Integrin endocytosis on elastic substrates mediates mechanosensing.

Tissue mechanics provides an appropriate niche for cell growth and functions. Integrin proteins play a pivotal role in mechanosensing associated with both extracellular matrix and intracellular cytoskeleton proteins. Endocytosis of integrin β1 of BMMSCs on collagen I-coated soft substrates promotes cell differentiation, providing a mechanism that cell senses elasticity through integrin. To determine whether other integrin subunits act the same way in BMMSCs, we carried on immunocytochemical staining and biotin labeling experiments to assay their subcellular distribution on stiff and soft hydrogels. Our results indicate that, consistent with our previous studies conducted on β1 integrin, more integrin α1 and α2 were internalized on collagen I-coated soft substrates compared with stiff substrate counterparts. This internalization is mainly mediated by caveolin-dependent endocytosis and would involve in soft matrix-promoted neurogentic lineage commitment. Cells on hydrogels coated by fibronectin and laminin, respective ligands of integrin α5 and α6, demonstrated no apparent soft substrate inducing endocytosis of these two subunits. These findings suggest that integrin-mediated mechanosensing is coupling with ECM ligands.