Neutrophil recruitment mediated by sphingosine 1-phosphate (S1P)/S1P receptors during chronic liver injury

Sphingosine 1-phosphate receptor 1signaling in macrophages reduces atherosclerosis in LDL receptor-deficient mice

Sphingosine 1-phosphate (S1P) is a lysosphingolipid with antiatherogenic properties, but mechanisms underlying its effects remain unclear. We here investigated atherosclerosis development in cholesterol-rich diet-fed LDL receptor-deficient mice with high or low overexpression levels of S1P receptor 1 (S1P1) in macrophages. S1P1-overexpressing macrophages showed increased activity of transcription factors PU.1, interferon regulatory factor 8 (IRF8), and liver X receptor (LXR) and were skewed toward an M2-distinct phenotype characterized by enhanced production of IL-10, IL-1RA, and IL-5; increased ATP-binding cassette transporter A1- and G1-dependent cholesterol efflux; increased expression of MerTK and efferocytosis; and reduced apoptosis due to elevated B cell lymphoma 6 and Maf bZIP B. A similar macrophage phenotype was observed in mice administered S1P1-selective agonist KRP203. Mechanistically, the enhanced PU.1, IRF8, and LXR activity in S1P1-overexpressing macrophages led to downregulation of the cAMP-dependent PKA and activation of the signaling cascade encompassing protein kinases AKT and mTOR complex 1 as well as the late endosomal/lysosomal adaptor MAPK and mTOR activator 1. Atherosclerotic lesions in aortic roots and brachiocephalic arteries were profoundly or moderately reduced in mice with high and low S1P1 overexpression in macrophages, respectively. We conclude that S1P1 signaling polarizes macrophages toward an antiatherogenic functional phenotype and countervails the development of atherosclerosis in mice.

Protective Effects and Mechanisms of Inhibiting Endoplasmic Reticulum Stress on Cold Seawater Immersion Combined with Hemorrhagic Shock

Purpose

Cold seawater immersion aggravates hemorrhagic shock-induced homeostasis imbalance and organ dysfunction, leading to increased mortality. Previous studies have shown that treatments targeting oxidative stress and mitochondrial dysfunction have limited efficacy for cold seawater immersion combined with hemorrhagic shock (SIHS). Thus, the mechanisms responsible for SIHS need further investigation.

Methods and Results

Data from the hemorrhagic shock transcriptome and cold seawater immersion targets used for bioinformatics analysis revealed the involvement of endoplasmic reticulum stress (ERS) in SIHS occurrence and progression. Based on these findings, the effects and possible mechanism of inhibiting ERS in SIHS rats were investigated. SIHS causes a lethal triad and impairment of vital organ function, leading to death. Compared to lactated Ringer's solution, the ERS inhibitor 4-phenylbutyric acid (PBA)significantly ameliorated acidosis and coagulopathy and protected vital organ function while prolonging survival and the golden treatment time. Through target screening and validation, 7 targets were identified for the ERS inhibitor PBA for the treatment of SIHS, among which S1PR1, MMP8 and CFTR may play more important roles.

Conclusion

ERS plays a crucial role in the progression of SIHS. Inhibition of ERS caused by SIHS alleviates the lethal triad, protects organ function, and prolongs survival and the golden treatment time. The ERS inhibitor PBA may be an effective therapeutic measure for treating SIHS.

Therapeutic Potential of Hydrogen Sulfide in Ischemia and Reperfusion Injury

Ischemia-reperfusion (I/R) injury, a prevalent pathological condition in medical practice, presents significant treatment challenges. Hydrogen sulfide (H2S), acknowledged as the third gas signaling molecule, profoundly impacts various physiological and pathophysiological processes. Extensive research has demonstrated that H2S can mitigate I/R damage across multiple organs and tissues. This review investigates the protective effects of H2S in preventing I/R damage in the heart, brain, liver, kidney, intestines, lungs, stomach, spinal cord, testes, eyes, and other tissues. H2S provides protection against I/R damage by alleviating inflammation and endoplasmic reticulum stress; inhibiting apoptosis, oxidative stress, and mitochondrial autophagy and dysfunction; and regulating microRNAs. Significant advancements in understanding the mechanisms by which H2S reduces I/R damage have led to the development and synthesis of H2S-releasing agents such as diallyl trisulfide-loaded mesoporous silica nanoparticles (DATS-MSN), AP39, zofenopril, and ATB-344, offering a new therapeutic avenue for I/R injury.

How do sphingosine-1-phosphate affect immune cells to resolve inflammation?

Inflammation is an important immune response of the body. It is a physiological process of self-repair and defense against pathogens taken up by biological tissues when stimulated by damage factors such as trauma and infection. Inflammation is the main cause of high morbidity and mortality in most diseases and is the physiological basis of the disease. Targeted therapeutic strategies can achieve efficient toxicity clearance at the inflammatory site, reduce complications, and reduce mortality. Sphingosine-1-phosphate (S1P), a lipid signaling molecule, is involved in immune cell transport by binding to S1P receptors (S1PRs). It plays a key role in innate and adaptive immune responses and is closely related to inflammation. In homeostasis, lymphocytes follow an S1P concentration gradient from the tissues into circulation. One widely accepted mechanism is that during the inflammatory immune response, the S1P gradient is altered, and lymphocytes are blocked from entering the circulation and are, therefore, unable to reach the inflammatory site. However, the full mechanism of its involvement in inflammation is not fully understood. This review focuses on bacterial and viral infections, autoimmune diseases, and immunological aspects of the Sphks/S1P/S1PRs signaling pathway, highlighting their role in promoting intradial-adaptive immune interactions. How S1P signaling is regulated in inflammation and how S1P shapes immune responses through immune cells are explained in detail. We teased apart the immune cell composition of S1P signaling and the critical role of S1P pathway modulators in the host inflammatory immune system. By understanding the role of S1P in the pathogenesis of inflammatory diseases, we linked the genomic studies of S1P-targeted drugs in inflammatory diseases to provide a basis for targeted drug development.

Reversal of cholestatic liver disease by the inhibition of sphingosine 1-phosphate receptor 2 signaling

Aims

The objective of this study is to examine the impact of inhibiting Sphingosine 1-phosphate receptor 2 (S1PR2) on liver inflammation, fibrogenesis, and changes of gut microbiome in the context of cholestasis-induced conditions.

Methods

The cholestatic liver injury model was developed by common bile duct ligation (CBDL). Sprague-Dawley rats were randomly allocated to three groups, sham operation, CBDL group and JTE-013 treated CBDL group. Biochemical and histological assessments were conducted to investigate the influence of S1PR2 on the modulation of fibrogenic factors and inflammatory infiltration. We conducted an analysis of the fecal microbiome by using 16S rRNA sequencing. Serum bile acid composition was evaluated through the utilization of liquid chromatography-mass spectrometry techniques.

Results

In the BDL rat model, the study findings revealed a significant increase in serum levels of conjugated bile acids, accompanied by an overexpression of S1PR2. Treatment with the specific inhibitor of S1PR2, known as JTE-013, resulted in a range of specific effects on the BDL rats. These effects included the improvement of liver function, reduction of liver inflammation, inhibition of hepatocyte apoptosis, and suppression of NETosis. These effects are likely mediated through the TCA/S1PR2/NOX2/NLRP3 pathway. Furthermore, the administration of JTE-013 resulted in an augmentation of the diversity of the bacterial community's diversity, facilitating the proliferation of advantageous species while concurrently inhibiting the prevalence of detrimental bacteria.

Conclusions

The results of our study suggest that the administration of JTE-013 may have a beneficial effect in alleviating cholestatic liver disease and restoring the balance of intestinal flora.

Long non-coding RNA HOX transcript antisense intergenic RNA depletion protects against alcoholic hepatitis through the microRNA-148a-3p/sphingosine 1-phosphate receptor 1 axis

The aggravating role of long noncoding RNA (lncRNA) HOTAIR has been indicated in liver injury caused by hepatic ischemia/reperfusion. However, under the condition of alcoholic hepatitis (AH), its effects remain unclear. The present study aimed to examine the effect of lncRNA HOTAIR on hepatic stellate cell viability and apoptosis during liver injury caused by AH. In the liver tissues of AH rats, HOTAIR and S1PR1 were overexpressed, and microRNA (miR)-148a-3p was poorly expressed. Loss-of-function assays revealed that silencing of HOTAIR alleviated liver injury in AH by inhibiting the activated phenotype of hepatic stellate cells, inflammation, and fibrosis. Using the bioinformatics databases, dual-luciferase, RIP, and FISH assays, we observed that HOTAIR was mainly localized in the cytoplasm of hepatic stellate cells, and HOTAIR could bind specifically to miR-148a-3p. In addition, miR-148a-3p could target S1PR1 expression. Rescue experiments showed that silencing of miR-148a-3p or overexpression of S1PR1 reversed the alleviating effects of HOTAIR silencing on liver injury. Taken together, our findings revealed that HOTAIR regulates hepatic stellate cell proliferation via the miR-148a-3p/S1PR1 axis in liver injury, which may serve as the basis for developing novel therapeutic strategies to treat AH.

Farnesoid X receptor prevents neutrophil extracellular traps via reduced sphingosine-1-phosphate in chronic kidney disease

Farnesoid X receptor (FXR) activation reduces renal inflammation, but the underlying mechanisms remain elusive. Neutrophil extracellular traps (NETs) are webs of DNA formed when neutrophils undergo specialized programmed cell death (NETosis). The signaling lipid sphingosine-1-phosphate (S1P) stimulates NETosis via its receptor on neutrophils. Here, we identify FXR as a negative regulator of NETosis via repressing S1P signaling. We determined the effects of the FXR agonist obeticholic acid (OCA) in mouse models of adenosine phosphoribosyltransferase (APRT) deficiency and Alport syndrome, both genetic disorders that cause chronic kidney disease. Renal FXR activity is greatly reduced in both models, and FXR agonism reduces disease severity. Renal NETosis and sphingosine kinase 1 (Sphk1) expression are increased in diseased mice, and they are reduced by OCA in both models. Genetic deletion of FXR increases Sphk1 expression, and Sphk1 expression correlates with NETosis. Importantly, kidney S1P levels in Alport mice are two-fold higher than controls, and FXR agonism restores them back to baseline. Short-term inhibition of sphingosine synthesis in Alport mice with severe kidney disease reverses NETosis, establishing a causal relationship between S1P signaling and renal NETosis. Finally, extensive NETosis is present in human Alport kidney biopsies (six male, nine female), and NETosis severity correlates with clinical markers of kidney disease. This suggests the potential clinical relevance of the newly identified FXR-S1P-NETosis pathway. In summary, FXR agonism represses kidney Sphk1 expression. This inhibits renal S1P signaling, thereby reducing neutrophilic inflammation and NETosis.NEW & NOTEWORTHY Many preclinical studies have shown that the farnesoid X receptor (FXR) reduces renal inflammation, but the mechanism is poorly understood. This report identifies FXR as a novel regulator of neutrophilic inflammation and NETosis via the inhibition of sphingosine-1-phosphate signaling. Additionally, NETosis severity in human Alport kidney biopsies correlates with clinical markers of kidney disease. A better understanding of this signaling axis may lead to novel treatments that prevent renal inflammation and chronic kidney disease.

Aralia saponin A isolated from Achyranthes bidentata Bl. ameliorates LPS/D-GalN induced acute liver injury via SPHK1/S1P/S1PR1 pathway in vivo and in vitro

OBJECTIVE

Acute liver injury (ALI) refers to a disease in which the liver is affected by factors such as chemical substances, alcohol, and virus infection in a short time, resulting in damage to liver cells. Achyranthes bidentata Bl. with the hepatoprotective activity has attracted great attention. In this study, a pentacyclic triterpenoid (Aralia saponin A, AsA) was isolated from roots of Achyranthes bidentata Bl. and its anti-ALI activity, as well as the mechanisms, were investigated for the first time.

METHODS

AsA (10 or 20 mg/kg, i.g.) was administered over a period of 1 weeks, following which liver injury was induced by LPS (10 µg/kg)/D-GalN (700 mg/kg). H&E staining of liver, Aspartate amino transferase (AST), Alanine transaminase (ALT) and cytokines was employed to investigate ALI relevant features. The mitochondrial morphology and levels of mitochondrial membrane potential (MMP), oxidative stress balance, apoptosis, average fluorescence intensity of 2-DG, natural killer (NK) cells in liver tissues were determined to assess the oxidative stress damage and inflammatory injury. Transcriptomics and metabonomics analysis were employed to clarify the mechanisms. Additionally, the mRNA and protein expression levels of Sphingosine 1-phosphate (S1P), Sphingosine kinase-1 (SPKH1), Sphingosine 1 phosphate receptor 1 (S1PR1), Sphingosine 1 phosphate receptor 3 (S1PR3), TNF receptor associated factor 2 (TRAF-2), Phospho-NF- kappaB p65 (p-P65), NF- kappaB p65 (P65), Proto-oncogene ras (Ras), Ras-related C3 botulinum toxin substrate (Rac), Phospholipase C (PLC), Interleukin 6 (IL-6), Tumor necrosis factor α (TNF-α), Interleukin 1β (IL-1β), Vascular cell adhesion molecule 1 (Vcam1), CC chemokine ligand-2 (Ccl2) were analyzed. The mediating role of SPHK1 in the observed effects caused by AsA was assessed by investigatin SPHK1 transfection silencing/overexpression against AsA in AML12 cells induced by LPS/D-GalN.

RESULTS

AsA can ameliorate liver function, inflammation, mitochondrial structure and oxidative stress in the ALI model. Meanwhile, AsA led to downregulated expression of proteins associated with sphingolipid signaling pathway. Silencing of SPHK1 led to enhanced protective effects of AsA, while over-expression of SPHK1 led to degraded protective effects of AsA in LPS/D-GalN-induced AML12 cells, suggesting that ALI is regulated by active molecules of AsA by means of SPHK1 mediation.

CONCLUSIONS

AsA can ameliorate LPS/D-GalN-induced ALI by inhibiting inflammation and oxidative stress via the SPHK1/S1P/S1PR1 pathway. In this way, a molecular justification is provided for AsA application in ALI treatment.

The double-edged role of neutrophil heterogeneity in inflammatory diseases and cancers

Neutrophils are important immune cells act as the body's first line of defense against infection and respond to diverse inflammatory cues. Many studies have demonstrated that neutrophils display plasticity in inflammatory diseases and cancers. Clarifying the role of neutrophil heterogeneity in inflammatory diseases and cancers will contribute to the development of novel treatment strategies. In this review, we have presented a review on the development of the understanding on neutrophil heterogeneity from the traditional perspective and a high-resolution viewpoint. A growing body of evidence has confirmed the double-edged role of neutrophils in inflammatory diseases and tumors. This may be due to a lack of precise understanding of the role of specific neutrophil subsets in the disease. Thus, elucidating specific neutrophil subsets involved in diseases would benefit the development of precision medicine. Thusly, we have summarized the relevance and actions of neutrophil heterogeneity in inflammatory diseases and cancers comprehensively. Meanwhile, we also discussed the potential intervention strategy for neutrophils. This review is intended to deepen our understanding of neutrophil heterogeneity in inflammatory diseases and cancers, while hold promise for precise treatment of neutrophil-related diseases.

The role of sphingosine-1-phosphate in the gut mucosal microenvironment and inflammatory bowel diseases

Sphingosine-1-phosphate (S1P), a type of bioactive sphingolipid, can regulate various cellular functions of distinct cell types in the human body. S1P is generated intracellularly by the catalysis of sphingosine kinase 1/2 (SphK1/2). S1P is transferred to the extracellular environment via the S1P transporter, binds to cellular S1P receptors (S1PRs) and subsequently activates S1P-S1PR downstream signaling. Dysbiosis of the intestinal microbiota, immune dysregulation and damage to epithelial barriers are associated with inflammatory bowel disease (IBD). Generally, S1P mainly exerts a proinflammatory effect by binding to S1PR1 on lymphocytes to facilitate lymphocyte migration to inflamed tissues, and increased S1P was found in the intestinal mucosa of IBD patients. Notably, there is an interaction between the distribution of gut bacteria and SphK-S1P signaling in the intestinal epithelium. S1P-S1PR signaling can also regulate the functions of intestinal epithelial cells (IECs) in mucosa, including cell proliferation and apoptosis. Additionally, increased S1P in immune cells of the lamina propria aggravates the inflammatory response by increasing the production of proinflammatory cytokines. Several novel drugs targeted at S1PRs have recently been used for IBD treatment. This review provides an overview of the S1P-S1PR signaling pathway and, in particular, summarizes the various roles of S1P in the gut mucosal microenvironment to deeply explore the function of S1P-S1PR signaling during intestinal inflammation and, more importantly, to identify potential therapeutic targets for IBD in the SphK-S1P-S1PR axis.

Dissecting the Therapeutic Mechanisms of Sphingosine-1-Phosphate Receptor Agonism during Ischaemia and Reperfusion

Sphingosine 1-phosphate (S1P) and S1P receptors (S1PR) regulate many cellular processes, including lymphocyte migration and endothelial barrier function. As neutrophils are major mediators of inflammation, their transendothelial migration may be the target of therapeutic approaches to inflammatory conditions such as ischaemia-reperfusion injury (IRI). The aim of this project was to assess whether these therapeutic effects are mediated by S1P acting on neutrophils directly or indirectly through the endothelial cells. First, our murine model of peritoneum cell recruitment demonstrated the ability of S1P to reduce CXCL8-mediated neutrophil recruitment. Mechanistic in vitro studies revealed that S1P signals in neutrophils mainly through the S1PR1 and 4 receptors and induces phosphorylation of ERK1/2; however, this had no effect on neutrophil transmigration and adhesion. S1P treatment of endothelial cells significantly reduced TNF-α-induced neutrophil adhesion under flow (p < 0.01) and transendothelial migration towards CXCL8 during in vitro chemotaxis assays (p < 0.05). S1PR1 agonist CYM5442 treatment of endothelial cells also reduced neutrophil transmigration (p < 0.01) and endothelial permeability (p < 0.005), as shown using in vitro permeability assays. S1PR3 agonist had no effects on chemotaxis or permeability. In an in vivo mouse model of renal IRI, S1PR agonism with CYM5442 reduced endothelial permeability as shown by reduced Evan's Blue dye extravasation. Western blot was used to assess phosphorylation at different sites on vascular endothelial (VE)-cadherin and showed that CYM5442 reduced VEGF-mediated phosphorylation. Taken together, the results of this study suggest that reductions in neutrophil infiltration during IRI in response to S1P are mediated primarily by S1PR1 signalling on endothelial cells, possibly by altering phosphorylation of VE-cadherin. The results also demonstrate the therapeutic potential of S1PR1 agonist during IRI.

Functional roles of sphingolipids in immunity and their implication in disease

Sphingolipids, which are components of cellular membranes and organ tissues, can be synthesized or degraded to modulate cellular responses according to environmental cues, and the balance among the different sphingolipids is important for directing immune responses, regardless of whether they originate, as intra- or extracellular immune events. Recent progress in multiomics-based analyses and methodological approaches has revealed that human health and diseases are closely related to the homeostasis of sphingolipid metabolism, and disease-specific alterations in sphingolipids and related enzymes can be prognostic markers of human disease progression. Accumulating human clinical data from genome-wide association studies and preclinical data from disease models provide support for the notion that sphingolipids are the missing pieces that supplement our understanding of immune responses and diseases in which the functions of the involved proteins and nucleotides have been established. In this review, we analyze sphingolipid-related enzymes and reported human diseases to understand the important roles of sphingolipid metabolism. We discuss the defects and alterations in sphingolipid metabolism in human disease, along with functional roles in immune cells. We also introduce several methodological approaches and provide summaries of research on sphingolipid modulators in this review that should be helpful in studying the roles of sphingolipids in preclinical studies for the investigation of experimental and molecular medicines.

Isoliquiritigenin alleviates the development of alcoholic liver fibrosis by inhibiting ANXA2

The study aimed to investigate the effect of isoliquiritigenin (ISL) on model of alcoholic liver fibrosis (ALF). C57BL/6 mice were used to establish animal model of ALF, HSC-T6 cells were used to establish alcohol-activated cell model, and tandem mass tag (TMT) assays were used to analyze the proteome. The results showed that ISL obviously alleviated hepatic fibrosis in model mice. ISL visually improved the area of liver pathological stasis and deposition of fibrillar collagen (Sirius Red staining, Masson staining), inhibited the mRNA expression levels of interleukin 6 (IL-6), tumor necrosis factor α (TNF-α) and interleukin 1β (IL-1β) in liver tissues. ISL down-regulated the mRNA expression levels of IL-6 and transforming growth factor-β1(TGF-β1) in activated hepatic stellate cells (HSCs). And ISL significantly reduced annexin A2 (ANXA2) in vitro detected by TMT proteomics technology. Interestingly, it was found for the first time that ISL could inhibit ANXA2 expression both in vivo and in vitro, block the sphingosine kinases (SPHKs)/sphingosine-1-phosphate (S1P)/interleukin 17 (IL-17) signaling pathway and regulate the expression of α-smooth muscle actin (α-SMA) by inhibiting the phosphorylation of signal transducer and activator of transcription 3 (STAT3) at the downstream signal to finally reverse HSCs activation and hepatic fibrosis. Thus, we demonstrated that ISL is a drug monomer with notable anti-hepatic fibrosis activity.

Neutrophil CEACAM1 determines susceptibility to NETosis by regulating the S1PR2/S1PR3 axis in liver transplantation

Neutrophils, the largest innate immune cell population in humans, are the primary proinflammatory sentinel in the ischemia-reperfusion injury (IRI) mechanism in orthotopic liver transplantation (OLT). Carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1, CC1, or CD66a) is essential in neutrophil activation and serves as a checkpoint regulator of innate immune-driven IRI cascade in OLT. Although CC1 alternative splicing generates two functionally distinct short and long cytoplasmic isoforms, their role in neutrophil activation remains unknown. Here, we undertook molecular and functional studies to interrogate the significance of neutrophil CC1 signaling in mouse and human OLT recipients. In the experimental arm, we employed a mouse OLT model to document that ablation of recipient-derived neutrophil CC1-long (CC1-L) isotype aggravated hepatic IRI by promoting neutrophil extracellular traps (NETs). Notably, by regulating the S1P-S1PR2/S1PR3 axis, neutrophil CC1-L determined susceptibility to NET formation via autophagy signaling. In the clinical arm, liver grafts from 55 transplant patients selectively enriched for neutrophil CC1-L showed relative resistance to ischemia-reperfusion (IR) stress/tissue damage, improved hepatocellular function, and clinical outcomes. In conclusion, despite neutrophils being considered a principal villain in peritransplant tissue injury, their CC1-L isoform may serve as a regulator of IR stress resistance/NETosis in human and mouse OLT recipients.

Differential Upregulation and Functional Activity of S1PR1 in Human Peripheral Blood Basophils of Atopic Patients

Basophils are key effector cells in atopic diseases, and the signaling sphingolipid Sphigosine-1-phosphate (S1P) is emerging as an important mediator in these conditions. The possible interaction of S1P and basophils and the resulting biological effects have not yet been studied. We hypothesize that S1P influences the function of basophils in atopy and aim to elucidate the modes of interaction. S1P receptor (S1PR) expression in human peripheral blood basophils from atopic and non-atopic patients was assessed through qRT-PCR and flow cytometry analysis. Functional effects of S1P were assessed through a basophil activation test (BAT), calcium flux, apoptosis, and chemotaxis assays. Immunofluorescence staining was performed to visualize intracellular S1P. Human basophils express S1PR1, S1PR2, S1PR3, and S1PR4 on the mRNA level. 0.1 µM S1P have anti-apoptotic, while 10 µM exhibits apoptotic effects on basophils. Basophils from atopic patients show less chemotactic activity in response to S1P than those from healthy donors. Protein expression of S1PR1 is downregulated in atopic patients, and basophils in lesional AD skin possess intracellular S1P. These findings suggest that the interaction of S1P and basophils might be an important factor in the pathophysiology of atopy.

Bile acids as inflammatory mediators and modulators of intestinal permeability

Bile acids are critical for the digestion and absorption of lipids and fat-soluble vitamins; however, evidence continues to emerge supporting additional roles for bile acids as signaling molecules. After they are synthesized from cholesterol in the liver, primary bile acids are modified into secondary bile acids by gut flora contributing to a diverse pool and making the composition of bile acids highly sensitive to alterations in gut microbiota. Disturbances in bile acid homeostasis have been observed in patients with Inflammatory Bowel Diseases (IBD). In fact, a decrease in secondary bile acids was shown to occur because of IBD-associated dysbiosis. Further, the increase in luminal bile acids due to malabsorption in Crohn's ileitis and ileal resection has been implicated in the induction of diarrhea and the exacerbation of inflammation. A causal link between bile acid signaling and intestinal inflammation has been recently suggested. With respect to potential mechanisms related to bile acids and IBD, several studies have provided strong evidence for direct effects of bile acids on intestinal permeability in porcine and rodent models as well as in humans. Interestingly, different bile acids were shown to exert distinct effects on the inflammatory response and intestinal permeability that require careful consideration. Such findings revealed a potential effect for changes in the relative abundance of different bile acids on the induction of inflammation by bile acids and the development of IBD. This review summarizes current knowledge about the roles for bile acids as inflammatory mediators and modulators of intestinal permeability mainly in the context of inflammatory bowel diseases.

Sphingosine 1-phosphate receptor 2 mediated early stages of pancreatic and systemic inflammatory responses via NF-kappa B activation in acute pancreatitis

In acute pancreatitis, activation of inflammatory signaling, including the nuclear factor-kappa B (NF-κB) pathway, within acinar cells is known to be an early intracellular event occurring in parallel with pathologic trypsinogen activation. Sphingosine 1-phosphate receptor 2 (S1PR2) plays a critical role in endothelial inflammation, and our previous studies reported that S1PR2 deficiency significantly reduced the inflammatory response in liver injury under cholestasis conditions. However, the role of S1PR2 in inflammatory signaling activation within acinar cells and inflammatory responses during acute pancreatitis has not been elucidated. Here we report that S1PR2 was upregulated in the whole pancreas during acute pancreatitis. Blockade of S1PR2 by pharmacologic inhibition of S1PR2 by JTE-013 or AAV-mediated knockdown of S1PR2 improved the severity of pancreatic injury, as indicated by a significant reduction in inflammation and acinar cells death in acute pancreatitis mice. Moreover, S1PR2 is the predominant S1PRs expressed in pancreatic acinar cells and mediates NF-κB activation and the early inflammatory response within acinar cells under acute pancreatitis conditions via ROCK signaling pathways, not extracellular signal-regulated kinase pathways or p38 mitogen-activated protein kinase pathways. In addition, S1PR2 mediated macrophage NF-κB activation, migration and polarization toward the M1 phenotype. Therefore, these results demonstrated that the S1PR2-mediated early inflammatory response in acinar cells promotes the progression of acute pancreatitis, successfully linking local events to the systematic inflammatory response and leading to a novel therapeutic target for acute pancreatitis aimed at halting the progression of the inflammatory response.

Activated Neutrophils Secrete Chitinase-Like 1 and Attenuate Liver Inflammation by Inhibiting Pro-Inflammatory Macrophage Responses

Excessive activation and recruitment of neutrophils are generally considered to be associated with pathological aggravation of multiple diseases. However, as the role of neutrophils in tissue injury repair is receiving increasing attention, it is necessary to further explore the beneficial role of activated neutrophils in promoting the resolution of inflammation after injury. In this study, we found that activated neutrophils have a crucial function in suppressing liver inflammation. In methionine-choline-deficient and high-fat (MCDHF) diet induced liver inflammation in mice, tail vein injection of activated neutrophils (A-Neu, stimulated by sphingosine 1-phosphate) inhibited the expressions of pro-inflammatory cytokines in the liver, including C-C chemokine motif ligand 4, tumor necrosis factor and nitric oxide synthase 2, and attenuated liver injury. However, non-activated neutrophils (N-Neu) did not have these effects. In vitro, pro-inflammatory macrophages were co-cultured with N-Neu or A-Neu by transwell, respectively. A-Neu was found to suppress the pro-inflammatory phenotype of macrophages by using RT-qPCR, western blot and cytometric bead array. Microarray analysis showed that there were systematic variations in transcript expression levels between N-Neu and A-Neu. GeneVenn software was used to show the gene expression overlap between GO terms including Regulation of Cell Communication, Cytokine Secretion, Inflammatory Response and Extracellular Space clusters. We identified that Chitinase-like 1 (CHIL1) secreted by S1P activated neutrophils may be an important mediators affecting the pro-inflammatory macrophage responses. In the injured liver of mice induced by MCDHF diet, the expression of Chil1 mRNA increased and was positively correlated with the neutrophil marker Ly6g. Moreover, the secretion of CHIL1 in A-Neu increased significantly. Strikingly, the effect of A-Neu on macrophage response was reproduced by incubating pro-inflammatory macrophages with recombinant CHIL1. A-Neu conditioned medium were incubated with CHIL1 antibody-conjugated protein G beads, magnetically separated to immunodepletion CHIL1 from the A-Neu supernatant, which can partially weaken its inhibitory effect of A-Neu on the production of macrophage pro-inflammatory cytokines. Together, the conclusions indicated that A-Neu could inhibit the pro-inflammatory macrophage responses by secreting CHIL1, thereby effectively inhibiting liver inflammation.