Ultraviolet A radiation-induced biological effects in human skin: relevance for photoaging and photodermatosis
Introduction
The solar spectrum that reaches the earth consists of short wavelength UVC (<280 nm), intermediate wavelength UVB (280–320 nm) and long wavelength UVA (320–400 nm). Under physiological conditions, human cells are exclusively exposed to UVB and UVA radiation, because ozone in the stratosphere completely absorbs wavelengths <290 nm. The amount of UVA radiation reaching the earth’s surface is approximately 20 times greater than that of UVB radiation, and solar UVA radiation contributes to photoaging and photocarcinogenesis. It is also responsible for triggering the most frequent photodermatoses, that is polymorphous light eruption. Analysis of the photobiological and molecular mechanisms which are exerted in human skin cells by UVA radiation are thus of critical importance for understanding these detrimental effects of UVA radiation.
Section snippets
New insights into the pathogenesis of polymorphous light eruption: UVA radiation-induced gene expression in human keratinocytes
Ultraviolet radiation (UVR)-induced expression of proinflammatory genes in human keratinocytes is thought to be important for the pathogenesis of photosensitive skin diseases such as polymorphous light eruption [1]. This is consistent with recent observations of an increased expression of keratinocyte-derived proinflammatory cytokines (IL-1, IL-8) and adhesion molecules (ICAM-1) in lesional skin of patients with polymorphous light eruption [2], [3]. In previous years, extensive research has
The relevance of UVA radiation-induced mitochondrial DNA mutations in photoaging of human skin
One of the main functions of mitochondria is to supply the cell with energy via oxidative phosphorylation, carried out by five protein complexes in the inner mitochondrial (mt) membrane. Erroneous oxidative phosphorylation can lead to the generation of reactive oxygen species (ROS) which is why mitochondria are the place with the highest ROS turnover in the cell. Oxidative phosphorylation is encoded by mt DNA. Mutations of mt DNA have initially been found in degenerative diseases. It has been
Conclusion
Our studies identify a previously unrecognized role of singlet oxygen in mediating UVA radiation-induced inflammation and photoaging. It is thus possible that the generation of singlet oxygen in human skin is of central importance for the capacity of UVA radiation to exert detrimental effects. Singlet oxygen quenching may thus represent an effective strategy to protect human skin from photoaging and PLE patients from developing skin lesions.
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