The importance of 12R‐lipoxygenase and transglutaminase activities in the hydration‐dependent ex vivo maturation of corneocyte envelopes

Abstract

BackgroundTerminally differentiated keratinocytes acquire corneocyte protein envelopes (CPE) complexed with corneocyte lipid envelopes (CLE). These two structural components of the corneocyte envelopes (CEs) undergo maturation by gaining in hydrophobicity, rigidity and surface area. Linoleoyl acylceramides are processed by 12R‐lipoxygenase (12R‐LOX) and other enzymes before transglutaminase (TG) attaches ω‐hydroxyceramides to involucrin in the CPE. Concurrently, structural proteins are cross‐linked by TG that has been activated by cathepsin D (CathD).ObjectivesThe primary aim of this work was to demonstrate the impact of relative humidity (RH) during ex vivo CE maturation. Low, optimal and high RH were selected to investigate the effect of protease inhibitors (PIs) on CE maturation and TG activity; in addition, 12R‐LOX and CathD activity were measured at optimal RH. Finally, the effect of glycerol on ex vivo CE maturation was tested at low, optimal and high RH.MethodsThe first and ninth tape strip of photo‐exposed (PE) cheek and photo‐protected (PP) post‐auricular sites of healthy volunteers were selected. Ex vivo CE maturation was assessed via the relative CE maturity (RCEM) approach based on CE rigidity and hydrophobicity. The second and eighth tapes were exposed to RH in the presence of inhibitors.ResultsIrrespective of tape stripping depth, CEs from PE samples attained CE rigidity to the same extent as mature CEs from the PP site, but such improvement was lacking for CE hydrophobicity. 70% RH was optimal for ex vivo CE maturation. The inhibition of 12R‐LOX activity resulted in enhanced CE rigidity which was reduced by the TG inhibitor. CE hydrophobicity remained unchanged during ex vivo maturation in the presence of TG or 12R‐LOX inhibition. CE hydrophobicity was enhanced in the presence of glycerol at 44% RH and 100% RH but not at 70% RH. Furthermore, TG activity was significantly diminished at 100% RH compared to the commercial inhibitor LDN‐27219. However, a protease inhibitor mix reversed the negative effect of overhydration.ConclusionThe study adds to the understanding of the roles of 12R‐LOX and TG activity in CE maturation and gives further insight into the effect of glycerol on the SC.

Changes in nano-mechanical properties of human epidermal cornified cells in children with atopic dermatitis

“…Cornified cell envelopes undergo progressive maturation within the SC that results in increase of the cell stiffness ( Michel et al ., 1988 ; Milani et al ., 2018 ). This process appears to rely largely on hydration-dependent activities of transglutaminase 1 and 12R-lipoxygenase ( Guneri et al ., 2019 ). It is, therefore, not surprising that in AD, characterized by low NMF content and, consequently, reduced hydration, expression of mRNA and the corresponding proteins composing CE is decreased ( Trzeciak et al ., 2017 ).…”

“…Indirectly, filaggrin influences the SC mechanical integrity through its degradation products, which contribute to a pool of hygroscopic molecules collectively called natural moisturizing factors (NMF). NMF regulate SC hydration, crucial for the plasticity of the skin, its pH and activity of enzymes involved in key homeostatic processes in the SC including lipid synthesis, maturation of CE and desquamation ( Guneri et al ., 2019 ; Rawlings, 2014 ). Therefore, deficiency of filaggrin will likely affect mechanical stability of the SC and its resistance to cracking and chapping, common hallmarks of AD skin.…”

Changes in levels of omega‐O‐acylceramides and related processing enzymes of sun‐exposed and sun‐protected facial stratum corneum in differently pigmented ethnic groups

“…Omega-O-acylceramides, especially the linoleate-containing ones, are used in a complex enzymatic process to attach ceramides to the corneocyte protein envelope (CPE) [13][14][15][16][17][18]. Reduced levels of 12R-LOX and eLOX3 were reported in photodamaged cheek SC previously from Caucasian women and 12R-LOX in Chinese subjects [38][39][40]. In this study, we observed that the mass levels of 12R-LOX and eLOX3 were equivocal in all three ethnic groups indicating a lipoxygenase-relevant corneocyte maturation insufficiency in all ethnicities (Table 1A-C).…”

Facial skin mapping: from single point bio‐instrumental evaluation to continuous visualization of skin hydration, barrier function, skin surface pH, and sebum in different ethnic skin types

“…Compared to other body sites, facial skin shows elevated transepidermal water loss (TEWL, a measure of skin barrier function), and increased SC cohesion together with lower levels of SC ceramides and natural moisturising factors and higher serine, aspartic and matrix metalloprotease protease activity resulting in premature corneodesmosomal degradation and thinning of the SC [1,[20][21][22][23][24][25][26][27][28][29][30]. Relating to the immaturity of the cells, reduced loricrin levels together with lowered transglutaminase and 12Rlipoxygenase activities have been reported in photodamaged facial skin [31][32][33]. A summary of this biochemistry is described in Fig.…”