Schistosoma japonicum attenuates dextran sodium sulfate-induced colitis in mice via reduction of endoplasmic reticulum stress

Abstract

Aim: To elucidate the impact of Schistosoma (S.) japonicum infection on inflammatory bowel disease by studying the effects of exposure to S. japonicum cercariae on dextran sodium sulfate (DSS)-induced colitis.

Methods: Infection was percutaneously established with 20 ± 2 cercariae of S. japonicum, and colitis was induced by administration of 3% DSS at 4 wk post infection. Weight change, colon length, histological score (HS) and disease activity index (DAI) were evaluated. Inflammatory cytokines, such as IL-2, IL-10 and IFN-γ, were tested by a cytometric bead array and real-time quantitative polymerase chain reaction (RT-PCR). Protein and mRNA levels of IRE1α, IRE1β, GRP78, CHOP, P65, P-P65, P-IκBα and IκBα in colon tissues were examined by Western blot and RT-PCR, respectively. Terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling positive cells, cleaved-caspase 3 expression and Bcl2/Bax were investigated to assess the apoptosis in colon tissues.

Results: Mice infected with S. japonicum cercariae were less susceptible to DSS. Mice infected with S. japonicum cercariae and treated with DSS showed decreased weight loss, longer colon, and lower HS and DAI compared with mice treated with DSS alone. A substantial decrease in Th1/Th2/Th17 response was observed after infection with S. japonicum. Endoplasmic reticulum (ER) stress and the nuclear factor-kappa B (NF-κB) pathway were reduced in mice infected with S. japonicum cercariae and treated with DSS, along with ameliorated celluar apoptosis, in contrast to mice treated with DSS alone.

Conclusion: Exposure to S. japonicum attenuated inflammatory response in a DSS-induced colitis model. In addition to the Th1/Th2/Th17 pathway and NF-κB pathway, ER stress was shown to be involved in mitigating inflammation and decreasing apoptosis. Thus, ER stress is a new aspect in elucidating the relationship between helminth infection and inflammatory bowel disease (IBD), which may offer new therapeutic methods for IBD.

Keywords: Colitis; Endoplasmic reticulum stress; Schistosoma japonicum.

Figure 1

Treatment with S. japonicum cercariae results in reduced susceptibility to dextran sodium sulfate-induced colitis in mice. Mice were infected with 20 ± 2 S. japonicum cercariae percutaneously, and experimental colitis was induced by administration of 3% DSS at 4 wk post infection. A: Weight change in percent; B: DAI based on weight change, stool characteristics and bleeding; C and D: Colon length; E: H and E staining was performed in colonic sections (original magnification, × 200 and × 400); F: HS was scored as described in Materials and Methods. n = 6. The mice infected with S. japonicum cercariae presented longer colons, decreased weight loss and lower DAI and HS after being induced with DSS compared to those without parasite infection. DSS: Dextran sodium sulfate treatment alone; CER + DSS: Infection with S. japonicum before DSS treatment; CER: S. japonicum infection alone.

Figure 2

Infection with S. japonicum decreases infiltration of inflammatory cells in colon tissues. A: Immunofluorescence staining of CD3 and Ly6G in the colon sections; B and C: Respective quantification of CD3 and Ly6G positive cells. n = 3. DSS: Dextran sodium sulfate treatment alone; CER + DSS: Infection with S. japonicum before DSS treatment; CER: S. japonicum infection alone.

Figure 3

Administration of S. japonicum leads to lowered inflammatory cytokines in dextran sodium sulfate-induced colitis mice. A: The production of IL-2, IL-6, IL-10, IL-17A, TNFα and IFN-γ in blood samples was detected by CBA and flow cytometry; B: IL-1β, IL-6, IL-10, IL-17a, IFN-γ, TNFα and TGFβ levels in colon tissues were tested by RT-PCR. n = 3 or 4. Exposure to S. japonicum protected mice from DSS-induced colitis with down-regulation of the Th1/Th2/Th17 pathway. DSS: Dextran sodium sulfate treatment alone; CER + DSS: Infection with S. japonicum before DSS treatment; CER: S. japonicum infection alone.

Figure 4

Infection with S. japonicum decreases the expression of phosphorylated-p65 in mice treated with dextran sodium sulfate. A: The expression of P-P65 and P65 in colon tissues was examined by Western blot; B and C: Respective quantification of P-P65 and P65; D and E: Respective quantification of P-IKBα and IKBα. n = 3. DSS: Dextran sodium sulfate treatment alone; CER + DSS: Infection with S. japonicum before DSS treatment; CER: S. japonicum infection alone.

Figure 5

Endoplasmic reticulum stress markers are downregulated in mice induced with dextran sodium sulfate after infection. A: The expression of IRE1α, IRE1β, GRP78 and CHOP in colon tissues was examined by Western blot; B-E: Respective quantification of IRE1α, IRE1β, GRP78 and CHOP. n = 4. DSS: Dextran sodium sulfate treatment alone; CER + DSS: Infection with S. japonicum before DSS treatment; CER: S. japonicum infection alone.

Figure 6

Apoptosis in colitic mice after infection with S. japonicum. A: Immunofluorescence staining of cleaved-caspase3 (C-C3) and TUNEL staining; B and C: Respective quantification of C-C3 and TUNEL positive cells; D: Bax and Bal-2 were tested by Western blot; E and F: Respective quantification of Bax and Bal-2. n = 3. DSS: Dextran sodium sulfate treatment alone; CER + DSS: Infection with S. japonicum before DSS treatment; CER: S. japonicum infection alone.