| Understanding cell mechanics in the context of cellular processes is essential as the constitutive cells in the human body are constantly subjected to mechanical stresses and often presented with situations where cellular adaptations are critical for their proliferation. For example, during wound healing, the initial onset of wounding causes cells residing in the extravascular space to be subjected to mechanical shear stress from vascular blood flow. Subsequent loss of cell-cell contacts may cause epithelial cells to undergo epithelial-mesenchymal transition (EMT), a process that turns the cells more fibroblast-like, changing not only morphology, but also increasing motility. Mechanical adaptations in response to shear stress or to increase cellular migration have been studied mainly though visualization of changes in cytoskeletal structures and understanding the corresponding signaling pathways. These observations are informative in elucidating regulating proteins and cellular phenotype, but do not offer insights to the effects of these cellular changes and regulations. A few important questions remain: (1) what are the corresponding mechanical changes, (2) how do these mechanical changes help the cell adapt, (3) is it possible these adaptations result in unforeseen consequences, and (4) if so, do they result in disease?; Due to technical limitations, only a portion of the answers have been explored to date. In an attempt to answer these questions, we examine changes in intracellular and intranuclear mechanics as a result of changes in cytoskeletal organization. We also document consequences of these changes, such as difference in cell migration, nucleus movement, and centrosome polarity. By first observing Swiss 3T3 fibroblasts, the quintessential cytoskeletal model system, we were able to develop original assays and gain an extensive foundation of knowledge. We reveal that adherent cells subjected to fluid shear stress strengthen their cytoskeleton and identify Rho-kinase as a key factor in the mechanotransduction pathway that controls the cytoskeleton mechanical response of cells to shear. In addition, we establish Cdc42 as a molecular regulator of shear induced microtubule-dependent polarity-driven nucleus movement in Swiss 3T3 fibroblasts.; We then applied this knowledge to further understand the role of cellular mechanics, beyond that of wound healing, in human diseases. For laminopathies, we examined lamin A/C knockout mouse embryo fibroblasts and find that intracellular mechanics depends critically on the integrity of the nuclear lamina. Loss of lamin A/C perturbed both cell motility and polarization, suggesting the existence of a functional connection between the nucleus and the cytoskeleton. In addition, preliminary data indicates that cell mechanics may be used, in conjunction with further tests of RhoGTPase mediation of EMT and migration pathways, to offer an alternative pathogenesis of high grade ovarian cancer. |
