Abstract:

Objective To employ Helicobacter hepaticus (H.hepaticus, H.h) to induce intestinal fibrosis in vitamin D receptor deletion (VDR^-/-) mice, thereby establishing a model of inflammatory bowel disease to investigate its pathological characteristics and underlying mechanisms. Methods Five male WT and five male VDR^-/- mice were orally administered a suspension containing 2×10⁸ CFU of H.hepaticus (referred to as the WT+H.h group and the VDR^-/-+H.h group, respectively), with treatments occurring every other day for three administrations. Concurrently, two uninfected control groups were established, consisting of five WT and five VDR^-/- mice, which were administered an equivalent volume of PBS. Seven days after the final administration, the infection status of the mice was assessed, and their body weight was recorded weekly. At the 16^th week post-infection, the mice were dissected, and the length of the colon tissue was measured, with fecal moisture content analyzed. The colon tissue was partitioned into four parts: one for paraffin embedding for HE, alcian blue-periodic acid Schiff (AB-PAS), Masson's trichrome staining, and immunohistochemical analysis; one for DNA extraction to evaluate the colonization levels of H.hepaticus through real-time fluorescent quantitative polymerase chain reaction (RFQ-PCR), thereby assessing the impact of the infection; one for RNA extraction to analyze cytokine expression via reverse transcription-PCR (RT-PCR); and one for protein extraction to measure the expression levels of alpha smooth muscle actin (α-SMA) and interleukin (IL)-33 using Western blotting. Results All mice in the infected groups successfully were infected with H. hepaticus after three oral gavages. Compared to VDR^-/- control group, VDR^-/- mice exhibited significant weight loss (P<0.05), intestinal hemorrhage, and higher fecal water content after 16 weeks of H. hepaticus infection than the uninfected control group and the WT+H.h group (P<0.05). Compared to the WT+H.h group, HE staining of the VDR^-/-+H.h group showed inflammatory cell infiltration, AB-PAS staining revealed irregular atrophy of intestinal glands and reduced acini, and Masson staining showed increased collagen area. RT-PCR demonstrated that the transcription levels of inflammation and fibrosis-related genes, including IL-6, IL-33, tumor necrosis factor-α (TNF-α), and α-SMA (P < 0.000 1), were significantly upregulated in the colon tissues of VDR^-/-+H.h group. Additionally, immunohistochemical analysis and Western blotting showed that the protein expression levels of IL-33 and α-SMA were markedly increased (P<0.001) in the VDR^-/-+H.h group. Conclusion VDR^-/- mice infected with H.hepaticus exhibit more severe inflammatory responses, including mucosal inflammatory infiltration, impaired mucosal tissue function, and collagen deposition, indicating successful construction of the inflammatory bowel disease model. Further research suggests that VDR deficiency may exacerbate the intestinal fibrosis process associated with inflammatory bowel disease by affecting IL-33 expression.

Key words: Helicobacter hepaticus, Intestinal fibrosis, Inflammatory bowel disease model, Vitamin D receptor, Mice