Time course of actin cytoskeleton stiffness and matrix adhesion molecules in human bronchial epithelial cell cultures.

Human bronchial epithelial (HBE) cells adhere to underlying extracellular matrix (ECM) via integrin-type transmembrane receptors. Integrins link the ECM to the cytoskeleton (CSK), establishing a mechanical continuum by which forces are transmitted between the outside and the inside of the cells. The present study investigates the time course of global and actin CSK stiffness of HBE cells (16HBE14o-) growing on various matrix substrates as a function of culture time until confluence, and the concomitant time course of F-actin and adhesion molecule distribution. Our results showed a progressive increase in actin CSK stiffness from cell seeding to confluence, related to acquisition of highly polymerized cortical and cytosolic F-actin organization and up-regulation of certain matrix ligands, such as beta 1-, alpha 5-, and alpha v-integrin subunit expression. Moreover, compared to fibrillar type I collagen, reticular type IV collagen used as matrix substrate, appeared to amplify actin CSK stiffness of HBE confluent cells probably in relation to up-regulation of alpha 3-integrin subunit. Taken together, these results support the concept of a close interaction among actin CSK stiffness, structural actin organization, specific integrin molecule involvement, cell spreading, and extracellular matrix.

Negative impact of DEP exposure on human airway epithelial cell adhesion, stiffness, and repair.

Epidemiological and experimental studies suggest that diesel exhaust particles (DEPs) may be associated with increased respiratory mortality and morbidity. Several recent studies have also shown that DEPs increase the production of inflammatory cytokines by human bronchial epithelium (HBE) cells in vitro. The present study investigates the effects of DEPs on the interaction of l-HBE cells (16HBE14o-) with the cell and matrix microenvironment based on evaluation of integrin-type cell/matrix ligand expression, cytoskeleton (CSK) stiffness, and matrix remodeling via matrix metalloproteinase (MMP)-1, MMP-2, and MMP-9 expression. The results showed that DEP exposure induced: 1) a net dose-dependent decrease in CSK stiffness through actin fibers, 2) a concomitant specific reduction of both alpha(3)- and beta(1)-integrin subunits extensively expressed on the HBE cell surface, 3) a decrease in the level of CD44, which is a major HBE cell-cell and HBE cell-matrix adhesion molecule; and 4) an isolated decrease in MMP-1 expression without any change in tissue inhibitor of matrix metalloproteinase (TIMP)-1 or TIMP-2 tissue inhibitors. Restrictive modulation of cell-matrix interaction, cell-cell connection, CSK stiffness, and fibrillary collagen remodeling results in a decreased wound closure capacity and an increased deadhesion capacity. In conclusion, on the basis of these results, we can propose that, in addition to their ability to increase the production of inflammatory cytokines, DEPs could also alter the links between actin CSK and the extracellular matrix, suggesting that they might facilitate HBE cell detachment in vivo.