A histological study of human wrinkle structures: comparison between sun-exposed areas of the face, with or without wrinkles, and sun-protected areas

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Abstract
Wrinkles are a major topic in dermocosmetology; the purpose of this work has been to go deeper into the knowledge of cutaneous damage underlying these modifications of skin surface. Up to now, the number of published works about the histological structure of wrinkles is not very large. Therefore to complete the findings, we studied 46 subjects of both sexes, between 57 and 98-year-old, enabling us to obtain 157 skin biopsies of wrinkles (face) and sun-protected areas (abdomen). We used different histological techniques involving histochemistry, immunohistochemistry, electron microscopy and quantification by image analysis in addition to classic standard techniques. This study has allowed us to confirm published structural modifications of wrinkles, but also to display many other original alterations. The increased thinning of the epidermis atrophied with age is confirmed by the study of desmoplakins outlining the cellular contours of keratinocytes. Such a thinning is accompanied by a decrease in several markers of epidermal differentiation at the bottom of the wrinkles: filaggrin, keratohyalin granules and transglutaminase I, disturbing desquamation and the capacity of the horny layer to retain water. The dermoepidermal junction is modified by a decrease of collagen IV and VII, which, combined with fewer and fewer oxytalan fibres under wrinkles, weakens this interface. The deposition of abnormal elastotic tissue in the dermis, with an interruption of these deposits under wrinkles and an atrophy of dermal collagen more pronounced under wrinkles, boosts the magnitude and depth of wrinkles. The composition of the other dermal constituents is also altered with, more particularly, a marked decrease of chondroitin sulphates in the papillary dermis under wrinkles, combined with an asymmetrical variation of glycosaminoglycans on both edges of wrinkles. The atrophy of the hypodermis, also more marked under wrinkles, with a thickening of fibrous lines, also makes the depth of wrinkles more pronounced. Wrinkle formation appears at the same time as numerous modifications in different cutaneous structures, which may be mutually amplified. Such a study by pointing out altered elements in skin physiology, makes the development of specific treatments possible in order to mitigate this unwelcome cutaneous deterioration.