Sun-protected Skin Research Articles

Alterations of Matrisome Gene Expression in Naturally Aged and Photoaged Human Skin In Vivo.

The main component of human skin is a collagen-rich extracellular matrix (ECM), known as the matrisome. The matrisome is essential for maintaining the structural integrity and mechanical properties of the skin. Recently, we reported notable decreases in matrisome proteins in natural aging and photoaging human skin. This study aims to investigate the mRNA expression of the core matrisome proteins in human skin, comparing young versus aged and sun-protected versus sun-exposed skin by quantitative real-time PCR and immunostaining. Our findings reveal a notable decrease in core matrisome transcription in aged skin. The mRNA expression of the core matrisome, such as collagen 1A1 (COL1A1), decorin, and dermatopontin, is significantly reduced in aged skin compared to its young skin. Yet, the majority of collagen mRNA expression levels of aged sun-exposed skin are similar to those found in young sun-exposed skin. This discrepancy is primarily attributable to a substantial decrease in collagen transcription in young sun-exposed skin, suggesting early molecular changes in matrisome transcription due to sun exposure, which preceded the emergence of clinical signs of photoaging. These findings shed light on the mRNA transcript profile of major matrisome proteins and their alterations in naturally aged and photoaged human skin, offering valuable insights into skin matrisome biology.

Expression of mast cell tryptase and immunoglobulin E is increased in cutaneous photodamage: implications for carcinogenesis

Purpose: Mast cells, their serine proteinase tryptase, and immunoglobulin E (IgE) can be involved in cutaneous carcinogenesis. Materials and methods: To study the association of tryptase+ and IgE+ cells with photodamage and skin cancers 385 adult patients (201 males, 184 females, 75 with immunosuppression) at risk of any type of skin cancer were examined. Skin biopsies were taken from the sun-protected medial arm and from the photodamaged dorsal forearm skin followed by immunohistochemical staining for tryptase and IgE. Results: The results show that tryptase+ and IgE+ cells are significantly higher in number in the photodamaged than sun-protected skin, both in immunocompetent and -compromised subjects, and there is a strong correlation between tryptase+ and IgE+ cells. The numbers of forearm tryptase+ and especially IgE+ cells associated significantly with the forearm photodamage severity. In the logistic regression analysis, the forearm to upper arm ratio of IgE+ cells produced a univariate odds ratio of 1.521 (p = .010) and a multivariate one of 3.875 (p = .047) for the history of squamous cell carcinoma. The serum level of total IgE correlated significantly to the IgE to tryptase ratio in both skin sites. Conclusions: Therefore, IgE+ mast cells participate in photodamage and carcinogenesis, though it is unclear whether they are tumor-protective or -causative.

Age-related changes in dermal collagen physical properties in human skin.

Collagen is the major structural protein in the skin. Fragmentation and disorganization of the collagen fibrils are the hallmarks of the aged human skin dermis. These age-related alterations of collagen fibrils impair skin structural integrity and make the tissue microenvironment more prone to skin disorders. As the biological function of collagen lies predominantly in its physical properties, we applied atomic force microscopy (AFM) and nanoindentation to evaluate the physical properties (surface roughness, stiffness, and hardness) of dermal collagen in young (25±5 years, N = 6) and aged (75±6 years, N = 6) healthy sun-protected hip skin. We observed that in the aged dermis, the surface of collagen fibrils was rougher, and fiber bundles were stiffer and harder, compared to young dermal collagen. Mechanistically, the age-related elevation of matrix metalloproteinase-1 (MMP-1) and advanced glycation end products (AGEs) are responsible for rougher and stiffer/harder dermal collagen, respectively. Analyzing the physical properties of dermal collagen as a function of age revealed that alterations of the physical properties of collagen fibrils changed with age (22-89 years, N = 18). We also observed that the reticular dermis is rougher and mechanically stiffer and harder compared to the papillary dermis in human skin. These data extend the current understanding of collagen beyond biological entities to include biophysical properties.

Phototherapy Restores Deficient Type I IFN Production and Enhances Antitumor Responses in Mycosis Fungoides

Transcriptional profiling demonstrated markedly reduced type I IFN gene expression in untreated mycosis fungoides (MF) skin lesions compared with that in healthy skin. Type I IFN expression in MF correlated with antigen-presenting cell-associated IRF5 before psoralen plus UVA therapy and epithelial ULBP2 after therapy, suggesting an enhancement of epithelial type I IFN. Immunostains confirmed reduced baseline type I IFN production in MF and increased levels after psoralen plus UVA treatment in responding patients. Effective tumor clearance was associated with increased type I IFN expression, enhanced recruitment of CD8+ T cells into skin lesions, and expression of genes associated with antigen-specific T-cell activation. IFNk, a keratinocyte-derived inducer of type I IFNs, was increased by psoralen plus UVA therapy and expression correlated with upregulation of other type I IFNs. Invitro, deletion of keratinocyte IFNk decreased baseline and UVA-induced expression of type I IFN and IFN response genes. In summary, we find a baseline deficit in type I IFN production in MF that is restored by psoralen plus UVA therapy and correlates with enhanced antitumor responses. This may explain why MF generally develops in sun-protected skin and suggests that drugs that increase epithelial type I IFNs, including topical MEK and EGFR inhibitors, may be effective therapies for MF.

Ultrastructural and morphological analysis during progression of Bowen disease reveals a complex interplay between hyperkeratosis, cytokeratin expression, host immunity and amyloid deposition.

Bowen disease, one of the common skin cancers, is defined as squamous cell carcinoma in situ, characterized by atypical keratinocytes occupying the full thickness of the epidermis, and predominantly occurs on sun-protected skin. There is no existing data on the impact of tumour and immune cell interactions or cytokeratin expression on the pathology of Bowen disease. We analysed dynamic changes in cytokeratin expression and immune cell composition during the development and progression of Bowen disease. Analysis was performed using immunohistochemistry and electron microscopy for samples from 140 patients with Bowen disease and 20 patients with invasive squamous cell carcinoma. We evaluated cytokeratin expression, the number of infiltrating immune cells and amyloid deposition by immunohistochemistry, and the ultrastructural relationship between tumour cells and immune cells by electron microscopy. The results showed that the expression of CK14 is associated with tumour progression, keratotic status and amyloid deposition and that the expression of CK10 is associated with accumulation of immune cells in Bowen disease. The findings of electron microscopy indicated repeated battles involving immune cells in response to tumour invasion. The expression of cytokeratins, hyperkeratosis, inflammatory infiltration and amyloid deposition are useful findings indicating the "stage" in Bowen disease.

CircRNA-406918 enhances the degradation of advanced glycation end products in photoaged human dermal fibroblasts via targeting cathepsin D.

Lysosomal cathepsin D (CTSD) can degrade internalized advanced glycation end products (AGEs) in dermal fibroblasts. CTSD expression is decreased in photoaged fibroblasts, which contributes to intracellular AGEs deposition and further plays a role in AGEs accumulation of photoaged skin. The mechanism under downregulated CTSD expression is unclear. To explore possible mechanism of regulating CTSD expression in photoaged fibroblasts. Dermal fibroblasts were induced into photoaging with repetitive ultraviolet A (UVA) irradiation. The competing endogenous RNA (ceRNA) networks were constructed to predict candidate circRNAs or miRNAs related with CTSD expression. AGEs-BSA degradation by fibroblasts was studied with flow cytometry, ELISA, and confocal microscopy. Effects of overexpressing circRNA-406918 via lentiviral transduction on CTSD expression, autophagy, AGE-BSA degradation were analyzed in photoaged fibroblasts. The correlation between circRNA-406918 and CTSD expression or AGEs accumulation in sun-exposed and sun-protected skin was studied. CTSD expression, autophagy, and AGEs-BSA degradation were significantly decreased in photoaged fibroblasts. CircRNA-406918 was identified to regulate CTSD expression, autophagy, and senescence in photoaged fibroblasts. Overexpressing circRNA-406918 potently decreased senescence and increased CTSD expression, autophagic flux, and AGEs-BSA degradation in photoaged fibroblasts. Moreover, circRNA-406918 level was positively correlated with CTSD mRNA expression and negatively associated with AGEs accumulation in photodamaged skin. Further, circRNA-406918 was predicted to mediate CTSD expression through sponging eight miRNAs. These findings suggest that circRNA-406918 regulates CTSD expression and AGEs degradation in UVA-induced photoaged fibroblasts and might exert a role in AGEs accumulation in photoaged skin.

686 Quantification of perception toward skin complexion on sun-exposed vs. sun-protected skin using an artificial neural network

686 Quantification of perception toward skin complexion on sun-exposed vs. sun-protected skin using an artificial neural network

Characterizing Dermal Transcriptional Change in the Progression from Sun-Protected Skin to Actinic Keratosis

Understanding early tumorigenic events have obvious diagnostic and prognostic implications, particularly in the skin since this is the site of more US cancer diagnoses than any other organ (Rogers et al., 2015). Actinic keratosis (AK) are dysplastic keratinocyte lesions characterized by irregularly shaped scaly papules frequently manifesting on sun-damaged skin, and are considered precursor lesions which can develop into cutaneous squamous cell carcinoma (cSCC), the second most common keratinocyte cancer (Siegel et al., 2017).

Lymphocyte subsets and Langerhans cells in the skin of kidney transplant recipients under three different immunosuppressive regimens.

Renal transplant recipients (RTRs) are at increased risk of developing skin cancer; however, the role of immunosuppression is not yet fully understood. In this study, we evaluated the immunohistochemical changes in the skin of RTRs under three different immunosuppression regimens: mTOR inhibitors (mTORi), sirolimus or everolimus, mycophenolic acid (MPA) precursors such as mycophenolate sodium or mofetil, or azathioprine (AZA). We evaluated biopsies of sun-exposed and sun-protected skin for immunohistochemical quantification of B lymphocytes (CD20+ ), T lymphocytes (CD3+ , CD4+ , and CD8+ ), and Langerhans cells (LCs) (CD1a+ ) in 30 RTRs and 10 healthy controls. The RTRs were divided into three groups: mTORi (n = 10), MPA (n = 10), and AZA (n = 10). No differences were observed in the number of B lymphocytes. However, a significant decrease in the number of T lymphocytes and LCs was observed in both sun-protected and sun-exposed skin in the AZA and MPA groups, although to a lesser degree in the latter group. The skin of the mTORi group did not differ from that of the control group in terms of the number of B and T lymphocytes and LCs. Patients treated with mTORi exhibit preserved cellular elements related to cutaneous immune surveillance. The use of AZA induced a greater degree of skin immunosuppression than in the control group, as demonstrated by the decrease in T lymphocytes and LCs.

129 Pervasive immune dysfunction characterizes photoaged skin

Long-term sun exposure markedly accelerates the skin changes of chronological aging, leading to deterioration of skin function and appearance in a process termed Photoaging. The molecular mechanisms underlying photoaging remain incompletely defined, due largely to the limitations of ex vivo studies. To interrogate this phenomenon in vivo, we performed single-cell RNA-seq of sun-protected and sun-exposed skin from four ∼20-year-old (yo) and four ∼90yo donors. Clustering and annotation of the resulting cells revealed pervasive immune dysfunction in photoaged skin.

Assessing the Role of Carbonyl Adducts, Particularly Malondialdehyde Adducts, in the Development of Dermis Yellowing Occurring during Skin Photoaging.

Solar elastosis is associated with a diffuse yellow hue of the skin. Photoaging is related to lipid peroxidation leading to the formation of carbonyl groups. Protein carbonylation can occur by addition of reactive aldehydes, such as malondialdehyde (MDA), 4-hydroxy-nonenal (4-HNE), and acrolein. All the proteins concerned with this modification, and the biological consequences of adduct formation, are not completely identified. The link between yellowish skin and dermal carbonylated proteins induced by aldehyde adducts was investigated. The study was carried out on ex vivo skin samples from sun-exposed or sun-protected areas and on in vitro dermal equivalent models incubated with 5 mM MDA, 4-HNE, or acrolein. The yellow color and the level of MDA, 4-HNE, and acrolein adducts were evaluated. Yellowish color differences were detected in the dermis of sun-exposed skin compared to sun-protected skin and in in vitro models following addition of MDA, 4-HNE, or acrolein. The yellowing was correlated with the carbonyl adducts increasing in the dermis and in in vitro models incubated with aldehydes. The stronger yellowing seemed to be mediated more by MDA than 4-HNE and acrolein. These observations suggest that dermal carbonylation especially induced by MDA result in the yellow hue of dermis and is involved, in part, in the yellowing observed during skin photoaging.

Reduced expression of Collagen 17A1 in naturally aged, photoaged, and UV-irradiated human skin in vivo: Potential links to epidermal aging

Collagen 17A1 (COL17A1) is atransmembrane structural component of the hemidesmosome that mediate adhesion of keratinocytes to the underlying membrane. Recent work in mouse showed that COL17A1 deficiency leads to premature skin aging. Although the role COL17A1 in skin aging is becoming recognized in mouse models, its connection to human skin natural aging/photoaging/ultraviolet (UV)-irradiated human skin has received little attention. To determine COL17A1 expression in naturally aged and photoaged as well as acutely UV irradiated human skin, skin samples were obtained from: (1) young (N = 10, 26.7±1.3 years) and aged (N = 10, 84.0 ± 1.7 years) sun-protected buttock skin; (2) photoaged extensor forearm and subject matched sun-protected underarm skin (N = 6, 56.0 ± 3.4 years); (3) solar-simulated UV-irradiated buttock skin (N = 6, 51.2 ± 3.6 years). COL17A1 levels were determined by immunohistology and RT-PCR, and the potential role of COL17A1 in epidermal aging was investigated by immunostaining of the marker for interfollicular epidermal stem cells and keratinocytes proliferation. We found that COL17A1 is specifically expressed in interfollicular epidermal stem cell niches, and that significantly reduced in naturally aged, photoaged, and acute UV-irradiated human skin in vivo. COL17A1 is identified as keratinocyte-specific collagen, and UV irradiation significantly downregulates COL17A1 expression in keratinocytes. Reduced expression of COL17A1 is positively correlated with impaired regeneration of keratinocytes and reduced dermal-epidermal junction as well as thin epidermis in aged human skin (epidermal aging). We also confirmed that keratinocyte-specific integrin β4 (ITGB4), which interacts with COL17A1, is reduced in aged human skin. Mechanistically, we found that matrix metalloproteinases (MMPs) are responsible for UV-mediated COL17A1 degradation in both in vitro keratinocytes and in vivo mouse skin. These data suggest the possible links between reduced expression of COL17A1 and epidermal aging in human skin.

Infiltration of subcutaneous adipose layer into the dermal layer with aging.

The elasticity of the dermal layer decreases with aging, leading to ulcer formation and wrinkling, but the mechanism of this change is not fully understood, because it is difficult to access the complex three-dimensional (3D) internal structure of the dermis. To clarify age-dependent changes in the overall 3D structure of the dermal layer by means of 3D analysis technology. We observed sun-protected human skin by means of X-ray micro CT, identified the layers of the skin, and reconstructed the 3D structure on computer. Age-dependent structural changes of the dermal layer were evaluated by statistical comparison of young and aged skin. Histological observations suggested the presence of two types of ectopic fat deposits, namely infiltrated subcutaneous fat and isolated fat, in the lower region of the reticular dermal layer in aged skin. To elucidate their nature, we observed skin specimens by X-ray microCT. The epidermis, dermal layer, and subcutaneous adipose layer were well differentiated on CT images, and 3D skin was digitally reconstructed on computer. This method clearly showed that the isolated fat observed histologically was in fact connected to the subcutaneous fat, namely all ectopic fat is connected to the subcutaneous adipose layer. Statistical analysis showed that the severity of fat infiltration into dermal layer is significantly increased in aged skin compared with young skin. Our findings indicate that subcutaneous fat infiltrates into the dermal layer of aged skin. Our 3D analysis approach is advantageous to understand changes of complex internal skin structures with aging.

Lupus band test for diagnostic evaluation in systemic lupus erythematosus

The lupus band test (LBT) using a sample of clinically normal skin was proposed as a useful diagnostic test for systemic lupus erythematosus (SLE). It is mostly performed to help diagnosing SLE in patients with insufficient clinical and serological profiles. However, most published studies on its utility are outdated and the results remain controversial. To determine the diagnostic performance of LBT on non-lesion sun-protected (NLSP) and sun-exposed (NLSE) skin for SLE. Consecutively presenting patients with clinical and serological suspicion of SLE who had LBT performed on non-lesion skin during January 2012 to August 2021 were retrospectively studied. LBT performed on either NLSE or NLSP skin biopsies were all included. Laboratory characteristics, number, types and patterns of deposited immunoreactants and disease activity were also assessed. LBT was performed in 57 patients with suspected SLE. LBT was positive in 18/57, 9/28 and 6/21 patients in overall non-lesion, NLSE and NLSP, respectively. Of all patients, 23 patients were diagnosed with SLE and 34 patients with other diseases. Overall, the sensitivity and specificity of LBT on non-lesion skin was 56.5% and 88.2%, respectively. The ability of the test to discriminate between those with and without SLE, assessed by the area under the Receiver-Operating Characteristic curve, was 0.72 (0.61-0.84). The sensitivity and specificity of LBT on NLSE skin was 58.3% and 87.5% while those of NLSP skin, were 57.1% and 85.7%, respectively. We found no significant correlation between the positivity of LBT and overall disease activity. Types, number and pattern of deposited immunoreactants also showed no correlation with disease activity (all p > 0.05). Used as a diagnostic adjunct, non-lesion LBT is still of value for diagnosing SLE in inconclusive cases.

Sun protecting factor value of the Ficus benjamina Linn. fruits extract

Sun Protection Factor or SPF is defined as the ratio between the amount of sunlight energy (UV-B) needed to cause minimal erythema on sun-protected skin with the amount of energy required to cause minimal erythema on the skin that is not protected by sunscreen. This study aims to determine the SPF value of the n-hexane fraction, the ethyl acetate fraction, methanol fraction, ethanol fraction, and butanol fraction from the Ficus benjamina Linn. fruits. SPF measurements can be done using UV-Vis spectrophotometry. The result is the SPF value of n-hexane fraction is 4.935, the ethyl acetate fraction is 19.917, methanol fraction is 4.056, ethanol fraction is 8.342, and butanol fraction is 0,422. The ethyl acetate fraction of Ficus benjamina Linn. fruits has the highest SPF value, and it’s categorized as high-protection.

Basement Membrane Helps Maintain Epidermal Hyaluronan Content

Hyaluronan (HA) is the major glycosaminoglycan in the extracellular matrix of most mammalian tissues, including the epidermis. It is synthesized in epidermis, and mainly metabolized after transfer to the liver via lymphatic vessels in the dermis following its passage through the basement membrane (BM) at the dermal-epidermal junction. The aim of the present study was to investigate the influence of BM integrity on the level of HA in the epidermis. Epidermal HA content was decreased in sun-exposed skin of older subjects, whose BM structure was impaired, compared with sun-exposed young skin and sun-protected skin, in which BM integrity was well maintained. In an organotypic culture model of sun-exposed facial skin, epidermal HA was increased in the presence of inhibitors of BM-degrading matrix metalloproteinases and heparanase. In a skin equivalent model treated with these inhibitors, HA content was increased in the epidermis, but decreased in conditioned medium. These findings suggest that the BM at the dermal-epidermal junction plays an important role in maintaining epidermal HA levels.

Increased PD-L1 Expression in Human Skin Acutely and Chronically Exposed to UV Irradiation.

Overexpression of PD-L1 (CD274) on tumor cells may represent a hallmark of immune evasion, and overexpression has been documented in several tumors including cutaneous squamous cell carcinoma (cSCC). While PD-L1/PD-1 activity in the skin has been primarily described in inflammatory models, our goal was to examine PD-L1 expression in human keratinocytes exposed to UV irradiation. We assessed PD-L1 expression in human sun-protected (SP) and sun-damaged (SD) skin, actinic keratosis (AK), and cSCC using IHC and protein microarray. Both methods found low baseline levels of PD-L1 in SP and SD skin and significantly increased expression in cSCC. Next, we examined PD-L1 expression in acute models of UV exposure. In human SP skin exposed to 2-3 MED of UV (n=20), epidermal PD-L1 was induced in 70% of subjects after 24h (P=0.0001). SKH-1 mice exposed to acute UV also showed significant epidermal PD-L1 induction at 16, 24 and 48h. A time- and dose-dependent induction of PD-L1 was confirmed in cultured human keratinocytes after UV, which was markedly reduced in the presence of MEK/ERK, JNK or STAT3 inhibitors. These findings suggest that UV induces upregulation of PD-L1 through established, pharmacologically targetable stress-signaling pathways in keratinocytes.

Rejuvenation of Aged Human Skin by Injection of Cross-linked Hyaluronic Acid.

Dermal injection of chemically cross-linked hyaluronic acid (CL-HA) is a common procedure to smooth wrinkles and add fullness to the face. Due to its physical properties, CL-HA both fills space and exerts mechanical forces within the dermis. Dermal fibroblasts produce the collagen-rich extracellular matrix (ECM), which comprises the bulk of skin. Attachment to the ECM allows fibroblasts to achieve a stretched, morphology, which confers a functional phenotype that maintains collagen production. In aged/photoaged skin, collagen fibril fragmentation impairs fibroblast attachment, resulting in a collapsed morphology and reduced collagen production. This article describes investigations of the impact of CL-HA injection on fibroblast morphology and function in the aged/photoaged human skin. Fifty-three subjects, age 70 years or older, received a single injection of saline (vehicle control) and CL-HA (0.5 ml each) in separate adjacent skin sites on photodamaged forearm or sun-protected buttock skin. Full-thickness punch biopsies were obtained from injected skin sites at various times and analyzed for molecular and cellular changes. Injected CL-HA forms discreet pockets that localize to areas of the dermis that contain fragmented, loosely organized collagen fibrils. These CL-HA pockets fill space and apply mechanical forces on adjacent ECM that induce stretching of fibroblasts. This stretching is associated with increased collagen gene expression and deposition of mature collagen fibril bundles, which resemble those observed in young skin. CL-HA injected into aged/photoaged human dermis acts by both filling space and inducing production of collagen by dermal fibroblasts. Deposition of mature collagen, which remains in the skin for decades, likely confers long-term benefits. Reduced collagen production in aged/photoaged skin is an adaptive response of fibroblasts to ECM fragmentation, rather than inherent cellular aging mechanisms.

Single-Cell RNA Sequencing Unravels Heterogeneity of the Stromal Niche in Cutaneous Melanoma Heterogeneous Spheroids

Simple SummaryCutaneous malignant melanoma is one of the most dangerous forms of skin cancer affecting humans. Frequently, it is linked to DNA damage due to ultraviolet radiation. Photoageing along with chronological ageing are therefore critically important factors in melanoma biology. The tissue microenvironment is also heavily affected by induced senescence. There is growing evidence that senescent dermal fibroblasts can consequently promote tumour progression. We focused on the analysis of microenvironmental factors represented in melanoma heterogeneous spheroids by either photodamaged or normal dermal fibroblasts. Our effort was primarily focused on the determination of the functional diversity of fibroblasts in heterogeneous spheroids. Therefore, we analysed these 3D models by single-cell RNA sequencing and advanced bioinformatic analysis. We aimed to map the fibroblast diversity resulting from previously acquired damage caused by exposure to extrinsic and intrinsic stimuli. Using this robust methodology, we highlighted molecules that could become important for the control of melanoma cell–cancer-associated fibroblast interaction as an essential part of the tumour microenvironment.Heterogeneous spheroids have recently acquired a prominent position in melanoma research because they incorporate microenvironmental cues relevant for melanoma. In this study, we focused on the analysis of microenvironmental factors introduced in melanoma heterogeneous spheroids by different dermal fibroblasts. We aimed to map the fibroblast diversity resulting from previously acquired damage caused by exposure to extrinsic and intrinsic stimuli. To construct heterogeneous melanoma spheroids, we used normal dermal fibroblasts from the sun-protected skin of a juvenile donor. We compared them to the fibroblasts from the sun-exposed photodamaged skin of an adult donor. Further, we analysed the spheroids by single-cell RNA sequencing. To validate transcriptional data, we also compared the immunohistochemical analysis of heterogeneous spheroids to melanoma biopsies. We have distinguished three functional clusters in primary human fibroblasts from melanoma spheroids. These clusters differed in the expression of (a) extracellular matrix-related genes, (b) pro-inflammatory factors, and (c) TGFβ signalling superfamily. We observed a broader deregulation of gene transcription in previously photodamaged cells. We have confirmed that pro-inflammatory cytokine IL-6 significantly enhances melanoma invasion to the extracellular matrix in our model. This supports the opinion that the aspects of ageing are essential for reliable melanoma 3D modelling in vitro.

Decrease of laminin-511 in the basement membrane due to photoaging reduces epidermal stem/progenitor cells

Daily sunlight exposure damages the epidermal basement membrane (BM) and disrupts epidermal homeostasis. Inter-follicular epidermal stem cells (IFE-SCs) regulate epidermal proliferation and differentiation, which supports epidermal homeostasis. Here, we examine how photoaging affects the function of IFE-SCs and we identify key components in their cellular environment (niche). We found that sun-exposed skin showed a decrease of MCSP-positive and β1-integrin-positive cells concomitantly with a decrease of laminin-511 at the dermal–epidermal junction (DEJ), as compared with sun-protected skin. Higher levels of laminin-511 were associated with not only increased efficiency of colony formation, but also higher expression levels of MCSP as well as other stem cell markers such as Lrig1, ITGB1, CD44, CD46, DLL1, and K15 in keratinocytes from skin of 12- to 62-year-old subjects. UVB exposure to cultured human skin impaired laminin-511 integrity at the dermal–epidermal junction and reduced MCSP-positive basal epidermal cells as well as K15-positive cells. Combined treatment with matrix metalloproteinase and heparanase inhibitors protected the integrity of laminin-511 and inhibited the reduction of MCSP-positive cells and K15-positive cells. These results suggest that photoaging may reduce the levels of MCSP-positive and K15-positive epidermal stem/progenitor cells in the epidermis via loss of laminin-511 at the dermal–epidermal junction.