The dermis of normal (wrinkle-free) skin is composed of abundant amounts of type I collagen and type VII collagen, as well as elastin, which provide tissue strength, resiliency and recoil. An illustration of the role of these key proteins in the skin is shown below.
During innate (normal) aging, aged dermal fibroblasts produce increased amounts of enzymes called matrix metalloprotienases (MMPs), which degrade collagen and elastin. To make matters worse, the amount of collagen and elastin produced by dermal fibroblasts decreases as the cells age. Thus, the overall loss of collagen and elastin results in skin laxity and fragility, which is visible in the form of wrinkles. The ability of a compound to reduce senescence (cell aging) or to stimulate aged fibroblasts to produce increased levels of Col I/VII and elastin, as well as inhibit the production of MMPs, would lead to an effective decrease, if not reversal, of the aging process. An illustration of the molecular changes that occur during aging is below.
During photoaging, exposure of dermal fibroblasts to ultraviolet radiation results in the increased expression of MMP’s and elastin. The overall loss of collagen, due to degradation by MMP’s, leads to skin laxity. Further, overexpression of elastin results in irregularly formed "knots" of elastin, called elastosis. Therefore, inhibition of the overexpression of MMPs and an increase in the production of collagen by a potential compound would result in an overall reduction, and possibly reversal, of photoaging. An illustration of the molecular changes that occur during photoaging is shown below.
As was the case for searching for compounds that can inhibit inflammatory processes, a similar type of cell culture based screening program must be developed when searching for chemical compounds that can improve skin in either intrinsically-aged or photoaged skin. The screening process for any candidate molecule typically involves a three step process which includes:
- Assessing the effects of a candidate compound on the expression of key aging proteins (e.g. collagen, elastin) under normal and UV-induced aging conditions (RT-PCR and Western analysis).
- Determining the effect of a candidate anti-aging compound on the expression of MMP’s (enzymes that destroy the dermal matrix) and TIMPS ( proteins that block MMPs) using an Antibody Array method.
- Examining the effects of a candidate compound on cell senescence by use of the b-galactosidase assay.
A typical anti-aging screening strategy is summarized in the flow chart entitled Anti-Aging Screening found below.
This screening strategy allows for the selection of a bioactive that can cause a marked improvement in the appearance of skin regardless of whether or not the skin has undergone photodamaged.