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.

These results confirm a marked increase of AGEs during intrinsic ageing in normal human skin and also suggest that glycation is enhanced in photoaged skin.

No abstract

The epidermis, the outermost structure of the skin, fulfils important roles as a physical barrier between the organism and its environment and as a neuroendocrine, immune and sensory organ. It is innervated by unmyelinated sensory fibres conveying nociceptive and thermoceptive information. Little is known concerning the functional interactions between these sensory fibres and the keratinocytes, which constitute 95% of the epidermal cells. We have developed a coculture model of primary rat sensory neurons and keratinocytes, as well as of equivalent cell-lines: ND7-23 neurons and A431 keratinocytes. We show that primary dorsal root ganglion neurons survive well in a standard keratinocyte reference medium containing a low concentration of calcium, but fail to extend axons. However, when neurons are cocultured with keratinocytes, axonal outgrowth is strongly stimulated. The use of a Transwell culture system indicated that the stimulation of axonal growth depends on a soluble factor secreted by keratinocytes. Axon outgrowth was also induced by nerve growth factor or brain-derived neurotrophic factor, but not by neurotrophin 3 or glial cell-derived neurotrophic factor. Neurons cocultured with keratinocytes did not change their responses to ATP, capsaicin or high potassium solution, as measured by calcium imaging. The trophic effect of keratinocytes concerned essentially a population of medium-sized (17-25 microm) neurons, some of which expressed substance P-like immunoreactivity and responded to capsaicin. Our preparation, in which cells are maintained at low external calcium concentration, could represent a useful in vitro model for characterizing the effect of skin-derived guidance and trophic factors.

The aim of this study was to evaluate the influence of the depth of the dermis on the measured collagen and elastin levels and to establish the correlation between the amount of these two extracellular matrix (ECM) components and age. Multiphoton Microscopy (MPM) that measures the autofluorescence (AF) and second harmonic generation (SHG) was used to quantify the levels of elastin and collagen and to determine the SAAID (SHG-to-AF Aging Index of Dermis) at two different skin depths. A 50 MHz ultrasound scanner was used for the calculation of the Sub Epidermal Non Echogenic Band (SENEB). The measurements of the skin mechanical properties were done with a cutometer. All measurements were performed on two groups of 30 healthy female volunteers. The MPM showed a decrease of the quantity of collagen and elastin as a function of depth of the dermis as well as age. The SAAID was lower for the older skin in the deeper dermis. Ultrasound imaging revealed a significant decrease of SENEB as a function of aging. The mechanical properties confirmed a loss of cutaneous elasticity and firmness. Although multiphoton microscopy is a powerful technique to study the characteristics of the dermis and its age-related damage, the location of the measurements (depth) remains very