A critical role of the transcription factor fli-1 in murine lupus development by regulation of interleukin-6 expression

A Non-Coding Variant in SLC15A4 Modulates Enhancer Activity and Lysosomal Deacidification Linked to Lupus Susceptibility

Systemic lupus erythematosus (SLE) is a complex autoimmune disease with a strong genetic basis. Despite the identification of several single nucleotide polymorphisms (SNPs) near the SLC15A4 gene that are significantly associated with SLE across multiple populations, specific causal SNP(s) and molecular mechanisms responsible for disease susceptibility are unknown. To address this gap, we employed bioinformatics, expression quantitative trait loci (eQTLs), and 3D chromatin interaction analysis to nominate a likely functional variant, rs35907548, in an active intronic enhancer of SLC15A4. Through luciferase reporter assays followed by chromatin immunoprecipitation (ChIP)-qPCR, we observed significant allele-specific enhancer effects of rs35907548 in diverse cell lines. The rs35907548 risk allele T is associated with increased regulatory activity and target gene expression, as shown by eQTLs and chromosome conformation capture (3C)-qPCR. The latter revealed long-range chromatin interactions between the rs35907548 enhancer and the promoters of SLC15A4, GLTLD1, and an uncharacterized lncRNA. The enhancer-promoter interactions and expression effects were validated by CRISPR/Cas9 knock-out (KO) of the locus in HL60 promyeloblast cells. KO cells also displayed dramatically dysregulated endolysosomal pH regulation. Together, our data show that the rs35907548 risk allele affects multiple aspects of cellular physiology and may directly contribute to SLE.

Role of the transcription factor Fli-1 on the CXCL10/CXCR3 Axis

The transcription factor Fli-1, a member of the ETS family of transcription factors, is implicated in the pathogenesis of lupus disease. Reduced Fli-1 expression in lupus mice leads to decreased renal Cxcl10 mRNA levels and renal infiltrating CXCR3+ T cells that parallels reduced renal inflammatory cell infiltration and renal damage. Inflammatory chemokine CXCL10 is critical for attracting inflammatory cells expressing the chemokine receptor CXCR3. The CXCL10/CXCR3 axis plays a role in the pathogenesis of various inflammatory diseases including lupus. Our data here demonstrate that renal CXCL10 protein levels are significantly lower in Fli-1 heterozygous MRL/lpr mice compared to wild-type MRL/lpr mice. Knockdown of Fli-1 significantly reduced CXCL10 secretion in mouse and human endothelial cells, and human mesangial cells, upon LPS or TNFα stimulation. The Fli-1 inhibitor, Camptothecin, significantly reduced CXCL10 production in human monocyte cells upon interferon stimulation. Four putative Ets binding sites in the Cxcl10 promoter showed significant enrichment for FLI-1; however, FLI-1 did not directly drive transcription from the human or mouse promoters, suggesting FLI-1 may regulate CXCL10 expression indirectly. Our results also suggest that the DNA binding domain of FLI-1 is necessary for regulation of human hCXCR3 promotor activity in human T cells and interactions with co-activators. Together, these results support a role for FLI-1 in modulating the CXCL10-CXCR3 axis by directly or indirectly regulating the expression of both genes to impact lupus disease development. Signaling pathways or drugs that reduce FLI-1 expression may offer novel approaches to lupus treatment.

A Non-Coding Variant in SLC15A4 Modulates Enhancer Activity and Lysosomal Deacidification Linked to Lupus Susceptibility

Systemic lupus erythematosus (SLE) is a complex autoimmune disease with a strong genetic basis. Despite the identification of several single nucleotide polymorphisms (SNPs) near the SLC15A4 gene that are significantly associated with SLE across multiple populations, specific causal SNP(s) and molecular mechanisms responsible for disease susceptibility are unknown. To address this gap, we employed bioinformatics, expression quantitative trait loci (eQTLs), and 3D chromatin interaction analysis to nominate a likely functional variant, rs35907548, in an active intronic enhancer of SLC15A4 . Through luciferase reporter assays followed by chromatin immunoprecipitation (ChIP)-qPCR, we observed significant allele-specific enhancer effects of rs35907548 in diverse cell lines. The rs35907548 risk allele T is associated with increased regulatory activity and target gene expression, as shown by eQTLs and chromosome conformation capture (3C)-qPCR. The latter revealed long-range chromatin interactions between the rs35907548 enhancer and the promoters of SLC15A4, GLTLD1 , and an uncharacterized lncRNA. The enhancer-promoter interactions and expression effects were validated by CRISPR/Cas9 knock-out (KO) of the locus in HL60 promyeloblast cells. KO cells also displayed dramatically dysregulated endolysosomal pH regulation. Together, our data show that the rs35907548 risk allele affects multiple aspects of cellular physiology and may directly contribute to SLE.

Transcription factor Fli-1 impacts the expression of CXCL13 and regulates immune cell infiltration into the kidney in MRL/lpr mouse

OBJECTIVE

Friend leukaemia virus integration 1 (Fli-1) regulates chemokine/cytokine expression and thus plays an important role in the development of lupus nephritis. Chemokine CXC ligand 13 (CXCL13) is a chemokine that promotes the formation of ectopic lymphoid structures and has been reported to be associated with the pathogenesis of lupus nephritis. The relationship between Fli-1 and CXCL13 is unknown. This study aims to elucidate whether Fli-1 impacts CXCL13 expression and contributes to the progression of lupus-like nephritis in adult MRL/lpr mouse.

METHODS

Serum CXCL13 levels were measured in adult wild-type (WT) MRL/lpr mice and Fli-1 heterozygote knockout (Fli-1^+/-) MRL/lpr mice (4 months old or older) using ELISA. Renal mRNA expression (CXCL13 and related molecules) was measured using real-time PCR method. Kidneys were removed, stained and evaluated using a pathology scoring system. The grade of CXCL13 or CXC-chemokine receptor type 5 (CXCR5)-positive immune cell infiltration into the kidney was evaluated using immunostaining with anti-CXCL13 or anti-CXCR5 antibodies. We also used immunofluorescence staining with CXCL13- and CD11b-specific antibodies to detect the infiltration of CXCL13/CD11b double-positive immune cells.

RESULTS

Serum CXCL13 levels in Fli-1^+/- MRL/lpr mice were significantly lower than that in WT MRL/lpr mice (545.5 and 960.5 pg/mL, p=0.02). Renal expression of CXCL13 mRNA and SRY-related HMG box4 (Sox4) (an important factor for B-cell development) levels were significantly lower in Fli-1^+/- MRL/lpr mice. Renal histology scores in WT MRL/lpr mice revealed significantly increased glomerular inflammation. Despite similar interstitial immune cell infiltration into the kidney, the number of CXCL13- and CXCR5-positive cells was significantly lower in Fli-1^+/- MRL/lpr mice than in WT mice. Furthermore, immunofluorescence staining revealed that Fli-1^+/-MRL/lpr mice had significantly fewer CXCL13/CD11b double-positive immune cells.

CONCLUSION

Fli-1 regulates renal Sox4 mRNA expression and infiltration of CXCR5-positive cells as well as CXCL13/CD11b double-positive immune cells into the kidney, which affects CXCL13 expression and lupus-like nephritis.

Potential Therapeutic Value of the STING Inhibitors

The stimulator of interferon genes (STING) is a critical protein in the activation of the immune system in response to DNA. It can participate the inflammatory response process by modulating the inflammation-preferred translation program through the STING-PKR-like endoplasmic reticulum kinase (PERK)-eIF2α pathway or by inducing the secretion of type I interferons (IFNs) and a variety of proinflammatory factors through the recruitment of TANK-binding kinase 1 (TBK1) and interferon regulatory factor 3 (IRF3) or the regulation of the nuclear factor kappa-B (NF-κB) pathway. Based on the structure, location, function, genotype, and regulatory mechanism of STING, this review summarizes the potential value of STING inhibitors in the prevention and treatment of infectious diseases, psoriasis, systemic lupus erythematosus, non-alcoholic fatty liver disease, and other inflammatory and autoimmune diseases.

The expression of Ets-1 and Fli-1 is associated with interferon-inducible genes in peripheral blood mononuclear cells from Japanese patients with systemic lupus erythematosus

Transcription factors E26 transformation-specific-1 (Ets-1) and Friend leukemia insertion site-1 (Fli-1) and type I interferon (IFN) have been implicated in systemic lupus erythematosus (SLE). We examined the expression of these genes in peripheral blood mononuclear cells (PBMCs) from Japanese patients with SLE and analyzed their association with SLE. We enrolled 53 Japanese patients with SLE, 42 patients with rheumatoid arthritis (RA), and 30 healthy donors (HDs) (as controls) in this study. PBMCs were collected from all participants, and the expressions of Ets-1, Fli-1, and three interferon-inducible genes (IFIGs) (interferon-inducible protein with tetratricopeptide 1 [IFIT1], interferon-inducible protein 44 [IFI44], and eukaryotic translation initiation factor 2 alpha kinase 2 [EIF2AK2]) were measured using real-time polymerase chain reaction (PCR). The relationships of each molecule with clinical symptoms, laboratory data, and treatments were analyzed. The expression of Ets-1 and Fli-1 was significantly lower in the PBMCs from patients with SLE than that in the PBMCs from patients with RA and HDs. The expression of the three IFIGs was significantly higher in the PBMCs from patients with SLE than that in the PBMCs from patients with RA and HDs. For patients with SLE, significantly positive correlations were found between Ets-1 and three IFIGs; a similar trend was observed between Fli-1 and IFIGs. IFIG expression in the PBMCs was significantly higher in patients with SLE than that in other participants, and the expression of Ets-1 and Fli-1 was positively associated with IFN expression. Therefore, it was suggested that Ets-1 and Fli-1 were associated with the pathophysiology of SLE by regulating the type I IFN pathway.

The druggable transcription factor Fli-1 regulates T cell immunity and tolerance in graft-versus-host disease

Graft-versus-host disease (GVHD), manifesting as either acute (aGVHD) or chronic (cGVHD), presents significant life-threatening complications following allogeneic hematopoietic cell transplantation. Here, we investigated Friend virus leukemia integration 1 (Fli-1) in GVHD pathogenesis and validated Fli-1 as a therapeutic target. Using genetic approaches, we found that Fli-1 dynamically regulated different T cell subsets in allogeneic responses and pathogenicity in the development of aGVHD and cGVHD. Compared with homozygous Fli1-deficient or WT T cells, heterozygous Fli1-deficient T cells induced the mildest GVHD, as evidenced by the lowest Th1 and Th17 cell differentiation. Single-cell RNA-Seq analysis revealed that Fli-1 differentially regulated CD4+ and CD8+ T cell responses. Fli-1 promoted the transcription of Th1/Th17 pathways and T cell receptor-inducible (TCR-inducible) transcription factors in CD4+ T cells, while suppressing activation- and function-related gene pathways in CD8+ T cells. Importantly, a low dose of camptothecin, topotecan, or etoposide acted as a potent Fli-1 inhibitor and significantly attenuated GVHD severity, while preserving the graft-versus-leukemia (GVL) effect. This observation was extended to a xenograft model, in which GVHD was induced by human T cells. In conclusion, we provide evidence that Fli-1 plays a crucial role in alloreactive CD4+ T cell activation and differentiation and that targeting Fli-1 may be an attractive strategy for treating GVHD without compromising the GVL effect.

Systems biology approach delineates critical pathways associated with disease progression in rheumatoid arthritis

Rheumatoid Arthritis (RA) is a chronic systemic autoimmune disease leading to inflammation, cartilage cell death, synoviocyte proliferation, and increased and impaired differentiation of osteoclasts and osteoblasts leading to joint erosions and deformities. Transcriptomics, proteomics, and metabolomics datasets were analyzed to identify the critical pathways that drive the RA pathophysiology. Single nucleotide polymorphisms (SNPs) associated with RA were analyzed for the functional implications, clinical outcomes, and blood parameters later validated by literature. SNPs associated with RA were grouped into pathways that drive the immune response and cytokine production. Further gene set enrichment analysis (GSEA) was performed on gene expression omnibus (GEO) data sets of peripheral blood mononuclear cells (PBMCs), synovial macrophages, and synovial biopsies from RA patients showed enrichment of Th1, Th2, Th17 differentiation, viral and bacterial infections, metabolic signalling and immunological pathways with potential implications for RA. The proteomics data analysis presented pathways with genes involved in immunological signaling and metabolic pathways, including vitamin B12 and folate metabolism. Metabolomics datasets analysis showed significant pathways like amino-acyl tRNA biosynthesis, metabolism of amino acids (arginine, alanine aspartate, glutamate, glutamine, phenylalanine, and tryptophan), and nucleotide metabolism. Furthermore, our commonality analysis of multi-omics datasets identified common pathways with potential implications for joint remodeling in RA. Disease-modifying anti-rheumatic drugs (DMARDs) and biologics treatments were found to modulate many of the pathways that were deregulated in RA. Overall, our analysis identified molecular signatures associated with the observed symptoms, joint erosions, potential biomarkers, and therapeutic targets in RA. Communicated by Ramaswamy H. Sarma.

Repurposing Multiple-Molecule Drugs for COVID-19-Associated Acute Respiratory Distress Syndrome and Non-Viral Acute Respiratory Distress Syndrome via a Systems Biology Approach and a DNN-DTI Model Based on Five Drug Design Specifications

The coronavirus disease 2019 (COVID-19) epidemic is currently raging around the world at a rapid speed. Among COVID-19 patients, SARS-CoV-2-associated acute respiratory distress syndrome (ARDS) is the main contribution to the high ratio of morbidity and mortality. However, clinical manifestations between SARS-CoV-2-associated ARDS and non-SARS-CoV-2-associated ARDS are quite common, and their therapeutic treatments are limited because the intricated pathophysiology having been not fully understood. In this study, to investigate the pathogenic mechanism of SARS-CoV-2-associated ARDS and non-SARS-CoV-2-associated ARDS, first, we constructed a candidate host-pathogen interspecies genome-wide genetic and epigenetic network (HPI-GWGEN) via database mining. With the help of host-pathogen RNA sequencing (RNA-Seq) data, real HPI-GWGEN of COVID-19-associated ARDS and non-viral ARDS were obtained by system modeling, system identification, and Akaike information criterion (AIC) model order selection method to delete the false positives in candidate HPI-GWGEN. For the convenience of mitigation, the principal network projection (PNP) approach is utilized to extract core HPI-GWGEN, and then the corresponding core signaling pathways of COVID-19-associated ARDS and non-viral ARDS are annotated via their core HPI-GWGEN by KEGG pathways. In order to design multiple-molecule drugs of COVID-19-associated ARDS and non-viral ARDS, we identified essential biomarkers as drug targets of pathogenesis by comparing the core signal pathways between COVID-19-associated ARDS and non-viral ARDS. The deep neural network of the drug–target interaction (DNN-DTI) model could be trained by drug–target interaction databases in advance to predict candidate drugs for the identified biomarkers. We further narrowed down these predicted drug candidates to repurpose potential multiple-molecule drugs by the filters of drug design specifications, including regulation ability, sensitivity, excretion, toxicity, and drug-likeness. Taken together, we not only enlighten the etiologic mechanisms under COVID-19-associated ARDS and non-viral ARDS but also provide novel therapeutic options for COVID-19-associated ARDS and non-viral ARDS.

Suppression of Fli-1 protects against pericyte loss and cognitive deficits in Alzheimer's disease

Brain pericytes regulate cerebral blood flow, maintain the integrity of the blood-brain barrier (BBB) and facilitate the removal of amyloid β (Aβ) which is critical to healthy brain activity. Pericyte loss has been observed in brains from patients with Alzheimer's disease (AD) and animal models. Our previous data demonstrated that friend leukemia virus integration 1 (Fli-1), an ETS transcription factor, governs pericyte viability in murine sepsis; however, the role of Fli-1 and its impact on pericyte loss in AD remains unknown. Here, we demonstrated that Fli-1 expression was up-regulated in postmortem brains from a cohort of human AD donors and in 5xFAD mice, which corresponded with a decreased pericyte number, elevated inflammatory mediators, and increased Aβ accumulation as compared to cognitively normal individuals and WT mice. Antisense oligonucleotide Fli-1 Gapmer administrated via intrahippocampal injection decelerated pericyte loss, decreased inflammatory response, ameliorated cognitive deficits, improved BBB dysfunction, and reduced Aβ deposition in 5xFAD mice. Fli-1 Gapmer-mediated inhibition of Fli-1 protected against Aβ accumulation-induced human brain pericyte apoptosis in vitro. Overall, these studies indicate that Fli-1 contributes to pericyte loss, inflammatory response, Aβ deposition, vascular dysfunction and cognitive decline, and suggest that inhibition of Fli-1 may represent novel therapeutic strategies for AD.

Phase II, randomised, double-blind, multicentre study evaluating the safety and efficacy of filgotinib and lanraplenib in patients with lupus membranous nephropathy

Objectives

Patients with lupus membranous nephropathy (LMN) are at risk for prolonged proteinuria and progressive chronic kidney disease. There are no proven effective treatments for LMN, and controlled trials are lacking. This trial assessed the preferential Janus kinase 1 (JAK1) inhibitor filgotinib and the spleen tyrosine kinase inhibitor lanraplenib in patients with LMN.

Methods

This was a phase II, randomised, double-blind trial conducted at 15 centres in the USA to evaluate the safety and efficacy of filgotinib or lanraplenib for the treatment of LMN. Eligible patients were randomised 1:1 to receive either filgotinib or lanraplenib in a blinded fashion for up to 52 weeks. The primary endpoint was the per cent change in 24-hour urine protein from baseline to week 16.

Results

Nine patients were randomised to receive filgotinib (n=5) or lanraplenib (n=4). Four patients in the filgotinib group and one patient in the lanraplenib group completed week 16. There was a median reduction of 50.7% in 24-hour urine protein after 16 weeks of treatment with filgotinib (n=4), and the median Systemic Lupus Erythematosus Disease Activity Index from the Safety of Estrogens in Lupus National Assessment score remained stable. Filgotinib treatment was well tolerated. Limited conclusions can be drawn about treatment with lanraplenib.

Conclusion

The number of patients treated in this study was small, and only limited conclusions can be drawn. There may be a therapeutic benefit with filgotinib treatment, which may support future investigations with filgotinib or other JAK inhibitors in patients with LMN.

Trial registration number

NCT03285711.

Camptothecin and Topotecan, Inhibitors of Transcription Factor Fli-1 and Topoisomerase, Markedly Ameliorate Lupus Nephritis in (NZB × NZW)F1 Mice and Reduce the Production of Inflammatory Mediators in Human Renal Cells

OBJECTIVE

To examine the therapeutic effects of camptothecin (CPT) and topotecan (TPT), inhibitors of transcription factor Fli-1 and topoisomerase, on lupus nephritis in (NZB × NZW)F1 (NZBWF1) mice, and to examine the effects of CPT and TPT on inflammatory mediators in human renal cells.

METHODS

Female NZBWF1 mice were treated with vehicle, cyclophosphamide (CYC), CPT (1 mg/kg or 2 mg/kg), or TPT (0.03 mg/kg, 0.1 mg/kg, or 0. 3 mg/kg) by intraperitoneal injection twice a week, beginning at the age of 25 weeks (n = 8-10 mice per group). Blood and urine were collected for monitoring autoantibodies and proteinuria. Mice were euthanized at 40 weeks, and renal pathology scores were assessed. Human renal endothelial and mesangial cells were treated with CPT or TPT, and cytokine expression was measured.

RESULTS

None of the NZBWF1 mice treated with 1 mg/kg or 2 mg/kg of CPT or 0.3 mg/kg of TPT had proteinuria >100 mg/dl at the age of 40 weeks. One of 8 mice treated with 0.1 mg/kg of TPT and 1 of 10 mice treated with CYC had proteinuria >300 mg/dl, whereas 90% of the mice treated with vehicle had proteinuria >300 mg/dl. Compared to vehicle control, mice treated with 1 mg/kg or 2 mg/kg of CPT, 0.1 mg/kg or 0.3 mg/kg of TPT, or CYC had significantly prolonged survival, attenuated renal injury, diminished splenomegaly, reduced anti-double-stranded DNA autoantibody levels, and reduced IgG and C3 deposits in the glomeruli (all P < 0.05). Human renal cells treated with CPT or TPT had reduced expression of Fli-1 and decreased monocyte chemotactic protein 1 production following stimulation with interferon-α (IFNα) or IFNγ.

CONCLUSION

Our findings indicate that low-dose CPT and TPT could be repurposed to treat lupus nephritis.

Expression of GM-CSF Is Regulated by Fli-1 Transcription Factor, a Potential Drug Target

Friend leukemia virus integration 1 (Fli-1) is an ETS transcription factor and a critical regulator of inflammatory mediators, including MCP-1, CCL5, IL-6, G-CSF, CXCL2, and caspase-1. GM-CSF is a regulator of granulocyte and macrophage lineage differentiation and a key player in the pathogenesis of inflammatory/autoimmune diseases. In this study, we demonstrated that Fli-1 regulates the expression of GM-CSF in both T cells and endothelial cells. The expression of GM-CSF was significantly reduced in T cells and endothelial cells when Fli-1 was reduced. We found that Fli-1 binds directly to the GM-CSF promoter using chromatin immunoprecipitation assay. Transient transfection assays indicated that Fli-1 drives transcription from the GM-CSF promoter in a dose-dependent manner, and mutation of the Fli-1 DNA binding domain resulted in a significant loss of transcriptional activation. Mutation of a known phosphorylation site within the Fli-1 protein led to a significant increase in GM-CSF promoter activation. Thus, direct binding to the promoter and phosphorylation are two important mechanisms behind Fli-1-driven activation of the GM-CSF promoter. In addition, Fli-1 regulates GM-CSF expression in an additive manner with another transcription factor Sp1. Finally, we demonstrated that a low dose of a chemotherapeutic drug, camptothecin, inhibited expression of Fli-1 and reduced GM-CSF production in human T cells. These results demonstrate novel mechanisms for regulating the expression of GM-CSF and suggest that Fli-1 is a critical druggable regulator of inflammation and immunity.

Emerging role of Fli1 in autoimmune diseases

The Ets transcription factor family exerts crucial role in cell proliferation, apoptosis, differentiation and migration. Friend leukemia integration 1 (Fli1), a member of the Ets family, is expressed in fibroblasts, endothelial cells and immune cells. Fli1 gene is participated in the development, proliferation, activation, migration and other processes of immune cells. Fli1 can also affect the function of immune cells by regulating cytokines and chemokines. Emerging evidence has shown that Fli1 is implicated in the etiology of several autoimmune diseases, including systemic sclerosis (SSc) and systemic lupus erythematosus (SLE). In this review, we mainly discuss the current evidence for the role of Fli1 in these diseases.

Ets Family Transcription Factor Fli-1 Promotes Leukocyte Recruitment and Production of IL-17A in the MRL/Lpr Mouse Model of Lupus Nephritis

The transcription factor Friend leukemia integration 1 (Fli-1) regulates the expression of numerous cytokines and chemokines and alters the progression of lupus nephritis in humans and in the MRL/MpJ-Fas^lpr (MRL/lpr) mouse model. Th17-mediated immune responses are notably important as they promote ongoing inflammation. The purpose of this study is to determine the impact of Fli-1 on expression of interleukin-17A (IL-17A) and the infiltration of immune cells into the kidney. IL-17A concentrations were measured by ELISA in sera collected from MRL/lpr Fli-1-heterozygotes (Fli-1^+/−) and MRL/lpr Fli-1^+/+ control littermates. Expression of IL-17A and related proinflammatory mediators was measured by real-time polymerase chain reaction (RT-PCR). Immunofluorescence staining was performed on renal tissue from MRL/lpr Fli-1^+/− and control littermates using anti-CD3, anti-CD4, and anti-IL-17A antibodies to detect Th17 cells and anti-CCL20 and anti-CD11b antibodies to identify CCL20⁺ monocytes. The expression of IL-17A in renal tissue was significantly reduced; this was accompanied by decreases in expression of IL-6, signal transducer and activator of transcription 3 (STAT3), and IL-1β. Likewise, we detected fewer CD3⁺IL-17⁺ and CD4⁺IL-17⁺ cells in renal tissue of MLR/lpr Fli-1^+/− mice and significantly fewer CCL20⁺CD11b⁺ monocytes. In conclusion, partial deletion of Fli-1 has a profound impact on IL-17A expression and on renal histopathology in the MRL/lpr mouse.

Fli-1 transcription factor regulates the expression of caspase-1 in lung pericytes

Our previous data demonstrated that Friend leukemia virus integration 1 (Fli-1), an ETS transcription factor, governs pericyte loss and vascular dysfunction in cecal ligation and puncture-induced murine sepsis by regulating essential pyroptosis markers including caspase-1. However, whether Fli-1 regulates caspase-1 expression levels in vitro and how Fli-1 regulates caspase-1 remain unknown. Our present work further demonstrated that overexpressed Fli-1 significantly increased caspase-1 and IL-18 expression levels in cultured mouse lung pericytes. Bacterial outer membrane vesicles (OMVs) have been found to induce cell pyroptosis through transferring LPS intracellularly. Using OMVs to induce an in vitro model of pyroptosis, we observed that OMVs significantly increased protein levels of Fli-1 in mouse lung pericytes. Furthermore, knockdown of Fli-1 by siRNA blocked OMVs-induced caspase-1, caspase-11 and IL-18 expression levels. As caspase-1 was predicted as a potential target of Fli-1, we cloned murine caspase-1 promoter into a luciferase construct. Our data demonstrate for the first time that Fli-1 regulates caspase-1 expression by directly binding to its promoter regions measured by chromatin immunoprecipitation (ChIP) assay and luciferase reporter system. In summary, our findings demonstrated a novel role and mechanism of Fli-1 in regulating caspase-1 expression in lung pericytes.

Fli-1 Governs Pericyte Dysfunction in a Murine Model of Sepsis

Background

Pericytes are vascular mural cells and are embedded in the basement membrane of the microvasculature. Recent studies suggest a role for pericytes in lipopolysaccharide (LPS)-induced microvascular dysfunction and mortality, but the mechanisms of pericyte loss in sepsis are largely unknown.

Methods

By using a cecal ligation and puncture (CLP)-induced murine model of sepsis, we observed that CLP led to lung and renal pericyte loss and reduced lung pericyte density and pericyte/endothelial cell (EC) coverage.

Results

Up-regulated Friend leukemia virus integration 1 (Fli-1) messenger ribonucleic acid (RNA) and protein levels were found in lung pericytes from CLP mice in vivo and in LPS-stimulated lung pericytes in vitro. Knockout of Fli-1 in Foxd1-derived pericytes prevented CLP-induced pericyte loss, vascular leak, and improved survival. Disrupted Fli-1 expression by small interfering RNA inhibited LPS-induced inflammatory cytokines and chemokines in cultured lung pericytes. Furthermore, CLP-induced pericyte pyroptosis was mitigated in pericyte Fli-1 knockout mice.

Conclusions

Our findings suggest that Fli-1 is a potential therapeutic target in sepsis.

In vivo Proinflammatory Cytokine Production by CD-1 Mice in Response to Equipotential Doses of Rhodobacter capsulatus PG and Salmonella enterica Lipopolysaccharides

The capacities of relatively nontoxic lipopolysaccharide (LPS) from Rhodobacter capsulatus PG and highly potent LPS from Salmonella enterica serovar Typhimurium to evoke proinflammatory cytokine production have been compared in vivo. Intravenous administration of S. enterica LPS at a relatively low dose (1 mg/kg body weight) led to upregulation of TNF-α, IL-6, and IFN-γ production by non-sensitized CD-1 mice. LPS from R. capsulatus PG used at a four-times higher dose than that from S. enterica elicited production of almost the same amount of systemic TNF-α; therefore, the doses of 4 mg/kg LPS from R. capsulatus PG and 1 mg/kg LPS from S. enterica were considered to be approximately equipotential doses with respect to the LPS-dependent TNF-α production by CD-1 mice. Rhodobacter capsulatus PG LPS was a weaker inducer of the production of TNF-α, IL-6, and IFN-γ, as compared to the equipotential dose of S. enterica LPS. Administration of R. capsulatus PG LPS before S. enterica LPS decreased production of IFN-γ, but not of TNF-α and IL-6, induced by S. enterica LPS. Rhodobacter capsulatus PG LPS also suppressed IFN-γ production induced by S. enterica LPS when R. capsulatus PG LPS had been injected as little as 10 min after S. enterica LPS, but to a much lesser extent. Rhodobacter capsulatus PG LPS did not affect TNF-α and IL-6 production induced by the equipotential dose of S. enterica LPS. In order to draw conclusion on the endotoxic activity of particular LPSs, species-specific structure or arrangement of the animal or human immune systems should be considered.

Mouse models of lupus: what they tell us and what they don't

Lupus is a complex heterogeneous disease characterised by autoantibody production and immune complex deposition followed by damage to target tissues. Animal models of human diseases are an invaluable tool for defining pathogenic mechanisms and testing of novel therapeutic agents. There are perhaps more applicable murine models of lupus than any other human disease. There are spontaneous models of lupus, inducible models of lupus, transgenic-induced lupus, gene knockout induced lupus and humanised mouse models of lupus. These mouse models of lupus have contributed significantly to our knowledge of the pathogenesis of lupus and served as valuable preclinical models for proof of concept for new therapies. Despite their utility, mouse models of lupus have their distinct limitations. Although similar, mouse and human immune systems are different and thus one cannot assume a mechanism for disease in one is translatable to the other. Efficacy and toxicity of compounds can vary significantly between humans and mice, also limiting direct translation. Finally, the heterogeneous aspects of human lupus, both in clinical presentation, underlying pathogenesis and genetics, are not completely represented in current mouse models. Thus, proving a therapy or mechanism of disease in one mouse model is similar to proving a mechanism/therapy in a limited subset of human lupus. These limitations, however, do not marginalise the importance of animal models nor the significant contributions they have made to our understanding of lupus.

Characterization of gene expression and genetic variation of horse ERBB receptor feedback inhibitor 1 in Thoroughbreds

Objective

This study aimed to test the expression patterns of ERBB receptor feedback inhibitor 1 (ERRFI1) before and after exercise and the association of non-synonymous single-nucleotide polymorphisms (nsSNPs) of horse ERRFI1 with racing traits in Thoroughbreds.

Methods

We performed bioinformatics and gene expression analyses for horse ERRFI1. Transcription factor (TF) binding sites in the 5′-regulatory region of this gene were identified through a tool for prediction of TF-binding site (PROMO). A general linear model was used to detect the association between the nsSNP (LOC42830758 A to G) and race performance.

Results

Quantitative polymerase chain reaction analysis showed that expression level of ERRFI1 after exercise was 1.6 times higher than that before exercise. Ten transcription factors were predicted from the ERRFI1 regulatory region. A novel nsSNP (LOC42830758 A to G) was found in ERRFI1, which was associated with three racing traits including average prize money, average racing index, and 3-year-old starts percentile ranking.

Conclusion

Our analysis will be helpful as a basis for studying genes and SNPs that affect race performance in racehorses.

Loss of PAFR prevents neuroinflammation and brain dysfunction after traumatic brain injury

Traumatic brain injury (TBI) is a principal cause of death and disability worldwide, which is a major public health problem. Death caused by TBI accounts for a third of all damage related illnesses, which 75% TBI occurred in low and middle income countries. With the increasing use of motor vehicles, the incidence of TBI has been at a high level. The abnormal brain functions of TBI patients often show the acute and long-term neurological dysfunction, which mainly associated with the pathological process of malignant brain edema and neuroinflammation in the brain. Owing to the neuroinflammation lasts for months or even years after TBI, which is a pivotal causative factor that give rise to neurodegenerative disease at late stage of TBI. Studies have shown that platelet activating factor (PAF) inducing inflammatory reaction after TBI could not be ignored. The morphological and behavioral abnormalities after TBI in wild type mice are rescued by general knockout of PAFR gene that neuroinflammation responses and cognitive ability are improved. Our results thus define a key inflammatory molecule PAF that participates in the neuroinflammation and helps bring about cerebral dysfunction during the TBI acute phase.

The Fli-1 transcription factor is a critical regulator for controlling the expression of chemokine C-X-C motif ligand 2 (CXCL2)

Mammalian cells produce inflammatory cytokines and chemokines in response to innate immune signals and their expression is tightly regulated. Chemokine (C-X-C motif) ligand 2 (CXCL2), also known as macrophage inflammatory protein 2-alpha (MIP2-alpha), is an inflammatory chemokine belonging to the CXC chemokine family. CXCL2 is chemotactic for neutrophils and elevated expression of CXCL2 is associated with many inflammatory and autoimmune diseases. The Fli-1 gene belongs to the large Ets transcription factor family, whose members regulate a wide variety of cellular functions including the immune response. In this study, we demonstrate that endothelial cells transfected with Fli-1 specific siRNA produce significantly less CXCL2 compared to cells transfected with control siRNA after stimulation by the Toll-like receptor (TLR) 4 ligands, lipopolysaccharide (LPS) and tumor necrosis factor alpha (TNF-α). The production of CXCL2 in endothelial cells stimulated with LPS stimulation is dose-dependent. We found that Fli-1 binds to the CXCL2 promoter as established by Chromatin immunoprecipitation‎ (ChIP) assay. Transient transfection assays show that Fli-1 drives transcription from the CXCL2 promoter in a dose-dependent manner and Fli-1 regulates the expression of CXCL2 largely by directly binding to the promoter. Targeted knockdown and transient transfection experiments suggest that both Fli-1 and the p65 subunit of NF-κB affect the activation of CXCL2 in an additive manner. These results indicate that Fli-1 is a novel, critical transcription factor that regulates the expression of the inflammatory chemokine CXCL2.

Acetylation impacts Fli-1-driven regulation of granulocyte colony stimulating factor

Fli-1 has emerged as a critical regulator of inflammatory mediators, including MCP-1, CCL5, and IL-6. The cytokine, granulocyte colony stimulating factor (G-CSF) regulates neutrophil precursor maturation and survival, and activates mature neutrophils. Previously, a significant decrease in neutrophil infiltration into the kidneys of Fli-1^+/- lupus-prone mice was observed. In this study, a significant decrease in G-CSF protein expression was detected in stimulated murine and human endothelial cells when expression of Fli-1 was inhibited. The murine G-CSF promoter contains numerous putative Fli-1 binding sites and several regions within the proximal promoter are significantly enriched for Fli-1 binding. Transient transfection assays indicate that Fli-1 drives transcription from the G-CSF promoter and mutation of the Fli-1 DNA binding domain resulted in a 94% loss of transcriptional activation. Mutation of a known acetylation site, led to a significant increase in G-CSF promoter activation. The histone acetyltransferases p300/CBP and p300/CBP associated factor (PCAF) significantly decrease Fli-1 specific activation of the G-CSF promoter. Thus, acetylation appears to be an important mechanism behind Fli-1 driven activation of the G-CSF promoter. These results further support the theory that Fli-1 plays a major role in the regulation of several inflammatory mediators, ultimately affecting inflammatory disease pathogenesis.

Transcription factor Fli-1 positively regulates lipopolysaccharide-induced interleukin-27 production in macrophages

IL-27 is an important regulator of TLR4-activated innate immune. The mechanism by which IL-27 production is regulated in TLR4-activated innate immune remains largely unclear. Here we show that expression of transcription factor Fli-1 at protein level is increased in macrophages following LPS stimulation. Fli-1 overexpression increases LPS-activated IL-27 production in macrophages. Consistently, Fli-1 knockdown inhibits LPS-induced IL-27 production in macrophages. Chromatin immunoprecipitation (ChIP) assay reveals that Fli-1 binds the promoter of IL-27 p28 subunit. Further experiments manifest that Fli-1 binds the region between -250 and -150 bp upstream of the transcriptional start site of p28 gene and increases p28 gene promoter-controlled transcription. These results demonstrate that Fli-1 positively regulates IL-27 production in TLR4-activated immune response by promoting transcription of IL-27 p28 gene.

Regulation of IL-6 in Immunity and Diseases

Interleukin-6 (IL-6) is a prototypical cytokine with functional pleiotropy and plays an important role in host defense. When infections or tissue injuries occur, IL-6 is promptly produced by monocytes and macrophages and contributes to removal of infectious agents and restoration of damaged tissues through activation of immune, hematological, and acute-phase responses. Once stress is removed from the host, IL-6 synthesis ends, but uncontrolled excessive or persistent IL-6 production plays a pathological role in the development of various inflammatory diseases and cancers, indicating that IL-6 is a double-edged sword for the host. Thus, the proper IL-6 expression is very important for host defense and is strictly controlled by chromatin structure, transcriptional regulation, and posttranscriptional modification. Differentiation status of cells, various transcription factors, RNA-binding proteins, and microRNAs are involved in this process. Since it is assumed that dysregulation of any of these regulatory molecules may cause abnormal IL-6 expression in a particular disease, further elucidation of the factors and processes involved in IL-6 expression can be expected to facilitate to clarification of pathogenesis and to identification of novel target molecule(s) for specific diseases.

FLI1 Levels Impact CXCR3 Expression and Renal Infiltration of T Cells and Renal Glycosphingolipid Metabolism in the MRL/lpr Lupus Mouse Strain

The ETS factor Friend leukemia virus integration 1 (FLI1) is a key modulator of lupus disease expression. Overexpressing FLI1 in healthy mice results in the development of an autoimmune kidney disease similar to that observed in lupus. Lowering the global levels of FLI1 in two lupus strains (Fli1(+/-)) significantly improved kidney disease and prolonged survival. T cells from MRL/lpr Fli1(+/-) lupus mice have reduced activation and IL-4 production, neuraminidase 1 expression, and the levels of the glycosphingolipid lactosylceramide. In this study, we demonstrate that MRL/lpr Fli1(+/-) mice have significantly decreased renal neuraminidase 1 and lactosylceramide levels. This corresponds with a significant decrease in the number of total CD3(+) cells, as well as CD4(+) and CD44(+)CD62L(-) T cell subsets in the kidney of MRL/lpr Fli1(+/-) mice compared with the Fli1(+/+) nephritic mice. We further demonstrate that the percentage of CXCR3(+) T cells and Cxcr3 message levels in T cells are significantly decreased and correspond with a decrease in renal CXCR3(+) cells and in Cxcl9 and Cxcl10 expression in the MRL/lpr Fli1(+/-) compared with the Fli1(+/+) nephritic mice. Our results suggest that reducing the levels of FLI1 in MRL/lpr mice may be protective against development of nephritis in part through downregulation of CXCR3, reducing renal T cell infiltration and glycosphingolipid levels.