[Study on the effect of high-intensity interval exercise on ulcerative colitis in mice]

Objective: This study aims to systematically explore the protective effect and its underlying mechanism of high-intensity interval exercise (HIE) on the mouse model of ulcerative colitis (UC) induced by dextran sulfate sodium (DSS) through regulating the structure and function of gut microbiota. Methods: A simple randomized controlled allocation method was adopted. From July to August 2024, 24 male C57BL/6 mice were divided into the control group (Con), ulcerative colitis group (DSS), high-intensity interval exercise group (HIE), and high-intensity interval exercise-ulcerative colitis group (HIE-DSS) in the experimental animal room of the Second Department of Infectious Disease Prevention and Control in the Disease Prevention and Control Center of the Eastern Theater Command, with six mice in each group. During the experimental stage, the mice in the HIE and HIE-DSS groups first received 5-week high-intensity interval exercise training. Then, the mice in the DSS and HIE-DSS groups were given free access to a 3% DSS solution for 7 days to induce the UC model. The diarrhea status, body weight changes of the mice were observed, and the colon length was measured. The histopathology and morphology of the colon tissues were scored. H&E staining was used to observe the pathological changes in the colon tissues. An enzyme-linked immunosorbent assay (ELISA) was used to analyze the expression levels of interleukin (IL) IL-10, IL-1β, IL-6 and tumor necrosis factor-α (TNF-α) in the peripheral serum of the mice in each group. Real-time fluorescent quantitative PCR (qRT-PCR) was used to monitor the changes in the levels of IL-1 mRNA, IL-6 mRNA, IL-10 mRNA, and TNF-α mRNA in the mouse colon tissues. Kits were used to detect the changes in malondialdehyde (MDA), myeloperoxidase (MPO), catalase (CAT), glutathione (GSH), total superoxide dismutase (T-SOD), and reactive oxygen species (ROS) in the mouse colon tissues. 16S rRNA sequencing and gas chromatography-mass spectrometry (GC-MS) techniques were used to detect the changes in the gut microbiota and fecal metabolites. Immunohistochemical techniques and bacterial translocation experiments were used to evaluate the changes in the gut mucosal proteins Occludin and Muc2 and the gut barrier function. One-way analysis of variance (One-way ANOVA) was used for statistical analysis. Newman-Keuls multiple comparison test was used to evaluate the differences between groups. Results: The weight changes (g) of the Con group, DSS group, HIE group, and HIE-DSS group were (28.29±0.71), (23.71±0.67), (27.61±1.20), and (25.63±0.78) respectively; the colon lengths (cm) were (7.67±0.41), (4.87±0.18), (7.08±0.22), and (6.53±0.14) respectively; the morphological scores of colon tissues were (1.26±0.62), (2.01±0.41), (1.25±0.70), and (1.57±0.28) respectively; the pathological scores were (0.66±0.31), (1.33±0.42), (0.81±0.19), and (1.03±0.32) respectively. The weight change, colon length, colon morphological score, and colon tissue pathological score of the DSS group were significantly lower than those of the HIE-DSS group, with statistically significant differences (t=3.195, P=0.036), (t=4.478, P=0.008 6), (t=3.745, P=0.007 1), and (t=4.106, P=0.006 9).The contents of IL-1β (pg/ml) in the serum of the Con group, DSS group, HIE group, and HIE-DSS group were 19.10±0.89, 26.26±1.86, 221.65±1.43, and 22.46±1.54 respectively; the expression levels of IL-6 (pg/ml) were 30.82±7.15, 71.90±14.42, 28.70±6.62, and 37.40±4.58 respectively; the expression levels of TNF-α (pg/ml) were 22.78±6.11, 37.86±7.12, 24.68±4.07, and 27.75±6.32 respectively; the expression levels of IL-10 (pg/ml) were 59.13±9.02, 43.38±6.72, 53.17±5.27, and 51.92±4.18 respectively. Compared with the Con group, the expression levels of IL-1β, IL-6, and TNF-α in the serum of the DSS group were significantly increased, while the expression level of IL-10 was significantly decreased, with statistically significant differences (t=6.345, P=0.044), (t=5.115, P=0.038), (t=8.931, P=0.021), (t=6.612, P=0.039). The expression levels of IL-1β, IL-6, and TNF-α in the HIE-DSS group were significantly lower than those in the DSS group, while the expression level of IL-10 was significantly higher, with statistically significant differences (t=7.749, P=0.000 8), (t=5.327, P=0.007 4), (t=10.140, P=0.000 6), (t=7.718, P=0.000 5).The relative expression levels of ROS (U/mol) in the colon tissues of the Con group, DSS group, HIE group, and HIE-DSS group were 111.83±10.90, 185.16±25.56, 118.83±16.43, and 135.83±11.81 respectively; the expression levels of MPO (U/mgport) were 0.71±0.85, 2.76±0.62, 0.90±0.43, and 1.56±1.33 respectively; the expression levels of CAT (U/mgport) were 0.44±0.31, 0.08±0.21, 0.37±0.25, and 0.30±0.22 respectively; the expression levels of MDA (nmol/mgport) were 0.38±0.12, 0.92±0.22, 0.46±0.18, and 0.57±0.19 respectively; the expression levels of GSH (mg/port) were 17.80±6.12, 6.11±2.82, 14.71±4.18, and 12.28±5.011 respectively; the expression levels of T-SOD (U/mgport) were 3.69±2.12, 1.25±0.61, 3.23±0.55, and 2.73±0.47 respectively. Compared with the HIE-DSS group, the expression levels of ROS, MPO, and MDA in the colon of the DSS group were significantly increased, while the expression levels of CAT, GSH, and T-SOD were significantly decreased, with statistically significant differences (t=3.915, P=0.005 4), (t=4.543, P=0.000 4), (t=8.018, P=0.000 7), (t=12.510, P=0.000 6), (t=6.703, P=0.000 5), (t=5.784, P=0.000 8).The expression levels (IOD) of tight-junction protein Muc2 in the colon tissues of the Con group, DSS group, HIE group, and HIE-DSS group were 3 019.51±23.26, 2 080.25±11.18, 2 690.32±17.24, and 2 473.50±16.04 respectively; the expression levels (IOD) of Occludin were 2 881.04±12.07, 2 198.30±10.05, 2 720.30±14.02, and 2 680.30±11.23 respectively. The expression levels of Muc2 and Occludin in the DSS group were significantly lower than those in the HIE-DSS and Con groups, with statistically significant differences (t=8.743, P=0.000 7), (t=9.634, P=0.000 9). Conclusion: As an emerging exercise mode, high-intensity interval training may participate in alleviating the pathogenesis of ulcerative colitis by regulating gut microbiota and their metabolites.