Force spectroscopy of membrane hardness of SH-SY5Y neuroblastoma cells before and after differentiation

Atomic force microscopy (AFM) is utilized in many studies for measuring the structure and the physical characteristics of soft and bio materials. In particular, the force spectroscopy function in the AFM system allows us to explore the mechanical properties of bio cells. In this study, we probe the variation in the membrane hardness of human neuroblastoma SH-SY5Y cells (SH-cells) before and after differentiation by using force spectroscopy. The SH-cell, which is usually differentiated by using a chemical treatment with retinoic acid (RA), is a neuronal cell line employed widely as an in-vitro model for neuroscience research. In force spectroscopy, the force-distance curves are obtained from both the original and the RA-treated cells while the AFM tip approaches and pushes on the cell membranes. The slope deduced from linear region in the force-distance curve is the spring constant and corresponds to the hardness of the cell membrane. The spring constant of the RA-treated cells (0.597 ± 0.010 nN/nm) was smaller than that of the original cells (0.794 ± 0.010 nN/nm), reflecting a hardness decrease in the cells differentiated with the RA treatments. The results clearly demonstrated that the differentiated cells are softer than the original cells. The change in the elasticity of the differentiated cells might be caused by morphological modification during differentiation process. We suggest that force spectroscopy can be employed as a novel method to determine the degree of differentiation of stem cells into various functional cells.