Signalling pathways activated by ultraviolet radiation: role in ocular and cutaneous health.

The eye and the skin are protected by a multi-layered epithelial barrier that provides the first line of defence against invading pathogens and environmental stresses such as damaging solar ultraviolet radiation. Extensive epidemiological findings supported by compelling experimental evidence in culture and animal models suggest that ultraviolet radiation is the most important environmental carcinogen leading to the development of a variety of benign and malignant ocular and cutaneous conditions. Epithelial cells have evolved several key defence mechanisms to prevent ultraviolet radiation-induced DNA mutations from stably entering the genome and ultraviolet radiation-damaged cells from establishing themselves in an otherwise normal microenvironment. Firstly, through the process excision repair, cells have the ability to correct carcinogen-induced DNA damage. Secondly, severely damaged cells are eliminated from healthy tissues by molecular programs that trigger cell death. These processes are activated through complex intracellular signalling circuits that ensure that organs such as the eyes and skin are maintained in a disease-free state. Finally, abnormal cells can be recognized, targeted and destroyed by surveillance from the immune system, however this is complicated further by the immunosuppressive effects of ultraviolet radiation that promote tumour growth. This review will discuss in greater detail some of the processes and pathways that are activated in response to ultraviolet radiation and their effect on ocular and cutaneous health.