Lateral Phase Behavior of Human Skin Lipids
Michael J. Counihan '16, Gettysburg College
The human stratum corneum (SC) is the outermost layer of the epidermis, the first barrier against the environment. This largely impenetrable layer consists of anucleated, flattened, protein-rich cells called corneocytes suspended in an extracellular lipid matrix. This lipid matrix is composed of ceramides (Cers), cholesterol (Chol), and free fatty acids (FFAs). The SC lipids are unique from other biologically relevant lipids commonly found in cell membranes in that the Cers and FFAs have very long (>20 carbons) fatty acid chains, nearly all of which are fully saturated. Lateral packing and domain formation within Langmuir monolayers of the individual Cer, Chol, and FFA components and their binary and ternary mixtures were investigating using surface pressure vs. molecular area isotherms and fluorescence microscopy to determine the role of each component in the material properties of the SC layer. Particular attention was paid to the effect of FFA length on membrane fluidity – FFA chains ranging from 16 to 30 carbons (24 carbons being the most common in the SC) were studied. A physiologically accurate mixture of several FFAs with different chain lengths (FFAmix) is shown to be more stable to compression-expansion cycling than any single FFA. Longer chain FFAs have a condensing effect in Cer monolayers, while Chol tends to disrupt the Cer-FFA organization. The trans double bond in the sphingosine backbone of certain SC Cers allows close lateral lipid packing, stiffening the layer. Additionally, there are significant differences between the canonical 1:1:1 Cer:Chol:FFA mixture and a more physiologically accurate 10:9:4 mixture with more representative Cers and FFAmix. Including a higher ratio of Cers and a lower one of FFAs in such mixtures condenses the monolayer despite FFAs being more incompressible than Cers alone, indicating that ternary SC lipid mixtures experience non-additive complex lipid interactions.
Counihan, Michael J. and Shelli F. Frey. "Lateral Phase Behavior of Human Skin Lipids." Presentation at the Biophysical Society Meeting in San Fransisco, CA, February 17-21, 2018.