arTicle | FUTURISTIC APPROACHES TO SKIN CARE |
as people age
intrinsically, the renewal rate of epidermal cells decreases. cellular turnover in the skin requires 40 to 60 days in the elderly, compared to 28 days in young adults.
As stated earlier, stem cells are influenced by
intercellular signals. One important pathway is “Notch” signaling, whose genes are named after the notched wing phenotype of the Drosophila fruit fly (8). Notch signaling is associated with the commitment of keratinocytes to differentiate and the suppression of tumorigenesis (9,10). Notch signaling also promotes differentiation of the sebaceous glands and hair follicle (11). The Notch pathway includes receptors, negative and positive modifiers, ligands, and transcription factors. Four Notch receptors (Notch 1–4) have been found in mammals (8). P63, a close homolog of the p53 tumor suppressor
protein, is associated with keratinocyte cell fate and self renewal of epithelial cells (9,12). The p63 transcription factor is necessary for regenerative proliferation in the development of epithelium (13,14). In the mature epidermis, p63 has two roles: (1) to initiate epithelial stratification during development and (2) to maintain the proliferative potential of basal keratinocytes (14). Since p63 also counteracts the promotion of differentiation by Notch signaling, a mutual antagonism between p63 and Notch signaling may be an important factor in epidermal homeostasis (9,11).
Ageing and stem cells As people age intrinsically, the renewal rate of epidermal cells decreases. Cellular turnover in the skin requires 40 to 60 days in the elderly, compared to 28 days in young adults (15,16). Reduced cellular turnover reduces epidermal thickness and compromises skin barrier function. Cell exfoliation is also adversely affected. The dermal–epidermal junction becomes flattened, increasing skin fragility. In the dermis, the number of fibroblasts decreases, as does the synthesis of collagen and elastin. Glycosaminoglycans (GAGs) and fibronectin (3) are also reduced as the functional ability of fibroblasts diminishes. Subdermal fat tissue decreases, microvasculature is reduced, and sebaceous glands are lost. The overall result is wrinkling, loss of elasticity,
24 ❚ March 2011 |
prime-journal.com
dryness, thinning, and increased susceptibility to trauma and bruising (15,17,18). Extrinsic ageing is essentially due to prolonged
exposure to ultraviolet (UV) light, particularly longer wavelengths (340–400 nm). Collagen synthesis in photodamaged skin is reduced compared to sun- protected skin (19). UV radiation also damages keratinocyte stem cells (20). With ageing, the regenerative potential of their adult
stem cells declines (3,21), possibly due to deletion of a DNA-damage response gene (3). The number of stem cells and their ability to renew themselves does not necessarily change with ageing, but the ability of stem cells to produce precursors and differentiated effector cells decreases (22). Wound healing is also impaired in aged skin, suggesting that either mobilization of stem cells is slower or the number of stem cells that respond to replicative signals is low. The latter would be consistent with the findings of Barrandon and Green (23) in which colony-forming keratinocytes from older donors, compared to similar cells of younger donors, gave rise to a lower proportion of clones of cells with the greatest proliferative capacity (holoclones) and a higher proportion of clones of cells with reduced proliferative capacity (paraclones). People seeking to improve the appearance of ageing
skin spend more than $230 per year worldwide on cosmetics and over-the-counter cosmetics and cosmeceuticals (15). Cosmeceuticals are the most rapidly growing segment in the skin care market (15,24). At the time of this writing, stem cell-based skin care products include Amatokin (Voss Laboratories), SimulCell (NV Perricone), and Dior Capture Totale XP Ultimate Wrinkle Restoring Cream. The importance of clinical testing to substantiate
claims cannot be overestimated. The remainder of this article focuses on the application of scientific methods in the development of products to combat ageing and cellulite.
People
seeking to improve the appearance of ageing skin spend more than $230 per year worldwide on cosmetics and over-the-counter cosmetics and cosmeceuticals.
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