Background and Purpose: The ionotropic purinergic trimeric receptor P2X3 is a new drug target other than the opioid receptor for the treatment of refractory chronic cough (RCC). However, the only marketed P2X3 antagonist, Gefapixant/AF-219, has a side effect of taste disorders due to simultaneous action on the human P2X2/3 (hP2X2/3) heterotrimer. Therefore, selective molecules with high affinity for the hP2X3 homotrimer and low affinity for the hP2X2/3 heterotrimer have potential in iteration 2.0 RCC drug development, such as Sivopixant/S-600918, a clinical phase II RCC candidate with lower taste disturbance than Gefapixant. S-600918 and its analogue (3-(4-((3-chloro-4-isopropoxyphenyl)amino)-3-(4-methylbenzyl)-2,6-dioxo-3,6-dihydro-1,3,5-triazin-1(2H)-yl)propanoic acid (DDTPA) exhibit both high affinity and high selectivity for hP2X3 homotrimers compared to hP2X2/3 heterotrimer. The mechanism of its druggable site and this high selectivity is not clear. Experimental Approach: Here, we reveal a novel allosteric mechanism that distinguishes this drug candidate from other P2X3 inhibitors through chimera construction, site covalent occupation, metadynamics, mutagenesis, and electrophysiology. Key Results: We suggest that the tri-symmetric site adjacent to the upper vestibule determines the high affinity and selectivity of S-600918/DDTPA for hP2X3. Only four amino acids of the hP2X2 upper body domain swapped with hP2X3, allow the hP2X2/3 heterotrimer to gain comparable affinity for S-600918/DDTPA as the hP2X3 homotrimer. Conclusion and Implications: Thus, we have revealed the molecular basis for the cough suppressive effects and reduced side effects of new RCC clinical candidates from the perspective of receptor-ligand recognition, which may provide information critical for the development of new drugs targeting P2X3 for indications such as RCC, idiopathic pulmonary fibrosis (IPF), and primary hypertension.
Background: Ticagrelor is labelled as a reversible, direct-acting platelet P2Y12 receptor (P2Y12R) antagonist that is indicated clinically for the prevention of thrombotic events in patients with acute coronary syndrome (ACS). As with many antiplatelet drugs, ticagrelor therapy increases bleeding risk in patients which in emergency situations requires platelet transfusion although there is ongoing debate on its effectiveness following ticagrelor therapy. The aim of this study was to further examine the reversibility of ticagrelor at the P2Y12R. Methods: Studies were performed in human platelets with both P2Y12R-stimulated GTPase activity and platelet aggregation assessed. Cell-based bioluminescence resonance energy transfer (BRET) assays were also undertaken to assess G protein subunit activation downstream of P2Y12R activation. Results: Initial studies revealed a range of P2Y12R ligands including ticagrelor displayed inverse agonist activity at the P2Y12R. Of these only ticagrelor was resistant to wash-out. In both human platelets and cell-based assays, washing failed to reverse ticagrelor-dependent inhibition of ADP-stimulated P2Y12R function in contrast to other P2Y12R antagonists. The P2Y12R agonist 2MeSADP, which was also resistant to wash-out, was able to effectively compete with ticagrelor. In silico docking revealed that ticagrelor and 2MeSADP penetrated more deeply into the orthosteric binding pocket of the P2Y12R than other P2Y12R ligands. Conclusion: Ticagrelor binding to the P2Y12R is prolonged and more akin to that of an irreversible antagonist especially versus the endogenous P2Y12R agonist ADP. This study highlights the potential clinical need for novel ticagrelor reversal strategies in patients with spontaneous major bleeding and bleeding associated with urgent invasive procedures.
Background and Purpose: Chronic pain is a devastating problem affecting 1 in 5 individuals around the globe, with neuropathic pain the most debilitating and poorly treated type of chronic pain. Advances in transcriptomics and data mining have contributed to cataloging diverse cellular pathways and transcriptomic alterations in response to peripheral nerve injury but have focused on phenomenology and classifying transcriptomic responses. Experimental approach: Here, with the goal of identifying new types of pain-relieving agents, we compared transcriptional reprogramming changes in the dorsal spinal cord after peripheral nerve injury cross-sex and cross-species and imputed commonalities, as well as differences in cellular pathways and gene regulation. Key Results: We identified 93 transcripts in the dorsal horn that were increased by peripheral nerve injury in male and female mice and rats. Following gene ontology and transcription factor analyses, we constructed a pain interactome for the proteins encoded by the differentially expressed genes, discovering new, conserved signaling nodes. We interrogated the interactome with the Drug-Gene database to predict FDA-approved medications that may modulate key nodes within the network. The top hit from the analysis was fostamatinib, the molecular target of which is the non-receptor tyrosine kinase Syk, which our analysis had identified as a key node in the interactome. Conclusions & Implications : We found that intrathecally administrating the active metabolite of fostamatinib, R406, significantly reversed pain hypersensitivity in both sexes. Thus, we have identified and shown the efficacy of an agent that could not have been previously predicted to have analgesic properties.
Autism is a neurodevelopmental condition with a range of symptoms that vary in intensity and severity from person to person. Genetic sequencing has identified thousands of genes containing mutations in autistic individuals, which may contribute to the development of autistic symptoms. Several of these genes encode G protein-coupled receptors (GPCRs) which are cell surface expressed proteins that transduce extracellular messages to the intracellular space. Mutations in GPCRs can impact their function, resulting in aberrant signalling within cells, and across neurotransmitter systems in the brain. This review summarises the current knowledge on autism-associated single nucleotide variations encoding missense mutations in GPCRs, and the impact of these genetic mutations on GPCR function. For some autism-associated mutations, changes in GPCR expression levels, ligand affinity, potency and efficacy have been observed; however, for many the functional consequences remain unknown. Thus, further work to characterise the functional impacts of the genetically identified mutations is required.
Background and Purpose: Sepsis-surviving adult individuals commonly develop immunosuppression and increased susceptibility to secondary infections, outcome mediated by the axis IL-33/ILC2s/M2 macrophages/Tregs. Nonetheless, the long-term immune consequences of pediatric sepsis are indeterminate. We sought to investigate the role of age in the genesis of immunosuppression following sepsis. Experimental Approach: Here, we compared the frequency of Tregs, the activation of the IL33/ILC2s axis in M2 macrophages, and the DNA methylation of epithelial lung cells from post-septic infant and adult mice. Likewise, sepsis-surviving mice were inoculated intranasally with Pseudomonas aeruginosa or by subcutaneous inoculation of the B16 melanoma cell line. Finally, blood samples from sepsis-surviving patients were collected and the concentrations of IL-33 and Tregs frequency were assessed. Key Results: In contrast to 6-week-old, 2-week-old mice were resistant to secondary infection and did not show impairment in tumour controls upon melanoma challenge. Mechanistically, increased IL-33 levels, Tregs expansion, and activation of ILC2s and M2-macrophages were observed in 6-week-old but not 2-week-old post-septic mice. Moreover, impaired IL-33 production in 2-week-old post-septic mice was associated with increased DNA methylation in lung epithelial cells. Notably, IL-33 treatment boosted the expansion of Tregs and induced immunosuppression in 2-week-old mice. Clinically, adults but not pediatric post-septic patients exhibited higher counts of Tregs and sera IL-33 levels. Conclusion and Implications: These findings demonstrate a crucial and age-dependent role for IL-33 in post-sepsis immunosuppression. Thus, a better understanding of this process could lead to differential treatments for adult and pediatric sepsis.
Background and Purpose: Peripheral nerve trauma-induced dysregulation of pain-associated genes in the primary sensory neurons of dorsal root ganglion (DRG) contributes to neuropathic pain genesis. RNA-binding proteins participate in gene transcription. We hypothesized that RALY, an RNA-binding protein, participated in nerve trauma-induced dysregulation of DRG pain-associated genes and nociceptive hypersensitivity. Methods and results: Immunohistochemistry staining showed that RALY was expressed exclusively in the nuclei of DRG neurons. Peripheral nerve trauma caused by chronic constriction injury (CCI) of unilateral sciatic nerve produced time-dependent increases in the levels of Raly mRNA and RALY protein in injured DRG. Blocking this increase through DRG microinjection of adeno-associated virus 5 (AAV5)-expressing Raly shRNA reduced the CCI-induced elevation in the amount of eukaryotic initiation factor 4 gamma 2 (eIF4G2) mRNA and eIF4G2 protein in injured DRG and mitigated the development and maintenance of CCI-induced nociceptive hypersensitivity, without altering basal (acute) response to noxious stimuli and locomotor activity. Mimicking DRG increased RALY through DRG microinjection of AAV5 expressing Raly mRNA upregulated the expression of eIF4G2 mRNA and eIF4G2 protein in the DRG and led to hypersensitive responses to noxious stimuli in the absence of nerve trauma. Mechanistically, CCI promoted the binding of RALY to the promoter of eIF4G2 gene and triggered its transcriptional activity. Conclusion and Implications: Our findings indicate that RALY participates in nerve trauma-induced nociceptive hypersensitivity likely through transcriptionally triggering eIF4G2 expression in the DRG. RALY may be a potential target in neuropathic pain management.
Biased signaling is a natural result of GPCR allosteric function and should be expected from any and all synthetic agonists. Therefore, it may be encountered in all agonist discovery projects and must be considered as a beneficial (or possible detrimental) feature of new candidate molecules. While bias is easily detected , the synoptic nature of GPCR signaling makes translation of simple in vitro bias to complex in vivo systems problematic. The practical outcome of this is a difficulty in predicting the therapeutic value of biased signaling due to the failure of translation of identified biased signaling to in vivo agonism. This is discussed in this review as well as some new ways forward to improve this translation process and better exploit this powerful pharmacologic activity.
The KEAP1-NRF2 system plays a central role in cytoprotection and defense mechanisms against oxidative stress. Because KEAP1 serves as a biosensor for electrophiles by using its reactive thiols and because NRF2 is a transcriptional factor regulating genes involved in the sulfur-mediated redox reactions, the KEAP1-NRF2 system has been regarded as a sulfur-utilizing cytoprotective mechanism. NRF2 is a key regulator of cytoprotective genes, such as antioxidant and detoxification genes, and also to possess potent anti-inflammatory activity. NRF2 has been recently focused as a great modifier/regulator for the cellular metabolism and mitochondrial function. Particularly, the NRF2-mediated regulatory mechanisms of metabolites and mitochondria has been considered diverse, but has not been fully-clarified yet. This review article provides an overview of the molecular mechanisms that regulate NRF2 signaling and its cytoprotective roles, and also highlights NRF2 contribution to the cellular metabolism, particularly in the context of mitochondrial function and newly found sulfur metabolism.
Background and Purpose: How to prevent the damage of ionizing radiation to testis has become an urgent problem to be solved. The present aim is to investigate whether inhibition of p38MAPK signaling can alleviate radiation-induced testicular damage. Experimental Approaches: HE staining was used to measure the morphological changes of epididymis and testis. Immunohistochemistry staining was used to assess the expression of PLZF, SOX9, p-p38MAPK. RNA-Seq was used to profile gene expression. The expression of Mapk14, Atf2, Ddit3 and Ap1m1 genes was detected by qPCR. Western blotting was used to detect the protein expression of p38MAPK and p-p38MAPK. Key Results: There was a dose-response relationship between testicular injury and ionizing radiation. The sperm quality was significantly decreased at 6 and 8 weeks after 6Gy of radiation. Radiation led to the decrease of PLZF+ cells and increase of SOX9+ cells in testis. RNA-Seq data showed radiation induced 969 genes changed in the testis. The expression of genes related to p38MAPK signal pathway enriched by GO was significantly increased by qPCR. The expression of p-p38MAPK in testis was significantly increased at 4 weeks after irradiation. SB203580 treatment increased numbers of spermatozoa, the area and diameter of seminiferous tubules and numbers of SOX9+ cells in irradiated mice, which were consistent with the increased sperm movement rate and density under radiation with SB203580 administration. Conclusions and Implications: Ionizing radiation significantly changes testicular gene expression, in which p38MAPK signal pathway is activated. p38MAPK inhibitor SB203580 partially alleviates the testicular damage caused by radiation and accelerate the recovery of sperm quality.
Chronic Obstructive Pulmonary Disease (COPD) is a major incurable health burden, ranking as the 3rd leading cause of death worldwide, mainly driven by cigarette smoking. COPD is characterised by persistent airway inflammation, lung function decline, and premature aging with the presence of pulmonary senescent cells. This review proposes that cellular senescence, a state of stable cell cycle arrest linked to ageing; induced by inflammation and oxidative stress in COPD, extends beyond the lungs and impacts the systemic circulation. This “spill over” of senescent cells contributes to brain inflammation and damage, increasing the risk of neurological comorbidities, such as stroke, cerebral small vessel disease, and Alzheimer’s disease. The review explores the role of cellular senescence in COPD-associated brain conditions and investigates the relationship between cellular senescence and circadian rhythm in COPD. Additionally, it discusses potential therapies, including senomorphic and senolytic treatments, as novel strategies to halt or improve COPD progression.
Background and Purpose: P2X4 receptors (P2X4R) are ligand gated cation channels that are activated by extracellular adenosine 5′-triphosphate (ATP) released by neurons and glia. The receptors are widely expressed in the brain and have fractional calcium currents comparable to NMDA receptors. Although P2X4Rs were described to modulate synaptic transmission and plasticity, their involvement in shaping neuronal network activity remains to be elucidated. Exp. Approach: We investigated the effects of P2X receptors on network and synaptic level using local field potential electrophysiology, whole cell patch clamp recordings and calcium imaging in fast spiking parvalbumin positive interneurons (PVINs) in rat and mice hippocampal slices. The stable ATP analogue ATPγS, selective antagonists and P2X4R knockout mice were used. Key results: The P2XR agonist ATPγS reversibly decreased the power of gamma oscillations. This inhibition could be antagonized by the selective P2X4R antagonist PSB-12062 and was not observed in P2X4-/- mice. The phasic excitatory inputs of CA3 PVINs were one of the main regulators of the gamma power. Associational fibre compound excitatory postsynaptic currents (cEPSCs) in CA3 PVINs were inhibited by P2X4R activation. This effect was reversible, dependent on intracellular calcium and dynamin-dependent internalization of AMPA receptors. Conclusions and Implications: The results indicate that P2X4Rs are an important source of dendritic calcium in CA3 PVINs, thereby regulating excitatory synaptic inputs onto the cells and the state of gamma oscillations in the hippocampus. P2X4Rs represent an effective target to modulate hippocampal network activity in pathophysiological conditions such as Alzheimer’s disease and schizophrenia.
Editorial. Platelet purinergic receptors and non-thrombotic diseases.Simon C. Pitchford1* and Dingxin Pan.11Pulmonary Pharmacology Unit, Institute of Pharmaceutical Science, King’s College London, London, UK.*Author for correspondence and reprint requests:Dr Simon PitchfordPulmonary Pharmacology UnitInstitute of Pharmaceutical Science5.43 Franklin Wilkins Building150 Stamford StreetWaterloo CampusKing’s College LondonLondon UKSE1 9NHPhone: +44 2078484266Fax: +44 207 8484788Simon.firstname.lastname@example.org