All Stressed Out: Mammalian Cells Subject to Adhesive and Hydrodynamic Stress Par Pr. Gerald G. Fuller

Mammalian cells are frequently (and in some cases, constantly) subjected to mechanical stress. This presentation examines two such problems: mechanotransduction of endothelial cells in flowing environments and biofilm-bladder cell adhesion. Vascular endothelial cells are nature's "rheologists" and line the interior walls of our blood vessels and are sensitive to surface shear stresses. These stresses are known to affect the shape and orientation of endothelial cells. There is increasing evidence that local flow kinematics are central to triggers that initiate valve formation. Experiments are described where stagnation point flows and constriction flows are used to create regions of well controlled spatial variations of wall shear stresses. Live-cell imaging is used to reveal migration dynamics that create remarkable patterns of orientation and cell densification. The observed mechano-transduction responses, along with elevated expression of the Prox1 transcription factor are shown to be well-matched to what is observed during valvulogenesis.

Bacterial adhesion to host cells is often a first step in the infection process. For example, uropathogenic Escherichia coli, the major causative agent of urinary tract infection, bind to host bladder-epithelial cells and initiate cell invasion. This triggers a subsequent pathogenic cascade characterized by recurrent infection. There is currently growing interest in developing new antimicrobials that, instead of targeting bacterial survival and placing high selective pressure for drug-resistant mutations, target mechanisms promoting infection such as binding to host cells. This new therapeutic strategy requires a detailed understanding of the factors that contribute to bacterial adhesion. To address this issue, we developed a live cell monolayer rheometer to measure adhesion between a monolayer of bladder-epithelial cells and a layer of bacteria. The bacterial strain used in this study is UTI89, a uropathogenic strain of E. coli that is capable of expressing several different extracellular components such as type 1 pili, curli, and cellulose. Using this approach, we can quantitatively compare the extent to which these different extracellular components affect bacterial adhesion to the cell monolayer. Additionally, we can use these measurements to assess the effectiveness of various small molecules in preventing binding to host cells.

Par Pr. Gerald G. Fuller

Chemical Engineering

Stanford University

Stanford, CA

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