IL-1 beta -converting enzyme (caspase-1) in intestinal inflammation

Abstract

IL-1 beta-converting enzyme (ICE; caspase-1) is the intracellular protease that cleaves the precursors of IL-1 beta and IL-18 into active cytokines. In the present study, the effect of ICE deficiency was evaluated during experimental colitis in mice. In acute dextran sulfate sodium-induced colitis, ICE-deficient (ICE KO) mice exhibited a greater than 50% decrease of the clinical scores weight loss, diarrhea, rectal bleeding, and colon length, whereas daily treatment with IL-1 receptor antagonist revealed a modest reduction in colitis severity. To further characterize the function of ICE and its role in intestinal inflammation, chronic colitis was induced over a 30-day time period. During this chronic time course, ICE KO mice exhibited a near complete protection, as reflected by significantly reduced clinical scores and almost absent histological signs of colitis. Consistently, colon shortening occurred only in dextran sulfate sodium-exposed wild-type mice but not in ICE KO mice. Protection was accompanied by reduced spontaneous release of the proinflammatory cytokines IL-18, IL-1 beta, and IFN-gamma from total colon cultures. In addition, flow cytometric analysis of isolated mesenteric lymph node cells revealed evidence of reduced cell activation in ICE KO mice as evaluated by surface expression of CD3 CD69 and CD4 CD25. We conclude that inhibition of ICE represents a novel anti-inflammatory strategy for intestinal inflammation.

Figure 1

Effect of ICE deficiency and IL-1Ra treatment during acute colitis. Untreated or hyaluronic acid-treated WT, ICE KO, and WT mice injected i.p. with IL-1Ra (100 mg/kg) once daily were fed with 3.5% DSS for 5 days followed by 5 days of regular drinking water. (A) Change in body weight. (B) Diarrhea score. (C) Bleeding score. Each score was assessed daily as described in Materials and Methods. Non-DSS control mice, either ICE KO or WT, are summarized as controls, as no differences among these groups could be detected. Data are mean ± SEM. *, P < 0.05; **, P < 0.01; ***, P <0.001 vs. DSS WT.

Figure 2

Effect of ICE deficiency on chronic colitis. WT and ICE KO mice were fed with 2% DSS for 5 days followed by 5 days of regular water. This cycle was repeated three time resulting in a 30-day experimental period. (A) Change in body weight. (B) Diarrhea score. (C) Bleeding score. Each score was assessed every other day as described in Materials and Methods. Data are mean ± SEM. *, P < 0.05; **, P < 0.01; ***, P <0.001 vs. DSS WT.

Figure 3

Histological score in the chronic DSS model. WT and ICE KO mice were fed with 2% DSS for 5 days followed by 5 days of regular water. This cycle was repeated three times, resulting in a 30-day experimental period. A 1-cm segment of the transverse colon was fixed in 10% buffered formalin. Paraffin sections were stained with hematoxylin/eosin. (Magnifications are 52-, 130-, and 325-fold.) Histologic scoring was performed in a blinded fashion as described in Materials and Methods. (Upper) Histological sections from DSS-fed WT and ICE KO mice with increasing magnifications are shown. As there was no difference between the DSS-exposed ICE KO and non-DSS control mice, control sections are not shown. Bars are mean ± SEM. ***, P < 0.001 vs. DSS WT.

Figure 4

Spontaneous colon cytokine production after chronic DSS-induced colitis. WT and ICE KO mice were fed with 2% DSS for 5 days followed by 5 days of regular water. This cycle was repeated three times, resulting in a 30-day experimental period. The colon was removed and washed extensively, and 1-cm² pieces were cultured for 24 h. Cytokines were measured in the supernatant, and protein concentration was determined as described in Materials and Methods. Bars are mean ± SEM. **, P < 0.01; ***, P < 0.001 vs. DSS WT.

Figure 5

Flow cytometric analysis of CD4 CD25 and CD3 CD69 expression of MLNs. WT and ICE KO mice were fed with 2% DSS for 5 days followed by 5 days of regular water. This cycle was repeated three times, resulting in a 30-day experimental period. MLNs were prepared, and cells were isolated and double-stained for either CD4 CD25 or CD3 CD69 for flow cytometry as described in Materials and Methods. (A) Representative staining for each experimental group. (B) Mean ± SEM of five mice per group. **, P < 0.01 vs. WT.