Plasma Membrane Disruption: Repair, Prevention, Adaptation

Impact of Silk-Ionomer Encapsulation on Immune Cell Mechanical Properties and Viability

Encapsulation of single cells is a powerful technique used in various fields, such as regenerative medicine, drug delivery, tissue regeneration, cell-based therapies, and biotechnology. It offers a method to protect cells by providing cytocompatible coatings to strengthen cells against mechanical and environmental perturbations. Silk fibroin, derived from the silkworm Bombyx mori, is a promising protein biomaterial for cell encapsulation due to the cytocompatibility and capacity to maintain cell functionality. Here, THP-1 cells, a human leukemia monocytic cell line, were encapsulated with chemically modified silk polyelectrolytes through electrostatic layer-by-layer deposition. The effectiveness of the silk nanocoating was assessed using scanning electron microscopy (SEM) and confocal microscopy and on cell viability and proliferation by Alamar Blue assay and live/dead staining. An analysis of the mechanical properties of the encapsulated cells was conducted using atomic force microscopy nanoindentation to measure elasticity maps and cellular stiffness. After the cells were encapsulated in silk, an increase in their stiffness was observed. Based on this observation, we developed a mechanical predictive model to estimate the variations in stiffness in relation to the thickness of the coating. By tuning the cellular assembly and biomechanics, these encapsulations promote systems that protect cells during biomaterial deposition or processing in general.

Polyvinylpyrrolidone can prevent oolemma lysis caused by abnormal rupture of the plasma membrane in Piezo-ICSI

The aim of this study was to investigate whether it is possible to prevent oolemma lysis after Piezo-assisted intracytoplasmic sperm injection (Piezo-ICSI) caused by abnormal membrane rupture. A total of 489 mature oocytes were obtained from 85 patients who underwent Piezo-ICSI in an infertility clinic. Inseminated oocytes were classified into the following two groups: normal rupture and abnormal rupture, and a portion of abnormally ruptured oocytes was randomly exposed to 7% PVP solution. Normal fertilization rate, degeneration rate, proportion of high-quality embryos on day 3, blastocyst formation, and morphologically high-quality blastocysts were compared. Abnormal rupture was defined as cytoplasmic membrane rupture before piezo pulse driving. Among the abnormal rupture groups, the normal fertilization and degeneration rates were compared between the high-stretched (ruptured at ≥ 50% during oocyte membrane stretching) and low-stretched (< 50% position) oocytes.The degeneration rate was significantly higher in abnormally ruptured oocytes than in normally ruptures oocytes (14.3% vs 1.3%, p < 0.001), and there was no significant difference in embryonic development after fertilization. PVP treatment immediately after oolemma rupture significantly decreased the degeneration rate (6.0% vs 19.7%, p = 0.031) and increased the normal fertilization rate. Similarly, there were no significant differences in the developmental potential. Furthermore, pregnancy outcome data showed no significant differences in pregnancy and live birth rates. The degeneration rate was reduced by treating low-stretched oocytes with PVP.Exposure to polyvinylpyrrolidone (PVP) immediately after abnormal membrane rupture represents an effective strategy to prevent oocyte degeneration. This is the first study to propose a strategy for the prevention of oocyte degeneration in Piezo-ICSI. These findings are expected to reduce the oocyte degeneration rate and increase normal fertilization rate as well as assist patients who can only acquire oocytes with weak plasma membranes.

Micronano Synergetic Three-Dimensional Bioelectronics: A Revolutionary Breakthrough Platform for Cardiac Electrophysiology

Cardiovascular diseases (CVDs) are the leading cause of mortality and therefore pose a significant threat to human health. Cardiac electrophysiology plays a crucial role in the investigation and treatment of CVDs, including arrhythmia. The long-term and accurate detection of electrophysiological activity in cardiomyocytes is essential for advancing cardiology and pharmacology. Regarding the electrophysiological study of cardiac cells, many micronano bioelectric devices and systems have been developed. Such bioelectronic devices possess unique geometric structures of electrodes that enhance quality of electrophysiological signal recording. Though planar multielectrode/multitransistors are widely used for simultaneous multichannel measurement of cell electrophysiological signals, their use for extracellular electrophysiological recording exhibits low signal strength and quality. However, the integration of three-dimensional (3D) multielectrode/multitransistor arrays that use advanced penetration strategies can achieve high-quality intracellular signal recording. This review provides an overview of the manufacturing, geometric structure, and penetration paradigms of 3D micronano devices, as well as their applications for precise drug screening and biomimetic disease modeling. Furthermore, this review also summarizes the current challenges and outlines future directions for the preparation and application of micronano bioelectronic devices, with an aim to promote the development of intracellular electrophysiological platforms and thereby meet the demands of emerging clinical applications.

A computational study of cell membrane damage and intracellular delivery in a cross-slot microchannel

We propose a three-dimensional computational framework to simulate the flow-induced cell membrane damage and the resulting enhanced intracellular mass transport in a cross-slot microchannel. We model the cell as a liquid droplet enclosed by a viscoelastic membrane and solve the cell deformation using a well-tested immersed-boundary lattice-Boltzmann method. The cell membrane damage, which is directly related to the membrane permeability, is considered using continuum damage mechanics. The transport of the diffusive solute into the cell is solved by a lattice-Boltzmann model. After validating the computational framework against several benchmark cases, we consider a cell flowing through a cross-slot microchannel, focusing on the effects of the flow strength, channel fluid viscosity and cell membrane viscosity on the membrane damage and enhanced intracellular transport. Interestingly, we find that under a comparable pressure drop across the device, for cells with low membrane viscosity, the inertial flow regime, which can be achieved by driving a low-viscosity liquid at a high speed, often leads to much larger membrane damage, compared with the high-viscosity low-speed viscous flow regime. However, the enhancement can be significantly reduced or even reversed by an increase of the cell membrane viscosity, which limits cell deformation, particularly in the inertial flow regime. Our computational framework and simulation results may guide the design and optimisation of microfluidic devices, which use cross-slot geometry to disrupt cell membranes to enhance intracellular delivery of solutes.

Plasma membrane repair empowers the necrotic survivors as innate immune modulators

The plasma membrane is crucial to the survival of animal cells, and damage to it can be lethal, often resulting in necrosis. However, cells possess multiple mechanisms for repairing the membrane, which allows them to maintain their integrity to some extent, and sometimes even survive. Interestingly, cells that survive a near-necrosis experience can recognize sub-lethal membrane damage and use it as a signal to secrete chemokines and cytokines, which activate the immune response. This review will present evidence of necrotic cell survival in both in vitro and in vivo systems, including in C. elegans, mouse models, and humans. We will also summarize the various membrane repair mechanisms cells use to maintain membrane integrity. Finally, we will propose a mathematical model to illustrate how near-death experiences can transform dying cells into innate immune modulators for their microenvironment. By utilizing their membrane repair activity, the biological effects of cell death can extend beyond the mere elimination of the cells.

Bilayer Charge Asymmetry and Oil Residues Destabilize Membranes upon Poration

Transmembrane asymmetry is ubiquitous in cells, particularly with respect to lipids, where charged lipids are mainly restricted to one monolayer. We investigate the influence of anionic lipid asymmetry on the stability of giant unilamellar vesicles (GUVs), minimal plasma membrane models. To quantify asymmetry, we apply the fluorescence quenching assay, which is often difficult to reproduce, and caution in handling the quencher is generally underestimated. We first optimize this assay and then apply it to GUVs prepared with the inverted emulsion transfer protocol by using increasing fractions of anionic lipids restricted to one leaflet. This protocol is found to produce highly asymmetric bilayers but with ∼20% interleaflet mixing. To probe the stability of asymmetric versus symmetric membranes, we expose the GUVs to porating electric pulses and monitor the fraction of destabilized vesicles. The pulses open macropores, and the GUVs either completely recover or exhibit leakage or bursting/collapse. Residual oil destabilizes porated membranes, and destabilization is even more pronounced in asymmetrically charged membranes. This is corroborated by the measured pore edge tension, which is also found to decrease with increasing charge asymmetry. Using GUVs with imposed transmembrane pH asymmetry, we confirm that poration-triggered destabilization does not depend on the approach used to generate membrane asymmetry.

Plasma membrane damage limits replicative lifespan in yeast and induces premature senescence in human fibroblasts

Plasma membrane damage (PMD) occurs in all cell types due to environmental perturbation and cell-autonomous activities. However, cellular outcomes of PMD remain largely unknown except for recovery or death. In this study, using budding yeast and normal human fibroblasts, we found that cellular senescence-stable cell cycle arrest contributing to organismal aging-is the long-term outcome of PMD. Our genetic screening using budding yeast unexpectedly identified a close genetic association between PMD response and replicative lifespan regulations. Furthermore, PMD limits replicative lifespan in budding yeast; upregulation of membrane repair factors ESCRT-III (SNF7) and AAA-ATPase (VPS4) extends it. In normal human fibroblasts, PMD induces premature senescence via the Ca2+-p53 axis but not the major senescence pathway, DNA damage response pathway. Transient upregulation of ESCRT-III (CHMP4B) suppressed PMD-dependent senescence. Together with mRNA sequencing results, our study highlights an underappreciated but ubiquitous senescent cell subtype: PMD-dependent senescent cells.

Annexins-a family of proteins with distinctive tastes for cell signaling and membrane dynamics

Annexins are cytosolic proteins with conserved three-dimensional structures that bind acidic phospholipids in cellular membranes at elevated Ca2+ levels. Through this they act as Ca2+-regulated membrane binding modules that organize membrane lipids, facilitating cellular membrane transport but also displaying extracellular activities. Recent discoveries highlight annexins as sensors and regulators of cellular and organismal stress, controlling inflammatory reactions in mammals, environmental stress in plants, and cellular responses to plasma membrane rupture. Here, we describe the role of annexins as Ca2+-regulated membrane binding modules that sense and respond to cellular stress and share our view on future research directions in the field.

Caveolae disassemble upon membrane lesioning and foster cell survival

Repair of lesions in the plasma membrane is key to sustaining cellular homeostasis. Cells maintain cytoplasmic as well as membrane-bound stores of repair proteins that can rapidly precipitate at the site of membrane lesions. However, little is known about the origins of lipids and proteins for resealing and repair of the plasma membrane. Here we study the dynamics of caveolar proteins after laser-induced lesioning of plasma membranes of mammalian C2C12 tissue culture cells and muscle cells of intact zebrafish embryos. Single-molecule diffusivity measurements indicate that caveolar clusters break up into smaller entities after wounding. Unlike Annexins and Dysferlin, caveolar proteins do not accumulate at the lesion patch. In caveolae-depleted cavin1a knockout zebrafish embryos, lesion patch formation is impaired, and injured cells show reduced survival. Our data suggest that caveolae disassembly releases surplus plasma membrane near the lesion to facilitate membrane repair after initial patch formation for emergency sealing.

Mechanosensitivity and mechanotransductive properties of osteoclasts

Mechanical loading is essential for maintaining bone health. Here, we aimed to investigate the role of ATP and ADP in the mechanotransduction of bone-resorptive osteoclasts. Single osteoclast in primary cultures from 10 to 12-wk-old mice was mechanically stimulated by a gentle touch with a micropipette. Changes in cytosolic free calcium [Ca2+]i were analyzed in Fura-2 loaded osteoclasts. The cell injury was assessed by analyzing the cellular Fura-2 loss and classified as severe or mild using k-means. Osteoclasts responded to mechanical stimuli with transient calcium elevation (primary responders) and transduced these signals to neighboring cells, which responded with delayed calcium elevations (secondary responders). Severely injured osteoclasts had higher calcium transients than mildly injured cells. Fluid shear stress similarly induced reversible cell injury in osteoclasts. Secondary responses were abolished by treatment with A-804598, a specific inhibitor of P2X7, but not suramin, a broad P2 receptor blocker. Osteoclasts responded to ATP and ADP with concentration-dependent changes in [Ca2+]i. We performed osteoclast micropipette stimulation in the presence of phosphoenolpyruvate and pyruvate kinase which converted all ADP in solution to ATP, or with hexokinase converting all ATP to ADP. Osteoclasts with mild membrane injury demonstrated similar calcium responses in ATP and ADP-rich environments. However, when the mechanotransductive signal to severe osteoclast injury was converted to ADP, the fraction of secondary responders and their [Ca2+]i amplitude was higher. This study suggests the importance of osteoclast mechanobiology and the role of ADP-mediated signaling in conditions of altered mechanical loading associated with bone loss.NEW & NOTEWORTHY Osteoclasts are rarely considered as cells that participate in mechanical signaling in bone. We show that osteoclasts are capable of sensing and transmitting mechanical signals to neighboring cells. Mechanical stimulation commonly induces minor repairable membrane injury in osteoclasts. ATP and especially ADP were found to play important roles in the mechanoresponsiveness of osteoclasts. This study highlights the importance of osteoclast mechanobiology especially in conditions of altered mechanical loading associated with bone loss, such as in microgravity.

Optimizing the Cell-Nanostructure Interface: Nanoconcave/Nanoconvex Device for Intracellular Recording of Cardiomyocytes

Nanostructures are powerful components for the development of high-performance nanodevices. Revealing and understanding the cell-nanostructure interface are essential for improving and guiding nanodevice design for investigations of cell physiology. For intracellular electrophysiological detection, the cell-nanostructure interface significantly affects the quality of recorded intracellular action potentials and the application of nanodevices in cardiology research and pharmacological screening. Most of the current investigations of biointerfaces focus on nanovertical structures, and few involve nanoconcave structures. Here, we design both nanoconvex and nanoconcave devices to perform intracellular electrophysiological recordings. The amplitude, signal-to-noise ratio, duration, and repeatability of the recorded intracellular electrophysiological signals provide a multifaceted characterization of the cell-nanostructure interface. We demonstrate that devices based on both convex and concave nanostructures can create tight coupling, which facilitates high-quality and stable intracellular recordings and paves the way for precise electrophysiological study.

Inhibition of the membrane repair protein annexin-A2 prevents tumor invasion and metastasis

Cancer cells are exposed to major compressive and shearing forces during invasion and metastasis, leading to extensive plasma membrane damage. To survive this mechanical stress, they need to repair membrane injury efficiently. Targeting the membrane repair machinery is thus potentially a new way to prevent invasion and metastasis. We show here that annexin-A2 (ANXA2) is required for membrane repair in invasive breast and pancreatic cancer cells. Mechanistically, we show by fluorescence and electron microscopy that cells fail to reseal shear-stress damaged membrane when ANXA2 is silenced or the protein is inhibited with neutralizing antibody. Silencing of ANXA2 has no effect on proliferation in vitro, and may even accelerate migration in wound healing assays, but reduces tumor cell dissemination in both mice and zebrafish. We expect that inhibiting membrane repair will be particularly effective in aggressive, poor prognosis tumors because they rely on the membrane repair machinery to survive membrane damage during tumor invasion and metastasis. This could be achieved either with anti-ANXA2 antibodies, which have been shown to inhibit metastasis of breast and pancreatic cancer cells, or with small molecule drugs.

Mechanisms of Endothelial Cell Membrane Repair: Progress and Perspectives

Endothelial cells are the crucial inner lining of blood vessels, which are pivotal in vascular homeostasis and integrity. However, these cells are perpetually subjected to a myriad of mechanical, chemical, and biological stresses that can compromise their plasma membranes. A sophisticated repair system involving key molecules, such as calcium, annexins, dysferlin, and MG53, is essential for maintaining endothelial viability. These components orchestrate complex mechanisms, including exocytosis and endocytosis, to repair membrane disruptions. Dysfunctions in this repair machinery, often exacerbated by aging, are linked to endothelial cell death, subsequently contributing to the onset of atherosclerosis and the progression of cardiovascular diseases (CVD) and stroke, major causes of mortality in the United States. Thus, identifying the core machinery for endothelial cell membrane repair is critically important for understanding the pathogenesis of CVD and stroke and developing novel therapeutic strategies for combating CVD and stroke. This review summarizes the recent advances in understanding the mechanisms of endothelial cell membrane repair. The future directions of this research area are also highlighted.

Biofilms as Battlefield Armor for Bacteria against Antibiotics: Challenges and Combating Strategies

Bacterial biofilms are formed by communities, which are encased in a matrix of extracellular polymeric substances (EPS). Notably, bacteria in biofilms display a set of 'emergent properties' that vary considerably from free-living bacterial cells. Biofilms help bacteria to survive under multiple stressful conditions such as providing immunity against antibiotics. Apart from the provision of multi-layered defense for enabling poor antibiotic absorption and adaptive persistor cells, biofilms utilize their extracellular components, e.g., extracellular DNA (eDNA), chemical-like catalase, various genes and their regulators to combat antibiotics. The response of biofilms depends on the type of antibiotic that comes into contact with biofilms. For example, excessive production of eDNA exerts resistance against cell wall and DNA targeting antibiotics and the release of antagonist chemicals neutralizes cell membrane inhibitors, whereas the induction of protein and folic acid antibiotics inside cells is lowered by mutating genes and their regulators. Here, we review the current state of knowledge of biofilm-based resistance to various antibiotic classes in bacteria and genes responsible for biofilm development, and the key role of quorum sensing in developing biofilms and antibiotic resistance is also discussed. In this review, we also highlight new and modified techniques such as CRISPR/Cas, nanotechnology and bacteriophage therapy. These technologies might be useful to eliminate pathogens residing in biofilms by combating biofilm-induced antibiotic resistance and making this world free of antibiotic resistance.

Ultrasound meets the cell membrane: for enhanced endocytosis and drug delivery

Endocytosis plays a crucial role in drug delivery for precision therapy. As a non-invasive and spatiotemporal-controllable stimulus, ultrasound (US) has been utilized for improving drug delivery efficiency due to its ability to enhance cell membrane permeability. When US meets the cell membrane, the well-known cavitation effect generated by US can cause various biophysical effects, facilitating the delivery of various cargoes, especially nanocarriers. The comprehension of recent progress in the biophysical mechanism governing the interaction between ultrasound and cell membranes holds significant implications for the broader scientific community, particularly in drug delivery and nanomedicine. This review will summarize the latest research results on the biological effects and mechanisms of US-enhanced cellular endocytosis. Moreover, the latest achievements in US-related biomedical applications will be discussed. Finally, challenges and opportunities of US-enhanced endocytosis for biomedical applications will be provided.

Coarse-grained molecular simulation of extracellular vesicle squeezing for drug loading

In recent years, extracellular vesicles have become promising carriers as next-generation drug delivery platforms. Effective loading of exogenous cargos without compromising the extracellular vesicle membrane is a major challenge. Rapid squeezing through nanofluidic channels is a widely used approach to load exogenous cargoes into the EV through the nanopores generated temporarily on the membrane. However, the exact mechanism and dynamics of nanopore opening, as well as cargo loading through nanopores during the squeezing process remains unknown and it is impossible to visualize or quantify it experimentally due to the small size of the EV and the fast transient process. This paper developed a systemic algorithm to simulate nanopore formation and predict drug loading during extracellular vesicle (EV) squeezing by leveraging the power of coarse-grain (CG) molecular dynamics simulations with fluid dynamics. The EV CG beads are coupled with implicit the fluctuating lattice Boltzmann solvent. The effects of EV properties and various squeezing test parameters, such as EV size, flow velocity, channel width, and length, on pore formation and drug loading efficiency are analyzed. Based on the simulation results, a phase diagram is provided as a design guide for nanochannel geometry and squeezing velocity to generate pores on the membrane without damaging the EV. This method can be utilized to optimize the nanofluidic device configuration and flow setup to obtain desired drug loading into EVs.

Early Endosomes Act as Local Exocytosis Hubs to Repair Endothelial Membrane Damage

The plasma membrane of a cell is subject to stresses causing ruptures that must be repaired immediately to preserve membrane integrity and ensure cell survival. Yet, the spatio-temporal membrane dynamics at the wound site and the source of the membrane required for wound repair are poorly understood. Here, it is shown that early endosomes, previously only known to function in the uptake of extracellular material and its endocytic transport, are involved in plasma membrane repair in human endothelial cells. Using live-cell imaging and correlative light and electron microscopy, it is demonstrated that membrane injury triggers a previously unknown exocytosis of early endosomes that is induced by Ca²⁺ entering through the wound. This exocytosis is restricted to the vicinity of the wound site and mediated by the endosomal soluble N-ethylmaleimide sensitive factor attachment protein receptor (SNARE) VAMP2, which is crucial for efficient membrane repair. Thus, the newly identified Ca²⁺ -evoked and localized exocytosis of early endosomes supplies the membrane material required for rapid resealing of a damaged plasma membrane, thereby providing the first line of defense against damage in mechanically challenged endothelial cells.

Pathogenic Mutations in the C2A Domain of Dysferlin form Amyloid that Activates the Inflammasome

Limb-Girdle Muscular Dystrophy Type-2B/2R is caused by mutations in the dysferlin gene ( DYSF ). This disease has two known pathogenic missense mutations that occur within dysferlin's C2A domain, namely C2A ^W52R and C2A ^V67D . Yet, the etiological rationale to explain the disease linkage for these two mutations is still unclear. In this study, we have presented evidence from biophysical, computational, and immunological experiments which suggest that these missense mutations interfere with dysferlin's ability to repair cells. The failure of C2A ^W52R and C2A ^V67D to initiate membrane repair arises from their propensity to form stable amyloid. The misfolding of the C2A domain caused by either mutation exposes β-strands, which are predicted to nucleate classical amyloid structures. When dysferlin C2A amyloid is formed, it triggers the NLRP3 inflammasome, leading to the secretion of inflammatory cytokines, including IL-1β. The present study suggests that the muscle dysfunction and inflammation evident in Limb-Girdle Muscular Dystrophy types-2B/2R, specifically in cases involving C2A ^W52R and C2A ^V67D , as well as other C2 domain mutations with considerable hydrophobic core involvement, may be attributed to this mechanism.

Structural basis for TRIM72 oligomerization during membrane damage repair

Tripartite Motif Protein 72 (TRIM72, also named MG53) mediates membrane damage repair through membrane fusion and exocytosis. During injury, TRIM72 molecules form intermolecular disulfide bonds in response to the oxidative environment and TRIM72 oligomers are proposed to connect vesicles to the plasma membrane and promote membrane fusion in conjunction with other partners like dysferlin and caveolin. However, the detailed mechanism of TRIM72 oligomerization and action remains unclear. Here we present the crystal structure of TRIM72 B-box-coiled-coil-SPRY domains (BCC-SPRY), revealing the molecular basis of TRIM72 oligomerization, which is closely linked to disulfide bond formation. Through structure-guided mutagenesis, we have identified and characterized key residues that are important for the membrane repair function of TRIM72. Our results also demonstrate that TRIM72 interacts with several kinds of negatively charged lipids in addition to phosphatidylserine. Our work provides a structural foundation for further mechanistic studies as well as the clinical application of TRIM72.

Repair of traumatic lesions to the plasmalemma of neurons and other cells: Commonalities, conflicts, and controversies

Neuroscientists and Cell Biologists have known for many decades that eukaryotic cells, including neurons, are surrounded by a plasmalemma/axolemma consisting of a phospholipid bilayer that regulates trans-membrane diffusion of ions (including calcium) and other substances. Cells often incur plasmalemmal damage via traumatic injury and various diseases. If the damaged plasmalemma is not rapidly repaired within minutes, activation of apoptotic pathways by calcium influx often results in cell death. We review publications reporting what is less-well known (and not yet covered in neuroscience or cell biology textbooks): that calcium influx at the lesion sites ranging from small nm-sized holes to complete axonal transection activates parallel biochemical pathways that induce vesicles/membrane-bound structures to migrate and interact to restore original barrier properties and eventual reestablishment of the plasmalemma. We assess the reliability of, and problems with, various measures (e.g., membrane voltage, input resistance, current flow, tracer dyes, confocal microscopy, transmission and scanning electron microscopy) used individually and in combination to assess plasmalemmal sealing in various cell types (e.g., invertebrate giant axons, oocytes, hippocampal and other mammalian neurons). We identify controversies such as plug versus patch hypotheses that attempt to account for currently available data on the subcellular mechanisms of plasmalemmal repair/sealing. We describe current research gaps and potential future developments, such as much more extensive correlations of biochemical/biophysical measures with sub-cellular micromorphology. We compare and contrast naturally occurring sealing with recently-discovered artificially-induced plasmalemmal sealing by polyethylene glycol (PEG) that bypasses all natural pathways for membrane repair. We assess other recent developments such as adaptive membrane responses in neighboring cells following injury to an adjacent cell. Finally, we speculate how a better understanding of the mechanisms involved in natural and artificial plasmalemmal sealing is needed to develop better clinical treatments for muscular dystrophies, stroke and other ischemic conditions, and various cancers.

Development of a novel fluorescence assay for studying lipid bilayer perturbation induced by amyloidogenic peptides using cell plasma membrane vesicles

Numerous pathophysiological conditions are associated with the misfolding and aggregation of proteins into insoluble amyloid fibrils. The mechanisms by which this process leads to cellular dysfunction remain elusive, though several hypotheses point toward the perturbation of the cell plasma membrane by pre-fibrillar intermediates and/or amyloid growth. However, current models to study membrane perturbations are largely limited to synthetic lipid vesicles and most of experimental approaches cannot be transposed to complex cell-derived plasma membrane systems. Herein, vesicles originating from the plasma membrane of erythrocytes and β-pancreatic cells were used to study the perturbations induced by an amyloidogenic peptide, the islet amyloid polypeptide (IAPP). These biologically relevant lipid vesicles displayed a characteristic clustering in the presence of the amyloidogenic peptide, which was able to rupture membranes. By exploiting Förster resonance energy transfer (FRET), a rapid, simple, and potentially high-throughput assay to detect membrane perturbations of intact mammalian cell plasma membrane vesicles was implemented. The FRET kinetics of membrane perturbations closely correlated with the kinetics of thioflavin-T fluorescence associated with amyloid formation. This novel kinetics assay expands the toolbox available to study amyloid-associated membrane damage, bridging the gap between synthetic lipid vesicles and living cells.

Orientation of the Dysferlin C2A Domain is Responsive to the Composition of Lipid Membranes

Dysferlin is a 230 kD protein that plays a critical function in the active resealing of micron-sized injuries to the muscle sarcolemma by recruiting vesicles to patch the injured site via vesicle fusion. Muscular dystrophy is observed in humans when mutations disrupt this repair process or dysferlin is absent. While lipid binding by dysferlin's C2A domain (dysC2A) is considered fundamental to the membrane resealing process, the molecular mechanism of this interaction is not fully understood. By applying nonlinear surface-specific vibrational spectroscopy, we have successfully demonstrated that dysferlin's N-terminal C2A domain (dysC2A) alters its binding orientation in response to a membrane's lipid composition. These experiments reveal that dysC2A utilizes a generic electrostatic binding interaction to bind to most anionic lipid surfaces, inserting its calcium binding loops into the lipid surface while orienting its β-sheets 30-40° from surface normal. However, at lipid surfaces, where PI(4,5)P2 is present, dysC2A tilts its β-sheets more than 60° from surface normal to expose a polybasic face, while it binds to the PI(4,5)P2 surface. Both lipid binding mechanisms are shown to occur alongside dysC2A-induced lipid clustering. These different binding mechanisms suggest that dysC2A could provide a molecular cue to the larger dysferlin protein as to signal whether it is bound to the sarcolemma or another lipid surface.

Interplay of membrane crosslinking and curvature induction by annexins

Efficient plasma membrane repair (PMR) is required to repair damage sustained in the cellular life cycle. The annexin family of proteins, involved in PMR, are activated by Ca²⁺ influx from extracellular media at the site of injury. Mechanistic studies of the annexins have been overwhelmingly performed using a single annexin, despite the recruitment of multiple annexins to membrane damage sites in living cells. Hence, we investigate the effect of the presence of the crosslinking annexins, annexin A1, A2 and A6 (ANXA1, ANXA2 and ANXA6) on the membrane curvature induction of annexin A4 (ANXA4) in model membrane systems. Our data support a mechanistic model of PMR where ANXA4 induced membrane curvature and ANXA6 crosslinking promotes wound closure. The model now can be expanded to include ANXA1 and ANXA2 as specialist free edge membrane crosslinkers that act in concert with ANXA4 induced curvature and ANXA6 crosslinking.

Sum frequency spectroscopy studies on cell membrane fusion induced by divalent cations

Cell membrane fusion is a fundamental biological process involved in a number of cellular living functions. Regarding this, divalent cations can induce fusion of the lipid bilayers through binding and bridging of divalent cations to the charged lipids, thus leading to the cell membrane fusion. How-ever, the elaborate mechanism of cell membrane fusion induced by divalent cations is still needed to be elucidated. Here, surface/interface sensitive sum frequency generation vibrational spectroscopy (SFG-VS) and dynamic light scattering (DLS) were applied in this research to study the responses of phospholipid monolayer to the exposure of divalent metal ions i.e. Ca2+ and Mg2+. According to the particle size distribution results measured by DLS experiments, it was found that Ca2+ could induce inter-vesicular fusion while Mg2+ could not. An octadecyltrichlorosilane self-assembled monolayer (OTS SAM)-lipid monolayer system was designed to model the cell membrane for the SFG-VS experiment. Ca2+ could interact with the lipid PO2− head groups more strongly, resulting in cell membrane fusion more easily, in comparison with Mg2+. No specific interaction between the two metal cations and the C=O groups was observed. However, the C=O orientations changed more after Ca2+-PO2− binding than Mg2+ mediation on lipid monolayer. Meanwhile, Ca2+ could induce dehydration of the lipids (which should be related to the strong Ca2+-PO2− interaction), leading to the reduced hindrance for cell membrane fusion.

Plantaricin NC8 αβ rapidly and efficiently inhibits flaviviruses and SARS-CoV-2 by disrupting their envelopes

Potent broad-spectrum antiviral agents are urgently needed to combat existing and emerging viral infections. This is particularly important considering that vaccine development is a costly and time consuming process and that viruses constantly mutate and render the vaccine ineffective. Antimicrobial peptides (AMP), such as bacteriocins, are attractive candidates as antiviral agents against enveloped viruses. One of these bacteriocins is PLNC8 αβ, which consists of amphipathic peptides with positive net charges that display high affinity for negatively charged pathogen membrane structures, including phosphatidylserine rich lipid membranes of viral envelopes. Due to the morphological and physiological differences between viral envelopes and host cell plasma membranes, PLNC8 αβ is thought to have high safety profile by specifically targeting viral envelopes without effecting host cell membranes. In this study, we have tested the antiviral effects of PLNC8 αβ against the flaviviruses Langat and Kunjin, coronavirus SARS-CoV-2, influenza A virus (IAV), and human immunodeficiency virus-1 (HIV-1). The concentration of PLNC8 αβ that is required to eliminate all the infective virus particles is in the range of nanomolar (nM) to micromolar (μM), which is surprisingly efficient considering the high content of cholesterol (8-35%) in their lipid envelopes. We found that viruses replicating in the endoplasmic reticulum (ER)/Golgi complex, e.g. SARS-CoV-2 and flaviviruses, are considerably more susceptible to PLNC8 αβ, compared to viruses that acquire their lipid envelope from the plasma membrane, such as IAV and HIV-1. Development of novel broad-spectrum antiviral agents can significantly benefit human health by rapidly and efficiently eliminating infectious virions and thereby limit virus dissemination and spreading between individuals. PLNC8 αβ can potentially be developed into an effective and safe antiviral agent that targets the lipid compartments of viral envelopes of extracellular virions, more or less independent of virus antigenic mutations, which faces many antiviral drugs and vaccines.

Landscape of Cellular Bioeffects Triggered by Ultrasound-Induced Sonoporation

Sonoporation is the process of transient pore formation in the cell membrane triggered by ultrasound (US). Numerous studies have provided us with firm evidence that sonoporation may assist cancer treatment through effective drug and gene delivery. However, there is a massive gap in the body of literature on the issue of understanding the complexity of biophysical and biochemical sonoporation-induced cellular effects. This study provides a detailed explanation of the US-triggered bioeffects, in particular, cell compartments and the internal environment of the cell, as well as the further consequences on cell reproduction and growth. Moreover, a detailed biophysical insight into US-provoked pore formation is presented. This study is expected to review the knowledge of cellular effects initiated by US-induced sonoporation and summarize the attempts at clinical implementation.

Hydrodynamic dissection of Stentor coeruleus in a microfluidic cross junction

Stentor coeruleus, a single-cell ciliated protozoan, is a model organism for wound healing and regeneration studies. Despite Stentor's large size (up to 2 mm in extended state), microdissection of Stentor remains challenging. In this work, we describe a hydrodynamic cell splitter, consisting of a microfluidic cross junction, capable of splitting Stentor cells in a non-contact manner at a high throughput of ∼500 cells per minute under continuous operation. Introduction of asymmetry in the flow field at the cross junction leads to asymmetric splitting of the cells to generate cell fragments as small as ∼8.5 times the original cell size. Characterization of cell fragment viability shows reduced 5-day survival as fragment size decreases and as the extent of hydrodynamic stress imposed on the fragments increases. Our results suggest that cell fragment size and composition, as well as mechanical stress, play important roles in the long-term repair of Stentor cells and warrant further investigations. Nevertheless, the hydrodynamic splitter can be useful for studying phenomena immediately after cell splitting, such as the closure of wounds in the plasma membrane which occurs on the order of 100-1000 seconds in Stentor.

Wrangling Actin Assemblies: Actin Ring Dynamics during Cell Wound Repair

To cope with continuous physiological and environmental stresses, cells of all sizes require an effective wound repair process to seal breaches to their cortex. Once a wound is recognized, the cell must rapidly plug the injury site, reorganize the cytoskeleton and the membrane to pull the wound closed, and finally remodel the cortex to return to homeostasis. Complementary studies using various model organisms have demonstrated the importance and complexity behind the formation and translocation of an actin ring at the wound periphery during the repair process. Proteins such as actin nucleators, actin bundling factors, actin-plasma membrane anchors, and disassembly factors are needed to regulate actin ring dynamics spatially and temporally. Notably, Rho family GTPases have been implicated throughout the repair process, whereas other proteins are required during specific phases. Interestingly, although different models share a similar set of recruited proteins, the way in which they use them to pull the wound closed can differ. Here, we describe what is currently known about the formation, translocation, and remodeling of the actin ring during the cell wound repair process in model organisms, as well as the overall impact of cell wound repair on daily events and its importance to our understanding of certain diseases and the development of therapeutic delivery modalities.

Evidence of an Annexin A4 mediated plasma membrane repair response to biomechanical strain associated with glaucoma pathogenesis

Glaucoma is a common neurodegenerative blinding disease that is closely associated with chronic biomechanical strain at the optic nerve head (ONH). Yet, the cellular injury and mechanosensing mechanisms underlying the resulting damage have remained critically unclear. We previously identified Annexin A4 (ANXA4) from a proteomic analyses of human ONH astrocytes undergoing pathological biomechanical strain that mimics glaucomatous conditions. Annexins are a family of calcium-dependent phospholipid binding proteins with key functions in plasma membrane repair (PMR); an active mechanism to limit and mend cellular injury that involves membrane and cytoskeletal reorganizations. However, a role for direct membrane damage and PMR has not been well studied in the context of biomechanical strain, such as that associated with glaucoma. Here we report that this moderate strain surprisingly damages cell membranes to increase permeability in a calcium-dependent manner, and induces rapid aggregation of ANXA4 at injury sites. ANXA4 loss-of-function increases permeability, while exogenous ANXA4 reduces it. Furthermore, ANXA4 aggregation is associated with F-actin dynamics in vitro, and remarkably this interaction and aggregation signature is also observed in the glaucomatous ONH in patient samples. Together these studies link moderate biomechanical strain with direct membrane damage and actin dynamics, and identify an active PMR role for ANXA4 in new model of cell injury associated with glaucoma pathogenesis.

Impairment of Ceramide-Mediated Endothelial Instant Membrane Resealing During Diabetes Mellitus

Recent studies have indicated that instant cell membrane resealing (ICMR) controls the activation of NOD-like receptor pyrin domain containing 3 (Nlrp3) inflammasomes in endothelial cells, thereby initiating and promoting vascular inflammation. It remains unknown whether this impaired ICMR occurs under diabetic condition or hyperglycemia contributing to endothelial dysfunction leading to vascular inflammation, a hallmark of diabetic vascular injury. The present study aims to examine whether ICMR occurs during in control and diabetic mice and to explore related molecular mechanisms associated with acid sphingomyelinase (ASM)-mediated ceramide production. Using confocal microscopy, we demonstrated that mouse aortic endothelial cells (MAECs) exposed to high glucose levels exhibited much more retarded ICMR after laser-induced membrane injury, compared to that in control cells. The high glucose-induced impairment of membrane resealing in MAECs was prevented when these cells were pretreated with sphingomyelin or C24-ceramide. Mechanistically, high glucose treatment decreased association of membrane ceramide with annexin A5, an essential element of membrane repair machinery. Consistently, the association of ceramide with annexin A5 was significantly reduced in the coronary arterial endothelium of mice with streptozotocin-induced diabetes mellitus compared to that in non-diabetic control mice. Moreover, a marked reduction of the association of ceramide with annexin A5 was observed in coronary arterial endothelium of ASM knockout mice regardless of their diabetic status. Lastly, high glucose treatment or ASM gene deletion substantially impaired ICMR in coronary arterial endothelium of mice receiving membrane puncturing agents. Collectively, our data suggest that ceramide-mediated ICMR in vascular endothelial cells is impaired during diabetes mellitus due to dissociation of ceramide with annexin A5 and ASM play a critical role in this ICMR.

Fluorescent dendrimer-based probes for cell membrane imaging: Zebrafish epidermal labeling-based toxicity evaluation

Visualizing the plasma membrane of living mammalian cells both in vitro and in vivo is crucial for tracking their cellular activities. However, due to the complex and dynamic nature of the plasma membrane, most commercial dyes for membrane staining can only realize very limited imaging performance. Thus, precise and stable plasma membrane imaging remains technically challenging. Here, by taking advantage of the small, well-defined, and amine-rich dendrimers, we prepared poly(ethylene glycol)-cholesterol (PEG-Chol)-conjugated and cyanine dye (e.g., cyanine2, cyanine3, and cyanine5)-labeled dendrimer nanoprobes (termed DPC-Cy2, DPC-Cy3, and DPC-Cy5 NPs). It was revealed that these probes enabled universal, wash-free, long-term (at least 8 h), and multicolor (green, yellow, and red) plasma membrane labeling of a variety of live mammalian cells. Further, we confirmed that the nanoprobes (using DPC-Cy5 as a representative) could achieve high-quality, wash-free, and stable cell surface labeling of live zebrafish embryos. More importantly, we demonstrated that our probes could act as biosensors to visualize the toxicity of metal-organic frameworks (MOFs) toward the epidermal cells of zebrafish embryos, and thus they hold great potential for identifying the toxic effect of drugs/materials at the single-cell scale or in live animals. The present work highlights the advantages of utilizing dendrimers for constructing functional imaging materials, and it is also believed that the fluorescent dendrimer nanoprobes developed in this work may find wide applications like cell imaging, drug toxicity evaluation, and cellular state monitoring.

Spatiotemporal Dynamics and Mechanisms of Actin Cytoskeletal Re-modeling in Cells Perforated by Ultrasound-Driven Microbubbles

To develop new strategies for improving the efficacy and biosafety of sonoporation-based macromolecule delivery, it is essential to understand the mechanisms underlying plasma membrane re-sealing and function recovery of the cells perforated by ultrasound-driven microbubbles. However, we lack a clear understanding of the spatiotemporal dynamics of the disrupted actin cytoskeleton and its role in the re-sealing of sonoporated cells. Here we used a customized experimental setup for single-pulse ultrasound (133.33-µs duration and 0.70-MPa peak negative pressure) exposure to microbubbles and for real-time recording of single-cell (human umbilical vein endothelial cell) responses by laser confocal microscopic imaging. We found that in reversibly sonoporated cells, the locally disrupted actin cytoskeleton, which was spatially correlated with the perforated plasma membrane, underwent three successive phases (expansion; contraction and re-sealing; and recovery) to re-model and that each phase of the disrupted actin cytoskeleton was approximately synchronized with that of the perforated plasma membrane. Moreover, compared with the closing time of the perforated plasma membrane, the same time was used for the re-sealing of the actin cytoskeleton in mildly sonoporated cells and a longer time was required in moderately sonoporated cells. Further, the generation, directional migration, accumulation and re-polymerization of globular actin polymers during the three phases drove the re-modeling of the actin cytoskeleton. However, in irreversibly sonoporated cells, the actin cytoskeleton, which underwent expansion and no contraction, was progressively de-polymerized and could not be re-sealed. Finally, we found that intracellular calcium transients were essential for the recruitment of globular actin and the re-modeling of the actin cytoskeleton. These results provide new insight into the role of actin cytoskeleton dynamics in the re-sealing of sonoporated cells and serve to guide the design of new strategies for sonoporation-based delivery.

The cellular response to plasma membrane disruption for nanomaterial delivery

Delivery of nanomaterials into cells is of interest for fundamental cell biological research as well as for therapeutic and diagnostic purposes. One way of doing so is by physically disrupting the plasma membrane (PM). Several methods that exploit electrical, mechanical or optical cues have been conceived to temporarily disrupt the PM for intracellular delivery, with variable effects on cell viability. However, apart from acute cytotoxicity, subtler effects on cell physiology may occur as well. Their nature and timing vary with the severity of the insult and the efficiency of repair, but some may provoke permanent phenotypic alterations. With the growing palette of nanoscale delivery methods and applications, comes a need for an in-depth understanding of this cellular response. In this review, we summarize current knowledge about the chronology of cellular events that take place upon PM injury inflicted by different delivery methods. We also elaborate on their significance for cell homeostasis and cell fate. Based on the crucial nodes that govern cell fitness and functionality, we give directions for fine-tuning nano-delivery conditions.

Trafficking of Annexins during Membrane Repair in Human Skeletal Muscle Cells

Defects in membrane repair contribute to the development of muscular dystrophies, such as Miyoshi muscular dystrophy 1, limb girdle muscular dystrophy (LGMD), type R2 or R12. Deciphering membrane repair dysfunctions in the development of muscular dystrophies requires precise and detailed knowledge of the membrane repair machinery in healthy human skeletal muscle cells. Using correlative light and electron microscopy (CLEM), we studied the trafficking of four members of the annexin (ANX) family, in myotubes damaged by laser ablation. Our data support a model in which ANXA4 and ANXA6 are recruited to the disruption site by propagating as a wave-like motion along the sarcolemma. They may act in membrane resealing by proceeding to sarcolemma remodeling. On the other hand, ANXA1 and A2 exhibit a progressive cytoplasmic recruitment, likely by interacting with intracellular vesicles, in order to form the lipid patch required for membrane resealing. Once the sarcolemma has been resealed, ANXA1 is released from the site of the membrane injury and returns to the cytosol, while ANXA2 remains accumulated close to the wounding site on the cytoplasmic side. On the other side of the repaired sarcolemma are ANXA4 and ANXA6 that face the extracellular milieu, where they are concentrated in a dense structure, the cap subdomain. The proposed model provides a basis for the identification of cellular dysregulations in the membrane repair of dystrophic human muscle cells.

Secreted acid sphingomyelinase as a potential gene therapy for limb girdle muscular dystrophy 2B

Efficient sarcolemmal repair is required for muscle cell survival, with deficits in this process leading to muscle degeneration. Lack of the sarcolemmal protein dysferlin impairs sarcolemmal repair by reducing secretion of the enzyme acid sphingomyelinase (ASM), and causes limb girdle muscular dystrophy 2B (LGMD2B). The large size of the dysferlin gene poses a challenge for LGMD2B gene therapy efforts aimed at restoring dysferlin expression in skeletal muscle fibers. Here, we present an alternative gene therapy approach targeting reduced ASM secretion, the consequence of dysferlin deficit. We showed that the bulk endocytic ability is compromised in LGMD2B patient cells, which was addressed by extracellularly treating cells with ASM. Expression of secreted human ASM (hASM) using a liver-specific adeno-associated virus (AAV) vector restored membrane repair capacity of patient cells to healthy levels. A single in vivo dose of hASM-AAV in the LGMD2B mouse model restored myofiber repair capacity, enabling efficient recovery of myofibers from focal or lengthening contraction-induced injury. hASM-AAV treatment was safe, attenuated fibro-fatty muscle degeneration, increased myofiber size, and restored muscle strength, similar to dysferlin gene therapy. These findings elucidate the role of ASM in dysferlin-mediated plasma membrane repair and to our knowledge offer the first non-muscle-targeted gene therapy for LGMD2B.

The Donnan-dominated resting state of skeletal muscle fibers contributes to resilience and longevity in dystrophic fibers

Duchenne muscular dystrophy (DMD) is an X-linked dystrophin-minus muscle-wasting disease. Ion homeostasis in skeletal muscle fibers underperforms as DMD progresses. But though DMD renders these excitable cells intolerant of exertion, sodium overloaded, depolarized, and spontaneously contractile, they can survive for several decades. We show computationally that underpinning this longevity is a strikingly frugal, robust Pump-Leak/Donnan (P-L/D) ion homeostatic process. Unlike neurons, which operate with a costly “Pump-Leak–dominated” ion homeostatic steady state, skeletal muscle fibers operate with a low-cost “Donnan-dominated” ion homeostatic steady state that combines a large chloride permeability with an exceptionally small sodium permeability. Simultaneously, this combination keeps fiber excitability low and minimizes pump expenditures. As mechanically active, long-lived multinucleate cells, skeletal muscle fibers have evolved to handle overexertion, sarcolemmal tears, ischemic bouts, etc.; the frugality of their Donnan dominated steady state lets them maintain the outsized pump reserves that make them resilient during these inevitable transient emergencies. Here, P-L/D model variants challenged with DMD-type insult/injury (low pump-strength, overstimulation, leaky Nav and cation channels) show how chronic “nonosmotic” sodium overload (observed in DMD patients) develops. Profoundly severe DMD ion homeostatic insult/injury causes spontaneous firing (and, consequently, unwanted excitation–contraction coupling) that elicits cytotoxic swelling. Therefore, boosting operational pump-strength and/or diminishing sodium and cation channel leaks should help extend DMD fiber longevity.

Innovation in culture systems to study muscle complexity

Endogenous skeletal muscle development, regeneration, and pathology are extremely complex processes, influenced by local and systemic factors. Unpinning how these mechanisms function is crucial for fundamental biology and to develop therapeutic interventions for genetic disorders, but also conditions like sarcopenia and volumetric muscle loss. Ex vivo skeletal muscle models range from two- and three-dimensional primary cultures of satellite stem cell-derived myoblasts grown alone or in co-culture, to single muscle myofibers, myobundles, and whole tissues. Together, these systems provide the opportunity to gain mechanistic insights of stem cell behavior, cell-cell interactions, and mature muscle function in simplified systems, without confounding variables. Here, we highlight recent advances (published in the last 5 years) using in vitro primary cells and ex vivo skeletal muscle models, and summarize the new insights, tools, datasets, and screening methods they have provided. Finally, we highlight the opportunity for exponential advance of skeletal muscle knowledge, with spatiotemporal resolution, that is offered by guiding the study of muscle biology and physiology with in silico modelling and implementing high-content cell biology systems and ex vivo physiology platforms.

Actin Cytoskeletal Dynamics in Single-Cell Wound Repair

The plasma membrane protects the eukaryotic cell from its surroundings and is essential for cell viability; thus, it is crucial that membrane disruptions are repaired quickly to prevent immediate dyshomeostasis and cell death. Accordingly, cells have developed efficient repair mechanisms to rapidly reseal ruptures and reestablish membrane integrity. The cortical actin cytoskeleton plays an instrumental role in both plasma membrane resealing and restructuring in response to damage. Actin directly aids membrane repair or indirectly assists auxiliary repair mechanisms. Studies investigating single-cell wound repair have often focused on the recruitment and activation of specialized repair machinery, despite the undeniable need for rapid and dynamic cortical actin modulation; thus, the role of the cortical actin cytoskeleton during wound repair has received limited attention. This review aims to provide a comprehensive overview of membrane repair mechanisms directly or indirectly involving cortical actin cytoskeletal remodeling.

Endoplasmic reticulum maintains ion homeostasis required for plasma membrane repair

Of the many crucial functions of the ER, homeostasis of physiological calcium increase is critical for signaling. Plasma membrane (PM) injury causes a pathological calcium influx. Here, we show that the ER helps clear this surge in cytoplasmic calcium through an ER-resident calcium pump, SERCA, and a calcium-activated ion channel, Anoctamin 5 (ANO5). SERCA imports calcium into the ER, and ANO5 supports this by maintaining electroneutrality of the ER lumen through anion import. Preventing either of these transporter activities causes cytosolic calcium overload and disrupts PM repair (PMR). ANO5 deficit in limb girdle muscular dystrophy 2L (LGMD2L) patient cells compromises their cytosolic and ER calcium homeostasis. By generating a mouse model of LGMD2L, we find that PM injury causes cytosolic calcium overload and compromises the ability of ANO5-deficient myofibers to repair. Addressing calcium overload in ANO5-deficient myofibers enables them to repair, supporting the requirement of the ER in calcium homeostasis in injured cells and facilitating PMR.

Tension modulation of actomyosin ring assembly and RhoGTPases activity: Perspectives from the Xenopus oocyte wound healing model

Cells are remarkably resilient structures; they are able to recover from injuries to their plasma membrane (PM) and cytoskeleton that would normally constitute existential threats. This capacity is exemplified by Xenopus laevis oocytes which can recover from very large PM defects through exocytotic and endocytic events and can repair damaged cortical cytoskeleton structures through the formation of a contractile actomyosin ring (AMR). Formation of the AMR involves the localized Ca²⁺ -dependent activation of RhoA and Cdc42, and the pre-patterning of guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs). However, this model fails to account for observations that suggest a link between cytoskeletal dynamics, intracellular tension, and AMR formation. It also does not explain why the formation of an AMR is not involved in the cytoskeletal repair program of adherent cells. We show here evidence for the support of tension as an essential regulatory signal for the formation of AMR. Indeed, oocytes in which global tension has been experimentally reduced were unable to form a functional AMR following injury, showing severely diminished RhoA activity at the wound site. These new insights place the cytoskeleton at the center of events involving changes in cell shape such as cytokinesis which also involves the formation and closure of an AMR.

Ca2+ roles in electroporation-induced changes of cancer cell physiology: From membrane repair to cell death

The combination of Ca²⁺ ions and electroporation has gained attention as potential alternative to electrochemotherapy. Ca²⁺ is an important component of the cell membrane repair system and its presence directly influences the dynamics of the pore cycle after electroporation which can be exploited for cancer therapies. Here, the influence of Ca²⁺ concentration is investigated on small molecule electrotransfer and release of Calcein from 4T1, MX-1, B16F10, U87 cancer cells after cell exposure to microsecond electric pulses. Moreover, we investigated simultaneous molecule electrotransfer and intracellular calcium ion influx when media was supplemented with different Ca²⁺ concentrations. Results show that increased concentrations of calcium ions reduce the electrotransfer of small molecules to different lines of cancer cells as well as the release of Calcein. These effects are related with an enhanced membrane repair mechanism. Overall, we show that the efficiency of molecular electrotransfer can be controlled by regulating Ca²⁺ concentration in the electroporation medium. For the first time, the cause of cancer cell death in vitro from 1 mM CaCl₂ concentrations is related to the irreversible loss of Ca²⁺ homeostasis after cell electroporation. Our findings provide fundamental insight on the mechanisms of Ca²⁺ electroporation that might lead to improved therapeutic outcomes.

Splitting up to heal: mitochondrial shape regulates signaling for focal membrane repair

Mitochondria are central to the health of eukaryotic cells. While commonly known for their bioenergetic role, mitochondria also function as signaling organelles that regulate cell stress responses capable of restoring homeostasis or leading the stressed cell to eventual death. Damage to the plasma membrane is a potentially fatal stressor incurred by all cells. Repairing plasma membrane damage requires cells to mount a rapid and localized response to injury. Accumulating evidence has identified a role for mitochondria as an important facilitator of this acute and localized repair response. However, as mitochondria are organized in a cell-wide, interconnected network, it is unclear how they collectively sense and respond to a focal injury. Here we will discuss how mitochondrial shape change is an integral part of this localized repair response. Mitochondrial fragmentation spatially restricts beneficial repair signaling, enabling a localized response to focal injury. Conservation of mitochondrial fragmentation in response to cell and tissue damage across species demonstrates that this is a universal pro-survival adaptation to injury and suggests that mitochondrial fragmentation may provide cells a mechanism to facilitate localized signaling in contexts beyond repairing plasma membrane injury.

Microfluidic and Nanofluidic Intracellular Delivery

Innate cell function can be artificially engineered and reprogrammed by introducing biomolecules, such as DNAs, RNAs, plasmid DNAs, proteins, or nanomaterials, into the cytosol or nucleus. This process of delivering exogenous cargos into living cells is referred to as intracellular delivery. For instance, clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9 gene editing begins with internalizing Cas9 protein and guide RNA into cells, and chimeric antigen receptor-T (CAR-T) cells are prepared by delivering CAR genes into T lymphocytes for cancer immunotherapies. To deliver external biomolecules into cells, tools, including viral vectors, and electroporation have been traditionally used; however, they are suboptimal for achieving high levels of intracellular delivery while preserving cell viability, phenotype, and function. Notably, as emerging solutions, microfluidic and nanofluidic approaches have shown remarkable potential for addressing this open challenge. This review provides an overview of recent advances in microfluidic and nanofluidic intracellular delivery strategies and discusses new opportunities and challenges for clinical applications. Furthermore, key considerations for future efforts to develop microfluidics- and nanofluidics-enabled next-generation intracellular delivery platforms are outlined.

Plasma membrane disruption (PMD) formation and repair in mechanosensitive tissues

Mammalian cells employ an array of biological mechanisms to detect and respond to mechanical loading in their environment. One such mechanism is the formation of plasma membrane disruptions (PMD), which foster a molecular flux across cell membranes that promotes tissue adaptation. Repair of PMD through an orchestrated activity of molecular machinery is critical for cell survival, and the rate of PMD repair can affect downstream cellular signaling. PMD have been observed to influence the mechanical behavior of skin, alveolar, and gut epithelial cells, aortic endothelial cells, corneal keratocytes and epithelial cells, cardiac and skeletal muscle myocytes, neurons, and most recently, bone cells including osteoblasts, periodontal ligament cells, and osteocytes. PMD are therefore positioned to affect the physiological behavior of a wide range of vertebrate organ systems including skeletal and cardiac muscle, skin, eyes, the gastrointestinal tract, the vasculature, the respiratory system, and the skeleton. The purpose of this review is to describe the processes of PMD formation and repair across these mechanosensitive tissues, with a particular emphasis on comparing and contrasting repair mechanisms and downstream signaling to better understand the role of PMD in skeletal mechanobiology. The implications of PMD-related mechanisms for disease and potential therapeutic applications are also explored.

Phospholipids: Identification and Implication in Muscle Pathophysiology

Phospholipids (PLs) are amphiphilic molecules that were essential for life to become cellular. PLs have not only a key role in compartmentation as they are the main components of membrane, but they are also involved in cell signaling, cell metabolism, and even cell pathophysiology. Considered for a long time to simply be structural elements of membranes, phospholipids are increasingly being viewed as sensors of their environment and regulators of many metabolic processes. After presenting their main characteristics, we expose the increasing methods of PL detection and identification that help to understand their key role in life processes. Interest and importance of PL homeostasis is growing as pathogenic variants in genes involved in PL biosynthesis and/or remodeling are linked to human diseases. We here review diseases that involve deregulation of PL homeostasis and present a predominantly muscular phenotype.

Proteolytic activation of Growth-blocking peptides triggers calcium responses through the GPCR Mthl10 during epithelial wound detection

The presence of a wound triggers surrounding cells to initiate repair mechanisms, but it is not clear how cells initially detect wounds. In epithelial cells, the earliest known wound response, occurring within seconds, is a dramatic increase in cytosolic calcium. Here, we show that wounds in the Drosophila notum trigger cytoplasmic calcium increase by activating extracellular cytokines, Growth-blocking peptides (Gbps), which initiate signaling in surrounding epithelial cells through the G-protein-coupled receptor Methuselah-like 10 (Mthl10). Latent Gbps are present in unwounded tissue and are activated by proteolytic cleavage. Using wing discs, we show that multiple protease families can activate Gbps, suggesting that they act as a generalized protease-detector system. We present experimental and computational evidence that proteases released during wound-induced cell damage and lysis serve as the instructive signal: these proteases liberate Gbp ligands, which bind to Mthl10 receptors on surrounding epithelial cells, and activate downstream release of calcium.

An Aerolysin-like Pore-Forming Protein Complex Targets Viral Envelope to Inactivate Herpes Simplex Virus Type 1

Because most of animal viruses are enveloped, cytoplasmic entry of these viruses via fusion with cellular membrane initiates their invasion. However, the strategies in which host cells counteract cytoplasmic entry of such viruses are incompletely understood. Pore-forming toxin aerolysin-like proteins (ALPs) exist throughout the animal kingdom, but their functions are mostly unknown. In this study, we report that βγ-crystallin fused aerolysin-like protein and trefoil factor complex (βγ-CAT), an ALP and trefoil factor complex from the frog Bombina maxima, directly blocks enveloped virus invasion by interfering with cytoplasmic entry. βγ-CAT targeted acidic glycosphingolipids on the HSV type 1 (HSV-1) envelope to induce pore formation, as indicated by the oligomer formation of protein and potassium and calcium ion efflux. Meanwhile, βγ-CAT formed ring-like oligomers of ∼10 nm in diameter on the liposomes and induced dye release from liposomes that mimic viral envelope. Unexpectedly, transmission electron microscopy analysis showed that the βγ-CAT-treated HSV-1 was visibly as intact as the vehicle-treated HSV-1, indicating that βγ-CAT did not lyse the viral envelope. However, the cytoplasmic entry of the βγ-CAT-treated HSV-1 into HeLa cells was totally hindered. In vivo, topical application of βγ-CAT attenuated the HSV-1 corneal infection in mice. Collectively, these results uncovered that βγ-CAT possesses the capacity to counteract enveloped virus invasion with its featured antiviral-acting manner. Our findings will also largely help to illustrate the putative antiviral activity of animal ALPs.

Numerical simulation of intracellular drug delivery via rapid squeezing

Intracellular drug delivery by rapid squeezing is one of the most recent and simple cell membrane disruption-mediated drug encapsulation approaches. In this method, cell membranes are perforated in a microfluidic setup due to rapid cell deformation during squeezing through constricted channels. While squeezing-based drug loading has been successful in loading drug molecules into various cell types, such as immune cells, cancer cells, and other primary cells, there is so far no comprehensive understanding of the pore opening mechanism on the cell membrane and the systematic analysis on how different channel geometries and squeezing speed influence drug loading. This article aims to develop a three-dimensional computational model to study the intracellular delivery for compound cells squeezing through microfluidic channels. The Lattice Boltzmann method, as the flow solver, integrated with a spring-connected network via frictional coupling, is employed to capture compound capsule dynamics over fast squeezing. The pore size is proportional to the local areal strain of triangular patches on the compound cell through mathematical correlations derived from molecular dynamics and coarse-grained molecular dynamics simulations. We quantify the drug concentration inside the cell cytoplasm by introducing a new mathematical model for passive diffusion after squeezing. Compared to the existing models, the proposed model does not have any empirical parameters that depend on operating conditions and device geometry. Since the compound cell model is new, it is validated by simulating a nucleated cell under a simple shear flow at different capillary numbers and comparing the results with other numerical models reported in literature. The cell deformation during squeezing is also compared with the pattern found from our compound cell squeezing experiment. Afterward, compound cell squeezing is modeled for different cell squeezing velocities, constriction lengths, and constriction widths. We reported the instantaneous cell center velocity, variations of axial and vertical cell dimensions, cell porosity, and normalized drug concentration to shed light on the underlying physics in fast squeezing-based drug delivery. Consistent with experimental findings in the literature, the numerical results confirm that constriction width reduction, constriction length enlargement, and average cell velocity promote intracellular drug delivery. The results show that the existence of the nucleus increases cell porosity and loaded drug concentration after squeezing. Given geometrical parameters and cell average velocity, the maximum porosity is achieved at three different locations: constriction entrance, constriction middle part, and outside the constriction. Our numerical results provide reasonable justifications for experimental findings on the influences of constriction geometry and cell velocity on the performance of cell-squeezing delivery. We expect this model can help design and optimize squeezing-based cargo delivery.