Collagen Damage Induced by Chronic Exposure to Sunlight
Because of its lack of a protective fur, human skin is readily susceptible to external elements, including ultraviolet radiations from sunlight. In fair-skinned and mildly pigmented individuals, ultraviolet radiations have severe damaging effects: they are responsible for premature aging of the skin (photoaging) and for tumorigenesis. This chapter details our current knowledge of how ultraviolet radiations affect the dermis (the nutritional and supportive layer of the skin) and, particularly, its collagen network. Dermal collagen provides strength and resiliency to the skin and is an important substrate for cell migration during wound repair. Altered collagen structure is a hallmark of aged dermis that can no longer exert its supportive function. Here, we review the molecular mechanisms by which ultraviolet light-induced signaling cascades transiently affect collagen homeostasis, we detail our understanding of how repeated exposure to sunlight leads to a sustained presence of damaged collagen fibers, and we explain why photoaging should be viewed as a self-sustained process. In all, we highlight many molecular targets to be considered by scientists aiming to restore the structure and function of photoaged skin.