SPINK5 knockdown in organotypic human skin culture as a model system for Netherton syndrome: effect of genetic inhibition of serine proteases kallikrein 5 and kallikrein 7

Netherton syndrome (NS; OMIM 256500) is a genetic skin disease resulting from defects in the serine protease inhibitor Kazal-type 5 (SPINK5) gene, which encodes the protease inhibitor lympho-epithelial Kazal type inhibitor (LEKTI). We established a SPINK5 knockdown skin model by transfecting SPINK5 small interfering RNA (siRNA) into normal human epidermal keratinocytes, which were used together with fibroblast-populated collagen gels to generate organotypic skin cultures. This model recapitulates some of the NS skin morphology: thicker, parakeratotic stratum corneum frequently detached from the underlying epidermis and loss of corneodesmosomes. As enhanced serine protease activity has been implicated in the disease pathogenesis, we investigated the impact of the kallikreins KLK5 [stratum corneum trypsin-like enzyme (SCTE)] and KLK7 [stratum corneum chymotrypsin-like enzyme (SCCE)] on the SPINK5 knockdown phenotype by generating double knockdowns in the organotypic model. Knockdown of KLK5 or KLK7 partially ameliorated the epidermal architecture: increased epidermal thickness and expression of desmocollin 1 (DSC1), desmoglein 1 (DSG1) and (pro) filaggrin. Thus, inhibition of serine proteases KLK5 and KLK7 could be therapeutically beneficial in NS.