Sclerotic atrophic plaques associated with a tattoo

Lichen sclerosus is a chronic inflammatory disease, usually of the anogenital area, that causes intractable itching and soreness. Less commonly, it may have extragenital involvement in 15 to 20% of cases. Lichen sclerosus has been reported at sites of injury as a Koebner phenomenon. We report a case of lichen sclerosus at the site of a tattoo with simultaneous genital involvement.

Cutaneous pigmentation in health and disease: novel and well-established players

Cutaneous pigment formation and aberration in disease are addressed. Dynoodt et al. (this issue) present data on a specific micro RNA that downregulates proteins involved in melanogenesis and melanosome movement. Kim et al. (this issue) present data showing that Wnt signaling is involved in the pathogenesis of melasma. Both articles enhance our understanding of cutaneous pigmentation and point to targets in the development of novel therapeutic modalities.

Telomeric DNA induces p53-dependent reactive oxygen species and protects against oxidative damage

BACKGROUND

Reactive oxygen species (ROS) are generated by cellular metabolism as well as by exogenous agents. While ROS can promote cellular senescence, they can also act as signaling molecules for processes that do not lead to senescence. Telomere homolog oligonucleotides (T-oligos) induce adaptive DNA damage responses including increased DNA repair capacity and these effects are mediated, at least in part, through p53.

OBJECTIVE

Studies were undertaken to determine whether such p53-mediated protective responses include enhanced antioxidant defenses.

METHODS

Normal human fibroblasts as well as R2F fibroblasts expressing wild type or dominant negative p53 were treated with an 11-base T-oligo, a complementary control oligo or diluents alone and then examined by western blot analysis, immunofluorescence microscopy and various biochemical assays.

RESULTS

We now report that T-oligo increases the level of the antioxidant enzymes superoxide dismutase 1 and 2 and protects cells from oxidative damage; and that telomere-based gammaH2AX (DNA damage) foci that form in response to T-oligos contain phosphorylated ATM and Chk2, proteins known to activate p53 and to mediate cell cycle arrest in response to oxidative stress. Further, T-oligo increases cellular ROS levels via a p53-dependent pathway, and these increases are abrogated by the NAD(P)H oxidase inhibitor diphenyliodonium chloride.

CONCLUSION

These results suggest the existence of innate telomere-based protective responses that act to reduce oxidative damage to cells. T-oligo treatment induces the same responses and offers a new model for studying intracellular ROS signaling and the relationships between DNA damage, ROS, oxidative stress, and cellular defense mechanisms.

p75NTR antagonistic cyclic peptide decreases the size of beta amyloid-induced brain inflammation

Amyloid beta (Abeta) was shown to bind the 75 kD neurotrophin receptor (p75(NTR)) to induce neuronal death. We synthesized a p75(NTR) antagonistic peptide (CATDIKGAEC) that contains the KGA motif that is present in the toxic part of Abeta and closely resembles the binding site of NGF for p75(NTR). In vivo injections of Abeta into the cerebral cortex of B57BL/6 mice together with the peptide produced significantly less inflammation than simultaneous injections of Abeta and a control (CKETIADGAC, scrambled) peptide injected into the contralateral cortex. These data suggest that blocking the binding of Abeta to p75(NTR) may reduce neuronal loss in Alzheimer's disease.

Lymphangiogenesis and angiogenesis in non-phymatous rosacea

BACKGROUND

Our study evaluated the expression of vascular endothelial growth factor (VEGF), CD31 and D2-40 in involved and uninvolved skin of 18 patients with rosacea.

METHODS

Immunostaining of facial skin specimens with VEGF, CD31 and D2-40 was compared between the lesional and the non-lesional skin of patients with erythemotelangiectatic and papulopustular rosacea.

RESULTS

Significantly increased dermal expression of VEGF in lesional vs. non-lesional skin (88.9% and 55.6%) was observed. Dermal expression of CD31 and D2-40 was also increased in lesional vs. non-lesional skin. There was no statistically significant difference in cutaneous expression of VEGF, CD31 and D2-40 between patients with papulopustular and erythemotelangiectatic rosacea, and no correlation was found between disease duration and immunoreactivity of VEGF, CD31or D2-40.

CONCLUSIONS

Our study showed marked immunostaining of lesional skin with VEGF, CD31 and D2-40 compared with non-lesional skin. Increased immunoreactivity of D2-40 in lesional skin is interesting, given that none of the patients had facial edema. There are no published data regarding the role of lymphangiogenesis in patients with non-phymatous rosacea; thus, our study represents a new understanding of its pathogenesis. Lack of correlation between D2-40 expression and disease duration suggests that lymphatics are involved early in the pathogenesis of rosacea and do not constitute a late event.

Photoageing: mechanism, prevention and therapy

Photoageing is the superposition of chronic ultraviolet (UV)-induced damage on intrinsic ageing and accounts for most age-associated changes in skin appearance. It is triggered by receptor-initiated signalling, mitochondrial damage, protein oxidation and telomere-based DNA damage responses. Photodamaged skin displays variable epidermal thickness, dermal elastosis, decreased/fragmented collagen, increased matrix-degrading metalloproteinases, inflammatory infiltrates and vessel ectasia. The development of cosmetically pleasing sunscreens that protect against both UVA and UVB irradiation as well as products such as tretinoin that antagonize the UV signalling pathways leading to photoageing are major steps forward in preventing and reversing photoageing. Improved understanding of the skin's innate UV protective mechanisms has also given rise to several novel treatment concepts that promise to revolutionize this field within the coming decade. Such advances should not only allow for the improved appearance of skin in middle age and beyond, but also greatly reduce the accompanying burden of skin cancer.

A cyclic peptide that binds p75(NTR) protects neurones from beta amyloid (1-40)-induced cell death

The current study determined the ability of a p75(NTR) antagonistic cyclic peptide to rescue cells from beta amyloid (Abeta) (1-40)-induced death. p75(NTR)-, p140(trkA)-NIH-3T3 cells or E17 foetal rat cortical neurones were incubated with 125I-NGF or 125I-Abeta (1-40) and increasing concentrations of the cyclic peptide (CATDIKGAEC). Peptide ability to displace 125I-NGF or 125I-Abeta (1-40) binding was determined. Duplicate cultures were preincubated with CATDIKGAEC (250 nM) or diluent and then stimulated with Abeta (1-40). Peptide ability to displace Abeta (1-40) binding, interfere with Abeta (1-40)-induced signalling and rescue cells from Abeta-mediated toxicity was determined by immunoprecipitation and autoradiography, Northern blotting, JNK activation, MTT and trypan blue assays. The peptide inhibited NGF and Abeta (1-40) binding to p75(NTR), but not to p140(trkA). Abeta (1-40) induced c-jun transcription (57.3% +/- 0.07%) in diluent-treated p75(NTR)-cells, but not in cells preincubated with the cyclic peptide. Also, at 250 nM, the peptide reduced Abeta (1-40)-induced phosphorylation of JNK by 71.8% +/- 0.03% and protected neurones against Abeta-induced toxicity as determined by: trypan blue exclusion assay (53% +/- 11% trypan blue-positive cells in diluent pretreated cultures vs. 28% +/- 5% in cyclic peptide-pretreated cultures); MTT assay (0.09 +/-0.03 units in diluent-pretreated cells vs. 0.12 +/- 0.004 units in cyclic peptide-pretreated cells); and visualization of representative microscopic fields. Our data suggest that a cyclic peptide homologous to amino acids 28-36 of NGF known to mediate binding to p75(NTR) can interfere with Abeta (1-40) signalling and rescue neurones from Abeta (1-40)-induced toxicity.

Telomeric DNA induces apoptosis and senescence of human breast carcinoma cells

INTRODUCTION

Cancer is a leading cause of death in Americans. We have identified an inducible cancer avoidance mechanism in cells that reduces mutation rate, reduces and delays carcinogenesis after carcinogen exposure, and induces apoptosis and/or senescence of already transformed cells by simultaneously activating multiple overlapping and redundant DNA damage response pathways.

METHODS

The human breast carcinoma cell line MCF-7, the adriamycin-resistant MCF-7 (Adr/MCF-7) cell line, as well as normal human mammary epithelial (NME) cells were treated with DNA oligonucleotides homologous to the telomere 3' overhang (T-oligos). SCID mice received intravenous injections of MCF-7 cells followed by intravenous administration of T-oligos.

RESULTS

Acting through ataxia telangiectasia mutated (ATM) and its downstream effectors, T-oligos induced apoptosis and senescence of MCF-7 cells but not NME cells, in which these signaling pathways were induced to a far lesser extent. In MCF-7 cells, experimental telomere loop disruption caused identical responses, consistent with the hypothesis that T-oligos act by mimicking telomere overhang exposure. In vivo, T-oligos greatly prolonged survival of SCID mice following intravenous injection of human breast carcinoma cells.

CONCLUSION

By inducing DNA damage-like responses in MCF-7 cells, T-oligos provide insight into innate cancer avoidance mechanisms and may offer a novel approach to treatment of breast cancer and other malignancies.

Features that determine telomere homolog oligonucleotide-induced therapeutic DNA damage-like responses in cancer cells

Cancer is the second leading cause of death in the USA, with metastatic disease proving a particular management challenge. Treatment modalities for patients with metastatic disease are limited, and survival beyond 5 years is uncommon. We have reported that an 11-base DNA oligonucleotide 100% homologous to the telomere 3' overhang can induce apoptosis, senescence and/or differentiation of several types of malignant cells in vitro and in vivo, while having minimal effect on normal cells. We now report that 22 oligonucleotides, 9-20 bases in length, with or without a 5' phosphate group and with varying homology (40-100%) to the 3' overhang, inhibit growth and induce apoptosis of human cell lines derived from breast cancers, pancreatic and ovarian carcinomas, and malignant melanoma, lines that lack p53 and/or p16 and harbor a variety of other abnormalities in key regulatory signaling pathways. Cytosine (C) content adversely affected oligonucleotide efficacy, decreasing their effect on cellular apoptosis by > or =80%. These data confirm and expand our earlier work suggesting that such telomere homolog oligonucleotides (T-oligos) target an innate anti-cancer defense system in human cells and may provide an effective treatment for cancers of multiple different cellular origins and genetic profile.

Cutaneous Immunoreactivity of D2-40 Antibody Beyond the Lymphatics

Recent research suggests that the D2-40 monoclonal antibody recognizes the 40,000 Da O-linked sialoglycoprotein podoplanin. Podoplanin not only is highly expressed in lymphatic endothelium but also in other cell types, including sebaceous carcinoma cells. Using the D2-40 antibody, our purpose was to evaluate expression of podoplanin in sebaceous glands of normal skin. Twenty-four formalin-fixed, paraffin-embedded normal skin specimens (10 from scalp and 14 from cheeks) were immunostained using the D2-40 mouse monoclonal antibody. Strong immunostaining with D2-40 antibody was observed at the periphery of sebaceous glands and in skin lymphatic endothelium of all specimens, demonstrating that podoplanin is expressed in sebaceous glands of normal skin.

Bone Morphogenetic Protein-4, a Novel Modulator of Melanogenesis

Bone morphogenetic proteins (BMPs), members of the transforming growth factor-beta family, signal in many cells including neural precursors. Two receptors, types 1 and 2, coordinately mediate BMP signaling, and type 1 receptor has two forms: A and B. Using RT-PCR we found that neural crest-derived human melanocytes express BMP receptor-1A, -1B, and -2. Furthermore, melanocytes and the surrounding keratinocytes express BMP-4, suggesting both autocrine and paracrine effects of this molecule. Moreover, BMP-4 supplementation of cultured human melanocytes decreases melanin synthesis, tyrosinase mRNA, and protein. The mechanism of this BMP-4 effect on tyrosinase and ultimately on melanogenesis involves modest decreases of tyrosinase transcription rate and mRNA stability. Moreover, ultraviolet irradiation, the best recognized environmental stimulator of melanogenesis, down-regulated the mRNA of BMP receptor-1B in melanocytes. Our data provide evidence of a novel regulatory pathway for melanogenesis in human skin.

Neurotrophins in Skin Biology and Pathology

Neurotrophins (NTs) belong to a family of growth factors, which control the development, maintenance, and apoptotic death of neurons and also fulfill multiple regulatory functions outside the nervous system. Biological effects induced by NTs strongly depend on the pattern of NT receptor/co-receptors expression in target cells, as well as on the set of intracellular adaptor molecules that link NT signalling to distinct biochemical pathways. In this review, we summarize data on the molecular mechanisms underlying the involvement of NTs in the control of non-neuronal functions in normal skin (e.g. keratinocyte proliferation, melanocyte development and apoptosis, hair growth). We also review the data on the role for NTs and their receptors in a number of pathological skin conditions (stress-induced hair loss, psoriasis, atopic dermatitis). Although additional efforts are required to fully understand mechanisms underlying the involvement of NTs and their receptors in controlling functions of normal and pathologically altered skin cells, substantial evidence suggests that modulation of NT signalling by NTs receptor agonists/antagonists may be developed as intervention modalities in distinct skin and hair growth pathologies.

Keratin 16 Expression in Epidermal Melanocytes of Normal Human Skin

Although the prevailing dogma states that keratin filaments are the hallmark of keratinocytes and other epithelial cells, recent publications suggest that they may be expressed by a variety of normal and malignant cells of different embryonic origin. Keratin expression has been reported in fibroblasts and endothelial cells as well as in various sarcomas. Also, some human melanomas express keratins in addition to the traditional diagnostic markers of differentiation, such as S-100 and melanocyte-specific antigens. Many studies have shown that cultured cells obtained from various melanomas express keratin. Most recently, keratin expression has also been shown in cultured melanocytes of normal skin. We now report that normal human melanocytes in vivo express keratin 16 (K16) but not keratins 1, 5, 8, 10, 14, or even keratin 6, the type II partner that is normally expressed with K16 in keratinocytes. Similarly, melanocytes in vitro express K16 but not K6. Keratin 16 expression in vivo was present in basal melanocytes in specimens derived from donors (0-77 years) and from different anatomic locations, suggesting that keratin 16 is constitutively expressed by all melanocytes. It appears that keratin expression may be more prevalent than previously assumed, and that these cytoskeletal filaments may play important roles in tissues and cells other than epithelia.

Modulation of vascular endothelial growth factor receptors in melanocytes

Vascular endothelial growth factor (VEGF) is constitutively produced by keratinocytes, but has no known epidermal target cell. We now report that normal human melanocytes (Mc) maintained in serum-free, hormone-, and growth factor-supplemented medium lacking phorbol ester and choleragen constitutively express VEGF receptor-1 (VEGFR-1), VEGFR-2, and neuropilin-1. Furthermore, stimulation of Mc with VEGF165 isoform leads to phosphorylation of VEGFR-2, the receptor responsible for most of the VEGF-mediated effects in endothelial cells, suggesting that the receptor is functional. Interestingly, in Mc, VEGFR-2 expression is induced by ultraviolet irradiation and is downregulated by VEGF and tumor necrosis factor-alpha. Prolonged culture (>8 weeks) in the presence of phorbol ester abrogates VEGFR-2 expression, explaining previous reports that Mc do not express VEGFR-1 and VEGFR-2. These data suggest that VEGF may play a role in Mc behavior in skin.

Estradiol induces proliferation of keratinocytes via a receptor mediated mechanism

In this study, we investigated the effects of estradiol on the proliferation of neonatal keratinocytes, the expression of estrogen receptor isoforms, and the signaling mechanisms by which estradiol mediates cell growth. We demonstrate that estradiol binds neonatal keratinocytes with high affinity (Kd=5.2nM) and limited capacity (Bmax of 14.2fmol/mg of protein), confirming the presence of estrogen binding sites. Using specific antibodies, we demonstrate that keratinocytes express both estrogen receptor (ER)-alpha and ER-beta. At physiological concentrations, estradiol up-regulates the level of ER-alpha receptors in keratinocytes and induces keratinocyte proliferation. The proliferative effect of estradiol requires the availability of functional estrogen receptors, as it is abrogated by anti-estrogen administration. Estradiol effect on keratinocyte proliferation is most likely mediated in part by activation of a nongenomic, membrane-associated, signaling pathway involving activation of the extracellular signal regulated kinases 1 and 2 and in part by the genomic signaling pathway through activation of nuclear receptors.

A Trial of Short Incubation, Broad-Area Photodynamic Therapy for Facial Actinic Keratoses and Diffuse Photodamage

BACKGROUND

There is no completely satisfactory treatment for multiple actinic keratoses (AKs).

OBJECTIVE

To evaluate the efficacy of short incubation, broad-area application of delta-aminolevulinic acid followed by exposure to activating light-photodynamic therapy (delta-ALA/PDT) for treatment of AKs and background photodamage. The benefit of pretreatment with 40% urea cream to enhance penetration and the use of topical 3% lidocaine hydrochloride to decrease discomfort were also evaluated.

METHODS

Eighteen patients with at least 4 nonhypertrophic facial AKs and mild to moderate diffuse facial photodamage were enrolled in the study. For 7 days, 40% urea cream or vehicle was applied to half of the treatment area, and then delta-ALA was applied to the entire area for 1, 2, or 3 hours. Lidocaine hydrochloride (3%) or vehicle cream was also applied to the entire area 45 minutes before exposure to 10 J/cm(2) of blue light. Pain,phototoxic reactions, AK counts, and photodamage improvement were evaluated 1 day, 1 week, and 1 month after treatment in all patients and after 5 months in 10 patients.

RESULTS

All patients experienced mild to moderate discomfort during treatment and moderate phototoxic effects for 1 week. At 1 and 5 months there was significant reduction in AKs in all groups and significant improvement of several photodamage parameters. Different delta-ALA application times and pretreatment with urea cream or lidocaine had no significant effect on the results.

CONCLUSIONS

This delta-ALA/PDT protocol is safe and effective for AK treatment as well as for improving photodamage. Further studies with a larger cohort, longer follow-up, and histologic confirmation of the clinical data would be of value.

Solar-simulated irradiation evokes a persistent and biphasic IL-1alpha response

Exposure of skin to solar-simulated irradiation generates a multitude of adaptive responses including cytokine transcription, synthesis and secretion. Interleukin-1 (IL-1) is one of the cytokines induced in epidermal cells in response to UV irradiation. It displays a broad range of mitogenic and inflammatory activities including fibroblast proliferation and T-cell activation. There are two forms, IL-1alpha and IL-1beta; and IL-1alpha is the predominant form secreted by epidermal keratinocytes. UV-induced modulations of IL-1alpha message levels have been extensively studied within the first 48 h after irradiation, but longer term changes and impact on IL-1alpha cellular protein levels are virtually unexplored. We now report that cells of keratinocyte origin (SCC 12F) respond to a single physiologic dose of solar-simulated irradiation with both early (8 h) and late (72 h) peaks of IL-1alpha mRNA induction. UV-stimulated IL-1alpha secretion is increased above sham-irradiated control secretion for at least 96 h after irradiation. Our study provides evidence that UV-induced adaptive cutaneous responses persist for at least several days, and suggests that different mechanisms may mediate the early vs. late inductions.

Modulations of nerve growth factor and Bcl-2 in ultraviolet-irradiated human epidermis

BACKGROUND

Ultraviolet (UV) irradiation to the skin causes apoptosis of keratinocytes. Melanocytes are more resistant to UV-induced apoptosis, due, in part, to high levels of antiapoptotic proteins such as Bcl-2. In vitro studies have shown that nerve growth factor (NGF), a neurotrophic polypeptide, is produced by keratinocytes and exerts a protective role for melanocytes by upregulating Bcl-2. The purpose of this study was to determine NGF and Bcl-2 modulations in UV-irradiated human skin.

METHODS

Nine volunteers were irradiated with two minimal erythema doses using solar-simulated UV irradiation. Seventy-two hours post irradiation, skin biopsies were obtained from irradiated and sun-protected skin. The skin specimens were stained with anti-tyrosinase-related protein-1 monoclonal antibody IgG2a (Mel-5), anti-Bcl-2 (monoclonal antibody IgG-kappa), and with anti-NGF (polyclonal antibody IgG).

RESULTS

NGF staining was identified within the cytoplasm of epidermal melanocytes, similar to the staining observed for TRP-1 and Bcl-2. While no significant difference in the number of TRP-1- and Bcl-2-positive melanocytes was observed between irradiated and non-irradiated skin within 72 h, the number of NGF-positive melanocytes decreased significantly, 72 h after UV irradiation (p < 0.024). NGF was also identified within keratinocytes, and while non-irradiated skin exhibited cytoplasmic NGF staining throughout the epidermis, NGF staining was reduced in the lower epidermal layers after UV irradiation.

CONCLUSIONS

This is the first in vivo study showing NGF to be present in melanocytes, as well as showing modulations of NGF and Bcl-2 in melanocytes, following solar-simulated UV irradiation.

UV induces VEGF through a TNF-alpha independent pathway

Vascular endothelial growth factor (VEGF) is a potent keratinocyte-derived angiogenic factor. Prior reports suggest that following UV irradiation VEGF in keratinocytes is induced primarily by tumor necrosis factor (TNF)- alpha, a cytokine synthesized and secreted by keratinocytes after UV irradiation. We investigated whether blocking TNF-alpha binding to its receptors would inhibit UV-induced VEGF expression and secretion in the keratinocyte-derived line SCC-12F. Irradiation with physiologic UV doses (30 mJ/cm2) substantially induced VEGF mRNA in this cell line, as expected, and mRNA induction was followed by increased VEGF in medium conditioned by UV-irradiated cells. Also as expected, TNF-alpha induced VEGF expression and secretion in a dose-dependent manner. Addition of a hexapeptide (Ac-KWIIVW-NH2), known to block TNF-alpha binding to its receptors, abrogated this TNF-alpha effect on VEGF mRNA induction. However, addition of the peptide to cells immediately after UV irradiation did not substantially affect VEGF mRNA induction or secretion into the medium. Our results suggest that VEGF induction after UV irradiation is mediated by multiple mechanisms and that blocking a single pathway does not affect the response.

Fifty years of skin aging

In developed countries, interest in cutaneous aging is in large part the result of a progressive, dramatic rise over the past century in the absolute number and the proportion of the population who are elderly (Smith et al, 2001). The psychosocial as well as physiologic effects of skin aging on older individuals have created a demand for better understanding of the process and particularly for effective interventions. Skin aging is a complex process determined by the genetic endowment of the individual as well as by environmental factors. The appearance of old skin and the clinical consequences of skin aging have been well known for centuries, but only in the past 50 y have mechanisms and mediators been systematically pursued. Still, within this relatively short time there has been tremendous progress, a progress greatly enhanced by basic gerontologic research employing immunologic, biochemical, and particularly molecular biologic approaches (Figs 1, 2).

Effect of sunscreen application on UV-induced thymine dimers

BACKGROUND

Exposure to UV radiation is a major risk factor for skin cancer, including malignant melanoma. Photocarcinogenesis is caused largely by mutations at sites of incorrectly repaired DNA photoproducts, of which the most common is the thymine dimer. Over the past decade, controversy has arisen over the use of sunscreens to prevent UV-induced skin cancer.

OBJECTIVES

To determine if daily application of a broad-spectrum sunscreen with a sun protection factor (SPF) of 15 protects human skin against UV-induced DNA damage as determined by the formation of thymine dimers after repeated exposures to simulated solar light and, if so, to determine whether daily applications are required to achieve this protective effect.

METHODS

Over 4 consecutive days, an SPF 15 sunscreen was applied homogeneously to each of 4 buttock sites of 18 women 30 minutes before exposure to 2 minimum erythemal doses of UV radiation. Of these 4 sites, 1 was treated with SPF 15 daily, and the remaining 3 were treated on 3 of the 4 irradiation days, skipping application on day 2, 3, or 4. A fifth site served as the untreated control and was also not irradiated. The number of cells per square millimeter positive for thymine dimer formation was determined using immunohistochemical and image analyses.

RESULTS

There was no significant difference in thymine dimer formation between nonirradiated and irradiated skin when application of sunscreen preceded each irradiation. However, when sunscreen application was omitted even once prior to irradiation, a statistically significant increase in thymine dimer formation was apparent. At 48 hours after irradiation of unprotected skin, 50% of epidermal dimers present 24 hours after irradiation had been removed; at 72 hours, more than 75% were gone.

CONCLUSIONS

Our study indicates that regular use of a broad-spectrum sunscreen is effective in preventing a major form of UV-induced DNA damage. Irregular and inadequate use of sunscreen during exposure to UV radiation results in thymine dimer formation, which may lead to mutation and subsequent cancer development.

Amyloid beta binds trimers as well as monomers of the 75-kDa neurotrophin receptor and activates receptor signaling

p75(NTR), a nerve growth factor co-receptor that has been implicated in apoptosis of neurons, is structurally related to Fas and the receptors for tumor necrosis factor-alpha that display ligand independent assembly into trimers. Using embryonic day 17 fetal rat cortical neurons and p75(NTR)-expressing NIH-3T3 cells, we now show that p75(NTR) exists as a trimer as well as a monomer. Furthermore, we have reported and others have confirmed that amyloid beta binds p75(NTR), and that this binding leads to apoptotic cell death. We now report that amyloid beta binds to trimers of p75(NTR) as well as to p75(NTR) monomers but not to the p140(trkA), the nerve growth factor co-receptor that mediates neuronal survival. Furthermore, amyloid beta activates p75(NTR), strongly inducing the transcription of c-Jun mRNA and stimulating the stress-activated c-Jun NH(2)-terminal kinase, as measured by phosphorylation of its substrate (glutathione S-transferase-c-Jun-(1-79)). Our data suggest that p75(NTR) may be present as a preformed trimer that binds amyloid beta to induce receptor activation, and support the hypothesis that p75(NTR) activation by amyloid beta is causally related to Alzheimer's disease.

Tyrosinase gene expression is regulated by p53

Tyrosinase, the rate-limiting enzyme for melanin synthesis, is induced after ultraviolet irradiation as part of the tanning response, the major recognized photoprotective response of human skin. Other DNA-damaging agents and DNA fragments such as thymidine dinucleotides also induce tyrosinase gene expression. Moreover, like ultraviolet light they also activate p53. To determine whether p53 activation is required for this increased tyrosinase expression, we employed two experimental systems: (i) a human melanoma line (WM35) known to express wild-type p53 versus WM35 cells engineered to express a transcriptionally inactive dominant-negative p53 (WM35-p53DN) or the empty vector alone (WM35-pCMV7) and (ii) mice with wild-type p53 versus p53 knockout mice. In WM35-p53DN cells, the baseline p53 protein level was higher than in WM35 or WM35-pCMV7 cells, and tyrosinase transcripts were lower. After ultraviolet irradiation, in all cell lines the p53 protein level increased within the first 24 h, as expected; and at 24 h tyrosinase mRNA levels were decreased. Consistent with the literature, these data in combination suggest that increased p53 protein level downregulates tyrosinase mRNA. In WM35 and WM35-pCMV7 cells at 48 and 72 h, however, whereas p53 levels remained elevated, tyrosinase mRNA levels compared to pre-irradiation levels tripled, whereas in WM35-p53DN cells levels remained below baseline. In thymidine-dinucleotide-treated WM35 and WM35-pCMV7 cells there was a comparable upregulation of tyrosinase mRNA within 24 h that persisted through 72 h, but there was no upregulation of tyrosinase mRNA in WM35-p53DN cells any time after ultraviolet irradiation or thymidine dinucleotide treatment. In ear skin of p53 wild-type mice, topical application of thymidine dinucleotide induced a 4-5-fold increase in epidermal melanin content after 3 wk, but in p53 knockout mice thymidine dinucleotide application caused no detectable increase in melanin. Together, these data demonstrate that p53 activation increases tyrosinase mRNA level and subsequently pigmentation. The data further suggest that tanning is part of a p53-mediated adaptive response of mammalian skin to DNA damage from ultraviolet irradiation.

Skin aging: postulated mechanisms and consequent changes in structure and function

Aging is a complex process influenced by telomere shortening and damage to cellular DNA. New insights into age-associated decrements in DNA damage repair are reviewed. Age-associated gross, histologic, and functional cutaneous deficits are delineated. Different treatment options for aged skin are examined.

Ageing and photoageing of keratinocytes and melanocytes

An overview of keratinocyte and melanocyte function is provided. The processes of cutaneous ageing and photoageing are defined, and age-associated modulations in gene expression are described. The changes in keratinocytes and melanocytes that occur with skin ageing and photoageing and the characteristics of chronologically aged vs. photoaged skin are delineated. Mutations that are found in malignant and premalignant tumors of epidermal origin are described.

Solar simulated irradiation modulates gene expression and activity of antioxidant enzymes in cultured human dermal fibroblasts

Exposure of skin to solar irradiation generates reactive oxygen species that damage DNA, membranes, mitochondria and proteins. To protect against such damage, skin cells have evolved antioxidant enzymes including glutathione peroxidase (GSH-Px), copper and zinc-dependent superoxide dismutase (SOD1), the mitochondrial manganese-dependent superoxide dismutase (SOD2), and catalase. This report examines the effect of a single low or moderate dose exposure to solar-simulating combined UVB and UVA irradiation on the gene expression and activities of these antioxidant enzymes in cultured normal human fibroblasts. We find that both doses initially decrease GSH-Px, SOD2 and catalase activities, but within 5 days after irradiation the activities of the enzymes return to pre-irradiation level (catalase) or are induced slightly (SOD1, GSH-Px) or substantially (SOD2) above the basal level. For SOD1, SOD2 and catalase, the higher dose also detectably modulates the mRNA level of these enzymes. Our results indicate that the effects of a single physiologic solar simulated irradiation dose persist for at least several days and suggest that skin cells prepare for subsequent exposure to damaging irradiation by upregulating this antioxidant defense system, in particular the mitochondrial SOD2. Our findings are consistent with the existence of a broad-based SOS-like response in irradiated human skin.

Effect of daily versus intermittent sunscreen application on solar simulated UV radiation-induced skin response in humans

BACKGROUND

Acute and chronic skin damage occurs as a consequence of solar UV radiation exposure. To diminish such skin damage, the dermatologic community advocates the daily use of sunscreens as part of a sun avoidance strategy.

OBJECTIVE

We determined the effectiveness of a sunscreen product with a sunscreen protection factor (SPF) of 15 applied daily in preventing UV-induced histologic damage in human skin compared with the protection afforded by sunscreens with equal or higher SPF applied intermittently.

METHODS

Twenty-four subjects were exposed to 2 minimal erythema doses of solar-simulated UV on 4 consecutive days. Three sunscreen products were applied to the buttock of each subject. One SPF 15 product was applied daily before exposure to UV and, to simulate intermittent product use, an SPF 15 or SPF 29 product was applied on 3 of 4 days, with one missed application on days 2, 3, or 4. Skin biopsy specimens were taken and processed for routine and immunohistochemical staining. Changes in number of sunburn cells and Langerhans cells as well as degree of inflammatory infiltrate and lysozyme immunostaining were determined.

RESULTS

There was a statistically significant increase in the number of sunburn cells, degree of inflammation, and intensity of lysozyme staining, and there was a decrease in the number of Langerhans cells at sites where sunscreen application was missed as compared with unirradiated control and daily SPF 15 sunscreen-treated sites.

CONCLUSION

Our data suggest that daily use of a sunscreen reduces the skin damage produced by UV exposure compared with intermittent use of equal or higher SPF products. The daily application of sunscreens in appropriate quantities reduces the harmful effects of solar UV radiation on skin. Compliance is essential for maximal benefit of sunscreens.

Mechanisms and implications of the age-associated decrease in DNA repair capacity

Skin cancer incidence is clearly linked to UV irradiation and increases exponentially with age. We studied the rate of removal of thymine dimers and (6-4) photoproducts in UV-irradiated human dermal fibroblasts derived from donors of different ages. There was a significant decrease with aging in the repair rates of both thymine dimers and (6-4) photoproducts (P<0.001). In addition, there was an age-associated decrease in the protein levels of ERCC3, PCNA, RPA, XPA, and p53 that participate in nucleotide excision repair. Moreover, the mRNA levels of XPA, ERCC3, and PCNA were significantly reduced with aging, suggesting that these decreases are often regulated at the mRNA level. Furthermore, with age induction of p53 after UV irradiation was significantly reduced. Taken together, our data suggest that the age-associated decrease in the repair of UV-induced DNA damage results at least in part from decreased levels of proteins that participate in the repair process.

Role of cytoplasmic dynein in melanosome transport in human melanocytes

Cytoplasmic dynein is a microtubule-associated retrograde-directed motor molecule for transport of membrane-bound organelles. To determine whether cytoplasmic dynein is expressed in melanocytes, we performed reverse transcriptase polymerase chain reaction using melanocyte cDNA and primers complementary to human brain cytoplasmic dynein heavy chain. A polymerase chain reaction product of the expected molecular size was generated and the identity was confirmed by sequence analysis. Western blotting of total melanocyte proteins reacted with an anti-intermediate chain cytoplasmic dynein antibody identified the appropriate 74 kDa band. To determine whether cytoplasmic dynein plays a role in melanosome transport, duplicate cultures were treated with cytoplasmic dynein antisense or sense (control) oligodeoxynucleotides and the cells were observed by high-resolution time-lapse microscopy, which allows visualization of melanosomal aggregates and individual melanosomes. Antisense-treated melanocytes demonstrated a strong anterograde transport of melanosomes from the cell body into the dendrites, whereas melanosome distribution was not affected in sense-treated melanocytes. To determine whether ultraviolet irradiation modifies cytoplasmic dynein expression, melanocyte cultures were exposed to increasing doses of solar-simulated irradiation, equivalent to a mild to moderate sunburn exposure for intact skin. Within 24 h, doses of 5 and 10 mJ per cm2 induced cytoplasmic dynein protein, whereas doses of 30 mJ per cm2 or more were associated with decreased levels of cytoplasmic dynein compared with sham-irradiated controls. Our data show that cytoplasmic dynein participates in retrograde melanosomal transport in human melanocytes and suggest that the altered melanosomal distribution in skin after sun exposure is due, at least in part, to decreased cytoplasmic dynein levels resulting in augmented anterograde transport.

Kinesin participates in melanosomal movement along melanocyte dendrites

Movement of melanosomes along melanocyte dendrites is necessary for the transfer of melanin pigment from melanocytes to basal and suprabasal keratinocytes, an event critical to epidermal photoprotection and maintenance of normal skin color. Recent murine data suggest that in melanocyte dendrites the microtubule-associated melanosome movement is bidirectional and that actin-associated myosin V secures the peripheral melanosomes, preparing them to be transferred to surrounding keratinocytes. We now report that human melanocytes express high levels of kinesin, a molecule that participates in microtubule-associated transport of organelles in other cell types, and that ultrastructurally kinesin molecules are closely associated with melanosomes. To determine whether kinesin participates in melanosomal transport, cultured melanocytes were treated with sense or antisense oligonucleotides complementary to kinesin heavy chain sequences. Antisense oligonucleotides decreased kinesin protein levels and inhibited the bidirectional movement of the melanosomes, promoting their backward movement. Furthermore, guinea pigs were exposed to ultraviolet B irradiation, known to enhance transport of melanosomes from melanocytes to epidermal keratinocytes, and then were treated with kinesin sense or antisense oligonucleotides. The areas that were treated with kinesin antisense oligonucleotides showed significantly less pigmentation clinically and histologically than control (sense) oligonucleotide-treated areas. As observed ultrastructurally, in antisense-treated areas melanosomes remained in melanocyte dendrites but over several days were not transferred to the surrounding keratinocytes. Our study supports a major role for kinesin in microtubule-associated anterograde melanosomal transport in human melanocyte dendrites.

Thymidine dinucleotides inhibit contact hypersensitivity and activate the gene for tumor necrosis factor alpha1

DNA is a target for ultraviolet-B-induced inhibition of contact hypersensitivity, and small DNA fragments such as thymidine dinucleotides (pTpT) can simulate several ultraviolet-induced effects. To determine whether pTpT mimics the suppressive influence of ultraviolet-B on contact hypersensitivity, we compared the effects of topical application of pTpT with those of ultraviolet-B irradiation on C57BL/6 mice sensitized to dinitrofluorobenzene. Mice pretreated with pTpT or ultraviolet-B irradiation showed markedly suppressed ear swelling responses to dinitrofluorobenzene challenge. Because tumor necrosis factor alpha mediates ultraviolet-B-induced suppression of contact hypersensitivity, and because pTpT exerts many ultraviolet-mimetic effects by augmenting mRNA and protein levels of effector molecules, we asked if pTpT mimics ultraviolet-B's upregulatory influence on tumor necrosis factor alpha expression. Using transgenic mice carrying a chloramphenicol acetyl transferase reporter linked to the tumor necrosis factor alpha promoter, we examined effects of ultraviolet-B irradiation versus intradermal injection of pTpT on tumor necrosis factor alpha gene transcription. Both treatments induced cutaneous chloramphenicol acetyl transferase activity. Ultra- violet-B or pTpT treatment of cultured dermal fibroblasts from these mice also stimulated chloramphenicol acetyl transferase activity. To determine whether human cells responded similarly, a well- differentiated ultraviolet-responsive human squamous cell carcinoma line was treated with pTpT. pTpT increased tumor necrosis factor alpha mRNA expression and protein secretion in a dose-dependent manner. Our findings expand the spectrum of ultraviolet effects mimicked by pTpT to include inhibition of contact hypersensitivity and activation of the tumor necrosis factor alpha gene. These results support the hypothesis that DNA photoproducts and/or their repair intermediates trigger many of the biologic consequences of ultraviolet irradiation.

Thymidine dinucleotide mimics the effect of solar simulated irradiation on p53 and p53-regulated proteins

The tumor suppressor protein p53 participates in DNA repair and cell cycle regulation in response to injuries like ultraviolet (UV) irradiation. We have previously reported that the thymidine dinucleotide (pTpT), a common target for DNA photoproduct formation by UV light, mimics many effects of UV irradiation in cultured skin-derived cells, at least in part through the activation of p53. In this report we compare the effects of solar-simulated irradiation and pTpT on p53 and p53-regulated proteins involved in cellular growth arrest and DNA repair in cultured human dermal fibroblasts. We find that, like UV irradiation, pTpT increases the levels of p53, p21, and proliferating-cell nuclear antigen. The magnitude and time course of the inductions are UV dose dependent and consistent with known regulatory interactions among these nuclear proteins. These data confirm and expand previous studies of UV effects on nuclear proteins involved in cell cycle regulation and DNA repair. Our observations suggest that such protective effects can also be induced by pTpT in the absence of initial DNA damage, rendering cells more capable of responding to subsequent DNA damage.

Aging versus photoaging: postulated mechanisms and effectors

The differences between intrinsic aging and photoaging are reviewed. The various model systems currently employed for the studies of aging and photoaging are discussed. Findings on age associated decrements in receptor/ligand mediated signaling as well as changes during cellular senescence in the expression of nuclear transcription factors are described. The role of telomere shortening and oxidative damage in the aging process is explained. At the cellular level, genetic and behavioral differences between aging and photoaging are illustrated with particular emphasis on changes in the structure and function of the tumor suppressor gene p53.

Post-transcriptional regulation of UV induced TNF-alpha expression

Ultraviolet (UV) irradiation exerts multiple effects on skin cells, including the induction of several cytokines involved in immunomodulation. Specifically, UV irradiation has been shown to upregulate the level of tumor necrosis factor-alpha (TNF-alpha) mRNA in keratinocytes. To determine whether the induction of TNF-alpha mRNA is regulated by transcriptional or post-transcriptional mechanisms, we examined cells of keratinocytic lineage (SCC12F) for steady state level, transcription rate, and stability of TNF-alpha mRNA after UV irradiation. Within 4 h there was a 20-40-fold induction of TNF-alpha mRNA that persisted at lower levels through 48 h. Consistently, TNF-alpha protein secretion increased at 24 and 48 h after UV irradiation. UV irradiation increased the half-life of TNF-alpha mRNA from approximately 35 min to approximately 10 h. Conversely, the transcription rate of the TNF-alpha gene increased < 2-fold at the time of peak mRNA steady state levels. Thus, post-transcriptional mechanisms play a major role in UV induced TNF-alpha transcript level.