DSS-induced inflammation in the colon drives a proinflammatory signature in the brain that is ameliorated by prophylactic treatment with the S100A9 inhibitor paquinimod

1,3-Dioleoyl-2-palmitoyl-glycerol and 1-oleoyl-2-palmitoyl-3-linoleoyl-glycerol: Structure-function relationship, triacylglycerols preparation, nutrition value

Based on multivariate statistics, this review compared major triacylglycerols (TAGs) in animal milk and human milk fat from China and other countries. Human milk fat differs from animal milk fat in that it has longer acyl chains and higher concentrations of 1,3-dioleoyl-2-palmitoyl-glycerol (O-P-O) and 1-oleoyl-2-palmitoyl-3-linoleoylglycerol (O-P-L). O-P-L is a significant and distinct TAG in human milk fat, particularly in China. 1-oleoyl-2-palmitoyl-3-linoleoylglycerol (OPL) is human milk's major triglyceride molecule of O-P-L, accounting for more than 70%. As a result, OPL has piqued the interest of Chinese academics. The synthesis process and nutritional outcomes of OPL have been studied, including changes in gut microbiota, serum lipid composition, improved fatty acid and calcium absorption, and increased total bile acid levels. However, current OPL research is limited. Therefore, this review discussed enzymatic preparation of 1,3-dioleoyl-2-palmitoyl-glycerol (OPO) and OPL and their nutritional and physiological activity to direct future research direction for sn-2 palmitate and OPL.

Subclinical peripheral inflammation has systemic effects impacting central nervous system proteome in budgerigars

Regulation of neuroimmune interactions varies across avian species. Little is presently known about the interplay between periphery and central nervous system (CNS) in parrots, birds sensitive to neuroinflammation. Here we investigated the systemic and CNS responses to dextran sulphate sodium (DSS)- and lipopolysaccharide (LPS)-induced subclinical acute peripheral inflammation in budgerigar (Melopsittacus undulatus). Three experimental treatment groups differing in DSS and LPS stimulation were compared to controls. Individuals treated with DSS showed significant histological intestinal damage. Through quantitative proteomics we described changes in plasma (PL) and cerebrospinal fluid (CSF) composition. In total, we identified 180 proteins in PL and 978 proteins in CSF, with moderate co-structure between the proteomes. Between treatments we detected differences in immune, coagulation and metabolic pathways. Proteomic variation was associated with the levels of pro-inflammatory cytokine mRNA expression in intestine and brain. Our findings shed light on systemic impacts of peripheral low-grade inflammation in birds.

BPOZ-2-deficient mice exhibit aggravated inflammation-associated tissue damage after acute dextran sodium sulfate or diethylnitrosamine exposure

An excessive inflammatory response plays an important role in pathological tissue damage associated with pathogen infection and tumorigenesis. Blood POZ-containing gene type 2 (BPOZ-2), an adaptor protein for the E3 ubiquitin ligase scaffold protein CUL3, is a negative regulator of the inflammatory response. In this study, we investigated the pathophysiological functions of BPOZ-2 in dextran sodium sulfate (DSS)-induced colon injury and diethylnitrosamine (DEN)-induced liver damage. Our results indicated that BPOZ-2 deficiency increased IL-1β induction after DSS and DEN treatment. In addition, BPOZ-2-deficient mice were more susceptible to DSS-induced colitis. Notably, BPOZ-2 deficiency aggravated DEN-induced acute liver injury. These results revealed that BPOZ-2 protected against pathological tissue damage with a dysregulated inflammatory response.

Sex-dependent effects of carbohydrate source and quantity on caspase-1 activity in the mouse central nervous system

BACKGROUND

Mounting evidence links glucose intolerance and diabetes as aspects of metabolic dysregulation that are associated with an increased risk of developing dementia. Inflammation and inflammasome activation have emerged as a potential link between these disparate pathologies. As diet is a key factor in both the development of metabolic disorders and inflammation, we hypothesize that long term changes in dietary factors can influence nervous system function by regulating inflammasome activity and that this phenotype would be sex-dependent, as sex hormones are known to regulate metabolism and immune processes.

METHODS

5-week-old male and female transgenic mice expressing a caspase-1 bioluminescent reporter underwent cranial window surgeries and were fed control (65% complex carbohydrates, 15% fat), high glycemic index (65% carbohydrates from sucrose, 15% fat), or ketogenic (1% complex carbohydrates, 79% fat) diet from 6 to 26 weeks of age. Glucose regulation was assessed with a glucose tolerance test following a 4-h morning fast. Bioluminescence in the brain was quantified using IVIS in vivo imaging. Blood cytokine levels were measured using cytokine bead array. 16S ribosomal RNA gene amplicon sequencing of mouse feces was performed to assess alterations in the gut microbiome. Behavior associated with these dietary changes was also evaluated.

RESULTS

The ketogenic diet caused weight gain and glucose intolerance in both male and female mice. In male mice, the high glycemic diet led to increased caspase-1 biosensor activation over the course of the study, while in females the ketogenic diet drove an increase in biosensor activation compared to their respective controls. These changes correlated with an increase in inflammatory cytokines present in the serum of test mice and the emergence of anxiety-like behavior. The microbiome composition differed significantly between diets; however no significant link between diet, glucose tolerance, or caspase-1 signal was established.

CONCLUSIONS

Our findings suggest that diet composition, specifically the source and quantity of carbohydrates, has sex-specific effects on inflammasome activation in the central nervous system and behavior. This phenotype manifested as increased anxiety in male mice, and future studies are needed to determine if this phenotype is linked to alterations in microbiome composition.

Mitochondrial transplantation confers protection against the effects of ischemic stroke by repressing microglial pyroptosis and promoting neurogenesis

JOURNAL/nrgr/04.03/01300535-202406000-00037/inline-graphic1/v/2023-10-30T152229Z/r/image-tiff

Transferring healthy and functional mitochondria to the lateral ventricles confers neuroprotection in a rat model of ischemia-reperfusion injury. Autologous mitochondrial transplantation is also beneficial in pediatric patients with cardiac ischemia-reperfusion injury. Thus, transplantation of functional exogenous mitochondria may be a promising therapeutic approach for ischemic disease. To explore the neuroprotective effect of mitochondria transplantation and determine the underlying mechanism in ischemic stroke, in this study we established a photo-thrombosis-induced mouse model of focal ischemia and administered freshly isolated mitochondria via the tail vein or to the injury site (in situ). Animal behavior tests, immunofluorescence staining, 2,3,5-triphenyltetrazolium chloride (TTC) staining, mRNA-seq, and western blotting were used to assess mouse anxiety and memory, cortical infarct area, pyroptosis, and neurogenesis, respectively. Using bioinformatics analysis, western blotting, co-immunoprecipitation, and mass spectroscopy, we identified S100 calcium binding protein A9 (S100A9) as a potential regulator of mitochondrial function and determined its possible interacting proteins. Interactions between exogenous and endogenous mitochondria, as well as the effect of exogenous mitochondria on recipient microglia, were assessed in vitro. Our data showed that: (1) mitochondrial transplantation markedly reduced mortality and improved emotional and cognitive function, as well as reducing infarct area, inhibiting pyroptosis, and promoting cortical neurogenesis; (2) microglial expression of S100A9 was markedly increased by ischemic injury and regulated mitochondrial function; (3) in vitro, exogenous mitochondria enhanced mitochondrial function, reduced redox stress, and regulated microglial polarization and pyroptosis by fusing with endogenous mitochondria; and (4) S100A9 promoted internalization of exogenous mitochondria by the microglia, thereby amplifying their pro-proliferation and anti-inflammatory effects. Taken together, our findings show that mitochondrial transplantation protects against the deleterious effects of ischemic stroke by suppressing pyroptosis and promoting neurogenesis, and that S100A9 plays a vital role in promoting internalization of exogenous mitochondria.

Alleviating depressive-like behavior in DSS-induced colitis mice: Exploring naringin and poncirin from Poncirus trifoliata extracts

Patients with inflammatory bowel diseases (IBDs), including ulcerative colitis (UC) and Crohn's disease (CD), often have concomitant mental disorders such as depression and anxiety. Therefore, a bidirectional approach involving the gut and brain axes is necessary for the prevention and treatment thereof. In this study, we explored the potential of Poncirus trifoliata extract (PT), traditionally known for its neuroprotective effects against gastrointestinal diseases, as a natural treatment agent for IBD in a dextran sulfate sodium (DSS)-induced colitis model. Oral administration of PT ameliorated weight loss and inflammatory responses in mice with DSS-induced colitis. Furthermore, PT treatment effectively restored the colon length and ameliorated enterocyte death by inhibiting DSS-induced reactive oxygen species (ROS)-mediated necroptosis. The main bioactive components of PT, poncirin and naringin, confirmed using ultra-performance liquid chromatography-quadrupole time-of-flight (UPLC-qTOF), can be utilized to regulate necroptosis. The antidepressant-like effects of PT were confirmed using open field test (OFT) and tail suspension test (TST). PT treatment also restored vascular endothelial cell integrity in the hippocampus. In the Cornu Ammonis 1 (CA1) and dentate gyrus (DG) regions of the hippocampus, PT controlled the neuroinflammatory responses of proliferated microglia. In conclusion, PT, which contains high levels of poncirin and naringin, has potential as a bidirectional therapeutic agent that can simultaneously improve IBD-associated intestinal and mental disorders.

Sex-dependent interactions between prodromal intestinal inflammation and LRRK2 G2019S in mice promote endophenotypes of Parkinson's disease

Gastrointestinal (GI) disruptions and inflammatory bowel disease (IBD) are commonly associated with Parkinson's disease (PD), but how they may impact risk for PD remains poorly understood. Herein, we provide evidence that prodromal intestinal inflammation expedites and exacerbates PD endophenotypes in rodent carriers of the human PD risk allele LRRK2 G2019S in a sex-dependent manner. Chronic intestinal damage in genetically predisposed male mice promotes α-synuclein aggregation in the substantia nigra, loss of dopaminergic neurons and motor impairment. This male bias is preserved in gonadectomized males, and similarly conferred by sex chromosomal complement in gonadal females expressing human LRRK2 G2019S. The early onset and heightened severity of neuropathological and behavioral outcomes in male LRRK2 G2019S mice is preceded by increases in α-synuclein in the colon, α-synuclein-positive macrophages in the colonic lamina propria, and loads of phosphorylated α-synuclein within microglia in the substantia nigra. Taken together, these data reveal that prodromal intestinal inflammation promotes the pathogenesis of PD endophenotypes in male carriers of LRRK2 G2019S, through mechanisms that depend on genotypic sex and involve early accumulation of α-synuclein in myeloid cells within the gut.

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.

Colitis reduces active social engagement in mice and is ameliorated by supplementation with human microbiota members

Multiple neurological disorders are associated with gastrointestinal (GI) symptoms, including autism spectrum disorder (ASD). However, it is unclear whether GI distress itself can modify aspects of behavior. Here, we show that mice that experience repeated colitis have impaired active social engagement, as measured by interactions with a foreign mouse, even though signs of colitis were no longer present. We then tested the hypothesis that individuals with ASD harbor a microbiota that might differentially influence GI health by performing microbiota transplantation studies into male germfree animals, followed by induction of colitis. Animals that harbor a microbiota from ASD individuals have worsened gut phenotypes when compared to animals colonized with microbiotas from familial neurotypical (NT) controls. We identify the enrichment of Blautia species in all familial NT controls and observe an association between elevated abundance of Bacteroides uniformis and reductions in intestinal injury. Oral treatment with either of these microbes reduces colon injury in mice. Finally, provision of a Blautia isolate from a NT control ameliorates gut injury-associated active social engagement in mice. Collectively, our data demonstrate that past intestinal distress is associated with changes in active social behavior in mice that can be ameliorated by supplementation of members of the human microbiota.

From gut to brain: understanding the role of microbiota in inflammatory bowel disease

With the proposal of the "biological-psychological-social" model, clinical decision-makers and researchers have paid more attention to the bidirectional interactive effects between psychological factors and diseases. The brain-gut-microbiota axis, as an important pathway for communication between the brain and the gut, plays an important role in the occurrence and development of inflammatory bowel disease. This article reviews the mechanism by which psychological disorders mediate inflammatory bowel disease by affecting the brain-gut-microbiota axis. Research progress on inflammatory bowel disease causing "comorbidities of mind and body" through the microbiota-gut-brain axis is also described. In addition, to meet the needs of individualized treatment, this article describes some nontraditional and easily overlooked treatment strategies that have led to new ideas for "psychosomatic treatment".

Locus coeruleus injury modulates ventral midbrain neuroinflammation during DSS-induced colitis

Parkinson's disease (PD) is characterized by a decades-long prodrome, consisting of a collection of non-motor symptoms that emerges prior to the motor manifestation of the disease. Of these non-motor symptoms, gastrointestinal dysfunction and deficits attributed to central norepinephrine (NE) loss, including mood changes and sleep disturbances, are frequent in the PD population and emerge early in the disease. Evidence is mounting that injury and inflammation in the gut and locus coeruleus (LC), respectively, underlie these symptoms, and the injury of these systems is central to the progression of PD. In this study, we generate a novel two-hit mouse model that captures both features, using dextran sulfate sodium (DSS) to induce gut inflammation and N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) to lesion the LC. We first confirmed the specificity of DSP-4 for central NE using neurochemical methods and fluorescence light-sheet microscopy of cleared tissue, and established that DSS-induced outcomes in the periphery, including weight loss, gross indices of gut injury and systemic inflammation, the loss of tight junction proteins in the colonic epithelium, and markers of colonic inflammation, were unaffected with DSP-4 pre-administration. We then measured alterations in neuroimmune gene expression in the ventral midbrain in response to DSS treatment alone as well as the extent to which prior LC injury modified this response. In this two-hit model we observed that DSS-induced colitis activates the expression of key cytokines and chemokines in the ventral midbrain only in the presence of LC injury and the typical DSS-associated neuroimmune is blunted by pre-LC lesioning with DSP-4. In all, this study supports the growing appreciation for the LC as neuroprotective against inflammation-induced brain injury and draws attention to the potential for NEergic interventions to exert disease-modifying effects under conditions where peripheral inflammation may compromise ventral midbrain dopaminergic neurons and increase the risk for development of PD.

A leaky gut dysregulates gene networks in the brain associated with immune activation, oxidative stress, and myelination in a mouse model of colitis

The gut and brain are increasingly linked in human disease, with neuropsychiatric conditions classically attributed to the brain showing an involvement of the intestine and inflammatory bowel diseases (IBDs) displaying an ever-expanding list of neurological comorbidities. To identify molecular systems that underpin this gut-brain connection and thus discover therapeutic targets, experimental models of gut dysfunction must be evaluated for brain effects. In the present study, we examine disturbances along the gut-brain axis in a widely used murine model of colitis, the dextran sodium sulfate (DSS) model, using high-throughput transcriptomics and an unbiased network analysis strategy coupled with standard biochemical outcome measures to achieve a comprehensive approach to identify key disease processes in both colon and brain. We examine the reproducibility of colitis induction with this model and its resulting genetic programs during different phases of disease, finding that DSS-induced colitis is largely reproducible with a few site-specific molecular features. We focus on the circulating immune system as the intermediary between the gut and brain, which exhibits an activation of pro-inflammatory innate immunity during colitis. Our unbiased transcriptomics analysis provides supporting evidence for immune activation in the brain during colitis, suggests that myelination may be a process vulnerable to increased intestinal permeability, and identifies a possible role for oxidative stress and brain oxygenation. Overall, we provide a comprehensive evaluation of multiple systems in a prevalent experimental model of intestinal permeability, which will inform future studies using this model and others, assist in the identification of druggable targets in the gut-brain axis, and contribute to our understanding of the concomitance of intestinal and neuropsychiatric dysfunction.

Locus coeruleus injury modulates ventral midbrain neuroinflammation during DSS-induced colitis

Parkinson's disease (PD) is characterized by a decades-long prodrome, consisting of a collection of non-motor symptoms that emerges prior to the motor manifestation of the disease. Of these non-motor symptoms, gastrointestinal dysfunction and deficits attributed to central norepinephrine (NE) loss, including mood changes and sleep disturbances, are frequent in the PD population and emerge early in the disease. Evidence is mounting that injury and inflammation in the gut and locus coeruleus (LC), respectively, underlie these symptoms, and the injury of these systems is central to the progression of PD. In this study, we generate a novel two-hit mouse model that captures both features, using dextran sulfate sodium (DSS) to induce gut inflammation and N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) to lesion the LC. We first confirmed the specificity of DSP-4 for central NE using neurochemical methods and fluorescence light-sheet microscopy of cleared tissue, and established that DSS-induced outcomes in the periphery, including weight loss, gross indices of gut injury and systemic inflammation, the loss of tight junction proteins in the colonic epithelium, and markers of colonic inflammation, were unaffected with DSP-4 pre-administration. We then measured alterations in neuroimmune gene expression in the ventral midbrain in response to DSS treatment alone as well as the extent to which prior LC injury modified this response. In this two-hit model we observed that DSS-induced colitis activates the expression of key cytokines and chemokines in the ventral midbrain only in the presence of LC injury and the typical DSS-associated neuroimmune is blunted by pre-LC lesioning with DSP-4. In all, this study supports the growing appreciation for the LC as neuroprotective against inflammation-induced brain injury and draws attention to the potential for NEergic interventions to exert disease-modifying effects under conditions where peripheral inflammation may compromise ventral midbrain dopaminergic neurons and increase the risk for development of PD.

Psychiatric Comorbidities of Inflammatory Bowel Disease: It Is a Matter of Microglia's Gut Feeling

Inflammatory bowel disease (IBD), a common term for Crohn's disease and ulcerative colitis, is a chronic, relapse-remitting condition of the gastrointestinal tract that is increasing worldwide. Psychiatric comorbidities, including depression and anxiety, are more prevalent in IBD patients than in healthy individuals. Evidence suggests that varying levels of neuroinflammation might underlie these states in IBD patients. Within this context, microglia are the crucial non-neural cells in the brain responsible for innate immune responses following inflammatory insults. Alterations in microglia's functions, such as secretory profile, phagocytic activity, and synaptic pruning, might play significant roles in mediating psychiatric manifestations of IBD. In this review, we discuss the role played by microglia in IBD-associated comorbidities.

Triggerable Prodrug Nanocoating Enables On-Demand Activation of Microbial and Small-Molecular Therapeutics for Combination Treatment

The synergy of living microbial and small-molecular therapeutics has been widely explored for treating a variety of diseases, while current combination strategies often suffer from low bioavailability, heterogeneous spatiotemporal distribution, and premature drug release. Here, the use of a triggerable prodrug nanocoating is reported to enable the on-demand activation of microbial and small-molecular therapeutics for combination treatment. As a proof-of-concept study, a reactive oxygen species-responsive aromatic thioacetal linker is employed to prepare cationic chitosan-drug conjugates, which can form a nanocoating on the surface of living bacteria via electrostatic interaction. Following administration, the wrapped bacteria can be prevented from in vivo insults by the shielding effect of the nanocoating and be co-delivered with the conjugated drug in a spatiotemporally synchronous manner. Upon reaching the lesion site, the upgraded reactive oxygen species trigger in situ cleavage of the thioacetal linker, resulting in the release of the conjugated drug and a linker-derived therapeutic cinnamaldehyde. Meanwhile, a charge reversal achieved by the generation of negatively charged thiolated chitosan induces the dissociation of the nanocoating, leading to synchronous release of the living bacteria. The adequate activation of the combined therapeutics at the lesion site exhibits superior synergistic treatment efficacy, as demonstrated by an in vivo assessment using a mouse model of colitis. This work presents an appealing approach to combine living microbial and small-molecular therapeutics for advanced therapy of diseases.

Altered peripheral taste function in a mouse model of inflammatory bowel disease

Increased sugar intake and taste dysfunction have been reported in patients with inflammatory bowel disease (IBD), a chronic disorder characterized by diarrhea, pain, weight loss and fatigue. It was previously unknown whether taste function changes in mouse models of IBD. Mice consumed dextran sodium sulfate (DSS) during three 7-day cycles to induce chronic colitis. DSS-treated mice displayed signs of disease, including significant weight loss, diarrhea, loss of colon architecture, and inflammation of the colon. After the last DSS cycle we assessed taste function by recording electrophysiological responses from the chorda tympani (CT) nerve, which transmits activity from lingual taste buds to the brain. DSS treatment significantly reduced neural taste responses to natural and artificial sweeteners. Responses to carbohydrate, salt, sour or bitter tastants were unaffected in mice with colitis, but umami responses were modestly elevated. DSS treatment modulated the expression of receptor subunits that transduce sweet and umami stimuli in oral taste buds as a substrate for functional changes. Dysregulated systemic cytokine responses or dysbiosis that occurs during chronic colitis may be upstream from changes in oral taste buds. We demonstrate for the first time that colitis alters taste input to the brain, which could exacerbate malnutrition in IBD patients.

Vitamin D3 affects the gut microbiota in an LPS-stimulated systemic inflammation mouse model

Although gut dysbiosis contributes to systemic inflammation, the counteractive effect of systemic inflammation on gut microbiota is unknown. Vitamin D may exert anti-inflammatory effects against systemic inflammation, but its regulation of the gut microbiota is poorly understood. In this study, mice were intraperitoneally injected with lipopolysaccharide (LPS) to create a systemic inflammation model and received vitamin D3 treatment orally for 18 continuous days. Then, body weight, morphological changes in the colon epithelium, and gut microbiota (n = 3) were evaluated. We verified that LPS stimulation caused inflammatory changes in the colon epithelium, which could be obviously attenuated by vitamin D3 treatment (10 μg/kg/day) in mice. Then, 16S rRNA gene sequencing of the gut microbiota first revealed that LPS stimulation induced a large number of operational taxonomic units, and vitamin D3 treatment reduced the number. In addition, vitamin D3 had distinctive effects on the community structure of the gut microbiota, which was obviously changed after LPS stimulation. However, neither LPS nor vitamin D3 affected the alpha and beta diversity of the gut microbiota. Furthermore, statistical analysis of differential microorganisms showed that the relative abundance of microorganisms in the phylum Spirochaetes decreased, the family Micrococcaceae increased, the genus [Eubacterium]_brachy_group decreased, the genus Pseudarthrobacter increased, and the species Clostridiales_bacterium_CIEAF_020 decreased under LPS stimulation, but vitamin D3 treatment significantly reversed the LPS-induced changes in the relative abundance of these microorganisms. In conclusion, vitamin D3 treatment affected the gut microbiota and alleviated inflammatory changes in the colon epithelium in the LPS-stimulated systemic inflammation mouse model.

Systematic analysis and characterization of long non-coding RNA genes in inflammatory bowel disease

The cases of inflammatory bowel disease (IBD) are increasing rapidly around the world. Due to the multifactorial causes of IBD, there is an urgent need to understand the pathogenesis of IBD. As such, the usage of high-throughput techniques to profile genetic mutations, microbiome environments, transcriptome and proteome (e.g. lipidome) is increasing to understand the molecular changes associated with IBD, including two major etiologies of IBD: Crohn disease (CD) and ulcerative colitis (UC). In the case of transcriptome data, RNA sequencing (RNA-seq) technique is used frequently. However, only protein-coding genes are analyzed, leaving behind all other RNAs, including non-coding RNAs (ncRNAs) to be unexplored. Among these ncRNAs, long non-coding RNAs (lncRNAs) may hold keys to understand the pathogenesis of IBD as lncRNAs are expressed in a cell/tissue-specific manner and dysregulated in a disease, such as IBD. However, it is rare that RNA-seq data are analyzed for lncRNAs. To fill this gap in knowledge, we re-analyzed RNA-seq data of CD and UC patients compared with the healthy donors to dissect the expression profiles of lncRNA genes. As inflammation plays key roles in the pathogenesis of IBD, we conducted loss-of-function experiments to provide functional data of IBD-specific lncRNA, lung cancer associated transcript 1 (LUCAT1), in an in vitro model of macrophage polarization. To further facilitate the lncRNA research in IBD, we built a web database, IBDB (https://ibd-db.shinyapps.io/IBDB/), to provide a one-stop-shop for expression profiling of protein-coding and lncRNA genes in IBD patients compared with healthy donors.

Altered peripheral taste function in a mouse model of inflammatory bowel disease

Increased sugar intake and taste dysfunction have been reported in patients with inflammatory bowel disease (IBD), a chronic disorder characterized by diarrhea, pain, weight loss and fatigue. It was previously unknown whether taste function changes in mouse models of IBD. Mice consumed dextran sodium sulfate (DSS) during three 7-day cycles to induce chronic colitis. DSS-treated mice displayed signs of disease, including significant weight loss, diarrhea, loss of colon architecture, and inflammation of the colon. After the last DSS cycle we assessed taste function by recording electrophysiological responses from the chorda tympani (CT) nerve, which transmits activity from lingual taste buds to the brain. DSS treatment significantly reduced neural taste responses to natural and artificial sweeteners. Responses to carbohydrate, salt, sour or bitter tastants were unaffected in mice with colitis, but umami responses were modestly elevated. DSS treatment modulated the expression of receptor subunits that transduce sweet and umami stimuli in oral taste buds as a substrate for functional changes. Dysregulated systemic cytokine responses, or dysbiosis that occurs during chronic colitis may be upstream from changes in oral taste buds. We demonstrate for the first time that colitis alters taste input to the brain, which could exacerbate malnutrition in IBD patients.

Repeated closed-head mild traumatic brain injury-induced inflammation is associated with nociceptive sensitization

BACKGROUND

Individuals who have experienced mild traumatic brain injuries (mTBIs) suffer from several comorbidities, including chronic pain. Despite extensive studies investigating the underlying mechanisms of mTBI-associated chronic pain, the role of inflammation in long-term pain after mTBIs is not fully elucidated. Given the shifting dynamics of inflammation, it is important to understand the spatial-longitudinal changes in inflammatory processes following mTBIs and their effects on TBI-related pain.

METHODS

We utilized a recently developed transgenic caspase-1 luciferase reporter mouse model to monitor caspase-1 activation through a thinned skull window in the in vivo setting following three closed-head mTBI events. Organotypic coronal brain slice cultures and acutely dissociated dorsal root ganglion (DRG) cells provided tissue-relevant context of inflammation signal. Mechanical allodynia was assessed by mechanical withdrawal threshold to von Frey and thermal hyperalgesia withdrawal latency to radiant heat. Mouse grimace scale (MGS) was used to detect spontaneous or non-evoked pain. In some experiments, mice were prophylactically treated with MCC950, a potent small molecule inhibitor of NLRP3 inflammasome assembly to inhibit injury-induced inflammatory signaling. Bioluminescence spatiotemporal dynamics were quantified in the head and hind paws, and caspase-1 activation was confirmed by immunoblot. Immunofluorescence staining was used to monitor the progression of astrogliosis and microglial activation in ex vivo brain tissue following repetitive closed-head mTBIs.

RESULTS

Mice with repetitive closed-head mTBIs exhibited significant increases of the bioluminescence signals within the brain and paws in vivo for at least one week after each injury. Consistently, immunoblotting and immunofluorescence experiments confirmed that mTBIs led to caspase-1 activation, astrogliosis, and microgliosis. Persistent changes in MGS and hind paw withdrawal thresholds, indicative of pain states, were observed post-injury in the same mTBI animals in vivo. We also observed enhanced inflammatory responses in ex vivo brain slice preparations and DRG for at least 3 days following mTBIs. In vivo treatment with MCC950 significantly reduced caspase-1 activation-associated bioluminescent signals in vivo and decreased stimulus-evoked and non-stimulus evoked nociception.

CONCLUSIONS

Our findings suggest that the inflammatory states in the brain and peripheral nervous system following repeated mTBIs are coincidental with the development of nociceptive sensitization, and that these events can be significantly reduced by inhibition of NLRP3 inflammasome activation.

A leaky gut dysregulates gene networks in the brain associated with immune activation, oxidative stress, and myelination in a mouse model of colitis

The gut and brain are increasingly linked in human disease, with neuropsychiatric conditions classically attributed to the brain showing an involvement of the intestine and inflammatory bowel diseases (IBDs) displaying an ever-expanding list of neurological comorbidities. To identify molecular systems that underpin this gut-brain connection and thus discover therapeutic targets, experimental models of gut dysfunction must be evaluated for brain effects. In the present study, we examine disturbances along the gut-brain axis in a widely used murine model of colitis, the dextran sodium sulfate (DSS) model, using high-throughput transcriptomics and an unbiased network analysis strategy coupled with standard biochemical outcome measures to achieve a comprehensive approach to identify key disease processes in both colon and brain. We examine the reproducibility of colitis induction with this model and its resulting genetic programs during different phases of disease, finding that DSS-induced colitis is largely reproducible with a few site-specific molecular features. We focus on the circulating immune system as the intermediary between the gut and brain, which exhibits an activation of pro-inflammatory innate immunity during colitis. Our unbiased transcriptomics analysis provides supporting evidence for immune activation in the brain during colitis, suggests that myelination may be a process vulnerable to increased intestinal permeability, and identifies a possible role for oxidative stress and brain oxygenation. Overall, we provide a comprehensive evaluation of multiple systems in a prevalent experimental model of intestinal permeability, which will inform future studies using this model and others, assist in the identification of druggable targets in the gut-brain axis, and contribute to our understanding of the concomitance of intestinal and neuropsychiatric dysfunction.

Mutant LRRK2 exacerbates immune response and neurodegeneration in a chronic model of experimental colitis

The link between the gut and the brain in Parkinson's disease (PD) pathogenesis is currently a subject of intense research. Indeed, gastrointestinal dysfunction is known as an early symptom in PD and inflammatory bowel disease (IBD) has recently been recognised as a risk factor for PD. The leucine-rich repeat kinase 2 (LRRK2) is a PD- and IBD-related protein with highest expression in immune cells. In this study, we provide evidence for a central role of LRRK2 in gut inflammation and PD. The presence of the gain-of-function G2019S mutation significantly increases the disease phenotype and inflammatory response in a mouse model of experimental colitis based on chronic dextran sulphate sodium (DSS) administration. Bone marrow transplantation of wild-type cells into G2019S knock-in mice fully rescued this exacerbated response, proving the key role of mutant LRRK2 in immune cells in this experimental colitis model. Furthermore, partial pharmacological inhibition of LRRK2 kinase activity also reduced the colitis phenotype and inflammation. Moreover, chronic experimental colitis also induced neuroinflammation and infiltration of peripheral immune cells into the brain of G2019S knock-in mice. Finally, combination of experimental colitis with overexpression of α-synuclein in the substantia nigra aggravated motor deficits and dopaminergic neurodegeneration in G2019S knock-in mice. Taken together, our results link LRRK2 with the immune response in colitis and provide evidence that gut inflammation can impact brain homeostasis and contribute to neurodegeneration in PD.

Lipocalin 2 in the Paraventricular Thalamic Nucleus Contributes to DSS-Induced Depressive-Like Behaviors

The incidence rate of anxiety and depression is significantly higher in patients with inflammatory bowel diseases (IBD) than in the general population. The mechanisms underlying dextran sulfate sodium (DSS)-induced depressive-like behaviors are still unclear. We clarified that IBD mice induced by repeated administration of DSS presented depressive-like behaviors. The paraventricular thalamic nucleus (PVT) was regarded as the activated brain region by the number of c-fos-labeled neurons. RNA-sequencing analysis showed that lipocalin 2 (Lcn2) was upregulated in the PVT of mice with DSS-induced depressive behaviors. Upregulating Lcn2 from neuronal activity induced dendritic spine loss and the secreted protein induced chemokine expression and subsequently contributed to microglial activation leading to blood-brain barrier permeability. Moreover, Lcn2 silencing in the PVT alleviated the DSS-induced depressive-like behaviors. The present study demonstrated that elevated Lcn2 in the PVT is a critical factor for DSS-induced depressive behaviors.

Effect of Systemic Inflammation in the CNS: A Silent History of Neuronal Damage

Central nervous system (CNS) infections including meningitis and encephalitis, resulting from the blood-borne spread of specific microorganisms, provoke nervous tissue damage due to the inflammatory process. Moreover, different pathologies such as sepsis can generate systemic inflammation. Bacterial lipopolysaccharide (LPS) induces the release of inflammatory mediators and damage molecules, which are then released into the bloodstream and can interact with structures such as the CNS, thus modifying the blood-brain barrier's (BBB´s) and blood-cerebrospinal fluid barrier´s (BCSFB´s) function and inducing aseptic neuroinflammation. During neuroinflammation, the participation of glial cells (astrocytes, microglia, and oligodendrocytes) plays an important role. They release cytokines, chemokines, reactive oxygen species, nitrogen species, peptides, and even excitatory amino acids that lead to neuronal damage. The neurons undergo morphological and functional changes that could initiate functional alterations to neurodegenerative processes. The present work aims to explain these processes and the pathophysiological interactions involved in CNS damage in the absence of microbes or inflammatory cells.

Blockage of S100A8/A9 ameliorates septic nephropathy in mice

Septic acute kidney injury (AKI) is the commonest cause of complication of sepsis in intensive care units, but its pathophysiology remains unclear. Calprotectin (S100A8/A9), which is a damage-associated molecular patterns (DAMPs) molecule, exerts a critical role in modulating leukocyte recruitment and inflammatory response during various diseases. However, role of S100A8/A9 in septic AKI is largely unknown. In this research, Septic AKI was triggered by cecal ligation and puncture (CLP) operation in wild-type mice, which treated with or without an S100A9 inhibitor, Paquinimod (Paq, 10 mg/kg) that prevents S100A8/A9 to bind to Toll-like receptor 4 (TLR4). Renal function, pathological changes, cell death, and oxidative stress were evaluated. Our research indicated that the mRNA and protein expression of S100A9 are time-dependently elevated in the kidney following CLP. Moreover, the administration of Paq for 24 h significantly improved CLP-induced renal dysfunction and pathological alterations compared with vehicle treatment in mice. These beneficial effects were associated with the inhibition of CLP-triggered renal tubular epithelial cell apoptosis, inflammation, superoxide production, and mitochondrial dynamic imbalance. What's more, we further confirmed the above findings by cell co-culture experiments. Our study demonstrates that S100A9 is a prominent protein to lead to septic AKI, and the selective inhibition of S100A9 could represent a new therapeutic approach which can treat septic AKI.

Proinflammatory activation of microglia in the cerebellum hyperexcites Purkinje cells to trigger ataxia

Specific medications to combat cerebellar ataxias, a group of debilitating movement disorders characterized by difficulty with walking, balance and coordination, are still lacking. Notably, cerebellar microglial activation appears to be a common feature in different types of ataxic patients and rodent models. However, direct evidence that cerebellar microglial activation in vivo is sufficient to induce ataxia is still lacking. Here, by employing chemogenetic approaches to manipulate cerebellar microglia selectively and directly, we found that specific chemogenetic activation of microglia in the cerebellar vermis directly leads to ataxia symptoms in wild-type mice and aggravated ataxic motor deficits in 3-acetylpyridine (3-AP) mice, a classic mouse model of cerebellar ataxia. Mechanistically, cerebellar microglial proinflammatory activation induced by either chemogenetic M3D(Gq) stimulation or 3-AP modeling hyperexcites Purkinje cells (PCs), which consequently triggers ataxia. Blockade of microglia-derived TNF-α, one of the most important proinflammatory cytokines, attenuates the hyperactivity of PCs driven by microglia. Moreover, chemogenetic inhibition of cerebellar microglial activation or suppression of cerebellar microglial activation by PLX3397 and minocycline reduces the production of proinflammatory cytokines, including TNF-α, to effectively restore the overactivation of PCs and alleviate motor deficits in 3-AP mice. These results suggest that cerebellar microglial activation may aggravate the neuroinflammatory response and subsequently induce dysfunction of PCs, which in turn triggers ataxic motor deficits. Our findings thus reveal a causal relationship between proinflammatory activation of cerebellar microglia and ataxic motor symptoms, which may offer novel evidence for therapeutic intervention for cerebellar ataxias by targeting microglia and microglia-derived inflammatory mediators.

Anti-Inflammatory Effects of Allocryptopine via the Target on the CX3CL1-CX3CR1 axis/GNB5/AKT/NF-κB/Apoptosis in Dextran Sulfate-Induced Mice

Allocryptopine (ALL) is an isoquinoline alkaloid extracted from Macleaya cordata(Willd). R. Br., which has been claimed to have anti-inflammatory and neuroprotection properties. However, the mechanism by which ALL ameliorates inflammatory bowel disease (IBD) remains unclear. Here, we used network pharmacology and quantitative proteomic approaches to investigate the effect of ALL on IBD pathogenesis. Network pharmacology predicted potential targets and signaling pathways of ALL's anti-IBD effects. As predicted by network pharmacology, gene ontology (GO) analysis, in terms of the proteomic results, showed that the immune response in mucosa and antimicrobial humoral response were enriched. Further study revealed that the ALL-related pathways were the chemokine signaling pathway and apoptosis in the Kyoto Encyclopedia of Genes and Genomes (KEGG). In addition, we identified AKT1 as a hub for the critical pathways through protein-protein interaction (PPI) network analysis. Similar to mesalazine (MES), Western blot verified that ALL downregulated upstream chemokine CX3CL1 and GNB5 content to reduce phosphorylation of AKT and NF-κB, as well as the degree of apoptosis, to improve inflammatory response in the colon. Our research may shed light on the mechanism by which ALL inhibits the CX3CL1/GNB5/AKT2/NF-κB/apoptosis pathway and improves the intestinal barrier to reduce colitis response and act on the CX3CL1-CX3CR1 axis to achieve neuroprotection.

Inflammatory Animal Models of Parkinson’s Disease

Accumulating evidence suggests that microglia and peripheral immune cells may play determinant roles in the pathogenesis of Parkinson’s disease (PD). Consequently, there is a need to take advantage of immune-related models of PD to study the potential contribution of microglia and peripheral immune cells to the degeneration of the nigrostriatal system and help develop potential therapies for PD. In this review, we have summarised the main PD immune models. From a historical perspective, we highlight first the main features of intranigral injections of different pro-inflammogens, including lipopolysaccharide (LPS), thrombin, neuromelanin, etc. The use of adenoviral vectors to promote microglia-specific overexpression of different molecules in the ventral mesencephalon, including α-synuclein, IL-1β, and TNF, are also presented and briefly discussed. Finally, we summarise different models associated with peripheral inflammation whose contribution to the pathogenesis of neurodegenerative diseases is now an outstanding question. Illustrative examples included systemic LPS administration and dextran sulfate sodium-induced colitis in rodents.

The Gut–Immune–Brain Axis: An Important Route for Neuropsychiatric Morbidity in Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) comprises Crohn’s disease (CD) and ulcerative colitis (UC) and is associated with neuropsychiatric symptoms like anxiety and depression. Both conditions strongly worsen IBD disease burden. In the present review, we summarize the current understanding of the pathogenesis of depression and anxiety in IBD. We present a stepwise cascade along a gut–immune–brain axis initiated by evasion of chronic intestinal inflammation to pass the epithelial and vascular barrier in the gut and cause systemic inflammation. We then summarize different anatomical transmission routes of gut-derived peripheral inflammation into the central nervous system (CNS) and highlight the current knowledge on neuroinflammatory changes in the CNS of preclinical IBD mouse models with a focus on microglia, the brain-resident macrophages. Subsequently, we discuss how neuroinflammation in IBD can alter neuronal circuitry to trigger symptoms like depression and anxiety. Finally, the role of intestinal microbiota in the gut–immune–brain axis in IBD will be reviewed. A more comprehensive understanding of the interaction between the gastrointestinal tract, the immune system and the CNS accounting for the similarities and differences between UC and CD will pave the path for improved prediction and treatment of neuropsychiatric comorbidities in IBD and other inflammatory diseases.

Prior episode of colitis impairs contextual fear memory

Accumulating evidence has shown that intestinal inflammations in inflammatory bowel disease (IBD) also drive pathological responses in organs outside the intestine, including the brain. Previous studies using the dextran sodium sulfate (DSS)-induced colitis model have shown that colonic inflammation contributes to the development of anxiety- and depression-related behaviors; however, little is known about whether memory function is affected. Here, we subjected male and female C57BL/6J mice to DSS-induced colitis for 6 days, followed by Pavlovian conditioned fear (CF) tests 15 days after the start of inflammation, when local colonic inflammation has receded. The contextual and cued CF tests were used to assess associative fear memory. We found that DSS-induced colitis led to significant impairment in contextual fear memory in both male and female mice; on the other hand, auditory cued fear memories were comparable between control and DSS-treated mice. There were marked signs of astrogliosis in the hippocampal regions 17 days (D17) after colitis induction. Furthermore, molecular characterization of hippocampi showed marked but transient increases in the expression of inflammatory genes Nfkb, Trem2 (microglial marker), GFAP (astrocyte marker), Il1b, and S100a8 in DSS-treated mice. While the expression of Nfkb, Trem2, and GFAP showed a peak on day 10, the S100a8 expression was high on days 10 and 17 and subsided on day 42. Interestingly, expression of Bdnf remained elevated in the times assessed (D10, 17, 42). Together, these results demonstrated that DSS-induced colitis could induce prolonged neuroinflammation and impaired contextual fear memory.

PARK7/DJ-1 as a Therapeutic Target in Gut-Brain Axis Diseases

It is increasingly known that Parkinson's (PD) and Alzheimer's (AD) diseases occur more frequently in patients with inflammatory gastrointestinal diseases including inflammatory bowel (IBD) or celiac disease, indicating a pathological link between them. Although epidemiological observations suggest the existence of the gut-brain axis (GBA) involving systemic inflammatory and neural pathways, little is known about the exact molecular mechanisms. Parkinson's disease 7 (PARK7/DJ-1) is a multifunctional protein whose protective role has been widely demonstrated in neurodegenerative diseases, including PD, AD, or ischemic stroke. Recent studies also revealed the importance of PARK7/DJ-1 in the maintenance of the gut microbiome and also in the regulation of intestinal inflammation. All these findings suggest that PARK7/DJ-1 may be a link and also a potential therapeutic target in gut and brain diseases. In this review, therefore, we discuss our current knowledge about PARK7/DJ-1 in the context of GBA diseases.

Monitoring of inflammation using novel biosensor mouse model reveals tissue- and sex-specific responses to Western diet

Obesity is an epidemic, and it is characterized by a state of low-grade systemic inflammation. A key component of inflammation is the activation of inflammasomes, multiprotein complexes that form in response to danger signals and that lead to activation of caspase-1. Previous studies have found that a Westernized diet induces activation of inflammasomes and production of inflammatory cytokines. Gut microbiota metabolites, including the short-chain fatty acid butyrate, have received increased attention as underlying some obesogenic features, but the mechanisms of action by which butyrate influences inflammation in obesity remain unclear. We engineered a caspase-1 reporter mouse model to measure spatiotemporal dynamics of inflammation in obese mice. Concurrent with increased capsase-1 activation in vivo, we detected stronger biosensor signal in white adipose and heart tissues of obese mice ex vivo and observed that a short-term butyrate treatment affected some, but not all, of the inflammatory responses induced by Western diet. Through characterization of inflammatory responses and computational analyses, we identified tissue- and sex-specific caspase-1 activation patterns and inflammatory phenotypes in obese mice, offering new mechanistic insights underlying the dynamics of inflammation.

Mitochondrial damage-associated molecular patterns trigger arginase-dependent lymphocyte immunoregulation

Tissue damage leads to loss of cellular and mitochondrial membrane integrity and release of damage-associated molecular patterns, including those of mitochondrial origin (mitoDAMPs). Here, we describe the lymphocyte response to mitoDAMPs. Using primary cells from mice and human donors, we demonstrate that natural killer (NK) cells and T cells adopt regulatory phenotypes and functions in response to mitoDAMPs. NK cell-mediated cytotoxicity, interferon gamma (IFN-γ) production, T cell proliferation, and in vivo anti-viral T cell activation are all interrupted in the presence of mitoDAMPs or mitoDAMP-rich irradiated cells in in vitro and in vivo assays. Mass spectrometry analysis of mitoDAMPs demonstrates that arginase and products of its enzymatic activity are prevalent in mitoDAMP preparations. Functional validation by arginase inhibition and/or arginine add-back shows that arginine depletion is responsible for the alteration in immunologic polarity. We conclude that lymphocyte responses to mitoDAMPs reflect a highly conserved mechanism that regulates inflammation in response to tissue injury.

Recruitment of α4β7 monocytes and neutrophils to the brain in experimental colitis is associated with elevated cytokines and anxiety-like behavior

Background

Behavioral comorbidities, such as anxiety and depression, are a prominent feature of IBD. The signals from the inflamed gut that cause changes in the brain leading to these behavioral comorbidities remain to be fully elucidated. We tested the hypothesis that enhanced leukocyte–cerebral endothelial cell interactions occur in the brain in experimental colitis, mediated by α4β7 integrin, to initiate neuroimmune activation and anxiety-like behavior.

Methods

Female mice treated with dextran sodium sulfate were studied at the peak of acute colitis. Circulating leukocyte populations were determined using flow cytometry. Leukocyte–cerebral endothelial cell interactions were examined using intravital microscopy in mice treated with anti-integrin antibodies. Brain cytokine and chemokines were assessed using a multiplex assay in animals treated with anti-α4β7 integrin. Anxiety-like behavior was assessed using an elevated plus maze in animals after treatment with an intracerebroventricular injection of interleukin 1 receptor antagonist.

Results

The proportion of classical monocytes expressing α4β7 integrin was increased in peripheral blood of mice with colitis. An increase in the number of rolling and adherent leukocytes on cerebral endothelial cells was observed, the majority of which were neutrophils. Treatment with anti-α4β7 integrin significantly reduced the number of rolling leukocytes. After anti-Ly6C treatment to deplete monocytes, the number of rolling and adhering neutrophils was significantly reduced in mice with colitis. Interleukin-1β and CCL2 levels were elevated in the brain and treatment with anti-α4β7 significantly reduced them. Enhanced anxiety-like behavior in mice with colitis was reversed by treatment with interleukin 1 receptor antagonist.

Conclusions

In experimental colitis, α4β7 integrin-expressing monocytes direct the recruitment of neutrophils to the cerebral vasculature, leading to elevated cytokine levels. Increased interleukin-1β mediates anxiety-like behavior.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02431-z.

Neuroinflammation as an etiological trigger for depression comorbid with inflammatory bowel disease

Patients with inflammatory bowel disease (IBD) suffer from depression at higher rates than the general population. An etiological trigger of depressive symptoms is theorised to be inflammation within the central nervous system. It is believed that heightened intestinal inflammation and dysfunction of the enteric nervous system (ENS) contribute to impaired intestinal permeability, which facilitates the translocation of intestinal enterotoxins into the blood circulation. Consequently, these may compromise the immunological and physiological functioning of distant non-intestinal tissues such as the brain. In vivo models of colitis provide evidence of increased blood–brain barrier permeability and enhanced central nervous system (CNS) immune activity triggered by intestinal enterotoxins and blood-borne inflammatory mediators. Understanding the immunological, physiological, and structural changes associated with IBD and neuroinflammation may aid in the development of more tailored and suitable pharmaceutical treatment for IBD-associated depression.