Flowtaxis of osteoblast migration under fluid shear and the effect of RhoA kinase silencing

• Published in: PloS one Vol. 12; no. 2; p. e0171857
• Main Authors: Riehl, Brandon D, Lee, Jeong Soon, Ha, Ligyeom, Kwon, Il Keun, Lim, Jung Yul
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 15.02.2017; Public Library of Science (PLoS)
• Subjects: Animals; Biocompatibility; Biology and Life Sciences; Bone remodeling; Bone remodelling; Cell adhesion & migration; Cell migration; Cell Movement; Cells, Cultured; Coefficients; Cytoskeleton; Directional sensitivity; Driving ability; Fluid flow; Homeostasis; Kinases; Mechanical stimuli; Medicine and Health Sciences; Mesenchymal stem cells; Mesenchymal Stem Cells - cytology; Mesenchymal Stem Cells - metabolism; Mesenchyme; Mice; Osteoblasts; Osteoblasts - cytology; Osteoblasts - enzymology; Osteoblasts - metabolism; Phosphotransferases; Physical Sciences; rho-Associated Kinases - antagonists & inhibitors; rho-Associated Kinases - genetics; rho-Associated Kinases - metabolism; RhoA protein; RNA Interference; RNA, Small Interfering - metabolism; Rocks; Sensitivity; Shear Strength; Shear stress; Shear stresses; Signal Transduction; Signaling; Steady flow; Stem cells; Stress, Mechanical; Time-Lapse Imaging; United States > US
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0171857

Despite the important role of mechanical signals in bone remodeling, relatively little is known about how fluid shear affects osteoblastic cell migration behavior. Here we demonstrated that MC3T3-E1 osteoblast migration could be activated by physiologically-relevant levels of fluid shear in a shear stress-dependent manner. Interestingly, shear-sensitive osteoblast migration behavior was prominent only during the initial period after the onset of the steady flow (for about 30 min), exhibiting shear stress-dependent migration speed, displacement, arrest coefficient, and motility coefficient. For example, cell speed at 1 min was 0.28, 0.47, 0.51, and 0.84 μm min-1 for static, 2, 15, and 25 dyne cm-2 shear stress, respectively. Arrest coefficient (measuring how often cells are paused during migration) assessed for the first 30 min was 0.40, 0.26, 0.24, and 0.12 respectively for static, 2, 15, and 25 dyne cm-2. After this initial period, osteoblasts under steady flow showed decreased migration capacity and diminished shear stress dependency. Molecular interference of RhoA kinase (ROCK), a regulator of cytoskeletal tension signaling, was found to increase the shear-sensitive window beyond the initial period. Cells with ROCK-shRNA had increased migration in the flow direction and continued shear sensitivity, resulting in greater root mean square displacement at the end of 120 min of measurement. It is notable that the transient osteoblast migration behavior was in sharp contrast to mesenchymal stem cells that exhibited sustained shear sensitivity (as we recently reported, J. R. Soc. Interface. 2015; 12:20141351). The study of fluid shear as a driving force for cell migration, i.e., "flowtaxis", and investigation of molecular mechanosensors governing such behavior (e.g., ROCK as tested in this study) may provide new and improved insights into the fundamental understanding of cell migration-based homeostasis.