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

Together, the costal and crural diaphragm constitute the primary respiratory muscle in mammals, but functionally, they are distinct. The crural segment has additional gastrointestinal function, wrapped around the esophagus at the esophagogastric junction, contributing to the esophageal sphincter. Emesis is an expulsive process that requires the coordinated action of multiple muscles to rapidly force out gastric contents. The simultaneous mechanical action and neural activation of the diaphragm segments during the process of emesis, especially expulsion, is uncertain. Detailed divergence of the crural diaphragm to sphincter function during emesis has not been studied. In six awake, spontaneously breathing canines, electrical activity and corresponding muscle shortening of the costal and crural diaphragm were measured at five phases of emesis (rest, early prodrome, mid prodrome, late prodrome, and expulsion) induced by apomorphine. Overall, baseline muscle length decreased and baseline EMG increased progressively from rest through prodrome for both costal and crural, but at expulsion, the crural segment diverged, lengthening abruptly. Shortening and EMG activity per breath for costal changed slightly throughout emesis; crural shortening and EMG activity increased abruptly at expulsion. The divergent action of crural during expulsion developed sequentially through each breath. Also, neuromechanical coupling of the segments reversed at expulsion, with contractility of the crural surpassing that of the costal. These measurements confirm a disparate action of crural diaphragm, compared with costal, to facilitate expulsion. During the process of emesis, although the costal persists as an obligatory respiratory muscle, the crural converts from respiratory muscle to opening sphincter.NEW & NOTEWORTHY Although the diaphragm is known as a primary respiratory muscle, the two diaphragm sections, the costal and crural, have notably different functions. This study elucidates the essential role of the crural diaphragm during emesis, a gastrointestinal process. During emesis, the crural diaphragm abandons respiratory function and transmutes to act as an esophageal sphincter. Meanwhile, the costal diaphragm continues ventilatory function.

Patatin-like phospholipase domain-containing protein 3 (PNPLA3) p.I148M is a well-established variant associated with metabolic dysfunction-associated steatotic liver disease (MASLD) and metabolic dysfunction-associated steatohepatitis (MASH). Conflicting in vitro and in vivo data about the impact of the variant suggest that the PNPLA3 p.I148M variant could be gain- or loss-of-function, or neomorphic. Most in vitro models used to study MASLD are cancer-derived hepatoma cell lines such as HepG2 and Huh7, which already endogenously express the homozygous PNPLA3 p.I148M variant. This highlights the need to develop models that better reflect disease and allow comparisons with wild-type cells. Clustered regularly interspaced short palindromic repeats (CRISPR) prime editing was used to introduce the PNPLA3 p.I148M gene variant into a healthy-derived immortalized human hepatocyte (IHH) cell line to generate a new in vitro model of MASLD that would better reflect PNPLA3-associated MASLD/MASH. Heterozygous and homozygous PNPLA3 p.I148M IHH cell lines were generated and validated with Sanger sequencing. Mutant cell lines exhibited lipid accumulation, increased cluster of differentiation 36 (CD36) gene expression and a decline in carnitine palmitoyltransferase 1 alpha (CPT1A) gene expression compared with the wild-type control, basally or in the presence of free fatty acid (FFA)-induced steatosis. The homozygous PNPLA3 p.I148M IHH cell line also demonstrated reduced PNPLA3 gene and protein expression compared with the wild-type control. We have developed a new human hepatocyte cell line and in vitro model to help understand PNPLA3-associated steatotic liver disease and provide a new resource for developing potential therapeutics.NEW & NOTEWORTHY We have developed a novel in vitro model for studying the PNPLA3 p.I148M variant in steatotic liver disease using a normal, healthy-derived hepatocyte cell line, which does not endogenously express the variant. We show that carrying the homozygous PNPLA3 p.I148M variant results in reduced PNPLA3 gene and protein expression, more lipid accumulation, increased lipid uptake, and reduced mitochondrial lipid oxidation-associated gene expressions and altered expression of genes associated with lipid synthesis and transport.

Metabolic dysfunction-associated steatotic liver disease (MASLD) affects ∼40% of adults, but causal mechanisms remain elusive. Preclinical models implicate the gut microbiota in MASLD pathogenesis, yet translation to humans is hampered by variability in microbial composition. We addressed this gap by investigating whether stable, quantitative gut phenotypes, including microbiota encroachment, are pathological features of MASLD. Sigmoid colon biopsies were collected from participants with and without imaging-defined MASLD. Mucus immunostaining was paired with fluorescent in situ hybridization to image and quantify the distance separating bacteria from the colonic epithelium (i.e., encroachment). Secondary outcomes included intestinal permeability, colon histopathology, and insulin resistance. RNA sequencing was combined with weighted gene network correlation analysis to explore correlations between colonic gene expression and clinical endpoints. Microbiota encroachment did not differentiate participants with MASLD (n = 13 with simple steatosis, n = 13 with fibrosis stage <4) from controls (n = 12; P = 0.20). Circulating lipopolysaccharide and flagellin-specific immunoglobulins (intestinal permeability), and colon histopathology were similar across cohorts (P = 0.23, P = 0.11, and P = 0.73, respectively). Microbiota encroachment and adipose tissue insulin resistance (Adipo-IR) were correlated with a colonic gene network regulating insulin and lipid metabolism (Pearson's r = -0.33, P = 0.04 and r = 0.47, P = 0.003, respectively). Pathway analysis of this network revealed genes involved in hepatic steatosis (P = 3.95E-06) and liver cell proliferation (P = 0.0003), suggesting a gut-adipose-liver cross talk. Microbiota encroachment and related gut phenotypes do not correlate with MASLD severity. However, colonic expression of genes related to insulin signaling and lipid metabolism links microbiota encroachment to Adipo-IR and MASLD. Future research should investigate how colonic gene products interact with microbiota-focused MASLD mechanisms.NEW & NOTEWORTHY In a first-in-human study, we observed that colonic expression of insulin and lipid-related genes may bridge the pathophysiology of colonic microbiota encroachment with adipose tissue insulin resistance and metabolic dysfunction-associated steatotic liver disease.

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.