The skin barrier: Epidermis vs environment

Comparative genomics of sirenians reveals evolution of filaggrin and caspase-14 upon adaptation of the epidermis to aquatic life

The mammalian epidermis has evolved to protect the body in a dry environment. Genes of the epidermal differentiation complex (EDC), such as FLG (filaggrin), are implicated in the barrier function of the epidermis. Here, we investigated the molecular evolution of the EDC in sirenians (manatees and dugong), which have adapted to fully aquatic life, in comparison to the EDC of terrestrial mammals and aquatic mammals of the clade Cetacea (whales and dolphins). We show that the main subtypes of EDC genes are conserved or even duplicated, like late cornified envelope (LCE) genes of the dugong, whereas specific EDC genes have undergone inactivating mutations in sirenians. FLG contains premature stop codons in the dugong, and the ortholog of human CASP14 (caspase-14), which proteolytically processes filaggrin, is pseudogenized in the same species. As FLG and CASP14 have also been lost in whales, these mutations represent convergent evolution of skin barrier genes in different lineages of aquatic mammals. In contrast to the dugong, the manatee has retained functional FLG and CASP14 genes. FLG2 (filaggrin 2) is truncated in both species of sirenians investigated. We conclude that the land-to-water transition of sirenians was associated with modifications of the epidermal barrier at the molecular level.

Mechanical Characterization of Anchoring Devices for the Prevention of Driveline Infection in Left Ventricular Assist Device Patients

Driveline infection (DLI) is associated with increased mortality and morbidity in left ventricular assist device (LVAD) patients. Because trauma to the driveline exit-site (DLES) is a risk factor for DLI, adhesive anchoring devices are used to immobilize the DL. In this study, commonly used products (identified through literature review and contact with nine international VAD implantation centers) were mechanically characterized to evaluate their effectiveness in preventing DLES trauma. Eight devices were tested in an in vitro abdominal model of the DLES, where a tensile force (10 N) was applied to a HeartMate 3 DL, whereas the resulting force ( FTotal ) on the DLES was recorded using a three-axis load cell. Four devices (CathGrip: FTotal = 2.1 ± 0.4 N, Secutape: FTotal = 2.6 ± 0.3 N, Hollister: FTotal = 2.7 ± 0.5 N, Tubimed: FTotal = 2.9 ± 0.2 N) were significantly ( p < 0.05) better at preventing tensile forces at the DLES compared to the other four devices (Main-Lock: FTotal = 3.7 [0.7] N, Secutape sensitive: FTotal = 3.9 ± 0.4 N, Foley Anchor: FTotal = 4.3 ± 0.5 N, Grip-Lok: FTotal = 5.4 ± 0.8 N). Immobilization of the DL with each anchoring device resulted in lower tensile force on the DLES than without an anchor ( FTotal = 8.2 ± 0.3 N). In conclusion, the appropriate selection of anchoring devices plays a critical role in reducing the risk of DLI, whereas the CathGrip, Secutape, Hollister, or Tubimed were superior in preventing trauma to the DLES in this study.

Comparative immunohistochemical analysis suggests a conserved role of EPS8L1 in epidermal and hair follicle barriers of mammals

The mammalian skin and its appendages depend on tightly coordinated differentiation of epithelial cells. Epidermal growth factor receptor (EGFR) pathway substrate 8 (EPS8) like 1 (EPS8L1) is enriched in the epidermis among human tissues and has also been detected in the epidermis of lizards. Here, we show by the analysis of single-cell RNA-sequencing data that EPS8L1 mRNA is co-expressed with filaggrin and loricrin in terminally differentiated human epidermal keratinocytes. Comparative genomics indicated that EPS8L1 is conserved in all main clades of mammals, whereas the orthologous gene has been lost in birds. Using a polyclonal antibody against EPS8L1, we performed an immunohistochemical screening of skin from diverse mammalian species and immuno-electron microscopy of human skin. EPS8L1 was detected predominantly in the granular layer of the epidermis in monotremes, marsupial, and placental mammals. The labeling was partly associated with cell membranes, and it was evident along the perimeter of keratinocytes at the transition with the cornified layer of the epidermis, similar to involucrin distribution. Basal, spinous, and the fully mature cornified layers lacked immunolabeling of EPS8L1. In addition to the epidermis, the hair follicle inner root sheath (IRS) was immunolabeled. Both epidermal granular layer and IRS contribute to the barrier function of the skin, suggesting that EPS8L1 is involved in the regulation of these barriers.

The study of wound healing activity of Thespesia populnea L. bark, an approach for accelerating healing through nanoparticles and isolation of main active constituents

The present study provides an evaluation for the wound healing activity of the ethanolic extract of Thespesia populnea L. bark (EBE) and its successive fractions in two doses level (1&2%), designed for determining the most bioactive fraction and the suitable dose. Furthermore, development of the most convenient formulation for these bioactive fractions through either their direct incorporation into hydrogel formulations or incorporation of chitosan-loaded nanoparticles with these bioactive fractions into hydrogel formulations. The highest excision wound healing activity was observed in petroleum ether (Pet-B) followed by ethyl acetate (Etac-B) fractions at the high dose (2%). The most suitable formulation designed for the Etac-B fraction was found to be the chitosan-loaded nanoparticles incorporated in the hydrogel formulation, while the conventional hydrogel formulation was observed to be the highly acceptable formulation for Pet-B fraction. Further phytochemical studies of the bioactive fractions led to the isolation of many compounds of different chemical classes viz; beta-sitosterol and lupeol acetate isolated from the Pet-B, in addition to cyanidin and delphinidin from the Etac-B. Our results revealed that EBE and its bioactive fractions (Pet-B & Etac-B) could be considered as strong wound healers through their anti-oxidant and anti-inflammatory activities, in addition to stimulating collagen synthesis.

Comparative genomics of monotremes provides insights into the early evolution of mammalian epidermal differentiation genes

The function of the skin as a barrier against the environment depends on the differentiation of epidermal keratinocytes into highly resilient corneocytes that form the outermost skin layer. Many genes encoding structural components of corneocytes are clustered in the epidermal differentiation complex (EDC), which has been described in placental and marsupial mammals as well as non-mammalian tetrapods. Here, we analyzed the genomes of the platypus (Ornithorhynchus anatinus) and the echidna (Tachyglossus aculeatus) to determine the gene composition of the EDC in the basal clade of mammals, the monotremes. We report that mammal-specific subfamilies of EDC genes encoding small proline-rich proteins (SPRRs) and late cornified envelope proteins as well as single-copy EDC genes such as involucrin are conserved in monotremes, suggesting that they have originated in stem mammals. Monotremes have at least one gene homologous to the group of filaggrin (FLG), FLG2 and hornerin (HRNR) in placental mammals, but no clear one-to-one pairwise ortholog of either FLG, FLG2 or HRNR. Caspase-14, a keratinocyte differentiation-associated protease implicated in the processing of filaggrin, is encoded by at least 3 gene copies in the echidna. Our results reveal evolutionarily conserved and clade-specific features of the genetic regulation of epidermal differentiation in monotremes.

Development-Associated Genes of the Epidermal Differentiation Complex (EDC)

The epidermal differentiation complex (EDC) is a cluster of genes that encode protein components of the outermost layers of the epidermis in mammals, reptiles and birds. The development of the stratified epidermis from a single-layered ectoderm involves an embryo-specific superficial cell layer, the periderm. An additional layer, the subperiderm, develops in crocodilians and over scutate scales of birds. Here, we review the expression of EDC genes during embryonic development. Several EDC genes are expressed predominantly or exclusively in embryo-specific cell layers, whereas others are confined to the epidermal layers that are maintained in postnatal skin. The S100 fused-type proteins scaffoldin and trichohyalin are expressed in the avian and mammalian periderm, respectively. Scaffoldin forms the so-called periderm granules, which are histological markers of the periderm in birds. Epidermal differentiation cysteine-rich protein (EDCRP) and epidermal differentiation protein containing DPCC motifs (EDDM) are expressed in the avian subperiderm where they are supposed to undergo cross-linking via disulfide bonds. Furthermore, a histidine-rich epidermal differentiation protein and feather-type corneous beta-proteins, also known as beta-keratins, are expressed in the subperiderm. The accumulating evidence for roles of EDC genes in the development of the epidermis has implications on the evolutionary diversification of the skin in amniotes.

Dietary supplementation with a wheat polar lipid complex improves skin conditions in women with dry skin and mild-to-moderate skin aging

BACKGROUND

Aging, menopause, and seasonal changes alter the lipid composition of the outermost skin layer, the stratum corneum, resulting in dry and itchy skin.

AIMS

This clinical trial aimed at evaluating the effects of a wheat polar lipid complex (WPLC) on skin characteristics in women showing dry and wrinkled skin, investigating its effects in a subgroup of postmenopausal women, and assessing if benefits were maintained after supplementation.

METHODS

Seventy-two women with dry and wrinkled skin were recruited in this double-blind, randomized, parallel-group study, and allocated to three groups of 24 subjects, each including at least 10 postmenopausal women. For 56 days, subjects consumed the WPLC supplement (oil or powder), or the placebo. Skin hydration, transepidermal water loss (TEWL), elasticity, and profilometry were evaluated at baseline, after 14, 28, and 56 days of supplementation, and 56 days after the end of supplementation. Additionally, a lipidomic analysis was performed to examine changes in superficial skin layers over 56 days.

RESULTS

Dietary supplementation with WPLC rapidly improved all parameters. It increased skin hydration, smoothness, and elasticity while decreasing TEWL, roughness, and wrinkle depth after only 14 days of supplementation. These effects were also observed in the subpopulation of postmenopausal women and led to an improved self-perception of skin. For all the parameters, outcomes were not maintained after the supplementation was stopped. The lipidomic analysis revealed 10 compounds evolving over the 56 days of WPLC supplementation.

CONCLUSION

WPLC supplementation improved skin hydration, smoothness, elasticity, and wrinkledness within 14 days and, as expected, did not last after supplementation was stopped.

Cornification of keratinocytes is associated with differential changes in the catalytic activity and the immunoreactivity of transglutaminase-1

Transglutaminase 1 (TGM1) plays an essential role in skin barrier formation by cross-linking proteins in differentiated keratinocytes. Here, we established a protocol for the antibody-dependent detection of TGM1 protein and the parallel detection of TGM activity. TGM1 immunoreactivity initially increased and co-localized with membrane-associated TGM activity during keratinocyte differentiation. TGM activity persisted upon further differentiation of keratinocytes, whereas TGM1 immunoreactivity was lost under standard assay conditions. Pretreatment of tissue sections with the proteases trypsin or proteinase K enabled immunodetection of TGM1 in cornified keratinocytes, indicating that removal of other proteins was a prerequisite for TGM1 immunolabeling after cornification. The increase of TGM activity and subsequent loss of TGM1 immunoreactivity could be replicated in HEK293T cells transfected with TGM1, suggesting that protein cross-linking mediated by TGM1 itself may lead to reduced recognition of TGM1 by antibodies. To screen for proteins potentially regulating TGM1, we performed Virotrap experiments and identified the CAPNS1 subunit of calpain as an interaction partner of TGM1. Treatment of keratinocytes and TGM1-transfected HEK293T cells with chemical inhibitors of calpain suppressed transglutamination. Our findings suggest that calpain contributes to the control of TGM1-mediated transglutamination and proteins cross-linked by transglutamination mask epitopes of TGM1.

Iron Metabolism of the Skin: Recycling versus Release

The skin protects the body against exogenous stressors. Its function is partially achieved by the permanent regeneration of the epidermis, which requires high metabolic activity and the shedding of superficial cells, leading to the loss of metabolites. Iron is involved in a plethora of important epidermal processes, including cellular respiration and detoxification of xenobiotics. Likewise, microorganisms on the surface of the skin depend on iron, which is supplied by the turnover of epithelial cells. Here, we review the metabolism of iron in the skin with a particular focus on the fate of iron in epidermal keratinocytes. The iron metabolism of the epidermis is controlled by genes that are differentially expressed in the inner and outer layers of the epidermis, establishing a system that supports the recycling of iron and counteracts the release of iron from the skin surface. Heme oxygenase-1 (HMOX1), ferroportin (SLC40A1) and hephaestin-like 1 (HEPHL1) are constitutively expressed in terminally differentiated keratinocytes and allow the recycling of iron from heme prior to the cornification of keratinocytes. We discuss the evidence for changes in the epidermal iron metabolism in diseases and explore promising topics of future studies of iron-dependent processes in the skin.

Photoprotective Effect of Fermented and Aged Mountain-Cultivated Ginseng Sprout (Panax ginseng) on Ultraviolet Radiation-Induced Skin Aging in a Hairless Mouse Model

Interest in foods that promote inner beauty increases with increases in exposure to ultraviolet (UV) rays and with improvements in quality of life. This study was performed to evaluate the efficacy of fermented and aged mountain-cultivated ginseng sprouts (FAMCGSs), which have higher anti-inflammatory and antioxidant effects compared to mountain-cultivated ginseng sprouts (MCGSs), as an inner beauty enhancing food. The effect of orally administered FAMCGSs on UV type B (UVB) radiation-induced skin aging was investigated in a hairless mouse model through analyzing skin parameters including epidermal thickness, transepidermal water loss (TEWL), roughness, moisture, elasticity, and collagen contents. The mice exposed to UVB had markedly greater epidermal thickness, TEWL, and skin roughness than those of the normal control (NC) group. In addition, the levels of collagen, skin moisture, and dermal elasticity were lower in the UVB radiation group than the NC group. These UVB-induced skin aging parameters were significantly lower in the groups administered FAMCGSs than in the groups not administered FAMCGSs (p < 0.05). These results show that FAMCGSs exhibit a photoprotective effect in mice exposed to UVB and suggest that FAMCGSs can be used as a food that promotes inner beauty and protects skin from UVB-induced photoaging.

The role of sirtuins in dermal fibroblast function

The sirtuins are a family of seven proteins that perform a variety of dermatological functions and help maintain both the structure and function of the skin. More specifically, the sirtuins have been shown to be altered in multiple dermal cell types including dermal fibroblasts. The functions of dermal fibroblasts are extensive, and include playing a significant role in wound healing as well as helping to maintain the integrity of the skin. As dermal fibroblasts age, they can undergo a state of permanent cell cycle arrest, known as cellular senescence. This senescent process can occur as a result of various stressors, including oxidative stress, ultraviolet radiation -induced stress, and replicative stress. In recent years, there has been a growing interest in both enhancing the cutaneous fibroblast’s ability to facilitate wound healing and altering fibroblast cellular senescence. Thus, in this review, we examine the relationship between sirtuin signaling and dermal fibroblasts to understand how this family of proteins may modulate skin conditions ranging from the wound healing process to photocarcinogenesis associated with fibroblast senescence. Additionally, we offer supporting data from experiments examining the relationship between fibroblast senescence and sirtuin levels in an oxidative stress model indicating that senescent dermal fibroblasts exhibit diminished sirtuin levels. Furthermore, we survey the research on the role of sirtuins in specific dermatological disease states that where dermal fibroblast function has been implicated. Finally, we conclude with outlining potential clinical applications of sirtuins in dermatology. In sum, we find that the literature on the involvement of sirtuins in dermal fibroblasts is limited, with research still in its early stages. Nevertheless, intriguing preliminary findings merit additional investigation into the clinical implications of sirtuins in dermatology.

Heme Oxygenase-1 Is Upregulated during Differentiation of Keratinocytes but Its Expression Is Dispensable for Cornification of Murine Epidermis

The epidermal barrier of mammals is initially formed during embryonic development and continuously regenerated by the differentiation and cornification of keratinocytes in postnatal life. Cornification is associated with the breakdown of organelles and other cell components by mechanisms which are only incompletely understood. Here, we investigated whether heme oxygenase 1 (HO-1), which converts heme into biliverdin, ferrous iron and carbon monoxide, is required for normal cornification of epidermal keratinocytes. We show that HO-1 is transcriptionally upregulated during the terminal differentiation of human keratinocytes in vitro and in vivo. Immunohistochemistry demonstrated expression of HO-1 in the granular layer of the epidermis where keratinocytes undergo cornification. Next, we deleted the Hmox1 gene, which encodes HO-1, by crossing Hmox1-floxed and K14-Cre mice. The epidermis and isolated keratinocytes of the resulting Hmox1f/f K14-Cre mice lacked HO-1 expression. The genetic inactivation of HO-1 did not impair the expression of keratinocyte differentiation markers, loricrin and filaggrin. Likewise, the transglutaminase activity and formation of the stratum corneum were not altered in Hmox1f/f K14-Cre mice, suggesting that HO-1 is dispensable for epidermal cornification. The genetically modified mice generated in this study may be useful for future investigations of the potential roles of epidermal HO-1 in iron metabolism and responses to oxidative stress.

Ferroptosis Activation Contributes to the Formation of Skin Lesions in Psoriasis Vulgaris

(1) Background: Ferroptosis is a newly coined form of programmed cell death marked by lethal accumulation of lipid peroxidation and ferrous iron overload. A few studies on the specific mechanism of ferroptosis in the genesis and development of psoriasis are available. (2) Methods: Levels of lipid reactive oxygen species (ROS) and ferrous iron were measured by flow cytometry. Ultrastructure analysis was performed by transmission electron microscopy. Imiquimod-induced psoriasis-like mice were treated with a ferroptosis inducer. The expressions of mRNA of genes were measured by qRT-PCR. HaCaT cells were used to explore the function of Cyb561d2. (3) Results: In this work, we observed that levels of lipid ROS and ferrous iron in the epidermis of psoriasis vulgaris (PV) patients were increased. The existence of ferroptosis activation in the epidermis of individuals with PV was confirmed by transmission electron microscope both in patients with PV and psoriasis-like mice models. Intradermal injection of the ferroptosis inducer RSL3 in psoriasis-like mice significantly promoted and aggravated the development of psoriasis-like dermatitis, and the level of serum transferrin was also increased in PV samples. Moreover, abnormal expression of some genes related to iron metabolism was also proved in the epidermis of PV cases, among which Cyb561d2 was shown to promote ferrous iron overload and lipid peroxidation accumulation in HaCaT cells. (4) Conclusions: In summary, our study suggested that ferroptosis activation owing to iron overload may be a novel mechanism underlying the formation of skin lesions in individuals with PV.

Mechanism of action and therapeutic effects of oxidative stress and stem cell-based materials in skin aging: Current evidence and future perspectives

Aging is associated with multiple degenerative diseases, including atherosclerosis, osteoporosis, and Alzheimer's disease. As the most intuitive manifestation of aging, skin aging has received the most significant attention. Skin aging results from various intrinsic and extrinsic factors. Aged skin is characterized by wrinkles, laxity, elastosis, telangiectasia, and aberrant pigmentation. The underlying mechanism is complex and may involve cellular senescence, DNA damage, oxidative stress (OS), inflammation, and genetic mutations, among other factors. Among them, OS plays an important role in skin aging, and multiple antioxidants (e.g., vitamin C, glutathione, and melatonin) are considered to promote skin rejuvenation. In addition, stem cells that exhibit self-replication, multi-directional differentiation, and a strong paracrine function can exert anti-aging effects by inhibiting OS. With the further development of stem cell technology, treatments related to OS mitigation and involving stem cell use may have a promising future in anti-skin aging therapy.

Grp94 Inhibitor HCP1 Inhibits Human Dermal Fibroblast Senescence

Researchers are paying more and more attention to aging, especially skin aging. Therefore, it is urgent to find an effective way to inhibit aging. Here, we report a small chemical molecule, HCP1, that inhibited the senescence of human dermal fibroblasts (HDFs). First, we performed morphological experiment and found that HCP1-treated HDFs were no longer elongated and flat compared to DMSO-treated groups. Next, we found that the number of β-gal positive cells decreased compared to DMSO-treated groups. Through flow cytometry, western blot, and immunofluorescence, we found that HCP1 could inhibit the senescence of HDFs. In the study of the mechanism, we found that HCP1 could regulate the AMPK/mTOR signal pathway through glucose-regulated protein 94 (Grp94). In addition, we found that HCP1 could promote the interaction between Grp94 and lysosomes, which led to an increase in the activity of lysosomes and inhibited the senescence of HDFs. At the same time, we found that HCP1 decreased the concentration of Ca²⁺ in mitochondria, inhibiting the senescence of HCP1. Therefore, we propose that HCP1 is a potential aging-inhibiting compound, and provide a new idea for the development of senescence-inhibiting drugs.

Ross J, Scott Herron G. Genetic and Epigenetic Influences on Cutaneous Cellular Senescence

Skin is the largest human organ system, and its protective function is critical to survival. The epithelial, dermal, and subcutaneous compartments are heterogeneous mixtures of cell types, yet they all display age-related skin dysfunction through the accumulation of an altered phenotypic cellular state called senescence. Cellular senescence is triggered by complex and dynamic genetic and epigenetic processes. A senescence steady state is achieved in different cell types under various and overlapping conditions of chronological age, toxic injury, oxidative stress, replicative exhaustion, DNA damage, metabolic dysfunction, and chromosomal structural changes. These inputs lead to outputs of cell-cycle withdrawal and the appearance of a senescence-associated secretory phenotype, both of which accumulate as tissue pathology observed clinically in aged skin. This review details the influence of genetic and epigenetic factors that converge on normal cutaneous cellular processes to create the senescent state, thereby dictating the response of the skin to the forces of both intrinsic and extrinsic aging. From this work, it is clear that no single biomarker or process leads to senescence, but that it is a convergence of factors resulting in an overt aging phenotype.

Evolutionary diversification of epidermal barrier genes in amphibians

The epidermal differentiation complex (EDC) is a cluster of genes encoding components of the skin barrier in terrestrial vertebrates. EDC genes can be categorized as S100 fused-type protein (SFTP) genes such as filaggrin, which contain two coding exons, and single-coding-exon EDC (SEDC) genes such as loricrin. SFTPs are known to be present in amniotes (mammals, reptiles and birds) and amphibians, whereas SEDCs have not yet been reported in amphibians. Here, we show that caecilians (Amphibia: Gymnophiona) have both SFTP and SEDC genes. Two to four SEDC genes were identified in the genomes of Rhinatrema bivittatum, Microcaecilia unicolor and Geotrypetes seraphini. Comparative analysis of tissue transcriptomes indicated predominant expression of SEDC genes in the skin of caecilians. The proteins encoded by caecilian SEDC genes resemble human SEDC proteins, such as involucrin and small proline-rich proteins, with regard to low sequence complexity and high contents of proline, glutamine and lysine. Our data reveal diversification of EDC genes in amphibians and suggest that SEDC-type skin barrier genes have originated either in a common ancestor of tetrapods followed by loss in Batrachia (frogs and salamanders) or, by convergent evolution, in caecilians and amniotes.

Diagnostic and Therapeutic Roles of Extracellular Vesicles in Aging-Related Diseases

Aging shows a decline in overall physical function, and cellular senescence is the powerful catalyst leading to aging. Considering that aging will be accompanied with the emergence of various aging-related diseases, research on new antiaging drugs is still valuable. Extracellular vesicles (EVs), as tools for intercellular communication, are important components of the senescence-associated secretory phenotype (SASP), and they can play pathological roles in the process of cellular senescence. In addition, EVs are similar to their original cells in functions. Therefore, EVs derived from pathological tissues or body fluids may be closely related to the progression of diseases and become potential biomarkers, while those from healthy cells may have therapeutic effects. Moreover, EVs are satisfactory drug carriers. At present, numerous studies have supported the idea that engineered EVs could improve drug targeting ability and utilization efficiency. Here, we summarize the characteristics of EVs and cellular senescence and focus on the diagnostic and therapeutic potential of EVs in various aging-related diseases, including Alzheimer disease, osteoporosis, cardiovascular disease, diabetes mellitus and its complications, and skin aging.

UVB-Induced Microvesicle Particle Release and Its Effects on the Cutaneous Microenvironment

Ultraviolet B radiation (UVB) has profound effects on human skin that results in a broad spectrum of immunological local and systemic responses and is the major cause of skin carcinogenesis. One important area of study in photobiology is how UVB is translated into effector signals. As the skin is exposed to UVB light, subcellular microvesicle particles (MVP), a subtype of bioactive extracellular vesicles, are released causing a variety of local and systemic immunological effects. In this review, we highlight keratinocyte MVP release in keratinocytes in response to UVB. Specifically, Platelet-activating factor receptor agonists generated by UVB result in MVP released from keratinocytes. The downstream effects of MVP release include the ability of these subcellular particles to transport agents including the glycerophosphocholine-derived lipid mediator Platelet-activating factor (PAF). Moreover, even though UVB is only absorbed in the epidermis, it appears that PAF release from MVPs also mediates systemic immunosuppression and enhances tumor growth and metastasis. Tumor cells expressing PAF receptors can use this mechanism to evade chemotherapy responses, leading to treatment resistance for advanced cancers such as melanoma. Furthermore, novel pharmacological agents provide greater insight into the UVB-induced immune response pathway and a potential target for pharmacological intervention. This review outlines the need to more clearly elucidate the mechanism linking UVB-irradiation with the cutaneous immune response and its pathological manifestations. An improved understanding of this process can result in new insights and treatment strategies for UVB-related disorders from carcinogenesis to photosensitivity.

Decellularized Tissues for Wound Healing: Towards Closing the Gap Between Scaffold Design and Effective Extracellular Matrix Remodeling

The absence or damage of a tissue is the main cause of most acute or chronic diseases and are one of the appealing challenges that novel therapeutic alternatives have, in order to recover lost functions through tissue regeneration. Chronic cutaneous lesions are the most frequent cause of wounds, being a massive area of regenerative medicine and tissue engineering to have efforts to develop new bioactive medical products that not only allow an appropriate and rapid healing, but also avoid severe complications such as bacterial infections. In tissue repair and regeneration processes, there are several overlapping stages that involve the synergy of cells, the extracellular matrix (ECM) and biomolecules, which coordinate processes of ECM remodeling as well as cell proliferation and differentiation. Although these three components play a crucial role in the wound healing process, the ECM has the function of acting as a biological platform to permit the correct interaction between them. In particular, ECM is a mixture of crosslinked proteins that contain bioactive domains that cells recognize in order to promote migration, proliferation and differentiation. Currently, tissue engineering has employed several synthetic polymers to design bioactive scaffolds to mimic the native ECM, by combining biopolymers with growth factors including collagen and fibrinogen. Among these, decellularized tissues have been proposed as an alternative for reconstructing cutaneous lesions since they maintain the complex protein conformation, providing the required functional domains for cell differentiation. In this review, we present an in-depth discussion of different natural matrixes recently employed for designing novel therapeutic alternatives for treating cutaneous injuries, and overview some future perspectives in this area.

The potential inhibitory effect of ginsenoside Rh2 on mitophagy in UV-irradiated human dermal fibroblasts

Background

In addition to its use as a health food, ginseng is used in cosmetics and shampoo because of its extensive health benefits. The ginsenoside, Rh2, is a component of ginseng that inhibits tumor cell proliferation and differentiation, promotes insulin secretion, improves insulin sensitivity, and shows antioxidant effects.

Methods

The effects of Rh2 on cell survival, extracellular matrix (ECM) protein expression, and cell differentiation were examined. The antioxidant effects of Rh2 in UV-irradiated normal human dermal fibroblast (NHDF) cells were also examined. The effects of Rh2 on mitochondrial function, morphology, and mitophagy were investigated in UV-irradiated NHDF cells.

Results

Rh2 treatment promoted the proliferation of NHDF cells. Additionally, Rh2 increased the expression levels of ECM proteins and growth-associated immediate-early genes in ultraviolet (UV)-irradiated NHDF cells. Rh2 also affected antioxidant protein expression and increased total antioxidant capacity. Furthermore, treatment with Rh2 ameliorated the changes in mitochondrial morphology, induced the recovery of mitochondrial function, and inhibited the initiation of mitophagy in UV-irradiated NHDF cells.

Conclusion

Rh2 inhibits mitophagy and reinstates mitochondrial ATP production and membrane potential in NHDF cells damaged by UV exposure, leading to the recovery of ECM, cell proliferation, and antioxidant capacity.

Wounding Therapies for Prevention of Photocarcinogenesis

The occurrence of non-melanoma skin cancer (NMSC) is closely linked with advanced age and ultraviolet-B (UVB) exposure. More specifically, the development of NMSC is linked to diminished insulin-like growth factor-1 (IGF-1) signaling from senescent dermal fibroblasts in geriatric skin. Consequently, keratinocyte IGF-1 receptor (IGF-1R) remains inactive, resulting in failure to induce appropriate protective responses including DNA repair and cell cycle checkpoint signaling. This allows UVB-induced DNA damage to proliferate unchecked, which increases the likelihood of malignant transformation. NMSC is estimated to occur in 3.3 million individuals annually. The rising incidence results in increased morbidity and significant healthcare costs, which necessitate identification of effective treatment modalities. In this review, we highlight the pathogenesis of NMSC and discuss the potential of novel preventative therapies. In particular, wounding therapies such as dermabrasion, microneedling, chemical peeling, and fractionated laser resurfacing have been shown to restore IGF-1/IGF-1R signaling in geriatric skin and suppress the propagation of UVB-damaged keratinocytes. This wounding response effectively rejuvenates geriatric skin and decreases the incidence of age-associated NMSC.

Promises and challenges of senolytics in skin regeneration, pathology and ageing

The research of the last two decades has defined a crucial role of cellular senescence in both the physiology and pathology of skin, and senescent cells have been detected in conditions including development, regeneration, aging, and disease. The pathophysiology of cellular senescence in skin is complex as the phenotype of senescence pertains to several different cell types including fibroblasts, keratinocytes and melanocytes, among others. Paradoxically, the transient presence of senescent cells is believed to be beneficial in the context of development and wound healing, while the chronic presence of senescent cells is detrimental in the context of aging, diseases, and chronic wounds, which afflict predominantly the elderly. Identifying strategies to prevent senescence induction or reduce senescent burden in the skin could broadly benefit the aging population. Senolytics, drugs known to specifically eliminate senescent cells while preserving non-senescent cells, are being intensively studied for use in the clinical setting. Here, we review recent research on skin senescence, on the methods for the detection of senescent cells and describe promises and challenges related to the application of senolytic drugs. This article is part of the Special Issue - Senolytics - Edited by Joao Passos and Diana Jurk.

Protective Effect of Potentilla glabra in UVB-Induced Photoaging Process

Maintaining skin homeostasis is one of the most important factors for skin health. UVB-induced skin photoaging is a difficult problem that has negative impacts on skin homeostasis. So far, a number of compounds have been discovered that improve human skin barrier function and hydration, and are thought to be effective ways to protect skin homeostasis. Potentilla glabra var. mandshurica (Maxim.) Hand.-Mazz. Ethanol Extract (Pg-EE) is a compound that has noteworthy anti-inflammatory properties. However, its skin-protective effects are poorly understood. Therefore, we evaluated the capacity of Pg-EE to strengthen the skin barrier and improve skin hydration. Pg-EE can enhance the expression of filaggrin (FLG), transglutaminase (TGM)-1, hyaluronic acid synthase (HAS)-1, and HAS-2 in human keratinocytes. Moreover, Pg-EE down-regulated the expression of pro-inflammatory cytokines and up-regulated the production of FLG, HAS-1, and HAS-2 suppressed by UVB through inhibition of p38 mitogen-activated protein kinase (MAPK) and extracellular signal-regulated kinase (ERK) pathways. Given the above, since Pg-EE can improve skin barrier, hydration and reduce the UVB-induced inflammation on skin, it could therefore be a valuable natural ingredient for cosmetics or pharmaceuticals to treat skin disorders.

Keratinocyte Growth Factor 2 Ameliorates UVB-Induced Skin Damage via Activating the AhR/Nrf2 Signaling Pathway

Objective: Exposure to ultraviolet B (UVB) can cause skin damage through oxidative stress, DNA damage, and apoptosis. Keratinocyte growth factor (KGF) has been shown to reduce the content of intracellular reactive oxygen species (ROS) following UVB exposure, a role that is crucial for the efficient photoprotection of skin. The present study evaluated the photoprotective effect of KGF-2 on UVB-induced skin damage and explored its potential molecular mechanism.

Methods: To evaluate the effect of KGF-2 on UVB-induced damage ex vivo, a human epidermal full-thickness skin equivalent was pretreated without or with KGF-2 and then exposed to UVB and the levels of histopathological changes, DNA damage, inflammation, and apoptosis were then evaluated. The ability of KGF-2 to protect the cells against UVB-inflicted damage and its effect on ROS production, apoptosis, and mitochondrial dysfunction were determined in HaCaT cells.

Results: Pretreatment of the epidermis with KGF-2 ameliorated the extent of photodamage. At the cellular level, KGF-2 could attenuate ROS production, apoptosis, DNA damage, and mitochondrial dysfunction caused by UVB exposure. KGF-2 could also activate the aryl hydrocarbon receptor (AhR) to trigger the Nrf2 signaling pathway.

Conclusion: Taken together, our findings suggested that KGF-2 could ameliorate UVB-induced skin damage through inhibiting apoptosis, reducing oxidative stress, and preventing DNA damage and mitochondrial dysfunction via regulating AhR/Nrf2 signaling pathway.

Akt1-associated actomyosin remodelling is required for nuclear lamina dispersal and nuclear shrinkage in epidermal terminal differentiation

Keratinocyte cornification and epidermal barrier formation are tightly controlled processes, which require complete degradation of intracellular organelles, including removal of keratinocyte nuclei. Keratinocyte nuclear destruction requires Akt1-dependent phosphorylation and degradation of the nuclear lamina protein, Lamin A/C, essential for nuclear integrity. However, the molecular mechanisms that result in complete nuclear removal and their regulation are not well defined. Post-confluent cultures of rat epidermal keratinocytes (REKs) undergo spontaneous and complete differentiation, allowing visualisation and perturbation of the differentiation process in vitro. We demonstrate that there is dispersal of phosphorylated Lamin A/C to structures throughout the cytoplasm in differentiating keratinocytes. We show that the dispersal of phosphorylated Lamin A/C is Akt1-dependent and these structures are specific for the removal of Lamin A/C from the nuclear lamina; nuclear contents and Lamin B were not present in these structures. Immunoprecipitation identified a group of functionally related Akt1 target proteins involved in Lamin A/C dispersal, including actin, which forms cytoskeletal microfilaments, Arp3, required for actin filament nucleation, and Myh9, a component of myosin IIa, a molecular motor that can translocate along actin filaments. Disruption of actin filament polymerisation, nucleation or myosin IIa activity prevented formation and dispersal of cytoplasmic Lamin A/C structures. Live imaging of keratinocytes expressing fluorescently tagged nuclear proteins showed a nuclear volume reduction step taking less than 40 min precedes final nuclear destruction. Preventing Akt1-dependent Lamin A/C phosphorylation and disrupting cytoskeletal Akt1-associated proteins prevented nuclear volume reduction. We propose keratinocyte nuclear destruction and differentiation requires myosin II activity and the actin cytoskeleton for two intermediate processes: Lamin A/C dispersal and rapid nuclear volume reduction.

Tracing skin aging process: a mini- review of in vitro approaches

Skin is a rather complex, yet useful organ of our body. Besides, skin aging is a complicated process that gains a growing interest as mediates many molecular processes in our body. Thus, an efficient skin model is important to understand skin aging function as well as to develop an effective innovative product for skin aging treatment. In this mini review, we present in vitro methods for assessments of skin aging in an attempt to pinpoint basic molecular mechanisms behind this process achieving both a better understanding of aging function and an effective  evaluation of potential products or ingredients that counteract aging. Specifically, this study presents in vitro assays such as 2D or 3D skin models, to evaluate skin aging-related processes such as skin moisturization, photoaging, wound healing, menopause, and skin microbiome as novel efforts in the designing of efficacy assessments in the development of skincare products.

Imaging of metabolic activity adaptations to UV stress, drugs and differentiation at cellular resolution in skin and skin equivalents - Implications for oxidative UV damage

The epidermis is a multi-layered epithelium that consists mainly of keratinocytes which proliferate in its basal layer and then differentiate to form the stratum corneum, the skin's ultimate barrier to the environment. During differentiation keratinocyte function, chemical composition, physical properties, metabolism and secretion are profoundly changed. Extrinsic or intrinsic stressors, like ultraviolet (UV) radiation thus may differently affect the epidermal keratinocytes, depending on differentiation stage. Exposure to UV elicits the DNA damage responses, activation of pathways which detoxify or repair damage or induction of programmed cell death when the damage was irreparable. Recently, rapid diversion of glucose flux into the pentose phosphate pathway (PPP) was discovered as additional mechanism by which cells rapidly generate reduction equivalents and precursors for nucleotides - both being in demand after UV damage. There is however little known about the correlation of such metabolic activity with differentiation state, cell damage and tissue localization of epidermal cells. We developed a method to correlate the activity of G6PD, the first and rate-limiting enzyme of this metabolic UV response, at cellular resolution to cell type, differentiation state, and cell damage in human skin and in organotypic reconstructed epidermis. We thereby could verify rapid activation of G6PD as an immediate UVB response not only in basal but also in differentiating epidermal keratinocytes and found increased activity in cells which initiated DNA damage responses. When keratinocytes had been UVB irradiated before organotypic culture, their distribution within the skin equivalent was abnormal and the G6PD activity was reduced compared to neighboring cells. Finally, we found that the anti-diabetic and potential anti-aging drug metformin strongly induced G6PD activity throughout reconstructed epidermis. Activation of the protective pentose phosphate pathway may be useful to enhance the skin's antioxidant defense systems and DNA damage repair capacity on demand.

Biomarkers, oxidative stress and autophagy in skin aging

Aging is a major cause of many degenerative diseases. The most intuitive consequence of aging is mainly manifested on the skin, resulting in cumulative changes in skin structure, function and appearance, such as increased wrinkles, laxity, elastosis, telangiectasia, and aberrant pigmentation of the skin. Unlike other organs of the human body, skin is not only inevitably affected by the intrinsic aging process, but also affected by various extrinsic environmental factors to accelerate aging, especially ultraviolet (UV) radiation. Skin aging is a highly complex and not fully understood process, and the lack of universal biomarkers for the definitive detection and evaluation of aging is also a major research challenge. Oxidative stress induced by the accumulation of reactive oxygen species (ROS) can lead to lipid, protein, nucleic acid and organelle damage, thus leading to the occurrence of cellular senescence, which is one of the core mechanisms mediating skin aging. Autophagy can maintain cellular homeostasis when faced with different stress conditions and is one of the survival mechanisms of cell resistance to intrinsic and extrinsic stress. Autophagy and aging have many features in common and may be associated with skin aging mediated by different factors. Here, we summarize the changes and biomarkers of skin aging, and discuss the effects of oxidative stress and autophagy on skin aging.

Major challenges and perspectives in the diagnostics and treatment of dermatophyte infections

Dermatophytes are the aetiological factors of a majority of superficial fungal infections. What distinguishes them from other pathogenic filamentous fungi is their unique ability to degrade keratin. The remarkable ability of this group of fungi to survive in different ecosystems results from their morphological and ecological diversity as well as high adaptability to changing environmental conditions. Paradoxically, despite the progress in medicine, the prevalence of dermatophyte infections is increasing from year to year. At the beginning of the third millennium, practical diagnostic and therapeutic options are still very limited. This review focuses on understanding the major problems in this aspect of dermatophyte infections and indicates future strategies and perspectives for novel approaches to identification and drugs for elimination of dermatophytes. Particular importance is placed on development of a strategy for a diagnostic pathway and implementation of rapid and reliable diagnostics methods designed by international teams. Furthermore, among compounds that currently arouse great interest, representatives of terpenoids, alkaloids, saponins, flavonoids and essential oils deserve attention. Many of these compounds are undergoing clinical trials as potential antifungal agents, and future research should focus on attempts at determination of the applicability of tested substances. Finally, the advantages and disadvantages in implementation of new diagnostic paths and medicinal substances for routine use are indicated.

The Skin Epilipidome in Stress, Aging, and Inflammation

Lipids are highly diverse biomolecules crucial for the formation and function of cellular membranes, for metabolism, and for cellular signaling. In the mammalian skin, lipids additionally serve for the formation of the epidermal barrier and as surface lipids, together regulating permeability, physical properties, acidification and the antimicrobial defense. Recent advances in accuracy and specificity of mass spectrometry have allowed studying enzymatic and non-enzymatic modifications of lipids-the epilipidome-multiplying the known diversity of molecules in this class. As the skin is an organ that is frequently exposed to oxidative-, chemical- and thermal stress, and to injury and inflammation, it is an ideal organ to study epilipidome dynamics, their causes, and their biological consequences. Recent studies uncover loss or gain in biological function resulting from either specific modifications or the sum of the modifications of lipids. These studies suggest an important role for the epilipidome in stress responses and immune regulation in the skin. In this minireview we provide a short survey of the recent developments on causes and consequences of epilipidomic changes in the skin or in cell types that reside in the skin.

Cell aging and cellular senescence in skin aging - Recent advances in fibroblast and keratinocyte biology

The aging of the skin is the most visible and obvious manifestation of organismal aging and may serve as a predictor of life expectancy and health. It is, however, also the human desire for long-lasting beauty that further raises interests in the topic, and thus considerable means and efforts are put into studying the mechanisms of skin aging in basic and applied research. Both medical und non-medical interests are of benefit for skin research in general because the results from these studies help to deepen our understanding of the complex molecular, biological, cell signaling, developmental and immunological processes in this organ. In fact, the skin is an ideal organ to observe and analyze the impact of extrinsic and intrinsic drivers of aging. Within the past five years technological advances like lineage tracing of cells in model organisms, intra-vital microscopy, nucleic acid sequencing at the single cell level, and high resolution mass spectrometry have allowed to study aging and senescence of individual skin cells within the tissue context, their signaling and communication, and to derive new hypotheses for experimental studies in vitro. In this short review we will discuss very recent developments that promise to extend the existing knowledge on cell aging and senescence of dermal fibroblasts and epidermal keratinocytes in skin aging.

Fucoidan from Undaria pinnatifida Ameliorates Epidermal Barrier Disruption via Keratinocyte Differentiation and CaSR Level Regulation

The epidermal barrier acts as a line of defense against external agents as well as helps to maintain body homeostasis. The calcium concentration gradient across the epidermal barrier is closely related to the proliferation and differentiation of keratinocytes (KCs), and the regulation of these two processes is the key to the repair of epidermal barrier disruption. In the present study, we found that fucoidan from Undaria pinnatifida (UPF) could promote the repair of epidermal barrier disruption in mice. The mechanistic study demonstrated that UPF could promote HaCaT cell differentiation under low calcium condition by up-regulating the expression of calcium-sensing receptor (CaSR), which could then lead to the activation of the Catenin/PLCγ1 pathway. Further, UPF could increase the expression of CaSR through activate the ERK and p38 pathway. These findings reveal the molecular mechanism of UPF in the repair of the epidermal barrier and provide a basis for the development of UPF into an agent for the repair of epidermal barrier repair.

Dissolving undercut microneedle arrays for multicomponent cutaneous vaccination

The skin is an attractive tissue target for vaccination, as it is readily accessible and contains a dense population of antigen-presenting and immune-accessory cells. Microneedle arrays (MNAs) are emerging as an effective tool for in situ engineering of the cutaneous microenvironment to enable diverse immunization strategies. Here, we present novel dissolving undercut MNAs and demonstrate their application for effective multicomponent cutaneous vaccination. The MNAs are composed of micron-scale needles featuring pyramidal heads supported by undercut stem regions with filleted bases to ensure successful skin penetration and retention during application. Prior efforts to fabricate dissolving undercut microstructures were limited and required complex and lengthy processing and assembly steps. In the current study, we strategically combine three-dimensional (3D) laser lithography, an emerging micro-additive manufacturing method with unique geometric capabilities and nanoscale resolution, and micromolding with favorable materials. This approach enables reproducible production of dissolving MNAs with undercut microneedles that can be tip-loaded with multiple biocargos, such as antigen (ovalbumin) and adjuvant (Poly(I:C)). The resulting MNAs fulfill the geometric (sharp tips and smooth edges) and mechanical-strength requirements for failure-free penetration of human and murine skin to simultaneously deliver multicomponent (antigen plus adjuvant) vaccines to the same cutaneous microenvironment. Cutaneous vaccination of mice using these MNAs induces more potent antigen-specific cellular and humoral immune responses than those elicited by traditional intramuscular injection. Together, the unique geometric features of these undercut MNAs and the associated manufacturing strategy, which is compatible with diverse drugs and biologics, could enable a broad range of non-cutaneous and cutaneous drug delivery applications, including multicomponent vaccination.

The non-homogenous distribution and aggregation of carotenoids in the stratum corneum correlates with the organization of intercellular lipids in vivo

The human stratum corneum (SC) contains an abundant amount of carotenoid antioxidants, quenching free radicals and thereby protecting the skin. For the precise measurements of the depth-dependent carotenoid concentration, confocal Raman microscopy is a suitable method. The quantitative concentration can be determined by the carotenoid-related peak intensity of a Gaussian function approached at ≈1524 cm^-1 using non-linear regression. Results show that the carotenoid concentration is higher at the superficial layers of the SC then decreases to a minimum at 20% SC depth and increases again towards the bottom of the SC. In the present work, two carotenoid penetration pathways into the SC are postulated. The first pathway is from the stratum granulosum to the bottom of the SC, while in the second pathway, the carotenoids are delivered to the skin surface by sweat and/or sebum secretion and penetrate from outside. The carotenoids are aggregated at the superficial layers, which are shown by high correlation between the aggregation states of carotenoids and the lateral organization of lipids. At the 30%-40% SC depths, the ordered and dense lipid molecules intensify the lipid-carotenoid interactions and weaken the carotenoid-carotenoid interaction and thus exhibit the disaggregation of carotenoids. At 90%-100% SC depths, the carotenoid-lipid interaction is weakened and the carotenoids have a tendency to be aggregated. Thus, the molecular structural correlation of carotenoid and SC lipid might be reserved in the intercellular space of the SC and also serves as the skeleton of the intercellular lipids.

Autophagic Control of Skin Aging

The skin forms the barrier to the environment. Maintenance of this barrier during aging requires orchestrated responses to variable types of stress, the continuous renewal of the epithelial compartment, and the homeostasis of long-lived cell types. Recent experimental evidence suggests that autophagy is critically involved in skin homeostasis and skin aging is associated with and partially caused by defects of autophagy. In the outer skin epithelium, autophagy is constitutively active during cornification of keratinocytes and increases the resistance to environmental stress. Experimental suppression of autophagy in the absence of stress is tolerated by the rapidly renewing epidermal epithelium, whereas long-lived skin cells such as melanocytes, Merkel cells and secretory cells of sweat glands depend on autophagy for cellular homeostasis and normal execution of their functions during aging. Yet other important roles of autophagy have been identified in the dermis where senescence of mesenchymal cells and alterations of the extracellular matrix (ECM) are hallmarks of aging. Here, we review the evidence for cell type-specific roles of autophagy in the skin and their differential contributions to aging.

A Stress Response Program at the Origin of Evolutionary Innovation in the Skin

The skin epithelium, ie, the epidermis, of dolphins and whales (cetaceans) is up to 50 times thicker than that of humans and other mammals living on land. Recently, comparative genomics revealed further striking differences in the cytoskeleton of the outer layers of the epidermis in aquatic and terrestrial mammals. Cetaceans lack the cytoskeletal keratins, which make up more than half of the total protein mass in the cornified epidermal layer of terrestrial mammals under homeostatic conditions. By contrast, orthologs of stress-inducible epithelial keratins are conserved in cetaceans and these keratins are constitutively expressed in their skin. Thus, the epidermal stress response program of a terrestrial common ancestor of modern mammals has become the default program of epidermal differentiation and a central component of the unique cutaneous organization of cetaceans. We propose that phenotypic plasticity during stress responses plays important roles in the evolution of the skin.

Host- and pathogen-dependent susceptibility and predisposition to dermatophytosis

Dermatophytes are a highly specialized group of keratinophilic and keratinolytic filamentous fungi causing a ringworm disease called dermatophytosis or superficial mycoses. Although dermatophyte infections do not threaten the host's life, they lower its quality in humans by causing discomfort related to cosmetic problems and through their epidemiological significance, whereas in farm animals they are responsible for economic losses and constitute a source of the spread of spores. Evidence from countless observational studies that have been conducted over the last 90 years indicates that dermatophytes infect humans of every age, race, gender and socioeconomic status with strikingly high rates, as well as both farmed and wild animals in various health conditions and with various epidemiological statuses. However, the prevalence of superficial fungal infections is highly variable, since it depends on several parameters associated with the infected individual and the dermatophyte, their mutual interactions, and epidemiological and geographical factors. The curious disparity in dermatophyte infection patterns has prompted many investigators to search for a link between the host, the host's predispositions and susceptibility to the disease, and the dermatophyte species and virulence. Thus, the question arises as to whether, in addition to the generally recognized factors predisposing hosts to diseases, there are some other predispositions to dermatophyte infections in a species-specific host. In this review, we describe recent findings about the mechanism of dermatophyte infections, focusing on the adaptation of the fungi to the host and conditions predisposing each side to the disease.