Cell Mechanobiology: The Forces Applied to Cells and Generated by Cells
Many types of cells live in a mechanical environment and are sensitive to changes in mechanical forces. A few examples of these mechanical load-responsive cells include ™broblasts in skin, osteocytes in bones, chondrocytes in cartilage, and endothelial cells lining the blood vessels. These cells in vivo are subjected to tension, compression, shear stresses, hydrostatic pressure, or a combination of these forces (Figure 12.1). Mechanical forces on cells regulate a wide range of cellular events, including proliferation, differentiation, gene expression, and protein secretion.13,23,35,52,67,72,128,132,135,161,175 As such, mechanical forces on cells have a profound effect on tissue homeostasis and pathophysiology. Therefore, in vitro model systems have been developed over the years to investigate cellular mechanobiological responses under well-controlled mechanical loading conditions.21,68
Besides external mechanical forces that act on cells, cells themselves generate internal mechanical forces, which are then transmitted to the ECM and are referred to as CTFs. CTFs are necessary for cells to migrate, maintain shape, organize ECM, probe physical environments, and generate mechanical signals. Hence, CTFs play a fundamental role in many biological processes including tissue homeostasis, wound healing, angiogenesis, and metastasis.175 Quantitative analysis of CTFs, therefore, enables better understanding of these physiological and pathological events at the tissue and organ levels.