From static to dynamic: The influence of mechanotransduction on skin equivalents analyzed by bioimaging and RNAseq

In this study, we explore the impact of mechanical stimuli on skin models using an innovative skin-on-a-chip platform, addressing the limitations of conventional transwell-cultured skin equivalents. This platform facilitates cyclic mechanical stimulation through compression and stretching, combined with automated media perfusion. Our findings, using bioimaging and bulk RNA sequencing, reveal increased expression of Keratin 10 and Keratin 14, indicating enhanced skin differentiation and mechanical integrity. The increase in desmosomes and tight junctions, observed through Claudin-1 and Desmoplakin 1 & 2 analysis, suggests improved keratinocyte differentiation due to mechanical stimulation. Gene expression analyses reveal a nuanced regulatory response, suggesting a potential connection to the Hippo pathway, indicative of a significant cellular reaction to mechanical stimuli. The results show the important influence of mechanical stimulation on skin model integrity and differentiation, demonstrating the potential of our microfluidic platform in advancing skin biology research and pharmaceutical testing.

Novel Chip for Applying Mechanical Forces on Human Skin Models Under Dynamic Culture Conditions

In recent years the need for in vitro skin models as a replacement for animal studies has resulted in significant progress in the development of skin-on-a-chip models. These devices allow the fine control of the microenvironment of the model and the incorporation of chemical and physical stimuli. In this study, we describe the development of an easy and low-budget open-top dynamic microfluidic device for skin-on-a-chip experiments using polydimethylsiloxane and a porous polyethylene terephthalate membrane. The chip allows the incorporation of compressive stimuli during the cultivation period by the use of syringe pumps. Proof-of-concept results show the successful differentiation of the cells and establishment of the skin structure in the chip. The microfluidic skin-on-a-chip models presented in this study can serve as a platform for future drug and feasibility studies.

Structural characterization of solvent-based food preparation of jellyfish

Jellyfish as a potential sustainable food material has recently gained increasing interest. However, with their soft gel-like texture and easy spoilage, it remains challenging to achieve desirable edible structures from jellyfish. The culinary preparation of jellyfish is a complex process and extends beyond conventional cooking methods. In this study, we investigate the transformation of jellyfish into crispy-like structures by manipulating their microstructural and mechanical properties through a solvent-based preparation. The study focuses on the use of "poor solvents", namely ethanol and acetone, and employs rheology measurements and quantitative microscopy techniques to analyze the effects of these solvents on the mechanical properties and microstructure of jellyfish. Our findings reveal that both ethanol and acetone lead to a significant increase in jellyfish hardness and deswelling. Notably, a micro-scale network is formed within the jellyfish matrix, and this network is then mechanically reinforced before a crispy-like texture can be obtained. Our study points to solvent polarity as also being a crucial factor for creating these effects and determines an upper polarity limit in the range of 12.2-12.9 MPa1/2 for added solvents, corresponding to approximately 60% of added ethanol or 70% of added acetone. Our study highlights that solvent-based preparation serves as a "reverse cooking" technique, where mechanical modification rather than traditional softening mechanisms are employed to stabilize and strengthen the microstructures and fibers of jellyfish. By elucidating the underlying mechanisms of solvent-induced stabilization, our findings may facilitate the development of innovative and sustainable culinary practices, paving the way for broader applications of jellyfish and other soft edible materials in the gastronomic landscape.

pH-Dependence Cytotoxicity Evaluation of Artepillin C against Tumor Cells

Brazilian green propolis is a well-known product that is consumed globally. Its major component, Artepillin C, showed potential as an antitumor product. This study explored the impact of Artepillin C on fibroblast and glioblastoma cell lines, used as healthy and very aggressive tumor cell lines, respectively. The focus of the study was to evaluate the pH-dependence of Artepillin C cytotoxicity, since tumor cells are known to have a more acidic extracellular microenvironment compared to healthy cells, and Artepillin C was shown to become more lipophilic at lower pH values. Investigations into the pH-dependency of Artepillin C (6.0-7.4), through viability assays and live cell imaging, revealed compelling insights. At pH 6.0, MTT assays showed the pronounced cytotoxic effects of Artepillin C, yielding a notable reduction in cell viability to less than 12% among glioblastoma cells following a 24 h exposure to 100 µM of Artepillin C. Concurrently, LDH assays indicated significant membrane damage, affecting approximately 50% of the total cells under the same conditions. Our Laurdan GP analysis suggests that Artepillin C induces autophagy, and notably, provokes a lipid membrane packing effect, contributing to cell death. These combined results affirm the selective cytotoxicity of Artepillin C within the acidic tumor microenvironment, emphasizing its potential as an effective antitumor agent. Furthermore, our findings suggest that Artepillin C holds promise for potential applications in the realm of anticancer therapies given its pH-dependence cytotoxicity.

Fate of microplastic captured in the marine demosponge Halichondria panicea

Microplastic particles are widespread pollutants in the sea and filter-feeding sponges have recently been suggested as useful monitoring organisms. However, the fate of microplastic particles in sponges is poorly understood, yet crucial for interpreting monitoring data. The present study aims to help develop sponges as more useful monitoring organisms for microplastic in the sea. Here, we describe the fate of inedible (2 and 10 μm) plastic beads compared to that of edible bacteria and algal cells captured in the marine demosponge Halichondria panicea. Small Cyanobium bacillare cells entered the choanocyte chambers and were phagocytized by choanocytes, while larger Rhodomonas salina cells were captured in incurrent canals and phagocytized in the mesohyl. Small 2 μm-beads were captured by choanocytes and subsequently expelled into the excurrent canals after 58 ± 34 min. Larger 10 μm-beads were captured in the incurrent canals and transferred to the mesohyl, where amoeboid cells moved them across the mesohyl before they were expelled into the excurrent canal after 95 ± 36 min. SEM observations further indicated engulfment of plastic beads on the outer sponge surface. This insight provides useful information on how sponges, in general, treat microplastic particles of various sizes. It helps us understand actual measured sizes and concentrations of microplastic particles in sponges in relation to those in the ambient water.

Helium Ion Microscopy and Sectioning of Spider Silk

Focused ion beams have recently emerged as a powerful tool for ultrastructural imaging of biological samples. In this article, we show that helium ion microscopy (HIM), in combination with ion milling, can be used to visualize the inner structure of both major and minor ampullate silk fibers of the orb-web weaving spider Nephila madagascariensis. The internal nanofibrils were imaged in pristine silk fibers, with little or no damage to the sample structure observed. Furthermore, a method to cut/rupture the fibers using He⁺ ions combined with internal sample tension is presented. This showed that the stretching and rupturing of spider silk is a highly dynamic process with considerable material reorganization.

Nanoscale imaging of major and minor ampullate silk from the orb-web spider Nephila Madagascariensis

Spider silk fibres have unique mechanical properties due to their hierarchical structure and the nanoscale organization of their proteins. Novel imaging techniques reveal new insights into the macro- and nanoscopic structure of Major (MAS) and Minor (MiS) Ampullate silk fibres from pristine samples of the orb-web spider Nephila Madagascariensis. Untreated threads were imaged using Coherent Anti-Stokes Raman Scattering and Confocal Microscopy, which revealed an outer lipid layer surrounding an autofluorescent protein core, that is divided into two layers in both fibre types. Helium ion imaging shows the inner fibrils without chemical or mechanical modifications. The fibrils are arranged parallel to the long axis of the fibres with typical spacing between fibrils of 230 nm ± 22 nm in the MAS fibres and 99 nm ± 24 nm in the MiS fibres. Confocal Reflection Fluorescence Depletion (CRFD) microscopy imaged these nano-fibrils through the whole fibre and showed diameters of 145 nm ± 18 nm and 116 nm ± 12 nm for MAS and MiS, respectively. The combined data from HIM and CRFD suggests that the silk fibres consist of multiple nanoscale parallel protein fibrils with crystalline cores oriented along the fibre axes, surrounded by areas with less scattering and more amorphous protein structures.

Dissolvable microneedles for transdermal drug delivery showing skin pentation and modified drug release

Topical therapies for chronic skin diseases suffer from a low patient compliance due to the inconvenient treatment regimens of available products. Dissolvable microneedles (MN) with modified release offer an interesting possibility to increase the compliance by acting as a depot in the skin and thereby decreasing the dosing frequency. Furthermore, the bioavailability can be increased significantly by bypassing the barrier of the skin by the direct penetration of the MN into the skin. In this study the depot effect and skin penetration of an innovative dissolvable MN patch was assessed by insertion in ex vivo human skin and in vivo using minipigs. The MN patches are based on biodegradable polymers and the active pharmaceutical ingredients calcipotriol (Calci) and betamethasone-17-21-dipropionate (BDP) used to treat psoriasis. Using computed tomography (CT) and Coherent anti-Stokes Raman scattering (CARS) microscopy it was possible to visualize the skin penetration and follow the morphology of the MN as function of time in the skin. The depot effect was assessed by studying the modified in vitro release in an aqueous buffer and by comparing the drug release of a single application of a patch both ex vivo and in vivo to daily application of a marketed oleogel containing the same active pharmaceutical ingredients. The CT and CARS images showed efficient penetration of the MN patches into the upper dermis and a slow swelling process of the drug containing tip over a period of 8 days. Furthermore, CARS demonstrated that it can be used as a noninvasive technique with potential applicability in clinical settings. The in vitro release studies show a release of 54% over a time period of 30 days. The pharmacological relevance of MNs was confirmed in human skin explants and in vivo after single application and showed a similar response on calcipotriol and BDP mediated signaling events compared to daily application of the active oleogel. Altogether it was demonstrated that the MN can penetrate the skin and have the potential to provide a depot effect.

Spectral Unmixing for Label-Free, In-Liquid Characterization of Biomass Microstructure and Biopolymer Content by Coherent Raman Imaging

Characterization of lignocellulosic biomass microstructure with chemical specificity and under physiological conditions could provide invaluable insights to our understanding of plant tissue development, microstructure, origins of recalcitrance, degradation, and solubilization. However, most methods currently available are either destructive, are not compatible with hosting a physiological environment, or introduces exogenous probes, complicating their use for studying changes in microstructure and mechanisms of plant development, recalcitrance, or degradation in situ. To address these challenges, we here present a multi-modal chemically specific imaging technique based on coherent anti-Stokes Raman scattering (CARS) microspectroscopy with simplex maximization and entropy-based spectral unmixing enabling label-free, chemically specific characterization of plant microstructure in liquid. We describe how spatial drift of samples suspended in liquid can introduce artifacts in spectral unmixing procedures for single-frequency CARS and propose a mitigative strategy toward these effects using simultaneously acquired forward-scattered CARS signals and epi-detected autofluorescence. We further apply the technique for chemical and microstructural characterization of untreated and liquid hot water pretreated rapeseed straw by CARS and show how the framework can be extended for 3D imaging with chemical specificity. Finally, we provide examples of the intricate chemical and microstructural details recovered by this hybrid imaging technique, including discerning between primary and secondary cell walls, localization of aqueous components to cell lumina, and the presence of funnel-type pits in samples ofBrassica napus.

Multilayer diffusion modeling and Coherent anti-Stokes Raman scattering microscopy for spatially resolved water diffusion measurements in human skin

In this work using Coherent anti-Stokes Raman Scattering microscopy, it was possible to directly measure the time dependent, spatially resolved change in concentration of water (D₂ O) in intact skin tissue with a spatial resolution of under 1 μm, and combined with a multilayer diffusion model, diffusion coefficients at different depths in the tissue were extracted. The results show that the diffusion varies at different layers throughout the Stratum Corneum (SC), indicating that the SC is not a homogeneous barrier but a complicated heterogeneous structure. Interestingly, averaging over the diffusion at the different depths and samples gave a relatively constant value of 0.047 ± 0.01 μm² /second. Treating the skin with acetone or tape stripping led to an increased diffusion coefficient of 0.064 ± 0.02 μm² /second and 0.079 ± 0.03 μm² /second, respectively. The combined method and model presented here shows potential for wide applications for measuring spatially resolved diffusion of different substances in a variety of different samples.

The ROC skin model: a robust skin equivalent for permeation and live cell imaging studies

Rat Epidermal Keratinocyte (REK) Organotypic Culture (ROC) is an epidermis model that is robust and inexpensive to develop and maintain, and it has in previous studies been shown to have permeability characteristics close to those of human skin. Here, we characterize the model further by structural comparison to native human and rat skin and by investigating functional characteristics of lipid packing, polarity, and permeability coefficients. We show that the ROC model has structural similarities to native human skin and observe human skin-like permeability coefficients for testosterone and mannitol. We develop a transwell device that allows live cell microscopy of the tissue at the air-liquid interface and establish transgenic cell lines expressing different fluorescently tagged proteins. This enables showing the migration of keratinocytes during the first days after seeding, finding that keratinocytes have a higher mean migration rate in the earlier days of development. Collectively, our results show that the ROC model is an inexpensive and robust epidermis model that works reproducibly across laboratories.

Polarized α-synuclein trafficking and transcytosis across brain endothelial cells via Rab7-decorated carriers

Parkinson’s disease is mainly caused by aggregation of α-synuclein (α-syn) in the brain. Exchange of α-syn between the brain and peripheral tissues could have important pathophysiological and therapeutic implications, but the trafficking mechanism of α-syn across the blood brain-barrier (BBB) remains unclear. In this study, we therefore investigated uptake and transport mechanisms of α-syn monomers and oligomers across an in vitro BBB model system. Both α-syn monomers and oligomers were internalized by primary brain endothelial cells, with increased restriction of oligomeric over monomeric transport. To enlighten the trafficking route of monomeric α-syn in brain endothelial cells, we investigated co-localization of α-syn and intracellular markers of vesicular transport. Here, we observed the highest colocalization with clathrin, Rab7 and VPS35, suggesting a clathrin-dependent internalization, preferentially followed by a late endosome retromer-connected trafficking pathway. Furthermore, STED microscopy revealed monomeric α-syn trafficking via Rab7-decorated carriers. Knockdown of Caveolin1, VPS35, and Rab7 using siRNA did not affect monomeric α-syn uptake into endothelial cells. However, it significantly reduced transcytosis of monomeric α-syn in the luminal-abluminal direction, suggesting a polarized regulation of monomeric α-syn vesicular transport. Our findings suggest a direct role for Rab7 in polarized trafficking of monomeric α-syn across BBB endothelium, and the potential of Rab7 directed trafficking to constitute a target pathway for new therapeutic strategies against Parkinson’s disease and related synucleinopathies.

Fractional CO2 laser ablation leads to enhanced permeation of a fluorescent dye in healthy and mycotic nails-An imaging investigation of laser-tissue effects and their impact on ungual drug delivery

Purpose

Conventional oral antifungal therapies for onychomycosis (OM) often do not achieve complete cure and may be associated with adverse effects, medical interactions, and compliance issues restricting their use in a large group of patients. Topical treatment can bypass the systemic side effects but is limited by the physical barrier of the nail plate. Ablative fractional laser (AFL) treatment can be used to improve the penetration of topical drugs into the nail. This study visualized the effects of laser ablation of nail tissue and assessed their impact on the biodistribution of a fluorescent dye in healthy and fungal nail tissue.

Methods

For the qualitative assessment of CO₂ AFL effects on healthy nail tissue, scanning electron microscopy (SEM), coherent anti‐Stokes Raman scattering microscopy (CARS‐M), and widefield fluorescence microscopy (WFM) were used. To quantitate the effect of laser‐pretreatment on the delivery of a fluorescent dye, ATTO‐647N, into healthy and fungal nail tissue, ablation depth, nail plate thickness, and ATTO‐647N fluorescence intensity in three nail plate layers were measured using WFM. A total of 30 nail clippings (healthy n = 18, fungal n = 12) were collected. An aqueous ATTO‐647N solution was directly applied to the dorsal surface of 24 nail samples (healthy n = 12, fungal n = 12) and incubated for 4 hours, of which half (healthy n = 6, fungal n = 6) had been pretreated with AFL (30 mJ/mb, 15% density, 300 Hz, pulse duration <1 ms).

Results

Imaging revealed a three‐layered nail structure, an AFL‐induced porous ablation crater, and changes in autofluorescence. While intact fungal samples showed a 106% higher ATTO‐647N signal intensity than healthy controls, microporation led to a significantly increased fluorophore permeation in all samples (p < 0.0001). AFL processing of nail tissue enhanced topical delivery of ATTO‐647N in all layers, (average increase: healthy +108%, fungal +33%), most pronounced in the top nail layer (healthy +122%, fungal +68%). While proportionally deeper ablation craters correlated moderately with higher fluorescence intensities in healthy nail tissue, fungal samples showed no significant relationship.

Conclusion

Fractional CO₂ laser microporation is a simple way of enhancing the passive delivery of topically applied ATTO‐647N. Although the impaired nail plate barrier in OM leads to greater diffusion of the aqueous solution, AFL can increase the permeability of both structurally deficient and intact nails.

Evaluation of native and non‐native biomaterials for engineering human skin tissue

A variety of human skin models have been developed for applications in regenerative medicine and efficacy studies. Typically, these employ matrix molecules that are derived from non‐human sources along with human cells. Key limitations of such models include a lack of cellular and tissue microenvironment that is representative of human physiology for efficacy studies, as well as the potential for adverse immune responses to animal products for regenerative medicine applications. The use of recombinant extracellular matrix proteins to fabricate tissues can overcome these limitations. We evaluated animal‐ and non‐animal‐derived scaffold proteins and glycosaminoglycans for the design of biomaterials for skin reconstruction in vitro. Screening of proteins from the dermal‐epidermal junction (collagen IV, laminin 5, and fibronectin) demonstrated that certain protein combinations when used as substrates increase the proliferation and migration of keratinocytes compared to the control (no protein). In the investigation of the effect of components from the dermal layer (collagen types I and III, elastin, hyaluronic acid, and dermatan sulfate), the primary influence on the viability of fibroblasts was attributed to the source of type I collagen (rat tail, human, or bovine) used as scaffold. Furthermore, incorporation of dermatan sulfate in the dermal layer led to a reduction in the contraction of tissues compared to the control where the dermal scaffold was composed primarily of collagen type I. This work highlights the influence of the composition of biomaterials on the development of complex reconstructed skin models that are suitable for clinical translation and in vitro safety assessment.

SSX2 promotes the formation of a novel type of intranuclear lamin bodies

SSX proteins are normally restricted to spermatogenic cells, but ectopic expression can be observed in many types of human cancer. We recently demonstrated that SSX family members may contribute to tumorigenesis by modifying chromatin structure and, in specific settings, compromise chromatin stability. Here, we used normal and tumorigenic breast epithelial cell line models to further study the effect of ectopic expression of SSX2 on nuclear organization. We show that SSX2 induces the formation of a novel type of nucleoplasmic lamin bodies. Ectopic expression of SSX2 in various breast epithelial cell lines led to the formation of a previously undescribed type of intranuclear bodies containing both A and B type lamins but no other components of the nuclear lamina. SSX2-expressing cells contained a highly variable number of lamin bodies distributed throughout the nuclear space. SSX2-mediated establishment of intranuclear lamin bodies could not be linked to previous molecular interactions of SSX proteins, including polycomb proteins and the Mediator complex, but was, however, dependent on S-phase progression. These results reveal a novel interaction between SSX2 and lamins in the nucleoplasmic space. They further suggest that SSX2 promotes the formation of chromatin neighborhoods supporting the organization of lamins into nuclear bodies. We speculate that this may have implications for the organization and functional regulation of chromatin in cancer cells. Our study contributes to the further understanding of the biology of SSX proteins in tumorigenesis.

Enhancing the sweat resistance of sunscreens

BACKGROUND

While sunbathing of performing outdoor sport activities, sunscreens are important for protection of uncovered skin against ultraviolet (UV) radiation. However, perspiration negatively affects the performance of a sunscreen film by weakening its substantivity and uniformity through the activation of two mechanisms, namely sunscreen wash-off and sunscreen redistribution.

MATERIAL AND METHODS

We used a perspiring skin simulator to investigate the effect of sunscreen formulation on its efficiency upon sweating. Specifically, we modified the sunscreen formulation by incorporating a hydrophobic film former and adding water-absorbing particles. Sunscreen performance before and after perspiration is assessed by in vitro sun protection factor measurements, direct detection of changes in the sunscreen distribution using UV reflectance imaging, and by coherent anti-Stokes Raman scattering (CARS) microscopy for microscopic characterization of the UV filter relocation.

RESULTS

The results show that incorporating a hydrophobic film former can decrease sunscreen wash-off due to sweating, while an excessive amount of film former might negatively affect the sunscreen distribution. The addition of water-absorbing particles, on the other hand, had either a negative or positive impact on the sunscreen substantivity, depending on the particle properties. While the addition of large water-absorbing particles appeared to increase sunscreen redistribution, smaller particles that could form a gel-like structure upon contact with water, appeared to change sunscreen wetting and sweat droplet spreading, thereby decreasing sunscreen wash-off and sunscreen redistribution.

CONCLUSIONS

We find that using a combination of hydrophobic film formers, which increase water resistance, and small water-absorbing particles, which change the wetting behavior, can make sunscreen formulations more sweat-resistant and less runny.

In vitro skin model for characterization of sunscreen substantivity upon perspiration

OBJECTIVE

The resistance of sunscreens to the loss of ultraviolet (UV) protection upon perspiration is important for their practical efficacy. However, this topic is largely overlooked in evaluations of sunscreen substantivity due to the relatively few well-established protocols compared to those for water resistance and mechanical wear.

METHODS

In an attempt to achieve a better fundamental understanding of sunscreen behaviour in response to sweat exposure, we have developed a perspiring skin simulator, containing a substrate surface that mimics sweating human skin. Using this perspiring skin simulator, we evaluated sunscreen performance upon perspiration by in vitro sun protection factor (SPF) measurements, optical microscopy, ultraviolet (UV) reflectance imaging and coherent anti-Stokes Raman scattering (CARS) microscopy.

RESULTS AND CONCLUSION

Results indicated that perspiration reduced sunscreen efficiency through two mechanisms, namely sunscreen wash-off (impairing the film thickness) and sunscreen redistribution (impairing the film uniformity). Further, we investigated how the sweat rate affected these mechanisms and how sunscreen application dose influenced UV protection upon perspiration. As expected, higher sweat rates led to a large loss of UV protection, while a larger application dose led to larger amounts of sunscreen being washed-off and redistributed but also provided higher UV protection before and after sweating.

Multiple Na,K-ATPase Subunits Colocalize in the Brush Border of Mouse Choroid Plexus Epithelial Cells

(1) Background: The unusual accumulation of Na,K-ATPase complexes in the brush border membrane of choroid plexus epithelial cells have intrigued researchers for decades. However, the full range of the expressed Na,K-ATPase subunits and their relation to the microvillus cytoskeleton remains unknown. (2) Methods: RT-PCR analysis, co-immunoprecipitation, native PAGE, mass spectrometry, and differential centrifugation were combined with high-resolution immunofluorescence histochemistry, proximity ligase assays, and stimulated emission depletion (STED) microscopy on mouse choroid plexus cells or tissues in order to resolve these issues. (3) Results: The choroid plexus epithelium expresses Na,K-ATPase subunits α1, α2, β1, β2, β3, and phospholemman. The α1, α2, β1, and β2, subunits are all localized to the brush border membrane, where they appear to form a complex. The ATPase complexes may stabilize in the brush border membrane via anchoring to microvillar actin indirectly through ankyrin-3 or directly via other co-precipitated proteins. Aquaporin 1 (AQP1) may form part of the proposed multi-protein complexes in contrast to another membrane protein, the Na-K-2Cl cotransporter 1 (NKCC1). NKCC1 expression seems necessary for full brush border membrane accumulation of the Na,K-ATPase in the choroid plexus. (4) Conclusion: A multitude of Na,K-ATPase subunits form molecular complexes in the choroid plexus brush border, which may bind to the cytoskeleton by various alternative actin binding proteins.

Substituted 9-Diethylaminobenzo[a]phenoxazin-5-ones (Nile Red Analogues): Synthesis and Photophysical Properties

Nile Red is a benzo[a]phenoxazone dye containing a diethylamino substituent at the 9-position. In recent years, it has become a popular histological stain for cellular membranes and lipid droplets due to its unrivaled fluorescent properties in lipophilic environments. This makes it an attractive lead for chemical decoration to tweak its attributes and optimize it for more specialized microscopy techniques, e.g., fluorescence lifetime imaging or two-photon excited fluorescence microscopy, to which Nile Red has never been optimized. Herein, we present synthesis approaches to a series of monosubstituted Nile Red derivatives (9-diethylbenzo[a]phenoxazin-5-ones) starting from 1-naphthols or 1,3-naphthalenediols. The solvatochromic responsiveness of these fluorophores is reported with focus on how the substituents affect the absorption and emission spectra, luminosity, fluorescence lifetimes, and two-photon absorptivity. Several of the analogues emerge as strong candidates for reporting the polarity of their local environment. Specifically, the one- and two-photon excited fluorescence of Nile Red turns out to be very responsive to substitution, and the spectroscopic features can be finely tuned by judiciously introducing substituents of distinct electronic character at specific positions. This new toolkit of 9-diethylbenzo[a]phenoxazine-5-ones constitutes a step toward the next generation of optical molecular probes for advancing the understanding of lipid structures and cellular processes.

Vibrational Spectroscopic Characterization and Coherent Anti-Stokes Raman Spectroscopy (CARS) Imaging of Artepillin C

In the following work, the vibrational spectroscopic characteristics of artepillin C are reported by means of Fourier transform infrared (FT-IR) and Raman spectroscopies, surface-enhanced Raman scattering (SERS), and coherent anti-Stokes Raman scattering (CARS) microscopy. Artepillin C is an interesting compound due to its pharmacological properties, including antitumor activity. It is found as the major component of Brazilian green propolis, a resinous mixture produced by bees to protect their hives against intruders. Vibrational spectroscopic techniques have shown a strong peak at 1599 cm^-1, assigned to C=C stretching vibrations from the aromatic ring of artepillin C. From these data, direct visualization of artepillin C could be assessed by means of CARS microscopy, showing differences in the film hydration obtained for its neutral and deprotonated states. Raman-based methods show potential to visualize the uptake and action of artepillin C in biological systems, triggering its interaction with biological systems that are needed to understand its mechanism of action.

Drinking and Water Handling in the Medaka Intestine: A Possible Role of Claudin-15 in Paracellular Absorption?

When euryhaline fish move between fresh water (FW) and seawater (SW), the intestine undergoes functional changes to handle imbibed SW. In Japanese medaka, the potential transcellular aquaporin-mediated conduits for water are paradoxically downregulated during SW acclimation, suggesting paracellular transport to be of principal importance in hyperosmotic conditions. In mammals, intestinal claudin-15 (CLDN15) forms paracellular channels for small cations and water, which may participate in water transport. Since two cldn15 paralogs, cldn15a and cldn15b, have previously been identified in medaka, we examined the salinity effects on their mRNA expression and immunolocalization in the intestine. In addition, we analyzed the drinking rate and intestinal water handling by adding non-absorbable radiotracers, 51-Cr-EDTA or 99-Tc-DTPA, to the water. The drinking rate was >2-fold higher in SW than FW-acclimated fish, and radiotracer experiments showed anterior accumulation in FW and posterior buildup in SW intestines. Salinity had no effect on expression of cldn15a, while cldn15b was approximately 100-fold higher in FW than SW. Despite differences in transcript dynamics, Cldn15a and Cldn15b proteins were both similarly localized in the apical tight junctions of enterocytes, co-localizing with occludin and with no apparent difference in localization and abundance between FW and SW. The stability of the Cldn15 protein suggests a physiological role in water transport in the medaka intestine.

Label free noninvasive spatially resolved NaCl concentration measurements using Coherent Anti-Stokes Raman Scattering microscopy applied to butter

Imaging the microstructure of opaque composite foodstuffs and extracting quantitative chemical information about specific localized components is challenging. Herein, a method has been developed to determine spatially resolved concentrations of aqueous salt and applied to measure salt concentrations of water droplets in butter samples. This was done using Coherent Anti-Stokes Raman Scattering (CARS) microscopy which achieves non-invasive label free imaging based on visualization of specific chemical-bond vibrations. The concentration of salt in the dispersed water droplets in butter was determined based on the relative change in intensity of the CARS-signal at two distinct wavenumbers, which have been shown to be dependent on the inter-molecular coupling of water molecules and salt. The results provide the size and salt concentration distribution of the droplets in the samples. It is further shown that the average salt concentration in the whole sample can correctly be inferred from the concentration measured within the water droplets.

Strain-Dependent Structural Changes in Major and Minor Ampullate Spider Silk Revealed by Two-Photon Excitation Polarization

Spider silk's mechanical properties make it an interesting material for many industrial applications. The structure and nanoscopic organization of its proteins are the basis of these qualities. In this study, the emission maxima of the autofluorescence from the protein core of major and minor ampullate silk fibers from the orb-web-weaving spider Nephila madagascariensis are determined and found to be 534 ± 11 and 547 ± 19 nm, respectively. Molecular conformational changes during applied strain are observed in both fiber types using two-photon excitation polarization measurements. Our findings showed that within the fibers the autofluorescent dipoles are separated into two distinct populations, one randomly orientated (amorphous regions) and one with aligned dipoles as found in crystalline structures. The crystalline-amorphous ratio was determined, and it was found that the crystalline dipoles made up around 30 and 20% of the autofluorescent dipoles in major and minor ampullate silk fibers, respectively. Using two-photon polarization measurements, it is possible to directly observe that the major and minor ampullate silk fibers structurally adapt to the applied stress, as well as discern different molecular conformational changes between major and minor ampullates. It was seen that the crystalline-amorphous ratio increased, with up to 9% for major fibers and 6% for minor fibers, as strain was applied, suggesting a conformational adaptation of the fiber, interpreted as noncrystalline 3₁₀-helices transforming into crystalline β-sheets.

Assessing Collagen and Elastin Pressure-dependent Microarchitectures in Live, Human Resistance Arteries by Label-free Fluorescence Microscopy

The pathogenic contribution of resistance artery remodeling is documented in essential hypertension, diabetes and the metabolic syndrome. Investigations and development of microstructurally motivated mathematical models for understanding the mechanical properties of human resistance arteries in health and disease have the potential to aid understanding how disease and medical treatments affect the human microcirculation. To develop these mathematical models, it is essential to decipher the relationship between the mechanical and microarchitectural properties of the microvascular wall. In this work, we describe an ex vivo method for passive mechanical testing and simultaneous label-free three-dimensional imaging of the microarchitecture of elastin and collagen in the arterial wall of isolated human resistance arteries. The imaging protocol can be applied to resistance arteries of any species of interest. Image analyses are described for quantifying i) pressure-induced changes in internal elastic lamina branching angles and adventitial collagen straightness using Fiji and ii) collagen and elastin volume densities determined using Ilastik software. Preferably all mechanical and imaging measurements are performed on live, perfused arteries, however, an alternative approach using standard video-microscopy pressure myography in combination with post-fixation imaging of re-pressurized vessels is discussed. This alternative method provides users with different options for analysis approaches. The inclusion of the mechanical and imaging data in mathematical models of the arterial wall mechanics is discussed, and future development and additions to the protocol are proposed.

Dynamic Changes in the Protein Localization in the Nuclear Environment in Pancreatic β-Cell after Brief Glucose Stimulation

Characterization of molecular mechanisms underlying pancreatic β-cell function in relation to glucose-stimulated insulin secretion is incomplete, especially with respect to global response in the nuclear environment. We focus on the characterization of proteins in the nuclear environment of β-cells after brief, high glucose stimulation. We compared purified nuclei derived from β-cells stimulated with 17 mM glucose for 0, 2, and 5 min using quantitative proteomics, a time frame that most likely does not result in translation of new protein in the cell. Among the differentially regulated proteins, we identified 20 components of the nuclear organization processes, including nuclear pore organization, ribonucleoprotein complex, and pre-mRNA transcription. We found alteration of the nuclear pore complex, together with calcium/calmodulin-binding chaperones that facilitate protein and RNA import or export to/from the nucleus to the cytoplasm. Putative insulin mRNA transcription-associated factors were identified among the regulated proteins, and they were cross-validated by Western blotting and confocal immunofluorescence imaging. Collectively, our data suggest that protein translocation between the nucleus and the cytoplasm is an important process, highly involved in the initial molecular mechanism underlying glucose-stimulated insulin secretion in pancreatic β-cells.

Imaging and modeling of acute pressure-induced changes of collagen and elastin microarchitectures in pig and human resistance arteries

The impact of disease-related changes in the extracellular matrix (ECM) on the mechanical properties of human resistance arteries largely remains to be established. Resistance arteries from both pig and human parietal pericardium (PRA) display a different ECM microarchitecture compared with frequently used rodent mesenteric arteries. We hypothesized that the biaxial mechanics of PRA mirror pressure-induced changes in the ECM microarchitecture. This was tested using isolated pig PRA as a model system, integrating vital imaging, pressure myography, and mathematical modeling. Collagenase and elastase digestions were applied to evaluate the load-bearing roles of collagen and elastin, respectively. The incremental elastic modulus linearly related to the straightness of adventitial collagen fibers circumferentially and longitudinally (both R2 ≥ 0.99), whereas there was a nonlinear relationship to the internal elastic lamina elastin fiber branching angles. Mathematical modeling suggested a collagen recruitment strain (means ± SE) of 1.1 ± 0.2 circumferentially and 0.20 ± 0.01 longitudinally, corresponding to a pressure of ~40 mmHg, a finding supported by the vital imaging. The integrated method was tested on human PRA to confirm its validity. These showed limited circumferential distensibility and elongation and a collagen recruitment strain of 0.8 ± 0.1 circumferentially and 0.06 ± 0.02 longitudinally, reached at a distending pressure below 20 mmHg. This was confirmed by vital imaging showing negligible microarchitectural changes of elastin and collagen upon pressurization. In conclusion, we show here, for the first time in resistance arteries, a quantitative relationship between pressure-induced changes in the extracellular matrix and the arterial wall mechanics. The strength of the integrated methods invites for future detailed studies of microvascular pathologies.

NEW & NOTEWORTHY This is the first study to quantitatively relate pressure-induced microstructural changes in resistance arteries to the mechanics of their wall. Principal findings using a pig model system were confirmed in human arteries. The combined methods provide a strong tool for future hypothesis-driven studies of microvascular pathologies.

Biochemical and Bioimaging Evidence of Cholesterol in Acquired Cholesteatoma

OBJECTIVES

To quantify the barrier sterols and image the lipid structures in the matrix of acquired cholesteatoma and compare the distribution with that found in stratum corneum from normal skin, with the goal to resolve their potential influence on cholesteatoma growth.

METHODS

High-performance thin-layer chromatography (HPTLC) was used to achieve a quantitative biochemical determination of the sterols. The intercellular lipids were visualized by Coherent Anti-Stokes Raman scattering (CARS) microscopy, which enables label-free imaging of the lipids in intact tissue samples.

RESULTS

The results show that the total lipid content of the cholesteatoma matrix is similar to that of stratum corneum from skin and that the cholesteatoma matrix unquestionably contains cholesterol. The cholesterol content in the cholesteatoma matrix is increased by over 30% (w/w dry weight) compared to the control. The cholesterol sulfate content is below 1% of the total lipids in both the cholesteatoma and the control. Cholesterol ester was reduced by over 30% when compared to the control.

CONCLUSIONS

The content of cholesterol in the cholesteatoma matrix is significantly different from that in stratum corneum from skin, and we confirm that the main structure of the cholesteatoma resembles very thick stratum corneum.

Endothelin-1 shifts the mediator of bradykinin-induced relaxation from NO to H2 O2 in resistance arteries from patients with cardiovascular disease

BACKGROUND AND PURPOSE

We tested the hypothesis that in resistance arteries from cardiovascular disease (CVD) patients, effects of an endothelium-dependent vasodilator depend on the contractile stimulus.

EXPERIMENTAL APPROACH

Arteries dissected from parietal pericardium of cardiothoracic surgery patients were studied by myography and imaging techniques. Segments were sub-maximally contracted by K(+) , the TxA2 analogue U46619 or endothelin-1 (ET-1).

KEY RESULTS

Relaxing effects of Na-nitroprusside were comparable, but those of bradykinin (BK) were bigger in the presence of ET-1 compared with K(+) or U46619. BK-induced relaxation was (i) abolished by L-NAME in K(+) -contracted arteries, (ii) partly inhibited by L-NAME in the presence of U46619 and (iii) not altered by indomethacin, L-NAME plus inhibitors of small and intermediate conductance calcium-activated K(+) channels, but attenuated by catalase, in ET-1-contracted arteries. This catalase-sensitive relaxation was unaffected by inhibitors of NADPH oxidases or allopurinol. Exogenous H2 O2 caused a larger relaxation of ET-1-induced contractions than those evoked by K(+) or U46619 in the presence of inhibitors of other endothelium-derived relaxing factors. Catalase-sensitive staining of cellular ROS with CellROX Deep Red was significantly increased in the presence of both 1 μM BK and 2 nM ET-1 but not either peptide alone.

CONCLUSIONS AND IMPLICATIONS

In resistance arteries from patients with CVD, exogenous ET-1 shifts the mediator of relaxing responses to the endothelium-dependent vasodilator BK from NO to H2 O2 and neither NADPH oxidases, xanthine oxidase nor NOS appear to be involved in this effect. This might have consequences for endothelial dysfunction in conditions where intra-arterial levels of ET-1 are enhanced.

Superresolution and Fluorescence Dynamics Evidence Reveal That Intact Liposomes Do Not Cross the Human Skin Barrier

In this study we use the combination of super resolution optical microscopy and raster image correlation spectroscopy (RICS) to study the mechanism of action of liposomes as transdermal drug delivery systems in human skin. Two different compositions of liposomes were applied to newly excised human skin, a POPC liposome and a more flexible liposome containing the surfactant sodium cholate. Stimulated emission depletion microscopy (STED) images of intact skin and cryo-sections of skin treated with labeled liposomes were recorded displaying an optical resolution low enough to resolve the 100 nm liposomes in the skin. The images revealed that virtually none of the liposomes remained intact beneath the skin surface. RICS two color cross correlation diffusion measurements of double labeled liposomes confirmed these observations. Our results suggest that the liposomes do not act as carriers that transport their cargo directly through the skin barrier, but mainly burst and fuse with the outer lipid layers of the stratum corneum. It was also found that the flexible liposomes showed a greater delivery of the fluorophore into the stratum corneum, indicating that they functioned as chemical permeability enhancers.

Slow Relaxation of Shape and Orientational Texture in Membrane Gel Domains

Gel domains in lipid bilayers are structurally more complex than fluid domains. Growth dynamics can lead to noncircular domains with a heterogeneous orientational texture. Most model membrane studies involving gel domain morphology and lateral organization assume the domains to be static. Here we show that rosette shaped gel domains, with heterogeneous orientational texture and a central topological defect, after early stage growth, undergo slow relaxation. On a time scale of days to weeks domains converge to circular shapes and approach uniform texture. 1,2-Dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) enriched gel domains are grown by cooling 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC):DPPC bilayers into the solid-liquid phase coexistence region and are visualized with fluorescence microscopy. The relaxation of individual domains is quantified through image analysis of time-lapse image series. We find a shape relaxation mechanism which is inconsistent with Ostwald ripening and coalescence as observed in membrane systems with coexisting liquid phases. Moreover, domain texture changes in parallel with the changes in domain shape, and selective melting and growth of particular subdomains cause the texture to become more uniform. We propose a relaxation mechanism based on relocation of lipids from high-energy lattice positions, through evaporation-condensation and edge diffusion, to low-energy positions. The relaxation process is modified significantly by binding Shiga toxin, a bacterial toxin from Shigella dysenteriae, to the membrane surface. Binding alters the equilibrium shape of the gel domains from circular to eroded rosettes with disjointed subdomains. This observation may be explained by edge diffusion while evaporation-condensation is restricted, and it provides further support for the proposed overall relaxation mechanism.

Membrane orientation and lateral diffusion of BODIPY-cholesterol as a function of probe structure

Cholesterol tagged with the BODIPY fluorophore via the central difluoroboron moiety of the dye (B-Chol) is a promising probe for studying intracellular cholesterol dynamics. We synthesized a new BODIPY-cholesterol probe (B-P-Chol) with the fluorophore attached via one of its pyrrole rings to carbon-24 of cholesterol (B-P-Chol). Using two-photon fluorescence polarimetry in giant unilamellar vesicles and in the plasma membrane (PM) of living intact and actin-disrupted cells, we show that the BODIPY-groups in B-Chol and B-P-Chol are oriented perpendicular and almost parallel to the bilayer normal, respectively. B-Chol is in all three membrane systems much stronger oriented than B-P-Chol. Interestingly, we found that the lateral diffusion in the PM was two times slower for B-Chol than for B-P-Chol, although we found no difference in lateral diffusion in model membranes. Stimulated emission depletion microscopy, performed for the first time, to our knowledge, with fluorescent sterols, revealed that the difference in lateral diffusion of the BODIPY-cholesterol probes was not caused by anomalous subdiffusion, because diffusion of both analogs in the PM was free but not hindered. Our combined measurements show that the position and orientation of the BODIPY moiety in cholesterol analogs have a severe influence on lateral diffusion specifically in the PM of living cells.

Insights into the cellular response triggered by silver nanoparticles using quantitative proteomics

The use of nanoparticles in foods, materials, and clinical treatments has increased dramatically in the past decade. Because of the possibility of human exposure to nanoparticles, there is an urgent need to investigate the molecular mechanisms underlying the cellular responses that might be triggered. Such information is necessary to assess potential health risks arising from the use of nanoparticles, and for developing new formulations of next generation nanoparticles for clinical treatments. Using mass spectrometry-based proteomic technologies and complementary techniques (e.g., Western blotting and confocal laser scanning microscopy), we present insights into the silver nanoparticle-protein interaction in the human LoVo cell line. Our data indicate that some unique cellular processes are driven by the size. The 100 nm nanoparticles exerted indirect effects via serine/threonine protein kinase (PAK), mitogen-activated protein kinase (MAPK), and phosphatase 2A pathways, and the 20 nm nanoparticles induced direct effects on cellular stress, including generation of reactive oxygen species and protein carbonylation. In addition, we report that proteins involved in SUMOylation were up-regulated after exposure to 20 nm silver nanoparticles. These results were further substantiated by the observation of silver nanoparticles entering the cells; however, data indicate that this was determined by the size of the nanoparticles, since 20 nm particles entered the cells while 100 nm particles did not.

Effect of detergents on the physicochemical properties of skin stratum corneum: a two-photon excitation fluorescence microscopy study

OBJECTIVE

Understanding the structural and dynamical features of skin is critical for advancing innovation in personal care and drug discovery. Synthetic detergent mixtures used in commercially available body wash products are thought to be less aggressive towards the skin barrier when compared to conventional detergents. The aim of this work is to comparatively characterize the effect of a mild synthetic cleanser mixture (SCM) and sodium dodecyl sulphate (SDS) on the hydration state of the intercellular lipid matrix and on proton activity of excised skin stratum corneum (SC).

METHOD

Experiments were performed using two-photon excitation fluorescence microscopy. Fluorescent images of fluorescence reporters sensitive to proton activity and hydration of SC were obtained in excised skin and examined in the presence and absence of SCM and SDS detergents.

RESULTS

Hydration of the intercellular lipid matrix to a depth of 10 μm into the SC was increased upon treatment with SCM, whereas SDS shows this effect only at the very surface of SC. The proton activity of SC remained unaffected by treatment with either detergent.

CONCLUSION

While our study indicates that the SC is very resistant to external stimuli, it also shows that, in contrast to the response to SDS, SCM to some extent modulates the in-depth hydration properties of the intercellular lipid matrix within excised skin SC.

Hydrophobic Mismatch Triggering Texture Defects in Membrane Gel Domains

The orientational texture of gel-phase lipid bilayers is a phenomenon that can structure membrane domains. Using two-photon polarized fluorescence microscopy and image analysis, we map the lateral variation of the lipid orientation (the texture) in single domains. With this method, we uncover a lipid-induced transition between vortex and uniform textures in binary phospholipid bilayers. By tuning the lipid composition, the hydrophobic mismatch at the domain boundary can be varied systematically as monitored by AFM. Low hydrophobic mismatch correlates with domains having uniform texture, while higher mismatch values correlate with a vortex-type texture. The defect pattern created during early growth persists in larger domains, and a minimal model incorporating the anisotropic line tension and the vortex energy can rationalize this finding. The results suggest that the lipid composition and the domain nucleation process are critical factors that determine the texture pattern of membrane domains.

Multi-color single particle tracking with quantum dots

Quantum dots (QDs) have long promised to revolutionize fluorescence detection to include even applications requiring simultaneous multi-species detection at single molecule sensitivity. Despite the early promise, the unique optical properties of QDs have not yet been fully exploited in e. g. multiplex single molecule sensitivity applications such as single particle tracking (SPT). In order to fully optimize single molecule multiplex application with QDs, we have in this work performed a comprehensive quantitative investigation of the fluorescence intensities, fluorescence intensity fluctuations, and hydrodynamic radii of eight types of commercially available water soluble QDs. In this study, we show that the fluorescence intensity of CdSe core QDs increases as the emission of the QDs shifts towards the red but that hybrid CdSe/CdTe core QDs are less bright than the furthest red-shifted CdSe QDs. We further show that there is only a small size advantage in using blue-shifted QDs in biological applications because of the additional size of the water-stabilizing surface coat. Extending previous work, we finally also show that parallel four color multicolor (MC)-SPT with QDs is possible at an image acquisition rate of at least 25 Hz. We demonstrate the technique by measuring the lateral dynamics of a lipid, biotin-cap-DPPE, in the cellular plasma membrane of live cells using four different colors of QDs; QD565, QD605, QD655, and QD705 as labels.

Potential of ultraviolet wide-field imaging and multiphoton microscopy for analysis of dehydroergosterol in cellular membranes

Dehydroergosterol (DHE) is an intrinsically fluorescent sterol with absorption/emission in the ultraviolet (UV) region and biophysical properties similar to those of cholesterol. We compared the potential of UV-sensitive low-light-level wide-field (UV-WF) imaging with that of multiphoton (MP) excitation microscopy to monitor DHE in living cells. Significantly reduced photobleaching in MP microscopy of DHE enabled us to acquire three-dimensional z-stacks of DHE-stained cells and to obtain high-resolution maps of DHE in surface ruffles, nanotubes, and the apical membrane of epithelial cells. We found that the lateral resolution of MP microscopy is ∼1.5-fold higher than that of UV-WF deconvolution microscopy, allowing for improved spatiotemporal analysis of plasma membrane sterol distribution. Surface intensity patterns of DHE with a diameter of 0.2 μm persisting over several minutes could be resolved by MP time-lapse microscopy. Diffusion coefficients of 0.25-μm-diameter endocytic vesicles containing DHE were determined by MP spatiotemporal image correlation spectroscopy. The requirement of extremely high laser power for visualization of DHE by MP microscopy made this method less potent for multicolor applications with organelle markers like green fluorescent protein-tagged proteins. The signal-to-noise ratio obtainable by UV-WF imaging could be significantly improved by pixelwise bleach rate fitting and calculation of an amplitude image from the decay model and by frame averaging after pixelwise bleaching correction of the image stacks. We conclude that UV-WF imaging and MP microscopy of DHE provide complementary information regarding membrane distribution and intracellular targeting of sterols.

Organic molecular nanotechnology

A new route to bottom-up organic nanotechnology is presented. Molecular building blocks with specific optoelectronic properties are designed and grown via directed self-assembly arrays of morphologically controlled light-emitting organic nanofibers on template surfaces. The fibers can be easily transferred from the growth substrate to device platforms either as single entities or as ordered arrays. Due to the extraordinary flexibility in the design of their optoelectronic properties they serve as key elements in next-generation nanophotonic devices.