Assembly of Human Stratum Corneum Lipids In Vitro: Fluidity Matters

Fluid lipid membranes are vital for living systems. In contrast, the skin barrier lipids are primarily rigid and tightly packed. While this unusual lipid rigidity makes sense for restricting water loss and preventing the penetration of harmful substances, it is less conceivable how such lipids attain their complex architecture. Our in vitro experiments on isolated human stratum corneum lipids suggest that the essential skin barrier structure, the long periodicity phase, LPP, is a robust assembly highly favored by the lipids without the need for fluidization or a template. However, to reduce nanoscopic packing defects and improve the barrier properties, the lipids need to undergo temporary fluidization. This finding may be relevant to the function of the corneocyte lipid envelope in vivo, as these covalent lipids may help orient the free lipids in a controlled manner to seal their lateral packing defects.