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

Malnutrition decreases intestinal bile acids, resulting in inefficient nutrient absorption and impaired catch-up growth. Mechanisms by which bile acid depletion occurs in malnutrition are unknown. Using a mouse model of early-life malnutrition, we explored bile acid homeostasis, focusing on transcriptional repression of oxysterol 7α-hydroxylase (CYP7B1), a rate-limiting enzyme in the alternative pathway of bile acid biosynthesis, by sterol regulatory element-binding protein-1c (SREBP-1c), a master regulator of lipid metabolism. Mice were maintained on a low-protein, low-fat, or isocaloric control chow until 8 wk of age, when livers were harvested for proteome profiling, western blot, reverse transcription quantitative real-time PCR, and chromatin immunoprecipitation. Cultured hepatocytes and mice were treated with the SREBP-1c inhibitors fatostatin and betulin to determine whether this therapeutic strategy rescues CYP7B1 expression and bile acid synthesis in malnutrition. Malnutrition decreased the bile acid pool size and altered the expression of multiple hepatic cytochrome P450 enzymes, with profound depletion of CYP7B1, in males but not females. Malnutrition activated SREBP-1c and led to its enrichment at a Cyp7b1 gene regulatory region that featured loss of binding by the basal transcriptional activator specificity protein 1 (SP1). Treatment of cultured hepatocytes or malnourished mice with the SREBP-1c inhibitors fatostatin or betulin increased CYP7B1 expression. Both drugs rescued the bile acid pool size in malnourished mice. These results suggest that malnutrition impairs bile acid synthesis via transcriptional repression of Cyp7b1 by SREBP-1c. SREBP-1c inhibitors restore hepatic CYP7B1 expression and bile acid synthesis.NEW & NOTEWORTHY We applied liver proteomics to a unique mouse model of early-life malnutrition to reveal a novel mechanism of suppression of bile acid synthesis. Malnutrition activates the nuclear protein SREBP-1c, which displaces the transcriptional activator SP1 from the promoter of the Cyp7b1 gene. Two different SREBP-1c inhibitors rescue CYP7B1 expression in vitro and rescue the bile acid pool in malnourished mice. This discovery might facilitate novel adjunct therapies to enhance nutritional rehabilitation in malnourished children.

Prostaglandin E₂ (PGE₂) actions on intestinal motility are complex due to the differential expression of the PGE₂ receptors EP₁-EP₄. We sought to determine the actions of PGE₂ on electrical pacemaker and contractile activity of the circular and longitudinal muscle layers of the murine small intestine. Intracellular microelectrode and isometric force measurements were performed to examine the effects of PGE₂ receptor activation on circular and longitudinal muscle layers. In the two muscle layers, PGE₂ produced differential responses. In the circular muscle layer, PGE₂ caused dose-dependent membrane hyperpolarization and a reduction in slow-wave amplitude, accompanied by a decrease in the amplitude of phasic contractions. Membrane hyperpolarization and the reduction in slow-wave amplitude and phasic contractions were insensitive to tetrodotoxin (TTX) and N^ω-nitro-l-arginine (l-NNA) but inhibited by the K_ATP channel antagonist glibenclamide. The actions of PGE₂ on the circular muscle layer were mimicked by the selective EP₂ and EP₄ agonists ONO AE1-259 and ONO AE1-329, respectively. The actions of PGE₂ were partially inhibited by the EP₄ antagonist ONO AE3-208. The EP₁ agonist ONO-DI-004 produced little effect, whereas the EP3 agonist ONO-AE-248 caused dose-dependent membrane depolarization. In comparison, PGE₂ produced increased tone and phasic contractions in the longitudinal muscle layer that was mimicked by ONO-DI-004 and ONO-AE-248, whereas EP₂ and EP₄ agonists had little effect on contractile activity. These data suggest that differential expression of PGE₂ receptors on intestinal muscle layers can produce antagonistic actions on intestinal motility.NEW & NOTEWORTHY Prostaglandins are lipid mediators that have complex actions on gastrointestinal motility that are highly dependent on the expression of the receptor subtypes where they exert their actions. PGE₂ has inhibitory or excitatory effects on circular or longitudinal muscle layers of the small intestine. Despite many studies of the effects of prostaglandins on tissue contractility, little is known about the specific receptors eliciting these effects. The present study examines functional receptor expression in the small intestine.

Inflammatory bowel diseases (IBDs), mainly involving the disease states of ulcerative colitis (UC) and Crohn's disease (CD), are characterized by chronic, relapsing inflammation of the gastrointestinal tract. IBD has an unclear etiology and likely develops from a complex interaction between the host's genetic predisposition, the gut microbiota, the immune system, and elements within the environment. In the United States alone, the estimated health care cost for IBD, according to a recent study, exceeds $25 billion. More than 200 genetic loci have been identified to be associated with IBD, highlighting its complex pathophysiology. Although existing treatments for IBD are generally supportive, they are not curative, underscoring the need to identify the causative agents that drive disease pathogenesis. Several studies have reported metabolic alterations in the pathogenesis of IBD. In all living cells, the central action of nicotinamide adenine dinucleotide (NAD⁺) plays a pivotal role in the regulation of energy metabolism and cell signaling. Dysregulated NAD⁺ metabolism is reported in patients with IBD. Sirtuins, a protein family of posttranslational modifiers, need NAD⁺ as a cofactor to perform enzymatic reactions such as deacylation and ADP-ribosylation of not only histones, but also of various other key cellular proteins. Therefore, sirtuins play a vital and central role as stress-responsive metabolic sensors in cells. In this review, we address novel mechanisms by which sirtuins play a role in IBD pathogenesis, thus exposing a potential therapeutic role of this group of enzymes that might be useful in curtailing IBD and several other debilitating gastrointestinal inflammatory disorders.

Inflammatory bowel diseases (IBDs) and gut barrier impairment are associated with changes in dietary tryptophan and arginine metabolism, but mechanisms of barrier perturbation and restoration are unclear. We show here that the widely consumed probiotic Lacticaseibacillus rhamnosus GG (LGG) enhances gut barrier functions in part through stimulating the intestinal arginine metabolic pathway, and this mechanism depends on the sufficiency of dietary tryptophan in the host. Specifically, LGG markedly upregulates argininosuccinate lyase (ASL), the enzyme that breaks down argininosuccinate into arginine. ASL expression is markedly reduced during experimental colitis with an accumulation of serum argininosuccinate. LGG colonization in mice reduces serum argininosuccinate, a metabolite that inversely correlates with tight junction gene expression, impairs barrier function, and exacerbates dextran sodium sulfate colitis. We show that LGG-derived indoles as well as arginine metabolites enhanced argininosuccinate lyase (ASL) and nitric oxide synthase (NOS2) expression, linking microbial metabolism to nitric oxide production and epithelial homeostasis. Patients with IBD have increased ASS1 and decreased ASL expression, suggesting a metabolic bottleneck driving ASA accumulation. We propose that signaling pathways underlying LGG and tryptophan-mediated ASL upregulation can be useful therapeutic targets to normalize arginine metabolism in select patients with IBD.NEW & NOTEWORTHY This study identifies a novel probiotic-driven mechanism linking dietary tryptophan and host arginine metabolism. Lacticaseibacillus rhamnosus GG, in synergy with tryptophan, enhances gut barrier integrity by upregulating argininosuccinate lyase (ASL), a critical enzyme in arginine biosynthesis. Furthermore, we uncover ASL downregulation and serum argininosuccinate elevation in experimental colitis in mice, suggesting a target to guide precision probiotics.

Intestinal hyperpermeability, which refers to translocation of microbial factors into the bloodstream, is associated with many chronic diseases. Increased intestinal permeability may contribute to the pathophysiology of these diseases by promoting systemic inflammation. Although early work on the health implications of increased intestinal permeability focused on diseases of the gastrointestinal tract, subsequent preclinical and cross-sectional data identified that various types of cardiometabolic and cardiovascular diseases (CVDs) are linked to gut barrier dysfunction. More recently, a body of epidemiological studies has emerged, indicating that elevated biomarkers of intestinal permeability are prospectively linked to incident CVD and CVD events, such as myocardial infarction and stroke, even after controlling for traditional CVD risk factors. In this brief review, we discuss gut barrier function in health and disease, highlight methodologies used to assess intestinal permeability, and review the emerging literature demonstrating that measures of intestinal permeability predict future CVD across several populations.

Homeostasis of the mammalian intestinal epithelium is tightly regulated by multiple factors, including cellular polyamines, but the exact mechanism underlying polyamines in this process remains largely unknown. Mitochondria are the powerhouse of cells and can also function as signaling organelles by releasing metabolic by-products. Here, we determined whether polyamines regulate intestinal epithelial renewal and wound healing by altering mitochondrial activity. Depletion of cellular polyamines by inhibiting ornithine decarboxylase with α-difluoromethylornithine (DFMO) resulted in mitochondrial dysfunction as evidenced by decreases in basal and maximal respiration levels, ATP production, and spare respiration capacity. Polyamine depletion by DFMO also decreased the levels of mitochondria-associated proteins prohibitin 1 and COX-IV. Mitochondrial dysfunction induced by DFMO was associated with an inhibition of intestinal organoid growth and epithelial repair after wounding, and this inhibition was ameliorated by administration of the mitochondrial activator Mito-Tempo or exogenous polyamine putrescine. These results indicate that polyamines are necessary for mitochondrial metabolism, in turn, controlling constant intestinal mucosal growth and epithelial repair after acute injury. NEW & NOTEWORTHY Our results indicate that polyamines are required for maintaining mitochondrial integrity in intestinal epithelial cells. Polyamine depletion led to mitochondrial dysfunction, along with an inhibition of intestinal epithelial renewal and delayed wound healing. Reinforcing mitochondrial activity by Mito-Tempo ameliorated reduced epithelial renewal and delayed healing in polyamine-deficient cells, demonstrating the importance of mitochondrial metabolism in polyamine-regulated mucosal growth and repair after injury.

Eosinophilic esophagitis (EoE) is a chronic allergic inflammatory disease of the esophagus that exerts a significant clinical and financial burden in developed countries. Despite an emerging interest in this disease, the cellular and molecular mechanisms driving EoE pathogenesis remain elusive. Addressing this knowledge gap is critical to guide the development of novel approaches for diagnosis, monitoring, and therapy in patients with EoE. As EoE is an allergic inflammatory disorder that results in esophageal inflammation and tissue remodeling, in vivo studies are critical to develop a better understanding of this disease. Here, we provide a review of murine models of EoE, highlighting the mechanistic and translational insights into EoE pathogenesis and therapeutic approaches that studies using these models have uncovered. We further discuss the strengths and limitations of EoE mouse models, as well as opportunities for future in vivo approaches to study EoE. Overall, this article reviews the progress, challenges, unmet needs, and opportunities in murine modeling of EoE.

The gastric proton pump H⁺/K⁺-ATPase (HKA) is the highly conserved acid secretory mechanism of the gnathostome stomach. HKA is a heterodimeric pump composed of α and β-subunits. In this study, we have explored the involvement of this enzyme in the transcriptional regulation of pathways linked to acid secretion (Cl^- and K⁺ movement across the cell membrane) and peptic digestion (pepsinogens) in the stomach of the teleost Astyanax mexicanus. To this end, we generated the first nonmammalian knockout line for the gastric proton pump, atp4a (HKA-α-subunit), in A. mexicanus using CRISPR-Cas9 gene editing. Homozygous mutant atp4a^-/- fish appeared healthy but were achlorhydric. The transcript and protein levels of the HKA-β-subunit remained unaltered despite the absence of α-subunit protein. Pepsinogen (pga and pgc) transcript levels were reduced, together with kcne2, kcc4 (involved in apical K⁺ recycling), and clcn2 (involved in the acid-coupled Cl^- secretion mechanism) mRNA levels. The cftr and slc4a2b transcript levels were significantly increased in knockout stomachs. The gastric morphology and cytology of atp4a^-/- characterized through bright-field and electron microscopy show that the lumen of the gastric glands of atp4a^-/- fish was dilated and the oxynticopeptic cells had large cytoplasmic inclusions that were absent in wild-type animals. The tubulovesicular system of knockouts was less developed relative to wild-type animals. Our findings provide novel evidence of the highly conservative nature of the gastric acid-peptic pathways across diverse vertebrates. Furthermore, this work highlights the potential for the use of nontraditional models in biomedical research.NEW & NOTEWORTHY We have knocked out stomach acidification in a nonmammalian gnathostome for the first time using CRISPR-Cas9 gene editing in the teleost fish Astyanax mexicanus targeting the gastric proton pump. This offers a novel and insightful alternative to murine models, having larger offspring numbers, rapid development, and ease of maintenance. In accordance, we present the first demonstration in a knockout animal of how diverse chloride and potassium transporters dynamically respond to-and are directly altered by-acidification.