Atomic Force Microscopy-Based Nanoscopy of Chondrogenically Differentiating Human Adipose-Derived Stem Cells: Nanostructure and Integrin β1 Expression

Integrin 1 is known to be involved in differentiation, migration, proliferation, wound repair, tissue development, and organogenesis. In order to analyze the binding probability between integrin 1 ligand and cluster of differentiation 29 (CD29) receptors, atomic force microscopy (AFM) was used to detect native integrin 1-coupled receptors on the surface of human adipose-derived stem cells (hADSc). The binding probability of integrin 1 ligand-receptor interaction was probed by integrin 1-functionalized tips on hADSc during early chondrogenic differentiation at the two-dimensional cell culture level. Cell morphology and ultrastructure of hADSc were measured by AFM, which demonstrated that long spindled cells became polygonal cells with decreased length/width ratios and increased roughness during chondrogenic induction. The binding of integrin 1 ligand and CD29 receptors was detected by 1-functionalized tips for living hADSc. A total of 1200 curves were recorded at 0, 6, and 12days of chondrogenic induction. Average rupture forces were, respectively, 61.8 +/- 22.2pN, 60 +/- 20.2pN, and 67.2 +/- 22.0pN. Rupture events were 19.58 +/- 1.74%, 28.03 +/- 2.05%, and 33.4 +/- 1.89%, respectively, which demonstrated that binding probability was increased between integrin 1 ligand and receptors on the surface of hADSc during chondrogenic induction. Integrin 1 and the -catenin/SOX signaling pathway were correlated during chondrogenic differentiation. The results of this investigation imply that AFM offers kinetic and visual insight into the changes in integrin 1 ligand-CD29 receptor binding on hADSc during chondrogenesis. Changes in cellular morphology, membrane ultrastructure, and the probability of ligand-transmembrane receptor binding were demonstrated to be useful markers for evaluation of the chondrogenic differentiation process.