Abstract
Epidermal barrier function is provided by the highly keratinised stratum corneum and also by tight junctions (TJs) in the granular layer of skin. The development of the TJ barrier significantly deteriorates in response to ultraviolet B radiation (UVB). Following exposure to UVB, keratinocytes accumulate organic osmolytes, which are known to preserve cell volume during water stress. Since TJs are intimately associated with control of water homeostasis in skin, we hypothesised that there may be a direct influence of osmolytes on TJ development. Exposure of rat epidermal keratinocytes (REKs) to a single dose of UVB reduced the function of developing TJs. This was concomitant with dislocalisation of claudin-1 and claudin-4 from the keratinocyte plasma membrane, phosphorylation of occludin and elevation of reactive oxygen species (ROS). In the presence of organic osmolytes, these effects were negated but were independent of the effects of these molecules on cell volume, elevation of ROS or the gene expression of TJ proteins. These data suggest that organic osmolytes affect TJs via post-translational mechanism(s) possibly involving protection of the native conformation of TJ proteins.
Highlights
Epidermal barrier function is provided by the highly keratinised stratum corneum and by tight junctions (TJs) in the granular layer of skin
This study aimed to investigate the potential role of organic osmolytes in maintaining the integrity of developing TJs following ultraviolet B radiation (UVB)-induced disruption in the rat epidermal keratinocyte (REK) cell line
We first investigated the basic cellular responses of rat epidermal keratinocytes to exposure to a single, sublethal dose of 10 mJ/cm[2] UVB (Supplementary Fig. S1). This resulted in a significant decrease in cell volume 24 hours post irradiation (Fig. 1a,b). This was accompanied by an elevation in the level of reactive oxygen species (ROS) as indicated by the significant increase in the fluorescence intensity of the 2′−7′- dichlorofluorescein (DCF) probe in irradiated keratinocytes compared with non-irradiated cells (Fig. 1c)
Summary
Epidermal barrier function is provided by the highly keratinised stratum corneum and by tight junctions (TJs) in the granular layer of skin. In the presence of organic osmolytes, these effects were negated but were independent of the effects of these molecules on cell volume, elevation of ROS or the gene expression of TJ proteins. During the process of evolution, a major requirement for terrestrial organisms was the development of mechanisms to reduce water loss Of importance in this regard was the evolution of the skin, the epidermis of which provides a tough, waterproof barrier to limit water loss[1,2]. Tight junctions (TJs) have been shown to play an important role in sealing the gaps between cells to prevent water loss, controlling the extracellular passage of molecules, ions and water[9,10,11,12]. In keratinocytes, TJs have a direct role in forming a barrier to water loss[29]
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