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The Biosynthesis, Signaling, and Neurological Functions of Bile Acids. Biomolecules 2019; 9:biom9060232. [PMID: 31208099 PMCID: PMC6628048 DOI: 10.3390/biom9060232] [Citation(s) in RCA: 108] [Impact Index Per Article: 21.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2019] [Revised: 06/13/2019] [Accepted: 06/14/2019] [Indexed: 12/13/2022] Open
Abstract
Bile acids (BA) are amphipathic steroid acids synthesized from cholesterol in the liver. They act as detergents to expedite the digestion and absorption of dietary lipids and lipophilic vitamins. BA are also considered to be signaling molecules, being ligands of nuclear and cell-surface receptors, including farnesoid X receptor and Takeda G-protein receptor 5. Moreover, BA also activate ion channels, including the bile acid-sensitive ion channel and epithelial Na+ channel. BA regulate glucose and lipid metabolism by activating these receptors in peripheral tissues, such as the liver and brown and white adipose tissue. Recently, 20 different BA have been identified in the central nervous system. Furthermore, BA affect the function of neurotransmitter receptors, such as the muscarinic acetylcholine receptor and γ-aminobutyric acid receptor. BA are also known to be protective against neurodegeneration. Here, we review recent findings regarding the biosynthesis, signaling, and neurological functions of BA.
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Abstract
Bile acids facilitate nutrient absorption and are endogenous ligands for nuclear receptors that regulate lipid and energy metabolism. The brain-gut-liver axis plays an essential role in maintaining overall glucose, bile acid, and immune homeostasis. Fasting and feeding transitions alter nutrient content in the gut, which influences bile acid composition and pool size. In turn, bile acid signaling controls lipid and glucose use and protection against inflammation. Altered bile acid metabolism resulting from gene mutations, high-fat diets, alcohol, or circadian disruption can contribute to cholestatic and inflammatory diseases, diabetes, and obesity. Bile acids and their derivatives are valuable therapeutic agents for treating these inflammatory metabolic diseases.
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Affiliation(s)
- John Y L Chiang
- Department of Integrative Medical Sciences, Northeast Ohio Medical University, Rootstown, Ohio 44272;
| | - Jessica M Ferrell
- Department of Integrative Medical Sciences, Northeast Ohio Medical University, Rootstown, Ohio 44272;
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53
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McMillin M, Grant S, Frampton G, Petrescu AD, Williams E, Jefferson B, Thomas A, Brahmaroutu A, DeMorrow S. Elevated circulating TGFβ1 during acute liver failure activates TGFβR2 on cortical neurons and exacerbates neuroinflammation and hepatic encephalopathy in mice. J Neuroinflammation 2019; 16:69. [PMID: 30940161 PMCID: PMC6446280 DOI: 10.1186/s12974-019-1455-y] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2018] [Accepted: 03/18/2019] [Indexed: 12/11/2022] Open
Abstract
BACKGROUND Acute liver failure resulting from drug-induced liver injury can lead to the development of neurological complications called hepatic encephalopathy (HE). Hepatic transforming growth factor beta 1 (TGFβ1) is upregulated due to liver failure in mice and inhibiting circulating TGFβ reduced HE progression. However, the specific contributions of TGFβ1 on brain cell populations and neuroinflammation during HE are not known. Therefore, the aim of this study was to characterize hepatic and brain TGFβ1 signaling during acute liver failure and its contribution to HE progression using a combination of pharmacological and genetic approaches. METHODS C57Bl/6 or neuron-specific transforming growth factor beta receptor 2 (TGFβR2) null mice (TGFβR2ΔNeu) were treated with azoxymethane (AOM) to induce acute liver failure and HE. The activity of circulating TGFβ1 was inhibited in C57Bl/6 mice via injection of a neutralizing antibody against TGFβ1 (anti-TGFβ1) prior to AOM injection. In all mouse treatment groups, liver damage, neuroinflammation, and neurological deficits were assessed. Inflammatory signaling between neurons and microglia were investigated in in vitro studies through the use of pharmacological inhibitors of TGFβ1 signaling in HT-22 and EOC-20 cells. RESULTS TGFβ1 was expressed and upregulated in the liver following AOM injection. Pharmacological inhibition of TGFβ1 after AOM injection attenuated neurological decline, microglia activation, and neuroinflammation with no significant changes in liver damage. TGFβR2ΔNeu mice administered AOM showed no effect on liver pathology but significantly reduced neurological decline compared to control mice. Microglia activation and neuroinflammation were attenuated in mice with pharmacological inhibition of TGFβ1 or in TGFβR2ΔNeu mice. TGFβ1 increased chemokine ligand 2 (CCL2) and decreased C-X3-C motif ligand 1 (CX3CL1) expression in HT-22 cells and reduced interleukin-1 beta (IL-1ß) expression, tumor necrosis factor alpha (TNFα) expression, and phagocytosis activity in EOC-20 cells. CONCLUSION Increased circulating TGFβ1 following acute liver failure results in activation of neuronal TGFβR2 signaling, driving neuroinflammation and neurological decline during AOM-induced HE.
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Affiliation(s)
- Matthew McMillin
- Central Texas Veterans Health Care System, Temple, TX, USA.,Department of Medical Physiology, College of Medicine, Texas A&M University Health Science Center, Temple, TX, USA.,Department of Internal Medicine, Dell Medical School, The University of Texas at Austin, Austin, TX, USA
| | - Stephanie Grant
- Central Texas Veterans Health Care System, Temple, TX, USA.,Department of Medical Physiology, College of Medicine, Texas A&M University Health Science Center, Temple, TX, USA.,Division of Pharmacology and Toxicology, College of Pharmacy, The University of Texas at Austin, Austin, TX, USA
| | - Gabriel Frampton
- Central Texas Veterans Health Care System, Temple, TX, USA.,Department of Medical Physiology, College of Medicine, Texas A&M University Health Science Center, Temple, TX, USA.,Department of Internal Medicine, Dell Medical School, The University of Texas at Austin, Austin, TX, USA
| | - Anca D Petrescu
- Central Texas Veterans Health Care System, Temple, TX, USA.,Department of Medical Physiology, College of Medicine, Texas A&M University Health Science Center, Temple, TX, USA.,Division of Pharmacology and Toxicology, College of Pharmacy, The University of Texas at Austin, Austin, TX, USA
| | - Elaina Williams
- Central Texas Veterans Health Care System, Temple, TX, USA.,Department of Medical Physiology, College of Medicine, Texas A&M University Health Science Center, Temple, TX, USA.,Division of Pharmacology and Toxicology, College of Pharmacy, The University of Texas at Austin, Austin, TX, USA
| | - Brandi Jefferson
- Central Texas Veterans Health Care System, Temple, TX, USA.,Department of Medical Physiology, College of Medicine, Texas A&M University Health Science Center, Temple, TX, USA
| | - Alison Thomas
- Department of Medical Physiology, College of Medicine, Texas A&M University Health Science Center, Temple, TX, USA
| | - Ankita Brahmaroutu
- Department of Medical Physiology, College of Medicine, Texas A&M University Health Science Center, Temple, TX, USA
| | - Sharon DeMorrow
- Central Texas Veterans Health Care System, Temple, TX, USA. .,Department of Medical Physiology, College of Medicine, Texas A&M University Health Science Center, Temple, TX, USA. .,Division of Pharmacology and Toxicology, College of Pharmacy, The University of Texas at Austin, Austin, TX, USA. .,Department of Internal Medicine, Dell Medical School, The University of Texas at Austin, Austin, TX, USA.
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54
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Modulation of sphingosine-1-phosphate receptor by FTY720 contributes in improvement of hepatic encephalopathy induced by bile duct ligation. Brain Res Bull 2019; 146:253-269. [DOI: 10.1016/j.brainresbull.2019.01.012] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2018] [Revised: 12/17/2018] [Accepted: 01/13/2019] [Indexed: 12/11/2022]
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55
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Zhang Y, Lu Y, Ji H, Li Y. Anti-inflammatory, anti-oxidative stress and novel therapeutic targets for cholestatic liver injury. Biosci Trends 2019; 13:23-31. [PMID: 30814402 DOI: 10.5582/bst.2018.01247] [Citation(s) in RCA: 37] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Cholestasis is a pathological process in which bile drainage is poor for a variety of reasons. Many studies have shown that cholestatic liver injury is a neutrophil-mediated inflammatory response, and oxidative stress induced by neutrophils is the main mechanism of liver cell death. The literature summarizes the bile acid signaling pathway, the neutrophil chemotaxis recruitment process during cholestasis, and the oxidative stress damage produced by neutrophil activation, summarizes the latest research progress. Sphingosine-1-phosphate receptor (S1PR) is a potential therapeutic target for cholestasis that reduces neutrophil aggregation without inhibiting systemic immune status. Early growth response factor 1 (Egr-1) may play a central role in the inflammation induced by cholestasis, and it is also a potential therapeutic target to inhibit the inflammation induced by cholestasis. Strengthening the antioxidant system of hepatocytes to cope with oxidative stress of neutrophils is a feasible treatment for cholestatic liver injury.
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Affiliation(s)
- Yafei Zhang
- Department of General Surgery, Second Affiliated Hospital of Xi'an Jiaotong University
| | - Yuxuan Lu
- The High School Affiliated to xi'an Jiaotong University
| | - Hong Ji
- Department of General Surgery, Second Affiliated Hospital of Xi'an Jiaotong University
| | - Yiming Li
- Department of General Surgery, Second Affiliated Hospital of Xi'an Jiaotong University
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Abstract
Hepatic encephalopathy describes the array of neurological complications that arise due to liver insufficiency and/or portal-systemic shunt. The pathogenesis of hepatic encephalopathy shares a longstanding association with hyperammonemia and inflammation. Recently, aberrant bile acid signaling has been implicated in the development of key features of hepatic encephalopathy due to acute liver failure including neuronal dysfunction, neuroinflammation and blood-brain barrier permeability. This review summarizes the findings of recent studies demonstrating a role for bile acids in hepatic encephalopathy and speculates on the possible downstream consequences of bile acid signaling.
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Key Words
- ASBT, Apical Sodium-Dependent Bile Acid Transporter
- CCL2, Chemokine Ligand 2
- CCR2, Chemokine Receptor 2
- Cyp46A1, Cytochrome p450 46A1
- FXR, Farnesoid X Receptor
- GR, Glucocorticoid Receptor
- NTCP, Sodium Taurocholate Cotransporting Polypeptide
- PXR, Pregnane X Receptor
- S1P2R, Sphingosine 1 Phosphate Receptor 2
- TGR5, Takeda G-Protein Receptor 5
- Takeda G-protein coupled receptor 5 (TGR5)
- VDR, Vitamin D Receptor
- blood–brain barrier
- farnesoid X receptor
- neuroinflammation
- sphingosine-1-phosphate receptor 2
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57
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Bile Acid-Activated Receptors: GPBAR1 (TGR5) and Other G Protein-Coupled Receptors. Handb Exp Pharmacol 2019; 256:19-49. [PMID: 31302759 DOI: 10.1007/164_2019_230] [Citation(s) in RCA: 64] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
The BA-responsive GPCRs S1PR2 and TGR5 are almost ubiquitously expressed in human and rodent tissues. In the liver, S1PR2 is expressed in all cell types, while TGR5 is predominately found in non-parenchymal cells. In contrast to S1PR2, which is mainly activated by conjugated bile acids (BAs), all BAs serve as ligands for TGR5 irrespective of their conjugation state and substitution pattern.Mice with targeted deletion of either S1PR2 or TGR5 are viable and develop no overt phenotype. In liver injury models, S1PR2 exerts pro-inflammatory and pro-fibrotic effects and thus aggravates liver damage, while TGR5 mediates anti-inflammatory, anti-cholestatic, and anti-fibrotic effects. Thus, inhibitors of S1PR2 signaling and agonists for TGR5 have been employed to attenuate liver injury in rodent models for cholestasis, nonalcoholic steatohepatitis, and fibrosis/cirrhosis.In biliary epithelial cells, both receptors activate a similar signaling cascade resulting in ERK1/2 phosphorylation and cell proliferation. Overexpression of both S1PR2 and TGR5 was found in human cholangiocarcinoma tissue as well as in CCA cell lines, where stimulation of both GPCRs resulted in transactivation of the epidermal growth factor receptor and triggered cell proliferation as well as increased cell migration and invasiveness.This chapter will focus on the function of S1PR2 and TGR5 in different liver cell types and summarizes current knowledge on the role of these receptors in liver disease models.
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58
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Al-Khaifi A, Straniero S, Voronova V, Chernikova D, Sokolov V, Kumar C, Angelin B, Rudling M. Asynchronous rhythms of circulating conjugated and unconjugated bile acids in the modulation of human metabolism. J Intern Med 2018; 284:546-559. [PMID: 29964306 DOI: 10.1111/joim.12811] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
BACKGROUND AND OBJECTIVES Bile acids (BAs) traversing the enterohepatic circulation (EHC) influence important metabolic pathways. By determining individual serum BAs in relation to markers of metabolic activity, we explored how diurnal variations in their EHC relate to hepatic metabolism in normal humans. METHODS Serum BAs, fibroblast growth factor 19 (FGF19), lipoproteins, glucose/insulin and markers of cholesterol and BA syntheses were monitored for 32 h in 8 healthy males. Studies were conducted at basal state and during initiation of cholestyramine treatment, with and without atorvastatin pretreatment. Time series cross-correlation analysis, Bayesian structural model and Granger causality test were applied. RESULTS Bile acids synthesis dominated daytime, and cholesterol production at night. Conjugated BAs peaked after food intake, with subsequent FGF19 elevations. BA synthesis was reduced following conjugated BA and FGF19 peaks. Cholestyramine reduced conjugated BAs and FGF19, and increased BA and cholesterol production; the latter effects attenuated by atorvastatin. The relative importance of FGF19 vs. conjugated BAs in this feedback inhibition could not be discriminated. Unconjugated BAs displayed one major peak late at night/early morning that was unrelated to FGF19 and BA synthesis, and abolished by cholestyramine. The normal suppression of serum triglycerides, glucose and insulin observed at night was attenuated by cholestyramine. CONCLUSIONS Conjugated and unconjugated BAs have asynchronous rhythms of EHC in humans. Postprandial transintestinal flux of conjugated BAs increases circulating FGF19 levels and suppresses BA synthesis. Unconjugated BAs peak late at night, indicating a non-postprandial diurnal change in human gut microflora, the physiological implications of which warrants further study.
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Affiliation(s)
- A Al-Khaifi
- Metabolism Unit, Endocrinology, Metabolism and Diabetes, Department of Medicine, Karolinska Institutet at Karolinska University Hospital Huddinge, Stockholm, Sweden.,Department of Medicine, Karolinska Institutet/AstraZeneca Integrated CardioMetabolic Center (KI/AZ ICMC), Novum, Stockholm, Sweden.,Department of Biochemistry, College of Medicine, Sultan Qaboos University, Muscat 123, Oman
| | - S Straniero
- Metabolism Unit, Endocrinology, Metabolism and Diabetes, Department of Medicine, Karolinska Institutet at Karolinska University Hospital Huddinge, Stockholm, Sweden.,Department of Medicine, Karolinska Institutet/AstraZeneca Integrated CardioMetabolic Center (KI/AZ ICMC), Novum, Stockholm, Sweden
| | | | | | | | - C Kumar
- Department of Medicine, Karolinska Institutet/AstraZeneca Integrated CardioMetabolic Center (KI/AZ ICMC), Novum, Stockholm, Sweden.,Translational Sciences, Cardiovascular, Renal and Metabolism, IMED Biotech Unit, AstraZeneca, Gothenburg, Sweden
| | - B Angelin
- Metabolism Unit, Endocrinology, Metabolism and Diabetes, Department of Medicine, Karolinska Institutet at Karolinska University Hospital Huddinge, Stockholm, Sweden.,Department of Medicine, Karolinska Institutet/AstraZeneca Integrated CardioMetabolic Center (KI/AZ ICMC), Novum, Stockholm, Sweden
| | - M Rudling
- Metabolism Unit, Endocrinology, Metabolism and Diabetes, Department of Medicine, Karolinska Institutet at Karolinska University Hospital Huddinge, Stockholm, Sweden.,Department of Medicine, Karolinska Institutet/AstraZeneca Integrated CardioMetabolic Center (KI/AZ ICMC), Novum, Stockholm, Sweden
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59
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Complement System as a Target for Therapies to Control Liver Regeneration/Damage in Acute Liver Failure Induced by Viral Hepatitis. J Immunol Res 2018; 2018:3917032. [PMID: 30402508 PMCID: PMC6196788 DOI: 10.1155/2018/3917032] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2018] [Accepted: 08/28/2018] [Indexed: 02/06/2023] Open
Abstract
The complement system plays an important role in innate immunity inducing liver diseases as well as signaling immune cell activation in local inflammation regulating immunomodulatory effects such as liver damage and/or liver regeneration. Our aim is to evaluate the role of complement components in acute liver failure (ALF) caused by viral hepatitis, involving virus-induced ALF in human subjects using peripheral blood, samples of liver tissues, and ex vivo assays. Our findings displayed low levels of C3a in plasma samples with high frequency of C3a, C5a, and C5b/9 deposition in liver parenchyma. Meanwhile, laboratory assays using HepG2 (hepatocyte cell line) showed susceptibility to plasma samples from ALF patients impairing in vitro cell proliferation and an increase in apoptotic events submitting plasma samples to heat inactivation. In summary, our data suggest that the complement system may be involved in liver dysfunction in viral-induced acute liver failure cases using ex vivo assays. In extension to our findings, we provide insights into future studies using animal models for viral-induced ALF, as well as other associated soluble components, which need further investigation.
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60
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Grant S, McMillin M, Frampton G, Petrescu AD, Williams E, Jaeger V, Kain J, DeMorrow S. Direct Comparison of the Thioacetamide and Azoxymethane Models of Type A Hepatic Encephalopathy in Mice. Gene Expr 2018; 18:171-185. [PMID: 29895352 PMCID: PMC6190119 DOI: 10.3727/105221618x15287315176503] [Citation(s) in RCA: 31] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Acute liver failure is a devastating consequence of hepatotoxic liver injury that can lead to the development of hepatic encephalopathy. There is no consensus on the best model to represent these syndromes in mice, and therefore the aim of this study was to classify hepatic and neurological consequences of azoxymethane- and thioacetamide-induced liver injury. Azoxymethane-treated mice were euthanized at time points representing absence of minor and significant stages of neurological decline. Thioacetamide-treated mice had tissue collected at up to 3 days following daily injections. Liver histology, serum chemistry, bile acids, and cytokine levels were measured. Reflexes, grip strength measurement, and ataxia were calculated for all groups. Brain ammonia, bile acid levels, cerebral edema, and neuroinflammation were measured. Finally, in vitro and in vivo assessments of blood-brain barrier function were performed. Serum transaminases and liver histology demonstrate that both models generated hepatotoxic liver injury. Serum proinflammatory cytokine levels were significantly elevated in both models. Azoxymethane-treated mice had progressive neurological deficits, while thioacetamide-treated mice had inconsistent neurological deficits. Bile acids and cerebral edema were increased to a higher degree in azoxymethane-treated mice, while cerebral ammonia and neuroinflammation were greater in thioacetamide-treated mice. Blood-brain barrier permeability exists in both models but was likely not due to direct toxicity of azoxymethane or thioacetamide on brain endothelial cells. In conclusion, both models generate acute liver injury and hepatic encephalopathy, but the requirement of a single injection and the more consistent neurological decline make azoxymethane treatment a better model for acute liver failure with hepatic encephalopathy.
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Affiliation(s)
- Stephanie Grant
- *Department of Medical Physiology, Texas A&M Health Science Center College of Medicine, Temple, TX, USA
| | | | - Gabriel Frampton
- *Department of Medical Physiology, Texas A&M Health Science Center College of Medicine, Temple, TX, USA
| | - Anca D. Petrescu
- *Department of Medical Physiology, Texas A&M Health Science Center College of Medicine, Temple, TX, USA
| | - Elaina Williams
- *Department of Medical Physiology, Texas A&M Health Science Center College of Medicine, Temple, TX, USA
| | - Victoria Jaeger
- *Department of Medical Physiology, Texas A&M Health Science Center College of Medicine, Temple, TX, USA
- †Central Texas Veterans Healthcare System, Temple, TX, USA
- ‡Baylor Scott & White Medical Center, Temple, TX, USA
| | - Jessica Kain
- *Department of Medical Physiology, Texas A&M Health Science Center College of Medicine, Temple, TX, USA
| | - Sharon DeMorrow
- *Department of Medical Physiology, Texas A&M Health Science Center College of Medicine, Temple, TX, USA
- †Central Texas Veterans Healthcare System, Temple, TX, USA
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61
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Deoxycholic Acid-Mediated Sphingosine-1-Phosphate Receptor 2 Signaling Exacerbates DSS-Induced Colitis through Promoting Cathepsin B Release. J Immunol Res 2018; 2018:2481418. [PMID: 29854830 PMCID: PMC5966668 DOI: 10.1155/2018/2481418] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2017] [Accepted: 01/08/2018] [Indexed: 01/07/2023] Open
Abstract
We recently have proved that excessive fecal DCA caused by high-fat diet may serve as an endogenous danger-associated molecular pattern to activate NLRP3 inflammasome and thus contributes to the development of inflammatory bowel disease (IBD). Moreover, the effect of DCA on inflammasome activation is mainly mediated through bile acid receptor sphingosine-1-phosphate receptor 2 (S1PR2); however, the intermediate process remains unclear. Here, we sought to explore the detailed molecular mechanism involved and examine the effect of S1PR2 blockage in a colitis mouse model. In this study, we found that DCA could dose dependently upregulate S1PR2 expression. Meanwhile, DCA-induced NLRP3 inflammasome activation is at least partially achieved through stimulating extracellular regulated protein kinases (ERK) signaling pathway downstream of S1PR2 followed by promoting of lysosomal cathepsin B release. DCA enema significantly aggravated DSS-induced colitis in mice and S1PR2 inhibitor as well as inflammasome inhibition by cathepsin B antagonist substantially reducing the mature IL-1β production and alleviated colonic inflammation superimposed by DCA. Therefore, our findings suggest that S1PR2/ERK1/2/cathepsin B signaling plays a critical role in triggering inflammasome activation by DCA and S1PR2 may represent a new potential therapeutic target for the management of intestinal inflammation in individuals on a high-fat diet.
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McMillin M, Grant S, Frampton G, Petrescu AD, Kain J, Williams E, Haines R, Canady L, DeMorrow S. FXR-Mediated Cortical Cholesterol Accumulation Contributes to the Pathogenesis of Type A Hepatic Encephalopathy. Cell Mol Gastroenterol Hepatol 2018; 6:47-63. [PMID: 29928671 PMCID: PMC6008252 DOI: 10.1016/j.jcmgh.2018.02.008] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/01/2018] [Accepted: 02/26/2018] [Indexed: 12/13/2022]
Abstract
BACKGROUND & AIMS Hepatic encephalopathy is a serious neurologic complication of acute and chronic liver diseases. We previously showed that aberrant bile acid signaling contributes to the development of hepatic encephalopathy via farnesoid X receptor (FXR)-mediated mechanisms in neurons. In the brain, a novel alternative bile acid synthesis pathway, catalyzed by cytochrome p450 46A1 (Cyp46A1), is the primary mechanism by which the brain regulates cholesterol homeostasis. The aim of this study was to determine if FXR activation in the brain altered cholesterol homeostasis during hepatic encephalopathy. METHODS Cyp7A1-/- mice or C57Bl/6 mice pretreated with central infusion of FXR vivo morpholino, 2-hydroxypropyl-β-cyclodextrin, or fed a cholestyramine-supplemented diet were injected with azoxymethane (AOM). Cognitive and neuromuscular impairment as well as liver damage and expression of Cyp46A1 were assessed using standard techniques. The subsequent cholesterol content in the frontal cortex was measured using commercially available kits and by Filipin III and Nile Red staining. RESULTS There was an increase in membrane-bound and intracellular cholesterol in the cortex of mice treated with AOM that was associated with decreased Cyp46A1 expression. Strategies to inhibit FXR signaling prevented the down-regulation of Cyp46A1 and the accumulation of cholesterol. Treatment of mice with 2-hydroxypropyl-β-cyclodextrin attenuated the AOM-induced cholesterol accumulation in the brain and the cognitive and neuromuscular deficits without altering the underlying liver pathology. CONCLUSIONS During hepatic encephalopathy, FXR signaling increases brain cholesterol and contributes to neurologic decline. Targeting cholesterol accumulation in the brain may be a possible therapeutic target for the management of hepatic encephalopathy.
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Key Words
- 2-HβC, 2-hypdroxypropyl-β-cyclodextrin
- AOM, azoxymethane
- Acute Liver Failure
- Azoxymethane
- CYP46A1, cytochrome p450 46A1
- CYP7A1, cytochrome p450 7A1
- Cytochrome p450 46A1
- FXR, farnesoid X receptor
- Farnesoid X Receptor
- GAPDH, glyceraldehyde-3-phosphate dehydrogenase
- PBS, phosphate-buffered saline
- PFA, paraformaldehyde
- RT-PCR, reverse-transcription polymerase chain reaction
- WT, wild-type
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Affiliation(s)
- Matthew McMillin
- Central Texas Veterans Healthcare System, Temple, Texas,Department of Medical Physiology, Texas A&M College of Medicine, Temple, Texas
| | - Stephanie Grant
- Central Texas Veterans Healthcare System, Temple, Texas,Department of Medical Physiology, Texas A&M College of Medicine, Temple, Texas
| | - Gabriel Frampton
- Central Texas Veterans Healthcare System, Temple, Texas,Department of Medical Physiology, Texas A&M College of Medicine, Temple, Texas
| | - Anca D. Petrescu
- Central Texas Veterans Healthcare System, Temple, Texas,Department of Medical Physiology, Texas A&M College of Medicine, Temple, Texas
| | - Jessica Kain
- Central Texas Veterans Healthcare System, Temple, Texas,Department of Medical Physiology, Texas A&M College of Medicine, Temple, Texas
| | - Elaina Williams
- Central Texas Veterans Healthcare System, Temple, Texas,Department of Medical Physiology, Texas A&M College of Medicine, Temple, Texas
| | - Rebecca Haines
- Department of Medical Physiology, Texas A&M College of Medicine, Temple, Texas
| | - Lauren Canady
- Department of Medical Physiology, Texas A&M College of Medicine, Temple, Texas
| | - Sharon DeMorrow
- Central Texas Veterans Healthcare System, Temple, Texas,Department of Medical Physiology, Texas A&M College of Medicine, Temple, Texas,Correspondence Address correspondence to: Sharon DeMorrow, PhD, Department of Medical Physiology, Texas A&M Health Science Center, Central Texas Veterans Health Care System, Building 205, 1901 South 1st Street, Temple, Texas 76504. fax: (254) 743-0378.
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63
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Mertens KL, Kalsbeek A, Soeters MR, Eggink HM. Bile Acid Signaling Pathways from the Enterohepatic Circulation to the Central Nervous System. Front Neurosci 2017; 11:617. [PMID: 29163019 PMCID: PMC5681992 DOI: 10.3389/fnins.2017.00617] [Citation(s) in RCA: 178] [Impact Index Per Article: 25.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2017] [Accepted: 10/23/2017] [Indexed: 12/14/2022] Open
Abstract
Bile acids are best known as detergents involved in the digestion of lipids. In addition, new data in the last decade have shown that bile acids also function as gut hormones capable of influencing metabolic processes via receptors such as FXR (farnesoid X receptor) and TGR5 (Takeda G protein-coupled receptor 5). These effects of bile acids are not restricted to the gastrointestinal tract, but can affect different tissues throughout the organism. It is still unclear whether these effects also involve signaling of bile acids to the central nervous system (CNS). Bile acid signaling to the CNS encompasses both direct and indirect pathways. Bile acids can act directly in the brain via central FXR and TGR5 signaling. In addition, there are two indirect pathways that involve intermediate agents released upon interaction with bile acids receptors in the gut. Activation of intestinal FXR and TGR5 receptors can result in the release of fibroblast growth factor 19 (FGF19) and glucagon-like peptide 1 (GLP-1), both capable of signaling to the CNS. We conclude that when plasma bile acids levels are high all three pathways may contribute in signal transmission to the CNS. However, under normal physiological circumstances, the indirect pathway involving GLP-1 may evoke the most substantial effect in the brain.
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Affiliation(s)
- Kim L Mertens
- Master's Program in Biomedical Sciences, University of Amsterdam, Amsterdam, Netherlands
| | - Andries Kalsbeek
- Department of Endocrinology and Metabolism, Academic Medical Center, University of Amsterdam, Amsterdam, Netherlands.,Laboratory of Endocrinology, Department Clinical Chemistry, Academic Medical Centre, University of Amsterdam, Amsterdam, Netherlands.,Department of Hypothalamic Integration Mechanisms, Netherlands Institute for Neuroscience, Amsterdam, Netherlands
| | - Maarten R Soeters
- Department of Endocrinology and Metabolism, Academic Medical Center, University of Amsterdam, Amsterdam, Netherlands
| | - Hannah M Eggink
- Department of Endocrinology and Metabolism, Academic Medical Center, University of Amsterdam, Amsterdam, Netherlands.,Department of Hypothalamic Integration Mechanisms, Netherlands Institute for Neuroscience, Amsterdam, Netherlands
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