The inflammatory and proliferative response of normal skin in a model for acute chemical injury: ornithine decarboxylase induction as a common feature in various models for acute skin injury

Psoriasis risk genes of the late cornified envelope-3 group are distinctly expressed compared with genes of other LCE groups

Deletion of the late cornified envelope (LCE) genes LCE3B and LCE3C has recently been identified as a risk factor for psoriasis. Expression of 16 LCE genes of LCE groups 1, 2, 3, 5, and 6 was examined in vivo and in vitro. Quantitative PCR demonstrated that moderate to high LCE expression was largely confined to skin and a few oropharyngeal tissues. Genes of the LCE3 group demonstrated increased expression in lesional psoriatic epidermis and were induced after superficial injury of normal skin, whereas expression of members of other LCE groups was down-regulated under these conditions. Immunohistochemistry and immunoelectron microscopy demonstrated that LCE2 protein expression was restricted to the uppermost granular layer and the stratum corneum. Stimulation of in vitro reconstructed skin by several psoriasis-associated cytokines resulted in induction of LCE3 members. The data suggest that LCE proteins of groups 1, 2, 5, and 6 are involved in normal skin barrier function, whereas LCE3 genes encode proteins involved in barrier repair after injury or inflammation. These findings may provide clues to the mechanistic role of LCE3B/C deletion in psoriasis.

Topical dorsal skin immersion in seawater induces apoptosis and proliferation in hairless mice

Recreational and occupational exposure to seawater (SW), have increased but the effect of SW on skin has not been elucidated. The purpose of present study was to assess the effects of SW immersion on the dorsal skin in hairless mice. Adult hairless mice were individually immersed in SW for 3 h, 6 h and 12 h; then, full-thickness dorsal skin of 2 cm diameter was excised for pathological examination (light microscope), apoptosis detection (terminal deoxynucleotidyl transferase-mediated 2'-deoxyuridine 5'-triphosphate nick end labeling [TUNEL]) and proliferation index evaluation (immunohistochemistry). Normal and normal saline (NS)-immersed skin were used as controls. Histological examination revealed that there were randomly distributed cell deaths, presenting cell shrinkage, condensation of nuclear chromatin and eosinophilic cytoplasm in the epidermis, and neutrophil infiltration in the dermis, after SW immersion. Moreover, TUNEL showed low levels of apoptosis in normal (9.07 +/- 0.70%) and NS-immersed skin (9.99 +/- 1.22%). There was an apparent increase in the 6-h and 12-h SW immersed groups (29.90 +/- 6.85%, P < 0.01; 45.46 +/- 6.12%, P < 0.01, respectively). Ki-67 antigen was located in the basal layer of the epidermis and hair follicles, the rates of Ki-67-positive cells were 7.90 +/- 1.45% and 7.76 +/- 1.52% in normal and NS-immersed skin, respectively, and in the 12-h SW immersed group, the rate of Ki-67-positive cells reached 23.85 +/- 4.21% (threefold, P < 0.01). In each group, the rate of apoptosis was higher than that of proliferation. We conclude that SW immersion can cause time-dependent apoptosis and proliferation in the epidermis, and the overall effect of SW immersion is injury to the epidermis.

Response of mouse skin to tattooing: use of SKH-1 mice as a surrogate model for human tattooing

Tattooing is a popular cosmetic practice involving more than 45 million US citizens. Since the toxicology of tattoo inks and pigments used to formulate tattoo inks has not been reported, we studied the immunological impact of tattooing and determined recovery time from this trauma. SKH-1 hairless mice were tattooed using commercial tattoo inks or suspensions of titanium dioxide, cadmium sulfide, or iron oxide, and sacrificed at 0.5, 1, 3, 4, 7, or 14 days post-tattooing. Histological evaluation revealed dermal hemorrhage at 0.5 and 1 day. Acute inflammation and epidermal necrosis were initiated at 0.5 day decreasing in incidence by day 14. Dermal necrosis and epidermal hyperplasia were prominent by day 3, reducing in severity by day 14. Chronic active inflammation persisted in all tattooed mice from day 3 to 14 post-tattooing. Inguinal and axillary lymph nodes were pigmented, the inguinal being most reactive as evidenced by lymphoid hyperplasia and polymorphonuclear infiltration. Cutaneous nuclear protein concentrations of nuclear factor-kappa B were elevated between 0.5 and 4 days. Inflammatory and proliferative biomarkers, cyclooxygenase-1, cyclooxygenase-2, and ornithine decarboxylase protein levels were elevated between 0.5 and 4 days in the skin and decreased to control levels by day 14. Interleukin-1 beta and interleukin-10 were elevated in the lymph nodes but suppressed in the tattooed skin, with maximal suppression occurring between days 0.5 and 4. These data demonstrate that mice substantially recover from the tattooing insult by 14 days, leaving behind pigment in the dermis and the regional lymph nodes. The response seen in mice is similar to acute injury seen in humans, suggesting that the murine model might be a suitable surrogate for investigating the toxicological and phototoxicological properties of ingredients used in tattooing.

In situ demonstration of phosphorylated c-jun and p38 MAP kinase in epidermal keratinocytes following ultraviolet B irradiation of human skin

Ultraviolet B (UVB) irradiation is known to induce activation of cellular stress response pathways in cultured cells or intact human skin, as demonstrated by phosphorylation of MAP kinase family members and up- or down-stream targets, using biochemical assays. This study demonstrates by immunohistochemistry that low-dose UVB irradiation of normal human skin induces rapid and reversible phosphorylation of c-jun (a target of c-jun N-terminal kinase) and p38 mitogen activated protein kinase (p38 MAP kinase). Phosphorylation was maximal at 4-8 h and returned to normal levels at 48 h after irradiation. Nuclear localization of these phosphorylated substrates was found using antisera against the epitope containing the phosphorylated serine-73 of c-jun, and the dually phosphorylated epitope (threonine-180 and tyrosine-182) of p38 MAP kinase. Nearly all epidermal cells were positive for c-jun phosphorylation, whereas p38 phosphorylation was seen predominantly in the differentiated layers. In contrast to the massive activation of c-jun and p38, only a small population of the suprabasal cells showed nuclear translocation of nuclear factor kappa B (NFkappaB), and a few scattered cells became apoptotic, as determined by TUNEL (TdT mediated dUTP nick end labelling) staining. The expression of involucrin and skin-derived anti-leukoproteinase (SKALP)/elafin, two genes putatively under control of the c-jun and p38 pathways, was found to be increased. These findings establish the first cellular localization of UVB-induced protein phosphorylation of stress response proteins in human epidermis, thereby providing a link between cellular activation and gene expression in defined cell populations.

Elevated expression of epidermal ornithine decarboxylase mRNA in scleroderma

Using in situ hybridization techniques, we examined the expression of ornithine decarboxylase (ODC) mRNA in the skin of five patients with systemic sclerosis (SSc) and five normal controls. Sections treated with an anti-sense probe showed concentrated grains exclusively in the epidermis of SSc patients, but not in that of normal controls. Because our subcloned anti-sense probe specifically hybridizes with ODC mRNA, these findings indicate that the expression of ODC mRNA is elevated in SSc epidermis. Possibly polyamines have an important part to play in the skin changes of SSc.

Towards a molecular definition of keratinocyte activation after acute injury to stratified epithelia

While in recent years we have come to increasingly appreciate the multifaceted role of skin, probably none of these novel contributions is as vital as its barrier function, inferred centuries ago. In human skin this function is fulfilled nearly entirely by the epidermis, a thin stratified squamous epithelium made up primarily of keratinocytes and located at the skin surface. Disruption of the integrity of epidermis triggers a homeostatic response involving blood-derived elements and resident skin cell types that is designed to rapidly restore a functional epithelial lining over the wound site. This article is focused on the process of recruitment of keratinocytes from intact skin tissue at the proximal wound edges to participate in re-epithelialization.

Changes in keratinocyte differentiation following mild irritation by sodium dodecyl sulphate

Although the induction of acute irritant dermatitis by detergents has been studied extensively in recent years, our understanding of the cell biological events in the repair phase, and its relevance for the development of chronic irritant dermatitis is limited. Here we studied the reaction pattern of human skin to short-term application of sodium dodecyl sulphate (SDS) in a model that induced a minimal acute inflammatory reaction (absence of polymorphonuclear leucocytes, PMN) and did not have cytopathic effects on the epidermal keratinocytes as determined by histological investigation. All parameters were measured up to 14 days after exposure to SDS. Application of SDS caused disturbances of barrier function as measured by transepidermal water loss and had vascular effects as judged by erythema. Several cell biological markers for epidermal growth and differentiation were examined by immunohistochemistry. A rapid and strong induction of the cornified envelope precursor protein involucrin was seen in the stratum spinosum, with a peak at 24 h. Within 24 h a strong upregulation of epidermal fatty acid binding protein (E-FABP) was noted, with a peak at 7 days after injury. Cellular proliferation in the basal layer was increased fivefold as assessed by nuclear staining for the Ki-67 antigen, showing a peak at 48 h. Surprisingly, no significant induction of cytokeratin 16 and SKALP/elafin expression, two markers associated with epidermal hyper-proliferation and inflammation, was seen. These findings suggest that the cellular changes following exposure to detergent are distinct from those seen in other forms of skin injury. We would speculate that the epidermal response to detergent exposure is primarily directed at restoration of barrier function.