Microbiota-derived Short-chain Fatty Acids Research Articles

Salmonella virulence factors induce amino acid malabsorption in the ileum to promote ecosystem invasion of the large intestine

The gut microbiota produces high concentrations of antimicrobial short-chain fatty acids (SCFAs) that restrict the growth of invading microorganisms. The enteric pathogen Salmonella enterica serovar (S.) Typhimurium triggers inflammation in the large intestine to ultimately reduce microbiota density and bloom, but it is unclear how the pathogen gains a foothold in the homeostatic gut when SCFA-producing commensals are abundant. Here, we show that S. Typhimurium invasion of the ileal mucosa triggers malabsorption of dietary amino acids to produce downstream changes in nutrient availability in the large intestine. In gnotobiotic mice engrafted with a community of 17 human Clostridia isolates, S. Typhimurium virulence factors triggered marked changes in the cecal metabolome, including an elevated abundance of amino acids. In an ex vivo fecal culture model, we found that two of these amino acids, lysine and ornithine, countered SCFA-mediated growth inhibition by restoring S. Typhimurium pH homeostasis through the inducible amino acid decarboxylases CadA and SpeF, respectively. In a mouse model of gastrointestinal infection, S. Typhimurium CadA activity depleted dietary lysine to promote cecal ecosystem invasion in the presence of an intact microbiota. From these findings, we conclude that virulence factor-induced malabsorption of dietary amino acids in the small intestine changes the nutritional environment of the large intestine to provide S. Typhimurium with resources needed to counter growth inhibition by microbiota-derived SCFAs.

Protective role of short-chain fatty acids on intestinal oxidative stress induced by TNF-α.

Inflammatory bowel diseases (IBD) are driven by an exaggerated inflammatory response, which leads to a marked increase in oxidative stress. This, in turn, exacerbates the inflammatory process and causes significant cellular and tissue damage. Intestinal dysbiosis, a common observation in IBD patients, alters the production of bacterial metabolites, including short-chain fatty acids (SCFAs), which are key by-products of dietary fiber fermentation. While the role of SCFAs in intestinal physiology is still being elucidated, this study aimed to investigate their effects on intestinal oxidative stress, particularly under inflammatory conditions induced by the proinflammatory mediator tumour necrosis factor alpha (TNF-α). The Caco-2/TC7 cell line was employed as an in vitro model of the intestinal epithelium, and the cells were treated with a range of SCFAs, including acetate, propionate, and butyrate. The levels of protein and lipid oxidation were quantified, as well as the activity of antioxidant enzymes. Our findings demonstrate that microbiota-derived SCFAs can effectively mitigate TNF-α-induced oxidative stress by modulating antioxidant enzyme activity. The proinflammatory mediator TNF-α induces lipid peroxidation by inhibiting catalase and glutathione peroxidase activities. SCFAs are able to upregulate antioxidant enzyme activity to restore lipid oxidative levels. These results underscore the critical role of the gut microbiota in maintaining intestinal homeostasis and highlight the therapeutic potential of SCFAs in managing oxidative stress-related pathologies.

The role for ω-3 polyunsaturated and short chain fatty acids in hypertension: an updated view on the interaction with gut microbiota

As of 2024, arterial hypertension is still considered the leading modifiable cardiovascular risk factor and, due to high rates of undertreatment and poor blood pressure control, the major contributor to human morbidity and mortality. Development of new treatment options and better interventions in lifestyle correction have become a priority of experimental and clinical research. In the last decades, dietary supplementation of omega-3 polyunsaturated fatty acids (ω-3 PUFAs) and generation of gut microbiota-derived short chain fatty acids (SCFAs) have surged as potential and promising interventions for hypertension and cardiovascular prevention. ω-3 PUFAs are considered “essential” fatty acids that can be obtained only from dietary sources. Although previous intervention trials were not consistent in reporting a significant benefit of ω-3 PUFAs, the recent REDUCE-IT trial has provided robust evidence in support of their role in cardiovascular prevention. Recent studies have also identified the intestinal microbiota as a potential player in the pathophysiology and progression of hypertension. Although this might occur through many pathways, generation of SCFAs that is highly dependent on dietary fiber intake is primarily involved, providing an additional target for the development of novel therapeutic strategies. For these reasons, some scientific societies currently recommend dietary supplementation of ω-3 PUFAs and fiber-containing foods in patients with hypertension. In this narrative review, we summarize the results of studies that examined the effects of ω-3 PUFAs and SCFAs on blood pressure, highlighting the mechanisms of action on the vascular system and their possible impact on hypertension, hypertension-related organ damage and, ultimately, cardiovascular outcomes.

Microbiota-derived short chain fatty acids in pediatric health and diseases: from gut development to neuroprotection.

The infant gut microbiota undergoes significant changes during early life, which are essential for immune system maturation, nutrient absorption, and metabolic programming. Among the various microbial metabolites, short-chain fatty acids (SCFAs), primarily acetate, propionate, and butyrate, produced through the fermentation of dietary fibers by gut bacteria, have emerged as critical modulators of host-microbiota interactions. SCFAs serve as energy sources for colonic cells and play pivotal roles in regulating immune responses, maintaining gut barrier integrity, and influencing systemic metabolic pathways. Recent research highlights the potential neuroprotective effects of SCFAs in pediatric populations. Disruptions in gut microbiota composition and SCFA production are increasingly associated with a range of pediatric health issues, including obesity, allergic disorders, inflammatory bowel disease (IBD), and neurodevelopmental disorders. This review synthesizes current knowledge on the role of microbiota-derived SCFAs in pediatric health, emphasizing their contributions from gut development to neuroprotection. It also underscores the need for further research to unravel the precise mechanisms by which SCFAs influence pediatric health and to develop targeted interventions that leverage SCFAs for therapeutic benefits.

Effects of Oral Butyrate on Blood Pressure in Patients With Hypertension: A Randomized, Placebo-Controlled Trial.

The microbiota-derived short chain fatty acid butyrate has been shown to lower blood pressure (BP) in rodent studies. Nonetheless, the net effect of butyrate on hypertension in humans remains uncovered. In this study, for the first time, we aimed to determine the effect of oral butyrate on BP in patients with hypertension. We performed a double-blind randomized placebo-controlled trial including 23 patients with hypertension. Antihypertensive medication was discontinued for the duration of the study with a washout period of 4 weeks before starting the intervention. Participants received daily oral capsules containing either sodium butyrate or placebo with an equivalent dosage of sodium chloride for 4 weeks. The primary outcome was daytime 24-hour systolic BP. Differences between groups over time were assessed using linear mixed models (group-by-time interaction). Study participants (59.0±3.7 years; 56.5% female) had an average baseline office systolic BP of 143.5±14.6 mm Hg and diastolic BP of 93.0±8.3 mm Hg. Daytime 24-hour systolic and diastolic BP significantly increased over the intervention period in the butyrate compared with the placebo group, with an increase of +9.63 (95% CI, 2.02-17.20) mm Hg in daytime 24-hour systolic BP and +5.08 (95% CI, 1.34-8.78) mm Hg in diastolic BP over 4 weeks. Butyrate levels significantly increased in plasma, but not in feces, upon butyrate intake, underscoring its absorption. Four-week treatment with oral butyrate increased daytime systolic and diastolic BP in subjects with hypertension. Our findings implicate that butyrate does not have beneficial effects on human hypertension, which warrants caution in future butyrate intervention studies. URL: https://onderzoekmetmensen.nl/; Unique identifier: NL8924.

Nutraceutical Capsules LL1 and Silymarin Supplementation Act on Mood and Sleep Quality Perception by Microbiota-Gut-Brain Axis: A Pilot Clinical Study.

Stress, unhealthy lifestyle, and sleep disturbance worsen cognitive function in mood disorders, prompting a rise in the development of integrative health approaches. The recent investigations in the gut-brain axis field highlight the strong interplay among microbiota, inflammation, and mental health. Thus, this study aimed to investigate a new nutraceutical formulation comprising prebiotics, minerals, and silymarin's impact on microbiota, inflammation, mood, and sleep quality. The study evaluated the LL1 + silymarin capsule supplementation over 180 days in overweight adults. We analyzed the fecal gut microbiota using partial 16S rRNA sequences, measured cytokine expression via CBA, collected anthropometric data, quality of life, and sleep questionnaire responses, and obtained plasma samples for metabolic and hormonal analysis at baseline (T0) and 180 days (T180) post-supplementation. Our findings revealed significant reshaping in gut microbiota composition at the phylum, genus, and species levels, especially in the butyrate-producer bacteria post-supplementation. These changes in gut microbiota were linked to enhancements in sleep quality, mood perception, cytokine expression, and anthropometric measures which microbiota-derived short-chain fatty acids might enhance. The supplementation tested in this study seems to be able to improve microbiota composition, reflecting anthropometrics and inflammation, as well as sleep quality and mood improvement.

Different Short-Chain Fatty Acids Unequally Modulate Intestinal Homeostasis and Reverse Obesity-Related Symptoms in Lead-Exposed High-Fat Diet Mice.

Our previous study showed that heavy metal lead (Pb) exposure exacerbates high-fat-diet (HFD)-induced metabolic damage and significantly depletes the gut microbiota-derived metabolite short-chain fatty acid (SCFA) levels. However, it remains unclear whether SCFA is a key metabolite involved in accelerating adverse consequences after Pb exposure. In this study, we explored the effects of exogenous supplementation of acetate, propionate, and butyrate on a metabolic disorder model in Pb-exposed HFD mice. We found that three SCFA interventions attenuated glycolipid metabolism disorders and liver damage, with butyrate performing the best effects in improving obesity-related symptoms. All three SCFA promoted the abundance of Muribaculaceae and Muribaculum, acetate specifically enriched Christensenellaceae, Blautia, and Ruminococcus, and butyrate specifically enriched Parasutterella, Rikenella, Prevotellaceae_UCG-001, and Bacteroides, which contributed to the positive promotion of SCFA production forming a virtuous cycle. Besides, butyrate inhibited Gram-negative bacteria Escherichia-Shigella. All of these events alleviated the intestinal Th17/Treg imbalance and inflammatory response through crosstalk between the G protein-coupled receptor (GPR)/histone deacetylase 3 (HDAC3) and lipopolysaccharide (LPS)/toll-like receptors 4 (TLR4)/nuclear factor κ-B (NF-κB) pathways and ultimately improved the intestinal barrier function. SCFA further upregulated the monocarboxylate transporter 1 (MCT1) and GPR43/adenosine 5'-monophosphate-activated protein kinase (AMPK) pathways to inhibit hepatic lipid accumulation. Overall, SCFA, especially butyrate, is an effective modulator to improve metabolic disorders in obese individuals exposed to heavy metals by targeting gut microecology.

Broad-spectrum antibiotics disrupt homeostatic efferocytosis.

The clearance of apoptotic cells, termed efferocytosis, is essential for tissue homeostasis and prevention of autoimmunity1. Although past studies have elucidated local molecular signals that regulate homeostatic efferocytosis in a tissue2,3, whether signals arising distally also regulate homeostatic efferocytosis remains elusive. Here, we show that large peritoneal macrophage (LPM) display impairs efferocytosis in broad-spectrum antibiotics (ABX)-treated, vancomycin-treated and germ-free mice in vivo, all of which have a depleted gut microbiota. Mechanistically, the microbiota-derived short-chain fatty acid butyrate directly boosts efferocytosis efficiency and capacity in mouse and human macrophages, and rescues ABX-induced LPM efferocytosis defects in vivo. Bulk messenger RNA sequencing of butyrate-treated macrophages in vitro and single-cell messenger RNA sequencing of LPMs isolated from ABX-treated and butyrate-rescued mice reveals regulation of efferocytosis-supportive transcriptional programmes. Specifically, we find that the efferocytosis receptor T cell immunoglobulin and mucin domain containing 4 (TIM-4, Timd4) is downregulated in LPMs of ABX-treated mice but rescued by oral butyrate. We show that TIM-4 is required for the butyrate-induced enhancement of LPM efferocytosis capacity and that LPM efferocytosis is impaired beyond withdrawal of ABX. ABX-treated mice exhibit significantly worse disease in a mouse model of lupus. Our results demonstrate that homeostatic efferocytosis relies on distal metabolic signals and suggest that defective homeostatic efferocytosis may explain the link between ABX use and inflammatory disease4-7.

The attenuation of gut microbiota-derived short-chain fatty acids elevates lipid transportation through suppression of the intestinal HDAC3-H3K27ac-PPAR-γ axis in gestational diabetes mellitus

Gut flora is considered to modulate lipid transport from the intestine into the bloodstream, and thus may potentially participate in the development of GDM. Although previous studies have shown that the intestinal microbiota influences lipid transport and metabolism in GDM, the precise mechanisms remain elusive. To address this, we used a high-fat diet (HFD)-induced GDM mouse model and conducted 16s rRNA sequencing and fecal metabolomics to assess gut microbial community shifts and associated metabolite changes. Western blot, ELISA, and chromatin immunoprecipitation (ChIP) were utilized to elucidate how gut microbiota affect intestinal lipid transport and the insulin sensitivity of hepatic, adipose, and skeletal muscle tissues. We found that HFD impaired the oral glucose tolerance test (OGTT) and insulin tolerance test (ITT) in pregnant mice. 16s rRNA sequencing demonstrated profound compositional changes, especially in the relative abundances of Firmicutes and Bacteroidetes. Metabolomics analysis presented a decline in the concentration of short-chain fatty acids (SCFAs) in the GDM group. Western blot analyses showed an upregulation of HDAC3 and a concurrent reduction in H3K27 acetylation in the intestine. ChIP-qPCR showed that PPAR-γ was inhibited, which in turn activated lipid-transporter CD36. ELISA and insulin signaling pathway detection in insulin-target organs showed high concentrations of circulating fatty acids and triglycerides and insulin resistance in insulin-target organs. Our results suggest that gut microbiota is closely associated with the development of GDM, partly because decreased gut flora-associated SCFAs activate CD36 by suppressing the HDAC3-H3K27ac-PPAR-γ axis to transport excessive fatty acids and triglycerides into blood circulation, thereby dysregulating the insulin sensitivity of insulin target organs.

Microbiota-Derived Short-Chain Fatty Acids Boost Antitumoral Natural Killer Cell Activity.

Background: The intestinal microbiota can regulate numerous host functions, including the immune response. Through fermentation, the microbiota produces and releases microbial metabolites such as short-chain fatty acids (SCFAs), which can affect host homeostasis. There is growing evidence that the gut microbiome can have a major impact on cancer. Specific gut microbial composition and metabolites are associated with tumor status in the host. However, their effects on the antitumor response have scarcely been investigated. Natural killer (NK) cells play an important role in antitumor immunity due to their ability to directly identify and eliminate tumor cells. Methods: The aim of this study was to investigate the effects of SCFAs on antitumoral NK cell activity, using NK-92 cell line. Results: Here, we describe how SCFAs can boost antitumoral NK cell activity. The SCFAs induced the release of NK extracellular vesicles and reduced the secretion of the anti-inflammatory cytokine IL-10. The SCFAs also increased the cytotoxicity of the NK cells against multiple myeloma cells. Conclusions: Our results indicate, for the first time, the enormous potential of SCFAs in regulating antitumoral NK cell defense, where modulation of the SCFAs' production could play a fundamental role in cancer immunotherapy.

Effects of gut microbiota-derived short-chain fatty acids on cognitive impairment: An in-silico study

Increasing evidence suggests that gut microbiota-derived metabolites affect cognitive function, but the underlying molecular mechanisms remain unclear. In this study, mechanisms of cognitive dysfunction that can be targeted by acetic acid and butyric acid were analyzed using literature review, Metascape, Mienturnent, Passonline, and WissADME. We found that acetic acid and butyric acid may regulate important genes (PPARG, CASP3, IL1B, SOD2, and TNF) that protect against cognitive decline. We also found microRNAs (hsa-miR-17-5p and hsa-miR-20a-5p) and transcription factors (RELA and NFKB1) that play a critical role in this protective mechanism. The AGE-RAGE signaling pathway and apoptosis pathways also emerged as crucial to understanding the underlying pathophysiological mechanisms. Our findings are further supported by the physicochemical properties and pharmacokinetic profiles of acetic acid and butyric acid, which demonstrate remarkable intestinal absorption, ability to penetrate the blood-brain barrier, and non-inhibition of CYP450 enzymes. Our study provides further evidence of the therapeutic potential of butyric acid in managing cognitive impairment, including its anti-inflammatory properties, stimulation of insulin synthesis, and regulation of lipid metabolism. We also identified several promising treatments for cognitive impairment, including miRNA sponges, mesalazine, omega-3 fatty acids, pomalidomide, and andrographolide. Focused investigations into the apoptosis and AGE-RAGE signaling pathways, miRNA sponges, promising drugs, and the role of gut microbiota in cognitive function are warranted.

Recognizing depression as an inflammatory disease: the search for endotypes.

Major depressive disorder (MDD) affects millions of individuals worldwide, leading to considerable social and economic costs. Despite advancements in pharmacological treatments, achieving remission remains a key challenge, with a substantial number of patients showing resistance to existing therapies. This resistance is often associated with elevated levels of proinflammatory cytokines, suggesting a connection between inflammation, MDD pathophysiology, and treatment efficacy. The observation of increased immune activation in about a quarter of patients with MDD resulted in the distinction between inflammatory and noninflammatory endotypes. Although anti-inflammatory treatments show promise in alleviating depression-like symptoms, responses are heterogeneous, thus highlighting the importance of identifying distinct inflammatory endotypes to tailor effective therapeutic strategies. The intestinal microbiome emerges as a crucial modulator of mental health, mediating its effects partially through different immune pathways. Microbiota-derived short-chain fatty acids (SCFAs) significantly impact innate and adaptive immune cells, regulating their differentiation, function, and cellular response. Furthermore, gut-educated immune cells reach the border regions of the central nervous system (CNS), regulating glial cell functions. Although the CNS modulates immune responses via efferent parts of the vagus nerve, afferent tracts concurrently transport information on peripheral inflammation back to the brain. This bidirectional communication is particularly relevant in depression, allowing for therapeutic stimulation of the vagus nerve in the context of inflammatory depression endotypes. In this review, we explore the intricate relationship between inflammation and depression, discuss how inflammatory signals are translated into depressive-like symptoms, and highlight immune-modulating therapeutic avenues.

Short-chain fatty acids mitigate Methamphetamine-induced hepatic injuries in a Sigma-1 receptor-dependent manner

Methamphetamine (Meth) is a potent psychostimulant with well-established hepatotoxicity. Gut microbiota-derived short-chain fatty acids (SCFAs) have been reported to yield beneficial effects on the liver. In this study, we aim to further reveal the mechanisms of Meth-induced hepatic injuries and investigate the potential protective effects of SCFAs. Herein, mice were intraperitoneally injected with 15 mg/kg Meth to induce hepatic injuries. The composition of fecal microbiota and SCFAs was profiled using 16 S rRNA sequencing and Gas Chromatography/Mass Spectrometry (GC/MS) analysis, respectively. Subsequently, SCFAs supplementation was performed to evaluate the protective effects against hepatic injuries. Additionally, Sigma-1 receptor knockout (S1R-/-) mice and fluvoxamine (Flu), an agonist of S1R, were introduced to investigate the mechanisms underlying the protective effects of SCFAs. Our results showed that Meth activated S1R and induced hepatic autophagy, inflammation, and oxidative stress by stimulating the MAPK/ERK pathway. Meanwhile, Meth disrupted SCFAs product-related microbiota, leading to a reduction in fecal SCFAs (especially Acetic acid and Propanoic acid). Accompanied by the optimization of gut microbiota, SCFAs supplementation normalized S1R expression and ameliorated Meth-induced hepatic injuries by repressing the MAPK/ERK pathway. Effectively, S1R knockout repressed Meth-induced activation of the MAPK/ERK pathway and further ameliorated hepatic injuries. Finally, the overexpression of S1R stimulated the MAPK/ERK pathway and yielded comparable adverse phenotypes to Meth administration. These findings suggest that Meth-induced hepatic injuries relied on the activation of S1R, which could be alleviated by SCFAs supplementation. Our study confirms the crucial role of S1R in Meth-induced hepatic injuries for the first time and provides a potential preemptive therapy.

Gut microbiota promoting propionic acid production accompanies caloric restriction-induced intentional weight loss in cats

Rodent models and human clinical studies have shown gut microbiota-derived short-chain fatty acids (SCFAs) play roles in obesity and insulin resistance. These roles have been minimally explored in cats, where in the USA an estimated 60% of cats are overweight or obese. Overweight/obese research cats (n = 7) were transitioned from a maintenance diet to a reduced calorie diet fed ad libitum for 7 days, then calories were restricted to achieve 1–2% weight loss per week for an additional 77 days. Cats then received their original maintenance diet again for 14 days. Significant intentional weight loss was noted after calorie restriction (adjusted p < 0.0001). 16S rRNA gene amplicon sequencing and targeted SCFA metabolomics were performed on fecal samples. Fecal microbial community structure significantly differed between the four study phases (PERMANOVA p = 0.011). Fecal propionic acid was significantly higher during caloric restriction-induced weight loss (adjusted p < 0.05). Repeated measures correlation revealed the relative abundances of Prevotella 9 copri (correlation coefficient = 0.532, 95% CI (0.275, 0.717), p = 0.0002) significantly correlated with propionic acid composition. Like humans, obese cats experienced an altered microbial community structure and function, favoring propionic acid production, during caloric restriction-induced weight loss.

Donepezil ameliorates gut barrier disruption in doxorubicin-treated rats

An impact of donepezil against doxorubicin-induced gut barrier disruption and gut dysbiosis has never been investigated. Twenty-four male Wistar rats were divided into three groups. Each group was treated with either vehicle as a control, doxorubicin, or doxorubicin-cotreated with donepezil. Heart rate variability was assessed to reflect the impact of doxorubicin and donepezil. Then, animals were euthanized, and the ileum and its contents were collected in each case to investigate the gut barrier and gut microbiota, respectively. The microbiota-derived endotoxin, trimethylamine N-oxide (TMAO), and short-chain fatty acids (SCFAs) in the serum were determined. An increase in the sympathetic tone, endotoxins, and TMAO levels with disruption of the gut barrier and a decrease in SCFAs levels were observed in doxorubicin-treated rats. Gut microbiota of doxorubicin-treated rats was significantly different from that of the control group. Donepezil treatment significantly decreased the sympathetic tone, restored the gut barrier, and reduced endotoxin and TMAO levels in doxorubicin-treated rats. Nonetheless, donepezil administration did not alter the gut microbiota profile and levels of SCFAs in doxorubicin-treated rats. Doxorubicin impaired the autonomic balance and the gut barrier, and induced gut dysbiosis, resulting in gut toxicity. Donepezil partially improved the doxorubicin-induced gut toxicity through balancing the autonomic disturbance.

Short-Chain Fatty Acid Butyrate Is an Inotropic Agent With Vasorelaxant and Cardioprotective Properties.

The heart can metabolize the microbiota-derived short-chain fatty acid butyrate. Butyrate may have beneficial effects in heart failure, but the underlying mechanisms are unknown. We tested the hypothesis that butyrate elevates cardiac output by mechanisms involving direct stimulation of cardiac contractility and vasorelaxation in rats. We examined the effects of butyrate on (1) invivo hemodynamics using parallel echocardiographic and invasive blood pressure measurements, (2) isolated perfused hearts in Langendorff systems under physiological conditions and after ischemia and reperfusion, and (3) isolated coronary arteries mounted in isometric wire myographs. We tested Na-butyrate added to injection solutions or physiological buffers and compared its effects with equimolar doses of NaCl. Butyrate at plasma concentrations of 0.56 mM increased cardiac output by 48.8±14.9%, stroke volume by 38.5±12.1%, and left ventricular ejection fraction by 39.6±6.2%, and lowered systemic vascular resistance by 33.5±6.4% without affecting blood pressure or heart rate invivo. In the range between 0.1 and 5 mM, butyrate increased left ventricular systolic pressure by up to 23.7±3.4% in isolated perfused hearts and by 9.4±2.9% following ischemia and reperfusion, while reducing myocardial infarct size by 81.7±16.9%. Butyrate relaxed isolated coronary septal arteries concentration dependently with an EC50=0.57 mM (95% CI, 0.23-1.44). We conclude that butyrate elevates cardiac output through mechanisms involving increased cardiac contractility and vasorelaxation. This effect of butyrate was not associated with adverse myocardial injury in damaged hearts exposed to ischemia and reperfusion.

Bioinformatics Approach to Identify the Pathogenetic Link of Gut Microbiota-Derived Short-Chain Fatty Acids and Ischemic Stroke.

Stroke is a life-threatening condition that impairs the arteries and causes neurological impairment. The incidence of stroke is increasing year by year with the arrival of the aging population. Thus, there is an urgent need for early stroke diagnosis. Short-chain fatty acids (SCFAs) can modulate the central nervous system and directly and indirectly impact behavioral and cognitive functions. This study aimed to investigate the connection between SCFA metabolism and stroke development via bioinformatic analysis. Initially, the Gene Set Enrichment Analysis (GSEA) and immune cell infiltration analysis were performed based on RNA data from stroke patients to comprehend the mechanisms governing stroke pathogenesis. The functional analysis, including Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG), and Protein-Protein Interaction (PPI), was performed based on the Differentially Expressed Gene (DEG) selected by the limma package. 1220 SCFA metabolism-related genes screened from Genecards databases were intersected with 242 genes in main modules determined by Weighted Gene Co-Expression Network Analysis (WGCNA), and the final 10 SCFA key genes were obtained. GO analysis revealed that these genes were involved in immune response processes. Through lasso regression analyses, we established a stroke early diagnosis model and selected 6 genes with diagnostic value. The genes were validated by the area under curve (AUC) values and had a relatively good diagnostic performance. Finally, 4 potential therapeutic drugs targeting these genes were predicted using the Drug Signatures Database (DSigDB) via Enrichr. In conclusion, this paper analyzes the involvement of SCFAs in the complex gut-brain axis mechanism, which contributes to developing new targets for treating central nervous system diseases and provides new ideas for early ischemic stroke diagnosis.

Microbiota-derived acetate attenuates neuroinflammation in rostral ventrolateral medulla of spontaneously hypertensive rats.

Increased neuroinflammation in brain regions regulating sympathetic nerves is associated with hypertension. Emerging evidence from both human and animal studies suggests a link between hypertension and gut microbiota, as well as microbiota-derived metabolites short-chain fatty acids (SCFAs). However, the precise mechanisms underlying this gut-brain axis remain unclear. The levels of microbiota-derived SCFAs in spontaneously hypertensive rats (SHRs) were determined by gas chromatography-mass spectrometry. To observe the effect of acetate on arterial blood pressure (ABP) in rats, sodium acetate was supplemented via drinking water for continuous 7 days. ABP was recorded by radio telemetry. The inflammatory factors, morphology of microglia and astrocytes in rostral ventrolateral medulla (RVLM) were detected. In addition, blood-brain barrier (BBB) permeability, composition and metabolomics of the gut microbiome, and intestinal pathological manifestations were also measured. The serum acetate levels in SHRs are lower than in normotensive control rats. Supplementation with acetate reduces ABP, inhibits sympathetic nerve activity in SHRs. Furthermore, acetate suppresses RVLM neuroinflammation in SHRs, increases microglia and astrocyte morphologic complexity, decreases BBB permeability, modulates intestinal flora, increases fecal flora metabolites, and inhibits intestinal fibrosis. Microbiota-derived acetate exerts antihypertensive effects by modulating microglia and astrocytes and inhibiting neuroinflammation and sympathetic output.

The emergence of inflammatory microglia during gut inflammation is not affected by FFAR2 expression in intestinal epithelial cells or peripheral myeloid cells

Gut inflammation can trigger neuroinflammation and is linked to mood disorders. Microbiota-derived short-chain fatty acids (SCFAs) can modulate microglia, yet the mechanism remains elusive. Since microglia do not express free-fatty acid receptor (FFAR)2, but intestinal epithelial cells (IEC) and peripheral myeloid cells do, we hypothesized that SCFA-mediated FFAR2 activation within the gut or peripheral myeloid cells may impact microglia inflammation. To test this hypothesis, we developed a tamoxifen-inducible conditional knockout mouse model targeting FFAR2 exclusively on IEC and induced intestinal inflammation with dextran sodium sulfate (DSS), a well-established colitis model. Given FFAR2′s high expression in myeloid cells, we also investigated its role by selectively deleting it in these populations of cells. In an initial study, male and female wild-type mice received 0 or 2% DSS for 5d and microglia were isolated 3d later to assess inflammatory status. DSS induced intestinal inflammation and upregulated inflammatory gene expression in microglia, indicating inflammatory signaling via the gut-brain axis. Despite the lack of significant effects of sex in the intestinal phenotype, male mice showed higher microglial inflammatory response than females. Subsequent studies using FFAR2 knockout models revealed that FFAR2 expression in IECs or immune myeloid cells did not affect DSS-induced colonic pathology (i.e. clinical and histological scores and colon length), or colonic expression of inflammatory genes. However, FFAR2 knockout led to an upregulation of several microglial inflammatory genes in control mice and downregulation in DSS-treated mice, suggesting that FFAR2 may constrain neuroinflammatory gene expression under healthy homeostatic conditions but may permit it during intestinal inflammation. No interactions with sex were observed, suggesting sex does not play a role on FFAR2 potential function in gut-brain communication in the context of colitis. To evaluate the role of FFAR2 activated by microbiota-derived SCFAs, we employed the same knockout and DSS models adding fermentable dietary fiber (0 or 2.5% inulin for 8 wks). Despite no genotype or fiber main effects, contrary to our hypothesis, inulin feeding augmented DSS-induced inflammation and signs of colitis, suggesting context-dependent effects of fiber. These findings highlight microglial involvement in colitis-associated neuroinflammation and advance our understanding of FFAR2′s role in the gut-brain axis. Although not integral, we observed that the role of FFAR2 differs between homeostatic and inflammatory conditions, underscoring the need to consider different inflammatory conditions and disease contexts when investigating the role of FFAR2 and SCFAs in the gut-brain axis.

GPR41 and GPR43 regulate CD8+ T cell priming during herpes simplex virus type 1 infection.

Naïve CD8+ T cells need to undergo a complex and coordinated differentiation program to gain the capacity to control virus infections. This not only involves the acquisition of effector functions, but also regulates the development of a subset of effector CD8+ T cells into long-lived and protective memory cells. Microbiota-derived metabolites have recently gained interest for their influence on T cells, but much remains unclear about their role in CD8+ T cell differentiation. In this study, we investigated the role of the G protein-coupled receptors (GPR)41 and GPR43 that can bind microbiota-derived short chain fatty acids (SCFAs) in CD8+ T cell priming following epicutaneous herpes simplex virus type 1 (HSV-1) infection. We found that HSV-specific CD8+ T cells in GPR41/43-deficient mice were impaired in the antigen-elicited production of interferon-gamma (IFN-γ), tumour necrosis factor-alpha (TNF-α), granzyme B and perforin, and failed to differentiate effectively into memory precursors. The defect in controlling HSV-1 at the site of infection could be restored when GPR41 and GPR43 were expressed exclusively by HSV-specific CD8+ T cells. Our findings therefore highlight roles for GPR41 and GPR43 in CD8+ T cell differentiation, emphasising the importance of metabolite sensing in fine-tuning anti-viral CD8+ T cell priming.