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Objective: Disruption of B cell homeostasis and subsequent dominance of effector B cell subsets are critical for the development of systemic lupus erythematosus (SLE). Revealing the key intrinsic regulators involved in the homeostatic control of B cells has important therapeutic value for SLE. This study was undertaken to determine the regulatory role of the transcription factor Pbx1 in B cell homeostasis and lupus pathogenesis. Methods: We constructed mice with B cell–specific deletion of Pbx1. T cell–dependent and T cell–independent humoral responses were induced by intraperitoneal injection of nitrophenyl‐containing hapten (NP) conjugated to keyhole limpet hemocyanin or NP‐Ficoll. The regulatory effects of Pbx1 on autoimmunity were observed in a Bm12‐induced lupus murine model. We investigated mechanisms of Pbx1 using RNA sequencing, the cleavage under targets and tagmentation assay, and chromatin immunoprecipitation–quantitative polymerase chain reaction assay. We transduced B cells from SLE patients with plasmids that overexpressed PBX1 to explore the in vitro therapeutic efficacy of PBX1. Results: Pbx1 was specifically down‐regulated in autoimmune B cells and negatively correlated with disease activity. The deficiency of Pbx1 in B cells resulted in excessive humoral responses following immunization. In the Bm12‐induced lupus model, mice with B cell–specific Pbx1 deficiency displayed enhancements in germinal center responses, plasma cell differentiation, and autoantibody production. Pbx1‐deficient B cells had increased survival and proliferative advantages after activation. Pbx1 regulated genetic programs by directly targeting critical components of the proliferation and apoptosis pathways. In SLE patients, PBX1 expression was negatively correlated with effector B cell expansion; when PBX1 expression was enforced, the survival and proliferative capacity of SLE B cells were attenuated. Conclusion: Our study reveals the regulatory function and mechanism of Pbx1 in adjusting B cell homeostasis and highlights Pbx1 as a therapeutic target in SLE. [ABSTRACT FROM AUTHOR]

Objective: Emerging evidence indicates that a distinct CD11c+T‐bet+ B cell subset, termed age/autoimmune‐associated B cells (ABCs), is the major pathogenic autoantibody producer in lupus. Human lupus is associated with significant metabolic alterations, but how ABCs orchestrate their typical transcription factors and metabolic programs to meet specific functional requirements is unclear. We undertook this study to characterize the metabolism of ABCs and to identify the regulators of their metabolic pathways in an effort to develop new therapies for ABC‐mediated autoimmunity. Methods: We developed a T‐bet–tdTomato reporter mouse strain to trace live T‐bet+ B cells and adoptively transferred CD4+ T cells from bm12 mice to induce lupus. We next sorted CD11c+tdTomato+ B cells and conducted RNA sequencing and an extracellular flux assay. A metabolic restriction to constrain ABC formation was tested in human and mouse B cells. We used a bm12‐induced lupus mouse model to conduct the metabolic intervention. Results: ABCs exhibited a hypermetabolic state with enhanced glycolytic capacity. The increased glycolytic rate in ABCs was promoted by interferon‐γ (IFNγ) signaling. T‐bet, a downstream transcription factor of IFNγ, regulated the gene program of the glycolysis pathway in ABCs by repressing the expression of Bcl6. Functionally, glycolysis restriction could impair ABC formation. The engagement of glycolysis promoted survival and terminal differentiation of antibody‐secreting cells. Administration of a glycolysis inhibitor ameliorated ABC accumulation and autoantibody production in the lupus‐induced bm12 mouse model. Conclusion: T‐bet can couple immune signals and metabolic programming to establish pathogenic ABC formation and functional capacities. Modulation of ABCs favored a metabolic program that could be a novel therapeutic approach for lupus. [ABSTRACT FROM AUTHOR]

Objective: Increased Toll‐like receptor 7 (TLR‐7) signaling leading to the production of type I interferon (IFN) is an important contributor to human systemic lupus erythematosus (SLE). Protein kinase C and casein kinase substrate in neurons 1 (PACSIN1), a molecule that regulates synaptic vesicle recycling, has been linked to TLR‐7/TLR‐9–mediated type I IFN production in humans and mice, but the underlying mechanism is unknown. We undertook this study to explore the pathogenicity and underlying mechanism of a de novo PACSIN1 missense variant identified in a child with SLE. Methods: PACSIN1 Q59K de novo and null variants were introduced into a human plasmacytoid dendritic cell line and into mice using CRISPR/Cas9 editing. The effects of the variants on TLR‐7/TLR‐9 signaling in human and mouse cells, as well as PACSIN1 messenger RNA and IFN signature in SLE patients, were assessed using real‐time polymerase chain reaction and flow cytometry. Mechanisms were investigated using luciferase reporter assays, RNA interference, coimmunoprecipitation, and immunofluorescence. Results: We established that PACSIN1 forms a trimolecular complex with tumor necrosis factor receptor–associated factor 4 (TRAF4) and TRAF6 that is important for the regulation of type I IFN. The Q59K mutation in PACSIN1 augments binding to neural Wiskott‐Aldrich syndrome protein while it decreases binding to TRAF4, leading to unrestrained TRAF6‐mediated activation of type I IFN. Intriguingly, PACSIN1 Q59K increased TLR‐7 but not TLR‐9 signaling in human cells, leading to elevated expression of IFNβ and IFN‐inducible genes. Untreated SLE patients had high PACSIN1 expression in peripheral blood cells that correlated positively with IFN‐related genes. Introduction of the Pacsin1 Q59K mutation into mice caused increased surface TLR‐7 and TRAIL expression in B cells. Conclusion: PACSIN1 Q59K increases IFNβ activity through the impairment of TRAF4‐mediated inhibition of TLR‐7 signaling, possibly contributing to SLE risk. [ABSTRACT FROM AUTHOR]

Objective: Type I interferons (IFNs) are critical in the development of systemic lupus erythematosus (SLE). Metabolic abnormalities cause dysregulation of multiple immune cells, but the metabolic regulation of type I IFN production is not well clarified in SLE. We undertook this study to define amino acid metabolism features in SLE and to explore the function of disease‐relevant metabolites in the control of plasmacytoid dendritic cell (pDC)–mediated type I IFN production and the progression of SLE. Methods: Metabolomic profiling of the serum from SLE patients and healthy controls was performed by mass spectrometry. The effects of SLE‐related metabolites on type I IFN production were explored in human and mouse pDCs. The reactive oxygen species (ROS) levels of pDCs from wild‐type and Ncf1−/− mice were measured by flow cytometry. Mechanisms were investigated by RNA sequencing and immunoblotting. In vivo effects of SLE‐relevant metabolites were systemically analyzed in B6.Cg‐Sle1NZM2410/Aeg Yaa/DcrJ mice. Results: Taurine was higher in the serum from SLE patients compared to healthy controls (P < 0.001) and rheumatoid arthritis patients (P < 0.001). Taurine content was positively correlated with disease activity and the expression of IFN signature genes. The addition of taurine facilitated IFN regulatory factor 7 phosphorylation and enhanced type I IFN production by reducing the ROS levels in pDCs in a neutrophil cytosolic factor 1–dependent manner. Taurine supplementation promoted expression of type I IFN–induced genes, activated lymphocytes, and increased autoantibodies and proteinuria, leading to more serious nephritis. Conclusion: Taurine metabolism is involved in the development of SLE by enhancing pDC‐mediated type I IFN production. Targeted inhibition of taurine or implementation of a taurine‐restricted diet has therapeutic potential in SLE. [ABSTRACT FROM AUTHOR]

Objective: Reactive arthritis (ReA) is an inflammatory disorder occurring several weeks after gastrointestinal or genitourinary tract infections. HLA–B27 positivity is considered a risk factor, although it is not necessarily predictive of disease incidence. Among nongenetic factors, the intestinal microbiome may play a role in disease susceptibility. The objective of this study was to characterize the gut microbiota and host gene interactions in ReA and postinfectious spondyloarthritis. Methods: Adult subjects with peripheral spondyloarthritis and control subjects with preceding infections who did not develop arthritis were prospectively recruited from a geographic region with a high prevalence of ReA. Clinical variables, HLA status, and 16S ribosomal RNA gene sequencing of intestinal microbiota were analyzed. Results: Subjects with ReA showed no significant differences from controls in gut bacterial richness or diversity. However, there was a significantly higher abundance of Erwinia and Pseudomonas and an increased prevalence of typical enteropathogens associated with ReA. Subjects with ultrasound evidence of enthesitis were enriched in Campylobacter, while subjects with uveitis and radiographic sacroiliitis were enriched in Erwinia and unclassified Ruminococcaceae, respectively; both were enriched in Dialister. Host genetics, particularly HLA–A24, were associated with differences in gut microbiota diversity irrespective of disease status. We identified several co‐occurring taxa that were also predictive of HLA–A24 status. Conclusion: This is the first culture‐independent study characterizing the gut microbial community in postinfectious arthritis. Although bacterial factors correlated with disease presence and clinical features of ReA, host genetics also appeared to be a major independent driver of intestinal community composition. Understanding of these gut microbiota–host genetic relationships may further clarify the pathogenesis of postinfectious spondyloarthritides. [ABSTRACT FROM AUTHOR]

MicroRNAs are universal post-transcriptional regulators in genomes. They have the ability of buffering gene expressional programs, contributing to robustness of biological systems and playing important roles in development, physiology and diseases. Here, we identified a microRNA, miR-125a, as a positive regulator of granulopoiesis. MiR125a knockout mice show reduced infiltration of neutrophils in the lung and alleviated tissue destruction after endotoxin challenge as a consequence of decreased neutrophil numbers. Furthermore, we demonstrated that this significant reduction of neutrophils was due to impaired development of granulocyte precursors to mature neutrophils in an intrinsic manner. We showed that Socs3, a critical repressor for granulopoiesis, was a target of miR-125a. Overall, our study revealed a new microRNA regulating granulocyte development and supported a model in which miR-125a acted as a fine-tuner of granulopoiesis. [ABSTRACT FROM AUTHOR]

Cyclic GMP-AMP (cGAMP) synthase (cGAS, a.k.a. MB21D1), a cytosolic DNA sensor, catalyzes formation of the second messenger 2’3’-cGAMP that activates the stimulator of interferon genes (STING) signaling. How the cGAS activity is modulated remains largely unknown. Here, we demonstrate that sentrin/SUMO-specific protease 7 (SENP7) interacted with and potentiated cGAS activation. The small ubiquitin-like modifier (SUMO) was conjugated onto the lysine residues 335, 372 and 382 of cGAS, which suppressed its DNA-binding, oligomerization and nucleotidyl-transferase activities. SENP7 reversed this inhibition via catalyzing the cGAS de-SUMOylation. Consistently, silencing of SENP7 markedly impaired the IRF3-responsive gene expression induced by cGAS-STING axis. SENP7-knockdown mice were more susceptible to herpes simplex virus 1 (HSV-1) infection. SENP7 was significantly up-regulated in patients with SLE. Our study highlights the temporal modulation of the cGAS activity via dynamic SUMOylation, uncovering a novel mechanism for fine-tuning the STING signaling in innate immunity. [ABSTRACT FROM AUTHOR]

Objective Type I interferon (IFN) is a critical pathogenic factor during the progression of lupus nephritis (LN). Although microRNAs (miRNAs) have been shown to control the IFN response in immune cells in LN, the role of miRNAs in resident renal cells remains unclear. We undertook this study to investigate the role of microRNA-130b (miR-130b) in the IFN pathway in renal cells as well as its therapeutic effect in LN. Methods Kidney tissues from patients and (NZB × NZW)F1 lupus-prone mice were collected for detecting miR-130b levels. Primary renal mesangial cells (RMCs) were used to determine the role of miR-130b in the IFN pathway. We overexpressed miR-130b by administering miR-130b agomir in a mouse model of IFNα-accelerated LN to test its therapeutic efficacy. Results Down-regulated miR-130b expression was observed in kidney tissues from patients and lupus-prone mice. Further analysis showed that underexpression of miR-130b correlated negatively with abnormal activation of the IFN response in LN patients. In vitro, overexpressing miR-130b suppressed signaling downstream from the type I IFN pathway in RMCs by targeting IFN regulatory factor 1 (IRF-1). The opposite effect was observed when endogenous miR-130b expression was inhibited. The inverse correlation between IRF1 and miR-130b levels was detected in renal biopsy samples from LN patients. More importantly, in vivo administration of miR-130b agomir reduced IFNα-accelerated progression of LN, with decreased proteinuria, lower levels of immune complex deposition, and lack of glomerular lesions. Conclusion MicroRNA-130b is a novel negative regulator of the type I IFN pathway in renal cells. Overexpression of miR-130b in vivo ameliorates IFNα-accelerated LN, providing potential novel strategies for therapeutic intervention in LN. [ABSTRACT FROM AUTHOR]

Objective Diffuse alveolar hemorrhage (DAH) is a rare but life-threatening complication of systemic lupus erythematosus (SLE). Pristane-treated B6 mice develop severe DAH within 2 weeks of treatment. MicroRNA-155 (miR-155) is a pleiotropic microRNA that plays a crucial role in the regulation of immune responses. Recent studies have revealed a pathogenic role of miR-155 in various autoimmune disorders. The purpose of this study was to examine the role of miR-155 in the development of DAH in pristane-induced lupus using miR-155-knockout (miR-155−/−) mice and miR-155 antagomir to silence miR-155. Methods DAH was induced by an intraperitoneal injection of 0.5 ml of pristane. MicroRNA-155 antagomir was administered intravenously to silence miR-155 expression. Lung tissues were collected for RNA extraction and were embedded in paraffin for sectioning. Gene expression profiling data were analyzed using Ingenuity Pathway Analysis. Real-time quantitative polymerase chain reaction analysis was used for single-gene validation. Luciferase reporter assay and argonaute 2 immunoprecipitation were performed for target validation. Results MicroRNA-155 expression was significantly increased during the development of DAH. Disease progression was reduced in miR-155−/− mice as well as by in vivo silencing of miR-155 using a miR-155 antagomir. MicroRNA-155 silencing dampened pristane-induced ectopic activation of multiple inflammatory pathways and reduced the expression of proinflammatory cytokines. Several negative regulators of NF-κB signaling were inhibited by pristane and were reactivated in miR-155−/− mice. In particular, the antiinflammatory factor peroxisome proliferator-activated receptor α was identified as a direct target of miR-155. Conclusion MicroRNA-155 promotes pristane-induced lung inflammation. It contributes to ectopic activation of NF-κB signaling pathways by targeting multiple negative regulators. MicroRNA-155 antagomir may be a promising therapeutic strategy for treating acute lung inflammation in lupus. [ABSTRACT FROM AUTHOR]

Objective MicroRNAs (miRNAs) function to fine-tune the control of immune cell signaling. It is well established that there are abnormalities in the interleukin-2 (IL-2)-related signaling pathways in systemic lupus erythematosus (SLE). The miR-31 microRNA has been found to be markedly underexpressed in patients with SLE, and thus the present study was undertaken to investigate the role of miR-31 in IL-2 defects in lupus T cells. Methods Expression levels of miR-31 were quantitated using TaqMan miRNA assays. Transfection and stimulation of cultured cells followed by TaqMan quantitative polymerase chain reaction, enzyme-linked immunosorbent assay, and reporter gene assays were conducted to determine the biologic function of miR-31. NF-AT nuclear translocation and expression were quantitatively measured using an ImageStream cytometer. Bioinformatics analysis, small interfering RNA (siRNA) knockdown, and Western blotting were performed to validate miR-31 targets and effects. Results The expression of miR-31 was significantly decreased in lupus T cells, and this was positively correlated with the expression of IL-2. Overexpression of miR-31 in T cells increased the production of IL-2 by altering NF-AT nuclear expression and IL2 promoter activity, while knockdown of endogenous miR-31 reduced IL-2 production. RhoA expression was directly repressed by miR-31 in T cells. Of note, siRNA-mediated knockdown of RhoA enhanced IL2 promoter activity and, consequently, up-regulated IL-2 production. RhoA expression was consistently up-regulated and negatively correlated with the levels of miR-31 in lupus T cells. Manipulation of miR-31 expression in lupus T cells restored the expression of IL-2 at both the messenger RNA and protein levels. Conclusion MicroRNA-31 is a novel enhancer of IL-2 production during T cell activation. Dysregulation of miR-31 and its target, RhoA, could be a novel molecular mechanism underlying the IL-2 deficiency in patients with SLE. [ABSTRACT FROM AUTHOR]

The article focuses on a study of MicroRNA-146a which contributes to abnormal activation of the type I interferon pathway in patients with systematic lupus erythematosus (SLE). SLE is a complex autoimmune disease that is characterized by chronic immune activation and multiple immunologic phenotypes. MicroRNA is identified as regulators that modulate target gene expression, which contributes to the pathogenesis of (SLE). Details on the biologic function of miR-146a are discussed.

A response by Jia Li and colleagues is presented to a letter to the editor about their article "Interferon-&alpha priming promotes lipid uptake and macrophage-derived foam cell formation: A novel link between interferon-&alpha and atherosclerosis in lupus" in the February 2011 issue.

Long non-coding RNAs (lncRNAs) have emerged as key epigenetic regulators that govern gene expression and influence multiple biological processes. Accumulating evidence demonstrates that lncRNAs have critical roles in immune cell development and function. In this Review, the molecular mechanisms of gene expression regulation by lncRNAs are described and current knowledge of the role of lncRNAs in immune regulation and inflammation are presented, highlighting strategies for defining the roles of lncRNAs in the pathogenesis of multiple rheumatic diseases. Finally, research progress in understanding the role of lncRNAs in rheumatic diseases is discussed. [ABSTRACT FROM AUTHOR]

Summary Iron deposition is frequently observed in human autoinflammatory diseases, but its functional significance is largely unknown. Here we showed that iron promoted proinflammatory cytokine expression in T cells, including GM-CSF and IL-2, via regulating the stability of an RNA-binding protein PCBP1. Iron depletion or Pcbp1 deficiency in T cells inhibited GM-CSF production by attenuating Csf2 3′ untranslated region (UTR) activity and messenger RNA stability. Pcbp1 deficiency or iron uptake blockade in autoreactive T cells abolished their capacity to induce experimental autoimmune encephalomyelitis, an animal model for multiple sclerosis. Mechanistically, intracellular iron protected PCBP1 protein from caspase-mediated proteolysis, and PCBP1 promoted messenger RNA stability of Csf2 and Il2 by recognizing UC-rich elements in the 3′ UTRs. Our study suggests that iron accumulation can precipitate autoimmune diseases by promoting proinflammatory cytokine production. RNA-binding protein-mediated iron sensing may represent a simple yet effective means to adjust the inflammatory response to tissue homeostatic alterations. [ABSTRACT FROM AUTHOR]