Ultraviolet-induced photoaging in the skin: The role of inflammatory cytokine, macrophage migration inhibitory factor

The human Skin is continuously challenged by different adverse influences such as solar radiation, chemicals and oxidative stress. The most common cause of physical injury to the skin is solar ultraviolet (UV) irradiation, which causes long-term detrimental effects, such as cutaneous photoaging. Photoaged skin is clinically characterized by wrinkles, laxity, coarseness, and the loss of skin tone and biochemically characterized by a predominance of abnormal elastic fibers in the dermis and a dramatic decrease in specific collagen types. Ultraviolet radiation induced changes in the dermal extracellular matrix proteins; the accumulation of disorganized elastin and the loss of interstitial collagens are also thought to be responsible for photo damage of the skin. Chronic skin exposure to ultraviolet radiation stimulates the production of cytokines known to play a key role in the process of photoaging and initiation of skin cancer. Macrophage migration inhibitory factor (MIF) has long been considered to be a lymphokine that concentrates macrophages at inflammatory loci, and it is a potent activator of macrophages in vivo, which are considered to play an important role in cell-mediated immunity. Subsequently, MIF was reevaluated and described to be a pro-inflammatory cytokine and pituitary-derived hormone that potentiates endotoxemia. MIF is expressed in the epidermis of the skin, particularly in the basal layer, and enhanced MIF production is observed in the skin after UV irradiation. This chapter will focus on the biological effects and the latest findings on the role of MIF in photoaging following UV exposure.