Vanessa A. Leone

Metabolic dysfunction–associated steatohepatitis (MASH) is increasingly linked to disruptions of the gut/liver axis, yet the microbial mechanisms driving disease progression remain incompletely defined. Here, Qu et al. have identified ileal microbial ammonia production by Clostridium perfringens as a mechanistic driver of epithelial barrier dysfunction and hepatic CD8 ⁺ T cell remodeling in MASH. In nonhuman primate and mouse models of MASH, the authors demonstrated that the glycine-based tripeptide DT-109 restored gut barrier integrity and attenuated FosB-mediated CCL5 expression in CD8 ⁺ T cells via inhibition of bacterial nitrite reductase A–mediated microbial ammonia production. These findings position microbial nitrogen metabolism as a tractable therapeutic target and highlight metabolite-focused microbiome interventions as a potential MASH intervention.

Metabolic dysfunction-associated steatotic liver disease (MASLD) affects approximately one-third of the global population and can progress to metabolic dysfunction-associated steatohepatitis (MASH) with fibrosis, increasing the risk of cirrhosis, hepatocellular carcinoma, and mortality. Gut microbes driven by diets high in saturated fat, simple sugar, and cholesterol contribute to disease progression, yet the underlying mechanisms remain undefined. We explored the independent and synergistic effects of dietary saturated fat and cholesterol on MASH development using specific pathogen-free (SPF) and germ-free (GF) mice. We demonstrate that (1) both dietary cholesterol and saturated fat are required to induce fibrosing MASH in SPF mice, whereas GF mice are protected, (2) saturated fat and cholesterol individually alter gut microbial membership, potentially via altered bile acid metabolism, while their combination promotes a distinct composition, including an increase in Parasutterella spp. which correlates with hepatic fibrosis, and (3) diluted cecal contents from SPF, but not GF, mice fed high-fat, high-cholesterol diets are enriched in deoxycholic acid and activate human hepatic stellate cells in vitro, suggesting a mechanistic link between dietary lipid-induced microbiota and liver fibrogenesis. These findings reveal how specific Western dietary components shape the gut microbiota and contribute to hepatic fibrosis via stellate cell activation, offering potential targets for therapeutic interventions against MASLD/MASH.

BACKGROUND: Gut microbes and their metabolites contribute to the host circulating metabolome and exhibit diurnal variation influenced by sleep-wake cycles and meal timing. Sleep deprivation alters the rhythmic circulating metabolome, but its impact on microbial metabolites remains unclear. We tested whether 24-hour circulating metabolite profiles, including those of microbial origin, differ under normal (habitual) versus short-term restricted sleep. METHODS: In a randomized crossover design, 9 healthy adults completed 2 in-lab 24-hour blood sampling sessions (q120): one following 3 nights of normal sleep (8.5 hours/night), the other following 3 nights of sleep restriction (4.5 hours/night). Meal timing and caloric intake were held constant. Serum metabolites were characterized using untargeted reverse-phase liquid chromatography–mass spectrometry and rhythmicity was assessed using empirical JTK_CYCLE analysis. RESULTS: We identified 90 metabolites, including 14 of microbial origin or derived from host metabolism of microbial products, e.g., butyrate and tryptophan derivatives. Sleep restriction significantly altered serum metabolite composition compared with normal sleep. While many compounds maintained rhythmicity across conditions, sleep restriction disrupted rhythms of several key compounds, including microbe-derived metabolites. Notably, butyrate and indole-3–propionic acid lost rhythmicity, whereas new rhythms emerged in the tryptophan catabolite, kynurenine, and lipid metabolism intermediates. CONCLUSION: We provide evidence that microbial metabolites are detectable in human blood and exhibit sleep-dependent rhythmicity. Sleep restriction alters diurnal circulating microbial and host-derived metabolite rhythms even under constant meal timing, composition, and calories. These findings support links between host sleep patterns and gut microbial metabolism and suggest microbial metabolites as potential biomarkers or mediators of sleep loss–associated health risks. TRIAL REGISTRATION: NCT00989976. FUNDING: NIH/NCRR KL2RR025000; R56DK102872-01A1, P30DK020595; P30DK042086; K01DK111785; F31DK122714; DOD W81XWH-07-2-0071.

Hypercholesterolemia contributes to the development of atherosclerosis and is a major risk factor for cardiovascular diseases (CVD). Dietary fiber can attenuate CVD, at least in part, by serving as a fermentable substrate for gut bacteria, leading to the production of short-chain fatty acids (SCFAs), such as butyrate and propionate, which have been linked to atheroprotective effects. SCFAs are sensed by G-protein coupled receptors including GPR41, GPR43, and GPR109A. To explore the role of these receptors in hypercholesterolemia and CVD, we examined atherosclerosis progression and lipid metabolism in Gpr41^-/-, Gpr43^-/-, and Gpr109a^-/- mice using a proprotein convertase subtilisin/kexin type 9 adeno-associated virus (PCSK9-AAV) model of hypercholesterolemia. Deficiency of any single SCFA receptor did not significantly affect atherosclerotic plaque burden compared with wild-type (WT) littermates. However, male Gpr41^-/- mice exhibited decreased gonadal fat, plasma triacylglycerol, and low-density lipoprotein cholesterol levels compared to their WT littermates. GPR41 deficiency in males was also associated with increased cecal propionate levels, reduced ileal expression of nutrient transporters such as Npc1l1 and a trend toward increased gut motility. In addition, male Gpr41^-/- mice displayed altered gut microbiota composition and lower levels of microbially generated bile acids relative to their WT counterparts. Together, these findings highlight GPR41 as a key intestinal chemosensor regulating nutrient uptake, lipid storage, and microbiota composition.

Circadian rhythms govern glucose homeostasis, and their dysregulation leads to complex metabolic diseases. Gut microbes exhibit diurnal rhythms that influence host circadian networks and metabolic processes, yet underlying mechanisms remain elusive. Here, we showed hierarchical, bidirectional communication among the liver circadian clock, gut microbes, and glucose homeostasis in mice. To assess this relationship, we utilized mice with liver-specific deletion of the core circadian clock gene Bmal1 via Albumin-cre maintained in either conventional or germ-free housing conditions. The liver clock, but not the forebrain clock, required gut microbes to drive glucose clearance and gluconeogenesis. Liver clock dysfunctionality expanded proportions and abundances of oscillating microbial features by 2-fold relative to that in controls. The liver clock was the primary driver of differential and rhythmic hepatic expression of glucose and fatty acid metabolic pathways. Absent the liver clock, gut microbes provided secondary cues that dampened these rhythms, resulting in reduced lipid fuel utilization relative to carbohydrates. All together, the liver clock transduced signals from gut microbes that were necessary for regulating glucose and lipid metabolism and meeting energy demands over 24 hours.

The mammalian gut secretes a family of multifunctional peptides that affect appetite, intestinal secretions, and motility whereas others regulate the microbiota. We have found that peptide YY (PYY _1-36 ), but not endocrine PYY _3-36 , acts as an antimicrobial peptide (AMP) expressed by gut epithelial paneth cells (PC). PC-PYY is packaged into secretory granules and is secreted into and retained by surface mucus, which optimizes PC-PYY activity. Although PC-PYY shows some antibacterial activity, it displays selective antifungal activity against virulent Candida albicans hyphae—but not the yeast form. PC-PYY is a cationic molecule that interacts with the anionic surfaces of fungal hyphae to cause membrane disruption and transcriptional reprogramming that selects for the yeast phenotype. Hence, PC-PYY is an antifungal AMP that contributes to the maintenance of gut fungal commensalism.

Nonalcoholic fatty liver disease (NAFLD) is multifactorial in nature, affecting over a billion people worldwide. The gut microbiome has emerged as an associative factor in NAFLD, yet mechanistic contributions are unclear. Here, we show fast food (FF) diets containing high fat, added cholesterol, and fructose/glucose drinking water differentially impact short- vs. long-term NAFLD severity and progression in conventionally-raised, but not germ-free mice. Correlation and machine learning analyses independently demonstrate FF diets induce early and specific gut microbiota changes that are predictive of NAFLD indicators, with corresponding microbial community instability relative to control-fed mice. Shotgun metagenomics showed FF diets containing high cholesterol elevate fecal pro-inflammatory effectors over time, relating to a reshaping of host hepatic metabolic and inflammatory transcriptomes. FF diet-induced gut dysbiosis precedes onset and is highly predictive of NAFLD outcomes, providing potential insights into microbially-based pathogenesis and therapeutics. Highlights Germ-free mice are protected from fast-food diet-induced NAFLD. Fast-food diets rapidly shift gut microbiota composition and function. Increasing dietary cholesterol exacerbates hepatic inflammation only in SPF mice. Fast-food diet-induced gut dysbiosis precedes and predicts late-stage NAFLD severity.

Host–microorganism circadian dynamics are key contributors to metabolic health. In addition, diet composition and timed feeding affect gut microbiota diurnal rhythms, with high-fat diets altering the composition of the gut microbiota and dampening circadian rhythms throughout the intestine. A recent study shows that time-restricted feeding of a high-fat diet restores the rhythms of small bowel host–microorganism interactions, preventing diet-induced obesity in mice.