Schistosoma japonicum ova maintains epithelial barrier function during experimental colitis

Abstract

Aim: To evaluate the impacts of Schistosoma japonicum (S. japonicum) ova on the tight junction barriers in a trinitrobenzenesulfonic acid (TNBS)-induced colitis model.

Methods: Balb/c mice were randomly divided into three groups: control group; TNBS(+)ova(-) group and TNBS(+)ova(+) group. TNBS was used intracolonic to induce colitis and mice of the TNBS(+)ova(+) group were pre-exposed to S. japonicum ova as a prophylactic intervention. Colon inflammation was quantified using following variables: mouse mortality, weight loss, colon extent and microscopic inflammation score. Serum expression of tumor necrosis factor-α and interferon-γ were assessed to evaluate the systemic inflammatory response. NOD2 and its mRNA were also tested. Bacterial translocations were tested by culturing blood and several tissues. ZO-1 and occludin were chosen as the representations of tight junction proteins. Both the proteins and mRNA were assessed.

Results: Ova pre-treatment contributed to the relief of colitis and decreased the mortality of the models. NOD2 expression was significantly downregulated when pretreated with the ova. The TNBS injection caused a significant downregulation of ZO-1 and occludin mRNA together with their proteins in the colon; ova pre-exposure reversed these alterations. Treatment with S. japonicum ova in the colitis model caused lower intestinal bacterial translocation frequency.

Conclusion: S. japonicum ova can maintain epithelial barrier function through increasing tight junction proteins, thus causing less exposure of NOD2 to the luminal antigens which may activate a series of inflammatory factors and induce colitis.

Keywords: Crohn’s disease; Occludin; Schistosoma japonicum ova; Tight junction protein; ZO-1.

Figure 1

The evaluations of colitis. The initial weight of each group (A) and variations of weight (B), colon extent (C) and microscopic colonic scoring (D) on day 22. Data are presented as mean ± SD. n = 10, ^aP < 0.05 vs the other two groups; ^bP < 0.01 vs the other two groups. TNBS: Trinitrobenzenesulfonic acid.

Figure 2

The histology of the colon in different group of mice (HE, × 10). Rare inflammation was found in controls (A). Transmural chronic inflammation was observed in TNBS-induced colitis (B). The inflammation was significantly relieved in schistosome ova treated mice (C). HE: Hematoxylin and eosin; TNBS: Trinitrobenzenesulfonic acid.

Figure 3

The serum levels of tumor necrosis factor-α (white bar) and interferon-γ (black bar). Data are presented as mean ± SD. There were 20 animals in the control group and the TNBS⁺ova^- group and 24 in the TNBS⁺ova⁺ group. ^aP < 0.05 vs the other two groups. TNBS: Trinitrobenzenesulfonic acid.

Figure 4

Effect of Schistosoma japonicum ova on the expression of NOD2, ZO-1 and occludin (Western blotting). White bar represents the control group (N), grey bar represents the TNBS⁺ova^- group (T), black bar represents the TNBS⁺ova⁺ group (S). Data are presented as mean ± SE. n = 10. ^aP < 0.05 vs the other two groups. NOD2: Nucleotide-binding-oligomerization domain 2; TNBS: Trinitrobenzenesulfonic acid; GAPDH: Glyceraldehyde phosphate dehydrogenase.

Figure 5

Effect of Schistosoma japonicum ova on the expression of NOD2 mRNA (Realtime-PCR). M: Marker; G: GAPDH; N: Control group; T: TNBS⁺ova^- group; S: TNBS⁺ova⁺ group. Data are presented as mean ± SE. n = 10. ^aP < 0.05 vs the other two groups. GAPDH: Glyceraldehyde phosphate dehydrogenase; TNBS: Trinitrobenzenesulfonic acid.

Figure 6

Effect of Schistosoma japonicum ova on the expression of ZO-1 and occludin mRNA (Realtime-PCR). White bar represents the control group (N), grey bar represents the TNBS⁺ova^- group (T), black bar represents the TNBS⁺ova⁺ group (S). M: Marker; G: GAPDH. Data are presented as mean ± SE. n = 10. ^aP < 0.05 vs the other two groups. GAPDH: Glyceraldehyde phosphate dehydrogenase. TNBS: Trinitrobenzenesulfonic acid.