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

Mammalian cells are frequently (and in some cases, constantly) subjected to mechanical stress. This presentation examines two of these issues: the mechanotransduction of endothelial cells in flow environments and the adhesion of biofilms to bladder cells. Vascular endothelial cells are nature's "rheologists" and line the inner walls of our blood vessels, being sensitive to surface shear stresses. It is known that these stresses affect the shape and orientation of endothelial cells. There is growing evidence that the local flow kinematics are fundamental to the triggers that initiate valve formation. Experiments are described in which stagnation point flows and constriction flows are used to create regions with well-controlled spatial variations in wall shear stresses. Live-cell imaging is used to reveal migration dynamics that create striking patterns of cell orientation and densification. It is shown that the observed mechanotransduction responses, together with elevated expression of the transcription factor Prox1, match well with what is observed during valvulogenesis.

Bacterial adhesion to host cells is often a first step in the infection process. For example, the Escherichia coli uropathogen, the main causative agent of urinary tract infection, adheres to the epithelial cells of the host bladder and initiates cellular invasion. This triggers a subsequent pathogenic cascade characterized by recurrent infection. There is currently growing interest in developing new antimicrobials that, rather than targeting bacterial survival and exerting high selective pressure for drug-resistant mutations, target mechanisms that promote 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 problem, 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 capable of expressing several different extracellular components, such as type 1 fimbriae, curli and cellulose. Using this approach, we can quantitatively compare the degree to which these different extracellular components affect bacterial adhesion to the cell monolayer. In addition, we can use these measurements to assess the effectiveness of various small molecules in preventing binding to host cells.

By Prof. Gerald G. Fuller

Chemical Engineering

Stanford University

Stanford, CA