Cadherins Mediate Intercellular Mechanical Signaling in Fibroblasts by Activation of Stretch-sensitive Calcium-permeable Channels

Abstract

Cells in mechanically active environments form extensive, cadherin-mediated intercellular junctions that are important in tissue remodeling and differentiation. Currently, it is unknown whether adherens junctions in connective tissue fibroblasts transmit mechanical signals and coordinate multicellular adaptations to physical forces. We hypothesized that cadherins mediate intercellular mechanotransduction by activating calcium-permeable, stretch-sensitive channels. Human gingival fibroblasts in suspension were plated on established homotypic monolayer cultures. The cells formed intercellular adherens junctions. Controlled mechanical forces were applied to intercellular junctions by electromagnets acting on cells containing internalized magnetite beads. At early but not later stages of intercellular attachment, force application visibly displaced magnetite bead-loaded cells and induced robust Ca2+ transients (65 ± 9.4 nM above base line). Similar Ca2+ transients were induced by force application to anti-N-cadherin antibody-coated magnetite beads. Ca2+ responses depended on influx of extracellular Ca2+ through mechanosensitive channels because both Ca2+ chelation and gadolinium chloride abolished the response and MnCl2 quenched fura-2 fluorescence after force application. Force application induced accumulation of microinjected rhodamine-actin at intercellular contacts; actin assembly was inhibited by buffering intracellular calcium fluxes. Our results indicate that mechanical forces applied to adherens junctions activate stretch-sensitive calcium-permeable channels and increase actin polymerization. We suggest that N-cadherins in fibroblasts are intercellular mechanotransducers.