Serum Amyloid A Isoforms Research Articles

Deficiency of Acute-Phase Serum Amyloid A Exacerbates Sepsis-Induced Mortality and Lung Injury in Mice.

Serum amyloid A (SAA) is a family of proteins, the plasma levels of which may increase >1000-fold in acute inflammatory states. We investigated the role of SAA in sepsis using mice deficient in all three acute-phase SAA isoforms (SAA-TKO). SAA deficiency significantly increased mortality rates in the three experimental sepsis mouse models: cecal ligation and puncture (CLP), cecal slurry (CS) injection, and lipopolysaccharide (LPS) treatments. SAA-TKO mice had exacerbated lung pathology compared to wild-type (WT) mice after CLP. A bulk RNA sequencing performed on lung tissues excised 24 h after CLP indicated significant enrichment in the expression of genes associated with chemokine production, chemokine and cytokine-mediated signaling, neutrophil chemotaxis, and neutrophil migration in SAA-TKO compared to WT mice. Consistently, myeloperoxidase activity and neutrophil counts were significantly increased in the lungs of septic SAA-TKO mice compared to WT mice. The in vitro treatment of HL-60, neutrophil-like cells, with SAA or SAA bound to a high-density lipoprotein (SAA-HDL), significantly decreased cellular transmigration through laminin-coated membranes compared to untreated cells. Thus, SAA potentially prevents neutrophil transmigration into injured lungs, thus reducing exacerbated tissue injury and mortality. In conclusion, we demonstrate for the first time that endogenous SAA plays a protective role in sepsis, including ameliorating lung injury.

Renal involvement in monogenic autoinflammatory diseases: A narrative review.

Autoinflammatory diseases (AIDs) are mostly caused by dysfunctions in single genes encoding for proteins with a prominent role in the regulation of innate immunity, such as complement factors, inflammasome components, tumour necrosis factor (TNF)-α, and proteins belonging to type I-interferon (IFN) signalling pathways. Due to the deposition of amyloid A (AA) fibrils in the glomeruli, unprovoked inflammation in AIDs frequently affects renal health. In fact, secondary AA amyloidosis is the most common form of amyloidosis in children. It is caused by the extracellular deposition of fibrillar low-molecular weight protein subunits resulting from the degradation and accumulation of serum amyloid A (SAA) in numerous tissues and organs, primarily the kidneys. The molecular mechanisms underlying AA amyloidosis in AIDs are the elevated levels of SAA, produced by the liver in response to pro-inflammatory cytokines, and a genetic predisposition due to specific SAA isoforms. Despite the prevalence of amyloid kidney disease, non-amyloid kidney diseases may also be responsible for chronic renal damage in children with AIDs, albeit with distinct characteristics. Glomerular damage can result in various forms of glomerulonephritis with distinct histologic characteristics and a different underlying pathophysiology. This review aims to describe the potential renal implications in patients with inflammasomopathies, type-I interferonopathies, and other rare AIDs in an effort to improve the clinical course and quality of life in paediatric patients with renal involvement.

Serum amyloid A augments the atherogenic effects of cholesteryl ester transfer protein

Serum amyloid A (SAA) is predictive of CVD in humans and causes atherosclerosis in mice. SAA has many proatherogenic effects in vitro. However, HDL, the major carrier of SAA in the circulation, masks these effects. The remodeling of HDL by cholesteryl ester transfer protein (CETP) liberates SAA restoring its proinflammatory activity. Here, we investigated whether deficiency of SAA suppresses the previously described proatherogenic effect of CETP. ApoE−/− mice and apoE−/− mice deficient in the three acute-phase isoforms of SAA (SAA1.1, SAA2.1, and SAA3; “apoE−/− SAA-TKO”) with and without adeno-associated virus-mediated expression of CETP were studied. There was no effect of CETP expression or SAA genotype on plasma lipids or inflammatory markers. Atherosclerotic lesion area in the aortic arch of apoE−/− mice was 5.9 ± 1.2%; CETP expression significantly increased atherosclerosis in apoE−/− mice (13.1 ± 2.2%). However, atherosclerotic lesion area in the aortic arch of apoE−/− SAA-TKO mice (5.1 ± 1.1%) was not significantly increased by CETP expression (6.2 ± 0.9%). The increased atherosclerosis in apoE−/− mice expressing CETP was associated with markedly increased SAA immunostaining in aortic root sections. Thus, SAA augments the atherogenic effects of CETP, which suggests that inhibiting CETP may be of particular benefit in patients with high SAA.

Signal peptide stabilizes folding and inhibits misfolding of serum amyloid A.

Signal peptide (SP) plays an important role in membrane targeting for insertion of secretory and membrane proteins during translocation processes in prokaryotes and eukaryotes. Beside the targeting functions, SP has also been found to affect the stability and folding of several proteins. Serum amyloid A (SAA) proteins are apolipoproteins responding to acute-phase inflammation. The fibrillization of SAA results in a protein misfolding disease named amyloid A (AA) amyloidosis. The main disease-associated isoform of human SAA, SAA1.1, is expressed as a precursor protein with an N-terminal signal peptide composed of 18 residues. The cleavage of the SP generates mature SAA1.1. To investigate whether the SP affects properties of SAA1.1, we systematically examined the structure, protein stability, and fibrillization propensity of pre-SAA1.1, which possesses the SP, and Ser-SAA1.1 without the SP but containing with an additional N-terminal serine residue. We found that the presence of the SP did not significantly affect the predominant helical structure but changed the tertiary conformation as evidenced by intrinsic fluorescence and exposed hydrophobic surfaces. Pre-SAA1.1 and Ser-SAA1.1 formed distinct oligomeric assemblies in which pre-SAA1.1 populated as tetramer and octamer, whereas Ser-SAA1.1 existed as a predominant hexamer. Pre-SAA1.1 was found significantly more stable than Ser-SAA1.1 upon thermal and chemical unfolding. Ser-SAA1.1, but not pre-SAA1.1, is capable of forming amyloid fibrils in protein misfolding study, indicating a protective role of the SP. Altogether, our results demonstrated a novel role of the SP in SAA folding and misfolding and provided a novel direction for therapeutic development of AA amyloidosis.

Maternal siRNA silencing of placental SAA2 mitigates preterm birth following intrauterine inflammation.

The placental inflammatory processes induced maternally result in preterm birth (PTB). Serum amyloid A (SAA) is a well-known biomarker of inflammation. The objective of this study was to investigate whether murine placental SAA isoforms (SAA1–4) participate in the mechanism of spontaneous PTB and whether maternal regulation of SAA production may serve as a therapeutic approach. During the gestation, all isoforms of SAA were detectable except SAA2. The mouse model of intrauterine inflammation was established using LPS infusion to the uterus. Following intrauterine inflammation, placental SAA2 increased significantly. Inhibition of Saa2, using siSaa2, markedly decreased PTB. The increased placental expression of pro-inflammatory cytokines Il1β, Il6, and Tnfα were downregulated by siSaa2 treatment. Maternal inhibition of Saa2 did not change the expression of Saa1–4 in the fetal brain. Explant inflammatory culture of placentas with siSaa2 showed similar results to our in vivo experiments. This study demonstrates the highly expressed placental SAA2 as a novel therapeutic target, and maternal administration of siRNA as a promising approach to alleviate PTB.

Abstract 447: Deficiency Of Serum Amyloid A Exacerbates Sepsis-induced Acute Lung Injury In Mice

Objectives: Serum Amyloid A (SAA) is a family of proteins whose plasma levels increase > 1000-fold in acute inflammatory states such as sepsis. We and others have demonstrated that SAA plays a causal role in mouse models of atherosclerosis. However, SAA may not be a valid therapeutic target if it is needed for host defense in inflammation. Here, we investigated the role of SAA in sepsis using mice deficient in all three acute-phase SAA isoforms (TKO). Approach and results: SAA deficiency significantly increased mortality rates in three experimental sepsis models. Survival rates in TKO and wild-type (WT) mice were: 25% and 55% after cecal ligation and puncture (CLP; p=0.02; n=10 each strain/gender); 0% and 45% after cecal slurry injection (p<0.0001; n=9 each strain); and 55% and 90 % after lipopolysaccharide injection (p<0.0001; n=10 each strain/gender). 24-hours after CLP, there were no apparent differences in liver, heart or kidney histology between genotypes. However, TKO mice had exacerbated lung pathology, including consolidation of lung tissues and atelectasis, compared to WT mice. RNAseq analysis of lungs excised 24-hours after CLP identified 664 genes differentially expressed (404 upregulated and 260 downregulated) in TKO compared to WT (p<0.05). Some of the genes that showed profound induction in the lungs of TKO compared to the WT were Proz, Dbp, Cxcl1, Cxcl2, Arg1 and Ackr1 . Gene ontology analysis revealed a significant enrichment of differentially expressed genes associated with chemokine production, chemokine and cytokine-mediated signaling, neutrophil chemotaxis and neutrophil migration in TKO lung tissues compared to WT tissues (p<0.01). Conclusions: SAA protects mice against sepsis-induced mortality, potentially by protecting the lung from tissue damage. Thus, the risk of infection should be considered when targeting SAA to ameliorate atherosclerosis.

Abstract P101: Suppression Of Serum Amyloid A Limits Progression Of Obesity Associated Abdominal Aortic Aneurysms

Obesity increases the risk for abdominal aortic aneurysms (AAA) in humans, and enhances angiotensin II (AngII)-induced AAA formation in C57BL/6 mice. Obesity is also associated with increases in serum amyloid A (SAA). We previously reported that deficiency of SAA significantly reduces AngII-induced inflammation and AAA in apoE-deficient mice. In this study we investigated whether SAA plays a role in progression of an established AAA in obese C57BL/6 mice. Approach and Results: Male C57BL/6 mice were fed a high fat diet (60% kcal as fat) throughout the study. After 4 months of diet the mice were infused with angiotensin II (AngII) at 1000ng/kg/min until the end of the study. Ultrasound (US) was performed in all mice before and after 28 days of AngII infusion, and mice that had at least a 25% increase in the luminal diameter of the abdominal aorta were stratified by luminal diameter into 3 groups. Group 1 was killed to establish baseline AAA. Groups 2 and 3 continued to receive AngII for a further 8 weeks along with an antisense oligonucleotide (ASO) that suppresses all 3 acute phase SAA isoforms (SAA-ASO), or a control ASO (5 mg/kg/wk). US was repeated at study end to assess AAA progression. Plasma SAA at the end of the experiment was 89.2±83.2 mg/L in the control ASO group, and 18.6±0.7 mg/L in the SAA-ASO group (mean±SD , p=0.008). There was no impact of SAA suppression on body weight, body fat, or blood pressure. After the first 4 weeks of AngII infusion, the average luminal diameter in all mice was 1.81±0.40 mm (mean±SD). Mice that received the control ASO had continued aortic dilation (average luminal aortic diameter 2.06±0.42 mm), whereas the mice that received the SAA-ASO had a significant reduction in progression of aortic dilation (average luminal diameter 1.64±0.43 mm, p=0.0015 for interaction between time and group). Conclusions: We demonstrate for the first time that suppression of SAA protects obese C57BL/6 mice from progression of AngII-induced AAA. Suppression of SAA may be a therapeutic approach to limit AAA progression.

Serum amyloid A3 is required for caerulein-induced acute pancreatitis through induction of RIP3-dependent necroptosis.

Serum amyloid A (SAA) is an early and sensitive biomarker of inflammatory diseases, but its role in acute pancreatitis (AP) is still unclear. Here, we used a caerulein-induced mouse model to investigate the role of SAA in AP and other related inflammatory responses. In our study, we found that the expression of a specific SAA isoform, SAA3, was significantly elevated in a caerulein-induced AP animal model. In addition, SAA3-knockout (Saa3-/- ) mice showed lower serum levels of amylase and lipase, tissue damage and proinflammatory cytokine production in the pancreas compared with those of wild-type mice in response to caerulein administration. AP-associated acute lung injury was also significantly attenuated in Saa3-/- mice. In our in vitro experiments, treatment with cholecystokinin and recombinant SAA3 significantly induced necroptosis and cytokine production. Moreover, we found that the regulatory effect of SAA3 on acinar cell necroptosis was through a receptor-interacting protein 3 (RIP3)-dependent manner. Collectively, our findings indicate that SAA3 is required for AP by inducing an RIP3-dependent necroptosis pathway in acinar cells and is a potential drug target for AP.

Targeted mass spectrometry for Serum Amyloid A (SAA) isoform profiling in sequential blood samples from experimentally Staphylococcus aureus infected pigs

Serum amyloid A (SAA) is a well-described acute phase protein induced during the acute phase response (APR) to infection. Four isoform specific genes are found in most mammals. Depending on species, SAA3 and SAA4 are generally preferentially expressed extrahepatically whereas SAA1 and SAA2 are hepatic isoforms dominating the SAA serum pool. Little is known about how specific infections affect the serum SAA isoform profile, as SAA isoform discriminating antibodies are not generally available. An antibody independent, quantitative targeted MS method (Selected Reaction Monitoring, SRM) based on available information on porcine SAA isoform genes was developed and used to profile SAA in serum samples from pigs experimentally infected with Staphylococcus aureus (Sa). While results suggest SAA2 as the main circulating porcine SAA isoform, induced around 10 times compared to non-infected controls, total SAA serum concentrations reached only around 4 μg/mL, much lower than established previously by immunoassays. This might suggest that SAA isoform variants not detected by the SRM method might be present in porcine serum. The assay allows monitoring host responses to experimental infections, infectious diseases and inflammation states in the pig at an unprecedented level of detail. It can also be used in a non-calibrated (relative quantification) format. SignificanceWe developed an SRM MS method which for the first time allowed the specific quantification of each of the circulating porcine SAA isoforms (SAA2, SAA3, SAA4). It was found that SAA2 is the dominating circulating isoform of SAA in the pig and that, during the acute phase response to Sa infection SAA2, SAA3 and SAA4 are induced approx. 10, 15 and 2 times, respectively. Absolute levels of the isoforms as determined by SRM MS were much lower than reported previously for total SAA quantified by immunosassays, suggesting the existence of hitherto non-described SAA variants. SRM MS holds great promise for the study of the basic biology of SAA isoforms with the potential to study an even broader range of SAA variants.

Differential expression of serum amyloid A1 and A3 in bovine epithelia.

Serum amyloid A (SAA) is both an amyloidogenic protein of amyloid A amyloidosis and an acute phase protein in most animal species. Although SAA isoforms, such as SAA1, 2, 3, and 4, have been identified in cattle, their biological functions are not completely understood. Previous studies using mice indicated that SAA3 mRNA expression increased by stimulation with Escherichia coli and lipopolysaccharide (LPS) in colonic epithelial cells, and subsequently the SAA3 protein enhanced the expression of mucin2 (MUC2) mRNA, which is the major component of the colonic mucus layer. These results suggest that SAA3 plays a role in host innate immunity against bacterial infection in the intestine. In this study, a novel anti-bovine SAA3 monoclonal antibody was produced and SAA3 expression levels in bovine epithelia were examined in vitro and in vivo using real-time PCR and immunohistochemistry (IHC). SAA3 mRNA expression, but not that of SAA1, was enhanced by LPS stimulus in bovine small intestinal and mammary glandular epithelial cells in vitro. Moreover, in bovine epithelia (small intestine, mammary gland, lung, and uterus) obtained from four Holstein dairy cows from a slaughterhouse, SAA3 mRNA expression was higher than that of SAA1. Furthermore, using IHC, SAA3 protein expression was observed in bovine epithelia, whereas SAA1 protein was not. These results suggest that in cattle, SAA3 plays an immunological role against bacterial infection in epithelial tissues, including the small intestine, mammary gland, lung, and uterus.

Comparative Study on Hyaluronic Acid Binding to Murine SAA1.1 and SAA2.2

Persistently high plasma levels of serum amyloid A (SAA) may induce AA amyloidosis in various organs causing their dysfunction. Although SAA isoforms share a high degree of homology, only the SAA1.1 isoform is found in amyloid deposits. SAA1.1 misfolding is a nucleation-dependent process with dimer and trimer formation playing a major role in SAA fibril formation through self-catalyzed recruitment of native SAA molecules. Yet, a structural model of initial SAA oligomerization is still missing. In this study, we constructed a loosely associated model for murine SAA1.1 and SAA2.2 dimers in the presence or absence of hyaluronic acid as an exemplary glycosaminoglycan, a factor known to facilitate SAA fibril formation. Molecular dynamics simulations predicted that hyaluronic acid finally stabilized in a different binding pocket of the pathogenic SAA1.1 dimer compared to the nonpathogenic SAA2.2 dimer. Besides, Markov state modeling points to dynamic behavioral differences between the linker region of SAA1.1 and SAA2.2 and identifies a state unique to pathogenic SAA1.1 while bound to hyaluronic acid. The presence or absence of hyaluronic acid, as well as the dimer interface switch, affects dynamic behavior and possible oligomeric states, proposing a conceivable clue to the deviant pathogenicity of the two SAA isoforms.

Elevated Expression of Serum Amyloid A 3 Protects Colon Epithelium Against Acute Injury Through TLR2-Dependent Induction of Neutrophil IL-22 Expression in a Mouse Model of Colitis.

Induced expression of serum amyloid A (SAA) is a hallmark of many inflammatory diseases, but whether SAA exacerbates inflammation or protects tissues against injury remains unclear. In dextran sulfate sodium (DSS)-induced colitis, SAA3 is the predominant isoform of inducible SAA proteins that also include SAA1 and SAA2, and mice with genetic deletion of Saa3 exhibits increased production of proinflammatory cytokines, decreased expression of IL-22 along with aggravated epithelium disruption, and reduced colon length compared with wild-type littermates. Colonic neutrophils have been identified as a major source of IL-22 in these mice. Administration of exogenous SAA3 as recombinant protein to Saa3−/− mice improves neutrophil IL-22 production, colonic epithelial integrity, and secretion of the antimicrobial peptides Reg3β and Reg3γ. Stimulation of mouse bone marrow neutrophils with mouse SAA3 or human SAA1 leads to expansion of IL-22-producing neutrophils. Unlike previously reported IL-22 induction through IL-23, the SAA3-induced neutrophil IL-22 expression utilizes a TLR2-dependent mechanism that does not depend on IL-23. Adoptive transfer of the SAA3-treated neutrophils to Saa3−/− mice ameliorates DSS-induced colitis and improves colonic epithelial integrity. These findings suggest that in the DSS-induced mouse colitis model, SAA isoforms are expressed to different extent in colon and deletion of Saa3 renders these mice more susceptible to DSS-induced injury. The presence of SAA3 in the inflamed colon mucosal serves to protect epithelial barrier in part through expansion of IL-22-producing neutrophils. It is speculated that SAA3 stimulation of autologous neutrophils may have therapeutic potential for inflammatory bowel disease.

Serum amyloid A3 is a high density lipoprotein-associated acute-phase protein

Serum amyloid A (SAA) is a family of acute-phase reactants. Plasma levels of human SAA1/SAA2 (mouse SAA1.1/2.1) can increase ≥1,000-fold during an acute-phase response. Mice, but not humans, express a third relatively understudied SAA isoform, SAA3. We investigated whether mouse SAA3 is an HDL-associated acute-phase SAA. Quantitative RT-PCR with isoform-specific primers indicated that SAA3 and SAA1.1/2.1 are induced similarly in livers (∼2,500-fold vs. ∼6,000-fold, respectively) and fat (∼400-fold vs. ∼100-fold, respectively) of lipopolysaccharide (LPS)-injected mice. In situ hybridization demonstrated that all three SAAs are produced by hepatocytes. All three SAA isoforms were detected in plasma of LPS-injected mice, although SAA3 levels were ∼20% of SAA1.1/2.1 levels. Fast protein LC analyses indicated that virtually all of SAA1.1/2.1 eluted with HDL, whereas ∼15% of SAA3 was lipid poor/free. After density gradient ultracentrifugation, isoelectric focusing demonstrated that ∼100% of plasma SAA1.1 was recovered in HDL compared with only ∼50% of SAA2.1 and ∼10% of SAA3. Thus, SAA3 appears to be more loosely associated with HDL, resulting in lipid-poor/free SAA3. We conclude that SAA3 is a major hepatic acute-phase SAA in mice that may produce systemic effects during inflammation.

Porcine serum amyloid A3 is expressed in extrahepatic tissues and facilitates viral replication during porcine respiratory and reproductive syndrome virus infection

Serum amyloid A (SAA) is an acute phase protein that is expressed rapidly in response to infection and inflammation in vertebrates. Here, we detected the expression of porcine SAA3, an isoform of porcine SAA, during porcine respiratory and reproductive syndrome virus (PRRSV) infection, which is a major threat to the pig industry. In response to PRRSV infection, porcine SAA3 expression was upregulated significantly in porcine pulmonary alveolar macrophages and in extrahepatic tissues, including the lungs and inguinal, mandibular, and hilar lymph nodes, which were affected mainly by PRRSV infection, demonstrating that porcine SAA3 is a tissue-derived isoform that is induced in extrahepatic tissues during the acute phase response. Overexpression of porcine SAA3 increased PRRSV titers in cultured cells, and the exogenous administration of porcine SAA3 facilitated PRRSV adsorption to cells, suggesting that porcine SAA3 assists PRRSV replication. Our data provide insights into the role of porcine SAA3 during PRRSV infection.

The N-terminal region of serum amyloid A3 protein activates NF-κB and up-regulates MUC2 mucin mRNA expression in mouse colonic epithelial cells.

Serum amyloid A (SAA) is the major acute-phase protein and a precursor of amyloid A (AA) in AA amyloidosis in humans and animals. SAA isoforms have been identified in a wide variety of animals, such as SAA1, SAA2, SAA3, and SAA4 in mouse. Although the biological functions of SAA isoforms are not completely understood, recent studies have suggested that SAA3 plays a role in host defense. Expression of SAA3 is increased on the mouse colon surface in the presence of microbiota in vivo, and it increases mRNA expression of mucin 2 (MUC2) in murine colonic epithelial cells in vitro, which constitutes a protective mucus barrier in the intestinal tract. In this study, to identify responsible regions in SAA3 for MUC2 expression, recombinant murine SAA1 (rSAA1), rSAA3, and rSAA1/3, a chimera protein constructed with mature SAA1 (amino acids 1–36) and SAA3 (amino acids 37–103), and vice versa for rSAA3/1, were added to murine colonic epithelial CMT-93 cells, and the mRNA expressions of MUC2 and cytokines were measured. Inhibition assays with NF-κB inhibitor or TLR4/MD2 inhibitor were also performed. Up-regulation of MUC2 mRNA expression was strongly stimulated by rSAA3 and rSAA3/1, but not by rSAA1 or rSAA1/3. Moreover, NF-κB and TLR4/MD2 inhibitors suppressed the increase of MUC2 mRNA expression. These results suggest that the major responsible region for MUC2 expression exists in amino acids 1–36 of SAA3, and that up-regulations of MUC2 expression by SAA3 and SAA3/1 are involved with activation of NF-κB via the TLR4/MD2 complex.

Impact of individual acute phase serum amyloid A isoforms on HDL metabolism in mice

The acute phase (AP) reactant serum amyloid A (SAA), an HDL apolipoprotein, exhibits pro-inflammatory activities, but its physiological function(s) are poorly understood. Functional differences between SAA1.1 and SAA2.1, the two major SAA isoforms, are unclear. Mice deficient in either isoform were used to investigate plasma isoform effects on HDL structure, composition, and apolipoprotein catabolism. Lack of either isoform did not affect the size of HDL, normally enlarged in the AP, and did not significantly change HDL composition. Plasma clearance rates of HDL apolipoproteins were determined using native HDL particles. The fractional clearance rates (FCRs) of apoA-I, apoA-II, and SAA were distinct, indicating that HDL is not cleared as intact particles. The FCRs of SAA1.1 and SAA2.1 in AP mice were similar, suggesting that the selective deposition of SAA1.1 in amyloid plaques is not associated with a difference in the rates of plasma clearance of the isoforms. Although the clearance rate of SAA was reduced in the absence of the HDL receptor, scavenger receptor class B type I (SR-BI), it remained significantly faster compared with that of apoA-I and apoA-II, indicating a relatively minor role of SR-BI in SAA's rapid clearance. These studies enhance our understanding of SAA metabolism and SAA's effects on AP-HDL composition and catabolism.

Abstract 388: Impact of Individual Acute Phase Serum Amyloid A Isoforms on HDL Metabolism in Mice

The acute phase reactant serum amyloid A (SAA) is an HDL apolipoprotein that exhibits biological activities as a pro-inflammatory mediator, but its physiological function(s) are poorly understood. Possible functional differences between SAA1.1 and SAA2.1, the two major SAA isoforms, are also unclear. Mice deficient in either SAA1.1 or SAA2.1 were used to investigate SAA isoform plasma clearance rates and effects on HDL structure, composition and apolipoprotein catabolism. The absence of either isoform did not affect the size of the normally enlarged HDL found in acute phase wild type mice, and did not result in significant changes in HDL lipid composition. Plasma clearance rates of normal and acute phase HDL apolipoproteins were determined using native HDL particles. The fractional clearance rates (FCR’s) of apoA-I, apoA-II and SAA were distinct, indicating that neither normal nor acute phase particles are cleared as intact particles. No significant difference was found between the FCR’s of SAA1.1 and SAA2.1 in acute phase mice, suggesting that the selective deposition of SAA1.1 observed in amyloid plaques is not associated with a difference in the rates of plasma clearance of the isoforms. In the absence of the HDL receptor SR-BI, the clearance rate of SAA was reduced by about 30% and remained significantly greater compared to that of apoA-I and apoA-II, indicating a relatively minor role of SR-BI in SAA clearance. These studies contribute to our understanding of the metabolism of SAA and its effects on acute phase HDL composition and catabolism.

Production of serum amyloid A in equine articular chondrocytes and fibroblast-like synoviocytes treated with proinflammatory cytokines and its effects on the two cell types in culture.

To investigate the role of the major equine acute phase protein serum amyloid A (SAA) in inflammation of equine intraarticular tissues. Articular chondrocytes and fibroblast-like synoviocytes (FLSs) from 8 horses (4 horses/cell type). Chondrocytes and FLSs were stimulated in vitro for various periods up to 48 hours with cytokines (recombinant interleukin [IL]-1β, IL-6, tumor necrosis factor-α, or a combination of all 3 [IIT]) or with recombinant SAA. Gene expression of SAA, IL-6, matrix metalloproteinases (MMP)-1 and -3, and cartilage-derived retinoic acid-sensitive protein were assessed by quantitative real-time PCR assay; SAA protein was evaluated by immunoturbidimetry and denaturing isoelectric focusing and western blotting. All cytokine stimulation protocols increased expression of SAA mRNA and resulted in detectable SAA protein production in chondrocytes and FLSs. Isoforms of SAA in lysed chondrocytes and their culture medium corresponded to those previously detected in synovial fluid from horses with joint disease. When exposed to SAA, chondrocytes and FLSs had increased expression of IL-6, SAA, and MMP3, and chondrocytes had increased expression of MMP-1. Chondrocytes had decreased expression of cartilage-derived retinoic acid-sensitive protein. Upregulation of SAA in chondrocytes and FLSs stimulated with proinflammatory cytokines and the proinflammatory effects of SAA suggested that SAA may be involved in key aspects of pathogenesis of the joint inflammation in horses.

Consequences of hepatic damage after traumatic brain injury: current outlook and potential therapeutic targets.

Consequences of hepatic damage after traumatic brain injury: current outlook and potential therapeutic targets.

Acute Phase Proteins: How they portray Mastitis – A review

Acute Phase Proteins are blood proteins primarily synthesized by hepatocytes as part of the acute phase response (APR). APR to disease is accompanied by an increase in the circulating concentration of a number of plasma proteins which are collectively known as the Acute Phase Proteins. According to the concentration, APPs are classified in positive APP, if they increase or negative APP, if they decrease. During mastitis, APPs move from the systemic circulation to mammary gland or there could be de-novo synthesis of the APP within mammary gland tissues. Among the APPs, Serum Amyloid A (SAA), Haptoglobin (Hp), Alpha 1-acid glycoprotein and Lipopolysaccharide binding protein play a major role during mastitis in cattle and their concentration will increase with the severity of the infection, inflammation or trauma. SAA is involved in defense against Gram positive and Gram negative pathogens. SAA acts by modulating innate immune system and by acting as an opsonin. Among the SAA isoforms, mammary associated SAA3 (m-SAA3) is important. The blood concentration of SAA and Hp increases dramatically after LPS infusion, with SAA (acute and middle phase of APR) appearing before Hp (Late phase of APR). The herd level APP might be useful for determining the prevalence of clinical and subclinical infections indicated by the high serum concentration of selected APP and by serving as the prognostic tool. APPs, used as markers of animal health may possibly be influenced by environmental factors, handling procedures and other types of stress in the absence of disease.