Final Report

Dysregulated Host/microbial interactions have been shown to result in the development and/or perpetuation of inflammatory bowel disease (IBD) by inducing uncontrolled activation of acquired immune responses. Innate immune responses mediated by colonic epithelial cells (CEC) and phagocytic cells such as macrophages (Mf) play a crucial role in the initial defense to maintain the appropriate host/microbial interactions.   Activation of signal transducer and activator of transcription (STAT) 3 is required to enhance and maintain not only the barrier function of epithelial cells but also the activation of Mf. Therefore, disruption of innate immune responses by genetically engineered inactivation of STAT3 cascade in the intestinal epithelial cells or Mf induces a spontaneous development of intestinal inflammation. In contrast, activation of IL-6/STAT3 cascade can also induce prolonged survival of pathogenic T cells and disruption of immune tolerance and, indeed, inactivation of this cascade contributes to the suppression of acquired immune (T-cell) mediated colitis. Therefore, STAT3 activation plays distinctly different roles: regulatory role in innate inflammation versus the pathogenic role in acquired inflammation. Since it is believed that both innate and acquired immunities are simultaneously involved in the IBD pathogenesis, a combined therapeutic approach designed to preserve STAT3 activation in innate cells (such as CEC) and simultaneously downregulate activation of STAT3 in acquired cells (T cells) may be a more effective way for amelioration of IBD.   Through our molecular screening utilizing DNA microarray and real-time PCR analyses, we have found that IL-22 expression in the colonic LP is induced under intestinal inflammatory conditions in both human and mouse. In addition, neutralization of IL-22 activity leads to exacerbation of experimental acute colitis. Furthermore, direct gene delivery of IL-22 into the colon leads to attenuation of chronic colitis. Importantly, IL-22 specifically activates STAT3 in innate cells such as CEC and Mf, consistent with recent reports that the target of IL-22 is innate, but not acquired, cells. Therefore, we hypothesize that IL-22 plays a crucial role in the suppression of intestinal inflammation by maintaining an appropriate host/microbial interaction that is controlled by the STAT3-induced activation of innate immunity. The following Aims are designed to test our hypothesis.

 

Aim I: To examine the role of IL-22 in mucin-associated protein expressions by human colonic epithelial cells.   

 

Aim II: To examine the role of IL-22 in experimental colitis models and to determine whether IL-22 gene delivery can be used as a therapeutic approach for IBD.

 

All studies proposed in the Aims of BMRP grant application have been fully completed. As a result, we have identified the unexpected novel function of IL-22 for reinforcing intestinal mucus layer formation under intestinal inflammatory condition in a signal transducer and activator of transcription (STAT) 3-dependent manner. In addition, we have found that supplementation of IL-22 expression by lipid-based local gene delivery system, which has the potential to perform in humans through the approach used for endoscopic mucosal resection (EMR), leads to rapid amelioration of chronic UC-like experimental colitis in association with significant goblet cell restitution.   The results obtained have been published in J Clin Invest 2008, 118:534-544. The significant results are summarized in the section (iii).

 

1. IL-22 has generally been believed to play a pathogenic role in IBD due to the ability to activate Erk1/2 in cancer cell lines to induce the production of IL-8 and due to the production of IL-22 by T helper (Th) 17 T cell subset involved in the pathogenesis of several inflammatory responses. However, our data clearly demonstrate that IL-22 rather serves as a regulatory cytokine for improving UC-like experimental colitis. 

 

2. Previous in vitro studies using cancer cell lines have demonstrated the ability of IL-22 to activate both STAT3 and Erk. However, we find in surgical samples of human colons and freshly isolated colonic epithelial cells from wild type mice that IL-22 can activate STAT3 but not Erk1/2 in normal (without carcinogenic change) colonic epithelial cells of humans and mice.

 

3. IL-22 has previously been demonstrated to induce the production of anti-bacterial peptide and IL-10. We identify an additional novel function of IL-22 for inducing the expression of mucus-associated molecules such as mucin (MUC) 1, 3 and 13 by colonic epithelial cells in humans and mice. Importantly, we also find that the reinforcement of colonic mucus layer formation, which contributes for enhancing intestinal defense against enteric microorganisms, represents the major determinant for IL-22-induced rapid amelioration of chronic colitis.

 

4. IL-22 binding protein (IL-22BP) has previously been shown to possess the ability to neutralize IL-22 activity in vitro. We further demonstrate that IL-22BP serves as a very strong inhibitor of IL-22 in vivo.

 

5. We establish a lipid-based local gene delivery system that is capable of targeting the restricted region such as inflamed mucosa within colon for inducing the expression of genes of interest. This system is achieved through injecting the lipid-coupled genes into the space between mucosal and muscular layers where is also targeted by endoscopic mucosal resection (EMR) that has been widely used in humans to remove early phase of cancer. Therefore, the local gene delivery system developed in mice may apply to human in future. 

 

Inflammatory bowel disease (IBD) is a group of chronic, relapsing and remitting inflammatory conditions that affect individuals throughout the life.   Undesired responses of host to intestinal bacteria play an important role in the development, exacerbation and perpetuation of IBD. For preventing the development of the undesired host responses, epithelial cells have generally been considered to represent the key player because they anatomically make a barrier between intestinal bacteria and host. Therefore, it could be predicted that the activation of epithelial cells significantly contributes to the suppression of IBD.   Several factors have been identified to induce the activation of epithelial cells. However, one of major concerns regarding the previously identified factors is that they simultaneously activate epithelial cells and other cells that serve as a bad guy in IBD.   Therefore, it is reasonable to consider that specific activation of epithelial cells represents an ideal and effective therapeutic approach for IBD. In this regard, we have identified by the support from BMRP that a new factor termed interleukin-22 has the potential to rapidly and efficiently improve ulcerative colitis by specifically activating epithelial cells. Interestingly, we have also found that IL-22 provides significant contributions to enhance host defense against enteric microorganisms that are required for the development and exacerbation of chronic colitis. In addition, we have developed a local gene delivery system in mice that is capable of targeting the inflamed colon for enhancing the defense against enteric bacteria. Since the procedure employed for the gene delivery system is similar to that used for endoscopic mucosal resection (EMR) that has been widely used for treating the patients with gastric and colonic cancer, we hope that the gene delivery system developed in mice would apply to IBD patients in future.