Biological Effects Induced by Ultraviolet Radiation in Human Fibroblasts

Abstract

As the most superficial body organ, skin plays an important role in protecting the body from environmental damage. The skin is composed of three layers: the epidermis, dermis and subcutaneous tissue. The epidermis, the outermost layer, has as main functions to protect the body against harmful environmental stimuli and to reduce fluid loss. It is a stratified squamous epithelium with several layers and its major cell type is the keratinocyte. This tissue is constantly being renewed by keratinization, a process of detachment of cornified cells (Blumenberg & Tomic-Canic, 1997). Located under the epidermis are the dermis and the dermal connective tissue, with extracellular matrix proteins such as collagen, elastic fibers, fibronectin, glycosaminoglycans and proteoglycans, which are produced and secreted into the extracellular space by fibroblasts, the major cell type found in this tissue (Makrantonaki & Zouboulis, 2007). The extracellular matrix proteins in the dermal connective tissue contribute for maintaining skin preservation and integrity (Hwang et al., 2011). Stromal fibroblasts play an important role in tissue homeostasis regulation and wound repair via protein synthesis and secretion of growth factors or cytokines of paracrine action with direct effect on proliferation and differentiation of adjacent epithelial tissues (Andriani et al., 2011). Solar ultraviolet (UV) radiation is a predictable epidemiologic risk factor for melanoma and non-melanoma skin cancers. (Katiyar et al., 2011). UV irradiation can impair cellular functions by directly damaging DNA to induce apoptosis (Waster & Ollinger, 2009). Among other things, longer UV wavelengths (UVB, UVA) induce oxidative stress and protein denaturation whereas short wavelength UV radiation (UVC) causes predominantly DNA damage to cells in the form of pyrimidine dimers, 6-4 photoproducts and apoptosis (Armstrong & Kricker, 2001; Gruijl et al., 2001). UVB irradiation damages skin cells by the formation of ROS (Reactive Oxygen Species) resulting in oxidative stress, an important mediator of damage to cell structures, including lipids and membranes, proteins, and DNA (Waster & Ollinger, 2009). However, it has less penetrating power than UVA and acts mainly on the epidermal basal layer of the skin. UVC, on the other hand, is extremely damaging to the skin because its wavelengths have enormous energy and induce genotoxic