Fluorescence labeling strategies for cell surface expression of TRPV1.

Regulation of ion channel expression on the plasma membrane is a major determinant of neuronal excitability, and identifying the underlying mechanisms of this expression is critical to our understanding of neurons. Here, we present two orthogonal strategies to label extracellular sites of the ion channel TRPV1 that minimally perturb its function. We use the amber codon suppression technique to introduce a non-canonical amino acid (ncAA) with tetrazine click chemistry, compatible with a trans-cyclooctene coupled fluorescent dye. Additionally, by inserting the circularly permutated HaloTag (cpHaloTag) in an extracellular loop of TRPV1, we can incorporate a fluorescent dye of our choosing. Optimization of ncAA insertion sites was accomplished by screening residue positions between the S1 and S2 transmembrane domains with elevated missense variants in the human population. We identified T468 as a rapid labeling site (∼5 min) based on functional and biochemical assays in HEK293T/17 cells. Through adapting linker lengths and backbone placement of cpHaloTag on the extracellular side of TRPV1, we generated a fully functional channel construct, TRPV1exCellHalo, with intact wild-type gating properties. We used TRPV1exCellHalo in a single molecule experiment to track TRPV1 on the cell surface and validate studies that show decreased mobility of the channel upon activation. The application of these extracellular label TRPV1 (exCellTRPV1) constructs to track surface localization of the channel will shed significant light on the mechanisms regulating its expression and provide a general scheme to introduce similar modifications to other cell surface receptors.

The Influence of Sex Steroid Hormone Fluctuations on Capsaicin-Induced Pain and TRPV1 Expression.

Sexual dimorphism among mammals includes variations in the pain threshold. These differences are influenced by hormonal fluctuations in females during the estrous and menstrual cycles of rodents and humans, respectively. These physiological conditions display various phases, including proestrus and diestrus in rodents and follicular and luteal phases in humans, distinctly characterized by varying estrogen levels. In this study, we evaluated the capsaicin responses in male and female mice at different estrous cycle phases, using two murine acute pain models. Our findings indicate that the capsaicin-induced pain threshold was lower in the proestrus phase than in the other three phases in both pain assays. We also found that male mice exhibited a higher pain threshold than females in the proestrus phase, although it was similar to females in the other cycle phases. We also assessed the mRNA and protein levels of TRPV1 in the dorsal root and trigeminal ganglia of mice. Our results showed higher TRPV1 protein levels during proestrus compared to diestrus and male mice. Unexpectedly, we observed that the diestrus phase was associated with higher TRPV1 mRNA levels than those in both proestrus and male mice. These results underscore the hormonal influence on TRPV1 expression regulation and highlight the role of sex steroids in capsaicin-induced pain.

Nociceptive transient receptor potential ankyrin 1 (TRPA1) in sensory neurons are targets of the antifungal drug econazole.

BACKGROUND: Econazole is a widely used imidazole derivative antifungal for treating skin infections. The molecular targets for its frequent adverse effects of skin irritation symptoms, such as pruritus, burning sensation, and pain, have not been clarified. Transient receptor potential (TRP) channels, non-selective cation channels, are mainly expressed in peripheral sensory neurons and serve as sensors for various irritants. METHODS: We investigated the effect of econazole on TRP channel activation by measuring intracellular calcium concentration ([Ca2+]i) through fluorescent ratio imaging in mouse dorsal root ganglion (DRG) neurons isolated from wild-type, TRPA1(-/-) and TRPV1(-/-) mice, as well as in heterologously TRP channel-expressed cells. A cheek injection model was employed to assess econazole-induced itch and pain in vivo. RESULTS: Econazole evoked an increase in [Ca2+]i, which was abolished by the removal of extracellular Ca2+ in mouse DRG neurons. The [Ca2+]i responses to econazole were suppressed by a TRPA1 blocker but not by a TRPV1 blocker. Attenuation of the econazole-induced [Ca2+]i responses was observed in the TRPA1(-/-) mouse DRG neurons but was not significant in the TRPV1(-/-) neurons. Econazole increased the [Ca2+]i in HEK293 cells expressing TRPA1 (TRPA1-HEK) but not in those expressing TRPV1, although at higher concentrations, it induced Ca2+ mobilization from intracellular stores in untransfected naïve HEK293 cells. Miconazole, which is a structural analog of econazole, also increased the [Ca2+]i in mouse DRG neurons and TRPA1-HEK, and its nonspecific action was larger than econazole. Fluconazole, a triazole drug failed to activate TRPA1 and TRPV1 in mouse DRG neurons and TRPA1-HEK. Econazole induced itch and pain in wild-type mice, with reduced responses in TRPA1(-/-) mice. CONCLUSIONS: These findings suggested that the imidazole derivatives econazole and miconazole may induce skin irritation by activating nociceptive TRPA1 in the sensory neurons. Suppression of TRPA1 activation may mitigate the adverse effects of econazole.

Hot topic: Mapping of the human intranasal mucosal thermal sensitivity: A clinical study on thermal threshold and trigeminal receptors.

INTRODUCTION: The olfactory and trigeminal system are closely interlinked. Existing literature has primarily focused on characterizing trigeminal stimulation through mechanical and chemical stimulation, neglecting thermal stimulation thus far. The present study aimed to characterize the intranasal sensitivity to heat and the expression of trigeminal receptors (transient receptor potential channels, TRP). METHODS: A total of 20 healthy participants (aged 21-27 years, 11 women) were screened for olfactory function and trigeminal sensitivity using several tests. Under endoscopic control, a thermal stimulator was placed in 7 intranasal locations: anterior septum, lateral vestibulum, interior nose tip, lower turbinate, middle septum, middle turbinate, and olfactory cleft to determine the thermal threshold. Nasal swabs were obtained in 3 different locations (anterior septum, middle turbinate, olfactory cleft) to analyze the expression of trigeminal receptors TRP: TRPV1, TRPV3, TRPA1, TRPM8. RESULTS: The thermal threshold differed between locations (p = 0.018), with a trend for a higher threshold at the anterior septum (p = 0.092). There were no differences in quantitative receptor expression (p = 0.46) at the different sites. The highest overall receptor RNA expression was detected for TRPV1 over all sites (p<0.001). The expression of TRPV3 was highest at the anterior septum compared to the middle turbinate or the olfactory cleft. The thermal sensitivity correlated with olfactory sensitivity and results from tests were related to trigeminal function like intensity ratings of ammonium, a questionnaire regarding trigeminal function, nasal patency, and CO2 thresholds. However, no correlation was found between receptor expression and psychophysical measures of trigeminal function. DISCUSSION: This study provided the first insights about intranasal thermal sensitivity and suggested the presence of topographical differences in thermal thresholds. There was no correlation between thermal sensitivity and trigeminal mRNA receptor expression. However, thermal sensitivity was found to be associated with psychophysical measures of trigeminal and olfactory function.

Gastric Carcinogenesis and Potential Role of the Transient Receptor Potential Vanilloid 1 (TRPV1) Receptor: An Observational Histopathological Study.

The potential role of the transient receptor potential Vanilloid 1 (TRPV1) non-selective cation channel in gastric carcinogenesis remains unclear. The main objective of this study was to evaluate TRPV1 expression in gastric cancer (GC) and precursor lesions compared with controls. Patient inclusion was based on a retrospective review of pathology records. Patients were subdivided into five groups: Helicobacter pylori (H. pylori)-associated gastritis with gastric intestinal metaplasia (GIM) (n = 12), chronic atrophic gastritis (CAG) with GIM (n = 13), H. pylori-associated gastritis without GIM (n = 19), GC (n = 6) and controls (n = 5). TRPV1 expression was determined with immunohistochemistry and was significantly higher in patients with H. pylori-associated gastritis compared with controls (p = 0.002). TRPV1 expression was even higher in the presence of GIM compared with patients without GIM and controls (p < 0.001). There was a complete loss of TRPV1 expression in patients with GC. TRPV1 expression seems to contribute to gastric-mucosal inflammation and precursors of GC, which significantly increases in cancer precursor lesions but is completely lost in GC. These findings suggest TRPV1 expression to be a potential marker for precancerous conditions and a target for individualized treatment. Longitudinal studies are necessary to further address the role of TRPV1 in gastric carcinogenesis.

Structural basis of TRPV1 inhibition by SAF312 and cholesterol.

Transient Receptor Potential Vanilloid 1 (TRPV1) plays a central role in pain sensation and is thus an attractive pharmacological drug target. SAF312 is a potent, selective, and non-competitive antagonist of TRPV1 and shows promising potential in treating ocular surface pain. However, the precise mechanism by which SAF312 inhibits TRPV1 remains poorly understood. Here, we present the cryo-EM structure of human TRPV1 in complex with SAF312, elucidating the structural foundation of its antagonistic effects on TRPV1. SAF312 binds to the vanilloid binding pocket, preventing conformational changes in S4 and S5 helices, which are essential for channel gating. Unexpectedly, a putative cholesterol was found to contribute to SAF312's inhibition. Complemented by mutagenesis experiments and molecular dynamics simulations, our research offers substantial mechanistic insights into the regulation of TRPV1 by SAF312, highlighting the interplay between the antagonist and cholesterol in modulating TRPV1 function. This work not only expands our understanding of TRPV1 inhibition by SAF312 but also lays the groundwork for further developments in the design and optimization of TRPV1-related therapies.

A chemogenetic screen reveals that Trpv1-expressing neurons control regulatory T cells in the gut.

Neuroimmune cross-talk participates in intestinal tissue homeostasis and host defense. However, the matrix of interactions between arrays of molecularly defined neuron subsets and of immunocyte lineages remains unclear. We used a chemogenetic approach to activate eight distinct neuronal subsets, assessing effects by deep immunophenotyping, microbiome profiling, and immunocyte transcriptomics in intestinal organs. Distinct immune perturbations followed neuronal activation: Nitrergic neurons regulated T helper 17 (TH17)-like cells, and cholinergic neurons regulated neutrophils. Nociceptor neurons, expressing Trpv1, elicited the broadest immunomodulation, inducing changes in innate lymphocytes, macrophages, and RORγ+ regulatory T (Treg) cells. Neuroanatomical, genetic, and pharmacological follow-up showed that Trpv1+ neurons in dorsal root ganglia decreased Treg cell numbers via the neuropeptide calcitonin gene-related peptide (CGRP). Given the role of these neurons in nociception, these data potentially link pain signaling with gut Treg cell function.

Genetic code expansion, click chemistry, and light-activated PI3K reveal details of membrane protein trafficking downstream of receptor tyrosine kinases.

Ligands such as insulin, epidermal growth factor, platelet-derived growth factor, and nerve growth factor (NGF) initiate signals at the cell membrane by binding to receptor tyrosine kinases (RTKs). Along with G-protein-coupled receptors, RTKs are the main platforms for transducing extracellular signals into intracellular signals. Studying RTK signaling has been a challenge, however, due to the multiple signaling pathways to which RTKs typically are coupled, including MAP/ERK, PLCγ, and Class 1A phosphoinositide 3-kinases (PI3K). The multi-pronged RTK signaling has been a barrier to isolating the effects of any one downstream pathway. Here, we used optogenetic activation of PI3K to decouple its activation from other RTK signaling pathways. In this context, we used genetic code expansion to introduce a click chemistry noncanonical amino acid into the extracellular side of membrane proteins. Applying a cell-impermeant click chemistry fluorophore allowed us to visualize delivery of membrane proteins to the plasma membrane in real time. Using these approaches, we demonstrate that activation of PI3K, without activating other pathways downstream of RTK signaling, is sufficient to traffic the TRPV1 ion channels and insulin receptors to the plasma membrane.

Involvement of TRPV4 in temperature-dependent perspiration in mice.

Reports indicate that an interaction between TRPV4 and anoctamin 1 (ANO1) could be widely involved in water efflux of exocrine glands, suggesting that the interaction could play a role in perspiration. In secretory cells of sweat glands present in mouse foot pads, TRPV4 clearly colocalized with cytokeratin 8, ANO1, and aquaporin-5 (AQP5). Mouse sweat glands showed TRPV4-dependent cytosolic Ca2+ increases that were inhibited by menthol. Acetylcholine-stimulated sweating in foot pads was temperature-dependent in wild-type, but not in TRPV4-deficient mice and was inhibited by menthol both in wild-type and TRPM8KO mice. The basal sweating without acetylcholine stimulation was inhibited by an ANO1 inhibitor. Sweating could be important for maintaining friction forces in mouse foot pads, and this possibility is supported by the finding that wild-type mice climbed up a slippery slope more easily than TRPV4-deficient mice. Furthermore, TRPV4 expression was significantly higher in controls and normohidrotic skin from patients with acquired idiopathic generalized anhidrosis (AIGA) compared to anhidrotic skin from patients with AIGA. Collectively, TRPV4 is likely involved in temperature-dependent perspiration via interactions with ANO1, and TRPV4 itself or the TRPV4/ANO 1 complex would be targeted to develop agents that regulate perspiration.

Stress, spicy foods and elevated temperatures can all trigger specialized gland cells to move water to the skin ­ in other words, they can make us sweat. This process is one of the most important ways by which our bodies regulate their temperature and avoid life-threatening conditions such as heatstroke. Disorders in which this function is impaired, such as AIGA (acquired idiopathic generalized anhidrosis), pose significant health risks. Finding treatments for sweat-related diseases requires a detailed understanding of the molecular mechanisms behind sweating, which has yet to be achieved. Recent research has highlighted the role of two ion channels, TRPV4 and ANO1, in regulating fluid secretion in glands that produce tears and saliva. These gate-like proteins control how certain ions move in or out of cells, which also influences water movement. Once activated by external stimuli, TRPV4 allows calcium ions to enter the cell, causing ANO1 to open and chloride ions to leave. This results in water also exiting the cell through dedicated channels, before being collected in ducts connected to the outside of the body. TRPV4, which is activated by heat, is also present in human sweat gland cells. This prompted Kashio et al. to examine the role of these channels in sweat production, focusing on mice as well as AIGA patients. Probing TRPV4, ANO1 and AQP5 (a type of water channel) levels using fluorescent antibodies confirmed that these channels are all found in the same sweat gland cells in the foot pads of mice. Further experiments highlighted that TRPV4 mediates sweat production in these animals via ANO1 activation. As rodents do not regulate their body temperature by sweating, Kashio et al. explored the biological benefits of having sweaty paws. Mice lacking TRPV4 had reduced sweating and were less able to climb a slippery slope, suggesting that a layer of sweat helps improve traction. Finally, Kashio et al. compared samples obtained from healthy volunteers with those from AIGA patients and found that TRPV4 levels are lower in individuals affected by the disease. Overall, these findings reveal new insights into the underlying mechanisms of sweating, with TRPV4 a potential therapeutic target for conditions like AIGA. The results also suggest that sweating could be controlled by local changes in temperature detected by heat-sensing channels such as TRPV4. This would depart from our current understanding that sweating is solely controlled by the autonomic nervous system, which regulates involuntary bodily functions such as saliva and tear production.

LPS exacerbates TRPV4-mediated itch through the intracellular TLR4-PI3K signalling.

Pruritus is often accompanied with bacterial infections, but the underlying mechanism is not fully understood. Although previous studies revealed that lipopolysaccharides (LPS) could directly activate TRPV4 channel and TRPV4 is involved in the generation of both acute itch and chronic itch, whether and how LPS affects TRPV4-mediated itch sensation remains unclear. Here, we showed that LPS-mediated TRPV4 sensitization exacerbated GSK101-induced scratching behaviour in mice. Moreover, this effect was compromised in TLR4-knockout mice, suggesting LPS acted through a TLR4-dependent mechanism. Mechanistically, LPS enhanced GSK101-evoked calcium influx in mouse ear skin cells and HEK293T cells transfected with TRPV4. Further, LPS sensitized TRPV4 channel through the intracellular TLR4-PI3K-AKT signalling. In summary, our study found a modulatory role of LPS in TRPV4 function and highlighted the TLR4-TRPV4 interaction in itch signal amplification.

Role of Piezo2 in Schwann Cell Volume Regulation and Its Impact on Neurotrophic Release Regulation.

BACKGROUND/AIMS: Tactile perception relies on mechanoreceptors and nerve fibers, including c-fibers, Aß-fibers and Aδ-fibers. Schwann cells (SCs) play a crucial role in supporting nerve fibers, with non-myelinating SCs enwrapping c-fibers and myelinating SCs ensheathing Aß and Aδ fibers. Recent research has unveiled new functions for cutaneous sensory SCs, highlighting the involvement of nociceptive SCs in pain perception and Meissner corpuscle SCs in tactile sensation. Furthermore, Piezo2, previously associated with Merkel cell tactile sensitivity, has been identified in SCs. The goal of this study was to investigate the channels implicated in SC mechanosensitivity and the release process of neurotrophic factor secretion. METHODS: Immortalized IFRS1 SCs and human primary SCs generated two distinct subtypes of SCs: undifferentiated and differentiated SCs. Quantitative PCR was employed to evaluate the expression of differentiation markers and mechanosensitive channels, including TRP channels (TRPV4, TRPM7 and TRPA1) and Piezo channels (Piezo1 and Piezo2). To validate the functionality of specific mechanosensitive channels, Ca2+ imaging and electronic cell sizing experiments were conducted under hypotonic conditions, and inhibitors and siRNAs were used. Protein expression was assessed by Western blotting and immunostaining. Additionally, secretome analysis was performed to evaluate the release of neurotrophic factors in response to hypotonic stimulation, with BDNF, a representative trophic factor, quantified using ELISA. RESULTS: Induction of differentiation increased Piezo2 mRNA expression levels both in IFRS1 and in human primary SCs. Both cell types were responsive to hypotonic solutions, with differentiated SCs displaying a more pronounced response. Gd3+ and FM1-43 effectively inhibited hypotonicity-induced Ca2+ transients in differentiated SCs, implicating Piezo2 channels. Conversely, inhibitors of Piezo1 and TRPM7 (Dooku1 and NS8593, respectively) had no discernible impact. Moreover, Piezo2 in differentiated SCs appeared to participate in regulatory volume decreases (RVD) after cell swelling induced by hypotonic stimulation. A Piezo2 deficiency correlated with reduced RVD and prolonged cell swelling, leading to heightened release of the neurotrophic factor BDNF by upregulating the function of endogenously expressed Ca2+-permeable TRPV4. CONCLUSION: Our study unveils the mechanosensitivity of SCs and implicates Piezo2 channels in the release of neurotrophic factors from SCs. These results suggest that Piezo2 may contribute to RVD, thereby maintaining cellular homeostasis, and may also serve as a negative regulator of neurotrophic factor release. These findings underscore the need for further investigation into the role of Piezo2 in SC function and neurotrophic regulation.

Multicenter integration analysis of TRP channels revealed potential mechanisms of immunosuppressive microenvironment activation and identified a machine learning-derived signature for improving outcomes in gliomas.

AIM: This study aimed to explore the mechanisms of transient receptor potential (TRP) channels on the immune microenvironment and develop a TRP-related signature for predicting prognosis, immunotherapy response, and drug sensitivity in gliomas. METHODS: Based on the unsupervised clustering algorithm, we identified novel TRP channel clusters and investigated their biological function, immune microenvironment, and genomic heterogeneity. In vitro and in vivo experiments revealed the association between TRPV2 and macrophages. Subsequently, based on 96 machine learning algorithms and six independent glioma cohorts, we constructed a machine learning-based TRP channel signature (MLTS). The performance of the MLTS in predicting prognosis, immunotherapy response, and drug sensitivity was evaluated. RESULTS: Patients with high expression levels of TRP channel genes had worse prognoses, higher tumor mutation burden, and more activated immunosuppressive microenvironment. Meanwhile, TRPV2 was identified as the most essential regulator in TRP channels. TRPV2 activation could promote macrophages migration toward malignant cells and alleviate glioma prognosis. Furthermore, MLTS could work independently of common clinical features and present stable and superior prediction performance. CONCLUSION: This study investigated the comprehensive effect of TRP channel genes in gliomas and provided a promising tool for designing effective, precise treatment strategies.

Molecular mechanisms of two novel and selective TRPV1 channel activators.

Venomous toxins hold immense value as tools in elucidating the intricate structure and underlying mechanisms of ion channels. In this article, we identified of two novel toxins, Hainantoxin-XXI (HNTX-XXI) and Hainantoxin-XXII (HNTX-XXII), derived from the venom of the Chinese spider Ornithoctonus hainana. HNTX-XXI, boasting a molecular weight of 6869.095 Da, comprises 64 amino acid residues and contains 8 cysteines. Meanwhile, HNTX-XXII, with a molecular weight of 8623.732 Da, comprises 77 amino acid residues and contains 12 cysteines. Remarkably, we discovered that both HNTX-XXI and HNTX-XXII possess the ability to activate TRPV1. They activated TRPV1 with EC50 values of 3.6 ± 0.19 µM and 862 ± 56 nM, respectively. Furthermore, the current generated by the activation of TRPV1 by these toxins can be rapidly blocked by ruthenium red. Intriguingly, our analysis revealed that the interaction between HNTX-XXI and TRPV1 is mediated by three key amino acid residues: L465, V469, and D471. Similarly, the interaction between HNTX-XXII and TRPV1 is facilitated by four key amino acid residues: A657, F659, E600, and R601. These findings provide profound insights into the molecular basis of toxin-TRPV1 interactions and pave the way for future research exploring the therapeutic potential of these toxic peptides.

Ginger Extract and Omega-3 Fatty Acids Supplementation: A Promising Strategy to Improve Diabetic Cardiomyopathy.

Diabetic cardiomyopathy may result from the overproduction of ROS, TRPM2 and TRPV2. Moreover, the therapeutic role of ginger, omega-3 fatty acids, and their combinations on the expression of TRPM2 and TRPV2 and their relationship with apoptosis, inflammation, and oxidative damage in heart tissue of rats with type 2 diabetes have not yet been determined. Therefore, this study aimed to investigate the therapeutic effects of ginger and omega-3 fatty acids on diabetic cardiomyopathy by evaluating the cardiac gene expression of TRPM2 and TRPV2, oxidative damage, inflammation, and apoptosis in male rats. Ninety adult male Wistar rats were equally divided into nine control, diabetes, and treated diabetes groups. Ginger extract (100 mg/kg) and omega-3 fatty acids (50, 100, and 150 mg/kg) were orally administrated in diabetic rats for 6 weeks. Type 2 diabetes was induced by feeding a high-fat diet and a single dose of STZ (40 mg/kg). Glucose, cardiac troponin I (cTnI), lipid profile, insulin in serum, and TNF-alpha IL-6, SOD, MDA, and CAT in the left ventricle of the heart were measured. The cardiac expression of TRPM2, TRPV2, NF-kappaB, Bcl2, Bax, Cas-3, and Nrf-2 genes was also measured in the left ventricle of the heart. An electrocardiogram (ECG) was continuously recorded to monitor arrhythmia at the end of the course. The serum levels of cTnI, glucose, insulin, and lipid profile, and the cardiac levels of MDA, IL-6, and TNF-alpha increased in the diabetic group compared to the control group (p<0.05). Moreover, the cardiac levels of SOD and CAT decreased in the diabetic group compared to the control group (p<0.05). The cardiac expression of TRPM2, TRPV2, NF-kappaB, Bax, and Cas-3 increased and Bcl2 and Nrf-2 expression decreased in the diabetic group compared to the control group (p<0.05). However, simultaneous and separate treatment with ginger extract and omega-3 fatty acids (50, 100, and 150 mg/kg) could significantly moderate these changes (p<0.05). The results also showed that the simultaneous treatment of ginger extract and different doses of omega-3 fatty acids have improved therapeutic effects than their individual treatments (p<0.05). It can be concluded that ginger and omega-3 fatty acids showed protective effects against diabetic cardiomyopathy by inhibiting inflammation, apoptosis and oxidative damage of the heart and reducing blood glucose and cardiac expression of TRPM2 and TRPV2. Combining ginger and omega-3 in the diet may provide a natural approach to reducing the risk or progression of diabetic cardiomyopathy while preserving heart structure and function.

Aqp4a and Trpv4 mediate regulatory cell volume increase for swimming maintenance of marine fish spermatozoa.

Volume regulation is essential for cell homeostasis and physiological function. Amongst the sensory molecules that have been associated with volume regulation is the transient receptor potential vanilloid 4 (TRPV4), which is a non-selective cation channel that in conjunction with aquaporins, typically controls regulatory volume decrease (RVD). Here we show that the interaction between orthologous AQP4 (Aqp4a) and TRPV4 (Trpv4) is important for regulatory volume increase (RVI) in post-activated marine fish spermatozoa under high osmotic stress. Based upon electrophysiological, volumetric, and in vivo and ex vivo functional experiments using the pharmacological and immunological inhibition of Aqp4a and Trpv4 our model suggests that upon ejaculation and exposure to the hypertonic seawater, spermatozoon shrinkage is initially mediated by water efflux through Aqp1aa in the flagellar tail. The shrinkage results in an increase in intracellular Ca2+ concentration, and the activation of sperm motility and a Na+/K+/2Cl- (NKCC1) cotransporter. The activity of NKCC1 is required for the initiation of cell swelling, which secondarily activates the Aqp4a-Trpv4 complex to facilitate the influx of water via Aqp4a-M43 and Ca2+ via Trpv4 and L-type channels for the mediation of RVI. The inhibitory experiments show that blocking of each of these events prevents either shrinkage or RVI. Our data thus reveal that post-activated marine fish spermatozoa are capable of initiating RVI under a high hypertonic stress, which is essential for the maintenance of sperm motility.

TRPV4 activation in human corneal epithelial cells promotes membrane mucin production.

Given that the corneal epithelium is situated on the outermost part of the eye, its functions can be influenced by external temperatures and chemical substances. This study aimed to elucidate the expression profile of chemosensory receptors in corneal epithelial cells and analyze their role in eye function regulation. A comprehensive analysis of 425 chemosensory receptors in human corneal epithelial cells-transformed (HCE-T) revealed the functional expression of TRPV4. The activation of TRPV4 in HCE-T cells significantly increased the expression of membrane-associated mucins MUC1, MUC4, and MUC16, which are crucial for stabilizing tear films, with efficacy comparable to the active components of dry eye medications. The present study suggests that TRPV4, which is activated by body temperature, regulates mucin expression and proposes it as a novel target for dry eye treatment.

The chondrocyte "mechanome": Activation of the mechanosensitive ion channels TRPV4 and PIEZO1 drives unique transcriptional signatures.

The mechanosensitive ion channels Transient Receptor Potential Vanilloid 4 (TRPV4) and PIEZO1 transduce physiologic and supraphysiologic magnitudes of mechanical signals in the chondrocyte, respectively. TRPV4 activation promotes chondrogenesis, while PIEZO1 activation by supraphysiologic deformations drives cell death. The mechanisms by which activation of these channels discretely drives changes in gene expression to alter cell behavior remain to be determined. To date, no studies have contrasted the transcriptomic response to activation of these channels nor has any published data attempted to correlate these transcriptomes to alterations in cellular function. This study used RNA sequencing to comprehensively investigate the transcriptomes associated with activation of TRPV4 or PIEZO1, revealing that TRPV4 and PIEZO drive distinct transcriptomes and also exhibit unique co-regulated clusters of genes. Notably, activation of PIEZO1 through supraphysiologic deformation induced a transient inflammatory profile that overlapped with the interleukin (IL)-1-responsive transcriptome and contained genes associated with cartilage degradation and osteoarthritis progression. However, both TRPV4 and PIEZO1 were also shown to elicit anabolic effects. PIEZO1 expression promoted a pro-chondrogenic transcriptome under unloaded conditions, and daily treatment with PIEZO1 agonist Yoda1 significantly increased sulfated glycosaminoglycan deposition in vitro. These findings emphasize the presence of a broad "mechanome" with distinct effects of TRPV4 and PIEZO1 activation in chondrocytes, suggesting complex roles for PIEZO1 in both the physiologic and pathologic responses of chondrocytes. The identification of transcriptomic profiles unique to or shared by PIEZO1 and TRPV4 (distinct from IL-1-induced inflammation) could inform future therapeutic designs targeting these channels for the management and treatment of osteoarthritis.

TRPV1 and mast cell involvement in repeated variate stress-induced urinary bladder dysfunction in adult female mice.

The etiology of interstitial cystitis/bladder pain syndrome (IC/BPS) is unknown but likely multifactorial. IC/BPS symptoms can be exacerbated by psychological stress, but underlying mechanisms remain to be defined. Transient receptor potential vanilloid 1 (TRPV1) channels, expressed on nerve fibers, have been implicated in bladder dysfunction and colonic hypersensitivity with stress in rodents. Histamine/H1R activation of TRPV1+ nerves increases bladder afferent fiber sensitivity to distension. TRPV1 channels are also expressed on mast cells, previously implicated in contributing to IC/BPS etiology and symptoms. We have examined the contribution of TRPV1 and mast cells to bladder dysfunction after repeated variate stress (RVS). RVS increased (P ≤ 0.05) serum and fecal corticosterone expression and induced anxiety-like behavior in wild-type (WT) mice. Intravesical instillation of the selective TRPV1 antagonist capsazepine (CPZ) rescued RVS-induced bladder dysfunction in WT mice. Trpv1 knockout (KO) mice did not increase voiding frequency with RVS and did not exhibit increased serum corticosterone expression despite exhibiting anxiety-like behavior. Mast cell-deficient mice (B6.Cg-Kitw-sh) failed to demonstrate RVS-induced increased voiding frequency or serum corticosterone expression, whereas control (no stress) mast cell-deficient mice had similar functional bladder capacity to WT mice. TRPV1 protein expression was significantly increased in the rostral lumbar (L1-L2) spinal cord and dorsal root ganglia (DRG) in WT mice exposed to RVS, but no changes were observed in lumbosacral (L6-S1) spinal segments or DRG. These studies demonstrated TRPV1 and mast cell involvement in RVS-induced increased voiding frequency and suggest that TRPV1 and mast cells may be useful targets to mitigate stress-induced urinary bladder dysfunction.NEW & NOTEWORTHY Using pharmacological tools and transgenic mice in a repeated variate stress (RVS) model in female mice, we demonstrate that transient receptor potential vanilloid 1 (TRPV1) and mast cells contribute to the increased voiding frequency observed following RVS. TRPV1 and mast cells should continue to be considered as targets to improve bladder function in stress-induced bladder dysfunction.

Butyrate promotes visceral hypersensitivity in IBS model via mast cell-derived DRG neuron lincRNA-01028-PKC-TRPV1 pathway.

Emerging evidence indicates that gut dysbiosis is involved in the pathogenesis of visceral hypersensitivity (VH). However, how gut microbiota contributes to the development of VH is unknown. Here, we sought to examine the signal transduction pathways from gut to dorsal root ganglion (DRG) responsible for this. Therefore, abdominal withdrawal reflex (AWR) scores, fecal output, fecal water content, and total gastrointestinal transit time (TGITT) were assessed in Con rats, VH rats, rats treated with NaB, and VH rats treated with VSL#3. Fecal microbiota and its metabolite (short-chain fatty acids, SCFAs), mast cell degranulation in colon, lincRNA-01028, miR-143, and protease kinase C (PKC) and TRPV1 expression in DRGs were further detected. VH rats showed an increased fecal water content, a shortened TGITT, an increased abundance of Clostridium sensu stricto 1 and increased butyrate in fecal samples, an increased mast cell degranulation, an increased expression of lincRNA-01028, PKC, and TRPV1, and a decreased expression of miR-143 in DRGs compared with control rats, which could be restored by the application of probiotic VSL#3. The above-mentioned detection in rats treated with butyrate was similar to that of VH rats. We further confirm whether butyrate sensitized DRG neurons by a lincRNA-01028, miR-143, and PKC-dependent mechanism via mast cell in vitro. In co-cultures, MCs treated with butyrate elicited a higher TRPV1 current, a higher expression of lincRNA-01028, PKC, and a lower expression of miR-143 in DRG neurons, which could be inhibited by a lincRNA-01028 inhibitor. These findings indicate that butyrate promotes visceral hypersensitivity via mast cell-derived DRG neuron lincRNA-01028-PKC-TRPV1 pathway.IMPORTANCEIrritable bowel syndrome (IBS), characterized by visceral hypersensitivity, is a common gastrointestinal dysfunction syndrome. Although the gut microbiota plays a role in the pathogenesis and treatment of irritable bowel syndrome (IBS), the possible underlying mechanisms are unclear. Therefore, it is of critical importance to determine the signal transduction pathways from gut to DRG responsible for this in vitro and in vivo assay. This study demonstrated that butyrate sensitized TRPV1 in DRG neurons via mast cells in vivo and in vitro by a lincRNA-01028, miR-143, and PKC-dependent mechanism. VH rats similarly showed an increased abundance of Clostridium sensu stricto 1, an increased fecal butyrate, an increased mast cell degranulation, and increased expression of TRPV1 compared with control rats, which could be restored by the application of VSL#3. In conclusion, butyrate produced by the altered intestinal microbiota is associated with increased VH.

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OBJECTIVES: To observe the effect of moxibustion at "Xinshu" (BL15) and "Feishu" (BL13) on transient receptor potential vanilloid type 1(TRPV1), calcitonin gene-related peptide (CGRP), and serum interleukin-10 (IL-10) in the myocardial tissue of rats with chronic heart failure (CHF), so as to explore its underlying mechanisms in improvement of CHF. METHODS: Male SD rats were randomly divided into the normal, model, moxibustion, capsaicin, moxibustion + capsaicin, and moxibustion + solvent groups, with 10 rats in each group. The CHF model was established by permanent ligation of the anterior descending branch of the left coronary artery. Mild moxibustion was applied to bilateral BL13 and BL15 for 30 min once daily for 4 weeks. Rats in the capsaicin group were smeared with capsaicin in the acupoint area once a day for 4 weeks. For rats of the moxibustion + capsaicin and moxibustion + solvent groups, capsaicin and solvent were applied to the acupoint area before moxibustion for 4 weeks, respectively. The ejection fraction (EF) and left ventricular fractional shortening rate (FS) were examined by echocardiography. HE staining was used to observe the myecardial morphological structure. The mRNA and protein expression levels of TRPV1, CGRP and galectin-3 (Gal-3) in myocardial tissue were detected by real-time quantitative PCR and Western blot, respectively. The content of IL-10 in serum was detected by ELISA. RESULTS: After modeling, the pathological changes of myocardium (as cardiac muscle fiber disorder, inflammatory cell infiltration, etc.) were obvious, and the EF, FS, serum IL-10, protein and mRNA exspression of TRPV1 and CGRP were significantly decreased (P<0.01) in the model group compared with the normal group, while the protein and mRNA exspression of Gal-3 were significantly up-regulated (P<0.01). Following the interventions, the above-mentioned indexes were all reversed in moxibustion, capsaicin, and moxibustion + capsaicin groups (P<0.01), and the effect of moxibustion + capsaicin was the best (P<0.05, P<0.01). CONCLUSIONS: Moxibustion can reduce myocardial injury and improve cardiac function in CHF rats, which may be related to its effects in up-regulating the expression of TRPV1 and CGRP, and down-regulating the expression of Gal-3 to alleviate myocardial fibrosis.