Abstract
MicroRNAs are critical post-transcriptional regulators of gene expression and key mediators of pathophysiology of inflammatory bowel disease (IBD). This study is aimed to study the role of miR-665 in the progression of IBD. Real-time PCR analysis was used to determine miR-665 expression in 89 freshly isolated IBD samples and dextran sulfate sodium (DSS)-induced colonic mucosal tissues. The role of miR-665 in inducing apoptosis and colitis were examined by Annexin V, TUNEL (terminal deoxynucleotidyl transferase dUTP nick-end labeling) staining, colony formation in vitro and DSS-induced colitis mice model in vivo. Moreover, luciferase reporter assay, western blot analysis and microribonucleoprotein immunoprecipitation were performed to determine that miR-665 directly repressed XBP1 (X-box-binding protein-1) and ORMDL3 expression. Herein, our results revealed that miR-665 was markedly upregulated in active colitis. Gain-of-function and loss-of-function studies showed that ectopic expression of miR-665 promoted apoptosis under different inflammatory stimuli. Importantly, delivery of miR-665 mimic promoted, while injection of antagomiR-665 markedly impaired DSS-induced colitis in vivo. Mechanistically, we demonstrated that miR-665 induced apoptosis by inhibiting XBP1 and ORMDL3. Taken together, our findings reveal a new regulatory mechanism for ER stress signaling and suggest that miR-665 might be a potential target in IBD therapy.
Highlights
Inflammatory bowel disease (IBD) is a complex disease characterized by chronic or recurrent inflammation in the gastrointestinal tract
endoplasmic reticulum (ER) stress is observed in many human diseases, such as inflammation, neurodegenerative diseases, metabolic diseases and cancers, and it is identified that the unfolded protein response (UPR), a three-pronged signaling axis, to preserve ER homeostasis.[16]
For the intestinal epithelium, ER stress is characteristically induced by primary causes associated with the UPR, such as X-box-binding protein-1 (XBP1), ORMDL3 and ARG2, or secondary factors, including bacterial toxins, mucins (e.g., MUC2), autophagic proteins (e.g., ATG16L1) and cytokines (e.g., tumor necrosis factor-α (TNF-α) and interleukin-10), and the interplay of these factors initiates the cascades of inflammation that can cause or exacerbate homeostatic ER stress.[18]
Summary
Inflammatory bowel disease (IBD) is a complex disease characterized by chronic or recurrent inflammation in the gastrointestinal tract. The X-box-binding protein-1 (XBP1), a potent inducer of a subset of UPR target genes, is required for the constitutive maintenance of ER function in all cell types, and XBP1 deletion in intestinal epithelial cells (IECs) results in spontaneous enteritis.[3,4] the ORMDL3 protein is located primarily in the ER and regulates Ca2+ uptake from the cytosol and ER-mediated Ca2+ signaling.[5,6] Recently, genome-wide association studies identified ORMDL3 as another genetic risk factor of CD and UC.[7] Loss of XBP1 or ORMDL3 expression has been reported to promote colitis and increase hypersensitivity to cytokineinduced apoptosis via c-Jun N-terminal kinase (JNK) signaling.[2,3,8] Regarding their critical roles in ER stress and pathogenesis of IBD, better understanding of the regulation of XBP1 and ORMDL3 might provide new clues for the prognosis and therapy of IBD. We demonstrated that miR-665 downregulated XBP1 and ORMDL3 expression by directly targeting their 3′-UTRs, resulting in the Received 09.8.16; revised 15.12.16; accepted 24.1.17; Edited by G Calin
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