Skin cell management: the NICE approach

Characterised by a decrease in functional capacity and increased susceptibility to certain diseases and environmental insults it includes skin changes such as wrinkling, laxity, dryness, general thinning, and a flattening of the dermal/epidermal interface.1 Many of the skin collagen bundles appear, in fact, atrophic and elastic fibres are fewer and fragmented (Fig. 1). Thus, for formulating and producing anti-ageing cosmeceuticals and nutraceuticals capable of rejuvenating the skin, it should be necessary to know the intimate organisation of this important organ and, therefore, the global life-cycle of all its cells.2-4

The skin

The skin is a multicellular organ comprising three distinct major compartments: the epidermis, dermis and hypodermis (Fig. 2).5 It has blood and nerve systems and contains many related appendages, some of which have an opening to its surface, such as pilosebaceous units and eccrine glands. The epidermis contains three main cell types: the keratinocyte, the melanocyte and the Langerhans cell. Keratinocytes, continually migrating from the basement membrane (basal cells) differentiate themselves as outermost corneocytes which, embedded in lipid lamellae, give rise to the stratum corneum (SC). This dynamic structure, adapting to any environmental condition, represents the skin defensive barrier.6,7 Another major characteristic concerning the epidermis is that its cells can produce the cytokine-messengers (signals), following stimulation. In this way it represents a key part of the body’s early signal responses.8 The dermis is a composite system of insoluble fibrils and soluble polymers which take the stresses of movement and maintain shape. The fibrils are collagen and elastin (composed of aminoacids), while the major soluble polymers (macromolecules) are proteoglycans and hyaluronan, which bind vast amounts of water, and thus occupy a large volume. This diverse family of macromolecules helps to regulate cellular growth, adhesion, migration and differentiation. The hypodermis (subcutaneous tissue), an adipose fatty layer is composed mainly of tryglicerides (fatty acids) and represents a potential energy store. Moreover, it provides insulation against the cold, maintaining body temperature and the enzymatic function. The exact composition of fatty acids reflects diet and environmental conditions. In conclusion, the skin’s homeostatic central mechanism is represented by a complex network of cytokines (peptidesmessengers) mediating interactions between resident keratinocytes, Langerhans cells, T-lymphocytes, neutrophils and macrophages. Each peptide-messenger may be produced by many target cells which in turn may exert an effect on many cell types, binding to specific cell surface receptors to produce soon after a second message. This peptide activates the surface receptor proteins which, acting as intracellular signals, alter the behaviour of the target cell.