Molecular pathogenesis of Helicobacter hepaticus induced liver disease

Thesis (Ph. D. in Molecular and Systems Bacterial Pathogenesis)--Massachusetts Institute of Technology, Biological Engineering Division, 2005.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references.Helicobacter hepaticus infection of A/JCr mice is a model of liver cancer resulting from chronic active inflammation. We monitored hepatic global gene expression profiles and correlated them to histological liver lesions in H. hepaticus infected and control male A/JCr mice at 3 months, 6 months, and 1 year of age. We used an Affymetrix-based oligonucleotide microarray platform on the premise that a specific genetic expression signature at isolated time points would be indicative of disease status. Model based expression index comparisons generated by dChip yielded consistent profiles of differential gene expression for H. hepaticus infected male mice with progressive liver disease versus uninfected control mice within each age group. Linear discriminant analysis and principal component analysis allowed segregation of mice based on combined age and lesion status, or age alone. Up-regulated genes present throughout the 12 month study involved inflammation, tissue repair, and host immune function. Upregulation of putative tumor and proliferation markers correlated with advancing hepatocellular dysplasia. Transcriptionally down-regulated genes in mice with liver lesions included those related to peroxisome proliferator, cholesterol, and steroid metabolism pathways. Transcriptional profiling of hepatic genes documented gene expression signatures in the livers of H. hepaticus infected male A/JCr mice with chronic progressive hepatitis and preneoplastic liver lesions, complemented the histopathological diagnosis, and suggested molecular targets for the monitoring and intervention of disease progression prior to the onset of hepatocellular neoplasia. Our laboratory, in collaboration with Professors Suerbaum and Schauer, recently identified a(cont.) 70kb genomic island in Helicobacter hepaticus strain ATCC 51488 as a putative pathogenicity island (HhPAI) (Suerbaum et al, PNAS, 2003). This region within H. hepaticus contains genes HH0233-HH0302, a differential GC content, several long tandem repeats but no flanking repeats, and three components of a type IV secretion system (T4SS). A/JCr mice were experimentally infected with three naturally occurring strains of H. hepaticus including the type strain H. hepaticus ATCC 51488 strain (Hh 3B1) isolated from A/JCr mice, MIT 96-1809 (Hh NET) isolated from mice shipped from the Netherlands, and MIT-96-284 (HhG) isolated from mice acquired from Germany.4 HhNET (missing most of the HhPAI) infected male A/JCR mice exhibited a significantly lower prevalence (p<.05) of hepatic lesions at 6 months post infection than Hh 3B1 with an intact HhPAI. Hh G also has a large segment of the genomic island deleted, but not as many genes are deleted as compared to Hh NET. Hh G also demonstrated a lower prevalence of hepatic lesions. This variable pathological effect was evident in male mice only. The severity of chronic active inflammation in the liver of the H. hepaticus infected A/JCr mice depended on H. hepaticus liver colonization levels. The in vivo results support the presence of the HhPAI as a legitimate virulence determinant and predictor of severity of liver lesions in H. hepaticus infected A/JCr male mice. To further determine the differences in virulence of the H. hepaticus strains Hh 3B1, Hh NET, Hh G and an isogenic mutant H. ...by Samuel R. Boutin.Ph.D.in Molecular and Systems Bacterial Pathogenesi