Elucidating the role of Transient Receptor Potential Ankyrin 1 (TRPA1) in Aldara™-induced skin inflammation model

Psoriasis is a common chronic skin disease, affecting 2-3% of the UK population (1). As Transient Receptor Potential Ankyrin 1 (TRPA1) has been implicated in many inflammatory diseases, including colitis (2), this study used genetics approach to investigate the role ofTRPA1 using Aldara™-induced psoriasis model in mice (3). We hypothesised that TRPA1is involved in driving skin inflammation in this model.

In vivo procedures were carried out according to the UK Home Office Animals (Scientific Procedures) Act 1986. Male C57BL/6J mice or TRPA1 WT/ KO (n=4-5; 6-8 weeks; mixed background) mice were used in recovery procedures performed under 2% isoflurane. Dorsal skin hair was removed prior to measuring blood flow using Full-field Laser Perfusion Imager (4). Doublefold skin thickness was measured and epidermal thickness confirmed by H&E staining. 75mg of Aldara™ (5% imiquimod) cream (Meda Pharma, UK) or Vaseline (for control) was applied over a 2x2cm2 area daily for 4 days. Skin samples were frozen at -20oC until further analysis. Data were analysed using 2-way or repeated measures ANOVA followed by Bonferonni post-hoc test.

In contrast to the skin inflammatory response observed in C57BL/6J mice, with enhanced blood flow in Aldara™-treated vs vaseline-treated mice (397.2±46.2 vs 708.2±43.0 flux units, p<0.001) and increased doublefold skin thickness (0.10±0.06 vs 0.6±0.06 mm, p<0.001), TRPA1 WT showed weaker response to Aldara™-induced skin inflammation, with only a trend of increased blood flow and epidermal thickness (Table 1). Interestingly, TRPA1 KO mice showed significantly enhanced inflammatory response compared to TRPA1 WT in all the parameters described below (Table 1).

In conclusion, we developed a feasible model with characteristics of psoriasis in C57BL/6J mice, this model is sensitive to the mouse strain. Our current results suggest thatTRPA1 may play a protective, rather than damaging role, based on our results to date.

Table 1:Aldara™-induced skin inflammation in TRPA1 WT and KO mice. Results shown for blood flow and doublefold skin thickness from 24-hour post-day 4 treatment. ** p<0.01, *** p<0.001 between vaselinevs Aldara™ of the same genotype group. # p<0.05, ## p<0.01, ### p<0.001 between WT vs KO groups.

1. Nestle, FO (2009). New Eng J Med 361: 496-509

2. Engel, MA (2011). Gastroenterol 141: 1346-1358

3. Van der Fits, L et al. (2009). J Immunol 182: 5836-5845

4. Aubdool, AA et al. (2014). Nat Comms 5: 5732

XK is supported by British Pharmacological Society’s AJ Clark Studentship