Solar simulated radiation induces loss of Claudin – 1 from primary human keratinocytes: a mechanistic study 


Claudin-1 is a major barrier forming protein of tight junctions (TJs) in the epidermal granular layer. The function of claudin-1 in other epidermal layers is poorly understood. However, claudin-1 is reduced in conditions induced by ultraviolet radiation (UVR) including polymorphic light eruption and photoageing. The aim of this study was to investigate the mechanisms whereby UV could induce loss of claudin-1 from keratinocytes.

Using western blotting for claudin-1 of primary human keratinocytes exposed to solar-simulated radiation (SSR) at 10 or 20J/cm2, we showed that claudin-1 abundance was reduced by 50% at 72h post irradiation. However, RT-PCR showed no loss claudin-1 expression. Bioinformatics analysis suggested that claudin-1 may contain cleavage sites for MMP’s 3 or 9 and elastase, all of which are known to be UV-inducible. Treatment of keratinocytes with these enzymes resulted in a decrease in the abundance of claudin-1 protein and the UV-induced loss of claudin-1 could be inhibited by pre-treatment of keratinocytes with an MMP inhibitor (Marimastat) and but not by antioxidant (glutathione) or elastase inhibitor (Sivelestat). Using gelatine zymography, there was a significant shift of MMP-9 from the pro form to the active isoform in a time concomitant with loss of claudin-1 from the keratinocytes. These data suggest that SSR induces loss of claudin-1 via MMP mediated proteolysis but not elastase mediated proteolysis or photo-dynamic oxidation.  We speculate that Claudin-1 outside of the TJ may act as a ‘sacrificial protein’, acting as a substrate for UV induced enzymes and so protecting other more vulnerable proteins from degradation.

Solar simulated radiation induces loss of claudin – 1 from primary human keratinocytes: a mechanistic study