Ultraviolet B irradiation increases endothelin-1 and endothelin receptor expression in cultured human keratinocytes

UV light exposure versus vitamin D supplementation: A comparison of health benefits and vitamin D metabolism in a pig model

There is limited data on the effect of UV light exposure versus orally ingested vitamin D3 on vitamin D metabolism and health. A 4-week study with 16 pigs (as a model for human physiology) was conducted. The pigs were either supplemented with 20 µg/d vitamin D3 or exposed to UV light for 19 min/d to standardize plasma 25-hydroxyvitamin D3 levels. Important differences were higher levels of stored vitamin D3 in skin and subcutaneous fat, higher plasma concentrations of 3-epi-25-hydroxyvitamin D3 and increases of cutaneous lumisterol3 in UV-exposed pigs compared to supplemented pigs. UV light exposure compared to vitamin D3 supplementation resulted in lower hepatic cholesterol, higher circulating plasma nitrite, a marker of the blood pressure-lowering nitric oxide, and a reduction in the release of pro- and anti-inflammatory cytokines from stimulated peripheral blood mononuclear cells. However, plasma metabolome and stool microbiome analyses did not reveal any differences between the two groups. To conclude, the current data show important health relevant differences between oral vitamin D3 supplementation and UV light exposure. The findings may also partly explain the different vitamin D effects on health parameters obtained from association and intervention studies.

Neuro-immune communication regulating pruritus in atopic dermatitis

Atopic dermatitis (AD) is a common, chronic-relapsing inflammatory skin disease with significant disease burden. Genetic and environmental trigger factors contribute to AD, activating two of our largest organs, the nervous and immune system. Dysregulation of neuro-immune circuits plays a key role in the pathophysiology of AD causing inflammation, pruritus, pain, and barrier dysfunction. Sensory nerves can be activated by environmental or endogenous trigger factors transmitting itch stimuli to the brain. Upon stimulation, sensory nerve endings also release neuromediators into the skin contributing again to inflammation, barrier dysfunction and itch. Additionally, dysfunctional peripheral and central neuronal structures contribute to neuroinflammation, sensitization, nerve elongation, neuropathic itch, thus chronification and therapy-resistance. Consequently, neuro-immune circuits in skin and central nervous system may be targets to treat pruritus in AD. Cytokines, chemokines, proteases, lipids, opioids, ions excite/sensitize sensory nerve endings not only induce itch but further aggravate/perpetuate inflammation, skin barrier disruption, and pruritus. Thus, targeted therapies for neuro-immune circuits as well as pathway inhibitors (e.g., kinase inhibitors) may be beneficial to control pruritus in AD either in systemic and/or topical form. Understanding neuro-immune circuits and neuronal signaling will optimize our approach to control all pathological mechanisms in AD, inflammation, barrier dysfunction and pruritus.

Pruritus: A Sensory Symptom Generated in Cutaneous Immuno-Neuronal Crosstalk

Pruritus or itch generated in the skin is one of the most widespread symptoms associated with various dermatological and systemic (immunological) conditions. Although many details about the molecular mechanisms of the development of both acute and chronic itch were uncovered in the last 2 decades, our understanding is still incomplete and the clinical management of pruritic conditions is one of the biggest challenges in daily dermatological practice. Recent research revealed molecular interactions between pruriceptive sensory neurons and surrounding cutaneous cell types including keratinocytes, as well as resident and transient cells of innate and adaptive immunity. Especially in inflammatory conditions, these cutaneous cells can produce various mediators, which can contribute to the excitation of pruriceptive sensory fibers resulting in itch sensation. There also exists significant communication in the opposite direction: sensory neurons can release mediators that maintain an inflamed, pruritic tissue-environment. In this review, we summarize the current knowledge about the sensory transduction of pruritus detailing the local intercellular interactions that generate itch. We especially emphasize the role of various pruritic mediators in the bidirectional crosstalk between cutaneous non-neuronal cells and sensory fibers. We also list various dermatoses and immunological conditions associated with itch, and discuss the potential immune-neuronal interactions promoting the development of pruritus in the particular diseases. These data may unveil putative new targets for antipruritic pharmacological interventions.

Endothelin receptor type A is involved in the development of oxaliplatin-induced mechanical allodynia and cold allodynia acting through spinal and peripheral mechanisms in rats

Oxaliplatin, a platinum-based chemotherapeutic agent, frequently causes severe neuropathic pain typically encompassing cold allodynia and long-lasting mechanical allodynia. Endothelin has been shown to modulate nociceptive transmission in a variety of pain disorders. However, the action of endothelin varies greatly depending on many variables, including pain causes, receptor types (endothelin type A (ET_A) and B (ET_B) receptors) and organs (periphery and spinal cord). Therefore, in this study, we investigated the role of endothelin in a Sprague–Dawley rat model of oxaliplatin-induced neuropathic pain. Intraperitoneal administration of bosentan, a dual ET_A/ET_B receptor antagonist, effectively blocked the development or prevented the onset of both cold allodynia and mechanical allodynia. The preventive effects were exclusively mediated by ET_A receptor antagonism. Intrathecal administration of an ET_A receptor antagonist prevented development of long-lasting mechanical allodynia but not cold allodynia. In marked contrast, an intraplantar ET_A receptor antagonist had a suppressive effect on cold allodynia but only had a partial and transient effect on mechanical allodynia. In conclusion, ET_A receptor antagonism effectively prevented long-lasting mechanical allodynia through spinal and peripheral actions, while cold allodynia was prevented through peripheral actions.

The Nax (SCN7A) channel: an atypical regulator of tissue homeostasis and disease

Within an articulately characterized family of ion channels, the voltage-gated sodium channels, exists a black sheep, SCN7A (Nax). Nax, in contrast to members of its molecular family, has lost its voltage-gated character and instead rapidly evolved a new function as a concentration-dependent sensor of extracellular sodium ions and subsequent signal transducer. As it deviates fundamentally in function from the rest of its family, and since the bulk of the impressive body of literature elucidating the pathology and biochemistry of voltage-gated sodium channels has been performed in nervous tissue, reports of Nax expression and function have been sparse. Here, we investigate available reports surrounding expression and potential roles for Nax activity outside of nervous tissue. With these studies as justification, we propose that Nax likely acts as an early sensor that detects loss of tissue homeostasis through the pathological accumulation of extracellular sodium and/or through endothelin signaling. Sensation of homeostatic aberration via Nax then proceeds to induce pathological tissue phenotypes via promotion of pro-inflammatory and pro-fibrotic responses, induced through direct regulation of gene expression or through the generation of secondary signaling molecules, such as lactate, that can operate in an autocrine or paracrine fashion. We hope that our synthesis of much of the literature investigating this understudied protein will inspire more research into Nax not simply as a biochemical oddity, but also as a potential pathophysiological regulator and therapeutic target.

Inhibition of mite-induced dermatitis, pruritus, and nerve sprouting in mice by the endothelin receptor antagonist bosentan

BACKGROUND

Endothelin-1 (EDN1) can evoke histamine-independent pruritus in mammals and is upregulated in the lesional epidermis of atopic dermatitis (AD). EDN1 increases the production of interleukin 25 (IL-25) from keratinocytes to accelerate T helper type 2 immune deviation. Plasma EDN1 levels are positively correlated with the clinical severity and itch intensity of AD. Therefore, we hypothesized that the inhibition of EDN1 might be useful for treating atopic inflammation and itch and investigated the effects of the topical application of the EDN1 receptor antagonist bosentan on the skin inflammation and itch in a murine AD model.

METHODS

We analyzed the mite-induced AD-like NC/Nga murine model, which was topically applied with bosentan or ethanol control every day for 3 weeks. We also subjected in vitro primary sensory neuron culture systems to nerve elongation and branching assays after EDN1 stimulation.

RESULTS

Topical application of bosentan significantly attenuated the development of mite-induced AD-like skin inflammation, dermatitis scores, ear thickness, scratching bouts, and serum level of thymus and activation-regulated chemokine in NC/Nga mice. Bosentan application also significantly reduced the gene expression of Il13, Il17, and Ifng in the treated lesions. Histologically, the number of infiltrated dermal cells, the epidermal EDN1 expression, and the number of intraepidermal nerve fibers were significantly inhibited upon bosentan application. While EDN1 significantly elongated the neurites of dorsal root ganglion cells in a dose- and time-dependent manner, bosentan treatment attenuated this.

CONCLUSIONS

EDN1 plays a significant role in mite-induced inflammation and itch. Topical bosentan is a potential protective candidate for AD.

A deep dive into UV-based phototherapy: Mechanisms of action and emerging molecular targets in inflammation and cancer

UV-based phototherapy (including psoralen plus UVA (PUVA), UVB and UVA1) has a long, successful history in the management of numerous cutaneous disorders. Photoresponsive diseases are etiologically diverse, but most involve disturbances in local (and occasionally systemic) inflammatory cells and/or abnormalities in keratinocytes that trigger inflammation. UV-based phototherapy works by regulating the inflammatory component and inducing apoptosis of pathogenic cells. This results in a fascinating and complex network of simultaneous events-immediate transcriptional changes in keratinocytes, immune cells, and pigment cells; the emergence of apoptotic bodies; and the trafficking of antigen-presenting cells in skin-that quickly transform the microenvironment of UV-exposed skin. Molecular elements in this system of UV recognition and response include chromophores, metabolic byproducts, innate immune receptors, neurotransmitters and mediators such as chemokines and cytokines, antimicrobial peptides, and platelet activating factor (PAF) and PAF-like molecules that simultaneously shape the immunomodulatory effects of UV and their interplay with the microbiota of the skin and beyond. Phototherapy's key effects-proapoptotic, immunomodulatory, antipruritic, antifibrotic, propigmentary, and pro-prebiotic-promote clinical improvement in various skin diseases such as psoriasis, atopic dermatitis (AD), graft-versus-host disease (GvHD), vitiligo, scleroderma, and cutaneous T-cell lymphoma (CTCL) as well as prevention of polymorphic light eruption (PLE). As understanding of phototherapy improves, new therapies (UV- and non-UV-based) are being developed that will modify regulatory T-cells (Treg), interact with (resident) memory T-cells and /or utilize agonists and antagonists as well as antibodies targeting soluble molecules such as cytokines and chemokines, transcription factors, and a variety of membrane-associated receptors.

Topical application of endothelin receptor a antagonist attenuates imiquimod-induced psoriasiform skin inflammation

Endothelin-1 (ET-1) is well known as the most potent vasoconstrictor, and can evoke histamine-independent pruritus. Recently, its involvement in cutaneous inflammation has begun to draw attention. The upregulation of ET-1 expression in the epidermis of human psoriasis patients has been reported. It was also demonstrated that ET-1 can stimulate dendritic cells to induce Th17/1 immune responses. However, the role of the interaction between ET-1 and ET-1 receptors in the pathogenesis of psoriasis remains elusive. Here, we investigated the effects of ET-1 receptor antagonist on imiquimod (IMQ) -induced psoriasiform dermatitis in mouse. Psoriasis-related cytokines such as IL-17A and TNF-α induced ET-1 expression in human keratinocytes. Topical application of selective endothelin A receptor (ETAR) antagonist ambrisentan significantly attenuated the development of IMQ-induced psoriasiform dermatitis and also significantly inhibited the histological inflammation and cytokine expression (TNF-α, IL-12p40, IL-12 p19, and IL-17) in the lesional skin of the mouse model. Furthermore, topical application of ambrisentan suppressed phenotypic and functional activation of dendritic cells in lymph nodes. Our findings indicate that the ET-1 and ETAR axis plays an important role in the pathogenesis of psoriasis and is a potential therapeutic target for treating psoriasis.

Lifting the veil on the keratinocyte contribution to cutaneous nociception

Cutaneous nociception is essential to prevent individuals from sustaining injuries. According to the conventional point of view, the responses to noxious stimuli are thought to be exclusively initiated by sensory neurons, whose activity would be at most modulated by keratinocytes. However recent studies have demonstrated that epidermal keratinocytes can also act as primary nociceptive transducers as a supplement to sensory neurons. To enlighten our understanding of cutaneous nociception, this review highlights recent and relevant findings on the cellular and molecular elements that underlie the contribution of epidermal keratinocytes as nociceptive modulators and noxious sensors, both under healthy and pathological conditions.

The pruritogenic mediator endothelin-1 shifts the dendritic cell-T-cell response toward Th17/Th1 polarization

Endothelin-1 (ET-1) is associated with skin diseases such as atopic dermatitis (AD) and psoriasis. ET-1 is enhanced in the skin of patients AD and psoriasis. In addition, plasma levels of ET-1 are elevated in AD and psoriasis. Although both AD and psoriasis are T-cell-mediated skin diseases, the association between ET-1 and the T-cell immune response has not been clarified. To evaluate the role of ET-1 in inflammatory skin disease, we sought to investigate the effects of ET-1 on the functions of dendritic cells (DCs) and subsequent immune responses. For this purpose, we immunohistochemically confirmed the upregulation of ET-1 in the epidermis of patients with AD or psoriasis. ET-1 directly induced phenotypic maturation of bone marrow-derived DCs (BMDCs). In addition, ET-1 augmented the production of several cytokines and allogeneic stimulatory capacity of BMDCs. Interestingly, ET-1-activated BMDCs primed T cells to produce Th1 and Th17 cytokines, but not Th2 cytokines. These findings indicate that ET-1 polarizes the DC-T-cell response toward Th17/1 differentiation and may augment the persistent course of inflammatory skin diseases.

Effect of radiation on brain tissue endothelin-1 level and tumor development

BACKGROUND

Radiotherapy causes injury in the endothelial cells of blood vessels and the production of vasoactive amines such as endothelin-1 (ET-1). ET-1 is an important peptide in cancer development. In this study, the effects of radiation on brain tissue ET-1 level were evaluated. Is it possible to suggest a mechanism using ET-1 level in the production of this adverse effect? In this paper, the relationship between the development of brain tumors and the ET-1 level has been discussed.

MATERIALS AND METHODS

Twenty-eight adult Sprague Dawley rats were used in the experiments. The rats were divided into four groups (n = 7) as follows: control group: radiation was not applied during the experiment; Group 1: Decapitated on the 1^st day following radiation; Group 2: Decapitated on the 7^th day following radiation; and Group 3: Decapitated on the 30^th day following radiation. ET-1 levels were measured with enzyme-linked immunosorbent assay (ELISA) method. The t-test, variance analysis, and Tukey honestly significant difference (HSD) tests were used in the statistical analysis. A value of P < 0.05 was accepted as significant.

RESULTS

No statistical differences were observed in the tissue ET-1 levels between the control group and other groups. According to the variance analysis and Tukey test, the differences between the groups were not significant.

CONCLUSION

We observed in this study that the effects of radiation on brain tumor development or malignant transformation are not mediated by ET-1 levels. In addition, these results support the hypothesis of the fact that medical treatment with ET-1 antagonists in clinical cases receiving radiotheraphy is unnecessary.

Mutual upregulation of endothelin-1 and IL-25 in atopic dermatitis

BACKGROUND

Endothelin-1 (ET-1) has been reported to evoke histamine-independent pruritus in mammals. However, its association with pruritus or inflammation of atopic dermatitis (AD) has not been clarified. We sought to investigate the role of ET-1 in the skin inflammation of AD.

METHODS

To examine the role of ET-1 in AD, we investigated the expression of ET-1 and IL-25 in the skin of an AD mouse model and patients with AD and examined the mutual regulatory relationship between ET-1 and IL-25, one of the important cytokines in AD, using the human HaCaT keratinocyte cell line.

RESULTS

We immunohistochemically confirmed the upregulation of ET-1 and IL-25 expression in the epidermis of both the AD mouse model and patients with AD. In vitro, IL-25 upregulated ET-1 mRNA and protein expression in a concentration- and time-dependent fashion in HaCaT cells. This IL-25-induced ET-1 expression was inhibited by ERK1/2 or JNK inhibitor. In a reciprocal manner, ET-1 also induced IL-25 upregulation. The enhancing effect of ET-1 on IL-25 was inhibited by an endothelin A receptor antagonist, ERK1/2 inhibitor, or p38 inhibitor, but not by an endothelin B receptor antagonist or JNK inhibitor.

CONCLUSION

These findings suggest that mutual upregulation of ET-1 and IL-25 takes place in the epidermis of AD, which may be a future target for antipruritic agents.

Mast cells are required for phototolerance induction and scratching abatement

Dermal mast cells protect the skin from inflammatory effects of ultraviolet (UV) radiation and are required for UV-induced immune suppression. We sought to determine a potential mechanistic role of mast cells in reducing the sensitivity to UV radiation (i.e. phototolerance induction) through photohardening. We administered single UV exposures as well as a chronic UV irradiation regime to mast cell-deficient Kit(W-Sh/W-Sh) mice and their controls. The chronic irradiation protocol was similar to that given for prophylaxis in certain photodermatoses in humans. Compared to controls, UV-exposed Kit(W-Sh/W-Sh) mice were more susceptible to epidermal hyperplasia and dermal oedema which was linked to blood vessel dilation. Unexpectedly, Kit(W-Sh/W-Sh) mice exhibited an excessive scratching behaviour following broadband UVB plus UVA or solar simulated UV irradiation at doses far below their minimal skin-swelling dose. Protection from this UV-induced scratching phenotype was dependent on mast cells, as engraftment of bone marrow-derived cultured mast cells abated it entirely. Kit(W-Sh/W-Sh) mice were entirely resistant to phototolerance induction by photohardening treatment. Compared to controls, these mice also showed reduced numbers of regulatory T cells and neutrophils in the skin 24 h after UV irradiation. While it is well known that mast cell-deficient mice are resistant to UV-induced immune suppression, we have discovered that they are prone to develop photo-itch and are more susceptible to UV-induced epidermal hyperplasia and skin oedema.

UVB radiation generates sunburn pain and affects skin by activating epidermal TRPV4 ion channels and triggering endothelin-1 signaling

At our body surface, the epidermis absorbs UV radiation. UV overexposure leads to sunburn with tissue injury and pain. To understand how, we focus on TRPV4, a nonselective cation channel highly expressed in epithelial skin cells and known to function in sensory transduction, a property shared with other transient receptor potential channels. We show that following UVB exposure mice with induced Trpv4 deletions, specifically in keratinocytes, are less sensitive to noxious thermal and mechanical stimuli than control animals. Exploring the mechanism, we find that epidermal TRPV4 orchestrates UVB-evoked skin tissue damage and increased expression of the proalgesic/algogenic mediator endothelin-1. In culture, UVB causes a direct, TRPV4-dependent Ca(2+) response in keratinocytes. In mice, topical treatment with a TRPV4-selective inhibitor decreases UVB-evoked pain behavior, epidermal tissue damage, and endothelin-1 expression. In humans, sunburn enhances epidermal expression of TRPV4 and endothelin-1, underscoring the potential of keratinocyte-derived TRPV4 as a therapeutic target for UVB-induced sunburn, in particular pain.

Dermal mast cells affect the development of sunlight-induced skin tumours

Ultraviolet (UV) radiation contained in sunlight is considered a major risk in the induction of skin cancer. While mast cells are best known for their role in allergic responses, they have also been shown to play a crucial role in suppressing the anti-tumour immune response following UV exposure. Evidence is now emerging that UV may also trigger mast cell release of cutaneous tissue remodelling and pro-angiogenic factors. In this review, we will focus on the cellular and molecular mechanisms by which UV recruits and then activates mast cells to initiate and promote skin cancer development.

At the heart of tissue: endothelin system and end-organ damage

ET (endothelin)-1 was first described as a potent vasoconstrictor. Since then, many other deleterious properties mediated via its two receptors, ETA and ETB, have been described, such as inflammation, fibrosis and hyperplasia. These effects, combined with a wide tissue distribution of the ET system, its up-regulation in pathological situations and a local autocrine/paracrine activity due to a high tissue receptor binding, make the tissue ET system a key local player in end-organ damage. Furthermore, ET-1 interacts in tissues with other systems such as the RAAS (renin-angiotensin-aldosterone system) to exert its effects. In numerous genetically modified animal models, non-specific or organ-targeted ET-1 overexpression causes intense organ damage, especially hypertrophy and fibrosis, in the absence of haemodynamic changes, confirming a local activity of the ET system. ET receptor antagonists have been shown to prevent and sometimes reverse these tissue alterations in an organ-specific manner, leading to long-term benefits and an improvement in survival in different animal models. Potential for such benefits going beyond a pure haemodynamic effect have also been suggested by clinical trial results in which ET receptor antagonism decreased the occurrence of new digital ulcers in patients with systemic sclerosis and delayed the time to clinical worsening in patients with PAH (pulmonary arterial hypertension). The tissue ET system allows therapeutic interventions to provide organ selectivity and beneficial effects in diseases associated with tissue inflammation, hypertrophy or fibrosis.

PGE(2) is a UVR-inducible autocrine factor for human melanocytes that stimulates tyrosinase activation

Prostaglandins activate signalling pathways involved in growth, differentiation and apoptosis. Prostaglandin E(2) (PGE(2)) is released by keratinocytes following ultraviolet irradiation (UVR) and stimulates the formation of dendrites in melanocytes. We show that multiple irradiations of human melanocytes with UVR-activated cPLA(2), the rate-limiting enzyme in eicosanoid synthesis and stimulated PGE(2) secretion. PGE(2) increased cAMP production, tyrosinase activity and proliferation in melanocytes. PGE(2) binds to four distinct G-protein coupled receptors (EP(1-4)). We show that PGE(2) stimulates EP(4) receptor signalling in melanocytes, resulting in cAMP production. Conversely, PGE(2) also stimulated the EP(3) receptor in melanocytes, resulting in lowered basal cAMP levels. These data suggest that relative levels or activity of these receptors controls effects of PGE(2) on cAMP in melanocytes. The data are the first to identify PGE(2) as an UVR-inducible autocrine factor for melanocytes. These data also show that PGE(2) activates EP(3) and EP(4) receptor signalling, resulting in opposing effects on cAMP production, a critical signalling pathway that regulates proliferation and melanogenesis in melanocytes.

High doses of ultraviolet-C irradiation increases vasoactive intestinal contractor/endothelin-2 expression in keratinocytes of the newborn mouse epidermis

We examined the expression profiles of vasoactive intestinal contractor/endothelin-2 (VIC/ET-2) at both gene and peptide level in skin irradiated with different ultraviolet wavelengths. We found that VIC/ET-2 gene expression is sensitive only to ultraviolet-C (UVC) irradiation and has an immediate response. These results provide direct evidence that high doses of UVC irradiation induce an increase in gene expression and protein production of VIC/ET-2 and endothelin (ET) receptors in a dose-dependent manner in epidermal keratinocytes. We suggest that VIC/ET-2 can play an essential role in the maintenance, protection and hyperpigmentation of the epidermis exposed to UVC irradiation from artificial or natural sources.

Endothelin-2/vasoactive Intestinal Contractor via ROCK regulates transglutaminase 1 on differentiation of mouse keratinocytes

We previously found that endothelin-2/vasoactive intestinal contractor (ET-2/VIC) greatly increased in mouse epidermis after birth. In the present study, we evaluated whether ET-2/VIC expression was associated with the calcium-induced differentiation of cultured mouse keratinocytes. The differentiation induction was revealed by morphological change, cornified envelope (CE) formation, and involucrin and transglutaminase 1 (TG 1) expressions. ET-2/VIC gene expression and peptide production subsequently increased in the induction of the differentiation. We also found that Y-27632, a Rho-associated coiled-coil forming protein serine/threonine kinase (ROCK) inhibitor, suppressed up-regulation of ET-2/VIC gene expression, the induction of morphological change, the CE formation, and TG 1 expression, but not involucrin expression. These results indicate new three findings, (1) ET-2/VIC expression increases and has potential as a differentiation marker, (2) ET-2/VIC expression is mediated by ROCK, and (3) the ROCK regulated TG 1 expression, on the calcium-induced differentiation of mouse keratinocytes.

Inflammatory murine skin responses to UV-B light are partially dependent on endothelin-1 and mast cells

Endothelin (ET-1) has been shown to crucially contribute to UV-induced skin responses such as tanning. To test whether ET-1 is also involved in early cutaneous reactions to UV, we assessed ET-1 skin levels in UV-irradiated mice. In correlation with the levels of UV-induced skin inflammation, ET-1 concentrations increased substantially and continually. Moreover, blocking of ET-1 receptors (ETA) resulted in significantly decreased cutaneous inflammation following UV irradiation. When we assessed skin responses to ET-1 injections, we observed prominent mast cell degranulation and mast cell-dependent inflammation. Since mast cells also critically contributed to UV-induced inflammation, we determined the ET-1-dependent inflammatory response to UV in the absence and presence of these cells. Interestingly, ETA blockade did not decrease UV-induced inflammation in mast cell-deficient mice, unless these mice had been adoptively transferred with mast cells before irradiation. This indicates that skin inflammation due to UV irradiation is caused in part by ET-1 acting on skin mast cells.

Differential expression of melanoma-associated growth factors in keratinocytes and fibroblasts by ultraviolet A and ultraviolet B radiation

BACKGROUND

Besides the direct DNA-damaging effects of ultraviolet (UV) radiation on cells, indirect effects on the microenvironment of the skin may facilitate melanoma development. A stimulation of growth factor production by cells in the immediate environment of melanocytes may lead to a paracrine activation and proliferation of melanocytes that in turn become more susceptible to transformation.

OBJECTIVES

We investigated whether the expression of growth factors for melanocytes can be modulated in keratinocytes and fibroblasts by UVA or UVB.

METHODS

After irradiation with different doses of UVA or UVB, protein expression of basic fibroblast growth factor (bFGF), endothelin (ET)-1, transforming growth factor (TGF)-beta1, platelet-derived growth factor (PDGF)-AA, stem cell factor (SCF) and hepatocyte growth factor (HGF) was analysed by quantitative enzyme-linked immunosorbent assay. The mRNA expression of bFGF and ET-1 was analysed by quantitative real-time reverse transcriptase-polymerase chain reaction.

RESULTS

In keratinocytes, UVB and UVA increased bFGF protein levels up to 2.6-fold. This increase was paralleled by elevated mRNA levels. UVB also induced ET-1 protein up to 1.8-fold, while UVA led to an 80% decrease. Secreted TGF-beta1 and PDGF-AA were downregulated by UVA by less than 50%, while there was no significant alteration by UVB. Secreted SCF was not changed significantly by UVA or UVB. In fibroblasts, bFGF protein levels were increased 11-64-fold by UVA and 34-61-fold by UVB. This was paralleled by elevated mRNA levels for bFGF up to 2.7-fold. HGF protein was stimulated by UVA up to 2.8-fold and by UVB up to 6.7-fold, while TGF-beta1 protein was increased up to 2.7-fold by UVB and 1.7-fold by UVA.

CONCLUSIONS

UVA and UVB can stimulate and inhibit the production of growth factors for melanocytes in keratinocytes and fibroblasts dependent on the cell type and wavelength. We show for the first time that UVA and UVB can activate bFGF, HGF and TGF-beta1 in fibroblasts, while bFGF was the most inducible factor both in fibroblasts and in keratinocytes. The induction of bFGF and HGF in fibroblasts by UVA suggests that stroma cells in the dermis may be involved in the UV activation of melanocytes via paracrine ways and thus promote melanoma development.

Pigmentation in basal cell carcinoma involves enhanced endothelin-1 expression

Basal cell carcinoma (BCC) is the most prevalent malignant skin tumor. In Asian patients, marked pigmentation in BCC lesions is often observed. Recently, endothelins (ETs) have been implicated to participate in the pigmentation process of BCC. Therefore, we set out to investigate the involvement of ET in the pigmentation process of BCC and the potential regulators in the pigmentation pathway. We explored the effects of an established BCC cell line on melanocytes. The growth factor profiles of BCC culture supernatant and effects of supernatant on melanocytes were documented. Potential regulators involved in the pigmentation pathway were also studied. The immunohistochemical staining of pigmented and non-pigmented BCC specimens was performed to confirm our in vitro findings. Our results showed that BCC supernatant contained significant amount of ET-1, basic fibroblast growth factor, and nerve growth factor. Furthermore, BCC supernatant stimulated melanin formation of cultured melanocytes. Addition of ET-receptor antagonist abrogated the melanogenic effect of BCC supernatant on melanocytes. Introduction of UVB irradiation decreased the ET-1 secretion by BCC cells. Immunohistochemical staining of the pigmented facial BCC specimens showed prominent expression of ET-1 on pigmented BCC, while the non-pigmented facial BCC specimens showed little ET-1 reactivity. Tumor necrosis factor-alpha (TNF-alpha) staining showed little expression on BCC specimens, regardless of pigmentation status. In summary, our results indicate that enhanced ET-1 expression in pigmented BCC plays an important role in the hyperpigmentation of this tumor. Moreover, this enhanced ET-1 cascade showed little correlation with UV irradiation and TNF-alpha expression in our study.

Proteinase-activated receptor-2 stimulates prostaglandin production in keratinocytes: analysis of prostaglandin receptors on human melanocytes and effects of PGE2 and PGF2alpha on melanocyte dendricity

Prostaglandins (PG) are key mediators of diverse functions in the skin and several reports suggest that PG mediate post-inflammatory pigmentary changes through modulation of melanocyte dendricity and melanin synthesis. The proteinase-activated receptor 2 (PAR-2) is important for skin pigmentation because activation of keratinocyte PAR-2 stimulates uptake of melanosomes through phagocytosis in a Rho-dependent manner. In this report, we show that activation of keratinocyte PAR-2 stimulates release of PGE(2) and PGF(2alpha) and that PGE(2) and PGF(2alpha) act as paracrine factors that stimulate melanocyte dendricity. We characterized the expression of the EP and FP receptors in human melanocytes and show that human melanocytes express EP1 and EP3, and the FP receptor, but not EP2 and EP4. Treatment of melanocytes with EP1 and EP3 receptor agonists resulted in increased melanocyte dendricity, indicating that both EP1 and EP3 receptor signaling contribute to PGE(2)-mediated melanocyte dendricity. Certain EP3 receptor subtypes have been shown to increase adenosine 3',5'-cyclic monophosphate (cAMP) through coupling to Gs, whereas EP1 is known to couple to Gq to activate phospholipase C with elevation in Ca(2+). The cAMP/protein kinase A system is known to modulate melanocyte dendrite formation through modulation of Rac and Rho activity. Neither PGF(2alpha) or PGE(2) elevated cAMP in human melanocytes showing that dendricity observed in response to PGE(2) and PGF(2alpha) is cAMP-independent. Our data suggest that PAR-2 mediates cutaneous pigmentation both through increased uptake of melanosomes by keratinocytes, as well as by release of PGE(2) and PGF(2alpha) that stimulate melanocyte dendricity through EP1, EP3, and FP receptors.

Local injection of a selective endothelin-B receptor agonist inhibits endothelin-1-induced pain-like behavior and excitation of nociceptors in a naloxone-sensitive manner

We showed previously that subcutaneous injection of the injury-associated peptide mediator endothelin-1 (ET-1) into the rat plantar hindpaw produces pain behavior and selective excitation of nociceptors, both through activation of ET(A) receptors likely on nociceptive terminals. The potential role of ET(B) receptor activation in these actions of ET-1-has not been examined. Therefore, in these experiments, we studied the effect of blocking or activating ET(B) receptors on ET-1-induced hindpaw flinching and excitation of nociceptors in rats. An ET(B) receptor-selective antagonist, BQ-788 (3 mm), coinjected with ET-1 (200 microm) reduced the time-to-peak of flinching and significantly enhanced the average maximal flinch frequency (MFF). In contrast, coinjection of an ET(B) receptor selective agonist, IRL-1620 (100 or 200 microm), with ET-1 reduced the average MFF and the average total number of flinches. Interestingly, this unexpected inhibitory effect of IRL-1620 was prevented by the nonselective opioid receptor antagonist naloxone (2.75 mm). To confirm these inhibitory actions, we studied the effects of IRL-1620 on ET-1-induced spike responses in single, physiologically characterized nociceptive C-fibers. IRL-1620 suppressed spike responses to ET-1 in all (n = 12) C-units, with mean and maximum response frequencies of 0.08 +/- 0.02 and 1.5 +/- 0.4 impulses/sec versus 0.32 +/- 0.07 and 4.17 +/- 0.17 impulses/sec for ET-1 alone. In additional support of the behavioral results, coinjection of naloxone (2.75 mm) completely prevented this inhibitory action of IRL-1620. These results establish that ET(B) receptor activation inhibits ET-1-induced pain behavior and nociception in a naloxone-sensitive manner and point to a previously unrecognized dual modulation of acute nociceptive signaling by ET(A) and ET(B) receptors in cutaneous tissues.

Biochemical characterization of endothelin-converting enzyme-1alpha in cultured skin-derived cells and its postulated role in the stimulation of melanogenesis in human epidermis

The vasoconstrictive peptide endothelin-1 (ET-1) is expressed in human epidermis at the gene and protein levels and plays an important role in stimulating pigmentation via its increased secretion by keratinocytes following ultraviolet B (UVB) irradiation. However, one or more biological mechanisms underlying the secretion of ET-1 by keratinocytes in human skin have never been evaluated. In mammalian endothelial cells, a membrane-bound neutral metalloproteinase, termed endothelin-converting enzyme (ECE), catalyzes the specific cleavage of the inactive precursor Big ET to produce mature active ET, which leads in turn to the secretion of ET by those cells. To clarify the potential involvement of ECE in the processing and secretion of ET-1 by human keratinocytes, we synthesized the N-terminal peptide of human ECE-1alpha and generated a rabbit polyclonal antibody (alphaPEPT6) that specifically recognizes ECE-1alpha. Reverse transcription PCR and Western blotting analysis revealed that significant expression of ECE-1 transcripts and ECE-1alpha protein occurs in human keratinocytes. When ECE activity was assayed in extracts of human keratinocytes at pHs ranging from 5.0 to 8.0, the enzymatic profile had an optimal neutral pH of 7.0 and was sharply pH-dependent. Furthermore, when extracts of human keratinocytes were treated with alphaPEPT6, ECE activity was significantly reduced compared with extracts treated with the prebleed serum of alphaPEPT6, which supports the notion that ECE-1alpha is a major metalloproteinase with ECE activity in human keratinocytes. The exogenous addition of the pro-inflammatory cytokine interleukin-1alpha significantly increased expression of ECE-1 transcripts in cultured human keratinocytes, which suggests an association with post-inflammatory hyperpigmentation. Collectively, our results demonstrate for the first time that ECE-1alpha is expressed at significant levels in various types of human skin cells (including keratinocytes) and that it plays a constitutive role in the processing and UVB-inducible secretion of ET-1 by human keratinocytes, which leads to the stimulation of pigmentation in the epidermis.

The expression of endothelin-1 and its binding sites in mouse skin increased after ultraviolet B irradiation or local injection of tumor necrosis factor alpha

Endothelin (ET)-1 is a 21-amino acid peptide which has vasoconstrictor and growth regulatory activity. Recently, cultured keratinocytes have been reported to express ET-1 and its receptor when irradiated by ultraviolet (UV) B. In order to further understand the role of ET-1 in vivo during UVB-induced inflammation, we examined the localization, intensity and time course of the expression levels of ET-1 and its binding sites in UVB-exposed BALB/c mouse skin. Frozen and paraffin sections prepared from mouse skin 48 h after treatment with UVB irradiation (0.36 or 0.72 J/cm2) or after injection with tumor necrosis factor (TNF)-alpha (1.0 microgram) or interleukin (IL)-1 alpha (0.05 microgram) were incubated with monoclonal anti-ET-1 IgG and then visualized by peroxidase staining. In normal skin, faint ET-1 immunoreactivity was observed in the epidermis, pilosebaceous structures and blood vessels. Upon exposure to UVB irradiation or administration of TNF-alpha injection or IL-1 alpha injection, such immunoreactivity was found to be significantly enhanced. Subsequently, the frozen sections were incubated with 125I ET-1 for 30 min, and visualized by autoradiographic technique. In normal skin, ET-1 weakly bound to the skin, while UVB irradiation and TNF-alpha injection significantly enhanced ET-1 binding in the epidermis, pilosebaceous structures and blood vessels. Time course experiments (1, 2, 4 and 7 days) indicated that ET-1 immunoreactivity and ET-1 binding peaked 1 or 2 days after UVB irradiation or TNF-alpha injection. These results suggest that the up-regulated expression of ET-1 and its binding sites in the epidermis and pilosebaceous structures may act as an autocrine/paracrine factor during UVB-induced inflammation.

Increase of particulate nitric oxide synthase activity and peroxynitrite synthesis in UVB-irradiated keratinocyte membranes

Here we demonstrate that human keratinocytes possess a Ca2+/calmodulin-dependent particulate NO synthase that can be activated to release NO after exposure to UVB radiation. UVB irradiation (up to 20 mJ/cm2) of human keratinocyte plasma membranes resulted in a dose-dependent increase in NO and L-[3H]citrulline production that was inhibited by approx. 90% in the presence of N-monomethyl-L-arginine (L-NMMA). In time-course experiments with UVB-irradiated plasma membranes the changes in NO production were followed by analogous changes in soluble guanylate cyclase (sGC) activity. In reconstitution experiments, when particulate NO synthase was added to purified sGC isolated from keratinocyte cytosol, a 4-fold increase in cGMP was observed; the cGMP was increased by NO synthesized after UVB irradiation (up to 20 mJ/cm2) of particulate NO synthase. A 5-fold increase in superoxide (O2-) and a 7-fold increase in NO formation followed by an 8-fold increase in peroxynitrite (ONOO-) production by UVB (20 mJ/cm2)-irradiated keratinocyte microsomes was observed. UVB radiation (20 mJ/cm2) decreased plasma membrane lipid fluidity as indicated by steady-state fluorescence anisotropy. Membrane fluidity changes were prevented by L-NMMA. Changes in Arrhenius plots of particulate NO synthase in combination with changes in its allosteric properties induced by UVB radiation are consistent with a decreased fluidity of the lipid microenvironment of the enzyme. The present studies provide important new clues to the role of NO and ONOO- released by UVB-irradiated human keratinocytes in skin erythema and inflammation.