SUCNR1-deficient mice are protected from colitis. Acute colitis was induced in both wild type (WT, n = 23) and Sucnr1 −/− mice (n = 25) by intrarectal administration of TNBS (3.5 mg per 20 g mice) or vehicle (EtOH 40%, Vh). Mice were killed 2 days after TNBS-administration. Graphs show: a body weight as a percentage of starting weight, measured daily; b colon length; c histological damage score (according to the Wallace score parameters) and representative photographs of the mucosa; d Sucnr1 mRNA expression in intestinal tissue (expressed as fold induction); e Relative mRNA expression levels of M1 markers (Cd86, CcrR7, Cd11c, and iNOS), M2 markers (Cd206, Fizz1, Ym1, and Arg1) and proinflammatory (Tnfα, Il-6 and Il-1β) and anti-inflammatory cytokines (Il-10) in both vehicle-and damaged-colon of TNBS-treated mice vs the housekeeping gene β-actin and represented as fold induction vs vehicle WT group. Points or bars in graphs represent mean ± s.e.m. Significant differences in relation to the WT vehicle-treated group are shown by *P < 0.05 and **P < 0.01; from the WT TNBS-treated mice by #P < 0.05 and ##P < 0.01 and from the Sucnr1 −/− vehicle-treated group by &&P < 0.01

SUCNR1-deficient mice are protected from colitis. Acute colitis was induced in both wild type (WT, n = 23) and Sucnr1 −/− mice (n = 25) by intrarectal administration of TNBS (3.5 mg per 20 g mice) or vehicle (EtOH 40%, Vh). Mice were killed 2 days after TNBS-administration. Graphs show: a body weight as a percentage of starting weight, measured daily; b colon length; c histological damage score (according to the Wallace score parameters) and representative photographs of the mucosa; d Sucnr1 mRNA expression in intestinal tissue (expressed as fold induction); e Relative mRNA expression levels of M1 markers (Cd86, CcrR7, Cd11c, and iNOS), M2 markers (Cd206, Fizz1, Ym1, and Arg1) and proinflammatory (Tnfα, Il-6 and Il-1β) and anti-inflammatory cytokines (Il-10) in both vehicle-and damaged-colon of TNBS-treated mice vs the housekeeping gene β-actin and represented as fold induction vs vehicle WT group. Points or bars in graphs represent mean ± s.e.m. Significant differences in relation to the WT vehicle-treated group are shown by *P < 0.05 and **P < 0.01; from the WT TNBS-treated mice by #P < 0.05 and ##P < 0.01 and from the Sucnr1 −/− vehicle-treated group by &&P < 0.01

Source publication
Article
Full-text available
Succinate, an intermediate of the tricarboxylic acid cycle, is accumulated in inflamed areas and its signaling through succinate receptor (SUCNR1) regulates immune function. We analyze SUCNR1 expression in the intestine of Crohn's disease patients and its role in murine intestinal inflammation and fibrosis. We show that both serum and intestinal su...

Contexts in source publication

Context 1
... of inflammatory bowel disease based on the intrarectal administration of TNBS to mice. This sensitizing agent induced, 2 days after its administration, a loss-of-body weight, a diminution in colon length and an increase of the histological damage score due to the inflammatory infiltrate and the slight disruption of the epithelial architecture (Fig. 3a-c). A significant increased mRNA expression of Sucnr1 was detected in the colon of TNBS-treated mice compared with levels detected in vehicle-treated mice (Fig. 3d). Administration of TNBS to Sucnr1 −/ − mice showed that the loss-of-body weight was significantly attenuated compared with the one detected in TNBS-treated WT mice and the ...
Context 2
... weight, a diminution in colon length and an increase of the histological damage score due to the inflammatory infiltrate and the slight disruption of the epithelial architecture (Fig. 3a-c). A significant increased mRNA expression of Sucnr1 was detected in the colon of TNBS-treated mice compared with levels detected in vehicle-treated mice (Fig. 3d). Administration of TNBS to Sucnr1 −/ − mice showed that the loss-of-body weight was significantly attenuated compared with the one detected in TNBS-treated WT mice and the histological damage and the reduction in colon length were significantly prevented (Fig. ...
Context 3
... colon of TNBS-treated mice compared with levels detected in vehicle-treated mice (Fig. 3d). Administration of TNBS to Sucnr1 −/ − mice showed that the loss-of-body weight was significantly attenuated compared with the one detected in TNBS-treated WT mice and the histological damage and the reduction in colon length were significantly prevented (Fig. ...
Context 4
... days after TNBS administration, a significant increase in the expression of M1 markers (Cd11c and iNOS), and pro-inflammatory cytokines (Il1β, Il6, and Tnfα,) was detected in colonic tissue from WT mice compared with vehicle-treated mice while the expression of M2 markers (Cd206, Fizz1, Ym1, and ArgI) was not significantly modified (Fig. 3e). In Sucnr1 −/− mice, TNBS failed to significantly modify the expression of M1 markers, pro-inflammatory cytokines and M2 markers with the exception of Fizz1 that it was significantly reduced (Fig. 3e). A detailed analysis between TNBS-treated WT and Sucnr1 −/− mice revealed a different expression of Cd11c, iNOS, Fizz1, Tnfα, Il1β, Il6, ...
Context 5
... from WT mice compared with vehicle-treated mice while the expression of M2 markers (Cd206, Fizz1, Ym1, and ArgI) was not significantly modified (Fig. 3e). In Sucnr1 −/− mice, TNBS failed to significantly modify the expression of M1 markers, pro-inflammatory cytokines and M2 markers with the exception of Fizz1 that it was significantly reduced (Fig. 3e). A detailed analysis between TNBS-treated WT and Sucnr1 −/− mice revealed a different expression of Cd11c, iNOS, Fizz1, Tnfα, Il1β, Il6, and Il10 (Fig. 3e). In vehicle-treated Sucnr1 −/− mice, higher mRNA levels of the M2 markers were detected compared with vehicle-treated WT mice, which reached statistical significance for Cd206 and ...
Context 6
... In Sucnr1 −/− mice, TNBS failed to significantly modify the expression of M1 markers, pro-inflammatory cytokines and M2 markers with the exception of Fizz1 that it was significantly reduced (Fig. 3e). A detailed analysis between TNBS-treated WT and Sucnr1 −/− mice revealed a different expression of Cd11c, iNOS, Fizz1, Tnfα, Il1β, Il6, and Il10 (Fig. 3e). In vehicle-treated Sucnr1 −/− mice, higher mRNA levels of the M2 markers were detected compared with vehicle-treated WT mice, which reached statistical significance for Cd206 and Fizz1 (Fig. ...
Context 7
... 3e). A detailed analysis between TNBS-treated WT and Sucnr1 −/− mice revealed a different expression of Cd11c, iNOS, Fizz1, Tnfα, Il1β, Il6, and Il10 (Fig. 3e). In vehicle-treated Sucnr1 −/− mice, higher mRNA levels of the M2 markers were detected compared with vehicle-treated WT mice, which reached statistical significance for Cd206 and Fizz1 (Fig. ...

Citations

... SUNCR1 is expressed on various types of cells including immune cells (3). Via the succinate-SUNCR1 signaling axis, succinate triggered proinflammatory response in macrophages during antigeninduced arthritis and induced a type 2 immune response in the small intestine (4)(5)(6). In the lipopolysaccharide (LPS)-stimulated macrophages, succinate acted as a metabolite in innate immune signaling to enhance interleukin-1b production through hypoxia-inducible factor-1a (7). ...
Article
Full-text available
Succinate is at the crossroads of multiple metabolic pathways and plays a role in several immune responses acting as an inflammation signal. However, whether succinate regulates antiviral immune response remains unclear. Here, we found that the production of succinate was reduced in RAW264.7 cells during vesicular stomatitis virus (VSV) infection. Using diethyl succinate to pretreat the mouse peritoneal macrophages and RAW264.7 cells before VSV infection, the production of interferon-β (IFN-β), chemokine (C-X-C motif) ligand 10 (CXCL-10), and IFN-stimulated genes 15 (ISG15) was significantly decreased, following which the VSV replication in diethyl succinate-pretreated cells was obviously increased. Moreover, succinate decreased the expression of IFN-β in serum, lung, and spleen derived from the VSV-infected mice. The overall survival rate in the VSV-infected mice with diethyl succinate pretreatment was also remarkably downregulated. Furthermore, we identified that succinate inhibited the activation of MAVS-TBK1-IRF3 signaling by suppressing the formation of MAVS aggregates. Our findings provide previously unrecognized roles of succinate in antiviral immune response and establish a novel link between metabolism and innate immune response.
... Beyond the role of succinate as an energy supplier, this amino acid is an inflammation mediator; it selectively binds to and activates the succinate receptor-1 (SUCNR1), which promotes pro-inflammatory signaling pathways (Mills and O'Neill, 2014). In patients with CD, hypoxia, inflammation, and necrosis promote the accumulation of succinate in gut inflamed areas, with a further activation and infiltration of macrophages and fibroblasts, the overexpression of pro-inflammatory cytokines, and ultimately the acceleration of fibrosis (Macias-Ceja et al., 2019). ...
Article
Full-text available
The integrity of the gastrointestinal tract structure and function is seriously compromised by two pathological conditions sharing, at least in part, several pathogenetic mechanisms: inflammatory bowel diseases (IBD) and coronavirus disease 2019 (COVID-19), caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. IBD and COVID-19 are marked by gut inflammation, intestinal barrier breakdown, resulting in mucosal hyperpermeability, gut bacterial overgrowth, and dysbiosis together with perturbations in microbial and human metabolic pathways originating changes in the blood and fecal metabolome. This review compared the most relevant metabolic and microbial alterations reported from the literature in patients with IBD with those in patients with COVID-19. In both diseases, gut dysbiosis is marked by the prevalence of pro-inflammatory bacterial species and the shortfall of anti-inflammatory species; most studies reported the decrease in Firmicutes, with a specific decrease in obligately anaerobic producers short-chain fatty acids (SCFAs), such as Faecalibacterium prausnitzii. In addition, Escherichia coli overgrowth has been observed in IBD and COVID-19, while Akkermansia muciniphila is depleted in IBD and overexpressed in COVID-19. In patients with COVID-19, gut dysbiosis continues after the clearance of the viral RNA from the upper respiratory tract and the resolution of clinical symptoms. Finally, we presented and discussed the impact of gut dysbiosis, inflammation, oxidative stress, and increased energy demand on metabolic pathways involving key metabolites, such as tryptophan, phenylalanine, histidine, glutamine, succinate, citrate, and lipids.
... In recent years, succinate, an intermediate metabolite of the tricarboxylic acid (TCA) cycle, acting through the G-protein-coupled receptor SUCNR1, has been involved in several inflammatory and metabolic pathologies [22][23][24][25][26]. This receptor, initially named GPR91, is expressed in several cell types, such as hepatic stellate cells, cardiomyocytes, platelets, dendritic cells, macrophages, epithelial cells and fibroblasts, and is found in several tissues, including liver, heart, kidney, retina, immune system and the gastrointestinal tract [27]. ...
... Moreover, the present data extend these observations by showing that SUCNR1 regulated the basal phosphorylation of the well-known proinflammatory transcription factor NFкB in intestinal epithelial cells (Figure 7). These observations may help to explain the reduced expression of proinflammatory cytokines detected in resting macrophages by several studies [26,30]. Growing evidence has demonstrated that NFкB induces the transcription of several inflammasome components such as Nlrp1, Nlrp3, and IL-1B [45]. ...
... Unexpectedly, they both failed to significantly increase the extracellular levels of succinate, in contrast to that reported in BMDMs [30]. It is important to note that differences in succinate levels between cell lines and primary cells have been reported [42]; we found that, in HT29 cells, levels of this metabolite were on the order of ten times higher than those detected in blood from carcinoma [49] or Crohn's Disease patients [26]. Therefore, we suggest that, in intestinal epithelial HT29 cells, SUCNR1 (rather than succinate levels) might be the limiting factor for the activation of the proinflammatory signalling pathway. ...
Article
Full-text available
Intestinal epithelial cells (IECs) constitute a defensive physical barrier in mucosal tissues and their disruption is involved in the etiopathogenesis of several inflammatory pathologies, such as Ulcerative Colitis (UC). Recently, the succinate receptor SUCNR1 was associated with the activation of inflammatory pathways in several cell types, but little is known about its role in IECs. We aimed to analyze the role of SUCNR1 in the inflammasome priming and its relevance in UC. Inflammatory and inflammasome markers and SUCNR1 were analyzed in HT29 cells treated with succinate and/or an inflammatory cocktail and transfected with SUCNR1 siRNA in a murine DSS model, and in intestinal resections from 15 UC and non-IBD patients. Results showed that this receptor mediated the inflammasome, priming both in vitro in HT29 cells and in vivo in a murine chronic DSS-colitis model. Moreover, SUNCR1 was also found to be involved in the activation of the inflammatory pathways NFкB and ERK pathways, even in basal conditions, since the transient knock-down of this receptor significantly reduced the constitutive levels of pERK-1/2 and pNFкB and impaired LPS-induced inflammation. Finally, UC patients showed a significant increase in the expression of SUCNR1 and several inflammasome components which correlated positively and significantly. Therefore, our results demonstrated a role for SUCNR1 in basal and stimulated inflammatory pathways in intestinal epithelial cells and suggested a pivotal role for this receptor in inflammasome activation in UC.
... There is evidence of this when looking at the genetic differences between the two Campylobacter lineages found within the human host, specifically the dcuB gene that encodes a fumarate/succinate active antiporter under low oxygen conditions that can also import aspartate [27]. Succinate concentrations in the gastrointestinal tract have been shown to increase during gut dysbiosis [28] and inflammation [29], but it remains to be determined if these conditions affect fumarate or aspartate concentrations. The New Zealand patient's gastrointestinal tract showed a large amount of variation in inflammation plus variation in the microbiota composition and these may be influencing the concentration of succinate and possibly other metabolites. ...
Article
Full-text available
Background Campylobacter is a genus of bacteria that has been isolated from the gastrointestinal tract of humans and animals, and the environments they inhabit around the world. Campylobacter adapt to new environments by changes in their gene content and expression, but little is known about how they adapt to long-term human colonization. In this study, the genomes of 31 isolates from a New Zealand patient and 22 isolates from a United Kingdom patient belonging to Campylobacter jejuni sequence type 45 (ST45) were compared with 209 ST45 genomes from other sources to identify the mechanisms by which Campylobacter adapts to long-term human colonization. In addition, the New Zealand patient had their microbiota investigated using 16S rRNA metabarcoding, and their level of inflammation and immunosuppression analyzed using biochemical tests, to determine how Campylobacter adapts to a changing gastrointestinal tract. Results There was some evidence that long-term colonization led to genome degradation, but more evidence that Campylobacter adapted through the accumulation of non-synonymous single nucleotide polymorphisms (SNPs) and frameshifts in genes involved in cell motility, signal transduction and the major outer membrane protein (MOMP). The New Zealand patient also displayed considerable variation in their microbiome, inflammation and immunosuppression over five months, and the Campylobacter collected from this patient could be divided into two subpopulations, the proportion of which correlated with the amount of gastrointestinal inflammation. Conclusions This study demonstrates how genomics, phylogenetics, 16S rRNA metabarcoding and biochemical markers can provide insight into how Campylobacter adapts to changing environments within human hosts. This study also demonstrates that long-term human colonization selects for changes in Campylobacter genes involved in cell motility, signal transduction and the MOMP; and that genetically distinct subpopulations of Campylobacter evolve to adapt to the changing gastrointestinal environment.
... The presence of SUCNR1 has been confirmed in a wide range of tissues such as liver, retina, kidney, blood cell and adipose tissue [5,6]. Existing reports from our group [7] and others [8][9][10][11][12][13][14][15] suggest a pro-inflammatory response upon SUCNR1 activation in various tissues. The fact that the succinate receptor is expressed in different types of immune cells indicates SUCNR1 activation could be a common reaction during immune responses. ...
Article
Full-text available
Succinate is a metabolite in the tricarboxylic acid cycle (TCA) which plays a central role in mitochondrial activity. Excess succinate is known to be transported out of the cytosol, where it activates a succinate receptor (SUCNR1) to enhance inflammation through macrophages in various contexts. In addition, the intracellular role of succinate beyond an intermediate metabolite and prior to its extracellular release is also important to the polarization of macrophages. However, the role of succinate in microglial cells has not been characterized. Lipopolysaccharide (LPS) stimulates the elevation of intracellular succinate levels. To reveal the function of intracellular succinate associated with LPS-stimulated inflammatory response in microglial cells, we assessed the levels of ROS, cytokine production and mitochondrial fission in the primary microglia pretreated with cell-permeable diethyl succinate mimicking increased intracellular succinate. Our results suggest that elevated intracellular succinate exerts a protective role in the primary microglia by preventing their conversion into the pro-inflammatory M1 phenotype induced by LPS. This protective effect is SUCNR1-independent and mediated by reduced mitochondrial fission and cellular ROS production.
... Succinate may act as a pro-inflammatory stimulus [33,35], and its basolateral elevation in the infected colonoids might contribute to the inflammatory responses by lamina propria cells. Thus, an increase in both serum and intestinal succinate levels has been reported in patients with Crohn's disease when compared with healthy subjects [36]. The mechanism of succinate release into the basolateral media thus might be an important target in inflammatory diseases. ...
Article
Full-text available
Colonic epithelium–commensal interactions play a very important role in human health and disease development. Colonic mucus serves as an ecologic niche for a myriad of commensals and provides a physical barrier between the epithelium and luminal content, suggesting that communication between the host and microbes occurs mainly by soluble factors. However, the composition of epithelia-derived metabolites and how the commensal flora influences them is less characterized. Here, we used mucus-producing human adult stem cell-derived colonoid monolayers exposed apically to probiotic E. coli strain Nissle 1917 to characterize the host–microbial communication via small molecules. We measured the metabolites in the media from host and bacterial monocultures and from bacteria-colonoid co-cultures. We found that colonoids secrete amino acids, organic acids, nucleosides, and polyamines, apically and basolaterally. The metabolites from host-bacteria co-cultures markedly differ from those of host cells grown alone or bacteria grown alone. Nissle 1917 affects the composition of apical and basolateral metabolites. Importantly, spermine, secreted apically by colonoids, shows antibacterial properties, and inhibits the growth of several bacterial strains. Our data demonstrate the existence of a cross-talk between luminal bacteria and human intestinal epithelium via metabolites, which might affect the numbers of physiologic processes including the composition of commensal flora via bactericidal effects.
... Excessively produced citrate causes an increase in the generation of pro-inflammatory molecules such as NO and prostaglandin [32]. Succinate is another metabolite accumulated from the broken TCA cycle and associated with the pro-inflammatory function of M1 macrophages [33,34]. By contrast, glutamine formation from glutamate is important to M2 macrophage function, pointing out the relevance of glutamine metabolism in this polarization [35]. ...
Article
Full-text available
Fibrosis is a pathophysiological process of wound repair that leads to the deposit of connective tissue in the extracellular matrix. This complication is mainly associated with different pathologies affecting several organs such as lung, liver, heart, kidney, and intestine. In this fibrotic process, macrophages play an important role since they can modulate fibrosis due to their high plasticity, being able to adopt different phenotypes depending on the microenvironment in which they are found. In this review, we will try to discuss whether the macrophage phenotype exerts a pivotal role in the fibrosis development in the most important fibrotic scenarios.
... In line with observations in other models and in human SH, elevated succinate is a signal of liver damage. It can bind to a G-protein-coupled succinate receptor, SUCNR1 [106], that activates hepatic stellate cells [107][108][109], triggers an immune response [56, 110,111], and impairs the mitochondrial quality control machinery [112]. Moreover, it has been demonstrated in an acetaminophen-toxicity model that, by uncoupling the succinate dehydrogenase and quinone reductase activities of SQR with methylene blue, the adverse effects of SQR inhibition can be relieved [113]. ...
Article
Full-text available
Understanding the pathomechanism of steatohepatitis (SH) is hampered by the difficulty of distinguishing between causes and consequences, by the broad spectrum of aetiologies that can produce the phenotype, and by the long time-span during which SH develops, often without clinical symptoms. We propose that SH develops in four phases with transitions: (i) priming lowers stress defence; (ii) triggering leads to acute damage; (iii) adaptation, possibly associated with cellular senescence, mitigates tissue damage, leads to the phenotype, and preserves liver function at a lower level; (iv) finally, senescence prevents neoplastic transformation but favours fibrosis (cirrhosis) and inflammation and further reduction in liver function. Escape from senescence eventually leads to hepatocellular carcinoma. This hypothesis for a pathomechanism of SH is supported by clinical and experimental observations. It allows organizing the various findings to uncover remaining gaps in our knowledge and, finally, to provide possible diagnostic and intervention strategies for each stage of SH development.
... Moreover, our experiments unraveled increased SUCNR1 expression in GDM placenta tissue lysates. Likewise, upregulated SUCNR1 expression has been highlighted in other pathologies of immunological etiologies [32,33]. Whereas succinate-SUCNR1 interplay has been proposed as a molecular mechanism in diabetic neuroretinal angiopathy [20] as well as nephropathy [34], our data imply a role of this pathway also in placental angiogenesis through VEGF. ...
Article
Full-text available
Placental hypervascularization has been reported in pregnancy-related pathologies such as gestational diabetes mellitus (GDM). Nevertheless, the underlying causes behind this abnormality are not well understood. In this study, we addressed the expression of SUCNR1 (cognate succinate receptor) in human placental endothelial cells and hypothesized that the succinate–SUCNR1 axis might play a role in the placental hypervascularization reported in GDM. We measured significantly higher succinate levels in placental tissue lysates from women with GDM relative to matched controls. In parallel, SUCNR1 protein expression was upregulated in GDM tissue lysates as well as in isolated diabetic fetoplacental arterial endothelial cells (FpECAds). A positive correlation of SUCNR1 and vascular endothelial growth factor (VEGF) protein levels in tissue lysates indicated a potential link between the succinate–SUCNR1 axis and placental angiogenesis. In our in vitro experiments, succinate prompted hallmarks of angiogenesis in human umbilical vein endothelial cells (HUVECs) such as proliferation, migration and spheroid sprouting. These results were further validated in fetoplacental arterial endothelial cells (FpECAs), where succinate induced endothelial tube formation. VEGF gene expression was increased in response to succinate in both HUVECs and FpECAs. Yet, knockdown of SUCNR1 in HUVECs led to suppression of VEGF gene expression and abrogated the migratory ability and wound healing in response to succinate. In conclusion, our data underline SUCNR1 as a promising metabolic target in human placenta and as a potential driver of enhanced placental angiogenesis in GDM.
... An increased abundance of potential opportunistic pathogens (Anaeroplasma, Desulfovibrio, Mucispirillum, and Paraprevotella) was seen in S839I ( Fig. 5 D). Members of the genus Paraprevotella are associated with colonic CD and produce succinic acid, increased levels of which are reported to be associated with microbiome dysbiosis and intestinal inflammation in patients with IBD and animal models of chronic colitis (Macias-Ceja et al., 2019;Walters et al., 2014). The genus Mucispirillum is also significantly higher in S839I mice (Fig. 5 D). ...
Article
Full-text available
Activating mutations in receptor guanylyl cyclase C (GC-C), the target of gastrointestinal peptide hormones guanylin and uroguanylin, and bacterial heat-stable enterotoxins cause early-onset diarrhea and chronic inflammatory bowel disease (IBD). GC-C regulates ion and fluid secretion in the gut via cGMP production and activation of cGMP-dependent protein kinase II. We characterize a novel mouse model harboring an activating mutation in Gucy2c equivalent to that seen in an affected Norwegian family. Mutant mice demonstrated elevated intestinal cGMP levels and enhanced fecal water and sodium content. Basal and linaclotide-mediated small intestinal transit was higher in mutant mice, and they were more susceptible to DSS-induced colitis. Fecal microbiome and gene expression analyses of colonic tissue revealed dysbiosis, up-regulation of IFN-stimulated genes, and misregulation of genes associated with human IBD and animal models of colitis. This novel mouse model thus provides molecular insights into the multiple roles of intestinal epithelial cell cGMP, which culminate in dysbiosis and the induction of inflammation in the gut.