Dynamic single-vesicle tracking of cell-bound membrane vesicles on resting, activated, and cytoskeleton-disrupted cells

Analysis of lipid composition of cell-bound membrane vesicles (CBMVs) derived from endothelial cells

Cell-bound membrane vesicles (CBMVs), a novel type of membrane vesicles, have been identified through a series of characterization tools. However, the lipid composition of CBMVs has not yet been characterized. This study focuses on the differences in lipid composition between CBMVs and cell membranes. In order to determine the lipid composition of CBMVs and cell membranes of Human umbilical vein endothelial cells (HUVECs) and find out differential metabolites, this study was carried out by isolating CBMVs lipids and characterizing them using high-performance liquid chromatography tandem secondary mass spectrometry (LC-MS/MS). The results showed the presence of 213 up-regulated and 726 down-regulated lipids in CBMVs compared to cell membranes which produced CBMVs. There are lipids expressed in CBMVs and not in cell membranes: DGDG 18:0_8:0, DGDG O-8:0_16:1, DGDG O-26:7_26:7, DGDG O-16:3_26:7, TG 15:4_21:5_22:5; 4O, PC 49:11, PG 19:5_38:10, PI 60:14, PI 44:9, PI 25:2, PI 43:5, PI 50:10, PS 55:10. DGDG (digalactosyl diglyceride), MGDG (monogalactosyl diglyceride) belongs to galactosyl diglyceride, promotes fat catabolism, which also has antioxidant and anti-inflammatory effects, and unsaturated diacylglycerols are a class of antioxidant compounds, which enables CBMVs to have a therapeutic potential.

Quantitative phase velocimetry measures bulk intracellular transport of cell mass during the cell cycle

Transport of mass within cells helps maintain homeostasis and is disrupted by disease and stress. Here, we develop quantitative phase velocimetry (QPV) as a label-free approach to make the invisible flow of mass within cells visible and quantifiable. We benchmark our approach against alternative image registration methods, a theoretical error model, and synthetic data. Our method tracks not just individual labeled particles or molecules, but the entire flow of bulk material through the cell. This enables us to measure diffusivity within distinct cell compartments using a single approach, which we use here for direct comparison of nuclear and cytoplasmic diffusivity. As a label-free method, QPV can be used for long-term tracking to capture dynamics through the cell cycle.

TiO2 nanotubes regulate histone acetylation through F-actin to induce the osteogenic differentiation of BMSCs

Bone integration on the surface of titanium prosthesis is critical to the success of implant surgery. Good Bone integration at the contact interface is the basis of long-term stability. TiO2 nanotubes have become one of the most commonly used modification techniques for artificial joint prostheses and bone defect implants due to their good biocompatibility, mechanical properties and chemical stability. TiO2 nanotubes can promote F-actin polymerization in bone mesenchymal stem cells (BMSCs) and osteogenic differentiation. The possibility of F-actin as an upstream part to regulate GCN5 initiation of osteogenesis was discussed. The results of gene loss and functional acquisition assay, immunoblotting assay and fluorescence staining assay showed that TiO2 nanotubes could promote the differentiation of BMSCs into osteoblasts. The intervention of TiO2 nanotubes can make BMSCs form stronger F-actin fibre bundles, which can drive the differentiation process of osteogenesis. Our results showed that F-actin mediated nanotube-induced cell differentiation through promoting the expression of GCN5 and enhancing the function of GCN5 and GCN5 was a key regulator of the osteogenic differentiation of BMSCs induced by TiO2 nanotubes as a downstream mediated osteogenesis of F-actin, providing a novel insight into the study of osteogenic differentiation on surface of TiO2 nanotubes.

Methyl-β-cyclodextrin suppresses the monocyte-endothelial adhesion triggered by lipopolysaccharide (LPS) or oxidized low-density lipoprotein (oxLDL)

CONTEXT

Recent studies demonstrated the anti-atherosclerotic efficacy of cyclodextrin. However, it remains unclear whether cyclodextrin exerts the anti-atherosclerotic effect via regulating monocyte-endothelial adhesion.

OBJECTIVE

To answer that question by recruiting methyl-β-cyclodextrin (MβCD) as a cyclodextrin representative.

MATERIALS AND METHODS

Human umbilical vein endothelial cells (HUVECs) were not treated, or treated with 1 µg/mL liposaccharide (LPS) or 50 µg/mL oxidized low-density lipoprotein (oxLDL) for 12 h, 5 mM MβCD for 1 h, and LPS/oxLDL (1 and 50 µg/mL, respectively for 12 h) plus MβCD (5 mM for 1 h), respectively. The effects of MβCD on LPS/oxLDL-triggered monocyte-endothelial adhesion and related molecules in signalling pathways were evaluated via confocal microscopy, flow cytometry, RT-PCR, western blotting, and cell adhesion assay.

RESULTS

MβCD with an IC₅₀ of 27.66 mM (1 h treatment) exerted no significant cytotoxicity at ≤5 mM for ≤2 h. Compared with the control, both LPS and oxLDL induced an ∼2-3-fold increase in adhesion molecule expression (ICAM-1 and VCAM-1 at protein and mRNA levels) and NF-κB phosphorylation (p-NF-κB/pP65), an increase in IκB kinase (IKK), and a decrease in phosphorylated protein kinase B (p-Akt), respectively. Moreover, more monocytes (2-fold higher for LPS and 15% higher for oxLDL) were attached on LPS/oxLDL-stimulated HUVECs. 5 mM MβCD reversed the LPS/oxLDL-induced changes back to the control levels.

CONCLUSIONS

MβCD significantly suppresses the LPS/oxLDL-triggered monocyte-endothelial adhesion by downregulating adhesion molecule expression probably via LPS-IKK-NF-κB or oxLDL-Akt-NF-κB pathway. This study demonstrates a potential mechanism of the anti-atherosclerotic efficacy of cyclodextrin from the angle of monocyte-endothelial adhesion.

Numerical analysis of the impact of cytoskeletal actin filament density alterations onto the diffusive vesicle-mediated cell transport

The interior of a eukaryotic cell is a highly complex composite material which consists of water, structural scaffoldings, organelles, and various biomolecular solutes. All these components serve as obstacles that impede the motion of vesicles. Hence, it is hypothesized that any alteration of the cytoskeletal network may directly impact or even disrupt the vesicle transport. A disruption of the vesicle-mediated cell transport is thought to contribute to several severe diseases and disorders, such as diabetes, Parkinson’s and Alzheimer’s disease, emphasizing the clinical relevance. To address the outlined objective, a multiscale finite element model of the diffusive vesicle transport is proposed on the basis of the concept of homogenization, owed to the complexity of the cytoskeletal network. In order to study the microscopic effects of specific nanoscopic actin filament network alterations onto the vesicle transport, a parametrized three-dimensional geometrical model of the actin filament network was generated on the basis of experimentally observed filament densities and network geometries in an adenocarcinomic human alveolar basal epithelial cell. Numerical analyzes of the obtained effective diffusion properties within two-dimensional sampling domains of the whole cell model revealed that the computed homogenized diffusion coefficients can be predicted statistically accurate by a simple two-parameter power law as soon as the inaccessible area fraction, due to the obstacle geometries and the finite size of the vesicles, is known. This relationship, in turn, leads to a massive reduction in computation time and allows to study the impact of a variety of different cytoskeletal alterations onto the vesicle transport. Hence, the numerical simulations predicted a 35% increase in transport time due to a uniformly distributed four-fold increase of the total filament amount. On the other hand, a hypothetically reduced expression of filament cross-linking proteins led to sparser filament networks and, thus, a speed up of the vesicle transport.

Many vital processes in our eukaryotic cells and organs require an astonishingly precise routing of intermediate products to various intra- and extracellular destinations using vesicles as transporters. This can be illustrated by numerous examples, such as the production and destruction of proteins, the export of neurotransmitters or insulin to the extracellular domain, etc. However, the inside of a cell is tightly packed with numerous structural scaffoldings (filaments), which serve as obstacles and impede the vesicle motion. It is thought that any disturbances of the vesicle-mediated cell transport contribute to numerous degenerative diseases and disorders, which highlights the clinical relevance for investigating this intracellular transport mechanism by developing computational models and performing experimental studies. In this study, we numerically quantified how different specific alterations of the filament density inside a human lung cell—due to changed mechanical loadings or genetic disorders of proteins being responsible for filament branching—affect the diffusion of vesicles inside the intracellular fluid. Therefore, based on the concept of homogenization, a computationally efficient numerical method was developed and utilized to simulate the diffusion of vesicles inside the whole cell, considering the detailed structural information of the filament network.

Single-vesicle tracking reveals the potential correlation of the movement of cell-bound membrane vesicles (CBMVs) with cell migration

The movement of cell-bound membrane vesicles (CBMVs) on migrating cells is poorly understood. We hypothesized that the movement of CBMVs on migrating cells is different from that on non-migrating cells and can be interfered by external stimuli. To test it, single-vesicle tracking was performed to analyze motion type, speed, displacement, and direction of CBMVs on migrating cells treated with different reagents (Ang-1, TNF-α, LPS, VEGFα, endostatin, Cytochalasin D, and nocodazole) among which the former four promoted cell migration whereas the others inhibited cell migration. We found that cell migration changed CBMVs from non-directed to directed motion and that most CBMVs on untreated migrating cells moved along the migration axis. Interestingly, the migration-promoting reagents played positive roles in CBMV movement (improving directed motion, speed and/or maximal displacement, upregulating the amount of vesicles moving in migration direction) whereas the migration-inhibiting reagents played negative roles (impairing/abolishing directed motion, speed and/or maximal displacement, downregulating the vesicles moving forward or causing an even distribution of motion direction). The cytoskeleton (particularly microtubules) probably played vital roles in CBMV movement on migrating cells and mediated the effects of stimuli on vesicle movement. The data may provide important information for understanding the properties, behaviors, and functions of CBMVs.

Isolated cell-bound membrane vesicles (CBMVs) as a novel class of drug nanocarriers

BACKGROUND

Cell-bound membrane vesicles (CBMVs) are a type of membrane vesicles different from the well-known extracellular vesicles (EVs). In recent years, the applications of EVs as drug delivery systems have been studied widely. A question may arise whether isolated CBMVs also have the possibility of being recruited as a drug delivery system or nanocarrier?

METHODS

To test the possibility, CBMVs were isolated/purified from the surfaces of cultured endothelial cells, loaded with a putative antitumor drug doxorubicin (Dox), and characterized. Subsequently, cellular experiments and animal experiments using mouse models were performed to determine the in vitro and in vivo antitumor effects of Dox-loaded CBMVs (Dox-CBMVs or Dox@CBMVs), respectively.

RESULTS

Both Dox-free and Dox-loaded CBMVs were globular-shaped and nanometer-sized with an average diameter of ~ 300-400 nm. Dox-CBMVs could be internalized by cells and could kill multiple types of cancer cells. The in vivo antitumor ability of Dox-CBMVs also was confirmed. Moreover, Quantifications of blood cells (white blood cells and platelets) and specific enzymes (aspartate aminotransferase and creatine kinase isoenzymes) showed that Dox-CBMVs had lower side effects compared with free Dox.

CONCLUSIONS

The data show that the CBMV-entrapped Doxorubicin has the antitumor efficacy with lower side effects. This study provides evidence supporting the possibility of isolated cell-bound membrane vesicles as a novel drug nanocarrier.

Exogenous GM3 ganglioside inhibits atherosclerosis via multiple steps: A potential atheroprotective drug

Atherosclerosis is one of the leading causes of morbidity and mortality worldwide. A significant increase in ganglioside GM3 content generally happens in atherosclerotic plaques causing a GM3-enriched microenvironment. It remains unclear whether the GM3-enriched microenvironment influences atherogenesis. This study sought to answer the question by investigating exogenous GM3 effects on multiple steps involved in atherogenesis. First, the physicochemical properties of native low-density lipoprotein (LDL) and LDL enriched with exogenous GM3 (GM3-LDL) were characterized by dynamic laser scattering, atomic force microscopy, and agarose gel electrophoresis. Then, electrophoretic mobility, conjugated diene and malondialdehyde production, and amino group blockage of GM3-LDL/LDL were measured to determine LDL oxidation degrees and cellular recognition/internalization of GM3-LDL/GM3-oxLDL were detected via confocal microscopy and flow cytometry. Subsequently, influences of exogenous GM3 addition on the monocyte-adhering ability of endothelial cells and on lipid deposition in macrophages were investigated. Finally, exogenous GM3 effect on atherogenesis was evaluated using apoE^-/- mice fed a high-fat diet. We found that exogenous GM3 addition increased the size, charge, and stability of LDL particles, reduced LDL susceptibility to oxidation and its cellular recognition/internalization, impaired the monocyte-adhering ability of endothelial cells and lipid deposition in macrophages. Moreover, exogenous GM3 treatment also significantly decreased blood lipid levels and atherosclerotic lesion areas in atherosclerotic mice. The data imply that exogenous GM3 had an inhibitory effect on atherogenesis, suggesting a protective role of a GM3-enriched microenvironment in atherosclerotic plaques and implying a possibility of exogenous GM3 as an anti-atherosclerotic drug.

Image and data processing algorithms for identifying cell-bound membrane vesicle trajectories and movement information

This DIB article provides details about the trajectory identification and data processing algorithms used in the article “Dynamic single-vesicle tracking of cell-bound membrane vesicles on resting, activated, and cytoskeleton-disrupted cells” (Zhang et al.) [1]. The algorithm identifies vesicles on cell membranes from series of undyed grayscale images captured by the confocal microscope based on contrast differences and then trajectories of vesicles are obtained by analyzing their positions in consecutive images. Once the trajectories have been obtained, other quantitative movement information, such as moving speed, direction and acceleration, are derived by standard dynamic relations.