adenosine signaling pathways: A current view

Adenosine is an endogenous nucleoside that regulates many physiological and pathological processes. It is derived from either the intracellular or extracellular dephosphorylation of adenosine triphosphate and interacts with cell-surface G-protein-coupled receptors. Adenosine plays a substantial role in protecting against cell damage in areas of increased tissue metabolism and preventing organ dysfunction in pathological states. Targeting adenosine metabolism and receptor signaling may be an effective therapeutic approach for human diseases, including cardiovascular and central nervous system disorders, rheumatoid arthritis, asthma, renal diseases, and cancer. Several lines of evidence have shown that many drugs exert their beneficial effects by modulating adenosine signaling pathways but this knowledge urgently needs to be summarized, and most importantly, actualized. The present review collects pharmaceuticals and pharmacological or diagnostic tools that target adenosine signaling in their primary or secondary mode of action. We overviewed FDA-approved drugs as well as those currently being studied in clinical trials. Among them are already used in clinic A2A adenosine receptor modulators like istradefylline or regadenoson, but also plenty of anti-platelet, anti-inflammatory, or immunosuppressive, and anti-cancer drugs. On the other hand, we investigated dozens of specific adenosine pathway regulators that are tested in clinical trials to treat human infectious and noninfectious diseases. In conclusion, targeting purinergic signaling represents a great therapeutic challenge. The actual knowledge of the involvement of adenosinergic signaling as part of the mechanism of action of old drugs has open a path not only for drug-repurposing but also for new therapeutic strategies.

Autophagy may protect the brain against prolonged consequences of headache attacks: A narrative/hypothesis review

OBJECTIVE

To assess the potential of autophagy in migraine pathogenesis.

BACKGROUND

The interplay between neurons and microglial cells is important in migraine pathogenesis. Migraine-related effects, such as cortical spreading depolarization and release of calcitonin gene-related peptide, may initiate adenosine triphosphate (ATP)-mediating pro-nociceptive signaling in the meninges causing headaches. Such signaling may be induced by the interaction of ATP with purinergic receptor P2X 7 (P2X7R) on microglial cells leading to a Ca2+ -mediated pH increase in lysosomes and release of autolysosome-like vehicles from microglial cells indicating autophagy impairment.

METHODS

A search in PubMed was conducted with the use of the terms "migraine," "autophagy," "microglia," and "degradation" in different combinations.

RESULTS

Impaired autophagy in microglia may activate secretory autophagy and release of specific proteins, including brain-derived neurotrophic factor (BDNF), which can be also released through the pores induced by P2X7R activation in microglial cells. BDNF may be likewise released from microglial cells upon ATP- and Ca2+ -mediated activation of another purinergic receptor, P2X4R. BDNF released from microglia might induce autophagy in neurons to clear cellular debris produced by oxidative stress, which is induced in the brain as the response to migraine-related energy deficit. Therefore, migraine-related signaling may impair degradative autophagy, stimulate secretory autophagy in microglia, and degradative autophagy in neurons. These effects are mediated by purinergic receptors P2X4R and P2X7R, BDNF, ATP, and Ca2+ .

CONCLUSION

Different effects of migraine-related events on degradative autophagy in microglia and neurons may prevent prolonged changes in the brain related to headache attacks.

DT-0111: a novel P2X3 receptor antagonist

Extracellular adenosine 5'-triphosphate (ATP) acts as an autocrine and paracrine agent, the actions of which on affected cells are mediated by P2 receptors (P2R), which include trans cell-membrane cationic channels (P2XRs), and G protein coupled receptors (P2YRs). The mammalian P2X receptors form homotrimeric or heterotrimeric cationic channels, each of which contains three ATP-binding sites. There are seven homotrimeric P2X receptors (P2X1-7) and three heteromeric (P2X2/P2X3, P2X4/P2X6, P2X1/P2X5). In the lungs and airways, ATP activates P2X3 and P2X2/3 receptors (P2X3R, P2X2/3R, respectively) localized on vagal sensory nerve terminals resulting in bronchoconstriction, and cough, and probably also localized release of pro-inflammatory neuropeptides via the axon reflex. Currently, several P2X3R and P2X2/3R antagonists are being developed as drug-candidates for the treatment of chronic cough. This report presents the receptor affinity data of a novel water-soluble small molecule, DT-0111, that acts as a selective P2X3R antagonist.

Recent advances in the structure and activation mechanisms of metabolite-releasing Pannexin 1 channels

Pannexin 1 (PANX1) is a widely expressed large-pore ion channel located in the plasma membrane of almost all vertebrate cells. It possesses a unique ability to act as a conduit for both inorganic ions (e.g. potassium or chloride) and bioactive metabolites (e.g. ATP or glutamate), thereby activating varying signaling pathways in an autocrine or paracrine manner. Given its crucial role in cell-cell interactions, the activity of PANX1 has been implicated in maintaining homeostasis of cardiovascular, immune, and nervous systems. Dysregulation of PANX1 has also been linked to numerous diseases, such as ischemic stroke, seizure, and inflammatory disorders. Therefore, the mechanisms underlying different modes of PANX1 activation and its context-specific channel properties have gathered significant attention. In this review, we summarize the roles of PANX1 in various physiological processes and diseases, and analyze the accumulated lines of evidence supporting diverse molecular mechanisms associated with different PANX1 activation modalities. We focus on examining recent discoveries regarding PANX1 regulations by reversible post-translational modifications, elevated intracellular calcium concentration, and protein-protein interactions, as well as by irreversible cleavage of its C-terminal tail. Additionally, we delve into the caveats in the proposed PANX1 gating mechanisms and channel open-closed configurations by critically analyzing the structural insights derived from cryo-EM studies and the unitary properties of PANX1 channels. By doing so, we aim to identify potential research directions for a better understanding of the functions and regulations of PANX1 channels.

The AMP deaminase of the mollusk Helix pomatia is an unexpected member of the adenosine deaminase-related growth factor (ADGF) family

We report here the first occurrence of an adenosine deaminase-related growth factor (ADGF) that deaminates adenosine 5' monophosphate (AMP) in preference to adenosine. The ADGFs are a group of secreted deaminases found throughout the animal kingdom that affect the extracellular concentration of adenosine by converting it to inosine. The AMP deaminase studied here was first isolated and biochemically characterized from the roman snail Helix pomatia in 1983. Determination of the amino acid sequence of the AMP deaminase enabled sequence comparisons to protein databases and revealed it as a member of the ADGF family. Cloning and expression of its cDNA in Pichia pastoris allowed the comparison of the biochemical characteristics of the native and recombinant forms of the enzyme and confirmed they correspond to the previously reported activity. Uncharacteristically, the H. pomatia AMP deaminase was determined to be dissimilar to the AMP deaminase family by sequence comparison while demonstrating similarity to the ADGFs despite having AMP as its preferred substrate rather than adenosine.