Abstract
Recently been pointed out that changes in the shape of cell nuclei including DNA may affect various cellular
functions. Furthermore, the changes in the force on the nucleus associated with remodeling of the actin cytoskeleton has also been involved in osteogenic differentiation of cells. In such differentiation process of cells, the localization of actin cytoskeleton is changed and the shape of the nucleus is greatly changed. However, it has not been quantitatively clarified how actin exerts a force on the nucleus or how the structure of the nucleus changes during the process of osteogenic differentiation. Therefore, in this study, MC3T3-E1 osteoblast-like cells were cultured in osteoinductive medium to promote bone differentiation. An Atomic force microscopy (AFM) was used to examine the mechanical properties of the nucleus in detail, and to estimate the internal tension of actin cytoskeleton. We found that the internal tension of actin cytoskeleton significantly increased with actin remodeling in the early stage of osteogenic differentiation, consequently generated the intracellular compressive forces to the nucleus. The forces also induced the nucleus remodeling with stiffening and maturation of nuclear lamina. Then the tension reduction and actin stabilization were occurred in the latter term of osteogenic differentiation. The results indicate that such changes in the cellular
forces and structures may be important mechanical factors for osteogenic differentiation.
