MiR-223 is a key modulator of the regulation of myeloid cells, especially the differentiation and activation of neutrophils and macrophages . MiR-223 limits the function of neutrophils to avoid excessive immune responses in inflammatory diseases . For example, miR-223 is secreted in microvesicles from neutrophils that are recruited from the vasculature to sites of pulmonary inflammation and tissue injury and then shuttled to alveolar type II epithelial cells (ATII) to confer lung protection in acute respiratory distress syndrome (ARDS) . Recent studies have demonstrated the abnormal expression of miR-223 in IBD patients and experimental colitis mice [5–13]. In this study, we found that the expression of miR-223 in the terminal ileum and colon was increased in DSS-induced colitis mice. These results were similar to those of previous reports.
The pathogenesis of IBD is not completely clear and is related to dysregulated epithelial barrier function, increased bacterial translocation and an aberrant immune response . MiR-223 not only functions as a key modulator for the innate immunity, but also affects adaptive immunity, and immune dysregulation has been shown to contribute to IBD . It has been reported that miR-223 is involved in the pathogenesis of IBD by regulating various immune cells and signaling pathways [5–9]. Furthermore, miR-223 from human mast cells-1 (HMCs-1) inhibits CLDN8 expression to destroy intestinal barrier function in IBD .
The role of miR-223 in the pathogenesis of IBD is still controversial. Zhou et al showed that miR-223−/y mice developed more severe colitis in the DSS-induced colitis model, and concluded that miR-223 regulated DCs and macrophages by directly targeting C/EBPβ to maintain intestinal homeostasis . Neudecker V also reported that miR-223−/y mice exhibited exacerbated experimental colitis with elevated NLRP3 and IL-1β levels, and nanoparticle-mediated overexpression of miR-223 attenuated experimental colitis . Therefore, the researchers determined that miR-223 was an anti-inflammatory factor. In the present study, miR-223 expression in the colon was significantly upregulated and downregulated by the miR-223 agomir and antagomir, respectively. We also found that the clinical signs of experimental colitis were improved, MPO and proinflammatory cytokines (TNF-α, IL-6, IL-17) were downregulated and anti-inflammatory cytokine (IL-10) were upregulated after administration of the miR-223 agomir, and these changes were reversed after administration of the miR-223 antagomir. These results showed that miR-223 played an anti-inflammatory role in DSS-induced colitis. Interestingly, miR-223 has been reported to be proinflammatory by other studies. Wang et al identified miR-223 as a mediator of the crosstalk between the IL-23 signaling pathway and CLDN8 in the development of IBD, and the inhibition of miR-223 alleviated TNBS-induced colitis . Kim confirmed that miR-223 negatively regulated FOXO3a to enhance NF-κB signaling and promote the production of proinflammatory cytokines .
The IL-6/STAT3 signaling pathway plays an important role in the development of inflammation in the pathogenesis of IBD [18–20]. The present study showed that the levels of IL-6, IL-17, gp130, STAT3, p-STAT3, Bcl-2 and Bcl-x1 were upregulated in DSS-induced colitis, which was consistent with previously published data. IL-6 first binds to soluble IL-6 receptor (sIL-6R) on the membrane and then forms an IL-6 and sIL-6R complex. The IL-6/sIL-6R complex activates a homodimer of gp130, leading to Janus kinase (JAK) activation and the phosphorylation of STAT3 . P-STAT3 activates the NF-κB signaling pathway to regulate the expression of inflammatory cytokines . Furthermore, STAT3 inhibits the apoptosis of T lymphocytes by inducing the antiapoptotic genes Bcl-2 and Bcl-x1, ultimately leading to further production of inflammatory cytokines and continuous tissue destruction . IL-6/STAT3 is also involved in the differentiation of T helper 17 (Th17) cells and cytokine production, which promotes the inflammatory response [24, 25].
MiR-223 has been confirmed to participate in the IL-6/STAT3 pathway to regulate inflammatory cytokines [26, 27]. Chen suggested that IL-6/miR-223/STAT3 formed a positive feedback loop to promote the pathogenesis of inflammatory diseases .
Wu also found that miR-223 formed a complex regulatory network with proinflammatory factors and signaling pathways in adipose stem cells stimulated by lipopolysaccharide (LPS) . However, whether miR-223 is involved in IBD through the IL-6/STAT3 pathway is unclear. In the present study, we explored the mechanism of miR-223 in IBD, focusing on the IL-6/STAT3 pathway. After administration of the miR-223 agomir, the expression of miR-223 was increased, and the levels of IL-6, gp130, p-STAT3, Bcl-2 and Bcl-x1 were decreased. The miR-223 antagomir showed the opposite effects. These data demonstrated that miR-223 might inhibit the IL-6/STAT3 signaling pathway in DSS-induced colitis.