Abstract: BACKGROUND: The pathogenesis of ulcerative colitis is highly complex, necessitating the development of models that more closely mimic human physiological and pathological responses to study the mechanisms underlying its onset and progression. 
OBJECTIVE: To establish a mouse ulcerative colitis organoid model. 
METHODS: Colon organoids of C57BL/6J mice were extracted, cultured and passaged in vitro. Colon organoids from mice after three generations of passage were taken and incubated in lipopolysaccharide at varying concentrations [0 (control), 150, 175, 200, 225, 250, 275, 300, 325, and 350 μg/mL] to induce inflammation for 24 hours. The morphology of mouse colon organoids was observed under a microscope, and changes in proliferation viability were assessed using the cell counting kit-8 assay. After 24 hours of incubation with 0, 225, 250, and 275 μg/mL lipopolysaccharide, the expression levels of tumor necrosis factor-α, interleukins 6, 9, and 10 were measured via ELISA. Immunofluorescence was used to detect the expression of occludin and ZO-1. Quantitative PCR was employed to evaluate the mRNA levels of tumor necrosis factor-α, interleukins 6, 9, and tight junction proteins (occludin and ZO-1). 
RESULTS AND CONCLUSION: (1) Following 24-hour induction with lipopolysaccharide at concentrations ranging from 150 to 275 μg/mL, the colon organoids exhibited varying degrees of swelling under the microscope. However, when the concentration of lipopolysaccharide was 300-350 μg/mL, organoid growth and swelling were inhibited. Cell counting kit-8 results showed that proliferation viability of the colon organoids decreased to varying degrees after 24-hour induction with lipopolysaccharide at 150-350 μg/mL, with a significant reduction observed at 225-350 μg/mL. Based on the results of cell morphology and proliferation activity testing, 225, 250, and 275 μg/mL lipopolysaccharide were selected for ELISA testing. (2) After 24-hour induction with lipopolysaccharide at 225, 250, and 275 μg/mL, the levels of interleukin-6 and tumor necrosis factor-α were significantly elevated compared with the control group (P < 0.05). After induction with 275 μg/mL lipopolysaccharide, the level of interleukin-9 also showed a notable increase (P < 0.05). (3) Immunofluorescence staining revealed that, after 24-hour induction with 275 μg/mL lipopolysaccharide, the expression of ZO-1 and occludin was reduced compared with the control group. Quantitative PCR results showed that after 24-hour induction with 275 μg/mL lipopolysaccharide, the mRNA levels of interleukin-6 and tumor necrosis factor-α were significantly upregulated compared with the control group (P < 0.05), while the mRNA level of occludin was markedly downregulated (P < 0.05). There was no significant difference in the expression of interleukin-9 and ZO-1 (P > 0.05). All these findings indicate that an organoid-based in vitro mouse ulcerative colitis model was successfully constructed, providing a powerful tool for investigating the mechanisms of ulcerative colitis and screening effective therapeutic agents.

Key words: colon, organoid, inflammation models, lipopolysaccharide, inflammation factors, ulcerative colitis, mouse, crypt