The permeability barrier in mammalian epidermis

Area of Science:

• Dermatology
• Cell Biology
• Biophysics

Background:

• The mammalian epidermis provides a critical barrier against environmental factors and water loss.
• Understanding the structural basis of this permeability barrier is essential for dermatology and drug delivery.

Purpose of the Study:

• To elucidate the structural basis of the mammalian epidermis permeability barrier.
• To investigate the role of lamellar bodies and intercellular spaces in epidermal barrier function.

Main Methods:

• Tracer studies using horseradish peroxidase, lanthanum, and ferritin in neonatal mice and isolated epidermal sheets.
• Freeze-fracture electron microscopy to examine cellular and intercellular structures.
• Freeze-substitution techniques to confirm fracture plane pathways.

Main Results:

• Water-soluble tracers were impeded at the stratum granulosum by extruded lamellar body contents.
• Lamellar body contents formed sheets within the stratum corneum's intercellular spaces, revealing wider interstices (5-10x previously appreciated).
• Freeze-fracture revealed no tight junctions in granular cells, but complex, multilaminated intercellular faces in the stratum corneum.

Conclusions:

• The primary barrier to water loss originates in the stratum granulosum, mediated by intercellular deposition of lamellar bodies.
• A novel intercellular freeze-fracture plane exists within the stratum corneum.
• The expanded, complex intercellular regions of the stratum corneum are likely lipid-rich and play a role in percutaneous transport.