Aged Epidermis Research Articles

The Role of PGC-1α in Aging Skin Barrier Function.

Skin provides a physical and immune barrier to protect the body from foreign substances, microbial invasion, and desiccation. Aging reduces the barrier function of skin and its rate of repair. Aged skin exhibits decreased mitochondrial function and prolonged low-level inflammation that can be seen in other organs with aging. Peroxisome proliferator-activated receptor (PPAR)-γ coactivator-1α (PGC-1α), an important transcriptional coactivator, plays a central role in modulating mitochondrial function and antioxidant production. Mitochondrial function and inflammation have been linked to epidermal function, but the mechanisms are unclear. The aim of this review is to discuss the mechanisms by which PGC-1α might exert a positive effect on aged skin barrier function. Initially, we provide an overview of the function of skin under physiological and aging conditions, focusing on the epidermis. We then discuss mitochondrial function, oxidative stress, cellular senescence, and inflamm-aging, the chronic low-level inflammation observed in aging individuals. Finally, we discuss the effects of PGC-1α on mitochondrial function, as well as the regulation and role of PGC-1α in the aging epidermis.

Chronological aging impacts abundance, function and microRNA content of extracellular vesicles produced by human epidermal keratinocytes.

The disturbance of intercellular communication is one of the hallmarks of aging. The goal of this study is to clarify the impact of chronological aging on extracellular vesicles (EVs), a key mode of communication in mammalian tissues. We focused on epidermal keratinocytes, the main cells of the outer protective layer of the skin which is strongly impaired in the skin of elderly. EVs were purified from conditioned medium of primary keratinocytes isolated from infant or aged adult skin. A significant increase of the relative number of EVs released from aged keratinocytes was observed whereas their size distribution was not modified. By small RNA sequencing, we described a specific microRNA (miRNA) signature of aged EVs with an increase abundance of miR-30a, a key regulator of barrier function in human epidermis. EVs from aged keratinocytes were found to be able to reduce the proliferation of young keratinocytes, to impact their organogenesis properties in a reconstructed epidermis model and to slow down the early steps of skin wound healing in mice, three features observed in aged epidermis. This work reveals that intercellular communication mediated by EVs is modulated during aging process in keratinocytes and might be involved in the functional defects observed in aged skin.

Restoring Endoplasmic Reticulum Calcium Stores in Aged Epidermis Improves the Epidermal Calcium Gradient and Enhances FLG Expression

Aging impairs epidermal differentiation and barrier function, making aged skin susceptible to dryness, dermatitis and infection. Here, we show that pharmacologically enhancing endoplasmic reticulum Ca2+ stores with CDN 1163, a small molecular SERCA2b allosteric activator, corrects age-related defects in Ca2+ storage in aged keratinocytes, partially corrects the abnormal Ca2+ gradient seen in aged epidermis, and enhances filaggrin expression in aged skin samples.

Deletion of NRF2 disturbs composition, morphology, and differentiation of the murine tail epidermis in chronological aging.

NRF2 is a master regulator of the cellular protection against oxidative damage in mammals and of multiple pathways relevant in the mammalian aging process. In the epidermis of the skin NRF2 contributes additionally to the formation of an antioxidant barrier to protect from environmental insults and is involved in the differentiation process of keratinocytes. In chronological aging of skin, the capacity for antioxidant responses and the ability to restore homeostasis after damage are impaired. Surprisingly, in absence of extrinsic stressors, NRF2 deficient mice do not show any obvious skin phenotype, not even at old age. We investigated the differences in chronological epidermal aging of wild type and NRF2-deficient mice to identify the changes in aged epidermis that may compensate for absence of this important transcriptional regulator. While both genotypes showed elevated epidermal senescence markers (increased Lysophospholipids, decreased LaminB1 expression), the aged NRF2 deficient mice displayed disturbed epidermal differentiation manifested in irregular keratin 10 and loricrin expression. The tail skin displayed less age-related epidermal thinning and a less pronounced decline in proliferating basal epidermal cells compared to the wildtype controls. The stratum corneum lipid composition also differed, as we observed elevated production of barrier protective linoleic acid (C18:2) and reduced abundance of longer chain saturated lignoceric acid (C24:0) among the stratum corneum fatty acids in the aged NRF2-deficient mice. Thus, despite epidermal differentiation being disturbed in aged NRF2-deficient animals in homeostasis, adaptations in keratinocyte proliferation and barrier lipid synthesis could explain the lack of a more severe phenotype.

190 Down-regulation of the NOTCH pathway during skin aging contributes to functional epidermal defects through miR-30a activation

Skin aging is a complex biological process leading to multiple functional defects in the different structure of the skin tissues. Epidermal aging is especially characterized by an alteration of the tissue renewal associated to an impairment of the keratinocytes differentiation process. We have previously reported that the microRNA miR-30a is over-expressed in aged epidermis and we have shown in organotypic skin models that this induction impairs epidermal differentiation, induces cell apoptosis, increases oxidative stress and leads to strong defects of the epidermal barrier function.

Pgc-1α controls epidermal stem cell fate and skin repair by sustaining NAD+ homeostasis during aging

ObjectiveThe epidermal barrier is renewed by the activation, proliferation, and differentiation of keratinocyte stem cells after injury and aging impedes this repair process through undefined mechanisms. We previously identified a gene signature of metabolic dysfunction in aged murine epidermis, but the precise regulators of epidermal repair and age-related growth defects are not well established. Aged mouse models as well as mice with conditional epidermal loss of the metabolic regulator peroxisome proliferator-activated receptor gamma coactivator-1 alpha (Pgc-1α) were used to explore the cellular pathways which control skin repair after injury and stress. MethodsAged mice or those with epidermal Pgc-1α deletion (epiPgc-1α KO) and young or Pgc1afl/fl controls were subjected to wound injury, UVB exposure or the inflammatory agent TPA. In vivo and ex vivo analyses of wound closure, skin structure, cell growth and stem cell differentiation were used to understand changes in epidermal re-growth and repair resulting from aging or Pgc-1α loss. ResultsAging impairs epidermal re-growth during wound healing and results in lower expression of Pgc-1α. Mice with conditional deletion of epidermal Pgc-1α exhibit greater inflammation- and UVB-induced cell differentiation, reduced proliferation, and slower wound healing. epiPgc-1α KO mice also displayed reduced keratinocyte NAD+ levels, shorter telomeres, and greater poly ADP-ribosylation, resulting in enhanced stress-stimulated p53 and p21 signaling. When NAD+ was reduced by Pgc-1α loss or pharmacologic inhibition of NAD+ synthesis, there was reduced stress-induced proliferation, increased differentiation, and protection against DNA damage via enhanced epidermal shedding. Similarly, aged mice exhibit disrupted epidermal NAD+ homeostasis and enhanced p53 activation, resulting in p21 growth arrest after wounding. NAD+ precursor treatment restores epidermal growth from old skin to that of young. ConclusionsOur studies identify a novel role for epidermal Pgc-1α in controlling epidermal repair via its regulation of cellular NAD+ and downstream effects on p53-driven growth arrest. We also establish that parallel mechanisms are evident in aged epidermis, showing that NAD+ signaling is an important controller of physiologic skin repair and that dysfunction of this pathway contributes to age-related wound repair defects.

Facial skin ageing: Key concepts and overview of processes.

IntroductionThe face is a cosmetically sensitive region where the process of ageing is most clearly manifested. With increased focus on anti‐ageing and longevity, more anti‐senescent treatments are being proposed despite limited evidence. This study outlines the pathways and mechanisms underpinning the biological process of ageing in the face.MethodsComprehensive searches of MEDLINE, EMBASE, Cochrane Library and CINAHL from inception to 2020. Inclusion criteria included all empirical human research studies specific to facial ageing features, written in the English language.ResultsA total of 65 papers met inclusion criteria for analysis. Pathways were subdivided into intrinsic and extrinsic senescence mechanisms. Intrinsic pathways included genetics, generation of reactive oxygen species and hormonal changes. Extrinsic pathways included photoageing and damage to skin layers. The combined intrinsic and extrinsic pathway alterations result in wrinkles, higher laxity, slackness and thinning of the skin. Skin functions such as barrier immune function, wound healing, thermoregulation and sensory function are also impaired.ConclusionThe ageing process is unique to the individual and depends on the interplay between an individual's genetics and external environmental factors. Through understanding the molecular and cellular mechanisms, an appreciation of the consequent structural and functional changes can be achieved. Based on this knowledge, further research can focus on how to slow or impede the ageing process and identify specific targets to develop and evolve new treatment strategies.

Tideglusib promotes wound healing in aged skin by activating PI3K/Akt pathway

BackgroundAging disturbs the skin morphology and function, manifested as thinned epithelium and impaired wound healing. As a major type of skin cells, epidermal stem cells (EpiSCs) are inevitably affected by aging. The effect of age on EpiSCs and wound healing needs to be further explored.MethodsSkin RNA-seq data of young (5 months) and old (30 months) CB6F1 mice were obtained from GEO Series GSE35322 with 10 in each age group. Differentially expressed genes were analyzed, and EpiSCs-related pathways were enriched by KEGG. The age-related changes of the screened PI3K/Akt pathway were validated by Western Blot and immunofluorescence of epidermis of SD rats (2, 17, and 23 months, n = 6). The expression of upstream protein EGFR was assessed by immunofluorescence in skin of mice (4, 13, and 23 months, n = 6) and human (respectively, 23, 28, 30 years old in the young group and 69, 73, 78 years old in the old group) skin. Inhibitors of EGFR were used to verify its effects on EpiSCs and wound healing. The small molecule drug Tideglusib was tested for its effects on signaling pathways of EpiSCs and wound healing of aged rats. Western Blot was used for the detection of signaling pathways in in vitro experiments. Cell migration assays were used to assess cell migration ability. Flow cytometry was used to detect changes in cell cycle and apoptosis levels. Sulforhodamine B assay and CCK-8 assay were used to evaluate cell proliferation and viability, respectively. Student’s t test and one-way analysis of variance (ANOVA) followed by the multiple comparisons Bonferroni test were used for statistical analysis. The 0.05 level of confidence was accepted as a significant difference.ResultsEpiSCs-related PI3K/Akt pathway was enriched by KEGG and verified by decreased phosphorylation of Akt (32.1 ± 13.8%, P < 0.01) and mTOR (38.9 ± 11.8%, P < 0.01) in aged epidermis of rats. Furthermore, the expression of PI3K/Akt-upstream EGFR decreased with age in the epidermis of mouse (27.6 ± 5.5%, P < 0.01) and human (25.8 ± 9.3%, P < 0.01). With EGFR blocked by Erlotinib, EpiSCs showed reduced phosphorylation of Akt (30.4 ± 10.6%, P < 0.01) and mTOR (39.8 ± 12.8%, P < 0.01), impaired proliferation and migration after incubated for 24 h and 36 h (P < 0.05), and higher levels of apoptosis (11.9 ± 1.7%, P < 0.05), and rats showed slower wound healing from d7 to d14 after wounding (P < 0.01). In addition to slower wound healing rates, aged rats also showed a decrease in the efficacy of EGF, partly due to the downregulated EGFR expression. By activating PI3K/Akt pathway, Tideglusib promoted the proliferation and migration of EpiSCs with apoptosis inhibited (P < 0.01) and accelerated wound healing in aged rats from d7 to d14 after wounding (P < 0.05). Notably, the combined use of Tideglusib and EGF could further enhance wound healing in aged rats.ConclusionsThe decreased expression of EGFR in epidermis with age resulted in decreased activity of the PI3K/Akt pathway and limited EGF efficacy. Tideglusib could assist wound healing in aged rats via activating PI3K/Akt pathway, which may be considered as an ingredient for medical and cosmetics use.

Decreased Calcium-Sensing Receptor Expression Controls Calcium Signaling and Cell-To-Cell Adhesion Defects in Aged Skin

The calcium-sensing receptor (CaSR) drives essential calcium ion (Ca2+) and E-cadherin‒mediated processes in the epidermis, including differentiation, cell-to-cell adhesion, and epidermal barrier homeostasis in cells and inyoung adult mice. We now report that decreased CaSR expression leads to impaired Ca2+ signal propagation in aged mouse (aged >22 months) epidermis and human (aged >79 years, donor age) keratinocytes. Baseline cytosolic Ca2+ concentrations were higher, and capacitive Ca2+ entry was lower in aged than in young keratinocytes. As in Casr-knockout mice (EpidCaSR-/-), decreased CaSR expression led to decreased E-cadherin and phospholipase C-γ expression and to a compensatory upregulation of STIM1. Pretreatment with the CaSR agonist N-(3-[2-chlorophenyl]propyl)-(R)-alpha-methyl-3-methoxybenzylamine normalized Ca2+ propagation and E-cadherin organization after experimental wounding. These results suggest that age-related defects in CaSR expression dysregulate normal keratinocyte and epidermal Ca2+ signaling, leading to impaired E-cadherin expression, organization, and function. These findings show an innovative mechanism whereby Ca2+- and E-cadherin‒dependent functions are impaired in aging epidermis and suggest a new therapeutic approach by restoring CaSR function.

337 The calcium sensing receptor regulates epidermal intracellular Ca2+ signaling and re-epithelialization in aged epidermis

337 The calcium sensing receptor regulates epidermal intracellular Ca2+ signaling and re-epithelialization in aged epidermis

Ceramides metabolism and impaired epidermal barrier in cutaneous diseases and skin aging: focus on the role of the enzyme PNPLA1 in the synthesis of ω-O-acylceramides and its pathophysiological involvement in some forms of congenital ichthyoses

The outermost layer of the skin, the stratum corneum, is essential for the protective barrier functions of the skin. It results from the stacking of corneocytes, the dead flattened cells resulting from epidermal terminal differentiation of underlying living keratinocytes. The cornified lipid envelope, encapsulating corneocytes, and the extracellular mortar-like multilayered lipid matrix, called lamellae, are two crucial elements of the epidermal barrier. Stratum corneum extracellular lipids are mainly composed of ceramides, cholesterol and free fatty acids. Ceramides, and more specifically the epidermis specific ω-O-acylceramides, are essential for lipid-matrix organization into lamellae and formation of the corneocyte lipid envelope. Pathophysiological studies of inherited lipid metabolism disorders recently contributed to a better understanding of stratum corneum lipid metabolism. In the lab, our data from patients with Autosomal Recessive Congenital Ichthyosis and a murine knock-out model showed that the enzyme PNPLA1 is essential for the last step of synthesis of omega-O-acylceramides. Skin aging is a complex biological process caused by genetic and extrinsic factors e.g. sun exposure, smoke, and pollution. Aging skin is marked by a senescence-related decline in lipid and water content, which ultimately impairs epidermal barrier function. Thus, aged epidermis is prone to develop altered drug permeability, increased susceptibility to irritants contact dermatitis and severe xerosis. Ceramide deficiency may account, at least in part, for the dysfunction of the stratum corneum associated with ageing. Hence, treatments able to increase skin-ceramide levels could improve the epidermal barrier function in aged skin. Many animal testing and clinical trials are taken in that regard.

In vitro epidermis model mimicking IGF-1-specific age-related decline.

Ageing is a complex multifaceted process affecting skin functionality and structure. Several 3D organotypic skin culture models have reproduced ageing by inducing replicative senescence, glycation or oxidative stress. Yet, very few models have focused on hormonal ageing and especially the insulin-like growth factor 1 (IGF-1) signalling pathway, which has been associated with longevity in animal studies and is necessary for the early stages of skin development. In this study, we built an organotypic epidermis model with targeted IGF-1 receptor knockdown to reproduce some aspects of hormonal ageing on skin. Our model displayed morphological and functional features of aged epidermis, which were mostly attributed to a loss of function of the Stratum basale. IGF-1 receptor knockdown keratinocytes depicted an extended cell cycle, reduced proliferation potential and reduced adhesion capacities and greater sensitivity to oxidative stress than control cells. Altogether, this model represents an essential tool for further investigations into the mechanisms linked to some aspects of hormonal decline or when screening for potent anti-ageing compounds.

Aging-Associated Decline of Epidermal PSMD8 Contributes to Impaired Skin Function

Aging-Associated Decline of Epidermal PSMD8 Contributes to Impaired Skin Function

Lower levels of interleukin-1β gene expression are associated with impaired Langerhans' cell migration in aged human skin.

SummaryLangerhans’ cells (LC) play pivotal roles in skin immune responses, linking innate and adaptive immunity. In aged skin there are fewer LC and migration is impaired compared with young skin. These changes may contribute to declining skin immunity in the elderly, including increased skin infections and skin cancer. Interleukin‐1β (IL‐1β) and tumour necrosis factor‐α (TNF‐α) are mandatory signals for LC migration and previous studies suggest that IL‐1β signalling may be dysregulated in aged skin. Therefore, we sought to explore the mechanisms underlying these phenomena. In skin biopsies of photoprotected young (< 30 years) and aged (> 70 years) human skin ex vivo, we assessed the impact of trauma, and mandatory LC mobilizing signals on LC migration and gene expression. Biopsy‐related trauma induced LC migration from young epidermis, whereas in aged skin, migration was greatly reduced. Interleukin‐1β treatment restored LC migration in aged epidermis whereas TNF‐α was without effect. In uncultured, aged skin IL‐1β gene expression was lower compared with young skin; following culture, IL‐1β mRNA remained lower in aged skin under control and TNF‐α conditions but was elevated after culture with IL‐1β. Interleukin‐1 receptor type 2 (IL1R2) gene expression was significantly increased in aged, but not young skin, after cytokine treatment. Keratinocyte‐derived factors secreted from young and aged primary cells did not restore or inhibit LC migration from aged and young epidermis, respectively. These data suggest that in aged skin, IL‐1β signalling is diminished due to altered expression of IL1B and decoy receptor gene IL1R2.

471 NFAT-5 regulates the response to osmotic stress, clonogenic potential and differentiation of normal human keratinocytes and disappears in the aged epidermis

471 NFAT-5 regulates the response to osmotic stress, clonogenic potential and differentiation of normal human keratinocytes and disappears in the aged epidermis

339 Naturally occurring polysaccharides increase proliferation of stem cells from aged epidermis

339 Naturally occurring polysaccharides increase proliferation of stem cells from aged epidermis

Epidermal aging and anti-aging strategies

Epithelial senescence is a complex process depending on intrinsic as well as extrinsic factors (e.g., UV or IR light, tobacco smoke) and must be seen in the context of the aging process especially of the corium and the subcutis. Morphological alterations become apparent in the form of epithelial atrophy, structural changes within the basal membrane, and a decrease in cell count of melanocytes and Langerhans cells. Signs of cellular senescence are reduced proliferation of keratinocytes, cumulation of dysplastic keratinocytes, various mutations (e.g., c-Fos/c-Jun, STAT3, FoxO1), as well as multiple lipid or amino acid metabolic aberrations (e.g., production of advanced glycation endproducts). This causes functional changes within the physical (lipid deficiency, water distribution dysfunction, lack of hygroscopic substances), chemical (pH conditions, oxygen radicals), and immunological barrier. Prophylactically, barrier-protective care products, antioxidant substances (e.g., vitamin C, B3, E, polyphenols, flavonoids), sunscreen products/measurements, and retinoids are used. For correcting alterations in aged epidermis, chemical peelings (fruit acids, β-hydroxy acid, trichloroacetic acid, phenolic compounds), non-ablative (IPL, PDL, Nd:YAG) as well as ablative (CO2, Erbium-YAG) light-assisted methods are used.

A three-dimensional skin equivalent reflecting some aspects of in vivo aged skin.

Human skin undergoes morphological, biochemical and functional modifications during the ageing process. This study was designed to produce a 3-dimensional (3D) skin equivalent in vitro reflecting some aspects of in vivo aged skin. Reconstructed skin was generated by co-culturing skin fibroblasts and keratinocytes on a collagen-glycosaminoglycan-chitosan scaffold, and ageing was induced by the exposition of fibroblasts to Mitomycin-C (MMC). Recently published data showed that MMC treatment resulted in a drug-induced accelerated senescence (DIAS) in human dermal fibroblast cultures. Next to established ageing markers, histological changes were analysed in comparison with in vivo aged skin. In aged epidermis, the filaggrin expression is reduced in vivo and in vitro. Furthermore, in dermal tissue, the amount of elastin and collagen is lowered in aged skin in vivo as well as after the treatment of 3D skin equivalents with MMC in vitro. Our results show histological signs and some aspects of ageing in a 3D skin equivalent in vitro, which mimics aged skin in vivo.

Analysis of gene expression dynamics revealed delayed and abnormal epidermal repair process in aged compared to young skin.

With aging, epidermal homeostasis and barrier function are disrupted. In a previous study, we analyzed the transcriptomic response of young skin epidermis after stratum corneum removal, and obtained a global kinetic view of the molecular processes involved in barrier function recovery. In the present study, the same analysis was performed in aged skin in order to better understand the defects which occur with aging. Thirty healthy male volunteers (67 ± 4 years old) were involved. Tape-strippings were carried out on the inner face of one forearm, the other unstripped forearm serving as control. At 2, 6, 18, 30 and 72 h after stripping, TEWL measurements were taken, and epidermis samples were collected. Total RNA was extracted and analyzed using DermArray® cDNA microarrays. The results highlighted that barrier function recovery and overall kinetics of gene expression were delayed following stripping in aged skin. Indeed, the TEWL measurements showed that barrier recovery in the young group appeared to be dramatically significant during the overall kinetics, while there were no significant evolution in the aged group until 30 h. Moreover, gene expression analysis revealed that the number of modulated genes following tape stripping increased as a function of time and reached a peak at 6 h after tape stripping in young skin, while it was at 30 h in aged skin, showing that cellular activity linked to the repair process may be engaged earlier in young epidermis than in aged epidermis. A total of 370 genes were modulated in the young group. In the aged group, 382 genes were modulated, whose 184 were also modulated in the young group. Only eight genes that were modulated in both groups were significantly differently modulated. The characterization of these genes into 15 functional families helped to draw a scenario for the aging process affecting epidermal repair capacity.

Reversal of Murine Epidermal Atrophy by Topical Modulation of Calcium Signaling

Cytosolic Ca(2+) signals are performed by Ca(2+) releases from the endoplasmic reticulum and Ca(2+) influx from the extracellular medium. Releases rely on the refilling of the intracellular Ca(2+) stores by the Ca(2+) influx "Store-Operated Calcium Entry" (SOCE) via the channel Orai1. Here we show that Orai1 expression, SOCE amplitude, and epidermal proliferation are decreased in the epidermis of patients with skin fragility when compared with aged nonatrophic skin. Epidermal atrophy was induced in mice by the inhibition of Orai1 with small interfering RNA and the topical application of a SOCE blocker BTP2. The inhibition of Orai1 impaired the heparin-binding epidermal growth factor (HB-EGF)-induced Ca(2+) influxes and fully prevented the mitogen effect of HB-EGF in primary human keratinocytes. Importantly, epidermal proliferation correlated with Orai1 expression in mice. Conversely, the topical application of an Orai1 activator, the benzohydroquinone (BHQ), increased the epidermal thickness and proliferation, whereas the pro-proliferative effect of BHQ was prevented by the inhibition of Orai1. Finally, the topical application of BHQ reversed the epidermal atrophy induced by corticosteroids in mice. The topical modulation of Ca(2+) signals may thus be a promising therapeutic strategy in dermatology.