miR-155-overexpressing monocytes resemble HLAhighISG15+ synovial tissue macrophages from patients with rheumatoid arthritis and induce polyfunctional CD4+ T-cell activation.

MicroRNAs (miRs) are known to regulate pro-inflammatory effector functions of myeloid cells, and miR dysregulation is implicated in rheumatoid arthritis (RA), a condition characterized by inflammation and destruction of the joints. We showed previously that miR-155 is increased in myeloid cells in RA and induces pro-inflammatory activation of monocytes and macrophages; however, its role at the interface between innate and adaptive immunity was not defined. Here, RNA-sequencing revealed that overexpression of miR-155 in healthy donor monocytes conferred a specific gene profile which bears similarities to that of RA synovial fluid-derived CD14+ cells and HLAhighISG15+ synovial tissue macrophages, both of which are characterized by antigen-presenting pathways. In line with this, monocytes in which miR-155 was overexpressed, displayed increased expression of HLA-DR and both co-stimulatory and co-inhibitory molecules, and induced activation of polyfunctional T cells. Together, these data underpin the notion that miR-155-driven myeloid cell activation in the synovium contributes not only to inflammation but may also influence the adaptive immune response.

MicroRNA23a Overexpression in Crohn's Disease Targets Tumour Necrosis Factor Alpha Inhibitor Protein 3, Increasing Sensitivity to TNF and Modifying the Epithelial Barrier.

BACKGROUND AND AIMS: Mucosal healing is important in Crohn's disease therapies. Epithelial homeostasis becomes dysregulated in Crohn's, with increased permeability, inflammation, and diarrhoea. MicroRNAs are small non-coding RNAs that regulate gene expression and show changes in inflammatory bowel disease. Tumour necrosis factor alpha [TNFα] inhibitor protein 3 is raised in Crohn's and regulates TNFα-mediated activation of NFκB. We investigated TNFα regulation by microRNA in Crohn's disease [CD], and studied effects on epithelial permeability and inflammation. METHODS: Colonic epithelium from CD and healthy donor biopsies was isolated using laser capture microdissection, and microRNA was quantified. Tumour necrosis factor alpha inhibitor protein 3 was characterised immunohistochemically on serial sections. Expression effect of microRNA was confirmed with luciferase reporter assays. Functional barrier permeability studies and innate cytokine release were investigated with cell and explant culture studies. RESULTS: MicroRNA23a levels significantly increased in colonic Crohn's epithelium compared with healthy epithelium. Luciferase reporter assays in transfected epithelial cells confirmed that microRNA23a repressed expression via the 3' untranslated region of tumour necrosis factor alpha inhibitor protein 3 mRNA, coinciding with increased NFκB-mediated transcription. Immunohistochemical staining of TNFAIP3 protein in colonic biopsies was reduced or absent in adjacent Crohn's sections, correlating inversely with microRNA23a levels and encompassing some intercohort variation. Overexpression of microRNA23a increased epithelial barrier permeability in a colonic epithelial model and increased inflammatory cytokine release in cultured explant biopsies, mimicking Crohn's disease characteristics. CONCLUSIONS: MicroRNA23a overexpression in colonic Crohn's epithelium represses tumour necrosis factor alpha inhibitor protein 3, enhancing sensitivity to TNFα, with increased intestinal permeability and cytokine release.

Genome-Wide Posttranscriptional Dysregulation by MicroRNAs in Human Asthma as Revealed by Frac-seq.

MicroRNAs are small noncoding RNAs that inhibit gene expression posttranscriptionally, implicated in virtually all biological processes. Although the effect of individual microRNAs is generally studied, the genome-wide role of multiple microRNAs is less investigated. We assessed paired genome-wide expression of microRNAs with total (cytoplasmic) and translational (polyribosome-bound) mRNA levels employing subcellular fractionation and RNA sequencing (Frac-seq) in human primary bronchoepithelium from healthy controls and severe asthmatics. Severe asthma is a chronic inflammatory disease of the airways characterized by poor response to therapy. We found genes (i.e., isoforms of a gene) and mRNA isoforms differentially expressed in asthma, with novel inflammatory and structural pathophysiological mechanisms related to bronchoepithelium disclosed solely by polyribosome-bound mRNAs (e.g., IL1A and LTB genes or ITGA6 and ITGA2 alternatively spliced isoforms). Gene expression (i.e., isoforms of a gene) and mRNA expression analysis revealed different molecular candidates and biological pathways, with differentially expressed polyribosome-bound and total mRNAs also showing little overlap. We reveal a hub of six dysregulated microRNAs accounting for ∼90% of all microRNA targeting, displaying preference for polyribosome-bound mRNAs. Transfection of this hub in bronchial epithelial cells from healthy donors mimicked asthma characteristics. Our work demonstrates extensive posttranscriptional gene dysregulation in human asthma, in which microRNAs play a central role, illustrating the feasibility and importance of assessing posttranscriptional gene expression when investigating human disease.

A microRNA network dysregulated in asthma controls IL-6 production in bronchial epithelial cells.

MicroRNAs are short non-coding single stranded RNAs that regulate gene expression. While much is known about the effects of individual microRNAs, there is now growing evidence that they can work in co-operative networks. MicroRNAs are known to be dysregulated in many diseases and affect pathways involved in the pathology. We investigated dysregulation of microRNA networks using asthma as the disease model. Asthma is a chronic inflammatory disease of the airways characterized by bronchial hyperresponsiveness and airway remodelling. The airway epithelium is a major contributor to asthma pathology and has been shown to produce an excess of inflammatory and pro-remodelling cytokines such as TGF-ß, IL-6 and IL-8 as well as deficient amounts of anti-viral interferons. After performing microRNA arrays, we found that microRNAs -18a, -27a, -128 and -155 are down-regulated in asthmatic bronchial epithelial cells, compared to cells from healthy donors. Interestingly, these microRNAs are predicted in silico to target several components of the TGF-ß, IL-6, IL-8 and interferons pathways. Manipulation of the levels of individual microRNAs in bronchial epithelial cells did not have an effect on any of these pathways. Importantly, knock-down of the network of microRNAs miR-18a, -27a, -128 and -155 led to a significant increase of IL-8 and IL-6 expression. Interestingly, despite strong in silico predictions, down-regulation of the pool of microRNAs did not have an effect on the TGF-ß and Interferon pathways. In conclusion, using both bioinformatics and experimental tools we found a highly relevant potential role for microRNA dysregulation in the control of IL-6 and IL-8 expression in asthma. Our results suggest that microRNAs may have different roles depending on the presence of other microRNAs. Thus, interpretation of in silico analysis of microRNA function should be confirmed experimentally in the relevant cellular context taking into account interactions with other microRNAs when studying disease.

The interleukin 13 (IL-13) pathway in human macrophages is modulated by microRNA-155 via direct targeting of interleukin 13 receptor alpha1 (IL13Ralpha1).

Macrophages play a central role in the balance and efficiency of the immune response and are at the interface between innate and adaptive immunity. Their phenotype is a delicate equilibrium between the M1 (classical, pro-Th(1)) and M2 (alternative, pro-Th(2)) profiles. This balance is regulated by cytokines such as interleukin 13 (IL-13), a typical pro-M2-Th(2) cytokine that has been related to allergic disease and asthma. IL-13 binds to IL-13 receptor α1 (IL13Rα1), a component of the Type II IL-4 receptor, and exerts its effects by activating the transcription factor signal transducer and activator of transcription 6 (STAT6) through phosphorylation. MicroRNAs are short (∼22 nucleotide) inhibitory non-coding RNAs that block the translation or promote the degradation of their specific mRNA targets. By bioinformatics analysis, we found that microRNA-155 (miR-155) is predicted to target IL13Rα1. This suggested that miR-155 might be involved in the regulation of the M1/M2 balance in macrophages by modulating IL-13 effects. miR-155 has been implicated in the development of a healthy immune system and function as well as in the inflammatory pro-Th(1)/M1 immune profile. Here we have shown that in human macrophages, miR-155 directly targets IL13Rα1 and reduces the levels of IL13Rα1 protein, leading to diminished activation of STAT6. Finally we also demonstrate that miR-155 affects the IL-13-dependent regulation of several genes (SOCS1, DC-SIGN, CCL18, CD23, and SERPINE) involved in the establishment of an M2/pro-Th(2) phenotype in macrophages. Our work shows a central role for miR-155 in determining the M2 phenotype in human macrophages.

MicroRNA-155 targets SMAD2 and modulates the response of macrophages to transforming growth factor-{beta}.

Transforming growth factor-beta (TGF-ß) is a pleiotropic cytokine with important effects on processes such as fibrosis, angiogenesis, and immunosupression. Using bioinformatics, we identified SMAD2, one of the mediators of TGF-ß signaling, as a predicted target for a microRNA, microRNA-155 (miR-155). MicroRNAs are a class of small non-coding RNAs that have emerged as an important class of gene expression regulators. miR-155 has been found to be involved in the regulation of the immune response in myeloid cells. Here, we provide direct evidence of binding of miR-155 to a predicted binding site and the ability of miR-155 to repress SMAD2 protein expression. We employed a lentivirally transduced monocyte cell line (THP1-155) containing an inducible miR-155 transgene to show that endogenous levels of SMAD2 protein were decreased after sustained overexpression of miR-155. This decrease in SMAD2 led to a reduction in both TGF-ß-induced SMAD-2 phosphorylation and SMAD-2-dependent activation of the expression of the CAGA(12)LUC reporter plasmid. Overexpression of miR-155 altered the cellular responses to TGF-ß by changing the expression of a set of genes that is involved in inflammation, fibrosis, and angiogenesis. Our study provides firm evidence of a role for miR-155 in directly repressing SMAD2 expression, and our results demonstrate the relevance of one of the two predicted target sites in SMAD2 3'-UTR. Altogether, our data uncover an important role for miR-155 in modulating the cellular response to TGF-ß with possible implications in several human diseases where homeostasis of TGF-ß might be altered.

The novel RUNX3/p33 isoform is induced upon monocyte-derived dendritic cell maturation and downregulates IL-8 expression.

RUNX proteins are heterodimeric factors that play crucial roles during development and differentiation of cells of the immune system. The RUNX3 transcription factor controls lineage decisions during thymopoiesis and T-cell differentiation, and modulates myeloid cell effector functions. We now report the characterization of the human RUNX3/p33 isoform, generated by splicing out a Runt DNA-binding domain-encoding exon, and whose transcriptional activities differ from those of the prototypic RUNX3/p44 molecule. Unlike RUNX3/p44, RUNX3/p33 is induced upon maturation of monocyte-derived dendritic cells (MDDC), and is unable to transactivate the regulatory regions of the CD11a, CD11c and CD49e integrin genes. Overexpression of RUNX3/p33 in myeloid cell lines led to diminished expression of genes involved in inflammatory responses. Moreover, overexpression of RUNX3/p33 down-modulated the basal level of IL-8 production from immature monocyte-derived dendritic cells (MDDC). Besides, siRNA-mediated knock-down of RUNX3 led to diminished levels of IL-8 RNA in immature MDDC, and modulated the neutrophil-recruiting capacity of myeloid cell line supernatants. Since IL-8 promotes neutrophil chemotaxis and degranulation during inflammatory responses, and exerts mitogenic and angiogenic actions within tumor microenvironment, our results imply that myeloid RUNX3 expression regulates the recruitment of leukocytes towards inflammatory foci and might also contribute to human cancer progression.

MicroRNA-155 modulates the pathogen binding ability of dendritic cells (DCs) by down-regulation of DC-specific intercellular adhesion molecule-3 grabbing non-integrin (DC-SIGN).

MicroRNA-155 (miR-155) has been involved in the response to inflammation in macrophages and lymphocytes. Here we show how miR-155 participates in the maturation of human dendritic cells (DC) and modulates pathogen binding by down-regulating DC-specific intercellular adhesion molecule-3 grabbing non-integrin (DC-SIGN), after directly targeting the transcription factor PU.1. During the maturation of DCs, miR-155 increases up to 130-fold, whereas PU.1 protein levels decrease accordingly. We establish that human PU.1 is a direct target for miR-155 and localize the target sequence for miR-155 in the 3'-untranslated region of PU.1. Also, overexpression of miR-155 in the THP1 monocytic cell line decreases PU.1 protein levels and DC-SIGN at both the mRNA and protein levels. We prove a link between the down-regulation of PU.1 and reduced transcriptional activity of the DC-SIGN promoter, which is likely to be the basis for its reduced mRNA expression, after miR-155 overexpression. Finally, we show that, by reducing DC-SIGN in the cellular membrane, miR-155 is involved in regulating pathogen binding as dendritic cells exhibited the lower binding capacity for fungi and HIV protein gp-120 when the levels of miR-155 were higher. Thus, our results suggest a mechanism by which miR-155 regulates proteins involved in the cellular immune response against pathogens that could have clinical implications in the way pathogens enter the human organism.