Extracellular Vesicles in Human Skin: Cross-Talk from Senescent Fibroblasts to Keratinocytes by miRNAs

Elimination of damaged mitochondria during UVB-induced senescence is orchestrated by NIX-dependent mitophagy

Skin aging is the result of two types of aging, "intrinsic aging" an inevitable consequence of physiologic and genetically determined changes and "extrinsic aging," which is dependent on external factors such as exposure to sunlight, smoking, and dietary habits. UVB causes skin injury through the generation of free radicals and other oxidative byproducts, also contributing to DNA damage. Appearance and accumulation of senescent cells in the skin are considered one of the hallmarks of aging in this tissue. Mitochondria play an important role for the development of cellular senescence, in particular stress-induced senescence of human cells. However, many aspects of mitochondrial physiology relevant to cellular senescence and extrinsic skin aging remain to be unraveled. Here, we demonstrate that mitochondria damaged by UVB irradiation of human dermal fibroblasts (HDF) are eliminated by NIX-dependent mitophagy and that this process is important for cell survival under these conditions. Additionally, UVB-irradiation of human dermal fibroblasts (HDF) induces the shedding of extracellular vesicles (EVs), and this process is significantly enhanced in UVB-irradiated NIX-depleted cells. Our findings establish NIX as the main mitophagy receptor in the process of UVB-induced senescence and suggest the release of EVs as an alternative mechanism of mitochondrial quality control in HDF.

Role of epigenetics in the regulation of skin aging and geroprotective intervention: A new sight

Multiple epigenetic factors play a regulatory role in maintaining the homeostasis of cutaneous components and are implicated in the aging process of the skin. They have been associated with the activation of the senescence program, which is the primary contributor to age-related decline in the skin. Senescent species drive a series of interconnected processes that impact the immediate surroundings, leading to structural changes, diminished functionality, and heightened vulnerability to infections. Geroprotective medicines that may restore the epigenetic balance represent valid therapeutic alliances against skin aging. Most of them are well-known Western medications such as metformin, nicotinamide adenine dinucleotide (NAD+), rapamycin, and histone deacetylase inhibitors, while others belong to Traditional Chinese Medicine (TCM) remedies for which the scientific literature provides limited information. With the help of the Geroprotectors.org database and a comprehensive analysis of the referenced literature, we have compiled data on compounds and formulae that have shown potential in preventing skin aging and have been identified as epigenetic modulators.

The senescence-associated secretory phenotype and its physiological and pathological implications

Cellular senescence is a state of terminal growth arrest associated with the upregulation of different cell cycle inhibitors, mainly p16 and p21, structural and metabolic alterations, chronic DNA damage responses, and a hypersecretory state known as the senescence-associated secretory phenotype (SASP). The SASP is the major mediator of the paracrine effects of senescent cells in their tissue microenvironment and of various local and systemic biological functions. In this Review, we discuss the composition, dynamics and heterogeneity of the SASP as well as the mechanisms underlying its induction and regulation. We describe the various biological properties of the SASP, its beneficial and detrimental effects in different physiological and pathological settings, and its impact on overall health span. Finally, we discuss the use of the SASP as a biomarker and of SASP inhibitors as senomorphic interventions to treat cancer and other age-related conditions.

Extracellular vesicles from keratinocytes and other skin-related cells in psoriasis: A review

Psoriasis is a highly prevalent chronic inflammatory skin condition involving abnormal proliferation and differentiation of keratinocytes, together with substantial infiltration of immune cells. Extracellular vesicles (EVs), which are released spontaneously into the extracellular space by virtually all cell types, play a crucial role in cell-to-cell communication by delivering bioactive cargos such as mRNA nucleic acids and proteins to recipient cells. Numerous studies have highlighted the significant contributions of EVs to both the pathogenesis and treatment of psoriasis. This review provides a concise overview of skin-derived EVs and their involvement in the pathogenesis of psoriasis.

Hallmarks of Skin Aging: Update

Aging is defined as impaired physiological integrity, decreased function, increased susceptibility to external risk factors and various diseases. Skin, the largest organ in our body, may become more vulnerable to insult as time goes by and behave as aged skin. Here, we systemically reviewed three categories including seven hallmarks of skin aging. These hallmarks including genomic instability and telomere attrition, epigenetic alterations and loss of proteostasis, deregulated nutrient-sensing, mitochondrial damage and dysfunction, cellular senescence, stem cell exhaustion/dysregulation, and altered intercellular communication. These seven hallmarks can generally be divided into three categories including (i) causes of damages as primary hallmarks in skin aging; (ii) responses to damage as antagonistic hallmarks in skin aging; and (iii) culprits of the phenotype as integrative hallmarks in skin aging.

Progress in the Development of Stem Cell-Derived Cell-Free Therapies for Skin Aging

Introduction

The skin is a vital organ as the body's largest barrier, but its function declines with aging. Therefore, research into effective regeneration treatments must continue to advance. Stem cell transplantation, a cell-based therapy, has become a popular skin-aging treatment, although it comes with drawbacks like host immune reactions. Stem cell-derived cell-free therapies have emerged as an alternative, backed by promising preclinical findings. Stem cell secretomes and extracellular vesicles (EVs) are the key components in cell-free therapy from stem cells. However, comprehensive reviews on the mechanisms of such treatments for skin aging are still limited.

Purpose

This review discusses stem cell-derived cell-free therapy's potential mechanisms of action related to skin aging prevention by identifying specific molecular targets suitable for the interventions.

Methods

A search identified 27 relevant in vitro studies on stem cell-derived cell-free therapy interventions in skin aging model cells without restricting publication years using PubMed, Scopus, and Google Scholar.

Results

Stem cell-derived cell-free therapy can prevent skin aging through various mechanisms, such as (1) involvement of multiple regenerative pathways [NFkb, AP-1, MAPK, P-AKT, NRF2, SIRT-1]; (2) oxidative stress regulation [by reducing oxidants (HO-1, NQO1) and enhancing antioxidants (SOD1, CAT, GP, FRAP)]; (3) preventing ECM degradation [by increasing elastin, collagen, HA, TIMP, and reducing MMP]; (4) regulating cell activity [by reducing cell senescence (SA-β-gal), apoptosis, and cell cycle arrest (P53, P12, P16); and enhancing autophagy, cell migration, and cell proliferation (Ki67)] (5) Regulating the inflammatory pathway [by reducing IL-6, IL-1, TNF-⍺, and increasing TGF-β]. Several clinical trials have also revealed improvements in wrinkles, elasticity, hydration, pores, and pigmentation.

Conclusion

Stem cell-derived cell-free therapy is a potential novel treatment for skin aging by cell rejuvenation through various molecular mechanisms.

Quadruplexes and aging: G4-binding proteins regulate the presence of miRNA in small extracellular vesicles (sEVs)

The interaction between proteins and nucleic acids is a core element of life. Many proteins bind nucleic acids via a sequence-specific manner, but there are also many types of proteins that recognize various structural motifs. Researchers have recently found that proteins that can recognize DNA and RNA G-quadruplexes (G4s) are very important for basic cellular processes, particularly in eukaryotes. Some of these proteins are located outside the nucleus and interact with RNA, potentially affecting miRNA functions in intercellular communication, which is facilitated by small extracellular vesicles (sEVs). Imbalances in the production of sEVs are associated with various pathologies and senescence in humans. The distribution of miRNA into sEVs is regulated by two RNA-binding proteins, Alyref and FUS. Both proteins possess G-rich recognition motifs that are compatible with the formation of RNA parallel G4 structures. This lends credence to the new hypothesis that G4-formation in RNAs and their interaction with G4-binding proteins can affect the fate of miRNAs and control their distribution in sEVs that are associated with senescence and aging.

P-MSC-derived extracellular vesicles facilitate diabetic wound healing via miR-145-5p/ CDKN1A-mediated functional improvements of high glucose-induced senescent fibroblasts

Background

Persistent hyperglycaemia in diabetes causes functional abnormalities of human dermal fibroblasts (HDFs), partially leading to delayed skin wound healing. Extracellular vesicles (EVs) containing multiple pro-healing microRNAs (miRNAs) have been shown to exert therapeutic effects on diabetic wound healing. The present study aimed to observe the effects of EVs derived from placental mesenchymal stem cells (P-MSC-EVs) on diabetic wound healing and high glucose (HG)-induced senescent fibroblasts and to explore the underlying mechanisms.

Methods

P-MSC-EVs were isolated by differential ultracentrifugation and locally injected into the full-thickness skin wounds of diabetic mice, to observe the beneficial effects on wound healing in vivo by measuring wound closure rates and histological analysis. Next, a series of assays were conducted to evaluate the effects of low (2.28 x 1010 particles/ml) and high (4.56 x 1010 particles/ml) concentrations of P-MSC-EVs on the senescence, proliferation, migration, and apoptosis of HG-induced senescent HDFs in vitro. Then, miRNA microarrays and real-time quantitative PCR (RT-qPCR) were carried out to detect the differentially expressed miRNAs in HDFs after EVs treatment. Specific RNA inhibitors, miRNA mimics, and small interfering RNA (siRNA) were used to evaluate the role of a candidate miRNA and its target genes in P-MSC-EV-induced improvements in the function of HG-induced senescent HDFs.

Results

Local injection of P-MSC-EVs into diabetic wounds accelerated wound closure and reduced scar widths, with better-organized collagen deposition and decreased p16INK4a expression. In vitro, P-MSC-EVs enhanced the antisenescence, proliferation, migration, and antiapoptotic abilities of HG-induced senescent fibroblasts in a dose-dependent manner. MiR-145-5p was found to be highly enriched in P-MSC-EVs. MiR-145-5p inhibitors effectively attenuated the P-MSC-EV-induced functional improvements of senescent fibroblasts. MiR-145-5p mimics simulated the effects of P-MSC-EVs on functional improvements of fibroblasts by suppressing the expression of cyclin-dependent kinase inhibitor 1A and activating the extracellular signal regulated kinase (Erk)/protein kinase B (Akt) signaling pathway. Furthermore, local application of miR-145-5p agomir mimicked the effects of P-MSC-EVs on wound healing.

Conclusions

These results suggest that P-MSC-EVs accelerate diabetic wound healing by improving the function of senescent fibroblasts through the transfer of miR-145-5p, which targets cyclin-dependent kinase inhibitor 1A to activate the Erk/Akt signaling pathway. P-MSC-EVs are promising therapeutic candidates for diabetic wound treatment.

SMOOTH protocol: A pilot randomised prospective intra-patient single-blinded observational study for examining the mechanistic basis of ablative fractional carbon dioxide laser therapy in treating hypertrophic scarring

BACKGROUND

Burn injuries are the fourth most common type of trauma and are associated with substantial morbidity and mortality. The impact of burn injury is clinically significant as burn injuries often give rise to exuberant scarring. Hypertrophic scarring (HTS) is a particular concern as up to 70% of burns patients develop HTS. Laser therapy is used for treating HTS and has shown positive clinical outcomes, although the mechanisms remain unclear limiting approaches to improve its effectiveness. Emerging evidence has shown that fibroblasts and senescent cells are important modifiers of scarring. This study aims to investigate the cellular kinetics in HTS after laser therapy, with a focus on the association of scar reduction with the presence of senescent cells.

METHODS

We will conduct a multicentre, intra-patient, single-blinded, randomised controlled longitudinal pilot study with parallel assignments to achieve this objective. 60 participants will be recruited to receive 3 interventional ablative fractional CO2 laser treatments over a 12-month period. Each participant will have two scars randomly allocated to receive either laser treatment or standard care. Biopsies will be obtained from laser-treated, scarred-no treatment and non-scarred tissues for immune-histological staining to investigate the longitudinal kinetics of p16INK4A+-senescent cells and fibroblast subpopulations (CD90+/Thy1+ and αSMA+). Combined subjective scar assessments including Modified Vancouver Scar Scale, Patient and Observer Scar Assessment Scale and Brisbane Burn Scar Impact Profile; and objective assessment tools including 3D-Vectra-H1 photography, DermaScan® Cortex, Cutometer® and ColoriMeter®DSMIII will be used to evaluate clinical outcomes. These will then be used to investigate the association between senescent cells and scar reduction after laser therapy. This study will also collect blood samples to explore the systemic biomarkers associated with the response to laser therapy.

DISCUSSION

This study will provide an improved understanding of mechanisms potentially mediating scar reduction with laser treatment, which will enable better designs of laser treatment regimens for those living with HTS.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT04736251.

Context-specific regulation of extracellular vesicle biogenesis and cargo selection

To coordinate, adapt and respond to biological signals, cells convey specific messages to other cells. An important aspect of cell-cell communication involves secretion of molecules into the extracellular space. How these molecules are selected for secretion has been a fundamental question in the membrane trafficking field for decades. Recently, extracellular vesicles (EVs) have been recognized as key players in intercellular communication, carrying not only membrane proteins and lipids but also RNAs, cytosolic proteins and other signalling molecules to recipient cells. To communicate the right message, it is essential to sort cargoes into EVs in a regulated and context-specific manner. In recent years, a wealth of lipidomic, proteomic and RNA sequencing studies have revealed that EV cargo composition differs depending upon the donor cell type, metabolic cues and disease states. Analyses of distinct cargo 'fingerprints' have uncovered mechanistic linkages between the activation of specific molecular pathways and cargo sorting. In addition, cell biology studies are beginning to reveal novel biogenesis mechanisms regulated by cellular context. Here, we review context-specific mechanisms of EV biogenesis and cargo sorting, focusing on how cell signalling and cell state influence which cellular components are ultimately targeted to EVs.

Exploring the Communication of the SASP: Dynamic, Interactive, and Adaptive Effects on the Microenvironment

Cellular senescence is a complex cell state that can occur during physiological ageing or after exposure to stress signals, regardless of age. It is a dynamic process that continuously evolves in a context-dependent manner. Senescent cells interact with their microenvironment by producing a heterogenous and plastic secretome referred to as the senescence-associated secretory phenotype (SASP). Hence, understanding the cross-talk between SASP and the microenvironment can be challenging due to the complexity of signal exchanges. In this review, we first aim to update the definition of senescence and its associated biomarkers from its discovery to the present day. We detail the regulatory mechanisms involved in the expression of SASP at multiple levels and develop how SASP can orchestrate microenvironment modifications, by focusing on extracellular matrix modifications, neighboring cells' fate, and intercellular communications. We present hypotheses on how these microenvironmental events may affect dynamic changes in SASP composition in return. Finally, we discuss the various existing approaches to targeting SASP and clarify what is currently known about the biological effects of these modified SASPs on the cellular environment.

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.

PRPF19 modulates morphology and growth behavior in a cell culture model of human skin

The skin provides one of the most visual aging transformations in humans, and premature aging as a consequence of oxidative stress and DNA damage is a frequently seen effect. Cells of the human skin are continuously exposed to endogenous and exogenous DNA damaging factors, which can cause DNA damage in all phases of the cell cycle. Increased levels of DNA damage and/or defective DNA repair can, therefore, accelerate the aging process and/or lead to age-related diseases like cancer. It is not yet clear if enhanced activity of DNA repair factors could increase the life or health span of human skin cells. In previous studies, we identified and characterized the human senescence evasion factor (SNEV)/pre-mRNA-processing factor (PRPF) 19 as a multitalented protein involved in mRNA splicing, DNA repair pathways and lifespan regulation. Here, we show that overexpression of PRPF19 in human dermal fibroblasts leads to a morphological change, reminiscent of juvenile, papillary fibroblasts, despite simultaneous expression of senescence markers. Moreover, conditioned media of this subpopulation showed a positive effect on keratinocyte repopulation of wounded areas. Taken together, these findings indicate that PRPF19 promotes cell viability and slows down the aging process in human skin.

The role of extracellular vesicles in cellular senescence

Cellular senescence, an evolutionarily conserved mechanism that prevents the proliferation of damaged cells, is a very relevant cellular response involved in both physiological and pathological conditions. Even though senescent cells are stably growth arrested, they exhibit a complex and poorly understood secretory phenotype, known as senescence-associated secretory phenotype, composed of soluble proteins and extracellular vesicles (EVs). Extracellular vesicles were initially described as a waste management mechanism to remove damaged components of cellular metabolism, but increasing evidence shows that EVs could also play important roles in intercellular communication. Recently, some studies showed that EVs could have fundamental functions during cellular senescence. Our purpose in this review is to clarify the increasing literature on the role of EVs in cellular senescence as key mediators in cell-to-cell communication.

Fibroblast-Derived Extracellular Vesicle-Packaged Long Noncoding RNA Upregulated in Diabetic Skin Enhances Keratinocyte MMP-9 Expression and Delays Diabetic Wound Healing

Accurate communication between fibroblasts and keratinocytes is crucial for diabetic wound healing. Extracellular vesicles are being explored as essential mediators of intercellular communication in the skin. However, the mechanisms underlying wound healing mediated by fibroblast-derived extracellular vesicles (Fib-EVs) remain unclear. The present study evaluated the role of long noncoding RNA upregulated in diabetic skin (lnc-URIDS) packed in Fib-EVs in the wound healing of streptozotocin-induced diabetes and the potential mechanisms of the effects. We demonstrated that high glucose induced the enrichment of lnc-URIDS in Fib-EVs, facilitated the transfer of lnc-URIDS to primary rat epidermal keratinocytes, and increased the expression of matrix metalloproteinase-9. Mechanistically, the binding of lnc-URIDS to YTH domain family protein-2 enhanced the degradation of YTH domain family protein-2 in the lysosomes, which increased the translational activity of the messenger RNA of matrix metalloproteinase-9 and ultimately induced the degradation of collagen for wound healing. The results provided an insight into the crosstalk and cooperation between fibroblasts and keratinocytes in collagen homeostasis in diabetic wounds and clarified the mechanism by which lnc-URIDS degrades collagen for diabetic wound healing.

Extracellular Vesicles-Based Cell-Cell Communication in Melanoma: New Perspectives in Diagnostics and Therapy

Extracellular vesicles (EVs) are a heterogeneous group of cell-secreted particles that carry cargo of functional biomolecules crucial for cell-to-cell communication with both physiological and pathophysiological consequences. In this review, we focus on evidence demonstrating that the EV-mediated crosstalk between melanoma cells within tumor, between melanoma cells and immune and stromal cells, promotes immune evasion and influences all steps of melanoma development from local progression, pre-metastatic niche formation, to metastatic colonization of distant organs. We also discuss the role of EVs in the development of resistance to immunotherapy and therapy with BRAF^V600/MEK inhibitors, and shortly summarize the recent advances on the potential applications of EVs in melanoma diagnostics and therapy.

Fibroblast growth factor-2 bound to specific dermal fibroblast-derived extracellular vesicles is protected from degradation

Fibroblast growth factor-2 (FGF2) has multiple roles in cutaneous wound healing but its natural low stability prevents the development of its use in skin repair therapies. Here we show that FGF2 binds the outer surface of dermal fibroblast (DF)-derived extracellular vesicles (EVs) and this association protects FGF2 from fast degradation. EVs isolated from DF cultured in the presence of FGF2 harbor FGF2 on their surface and FGF2 can bind purified EVs in absence of cells. Remarkably, FGF2 binding to EVs is restricted to a specific subpopulation of EVs, which do not express CD63 and CD81 markers. Treatment of DF with FGF2-EVs activated ERK and STAT signaling pathways and increased cell proliferation and migration. Local injection of FGF2-EVs improved wound healing in mice. We further demonstrated that binding to EVs protects FGF2 from both thermal and proteolytic degradation, thus maintaining FGF2 function. This suggests that EVs protect soluble factors from degradation and increase their stability and half-life. These results reveal a novel aspect of EV function and suggest EVs as a potential tool for delivering FGF2 in skin healing therapies.

Circulating Exosomal miR-493-3p Affects Melanocyte Survival and Function by Regulating Epidermal Dopamine Concentration in Segmental Vitiligo

Circulating exosomal microRNAs have been used as potential biomarkers for various disorders. However, to date, the microRNA expression profile of circulating exosomes in patients with segmental vitiligo (SV) has not been identified. Thus, we aimed to identify the expression profile of circulating exosomal microRNAs and investigate their role in the pathogenesis of SV. Our study identified the expression profile of circulating exosomal microRNAs in SV and selected miR-493-3p as a candidate biomarker whose expression is significantly increased in circulating exosomes and perilesions in patients with SV. Circulating exosomes were internalized by human primary keratinocytes and increased dopamine secretion in vitro. Furthermore, miR-493-3p overexpression in keratinocytes increased dopamine concentration in the culture supernatant, which led to a significant increase in ROS and melanocyte apoptosis as well as a decrease in melanocyte proliferation and melanin synthesis in the coculture system by targeting HNRNPU. We also confirmed that HNRNPU could bind to and regulate COMT, a major degradative enzyme of dopamine. Hence, circulating exosomal miR-493-3p is a biomarker for SV, and the miR-493-3p/HNRNPU/COMT/dopamine axis may contribute to melanocyte dysregulation in the pathogenesis of SV.

Extracellular vesicle-associated microRNA-30b-5p activates macrophages through the SIRT1/ NF-κB pathway in cell senescence

Chronic inflammation is widely observed in aging, but it is unclear whether extracellular vesicles (EVs) play a role in chronic disease-associated senescence. In our study, LC/MS profiling revealed that senescent cell derived EVs (SEN EVs) activate the immune response pathways of macrophages. Significantly more EVs were found in the supernatant of SEN than of control (CON) cell cultures, and SEN EVs were enriched in miR-30b-5p, which directly target sirtuin1 (SIRT1). In vitro, we found that SEN EV treatment resulted in increased cellular levels of interleukin-1β (IL-1β) and IL-6 and decreased levels of SIRT1. Increased cytokine levels could be reversed by SIRT1 activation and miR-30b-5p inhibition. Furthermore, miR-30b-5p significantly increased with age in both mouse liver tissue and EVs harvested from the tissue, with differences in EVs observed both earlier and in the later magnitude of aging. Western blot and qPCR proved that miR-30b-5p downregulated the level of SIRT1 in mouse macrophages. Collectively, we propose that EVs carrying miR-30b-5p from SEN cells can induce chronic inflammation through macrophage activation. This occurs through the downregulation of SIRT1 and the corresponding activation of NF-κB pathways that enhance pro-inflammatory cytokine production. Collectively, these results demonstrate that EVs carrying pro-inflammatory signals are released by SEN cells and then activate immune cells in the SEN microenvironment, changing the inflammatory balance. Our results also explain why inflammation increases with age even though SEN cells can be immediately eliminated under rigorous immune surveillance.

Evaluation of Platelet-Derived Extracellular Vesicles in Gingival Fibroblasts and Keratinocytes for Periodontal Applications

Gingival regeneration aims at restoring the architecture and functionality of oral damaged tissue. Different biomaterials or biological materials have been tested for tissue repair, such as platelet concentrates such as PL. In this article, the use of extracellular vesicles (EVs) derived from platelet lysate (PL) and their combination with hyaluronic acid biomaterials (HA) in an in vitro wound healing assay is investigated. EVs were isolated by size exclusion chromatography from PL. In addition, HA gels were formulated with PL or EVs. EVs or HA combined with EVs (HA-EVs) were tested in vitro in gingival fibroblasts and keratinocytes for biocompatibility (LDH activity and metabolic activity) and by an in vitro wound-healing assay and gene expression analysis. EVs and EVs-HA treatments were biocompatible in gingival fibroblasts and keratinocytes and showed an increase in wound healing in vitro compared to control. Moreover, changes in gene expression related to extracellular matrix remodeling were observed after the treatment with EVs. EVs can be combined with HA biomaterials, showing good biocompatibility and preserving their activity and functionality. Therefore, platelet-derived EVs could emerge as a new application for periodontal regeneration in combination with biomaterials in order to enhance their clinical use.

Role of exosomes in skin diseases

BACKGROUND

Exosomes, as a family member of extracellular vesicles, are cell-secreted nanoscale structures that play pivotal roles in regulating physiological and pathophysiological processes of the skin. Exosomes induce communication between cells and are responsible for transporting cellular components such as microRNAs, mRNAs, DNA, lipids, metabolites, and cell-surface proteins. Numerous preclinical and clinical trials searched the contribution of exosomes to skin functions and disorders. Thus, exosomes are gaining increasing attention within investigational dermatology. In advance, stem-cell-derived exosomes were integrated into the functional cosmetics industry nominated as cell-free regenerative medicine.

OBJECTIVE

This review aims to demonstrate the roles of exosomes in inflammatory skin disorders, stem cell, and tumor biology through a comprehensive evaluation of the diagnostic, prognostic, and therapeutic perspectives.

METHODS

A comprehensive literature search was performed using electronic online databases "PubMed" and "Google Scholar" using key words ''exosomes'', ''skin'', ''wound healing''.

CONCLUSION

Exosomes are regarded as promising diagnostic and prognostic biomarkers for various skin diseases. Future prospects are repurposing exosomes to treat skin disorders, either as drug carriers or drugs themselves.

Zebrafish Melanoma-Derived Interstitial EVs Are Carriers of ncRNAs That Induce Inflammation

Extracellular vesicles (EVs) are membranous particles released by all cell types. Their role as functional carrier of bioactive molecules is boosted by cells that actively secrete them in biological fluids or in the intercellular space (interstitial EVs, iEVs). Here we have optimised a method for the isolation and characterization of zebrafish iEVs from whole melanoma tissues. Zebrafish melanoma iEVs are around 140 nm in diameter, as determined by nanoparticle tracking and transmission electron microscopy (TEM) analysis. Western blot analysis shows enrichment for CD63 and Alix in the iEV fraction, but not in melanoma cell lysates. Super resolution and confocal microscopy reveal that purified zebrafish iEVs are green fluorescent protein positive (GFP+), indicating that they integrate the oncogene GFP-HRAS^V12G used to induce melanoma in this model within their vesicular membrane or luminal content. Analysis of RNA-Seq data found 118 non-coding (nc)RNAs differentially distributed between zebrafish melanoma and their iEVs, with only 17 of them being selectively enriched in iEVs. Among these, the RNA components of RNAses P and MRP, which process ribosomal RNA precursors, mitochondrial RNAs, and some mRNAs, were enriched in zebrafish and human melanoma EVs, but not in iEVs extracted from brain tumours. We found that melanoma iEVs induce an inflammatory response when injected in larvae, with increased expression of interferon responsive genes, and this effect is reproduced by MRP- or P-RNAs injected into circulation. This suggests that zebrafish melanoma iEVs are a source of MRP- and P-RNAs that can trigger inflammation in cells of the innate immune system.

A time to heal: microRNA and circadian dynamics in cutaneous wound repair

Many biological systems have evolved circadian rhythms based on the daily cycles of daylight and darkness on Earth. Such rhythms are synchronised or entrained to 24-h cycles, predominantly by light, and disruption of the normal circadian rhythms has been linked to elevation of multiple health risks. The skin serves as a protective barrier to prevent microbial infection and maintain homoeostasis of the underlying tissue and the whole organism. However, in chronic non-healing wounds such as diabetic foot ulcers (DFUs), pressure sores, venous and arterial ulcers, a variety of factors conspire to prevent wound repair. On the other hand, keloids and hypertrophic scars arise from overactive repair mechanisms that fail to cease in a timely fashion, leading to excessive production of extracellular matrix (ECM) components such as such as collagen. Recent years have seen huge increases in our understanding of the functions of microRNAs (miRNAs) in wound repair. Concomitantly, there has been growing recognition of miRNA roles in circadian processes, either as regulators or targets of clock activity or direct responders to external circadian stimuli. In addition, miRNAs are now known to function as intercellular signalling mediators through extracellular vesicles (EVs). In this review, we explore the intersection of mechanisms by which circadian and miRNA responses interact with each other in relation to wound repair in the skin, using keratinocytes, macrophages and fibroblasts as exemplars. We highlight areas for further investigation to support the development of translational insights to support circadian medicine in the context of these cells.

miR-10a, miR-30c, and miR-451a encapsulated in small extracellular vesicles are pro-senescence factors in human dermal fibroblasts

Although small extracellular vesicles (sEV) have been reported to play an important role in cellular senescence and aging, little is known about the potential role and function of microRNAs (miRNAs) contained within the sEV. To determine senescence-associated factors secreted from sEV of human dermal fibroblasts (HDF), we isolated and characterized sEV from non-senescent vs. senescent HDF. Small RNA sequencing analysis identified many enriched miRNAs in sEV of senescent HDF, as shown by the upregulation of miR-10a, miR-30c, and miR-451a, and downregulation of miR-128, miR-184, miR-200c, and miR-125a. Overexpression of miR-10a, miR-30c, and miR-451a induced an aging phenotype in HDF, whereas inhibition of these miRNAs reduced senescent-like phenotypes in senescent HDF. Moreover, treatment with sEV or sEV-containing conditioned medium promoted cellular senescence in HDF, whereas sEV depletion abrogated pro-senescence effects of the senescent HDF secretome. Interestingly, pro-senescence sEV miRNAs were found to have an essential role in regulating reactive oxygen species production and mitophagy activation. Taken together, our results revealed miR-10a, miR-30c, and miR-451a as pro-senescence factors that are differentially expressed in sEV of senescent HDF, demonstrating the essential role of sEV miRNAs in the biological processes of aging.

Action Mechanisms of Small Extracellular Vesicles in Inflammaging

The accumulation process of proinflammatory components in the body due to aging influences intercellular communication and is known as inflammaging. This biological mechanism relates the development of inflammation to the aging process. Recently, it has been reported that small extracellular vesicles (sEVs) are mediators in the transmission of paracrine senescence involved in inflammatory aging. For this reason, their components, as well as mechanisms of action of sEVs, are relevant to develop a new therapy called senodrugs (senolytics and senomorphic) that regulates the intercellular communication of inflammaging. In this review, we include the most recent and relevant studies on the role of sEVs in the inflammatory aging process and in age-related diseases such as cancer and type 2 diabetes.

Characterization of MicroRNA Cargo of Extracellular Vesicles Isolated From the Plasma of Schistosoma japonicum-Infected Mice

Schistosoma is a genus of parasitic trematodes that undergoes complex migration in final hosts, finally developing into adult worms, which are responsible for egg production and disease dissemination. Recent studies documented the importance of extracellular vesicles (EVs) in the regulation of host-parasite interactions. Herein, we investigated the microRNA (miRNA) profiles of EVs isolated from host plasma at different stages of Schistosoma japonicum infection (lung stage: 3 days post-infection (dpi), and liver stages: 14 and 21 dpi) to identify miRNA cargo potentially involved in the pathogenesis and immune regulation of schistosomiasis. Characterization of the isolated plasma EVs revealed their diameter to be approximately 100 nm, containing typical EV markers such as Hsp70 and Tsg101. Deep sequencing analysis indicated the presence of 811 known and 15 novel miRNAs with an increasing number of differential miRNAs from the lung stage (27 miRNAs) to the liver stages (58 and 96 miRNAs at 14 and 21 dpi, respectively) in the plasma EVs of infected mice compared to EVs isolated from the uninfected control. In total, 324 plasma EV miRNAs were shown to be co-detected among different stages of infection and the validation of selected miRNAs showed trends of abundance similar to deep sequencing analysis. For example, miR-1a-3p and miR-122-5p showed higher abundance, whereas miR-150-3p and miR-126a showed lower abundance in the plasma EVs of infected mice at 3, 14, and 21 dpi as compared to those of uninfected mice. In addition, bioinformatic analysis combined with PCR validation of the miRNA targets, particularly those associated with the immune system and parasitic infectious disease, indicated a significant increase in the expression of Gbp7and Ccr5 in contrast to the decreased expression of Fermt3, Akt1, and IL-12a. Our results suggested that the abundance of miRNA cargo of the host plasma EVs was related to the stages of Schistosoma japonicum infection. Further studies on the roles of these miRNAs may reveal the regulatory mechanism of the host-parasite interaction. Moreover, the differentially abundant miRNA cargo in host EVs associated with S. japonicum infection may also provide valuable clues for identifying novel biomarkers for schistosomiasis diagnosis.

Construction of Yeast Display Libraries for Selection of Antigen-Binding Variants of Large Extracellular Loop of CD81, a Major Surface Marker Protein of Extracellular Vesicles

Over the last two decades, yeast display methodology has served as a popular tool for discovery, humanization, stability improvement, and affinity maturation of antibodies and antibody fragments, but also for development of diverse non-antibody protein scaffolds towards the ability of antigen recognition. Yeast display is particularly well suited for multiparametric analysis of properties of derivatized proteins, allowing the evolution of most diverse protein structures into antigen binding entities with favorable expression, stability, and folding properties. Here we present the methodological basics of a novel yeast display-based approach for the functionalization of the large extracellular loop of CD81 into a de novo antigen binding unit. CD81 is intrinsically overrepresented on the surface of extracellular vesicles (EVs), naturally occurring nanoparticle units that act as cell-to-cell messengers by delivering their intracellular cargo from the source cell into a recipient cell. This amazing feature makes them of highest biotechnological interest, yet methods for their targeted delivery are still in their infancy. As a novel approach for introducing EV surface modifications enabling specific target cell recognition and internalization, we have prepared yeast display libraries of CD81 large extracellular loop mutants, which are selected towards specific antigen binding and resulting mutants conveniently clicked into the full-length EV surface protein. Resulting EVs display wild-type-like characteristics regarding the expression level and distribution of recombinant proteins and are hence promising therapeutic tools.

Photoprotective Effects of a Hyperoside-Enriched Fraction Prepared from Houttuynia cordata Thunb. on Ultraviolet B-Induced Skin Aging in Human Fibroblasts through the MAPK Signaling Pathway

Ultraviolet-B (UVB) irradiation causes skin damage via deleterious effects including oxidative stress, inflammation, and collagen degradation. The photoprotective effects of a hyperoside-enriched fraction obtained from Houttuynia cordata Thunb. (H. cordata) on the attenuation of UVB-induced skin aging in human fibroblasts were investigated. The solvent-partition technique was used to establish the hyperoside-enriched fraction of H. cordata (HcEA). The active compounds identified in the H. cordata extracts were hyperoside, quercitrin, chlorogenic acid, and rutin. With regard to the photoprotective effects of H. cordata on UVB-irradiated dermal fibroblasts, HcEA and hyperoside inhibited intracellular ROS production and inflammatory cytokine secretions (IL-6 and IL-8), while increasing collagen type I synthesis along with downregulating MMP-1 gene and protein expressions. Mechanistically, the hyperoside-enriched fraction obtained from H. cordata inhibited UVB-irradiated skin aging through regulation of the MAPK signaling pathway by attenuating the activation of JNK/ERK/c-Jun in human dermal fibroblasts. The hyperoside-enriched fraction of H. cordata exerted potent anti-skin aging properties against UVB exposure. The findings of this study can be applied in the cosmetics industry, as H. cordata extract can potentially be used in pharmaceutical or cosmetic formulations as a photoprotective or anti-skin aging agent.

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

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

Extracellular Vesicles: Emerging Therapeutics in Cutaneous Lesions

Extracellular vesicles (EVs), as nanoscale membranous vesicles containing DNAs, RNAs, lipids and proteins, have emerged as promising diagnostic and therapeutic agents for skin diseases. Here, we summarize the basic physiology of the skin and the biological characteristic of EVs. Further, we describe the applications of EVs in the treatment of dermatological conditions such as skin infection, inflammatory skin diseases, skin repair and rejuvenation and skin cancer. In particular, plant-derived EVs and clinical trials are discussed. In addition, challenges and perspectives related to the preclinical and clinical applications of EVs are highlighted.

An engineered CD81-based combinatorial library for selecting recombinant binders to cell surface proteins: Laminin binding CD81 enhances cellular uptake of extracellular vesicles

The research of extracellular vesicles (EVs) has boomed in the last decade, with the promise of them functioning as target-directed drug delivery vehicles, able to modulate proliferation, migration, differentiation, and other properties of the recipient cell that are vital for health of the host organism. To enhance the ability of their targeted delivery, we employed an intrinsically overrepresented protein, CD81, to serve for recognition of the desired target antigen. Yeast libraries displaying mutant variants of the large extracellular loop of CD81 have been selected for binders to human placental laminin as an example target. Their specific interaction with laminin was confirmed in a mammalian display system. Derived sequences were reformatted to full-length CD81 and expressed in EVs produced by HeLa cells. These EVs were examined for the presence of the recombinant protein and were shown to exhibit an enhanced uptake into laminin-secreting mammalian cell lines. For the best candidate, the specificity of antigen interaction was demonstrated with a competition experiment. To our knowledge, this is the first example of harnessing an EV membrane protein as mediator of de novo target antigen recognition via in vitro molecular evolution, opening horizons to a broad range of applications in various therapeutic settings.

miRNAs as Regulators of the Early Local Response to Burn Injuries

In burn injuries, risk factors and limitations to treatment success are difficult to assess clinically. However, local cellular responses are characterized by specific gene-expression patterns. MicroRNAs (miRNAs) are single-stranded, non-coding RNAs that regulate mRNA expression on a posttranscriptional level. Secreted through exosome-like vesicles (ELV), miRNAs are intracellular signalers and epigenetic regulators. To date, their role in the regulation of the early burn response remains unclear. Here, we identified 43 miRNAs as potential regulators of the early burn response through the bioinformatics analysis of an existing dataset. We used an established human ex vivo skin model of a deep partial-thickness burn to characterize ELVs and miRNAs in dermal interstitial fluid (dISF). Moreover, we identified miR-497-5p as stably downregulated in tissue and dISF in the early phase after a burn injury. MiR-218-5p and miR-212-3p were downregulated in dISF, but not in tissue. Target genes of the miRNAs were mainly upregulated in tissue post-burn. The altered levels of miRNAs in dISF of thermally injured skin mark them as new biomarker candidates for burn injuries. To our knowledge, this is the first study to report miRNAs altered in the dISF in the early phase of deep partial-thickness burns.

Involvement of extracellular vesicles in aging process and their beneficial effects in alleviating aging-associated symptoms

Aging is a gradual and unavoidable physiological phenomenon that manifests in the natural maturation process and continues to progress from infanthood to adulthood. Many elderly people suffer from aging-associated hematological and nonhematological disorders. Recent advances in regenerative medicine have shown new revolutionary paths of treating such diseases using stem cells; however, aging also affects the quality and competence of stem and progenitor cells themselves and ultimately directs their death or apoptosis and senescence, leading to a decline in their regenerative potential. Recent research works show that extracellular vesicles (EVs) isolated from different types of stem cells may provide a safe treatment for aging-associated disorders. The cargo of EVs comprises packets of information in the form of various macromolecules that can modify the fate of the target cells. To harness the true potential of EVs in regenerative medicine, it is necessary to understand how this cargo contributes to the rejuvenation of aged stem and progenitor populations and to identify the aging-associated changes in the macromolecular profile of the EVs themselves. In this review, we endeavor to summarize the current knowledge of the involvement of EVs in the aging process and delineate the role of EVs in the reversal of aging-associated phenotypes. We have also analyzed the involvement of the molecular cargo of EVs in the generation of aging-associated disorders. This knowledge could not only help us in understanding the mechanism of the aging process but could also facilitate the development of new cell-free biologics to treat aging-related disorders in the future.

Flavonoids in Skin Senescence Prevention and Treatment

Skin aging is associated with the accumulation of senescent cells and is related to many pathological changes, including decreased protection against pathogens, increased susceptibility to irritation, delayed wound healing, and increased cancer susceptibility. Senescent cells secrete a specific set of pro-inflammatory mediators, referred to as a senescence-associated secretory phenotype (SASP), which can cause profound changes in tissue structure and function. Thus, drugs that selectively eliminate senescent cells (senolytics) or neutralize SASP (senostatics) represent an attractive therapeutic strategy for age-associated skin deterioration. There is growing evidence that plant-derived compounds (flavonoids) can slow down or even prevent aging-associated deterioration of skin appearance and function by targeting cellular pathways crucial for regulating cellular senescence and SASP. This review summarizes the senostatic and senolytic potential of flavonoids in the context of preventing skin aging.

The role of lipid-based signalling in wound healing and senescence

Lipid-based signalling modulates several cellular processes and intercellular communication during wound healing and tissue regeneration. Bioactive lipids include but are not limited to the diverse group of eicosanoids, phospholipids, and extracellular vesicles and mediate the attraction of immune cells, initiation of inflammatory responses, and their resolution. In aged individuals, wound healing and tissue regeneration are greatly impaired, resulting in a delayed healing process and non-healing wounds. Senescent cells accumulate with age in vivo, preferably at sites implicated in age-associated pathologies and their elimination was shown to alleviate many age-associated diseases and disorders. In contrast to these findings, the transient presence of senescent cells in the process of wound healing exerts beneficial effects and limits fibrosis. Hence, clearance of senescent cells during wound healing was repeatedly shown to delay wound closure in vivo. Recent findings established a dysregulated synthesis of eicosanoids, phospholipids and extracellular vesicles as part of the senescent phenotype. This intriguing connection between cellular senescence, lipid-based signalling, and the process of wound healing and tissue regeneration prompts us to compile the current knowledge in this review and propose future directions for investigation.

Faces of cellular senescence in skin aging

The skin is comprised of different cell types with different proliferative capacities. Skin aging occurs with chronological age and upon exposure to extrinsic factors such as photodamage. During aging, senescent cells accumulate in different compartments of the human skin, leading to impaired skin physiology. Diverse skin cell types may respond differently to senescence-inducing stimuli and it is not clear how this results in aging-associated skin phenotypes and pathologies. This review aims to examine and provide an overview of current evidence of cellular senescence in the skin. We will focus on cellular characteristics and behaviour of different skin cell types undergoing senescence in the epidermis and dermis, with a particular focus on the complex interplay between mitochondrial dysfunction, autophagy and DNA damage pathways. We will also examine how the dermis and epidermis cope with the accumulation of DNA damage during aging.

Extracellular Vesicles as Potential Theranostic Platforms for Skin Diseases and Aging

Extracellular vesicles (EVs), naturally secreted by cells, act as mediators for communication between cells. They are transported to the recipient cells along with cargoes such as nucleic acids, proteins, and lipids that reflect the changes occurring within the parent cells. Thus, EVs have been recognized as potential theranostic agents for diagnosis, treatment, and prognosis. In particular, the evidence accumulated to date suggests an important role of EVs in the initiation and progression of skin aging and various skin diseases, including psoriasis, systemic lupus erythematosus, vitiligo, and chronic wounds. This review highlights recent research that investigates the role of EVs and their potential as biomarkers and therapeutic agents for skin diseases and aging.

microRNA-106b derived from endothelial cell-secreted extracellular vesicles prevents skin wound healing by inhibiting JMJD3 and RIPK3

Intriguingly, microRNAs (miRs) transferred as cargo in extracellular vesicles (EVs) can modulate wound healing through their regulation of fibroblast functions. In this study, we investigated the effects of miR‐106b transfer via EVs derived from human umbilical vein endothelial cells (HUVECs) on skin wound healing. Dual‐luciferase reporter gene assay identified that miR‐106b could target and inhibit JMJD3. RT‐qPCR analysis showed EVs isolated from HUVECs had enriched expression of miR‐106b. LL29 fibroblast cells and HaCaT keratinocytes were co‐cultured with HUVEC‐derived EVs, in which miR‐106b had been up‐regulated or down‐regulated by its mimic or inhibitor. The co‐culture with HUVEC‐derived EVs increased miR‐106b expression, and reduced the viability and adhesion of LL29 and HaCaT cells, whereas the inhibition of miR‐106b in HUVEC‐derived EVs enhanced the viability and adhesion of LL29 and HaCaT cells through up‐regulation of JMJD3. Next, we showed that JMJD3 overexpression enhanced LL29 and HaCaT cell viability and adhesion through elevating RIPK3, which induced the phosphorylation of AKT during the wound‐healing process. We next developed a mouse skin wound model to investigate the actions of miR‐106b in vivo after 14 days. The delivery of miR‐106b via HUVEC‐derived EVs delayed wound healing through suppression of collagen I content and angiogenesis, but had no effects on pro‐inflammatory cytokines. In conclusion, miR‐106b from HUVEC‐derived EVs inhibits JMJD3 and RIPK3, leading to the inhibition of skin wound healing, thus constituting a new therapeutic target.

Skin Immunomodulation during Regeneration: Emerging New Targets

Adipose-Derived Stem Cells (ADSC) are present within the hypodermis and are also expected to play a pivotal role in wound healing, immunomodulation, and rejuvenation activities. They orchestrate, through their exosome, the mechanisms associated to cell differentiation, proliferation, and cell migration by upregulating genes implicated in different functions including skin barrier, immunomodulation, cell proliferation, and epidermal regeneration. ADSCs directly interact with their microenvironment and specifically the immune cells, including macrophages and T and B cells, resulting in differential inflammatory and anti-inflammatory mechanisms impacting, in return, ADSCs microenvironment and thus skin function. These useful features of ADSCs are involved in tissue repair, where the required cell proliferation, angiogenesis, and anti-inflammatory responses should occur rapidly in damaged sites. Different pathways involved have been reported such as Growth Differentiation Factor-11 (GDF11), Tumor Growth Factor (TGF)-β, Metalloproteinase (MMP), microRNA, and inflammatory cytokines that might serve as specific biomarkers of their immunomodulating capacity. In this review, we try to highlight ADSCs’ network and explore the potential indicators of their immunomodulatory effect in skin regeneration and aging. Assessment of these biomarkers might be useful and should be considered when designing new clinical therapies using ADSCs or their specific exosomes focusing on their immunomodulation activity.

Epilipidomics of Senescent Dermal Fibroblasts Identify Lysophosphatidylcholines as Pleiotropic Senescence-Associated Secretory Phenotype (SASP) Factors

During aging, skin accumulates senescent cells. The transient presence of senescent cells, followed by their clearance by the immune system, is important in tissue repair and homeostasis. The persistence of senescent cells that evade clearance contributes to the age-related deterioration of the skin. The senescence-associated secretory phenotype of these cells contains immunomodulatory molecules that facilitate clearance but also promote chronic damage. Here, we investigated the epilipidome-the oxidative modifications of phospholipids-of senescent dermal fibroblasts, because these molecules are among the bioactive lipids that were recently identified as senescence-associated secretory phenotype factors. Using replicative- and stress- induced senescence protocols, we identified lysophosphatidylcholines as universally elevated in senescent fibroblasts, whereas other oxidized lipids displayed a pattern that was characteristic for the used senescence protocol. When we tested the lysophosphatidylcholines for senescence-associated secretory phenotype activity, we found that they elicit chemokine release in nonsenescent fibroblasts but also interfere with toll-like receptor 2 and 6/CD36 signaling and phagocytic capacity in macrophages. Using matrix-assisted laser desorption/ionization Fourier transform ion cyclotron resonance mass spectrometry imaging, we localized two lysophosphatidylcholine species in aged skin. This suggests that lysophospholipids may facilitate immune evasion and low-grade chronic inflammation in skin aging.

[Functional integrity of aging skin, from cutaneous biology to anti-aging strategies]

The skin is a sentinel organ making easily visible the passing of time. Chronological and environmental aging weakens skin structure and functions. The skin barrier, the elastic and mechanical properties of the cutaneous tissue as well as its vascular reactivity are impacted by aging. The barrier dysfunction in aged skin is caused by defects in epidermal keratinocytes renewal and differentiation notably linked to abnormal expression of microRNAs regulating cell death and autophagy. An abnormal balance between synthesis and degradation of matrix proteins modifies the mechanical properties of the dermis in aged skin. Finally, a reduction of the vascular reactivity linked to endothelial dysfunctions is observed in elderly people. These biological processes can be targeted by therapeutic approaches either topical or systemic, especially using anti-oxydants or senolytics. These anti-aging strategies might contribute to restore, at least in part, the functional integrity of aged skin.

Targeting cellular senescence based on interorganelle communication, multilevel proteostasis, and metabolic control

Cellular senescence, a stable cell division arrest caused by severe damage and stress, is a hallmark of aging in vertebrates including humans. With progressing age, senescent cells accumulate in a variety of mammalian tissues, where they contribute to tissue aging, identifying cellular senescence as a major target to delay or prevent aging. There is an increasing demand for the discovery of new classes of small molecules that would either avoid or postpone cellular senescence by selectively eliminating senescent cells from the body (i.e., ‘senolytics’) or inactivating/switching damage‐inducing properties of senescent cells (i.e., ‘senostatics/senomorphics’), such as the senescence‐associated secretory phenotype. Whereas compounds with senolytic or senostatic activity have already been described, their efficacy and specificity has not been fully established for clinical use yet. Here, we review mechanisms of senescence that are related to mitochondria and their interorganelle communication, and the involvement of proteostasis networks and metabolic control in the senescent phenotype. These cellular functions are associated with cellular senescence in in vitro and in vivo models but have not been fully exploited for the search of new compounds to counteract senescence yet. Therefore, we explore possibilities to target these mechanisms as new opportunities to selectively eliminate and/or disable senescent cells with the aim of tissue rejuvenation. We assume that this research will provide new compounds from the chemical space which act as mimetics of caloric restriction, modulators of calcium signaling and mitochondrial physiology, or as proteostasis optimizers, bearing the potential to counteract cellular senescence, thereby allowing healthy aging.

miR-155 Contributes to Normal Keratinocyte Differentiation and Is Upregulated in the Epidermis of Psoriatic Skin Lesions

The role of microRNAs (miRNAs) during keratinocyte (KC) differentiation and in skin diseases with epidermal phenotypes has attracted strong interest over the past few years. However, combined mRNA and miRNA expression analyses to elucidate the intricate mRNA–miRNA networks of KCs at different stages of differentiation have not been performed yet. In the present study, we investigated the dynamics of miRNA and mRNA expression during KC differentiation in vitro and in normal and psoriatic epidermis. While we identified comparable numbers of up- and downregulated mRNAs (49% and 51%, respectively), miRNAs were predominantly upregulated (76% vs 24%) during KC differentiation. Further bioinformatics analyses suggested an important inhibitory role for miR-155 in KC differentiation, as it was repressed during KC differentiation in normal skin but strongly upregulated in the epidermis of psoriatic skin lesions. Mimicking the inflammatory milieu of psoriatic skin in vitro, we could show that the pro-inflammatory cytokines IL17, IL1β and INFγ synergistically upregulated miR-155 expression in KCs. Forced over-expression of miR-155 in human in vitro skin models specifically reduced the expression of loricrin (LOR) in KCs, indicating that miR-155 interferes with the establishment of a normal epidermal barrier. Together, our data indicate that downregulation of miR-155 during KC differentiation is a crucial step for epidermal barrier formation. Furthermore, its strong upregulation in psoriatic lesions suggests a contributing role of miR-155 in the altered keratinocyte differentiation observed in psoriasis. Therefore, miR-155 represents as a potential target for treating psoriatic skin lesions.

Modern isolation and separation techniques for extracellular vesicles

Extracellular vesicles (EVs) are heterogenous membrane-bound vesicles released from various origins. EVs play a crucial role in cellular communication and mediate several physiological and pathological processes, highlighting their potential therapeutic and diagnostic applications. Due to the rapid increase in interests and needs to elucidate EV properties and functions, numerous isolation and separation approaches for EVs have been developed to overcome limitations of conventional techniques, such as ultracentrifugation. This review focuses on recently emerging and modern EV isolation and separation techniques, including size-, charge-, and affinity-based techniques while excluding ultracentrifugation and precipitation-based techniques due to their multiple limitations. The advantages and drawbacks of each technique are discussed together with insights into their applications. Emerging approaches all share similar features in terms of being time-effective, easy-to-operate, and capable of providing EVs with suitable and desirable purity and integrity for applications of interest. Combination and hyphenation of techniques have been used for EV isolation and separation to yield EVs with the best quality. The most recent development using an automated on-line system including selective affinity-based trapping unit and asymmetrical flow field-flow fractionation allows reliable isolation and fractionation of EV subpopulations from human plasma.

The bright and dark side of skin senescence. Could skin rejuvenation anti-senescence interventions become a "bright" new strategy for the prevention of age-related skin pathologies?

The number of senescent cells in the skin is increasing with age. Numerous studies have attempted to elucidate the role of these cells in normal aging of the skin as well as in age-related skin conditions. In recent years, attempts have also been made to find treatments that aim either to cleanse the skin tissues of senescent cells or to neutralize their effects (referred to as senolytics and senomorphics respectively) and thus prevent the consequences, particularly on the skin's appearance in advanced age. Through this review, we have tried to gather data on the role of senescent cells in the skin, in treatments aimed at removing them, and we are asking a reasonable question as to whether anti-senescence treatments may contribute to the protection against age-related skin pathologies, including skin cancer, such as non-melanoma skin cancer, in addition to their involvement in skin rejuvenation.

Methotrexate reduces keratinocyte proliferation, migration and induces apoptosis in HaCaT keratinocytes in vitro and reduces wound closure in Skh1 mice in vivo

The aim of the present work was to evaluate MTX treatment (0.1, 1 and 10 μg mL^-1) in vitro in order to characterize its effects on cell proliferation alterations in cell cycle of HaCaT keratinocytes and wound healing in a Skh1 mice treated with MTX (low doses 30 mg kg^-1, high doses 200 mg kg^-1 and repeated doses at 1.5 mg kg^-1). We analyzed the cytotoxic effect of methotrexate by a resazurin assay. The effects in the proliferation, cell cycle and apoptosis of HaCaT cells were analyzed by flow cytometry. The effects of MTX on wound healing in vivo were also analyzed. A trend toward reduction in the resazurin assay was found (p > 0.05). Reduced proliferation was also identified in a clonogenic assay and a CFSE assay (p < 0.05) due to the MTX treatment. A reduction in the G₂/M and S phases was observed accompanied by apoptosis induction with increased sub G₀ phase and annexin V FITC staining. Effect of MTX was evidenced in vivo on the wound closure process after day 10 (p < 0.05) with alterations in tissue architecture and remodeling. There is a marked effect of MTX on wound healing in vivo in Skh1 mice with implications for long-term therapy and surgical interventions.

Shedding light on the role of keratinocyte-derived extracellular vesicles on skin-homing cells

Extracellular vesicles (EVs) are secretory lipid membranes with the ability to regulate cellular functions by exchanging biological components between different cells. Resident skin cells such as keratinocytes, fibroblasts, melanocytes, and inflammatory cells can secrete different types of EVs depending on their biological state. These vesicles can influence the physiological properties and pathological processes of skin, such as pigmentation, cutaneous immunity, and wound healing. Since keratinocytes constitute the majority of skin cells, secreted EVs from these cells may alter the pathophysiological behavior of other skin cells. This paper reviews the contents of keratinocyte-derived EVs and their impact on fibroblasts, melanocytes, and immune cells to provide an insight for better understanding of the pathophysiological mechanisms of skin disorders and their use in related therapeutic approaches.

Extracellular vesicles in Inflammatory Skin Disorders: from Pathophysiology to Treatment

Extracellular vesicles (EVs), naturally secreted by almost all known cell types into extracellular space, can transfer their bioactive cargos of nucleic acids and proteins to recipient cells, mediating cell-cell communication. Thus, they participate in many pathogenic processes including immune regulation, cell proliferation and differentiation, cell death, angiogenesis, among others. Cumulative evidence has shown the important regulatory effects of EVs on the initiation and progression of inflammation, autoimmunity, and cancer. In dermatology, recent studies indicate that EVs play key immunomodulatory roles in inflammatory skin disorders, including psoriasis, atopic dermatitis, lichen planus, bullous pemphigoid, systemic lupus erythematosus, and wound healing. Importantly, EVs can be used as biomarkers of pathophysiological states and/or therapeutic agents, both as carriers of drugs or even as a drug by themselves. In this review, we will summarize current research advances of EVs from different cells and their implications in inflammatory skin disorders, and further discuss their future applications, updated techniques, and challenges in clinical translational medicine.

Plasma endothelial cells-derived extracellular vesicles promote wound healing in diabetes through YAP and the PI3K/Akt/mTOR pathway

Extracellular vesicles are involved in skin wound healing and diabetes. After enrichment and identification, plasma endothelial cells-derived-extracellular vesicles were cocultured with skin fibroblasts or HaCaT. The gain-and loss-of functions were performed to measure fibroblast proliferation, senescence, and reactive oxygen species. Levels of senescence-related proteins, senescence-associated secretory phenotypes, vascular markers, YAP and the PI3K/Akt/mTOR pathway-related proteins were determined. Diabetic mice were induced to establish skin wound model. After endothelial cells-derived-extracellular vesicles were injected into skin wound modeling mice, skin wound healing was evaluated. Endothelial cells-derived-extracellular vesicles treatment enhanced fibroblast proliferation, and decreased senescence through the elevation of YAP nuclear translocation and activation the PI3K/Akt/mTOR pathway. YAP inhibition reversed the effect of plasma endothelial cells-derived-extracellular vesicles on fibroblast proliferation. Endothelial cells-derived-extracellular vesicles also promoted wound healing in diabetic mice, increased microvascular density, collagen deposition, macrophage infiltration and positive rates of vascular markers, and inhibited YAP phosphorylation and senescence. Plasma endothelial cells-derived-extracellular vesicles prevent fibroblast senescence and accelerate skin wound healing in diabetic mice by reducing YAP phosphorylation and activating the PI3K/Akt/mTOR pathway. This study may provide novel insights for skin disorders in diabetic mice.

Tissue engineering to better understand senescence: Organotypics come of age

The recent advent of 'organs in a dish' has revolutionised the research landscape. These 3D culture systems have paved the way for translational, post genomics research by enabling scientists to model diseases in the laboratory, grow patient-derived organoids, and unite this technology with other cutting-edge methodologies such as drug discovery. Fields such as dermatology and neuroscience have revolutionised the development of robust 3D models, which faithfully recapitulate native physiology in vivo to provide important functional and mechanistic insights. These models have underpinned a rapid growth in the number of organs and myriad of human diseases that can be modelled in 3D, which currently includes breast, cerebral cortex, heart, intestine, kidney, liver, lung, neural tube, pancreas, prostate, skin and stomach, as well as patient derived tumours. However, so far, they have not yet been employed extensively in the study of fundamental cellular programmes such as senescence. Thus, tissue engineering and 3D culture offer an exciting opportunity to further understand the bright and dark sides of senescence in a more complex and physiologically relevant environment. Below, we will discuss previous approaches to investigating senescence and ageing using organotypic models, and some potential opportunities for future research.