Titushkin Igor, Cho Michael
Department of Bioengineering, University of Illinois, Chicago, Illinois 60607, USA.
Biophys J. 2007 Nov 15;93(10):3693-702. doi: 10.1529/biophysj.107.107797. Epub 2007 Aug 3.
Recognition of the growing role of human mesenchymal stem cells (hMSC) in tissue engineering and regenerative medicine requires a thorough understanding of intracellular biochemical and biophysical processes that may direct the cell's commitment to a particular lineage. In this study, we characterized the distinct biomechanical properties of hMSCs, including the average Young's modulus determined by atomic force microscopy (3.2 +/- 1.4 kPa for hMSC vs. 1.7 +/- 1.0 kPa for fully differentiated osteoblasts), and the average membrane tether length measured with laser optical tweezers (10.6 +/- 1.1 microm for stem cells, and 4.0 +/- 1.1 microm for osteoblasts). These differences in cell elasticity and membrane mechanics result primarily from differential actin cytoskeleton organization in these two cell types, whereas microtubules did not appear to affect the cellular mechanics. The membrane-cytoskeleton linker proteins may contribute to a stronger interaction of the plasma membrane with F-actins and shorter membrane tether length in osteoblasts than in stem cells. Actin depolymerization or ATP depletion caused a two- to threefold increase in the membrane tether length in osteoblasts, but had essentially no effect on the stem-cell membrane tethers. Actin remodeling in the course of a 10-day osteogenic differentiation of hMSC mediates the temporally correlated dynamical changes in cell elasticity and membrane mechanics. For example, after a 10-day culture in osteogenic medium, hMSC mechanical characteristics were comparable to those of mature bone cells. Based on quantitative characterization of the actin cytoskeleton remodeling during osteodifferentiation, we postulate that the actin cytoskeleton plays a pivotal role in determining the hMSC mechanical properties and modulation of cellular mechanics at the early stage of stem-cell osteodifferentiation.
认识到人间充质干细胞（hMSC）在组织工程和再生医学中日益重要的作用，需要深入了解可能引导细胞向特定谱系分化的细胞内生化和生物物理过程。在本研究中，我们对hMSC的独特生物力学特性进行了表征，包括通过原子力显微镜测定的平均杨氏模量（hMSC为3.2±1.4 kPa，完全分化的成骨细胞为1.7±1.0 kPa），以及用激光光镊测量的平均膜系链长度（干细胞为10.6±1.1微米，成骨细胞为4.0±1.1微米）。这两种细胞类型在细胞弹性和膜力学方面的差异主要源于肌动蛋白细胞骨架组织的不同，而微管似乎并未影响细胞力学。膜 - 细胞骨架连接蛋白可能导致成骨细胞中质膜与F - 肌动蛋白的相互作用更强，且膜系链长度比干细胞中的短。肌动蛋白解聚或ATP耗尽导致成骨细胞膜系链长度增加两到三倍，但对干细胞膜系链基本没有影响。hMSC在10天成骨分化过程中的肌动蛋白重塑介导了细胞弹性和膜力学在时间上相关的动态变化。例如，在成骨培养基中培养10天后，hMSC的力学特性与成熟骨细胞相当。基于对成骨分化过程中肌动蛋白细胞骨架重塑的定量表征，我们推测肌动蛋白细胞骨架在决定hMSC力学特性以及在干细胞成骨分化早期调节细胞力学方面起着关键作用。
