miR-135a Protects Dextran Sodium Sulfate-Induced Inflammation in Human Colorectal Cell Lines by Activating STAT3 Signal

Background/Aims: miR-135a is reduced in several cancers and has been suggested to mediate immune and inflammatory responses. However, the effect of miR-135a on inflammatory bowel diseases was obscure. This study firstly attempted to investigate the hypothesis that miR-135a alleviates dextran sodium sulfate (DSS)-induced inflammation in colonic cells and potential mechanisms are also studied. Methods: Caco-2 and HT-29 cells in this study were treated with DSS, miR-135a mimic, and S3I-201, and then CKK-8 assay was used to test cell viability. Expressions of miR-135a, cytokines, and signal transducers and activators of transcription factors (STATs) were determined by RT-PCR. Also, cytokine productions were further tested by using ELISA kits. Activation or inactivation of STAT3 signal was validated by western blotting analysis. Results: The results showed that DSS markedly downregulated miR-135a expression (P< 0.05) and induced inflammatory response in Caco-2 and HT-29 cells evidenced by the up regulations and productions of interleukin-1β (IL-1β) and tumor necrosis factor-ɑ (TNF-ɑ) (P< 0.05). Transfection with miR-135a mimic significantly alleviated DSS-induced upregulation and productions of IL-1β and TNF-ɑ in Caco-2 and HT-29 cells (P< 0.05). STATs were analyzed and miR-135a mimic treatment reversed STAT3 downregulation in DSS-challenged Caco-2 and HT-29 cells compared with the mimic control (P< 0.05). Also, STAT3 phosphorylation was inhibited in DSS-challenged Caco-2 cells and miR-135a mimic activated STAT3 signal (P< 0.05). S3I-201, an inhibitor of STAT3 signal, further used to inactivate STAT3 signal and the results showed that S3I-201 blocked the anti-inflammatory effect of miR-135a mimic on Caco-2 and HT-29 cells evidenced by the lowered expressions and productions of proinflammatory cytokines ((IL-1β and TNF-ɑ) (P< 0.05). Conclusion: Our results indicated that miR-135a alleviated DSS-induced inflammation and activated STAT3 signal in colonic cells. Inhibition of STAT3 reversed the anti-inflammatory function of miR-135a by regulating proinflammatory cytokines. Thus, STAT3 signal might serve, at least in part, as the potential mechanism of miR-135a-mediated anti-inflammatory effect in colonic cells.