Toll-Like Receptor-Complex in Intestinal Epith. Cells

Project: Research project

Project Details

Description

The intestinal epithelium is continually exposed to a high concentration of diverse bacteria. In spite of the
density of commensal bacteria, the normal intestine is not inflamed. Idiopathic inflammatory bowel disease
in humans and animals is characterized by aberrant host-microbial interactions. We wished to understand the
mechanism by which the normal epithelium guards against chronic inflammation in the presence of
commensal flora and thus understand how this may be perturbed in idiopathic inflammatory bowel disease.
Gut commensal flora consists of mixed gram-positive and gram-negative organisms (Naidu et al. 1999;
Dunne 2001). The cell wall of gram-negative bacteria contains lipopolysaccharide (LPS), a potent pro-
inflammatory molecule (Aderem and Ulevitch 2000). Cellular responses to LPS are mediated by the
interaction of LPS with toll-like receptor 4 (TLR4) and transduced via the IL- 1 receptor signaling complex to
activate NF-KB and pro-inflammatory cytokine secretion (Zhang et al. 1999; Bowie and O'Neill 2000; Jiang
et al. 2000; da Silva Correia et al. 2001). Data demonstrate that a novel, secreted protein, MD-2, is required
for TLR4 function (Shimazu et al. 1999; Yang et al. 2000). We hypothesize that the TLR co-receptor MD-2
is normally down-regulated in intestinal epithelial cells limiting pro-inflammatory gene expression in the
presence of LPS. We further hypothesize that increased expression of MD-2 in response to Thl cytokines
perpetuates bacterial hyper-reactivity in inflammatory bowel disease. We and others have recently described
that intestinal epithelial cells are unresponsive to purified, protein-free LPS as measured by NF-KB activation
and IL-8 secretion (Abreu et al. 2001; Naik et al. 2001). LPS unresponsiveness in intestinal epithelial cells is
due to low expression of TLR4 and MD-2. Preliminary data demonstrate that MD-2 expression is low in
normal intestinal epithelial cells in vivo and increased in patients with inflammatory bowel disease. Thl
cytokines increase expression of MD-2 and restore LPS responsiveness in intestinal epithelial cells. Cloning
of the MD-2 promoter demonstrates that MD-2 is transcriptionally regulated by IFN-y via the STAT
pathway. In this proposal, we will explore the molecular mechanisms by which MD-2 is transcriptionally
regulated in intestinal epithelial cells and the effect of this regulation on the function of toll-like receptor
signaling. The results of our studies have important implications for understanding host-microbial interactions
and the inter-relationship between the innate and adaptive immune systems in the gut.
StatusFinished
Effective start/end date7/1/0312/31/07

Funding

  • National Institute of Allergy and Infectious Diseases: $331,034.00
  • National Institute of Allergy and Infectious Diseases: $77,248.00
  • National Institute of Allergy and Infectious Diseases: $243,701.00
  • National Institute of Allergy and Infectious Diseases: $102,001.00
  • National Institute of Allergy and Infectious Diseases: $321,433.00
  • National Institute of Allergy and Infectious Diseases: $339,000.00

Fingerprint

Explore the research topics touched on by this project. These labels are generated based on the underlying awards/grants. Together they form a unique fingerprint.