Host-microbiota interaction in intestinal stem cell homeostasis.

Intestinal stem cells (ISCs) play a pivotal role in gut physiology by governing intestinal epithelium renewal through the precise regulation of proliferation and differentiation. The gut microbiota interacts closely with the epithelium through myriad of actions, including immune and metabolic interactions, which translate into tight connections between microbial activity and ISC function. Given the diverse functions of the gut microbiota in affecting the metabolism of macronutrients and micronutrients, dietary nutrients exert pronounced effects on host-microbiota interactions and, consequently, the ISC fate. Therefore, understanding the intricate host-microbiota interaction in regulating ISC homeostasis is imperative for improving gut health. Here, we review recent advances in understanding host-microbiota immune and metabolic interactions that shape ISC function, such as the role of pattern-recognition receptors and microbial metabolites, including lactate and indole metabolites. Additionally, the diverse regulatory effects of the microbiota on dietary nutrients, including proteins, carbohydrates, vitamins, and minerals (e.g. iron and zinc), are thoroughly explored in relation to their impact on ISCs. Thus, we highlight the multifaceted mechanisms governing host-microbiota interactions in ISC homeostasis. Insights gained from this review provide strategies for the development of dietary or microbiota-based interventions to foster gut health.

Postbiotics from Lactobacillus delbrueckii Alleviate Intestinal Inflammation by Promoting the Expansion of Intestinal Stem Cells in S. Typhimurium-Induced Mice.

Previous studies have demonstrated that L. delbrueckii plays beneficial roles in modulating the gut microbiota, enhancing the intestinal barrier, and promoting animal growth. Postbiotics have a similar or even superior effect in protecting intestinal health compared to probiotics due to their excellent stability, extended shelf life, and safety. However, the protective effects and underlying mechanism of postbiotics from L. delbrueckii in intestinal inflammation remain unclear. In this study, we demonstrated the beneficial impact of postbiotics from L. delbrueckii on intestinal health by establishing a S. Typhimurium-induced intestinal inflammation model in mice, which included inactivated bacteria and supernatant. The results revealed that the probiotics and postbiotics from L. delbrueckii increased the survival rate and body weight of S. Typhimurium-induced mice, increased the level of IL-10, and decreased the levels of TNF-α and IL-6, thereby alleviating intestinal inflammation. Meanwhile, treatment with postbiotics decreased the levels of D-LA, DAO, and LPS and promoted the expression of Occludin, ZO-1, and Claudin-1 in the serum and jejunum, suggesting an improvement in intestinal barrier function by postbiotics. Additionally, the postbiotics modulated gut microbial diversity, increased the ratio of Firmicutes and Bacteroidetes, and restored the abundance of Muribaculaceae, Lachnospiraceae_NK4a136_groups, and Alloprevotella in S. Typhimurium-infected mice. Moreover, postbiotics from L. delbrueckii promoted the expansion of intestinal stem cells (ISCs) and increased the numbers of Paneth and Goblet cells. Taken together, these data revealed the beneficial role of postbiotics from L. delbrueckii in protecting against intestinal inflammation by promoting the expansion of ISCs.

Effects of 2'-fucosyllactose on the composition and metabolic activity of intestinal microbiota from piglets after in vitro fermentation.

BACKGROUND: As indigestible carbohydrates, milk oligosaccharides possess various benefits for newborns, mainly through intestinal microbiota, among which 2'-fucosyllactose (2'-FL) is the most predominant milk oligosaccharide. However, knowledge about the fermentative characteristics of 2'-FL in the gut remains limited, especially in the small intestine. The aim of this study is to explore the differential fermentability of 2'-FL by the small and large intestinal microbiota of piglets using fructo-oligosaccharide (FOS) and lactose as controls in an in vitro batch fermentation experiment. During fermentation, microbial composition was characterized along with gas production and short-chain fatty acid production. RESULTS: 2'-Fucosyllactose showed differential fermentability in jejunal and colonic fermentation. Compared with the colon, 2'-FL produced less gas in the jejunum than in the FOS and lactose groups (P < 0.05). Meanwhile, 2'-FL exhibited a different influence on the microbial composition and metabolism in the jejunum and colon compared with FOS and lactose. In the jejunum, compared with the FOS and lactose groups, the 2'-FL group showed a higher abundance of Bacteroides, Prevotella, and Blautia, but a lower abundance of Streptococcus and Lactobacillus (P < 0.05), with a higher level of propionate and a lower level of lactate during fermentation (P < 0.05). In the colon, compared with the FOS and lactose groups, 2'-FL increased the abundance of Blautia, Faecalibacterium, and Lachnospiraceae FCS020, but decreased the abundance of Prevotella_9, Succinivibrio, and Megasphaera (P < 0.05) with an increase in acetate production (P < 0.05). CONCLUSION: Overall, the results suggested that the small intestinal microbiota had the potential to ferment milk oligosaccharides. Meanwhile, in comparison with FOS and lactose, 2'-FL selectively stimulated the growth of propionate-producing bacteria in the jejunum and acetate-producing bacteria in the colon. These results demonstrated the differences in fermentation properties of 2'-FL by small and large intestinal microbiota and provided new evidence for the application of 2'-FL in optimizing gut microbiota. © 2023 Society of Chemical Industry.

Succinate signaling attenuates high-fat diet-induced metabolic disturbance and intestinal barrier dysfunction.

Succinate is a vital signaling metabolite produced by the host and gut microbiota. Succinate has been shown to regulate host metabolic homeostasis and inhibit obesity-associated inflammation in macrophages by engaging its cognate receptor, SUCNR1. However, the contribution of the succinate-SUCNR1 axis to intestinal barrier dysfunction in obesity remains unclear. In the present study, we explored the effects of succinate-SUCNR1 signaling on high-fat diet (HFD)-induced intestinal barrier dysfunction. Using a SUCNR1-deficient mouse model under HFD feeding conditions, we identified the effects of succinate-SUCNR1 axis on obesity-associated intestinal barrier impairment. Our results showed that HFD administration decreased goblet cell numbers and mucus production, promoted intestinal pro-inflammatory responses, induced gut microbiota composition imbalance, increased intestinal permeability, and caused mucosal barrier dysfunction. Dietary succinate supplementation was sufficient to activate a type 2 immune response, trigger the differentiation of barrier-promoting goblet cells, suppress intestinal inflammation, restore HFD-induced mucosal barrier impairment and intestinal dysbiosis, and eventually exert anti-obesity effects. However, SUNNR1-deficient mice failed to improve the intestinal barrier function and metabolic phenotype in HFD mice. Our data indicate the protective role of the succinate-SUCNR1 axis in HFD-induced intestinal barrier dysfunction.

Succinate communicates pro-inflammatory signals to the host and regulates bile acid enterohepatic metabolism in a pig model.

Succinate is produced by both the host and microbiota with pleiotropic functions in the modulation of intestinal inflammation and metabolic homeostasis, but the mechanisms remain elusive. This study aimed to determine whether dietary succinate influences the intestinal inflammatory response and to analyze the possible mechanisms by which succinate regulates enterohepatic metabolism. Sixteen growing barrows were randomly assigned to two groups, fed with a basal diet that consisted of a typical commercial diet or fed with a basal diet supplemented with 1% sodium succinate. Our data showed that dietary succinate activated the expression of succinate receptor 1 (SUCNR1) and increased the concentrations of pro-inflammatory cytokines in the intestine. Dietary succinate inhibited the expression levels of the ileal Farnesol X receptor (FXR) and its target genes, promoted hepatic bile acid secretion, and altered the bile acid metabolic profile. Then, we demonstrated that the pro-inflammatory cytokines triggered by succinate disrupted the ability of bile acids to activate FXR and fibroblast growth factor 19. Furthermore, dietary succinate reduced the abundance of bile-salt hydrolase enriched bacteria in the ileum. Taken together, dietary succinate activated the pro-inflammatory response via SUCNR1 in the intestine, and the pro-inflammatory cytokines induced by succinate blocked the activation of FXR and its target genes and disturbed bile acid enterohepatic circulation.

SK3 in POMC neurons plays a sexually dimorphic role in energy and glucose homeostasis.

BACKGROUND: Pro-opiomelanocortin (POMC) neurons play a sexually dimorphic role in body weight and glucose balance. However, the mechanisms for the sex differences in POMC neuron functions are not fully understood. RESULTS: We detected small conductance calcium-activated potassium (SK) current in POMC neurons. Secondary analysis of published single-cell RNA-Seq data showed that POMC neurons abundantly express SK3, one SK channel subunit. To test whether SK3 in POMC neurons regulates POMC neuron functions on energy and glucose homeostasis, we used a Cre-loxP strategy to delete SK3 specifically from mature POMC neurons. POMC-specific deletion of SK3 did not affect body weight in either male or female mice. Interestingly, male mutant mice showed not only decreased food intake but also decreased physical activity, resulting in unchanged body weight. Further, POMC-specific SK3 deficiency impaired glucose balance specifically in female mice but not in male mice. Finally, no sex differences were detected in the expression of SK3 and SK current in total POMC neurons. However, we found higher SK current but lower SK3 positive neuron population in male POMC neurons co-expressing estrogen receptor α (ERα) compared to that in females. CONCLUSION: These results revealed a sexually dimorphic role of SK3 in POMC neurons in both energy and glucose homeostasis independent of body weight control, which was associated with the sex difference of SK current in a subpopulation of POMC + ERα + neurons.

Gabra5 plays a sexually dimorphic role in POMC neuron activity and glucose balance.

Pro-opiomelanocortin (POMC) neurons are important for the regulation of body weight and glucose balance. The inhibitory tone to POMC neurons is mediated primarily by the GABA receptors. However, the detailed mechanisms and functions of GABA receptors are not well understood. The α5 subunit of GABAA receptor, Gabra5, is reported to regulate feeding, and we found that Gabra5 is highly expressed in POMC neurons. To explore the function of Gabra5 in POMC neurons, we knocked down Gabra5 specifically from mature hypothalamic POMC neurons using the clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9 strategy. This POMC-specific knock-down of Gabra5 did not affect body weight or food intake in either male or female mice. Interestingly, the loss of Gabra5 caused significant increases in the firing frequency and resting membrane potential, and a decrease in the amplitude of the miniature inhibitory postsynaptic current (mIPSC) in male POMC neurons. However, the loss of Gabra5 only modestly decreased the frequency of mIPSC in female POMC neurons. Consistently, POMC-specific knock-down of Gabra5 significantly improved glucose tolerance in male mice but not in female mice. These results revealed a sexually dimorphic role of Gabra5 in POMC neuron activity and glucose balance, independent of body weight control.

Propionate stimulates the secretion of satiety hormones and reduces acute appetite in a cecal fistula pig model.

Short-chain fatty acids (SCFA) can regulate appetite by stimulating the secretion of satiety hormones. However, the impact of short-chain fatty acid propionate on the release of gut satiety hormones and appetite regulation in pigs is not completely understood. In this study, 16 pigs were infused with saline or sodium propionate through a fistula in the caecum during a 28-day experimental period. We characterized the effects of propionate administration on peptide YY (PYY) and glucagon-like peptide 1 (GLP-1) secretion from colonic tissue, and investigated the role of propionate infusion on the expression of appetite-related genes in the colon and hypothalamus. Further, the direct impact of propionate administration on the expression of orexigenic neuropeptide agouti-related protein (AgRP) in hypothalamic N38 cells was also examined. The results showed that intra-cecal infusion of propionate reduced the short-term feed intake (P < 0.05) but not the long-term feed intake in pigs (P > 0.05). Propionate administration stimulated PYY and GLP-1 release from colon tissue in vivo and ex vivo (P < 0.05). It also upregulated PYY expression in the colonic mucosa (P < 0.05). Meanwhile, the GLP-1 and PYY levels in the blood were increased after intra-cecal infusion of propionate at d 28 (P < 0.05). Additionally, intra-cecal infusion of propionate upregulated the mRNA and protein expression of free fatty acid receptor 2/3 (FFAR2/FFAR3) in the colonic mucosa (P < 0.05). Propionate infusion also downregulated the orexigenic AgRP mRNA expression (P < 0.05) and upregulated the anorexigenic cocaine-and amphetamine-regulated transcript (CART) mRNA expression (P = 0.09) in the hypothalamus. Moreover, propionate administration directly downregulated AgRP expression in hypothalamic N38 cells in a dose-dependent manner (P < 0.05). Collectively, these findings demonstrated that cecal propionate stimulated colonic secretion of satiety hormones and suppressed appetite to reduce the short-term feed intake in pigs. This study highlights that microbial-derived propionate exerts an important role in regulating the physical functions of the host.

Effects of Dietary Indole-3-carboxaldehyde Supplementation on Growth Performance, Intestinal Epithelial Function, and Intestinal Microbial Composition in Weaned Piglets.

As a microbial tryptophan metabolite, indole-3-carboxaldehyde (ICA) has been suggested to confer benefits to host, such as regulation of intestinal barrier function. This study aimed to elucidate the role of ICA in modulating intestinal homeostasis via using a weaned pig model. Twenty-four weaned piglets were randomly allocated into three groups: the control group (a basal diet), ICA100 group (the basal diet supplemented with 100 mg/kg ICA), and ICA200 group (the basal diet supplemented with 200 mg/kg ICA). The experiment lasted 14 d, and pigs from the control and ICA100 groups were slaughtered. The results showed no significant differences in the average daily gain (ADG) and average daily feed intake (ADFI) among the three groups (P > 0.05). However, the ICA100 group had a lower feed to gain ratio (F:G) (P < 0.05). Dietary ICA supplementation did not alter the villus height, crypt depth, and villus height/crypt depth ratio in the small intestine, and did not change the intestinal permeability and antioxidant parameters (P > 0.05). Intriguingly, ICA treatment significantly increased the jejunal, ileal and colonic indexes in piglets (P < 0.05). Besides, the expression of proliferating cell nuclear antigen (PCNA) in the intestine was up-regulated by ICA treatment. Moreover, in vitro experiments demonstrated that 15 µM ICA significantly accelerated the proliferation activity of IPEC-J2 cells, and increased the expression of the ICA receptor aryl hydrocarbon receptor (AHR) and the proliferation markers PCNA and Cyclin D1 (P < 0.05). In addition, dietary ICA supplementation modulated the intestinal flora, increasing the richness estimators and diversity index, decreasing the abundances of phylum Fibrobacterota and genera Alloprevotella, Prevotella, and Parabacteroides, and enriching the abundance of genera Butyrivibrio. These data reveal a beneficial role for the microbial metabolite ICA on intestinal epithelial proliferation, rather than intestinal barrier function, in weaned piglets.

An estrogen-sensitive hypothalamus-midbrain neural circuit controls thermogenesis and physical activity.

Estrogen receptor­α (ERα) expressed by neurons in the ventrolateral subdivision of the ventromedial hypothalamic nucleus (ERαvlVMH) regulates body weight in females, but the downstream neural circuits mediating this biology remain largely unknown. Here we identified a neural circuit mediating the metabolic effects of ERαvlVMH neurons. We found that selective activation of ERαvlVMH neurons stimulated brown adipose tissue (BAT) thermogenesis, physical activity, and core temperature and that ERαvlVMH neurons provide monosynaptic glutamatergic inputs to 5-hydroxytryptamine (5-HT) neurons in the dorsal raphe nucleus (DRN). Notably, the ERαvlVMH → DRN circuit responds to changes in ambient temperature and nutritional states. We further showed that 5-HTDRN neurons mediate the stimulatory effects of ERαvlVMH neurons on BAT thermogenesis and physical activity and that ERα expressed by DRN-projecting ERαvlVMH neurons is required for the maintenance of energy balance. Together, these findings support a model that ERαvlVMH neurons activate BAT thermogenesis and physical activity through stimulating 5-HTDRN neurons.

Hypothalamic steroid receptor coactivator-2 regulates adaptations to fasting and overnutrition.

The neuroendocrine system coordinates metabolic and behavioral adaptations to fasting, including reducing energy expenditure, promoting counterregulation, and suppressing satiation and anxiety to engage refeeding. Here, we show that steroid receptor coactivator-2 (SRC-2) in pro-opiomelanocortin (POMC) neurons is a key regulator of all these responses to fasting. POMC-specific deletion of SRC-2 enhances the basal excitability of POMC neurons; mutant mice fail to efficiently suppress energy expenditure during food deprivation. SRC-2 deficiency blunts electric responses of POMC neurons to glucose fluctuations, causing impaired counterregulation. When food becomes available, these mutant mice show insufficient refeeding associated with enhanced satiation and discoordination of anxiety and food-seeking behavior. SRC-2 coactivates Forkhead box protein O1 (FoxO1) to suppress POMC gene expression. POMC-specific deletion of SRC-2 protects mice from weight gain induced by an obesogenic diet feeding and/or FoxO1 overexpression. Collectively, we identify SRC-2 as a key molecule that coordinates multifaceted adaptive responses to food shortage.

5-HT recruits distinct neurocircuits to inhibit hunger-driven and non-hunger-driven feeding.

Obesity is primarily a consequence of consuming calories beyond energetic requirements, but underpinning drivers have not been fully defined. 5-Hydroxytryptamine (5-HT) neurons in the dorsal Raphe nucleus (5-HTDRN) regulate different types of feeding behavior, such as eating to cope with hunger or for pleasure. Here, we observed that activation of 5-HTDRN to hypothalamic arcuate nucleus (5-HTDRN → ARH) projections inhibits food intake driven by hunger via actions at ARH 5-HT2C and 5-HT1B receptors, whereas activation of 5-HTDRN to ventral tegmental area (5-HTDRN → VTA) projections inhibits non-hunger-driven feeding via actions at 5-HT2C receptors. Further, hunger-driven feeding gradually activates ARH-projecting 5-HTDRN neurons via inhibiting their responsiveness to inhibitory GABAergic inputs; non-hunger-driven feeding activates VTA-projecting 5-HTDRN neurons through reducing a potassium outward current. Thus, our results support a model whereby parallel circuits modulate feeding behavior either in response to hunger or to hunger-independent cues.

Stimulation of Gastric Transit Function Driven by Hydrolyzed Casein Increases Small Intestinal Carbohydrate Availability and Its Microbial Metabolism.

Gastrointestinal (GI) functions affect gut nutrient flow and microbial metabolism. Dietary peptides modulate GI functions and improve small intestinal health, but the mechanism remains elusive. This study aims to investigate whether dietary peptides affect small intestinal microbial metabolism, and the underlying mechanisms. An ileal-cannulated pig model is adopted to explore the relationship between gut nutrient flow and microbial metabolism after treatment with hydrolyzed casein (peptides) or intact casein (Control)-based diet. The results demonstrate that hydrolyzed casein enhances microbial carbohydrate metabolism with higher Streptococcus abundance and higher lactate level in the ileum. Meanwhile, hydrolyzed casein increases ileal flows of nutrients, especially carbohydrate, leading to a higher carbohydrate availability in ileal digesta. To unveil the mechanisms, it is found that the hydrolyzed casein enhances the ghrelin signal and improves development of interstitial cells of Cajal and muscular layer in gastric corpus, indicating the enhanced upper GI transit function. In addition, hydrolyzed casein improves small intestinal health, as indicated by higher villus heights and luminal lactate concentrations in the jejunum and ileum. In conclusion, hydrolyzed casein stimulates upper GI transit function, enhances gut nutrient flow, and increases small intestinal carbohydrate availability and its microbial metabolism, which favor the small intestinal health.

17ß-estradiol promotes acute refeeding in hungry mice via membrane-initiated ERα signaling.

OBJECTIVE: Estrogen protects animals from obesity through estrogen receptor α (ERα), partially by inhibiting overeating in animals fed ad libitum. However, the effects of estrogen on feeding behavior in hungry animals remain unclear. In this study, we examined the roles of 17ß-estradiol (E2) and ERα in the regulation of feeding in hungry female animals and explored the underlying mechanisms. METHODS: Wild-type female mice with surgical depletion of endogenous estrogens were used to examine the effects of E2 supplementation on acute refeeding behavior after starvation. ERα-C451A mutant mice deficient in membrane-bound ERα activity and ERα-AF20 mutant mice lacking ERα transcriptional activity were used to further examine mechanisms underlying acute feeding triggered by either fasting or central glucopenia (induced by intracerebroventricular injections of 2-deoxy-D-glucose). We also used electrophysiology to explore the impact of these ERα mutations on the neural activities of ERα neurons in the hypothalamus. RESULTS: In the wild-type female mice, ovariectomy reduced fasting-induced refeeding, which was restored by E2 supplementation. The ERα-C451A mutation, but not the ERα-AF20 mutation, attenuated acute feeding induced by either fasting or central glucopenia. The ERα-C451A mutation consistently impaired the neural responses of hypothalamic ERα neurons to hypoglycemia. CONCLUSION: In addition to previous evidence that estrogen reduces deviations in energy balance by inhibiting eating at a satiated state, our findings demonstrate the unexpected role of E2 that promotes eating in hungry mice, also contributing to the stability of energy homeostasis. This latter effect specifically requires membrane-bound ERα activity.

Estrogen receptor-α expressing neurons in the ventrolateral VMH regulate glucose balance.

Brain glucose-sensing neurons detect glucose fluctuations and prevent severe hypoglycemia, but mechanisms mediating functions of these glucose-sensing neurons are unclear. Here we report that estrogen receptor-α (ERα)-expressing neurons in the ventrolateral subdivision of the ventromedial hypothalamic nucleus (vlVMH) can sense glucose fluctuations, being glucose-inhibited neurons (GI-ERαvlVMH) or glucose-excited neurons (GE-ERαvlVMH). Hypoglycemia activates GI-ERαvlVMH neurons via the anoctamin 4 channel, and inhibits GE-ERαvlVMH neurons through opening the ATP-sensitive potassium channel. Further, we show that GI-ERαvlVMH neurons preferentially project to the medioposterior arcuate nucleus of the hypothalamus (mpARH) and GE-ERαvlVMH neurons preferentially project to the dorsal Raphe nuclei (DRN). Activation of ERαvlVMH to mpARH circuit and inhibition of ERαvlVMH to DRN circuit both increase blood glucose. Thus, our results indicate that ERαvlVMH neurons detect glucose fluctuations and prevent severe hypoglycemia in mice.

A POMC-originated circuit regulates stress-induced hypophagia, depression, and anhedonia.

Chronic stress causes dysregulations of mood and energy homeostasis, but the neurocircuitry underlying these alterations remain to be fully elucidated. Here we demonstrate that chronic restraint stress in mice results in hyperactivity of pro-opiomelanocortin neurons in the arcuate nucleus of the hypothalamus (POMCARH neurons) associated with decreased neural activities of dopamine neurons in the ventral tegmental area (DAVTA neurons). We further revealed that POMCARH neurons project to the VTA and provide an inhibitory tone to DAVTA neurons via both direct and indirect neurotransmissions. Finally, we show that photoinhibition of the POMCARH→VTA circuit in mice increases body weight and food intake, and reduces depression-like behaviors and anhedonia in mice exposed to chronic restraint stress. Thus, our results identified a novel neurocircuitry regulating feeding and mood in response to stress.

Hepatic Metabolomic and Transcriptomic Responses Induced by Cecal Infusion of Sodium Propionate in a Fistula Pig Model.

Short-chain fatty acids (SCFAs) are the major products of the microbial fermentation of indigestible carbohydrates. SCFAs are known to improve the host metabolism, but their underlying mechanism of action remains elusive. In this study, 16 growing pigs were infused with saline or sodium propionate solution (25 mL, 2 mol/L) through a cecal fistula twice a day during a 28 day experimental period. The results showed that the cecal infusion of the SCFA propionate decreased serum and liver triglyceride levels and increased serum PYY secretion in growing pigs. Hepatic metabolomics identified 12 metabolites that were significantly altered by propionate. These included decreased levels of lipid metabolism-related stearic acid and glycerol-2-phosphate; increased levels of TCA cycle components including malic acid, fructose-6-phosphate, and succinic acid; and decreased levels of the amino acid metabolism products aspartic acid and serine. Hepatic transcriptomics demonstrated that propionate inhibited fatty acid synthesis and promoted the lipid metabolic process. Pathway enrichment analysis showed that propionate accelerated gluconeogenesis and decreased glycolysis. Taken together, these data support a role of the SCFA propionate on host lipid and glucose metabolism.

Succinate Modulates Intestinal Barrier Function and Inflammation Response in Pigs.

Succinate is a metabolic intermediate of the tricarboxylic acid (TCA) cycle in all aerobic organisms, and is also a vital microbial metabolite in the gut. Although succinate is known to regulate intestinal metabolism and immune function, its role in the protection of the intestinal epithelial barrier function and inflammation is poorly characterized. In this study, we evaluated the effects of succinate on intestinal epithelial barrier function and inflammation in pigs. Twenty-four growing pigs were distributed into three groups (n = 8) and received either a basal diet (control group) or the same diet supplemented with 0.1% succinate or 1% succinate. The diet supplemented with 1% succinate led to alterations in the intestinal morphology. We confirmed in vitro that 5 mM succinate treatment modulated intestinal epithelial permeability by increased transepithelial electrical resistance (TEER) in intestinal porcine epithelial cell (IPEC)-J2 cells. Furthermore, succinate treatment increased the abundance of tight junction proteins claudin-1, zona occluden (ZO)-1, and ZO-2 in the jejunum in vivo and in vitro. In addition, dietary succinate supplementation promoted the expression of inflammatory cytokines interleukin (IL)-25, IL-10, IL-8, and IL-18 in the jejunum. Taken together, these data identify a novel role of succinate in the modulation of intestinal epithelial barrier function, which may be a nutritional target to improve gut health in animals.

Cecal Infusion of Sodium Propionate Promotes Intestinal Development and Jejunal Barrier Function in Growing Pigs.

Short-chain fatty acids (SCFAs) produced by microbial fermentation facilitate the differentiation and proliferation of intestinal epithelium. However, the role of individual SCFAs, such as propionate, on intestinal development is still unclear. In the present study, sixteen barrows fitted with a cecal fistula were randomly divided into two groups for cecal infusion of either saline (control group) or sodium propionate (propionate group). After 28 days, the length and the relative weight of intestinal segments were calculated, the intestinal morphology was assessed, and the expression of tight junction protein was measured using qPCR and Western blotting. Compared to the saline group, the length of the colon was significantly increased in the propionate group (p < 0.05). The jejunal villi length and villi/crypt ratio in the propionate group were significantly higher than in the saline group (p < 0.05). Furthermore, propionate infusion significantly upregulated the mRNA levels of Claudin-4 and the expression of Claudin-1, Claudin-4, and Occludin protein in the jejunal mucosa (p < 0.05). Collectively, these findings revealed that the short-chain fatty acid propionate in the hindgut contributed to intestinal development, and selectively enhanced jejunal tight junction protein expression.

Caecal infusion of the short-chain fatty acid propionate affects the microbiota and expression of inflammatory cytokines in the colon in a fistula pig model.

Short-chain fatty acids (SCFAs), particularly butyrate, are known to suppress inflammation, and regulate the gut bacterial ecology. However, little is known about propionate. We report here that propionate infusion in the caecum dramatically affected the structure of colonic microbiota of pigs based on 16s rRNA high-throughput sequencing. Sixteen pig models were perfused with saline or sodium propionate by a fistula in the caecum. At d 28, all pigs were slaughtered for analysing bacterial metabolites, colonic microbiota and the expression of genes related to inflammation. The results showed that caecal infusion of sodium propionate increased the concentration of propionate and decreased the butyrate concentration in colonic content. For biogenic amines, the tyramine concentration was increased, while the concentration of cadaverine was decreased by infusion of sodium propionate. Furthermore, at the level of phylum, propionate increased the abundance of Bacteroidetes and reduced the abundance of Firmicutes. Prevotella and Bacteroides counts were increased, while Turicibacter abundance was decreased at the level of genus. Real-time qPCR showed that the expression of NF-κB and IL-18 was upregulated by propionate infusion, whereas no significant differences were observed for the expression of other genes related to inflammatory processes. Taken together, these results provide a new evidence for the role of short-chain fatty acid propionate on the composition of microbial community and inflammatory cytokines.