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RESEARCH FACULTY - HECHT'S LAB
Pathophysiology of Enteric Pathogen Infections
Gail Hecht, MD, Chief and Professor of Medicine
Research Overview
The focus of our laboratory is to study the impact of infection by enteric bacterial pathogens on host intestinal epithelial cell function. The majority of our efforts are focused on the effects of enteropathogenic Escherichia coli (EPEC) on human intestinal epithelial physiology. EPEC is a predominant cause of enterocolitis worldwide and carries a high mortality rate. Although EPEC was the first E. coli to be linked to diarrhea, the mechanisms by which this pathogen causes diarrhea remain unknown. EPEC is an interesting pathogen as it is not invasive nor is it toxigenic. When it attaches to host cells, however, it causes the formation of an "attaching and effacing" lesion. This morphological change in the host cell is characterized by an elevation in the host cell membrane with a central depression at the site of microcolony attachment. Several signal transduction pathways are activated by EPEC attachment. The hypothesis of our studies is that following the attachment of EPEC to intestinal epithelial cells, specific signal transduction pathways which are activated are responsible for the induced changes in intestinal epithelial functions including active ion transport, tight junction barrier function, and gene expression, in particular for cytokines that direct the transepithelial migration of neutrophils. The long-term objective of these studies is to understand the mechanisms by which EPEC induces alteration in host intestinal epithelial physiology. The specific aims of our studies are:
- 1. To investigate the influence of EPEC on intestinal secretion and absorption of ions.
We have shown that EPEC infection does not stimulate chloride secretion, the usual paradigm associated with infectious diarrhea. In fact, EPEC infection attenuates the secretory response to classic secretagogues most likely by perturbing bicarbonate-dependent transport events.
- 2. To determine the mechanisms involved in the EPEC-induced disruption of tight junction barrier function.
Within 2-4 hours following EPEC attachment to intestinal epithelial monolayers, there is a significant drop in transepithelial electrical resistance which reflects an increase in tight junction permeability. This alteration in tight junction permeability is due to phosphorylation of myosin light chain by EPEC-activated myosin light chain kinase. Phosphorylated myosin light chain interacts with actin which activates myosin ATPase thus inducing contraction of the perijunctional actomyosin ring which directly underlies the tight junction. This force is transmitted to the tight junction causing it to become more leaky. We are also investigating the effect of EPEC on specific tight junction-associated proteins.
- 3. To elucidate the role of IL-8 in EPEC-stim
ulated neutrophil transmigration and determine the pathways through which EPEC regulates IL-8 gene expression. Our lab has shown that the inflammatory response-associated transcription factor, NF-kB, is activated by EPEC and that this activation is crucial for the expression of IL-8 in response to this infection. Interestingly, commensal strains of E. coli do not activate this transcription factor. We have shown instead that specific EPEC virulence genes are required for the initiation of this inflammatory response. We are examining the role of other relevant transcription factors in EPEC-induced IL-8 gene expression and comparing the patterns of transcription factor activation in response to other enteric bacterial pathogens with different mechanisms of action.
LAB STAFF:
Gail Hecht, MD
Kim Hodges, PhD
Sia Koutsouris, BS
Michelle M. Muza-Moons, PhD
Jennifer Roxas, BS
Sandy Royas, PhD
Andrew Weflen, BS
Contact Information:
Clinical Sciences Building
840 South Wood Street, 7th Floor
Phone: (312) 996-6651
Fax: (312) 996-5103
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