Geographical ancestry is a key determinant of epidermal morphology and dermal composition

Exploring physiological differences in injury response by skin tone: A scoping review

AIM

To explore existing literature examining physiological differences in pressure ulcer response among individuals with differing skin tones.

METHODS

This was a scoping review. Articles meeting the inclusion criteria were retrieved from electronic databases including PubMed, CINAHL, Scopus, Cochrane, and EMBASE, using the keywords "pressure ulcer," "skin pigmentation," "melanin," and "risk factor." Data were extracted using a predesigned data extraction tool and analysed using a narrative synthesis.

RESULTS

Five papers met the inclusion criteria. Analysis of findings suggests there are potential mechanisms which may influence the skin's ability to withstand mechanical stress and its inflammatory response to damage among those with different skin tones; the structure of the stratum corneum, collagen density, fibroblast activity, mast cell density, and transepidermal water loss (TEWL). The stratum corneum can compromise skin resilience, while collagen density and fibroblast activity may impact skin strength and repair. Mast cells affect inflammation, which can exacerbate pressure ulcer damage, and increased TEWL in those with dark skin tones can result in lower water content in the stratum corneum, affecting hydration.Conversely, factors like melanosome size, hair follicle and hair fiber characteristics, sebaceous gland activity, vitamin D production, UVR protection, and desquamation rate, although relevant to overall skin health, may not directly affect the mechanical processes leading to pressure ulcer formation.

CONCLUSIONS

Physiological differences in skin structure may contribute to alterations in the response to pressure ulcer development among individuals with dark skin. Recognising these differences is important for targeted prevention strategies within diverse populations. However, further research is needed to explore the mechanisms underlying this association in greater detail.

Retinoids in the treatment of photoageing: A histological study of topical retinoid efficacy in black skin

BACKGROUND

Photoageing describes complex cutaneous changes that occur due to chronic exposure to solar ultraviolet radiation (UVR). The 'gold standard' for the treatment of photoaged white skin is all-trans retinoic acid (ATRA); however, cosmetic retinol (ROL) has also proven efficacious. Recent work has identified that black skin is susceptible to photoageing, characterized by disintegration of fibrillin-rich microfibrils (FRMs) at the dermal-epidermal junction (DEJ). However, the impact of topical retinoids for repair of black skin has not been well investigated.

OBJECTIVES

To determine the potential of retinoids to repair photoaged black skin.

METHODS

An exploratory intervention study was performed using an in vivo, short-term patch test protocol. Healthy but photoaged black volunteers (>45 years) were recruited to the study, and participant extensor forearms were occluded with either 0.025% ATRA (n = 6; 4-day application due to irritancy) or ROL (12-day treatment protocol for a cosmetic) at concentrations of 0.3% (n = 6) or 1% (n = 6). Punch biopsies from occluded but untreated control sites and retinoid-treated sites were processed for histological analyses of epidermal characteristics, melanin distribution and dermal remodelling.

RESULTS

Treatment with ATRA and ROL induced significant acanthosis (all p < 0.001) accompanied by a significant increase in keratinocyte proliferation (Ki67; all p < 0.01), dispersal of epidermal melanin and restoration of the FRMs at the DEJ (all p < 0.01), compared to untreated control.

CONCLUSIONS

This study confirms that topical ATRA has utility for the repair of photoaged black skin and that ROL induces comparable effects on epidermal and dermal remodelling, albeit over a longer timeframe. The effects of topical retinoids on black photoaged skin are similar to those reported for white photoaged skin and suggest conserved biology in relation to repair of UVR-induced damage. Further investigation of topical retinoid efficacy in daily use is warranted for black skin.

Prediction, screening and characterization of novel bioactive tetrapeptide matrikines for skin rejuvenation

BACKGROUND

Extracellular matrices play a critical role in tissue structure and function and aberrant remodelling of these matrices is a hallmark of many age-related diseases. In skin, loss of dermal collagens and disorganization of elastic fibre components are key features of photoageing. Although the application of some small matrix-derived peptides to aged skin has been shown to beneficially affect in vitro cell behaviour and, in vivo, molecular architecture and clinical appearance, the discovery of new peptides has lacked a guiding hypothesis.

OBJECTIVES

To identify, using protease cleavage site prediction, novel putative matrikines with beneficial activities for skin composition and structure.

METHODS

Here, we present an in silico (peptide cleavage prediction) to in vitro (proteomic and transcriptomic activity testing in cultured human dermal fibroblasts) to in vivo (short-term patch test and longer-term split-face clinical study) discovery pipeline, which enables the identification and characterization of peptides with differential activities.

RESULTS

Using this pipeline we showed that cultured fibroblasts were responsive to all applied peptides, but their associated bioactivity was sequence-dependent. Based on bioactivity, toxicity and protein source, we further characterized a combination of two novel peptides, GPKG (glycine-proline-lysine-glycine) and LSVD (leucine-serine-valine-aspartate), that acted in vitro to enhance the transcription of matrix -organization and cell proliferation genes and in vivo (in a short-term patch test) to promote processes associated with epithelial and dermal maintenance and remodelling. Prolonged use of a formulation containing these peptides in a split-face clinical study led to significantly improved measures of crow's feet and firmness in a mixed population.

CONCLUSIONS

This approach to peptide discovery and testing can identify new synthetic matrikines, providing insights into biological mechanisms of tissue homeostasis and repair and new pathways to clinical intervention.

Rete ridges: Morphogenesis, function, regulation, and reconstruction

Rete ridges (RRs) are distinct undulating microstructures at the junction of the dermis and epidermis in the skin of humans and certain animals. This structure is essential for enhancing the mechanical characteristics of skin and preserving homeostasis. With the development of tissue engineering and regenerative medicine, artificial skin grafts have made great progress in the field of skin healing. However, the restoration of RRs has been often disregarded or absent in artificial skin grafts, which potentially compromise the efficacy of tissue repair and regeneration. Therefore, this review collates recent research advances in understanding the structural features, function, morphogenesis, influencing factors, and reconstruction strategies pertaining to RRs. In addition, the preparation methods and limitations of tissue-engineered skin with RRs are discussed. STATEMENT OF SIGNIFICANCE: The technology for the development of tissue-engineered skin (TES) is widely studied and reported; however, the preparation of TES containing rete ridges (RRs) is often ignored, with no literature reviews on the structural reconstruction of RRs. This review focuses on the progress pertaining to RRs and focuses on the reconstruction methods for RRs. In addition, it discusses the limitations of existing reconstruction methods. Therefore, this review could be a valuable reference for transferring TES with RR structure from the laboratory to clinical applications in skin repair.

Variations in genetics, biology, and phenotype of cutaneous disorders in skin of color - Part I: Genetic, biologic, and structural differences in skin of color

Skin of color (SOC) populations include those who identify as Black/African, Hispanic/Latinx, Asian/Pacific Islander, American Indian/Native Alaskan, Indigenous Australian, Middle Eastern, biracial/multiracial, or non-White; this list is far from exhaustive and may vary between and within cultures. Recent genetic and immunological studies have suggested that cutaneous inflammatory disorders (atopic dermatitis, psoriasis, and hidradenitis suppurativa) and malignancies (melanoma, basal cell carcinoma, and cutaneous T-cell lymphoma) may have variations in their immunophenotype among SOC. Additionally, there is growing recognition of the substantial role social determinants of health play in driving health inequalities in SOC communities. It is critically important to understand that social determinants of health often play a larger role than biologic or genetic factors attributed to "race" in health care outcomes. Herein, we describe the structural, genetic, and immunological variations and the potential implications of these variations in populations with SOC. This article underscores the importance of increasing the number of large, robust genetic studies of cutaneous disorders in SOC to create more targeted, effective therapies for this often underserved and understudied population. Part II of this CME will highlight the clinical differences in the phenotypic presentation of and the health disparities associated with the aforementioned cutaneous disorders in SOC.

Post-Inflammatory Hyperpigmentation in Dark Skin: Molecular Mechanism and Skincare Implications

Human skin is characterized by significant diversity in color and tone, which are determined by the quantity and distribution of melanin pigment in the epidermis. Melanin absorbs and reflects ultraviolet radiation (UVR), preventing the damage to genomic DNA in the epidermis and degradation of collagen in the dermis; therefore, darker skin types are thought to be well protected from the photodamage because of the high melanin content. However, increased content of melanin in combination with the extrinsic stress factors causing inflammation such as excess UVR, allergic reactions, or injury can also frequently lead to cosmetic problems resulting in discoloration and scarring. This review summarizes current knowledge on histopathology and likely molecular signatures of one of the most common problems, post-inflammatory hyperpigmentation (PIH). The mechanisms proposed so far are subsequently discussed in the context of other factors characterizing darker skin types. This includes the common cellular features, organization of upper skin layers, and major biomarkers, with particular emphasis on increased propensities to systemic and localized inflammation. Enhanced or prolonged inflammatory responses can not only affect the process of melanogenesis but also have been implicated in injury-related skin pathologies and aging. Finally, we summarize the major cosmetic treatments for PIH and their known anti-inflammatory targets, which can be beneficial for darker skin tones and combined with broad-spectrum filters against UVR.

Epidermal thickness in healthy humans: A systematic review and meta-analysis

Several skin diseases are characterised by epidermal alterations affecting epidermal thickness. Reference values of epidermal thickness in healthy humans and knowledge of possible differences regarding age, sex, skin phototype, and ethnic origin are essential in research and in clinical practice. The objectives of this systematic review were to provide epidermal thickness reference values for healthy human skin and describe possible effects of measurement methods, age, sex, ethnic origin, and skin phototype. A combined search in the databases Medline and Embase, and other sources was conducted. Searches covered a period from 1946 to 3^rd June 2020. Included studies were primary observational and interventional studies providing means and spread values of epidermal thickness estimates in healthy humans, with clear reporting of skin area, age and measurement method, and optional reporting of sex, ethnic origin and skin phototype. Data were extracted per skin area and pooled in random-effects models. 142 studies were included in the qualitative synthesis and 133 in the meta-analysis. Pooled epidermal thickness estimates were calculated for 37 skin areas. The lowest epidermal thickness of 31.2 (95% CI 27.8 to 34.6) μm was reported for the penis, and the highest of 596.6 (95% CI 443.9 to 749.3) μm for the plantar aspect of the foot. Differences of epidermal thickness estimates obtained by histology, optical coherence tomography and laser scanning microscopy were minor. High-frequency ultrasonography produces systematically higher values. Epidermis was thinner in aged skin. Differences between sexes and among ethnic origins where minor. Epidermal thickness reference values are provided for 37 skin areas. In conclusion, the epidermis tends to become thinner by ageing and does not seem to be influenced by sex. Histology, optical coherence tomography and laser scanning microscopy might be used interchangeably to measure epidermal thickness, whereas high-frequency ultrasound should not be used.

Development of a numerical multi-layer model of skin subjected to pulsed laser irradiation to optimise thermal stimulation in photorejuvenation procedure

BACKGROUND AND OBJECTIVE

This paper presents the development of a 3D physics-based numerical model of skin capable of representing the laser-skin photo-thermal interactions occurring in skin photorejuvenation treatment procedures. The aim of this model was to provide a rational and quantitative basis to control and predict temperature distribution within the layered structure of skin. Ultimately, this mathematical and numerical modelling platform will guide the design of an automatic robotic controller to precisely regulate skin temperature at desired depths and for specific durations.

METHODS

The Pennes bioheat equation was used to account for heat transfer in a 3D multi-layer model of skin. The effects of blood perfusion, skin pigmentation and various convection conditions are also incorporated in the proposed model. The photo-thermal effect due to pulsed laser light on skin is computed using light diffusion theory. The physics-based constitutive model was numerically implemented using a combination of finite volume and finite difference techniques. Direct sensitivity routines were also implemented to assess the influence of constitutive parameters on temperature. A stability analysis of the numerical model was conducted.

RESULTS

Finally, the numerical model was exploited to assess its ability to predict temperature distribution and thermal damage via a multi-parametric study which accounted for a wide array of biophysical parameters such as light coefficients of absorption for individual skin layers and melanin levels (correlated with ethnicity). It was shown how critical is the link between melanin content, laser light characteristics and potential thermal damage to skin.

CONCLUSIONS

The developed photo-thermal model of skin-laser interactions paves the way for the design of an automated simulation-driven photorejuvenation robot, thus alleviating the need for inconsistent and error-prone human operators.

Evaluation of elastin fibres in young and aged eyelids and abdominal skin using computational 3D structural analysis

Background

Aging‐related degeneration of elastic fibres causes skin wrinkles and loss of elasticity. A correlation has been reported between dermal elastic fibre degradation and wrinkles. However, the mechanism of wrinkle formation is complex and unclear. To establish methods for treating wrinkles, it is necessary to understand the aging‐related morphological alterations underlying elastin fibre degradation or disappearance.

Objectives

To image and analyse aging‐related three‐dimensional (3D) morphological alterations of elastic fibres in the eyelid and abdominal skin.

Methods

Excised human eyelid and abdominal skin tissues were examined. The structure of elastic fibres in the skin tissues was examined via nuclear, tropoelastin and fibrillin‐1 immunostaining. Then, 3D imaging was performed using a confocal laser microscope and tissue decolourization technology. Images were analysed using a computational method.

Results

The decolourization technology made it possible to image elastin fibres in 3D, and we devised a method for analyzing the elastin fibre structure using computational methods. It was quantitatively shown that the eyelid skin has a more complex fibrous structure than the abdomen, and the fibres became curved, shortened and thickened with age.

Conclusions

We provide a novel 3D analysis method for elastin fibres and report age‐related alterations in elastin fibre structure in the human eyelid and abdominal skin. This method contributes to the understanding of elastin fibre degeneration in more detail than conventional methods. Applying this 3D analysis method to skin tissues will contribute to a better understanding of age‐related changes in fibres and to the development of novel wrinkle treatments.

Differences between perceived age and chronological age in women: A multi-ethnic and multi-centre study

Objective

Accuracy in assessing age from facial cues is important in social perception given reports of strong negative correlations between perceived age and assessments of health and attractiveness. In a multi‐ethnic and multi‐centre study, we previously documented similar patterns of female facial age assessments across ethnicities, influenced by gender and ethnicity of assessors.

Methods

Here we extend these findings by examining differences between estimated age from digital portraits and chronological age (Δ age) for 180 women from three age groups (20–34, 35–49, 50–66 years) and five ethnicities (36 images of each ethnicity, assessed for age on a continuous scale by 120 female and male raters of each ethnicity).

Results

Across ethnicities, Δ age was smallest in French assessors and largest in South African assessors. Numerically, French women were judged oldest and Chinese women youngest relative to chronological age. In younger women, Δ age was larger than in middle‐aged and older women. This effect was particularly evident when considering the interaction of women's age with assessor gender and ethnicity, independently and together, on Δ age.

Conclusion

Collectively, our findings suggest that accuracy in assessments of female age from digital portraits depends on the chronological age and ethnicity of the photographed women and the ethnicity and gender of the assessor. We discuss the findings concerning ethnic variation in skin pigmentation and visible signs of ageing and comment on implications for cosmetic science.

Global differences in atopic dermatitis

Atopic dermatitis (AD) is a chronic inflammatory skin disorder, with a highly variable prevalence worldwide. Recent evidence, however, has shown an increase in prevalence in the Asia Pacific region. Nevertheless, most of the published literature has focused mainly on Western populations, and only few clinical trials have included subgroups of other ethnic populations. Reasons for the observed ethnic and geographical differences in AD are not well established. This calls into question the need for a better understanding of AD pathogenesis and inter-ethnic differences in clinical and immuno-phenotypes. These differences may reflect inherent variability in disease mechanisms between populations, which in turn may impact upon treatment responses such as biologics that are currently tailored mainly to a specific immuno-phenotype (T-helper type 2 dominant). In this article, we reviewed existing literature on the prevalence of AD globally, highlighting differences, if any, in the clinical and immuno-phenotypes of AD between different ethnicities. We discussed genetic and environmental factors that affect AD in different populations and therapeutic considerations. Our review highlights AD as a disease with ethnic-dependent clinical and immunological heterogeneity and calls for greater inclusion of ethnic diversity in future research in order to develop targeted treatments.

Heterogeneity of fibrillin-rich microfibrils extracted from human skin of diverse ethnicity

The dermal elastic fibre network is the primary effector of skin elasticity, enabling it to extend and recoil many times over the lifetime of the individual. Fibrillin-rich microfibrils (FRMs) constitute integral components of the elastic fibre network, with their distribution showing differential deposition in the papillary dermis across individuals of diverse skin ethnicity. Despite these differential findings in histological presentation, it is not known if skin ethnicity influences FRM ultrastructure. FRMs are evolutionarily highly conserved from jellyfish to man and, regardless of tissue type or species, isolated FRMs have a characteristic 'beads-on-a-string' ultrastructural appearance, with an average inter-bead distance (or periodicity) of 56 nm. Here, skin biopsies were obtained from the photoprotected buttock of healthy volunteers (18-27 years; African: n = 5; European: n = 5), and FRMs were isolated from the superficial papillary dermis and deeper reticular dermis and imaged by atomic force microscopy. In the reticular dermis, there was no significant difference in FRM ultrastructure between European and African participants. In contrast, in the more superficial papillary dermis, inter-bead periodicity was significantly larger for FRMs extracted from European participants than from African participants by 2.20 nm (p < .001). We next assessed whether these differences in FRM ultrastructure were present during early postnatal development by characterizing FRMs from full-thickness neonatal foreskin. Analysis of FRM periodicity identified no significant difference between neonatal cohorts (p = .865). These data suggest that at birth, FRMs are developmentally invariant. However, in adults of diverse skin ethnicity, there is a deviation in ultrastructure for the papillary dermal FRMs that may be acquired during the passage of time from child to adulthood. Understanding the mechanism by which this difference in papillary dermal FRMs arises warrants further study.

Remodelling of fibrillin-rich microfibrils by solar-simulated radiation: impact of skin ethnicity

Cutaneous fibrillin-rich microfibrils (FRMs) should be considered as two distinct populations that differentially accrue damage in response to SSR. Furthermore, FRMs derived from black African skin show greater change following UVR challenge.

Changes in epidermal morphology associated with dandruff

OBJECTIVE

Dandruff is a very common scalp condition characterized by flaking and pruritus usually with no visible signs of inflammation, such as redness and erythema. Dandruff is considered a multifactorial condition with both microbial colonization and host factors such as sebum production thought to play a role. There is evidence of changes in epidermal morphology in the scalp skin of dandruff sufferers, with reports of an increase in mean thickness and more nucleated cell layers. The underlying mechanisms driving these morphological changes are currently unclear. The objective of this study was to fully characterize epidermal morphology in dandruff compared to healthy scalp skin and to evaluate potential mechanisms underlying any changes observed.

METHODS

Scalp skin biopsies were taken from 22 healthy female subjects and 21 dandruff sufferers, from both lesional and non-lesional sites. Samples were processed, sectioned and stained using haematoxylin and eosin (H&E). To fully characterize epidermal morphology, measurements were taken of epidermal thickness, the convolution of the dermal-epidermal junction and the depth of epidermal rete ridges. To analyse changes in epidermal proliferation immunohistochemical staining was performed using Ki67, a well-established marker of cell proliferation, and quantified using image analysis.

RESULTS

Histochemical analysis of skin sections revealed that in dandruff lesional samples, the epidermis was thicker, had a more convoluted dermal epidermal junction and the rete ridges were elongated, compared to healthy scalp skin. Similar directional changes in epidermal morphology, were observed in non-lesional dandruff samples, albeit to a lesser extent. Image analysis of Ki67 expression in the epidermis revealed dandruff lesional skin contained significantly more Ki67-positive proliferating keratinocytes than healthy controls samples. This suggests dandruff scalp skin epidermal keratinocytes are in a hyper-proliferative state.

CONCLUSION

There were significant changes in epidermal morphology in dandruff lesional skin compared to healthy scalp skin including increased epidermal thickness, a more convoluted dermal-epidermal junction and elongation of rete ridges. Interestingly, we found there was evidence of an increase in the percentage of epidermal Ki67-positive cells, which has not been reported previously, and demonstrates dandruff is a condition displaying epidermal hyper-proliferation.

Skin characterization and immediate effects of different dermocosmetic treatments in French and Brazilian skin

BACKGROUND

All over the world, people face the same skin problems. However, their skin characteristics are different. Thus, it is a challenge to prescribe treatments that will be effective on different skin types. Therefore, it is very important to consider the skin biology when indicating a dermocosmetic treatment.

OBJECTIVES

To assess skin biophysical parameters in French and Brazilian subjects and to verify the efficacy of four dermocosmetic treatments in these populations.

METHODS

Five test areas were defined on each volar forearm of the eighteen Brazilian and eighteen French participants using a randomized design. Biophysical measurements in terms of skin hydration, skin barrier function, skin brightness, and skin viscoelasticity were performed before and after 60 minutes of treatment.

RESULTS

Skin biophysical differences between populations were found. French skin has been shown to be more hydrated regarding epidermal mechanic properties and stratum corneum water content and more radiant when compared with Brazilian skin. However, it showed more signs of cutaneous aging and fatigue effects on skin. The Brazilian skin showed better skin barrier function. In addition, the treatments were effective in both populations.

CONCLUSIONS

Despite the differences found in French and Brazilian skin, the proposed dermocosmetic treatments showed effective in both populations.

Reconstructed Skin Models Revealed Unexpected Differences in Epidermal African and Caucasian Skin

Clinical observations of both normal and pathological skin have shown that there is a heterogeneity based on the skin origin type. Beside external factors, intrinsic differences in skin cells could be a central element to determine skin types. This study aimed to understand the in vitro behaviour of epidermal cells of African and Caucasian skin types in the context of 3D reconstructed skin. Full-thickness skin models were constructed with site matched human keratinocytes and papillary fibroblasts to investigate potential skin type related differences. We report that reconstructed skin epidermis exhibited remarkable differences regarding stratification and differentiation according to skin types, as demonstrated by histological appearance, gene expression analysed by DNA microarray and quantitative proteomic analysis. Signalling pathways and processes related to terminal differentiation and lipid/ceramide metabolism were up-regulated in epidermis constructed with keratinocytes from Caucasian skin type when compared to that of keratinocytes from African skin type. Specifically, the expression of proteins involved in the processing of filaggrins was found different between skin models. Overall, we show unexpected differences in epidermal morphogenesis and differentiation between keratinocytes of Caucasian and African skin types in in vitro reconstructed skin containing papillary fibroblasts that could explain the differences in ethnic related skin behaviour.

Aging in Skin of Color: Disruption to Elastic Fiber Organization Is Detrimental to Skin's Biomechanical Function

Skin aging is a complex process involving the additive effects of time-dependent intrinsic aging and changes elicited via skin's interaction with the environment. Maintaining optimal skin function is essential for healthy aging across global populations; yet most research focuses on lightly pigmented skin (Fitzpatrick phototypes I-III), with little emphasis on skin of color (Fitzpatrick phototypes V-VI). Here, we explore the biomechanical and histologic consequences of aging in black African-American volunteers. We found that healthy young buttock and dorsal forearm skin was biomechanically resilient, highly elastic, and characterized histologically by strong interdigitation of rete ridges, abundant organized fibrillar collagen, and plentiful arrays of elastic fibers. In contrast, intrinsically aged buttock skin was significantly less resilient, less elastic, and was accompanied by effacement of rete ridges with reduced deposition of both elastic fibers and fibrillar collagens. In chronically photoexposed dorsal forearm, significant impairment of all biomechanical functions was identified, with complete flattening of rete ridges and marked depletion of elastic fibers and fibrillar collagens. We conclude that in skin of color, both intrinsic aging and photoaging significantly impact skin function and composition, despite the additional photoprotective properties of increased melanin. Improved public health advice regarding the consequences of chronic photoexposure and the importance of multimodal photoprotection use for all is of global significance.

Differential reorganisation of cutaneous elastic fibres: a comparison of the in vivo effects of broadband ultraviolet B versus solar simulated radiation

Long-term exposure of human skin to ultraviolet radiation (UVR) in sunlight negatively impacts its appearance and function with photoaged skin having a characteristic leathery, rough appearance, with deep wrinkles. These clinical features of photodamage are thought to result from UVR-induced remodelling of the dermal extracellular matrix, particularly the elastic fibre system. There are few in vivo human data on the impact of acute UVR exposure on this fibre system and particularly solar-simulated radiation (SSR)-mediated effects. We examined the differential effect of broadband UVB and SSR on the human dermal elastic fibre system, and specifically the microfibrillar components fibrillin-1, fibulin-2 and fibulin-5. Healthy white Caucasian adults (skin type II-III) were recruited and irradiated with 3× their minimal erythema dose of broadband UVB (n = 6) or SSR (n = 6) on photoprotected buttock skin. Punch biopsies were taken 24 h after irradiation and from unirradiated control skin. Overall, histological assessment of elastic fibres revealed significantly less elastic fibre staining in broadband UVB (P = 0.004) or SSR (P = 0.04) irradiated skin compared to unirradiated control skin. Significantly less staining of fibrillin-1-positive microfibrils was also observed in the papillary dermis of UVB irradiated skin (P = 0.02) but not skin exposed to SSR. Conversely, immunohistochemistry for fibulin-5-positive microfibrils revealed significantly less expression in skin exposed to SSR (P = 0.04) but not to broadband UVB. There was no significant change in fibulin-2-positive microfibrils following either broadband UVB or SSR irradiation. Thus, broadband UVB and SSR mediate differential effects on individual components of the dermal elastic fibre network in human skin. Further human studies are required to explore the mechanisms underlying these findings and the impact of potential photoprotective agents.

Organization of the dermal matrix impacts the biomechanical properties of skin

BACKGROUND

Human skin has the crucial roles of maintaining homeostasis and protecting against the external environment. Skin offers protection against mechanical trauma due to the reversible deformation of its structure; these biomechanical properties are amenable to dynamic testing using noninvasive devices.

OBJECTIVES

To characterize the biomechanical properties of young, black African/African-Caribbean and white Northern European skin from different anatomical sites, and to relate underlying skin architecture to biomechanical function.

METHODS

Using cutometry and ballistometry, the biomechanical properties of buttock and dorsal forearm skin were determined in black African/African-Caribbean (n = 18) and white Northern European (n = 20) individuals aged 18-30 years. Skin biopsies were obtained from a subset of the volunteers (black African/African-Caribbean, n = 5; white Northern European, n = 6) and processed for histological and immunohistochemical detection of the major elastic fibre components and fibrillar collagens.

RESULTS

We have determined that healthy skin from young African and white Northern European individuals has similar biomechanical properties (F3): the skin is resilient (capable of returning to its original position following deformation, R1), exhibits minimal fatigue (R4) and is highly elastic (R2, R5 and R7). At the histological level, skin with these biomechanical properties is imbued with strong interdigitation of the rete ridges at the dermoepidermal junction (DEJ) and candelabra-like arrays of elastic fibres throughout the papillary dermis. Dramatic disruption to this highly organized arrangement of elastic fibres, effacement of the rete ridges and alterations to the alignment of the fibrillar collagens is apparent in the white Northern European forearm and coincides with a marked decline in biomechanical function.

CONCLUSIONS

Maintenance of skin architecture - both epidermal morphology and elastic fibre arrangement - is essential for optimal skin biomechanical properties. Disruption to underlying skin architecture, as observed in the young white Northern European forearm, compromises biomechanical function.

African ancestry is associated with facial melasma in women: a cross-sectional study

Background

Melasma is a chronic acquired focal hypermelanosis affecting photoexposed areas, especially for women during fertile age. Several factors contribute to its development: sun exposure, sex steroids, medicines, and family history. Melanic pigmentation pathway discloses several SNPs in different populations. Here, we evaluated the association between genetic ancestry and facial melasma.

Methods

A cross-sectional study involving women with melasma and an age-matched control group from outpatients at FMB-Unesp, Botucatu-SP, Brazil was performed. DNA was extracted from oral mucosa swabs and ancestry determined by studying 61 INDELs. The genetic ancestry components were adjusted by other known risk factors by multiple logistic regression.

Results

We evaluated 119 women with facial melasma and 119 controls. Mean age was 39 ± 9 years. Mean age at beginning of disease was 27 ± 8 years. Pregnancy (40%), sun exposure (37%), and hormonal oral contraception (22%) were the most frequently reported melasma triggers. All subjects presented admixed ancestry, African and European genetic contributions were significantly different between cases and controls (respectively 10% vs 6%; 77% vs 82%; p < 0.05). African ancestry (OR = 1.04; 95% CI 1.01 to 1.07), first generation family history (OR = 3.04; 95% CI 1.56 to 5.94), low education level (OR = 4.04; 95% CI 1.56 to 5.94), and use of antidepressants by individuals with affected family members (OR = 6.15; 95% CI 1.13 to 33.37) were associated with melasma, independently of other known risk factors.

Conclusions

Facial melasma was independently associated with African ancestry in a highly admixed population.

Electronic supplementary material

The online version of this article (doi:10.1186/s12881-017-0378-7) contains supplementary material, which is available to authorized users.

Thyroid Hormones Enhance Mitochondrial Function in Human Epidermis

Since it is unknown whether thyroid hormones (THs) regulate mitochondrial function in human epidermis, we treated organ-cultured human skin, or isolated cultured human epidermal keratinocytes, with triiodothyronine (100 pmol/L) or thyroxine (100 nmol/L). Both THs significantly increased protein expression of the mitochondrially encoded cytochrome C oxidase I (MTCO1), complex I activity, and the number of perinuclear mitochondria. Triiodothyronine also increased mitochondrial transcription factor A (TFAM) protein expression, and thyroxine stimulated complex II/IV activity. Increased mitochondrial function can correlate with increased reactive oxygen species production, DNA damage, and accelerated tissue aging. However, THs neither raised reactive oxygen species production or matrix metalloproteinase-1, -2 and -9 activity nor decreased sirtuin1 (Sirt1) immunoreactivity. Instead, triiodothyronine increased sirtuin-1, fibrillin-1, proliferator-activated receptor-gamma 1-alpha (PGC1α), collagen I and III transcription, and thyroxine decreased cyclin-dependent kinase inhibitor 2A (p16(ink4)) expression in organ-cultured human skin. Moreover, TH treatment increased intracutaneous fibrillin-rich microfibril and collagen III deposition and decreased mammalian target of rapamycin (mTORC1/2) expression ex vivo. This identifies THs as potent endocrine stimulators of mitochondrial function in human epidermis, which down-regulates rather than enhance the expression of skin aging-related biomarkers ex vivo. Therefore, topically applied THs deserve further exploration as candidate agents for treating skin conditions characterized by reduced mitochondrial function.

The dynamic anatomy and patterning of skin

The skin is often viewed as a static barrier that protects the body from the outside world. Emphasis on studying the skin's architecture and biomechanics in the context of restoring skin movement and function is often ignored. It is fundamentally important that if skin is to be modelled or developed, we do not only focus on the biology of skin but also aim to understand its mechanical properties and structure in living dynamic tissue. In this review, we describe the architecture of skin and patterning seen in skin as viewed from a surgical perspective and highlight aspects of the microanatomy that have never fully been realized and provide evidence or concepts that support the importance of studying living skin's dynamic behaviour. We highlight how the structure of the skin has evolved to allow the body dynamic form and function, and how injury, disease or ageing results in a dramatic changes to the microarchitecture and changes physical characteristics of skin. Therefore, appreciating the dynamic microanatomy of skin from the deep fascia through to the skin surface is vitally important from a dermatological and surgical perspective. This focus provides an alternative perspective and approach to addressing skin pathologies and skin ageing.