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

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.

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.

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.

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.

Overactivation of hepatic de novo lipogenesis (DNL) contributes to fatty liver disease. Although glucose and fructose strongly promote DNL, diary-rich galactose is only weakly lipogenic. However, whether and how it regulates hepatic DNL remains unclear. In this study, we investigated whether low-dose galactose supplementation attenuates glucose- or fructose-induced DNL activation and protects against fatty liver diseases driven by DNL overactivation, such as alcohol-associated liver disease (ALD). In this study, we used integrated hepatocyte and mouse models to assess hepatic DNL and related signaling under high-glucose or high-fructose conditions, with or without low-dose galactose. Pharmacological and genetic interventions targeting the Leloir and hexosamine biosynthetic pathways (HBP) defined underlying mechanisms. For in vivo validation, male C57BL/6 mice were fed an isocaloric control or ethanol-containing diet for 4 wk. We found that glucose engages the HBP-mTORC1-SREBP-1c axis to stimulate hepatic DNL, whereas fructose acts predominantly through carbohydrate-responsive element-binding protein (ChREBP). Low-dose galactose selectively suppressed glucose-induced hepatic fat accumulation, concomitant with the inhibition of the HBP-mTORC1-SERBP-1c pathway. These effects required an intact Leloir pathway for galactose metabolism and were not observed with fructose. In alcohol-fed mice, hepatic HBP-mTORC1-SREBP-1c signaling was markedly upregulated, contributing to steatosis and liver injury. Replacing even a small fraction of dietary glucose with galactose normalized these alterations, attenuating hepatic lipid accumulation and injury without altering systemic glucose levels. In conclusion, glucose-induced hepatic lipogenesis involves the HBP-mTORC1-SREBP-1c pathway, which is also activated during chronic alcohol exposure. Low-dose galactose, obtainable from dairy sources, attenuates this pathway, thereby limiting excessive lipogenesis and protecting against early-stage ALD.NEW & NOTEWORTHY This study demonstrates that low-dose galactose, a dairy-derived monosaccharide, regulates hepatic de novo lipogenesis (DNL) by selectively inhibiting glucose-induced DNL activation. Mechanistically, low-dose galactose suppresses hexosamine biosynthetic pathway (HBP) flux, protein O-GlcNAcylation, and mTORC1 signaling, thereby inhibiting SREBP-1c activation in a Leloir pathway-dependent manner. Notably, galactose supplementation prevented early-stage alcohol-related liver disease by attenuating hepatic HBP-O-GlcNAcylation-SREBP-1c signaling.

Gastrointestinal motility is regulated primarily by the enteric and the central nervous systems. Our previous studies revealed that central circuits regulating colorectal motility partially overlap with those involved in pain modulation, suggesting functional interactions between the nociceptive modulatory pathway and the autonomic regulatory pathway of colorectal motility. Here, we examined whether peripheral inflammatory pain alters the neural components of the descending pathway regulating colorectal motility. Complete Freund's adjuvant (CFA) was administered unilaterally into the hind paw of rats to induce inflammation. Colorectal motility was assessed in vivo under anesthesia with α-chloralose and ketamine. In sham-treated rats, intraluminal administration of capsaicin, a noxious stimulus to the colorectal lumen, enhanced colorectal motility. In contrast, the capsaicin-induced colorectal motility response was suppressed in rats 3 days after CFA treatment. This suppression was rescued by the intrathecal administration of a GABA_A receptor antagonist or an oxytocin (OXT) receptor antagonist. Furthermore, spinal OXT administration and chemogenetic activation of OXT neurons in naïve rats elicited a marked inhibition of capsaicin-induced motility responses of the colorectum. Notably, the inhibitory effect of activated OXT neurons was abolished by the intrathecal administration of a GABA_A receptor antagonist. These results indicate that the descending OXT pathway becomes operative in response to persistent pain caused by peripheral inflammation and that the inhibitory effect on colorectal motility may involve local GABAergic transmission within the spinal cord. These changes may reduce parasympathetic outflow to the colorectum and contribute to defecation disorders involving central neural mechanisms.NEW & NOTEWORTHY This study focused on the remodeling of the neural pathways regulating colorectal motility and examined whether peripheral inflammation outside the gastrointestinal tract affects this process. In rats administered a complete Freund's adjuvant into their hind paw, colorectal motility responses induced by intracolonic administration of capsaicin were suppressed. This suppression involved oxytocinergic and GABAergic transmission in the spinal cord. These results demonstrate that inflammatory pain in the hind paw induces remodeling of the neural pathways regulating colorectal motility.

Pancreatitis is an inflammatory disorder of the pancreas that occurs in acute, recurrent acute, and chronic forms, often leading to severe complications and long-term functional impairment. The disease develops through multiple pathological mechanisms, including the premature activation of the digestive proenzyme trypsinogen within the pancreas. Conversion of trypsinogen to its active form trypsin may be catalyzed by the lysosomal protease cathepsin B or may occur through autoactivation, a self-amplifying reaction in which trypsin activates trypsinogen. Accumulating evidence from genetic, biochemical, and animal model studies on trypsinogen mutations associated with human pancreatitis strongly supports autoactivation as a key driver of disease pathogenesis, whereas cathepsin B-mediated activation may play a context-dependent, lesser role. This review explores the biochemical pathways of intrapancreatic trypsinogen activation and discusses their respective contributions to the multifactorial pathogenesis of pancreatitis.

Serotonin (5-HT) is a multifunctional signaling molecule in the gastrointestinal (GI) tract. 5-HT synthesis is regulated by the gut microbiota. Microbial dysbiosis has been implicated in visceral pain and persistent alterations in gut function that occur following inflammation. Here, we tested the hypothesis that alterations in gut microbiota in a postinflammatory model of visceral pain contribute to dysregulated 5-HT signaling. We used mice treated with dextran sodium sulfate (DSS) 42 days earlier (postcolitis) or untreated mice as donors for fecal microbiota transplants (FMTs) into germ-free mice to explore changes in enterochromaffin (EC) cell populations, expression of 5-HT synthesis, transport, and degradation genes, levels of 5-HT and its major metabolite, 5-hydroxyindoleacetic acid (5-HIAA), and 5-HT release. Significant differences were observed in EC cells, Tph1, Slc6a4, and Maoa gene expression, 5-HT and 5-HIAA levels, and 5-HT release between germ-free mice and mice receiving an FMT from either control or postcolitis donor mice. We observed no differences in the total number of EC cells, Tph1, or Slc6a4 gene expression of mice after FMT from postcolitis or control mice. However, there was a significant increase in Maoa gene expression in the terminal ileum, an increased 5-HIAA/5-HT ratio in the proximal colon, and reduced 5-HT release to mechanical and chemical stimulation in the proximal and distal colon after FMT from postcolitis mice. Collectively, these findings provide additional evidence that the gut microbiota regulates 5-HT signaling. Moreover, they reveal functional changes in EC cell sensitivity in the presence of an altered microbiota after recovery from inflammation. NEW & NOTEWORTHY The gut microbiota regulates serotonin biosynthesis in enterochromaffin cells. Here, we show that a dysbiotic gut microbiota that occurs after recovery from inflammation alters serotonin signaling and produces functional changes in enterochromaffin cell sensitivity.

Sterile inflammation, resulting from hepatocyte death and subsequent release of damage-associated molecular patterns (DAMPs), significantly contributes to liver disease pathogenesis. Neutrophils, as primary responders to liver injury, undergo NETosis-an immune response generating neutrophil extracellular traps (NETs), further amplifying inflammatory damage. Extracellular DNA (ecDNA), a major constituent of NETs and released cell fragments, potentiates inflammation through pattern recognition receptor activation. Mitochondrial DNA, released during hepatocyte damage, especially provokes robust immune responses due to its bacterial DNA-like structure and unmethylated CpG motifs. Concurrently, purinergic signaling-particularly via ATP release and its conversion into adenosine by ectonucleotidases CD39 and CD73-critically modulates immune homeostasis and inflammatory responses. Dysregulated expression of CD39/CD73, driven by altered aryl hydrocarbon receptor (AhR) signaling, exacerbates inflammatory states through disturbed regulatory T (Treg) and T helper (Th) 17 cell balance. Recent insights highlight that neutrophils and NETs not only drive innate inflammatory responses but significantly influence adaptive immunity by modulating T cell differentiation. NET components, such as cathelicidin and histones, actively promote Th17 differentiation while simultaneously impairing Treg functions, thereby sustaining inflammatory conditions. In addition, T cells reciprocally influence neutrophil activation and recruitment, predominantly through interleukin-17A (IL-17A) production. Detailed mechanisms underlying neutrophil-T cell cross talk in autoimmune hepatitis, acute liver failure, ischemia/reperfusion injury, alcoholic liver disease, and metabolic dysfunction-associated steatotic liver disease underscore potential therapeutic targets. Future strategies targeting NET formation, ecDNA clearance via DNase therapy, purinergic receptor modulation, and restoring AhR signaling hold promise for effectively attenuating sterile inflammation and immune dysregulation in liver diseases.