American journal of physiology. Gastrointestinal and liver physiology最新文献

Transient receptor potential vanilloid 6 (TRPV6) is a highly Ca²⁺-permeable cation channel predominantly expressed in the intestinal epithelium. It plays a crucial role in maintaining systemic calcium homeostasis by regulating Ca²⁺ absorption in the intestine. However, its local physiological and pathophysiological roles in the intestine remain unexplored. The exact cause of inflammatory bowel disease is not fully understood; however, disruption of the intestinal epithelial barrier is a key pathogenic mechanism. In this study, we aimed to elucidate the role of TRPV6 in the pathogenesis of colitis. Experimental colitis was induced in TRPV6-deficient (KO) and wild-type (WT) mice by administering 2% dextran sulfate sodium solution (DSS) in drinking water for 7 days. DSS treatment resulted in weight loss, diarrhea/bloody stool, histological colonic injury, and colon shortening. The systemic symptoms and colonic injury were significantly worse in TRPV6KO mice than in WT mice. DSS treatment increased tumor necrotic factor-α, interleukin-1β, interleukin-6 mRNA expressions, and myeloperoxidase activity, and these responses were significantly enhanced in TRPV6KO mice compared with WT mice. Under normal (no-DSS-treated) conditions, TRPV6KO mice exhibited increased intestinal permeability compared with WT mice. No difference was observed in the number of goblet cells between WT and TRPV6KO mice; however, the expression of intercellular junction proteins, including E-cadherin, claudin-3, and occludin, was significantly suppressed in TRPV6KO mice compared with WT mice. These findings suggest that TRPV6 protects against DSS-induced colitis, potentially by regulating epithelial barrier function through intracellular junction protein expressions.

Visceral hypersensitivity is a pivotal mechanism in pain associated with irritable bowel syndrome (IBS). Calcitonin gene-related peptide (CGRP) is expressed by visceral afferents. The aim of this study was to evaluate the efficacy of rimegepant, a CGRP antagonist, on abdominal pain, rectal compliance and sensation, gut transit, and safety in participants with non-constipation IBS with pain. We conducted a pilot, randomized, double-blind placebo-controlled, parallel-group design trial (NCT06221111) of oral rimegepant 75 mg every other day (as approved for migraine prophylaxis) in adults with non-constipation IBS-pain. The trial consisted of 3 periods: 2-week run-in, 4-week treatment, and 4-week post-treatment with diary recording of daily abdominal pain (primary endpoint) and bowel movements (BM). Rectal compliance and sensation were measured using barostat distensions and gastrointestinal and colonic transit by scintigraphy. Statistical analysis compared rimegepant to placebo using ANCOVA with sex, level of anxiety, and baseline measurements as covariates. Twenty-four participants were randomized to rimegepant (n=12) or placebo (n=12); baseline demographics, rectal sensation and compliance were similar between the groups. Rimegepant did not significantly reduce abdominal pain, daily BM frequency, or BM consistency relative to baseline. Compared to placebo, rimegepant significantly reduced sensations of gas, urgency, pain during 24mmHg, and gas and urgency sensations during 36mmHg rectal distension (all P <0.05 unadjusted). Rimegepant decreased rectal compliance. No significant effects were noted during washout. There were no serious adverse events or adverse events of ≥ Grade 3 severity. Rimegepant's effects on rectal sensation suggest further studies in non-constipation IBS pain are warranted.

Primary aging associates with an imbalanced gut microbiome and cardiovascular disease (CVD) risk in mice and humans. Strong evidence from clinical and pre-clinical studies supports that habitual physical exercise improves cardiovascular function and intestinal health in adults. Here we tested the hypothesis that exercise training, even when initiated late-in-life, re-establishes a beneficial and cooperative intestinal microbiome to an extent that associates with reduced risk for CVD. At 21-months of age, male C57BL/6 mice started a progressive resistance treadmill-training program 6-days per week (Old+ETR) for 12-weeks. Twenty-one month old (Old) and 4-month old (Adult) male mice remained sedentary. First, reductions in exercise capacity and soleus muscle citrate synthase activity displayed by Old vs. Adult mice were restored in Old+ETR animals. Next, systolic function (fractional shortening, FS), diastolic function (E/A ratio), and overall left-ventricular function (myocardial performance index, MPI) otherwise depressed in Old vs. Adult mice were normalized in Old+ETR animals. Third, elevated trimethylamine (TMA) and TMA N-oxide (TMAO), and heightened inflammatory markers [e.g., interferon (IFN)-g and keratinocyte-derived chemokine (KC)], observed in Old vs. Adult mice were lowered in Old+ETR animals. Importantly, the abundance of beneficial microbial features, including Bacteroides, Muribaculaceae, Parabacteroides, and the Rikenellaceae RC9 gut group, otherwise depressed by aging, was normalized in Old+ETR mice. Finally, the Rikenellaceae RC9 gut group positively correlated with FS, and Parabacteroides negatively correlated with IFN-γ. These findings support that late-in-life exercise training beneficially remodels the gut microbiome to an extent that associates with reduced CVD risk in male mice.

Classically known for their roles in facilitating lipid digestion and absorption, bile acids are now also appreciated as enterocrine hormones that modulate many aspects of intestinal physiology. We have previously shown lithocholic acid (LCA), a secondary bile acid, to be protective against colonic inflammation. Here, we investigated whether LCA also regulates colonic epithelial fluid and electrolyte transport. T₈₄ cell monolayers were mounted in Ussing chambers for measurements of transepithelial Cl^- secretion. CFTR mRNA and protein expression were analyzed by qRT-PCR and Western blotting in T₈₄ cells and human-derived colonic organoids. CFTR promoter activity was assessed using a luciferase promoter/reporter assay in HEK293 cells. Pretreatment of T₈₄ cells with LCA inhibited Cl^- secretory responses to the cAMP-dependent agonist, forskolin (FSK), with maximal effects occurring at a concentration of 10 µM after 24 h of treatment. Under these conditions, LCA also inhibited responses to the Ca²⁺-dependent secretagogues, thapsigargin, and histamine. In nystatin-permeabilized T₈₄ monolayers, LCA reduced FSK-stimulated apical Cl^- conductances, an effect that correlated with reduced CFTR Cl^- channel expression. Although LCA activated both farnesoid X receptor (FXR) and vitamin D receptor (VDR), its effects on CFTR expression and Cl^- conductances were mimicked only by an FXR agonist, GW4064, and not by a VDR agonist, calcitriol. Finally, LCA inhibited CFTR promoter activity in HEK3 cells, but only when FXR was expressed. LCA, at physiologically relevant concentrations, chronically inhibits colonic epithelial Cl^- secretion, likely via FXR-induced downregulation of CFTR. These data broaden our knowledge of the regulatory roles of LCA in the colon and highlight its potential as a therapeutic target for intestinal disorders.NEW & NOTEWORTHY This study reveals a previously unrecognized role for lithocholic acid (LCA) in chronically suppressing colonic epithelial chloride secretion. We demonstrate a genomic mechanism of action for LCA that is likely mediated by FXR-induced downregulation of CFTR expression and function. These findings highlight LCA as a key modulator of intestinal fluid and electrolyte transport and underline the therapeutic potential of targeting bile acids and their receptors for the treatment of diarrheal diseases.

Parkinson's disease is a neurodegenerative disorder pathologically characterized by accumulation of misfolded α-synuclein in the central and peripheral nervous systems, influencing symptomology at both sites. Calcitonin gene-related peptide (CGRP), a neuropeptide produced in the brain and intestine, has been linked with altered α-synuclein aggregation. This study examines the role of calcitonin gene-related peptide in modulating enteric α-synuclein accumulation and enteric glial cell reactivity using an ex vivo slice culture model from A53T^+/- human α-synuclein mutant mice. In slices treated with calcitonin gene-related peptide, α-synuclein immunoreactivity was elevated in myenteric neurons within 24 h. A stark elevation in gut mucosal calcitonin gene-related peptide immunoreactivity was revealed to be predominantly S100β+ enteric glia cells rather than neuronal fibers, pointing toward a reactive enteric glial cell phenotype. In addition, CGRP treatment increased enteric glial cell count in the mucosa in wildtype colon slices without evidence of incorporation of the DNA synthesis marker 5-ethynyl-2'-deoxyuridine indicating a lack of cell proliferation. Mucosal increases in enteric glial cell counts were accompanied by a decrease in these cells in the submucosa. This supports the idea that an inflamed gut environment may shift enteric glial cells to a reactive phenotype, inducing alterations in their number and anatomic localization. These data implicate calcitonin gene-related peptide in the accumulation of enteric α-synuclein, an effect potentially driven by an inflammatory environment that we hypothesize is due in part to enteric glial cell activation.NEW & NOTEWORTHY Gastrointestinal symptoms of Parkinson's disease (PD) are an emerging area of investigation with implications for disease etiology. Utilizing intestinal ex vivo slices from a PD mouse model, Templeton et al., identify calcitonin gene-related peptide (CGRP) as a key modulator of enteric α-synuclein accumulation and enteric glial reactivity. These findings suggest that targeting peripheral CGRP signaling pathways in the enteric nervous system may represent a novel therapeutic approach for early intervention in PD.

Hookworm infects over 400 million people globally and causes gastrointestinal morbidity, yet its physiological effects remain poorly defined. Controlled human hookworm infection is also being explored as a therapy for gut diseases. We performed an exploratory study to evaluate the impact of experimental Necator americanus infection on gastrointestinal transit, motility, and luminal pH in 10 healthy adults (mean age 41 yr, 60% females) infected with 30 larvae via skin application. Assessments using the SmartPill Wireless Motility Capsule were performed at baseline, week 6 (acute infection), and week 24 or 48 (chronic infection). Parameters included gastric emptying time, small bowel and colonic transit, whole gut transit, intraluminal pressures, contraction frequency, motility index, and segmental pH, analyzed with paired t tests or ANOVA. All participants developed patent infections. No significant differences were observed in gastric emptying, small bowel, colonic, or whole gut transit times, nor in motility indices or contraction frequencies. However, during acute infection, duodenal (6.14 ± 0.19 vs. 5.80 ± 0.24, P < 0.05) and small bowel pH (6.96 ± 0.37 vs. 6.50 ± 0.37, P < 0.05) were significantly reduced compared with baseline, normalizing by the chronic phase. No other significant pH alterations were detected. Thus, these data suggest that controlled N. americanus infection in healthy adults induces a transient reduction in duodenal and small-intestinal pH without affecting gastrointestinal transit or motility. This acidification may contribute to acute-phase symptoms and nutrient malabsorption in endemic settings, whereas the absence of sustained motility disturbance supports the safety of controlled hookworm infection for therapeutic investigation.NEW & NOTEWORTHY This exploratory study using SmartPill technology found that controlled hookworm infection in healthy adults caused a transient drop in duodenal and small-intestinal pH during the acute phase, but no lasting changes in gut motility or transit. The findings, the first of their kind in humans, suggest that the physiological effects of controlled doses of hookworm are subtle and short-lived, offering reassurance for therapeutic trials while highlighting a potential mechanism for symptoms and malabsorption in endemic regions.

Epigenetic regulations link environmental factors to the development of obesity and metabolic dysfunction-associated steatotic liver disease (MASLD). We determined the role of hepatocyte histone deacetylase 4 (HDAC4) in the pathogenesis of MASLD. Male and female hepatocyte-specific Hdac4 knockout (Hdac4^HKO) mice and control Hdac4 floxed (Hdac4^fl/fl) mice were fed a high-fat, high-sucrose, high-cholesterol diet for 16 wk to induce obesity and MASLD. The loss of hepatic Hdac4 increased serum alanine transaminase activity and exacerbated hepatic steatosis with higher liver weights and triglyceride levels than Hdac4^fl/fl mice in males. Hepatic expression of lipogenic genes was significantly higher in male and female Hdac4^HKO mice than in controls. Moreover, primary hepatocytes and the liver of Hdac4^HKO mice exhibited perturbed insulin signaling, characterized by reduced phosphorylated AKT2. Interestingly, hepatocyte Hdac4 loss increased inflammatory and fibrogenic genes in gonadal white adipose tissue (gWAT). Serum cytokine array and proteomic analysis demonstrated alterations in several serum factors, which may contribute to crosstalk between the liver and WAT in Hdac4^HKO, leading to obesity-induced metabolic dysfunction in gWAT. In conclusion, hepatocyte Hdac4 loss exacerbates hepatic steatosis, accompanied by disturbed insulin signaling and WAT inflammation and fibrosis in obese mice, underscoring its crucial role in liver-WAT crosstalk.NEW & NOTEWORTHY We examined the role of hepatocyte histone deacetylase 4 (HDAC4) in the development of obesity and metabolic dysfunction-associated steatotic liver disease (MASLD) using Hdac4-deficient mice with hepatocyte-specific deletion. We found that deleting Hdac4 in hepatocytes worsens hepatic steatosis and disrupts insulin signaling in the liver. In addition, this deletion caused inflammation and fibrosis in the white adipose tissue of obese mice, highlighting the role of HDAC4 in the liver-adipose axis.

A growing proportion of the non-celiac population experiences adverse symptoms to gluten. The pathogenesis of non-celiac gluten sensitivity (NCGS) is unclear, but elevated duodenal eosinophils and altered mucosa-associated microbiota (MAM) populations have been reported. Given the microbiome's role in gluten digestion and its susceptibility to antibiotics, we hypothesized that altering the microbiome with antibiotics would modify immune responses to gluten in mice. BALB/C mice consuming gluten-free chow received amoxicillin/clavulanate (5 mg/kg) or PBS-vehicle daily for 5 days. Mice were then treated with a 3-mg wheat-gluten suspension, or vehicle, on days 4 and 5 before euthanasia on day 7. Duodenal immune cells were analyzed by histology and flow cytometry, whereas the duodenal MAM and fecal microbiome were characterized via 16S rRNA and shotgun metagenomic sequencing, respectively. Antibiotic treatment followed by gluten reintroduction significantly reduced Staphylococcus in the duodenal MAM, enriched Bacteroides in feces, and resulted in altered microbial carbohydrate and lipid metabolism, compared with vehicle controls. Treatment with antibiotics and gluten also increased duodenal eosinophils, which positively correlated with the genus Blautia. Flow cytometry revealed that sequential antibiotic and gluten treatment resulted in a greater proportion of active eosinophils and epithelial γδ T-cells, compared with vehicle control mice. This study demonstrated that modulating the microbiome with antibiotics was sufficient to alter the immune response to gluten in mice, suggesting that the microbiome may determine the capacity for gluten to induce immune responses. These findings contribute valuable insights into possible microbial mechanisms underlying NCGS, such as altered gluten metabolism or production of immunomodulatory metabolites.NEW & NOTEWORTHY A mouse model examined how microbial modulation affects immune responses to gluten. Antibiotic treatment followed by gluten reintroduction reduced duodenal Staphylococcus and altered microbial carbohydrate and lipid metabolism pathways in the fecal microbiome. Antibiotics and gluten treatment resulted in increased abundance and activation of duodenal eosinophils and elevated γδ T-cells in the duodenal epithelium. These findings highlight the role the microbiome plays in gluten-induced immune responses, providing insights into mechanisms behind non-celiac gluten sensitivity.

Liver fibrosis is driven by the accumulation of scar tissue in response to injury. Activated hepatic stellate cells (HSCs) secrete fibrogenic proteins that deposit into the extracellular matrix, leading to fibrosis. Increased production of fibrogenic proteins by HSCs leads to endoplasmic reticulum (ER) stress, triggering the unfolded protein response (UPR). The UPR is important in regulating HSC activation and fibrogenesis, but mechanisms driving this regulation are unclear. A key process regulated by the UPR is degradation of misfolded proteins through various pathways, including ER-to-lysosome-associated degradation (ERLAD). ERLAD targets proteins for lysosomal degradation and can involve autophagosomes engulfing portions of the ER, termed ER-phagy. ER-phagy is implicated in degradation of misfolded fibrillar collagen, but its role in fibrogenesis is unknown. We show that collagen I levels are posttranslationally regulated by autophagy, and this correlates with ER-phagy receptor expression. Furthermore, activation of HSCs induces ER-phagy flux and expression of ER-phagy receptors, including FAM134B, in a process dependent on UPR transducer ATF6α. Loss of FAM134B decreases intracellular collagen I without affecting COL1A1 mRNA. Moreover, FAM134B deletion blocks transforming growth factor β-induced collagen I deposition despite increased secretion. Together, we show that ER-phagy receptor FAM134B is pivotal for collagen I deposition during fibrogenesis.NEW & NOTEWORTHY We show for the first time that TGFβ-mediated activation of HSCs induces selective autophagy of the endoplasmic reticulum (ER-phagy), through upregulation of ER-phagy receptors and ER-phagic flux. We further show that the unfolded protein response is critical for this effect. Finally, we identify the ER-phagy receptor FAM134B as a critical regulator of collagen I dynamics and fibrogenesis, with loss of FAM134B dysregulating collagen I secretion and deposition.