Transcriptional regulation of serum amyloid A1 gene expression in human aortic smooth muscle cells involves CCAAT/enhancer binding proteins (C/EBP) and is distinct from HepG2 cells

Serum amyloid A - a review

Serum amyloid A (SAA) proteins were isolated and named over 50 years ago. They are small (104 amino acids) and have a striking relationship to the acute phase response with serum levels rising as much as 1000-fold in 24 hours. SAA proteins are encoded in a family of closely-related genes and have been remarkably conserved throughout vertebrate evolution. Amino-terminal fragments of SAA can form highly organized, insoluble fibrils that accumulate in “secondary” amyloid disease. Despite their evolutionary preservation and dynamic synthesis pattern SAA proteins have lacked well-defined physiologic roles. However, considering an array of many, often unrelated, reports now permits a more coordinated perspective. Protein studies have elucidated basic SAA structure and fibril formation. Appreciating SAA’s lipophilicity helps relate it to lipid transport and metabolism as well as atherosclerosis. SAA’s function as a cytokine-like protein has become recognized in cell-cell communication as well as feedback in inflammatory, immunologic, neoplastic and protective pathways. SAA likely has a critical role in control and possibly propagation of the primordial acute phase response. Appreciating the many cellular and molecular interactions for SAA suggests possibilities for improved understanding of pathophysiology as well as treatment and disease prevention.

Glucocorticoids and Toll-like receptor 2 cooperatively induce acute-phase serum amyloid A

Serum amyloid A (SAA) is a highly conserved acute-phase protein and extrahepatic produced SAA1/2 contributes to cutaneous inflammation. Prolonged systemic or topical treatment with glucocorticoids can provoke skin diseases such as steroid-induced acne. Glucocorticoids increase Toll-like receptor 2 (TLR2) expression, however, an inflammatory mediator linked to this side effect remains elusive. We report that TLR2 agonists in combination with dexamethasone substantially increase SAA expression and production in human keratinocytes and epithelial cells. Dexamethasone-mediated SAA1 induction depends on the glucocorticoid receptor (GR). In response to Propionibacterium acnes, TLR2-activated signal transducer and activator of transcription 3 (STAT3) and nuclear factor κB (NF-κB) signaling pathways are critically involved in dexamethasone-induced SAA1 production. The formation of transcription factor complexes between GR or p300 and phospho-STAT3 was confirmed by co-immunoprecipitation in dexamethasone- and P. acnes-stimulated keratinocytes. Furthermore, dexamethasone and P. acnes-increased TLR2 and mitogen-activated protein kinase phosphatase-1 (MKP-1) contribute to induction of SAA1 and 2. Likewise, tumor necrosis factor (TNF) induces SAA1 in combination with dexamethasone. GR, transcription factors STAT3 and NF-κB, but not MKP-1, mediate TNF- and dexamethasone-induced SAA1. Conclusively, we provide evidence that glucocorticoids promote SAA1 production under infectious and sterile inflammatory conditions which may provide significant insights to the pathogenesis of steroid-induced acne.

SAA1 polymorphisms are associated with variation in antiangiogenic and tumor-suppressive activities in nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is a cancer that occurs in high frequency in Southern China. A previous functional complementation approach and the subsequent cDNA microarray analysis have identified that serum amyloid A1 (SAA1) is an NPC candidate tumor suppressor gene. SAA1 belongs to a family of acute-phase proteins that are encoded by five polymorphic coding alleles. The SAA1 genotyping results showed that only three SAA1 isoforms (SAA1.1, 1.3 and 1.5) were observed in both Hong Kong NPC patients and healthy individuals. This study aims to determine the functional role of SAA1 polymorphisms in tumor progression and to investigate the relationship between SAA1 polymorphisms and NPC risk. Indeed, we have shown that restoration of SAA1.1 and 1.3 in the SAA1-deficient NPC cell lines could suppress tumor formation and angiogenesis in vitro and in vivo. The secreted SAA1.1 and SAA1.3 proteins can block cell adhesion and induce apoptosis in the vascular endothelial cells. In contrast, the SAA1.5 cannot induce apoptosis or inhibit angiogenesis because of its weaker binding affinity to αVβ3 integrin. This can explain why SAA1.5 has no tumor-suppressive effects. Furthermore, the NPC tumors with this particular SAA1.5/1.5 genotype showed higher levels of SAA1 gene expression, and SAA1.1 and 1.3 alleles were preferentially inactivated in tumor tissues that were examined. These findings further strengthen the conclusion for the defective function of SAA1.5 in suppression of tumor formation and angiogenesis. Interestingly, the frequency of the SAA1.5/1.5 genotype in NPC patients was ~2-fold higher than in the healthy individuals (P=0.00128, odds ratio=2.28), which indicates that this SAA1 genotype is significantly associated with a higher NPC risk. Collectively, this homozygous SAA1.5/1.5 genotype appears to be a recessive susceptibility gene, which has lost the antiangiogenic function, whereas SAA1.1 and SAA1.3 are the dominant alleles of the tumor suppressor phenotype.

Acute-phase serum amyloid a in osteoarthritis: regulatory mechanism and proinflammatory properties

Objective

To determine if serum amyloid A (A-SAA) could be detected in human osteoarthritic (OA) joints and further clarify if high A-SAA level in joints result from a local production or from a diffusion process from abnormally elevated plasma concentration. Regulatory mechanism of A-SAA expression and its pro-inflammatory properties were also investigated.

Methods

A-SAA levels in serum and synovial fluid of OA (n = 29) and rheumatoid arthritis (RA) (n = 27) patients were measured and compared to matched-healthy volunteers (HV) (n = 35). In vitro cell cultures were performed on primary joint cells provided from osteoarthritis patients. Regulatory mechanisms were studied using Western-blotting, ELISA and lentiviral transfections.

Results

A-SAA was statistically increased in OA plasma patients compared to HV. Moreover, A-SAA level in OA plasma and synovial fluid increased with the Kellgren & Lauwrence grade. For all OA and RA patients, A-SAA plasma level was higher and highly correlated with its corresponding level in the synovial fluid, therefore supporting that A-SAA was mainly due to the passive diffusion process from blood into the joint cavity. However, A-SAA expression was also observed in vitro under corticosteroid treatment and/or under IL-1beta stimuli. A-SAA expression was down-regulated by PPAR-γ agonists (genistein and rosiglitazone) and up-regulated by TGF-β1 through Alk1 (Smad1/5) pathway. RhSAA induced proinflammatory cytokines (IL-6, IL-8, GRO-α and MCP-1) and metalloproteinases (MMP-1, MMP-3 and MMP-13) expression in FLS and chondrocytes, which expression was downregulated by TAK242, a specific TLR4 inhibitor.

Conclusion

Systemic or local A-SAA expression inside OA joint cavity may play a key role in inflammatory process seen in osteoarthritis, which could be counteracted by TLR4 inhibition.

Serum amyloid A in atherosclerosis

PURPOSE OF REVIEW

Serum amyloid A (SAA) is a family of acute-phase proteins which are shown to correlate with cardiovascular disease, but whether this SAA contributes causally to atherosclerosis development or reflects underlying disease or risk factors remains unclear.

RECENT FINDINGS

SAA has been detected within atherosclerotic lesions and within adipose tissue where it is hypothesized that it may play a contributory role in disease development. In the acute-phase response SAA is synthesized by the liver and transported primarily in association with HDL. However, there is a growing literature suggesting that localized synthesis of SAA within the vasculature, or adipose tissue, may play a distinct role in disease development. Furthermore, SAA can be found in association with apoB-containing lipoproteins, in which its biological activity may be different.

SUMMARY

This review will discuss recent experimental evidence supporting a causal role of SAA with atherosclerosis.

Understanding Haemophilus parasuis infection in porcine spleen through a transcriptomics approach

Background

Haemophilus parasuis (HPS) is an important swine pathogen that causes Glässer's disease, which is characterized by fibrinous polyserositis, meningitis and arthritis. The molecular mechanisms that underlie the pathogenesis of the disease remain poorly understood, particularly the resistance of porcine immune system to HPS invasion. In this study, we investigated the global changes in gene expression in the spleen following HPS infection using the Affymetrix Porcine Genechip™.

Results

A total of 931 differentially expressed (DE) transcripts were identified in the porcine spleen 7 days after HPS infection; of these, 92 unique genes showed differential expression patterns based on analysis using BLASTX and Gene Ontology. The DE genes involved in the immune response included genes for inflammasomes (RETN, S100A8, S100A9, S100A12), adhesion molecules (CLDN3, CSPG2, CD44, LGALS8), transcription factors (ZBTB16, SLC39A14, CEBPD, CEBPB), acute-phase proteins and complement (SAA1, LTF, HP, C3), differentiation genes for epithelial cells and keratinocytes (TGM1, MS4A8B, CSTA), and genes related to antigen processing and presentation (HLA-B, HLA-DRB1). Further immunostimulation analyses indicated that mRNA levels of S100A8, S100A9, and S100A12 in porcine PK-15 cells increased within 48 h and were sustained after administration of lipopolysaccharide (LPS) and Poly(I:C) respectively. In addition, mapping of DE genes to porcine health traits QTL regions showed that 70 genes were distributed in 7 different known porcine QTL regions. Finally, 10 DE genes were validated by quantitative PCR.

Conclusion

Our findings demonstrate previously unrecognized changes in gene transcription that are associated with HPS infection in vivo, and many potential cascades identified in the study clearly merit further investigation. Our data provide new clues to the nature of the immune response in mammals, and we have identified candidate genes that are related to resistance to HPS.

Exocytosis of Neutrophil Formyl peptide receptor-like 1 (fPRL1) results in downregulation of cytoplasmic fPRL1 in patients with purulent dermatitis

N-Formyl peptide receptor-like 1 (fPRL1) is a member of the chemoattractant subfamily of G protein-coupled receptors and plays a key role in inflammation via chemotaxis and the regulation of mediator release from leukocytes. Activated fPRL1 has recently been shown to induce a complicated pattern of cellular signaling in vitro, but the details of the regulation and alteration of leukocyte cellular fPRL1 during inflammation in vivo remain unclear. To clarify the alteration of neutrophil fPRL1 during inflammation in vivo, the immunohistochemical staining of neutrophil fPRL1 in samples from patients with purulent dermatitis was performed. The in vitro morphological alteration of neutrophil fPRL1 on cellular membranes by stimulation with N-formylmethionyl-leucyl-phenylalanine (fMLP) was also examined. Both the cytoplasm and the cellular membranes of blood neutrophils stained strongly for fPRL1. On the other hand, the cellular membranes of neutrophils in dermatitis tissue stained strongly for fPRL1 but the cytoplasm stained weakly. The enhancement of neutrophil fPRL1 on cellular membranes by stimulation with fMLP indicates the exocytosis of neutrophil fPRL1-containing granules. In conclusion, we for the first time confirmed the alteration of neutrophil fPRL1 in clinical cases of purulent dermatitis. Cytoplasm that was weakly stained and cellular membranes that were well stained for fPRL1 were considered to be distinctive features of activated neutrophils in purulent dermatitis tissue.

Molecular interactions of acute phase serum amyloid A: possible involvement in carcinogenesis

Acute phase serum amyloid A (A-SAA) is a well-known marker of inflammation. The present review summarizes data on the regulation of A-SAA expression, signaling pathways which it is involved in, its effects, and possible influences on progression of malignant tumors.

Disease-specific expression and regulation of CCAAT/enhancer-binding proteins in asthma and chronic obstructive pulmonary disease

BACKGROUND

CCAAT/enhancer-binding proteins (C/EBPs) control cell proliferation; lack of C/EBPalpha correlates with increased proliferation of bronchial smooth muscle cells (BSMCs) of asthmatic patients.

OBJECTIVE

We sought to assess disease-specific expression of C/EBPalpha, beta, delta, and epsilon and the effects of budesonide (10(-8) mol/L) and formoterol (10(-8) mol/L).

METHODS

Expression and function of C/EBPalpha, beta, delta, and epsilon BSMCs of control subjects (n = 9), asthmatic patients (n = 12), and patients with chronic obstructive pulmonary disease (COPD; n = 10) were determined.

RESULTS

The control group expressed C/EBPalpha, beta, delta, and epsilon, which were upregulated by serum (5%). Budesonide completely inhibited C/EBPalpha and beta expression; formoterol increased C/EBPalpha expression (2-fold). C/EBPdelta and epsilon expression were not affected by the drugs. The asthmatic group did not appropriately express C/EBPalpha. Basal levels of C/EBPbeta, delta, and epsilon were upregulated by serum (5%). Budesonide and formoterol increased C/EBPbeta levels (3.4-fold and 2.5-fold, respectively), leaving C/EBPalpha, delta, and epsilon levels unaffected. The COPD group normally expressed C/EBPalpha, beta, and epsilon, which were upregulated by serum treatment (5%). Basal levels of C/EBPdelta were downregulated by serum in 7 of 10 BSMC lines. Budesonide inhibited C/EBPalpha and beta expression, upregulated C/EBPdelta (3.2-fold), and had no effect on C/EBPepsilon. Formoterol upregulated C/EBPalpha expression (3-fold) but not the other C/EBPs. Protein analysis and electrophoretic mobility shift assay confirmed the disease-specific expression pattern of C/EBPalpha in asthmatic patients and C/EBPdelta in patients with COPD.

CONCLUSIONS

The expression and regulation of C/EBPs in BSMCs of asthmatic patients and patients with COPD seems disease specific. Budesonide and formoterol modulate C/EBP expression in a drug- and disease-specific pattern.

CLINICAL IMPLICATIONS

The data could provide a method to discriminate between asthma and COPD at an early disease stage.

Inflammation-responsive transcription factor SAF-1 activity is linked to the development of amyloid A amyloidosis

Abundantly expressed serum amyloid A (SAA) protein under chronic inflammatory conditions gives rise to insoluble aggregates of SAA derivatives in multiple organs resulting in reactive amyloid A (AA) amyloidosis, a consequence of rheumatoid arthritis, Crohn's disease, ankylosing spondylitis, familial Mediterranean fever, and Castleman's disease. An inflammation-responsive transcription factor, SAF (for SAA activating factor), has been implicated in the sustained expression of amyloidogenic SAA under chronic inflammatory conditions. However, its role in the pathogenesis of AA amyloidosis has thus far remained obscure. In this paper we have shown that SAF-1, a major member of the SAF family, is abundantly present in human AA amyloidosis patients. To assess whether SAF-1 is directly linked to the pathogenesis of AA amyloidosis, we have developed a SAF-1 transgenic mouse model. SAF-1-overexpressing mice spontaneously developed AA amyloidosis at the age of 14 mo or older. Immunohistochemical analysis confirmed the nature of the amyloid deposits as an AA type derived from amyloidogenic SAA1. Furthermore, SAF-1 transgenic mice rapidly developed severe AA amyloidosis in response to azocasein injection, indicating increased susceptibility to inflammation. Also, during inflammation SAF-1 transgenic mice exhibited a prolonged acute phase response, leading to an extended period of SAA synthesis. Together, these results provide direct evidence that SAF-1 plays a key role in the development of AA amyloidosis, a consequence of chronic inflammation.

Human paraoxonase-1 gene expression by HepG2 cells is downregulated by interleukin-1beta and tumor necrosis factor-alpha, but is upregulated by interleukin-6

Recent studies have demonstrated that human paraoxonase-1 (PON1) associated with HDL, plays a role for anti-atherosclerotic effects of HDL, however, the relationships between PON1 and inflammatory cytokines remain unclear. To clarify this point, we evaluated the transcriptional regulation of PON1 gene by IL-1beta, IL-6 and TNF-alpha in HepG2 cells using luciferase reporter gene assay. We determined the nucleotide sequence of upstream of PON1 gene, and constructed plasmids containing various lengths of upstream region. In the plasmid constructs of U39 (PON1 upstream -1232/-6), U682 (-589/-6), U797 (-472/-6) and U953 (-318/-6), U953 showed a stepwise upregulation in basal promoter activity. The relative promoter activities using U682 plasmid were generally downregulated by IL-1beta and TNF-alpha, but were upregulated by IL-6. By the combination of IL-1beta, IL-6 and/or TNF-alpha, the promoter activities were proportionally regulated. The result of PON1 transcriptional regulation by cytokines in HepG2 cells was confirmed to be concordant with that of regulation of PON1 mRNA expression by cytokines. These results suggest that PON1 mRNA expression by hepatocytes is regulated by proinflammatory cytokines and that proinflammatory cytokines secreted in a disease state, may play a role in the development of atherosclerotic lesion via modification of PON1 mRNA expression affecting on the anti-oxidative property of HDL.