PNAS October 1, 2012
Krysta Biniek, Kemal Levi, and Reinhold H. Dauskardt dauskardt at stanford.edu
Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305
Edited by John W. Hutchinson, Harvard University, Cambridge, MA, and approved August 31, 2012 (received for review April 25, 2012)
The ubiquitous presence of solar UV radiation in human life is essential for vitamin D production but also leads to skin photoaging, damage, and malignancies. Photoaging and skin cancer have been extensively studied, but the effects of UV on the critical mechanical barrier function of the outermost layer of the epidermis, the stratum corneum (SC), are not understood. The SC is the first line of defense against environmental exposures like solar UV radiation, and its effects on UV targets within the SC and subsequent alterations in the mechanical properties and related barrier function are unclear. Alteration of the SC’s mechanical properties can lead to severe macroscopic skin damage such as chapping and cracking and associated inflammation, infection, scarring, and abnormal desquamation. Here, we show that UV exposure has dramatic effects on cell cohesion and mechanical integrity that are related to its effects on the SC’s intercellular components, including intercellular lipids and corneodesmosomes. We found that, although the keratin-controlled stiffness remained surprisingly constant with UV exposure, the intercellular strength, strain, and cohesion decreased markedly. We further show that solar UV radiation poses a double threat to skin by both increasing the biomechanical driving force for damage while simultaneously decreasing the skin’s natural ability to resist, compromising the critical barrier function of the skin.
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Cadavers have no method of skin repair.
- = 60 continuous days of solar UVB radiation
- > 14,000 times the average broadband UVB minimal erythema dose