Gérald Pierard

Bio: Gérald Pierard is an academic researcher from University of Liège. The author has contributed to research in topics: Stratum corneum & Varicella zoster virus. The author has an hindex of 56, co-authored 893 publications receiving 15376 citations. Previous affiliations of Gérald Pierard include Johnson & Johnson & United Laboratories.

Interaction Between Collagen Type I and Type III in Conditioning Bundles Organization

Abstract: Type I and type III collagen extracted from skin was purified by differential salt precipitation and chromatography. By heating to 37°, type I formed after a lag phase a floppy and opalescent gel of high optical density and type III formed more rapidly a translucent and rigid gel of low optical density. Addition of typs III to type I resulted in formation of gels of reduced optical density and lag phase related to the proportion of typs III added. Phase contrast and scanning electronmicroscopy demonstrated the formation of thick bundles of type I, thin fibers of type III and bundles of intermediate size related to the proportion of type III. The relationship between collagen type and bundle architecture might prove most significant in conditioning the mechanical properties of the connective tissues in normal and pathological conditions.

Macrophages and tumor necrosis factor alpha in toxic epidermal necrolysis.

Abstract: Background: We studied the immunopathologic characteristics of five cases of toxic epidermal necrolysis by using a large panel of antibodies. Observations: The pattern and amount of the inflammatory cell infiltrate varied according to the stage of the disease. The main constant feature was the prominent involvement of the monocyte-macrophage lineage, including factor XIIIa+HLA-DR+dendrocytes and CD68+Mac 387+macrophages, before and during the epidermal ne- crosis. The number of CD4+and CD8+lymphocytes was comparatively small. This was associated with a dense labeling of the epidermis for tumor necrosis factor a. Conclusions: Cells of the monocyte-macrophage lineage largely outnumber lymphocytes in the lesions of toxic epidermal necrolysis. Tumor necrosis factor a is likely a major cytokine that is responsible for necrosis. (Arch Dermatol. 1994;130:605-608)

Cellulite: From Standing Fat Herniation to Hypodermal Stretch Marks

Abstract: There are glaring discrepancies in the microanatomical descriptions of cellulite in the literature. We revisited this common skin condition in women with a microscopic examination of 39 autopsy specimens. A control group consisted of 4 women and 11 men showing no evidence of cellulite. The lumpy aspect of the dermohypodermal interface appeared to represent a gender-linked characteristic of the thighs and buttocks without being a specific sign of cellulite. Incipient cellulite identified by the mattress phenomenon was related to the presence of focally enlarged fibrosclerotic strands partitioning the subcutis. Such strands possibly serve as a physiologic buttress against fat herniation limiting the outpouching of fat lobules on pinching the skin. These structures might represent a reactive process to sustained hypodermal pressure caused by fat accumulation. Full-blown cellulite likely represents subjugation of the hypertrophic response when connective tissue is overcome by progressive fat accumulation. Histologic aspects reminiscent of stretch marks are identified within the hypodermal strands, resulting in clinical skin dimpling.

EEMCO guidance to the in vivo assessment of tensile functional properties of the skin. Part 1: relevance to the structures and ageing of the skin and subcutaneous tissues.

Abstract: From an engineering point of view, the skin and subcutaneous tissue represent an integrated load-transmitting structure. It is subjected to intrinsic and environmental influences. An attempt to use a four-layered model is offered to explain how the integument withstands and transmits loads through deforming appropriately. The stratum corneum, the association between the living epidermis and papillary dermis, the reticular dermis and the hypodermis have each their own intimate structures whose tensile functions are ideally balanced to respond adequately to the casual mechanical demands. A series of physiological variables, ageing and skin diseases alter the tensile functions of the organ. In the overall analysis, truly comprehensive multidisciplinary approaches in this field have brought advances in the understanding of functional skin biology. The assessment of tensile functions of skin also provides incentives for progress in skin care.

Classical Ehlers-Danlos syndrome caused by a mutation in type I collagen

Abstract: Classical Ehlers-Danlos syndrome (EDS) is characterized by skin hyperelasticity, joint hypermobility, increased tendency to bruise, and abnormal scarring. Mutations in type V collagen, a regulator of type I collagen fibrillogenesis, have been shown to underlie this type of EDS. However, to date, mutations have been found in only a limited number of patients, which suggests genetic heterogeneity. In this article, we report two unrelated patients with typical features of classical EDS, including excessive skin fragility, in whom we found an identical arginine→cysteine substitution in type I collagen, localized at position 134 of the α1(I) collagen chain. The arginine residue is highly conserved and localized in the X position of the Gly-X-Y triplet. As a consequence, intermolecular disulfide bridges are formed, resulting in type I collagen aggregates, which are retained in the cells. Whereas substitutions of glycine residues in type I collagen invariably result in osteogenesis imperfecta, substitutions of nonglycine residues in type I collagen have not yet been associated with a human disease. In contrast, arginine→cysteine substitutions in type II collagen have been identified in a variety of chondrodysplasias. Our findings show that mutations in other fibrillar collagens can be causally involved in classical EDS and point to genetic heterogeneity of this disorder.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

The skin microbiome

Abstract: The skin is the human body's largest organ, colonized by a diverse milieu of microorganisms, most of which are harmless or even beneficial to their host. Colonization is driven by the ecology of the skin surface, which is highly variable depending on topographical location, endogenous host factors and exogenous environmental factors. The cutaneous innate and adaptive immune responses can modulate the skin microbiota, but the microbiota also functions in educating the immune system. The development of molecular methods to identify microorganisms has led to an emerging view of the resident skin bacteria as highly diverse and variable. An enhanced understanding of the skin microbiome is necessary to gain insight into microbial involvement in human skin disorders and to enable novel promicrobial and antimicrobial therapeutic approaches for their treatment.

Role of collagenous matrices in the adhesion and growth of cells.

Abstract: It has long been appreciated that, for many types of cells, attachment to a substrate is required for their replication. Collagen substrates enhance the growth (64, 70, 109, 238) as well as the differentiation (40, 69, 85, 86, 146, 161, 184), of many cells in culture above that observed with other substrates such as plastic and glass. As discussed in this report, many cultured cells including fibroblasts, myoblasts, hepatocytes, chondrocytes, and certain epithelial cells are thought not to bind directly to the collagen substrate or to the plastic surface of culture dishes (31, 73, 74, 76, 77, 89, 93, 113, 164, 220) . Instead, extracellular glycoproteins bind the cells to the substrate. One of these attachment proteins, fibronectin, has been extensively studied (99, 151, 166, 227, 228, 244) . Fibronectin is produced by fibroblasts (13, 197, 246) and endothelial cells (102, 140) as well as some other cell types . It is also present in high concentrations in blood and serum (152) . In culture, serum fibronectin, as well as that produced by the cells, can bind to both the collagen substrates and the tissue culture plastic surface and mediate the attachment of cells (73, 113, 164, 242) . Circulating fibronectin participates in a variety of reactions important to wound healing, including the adhesion and spreading of platelets on collagen (10, 14, 75, 100, 204), binding to the fibrin clot (74, 150, 198) and to collagen (37, 46, 94, 103, 119), promoting opsonization reactions by phagocytic cells (18, 94, 201), and promoting fibroblast migration (6, 61) . Thus, fibronectin not only functions as an attachment protein, but also may play an important role in repair reactions . In the case of certain differentiated cells, such as chondrocytes (89) and epithelial cells (159, 220), glycoproteins different from fibronectin are active in attachment. The components of these extracellular matrices of fibroblasts, chondrocytes, and epithelial cells differ with the cell type, and they require separate attachment proteins to provide additional specificity to the interaction ofthe cell with its matrix. Alterations in cellsubstratum interactions are observed in differentiating cells and after spontaneous transformation of cells or exposure to oncogenic agents (99, 228) . This review will briefly outline our current knowledge of the types of collagen and their distribution and biosynthesis. Then, the interaction of cells with colREVIEW