Reduced expression of purinergic P2X4 receptors increases voluntary ethanol intake in C57BL/6J mice

Suppression of P2X4 and P2X7 by Lactobacillus rhamnosus vitaP1: effects on hangover symptoms

This study aimed to identify substances including Lactobacillus rhamnosus vitaP1 (KACC 92054P) that alleviate hangover-induced emotional anxiety and liver damage. The association between emotional anxiety caused by hangover and the genes P2X4, P2X7, SLC6A4 was investigated. In vitro and in vivo analyses were conducted to assess the influence of free-panica on alcohol-induced upregulated gene expression. Additionally, the concentration of AST, ALT, alcohol, and acetaldehyde in blood was measured. Free-panica, consisting of five natural products (Phyllanthus amarus, Phoenix dactylifera, Vitis vinifera, Zingiber officinale, and Lactobacillus rhamnosus), were evaluated for their regulatory effects on genes involved in alcohol-induced emotional anxiety and liver damage. The combination of these natural products in free-panica successfully restored emotional anxiety, and the concentration of AST, ALT, alcohol, and acetaldehyde in blood to those of the normal control group. These findings support the potential development of free-panica as a health functional food or medicinal intervention for relieving hangover symptoms and protecting liver from alcohol consumption.

P2 receptor-mediated signaling in the physiological and pathological brain: From development to aging and disease

The purinergic pathway mediates both pro-inflammatory and anti-inflammatory responses, whereas the breakdown of adenosine triphosphate (ATP) is in a critical equilibrium. Under physiological conditions, extracellular ATP is maintained at a nanomolar concentration. Whether released into the medium following tissue damage, inflammation, or hypoxia, ATP is considered a clear indicator of cell damage and a marker of pathological conditions. In this overview, we provide an update on the participation of P2 receptor-mediated purinergic signaling in normal and pathological brain development, with special emphasis on neurodevelopmental psychiatric disorders. Since purinergic signaling is ubiquitous, it is not surprising that it plays a prominent role in developmental processes and pathological alterations. The main aim of this review is to conceptualize the time-dependent dynamic changes in the participation of different players in the purinome in shaping the normal and aberrant developmental patterns and diseases of the central nervous system over one's lifespan.

Increased ATP Release and Higher Impact of Adenosine A2A Receptors on Corticostriatal Plasticity in a Rat Model of Presymptomatic Parkinson's Disease

Extracellular ATP can be a danger signal, but its role in striatal circuits afflicted in Parkinson's disease (PD) is unclear and was now investigated. ATP was particularly released at high stimulation intensities from purified striatal nerve terminals of mice, which were endowed with different ATP-P2 receptors (P2R), although P2R antagonists did not alter corticostriatal transmission or plasticity. Instead, ATP was extracellularly catabolized into adenosine through CD73 to activate adenosine A_2A receptors (A_2AR) modulating corticostriatal long-term potentiation (LTP) in mice. In the presymptomatic phase of a 6-hydroxydopamine rat model of PD, ATP release from striatal nerve terminals was increased and was responsible for a greater impact of CD73 and A_2AR on corticostriatal LTP. These observations identify increased ATP release and ATP-derived formation of extracellular adenosine bolstering A_2AR activation as a key pathway responsible for abnormal synaptic plasticity in circuits involved in the onset of PD motor symptoms. The translation of these findings to humans prompts extending the use of A_2AR antagonists from only co-adjuvants of motor control in Parkinsonian patients to neuroprotective drugs delaying the onset of motor symptoms.

Ethanol antagonizes P2X4 receptors in ventral tegmental area neurons

P2X4 receptors are found throughout the central nervous system, and studies have shown that these purinergic receptors are important regulators of alcohol intake. The ventral tegmental area (VTA) is an important region for the rewarding and reinforcing properties of alcohol, but the role of P2X4 receptors in this region is unknown. Using both immunohistochemical and electrophysiological methods, we examined the interaction between P2X4 receptors and alcohol on VTA neurons. Incubation of brain slices containing the VTA for 2 h with siRNA targeting P2X4 receptors resulted in about a 25% reduction in P2X4 immunoreactivity in tyrosine hydroxylase positive VTA neurons. In electrophysiological experiments, ATP (0.5-3 mM) produced a reduction in the spontaneous firing rate, and ethanol significantly reduced this inhibition. Exposure to siP2X4 for 2 h via the recording micropipette resulted in a suppression of the response of VTA neurons to ATP, but no significant reduction in the ethanol inhibition of the ATP response was observed after this P2X4 downregulation. These results support the idea that VTA neurons are inhibited by ATP, ethanol antagonizes this inhibition, and the ethanol-sensitive component of ATP inhibition is mediated by P2X4 receptors. This interaction of ethanol with P2X4 receptors may be an important regulator of the rewarding effects of ethanol, making P2X4 receptors an intriguing target for the development of agents to treat alcohol use disorders.

Microglia: The Missing Link to Decipher and Therapeutically Control MS Progression?

Therapeutically controlling chronic progression in multiple sclerosis (MS) remains a major challenge. MS progression is defined as a steady loss of parenchymal and functional integrity of the central nervous system (CNS), occurring independent of relapses or focal, magnetic resonance imaging (MRI)-detectable inflammatory lesions. While it clinically surfaces in primary or secondary progressive MS, it is assumed to be an integral component of MS from the very beginning. The exact mechanisms causing progression are still unknown, although evolving evidence suggests that they may substantially differ from those driving relapse biology. To date, progression is assumed to be caused by an interplay of CNS-resident cells and CNS-trapped hematopoietic cells. On the CNS-resident cell side, microglia that are phenotypically and functionally related to cells of the monocyte/macrophage lineage may play a key role. Microglia function is highly transformable. Depending on their molecular signature, microglia can trigger neurotoxic pathways leading to neurodegeneration, or alternatively exert important roles in promoting neuroprotection, downregulation of inflammation, and stimulation of repair. Accordingly, to understand and to possibly alter the role of microglial activation during MS disease progression may provide a unique opportunity for the development of suitable, more effective therapeutics. This review focuses on the current understanding of the role of microglia during disease progression of MS and discusses possible targets for therapeutic intervention.

Increased surface P2X4 receptor regulates anxiety and memory in P2X4 internalization-defective knock-in mice

ATP signaling and surface P2X4 receptors are upregulated selectively in neurons and/or glia in various CNS disorders including anxiety, chronic pain, epilepsy, ischemia, and neurodegenerative diseases. However, the cell-specific functions of P2X4 in pathological contexts remain elusive. To elucidate P2X4 functions, we created a conditional transgenic knock-in P2X4 mouse line (Floxed P2X4mCherryIN) allowing the Cre activity-dependent genetic swapping of the internalization motif of P2X4 by the fluorescent mCherry protein to prevent constitutive endocytosis of P2X4. By combining molecular, cellular, electrophysiological, and behavioral approaches, we characterized two distinct knock-in mouse lines expressing noninternalized P2X4mCherryIN either exclusively in excitatory forebrain neurons or in all cells natively expressing P2X4. The genetic substitution of wild-type P2X4 by noninternalized P2X4mCherryIN in both knock-in mouse models did not alter the sparse distribution and subcellular localization of P2X4 but increased the number of P2X4 receptors at the surface of the targeted cells mimicking the pathological increased surface P2X4 state. Increased surface P2X4 density in the hippocampus of knock-in mice altered LTP and LTD plasticity phenomena at CA1 synapses without affecting basal excitatory transmission. Moreover, these cellular events translated into anxiolytic effects and deficits in spatial memory. Our results show that increased surface density of neuronal P2X4 contributes to synaptic deficits and alterations in anxiety and memory functions consistent with the implication of P2X4 in neuropsychiatric and neurodegenerative disorders. Furthermore, these conditional P2X4mCherryIN knock-in mice will allow exploring the cell-specific roles of P2X4 in various physiological and pathological contexts.

Inhibiting the P2X4 Receptor Suppresses Prostate Cancer Growth In Vitro and In Vivo, Suggesting a Potential Clinical Target

Prostate cancer (PCa) is the most frequently diagnosed cancer in men, causing considerable morbidity and mortality. The P2X4 receptor (P2X4R) is the most ubiquitously expressed P2X receptor in mammals and is positively associated with tumorigenesis in many cancer types. However, its involvement in PCa progression is less understood. We hypothesized that P2X4R activity enhanced tumour formation by PCa cells. We showed that P2X4R was the most highly expressed, functional P2 receptor in these cells using quantitative reverse transcription PCR (RT-PCR) and a calcium influx assay. The effect of inhibiting P2X4R on PCa (PC3 and C4-2B4 cells) viability, proliferation, migration, invasion, and apoptosis were examined using the selective P2XR4 antagonists 5-BDBD and PSB-12062. The results demonstrated that inhibiting P2X4R impaired the growth and mobility of PCa cells but not apoptosis. In BALB/c immunocompromised nude mice inoculated with human PC3 cells subcutaneously, 5-BDBD showed anti-tumourigenic effects. Finally, a retrospective analysis of P2RX4 expression in clinical datasets (GDS1439, GDS1746, and GDS3289) suggested that P2X4R was positively associated with PCa malignancy. These studies suggest that P2X4R has a role in enhancing PCa tumour formation and is a clinically targetable candidate for which inhibitors are already available and have the potential to suppress disease progression.

A long non-coding RNA (Lrap) modulates brain gene expression and levels of alcohol consumption in rats

LncRNAs are important regulators of quantitative and qualitative features of the transcriptome. We have used QTL and other statistical analyses to identify a gene coexpression module associated with alcohol consumption. The "hub gene" of this module, Lrap (Long non-coding RNA for alcohol preference), was an unannotated transcript resembling a lncRNA. We used partial correlation analyses to establish that Lrap is a major contributor to the integrity of the coexpression module. Using CRISPR/Cas9 technology, we disrupted an exon of Lrap in Wistar rats. Measures of alcohol consumption in wild type, heterozygous and knockout rats showed that disruption of Lrap produced increases in alcohol consumption/alcohol preference. The disruption of Lrap also produced changes in expression of over 700 other transcripts. Furthermore, it became apparent that Lrap may have a function in alternative splicing of the affected transcripts. The GO category of "Response to Ethanol" emerged as one of the top candidates in an enrichment analysis of the differentially expressed transcripts. We validate the role of Lrap as a mediator of alcohol consumption by rats, and also implicate Lrap as a modifier of the expression and splicing of a large number of brain transcripts. A defined subset of these transcripts significantly impacts alcohol consumption by rats (and possibly humans). Our work shows the pleiotropic nature of non-coding elements of the genome, the power of network analysis in identifying the critical elements influencing phenotypes, and the fact that not all changes produced by genetic editing are critical for the concomitant changes in phenotype.

The macrocyclic lactones ivermectin and moxidectin show differential effects on rotational behavior in the 6-hydroxydopamine mouse model of Parkinson's disease

Parkinson's disease (PD) is a common neurodegenerative disease characterized by motor and cognitive deficits, the result of dopamine (DA)-depletion within the basal ganglia. Currently, DA replacement therapy in the form of Sinemet (L-DOPA plus Carbidopa) provides symptomatic motor benefits and remains the "gold standard" for treatment. Several pharmacological approaches can enhance DA neurotransmission including the administration of DA receptor agonists, the inhibition of DA metabolism, and enhancing pre-synaptic DA release. DA neurotransmission is regulated by several receptor subtypes including signaling through the purinergic system. P2 × 4 receptors (P2 × 4Rs) are a class of cation-permeable ligand-gated ion channels activated by the synaptic release of extracellular adenosine 5'-triphosphate (ATP). P2 × 4Rs are expressed throughout the central nervous system including the dopaminergic circuitry of the substantia nigra, basal ganglia, and related reward networks. Previous studies have demonstrated that P2 × 4Rs can modulate several DA-dependent characteristics including motor, cognitive, and reward behaviors. Ivermectin (IVM) and moxidectin (MOX) are two macrocyclic lactones that can potentiate P2 × 4Rs. In this study, we sought to investigate the role of P2 × 4Rs in mediating DA neurotransmission by exploring their impact on DA-dependent behavior, specifically rotation frequency in the unilateral 6-hydroxydopamine-lesioned mouse model of DA-depletion. While we did not observe any differences in the degree of lesioning based on immunostaining for tyrosine hydroxylase between sexes, male mice displayed a greater number of rotations with L-DOPA compared to female mice. In contrast, we observed that IVM plus L-DOPA increased the number of rotations (per 10 min) in female, but not male mice. These findings highlight the potential role of pharmacologically targeting the purinergic receptor system in modulating DA neurotransmission as well as the importance of sex differences impacting outcome measures.

Contribution of P2X4 Receptors to CNS Function and Pathophysiology

The release and extracellular action of ATP are a widespread mechanism for cell-to-cell communication in living organisms through activation of P2X and P2Y receptors expressed at the cell surface of most tissues, including the nervous system. Among ionototropic receptors, P2X4 receptors have emerged in the last decade as a potential target for CNS disorders such as epilepsy, ischemia, chronic pain, anxiety, multiple sclerosis and neurodegenerative diseases. However, the role of P2X4 receptor in each pathology ranges from beneficial to detrimental, although the mechanisms are still mostly unknown. P2X4 is expressed at low levels in CNS cells including neurons and glial cells. In normal conditions, P2X4 activation contributes to synaptic transmission and synaptic plasticity. Importantly, one of the genes present in the transcriptional program of myeloid cell activation is P2X4. Microglial P2X4 upregulation, the P2X4⁺ state of microglia, seems to be common in most acute and chronic neurodegenerative diseases associated with inflammation. In this review, we summarize knowledge about the role of P2X4 receptors in the CNS physiology and discuss potential pitfalls and open questions about the therapeutic potential of blocking or potentiation of P2X4 for different pathologies.

To Inhibit or Enhance? Is There a Benefit to Positive Allosteric Modulation of P2X Receptors?

The family of ligand-gated ion channels known as P2X receptors were discovered several decades ago. Since the cloning of the seven P2X receptors (P2X1-P2X7), a huge research effort has elucidated their roles in regulating a range of physiological and pathophysiological processes. Transgenic animals have been influential in understanding which P2X receptors could be new therapeutic targets for disease. Furthermore, understanding how inherited mutations can increase susceptibility to disorders and diseases has advanced this knowledge base. There has been an emphasis on the discovery and development of pharmacological tools to help dissect the individual roles of P2X receptors and the pharmaceutical industry has been involved in pushing forward clinical development of several lead compounds. During the discovery phase, a number of positive allosteric modulators have been described for P2X receptors and these have been useful in assigning physiological roles to receptors. This review will consider the major physiological roles of P2X1-P2X7 and discuss whether enhancement of P2X receptor activity would offer any therapeutic benefit. We will review what is known about identified compounds acting as positive allosteric modulators and the recent identification of drug binding pockets for such modulators.

Knockout and Knock-in Mouse Models to Study Purinergic Signaling

Purinergic signaling involves extracellular purines and pyrimidines acting upon specific cell surface purinoceptors classified into the P1, P2X, and P2Y families for nucleosides and nucleotides. This widespread signaling mechanism is active in all major tissues and influences a range of functions in health and disease. Orthologs to all but one of the human purinoceptors have been found in mouse, making this laboratory animal a useful model to study their function. Indeed, analyses of purinoceptors via knock-in or knockout approaches to produce gain or loss of function phenotypes have revealed several important therapeutic targets. None of the homozygous purinoceptor knockouts proved to be developmentally lethal, which suggest that either these receptors are not involved in key developmental processes or that the large number of receptors in each family allowed for functional compensation. Different models for the same purinoceptor often show compatible phenotypes but there have been examples of significant discrepancies. These revealed unexpected differences in the structure of human and mouse genes and emphasized the importance of the genetic background of different mouse strains. In this chapter, we provide an overview of the current knowledge and new trends in the modifications of purinoceptor genes in vivo. We discuss the resulting phenotypes, their applications and relative merits and limitations of mouse models available to study purinoceptor subtypes.

‬The expression of purinergic P2X4 and P2X7 receptors in selected mesolimbic structures during morphine withdrawal in rats

Morphine is one of the most potent analgesics used in medicine and it's long-term use is associated with the risk of the state of dependence. The cessation of chronic morphine administration leads to withdrawal signs which are associated with neurotransmitter dysregulations within mesolimbic system. Adenosine 5'-triphosphate (ATP) and purinergic system play an important role in the activity of central nervous system (CNS). Purinergic receptors are widely distributed in neurons and glial cells throughout the CNS taking part in integration of functional activity between neurons, glial and vascular cells. In the present study the mRNA and protein expression of purinergic P2X4 and P2X7 receptors in selected mesolimbic structures (striatum, hippocampus and prefrontal cortex) during morphine withdrawal in rats was investigated by RT-PCR and Western Blot analysis. Two experimental models of morphine withdrawal were studied: single and repeated morphine withdrawal. We demonstrated that expression of P2X4 and P2X7 receptors was altered during morphine withdrawal period in rats. These alterations were varied in particular mesolimbic areas depending on the scheme of morphine administration. Our results extend the current knowledge on morphine withdrawal and for the first time high-light interactions between purinergic system and morphine withdrawal. It seems, the purinergic system may be a new, valuable tool in searching for a new strategy of management of opioid dependence.

Role of P2 receptors in normal brain development and in neurodevelopmental psychiatric disorders

The purinergic signaling system, including P2 receptors, plays an important role in various central nervous system (CNS) disorders. Over the last few decades, a substantial amount of accumulated data suggest that most P2 receptor subtypes (P2X1, 2, 3, 4, 6, and 7, and P2Y₁, ₂, ₆, ₁₂, and ₁₃) regulate neuronal/neuroglial developmental processes, such as proliferation, differentiation, migration of neuronal precursors, and neurite outgrowth. However, only a few of these subtypes (P2X2, P2X3, P2X4, P2X7, P2Y₁, and P2Y₂) have been investigated in the context of neurodevelopmental psychiatric disorders. The activation of these potential target receptors and their underlying mechanisms mainly influence the process of neuroinflammation. In particular, P2 receptor-mediated inflammatory cytokine release has been indicated to contribute to the complex mechanisms of a variety of CNS disorders. The released inflammatory cytokines could be utilized as biomarkers for neurodevelopmental and psychiatric disorders to improve the early diagnosis intervention, and prognosis. The population changes in gut microbiota after birth are closely linked to neurodevelopmental/neuropsychiatric disorders in later life; thus, the dynamic expression and function of P2 receptors on gut epithelial cells during disease processes indicate a novel avenue for the evaluation of disease progression and for the discovery of related therapeutic compounds.

Preclinical evaluation of avermectins as novel therapeutic agents for alcohol use disorders

The deleterious effects of alcohol use disorders (AUDs) on human health have been documented worldwide. The enormous socioeconomic burden coupled with lack of efficacious pharmacotherapies underlies the need for improved treatment strategies. At present, there is a growing body of preclinical evidence that demonstrates the potential of avermectins [ivermectin (IVM), selamectin (SEL), abamectin (ABM), and moxidectin (MOX)] in treatment of AUDs. Avermectins are derived by fermentation of soil micro-organism, Streptomyces avermitilis, and have been extensively used for treatment of parasitic infections. From the mechanistic standpoint, avermectins are positive modulators of purinergic P2X4 receptors (P2X4Rs). P2X4Rs belong to P2X superfamily of cation-permeable ion channels gated by adenosine 5'-triphosphate (ATP). Building evidence has implicated a role for P2X4Rs in regulation of ethanol intake and that ethanol can inhibit ATP-gated currents in P2X4Rs. Investigations using recombinant cell models and animal models of alcohol drinking have reported that IVM, ABM, and MOX, but not SEL, were able to antagonize the inhibitory effects of ethanol on P2X4Rs in vitro and reduce ethanol intake in vivo. Furthermore, IVM was shown to reduce ethanol consumption via P2X4R potentiation in vivo, supporting the involvement of P2X4Rs in IVM's anti-alcohol effects and that P2X4Rs can be used as a platform for developing novel anti-alcohol compounds. Taken together, these findings support the utility of avermectins as a novel class of drug candidates for treatment of AUDs.