Hepatic serum amyloid A1 aggravates T cell-mediated hepatitis by inducing chemokines via Toll-like receptor 2 in mice

Shared inflammatory glial cell signature after stab wound injury, revealed by spatial, temporal, and cell-type-specific profiling of the murine cerebral cortex

Traumatic brain injury leads to a highly orchestrated immune- and glial cell response partially responsible for long-lasting disability and the development of secondary neurodegenerative diseases. A holistic understanding of the mechanisms controlling the responses of specific cell types and their crosstalk is required to develop an efficient strategy for better regeneration. Here, we combine spatial and single-cell transcriptomics to chart the transcriptomic signature of the injured male murine cerebral cortex, and identify specific states of different glial cells contributing to this signature. Interestingly, distinct glial cells share a large fraction of injury-regulated genes, including inflammatory programs downstream of the innate immune-associated pathways Cxcr3 and Tlr1/2. Systemic manipulation of these pathways decreases the reactivity state of glial cells associated with poor regeneration. The functional relevance of the discovered shared signature of glial cells highlights the importance of our resource enabling comprehensive analysis of early events after brain injury.

Integrated untargeted and targeted proteomics to unveil plasma prognostic markers for patients with acute paraquat poisoning: A pilot study

Paraquat (PQ) is a widely used but strongly toxic herbicide, which can induce multiple organ failure. The overall survival rate of the poisoned patients was only 54.4% due to lack of specific antidotes. Besides, the definite pathogenic mechanism of PQ is still not fully understood. In this pilot study, untargeted and targeted proteomics were integrated to explore the expression characteristics of plasma protein in PQ poisoned patients, and identify the differentially expressed proteins between survivors and non-survivors. A total of 494 plasma proteins were detected, and of which 47 were upregulated and 44 were downregulated in PQ poisoned patients compared to healthy controls. Among them, five differential plasma proteins (S100A9, S100A8, MB, ACTB and RAB11FIP3) were further validated by multiple reaction monitoring (MRM)-based targeted proteomic approach, and three of them (S100A9, S100A8 and ACTB) were confirmed to be correlated with PQ poisoning. Meanwhile, 84 dysregulated plasma proteins were identified in non-survivors compared with survivors. Moreover, targeted proteomic and ROC analysis suggested that ACTB had a good performance in predicting the prognosis of PQ poisoned patients. These findings highlighted the value of label-free and mass spectrometry-based proteomics in screening prognostic biomarkers of PQ poisoning and studying the mechanism of PQ toxicity.

Natural deletion of mouse carboxylesterases Ces1c/d/e impacts drug metabolism and metabolic syndrome development

Mammalian carboxylesterase 1 enzymes can hydrolyze many xenobiotic chemicals and endogenous lipids. We here identified and characterized a mouse strain (FVB/NKI) in which three of the eight Ces1 genes were spontaneously deleted, removing Ces1c and Ces1e partly, and Ces1d entirely. We studied the impact of this Ces1c/d/e deficiency on drug and lipid metabolism and homeostasis. Ces1c/d/e-/- mice showed strongly impaired conversion of the anticancer prodrug irinotecan to its active metabolite SN-38 in plasma, spleen and lung. Plasma hydrolysis of the oral anticancer prodrug capecitabine to 5-DFCR was also profoundly reduced in Ces1c/d/e-/- mice. Our findings resolved previously unexplained FVB/NKI pharmacokinetic anomalies. On a medium-fat diet, Ces1c/d/e-/- female mice exhibited moderately higher body weight, mild inflammation in gonadal white adipose tissue (gWAT), and increased lipid load in brown adipose tissue (BAT). Ces1c/d/e-/- males showed more pronounced inflammation in gWAT and an increased lipid load in BAT. On a 5-week high-fat diet exposure, Ces1c/d/e deficiency predisposed to developing obesity, enlarged and fatty liver, glucose intolerance and insulin resistance, with severe inflammation in gWAT and increased lipid load in BAT. Hepatic proteomics analysis revealed that the acute phase response, involved in the dynamic cycle of immunometabolism, was activated in these Ces1c/d/e-/- mice. This may contribute to the obesity-related chronic inflammation and adverse metabolic disease in this strain. While Ces1c/d/e deficiency clearly exacerbated metabolic syndrome development, long-term (18-week) high-fat diet exposure overwhelmed many, albeit not all, observed phenotypic differences.

Serum amyloid A and metabolic disease: evidence for a critical role in chronic inflammatory conditions

Serum amyloid A (SAA) subtypes 1-3 are well-described acute phase reactants that are elevated in acute inflammatory conditions such as infection, tissue injury, and trauma, while SAA4 is constitutively expressed. SAA subtypes also have been implicated as playing roles in chronic metabolic diseases including obesity, diabetes, and cardiovascular disease, and possibly in autoimmune diseases such as systemic lupus erythematosis, rheumatoid arthritis, and inflammatory bowel disease. Distinctions between the expression kinetics of SAA in acute inflammatory responses and chronic disease states suggest the potential for differentiating SAA functions. Although circulating SAA levels can rise up to 1,000-fold during an acute inflammatory event, elevations are more modest (∼5-fold) in chronic metabolic conditions. The majority of acute-phase SAA derives from the liver, while in chronic inflammatory conditions SAA also derives from adipose tissue, the intestine, and elsewhere. In this review, roles for SAA subtypes in chronic metabolic disease states are contrasted to current knowledge about acute phase SAA. Investigations show distinct differences between SAA expression and function in human and animal models of metabolic disease, as well as sexual dimorphism of SAA subtype responses.

Neutralizing serum amyloid a protects against sinusoidal endothelial cell damage and platelet aggregation during acetaminophen-induced liver injury

Serum amyloid A (SAA) is an acute response protein that mainly produced by hepatocytes, and it can promote endothelial dysfunction via a pro-inflammatory and pro-thrombotic effect in atherosclerosis and renal disease. Overdose of Acetaminophen (APAP) will cause hepatotoxicity accompany with hepatocyte necrosis, liver sinusoidal endothelial cells (LSECs) damage and thrombosis in liver. However, whether SAA plays a role in APAP-induced liver toxicity remains unclear. Here, we evaluated the Saa1/2 expression in APAP-induced liver injury, and found that Saa1/2 production was significantly increased in an autocrine manner in APAP injury model. Moreover, we used neutralizing antibody (anti-SAA) to block the function of serum Saa1/2. We found that neutralizing serum Saa1/2 protected against APAP-induced liver injuries and increased the survival rate of mice that were treated with lethal dose APAP. Further investigations showed that blocking Saa1/2 reduced APAP-induced sinusoidal endothelium damage, hemorrhage and thrombosis. In addition, in vitro experiments showed that Saa1/2 augmented the toxic effect of APAP on LSECs, and Saa1/2 promoted platelets aggregation on LSECs cell membrane. Taken together, this study suggests that Saa1/2 may play a critical role in APAP-induced liver damages through platelets aggregation and sinusoidal damage. Therefore, we conceptually demonstrate that inhibition of SAA may be a potential intervention for APAP-directed acute liver injuries.

Hepatitis C Core Protein Induces a Genotype-Specific Susceptibility of Hepatocytes to TNF-Induced Death In Vitro and In Vivo

Hepatitis C virus (HCV) core protein is a multifunctional protein that is involved in the proliferation, inflammation, and apoptosis mechanism of hepatocytes. HCV core protein genetic variability has been implicated in various outcomes of HCV pathology and treatment. In the present study, we aimed to analyze the role of the HCV core protein in tumor necrosis factor α (TNFα)-induced death under the viewpoint of HCV genetic variability. Immortalized hepatocytes (IHH), and not the Huh 7.5 hepatoma cell line, stably expressing HCV subtype 4a and HCV subtype 4f core proteins showed that only the HCV 4a core protein could increase sensitivity to TNFα-induced death. Development of two transgenic mice expressing the two different core proteins under the liver-specific promoter of transthyretin (TTR) allowed for the in vivo assessment of the role of the core in TNFα-induced death. Using the TNFα-dependent model of lipopolysaccharide/D-galactosamine (LPS/Dgal), we were able to recapitulate the in vitro results in IHH cells in vivo. Transgenic mice expressing the HCV 4a core protein were more susceptible to the LPS/Dgal model, while mice expressing the HCV 4f core protein had the same susceptibility as their littermate controls. Transcriptome analysis in liver biopsies from these transgenic mice gave insights into HCV core molecular pathogenesis while linking HCV core protein genetic variability to differential pathology in vivo.

Toll-like receptor 2 signaling in liver pathophysiology

Chronic liver diseases (CLD) are among the major cause of mortality and morbidity worldwide. Despite current achievements in the area of hepatitis virus, chronic alcohol abuse and high-fat diet are still fueling an epidemic of severe liver disease, for which, an effective therapy has yet not been discovered. In particular, the therapeutic regimens that could prevent the progression of fibrosis and, in turn, aid cirrhotic liver to develop a robust regenerative capability are intensively needed. To this context, a better understanding of the signaling pathways regulating hepatic disease development may be of critical value. In general, the liver responds to various insults with an orchestrated healing process involving variety of signaling pathways. One such pathway is the TLR2 signaling pathway, which essentially regulates adult liver pathogenesis and thus has emerged as an attractive target to treat liver disease. TLR2 is expressed by different liver cells, including Kupffer cells (KCs), hepatocytes, and hepatic stellate cells (HSCs). From a pathologic perspective, the crosstalk between antigens and TLR2 may preferentially trigger a distinctive set of signaling mechanisms in these liver cells and, thereby, induce the production of inflammatory and fibrogenic cytokines that can initiate and prolong liver inflammation, ultimately leading to fibrosis. In this review, we summarize the currently available evidence regarding the role of TLR2 signaling in hepatic disease progression. We first elaborate its pathological involvement in liver-disease states, such as inflammation, fibrosis, and cirrhosis. We then discuss how therapeutic targeting of this pathway may help to alleviate its disease-related functioning.

The turning away of serum amyloid A biological activities and receptor usage

Serum amyloid A (SAA) is an acute-phase protein (APP) to which multiple immunological functions have been attributed. Regardless, the true biological role of SAA remains poorly understood. SAA is remarkably conserved in mammalian evolution, thereby suggesting an important biological function. Since its discovery in the 1970s, the majority of researchers have investigated SAA using recombinant forms made available through bacterial expression. Nevertheless, recent studies indicate that these recombinant forms of SAA are unreliable. Indeed, commercial SAA variants have been shown to be contaminated with bacterial products including lipopolysaccharides and lipoproteins. As such, biological activities and receptor usage (TLR2, TLR4) revealed through the use of commercial SAA variants may not reflect the inherent nature of this APP. Within this review, we discuss the biological effects of SAA that have been demonstrated through more solid experimental approaches. SAA takes part in the innate immune response via the recruitment of leucocytes and executes, through pathogen recognition, antimicrobial activity. Knockout animal models implicate SAA in a range of functions, such as regulation of T-cell-mediated responses and monopoiesis. Moreover, through its structural motifs, not only does SAA function as an extracellular matrix protein, but it also binds extracellular matrix proteins. Finally, we here also provide an overview of definite SAA receptor-mediated functions and highlight those that are yet to be validated. The role of FPR2 in SAA-mediated leucocyte recruitment has been confirmed; nevertheless, SAA has been linked to a range of other receptors including CD36, SR-BI/II, RAGE and P2RX7.

Toll-like receptor 2 activation and up-regulation by high mobility group box-1 contribute to post-operative neuroinflammation and cognitive dysfunction in mice

Post-operative cognitive dysfunction (POCD) is common and is associated with poor clinical outcome. Toll-like receptor (TLR) 3 and 4 have been implied in the development of POCD. The role of TLR2, a major brain TLR, in POCD is not clear. High mobility group box-1 (HMGB1) is a delayed inflammatory mediator and may play a role in POCD. The interaction between HMGB1 and TLRs in the perioperative period is not known. We hypothesize that TLR2 contributes to the development of POCD and that HMGB1 regulates TLR2 for this effect. To test these hypotheses, 6- to 8-week old male mice were subjected to right carotid artery exposure under isoflurane anesthesia. CU-CPT22, a TLR1/TLR2 inhibitor, at 3 mg/kg was injected intraperitoneally 30 min before surgery and 1 day after surgery. Glycyrrhizin, a HMGB1 antagonist, at 200 mg/kg was injected intraperitoneally 30 min before surgery. Mice were subjected to Barnes maze and fear conditioning tests from 1 week after surgery. Hippocampus and cerebral cortex were harvested 6 hr or 12 hr after the surgery for Western blotting, ELISA, immunofluorescent staining, and chromatin immunoprecipitation. There were neuroinflammation and impairment of learning and memory in mice with surgery. Surgery increased the expression of TLR2 and TLR4 but not TLR9 in the brain of CD-1 male mice. CU-CPT22 attenuated surgery-induced neuroinflammation and cognitive impairment. Similarly, surgery induced neuroinflammation and cognitive dysfunction in C57BL/6J mice but not in TLR2^-/- mice. TLR2 staining appeared in neurons and microglia. Surgery increased HMGB1 in the cell nuclei of the cerebral cortex and hippocampus. Glycyrrhizin ameliorated this increase and the increase of TLR2 in the hippocampus after surgery. Surgery also increased the amount of tlr2 DNA precipitated by an anti-HMGB1 antibody in the hippocampus. Our results suggest that TLR2 contributes to surgery-induced neuroinflammation and cognitive impairment. HMGB1 up-regulates TLR2 expression in the hippocampus after surgery to facilitate this contribution. Thus, TLR2 and HMGB1 are potential targets for reducing POCD.

SAA1/TLR2 axis directs chemotactic migration of hepatic stellate cells responding to injury

Hepatic stellate cells (HSCs) are crucial for liver injury repair and cirrhosis. However, the mechanism of chemotactic recruitment of HSCs into injury loci is still largely unknown. Here, we demonstrate that serum amyloid A1 (SAA1) acts as a chemokine recruiting HSCs toward injury loci signaling via TLR2, a finding proven by gene manipulation studies in cell and mice models. The mechanistic investigations revealed that SAA1/TLR2 axis stimulates the Rac GTPases through PI3K-dependent pathways and induces phosphorylation of MLC (pSer19). Genetic deletion of TLR2 and pharmacological inhibition of PI3K diminished the phosphorylation of MLCpSer19 and migration of HSCs. In brief, SAA1 serves as a hepatic endogenous chemokine for the TLR2 receptor on HSCs, thereby initiating PI3K-dependent signaling and its effector, Rac GTPases, which consequently regulates actin filament remodeling and cell directional migration. Our findings provide novel targets for anti-fibrosis drug development.

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SAA1 serves as a chemokine to guide migration of HSCs toward injury locus

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TLR2 acts as a functional receptor for SAA1 in HSCs

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SAA1/TLR2 axis-mediated migration of HSCs operates through PI3K/Rac1 signaling

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SAA1/TLR2 axis provides a link for the cross talk between hepatocytes and HSCs

Overexpression of hepatic serum amyloid A1 in mice increases IL-17-producing innate immune cells and decreases bone density

Serum amyloid A (SAA) is an acute-phase protein produced primarily in the liver that plays a key role in both the initiation and maintenance of inflammation. Rapidly secreted SAA induces neutrophilia at inflammatory sites, initiating inflammation and inducing the secretion of various cytokines, including TNF-α, IL-6, and IL-17. IL-17 is expressed in several inflammatory cells, including innate immune cells such as γδT cells, ILC3 cells, and neutrophils. Increased IL-17 levels exacerbate various inflammatory diseases. Among other roles, IL-17 induces bone loss by increasing receptor activator of nuclear factor-κB ligand (RANKL) secretion, which stimulates osteoclast differentiation. Several studies have demonstrated that chronic inflammation induces bone loss, suggesting a role for SAA in bone health. To test this possibility, we observed an increase in IL-17-producing innate immune cells, neutrophils, and γδT cells in these mice. In 6-month-old animals, we detected increased osteoclast-related gene expression and IL-17 expression in bone lysates. We also observed an increase in neutrophils that secreted RANKL in the bone marrow of TG mice. Finally, we demonstrated decreased bone mineral density in these transgenic (TG) mice. Our results revealed that the TG mice have increased populations of IL-17-producing innate immune cells, γδT cells, and neutrophils in TG mice. We additionally detected increased RANKL and IL-17 expression in the bone marrow of 6-month-old TG mice. Furthermore, we confirmed significant increases in RANKL-expressing neutrophils in TG mice and decreased bone mineral density. Our results provide evidence that chronic inflammation induced by SAA1 causes bone loss via IL-17-secreting innate immune cells.

Effects of serum amyloid protein A on influenza A virus replication and viral interactions with neutrophils

Innate immunity is vital for the early control of influenza A virus (IAV) infection. Serum amyloid A (SAA1) is an acute phase reactant produced in the liver and lung that rises dramatically during IAV infection. The potential role of SAA1 in host defense against IAV is unknown. SAA1 has been reported to directly activate neutrophils and to recruit them to the lung during infectious and inflammatory processes. Neutrophils are the most abundant cell recruited to the lung in the early phase of IAV infection. There are different forms and preparations of SAA1 that have found to have different effects on phagocyte responses, through various receptors. In this paper, we test the direct effects of various preparations of serum derived or recombinant SAA on IAV and how it modulates the interactions of IAV with neutrophils. All SAA preparations bound to IAV in vitro but caused minimal hemagglutination inhibition or viral aggregation. The human serum‐derived SAA1 or the complex of SAA1 with HDL did have IAV neutralizing activity in vitro, whereas the recombinant SAA1 preparations did not. We found that different SAA preparations also had markedly different effects on neutrophil functions, with E. coli‐derived SAA1 triggering some responses in neutrophils on its own or in presence of IAV whereas mammalian cell‐derived SAA1 did not. This discrepancy could be explained by the reported contamination of the former preparation with bacterial components. Of interest, however, serum SAA alone, serum SAA complexed with HDL, or HDL alone potentiated some neutrophil responses to IAV. Our results suggest that SAA may play some role in host response to IAV, but further work needs to be done to clarify the role of different variants of SAA alone or complexed with HDL.

Serum Amyloid A1 (SAA1) Revisited: Restricted Leukocyte-Activating Properties of Homogeneous SAA1

Infection, sterile injury, and chronic inflammation trigger the acute phase response in order to re-establish homeostasis. This response includes production of positive acute phase proteins in the liver, such as members of the serum amyloid A (SAA) family. In humans the major acute phase SAAs comprise a group of closely related variants of SAA1 and SAA2. SAA1 was proven to be chemotactic for several leukocyte subtypes through activation of the G protein-coupled receptor FPRL1/FPR2. Several other biological activities of SAA1, such as cytokine induction, reported to be mediated via TLRs, have been debated recently. Especially commercial SAA1, recombinantly produced in Escherichia coli, was found to be contaminated with bacterial products confounding biological assays performed with this rSAA1. We purified rSAA1 by RP-HPLC to homogeneity, removing contaminants such as lipopolysaccharides, lipoproteins and formylated peptides, and re-assessed several biological activities attributed to SAA1 (chemotaxis, cytokine induction, MMP-9 release, ROS generation, and macrophage differentiation). The homogeneous rSAA1 (hrSAA1) lacked most cell-activating properties, but its leukocyte-recruiting capacity in vivo and it’s in vitro synergy with other leukocyte attractants remained preserved. Furthermore, hrSAA1 maintained the ability to promote monocyte survival. This indicates that pure hrSAA1 retains its potential to activate FPR2, whereas TLR-mediated effects seem to be related to traces of bacterial TLR ligands in the E. coli-produced human rSAA1.

Plasma proteomic analysis of autoimmune hepatitis in an improved AIH mouse model

Background

The prevalence of autoimmune hepatitis (AIH) is increasing, and its early clinical diagnosis is difficult. The pathogenesis of AIH remains unclear, and AIH-related studies are largely limited because of lack of suitable mouse models.

Methods

To obtain a good tool for research on AIH, we first established an improved immune-mediated mouse model that can mimic the pathological process of AIH as in the human body, through repeated injections of human cytochrome P450 2D6 (CYP2D6) plasmid. Next, a proteomic analysis based on isobaric tag (IBT) technology was performed to detect the differentially expressed proteins (DEPs), and related biological functions and pathways in the plasma of AIH and normal mice. Finally, we performed enzyme-linked immunosorbent assay (ELISA) to further confirm the most abundant DEP in the plasma of patients with AIH.

Results

Autoantibodies and the characteristic pathology of AIH were observed in our mouse model. Inflammatory infiltration also increased in the livers of AIH mice over time and plateaued by day 42 post the first injection. Chronic hepatitis was most severe on day 35 with the development of fibrosis as well, and the plasma of AIH mice were collected for proteomic analysis. A total of 176 DEPs were found in this experiment, of which 148 DEPs were up-regulated and 28 DEPs were down-regulated. Thirty significant Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways (P < 0.05) were detected. Arginine biosynthesis was found to be the most significant pathway involved in the AIH process. During the Gene Ontology (GO) analysis, most DEPs were found to be involved in the binding, cellular, and metabolic processes. Using ELISA, the most overexpressed DEP, serum amyloid A 1 (SAA1), was confirmed to be increased specifically in the plasma of patients with AIH compared to other chronic hepatitis. Different plasma levels of SAA1 were also found related to different grades of inflammation and stages of fibrosis in the liver of patients with AIH.

Conclusions

Our study is the first to describe the proteomics analysis of a true sense of AIH mouse model, which is beneficial for a better understanding of AIH pathogenesis and identifying potential biomarkers for its clinical diagnosis.

The JAK inhibitor tofacitinib ameliorates immune‑mediated liver injury in mice

The prevalence of immune-mediated liver diseases such as autoimmune liver disease or viral hepatitis has increased in recent years, and the side effects of pre-existing treatments are a worldwide problem. Regulatory T cells (Tregs) and T helper 17 (Th17) cells play important roles in the development of immune-mediated hepatitis and may serve as potential therapeutic targets. Tofacitinib, a new Janus kinase (JAK) inhibitor, is under investigation for the treatment of rheumatoid arthritis; it is also helpful in treating ulcerative colitis and psoriasis. The roles of tofacitinib were investigated in conferring protection against immune-mediated liver injury in mice. T cell-mediated hepatitis was induced by concanavalin A (ConA). The mice in the treatment groups were administered with tofacitinib intragastrically before the ConA injection. Histopathological examination was performed by hematoxylin and eosin (H&E) staining, and the serum transaminase and inflammatory cytokine levels were determined using an automatic biochemistry analysis apparatus or cytometric bead array (CBA) kits. Flow cytometric analysis was used to detect Tregs and Th17 cells. Tofacitinib significantly decreased the hepatic injury induced by ConA and prominently decreased the liver transaminase level. The secretion of several anti-inflammatory cytokines such as interleukin (IL)-10 was upregulated in mice from the treatment group, compared to that in mice treated with ConA alone, while the expression of interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α) decreased. Tofacitinib treatment increased the number of Tregs and reduced the number of Th17 cells. Furthermore, tofacitinib could relieve liver fibrosis under conditions of autoimmune hepatitis (AIH). The present results indicated that tofacitinib improved immune-mediated hepatitis and restored the impaired Treg/Th17 cell ratio, which suggests that it may serve as a novel treatment approach for immune-mediated liver diseases.

Serum amyloid A1 is involved in amyloid plaque aggregation and memory decline in amyloid beta abundant condition

Alzheimer's disease (AD) is a neurodegenerative disorder, characterized by cognitive impairment, progressive neurodegeneration, and amyloid-β (Aβ) lesion. In the neuronal death and disease progression, inflammation is known to play an important role. Our previous study on acute-phase protein serum amyloid A1 (SAA1) overexpressed mice showed that the liver-derived SAA1 accumulated in the brain by crossing the brain blood barrier (BBB) and trigger the depressive-like behavior on mouse. Since SAA1 involved in immune responses in other diseases, we focused on the possibility that SAA1 may exacerbate the neuronal inflammation related to Alzheimer's disease. A APP/SAA overexpressed double transgenic mouse was generated using amyloid precursor protein overexpressed (APP)-c105 mice and SAA1 overexpressed mice to examine the function of SAA1 in Aβ abundant condition. Comparisons between APP and APP/SAA1 transgenic mice showed that SAA1 exacerbated amyloid aggregation and glial activation; which lead to the memory decline. Behavior tests also supported this result. Overall, overexpression of SAA1 intensified the neuronal inflammation in amyloid abundant condition and causes the greater memory decline compared to APP mice, which only expresses Aβ 1-42.

Hepatic serum amyloid A1 upregulates interleukin-17 (IL-17) in γδ T cells through Toll-like receptor 2 and is associated with psoriatic symptoms in transgenic mice

Serum amyloid A (SAA) is an acute phase protein with pro-inflammatory cytokine-like properties. Recent studies have revealed that SAA promoted interleukin-17 (IL-17) production by various cells, including γδ T cells. γδ T cells are innate immune cells and express Toll-like receptor 2 (TLR2) on their surface, which is one of the SAA receptors. In this study, we investigated the relationship between γδ T cells and SAA1 through TLR2, by using hepatic SAA1-overexpressing transgenic (TG) mice. By injecting CU-CPT22, which is a TLR2 inhibitor, into the mice, we confirmed that SAA1 induced IL-17 in γδ T cells through TLR2. In vitro studies have confirmed that SAA1 increased IL-17 secretion in γδ T cells in combination with IL-23. We also observed a thickened epidermis layer and granulocyte penetration into the skin similar to the pathology of psoriasis in TG mice. In addition, strongly expressed SAA1 and penetration of γδ T cells in the skin of TG mice were detected. The exacerbation of psoriasis is associated with an increase in IL-17 levels. Therefore, these symptoms were induced by IL-17-producing γδ T cells increased by SAA1. Our study confirmed that SAA1 was a prominent protein that increased IL-17 levels through TLR2 in γδ T cells, confirming the possibility that SAA1 may exacerbate inflammatory diseases through γδ T cells.

Secondary, AA, Amyloidosis

Secondary, AA, amyloidosis is a rare systemic complication that can develop in any long-term inflammatory disorder, and is characterized by the extracellular deposition of fibrils derived from serum amyloid A (SAA) protein. SAA is an acute-phase reactant synthetized largely by hepatocytes under the transcriptional regulation of proinflammatory cytokines. The kidney is the major involved organ with proteinuria as first clinical manifestation; renal biopsy is the commonest diagnostic investigation. Targeted anti-inflammatory treatment promotes normalization of circulating SAA levels preventing amyloid deposition and renal damage. Novel therapies aimed at promoting clearance of existing amyloid deposits soon may be an effective treatment approach.

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.

Serum amyloid A primes microglia for ATP-dependent interleukin-1β release

BACKGROUND

Acute-phase response is a systemic reaction to environmental/inflammatory insults and involves production of acute-phase proteins, including serum amyloid A (SAA). Interleukin-1β (IL-1β), a master regulator of neuroinflammation produced by activated inflammatory cells of the myeloid lineage, in particular microglia, plays a key role in the pathogenesis of acute and chronic diseases of the peripheral nervous system and CNS. IL-1β release is promoted by ATP acting at the purinergic P2X₇ receptor (P2X₇R) in cells primed with toll-like receptor (TLR) ligands.

METHODS

Purified (> 99%) microglia cultured from neonatal rat cortex and cerebellum were first primed with the putative TLR4/TLR2 agonist SAA (recombinant human Apo-SAA) or the established TLR4 agonist lipopolysaccharide (LPS) followed by addition of ATP. Expression of genes for the NLRP3 inflammasome, IL-1β, tumor necrosis factor-α (TNF-α), and SAA1 was measured by quantitative real-time polymerase chain reaction (q-PCR). Intracellular and extracellular amounts of IL-1β were determined by ELISA.

RESULTS

Apo-SAA stimulated, in a time-dependent manner, the expression of NLRP3, IL-1β, and TNF-α in cortical microglia, and produced a concentration-dependent increase in the intracellular content of IL-1β in these cells. A 2-h 'priming' of the microglia with Apo-SAA followed by addition of ATP for 1 h, resulting in a robust release of IL-1β into the culture medium, with a concomitant reduction in its intracellular content. The selective P2X₇R antagonist A740003 blocked ATP-dependent release of IL-1β. Microglia prepared from rat cerebellum displayed similar behaviors. As with LPS, Apo-SAA upregulated SAA1 and TLR2 mRNA, and downregulated that of TLR4. LPS was less efficacious than Apo-SAA, perhaps reflecting an action of the latter at TLR4 and TLR2. The TLR4 antagonist CLI-095 fully blocked the action of LPS, but only partially that of Apo-SAA. Although the TLR2 antagonist CU-CPT22 was inactive against Apo-SAA, it also failed to block the TLR2 agonist Pam₃CSK₄.

CONCLUSIONS

Microglia are central to the inflammatory process and a major source of IL-1β when activated. P2X₇R-triggered IL-1β maturation and export is thus likely to represent an important contributor to this cytokine pool. Given that SAA is detected in Alzheimer disease and multiple sclerosis brain, together with IL-1β-immunopositive microglia, these findings propose a link between P2X₇R, SAA, and IL-1β in CNS pathophysiology.

Amantadine attenuates sepsis-induced cognitive dysfunction possibly not through inhibiting toll-like receptor 2

Amantadine has been shown to reduce anesthesia and surgery-induced neuroinflammation and cognitive dysfunction. It is known that sepsis can impair brain function. We determined whether amantadine-attenuated sepsis-induced neuroinflammation and dysfunction of learning and memory and whether toll-like receptors (TLRs) play a role in the effects. Six- to eight-week-old mice were subjected to cecal ligation and puncture (CLP). Amantadine at 30 mg/kg/day was injected intraperitoneally for 3 days. CU-CPT22, a TLR1/TLR2 inhibitor, at 3 mg/kg/day was injected intraperitoneally for 2 days. Mice were subjected to Barnes maze and fear conditioning tests from 1 week after CLP. CLP induced neuroinflammation and cognitive dysfunction. CLP also increased the expression of toll-like receptor 2 (TLR2), TLR4, and TLR9, three major TLRs in the brain, in CD-1 male mice. Amantadine attenuated CLP-induced neuroinflammation and dysfunction of learning and memory but did not have significant effects on the expression of TLRs. CU-CPT22 also attenuated sepsis-induced neuroinflammation and cognitive dysfunction. Similarly, sepsis induced neuroinflammation and cognitive dysfunction in the C57BL/6J mice. Interestingly, sepsis also induced neuroinflammation and cognitive dysfunction in the TLR2 knockout mice. The effects of amantadine on the neuroinflammation and cognitive dysfunction were still apparent in these knockout mice. TLR2 contributes to sepsis-induced neuroinflammation and cognitive dysfunction. However, inhibiting TLR2 may not be a major mechanism for amantadine to inhibit sepsis-induced neuroinflammation and cognitive dysfunction.

KEY MESSAGES

Sepsis induces neuroinflammation and cognitive impairment, which were attenuated by amantadine. Toll-like receptors 2 mediates these sepsis effects but may not be the major target for amantadine to reduce these effects.

Serum Amyloid A1 Is an Epithelial Prorestitutive Factor

Several proteins endogenously produced during the process of intestinal wound healing have demonstrated prorestitutive properties. The presence of serum amyloid A1 (SAA1), an acute-phase reactant, within inflamed tissues, where it exerts chemotaxis of phagocytes, is well recognized; however, a putative role in intestinal wound repair has not been described. Herein, we show that SAA1 induces intestinal epithelial cell migration, spreading, and attachment through a formyl peptide receptor 2-dependent mechanism. Induction of the prorestitutive phenotype is concentration and time dependent and is associated with epithelial reactive oxygen species production and alterations in p130 Crk-associated substrate staining. In addition, using a murine model of wound recovery, we provide evidence that SAA1 is dynamically and temporally regulated, and that the elaboration of SAA1 within the wound microenvironment correlates with the influx of SAA1/CD11b coexpressing immune cells and increases in cytokines known to induce SAA expression. Overall, the present work demonstrates an important role for SAA in epithelial wound recovery and provides evidence for a physiological role in the wound environment.

Serum SAA1 and APOE are novel indicators for human cytomegalovirus infection

Human cytomegalovirus (HCMV) infection is a global concern and highly infectious. HCMV-infected individuals are often carriers with damaged immunity. However few diagnostic indicators block HMCV control and prevention. Thus, we measured 21 serum proteins related to HCMV infection using iTRAQ-labeling based quantitative proteomic approaches and SAA1 and APOE were confirmed as candidate serum indicators for identification of HMCV infection according to ROC curve analysis and that co-occurrence of SAA1 and APOE are better markers than individual proteins.

Diabetes increases the susceptibility to acute kidney injury after myocardial infarction through augmented activation of renal Toll-like receptors in rats

Acute kidney injury (AKI) after acute myocardial infarction (MI) worsens the prognosis of MI patients. Although type 2 diabetes mellitus (DM) is a major risk factor of AKI after MI, the underlying mechanism remains unclear. Here, we examined the roles of renal Toll-like receptors (TLRs) in the impact of DM on AKI after MI. MI was induced by coronary artery ligation in Otsuka-Long-Evans-Tokushima fatty (OLETF) rats, a rat DM model, and Long-Evans-Tokushima-Otsuka (LETO) rats, nondiabetic controls. Sham-operated rats served as no-MI controls. Renal mRNA levels of TLR2 and myeloid differentiation factor 88 (MyD88) were significantly higher in sham-operated OLETF rats than in sham-operated LETO rats, although levels of TLR1, TLR3, and TLR4 were similar. At 12 h after MI, protein levels of kidney injury molecule-1 (KIM-1) and neutrophil gelatinase-associated lipocalin (NGAL) in the kidney were elevated by 5.3- and 4.0-fold, respectively, and their mRNA levels were increased in OLETF but not LETO rats. The increased KIM-1 and NGAL expression levels after MI in the OLETF kidney were associated with upregulated expression of TLR1, TLR2, TLR4, MyD88, IL-6, TNF-α, chemokine (C-C motif) ligand 2, and transforming growth factor-β₁ and also with activation of p38 MAPK, JNK, and NF-κB. Cu-CPT22, a TLR1/TLR2 antagonist, administered before MI significantly suppressed MI-induced upregulation of KIM-1, TLR2, TLR4, MyD88, and chemokine (C-C motif) ligand 2 levels and activation of NF-κB, whereas NGAL levels and IL-6 and TNF-α expression levels were unchanged. The results suggest that DM increases the susceptibility to AKI after acute MI by augmented activation of renal TLRs and that TLR1/TLR2-mediated signaling mediates KIM-1 upregulation after MI.NEW & NOTEWORTHY This is the first report to demonstrate the involvement of Toll-like recpetors (TLRs) in diabetes-induced susceptibility to acute kidney injury after acute myocardial infarction. We propose that the TLR1/TLR2 heterodimer may be a new therapeutic target for the prevention of acute kidney injury in diabetic patients.

Genomic variants link to hepatitis C racial disparities

Chronic liver diseases are one of the major public health issues in United States, and there are substantial racial disparities in liver cancer-related mortality. We previously identified racially distinct alterations in the expression of transcripts and proteins of hepatitis C (HCV)-induced hepatocellular carcinoma (HCC) between Caucasian (CA) and African American (AA) subgroups. Here, we performed a comparative genome-wide analysis of normal vs. HCV+ (cirrhotic state), and normal adjacent tissues (HCCN) vs. HCV+HCC (tumor state) of CA at the gene and alternative splicing levels using Affymetrix Human Transcriptome Array (HTA2.0). Many genes and splice variants were abnormally expressed in HCV+ more than in HCV+HCC state compared with normal tissues. Known biological pathways related to cell cycle regulations were altered in HCV+HCC, whereas acute phase reactants were deregulated in HCV+ state. We confirmed by quantitative RT-PCR that SAA1, PCNA-AS1, DAB2, and IFI30 are differentially deregulated, especially in AA compared with CA samples. Likewise, IHC staining analysis revealed altered expression patterns of SAA1 and HNF4α isoforms in HCV+ liver samples of AA compared with CA. These results demonstrate that several splice variants are primarily deregulated in normal vs. HCV+ stage, which is certainly in line with the recent observations showing that the pre-mRNA splicing machinery may be profoundly remodeled during disease progression, and may, therefore, play a major role in HCV racial disparity. The confirmation that certain genes are deregulated in AA compared to CA tissues also suggests that there is a biological basis for the observed racial disparities.

Western Diet-Induced Dysbiosis in Farnesoid X Receptor Knockout Mice Causes Persistent Hepatic Inflammation after Antibiotic Treatment

Patients who have liver cirrhosis and liver cancer also have reduced farnesoid X receptor (FXR). The current study analyzes the effect of diet through microbiota that affect hepatic inflammation in FXR knockout (KO) mice. Wild-type and FXR KO mice were on a control (CD) or Western diet (WD) for 10 months. In addition, both CD- and WD-fed FXR KO male mice, which had hepatic lymphocyte and neutrophil infiltration, were treated by vancomycin, polymyxin B, and Abx (ampicillin, neomycin, metronidazole, and vancomycin). Mice were subjected to morphological analysis as well as gut microbiota and bile acid profiling. Male WD-fed FXR KO mice had the most severe steatohepatitis. FXR KO also had reduced Firmicutes and increased Proteobacteria, which could be reversed by Abx. In addition, Abx eliminated hepatic neutrophils and lymphocytes in CD-fed, but not WD-fed, FXR KO mice. Proteobacteria and Bacteroidetes persisted in WD-fed FXR KO mice even after Abx treatment. Only polymyxin B could reduce hepatic lymphocytes in WD-fed FXR KO mice. The reduced hepatic inflammation by antibiotics was accompanied by decreased free and conjugated secondary bile acids as well as changes in gut microbiota. Our data revealed that Lactococcus, Lactobacillus, and Coprococcus protect the liver from inflammation.

Suppression of Lipopolysaccharide-Induced Inflammatory Response by Fragments from Serum Amyloid A

Serum amyloid A (SAA) is known as an acute-phase protein and a biomarker for inflammatory diseases. Published studies have shown that SAA possesses proinflammatory cytokine-like activity and is chemotactic for phagocytes, but the structural basis for these activities remains unidentified. In this article, we report that truncated SAA1 proteins lacking N- and C-terminal sequences exhibit reduced proinflammatory activity and strongly suppress LPS-induced expression of IL-1β, IL-6, and TNF-α in macrophages. A truncated SAA1 containing aa 11-58 was examined further and found to facilitate p38 MAPK phosphorylation while reducing LPS-stimulated phosphorylation of ERK and JNK. In LPS-challenged mice, aa 11-58 reduced the severity of acute lung injury, with significantly less neutrophil infiltration in the lungs and attenuated pulmonary expression of IL-1β, IL-6, and TNF-α. Coadministration of aa 11-58 markedly improved mouse survival in response to a lethal dose of LPS. A potent induction of IL-10 was observed in a TLR2-dependent, but TLR4-independent, manner in macrophages stimulated with aa 11-58. However, the aa 11-58 fragment of SAA1 was unable to induce chemotaxis or calcium flux through formyl peptide receptor 2. These results indicate that the N- and C-terminal sequences contain structural determinants for the proinflammatory and chemotactic activities of SAA1, and their removal switches SAA1 to an anti-inflammatory role. Given that proteolytic processing of SAA is associated with the pathological changes in several diseases, including secondary amyloidosis, our findings may shed light on the structure-function relationship of SAA1 with respect to its role in inflammation.

Resveratrol Pretreatment Attenuates Concanavalin A-induced Hepatitis through Reverse of Aberration in the Immune Response and Regenerative Capacity in Aged Mice

Loss of regenerative capacity plays a critical role in age-related autoimmune hepatitis. Evidence implicates SIRT1 and p66^shc in cell senescence, apoptosis, oxidative stress, and proliferation. This study investigated the effect of resveratrol on concanavalin A (Con A)-induced hepatitis in aged mice and the roles of SIRT1 and p66^shc. Aged mice were administrated resveratrol (30 mg/kg orally) seven times at an interval of 12 h before a single intravenous injection of Con A (20 mg/kg). Results showed that the cytokines, TNF-α, IL-6, IFN-γ, and MCP-1, as well as infiltration of macrophages, neutrophils, and T lymphocytes in liver were dramatically enhanced in the mice given only Con A. The aged mouse livers showed markedly raised oxidative stress and cell apoptosis. This oxidative stress further aggravated regenerative dysfunction as indicated by the decreased levels of Ki67, PCNA, Cyclin D1, and Cdk2. Conversely, these phenomena were attenuated by pretreatment with resveratrol. Moreover, resveratrol suppressed the elevation of p66^shc in the liver by reversing Con-A-mediated downregulation of SIRT1. The findings suggest that resveratrol protected against Con A-induced hepatitis in aged mice by attenuating an aberration of immune response and liver regeneration, partially via the mechanism of SIRT1-mediated repression of p66^shc expression.

Overexpression of serum amyloid a 1 induces depressive-like behavior in mice

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by loss of memory and cognitive abilities. In AD, amyloid β (Aβ) protein aggregates in the brain of patients, forming amyloid plaques. Aβ plaques are known to be surrounded by activated microglial cells. Serum amyloid A (SAA) is elevated from several hundred to 1000-fold as part of the immune response against various injuries, including trauma, infection, and inflammation. Additionally, continuous elevation of SAA is related to the development of amyloidosis. This study was designed to identify the relationship between SAA1 and AD using liver specific SAA1 overexpressing mice (TG), because SAA1 is expressed in the liver during the acute phase. We detected exogenous SAA1 expression in the brain of TG mice. This result implies that liver-derived SAA1 migrates to the brain tissues. Thus, we confirmed that the blood brain barrier (BBB) functioned normally using Evans-blue staining and CARS. Furthermore, our results show an increase in the accumulation of the 87kDa form of Aβ in TG mice compared to wild type mice (WT). Additionally, the number of microglial cells and levels of pro-inflammatory cytokines were increased. Next, we investigated the relationship between SAA1 and depression by performing social interaction tests. The results showed that TG mice have a tendency to avoid stranger mice and an impaired social recognition. In conclusion, the SAA1 TG mouse model is a valuable model to study depression.

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.

Serum amyloid A1: Structure, function and gene polymorphism

Inducible expression of serum amyloid A (SAA) is a hallmark of the acute-phase response, which is a conserved reaction of vertebrates to environmental challenges such as tissue injury, infection and surgery. Human SAA1 is encoded by one of the four SAA genes and is the best-characterized SAA protein. Initially known as a major precursor of amyloid A (AA), SAA1 has been found to play an important role in lipid metabolism and contributes to bacterial clearance, the regulation of inflammation and tumor pathogenesis. SAA1 has five polymorphic coding alleles (SAA1.1-SAA1.5) that encode distinct proteins with minor amino acid substitutions. Single nucleotide polymorphism (SNP) has been identified in both the coding and non-coding regions of human SAA1. Despite high levels of sequence homology among these variants, SAA1 polymorphisms have been reported as risk factors of cardiovascular diseases and several types of cancer. A recently solved crystal structure of SAA1.1 reveals a hexameric bundle with each of the SAA1 subunits assuming a 4-helix structure stabilized by the C-terminal tail. Analysis of the native SAA1.1 structure has led to the identification of a competing site for high-density lipoprotein (HDL) and heparin, thus providing the structural basis for a role of heparin and heparan sulfate in the conversion of SAA1 to AA. In this brief review, we compares human SAA1 with other forms of human and mouse SAAs, and discuss how structural and genetic studies of SAA1 have advanced our understanding of the physiological functions of the SAA proteins.

Combination of double negative T cells and anti-thymocyte serum reverses type 1 diabetes in NOD mice

Background

Double-negative (DN) T cells could delay the onset and the progression of autoimmune diabetes, yet they were less efficient on reversing autoimmune diabetes. The aim of this study was to investigate whether the combination of DN T cells and anti-thymocyte serum (ATS) could reverse new-onset diabetes in NOD mice.

Methods

The regulation of different subsets of T cells in vitro and in vivo by ATS and DN T cells were examined using flow cytometry. At the day of diabetes onset, ATS was administered on the same day and 2 days later, and DN T cells were transferred at day 7. The reversion of diabetes was assessed by monitoring blood glucose levels.

Results

The efficacy of inhibition of DN T cells on CD8⁺ T cells was lower than that on CD4⁺ T cells both in vitro and in vivo. ATS resulted in a significant depletion of CD8⁺ T cells, while DN T cells were less sensitive to ATS depletion. 80 % diabetic NOD mice achieved long term (6 months) reversion of diabetes by combined ATS and DN T cells treatment, compared to 16 % in ATS single treatment and none in DN T cell single treatment. DN T cells preferentially resided in spleen and pancreatic draining lymph nodes in ATS plus DN T cells treated NOD mice.

Conclusions

DN T cells plus ATS therapy show promising reversion effects on diabetic NOD mice due to a shift of balance from a destructive T cell response to one that favors DN T cell regulation.