Chapter 2.2: Mechanics of the Cytoskeleton

The cytoskeleton, the system of protein filaments that permeate the cytoplasmic space of all eukaryotic cells, is primarily responsible for the structural integrity exhibited by a cell and determines its deformation in response to a given stress. This fibrous matrix is instrumental to a wide variety of essential cell functions ranging from migration to adhesion to mitosis to mechanotransduction (the genetic response of a cell to mechanical stimuli). For some cells, their intrinsic elasticity determines their deformation in response to external forces. Cells such as those circulating within or lining the walls of the vascular system are subjected to fluid dynamic forces and change shape as a direct consequence of those forces. In other cells, such as those surrounded by a stiffer extracellular matrix, their shape is dictated by the deformation of the structures in which they are embedded and the cell’s own elastic characteristics play little role in determining the magnitude of those deformations. Even in these, however, externally-imposed deformations produce intercellular forces that can influence cell secretions, gene expression and protein synthesis. Cell migration results from an interaction between the forces of adhesion to structures external to the cell (extracellular matrix in vivo or cell culture substrate for in vitro preparations), and the cell’s own intrinsic stiffness in response to internally generated forces. As will be shown in Chapter 2.3, the speed of migration depends on a critical balance between cell stiffness and adhesion strength such that migration speed is reduced when the cell is either too rigid or too compliant. Mechanotransduction is the term used to describe gene expression in response to cellular deformations or forces acting on the cell. This appears to be a property of nearly all eukaryotic