Elastase 2 is expressed in human and mouse epidermis and impairs skin barrier function in Netherton syndrome through filaggrin and lipid misprocessing
Chrystelle Bonnart, Céline Deraison, Matthieu Lacroix, Yoshikazu Uchida, Céline Besson, Aurélie Robin, Anaïs Briot, Marie Gonthier, Laurence Lamant, Pierre Dubus, Bernard Monsarrat, Alain Hovnanian
Chrystelle Bonnart, Céline Deraison, Matthieu Lacroix, Yoshikazu Uchida, Céline Besson, Aurélie Robin, Anaïs Briot, Marie Gonthier, Laurence Lamant, Pierre Dubus, Bernard Monsarrat, Alain Hovnanian
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Research Article Dermatology

Elastase 2 is expressed in human and mouse epidermis and impairs skin barrier function in Netherton syndrome through filaggrin and lipid misprocessing

Abstract

The human epidermis serves 2 crucial barrier functions: it protects against water loss and prevents penetration of infectious agents and allergens. The physiology of the epidermis is maintained by a balance of protease and antiprotease activities, as illustrated by the rare genetic skin disease Netherton syndrome (NS), in which impaired inhibition of serine proteases causes severe skin erythema and scaling. Here, utilizing mass spectrometry, we have identified elastase 2 (ELA2), which we believe to be a new epidermal protease that is specifically expressed in the most differentiated layer of living human and mouse epidermis. ELA2 localized to keratohyalin granules, where it was found to directly participate in (pro-)filaggrin processing. Consistent with the observation that ELA2 was hyperactive in skin from NS patients, transgenic mice overexpressing ELA2 in the granular layer of the epidermis displayed abnormal (pro-)filaggrin processing and impaired lipid lamellae structure, which are both observed in NS patients. These anomalies led to dehydration, implicating ELA2 in the skin barrier defect seen in NS patients. Thus, our work identifies ELA2 as a major new epidermal protease involved in essential pathways for skin barrier function. These results highlight the importance of the control of epidermal protease activity in skin homeostasis and designate ELA2 as a major protease driving the pathogenesis of NS.

Authors

Chrystelle Bonnart, Céline Deraison, Matthieu Lacroix, Yoshikazu Uchida, Céline Besson, Aurélie Robin, Anaïs Briot, Marie Gonthier, Laurence Lamant, Pierre Dubus, Bernard Monsarrat, Alain Hovnanian

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Figure 6

Abnormal epidermal lipid organization and quantification.

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Abnormal epidermal lipid organization and quantification. (A) Nile red s...
(A) Nile red staining of mouse and human skin cryosections. In normal mouse (WT) and human (healthy) skin, extracellular lipid lamellae appear as yellow parallel lines. In the epidermis of newborn Tg-ELA2 mice (Tgnb), no abnormality is detectable, but numerous yellow lipid droplets are observed at P4 (TgP4). In KOnb mice, lipid droplets are visible in the central layers of the SC. In KOg, the staining reveals numerous lipid droplets and no extracellular lamellae. NS patient epidermis shows similar abnormal lipid droplets. Scale bar: 10 μm. (B) Structure of intercellular lipids revealed with RuO4 postfixation in 4-day-old WT and Tg-ELA2 epidermis. Note broad and compact lipid bilayers in WT SC (bracket). In contrast, unprocessed lipids are seen in the SC intercellular space in Tg-ELA2. At the SG-SC interface of WT epidermis, LB are observed. In Tg-ELA2, lipid material remains globular and disorganized (asterisk) and dilates the extracellular space. Scale bar: 10 nm. (C) Epidermal lipid content in 4-day-old Tg-ELA2 compared with WT animals. ω-hydroxy Cers, ω-OH Cer in CLE; ω-hydroxy fatty acids, ω-OH FA in CLE. Quantification shows a significant decrease in FFA, SM, and ω-OH FA amount in Tg-ELA2 epidermis, while GlcCer amount is significantly increased. Results represent the mean ± SD of 4 WT and 4 transgenic epidermis. Significant P values are indicated.