Cell alignment is induced by cyclic changes in cell length: studies of cells grown in cyclically stretched substrates

Abstract

Many types of cells, when grown on the surface of a cyclically stretched substrate, align away from the stretch direction. Although cell alignment has been described as an avoidance response to stretch, the specific deformation signal that causes a cell population to become aligned has not been identified. Planar surface deformation is characterized by three strains: two normal strains describe the length changes of two initially perpendicular lines and one shear strain describes the change in the angle between the two lines. The present study was designed to determine which, if any, of the three strains was the signal for cell alignment. Human fibroblasts and osteoblasts were grown in deformable, rectangular, silicone culture dishes coated with ProNectin, a biosynthetic polymer containing the RGD ligand of fibronectin. 24 h after plating the cells, the dishes were cyclically stretched at 1 Hz to peak dish stretches of 0% (control), 4"%, 8%. and 12% After 24 h of stretching, the cells were fixed, stained, and their orientations measured. The cell orientation distribution was determined by calculating the percent of cells whose orientation was within each of eighteen 5" angular intervals. We found that the alignment response was primarily driven by the substrate strain which tended to lengthen the cell (axial strain). We also found that for each cell type there was an axial strain limit above which few cells were found. The axial strain limit for fibroblasts, 4.2&0.4% (mean & 95% confidence), was lower than for osteoblasts, 6.4 * O.6' Li . We suggest that the fibroblasts are more responsive to stretch because of their more highly developed actin cytoskeleton.

A thermodynamically motivated model for stress-fiber reorganization

“…The in-plane strains in the cell are spatially uniform, consistent with experimental observations; see for example Neidlinger-Wilke et al (2001). With the cells subjected to a spatially uniform state, ̂= 1 throughout the cell and ̂̇= 0, i.e.…”

“…Experiments regarding cytoskeletal arrangements in response to cyclic mechanical stimuli were initially performed on cells seeded on two-dimensional substrates that were stiff relative to the cells (Neidlinger-Wilke et al 2001;Kaunas et al 2005). In these experiments the cytoskeletal network formed perpendicular to the imposed cyclic strains and this was interpreted as strain avoidance (Buck 1980).…”

Conditions for Osteoblast Arrangement Induced under Long-Term Cyclic Stretching

“…Both the stretch frequency and magnitude are considered to have an effect on the change of cell direction. For osteoblasts, a stretch amplitude threshold for cell morphological change has been proposed as 4%, 13) which is consistent with our results showing that 4% stretching is best suited for sustained cell alignment. However, the combined conditions of 5 cycles/min frequency and 4% magnitude resulted in excess stress for osteoblasts in long-term cultivation, resulting in apoptosis.…”

Cooperative effects of Rho and mechanical stretch on stress fiber organization

“…Cyclic uniaxial stretch can cause cells and their stress fibers to orient perpendicular to the direction of stretch in nonconfluent osteoblasts and fibroblasts (29), nonconfluent vascular smooth muscle cells (30), and confluent airway smooth muscle cells (31). It has been shown that stretch-induced perpendicular orientation of stress fibers in nonconfluent and confluent ECs requires Rho and Rho-kinase activity (16,17).…”