We have discussed a lot about the importance of maintaining healthy skin, about the causes of aging, about the intrinsic and extrinsic actions of factors that directly affect the layers that make up the skin. Therefore, I think that special attention should be given to the main actress. An actress that we know we should take good care of, and even pamper, but we know little about how she truly is.
The skin, the largest organ of our body that outlines the shape of our features, protects us against environmental events and is responsible for the constant maintenance of internal balance. The skin controls body temperature, produces vitamin D, protects us against aggressors and external agents, absorbs UV radiation, and is a waterproof barrier. To perform these complex functions, it has a very specific recognition and signal integration system to trigger a protective response in our body.
Thus, among its layers, known as the epidermis and dermis, there are sensory, pigment, and defense cells that react to stimuli such as temperature, radiation, and microorganisms, respectively. In addition, there is a very specific organization in each stratum to maintain its integrity. Between the contact with connective tissue, there is a region known as the basement membrane, which is primarily formed by collagen and glycoproteins.
The skin's ability to function as a protective barrier is given by a very peculiar architecture of the extracellular space of its uppermost layer, in direct contact with the external environment, called the stratum corneum. This lipid structure is formed by a heterogeneous mixture of lipids such as free fatty acids (FFA), saturated fats, long-chain ceramides (CER), and cholesterol (CHOL).
Since it was discovered in 1970 that the stratum corneum is composed of lipids, it has been the subject of various studies regarding its structure. The study, particularly, of its molecular structure is of great interest to scientists and the cosmetic industry as it is the layer that is in direct contact with the external environment and that receives the first contact with products applied to it.
Thus, in 2012, the group of Iwai and collaborators used a methodology based on cryo-electron microscopy of a vitreous skin section (CEMOVIS) combined with molecular modeling and electron microscopy to investigate the molecular organization of the skin's lipid matrix close to its native state. With this method, it was possible to observe the three-dimensional molecular structure of the skin as the intensity of the captured images was directly related to the local electronic density of the sample.
They found that the lipid matrix is flexible and organized in a stacked bilipid form filled with fully extended ceramides (CER), with cholesterol molecules associated with the sphingoid portion of the ceramide (CER) - the ceramide molecule is formed by two parts, one called the sphingoid base and the other called the fatty acid.
This condensed yet flexible organization of the lipid bilayer with extended ceramides and asymmetrically arranged collagens explains the low permeability of the skin to water and to hydrophilic and lipophilic substances. Furthermore, from understanding the organization of the skin, one can also understand how it manages to maintain the robustness of its barrier concerning hydration and dehydration, temperature maintenance, and changes in pressure, compression, and bending.
According to the researchers, the relevance of the work lies in how future studies can be directed. The molecular description of the stratum corneum allows for more detailed and targeted studies using in silico models to verify the interaction between chemical components and the lipid layer and the selection of specific products for drug delivery and tissue repair.
Consulted and Suggested Bibliographic References
Iwai I, Han H, den Hollander L, Svensson S, Ofverstedt LG, Anwar J, Brewer J,
Bloksgaard M, Laloeuf A, Nosek D, Masich S, Bagatolli LA, Skoglund U, Norlén L. The human skin barrier is organized as stacked bilayers of fully extended ceramides with cholesterol molecules associated with the ceramide sphingoid moiety. J Invest Dermatol. 2012 Sep;132(9):2215-25.
Norlén L, Oktem O, Skoglund U. Molecular cryo-electron tomography of vitreous tissue sections: current challenges. Microsc. 2009 Sep;235(3):293-307.
