Many chameleons, and panther chameleons in particular, have the remarkable ability to exhibit complex and rapid colour changes during social interactions such as male contests or courtship. It is ...generally interpreted that these changes are due to dispersion/aggregation of pigment-containing organelles within dermal chromatophores. Here, combining microscopy, photometric videography and photonic band-gap modelling, we show that chameleons shift colour through active tuning of a lattice of guanine nanocrystals within a superficial thick layer of dermal iridophores. In addition, we show that a deeper population of iridophores with larger crystals reflects a substantial proportion of sunlight especially in the near-infrared range. The organization of iridophores into two superposed layers constitutes an evolutionary novelty for chameleons, which allows some species to combine efficient camouflage with spectacular display, while potentially providing passive thermal protection.
•Cutaneous pigmentation is regulated by a complex dermal-epidermal network.•Fibroblasts interact with melanocytes via the synthesis of biochemical factors.•Fibroblasts-derived factors bind to ...melanocyte receptors and modulate intracellular melanogenic pathways.•The importance of fibroblasts-derived factors is demonstrated by skin pigmentary changes.
Dermal fibroblasts are traditionally recognized as synthesizing, remodeling and depositing collagen and extracellular matrix, the structural framework for tissues, helping to bring thickness and firmness to the skin. However, the role of fibroblasts on skin pigmentation arouses concern recently. More is known about the interactions between epidermal melanocytes and keratinocytes.
This review highlights the importance of fibroblast-derived melanogenic paracrine mediators in the regulation of melanocyte activities. Fibroblasts act on melanocytes directly and indirectly through neighboring cells by secreting a large number of cytokines (SCF), proteins (DKK1, sFRP, Sema7a, CCN, FAP-α) and growth factors (KGF, HGF, bFGF, NT-3, NRG-1, TGF-β) which bind to receptors and modulate intracellular signaling cascades (MAPK/ERK, cAMP/PKA, Wnt/β-catenin, PI3K/Akt) related to melanocyte functions. These factors influence the growth, the pigmentation of melanocytes via the expression of melanin-producing enzymes and melanosome transfer, as well as their dendricity, mobility and adhesive properties. Thus, fibroblasts are implicated in both skin physiological and pathological pigmentation. In order to investigate their contribution, various in vitro models have been developed, based on cellular senescence. UV exposure, a major factor implicated in pigmentary disorders, may affect the secretory crosstalk between dermal and epithelial cells.
Therefore, identification of the interactions between fibroblasts and melanocytes could provide novel insights not only for the development of melanogenic agents in the clinical and cosmetic fields, but also for a better understanding of the melanocyte biology and melanogenesis regulation.
Skin pigmentation is a classic example of a polygenic trait that has experienced directional selection in humans. Genome-wide association studies have identified well over a hundred ...pigmentation-associated loci, and genomic scans in present-day and ancient populations have identified selective sweeps for a small number of light pigmentation-associated alleles in Europeans. It is unclear whether selection has operated on all of the genetic variation associated with skin pigmentation as opposed to just a small number of large-effect variants. Here, we address this question using ancient DNA from 1,158 individuals from West Eurasia covering a period of 40,000 y combined with genome-wide association summary statistics from the UK Biobank. We find a robust signal of directional selection in ancient West Eurasians on 170 skin pigmentation-associated variants ascertained in the UK Biobank. However, we also show that this signal is driven by a limited number of large-effect variants. Consistent with this observation, we find that a polygenic selection test in present-day populations fails to detect selection with the full set of variants. Our data allow us to disentangle the effects of admixture and selection. Most notably, a large-effect variant at
was introduced to Western Europe by migrations of Neolithic farming populations but continued to be under selection post-admixture. This study shows that the response to selection for light skin pigmentation in West Eurasia was driven by a relatively small proportion of the variants that are associated with present-day phenotypic variation.
The primary biological role of human skin pigmentation is as a mediator of penetration of ultraviolet radiation (UVR) into the deep layers of skin and the cutaneous circulation. Since the origin of ...Homo sapiens, dark, protective constitutive pigmentation and strong tanning abilities have been favored under conditions of high UVR and represent the baseline condition for modern humans. The evolution of partly depigmented skin and variable tanning abilities has occurred multiple times in prehistory, as populations have dispersed into environments with lower and more seasonal UVR regimes, with unique complements of genes and cultural practices. The evolution of extremes of dark pigmentation and depigmentation has been rare and occurred only under conditions of extremely high or low environmental UVR, promoted by positive selection on variant pigmentation genes followed by limited gene flow. Over time, the evolution of human skin pigmentation has been influenced by the nature and course of human dispersals and modifications of cultural practices, which have modified the nature and actions of skin pigmentation genes. Throughout most of prehistory and history, the evolution of human skin pigmentation has been a contingent and non‐deterministic process.
Skin complexion is among the most recognizable phenotypes between individuals and is mainly determined by the amount and type of melanin pigment deposited in the epidermis. Persons with dark skin ...complexion have more of a brown/black pigment known as eumelanin in their epidermis whereas those with fair skin complexions have less. Epidermal eumelanin acts as a natural sunblock by preventing incoming UV photons from penetrating into the skin and therefore protects against UV mutagenesis. By understanding the signaling pathways and regulation of pigmentation, strategies can be developed to manipulate skin pigmentation to improve UV resistance and to diminish skin cancer risk.
Ultraviolet (UV)‐induced pigmentation is very common in clinical practice, but the current treatments are rarely effective, accompanied by some side effects. Ganoderma lucidum polysaccharide (GLP) is ...a natural antioxidant with no toxic side effects, which can antagonize UVB‐induced fibroblast photo aging. The study aims to explore the role of GLP in inhibiting UVB‐induced melanogenesis and its possible mechanism. The expression of melanogenesis genes such as microphthalmia‐associated transcription factor (MITF), tyrosine (TYR), tyrosinase related protein 1 (TYRP1), tyrosinase related protein 2 (TYRP2), ras‐related protein Rab‐27A (Rab27A), and Myosin shows an upward trend after exposure of B16F10 and PIG1 cells to UVB irradiation, but GLP can downregulate the expression of genes related to UVB‐induced melanogenesis. GLP can inhibit UVB‐activated protein kinase A (PKA) and mitogen‐activated protein kinase (MAPK) signaling pathways. Besides, GLP protects mitochondria from UVB damage and inhibits reactive oxygen species (ROS) production. Also, UVB‐induced cyclic adenosine monophosphate (cAMP) can be inhibited. It has been found in the experiments of UVB‐induced skin pigmentation in zebrafish that GLP is capable of inhibiting UVB‐induced skin pigmentation. Meanwhile, it can greatly relieve erythema reaction in guinea pig skin caused by high‐dosage UVB irradiation. In conclusion, this study shows that GLP can inhibit UVB‐induced melanogenesis by antagonizing cAMP/PKA and ROS/MAPK signaling pathways and is a potential natural safe whitening sunscreen additive.
This study is the first to explore the role of Ganoderma lucidum polysaccharide (GLP) in inhibiting Ultraviolet B (UVB)‐induced melanogenesis and its possible mechanism. we found that GLP could inhibit UVB‐induced melanogenesis by antagonizing cyclic adenosine monophosphate/protein kinase A (cAMP/PKA) and reactive oxygen species/mitogen‐activated protein kinase (ROS/MAPK) signaling pathways and is a potential natural safe whitening sunscreen additive
Ultraviolet (UV) light and incompletely understood genetic and epigenetic variations determine skin color. Here we describe an UV- and microphthalmia-associated transcription factor ...(MITF)-independent mechanism of skin pigmentation. Targeting the mitochondrial redox-regulating enzyme nicotinamide nucleotide transhydrogenase (NNT) resulted in cellular redox changes that affect tyrosinase degradation. These changes regulate melanosome maturation and, consequently, eumelanin levels and pigmentation. Topical application of small-molecule inhibitors yielded skin darkening in human skin, and mice with decreased NNT function displayed increased pigmentation. Additionally, genetic modification of NNT in zebrafish alters melanocytic pigmentation. Analysis of four diverse human cohorts revealed significant associations of skin color, tanning, and sun protection use with various single-nucleotide polymorphisms within NNT. NNT levels were independent of UVB irradiation and redox modulation. Individuals with postinflammatory hyperpigmentation or lentigines displayed decreased skin NNT levels, suggesting an NNT-driven, redox-dependent pigmentation mechanism that can be targeted with NNT-modifying topical drugs for medical and cosmetic purposes.
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•Identification of a redox-dependent skin pigmentation mechanism•Modification of NNT affects ubiquitin-proteasome-mediated tyrosinase degradation•Alteration of NNT levels affects skin pigmentation through melanosome maturation•Human NNT SNPs are associated with skin pigmentation, tanning, and use of sun protection
Nicotinamide nucleotide transhydrogenase (NNT) is a mitochondrial redox-regulating enzyme that mediates pigmentation via a UVB- and MITF-independent mechanism.
The production of melanin pigments by melanocytes and their quantity, quality, and distribution play a decisive role in determining human skin, eye, and hair color, and protect the skin from adverse ...effects of ultraviolet radiation (UVR) and oxidative stress from various environmental pollutants. Melanocytes reside in the basal layer of the interfollicular epidermis and are compensated by melanocyte stem cells in the follicular bulge area. Various stimuli such as eczema, microbial infection, ultraviolet light exposure, mechanical injury, and aging provoke skin inflammation. These acute or chronic inflammatory responses cause inflammatory cytokine production from epidermal keratinocytes as well as dermal fibroblasts and other cells, which in turn stimulate melanocytes, often resulting in skin pigmentation. It is confirmed by some recent studies that several interleukins (ILs) and other inflammatory mediators modulate the proliferation and differentiation of human epidermal melanocytes and also promote or inhibit expression of melanogenesis-related gene expression directly or indirectly, thereby participating in regulation of skin pigmentation. Understanding of mechanisms of skin pigmentation due to inflammation helps to elucidate the relationship between inflammation and skin pigmentation regulation and can guide development of new therapeutic pathways for treating pigmented dermatosis. This review covers the mechanistic aspects of skin pigmentation caused by inflammation.
Interventions for vitiligo Whitton, Maxine E; Pinart, Mariona; Batchelor, Jonathan ...
Cochrane database of systematic reviews,
02/2015
2
Journal Article
Recenzirano
Odprti dostop
Vitiligo is a chronic skin disorder characterised by patchy loss of skin colour. Some people experience itching before the appearance of a new patch. It affects people of any age or ethnicity, more ...than half of whom develop it before the age of 20 years. There are two main types: generalised vitiligo, the common symmetrical form, and segmental, affecting only one side of the body. Around 1% of the world's population has vitiligo, a disease causing white patches on the skin. Several treatments are available. Some can restore pigment but none can cure the disease.
To assess the effects of all therapeutic interventions used in the management of vitiligo.
We updated our searches of the following databases to October 2013: the Cochrane Skin Group Specialised Register, CENTRAL in The Cochrane Library (2013, Issue 10), MEDLINE, Embase, AMED, PsycINFO, CINAHL and LILACS. We also searched five trials databases, and checked the reference lists of included studies for further references to relevant randomised controlled trials (RCTs).
Randomised controlled trials (RCTs) assessing the effects of treatments for vitiligo.
At least two review authors independently assessed study eligibility and methodological quality, and extracted data.
This update of the 2010 review includes 96 studies, 57 from the previous update and 39 new studies, totalling 4512 participants. Most of the studies, covering a wide range of interventions, had fewer than 50 participants. All of the studies assessed repigmentation, however only five reported on all of our three primary outcomes which were quality of life, > 75% repigmentation and adverse effects. Of our secondary outcomes, six studies measured cessation of spread but none assessed long-term permanence of repigmentation resulting from treatment at two years follow-up.Most of the studies assessed combination therapies which generally reported better results. New interventions include seven new surgical interventions.We analysed the data from 25 studies which assessed our primary outcomes. We used the effect measures risk ratio (RR), and odds ratio (OR) with their 95% confidence intervals (CI) and where N is the number of participants in the study.We were only able to analyse one of nine studies assessing quality of life and this showed no statistically significant improvement between the comparators.Nine analyses from eight studies reported >75% repigmentation. In the following studies the repigmentation was better in the combination therapy group: calcipotriol plus PUVA (psoralen with UVA light) versus PUVA (paired OR 4.25, 95% CI 1.43 to 12.64, one study, N = 27); hydrocortisone-17-butyrate plus excimer laser versus excimer laser alone (RR 2.57, 95% CI 1.20 to 5.50, one study, N = 84); oral minipulse of prednisolone (OMP) plus NB-UVB (narrowband UVB) versus OMP alone (RR 7.41, 95% CI 1.03 to 53.26, one study, N = 47); azathioprine with PUVA versus PUVA alone (RR 17.77, 95% CI 1.08 to 291.82, one study, N = 58) and 8-Methoxypsoralen (8-MOP ) plus sunlight versus psoralen (RR 2.50, 95% CI 1.06 to 5.91, one study, N = 168). In these three studies ginkgo biloba was better than placebo (RR 4.40, 95% CI 1.08 to 17.95, one study, N = 47); clobetasol propionate was better than PUVAsol (PUVA with sunlight) (RR 4.70, 95% CI 1.14 to 19.39, one study, N = 45); split skin grafts with PUVAsol was better than minipunch grafts with PUVAsol (RR 1.89, 95% CI 1.25 to 2.85, one study, N = 64).We performed one meta-analysis of three studies, in which we found a non-significant 60% increase in the proportion of participants achieving >75% repigmentation in favour of NB-UVB compared to PUVA (RR 1.60, 95% CI 0.74 to 3.45; I² = 0%).Studies assessing topical preparations, in particular topical corticosteroids, reported most adverse effects. However, in combination studies it was difficult to ascertain which treatment caused these effects. We performed two analyses from a pooled analysis of three studies on adverse effects. Where NB-UVB was compared to PUVA, the NB-UVB group reported less observations of nausea in three studies (RR 0.13, 95% CI 0.02 to 0.69; I² = 0% three studies, N = 156) and erythema in two studies (RR 0.73, 95% CI 0.55 to 0.98; I² = 0%, two studies, N = 106), but not itching in two studies (RR 0.57, 95% CI 0.20 to 1.60; I² = 0%, two studies, N = 106).Very few studies only assessed children or included segmental vitiligo. We found one study of psychological interventions but we could not include the outcomes in our statistical analyses. We found no studies evaluating micropigmentation, depigmentation, or cosmetic camouflage.
This review has found some evidence from individual studies to support existing therapies for vitiligo, but the usefulness of the findings is limited by the different designs and outcome measurements and lack of quality of life measures. There is a need for follow-up studies to assess permanence of repigmentation as well as high- quality randomised trials using standardised measures and which also address quality of life.
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