In situ AFM detection of the stiffness of the in situ exposed cell nucleus

Biomechanical properties of the cell nucleus play critical roles in cell behaviors and functions. As one important biomechanical property, the stiffness (or Young's modulus) of the cell nucleus has been widely investigated by different techniques including atomic force microscopy (AFM). In most of previous studies, the stiffness of the nuclear region of an intact cell or the stiffness of the isolated nucleus was detected. In this study, we developed a strategy for in situ detecting the stiffness of the cell nucleus via AFM. The extranuclear components of adherent cells (endothelial cells) were in situ removed by Triton X-100 treatment and the bare, adherent nuclei were exposed for in situ AFM force measurement. We found that the nuclear regions of intact cells (5.59 +/- 1.55 kPa) had a relatively higher average Young's modulus than the nonnuclear regions (1.47 +/- 0.77 kPa) and that the in situ exposed nuclei (22.06 +/- 7.29 kPa) were much stiffer than the nuclear regions of intact cells. This strategy is very simple and effective for detecting the stiffness of the cell nucleus and potentially is promising for a wide application.