In a three-dimensional reconstructed human epidermis filaggrin-2 is essential for proper cornification

Atopic dermatitis is a chronic inflammatory skin disease with defects in the epidermal barrier. In a cohort of African-American children, a FLG2 nonsense mutation has been associated with the disease. In the epidermis of European patients, the expression of filaggrin-2, the filaggrin-related protein encoded by FLG2, is decreased. To describe the function of filaggrin-2 and evaluate the impact of its deficiency, its expression was downregulated using lentivirus-mediated shRNA interference in a three-dimensional reconstructed human epidermis (RHE) model. This resulted in parakeratosis and a compact stratum corneum, presence of abnormal vesicles inside the corneocytes, increased pH and reduced amounts of free amino acids at the RHE surface, leading to increased sensitivity to UVB radiations. The expression of differentiation markers was slightly modified. However, we observed reduced proteolytic processing of corneodesmosin, hornerin and filaggrin in parallel with reduced amounts of caspase-14 and bleomycin hydrolase. Our data demonstrated that filaggrin-2 is important for a proper cornification and a functional stratum corneum. Its downregulation in atopic patients may be involved in the disease-associated epidermis impairment.