Insights into the pathogenesis of enteropathogenic E. coli using an improved intestinal enterocyte model

Enteropathogenic E. coli (EPEC) is a human pathogen that targets the small intestine, causing severe and often fatal diarrhoea in infants. A defining feature of EPEC disease is the loss (effacement) of absorptive microvilli (MV) from the surface of small intestinal enterocytes. Much of our understanding of EPEC pathogenesis is derived from studies using cell lines such as Caco-2 - the most extensively used small intestinal model. However, previous work has revealed fundamental differences between Caco-2 cells and in vivo differentiated enterocytes in relation to MV effacement. This, and the high heterogeneity and low transfection efficiency of the Caco-2 cell line prompted the isolation of several sub-clones (NCL-1-12) to identify a more tractable and improved in vivo-like cell model. Along with established Caco-2 clones (TC-7, BBE1), sub-clones were assessed for growth rate, apical surface morphology, epithelial barrier function and transfection efficiency. TC-7 cells provided the best all-round clone and exhibited highest levels of ectopic gene expression following cell polarisation. Novel alterations in EGFP-labelled mitochondria, that were not previously documented in non-polarised cell types, highlighted the potential of the TC-7 model for defining dynamic enterocyte-specific changes during infection. Crucially, the TC-7 cell line also mimicked ex vivo derived enterocytes with regard to MV effacement, enabling a better dissection of the process. Effacement activity caused by the EPEC protein Map in the Caco-2 but not ex vivo model, was linked to a defect in suppressing its Cdc42-dependent functionality. MV effacement activity of the EPEC protein EspF in the TC-7 model was dependent on its N-WASP binding motif, which is also shown to play an essential role in epithelial barrier dysfunction. Together, this study highlights the many advantages of using TC-7 cells as a small intestinal model to study host-pathogen interactions.