The cell manages to lose polarity shortly after the onset of cyclic stretching ((stretch parameters as in (a)). measured over a wide range of experimental conditions, thus elucidating a basic aspect of mechanosensitivity. Cells throughout our body constantly interact with their microenvironment. While biochemical communication has 4-Aminopyridine been extensively studied for a long time, the importance of mechanical interactions (i.e. cells ability to apply, sense and respond to forces) has been recognized only recently 1C4. Precise mechanical conditions, from the subcellular level and up to the organ scale, are critical for tissue development 5,6, function 7,8, remodeling and healing 9,10. Here we focus on the response of cells to cyclic stretching of the underlying substrate which mimics vital physiological conditions (e.g. heart beating, pulsating blood vessels and breathing). In response to these external forces, adherent cells – starting from naturally random orientations – reorient to a well-defined and uniform angle 11 which depends on the applied stretching 12C15. Moreover, at the subcellular level, the cytoskeleton and most notably stress fibres (SFs) generate internal contractile forces 16 even as they polarize, apparentlypreceding cell reorientation to a similar angle 14,17. This outstanding process reveals high cellular sensitivity and accuracy in response to external forces. Nevertheless, the mechanisms underlying it, as well as the validity of current theoretical models describing it 18C22, still remain unclear. In this study, we experimentally and theoretically study cell reorientation in response to cyclic stretching of the underlying substrate. We first report on detailed experimental measurements of cell reorientation and demonstrate that they cannot be quantitatively explained by the existing models. We then develop a new theory, which takes into 4-Aminopyridine account both the passive mechanical response of the cells to substrate deformation and the active remodeling of their actin cytoskeleton and focal adhesions (FAs), highlighting a fascinating interplay between structure, elasticity and molecular kinetics in the reorientation process. This theory is in excellent quantitative agreement with all of the extensive experimental data, predicting the complete temporal reorientation dynamics. Moreover, it elucidates mechanisms involved in cell readout of external substrate deformation, an important aspect of cellular mechanosensitivity. Finally, we address the biological and physical significance of the only two cellular parameters appearing in the theory, and discuss the non-trivial predictions that emerge. Results Reorientation deviates from current theoretical predictions We set out first to quantitatively study the reorientation process over a wide range of experimental conditions. REF-52 fibroblasts, which usually grow as polarized cells with long and well separated SFs, were plated onto a fibronectin-coated poly(dimethylsiloxane) (PDMS) chamber. After pre-incubation, the elastic chamber was cyclically stretched, effectively biaxially, in a custom built device 13 at chosen strain amplitudes and defined frequency, f. Specifically, Rabbit polyclonal to ERK1-2.ERK1 p42 MAP kinase plays a critical role in the regulation of cell growth and differentiation.Activated by a wide variety of extracellular signals including growth and neurotrophic factors, cytokines, hormones and neurotransmitters. the magnitudes of the linear elastic principal strains in the substrate, and ? A widespread and intuitive approach suggests that the rod-like SFs realign, under cyclic stretching, along the zero (or minimal) matrix strain directions 19C21, where they effectively maintain their initial unperturbed state. These zero strain models therefore predict 19 (?< <). The angle is measured relative to the direction of the principal strain (in our experiments is usually extensional and compressive with 0 1) (see Fig. 2a). A different approach 18,20, based on measurements of cell traction forces 23, suggests that SFs reorient in the minimal matrix stress direction and as our impartial control parameters. 4-Aminopyridine Consequently, a wide range of final orientations (45-80) was achieved by modifying the value of (was controlled by changing the clamping geometry at the chambers edges as depicted in Fig. 2b). Surprisingly, the measured angles (Fig. 2c) systematically deviate from the zero strain prediction of Eq. 1 (see also 14), reaching a deviation of ~10 degrees at low values (20 fold higher than the error bars). An even more dramatic deviation from the zero stress prediction of Eq. 2 is observed (Fig. 2c). Moreover, the statistical variation of the measured final orientations is very narrow (Fig. 4-Aminopyridine 1d and Fig. 2c, inset) and cannot account for the discrepancy with the zero strain/stress predictions. We conclude, therefore, that these results call for a new theoretical model. New theory of cell reorientation The above results demonstrate how SF reorientation depends on the spatiotemporal deformation pattern of the.