Inflammation enhances resection-induced intestinal adaptive growth in IL-10 null mice

Abstract

Background: Surgical resection of the ileum, cecum, and proximal right colon (ICR) is common in the management of Crohn's disease, yet little is known about the effect of active inflammation on the adaptive response following intestinal loss. We recently developed a surgical model of ICR in germ-free (GF) IL-10 null mice that develop small intestinal inflammation only when mice undergo conventionalization with normal fecal microflora (CONV) before surgical intervention. In this study, we examined the effects of postsurgical small bowel inflammation on adaptive growth after ICR.

Methods: GF 129SvEv IL-10 null mice, 8-10 wk old, were allocated to GF or CONV groups. Nonoperated GF and CONV mice provided baseline controls. Two wk later, GF and CONV mice were further allocated to ICR or sham operation. Small intestine and colon were harvested 7 d after surgery for histological analysis.

Results: All mice within the gnotobiotic facility maintained GF status and did not develop small intestinal or colonic inflammation. CONV resulted in colitis in all groups, whereas small intestinal inflammation was only observed following ICR. Resection-induced small intestinal inflammation in CONV mice was associated with increases in proliferation, crypt depth, and villus height compared with GF mice after ICR. Resection-induced increases in crypt fission only occurred in CONV mice.

Conclusion: ICR-dependent small intestinal inflammation in CONV IL-10 null mice dramatically enhances early adaptive growth of the small intestine. Additional studies utilizing our model may provide clinical insight leading to optimal therapies in managing IBD patients after surgical resection.

Figure 1. Surgical Isolator in UNC Gnotobiotic Facility

The surgical isolator allows GF mice to undergo the exact same operative procedure as CONV mice while remaining free of all microbiota post-operatively.

Figure 2. Non-operative BrdU Immunohistochemistry

Representative BrdU immunostained sections from the jejunum of non-operative GF and CONV IL-10 null mice (20x). Note the increase in BrdU labeled cells in the CONV mouse compared to GF.

Figure 3. Operative BrdU Immunohistochemistry

Representative BrdU immunostained sections from the jejunum of sham-operated and ICR mice 7d following operation (20x). Note the increases in BrdU labeled cells and crypt depth that occur in both GF and CONV mice after ICR. In addition, marked submucosal inflammation (bracket) is only present in the CONV mouse after ICR when compared to GF and sham-operated groups.

Figure 4. Proliferative Index

Proliferative index is determined by the percent BrdU labeled cells per crypt in non-operative, sham-operative and ICR CONV and GF IL-10 null mice. ** represents statistically significant differences comparing ICR and sham-operated to non-operated mice (p < 0.01), # represents significant difference between CONV and GF IL-10 null mice after ICR (p < 0.01). Error bars represent ± SEM.

Figure 5

A. Crypt Depth and B. Villus Height represented as the percent change compared to non-operative controls (Table 1). * significant difference Sham: ICR (p<0.02), # significant difference GF ICR: CONV ICR (p<0.01). Error bars represent ± SEM.

Figure 6. Crypt Fission

Representative histological H&E sections of jejunum (20x) demonstrating normal crypt morphology in GF IL-10 null mice compared to the observation of increased crypt fission and inflammation in CONV IL-10 null mice after ICR. Arrows denote bifurcating crypts.

Figure 7. Percent Change in Crypt Fission

Percent increase in crypt fission observed following sham-operation or ICR, normalized to non-operative GF and CONV levels. * represents significant difference between CONV Sham and ICR (p<0.02), # represents significant difference between GF and CONV IL-10 null mice 7d after ICR (p<0.01). Error bars represent ± SEM.