Association of functional polymorphisms in interferon regulatory factor 2 (IRF2) with susceptibility to systemic lupus erythematosus: a case-control association study

Regulation of IFNβ expression: focusing on the role of its promoter and transcription regulators

IFNβ is a single-copy gene without an intron. Under normal circumstances, it shows low or no expression in cells. It is upregulated only when the body needs it or is stimulated. Stimuli bind to the pattern recognition receptors (PRRs) and pass via various signaling pathways to several basic transcriptional regulators, such as IRFs, NF-кB, and AP-1. Subsequently, the transcriptional regulators enter the nucleus and bind to regulatory elements of the IFNβ promoter. After various modifications, the position of the nucleosome is altered and the complex is assembled to activate the IFNβ expression. However, IFNβ regulation involves a complex network. For the study of immunity and diseases, it is important to understand how transcription factors bind to regulatory elements through specific forms, which elements in cells are involved in regulation, what regulation occurs during the assembly of enhancers and transcription complexes, and the possible regulatory mechanisms after transcription. Thus, this review focuses on the various regulatory mechanisms and elements involved in the activation of IFNβ expression. In addition, we discuss the impact of this regulation in biology.

LncRNA XIST, as a ceRNA of miR-204, aggravates lipopolysaccharide-induced acute respiratory distress syndrome in mice by upregulating IRF2

BACKGROUND

Acute respiratory distress syndrome (ARDS) is a common clinical syndrome with high a mortality rate, which is associated with diffuse alveolar injury and capillary endothelial damage. In recent years, numerous studies have been performed to explore the roles of long non-coding RNAs (lncRNAs) in various diseases in which lncRNA serves as a microRNA (miRNA) sponge to regulate targeted gene expression. However, whether lncRNAs participate in ARDS progression remains unclear.

MATERIALS/METHODS

The dual-luciferase reporter assay was employed to identify the interaction between lncRNA XIST and miR-204, as well as the correlation between miR-204 and interferon regulatory factor 2 (IRF2). Then, PaO₂/FiO₂ was determined in lipopolysaccharide (LPS)-induced ARDS. In addition, the concentrations of cytokines, including IFN-γ, IL-6, IL-17, TNF-α, IL-1β, and IL-6R were analyzed by ELISA. lncRNA XIST, miR-204, and IRF2 levels were determined by qRT-PCR assay, and the IRF2 expression was evaluated by western blot. Furthermore, levels of inflammation and conditions of alveoli were evaluated by hematoxylin (H&E)-staining in LPS-induced ARDS.

RESULTS

Our findings indicated that lncRNA XIST served as a sponge for miR-204. miR-204 directly regulated IRF2, andlncRNA XIST upregulated IRF2 expression by targeting miR-204. LncRNA XIST and miR-204 inhibitors significantly decreased the PaO₂/FiO₂ ratio, whereas miR-204 and silencing of IRF2 significantly increased the PaO₂/FiO₂ ratio in LPS-induced ARDS. In addition, lncRNA XIST and miR-204 inhibitors significantly increased levels of IFN-γ, IL-6, IL-17, TNF-α, IL-1β, and IL-6R, whereas miR-204 and silencing of IRF2 dramatically decreased related cytokines in LPS-induced ARDS. Furthermore, we demonstrated that lncRNA XIST and miR-204 inhibitors aggravated inflammatory cell infiltration, alveolitis, and the degree of fibrosis, whereas miR-204 and silencing of IRF2 alleviated inflammation and conditions of the alveoli.

CONCLUSION

In this study, we verified that lncRNA XIST serves as a sponge for miR-204 to aggravate LPS-induced ARDS in mice by upregulating IRF2.

Therapeutic Targeting of IRFs: Pathway-Dependence or Structure-Based?

The interferon regulatory factors (IRFs) are a family of master transcription factors that regulate pathogen-induced innate and acquired immune responses. Aberration(s) in IRF signaling pathways due to infection, genetic predisposition and/or mutation, which can lead to increased expression of type I interferon (IFN) genes, IFN-stimulated genes (ISGs), and other pro-inflammatory cytokines/chemokines, has been linked to the development of numerous diseases, including (but not limited to) autoimmune and cancer. What is currently lacking in the field is an understanding of how best to therapeutically target these transcription factors. Many IRFs are regulated by post-translational modifications downstream of pattern recognition receptors (PRRs) and some of these modifications lead to activation or inhibition. We and others have been able to utilize structural features of the IRFs in order to generate dominant negative mutants that inhibit function. Here, we will review potential therapeutic strategies for targeting all IRFs by using IRF5 as a candidate targeting molecule.

IRF-2 haploinsufficiency causes enhanced imiquimod-induced psoriasis-like skin inflammation

BACKGROUNDS

IFN regulatory factor (IRF)-2 is one of the potential susceptibility genes for psoriasis, but how this gene influences psoriasis pathogenesis is unclear. Topical application of imiquimod (IMQ), a TLR7 ligand, induces psoriasis-like skin lesions in mice.

OBJECTIVE

The aim of this study was to investigate whether IRF-2 gene status would influence severity of skin disease in IMQ-treated mice.

METHODS

Imiquimod-induced psoriasis-like skin inflammation was assessed by clinical findings, histology, and cytokine expression. The effects of imiquimod or IFN on peritoneal macrophages were analyzed in vitro.

RESULTS

IMQ-induced skin inflammation assessed by clinical findings and histology was more severe in IRF-2^+/- mice than in wild-type mice. In inflamed skin, mRNA expression levels of tumor necrosis factor (TNF)-α, IL-12/23p40, IL-17A, and IL-22 were significantly elevated in IRF-2^+/- mice compared to wild-type mice. Stimulation of peritoneal macrophages by IMQ significantly increased mRNA levels of TNF-α, IL-12/23p40, IL-23p19, IL-12p35, and IL-36. Interestingly, macrophages from IRF-2^+/- mice expressed higher levels of TNF-α, IL-12/23p40, and IL-36 compared to those from wild-type mice 24 h after stimulation, while they expressed similar levels of IL-12p35 and IL-23p19. Moreover, elevated mRNA expression of inducible nitric oxide synthase was observed only in IMQ-stimulated macrophages derived from IRF-2^+/- mice, which correlated with angiogenesis in IMQ-treated ears of IRF-2^+/- mice.

CONCLUSIONS

These results suggest that IRF-2 haploinsufficiency creates heightened biologic responses to IFN-α that phenotypically lead to enhanced angiogenesis and psoriasis-like inflammation within skin.

Interferon regulatory factor signaling in autoimmune disease

Interferon regulatory factors (IRFs) play critical roles in pathogen-induced innate immune responses and the subsequent induction of adaptive immune response. Dysregulation of IRF signaling is therefore thought to contribute to autoimmune disease pathogenesis. Indeed, numerous murine in vivo studies have documented protection from or enhanced susceptibility to particular autoimmune diseases in Irf-deficient mice. What has been lacking, however, is replication of these in vivo observations in primary immune cells from patients with autoimmune disease. These types of studies are essential as the majority of in vivo data support a protective role for IRFs in Irf-deficient mice, yet IRFs are often found to be overexpressed in patient immune cells. A significant body of work is beginning to emerge from both of these areas of study - mouse and human.

Applications of Next-generation Sequencing in Systemic Autoimmune Diseases

Systemic autoimmune diseases are a group of heterogeneous disorders caused by both genetic and environmental factors. Although numerous causal genes have been identified by genome-wide association studies (GWAS), these susceptibility genes are correlated to a relatively low disease risk, indicating that environmental factors also play an important role in the pathogenesis of disease. The intestinal microbiome, as the main symbiotic ecosystem between the host and host-associated microorganisms, has been demonstrated to regulate the development of the body’s immune system and is likely related to genetic mutations in systemic autoimmune diseases. Next-generation sequencing (NGS) technology, with high-throughput capacity and accuracy, provides a powerful tool to discover genomic mutations, abnormal transcription and intestinal microbiome identification for autoimmune diseases. In this review, we briefly outlined the applications of NGS in systemic autoimmune diseases. This review may provide a reference for future studies in the pathogenesis of systemic autoimmune diseases.

B-Cell and Monocyte Contribution to Systemic Lupus Erythematosus Identified by Cell-Type-Specific Differential Expression Analysis in RNA-Seq Data

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by complex interplay among immune cell types. SLE activity is experimentally assessed by several blood tests, including gene expression profiling of heterogeneous populations of cells in peripheral blood. To better understand the contribution of different cell types in SLE pathogenesis, we applied the two methods in cell-type-specific differential expression analysis, csSAM and DSection, to identify cell-type-specific gene expression differences in heterogeneous gene expression measures obtained using RNA-seq technology. We identified B-cell-, monocyte-, and neutrophil-specific gene expression differences. Immunoglobulin-coding gene expression was altered in B-cells, while a ribosomal signature was prominent in monocytes. On the contrary, genes differentially expressed in the heterogeneous mixture of cells did not show any functional enrichment. Our results identify antigen binding and structural constituents of ribosomes as functions altered by B-cell- and monocyte-specific gene expression differences, respectively. Finally, these results position both csSAM and DSection methods as viable techniques for cell-type-specific differential expression analysis, which may help uncover pathogenic, cell-type-specific processes in SLE.