Intestinal Serotonin Transporter Inhibition by Toll-Like Receptor 2 Activation. A Feedback Modulation

Modulation of Serotonin-Related Genes by Extracellular Vesicles of the Probiotic Escherichia coli Nissle 1917 in the Interleukin-1β-Induced Inflammation Model of Intestinal Epithelial Cells

Inflammatory bowel disease (IBD) is a chronic inflammatory condition involving dysregulated immune responses and imbalances in the gut microbiota in genetically susceptible individuals. Current therapies for IBD often have significant side-effects and limited success, prompting the search for novel therapeutic strategies. Microbiome-based approaches aim to restore the gut microbiota balance towards anti-inflammatory and mucosa-healing profiles. Extracellular vesicles (EVs) from beneficial gut microbes are emerging as potential postbiotics. Serotonin plays a crucial role in intestinal homeostasis, and its dysregulation is associated with IBD severity. Our study investigated the impact of EVs from the probiotic Nissle 1917 (EcN) and commensal E. coli on intestinal serotonin metabolism under inflammatory conditions using an IL-1β-induced inflammation model in Caco-2 cells. We found strain-specific effects. Specifically, EcN EVs reduced free serotonin levels by upregulating SERT expression through the downregulation of miR-24, miR-200a, TLR4, and NOD1. Additionally, EcN EVs mitigated IL-1β-induced changes in tight junction proteins and oxidative stress markers. These findings underscore the potential of postbiotic interventions as a therapeutic approach for IBD and related pathologies, with EcN EVs exhibiting promise in modulating serotonin metabolism and preserving intestinal barrier integrity. This study is the first to demonstrate the regulation of miR-24 and miR-200a by probiotic-derived EVs.

Safety evaluation of a heat-treated Bifidobacterium bifidum OLB6378 concentrate

Several bacterial strains, including probiotic strains, have undergone evaluations for their safety and potential beneficial health effects. Some of these strains have been introduced into various markets, including that for infant products. However, certain probiotic strains have been linked to serious infections in infants, such as septicemia and meningitis. Given this, it is crucial to assess the safety of each probiotic strain, including those of Bifidobacterium, which is a common genus of probiotics. One such strain, Bifidobacterium bifidum OLB6378 (NITE BP-31), referred to as OLB6378 hereafter, has been selected for use in infants. To determine its genotoxicity and general toxicity potential, a heat-treated OLB6378 concentrate was subjected to various tests, including the bacterial reverse mutation test, in vitro chromosome aberration test, in vivo micronucleus test, and single- and 90-day oral gavage toxicity studies in rats. No significant differences were observed compared with negative controls in any of genotoxicity tests. The single-dose toxicity study employed dose levels of 560, 1,693, and 5,092 mg/kg, representing the total solid contents of culture concentrates containing OLB6378 (equivalent to 8.1 × 1011, 2.4 × 1012, and 7.4 × 1012 cells/kg of Bifidobacterium, respectively). In the 90-day toxicity study, dose levels of 280, 853, and 2,546 mg/kg/day were used (equivalent to 4.0 × 1011, 1.2 × 1012, and 3.7 × 1012 cells/kg/day, respectively). Importantly, the heat-treated OLB6378 concentrate did not induce any signs of toxicity in any of the conducted toxicity studies. In conclusion, the heat-treated OLB6378 concentrate exhibited no genotoxicity potential, and the no-observed-adverse-effect level in the 90-day toxicity study was determined to be 2,546 mg/kg/day (equivalent to 3.7 × 1012 cells/kg/day). This suggests that heat-treated OLB6378 can be safely utilized as a food source.

Epstein-Barr virus-acquired immunodeficiency in myalgic encephalomyelitis-Is it present in long COVID?

Both myalgic encephalomyelitis or chronic fatigue syndrome (ME/CFS) and long COVID (LC) are characterized by similar immunological alterations, persistence of chronic viral infection, autoimmunity, chronic inflammatory state, viral reactivation, hypocortisolism, and microclot formation. They also present with similar symptoms such as asthenia, exercise intolerance, sleep disorders, cognitive dysfunction, and neurological and gastrointestinal complaints. In addition, both pathologies present Epstein-Barr virus (EBV) reactivation, indicating the possibility of this virus being the link between both pathologies. Therefore, we propose that latency and recurrent EBV reactivation could generate an acquired immunodeficiency syndrome in three steps: first, an acquired EBV immunodeficiency develops in individuals with "weak" EBV HLA-II haplotypes, which prevents the control of latency I cells. Second, ectopic lymphoid structures with EBV latency form in different tissues (including the CNS), promoting inflammatory responses and further impairment of cell-mediated immunity. Finally, immune exhaustion occurs due to chronic exposure to viral antigens, with consolidation of the disease. In the case of LC, prior to the first step, there is the possibility of previous SARS-CoV-2 infection in individuals with "weak" HLA-II haplotypes against this virus and/or EBV.

Antibiotic-induced microbial depletion enhances murine small intestinal epithelial growth in a serotonin-dependent manner

Regulation of small intestinal epithelial growth by endogenous and environmental factors is critical for intestinal homeostasis and recovery from insults. Depletion of the intestinal microbiome increases epithelial proliferation in small intestinal crypts, similar to the effects observed in animal models of serotonin potentiation. Based on prior evidence that the microbiome modulates serotonin activity, we hypothesized that microbial depletion-induced epithelial proliferation is dependent on host serotonin activity. A mouse model of antibiotic-induced microbial depletion (AIMD) was employed. Serotonin potentiation was achieved through either genetic knockout of the serotonin transporter (SERT) or pharmacological SERT inhibition, and inhibition of serotonin synthesis was achieved with para-chlorophenylalanine. AIMD and serotonin potentiation increased intestinal villus height and crypt proliferation in an additive manner, but the epithelial proliferation observed after AIMD was blocked in the absence of endogenous serotonin. Using Lgr5-EGFP-reporter mice, we evaluated intestinal stem cell (ISC) quantity and proliferation. AIMD increased the number of ISCs per crypt and ISC proliferation compared with controls, and changes in ISC number and proliferation were dependent on the presence of host serotonin. Furthermore, Western blotting demonstrated that AIMD reduced epithelial SERT protein expression compared with controls. In conclusion, host serotonin activity is necessary for microbial depletion-associated changes in villus height and ISC proliferation in crypts, and microbial depletion produces a functional serotonin-potentiated state through reduced SERT protein expression. These findings provide an understanding of how changes to the microbiome contribute to intestinal pathology and can be applied therapeutically.NEW & NOTEWORTHY Antibiotic-induced microbial depletion of the murine small intestine results in a state of potentiated serotonin activity through reduced epithelial expression of the serotonin transporter. Specifically, serotonin-dependent mechanisms lead to increased intestinal surface area and intestinal stem cell proliferation. Furthermore, the absence of endogenous serotonin leads to blunting of small intestinal villi, suggesting that serotonin signaling is required for epithelial homeostasis.

Mode of action of Akkermansia muciniphila in the intestinal dialogue: role of extracellular proteins, metabolites and cell envelope components

Akkermansia muciniphila is a promising next-generation beneficial microbe due to its natural presence in the mucus layer of the gut, its symbiotic ability to degrade mucus, and its capacity to improve the intestinal barrier function. A. muciniphila is able to counteract weight gain and immuno-metabolic disturbances in several animal models. Many of these disorders, including obesity and auto-immune diseases, have been associated with decreased gut barrier function and consequent increased inflammation. Since A. muciniphila was found to normalize these changes and strengthen the gut barrier function, it is hypothesized that other beneficial effects of A. muciniphila might be caused by this restoration. In search for A. muciniphila's mode of action in enhancing the gut barrier function and promoting health, we reasoned that secreted components or cell envelope components of A. muciniphila are interesting candidates as they can potentially reach and interact with the epithelial barrier. In this review, we focus on the potential mechanisms through which A. muciniphila can exert its beneficial effects on the host by the production of extracellular and secreted proteins, metabolites and cell envelope components. These products have been studied in isolation for their structure, signaling capacity, and in some cases, also for their effects in preclinical models. This includes the protein known as Amuc_1100, which we here rename as pilus-associated signaling (PAS) protein , the P9 protein encoded by Amuc_1631, the short-chain fatty acids acetate and propionate, and cell envelope components, such as phosphatidylethanolamine and peptidoglycan.

Peripheral Serotonin: Cultivating Companionship with Gut Microbiota in Intestinal Homeostasis

Serotonin, also known as 5-hydroxytryptamine (5-HT), is an evolutionarily ancient and phylogenetically conserved monoamine that regulates multifaceted physiological functions in mammals. 5-HT was, at one time, most extensively studied as a neurotransmitter within the central nervous system but is now known to regulate non-neuronal functions including immune responses in an autocrine-paracrine-endocrine manner. Compelling evidence from intervention studies using germ-free mice or antibiotic-associated microbiota perturbation suggests that novel interactions between 5-HT and the gut microbiota are essential in maintaining intestinal homeostasis. Importantly, recent studies reveal that bidirectional host-microbial interactions mediated by the host serotonergic system can promote distinct changes within the gut microbiota. These changes may potentially lead to a state known as 'dysbiosis' which has been strongly associated with various gut pathologies including inflammatory bowel disease (IBD). In this review, we update the current understanding of host-microbiota interaction by focusing on the impact of peripheral 5-HT signaling within this dynamic. We also briefly highlight key environmental risk factors for IBD, such as Western diet, and draw attention to the interaction of synthetic food colorants with 5-HT signaling that may facilitate future research.

Mucosal Serotonin Reuptake Transporter Expression in Irritable Bowel Syndrome Is Modulated by Gut Microbiota Via Mast Cell-Prostaglandin E2

BACKGROUND & AIMS

Increased colonic serotonin (5-HT) level and decreased serotonin reuptake transporter (SERT) expression in irritable bowel syndrome (IBS) may contribute to diarrhea and visceral hypersensitivity. We investigated whether mucosal SERT is modulated by gut microbiota via a mast cell-prostaglandin E2 (PGE2) pathway.

METHODS

C57Bl/6 mice received intracolonic infusion of fecal supernatant (FS) from healthy controls or patients with diarrhea-predominant irritable bowel syndrome (IBS-D). The role of mast cells was studied in mast cell-deficient mice. Colonic organoids and/or mast cells were used for in vitro experiments. SERT expression was measured by quantitative polymerase chain reaction and Western blot. Visceromotor responses to colorectal distension and colonic transit were assessed.

RESULTS

Intracolonic infusion of IBS-D FS in mice caused an increase in mucosal 5-HT compared with healthy control FS, accompanied by ∼50% reduction in SERT expression. Mast cell stabilizers, cyclooxygenase-2 inhibitors, and PGE2 receptor antagonist prevented SERT downregulation. Intracolonic infusion of IBS-D FS failed to reduce SERT expression in mast cell-deficient (W/Wv) mice. This response was restored by mast cell reconstitution. The downregulation of SERT expression evoked by IBS FS was prevented by lipopolysaccharide (LPS) antagonist LPS from Rhodobacter sphaeroides and a bacterial trypsin inhibitor. In vitro LPS treatment caused increased cyclooxygenase-2 expression and PGE2 release from cultured mouse mast cells. Intracolonic infusion of IBS-D FS in mice reduced colonic transit, increased fecal water content, and increased visceromotor responses to colorectal distension. Ondansetron prevented these changes.

CONCLUSIONS

Fecal LPS acting in concert with trypsin in patients with IBS-D stimulates mucosal mast cells to release PGE2, which downregulates mucosal SERT, resulting in increased mucosal 5-HT. This may contribute to diarrhea and abdominal pain common in IBS.

Goblet cell hyperplasia is not epithelial-autonomous in the Cftr knockout intestine

Goblet cell hyperplasia is an important manifestation of cystic fibrosis (CF) disease in epithelial-lined organs. Explants of CF airway epithelium show normalization of goblet cell numbers; therefore, we hypothesized that small intestinal enteroids from Cftr knockout (KO) mice would not exhibit goblet cell hyperplasia. Toll-like receptors 2 and 4 (Tlr2 and Tlr4) were investigated as markers of inflammation and influence on goblet cell differentiation. Ex vivo studies found goblet cell hyperplasia in Cftr KO jejunum compared with wild-type (WT) mice. IL-13, SAM pointed domain-containing ETS transcription factor (Spdef), Tlr2, and Tlr4 protein expression were increased in Cftr KO intestine relative to WT. In contrast, WT and Cftr KO enteroids did not exhibit differences in basal or IL-13-stimulated goblet cell numbers, or differences in expression of Tlr2, Tlr4, and Spdef. Ileal goblet cell numbers in Cftr KO/Tlr4 KO and Cftr KO/Tlr2 KO mice were not different from Cftr KO mice, but enumeration was confounded by altered mucosal morphology. Treatment with Tlr4 agonist LPS did not affect goblet cell numbers in WT or Cftr KO enteroids, whereas the Tlr2 agonist Pam3Csk4 stimulated goblet cell hyperplasia in both genotypes. Pam3Csk4 stimulation of goblet cell numbers was associated with suppression of Notch1 and Neurog3 expression and upregulated determinants of goblet cell differentiation. We conclude that goblet cell hyperplasia and inflammation of the Cftr KO small intestine are not exhibited by enteroids, indicating that this manifestation of CF intestinal disease is not epithelial-automatous but secondary to the altered CF intestinal environment.NEW & NOTEWORTHY Studies of small intestinal organoids from cystic fibrosis (CF) mice show that goblet cell hyperplasia and increased Toll-like receptor 2/4 expression are not primary manifestations of the CF intestine. Intestinal goblet cell hyperplasia in the CF mice was not strongly altered by genetic ablation of Tlr2 and Tlr 4, but could be induced in both wild-type and CF intestinal organoids by a Tlr2-dependent suppression of Notch signaling.

Enteropathogenic infections modulate intestinal serotonin transporter (SERT) function by activating Toll-like receptor 2 (TLR-2) in Crohn's disease

Serotonin (5-hydroxytryptamine [5-HT]) is an intestinal neuromodulator that regulates several essential enteric physiological functions such as absorption or secretion of fluids, and peristaltic reflexes. Availability of the intestinal 5-HT is dependent on serotonin transporter (SERT), which uptakes 5-HT and facilitates its degradation. Interestingly, Toll-like receptor 2 (TLR-2) is co-localized with 5-HT, which suggests a possible impact of neuroendocrine cells in the inflammatory response through TLR-2 activation. Serum 5-HT levels were measured in 80 Crohn's disease (CD) patients and 40 healthy control subjects. Additionally, fully differentiated Caco-2 monolayers were infected with Mycobacteria paratuberculosis (MAP), L. monocytogenes, or M. smegmatis in the presence of exogenous 5-HT at different concentrations. Cells were subsequently harvested and used for measuring SERT activity, RNA isolation followed by RT-PCR, protein quantification, and tissue damage markers (DHE, LDH, GSH and MDA). TLR-2 intracellular signaling pathways were assessed by pre-incubating Caco-2 monolayers with selective blockers of ERK, cAMP/PKA, p38 MAPK, and 5-HT₃ receptors. MAP-infected CD patients (N = 40) had higher serum 5-HT levels (462.95 ± 8.55 ng/mL, N = 40) than those without MAP infection (385.33 ± 10.3 ng/mL, N = 40). TLR-2 activation by enteropathogenic bacteria inhibited SERT activity in the presence of exogenous 5-HT by up to 50%. These effects were increasing gradually over 72 h, and MAP infection had the greatest effect on SERT inhibition when cells were exposed to 5-HT in a concentration dependent manner. Additionally, inhibition of SERT activity was accompanied with higher levels of pro-inflammatory cytokines (TNF-α, IL-6, IL-8) and oxidative stress markers (DHE, LDH and MDA), whereas SERT expression and protein level were downregulated. Consequently, inhibition of TLR-2 and p38 MAPK signaling or blocking 5-HT₃ receptors restored SERT activity and reduced the production of pro-inflammatory cytokines, as reflected by the downregulation of oxidative stress and tissue damage markers. The involvement of TLR-2 in the intestinal pathology might be concluded not only from its innate immune role, but also from its effect on modulating the intestinal serotonergic response. Ultimately, regulating the intestinal serotonergic system can be therapeutically exploited to mitigate other enteropathogenic infections, which will help in understanding the gut-microbiome-brain connection.

Limosilactobacillus reuteri ATCC 6475 metabolites upregulate the serotonin transporter in the intestinal epithelium

The serotonin transporter (SERT) readily takes up serotonin (5-HT), thereby regulating the availability of 5-HT within the intestine. In the absence of SERT, 5-HT remains in the interstitial space and has the potential to aberrantly activate the many 5-HT receptors distributed on the epithelium, immune cells and enteric neurons. Perturbation of SERT is common in many gastrointestinal disorders as well as mouse models of colitis. Select commensal microbes regulate intestinal SERT levels, but the mechanism of this regulation is poorly understood. Additionally, ethanol upregulates SERT in the brain and dendritic cells, but its effects in the intestine have never been examined. We report that the intestinal commensal microbe Limosilactobacillus (previously classified as Lactobacillus) reuteri ATCC PTA 6475 secretes 83.4 mM ethanol. Consistent with the activity of L. reuteri alcohol dehydrogenases, we found that L. reuteri tolerated various levels of ethanol. Application of L. reuteri conditioned media or exogenous ethanol to human colonic T84 cells was found to upregulate SERT at the level of mRNA. A 4-(4-(dimethylamino) phenyl)-1-methylpyridinium (APP+) uptake assay confirmed the functional activity of SERT. These findings were mirrored in mouse colonic organoids, where L. reuteri metabolites and ethanol were found to upregulate SERT at the apical membrane. Finally, in a trinitrobenzene sulphonic acid model of acute colitis, we observed that mice treated with L. reuteri maintained SERT at the colon membrane compared with mice receiving phosphate buffered saline vehicle control. These data suggest that L. reuteri metabolites, including ethanol, can upregulate SERT and may be beneficial for maintaining intestinal homeostasis with respect to serotonin signalling.

Crosstalk Between Intestinal Serotonergic System and Pattern Recognition Receptors on the Microbiota-Gut-Brain Axis

Disruption of the microbiota-gut-brain axis results in a wide range of pathologies that are affected, from the brain to the intestine. Gut hormones released by enteroendocrine cells to the gastrointestinal (GI) tract are important signaling molecules within this axis. In the search for the language that allows microbiota to communicate with the gut and the brain, serotonin seems to be the most important mediator. In recent years, serotonin has emerged as a key neurotransmitter in the gut-brain axis because it largely contributes to both GI and brain physiology. In addition, intestinal microbiota are crucial in serotonin signaling, which gives more relevance to the role of the serotonin as an important mediator in microbiota-host interactions. Despite the numerous investigations focused on the gut-brain axis and the pathologies associated, little is known regarding how serotonin can mediate in the microbiota-gut-brain axis. In this review, we will mainly discuss serotonergic system modulation by microbiota as a pathway of communication between intestinal microbes and the body on the microbiota-gut-brain axis, and we explore novel therapeutic approaches for GI diseases and mental disorders.

The gut, its microbiome, and the brain: connections and communications

Modern research on gastrointestinal behavior has revealed it to be a highly complex bidirectional process in which the gut sends signals to the brain, via spinal and vagal visceral afferent pathways, and receives sympathetic and parasympathetic inputs. Concomitantly, the enteric nervous system within the bowel, which contains intrinsic primary afferent neurons, interneurons, and motor neurons, also senses the enteric environment and controls the detailed patterns of intestinal motility and secretion. The vast microbiome that is resident within the enteric lumen is yet another contributor, not only to gut behavior, but to the bidirectional signaling process, so that the existence of a microbiota-gut-brain "connectome" has become apparent. The interaction between the microbiota, the bowel, and the brain now appears to be neither a top-down nor a bottom-up process. Instead, it is an ongoing, tripartite conversation, the outline of which is beginning to emerge and is the subject of this Review. We emphasize aspects of the exponentially increasing knowledge of the microbiota-gut-brain "connectome" and focus attention on the roles that serotonin, Toll-like receptors, and macrophages play in signaling as exemplars of potentially generalizable mechanisms.

Nitrogen pollution promotes changes in the niche space of fish communities

Historically, anthropogenic fixed nitrogen has been purposely increased to benefit food production and global development. One consequence of this increase has been to raise concentrations of nitrogen in aquatic ecosystems. To evaluate whether nitrogen pollution promotes changes in the estimates of niche space of fish communities, we examined 16 sites along a Brazilian river basin highly impacted by anthropogenic activities, especially discharge of domestic and industrial sewage from a region with more than 5 million inhabitants. We analysed the carbon (δ¹³C) and nitrogen (δ¹⁵N) isotope ratios of fish species and both autochthonous (periphyton) and allochthonous (course and fine particulate organic matter) basal food resources. To estimate the magnitude of nitrogen pollution, we measured the nitrate and ammonium concentrations at each site. Sampling was conducted in the dry and wet seasons to evaluate the influence of seasonality. Nitrogen pollution generally increased estimates of niche space, and seasonality influenced only the niche estimates of fish communities from polluted sites. In addition, isotopic analyses of nitrogen polluted sites yielded unrealistic estimates of trophic positioning (detritivores at the top of the food web). We conclude that changes in niche space estimates reflect both alterations in baseline isotopic values and differential trophic behaviour among fishes. Our study suggests that under conditions of high pollution, other factors appear to influence isotopic estimates of niche, such as isotopically distinct sources that have not been sampled, and/or differences in δ¹⁵N turnover rates between fish tissue and basal resources, creating isotopic baselines that are challenging to interpret.

Neurotransmitter Dysfunction in Irritable Bowel Syndrome: Emerging Approaches for Management

Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder whose aetiology is still unknown. Most hypotheses point out the gut-brain axis as a key factor for IBS. The axis is composed of different anatomic and functional structures intercommunicated through neurotransmitters. However, the implications of key neurotransmitters such as norepinephrine, serotonin, glutamate, GABA or acetylcholine in IBS are poorly studied. The aim of this review is to evaluate the current evidence about neurotransmitter dysfunction in IBS and explore the potential therapeutic approaches. IBS patients with altered colorectal motility show augmented norepinephrine and acetylcholine levels in plasma and an increased sensitivity of central serotonin receptors. A decrease of colonic mucosal serotonin transporter and a downregulation of α2 adrenoceptors are also correlated with visceral hypersensitivity and an increase of 5-hydroxyindole acetic acid levels, enhanced expression of high affinity choline transporter and lower levels of GABA. Given these neurotransmitter dysfunctions, novel pharmacological approaches such as 5-HT₃ receptor antagonists and 5-HT₄ receptor agonists are being explored for IBS management, for their antiemetic and prokinetic effects. GABA-analogous medications are being considered to reduce visceral pain. Moreover, agonists and antagonists of muscarinic receptors are under clinical trials. Targeting neurotransmitter dysfunction could provide promising new approaches for IBS management.

The outer membrane protein Amuc_1100 of Akkermansia muciniphila promotes intestinal 5-HT biosynthesis and extracellular availability through TLR2 signalling

Akkermansia muciniphila is a probiotic inhabiting host intestinal mucus layers and displays evident easing or therapeutic effects on host enteritis and metabolic disorders such as obesity and diabetes. The outer membrane protein Amuc_1100 of A. muciniphila is likely to play a crucial role during the interaction with the host. 5-HT is a neurotransmitter and a key signal molecule regulating the gastrointestinal tract functions and other organs, which is involved in diverse physiological and pathological processes. This study demonstrated that Amuc_1100 could promote the expression of the 5-HT synthesis rate-limiting enzyme Tph1 in RIN-14B cells and reduce the expression of the serotonin reuptake transporter (SERT) in Caco-2 cells through direct interaction with TLR2, thereby improving 5-HT biosynthesis and extracellular availability. Using antibiotic-treated mice as animal models, we found that after gavage with A. muciniphila or Amuc_1100, Tph1 expression increased and SERT expression decreased in colon tissues. The 5-HT concentrations in colon tissues and blood were markedly elevated simultaneously. We also found that A. muciniphila or Amuc_1100 improved the gastrointestinal motility function and restored gut microbiota abundance and species diversity in antibiotic-treated mice. These results suggest that A. muciniphila can regulate the host intestinal 5-HT system via its outer membrane protein Amuc_1100 and TLR2. This mechanism represented an important approach through which A. muciniphila interacts with the host and further influences 5-HT-related physiological functions. These results advance the understanding of interplay mechanisms between the gut microbiota and the host, which could be the basis for new intervention strategies for related diseases.

Oxidized phospholipids affect small intestine neuromuscular transmission and serotonergic pathways in juvenile mice

BACKGROUND

Oxidized phospholipid derivatives (OxPAPCs) act as bacterial lipopolysaccharide (LPS)-like damage-associated molecular patterns. OxPAPCs dose-dependently exert pro- or anti-inflammatory effects by interacting with several cellular receptors, mainly Toll-like receptors 2 and 4. It is currently unknown whether OxPAPCs may affect enteric nervous system (ENS) functional and structural integrity.

METHODS

Juvenile (3 weeks old) male C57Bl/6 mice were treated intraperitoneally with OxPAPCs, twice daily for 3 days. Changes in small intestinal contractility were evaluated by isometric neuromuscular responses to receptor and non-receptor-mediated stimuli. Alterations in ENS integrity and serotonergic pathways were assessed by real-time PCR and confocal immunofluorescence microscopy in longitudinal muscle-myenteric plexus whole-mount preparations (LMMPs). Tissue levels of serotonin (5-HT), tryptophan, and kynurenine were measured by HPLC coupled to UV/fluorescent detection.

KEY RESULTS

OxPAPC treatment induced enteric gliosis, loss of myenteric plexus neurons, and excitatory hypercontractility, and reduced nitrergic neurotransmission with no changes in nNOS⁺ neurons. Interestingly, these changes were associated with a higher functional response to 5-HT, altered immunoreactivity of 5-HT receptors and serotonin transporter (SERT) together with a marked decrease in 5-HT levels, shifting tryptophan metabolism toward kynurenine production.

CONCLUSIONS AND INFERENCES

OxPAPC treatment disrupted structural and functional integrity of the ENS, affecting serotoninergic tone and 5-HT tissue levels toward a higher kynurenine content during adolescence, suggesting that changes in intestinal lipid metabolism toward oxidation can affect serotoninergic pathways, potentially increasing the risk of developing functional gastrointestinal disorders during critical stages of development.

Enteric neuroplasticity and dysmotility in inflammatory disease: key players and possible therapeutic targets

Intestinal functions, including motility and secretion, are locally controlled by enteric neural networks housed within the wall of the gut. The fidelity of these functions depends on the precision of intercellular signaling among cellular elements, including enteric neurons, epithelial cells, immune cells, and glia, all of which are vulnerable to disruptive influences during inflammatory events. This review article describes current knowledge regarding inflammation-induced neuroplasticity along key elements of enteric neural circuits, what is known about the causes of these changes, and possible therapeutic targets for protecting and/or repairing the integrity of intrinsic enteric neurotransmission. Changes that have been detected in response to inflammation include increased epithelial serotonin availability, hyperexcitability of intrinsic primary afferent neurons, facilitation of synaptic activity among enteric neurons, and attenuated purinergic neuromuscular transmission. Dysfunctional propulsive motility has been detected in models of colitis, where causes include the changes described above, and in models of multiple sclerosis and other autoimmune conditions, where autoantibodies are thought to mediate dysmotility. Other cells implicated in inflammation-induced neuroplasticity include muscularis macrophages and enteric glia. Targeted treatments that are discussed include 5-hydroxytryptamine receptor 4 agonists, cyclooxygenase inhibitors, antioxidants, B cell depletion therapy, and activation of anti-inflammatory pathways.

Poor Bifidobacterial Colonization Is Associated with Late Provision of Colostrum and Improved with Probiotic Supplementation in Low Birth Weight Infants

This study aimed to evaluate the association between bifidobacterial colonization in low birth weight infants and perinatal factors, including the timing of initial colostrum and the effect of probiotics on this colonization. In this non-randomized controlled trial, we enrolled 98 low-birth-weight infants from a neonatal intensive care unit (NICU) in Japan. Infants were divided into three groups: group N (no intervention), group H (received non-live bifidobacteria), and group L (received live bifidobacteria). The number of bifidobacteria in the infants’ stools at 1 month of age was measured using real-time polymerase chain reaction (PCR). We divided infants into “rich bifidobacteria” (≥10^4.8 cells/g feces) and “poor bifidobacteria” (<10^4.8 cells/g feces) subgroups. The ratio of “rich bifidobacteria” infants was 20/31, 34/36, and 30/30 in groups N, H, and L, respectively. In group N, the “rich bifidobacteria” group received first colostrum significantly earlier than the “poor bifidobacteria” group (1 day vs. 4 days, P < 0.05). Compared with the N group, both groups H and L had a significantly high proportion of “rich bifidobacteria” infants (P < 0.05). Bifidobacterial colonization was poor in premature infants at 1 month compared with term infants, and the level of colonization was associated with the timing of initial provision of colostrum. Providing probiotics to premature infants can improve bifidobacterial colonization.

Microbiome-Gut-Brain Axis and Toll-Like Receptors in Parkinson's Disease

Parkinson’s disease (PD) is a progressively debilitating neurodegenerative disease characterized by α-synucleinopathy, which involves all districts of the brain-gut axis, including the central, autonomic and enteric nervous systems. The highly bidirectional communication between the brain and the gut is markedly influenced by the microbiome through integrated immunological, neuroendocrine and neurological processes. The gut microbiota and its relevant metabolites interact with the host via a series of biochemical and functional inputs, thereby affecting host homeostasis and health. Indeed, a dysregulated microbiota-gut-brain axis in PD might lie at the basis of gastrointestinal dysfunctions which predominantly emerge many years prior to the diagnosis, corroborating the theory that the pathological process is spread from the gut to the brain. Toll-like receptors (TLRs) play a crucial role in innate immunity by recognizing conserved motifs primarily found in microorganisms and a dysregulation in their signaling may be implicated in α-synucleinopathy, such as PD. An overstimulation of the innate immune system due to gut dysbiosis and/or small intestinal bacterial overgrowth, together with higher intestinal barrier permeability, may provoke local and systemic inflammation as well as enteric neuroglial activation, ultimately triggering the development of alpha-synuclein pathology. In this review, we provide the current knowledge regarding the relationship between the microbiota-gut⁻brain axis and TLRs in PD. A better understanding of the dialogue sustained by the microbiota-gut-brain axis and innate immunity via TLR signaling should bring interesting insights in the pathophysiology of PD and provide novel dietary and/or therapeutic measures aimed at shaping the gut microbiota composition, improving the intestinal epithelial barrier function and balancing the innate immune response in PD patients, in order to influence the early phases of the following neurodegenerative cascade.

Increase in Processing Factors Is Involved in Skewed MicroRNA Expression in Patients with Ulcerative Colitis Who Develop Small Intestine Inflammation after Pouch Surgery

BACKGROUND

A large-scale increase in microRNA (miRNA) expression was observed in patients with ulcerative colitis who underwent pouch surgery and developed inflammation of the pouch (pouchitis). In this study, we assessed miRNA expression in these patients and investigated how regulation of its expression changes in the setting of pouchitis.

METHODS

Autologous samples that included mucosal biopsies, peripheral blood cells, and plasma were collected from the patients. Candidate primary and mature miRNA expressions were analyzed by quantitative polymerase chain reaction. A human intestinal epithelial cell line was used to test DICER activity, and the expression of key miRNA processing factors was analyzed by Western blot. miRNA-424 and its potential target serotonin reuptake transporter (SERT) expressions were examined by quantitative reverse transcription polymerase chain reaction and Western blot in human pouch tissues and in a human intestinal epithelial cell line stimulated with inflammatory cytokines TNF-α, IL-1β, and INF-γ.

RESULTS

Candidate miRNA expression and protein expression of DICER-1, EXPORTIN-5, and AGO-2 were increased in association with pouch inflammation. Similarly, inflammatory cytokines increased protein expression of DICER-1, EXPORTIN-5, and AGO-2 and DICER activity in the epithelial cell line. The miRNA-424 expression increased whereas SERT expression decreased in the patients' mucosa. Similarly, incubation of the epithelial cell line with inflammatory cytokines resulted in increased miRNA-424 and decreased SERT mRNA and protein expression.

CONCLUSIONS

The miRNA expression and processing are augmented in the inflamed intestinal mucosa of patients with pouchitis. These alterations are accompanied by increased expression of proteins involved in miRNA processing, suggesting that pouch inflammation contributes to miRNA processing and expression.

Manipulation of intestinal dysbiosis by a bacterial mixture ameliorates loperamide-induced constipation in rats

Constipation has a significant influence on quality of life. Patients with constipation have slow waves in their gastrointestinal smooth muscles and less faecal water contents, which are closely associated with down-regulation of the interstitial cells of Cajal (ICC) in the gastrointestinal muscles and the aquaporin protein AQP3 expressed in colon epithelial cells. Recent studies supported that patients with constipation have altered intestinal microbial structures compared with healthy controls. Intestinal dysbiosis might be one possible pathophysiological mechanism causing constipation. Bacterial strains, such as Lactobacillus spp., have shown many beneficial effects on the amelioration of constipation. However, few studies reported the structural changes of intestinal microbiota post-intervention of probiotics. In this study, a bacterial mixture was administrated to rats with loperamide-induced constipation. Effects of the bacterial mixture on small intestine transit (SIT), faecal water content, and the intestinal microbiome in rats were evaluated. Meanwhile, we investigated several factors involved in signalling pathways that regulate function of ICC and expression of AQP3 to discuss the possible underlying molecular mechanisms. Intervention of the bacterial mixture improved SIT and faecal water content in constipated rats. The up-regulation of C-kit/SP signalling pathways in ICC and AQP3 significantly contributed to improvements. These changes were closely associated with the manipulation of intestinal dysbiosis in constipated rats. Furthermore, our results revealed the important role of intestinal microbiota in affecting gut motility through regulation of serotonin biosynthesis. This monoamine neurotransmitter, secreted from enterochromaffin cells, up-regulated both substance P/neurokinin 1 receptors pathway of ICC and the expression of AQP3 in intestinal epithelial cells. Our study suggested that the disrupted microbiome in patients could be a potential therapeutic target for the improvement of constipation.

Interplay Between the Gut-Brain Axis, Obesity and Cognitive Function

Obesity continues to be one of the major public health problems due to its high prevalence and co-morbidities. Common co-morbidities not only include cardiometabolic disorders but also mood and cognitive disorders. Obese subjects often show deficits in memory, learning and executive functions compared to normal weight subjects. Epidemiological studies also indicate that obesity is associated with a higher risk of developing depression and anxiety, and vice versa. These associations between pathologies that presumably have different etiologies suggest shared pathological mechanisms. Gut microbiota is a mediating factor between the environmental pressures (e.g., diet, lifestyle) and host physiology, and its alteration could partly explain the cross-link between those pathologies. Westernized dietary patterns are known to be a major cause of the obesity epidemic, which also promotes a dysbiotic drift in the gut microbiota; this, in turn, seems to contribute to obesity-related complications. Experimental studies in animal models and, to a lesser extent, in humans suggest that the obesity-associated microbiota may contribute to the endocrine, neurochemical and inflammatory alterations underlying obesity and its comorbidities. These include dysregulation of the HPA-axis with overproduction of glucocorticoids, alterations in levels of neuroactive metabolites (e.g., neurotransmitters, short-chain fatty acids) and activation of a pro-inflammatory milieu that can cause neuro-inflammation. This review updates current knowledge about the role and mode of action of the gut microbiota in the cross-link between energy metabolism, mood and cognitive function.

NOD1 downregulates intestinal serotonin transporter and interacts with other pattern recognition receptors

Serotonin (5-HT) is an essential gastrointestinal modulator whose effects regulate the intestinal physiology. 5-HT effects depend on extracellular 5-HT bioavailability, which is controlled by the serotonin transporter (SERT) expressed in both the apical and basolateral membranes of enterocytes. SERT is a critical target for regulating 5-HT levels and consequently, modulating the intestinal physiology. The deregulation of innate immune receptors has been extensively studied in inflammatory bowel diseases (IBD), where an exacerbated defense response to commensal microbiota is observed. Interestingly, many innate immune receptors seem to affect the serotonergic system, demonstrating a new way in which microbiota could modulate the intestinal physiology. Therefore, our aim was to analyze the effects of NOD1 activation on SERT function, as well as NOD1's interaction with other immune receptors such as TLR2 and TLR4. Our results showed that NOD1 activation inhibits SERT activity and expression in Caco-2/TC7 cells through the extracellular signal-regulated kinase (ERK) signaling pathway. A negative feedback between 5-HT and NOD1 expression was also described. The results showed that TLR2 and TLR4 activation seems to regulate NOD1 expression in Caco-2/TC7 cells. To assess the extend of cross-talk between NOD1 and TLRs, NOD1 expression was measured in the intestinal tract (ileum and colon) of wild type mice and mice with individual knockouts of TLR2, and TLR4 as well as double knockout TLR2/TLR4 mice. Hence, we demonstrate that NOD1 acts on the serotonergic system decreasing SERT activity and molecular expression. Additionally, NOD1 expression seems to be modulated by 5-HT and other immune receptors as TLR2 and TLR4. This study could clarify the relation between both the intestinal serotonergic system and innate immune system, and their implications in intestinal inflammation.

Bifidobacterium pseudocatenulatum CECT 7765 Ameliorates Neuroendocrine Alterations Associated with an Exaggerated Stress Response and Anhedonia in Obese Mice

Obesity, besides being a problem of metabolic dysfunction, constitutes a risk factor for psychological disorders. Experimental models of diet-induced obesity have revealed that obese animals are prone to anxious and depressive-like behaviors. The present study aimed to evaluate whether Bifidobacterium pseudocatenulatum CECT 7765 could reverse the neurobehavioral consequences of obesity in a high-fat diet (HFD) fed mouse model via regulation of the gut-brain axis. Adult male wild-type C57BL-6 mice were fed a standard diet or HFD, supplemented with either placebo or the bifidobacterial strain for 13 weeks. Behavioral tests were performed, and immune and neuroendocrine parameters were analyzed including leptin and corticosterone and their receptors, Toll-like receptor 2 (TLR2) and neurotransmitters. We found that obese mice showed anhedonia (p < 0.050) indicative of a depressive-like behavior and an exaggerated hypothalamic-pituitary axis (HPA)-mediated stress response to acute physical (p < 0.001) and social stress (p < 0.050), but these alterations were ameliorated by B. pseudocatenulatum CECT 7765 (p < 0.050). These behavioral effects were parallel to reductions of the obesity-associated hyperleptinemia (p < 0.001) and restoration of leptin signaling (p < 0.050), along with fat mass loss (p < 0.010). B. pseudocatenulatum CECT 7765 administration also led to restoration of the obesity-induced reductions in adrenaline in the hypothalamus (p < 0.010), involved in the hypothalamic control of energy balance. Furthermore, the bifidobacterial strain reduced the obesity-induced upregulation of TLR2 protein or gene expression in the intestine (p < 0.010) and the hippocampus (p < 0.050) and restored the alterations of 5-HT levels in the hippocampus (p < 0.050), which could contribute to attenuating the obesity-associated depressive-like behavior (p < 0.050). In summary, the results indicate that B. pseudocatenulatum CECT 7765 could play a role in depressive behavior comorbid with obesity via regulation of endocrine and immune mediators of the gut-brain axis.

Toll-like receptors 2 and 4 modulate intestinal IL-10 differently in ileum and colon

Background

Inflammatory bowel diseases are consequence of an intestinal homeostasis breakdown in which innate immune dysregulation is implicated. Toll-like receptor (TLR)2 and TLR4 are immune recognition receptors expressed in the intestinal epithelium, the first physical-physiological barrier for microorganisms, to inform the host of the presence of Gram-positive and Gram-negative organisms. Interleukin (IL)-10 is an essential anti-inflammatory cytokine that contributes to maintenance of intestinal homeostasis.

Aim

Our main aim was to investigate intestinal IL-10 synthesis and release, and whether TLR2 and TLR4 are determinants of IL-10 expression in the intestinal tract.

Methods

We used Caco-2 cell line as an enterocyte-like cell model, and also ileum and colon from mice deficient in TLR2, TLR4 or TLR2/4 to test the involvement of TLR signaling.

Results

Intestinal epithelial cells are able to synthesize and release IL-10 and their expression is increased after TLR2 or TLR4 activation. IL-10 regulation seems to be tissue specific, with IL-10 expression in the ileum regulated by a compensation between TLR2 and TLR4 expression, whereas in the colon, TLR2 and TLR4 affect IL-10 expression independently.

Conclusions

Intestinal epithelial cells could release IL-10 in response to TLR activation, playing an intestinal tissue-dependent and critical intestinal immune role.