Time-dependent deformations in bone cells exposed to fluid flow in vitro: investigating the role of cellular deformation in fluid flow-induced signaling

Abstract

Numerous experiments have shown fluid flow to be a potent stimulator of bone cells in vitro, suggesting that fluid flow is an important physical signal in bone mechanotransduction. In fluid flow experiments, bone cells are exposed to both time-dependent (e.g. oscillating or pulsing) and timeindependent (e.g. steady) flow profiles. Interestingly, the signaling response of bone cells shows dependence on loading frequency and/or rate that has been postulated to be due to viscoelastic behavior. Thus, the objective of this study was to investigate the time-dependent deformations of bone cells exposed to fluid flow in vitro. Specifically, our goal was to characterize the mechanical response of bone cells exposed to oscillatory flow from 0.5-2.0Hz and steady flow, since these flow profiles have previously been shown to induce different morphological and biochemical responses in vitro. By tracking cell-bound sulfate and collagen coated fluorescent beads of varying sizes, we quantified the normalized peak deformation (peak displacement normalized by the maximum peak displacement observed for all frequencies) and phase lag in bone cells exposed to 1.0Pa oscillating flow at frequencies of 0.5-2.0Hz. The phase lag was small (3~10°) and frequency dependent, while the normalized peak displacements decreased as a weak power law of frequency (~f -0.2 ). During steady flow, the cells exhibited a nearly instantaneous deformation, followed by creep. Our results suggest that while substantial viscous deformation may occur during steady flow (compared to oscillating flow at ~1Hz), bone cells behave primarily as elastic bodies when exposed to flow at frequencies associated with habitual loading.

Integrative transcriptomic and proteomic analysis of osteocytic cells exposed to fluid flow reveals novel mechano-sensitive signaling pathways

“…However, these studies are generally constrained to a limited set of candidate genes or proteins as part of known or suspected signaling pathways. Osteocytic cells elastically deform when subject to physiological peak fluid shear stresses up to 5 Pa (Kwon and Jacobs, 2007; Price et al, 2011), initiating the rapid release of adenosine triphosphate (ATP) and prostaglandin E 2 via gap junctions or hemichannels (Batra et al, 2012; Cherian et al, 2005; Genetos et al, 2007; Klein-Nulend et al, 1995). In turn, these factors contribute to cell network propagation of intracellular calcium waves in proportion to flow-induced shear stress in vitro (Huo et al, 2008; Lu et al, 2012) as well as during in situ dynamic bone loading (Jing et al, 2013).…”

Measurement of Spatiotemporal Intracellular Deformation of Cells Adhered to Collagen Matrix During Freezing of Biomaterials

“…It was also reported that the pore size of the cytoplasm is around tens of nm [39], and particles of comparable or larger size are trapped in the cytoskeletal structure and do not undergo diffusive motion. In a previous study to characterize flow-induced deformation in bone cells, the displacements of cellbound microbeads were measured [40], where the cells were attached to a fibronectin-coated quartz slide. These previous studies, and the effect of particle size on deformation measurements reported in this work, confirm that microbead movement in the cell during cell deformation closely reflects cytoplasmic deformation in a short time interval.…”

Bone Cells Grown on Micropatterned Surfaces are More Sensitive to Fluid Shear Stress

“…understanding how cellular mechanotransduction occurs. 19,23 Other studies have suggested that in addition to maintaining the cell's mechanical integrity, the cytoskeleton plays a central role in sensing mechanical stimuli. 26,28,29 Nevertheless, the role of mechanical tension in the cytoskeleton in bone cell mechanotransduction, as distinguished from the existence of an intact cytoskeleton itself.…”