Acute P38-Mediated Enhancement of P2X3 Receptor Currents by TNF-α in Rat Dorsal Root Ganglion Neurons

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.

Gefapixant, a Novel P2X3 Antagonist, Protects against Post Myocardial Infarction Cardiac Dysfunction and Remodeling Via Suppressing NLRP3 Inflammasome

OBJECTIVE

The ATP responsive P2 purinergic receptors can be subdivided into metabotropic P2X family and ionotropic P2Y family. Among these, P2X3 is a type of P2X receptor which is specifically expressed on nerves, especially on pre-ganglionic sensory fibers. This study investigates whether gefapixant possesses the potential of inhibiting cardiac sympathetic hypersensitivity to protect against cardiac remodeling in the context of myocardial infarction.

METHODS

The Sprague-Dawley rats were divided randomly into three groups: sham group-myocardial infarction group, and myocardial infarction with gefapixant treatment group. Myocardial infarction was induced by left anterior descending branch ligation. The gefapixant solution was intraperitoneally injected each time per day for 7 days and the appropriate dosage of gefapixant was determined according to the results of hematoxylin-eosin (HE) staining and myocardial injury biomarkers. Conditions of cardiac function were assessed by echocardiograph and cardiac fibrosis was evaluated by Western blotting and immunofluorescence staining of collagen I and collagen III. The sympathetic innervation was detected by norepinephrine concentration (pg/mL), in-vivo electrophysiology, and typical sympathetic biomarkers. Inflammatory cell infiltration was shown from immunofluorescence staining and pro-inflammatory signaling pathway activation was checked by immunohistology, quantitative realtime PCR (qPCR) and Western blotting.

RESULTS

It was found that gefapixant injection of 10 mg/kg per day had the highest dosage-efficacy ratio. Furthermore, gefapixant treatment improved cardiac pump function as shown by increased LVEF and LVFS, and decreased LVIDd and LVIDs. The expression levels of collagen I and collagen III, and TNF-α were all decreased by P2X3 inhibition. Mechanistically, the decreased activation of nucleotide-binding and oligomerization domain-like receptors family pyrin-domain-containing 3 (NLRP3) inflammasome and subsequent cleavage of caspase-1 which modulated interleukin-1β (IL-1β) and IL-18 level in heart after gefapixant treatment were associated with the suppressed cardiac inflammation.

CONCLUSION

It is suggested that P2X3 inhibition by gefapixant ameliorates post-infarct autonomic nervous imbalance, cardiac dysfunction, and remodeling possibly via inactivating NLRP3 inflammasome.

TNF-α enhances sensory DRG neuron excitability through modulation of P2X3 receptors in an acute colitis model

Previous studies have demonstrated that acute colonic inflammation leads to an increase in dorsal root ganglia (DRG) neuronal excitability. However, the signaling elements implicated in this hyperexcitability have yet to be fully unraveled. Extracellular adenosine 5’-triphosphate (ATP) is a well-recognized sensory signaling molecule that enhances the nociceptive response after inflammation through activation of P2X3 receptors, which are expressed mainly by peripheral sensory neurons. The aim of this study is to continue investigating how P2X3 affects neuronal hypersensitivity in an acute colitis animal model. To achieve this, DNBS (Dinitrobenzene sulfonic acid; 200 mg/kg) was intrarectally administered to C57BL/6 mice, and inflammation severity was assessed according to the following parameters: weight loss, macroscopic and microscopic scores. Perforated patch clamp technique was used to evaluate neuronal excitability via measuring changes in rheobase and action potential firing in T8-L1 DRG neurons. A-317491, a well-established potent and selective P2X3 receptor antagonist, served to dissect their contribution to recorded responses. Protein expression of P2X3 receptors in DRG was evaluated by western blotting and immunofluorescence. Four days post-DNBS administration, colons were processed for histological analyses of ulceration, crypt morphology, goblet cell density, and immune cell infiltration. DRG neurons from DNBS-treated mice were significantly more excitable compared with controls; these changes correlated with increased P2X3 receptor expression. Furthermore, TNF-α mRNA expression was also significantly higher in inflamed colons compared to controls. Incubation of control DRG neurons with TNF-α resulted in similar cell hyperexcitability as measured in DNBS-derived neurons. The selective P2X3 receptor antagonist, A-317491, blocked the TNF-α-induced effect. These results support the hypothesis that TNF-α enhances colon-innervating DRG neuron excitability via modulation of P2X3 receptor activity.

Association between P2X3 receptors and neuropathic pain: As a potential therapeutic target for therapy

Neuropathic pain is a common clinical symptom of various diseases, and it seriously affects the physical and mental health of patients. Owing to the complex pathological mechanism of neuropathic pain, clinical treatment of pain is challenging. Therefore, there is growing interest among researchers to explore potential therapeutic strategies for neuropathic pain. A large number of studies have shown that development of neuropathic pain is related to nerve conduction and related signaling molecules. P2X3 receptors (P2X3R) are ATP-dependent ion channels that participate in the transmission of neural information and related signaling pathways, sensitize the central nervous system, and play a key role in the development of neuropathic pain. In this paper, we summarized the structure and biological characteristics of the P2X3R gene and discussed the role of P2X3R in the nervous system. Moreover, we outlined the related pathological mechanisms of pain and described the relationship between P2X3R and chronic pain to provide valuable information for development of novel treatment strategies for pain.

Molecular and cellular mechanisms of itch and pain in atopic dermatitis and implications for novel therapeutics

Atopic dermatitis is a chronic inflammatory skin disease. Patients with atopic dermatitis experience inflammatory lesions associated with intense itch and pain, which lead to sleep disturbance and poor mental health and quality of life. We review the molecular mechanisms underlying itch and pain symptoms in atopic dermatitis and discuss the current clinical development of treatments for moderate‐to‐severe atopic dermatitis. The molecular pathology of atopic dermatitis includes aberrant immune activation involving significant cross‐talk among the skin and immune and neuronal cells. Exogenous and endogenous triggers modulate stimulation of mediators including cytokine/chemokine expression/release by the skin and immune cells, which causes inflammation, skin barrier disruption, activation and growth of sensory neurons, itch and pain. These complex interactions among cell types are mediated primarily by cytokines, but also involve chemokines, neurotransmitters, lipids, proteases, antimicrobial peptides, agonists of ion channels or various G protein–coupled receptors. Patients with atopic dermatitis have a cytokine profile characterised by abnormal levels of interleukins 4, 12, 13, 18, 22, 31 and 33; thymic stromal lymphopoietin; and interferon gamma. Cytokine receptors mainly signal through the Janus kinase/signal transducer and activator of transcription pathway. Among emerging novel therapeutics, several Janus kinase inhibitors are being developed for topical or systemic treatment of moderate‐to‐severe atopic dermatitis because of their potential to modulate cytokine expression and release. Janus kinase inhibitors lead to changes in gene expression that have favourable effects on local and systemic cytokine release, and probably other mediators, thus successfully modulating molecular mechanisms responsible for itch and pain in atopic dermatitis.

Suppression of P2X3 receptor-mediated currents by the activation of α2A -adrenergic receptors in rat dorsal root ganglion neurons

Aims

The α₂‐adrenergic receptor (α₂‐AR) agonists have been shown to be effective in the treatment of various pain. For example, dexmedetomidine (DEX), a selective α_2A‐AR agonist, can be used for peripheral analgesia. However, it is not yet fully elucidated for the precise molecular mechanisms. P2X3 receptor is a major receptor processing nociceptive information in primary sensory neurons. Herein, we show that a functional interaction of α_2A‐ARs and P2X3 receptors in dorsal root ganglia (DRG) neurons could contribute to peripheral analgesia of DEX.

Methods

Electrophysiological recordings were carried out on rat DRG neurons, and nociceptive behavior was quantified in rats.

Results

The activation of α_2A‐ARs by DEX suppressed P2X3 receptor‐mediated and α,β‐methylene‐ATP (α,β‐meATP)‐evoked inward currents in a concentration‐dependent and voltage‐independent manner. Pre‐application of DEX shifted the α,β‐meATP concentration‐response curve downwards, with a decrease of 50.43 ± 4.75% in the maximal current response of P2X3 receptors to α,β‐meATP in the presence of DEX. Suppression of α,β‐meATP‐evoked currents by DEX was blocked by the α_2A‐AR antagonist BRL44408 and prevented by intracellular application of the G_i/o protein inhibitor pertussis toxin, the adenylate cyclase activator forskolin, and the cAMP analog 8‐Br‐cAMP. DEX also suppressed α,β‐meATP‐evoked action potentials through α_2A‐ARs in rat DRG neurons. Finally, the activation of peripheral α_2A‐ARs by DEX had an analgesic effect on the α,β‐meATP‐induced nociception.

Conclusions

These results suggested that activation of α_2A‐ARs by DEX suppressed P2X3 receptor‐mediated electrophysiological and behavioral activity via a G_i/o proteins and cAMP signaling pathway, which was a novel potential mechanism underlying analgesia of peripheral α_2A‐AR agonists.