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

Some forms of gastroesophageal reflux disease (GERD) are associated with crural diaphragm (CD) dysfunction, suggesting that GERD may be influenced by skeletal muscle deficiencies. Skeletal muscle atrophy has been strongly linked to alterations in the ubiquitin-proteasome system, the primary pathway for protein degradation. This study aimed to assess the expression of muscle atrophy-related proteins in the CD of patients with reflux esophagitis compared with those without esophagitis. In addition, we examined the correlation between these proteins, esophagitis severity, and esophageal acid exposure. CD biopsies were obtained from 15 volunteers (8 males, 7 females; mean age 43 yr) during antireflux laparoscopic Nissen fundoplication (GERD group) or gallbladder surgery (control group). The GERD group was further classified based on the Los Angeles classification into grades A (n = 5), B (n = 7), and C (n = 3). We analyzed key signaling pathways involved in muscle atrophy, including AKT, phosphorylated AKT (pAKT), muscle-specific RING finger 1 protein (MuRF-1), and muscle atrophy F-box (MAFbx/atrogin-1), normalized to glyceraldehyde 3-phosphate dehydrogenase (GAPDH). No significant differences were observed in MuRF-1, pAKT/AKT ratio, or MAFbx/atrogin-1 expression between the control and GERD groups. However, MuRF-1 expression was significantly elevated in the GERD C group compared with GERD B group. The control group showed no differences from GERD A or B. Notably, MuRF-1 expression correlated with esophageal total reflux time in the supine position. These findings suggest that increased MuRF-1 expression may contribute to CD fiber atrophy and weakness in patients with GERD, potentially impairing gastroesophageal junction function and influencing disease progression.NEW & NOTEWORTHY This study demonstrated, for the first time, an increased activation of the ubiquitin-proteasome pathway and elevated MuRF-1 expression in the crural diaphragm of humans with moderate reflux esophagitis. It showed a positive correlation between the supine reflux time and MuRF-1 expression, suggesting a molecular mechanism associated with diaphragm fiber atrophy and weakness. These findings highlight a potential link between diaphragm degradation and reflux esophagitis, which may modulate gastroesophageal reflux and symptoms.

Fructose consumption contributes to metabolic dysfunction-associated steatohepatitis (MASH). Retatrutide is a novel triple receptor agonist that improves obesity and hepatic steatosis in humans. The aims of this study were to develop a shortened and clinically relevant dietary mouse model of diet-induced steatohepatitis, and to evaluate the effects of a retatrutide intervention in this model. C57BL/6N mice were subjected to a single fructose binge (10 mg/g body wt), or a new 31-day mouse model of diet-induced steatohepatitis using a Western diet, fructose, and sucrose in the drinking water, and a final fructose binge with or without retatrutide. A single fructose binge resulted in significantly elevated alanine aminotransferase (ALT) and hepatic triglyceride levels in female mice after 6 h; male mice showed less hepatotoxicity. The novel 31-day feeding model significantly increased body weight, ALT levels, hepatic triglycerides and cholesterol, and hepatic inflammatory markers in female and male mice compared with their chow-fed controls. The overall hepatic gene expression profile per RNA sequencing of treated mice correlated with that of human MASH in children and adults. Retatrutide intervention over the final 2 weeks of the 31-day mouse model significantly reduced body weight, ALT levels, hepatic triglycerides and cholesterol, and hepatic inflammatory markers in female mice compared with their vehicle-treated counterparts. Our findings indicate that female mice develop more severe liver injury due to a single fructose binge than males. The novel 31-day mouse model induces robust steatohepatitis and correlates with human disease. An intervention with retatrutide improves steatohepatitis in this shortened mouse model.NEW & NOTEWORTHY Female mice are more prone to liver injury due to a single fructose binge compared with male mice. The new 31-day mouse model induces robust steatohepatitis in mice and correlates with MASLD in children and adults. An intervention with retatrutide improves steatohepatitis in this novel mouse model, indicating despite its short duration, the model can be used to trial pharmacological interventions.

Lithogenic diet exposure disrupts biliary lipid homeostasis to promote precipitation of excess biliary cholesterol; however, the underlying pathogenic signaling mechanism remains unclear. Protein kinase Cbeta (PKCβ) is involved in regulating hepatic cholesterol and bile acid metabolism. In this study, we aimed to identify the initiating signaling and biological changes in the liver upon loss of hepatic PKCβ function under lithogenic stress. Transcriptome analysis of the liver revealed that hepatic deletion of PKCβ altered the expression of 183 liver genes, 118 of which were upregulated and 65 were downregulated. We identified marked increases in the expression of genes involved in bile acid biosynthesis (Cyp7a1 and Cyp8b1) and a decrease in retinol metabolism (Cyp26b1) as the most relevant changes, with blunted expression of genes involved in bile acid and phosphatidylcholine transporters. Mechanistic studies revealed that the hepatic PKCβ deficiency was associated with reduced ERK1/2 phosphorylation in concert with increased p38^MAPK phosphorylation in the liver. Overexpression of PKCβ in the liver blocked p38^MAPK activation as well as resulted in increased ERK1/2 phosphorylation and was accompanied by suppression of both Cyp7a1 and Cyp8b1 expression, demonstrating that hepatic PKCβ functions as a positive regulator of ERK1/2 to suppress the expression of both genes by antagonizing p38^MAPK. Furthermore, depletion of liver p38^MAPK in PKCβ^Liv-/- mice resulted in enhanced ERK1/2 phosphorylation and suppression of Cyp7a1 and Cyp8b1 expression. The findings yielded by this study support our understanding of the intricate interplay among PKCβ, p38^MAPK, and ERK1/2 signaling in vivo and provide valuable insights into potential therapeutic targets for the development of novel strategies to combat cholelithiasis.NEW & NOTEWORTHY This study underscores the pivotal role of hepatic PKCβ in controlling biliary lipid composition under lithogenic stress. Our findings on the distinct and combined effects of downstream p38^MAPK and ERK1/2 offer key insights into the mechanisms driving lithogenic diet-induced dysregulation of biliary lipid composition. This research reveals that the potential of PKCβ/p38^MAPK/ERK1/2 signaling axis offers the possibility for the integration of different inputs to modulate the signaling output balancing in a way most appropriate for context.

Mucosal homeostasis requires coordinated immune regulation and epithelial repair. Inflammatory bowel disease (IBD) arises from disrupted coordination between the immune system and intestinal epithelium, where resolution and repair must occur in parallel. Interleukin-6 (IL-6) plays a dual role: it promotes epithelial regeneration but destabilizes regulatory T cells (Tregs). We aimed to determine the contribution of Treg IL-6 receptor (IL-6R) signaling to intestinal inflammation and epithelial integrity. We developed a conditional knockout mouse model in which IL-6R was deleted from Tregs (Treg IL-6R knockout). These mice were subjected to dextran sodium sulfate (DSS)-induced colitis and a T cell transfer model of colitis. Soluble IL-6R production by Tregs was assessed in vitro, and transcriptional changes in epithelial cells were analyzed by RNA-seq. Human colonic organoids from patients with IBD were treated with IL-6 or hyper-IL-6 (IL-6/sIL-6R fusion protein) to test downstream signaling effects. Tregs lacking IL-6R improved colitis to a similar extent as control Tregs in the adoptive transfer model, indicating intact suppressive function. However, Treg IL-6R knockout mice were more susceptible to DSS colitis than controls, suggesting a physiologic role for Treg IL-6R signaling in epithelial protection. In vitro, Tregs shed soluble IL-6R, enabling IL-6 trans-signaling to epithelial cells. Intestinal epithelial cells from Treg IL-6R knockout mice compared with WTcre controls revealed widespread transcriptional downregulation of genes related to survival and repair pathways at baseline, and impaired transcriptional responses following DSS treatment. In human organoids, IL-6 trans-signaling elicited stronger STAT3 activation than IL-6 alone. These findings reveal a previously unrecognized role for Treg-derived IL-6R in promoting epithelial resilience and maintaining mucosal homeostasis.NEW & NOTEWORTHY This study reveals a novel role for Treg-derived IL-6R in supporting epithelial repair. Despite preserved immune-suppressive capacity, deletion of IL-6R from Tregs impairs epithelial transcription and worsens injury in colitis. We demonstrate that human intestinal organoids preferentially respond to trans- over classic IL-6 signaling. These findings introduce a Treg-specific role in immune-epithelial cross talk relevant to mucosal healing and inflammatory bowel disease.

Excessive intake of fructose and fats disrupts hepatocyte function by overwhelming endoplasmic reticulum (ER) capacity, leading to unresolved protein stress and progression to metabolic dysfunction-associated steatohepatitis (Shepherd EL, Saborano R, Northall E, Matsuda K, Ogino H, Yashiro H, Pickens J, Feaver RE, Cole BK, Hoang SA, Lawson MJ, Olson M, Figler RA, Reardon JE, Nishigaki N, Wamhoff BR, Günther UL, Hirschfield G, Erion DM, Lalor PF. JHEP Rep 3: 100217, 2021). Ketohexokinase (KHK), the primary enzyme for fructose metabolism, is increasingly recognized for nonmetabolic roles (Peng C, Yang P, Zhang D, Jin C, Peng W, Wang T, Sun Q, Chen Z, Feng Y, Sun Y. Acta Pharm Sin B 14: 2959-2976, 2024; Li X, Qian X, Peng LX, Jiang Y, Hawke DH, Zheng Y, Xia Y, Lee JH, Cote G, Wang H, Wang L, Qian CN, Lu Z. Nat Cell Biol 18: 561-571, 2016), but its function in regulating ER proteostasis under nutrient stress remains unclear. We show that steatogenic conditions synergistically induce lipid accumulation and robust KHK expression, accompanied by activation of the IRE1α-XBP1 branch of the unfolded protein response. This adaptive axis was observed in HepG2 cells, primary hepatocytes from Gubra Amylin NASH, (GAN) diet-fed mice, and liver biopsies from MASLD patients, establishing a conserved KHK-IRE1α axis across species. Khk knockdown disrupted this balance, causing accumulation of misfolded and ubiquitinated proteins, proteotoxic stress, and a shift toward PERK-CHOP-driven apoptosis. Similar signatures in Khk-deficient mouse livers further underscore KHK's role in sustaining ER homeostasis. Our findings identify KHK as a dual-function enzyme: a metabolic gatekeeper of fructose flux and a proteostatic regulator that safeguards hepatocyte survival. Although KHK contributes to steatosis, its complete loss destabilizes ER proteostasis, suggesting that selective inhibition of KHK enzymatic activity may offer therapeutic benefit without compromising ER function.NEW & NOTEWORTHY This study uncovers a noncanonical role for ketohexokinase (KHK) in maintaining ER proteostasis during nutrient overload. In hepatocytes exposed to fructose and saturated fat, KHK promotes adaptive IRE1α-XBP1 signaling and prevents proteotoxic stress and apoptosis. These findings position KHK as a metabolic checkpoint linking fructose metabolism to ER stress resolution and offer new insight into liver survival pathways relevant to MASLD and MASH.

Peritonitis is a well-known complication of bowel perforation and abdominal surgery, leading to sepsis and high mortality. Despite its prevalence and severity, the pathogenesis of peritonitis remains incompletely understood, limiting our ability to develop targeted medical therapies. Specifically, little is known about the determinants of the peritoneal nutrient environment for pathogens. The gut microbiome is a well-established source of infectious bacteria in peritonitis, but whether it also modulates levels of nutrients that enable and sustain these infections remains unknown. Using multiple murine models of peritonitis (lipopolysaccharide and cecal slurry), multiple methods of microbiome modulation (germ-free mice and antibiotic-treated mice), novel ex vivo modeling of peritonitis, and nuclear magnetic resonance (NMR) metabolomics of the peritoneal microenvironment, we performed a series of experiments to determine how the gut microbiome influences peritoneal metabolite concentration during peritonitis. We found that both lipopolysaccharide and cecal slurry peritonitis caused consistent changes in high-abundance peritoneal metabolites and that many of these changes were blunted or completely abrogated in antibiotic-treated and germ-free mice. Moreover, we found that peritoneal washings from septic, microbiome-depleted animals supported less bacterial growth of common intra-abdominal pathogens compared with washings from septic conventional animals. We identified the peritoneal nutrients consumed by two common pathogens from the Enterobacteriaceae family and found that supplementation of gut microbiome-mediated nutrients was sufficient to alter bacterial growth in an ex vivo model. Taken together, we identify the gut microbiome as a key driver of the peritoneal nutrient environment, mediating pathogen growth. These findings suggest that microbiome-targeted therapies could mitigate peritonitis risk.NEW & NOTEWORTHY Peritonitis induced via cecal slurry or LPS induced similar changes in prevalent metabolites in the murine peritoneal microenvironment, increasing glutamine and pyruvate and decreasing glucose and butyrate. Gut microbiome depletion using germ-free mice or antibiotic pretreatment blunted many of these peritoneal metabolite changes. Peritoneal fluid from microbiome-depleted LPS-treated mice exhibited reduced bacterial growth of two Enterobacteriaceae commensals in an ex vivo peritonitis model compared with fluid from conventional LPS-treated animals.

Early-life adversity, including abrupt weaning, imposes significant psychosocial and environmental stress during a critical window of gastrointestinal (GI) development, leading to long-term consequences for gut function and disease susceptibility. In piglets, early weaning profoundly disrupts GI development, altering the intestinal epithelial barrier, reshaping immune function, and inducing lasting changes in the enteric nervous system. Despite these adverse outcomes, the early molecular mechanisms that initiate these alterations and set the gut on a divergent developmental trajectory remain poorly understood. Here, we used RNA sequencing and bioinformatic analyses to delineate early transcriptional changes in the jejunal mucosa of early-weaned male castrates compared with unweaned littermates. Ex vivo Ussing chamber experiments validated functional changes associated with these transcriptional alterations. Weaning triggered rapid transcriptional shifts observable within 3 h, including suppressed mitochondrial energy production and increased glucose transporter expression. Pathway analysis revealed upregulation of ion channel transport genes (KCN, SCN, TRP, SLC) and neurotransmitter receptors (cholinergic, dopaminergic, GABAergic, glutamatergic), indicating early neuronal adaptations. Functional assays confirmed enhanced SGLT-mediated glucose transport and neural-evoked secretory responses 24 h postweaning, supporting transcriptomic findings. These findings reveal previously unexamined early transcriptional and functional changes that may serve as inciting mechanisms altering gut trajectory during this critical developmental window, providing new insight into how psychosocial stress and early weaning contribute to long-term gut dysfunction, with broader implications for preterm birth, neonatal GI injury, and other early-life stressors that impact lifelong GI health.NEW & NOTEWORTHY Early-life stress is linked to long-term gut dysfunction, but the initiating events remain unclear. This study shows that early weaning triggers a rapid, integrated jejunal response involving metabolic suppression, altered glucose transport, and heightened enteric nervous system activity. These findings identify a critical developmental inflection point in gut maturation and offer new mechanistic insight into how early adversity shapes lifelong gastrointestinal health, informing strategies to prevent chronic disease in animals and humans.

Mitochondrial bioenergetics and hydrogen peroxide (H₂O₂) production play a central role in maintaining liver metabolic function and redox balance. Understanding sex dimorphism and substrate dependency in these mitochondrial processes is crucial for elucidating the regulatory mechanisms that govern male versus female differences in liver physiology in health and disease. This study aimed at investigating sex-specific and substrate-dependent alterations in liver mitochondrial respiratory rates (Jo₂), membrane potential (ΔΨ), and H₂O₂ production and their metabolic regulation. Liver mitochondria were isolated from adult male and female Sprague-Dawley rats. Four substrate combinations-pyruvate + malate (PM), glutamate + malate (GM), succinate, and succinate with complex I inhibitor rotenone-were used to determine their impact on the activities of the electron transport chain (ETC) and TCA cycle complexes. Adenosine diphosphate (ADP) was added to determine the influence of substrates on oxidative phosphorylation (OxPhos). Jo₂ and ΔΨ were measured simultaneously using an Oroboros Oxygraph-2k respirometer with the cationic rhodamine dye tetramethylrhodamine methyl ester. H₂O₂ production was measured spectrofluorometrically using the Amplex Red and horseradish peroxidase assay. Our results show that male and female liver mitochondria displayed distinct respiratory patterns for different substrates. GM and succinate yielded higher Jo₂, whereas PM yielded the lowest Jo₂. Notably, female mitochondria exhibited higher Jo₂ than males across all substrates. Both ΔΨ and H₂O₂ production showed substrate-dependent patterns, with females exhibiting higher values than males across all substrates. These findings reveal sex-specific differences in liver mitochondrial function, driven by substrate-dependent engagement of the ETC and TCA cycle complexes toward OxPhos, with females showing higher respiratory capacity and H₂O₂ production.NEW & NOTEWORTHY We examined sex-specific and substrate-dependent differences in liver mitochondrial function of adult SD rats. Liver mitochondria preferentially use GM over PM for respiration, whereas PM produces more H₂O₂. Female mitochondria exhibited higher respiration and H₂O₂ production than males across all substrates, likely driven by hormonal factors and sex-specific regulatory pathways. These findings highlight the importance of both substrate and sex in shaping liver mitochondrial bioenergetics and redox function, offering insight into intrinsic metabolic differences.