SAA1 Levels Research Articles

Causal associations of genetically predicted gut microbiota and blood metabolites with inflammatory states and risk of infections: a Mendelian randomization analysis.

Inflammation serves as a key pathologic mediator in the progression of infections and various diseases, involving significant alterations in the gut microbiome and metabolism. This study aims to probe into the potential causal relationships between gut microbial taxa and human blood metabolites with various serum inflammatory markers (CRP, SAA1, IL-6, TNF-α, WBC, and GlycA) and the risks of seven common infections (gastrointestinal infections, dysentery, pneumonia, bacterial pneumonia, bronchopneumonia and lung abscess, pneumococcal pneumonia, and urinary tract infections). Two-sample Mendelian randomization (MR) analysis was performed using inverse variance weighted (IVW), maximum likelihood, MR-Egger, weighted median, and MR-PRESSO. After adding other MR models and sensitivity analyses, genus Roseburia was simultaneously associated adversely with CRP (Beta IVW = -0.040) and SAA1 (Beta IVW = -0.280), and family Bifidobacteriaceae was negatively associated with both CRP (Beta IVW = -0.034) and pneumonia risk (Beta IVW = -0.391). After correction by FDR, only glutaroyl carnitine remained significantly associated with elevated CRP levels (Beta IVW = 0.112). Additionally, threonine (Beta IVW = 0.200) and 1-heptadecanoylglycerophosphocholine (Beta IVW = -0.246) were found to be significantly associated with WBC levels. Three metabolites showed similar causal effects on different inflammatory markers or infectious phenotypes, stearidonate (18:4n3) was negatively related to SAA1 and urinary tract infections, and 5-oxoproline contributed to elevated IL-6 and SAA1 levels. In addition, 7-methylguanine showed a positive correlation with dysentery and bacterial pneumonia. This study provides novel evidence confirming the causal effects of the gut microbiome and the plasma metabolite profile on inflammation and the risk of infection. These potential molecular alterations may aid in the development of new targets for the intervention and management of disorders associated with inflammation and infections.

Single-Cell RNA Sequencing Reveals a Unique Fibroblastic Subset and Immune Disorder in Lichen Sclerosus Urethral Stricture.

Lichen sclerosus urethral stricture disease (LS USD) is a refractory and progressive disease primarily affecting the anterior urethra in males. Various potential etiological factors, such as genetics, autoimmunity, infection, and exposure to infectious urine, have been suggested. However, the accurate etiology of LS in the male urethra remains unclear. In this study, we conducted single-cell RNA sequencing to identify the transcriptional profiles of three patients with LS USD and three patients with non-LS USD. Immunofluorescence was used to confirm the single-cell sequence results. Our study revealed distinct subsets of vein endothelial cells (ECs), smooth muscle cells (SMCs), and fibroblasts (FBs) with high proportions in LS USD, contributing to the tissue microenvironment primarily involved in proinflammatory and immune responses. In particular, FBs displayed a unique subset, Fib7, which is exclusively present in LS USD, and exhibited high expression levels of SAA1 and SAA2. The accumulation of macrophages, along with the dysregulated ratios of M1/M2-like phenotype macrophages, may be engaged in the pathogenesis of LS USD. Through cell-cell communication analysis, we identified significant interactions involving CXCL8/ACKR1 and CCR7/CCL19 in LS USD. Remarkably, Fib7 exhibited exclusive communication with IL-1B macrophages through the SAA1/FPR2 receptor-ligand pair. Our study provides a profound understanding of the tissue microenvironment in LS USD, which may be valuable for understanding the pathogenesis of LS USD.

Serum Amyloid A as a Potential Biomarker for Disease Activity in Chronic Spontaneous Urticaria

Chronic spontaneous urticaria (CSU) is an inflammatory skin disease with a complex physiopathology. Serum amyloid A (SAA), an acute-phase reactant, has been proposed as a potential biomarker in urticaria but has yet to be studied in a population with CSU or correlated with disease activity as indicated by the Urticaria Activity Score summed over 7 days (UAS7). We sought to determine SAA-1 levels in patients with CSU and correlate them with its activity and control, as well as with clinical features of CSU and other potential blood biomarkers. We conducted a retrospective multicenter study of 67 patients with CSU, from whom we obtained demographic and clinical data, UAS7 as an indicator of CSU activity, and blood and serum markers. SAA-1 levels positively correlated with UAS7 (rs=0.47, P < .001). SAA-1 levels were higher in patients with noncontrolled (UAS7 > 6) CSU than in those with controlled (UAS ≤ 6) CSU (P < .001) and were also higher in patients with concomitant angioedema (P= .003) or delayed pressure urticaria (P= .003). We propose SAA-1 as a potential biomarker for activity in CSU. Further studies are required to evaluate its potential role as a biomarker for other CSU outcomes, such as response to treatment.

Correlation of serum amyloid A1 and interleukin-1beta in response to anti-tubercular therapy

BackgroundHost biomarkers are needed to monitor the response to anti-tubercular therapy (ATT) for ensuring effective therapy and preventing drug-resistant tuberculosis. We sought to find the correlation between the serum levels of SAA1 and IL-1beta in response to ATT in adult patients with pulmonary TB (PTB) or extra-pulmonary TB (EPTB). MethodsBlood samples of 32 patients with PTB and 28 patients with EPTB were analyzed. The blood samples were collected at baseline, two months and six months following treatment initiation. SAA1 and IL-1beta levels were measured by enzyme linked immunosorbent assay (ELISA). ResultsIn the PTB group, the mean levels of SAA1 decreased significantly (p <0.001) after the intensive phase (two months) and continuous phase (six months) of ATT in comparison with the baseline value. IL-1beta values also decreased significantly (p = 0.005) after the intensive phase (two months) compared with the baseline values. In the EPTB group, there was a significant reduction in the mean serum level of SAA1 (p <0.001) and IL-1beta (p = 0.001) after the intensive phase (two months) in comparison with the baseline value, whereas the reduction at six months was not significant. ConclusionsSAA1 and IL-1beta may be useful potential treatment-monitoring biomarkers, especially in the intensive phase of therapy for both PTB and EPTB.

Quantitative Rapid Test for Detection and Monitoring of Active Pulmonary Tuberculosis in Nonhuman Primates.

Simple SummaryTuberculosis (TB), caused by Mycobacterium tuberculosis (MTB), is the most lethal infectious disease from a single pathogen for which there is no effective vaccine available. Rhesus macaques are extremely susceptible to MTB and therefore represent relevant models to study the pathogenesis of TB and assess the potential of TB drugs and vaccines. However, there are no diagnostic tools currently available that allow rapid, user-friendly detection of TB for either TB research purposes or monitoring nonhuman primate colonies. To develop a rapid diagnostic test, we investigated whether low complexity lateral flow assays (LFAs) that we recently developed for rapid and quantitative detection of human serum proteins are applicable to detect and monitor active pulmonary TB in NHPs. We found that serum levels of SAA1, IP-10, and IL-6 detected by LFAs were significantly increased after MTB infection in rhesus macaques. Moreover, levels of these biomarkers correlated with disease severity as determined by pathology scoring and allowed detection of the effect of vaccination and drug treatment in experimentally MTB infected macaques. These UCP-LFAs thus offer a low-cost, convenient, and minimally invasive diagnostic tool that can be used to assess new therapeutic and prophylactic treatment methods in macaques to tackle TB.Nonhuman primates (NHPs) are relevant models to study the pathogenesis of tuberculosis (TB) and evaluate the potential of TB therapies, but rapid tools allowing diagnosis of active pulmonary TB in NHPs are lacking. This study investigates whether low complexity lateral flow assays utilizing upconverting reporter particles (UCP-LFAs) developed for rapid detection of human serum proteins can be applied to detect and monitor active pulmonary TB in NHPs. UCP-LFAs were used to assess serum proteins levels and changes in relation to the MTB challenge dosage, lung pathology, treatment, and disease outcome in experimentally MTB-infected macaques. Serum levels of SAA1, IP-10, and IL-6 showed a significant increase after MTB infection in rhesus macaques and correlated with disease severity as determined by pathology scoring. Moreover, these biomarkers could sensitively detect the reduction of bacterial levels in the lungs of macaques due to BCG vaccination or drug treatment. Quantitative measurements by rapid UCP-LFAs specific for SAA1, IP-10, and IL-6 in serum can be utilized to detect active progressive pulmonary TB in macaques. The UCP-LFAs thus offer a low-cost, convenient, and minimally invasive diagnostic tool that can be applied in studies on TB vaccine and drug development involving macaques.

A Targetable Bone Marrow-Niche Axis for the Treatment of Acute Myeloid Leukemia

Converging lines of evidence show that the endosteal niche within the bone marrow (BM) microenvironment plays a crucial role in the pathogenesis and chemoresistance of myeloid malignancies. Dysplastic cells can exploit niche-dependent, cell non-autonomous pathways to favor their growth. Molecular delineation and targeting of those pathways may help overcome resistance to targeted therapies. In particular, acute myeloid leukemia (AML) remains recalcitrant to conventional chemo- and targeted-therapies leading to relapse and low overall survival rates (5-year survival rate <30%). These shortcomings highlight the urgency of proposing novel and adapted therapies for the disease.Leveraging genetic mouse models, patient-derived xenografts (PDX), and patient samples, herein we show the mechanism and therapeutic targeting of a cell non-autonomous progression pathway in AML. Specifically, we show that conditional ablation of serotonin receptor 1b (HTR1B) in osteoblasts -during or after AML engraftment- hampers or even prevents AML progression, increasing overall survival. Mass spectrometry-based untargeted metabolomics identified the tryptophan catabolite kynurenine (Kyn) as an oncometabolite secreted by AML cells. Remarkably, the AML proliferative pathway that exploits peripheral serotonin signaling in osteoblasts, is not driven by serotonin but by Kyn, which acts as a previously unrecognized HTR1B ligand.To explore in vivo the significance of Kyn for leukemia progression, we inhibited its synthesis by suppressing indoleamine 2,3-dioxygenase-1 (IDO1) activity in mouse and human AML cells. CRISPR-Cas9-mediated Ido1 targeting suppressed AML growth in a dose-dependent manner. Next, we sought to identify the downstream molecular targets of Kyn in human osteoblasts that render the BM niche permissive to AML engraftment and support proliferation of leukemia cells. RNAseq analysis of co-cultures between primary human osteoblasts and leukemia cells shows that AML cells induce a pro-inflammatory remodeling of the osteoblastic niche that depends on HTR1B engagement by Kyn. Among the plethora of secreted pro-inflammatory molecules induced in osteoblasts, AML-secreted Kyn (but not the canonical HTR1B ligand serotonin) induces secretion of the acute-phase protein serum amyloid-A (SAA), which in turn acts in a positive feedback-loop on leukemia cells by increasing IDO1 expression, the rate-limiting enzyme for Kyn synthesis. Acting in an autocrine manner -in a mode distinct from its established immunomodulatory properties in cancer- Kyn activates the aryl hydrocarbon receptor (AHR), thereby supporting further AML proliferation.Highlighting a clinical relevance of these findings, the Kyn-HTR1B-SAA-IDO1 AML-promoting axis identified in leukemia mouse models, is recapitulated in PDX as well as myelodysplastic syndromes (MDS) and AML patients. Preferential and progressive production of Kyn over serotonin by leukemic cells, as well as increased levels of SAA1 in the BM plasma, occur as the disease pathogenesis proceeds from MDS to AML in patients. Moreover, genetic or pharmacological (Epacadostat) IDO1 inhibition hinders AML progression in PDX models. Of note, inhibition of IDO1 synergizes with chemotherapy to reduce AML burden. Overall, these data suggest that the leukemia-osteoblast crosstalk conferred by the Kyn-HTR1B-SAA-IDO1 axis has potential as a therapeutic target. This niche-dependent, cell non-autonomous AML axis, may impact the management of myeloid malignancies, opening also new opportunities for cancer treatment in conjunction with chemo/immunotherapies. DisclosuresBorot: Vor Biopharma: Consultancy, Patents & Royalties: coinventor on issued and pending patent applications licensed to Vor Biopharm. Ali: Vor Biopharma: Consultancy, Patents & Royalties: coinventor on issued and pending patent applications licensed to Vor Biopharm. Roth: UNC: Patents & Royalties: UNC has licensed a patent with B.L.R. listed as an inventor on biased opioid compounds. . Mukherjee: Vor Biopharma: Current equity holder in publicly-traded company, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties: coinventor on issued and pending patent applications licensed to Vor Biopharma. S.M. has equity ownership and is on the Scientific Advisory Board of Vor Biopharma., Research Funding. Rabadan: AimedBio: Membership on an entity's Board of Directors or advisory committees; Genotwin: Other: Raul Rabadan is founder of Genotwin. Carroll: Incyte Pharmaceuticals: Research Funding; Janssen Pharmaceutical: Consultancy. Raza: Celgene Inc: Research Funding, Speakers Bureau; Novartis: Speakers Bureau; Genoptix: Speakers Bureau; Kura Oncology: Research Funding; Janssen R&D: Research Funding; Syros Pharmaceuticals: Research Funding; Onconova Therapeutics: Research Funding, Speakers Bureau.

Serum Amyloid A1/Toll-Like Receptor-4 Axis, an Important Link between Inflammation and Outcome of TBI Patients.

Traumatic brain injury (TBI) is one of the leading causes of mortality and disability worldwide without any validated biomarker or set of biomarkers to help the diagnosis and evaluation of the evolution/prognosis of TBI patients. To achieve this aim, a deeper knowledge of the biochemical and pathophysiological processes triggered after the trauma is essential. Here, we identified the serum amyloid A1 protein-Toll-like receptor 4 (SAA1-TLR4) axis as an important link between inflammation and the outcome of TBI patients. Using serum and mRNA from white blood cells (WBC) of TBI patients, we found a positive correlation between serum SAA1 levels and injury severity, as well as with the 6-month outcome of TBI patients. SAA1 levels also correlate with the presence of TLR4 mRNA in WBC. In vitro, we found that SAA1 contributes to inflammation via TLR4 activation that releases inflammatory cytokines, which in turn increases SAA1 levels, establishing a positive proinflammatory loop. In vivo, post-TBI treatment with the TLR4-antagonist TAK242 reduces SAA1 levels, improves neurobehavioral outcome, and prevents blood–brain barrier disruption. Our data support further evaluation of (i) post-TBI treatment in the presence of TLR4 inhibition for limiting TBI-induced damage and (ii) SAA1-TLR4 as a biomarker of injury progression in TBI patients.

High SAA1 Expression Predicts Advanced Tumors in Renal Cancer.

Renal cell carcinoma (RCC) is the most frequent malignant tumor of the kidney. 30% of patients with RCC are diagnosed at an advanced stage. Clear cell renal cell carcinoma (ccRCC) is the most common pathological subtype of RCC. Currently, advanced ccRCC lacks reliable diagnostic and prognostic markers. We explored the potential of SAA1 as a diagnostic and prognostic marker for advanced ccRCC. In this study, we mined and analyzed the public cancer databases (TCGA, UALCAN and GEPIA) to conclude that SAA1 was up-regulated at mRNA and protein levels in advanced ccRCC. We further found that hypomethylation of SAA1 promoter region was responsible for its high expression in ccRCC. Receiver operating characteristic curve (ROC) indicated that high SAA1 levels could distinguish advanced ccRCC patients from normal subjects (p < 0.0001). Kaplan-Meier curve analysis showed that high SAA1 levels predicted poor overall survival time (p < 0.0001) and poor disease-free survival time (p = 0.0003). Finally, the functional roles of SAA1 were examined using a si-SAA1 knockdown method in RCC cell lines. Our results suggest that SAA1 may possess the potential to serve as a diagnostic and prognostic biomarker for advanced ccRCC patients. Moreover, targeting SAA1 may represent as a novel therapeutic target for advanced ccRCC patients.

Serum amyloid A1 can be a novel biomarker for evaluating the presence and severity of acute coronary syndrome

BackgroundSerum amyloid A (SAA) is an acute phase protein and a novel inflammatory biomarker of cardiovascular diseases. Of the four subtypes, SAA1 is the most representative biomarker. In this study, we aimed to assess the value of SAA1 as a novel biomarker for evaluating the presence and severity of acute coronary syndrome (ACS) in Chinese patients. Methods and resultsA total of 140 ACS patients and 88 non-ACS patients (including 36 stable coronary artery disease (SCAD) patients and 52 healthy controls) who underwent coronary angiography were enrolled. The SAA1 level was significantly higher in ACS patients compared with the SCAD and healthy control subgroups (P < 0.001, respectively), and was significantly higher in the high SYNTAX Score II (SS II) group compared with the medium SS II group and low SS II group (P < 0.001, respectively) in ACS patients. The cutoff level of SAA1 for indicating the presence of ACS was 324.65 ng/mL (sensitivity of 77.9%, specificity of 60.2% and an area under the curve of 0.717). The increased SAA1 levels were positively associated with the presence (OR = 1.013, P < 0.001) and severity (OR = 1.023, P < 0.001) of ACS. Furthermore, there was a positive correlation between SAA1 levels and SS II (r = 0.467, P < 0.001). ConclusionsOur results suggest that elevated SAA1 levels may be a novel biomarker for evaluating the presence of ACS and the severity of CAD in ACS patients. Measuring SAA1 levels makes it possible to evaluate the presence of ACS and severity of CAD in ACS patients.

Presence of serum amyloid A3 in mouse plasma is dependent on the nature and extent of the inflammatory stimulus

Serum amyloid A3 (Saa3) derives mainly from extrahepatic tissue and is not detected in plasma from moderately inflamed obese mice. In contrast, it is present in plasma from mice acutely inflamed by injection of high dose of lipopolysaccharide (LPS). To reconcile these differences, we evaluated whether different acute inflammatory stimuli could affect the presence of Saa3 in plasma. Saa3 appeared dose dependently in plasma after LPS injection. In contrast, only very low levels were detected after sterile inflammation with silver nitrate despite levels of Saa1 and Saa2 being comparable to high dose LPS. Saa3 was not detected in plasma following casein administration. Although most Saa3 was found in HDL, a small amount was not lipoprotein associated. Gene expression and proteomic analysis of liver and adipose tissue suggested that a major source of Saa3 in plasma after injection of LPS was adipose tissue rather than liver. We conclude that Saa3 only appears in plasma after induction of acute inflammation by some but not all inflammatory stimuli. These findings are consistent with the observation that Saa3 is not detectable in plasma in more moderate chronic inflammatory states such as obesity.

Serum Amyloid A Induces Inflammation, Proliferation and Cell Death in Activated Hepatic Stellate Cells.

Serum amyloid A (SAA) is an evolutionary highly conserved acute phase protein that is predominantly secreted by hepatocytes. However, its role in liver injury and fibrogenesis has not been elucidated so far. In this study, we determined the effects of SAA on hepatic stellate cells (HSCs), the main fibrogenic cell type of the liver. Serum amyloid A potently activated IκB kinase, c-Jun N-terminal kinase (JNK), Erk and Akt and enhanced NF-κB-dependent luciferase activity in primary human and rat HSCs. Serum amyloid A induced the transcription of MCP-1, RANTES and MMP9 in an NF-κB- and JNK-dependent manner. Blockade of NF-κB revealed cytotoxic effects of SAA in primary HSCs with signs of apoptosis such as caspase 3 and PARP cleavage and Annexin V staining. Serum amyloid A induced HSC proliferation, which depended on JNK, Erk and Akt activity. In primary hepatocytes, SAA also activated MAP kinases, but did not induce relevant cell death after NF-κB inhibition. In two models of hepatic fibrogenesis, CCl4 treatment and bile duct ligation, hepatic mRNA levels of SAA1 and SAA3 were strongly increased. In conclusion, SAA may modulate fibrogenic responses in the liver in a positive and negative fashion by inducing inflammation, proliferation and cell death in HSCs.

Serum amyloid A1 levels and amyloid deposition following a high-fat diet challenge in transgenic mice overexpressing hepatic serum amyloid A1

Serum amyloid A (SAA) is an acute-phase response protein in the liver, and SAA1 is the major precursor protein involved in amyloid A amyloidosis. This amyloidosis has been reported as a complication in chronic inflammatory conditions such as arthritis, lupus, and Crohn's disease. Obesity is also associated with chronic, low-grade inflammation and sustained, elevated levels of SAA1. However, the contribution of elevated circulating SAA1 to metabolic disturbances and their complications is unclear. Furthermore, in several recent studies of transgenic (TG) mice overexpressing SAA1 that were fed a high-fat diet (HFD) for a relatively short period, no relationship was found between SAA1 up-regulation and metabolic disturbances. Therefore, we generated TG mice overexpressing SAA1 in the liver, challenged these mice with an HFD, and investigated the influence of elevated SAA1 levels. Sustained, elevated levels of SAA1 were correlated with metabolic parameters and local cytokine expression in the liver following 16 weeks on the HFD. Moreover, prolonged consumption (52 weeks) of the HFD was associated with impaired glucose tolerance and elevated SAA1 levels and resulted in systemic SAA1-derived amyloid deposition in the kidney, liver, and spleen of TG mice. Thus, we concluded that elevated SAA1 levels under long-term HFD exposure result in extensive SAA1-derived amyloid deposits, which may contribute to the complications associated with HFD-induced obesity and metabolic disorders.

Abstract 366: Inhibition of Interleukin-1ß by a Monoclonal Antibody Therapy Reduces Vascular Calcification in Ldlr-/- Mice

Objective: Given the link between cholesterol and activation of inflammation via interleukin-1β, we thus tested the effects of IL-1β inhibition on atherosclerotic calcification in mice. Methods and Results: A mouse monoclonal antibody (mAB) against IL-1β or placebo was administered subcutaneously to Ldlr-/- and Tg(Pcsk9) models fed a Western diet. Drug level, anthropometric, lipid and glucose profiles were determined. PCSK9, SAA1 and cytokine expressions were measured by ELISA. Aortic calcification was determined by micro-CT and X-Ray densitometry and aortic flow velocity was assessed by ultrasound. Circulating levels of IL-1β in Ldlr-/- mice were significant twice that observed in Tg(Pcsk9) mice. Both mAb and placebo treated mice did not differ in their growth, lipid, glucose profiles and other cytokines while plasma SAA1 levels were lower in mAb-treated mice. Calcifications were significantly diminished in mAb-treatment Ldlr-/- mice (a reduction of 75% by X-ray and 96% by micro-CT) and reduced insignificantly in mAb-treatment Tg(Pcsk9) mice, whereas aortic flow velocity was unchanged in both models. Conclusions: Herein we demonstrate that aortic calcifications can be inhibited by IL-1β mAb in LDL-receptor deficient mice. These results have a translational component to prevent vascular calcification in human and represent new evidence to rationalize targeting inflammation in cardiovascular disease.

Serum amyloid A and pairing formyl peptide receptor 2 are expressed in corneas and involved in inflammation-mediated neovascularization.

To solidify the involvement of Saa-related pathway in corneal neovascularization (CorNV). The pathogenesis of inflammatory CorNV is not fully understood yet, and our previous study implicated that serum amyloid A (Saa) 1 (Saa1) and Saa3 were among the genes up-regulated upon CorNV induction in mice. Microarray data obtained during our profiling project on CorNV were analyzed for the genes encoding the four SAA family members (Saa1-4), six reported SAA receptors (formyl peptide receptor 2, Tlr2, Tlr4, Cd36, Scarb1, P2rx7) and seven matrix metallopeptidases (Mmp) 1a, 1b, 2, 3, 9, 10, 13 reportedly to be expressed upon SAA pathway activation. The baseline expression or changes of interested genes were further confirmed in animals with CorNV using molecular or histological methods. CorNV was induced in Balb/c and C57BL/6 mice by placing either three interrupted 10-0 sutures or a 2 mm filter paper soaked with sodium hydroxide in the central area of the cornea. At desired time points, the corneas were harvested for histology examination or for extraction of mRNA and protein. The mRNA levels of Saa1, Saa3, Fpr2, Mmp2 and Mmp3 in corneas were detected using quantitative reverse transcription-PCR, and SAA3 protein in tissues detected using immunohistochemistry or western blotting. Microarray data analysis revealed that Saa1, Saa3, Fpr2, Mmp2, Mmp3 messengers were readily detected in normal corneas and significantly up-regulated upon CorNV induction. The changes of these five genes were confirmed with real-time PCR assay. On the contrary, other SAA members (Saa2, Saa4), other SAA receptors (Tlr2, Tlr4, Cd36, P2rx7, etc), or other Mmps (Mmp1a, Mmp1b, Mmp9, Mmp10, Mmp13) did not show consistent changes. Immunohistochemistry study and western blotting further confirmed the expression of SAA3 products in normal corneas as well as their up-regulation in corneas with CorNV. SAA-FPR2 pathway composing genes were expressed in normal murine corneas and, upon inflammatory stimuli challenge to the corneas, their expressions were up-regulated, suggesting their roles in pathogenesis of CorNV. The potential usefulness of SAA-FPR2 targets in future management of CorNV-related diseases deserves investigation.

Serum Amyloid A Facilitates the Binding of High-Density Lipoprotein From Mice Injected With Lipopolysaccharide to Vascular Proteoglycans

Levels of serum amyloid A (SAA), an acute-phase protein carried on high-density lipoprotein (HDL), increase in inflammatory states and are associated with increased risk of cardiovascular disease. HDL colocalizes with vascular proteoglycans in atherosclerotic lesions. However, its major apolipoprotein, apolipoprotein A-I, has no proteoglycan-binding domains. Therefore, we investigated whether SAA, which has proteoglycan-binding domains, plays a role in HDL retention by proteoglycans. HDL from control mice and mice deficient in both SAA1.1 and SAA2.1 (SAA knockout mice) injected with bacterial lipopolysaccharide (LPS) was studied. SAA mRNA expression in the liver and plasma levels of SAA increased dramatically in C57BL/6 mice after LPS administration, although HDL cholesterol did not change. Fast protein liquid chromatography analysis showed most of the SAA to be in HDL. Mass spectrometric analysis indicated that HDL from LPS-injected control mice had high levels of SAA1.1/2.1 and reduced levels of apolipoprotein A-I. HDL from LPS-injected control mice demonstrated high-affinity binding to biglycan relative to normal mouse HDL. In contrast, HDL from LPS-injected SAA knockout mice showed very little binding to biglycan, consistent with SAA facilitating the binding of HDL to vascular proteoglycans. SAA enrichment of HDL under inflammatory conditions plays an important role in the binding of HDL to vascular proteoglycans.

Expression of Mouse Acute-Phase (SAA1.1) and Constitutive (SAA4) Serum Amyloid A Isotypes

The serum amyloid A (SAA) family of proteins consists of inducible acute-phase members and a constitutive member that are minor apolipoproteins of normal high density lipoprotein (HDL). During inflammation, HDL cholesterol and apolipoprotein A-I (apoA-I) protein are decreased, and these changes are thought to be partly related to the increase in acute-phase SAA proteins that associate with the HDL particle to become the major apolipoprotein species. To determine the specific role of SAA in the alteration of HDL in the absence of a generalized acute-phase response, acute-phase Saa1.1 transgene expression was directed via an inducible mouse metallothionein promoter. Elevated levels of SAA1.1 (28+/-9 mg/dL) comparable to a moderate acute-phase response were achieved over a 5-day period. SAA association with the HDL particles at this concentration did not significantly alter the apoA-I or HDL cholesterol levels or change the lipoprotein profiles in the transgenic mice compared with wild-type mice. In addition, we used adenoviral vectors to increase the SAA expression to levels seen in a major acute-phase response. Injection of adenovirus expressing the mouse SAA1.1 protein resulted in high-level expression (72+/-8 mg/dL) but did not alter apoA-I levels. However, the SAA associated with the HDL particle gave rise to significantly larger HDL particles ( approximately 10%). Adenoviral expression of the constitutive SAA4 protein resulted in an increase in HDL size ( approximately 10%) and an increase in very low density lipoprotein levels (20-fold) and triglyceride levels (1.7-fold). These studies suggest that increases in acute-phase SAA proteins alone are insufficient to alter HDL cholesterol or apoA-I levels during inflammation. A role for constitutive SAA4 in HDL-very low density lipoprotein interactions should be considered.

Amyloidogenesis. One serum amyloid A isotype is selectively removed from the circulation.

The deposits of fibrils found in amyloidosis of the A type are derived from only one of the three serum amyloid A (SAA) gene products, namely SAA2. In order to explore the mechanism of SAA isotype-specific amyloid protein AA deposition, the molecular kinetics of the serum amyloid proteins were examined in CBA mice during casein induction of amyloidosis. The presence of SAA mRNA in spleen was searched for; hepatic SAA1 and SAA2 mRNA levels, rates of specific protein synthesis and secretion by hepatocytes, and serum levels were measured during a 20-d period of amyloid induction. We observed the following: small amounts of amyloid substance appeared in the spleen by day 5 and increased steadily over the ensuing 15 d to occupy nearly 30% of splenic volume by day 20. No SAA mRNA was detected in spleen at any time during induction of amyloid formation. Total serum SAA levels peaked 1 d after we began casein treatment, and thereafter declined. This decline was accounted for entirely by a dramatic fall in SAA2, while SAA1 levels remained nearly constant throughout. The ratios of hepatic SAA2:SAA1 mRNA, as determined by in vitro translation, remained constant during the 20-d period, as did amounts of SAA1 and SAA2 synthesized and secreted by freshly isolated hepatocytes. These data indicate that the deposition of amyloid A protein derived from SAA2 is not due to local SAA production in spleen, nor excessive SAA2 production compared with SAA1, but involves the selective and accelerated removal of SAA2 from the circulating pool of both SAA1 and SAA2.