O13 JAK inhibitors to restore skin barrier function in ARCI

Abstract The autosomal recessive congenital ichthyoses (ARCI) are a group of chronic conditions where there is unmet therapeutic need. Harlequin ichthyosis (HI) is the most severe form of ARCI, with aberrant differentiation of the epidermis leading to a severe barrier defect. It is caused by mutations in ABCA12, a lipid transporter involved in the transport of glucosylceramides from the lamellar body to the lipid lamellae. Lamellar ichthyosis is caused by mutations in TGM1. Several Janus kinase (JAK) inhibitors (JAKi) inhibiting the JAK–STAT pathway are now licensed for atopic dermatitis. Previous work from our group in an in vitro HI model showed that tofacitinib had a restorative effect on the lipid barrier. We hypothesized that JAKi A, B and C could restore the epidermal barrier in both HI three-dimensional (3D) organotypic models (OTs) made using ABCA12 CrispR-Cas9 knockout and wild-type keratinocytes and ARCI 3D OTs generated with short hairpin RNA knock down of TGM1. The JAKi were tested at three concentrations in the 3D models (20, 50 and 500 nmol L–1 for JAKiA; 10, 50 and 250 nmol L–1 for JAKiB; 2, 25 and 125 nmol L–1 for JAKiC) and vehicle only was used as the control. The OTs were stained with haematoxylin and eosin, Nile red and differentiation markers such as K10, K14, transglutaminase 1 (TGM1) and involucrin. All three JAKi had a positive effect on the epidermal barrier. The epidermal structure looked more organized and uniform, with an increase in neutral and polar lipids in the upper epidermis. The differentiation markers showed normalization of the expression of involucrin, K10 and TGM1 at the same drug concentrations. These results suggest that JAKi have a generalized positive effect on the skin barrier and will be further investigated in an in vivo mouse model of HI.