Relationship of matrix stiffness and cell morphology in regulation of osteogenesis and adipogenesis of BMSCs.

Backgrounds: Matrix stiffness has been found to regulate cell morphology, while both cell morphology and matrix stiffness are verified as important factors directing BMSCs (bone marrow mesenchymal stem cells) differentiation. This study aimed to investigate whether matrix stiffness depended on cell morphology to regulate osteogenesis and adipogenesis of BMSCs on 2D substrates.

Methods And Results: First, we seeded BMSCs on tissue culture plates (TCPs) with different fibronectin (FN) concentrations and cytoskeleton inhibitor cytochalasin D, and FN was found to promote cell spreading and osteogenesis while inhibiting adipogenesis of BMSCs through F-actin reorganization. Based on these, we modulated BMSCs morphology on 0.5 kPa and 32 kPa CytoSoft® substrates through FN. High concentration of FN (300 μg/ml) coated on 0.5 kPa substrates promoted cell spreading to similar levels with 32 kPa substrates coated with 100 μg/ml of FN, and cells in both groups dominantly commit osteogenesis. On the other hand, low FN concentration (30 μg/ml) on 32 kPa substrates induced restricted cell morphology similar with 0.5 kPa substrates coated with 100 μg/ml of FN, and cells in both groups mainly commit adipogenesis. Immunofluorescence indicated nuclear translocation and higher intensity of YAP/TAZ when cells spread to larger areas, regardless of matrix stiffness. However, when cell spreading areas were fixed as similar levels, matrix stiffness didn't significantly affect YAP/TAZ intensity or location.

Conclusions: Matrix stiffness failed to regulate BMSCs differentiation and YAP/TAZ activity without corresponding cell morphology. Cell spreading area could mediate effects of matrix stiffness on osteogenesis and adipogenesis of BMSCs.