TEXAS ENGINEERING EXPERIMENT STATION

"Most cells generate intracellular forces that are transmitted to, and countered by, forces in the extracellular matrix. This mechanical force balance is necessary for maintaining both mechanical and biochemical cell equilibrium, i.e. homeostasis. When this balance is disturbed, the cell cytoskeleton reorganizes in an attempt to reestablish homeostasis. A relevant example of this reestablishment of equilibrium is the alignment of cells and their actin stress fibers perpendicular to the direction of cyclic matrix stretch. Arterial endothelial cells, which are elongated and aligned with the vessel axis in most of the arterial tree, lack such alignment at regions prone to atherosclerosis. The Principal Investigator has previously shown that cyclic stretching of endothelial cells induces activation of JNK - a signaling protein involved in regulating pro-atherogenic gene expression - but that JNK activation subsides as cells and their stress fibers align perpendicular to stretch. Other studies, both in vitro and in vivo, support a relationship between cell alignment and an anti atherogenic cell phenotype; however, the mechanism remains obscure. The goals of this project are to 1) develop a mechanical model that incorporates actin turnover and actin-myosin interactions to describe the dynamic relationships between deformations in the matrix and associated reactive reorganization of the actin cytoskeleton; and 2) test and refine the model using traction microscopy, femtasecond laser ablation, and microscopy of live cells expressing fluorescently-labeled actin. The model developed during this project will provide a novel and comprehensive framework for understanding the roles of mechanical stretch and cytoskeletal remodeling on cell mechanics, signal transduction, and cell function. This effort will result in an unprecedented capability to model the dynamic changes in the actin cytoskeleton that occur in response to diverse spatial and temporal patterns of stretch. Further, a quantitative model will result in an improved ability to reinterpret existing data, as well as generate new experiments to elucidate the mechanisms of stretch-induced cytoskeletal reorganization. Importantly, this project will provide the foundation for models of signal transduction where the inputs are mechanical stimuli, rather than biochemical ligands. The proposed model provides a tool to understand how the mechanical properties of adherent cells change with time through cytoskeletal remodeling. Such knowledge will provide guidance toward the use of mechanical stimuli to regulate cell function in tissue engineering, surgical decision-making, and prognosis of cardiovascular disease. The model will be broadly disseminated by providing public access to the model software and incorporating the concepts developed in this project into undergraduate and graduate courses. Further, the proposed project will provide additional opportunities for undergraduate and graduate research, including students from underrepresented groups, in the laboratory of the Principal Investigator. "

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