Lipid Lamellae Research Articles

Lipophilic penetration enhancers and their impact to the bilayer structure of stratum corneum lipid model membranes: Neutron diffraction studies based on the example Oleic Acid

The present study analyzes the effect of the lipophilic penetration enhancer oleic acid on the bilayer structure of stratum corneum (SC) lipid model membranes based on Ceramide AP by using the neutron diffraction technique. Our results indicate the formation of a single lamellar phase in the presence of oleic acid under the chosen experimental conditions; a separated fluid-like oleic acid-rich phase was not detected in the present study. By comparing the internal membrane structure received from Fourier synthesis with the model system lacking oleic acid, considerable structural changes in terms of impairment of the lamellar order were found after incorporation of the penetration enhancer into the bilayers. In addition, by using specifically deuterated oleic acid we were able to prove the integration of the enhancer molecules into the model bilayers and moreover, to determine the exact position of oleic acid inside the SC lipid model membrane. From the present results we conclude a strong perturbation of lamellar SC lipid arrangement due to the intercalated penetration enhancer which can account for the promoting effects on drug penetration across the SC known for oleic acid.

Infrared spectroscopic studies of sodium dodecyl sulphate permeation and interaction with stratum corneum lipids in skin

The barrier function of skin is primarily provided by the lamellar lipid matrix of the stratum corneum (SC), which has been shown in previous infrared (IR) and related studies to consist predominantly of ordered lipids packed in orthorhombic and hexagonal domains. In the current work, we investigate the effects of the anionic surfactant, sodium dodecyl sulphate (SDS), on SC lipid packing and phase behaviour, using FT-IR spectroscopy. The use of acyl chain perdeuterated SDS allows unequivocal spectroscopic detection of both endogenous lipid and exogenous material in intact tissue. IR spectra were acquired as a function of temperature from isolated human SC exposed to SDS for various incubation periods at 34°C. SDS is found to enter the SC and is observed to be in a more ordered state in the SC than in solution, indicating that the SDS interacts with the ordered SC lipids. The results reveal that SDS reduces the amount of orthorhombic phase in the SC and increases the amount of hexagonally packed lipid at physiologically relevant temperatures. In addition, a small decrease in the lipid T(m) (acyl chain melting temperature) is observed. Furthermore, these SDS-induced changes were found to be strongly dependent on the time of exposure.

Supramolecular polymorphism of DNA in non-cationic Lα lipid phases

The structure of a complex between hydrated DNA and a non-cationic lipid is studied, including its phase diagram. The complex is spontaneously formed by adding DNA fragments (ca. 150 base pairs in length) to non-cationic lipids and water. The self-assembly process often leads to highly ordered structures. The structures were studied by combining X-ray scattering, fluorescence and polarized microscopy, as well as freeze-fracture experiments with transmission electron microscopy. We observe a significant increase of the smectic order as DNA is incorporated into the water layers of the lamellar host phase, and stabilization of single phase domains for large amounts of DNA. The effect of confinement on DNA ordering is investigated by varying the water content, following three dilution lines. A rich polymorphism is found, ranging from weakly correlated DNA-DNA in-plane organizations to highly ordered structures, where transmembrane correlations lead to the formation of columnar rectangular and columnar hexagonal superlattices of nucleotides embedded between lipid lamellae. From these observations, we suggest that addition of DNA to the lamellar phase significantly restricts membrane fluctuations above a certain concentration and helps the formation of the lipoplex. The alteration of membrane steric interactions, together with the appearance of interfacial interactions between membranes and DNA molecules may be a relevant mechanism for the emergence of highly ordered structures in the concentrated regime.

Is the skin barrier abnormal in dogs with atopic dermatitis?

In mammalian skin, the stratum corneum exerts a barrier function that protects from transepidermal water loss and the penetration of exogenous molecules, such as allergens, from the environment. Recently, skin barrier defects have been shown to be of prime importance in the pathogenesis of human atopic dermatitis. In this review, we summarize the latest research data pertinent to the stratum corneum and barrier function of dogs with atopic dermatitis. At the time of this writing, there is increasing evidence that a skin barrier defect likely exists in dogs with atopic dermatitis. This barrier dysfunction is characterized by abnormal intercellular stratum corneum lipid lamellae, abnormal stratum corneum morphology, reduced and abnormal ceramide content and, in some but not all dogs, abnormal filaggrin expression. In association with these changes, there is higher transepidermal water loss in atopic than in normal canine skin. Furthermore, atopic inflammation appears to worsen transepidermal water loss and filaggrin expression. It remains unknown, however, if the changes observed are primary (i.e. of genetic origin) or secondary to atopic inflammation that also exists even in clinically normal skin. Finally, whether or not a therapeutic intervention aimed at restoring a dysfunctional skin barrier is of any clinical benefit to atopic dogs has not yet been proven unequivocally.

Analysis of epidermal lipids in normal and atopic dogs, before and after administration of an oral omega-6/omega-3 fatty acid feed supplement. A pilot study

Alterations of the lipid expression in the skin of human and canine atopic subjects may be one of the key factors in the disease development. We have analyzed the ultrastructure of the clinically uninvolved skin of atopic dogs and compared it with the lipid composition of their tape-stripped stratum corneum (SC). The effect of a 2 month treatment of atopic dogs by food supplementation with a mixture of essential fatty acids was evaluated on skin samples taken before and after the treatment period. Electron microscopy revealed that the non-lesional skin of atopic dogs exhibited an abnormal and largely incomplete structure of the lamellar lipids with little cohesion between the corneocyte strata. The SC of atopic dogs was characterized by a significant decrease in the lipid content when compared to the healthy controls. Following oral supplementation with the mixture of essential fatty acids, the overall lipid content of the SC markedly increased. This feature was observed both with the free and, most importantly, with the protein-bound lipids (cholesterol, fatty acids and ceramides), the latter constituting the corneocyte-bound scaffold for ordinate organisation of the extracellular lipid bi-layers. Indeed, the semi-quantitative electron microscopy study revealed that the treatment resulted in a significantly improved organization of the lamellar lipids in the lower SC, comparable to that of the healthy dogs. Our results indicate the potential interest of long-term alimentary supplementation with omega-6 and omega-3 essential fatty acids in canine atopic dermatitis.

Topical emulsions containing ceramides: Effects on the skin barrier function and anti‐inflammatory properties

AbstractThe barrier properties of the stratum corneum (SC) are largely dependent on the intactness of the lipid lamellae that surround the corneocytes. Ceramides, fatty acids, and cholesterol together with hydrocortisone (HC) have thus been proposed as protective or therapeutic agents against xerosis and atopic dermatitis (AD). However, topical delivery of these substances is still a challenge because of the excellent barrier function of the skin. The aim of the present study was to develop a formulation with combined anti‐inflammatory/barrier repair properties. In order to achieve this goal, a new non‐ionic O/W emulsion (CerEmulsion) containing skin barrier lipids and HC was prepared. Its physicochemical and microbiological stability and skin permeation performance were compared to a blank emulsion (NoCerEmulsion). Placebos described as PlaceboCerEmulsion and PlaceboNoCerEmulsion of CerEmulsion and NoCerEmulsion, respectively, were also prepared in order to study the transepidermal water loss (TEWL) profiles. The emulsions presented white glossy and pourable characteristics with an acidic pH. CerEmulsion showed smaller droplet sizes and higher viscosity values (5000 mPas) while NoCerEmulsion presented viscosity values of 2000 mPas. Crystalline structures were prominent in both emulsions. The microbiological analysis showed that the results were within the established specification limits. CerEmulsion and NoCerEmulsion have shown similar release profiles and CerEmulsion presented a similar anti‐inflammatory activity in vivo when compared with a commercially available 1% HC emulsion. Both emulsions were chemically, physically, and microbiologically stable. TEWL was significantly lower for the group treated with PlaceboCerEmulsion, suggesting that skin hydration was higher with this ceramide‐containing formulation.Practical applications: In this work, the authors develop and characterize a new non‐ionic HC/ceramide‐dominant O/W emulsion as a topical therapy for the improvement of skin barrier abnormalities in atopic dermatitis (AD). This unique formulation includes high concentrations of three lipids (ceramides, cholesterol, and free fatty acids) and paraffin. Its use is recommended for AD patients ≥6 months of age. It is also indicated for the management and relief of burning and itching associated with various dermatoses, including AD, irritant contact dermatitis, and radiation dermatitis.

Altered epidermal lipid layers induced by long‐term exposure to suberythemal‐dose ultraviolet

Although several studies have reported on the biological effects of ultraviolet (UV) radiation, there have been only a few reports on the changes in epidermal lipids following long-term UV irradiation at suberythemal dose (SED), to which people are usually exposed during their lifetime. To investigate the changes of epidermal lipid properties after long-term UV radiation with SED. Hairless mice were irradiated three times weekly for 15 weeks at an SED of UV (UVB: 20 mJ/cm(2) ; UVA: 14 J/cm(2) ). Every three weeks, transepidermal water loss (TEWL) was measured by a Tewameter. The morphological alterations of stratum corneum (SC) lipid lamellae were examined by electron microscopy (EM). Activities of three key enzymes for mRNA of serine palmitoyl transferase, fatty acid synthase, and HMG CoA reductase were analyzed with real time reverse transcriptase-polymerase chain reaction. We also measured the amount of ceramide, cholesterol sulfate, and free fatty acid in the SC by high-performance thin-layer chromatography with exposed times. The SED UV-irradiated group showed increased TEWL after 12 weeks. Following the irradiation period, EM revealed incomplete and separated lamellae at SC intercellular space. mRNA of three key enzymes was increased until six weeks of UV irradiation and decreased thereafter. However, three major lipid amounts gradually decreased throughout the exposed period, with a notable decrease in ceramide. Long-term UV irradiation even with SED influences skin barrier function and structure with prominent ceramide decrease in SC intercellular lipid.

Sesquiterpene components of volatile oils as skin penetration enhancers for the hydrophilic permeant 5-fluorouracil.

Twelve sesquiterpene compounds, derived from natural volatile oils, were investigated as putative skin penetration enhancers for human skin. Pretreatment of epidermal membranes with sesquiterpene oils, or solid sesquiterpenes saturated in dimethyl isosorbide, increased the rate of absorption of the model hydrophilic permeant, 5-fluorouracil (5-FU). Enhancers with polar functional groups were generally more potent than pure hydrocarbons. Furthermore, enhancers with the least bunched structures were the most active. The largest effect was observed following pretreatment with nerolidol, which increased pseudo-steady-state 5-FU flux over 20-fold. Molecular modelling suggested that terpenes with structures suitable for alignment within lipid lamellae were the most potent enhancers. Sesquiterpene enhancers had long durations of action implying that they did not wash out of the skin easily. This study attempted to improve enhancer clearance by replacing the aqueous donor and receptor phases by ethanol:water (1:1) solutions. Ethanol increased the permeability coefficient for 5-FU 13-fold, demonstrating that, in aqueous solution, it is a moderately potent penetration enhancer. Sesquiterpene and ethanol enhancement effects were approximately additive. Sesquiterpene effects were almost fully maintained for at least 4.5 days following pretreatment, illustrating poor reversibility. Stratum corneum/water drug partitioning studies suggested that an important mechanism of action of the enhancers was to increase the apparent drug diffusivity in the stratum corneum. Increases in drug partitioning into the entire stratum corneum following enhancer pretreatment were relatively small. Diffusivity increases were directly related to overall rises in permeability. This study has shown that sesquiterpene compounds, which are of low toxicity and cutaneous irritancy, can promote 5-FU absorption across human skin. Sesquiterpene compounds, therefore, show promise as clinically-acceptable skin penetration enhancers.

Cytosolic StAR-related lipid transfer domain 4 (STARD4) protein influences keratinocyte lipid phenotype and differentiation status

Terminally differentiating keratinocytes actively synthesize and accumulate cholesterol, which is a key constituent of intercellular lipid lamellae which contribute to the epidermal permeability barrier. While the pathway for cholesterol biosynthesis is established, intracellular transport mechanisms for this lipid are poorly understood, despite their importance in regulating organelle sterol content, keratinocyte differentiation status and the activity of lipid-responsive transcription factors involved in skin health, repair and disease. Recent data implicate proteins containing a steroidogenic acute regulatory protein (StAR)-related lipid transfer (START) domain in cellular cholesterol homeostasis. To investigate gene expression of cytosolic, cholesterol-binding StAR-related lipid transfer domain 4 (STARD4) protein in primary human keratinocytes and differentiating HaCaT keratinocytes and, by overexpression of this protein, the function of STARD4 in HaCaT keratinocyte lipid phenotype and differentiation status. Quantitative polymerase chain reaction was utilized to measure gene expression of STARD4 relative to the housekeeping gene GAPDH. Following transient (48 h) overexpression of STARD4, keratinocyte lipid mass and lipogenesis were measured, along with expression of genes involved in cholesterol homeostasis and those encoding a range of keratinocyte differentiation markers. Cholesterol-binding protein STARD4 is expressed in both primary and immortalized HaCaT keratinocytes, and is repressed during Ca(2+) -dependent differentiation of the latter. Transient overexpression of STARD4 reduces endogenous [(14) C]cholesterol and cholesteryl ester biosynthesis, and triggers increased expression of SREBF2, ABCG4 and LOR, while repressing expression of ABCA1. The cytosolic cholesterol-sensing protein STARD4 modulates both keratinocyte cholesterol homeostasis and differentiation status, increasing the efficiency of cholesterol trafficking within the cell, and amplifying and 'fine-tuning' cellular responses to this sterol. Modulation of expression of STARD4, and other members of the START family of lipid trafficking proteins, may prove useful in resolving imbalances in lipid metabolism associated with loss of epidermal barrier function in psoriasis and atopic dermatitis.

Antimicrobial Peptide Recognition of Bacterial Membranes

In the face of increasing clinical resistance to existing antibiotic drugs, antimicrobial peptides (AMP) are seen as a source of new antibiotics. Since these AMP have high affinities for bacterial membranes, but with highly variable activities over different strains, a multidisciplinary approach combining solid-state NMR, microbiology and lipidomics has been taken to decipher their specific recognition. Most studies of AMP have been carried out using model membrane systems, such as phosphatidylcholine (PC) and phosphatidylglycerol (PG) bilayers, which bear questionable resemblance to bacterial membranes. We have expanded these studies to include other bacterial phospholipids, e.g. phosphatidylethanolamine, cardiolipin (CL) and natural lipid extracts. Model membranes prepared from bacterial lipid extracts and live pathogenic bacteria are being used to help determine the mechanism of action of a class of AMP obtained from Australian tree frogs. The aims are to determine at which growth stage of the bacteria the peptides are active and to correlate with the membrane composition at each stage using mass spectrometry of the extracted phospholipids (lipidomics). Ongoing solid-state NMR experiments are providing in vivo AMP activity spectra at atomic resolution. This includes monitoring of phospholipid-peptide association and identification of specific bacterial features, such as acyl chain lipid composition, as critical mechanisms of antibiotic resistance. We report AMPs that have shown a better affinity for CL-containing vesicles, than for PC or a PC/PG mixture, and promote lamellar lipid organization to break into isotropic, as yet unsolved, structures. These correlate with the lower minimum inhibitory concentration assays done on a range of bacteria and circular dichroism experiments of AMP with specific lipid composition as those used in preliminary in vivo NMR experiments.

Application of Neutron Diffraction for Localization of Specifically Deuterated Penetration Enhancers in Oriented Stratum Corneum Model Membranes

The unique lamellar lipid matrix of the stratum corneum (SC) is known to play a key role in forming the main protecting barrier of the mammalian skin. This barrier function can be influenced e.g. by application of penetration enhancers. To learn more about their mode of action, the present study aimed at the characterization of the influence of lipophilic penetration enhancers like oleic acid (OA) on the bilayer structure of highly oriented SC model membranes. For exact localization of the enhancer molecules inside the bilayers of the studied quaternary SC models, we applied specifically deuterated penetration enhancers (e.g. OA-9,10-D2 and isopropyl myristate-14,14,14,13,13-D5) to the samples which were investigated by means of neutron diffraction. Benefitting from the advantages offered by the neutron diffraction technique, we could evaluate the exact position of the deuterium labels inside the membrane. Furthermore, hydration properties of the membrane could be studied and the bilayer architecture was elucidated by calculating the neutron scattering length density (neutron SLD) profiles using Fourier transform.View Large Image | View Hi-Res Image | Download PowerPoint Slide

Molecular dynamics simulations of phase transition of lamellar lipid membrane in water under an electric field

Molecular dynamics simulations were conducted to investigate phase behaviors of lamellar lipid membranes in water under a uniform external electric field. Poration, deformation and fusion of membranes were induced and water/membrane interfaces changed from perpendicular to parallel to the electric field. The hydration level of the lipids determined whether the final phase was the lamellar or inverted columnar structure. The simulations provide insights into phase transitions of amphiphile solutions in electric fields and mechanisms of cell electrofusion.

Physicochemical Analysis of Liposome Membranes Consisting of Model Lipids in the Stratum Corneum

Lamellar lipid layers in the stratum corneum (SC), the outermost layer of the skin, act as a primary permeability barrier to protect the body. The roles of SC lipid composition and membrane structure in skin barrier function have been extensively investigated using ex-vivo SC samples and reconstructed SC lipids in the form of multi-lamellar lipids or liposomes. The primary lipids, especially ceramide, have been found to be highly important. Atopic dermatitis (AD) is a well-known chronic inflammatory skin disease with immunologic and epidermal abnormalities of the permeability barrier; therefore, a comparison of SC lipids in AD skin with those in normal skin is a promising method to explore the mechanisms of skin barrier function. Here, we focused on the effect of sphingoids (ceramide metabolites and a minor component of the SC lipids) and their content/species on skin barrier function. A significant difference in the leakage ratio was observed between model SC lipid liposomes with a different sphingolipid ratio (sphingosine/sphinganine), with a value of 5.43 for normal skin vs. 14.3 for AD skin. This result shows a good concordance with AD mouse experiments. Therefore, an alteration in the composition of minor SC lipids resulting from a ceramide metabolic abnormality can affect the membrane integrity (i.e., skin barrier function). Small angle X-ray scattering (SAXS) measurements revealed no distinct differences in the SAXS pattern between the 3 models, with all models forming a rigid membrane (i.e., a nearly hydrated solid). According to increasing the temperature, the peaks indicated that the lamellar structures decreased in all models and that the lateral packing of lipids decreased, which suggested annealing or melting of the gel to a liquid crystal, although no distinct phase transition was observed through fluorescence anisotropy measurements. Hence, we assume that the altered sphingoid composition triggers local membrane structural changes (i.e., formation of domains or clusters).

Lipid Polymorphism Induced by Surfactant Peptide SP-B1-25

Pulmonary surfactant protein B (SP-B) is an essential protein for lowering surface tension in the alveoli. SP-B1-25, a peptide comprised of the N-terminal 25 amino-acid residues of SP-B, is known to retain much of the biological activity of SP-B. Circular dichroism has shown that when SP-B1-25 interacts with negatively charged lipid vesicles, it contains significant helical structure for the lipid compositions and peptide/lipid ratios studied here. The effect of SP-B1-25 on lipid organization and polymorphisms was investigated via DSC, dynamic light scattering, transmission electron microscopy, and solid-state NMR spectroscopy. At 1-3 mol% peptide and physiologic temperature, SP-B1-25 partitions at the interface of negatively charged PC/PG lipid bilayers. In lipid mixtures containing 1-5 mol% peptide, the structure of SP-B1-25 remains constant, but 2H and 31P NMR spectra show the presence of an isotropic lipid phase in exchange with the lamellar phase below the Tm of the lipids. This behavior is observed for both DPPC/POPG and POPC/POPG lipid mixtures as well as for both the PC and PG components of the mixtures. For 1-3 mol% SP-B1-25, a return to a single lamellar phase above the lipid mixture Tm is observed, but for 5 mol% SP-B1-25 a significant isotropic component is observed at physiologic temperatures for DPPC and exchange broadening is observed in 2H and 31P NMR spectra of the other lipid components in the two mixtures. DLS and TEM rule out the formation of micellar structures and suggest that SP-B1-25 promotes the formation of a fluid isotropic phase. The ability of SP-B1-25 to fuse lipid lamellae via this mechanism, particularly those enriched in DPPC, suggests a specific role for the highly conserved N-terminus of SP-B in the packing of lipid lamellae into surfactant lamellar bodies or in stabilizing multilayer structures at the air-liquid interface. Importantly, this behavior has not been seen for the other SP-B fragments of SP-B8-25 and SP-B59-80, indicating a critical role for the proline rich first seven amino acids in this protein.

Expression of Antimicrobial Peptides Such as LL-37 and hBD-2 in Nonlesional Skin of Atopic Individuals

Recurrent skin infection is one of the major complications of atopic dermatitis and can be partly explained by decreased expression of antimicrobial peptides such as human beta-defensin-2 and cathelicidin (LL-37). In the human epidermis, human beta-defensin-2 is packed in the lamellar body and LL-37 is co-localized with intercellular lipid lamellae of the stratum corneum; together, these antimicrobial peptides constitute the primary defense system. IL-1alpha, a potent inducer of LL-37 and human beta-defensin-2, is also secreted from the disrupted epidermis for barrier homeostasis. In this study, we investigated whether expression of human beta-defensin-2 and LL-37 is constitutively decreased in the skin of atopic individuals. Nonlesional foreskins from atopic (n=7) and nonatopic (n=7) individuals were analyzed. The expression of LL-37, human beta-defensin-2 and IL-1alpha was analyzed using immunohistochemical staining, Western blot, and real-time polymerase chain reaction. Lamellar body density and secretion were evaluated by electron microscope. Quantitative analysis showed that the expression of each parameter was not significantly different between groups. Thus, basal expression of LL-37 and human beta-defensin-2 was not changed in atopic individuals. These results indicate that the expression of antimicrobial peptides at baseline was not different between nonlesional skin of atopic individuals and normal skin of nonatopic individuals.

OSBP-related protein 11 (ORP11) dimerizes with ORP9 and localizes at the Golgi–late endosome interface

We characterize here ORP11, a member of the oxysterol-binding protein family. ORP11 is present at highest levels in human ovary, testis, kidney, liver, stomach, brain, and adipose tissue. Immunohistochemistry demonstrates abundant ORP11 in the epithelial cells of kidney tubules, testicular tubules, caecum, and skin. ORP11 in HEK293 cells resides on Golgi complex and LE, co-localizing with GFP-Rab9, TGN46, GFP-Rab7, and a fluorescent medial-trans-Golgi marker. Under electron microscopic observation, cells overexpressing ORP11 displayed lamellar lipid bodies associated with vacuolar structures or the Golgi complex, indicating a disturbance of lipid trafficking. N-terminal fragment of ORP11 (aa 1–292) localized partially to Golgi, but displayed enhanced localization on Rab7- and Rab9-positive LE, while the C-terminal ligand-binding domain (aa 273–747) was cytosolic, demonstrating that the membrane targeting determinants are N-terminal. Yeast two-hybrid screen revealed interaction of ORP11 with the related ORP9. The interacting region was delineated within aa 98–372 of ORP9 and aa 154–292 of ORP11. Overexpressed ORP9 was able to recruit EGFP-ORP11 to membranes, and ORP9 silencing inhibited ORP11 Golgi association. The results identify ORP11 as an OSBP homologue distributing at the Golgi–LE interface and define the ORP9-ORP11 dimer as a functional unit that may act as an intracellular lipid sensor or transporter.

Self-Assembly of Lamellar Lipid−DNA Complexes Simulated by Explicit Solvent Counterion Model

The dissipative particle dynamics simulations with explicit solvent and counterions are used to mimic the self-assembly of lamellar cationic lipid-DNA (CL-DNA)complexes. We found that the formation of the complexes is associated with the releasing of 70% DNA counterions and 90% lipid counterions. The trapped DNA and CL charges together with their counterions inside the complex still keep the interior neutral, which stabilized the structure. Simulations in constant pressure ensemble following the self-assembly show that the DNA interaxial spacing as a function of the inversed CL concentrations 1/phi(c) is linear at low phi(c) and nonlinear at high phi(c). The attraction between the DNA and the CLs as well as the repulsion between the DNA strands impose stretching stress on the membrane so that the averaged area per lipid is dependent on the CL concentration, which in turn determines the behavior of the DNA spacing.

A coarse-grained model for amorphous and crystalline fatty acids.

Fatty acids constitute one of the main components of the lipid lamellae in the top layer of the skin, known as the stratum corneum, which acts as a barrier to foreign substances entering the body and to water leaving the body. To better understand the mechanics of the skin, a molecular-level understanding of the structure of the lamellae needs to be investigated. As a first step toward this goal, the current work involves the development of a coarse-grained model for fatty acids in an amorphous and a crystalline state. In order to retain the structural details of the atomistic molecules, radial distribution functions have been used to provide target data against which the coarse-grained force field is optimized. The optimization was achieved using the method developed by Reith, Putz, and Muller-Plathe with a damping factor introduced into the updating scheme to facilitate the convergence against the crystalline radial distribution functions. Using this approach, a transferable force field has been developed for both crystalline and amorphous systems that can be used to describe fatty acids of different chain lengths. We are unaware of any other coarse-grained model in the literature that has been developed to study solid phases. Additionally, the amorphous force field has been shown to accurately model mixtures of different free fatty acids based on the potentials derived from pure lipid systems.

Elastase 2 is expressed in human and mouse epidermis and impairs skin barrier function in Netherton syndrome through filaggrin and lipid misprocessing

The human epidermis serves 2 crucial barrier functions: it protects against water loss and prevents penetration of infectious agents and allergens. The physiology of the epidermis is maintained by a balance of protease and antiprotease activities, as illustrated by the rare genetic skin disease Netherton syndrome (NS), in which impaired inhibition of serine proteases causes severe skin erythema and scaling. Here, utilizing mass spectrometry, we have identified elastase 2 (ELA2), which we believe to be a new epidermal protease that is specifically expressed in the most differentiated layer of living human and mouse epidermis. ELA2 localized to keratohyalin granules, where it was found to directly participate in (pro-)filaggrin processing. Consistent with the observation that ELA2 was hyperactive in skin from NS patients, transgenic mice overexpressing ELA2 in the granular layer of the epidermis displayed abnormal (pro-)filaggrin processing and impaired lipid lamellae structure, which are both observed in NS patients. These anomalies led to dehydration, implicating ELA2 in the skin barrier defect seen in NS patients. Thus, our work identifies ELA2 as a major new epidermal protease involved in essential pathways for skin barrier function. These results highlight the importance of the control of epidermal protease activity in skin homeostasis and designate ELA2 as a major protease driving the pathogenesis of NS.

Mass spectrometry imaging of mating Tetrahymena show that changes in cell morphology regulate lipid domain formation

Mass spectrometry imaging has been used here to suggest that changes in membrane structure drive lipid domain formation in mating single-cell organisms. Chemical studies of lipid bilayers in both living and model systems have revealed that chemical composition is coupled to localized membrane structure. However, it is not clear if the lipids that compose the membrane actively modify membrane structure or if structural changes cause heterogeneity in the surface chemistry of the lipid bilayer. We report that time-of-flight secondary ion mass spectrometry images of mating Tetrahymena thermophila acquired at various stages during mating demonstrate that lipid domain formation, identified as a decrease in the lamellar lipid phosphatidylcholine, follows rather than precedes structural changes in the membrane. Domains are formed in response to structural changes that occur during cell-to-cell conjugation. This observation has wide implications in all membrane processes.