Keratinocyte apoptosis in epidermal development and disease

Sargaquinoic acid and sargachromenol, extracts of Sargassum sagamianum, induce apoptosis in HaCaT cells and mice skin: Its potentiation of UVB-induced apoptosis

The plastoquinones sargaquinoic acid and sargachromenol are major components of brown alga Sargassum sagamianum and are known to be involved in neurite growth and survival. In this study, we describe their novel pro-apoptotic activities in vitro and in vivo. In vitro, treatment with sargaquinoic acid or sargachromenol promoted cell death and activation of caspase-3, caspase-8, caspase-9 and poly (ADP-ribose) polymerase (PARP) in a concentration-dependent manner. Sargaquinoic acid- or sargachromenol-induced apoptosis was enhanced by co-treatment with UVB irradiation. It showed much higher levels of cleaved caspase-3, caspase-8, caspase-9, and PARP than with sargaquinoic acid and sargachromenol alone, while it had no effect on Bcl-2 and Bax expression level. Examination by terminal deoxynucleotidyl transferase-mediated nick-end labeling (TUNEL) and immunohistochemistry showed that topical application of sargaquinoic acid (1 mg/ml) before UVB irradiation (2.5 kJ/m(2)) of hairless mice also enhanced apoptosis including activation of caspase-3. Since a combination of phototherapy using UVB with topical reagents has been clinically applied to treat hyperproliferative skin disease, these results suggest that sargaquinoic acid and sargachromenol could be effective therapeutic agents.

DNA damage, apoptosis and langerhans cells--Activators of UV-induced immune tolerance

Solar UVR is highly mutagenic but is only partially absorbed by the outer stratum corneum of the epidermis. UVR can penetrate into the deeper layers of the epidermis, depending on melanin content, where it induces DNA damage and apoptosis in epidermal cells, including those in the germinative basal layer. The cellular decision to initiate either cellular repair or undergo apoptosis has evolved to balance the acute need to maintain skin barrier function with the long-term risk of retaining precancerous cells. Langerhans cells (LCs) are positioned suprabasally, where they may sense UV damage directly, or indirectly through recognition of apoptotic vesicles and soluble mediators derived from surrounding keratinocytes. Apoptotic vesicles will contain UV-induced altered proteins that may be presented to the immune system as foreign. The observation that UVR induces immune tolerance to skin-associated antigens suggests that this photodamage response has evolved to preserve the skin barrier by protecting it from autoimmune attack. LC involvement in this process is not clear and controversial. We will highlight some basic concepts of photobiology and review recent advances pertaining to UV-induced DNA damage, apoptosis regulation, novel immunomodulatory mechanisms and the role of LCs in generating antigen-specific regulatory T cells.

Hypericin phototoxicity induces different modes of cell death in melanoma and human skin cells

Hypericin, the major component of St. John's Wort, absorbs light in the UV and visible ranges whereupon it becomes phototoxic through the production of reactive oxygen species. Although photodynamic mechanisms (i.e. through endogenous photosensitizers) play a role in UVA phototherapy for the treatment of skin disorders such as eczema and psoriasis, photodynamic therapy employing exogenous photosensitizers are currently being used only for the treatment of certain forms of non-melanoma skin cancers and actinic keratoses. There are few reports however on its use in treating melanomas. This in vitro study analyses the phototoxic effect of UVA (400-315 nm) - activated hypericin in human pigmented and unpigmented melanomas and immortalised keratinocytes and melanocytes. We show that neither hypericin exposure nor UV irradiation alone reduces cell viability. We show that an exposure to 1 microM UVA-activated hypericin does not bring about cell death, while 3 microM activated hypericin induces a necrotic mode of cell death in pigmented melanoma cells and melanocytes and an apoptotic mode of cell death in non-pigmented melanoma cells and keratinocytes. We hypothesis that the necrotic mode of cell death in the pigmented cells is possibly related to the presence of melanin-containing melanosomes in these cells and that the hypericin-induced increase in reactive oxygen species leads to an increase in permeability of melanosomes. This would result in toxic melanin precursors (of an indolic and phenolic nature) leaking into the cytoplasm which in turn leads to cell death. Hypericin localisation in the endoplasmic reticulum in these cells shown by fluorescent microscopy, further support a disruption in cellular processing and induction of cell death. In contrast, this study shows that cells that do not contain melanosomes (non-pigmented melanoma cells and keratinocytes) die by apoptosis. Further, using a mitochondrial-specific fluorescent dye, we show that intracellular accumulation of hypericin induces a mitochondrial-associated caspase-dependent apoptotic mode of cell death. This work suggests that UVA is effective in activating hypericin and that this phototoxicity may be considered as treatment option in some cases of lentigo maligna or lentigo maligna melanoma that are too large for surgical resection.

Dermatomyositis

Dermatomyositis (DM) is a chronic inflammatory disorder of the skin and muscles. Although thought to be autoimmune in origin, many questions remain as to the etiopathogenesis of this disease. DM has classically been considered a humorally mediated disease. Current evidence, however, seems to increasingly support alternative (though not mutually exclusive) mechanisms of pathogenesis, including cell-mediated and innate immune system dysfunction. Pathologic findings of DM in muscle include infarcts, perifascicular atrophy, endothelial cell swelling and necrosis, vessel wall membrane attack complex deposition, and myocyte-specific MHC I upregulation. As for the skin, histopathologic findings include hyperkeratosis, epidermal basal cell vacuolar degeneration and apoptosis, increased dermal mucin deposition, and a cell-poor interface dermatitis. Autoantibodies, particularly those that bind nuclear or cytoplasmic ribonucleoprotein antigens, are also commonly found in DM, although their importance in pathogenesis remains unclear. Defective cellular clearance, genetic predilection and environmental exposures, such as viral infection, may also play an important role in the pathogenesis of DM. The seminal work regarding the pathogenesis of DM is reviewed and an update on the recent basic and molecular advances in the field is provided.

Fas ligand-induced proinflammatory transcriptional responses in reconstructed human epidermis. Recruitment of the epidermal growth factor receptor and activation of MAP kinases

Fas ligand (FasL) exerts potent proapoptotic and proinflammatory actions on epidermal keratinocytes and has been implicated in the pathogenesis of eczema, toxic epidermal necrolysis, and drug-induced skin eruptions. We used reconstructed human epidermis to investigate the mechanisms of FasL-induced inflammatory responses and their relationships with FasL-triggered caspase activity. Caspase activity was a potent antagonist of the pro-inflammatory gene expression triggered by FasL prior to the onset of cell death. Furthermore, we found that FasL-stimulated autocrine production of epidermal growth factor receptor (EGFR) ligands, and the subsequent activation of EGFR and ERK1 and ERK2 mitogen-activated protein kinases, were obligatory extracellular steps for the FasL-induced expression of a subset of inflammatory mediators, including CXCL8/interleukin (IL)-8, ICAM-1, IL-1alpha, IL-1beta, CCL20/MIP-3alpha, and thymic stromal lymphopoietin. These results expand the known physiological role of EGFR and its ligands from promoting keratinocyte mitogenesis and survival to mediating FasL-induced epidermal inflammation.

Loss of the Atp2c1 secretory pathway Ca(2+)-ATPase (SPCA1) in mice causes Golgi stress, apoptosis, and midgestational death in homozygous embryos and squamous cell tumors in adult heterozygotes

Loss of one copy of the human ATP2C1 gene, encoding SPCA1 (secretory pathway Ca(2+)-ATPase isoform 1), causes Hailey-Hailey disease, a skin disorder. We performed targeted mutagenesis of the Atp2c1 gene in mice to analyze the functions of this Golgi membrane Ca(2+) pump. Breeding of heterozygous mutants yielded a normal Mendelian ratio among embryos on gestation day 9.5; however, null mutant (Spca1(-/-)) embryos exhibited growth retardation and did not survive beyond gestation day 10.5. Spca1(-/-) embryos had an open rostral neural tube, but hematopoiesis and cardiovascular development were ostensibly normal. Golgi membranes of Spca1(-/-) embryos were dilated, had fewer stacked leaflets, and were expanded in amount, consistent with increased Golgi biogenesis. The number of Golgi-associated vesicles was also increased, and rough endoplasmic reticulum had fewer ribosomes. Coated pits, junctional complexes, desmosomes, and basement membranes appeared normal in mutant embryos, indicating that processing and trafficking of proteins in the secretory pathway was not massively impaired. However, apoptosis was increased, possibly the result of secretory pathway stress, and a large increase in cytoplasmic lipid was observed in mutant embryos, consistent with impaired handling of lipid by the Golgi. Adult heterozygous mice appeared normal and exhibited no evidence of Hailey-Hailey disease; however, aged heterozygotes had an increased incidence of squamous cell tumors of keratinized epithelial cells of the skin and esophagus. These data show that loss of the Golgi Ca(2+) pump causes Golgi stress, expansion of the Golgi, increased apoptosis, and embryonic lethality and demonstrates that SPCA1 haploinsufficiency causes a genetic predisposition to cancer.

Histological and proteomic analysis of reversible H-RasV12G expression in transgenic mouse skin

We have used a two-transgene tetracycline system to reversibly express oncogenic H-Ras(V12G) in mouse skin and primary keratinocytes culture using the bovine keratin 5 promoter. Induction of H-Ras(V12G) expression in skin at 30 days after birth causes epidermal basal cell hyperplasia, an eruption of keratinous cysts and loss of hair follicles by 3 weeks. Subsequent H-Ras(V12G) de-induction for 3 days results in massive apoptosis in the non-H-Ras(V12G)-expressing stroma as well as in the suprabasal cells of the epidermis. Several procaspases such as CASP3, 1alpha, 5 and 12 disappeared, whereas the pro-apoptotic proteins AIF, Bax and Fas ligand were induced in H-Ras(V12G) de-induction skin. This process is followed by a wave of cell division at 14 days as hair follicles regrew, returning to near normal histology and skin appearance by 30 days. Using Kinetworkstrade mark multi-immunoblotting screens, the phosphorylation status of 37 proteins and expression levels of 75 protein kinases in the skin were determined in three samples: (i) wild-type skin, (ii) hyperplastic H-Ras(V12G)-expressing skin and (iii) skin where H-Ras(V12G) expression was suppressed for 7 days. Following H-Ras(V12G) induction, 16 kinases were increased over 2-fold, and 2 kinases were reduced over 50%. This included increased phosphorylation of both known downstream H-Ras(V12G) targets and unknown H-Ras(V12G) targets. After H-Ras(V12G) suppression, many but not all protein changes were reversed. These results from skin and primary keratinocytes are organized to reflect the molecular events that cause the histological changes observed. These proteomic changes identify markers that may mediate the oncogenic addiction paradigm.

Terminal differentiation of nail matrix keratinocytes involves up-regulation of DNase1L2 but is independent of caspase-14 expression

Terminal differentiation of keratinocytes in the epidermis and in epidermal appendages results in specialized forms of cell death. Keratinocytes of the nail matrix differentiate into nail corneocytes, the building blocks of the nail plate. Here, we show that, in contrast to the abrupt breakdown of the nucleus during corneocyte formation of epidermal keratinocytes, chromatin undergoes progressive condensation over several nail matrix cell layers below the transition zone to the nail plate, where nuclear DNA disappears. Virtually all keratinocytes in the cell layer immediately beneath the nail plate contained terminal deoxynucleotidyl transferase-mediated fluorescein-dUTP nick end labeling-positive DNA fragments. Nail matrix keratinocytes lacked processed caspase-3, a marker of apoptosis, and did not express caspase-14, a protease up-regulated during terminal differentiation of epidermal keratinocytes. By contrast, DNase1L2, which is also up-regulated during the differentiation of epidermal keratinocytes and plays an essential role in differentiation-associated degradation of nuclear DNA in epidermal keratinocytes, was strongly expressed in the nail matrix-nail plate transition layer. Our results show that caspase-14 is not strictly, if at all, required for differentiation-associated keratinocyte cell death and implicates DNase1L2 in terminal differentiation of nail matrix keratinocytes.

Cyclooxygenase-2 deficiency increases epidermal apoptosis and impairs recovery following acute UVB exposure

The cyclooxygenases, COX-1 and COX-2, are involved in cutaneous responses to both acute and chronic UV exposure. In the present study, wild-type (WT), COX-1-/- and COX-2-/- mice were used to determine the influence of the individual isoform on mouse skin responses to acute UVB treatment. Immunohistochemistry and Western analysis indicated that COX-2, and not COX-1, was induced by UVB (2.5 or 5.0 kJ/m2), but that COX-1 remained the major source of prostaglandin E2 production. UVB exposure significantly increased epidermal apoptosis in all genotypes compared to untreated mice. However, while the number of apoptotic cells in WT and COX-1-/- mice were about equal, the number of apoptotic cells was 2.5-fold greater in COX-2-/- mice. Apoptosis in WT and COX-2-/- mice peaked at 24 h post-exposure. The increased apoptosis and reduced proliferation in COX-2-/- mice resulted in about a 50% decrease in epidermal thickness at 24-48 h post-exposure compared to about a 50% increase in epidermal thickness in WT mice. UVB-induced cell replication, as measured by BrdU labeling, was reduced in COX-2-/- compared to WT mice at 24-96 h. However, by 96 h post-exposure, both WT and COX-2-/- mice showed epidermal hyperplasia. The data indicate that COX-2 induction initially protects against the acute sunburn effects of UVB, but that continuous induction of COX-2 may contribute to skin cancer in chronic UVB exposure.

Activation of dual apoptotic pathways in human melanocytes and protection by survivin

Apoptosis resistance in melanoma is a primary cause of treatment failure. Apoptotic pathways in melanocytes, from which melanoma arises, are poorly characterized. Human melanocytes were susceptible to apoptosis following exposure to UV radiation (UVB, 24-48 hours), 4-tert-butylphenol (4-TBP, 1-4 hours), and cisplatin (24-48 hours). These responses were associated with Bid cleavage, caspase activation (caspases 3, 8, and 9), mitochondrial depolarization and release of cytochrome c, Smac/DIABLO, and apoptosis-inducing factor (AIF), but not endonuclease G. The apoptotic responses and AIF release were caspase-independent, as they were not blocked by zVal-Ala-Asp(OMe)-fluoromethyl ketone (zVAD-fmk). While RNA interference-mediated knockdown of AIF protected melanocytes against apoptosis induced by serum withdrawal, apoptotic responses to UVB, cisplatin, and 4-TBP were not compromised by AIF knockdown, even in the presence of zVAD-fmk. Finally, adenoviral-mediated expression of Survivin, an inhibitor of apoptosis expressed in melanoma but not melanocytes, protected melanocytes against UVB-induced apoptosis. Survivin expression in melanocytes partially blocked caspase activation and release of mitochondrial release of AIF, cytochrome c, and Smac induced by UVB. These data indicate that multiple stimuli can activate both caspase-dependent and caspase-independent apoptotic pathways in melanocytes, and that endogenous expression of Survivin in melanoma may contribute to apoptosis resistance by multiple mechanisms.