Total Internal Reflection Fluorescence Research Articles

Cytotoxicity and cell membrane interactions of choline-based ionic liquids: comparing amino acids, acetate, and geranate anions

Ionic liquids (ILs) have found diverse applications in research and industry. Biocompatible ILs, a subset considered less toxic than traditional ILs, have expanded their applications into biomedical fields. However, there is limited understanding of the toxicity profiles, safe concentrations, and underlying factors driving their toxicity. In this study, we investigated the cytotoxicity of 13 choline-based ILs using four different cell lines: Human dermal fibroblasts (HDF), epidermoid carcinoma cells (A431), cervical cancer cells (HeLa), and gastric cancer cells (AGS). Additionally, we explored the haemolytic activity of these ILs. Our findings showed that the cytotoxic and haemolytic activities of ILs can be attributed to the hydrophobicity of the anions and the pH of the IL solutions. Furthermore, utilising quartz crystal microbalance with dissipation (QCM-D) technique, we delved into the interaction of selected ILs, including choline acetate [Cho][Ac] and choline geranate [Cho][Ge], with model cell membranes composed of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC). The QCM-D data showed that ILs with higher toxicities exhibited more pronounced interactions with membranes. Increased variations in frequency and dissipation reflected substantial changes in membrane fluidity and mass following the addition of the more toxic ILs. Furthermore, total internal reflection fluorescence microscopy study revealed that [Cho][Ac] could cause lipid rearrangements and pore formation in the membrane, while [Cho][Ge] disrupted the bilayer packing. This study advances our understanding of the cellular toxicities associated with choline-based ILs and provides valuable insights into their mechanisms of action concerning IL-membrane interactions. These findings have significant implications for the safe and informed utilisation of biocompatible ILs in the realm of drug delivery and biotechnology.

C2-domain abscisic acid-related proteins regulate the dynamics of a plasma membrane H+-ATPase in response to alkali stress.

Arabidopsis (Arabidopsis thaliana) H+-ATPase1 (AHA1), a plasma membrane (PM)-localized H+-ATPase, plays a key role in plant alkali stress tolerance by pumping protons from the cytoplasm to the apoplast. However, its molecular dynamics are poorly understood. We report that many C2-domain ABA-related (CAR) protein family members interact with AHA1 in Arabidopsis. Single or double mutants of CAR1, CAR6, and CAR10 had no obvious phenotype of alkali stress tolerance, while their triple mutants showed significantly higher tolerance to this stress. The disruption of AHA1 largely compromised the increased alkali stress tolerance of the car1car6car10 mutant, revealing a key role of CARs in AHA1 regulation during the plant's response to a high alkali pH. Furthermore, variable angle total internal reflection fluorescence microscopy was used to observe AHA1-mGFP5 in intact Arabidopsis seedlings, revealing the presence of heterogeneous diffusion coefficients and oligomerization states in the AHA1 spots. In the aha1 complementation lines, alkali stress curtailed the residence time of AHA1 at the PM and increased the diffusion coefficient and particle velocity of AHA1. In contrast, the absence of CAR proteins decreased the restriction of the dynamic behavior of AHA1. Our results suggest that CARs play a negative role in plant alkali stress tolerance by interacting with AHA1 and provide a perspective to investigate the regulatory mechanism of PM H+-ATPase activity at the single-particle level.

The mutual influence of microtubules and the cortical ER on their coordinated organisation.

The endoplasmic reticulum (ER) is the largest organelle in terms of membrane content, occupying the entire cytoplasmic volume. It is tethered to the cell cortex through ER-plasma membrane contact sites (EPCS). Previous studies have shown that EPCSs labelled by VAP27 align with cortical microtubules, and that ER tubules elongate along microtubules. Here, we addressed the question whether this relationship is bidirectional, with EPCSs influencing microtubule organisation. Using TIRF microscopy to track EPCSs and microtubule dynamics simultaneously, we demonstrate that while EPCSs remain stable, microtubules are highly dynamic and can adjust their positioning based on nearby EPCS in Arabidopsis cotyledon epidermis. In lobes of epidermal cells enclosed by two indentations, where microtubules bundle together, EPCSs flank the bundles and exhibit a distinctive arrangement, forming symmetric arcs in relation to the lobe axis. In guard cells, transversely oriented ER tubules co-align with microtubules. Disrupting microtubules with the drug oryzalin leads to transient guard cells-ER remodelling, followed by its reorganisation into transverse tubules before microtubule recovery. Taken together our observations suggest, that the positioning of EPCSs and cortical microtubules, can affect each other and the organisation of cortical ER.

Degradation of Amyloid-β Species by Multi-Copper Oxidases.

Reduction of the production of amyloid-β (Aβ) species has been intensively investigated as potential therapeutic approaches for Alzheimer's disease (AD). However, the degradation of Aβ species, another potential beneficial approach, has been far less explored. To investigate the potential of multi-copper oxidases (MCOs) in degrading Aβ peptides and their potential benefits for AD treatment. We investigated the degradation efficiency of MCOs by using electrophoresis and validated the ceruloplasmin (CP)-Aβ interaction using total internal reflection fluorescence microscopy, fluorescence photometer, and fluorescence polarization measurement. We also investigated the therapeutic effect of ascorbate oxidase (AO) by using induced pluripotent stem (iPS) neuron cells and electrophysiological analysis with brain slices. We discovered that CP, an important MCO in human blood, could degrade Aβ peptides. We also found that other MCOs could induce Aβ degradation as well. Remarkably, we revealed that AO had the strongest degrading effect among the tested MCOs. Using iPS neuron cells, we observed that AO could rescue neuron toxicity which induced by Aβ oligomers. In addition, our electrophysiological analysis with brain slices suggested that AO could prevent an Aβ-induced deficit in synaptic transmission in the hippocampus. To the best of our knowledge, our report is the first to demonstrate that MCOs have a degrading function for peptides/proteins. Further investigations are warranted to explore the possible benefits of MCOs for future AD treatment.

Observing multi-frequency structured illumination patterns based on an evanescent field in a millimeter-scale polymer slide.

Millimeter-scale slide optical waveguides (OWGs) show the potential to break the barrier of easy-to-use and versatility for total internal reflection (TIR) fluorescence technology. In this paper, multi-frequency structured illumination (SI) patterns resulting from the evanescent field (EF) on the surface of a millimeter-scale polymer slide OWG are observed by measuring the fluorescence intensity distribution of fluorescent dyes deposited on the top of the OWG. The frequency, intensity, and stability of the SI patterns show a strong dependence on the coupling angle of the incident light (changing with the incident position). The distribution of multi-frequency SI patterns in the frequency space is demonstrated for different numerical aperture (NA) imaging systems (NA = 0.3, 0.6, and 0.8), indicating the potential for enhanced resolution for low NA systems with a simple and cheap polymer slide.

Waveguide-based microscope slide for label-free high-resolution imaging

Waveguide-based total internal reflection fluorescence microscopy has been widely adopted due to its excellent signal-to-noise ratio over a large field of view. However, with the increasing demand for label-free imaging, waveguide-based evanescent light scattering microscopy (ESM) has also garnered significant attention. Here, we present a low-cost waveguide-based microscope slide that offers easier integration with conventional optical microscopy. This microscope slide uses an incoherent light source coupled to a lithium tantalate (LT) planar waveguide to generate an evanescent light that illuminates samples located within a few hundred nanometers of the waveguide surface. We perform its application for imaging chromium nanoholes and polystyrene nanospheres, demonstrating its label-free, high-resolution, high-contrast imaging performance. LT waveguide microscope slides provide a simple and effective solution for ESM.

Molecular basis of product recognition during PIP5K-mediated production of PI(4,5)P2 with positive feedback

The ability for cells to localize and activate peripheral membrane binding proteins is critical for signal transduction. Ubiquitously important in these signaling processes are phosphatidylinositol phosphate (PIP) lipids, which are dynamically phosphorylated by PIP lipid kinases on intracellular membranes. Functioning primarily at the plasma membrane, phosphatidylinositol-4-phosphate 5-kinases (PIP5K) catalyzes the phosphorylation of PI(4)P to generate most of the PI(4,5)P2 lipids found in eukaryotic plasma membrane. Recently, we determined that PIP5K displays a positive feedback loop based on membrane-mediated dimerization and cooperative binding to its product, PI(4,5)P2. Here, we examine how two motifs contribute to PI(4,5)P2 recognition to control membrane association and catalysis of PIP5K. Using a combination of single molecule TIRF microscopy and kinetic analysis of PI(4)P lipid phosphorylation, we map the sequence of steps that allow PIP5K to cooperatively engage PI(4,5)P2. We find that the specificity loop regulates the rate of PIP5K membrane association and helps orient the kinase to more effectively bind PI(4,5)P2 lipids. After correctly orienting on the membrane, PIP5K transitions to binding PI(4,5)P2 lipids near the active site through a motif previously referred to as the substrate or PIP binding motif (PIPBM). The PIPBM has broad specificity for anionic lipids and serves a role in regulating membrane association in vitro and in vivo. Overall, our data supports a two-step membrane binding model where the specificity loop and PIPBM act in concert to help PIP5K orient and productively engage anionic lipids to drive the positive feedback during PI(4,5)P2 production.

Unraveling the influence of CRISPR/Cas13a reaction components on enhancing trans-cleavage activity for ultrasensitive on-chip RNA detection.

The CRISPR/Cas13 nucleases have been widely documented for nucleic acid detection. Understanding the intricacies of CRISPR/Cas13's reaction components is pivotal for harnessing its full potential for biosensing applications. Herein, we report onthe influence of CRISPR/Cas13a reaction components on its trans-cleavage activity and the development of an on-chip total internal reflection fluorescence microscopy (TIRFM)-powered RNA sensing system. We used SARS-CoV-2 synthetic RNA and pseudovirus as a model system. Our results show that optimizing Mg2+ concentration, reporter length, and crRNA combination significantly improves the detection sensitivity. Under optimized conditions, we detected 100 fM unamplified SARS-CoV-2 synthetic RNA using a microtiter plate reader. To furtherimprove sensitivity and provide a new amplification-free RNA sensing toolbox, we developed a TIRFM-based amplification-free RNA sensing system. We were able to detect RNA down to 100 aM. Furthermore, the TIRM-based detection system developed in this study is 1000-fold more sensitive than the off-coverslip assay. The possible clinical applicability of the system was demonstrated by detecting SARS-CoV-2 pseudovirus RNA. Our proposed sensing system has the potential to detect any target RNA with slight modifications to the existing setup, providing a universal RNA detection platform.

Determination of the Localized Surface Plasmon Resonance Alteration of AgNPs via Multiwavelength Evanescent Scattering Microscopy for Pb(II) Detection.

We developed multiwavelength evanescent scattering microscopy (MWESM), which can acquire plasmonic nanoparticle images at the particle level using the evanescent field as the incident source and distinguish different LSPR (localized surface plasmon resonance) spectral peaks among four wavelengths. Our microscope could be easily and simply built by modifying a commercial total internal reflection fluorescence microscope (TIRFM) with the substitution of a beamsplitter and the addition of a semicircular stop. The ultrathin depth of illumination and rejection of the reflected incident source together contribute to the high sensitivity and contrast of single nanoparticle imaging. We first validated the capability of our imaging system in distinguishing plasmonic nanoparticles bearing different LSPR spectral peaks, and the results were consistent with the scattering spectra results of hyperspectral imaging. Moreover, we demonstrated high imaging quality from the aspects of the signal/noise ratio and point spread function of the single-particle images. Meaningfully, the system can be utilized in rapidly determining the concentration of toxic lead ions in environmental and biological samples with good linearity and sensitivity, based on single-particle evanescent scattering imaging through the detection of the alteration of the LSPR of silver nanoparticles. This system holds the potential to advance the field of nanoparticle imaging and foster the application of nanomaterials as sensors.

IL-1β Induces LDL Transcytosis by a Novel Pathway Involving LDLR and Rab27a.

In early atherosclerosis, circulating LDLs (low-density lipoproteins) traverse individual endothelial cells by an active process termed transcytosis. The CANTOS trial treated advanced atherosclerosis using a blocking antibody for IL-1β (interleukin-1β); this significantly reduced cardiovascular events. However, whether IL-1β regulates early disease, particularly LDL transcytosis, remains unknown. We used total internal reflection fluorescence microscopy to quantify transcytosis by human coronary artery endothelial cells exposed to IL-1β. To investigate transcytosis in vivo, we injected wild-type and knockout mice with IL-1β and LDL to visualize acute LDL deposition in the aortic arch. Exposure to picomolar concentrations of IL-1β induced transcytosis of LDL but not of albumin by human coronary artery endothelial cells. Surprisingly, expression of the 2 known receptors for LDL transcytosis, ALK-1 (activin receptor-like kinase-1) and SR-BI (scavenger receptor BI), was unchanged or decreased. Instead, IL-1β increased the expression of the LDLR (LDL receptor); this was unexpected because LDLR is not required for LDL transcytosis. Overexpression of LDLR had no effect on basal LDL transcytosis. However, knockdown of LDLR abrogated the effect of IL-1β on transcytosis rates while the depletion of Cav-1 (caveolin-1) did not. Since LDLR was necessary but overexpression had no effect, we reasoned that another player must be involved. Using public RNAseq data to curate a list of Rab GTPases affected by IL-1β, we identified Rab27a. Overexpression of Rab27a alone had no effect on basal transcytosis, but its knockdown prevented induction by IL-1β. This was phenocopied by depletion of the Rab27a effector JFC1. In vivo, IL-1β increased LDL transcytosis in the aortic arch of wild-type but not Ldlr-/- or Rab27a-deficient mice. The JFC1 inhibitor nexinhib20 also blocked IL-1β-induced LDL accumulation in the aorta. IL-1β induces LDL transcytosis by a distinct pathway requiring LDLR and Rab27a; this route differs from basal transcytosis. We speculate that induction of transcytosis by IL-1β may contribute to the acceleration of early disease.

Correlative single-molecule and structured illumination microscopy of fast dynamics at the plasma membrane

Total internal reflection fluorescence (TIRF) microscopy offers powerful means to uncover the functional organization of proteins in the plasma membrane with very high spatial and temporal resolution. Traditional TIRF illumination, however, shows a Gaussian intensity profile, which is typically deteriorated by overlaying interference fringes hampering precise quantification of intensities—an important requisite for quantitative analyses in single-molecule localization microscopy (SMLM). Here, we combine flat-field illumination by using a standard πShaper with multi-angular TIR illumination by incorporating a spatial light modulator compatible with fast super-resolution structured illumination microscopy (SIM). This distinct combination enables quantitative multi-color SMLM with a highly homogenous illumination. By using a dual camera setup with optimized image splitting optics, we achieve a versatile combination of SMLM and SIM with up to three channels. We deploy this setup for establishing robust detection of receptor stoichiometries based on single-molecule intensity analysis and single-molecule Förster resonance energy transfer (smFRET). Homogeneous illumination furthermore enables long-term tracking and localization microscopy (TALM) of cell surface receptors identifying spatial heterogeneity of mobility and accessibility in the plasma membrane. By combination of TALM and SIM, spatially and molecularly heterogenous diffusion properties can be correlated with nanoscale cytoskeletal organization and dynamics.

Insulin-Mimetic Activity of Herbal Extracts Identified with Large-Scale Total Internal Reflection Fluorescence Microscopy.

Diabetes mellitus is a spreading global pandemic. Type 2 diabetes mellitus (T2DM) is the predominant form of diabetes, in which a reduction in blood glucose uptake is caused by impaired glucose transporter 4 (GLUT4) translocation to the plasma membrane in adipose and muscle cells. Antihyperglycemic drugs play a pivotal role in ameliorating diabetes symptoms but often are associated with side effects. Hence, novel antidiabetic compounds and nutraceutical candidates are urgently needed. Phytogenic therapy can support the prevention and amelioration of impaired glucose homeostasis. Using total internal reflection fluorescence microscopy (TIRFM), 772 plant extracts of an open-access plant extract library were screened for their GLUT4 translocation activation potential, resulting in 9% positive hits. Based on commercial interest and TIRFM assay-based GLUT4 translocation activation, some of these extracts were selected, and their blood glucose-reducing effects in ovo were investigated using a modified hen's egg test (Gluc-HET). To identify the active plant part, some of the available candidate plants were prepared in-house from blossoms, leaves, stems, or roots and tested. Acacia catechu (catechu), Pulmonaria officinalis (lungwort), Mentha spicata (spearmint), and Saponaria officinalis (common soapwort) revealed their potentials as antidiabetic nutraceuticals, with common soapwort containing GLUT4 translocation-activating saponarin.

An atomic force microscopy and total internal reflection fluorescence microscopy correlated system (AFM-TIRF) for fluorescence imaging and spectroscopy of a single particle.

Combining atomic force microscopy (AFM) with other optical microscopic techniques is pivotal in nanoscale investigations, particularly leveraging the surface-sensitive properties of total internal reflection fluorescence microscopy (TIRF). A novel design that integrates AFM with a multi-wavelength TIRF is displayed, providing simultaneous fluorescence imaging and spectral acquisition capabilities. We elaborate on the considerations in the instrument design process and demonstrate the performance and potential applications of the instrument through fluorescence imaging and spectroscopy testing of individual nanoparticles. This AFM and TIRF correlated system (AFM-TIRF) emerges as a promising option for single-molecule fluorescence studies, enabling simultaneous manipulation and detection of fluorescence from individual molecules.

Freestanding bilayer microscope for single-molecule imaging of membrane proteins.

Integral membrane proteins (IMPs) constitute a large fraction of organismal proteomes, playing fundamental roles in physiology and disease. Despite their importance, the mechanisms underlying dynamic features of IMPs, such as anomalous diffusion, protein-protein interactions, and protein clustering, remain largely unknown due to the high complexity of cell membrane environments. Available methods for in vitro studies are insufficient to study IMP dynamics systematically. This publication introduces the freestanding bilayer microscope (FBM), which combines the advantages of freestanding bilayers with single-particle tracking. The FBM, based on planar lipid bilayers, enables the study of IMP dynamics with single-molecule resolution and unconstrained diffusion. This paper benchmarks the FBM against total internal reflection fluorescence imaging on supported bilayers and is used here to estimate ion channel open probability and to examine the diffusion behavior of an ion channel in phase-separated bilayers. The FBM emerges as a powerful tool to examine membrane protein/lipid organization and dynamics to understand cell membrane processes.

DNA Framework-Guided Self-Limiting Aggregation for Highly Luminescent Metal Cluster Nanoaggregates.

The photoluminescent properties of atomically precise metal nanoclusters (MCs) have garnered significant attention in the fields of chemical sensing and biological imaging. However, the limited brightness of single-component nanoclusters hinders their practical applications, and the conventional ligand engineering approaches have proven insufficient in enhancing the emission efficiency of MCs. Here, we present a DNA framework-guided strategy to prepare highly luminescent metal cluster nanoaggregates. Our approach involves an amphiphilic DNA framework comprising a hydrophobic alkyl core and a rigid DNA framework shell, serving as a nucleation site and providing well-defined nanoconfinements for the self-limiting aggregation of MCs. Through this method, we successfully produced homogeneous MC nanoaggregates (10.1 ± 1.2 nm) with remarkable nanoscale precision. Notably, this strategy proves adaptable to various MCs, leading to a substantial enhancement in emission and quantum yield, up to 3011- and 87-fold, respectively. Furthermore, our investigation using total internal reflection fluorescence microscopy at the single-particle level uncovered a more uniform photon number distribution and higher photostability for MC nanoaggregates compared to template-free counterparts. This DNA-templating strategy introduces a conceptually innovative approach for studying the photoluminescent properties of aggregates with nanoscale precision and holds promise for constructing highly luminescent MC nanoparticles for diverse applications.

Abstract A013: NF1 loss is syntetic lethal with Trastuzumab emtansine

Abstract There is great interest in the identification of biomarkers to guide development of antibody-drug conjugates (ADC). Most research has focused on target expression, but key predictors of payload efficacy have not been indeitifed. NF1 is a tumor suppressor classically considered as an inhibitor of RAS signaling, and often mutated in metastatic HER2+ breast cancer (BC). We screened multiple approved drugs for differential sensitivityin CRISPR-engineeredf NF1 KO cells. HER2-targeted agents (small molecules or antibodies) were found to be less effective upon NF1 loss; surprisingly, we identified increased sensitivity to the approved ADC T-DM1, but not to Trastuzumab Deruxtecan (T-Dxd). We then elucidated the underlying molecular cause employing in vivo, in vitro and in vitro reductionist systems. To measure in vivo MT dynamics, we transiently transfected the MT end-binding protein EB3- GFP and reconstructed MT trajectories by live-cell imaging. Upon DM1 treatment, KO cells showed a highly significant reduction in MT speed, demonstrating a direct role for NF1 on MT dynamics in cells. In tubulin polymerization assays, recombinant NF1 greatly accelerated polymerization and completely rescued DM1-induced inhibition. NF1 induced significant MT bundling, a defining feature of many MT-associated proteins, which generates signal indistinguishable from true MT polymerization in turbidity assays. To follow the dynamics of individual microtubules, we applied Total Internal Reflection (TIRF) microscopy on glass-immobilized MTs. As expected, polymerization in the presence of NF1 led to a dose-dependent significant increase in MT dynamics (fraction of elongating MTs, elongation speed, catastrophe rate). Expectedly, DM1 led to significant reduction in the fraction of elongating MTs and speed, but these defects were completely or partially rescued by NF1. Importantly, DM1 did not only lead to MT shortening (as proposed by the current model), but also to clear and frequent MT fracturing, indicating that the drug is not only engaging MT ends but also intra-tubular binding sites. This is consistent with recent models of MT formation which incorporate the frequent presence of areas of discontinuity or damage induced by mechanical stress, exposing intratubular DM1 binding sites. Interestingly, adding NF1 to DM1-treated MTs generated areas of de novo intra-tubular tubulin insertion, coincident with damaged sites, suggesting an entirely novel role for NF1 in MT repair. In conclusion, we provide evidence for a model in which maytansinoids bind not only to soluble tubulin dimers and MT ends, but also to intratubular damaged sites. Thus, the number of binding sites in cells would be proportional to MT damage, suggesting a mechanism for differential efficacy across tumor types and a potential avenue for combinatorial drug development. These results prompt the use of NF1 as a biomarker to select patients for ADC treatment. Funding: FIEO fellowship 2023, AIRC (n25791), Italian MoH-Ricerca Corrente di Rete (ACCORD) 2022, Next Generation EU – PNRR M6C2 – PNRR-MAD-2022-12376934 Citation Format: Eleonora Messuti, Bruno Achutti Duso, Alessia Castiglioni, Giulia Tini, Emanuele Bonetti, Giuseppe Ciossani, Silvia Monzani, Daria Khuntsariya, Marcus Braun, Zdenek Lansky, Luigi Scietti, Luca Mazzarella. NF1 loss is syntetic lethal with Trastuzumab emtansine [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Expanding and Translating Cancer Synthetic Vulnerabilities; 2024 Jun 10-13; Montreal, Quebec, Canada. Philadelphia (PA): AACR; Mol Cancer Ther 2024;23(6 Suppl):Abstract nr A013.

Imbalance of APOB Lipoproteins and Large HDL in Type 1 Diabetes Drives Atherosclerosis.

Individuals with type 1 diabetes (T1D) generally have normal or even higher HDL (high-density lipoprotein)-cholesterol levels than people without diabetes yet are at increased risk for atherosclerotic cardiovascular disease (CVD). Human HDL is a complex mixture of particles that can vary in cholesterol content by >2-fold. To investigate if specific HDL subspecies contribute to the increased atherosclerosis associated with T1D, we created mouse models of T1D that exhibit human-like HDL subspecies. We also measured HDL subspecies and their association with incident CVD in a cohort of people with T1D. We generated LDL receptor-deficient (Ldlr-/-) mouse models of T1D expressing human APOA1 (apolipoprotein A1). Ldlr-/-APOA1Tg mice exhibited the main human HDL subspecies. We also generated Ldlr-/-APOA1Tg T1D mice expressing CETP (cholesteryl ester transfer protein), which had lower concentrations of large HDL subspecies versus mice not expressing CETP. HDL particle concentrations and sizes and proteins involved in lipoprotein metabolism were measured by calibrated differential ion mobility analysis and targeted mass spectrometry in the mouse models of T1D and in a cohort of individuals with T1D. Endothelial transcytosis was analyzed by total internal reflection fluorescence microscopy. Diabetic Ldlr-/-APOA1Tg mice were severely hyperglycemic and hyperlipidemic and had markedly elevated plasma APOB levels versus nondiabetic littermates but were protected from the proatherogenic effects of diabetes. Diabetic Ldlr-/-APOA1Tg mice expressing CETP lost the atheroprotective effect and had increased lesion necrotic core areas and APOB accumulation, despite having lower plasma APOB levels. The detrimental effects of low concentrations of larger HDL particles in diabetic mice expressing CETP were not explained by reduced cholesterol efflux. Instead, large HDL was more effective than small HDL in preventing endothelial transcytosis of LDL mediated by scavenger receptor class B type 1. Finally, in humans with T1D, increased concentrations of larger HDL particles relative to APOB100 negatively predicted incident CVD independently of HDL-cholesterol levels. Our results suggest that the balance between APOB lipoproteins and the larger HDL subspecies contributes to atherosclerosis progression and incident CVD in the setting of T1D and that larger HDLs exert atheroprotective effects on endothelial cells rather than by promoting macrophage cholesterol efflux.

Quantification of membrane fluidity in bacteria using TIR-FCS

Plasma membrane fluidity is an important phenotypic feature that regulates the diffusion, function, and folding of transmembrane and membrane-associated proteins. In bacterial cells, variations in membrane fluidity are known to affect respiration, transport, and antibiotic resistance. Membrane fluidity must therefore be tightly regulated to adapt to environmental variations and stresses such as temperature fluctuations or osmotic shocks. Quantitative investigation of bacterial membrane fluidity has been, however, limited due to the lack of available tools, primarily due to the small size and membrane curvature of bacteria that preclude most conventional analysis methods used in eukaryotes. Here, we develop an assay based on total internal reflection-fluorescence correlation spectroscopy (TIR-FCS) to directly measure membrane fluidity in live bacteria via the diffusivity of fluorescent membrane markers. With simulations validated by experiments, we could determine how the small size, high curvature, and geometry of bacteria affect diffusion measurements and correct subsequent measurements for unbiased diffusion coefficient estimation. We used this assay to quantify the fluidity of the cytoplasmic membranes of the Gram-positive bacteria Bacillus subtilis (rod-shaped) and Staphylococcus aureus (coccus) at high (37°C) and low (20°C) temperatures in a steady state and in response to a cold shock, caused by a shift from high to low temperature. The steady-state fluidity was lower at 20°C than at 37°C, yet differed between B. subtilis and S. aureus at 37°C. Upon cold shock, the membrane fluidity decreased further below the steady-state fluidity at 20°C and recovered within 30 min in both bacterial species. Our minimally invasive assay opens up exciting perspectives for the study of a wide range of phenomena affecting the bacterial membrane, from disruption by chemicals or antibiotics to viral infection or change in nutrient availability.

Propafenone-induced connexin-43 protein accumulation and intracellular dynamics

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): China Scholarship Council Background Connexin-43 (Cx43) plays a pivotal role in intercellular communication through gap junctions. It is instrumental in propagating electrical signals and allowing ions to flow between neighboring cardiomyocytes. This synchronized electrical activity allows the heart to work as a functional syncytium. Any disruption or malfunction of Cx43 can lead to arrhythmias and other cardiac issues. Understanding the functions and regulation of Cx43 is vital in both basic research and clinical contexts. Propafenone, a class Ic antiarrhythmic drug, has shown promise in rhythm control; however, its precise impact on cardiac cellular physiology, particularly regarding Cx43, remains incompletely understood. Purpose To investigate propafenone’s effect on Cx43 expression, physiology, and underlying mechanisms in cell systems. Methods Used cell lines include human embryonic kidney HEK293 cells transfected with Cx43; differentiated murine embryonic carcinoma EPI7 cells with an epithelioid morphology and visceral endoderm-like END2 cells, endogenously expressing high amounts of functional Cx43. Cx43 protein expression levels were determined by Western blot analysis, whereas immunofluorescence (IF) imaged by a Total Internal Reflection Fluorescence (TIRF) microscope was used to assess the subcellular localization of Cx43 proteins. Dye injections were used to gain insight into the effects of propafenone on Cx43 metabolic coupling. Results and Conclusion Full length Cx43 protein levels were increased after treatment with propafenone and IF microscopy showed an intracellular accumulation of Cx43 protein, both on ectopically and endogenously expressed Cx43. Propafenone did not alter Cx43 half-life, in contrast to the lysosomal inhibitor chloroquine. Finally, gap-junctional coupling was decreased by chronic propafenone treatment. We conclude that the class 1c antiarrhythmic drug propanone increases Cx43 protein expression, resulting in its intracellular accumulation, as a side effect.

Zero-shot learning enables instant denoising and super-resolution in optical fluorescence microscopy.

Computational super-resolution methods, including conventional analytical algorithms and deep learning models, have substantially improved optical microscopy. Among them, supervised deep neural networks have demonstrated outstanding performance, however, demanding abundant high-quality training data, which are laborious and even impractical to acquire due to the high dynamics of living cells. Here, we develop zero-shot deconvolution networks (ZS-DeconvNet) that instantly enhance the resolution of microscope images by more than 1.5-fold over the diffraction limit with 10-fold lower fluorescence than ordinary super-resolution imaging conditions, in an unsupervised manner without the need for either ground truths or additional data acquisition. We demonstrate the versatile applicability of ZS-DeconvNet on multiple imaging modalities, including total internal reflection fluorescence microscopy, three-dimensional wide-field microscopy, confocal microscopy, two-photon microscopy, lattice light-sheet microscopy, and multimodal structured illumination microscopy, which enables multi-color, long-term, super-resolution 2D/3D imaging of subcellular bioprocesses from mitotic single cells to multicellular embryos of mouse and C. elegans.