‘Memory’ of the stratum corneum: exploration of the epidermis’ past

Abstract

Summary The stratum corneum (SC) is the final product of the process of epidermal differentiation. Besides its crucial protective role as a physical permeability barrier, this composite structure made of cornified keratinocytes embedded in a layered lipid matrix is also, by nature, a tissue that keeps track of past events occurring in the outermost living layers. In normal human epidermis, formation of the SC is very rapid, and during this cornification process several structures expressed by the last granular layer of keratinocytes become entrapped and immobilized at the cells’ periphery. Cell–cell junctions are obvious targets of transglutaminases that cross‐link junctions’ components within the corneocyte envelopes. Thus, desmosomes and tight junctions (TJs) in living cells become fixed at the corneocyte periphery and cannot be recycled anymore. We have quantified the TJ‐like structures residing in the SC of human skin explants subjected to environmental stress and compared these results with fresh skin controls. Significant overexpression of TJ‐like cell–cell envelope fusions has been observed in the stressed epidermis and in two different hereditary skin diseases characterized by increased SC cohesion. Quantitation of TJ‐like structures has contributed to the interpretation of the diseases’ physiopathology. Other examples of information retrieved from the SC concern fluctuating lipid expression in the course of atopic dermatitis and patterns of corneodesmosome breakdown influencing SC desquamation. It is, therefore, possible to analyse and quantify the traces left in the SC and to draw conclusions on the dynamics of living tissue over the past several days.

Assessing the skin barrier via corneocyte morphometry

“…The change in humidity, shape and protein levels is collectively called maturation, ultimately leading to death . During maturation, corneocytes collect intrinsic as well as external influences and can hence be regarded as messengers from inside, representing a kind of skin “memory” …”

“…[18] During maturation, corneocytes collect intrinsic as well as external influences and can hence be regarded as messengers from inside, representing a kind of skin "memory". [19]…”

“…as well as external influences (toxins, bacteria, UV light, etc.). [19] According to functional anatomy, it can be postulated, that any change in function leaves minute traces in the shape-it is just a question of resolution, whether they can be observed. As highresolution techniques are available, the race is on to identify the underlying mechanisms of morphological changes.…”

Lycopene presence in facial skin corneocytes and sebum and its association with circulating lycopene isomer profile: Effects of age and dietary supplementation

“…Our substudy with lycopene supplementation showed different patterns of lycopene accumulation in desquamated corneocytes and surrounding sebum (Figure ). This difference appears to be easy to explain by the physiological necessity of the transit of terminally differentiated corneocytes through the SC that takes approximately 14 days (Haftek, ). Therefore, desquamation of the first corneocytes enriched with lycopene should start only by the end of the second week of supplementation and is likely to be fully manifested later as we observe (Figure a).…”

Applications of human skin in vitro

“…The keratinocytes of the epidermis stem from epidermal stem cells which are present in the stratum basale. By dividing they give rise to the transit amplifying cell compartment that ultimately undergoes terminal differentiation and cell death to form the stratum corneum of densely packed cell membranes of keratinocytes (3). Keratinocytes express specific sets of keratins during their passage through the epidermis.…”