Indication of fibroblast apoptosis during the maturation of disc-shaped mechanically stressed collagen lattices

Human dermal fibroblasts seeded in tense disc-shaped collagen gels organized gradually into a tissue composed of three distinct superimposed layers of cells: a basal layer of aligned myofibroblasts, a middle layer of unoriented fibroblasts, and an upper layer of myofibroblasts oriented orthogonally to the basal myofibroblasts. Confocal observation of alpha-smooth muscle actin (alpha-SMA) immunolabelling as a marker of myofibroblasts showed that the upper myofibroblasts disappeared during maturation of the lattices. Observation of morphological modifications of cells, typical chromatin condensation identified by Hoechst 33258 staining, and detection of ssDNA after formamide-induced denaturation suggested the involvement of apoptosis in myofibroblast disappearance. It is suggested that the model of disc-shaped stressed collagen lattice is thus able to mimic conditions in wound repair: on the one hand, wound contraction during which fibroblasts undergo mechanical stress and, on the other, apoptotic disappearance of cells at the end of tissue retraction.