Intracellular apolipoprotein E affects Amyloid Precursor Protein processing and amyloid Abeta production in COS-1 cells

The apoE gene has been identified as a major susceptibility locus for late-onset Alzheimer's disease (LOAD). The epsilon4 allele greatly reduces age of onset of LOAD as compared to the wild-type 3 allele. The molecular mechanism(s) underlying the association has not yet been fully elucidated. The apoE protein has been shown to physically interact with the Abeta region of the Amyloid Precursor Protein (APP), but also with the ectodomain of the APP holoprotein itself. In this study we have used apoE fusion proteins containing either the ER retention sequence KDEL or trans-Golgi network (TGN) signal sequence in order to define potential apoE-mediated alterations in APP protein processing. Co-expression and pulse-chase experiments showed that a functional apoE:APP interaction occurs intracellularly which directly affects maturation and subsequently the secretion kinetics of APP. In addition, an epsilon4 allele-specific induction of Abeta production has been demonstrated. apoE3 resulted in increased Abeta production only when targeted to the ER, as observed in cells transfected with an apoE3KDEL fusion protein as well as following treatment with brefeldin A. The findings suggest that in cells that express both apoE and APP, such as astrocytes and microglia, a functional apoE:APP interaction may occur which modulates APP processing and Abeta production.

Serum amyloid A (apoSAA) expression is up-regulated in rheumatoid arthritis and induces transcription of matrix metalloproteinases

The acute-phase reactant rabbit serum amyloid A 3 (SAA3) was identified as the major difference product in Ag-induced arthritis in the rabbit, a model resembling in many aspects the clinical characteristics of rheumatoid arthritis (RA) in humans. In Ag-induced arthritis, up-regulated SAA3 transcription in vivo was detected in cells infiltrating into the inflamed joint, in the area where pannus formation starts and, most notably, also in chondrocytes. The proinflammatory cytokine IL-1beta induced SAA3 transcription in primary rabbit chondrocytes in vitro. Furthermore, rSAA3 protein induced transcription of matrix metalloproteinases in rabbit chondrocytes in vitro. In the human experimental system, IL-1beta induced transcription of acute-phase SAA (A-SSA; encoded by SAA1/SAA2) in primary chondrocytes. Similar to the rabbit system, recombinant human A-SAA protein was able to induce matrix metalloproteinases' transcription in chondrocytes. Further, immunohistochemistry demonstrated that A-SAA was highly expressed in human RA synovium. A new finding of our study is that A-SSA expression was also detected in cartilage in osteoarthritis. Our data, together with previous findings of SAA expression in RA synovium, suggest that A-SAA may play a role in cartilage destruction in arthritis.

Dexamethasone, but not IL-1 alone, upregulates acute-phase serum amyloid A gene expression and production by cultured human aortic smooth muscle cells

Although the SAA1 and SAA2 protein isoforms (A-SAA) of the serum amyloid A (SAA) family of acute phase reactants have been found in a number of extrahepatic tissues; the site of synthesis of extrahepatic SAA remains to be clarified. To investigate site(s) of synthesis of the SAA protein localized to atherosclerotic plaque, expression of the SAA1 and SAA2 genes by cultured human aortic smooth muscle cells (HASMC) was investigated. A-SAA protein isoforms were detectable by immunoblot analysis in the culture medium of HASMC. Both A-SAA and C-SAA (SAA4) mRNA isoforms were constitutively expressed by HASMC, but not, however, by the human umbilical vein endothelial cells. Expression of A-SAA mRNA by HASMC was upregulated by corticoid hormones including dexamethasone (Dex), corticosterone, hydrocortisone, and aldosterone, but not by the cytokines interleukin (IL)-1, IL-6, and tumour necrosis factor (TNF)-alpha alone. Dex stimulation of A-SAA mRNA was time and dose dependent from 6 to 48 h. The threshold concentration for upregulation of A-SAA mRNA in HASMC by Dex was between 0.1 and 1 nM. IL-1, known to upregulate extrahepatic A-SAA gene expression in other cell systems only slightly, if at all, upregulated Dex-induced A-SAA expression by HASMC. Thus, it is possible that some of the A-SAA protein in the vascular wall (atherosclerotic plaques) can originate from smooth muscle cells. In consideration of recent reports that A-SAA modulates the inflammatory process and lipid synthesis, A-SAA can potentially serve as a physiological regulator of smooth muscle cell homeostasis within that, in a disease state, participates in the formation of atherosclerotic plaques.

Serum amyloid A protein in an echinoderm: its primary structure and expression during intestinal regeneration in the sea cucumber Holothuria glaberrima

Serum amyloid A (SAA) proteins comprise a family of highly conserved apolipoproteins found in all mammals thus far investigated, and also in ducks and salmonid fishes. However, no invertebrate SAA homologues have been detected to date. Here we report the characterization of the first SAA homologue in a nonvertebrate deuterostome, the echinoderm Holothuria glaberrima. A 971-base-pair cDNA was obtained from a regenerating intestine cDNA library. The clone contains a 369-nucleotide open reading frame corresponding to a 122-amino-acid protein exhibiting a high degree of homology to members of the SAA superfamily. Sequence alignments of the holothuroid and vertebrate SAA proteins make evident a remarkable degree of conservation, even between phylogenetically disparate groups. Northern blots and immunohistochemistry show that SAA expression increases during regeneration of the holothuroid digestive tract as compared with normal nonregenerating tissue, and that the SAA protein is expressed by cells of the coelomic epithelium of the regenerating intestine. While SAA expression during the initial wound healing stage of regeneration is minimal, it increases during subsequent stages, peaking at day 15 of regeneration, concomitantly with lumen formation and the organization of the muscular layers of the regenerating digestive tract. Although in vertebrates SAA proteins may be part of a well-conserved anti-inflammatory mechanism, their exact biological function remains obscure. Our results suggest the possibility that SAA proteins, although structurally conserved, may possess enough functional diversity to participate in processes other than anti-inflammatory responses.

Serum amyloid A transcription in Atlantic salmon (Salmo salar L.) hepatocytes is enhanced by stimulation with macrophage factors, recombinant human IL-1 beta, IL-6 and TNF alpha or bacterial lipopolysaccharide

Serum amyloid A (A-SAA) has previously been reported to be an acute-phase protein in salmonids. Hepatocytes represent a major source of A-SAA in salmonids, but nothing is known about hepatocyte SAA synthesis in fish. In the present work, the expression of A-SAA transcripts in primary cultures of Atlantic salmon hepatocytes in response to macrophage derived cytokines, human recombinant cytokines and bacterial lipopolysaccharide (LPS) was studied by Northern blot analysis. The macrophage supernatants were prepared by stimulating Atlantic salmon head kidney macrophages with LPS, yeast glucan or a leukocyte derived macrophage activating factor (MAF). The supernatants from glucan- or MAF-stimulated macrophages had no effect on A-SAA expression of the hepatocytes, while supernatants from LPS-stimulated macrophages gave about a 2-fold increase in expression. The combination of either glucan and MAF, or LPS and MAF were more effective and these supernatants gave a 3.4- and 5.2-fold increase in A-SAA expression, respectively. The hepatocytes were also treated with the human recombinant cytokines TNFalpha, IL-1beta and IL-6, alone or in combination. The A-SAA response to each of them alone was modest, but TNFalpha and IL-6 or IL-1beta and IL-6 in combination gave a higher response than each cytokine alone. These data suggest that the expression of A-SAA by hepatocytes from Atlantic salmon is induced by cytokine-like molecules. Interestingly, hepatocytes treated directly with LPS gave a more than 10-fold increase in SAA mRNA expression, but it is not known if this is a direct effect of LPS on the hepatocytes or if it is mediated by other contaminating cell types.

Serum amyloid A secretion from monocytic leukaemia cell line THP-1 and cultured human peripheral monocytes

Serum amyloid A (SAA), an acute-phase protein and a precursor of fibrous components in reactive amyloid deposits, is synthesized mainly in the liver under the stimulation of inflammation-related cytokines. In addition, the SAA gene is expressed in monocytes/macrophages, which are believed to play a central role in amyloid fibrillogenesis. Consequently, the pathogenic implication of SAA produced from these cells has been of major concern. Because SAA synthesis at the protein level in such cells has never been analyzed quantitatively, in this study an enzyme-linked immunosorbent assay was generated with a detection level sufficiently high to measure SAA concentrations in the culture supernatants of the human monocytic leukaemia cell line THP-1. SAA secretion by THP-1 with interleukin (IL)-1beta required the presence of dexamethasone as proposed previously. We also found that unidentified components in fetal calf serum (FCS) could induce SAA production by THP-1 in the presence of dexamethasone. These findings are in contrast to the results obtained from hepatoma cell line HepG2, in which IL-1beta alone could induce SAA secretion, while dexamethasone-supplemented FCS could not. The method was able to quantify SAA secreted from cultured human peripheral monocytes. The findings suggest that monocytes produce SAA in almost the same manner as THP-1. Thus, THP-1 cells can be utilized to investigate a distinctive manner of SAA production from monocytes.

Enhancement of AA-amyloid formation in mice by transthyretin amyloid fragments and polyethylene glycol

The mechanism behind amyloid formation is unknown in all types of amyloidosis. Several substances can enhance amyloid formation in animal experiments. To induce secondary systemic amyloid (AA-type amyloid) formation, we injected silver nitrate into mice together with either amyloid fibrils obtained from patients with familial polyneuropathy (FAP) type I or polyethylene glycol (PEG). Mice injected with silver nitrate only served as controls. Amyloid deposits were detectable at day 3 in animals injected with amyloid fibrils and in those injected with PEG, whereas in control mice, deposits were not noted before day 12. Our results indicate that amyloid fibrils from FAP patients and even a non-sulfate containing polysaccharide (PEG) have the potential to act as amyloid-enhancing factors.

Expression of SAA and amyloidogenesis in congenic mice of CE/J and C57BL/6 strains

Inbred strains of mice display different susceptibilities to experimental induction of reactive amyloidosis. CBA/J, C57BL/6, and ICR are among the most susceptible strains, while CE/J mice appear to be totally resistant. In contrast to amyloidogenic strains which express two major acute phase serum amyloid A proteins (SAA1 and SAA2), CE/J mice produce only a single isoform, designated SAA2.2. Studies indicate that CE/J x CBA/J hybrid mice expressing both SAA2.2 and SAA1.1/SAA2.1 are amyloid resistant, and this has led to the hypothesis that SAA2.2 may protect mice against amyloid formation even in the presence of fibrillogenic SAA1.1. We have tested this hypothesis in mice derived from CE/J and C57BL/6 strains. CE/J mice were mated with C57BL/6 mice to produce F1 hybrids. Congenic mice were then produced by backcrossing each successive generation to C57BL/6 mice. Representative mice from F2 and F3 generations were analyzed to determine SAA genotype and susceptibility to amyloid induction by repeated casein injections. All F2 and F3 mice examined, including those which carried the SAA2.2 gene, developed extensive splenic AA amyloid. Expression of SAA2.2 in mice testing positive for the SAA2.2 gene was confirmed by sequence analysis of HDL-associated SAA proteins. These results demonstrate that the presence of SAA2.2 is not sufficient to protect CE/J x C57BL/6 hybrid mice from amyloid development. This is consistent with our observation that macrophage cultures, derived from C57BL/6, CBA/J, or CE/J mice, undergo amyloid deposition when treated with SAA1.1 alone or with equal amounts of SAA1.1 and SAA2.2, but show no deposition when treated solely with SAA2.2. We conclude from these studies that while SAA2.2 is non-fibrillogenic, its physical presence is not sufficient for protection against amyloid formation.

Amyloid formation in the rat: adenoviral expression of mouse serum amyloid A proteins

Serum amyloid A (SAA) proteins are acute-phase apolipoproteins that are associated with high-density lipoprotein (HDL) particles: SAA proteins are precursors to secondary amyloid fibril proteins and under certain conditions of chronic or recurrent inflammation these proteins are deposited as amyloid fibrils. Of two isotypes found in mouse, SAA1.1 and SAA2.1, only SAA1.1 is deposited into amyloid. The CE/J mouse is unique, in that the only isoform identified is a hybrid between SAA1.1 and SAA2.1 and the mouse does not show amyloid deposition. In the rat, a deletion in the SAA1/SAA2 gene is associated with the absence of protein in the plasma and subsequently no amyloid deposition is detected. We have generated adenoviral vectors to study the expression of SAA proteins on HDL metabolism and amyloid formation. Injection of SAA viruses into rats resulted in expression of the mouse SAA proteins in the plasma with specific association of the SAA with HDL particles. The induction of SAA proteins was comparable to that seen in mice presented with the inflammatory agent, bacterial lipopolysaccharide (LPS). Adenoviral induced SAA levels were maintained for up to several weeks without a significant decrease in SAA expression. Injection of rats with the mouse SAA1.1 adenoviral vector, followed by amyloid enhancing factor (AEF) and silver nitrate resulted in the deposition of amyloid fibrils in the spleen. After 2 weeks, amyloid could be detected in other tissues, including the heart, liver, kidneys and lungs. When animals were injected with null or the SAA2.2 virus no amyloid was detected. These studies demonstrate that the inability of the rat to develop AA amyloid is due to the lack of synthesizing an amyloidogenic SAA protein. Furthermore, the expression of the adenoviral SAA protein from the liver and incorporation onto HDL particles further supports the hypothesis that AA amyloid is derived from circulating SAA protein. The ease of use of the adenoviral vectors and the rat provide an excellent model to study the function of SAA proteins.

Synergistic induction of mouse serum amyloid A3 promoter by the inflammatory mediators IL-1 and IL-6

Serum amyloid A (SAA), one of the major acute-phase proteins, increases several hundredfold in concentration in plasma following acute inflammation, primarily as a result of a 200-fold increase in its transcription rate. We have previously demonstrated that a 350-bp promoter fragment from the mouse SAA3 gene could confer conditioned medium-induced expression in cultured cells. The induction is mediated through a 42-bp distal response element (DRE) consisting of three functional regulatory elements. In this study, we show that interleukin-1 (IL-1) is the major cytokine in the conditioned medium responsible for SAA3 induction, and the induction by IL-1 can be effectively blocked by H-7, a protein kinase C inhibitor. Although IL-6 alone had no effect on SAA3 promoter activity, the addition of IL-6 and IL-1 resulted in dramatic synergistic activation of the reporter gene. We further show that the DRE is both necessary and sufficient to confer synergistic induction by IL-1 and IL-6. Moreover, individual mutation of the three regulatory elements within DRE either abolished or drastically reduced the synergistic induction. Our results indicate that synergistic activation of SAA3 promoter by IL-1 and IL-6 is achieved through integration of signals triggered by these two cytokines onto the DRE and that all three functionally distinct regulatory elements in the DRE are required to effectively and fully activate SAA3 gene transcription.

A search within the IL-1 type I receptor reveals a peptide with hydropathic complementarity to the IL-1beta trigger loop which binds to IL-1 and inhibits in vitro responses

In previous research, we were able to demonstrate that a seven amino acid residue peptide (VITFFSL), designed as an antisense peptide of the beta-bulge trigger loop region of interleukin 1beta (IL-1beta) (QGEESND; residues 48-54 [mature protein sequence]), was able to interact with IL-1 specifically and inhibit the response to IL-1 in an in vitro bioassay. The evidence was consistent with a specific interaction ocurring between antisense peptide and the trigger loop region. On the basis that antisense peptides are able to interact with their corresponding sense peptide sequences as a result of their mutually complementary hydropathic profiles (Fassina G., Verdoliva, A., Cassani, G., Melli, M., 1994. Binding of type I IL-1 receptor fragment 151-162 to IL-1. Growth Factors 10, 99-106; Maier, C.C., Moseley, H.N.B., Zhou, S., Whitaker, J.N., Blalock, J.E., 1994. Indentification of interactive determinants on idiotypic-anti-idiotypic antibodies through comparison of their hydropathic profiles. Immunomethods 5, 107-113), we devised a computer program (FINDH) to search the amino acid residue sequence of interleukin-1 type 1 receptor (IL-1 R1) for peptide motifs possessing hydropathic complementarity to the trigger loop sequence. The most complementary "best-fit peptide" motif (LITVLNI) was located in the third extracellular domain of IL-1 R1. A best-fit peptide corresponding to this motif was synthesised and found to bind to IL-1beta as well as inhibit the response to IL-1 in two independent in vitro bioassays (monitoring IL-1 dependent serum amyloid A synthesis and IL-1 dependent alkaline phosphatase activity, respectively). A second peptide motif (VIEFITL) was identified and the corresponding peptide synthesised along with a reordered version (LTILINV) of the best fit peptide. Both failed to bind measurably with IL-1beta or inhibit the response to IL-1 in the two bioassays. This best fit peptide behaved very similarly, in terms of IL-1 binding and inhibition behaviour, to the original trigger loop antisense peptide. Reference to the recently released X-ray crystal structure of IL-1beta and the IL1-R1 extracellular domain shows that the best fit peptide motif in IL-1 R1 is not apparantly interacting with the IL-1 trigger loop, although both are close in space. The intriguing possibility exists that the best fit peptide motif could represent an alternative site for IL-1beta receptor interaction which has not thus far been identified.

An upstream repressor element that contributes to hepatocyte-specific expression of the rat serum amyloid A1 gene

Serum amyloid A (SAA) is a major acute-phase protein whose expression can be dramatically induced in response to tissue damage, infection, and inflammation. Its expression is highly tissue-specific, restricted almost exclusively to liver hepatocytes. We have shown that a 320-bp fragment of the rat SAA1 promoter could confer liver-cell-specific expression on a reporter gene when transfected into cultured cells. Here we report the identification of a 29-bp regulatory element that possesses inhibitory activities on SAA1 promoter in HeLa cells but has no such effects in liver cells. Moreover, this regulatory element has properties of a transcriptional repressor; in that, it can function with a heterologous promoter and is independent of orientation and distance from the transcription initiation site. Protein binding studies showed that this regulatory element can form specific protein-DNA complexes with nuclear proteins from several nonliver cell lines (HeLa, 10T(1/2), and C2) and placenta. However, the same DNA-protein complex was not detected in extracts from liver or liver-derived cell lines (HepG2 and Hep3B). Taken together, our results demonstrate the presence of a DNA-binding protein, termed tissue-specific repressor, found only in nonhepatocytes which may function to repress SAA1 gene expression by interacting with a repressor element. Thus, liver-specific expression of the SAA1 gene is apparently regulated by both positive and negative regulatory elements and their interacting transcription factors to ensure that it is expressed only in suitable cell types.

Posttranscriptional regulation of acute phase serum amyloid A2 expression by the 5'- and 3'-untranslated regions of its mRNA

Human acute-phase serum amyloid A protein (A-SAA) is a major acute phase reactant, the concentration of which increases dramatically as part of the body's early response to inflammation. A-SAA is the product of two almost identical genes, SAA1 and SAA2, which are induced by the pro-inflammatory cytokines, IL-1 and IL-6. In this study, we examine the roles played by the 5'- and 3'-untranslated regions (UTRs) of the SAA2 mRNA in regulating A-SAA2 expression. SAA2 promoter-driven luciferase reporter gene constructs carrying the SAA2 5'-UTR and/or 3'-UTR were transiently transfected into the HepG2 human hepatoma cell line. After induction of chimeric mRNA with IL-1beta and IL-6, the SAA2 5'- and 3'-UTRs were both able to posttranscriptionally modify the expression of the luciferase reporter. The SAA2 5'-UTR promotes efficient translation of the chimeric luciferase transcripts, whereas the SAA2 3'-UTR shares this property and also significantly accelerates the rate of reporter mRNA degradation. Our data strongly suggest that the SAA2 5'- and 3'-UTRs each play significant independent roles in the posttranscriptional regulation of A-SAA2 protein synthesis.

Novel neurotrophin-1/B cell-stimulating factor-3: a cytokine of the IL-6 family

We have identified a cytokine of the IL-6 family and named it novel neurotrophin-1/B cell-stimulating factor-3 (NNT-1/BSF-3). NNT-1/BSF-3 cDNA was cloned from activated Jurkat human T cell lymphoma cells. Its sequence predicts a 225-aa protein with a 27-aa signal peptide, a molecular mass of 22 kDa in mature form, and the highest homology to cardiotrophin-1 and ciliary neurotrophic factor. The gene for NNT-1/BSF-3 is on chromosome 11q13. A murine equivalent to NNT-1/BSF-3 also was identified, which shows 96% homology to human NNT-1/BSF-3. NNT-1/BSF-3 mRNA is found mainly in lymph nodes and spleen. NNT-1/BSF-3 induces tyrosine phosphorylation of glycoprotein 130 (gp130), leukemia inhibitory factor receptor beta, and signal transducer and activator of transcription 3 in the SK-N-MC human neuroblastoma cells. NNT-1/BSF-3 shows activities typical of IL-6 family members. In vitro, it supports the survival of chicken embryo motor and sympathetic neurons. In mice, it induces serum amyloid A, potentiates the induction by IL-1 of corticosterone and IL-6, and causes body weight loss and B cell hyperplasia with serum IgG and IgM increase. NNT-1/BSF-3 is a gp130 activator with B-cell stimulating capability.

Lipopolysaccharide binding protein and serum amyloid A secretion by human intestinal epithelial cells during the acute phase response

The acute phase proteins LPS binding protein (LBP) and serum amyloid A (SAA) are produced by the liver and are present in the circulation. Both proteins have been shown to participate in the immune response to endotoxins. The intestinal mucosa forms a large surface that is continuously exposed to these microbial products. By secretion of antimicrobial and immunomodulating agents, the intestinal epithelium contributes to the defense against bacteria and their products. The aim of this study was to explore the influence of the inflammatory mediators TNF-alpha, IL-6, and IL-1beta on the release of LBP and SAA by intestinal epithelial cells (IEC). In addition, the induction of LBP and SAA release by cell lines of intestinal epithelial cells and hepatic cells was compared. The data obtained show that in addition to liver cells, IEC also expressed LBP mRNA and released bioactive LBP and SAA upon stimulation. Regulation of LBP and SAA release by IEC and hepatocytes was typical for class 1 acute phase proteins, although differences in regulation between the cell types were observed. Endotoxin did not induce LBP and SAA release. Glucocorticoids were demonstrated to strongly enhance the cytokine-induced release of LBP and SAA by IEC, corresponding to hepatocytes. The data from this study, which imply that human IEC can produce LBP and SAA, suggest a role for these proteins in the local defense mechanism of the gut to endotoxin. Furthermore, the results demonstrate that tissues other than the liver are involved in the acute phase response.

Persistent expression of serum amyloid A during experimentally induced chronic inflammatory condition in rabbit involves differential activation of SAF, NF-kappa B, and C/EBP transcription factors

The serum amyloid A (SAA) protein has been implicated in the pathogenesis of several chronic inflammatory diseases. Its induction mechanism in response to a chronic inflammatory condition was investigated in rabbits following multiple s.c. injections of AgNO3 over a period of 35 days. During unremitting exposure to inflammatory stimulus, a persistently higher than normal level of SAA2 expression was seen in multiple tissues. Induction of SAA was correlated with higher levels of several transcription factor activities. Increased SAA-activating factor (SAF) activity was detected in the liver, lung, and brain tissues under both acute and chronic inflammatory conditions. In the heart, kidney, and skeletal muscle tissues, this activity remained virtually constant. In contrast, CCAAT enhancer binding protein (C/EBP) DNA-binding activity was transiently induced in selective tissues. Higher than normal NF-kappa B DNA-binding activity was detected in the lung and to a lesser extent in the liver and kidney tissues under both acute and chronic conditions. This result suggested that C/EBP, SAF, and NF-kappa B are required for transient acute phase induction of SAA whereas SAF and NF-kappa B activities are necessary for persistent SAA expression during chronic inflammatory conditions.

Effects of cytokines, butyrate and dexamethasone on serum amyloid A and apolipoprotein A-I synthesis in human HUH-7 hepatoma cells

Serum amyloid A (SAA) and apolipoprotein A-I (apo A-I) are secreted by the liver. As concentrations of both apolipoproteins are inversely related under normal and acute-phase conditions, human HUH-7 hepatoma cells were stimulated with interleukin (IL)-1alpha (100 and 200 U), IL-6 (50 and 100 U), butyrate (2 mM) and dexamethasone (2 x 10(-7)M and 1 x 10(-6)M), alone or in combination. Changes in SAA and apo A-I synthesis were monitored after metabolic labelling of the cells with [35S]-methionine. Intracellular and secreted SAA and apo A-I were immunoprecipitated, separated by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE), and the radioactivity in the corresponding bands was counted. Intracellular apolipoprotein levels were increased by all stimuli, either alone or in combination, between 2.7- and 5.5-fold (SAA) and between 2.8- and 4.1-fold (apo A-I), respectively. In a similar manner, apolipoprotein levels secreted by HUH-7 cells were increased between 3.1- and 4.3-fold (SAA) and between 1.9- and 3. 3-fold (apo A-I). Co-administration of cytokines, butyrate and/or dexamethasone had no pronounced synergistic effect on intracellular biosynthesis and secretion of SAA and apo A-I. The results from the present study suggest that apo A-I must not necessarily be considered as a negative acute-phase reactant.

Expression of recombinant feline serum amyloid A (SAA) protein

Feline serum amyloid A (SAA) cDNA clone was isolated from a hepatic mRNA of a mixed-breed cat. The feline SAA cDNA clone contains 333 nucleotides and deduced amino acid sequence shows 87.4%, 73.9%, and 65.8% homology with dog, human and mouse SAA respectively. Relative to the human and mouse SAA proteins, an additional peptide of eight amino acids is specified in the feline cDNA clone. Recombinant feline SAA (rfSAA) was expressed at high levels using pGEX bacterial expression system. Cleavage from the fusion moiety, and purification using glutathione-sepharose yielded pure soluble form of rfSAA. Antibodies generated against rfSAA were specific for feline SAA and showed no cross-reactivity with human SAA. Furthermore, antibodies against human SAA did not react with feline SAA. These results indicate that antigenicity of feline SAA is totally different from human SAA.

Augmentation of type I IL-1 receptor expression and IL-1 signaling by IL-6 and glucocorticoid in murine hepatocytes

IL-1 signal is transduced through type I receptor (IL-1RI). We have recently reported that LPS augments IL-1RI mRNA expression in the hepatocytes of mice in vivo, and the augmentation is mediated by the interaction of IL-1, IL-6, and glucocorticoid (GC). In this study, we examined whether IL-1RI mRNA expression level in the hepatocytes reflects those of cell surface molecule and IL-1 signaling. When primary cultured murine hepatocytes were treated with dexamethasone (Dex) or IL-6, these two reagents synergistically up-regulated IL-1RI mRNA expression in the cells. 125I-labeled IL-1 binding experiment showed that the level of binding was also up-regulated by the treatment with Dex and IL-6. Scatchard analysis revealed that the number of IL-1R increased. The increased binding of IL-1 was completely inhibited by an Ab against murine IL-1RI, indicating that Dex and IL-6 augmented the expression of cell surface IL-1RI molecule. When hepatocytes were pretreated with Dex and IL-6, the activation of IL-1R-associated kinase was augmented in response to IL-1, indicating that IL-1 signaling was also augmented. In addition, IL-1 treatment following administration of the combination of Dex and IL-6 into mice markedly increased the serum level of serum amyloid A. These results indicate that GC and IL-6 augment the expression of cell surface IL-1RI in hepatocytes, as well as IL-1 signaling and IL-1R-associated kinase activation, through up-regulation of IL-1RI mRNA level, which represents a novel regulatory network between IL-1, GC, and IL-6.

The kinetics and magnitude of the synergistic activation of the serum amyloid A promoter by IL-1 beta and IL-6 is determined by the order of cytokine addition

Human serum amyloid A protein (A-SAA) is a major hepatic acute-phase protein, the concentration of which increases by up to 1000-fold during inflammation. This induction is primarily due to synergistic transcriptional up-regulation by pro-inflammatory cytokines, principally interleukin (IL)-1 and IL-6. Using HepG2 hepatoma cells transfected with pGL2-SAA2pt, a cytokine-responsive human SAA2 promoter/luciferase reporter gene construct, we show that stimulation with IL-1 beta prior to IL-6 is essential for maximal synergistic transcriptional induction of the SAA2 gene. The reciprocal treatment, i.e. stimulation of the promoter with IL-6 before IL-1 beta results in significantly less synergistic activation of the SAA2 promoter. These findings strongly suggest that in vitro studies of acute-phase-protein induction using combinations of cytokines should be designed to reflect the chronology of their participation in the cytokine cascade.

The acute phase protein serum amyloid A (SAA) as an inflammatory marker in equine influenza virus infection

The acute phase protein serum amyloid A (SAA) has proven potentially useful as an inflammatory marker in the horse, but the knowledge of SAA responses in viral diseases is limited. The aim of this study was to evaluate SAA as a marker for acute equine influenza A2 (H3N8) virus infection. This is a highly contagious, serious condition that inflicts suffering on affected horses and predisposes them to secondary bacterial infections and impaired performance. Seventy horses, suffering from equine influenza, as verified by clinical signs and seroconversion, were sampled in the acute (the first 48 h) and convalescent (days 11-22) stages of the disease, and SAA concentrations were determined. Clinical signs and rectal temperature were recorded. Secondary infections, that could have influenced SAA concentrations, were clinically suspected in 4 horses. SAA concentrations were higher in the acute stage than in the convalescent stage, and there was a statistically positive relationship between acute stage SAA concentrations and clinical signs and between acute stage SAA concentrations and maximal rectal temperature. Horses sampled early in the acute stage had lower SAA concentrations than those sampled later, indicating increasing concentrations during the first 48 h. There was a statistically positive relationship between convalescent SAA concentrations and degree of clinical signs during the disease process. The results of this investigation indicate that equine SAA responds to equine influenza infection by increasing in concentration during the first 48 h of clinical signs and returning to baseline within 11-22 days in uncomplicated cases.

Mechanism of minimally modified LDL-mediated induction of serum amyloid A gene in monocyte/macrophage cells

Minimally modified low-density lipoprotein (MM-LDL) is regarded as a major risk factor for the development of atherosclerosis. In this report, we show that this lipoprotein complex can induce expression of an inflammatory protein, serum amyloid A (SAA), in monocyte/macrophage cells, a key cell type implicated in the pathogenesis of atherosclerosis. By promoter function analysis and site-directed mutagenesis, we have located promoter regions responsive to MM-LDL action. Using electrophoretic mobility shift, antibody ablation/supershift, and Western blot assays, we showed that induction of SAA by MM-LDL is mediated via activation of SAS binding factor (SAF) and C/EBP transcription factors. We further show that tamoxifen, a downregulator of CD36, one of the major scavenger receptors which binds MM-LDL, can inhibit MM-LDL-mediated SAA induction in THP-1 cells. This finding suggests that CD36 participates in the manifestation of the inflammatory effects of MM-LDL. Our experiments provide the first evidence for transcription factor activation by MM-LDL.

Intracerebroventricular injection of anti-Fas activates the hypothalamus-pituitary-adrenal axis and induces peripheral interleukin-6 and serum amyloid A in mice: comparison with other ligands of the tumor necrosis factor/nerve growth factor receptor superfamily

Fas is a receptor of the tumor necrosis factor (TNF)/ nerve growth factor (NGF) receptor superfamily that mediates apoptosis and some inflammatory changes. As the central administration of TNF is known to activate the hypothalamus-pituitary-adrenal axis (HPAA) and to induce peripheral responses including induction of serum interleukin (IL)-6 and serum amyloid A (SAA), we investigated the effects of intracerebroventricular (i.c.v.) administration of agonist anti-Fas monoclonal antibody Jo2. Centrally administered anti-Fas (1 microg/mouse, i.c.v.) induced elevated levels of corticosterone, IL-6, and SAA comparable to those observed after i.c.v. administration of recombinant murine TNF. On the other hand, administration of murine NGF did not elevate serum corticosterone or IL-6, but induced SAA. Thus, Fas can trigger a centrally mediated anti-inflammatory response (HPAA activation) and induce a peripheral acute-phase response comparable to that induced with TNF, whereas NGF induces only acute-phase proteins.

Endotoxemia in mice stimulates production of complement C3 and serum amyloid A in mucosa of small intestine

We examined the effect of endotoxemia in mice on protein and mRNA levels for the acute phase proteins complement C3 and serum amyloid A (SAA) in jejunal mucosa. Endotoxemia was induced in mice by the subcutaneous injection of 250 microg lipopolysaccharide per mouse. Control mice were injected with saline. C3 and SAA were measured by ELISA. Messenger RNA levels were determined by Northern blot analysis or competitive PCR. Immunohistochemistry was performed to determine in which cell type(s) C3 and SAA were present. Mucosal C3 and SAA protein and mRNA levels were increased in endotoxemic mice. Immunohistochemistry showed that C3 was present in both enterocytes and cells of the lamina propria, whereas SAA was seen mainly in lamina propria cells. Results suggest that endotoxemia stimulates production of C3 and SAA in small intestinal mucosa. The response may be regulated at the transcriptional level and probably reflects increased synthesis of the acute phase proteins in both enterocytes and cells of the lamina propria.

Mucosal production of complement C3 and serum amyloid A is differentially regulated in different parts of the gastrointestinal tract during endotoxemia in mice

The effect of endotoxemia and sepsis on mucosal production of the acute-phase proteins complement component C3 and serum amyloid A (SAA) was studied in mice. In addition, the role of the proinflammatory cytokines tumor necrosis factor-alpha, interleukin (IL)(-1)beta, and IL-6 on mucosal C3 and SAA production was examined. Endotoxemia was induced by the subcutaneous injection of 250 microg/mouse of lipopolysaccharide. Control mice were injected with corresponding volumes of sterile saline solution. Sepsis was induced by cecal ligation and puncture, and sham-operated mice served as controls. Endotoxemia resulted in increased mucosal C3 levels in all parts of the gastrointestinal tract examined, from the stomach to the colon, with the most pronounced effects noticed in the proximal gastrointestinal tract. The influence of endotoxemia on mucosal SAA production was more differentiated with increased levels noted in the jejunum and ileum, and no changes seen in gastric and colonic mucosa. Sepsis resulted in similar changes in mucosal C3 and SAA levels as seen in endotoxemic mice, except that SAA levels were increased in colonic mucosa of septic mice. Among the cytokines, IL(-1)beta resulted in the most pronounced changes in mucosal acute-phase proteins. The increase in C3 and SAA levels in the mucosa of the small intestine during endotoxemia was partially blocked by IL(-1) receptor antagonist. The results suggest that endotoxemia is associated with increased mucosal C3 production in different parts of the gastrointestinal tract and increased SAA production in the mucosa of the small intestine. Mucosal acute-phase protein synthesis may, at least in part, be regulated by IL(-1)beta.

Leptin causes body weight loss in the absence of in vivo activities typical of cytokines of the IL-6 family

To investigate if leptin shares in vivo activities with interleukin (IL)-6 family cytokines, it was tested in normal mice for the ability, after a single injection, to induce the acute-phase protein serum amyloid A, to potentiate the induction by IL-1 of serum corticosterone and IL-6, and to inhibit the induction by lipopolysaccharide of serum tumor necrosis factor and, after seven daily injections, to cause body weight loss and to change peripheral blood cell counts. At a 0.5 mg/kg dose, leptin caused body weight loss but did not show any of the other activities above. At a dose of 5 mg/kg, which also caused body weight loss, leptin potentiated the induction by IL-1 of serum corticosterone and IL-6 but did not show any other activity. In addition to causing body weight loss, leptin shows only some of the in vivo activities typical of IL-6 family cytokines and only if used at a dose that exceeds the one sufficient to affect body weight. In vivo, leptin seems to chiefly control body weight and not inflammatory or hematopoietic processes.

Adenoviral expression of murine serum amyloid A proteins to study amyloid fibrillogenesis

Serum amyloid A (SAA) proteins are one of the most inducible acute-phase reactants and are precursors of secondary amyloidosis. In the mouse, SAA1 and SAA2 are induced in approximately equal quantities in response to amyloid induction models. These two isotypes differ in only 9 of 103 amino acid residues; however, only SAA2 is selectively deposited into amyloid fibrils. SAA expression in the CE/J mouse species is an exception in that gene duplication did not occur and the CE/J variant is a hybrid molecule sharing features of SAA1 and SAA2. However, even though it is more closely related to SAA2 it is not deposited as amyloid fibrils. We have developed an adenoviral vector system to overexpress SAA proteins in cell culture to determine the ability of these proteins to form amyloid fibrils, and to study the structural features in relation to amyloid formation. Both the SAA2 and CE/J SAA proteins were synthesized in large quantities and purified to homogeneity. Electron microscopic analysis of the SAA proteins revealed that the SAA2 protein was capable of forming amyloid fibrils, whereas the CE/J SAA was incapable. Radiolabelled SAAs were associated with normal or acute-phase high-density lipoproteins (HDLs); we examined them for their clearance from the circulation. In normal mice, SAA2 had a half-life of 70 min and CE/J SAA had a half-life of 120 min; however, in amyloid mice 50% of the SAA2 cleared in 55 min, compared with 135 min for the CE/J protein. When the SAA proteins were associated with acute-phase HDLs, SAA2 clearance was decreased to 60 min in normal mice compared with 30 min in amyloidogenic mice. Both normal and acute-phase HDLs were capable of depositing SAA2 into preformed amyloid fibrils, whereas the CE/J protein did not become associated with amyloid fibrils. This established approach opens the doors for large-scale SAA production and for the examination of specific amino acids involved in the fibrillogenic capability of the SAA2 molecule in vitro and in vivo.

Acceleration of amyloid protein A amyloidosis by amyloid-like synthetic fibrils

Amyloid protein A (AA) amyloidosis is a consequence of some long-standing inflammatory conditions, and subsequently, an N-terminal fragment of the acute phase protein serum AA forms beta-sheet fibrils that are deposited in different tissues. It is unknown why only some individuals develop AA amyloidosis. In the mouse model, AA amyloidosis develops after approximately 25 days of inflammatory challenge. This lag phase can be shortened dramatically by administration of a small amount of amyloid extract containing an as yet undefined amyloid-enhancing factor. In the present study, we show that preformed amyloid-like fibrils made from short synthetic peptides corresponding to parts of several different amyloid fibril proteins exert amyloidogenic enhancing activity when given i.v. to mice at the induction of inflammation. We followed i.v. administered, radiolabeled, heterologous, synthetic fibrils to the lung and to the perifollicular area in the spleen and found that new AA-amyloid fibrils developed on these preformed fibrils. Our findings thus show that preformed, synthetic, amyloid-like fibrils have an in vivo nidus activity and that amyloid-enhancing activity may occur, at least in part, through this mechanism. Our findings also show that fibrils of a heterologous chemical nature exert amyloid-enhancing activity.

The sphingomyelin-ceramide pathway participates in cytokine regulation of C-reactive protein and serum amyloid A, but not alpha-fibrinogen

Maximal induction of the acute-phase proteins C-reactive protein (CRP) and serum amyloid A (SAA) in the human hepatoma cell line Hep3B requires the combination of interleukin (IL)-6 and IL-1. In contrast, IL-1 inhibits fibrinogen induction by IL-6. To explore the possible participation of the sphingomyelin-ceramide pathway in the transduction of cytokine effects, the role of this pathway in expression of CRP, SAA and alpha-fibrinogen was investigated. The cell-permeable ceramide analogues C2 and C6 each greatly potentiated induction of both CRP and SAA mRNA by IL-6+IL-1beta but did not affect the responses of alpha-fibrinogen to IL-6 or to IL-6+IL-1beta. The combination of IL-6+IL-1beta led to increased turnover of sphingomyelin in Hep3B cells. D609, an inhibitor of ceramide production by acidic but not neutral sphingomyelinases, substantially inhibited induction of CRP and SAA by IL-6+IL-1beta. The ability of C2 and C6 to potentiate the effects of cytokines suggests that the sphingomyelin-ceramide pathway participates in induction of CRP and SAA by IL-6+IL-1beta under these experimental conditions, most likely by transducing the effects of IL-1beta. C2 and C6 were unable to substitute for IL-1beta in enhancing IL-6 effects on CRP and SAA, consistent with other reports indicating that the sphingomyelin-ceramide pathway is only a single component of multiple necessary converging pathways for induction of many genes. In contrast, this pathway does not appear to participate in mediating the inhibitory effects of IL-1beta on fibrinogen induction by IL-6.

Down-regulation of the major circulating precursors of proteins deposited in secondary amyloidosis by a recombinant mouse interleukin-1 receptor antagonist

An inflammatory response was induced in C57BL/6 mice using silver nitrate. Co-administration of a recombinant mouse interleukin-1 receptor antagonist (rmIL-1ra) significantly reduced the magnitude of hepatic induction of the mRNA specifying the serum amyloid A (A-SAA) isoforms A-SAA1 and A-SAA2 for up to 24 h. In relative terms, the amount by which the induction of serum A-SAA protein levels could be countered by the antagonist was less, probably reflecting extrahepatic A-SAA synthesis that is regulated independently of IL-1. Induction of hepatic serum amyloid P component (SAP) mRNA and other acute-phase reactant (APR) mRNA were all partially blocked by rmIL-1ra for up to 24 h, indicating that induction of these APR mRNA involves both IL-1 and additional factors acting independently of IL-1. Hepatic mRNA levels of the negative APR apolipoprotein A-I (apo A-I) and serum albumin were down-regulated by silver nitrate treatment; rmIL-1ra partially restored serum albumin mRNA levels but not those of apo A-I. The IL-1ra-mediated reduction in inflammation-induced hepatic mRNA and serum protein concentrations of A-SAA and SAP (the precursors of the main protein components of amyloid deposits in secondary amyloidosis) was, however, not sufficient to prevent or delay early amyloid deposition in the silver nitrate/amyloid enhancing factor model of accelerated amyloidosis. The rmIL-1ra may be a useful component in future therapies to control inflammation and secondary amyloidosis; in addition, it will be a useful tool for the detailed analysis of the IL-1-driven aspects of inflammation per se.

Regulation of extrahepatic apolipoprotein serum amyloid A (ApoSAA) gene expression by interleukin-1 alpha alone: synthesis and secretion of ApoSAA by cultured aortic smooth muscle cells

Serum amyloid A apolipoproteins (apoSAA) appear to compromise the ability of high density lipoprotein to protect against atherosclerosis and it is of interest to determine whether aortic smooth muscle cells can contribute to local pools of apoSAA in the presence of cytokines that are known to stimulate acute phase apoSAA (A-apoSAA) synthesis in the liver. In this study, the regulation of A-apoSAA synthesis was monitored in cultured neonatal rabbit aortic smooth muscle cells. Constitutive apoSAA3 gene expression was minimal, and only detectable by amplification of the mRNA by reverse transcriptase-polymerase chain reaction. ApoSAA3 gene expression and protein synthesis were stimulated by IL-1 alpha; as little as 0.01 ng/ml of IL-1 alpha stimulated an increase in steady state levels of apoSAA3 mRNA. Interestingly, IL-6 (which is required in addition to IL-1 alpha for the optimal synthesis of A-apoSAA by human hepatoma cells) had little if any effect on apoSAA3 synthesis by the smooth muscle cells. In a time course, it was shown that the stimulation of apoSAA3 mRNA levels was apparent by 1-2 h after the addition of cytokine, and that levels remained elevated in the presence of the cytokine for at least 48 h. Immunoprecipitation using an antiserum directed against apoSAA3 revealed that IL-1 alpha stimulated the synthesis and secretion of apoSAA3 protein in a manner that was consistent with apoSAA3 mRNA expression. The implications of these findings in atherogenesis are discussed.

An in vitro cellular system for generation of AA-amyloid

Different conditions for establishing a cell culture system for generation of AA-amyloid were investigated. The most effective system was based on peritoneal macrophages from CBA/J mice that had received repeated injections of Hammersten casein, with subsequent cultivation of the cells at high density, high levels of acute phase serum, and neutral pH. Staining with Congo red, thioflavin T, and anti-AA revealed amyloid-like structures associated with macrophage clusters. The structures increased in number and size from day 2 to 6 of cell cultivation. The concentration of apoSAA in the culture medium fell markedly in the amyloid-producing cell cultures, while the SAP concentration was not reduced. The described cell culture system can be useful in studies of the influence of chaperone molecules and other factors or the formation and degradation of amyloid fibrils.

[Production of inflammatory markers by HepG 2 cells stimulated with monocyte conditioned media: the effects of corticosteroid and other immunosuppressants]

Both C-reactive protein (CRP) and serum amyloid A protein (SAA) are determined as an indicator of inflammation and tissue damage. We found that CRP decreased extremely after administration of corticosteroid but SAA did not. However, the mechanism of the CRP decrease by corticosteroid therapy is unclear. In this study we have examined the effects of some immunosuppressive drugs and cytokines on the production of CRP and SAA by human hepatoma cells (HepG 2). A corticosteroid prednisolone did not enhance the production of CRP by HepG 2 cells but enhanced that of SAA, which indicate that prednisolone had no direct effect on the CRP production. Some immunosuppressants other than corticosteroids suppressed the SAA production but had no effect on the CRP production. IL-1 beta induced both CRP and SAA production but only in the co-presence of IL-6. A cytokine IL-6 induced the CRP production in the presence of IL-1 beta, but did not affect the constitutive production of SAA. Then we have examined the cytokine production by monocytes stimulated by lipopolysaccharide. Prednisolone inhibited the production of IL-1 alpha, IL-1 beta, IL-6 and TNF alpha.

Messenger RNA deadenylylation precedes decapping in mammalian cells

In yeast, the major mRNA degradation pathway is initiated by poly(A) tail shortening that triggers mRNA decapping. The mRNA is then degraded by 5'-to-3' exonucleolysis. In mammalian cells, even though poly(A) tail shortening also precedes mRNA degradation, the degradation pathway has not been elucidated. We have used a reverse transcription-PCR approach that relies on mRNA circularization to measure the poly(A) tail length of four mammalian mRNAs. This approach allows for the simultaneous analysis of the 5' and 3' ends of the same mRNA molecule. For all four mRNAs analyzed, this strategy permitted us to demonstrate the existence of small amounts of decapped mRNA species which have a shorter poly(A) tail than their capped counterparts. Kinetic analysis of one of these mRNAs indicates that the decapped species with a short poly(A) tail are mRNA degradation products. Therefore, our results indicate that decapping is preceded by a shortening of the poly(A) tail in mammalian cells, as it is in yeast, suggesting that this mRNA degradation pathway is conserved throughout eukaryotic evolution.

Response to local inflammation of IL-1 beta-converting enzyme- deficient mice

IL-1 beta-converting enzyme (ICE) cleaves pro-IL-1 beta to the mature, released form. Although other proteases can process pro-IL-1 beta, ICE-deficient (ICE -/-) mice do not release mature IL-1 beta in response to endotoxin. The purpose of our study was to investigate the response of ICE -/- mice in two models of local inflammation, turpentine-induced tissue damage and zymosan-induced peritonitis. No differences were observed in the development of the systemic acute phase response after turpentine administration between wild-type and ICE -/- mice, but this response was completely impaired in IL-1 beta -/- mice. Accordingly, the levels of mature IL-1 beta produced in response to turpentine did not differ between wild-type and ICE -/- mice. In contrast, following zymosan-induced peritonitis, the levels of mature IL-1 beta were significantly lower in ICE -/- mice. This was associated with a 50% decrease in cellular infiltrate in ICE -/- mice compared with that in wild-type controls. The reduced production of zymosan-induced mature IL-1 beta in ICE -/- mice was also observed from cultured peritoneal or spleen cells. Our results demonstrate that in turpentine-induced tissue necrosis, precursor IL-1 beta is processed by non-ICE proteases, but in complement-mediated inflammation, ICE participates in the processing of the IL-1 beta precursor.

Expression and regulation of constitutive and acute phase serum amyloid A mRNAs in hepatic and non-hepatic cell lines

'Acute phase' and 'constitutive' SAA (A-SAA and C-SAA, respectively) mRNA levels were measured in hepatic and non-hepatic cell lines after treatment with monocyte conditioned medium (MoCM), with or without dexamethasone (Dex). A-SAA mRNAs were detected in MoCM-treated hepatoma cell lines (PLC/PRF/5, HuH7, HepG2, and Hep3B), a fibroblast cell line (MRC5), six epithelial cell lines (RT4/ 31, SW13, Hela Ohio, HCT-8, CaCo2, and KB), and an endothelial cell line ECV304. In KB cells, Dex alone caused a dramatic increase in A-SAA mRNA levels. C-SAA was detected in all hepatic and non-hepatic cell lines. Two differentially regulated size classes of C-SAA mRNA were detected in the hepatoma cell lines. A-SAA mRNA levels were measured in ECV304 cells treated with IL-1 beta, IL-6, TNF alpha and Dex, in various combinations, and revealed different profiles to those seen for hepatic cells. The extent of polyadenylation of A-SAA mRNA in ECV304 and KB cells differed whereas the polyadenylation of C-SAA mRNA remained constant. These data suggest that the parameters that determine the steady state mRNA levels and post-transcriptional regulation of A-SAA and C-SAA mRNAs are different and are cell type specific.

Generation of soluble recombinant human acute phase serum amyloid A2 (A-SAA2) protein and its use in development of an A-SAA specific ELISA

Human acute phase serum amyloid A (the A-SAA2 isoform) was expressed at high levels using the pGEX bacterial expression system. A-SAA2 protein was expressed in E. coli NM544 as part of a fusion protein facilitating rapid purification. A-SAA2 was cleaved from the fusion moiety in the presence of a non-ionic detergent (Triton X-100) to release a soluble A-SAA2. Further purification using ion exchange chromatography yielded a pure A-SAA2 (3 mg per litre of culture). Antibodies generated against recombinant A-SAA2 were specific for the acute phase SAAs, A-SAA1 and A-SAA2 and showed no cross-reactivity with the constitutively expressed SAA (C-SAA). These antibodies were used to develop a rapid enzyme-linked immunosorbent assay (ELISA) specific for the measurement of A-SAA in serum.

C-reactive protein and serum amyloid A mRNA stability following induction by cytokines

We determined the effects of cytokine withdrawal on C-reactive protein (CRP) and serum amyloid A (SAA) mRNA abundance in Hep3B cells following 24 h of preinduction with interleukin 6 plus interleukin 1 beta. After cytokine withdrawal, CRP transcription rate rapidly fell to undetectable levels and mRNA levels fell with a half-disappearance time of about 2.5 h. In view of the relatively small amount of CRP transcription occurring at this time, it is likely that this value closely reflects the actual half-life of CRP mRNA. In contrast, substantial SAA transcription continued for at least 8 h, while SAA mRNA fell with a half-disappearance time of about 8.5 h. It is not possible, under these conditions, to determine SAA mRNA half-life, but it clearly was no greater than 8.5 h. Both Actinomycin D (ActD) and cycloheximide enhanced the stability of SAA mRNA, strongly suggesting that SAA mRNA degradation requires synthesis of a short-lived protein. CRP mRNA stability was also enhanced by ActD, but cycloheximide did not have a protracted stabilizing effect, suggesting complex regulatory processes. These studies provide insight into the stability of CRP and SAA mRNA following induction with [IL-6 + IL-1 beta] and into the mechanisms regulating their degradation.

Unstimulated peripheral blood mononuclear cells from patients with the hyper-IgD syndrome produce cytokines capable of potent induction of C-reactive protein and serum amyloid A in Hep3B cells

The hyper-IgD and periodic fever syndrome (HIDS) and familial Mediterranean fever (FMF) are both characterized by attacks of periodic fever accompanied by acute phase responses that are substantially higher in HIDS than in FMF. To determine whether this difference could be due to differences in production of acute phase protein-inducing mediators, we studied PBMC from HIDS and FMF patients in the inactive phase of disease. Unstimulated PBMC from patients with inactive HIDS released significantly more IL-1 beta, IL-6, and TNF-alpha than did PBMC from patients with FMF, but unstimulated PBMC from the latter group released significantly more IL-1 beta and IL-6 compared with controls. Conditioned medium (CM) derived from PBMC of patients with inactive HIDS induced significantly greater CRP production and significantly higher mRNAs for CRP and SAA in Hep3B cells than did CM derived from the PBMC of patients with inactive FMF. Stimulation of PBMC with LPS led to further increases in cytokine production and in acute phase protein-inducing ability in both patient groups and in controls. These findings suggest that the greater acute phase response seen in HIDS compared with FMF reflects greater production of acute phase protein-inducing cytokines in the former patients and indicates that PBMC from inactive HIDS patients are already activated in vivo. Finally, the finding of both quantitative and qualitative differences in cytokine production by unstimulated PBMC from HIDS and FMF patients supports the likelihood of different pathogeneses of these diseases.

Developmental regulation of expression of rabbit C-reactive protein and serum amyloid A genes

Serum amyloid A (SAA) and C-reactive protein (CRP) are acute phase plasma proteins which increases 100- to 1000-fold after inflammatory stimuli. In this study pregnant rabbits were given lipopolysaccharide (LPS) or subjected to laparotomy with fetal injections of LPS at different stages of gestation. Newborn rabbits were given LPS or saline. SAA and CRP mRNA were studied using Northern blot analyses and scanning densitometry. In vitro transcribed RNAs were used as standards for quantitative mRNA analyses. A gradual increase in LPS-induced SAA and CRP mRNA levels was observed during development, but only SAA mRNA induction was seen at gestational day 19. Fetal SAA and CRP mRNA induction was not seen after maternal LPS stimulation. The constitutive level of SAA and CRP mRNA was significantly lower in fetal rabbits than in adults. The control level of SAA mRNA in one-day-old rabbits was higher than the normal adult level, while the neonatal CRP mRNA level was lower. SAA2 seemed to be the major acute phase reactant in both fetal, neonatal and adult rabbits, while relatively more SAA3 was found during early developmental stages. The study demonstrated that CRP and three SAA genes are differentially regulated during development.

Reduced susceptibility to IL-1 and endotoxin in transgenic mice expressing IL-1 in their lens

To learn about the effects of chronic exposure to IL-1 we generated a transgenic (Tg) mouse line that expresses human IL-1 beta under the control of the lens alpha-A crystallin promoter. Expression of human IL-1 beta was restricted to the eye; neither the protein nor its mRNA were detected in various other organs of the Tg mice. The Tg mice develop severe ocular inflammation shortly after birth, which affects the lens and other eye tissues and apparently allows the release of IL-1 into the circulation. Here we report that the Tg mice exhibit decreased responsiveness to IL-1 and lipopolysaccharide (LPS), as compared to their wild-type littermate controls: (1) when injected with IL-1 the Tg mice produced lower levels of serum amyloid A than their controls; (2) thymocytes of the Tg mice responded less vigorously in culture to stimulation with IL-1; and (3) Tg mice showed lower morbidity and mortality than their controls when injected with toxic amounts of LPS. These data suggest that chronic exposure to IL-1 in the Tg mice induces partial resistance to this cytokine, analogous to the reduced responsiveness to IL-1 in animals pretreated with this proinflammatory cytokine.

A novel cis-acting element is essential for cytokine-mediated transcriptional induction of the serum amyloid A gene in nonhepatic cells

Serum amyloid A (SAA) is a plasma protein which has been associated with several diseases, including amyloidosis, arthritis, and atherosclerosis, and its abnormal expression, particularly in nonhepatic cells, is implicated in the pathogenesis of these diseases. Transfection and DNA-binding studies were performed to investigate the mechanism controlling cytokine-induced, nonhepatic expression of the SAA gene. We have identified a novel promoter, located between positions -280 and 224, that confers interleukin-6 (IL-6) inducibility to an SAA-chloramphenicol acetyltransferase reporter gene in both nonhepatic and hepatic cells. DNase I protection assays revealed, within this region, three homologous highly pyrimidine rich octanucleotide sequence motifs, termed SAA-activating sequences (SAS). Specific mutations within these three SAS motifs severely reduced IL-6-mediated induction of the reporter gene in transfected nonhepatic cells but not in liver cells. A nuclear factor activated by IL-6 in both hepatic and nonhepatic cells efficiently interacts with the SAS. The induction kinetics and cycloheximide sensitivity of this SAS-binding factor (SAF) suggested that de novo synthesis of this factor itself or an activator protein is essential. Loss of DNA-binding ability as a result of in vitro dephosphorylation, induction of SAA-chloramphenicol acetyltransferase reporter gene activity in the presence of genistein, a protein kinase inhibitor, further indicate that a phosphorylation step is necessary for the activation of SAF. Our results suggest that SAF is a key regulator of cytokine-mediated SAA gene expression in some nonhepatic cells.

Beta-nerve growth factor as a mediator of the acute phase response in vivo

Nerve growth factor (NGF) is increased during inflammation and stress. Stress-induced increases in specific serum proteins, such as serum amyloid A (SAA) and serum triglyceride (TG) levels, are part of the acute phase response which is mediated by cytokines. We now report the effect of systemic administration of beta-NGF on levels of serum lipids and SAA. Beta-NGF induced a rapid and sustained increase in serum TG and free fatty acid (FFA) in a dose dependent manner, while decreasing serum cholesterol levels in rats. Additionally, beta-NGF increased hepatic mRNA levels and serum concentrations of SAA at 16 hours in mice. Thus, beta-NGF joins the list of cytokines and growth factors that can mediate the acute phase response.

Cytokine-induced differential expression of serum amyloid A genes in fetal and neonatal rabbits

Serum amyloid A (SAA) is an acute-phase plasma protein which increases 100- to 1000-fold in response to inflammatory stimuli. In this study pregnant rabbits were subjected to laparotomy and their fetuses were injected with lipopolysaccharide (LPS) or various cytokines. Newborn rabbits were likewise stimulated. Hepatic SAA mRNA was studied using Northern blot analyses and scanning densitometry. In vitro derived RNA was used as standard for quantitative mRNA analyses. Cytokine concentrations in amniotic fluid and serum were analysed by biological assays. Fetal rabbits responded to cytokine stimulation by increased hepatic SAA mRNA expression, both during late gestation and in the early neonatal period. However, differences in dose-responses, kinetics and mRNA concentrations were seen dependent on gestational age. IL-1 and tumour necrosis factor (TNF) induced hepatic accumulation of both SAA1, SAA2 and SAA3, while only SAA1 and SAA2 mRNA accumulation was seen after IL-6 stimulation. High levels of IL-1 and TNF found in amniotic fluid from LPS-stimulated fetal rabbits corresponded with high levels in fetal, but not in maternal, serum. High levels of IL-1 and TNF, but no IL-6, were seen in newborn control sera and in adult serum 1 day after a normal delivery. The study details the complexity of the cytokine-induced in vivo response of SAA mRNA in fetal and neonatal rabbits.

Age-related changes of mRNA expression of amyloid precursor protein in the brain of senescence-accelerated mouse

APP695 mRNA is only expressed in the brains of SAM. The expression of APP mRNA in SAM P1 mice brains is more marked than that in SAM R1 mice brain. APP mRNA expression was increased with advancing age in all brain regions of SAM P1 mice compared with SAM R1. Especially, the changes of the amount of APP mRNA in the prosencephalon and the mesencephalon are significant at P value of 0.05. We suggest that overexpression of APP mRNA may be related to accelerated aging phenomenon in the SAM brain. This is the first report of age-related increase in the amount of APP mRNA in the SAM brain.

alpha 2-Macroglobulin gene expression during hibernation in ground squirrels is independent of acute phase response

alpha 2-Macroglobulin, a major acute phase reactant in many species, increases in the Richardson's ground squirrel (Spermophilus richarsonii) during hibernation at the level of both mRNA and protein. To determine if the pattern of liver gene expression known as the acute phase response is elicited as a normal part of the physiological adaptation of hibernation, acute phase reactants were identified in the Richardson's ground squirrel and were then assayed for changes in mRNA expression in the livers of active and hibernating ground squirrels. Our data demonstrate that alpha 1-antitrypsin, alpha 2-macroglobulin, ceruloplasmin, C-reactive protein, and serum amyloid A are acute phase reactants in the Richardson's ground squirrel. Of these, only alpha 2-macroglobulin (alpha 2M) mRNA increases during hibernation, demonstrating that the entire acute phase response is not elicited as a part of the adaptation for hibernation. Alternatively, data from blood clotting assays of serum from active and hibernating animals support a role for the increase in alpha 2M protein during hibernation in decreasing the coagulative properties of the blood.