Sebaceous-immunobiology is orchestrated by sebum lipids

Hair follicles modulate skin barrier function

Our skin provides a protective barrier that shields us from our environment. Barrier function is typically associated with the interfollicular epidermis; however, whether hair follicles influence this process remains unclear. Here, we utilize a potent genetic tool to probe barrier function by conditionally ablating a quintessential epidermal barrier gene, Abca12, which is mutated in the most severe skin barrier disease, harlequin ichthyosis. With this tool, we deduced 4 ways by which hair follicles modulate skin barrier function. First, the upper hair follicle (uHF) forms a functioning barrier. Second, barrier disruption in the uHF elicits non-cell-autonomous responses in the epidermis. Third, deleting Abca12 in the uHF impairs desquamation and blocks sebum release. Finally, barrier perturbation causes uHF cells to move into the epidermis. Neutralizing IL-17a, whose expression is enriched in the uHF, partially alleviated some disease phenotypes. Altogether, our findings implicate hair follicles as multi-faceted regulators of skin barrier function.

Sebaceous gland organoid engineering

Sebaceous glands (SGs), as holocrine-secreting appendages, lubricate the skin and play a central role in the skin barrier. Large full-thickness skin defects cause overall architecture disruption and SG loss. However, an effective strategy for SG regeneration is lacking. Organoids are 3D multicellular structures that replicate key anatomical and functional characteristics of in vivo tissues and exhibit great potential in regenerative medicine. Recently, considerable progress has been made in developing reliable procedures for SG organoids and existing SG organoids recapitulate the main morphological, structural and functional features of their in vivo counterparts. Engineering approaches empower researchers to manipulate cell behaviors, the surrounding environment and cell-environment crosstalk within the culture system as needed. These techniques can be applied to the SG organoid culture system to generate functionally more competent SG organoids. This review aims to provide an overview of recent advancements in SG organoid engineering. It highlights some potential strategies for SG organoid functionalization that are promising to forge a platform for engineering vascularized, innervated, immune-interactive and lipogenic SG organoids. We anticipate that this review will not only contribute to improving our understanding of SG biology and regeneration but also facilitate the transition of the SG organoid from laboratory research to a feasible clinical application.

A review of biomacromolecule-based 3D bioprinting strategies for structure-function integrated repair of skin tissues

When skin is damaged or affected by diseases, it often undergoes irreversible scar formation, leading to aesthetic concerns and psychological distress for patients. In cases of extensive skin defects, the patient's life can be severely compromised. In recent years, 3D printing technology has emerged as a groundbreaking approach to skin tissue engineering, offering promising solutions to various skin-related conditions. 3D bioprinting technology enables the precise fabrication of structures by programming the spatial arrangement of cells within the skin tissue and subsequently printing skin replacements either in a 3D bioprinter or directly at the site of the defect. This study provides a comprehensive overview of various biopolymer-based inks, with a particular emphasis on chitosan (CS), starch, alginate, agarose, cellulose, and fibronectin, all of which are natural polymers belonging to the category of biomacromolecules. Additionally, it summarizes artificially synthesized polymers capable of enhancing the performance of these biomacromolecule-based bioinks, thereby composing hybrid biopolymer inks aimed at better application in skin tissue engineering endeavors. This review paper examines the recent advancements, characteristics, benefits, and limitations of biological 3D bioprinting techniques for skin tissue engineering. By utilizing bioinks containing seed cells, hydrogels with bioactive factors, and biomaterials, complex structures resembling natural skin can be accurately fabricated in a layer-by-layer manner. The importance of biological scaffolds in promoting skin wound healing and the role of 3D bioprinting in skin tissue regeneration processes is discussed. Additionally, this paper addresses the challenges and constraints associated with current 3D bioprinting technologies for skin tissue and presents future perspectives. These include advancements in bioink formulations, full-thickness skin bioprinting, vascularization strategies, and skin appendages bioprinting.

Hair follicles modulate skin barrier function

Our skin provides a protective barrier that shields us from our environment. Barrier function is typically associated with interfollicular epidermis; however, whether hair follicles influence this process remains unclear. Here, we utilize a potent genetic tool to probe barrier function by conditionally ablating a quintessential epidermal barrier gene, Abca12, which is mutated in the most severe skin barrier disease, harlequin ichthyosis. With this tool, we deduced 4 ways by which hair follicles modulate skin barrier function. First, the upper hair follicle (uHF) forms a functioning barrier. Second, barrier disruption in the uHF elicits non-cell autonomous responses in the epidermis. Third, deleting Abca12 in the uHF impairs desquamation and blocks sebum release. Finally, barrier perturbation causes uHF cells to move into the epidermis. Neutralizing Il17a, whose expression is enriched in the uHF, partially alleviated some disease phenotypes. Altogether, our findings implicate hair follicles as multi-faceted regulators of skin barrier function.

Immune cell trafficking: a novel perspective on the gut-skin axis

Immune cell trafficking, an essential mechanism for maintaining immunological homeostasis and mounting effective responses to infections, operates under a stringent regulatory framework. Recent advances have shed light on the perturbation of cell migration patterns, highlighting how such disturbances can propagate inflammatory diseases from their origin to distal organs. This review collates and discusses current evidence that demonstrates atypical communication between the gut and skin, which are conventionally viewed as distinct immunological spheres, in the milieu of inflammation. We focus on the aberrant, reciprocal translocation of immune cells along the gut-skin axis as a pivotal factor linking intestinal and dermatological inflammatory conditions. Recognizing that the translation of these findings into clinical practices is nascent, we suggest that therapeutic strategies aimed at modulating the axis may offer substantial benefits in mitigating the widespread impact of inflammatory diseases.

Exploring Skin Wound Healing Models and the Impact of Natural Lipids on the Healing Process

Cutaneous wound healing is a complex biological process involving a series of well-coordinated events aimed at restoring skin integrity and function. Various experimental models have been developed to study the mechanisms underlying skin wound repair and to evaluate potential therapeutic interventions. This review explores the diverse array of skin wound healing models utilized in research, ranging from rodent excisional wounds to advanced tissue engineering constructs and microfluidic platforms. More importantly, the influence of lipids on the wound healing process is examined, emphasizing their role in enhancing barrier function restoration, modulating inflammation, promoting cell proliferation, and promoting remodeling. Lipids, such as phospholipids, sphingolipids, and ceramides, play crucial roles in membrane structure, cell signaling, and tissue repair. Understanding the interplay between lipids and the wound microenvironment provides valuable insights into the development of novel therapeutic strategies for promoting efficient wound healing and tissue regeneration. This review highlights the significance of investigating skin wound healing models and elucidating the intricate involvement of lipids in the healing process, offering potential avenues for improving clinical outcomes in wound management.

Biosignatures of defective sebaceous gland activity in sebum-rich and sebum-poor skin areas in adult atopic dermatitis

Atopic dermatitis (AD) is a composite disease presenting disruption of the skin permeability barrier (SPB) in the stratum corneum (SC). Recent evidence supports derangement of the sebaceous gland (SG) activity in the AD pathomechanisms. The objective of this study was to delineate profiles of both sebaceous and epidermal lipids and of aminoacids from SG-rich (SGR) and SG-poor (SGP) areas in AD. Both sebum and SC were sampled from SGR areas, while SC was sampled also from SGP areas in 54 adult patients with AD, consisting of 34 and 20 subjects, respectively with and without clinical involvement of face, and in 44 age and sex-matched controls. Skin biophysics were assessed in all sampling sites. Disruption of the SBP was found to be associated with dysregulated lipidome. Abundance of sapienate and lignocerate, representing, respectively, sebum and the SC type lipids, were decreased in sebum and SC from both SGR and SGP areas. Analogously, squalene was significantly diminished in AD, regardless the site. Extent of lipid derangement in SGR areas was correlated with the AD severity. The abundance of aminoacids in the SC from SGR areas was altered more than that determined in SGP areas. Several gender-related differences were found in both controls and AD subgroups. In conclusion, the SG activity was differently compromised in adult females and males with AD, in both SGR and SGP areas. In AD, alterations in the aminoacidome profiles were apparent in the SGR areas. Lipid signatures in association with aminoacidome and skin physical properties may serve the definition of phenotype clusters that associate with AD severity and gender.

A fast and non-invasive artificial intelligence olfactory-like system that aids diagnosis of Parkinson's disease

BACKGROUND AND PURPOSE

Several previous studies have shown that skin sebum analysis can be used to diagnose Parkinson's disease (PD). The aim of this study was to develop a portable artificial intelligence olfactory-like (AIO) system based on gas chromatographic analysis of the volatile organic compounds (VOCs) in patient sebum and explore its application value in the diagnosis of PD.

METHODS

The skin VOCs from 121 PD patients and 129 healthy controls were analyzed using the AIO system and three classic machine learning models were established, including the gradient boosting decision tree (GBDT), random forest and extreme gradient boosting, to assist the diagnosis of PD and predict its severity.

RESULTS

A 20-s time series of AIO system data were collected from each participant. The VOC peaks at a large number of time points roughly concentrated around 5-12 s were significantly higher in PD subjects. The gradient boosting decision tree model showed the best ability to differentiate PD from healthy controls, yielding a sensitivity of 83.33% and a specificity of 84.00%. However, the system failed to predict PD progression scored by Hoehn-Yahr stage.

CONCLUSIONS

This study provides a fast, low-cost and non-invasive method to distinguish PD patients from healthy controls. Furthermore, our study also indicates abnormal sebaceous gland secretion in PD patients, providing new evidence for exploring the pathogenesis of PD.

Advancements in Skin-Mediated Drug Delivery: Mechanisms, Techniques, and Applications

Skin-mediated drug delivery methods currently are receiving significant attention as a promising approach for the enhanced delivery of drugs through the skin. Skin-mediated drug delivery offers the potential to overcome the limitations of traditional drug delivery methods, including oral administration and intravenous injection. The challenges associated with drug permeation through layers of skin, which act as a major barrier, are explored, and strategies to overcome these limitations are discussed in detail. This review categorizes skin-mediated drug delivery methods based on the means of increasing drug permeation, and it provides a comprehensive overview of the mechanisms and techniques associated with these methods. In addition, recent advancements in the application of skin-mediated drug delivery are presented. The review also outlines the limitations of ongoing research and suggests future perspectives of studies regarding the skin-mediated delivery of drugs.

Spatial transcriptomics reveals altered lipid metabolism and inflammation-related gene expression of sebaceous glands in psoriasis and atopic dermatitis

Sebaceous glands drive acne, however, their role in other inflammatory skin diseases remains unclear. To shed light on their potential contribution to disease development, we investigated the spatial transcriptome of sebaceous glands in psoriasis and atopic dermatitis patients across lesional and non-lesional human skin samples. Both atopic dermatitis and psoriasis sebaceous glands expressed genes encoding key proteins for lipid metabolism and transport such as ALOX15B, APOC1, FABP7, FADS1/2, FASN, PPARG, and RARRES1. Also, inflammation-related SAA1 was identified as a common spatially variable gene. In atopic dermatitis, genes mainly related to lipid metabolism (e.g. ACAD8, FADS6, or EBP) as well as disease-specific genes, i.e., Th2 inflammation-related lipid-regulating HSD3B1 were differentially expressed. On the contrary, in psoriasis, more inflammation-related spatially variable genes (e.g. SERPINF1, FKBP5, IFIT1/3, DDX58) were identified. Other psoriasis-specific enriched pathways included lipid metabolism (e.g. ACOT4, S1PR3), keratinization (e.g. LCE5A, KRT5/7/16), neutrophil degranulation, and antimicrobial peptides (e.g. LTF, DEFB4A, S100A7-9). In conclusion, our results show that sebaceous glands contribute to skin homeostasis with a cell type-specific lipid metabolism, which is influenced by the inflammatory microenvironment. These findings further support that sebaceous glands are not bystanders in inflammatory skin diseases, but can actively and differentially modulate inflammation in a disease-specific manner.

The heterogeneity and complexity of skin surface lipids in human skin health and disease

The outermost epidermal layer of the skin, the stratum corneum, is not simply a barrier that safeguards skin integrity from external insults and invaders, it is also a delicately integrated interface composed of firm, essentially dead corneocytes and a distinctive lipid matrix. Together, the stratum corneum lipid matrix and sebum lipids derived from sebaceous glands give rise to a remarkably complex but quite unique blend of skin surface lipids that demonstrates tremendous heterogeneity and provides the skin with its indispensable protective coating. The stratum corneum lipid matrix is composed primarily of three major lipid classes: ceramides, non-esterified fatty acids and cholesterol, whereas sebum is a waxy mixture predominantly composed of acylglycerols, wax esters, non-esterified fatty acids, squalene, cholesterol and cholesterol esters. The balance of these skin surface lipids in terms of their relative abundance, composition, molecular organisation and dynamics, and their intricate interactions play a crucial role in the maintenance of healthy skin. For that reason, even minuscule alterations in skin surface lipid properties or overall lipid profile have been implicated in the aetiology of many common skin diseases including atopic dermatitis, psoriasis, xerosis, ichthyosis and acne. Novel lipid-based interventions aimed at correcting the skin surface lipid abnormalities have the potential to repair skin barrier integrity and the symptoms associated with such skin diseases, even though the exact mechanisms of lipid restoration remain elusive.

Thymic stromal lymphopoietin induces IL-4/IL-13 from T cells to promote sebum secretion and adipose loss

BACKGROUND

The cytokine TSLP promotes type 2 immune responses and can induce adipose loss by stimulating lipid loss from the skin through sebum secretion by sebaceous glands, which enhances the skin barrier. However, the mechanism by which TSLP upregulates sebaceous gland function is unknown.

OBJECTIVES

This study investigated the mechanism by which TSLP stimulates sebum secretion and adipose loss.

METHODS

RNA-sequencing analysis was performed on sebaceous glands isolated by laser capture microdissection and single-cell RNA-sequencing analysis was performed on sorted skin T cells. Sebocyte function was analyzed by histological analysis and sebum secretion in vivo and by measuring lipogenesis and proliferation in vitro.

RESULTS

This study found that TSLP sequentially stimulated the expression of lipogenesis genes followed by cell death genes in sebaceous glands to induce holocrine secretion of sebum. TSLP did not affect sebaceous gland activity directly. Rather, single-cell RNA-sequencing revealed that TSLP recruited distinct T-cell clusters that produce IL-4 and IL-13, which were necessary for TSLP-induced adipose loss and sebum secretion. Moreover, IL-13 was sufficient to cause sebum secretion and adipose loss in vivo and to induce lipogenesis and proliferation of a human sebocyte cell line in vitro.

CONCLUSIONS

This study proposes that TSLP stimulates T cells to deliver IL-4 and IL-13 to sebaceous glands, which enhances sebaceous gland function, turnover, and subsequent adipose loss.

A review of sebum in mammals in relation to skin diseases, skin function, and the skin microbiome

Diseases vary among and within species but the causes of this variation can be unclear. Immune responses are an important driver of disease variation, but mechanisms on how the body resists pathogen establishment before activation of immune responses are understudied. Skin surfaces of mammals are the first line of defense against abiotic stressors and pathogens, and skin attributes such as pH, microbiomes, and lipids influence disease outcomes. Sebaceous glands produce sebum composed of multiple types of lipids with species-specific compositions. Sebum affects skin barrier function by contributing to minimizing water loss, supporting thermoregulation, protecting against pathogens, and preventing UV-induced damage. Sebum also affects skin microbiome composition both via its antimicrobial properties, and by providing potential nutrient sources. Intra- and interspecific variation in sebum composition influences skin disease outcomes in humans and domestic mammal species but is not well-characterized in wildlife. We synthesized knowledge on sebum function in mammals in relation to skin diseases and the skin microbiome. We found that sebum composition was described for only 29 live, wild mammalian species. Sebum is important in dermatophilosis, various forms of dermatitis, demodicosis, and potentially white-nose syndrome. Sebum composition likely affects disease susceptibility, as lipid components can have antimicrobial functions against specific pathogens. It is unclear why sebum composition is species-specific, but both phylogeny and environmental effects may drive differences. Our review illustrates the role of mammal sebum function and influence on skin microbes in the context of skin diseases, providing a baseline for future studies to elucidate mechanisms of disease resistance beyond immune responses.

Investigating material basis and molecular mechanism of Qing Cuo formula in the treatment of acne based on animal experiments, UPLC-LTQ-Orbitrap-MS and network pharmacology

CONTEXT

Qing Cuo Formula (QCF) is a traditional Chinese medicine for treating acne, but its active compounds and molecular mechanisms are unclear.

OBJECTIVE

To investigate the material basis and molecular mechanism of QCF.

MATERIALS AND METHODS

In vivo experiments were conducted on 60 male golden hamsters with damp-heat acne, with a blank group, a spironolactone group and 3 QCF administration groups (given high, medium and low doses) over a 30-day period. Serum androgen and inflammatory cytokine levels were tested by ELISA. In vitro, chemical compositions of QCF were investigated by UPLC-LTQ-Orbitrap-MS. Network pharmacology approaches were used to analyse the protein-protein interaction (PPI) network and QCF active compounds-intersection targets-acne network. GO enrichment and KEGG pathway analysis was conducted subsequently.

RESULTS

Low-dose QCF group (11.4 g/kg/day) showed significantly reduced levels of serum T (4.94 ± 0.36; 5.51 ± 0.36 ng/mL), DHT (6.67 ± 0.61; 8.09 ± 0.59 nmol/L), E2 (209.01 ± 20.92; 237.08 ± 13.94 pg/mL), IL-1α (36.84 ± 3.23; 44.07 ± 4.00 pg/mL) and FFA (128.32 ± 10.94; 148.00 ± 12.12 µmol/L) compared to the blank group (p < 0.05). In vitro experiments identified 75 compounds in QCF decoction, with 27 active compounds absorbed in serum. Network pharmacology identified 6 active components connecting 17 targets. GO enrichment and KEGG pathway analysis indicated that QCF's anti-acne targets mainly regulate extracellular matrix function, inflammatory processes, immune response and endocrine function.

CONCLUSIONS

This study provides evidence of the molecular mechanism and material basis of QCF in treating androgen-related damp-heat acne, paving the way for further research on its potential in treating other conditions related to damp-heat constitution.

Mitochondrial dynamics and metabolism across skin cells: implications for skin homeostasis and aging

Aging of human skin is a complex process leading to a decline in homeostasis and regenerative potential of this tissue. Mitochondria are important cell organelles that have a crucial role in several cellular mechanisms such as energy production and free radical maintenance. However, mitochondrial metabolism as well as processes of mitochondrial dynamics, biogenesis, and degradation varies considerably among the different types of cells that populate the skin. Disturbed mitochondrial function is known to promote aging and inflammation of the skin, leading to impairment of physiological skin function and the onset of skin pathologies. In this review, we discuss the essential role of mitochondria in different skin cell types and how impairment of mitochondrial morphology, physiology, and metabolism in each of these cellular compartments of the skin contributes to the process of skin aging.

Are the Cutaneous Microbiota a Guardian of the Skin's Physical Barrier? The Intricate Relationship between Skin Microbes and Barrier Integrity

The skin is a tightly regulated, balanced interface that maintains our integrity through a complex barrier comprising physical or mechanical, chemical, microbiological, and immunological components. The skin's microbiota affect various properties, one of which is the establishment and maintenance of the physical barrier. This is achieved by influencing multiple processes, including keratinocyte differentiation, stratum corneum formation, and regulation of intercellular contacts. In this review, we summarize the potential contribution of Cutibacterium acnes to these events and outline the contribution of bacterially induced barrier defects to the pathogenesis of acne vulgaris. With the combined effects of a Westernized lifestyle, microbial dysbiosis, epithelial barrier defects, and inflammation, the development of acne is very similar to that of several other multifactorial diseases of barrier organs (e.g., inflammatory bowel disease, celiac disease, asthma, atopic dermatitis, and chronic rhinosinusitis). Therefore, the management of acne requires a complex approach, which should be taken into account when designing novel treatments that address not only the inflammatory and microbial components but also the maintenance and strengthening of the cutaneous physical barrier.

In vitro acne disease model from inertial focusing effect for studying the interactions between sebocyte glands and macrophages

Acne is one of the most widespread skin diseases. The acne mechanism is intricate, involving interactions between different types of cells (i.e., sebocytes and macrophages). One of the challenges in studying the mechanism of acne is that current in vitro culture methods cannot reflect the 3D cellular environment in the tissue, including inflammatory stimuli and cellular interactions especially the interactions between sebocytes and immune cells. To solve this issue, we generated an in vitro acne disease model consisting of 3D artificial sebocyte glands and macrophages through the inertial focusing effect method. Using this model, we produced a controllable inflammatory environment similar to the acne pathogenetic process in the skin. The 3D artificial sebocyte glands and macrophages can be separated for analyzing each cell type, assisting the in-depth understanding of the acne mechanism. This study indicates that proinflammatory macrophages promote lipid accumulation and induce oxidative stress in sebocyte glands. Additionally, in an inflammatory environment, sebocyte glands induce macrophage polarization into the M1 phenotype. Employing this model for drug screening, we also demonstrated that, cannabidiol (CBD), a clinically investigated drug, is effective in restoring lipid accumulation, oxidative stress, inflammatory cytokines and macrophage polarization in the acne disease.

Insights into acne and the skin barrier: Optimizing treatment regimens with ceramide-containing skincare

INTRODUCTION

Acne is a common, complex, multifactorial inflammatory skin disease associated with epidermal barrier dysfunction. Beginning in childhood, acne affects many adolescents and adults. Acne is associated with lower self-esteem, anxiety, and depression and may cause scars and pigmentary sequelae. The review explores the relationships between acne and the skin barrier function and discusses nuances in the prevention, treatment, and maintenance of acne and its impact on the skin barrier.

METHODS

The advisors' previous publications addressed prescription and nonprescription pediatric acne treatment and skincare using cleansers, moisturizers, and a practical algorithm for treatment and maintenance, including skincare recommendations for pediatric acne patients and an algorithm for skin of color patients with acne. Before the meeting, literature was culled on the relationship between the skin barrier and acne and current best practices in acne, addressing prescription and nonprescription acne products and skincare as monotherapy, adjunctive, and maintenance treatment.

RESULTS

After discussing 13 draft statements, the advisors applied the selected literature and drew from their clinical knowledge and experience, and agreed on five statements. The follicular epithelial barrier is directly involved with changes that occur during both comedogenesis and in stages of inflammation, especially with follicular rupture compromising the barrier's integrity. In acne-affected skin, sebaceous glands are larger, sebum excretion and filaggrin expression higher, and stratum corneum lipids are reduced. Educating patients and clinicians about inflammation's central role in acne and measures to reduce inflammation is essential. Skin irritation and xerosis from acne and treatments lead to poor treatment adherence. A skincare regimen should be included in the acne prevention, treatment, and maintenance care regimen and should be ongoing. Maintenance treatment with topical agents and skincare using gentle ceramide-containing cleansers and moisturizers is a recommended strategy after successfully controlling the disease.

CONCLUSIONS

Epidermal barrier dysfunction contributes to acne exacerbation. Using the appropriate treatment and skincare helps to minimize irritation and inflammation, enhance treatment adherence, and improve patient outcomes.

Skin properties associated with skin tears in older adults: A case-control study

BACKGROUND

The world population is growing rapidly and skin problems such as skin tears (STs) are more common in aging skin due to changes in the epidermis and dermis. Identification of ageing related skin properties, which are risk factors for STs, is essential for the development of ST prevention protocols.

OBJECTIVE

The aim of this study was to reveal the skin properties related to epidermal function and dermal associated with STs.

MATERIAL AND METHODS

A prospective case-control study was conducted with a sample of 36 older adults, 18 participants with ST and 18 participants without ST, in two elderly care centers. Tewameter TM 210 was used to measure transepidermal water loss, the Sebumeter SM810 was used to measure sebum, and Cutometer Dual MPA 580 was used to measure skin viscoelasticity (R0-R9). The differences of skin properties between groups were analyzed using the independent t-test and Mann-Whitney U test.

RESULTS

The case group had a mean age of 77,17 ± 9,7 and the control group had a mean age of 75,33 ± 6,8. It was determined that there were more ecchymosis (p < 0.000), hematoma (p = 0.008), and ST history (p = 0.001) in the case group. Older adults in the case group were more frail than the control group (p = 0.044). Regarding the score of the skin properties, the case group showed that the TEWL levels of the older adults in the case group were lower (p = 0.031) compared to the control groups. There was a significant difference between the groups and R0, R2, R5, and R7. While R0 was higher in the case group, R2, R5, and R7 were lower than the control group.

CONCLUSION

Older adults with ST showed differences in skin properties compared to those without ST, especially transepidermal water loss, and viscoelasticity (R0, R2, R5, R7). The results of this study suggest that some changes in skin properties may be a risk factor for STs.

Treatment of mild to severe acne with 1726 nm laser: A safe alternative to traditional acne therapies

INTRODUCTION

Acne is the most common reason for dermatology consultation in adolescents and young adults. Consultation is often delayed despite unsuccessful self-treatment. Postponing effective treatment places acne sufferers at higher risk for permanent acne scars and post-inflammatory pigment changes.

AIM

This review discusses clinical challenges with present therapeutic options for acne treatment and the role of a 1726 nm laser for acne.

METHODS

Current acne treatment guidelines were reviewed. A literature review was conducted for trials of light-based acne therapy. The selectivity of previous light-based therapies was reviewed.

RESULTS

Available acne therapy is effective, but treatment-related side effects are common. Acne treatment guidelines do not include recommendations for light-based treatments. Different types of light-based treatments have been tried but until now no wavelength specifically targeted sebaceous glands.

CONCLUSION

The 1726 nm laser is safe and effective for treating mild to severe acne in all Fitzpatrick skin types. Acne resolution is apparent within the first month and improves for up to 2 years beyond treatment.

Distinct mechanisms for sebaceous gland self-renewal and regeneration provide durability in response to injury

Sebaceous glands (SGs) release oils that protect our skin, but how these glands respond to injury has not been previously examined. Here, we report that SGs are largely self-renewed by dedicated stem cell pools during homeostasis. Using targeted single-cell RNA sequencing, we uncovered both direct and indirect paths by which resident SG progenitors ordinarily differentiate into sebocytes, including transit through a Krt5+PPARγ+ transitional basal cell state. Upon skin injury, however, SG progenitors depart their niche, reepithelialize the wound, and are replaced by hair-follicle-derived stem cells. Furthermore, following targeted genetic ablation of >99% of SGs from dorsal skin, these glands unexpectedly regenerate within weeks. This regenerative process is mediated by alternative stem cells originating from the hair follicle bulge, is dependent upon FGFR2 signaling, and can be accelerated by inducing hair growth. Altogether, our studies demonstrate that stem cell plasticity promotes SG durability following injury.

Bioprospecting the Skin Microbiome: Advances in Therapeutics and Personal Care Products

Bioprospecting is the discovery and exploration of biological diversity found within organisms, genetic elements or produced compounds with prospective commercial or therapeutic applications. The human skin is an ecological niche which harbours a rich and compositional diversity microbiome stemming from the multifactorial interactions between the host and microbiota facilitated by exploitable effector compounds. Advances in the understanding of microbial colonisation mechanisms alongside species and strain interactions have revealed a novel chemical and biological understanding which displays applicative potential. Studies elucidating the organismal interfaces and concomitant understanding of the central processes of skin biology have begun to unravel a potential wealth of molecules which can exploited for their proposed functions. A variety of skin-microbiome-derived compounds display prospective therapeutic applications, ranging from antioncogenic agents relevant in skin cancer therapy to treatment strategies for antimicrobial-resistant bacterial and fungal infections. Considerable opportunities have emerged for the translation to personal care products, such as topical agents to mitigate various skin conditions such as acne and eczema. Adjacent compound developments have focused on cosmetic applications such as reducing skin ageing and its associated changes to skin properties and the microbiome. The skin microbiome contains a wealth of prospective compounds with therapeutic and commercial applications; however, considerable work is required for the translation of in vitro findings to relevant in vivo models to ensure translatability.

Linoleic Acid Induced Changes in SZ95 Sebocytes-Comparison with Palmitic Acid and Arachidonic Acid

Linoleic acid (LA) is an essential omega-6 polyunsaturated fatty acid (PUFA) derived from the diet. Sebocytes, whose primary role is to moisturise the skin, process free fatty acids (FFAs) to produce the lipid-rich sebum. Importantly, like other sebum components such as palmitic acid (PA), LA and its derivative arachidonic acid (AA) are known to modulate sebocyte functions. Given the different roles of PA, LA and AA in skin biology, the aim of this study was to assess the specificity of sebocytes for LA and to dissect the different roles of LA and AA in regulating sebocyte functions. Using RNA sequencing, we confirmed that gene expression changes in LA-treated sebocytes were largely distinct from those induced by PA. LA, but not AA, regulated the expression of genes related to cholesterol biosynthesis, androgen and nuclear receptor signalling, keratinisation, lipid homeostasis and differentiation. In contrast, a set of mostly down-regulated genes involved in lipid metabolism and immune functions overlapped in LA- and AA-treated sebocytes. Lipidomic analyses revealed that the changes in the lipid profile of LA-treated sebocytes were more pronounced than those of AA-treated sebocytes, suggesting that LA may serve not only as a precursor of AA but also as a potent regulator of sebaceous lipogenesis, which may not only influence the gene expression profile but also have further specific biological relevance. In conclusion, we have shown that sebocytes are able to respond selectively to different lipid stimuli and that LA-induced effects can be both AA-dependent and independent. Our findings allow for the consideration of LA application in the therapy of sebaceous gland-associated inflammatory skin diseases such as acne, where lipid modulation and selective targeting of AA metabolism are potential treatment options.

The Role of Sirtuins in the Pathogenesis of Psoriasis

Psoriasis is the most common chronic inflammatory skin disease with a genetic basis. It is characterised by keratinocyte hyperproliferation, parakeratosis and inflammatory cell infiltration. Psoriasis negatively affects a patient's physical and emotional quality of life. Sirtuins (SIRTs; silent information regulators) are an evolutionarily conserved group of enzymes involved in the post-translational modification of proteins, including deacetylation, polyADP-ribosylation, demalonylation and lipoamidation. SIRTs are involved in a number of cellular pathways related to ageing, inflammation, oxidative stress, epigenetics, tumorigenesis, the cell cycle, DNA repair and cell proliferation, positioning them as an essential component in the pathogenesis of many diseases, including psoriasis. Activation of SIRT1 counteracts oxidative-stress-induced damage by inhibiting the mitogen-activated protein kinases (MAPK), nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and signal transducer and activator of transcription 3 (STAT3) pathways and may mitigate pathological events in psoriasis. There is a significant reduction in the expression of SIRT1, SIRT2, SIRT3, SIRT4 and SIRT5 and an increase in the expression of SIRT6 and SIRT7 in psoriasis. The aim of the review is to draw the attention of physicians and scientists to the importance of SIRTs in dermatology and to provide a basis and impetus for future discussions, research and pharmacological discoveries to modulate SIRT activity. In light of the analysis of the mode of action of SIRTs in psoriasis, SIRT1-SIRT5 agonists and SIRT6 and SIRT7 inhibitors may represent new therapeutic options for the treatment of psoriasis.

Effects of Moringa oleifera Seed Oil on Cultured Human Sebocytes In Vitro and Comparison with Other Oil Types

The seeds of Moringa oleifera (horseradish tree) contain about 40% of one of the most stable vegetable oils (Moringa seed oil). Therefore, the effects of Moringa seed oil on human SZ95 sebocytes were investigated and were compared with other vegetable oils. Immortalized human SZ95 sebocytes were treated with Moringa seed oil, olive oil, sunflower oil, linoleic acid and oleic acid. Lipid droplets were visualized by Nile Red fluorescence, cytokine secretion via cytokine antibody array, cell viability with calcein-AM fluorescence, cell proliferation by real-time cell analysis, and fatty acids were determined by gas chromatography. Statistical analysis was performed by the Wilcoxon matched-pairs signed-rank test, the Kruskal-Wallis test and Dunn's multiple comparison test. The vegetable oils tested stimulated sebaceous lipogenesis in a concentration-dependent manner. The pattern of lipogenesis induced by Moringa seed oil and olive oil was comparable to lipogenesis stimulated by oleic acid with also similar fatty acid secretion and cell proliferation patterns. Sunflower oil induced the strongest lipogenesis among the tested oils and fatty acids. There were also differences in cytokine secretion, induced by treatment with different oils. Moringa seed oil and olive oil, but not sunflower oil, reduced the secretion of pro-inflammatory cytokines, in comparison to untreated cells, and exhibited a low n-6/n-3 index. The anti-inflammatory oleic acid detected in Moringa seed oil probably contributed to its low levels of pro-inflammatory cytokine secretion and induction of cell death. In conclusion, Moringa seed oil seems to concentrate several desired oil properties on sebocytes, such as high content level of the anti-inflammatory fatty acid oleic acid, induction of similar cell proliferation and lipogenesis patterns compared with oleic acid, lipogenesis with a low n-6/n-3 index and inhibition of secretion of pro-inflammatory cytokines. These properties characterize Moringa seed oil as an interesting nutrient and a promising ingredient in skin care products.

Distinct mechanisms for sebaceous gland self-renewal and regeneration provide durability in response to injury

Sebaceous glands (SGs) release oils that protect our skin, but how these glands respond to injury has not been previously examined. Here, we report that SGs are largely self-renewed by dedicated stem cell pools during homeostasis. Using targeted single cell RNA-sequencing, we uncovered both direct and indirect paths by which these resident SG progenitors ordinarily differentiate into sebocytes, including transit through a PPARγ+Krt5+ transitional cell state. Upon skin injury, however, SG progenitors depart their niche, reepithelialize the wound, and are replaced by hair follicle-derived stem cells. Furthermore, following targeted genetic ablation of >99% of SGs from dorsal skin, these glands unexpectedly regenerate within weeks. This regenerative process is mediated by alternative stem cells originating from the hair follicle bulge, is dependent upon FGFR signaling, and can be accelerated by inducing hair growth. Altogether, our studies demonstrate that stem cell plasticity promotes SG durability following injury.

A comparison of the natural and groomed fingermark lipid composition of different donors using GC/MS

The lipid composition of natural fingermarks was studied and compared with the composition of groomed residue. Approximately 100 specimens were collected from 6 donors over three sessions (in October, December and July) and analysed using gas chromatography / mass spectrometry (GC/MS). The measured lipid content was generally lower and more variable in natural fingermarks than in groomed fingermarks. Some significant variability was noticed. Relative standard deviations were the highest between donors (generally above 100%) but were also relatively high within donor within a session (from 21% to 80%) and between sessions (from 34% to 126%). The fingermarks from one of the donors generally contained higher relative amounts of lipids in both groomed and natural residue compared to the others. All other fingermarks led to very variable amounts and did not allow classifying the other donors as constantly "good" or "poor" donors. Squalene was the major compound in all marks, particularly in groomed specimens. A correlation between squalene, cholesterol, myristic acid, palmitoleic acid, stearyl palmitoleate and pentadecanoic acid was highlighted. Oleic and stearic were also correlated together but generally more in natural than groomed marks. The obtained results may be particularly useful to better understand the detection mechanisms for techniques targeting lipids and to develop artificial fingermark secretions to further support the development of detection techniques.

No skin off your back: the sampling and extraction of sebum for metabolomics

INTRODUCTION

Sebum-based metabolomics (a subset of "sebomics") is a developing field that involves the sampling, identification, and quantification of metabolites found in human sebum. Sebum is a lipid-rich oily substance secreted by the sebaceous glands onto the skin surface for skin homeostasis, lubrication, thermoregulation, and environmental protection. Interest in sebomics has grown over the last decade due to its potential for rapid analysis following non-invasive sampling for a range of clinical and environmental applications.

OBJECTIVES

To provide an overview of various sebum sampling techniques with their associated challenges. To evaluate applications of sebum for clinical research, drug monitoring, and human biomonitoring. To provide a commentary of the opportunities of using sebum as a diagnostic biofluid in the future.

METHODS

Bibliometric analyses of selected keywords regarding skin surface analysis using the Scopus search engine from 1960 to 2022 was performed on 12th January 2023. The published literature was compartmentalised based on what the work contributed to in the following areas: the understanding about sebum, its composition, the analytical technologies used, or the purpose of use of sebum. The findings were summarised in this review.

RESULTS

Historically, about 15 methods of sampling have been used for sebum collection. The sample preparation approaches vary depending on the analytes of interest and are summarised. The use of sebum is not limited to just skin diseases or drug monitoring but also demonstrated for other systemic disease. Most of the work carried out for untargeted analysis of metabolites associated with sebum has been in the recent two decades.

CONCLUSION

Sebum has a huge potential beyond skin research and understanding how one's physiological state affects or reflects on the skin metabolome via the sebaceous glands itself or by interactions with sebaceous secretion, will open doors for simpler biomonitoring. Sebum acts as a sink to environmental metabolites and has applications awaiting to be explored, such as biosecurity, cross-border migration, localised exposure to harmful substances, and high-throughput population screening. These applications will be possible with rapid advances in volatile headspace and lipidomics method development as well as the ability of the metabolomics community to annotate unknown species better. A key issue with skin surface analysis that remains unsolved is attributing the source of the metabolites found on the skin surface before meaningful biological interpretation.

Desaturation of sebaceous-type saturated fatty acids through the SCD1 and the FADS2 pathways impacts lipid neosynthesis and inflammatory response in sebocytes in culture

Sebum is a lipid-rich mixture secreted by the sebaceous gland (SG) onto the skin surface. By penetrating through the epidermis, sebum may be involved in the regulation of epidermal and dermal cells in both healthy and diseased skin conditions. Saturated and monounsaturated fatty acids (FAs), found as free FAs (FFAs) and in bound form in neutral lipids, are essential constituents of sebum and key players of the inflammatory processes occurring in the pilosebaceous unit in acne-prone skin. Little is known on the interplay among uptake of saturated FFAs, their biotransformation, and induction of proinflammatory cytokines in sebocytes. In the human SG, palmitate (C16:0) is the precursor of sapienate (C16:1n-10) formed by insertion of a double bond (DB) at the Δ6 position catalysed by the fatty acid desaturase 2 (FADS2) enzyme. Conversely, palmitoleate (C16:1n-7) is formed by insertion of a DB at the Δ9 position catalysed by the stearoyl coenzyme A desaturase 1 (SCD1) enzyme. Other FFAs processed in the SG, also undergo these main desaturation pathways. We investigated lipogenesis and release of IL-6 and IL-8 pro-inflammatory cytokines in SZ95 sebocytes in vitro after treatment with saturated FFAs, that is, C16:0, margarate (C17:0), and stearate (C18:0) with or without specific inhibitors of SCD1 and FADS2 desaturase enzymes, and a drug with mixed inhibitory effects on FADS1 and FADS2 activities. C16:0 underwent extended desaturation through both SCD1 and FADS2 catalysed pathways and displayed the strongest lipoinflammatory effects. Inhibition of desaturation pathways proved to enhance lipoinflammation induced by SFAs in SZ95 sebocytes. Palmitate (C16:0), margarate (C17:0), and stearate (C18:0) are saturated fatty acids that induce different arrays of neutral lipids (triglycerides) and dissimilar grades of inflammation in sebocytes.

The epidermal lipid barrier in microbiome-skin interaction

The corneocyte layers forming the upper surface of mammalian skin are embedded in a lamellar-membrane matrix which repels harmful molecules while retaining solutes from subcutaneous tissues. Only certain bacterial and fungal taxa colonize skin surfaces. They have ways to use epidermal lipids as nutrients while resisting antimicrobial fatty acids. Skin microorganisms release lipophilic microbe-associated molecular pattern (MAMP) molecules which are largely retained by the epidermal lipid barrier. Skin barrier defects, as in atopic dermatitis, impair lamellar-membrane integrity, resulting in altered skin microbiomes, which then include the pathogen Staphylococcus aureus. The resulting increased penetration of MAMPs and toxins promotes skin inflammation. Elucidating how microorganisms manipulate the epidermal lipid barrier will be key for better ways of preventing inflammatory skin disorders.

Insulin Resistance and Acne: The Role of Metformin as Alternative Therapy in Men

The association between acne and insulin resistance has not been investigated as thoroughly in males as it has been in women, despite the fact that in adult men, acne prevalence has grown. On the face, sebaceous glands produce and secrete sebum, which lubricates the skin and protects it from friction. Metformin, an insulin-sensitizing medication, may modify the association between acne vulgaris and insulin resistance (IR). Individuals with IR, metabolic syndrome or with impaired glucose tolerance are sometimes treated 'off label' with Metformin. In these conditions, IR may be a leading factor in the pathogenesis of acne, and in men, Metformin treatment may reduce the Global Acne Grading System (GAGS) score by enhancing insulin sensitivity. However, additional clinical studies are required to corroborate these assumptions.

Skin Microbiome, Metabolome and Skin Phenome, from the Perspectives of Skin as an Ecosystem

Skin is a complex ecosystem colonized by millions of microorganisms, including bacteria, fungi, and viruses. Skin microbiota is believed to exert critical functions in maintaining host skin health. Profiling the structure of skin microbial community is the first step to overview the ecosystem. However, the community composition is highly individualized and extremely complex. To explore the fundamental factors driving the complexity of the ecosystem, namely the selection pressures, we review the present studies on skin microbiome from the perspectives of ecology. This review summarizes the following: (1) the composition of substances/nutrients in the cutaneous ecological environment that are derived from the host and the environment, highlighting their proposed function on skin microbiota; (2) the features of dominant skin commensals to occupy ecological niches, through self-adaptation and microbe-microbe interactions; (3) how skin microbes, by their structures or bioactive molecules, reshape host skin phenotypes, including skin immunity, maintenance of skin physiology such as pH and hydration, ultraviolet (UV) protection, odor production, and wound healing. This review aims to re-examine the host-microbe interactions from the ecological perspectives and hopefully to give new inspiration to this field.

Topical methylene blue nanoformulation for the photodynamic therapy of acne vulgaris

Acne vulgaris is a common skin disease caused by multifactorial reasons involving excessive sebum secretion and inflammation by Cutibacterium acnes (C. acnes). Various conventional therapies are available for the treatment of acne vulgaris; however, topical photodynamic therapy (PDT) has attracted much attention because of its great potential for sebum-reducing, anti-inflammatory, and antimicrobial activities. Although 5-aminolevulinic acid (ALA) has been broadly used as a photosensitizer for topical PDT, it has several limitations such as long incubation time, pain, and post-inflammatory hyperpigmentation. Here, we report a biocompatible nanoformulation consisting of methylene blue and salicylic acid (MBSD), as a potent PDT and acne therapeutics, enclosed within oleic acid. Photoactivated MBSD showed antimicrobial activity against C. acnes along with long-term stability. When 24 patients with acne were treated with MBSD and light irradiation 5 times at 1-week intervals, MBSD-based PDT exhibited a remarkable reduction in acne lesions and sebum production. In addition, the therapeutic procedure was painless and safe, without any adverse events. Therefore, MBSD is a promising topical PDT agent for biocompatible, safe, and effective acne treatment.

Sebaceous immunobiology - skin homeostasis, pathophysiology, coordination of innate immunity and inflammatory response and disease associations

This review presents several aspects of the innovative concept of sebaceous immunobiology, which summarizes the numerous activities of the sebaceous gland including its classical physiological and pathophysiological tasks, namely sebum production and the development of seborrhea and acne. Sebaceous lipids, which represent 90% of the skin surface lipids in adolescents and adults, are markedly involved in the skin barrier function and perifollicular and dermal innate immune processes, leading to inflammatory skin diseases. Innovative experimental techniques using stem cell and sebocyte models have clarified the roles of distinct stem cells in sebaceous gland physiology and sebocyte function control mechanisms. The sebaceous gland represents an integral part of the pilosebaceous unit and its status is connected to hair follicle morphogenesis. Interestingly, professional inflammatory cells contribute to sebocyte differentiation and homeostasis, whereas the regulation of sebaceous gland function by immune cells is antigen-independent. Inflammation is involved in the very earliest differentiation changes of the pilosebaceous unit in acne. Sebocytes behave as potent immune regulators, integrating into the innate immune responses of the skin. Expressing inflammatory mediators, sebocytes also contribute to the polarization of cutaneous T cells towards the Th17 phenotype. In addition, the immune response of the perifollicular infiltrate depends on factors produced by the sebaceous glands, mostly sebaceous lipids. Human sebocytes in vitro express functional pattern recognition receptors, which are likely to interact with bacteria in acne pathogenesis. Sex steroids, peroxisome proliferator-activated receptor ligands, neuropeptides, endocannabinoids and a selective apoptotic process contribute to a complex regulation of sebocyte-induced immunological reaction in numerous acquired and congenital skin diseases, including hair diseases and atopic dermatitis.

Paper Spray Ionization Ion Mobility Mass Spectrometry of Sebum Classifies Biomarker Classes for the Diagnosis of Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder, and identification of robust biomarkers to complement clinical diagnosis will accelerate treatment options. Here, we demonstrate the use of direct infusion of sebum from skin swabs using paper spray ionization coupled with ion mobility mass spectrometry (PS-IM-MS) to determine the regulation of molecular classes of lipids in sebum that are diagnostic of PD. A PS-IM-MS method for sebum samples that takes 3 min per swab was developed and optimized. The method was applied to skin swabs collected from 150 people and elucidates ∼4200 features from each subject, which were independently analyzed. The data included high molecular weight lipids (>600 Da) that differ significantly in the sebum of people with PD. Putative metabolite annotations of several lipid classes, predominantly triglycerides and larger acyl glycerides, were obtained using accurate mass, tandem mass spectrometry, and collision cross section measurements.

Inverse correlation between the expression of AMPK/SIRT1 and NAMPT in psoriatic skin: A pilot study

PURPOSE

Epidermal hyperplasia and the involvement of immune cells characterize the clinical picture of psoriasis. Among the several factors involved, attention has been focused on sirtuin 1 (SIRT1) - a deacetylase endowed with a variety of functions including the control of metabolic and inflammatory processes-, and on nicotinamide phosphoribosyltransferase (NAMPT), important for SIRT1 activation and involved in inflammatory events. The aim of the study was to analyze changes of SIRT1 and NAMPT expression in psoriatic skin.

PATIENTS AND METHODS

Samples from healthy controls and psoriatic patients were subjected to immunohistochemical analysis.

RESULTS

A strong downregulation of SIRT1 expression was observed in skin samples from psoriatic patients compared to healthy controls. This was accompanied by a parallel reduction of adenosine monophosphate-activated kinase (AMPK) expression and, more strikingly, by the disappearance of cells immunolabeled for its active, phosphorylated form (pAMPK). In both cases, analysis of the distribution of immunopositive cells revealed a shift towards reduced intensity of staining. In contrast, NAMPT expression was upregulated in psoriatic samples in line with its pro-inflammatory role. This was again more visible with an intensity-based distribution analysis that evidenced a shift towards more intensely immunostained cell populations.

CONCLUSIONS

The present data correlate in the same samples the expression of SIRT1, pAMPK/AMPK and NAMPT in psoriasis and open the way for novel pharmacological targets in the treatment of the disease.

Skin immunity: dissecting the complex biology of our body's outer barrier

Our skin contributes critically to health via its role as a barrier tissue, carefully regulating passage of key substrates while also providing defense against exogenous threats. Immunological processes are integral to almost every skin function and paramount to our ability to live symbiotically with skin commensal microbes and other environmental stimuli. While many parallels can be drawn to immunobiology at other mucosal sites, skin immunity demonstrates unique features that relate to its distinct topography, chemical composition and microbial ecology. Here we provide an overview of skin as an immune organ, with reference to the broader context of mucosal immunology. We review paradigms of innate as well as adaptive immune function and highlight how skin-specific structures such as hair follicles and sebaceous glands interact and contribute to these processes. Finally, we highlight for the mucosal immunology community a few emerging areas of interest for the skin immunity field moving forward.

A Brief Review on Factors Affecting the Tribological Interaction between Human Skin and Different Textile Materials

The application of tribology is not just limited to mechanical components of engineering systems. As a matter of fact, the understanding of friction and wear can be applied to everyday life. One of the important fields is skin tribology, as human skin interacts with various surfaces of different materials. This paper focuses on the friction behavior of the skin when in contact with the fabric and other materials in relative motion. The excessive friction at the fabric-skin interface may lead to discomfort, blistering, chafing, and pressure ulcers especially in athletes who experience higher friction due to rapid movement for an extended period. Other than understanding the fabric properties, it is equally important to understand the structure and properties of the skin to evaluate its function and interaction with the different fabric materials. The identification of the contributing factors of skin friction can help to design suitable fabric materials. An overview of skin functions and the factors that affect the friction on the skin-textile material interface are presented in this review article.

Bee Venom and Its Major Component Melittin Attenuated Cutibacterium acnes- and IGF-1-Induced Acne Vulgaris via Inactivation of Akt/mTOR/SREBP Signaling Pathway

Acne vulgaris is the most common disease of the pilosebaceous unit. The pathogenesis of this disease is complex, involving increased sebum production and perifollicular inflammation. Understanding the factors that regulate sebum production is important in identifying novel therapeutic targets for the treatment of acne. Bee Venom (BV) and melittin have multiple effects including antibacterial, antiviral, and anti-inflammatory activities in various cell types. However, the anti-lipogenic mechanisms of BV and melittin have not been elucidated. We investigated the effects of BV and melittin in models of Insulin-like growth factor-1 (IGF-1) or Cutibacterium acnes (C. acnes)-induced lipogenic skin disease. C. acnes or IGF-1 increased the expression of sterol regulatory element-binding protein-1 (SREBP-1) and proliferator-activated receptor gamma (PPAR-γ), transcription factors that regulate numerous genes involved in lipid biosynthesis through the protein kinase B (Akt)/mammalian target of rapamycin (mTOR)/SREBP signaling pathway. In this study using a C. acnes or IGF-1 stimulated lipogenic disease model, BV and melittin inhibited the increased expression of lipogenic and pro-inflammatory factor through the blockade of the Akt/mTOR/SREBP signaling pathway. This study suggests for the first time that BV and melittin could be developed as potential natural anti-acne agents with anti-lipogenesis, anti-inflammatory, and anti-C. acnes activity.

Small proline-rich proteins (SPRRs) are epidermally produced antimicrobial proteins that defend the cutaneous barrier by direct bacterial membrane disruption

Human skin functions as a physical barrier, preventing the entry of foreign pathogens while also accommodating a myriad of commensal microorganisms. A key contributor to the skin landscape is the sebaceous gland. Mice devoid of sebocytes are prone to skin infection, yet our understanding of how sebocytes function in host defense is incomplete. Here we show that the small proline-rich proteins, SPRR1 and SPRR2 are bactericidal in skin. SPRR1B and SPPR2A were induced in human sebocytes by exposure to the bacterial cell wall component lipopolysaccharide (LPS). Colonization of germ-free mice was insufficient to trigger increased SPRR expression in mouse skin, but LPS injected into mouse skin triggered the expression of the mouse SPRR orthologous genes, Sprr1a and Sprr2a, through stimulation of MYD88. Both mouse and human SPRR proteins displayed potent bactericidal activity against MRSA (methicillin-resistant Staphylococcus aureus), Pseudomonas aeruginosa and skin commensals. Thus, Sprr1a^-/-;Sprr2a^-/- mice are more susceptible to MRSA and Pseudomonas aeruginosa skin infection. Lastly, mechanistic studies demonstrate that SPRR proteins exert their bactericidal activity through binding and disruption of the bacterial membrane. Taken together, these findings provide insight into the regulation and antimicrobial function of SPRR proteins in skin and how the skin defends the host against systemic infection.

An explorative study comparing skin surface lipids in the West Highland white terrier dog with and without atopic dermatitis

Background

The skin barrier is important in the pathogenesis of atopic dermatitis and stratum corneum lipids have a critical role. Skin surface lipids have been largely overlooked but also contribute to barrier function. An untargeted approach was used to compare the skin surface lipids from atopic and non-atopic West Highland White terrier dogs (WHWT).

Objectives

The primary hypothesis was that a difference in the lipidome would exist. The secondary hypothesis was that affected and unaffected skin lipids would differ.

Animals and methods

This prospective, cross-sectional, case-controlled study included thirty-nine privately owned WHWTs. Dogs were assigned to one of four disease status groups based on strict criteria. Samples for lipid analysis were collected from the skin surface of unaffected and affected sites. Lipid analysis was by untargeted liquid chromatography/mass spectrometry and utilised lipid identification software packages. Principle component analysis (PCA) and partial least-squares discriminant analysis (sPLS-DA) statistical methods analysed the association between the relative lipid abundance and disease status and affected and unaffected skin.

Results

Samples for lipid analysis found 421 lipid soluble features of which ten lipids were positively identified. Statistical analysis could not distinguish between non-atopic and atopic dogs but did reveal a statistically significant difference in the lipid profiles from affected and non-affected skin irrespective of disease status.

Conclusions

A large array of unidentified lipids from the skin surface were found with a difference between affected and unaffected skin unrelated to disease status. Investigation into the lipidome of the skin surface is an emerging area of research with clinical and therapeutic applications.

Mammalian Epidermis: A Compendium of Lipid Functionality

Mammalian epidermis is a striking example of the role of lipids in tissue biology. In this stratified epithelium, highly specialized structures are formed that leverage the hydrophobic properties of lipids to form an impermeable barrier and protect the humid internal environment of the body from the dry outside. This is achieved through tightly regulated lipid synthesis that generates the molecular species unique to the tissue. Beyond their fundamental structural role, lipids are involved in the active protection of the body from external insults. Lipid species present on the surface of the body possess antimicrobial activity and directly contribute to shaping the commensal microbiota. Lipids belonging to a variety of classes are also involved in the signaling events that modulate the immune responses to environmental stress as well as differentiation of the epidermal keratinocytes themselves. Recently, high-resolution methods are beginning to provide evidence for the involvement of newly identified specific lipid molecules in the regulation of epidermal homeostasis. In this review we give an overview of the wide range of biological functions of mammalian epidermal lipids.

Research Techniques Made Simple: Lipidomic Analysis in Skin Research

Although lipids are crucial molecules for cell structure, metabolism, and signaling in most organs, they have additional specific functions in the skin. Lipids are required for the maintenance and regulation of the epidermal barrier, physical properties of the skin, and defense against microbes. Analysis of the lipidome-the totality of lipids-is of similar complexity to those of proteomics or other omics, with lipid structures ranging from simple, linear, to highly complex structures. In addition, the ordering and chemical modifications of lipids have consequences on their biological function, especially in the skin. Recent advances in analytic capability (usually with mass spectrometry), bioinformatic processing, and integration with other dermatological big data have allowed researchers to increasingly understand the roles of specific lipid species in skin biology. In this paper, we review the techniques used to analyze skin lipidomics and epilipidomics.

Skin pH varies among bat species and seasons and between wild and captive bats

Skin is a key aspect of the immune system in the defence against pathogens. Skin pH regulates the activity of enzymes produced both by hosts and by microbes on host skin, thus implicating pH in disease susceptibility. Skin pH varies inter- and intra-specifically and is influenced by a variety of intrinsic and extrinsic variables. Increased skin alkalinity is associated with a predisposition to cutaneous infections in humans and dogs, and inter-specific and inter-individual variation in skin pH is implicated in differential susceptibility to some skin diseases. The cutaneous pH of bats has not been characterized but is postulated to play a role in susceptibility to white-nose syndrome (WNS), a fungal infection that has decimated several Nearctic bat species. We used non-invasive probes to measure the pH of bat flight membranes in five species with differing susceptibility to WNS. Skin pH ranged from 4.67 to 8.59 and varied among bat species, geographic locations, body parts, age classes, sexes and seasons. Wild Eptesicus fuscus were consistently more acidic than wild Myotis lucifugus, Myotis leibii and Perimyotis subflavus. Juvenile bats had more acidic skin than adults during maternity season but did not differ during swarming. Male M. lucifugus were more acidic than females during maternity season, yet this trend reversed during swarming. Bat skin was more acidic in summer compared to winter, a pattern also reported in humans. Skin pH was more acidic in captive than wild E. fuscus, suggesting environmental impacts on skin pH. The pH of roosting substrates affects skin pH in captive bats and may partially explain seasonal patterns in wild bats that use different roost types across seasons. Future research on the influence of pH on microbial pathogenic factors and skin barrier function may provide valuable insights on new therapeutic targets for treating bat skin conditions.

Application of Sebum Lipidomics to Biomarkers Discovery in Neurodegenerative Diseases

Lipidomics is strategic in the discovery of biomarkers of neurodegenerative diseases (NDDs). The skin surface lipidome bears the potential to provide biomarker candidates in the detection of pathological processes occurring in distal organs. We investigated the sebum composition to search diagnostic and, possibly, prognostic, biomarkers of Alzheimer’s disease (AD) and Parkinson’s disease (PD). The observational study included 64 subjects: 20 characterized as “probable AD with documented decline”, 20 as “clinically established PD”, and 24 healthy subjects (HS) of comparable age. The analysis of sebum by GCMS and TLC retrieved the amounts (µg) of 41 free fatty acids (FFAs), 7 fatty alcohols (FOHs), vitamin E, cholesterol, squalene, and total triglycerides (TGs) and wax esters (WEs). Distributions of sebum lipids in NDDs and healthy conditions were investigated with multivariate ANOVA-simultaneous component analysis (ASCA). The deranged sebum composition associated with the PD group showed incretion of most composing lipids compared to HS, whereas only two lipid species (vitamin E and FOH14:0) were discriminant of AD samples and presented lower levels than HS sebum. Thus, sebum lipid biosynthetic pathways are differently affected in PD and AD. The characteristic sebum bio-signatures detected support the value of sebum lipidomics in the biomarkers search in NDDs.

Acne Syndromes and Mosaicism

Abnormal mosaicism is the coexistence of cells with at least two genotypes, by the time of birth, in an individual derived from a single zygote, which leads to a disease phenotype. Somatic mosaicism can be further categorized into segmental mosaicism and nonsegmental somatic mosaicism. Acne is a chronic illness characterized by inflammatory changes around and in the pilosebaceous units, commonly due to hormone- and inflammatory signaling-mediated factors. Several systemic disorders, such as congenital adrenal hyperplasia, polycystic ovarian syndrome, and seborrhoea-acne-hirsutism-androgenetic alopecia syndrome have classically been associated with acne. Autoinflammatory syndromes, including PAPA, PASH, PAPASH, PsAPASH, PsaPSASH, PASS, and SAPHO syndromes include acneiform lesions as a key manifestation. Mosaic germline mutations in the FGFR2 gene have been associated with Apert syndrome and nevus comedonicus, two illnesses that are accompanied by acneiform lesions. In this review, we summarize the concept of cutaneous mosaicism and elaborate on acne syndromes, as well as acneiform mosaicism.

Long-term effect of azelaic acid peel on sebum production in acne

Seborrhea and the associated oily skin are undoubtedly the problem of women and men around the world. The pathogenesis of acne vulgaris involves excessive activity of sebaceous glands, as well as disturbances in the composition of sebum. The aim of the study was to assess the severity of seborrhea in a group of acne vulgaris patients and to determine the effect of a 20% azelaic acid solution on the activity of sebaceous glands. Twenty seven women, aged 19-25 years, underwent a series of six treatments with the application of a 20% solution of azelaic acid to the face. The mean values of sebum level showed a decreasing tendency. On the forehead, the results were as follows-195.5 before the treatment and 162.7 2 weeks after the last treatment. Measurements of the right cheek decreased from 175.3 to 141.3 The measurements taken 3 months after the study were 151.3 on the forehead and 138.9 on the cheek. Similarly, the values determining the total number of acne lesions and the severity of the disease according to the IGA scale also changed significantly. Chemical peel with 20% azelaic acid shows long-term sebostatic action, which inhibits the formation of new acne lesions.

miR-146a modulates TLR1/2 and 4 induced inflammation and links it with proliferation and lipid production via the indirect regulation of GNG7 in human SZ95 sebocytes

Activation of Toll-like receptors (TLR) 1/2 and 4 are central in inducing inflammation in sebocytes by regulating the expression of protein coding mRNAs, however the microRNA (miRNA) profile in response to TLR activation and thus the possible role of miRNAs in modulating sebocyte functions has not been elucidated. In this work we identified miR-146a to have the highest induction in the TLR1/2 and 4 activated SZ95 sebocytes and found that its increased levels led to the down-regulation of IL-8 secretion, decreased the chemoattractant potential and stimulated the proliferation of sebocytes. Assessing the gene expression profile of SZ95 sebocytes treated with a miR-146a inhibitor, the induction of GNG7 was one of the highest, while when cells were treated with a miR-146a mimic, the expression of GNG7 was down-regulated. These findings correlated with our in situ hybridization results, that compared with control, miR-146a showed an increased, while GNG7 a decreased expression in sebaceous glands of acne samples. Further studies revealed, that when inhibiting the levels of GNG7 in SZ95 sebocytes, cells increased their lipid content and decreased their proliferation. Our findings suggest, that miR-146a could be a potential player in acne pathogenesis by regulating inflammation, inducing proliferation and, through the indirect down-regulation of GNG7, promoting the lipid production of sebocytes.

Transcriptional Differences in Lipid-Metabolizing Enzymes in Murine Sebocytes Derived from Sebaceous Glands of the Skin and Preputial Glands

Sebaceous glands are adnexal structures, which critically contribute to skin homeostasis and the establishment of a functional epidermal barrier. Sebocytes, the main cell population found within the sebaceous glands, are highly specialized lipid-producing cells. Sebaceous gland-resembling tissue structures are also found in male rodents in the form of preputial glands. Similar to sebaceous glands, they are composed of lipid-specialized sebocytes. Due to a lack of adequate organ culture models for skin sebaceous glands and the fact that preputial glands are much larger and easier to handle, previous studies used preputial glands as a model for skin sebaceous glands. Here, we compared both types of sebocytes, using a single-cell RNA sequencing approach, to unravel potential similarities and differences between the two sebocyte populations. In spite of common gene expression patterns due to general lipid-producing properties, we found significant differences in the expression levels of genes encoding enzymes involved in the biogenesis of specialized lipid classes. Specifically, genes critically involved in the mevalonate pathway, including squalene synthase, as well as the sphingolipid salvage pathway, such as ceramide synthase, (acid) sphingomyelinase or acid and alkaline ceramidases, were significantly less expressed by preputial gland sebocytes. Together, our data revealed tissue-specific sebocyte populations, indicating major developmental, functional as well as biosynthetic differences between both glands. The use of preputial glands as a surrogate model to study skin sebaceous glands is therefore limited, and major differences between both glands need to be carefully considered before planning an experiment.