Epidermal gene expression and ethnic pigmentation variations among individuals of Asian, European and African ancestry

Overview of Atopic Dermatitis in Different Ethnic Groups

Atopic dermatitis (AD) is a common chronic inflammatory skin disease with a high prevalence worldwide, including countries from Asia, Africa, and Latin America, and in different ethnic groups. In recent years, more attention has been placed on the heterogeneity of AD associated with multiple factors, including a patient's ethnic background, resulting in an increasing body of clinical, genetic, epidemiologic, and immune-phenotypic evidence that delineates differences in AD among racial groups. Filaggrin (FLG) mutations, the strongest genetic risk factor for the development of AD, are detected in up to 50% of European and 27% of Asian AD patients, but very rarely in Africans. Th2 hyperactivation is a common attribute of all ethnic groups, though the Asian endotype of AD is also characterized by an increased Th17-mediated signal, whereas African Americans show a strong Th2/Th22 signature and an absence of Th1/Th17 skewing. In addition, the ethnic heterogeneity of AD may hold important therapeutic implications as a patient's genetic predisposition may affect treatment response and, thereby, a tailored strategy that better targets the dominant immunologic pathways in each ethnic subgroup may be envisaged. Nevertheless, white patients with AD represent the largest ethnicity enrolled and tested in clinical trials and the most treated in a real-world setting, limiting investigations about safety and efficacy across different ethnicities. The purpose of this review is to describe the heterogeneity in the pathophysiology of AD across ethnicities and its potential therapeutic implications.

Commentary: Facial Aesthetic Dermatological Procedures and Photoprotection in Chinese Populations

The medical literature on aesthetic dermatology has primarily focused on a light-skinned patient population, yet patients of darker skin types have different needs and priorities. In Chinese individuals, key concerns include altered pigmentation, which is perceived to age the individual, and also relates to the Chinese cultural standard of beauty of fair skin; many seek aesthetic treatment for this. Non-invasive cosmetic procedures such as lasers and injections are also gaining in popularity in the Chinese market, but this population is prone to hyperpigmentation as an adverse effect of such procedures. Considered and tailored approaches, both to primary concerns of photoaging and the side effects of cosmetic treatments, are warranted.

Transcriptome analysis reveals intrinsic pro-inflammatory signaling in healthy African American skin

Differences in morphology and physiology of darkly pigmented compared to lightly pigmented skin are well recognized. There are also disparities in prevalence and clinical features for many inflammatory skin diseases including atopic dermatitis and psoriasis; however, the underlying mechanisms are largely unknown. We compared the baseline gene expression in full thickness skin biopsies from healthy individuals self-reporting as African American (AA) or White Non-Hispanic (WNH). Extensively validated RNA-Seq analysis identified 570 differentially expressed genes (DEG) in AA skin including immunoglobulins and their receptors such as FCER1G; pro-inflammatory genes such as TNFα, IL-32; EDC (epidermal differentiation cluster) and keratin genes. DEGs were functionally enriched for inflammatory responses, keratinization, cornified envelope formation. RNA-seq analysis of 3D human skin equivalents (HSE) made from AA and WNH primary keratinocytes revealed 360 DEGs (some shared with skin) which were enriched by similar functions. AA HSE appeared more responsive to TNFα pro-inflammatory effects. Finally, AA-specific DEGs in skin and HSE significantly overlapped with molecular signatures of skin in AD and psoriasis patients. Overall, these findings suggest the existence of intrinsic pro-inflammatory circuits in AA keratinocytes/skin that may account for disease disparities and will help to build a foundation for the development of targeted skin disease prevention.

Melanin Distribution in Human Skin: Influence of Cytoskeletal, Polarity, and Centrosome-Related Machinery of Stratum basale Keratinocytes

Melanin granules cluster within supra-nuclear caps in basal keratinocytes (KCs) of the human epidermis, where they protect KC genomic DNA against ultraviolet radiation (UVR) damage. While much is known about melanogenesis in melanocytes (MCs) and a moderate amount about melanin transfer from MC to KC, we know little about the fate of melanin once inside KCs. We recently reported that melanin fate in progenitor KCs is regulated by rare asymmetric organelle movement during mitosis. Here, we explore the role of actin, microtubules, and centrosome-associated machinery in distributing melanin within KCs. Short-term cultures of human skin explants were treated with cytochalasin-B and nocodazole to target actin filaments and microtubules, respectively. Treatment effects on melanin distribution were assessed by the Warthin-Starry stain, on centrosome-associated proteins by immunofluorescence microscopy, and on co-localisation with melanin granules by brightfield microscopy. Cytochalasin-B treatment disassembled supra-nuclear melanin caps, while nocodazole treatment moved melanin from the apical to basal KC domain. Centrosome and centriolar satellite-associated proteins showed a high degree of co-localisation with melanin. Thus, once melanin granules are transferred to KCs, their preferred apical distribution appears to be facilitated by coordinated movement of centrosomes and centriolar satellites. This mechanism may control melanin's strategic position within UVR-exposed KCs.

Melanosome transport and regulation in development and disease

Melanosomes are specialized membrane-bound organelles that synthesize and organize melanin, ultimately providing color to the skin, hair, and eyes. Disorders in melanogenesis and melanosome transport are linked to pigmentary diseases, such as Hermansky-Pudlak syndrome, Chediak-Higashi syndrome, and Griscelli syndrome. Clinical cases of these pigmentary diseases shed light on the molecular mechanisms that control melanosome-related pathways. However, only an improved understanding of melanogenesis and melanosome transport will further the development of diagnostic and therapeutic approaches. Herein, we review the current literature surrounding melanosomes with particular emphasis on melanosome membrane transport and cytoskeleton-mediated melanosome transport. We also provide perspectives on melanosome regulatory mechanisms which include hormonal action, inflammation, autophagy, and organelle interactions.

Impact of admixture and ancestry on eQTL analysis and GWAS colocalization in GTEx

BACKGROUND

Population structure among study subjects may confound genetic association studies, and lack of proper correction can lead to spurious findings. The Genotype-Tissue Expression (GTEx) project largely contains individuals of European ancestry, but the v8 release also includes up to 15% of individuals of non-European ancestry. Assessing ancestry-based adjustments in GTEx improves portability of this research across populations and further characterizes the impact of population structure on GWAS colocalization.

RESULTS

Here, we identify a subset of 117 individuals in GTEx (v8) with a high degree of population admixture and estimate genome-wide local ancestry. We perform genome-wide cis-eQTL mapping using admixed samples in seven tissues, adjusted by either global or local ancestry. Consistent with previous work, we observe improved power with local ancestry adjustment. At loci where the two adjustments produce different lead variants, we observe 31 loci (0.02%) where a significant colocalization is called only with one eQTL ancestry adjustment method. Notably, both adjustments produce similar numbers of significant colocalizations within each of two different colocalization methods, COLOC and FINEMAP. Finally, we identify a small subset of eQTL-associated variants highly correlated with local ancestry, providing a resource to enhance functional follow-up.

CONCLUSIONS

We provide a local ancestry map for admixed individuals in the GTEx v8 release and describe the impact of ancestry and admixture on gene expression, eQTLs, and GWAS colocalization. While the majority of the results are concordant between local and global ancestry-based adjustments, we identify distinct advantages and disadvantages to each approach.

The GTEx Consortium atlas of genetic regulatory effects across human tissues

The Genotype-Tissue Expression (GTEx) project was established to characterize genetic effects on the transcriptome across human tissues and to link these regulatory mechanisms to trait and disease associations. Here, we present analyses of the version 8 data, examining 15,201 RNA-sequencing samples from 49 tissues of 838 postmortem donors. We comprehensively characterize genetic associations for gene expression and splicing in cis and trans, showing that regulatory associations are found for almost all genes, and describe the underlying molecular mechanisms and their contribution to allelic heterogeneity and pleiotropy of complex traits. Leveraging the large diversity of tissues, we provide insights into the tissue specificity of genetic effects and show that cell type composition is a key factor in understanding gene regulatory mechanisms in human tissues.

Identification of a CDH12 potential candidate genetic variant for an autosomal dominant form of transgrediens and progrediens palmoplantar keratoderma in a Tunisian family

Molecular diagnosis of rare inherited palmoplantar keratoderma (PPK) is still challenging. We investigated at the clinical and genetic level a consanguineous Tunisian family presenting an autosomal dominant atypical form of transgrediens and progrediens PPK to better characterize this ultrarare disease and to identify its molecular etiology. Whole-exome sequencing (WES), filtering strategies, and bioinformatics analysis have been achieved. Clinical investigation and follow up over 13 years of this Tunisian family with three siblings formerly diagnosed as an autosomal recessive form of Mal de Melela-like conducted us to reconsider its initial phenotype. Indeed, the three patients presented clinical features that overlap both Mal de Meleda and progressive symmetric erythrokeratoderma (PSEK). The mode of inheritance was also reconsidered, since the mother, initially classified as unaffected, exhibited a similar expression of the disease. WES analysis showed the absence of potentially functional rare variants in known PPKs or PSEK-related genes. Results revealed a novel heterozygous nonsynonymous variant in cadherin-12 gene (CDH12, NM_004061, c.1655C > A, p.Thr552Asn) in all affected family members. This variant is absent in dbSNP and in 50 in-house control exomes. In addition, in silico analysis of the mutated 3D domain structure predicted that this variant would result in cadherin-12 protein destabilization and thermal instability. Functional annotation and biological network construction data provide further supporting evidence for the potential role of CDH12 in the maintenance of skin integrity. Taken together, these results suggest that CDH12 gene is a potential candidate gene for an atypical presentation of an autosomal dominant form of transgrediens and progrediens PPK.

Baumann Skin Type in the Korean Male Population

Background

Research into the Baumann skin type (BST) has recently expanded, with growing interest in the development of an efficient and effective skin type classification system for better understanding of this skin condition.

Objective

We aimed to identify male-specific skin type characteristics with investigation into the distribution of BST by age and region in the Korean male population and to determine the intrinsic and extrinsic factors related to skin type.

Methods

A questionnaire was administered to collect information about age, region, working behavior, drinking behavior, smoking behavior, usual habit of sun protection, medical history, and the BST which consisted of four parameters; oily (O) or dry (D), sensitive (S) or resistant (R), pigmented (P) or non-pigmented (N), and wrinkled (W) or tight (T).

Results

We surveyed 1,000 Korean males aged between 20 and 60 years who were divided equally by age and region. Of the total respondents, OSNW type accounted for the largest percentage and ORPW type the lowest. In terms of Baumann parameters, O type was 53.5%, S type was 56.1%, N type was 84.4% and W type was 57.5%. Several behavioral factors were found to have various relationships with the skin type.

Conclusion

The predominant skin type in the Korean male respondents was OSNW type, and the distribution of skin types with regards to age and region was reported to be distinct. Therefore, skin care should be customized based on detailed skin types considering the various environmental factors.

Transcriptome variation in human populations and its potential application in forensics

This review presents the state-of-the-art in the forensic application of genetic methods driven by the research in population transcriptomics. In the first part of the review, the constraints of using classical genomic markers are shortly reviewed. In the second part, the developments in the field of inter-population diversity at the transcriptomic level are presented. Subsequently, a potential of population-specific transcriptomic markers in forensic science applications, including ascertaining population affiliation of human samples and cell mixtures separation, are presented.

Transcriptomic Network Interactions in Human Skin Treated with Topical Glucocorticoid Clobetasol Propionate

Glucocorticoids are the most frequently used anti-inflammatory drugs in dermatology. However, the molecular signature of glucocorticoids and their receptor in human skin is largely unknown. Our validated bioinformatics analysis of human skin transcriptome induced by topical glucocorticoid clobetasol propionate (CBP) in healthy volunteers identified numerous unreported glucocorticoid-responsive genes, including over a thousand noncoding RNAs. We observed sexual and racial dimorphism in the CBP response including a shift toward IFN-α/IFN-γ and IL-6/Jak/Signal transducer and activator of transcription (STAT) 3 signaling in female skin; and a larger response to CBP in African-American skin. Weighted gene coexpression network analysis unveiled a dense skin network of 41 transcription factors including circadian Kruppel-like factor 9 (KLF9), and ∼260 of their target genes enriched for functional pathways representative of the entire CBP transcriptome. Using keratinocytes with Kruppel-like factor 9 knockdown, we revealed a feedforward loop in glucocorticoid receptor signaling, previously unreported. Interestingly, many of the CBP-regulated transcription factors were involved in the control of development, metabolism, circadian clock; and 80% of them were associated with skin aging showing similarities between glucocorticoid-treated and aged skin. Overall, these findings indicate that glucocorticoid receptor acts as an important regulator of gene expression in skin-both at the transcriptional and posttranscriptional level-via multiple mechanisms including regulation of noncoding RNAs and multiple core transcription factors.

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.

Racial differences in atopic dermatitis

OBJECTIVE

To summarize studies investigating ethnical and racial differences in atopic dermatitis (AD) epidemiology, clinical features, and skin and blood phenotypes.

DATA SOURCES

PubMed literature review (years 2000-2018).

STUDY SELECTIONS

Articles discussing primarily human disease.

RESULTS

Higher overall rates of AD were found in Africa and Oceania as opposed to India and Northern and Eastern Europe. In the United States, AD prevalence was found to be higher in African American (19.3%) compared with European American (16.1%) children. Although several studies have consistently found FLG loss-of-function mutations in up to 50% of European and 27% of Asian patients with AD, FLG mutations were 6 times less common in African American than in European American patients, even in patients with severe AD. Thus, FLG mutations seem to play less a pathogenic role in patients of African origin than in individuals of European or Asian ancestry. The immune phenotype of all ethnic groups was characterized by strong TH2 activation, but important differences in immune polarization exist among the different ethnicities. Asian patients with AD had stronger TH17/TH22 activation than African American and European American patients with AD, whereas African American patients had the highest serum IgE levels among all groups, while largely lacking TH1 and TH17 activation.

CONCLUSION

AD is a heterogeneous disease that has differences among various ethnic and racial groups, which might be important for the development of future, targeted treatments and for personalized medicine approaches.

The roles of vitamin D and cutaneous vitamin D production in human evolution and health

Most of the vitamin D necessary for the maintenance of human health and successful reproduction is made in the skin under the influence of a narrow portion of the electromagnetic spectrum emitted from the sun, namely ultraviolet B radiation (UVB). During the course of human evolution, skin pigmentation has evolved to afford protection against high levels of UVR while still permitting cutaneous production of vitamin D. Similar pigmentation phenotypes evolved repeatedly as the result of independent genetic events when isolated human populations dispersed into habitats of extremely low or high UVB. The gradient of skin color seen in modern human populations is evidence of the operation of two clines, one favoring photoprotection near the equator, the other favoring vitamin D production nearer the poles. Through time, human adaptations to different solar regimes have become more cultural than biological. Rapid human migrations, increasing urbanization, and changes in lifestyle have created mismatches between skin pigmentation and environmental conditions leading to vitamin D deficiency. The prevalence and significance for health of vitamin D deficiencies, and the definition of optimal levels of vitamin D in the bloodstream are subjects of intense research and debate, but two of the causes of vitamin D deficiency - lack of sun exposure and abandonment of vitamin D rich foods in the diet - are traceable to changes in human lifestyles accompanying urbanization in prehistory.

Clinical and Biological Characterization of Skin Pigmentation Diversity and Its Consequences on UV Impact

Skin color diversity is the most variable and noticeable phenotypic trait in humans resulting from constitutive pigmentation variability. This paper will review the characterization of skin pigmentation diversity with a focus on the most recent data on the genetic basis of skin pigmentation, and the various methodologies for skin color assessment. Then, melanocyte activity and amount, type and distribution of melanins, which are the main drivers for skin pigmentation, are described. Paracrine regulators of melanocyte microenvironment are also discussed. Skin response to sun exposure is also highly dependent on color diversity. Thus, sensitivity to solar wavelengths is examined in terms of acute effects such as sunburn/erythema or induced-pigmentation but also long-term consequences such as skin cancers, photoageing and pigmentary disorders. More pronounced sun-sensitivity in lighter or darker skin types depending on the detrimental effects and involved wavelengths is reviewed.

Transcriptomic population markers for human population discrimination

Background

Numerous studies have demonstrated significant differences in the expression level across continental human populations. Most of published results were performed on B-cell lines materials examined under specific laboratory conditions, without further validation in a primary biological material. The goal of our study was to identify mRNA markers characterized by a significant and stable difference in the gene expression profile in Caucasian and Chinese populations, both in the commercially available B-lymphocyte cell lines and in the primary samples of the peripheral blood.

Results

The preliminary selection of population-differentiating transcripts was based on Illumina expression microarray analysis of the representative group of ethnically-specified B-lymphocyte cell lines. Twenty genes with the inter-population difference in the mean expression characterized by the at least 1.5-fold change and FDR <  0.05 were identified. Subsequently, a two-step validation procedure was carried out. In the first step, a subset of selected population- differentiating transcripts was tested in the independent set of B-lymphocyte cell lines, using TLDA cards. Based on TLDA analysis, three transcripts representing Fch > 2 were chosen for validation. The differentiating status was confirmed for all of them: UTS2, UGT2B17 and SLC7A7. The mean expression of UTS2 was higher in CHB (25.8-fold change compared to CEU), while the expression of UGT2B17 and SLC7A7 was higher in CEU (3.2- and 2.2-fold change, respectively).

In the next validation step, two transcripts were verified in the primary biological material. As an ultimate result of our study, two mRNA markers (UTS2 and UGT2B17) exhibiting population differences in the expression level in both B-cell line and in the blood were identified. Further statistical analysis confirmed the discriminatory potential of these two markers.

Conclusions

An inter-population differences on the level of gene expression were identified in both B-cell lines and peripheral blood samples. These findings may have a practical application in the field of forensic science. In particular, these transcripts, targeted by specific probes, may be used as population-specific targets in the efforts aiming to separate mixture of blood from individuals of different populations. Notwithstanding, these results have to be confirmed on extended population group.

Electronic supplementary material

The online version of this article (10.1186/s12863-018-0663-2) contains supplementary material, which is available to authorized users.

High correlation between skin color based on CIELAB color space, epidermal melanocyte ratio, and melanocyte melanin content

Background

To treat skin color disorders, such as vitiligo or burns, melanocytes are transplanted for tissue regeneration. However, melanocyte distribution in the human body varies with age and location, making it difficult to select the optimal donor skin to achieve a desired color match. Determining the correlations with the desired skin color measurement based on CIELAB color, epidermal melanocyte numbers, and melanin content of individual melanocytes is critical for clinical application.

Method

Fifteen foreskin samples from Asian young adults were analyzed for skin color, melanocyte ratio (melanocyte proportion in the epidermis), and melanin concentration. Furthermore, an equation was developed based on CIELAB color with melanocyte ratio, melanin concentration, and the product of melanocyte ratio and melanin concentration. The equation was validated by seeding different ratios of keratinocytes and melanocytes in tissue-engineered skin substitutes, and the degree of fitness in expected skin color was confirmed.

Results

Linear regression analysis revealed a significant strong negative correlation (r =  − 0.847, R² = 0.717) between CIELAB L* value and the product of the epidermal melanocyte ratio and cell-based melanin concentration. Furthermore, the results showed that an optimal skin color match was achieved by the formula.

Discussion

We found that L* value was correlated with the value obtained from multiplying the epidermal melanocyte ratio (R) and melanin content (M) and that this correlation was more significant than either L* vs M or L* vs R. This suggests that more accurate prediction of skin color can be achieved by considering both R and M. Therefore, precise skin color match in treating vitiligo or burn patients would be potentially achievable based on extensive collection of skin data from people of Asian descent.

The colours of humanity: the evolution of pigmentation in the human lineage

Humans are a colourful species of primate, with human skin, hair and eye coloration having been influenced by a great variety of evolutionary forces throughout prehistory. Functionally naked skin has been the physical interface between the physical environment and the human body for most of the history of the genus Homo, and hence skin coloration has been under intense natural selection. From an original condition of protective, dark, eumelanin-enriched coloration in early tropical-dwelling Homo and Homo sapiens, loss of melanin pigmentation occurred under natural selection as Homo sapiens dispersed into non-tropical latitudes of Africa and Eurasia. Genes responsible for skin, hair and eye coloration appear to have been affected significantly by population bottlenecks in the course of Homo sapiens dispersals. Because specific skin colour phenotypes can be created by different combinations of skin colour-associated genetic markers, loss of genetic variability due to genetic drift appears to have had negligible effects on the highly redundant genetic 'palette' for the skin colour. This does not appear to have been the case for hair and eye coloration, however, and these traits appear to have been more strongly influenced by genetic drift and, possibly, sexual selection.This article is part of the themed issue 'Animal coloration: production, perception, function and application'.

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.

Molecular and histological characterization of age spots

Age spots, also called solar lentigines and lentigo senilis, are light brown to black pigmented lesions of various sizes that typically develop in chronically sun-exposed skin. It is well known that age spots are strongly related to chronic sun exposure and are associated with photodamage and an increased risk for skin cancer; however, the mechanisms underlying their development remain poorly understood. We used immunohistochemical analysis and microarray analysis to investigate the processes involved in their formation, focusing on specific markers associated with the functions and proliferation of melanocytes and keratinocytes. A total of 193 genes were differentially expressed in age spots, but melanocyte pigment genes were not among them. The increased expression of keratins 5 and 10, markers of basal and suprabasal keratinocytes, respectively, in age spots suggests that the increased proliferation of basal keratinocytes combined with the decreased turnover of suprabasal keratinocytes leads to the exaggerated formation of rete ridges in lesional epidermis which in turn disrupts the normal processing of melanin upwards from the basal layer. Based on our results, we propose a model for the development of age spots that explains the accumulation of melanin and the development of extensive rete ridges in those hyperpigmented lesions.

Variation in Hsp70-1A Expression Contributes to Skin Color Diversity

The wide range in human skin color results from varying levels of the pigment melanin. Genetic mechanisms underlying coloration differences have been explored, but identified genes do not account for all variation seen in the skin color spectrum. Post-transcriptional and post-translational regulation of factors that determine skin color, including melanin synthesis in epidermal melanocytes, melanosome transfer to keratinocytes, and melanosome degradation, is also critical for pigmentation. We therefore investigated proteins that are differentially expressed in melanocytes derived from either white or African American skin. Two-dimensional gel electrophoresis and mass spectrometry demonstrated that heat shock protein 70-1A (Hsp70-1A) protein levels were significantly higher in African American melanocytes compared with white melanocytes. Hsp70-1A expression significantly correlated with levels of tyrosinase, the rate-limiting melanogenic enzyme, consistent with a proposed role for Hsp70 family members in tyrosinase post-translational modification. In addition, pharmacologic inhibition and small interfering RNA-mediated downregulation of Hsp70-1A correlated with pigmentation changes in cultured melanocytes, modified human skin substitutes, and ex vivo skin. Furthermore, Hsp70-1A inhibition led to increased autophagy-mediated melanosome degradation in keratinocytes. Our data thus reveal that epidermal Hsp70-1A contributes to the diversity of skin color by regulating the amount of melanin synthesized in melanocytes and modulating autophagic melanosome degradation in keratinocytes.

Identification of Genes Expressed in Hyperpigmented Skin Using Meta-Analysis of Microarray Data Sets

More than 375 genes have been identified that are involved in regulating skin pigmentation, and those act during development, survival, differentiation and/or responses of melanocytes to the environment. Many of those genes have been cloned and disruptions of their functions are associated with various pigmentary diseases, however many remain to be identified. We have performed a series of microarray analyses of hyperpigmented compared to less pigmented skin to identify genes responsible for those differences. The rationale and goal for this study was to perform a meta-analysis on those microarray databases to identify genes that may be significantly involved in regulating skin phenotype either directly or indirectly that might not have been identified due to subtle differences by any of those individual studies alone. The meta-analysis demonstrates that 1,271 probes representing 921 genes are differentially expressed at significant levels in the 5 microarray datasets compared, which provides new insights into the variety of genes involved in determining skin phenotype. Immunohistochemistry was used to validate 2 of those markers at the protein level (TRIM63 and QPCT) and we discuss the possible functions of those genes in regulating skin physiology.