Clinical features of photodamaged human skin are associated with a reduction in collagen VII

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Abstract
Chronically sun-exposed or photodamaged human skin is characterized by a number of clinical features, including wrinkles. However, little is known about the molecular mechanisms that underlie these features. We investigated the hypothesis that the mechanism of wrinkle formation may involve loss of anchoring fibrils, composed mainly of collagen VII, which are important in maintaining dermal-epidermal junction integrity. Ten volunteers with moderate to severe photodamage of dorsal forearm skin were recruited to the study. Using immunohistochemistry, transmission electron microscopy and in situ hybridization, we compared collagen VII protein and mRNA content of photodamaged forearm skin with that of sun-protected hip and upper inner arm skin from the same subjects. Numbers of anchoring fibrils per linear microns of basement membrane (mean +/- SEM) were significantly lower in photodamaged skin (1.79 +/- 0.10) as compared with sun-protected hip (2.28 +/- 0.11) and upper inner arm skin (2.21 +/- 0.10) (P < 0.01), and similarly keratinocyte expression of collagen VII mRNA, quantitated as number of positively stained keratinocytes per high power field, was significantly reduced in photodamaged skin (6.3 +/- 2.5) as compared with sun-protected hip (20.0 +/- 5.6) and upper inner arm skin (17.7 +/- 4.9) (P < 0.001). Semiquantitative assessment of immunohistochemical staining for collagen VII showed a non-significant reduction in photodamaged skin as compared with sun-protected skin. We propose that reduced content of collagen VII in photodamaged skin contributes to wrinkle formation by weakening the bond between the dermis and epidermis.