Molecular responses of human dermal fibroblasts to dual cues: contact guidance and mechanical load.

Fibroblast contraction in wound healing involves the interaction of several cell types, cytokines, and extracellular matrix molecules. We have previously developed fibroblast alignment models using precise uniaxial mechanical loads in 3D culture and using contact guidance on fibronectin strands. Our aim here was to use contact guidance to place fibroblasts in their potentially most sensitive configuration, i.e., perpendicular to the axis of loading, to present cells with conflicting guidance cues. Gene expression at the mRNA level of cells recovered from different zones of the 3D collagen gel (with distinct orientation) was determined by quantitative RT-PCR for the matrix proteases MMP1, 2, and 3, and inhibitors TIMP1 and 2. Our results show a 2-, 4-, and 3-fold increase in MMP1, 2, and 3, respectively, in the non-aligned strain zone, relative to the aligned strain zone. These results suggest that cells unable to align to applied loads remodel their matrix far more rapidly than orientated cells. Where fibroblasts were held in an alignment perpendicular to the applied load by contact guidance, the fall in MMP mRNA expression was largely abolished, indicating that these cells remained in a mechano-activated state. The protease inhibitors TIMP1 and 2 were poorly mechano-responsive, further suggesting that changes in MMP expression result in functional matrix remodelling. These results indicate how mechanical loading in tissues may influence matrix remodelling, particularly under conflicting guidance cues. Copyright 2000 Wiley-Liss, Inc.