Sensitivity of desquamin to proteolytic degradation

Death penalty for keratinocytes: apoptosis versus cornification

Homeostasis implies a balance between cell growth and cell death. This balance is essential for the development and maintenance of multicellular organisms. Homeostasis is controlled by several mechanisms including apoptosis, a process by which cells condemned to death are completely eliminated. However, in some cases, total destruction and removal of dead cells is not desirable, as when they fulfil a specific function such as formation of the skin barrier provided by corneocytes, also known as terminally differentiated keratinocytes. In this case, programmed cell death results in accumulation of functional cell corpses. Previously, this process has been associated with apoptotic cell death. In this overview, we discuss differences and similarities in the molecular regulation of epidermal programmed cell death and apoptosis. We conclude that despite earlier confusion, apoptosis and cornification occur through distinct molecular pathways, and that possibly antiapoptotic mechanisms are implicated in the terminal differentiation of keratinocytes.

30-kDa trypsin-like proteases in the plantar stratum corneum

The casein digestible proteases in human plantar stratum corneum were determined to be about 75-kDa, 30-kDa and 25-kDa in molecular weight by zymography. The enzymatic activity of the 75-kDa and 25-kDa proteases was specifically inhibited by chymostatin, which is an inhibitor of chymotrypsin-like serine proteases, and the proteases around 30-kDa were inhibited by leupeptin, a trypsin-like serine protease inhibitor. The enzymatic activity of all these proteases was inhibited by aprotinin. The 30-kDa trypsin-like proteases were heat-stable; their enzymatic activity still remained even after heating at 100 degrees C for 60 minutes. Their optimal pH was around 9, and the activity was higher in the outer part of the stratum corneum than in the inner part.

Human stratum corneum lipids have a distorted orthorhombic packing at the surface of cohesive failure

The cohesive strength of the stratum corneum is determined by its unique molecular composition and structural architecture. Whereas the structure responsible for corneocyte cohesion has been visualized at the microscopic level, the structure of the intercellular domain has not been characterized at the molecular level. In this report, new insight into the molecular architecture of the stratum corneum has been provided by atomic force microscopy and x-ray photoelectron spectroscopy. The surface layer of human stratum corneum was stripped, yielding the characteristic polygonal corneocytes shown by scanning electron microscopy as well as low resolution atomic force microscopy. With atomic force microscopy, the resolution was increased to allow imaging of the molecular architecture of the stratum corneum. With the high resolution image, a repetitive pattern characteristic of lipids in an ordered state was visualized. The lattice appeared to be orthorhombic where the lattice distances were about 5.5 and 9 angstroms, and the lattice angle was close to 90 degrees. The atomic composition of the superficial layers was 82% carbon, 16.5% oxygen, and 1.4% nitrogen as determined by x-ray photoelectron spectroscopy. The high nitrogen content compared to the calculated stratum corneum lipid composition and measured model lipid composition suggests that proteins were detected. In summary, although proteins are present, the fracture plane of the stratum corneum is largely composed of lipids that appear to have a distorted orthorhombic packing.

Cohesion and desquamation of epidermal stratum corneum

This article attempts to provide a comprehensive review on the roles of various classes of molecules in the cohesion and desquamation of the stratum corneum. In the first part of this monograph we review the field of epidermal differentiation in vivo and vitro, describing the expression and functions of a number of key structural molecules that characterize the process. In the second part we emphasize terminal differentiation and the biogenesis of the stratum corneum. The stratum corneum is a cell layer unique to fully differentiated squamous epithelia such as skin. While it is a dead stratum, it nevertheless is in a homeostatic process of continual shedding and renewal in synchrony with basal cell replication. It is also a degradative layer containing many proteinases and glycosidases in which a variety of intracellular and intercellular macromolecules are degraded. We highlight the molecules localized within the intercorneal matrix that are most likely to play a role in cohesion and desquamation, including: glycoproteins, lipids and enzymes. Because it is difficult to study the stratum corneum and desquamation in the native tissue, we discuss a number of model systems that have been used. The stratum corneum can be dispersed into single squames in different ways; these include mechanical dispersion as well as agents such as detergents and enzymes. The solubilized molecules and the structures remaining can then be studied as to their specific roles in desquamation. Using this approach it is possible to reconstitute multilayered structures that resemble a real stratum corneum. We have shown that glycoproteins play a key role in squame reaggregation and that this process can be modulated with amino sugars in a lectin-like fashion. Cohesion and desquamation can also be studied in tissue culture. Depending on the culture system, the extent of terminal differentiation and squame accumulation varies. Yet desquamation does not normally occur. It can be induced however by the inclusion of exogenous agents such as IFN-gamma which are found in the native epidermis but are absent in vitro. Modulation of desquamation by other exogenous agents is likely to yield further knowledge of how shedding occurs in vivo. Insight has also come from studies of scaling skin disorders. The glycoprotein and lipid profiles are altered in the stratum corneum in many diseases of aberrant terminal differentiation. A number of abnormalities in the levels of cytokines and growth factors have also been reported in the lesional tissue of such diseases.(ABSTRACT TRUNCATED AT 400 WORDS)

Interferon-gamma modulates terminal differentiation and the expression of desquamin in cultured keratinocytes

Interferon (IFN)-gamma has been shown to modulate cell differentiation and the expression of cell surface molecules of cultured human keratinocytes; it also induces cell shedding. We have previously described the properties of desquamin, a cell surface adhesion molecule from the stratum corneum. We report here on the impact of IFN-gamma on the expression of desquamin. We document the related morphological changes in terminal differentiation. We cultured human keratinocytes in three different culture systems: in serum-free medium at low Ca2+ (0.1 mM), at high Ca2+ (1.5 mM), and at high Ca2+ with 10% serum. IFN-gamma (100 U/ml) was added to each culture system after overnight incubation. In all cases, IFN-gamma induced an altered phenotype, as shown by phase contrast and electron microscopy. We exposed cultured cells to antibodies to the desquamins (glycoproteins from the stratum corneum). Immunoflurescent localization and Western blotting showed that the desquamins were expressed only under culture conditions where both serum and IFN-gamma were present. The induction of desquamin expression by IFN-gamma coupled with an increase in cell shedding, suggests that we have developed a suitable culture system for the study of desquamation in vitro.