FIG. 1.

Transforming growth factor-β1 (TGF-β1) alters rheology of mesenchymal stem cell (MSC) cytosol. (A) The ensemble averaged mean squared displacements (MSDs) of 100-nm particles embedded in the cytoplasm of murine MSCs (isolated from Balb/C mouse bone marrow) incubated for 24 h in control media [CM (a)], 5 ng/mL PDGF (b), 5 ng/mL TGF-β1 (c), and combination of PDGF and TGF-β1—each 5 ng/mL [PDGF+TGF-β1 (d)]. (B) The time-dependent ensemble averaged MSDs of 100-nm particles embedded in the cytoplasm of MSCs were converted to frequency-dependent elastic (G′) and viscous (G″) moduli using a custom-written algorithm for Matlab software. (C) Brightfield images for soluble-factor-treated MSCs [conditions (a–d)] after 24 h stained with crystal violet. MSCs elongated dramatically in response to TGF-β1 individually and in combination with PDGF, whereas MSCs did not respond to PDGF treatment alone (scale bar=100 μm). (D) Phase angle (φ in degrees) proportional to the ratio of viscous to elastic modulus was calculated using G′ and G′′. (E) Cell shape factor (CSF) was determined by analysis of brightfield images with image J. CSF was used to characterize the elongation of the cell, with a shape factor of 1 indicating a perfect circle and 0 indicating a straight line. Results are reported as average±standard error of the mean (SEM, n=3). Statistical significances are indicated as (*) for p<0.05, (**) for p<0.005, and (***) for p<0.0005.