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

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.

Serine/threonine phosphatase 1 (PP1) and phosphatase 2A (PP2A) play important roles in mediating cellular signaling in different tissues to different stimuli, including in protein synthesis, growth, cell cycle regulation, and secretion. However, their roles in various pancreatic exocrine functions, such as pancreatic acinar fluid/electrolyte secretion, is still unclear. Therefore, in the present study, we examined the ability of vasoactive intestinal peptide (VIP) and secretin, which stimulate cAMP generation in pancreatic acini, to activate serine/threonine phosphatase 1 (PP1) and phosphatase 2A (PP2A), the signaling cascades involved, and their possible role in activating sodium-potassium adenosine triphosphatase (Na⁺-K⁺-ATPase). Our results demonstrate that VIP and secretin activate PP1 and PP2A. However, they differ in their signaling cascades. Both VIP and secretin stimulate PP1 through cAMP-stimulated activation of protein kinase A (PKA) and exchange protein directly activated by cAMP (EPAC). However, VIP stimulates PP2A through the activation of cAMP-mediated EPAC, whereas secretin does it through activation of PKA. Despite these differences, in cAMP effect on activation, both VIP and secretin activate PP2A through a p21-activated kinase 4 (PAK4)-mediated mechanism, without involvement of PAK2. Furthermore, PP1 and PP2A activation is needed for Na⁺-K⁺-ATPase activation, which mediates pancreatic acinar fluid and electrolyte secretion. These results support the conclusion that PP1 and PP2A play an important role in pancreatic acinar fluid and electrolyte secretion, mediated by a PAK4-dependent mechanism, which when combined with their recently described roles in pancreatic enzyme secretion, pancreatitis, and pancreatic acinar growth and cancer, demonstrate the important roles they play in both physiological and pathological responses in the exocrine pancreas, similar to their previously established roles in the endocrine pancreas.NEW & NOTEWORTHY The roles of the serine/threonine phosphatase 1/2A in mediating fluid/electrolyte secretion by pancreatic acinar cells remains unclear. This study demonstrates that PP1/PP2A are activated vasoactive intestinal peptide (VIP)/secretin in pancreatic acini. VIP/secretin both activate PP1/PP2A but differed for their ability to activate exchange protein directly activated by cAMP (EPAC) and protein kinase A (PKA). VIP/secretin require PAK4, not PAK2, activation to stimulate PP2A, not PP1; however, PP1/PP2A activation stimulate sodium-potassium adenosine triphosphatase (Na⁺-K⁺-ATPase) activity. This study shows that PP1/PP2A play important roles in VIP-secretin-stimulated pancreatic acinar fluid/electrolyte secretion.

The inflammatory process is a conserved and adaptive biological response to infection or tissue damage. Despite its substantial energy demands, inflammation triggers centrally regulated changes in behavior, commonly referred to as sickness behavior, which includes anorexia and consequent negative energy balance. Although these responses have been extensively modeled through infection or cytokine administration, they remain less explored in a more dynamic spectrum of clinical conditions, such as inflammatory bowel disease (IBD). In this study, we used the dextran sodium sulfate (DSS) model of colitis, which mimics key features of human IBD. We assessed food and water intake, locomotor activity, and body composition over the disease progression. We further assessed neuronal activation and transcriptional changes in metabolic-sensing brain regions at key disease stages. Acute DSS-induced disease progression was associated with metabolic alterations, including anorexia, energy conservation, reduced physical activity, and changes in body mass composition. A positive correlation between disease severity and neuronal activation in the hypothalamus and the caudal brainstem was also found. Transcriptomic analysis revealed changes in hypothalamic gene expression associated with the immune response. Furthermore, targeted colocalization studies identified the activation of hypothalamic hunger-promoting AgRP/NPY-expressing neurons as a neuronal population recruited during colitis, suggesting a role for these neurons in coordinating allostatic metabolic adaptations to intestinal inflammation. This study provides evidence that the DSS model is a clinically relevant, dynamic, and tractable tool for studying the progression of sickness-like behavior in IBD, as well as the underlying neurometabolic adaptations that extend beyond the gut.NEW & NOTEWORTHY By showing that experimental colitis induced by DSS in mice triggers metabolic adaptations and activation of brain regions regulating energy balance, this study expands the model's relevance beyond intestinal inflammation. These findings provide a framework to investigate gut-brain interactions and the neurometabolic components of sickness-like behavior in inflammatory bowel disease.

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.

Hepatocyte nuclear factor 4 A (HNF4A) is a transcription factor that regulates a diverse range of intestinal epithelial genes involved in tissue renewal, differentiation, and metabolism, among other functions. The HNF4A locus is associated with inflammatory bowel disease (IBD) susceptibility, and its deletion in the mouse intestine causes long-term chronic inflammation of the colon. However, it remains unclear whether HNF4A is part of the regulatory mechanisms involved in the inflammatory processes of the small intestine. Using a tamoxifen-inducible mouse intestinal knockout of Hnf4a, we observed a spontaneous increase in mucosal barrier permeability in the absence of HNF4A. However, when these mice were infected with the invasive-deficient Salmonella typhimurium SB103, this increase in permeability did not result in an increase in liver and spleen bacterial colonization compared with undeleted mice. Interestingly, ileal secretory cell lineage differentiation was favored when HNF4A was depleted during the early stages of infection. This resulted in increased production of ileal goblet cells and the expression of Muc2, as well as the expression of specific antimicrobial peptides such as Reg3g and Rtnlb. We conclude that epithelial HNF4A is sensitive to Salmonella in the ileum and that its reduction in expression during the early phase of infection may contribute to rapidly reinforcing the chemical barrier response to elicit mucosal threat from pathogens.NEW & NOTEWORTHY HNF4A is associated with inflammatory bowel disease susceptibility and protects against chronic colon inflammation. Whether HNF4A acts similarly in the small intestine remains speculative. Although its deletion led to an increase in paracellular permeability, exposure to an attenuated Salmonella typhimurium strain did not cause systemic infection. Ileal goblet cell lineage commitment was stimulated with increased expression of antimicrobial peptide genes. HNF4A reduction of expression may contribute to early mucosal protection against luminal pathogen burdens.