Probing Nonlinear Cellular Responses to Integrated Mechanical Signals Through Examining Cell Alignment

Cells are complex systems that continuously receive signals in a variety of forms including both physical and chemical. The ability of cells to integrate these signals and already be hard wired to have coupled responses indicates the complexity at which cells function in terms of signal integration. One of the important areas in signal response is in mechanical stimulation, which has been shown to influence many cellular functions through the cytoskeleton and most often induces various cellular alignment. Most studies generally probe the affects of mechanical stimulation on cell behaviour by one mode of mechanical stimulation, though cells in fact experience multiple modes of mechanical stimulation simultaneously. From this comes the question of how does the cell process these multiple mechanical inputs? In this study we probed the effects of uniaxial stretch and/or shear fluid flow on NIH 3T3 fibroblast behaviour, specifically cell alignment. We used fluorescence microscopy to examine the orientation of the actin cytoskeleton and observed alignment along the direction of force for both uniaxial stretching and shear fluid flow in comparison to cells exposed to both mechanical modes. The cellular response surprisingly revealed an alignment that was neither parallel nor perpendicular to the direction of force. Furthermore, the integration of these 2 modes revealed a nonlinear response to combinations of shear stress and uniaxial stretching. These intriguing results have potential implications in a variety of fields including bioengineering, mechanotransduction, and cell structure.