Transient receptor potential channels as an emerging target for the treatment of Alzheimer's disease: Unravelling the potential of pharmacological interventions

Alzheimer's disease (AD) is a devastating disorder with a multifaceted aetiology characterized by dementia, which later progresses to cognitive impairment. Significant efforts have been made to develop pharmacological interventions that slow down the pathogenesis of AD. However, conventional drugs have failed to satisfactorily treat AD and are more focussed towards symptomatic management. Thus, there is a gap in the literature regarding novel targets and modulators targeting them for the effective treatment of AD. Recent studies have demonstrated that modulation of transient receptor potential (TRP) channels has the potential to halt AD pathogenesis at an early stage and rescue hippocampal neurons from death. Amongst several members, TRP channels like TRPA1, TRPC6, TRPM2 and TRPV2 have shown promising results in the attenuation of neurobehavioural cognitive deficits as well as signalling pathways governing such cognitive decline. Furthermore, as these channels govern the ionic balance in the cell, their beneficial effects have also been known to maintain the homeostasis of Ca2+, which is the major culprit eliciting the vicious cycle of excitotoxicity, mitochondrial dysfunction, ROS generation and neurodegeneration. Despite such tremendous potential of TRP channel modulators, their clinical investigation remains elusive. Therefore, in the present review, we have discussed such agents in the light of TRP channels as molecular targets for the amelioration of AD both at the preclinical and clinical levels.

The role of G protein-coupled receptors and their ligands in animal domestication

The domestication of plants and animals has resulted in one of the most significant cultural and socio-economical transitions in human history. Domestication of animals, including human-supervised reproduction, largely uncoupled particular animal species from their natural, evolutionary history driven by environmental and ecological factors. The primary motivations for domesticating animals were, and still are, producing food and materials (e.g. meat, eggs, honey or milk products, wool, leather products, jewelry and medication products) to support plowing in agriculture or in transportation (e.g. horse, cattle, camel and llama) and to facilitate human activities (for hunting, rescuing, therapeutic aid, guarding behavior and protecting or just as a companion). In recent years, decoded genetic information from more than 40 domesticated animal species have become available; these studies have identified genes and mutations associated with specific physiological and behavioral traits contributing to the complex genetic background of animal domestication. These breeding-altered genomes provide insights into the regulation of different physiological areas, including information on links between e.g. endocrinology and behavior, with important pathophysiological implications (e.g. for obesity and cancer), extending the interest in domestication well beyond the field. Several genes that have undergone selection during domestication and breeding encode specific G protein-coupled receptors, a class of membrane-spanning receptors involved in the regulation of a number of overarching functions such as reproduction, development, body homeostasis, metabolism, stress responses, cognition, learning and memory. Here we summarize the available literature on variations in G protein-coupled receptors and their ligands and how these have contributed to animal domestication.

Identifying microRNAs Possibly Implicated in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome and Fibromyalgia: A Review

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) and fibromyalgia (FM) are chronic syndromes of unknown etiology, accompanied by numerous symptoms affecting neurological and physical conditions. Despite frequent revisions of the diagnostic criteria, clinical practice guidelines are often outdated, leading to underdiagnosis and ineffective treatment. Our aim was to identify microRNA (miRNA) biomarkers implicated in pathological mechanisms underlying these diseases. A comprehensive literature review using publicly accessible databases was conducted. Interesting miRNAs were extracted from relevant publications on ME/CFS and/or FM, and were then linked to pathophysiological processes possibly manifesting these chronic diseases. Dysregulated miRNAs in ME/CFS and FM may serve as promising biomarkers for these diseases. Key identified miRNAs, such as miR-29c, miR-99b, miR-128, miR-374b, and miR-766, were frequently mentioned for their roles in immune response, mitochondrial dysfunction, oxidative stress, and central sensitization, while miR-23a, miR-103, miR-152, and miR-320 were implicated in multiple crucial pathological processes for FM and/or ME/CFS. In summary, both ME/CFS and FM seem to share many dysregulated biological or molecular processes, which may contribute to their commonly shared symptoms. This miRNA-based approach offers new angles for discovering molecular markers urgently needed for early diagnosis or therapeutics to tackle the pathology of these medically unexplained chronic diseases.

Ca2+-sensing receptor-TRP channel-mediated Ca2+ signaling: Functional diversity and pharmacological complexity

The Ca2+-sensing receptor (CaSR) is a G-protein-coupled receptor activated by elevated concentrations of extracellular Ca2+, and was initially known for its regulation of parathyroid hormone (PTH) release. Ubiquitous expression of CaSR in different tissues and organs was later noted and CaSR participation in various physiological functions was demonstrated. Accumulating evidence has suggested that CaSR functionally interacts with transient receptor potential (TRP) channels, which are mostly non-selective cation channels involved in sensing temperature, pain and stress. This review describes the interactions of CaSR with TRP channels in diverse cell types to trigger a variety of biological responses. CaSR has been known to interact with different types of G proteins. Possible involvements of G proteins, other signaling and scaffolding protein intermediates in CaSR-TRP interaction are discussed. In addition, an attempt will be made to extend the current understanding of biased agonism of CaSR.

Complement Component C5a and Fungal Pathogen Induce Diverse Responses through Crosstalk between Transient Receptor Potential Channel (TRPs) Subtypes in Human Conjunctival Epithelial Cells

The conjunctiva has immune-responsive properties to protect the eye from infections. Its innate immune system reacts against external pathogens, such as fungi. The complement factor C5a is an important contributor to the initial immune response. It is known that activation of transient-receptor-potential-vanilloid 1 (TRPV1) and TRP-melastatin 8 (TRPM8) channels is involved in different immune reactions and inflammation in the human body. The aim of this study was to determine if C5a and mucor racemosus e voluminae cellulae (MR) modulate Ca2+-signaling through changes in TRPs activity in human conjunctival epithelial cells (HCjECs). Furthermore, crosstalk was examined between C5a and MR in mediating calcium regulation. Intracellular Ca2+-concentration ([Ca2+]i) was measured by fluorescence calcium imaging, and whole-cell currents were recorded using the planar-patch-clamp technique. MR was used as a purified extract. Application of C5a (0.05-50 ng/mL) increased both [Ca2+]i and whole-cell currents, which were suppressed by either the TRPV1-blocker AMG 9810 or the TRPM8-blocker AMTB (both 20 µM). The N-terminal peptide C5L2p (20-50 ng/mL) blocked rises in [Ca2+]i induced by C5a. Moreover, the MR-induced rise in Ca2+-influx was suppressed by AMG 9810 and AMTB, as well as 0.05 ng/mL C5a. In conclusion, crosstalk between C5a and MR controls human conjunctival cell function through modulating interactions between TRPV1 and TRPM8 channel activity.

TRP Channels in Stroke

Ischemic stroke is a devastating disease that affects millions of patients worldwide. Unfortunately, there are no effective medications for mitigating brain injury after ischemic stroke. TRP channels are evolutionally ancient biosensors that detect external stimuli as well as tissue or cellular injury. To date, many members of the TRP superfamily have been reported to contribute to ischemic brain injury, including the TRPC subfamily (1, 3, 4, 5, 6, 7), TRPV subfamily (1, 2, 3, 4) and TRPM subfamily (2, 4, 7). These TRP channels share structural similarities but have distinct channel functions and properties. Their activation during ischemic stroke can be beneficial, detrimental, or even both. In this review, we focus on discussing the interesting features of stroke-related TRP channels and summarizing the underlying cellular and molecular mechanisms responsible for their involvement in ischemic brain injury.

The impact of volatile anesthetics and propofol on phosphatidylinositol 4,5-bisphosphate signaling

Phosphatidylinositol 4,5-bisphosphate (PIP2), as well as other anionic phospholipids, play a pivotal role in various cellular processes, including ion channel regulation, receptor trafficking, and intracellular signaling pathways. The binding of volatile anesthetics and propofol to PIP2 leads to alterations in PIP2-mediated signaling causing modulation of ion channels such as ɣ-aminobutyric acid type A (GABAA) receptors, voltage-gated calcium channels, and potassium channels through various mechanisms. Additionally, the interaction between anionic phospholipids and G protein-coupled receptors plays a critical role in various anesthetic pathways, with these anesthetic-induced changes impacting PIP2 levels which cause cascading effects on receptor trafficking, including GABAA receptor internalization. This comprehensive review of various mechanisms of interaction provides insights into the intricate interplay between PIP2 signaling and anesthetic-induced changes, shedding light on the molecular mechanisms underlying anesthesia.

Widespread transcriptomic alterations of transient receptor potential channel genes in cancer

Ion channels, in particular transient-receptor potential (TRP) channels, are essential genes that play important roles in many physiological processes. Emerging evidence has demonstrated that TRP genes are involved in a number of diseases, including various cancer types. However, we still lack knowledge about the expression alterations landscape of TRP genes across cancer types. In this review, we comprehensively reviewed and summarised the transcriptomes from more than 10 000 samples in 33 cancer types. We found that TRP genes were widespreadly transcriptomic dysregulated in cancer, which was associated with clinical survival of cancer patients. Perturbations of TRP genes were associated with a number of cancer pathways across cancer types. Moreover, we reviewed the functions of TRP family gene alterations in a number of diseases reported in recent studies. Taken together, our study comprehensively reviewed TRP genes with extensive transcriptomic alterations and their functions will directly contribute to cancer therapy and precision medicine.

SARS-CoV-2, periodontal pathogens, and host factors: The trinity of oral post-acute sequelae of COVID-19

COVID-19 as a pan-epidemic is waning but there it is imperative to understand virus interaction with oral tissues and oral inflammatory diseases. We review periodontal disease (PD), a common inflammatory oral disease, as a driver of COVID-19 and oral post-acute-sequelae conditions (PASC). Oral PASC identifies with PD, loss of teeth, dysgeusia, xerostomia, sialolitis-sialolith, and mucositis. We contend that PD-associated oral microbial dysbiosis involving higher burden of periodontopathic bacteria provide an optimal microenvironment for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. These pathogens interact with oral epithelial cells activate molecular or biochemical pathways that promote viral adherence, entry, and persistence in the oral cavity. A repertoire of diverse molecules identifies this relationship including lipids, carbohydrates and enzymes. The S protein of SARS-CoV-2 binds to the ACE2 receptor and is activated by protease activity of host furin or TRMPSS2 that cleave S protein subunits to promote viral entry. However, PD pathogens provide additional enzymatic assistance mimicking furin and augment SARS-CoV-2 adherence by inducing viral entry receptors ACE2/TRMPSS, which are poorly expressed on oral epithelial cells. We discuss the mechanisms involving periodontopathogens and host factors that facilitate SARS-CoV-2 infection and immune resistance resulting in incomplete clearance and risk for 'long-haul' oral health issues characterising PASC. Finally, we suggest potential diagnostic markers and treatment avenues to mitigate oral PASC.

Inhibition of TRPM8 function by prostacyclin receptor agonists requires coupling to Gq/11 proteins

BACKGROUND AND PURPOSE

The TRPM8 ion channel is involved in innocuous cold sensing and has a potent anti-inflammatory action. Its activation by lower temperature or chemical agonists such as menthol and icilin induces analgesic effects, reversing hypersensitivity and reducing chronic pain. On the other hand, prostacyclin (PGI2) enhances pain and inflammation by activating the IP receptors. Due to the critical roles of TRPM8 and IP receptors in the regulation of inflammatory pain, and considering their overlapping expression pattern, we analysed the functional interaction between human TRPM8 and IP receptors.

EXPERIMENTAL APPROACH

We transiently expressed human TRPM8 channels and IP receptors in HEK293T cells and carried out intracellular calcium and cAMP measurements. Additionally, we cultured neurons from the dorsal root ganglia (DRGs) of mice and determined the increase in intracellular calcium triggered by the TRPM8 agonist, icilin, in the presence of the IP receptor agonist cicaprost, the IP receptor antagonist Cay10441, and the Gq/11 inhibitor YM254890.

KEY RESULTS

Activation of IP receptors by selective agonists (cicaprost, beraprost, and iloprost) inhibited TRPM8 channel function, independently of the Gs-cAMP pathway. The potent inhibition of TRPM8 channels by IP receptor agonists involved Gq/11 coupling. These effects were also observed in neurons isolated from murine DRGs.

CONCLUSIONS AND IMPLICATIONS

Our results demonstrate an unusual signalling pathway of IP receptors by coupling to Gq/11 proteins to inhibit TRPM8 channel function. This pathway may contribute to a better understanding of the role of TRPM8 channels and IP receptors in regulating pain and inflammation.

Evaluation of Urtica dioica Phytochemicals against Therapeutic Targets of Allergic Rhinitis Using Computational Studies

Allergic rhinitis (AR) is a prevalent inflammatory condition affecting millions globally, with current treatments often associated with significant side effects. To seek safer and more effective alternatives, natural sources like Urtica dioica (UD) are being explored. However, UD's mechanism of action remains unknown. Therefore, to elucidate it, we conducted an in silico evaluation of UD phytochemicals' effects on known therapeutic targets of allergic rhinitis: histamine receptor 1 (HR1), neurokinin 1 receptor (NK1R), cysteinyl leukotriene receptor 1 (CLR1), chemoattractant receptor-homologous molecule expressed on type 2 helper T cells (CRTH2), and bradykinin receptor type 2 (BK2R). The docking analysis identified amentoflavone, alpha-tocotrienol, neoxanthin, and isorhamnetin 3-O-rutinoside as possessing a high affinity for all the receptors. Subsequently, molecular dynamics (MD) simulations were used to analyze the key interactions; the free energy of binding was calculated through Generalized Born and Surface Area Solvation (MMGBSA), and the conformational changes were evaluated. Alpha-tocotrienol exhibited a high affinity while also inducing positive conformational changes across all targets. Amentoflavone primarily affected CRTH2, neoxanthin targeted NK1R, CRTH2, and BK2R, and isorhamnetin-3-O-rutinoside acted on NK1R. These findings suggest UD's potential to treat AR symptoms by inhibiting these targets. Notably, alpha-tocotrienol emerges as a promising multi-target inhibitor. Further in vivo and in vitro studies are needed for validation.

Single-Cell RNA-Seq Reveals Coronary Heterogeneity and Identifies CD133+TRPV4high Endothelial Subpopulation in Regulating Flow-Induced Vascular Tone in Mice

BACKGROUND

Single-cell RNA-Seq analysis can determine the heterogeneity of cells between different tissues at a single-cell level. Coronary artery endothelial cells (ECs) are important to coronary blood flow. However, little is known about the heterogeneity of coronary artery ECs, and cellular identity responses to flow. Identifying endothelial subpopulations will contribute to the precise localization of vascular endothelial subpopulations, thus enabling the precision of vascular injury treatment.

METHODS

Here, we performed a single-cell RNA sequencing of 31 962 cells and functional assays of 3 branches of the coronary arteries (right coronary artery/circumflex left coronary artery/anterior descending left coronary artery) in wild-type mice.

RESULTS

We found a compendium of 7 distinct cell types in mouse coronary arteries, mainly ECs, granulocytes, cardiac myocytes, smooth muscle cells, lymphocytes, myeloid cells, and fibroblast cells, and showed spatial heterogeneity between arterial branches. Furthermore, we revealed a subpopulation of coronary artery ECs, CD133+TRPV4high ECs. TRPV4 (transient receptor potential vanilloid 4) in CD133+TRPV4high ECs is important for regulating vasodilation and coronary blood flow.

CONCLUSIONS

Our study elucidates the nature and range of coronary arterial cell diversity and highlights the importance of coronary CD133+TRPV4high ECs in regulating coronary vascular tone.

Joint CB1 and NGF Receptor Activation Suppresses TRPM8 Activation in Etoposide-Resistant Retinoblastoma Cells

In childhood, retinoblastoma (RB) is the most common primary tumor in the eye. Long term therapeutic management with etoposide of this life-threatening condition may have diminishing effectiveness since RB cells can develop cytostatic resistance to this drug. To determine whether changes in receptor-mediated control of Ca2+ signaling are associated with resistance development, fluorescence calcium imaging, semi-quantitative RT-qPCR analyses, and trypan blue dye exclusion staining patterns are compared in WERI-ETOR (etoposide-insensitive) and WERI-Rb1 (etoposide-sensitive) cells. The cannabinoid receptor agonist 1 (CNR1) WIN55,212-2 (40 µM), or the transient receptor potential melastatin 8 (TRPM8) agonist icilin (40 µM) elicit similar large Ca2+ transients in both cell line types. On the other hand, NGF (100 ng/mL) induces larger rises in WERI-ETOR cells than in WERI-Rb1 cells, and its lethality is larger in WERI-Rb1 cells than in WERI-ETOR cells. NGF and WIN55,212-2 induced additive Ca2+ transients in both cell types. However, following pretreatment with both NGF and WIN55,212-2, TRPM8 gene expression declines and icilin-induced Ca2+ transients are completely blocked only in WERI-ETOR cells. Furthermore, CNR1 gene expression levels are larger in WERI-ETOR cells than those in WERI-Rb1 cells. Therefore, the development of etoposide insensitivity may be associated with rises in CNR1 gene expression, which in turn suppress TRPM8 gene expression through crosstalk.

TRPV4 is expressed by enteric glia and muscularis macrophages of the colon but does not play a prominent role in colonic motility

Background

Mechanosensation is an important trigger of physiological processes in the gastrointestinal tract. Aberrant responses to mechanical input are associated with digestive disorders, including visceral hypersensitivity. Transient Receptor Potential Vanilloid 4 (TRPV4) is a mechanosensory ion channel with proposed roles in visceral afferent signaling, intestinal inflammation, and gut motility. While TRPV4 is a potential therapeutic target for digestive disease, current mechanistic understanding of how TRPV4 may influence gut function is limited by inconsistent reports of TRPV4 expression and distribution.

Methods

In this study we profiled functional expression of TRPV4 using Ca2+ imaging of wholemount preparations of the mouse, monkey, and human intestine in combination with immunofluorescent labeling for established cellular markers. The involvement of TRPV4 in colonic motility was assessed in vitro using videomapping and contraction assays.

Results

The TRPV4 agonist GSK1016790A evoked Ca2+ signaling in muscularis macrophages, enteric glia, and endothelial cells. TRPV4 specificity was confirmed using TRPV4 KO mouse tissue or antagonist pre-treatment. Calcium responses were not detected in other cell types required for neuromuscular signaling including enteric neurons, interstitial cells of Cajal, PDGFRα+ cells, and intestinal smooth muscle. TRPV4 activation led to rapid Ca2+ responses by a subpopulation of glial cells, followed by sustained Ca2+ signaling throughout the enteric glial network. Propagation of these waves was suppressed by inhibition of gap junctions or Ca2+ release from intracellular stores. Coordinated glial signaling in response to GSK1016790A was also disrupted in acute TNBS colitis. The involvement of TRPV4 in the initiation and propagation of colonic motility patterns was examined in vitro.

Conclusions

We reveal a previously unappreciated role for TRPV4 in the initiation of distension-evoked colonic motility. These observations provide new insights into the functional role of TRPV4 activation in the gut, with important implications for how TRPV4 may influence critical processes including inflammatory signaling and motility.

Direct activation of airway sensory C-fibers by SARS-CoV-2 S1 spike protein

Respiratory viral infection can lead to activation of sensory afferent nerves as indicated by the consequential sore throat, sneezing, coughing, and reflex secretions. In addition to causing troubling symptoms, sensory nerve activation likely accelerates viral spreading. The mechanism how viruses activate sensory nerve terminals during infection is unknown. In this study, we investigate whether coronavirus spike protein activates sensory nerves terminating in the airways. We used isolated vagally-innervated mouse trachea-lung preparation for two-photon microscopy and extracellular electrophysiological recordings. Using two-photon Ca2+ imaging, we evaluated a total number of 786 vagal bronchopulmonary nerves in six experiments. Approximately 49% of the sensory fibers were activated by S1 protein (4 μg/mL intratracheally). Extracellular nerve recording showed the S1 protein evoked action potential discharge in sensory C-fibers; of 39 airway C-fibers (one fiber per mouse), 17 were activated. Additionally, Fura-2 Ca2+ imaging was performed on neurons dissociated from vagal sensory ganglia (n = 254 from 22 mice). The result showed that 63% of neurons responded to S1 protein. SARS-CoV-2 S1 protein can lead to direct activation of sensory C-fiber nerve terminals in the bronchopulmonary tract. Direct activation of C-fibers may contribute to coronavirus symptoms, and amplify viral spreading in a population.

Role of sonic hedgehog signaling pathway in the regulation of ion channels: focus on its association with cardio-cerebrovascular diseases

Sonic hedgehog (SHH) signaling is vital for cell differentiation and proliferation during embryonic development, yet its role in cardiac, cerebral, and vascular pathophysiology is under debate. Recent studies have demonstrated that several compounds of SHH signaling regulate ion channels, which in turn affect the behavior of target cells. Some of these ion channels are involved in the cardio-cerebrovascular system. Here, we first reviewed the SHH signaling cascades, then its interaction with ion channels, and their impact on cardio-cerebrovascular diseases. Considering the complex cross talk of SHH signaling with other pathways that also affect ion channels and their potential impact on the cardio-cerebrovascular system, we highlight the necessity of thoroughly studying the effect of SHH signaling on ion homeostasis, which could serve as a novel mechanism for cardio-cerebrovascular diseases. Activation of SHH signaling influence ion channels activity, which in turn influence ion homeostasis, membrane potential, and electrophysiology, could serve as a novel strategy for cardio-cerebrovascular diseases.

Differentiation, Transcriptomic Profiling, and Calcium Imaging of Human Hypothalamic Neurons

Neurons in the hypothalamus orchestrate homeostatic physiological processes and behaviors essential for life. Human pluripotent stem cells (hPSCs) can be differentiated into many types of hypothalamic neurons, progenitors, and glia. This updated unit includes published studies and protocols with new advances in the differentiation, maturation, and interrogation by transcriptomic profiling and calcium imaging of human hypothalamic cell populations. Specifically, new methods to freeze and thaw hypothalamic progenitors after they have been patterned and before substantial neurogenesis has occurred are provided that will facilitate experimental flexibility and planning. Also included are updated recipes and protocols for neuronal maturation, with details on the equipment and methods for examining their transcriptomic response and cell-autonomous properties in culture in the presence of synaptic blockers. Together, these protocols facilitate the adoption and use of this model system for fundamental biological discovery and therapeutic translation to human diseases such as obesity, diabetes, sleep disorders, infertility, and chronic stress. © 2023 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: hPSC maintenance Basic Protocol 2: Hypothalamic neuron differentiation Support Protocol 1: Cortical neuron (control) differentiation Basic Protocol 3: Neuronal maturation Support Protocol 2: Cryopreservation and thawing of neuronal progenitors Support Protocol 3: Quality control: Confirmation of hypothalamic patterning and neurogenesis Support Protocol 4: Bulk RNA sequencing of hypothalamic cultures Basic Protocol 4: Calcium imaging of hypothalamic neurons using Fura-2 AM Alternate Protocol: Calcium imaging of green fluorescent hypothalamic neurons using Rhod-3 AM.

Angiotensin-(1-7) mediated calcium signalling by MAS

The G protein-coupled receptor, MAS, is the receptor of the endogenous ligand, Angiotensin (Ang)-(1-7). It is a promising drug target since the Ang-(1-7)/MAS axis is protective in the cardiovascular system. Therefore, a characterization of MAS signalling is important for developing novel therapeutics for cardiovascular diseases. In this paper, we show that Ang-(1-7) increases intracellular calcium in transiently MAS-transfected HEK293 cells. The calcium influx induced by the activation of MAS is dependent on plasma membrane Ca²⁺ channels, phospholipase C, and protein kinase C. Specifically, we could demonstrate that MAS employs non-selective, transient receptor potential channels (TRPs) for calcium entry.

Energy metabolism disturbance in migraine: From a mitochondrial point of view

Migraine is a serious central nervous system disease with a high incidence rate. Its pathogenesis is very complex, which brings great difficulties for clinical treatment. Recently, many studies have revealed that mitochondrial dysfunction may play a key role in migraine, which affects the hyperosmotic of Ca²⁺, the excessive production of free radicals, the decrease of mitochondrial membrane potential, the imbalance of mPTP opening and closing, and the decrease of oxidative phosphorylation level, which leads to neuronal energy exhaustion and apoptosis, and finally lessens the pain threshold and migraine attack. This article mainly introduces cortical spreading depression, a pathogenesis of migraine, and then damages the related function of mitochondria, which leads to migraine. Oxidative phosphorylation and the tricarboxylic acid cycle are the main ways to provide energy for the body. 95 percent of the energy needed for cell survival is provided by the mitochondrial respiratory chain. At the same time, hypoxia can lead to cell death and migraine. The pathological opening of the mitochondrial permeability transition pore can promote the interaction between pro-apoptotic protein and mitochondrial, destroy the structure of mPTP, and further lead to cell death. The increase of mPTP permeability can promote the accumulation of reactive oxygen species, which leads to a series of changes in the expression of proteins related to energy metabolism. Both Nitric oxide and Calcitonin gene-related peptide are closely related to the attack of migraine. Recent studies have shown that changes in their contents can also affect the energy metabolism of the body, so this paper reviews the above mechanisms and discusses the mechanism of brain energy metabolism of migraine, to provide new strategies for the prevention and treatment of migraine and promote the development of individualized and accurate treatment of migraine.

Diversification of PAR signaling through receptor crosstalk

Protease activated receptors (PARs) are among the first receptors shown to transactivate other receptors: noticeably, these interactions are not limited to members of the same family, but involve receptors as diverse as receptor kinases, prostanoid receptors, purinergic receptors and ionic channels among others. In this review, we will focus on the evidence for PAR interactions with members of their own family, as well as with other types of receptors. We will discuss recent evidence as well as what we consider as emerging areas to explore; from the signalling pathways triggered, to the physiological and pathological relevance of these interactions, since this additional level of molecular cross-talk between receptors and signaling pathways is only beginning to be explored and represents a novel mechanism providing diversity to receptor function and play important roles in physiology and disease.

Sensitivity of Ca2+-sensing receptor-transient receptor potential-mediated Ca2+ influx to extracellular acidity in bEND.3 endothelial cells

Ca²⁺-sensing receptors (CaSRs) are G protein-coupled receptors activated by elevated concentrations of extracellular Ca²⁺. In our previous works, we showed protein and functional expression of CaSR in mouse cerebral endothelial cell (EC) (bEND.3); the CaSR response (high Ca²⁺-elicited cytosolic [Ca²⁺] elevation) was unaffected by suppression of phospholipase C but in part involved Ca²⁺ influx through transient receptor potential V1 (TRPV1) channels. In this work, we investigated if extracellular acidity affected CaSR-mediated Ca²⁺ influx triggered by high (3 mM) Ca²⁺ (CaSR agonist), 3 mM spermine (CaSR agonist), and 10 mM cinacalcet (positive allosteric modulator of CaSR). Extracellular acidosis (pH 6.8 and pH 6.0) strongly suppressed cytosolic [Ca²⁺] elevation triggered by high Ca²⁺, spermine, and cinacalcet; acidosis also inhibited Mn²⁺ influx stimulated by high Ca²⁺ and cinacalcet. Purinoceptor-triggered Ca²⁺ response, however, was not suppressed by acidosis. Extracellular acidity also did not affect membrane potential, suggesting suppressed CaSR-mediated Ca²⁺ influx in acidity did not result from the reduced electrical driving force for Ca²⁺. Our results suggest Ca²⁺ influx through a putative CaSR-TRP complex in bEND.3 EC was sensitive to extracellular pH.

Transient Receptor Potential Channels: Important Players in Ocular Pain and Dry Eye Disease

Dry eye disease (DED) is a multifactorial disorder in which the eyes respond to minor stimuli with abnormal sensations, such as dryness, blurring, foreign body sensation, discomfort, irritation, and pain. Corneal pain, as one of DED’s main symptoms, has gained recognition due to its increasing prevalence, morbidity, and the resulting social burden. The cornea is the most innervated tissue in the body, and the maintenance of corneal integrity relies on a rich density of nociceptors, such as polymodal nociceptor neurons, cold thermoreceptor neurons, and mechano-nociceptor neurons. Their sensory responses to different stimulating forces are linked to the specific expression of transient receptor potential (TRP) channels. TRP channels are a group of unique ion channels that play important roles as cellular sensors for various stimuli. These channels are nonselective cation channels with variable Ca²⁺ selectivity. TRP homologs are a superfamily of 28 different members that are subdivided into 7 different subfamilies based on differences in sequence homology. Many of these subtypes are expressed in the eye on both neuronal and non-neuronal cells, where they affect various stress-induced regulatory responses essential for normal vision maintenance. This article reviews the current knowledge about the expression, function, and regulation of TRPs in ocular surface tissues. We also describe their implication in DED and ocular pain. These findings contribute to evidence suggesting that drug-targeting TRP channels may be of therapeutic benefit in the clinical setting of ocular pain.

Role of Ion Channels in the Chemotransduction and Mechanotransduction in Digestive Function and Feeding Behavior

The gastrointestinal tract constantly communicates with the environment, receiving and processing a wide range of information. The contents of the gastrointestinal tract and the gastrointestinal tract generate mechanical and chemical signals, which are essential for regulating digestive function and feeding behavior. There are many receptors here that sense intestinal contents, including nutrients, microbes, hormones, and small molecule compounds. In signal transduction, ion channels are indispensable as an essential component that can generate intracellular ionic changes or electrical signals. Ion channels generate electrical activity in numerous neurons and, more importantly, alter the action of non-neurons simply and effectively, and also affect satiety, molecular secretion, intestinal secretion, and motility through mechanisms of peripheral sensation, signaling, and altered cellular function. In this review, we focus on the identity of ion channels in chemosensing and mechanosensing in the gastrointestinal tract.

Sustained endosomal release of a neurokinin-1 receptor antagonist from nanostars provides long-lasting relief of chronic pain

Soft polymer nanoparticles designed to disassemble and release an antagonist of the neurokinin 1 receptor (NK₁R) in endosomes provide efficacious yet transient relief from chronic pain. These micellar nanoparticles are unstable and rapidly release cargo, which may limit the duration of analgesia. We examined the efficacy of stable star polymer nanostars containing the NK₁R antagonist aprepitant-amine for the treatment of chronic pain in mice. Nanostars continually released cargo for 24 h, trafficked through the endosomal system, and disrupted NK₁R endosomal signaling. After intrathecal injection, nanostars accumulated in endosomes of spinal neurons. Nanostar-aprepitant reversed mechanical, thermal and cold allodynia and normalized nociceptive behavior more efficaciously than free aprepitant in preclinical models of neuropathic and inflammatory pain. Analgesia was maintained for >10 h. The sustained endosomal delivery of antagonists from slow-release nanostars provides effective and long-lasting reversal of chronic pain.

Angiotensin and Endothelin Receptor Structures With Implications for Signaling Regulation and Pharmacological Targeting

In conjunction with the endothelin (ET) type A (ETAR) and type B (ETBR) receptors, angiotensin (AT) type 1 (AT1R) and type 2 (AT2R) receptors, are peptide-binding class A G-protein-coupled receptors (GPCRs) acting in a physiologically overlapping context. Angiotensin receptors (ATRs) are involved in regulating cell proliferation, as well as cardiovascular, renal, neurological, and endothelial functions. They are important therapeutic targets for several diseases or pathological conditions, such as hypertrophy, vascular inflammation, atherosclerosis, angiogenesis, and cancer. Endothelin receptors (ETRs) are expressed primarily in blood vessels, but also in the central nervous system or epithelial cells. They regulate blood pressure and cardiovascular homeostasis. Pathogenic conditions associated with ETR dysfunctions include cancer and pulmonary hypertension. While both receptor groups are activated by their respective peptide agonists, pathogenic autoantibodies (auto-Abs) can also activate the AT1R and ETAR accompanied by respective clinical conditions. To date, the exact mechanisms and differences in binding and receptor-activation mediated by auto-Abs as opposed to endogenous ligands are not well understood. Further, several questions regarding signaling regulation in these receptors remain open. In the last decade, several receptor structures in the apo- and ligand-bound states were determined with protein X-ray crystallography using conventional synchrotrons or X-ray Free-Electron Lasers (XFEL). These inactive and active complexes provide detailed information on ligand binding, signal induction or inhibition, as well as signal transduction, which is fundamental for understanding properties of different activity states. They are also supportive in the development of pharmacological strategies against dysfunctions at the receptors or in the associated signaling axis. Here, we summarize current structural information for the AT1R, AT2R, and ETBR to provide an improved molecular understanding.

Preparation and application of taste bud organoids in biomedicine towards chemical sensation mechanisms

Taste is one of the most basic and important sensations that is able to monitor the food quality and avoid intake of potential danger materials. Whether as an inevitable symptom of aging or a complication of cancer treatment, taste loss very seriously affects the patient's life quality. Taste bud organoids provide an alternative and convenient approach for the research of taste functions and the underlying mechanisms due to their characteristics of availability, strong maneuverability, and high similarity to the in-vivo taste buds. This review gives a systemic and comprehensive introduction to the preparation and application of taste bud organoids towards chemical sensing mechanisms. For the first, the basic structure and functions of taste buds will be briefly introduced. Then, the currently available approaches for the preparation of taste bud organoids are summarized and discussed, which are mainly divided into two categories, i.e. the stem/progenitor cell-derived approach and the tissue-derived approach. For the next, different applications of taste bud organoids in biomedicine are outlined based on their central roles such as disease modeling, biological sensing, gene regulation, and signal transduction. Finally, the current challenges, future development trends and prospects of research in taste bud organoids are proposed and discussed. This article is protected by copyright. All rights reserved.

Diverse Roles of TRPV4 in Macrophages: A Need for Unbiased Profiling

Transient receptor potential vanilloid 4 (TRPV4) is a non-selective mechanosensitive ion channel expressed by various macrophage populations. Recent reports have characterized the role of TRPV4 in shaping the activity and phenotype of macrophages to influence the innate immune response to pathogen exposure and inflammation. TRPV4 has been studied extensively in the context of inflammation and inflammatory pain. Although TRPV4 activity has been generally described as pro-inflammatory, emerging evidence suggests a more complex role where this channel may also contribute to anti-inflammatory activities. However, detailed understanding of how TRPV4 may influence the initiation, maintenance, and resolution of inflammatory disease remains limited. This review highlights recent insights into the cellular processes through which TRPV4 contributes to pathological conditions and immune processes, with a focus on macrophage biology. The potential use of high-throughput and omics methods as an unbiased approach for studying the functional outcomes of TRPV4 activation is also discussed.

GPCRs Are Optimal Regulators of Complex Biological Systems and Orchestrate the Interface between Health and Disease

GPCRs arguably represent the most effective current therapeutic targets for a plethora of diseases. GPCRs also possess a pivotal role in the regulation of the physiological balance between healthy and pathological conditions; thus, their importance in systems biology cannot be underestimated. The molecular diversity of GPCR signaling systems is likely to be closely associated with disease-associated changes in organismal tissue complexity and compartmentalization, thus enabling a nuanced GPCR-based capacity to interdict multiple disease pathomechanisms at a systemic level. GPCRs have been long considered as controllers of communication between tissues and cells. This communication involves the ligand-mediated control of cell surface receptors that then direct their stimuli to impact cell physiology. Given the tremendous success of GPCRs as therapeutic targets, considerable focus has been placed on the ability of these therapeutics to modulate diseases by acting at cell surface receptors. In the past decade, however, attention has focused upon how stable multiprotein GPCR superstructures, termed receptorsomes, both at the cell surface membrane and in the intracellular domain dictate and condition long-term GPCR activities associated with the regulation of protein expression patterns, cellular stress responses and DNA integrity management. The ability of these receptorsomes (often in the absence of typical cell surface ligands) to control complex cellular activities implicates them as key controllers of the functional balance between health and disease. A greater understanding of this function of GPCRs is likely to significantly augment our ability to further employ these proteins in a multitude of diseases.

Mini-review: Dissecting receptor-mediated stimulation of TRPV4 in nociceptive and inflammatory pathways

Transient Receptor Potential Vanilloid 4 (TRPV4) is a polymodal, non-selective cation channel that detects thermal, mechanical, and environmental cues and contributes to a range of diverse physiological processes. The effects of chronic TRPV4 stimulation and gain-of-function genetic mutations suggest that TRPV4 may also be a valuable therapeutic target for pathophysiological events including neurogenic inflammation, peripheral neuropathies, and impaired wound healing. There has been significant interest in defining how and where TRPV4 may promote inflammation and pain. Endogenous stimuli such as osmotic stress and lipid binding are established TRPV4 activators. The TRP channel family is also well-known to be controlled by 'receptor-operated' pathways. For example, G protein-coupled receptors (GPCRs) expressed by primary afferent neurons or other cells in inflammatory pathways utilize TRPV4 as an effector protein to amplify nociceptive and inflammatory signaling. Contributing to disorders including arthritis, neuropathies, and pulmonary edema, GPCRs such as the protease-activated receptor PAR2 mediate activation of kinase signaling cascades to increase TRPV4 phosphorylation, resulting in sensitization and enhanced neuronal excitability. Phospholipase activity also leads to production of polyunsaturated fatty acid lipid mediators that directly activate TRPV4. Consistent with the contribution of TRPV4 to disease, pharmacological inhibition or genetic ablation of TRPV4 can diminish receptor-mediated inflammatory events. This review outlines how receptor-mediated signaling is a major endogenous driver of TRPV4 gating and discusses key signaling pathways and emerging TRPV4 modulators such as the mechanosensitive Piezo1 ion channel. A collective understanding of how endogenous stimuli can influence TRPV4 function is critical for future therapeutic endeavors to modulate this channel.

Glucosylsphingosine evokes pruritus via activation of 5-HT2A receptor and TRPV4 in sensory neurons

BACKGROUND AND PURPOSE

Glucosylsphingosine (GS), an endogenous sphingolipid, is highly accumulated in the epidermis of patients with atopic dermatitis (AD) due to abnormal ceramide metabolism. More importantly, GS can evoke scratching behaviors. However, the precise molecular mechanism by which GS induces pruritus has been elusive. Thus, the present study aimed to elucidate the molecular signaling pathway of GS, especially at the peripheral sensory neuronal levels.

EXPERIMENTAL APPROACH

Calcium imaging was used to investigate the responses of HEK293T cells or mouse dorsal root ganglion (DRG) neurons to application of GS. Scratching behavior tests were also performed with wild-type and Trpv4 knockout mice.

KEY RESULTS

GS activated DRG neurons in a manner involving both the 5-HT_2A receptor and TRPV4. Furthermore, GS-induced responses were significantly suppressed by various inhibitors, including ketanserin (5-HT_2A receptor antagonist), YM254890 (Gα_q/11 inhibitor), gallein (Gβγ complex inhibitor), U73122 (phospholipase C inhibitor), bisindolylmaleimide I (PKC inhibitor), and HC067047 (TRPV4 antagonist). Moreover, DRG neurons from Trpv4 knockout mice exhibited significantly reduced responses to GS. Additionally, GS-evoked scratching behaviors were greatly decreased by pretreatment with inhibitors of either 5-HT_2A receptor or TRPV4. As expected, GS-evoked scratching behavior was also significantly decreased in Trpv4 knockout mice.

CONCLUSION AND IMPLICATIONS

Overall, the present study provides evidence for a novel molecular signaling pathway for GS-evoked pruritus, which utilizes both 5-HT_2A receptor and TRPV4 in mouse sensory neurons. Considering the high accumulation of GS in the epidermis of patients with AD, GS could be another pruritogen in patients with AD.

Transient receptor potential ankyrin 1 and calcium: Interactions and association with disease (Review)

Calcium (Ca²⁺) is an essential signaling molecule in all cells. It is involved in numerous fundamental functions, including cell life and death. Abnormal regulation of Ca²⁺ homeostasis may cause human diseases. Usually known as a member of the transient receptor potential (TRP) family, TRP ankyrin 1 (TRPA1) is the only member of the ankyrin subfamily identified in mammals so far and widely expressed in cells and tissues. As it is involved in numerous sensory disorders such as pain and pruritus, TRPA1 is a potential target for the treatment of neuropathy. The functions of TRP family members are closely related to Ca²⁺. TRPA1 has a high permeability to Ca²⁺, sodium and potassium ions as a non-selective cation channel and the Ca²⁺ influx mediated by TRPA1 is involved in a variety of biological processes. In the present review, research on the relationship between the TRPA1 channel and Ca²⁺ ions and their interaction in disease-associated processes was summarised. The therapeutic potential of the TRPA1 channel is highlighted, which is expected to become a novel direction for the prevention and treatment of health conditions such as cancer and neurodegenerative diseases.

Beneficial effect of capsaicin via TRPV4/EDH signals on mesenteric arterioles of normal and colitis mice

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Capsaicin induced vasorelaxation of human colonic submucosal arterioles in vitro and in vitro.

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Capsaicin induced an endothelium-dependent vasorelaxation of human submucosal arterioles.

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Capsaicin induced an endothelium-dependent vasorelaxation of mouse mesenteric arterioles.

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Capsaicin induced vasorelaxation minily by TRPV1-mediated endothelial nitric oxide release.

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Capsaicin induced vasorelaxation mainly by TRPV4/endothelium-dependent hyperpolarization.

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Capsaicin exerted anti-colitis action in wide-type mice, but not in TRPV4 knock-out mice.

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Capsaicin rescued the impaired endothelium-dependent vasorelaxation via TRPV4/EDH pathway.

Introduction

Although capsaicin has long been used as food additive and medication worldwide, its actions on gastrointestinal tract as its most delivery pathway have not been well addressed.

Objectives

In the present study, we aimed to study GI actions of capsaicin on mesenteric arterioles in normal and colitis mice and to elucidate the underlying mechanisms.

Methods

Vasorelaxation of human submucosal arterioles and the mesenteric arterioles from wide-type (WT) mice, TRPV1^−/− and TRPV4^−/− (KO) mice were measured. The expression and function of TRPV channels in endothelial cells were examined by q-PCR, immunostaining, Ca²⁺ imaging and membrane potential measurements.

Results

Capsaicin dose-dependently induced vasorelaxation of human submucosal arterioles and mouse mesenteric arterioles in vitro and in vivo through endothelium-dependent hyperpolarization (EDH), nitric oxide (NO), and prostacyclin (PGI₂). Using TRPV1 and TRPV4 KO mice, we found that capsaicin-induced vasorelaxation was predominately through TRPV4/EDH, but marginally through TRPV1/NO/PGI₂. Capsaicin induced hyperpolarization through activation of endothelial TRPV4 channels and intermediate-conductance of Ca²⁺-activated K⁺ channels to finally stimulate vasorelaxation. Importantly, capsaicin exerted anti-colitis action by rescuing the impaired ACh-induced vasorelaxation in WT colitis mice but not in TRPV4 KO colitis mice.

Conclusions

Capsaicin increases intestinal mucosal blood perfusion to potentially prevent/treat colitis through a novel TRPV4/EDH-dependent vasorelaxation of submucosal arterioles in health and colitis. This study further supports our previous notion that TRPV4/EDH in mesenteric circulation plays a critical role in the pathogenesis of colitis.

A novel strategy for treating cancer: understanding the role of Ca2+ signaling from nociceptive TRP channels in regulating cancer progression

Cancer is an aging-associated disease and caused by genomic instability that is driven by the accumulation of mutations and epimutations in the aging process. Although Ca²⁺ signaling, reactive oxygen species (ROS) accumulation, DNA damage response (DDR) and senescence inflammation response (SIR) are processed during genomic instability, the underlying mechanism for the cause of genomic instability and cancer development is still poorly understood and needs to be investigated. Nociceptive transient receptor potential (TRP) channels, which firstly respond to environmental stimuli, such as microbes, chemicals or physical injuries, potentiate regulation of the aging process by Ca²⁺ signaling. In this review, the authors provide an explanation of the dual role of nociceptive TRP channels in regulating cancer progression, initiating cancer progression by aging-induced genomic instability, and promoting malignancy by epigenetic regulation. Thus, therapeutically targeting nociceptive TRP channels seems to be a novel strategy for treating cancers.

Long noncoding RNA LOC100911498 is a novel regulator of neuropathic pain in rats

INTRODUCTION

Neuropathic pain (NP) is the most debilitating of all clinical pain syndromes and may be a consequence of dysfunction in the somatosensory nervous system. Unfortunately, the pathogenesis of NP is not fully understood yet and it cannot be cured totally. Long noncoding RNA (lncRNA) is a type of RNA molecule greater than 200 nucleotides, and dysregulated expression of lncRNAs play a critical role in the facilitation of NP. Previous study showed the expression level of LOC100911498 in the spinal cords of spared nerve injury (SNI) rats were increased. This research was aimed at exploring what role LOC100911498 plays in the pathophysiological process of NP.

METHODS

The mechanical withdrawal threshold (MWT) of rats was measured by the von Frey test. The expression levels of P2X4 receptor (P2X4R), ionized calcium-binding adaptor molecule 1 (Iba-1), p-p38 and brain-derived neurotrophic factor (BDNF) in spinal cords were detected, respectively.

RESULTS

Our results suggested that the level of LOC100911498 in SNI rats was markedly higher than that in the sham group; the MWT values in rats were treated with LOC100911498siRNA were increased, and the expression levels of P2X4R, Iba-1, p-p38 and BDNF in SNI+ LOC100911498siRNA group were reduced compared with those in the SNI group.

CONCLUSION

Our study indicated the effects lncRNA LOC100911498 siRNA exerted on NP were mediated by P2X4R on microglia in the spinal cords of rats. Further, LOC100911498 may be a novel positive regulator of NP by regulating the expression and function of the P2X4R.

GPR151 in nociceptors modulates neuropathic pain via regulating P2X3 function and microglial activation

Neuropathic pain is a major health problem that affects up to 7-10% of the population worldwide. Currently, neuropathic pain is difficult to treat due to its elusive mechanisms. Here we report that orphan G protein-coupled receptor 151 (GPR151) in nociceptive sensory neurons controls neuropathic pain induced by nerve injury. GPR151 was mainly expressed in nonpeptidergic C-fiber dorsal root ganglion (DRG) neurons and highly upregulated after nerve injury. Importantly, conditional knockout of Gpr151 in adult nociceptive sensory neurons significantly alleviated chronic constriction injury (CCI)-induced neuropathic pain-like behavior but did not affect basal nociception. Moreover, GPR151 in DRG neurons was required for CCI-induced neuronal hyperexcitability and upregulation of colony-stimulating factor 1 (CSF1), which is necessary for microglial activation in the spinal cord after nerve injury. Mechanistically, GPR151 coupled with P2X3 ion channels and promoted their functional activities in neuropathic pain-like hypersensitivity. Knockout of Gpr151 suppressed P2X3-mediated calcium elevation and spontaneous pain behavior in CCI mice. Conversely, overexpression of Gpr151 significantly enhanced P2X3-mediated calcium elevation and DRG neuronal excitability. Furthermore, knockdown of P2X3 in DRGs reversed CCI-induced CSF1 upregulation, spinal microglial activation, and neuropathic pain-like behavior. Finally, the co-expression of GPR151 and P2X3 was confirmed in small-diameter human DRG neurons, indicating the clinical relevance of our findings. Together, our results suggest that GPR151 in nociceptive DRG neurons plays a key role in the pathogenesis of neuropathic pain and could be a potential target for treating neuropathic pain.

Serotonin-induced vascular permeability is mediated by transient receptor potential vanilloid 4 in the airways and upper gastrointestinal tract of mice

Endothelial and epithelial cells form physical barriers that modulate the exchange of fluid and molecules. The integrity of these barriers can be influenced by signaling through G protein-coupled receptors (GPCRs) and ion channels. Serotonin (5-HT) is an important vasoactive mediator of tissue edema and inflammation. However, the mechanisms that drive 5-HT-induced plasma extravasation are poorly defined. The Transient Receptor Potential Vanilloid 4 (TRPV4) ion channel is an established enhancer of signaling by GPCRs that promote inflammation and endothelial barrier disruption. Here, we investigated the role of TRPV4 in 5-HT-induced plasma extravasation using pharmacological and genetic approaches. Activation of either TRPV4 or 5-HT receptors promoted significant plasma extravasation in the airway and upper gastrointestinal tract of mice. 5-HT-mediated extravasation was significantly reduced by pharmacological inhibition of the 5-HT2A receptor subtype, or with antagonism or deletion of TRPV4, consistent with functional interaction between 5-HT receptors and TRPV4. Inhibition of receptors for the neuropeptides substance P (SP) or calcitonin gene-related peptide (CGRP) diminished 5-HT-induced plasma extravasation. Supporting studies assessing treatment of HUVEC with 5-HT, CGRP, or SP was associated with ERK phosphorylation. Exposure to the TRPV4 activator GSK1016790A, but not 5-HT, increased intracellular Ca2+ in these cells. However, 5-HT pre-treatment enhanced GSK1016790A-mediated Ca2+ signaling, consistent with sensitization of TRPV4. The functional interaction was further characterized in HEK293 cells expressing 5-HT2A to reveal that TRPV4 enhances the duration of 5-HT-evoked Ca2+ signaling through a PLA2 and PKC-dependent mechanism. In summary, this study demonstrates that TRPV4 contributes to 5-HT2A-induced plasma extravasation in the airways and upper GI tract, with evidence supporting a mechanism of action involving SP and CGRP release.

Effect of resolvins on sensitisation of TRPV1 and visceral hypersensitivity in IBS

OBJECTIVE

Resolvins (RvD1, RvD2 and RvE1) are endogenous anti-inflammatory lipid mediators that display potent analgesic properties in somatic pain by modulating transient receptor potential vanilloid 1 (TRPV1) activation. To what extent these molecules could also have a beneficial effect on TRPV1 sensitisation and visceral hypersensitivity (VHS), mechanisms involved in IBS, remains unknown.

DESIGN

The effect of RvD1, RvD2 and RvE1 on TRPV1 activation and sensitisation by histamine or IBS supernatants was assessed on murine dorsal root ganglion (DRG) neurons using live Ca²⁺ imaging. Based on the results obtained in vitro, we further studied the effect of RvD2 in vivo using a murine model of post-infectious IBS and a rat model of post-inflammatory VHS. Finally, we also tested the effect of RvD2 on submucosal neurons in rectal biopsies of patients with IBS.

RESULTS

RvD1, RvD2 and RvE1 prevented histamine-induced TRPV1 sensitisation in DRG neurons at doses devoid of an analgesic effect. Of note, RvD2 also reversed TRPV1 sensitisation by histamine and IBS supernatant. This effect was blocked by the G protein receptor 18 (GPR18) antagonist O-1918 (3-30 µM) and by pertussis toxin. In addition, RvD2 reduced the capsaicin-induced Ca²⁺ response of rectal submucosal neurons of patients with IBS. Finally, treatment with RvD2 normalised pain responses to colorectal distention in both preclinical models of VHS.

CONCLUSIONS

Our data suggest that RvD2 and GPR18 agonists may represent interesting novel compounds to be further evaluated as treatment for IBS.

FAM19A5l Affects Mustard Oil-Induced Peripheral Nociception in Zebrafish

Family with sequence similarity 19 (chemokine (C-C motif)-like) member A5 (FAM19A5) is a chemokine-like secretory protein recently identified as involved in the regulation of osteoclast formation, post-injury neointima formation, and depression. Although roles for FAM19A5 have been described in nervous system development and psychiatric disorders, its role in the nervous system remains poorly understood. Here, we analyzed the evolutionary history of FAM19A genes in vertebrates and identified FAM19A5l, a paralogous zebrafish gene originating from a common ancestral FAM19A5 gene. Further, zebrafish FAM19A5l is expressed in trigeminal and dorsal root ganglion neurons as well as distinct neuronal subsets of the central nervous system. Interestingly, FAM19A5l⁺ trigeminal neurons are nociceptive neurons that localized with TRPA1b and TRPV1 and respond to mustard oil treatment. Behavioral analysis further revealed that the nociceptive response to mustard oil decreases in FAM19A5l-knockout zebrafish larvae. In addition, TRPA1b and NGFa mRNA levels are down- and upregulated in FAM19A5l-knockout and -overexpressing transgenic zebrafish, respectively. Together, our data suggest that FAM19A5l plays a role in nociceptive responses to mustard oil by regulating TRPA1b and NGFa expression in zebrafish.

The role of the skin microbiota in the modulation of cutaneous inflammation-Lessons from the gut

Inflammation is a vital defense mechanism used to protect the body from invading pathogens, but dysregulation can lead to chronic inflammatory disorders such as psoriasis and atopic dermatitis. Differences in microbiota composition have been observed in patients with inflammatory skin conditions compared with healthy individuals, particularly within lesions. There is also increasing evidence accumulating to support the notion that the microbiome contributes to the onset or modulates the severity of inflammatory diseases. Despite the known protective effects of orally administered lactic acid bacteria against inflammation, few studies have investigated the potential protective effects of topical application of bacteria on skin health and even fewer have looked at the potential anti-inflammatory effects of skin commensals. If lack of diversity and reduction in the abundance of specific commensal strains is observed in inflammatory skin lesions, and it is known that commensal bacteria can produce anti-inflammatory compounds, we suggest that certain members of the skin microbiota have anti-inflammatory properties that can be harnessed for use as topical therapeutics in inflammatory skin disorders.

TRP Channels in Brain Tumors

Malignant glioma including glioblastoma (GBM) is the most common group of primary brain tumors. Despite standard optimized treatment consisting of extensive resection followed by radiotherapy/concomitant and adjuvant therapy, GBM remains one of the most aggressive human cancers. GBM is a typical example of intra-heterogeneity modeled by different micro-environmental situations, one of the main causes of resistance to conventional treatments. The resistance to treatment is associated with angiogenesis, hypoxic and necrotic tumor areas while heterogeneity would accumulate during glioma cell invasion, supporting recurrence. These complex mechanisms require a focus on potential new molecular actors to consider new treatment options for gliomas. Among emerging and underexplored targets, transient receptor potential (TRP) channels belonging to a superfamily of non-selective cation channels which play critical roles in the responses to a number of external stimuli from the external environment were found to be related to cancer development, including glioma. Here, we discuss the potential as biological markers of diagnosis and prognosis of TRPC6, TRPM8, TRPV4, or TRPV1/V2 being associated with glioma patient overall survival. TRPs-inducing common or distinct mechanisms associated with their Ca²⁺-channel permeability and/or kinase function were detailed as involving miRNA or secondary effector signaling cascades in turn controlling proliferation, cell cycle, apoptotic pathways, DNA repair, resistance to treatment as well as migration/invasion. These recent observations of the key role played by TRPs such as TRPC6 in GBM growth and invasiveness, TRPV2 in proliferation and glioma-stem cell differentiation and TRPM2 as channel carriers of cytotoxic chemotherapy within glioma cells, should offer new directions for innovation in treatment strategies of high-grade glioma as GBM to overcome high resistance and recurrence.

Reduction of Pressure Pain Sensitivity as Novel Non-pharmacological Therapeutic Approach to Type 2 Diabetes: A Randomized Trial

BACKGROUND

Autonomic nervous system dysfunction (ANSD) is known to affect glucose metabolism in the mammalian body. Tradition holds that glucose homeostasis is regulated by the peripheral nervous system, and contemporary therapeutic intervention reflects this convention.

OBJECTIVES

The present study tested the role of cerebral regulation of ANSD as consequence of novel understanding of glucose metabolism and treatment target in type 2 diabetes (T2D), suggested by the claim that the pressure pain sensitivity (PPS) of the chest bone periosteum may be a measure of cerebral ANSD.

DESIGN

In a randomized controlled trial of 144 patients with T2D, we tested the claim that 6 months of this treatment would reduce PPS and improve peripheral glucose metabolism.

RESULTS

In the active treatment group, mean glycated hemoglobin A1c (HbA1c) declined from 53.8 to 50.5 mmol/mol (intragroup p = 0.001), compared with the change from 53.8 to 53.4 mmol/mol in the control group, with the same level of diabetes treatment but not receiving the active treatment (between group p = 0.036). Mean PPS declined from 76.6 to 56.1 units (p < 0.001) in the active treatment group and from 77.5 to 72.8 units (p = 0.02; between group p < 0.001) in the control group. Changes of PPS and HbA1c were correlated (r = 0.37; p < 0.001).

CONCLUSION

We conclude that the proposed approach to treatment of T2D is a potential supplement to conventional therapy.

CLINICAL TRIAL REGISTRATION

www.clinicaltrials.gov (NCT03576430).

The use of zebrafish as a non-traditional model organism in translational pain research: the knowns and the unknowns

The ability of the nervous system to detect a wide range of noxious stimuli is crucial to avoid life-threatening injury and to trigger protective behavioral and physiological responses. Pain represents a complex phenomenon, including nociception associated with cognitive and emotional processing. Animal experimental models have been developed to understand the mechanisms involved in pain response, as well as to discover novel pharmacological and non-pharmacological anti-pain therapies. Due to the genetic tractability, similar physiology, low cost, and rich behavioral repertoire, the zebrafish (Danio rerio) has been considered a powerful aquatic model for modeling pain responses. Here, we summarize the molecular machinery of zebrafish to recognize painful stimuli, as well as emphasize how zebrafish-based pain models have been successfully used to understand specific molecular, physiological, and behavioral changes following different algogens and/or noxious stimuli (e.g., acetic acid, formalin, histamine, Complete Freund's Adjuvant, cinnamaldehyde, allyl isothiocyanate, and fin clipping). We also discuss recent advances in zebrafish-based studies and outline the potential advantages and limitations of the existing models to examine the mechanisms underlying pain responses from an evolutionary and translational perspective. Finally, we outline how zebrafish models can represent emergent tools to explore pain behaviors and pain-related mood disorders, as well as to facilitate analgesic therapy screening in translational pain research.

The role of TRPA1 and TRPV4 channels in bronchoconstriction and plasma extravasation in airways of rats treated with captopril

Angiotensin-converting enzyme inhibitors (ACEis) may cause adverse airway events, such as cough and angioedema, due to a reduction in bradykinin breakdown and consequent activation of bradykinin type 2 receptor (B₂ receptor). Recent studies have shown that bradykinin can also sensitize pro-inflammatory receptors such as the transient receptor potential ankyrin 1 (TRPA1) and vanilloid 4 (TRPV4), which are implicated in several inflammatory airway diseases. Based on these considerations, the aim of this study was to understand the role of TRPA1 and TRPV4 channels in the bronchoconstrictive response and plasma extravasation in the trachea of rats pretreated with captopril. Using methods to detect alterations in airway resistance and plasma extravasation, we found that intravenous (i.v.) administration of bradykinin (0.03-0.3 μmol/kg, B₂ receptor agonist), allyl isothiocyanate (100-1000 μmol/kg, TRPA1 agonist) or GSK1016790A (0.01-0.1 μmol/kg, TRPV4 agonist), but not des-arg⁹-bradykinin (DABK; 100-300 μmol/kg, B₁ receptor agonist), induced bronchoconstriction in anaesthetized rats. In doses that did not cause significant bronchoconstriction, bradykinin (0.03 μmol/kg) or allyl isothiocyanate (100 μmol/kg), but not GSK1016790A (0.01 μmol/kg) or DABK (300 μmol/kg) induced an increased bronchoconstrictive response in rats pretreated with captopril (2.5 mg/kg, i.v.). On the other hand, in rats pretreated with captopril (5 mg/kg, i.v.), an increased bronchoconstrictive response to GSK1016790A (0.01 μmol/kg) was observed. The bronchoconstrictive response induced by bradykinin in captopril-pretreated rats was inhibited by intratracheal treatment (i.t.) with HC030031 (300 μg/50 μl; 36 ± 9%) or HC067047 (300 μg/50 μl; 35.1 ± 16%), for TRPA1 and TRPV4 antagonists, respectively. However, the co-administration of both antagonists did not increase this inhibition. The bronchoconstriction induced by allyl isothiocyanate in captopril-pretreated rats (2.5 mg/kg) was inhibited (58.3 ± 8%) by the B₂ receptor antagonist HOE140 (10 nmol/50 μl, i.t.). Similarly, the bronchoconstriction induced by GSK1016790A in captopril-pretreated rats (5 mg/kg) was also inhibited (84.2 ± 4%) by HOE140 (10 nmol/50 μl, i.t.). Furthermore, the plasma extravasation induced by captopril on the trachea of rats was inhibited by pretreatment with HC030031 (47.2 ± 8%) or HC067047 (38.9 ± 8%). Collectively, these findings support the hypothesis that TRPA1 and TRPV4, via a B₂ receptor activation-dependent pathway, are involved in the plasma extravasation and bronchoconstriction induced by captopril, making them possible pharmacological targets to prevent or remediate ACEi-induced adverse respiratory reactions.

Effect of TRPM8 and TRPA1 Polymorphisms on COPD Predisposition and Lung Function in COPD Patients

Certain transient receptor potential (TRP) channels including TRPM8 and TRPA1 are widely expressed in the respiratory tract and have been shown to be the receptors of cigarette smoke and particulate matter-the main causative factors of chronic obstructive pulmonary disease (COPD). The aim of the study was to investigate the effect of TRPM8 and TRPA1 polymorphisms on COPD predisposition and lung function in COPD patients. The study enrolled 143 COPD patients and 104 smokers with post-bronchodilator forced expiratory volume in one second (FEV1)/forced vital capacity (FVC) > 70%. Lung function was measured by spirometry. TRPM8 and TRPA1 polymorphisms were genotyped by LATE-PCR. None of the polymorphisms significantly influenced COPD predisposition after correction for covariates and multiple testing. Among COPD patients, the TT genotype of TRPA1 rs7819749 was significantly associated with higher degree of bronchial obstruction. In addition, we established that carriers of the C allele of TRPM8 rs11562975 more commonly had post-bronchodilator FEV1 < 60% (OR 3.2, 95%CI (1.14-8.94), p = 0.03) and revealed the effect of TRPA1 rs959976 and TRPM8 rs17865682 on bronchodilator response in COPD. Thus, the obtained results suggest possible involvement of TRPM8 and TRPA1 in COPD pathogenesis, indicating the necessity to further investigate their functional role in this pathology.

A basophil-neuronal axis promotes itch

Itch is an evolutionarily conserved sensation that facilitates expulsion of pathogens and noxious stimuli from the skin. However, in organ failure, cancer, and chronic inflammatory disorders such as atopic dermatitis (AD), itch becomes chronic, intractable, and debilitating. In addition to chronic itch, patients often experience intense acute itch exacerbations. Recent discoveries have unearthed the neuroimmune circuitry of itch, leading to the development of anti-itch treatments. However, mechanisms underlying acute itch exacerbations remain overlooked. Herein, we identify that a large proportion of patients with AD harbor allergen-specific immunoglobulin E (IgE) and exhibit a propensity for acute itch flares. In mice, while allergen-provoked acute itch is mediated by the mast cell-histamine axis in steady state, AD-associated inflammation renders this pathway dispensable. Instead, a previously unrecognized basophil-leukotriene (LT) axis emerges as critical for acute itch flares. By probing fundamental itch mechanisms, our study highlights a basophil-neuronal circuit that may underlie a variety of neuroimmune processes.

Ascorbate-induced oxidative stress mediates TRP channel activation and cytotoxicity in human etoposide-sensitive and -resistant retinoblastoma cells

There are indications that pharmacological doses of ascorbate (Asc) used as an adjuvant improve the chemotherapeutic management of cancer. This favorable outcome stems from its cytotoxic effects due to prooxidative mechanisms. Since regulation of intracellular Ca2+ levels contributes to the maintenance of cell viability, we hypothesized that one of the effects of Asc includes disrupting regulation of intracellular Ca2+ homeostasis. Accordingly, we determined if Asc induced intracellular Ca2+ influx through activation of pertussis sensitive Gi/o-coupled GPCR which in turn activated transient receptor potential (TRP) channels in both etoposide-resistant and -sensitive retinoblastoma (WERI-Rb1) tumor cells. Ca2+ imaging, whole-cell patch-clamping, and quantitative real-time PCR (qRT-PCR) were performed in parallel with measurements of RB cell survival using Trypan Blue cell dye exclusion. TRPM7 gene expression levels were similar in both cell lines whereas TRPV1, TRPM2, TRPA1, TRPC5, TRPV4, and TRPM8 gene expression levels were downregulated in the etoposide-resistant WERI-Rb1 cells. In the presence of extracellular Ca2+, 1 mM Asc induced larger intracellular Ca2+ transients in the etoposide-resistant WERI-Rb1 than in their etoposide-sensitive counterpart. With either 100 µM CPZ, 500 µM La3+, 10 mM NAC, or 100 µM 2-APB, these Ca2+ transients were markedly diminished. These inhibitors also had corresponding inhibitory effects on Asc-induced rises in whole-cell currents. Pertussis toxin (PTX) preincubation blocked rises in Ca2+ influx. Microscopic analyses showed that after 4 days of exposure to 1 mM Asc cell viability fell by nearly 100% in both RB cell lines. Taken together, one of the effects underlying oxidative mediated Asc-induced WERI-Rb1 cytotoxicity stems from its promotion of Gi/o coupled GPCR mediated increases in intracellular Ca2+ influx through TRP channels. Therefore, designing drugs targeting TRP channel modulation may be a viable approach to increase the efficacy of chemotherapeutic treatment of RB. Furthermore, Asc may be indicated as a possible supportive agent in anti-cancer therapies.

The Ion Channel and GPCR Toolkit of Brain Capillary Pericytes

Brain pericytes reside on the abluminal surface of capillaries, and their processes cover ~90% of the length of the capillary bed. These cells were first described almost 150 years ago (Eberth, 1871; Rouget, 1873) and have been the subject of intense experimental scrutiny in recent years, but their physiological roles remain uncertain and little is known of the complement of signaling elements that they employ to carry out their functions. In this review, we synthesize functional data with single-cell RNAseq screens to explore the ion channel and G protein-coupled receptor (GPCR) toolkit of mesh and thin-strand pericytes of the brain, with the aim of providing a framework for deeper explorations of the molecular mechanisms that govern pericyte physiology. We argue that their complement of channels and receptors ideally positions capillary pericytes to play a central role in adapting blood flow to meet the challenge of satisfying neuronal energy requirements from deep within the capillary bed, by enabling dynamic regulation of their membrane potential to influence the electrical output of the cell. In particular, we outline how genetic and functional evidence suggest an important role for G_s-coupled GPCRs and ATP-sensitive potassium (K_ATP) channels in this context. We put forth a predictive model for long-range hyperpolarizing electrical signaling from pericytes to upstream arterioles, and detail the TRP and Ca²⁺ channels and G_q, G_i/o, and G_12/13 signaling processes that counterbalance this. We underscore critical questions that need to be addressed to further advance our understanding of the signaling topology of capillary pericytes, and how this contributes to their physiological roles and their dysfunction in disease.

Resolvins: Potent Pain Inhibiting Lipid Mediators via Transient Receptor Potential Regulation

Chronic pain is a serious condition that occurs in the peripheral nervous system (PNS) and the central nervous system (CNS). It is caused by inflammation or nerve damage that induces the release of inflammatory mediators from immune cells and/or protein kinase activation in neuronal cells. Both nervous systems are closely linked; therefore, inflammation or nerve damage in the PNS can affect the CNS (central sensitization). In this process, nociceptive transient receptor potential (TRP) channel activation and expression are increased. As a result, nociceptive neurons are activated, and pain signals to the brain are amplified and prolonged. In other words, suppressing the onset of pain signals in the PNS can suppress pain signals to the CNS. Resolvins, endogenous lipid mediators generated during the resolution phase of acute inflammation, inhibit nociceptive TRP ion channels and alleviate chronic pain. This paper summarizes the effect of resolvins in chronic pain control and discusses future scientific perspectives. Further study on the effect of resolvins on neuropathic pain will expand the scope of pain research.

The structural basis for an on-off switch controlling Gβγ-mediated inhibition of TRPM3 channels

TRPM3 channels play important roles in the detection of noxious heat and in inflammatory thermal hyperalgesia. The activity of these ion channels in somatosensory neurons is tightly regulated by µ-opioid receptors through the signaling of Gβγ proteins, thereby reducing TRPM3-mediated pain. We show here that Gβγ directly binds to a domain of 10 amino acids in TRPM3 and solve a cocrystal structure of this domain together with Gβγ. Using these data and mutational analysis of full-length proteins, we pinpoint three amino acids in TRPM3 and their interacting partners in Gβ1 that are individually necessary for TRPM3 inhibition by Gβγ. The 10-amino-acid Gβγ-interacting domain in TRPM3 is subject to alternative splicing. Its inclusion in or exclusion from TRPM3 channel proteins therefore provides a mechanism for switching on or off the inhibitory action that Gβγ proteins exert on TRPM3 channels.

Crotamiton, an Anti-Scabies Agent, Suppresses Histamine- and Chloroquine-Induced Itch Pathways in Sensory Neurons and Alleviates Scratching in Mice

Crotamiton is an anti-scabies drug, but it was recently found that crotamiton also suppresses non-scabietic itching in mice. However, the underlying mechanism is largely unclear. Therefore, aim of the study is to investigate mechanisms of the anti-pruritic effect of crotamiton for non-scabietic itching. Histamine and chloroquine are used as non-scabietic pruritogens. The effect of crotamiton was identified using fluorometric intracellular calcium assays in HEK293T cells and primary cultured dorsal root ganglion (DRG) neurons. Further in vivo effect was evaluated by scratching behavior tests. Crotamiton strongly inhibited histamine-induced calcium influx in HEK293T cells, expressing both histamine receptor 1 (H1R) and transient receptor potential vanilloid 1 (TRPV1), as a model of histamine-induced itching. Similarly, it also blocked chloroquine-induced calcium influx in HEK293T cells, expressing both Mas-related G-protein-coupled receptor A3 (MRGPRA3) and transient receptor potential A1 (TRPA1), as a model of histamine-independent itching. Furthermore, crotamiton also suppressed both histamine- and chloroquine-induced calcium influx in primary cultures of mouse DRG. Additionally, crotamiton strongly suppressed histamine- and chloroquine-induced scratching in mice. Overall, it was found that crotamiton has an anti-pruritic effect against non-scabietic itching by histamine and chloroquine. Therefore, crotamiton may be used as a general anti-pruritic agent, irrespective of the presence of scabies.