The epidermal tight junction (TJ) plays an important role as a barrier which protects the skin against dehydration and infection. Skin barrier function is known to decline with increasing age (Rabe et al., 2006). Human skin is subject to intrinsic (i.e. chronological) ageing and extrinsic (environmentally-induced) ageing. However, the role of TJs in the ageing process is still unknown. Therefore, in this study, using quantitative immunofluorescent staining TJ protein expression was investigated in intrinsically aged compared to young human skin. Since ultraviolet radiation (UVR) from sunlight is considered the major environmental insult to human skin, TJ proteins were also investigated in photoaged compared to photoprotected human skin, and in skin exposed to a single acute dose of UVR.In aged vs young skin, there was no significant difference either in the expression levels or localisation of TJ proteins.However, significant reduction in claudin-1 (cld-1) and increases in cld-7 and -12 expressions were demonstrated in chronically photoaged human skin suggesting differential regulation of clds in response to photoexposure. By contrast in acutely irradiated human skin, only a reduction in cld-1 expression was observed 24h after a single UVB dose. Moreover, in both chronic and acute UVR exposed human skin, cld-1 was most significantly reduced in the basal layer of the epidermis suggesting that the differentiation state of keratinocytes might be important in their response to UVR.To investigate these effects further, a normal human epidermal keratinocyte (NHEK) cell culture model was employed. A reduction in cld-1 expression and an increase in cld-4 were demonstrated in undifferentiated NHEK cells irradiated with sub lethal doses of UVR. Interestingly, no changes were observed in TJ protein expression in irradiated differentiated keratinocytes. However, when TJ function was measured in these cells using transepithelial electrical resistance (TEER) as a marker of TJ function, UVR induced a significant reduction in TEER. This coincided with an alteration in the organisation of cld-1 in irradiated differentiated keratinocytes.These data demonstrate that TJ protein expression is modulated by acute and chronic exposure to UVR. These observations may explain, at least in part, the decline in skin barrier function observed in response to UVR.
|Date of Award||1 Aug 2013|
- The University of Manchester
|Supervisor||Catherine O'Neill (Supervisor), Christopher Griffiths (Supervisor) & Rachel Watson (Supervisor)|