The mechanisms underlying UVB-induced clearance of psoriasis are incompletely understood. We compared the cellular and molecular effects of a clinically effective wavelength of UVB (311nm) with a clinically ineffective wavelength (290nm) in vivo and in vitro to distinguish bystander effects and utilised a systems biology approach to understand functional significance. 84 adult psoriatic patients were recruited. Biopsies were taken from lesional (plaque) skin before and 4-48h after irradiation with equi-erythemogenic doses of 311 and/or 290nm UVB (0.75-3.0 MED). A significant increase in the numbers of apoptotic epidermal cells (active-caspase-3+ cells) was seen after a single irradiation with 2-3 MEDs 311 nm UVB compared to 2-3 MEDs 290 nm UVB or untreated psoriasis (median 12/1000, 0/1000 and 0/1000 epidermal cells respectively; p<0.001). Routine clinical doses of 311nm also induced apoptosis. Immunochemistry and electron microscopy showed that the vast majority of apoptotic cells were keratinocytes. Live cell imaging of irradiated cultured keratinocytes and mathematical modelling showed that the rate of keratinocyte apoptosis observed in vivo was sufficient to account for clearance of psoriasis. Gene array analysis was used to examine differential gene regulation at these early time-points, prior to clinical response. Apoptosis and control of cell cycle pathways were affected by 311nm but not 290nm UVB. CDKN1A (WAF1/p21) showed the greatest fold change (27 fold up-regulation) following irradiation with 311nm UVB but not 290nm. Together these data provide evidence that epidermal keratinocyte apoptosis is a key mechanism in psoriasis resolution and identifies keratinocyte apoptosis as a potential target for future drug development.
|Number of pages||1|
|Journal||Journal of Investigative Dermatology|
|Issue number||Supplement 2|
|Publication status||Published - Sep 2011|
|Event||41st Annual Meeting of the European-Society-for-Dermatological-Research - Barcelona, Spain|
Duration: 7 Sep 2011 → 10 Sep 2011