A plaidoyer for cutaneous enzymology: our view of some important unanswered questions on the contributions of selected key enzymes to epidermal homeostasis

Fad Diets Past and Present - Including Taurine for Psoriasis, Diet Therapy for Atopic Dermatitis and the Role of Elimination Diets

The impact of diets and foods on cutaneous afflictions has never been a moot point. The number of enquiries from patients and the wider public about how certain foods have impacted upon, or indeed, caused their skin eruption is increasing. While this inquisition is at the forefront of people's and physicians mind in today's modern practice, this has long been a discussion in the scientific world. Metchnikoff alluded to this at the turn of the 20^th century. How foods and certain dietary programs impact on diseases has been postulated, although there is still more to learn, despite the patient's advocacy for a particular dietary regime. The study of the role of the microbiome is increasing. Gut dysbiosis, along with the interaction of the gastrointestinal tract, skin, and brain - gut-skin-brain axis is discussed . The role and impact of neuroendocrine transmitters and the skin are explored.

Involvement of the nuclear structural proteins in aging-related responses of human skin to the environmental stress

Human skin is a stratified endocrine organ with primary roles in protection against detrimental biochemical and biophysical factors in the environment. Environmental stress causes gradual accumulation of the macromolecular damage and clinical manifestations consistent with chronic inflammatory conditions and premature aging of the skin. Structural proteins of cell nucleus, the nuclear lamins and lamina-associated proteins, play an important role in the regulation of a number of signal transduction pathways associated with stress. The nuclear lamina proteins have been implicated in a number of degenerative disorders with frequent clinical manifestations of the skin conditions related to premature aging. Analysis of the molecular signatures in response of the skin to a range of damaging factors not only points at the likely involvement of the nuclear lamina in transmission of the signals between the environment and cell nucleus but also defines skin's sensitivity to stress, and therefore the capacities to counteract external damage in aging.

The gut-skin axis in health and disease: A paradigm with therapeutic implications

As crucial interface organs gut and skin have much in common. Therefore it is unsurprising that several gut pathologies have skin co-morbidities. Nevertheless, the reason for this remains ill explored, and neither mainstream gastroenterology nor dermatology research have systematically investigated the 'gut-skin axis'. Here, in reviewing the field, we propose several mechanistic levels on which gut and skin may interact under physiological and pathological circumstances. We focus on the gut microbiota, with its huge metabolic capacity, and the role of dietary components as potential principle actors along the gut-skin axis. We suggest that metabolites from either the diet or the microbiota are skin accessible. After defining open key questions around the nature of these metabolites, how they are sensed, and which cutaneous changes they can induce, we propose that understanding of these pathways will lead to novel therapeutic strategies based on targeting one organ to improve the health of the other.

Ultraviolet Radiation-Induced Skin Aging: The Role of DNA Damage and Oxidative Stress in Epidermal Stem Cell Damage Mediated Skin Aging

Skin is the largest human organ. Skin continually reconstructs itself to ensure its viability, integrity, and ability to provide protection for the body. Some areas of skin are continuously exposed to a variety of environmental stressors that can inflict direct and indirect damage to skin cell DNA. Skin homeostasis is maintained by mesenchymal stem cells in inner layer dermis and epidermal stem cells (ESCs) in the outer layer epidermis. Reduction of skin stem cell number and function has been linked to impaired skin homeostasis (e.g., skin premature aging and skin cancers). Skin stem cells, with self-renewal capability and multipotency, are frequently affected by environment. Ultraviolet radiation (UVR), a major cause of stem cell DNA damage, can contribute to depletion of stem cells (ESCs and mesenchymal stem cells) and damage of stem cell niche, eventually leading to photoinduced skin aging. In this review, we discuss the role of UV-induced DNA damage and oxidative stress in the skin stem cell aging in order to gain insights into the pathogenesis and develop a way to reduce photoaging of skin cells.

Yokukansan, a traditional Japanese medicine, adjusts glutamate signaling in cultured keratinocytes

Glutamate plays an important role in skin barrier signaling. In our previous study, Yokukansan (YKS) affected glutamate receptors in NC/Nga mice and was ameliorated in atopic dermatitis lesions. The aim of this study was to assess the effect of YKS on skin and cultured human keratinocytes. Glutamate concentrations in skin of YKS-treated and nontreated NC/Nga mice were measured. Then, glutamate release from cultured keratinocytes was measured, and extracellular glutamate concentrations in YKS-stimulated cultured human keratinocytes were determined. The mRNA expression levels of NMDA receptor 2D (NMDAR2D) and glutamate aspartate transporter (GLAST) were also determined in YKS-stimulated cultured keratinocytes. The glutamate concentrations and dermatitis scores increased in conventional mice, whereas they decreased in YKS-treated mice. Glutamate concentrations in cell supernatants of cultured keratinocytes increased proportionally to the cell density. However, they decreased dose-dependently with YKS. YKS stimulation increased NMDAR2D in a concentration-dependent manner. Conversely, GLAST decreased in response to YKS. Our findings indicate that YKS affects peripheral glutamate signaling in keratinocytes. Glutamine is essential as a transmitter, and dermatitis lesions might produce and release excess glutamate. This study suggests that, in keratinocytes, YKS controls extracellular glutamate concentrations, suppresses N-methyl-D-aspartate (NMDA) receptors, and activates glutamate transport.

A neuroendocrinological perspective on human hair follicle pigmentation

The role of neurohormones and neuropeptides in human hair follicle (HF) pigmentation extends far beyond the control of melanin synthesis by α-MSH and ACTH and includes melanoblast differentiation, reactive oxygen species scavenging, maintenance of HF immune privilege, and remodeling of the HF pigmentary unit (HFPU). It is now clear that human HFs are not only a target of multiple neuromediators, but also are a major non-classical production site for neurohormones such as CRH, proopiomelanocortin, ACTH, α-MSH, ß-endorphin, TRH, and melatonin. Moreover, human HFs have established a functional peripheral equivalent of the hypothalamic-pituitary-adrenal axis. By charting the author's own meanderings through the jungle of hair pigmentation research, the current perspectives essay utilizes four clinical observations - hair repigmentation, canities, poliosis, and 'overnight greying'- as points of entry into the enigmas and challenges of .pigmentary HF neuroendocrinology. After synthesizing key principles and defining major open questions in the field, selected research avenues are delineated that appear clinically most promising. In this context, novel neuroendocrinological strategies to retard or reverse greying and to reduce damage to the HFPU are discussed.

Keratinocytes: a source of the transmitter L-glutamate in the epidermis

Various glutamate receptors have been described in both keratinocytes and melanocytes. L-Glutamate is the physiological agonist of the glutamate receptor family. The source of this transmitter had not yet been identified. In normal human epidermal keratinocytes (NHEK) and HaCaT-keratinocytes, cell supernatants were sampled in various stages of cell density and the l-glutamate content photometrically determined. The following examination time-points were defined: non-confluent (ca. 33%), subconfluent (ca. 70%) and confluent (90-100%). The L-glutamate concentration originally in the culture medium was 14.7 mg/l (0.1 mm/l). The L-glutamate concentration in the cell supernatant increased in NHEK with increasing cell density: non-confluent 39.9 + or - 4 mg/l, subconfluent 60.6 + or - 15.8 mg/l, confluent 100.7 + or - 33.2 mg/l. A linear increase of L-glutamate concentration was also found for HaCaT cells. The investigations show that keratinocytes are capable of producing and releasing L-glutamate. Thus they are a source of L-glutamate which acts as a transmitter on epidermal glutamate receptors.

Impact of NAD(P)H:quinone oxidoreductase-1 on pigmentation

We obtained metastasized melanoma tissue from a primary acral lentiginous melanoma (ALM) patient and established a melanoma cell line named primary culture of melanoma cell derived from lymph node (PML)-1. PML-1 cells had a light brown color and decreased the expression of melanogenesis markers, including tyrosinase (TYR), microphthalmia-associated transcription factor, and tyrosinase-related protein-1. To identify genes differentially regulated in PML-1 melanoma cells, we performed DNA microarray and two-dimensional matrix-assisted laser desorption ionization-time of flight mass spectrometry analyses. Among the candidate genes identified, we chose NAD(P)H:quinone oxidoreductase-1 (NQO1) for further study. Reverse transcription-PCR and western blot analyses showed that NQO1 was markedly decreased in PML-1 cells and in several amelanotic melanoma cell lines. To investigate whether NQO1 affects the melanogenesis, we treated the cultured normal human melanocytes (NHMC) and zebrafish with NQO1 inhibitors, ES936 and dicoumarol. Interestingly, melanogenesis was significantly decreased by the addition of NQO1 inhibitors in both NHMC and zebrafish models. In contrast, overexpression of NQO1 using a recombinant adenovirus clearly induced melanogenesis, concomitantly with an increase of TYR protein level. These results suggest that NQO1 is a positive regulator of the pigmentation process.

What are melanocytes really doing all day long...?

Everyone knows and seems to agree that melanocytes are there to generate melanin - an intriguing, but underestimated multipurpose molecule that is capable of doing far more than providing pigment and UV protection to skin (1). What about the cell that generates melanin, then? Is this dendritic, neural crest-derived cell still serving useful (or even important) functions when no-one looks at the pigmentation of our skin and its appendages and when there is essentially no UV exposure? In other words, what do epidermal and hair follicle melanocytes do in their spare time - at night, under your bedcover? How much of the full portfolio of physiological melanocyte functions in mammalian skin has really been elucidated already? Does the presence or absence of melanocytes matter for normal epidermal and/or hair follicle functions (beyond pigmentation and UV protection), and for skin immune responses? Do melanocytes even deserve as much credit for UV protection as conventional wisdom attributes to them? In which interactions do these promiscuous cells engage with their immediate epithelial environment and who is controlling whom? What lessons might be distilled from looking at lower vertebrate melanophores and at extracutaneous melanocytes in the endeavour to reveal the 'secret identity' of melanocytes? The current Controversies feature explores these far too infrequently posed, biologically and clinically important questions. Complementing a companion viewpoint essay on malignant melanocytes (2), this critical re-examination of melanocyte biology provides a cornucopia of old, but under-appreciated concepts and novel ideas on the slowly emerging complexity of physiological melanocyte functions, and delineates important, thought-provoking questions that remain to be definitively answered by future research.