Gene expression profiles in psoriasis: analysis of impact of body site location and clinical severity

BACKGROUND

Psoriasis is characterized by symmetry of plaques and modulation of multiple genes within those plaques.

OBJECTIVES

We compared gene expression profiles of plaques of psoriasis at different anatomical sites for both symmetrical and asymmetrical disease to ascertain whether the same genes were expressed.

METHODS

Gene expression profiles were analysed in biopsies from lesional and uninvolved skin from two groups of patients with either predominantly symmetrical or truncal plaques of psoriasis vulgaris, and from normal skin of healthy volunteers. Genomic analyses were performed using cDNA array and kinetically monitored reverse transcriptase-initiated polymerase chain reaction (kRT-PCR) approaches. A cluster of genes upregulated in involved psoriasis skin as compared with normal skin was identified using each of these two technologies.

RESULTS

Clustering of patients based on their gene expression profile did not reveal any correlation with family history of psoriasis, age at onset or association of psoriasis with arthritis. There was no difference in gene expression profile between the type (symmetrical vs. truncal) or location (left vs. right side of body) of psoriatic plaques. Gene expression profiles of involved psoriatic skin analysed by kRT-PCR analysis did correlate with both global (Psoriasis Area and Severity Index) and local (erythema, desquamation and plaque elevation) clinical severity.

CONCLUSIONS

These results indicate that it may be feasible to analyse the molecular effects of pharmacological agents on psoriatic skin in 'minizone' protocols, that the obtained data can be correlated with clinical severity and that plaques of psoriasis in the same individual express the same genes.

Ultraviolet B induces hyperproliferation and modification of epidermal differentiation in normal human skin grafted on to nude mice

BACKGROUND

For ethical and technical reasons, the in vivo biological effects of ultraviolet (UV) radiation on skin are difficult to study in human volunteers. The use of human skin grafted on to nude mice may circumvent this difficulty.

OBJECTIVES

To investigate the effects of a single moderate UVB exposure on human skin grafted on to nude mice.

METHODS

Modifications of epidermal differentiation markers and patterns of keratin expression were assessed from 24 h to 14 days after a physiological UVB irradiation characterized by the induction of sunburn cells.

RESULTS

During the first 48 h postexposure, involucrin, loricrin, transglutaminase type I, filaggrin and keratin K2e expression were altered together with the formation of abnormal horny layers. Constitutive keratin K14 was increased while keratin K10 expression was delayed. Newly synthesized keratins K6, K16, K17 and K19 were induced in parallel with an increase in the epidermal proliferation rate. A progressive normalization of both keratinocyte proliferation and differentiation took place during the following days, reaching completion within 2 weeks.

CONCLUSIONS

Exposure of human skin to a UVB dose corresponding to a mild sunburn reaction induces epidermal hyperproliferation and alterations of several constitutive differentiation markers, as well as a drastic modification in the pattern of epidermal keratins. Although these modifications were shown to be progressively reversed in a single exposure model, the data also suggest that subsequent UV exposures occurring during the recovery period may lead to potentially deleterious long-term consequences, such as photoageing and photocarcinogenesis. Grafted human skin appeared to be an attractive and promising model for investigating the biological consequences of UVB radiation in vivo.

Localisation of members of the notch system and the differentiation of vibrissa hair follicles: receptors, ligands, and fringe modulators

Hair vibrissa follicle morphogenesis involves several cell segregation phases, in the dermis as well as in the epidermis. The expression of Notch-related genes, which are well established mediators of multiple cell segregation events in Drosophila development, was studied by in situ hybridisation during embryonic mouse vibrissa follicle morphogenesis and the first adult hair cycle. The results show that two receptors, Notch1 and -2, three ligands, Delta1, Serrate1, and -2, and the three Fringe regulators, Lunatic, Manic, and Radical, are expressed in different locations and morphogenetic stages. First, the appearance of hair vibrissa primordia involves the expression of complementary patterns of Notch2, Delta1, and Lunatic Fringe in the dermis and of Notch1, Serrate2, and Lunatic Fringe in the epidermis. Second, this expression pattern is no longer found after stage 3 in the dermis. Meanwhile, in the epidermis, the expression of Notch1, Serrate2, and Lunatic Fringe before the formation of the placode may be involved in determining two populations of epidermal cells in the developing follicle. Third, complementary expression patterns for Notch1, Manic, and Lunatic Fringe, as well as Serrate1 and -2 as previously shown (Powell et al., 1998), are progressively established from stage 4 of embryonic development both in the outer root sheath and in the hair matrix. These patterns are consistent with the one found in the adult anagen phase. During the hair vibrissa cycle, Notch1 and Manic Fringe display temporal and spatial changes of expression, suggesting that they may intervene as modulators of trichocyte activities.

Dermal cysts of the rhino mouse develop into unopened sebaceous glands

The rhino mouse (hr(rh)hr(rh)) is a mutant strain characterized by a wrinkled and hairless skin with epidermal utriculi (pseudocomedones) and dermal cysts. The epidermal cysts have been extensively studied. The present work focused on the dermal cysts. By electron microscopy it was found that they appear on day 20 after birth and that they originate from a pool of undifferentiated epithelial cells of the deepest part of the initial follicular unit. Progressively, the number of cells in these islets increased and a central cavity was formed. Peripheral cells differentiated into sebocyte-like cells and outer root sheath cells. Staining with Oil Red O solution indicated accumulation of lipid material in the central cavity. The dermal cysts of the adult rhino mouse were isolated and purified in several steps including enzyme digestion, centrifugation, and separation on Nylex sieves. The integrity of the isolated cysts was confirmed by histology and electron microscopy. Study of their keratin polypeptide pattern by gel electrophoresis indicated that they express the mouse keratins 5, 14, 6 and 17. Neutral lipid analysis of the dermal cyst contents showed that they were mainly composed of cholesterol esters, wax esters, lipid fractions which migrate between triglycerides and cholesterol esters but very small amounts of triglycerides, cholesterol and ceramides. In conclusion, the present results demonstrate that dermal cysts of the rhino mouse have strong similarities with sebaceous glands and outer root sheath cells. These structures can easily be isolated and could therefore serve as a 'closed sebaceous gland' model to study the physiology or differentiation of the sebaceous gland, or the effects of pharmacological agents.

Vla and alpha 6 beta 4 integrin expression in neuroendocrine carcinomas of the skin (their xenografts on nude mice and a corresponding primary culture)

Immunohistological expression of VLA1-5 and alpha 6 beta 4 integrins have been studied in 21 cases of primary neuroendocrine carcinomas of the skin (NECS), three xenografts on nude mice and one NECS cell culture. The phenotypic properties of NECS cells were largely maintained in NECS grafted on athymic nude-mice and in the corresponding cell line. Our results indicate that alpha 1 beta 1 and to a lesser extent alpha 3 beta 1, alpha 5 beta 1 are the main integrins expressed in NECS. In addition, VLA2, 4 and alpha 6 beta 4 are heterogeneously expressed in the same group of tumors and very sparsely present. These data suggest that like neuroblastoma and primitive peripheral neuroectodermal tumor (pPNET) the absence or the heterogeneous distribution of such integrins is correlated with the aggressive behaviour of NECS although long-term follow-up was not available for our cases. On the other hand, the alpha 1 expression could be regarded as a novel marker for differential diagnosis between NECS (alpha 1+) and pPNET (alpha 1-). The alpha 1 beta 1, alpha 2 beta 1, alpha 3 beta 1, alpha 5 beta 1 heterodimers in the 21 NECS studied showed an uniform pericellular staining of both the peripheral cells and central cells of the tumor islands. The predominant expression of alpha 1 beta 1 is consistent with the hypothesis of a primitive epithelial totipotential origin in NECS.

Induction of tolerance by administration of hapten-immunoglobulin conjugates is associated with decreased IL-2 and IL-4 production

Intravenous administration of trinitrophenyl-modified isologous immunoglobulin-induced nonresponsiveness to subsequent epicutaneous painting of sensitizing doses of trinitrochlorobenzene. Isologous immunoglobulin with various degrees of trinitrophenyl substitution (11.2, 14.3, 27 and 47.3) prevented sensitization. The suppression of contact hypersensitivity was dependent on the dose of tolerogen and was hapten specific. Tolerance was inducible in mice of the strains CBA (H-2k), C57BL/6 (H-2b), and DBA/2 (H-2d) but not in Balb/C (H-2d) mice, suggesting that this trait maps outside the murine major histocompatibility complex. Tolerance induced by trinitrophenyl-modified immunoglobulin was associated with decreased hapten-induced proliferation of draining lymph-node cells. Unlike in other models of tolerance in which a decreased interleukin-2 to interleukin-4 ratio can be observed, administration of tolerizing trinitrophenylated immunoglobulin was associated with deficient hapten-induced release of both interleukin-2 and interleukin-4.

Lipid composition and barrier function of human skin after grafting onto athymic nude mice

The barrier properties of human epidermis grafted for 1-3 months onto nude mice are compared with normal human skin. Beside penetration studies with tritiated water and measurements of transepidermal water loss (TEWL), we analyzed the epidermal lipids by high-performance thin layer chromatography and evaluated the ultrastructure of the intercorneocyte lipid arrangement by freeze fracture electron microscopy (FFEM). The permeability of human skin for tritiated water and the TEWL exhibit no significant changes after grafting onto nude mice. FFEM analysis showed that grafted epidermis has the same morphological pattern as normal human epidermis. Regular desmosomes and lamellar lipid structures are present. Grafting did not qualitatively affect the lipid composition of human epidermis. Ceramides which contribute largely to the barrier function, have the same distribution profile.

Peripherin, a neuronal intermediate protein, is stably expressed by neuroendocrine carcinomas of the skin, their xenograft on nude mice, and the corresponding primary cultures

The histogenesis of neuroendocrine carcinomas of the skin is still controversial. To determine the degree of neural differentiation of these neoplasias, we studied the expression of intermediate filament proteins in tumoral tissues. Expressions of peripherin, the neurofilament protein NF-L, vimentin, and cytokeratin 8 were analyzed by immunohistochemical methods on 12 human primary tumors and 3 tumor xenografts on nude mice. Peripherin was detected in 10 primary tumors by immunofluorescence. The protein and the corresponding messenger RNA were identified by two-dimensional gel electrophoresis and Northern analysis in extracts of an immunofluorescence-negative tumor. Peripherin, NF-L, and cytokeratin 8 were detected in tumoral cells, whereas vimentin was found exclusively in the stroma. The histological and ultrastructural properties of the original cells of neuroendocrine carcinomas of the skin, as well as coexpression of peripherin, cytokeratin 8, and neurofilament polypeptides, were preserved in tumor xenografts and their primary cultures in vitro. These results bring new elements to the knowledge of the biology of neuroendocrine carcinomas of the skin and indicate that peripherin constitutes a marker for tumor identification.

The role of fibroblasts in dermal vascularization and remodeling of reconstructed human skin after transplantation onto the nude mouse

The vascularization and the dermal remodeling of two different types of human skin reconstructed "in vitro" and grafted onto the nude mouse were studied. They were composed of human keratinocytes grown either on a human acellular deepidermized dermis (DED), or on a lattice composed of human fibroblasts embedded in bovine type I collagen, a living dermal equivalent (LDE). At different stages after grafting, the transplants were harvested and processed for an immunohistological study with species-specific and non-species-specific antibodies. At one month after grafting, the two types of grafted dermis contained blood vessels whose vascular basement membranes were labeled with a mouse-specific anti-type IV collagen antibody. With an antibody specific for human type IV collagen, a constant labeling of the vascular basement membrane was only observed in the LDE containing fibroblasts. In the DED, a constant association of the mouse endothelial cells with human type IV collagen was observed at early stages after grafting. At later stages, the human type IV collagen progressively disappeared. On the other hand, the dermal-epidermal junction underneath the human epidermis contained human type IV collagen in the two types of reconstructed skin. Labeling with the species-specific antibodies directed against human or murine type I collagen showed that the ratio murine type I collagen versus human type I collagen increased with time, suggesting that the DED is progressively invaded by mouse fibroblasts that produce the mouse collagen. On the other hand, in the LDE, the preexisting bovine type I collagen became progressively undetectable while both human type I collagen and elastic fibers were deposited by numerous human fibroblasts. Mouse type I collagen was not detected. Altogether, these observations made by grafting human skin reconstructed "in vitro" onto the nude mouse should be interesting for evaluating the usefulness of grafting a dermal substrate together with the epidermal sheet in the treatment of burns.

An immunohistological study of the revascularization process in human skin transplanted onto the nude mouse

The revascularization of human skin transplanted onto the nude mouse was studied by performing double-labeling immunofluorescence microscopy on human skin before transplantation and at different stages, ranging from one week to six months after grafting. With a crossreacting anti-factor-VIII antigen antibody used to identify the endothelial cells, and with human-specific monoclonal antibodies directed against vimentin or HLA-DR antigen, it appeared that the original human endothelial cells of transplanted skin progressively disappear, while murine endothelial cells invade the graft. Moreover, in double-labeling experiments with a crossreacting anti-factor-VIII antibody and a human-specific anti-type-IV-collagen antibody, anastomosis between host and graft vessels and a constant codistribution of graft endothelial cells with human type IV collagen were observed. Finally, double staining with species-specific antibodies directed against murine or human type IV collagen showed that mouse type IV collagen appeared progressively in the graft and was constantly colocalized with human type IV collagen. From these observations, it was concluded that revascularization of human skin transplanted onto the nude mouse proceeds as follows: inoculation; disappearance of human endothelial cells and migration of mouse endothelial cells into the graft over the basement membrane of preexisting human vessels; and production of a new vascular basement membrane by mouse endothelial cells on the original basement membrane of human graft vessels.

Further evidence for the self-reproducing capacity of Langerhans cells in human skin

The limited number of Langerhans cells (LC) in the epidermis is one of the main reasons for the technical difficulties in resolving the question of LC kinetics. In the present paper, we describe a method to evaluate the LC replication potential in epidermis. The procedure is based on the specific incorporation of bromodeoxyuridine (BrdU), a thymidine analogue, into the DNA during the S-phase of the cell cycle. Mice, bearing human skin grafts, were injected s.c. every 6 h for up to 17 days with BrdU. At different times, the incorporated BrdU as well as the human epidermal LC were revealed on skin sections using anti-BrdU and OKT-6 monoclonal antibodies, respectively. After 6 h, 4.9% of the LC were labeled with BrdU. Then, the number of OKT-6(+) BrdU(+) cells increased in a linear manner and achieved 34% at 120 h, 67% at 240 h, and 94% at 400 h during the course of continuous labeling procedures. Based on this result we calculated a total cell cycle time of 392 h (16.3 days) and 12 h for the S-phase for human epidermal LC. Applying this technique, we were able to show also that 48 h after local treatment with 12-O-tetradecanoylphorbol-13-acetate or after stripping, the number of BrdU-labeled LC was considerably increased. Furthermore, after i.p. injection of colchicine in the nude mouse, human epidermal LC undergoing mitosis were evidenced by electron microscopy in the graft. From these results we conclude that the LC are actively cycling--therewith a self-reproducing cell population in human epidermis.

Wound healing of human skin transplanted onto the nude mouse. I. An immunohistological study of the reepithelialization process

Two months after transplantation of human skin onto the nude mouse, excisional wounds were made through the entire thickness of the skin, at the center of the graft, using a 2-mm punch. At various time intervals thereafter, ranging from 2 days to 9 weeks, the graft sites were harvested and processed for an immunohistological study. With a monoclonal antibody directed against HLA-ABC antigens, it was demonstrated that the healing epidermis is of human origin. Moreover, with three different monoclonal antibodies directed against human keratins, named respectively AE1, AE3, and KL1 and with an anti-involucrin antiserum, it is reported that the keratinization and involucrin distribution patterns observed in normal human epidermis are reconstituted, 2 months after transplantation, in the major part of the grafted epidermis, undergo changes during the reepithelialization process, and are restored in the healed epidermis 9 weeks after injury. This study indicates that the nude mouse/human skin model could be a valuable tool to study a major aspect of regeneration such as the reepidermization of human skin without recourse to human volunteers.

Human Langerhans cells in epidermal cell culture, in vitro skin explants and skin grafts onto "nude" mice

In order to find a model system which best preserves human Langerhans cells (LC) outside of the human body, three possibilities were examined: epidermal cell culture, skin explants, and skin grafts onto "nude" mice. Using OKT-6 and anti-HLA-DR monoclonal antibodies, we quantified LC in epidermal sheets or epidermal cell cultures. All observations were carried out over a period of 4 weeks. We found that under epidermal cell culture conditions, LC rapidly disappeared, to the extent that after 10 days only rare HLA-DR-positive cells could be observed. In contrast, in the presence of intact dermis (explants and grafts), 60%-80% of the original number of LC, morphologically unchanged, dendritic and OKT-6 and HLA-DR-positive, were seen. These findings suggest that human LC are either a long-lived cell population or else can proliferate locally. The systems studied may be a useful tool for future investigation of LC function.

[Distribution of collagen, fibronectin, and laminin during morphogenesis of skin and cutaneous appendages in the chick embryo (author's transl)]

In the dermis of inter-appendage and glabrous skin, interstitial collagen types I, III, and V are abundant, while fibronectin is scarce. Conversely, in the morphogenetically active foci of cutaneous appendages, interstitial collagen is scarce or absent, whereas fibronectin is abundant. Type IV collagen and laminin are localized at the dermal-epidermal junction and distributed evenly.