Corneocytes undergo systematic changes in element concentrations across the human inner stratum corneum

Area of Science:

• Biophysics
• Cell Biology
• Dermatology

Background:

• The stratum corneum is the outermost layer of the skin, crucial for barrier function.
• Corneocytes, the cells of the stratum corneum, undergo significant structural and chemical changes during maturation.
• Understanding the elemental composition of corneocytes is key to understanding skin barrier development.

Purpose of the Study:

• To visualize and quantify the elemental composition of individual human corneocytes within the inner stratum corneum.
• To investigate the dynamic changes in ion concentrations (potassium, chloride, sodium, phosphorus) during corneocyte transit.
• To correlate elemental shifts with the chemical maturation of corneocytes, including filaggrin breakdown.

Main Methods:

• Analytical electron microscopy (AEM) was employed on freeze-dried cryosections of human skin.
• Elemental mapping and quantification were performed at the cellular level within the inner stratum corneum.
• Corneocyte position was correlated with elemental composition to track changes during transit.

Main Results:

• Phosphorus concentration drops sharply at the granular/stratum corneum interface.
• Potassium concentration declines more slowly than phosphorus, migrating further into the stratum corneum.
• Chloride concentration initially increases and then decreases, while sodium remains relatively constant.
• Oppositely directed movements of potassium and chloride suggest potential electrical charge imbalances.

Conclusions:

• Corneocytes exhibit position-dependent alterations in elemental composition, indicating intracellular chemical maturation.
• These elemental shifts are associated with key events like filaggrin breakdown, contributing to skin barrier formation.
• The study provides a detailed view of the dynamic ionic environment within maturing corneocytes.