p16INK4A is a robust in vivo biomarker of cellular aging in human skin

Immunomodulatory Nanosystems: Advanced Delivery Tools for Treating Chronic Wounds

The increasingly aging society led to a rise in the prevalence of chronic wounds (CWs), posing a significant burden to public health on a global scale. One of the key features of CWs is the presence of a maladjusted immune microenvironment characterized by persistent and excessive (hyper)inflammation. A variety of immunomodulatory therapies have been proposed to address this condition. Yet, to date, current delivery systems for immunomodulatory therapy remain inadequate and lack efficiency. This highlights the need for new therapeutic delivery systems, such as nanosystems, to manage the pathological inflammatory imbalance and, ultimately, improve the treatment outcomes of CWs. While a plethora of immunomodulatory nanosystems modifying the immune microenvironment of CWs have shown promising therapeutic effects, the literature on the intersection of immunomodulatory nanosystems and CWs remains relatively scarce. Therefore, this review aims to provide a comprehensive overview of the pathogenesis and characteristics of the immune microenvironment in CWs, discuss important advancements in our understanding of CW healing, and delineate the versatility and applicability of immunomodulatory nanosystems-based therapies in the therapeutic management of CWs. In addition, we herein also shed light on the main challenges and future perspectives in this rapidly evolving research field.

Senotherapeutic peptide treatment reduces biological age and senescence burden in human skin models

Cellular senescence is known to play a role in age-related skin function deterioration which potentially influences longevity. Here, a two-step phenotypic screening was performed to identify senotherapeutic peptides, leading to the identification of Peptide (Pep) 14. Pep 14 effectively decreased human dermal fibroblast senescence burden induced by Hutchinson-Gilford Progeria Syndrome (HGPS), chronological aging, ultraviolet-B radiation (UVB), and etoposide treatment, without inducing significant toxicity. Pep 14 functions via modulation of PP2A, an understudied holoenzyme that promotes genomic stability and is involved in DNA repair and senescence pathways. At the single-cell level, Pep 14 modulates genes that prevent senescence progression by arresting the cell cycle and enhancing DNA repair, which consequently reduce the number of cells progressing to late senescence. When applied on aged ex vivo skin, Pep 14 promoted a healthy skin phenotype with structural and molecular resemblance to young ex vivo skin, decreased the expression of senescence markers, including SASP, and reduced the DNA methylation age. In summary, this work shows the safe reduction of the biological age of ex vivo human skins by a senomorphic peptide.

Oral delivery of a highly stable superoxide dismutase as a skin aging inhibitor

As an effective antioxidant enzyme, superoxide dismutase (SOD) has been widely used as a food supplement, cosmetic additive, and therapeutic agent. However, oral delivery of SOD is challenging due to its relative instability, limited bioavailability, and low absorption efficiency in the gastrointestinal (GI) tract. We addressed these issues using a highly stable superoxide dismutase (hsSOD) generated from a hot spring microbial sample. This SOD exhibited a specific activity of 5000 IU/mg while retaining its enzymatic activity under low pH environments of an artificial GI system and in the presence of surfactants and various proteolytic enzymes. The inhibitory effects of hsSOD against skin-aging was evaluated under both in vitro and in vivo experiments using fibroblast cell and D-galactose induced aging-mouse models, respectively. Effective oral delivery of hsSOD promises wide applicability in pharmaceutical and food industries.

Skin aging from mechanisms to interventions: focusing on dermal aging

Skin aging is a multifaceted process that involves intrinsic and extrinsic mechanisms that lead to various structural and physiological changes in the skin. Intrinsic aging is associated with programmed aging and cellular senescence, which are caused by endogenous oxidative stress and cellular damage. Extrinsic aging is the result of environmental factors, such as ultraviolet (UV) radiation and pollution, and leads to the production of reactive oxygen species, ultimately causing DNA damage and cellular dysfunction. In aged skin, senescent cells accumulate and contribute to the degradation of the extracellular matrix, which further contributes to the aging process. To combat the symptoms of aging, various topical agents and clinical procedures such as chemical peels, injectables, and energy-based devices have been developed. These procedures address different symptoms of aging, but to devise an effective anti-aging treatment protocol, it is essential to thoroughly understand the mechanisms of skin aging. This review provides an overview of the mechanisms of skin aging and their significance in the development of anti-aging treatments.

Quantitative morphometric analysis of intrinsic and extrinsic skin ageing in individuals with Fitzpatrick skin types II-III

Skin ageing is an intricate physiological process affected by intrinsic and extrinsic factors. There is a demand to understand how the skin changes with age and photoexposure in individuals with Fitzpatrick skin types I-III due to accelerated photoageing and the risk of cutaneous malignancies. To assess the structural impact of intrinsic and extrinsic ageing, we analysed 14 skin parameters from the photoprotected buttock and photoexposed dorsal forearm of young and ageing females with Fitzpatrick skin types II-III (n = 20) using histomorphic techniques. Whilst the minimum viable epidermis (Emin ) remained constant (Q > 0.05), the maximum viable epidermis (Emax ) was decreased by both age and photoexposure (Q ≤ 0.05), which suggests that differences in epidermal thickness are attributed to changes in the dermal-epidermal junction (DEJ). Changes in Emax were not affected by epidermal cell proliferation. For the first time, we investigated the basal keratinocyte morphology with age and photoexposure. Basal keratinocytes had an increased cell size, cellular height and a more columnar phenotype in photoexposed sites of young and ageing individuals (Q ≤ 0.05), however no significant differences were observed with age. Some of the most striking changes were observed in the DEJ, and a decrease in the interdigitation index was observed with both age and photoexposure (Q ≤ 0.001), accompanied by a decreased height of rête ridges and dermal papilla. Interestingly, young photoexposed skin was comparable to ageing skin across many parameters, and we hypothesise that this is due to accelerated photoageing. This study highlights the importance of skin care education and photoprotection from an early age.

Senescence Induced by UVB in Keratinocytes Impairs Amino Acids Balance

Skin is one of the most exposed organs to external stress. Namely, UV rays are the most harmful stress that could induce important damage leading to skin aging and cancers. At the cellular level, senescence is observed in several skin cell types and contributes to skin aging. However, the origin of skin senescent cells is still unclear but is probably related to exposure to stresses. In this work, we developed an in vitro model of UVB-induced premature senescence in normal human epidermal keratinocytes. UVB-induced senescent keratinocytes display a common senescent phenotype resulting in an irreversible cell cycle arrest, an increase in the proportion of senescence-associated β-galactosidase‒positive cells, unrepaired DNA damage, and a long-term DNA damage response activation. Moreover, UVB-induced senescent keratinocytes secrete senescence-associated secretory phenotype factors that influence cutaneous squamous cell carcinoma cell migration. Finally, a global transcriptomic study highlighted that senescent keratinocytes present a decrease in the expression of several amino acid transporters, which is associated with reduced intracellular levels of glycine, alanine, and leucine. Interestingly, the chemical inhibition of the glycine transporter SLC6A9/Glyt1 triggers senescence features.

Cytotoxic CD4+ T cells eliminate senescent cells by targeting cytomegalovirus antigen

Senescent cell accumulation has been implicated in the pathogenesis of aging-associated diseases, including cancer. The mechanism that prevents the accumulation of senescent cells in aging human organs is unclear. Here, we demonstrate that a virus-immune axis controls the senescent fibroblast accumulation in the human skin. Senescent fibroblasts increased in old skin compared with young skin. However, they did not increase with advancing age in the elderly. Increased CXCL9 and cytotoxic CD4+ T cells (CD4 CTLs) recruitment were significantly associated with reduced senescent fibroblasts in the old skin. Senescent fibroblasts expressed human leukocyte antigen class II (HLA-II) and human cytomegalovirus glycoprotein B (HCMV-gB), becoming direct CD4 CTL targets. Skin-resident CD4 CTLs eliminated HCMV-gB+ senescent fibroblasts in an HLA-II-dependent manner, and HCMV-gB activated CD4 CTLs from the human skin. Collectively, our findings demonstrate HCMV reactivation in senescent cells, which CD4 CTLs can directly eliminate through the recognition of the HCMV-gB antigen.

Emerging Therapeutic Approaches to Target the Dark Side of Senescent Cells: New Hopes to Treat Aging as a Disease and to Delay Age-Related Pathologies

Life expectancy has drastically increased over the last few decades worldwide, with important social and medical burdens and costs. To stay healthy longer and to avoid chronic disease have become essential issues. Organismal aging is a complex process that involves progressive destruction of tissue functionality and loss of regenerative capacity. One of the most important aging hallmarks is cellular senescence, which is a stable state of cell cycle arrest that occurs in response to cumulated cell stresses and damages. Cellular senescence is a physiological mechanism that has both beneficial and detrimental consequences. Senescence limits tumorigenesis, lifelong tissue damage, and is involved in different biological processes, such as morphogenesis, regeneration, and wound healing. However, in the elderly, senescent cells increasingly accumulate in several organs and secrete a combination of senescence associated factors, contributing to the development of various age-related diseases, including cancer. Several studies have revealed major molecular pathways controlling the senescent phenotype, as well as the ones regulating its interactions with the immune system. Attenuating the senescence-associated secretory phenotype (SASP) or eliminating senescent cells have emerged as attractive strategies aiming to reverse or delay the onset of aging diseases. Here, we review current senotherapies designed to suppress the deleterious effect of SASP by senomorphics or to selectively kill senescent cells by "senolytics" or by immune system-based approaches. These recent investigations are promising as radical new controls of aging pathologies and associated multimorbidities.

The Extracellular Matrix Vitalizer RATM Increased Skin Elasticity by Modulating Mitochondrial Function in Aged Animal Skin

Oxidative stress-induced cellular senescence and mitochondrial dysfunction result in skin aging by increasing ECM levels-degrading proteins such as MMPs, and decreasing collagen synthesis. MMPs also destroy the basement membrane, which is involved in skin elasticity. The extracellular matrix vitalizer RATM (RA) contains various antioxidants and sodium hyaluronate, which lead to skin rejuvenation. We evaluated whether RA decreases oxidative stress and mitochondrial dysfunction, eventually increasing skin elasticity in aged animals. Oxidative stress was assessed by assaying NADPH oxidase activity, which is involved in ROS generation, and the expression of SOD, which removes ROS. NADPH oxidase activity was increased in aged skin and decreased by RA injection. SOD expression was decreased in aged skin and increased by RA injection. Damage to mitochondrial DNA and mitochondrial fusion markers was increased in aged skin and decreased by RA. The levels of mitochondrial biogenesis markers and fission markers were decreased in aged skin and increased by RA. The levels of NF-κB/AP-1 and MMP1/2/3/9 were increased in aged skin and decreased by RA. The levels of TGF-β, CTGF, and collagen I/III were decreased in aged skin and increased by RA. The expression of laminin and nidogen and basement membrane density were decreased in aged skin and increased by RA. RA increased collagen fiber accumulation and elasticity in aged skin. In conclusion, RA improves skin rejuvenation by decreasing oxidative stress and mitochondrial dysfunction in aged skin.

Identification of Apolipoprotein D as a Dermal Fibroblast Marker of Human Aging for Development of Skin Rejuvenation Therapy

The current understanding of skin aging is that senescent fibroblasts accumulate within the dermis and subcutaneous fat to cause abnormal tissue remodeling and extracellular matrix dysfunction, triggering a senescence-associated secretory phenotype (SASP). A novel therapeutic approach to prevent skin aging is to specifically eliminate senescent dermal fibroblasts; this requires the identification of specific protein markers for senescent cells. Apolipoprotein D (ApoD) is involved in lipid metabolism and antioxidant responses and is abundantly expressed in tissues affected by age-related diseases such as Alzheimer's disease and atherosclerosis. However, its behavior and role in skin aging remain unclear. In this study, we examined whether ApoD functions as a marker of aging using human dermal fibroblast aging models. In cellular senescence models induced through replicative aging and ionizing radiation exposure, ApoD expression was upregulated at the gene and protein levels and correlated with senescence-associated β-galactosidase activity and the decreased uptake of the proliferation marker bromodeoxyuridine, which was concomitant with the upregulation of SASP genes. Furthermore, ApoD-positive cells were found to be more abundant in the aging human dermis using fluorescence flow cytometry. These results suggest that ApoD is a potential clinical marker for identifying aging dermal fibroblasts.

Influence of the Mediterranean Diet on Healthy Aging

The life expectancy of the global population has increased. Aging is a natural physiological process that poses major challenges in an increasingly long-lived and frail population. Several molecular mechanisms are involved in aging. Likewise, the gut microbiota, which is influenced by environmental factors such as diet, plays a crucial role in the modulation of these mechanisms. The Mediterranean diet, as well as the components present in it, offer some proof of this. Achieving healthy aging should be focused on the promotion of healthy lifestyle habits that reduce the development of pathologies that are associated with aging, in order to increase the quality of life of the aging population. In this review we analyze the influence of the Mediterranean diet on the molecular pathways and the microbiota associated with more favorable aging patterns, as well as its possible role as an anti-aging treatment.

Hallmarks and Biomarkers of Skin Senescence: An Updated Review of Skin Senotherapeutics

Aging is a complex process characterized by an ongoing decline in physiological functions, leading to degenerative diseases and an increased probability of death. Cellular senescence has been typically considered as an anti-proliferative process; however, the chronic accumulation of senescent cells contributes to tissue dysfunction and aging. In this review, we discuss some of the most important hallmarks and biomarkers of cellular senescence with a special focus on skin biomarkers, reactive oxygen species (ROS), and senotherapeutic strategies to eliminate or prevent senescence. Although most of them are not exclusive to senescence, the expression of the senescence-associated beta-galactosidase (SA-β-gal) enzyme seems to be the most reliable biomarker for distinguishing senescent cells from those arrested in the cell cycle. The presence of a stable DNA damage response (DDR) and the accumulation of senescence-associated secretory phenotype (SASP) mediators and ROS are the most representative hallmarks for senescence. Senotherapeutics based on natural compounds such as quercetin, naringenin, and apigenin have shown promising results regarding SASP reduction. These compounds seem to prevent the accumulation of senescent cells, most likely through the inhibition of pro-survival signaling pathways. Although studies are still required to verify their short- and long-term effects, these therapies may be an effective strategy for skin aging.

Senolytic effect of high intensity interval exercise on human skeletal muscle

p16^INK4a expression is a robust biomarker of senescence for stem cells in human tissues. Here we examined the effect of exercise intensity on in vivo senescence in skeletal muscle, using a randomized counter-balanced crossover design. Biopsied vastus lateralis of 9 sedentary men (age 26.1 ± 2.5 y) were assessed before and after a single bout of moderate steady state exercise (SSE, 60% maximal aerobic power) and high intensity interval exercise (HIIE, 120% maximal aerobic power) on a cycloergometer accumulating same amount of cycling work (in kilojoule). Increases in cell infiltration (+1.2 folds), DNA strand break (+1.3 folds), and γ-H2AX⁺ myofibers (+1.1 folds) occurred immediately after HIIE and returned to baseline in 24 h (p < 0.05). Muscle p16^Ink4a mRNA decreased 24 h after HIIE (-57%, p < 0.05). SSE had no effect on cell infiltration, p16^Ink4a mRNA, and DNA strand break in muscle tissues. Senescence-lowering effect of HIIE was particularly prominent in the muscle with high pre-exercise p16INK4a expression, suggesting that exercise intensity determines the level of selection pressure to tissue stem cells at late senescent stage in human skeletal muscle. This evidence provides an explanation for the discrepancy between destructive nature of high intensity exercise and its anti-aging benefits.

Caloric restriction induced epigenetic effects on aging

Aging is the subject of many studies, facilitating the discovery of many interventions. Epigenetic influences numerous life processes by regulating gene expression and also plays a crucial role in aging regulation. Increasing data suggests that dietary changes can alter epigenetic marks associated with aging. Caloric restriction (CR)is considered an intervention to regulate aging and prolong life span. At present, CR has made some progress by regulating signaling pathways associated with aging as well as the mechanism of action of intercellular signaling molecules against aging. In this review, we will focus on autophagy and epigenetic modifications to elaborate the molecular mechanisms by which CR delays aging by triggering autophagy, epigenetic modifications, and the interaction between the two in caloric restriction. In order to provide new ideas for the study of the mechanism of aging and delaying aging.

Development of a Vascularized Human Skin Equivalent with Hypodermis for Photoaging Studies

Photoaging is an important extrinsic aging factor leading to altered skin morphology and reduced function. Prior work has revealed a connection between photoaging and loss of subcutaneous fat. Currently, primary models for studying this are in vivo (human samples or animal models) or in vitro models, including human skin equivalents (HSEs). In vivo models are limited by accessibility and cost, while HSEs typically do not include a subcutaneous adipose component. To address this, we developed an "adipose-vascular" HSE (AVHSE) culture method, which includes both hypodermal adipose and vascular cells. Furthermore, we tested AVHSE as a potential model for hypodermal adipose aging via exposure to 0.45 ± 0.15 mW/cm² 385 nm light (UVA). One week of 2 h daily UVA exposure had limited impact on epidermal and vascular components of the AVHSE, but significantly reduced adiposity by approximately 50%. Overall, we have developed a novel method for generating HSE that include vascular and adipose components and demonstrated potential as an aging model using photoaging as an example.

Current Understanding of the Role of Senescent Melanocytes in Skin Ageing

Melanocytes reside within the basal epidermis of human skin, and function to protect the skin from ultraviolet light through the production of melanin. Prolonged exposure of the skin to UV light can induce irreparable DNA damage and drive cells into senescence, a sustained cell cycle arrest that prevents the propagation of this damage. Senescent cells can also be detrimental and contribute to skin ageing phenotypes through their senescence-associated secretory phenotype. Senescent cells can act in both an autocrine and paracrine manner to produce widespread tissue inflammation and skin ageing. Recently, melanocytes have been identified as the main senescent cell population within the epidermis and have been linked to a variety of skin ageing phenotypes, such as epidermal thinning and the presence of wrinkles. However, the literature surrounding melanocyte senescence is limited and tends to focus on the role of senescence in the prevention of melanoma. Therefore, this review aims to explore the current understanding of the contribution of senescent melanocytes to human skin ageing.

The landscape of aging

Aging is characterized by a progressive deterioration of physiological integrity, leading to impaired functional ability and ultimately increased susceptibility to death. It is a major risk factor for chronic human diseases, including cardiovascular disease, diabetes, neurological degeneration, and cancer. Therefore, the growing emphasis on "healthy aging" raises a series of important questions in life and social sciences. In recent years, there has been unprecedented progress in aging research, particularly the discovery that the rate of aging is at least partly controlled by evolutionarily conserved genetic pathways and biological processes. In an attempt to bring full-fledged understanding to both the aging process and age-associated diseases, we review the descriptive, conceptual, and interventive aspects of the landscape of aging composed of a number of layers at the cellular, tissue, organ, organ system, and organismal levels.

Macrophages Are Polarized toward an Inflammatory Phenotype by their Aged Microenvironment in the Human Skin

Aging of the skin is accompanied by cellular as well as tissue environmental changes, ultimately reducing the ability of the tissue to regenerate and adequately respond to external stressors. Macrophages are important gatekeepers of tissue homeostasis, and it has been reported that their number and phenotype change during aging in a site-specific manner. How aging affects human skin macrophages and what implications this has for the aging process in the tissue are still not fully understood. Using single-cell RNA-sequencing analysis, we show that there is at least a 50% increase of macrophages in human aged skin, which appear to have developed from monocytes and exhibit more proinflammatory M1-like characteristics. In contrast, the cell-intrinsic ability of aged monocytes to differentiate into M1 macrophages was reduced. Using coculture experiments with aged dermal fibroblasts, we show that it is the aged microenvironment that drives a more proinflammatory phenotype of macrophages in the skin. This proinflammatory M1-like phenotype in turn negatively influenced the expression of extracellular matrix proteins by fibroblasts, emphasizing the impact of the aged macrophages on the skin phenotype.

Organotypic cultures as aging associated disease models

Aging remains a primary risk factor for a host of diseases, including leading causes of death. Aging and associated diseases are inherently multifactorial, with numerous contributing factors and phenotypes at the molecular, cellular, tissue, and organismal scales. Despite the complexity of aging phenomena, models currently used in aging research possess limitations. Frequently used in vivo models often have important physiological differences, age at different rates, or are genetically engineered to match late disease phenotypes rather than early causes. Conversely, routinely used in vitro models lack the complex tissue-scale and systemic cues that are disrupted in aging. To fill in gaps between in vivo and traditional in vitro models, researchers have increasingly been turning to organotypic models, which provide increased physiological relevance with the accessibility and control of in vitro context. While powerful tools, the development of these models is a field of its own, and many aging researchers may be unaware of recent progress in organotypic models, or hesitant to include these models in their own work. In this review, we describe recent progress in tissue engineering applied to organotypic models, highlighting examples explicitly linked to aging and associated disease, as well as examples of models that are relevant to aging. We specifically highlight progress made in skin, gut, and skeletal muscle, and describe how recently demonstrated models have been used for aging studies or similar phenotypes. Throughout, this review emphasizes the accessibility of these models and aims to provide a resource for researchers seeking to leverage these powerful tools.

Skin Aging in Long-Lived Naked Mole-Rats Is Accompanied by Increased Expression of Longevity-Associated and Tumor Suppressor Genes

Naked mole-rats (NMRs) (Heterocephalus glaber) are long-lived mammals that possess a natural resistance to cancer and other age-related pathologies, maintaining a healthy life span >30 years. In this study, using immunohistochemical and RNA-sequencing analyses, we compare skin morphology, cellular composition, and global transcriptome signatures between young and aged (aged 3‒4 vs. 19‒23 years, respectively) NMRs. We show that similar to aging in human skin, aging in NMRs is accompanied by a decrease in epidermal thickness; keratinocyte proliferation; and a decline in the number of Merkel cells, T cells, antigen-presenting cells, and melanocytes. Similar to that in human skin aging, expression levels of dermal collagens are decreased, whereas matrix metalloproteinase 9 and matrix metalloproteinase 11 levels increased in aged versus in young NMR skin. RNA-sequencing analyses reveal that in contrast to human or mouse skin aging, the transcript levels of several longevity-associated (Igfbp3, Igf2bp3, Ing2) and tumor-suppressor (Btg2, Cdkn1a, Cdkn2c, Dnmt3a, Hic1, Socs3, Sfrp1, Sfrp5, Thbs1, Tsc1, Zfp36) genes are increased in aged NMR skin. Overall, these data suggest that specific features in the NMR skin aging transcriptome might contribute to the resistance of NMRs to spontaneous skin carcinogenesis and provide a platform for further investigations of NMRs as a model organism for studying the biology and disease resistance of human skin.

Protective effects of the phenolic compounds from mung bean hull against H2O2-induced skin aging through alleviating oxidative injury and autophagy in HaCaT cells and HSF cells

To add value to food waste and seek skin aging suppressor, petroleum ether, ethyl acetate, n-butanol and water phenolic extracts were produced from mung bean hulls subjected to ultrasound-assisted ethanolic extraction. The four extracts all contained protocatechuic acid, isovitexin, vitexin, caffeic acid, 4-coumaric acid, ferulic acid, rutin and chlorogenic acid (revealed by UHPLC-MS/MS). The effects of the four extracts and their main phenolic compounds against H₂O₂-caused cell damage and aging in HaCaT and HSF cells were examined (including cell viability, ROS, MDA, SOD, GSH-px and β-galactosidase levels). The four extracts and the eight phenolic compounds exhibited different protective effects on H₂O₂-treated HaCaT/HSF cells viability, with the ethyl acetate extract among the extracts, and isovitexin and vitexin among the eight compounds, exerting the greatest protection. Therefore, isovitexin and vitexin may be the key oxidative stress and autophagy modulators of mung bean hull, and they inhibit skin aging and damage likely through suppressing Nrf2/keap1/HO-1 related oxidative damage and LC3II/p62/GATA4 related autophagy.

Targeting Cellular Senescence with Senotherapeutics: Development of New Approaches for Skin Care

SUMMARY

Aging of the skin is evidenced by increased wrinkles, age spots, dryness, and thinning with decreased elasticity. Extrinsic and intrinsic factors including UV, pollution, and inflammation lead to an increase in senescent cells (SnCs) in skin with age that contribute to these observed pathological changes. Cellular senescence is induced by multiple types of damage and stress and is characterized by the irreversible exit from the cell cycle with upregulation of cell cycle-dependent kinase inhibitors p16INK4a and p21CIP1. Most SnCs also developed an inflammatory senescence-associated secretory phenotype (SASP) that drives further pathology through paracrine effects on neighboring cells and endocrine effects on cells at a distance. Recently, compounds able to kill senescent cells specifically, termed senolytics, or suppress the SASP, termed senomorphics, have been developed that have the potential to improve skin aging as well as systemic aging in general. Here, we provide a summary of the evidence for a key role in cellular senescence in driving skin aging. In addition, the evidence for the potential application of senotherapeutics for skin treatments is presented. Overall, topical, and possibly oral senotherapeutic treatments have tremendous potential to eventually become a standard of care for skin aging and related skin disorders.

β2-microglobulin is overexpressed in buccal cells of elderly and correlated with expression of p16 and inflammatory genes

β2M (Beta 2 microglobulin) is a small protein that is found in all nucleated cells, previous finding showed that its levels increased in the serum of the elderly. Buccal cell samples are none invasive approach for assessing the expression of target genes. There was rationality to assess the expression of β2M in buccal cells of people of a different group of ages. Indeed, the expression of β2M increased significantly with fold change 3.40, 4.80, 6.60^**, 8.20^*** and 12.04^*** for the group of age 18–25 years, 26–35 years, 36–45 years, 46–55 years, and 56–70 years respectively. The same observation was seen with markers of biological aging (p16^INK4a) with fold change 3.19, 3.90, 4.80*, 8.50^*** and 12.40^*** for the group of age 18–25 years, 26–35 years, 36–45 years, 46–55 years, and 56–70 years respectively. As expected, there was an increase in the inflammatory genes (IL-1 β and IL-6) expression in the elderly. Moreover, there was a direct significant correlation (r = 90, p < 0.001) between β2M expression and age (years), and the same direct significant correlation between p16^INK4a expression and age (years) was also seen (r = 90, p < 0.001). In addition, a direct correlation between β2M and p16^INK4a was also seen (r = 0.8.3, p < 0.001), there was also direct correlation between β2M and IL-1 β and IL-6 with (r = 0.5, p < 0.001; r = 0.68, p < 0.001) respectively. This evidence showed that β2M increased in buccal cells of the elderly compared to younger, and thereby buccal cells can be exploited to assess biological aging by measuring β2M levels, however, large sample size and using another assessing method such as β2M protein levels should be performed to confirm the results.

Downregulation of senescence-associated secretory phenotype by knockdown of secreted frizzled-related protein 4 contributes to the prevention of skin aging

There is growing evidence that the appearance and texture of the skin that is altered during the aging process are considerably enhanced by the accumulation of senescent dermal fibroblasts. These senescent cells magnify aging via an inflammatory, histolytic, and senescence-associated secretory phenotype (SASP). Secreted frizzled-related protein 4 (SFRP4) was previously determined to be expressed in dermal fibroblasts of aging skin, and its increased expression has been shown to promote cellular senescence. However, its role in the SASP remains unknown. We found that SFRP4 was significantly expressed in p16ink4a-positive human skin fibroblasts and that treatment with recombinant SFRP4 promoted SASP and senescence, whereas siRNA knockdown of SFRP4 suppressed SASP. Furthermore, we found that knockdown of SFRP4 in mouse skin ameliorates age-related reduction of subcutaneous adipose tissue, panniculus carnosus muscle layer, and thinning and dispersion of collagen fibers. These findings suggest a potential candidate for the development of new skin rejuvenation therapies that suppress SASP.

Skin-Aging Pigmentation: Who Is the Real Enemy?

Skin aging is induced and sustained by chronological aging and photoaging. Aging skin pigmentation such as mottled pigmentation (senile lentigo) and melasma are typical signs of photoaging. The skin, like other human organs, undergoes cellular senescence, and senescent cells in the skin increase with age. The crosstalk between melanocytes as pigmentary cells and other adjacent types of aged skin cells such as senescent fibroblasts play a role in skin-aging pigmentation. In this review, we provide an overview of cellular senescence during the skin-aging process. The discussion also includes cellular senescence related to skin-aging pigmentation and the therapeutic potential of regulating the senescence process.

Synergism of BCL-2 family inhibitors facilitates selective elimination of senescent cells

Accumulation of senescent cells in tissues with advancing age participates in the pathogenesis of several human age-associated diseases. Specific senescent secretome, the resistance of senescent cells to apoptotic stimuli, and lack of immune system response contribute to the accumulation of senescent cells and their adverse effects in tissues. Inhibition of antiapoptotic machinery, augmented in senescent cells, by BCL-2 protein family inhibitors represents a promising approach to eliminate senescent cells from tissues. This study aimed to explore synergistic and selective senolytic effects of anti-apoptotic BCL-2 family targeting compounds, particularly BH3 mimetics.

Using human non-transformed cells RPE-1, BJ, and MRC-5 brought to ionizing radiation-, oncogene-, drug-induced and replicative senescence, we found synergy in combining MCL-1 selective inhibitors with other BH3 mimetics. In an attempt to uncover the mechanism of such synergy, we revealed that the surviving subpopulation of cells resistant to individually applied ABT-737/ABT-263, MIK665, ABT-199, and S63845 BCL-2 family inhibitors showed elevated MCL-1 compared to untreated control cells indicating the presence of a subset of cells expressing high MCL-1 levels and, therefore, resistant to BCL-2 inhibitors within the original population of senescent cells.

Overall, we found that combining BCL-2 inhibitors can be beneficial for eliminating senescent cells, thereby enabling use of lower, potentially less toxic, doses of drugs compared to monotherapy, thereby overcoming the resistance of the subpopulation of senescent cells to monotherapy.

Pharmacological Approaches to Decelerate Aging: A Promising Path

Biological aging or senescence is a course in which cellular function decreases over a period of time and is a consequence of altered signaling mechanisms that are triggered in stressed cells leading to cell damage. Aging is among the principal risk factors for many chronic illnesses such as cancer, cardiovascular disorders, and neurodegenerative diseases. Taking this into account, targeting fundamental aging mechanisms therapeutically may effectively impact numerous chronic illnesses. Selecting ideal therapeutic options in order to hinder the process of aging and decelerate the progression of age-related diseases is valuable. Along therapeutic options, life style modifications may well render the process of aging. The process of aging is affected by alteration in many cellular and signaling pathways amid which mTOR, SIRT1, and AMPK pathways are the most emphasized. Herein, we have discussed the mechanisms of aging focusing mainly on the mentioned pathways as well as the role of inflammation and autophagy in aging. Moreover, drugs and natural products with antiaging properties are discussed in detail.

Human placental extract activates a wide array of gene expressions related to skin functions

As skin aging is one of the most common dermatological concerns in recent years, scientific research has promoted treatment strategies aimed at preventing or reversing skin aging. Breakdown of the extracellular matrix (ECM), such as collagen and elastin fibers, in the skin results in decreased skin elasticity and tension. Cutaneous cells, especially fibroblasts in the dermis layer of the skin, mainly produce ECM proteins. Although clinical studies have demonstrated that placental extract (PE) has positive effects on skin health, the molecular mechanisms by which PE acts against skin aging are still largely unknown. In this study, we performed RNA-sequence analysis to investigate whether human PE (HPE) alters ECM-related gene expression in normal human dermal fibroblast (NHDF) cells. Gene ontology analysis showed that genes related to extracellular matrix/structure organization, such as COL1A1, COL5A3, ELN, and HAS2 were highly enriched, and most of these genes were upregulated. We further confirmed that the HPE increased the type I collagen, proteoglycan versican, elastin, and hyaluronan levels in NHDF cells. Our results demonstrate that HPE activates global ECM-related gene expression in NHDF cells, which accounts for the clinical evidence that the HPE affects skin aging.

The accelerated aging skin in rhino-like SHJHhr mice

SHJH^hr mice line is rhino-like mice with a nonsense Hairless (Hr) mutant, which shows the characteristic of shedding hair and wrinkled skin with increasing age. Though histological analysis and aging indexes detection, SHJH^hr mice show an increased thickness skin with degraded hair follicle and dermal cysts, and disorganized collagen fibers as well as decreased level of Hyp. Meanwhile, the aging markers p16 and p21 are significantly higher in SHJH^hr mouse skin than ICR mouse skin at same age. Moreover, the data of MDA and SOD show a higher oxidative stress in SHJH^hr mouse skin, and the levels of Nrf2 and its targets are significantly down-regulated, which suggests SHJH^hr mice have a faster aging skin and its reason maybe poor antioxidative protection. Overall, this study shows SHJH^hr mice with an accelerated aging skin, which suggests the role of Hr gene in skin aging.

A Comprehensive Overview of the Complex Role of Oxidative Stress in Aging, The Contributing Environmental Stressors and Emerging Antioxidant Therapeutic Interventions

Introduction

Aging is a normal, inevitable, irreversible, and progressive process which is driven by internal and external factors. Oxidative stress, that is the imbalance between prooxidant and antioxidant molecules favoring the first, plays a key role in the pathophysiology of aging and comprises one of the molecular mechanisms underlying age-related diseases. However, the oxidative stress theory of aging has not been successfully proven in all animal models studying lifespan, meaning that altering oxidative stress/antioxidant defense systems did not always lead to a prolonged lifespan, as expected. On the other hand, animal models of age-related pathological phenotypes showed a well-correlated relationship with the levels of prooxidant molecules. Therefore, it seems that oxidative stress plays a more complicated role than the one once believed and this role might be affected by the environment of each organism. Environmental factors such as UV radiation, air pollution, and an unbalanced diet, have also been implicated in the pathophysiology of aging and seem to initiate this process more rapidly and even at younger ages.

Aim

The purpose of this review is to elucidate the role of oxidative stress in the physiology of aging and the effect of certain environmental factors in initiating and sustaining this process. Understanding the pathophysiology of aging will contribute to the development of strategies to postpone this phenomenon. In addition, recent studies investigating ways to alter the antioxidant defense mechanisms in order to prevent aging will be presented.

Conclusions

Careful exposure to harmful environmental factors and the use of antioxidant supplements could potentially affect the biological processes driving aging and slow down the development of age-related diseases. Maybe a prolonged lifespan could not be achieved by this strategy alone, but a longer healthspan could also be a favorable target.

Focus on the Contribution of Oxidative Stress in Skin Aging

Skin aging is one of the most evident signs of human aging. Modification of the skin during the life span is characterized by fine lines and wrinkling, loss of elasticity and volume, laxity, rough-textured appearance, and pallor. In contrast, photoaged skin is associated with uneven pigmentation (age spot) and is markedly wrinkled. At the cellular and molecular level, it consists of multiple interconnected processes based on biochemical reactions, genetic programs, and occurrence of external stimulation. The principal cellular perturbation in the skin driving senescence is the alteration of oxidative balance. In chronological aging, reactive oxygen species (ROS) are produced mainly through cellular oxidative metabolism during adenosine triphosphate (ATP) generation from glucose and mitochondrial dysfunction, whereas in extrinsic aging, loss of redox equilibrium is caused by environmental factors, such as ultraviolet radiation, pollution, cigarette smoking, and inadequate nutrition. During the aging process, oxidative stress is attributed to both augmented ROS production and reduced levels of enzymatic and non-enzymatic protectors. Apart from the evident appearance of structural change, throughout aging, the skin gradually loses its natural functional characteristics and regenerative potential. With aging, the skin immune system also undergoes functional senescence manifested as a reduced ability to counteract infections and augmented frequency of autoimmune and neoplastic diseases. This review proposes an update on the role of oxidative stress in the appearance of the clinical manifestation of skin aging, as well as of the molecular mechanisms that underline this natural phenomenon sometimes accelerated by external factors.

Age-Related Changes in the Fibroblastic Differon of the Dermis: Role in Skin Aging

Skin aging is a multi-factorial process that affects nearly every aspect of skin biology and function. The processes developing in the skin during aging are based on fundamental molecular mechanisms associated with fibroblasts, the main cellular population of the dermis. It has been revealed that the amount of fibroblasts decreases markedly with age and their functional activity is also reduced. This inevitably leads to a decrease in the regenerative abilities of the skin and the progression of its aging. In this review we consider the mechanisms underlying these processes, mainly the changes observed with age in the stem/progenitor cells that constitute the fibroblastic differon of the dermis and form their microenvironment (niches). These changes lead to the depletion of stem cells, which, in turn, leads to a decrease in the number of differentiated (mature) dermal fibroblasts responsible for the production of the dermal extracellular matrix and its remodeling. We also describe in detail DNA damages, their cellular and systemic consequences, molecular mechanisms of DNA damage response, and also the role of fibroblast senescence in skin aging.

Modeling human gray hair by irradiation as a valuable tool to study aspects of tissue aging

As one of the earliest and most visible phenomenon of aging, gray hair makes it a unique model system for investigating the mechanism of aging. Ionizing radiation successfully induces gray hair in mice, and also provides a venue to establish an organ-cultured human gray hair model. To establish a suitable organ-cultured human gray HF model by IR, which imitates gray hair in the elderly, and to explore the mechanisms behind the model. By detecting growth parameters, melanotic and senescence markers of the model, we found that the model of 5 Gy accords best with features of elderly gray hair. Then, we investigated the formation mechanisms of the model by RNA-sequencing. We demonstrated that the model of organ-cultured gray HFs after 5 Gy irradiation is closest to the older gray HFs. Moreover, the 5 Gy inhibited the expression of TRP-1, Tyr, Pmel17, and MITF in hair bulbs/ORS of HFs. The 5 Gy also significantly induced ectopically pigmented melanocytes and increased the expression of DNA damage and senescence in HFs. Finally, RNA-seq analysis of the model suggested that IR resulted in cell DNA damage, and the accumulation of oxidative stress in the keratinocytes. Oxidative stress and DNA damage caused cell dysfunction and decreased melanin synthesis in the gray HFs. We found that HFs irradiated at 5 Gy successfully constructed an appropriate aging HF model. This may provide a useful model for cost-effective and predictable treatment strategies to human hair graying and the process of aging.

Mechanism of Ba Zhen Tang Delaying Skin Photoaging Based on Network Pharmacology and Molecular Docking

Purpose

To study the efficacy of Ba Zhen Tang in delaying skin photoaging and its potential mechanism based on network pharmacology and molecular docking.

Methods

First, we screened the active components and targets of Ba Zhen Tang by Traditional Chinese Medicine Database and Analysis Platform (TCMSP) and The Universal Protein Resource (UniProt). The target genes of skin photoaging were obtained from GeneCards and GeneMap database. Then, we analyzed the protein–protein interaction (PPI) by STRING database. The network map was constructed by Cytoscape. Finally, we performed Gene Ontology (GO) enrichment analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis by Metascape database. The molecular docking via Autodock Vina and Pymol. Furthermore, skin photoaging cellular models were established, and the effects of Ba Zhen Tang on ameliorating skin photoaging were investigated.

Results

A total of 160 active ingredients in Ba Zhen Tang and 60 targets of Ba Zhen Tang for delaying skin photoaging were identified. By GO enrichment analysis, 1153 biological process entries, 45 cellular component entries and 89 molecular functional entries were obtained. A total of 155 signal pathways were obtained by KEGG analysis. Ba Zhen Tang is related to MAPK signaling pathway, TNF signaling pathway and AGE-RAGE signaling pathway in diabetic complications, etc., which directly affect the key nodes of photoaging. The molecular docking results showed that there was a certain affinity between the main compounds (kaempferol, quercetin, β-sitosterol, naringenin) and core target genes (PTGS2, CASP3, MAPK1, MAPK3, TP53). Ba Zhen Tang-treated mouse serum inhibited the senescence and p16^INK4a expression of human immortalized keratinocyte (HaCaT) cells irradiated by ultraviolet-B (UVB).

Conclusion

Our study elucidated the potential pharmacological mechanism of Ba Zhen Tang in the treatment of photoaging through multiple targets and pathways. The therapeutic effects of Ba Zhen Tang on skin photoaging were validated in cellular models.

Attenuation of intrinsic aging of the skin via elimination of senescent dermal fibroblasts with senolytic drugs

BACKGROUND

Skin aging is caused by numerous factors that result in structural and functional changes in cutaneous components. Research has shown that senescent cells are known to accumulate in skin aging, however, the role of senescent cells in skin aging has not been defined.

OBJECTIVES

To elucidate the role of senescent cell in skin aging, we evaluated the effect of known senolytic drugs on senescent dermal fibroblasts.

METHODS

Primary human dermal fibroblasts (HDFs) were induced to senescence by long-term passaging, UV irradiation, and H2O2 treatment. Cell viability was measured after treatment of ABT-263 and ABT-737 on HDFs. Young and aged hairless mice were intradermally injected with drugs or vehicle on the dorsal skin for 10 days. Skin specimens were obtained and reverse-transcription quantitative PCR, western blotting, and histological analysis were performed.

RESULTS

We found that ABT-263 and ABT-737 induced selective clearance of senescent dermal fibroblasts, regardless of the method of senescence induction. Aged mouse skin treated with ABT-263 or ABT-737 showed increased collagen density, epidermal thickness, and proliferation of keratinocytes, as well as decreased senescence-associated secretory phenotypes, such as MMP-1 and IL-6.

CONCLUSIONS

Taken together, our results indicate that selective clearance of senescent skin cells can attenuate and improve skin aging phenotypes and that senolytic drugs may be of potential use as new therapeutic agents for treating aging of the skin.

Obesity Increases Gene Expression of Markers Associated With Immunosenescence in Obese Middle-Aged Individuals

Recently, it has been argued that obesity leads to a chronic pro-inflammatory state that can accelerate immunosenescence, predisposing to the early acquisition of an immune risk profile and health problems related to immunity in adulthood. In this sense, the present study aimed to verify, in circulating leukocytes, the gene expression of markers related to early immunosenescence associated with obesity and its possible relationships with the physical fitness in obese adults with type 2 diabetes or without associated comorbidities. The sample consisted of middle-aged obese individuals (body mass index (BMI) between 30-35 kg/m²) with type 2 diabetes mellitus (OBD; n = 17) or without associated comorbidity (OB; n = 18), and a control group of eutrophic healthy individuals (BMI: 20 - 25 kg/m²) of same ages (E; n = 18). All groups (OBD, OB and E) performed the functional analyses [muscle strength (1RM) and cardiorespiratory fitness (VO_2max)], anthropometry, body composition (Air Displacement Plethysmograph), blood collections for biochemical (anti-CMV) and molecular (gene expression of leptin, IL-2, IL-4, IL-6, IL-10, TNF-α, PD-1, P16^ink4a, CCR7, CD28 and CD27) analyses of markers related to immunosenescence. Increased gene expression of leptin, IL-2, IL-4, IL-10, TNF-α, PD-1, P16^ink4a, CCR7 and CD27 was found for the OBD and OB groups compared to the E group. Moreover, VO_2max for the OBD and OB groups was significantly lower compared to E. In conclusion, obesity, regardless of associated disease, induces increased gene expression of markers associated with inflammation and immunosenescence in circulating leukocytes in obese middle-aged individuals compared to a eutrophic group of the same age. Additionally, increased adipose tissue and markers of chronic inflammation and immunosenescence were associated to impairments in the cardiorespiratory capacity of obese middle-aged individuals.

Altered p16Ink4a, IL-1β, and Lamin b1 Protein Expression Suggest Cellular Senescence in Deep Endometriotic Lesions

Endometriosis causes immunological and cellular alterations. Endometriosis lesions have lower levels of lamin b1 than the endometrium. Moreover, high levels of pro-inflammatory markers are observed in the peritoneal fluid, follicular fluid, and serum in endometriosis lesions. Thus, we hypothesized that the accumulation of senescent cells in endometriosis tissues would facilitate endometriosis maintenance in an inflammatory microenvironment. To study senescent cell markers and the senescence-associated secretory phenotype (SASP) in endometriosis lesions, we conducted a cross-sectional study with 27 patients undergoing video laparoscopy for endometriosis resection and 19 patients without endometriosis. Endometriosis lesions were collected from patients with endometriosis, while eutopic endometrium was collected from patients both with and without endometriosis. Tissues were evaluated for senescence markers (p16Ink4a, lamin b1, and IL-1β) and interleukin concentrations. The expression of p16Ink4a increased in lesions compared to that in eutopic endometrium from endometriosis patients in the secretory phase. In the proliferative phase, lesions exhibited lower lamin b1 expression but higher IL-4 expression than the eutopic endometrium. Further, IL-1β levels were higher in the lesions than in the eutopic endometrium in both the secretory and proliferative phases. We believe that our findings may provide targets for better therapeutic interventions to alleviate the symptoms of endometriosis.

IL-34 Downregulation-associated M1/M2 Macrophage Imbalance is Related to Inflammaging in Sun-exposed Human Skin

Macrophages can be polarized into two subsets: a proinflammatory (M1) or an anti-inflammatory (M2) phenotype. In this study, we show that an increased M1-to-M2 ratio associated with a decrease in IL-34 induces skin inflammaging. The total number of macrophages in the dermis did not change, but the number of M2 macrophages was significantly decreased. Thus, the M1-to-M2 ratio was significantly increased in sun-exposed aged skin and positively correlated with the percentage of p21⁺ and p16⁺ senescent cells in the dermis. The supernatant of M1 macrophages increased the percentages of senescence-associated β-galactosidase‒positive cells, whereas the supernatant of M2 macrophages decreased the percentages of senescence-associated β-galactosidase‒positive cells in vitro. Among the mechanisms that could explain the increase in the M1-to-M2 ratio, we found that the number of IL-34⁺ cells was decreased in aged skin and negatively correlated with the M1-to-M2 ratio. Furthermore, IL-34 induced the expression of CD206 and IL-10, which are M2 macrophage markers, in an in vitro assay. Our results suggest that a reduction in epidermal IL-34 in aged skin may skew the M1/M2 balance in the dermis and lead to low-grade chronic inflammation and inflammaging.

Tissue engineering strategies to bioengineer the ageing skin phenotype in vitro

Human skin ageing is a complex and heterogeneous process, which is influenced by genetically determined intrinsic factors and accelerated by cumulative exposure to extrinsic stressors. In the current world ageing demographic, there is a requirement for a bioengineered ageing skin model, to further the understanding of the intricate molecular mechanisms of skin ageing, and provide a distinct and biologically relevant platform for testing actives and formulations. There have been many recent advances in the development of skin models that recapitulate aspects of the ageing phenotype in vitro. This review encompasses the features of skin ageing, the molecular mechanisms that drive the ageing phenotype, and tissue engineering strategies that have been utilised to bioengineer ageing skin in vitro.

Skin senescence: mechanisms and impact on whole-body aging

The skin is the largest organ and has a key protective role. Similar to any other tissue, the skin is influenced not only by intrinsic/chronological aging, but also by extrinsic aging, triggered by environmental factors that contribute to accelerating the skin aging process. Aged skin shows structural, cellular, and molecular changes and accumulation of senescent cells. These senescent cells can induce or accelerate the age-related dysfunction of other nearby cells from the skin, or from different origins. However, the extent and underlying mechanisms remain unknown. In this opinion, we discuss the possible relevant role of skin senescence in the induction of aging phenotypes to other organs/tissues, contributing to whole-body aging. Moreover, we suggest that topical administration of senolytics/senotherapeutics could counteract the overall whole-body aging phenotype.

Bullous pemphigoid: An immune disorder related to aging (Review)

Bullous pemphigoid (BP) is the most frequent subepidermal autoimmune blistering disease and is caused by autoantibodies directed against two principal antigens of the hemidesmosome, BP antigen 180 and BP antigen 230. The pathogenesis of BP is dependent upon the interaction between genetic predisposition, physiological skin alterations due to aging and specific triggers. Several triggers have already been reported to induce this disease and include drugs, thermal or electrical burns, surgical procedures, trauma, UV radiation, radiotherapy, chemicals and infections. Data from the current literature support the hypothesis that alterations of the skin barrier associated with aging increase individual susceptibility to these aforementioned triggers. Consequently, this has been reported to lead to the attack of autoantibodies, demonstrating the predilection of BP for the elderly population. The identification of triggering factors and comorbidities may aid in understanding the pathogenesis of BP and improve clinical management by encouraging their prompt recognition and removal. Moreover, the present review has indicated that current management of BP should be aimed at counteracting the detrimental effects of aging on the skin by restoring skin barrier integrity and maintaining cutaneous homeostasis, for example with systematic applications of topical emollients and photoprotection. This strategy could prove even more beneficial in the elderly, in which frequent comorbidities associated with age often narrow available immunosuppressive treatment options. Furthermore, the safety of treatment regimens may significantly affect outcome and prognosis.

An efficient, non-invasive approach for in-vivo sampling of hair follicles: design and applications in monitoring DNA damage and aging

In accordance with the 3 Rs principle (to replace, reduce and refine) animal models in biomedical research, we have developed and applied a new approach for sampling and analyzing hair follicles in various experimental settings. This involves use of a convenient device for non-invasive collection of hair follicles and processing methods that provide sufficient amounts of biological material to replace stressful and painful biopsies. Moreover, the main components of hair follicles are live cells of epithelial origin, which are highly relevant for most types of malignant tumors, so they provide opportunities for studying aging-related pathologies including cancer. Here, we report the successful use of the method to obtain mouse hair follicular cells for genotyping, quantitative PCR, and quantitative immunofluorescence. We present proof of concept data demonstrating its utility for routine genotyping and monitoring changes in quality and expression levels of selected proteins in mice after gamma irradiation and during natural or experimentally induced aging. We also performed pilot translation of animal experiments to human hair follicles irradiated ex vivo. Our results highlight the value of hair follicles as biological material for convenient in vivo sampling and processing in both translational research and routine applications, with a broad range of ethical and logistic advantages over currently used biopsy-based approaches.

Targeting microRNA for improved skin health

BACKGROUND

In human skin, miRNAs have important regulatory roles and are involved in the development, morphogenesis, and maintenance by influencing cell proliferation, differentiation, immune regulation, and wound healing. MiRNAs have been investigated for many years in various skin disorders such as atopic dermatitis, psoriasis, as well as malignant tumors. Only during recent times, cosmeceutical use of molecules/natural active ingredients to regulate miRNA expression for significant advances in skin health/care product development was recognized.

AIM

To review miRNAs with the potential to maintain and boost skin health and avoid premature aging by improving barrier function, preventing photoaging, hyperpigmentation, and chronological aging/senescence.

METHODS

Most of the cited articles were found through literature search on PubMed. The main search criteria was a keyword "skin" in combination with the following words: miRNA, photoaging, UV, barrier, aging, exposome, acne, wound healing, pigmentation, pollution, and senescence. Most of the articles reviewed for relevancy were published during the past 10 years.

RESULTS

All results are summarized in Figure 1, and they are based on cited references.

CONCLUSIONS

Thus, regulating miRNAs expression is a promising approach for novel therapy not only for targeting skin diseases but also for cosmeceutical interventions aiming to boost skin health.

Gremlin 2 suppresses differentiation of stem/progenitor cells in the human skin

INTRODUCTION

The skin is comprised of various kinds of cells and has three layers, the epidermis, dermis and subcutaneous adipose tissue. Stem cells in each tissue duplicate themselves and differentiate to supply new cells that function in the tissue, and thereby maintain the tissue homeostasis. In contrast, senescent cells accumulate with age and secrete senescence-associated secretory phenotype (SASP) factors that impair surrounding cells and tissues, which lowers the capacity to maintain homeostasis in each tissue. Previously, we found Gremlin 2 (GREM2) as a novel SASP factor in the skin and reported that GREM2 suppressed the differentiation of adipose-derived stromal/stem cells. In the present study, we investigated the effects of GREM2 on stem cells in the epidermis and dermis.

METHODS

To examine whether GREM2 expression and the differentiation levels in the epidermis and dermis are correlated, the expressions of GREM2, stem cell markers, an epidermal differentiation marker Keratin 10 (KRT10) and a dermal differentiation marker type 3 procollagen were examined in the skin samples (n = 14) randomly chosen from the elderly where GREM2 expression level is high and the individual differences of its expression are prominent. Next, to test whether GREM2 affects the differentiation of skin stem cells, cells from two established lines (an epidermal and a dermal stem/progenitor cell model) were cultured and induced to differentiate, and recombinant GREM2 protein was added.

RESULTS

In the human skin, the expression levels of GREM2 varied among individuals both in the epidermis and dermis. The expression level of GREM2 was not correlated with the number of stem cells, but negatively correlated with those of both an epidermal and a dermal differentiation markers. The expression levels of epidermal differentiation markers were significantly suppressed by the addition of GREM2 in the three-dimensional (3D) epidermis generated with an epidermal stem/progenitor cell model. In addition, by differentiation induction, the expressions of dermal differentiation markers were induced in cells from a dermal stem/progenitor cell model, and the addition of GREM2 significantly suppressed the expressions of the dermal differentiation markers.

CONCLUSIONS

GREM2 expression level did not affect the numbers of stem cells in the epidermis and dermis but affects the differentiation and maturation levels of the tissues, and GREM2 suppressed the differentiation of stem/progenitor cells in vitro. These findings suggest that GREM2 may contribute to the age-related reduction in the capacity to maintain skin homeostasis by suppressing the differentiation of epidermal and dermal stem/progenitor cells.

Skin Aging, Cellular Senescence and Natural Polyphenols

The skin, being the barrier organ of the body, is constitutively exposed to various stimuli impacting its morphology and function. Senescent cells have been found to accumulate with age and may contribute to age-related skin changes and pathologies. Natural polyphenols exert many health benefits, including ameliorative effects on skin aging. By affecting molecular pathways of senescence, polyphenols are able to prevent or delay the senescence formation and, consequently, avoid or ameliorate aging and age-associated pathologies of the skin. This review aims to provide an overview of the current state of knowledge in skin aging and cellular senescence, and to summarize the recent in vitro studies related to the anti-senescent mechanisms of natural polyphenols carried out on keratinocytes, melanocytes and fibroblasts. Aged skin in the context of the COVID-19 pandemic will be also discussed.