The stratum corneum comprises three layers with distinct metal-ion barrier properties

Akiharu Kubo,Keisuke Nagao,Hiroshi Kawasaki,Akiko Kubo,Yoshiharu Ohashi,Itsuko Ishizaki,Masayuki Amagai

doi:10.1038/srep01731

Abstract

The stratum corneum (SC), the outermost barrier of mammalian bodies, consists of layers of cornified keratinocytes with intercellular spaces sealed with lipids. The insolubility of the SC has hampered in-depth analysis, and the SC has been considered a homogeneous barrier. Here, we applied time-of-flight secondary ion mass spectrometry to demonstrate that the SC consists of three layers with distinct properties. Arginine, a major component of filaggrin-derived natural moisturizing factors, was concentrated in the middle layer, suggesting that this layer functions in skin hydration. Topical application of metal ions revealed that the outer layer allowed their passive influx and efflux, while the middle and lower layers exhibited distinct barrier properties, depending on the metal tested. Notably, filaggrin deficiency abrogated the lower layer barrier, allowing specific metal ions to permeate viable layers. These findings elucidate the multi-layered barrier function of the SC and its defects in filaggrin-deficient atopic disease patients.

Highlights

The stratum corneum (SC), the outermost barrier of mammalian bodies, consists of layers of cornified keratinocytes with intercellular spaces sealed with lipids
Muscles were visualized as actinhigh by immunofluorescence and potassium (K)high sodium (Na)low in TOF-SIMS, and connective tissues were visualized as collagen Ihigh in immunofluorescence and Klow Nahigh in TOF-SIMS (Fig. 2a–c), suggesting that cell-rich areas are Khigh Nalow and that matrix-rich areas are Klow Nahigh, probably due to the exchange of Na and K ions on the cell surface[16,17]
TOF-SIMS imaging and matrix-assisted laser desorption ionization (MALDI)-mass spectrometry (MS) imaging are similar techniques that have several advantages, including the lack of the need for fixation or chemical labeling, which avoids delocalization of unfixable molecules, and the ability to simultaneously image a variety of biological compounds in a single run[24,25]

Summary

Introduction

The stratum corneum (SC), the outermost barrier of mammalian bodies, consists of layers of cornified keratinocytes with intercellular spaces sealed with lipids. The insolubility of the SC and its densely packed and heavily cross-linked proteins has hampered the detailed analysis of its barrier nature by conventional imaging techniques To overcome these difficulties, we applied imaging mass spectrometry (MS) in this study to analyze the SC. In contrast to previous studies using MS14,15, our improved sample preparation method and TOF-SIMS enabled us to visualize the spatial distribution of natural substances and externally applied molecules simultaneously in submicron spatial resolution. This approach revealed that the SC consists of three sharply demarcated layers with distinct barrier properties

Methods

Results

Conclusion