Modelling and Implementation of Complex Systems

Abstract

Atopic dermatitis (AD) is a chronic inflammatory disease characterized by pruritus, eczematous lesions, increased transepidermal water loss and lichenification, and in some cases retained nuclei in the cornified layer (parakeratosis). Current evidence suggests that the primary defect is one of impaired barrier function, with mutations in the filaggrin gene being important. However not all patients with AD have filaggrin mutations, suggesting that other mechanisms may give rise to the barrier defect observed in these patients. We have detected loss of Akt1 activity in patients with AD. To investigate the role of Akt1 in cornified envelope formation, we knocked down Akt1 expression using small-interfering (si)RNA in rat epidermal keratinocytes (REK), creating an in vitro organotypic culture model that phenocopies AD. The knockdown rafts demonstrated the basket-weave hyperkeratosis characteristic of AD, filaggrin localization was altered, and processing to the monomeric form greatly reduced. Akt-1 inhibition reduced colocalization of filaggrin with HspB1, and reduced interaction between HspB1 and filaggrin while increasing the interaction between HspB1 and actin during confluent cell culture. These findings suggest a switch between HspB1-actin interaction to a HspB1-filaggrin interaction in the upper epidermis which is mediated by Akt1. There was also parakeratosis in our Akt1 siRNA-expressing organotypic cultures. Lamin A/C expression was maintained in the cornified layer, and lamin A/C degradation, thought to be an Akt-mediated process, was reduced in the siRNA-expressing cells. We provide evidence that Akt-1 controls both filaggrin processing and via lamin A/C degradation, nuclear degradation, key processes for forming strong cornified envelopes.