JVII Journal

1.        Keywords: Autoimmunity; Crohn’s Disease; IL-17; Inflammatory Bowel Disease; miR-301a; Pro-Inflammatory Cytokines; T Cells; TNF-α;Ulcerative Colitis 

2.            Commentary

CD4 T cells act as a key regulator of adaptive immunity and critically involves in the function of the immune system. CD4 T cells interact with various immune cells and suppress a broad range of pathogenic conditions via coordinating immune responses. CD4 T cells also play a major role to maintain immunogenic tolerance to avoid undesired immune response to self antigens. The activation and differentiation of naïve CD4+ T cells into distinct subsets such as TH1, TH2, TH17 and regulatory T cells (Tregs) are accomplished by various signals obtained from antigen-loaded MHC class II molecules, co-stimulatory molecules and polarizing cytokines. Diminished in number or defective in nature (phenotype) of CD4 T cells linked with various autoimmune diseases and pathological condition [1,2]. The autoimmunity is a multi defective immune cell process whichismainly associated with failure in central immune-tolerance with amendment of self-antigen expression levels.Recent studies suggest the development of autoimmune diseases such as Crohn’s Disease (CD), Ulcerative Colitis (UC), Inflammatory Bowel Disease (IBD), Systemic Lupus Erythematosus (SLE), Multiple Sclerosis (MS) and Rheumatoid Arthritis (RA) are linked with CD4 T subset cells[1-4]. Additionally, dysregulated immune system in autoimmune diseases are linked with various pro-inflammatory cytokines, which are mediated by CD4 T subset cells. For instance CD patients has been remarkably noticed with TH1 cell-mediated disease with high levels of pro-inflammatory cytokines such as tumor necrosis factor-α (TNF-α) and interferon-γ (IFN-γ). Another example, UC patients havebeen reported to be linked with TH2 cells. Additionally, recent evidence suggests that various autoimmune diseases, including IBD have been associated with TH17 cells[4,5]. 

TH17 cells are a distinct lineage of CD4 helper T cells, which secrete specific cytokines such as IL-17A, IL-17F, IL-21, GM-CSF and IL-22 and play a critical role in the pathogenesis of several autoimmune and allergic diseases. IL-17A producing TH17 express the surface IL-23 receptor (IL-23R) and lineage specific transcription factor RORC (RORγt in mice). RORC is key transcription factor play pivotal role in the differentiation TH17 cells[6, 7]. IL-17 is a pro-inflammatory cytokines and reported to be over expressed in a large set of autoimmune disease. Recent studies suggest that various microRNAs (miR-301a, miR-155 and miR-21) are directly or indirectly involve in TH17 differentiation and modulate the IL-17 production [4,8-15]. 

MicroRNAs (miRNAs) are conserved non-coding RNA sequences, approximately 18-25 nucleotides in length. miRNAs are fine tuners which act as negative regulator of the target genes via binding to 3’-untranslated region of mRNAs, leading to mRNA degradation or inhibition of mRNA translation[2]. miRNAs are tiny in size but effectively regulates various cellular and physiological processes and aberrant expression of miRNA has been linked to various pathologies including autoimmune diseases. Recent observationsby various research groups determine the role of various miRNAs in the function of the immune system and also provide evidences linked the development of autoimmunity and inflammatory diseases. Additionally, In recent years, significant efforts have been made the association of miRNAs with autoimmune disease, in particular IBD with TH17 mediated abnormal production pro-inflammatory cytokines.Recent observationpublished by Liu and colleaguessuggests that induced expression of miR-301 promotes TH17 cell differentiation via suppressing the expression of SNIP1 in inflamed mucosa of IBD patients[4].Idiopathic IBD is a chronic inflammation of the human digestive tract. CD and UC are the two main clinical type linked with IBD[4-7] (Figure 1).

Chong He et al. first investigated the expression of miR-301 in the inflamed mucosa and PBMC of patients with IBD and observed that miR-301 is over expressed in the inflamed mucosa and PBMC of both patients with CD and patients with UC compared with Healthy Controls (HC). Further, they examined the expression of miR-301 in inflamed and unaffected mucosa from the same patients and identified over expression in inflamed mucosa compared with the unaffected mucosa of the same patients. miR-301 expression is induced in CD4 T-cells compare with other subsets of immune cells in HC. Additionally, they also observed the expression of miR-301 was induced in CD4 T-cells and Intestinal Epithelial Cells (IECs) compare to B cells and Dendritic Cells (DCs) in normal intestinal mucosa patients with colon cancer. 

As evidence suggested that various pro-inflammatory cytokines expression such as TNF-α, IL-23 and IL-6 have been induced in mucosa of patients with IBD. The authors next aimed to understand the mechanism by which miR-301 was induced in IBD and identify the effect of cytokine on the miR-301 regulation. For this purpose, they stimulated CD4 T-cells (isolated from HC) using anti-CD3/CD28in presence of selected cytokines such as TNF-α, IL-17A, IL-23, IL-6, IFN-γ, IL-10 or IL-12. They observed thatmiR-301 expression was significantly induced in stimulated CD4 T-cells in the presence of IL-23, IL-6 and TNF-α (highest), suggested that miR-301 expression might be mediated by TNF-α. To examine this hypothesis Chong He et al. focused to understand the expression of miR-301 in mucosa ofCD patients with pre and post anti-TNF-αmAb (IFX) treatment. They observed miR-301 expression was suppressed with IFX treatment nd results suggested the correlation between miR-301 and TNF-α in patients with active CD.

Previous observation performed by another group suggested that miR-301a could induce TH17 cell differentiation in EAE [8]. The authors were aimed to address the effect of miR-301 on CD4 T-cell activation isolated from IBD or HC. For this purpose authors were primarily transduced CD4 T-cells with lentivirus-miR-301a or lentivirus-anti-miR-301a and then stimulated with anti-CD3/CD28. They obtained miR-301a conditional upregulation results in enhanced the expression of IL-17a, RORC and TNF-α in stimulated-CD4 T-cell in IBD and HC compare to control, and also observed down-regulated expression of these molecules with suppressed expression of miR-301a using lentivirus-anti-miR-301a. These observations revealed that the expression of miR-301a was positively correlated with IL-17a, RORC and TNF-α. Furthermore, the authors identified the SNIP1 as a putative target of miR-301a which they further validated using relative expression analysis in aforementioned experimental setups and additional method termed as dual-luciferase reporter assays, inin-vitro.These observations were further validated in in-vivo active patients with IBD (both, CD and UC) as well as clotis mice model. To understand the physiological effect of SNIP1, Authors performed forced suppression in the expression of SNIP1 using Lentivirus-SNIP1 siRNA in stimulated CD4 T-cells and observed that suppressed expression of IL-17a, RORC and TNF-α. Conditional suppression of SNIP1 promotes TH17 cell differentiation.

To summerise, these observations provide evidence induced expression of miR-301a in IBD facilitates the intestinal mucosal inflammation via promoting the induced expression of IL-17a, RORC and TNF-α. These observations also implicate that elevated expression of miR-301a in IBD regulates TH17 cell differentiation via suppressing the expression of SNIP1. Conclusive remarks of these observations are revealing that the miRNA-mediated regulation play pivotal role in IBD pathogenesis, and it would be worth to modulate the miR-301a expression and use in the treatment of IBD.

Figure 1: Regulation of miR-301a in Inflammatory Bowl Disease (IBD):Under pathological condition, miRNA regulation modulates. In IBD, expression of miR-301a were upregulated in all patients, which could positively regulated by inflammatory cytokines, such as Interleukin (IL)-6, IL-23 and TNF-α. Upregulated miR-301a promotes T_H17 differentiation via inducing the expression of RORC, IL-17a, and suppressing the expression of SNIP1 (negative regulation of T_H17 differentiation). Interestingly, miR-301a also regulates TNF-α production via positive feed-back loop. In conclusion, miR-301a play as a key regulator which modulates pro-inflammatory cytokine production in IBD. 

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