Acute-phase Response Gene Expression Research Articles

SMC-Derived Hyaluronan Modulates Vascular SMC Phenotype in Murine Atherosclerosis.

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CREBH: A Complex Array of Regulatory Mechanisms in Nutritional Signaling, Metabolic Inflammation, and Metabolic Disease.

The endoplasmic reticulum (ER)-resident basic leucine zipper (bZIP) transcription factor c-AMP responsive element binding protein H (CREBH/CREB3L3) is exclusively expressed in the liver and intestine. Physiologically, CREBH is intrinsically linked to nutritional homeostasis via its regulation on fatty acid β-oxidation, lipid droplet process, very low-density lipoprotein metabolism, gluconeogenesis, and iron metabolism. Pathologically, CREBH enhances hepatic acute-phase response gene expression (e.g., C-reactive protein and serum amyloid P-component) and mediates nutrient-surplus induced metabolic inflammation. Hyperactivation of CREBH in metabolic inflammation further contributes to the development of hyperlipidemia, lipotoxicity, non-alcoholic fatty liver disease, and potentially non-alcoholic steatohepatitis. This review highlights recent findings that delineate the interactions between CREBH and peroxisome proliferator activated receptor α (PPARα), fibroblast growth factor 21 (FGF21), fat-specific protein 27 (FSP27), and lipoprotein metabolism with a focus on the molecular and biochemical mechanisms that underlie the development of metabolic inflammation, non-alcoholic fatty liver disease and inflammatory associated bone disease.

Atranorin and lecanoric acid antagonize TCDD-induced xenobiotic response element-driven activity, but not xenobiotic response element-independent activity.

Lichens are symbiotic organisms that consist of fungi and photosynthetic symbionts (algae and/or cyanobacteria). Previous studies of their constituents suggested lichens produce many kinds of aromatic secondary metabolites, such as depsides, quinones, and dibenzofurans. In this study, we evaluated the aryl hydrocarbon receptor (AhR) antagonistic activity of 17 lichen substances and demonstrated that atranorin (1) and lecanoric acid (2), isolated from Parmotrema tinctorum Hale, showed an inhibitory effect on luciferase activity increased by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), using an XRE-driven pX4TK-Luc reporter gene assay. In addition, CYP1A1 mRNA and protein levels increased by TCDD were also suppressed by 1 and 2. Conversely, neither 1 nor 2 antagonized the suppressive effect of TCDD on interleukin (IL)-1β-induced acute-phase response (APR) gene expression. Thus, we concluded that 1 and 2 were selective AhR modulators that antagonize XRE-dependent activity, but not XRE-independent activity. However, 1 has different characteristics to 2 in that 1 alone showed a suppressive effect on IL-1β-induced APR gene expression in a similar fashion to TCDD.

Ah receptor represses acute-phase response gene expression without binding to its cognate response element

Repression of the nuclear factor-κB (NF-κB) pathway has been extensively researched because of its pivotal role in inflammation. We investigated the potential of the aryl hydrocarbon receptor (AHR) to suppress NF-κB regulated-gene expression, especially acute-phase genes, such as serum amyloid A (Saa). Using AHR mutants, it was determined that nuclear translocation and heterodimerization with AHR-nuclear translocator are essential, but DNA binding is not involved in AHR-mediated Saa repression. A number of AHR ligands were capable of repressing Saa3 expression. AHR activation leads to a decrease in RELA and C/EBP/β recruitment to and histone acetylation at Saa3 gene promoter. A battery of acute-phase genes (eg C-reactive protein and haptoglobin) induced by cytokine exposure was repressed by AHR activation in mouse hepatocytes. Dietary exposure to an AHR ligand represses cytokine-induced acute-phase response in the liver. Use of a human liver-derived cell line revealed similar repression of Saa mRNA levels and secreted protein. Repression of AHR expression also enhanced Saa induction in response to cytokines, suggesting that AHR is capable of constitutively repressing Saa gene expression. These results establish a role for AHR in inflammatory signaling within the liver, presenting a new therapeutic opportunity, and signify AHR's ability to function in a DNA-independent manner.

Oncostatin M pathway plays a major role in the renal acute phase response

The acute phase response is traditionally characterized by hepatic synthesis of proteins as an inflammatory response to injury, with interleukin-6 (IL-6) being the key mediator. In contrast, microarray studies in human renal transplant implantation biopsies indicate a strong acute phase response in the deceased donor kidney, associated with a significant upregulation of oncostatin M receptor beta (OSMR). The aim of this study was to determine whether the kidney can generate a strong acute phase response, mediated by the OSM/OSMR gateway. Genes associated with the IL-6 cytokine family and acute phase reactants were analyzed by real-time RT-PCR in four groups of human biopsies spanning a spectrum of renal injury. OSM, OSMR, and fibrinogen beta (FGB) were progressively more highly expressed from prenephrectomy, living donor, deceased donor, to discarded donor kidneys, suggesting correlation with severity of injury and local renal synthesis. Acute phase response gene expression was analyzed in human proximal tubular cells in culture in response to OSM. OSM induced a significant increase in expression of FGB, OSMR, serpin peptidase inhibitor A1, IL-6, and lipopolysaccharide binding protein, and a decrease in IL-6R. These changes were largely attenuated by coincubation with an OSMR blocking antibody, indicating the OSM effect was mediated through OSMR. OSM also resulted in a significantly altered expression of acute phase genes compared with IL-6 or leukemia inhibitory factor, suggesting that OSM is the predominant cytokine mediating the renal tubular acute phase response. In conclusion, the renal parenchyma is capable of generating a strong acute phase response, likely mediated via OSM/OSMR.

Systemic and Distal Repercussions of Liver-Specific Peroxisome Proliferator-Activated Receptor-α Control of the Acute-Phase Response

The acute-phase response is characterized by the modulation of liver expression of many proteins involved in a diversity of biological functions. Among them, some are associated with the pathology of atherosclerosis. We previously found that peroxisome proliferator-activated receptor-alpha (PPARalpha) agonists attenuate the IL-6 induction of acute-phase response gene expression in vitro and in vivo. In the current work, we found a PPARalpha-dependent regulation of hepatic acute-phase response stimulated by IL-1. We also found that IL-1-stimulated expression of secondary wave cytokines such as IL-6 is prevented upon PPARalpha activation in liver. Direct involvement of hepatic PPARalpha was demonstrated using a liver-restricted expression of PPARalpha in mice. IL-1- or IL-6-mediated acute-phase response was inhibited by fenofibrate treatment in liver-specific PPARalpha-expressing mice but not in PPARalpha-deficient mice. In addition, we demonstrated that PPARalpha exerts a general control of the acute-phase response by using an inflammation/infection model of lipopolysaccharide. In such a context, liver-specific PPARalpha-expressing mice displayed lower circulating levels of TNF, IL-1, and IL-6 cytokines. We found a distal repercussion of this lowering at the vascular wall level as illustrated by a decreased expression of adhesion molecules in aorta. In conclusion, we demonstrated that through a specific liver action, PPARalpha behaves as a modulator of systemic inflammation and of the associated vascular response.

IL-6 and the acute phase response in murine atherosclerosis

Numerous studies have implicated C-reactive protein (CRP) and the acute phase response (APR) in the development of atherosclerotic heart disease. Interleukin (IL)-6, which regulates both CRP expression and the APR, has also been identified as a risk factor for heart disease. To more directly evaluate the role of IL-6 in the development of atherosclerosis, IL-6 knockout mice were crossed with atherosclerosis prone LDL receptor (LDL-R) knockout mice. Lesion development was evaluated on Chow, Western type and Paigen diets. As anticipated, the Paigen diet stimulated the expression of APR genes in LDL-R[−/−] mice, but not IL-6[−/−]/LDL-R[−/−] mice. Despite this difference in acute phase response, only modest and statistically not significant differences were noted in the development of atherosclerotic lesions in LDL-R[−/−] and IL-6[−/−]/LDL-R[−/−] mice. These observations suggest that IL-6 and the acute phase response may not play as significant role in atherogenesis as other studies have indicated.

Global Suppression of IL-6-induced Acute Phase Response Gene Expression after Chronic in Vivo Treatment with the Peroxisome Proliferator-activated Receptor-α Activator Fenofibrate

The peroxisome proliferator-activated receptor alpha (PPARalpha), which is highly expressed in liver, plays key roles in lipid metabolism and inflammation. Interleukin-6 (IL-6) is the principal inducer of acute phase response (APR) gene expression. In the present study, we demonstrate that chronic treatment with the PPARalpha agonist fenofibrate fully prevents the IL-6-induced APR gene expression in wild-type but not in PPARalpha-deficient mice. PPARalpha prevents the IL-6-induced expression of the positive APR genes fibrinogen-alpha, -beta, -gamma, haptoglobulin, and serum amyloid A and the IL-6-induced suppression of the negative APR gene, major urinary protein. Furthermore, the effect of PPARalpha on the APR gene expression does not simply consist in a delayed systemic response to IL-6 but occurs directly at the transcriptional level. This global suppression of acute phase gene transcription may be explained by two PPARalpha-dependent in vivo effects: 1) PPARalpha activation results in the down-regulation of the IL-6 receptor components gp80 and gp130 in the liver, thereby reducing the phosphorylation and activation of the downstream transcription factors STAT3 and c-Jun that transduce the IL-6 signal; and 2) PPARalpha reduces the basal expression of the transcription factors CCAAT enhancer-binding protein-alpha, -beta, -delta, which are responsible for immediate and maintained transcription of APR genes. A similar global effect of fenofibrate on acute phase protein expression is observed in hyperlipidemic patients chronically treated with fenofibrate, which displayed decreased plasma concentrations of the positive APR proteins fibrinogen, C-reactive protein, serum amyloid A, plasminogen, and alpha2-macroglobulin and increased plasma concentrations of the negative APR albumin, underlining the clinical significance of our findings.

Involution of the mouse mammary gland is associated with an immune cascade and an acute-phase response, involving LBP, CD14 and STAT3.

Involution of the mammary gland is a complex process of controlled apoptosis and tissue remodelling. The aim of the project was to identify genes that are specifically involved in this process. We used Affymetrix oligonucleotide microarrays to perform a detailed transcript analysis on the mechanism of controlled involution after withdrawal of the pups at day seven of lactation. Some of the results were confirmed by semi-quantitative reverse transcriptase polymerase chain reaction, Western blotting or immunohistochemistry. We identified 145 genes that were specifically upregulated during the first 4 days of involution; of these, 49 encoded immunoglobulin genes. A further 12 genes, including those encoding the signal transducer and activator of transcription 3 (STAT3), the lipopolysaccharide receptor (CD14) and lipopolysaccharide-binding protein (LBP), were involved in the acute-phase response, demonstrating that the expression of acute-phase response genes can occur in the mammary gland itself and not only in the liver. Expression of LBP and CD14 was upregulated, at both the RNA and protein level, immediately after pup withdrawal; CD14 was strongly expressed in the luminal epithelial cells. Other genes identified suggested neutrophil activation early in involution, followed by macrophage activation late in the process. Immunohistochemistry and histological staining confirmed the infiltration of the involuting mammary tissue with neutrophils, plasma cells, macrophages and eosinophils. Oligonucleotide microarrays are a useful tool for identifying genes that are involved in the complex developmental process of mammary gland involution. The genes identified are consistent with an immune cascade, with an early acute-phase response that occurs in the mammary gland itself and resembles a wound healing process.

Lack of gp130 expression in hepatocytes promotes liver injury

Background & aims: Interleukin 6 (IL-6) contributes via its signal transducer gp130 to the acute phase response (APR) in hepatocytes. Recent studies indicated that IL-6 is involved in the regulation of different pathophysiologic conditions of the liver. To define the IL-6-dependent intracellular pathways more specifically, we generated a hepatocyte-specific gp130 knockout mouse. Methods: Hepatocyte-specific gp130-deficient mice were generated using the Cre-loxP system. Expression of the Cre recombinase was under the control of a hepatocyte-specific control element. Adult mice were challenged with IL-6, oncostatin M (OSM), and LPS. Results: Cre expression started at day 10.5 postconception, and a complete deletion of gp130 in hepatocytes was found at day 14 during liver development. The adult liver of these mice showed no abnormalities; however, after IL-6 and OSM stimulation, gp130-dependent pathways (STAT3, APR gene expression) were completely blocked in the liver of these animals. Additionally, challenging hepatocyte-specific gp130 knockout animals with lipopolysaccharides (LPS) lead to an onset of acute liver injury with an increase of hepatocyte apoptosis associated with elevated tumor necrosis factor α (TNF-α) serum levels and reduced nuclear factor κB (NF-κB) activation in hepatocytes. Conclusions: Our findings demonstrate that gp130 is of minor relevance for embryonal development of hepatocytes. However, the molecule has an essential role in controlling acute phase gene expression and provides hepatocellular protection after LPS challenge.

Down-Regulation of Cytochrome P450 2C Family Members and Positive Acute-Phase Response Gene Expression by Peroxisome Proliferator Chemicals

In this study, we show that peroxisome proliferator chemical (PPC) exposure leads to alterations in the expression of genes in rat liver regulated by the sex-specific growth hormone secretory pattern and induced during inflammation. Expression of the male-specific cytochrome P450 (P450) 2C11 and alpha2 urinary globulin (alpha2u) genes and the female-specific P450 2C12 gene was down-regulated by some PPC. Expression of P450 2C13, also under control by the sex-specific growth hormone secretory pattern, was not altered by PPC treatment, indicating that regulation of CYP2C family members does not involve perturbation of the growth hormone secretory pattern. In contrast to the increases in expression observed when inflammation was induced in male rats, two positive acute-phase response genes, alpha1-acid glycoprotein and beta-fibrinogen, were decreased by PPC exposure. The down-regulation of the P450 2C11 by WY-14,643 could be reproduced in cultured rat hepatocytes, indicating the down-regulation is a direct effect. Experiments in wild-type mice and mice that lacked a functional peroxisome proliferator-activated receptor-alpha gene showed that down-regulation by WY of alpha1-acid glycoprotein, beta-fibrinogen, and a mouse homologue of alpha2u was dependent on peroxisome proliferator-activated receptor-alpha expression. Our results demonstrate that PPC exposure leads to down-regulation of diverse liver-specific genes, including CYP2C family members important in hormonal homeostasis and acute-phase response genes important in inflammatory responses.

CCAAT/enhancer binding proteins beta and delta regulate alpha1-acid glycoprotein gene expression in rat intestinal epithelial cells.

Isoforms of CCAAT/enhancer binding protein (C/EBP) are expressed in rodent intestine as well as in the rat intestinal epithelial cell line IEC-6. However, no specific roles have been attributed to these isoforms in intestinal epithelial cells. To determine whether C/EBP family members could be implicated in the regulation of acute-phase response gene expression in intestinal epithelial cells, we have studied the effect of glucocorticoids on expression of the alpha1-acid glycoprotein gene and C/EBP isoforms in IEC-6 cells. Glucocorticoids induced alpha1-acid glycoprotein gene expression in these cells. This induction coincided with an increase of DNA-binding capacity of both C/EBPbeta and C/EBPdelta to the B1 and B2 C/EBP-interacting sites localized in the rat AGP promoter. Transforming growth factor beta, (TGFbeta), a cytokine involved in the transcriptional regulation of several acute-phase plasma proteins, antagonized the glucocorticoid-dependent induction of alpha1-acid glycoprotein gene expression. In parallel, TGFbeta downregulated the DNA-binding capacities of both the C/EBPbeta and C/EBPdelta isoforms. Mutations of the B1 or the B2 C/EBP-interacting site strongly reduced the responsiveness of the alpha1-acid glycoprotein promoter to glucocorticoids and TGFbeta. These results demonstrate a functional role for C/EBPbeta and C/EBPdelta in rat intestinal epithelial cells and suggest that these isoforms represent important modulators of the acute-phase response and of glucocorticoid, as well as TGFbeta, responsiveness.

Activation of cerebral cytokine gene expression and its correlation with onset of reactive astrocyte and acute-phase response gene expression in scrapie

The pathogenesis of scrapie, a transmissible subacute spongiform encephalopathy, is unclear. However, certain aspects of the known cellular and molecular neuropathology in scrapie led us to hypothesize that cytokines could mediate cerebral pathological changes in this neurodegenerative disease. Therefore, expression of multiple cytokine genes in the brain and peripheral organs of scrapie-infected mice was examined. Late in the course of scrapie, expression of tumor necrosis factor alpha (TNF-alpha), interleukin-1 alpha (IL-1 alpha), and IL-1 beta mRNA was markedly increased in the brain but not the spleen, kidneys, or liver. In time course studies, scrapie-infected mice exhibited increased cerebral expression of the TNF-alpha, IL-1 alpha, and IL-1 beta mRNAs by week 15 postinoculation--a time point that coincided with the onset of clinical symptoms. Thereafter, the levels of these cytokine transcripts increased progressively to the terminal stages of of the disease (week 25). To determine the relationship of the increased cerebral expression of the cytokine mRNAs to the development of pathological changes in scrapie, we examined the expression of the glial fibrillary acidic protein gene (a marker for astrocytosis) and the murine acute-phase response gene homologous to the alpha 1-antichymotrypsin gene (designated EB22/5.3). Markedly increased expression of both the glial fibrillary acidic protein and EB22/5.3 mRNAs was observed in the brain but not the peripheral organs of scrapie-infected mice. The increased expression of both these gene products also occurred at week 15 of infection and, thereafter, increased progressively to the terminal stages of the disease. Therefore, infection of mice with scrapie resulted in significant increases in the expression of the TNF-alpha, IL-1 alpha, and IL-1 beta gene products, whose pattern correlated with the onset and development of molecular and clinical pathological changes. Since scrapie is known not to evoke an immune response, the present findings strongly suggest the existence of a localized cerebral host response to the agent during which proinflammatory cytokines could be key pathogenic mediators.