Gastric adaptive relaxation (GAR) is impaired in ∼40% of functional dyspepsia (FD) patients, and nitric oxide (NO) released from inhibitory motor neurons plays an important role in this relaxation. Although the underlying molecular mechanism of GAR is poorly understood, transient receptor potential channel vanilloid 2 (TRPV2) mechano- and chemoreceptors are expressed in mouse intestinal inhibitory motor neurons and are involved in intestinal relaxation. The aim of this study was to evaluate the distribution of TRPV2 in inhibitory motor neurons throughout the mouse gastrointestinal tract and the contribution of TRPV2 to GAR. RT-PCR and immunohistochemical analyses were used to detect TRPV2 mRNA and protein, respectively. Intragastric pressure was determined with an isolated mouse stomach. Gastric emptying (GE) in vivo was determined using a test meal. TRPV2 mRNA was detected throughout the mouse gastrointestinal tract, and TRPV2 immunoreactivity was detected in 84.3% of neuronal nitric oxide synthase-expressing myenteric neurons in the stomach. GAR, which was expressed as the rate of decline of intragastric pressure in response to volume stimuli, was significantly enhanced by the TRPV2 activator probenecid, and the enhancement was inhibited by the TRPV2 inhibitor tranilast. GE was significantly accelerated by TRPV2 agonist applications, and the probenecid-induced enhancement was significantly inhibited by tranilast coapplication. Mechanosensitive TRPV2 was expressed in inhibitory motor neurons in the mouse stomach and contributed to GAR and GE. TRPV2 may be a promising target for FD patients with impaired GAR.

Transient receptor potential vanilloid 4-dependent calcium influx and ATP release in mouse and rat gastric epithelia

Background: Helicobacter pylori (HP) infection induces methylation silencing of specific genes in gastric epithelium. Various stimuli activate the nonselective cation channel TRPV4, which is expressed in gastric epithelium where it detects mechanical stimuli and promotes ATP release. As CpG islands in TRPV4 are methylated in HP‐infected gastric epithelium, we evaluated HP infection‐dependent changes in TRPV4 expression in gastric epithelium.Materials and Methods: Human gastric biopsy samples, a human gastric cancer cell line (AGS), and a normal gastric epithelial cell line (GES‐1) were used to detect TRPV4 mRNA and protein expression by RT‐PCR and Western blotting, respectively. Ca²⁺ imaging was used to evaluate TRPV4 ion channel activity. TRPV4 methylation status was assessed by methylation‐specific PCR (MSP). ATP release was measured by a luciferin‐luciferase assay.Results: TRPV4 mRNA and protein were detected in human gastric biopsy samples and in GES‐1 cells. MSP and demethylation assays showed TRPV4 methylation silencing in AGS cells. HP coculture directly induced methylation silencing of TRPV4 in GES‐1 cells. In human samples, HP infection was associated with TRPV4 methylation silencing that recovered after HP eradication in a time‐dependent manner.Conclusion: HP infection‐dependent DNA methylation suppressed TRPV4 expression in human gastric epithelia, suggesting that TRPV4 methylation may be involved in HP‐associated dyspepsia.

Adenosine triphosphate (ATP) modulates mechanosensitive vagal afferent nerves in the gastrointestinal tract. ATP is stored in secretory vesicles via the ATP transporter VNUT. Recently, the bisphosphate clodronate was reported to inhibit VNUT and was suggested to be a safe potent therapeutic option for chronic pain. Transient receptor potential vanilloid 4 (TRPV4) is activated by mechanical stimuli and some epoxyeicosatrienoic acids and becomes sensitized under inflammatory conditions. We have previously reported that TRPV4 and VNUT are expressed in mouse esophageal keratinocytes and that TRPV4 activation induces ATP release in gastric epithelial cells. Here we show the expression of TRPV4 and VNUT in normal human gastrointestinal cell derived cell lines (GES-1 and CCD 841) and in tissues from normal and VNUT-KO mice. TRPV4 agonists (GSK101 or 8,9-EET) induced an increase in cytosolic Ca²⁺ and/or current responses in mouse primary colonic epithelial cells and CCD 841 cells, but not in cells isolated from TRPV4-KO mice. TRPV4 agonists (GSK101 or 5.6-EET) also induced ATP release in GES-1 and CCD 841 cells, which could be blocked by the VNUT inhibitor, clodronate. Thus, VNUT inhibition with clodronate could represent a novel therapeutic option for visceral pain.

Background: Transient receptor potential vanilloid 4 (TRPV4) is activated by stretch (mechanical), warm temperature, some epoxyeicosatrienoic acids, and lipopolysaccharide. TRPV4 is expressed throughout the gastrointestinal epithelia and its activation induces adenosine triphosphate (ATP) exocytosis that is involved in visceral hypersensitivity. As an ATP transporter, vesicular nucleotide transporter (VNUT) mediates ATP storage in secretory vesicles and ATP release via exocytosis upon stimulation. Summary: TRPV4 is sensitized under inflammatory conditions by a variety of factors, including proteases and serotonin, whereas methylation-dependent silencing of TRPV4 expression is associated with various pathophysiological conditions. Gastrointestinal epithelia also release ATP in response to hypo-osmolality or acid through molecular mechanisms that remain unclear. These synergistically released ATP could be involved in visceral hypersensitivity. Low concentrations of the first generation bisphosphate, clodronate, were recently reported to inhibit VNUT activity and thus clodronate may be a safe and potent therapeutic option to treat visceral pain. Key Messages: This review focuses on: (1) ATP and TRPV4 activities in gastrointestinal epithelia; (2) factors that could modulate TRPV4 activity in gastrointestinal epithelia; and (3) the inhibition of VNUT as a potential novel therapeutic strategy for functional gastrointestinal disorders.

IBS is not considered to be an organic disease and usually shows no abnormality on lower gastrointestinal endoscopy, although biofilm formation, dysbiosis, and histological microinflammation have recently been reported in patients with IBS. In this study, we investigated whether an artificial intelligence (AI) colorectal image model can identify minute endoscopic changes, which cannot typically be detected by human investigators, that are associated with IBS. Study subjects were identified based on electronic medical records and categorized as IBS (Group I; n = 11), IBS with predominant constipation (IBS-C; Group C; n = 12), and IBS with predominant diarrhea (IBS-D; Group D; n = 12). The study subjects had no other diseases. Colonoscopy images from IBS patients and from asymptomatic healthy subjects (Group N; n = 88) were obtained. Google Cloud Platform AutoML Vision (single-label classification) was used to construct AI image models to calculate sensitivity, specificity, predictive value, and AUC. A total of 2479, 382, 538, and 484 images were randomly selected for Groups N, I, C and D, respectively. The AUC of the model discriminating between Group N and I was 0.95. Sensitivity, specificity, positive predictive value, and negative predictive value of Group I detection were 30.8%, 97.6%, 66.7%, and 90.2%, respectively. The overall AUC of the model discriminating between Groups N, C, and D was 0.83; sensitivity, specificity, and positive predictive value of Group N were 87.5%, 46.2%, and 79.9%, respectively. Using the image AI model, colonoscopy images of IBS could be discriminated from healthy subjects at AUC 0.95. Prospective studies are needed to further validate whether this externally validated model has similar diagnostic capabilities at other facilities and whether it can be used to determine treatment efficacy.