Ruxolitinib Alleviates DSS-Induced Acute Ulcerative Colitis by Inhibiting STAT1 Phosphorylation and Reducing MDSC Infiltration

Lu Xu¹Fangyue Xu²Vincent Kam Wai Wong^1*

• ¹Dr. Neher's Biophysics Laboratory for Innovative Drug Discovery, State Key Laboratory of Quality Research in Chinese Medicine, Macau University of Science and Technology, Macau, China
• ²Second Clinical Medical School, Zhejiang Chinese Medical University, Hangzhou, Jiangsu Province, China

Objective: This study aimed to evaluate the therapeutic effects of Ruxolitinib, a JAK1/2 inhibitor, on DSS-induced acute colitis in mice, with a focus on its impact on disease activity, inflammatory responses, modulation of myeloid-derived suppressor cells (MDSCs), and regulation of the JAK/STAT1 signaling pathway.Acute UC was induced in C57BL/6 mice by administering a 2.5% DSS solution.Mice were randomly assigned to three groups: the blank group (no DSS), the model group (DSS only), and the Ruxolitinib-treated group (DSS + 30 mg/kg Ruxolitinib by gavage for 14 consecutive days). Body weight, disease activity index (DAI) scores, spleen weight, and colon length were measured. Spleen index and the spleen weight-to-colon length ratio were calculated.Flow cytometry was used to assess the proportion of MDSCs in the blood. In vitro, CCD841 and Jurkat cells were pretreated with 50 IU/mL IFN-γ for 2 hours, followed by 24-hour treatment with Ruxolitinib. PCR array analysis was performed to identify transcriptional changes in JAK-STAT pathway-related genes. Electrophoretic mobility shift assay (EMSA) and Western blot were used to investigate the inhibition of STAT1 activation and phosphorylation.In vivo, DSS-induced acute colitis in the model group, and Ruxolitinib treatment significantly alleviated colitis as evidenced by reduced body weight loss (p < 0.05), decreased DAI scores in the later stages (p<0.05), a lower spleen index (p < 0.05), increased colon length (p < 0.01), and a reduced spleen weight-to-colon length ratio (p < 0.05). Flow cytometry revealed a significant reduction in the proportion of CD11b + Gr-1 + MDSCs in the blood of the Ruxolitinib group compared to the model group (p < 0.01). In vitro, PCR array analysis showed that Ruxolitinib notably downregulated the transcription of several JAK-STAT pathway-related genes, including B2M, IRF1, RQ1, SOCS1, STAT1, and STAT3, with STAT1 showing the most pronounced changes. EMSA and Western blot analysis confirmed that Ruxolitinib effectively inhibited IFN-γ-induced STAT1 activation and phosphorylation in a dose-dependent manner.Ruxolitinib effectively ameliorated DSS-induced acute colitis by reducing inflammation, modulating MDSC levels, and inhibiting STAT1 activation. These findings suggest that Ruxolitinib could be a promising therapeutic agent for UC, targeting both the immune response and the JAK/STAT1 signaling pathway.