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

Anticipation of daily recurring changes in the environment is critical for survival. When food access is limited to a few hours during the daytime, nocturnal rodents exhibit food-anticipatory activity, which appears a few hours before scheduled mealtime. The rodents are also known to exhibit anticipatory activity for time-restricted palatable meals under ad libitum access to chow. When 1 h of chocolate chip access was given during the day, mice exhibited robust anticipatory activity. In contrast, despite the peanut butter-fed mice eating two times the calories of peanut butter than the chocolate-fed mice did of chocolate chips, we observed only negligible anticipatory activity for daily 1 h peanut butter administration. In ex vivo explants, the phase of the liver in mice subjected to timed-chocolate chip access was significantly advanced, similarly to that in mice subjected to 4 h restricted feeding during the day. Similar to anticipatory activity, negligible phase changes in the liver were observed in the mice given 1 h of peanut butter access during the day. Therefore, robustness of palatable meal-anticipatory activity and phase advance in the liver are unlikely to be in direct response to increased calorie intake during the day. We measured food-seeking nose-poking behavior during food deprivation following daily 1 h chocolate chip access. Mice expressed anticipatory food seeking around the time that they had previously been given daily chocolate chips. This suggests that the time of chocolate chip access is encoded to the same circadian pacemaker that controls food-anticipatory activity.

Colonic motility is controlled by the enteric nervous system that is modulated by not only autonomic neurotransmitters but substances released from enteroendocrine cells. Glucagon-like peptide-1 (GLP-1) secreted from L cells accelerates peristalsis of the proximal colon, while somatostatin released from D cells inhibits GLP-1 secretion via the activation of somatostatin receptor subtype 5 (SST₅). Here, effects of somatostatin on GLP-1-mediated acceleration of colonic peristalsis were investigated. Cannulated segments of rat proximal colon were serosally perfused with oxygenated physiological salt solution and luminally perfused with degassed solution. Colonic wall motion was imaged and converted into spatio-temporal maps. Distributions of somatostatin and SST₅ receptors were assessed via immunohistochemistry. Intraluminal administration of somatostatin alone did not affect oro-aboral propagating peristaltic contractions, but prevented luminal-applied GLP-1 (30 nM)-induced acceleration of peristaltic waves. Somatostatin also prevented the prokinetic action of endogenous GLP-1 that was released upon the stimulation by luminal-applied short-chain fatty acids (SCFA, 3 mM) or lipopolysaccharide. In colonic segments that had been pretreated with selective SST₅ receptor antagonist 1, a lower concentration of GLP-1 (10 nM) or SCFA (300 µM) became capable of accelerating peristaltic waves. GLP-1-positive epithelial cells co-expressed SST₅ receptors, while GLP-1 receptor-positive epithelial cells and afferent neurons contained somatostatin. Thus, L cell-derived GLP-1 that accelerates colonic peristalsis may simultaneously stimulate D cells and afferents to release somatostatin that serves as a break on prokinetic actions of GLP-1 by activating SST₅ receptors on L cells. This interplay between GLP-1 and somatostatin would prevent excessive colonic motility.

Gastric slow waves fail to propagate through the pyloric sphincter (PS), thus isolating the specialized motility patterns of the stomach and small intestine. We investigated the role of interstitial cells of Cajal (ICC) in PS of mice. Ca²⁺ waves in ICC, events responsible for electrical slow waves, propagated along the gastric wall but failed to propagate into the PS. ICC in PS fired localized Ca²⁺ transients and displayed low expression of voltage-dependent Ca²⁺ conductances. These are properties of intramuscular ICC (ICC-IM) that cannot regenerate and propagate slow waves. A T-type Ca²⁺ channel antagonist had no effect on Ca²⁺ transients, but these events were blocked by thapsigargin and CPA, suggesting they result from Ca²⁺ release. PS ICC expressed ANO1, a Ca²⁺-activated Cl^- conductance. Ca²⁺ released from stores actives ANO1 channels, thus exerting a depolarizing influence on PS. Ani9, selective antagonist of ANO1 channels, hyperpolarized cells and reduced contractile tone. Electrical field stimulation (EFS) of intrinsic neurons yielded inhibitory junction potentials (IJPs), and cessation of EFS resulted in post-stimulus depolarization and contraction. L-NNA abolished relaxation responses to EFS and switched responses to contractions. Application of atropine or Ani9 (in the presence of L-NNA) abolished contraction during EFS. Our results describe new and fundamental functions of ICC-IM in the PS. The inability of these cells to propagate slow waves provides the insulator function of PS muscles and localized Ca²⁺ transients and activation of ANO1 regulates PS tone and mediates inputs from enteric neurons.

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.

Gastroesophageal reflux disease (GERD) is common and often medically refractory. Abnormal gastric myoelectrical function may contribute to pathogenesis. This prospective observational study with matched controls assessed if myoelectrical abnormalities measured using body surface gastric mapping were correlated with reflux measured by 24-h pH testing and symptom severity. Gastric Alimetry was performed simultaneously on patients undergoing 24-h pH testing for investigation of reflux symptoms, with a standardized 4.5-h test and validated symptom logging. Data were segmented into 15-min epochs. Forty subjects were recruited (mean age 46.5 yr, 60% female): 20 undergoing pH testing (12 with GERD and 8 symptomatic patients without) and 20 controls. Patients with GERD displayed lower gastric rhythm stability measured by the Gastric Alimetry Rhythm Index (GA-RI) when compared with controls (P = 0.011), but not with patients without GERD (P = 0.605). Lower gastric rhythm stability measured by GA-RI was associated with increased esophageal acid exposure (DeMeester score; r = -0.46, P = 0.042). Periods of decreased gastric rhythm stability measured by GA-RI were not temporally correlated with reflux (r = 0.08, P = 0.182) or heartburn severity (r = 0.04, P = 0.309) but were correlated with nausea (r = -0.22, P < 0.001) and excessive fullness (r = -0.28, P < 0.001). We demonstrated that gastric rhythm instability is associated with increased symptom severity and overall acid exposure in patients with GERD. Although there was no temporal link between rhythm instability and heartburn, rhythm instability was temporally associated with increased nausea and fullness. GA-RI therefore offers an emerging biomarker of concurrent gastric neuromuscular dysfunction in patients with GERD.NEW & NOTEWORTHY Gastroesophageal reflux disease (GERD) is common and often medically refractory. We assessed whether gastric myoelectrical function contributes to pathogenesis by simultaneously measuring myoelectrical activity with Gastric Alimetry and reflux events on 24-h pH testing in patients. We demonstrated that gastric rhythm instability is associated with increased symptom severity and acid exposure in patients with GERD. Although there was no temporal link between rhythm instability and heartburn found, rhythm instability was temporally associated with dyspepsia.

The global population is aging, with one in six people projected to be 65 yr or older by 2050. Since people aged 65 and older experience higher rates of morbidity and mortality after burn injury, there is an increased need to develop effective burn treatments in this age group. Heightened morbidity and risk of mortality may stem from increased gut leakiness and death of intestinal epithelial cells of aged individuals. Herein, we used our clinically relevant model of scald burn injury in young and aged mice to ascertain whether the colon, isolated colonic epithelium, and organoids grown from the colon have deficiencies in cell growth, senescence, and apoptosis pathways. Aged, burn-injured mice displayed increased senescence marker cdkn2a in the colon and isolated epithelium, and displayed a reduction in proliferation marker cdk4 in the colon when compared with young mice. Changes in senescence and proliferation coincided with a reduction in stem cell marker lgr5 in the colon and colonic epithelium, suggesting a burn-related reduction in the stemness of the epithelial crypt. Although we failed to see histological changes in the colonic epithelium, we observed an increase in proapoptotic cleaved caspase 3 and 9 within the colons of aged, burn-injured mice. Finally, there was a decrease in the expression of antimicrobial peptide ang4, and not camp in the colons of aged, burn-injured mice. Taken together, these data suggest that in the colon, disruption of proliferation and apoptosis in aged burn-injured mice occurs primarily in the nonepithelial compartment.NEW & NOTEWORTHY Aged mice have more senescent cells in their colons and burn injury in aged mice leads to suppression of proliferation markers in the colon, but not in epithelial cells or cultured organoids. Colonic expression of stem cell marker lgr5 is reduced in colon from aged, burn-injured mice, and a proapoptotic caspase cascade was seen in this cohort. Finally, antimicrobial peptide ang4 expression is decreased in colons from both aged and aged, burn-injured mice.

The gastrointestinal manifestations of cystic fibrosis (CF) are a continued source of morbidity and mechanistic uncertainty despite recent advances in CF care. We sought to characterize intestinal glucose demand in a mouse model of CF to better understand CF intestinal disease. We assessed in vivo systemic glucose uptake from circulation, including intestinal glucose demand, using ¹⁸F-fluorodeoxyglucose positron emission tomography (PET) imaging studies in wild-type (WT) and CF mice. RNA-sequencing studies with complementary assessments of protein expression and functional metabolism were performed to identify the responsible glucose transporter and relevant metabolic pathways. Finally, morphologic and histologic differences between the CF and WT small intestine were investigated. Increased glucose uptake from circulation to CF intestine was detected with the most prominent increases seen in CF jejunum and ileum. Increased mRNA and protein expression of GLUT1 was evident in whole intestinal tissue and isolated crypts, suggesting that GLUT1 is responsible for mediating the increased glucose uptake from the blood supply. We found transcriptional and functional enrichment of glycolysis in the CF jejunum and ileum. Proliferative intestinal adaptations, including increased intestinal length and weight, in addition to increased villi length and crypt depth, were observed in CF mice. The increased intestinal glucose uptake from circulation and increased glycolysis, in combination with the morphologic and histologic changes in the CF intestine, are suggestive of a proliferative adaptive response and increased intestinal glucose demand in CF. This work may yield novel markers of CF disease status and new therapeutic approaches. NEW & NOTEWORTHY We found transcriptional, protein level, and functional evidence of increased intestinal glucose uptake from circulation and increased glycolysis in a cystic fibrosis mouse model. These findings in the context of hyperplastic morphologic and histologic changes in the cystic fibrosis intestine are indicative of an adaptive response. Our work elucidates new mechanisms of intestinal disease in cystic fibrosis and identifies altered intestinal glucose uptake and glycolysis as potential markers of disease status and gastrointestinal cancer risk.

Fibroblast-like cells (FLCs) exist in the smooth muscle layers of visceral organs, yet in many instances their functional role(s) have not been identified. FLCs express platelet-derived growth factor receptor (PDGFR) α and are a novel class of excitable cells recently described in visceral organs. Crenolanib is a benzamidine quinolone derivative originally developed as an inhibitor of PDGFR to treat certain solid tumors with PDGFRα over-expression mutations. In the present study we used crenolanib to disrupt PDGFRα expression and signaling in the GI tracts of BALB/c mice. Intra-peritoneal injections of crenolanib (100 μg/g body weight) or DMSO control vehicle were given to littermates from postpartum P1 through P15. Crenolanib injected mice were smaller in size and weight. The gastrointestinal tracts were also shorter and appeared partially distended. qPCR revealed down-regulation of key gene transcripts involved in PDGFRα cell signaling including Pdgfrα, Kcnn3 and P2ry1. Confocal immunofluorescence demonstrated significant decreases in PDGFRα and SK3 protein expression. c-Kit expression was slightly inhibited but gastric, intestinal and colonic pacemaker activity was not affected by crenolanib. Purinergic inhibitory post-junctional motor responses were greatly attenuated in the GI tracts of crenolanib treated animals compared to vehicle treated controls in response to electric field evoked nerve stimulation. These data provide evidence for a functional role of PDGFRα⁺ cells in inhibitory neuroeffector motor responses throughout the gastrointestinal tract.

Radiation exposure impairs rapidly renewing tissues like the intestinal epithelium, yet translational insights from murine models have been limited by species-specific responses. Here, we use human intestinal organoids (HIOs) derived from jejunal epithelium to evaluate human epithelial responses to low-dose proton and photon (γ) radiation. γ irradiation induces a unique developmental and metabolic shift in crypt-like organoids, including enrichment of amino acid metabolism pathways and activation of fetal-associated transcription factors and morphology. Integrated multiomic profiling reveals serotonin biosynthesis as a central regenerative node. HIOs can complement animal models and are emerging as a powerful tool in modeling human radiation responses and identifying candidate biomarkers for intestinal injury.NEW & NOTEWORTHY Radiation damages the intestinal epithelium, but murine models often fail to capture human-specific responses. Using human intestinal organoids, we show that γ irradiation triggers a distinct developmental and metabolic reprogramming, including enrichment of amino acid metabolism and induction of fetal-associated transcription factors and morphology. These findings highlight human organoids as a translational platform to model radiation injury and uncover candidate biomarkers for intestinal damage.