Probing nanomechanics by direct indentation using Nanoendoscopy-AFM reveals the nuclear elasticity transition in cancer cells

The assessment of nuclear structural changes is considered a potential biomarker of metastatic cancer. However, accurately measuring nuclear elasticity remains challenging. Traditionally, nuclear elasticity has been measured by indenting the cell membrane with a bead-attached atomic force microscopy (AFM) probe or aspirating isolated nuclei with a micropipette tip. However, indentation using a bead-attached probe is influenced by the cell membrane and cytoskeleton, while measurements of isolated nuclei do not reflect their intact state. In this study, we used Nanoendoscopy-AFM, a technique in which a nanoneedle probe is inserted into a living cell to directly measure nuclear elasticity and map its distribution. Our findings show that nuclear elasticity increases under serum depletion but decreases when serum-depleted cells are treated with TGF-β, which induces epithelial-mesenchymal transition (EMT). Furthermore, we found that changes in nuclear elasticity correlate positively with trimethylation levels of histone H4 at lysine 20, rather than with nuclear lamins expression levels. These findings suggest that alterations in chromatin structure underlie changes in nuclear elasticity during cancer progression.