Cells sense forces from the extracellular matrix (ECM) and transduce them into biochemical signals. The molecules produced cause in turn remodeling of the ECM. Molecular altered expression will affect this force sensing mechanism changing cellular properties as migration, differentiation, etc. Therefore, cells mechanical properties can be used as a marker for the early diagnosis of pathologies as cancer or cardiovascular diseases. In this framework, Atomic Force Microscopy (AFM) represents an excellent tool to evaluate the mechanical properties of different cellular systems.

In this talk, we will analyze the mechanical properties of aortic valve interstitial cells (VICs), the predominant constituent of aortic valves, governing ECM structure and composition, in the onset of calcific aortic valve disease (CAVD).

In particular, we obtained adhesion polymeric substrates with different stiffness onto which human AoV VICs were plated, and subsequently investigated for the cytoskeleton dynamics and the activity of the mechanosensing-activated transcription factor YAP. We found that cells were subject to a reversible stiffness-dependent nuclear translocation of the transcription factor in concert with an increase in cytoskeleton tensioning and loading of the myofibroblast-specific protein $\alpha$SMA onto the F-actin cytoskeleton.\newline Then, we studied the interaction between porcine VICs and optically transparent, vertically aligned carbon nanotube (CNT) substrates, mimicking the chemical/morphological role of natural ECM. Here we found that the number of myofibroblasts (correlated to disease-associated phenotype) was similar to the case of healthy valves, and that fibroblasts on CNT matrix resulted in higher stiffness and higher number of focal adhesions, with respect to reference glass. AFM imaging of the inner membrane of VICs broken up by osmotic shock allowed to observe that CNTs are piercing and pinching the plasma membrane, in this way facilitating the creation of clusters of FAs that contribute to increase cellular rigidity.