Defining the structural characteristics of annexin V binding to a mimetic apoptotic membrane

Molecular Sensing and Manipulation of Protein Oligomerization in Membrane Nanotubes with Bolaamphiphilic Foldamers

Adaptive and reversible self-assembly of supramolecular protein structures is a fundamental characteristic of dynamic living matter. However, the quantitative detection and assessment of the emergence of mesoscale protein complexes from small and dynamic oligomeric precursors remains highly challenging. Here, we present a novel approach utilizing a short membrane nanotube (sNT) pulled from a planar membrane reservoir as nanotemplates for molecular reconstruction, manipulation, and sensing of protein oligomerization and self-assembly at the mesoscale. The sNT reports changes in membrane shape and rigidity caused by membrane-bound proteins as variations of the ionic conductivity of the sNT lumen. To confine oligomerization to the sNT, we have designed and synthesized rigid oligoamide foldamer tapes (ROFTs). Charged ROFTs incorporate into the planar and sNT membranes, mediate protein binding to the membranes, and, driven by the luminal electric field, shuttle the bound proteins between the sNT and planar membranes. Using Annexin-V (AnV) as a prototype, we show that the sNT detects AnV oligomers shuttled into the nanotube by ROFTs. Accumulation of AnV on the sNT induces its self-assembly into a curved lattice, restricting the sNT geometry and inhibiting the material uptake from the reservoir during the sNT extension, leading to the sNT fission. By comparing the spontaneous and ROFT-mediated entry of AnV into the sNT, we reveal how intricate membrane curvature sensing by small AnV oligomers controls the lattice self-assembly. These results establish sNT-ROFT as a powerful tool for molecular reconstruction and functional analyses of protein oligomerization and self-assembly, with broad application to various membrane processes.

Targeted delivery of LM22A-4 by cubosomes protects retinal ganglion cells in an experimental glaucoma model

Glaucoma, a major cause of irreversible blindness worldwide, is associated with elevated intraocular pressure (IOP) and progressive loss of retinal ganglion cells (RGCs) that undergo apoptosis. A mechanism for RGCs injury involves impairment of neurotrophic support and exogenous supply of neurotrophic factors has been shown to be beneficial. However, neurotrophic factors can have widespread effects on neuronal tissues, thus targeting neurotrophic support to injured neurons may be a better neuroprotective strategy. In this study, we have encapsulated LM22A-4, a small neurotrophic factor mimetic, into Annexin V-conjugated cubosomes (L4-ACs) for targeted delivery to injured RGCs in a model of acute IOP elevation, which is induced by acute IOP elevation. We have tested cubosomes formulations that encapsulate from 9% to 33% LM22A-4. Our data indicated that cubosomes encapsulating 9% and 17% LM22A-4 exhibited a mixture of Pn3m/Im3m cubic phase, whereas 23% and 33% showed a pure Im3m cubic phase. We found that 17% L4-ACs with Pn3m/Im3m symmetries showed better in-situ and in-vitro lipid membrane interactions than the 23% and 33% L4-ACs with Im3m symmetry. In vivo experiments showed that 17% L4-ACs targeted the posterior retina and the optic nerve head, which prevented RGCs loss and improved functional outcomes in a mouse model of acute IOP elevation. These results provide evidence that Annexin V-conjugated cubosomes-based LM22A-4 delivery may be a useful targeted approach to prevent the progression of RGCs loss in glaucoma. STATEMENT OF SIGNIFICANCE: Recent studies suggest that the therapy of effectively delivering neurotrophic factors to the injured retinal ganglion cells (RGCs) could promote the survival of RGCs in glaucoma. Our present work has for the first time used cubosomes as an active targeted delivery system and have successfully delivered a neuroprotective drug to the damaged RGCs in vivo. Our new cubosomal formulation can protect apoptotic cell death in vitro and in vivo, showing that cubosomes are a promising drug carrier system for ocular drug delivery and glaucoma treatment. We have further found that by controlling cubosomes in Pn3m phase we can facilitate delivery of neuroprotective drug through apoptotic membranes. This data, we believe, has important implications for future design and formulation of cubosomes for therapeutic applications.

A Quenched Annexin V-Fluorophore for the Real-Time Fluorescence Imaging of Apoptotic Processes In Vitro and In Vivo

Annexin-based probes have long been used to study apoptotic cell death, which is of key importance to many areas of biological research, drug discovery, and clinical applications. Although apoptosis is a dynamic biological event with cell-to-cell variations, current annexin-based probes are impractical for monitoring apoptosis in real-time. Herein, a quenched annexin V-near-infrared fluorophore conjugate (Q-annexin V) is reported as the first OFF-ON annexin protein-based molecular sensor for real-time near-infrared fluorescence imaging of apoptosis. Q-annexin V is non-fluorescent in the extracellular region, due to photoinduced electron transfer interactions between the conjugated dye and amino acid quenchers (tryptophan and tyrosine). The probe becomes highly fluorescent when bound to phosphatidylserines on the outer layer of cell membranes during apoptosis, thereby enabling apoptosis to be monitored in real-time in 2D and 3D cell structures. In particular, Q-annexin V shows superior utility for in vivo apoptosis fluorescence imaging in animal models of cisplatin-induced acute kidney injury and cancer immune therapy, compared to the conventional polarity-sensitive pSIVA-IANBD or annexin V-Alexa647 conjugates.

Annexin V Drives Stabilization of Damaged Asymmetric Phospholipid Bilayers

Annexins are soluble membrane-binding proteins that associate in a calcium dependent manner with anionic phospholipids. They play roles in membrane organization, signaling and vesicle transport and in several disease states including thrombosis and inflammation. Annexin V is believed to be involved in membrane repair. Mediated through binding to phosphatidylserine exposed at damaged plasma membrane, the protein forms crystalline networks that seal or stabilize small membrane tears. Herein, we model this biochemical mechanism to simulate membrane healing at microcavity array supported, transversally asymmetric, lipid bilayers (MSLBs) comprising 1,2-dioleoylsn-glycero-3-phosphocholine (DOPC) and 1,2-dioleoyl-sn-glycero-3-phospho-l-serine (DOPS). Varying annexin V concentration, lipid composition, and DOPS presence at each leaflet, fluorescence imaging and correlation spectroscopy confirmed that when DOPS was present at the external, annexin V, contacting leaflet, the protein assembled rapidly at the membrane interface to form a layer. From electrochemical impedance studies, the annexin layer decreased membrane capacitance while reducing resistance. With DOPS incorporated only at the lower (proximal) leaflet, no appreciable annexin assembly was observed over the first 21 h. This suggests that membrane asymmetry is preserved over this window and transversal diffusion of DOPS is slow. Intense laser light applied to the membrane, in which DOPS is initially isolated at the lower leaflet, was found to simulate membrane damage, stimulating the rapid assembly of annexin V at the membrane interface confirmed by fluorescence imaging, correlation spectroscopy, and electrochemical impedance measurements. The damage induced by light increased impedance and decreased membrane resistance. The resulting bilayer annexin V patched bilayer showed better temporal stability toward impedance changes when compared with that of the parent membrane. In summary, this simple model of annexin V assembly in a fluidic lipid membrane provides new insights into the assembly of annexins as well as an empirical basis for building patch-repair mechanisms into interfacial bilayer membrane assemblies.

Hormone-regulated PKA activity in porcine oviductal epithelial cells

The oviduct is a dynamic organ that suffers changes during the oestrous cycle and modulates gamete and embryo physiology. We analyse the possible existence of Protein kinase A (PKA)-dependent hormone-regulated pathways in porcine ampulla and primary cell cultures by 2D-electrophoresis/Western blot using anti-phospho PKA substrate antibodies. Differential phosphorylation was observed for ten proteins that were identified by mass spectrometry. The results were validated for five of the proteins: Annexin A5, Calumenin, Glyoxalase I and II and Enolase I. Immunofluorescence analyses show that Calumenin, Glyoxalase II and Enolase I change their localisation in the oviductal epithelium through the oestrus cycle. The results demonstrate the existence of PKA hormone-regulated pathways in the ampulla epithelium during the oestrus cycle.

Designing nanoparticles with improved tumor penetration: surface properties from the molecular architecture viewpoint

Cancer is the second most common cause of death, and nanomedicine is regarded as one of the strategies that may revolutionize cancer treatments. However, the tumor microenvironment (e.g., increased interstitial fluid pressure and dense extracellular matrix) hinders the penetration of nanomedicine into tumor cells, which leads to a short acting time and low drug concentration with tumors, eventually leading to a high recurrence rate and therapeutic failure in clinics. Developing a delivery system with deep penetration ability into the tumor has always been pursued and highly desirable for cancer treatments. Inspired by the high cellular uptake efficiency of enveloped viruses with rough and nanoscale surfaces, we constructed polystyrene nanoparticles (NPs) with similar sizes and charges, but with different surface topologies at the molecular level, by conjugating poly(propylene imine) (PPI) dendrimers with different generations onto the NPs. We found that subtle changes made to the surficial chemical properties led to changes in surface roughness and wettability, which considerably influenced the cellular internalization, endocytosis mechanism, and penetration into the tumor model both in vitro and in vivo. This will shed light on the future design of drug delivery vehicles and facilitate understanding the interactions between NP surfaces and cells, as well as tumor penetration.

Towards biomimics of cell membranes: Structural effect of phosphatidylinositol triphosphate (PIP3) on a lipid bilayer

Phosphoinositide (PIP) lipids are anionic phospholipids playing a fundamental role for the activity of several transmembrane and soluble proteins. Among all, phosphoinositol-3',4',5'-trisphosphate (PIP₃) is a secondary signaling messenger that regulates the function of proteins involved in cell growth and gene transcription. The present study aims to reveal the structure of PIP-containing lipid membranes, which so far has been little explored. For this purpose, supported lipid bilayers (SLBs) containing 1,2-dioleoyl-sn-glycero-3-phospho-(1'-myo-inositol-3',4',5'-trisphosphate (DOPIP₃) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) were used as mimics of biomembranes. Surface sensitive techniques, i.e. Quartz Crystal Microbalance with Dissipation monitoring (QCM-D), Atomic Force Microscopy (AFM) and Neutron Reflectometry (NR), provided detailed information on the formation of the SLB and the location of DOPIP₃ in the lipid membrane. Specifically, QCM-D and AFM were used to identify the best condition for lipid deposition and to estimate the total bilayer thickness. On the other hand, NR was used to collect experimental structural data on the DOPIP₃ location and orientation within the lipid membrane. The two bilayer leaflets showed the same DOPIP₃ concentration, thus suggesting the formation of a symmetric bilayer. The headgroup layer thicknesses of the pure POPC and the mixed POPC/DOPIP₃ bilayer suggest that the DOPIP₃-headgroups have a preferred orientation, which is not perpendicular to the membrane surface, but instead it is close to the surrounding lipid headgroups. These results support the proposed PIP₃ tendency to interact with the other lipid headgroups as PC, so far exclusively suggested by MD simulations.

Annexin V-containing cubosomes for targeted early detection of apoptosis in degenerative retinal tissue

ANX–PS–Phy cubosomes could be applied as a safe and robust drug delivery vehicle for targeting damaged, apoptotic cells in ocular diseases.