Mechanical forces induce scar remodeling. Study in non-pressure-treated versus pressure-treated hypertrophic scars

Abstract

Reparative process of second and third degree burns usually results in hypertrophic scar formation that can be treated by pressure. Although this method is efficient, its mechanisms of action are not known. In this work, we have studied the histological organization of hypertrophic scars submitted to pressure. Skin biopsies were performed 2 to 7 months after the onset of treatment in two adjacent regions of the scar, non-pressure- or pressure-treated and analyzed by immunohistochemistry and transmission electron microscopy for extracellular matrix organization and cellular morphology. In non-pressure-treated regions, fibrillin deposits did not present the classical candelabra-like pattern under epidermis and were reduced in dermis; in pressure-treated regions the amount was increased compared to non-pressure-treated regions but the organization was still disturbed. In non-pressure-treated regions, elastin was present in patch deposits; in pressure-treated regions elastin formed fibers, smaller than in normal dermis. Tenascin was present in the whole dermis in non-pressure-treated regions, whereas in pressure-treated regions it was observed only under epidermis and around vessels, as in normal skin. alpha-Smooth muscle actin-expressing myofibroblasts were absent in normal skin, present in large amounts in non-pressure-treated regions, and almost absent in pressure-treated regions. The disturbed ultrastructural organization of dermal-epidermal junction observed in non-pressure-treated regions disappeared after pressure therapy; typical features of apoptosis in fibroblastic cells and morphological aspects of collagen degradation were observed in pressure-treated regions. Our results show that, in hypertrophic scars, pressure therapy restores in part the extracellular matrix organization observed in normal scar and induces the disappearance of alpha-smooth muscle actin-expressing myofibroblasts, probably by apoptosis. We suggest that the pressure acts by accelerating the remission phase of the postburn reparative process.

Figure 1.

Gomori’s silver impregnation in non-pressure- and pressure-treated regions. In non-pressure-treated region (a), bundles of reticular collagen fibers are perpendicular to epidermis and there are a large amount of reticular collagen fibers in deep dermis. In pressure-treated region of the same patient (b), the reticular collagen fibers present a random arrangement without forming large bundles, similarly to that observed in normal skin. Scale bar, 50 μm.

Figure 2.

Fibrillin and elastin immunofluorescence. In normal skin (a), fibrillin labeling shows a typical candelabra-like pattern perpendicularly inserted onto the basal lamina (arrowheads); in reticular dermis, thicker fibers are visualized. In non-pressure-treated region (b), the candelabra-like pattern is not present and in deep dermis, the stained fibers show a fragmented aspect. In pressure-treated region of the same patient (c), the fibrillin-containing fibers present under the epidermis are thicker (arrows), perpendicular to the basal lamina but without showing the candelabra-like pattern; in deep dermis the stained fibers are small and arranged parallel to the epidermis, as in normal skin. In normal skin (d), elastin is observed in dermis as fibers arranged preferentially parallel to epidermis. In non-pressure-treated region (e), only sparse elastin deposits are present. In pressure-treated region (f), elastin deposits form small and thin fibers in deep dermis. Asterisks: epidermis. Scale bar, 40 μm.

Figure 3.

Tenascin immunofluorescence. In normal skin (a), tenascin is present in superficial papillary dermis and around blood vessels. In non-pressure-treated region (b), tenascin is observed in dermis with a non homogeneous distribution. In pressure-treated region of the same patient (c), tenascin is present only in dermal papilla and around blood vessels. Asterisks: epidermis. Scale bar, 30 μm.

Figure 4.

α-Smooth muscle actin immunofluorescence. In non-pressure-treated region (a), α-smooth muscle actin is present around vessels and in stromal myofibroblasts. In pressure-treated region of the same patient (b), α-smooth muscle actin is present only around vessels. Scale bar, 60 μm.

Figure 5.

Ultrastructure of the dermal-epidermal junction. In normal skin (a), the typical architecture is represented, with keratinocyte microfoot processes, regular hemidesmosomes, lamina lucida and anchoring filaments, lamina densa and anchoring fibrils. In non-pressure-treated region (b), the keratinocytic microfeet are almost absent, the lamina lucida is indinstinct and the lamina densa is thickened. The hemidesmosomes are not regularly distributed, and their subbasal dense plate is missing (arrowheads). In pressure-treated region of the same patient (c), keratinocyte microfoot processes are elongated, while hemidesmosomes, anchoring filaments and anchoring fibrils are well organized. Scale bar, 0.5 μm.

Figure 6.

Ultrastructure of dermal components. In non-pressure-treated region (a), an elaunin fiber is observed near a fibroblast (arrowhead). In pressure-treated region (b), an elastic fiber (star) and some bundles of regular collagen fibers are observed together with collagen fibers showing typical features of degradation (arrows). In pressure-treated region (c and d), fibroblastic cells presenting typical apoptotic features such as chromatin condensation and nuclei in part extruded from the cytoplasm are observed. Scale bars, 1 μm.