An investigation of circadian rhythms in psoriasis skin and time-of-day dependent response to ultraviolet B radiation

Humans have a built-in body clock that controls the expression of different genes and proteins over a 24-hour period, which we call our circadian rhythms. The skin is the largest organ in the body and forms an important interface with the environment. There is a huge variation between the day and night in our environmental exposures, including the amount of ultraviolet (UV) radiation we get from the sun, the risk of physical injury like cuts and burns, temperature changes and drying out of the skin. To help with this, the skin's cells have their own clock which we believe has evolved to help predict and better adapt to our environment. Research studies in mice have shown that skin growth and risk of damage from sunlight varies over the course of the day. We know that human skin growth also varies over the day but we don't know whether our sensitivity to sunlight varies too.

Whilst too much sunlight is dangerous for our skin, we have known for thousands of years that it can improve skin diseases like psoriasis. Psoriasis is a common skin condition which can be disabling, as well as leading to social rejection. It presents as red, thick and scaly plaques on visible areas of the skin. Phototherapy, which is where a safe part of the radiation from the sun is shone on the skin, is a good treatment for psoriasis because it is relatively safe and effective and often people prefer it to tablet treatments. However, it doesn't work for everyone, so we are continuing to look into this and work out why.

The aims of this study are:

1. To look into the circadian clock in psoriasis skin to see whether it is present and functions normally like in non-psoriasis skin
2. To discover new genes that cycle over the course of the day in psoriasis skin
3. To see how circadian rhythms change in psoriasis plaques as they get better with treatment
4. To investigate whether psoriasis skin is more sensitive to UV radiation in the morning compared with the afternoon

For the first part of the project, I will just look at the individual skin cells of patients with and without psoriasis and monitor the circadian clock in "real-time".

For the next part, I will take small, 6mm biopsies of skin from the psoriasis plaques of patients in the morning and afternoon, with and without UV radiation (four biopsies per patient). This skin will be stained to help compare the effects of UV radiation between time points. This skin will also be sent for gene expression profiling and analysis performed to see if the cells are behaving differently in the morning and afternoon. Sixteen patients will be required for this part of the study and this has been precisely calculated based on earlier data we have gathered.

Lastly, I will analyse gene expression data that has already been taken from a large multimillion pound study called PSORT (Psoriasis Stratification and Optimisation of Relevant Therapies), in which over 120 patients with psoriasis gave skin biopsies over the course of their treatment with a different medication called a biologic. These biopsies have the time they were taken recorded which means I can compare gene expression in a larger cohort and see what changes happen as their psoriasis clears.

I think this research is very important for three reasons. Firstly, psoriasis is very common, and so anything that improves our understanding of psoriasis can help many people worldwide. Secondly, this project has the potential to change the way we deliver phototherapy, meaning we can improve care of people with psoriasis. Lastly, learning about and applying circadian rhythms has a wider application. Chronotherapy - giving treatments at a particular time in the day for better outcomes - is emerging as a new and exciting concept in healthcare. What we learn about how we carry this research can be applied to other diseases to apply chronotherapy to those too.

I aim to undertake three experiments with a translational focus to investigate the circadian clock and circadian rhythms found in psoriasis skin and compare the response to UVB irradiation applied locally to psoriasis plaques in a powered clinical study.


Experiment 1: Mechanistic enquiry (10 patients)
Hypothesising that circadian rhythms are present in skin derived from psoriasis plaques, I will carry out lentiviral transduction of epidermal keratinocytes and dermal fibroblasts with a clock gene reporter and quantify the expression of this in real-time over 1 week via luminometry.

Experiment 2: Clinical study (16 patients)
I have generated pilot data suggesting that clock gene expression varies between the morning and afternoon, and that UVB irradiation to plaques of psoriasis will lead to significantly more DNA damage and keratinocyte apoptosis in the morning compared with the afternoon. To confirm these findings, I will carry out a larger clinical study of 16 patients (powered from pilot data). I will administer a standardised dose of UVB to individual plaques of psoriasis in the AM and PM, then take 6mm skin biopsies from these areas as well as similar non-irradiated areas (four biopsies per patient). I will also take AM/PM blood samples for future RNA and DNA analysis. I will process these biopsies to perform RNAseq and by immunohistochemistry to quantify AM/PM DNA damage and apoptosis.

Experiment 3: Bioinformatics enquiry
I will use the RNAseq data from my clinical study and also from an existing large cohort study (PSORT, >120 patients with timestamped biopsies) for AM/PM differential expressed gene (DEG) analysis and Ingenuity Pathway Analysis (IPA).


This Fellowship will greatly increase the current knowledge about circadian rhythms in psoriasis and provides built-in translational application to phototherapy, a commonly used treatment for psoriasis. Future aims would be a RCT comparing phototherapy outcomes for psoriasis patients.