Epithelium-Intrinsic MicroRNAs Contribute to Mucosal Immune Homeostasis by Promoting M-Cell Maturation

Role of microRNAs in immunoregulatory functions of epithelial cells

Epithelial cells (ECs) provide the first line of defense against microbial threats and environmental challenges. They participate in the host's immune responses via the expression and secretion of various immune-related molecules such as cytokines and chemokines, as well as interaction with immune cells. A growing body of evidence suggests that the dysregulated function of ECs can be involved in the pathophysiology of a broad range of infectious, autoimmune, and inflammatory diseases, including inflammatory bowel disease (IBD), asthma, multiple sclerosis, and rheumatoid arthritis. To maintain a substantial immunoregulatory function of ECs, precise expression of different molecules and their regulatory effects are indispensable. MicroRNAs (miRNAs, miRs) are small non-coding RNAs that regulate gene expression commonly at post-transcriptional level through degradation of target messenger RNAs (mRNAs) or suppression of protein translation. MiRNAs implicate as critical regulators in many cellular processes, including apoptosis, growth, differentiation, and immune response. Due to the crucial roles of miRNAs in such a vast range of biological processes, they have become the spotlight of biological research for more than two decades, but we are still at the beginning stages of the use of miRNA-based therapies in the improvement of human health. Hence, in the present paper, attempts are made to provide a comprehensive overview with regard to the roles of miRNAs in the immunoregulatory functions of ECs. A better understanding of the molecular mechanisms through which immunoregulatory properties of ECs are manifested, could aid the development of efficient strategies to prevent and treat multiple human diseases.

Goblet cell-associated antigen passage: A gatekeeper of the intestinal immune system

Effective delivery of luminal antigens to the underlying immune system is the initial step in generating antigen-specific responses in the gut. However, a large body of information regarding the immune response activation process remains unknown. Recently, goblet cells (GCs) have been reported to form goblet cell-associated antigen passages (GAPs). Luminal antigens can be transported inside GAPs and reach subepithelial immune cells to induce antigen-specific immune responses, contributing largely to gut homeostasis and the prevention of some intestinal diseases like allergic enteritis and bacterial translocation. In this article, we summarized recent observations on the formation of intestinal GAPs and their roles in mucosal immunity. We hope that this review can offer a fresh perspective and valuable insights for clinicians and researchers interested in studying the intestinal immune system.

MicroRNA-1297 participates in the repair of intestinal barrier injury in patients with HIV/AIDS via negative regulation of PLCβ1

To explore the role of the miRNA-1297/phospholipase Cβ1 (PLCβ1) axis in intestinal barrier injury. Abnormally expressed miR-1297 and its target gene PLCβ1 as well as their transcriptome sequencing were confirmed by bioinformatics analysis. Next, the intestinal barrier injury was induced by lipopolysaccharide (LPS) in the CCCHIE-2 cells. Subsequently, the impacts of miR-1297 and PLCβ1 on the transcriptome were estimated. QRT-PCR and Western blotting were conducted to detect the relative mRNA and protein expressions, respectively. The cell viability and permeability were analyzed by MTT assay and fluorescent yellow detection. miR-1297 was significantly upregulated in patients with human immunodeficiency virus/acquired immunodeficiency syndrome and targeted PLCβ1. Moreover, overexpressed PLCβ1 was mainly enriched in the transforming growth factor-beta signaling pathway, while the knockdown of miR-1297 was focused on the arginine biosynthesis pathway. The overexpression of miR-1297 could reduce the PLCβ1 expression and inhibit the viability of CCCHIE-2 cells injured by LPS, while the effect of the downregulation of miR-1297 was on the opposite. Western blotting and cell fluorescence localization experiments revealed that the inhibition of miR-1297 increased the expressions of PLCβ1 and ZO-1. In addition, the upregulation of miR-1297 strengthened the permeability in cells injured by LPS, as did the knockdown of PLCβ1. miR-1297 could restrain the repair of intestinal barrier injury via negatively regulating PLCβ1 and its tight junction downstream protein ZO-1 in CCC-HIE-2 cells injured by LPS, which indicated that PLCβ1 and miR-1297 might be important targets for the repair of intestinal barrier injury.

Nanoparticulate strategies for the delivery of miRNA mimics and inhibitors in anticancer therapy and its potential utility in oral submucous fibrosis

MicroRNAs (miRNAs) are naturally occurring noncoding RNAs with multiple functionalities. They are dysregulated in several conditions and can serve as disease biomarkers, therapeutic targets and therapeutic agents. Translation of miRNA therapeutics to the clinic poses several challenges related to the safe and effective delivery of these agents to the site of action. Nanoparticulate carriers hold promise in this area by enhancing targeting efficiency and reducing off-target effects. This paper reviews recent advances in the delivery strategies of miRNAs in anticancer therapy, with a focus on lipid-based, polymeric, inorganic platforms, cell membrane-derived vesicles and bacterial minicells. Additionally, this review explores the potentiality of miRNAs in the treatment of oral submucous fibrosis, a potentially premalignant condition of the oral cavity with no definitive treatment to date.

Intestinal miRNAs regulated in response to dietary lipids

The role of miRNAs in intestinal lipid metabolism is poorly described. The small intestine is constantly exposed to high amounts of dietary lipids, and it is under conditions of stress that the functions of miRNAs become especially pronounced. Approaches consisting in either a chronic exposure to cholesterol and triglyceride rich diets (for several days or weeks) or an acute lipid challenge were employed in the search for intestinal miRNAs with a potential role in lipid metabolism regulation. According to our results, changes in miRNA expression in response to fat ingestion are dependent on factors such as time upon exposure, gender and small intestine section. Classic and recent intestinal in vitro models (i.e. differentiated Caco-2 cells and murine organoids) partially mirror miRNA modulation in response to lipid challenges in vivo. Moreover, intestinal miRNAs might play a role in triglyceride absorption and produce changes in lipid accumulation in intestinal tissues as seen in a generated intestinal Dicer1-deletion murine model. Overall, despite some variability between the different experimental cohorts and in vitro models, results show that some miRNAs analysed here are modulated in response to dietary lipids, hence likely to participate in the regulation of lipid metabolism, and call for further research.

Exosome-mediated effects and applications in inflammatory bowel disease

Gut mucosal barriers, including chemical and physical barriers, spatially separate the gut microbiota from the host immune system to prevent unwanted immune responses that could lead to intestinal inflammation. In inflammatory bowel disease (IBD), there is mucosal barrier dysfunction coupled with immune dysregulation and dysbiosis. The discovery of exosomes as regulators of vital functions in both physiological and pathological processes has generated much research interest. Interestingly, exosomes not only serve as natural nanocarriers for the delivery of functional RNAs, proteins, and synthetic drugs or molecules, but also show potential for clinical applications in tissue repair and regeneration as well as disease diagnosis and prognosis. Biological or chemical modification of exosomes can broaden, change and enhance their therapeutic capability. We review the modulatory effects of exosomal proteins, RNAs and lipids on IBD components such as immune cells, the gut microbiota and the intestinal mucosal barrier. Mechanisms involved in regulating these factors towards attenuating IBD have been explored in several studies employing exosomes derived from different sources. We discuss the potential utility of exosomes as diagnostic markers and drug delivery systems, as well as the application of modified exosomes in IBD.

Comparative expression profiles of host circulating miRNAs in response to Trichinella spiralis infection

Trichinellosis is an important food-borne parasitic zoonosis throughout the world. At present, the mechanisms of Trichinella spiralis infection remain unclear. Acquiring detailed information on the host-Trichinella interaction would be beneficial for the development of new strategies for trichinellosis control. Circulating miRNAs are stably detectable in the blood of humans and animals infected with parasites. Circulating miRNAs might regulate the expression of target genes in pathological responses during infection and might be novel potential biomarkers of parasitic diseases. In the present study, a total of ten differentially expressed circulating mouse miRNAs with |log₂(fold change)| ≥ 1.0 and FDR < 0.01 were found during T. spiralis infection, of which five were upregulated and five were downregulated. GO and KEGG analyses showed that the target genes of the ten miRNAs were enriched in many signalling pathways, especially focal adhesion, MAPK pathway, and so on. The results of qRT-PCR showed that among the five upregulated miRNAs, mmu-miR-467a-3p and mmu-miR-467d-3p expression in mouse serum reached a peak at 30 days post-infection (dpi). The expression of mmu-miR-376b-3p and mmu-miR-664-3p increased significantly at 18 dpi and then decreased at 30 dpi. The expression of mmu-miR-292a-5p gradually decreased from 12 to 30 dpi. Among the 5 downregulated miRNAs, mmu-miR-199a-5p expression was significantly downregulated at 30 dpi, while the expression levels of the other four miRNAs (mmu-miR-455-5p, mmu-miR-125b-5p, mmu-miR-125a-5p, and mmu-miR-615-3p) were significantly lower compared with the control, showing a steady downregulation at different phases of infection. These findings will help to further understand the host-Trichinella interaction and provide promising serum biomarkers for trichinellosis.

MicroRNA Determines the Fate of Intestinal Epithelial Cell Differentiation and Regulates Intestinal Diseases

The rapid self-renewal of intestinal epithelial cells enhances intestinal function, promotes the nutritional needs of animals and strengthens intestinal barrier function to resist the invasion of foreign pathogens. MicroRNAs (miRNAs) are a class of short-chain, non-coding RNAs that regulate stem cell proliferation and differentiation by down-regulating hundreds of conserved target genes after transcription via seed pairing to the 3' untranslated regions. Numerous studies have shown that miRNAs can improve intestinal function by participating in the proliferation and differentiation of different cell populations in the intestine. In addition, miRNAs also contribute to disease regulation and therefore not only play a vital role in the gastrointestinal disease management but also act as blood or tissue biomarkers of disease. As changes to the levels of miRNAs can change cell fates, miRNA-mediated gene regulation can be used to update therapeutic strategies and approaches to disease treatment.

MicroRNA-mediated dynamic control of mucosal immunity

The gastrointestinal tract is a complex and important physiological and immunological organ embodying the first line of defense by which mucosal immunity regulates the immense number and diversity of naturally encountered antigens and commensal microflora. Effective microRNA (miRNA) control of transcription factors or mediators in mucosal immunity is essential to host defense and homeostasis in both physiologic and pathologic states. MiRNA biology has advanced our understanding of the immune regulatory system network at the level of post-transcriptional gene modification. Increasing knowledge on circulating miRNAs could potentially enhance diagnostic techniques in inflammatory bowel disease (IBD). Furthermore, recent findings on the dynamic role of exosomes vis-à-vis the intercellular transportation of miRNAs may provide insights on the use of miRNA as a target for treating IBD.

MicroRNA-mediated regulation of immune responses to intestinal helminth infections

Intestinal helminth infections are highly prevalent in the developing world, often resulting in chronic infection and inflicting high host morbidity. With the emergence of drug-resistant parasites, a limited number of chemotherapeutic drugs available and stalling vaccine efforts, an increased understanding of antihelminth immunity is essential to provide new avenues to therapeutic intervention. MicroRNAs are a class of small, nonprotein coding RNAs which negatively regulate mRNA translation, thus providing finite control over gene expression in a plethora of biological settings. The miRNA-mediated coordinated control of gene expression has been shown to be essential in infection and immunity, in promoting and fine-tuning the appropriate immune response. This review gathers together and discusses observations of miRNA-mediated effects on the immune system and the subsequent impact on our understanding of antihelminth immunity.

Regulatory aspects in the pharmaceutical development of nanoparticle drug delivery systems designed to cross the intestinal epithelium and M-cells

This article reviews the field of oral uptake of nanoparticles across the gastrointestinal epithelium for the period 2006-2016. Analysis is conducted from the viewpoint of i) M-cell genetics and model development, ii) drug targeting to Peyer's patches and M-cells, and iii) physicochemical interactions of nanoparticles in the intestinal milieu. In light of these recent developments, regulatory considerations in the development of orally-absorbable nanoparticle drug products are discussed and focused on Module 3.2.P sub-sections of the Common Technical Document. Particular attention is paid to novel excipients, ligands and the non-standard method of manufacture. The novelty of this drug delivery system demands not only a multi-disciplinary scientific and regulatory approach but also a risk-adjusted consideration for a system defined by both processes and specifications. Given the current state of scientific development in the field it is suggested (in the author's personal opinion) that the design of nanoparticulate drug delivery systems should be kept as simple as possible (from a regulatory and manufacturing perspective) and to target the entire gastrointestinal epithelium.

Post-Transcriptional Regulation of Toll-Interacting Protein in the Intestinal Epithelium

Immune responses against gut microbiota should be minimized to avoid unnecessary inflammation at mucosal surface. In this study, we analyzed the expression patterns of Toll-interacting protein (Tollip), an inhibitor of TLRs and IL-1 family cytokine-related intracellular signaling, in intestinal epithelial cells (IECs). Comparable mRNA expression was observed in murine small and large IECs (S-IECs and L-IECs). However, Tollip protein was only detected in L-IECs, but not in S-IECs. Similar results were obtained in germ-free mice, indicating that L-IEC-specific TOLLIP expression does not depend on bacterial colonization. Next, to understand the mechanisms underlying the post-transcriptional repression of Tollip, 3´-UTR-mediated translational regulation was evaluated. The region +1876/+2398 was responsible for the repression of Tollip expression. This region included the target sequence of miR-31. The inhibition of miR-31 restored the 3´-UTR-meditaed translational repression. In addition, miR-31 expression was significantly higher in S-IECs than in L-IECs, suggesting that miR-31 represses the translation of Tollip mRNA in S-IECs. Collectively, we conclude that the translation of Tollip is inhibited in S-IECs, at least in part, by miR-31 to yield L-IEC-specific high-level expression of the Tollip protein, which may contribute to the maintenance of intestinal homeostasis.