Submitted on August 16, 2007
Accepted on January 4, 2008
Decreased epithelial barrier function evoked by exposure to metabolic stress and non-pathogenic E. coli is enhanced by TNF
Kimberley Lewis1, Jackie Caldwell2, Van Phan2, David Prescott2, Aisha Nazli1, Arthur Wang2, Johan D Soderholm3, Mary H. Perdue4, Philip M. Sherman5, and Derek M McKay6*
1 McMaster University, Hamilton, Canada
2 University of Calgary, Calgary, Canada
3 Biomedicine and Surgery, Linkoping University, Linkoping, Sweden
4 Department of Pathology, Mcmaster University, Hamilton, Canada
5 University of Toronto; University of Toronto, United States
6 Physiology and Biophysics, University of Calgary, Calgary, Canada; , Canada
* To whom correspondence should be addressed. E-mail: dmckay{at}ucalgary.ca.
A defect in mitochondrial activity can contributes to disease. We found that monolayers of T84 epithelial cells exposed to dinitrophenol (DNP; uncouples oxidative phosphorylation) and non-pathogenic E. coli display decreased barrier function. Here the impact of DNP on macrophages and the effect of TNF 
, DNP and E. coli on epithelial permeability were assessed. DNP treatment of THP-1 macrophages resulted in reduced ATP, and although hypo-responsive to LPS, these macrophages produced IL-1
, IL-6 and TNF. Given the role of TNF in inflammatory bowel disease (IBD), and the association between increased permeability and IBD, TNF (10 ng/ml) was added to the DNP (0.1 mM)+E. coli (106 cfu) and this resulted in a significantly greater lincrease in epithelial permeability than that elicited by DNP+E. coli. This increased permeability was not due to epithelial death and the enhanced E. coli translocation was reduced by pharmacological inhibitors of NF
signaling (PTDC, NEMO-binding peptide and BAY 11-7082, and the proteosome inhibitor, MG132). In contrast, the drop in TER was unaffected by the inhibitors of NF. As an integrative model system, our findings support the induction of a positive feedback loop that can severely impair epithelial barrier function and contribute to existing inflammation or trigger relapses in IBD. Thus, metabolically-stressed epithelia display increased permeability in the presence of viable non-pathogenic E. coli that is exaggerated by TNF released by immune cells, such as macrophages, that retain this ability even if they also metabolically stressed.
