A microRNA upregulated in asthma airway T cells promotes TH2 cytokine production

MicroRNA in Immune Regulation

The immune system protects us from enormously diverse microbial pathogens but needs to be tightly regulated to avoid deleterious immune-mediated inflammation and tissue damage. A wide range of molecular determinants and cellular components work in concert to control the magnitude and duration of a given immune response. In the past decade, microRNAs (miRNAs), a major class of small non-coding RNA species, have been extensively studied as key molecular players in immune regulation. In this chapter, we will discuss how miRNAs function as negative regulators to restrict innate and adaptive immune responses. Moreover, we will review the current reports regarding miRNAs in human immunological diseases. Finally, we will also address the emerging roles of other non-coding RNAs, long non-coding RNAs (lncRNAs) in particular, in the regulation of the immune system.

miR-19a promotes colitis-associated colorectal cancer by regulating tumor necrosis factor alpha-induced protein 3-NF-κB feedback loops

Chronic inflammation is believed to have a crucial role in colon cancer development. MicroRNA (miRNA) deregulation is common in human colorectal cancers, but little is known regarding whether miRNA drives tumor progression by regulating inflammation. Here, we showed that miR-19a can promote colitis and colitis-associated colon cancer (CAC) development using a CAC mouse model and an acute colitis mouse model. Tumor necrosis factor-α (TNF-α) stimulation can increase miR-19a expression, and upregulated miR-19a can in turn activate nuclear factor (NF)-κB signaling and TNF-α production by targeting TNF alpha-induced protein 3 (TNFAIP3). miR-19a inhibition can also alleviate CAC in vivo. Moreover, the regulatory effects of miR-19a on TNFAIP3 and NF-κB signaling were confirmed using tumor samples from patients with colon cancer. These new findings demonstrate that miR-19a has a direct role in upregulating NF-κB signaling and that miR-19a has roles in inflammation and CAC.

Post-transcriptional regulation of interleukin-10 in peripheral B cells of airway allergy patients

The dysfunction of peripheral immune tolerance plays an important role in the pathogenesis of allergic diseases. Recent reports indicate that micro RNA (miR)-98 is associated with the process of aberrant immune responses. This study aims to test a hypothesis that miR-98 is associated with the pathogenesis of airway allergy via interfering with the development of regulatory B cells (Breg). In this study, patients with airway allergy were recruited into this study. The frequency of Bregs was assessed by flow cytometry. The levels of miR-98 in peripheral B cells were determined by RT-qPCR. A cell-culture model of B cells was developed to test the role of miR-98 in the repressing of interleukin (IL)-10 in B cells. The results showed that the levels of IL-10 in peripheral B cells were significantly lower in patients with airway allergy as compared with healthy subjects. High levels of miR-98 (one of the miR-98 members) were detected in peripheral B cells of patients with airway allergy, which was mimicked by stimulating B cells with IL-4. Histone acetyltransferase p300 was involved in the IL-4-induced miR-98 expression. miR-98 mediated the IL-4-inhibited IL-10 expression in B cells. In conclusion, miR-98 affects the expression of IL-10 in B cells and may be a novel therapeutic target for the treatment of allergic diseases.

Micro RNA-19a suppresses thrombospondin-1 in CD35+ B cells in the intestine of mice with food allergy

Disruption of immune tolerance is associated in the pathogenesis of allergy. Thrombospondin-1 (TSP1) plays a role in the maintenance of immune tolerance, which is compromised in allergic disorders. Micro RNA (miR) is involved in the regulation of immune responses. This study tests a hypothesis that miR-17-92 cluster is involved in the regulation of TSP1 in the intestinal CD35⁺ B cells. In this study, a food allergy mouse model was developed. The intestinal B cells were isolated to be analyzed for the expression of a miR-17-92 cluster and TSP1. The role of miR-19a in the suppression of TSP1 in B cells was tested in a cell culture model. We observed that the levels of TSP1 were significantly decreased; the levels of miR-19a were significantly increased in intestinal CD35⁺ B cells of mice sensitized to ovalbumin (OVA) as compared with naïve controls. Exposure to interleukin (IL)-4 suppressed the expression of TSP1 in B cells, which was abolished by inhibition of miR-19a. miR-19a mediated the effects of IL-4 on repressing TSP1 expression in B cells. We conclude that IL-4 suppresses the expression of TSP1 in the intestinal CD35⁺ B cells via up regulating miR-19a. The miR-19a may be a target to regulate the immune tolerant status in the body.

Role of MicroRNA in the Lung's Innate Immune Response

The immune response to respiratory pathogens must be robust enough to defend the host yet properly constrained such that inflammation-induced tissue damage is avoided. MicroRNA (miRNA) are small noncoding RNA which posttranscriptionally influence gene expression. In this review, we discuss recent experimental evidence of the contribution of miRNA to the lung's response to bacterial and viral pathogens.

The RNA Binding Protein Mex-3B Is Required for IL-33 Induction in the Development of Allergic Airway Inflammation

Allergic airway inflammation is one of the primary features of allergic asthma. Interleukin-33 (IL-33) is recognized as a key pro-inflammatory cytokine that mediates allergic airway inflammation, and its expression is elevated in this condition, but little is known about the regulatory mechanisms underlying IL-33 induction. Here, we show that the RNA binding protein Mex-3B plays a critical role in the induction of IL-33 in the development of allergic airway inflammation. We generated Mex3b(-/-) mice and found that they develop significantly less airway inflammation than wild-type mice due to reduced induction of IL-33. Furthermore, we show that Mex-3B directly upregulates IL-33 expression by inhibiting miR-487b-3p-mediated repression of IL-33. Moreover, we show that inhalation of an antisense oligonucleotide targeting Mex-3B suppresses allergic airway inflammation. Our data identify a signaling pathway that post-transcriptionally regulates IL-33 expression and suggest that Mex-3B could be a promising molecular target for the treatment of allergic asthma.

Regulation of B-cell development and tolerance by different members of the miR-17∼92 family microRNAs

The molecular mechanisms that regulate B-cell development and tolerance remain incompletely understood. In this study, we identify a critical role for the miR-17∼92 microRNA cluster in regulating B-cell central tolerance and demonstrate that these miRNAs control early B-cell development in a cell-intrinsic manner. While the cluster member miR-19 suppresses the expression of Pten and plays a key role in regulating B-cell tolerance, miR-17 controls early B-cell development through other molecular pathways. These findings demonstrate differential control of two closely linked B-cell developmental stages by different members of a single microRNA cluster through distinct molecular pathways.

MicroRNA cluster 17∼92 plays a critical role in B-cell differentiation. Here the authors show that miR-19 regulates B-cell tolerance via suppressing the expression of PTEN, whereas miR- 17 is essential for early B-cell development independently of Pten, Phlpp2, or Bim.

MicroRNA-mediated Th2 bias in methimazole-induced acute liver injury in mice

MicroRNA (miRNA) is a class of small non-coding RNAs containing approximately 20 nucleotides that negatively regulate target gene expression. Little is known about the role of individual miRNAs and their targets in immune- and inflammation-related responses in drug-induced liver injury. In the present study, involvement of miRNAs in the T helper (Th) 2-type immune response was investigated using a methimazole (MTZ)-induced liver injury mouse model. Co-administration of L-buthionine-S,R-sulfoximine and MTZ induced acute hepatocellular necrosis and elevated plasma levels of alanine aminotransferase (ALT) from 4h onward in female Balb/c mice. The hepatic mRNA expression of Th2 promotive factors was significantly increased concomitantly with plasma ALT levels. In contrast, the hepatic mRNA expression of Th2 suppressive factors was significantly decreased during the early phase of liver injury. Comprehensive profiling of hepatic miRNA expression was analyzed before the onset of MTZ-induced liver injury. Using in silico prediction of miRNAs that possibly regulate Th2-related genes and subsequent quantification, we identified up-regulation of expression of miR-29b-1-5p and miR-449a-5p. Among targets of these miRNAs, down-regulation of Th2 suppressive transcription factors, such as SRY-related HMG-box 4 (SOX4) and lymphoid enhancer factor-1 (LEF1), were observed from the early phase of liver injury. In conclusion, negative regulation of the expression of SOX4 by miR-29b-1-5p and that of LEF1 by miR-449a-5p is suggested to play an important role in the development of Th2 bias in MTZ-induced liver injury.

MicroRNA expression profiling in children with different asthma phenotypes

An improved understanding of the molecular mechanisms in asthma through exploring the role of microRNAs may offer promise to reveal new approaches for primary prevention and identification of new therapeutic targets in childhood asthma. The primary goal of this study is to identify the microRNAs that play a role in the pathogenesis of asthma in pediatric age group. The secondary goal is to analyze these microRNAs according to the asthma phenotype, atopic status, and severity of the disease exacerbation. To our knowledge, this is the first research project in the literature which studies the relationship between microRNA expression and the severity of childhood asthma. One hundred children between 6 and 18 years old with a diagnosis of asthma, and 100 age-matched healthy children were enrolled in this study, and the analyses of microRNA expression profiles were performed in the Medical Genetics Laboratories of Ege University between November 2009 and June 2010. The expression of 10 microRNAs were shown to be higher in patients with more severe asthma, and the expression of these microRNAs were also found to be higher in patients who present with more severe acute asthma exacerbation symptoms (P < 0.001). Also, five microRNAs were found to be expressed more than twofold in allergic patients when compared to non-allergic participants (P <0.001). Asthma is one of the best examples of complex genetic diseases, and further studies, which will investigate the relationship between these microRNA's and their target genes, are needed to learn more about the specific roles of microRNAs in respiratory diseases. Pediatr Pulmonol. 2016;51:582-587. © 2015 Wiley Periodicals, Inc.

Posttranscriptional and Translational Control of Gene Regulation in CD4+ T Cell Subsets

The immune system is under strict regulatory control to ensure homeostasis of inflammatory responses, lying dormant when not needed but quick to act when called upon. Small changes in gene expression can lead to drastic changes in lineage commitment, cellular function, and immunity. Conventional assessment of these changes centered on the analysis of mRNA levels through a variety of methodologies, including microarrays. However, mRNA synthesis does not always correlate directly to protein synthesis and downstream functional activity. Work conducted in recent years has begun to shed light on the various posttranscriptional changes that occur in response to a dynamic external environment that a given cell type encounters. We provide a critical review of key posttranscriptional mechanisms (i.e., microRNA) and translational mechanisms of regulation of gene expression in the immune system, with a particular emphasis on these regulatory processes in various CD4(+) T cell subsets.

Micro RNA-17-92 cluster mediates interleukin-4-suppressed IL-10 expression in B cells

The pathogenesis of allergen-related inflammation in the intestine is to be further understood. Micro RNA (miR) can regulate immune responses. This study aims to investigate the role of miR-17-92 cluster in the induction of food allergen-related inflammation in the intestine. In this study, a mouse model of food allergen-related intestinal inflammation was developed. Expression of miR-17-92 cluster in B cells of the intestinal mucosa was analyzed by real time quantitative RT-PCR. The results showed that the levels of miR-19a, one of the members of the miR-17-92 cluster, were detected in the B cells of the intestine of mice sensitized to ovalbumin, which was significantly higher than that in naïve control mice. The expression of IL-10 by B cells was significantly lower in the sensitized mice as compared with naive control mice. Exposure to IL-4 in the culture increased the expression of miR-19a as well as suppression the expression of IL-10 in B cells via remolding DNA structure at the IL-10 promoter locus. We conclude that B cells from sensitized mice show higher levels of miR-19a, which plays an important role in the suppression of IL-10 in the B cells.

Contribution of MicroRNAs to autoimmune diseases

MicroRNAs are a class of evolutionarily conserved, short non-coding RNAs that post-transcriptionally modulate the expression of multiple target genes. They are implicated in almost every biological process, including pathways involved in immune homeostasis, such as immune cell development, central and peripheral tolerance, and T helper cell differentiation. Alterations in miRNA expression and function can lead to major dysfunction of the immune system and mediate susceptibility to autoimmune disease. Here, we discuss the role of miRNAs in the maintenance of immune tolerance to self-antigens and the gain or loss of miRNA functions on tissue inflammation and autoimmunity.

MicroRNAs 24 and 27 Suppress Allergic Inflammation and Target a Network of Regulators of T Helper 2 Cell-Associated Cytokine Production

MicroRNAs (miRNAs) are important regulators of cell fate decisions in immune responses. They act by coordinate repression of multiple target genes, a property that we exploited to uncover regulatory networks that govern T helper-2 (Th2) cells. A functional screen of individual miRNAs in primary T cells uncovered multiple miRNAs that inhibited Th2 cell differentiation. Among these were miR-24 and miR-27, miRNAs coexpressed from two genomic clusters, which each functioned independently to limit interleukin-4 (IL-4) production. Mice lacking both clusters in T cells displayed increased Th2 cell responses and tissue pathology in a mouse model of asthma. Gene expression and pathway analyses placed miR-27 upstream of genes known to regulate Th2 cells. They also identified targets not previously associated with Th2 cell biology which regulated IL-4 production in unbiased functional testing. Thus, elucidating the biological function and target repertoire of miR-24 and miR-27 reveals regulators of Th2 cell biology.

Emerging Roles for MicroRNAs in T Follicular Helper Cell Differentiation

T follicular helper (Tfh) cells are essential for the formation of germinal centers (GCs) and the development of long-lived humoral immunity. Tfh cell differentiation is a multistep process driven by the balanced expression of key transcription factors that form a regulatory network in which small changes in gene expression determine the Tfh cell fate decision. Here, we review recent findings that have revealed that certain microRNAs act as important mediators within this network, with roles in tuning gene expression. We integrate these findings into the current understanding of the mechanisms governing T helper cell differentiation, and propose a model in which the establishment of Tfh cell identity is dependent on the differential expression and concerted action of distinct microRNAs and transcription factors.

Toll-Like Receptors in Cystic Fibrosis: Impact of Dysfunctional microRNA on Innate Immune Responses in the Cystic Fibrosis Lung

Toll-like receptors (TLRs) are a class of pattern recognition receptors that are particularly expressed in the sentinel and epithelial cells in the body, including the lung. They are central players in the innate immune system in response to microbial infection, and are the triggers of a complex pathway network that both promotes the inflammatory response and influences the adaptive immune response. These pathways are transiently and finely tuned by cellular factors, including a cell's microRNA response program. MicroRNAs are small, non-coding RNAs that specifically regulate gene expression. In this article, we review the disease-specific microRNA regulatory network of cystic fibrosis, a debilitating and ultimately fatal disease and, specifically, its effect on TLR signalling.

An integrated miRNA functional screening and target validation method for organ morphogenesis

The relative ease of identifying microRNAs and their increasing recognition as important regulators of organogenesis motivate the development of methods to efficiently assess microRNA function during organ morphogenesis. In this context, embryonic organ explants provide a reliable and reproducible system that recapitulates some of the important early morphogenetic processes during organ development. Here we present a method to target microRNA function in explanted mouse embryonic organs. Our method combines the use of peptide-based nanoparticles to transfect specific microRNA inhibitors or activators into embryonic organ explants, with a microRNA pulldown assay that allows direct identification of microRNA targets. This method provides effective assessment of microRNA function during organ morphogenesis, allows prioritization of multiple microRNAs in parallel for subsequent genetic approaches, and can be applied to a variety of embryonic organs.

Differential gene network analysis for the identification of asthma-associated therapeutic targets in allergen-specific T-helper memory responses

BACKGROUND

Asthma is strongly associated with allergic sensitization, but the mechanisms that determine why only a subset of atopics develop asthma are not well understood. The aim of this study was to test the hypothesis that variations in allergen-driven CD4 T cell responses are associated with susceptibility to expression of asthma symptoms.

METHODS

The study population consisted of house dust mite (HDM) sensitized atopics with current asthma (n = 22), HDM-sensitized atopics without current asthma (n = 26), and HDM-nonsensitized controls (n = 24). Peripheral blood mononuclear cells from these groups were cultured in the presence or absence of HDM extract for 24 h. CD4 T cells were then isolated by immunomagnetic separation, and gene expression patterns were profiled on microarrays.

RESULTS

Differential network analysis of HDM-induced CD4 T cell responses in sensitized atopics with or without asthma unveiled a cohort of asthma-associated genes that escaped detection by more conventional data analysis techniques. These asthma-associated genes were enriched for targets of STAT6 signaling, and they were nested within a larger coexpression module comprising 406 genes. Upstream regulator analysis suggested that this module was driven primarily by IL-2, IL-4, and TNF signaling; reconstruction of the wiring diagram of the module revealed a series of hub genes involved in inflammation (IL-1B, NFkB, STAT1, STAT3), apoptosis (BCL2, MYC), and regulatory T cells (IL-2Ra, FoxP3). Finally, we identified several negative regulators of asthmatic CD4 T cell responses to allergens (e.g. IL-10, type I interferons, microRNAs, drugs, metabolites), and these represent logical candidates for therapeutic intervention.

CONCLUSION

Differential network analysis of allergen-induced CD4 T cell responses can unmask covert disease-associated genes and pin point novel therapeutic targets.

The microRNA miR-148a functions as a critical regulator of B cell tolerance and autoimmunity

Autoreactive B cells have critical roles in a large diversity of autoimmune diseases, but the molecular pathways that control these cells remain poorly understood. We performed an in vivo functional screen of a lymphocyte-expressed microRNA library and identified miR-148a as a potent regulator of B cell tolerance. Elevated miR-148a expression impaired B cell tolerance by promoting the survival of immature B cells after engagement of the B cell antigen receptor by suppressing the expression of the autoimmune suppressor Gadd45α, the tumor suppressor PTEN and the pro-apoptotic protein Bim. Furthermore, increased expression of miR-148a, which occurs frequently in patients with lupus and lupus-prone mice, facilitated the development of lethal autoimmune disease in a mouse model of lupus. Our studies demonstrate a function for miR-148a as a regulator of B cell tolerance and autoimmunity.

Challenges and Current Efforts in the Development of Biomarkers for Chronic Inflammatory and Remodeling Conditions of the Lungs

This review discusses biomarkers that are being researched for their usefulness to phenotype chronic inflammatory lung diseases that cause remodeling of the lung's architecture. The review focuses on asthma, chronic obstructive pulmonary disease (COPD), and pulmonary hypertension. Bio-markers of environmental exposure and specific classes of biomarkers (noncoding RNA, metabolism, vitamin, coagulation, and microbiome related) are also discussed. Examples of biomarkers that are in clinical use, biomarkers that are under development, and biomarkers that are still in the research phase are discussed. We chose to present examples of the research in biomarker development by diseases, because asthma, COPD, and pulmonary hypertension are distinct entities, although they clearly share processes of inflammation and remodeling.

Targeting MicroRNA Function in Respiratory Diseases: Mini-Review

MicroRNAs (miRNAs) are small non-coding RNA molecules that modulate expression of the majority of genes by inhibiting protein translation. Growing literature has identified functional roles for miRNAs across a broad range of biological processes. As such, miRNAs are recognized as potential disease biomarkers and novel targets for therapies. While several miRNA-targeted therapies are currently in clinical trials (e.g., for the treatment of hepatitis C virus infection and cancer), no therapies have targeted miRNAs in respiratory diseases in the clinic. In this mini-review, we review the current knowledge on miRNA expression and function in respiratory diseases, intervention strategies to target miRNA function, and considerations specific to respiratory diseases. Altered miRNA expression profiles have been reported in a number of respiratory diseases, including asthma, chronic obstructive pulmonary disease, cystic fibrosis, and idiopathic pulmonary fibrosis. These include alterations in isolated lung tissue, as well as sputum, bronchoalveolar lavage fluids and peripheral blood or serum. The observed alterations in easily accessible body fluids (e.g., serum) have been proposed as new biomarkers that may inform disease diagnosis and patient management. In a subset of studies, miRNA-targeted interventions also improved disease outcomes, indicating functional roles for altered miRNA expression in disease pathogenesis. In fact, direct administration of miRNA-targeting molecules to the lung has yielded promising results in a number of animal models. The ability to directly administer compounds to the lung holds considerable promise and may limit potential off-target effects and side effects caused by the systemic administration required to treat other diseases.

miR-23∼27∼24 clusters control effector T cell differentiation and function

The miR-23∼27∼24 clusters control differentiation of effector T cells. In particular, miR-24 targets IL-4 and miR-27 targets GATA3, thus collaborating in the control of Th2 immunity.

Coordinated repression of gene expression by evolutionarily conserved microRNA (miRNA) clusters and paralogs ensures that miRNAs efficiently exert their biological impact. Combining both loss- and gain-of-function genetic approaches, we show that the miR-23∼27∼24 clusters regulate multiple aspects of T cell biology, particularly helper T (Th) 2 immunity. Low expression of this miRNA family confers proper effector T cell function at both physiological and pathological settings. Further studies in T cells with exaggerated regulation by individual members of the miR-23∼27∼24 clusters revealed that miR-24 and miR-27 collaboratively limit Th2 responses through targeting IL-4 and GATA3 in both direct and indirect manners. Intriguingly, although overexpression of the entire miR-23 cluster also negatively impacts other Th lineages, enforced expression of miR-24, in contrast to miR-23 and miR-27, actually promotes the differentiation of Th1, Th17, and induced regulatory T cells, implying that under certain conditions, miRNA families can fine tune the biological effects of their regulation by having individual members antagonize rather than cooperate with each other. Together, our results identify a miRNA family with important immunological roles and suggest that tight regulation of miR-23∼27∼24 clusters in T cells is required to maintain optimal effector function and to prevent aberrant immune responses.

Regulation of IL-4 Expression in Immunity and Diseases

IL-4 was first identified as a T cell-derived growth factor for B cells. Studies over the past several decades have markedly expanded our understanding of its cellular sources and function. In addition to T cells, IL-4 is produced by innate lymphocytes, such as NTK cells, and myeloid cells, such as basophils and mast cells. It is a signature cytokine of type 2 immune response but also has a nonimmune function. Its expression is tightly regulated at several levels, including signaling pathways, transcription factors, epigenetic modifications, microRNA, and long noncoding RNA. This chapter will review in detail the molecular mechanism regulating the cell type-specific expression of IL-4 in physiological and pathological type 2 immune responses.

Inhibition of the kinase ITK in a mouse model of asthma reduces cell death and fails to inhibit the inflammatory response

Interleukin-2 (IL-2)-inducible T cell kinase (ITK) mediates T cell receptor (TCR) signaling primarily to stimulate the production of cytokines, such as IL-4, IL-5, and IL-13, from T helper 2 (TH2) cells. Compared to wild-type mice, ITK knockout mice are resistant to asthma and exhibit reduced lung inflammation and decreased amounts of TH2-type cytokines in the bronchoalveolar lavage fluid. We found that a small-molecule selective inhibitor of ITK blocked TCR-mediated signaling in cultured TH2 cells, including the tyrosine phosphorylation of phospholipase C-γ1 (PLC-γ1) and the secretion of IL-2 and TH2-type cytokines. Unexpectedly, inhibition of the kinase activity of ITK during or after antigen rechallenge in an ovalbumin-induced mouse model of asthma failed to reduce airway hyperresponsiveness and inflammation. Rather, in mice, pharmacological inhibition of ITK resulted in T cell hyperplasia and the increased production of TH2-type cytokines. Thus, our studies predict that inhibition of the kinase activity of ITK may not be therapeutic in patients with asthma.

miR-155-SOCS1 as a Functional Axis: Satisfying the Burden of Proof

The importance of individual target genes for miRNA activity has been difficult to establish. In this issue of Immunity, Lu et al. (2015) disrupt the miR-155 binding site in the SOCS1 3' UTR in the mouse germline and show that this axis is important for T and NK cell function.

ncRNA-regulated immune response and its role in inflammatory lung diseases

Despite the greatly expanded knowledge on the regulation of immune response by protein molecules, there is increasing understanding that noncoding RNAs (ncRNAs) are also an integral component of this regulatory network. Abnormal immune response serves a central role in the initiation, progression, and exacerbation of inflammatory lung diseases, such as asthma, chronic obstructive pulmonary disease, cystic fibrosis, and acute respiratory distress syndrome/acute lung injury. Dysregulation of ncRNAs has been linked to various immunopathologies. In this review, we highlighted the role of ncRNAs in the regulation of innate and adaptive immunity and summarized recent findings that ncRNAs participate in the pathogenesis of inflammatory lung diseases via their regulation of pulmonary immunity. We also discussed therapeutic potentials for targeting ncRNAs to treat these lung disorders.

Noncoding RNAs and chronic inflammation: Micro-managing the fire within

Inflammatory responses are essential for the clearance of pathogens and the repair of injured tissues; however, if these responses are not properly controlled chronic inflammation can occur. Chronic inflammation is now recognized as a contributing factor to many age-associated diseases including metabolic disorders, arthritis, neurodegeneration, and cardiovascular disease. Due to the connection between chronic inflammation and these diseases, it is essential to understand underlying mechanisms behind this process. In this review, factors that contribute to chronic inflammation are discussed. Further, we emphasize the emerging roles of microRNAs (miRNAs) and other noncoding RNAs (ncRNA) in regulating chronic inflammatory states, making them important future diagnostic markers and therapeutic targets.

MicroRNA regulation of allergic inflammation and asthma

Allergic diseases are prevalent and clinically heterogeneous, and are the pathologic consequence of inappropriate or exaggerated type 2 immune responses. In this review, we explore the role of microRNAs (miRNAs) in regulating allergic inflammation. We discuss how miRNAs, acting through target genes to modulate gene expression networks, impact multiple facets of immune cell function critical for type 2 immune responses including cell survival, proliferation, differentiation, and effector functions. Human and mouse studies indicate that miRNAs are significant regulators of allergic immune responses. Finally, investigations of extracellular miRNAs offer promise for noninvasive biomarkers and therapeutic strategies for allergy and asthma.

Altered expression and editing of miRNA-100 regulates iTreg differentiation

RNA editing of miRNAs, especially in the seed region, adds another layer to miRNA mediated gene regulation which can modify its targets, altering cellular signaling involved in important processes such as differentiation. In this study, we have explored the role of miRNA editing in CD4⁺ T cell differentiation. CD4⁺ T cells are an integral component of the adaptive immune system. Naïve CD4⁺ T cells, on encountering an antigen, get differentiated either into inflammatory subtypes like Th1, Th2 or Th17, or into immunosuppressive subtype Treg, depending on the cytokine milieu. We found C-to-U editing at fifth position of mature miR-100, specifically in Treg. The C-to-U editing of miR-100 is functionally associated with at least one biologically relevant target change, from MTOR to SMAD2. Treg cell polarization by TGFβ1 was reduced by both edited and unedited miR-100 mimics, but percentage of Treg in PBMCs was only reduced by edited miR-100 mimics, suggesting a model in which de-repression of MTOR due to loss of unedited mir-100, promotes tolerogenic signaling, while gain of edited miR-100 represses SMAD2, thereby limiting the Treg. Such delicately counterbalanced systems are a hallmark of immune plasticity and we propose that miR-100 editing is a novel mechanism toward this end.

A Single miRNA-mRNA Interaction Affects the Immune Response in a Context- and Cell-Type-Specific Manner

MicroRNA (miRNA)-dependent regulation of gene expression confers robustness to cellular phenotypes and controls responses to extracellular stimuli. Although a single miRNA can regulate expression of hundreds of target genes, it is unclear whether any of its distinct biological functions can be due to the regulation of a single target. To explore in vivo the function of a single miRNA-mRNA interaction, we mutated the 3' UTR of a major miR-155 target (SOCS1) to specifically disrupt its regulation by miR-155. We found that under physiologic conditions and during autoimmune inflammation or viral infection, some immunological functions of miR-155 were fully or largely attributable to the regulation of SOCS1, whereas others could be accounted only partially or not at all by this interaction. Our data suggest that the role of a single miRNA-mRNA interaction is dependent on cell type and biological context.

Noncoding RNAs, cytokines, and inflammation-related diseases

Chronic inflammation is involved in the onset and development of many diseases, including obesity, atherosclerosis, type 2 diabetes, osteoarthritis, autoimmune and degenerative diseases, asthma, periodontitis, and cirrhosis. The inflammation process is mediated by chemokines, cytokines, and different inflammatory cells. Although the molecules and mechanisms that regulate this primary defense mechanism are not fully understood, recent findings offer a putative role of noncoding RNAs, especially microRNAs (miRNAs), in the progression and management of the inflammatory response. These noncoding RNAs are crucial for the stability and maintenance of gene expression patterns that characterize some cell types, tissues, and biologic responses. Several miRNAs, such as miR-126, miR-132, miR-146, miR-155, and miR-221, have emerged as important transcriptional regulators of some inflammation-related mediators. Additionally, little is known about the involvement of long noncoding RNAs, long intergenic noncoding RNAs, and circular RNAs in inflammation-mediated processes and the homeostatic imbalance associated with metabolic disorders. These noncoding RNAs are emerging as biomarkers with diagnosis value, in prognosis protocols, or in the personalized treatment of inflammation-related alterations. In this context, this review summarizes findings in the field, highlighting those noncoding RNAs that regulate inflammation, with emphasis on recognized mediators such as TNF-α, IL-1, IL-6, IL-18, intercellular adhesion molecule 1, VCAM-1, and plasminogen activator inhibitor 1. The down-regulation or antagonism of the noncoding RNAs and the administration of exogenous miRNAs could be, in the near future, a promising therapeutic strategy in the treatment of inflammation-related diseases.

MicroRNA regulation of lymphocyte tolerance and autoimmunity

Understanding the cell-intrinsic cues that permit self-reactivity in lymphocytes, and therefore autoimmunity, requires an understanding of the transcriptional and posttranscriptional regulation of gene expression in these cells. In this Review, we address seminal and recent research on microRNA (miRNA) regulation of central and peripheral tolerance. Human and mouse studies demonstrate that the PI3K pathway is a critical point of miRNA regulation of immune cell development and function that affects the development of autoimmunity. We also discuss how miRNA expression profiling in human autoimmune diseases has inspired mechanistic studies of miRNA function in the pathogenesis of multiple sclerosis, rheumatoid arthritis, systemic lupus erythematosus, type 1 diabetes, and asthma.

Prospects for Therapeutic Targeting of MicroRNAs in Human Immunological Diseases

MicroRNAs (miRNAs) are endogenous oligoribonucleotides with exciting therapeutic potential. Early studies established a clear role for miRNAs in leukocyte biology. The first miRNA-based therapy, miravirsen, is now in phase 2 clinical trials, making the reality of these therapies undeniable. The capacity for miRNAs to fine-tune inflammatory signaling make them attractive treatment targets for immunological diseases. Nonetheless, the degree of redundancy among miRNAs, coupled with the promiscuity of miRNA binding sites in the transcriptome, require consideration when designing miRNA-directed interventions. Altered miRNA expression occurs across a range of inflammatory conditions, including inflammatory bowel disease, arthritis, and diabetes. However, very few studies successfully treated murine models of immunological diseases with miRNA-based approaches. While discussing recent studies targeting miRNAs to treat immunological conditions, we also reflect on the risks of miRNA targeting and showcase some newer delivery systems that may improve the pharmacological profile of this class of therapeutics.

Targeting microRNAs for immunomodulation

microRNAs (miRNA) are small regulatory RNAs exerting pleiotropic functions in virtually any immune cell-type. Dozens of miRNAs with a known function in the immune system constitute interesting drug targets for immunomodulation. Chemical modifications of nucleic acid-based miRNA mimics and inhibitors largely solved instability issues but delivery to immune cells remains a major challenge. However, recent success targeting the acidic tumor microenvironment is very promising for inflammatory diseases. Moreover, small molecules are being explored as an interesting alternative. Although RNA is often considered 'undruggable' by small molecules recent progress modulating miRNA function through small molecules is encouraging. Computational approaches even allow predictions about specific small molecule/RNA interactions. Finally, recent clinical success demonstrates that drugs targeting RNAs work in humans.

Cross-regulation between cytokine and microRNA pathways in T cells

microRNA (miRNA) mediated regulation of protein expression has emerged as an important mechanism in T-cell physiology, from development and survival to activation, proliferation, and differentiation. One of the major classes of proteins involved in these processes are cytokines, which are both key input signals and major products of T-cell function. Here, we summarize the current data on the molecular cross-talk between cytokines and miRNAs: how cytokines regulate miRNA expression, and how specific miRNAs control cytokine production in T cells. We also describe the inflammatory consequences of deregulating the miRNA/cytokine axis in mice and humans. We believe this topical area will have key implications for immune modulation and treatment of autoimmune pathology.

Functional interactions among members of the miR-17-92 cluster in lymphocyte development, differentiation and malignant transformation

The miR-17-92 cluster is a prototypical example of a polycistronic miRNA gene. Recently, miR-17-92 has emerged as a pleiotropic regulator in immune system. Its loss or deregulation leads to defects in lymphocyte development and response, and lymphoma development. Although the six individual miRNAs of the cluster are expressed together from the same primary transcript, their relative abundance, functional contributions and interactions vary in different cellular contexts.

The role of microRNAs in equine medicine: a review

The search for new markers of diseases in human as well as veterinary medicine is ongoing. Recently, microRNAs (miRNAs or miRs) have emerged as potential new biomarkers. MiRNAs are short sequences of RNA (∼22 nucleotides) that regulate gene expression via their target messenger RNA (mRNA). Circulating miRNAs in blood can be used as novel diagnostic markers for diseases due to their evolutionary conservation and stability. As a consequence of their systemic and manifold effects on the gene expression in various target organs, the concept that miRNAs could function as hormones has been suggested. This review summarizes the biogenesis, maturation, and stability of miRNAs and discusses their use as potential biomarkers in equine medicine. To date, over 700 equine miRNAs are identified with distinct subsets of miRNAs differentially expressed in a tissue-specific manner. A physiological involvement of various miRNAs in the regulation of cell survival, steroidogenesis, and differentiation during follicle selection and ovulation in the monovular equine ovary has been demonstrated. Furthermore, miRNAs might be used as novel diagnostic markers for myopathies such as polysaccharide storage myopathy and recurrent exertional rhabdomyolysis as well as osteochondrosis. Preliminary data indicate that miRNAs in blood might play important roles in equine glucose metabolism pathway. Of note, breed differences have been reported regarding the normal equine miRNA signature. For disease prevention, it is of utmost importance to identify disease-associated biomarkers which help detect diseases before symptoms appear. As such, circulating miRNAs represent promising novel diagnostic markers in equine medicine.

Kinetics of microRNA Expression in Bronchoalveolar Lavage Fluid Samples

Levels of microRNAs (miRNAs) are increasingly assessed in biological fluids, for example, in samples obtained by bronchoalveolar lavage (BAL). "Post-collection kinetics" of miRNA expression levels, however, have not been investigated to date. In these experiments, we analyzed the dynamic expression profile of 5 different miRNAs (miR-17, miR-19b, miR-20b, miR-125a, and miR-223-3p) in BAL within the first 24 h following collection by routine bronchoscopy. miRNAs were quantified 0, 1, 4, 8, and 24 h after collection in samples that were kept at 4 °C or at room temperature. The expression of all five miRNAs was found to remain stable between the first 8 h after collection. 24 h after collection miRNAs faced substantial alterations in their expression profile. These data emphasize that BAL samples intended for further miRNA analysis can be handled at room temperature within the first 8 h after bronchoscopy.