Skin barrier fine-tuning through low-temperature lipid chain transition

The lipids in the mammalian stratum corneum (SC) adopt an unusually rigid arrangement to form a vital barrier preventing water loss and harmful environmental impacts. Just above the physiological temperature, a subset of barrier lipids undergoes a phase transition from a very tight orthorhombic to a looser hexagonal arrangement and vice versa. The purpose of this lipid transition in skin physiology is unknown. Permeability experiments on isolated human SC indicated that the transition affects the activation energy for a model compound that prefers lateral movement along lipid layers but not for water or a large polymer that would cross the SC via the pore pathway. The orthorhombic phase content of SC lipids, as determined by infrared spectroscopy, was also modulated by (de)hydration. Spontaneous rearrangement of human SC lipid monolayers into 10 nm higher multilamellar islets at 32 – 37°C, but not at room temperature, was revealed by atomic force microscopy. Our findings add to our knowledge of fundamental skin physiology suggesting a fine temperature- and hydration-controlled switch from fluid lipids required for lipid barrier assembly to rigid and tightly packed lipids in the mature SC necessary for the water and permeability barriers.