The hallmarks of fibroblast ageing

The Aryl Hydrocarbon Receptor (AhR) in the Aging Process: Another Puzzling Role for This Highly Conserved Transcription Factor

Aging is the most important risk factor for the development of major life-threatening diseases such as cardiovascular disorders, cancer, and neurodegenerative disorders. The aging process is characterized by the accumulation of damage to intracellular macromolecules and it is concurrently shaped by genetic, environmental and nutritional factors. These factors influence the functionality of mitochondria, which play a central role in the aging process. Mitochondrial dysfunction is one of the hallmarks of aging and is associated with increased fluxes of ROS leading to damage of mitochondrial components, impaired metabolism of fatty acids, dysregulated glucose metabolism, and damage of adjacent organelles. Interestingly, many of the environmental (e.g., pollutants and other toxicants) and nutritional (e.g., flavonoids, carotenoids) factors influencing aging and mitochondrial function also directly or indirectly affect the activity of a highly conserved transcription factor, the Aryl hydrocarbon Receptor (AhR). Therefore, it is not surprising that many studies have already indicated a role of this versatile transcription factor in the aging process. We also recently found that the AhR promotes aging phenotypes across species. In this manuscript, we systematically review the existing literature on the contradictory studies indicating either pro- or anti-aging effects of the AhR and try to reconcile the seemingly conflicting data considering a possible dependency on the animal model, tissue, as well as level of AhR expression and activation. Moreover, given the crucial role of mitochondria in the aging process, we summarize the growing body of evidence pointing toward the influence of AhR on mitochondria, which can be of potential relevance for aging.

The anti-skin-aging effect of oral administration of gelatin from the swim bladder of Amur sturgeon (Acipenser schrenckii)

Gelatin was extracted from the swim bladder of Amur sturgeon with hot water at 50 °C with acceptable yield (76.54%) and it showed type I collagen features. The degree of hydrolysis reached 70.42%, and 26.55% of collagen peptides (380.76 Da) survived, after simulating digestion, absorption and peripheral blood circulation in vitro. In situ single-pass intestinal perfusion showed that the AMW of the collagen peptides was about 1100 Da in the intestine and they were mainly absorbed in the jejunum (61.11%). A 12-month feeding experiment using rats demonstrated that gelatin improved the histological structure, increased the thickness of the dermis (18.45%) and the density of collagen fibers (22.17%), and decreased the ratio of type III to type I collagen (43.44%) of chronologically aged skin at 3.85 g per kg bw per d. Moreover, the antioxidant enzyme activities in skin were significantly enhanced, while the malondialdehyde content was reduced by 31.99%. These results provided new insights into the development of new nutraceuticals and functional foods for the anti-skin-aging effect.

Derivation of Cell-Engineered Nanovesicles from Human Induced Pluripotent Stem Cells and Their Protective Effect on the Senescence of Dermal Fibroblasts

Stem cells secrete numerous paracrine factors, such as cytokines, growth factors, and extracellular vesicles. As a kind of extracellular vesicle (EV), exosomes produced in the endosomal compartment of eukaryotic cells have recently emerged as a biomedical material for regenerative medicine, because they contain many valuable contents that are derived from the host cells, and can stably deliver those contents to other recipient cells. Although we have previously demonstrated the beneficial effects of human induced potent stem cell-derived exosomes (iPSC-Exo) on the aging of skin fibroblasts, low production yield has remained an obstacle for clinical applications. In this study, we generated cell-engineered nanovesicles (CENVs) by serial extrusion of human iPSCs through membrane filters with diminishing pore sizes, and explored whether the iPSC-CENV ameliorates physiological alterations of human dermal fibroblasts (HDFs) that occur by natural senescence. The iPSC-CENV exhibited similar characteristics to the iPSC-Exo, while the production yield was drastically increased compared to that of iPSC-derived EVs, including exosomes. The proliferation and migration of both young and senescent HDFs were stimulated by the treatment with iPSC-CENVs. In addition, it was revealed that the iPSC-CNEV restored senescence-related alterations of gene expression. Treatment with iPSC-CENVs significantly reduced the activity of senescence-associated-β-galactosidase (SA-β-Gal) in senescent HDFs, as well as suppressing the elevated expression of p53 and p21, key factors involved in cell cycle arrest, apoptosis, and cellular senescence signaling pathways. Taken together, these results suggest that iPSC-CENV could provide an excellent alternative to iPSC-exo, and be exploited as a resource for the treatment of signs of skin aging.

Novel approaches for managing aged skin and nonmelanoma skin cancer

The process of aging influences every bodily organ and tissue, and those with rapid epithelial cell turnover, are particularly affected. The most visible of these, however, is the skin (including the epidermis), the largest human organ that provides a barrier to external insults, structure to the body and its movements, facilitates thermoregulation, harbors immune cells, and incorporates sensory neurons (including mechanoreceptors, nociceptors, and thermoreceptors). Skin aging has traditionally been categorized into intrinsic and extrinsic, with the latter nearly exclusively restricted to "photoaging," (i.e., aging due to exposure to solar or artificial ultraviolet radiation). However, both intrinsic and extrinsic aging share similar causes, including oxidative damage, telomere shortening, and mitochondrial senescence. Also, like other malignancies, the risk of malignant and nonmalignant lesions increases with age. Herein, we review the most recent findings in skin aging and nonmelanoma skin cancer, including addition to traditional and developing therapies.

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.

The Hyaluronidase, TMEM2, Promotes ER Homeostasis and Longevity Independent of the UPRER

Cells have evolved complex mechanisms to maintain protein homeostasis, such as the UPR^ER, which are strongly associated with several diseases and the aging process. We performed a whole-genome CRISPR-based knockout (KO) screen to identify genes important for cells to survive ER-based protein misfolding stress. We identified the cell-surface hyaluronidase (HAase), Transmembrane Protein 2 (TMEM2), as a potent modulator of ER stress resistance. The breakdown of the glycosaminoglycan, hyaluronan (HA), by TMEM2 within the extracellular matrix (ECM) altered ER stress resistance independent of canonical UPR^ER pathways but dependent upon the cell-surface receptor, CD44, a putative HA receptor, and the MAPK cell-signaling components, ERK and p38. Last, and most surprisingly, ectopic expression of human TMEM2 in C. elegans protected animals from ER stress and increased both longevity and pathogen resistance independent of canonical UPR^ER activation but dependent on the ERK ortholog mpk-1 and the p38 ortholog pmk-1.

A dynamical systems model for the measurement of cellular senescence

Senescent cells provide a good in vitro model to study ageing. However, cultures of ‘senescent’ cells consist of a mix of cell subtypes (proliferative, senescent, growth-arrested and apoptotic). Determining the proportion of senescent cells is crucial for studying ageing and developing new anti-degenerative therapies. Commonly used markers such as doubling population, senescence-associated β-galactosidase, Ki-67, γH2AX and TUNEL assays capture diverse and overlapping cellular populations and are not purely specific to senescence. A newly developed dynamical systems model follows the transition of an initial culture to senescence tracking population doubling, and the proportion of cells in proliferating, growth-arrested, apoptotic and senescent states. Our model provides a parsimonious description of transitions between these states accruing towards a predominantly senescent population. Using a genetic algorithm, these model parameters are well constrained by an in vitro human primary fibroblast dataset recording five markers at 16 time points. The computational model accurately fits to the data and translates these joint markers into the first complete description of the proportion of cells in different states over the lifetime. The high temporal resolution of the dataset demonstrates the efficacy of strategies for reconstructing the trajectory towards replicative senescence with a minimal number of experimental recordings.

Do senescence markers correlate in vitro and in situ within individual human donors?

Little is known on how well senescence markers in vitro and in situ correlate within individual donors. We studied correlations between the same and different in vitro markers. Furthermore, we tested correlations between in vitro markers with in situ p16INK4a positivity.

From 100 donors (20-91 years), cultured dermal fibroblasts were assessed for reactive oxygen species (ROS), telomere-associated foci (TAF), p16INK4a and senescence-associated β-gal (SAβ-gal), with/ without 0.6 µM rotenone for 3 days (short-term). In fibroblasts from 40 donors, telomere shortening, ROS and SAβ-gal were additionally assessed, with/ without 20 nM rotenone for 7 weeks (long-term). In skin from 52 donors, the number of p16INK4a positive dermal cells was assessed in situ.

More than half of the correlations of the same senescence markers in vitro between duplicate experiments and between short-term versus long-term experiments were significant. Half of the different senescence marker correlations were significant within the short-term and within the long-term experiments. The different senescence markers in vitro were not significantly correlated intra-individually with in situ p16INK4a positivity.
In conclusion, the same and different senescence markers are frequently correlated significantly within and between in vitro experiments, but in vitro senescence markers are not correlated with p16INK4a positivity in situ.

Effects of Lycium barbarum Polysaccharides on Health and Aging of C. elegans Depend on daf-12/daf-16

As the global population ages, searching for drugs and functional foods which can slow down the aging process has attracted a number of researchers. In this paper, the Lycium barbarum polysaccharides (LBP) extracted from Lycium barbarum was characterized and the effects of LBP on the aging and health of C. elegans were studied. Results showed that LBP can prolong the lifespan, improve the abilities to withstand environmental stress, enhance reproductive potentials, and maintain muscle integrity of C. elegans. By using genetically mutated C. elegans strains, RNAi gene silencing, and measuring the mRNA expression level, it was demonstrated that the lifespan of C. elegans was extended by LBP mainly through sir-2.1, daf-12, and daf-16. The present study might provide a basis for further study of LBP as a food or drug to interfere with aging and reduce the incidence of age-related diseases.

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.

Aging-related increase in store-operated Ca2+ influx in human ventricular fibroblasts

Senescence-related fibrosis contributes to cardiac dysfunction. Profibrotic processes are Ca²⁺ dependent. The effect of aging on the Ca²⁺ mobilization processes of human ventricular fibroblasts (hVFs) is unclear. Therefore, we tested whether aging altered intracellular Ca²⁺ release and store-operated Ca²⁺ entry (SOCE). Disease-free hVFs from 2- to 63-yr-old trauma victims were assessed for cytosolic Ca²⁺ dynamics with fluo 3/confocal imaging. Angiotensin II or thapsigargin was used to release endoplasmic reticulum Ca²⁺ in Ca²⁺-free solution; CaCl₂ (2 mM) was then added to assess SOCE, which was normalized to ionomycin-induced maximal Ca²⁺. The angiotensin II experiments were repeated after phosphoenolpyruvate pretreatment to determine the role of energy status. The expression of genes encoding SOCE-related ion channel subunits was assessed by quantitative PCR, and protein expression was assessed by immunoblot analysis. Age groups of <50 and ≥50 yr were compared using unpaired t-test or regression analysis. Ca²⁺ release by angiotensin II or thapsigargin was not different between the groups, but SOCE was significantly elevated in the ≥50-yr group. Regression analysis showed an age-dependent phosphoenolpyruvate-sensitive increase in SOCE of hVFs. Aging did not alter the mRNA expression of SOCE-related genes. The profibrotic phenotype of hVFs was evident by sprouty1 downregulation with age. Thus, an age-associated increase in angiotensin II- and thapsigargin-induced SOCE occurs in hVFs, independent of receptor mechanisms or alterations of mRNA expression level of SOCE-related ion channel subunits but related to the cellular bioenergetics status. Elucidation of mechanisms underlying enhanced hVF SOCE with aging may refine SOCE targets to limit aging-related progression of Ca²⁺-dependent cardiac fibrosis. NEW & NOTEWORTHY Human ventricular fibroblasts exhibit an age-related increase in store-operated Ca²⁺ influx induced by angiotensin II, an endogenous vasoactive hormone, or thapsigargin, an inhibitor of endoplasmic reticulum Ca²⁺-ATPase, independent of receptor mechanisms or genes encoding store-operated Ca²⁺ entry-related ion channel subunits. Selective inhibition of this augmented store-operated Ca²⁺ entry could therapeutically limit aging-related cardiac fibrosis.

Human aging DNA methylation signatures are conserved but accelerated in cultured fibroblasts

Aging is associated with progressive and site-specific changes in DNA methylation (DNAm). These global changes are captured by DNAm clocks that accurately predict chronological age in humans but relatively little is known about how clocks perform in vitro. Here we culture primary human fibroblasts across the cellular lifespan (~6 months) and use four different DNAm clocks to show that age-related DNAm signatures are conserved and accelerated in vitro. The Skin & Blood clock shows the best linear correlation with chronological time (r = 0.90), including during replicative senescence. Although similar in nature, the rate of epigenetic aging is approximately 62x times faster in cultured cells than in the human body. Consistent with in vivo data, cells aged under hyperglycemic conditions exhibit an approximately three years elevation in baseline DNAm age. Moreover, candidate gene-based analyses further corroborate the conserved but accelerated biological aging process in cultured fibroblasts. Fibroblasts mirror the established DNAm topology of the age-related ELOVL2 gene in human blood and the rapid hypermethylation of its promoter cg16867657, which correlates with a linear decrease in ELOVL2 mRNA levels across the lifespan. Using generalized additive modeling on twelve timepoints across the lifespan, we also show how single CpGs exhibit loci-specific, linear and nonlinear trajectories that reach rates up to -47% (hypomethylation) to +23% (hypermethylation) per month. Together, these high-temporal resolution global, gene-specific, and single CpG data highlight the conserved and accelerated nature of epigenetic aging in cultured fibroblasts, which may constitute a system to evaluate age-modifying interventions across the lifespan.

Neuroendocrine Aspects of Skin Aging

Skin aging is accompanied by a gradual loss of function, physiological integrity and the ability to cope with internal and external stressors. This is secondary to a combination of complex biological processes influenced by constitutive and environmental factors or by local and systemic pathologies. Skin aging and its phenotypic presentation are dependent on constitutive (genetic) and systemic factors. It can be accelerated by environmental stressors, such as ultraviolet radiation, pollutants and microbial insults. The skin’s functions and its abilities to cope with external stressors are regulated by the cutaneous neuroendocrine systems encompassing the regulated and coordinated production of neuropeptides, neurohormones, neurotransmitters and hormones, including steroids and secosteroids. These will induce/stimulate downstream signaling through activation of corresponding receptors. These pathways and corresponding coordinated responses to the stressors decay with age or undergo pathological malfunctions. This affects the overall skin phenotype and epidermal, dermal, hypodermal and adnexal functions. We propose that skin aging can be attenuated or its phenotypic presentation reversed by the topical use of selected factors with local neurohormonal activities targeting specific receptors or enzymes. Some of our favorite factors include melatonin and its metabolites, noncalcemic secosteroids and lumisterol derivatives, because of their low toxicity and their desirable local phenotypic effects.

Hyaluronan as tunable drug delivery system

The hyaluronan (HA) polymer is an important macromolecule of extracellular matrix with remarkable structure and functions: it is a linear and unbranched polymer without sulphate or phosphate groups and has key role in several biological processes in mammals. It is ubiquitous in mammalian tissues with several and specific functions, influencing cell proliferation and migration as well as angiogenesis and inflammation. To exert these important functions in tissues HA modifies the concentration and size. Considering this HA content in tissues is carefully controlled by different mechanisms including covalent modification of the synthetic enzymes and epigenetic control of their gene expression. The function of HA is also critical in several pathologies including cancer, diabetes and chronic inflammation. Among these biological roles, the structural properties of HA allow to use this polymer in regenerative medicine including cosmetics and drug delivery. HA takes advantage from its capacity to form gels even at concentration of 1% producing scaffolds with very intriguing mechanical properties. These hydrogels are useful in regenerative medicine as biocompatible material for advanced therapeutic uses. In this review we highlight the biological aspects of HA addressing the mechanisms controlling the HA content in tissues and its role as drug delivery system.

Stem cells: past, present, and future

In recent years, stem cell therapy has become a very promising and advanced scientific research topic. The development of treatment methods has evoked great expectations. This paper is a review focused on the discovery of different stem cells and the potential therapies based on these cells. The genesis of stem cells is followed by laboratory steps of controlled stem cell culturing and derivation. Quality control and teratoma formation assays are important procedures in assessing the properties of the stem cells tested. Derivation methods and the utilization of culturing media are crucial to set proper environmental conditions for controlled differentiation. Among many types of stem tissue applications, the use of graphene scaffolds and the potential of extracellular vesicle-based therapies require attention due to their versatility. The review is summarized by challenges that stem cell therapy must overcome to be accepted worldwide. A wide variety of possibilities makes this cutting edge therapy a turning point in modern medicine, providing hope for untreatable diseases.

Dihydrocaffeic Acid Prevents UVB-Induced Oxidative Stress Leading to the Inhibition of Apoptosis and MMP-1 Expression via p38 Signaling Pathway

Chronic UVB exposure promotes oxidative stress, directly causes molecular damage, and induces aging-related signal transduction, leading to skin photoaging. Dihydrocaffeic acid (DHCA) is a phenolic compound with potential antioxidant capacity and is thus a promising compound for the prevention of UVB-induced skin photodamage. The aim of this study was to evaluate the antioxidant and protective effect of DHCA against oxidative stress, apoptosis, and matrix metalloproteinase (MMP) expression via the mitogen-activated protein kinase (MAPK) signaling pathway on L929 fibroblasts irradiated with UVB. DHCA exhibited high antioxidant capacity on 2,2-diphenyl-1-picrylhydrazyl (DPPH^•), 2,2-azinobis-3-ethylbenzothiazoline-6-sulphonic acid (ABTS^•+), and xanthine/luminol/xanthine oxidase (XOD) assays and reduced UVB-induced cell death in the neutral red assay. DHCA also modulated oxidative stress by decreasing intracellular reactive oxygen species (ROS) and extracellular hydrogen peroxide (H₂O₂) production, enhancing catalase (CAT) and superoxide dismutase (SOD) activities and reduced glutathione (GSH) levels. Hence, cellular damage was attenuated by DHCA, including lipid peroxidation, apoptosis/necrosis and its markers (loss of mitochondria membrane potential, DNA condensation, and cleaved caspase 9 expression), and MMP-1 expression. Furthermore, DHCA reduced the phosphorylation of MAPK p38. These findings suggest that DHCA can be used in the development of skin care products to prevent UVB-induced skin damage.

Sanshool improves UVB-induced skin photodamage by targeting JAK2/STAT3-dependent autophagy

Ultraviolet radiation is markedly increased because of pollution and the depletion of the stratospheric ozone layer. Excessive exposure to sunlight can negatively affect the skin, resulting in sunburn, photo-aging, or skin cancer. In this study, we first determined the photoprotective effect of sanshool, a major component in Zanthoxylum bungeanum, on UVB-irradiated responses in human dermal fibroblasts (HDFs) and nude mouse. We found that sanshool treatment can protect cells against the effects of UVB irradiation by (i) increasing cell viability, (ii) inhibiting MMP expression, and (iii) inducing autophagy. We also used the recombinant CSF2 or anti-CSF2 antibody co-cultured with human dermal fibroblasts (HDFs) and found that CSF2 contributes to sanshool-induced autophagy. Sanshool hindered the UVB-induced activation of JAK2-STAT3 signaling in HDFs, thereby inhibiting the expression of MMPs and activation of autophagic flux. Exposure of the dorsal skin of hairless mice to UVB radiation and subsequent topical application of sanshool delayed the progression of skin inflammation, leading to autophagy and inhibiting the activation of JAK2-STAT3 signaling. These results provide a basis for the study of the photoprotective effect of sanshool and suggest that it can be potentially used as an agent against UVB-induced skin damage in humans.

Predicting age from the transcriptome of human dermal fibroblasts

Biomarkers of aging can be used to assess the health of individuals and to study aging and age-related diseases. We generate a large dataset of genome-wide RNA-seq profiles of human dermal fibroblasts from 133 people aged 1 to 94 years old to test whether signatures of aging are encoded within the transcriptome. We develop an ensemble machine learning method that predicts age to a median error of 4 years, outperforming previous methods used to predict age. The ensemble was further validated by testing it on ten progeria patients, and our method is the only one that predicts accelerated aging in these patients.

Epigenetic Regulation of Skin Cells in Natural Aging and Premature Aging Diseases

Skin undergoes continuous renewal throughout an individual’s lifetime relying on stem cell functionality. However, a decline of the skin regenerative potential occurs with age. The accumulation of senescent cells over time probably reduces tissue regeneration and contributes to skin aging. Keratinocytes and dermal fibroblasts undergo senescence in response to several intrinsic or extrinsic stresses, including telomere shortening, overproduction of reactive oxygen species, diet, and sunlight exposure. Epigenetic mechanisms directly regulate skin homeostasis and regeneration, but they also mark cell senescence and the natural and pathological aging processes. Progeroid syndromes represent a group of clinical and genetically heterogeneous pathologies characterized by the accelerated aging of various tissues and organs, including skin. Skin cells from progeroid patients display molecular hallmarks that mimic those associated with naturally occurring aging. Thus, investigations on progeroid syndromes strongly contribute to disclose the causal mechanisms that underlie the aging process. In the present review, we discuss the role of epigenetic pathways in skin cell regulation during physiologic and premature aging.

Senescent fibroblasts drive ageing pigmentation: ​A potential therapeutic target for senile lentigo

Cutaneous ageing is an important extrinsic process that modifies the pigmentary system. Because cellular senescence is a fundamental ageing mechanism, we examined the role of senescent cells in ageing pigmentation.

Methods: Biopsies obtained from senile lentigo and perilesional normal skin were assayed for a marker of cellular senescence, p16^INK4A. To determine the secretory phenotypes of senescent fibroblasts, we performed microarray, RNA sequencing and methylation array analyses in senile lentigo and senescent fibroblasts. To further investigate the impact of senescent cells on ageing-related pigmentation, an intervention that targeted senescent cells using radiofrequency was performed.

Results:In vivo, senescent fibroblasts accumulated at the sites of age-related pigmentation. Phenotype switching of the cells resulted in the repression of stromal-derived factor 1 (SDF1) by promoter methylation. SDF1 induced melanocyte differentiation via stromal-epithelial interactions, ultimately driving skin pigmentation. Furthermore, the elimination of senescent fibroblasts from pigmented skin using radiofrequency was accompanied by skin lightening, rendering it a potential target for treatment.

Conclusion: Aged pigmented skin contains an increasing proportion of senescent fibroblasts. Cells with phenotype switching exhibited a loss of SDF1, which stimulates the melanogenic process and thereby contributes to aging pigmentation. These data may promote the development of new therapeutic paradigms, such as a stroma-targeting therapy for pigmentary disorders.

Lineage Identity and Location within the Dermis Determine the Function of Papillary and Reticular Fibroblasts in Human Skin

Human skin dermis is composed of the superficial papillary dermis and the reticular dermis in the lower layers, which can easily be distinguished histologically. In vitro analyses of fibroblasts from explant cultures from superficial and lower dermal layers suggest that human skin comprises at least two fibroblast lineages with distinct morphology, expression profiles, and functions. However, while for mouse skin cell surface markers have been identified, allowing the isolation of pure populations of one lineage or the other via FACS, this has not been achieved for human skin fibroblasts. We have now discovered two cell surface markers that discriminate between papillary and reticular fibroblasts. While FAP⁺CD90^- cells display increased proliferative potential, express PDPN and NTN1, and cannot be differentiated into adipocytes, FAP^-CD90⁺ fibroblasts express high levels of ACTA2, MGP, PPARγ, and CD36 and readily undergo adipogenic differentiation, a hallmark of reticular fibroblasts. Flow cytometric analysis of fibroblasts isolated from superficial and lower layers of human dermis showed that FAP⁺CD90^- cells are enriched in the papillary dermis. Altogether, functional analysis and expression profiling confirms that FAP⁺CD90^- cells represent papillary fibroblasts, whereas FAP^-CD90⁺ fibroblasts derive from the reticular lineage. Although papillary and reticular fibroblasts are enriched in the upper or lower dermis, respectively, they are not spatially restricted, and the microenvironment seems to affect their function.

SIRT4 interacts with OPA1 and regulates mitochondrial quality control and mitophagy

The stress-responsive mitochondrial sirtuin SIRT4 controls cellular energy metabolism in a NAD⁺-dependent manner and is implicated in cellular senescence and aging. Here we reveal a novel function of SIRT4 in mitochondrial morphology/quality control and regulation of mitophagy. We report that moderate overexpression of SIRT4, but not its enzymatically inactive mutant H161Y, sensitized cells to mitochondrial stress. CCCP-triggered dissipation of the mitochondrial membrane potential resulted in increased mitochondrial ROS levels and autophagic flux, but surprisingly led to increased mitochondrial mass and decreased Parkin-regulated mitophagy. The anti-respiratory effect of elevated SIRT4 was accompanied by increased levels of the inner-membrane bound long form of the GTPase OPA1 (L-OPA1) that promotes mitochondrial fusion and thereby counteracts fission and mitophagy. Consistent with this, upregulation of endogenous SIRT4 expression in fibroblast models of senescence either by transfection with miR-15b inhibitors or by ionizing radiation increased L-OPA1 levels and mitochondrial fusion in a SIRT4-dependent manner. We further demonstrate that SIRT4 interacts physically with OPA1 in co-immunoprecipitation experiments. Overall, we propose that the SIRT4-OPA1 axis is causally linked to mitochondrial dysfunction and altered mitochondrial dynamics that translates into aging-associated decreased mitophagy based on an unbalanced mitochondrial fusion/fission cycle.

Exosomes Derived from Human Induced Pluripotent Stem Cells Ameliorate the Aging of Skin Fibroblasts

Stem cells and their paracrine factors have emerged as a resource for regenerative medicine. Many studies have shown the beneficial effects of paracrine factors secreted from adult stem cells, such as exosomes, on skin aging. However, to date, few reports have demonstrated the use of exosomes derived from human pluripotent stem cells for the treatment of skin aging. In this study, we collected exosomes from the conditioned medium of human induced pluripotent stem cells (iPSCs) and investigated the effect on aged human dermal fibroblasts (HDFs). Cell proliferation and viability were determined by an MTT assay and cell migration capacity was shown by a scratch wound assay and a transwell migration assay. To induce photoaging and natural senescence, HDFs were irradiated by UVB (315 nm) and subcultured for over 30 passages, respectively. The expression level of certain mRNAs was evaluated by quantitative real-time PCR (qPCR). Senescence-associated-β-galactosidase (SA-β-Gal) activity was assessed as a marker of natural senescence. As a result, we found that exosomes derived from human iPSCs (iPSCs-Exo) stimulated the proliferation and migration of HDFs under normal conditions. Pretreatment with iPSCs-Exo inhibited the damages of HDFs and overexpression of matrix-degrading enzymes (MMP-1/3) caused by UVB irradiation. The iPSCs-Exo also increased the expression level of collagen type I in the photo-aged HDFs. In addition, we demonstrated that iPSCs-Exo significantly reduced the expression level of SA-β-Gal and MMP-1/3 and restored the collagen type I expression in senescent HDFs. Taken together, it is anticipated that these results suggest a therapeutic potential of iPSCs-Exo for the treatment of skin aging.

3' UTR lengthening as a novel mechanism in regulating cellular senescence

Cellular senescence has been viewed as a tumor suppression mechanism and also as a contributor to individual aging. Widespread shortening of 3' untranslated regions (3' UTRs) in messenger RNAs (mRNAs) by alternative polyadenylation (APA) has recently been discovered in cancer cells. However, the role of APA in the process of cellular senescence remains elusive. Here, we found that hundreds of genes in senescent cells tended to use distal poly(A) (pA) sites, leading to a global lengthening of 3' UTRs and reduced gene expression. Genes that harbor longer 3' UTRs in senescent cells were enriched in senescence-related pathways. Rras2, a member of the Ras superfamily that participates in multiple signal transduction pathways, preferred longer 3' UTR usage and exhibited decreased expression in senescent cells. Depletion of Rras2 promoted senescence, while rescue of Rras2 reversed senescence-associated phenotypes. Mechanistically, splicing factor TRA2B bound to a core "AGAA" motif located in the alternative 3' UTR of Rras2, thereby reducing the RRAS2 protein level and causing senescence. Both proximal and distal poly(A) signals showed strong sequence conservation, highlighting the vital role of APA regulation during evolution. Our results revealed APA as a novel mechanism in regulating cellular senescence.

Quantitative evaluation of collagen and elastic fibers after intense pulsed light treatment of mouse skin

BACKGROUND AND OBJECTIVE

The aging of human skin includes intrinsic aging and photo-aging, which are characterized by a decrease in collagen and the deposition of abnormal elastic fibers. Intense pulsed light (IPL) sources are widely used in medicine to treat various cosmetic problems, including photo-damaged skin. Few studies have examined the microscopic changes produced by IPL. The objective of this study was to quantitatively evaluate the effects of IPL on collagen and elastic fibers in mice.

MATERIALS AND METHODS

Forty female BALB/c mice were divided into four subgroups. Group 1 was the control group (n = 10), and groups 2, 3, and 4 were treatment groups (n = 10 in each group). Group 2 received one treatment, group 3 received two treatments, and group 4 received three treatments every 2 weeks. Skin tissue was obtained from irradiated areas 24 hours after the last treatment in each mouse. Collagen fibers were identified using the picrosirius red method. Elastic fibers were marked by Weigert-oxone stain. All samples were analyzed and quantified by a light microscope using analyzer system images.

RESULTS

Group 4, which received three IPL treatments, showed significant quantitative increases in both collagen fibers (P < 0.05) and elastic fibers (P < 0.01). Collagen fibers demonstrated a better parallel distribution in relation to the epidermis.

CONCLUSION

IPL treatment significantly increased the number of collagen and elastic fibers within the dermis and improved the parallel distribution of collagen fibers in relation to the epidermis. These results were evident after three IPL treatments. Lasers Surg. Med. © 2018 Wiley Periodicals, Inc.

A Trickster in Disguise: Hyaluronan's Ambivalent Roles in the Matrix

Hyaluronan (HA) is a simple but diverse glycosaminoglycan. It plays a major role in aging, cellular senescence, cancer, and tissue homeostasis. In which way HA affects the surrounding tissues greatly depends on the molecular weight of HA. Whereas high molecular weight HA is associated with homeostasis and protective effects, HA fragments tend to be linked to the pathologic state. Furthermore, the interaction of HA with its binding partners, the hyaladherins, such as CD44, is essential for sustaining tissue integrity and is likewise related to cancer. The naked mole rat, a rodent species, possesses a special form of very high molecular weight (vHMW) HA, which is associated with the extraordinary cancer resistance and longevity of those animals. This review addresses HA and its diverse facets: from HA synthesis to degradation, from oligomeric HA to vHMW-HA and from its beneficial properties to the involvement in pathologies. We further discuss the functions of HA in the naked mole rat and compare them to human conditions. Though intensively researched, this simple polymer bears some secrets that may hold the key for a better understanding of cellular processes and the development of diseases, such as cancer.

Role of Prion protein in premature senescence of human fibroblasts

Prion protein (PrP) is essentially known for its capacity to induce neurodegenerative prion diseases in mammals caused by a conformational change in its normal cellular isoform (PrP^C) into an infectious and disease-associated misfolded form, called scrapie isoform (PrP^Sc). Although its sequence is highly conserved, less information is available on its physiological role under normal conditions. However, increasing evidence supports a role for PrP^C in the cellular response to oxidative stress. In the present study, a new link between PrP and senescence is highlighted. The role of PrP in premature senescence induced by copper was investigated. WI-38 human fibroblasts were incubated with copper sulfate (CuSO₄) to trigger premature senescence. This induced an increase of PrP mRNA level, an increase of protein abundance of the normal form of PrP and a nuclear localization of the protein. Knockdown of PrP expression using specific small interfering RNA (siRNA) gave rise to appearance of several biomarkers of senescence as a senescent morphology, an increase of senescence associated β-galactosidase activity and a decrease of the cellular proliferative potential. Overall these data suggest that PrP protects cells against premature senescence induced by copper.

In vivo and in vitro ageing results in accumulation of de novo copy number variations in bulls

We have identified de novo copy number variations (CNVs) generated in bulls as they age. Blood samples from eight bulls were collected and SNP arrayed in a prospective design over 30 months allowing us to differentiate de novo CNVs from constant CNVs that are present throughout the sampling period. Quite remarkably, the total number of CNVs doubled over the 30-month period, as we observed an almost equal number of de novo and constant CNVs (107 and 111, respectively, i.e. 49% and 51%). Twice as many de novo CNVs emerged during the second half of the sampling schedule as in the first part. It suggests a dynamic generation of de novo CNVs in the bovine genome that becomes more frequent as the age of the animal progresses. In a second experiment de novo CNVs were detected through in vitro ageing of bovine fibroblasts by sampling passage #5, #15 and #25. De novo CNVs also became more frequent, but the proportion of them was only ~25% of the total number of CNVs (21 out of 85). Temporal generation of de novo CNVs resulted in increasing genome coverage. Genes and quantitative trait loci overlapping de novo CNVs were further investigated for ageing related functions.

A Holistic Approach to Antiaging as an Adjunct to Antiaging Procedures: A Review of the Literature

BACKGROUND

Aging is a multifactorial process and depends on both intrinsic and extrinsic factors. Procedural options for diminishing signs of intrinsic aging and cosmetic rejuvenation have expanded dramatically. However, less attention is paid to counseling patients on options for mitigating extrinsic factors related to aging.

OBJECTIVE

The objective of this study was to review changes that occur with intrinsic and extrinsic aging, and provide evidence-based holistic counseling recommendations that can be used synergistically with aesthetic procedures to maximize antiaging interventions.

MATERIALS AND METHODS

A PubMed search was conducted for articles on intrinsic and extrinsic aging as it relates to skin, fat, muscle, and bone. Key clinical trials and studies on the effect of diet, hormones, exercise, sleep, stress, dental hygiene, smoking, pollution, and oxidative stress on the aging process are reviewed, and treatment recommendations are summarized based on available evidence.

RESULTS

Conventional cosmetic procedures and cosmeceuticals work together with nutritious diet, exercise, dental hygiene, hormonal balance, stress reduction, smoking and pollution avoidance, and healthy sleep patterns for a better effect on antiaging.

CONCLUSION

A combination approach of multiple nonsurgical modalities along with healthy lifestyle recommendations to minimize intrinsic and extrinsic aging factors allows cosmetic practitioners to target multiple facets of aging concurrently and maximize the aesthetic interventions cosmetic dermatologists/practitioners provide.

The impact of cellular senescence in skin ageing: A notion of mosaic and therapeutic strategies

Cellular senescence is now recognized as one of the nine hallmarks of ageing. Recent data show the involvement of senescent cells in tissue ageing and some age-related diseases. Skin represents an ideal model for the study of ageing. Indeed, skin ageing varies between individuals depending on their chronological age but also on their exposure to various exogenous factors (mainly ultraviolet rays). If senescence traits can be detected with ageing in the skin, the senescent phenotype varies among the various skin cell types. Moreover, the origin of cellular senescence in the skin is still unknown, and multiple origins are possible. This reflects the mosaic of skin ageing. Senescent cells can interfere with their microenvironment, either via the direct secretion of factors (the senescence-associated secretory phenotype) or via other methods of communication, such as extracellular vesicles. Knowledge regarding the impact of cellular senescence on skin ageing could be integrated into dermatology research, especially to limit the appearance of senescent cells after photo(chemo)therapy or in age-related skin diseases. Therapeutic approaches include the clearance of senescent cells via the use of senolytics or via the cooperation with the immune system.

MicroRNA-15b regulates mitochondrial ROS production and the senescence-associated secretory phenotype through sirtuin 4/SIRT4

Mammalian sirtuins are involved in the control of metabolism and life-span regulation. Here, we link the mitochondrial sirtuin SIRT4 with cellular senescence, skin aging, and mitochondrial dysfunction. SIRT4 expression significantly increased in human dermal fibroblasts undergoing replicative or stress-induced senescence triggered by UVB or gamma-irradiation. In-vivo, SIRT4 mRNA levels were upregulated in photoaged vs. non-photoaged human skin. Interestingly, in all models of cellular senescence and in photoaged skin, upregulation of SIRT4 expression was associated with decreased levels of miR-15b. The latter was causally linked to increased SIRT4 expression because miR-15b targets a functional binding site in the SIRT4 gene and transfection of oligonucleotides mimicking miR-15b function prevented SIRT4 upregulation in senescent cells. Importantly, increased SIRT4 negatively impacted on mitochondrial functions and contributed to the development of a senescent phenotype. Accordingly, we observed that inhibition of miR-15b, in a SIRT4-dependent manner, increased generation of mitochondrial reactive oxygen species, decreased mitochondrial membrane potential, and modulated mRNA levels of nuclear encoded mitochondrial genes and components of the senescence-associated secretory phenotype (SASP). Thus, miR-15b is a negative regulator of stress-induced SIRT4 expression thereby counteracting senescence associated mitochondrial dysfunction and regulating the SASP and possibly organ aging, such as photoaging of human skin.

Raman and infrared spectroscopy differentiate senescent from proliferating cells in a human dermal fibroblast 3D skin model

Senescence-associated alterations were detected in biomolecules of 3D cultured cells and these cells were distinguished from 2D cultured cells.

Increased permeability of reconstructed human epidermis from UVB-irradiated keratinocytes

Extrinsic (photo) aging accelerates chronologically aging in the skin due to cumulative UV irradiation. Despite recent insights into the molecular mechanisms of fibroblast aging, age-related changes of the skin barrier function have been understudied. In contrast, the constantly increasing subpopulation of aged patients causes a clinical need for effective and safe (dermatological) treatment. Herein, we reconstructed human epidermis from UVB-irradiated keratinocytes (UVB-RHE). UVB-irradiated keratinocytes show higher activity of senescence associated β-galactosidase, less cell proliferation, and reduced viability. Higher amounts of β-galactosidase are also detectable in UVB-RHE. Moreover, UVB-RHE release more interleukin-1α and -8 into the culture medium and present altered differentiation with a thinner stratum corneum compared to normal RHE. For the first time, the permeation of testosterone and caffeine through UVB-irradiated RHE indicate a clear influence of the UVB stress on the skin barrier function. Impaired barrier function was confirmed by the increased permeation of testosterone and caffeine as well as by the increased penetration of dendritic core-multishell nanocarriers into the constructs. Taken together, UVB-RHE emulate hallmarks of skin aging and might contribute to an improved non-clinical development of medicinal or cosmetic products.

Distinct Cell Stress Responses Induced by ATP Restriction in Quiescent Human Fibroblasts

Quiescence is the prevailing state of many cell types under homeostatic conditions. Yet, surprisingly little is known about how quiescent cells respond to energetic and metabolic challenges. To better understand compensatory responses of quiescent cells to metabolic stress, we established, in human primary dermal fibroblasts, an experimental ‘energy restriction’ model. Quiescence was achieved by short-term culture in serum-deprived media and ATP supply restricted using a combination of glucose transport inhibitors and mitochondrial uncouplers. In aggregate, these measures led to markedly reduced intracellular ATP levels while not compromising cell viability over the observation period of 48 h. Analysis of the transcription factor (TF) landscape induced by this treatment revealed alterations in several signal transduction nodes beyond the expected biosynthetic adaptations. These included increased abundance of NF-κB regulated TFs and altered TF subsets regulated by Akt and p53. The observed changes in gene regulation and corresponding alterations in key signaling nodes are likely to contribute to cell survival at intracellular ATP concentrations substantially below those achieved by growth factor deprivation alone. This experimental model provides a benchmark for the investigation of cell survival pathways and related molecular targets that are associated with restricted energy supply associated with biological aging and metabolic diseases.

Multiplexed high-content analysis of mitochondrial morphofunction using live-cell microscopy

Mitochondria have a central role in cellular (patho)physiology, and they display a highly variable morphology that is probably coupled to their functional state. Here we present a protocol that allows unbiased and automated quantification of mitochondrial 'morphofunction' (i.e., morphology and membrane potential), cellular parameters (size, confluence) and nuclear parameters (number, morphology) in intact living primary human skin fibroblasts (PHSFs). Cells are cultured in 96-well plates and stained with tetramethyl rhodamine methyl ester (TMRM), calcein-AM (acetoxy-methyl ester) and Hoechst 33258. Next, multispectral fluorescence images are acquired using automated microscopy and processed to extract 44 descriptors. Subsequently, the descriptor data are subjected to a quality control (QC) algorithm based upon principal component analysis (PCA) and interpreted using univariate, bivariate and multivariate analysis. The protocol requires a time investment of ∼4 h distributed over 2 d. Although it is specifically developed for PHSFs, which are widely used in preclinical research, the protocol is portable to other cell types and can be scaled up for implementation in high-content screening.

Impaired DNA double-strand break repair contributes to the age-associated rise of genomic instability in humans

Failing to repair DNA double-strand breaks by either nonhomologous end joining (NHEJ) or homologous recombination (HR) poses a threat to genome integrity, and may have roles in the onset of aging and age-related diseases. Recent work indicates an age-related decrease of NHEJ efficiency in mouse models, but whether NHEJ and HR change with age in humans and the underlying mechanisms of such a change remain uncharacterized. Here, using 50 eyelid fibroblast cell lines isolated from healthy donors at the age of 16-75 years, we demonstrate that the efficiency and fidelity of NHEJ, and the efficiency of HR decline with age, leading to increased IR sensitivity in cells isolated from old donors. Mechanistic analysis suggests that decreased expression of XRCC4, Lig4 and Lig3 drives the observed, age-associated decline of NHEJ efficiency and fidelity. Restoration of XRCC4 and Lig4 significantly promotes the fidelity and efficiency of NHEJ in aged fibroblasts. In contrast, essential HR-related factors, such as Rad51, do not change in expression level with age, but Rad51 exhibits a slow kinetics of recruitment to DNA damage sites in aged fibroblasts. Further rescue experiments indicate that restoration of XRCC4 and Lig4 may suppress the onset of stress-induced premature cellular senescence, suggesting that improving NHEJ efficiency and fidelity by targeting the NHEJ pathway holds great potential to delay aging and mitigate aging-related pathologies.

How Wounding via Lasers Has Potential Photocarcinogenic Preventative Effects via Dermal Remodeling

As the incidence of non-melanoma skin cancer (NMSC) is increasing, there is a growing need to identify effective preventive strategies. A recently proposed hypothesis states that NMSC photocarcinogenesis is tightly linked to insufficient insulin growth factor-1 expression by agglomerated senescent fibroblasts in geriatric dermis. This paucity of IGF-1 expression in senile skin allows basal keratinocytes to mitotically propagate their UVB-altered genome and potentially initiate an actinic neoplasm. Here we review the role of the dermal microenvironment in NMSC pathogenesis, describe the impact of fibroblast senescence on this process and discuss how laser-induced dermal wounding can be effectively used to prevent NMSC development in geriatric patients.

Loss of fibronectin from the aged stem cell niche affects the regenerative capacity of skeletal muscle in mice

Age-related changes in the niche have long been postulated to impair the function of somatic stem cells. Here we demonstrate that the aged stem cell niche in skeletal muscle contains substantially reduced levels of fibronectin (FN), leading to detrimental consequences for the function and maintenance of muscle stem cells (MuSCs). Deletion of the gene encoding FN from young regenerating muscles replicates the aging phenotype and leads to a loss of MuSC numbers. By using an extracellular matrix (ECM) library screen and pathway profiling, we characterize FN as a preferred adhesion substrate for MuSCs and demonstrate that integrin-mediated signaling through focal adhesion kinase and the p38 mitogen-activated protein kinase pathway is strongly de-regulated in MuSCs from aged mice because of insufficient attachment to the niche. Reconstitution of FN levels in the aged niche remobilizes stem cells and restores youth-like muscle regeneration. Taken together, we identify the loss of stem cell adhesion to FN in the niche ECM as a previously unknown aging mechanism.