Netherton Syndrome (NS) is an autosomal recessive form of ichthyosis regarded as one of the most severe skin hereditary disorders affecting newborns, and patients present both cutaneous and immunological abnormalities. NS is caused by loss-of-function mutations in the SPINK5 gene, encoding the serine-protease inhibitor LEKTI, whose deficiency results in unrestricted activity of kallikreins (e.g. KLK5 and KLK7) that leads to degradation of corneodesmosomal proteins, thus producing the detachment of the stratum corneum and disruption of the epidermal barrier. Due to the limited availability of NS skin biopsies and ethical constraints of experimentation on human subjects we sought to develop a skin humanized mouse model for the disease based on the grafting of transgenic bioengineered human skin onto immunodeficient mice. In order to recapitulate the histopathological hallmarks of the condition we first considered an approach consisting in the overexpression of the KLK5 gene in human keratinocytes by lentiviral transduction. We have performed an initial characterization of the model through the analysis of histopathological markers associated to NS as well as KLK5 expression and activity. The study confirmed the alterations in the KLK5 pathway, which results in clear epidermal proliferation and differentiation alterations, similar to those observed in skin biopsies of NS patients. In a preliminary experiment, a topical formulation of a KLK5 inhibitory peptide was applied to KLK5 overexpressing grafts. The analysis of the treated grafts showed a lower activity of KLK5 and a certain degree of reversion of the main NS phenotypic markers. Establishing a reliable skin humanized mouse model for hyperkeratotic genodermatoses such as NS would enable to understand the underlying pathogenic mechanisms as well as developing novel therapeutic strategies to treat these conditions.

Development and characterization of a kallikrein 5 overexpressing skin humanized mouse model resembling Netherton Syndrome