Page 71 - Physico-Chemical Niche Conditions for Bone Cells

Therefore, it is entirely possible that also in the current study, PFF induced expression of small HSPs. In addition, evidence shows that sHSPs are involved in the protection and dynamics of the cytoskeleton [47]. For example, sHSPs can stabilize actin filaments and prevent their aggregation when the cell is treated by physical/chemical stimuli (e.g., oxidative stress, heat shock) [47]. sHSPs regulates the equilibrium between microtubules and tubulin via combining tubulin subunits [47].
Figure 7. Effect of 1 h PFF on F-actin distribution at the cell boundary, and schematic summary of the changes induced by PFF in MC3T3-E1 osteoblasts. (A) F-actin was visualized using phalloidin. Upper image: control cell. Lower image: PFF-treated cell. Bar = 25 μm. (B) PFF was sensed through integrins, which formed clusters of a and b-integrins. Paxillin changed from granular to short rods. F-actin was neatly arranged, and F-actin fluorescence intensity was increased by PFF. The morphology and volume of the cell body and nucleus changed in response to PFF, which might result in changed cell function. CON, control; PFF, pulsating fluid flow.
The change in F-actin distribution in response to PFF is likely due to the rearrangement of actin fibers. In a previous study [48], we already showed that in PFF-treated osteoblastic cells, the orientation and alignment of F-actin stress fiber bundles were more homogeneous than in static control cells, with F-actin bundles running roughly parallel to the cell long axis. The connections of F-actin bundles between PFF-treated cells appeared simpler and clearer than in static control cells. The F-actin stress fiber bundles were also clearly visible above the nuclei. This data is consistent with findings by Fredrick et al., who also found that mechanical stimuli promoted the development of F-actin stress fibers, which were oriented parallel to the cell long axis in osteoblasts, whereas the F-actin stress fibers in static control cells were
Chapter 3
69
3