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Animals; Epidermis, metabolism; Ichthyosis, metabolism; Intermediate Filament Proteins, metabolism; Lipids, immunology; Mice; Mice, Knockout; Protein Processing, Post-Translational, immunology; Rapamycin-Insensitive Companion of mTOR Protein, immunology; Signal Transduction, immunology
Abstract
Perturbation of epidermal barrier formation will profoundly compromise overall skin function, leading to a dry and scaly, ichthyosis-like skin phenotype, which is the hallmark of a broad range of skin diseases, including ichthyosis, atopic dermatitis, and a multitude of clinical eczema variants. An overarching molecular mechanism that orchestrates the multitude of factors controlling epidermal barrier formation and homeostasis remains to be elucidated.; Here we highlight a specific role of mammalian target of rapamycin complex 2 (mTORC2) signaling in epidermal barrier formation.; Epidermal mTORC2 signaling was specifically disrupted by deleting Rictor, encoding an essential subunit of mTORC2 in mouse epidermis (Ric; EKO; ). Epidermal structure and barrier function were investigated by a combination of gene expression, biochemical, morphological and functional analysis in Ric; EKO; and control mice.; Ric; EKO; newborns displayed an ichthyosis-like phenotype characterized by dysregulated epidermal de novo lipid synthesis, altered lipid lamellae structure, and aberrant filaggrin processing. Despite a compensatory transcriptional epidermal repair response, the protective epidermal function was impaired in Ric; EKO; mice as revealed by increased transepidermal water loss, enhanced corneocyte fragility, decreased dendritic epidermal T cells, and an exaggerated percutaneous immune response. Restoration of Akt-Ser473 phosphorylation in mTORC2-deficient keratinocytes by expression of constitutive Akt rescued filaggrin processing.; Our findings reveal a critical metabolic signaling relay of barrier formation where epidermal mTORC2 activity controls filaggrin processing and de novo epidermal lipid synthesis during cornification. Our findings provide novel mechanistic insights into epidermal barrier formation and could open up new therapeutic opportunities to restore defective epidermal barrier conditions.
