Inappropriate activation of the Toll-IL-1R (TL-IL-1) signaling by commensal bacteria contributes to the pathogenesis of inflammatory bowel diseases and colitis-associated cancer. Recent studies have identified SIGIRR as a negative regulator of TL-IL-1 signaling. It dampens intestinal inflammation and tumorigenesis in the colon. In this review, we will discuss the role of SIGIRR in different cell types and the mechanisms underlying its tumor suppressor function.
Interleukin 17 (IL-17) promotes expression of chemokines and cytokines via induction of gene transcription and post-transcriptional stabilization of mRNA. We show that IL-17 enhanced the stability of CXCL1 and other mRNAs through a pathway that involves Act1, TRAF2 or TRAF5 and the splicing factor SF2/ASF. TRAF2/TRAF5 were necessary for IL-17 to signal CXCL1 mRNA stabilization. Furthermore, IL-17 promoted formation of complexes between TRAF5/TRAF2, Act1 and SF2/ASF. Overexpression of SF2/ASF shortened while depletion of SF2/ASF prolonged CXCL1 mRNA half-life. SF2/ASF bound chemokine mRNA in unstimulated cells while the SF2/ASF-mRNA interaction was markedly diminished following stimulation with IL-17. These findings define an IL-17-induced signaling pathway that links to the stabilization of selected mRNAs through Act1, TRAF2/5 and the RNA binding protein SF2/ASF.
Intestinal microflora and inflammatory cell infiltrates play critical roles in the pathogenesis of acute colitis. Ceruloplasmin is an acute-phase plasma protein produced by hepatocytes and activated macrophages, and has ferroxidase with bactericidal activities. The goal is to understand the role of ceruloplasmin in colitis progression in a genetically modified murine model.
Experimental colitis was induced in ceruloplasmin null (Cp−/−) and wild-type (WT) mice by dextran sulphate sodium administration. The role of ceruloplasmin was further evaluated by transplantation of WT macrophages into Cp−/− mice.
Cp−/− mice rapidly lost weight and were moribund by day 14, while WT mice survived at least 30 days. Colon culture supernatants from Cp−/− mice exhibited elevated levels of TNFα, KC and MCP-1, indicative of increased inflammation and neutrophil and macrophage infiltration. Elevated leucocytes and severe histopathology were observed in Cp−/− mice. Elevated protein carbonyl content was detected in colons from Cp−/− mice suggesting ceruloplasmin antioxidant activity might contribute to its protective function. Unexpectedly, intraperitoneal administration of human ceruloplasmin into Cp−/− mice did not afford protection. Bone marrow transplantation from WT mice or injection of isolated peripheral blood monocytes markedly reduced severity of colitis and morbidity in Cp−/− mice.
Macrophage-derived ceruloplasmin contributes importantly to protection against inflammation and tissue injury in acute and chronic experimental colitis. The findings suggest that defects in ceruloplasmin expression or processing may influence the onset or progression of inflammatory bowel disease in patients.
Background and Aims
Dendroclimatology is playing an important role in understanding past climatic changes on the Tibetan Plateau. Forests, however, are mainly confined to the eastern Tibetan Plateau. On the central Tibetan Plateau, in contrast, shrubs and dwarf shrubs need to be studied instead of trees as a source of climate information. The objectives of this study were to check the dendrochronological potential of the dwarf shrub Wilson juniper (Juniperus pingii var. wilsonii) growing from 4740 to 4780 m a.s.l. and to identify the climatic factors controlling its radial growth.
Forty-three discs from 33 stems of Wilson juniper were sampled near the north-eastern shore of the Nam Co (Heavenly Lake). Cross-dating was performed along two directions of each stem, avoiding the compression-wood side as far as possible. A ring-width chronology was developed after a negative exponential function or a straight line of any slope had been fit to the raw measurements. Then, correlations were calculated between the standard ring-width chronology and monthly climate data recorded by a weather station around 100 km away.
Our study has shown high dendrochronological potential of Wilson juniper, based on its longevity (one individual was 324 years old), well-defined growth rings, reliable cross-dating between individuals and distinct climatic signals reflected by the ring-width variability. Unlike dwarf shrubs in the circum-arctic tundra ecosystem which positively responded to above-average temperature in the growing season, moisture turned out to be growth limiting for Wilson juniper, particularly the loss of moisture caused by high maximum temperatures in May–June.
Because of the wide distribution of shrub and dwarf shrub species on the central Tibetan Plateau, an exciting prospect was opened up to extend the presently existing tree-ring networks far up into one of the largest tundra regions of the world.
Central Tibetan Plateau; high altitude; Juniperus pingii var. wilsonii; dwarf shrub; cross-dating; dendrochronology; dendroclimatology; growth ring; tree ring; growth-limiting factor; climate proxy
Pathogens may signal through multiple TLRs with synergistic or antagonistic effects on the induction of cytokines, including type I IFN (IFN-I). IFN-I is typically induced by TLR9 but not TLR2. Moreover, we previously reported that TLR2 signaling by Mycobacterium tuberculosis or other TLR2 agonists inhibited TLR9 induction of IFN-I and IFN-I-dependent MHC-I Ag cross processing. The current studies revealed that lipopeptide-induced TLR2 signaling inhibited induction of first-wave IFN-α and IFN-β mRNA by TLR9, whereas induction of second wave IFN-I mRNA was not inhibited. TLR2 also inhibited induction of IFN-I by TLR7, another MyD88-dependent IFN-I-inducing receptor, but did not inhibit IFN-I induction by TLR3 or TLR4 (both TRIF-dependent, MyD88-independent). The inhibitory effect of TLR2 was not dependent on new protein synthesis or intercellular signaling. IRAK1 was depleted rapidly (within 10 min) by TLR2 agonist but not until later (e.g. 2 h) by TLR9 agonist. Since IRAK1 is required for TLR7/9 induced IFN-I production, we propose that TLR2 signaling induces rapid depletion of IRAK1, which impairs IFN-I induction by TLR7/9. This novel mechanism, whereby TLR2 inhibits IFN-I induction by TLR7/9, may shape immune responses to microbes that express ligands for both TLR2 and TLR7/TLR9, or responses to bacteria/virus co-infection.
Dendritic cell; type-I interferon; Toll-like receptor; IRAK1
Lipoprotein lipase (LPL) and serum 25-hydroxyvitamin D [25(OH)D] play important roles in the regulation of lipid metabolism. Although dyslipidemia is associated with insulin resistance (IR) and type 2 diabetes (T2D), there are limited data available regarding the relationship of LPL and 25(OH)D to IR and T2D at a population level. The objective of the present study is to investigate the associations of LPL and 25(OH)D with IR and T2D in a Chinese population.
The study cohort consisted of 2708 subjects (1326 males, 1382 females; mean age 48.5 ± 12.6 years) in main communities of Harbin, China. Serum 25(OH)D, LPL, free fatty acids (FFAs), fasting glucose (FG), fasting insulin, lipid profile, apoA and apoB concentrations were measured.
Serum 25(OH)D concentration was positively associated with LPL (β = 0.168, P < 0.001). LPL was inversely associated with IR and T2D. Subjects in the lowest quartile of LPL had the highest risk of IR [odds ratio (OR) = 1.85, 95% CI = 1.22-2.68] and T2D (OR = 1.65, 95% CI = 1.14-2.38). Serum 25(OH)D was also inversely associated with IR and T2D. Vitamin D deficiency [25(OH)D < 20 ng/ml] was associated with an increasing risk of IR (OR = 1.91, 95% CI = 1.23-2.76) and T2D (OR = 2.06, 95% CI = 1.37-3.24). The associations of 25(OH)D with IR and T2D were attenuated by further adjustment for LPL.
LPL is associated with serum 25(OH)D, IR and T2D in the Chinese population. These results suggest a potential mediating role of LPL in the associations of 25(OH)D with IR and T2D.
Lipoprotein lipase; Vitamin D; Diabetes; Insulin resistance; Lipid metabolism
The pathophysiology of interstitial cystitis (IC) is unknown. Deficits in urothelial cell layers and autoimmune mechanisms may play a role.
To examine whether immunization of mice with recombinant mouse uroplakin II (rmUPK2), a bladder-specific protein, would provoke an autoimmune response sufficient to create an IC phenotype.
Design, setting, and participants
RmUPK2 complementary DNA was generated, transferred into a bacterial expression vector, and the generated protein was purified. Eight-week-old SWXJ female mice were immunized with rmUPK2 protein via subcutaneous injection of 200 µg of rmUPK2 protein in 200 µl of an emulsion.
Mice were euthanized 5 wk after immunization. Axillary and inguinal lymph node cells were tested for antigen-specific responsiveness and cytokine production, serum isotype antibody titers against rmUPK2 were determined, and gene expression of inflammatory mediators was measured in the bladder and other organs. For functional analysis, mice were placed in urodynamic chambers for 24-h micturition frequency and total voided urine measurements.
Results and limitations
Immunization with rmUPK2 resulted in T-cell infiltration of the bladder urothelium and increased rmUPK2-specific serum antibody responses in the experimental autoimmune cystitis (EAC) mice models compared with controls. The ratio of bladder to body weight was increased in EAC mice. Quantitative reverse transcriptase polymerase chain reaction analysis showed elevated gene expression of tumor necrosis factor α, interferon γ, interleukin (IL)-17A, and IL-1β in bladder urothelium but not in other organs. Evaluation of 24-h micturition habits of EAC mice showed significantly increased urinary frequency (p < 0.02) and significantly decreased urine output per void (p < 0.021) when compared with control mice.
Our study showed that a bladder-specific autoimmune response sufficient to induce inflammation and EAC occurs in mice following immunization with rmUPK2. EAC mice displayed significant evidence of urinary frequency and decreased urine output per void. Further phenotype characterization of EAC mice should include evidence for pain and/or afferent hypersensitivity, and evidence of urothelial cell layer damage.
Autoimmune; Animal model; Bladder; Cystitis; T cell
Cuprizone inhibits mitochondrial function and induces demyelination in the corpus callosum which resembles pattern III lesions in multiple sclerosis (MS) patients. However, the molecular and cellular mechanism by which cuprizone induces demyelination remains unclear. Interleukin-17 (IL-17) secreted by T helper 17 (Th17) cells and γδT cells are essential in the development of experimental autoimmune encephalomyelitis (EAE). In this study, we examined the importance of IL-17 signaling in cuprizone-induced demyelination. We found that mice deficient in IL-17A, IL-17RC and adaptor protein Act1 (of IL-17R) all had reduced demyelination accompanied by lessened microglial and polydendrocyte cellular reactivity compared to that in wild-type mice in response to cuprizone feeding, demonstrating the essential role of IL-17-induced Act1-mediated signaling in cuprizone-induced demyelination. Importantly, specific deletion of Act1 in astrocytes reduced the severity of tissue injury in this model, indicating the critical role of CNS resident cells in the pathogenesis of cuprizone-induced demyelination. In cuprizone-fed mice IL-17 was produced by CNS CD3+ T cells suggesting a source of IL-17 in CNS upon cuprizone treatment.
Here, we report a novel porcine circovirus type 2a (PCV2a) strain with 11 nucleotides (nt) inserted in the origin of genome replication (Ori). This is the first report of a PCV2a strain with nucleotide insertion in Ori. Our study will help further epidemiological studies and extend our knowledge of evolutionary characteristics of PCV2.
Interleukin-17 (IL-17) and IL-25 signaling induce the expression of genes that encode inflammatory factors and they are implicated in the pathology of various inflammatory diseases. Nuclear factor κB (NF-κB) activator 1 (Act1) is an adaptor protein and E3 ubiquitin ligase that is critical for IL-17 and IL-25 signaling, and it is recruited to their receptors through heterotypic interactions between their SEFIR [SEF (similar expression to fibroblast growth factor genes)/IL-17R] domains. Modeling of SEFIR domains has shown their structural similarity with the Toll-IL-1 receptor (TIR) domains of Toll-like receptors (TLRs) and the IL-1R. Whereas the BB′ loop of TIR is required for TIR-TIR interactions, we found that deletion of the BB′ loop from Act1 or IL-17RA (a common subunit of IL-17R and IL-25R) did not affect Act1–IL-17RA interactions. Instead, deletion of the CC′ loop from Act1 or IL-17RA abolished the interaction between Act1 and IL-17RA, suggesting that SEFIR and TIR domains interact in different manners. Surface plasmon resonance measurements showed that a peptide corresponding to the CC′ loop bound directly to IL-17RA. A cell-permeable decoy peptide based on the CC′ loop sequence inhibited IL-17- and IL-25-mediated signaling, and it inhibited IL-17- and IL-25-induced responses in vitro and pulmonary inflammation in vivo. Together, these findings provide the molecular basis for the specificity of SEFIR versus TIR domain interactions and consequent signaling. Moreover, we suggest that the CC′ loop motif of SEFIR domains is a promising target for therapeutic strategies against IL-17- and IL-25-asssociated inflammatory diseases.
The human immunodeficiency virus (HIV) is spreading from high-risk groups, such as men who have sex with men (MSM) and sex workers, to the general population in China. This study examined the willingness of general residents in Heilongjiang, Northeast China, to participate in free HIV testing in the nearest health care setting, and the factors that may affect participation, including demographic characteristics, HIV-related knowledge, and stigma.
A cross-sectional study was conducted in Heilongjiang Province. All residents aged 15–69 years in two communities in urban areas (September 2007) and four villages in rural areas (April 2008) were recruited using stratified cluster sampling. A total of 4050 residents were interviewed using an anonymous questionnaire. Univariate and multivariate log-binomial regression were used to analyze factors affecting willingness to undergo HIV testing.
The proportions of participants who were willing to participate in free HIV testing was 73.0% in urban residents and 78.8% in rural residents. Multivariate regression analysis among urban participants showed that greater knowledge of HIV transmission misconceptions (relative risk (RR) = 1.02, 95% confidence interval (CI): 1.00–1.04, P = 0.021) and the awareness that an apparently healthy person can be an HIV carrier (RR = 1.12, 95%CI: 1.03–1.21, P = 0.007) was significantly associated with greater willingness to participate in free HIV testing. Among rural participants, greater knowledge of HIV transmission modes (RR = 1.03, 95%CI: 1.01–1.06 P = 0.001) and the awareness that an apparently healthy person can be an HIV carrier (RR = 1.07; 95%CI: 1.01–1.13 P = 0.019) was significantly associated with greater willingness to participate.
The overall level of willingness to accept free HIV testing is high, and is higher in rural residents than in urban residents in Heilongjiang. knowledge of HIV transmission misconceptions and that an apparently healthy person can be a carrier for HIV were associated with willingness to accept free HIV testing among urban residents, while knowledge of HIV transmission modes and that an apparently healthy person can be a carrier for HIV were associated with willingness to accept free HIV testing among rural residents.
HIV; Knowledge; Public stigma; Willingness; General individuals
Deep sequencing of the 16S rRNA gene provides a comprehensive view of bacterial communities in a particular environment and has expanded our ability to study the impact of the microflora on human health and disease. Current analysis methods rely on comparisons of the sequences generated with an expanding but limited set of annotated 16S rRNA sequences or phylogenic clustering of sequences based on arbitrary similarity cutoffs. We describe a novel approach to characterize bacterial composition using deep sequencing of 16S rRNA gene. Our method defines operational taxonomic units based on phylogenetic tree reconstruction and dynamic clustering of sequences using solely sequencing data. These OTUs can be used to identify differences in bacteria abundance between environments. This approach can perform better than previous phylogenetic methods and will significantly improve our understanding of the microfloral role on human diseases by providing a comprehensive analysis of the microbial composition from various bacterial communities.
microflora; massively parallel sequencing; 16s ribosomal RNA
Interleukin 17 (IL-17) plays a critical role in the pathogenesis of inflammatory and autoimmune diseases. Here we report that Act1, the key adaptor for IL-17R, forms a complex with IKKi upon IL-17 stimulation. Using IKKi-deficient mice, we show that IKKi was required for IL-17-induced inflammatory gene expression in primary airway epithelial cells, neutrophilia and pulmonary inflammation. IKKi deficiency abolished IL-17-induced Act1-TRAF2/5 complex formation, MAPK activation and mRNA stability, whereas the Act1-TRAF6-NFκB axis was retained. IKKi was required for IL-17-induced Act1 phosphorylation on serine 311, adjacent to a putative TRAF binding motif. S311A mutation impaired IL-17-mediated Act1-TRAF2/5 interaction and gene expression. Thus, IKKi is a novel kinase modulating IL-17 signaling through its impact on Act1 phosphorylation and consequent function.
Interleukin-1 receptor–associated kinase 2 (IRAK2) has been shown to be essential for lipopolysaccharide (LPS)-mediated posttranscriptional control of cytokine and chemokine production. In this study, we investigated the role of IRAK2 kinase activity in LPS-mediated posttranscriptional control by reconstituting IRAK2-deficient macrophages with either wild-type or kinase-inactive IRAK2. Compared with wild-type IRAK2 (IRAK2-WT) macrophages, kinase-inactive IRAK2 (IRAK2-KD) macrophages show reduced cytokine and chemokine mRNA stability and translation in response to LPS. Further, LPS-treated IRAK2-KD macrophages also show reduced activation of MKK3/6, MNK1, and eIF4E and attenuated toll-like receptor 4-induced tristetraprolin modification and stabilization. Taken together, these results suggest that the kinase activity of IRAK2 is required for the optimal activation of mitogen-activated protein kinase signaling, which regulates cytokine and chemokine production at posttranscriptional levels.
Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of the central nervous system (CNS). Experimental autoimmune encephalomyelitis (EAE) is widely used to dissect molecular mechanisms of MS and to develop new therapeutic strategies. The T helper 17 subset of CD4 T cells play a crucial role in the development of EAE. IL-17, a cytokine produced by Th17 cells, participates in EAE pathogenesis through induction inflammatory gene expression in target cells. Recent work has shown that Act1, a U-box E3 ubiquitin ligase, is recruited to IL-17 receptor (IL-17R) upon IL-17 stimulation and is required for IL-17-mediated signaling. Here, we review the molecular and cellular mechanisms by which IL-17 and Act1-mediated signaling contribute to EAE.
Toll-like receptors (TLRs) shape innate and adaptive immunity to microorganisms. The enzyme IRAK1 transduces signals from TLRs, but its activation and regulation mechanisms remain unknown. We show that TLR7 and TLR9 activated the isomerase Pin1, which then bound to IRAK1, resulting in IRAK1 activation and facilitating its release from the receptor complex to activate the transcription factor IRF7 and induce type I interferons. Consequently, Pin1-null cells and mice failed to mount TLR-mediated, interferon-dependent innate and adaptive immune responses. Given the critical role of aberrant IRAK1 activation and type I interferons in various immune diseases, controlling IRAK1 activation via Pin1 inhibition may represent a useful therapeutic approach.
Bone marrow-derived plasmacytoid dendritic cells (pDCs) from IRAK2-deficient mice produced more interferons than did wild-type pDCs upon stimulation with the TLR9 ligand CpG. Furthermore, in CpG-stimulated IRAK2-deficient pDCs there was increased nuclear translocation of interferon regulatory factor 7 (IRF7), the key transcription factor for interferon gene transcription in these cells. In IRAK2-deficient macrophages, enhanced NFκB activation and increased expression of CpG-induced genes were detected within 2 hours after treatment. However, at later times, NFκB activation was decreased and, in contrast to the results with interferon, there was less secretion of other pro-inflammatory cytokines (such as TNFα) and chemokines in CpG-stimulated IRAK2-deficient pDCs and macrophages. Therefore, although IRAK2 is a negative regulator of TLR9-mediated interferon production through its modulation of the transcriptional activity of IRF7, it is also a positive regulator of TLR9-mediated pro-inflammatory cytokine and chemokine production at some level subsequent to transcription.
Erythropoietin is known as the requisite cytokine for red blood cell production. Its receptor, expressed at a high level on erythroid progenitor/precursor cells, is also found on endothelial, neural, and other cell types. Erythropoietin and erythropoietin receptor expression in the developing and adult brain suggest their possible involvement in neurodevelopment and neuroprotection. During ischemic stress, erythropoietin, which is hypoxia inducible, can contribute to brain homeostasis by increasing red blood cell production to increase the blood oxygen carrying capacity, stimulate nitric oxide production to modulate blood flow and contribute to the neurovascular response, or act directly on neural cells to provide neuroprotection as demonstrated in culture and animal models. Clinical studies of erythropoietin treatment in stroke and other diseases provide insight on safety and potential adverse effects and underscore the potential pleiotropic activity of erythropoietin. Herein, we summarize the roles of EPO and its receptor in the developing and adult brain during health and disease, providing first a brief overview of the well-established EPO biology and signaling, its hypoxic regulation, and role in erythropoiesis.
Background & Aims
Commensal bacteria can activate signaling by the toll-like and interleukin-1 receptors (TLR and IL-1R) to mediate pathogenesis of inflammatory bowel diseases and colitis-associated cancer. We investigated the role of the single immunoglobulin IL-1 receptor-related (SIGIRR) molecule, a negative regulator of TLR and IL-1R signaling, as a tumor suppressor to determine whether SIGIRR controls cell cycle progression, genetic instability, and colon tumor initiation by modulating commensal TLR signaling in the gastrointestinal tract.
We analyzed Apcmin/+/Sigirr-/- mice for polyps, microadenomas, and anaphase bridge index. Commensal bacteria were depleted from mice with antibiotics. Akt, mTOR and β-catenin pathways were examined by immunoblotting and immunohistochemistry. Loss of heterozygosity (LOH) of Apc and expression of cytokines and proinflammatory mediators were measured by non-quantitative or quantitative PCR.
Apcmin/+/Sigirr-/- mice had increased LOH of Apc and microadenoma formation, resulting in spontaneous colonic polyposis, compared with Apc min/+/Sigirr+/+ mice. The increased colonic tumorigenesis that occurred in the Apcmin/+/Sigirr-/- mice depended on the presence of commensal bacteria in the gastrointestinal tract. Cell proliferation and chromosomal instability increased in colon crypt cells of the Apcmin/+/Sigirr-/- mice. Akt, mTOR and their substrates were hyper-activated in colon epithelium of Apcmin/+/Sigirr-/- mice in response to TLR or IL-1R ligands. Inhibition of the mTOR pathway by rapamycin reduced formation of microadenomas and polyps in the Apcmin/+/Sigirr-/- mice.
SIGIRR acts as a tumor suppressor in the colon by inhibiting TLR-induced, mTOR-mediated cell cycle progression and genetic instability.
TIR8; Cyclin D1; c-Myc; Stat3
This study was conducted to characterize the intracranial pressure response to non-penetrating ballistic impact using a "scalp-skull-brain" pig physical head model and live pigs. Forty-eight ballistic tests targeting the physical head model and anesthetized pigs protected by aramid plates were conducted with standard 9 mm bullets at low (279-297 m/s), moderate (350-372 m/s), and high (409-436 m/s) velocities. Intracranial pressure responses were recorded with pressure sensors embedded in similar brain locations in the physical head model and the anesthetized pigs. Three parameters of intracranial pressure were determined from the measured data: intracranial maximum pressure (Pmax), intracranial maximum pressure impulse (PImax), and the duration of the first positive phase (PPD). The intracranial pressure waves exhibited blast-like characteristics for both the physical model and l live pigs. Of all three parameters, Pmax is most sensitive to impact velocity, with means of 126 kPa (219 kPa), 178 kPa (474 kPa), and 241 kPa (751 kPa) for the physical model (live pigs) for low, moderate, and high impact velocities, respectively. The mean PPD becomes increasingly short as the impact velocity increases, whereas PImax shows the opposite trend. Although the pressure parameters of the physical model were much lower than those of the live pigs, good correlations between the physical model and the live pigs for the three pressure parameters, especially Pmax, were found using linear regression. This investigation suggests that Pmax is a preferred parameter for predicting the severity of the brain injury resulting from behind armor blunt trauma (BABT).
Intracranial pressure response; Non-penetrating ballistic impact; Pig physical head model; Live pigs
CD40L and BAFF, members of TNF superfamily, play critical roles in B cell survival and activation, and in the regulation of humoral immunity. We previously reported that the adaptor molecule Act1 functions as a negative regulator of CD40- and BAFF-mediated B cell survival. Here we demonstrated that mice deficient in Act1 developed systemic autoimmune disease with histological and serological features of human Sjogren’s syndrome, in association with SLE-like nephritis. Analyses of Act1−/−CD40−/− and Act1−/−BAFF−/− mice revealed that Act1 regulates different stages of the disease development through its impact on both CD40-and BAFF-mediated pathways. We found that Act1 modulates the survival of auto-reactive B cells mainly through its negative regulatory role in BAFF-mediated cell survival, while the effect of Act1 on autoantibody production is probably through its modulation on CD40-mediated T-cell dependent antibody response. The impact of Act1 on both BAFF and CD40 pathways establishes Act1−/− mice as a unique model to study distinct steps of autoimmunity and regulation of self-tolerance.
B cells; Autoimmunity; Systemic Lupus Erythematosus; Rheumatoid Arthritis; Autoantibodies
The transitional stage is a key check-point for elimination of autoreactive B cells in the periphery. This selection process requires fine regulation of signals received through B-cell receptor (BCR) and B cell activating factor receptor (BAFFR). We previously identified the adaptor molecule Act1 as a negative regulator of BAFF-mediated signaling. Deficiency of Act1 in mice results in peripheral B cell hyperplasia and development of autoimmunity. In this study we demonstrate that Act1 plays a critical role in the regulation of transitional B cell survival and maturation. We found that the ratio of late-transitional (T2) to early-transitional (T1) cells was increased in spleens from Act1-deficient mice. Moreover, BAFF stimulation induced better T1 cell survival and promoted more efficient maturation of T1 cells into T2 cells ex vivo in the absence of Act1. BAFF stimulation induced higher levels of the anti-apoptotic Bcl2-member Mc1-l in Act1-deficient T1 than that in wild-type control cells, suggesting that Mcl1 might be one of the key effector molecules for BAFF-mediated survival in the Act1-deficient transitional B cells. Importantly, co-stimulation with BAFF was able to rescue Act1-deficient T1 cells from BCR-induced apoptosis more effectively than Act1-suffienct T1 B cells. Finally, by using double transgenic HEL mice, we demonstrated that Act1 deficiency can promote the maturation of HEL-specific autoreactive B cells. Taken together, our results suggest that the transitional stage is a critical point of action for Act1 in the elimination of autoreactive B cells and in the regulation of peripheral B cell homeostasis.
Interleukin (IL)-17, a proinflammatory cytokine mainly produced by T-helper-17 (TH17) lineage, is required for host defense against bacteria and fungus infection and plays a critical role in the pathogenesis of inflammatory and autoimmune diseases. Act1 is an essential adaptor molecule in IL-17-mediated signaling pathway, recruited to IL-17 receptor (IL-17R) upon IL-17 stimulation through SEFIR-SEFIR domain interaction. Here we report that Act1 is a novel bona fide U-box E3 ubiquitin ligase, whose activity is essential for IL-17-mediated signaling pathways (including nuclear factor kappa B (NFκB), and partially required for Jun N-terminal Kinase (JNK) and extracellular signal-regulated kinase (ERK) activation) and inflammatory gene expression (KC (CXCL1), granulocyte macrophage colony stimulating factor (GM-CFS ) and IL-6) in mammalian cells. By utilizing Ubc13/Uev1A E2 complex, Act1 mediates Lys 63-linked ubiquitination of tumor necrosis factor receptor-associated factor 6 (TRAF6), an important signaling component of IL-17-mediated signaling pathway. Deletion and point mutations of the Act1 U-box abolish Act1-mediated ubiquitination of TRAF6 and impair the ability of Act1 to restore IL-17-dependent signaling and inflammatory gene expression in Act1−/− mouse embryonic fibroblasts (MEFs). Importantly, we demonstrate that the Lys 124 residue of TRAF6 is critical for efficient Act1-mediated TRAF6 ubiquitination and for the ability of TRAF6 to mediate IL-17-induced NFκB activation. Thus Act1 mediates IL-17-induced signaling pathways through its E3 ubiquitin ligase activity and TRAF6 is a critical substrate of Act1, indicating the importance of protein ubiquitination in IL-17-dependent inflammatory response.
Prostaglandin E2 (PGE2) has been reported to modulate angiogenesis, the process of new blood vessel formation, by promoting proliferation, migration and tube formation of endothelial cells. Endothelial progenitor cells are known as a subset of circulating bone marrow mononuclear cells that have the capacity to differentiate into endothelial cells. However, the mechanism underlying the stimulatory effects of PGE2 and its specific receptors on bone marrow-derived cells (BMCs) in angiogenesis has not been fully characterized. Treatment with PGE2 significantly increased the differentiation and migration of BMCs. Also, the markers of differentiation to endothelial cells, CD31 and von Willebrand factor, and the genes associated with migration, matrix metalloproteinases 2 and 9, were significantly upregulated. This upregulation was abolished by dominant-negative AMP-activated protein kinase (AMPK) and AMPK inhibitor but not protein kinase, a inhibitor. As a functional consequence of differentiation and migration, the tube formation of BMCs was reinforced. Along with altered BMCs functions, phosphorylation and activation of AMPK and endothelial nitric oxide synthase, the target of activated AMPK, were both increased which could be blocked by EP4 blocking peptide and simulated by the agonist of EP4 but not EP1, EP2 or EP3. The pro-angiogenic role of PGE2 could be repressed by EP4 blocking peptide and retarded in EP4+/− mice. Therefore, by promoting the differentiation and migration of BMCs, PGE2 reinforced their neovascularization by binding to the receptor of EP4 in an AMPK-dependent manner. PGE2 may have clinical value in ischemic heart disease.
By binding to the interleukin 17 receptor (IL-17R), TRAF3 blocks formation of the IL-17R–Act1–TRAF6 complex and inhibits downstream signaling.
Interleukin 17 (IL-17) plays critical roles in the pathogenesis of various autoimmune diseases, including experimental autoimmune encephalomyelitis (EAE). How the signals triggered by this powerful inflammatory cytokine are controlled to avoid abnormal inflammatory responses is not well understood. In this study, we report that TRAF3 is a receptor proximal negative regulator of IL-17 receptor (IL-17R) signaling. TRAF3 greatly suppressed IL-17–induced NF-κB and mitogen-activated protein kinase activation and subsequent production of inflammatory cytokines and chemokines. Mechanistically, the binding of TRAF3 to IL-17R interfered with the formation of the receptor signaling activation complex IL-17R–Act1–TRAF6, resulting in suppression of downstream signaling. TRAF3 markedly inhibited IL-17–induced expression of inflammatory cytokine and chemokine genes in vivo and consequently delayed the onset and greatly reduced the incidence and severity of EAE. Thus, TRAF3 is a negative regulator of IL-17R proximal signaling.