Molecular changes during skin aging and wound healing after fractional ablative photothermolysis

Photo-damaged skin is characterized by major alterations of the extracellular matrix and collagen network, leading to clinically obvious signs of skin aging. UV radiation increases the levels of matrix metalloproteinase (MMP) 1, which initiates the cleavage of fibrillar collagen types I and III. The developing collagen fragments are further degraded by MMPs 2 and 9. Various ablative, non-ablative, thermal and non-thermal rejuvenation modalities have been tested for their capacity to reverse epidermal and dermal signs of photo- and chronological-aging. Light and laser therapies are among the most effective treatment options for skin rejuvenation. Conventional laser therapy treats entire surface areas by selective photothermolysis or ablation. Recently, intervention with a fractional ablative laser leads to fast wound healing, and hence, a substantial amount of the target skin area is left untreated. It is not known if the efficacy of a particular ablative skin rejuvenation treatment depends on the extent of microwounding and/or the amount of heat produced. The underlying molecular changes are not fully understood but have been postulated to be induced by time-dependent changes in heat shock proteins, transforming growth factor beta, MMPs, hyaluronic acid synthethases, hyaluronidases and HA, among others.