REMODELING OF ACTIN CYTOSKELETONS INDUCED BY LOW-ENERGY SHOCK WAVE IRRADIATION
Megumi Baba1, Akira Tukamoto1, Toru Takahashi1, Keiichi Nakagawa2, Shigeru Tada1
1National Defense Academy of Japan, Japan;
2University of Tokyo, Japan
Low-energy shock waves (LESW), peak pressure of which is 10-20 MPa, induce cellular responses in various cell types including endothelial cells and osteoblasts. Comparing with peak pressure in Extracorporeal Shock Wave Lithotripsy, 50-100MPa, energy flux density is around 1/10. In our previous studies, LESW induced cellular responses including intracellular Ca2+ increase and mitochondria remodeling. Furthermore, in those cellular responses, actin cytoskeleton was involved. Thus, it was suggested that LESW interact with actin cytoskeleton before inducing various cellular responses. Mechanical stimulations, such as cyclic stretch and shear stress, remodel actin cytoskeleton. Here we hypothesized that LESW also remodel actin cytoskeleton as well. In this study, actin cytoskeletons were visualized by expressing pLifeAct-mTurquoise2 in murine osteoblastic MC3T3-E1 cells. Remodeling of actin cytoskeletons was observed every 15 min for 30 min, i.e. three time points after shock wave irradiation. Dependent on peak pressure and shot number of shock wave irradiation, shock wave irradiation induced various remodeling of actin cytoskeletons. Among the remodeling, newly appearances of filopodia-like or lamelipodia-like structures were typically observed. However, no apparent remodeling in stress fibers was observed during the observation time of 30 min. In the remodeling of actin cytoskeleton with other mechanical stimulation such as stretch and shear stress, remodeling of stress fibers is typically observed. Thus, it was suggested that LESW could induce remodeling in actin cytoskeleton. However, type of the remodeling could be rather different from those induced by other mechanical stimulations. To explain the difference, other parameters in LESW irradiation should be studied. Furthermore, mechanism by which LESW interact with actin cytoskeleton could be different from other mechanical stimulations. The difference in the mechanism is required to be investigated both in physical and biochemical aspects.