The role of fatty acid elongation in epidermal structure and function

RNAseq analysis of whole zebrafish (Danio rerio) larvae revealed the main cellular biological effects of geosmin and microcystin exposure at environmentally relevant concentrations

Cyanobacterial blooms are common events that releases secondary metabolites into water posing considerable threats to the environment, wildlife, and public health. Some of these metabolites, such as microcystin, have been extensively studied and associated with harmful effects in mammals and aquatic organisms, while the biological effects of others, like geosmin, remain much less investigated. Enhancing our understanding of cyanotoxins effects on organisms is especially relevant facing the complex scenarios projected due to global warming. The aim of this study was to assess the transcriptional modulation in whole zebrafish (Danio rerio) larvae (n = 9) in response to a 7-days immersion exposure to 3 μg L-1 MCLR or 5 μg L-1 geosmin. No mortality or differences in length gain were observed in zebrafish larvae exposed to environmentally realistic doses of both cyanotoxins. The exposure to MCLR and to geosmin caused the differential expression of 164 and 172 genes respectively, being 23 upregulated by MCLR and 98 upregulated by geosmin. Among the upregulated genes, 16 were shared, while 42 were shared among the downregulated genes. Over-representation analysis identified three enriched GO terms only among the genes upregulated by geosmin: organic hydroxy compound metabolic process (1901615), small molecule biosynthetic process (0044283), and lipid metabolic process (0006629). In fact, the expression of 12 of the 13 genes directly involved in the synthesis of cholesterol from acetyl-CoA was upregulated by geosmin. A chronic upregulation of cholesterol biosynthetic pathway is linked to several diseases and metabolic disorders, including alterations in sex-related hormones. Moreover, our results indicate that geosmin and MCLR acts through different mechanisms. Geosmin does not appear to provoke short-term adverse effects as MCLR but could disrupt the endocrine system by altering the lipid and steroid metabolism.

Exploring the apoptotic effects of sericin on HCT116 cells through comprehensive nanostring transcriptomics and proteomics analysis

Sericin, a silk protein from Bombyx mori (silkworms), has many applications, including cosmetics, anti-inflammation, and anti-cancer. Sericin complexes with nanoparticles have shown promise for breast cancer cell lines. Apoptosis, a programmed cell death mechanism, stops cancer cell growth. This study found that Sericin urea extract significantly affected HCT116 cell viability (IC50 = 42.00 ± 0.002 µg/mL) and caused apoptosis in over 80% of treated cells. S-FTIR analysis showed significant changes in Sericin-treated cells' macromolecule composition, particularly in the lipid and nucleic acid areas, indicating major cellular modifications. A transcriptomics study found upregulation of the apoptotic signaling genes FASLG, TNFSF10, CASP3, CASP7, CASP8, and CASP10. Early apoptotic proteins also showed that BAD, AKT, CASP9, p53, and CASP8 were significantly upregulated. A proteomics study illuminated Sericin-treated cells' altered protein patterns. Our results show that Sericin activated the extrinsic apoptosis pathway via the caspase cascade (CASP8/10 and CASP3/7) and the death receptor pathway, involving TNFSF10 or FASLG, in HCT116 cells. Upregulation of p53 increases CASP8, which activates CASP3 and causes HCT116 cell death. This multi-omics study illuminates the molecular mechanisms of Sericin-induced apoptosis, sheds light on its potential cancer treatment applications, and helps us understand the complex relationship between silk-derived proteins and cellular processes.

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.

Circulating Sphingolipids in Insulin Resistance, Diabetes and Associated Complications

Sphingolipids play an important role in the development of diabetes, both type 1 and type 2 diabetes, as well as in the development of both micro- and macro-vascular complications. Several reviews have been published concerning the role of sphingolipids in diabetes but most of the emphasis has been on the possible mechanisms by which sphingolipids, mainly ceramides, contribute to the development of diabetes. Research on circulating levels of the different classes of sphingolipids in serum and in lipoproteins and their importance as biomarkers to predict not only the development of diabetes but also of its complications has only recently emerged and it is still in its infancy. This review summarizes the previously published literature concerning sphingolipid-mediated mechanisms involved in the development of diabetes and its complications, focusing on how circulating plasma sphingolipid levels and the relative content carried by the different lipoproteins may impact their role as possible biomarkers both in the development of diabetes and mainly in the development of diabetic complications. Further studies in this field may open new therapeutic avenues to prevent or arrest/reduce both the development of diabetes and progression of its complications.

Association of Early Clinical Response to Laser Rejuvenation of Photoaged Skin with Increased Lipid Metabolism and Restoration of Skin Barrier Function

Laser resurfacing treatments for photoaged skin have improved dramatically over the past decades, but few studies have examined the molecular mechanisms underlying differences in clinical response. Seventeen white female participants with moderate-to-severe photoaging received nonablative fractional laser treatment on the face and forearm once monthly for 6 months. Biopsies for microarray analysis were performed at baseline and 7 days after facial treatment and at baseline and 1, 7, 14, and 29 days after forearm treatment in each participant, resulting in 119 total samples. Participants were stratified into fast (n = 11) and slow (n = 6) responders on the basis of the presence of clinical improvement after the first treatment. Microarray analysis revealed the upregulation of genes associated with matrix metalloproteinases, collagen and extracellular components, TGF-β signaling, double-stranded RNA signaling, and retinoic acid synthesis after treatment that did not differ significantly between fast and slow responders. Cluster and enrichment analyses suggested significantly greater activation of lipid metabolism and keratinocyte differentiation in fast responders, who showed greater upregulation of acyltransferases, fatty acid elongases, fatty acid 2-hydroxylase, fatty acid desaturases, and specific keratins that may contribute to epidermal barrier function. These results create, to our knowledge, a previously unreported atlas of molecular changes that correlate with improvements in photoaging after laser therapy.

Staphylococcus aureus causes aberrant epidermal lipid composition and skin barrier dysfunction

BACKGROUND

Staphylococcus (S) aureus colonization is known to cause skin barrier disruption in atopic dermatitis (AD) patients. However, it has not been studied how S. aureus induces aberrant epidermal lipid composition and skin barrier dysfunction.

METHODS

Skin tape strips (STS) and swabs were obtained from 24 children with AD (6.0 ± 4.4 years) and 16 healthy children (7.0 ± 4.5 years). Lipidomic analysis of STS samples was performed by mass spectrometry. Skin levels of methicillin-sensitive and methicillin-resistant S. aureus (MSSA and MRSA) were evaluated. The effects of MSSA and MRSA were evaluated in primary human keratinocytes (HEKs) and organotypic skin cultures.

RESULTS

AD and organotypic skin colonized with MRSA significantly increased the proportion of lipid species with nonhydroxy fatty acid sphingosine ceramide with palmitic acid ([N-16:0 NS-CER], sphingomyelins [16:0-18:0 SM]), and lysophosphatidylcholines [16:0-18:0 LPC], but significantly reduced the proportion of corresponding very long-chain fatty acids (VLCFAs) species (C22-28) compared to the skin without S. aureus colonization. Significantly increased transepidermal water loss (TEWL) was found in MRSA-colonized AD skin. S. aureus indirectly through interleukin (IL)-1β, tumor necrosis factor (TNF)-α, IL-6, and IL-33 inhibited expression of fatty acid elongase enzymes (ELOVL3 and ELOVL4) in HEKs. ELOVL inhibition was more pronounced by MRSA and resulted in TEWL increase in organotypic skin.

CONCLUSION

Aberrant skin lipid profiles and barrier dysfunction are associated with S. aureus colonization in AD patients. These effects are attributed to the inhibition of ELOVLs by S. aureus-induced IL-1β, TNF-α, IL-6, and IL-33 seen in keratinocyte models and are more prominent in MRSA than MSSA.

Maternal Pyrroloquinoline Quinone Supplementation Improves Offspring Liver Bioactive Lipid Profiles throughout the Lifespan and Protects against the Development of Adult NAFLD

Maternal obesity and consumption of a high-fat diet significantly elevate risk for pediatric nonalcoholic fatty liver disease (NAFLD), affecting 10% of children in the US. Almost half of these children are diagnosed with nonalcoholic steatohepatitis (NASH), a leading etiology for liver transplant. Animal models show that signs of liver injury and perturbed lipid metabolism associated with NAFLD begin in utero; however, safe dietary therapeutics to blunt developmental programming of NAFLD are unavailable. Using a mouse model of maternal Western-style diet (WD), we previously showed that pyrroloquinoline quinone (PQQ), a potent dietary antioxidant, protected offspring of WD-fed dams from development of NAFLD and NASH. Here, we used untargeted mass spectrometry-based lipidomics to delineate lipotoxic effects of WD on offspring liver and identify lipid targets of PQQ. PQQ exposure during pregnancy altered hepatic lipid profiles of WD-exposed offspring, upregulating peroxisome proliferator-activated receptor (PPAR) α signaling and mitochondrial fatty acid oxidation to markedly attenuate triglyceride accumulation beginning in utero. Surprisingly, the abundance of very long-chain ceramides, important in promoting gut barrier and hepatic function, was significantly elevated in PQQ-treated offspring. PQQ exposure reduced the hepatic phosphatidylcholine/phosphatidylethanolamine (PC/PE) ratio in WD-fed offspring and improved glucose tolerance. Notably, levels of protective n - 3 polyunsaturated fatty acids (PUFAs) were elevated in offspring exposed to PQQ, beginning in utero, and the increase in n - 3 PUFAs persisted into adulthood. Our findings suggest that PQQ supplementation during gestation and lactation augments pathways involved in the biosynthesis of long-chain fatty acids and plays a unique role in modifying specific bioactive lipid species critical for protection against NAFLD risk in later life.

Ceramide NPs Derived from Natural Oils of Korean Traditional Plants Enhance Skin Barrier Functions and Stimulate Expressions of Genes for Epidermal Homeostasis

BACKGROUND

New ceramide (CER) NPs were prepared by linking fatty acids derived from oils of Korean traditional plants to phytosphingosine(PHS). The oils of Korean traditional plants were extracted from the seeds of Panax ginseng, Camellia sinensis, Glycine max napjakong, Glycine max seoritae and Camellia japonica as sources of diverse fatty acids AIMS: To investigate signaling bioactivities of HP-C. sinensis ceramide NP that was column purified to remove any residual PHS and to evaluate the skin barrier functions of the HP-C. sinensis ceramide NP in human skin.

METHODS

The expressions of genes related with epidermal differentiation was analyzed in vitro by qPCR. Human studies were also performed to determine the skin barrier functions with respect of TEWL and SC cohesion.

RESULTS

The HP-C. sinensis CER NP significantly enhanced the expressions of FLG, CASP14 and INV indicates that the signaling biological activities of oil-derived ceramide NPs could be different depend on the natural oils. The control ceramide, C18-CER NP had no effect on the expression of the three genes. HP-C. sinensis CER NP was selected for the in vivo human studies. Application of 0.5% HP-C. sinensis CER NP cream stimulated significantly faster recovery of a disrupted skin barrier than that of the control C18-CER NP. A significant enhancement of SC cohesion of the skin treated with 0.5% HP-C. sinensis CER NP was also observed.

CONCLUSION

Taken all together, our results clearly demonstrate that HP-C. sinensis CER NP, P. ginseng CER NP and other oil-derived CER NP could be a better choice for developing moisturizers to improve skin barrier function as they more closely mimic the endogenous CER composition of the actual human skin barrier.

Decrease of ceramides with long-chain fatty acids in psoriasis: Possible inhibitory effect of interferon gamma on chain elongation

Reportedly, decreases in fatty acid (FA) chain length of ceramide (CER) are associated with interferon-γ (IFN-γ), which shows increased expression in psoriasis. However, the underlying mechanism of this association remains unclear. Therefore, in this study, we aimed to clarify this association between FA chain length of CER, IFN-γ, and the major transcriptional factors involving psoriasis. CER profiling according to FA chain length and class was performed in murine epidermis (n = 10 BALB/c mice topically treated with imiquimod, n = 10 controls) and human stratum corneum (SC) (n = 12 psoriasis, n = 11 controls). The expression of lipid synthetic enzymes, including elongases (ELOVLs), in murine epidermis was also measured using RT-PCR. Furthermore, the association of IFN-γ with various enzymes and transcription factors involved in the generation of long-chain CERs was also investigated using in vitro keratinocyte. A significant decrease in the percentage of long-chain CERs was observed in psoriasis-like murine epidermis and human psoriatic SC. Additionally, the expression levels of ELOVL1, ELOVL4, and ceramide synthase3 (CerS3) were significantly decreased in psoriasis-like murine epidermis and IFN-γ-treated keratinocyte. There was also a significant decrease in the expression of transcriptional factors, including peroxisome proliferator-activated receptor (PPAR), in IFN-γ treated keratinocyte. Thus, it could be suggested that IFN-γ may regulate ELOVL and CerS levels by down-regulating the transcriptional factors. Additionally, given the possible involvement of PPARs or liver X receptor agonist in the CER elongation process, they may serve as potential therapeutic agents for lengthening the CER FAs in psoriasis.

HCV poly U/UC sequence-induced inflammation leads to metabolic disorders in vulvar lichen sclerosis

Multi-omics analysis reveals the elevation of HCV poly U/UC sequences, which induces abnormal inflammation and related metabolic disorder in vulvar lichen sclerosis.

Vulvar lichen sclerosis (VLS) is a dermatologic disorder that affects women worldwide. Women with VLS have white, atrophic papules on the vulva. They suffer from life-long intense pruritus. Corticosteroids are the first-line of treatments and the most effective medicines for VLS. Although VLS has been speculated as an autoimmune disease for a long time, its pathogenesis and the molecular mechanism is largely unknown. We performed a comprehensive multi-omics analysis of paired samples from VLS patients as well as healthy donors. From the RNA-seq analysis, we found that VLS is correlated to abnormal antivirus response because of the presence of Hepatitis C Virus poly U/UC sequences. Lipidomic and metabolomic analysis revealed that inflammation-induced metabolic disorders of fatty acids and glutathione were likely the reasons for pruritus, atrophy, and pigment loss in the vulva. Thus, the present study provides an initial interpretation of the pathogenesis and molecular mechanism of VLS and suggests that metabolic disorders that affect the vulva may serve as therapeutic targets for VLS.

Rearrangements of Blood and Tissue Fatty Acid Profile in Colorectal Cancer - Molecular Mechanism and Diagnostic Potential

Colorectal cancer (CRC) is often diagnosed at an advanced stage due to the invasiveness of colonoscopy; thus, non-invasive CRC diagnostics are desirable. CRC is associated with lipid alterations. We aimed to verify whether fatty acid (FA) profiles in CRC patients may serve as a potential diagnostic tool for CRC diagnosis. FA profiles were assayed by GC-MS in cancer tissue, paired normal mucosa and serum from CRC patients and healthy controls. The levels of very long FAs – VLCFAs (26:0, 28:0 and 26:1) were the most highly increased FAs in cancer tissue compared to normal colon mucosa. Moreover, these FA were present in serum of CRC patients, they were absent in the serum of healthy subjects, or present in only trace amounts. To verify if cancer cells are the source of small amounts of these VLCFAs in the serum of patients we performed experiment in HT-29 CRC cells, which proved that CRC cells can produce and release VLCFAs into the blood. Most importantly, we defined a panel of FAs that may be assayed in a single analysis that definitely distinguishes CRC patients and healthy subjects, which was confirmed by PLS-DA and multivariate ROC analysis (AUC = 0.985). This study shows that selected FA panel may serve as a diagnostic marker for CRC.

Lipid Metabolic Events Underlying the Formation of the Corneocyte Lipid Envelope

Cornified cells of the stratum corneum have a monolayer of an unusual lipid covalently attached to the outer surface. This is referred to as the corneocyte lipid envelope (CLE). It consists of a monolayer of ω-hydroxyceramides covalently attached to the outer surface of the cornified envelope. The CLE is essential for proper barrier function of the skin and is derived from linoleate-rich acylglucosylceramides synthesized in the viable epidermis. Biosynthesis of acylglucosylceramide and its conversion to the cornified envelope is complex. Acylglucosylceramide in the bounding membrane of the lamellar granule is the precursor of the CLE. The acylglucosylceramide in the limiting membrane of the lamellar granule may be oriented with the glucosyl moiety on the inside. Conversion of the acylglucosylceramide to the CLE requires removal of the glucose by action of a glucocerebrosidase. The ester-linked fatty acid may be removed by an as yet unidentified esterase, and the resulting ω-hydroxyceramide may become ester linked to the outer surface of the cornified envelope through action of transglutaminase 1. Prior to removal of ester-linked fatty acids, linoleate is oxidized to an epoxy alcohol through action of 2 lipoxygenases. This can be further oxidized to an epoxy-enone, which can spontaneously attach to the cornified envelope through Schiff's base formation. Mutations of genes coding for enzymes involved in biosynthesis of the CLE result in ichthyosis, often accompanied by neurologic dysfunction. The CLE is recognized as essential for barrier function of skin, but many questions about details of this essentiality remain. What are the relative roles of the 2 mechanisms of lipid attachment? What is the orientation of acylglucosylceramide in the bounding membrane of lamellar granules? Some evidence supports a role for CLE as a scaffold upon which intercellular lamellae unfold, but other evidence does not support this role. There is also controversial evidence for a role in stratum corneum cohesion. Evidence is presented to suggest that covalently bound ω-hydroxyceramides serve as a reservoir for free sphingosine that can serve in communicating with the viable epidermis and act as a potent broad-acting antimicrobial at the skin surface. Many questions remain.

Dietary ceramide 2-aminoethylphosphonate, a marine sphingophosphonolipid, improves skin barrier function in hairless mice

Sphingolipids are one of the major components of cell membranes and are ubiquitous in eukaryotic organisms. Ceramide 2-aminoethylphosphonate (CAEP) of marine origin is a unique and abundant sphingophosphonolipid with a C-P bond. Although molluscs such as squids and bivalves, containing CAEP, are consumed globally, the dietary efficacy of CAEP is not understood. We investigated the efficacy of marine sphingophosphonolipids by studying the effect of dietary CAEP on the improvement of the skin barrier function in hairless mice fed a diet that induces severely dry-skin condition. The disrupted skin barrier functions such as an increase in the transepidermal water loss (TEWL), a decrease in the skin hydration index, and epidermal hyperplasia were restored by CEAP dietary supplementation. Correspondingly, dietary CAEP significantly increased the content of covalently bound ω-hydroxyceramide, and the expression of its biosynthesis-related genes in the skin. These effects of dietary CAEP mimic those of dietary plant glucosylceramide. The novel observations from this study show an enhancement in the skin barrier function by dietary CAEP and the effects could be contributed by the upregulation of covalently bound ω-hydroxyceramide synthesis in the skin.

Glucocerebrosidase: Functions in and Beyond the Lysosome

Glucocerebrosidase (GCase) is a retaining β-glucosidase with acid pH optimum metabolizing the glycosphingolipid glucosylceramide (GlcCer) to ceramide and glucose. Inherited deficiency of GCase causes the lysosomal storage disorder named Gaucher disease (GD). In GCase-deficient GD patients the accumulation of GlcCer in lysosomes of tissue macrophages is prominent. Based on the above, the key function of GCase as lysosomal hydrolase is well recognized, however it has become apparent that GCase fulfills in the human body at least one other key function beyond lysosomes. Crucially, GCase generates ceramides from GlcCer molecules in the outer part of the skin, a process essential for optimal skin barrier property and survival. This review covers the functions of GCase in and beyond lysosomes and also pays attention to the increasing insight in hitherto unexpected catalytic versatility of the enzyme.

Skin of atopic dermatitis patients shows disturbed β-glucocerebrosidase and acid sphingomyelinase activity that relates to changes in stratum corneum lipid composition

Patients with Atopic Dermatitis (AD) suffer from inflamed skin and skin barrier defects. Proper formation of the outermost part of the skin, the stratum corneum (SC), is crucial for the skin barrier function. In this study we analyzed the localization and activity of lipid enzymes β-glucocerebrosidase (GBA) and acid sphingomyelinase (ASM) in the skin of AD patients and controls. Localization of both the expression and activity of GBA and ASM in the epidermis of AD patients was altered, particularly at lesional skin sites. These changes aligned with the altered SC lipid composition. More specifically, abnormal localization of GBA and ASM related to an increase in specific ceramide subclasses [AS] and [NS]. Moreover we related the localization of the enzymes to the amounts of SC ceramide subclasses and free fatty acids (FFAs). We report a correlation between altered localization of active GBA and ASM and a disturbed SC lipid composition. Localization of antimicrobial peptide beta-defensin-3 (HBD-3) and AD biomarker Thymus and Activation Regulated Chemokine (TARC) also appeared to be diverging in AD skin compared to control. This research highlights the relation between correct localization of expressed and active lipid enzymes and a normal SC lipid composition for a proper skin barrier.

Phytosphingosine Increases Biosynthesis of Phytoceramide by Uniquely Stimulating the Expression of Dihydroceramide C4-desaturase (DES2) in Cultured Human Keratinocytes

Ceramide NP is known to be the most abundant class of 12 ceramide (CER) families that form a permeability barrier in the human skin barrier. However, not many studies have been reported on the regulation of the biosynthesis of ceramide NP. Recently, it has been reported that phytosphingosine (PHS) treatment in the cultured keratinocytes (KC) notably increased the content of ceramide NP. However, the mechanism behind the PHS-induced enhancement of ceramide NP has not been elucidated. In this study, we investigated the effects of PHS on the expression of several essential genes for the biosynthesis of CER. Also, we determined the molecular mechanism behind the unique enhancement of ceramide NP upon treatment of PHS in the cultured KC. The expressions of all of the three genes (SPT, ceramide synthase 3 [CERS3], and ELOVL4) and their respective proteins were markedly increased in PHS-treated KC. In addition, the expression of the dihydroceramide C4-desaturase (DES2) responsible for conversion of dihydroceramide into ceramide NP was uniquely enhanced only by PHS treatment. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis revealed that more than 20-fold increase of ceramide NP by PHS was observed while no significant enhancement of ceramide NS and NDS was observed. This study demonstrates that PHS plays a fundamental role in strengthening the epidermal permeability barrier by stimulating the overall processes of biosynthesis of all classes of CER in epidermis. The dramatic increase of ceramide NP upon PHS treatment seemed to be the outcome of transformation of dihydroceramide and/or ceramide NS by C4-hydroxylase activity.

Glycosylated sphingolipids and progression to kidney dysfunction in type 1 diabetes

BACKGROUND

Glycosphingolipids are important components of cell membranes, modulators of cell-cell interactions and cell recognition, and have recently emerged as bioactive molecules and important players in nearly all cell biological processes. We previously have shown that decreased plasma levels of long and very long species of ceramides were able to predict the development of macroalbuminuria (MA) in type 1 diabetes.

OBJECTIVE

This study proposed to examine whether plasma glycosphingolipids could predict development of diabetic nephropathy, assessed as MA or chronic kidney disease (CKD).

METHODS

Measurement of plasma hexosylceramides (H) and lactosylceramides (L) were conducted in the Lipidomics Core Facility of our Institution in a subcohort of 432 patients from the DCCT/Epidemiology of Diabetes Interventions and Complications cohort in plasma collected at entry into the study. Inverse probability weighted Cox proportional hazards regression models were used to assess the effect of glycosphingolipids levels on the risk of developing MA (albumin excretion rate ≥300 mg/24 hours) or CKD (glomerular filtration rate <60 mL/min) over a period of 21 to 28 years.

RESULTS

Decreases of several long and very long chain lactosylceramides were significantly associated with increased risk of progression to MA but not CKD. Among the hexosylceramides, the only significant association observed was between one of its minor species C18:1-H and CKD.

CONCLUSION

Our findings showed that decreased levels of long and very long lactosylceramides were able to predict the development of MA in type 1 diabetes. This finding is similar to previous findings showing that low levels of long and very long ceramides were also able to predict development of MA in the same cohort. Further studies are needed to determine the changes in sphingolipid metabolism leading to the development of complications.

ELOVL4-Mediated Production of Very Long-Chain Ceramides Stabilizes Tight Junctions and Prevents Diabetes-Induced Retinal Vascular Permeability

Tight junctions (TJs) involve close apposition of transmembrane proteins between cells. Although TJ proteins have been studied in detail, the role of lipids is largely unknown. We addressed the role of very long-chain (VLC ≥26) ceramides in TJs using diabetes-induced loss of the blood-retinal barrier as a model. VLC fatty acids that incorporate into VLC ceramides are produced by elongase elongation of very long-chain fatty acids protein 4 (ELOVL4). ELOVL4 is significantly reduced in the diabetic retina. Overexpression of ELOVL4 significantly decreased basal permeability, inhibited vascular endothelial growth factor (VEGF)- and interleukin-1β-induced permeability, and prevented VEGF-induced decrease in occludin expression and border staining of TJ proteins ZO-1 and claudin-5. Intravitreal delivery of AAV2-hELOVL4 reduced diabetes-induced increase in vascular permeability. Ultrastructure and lipidomic analysis revealed that ω-linked acyl-VLC ceramides colocalize with TJ complexes. Overall, normalization of retinal ELOVL4 expression could prevent blood-retinal barrier dysregulation in diabetic retinopathy through an increase in VLC ceramides and stabilization of TJs.

Transcription Factor CTIP1/ BCL11A Regulates Epidermal Differentiation and Lipid Metabolism During Skin Development

The epidermal permeability barrier (EPB) prevents organisms from dehydration and infection. The transcriptional regulation of EPB development is poorly understood. We demonstrate here that transcription factor COUP-TF-interacting protein 1 (CTIP1/BCL11A; hereafter CTIP1) is highly expressed in the developing murine epidermis. Germline deletion of Ctip1 (Ctip1^−/−) results in EPB defects accompanied by compromised epidermal differentiation, drastic reduction in profilaggrin processing, reduced lamellar bodies in granular layers and significantly altered lipid composition. Transcriptional profiling of Ctip1^−/− embryonic skin identified altered expression of genes encoding lipid-metabolism enzymes, skin barrier-associated transcription factors and junctional proteins. CTIP1 was observed to interact with genomic elements within the regulatory region of the gene encoding the differentiation-associated gene, Fos-related antigen2 (Fosl2) and lipid-metabolism-related gene, Fatty acid elongase 4 (Elvol4), and the expression of both was altered in Ctip1^−/− mice. CTIP1 appears to play a role in EPB establishment of via direct or indirect regulation of a subset of genes encoding proteins involved in epidermal differentiation and lipid metabolism. These results identify potential, CTIP1-regulated avenues for treatment of skin disorders involving EBP defects.

The Effect of Glycation on Epidermal Lipid Content, Its Metabolism and Change in Barrier Function

BACKGROUND/AIMS

Advanced glycation end products, which are linked to both aging and hyperglycemia, cause marked functional and structural alterations in human skin. Though it is well known that the metabolism of glucose is closely associated with that of fatty acid (FA), sharing the same energy-yielding reaction pathways as glucose, its effect on the epidermis has been unclear so far.

METHODS

Content of ceramides, cholesterol and FA in a reconstructed epidermal model glycated by glyoxal was analyzed by high-performance thin-layer chromatography. FA species extracted from HaCaT keratinocytes was determined by gas chromatography/mass spectrometry. Regulation of FA synthesis was analyzed by real-time PCR. For physiological analysis, excised mouse skin was glycated using a vertical diffusion cell and used for the evaluation of barrier function by transepidermal water loss measurement and observation of penetration of sodium fluorescein.

RESULTS

Saturated FA content was significantly increased in glycated epidermis, and glycation upregulated mRNA expression of FA elongases 2 and 3 and FA synthase in HaCaT cells. Further, both inside-out and outside-in barriers were disrupted in glycated excised skin.

CONCLUSION

Biological and physical change in the epidermis, especially upregulation of FA synthesis by glycation, contributed to barrier disruption, and inhibiting glycation may offer an effective treatment option for aged or glycated skin.

Modulation of stratum corneum lipid composition and organization of human skin equivalents by specific medium supplements

Our in-house human skin equivalents contain all stratum corneum (SC) barrier lipid classes, but have a reduced level of free fatty acids (FAs), of which a part is mono-unsaturated. These differences lead to an altered SC lipid organization and thereby a reduced barrier function compared to human skin. In this study, we aimed to improve the SC FA composition and, consequently, the SC lipid organization of the Leiden epidermal model (LEM) by specific medium supplements. The standard FA mixture (consisting of palmitic, linoleic and arachidonic acids) supplemented to the medium was modified, by replacing protonated palmitic acid with deuterated palmitic acid or by the addition of deuterated arachidic acid to the mixture, to determine whether FAs are taken up from the medium and are incorporated into SC of LEM. Furthermore, supplementation of the total FA mixture or that of palmitic acid alone was increased four times to examine whether this improves the SC FA composition and lipid organization of LEM. The results demonstrate that the deuterated FAs are taken up into LEMs and are subsequently elongated and incorporated in their SC. However, a fourfold increase in palmitic acid supplementation does not change the SC FA composition or lipid organization of LEM. Increasing the concentration of the total FA mixture in the medium resulted in a decreased level of very long chain FAs and an increased level of mono-unsaturated FAs, which lead to deteriorated SC lipid properties. These results indicate that SC lipid properties can be modulated by specific medium supplements.

The importance of free fatty acid chain length for the skin barrier function in atopic eczema patients

An important feature of atopic eczema (AE) is a decreased skin barrier function. The stratum corneum (SC) lipids - comprised of ceramides (CERs), free fatty acids (FFAs) and cholesterol - fulfil a predominant role in the skin barrier function. In this clinical study, the carbon chain length distribution of SC lipids (FFAs and CERs) and their importance for the lipid organization and skin barrier function were examined in AE patients and compared with control subjects. A reduction in FFA chain length and an increase in unsaturated FFAs are observed in non-lesional and lesional SC of AE patients. The reduction in FFA chain length associates with a reduced CER chain length, suggesting a common synthetic pathway. The lipid chain length reduction correlates with a less dense lipid organization and a decreased skin barrier function. All changes are more pronounced in lesional SC compared with non-lesional skin. No association was observed between lipid properties and filaggrin mutations, an important predisposing factor for developing AE. The results of this study demonstrate an altered SC lipid composition and signify the importance of these changes (specifically regarding the CER and FFA chain lengths) for the impaired skin barrier function in AE. This provides insights into epidermal lipid metabolism as well as new opportunities for skin barrier repair.

The important role of stratum corneum lipids for the cutaneous barrier function

The skin protects the body from unwanted influences from the environment as well as excessive water loss. The barrier function of the skin is located in the stratum corneum (SC). The SC consists of corneocytes embedded in a lipid matrix. This lipid matrix is crucial for the lipid skin barrier function. This paper provides an overview of the reported SC lipid composition and organization mainly focusing on healthy and diseased human skin. In addition, an overview is provided on the data describing the relation between lipid modulations and the impaired skin barrier function. Finally, the use of in vitro lipid models for a better understanding of the relation between the lipid composition, lipid organization and skin lipid barrier is discussed. This article is part of a Special Issue entitled The Important Role of Lipids in the Epidermis and their Role in the Formation and Maintenance of the Cutaneous Barrier. This article is part of a Special Issue entitled The Important Role of Lipids in the Epidermis and their Role in the Formation and Maintenance of the Cutaneous Barrier. Guest Editors: Kenneth R. Feingold and Peter Elias.

1-O-acylceramides are natural components of human and mouse epidermis

The lipid-rich stratum corneum functions as a barrier against pathogens and desiccation inter alia by an unbroken meshwork of extracellular lipid lamellae. These lamellae are composed of cholesterol, fatty acids, and ceramides (Cers) in an equimolar ratio. The huge class of skin Cers consists of three groups: group I, "classical" long and very long chain Cers; group II, ultra-long chain Cers; and group III, ω-esterified ultra-long chain Cers, which are esterified either with linoleic acid or with cornified envelope proteins and are required for the water permeability barrier. Here, we describe 1-O-acylceramides as a new class of epidermal Cers in humans and mice. These Cers contain, in both the N- and 1-O-position, long to very long acyl chains. They derive from the group I of classical Cers and make up 5% of all esterified Cers. Considering their chemical structure and hydrophobicity, we presume 1-O-acylceramides to contribute to the water barrier homeostasis. Biosynthesis of 1-O-acylceramides is not dependent on lysosomal phospholipase A2. However, glucosylceramide synthase deficiency was followed by a 7-fold increase of 1-O-acylceramides, which then contributed 30% to all esterified Cers. Furthermore, loss of neutral glucosylceramidase resulted in decreased levels of a 1-O-acylceramide subgroup. Therefore, we propose 1-O-acylceramides to be synthesized at endoplasmic reticulum-related sites.

Interferon-γ decreases ceramides with long-chain fatty acids: possible involvement in atopic dermatitis and psoriasis

Ceramide (CER) with long-chain fatty acids (FAs) in the human stratum corneum (SC) is important for the skin barrier functions. Changes in the CER profile have been associated with abnormal permeability of dermatoses such as atopic dermatitis (AD) and psoriasis. In addition, interferon-γ (IFN-γ) has been known to be abundant in both AD and psoriatic skin lesions. In this study, we aimed to identify the mechanism underlying the alteration of FA chain length of CERs in these diseases. Mass spectrometry analysis of CERs in the SC showed that the proportion of CERs with long-chain FAs was significantly lower in AD and psoriasis patients than in healthy controls, and this reduction was more pronounced in psoriasis than in AD. Using cultured human keratinocytes and epidermal sheets, we found that only IFN-γ among various cytokines decreased the mRNA expression of elongase of long-chain fatty acids (ELOVL) and ceramide synthase (CerS), enzymes involved in FA chain elongation. Furthermore, quantitative analysis showed that IFN-γ decreased the levels of CERs with long-chain FAs. These results suggest that IFN-γ decreases CERs with long-chain FAs through the downregulation of ELOVL and CerS and that this mechanism may be involved in the CER profile alteration observed in psoriasis and AD.

EGFR regulation of epidermal barrier function

Keratinocyte terminal differentiation is the process that ultimately forms the epidermal barrier that is essential for mammalian survival. This process is controlled, in part, by signal transduction and gene expression mechanisms, and the epidermal growth factor receptor (EGFR) is known to be an important regulator of multiple epidermal functions. Using microarray analysis of a confluent cell density-induced model of keratinocyte differentiation, we identified 2,676 genes that are regulated by epidermal growth factor (EGF), a ligand of the EGFR. We further discovered, and separately confirmed by functional assays, that EGFR activation abrogates all of the known essential processes of keratinocyte differentiation by 1) decreasing the expression of lipid matrix biosynthetic enzymes, 2) regulating numerous genes forming the cornified envelope, and 3) suppressing the expression of tight junction proteins. In organotypic cultures of skin, EGF acted to impair epidermal barrier integrity, as shown by increased transepidermal water loss. As defective epidermal differentiation and disruption of barrier function are primary features of many human skin diseases, we used bioinformatic analyses to identify genes that are known to be associated with skin diseases. Compared with non-EGF-regulated genes, EGF-regulated genes were significantly enriched for skin disease genes. These results provide a systems-level understanding of the actions of EGFR signaling to inhibit keratinocyte differentiation, providing new insight into the role of EGFR imbalance in skin pathogenesis.