Effects of lipid composition and solution conditions on the mechanical properties of membrane vesicles

Exogenous polyserine fibrils change membrane properties of phosphatidylcholine-liposome and red blood cells

The causative genes for neurodegenerative polyglutamine (polyQ) diseases produce homopolymeric polyglutamine (polyQ), polyserine (polyS), polyalanine (polyA), polycysteine (polyC), and polyleucine (polyL) sequences by repeat-associated non-AUG (RAN) translation. The cytotoxicity of the intracellular polyQ and RAN products has been extensively investigated. However, little is known about the toxicity of the extracellular polyQ and RAN products on the membranes of viable cells. Because polyQ aggregates induce a deflated morphology of a model membrane, we hypothesized that extracellular polyQ and RAN products might affect the membrane properties of viable cells. In this study, we demonstrated that exogenous polyS fibrils but not polyS or polyQ non-fibril aggregates altered the thermal phase transition behavior of a model membrane composed of a phosphatidylcholine bilayer using differential scanning calorimetry. PolyS fibrils induced morphological changes in viable red blood cells (RBCs). However, both polyS and polyQ non-fibril aggregates had no effects on RBCs. These results highlight the possibility that extracellular fibrils generated from RAN products may alter the properties of neuronal cell membranes, which may contribute to changes in the brain pathology.

Methods to mechanically perturb and characterize GUV-based minimal cell models

Cells shield organelles and the cytosol via an active boundary predominantly made of phospholipids and membrane proteins, yet allowing communication between the intracellular and extracellular environment. Micron-sized liposome compartments commonly known as giant unilamellar vesicles (GUVs) are used to model the cell membrane and encapsulate biological materials and processes in a cell-like confinement. In the field of bottom-up synthetic biology, many have utilized GUVs as substrates to study various biological processes such as protein-lipid interactions, cytoskeletal assembly, and dynamics of protein synthesis. Like cells, it is ideal that GUVs are also mechanically durable and able to stay intact when the inner and outer environment changes. As a result, studies have demonstrated approaches to tune the mechanical properties of GUVs by modulating membrane composition and lumenal material property. In this context, there have been many different methods developed to test the mechanical properties of GUVs. In this review, we will survey various perturbation techniques employed to mechanically characterize GUVs.

Facile generation of giant unilamellar vesicles using polyacrylamide gels

Giant unilamellar vesicles (GUVs) are model cell-sized systems that have broad applications including drug delivery, analysis of membrane biophysics, and synthetic reconstitution of cellular machineries. Although numerous methods for the generation of free-floating GUVs have been established over the past few decades, only a fraction have successfully produced uniform vesicle populations both from charged lipids and in buffers of physiological ionic strength. In the method described here, we generate large numbers of free-floating GUVs through the rehydration of lipid films deposited on soft polyacrylamide (PAA) gels. We show that this technique produces high GUV concentrations for a range of lipid types, including charged ones, independently of the ionic strength of the buffer used. We demonstrate that the gentle hydration of PAA gels results in predominantly unilamellar vesicles, which is in contrast to comparable methods analyzed in this work. Unilamellarity is a defining feature of GUVs and the generation of uniform populations is key for many downstream applications. The PAA method is widely applicable and can be easily implemented with commonly utilized laboratory reagents, making it an appealing platform for the study of membrane biophysics.

Anti-MRSA malleable liposomes carrying chloramphenicol for ameliorating hair follicle targeting

Pathogens usually invade hair follicles when skin infection occurs. The accumulated bacteria in follicles are difficult to eradicate. The present study aimed to assess the cutaneous and follicular delivery of chloramphenicol (Cm)-loaded liposomes and the antibacterial activity of these liposomes against methicillin-resistant Staphylococcus aureus (MRSA). Skin permeation was conducted by in vitro Franz diffusion cell. The anti-MRSA potential was checked using minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), a well diffusion test, and intracellular MRSA killing. The classic, dimyristoylphosphatidylcholine (DMPC), and deoxycholic acid (DA) liposomes had a vesicle size of 98, 132, and 239 nm, respectively. The incorporation of DMPC or DA into the liposomes increased the bilayer fluidity. The malleable vesicles containing DMPC and DA showed increased follicular Cm uptake over the control solution by 1.5- and 2-fold, respectively. The MIC and MBC of DA liposomes loaded with Cm were 62.5 and 62.5–125 μg/mL, comparable to free Cm. An inhibition zone about 2-fold higher was achieved by DA liposomes as compared to the free control at a Cm dose of 0.5 mg/mL. DA liposomes also augmented antibacterial activity on keratinocyte-infected MRSA. The deformable liposomes had good biocompatibility against keratinocytes and neutrophils (viability >80%). In vivo administration demonstrated that DA liposomes caused negligible toxicity on the skin, based on physiological examination and histology. These data suggest the potential application of malleable liposomes for follicular targeting and the treatment of MRSA-infected dermatologic conditions.

Physicochemical characterizations of functional hybrid liposomal nanocarriers formed using photo-sensitive lipids

With recent advances in the field of diagnostics and theranostics, liposomal technology has secured a fortified position as a potential nanocarrier. Specifically, radiation/photo-sensitive liposomes containing photo-polymerizable cross-linking lipids are intriguing as they can impart the vesicles with highly interesting properties such as response to stimulus and improved shell stability. In this work, 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphoethanolamine (DTPE) is used as a photo-polymerizable lipid to form functional hybrid-liposomes as it can form intermolecular cross-linking through the diacetylenic groups. Hybrid-liposomes were formulated using mixtures of DTPE and saturated lipids of different chain lengths (dipalmitoylphosphatidylcholine (DPPC) and dimirystoilphosphatidylcholine (DMPC)) at different molar ratios. The physico-chemical characteristics of the liposomes has been studied before and after UV irradiation using a combination of techniques: DSC, QCM-D and solid-state NMR. The results signify the importance of a subtle modification in alkyl chain length on the phase behavior of the hybrid-liposomes and on the degree of crosslinking in the shell.

The chain order of binary unsaturated lipid bilayers modulated by aromatic-residue-containing peptides: an ATR-FTIR spectroscopy study

It highlights the importance of aromatic residues in influencing peptide binding to the membrane, demonstrates that the stability of the membranes depends on the lipid composition and the sequence, structural context, and orientation of the peptides.

Reversible Morphological Control of Tubulin-Encapsulating Giant Liposomes by Hydrostatic Pressure

Liposomes encapsulating cytoskeletons have drawn much recent attention to develop an artificial cell-like chemical-machinery; however, as far as we know, there has been no report showing isothermally reversible morphological changes of liposomes containing cytoskeletons because the sets of various regulatory factors, that is, their interacting proteins, are required to control the state of every reaction system of cytoskeletons. Here we focused on hydrostatic pressure to control the polymerization state of microtubules (MTs) within cell-sized giant liposomes (diameters ∼10 μm). MT is the cytoskeleton formed by the polymerization of tubulin, and cytoskeletal systems consisting of MTs are very dynamic and play many important roles in living cells, such as the morphogenesis of nerve cells and formation of the spindle apparatus during mitosis. Using real-time imaging with a high-pressure microscope, we examined the effects of hydrostatic pressure on the morphology of tubulin-encapsulating giant liposomes. At ambient pressure (0.1 MPa), many liposomes formed protrusions due to tubulin polymerization within them. When high pressure (60 MPa) was applied, the protrusions shrank within several tens of seconds. This process was repeatedly inducible (around three times), and after the pressure was released, the protrusions regenerated within several minutes. These deformation rates of the liposomes are close to the velocities of migrating or shape-changing living cells rather than the shortening and elongation rates of the single MTs, which have been previously measured. These results demonstrate that the elongation and shortening of protrusions of giant liposomes is repeatedly controllable by regulating the polymerization state of MTs within them by applying and releasing hydrostatic pressure.