Repair of injured plasma membrane by rapid Ca2+-dependent endocytosis

The septin cytoskeleton is required for plasma membrane repair

Plasma membrane repair is a fundamental homeostatic process of eukaryotic cells. Here, we report a new function for the conserved cytoskeletal proteins known as septins in the repair of cells perforated by pore-forming toxins or mechanical disruption. Using a silencing RNA screen, we identified known repair factors (e.g. annexin A2, ANXA2) and novel factors such as septin 7 (SEPT7) that is essential for septin assembly. Upon plasma membrane injury, the septin cytoskeleton is extensively redistributed to form submembranous domains arranged as knob and loop structures containing F-actin, myosin IIA, S100A11, and ANXA2. Formation of these domains is Ca2+-dependent and correlates with plasma membrane repair efficiency. Super-resolution microscopy revealed that septins and F-actin form intertwined filaments associated with ANXA2. Depletion of SEPT7 prevented ANXA2 recruitment and formation of submembranous actomyosin domains. However, ANXA2 depletion had no effect on domain formation. Collectively, our data support a novel septin-based mechanism for resealing damaged cells, in which the septin cytoskeleton plays a key structural role in remodeling the plasma membrane by promoting the formation of SEPT/F-actin/myosin IIA/ANXA2/S100A11 repair domains.

Bacterial pore-forming toxin pneumolysin drives pathogenicity through host extracellular vesicles released during infection

Streptococcus pneumoniae is a global priority respiratory pathogen that kills over a million people annually. The pore-forming cytotoxin, pneumolysin (PLY) is a major virulence factor. Here, we found that recombinant PLY as well as wild-type pneumococcal strains, but not the isogenic PLY mutant, upregulated the shedding of extracellular vesicles (EVs) harboring membrane-bound toxin from human THP-1 monocytes. PLY-EVs induced cytotoxicity and hemolysis dose-dependently upon internalization by recipient monocyte-derived dendritic cells. Proteomics analysis revealed that PLY-EVs are selectively enriched in key inflammatory host proteins such as IFI16, NLRC4, PTX3, and MMP9. EVs shed from PLY-challenged or infected cells induced dendritic cell maturation and primed them to infection. In vivo, zebrafish administered with PLY-EVs showed pericardial edema and mortality. Adoptive transfer of bronchoalveolar-lavage-derived EVs from infected mice to healthy recipients induced lung damage and inflammation in a PLY-dependent manner. Our findings identify that host EVs released during infection mediate pneumococcal pathogenesis.

Calcium influx rapidly establishes distinct spatial recruitments of Annexins to cell wounds

To survive daily damage, the formation of actomyosin ring at the wound edge is required to rapidly close cell wounds. Calcium influx is one of the start signals for these cell wound repair events. Here, we find that the rapid recruitment of all 3 Drosophila calcium-responding and phospholipid-binding Annexin proteins (AnxB9, AnxB10, and AnxB11) to distinct regions around the wound is regulated by the quantity of calcium influx rather than their binding to specific phospholipids. The distinct recruitment patterns of these Annexins regulate the subsequent recruitment of RhoGEF2 and RhoGEF3 through actin stabilization to form a robust actomyosin ring. Surprisingly, while the wound does not close in the absence of calcium influx, we find that reduced calcium influx can still initiate repair processes, albeit leading to severe repair phenotypes. Thus, our results suggest that, in addition to initiating repair events, the quantity of calcium influx is important for precise Annexin spatiotemporal protein recruitment to cell wounds and efficient wound repair.

Biomodulatory Effects of Molecular Delivery in Human T Cells Using 3D-Printed Acoustofluidic Devices

OBJECTIVE

Cell-based therapies have shown significant promise for treating many diseases, including cancer. Current cell therapy manufacturing processes primarily utilize viral transduction to insert genomic material into cells, which has limitations, including variable transduction efficiency and extended processing times. Non-viral transfection techniques are also limited by high variability or reduced molecular delivery efficiency. Novel 3D-printed acoustofluidic devices are in development to address these challenges by delivering biomolecules into cells within seconds via sonoporation.

METHODS

In this study, we assessed biological parameters that influence the ultrasound-mediated delivery of fluorescent molecules (i.e., calcein and 150 kDa FITC-Dextran) to human T cells using flow cytometry and confocal imaging.

RESULTS

Low cell plating densities (100,000 cells/mL) enhanced molecular delivery compared to higher cell plating densities (p < 0.001), even though cells were resuspended at equal concentrations for acoustofluidic processing. Additionally, cells in the S phase of the cell cycle had enhanced intracellular delivery compared to cells in the G2/M phase (p < 0.001) and G0/G1 phase (p < 0.01), while also maintaining higher viability compared to G0/G1 phase (p < 0.001). Furthermore, the calcium chelator (EGTA) decreased overall molecular delivery levels. Confocal imaging indicated that the actin cytoskeleton had important implications on plasma membrane recovery dynamics after sonoporation. In addition, confocal imaging indicates that acoustofluidic treatment can permeabilize the nuclear membrane, which could enable rapid intranuclear delivery of nucleic acids.

CONCLUSIONS

The results of this study demonstrate that a 3D-printed acoustofluidic device can enhance molecular delivery to human T cells, which may enable improved techniques for non-viral processing of cell therapies.

Glucose and Oxygen Levels Modulate the Pore-Forming Effects of Cholesterol-Dependent Cytolysin Pneumolysin from Streptococcus pneumoniae

A major Streptococcus pneumoniae pathogenic factor is the cholesterol-dependent cytolysin pneumolysin, binding membrane cholesterol and producing permanent lytic or transient pores. During brain infections, vascular damage with variable ischemia occurs. The role of ischemia on pneumolysin's pore-forming capacity remains unknown. In acute brain slice cultures and primary cultured glia, we studied acute toxin lysis (via propidium iodide staining and LDH release) and transient pore formation (by analyzing increases in the intracellular calcium). We analyzed normal peripheral tissue glucose conditions (80 mg%), normal brain glucose levels (20 mg%), and brain hypoglycemic conditions (3 mg%), in combinations either with normoxia (8% oxygen) or hypoxia (2% oxygen). At 80 mg% glucose, hypoxia enhanced cytolysis via pneumolysin. At 20 mg% glucose, hypoxia did not affect cell lysis, but impaired calcium restoration after non-lytic pore formation. Only at 3 mg% glucose, during normoxia, did pneumolysin produce stronger lysis. In hypoglycemic (3 mg% glucose) conditions, pneumolysin caused a milder calcium increase, but restoration was missing. Microglia bound more pneumolysin than astrocytes and demonstrated generally stronger calcium elevation. Thus, our work demonstrated that the toxin pore-forming capacity in cells continuously diminishes when oxygen is reduced, overlapping with a continuously reduced ability of cells to maintain homeostasis of the calcium influx once oxygen and glucose are reduced.

Lysosomes in Cancer-At the Crossroad of Good and Evil

Although it has been known for decades that lysosomes are central for degradation and recycling in the cell, their pivotal role as nutrient sensing signaling hubs has recently become of central interest. Since lysosomes are highly dynamic and in constant change regarding content and intracellular position, fusion/fission events allow communication between organelles in the cell, as well as cell-to-cell communication via exocytosis of lysosomal content and release of extracellular vesicles. Lysosomes also mediate different forms of regulated cell death by permeabilization of the lysosomal membrane and release of their content to the cytosol. In cancer cells, lysosomal biogenesis and autophagy are increased to support the increased metabolism and allow growth even under nutrient- and oxygen-poor conditions. Tumor cells also induce exocytosis of lysosomal content to the extracellular space to promote invasion and metastasis. However, due to the enhanced lysosomal function, cancer cells are often more susceptible to lysosomal membrane permeabilization, providing an alternative strategy to induce cell death. This review summarizes the current knowledge of cancer-associated alterations in lysosomal structure and function and illustrates how lysosomal exocytosis and release of extracellular vesicles affect disease progression. We focus on functional differences depending on lysosomal localization and the regulation of intracellular transport, and lastly provide insight how new therapeutic strategies can exploit the power of the lysosome and improve cancer treatment.

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.

Wound Repair of the Cell Membrane: Lessons from Dictyostelium Cells

The cell membrane is frequently subjected to damage, either through physical or chemical means. The swift restoration of the cell membrane's integrity is crucial to prevent the leakage of intracellular materials and the uncontrolled influx of extracellular ions. Consequently, wound repair plays a vital role in cell survival, akin to the importance of DNA repair. The mechanisms involved in wound repair encompass a series of events, including ion influx, membrane patch formation, endocytosis, exocytosis, recruitment of the actin cytoskeleton, and the elimination of damaged membrane sections. Despite the absence of a universally accepted general model, diverse molecular models have been proposed for wound repair in different organisms. Traditional wound methods not only damage the cell membrane but also impact intracellular structures, including the underlying cortical actin networks, microtubules, and organelles. In contrast, the more recent improved laserporation selectively targets the cell membrane. Studies on Dictyostelium cells utilizing this method have introduced a novel perspective on the wound repair mechanism. This review commences by detailing methods for inducing wounds and subsequently reviews recent developments in the field.

The Septin Cytoskeleton is Required for Plasma Membrane Repair

Mammalian cells are frequently exposed to mechanical and biochemical stressors resulting in plasma membrane injuries. Repair mechanisms reseal the plasma membrane to restore homeostasis and prevent cell death. In the present work, a silencing RNA screen was performed to uncover plasma membrane repair mechanisms of cells exposed to a pore-forming toxin (listeriolysin O). This screen identified molecules previously known to repair the injured plasma membrane such as annexin A2 (ANXA2) as well as novel plasma membrane repair candidate proteins. Of the novel candidates, we focused on septin 7 (SEPT7) because the septins are an important family of conserved eukaryotic cytoskeletal proteins. Using diverse experimental approaches, we established for the first time that SEPT7 plays a general role in plasma membrane repair of cells perforated by pore-forming toxins and mechanical wounding. Remarkably, upon cell injury, the septin cytoskeleton is extensively redistributed in a Ca 2+ -dependent fashion, a hallmark of plasma membrane repair machineries. The septins reorganize into subplasmalemmal domains arranged as knob and loop (or ring) structures containing F-actin, myosin II, and annexin A2 (ANXA2) and protrude from the cell surface. Importantly, the formation of these domains correlates with the plasma membrane repair efficiency. Super-resolution microscopy shows that septins and actin are arranged in intertwined filaments associated with ANXA2. Silencing SEPT7 expression prevented the formation of the F-actin/myosin II/ANXA2 domains, however, silencing expression of ANXA2 had no observable effect on their formation. These results highlight the key structural role of the septins in remodeling the plasma membrane and in the recruitment of the repair molecule ANXA2. Collectively, our data support a novel model in which the septin cytoskeleton acts as a scaffold to promote the formation of plasma membrane repair domains containing contractile F-actin and annexin A2.

Enteropathogenic E. coli infection co-elicits lysosomal exocytosis and lytic host cell death

IMPORTANCE

Enteropathogenic Escherichia coli (EPEC) infection is a significant cause of gastroenteritis, mainly in children. Therefore, studying the mechanisms of EPEC infection is an important research theme. EPEC modulates its host cell life by injecting via a type III secretion machinery cell death modulating effector proteins. For instance, while EspF and Map promote mitochondrial cell death, EspZ antagonizes cell death. We show that these effectors also control lysosomal exocytosis, i.e., the trafficking of lysosomes to the host cell plasma membrane. Interestingly, the capacity of these effectors to induce or protect against cell death correlates completely with their ability to induce LE, suggesting that the two processes are interconnected. Modulating host cell death is critical for establishing bacterial attachment to the host and subsequent dissemination. Therefore, exploring the modes of LE involvement in host cell death is crucial for elucidating the mechanisms underlying EPEC infection and disease.

Cellular Uptake and Cytotoxicity of Clostridium perfringens Iota-Toxin

Clostridium perfringens iota-toxin is composed of two separate proteins: a binding protein (Ib) that recognizes a host cell receptor and promotes the cellular uptake of a catalytic protein and (Ia) possessing ADP-ribosyltransferase activity that induces actin cytoskeleton disorganization. Ib exhibits the overall structure of bacterial pore-forming toxins (PFTs). Lipolysis-stimulated lipoprotein receptor (LSR) is defined as a host cell receptor for Ib. The binding of Ib to LSR causes an oligomer formation of Ib in lipid rafts of plasma membranes, mediating the entry of Ia into the cytoplasm. Ia induces actin cytoskeleton disruption via the ADP-ribosylation of G-actin and causes cell rounding and death. The binding protein alone disrupts the cell membrane and induces cytotoxicity in sensitive cells. Host cells permeabilized by the pore formation of Ib are repaired by a Ca2+-dependent plasma repair pathway. This review shows that the cellular uptake of iota-toxin utilizes a pathway of plasma membrane repair and that Ib alone induces cytotoxicity.

Calcium influx rapidly establishes distinct spatial recruitments of Annexins to cell wounds

To survive daily damage, the formation of actomyosin ring at the wound periphery is required to rapidly close cell wounds. Calcium influx is one of the start signals for these cell wound repair events. Here, we find that rapid recruitment of all three Drosophila calcium responding and phospholipid binding Annexin proteins (AnxB9, AnxB10, AnxB11) to distinct regions around the wound are regulated by the quantity of calcium influx rather than their binding to specific phospholipids. The distinct recruitment patterns of these Annexins regulate the subsequent recruitment of RhoGEF2 and RhoGEF3 through actin stabilization to form a robust actomyosin ring. Surprisingly, we find that reduced extracellular calcium and depletion of intracellular calcium affect cell wound repair differently, despite these two conditions exhibiting similar GCaMP signals. Thus, our results suggest that, in addition to initiating repair events, both the quantity and sources of calcium influx are important for precise Annexin spatiotemporal protein recruitment to cell wounds and efficient wound repair.

The SNARE complex formed by RIC-4/SEC-22/SYX-2 promotes C. elegans epidermal wound healing

Maintaining cellular viability relies on the integrity of the plasma membrane, which must be repaired upon damage. Soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE)-mediated membrane fusion is a crucial mechanism involved in membrane repair. In C. elegans epidermal cell hyp 7, syntaxin-2 (SYX-2) facilitates large membrane wound repair; however, the underlying molecular mechanism remains unclear. Here, we found that SNAP-25 protein RIC-4 and synaptobrevin protein SEC-22 are required for SYX-2 recruitment at the wound site. They interact to form a SNARE complex to promote membrane repair in vivo and fusion in vitro. Moreover, we found that SEC-22 localized in multiple intracellular compartments, including endosomes and the trans-Golgi network, which recruited to the wounds. Furthermore, inhibition of RAB-5 disrupted SEC-22 localization and prevented its interaction with SYX-2. Our findings suggest that RAB-5 facilitates the formation of the RIC-4/SEC-22/SYX-2 SNARE complex and provides valuable insights into the molecular mechanism of how cells repair large membrane wounds.

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.

Investigations on Na+, K+-ATPase energy consumption in ion flow of hydrophilic pores by THz unipolar stimulation

Terahertz science and technology has recently shown new application prospects in artificial intelligence. It is found that terahertz unipolar stimulation can activate cell membrane hydrophilic pores. However, the behaviors of Na+, K+-ATPase and energy consumption during this period remain unknown. This paper investigates these behaviors by Na+, K+-ATPase and electroporation models, based on the interaction theory between terahertz fields and ions at the cellular level. The effective diameters of life ions are considered in the aqueous solution. From results, Na+, K+-ATPases can be activated and stay for a while before close after the stimulation. Their life ion flows are far lower than the flows via the pores. And their power dissipation is as low as 10-11 W in both rat neostriatal neurons and guinea pig ventricular myocytes. The results keep tenable in 0.1-1.2 THz. These lay the basis for investigations of information communication mechanisms in cells under terahertz stimulation.

Pore-forming activity of S. pneumoniae pneumolysin disrupts the paracellular localization of the epithelial adherens junction protein E-cadherin

Streptococcus pneumoniae, a common cause of community-acquired bacterial pneumonia, can cross the respiratory epithelial barrier to cause lethal septicemia and meningitis. S. pneumoniae pore-forming toxin pneumolysin (PLY) triggers robust neutrophil (PMN) infiltration that promotes bacterial transepithelial migration in vitro and disseminated disease in mice. Apical infection of polarized respiratory epithelial monolayers by S. pneumoniae at a multiplicity of infection (MOI) of 20 resulted in recruitment of PMNs, loss of 50% of the monolayer, and PMN-dependent bacterial translocation. Reducing the MOI to 2 decreased PMN recruitment two-fold and preserved the monolayer, but apical-to-basolateral translocation of S. pneumoniae remained relatively efficient. At both MOI of 2 and 20, PLY was required for maximal PMN recruitment and bacterial translocation. Co-infection by wild-type S. pneumoniae restored translocation by a PLY-deficient mutant, indicating that PLY can act in trans. Investigating the contribution of S. pneumoniae infection on apical junction complexes in the absence of PMN transmigration, we found that S. pneumoniae infection triggered the cleavage and mislocalization of the adherens junction (AJ) protein E-cadherin. This disruption was PLY-dependent at MOI of 2 and was recapitulated by purified PLY, requiring its pore-forming activity. In contrast, at MOI of 20, E-cadherin disruption was independent of PLY, indicating that S. pneumoniae encodes multiple means to disrupt epithelial integrity. This disruption was insufficient to promote bacterial translocation in the absence of PMNs. Thus, S. pneumoniae triggers cleavage and mislocalization of E-cadherin through PLY-dependent and -independent mechanisms, but maximal bacterial translocation across epithelial monolayers requires PLY-dependent neutrophil transmigration.

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.

Triggered Golgi membrane enrichment promotes PtdIns(4,5)P2 generation for plasma membrane repair

The maintenance of plasma membrane integrity and a capacity for efficiently repairing damaged membranes are essential for cell survival. Large-scale wounding depletes various membrane components at the wound sites, including phosphatidylinositols, yet little is known about how phosphatidylinositols are generated after depletion. Here, working with our in vivo C. elegans epidermal cell wounding model, we discovered phosphatidylinositol 4-phosphate (PtdIns4P) accumulation and local phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] generation at the wound site. We found that PtdIns(4,5)P2 generation depends on the delivery of PtdIns4P, PI4K, and PI4P 5-kinase PPK-1. In addition, we show that wounding triggers enrichment of the Golgi membrane to the wound site, and that is required for membrane repair. Moreover, genetic and pharmacological inhibitor experiments support that the Golgi membrane provides the PtdIns4P for PtdIns(4,5)P2 generation at the wounds. Our findings demonstrate how the Golgi apparatus facilitates membrane repair in response to wounding and offers a valuable perspective on cellular survival mechanisms upon mechanical stress in a physiological context.

Clostridium perfringens epsilon-toxin requires acid sphingomyelinase for cellular entry

OBJECTIVES

Clostridium perfringens epsilon-toxin is considered to be a crucial agent in enterotoxemia in domestic animals. Epsilon-toxin enters host cells via endocytosis and results in the formation of late endosome/lysosome-derived vacuoles. In the present study, we found that acid sphingomyelinase promotes the internalization of epsilon-toxin in MDCK cells.

METHODS

We measured the extracellular release of acid sphingomyelinase (ASMase) by epsilon-toxin. We examined the role of ASMase in epsilon-toxin-induced cytotoxicity using selective inhibitors and knockdown of ASMase. Production of ceramide after toxin treatment was determined by immunofluorescence technique.

RESULTS

Blocking agents of ASMase and exocytosis of lysosomes inhibited this epsilon-toxin-induced vacuole formation. Lysosomal ASMase was liberated to extracellular space during treatment of the cells with epsilon-toxin in the presence of Ca2+. RNAi-mediated attenuation of ASMase blocked epsilon-toxin-induced vacuolation. Moreover, incubation of MDCK cells with epsilon-toxin led to production of ceramide. The ceramide colocalized with lipid raft-binding cholera toxin subunit B (CTB) in the cell membrane, indicating that conversion of lipid raft associated sphingomyelin to ceramide by ASMase facilitates lesion of MDCK cells and internalization of epsilon-toxin.

CONCLUSIONS

Based on the present results, ASMase is required for efficient internalization of epsilon-toxin.

Aminopeptidase MNP-1 triggers intestine protease production by activating daf-16 nuclear location to degrade pore-forming toxins in Caenorhabditis elegans

Pore-forming toxins (PFTs) are effective tools for pathogens infection. By disrupting epithelial barriers and killing immune cells, PFTs promotes the colonization and reproduction of pathogenic microorganisms in their host. In turn, the host triggers defense responses, such as endocytosis, exocytosis, or autophagy. Bacillus thuringiensis (Bt) bacteria produce PFT, known as crystal proteins (Cry) which damage the intestinal cells of insects or nematodes, eventually killing them. In insects, aminopeptidase N (APN) has been shown to act as an important receptor for Cry toxins. Here, using the nematode Caenorhabditis elegans as model, an extensive screening of APN gene family was performed to analyze the potential role of these proteins in the mode of action of Cry5Ba against the nematode. We found that one APN, MNP-1, participate in the toxin defense response, since the mnp-1(ok2434) mutant showed a Cry5Ba hypersensitive phenotype. Gene expression analysis in mnp-1(ok2434) mutant revealed the involvement of two protease genes, F19C6.4 and R03G8.6, that participate in Cry5Ba degradation. Finally, analysis of the transduction pathway involved in F19C6.4 and R03G8.6 expression revealed that upon Cry5Ba exposure, the worms up regulated both protease genes through the activation of the FOXO transcription factor DAF-16, which was translocated into the nucleus. The nuclear location of DAF-16 was found to be dependent on mnp-1 under Cry5Ba treatment. Our work provides evidence of new host responses against PFTs produced by an enteric pathogenic bacterium, resulting in activation of host intestinal proteases that degrade the PFT in the intestine.

Leveraging Plasma Membrane Repair Therapeutics for Treating Neurodegenerative Diseases

Plasma membrane repair is an essential cellular mechanism that reseals membrane disruptions after a variety of insults, and compromised repair capacity can contribute to the progression of many diseases. Neurodegenerative diseases are marked by membrane damage from many sources, reduced membrane integrity, elevated intracellular calcium concentrations, enhanced reactive oxygen species production, mitochondrial dysfunction, and widespread neuronal death. While the toxic intracellular effects of these changes in cellular physiology have been defined, the specific mechanism of neuronal death in certain neurodegenerative diseases remains unclear. An abundance of recent evidence indicates that neuronal membrane damage and pore formation in the membrane are key contributors to neurodegenerative disease pathogenesis. In this review, we have outlined evidence supporting the hypothesis that membrane damage is a contributor to neurodegenerative diseases and that therapeutically enhancing membrane repair can potentially combat neuronal death.

Janus polymer-grafted nanoparticles mimicking membrane repair proteins for the prevention of lipid membrane rupture

Plasma membrane rupture often leads to cell damage, especially when there is a lack of membrane repair proteins near the wounds due to genetic mutations in organisms. To efficiently promote the repair of the injured lipid membrane, nanomedicines may act as a promising alternative to membrane repair proteins, but the related research is still in its infancy. Herein, using dissipative particle dynamics simulations, we designed a class of Janus polymer-grafted nanoparticles (PGNPs) that can mimic the function of membrane repair proteins. The Janus PGNPs comprise both hydrophobic and hydrophilic polymer chains grafted on nanoparticles (NPs). We track the dynamic process of the adsorption of Janus PGNPs at the damaged site in the lipid membrane and systematically assess the driving forces for this process. Our results reveal that tuning the length of the grafted polymer chains and the surface polarity of the NPs can efficiently enhance the adsorption of Janus PGNPs at the site of the damaged membrane to reduce membrane stress. After repair, the adsorbed Janus PGNPs can be successfully detached from the membrane, leaving the membrane untouched. These results provide valuable guidelines for designing advanced nanomaterials for the repair of damaged lipid membranes.

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.

Role of calcium-sensor proteins in cell membrane repair

Cell membrane repair is a critical process used to maintain cell integrity and survival from potentially lethal chemical, and mechanical membrane injury. Rapid increases in local calcium levels due to a membrane rupture have been widely accepted as a trigger for multiple membrane-resealing models that utilize exocytosis, endocytosis, patching, and shedding mechanisms. Calcium-sensor proteins, such as synaptotagmins (Syt), dysferlin, S100 proteins, and annexins, have all been identified to regulate, or participate in, multiple modes of membrane repair. Dysfunction of membrane repair from inefficiencies or genetic alterations in these proteins contributes to diseases such as muscular dystrophy (MD) and heart disease. The present review covers the role of some of the key calcium-sensor proteins and their involvement in membrane repair.

Membrane damage and repair: a thin line between life and death

Bilayered membranes separate cells from their surroundings and form boundaries between intracellular organelles and the cytosol. Gated transport of solutes across membranes enables cells to establish vital ion gradients and a sophisticated metabolic network. However, an advanced compartmentalization of biochemical reactions makes cells also particularly vulnerable to membrane damage inflicted by pathogens, chemicals, inflammatory responses or mechanical stress. To avoid potentially lethal consequences of membrane injuries, cells continuously monitor the structural integrity of their membranes and readily activate appropriate pathways to plug, patch, engulf or shed the damaged membrane area. Here, we review recent insights into the cellular mechanisms that underly an effective maintenance of membrane integrity. We discuss how cells respond to membrane lesions caused by bacterial toxins and endogenous pore-forming proteins, with a primary focus on the intimate crosstalk between membrane proteins and lipids during wound formation, detection and elimination. We also discuss how a delicate balance between membrane damage and repair determines cell fate upon bacterial infection or activation of pro-inflammatory cell death pathways.

Role of Ceramides and Lysosomes in Extracellular Vesicle Biogenesis, Cargo Sorting and Release

Cells have the ability to communicate with their immediate and distant neighbors through the release of extracellular vesicles (EVs). EVs facilitate intercellular signaling through the packaging of specific cargo in all type of cells, and perturbations of EV biogenesis, sorting, release and uptake is the basis of a number of disorders. In this review, we summarize recent advances of the complex roles of the sphingolipid ceramide and lysosomes in the journey of EV biogenesis to uptake.

Neutrophils as immune effector cells in antibody therapy in cancer

Tumor-targeting monoclonal antibodies are available for a number of cancer cell types (over)expressing the corresponding tumor antigens. Such antibodies can limit tumor progression by different mechanisms, including direct growth inhibition and immune-mediated mechanisms, in particular complement-dependent cytotoxicity, antibody-dependent cellular phagocytosis, and antibody-dependent cellular cytotoxicity (ADCC). ADCC can be mediated by various types of immune cells, including neutrophils, the most abundant leukocyte in circulation. Neutrophils express a number of Fc receptors, including Fcγ- and Fcα-receptors, and can therefore kill tumor cells opsonized with either IgG or IgA antibodies. In recent years, important insights have been obtained with respect to the mechanism(s) by which neutrophils engage and kill antibody-opsonized cancer cells and these findings are reviewed here. In addition, we consider a number of additional ways in which neutrophils may affect cancer progression, in particular by regulating adaptive anti-cancer immunity.

Pneumolysin boosts the neuroinflammatory response to Streptococcus pneumoniae through enhanced endocytosis

In pneumococcal meningitis, bacterial growth in the cerebrospinal fluid results in lysis, the release of toxic factors, and subsequent neuroinflammation. Exposure of primary murine glia to Streptococcus pneumoniae lysates leads to strong proinflammatory cytokine and chemokine production, blocked by inhibition of the intracellular innate receptor Nod1. Lysates enhance dynamin-dependent endocytosis, and dynamin inhibition reduces neuroinflammation, blocking ligand internalization. Here we identify the cholesterol-dependent cytolysin pneumolysin as a pro-endocytotic factor in lysates, its elimination reduces their proinflammatory effect. Only pore-competent pneumolysin enhances endocytosis in a dynamin-, phosphatidylinositol-3-kinase- and potassium-dependent manner. Endocytic enhancement is limited to toxin-exposed parts of the membrane, the effect is rapid and pneumolysin permanently alters membrane dynamics. In a murine model of pneumococcal meningitis, mice treated with chlorpromazine, a neuroleptic with a complementary endocytosis inhibitory effect show reduced neuroinflammation. Thus, the dynamin-dependent endocytosis emerges as a factor in pneumococcal neuroinflammation, and its enhancement by a cytolysin represents a proinflammatory control mechanism.

Piezo1 Mechano-Activation Is Augmented by Resveratrol and Differs between Colorectal Cancer Cells of Primary and Metastatic Origin

Cancer cells must survive aberrant fluid shear stress (FSS) in the circulation to metastasize. Herein, we investigate the role that FSS has on colorectal cancer cell apoptosis, proliferation, membrane damage, calcium influx, and therapeutic sensitization. We tested this using SW480 (primary tumor) and SW620 cells (lymph node metastasis) derived from the same patient. The cells were exposed to either shear pulses, modeling millisecond intervals of high FSS seen in regions of turbulent flow, or sustained shear to model average magnitudes experienced by circulating tumor cells. SW480 cells were significantly more sensitive to FSS-induced death than their metastatic counterparts. Shear pulses caused significant cell membrane damage, while constant shear decreased cell proliferation and increased the expression of CD133. To investigate the role of mechanosensitive ion channels, we treated cells with the Piezo1 agonist Yoda1, which increased intracellular calcium. Pretreatment with resveratrol further increased the calcium influx via the lipid-raft colocalization of Piezo1. However, minimal changes in apoptosis were observed due to calcium saturation, as predicted via a computational model of apoptosis. Furthermore, SW480 cells had increased levels of Piezo1, calcium influx, and TRAIL-mediated apoptosis compared to SW620 cells, highlighting differences in the mechano-activation of metastatic cells, which may be a necessary element for successful dissemination in vivo.

A conserved annexin A6-mediated membrane repair mechanism in muscle, heart, and nerve

Membrane instability and disruption underlie myriad acute and chronic disorders. Anxa6 encodes the membrane-associated protein annexin A6 and was identified as a genetic modifier of muscle repair and muscular dystrophy. To evaluate annexin A6’s role in membrane repair in vivo, we inserted sequences encoding green fluorescent protein (GFP) into the last coding exon of Anxa6. Heterozygous Anxa6gfp mice expressed a normal pattern of annexin A6 with reduced annexin A6GFP mRNA and protein. High-resolution imaging of wounded muscle fibers showed annexin A6GFP rapidly formed a repair cap at the site of injury. Injured cardiomyocytes and neurons also displayed repair caps after wounding, highlighting annexin A6–mediated repair caps as a feature in multiple cell types. Using surface plasmon resonance, we showed recombinant annexin A6 bound phosphatidylserine-containing lipids in a Ca²⁺- and dose-dependent fashion with appreciable binding at approximately 50 μM Ca²⁺. Exogenously added recombinant annexin A6 localized to repair caps and improved muscle membrane repair capacity in a dose-dependent fashion without disrupting endogenous annexin A6 localization, indicating annexin A6 promotes repair from both intracellular and extracellular compartments. Thus, annexin A6 orchestrates repair in multiple cell types, and recombinant annexin A6 may be useful in additional chronic disorders beyond skeletal muscle myopathies.

Recruitment of tetraspanin TSP-15 to epidermal wounds promotes plasma membrane repair in C. elegans

Maintaining the integrity of the plasma membrane after cellular damage is essential for cell survival. However, it is unclear how cells repair large membrane injuries in vivo. Here, we report that the tetraspanin protein, TSP-15, is recruited to large membrane wounds and forms a ring-like structure in C. elegans epidermis and promotes membrane repair after an injury. TSP-15 recruits from the adjacent region underneath the plasma membrane to the wound site in a RAB-5-dependent manner upon membrane damage. Genetic and live-imaging analysis suggested that the endosomal sorting complex required for transport III (ESCRT III) is necessary for recruiting TSP-15 from the early endosome to the damaged membrane. Moreover, TSP-15 interacts with and is required for the accumulation of t-SNARE protein Syntaxin-2, which facilitates membrane repair. These findings provide valuable insights into the role of the conserved tetraspanin TSP-15 in the cellular repair of large wounds resulting from environmental insults.

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.

The role of lysosomal cathepsins in neurodegeneration: Mechanistic insights, diagnostic potential and therapeutic approaches

Lysosomes are ubiquitous organelles with a fundamental role in maintaining cellular homeostasis by mediating degradation and recycling processes. Cathepsins are the most abundant lysosomal hydrolyses and are responsible for the bulk degradation of various substrates. A correct autophagic function is essential for neuronal survival, as most neurons are post-mitotic and thus susceptible to accumulate cellular components. Increasing evidence suggests a crucial role of the lysosome in neurodegeneration as a key regulator of aggregation-prone and disease-associated proteins, such as α-synuclein, β-amyloid and huntingtin. Particularly, alterations in lysosomal cathepsins CTSD, CTSB and CTSL can contribute to the pathogenesis of neurodegenerative diseases as seen for neuronal ceroid lipofuscinosis, synucleinopathies (Parkinson's disease, Dementia with Lewy Body and Multiple System Atrophy) as well as Alzheimer's and Huntington's disease. In this review, we provide an overview of recent evidence implicating CTSD, CTSB and CTSL in neurodegeneration, with a special focus on the role of these enzymes in α-synuclein metabolism. In addition, we summarize the potential role of lysosomal cathepsins as clinical biomarkers in neurodegenerative diseases and discuss potential therapeutic approaches by targeting lysosomal function.

Cellular and molecular mechanisms underlying plasma membrane functionality and integrity

The plasma membrane not only protects the cell from the extracellular environment, acting as a selective barrier, but also regulates cellular events that originate at the cell surface, playing a key role in various biological processes that are essential for the preservation of cell homeostasis. Therefore, elucidation of the mechanisms involved in the maintenance of plasma membrane integrity and functionality is of utmost importance. Cells have developed mechanisms to ensure the quality of proteins that inhabit the cell surface, as well as strategies to cope with injuries inflicted to the plasma membrane. Defects in these mechanisms can lead to the development or onset of several diseases. Despite the importance of these processes, a comprehensive and holistic perspective of plasma membrane quality control is still lacking. To tackle this gap, in this Review, we provide a thorough overview of the mechanisms underlying the identification and targeting of membrane proteins that are to be removed from the cell surface, as well as the membrane repair mechanisms triggered in both physiological and pathological conditions. A better understanding of the mechanisms underlying protein quality control at the plasma membrane can reveal promising and unanticipated targets for the development of innovative therapeutic approaches.

Gasdermins in Innate Host Defense Against Entamoeba histolytica and Other Protozoan Parasites

Gasdermins (GSDMs) are a group of proteins that are cleaved by inflammatory caspases to induce pore formation in the plasma membrane to cause membrane permeabilization and lytic cell death or pyroptosis. All GSDMs share a conserved structure, containing a cytotoxic N-terminal (NT) pore-forming domain and a C-terminal (CT) repressor domain. Entamoeba histolytica (Eh) in contact with macrophages, triggers outside-in signaling to activate inflammatory caspase-4/1 via the noncanonical and canonical pathway to promote cleavage of gasdermin D (GSDMD). Cleavage of GSDMD removes the auto-inhibition that masks the active pore-forming NT domain in the full-length protein by interactions with GSDM-CT. The cleaved NT-GSDMD monomers then oligomerize to form pores in the plasma membrane to facilitate the release of IL-1β and IL-18 with a measured amount of pyroptosis. Pyroptosis is an effective way to counteract intracellular parasites, which exploit replicative niche to avoid killing. To date, most GSDMs have been verified to perform pore-forming activity and GSDMD-induced pyroptosis is rapidly emerging as a mechanism of anti-microbial host defence. Here, we review our comprehensive and current knowledge on the expression, activation, biological functions, and regulation of GSDMD cleavage with emphases on physiological scenario and related dysfunctions of each GSDM member as executioner of cell death, cytokine secretion and inflammation against Eh and other protozoan parasitic infections.

Plasma Membrane Wounding and Repair Assays for Eukaryotic Cells

Damage to the plasma membrane and loss of membrane integrity are detrimental to eukaryotic cells. It is, therefore, essential that cells possess an efficient membrane repair system to survive. However, the different cellular and molecular mechanisms behind plasma membrane repair have not been fully elucidated. Here, we present three complementary methods for plasma membrane wounding, and measurement of membrane repair and integrity. The first protocol is based on real time imaging of cell membrane repair kinetics in response to laser-induced injury. The second and third protocols are end point assays that provide a population-based measure of membrane integrity, after either mechanical injury by vortex mixing with glass beads, or by detergent-induced injury by digitonin in sublytic concentrations. The protocols can be applied to most adherent eukaryotic cells in culture, as well as cells in suspension.

Cancer cells resist antibody-mediated destruction by neutrophils through activation of the exocyst complex

BACKGROUND

Neutrophils kill antibody-opsonized tumor cells using trogocytosis, a unique mechanism of destruction of the target plasma. This previously unknown cytotoxic process of neutrophils is dependent on antibody opsonization, Fcγ receptors and CD11b/CD18 integrins. Here, we demonstrate that tumor cells can escape neutrophil-mediated cytotoxicity by calcium (Ca2+)-dependent and exocyst complex-dependent plasma membrane repair.

METHODS

We knocked down EXOC7 or EXOC4, two exocyst components, to evaluate their involvement in tumor cell membrane repair after neutrophil-induced trogocytosis. We used live cell microscopy and flow cytometry for visualization of the host and tumor cell interaction and tumor cell membrane repair. Last, we reported the mRNA levels of exocyst in breast cancer tumors in correlation to the response in trastuzumab-treated patients.

RESULTS

We found that tumor cells can evade neutrophil antibody-dependent cellular cytotoxicity (ADCC) by Ca2+-dependent cell membrane repair, a process induced upon neutrophil trogocytosis. Absence of exocyst components EXOC7 or EXOC4 rendered tumor cells vulnerable to neutrophil-mediated ADCC (but not natural killer cell-mediated killing), while neutrophil trogocytosis remained unaltered. Finally, mRNA levels of exocyst components in trastuzumab-treated patients were inversely correlated to complete response to therapy.

CONCLUSIONS

Our results support that neutrophil attack towards antibody-opsonized cancer cells by trogocytosis induces an active repair process by the exocyst complex in vitro. Our findings provide insight to the possible contribution of neutrophils in current antibody therapies and the tolerance mechanism of tumor cells and support further studies for potential use of the exocyst components as clinical biomarkers.

Single-cell monitoring of dry mass and dry mass density reveals exocytosis of cellular dry contents in mitosis

Cell mass and composition change with cell cycle progression. Our previous work characterized buoyant mass dynamics in mitosis (Miettinen et al., 2019), but how dry mass and cell composition change in mitosis has remained unclear. To better understand mitotic cell growth and compositional changes, we develop a single-cell approach for monitoring dry mass and the density of that dry mass every ~75 s with 1.3% and 0.3% measurement precision, respectively. We find that suspension grown mammalian cells lose dry mass and increase dry mass density following mitotic entry. These changes display large, non-genetic cell-to-cell variability, and the changes are reversed at metaphase-anaphase transition, after which dry mass continues accumulating. The change in dry mass density causes buoyant and dry mass to differ specifically in early mitosis, thus reconciling existing literature on mitotic cell growth. Mechanistically, cells in early mitosis increase lysosomal exocytosis, and inhibition of lysosomal exocytosis decreases the dry mass loss and dry mass density increase in mitosis. Overall, our work provides a new approach for monitoring single-cell dry mass and dry mass density, and reveals that mitosis is coupled to extensive exocytosis-mediated secretion of cellular contents.

Reduced Sarcolemmal Membrane Repair Exacerbates Striated Muscle Pathology in a Mouse Model of Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is a common X-linked degenerative muscle disorder that involves mutations in the DMD gene that frequently reduce the expression of the dystrophin protein, compromising the structural integrity of the sarcolemmal membrane and leaving it vulnerable to injury during cycles of muscle contraction and relaxation. This results in an increased frequency of sarcolemma disruptions that can compromise the barrier function of the membrane and lead to death of the myocyte. Sarcolemmal membrane repair processes can potentially compensate for increased membrane disruptions in DMD myocytes. Previous studies demonstrated that TRIM72, a muscle-enriched tripartite motif (TRIM) family protein also known as mitsugumin 53 (MG53), is a component of the cell membrane repair machinery in striated muscle. To test the importance of membrane repair in striated muscle in compensating for the membrane fragility in DMD, we crossed TRIM72/MG53 knockout mice into the mdx mouse model of DMD. These double knockout (DKO) mice showed compromised sarcolemmal membrane integrity compared to mdx mice, as measured by immunoglobulin G staining and ex vivo muscle laser microscopy wounding assays. We also found a significant decrease in muscle ex vivo contractile function as compared to mdx mice at both 6 weeks and 1.5 years of age. As the DKO mice aged, they developed more extensive fibrosis in skeletal muscles compared to mdx. Our findings indicate that TRIM72/MG53-mediated membrane repair can partially compensate for the sarcolemmal fragility associated with DMD and that the loss of membrane repair results in increased pathology in the DKO mice.

Resisting attack by repairing the damage

Removing membrane pores may help cancer cells survive T cell assault.

An Overview of Cell Membrane Perforation and Resealing Mechanisms for Localized Drug Delivery

Localized and reversible plasma membrane disruption is a promising technique employed for the targeted deposition of exogenous therapeutic compounds for the treatment of disease. Indeed, the plasma membrane represents a significant barrier to successful delivery, and various physical methods using light, sound, and electrical energy have been developed to generate cell membrane perforations to circumvent this issue. To restore homeostasis and preserve viability, localized cellular repair mechanisms are subsequently triggered to initiate a rapid restoration of plasma membrane integrity. Here, we summarize the known emergency membrane repair responses, detailing the salient membrane sealing proteins as well as the underlying cytoskeletal remodeling that follows the physical induction of a localized plasma membrane pore, and we present an overview of potential modulation strategies that may improve targeted drug delivery approaches.

Membrane Dynamics and Remodelling in Response to the Action of the Membrane-Damaging Pore-Forming Toxins

Pore-forming protein toxins (PFTs) represent a diverse class of membrane-damaging proteins that are produced by a wide variety of organisms. PFT-mediated membrane perforation is largely governed by the chemical composition and the physical properties of the plasma membranes. The interaction between the PFTs with the target membranes is critical for the initiation of the pore-formation process, and can lead to discrete membrane reorganization events that further aids in the process of pore-formation. Punching holes on the plasma membranes by the PFTs interferes with the cellular homeostasis by disrupting the ion-balance inside the cells that in turn can turn on multiple signalling cascades required to restore membrane integrity and cellular homeostasis. In this review, we discuss the physicochemical attributes of the plasma membranes associated with the pore-formation processes by the PFTs, and the subsequent membrane remodelling events that may start off the membrane-repair mechanisms.

Membrane repair triggered by cholesterol-dependent cytolysins is activated by mixed lineage kinases and MEK

Repair of plasma membranes damaged by bacterial pore-forming toxins, such as streptolysin O or perfringolysin O, during septic cardiomyopathy or necrotizing soft tissue infections is mediated by several protein families. However, the activation of these proteins downstream of ion influx is poorly understood. Here, we demonstrate that following membrane perforation by bacterial cholesterol-dependent cytolysins, calcium influx activates mixed lineage kinase 3 independently of protein kinase C or ceramide generation. Mixed lineage kinase 3 uncouples mitogen-activated kinase kinase (MEK) and extracellular-regulated kinase (ERK) signaling. MEK signals via an ERK-independent pathway to promote rapid annexin A2 membrane recruitment and enhance microvesicle shedding. This pathway accounted for 70% of all calcium ion-dependent repair responses to streptolysin O and perfringolysin O, but only 50% of repair to intermedilysin. We conclude that mixed lineage kinase signaling via MEK coordinates microvesicle shedding, which is critical for cellular survival against cholesterol-dependent cytolysins.

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.

Ca2+ dependence and kinetics of cell membrane repair after electropermeabilization

Electroporation, in particular with nanosecond pulses, is an efficient technique to generate nanometer-size membrane lesions without the use of toxins or other chemicals. The restoration of the membrane integrity takes minutes and is only partially dependent on [Ca²⁺]. We explored the impact of Ca²⁺ on the kinetics of membrane resealing by monitoring the entry of a YO-PRO-1 dye (YP) in BPAE and HEK cells. Ca²⁺ was promptly removed or added after the electric pulse (EP) by a fast-step perfusion. YP entry increased sharply after the EP and gradually slowed down following either a single- or a double-exponential function. In BPAE cells permeabilized by a single 300- or 600-ns EP at 14 kV/cm in a Ca²⁺-free medium, perfusion with 2 mM of external Ca²⁺ advanced the 90% resealing and reduced the dye uptake about twofold. Membrane restoration was accomplished by a combination of fast, Ca²⁺-independent resealing (τ = 13-15 s) and slow, Ca²⁺-dependent processes (τ ~70 s with Ca²⁺ and ~ 110 s or more without it). These time constants did not change when the membrane damage was doubled by increasing EP duration from 300 to 600 ns. However, injury by microsecond-range EP (300 and 600 μs) took longer to recover even when the membrane initially was less damaged, presumably because of the larger size of pores made in the membrane. Full membrane recovery was not prevented by blocking both extra- and intracellular Ca²⁺ (by loading cells with BAPTA or after Ca²⁺ depletion from the reticulum), suggesting the recruitment of unknown Ca²⁺-independent repair mechanisms.

A single dual-targeting fluorescent probe enables exploration of the correlation between the plasma membrane and lysosomes

The interactions between organelles can maintain normal cell activity. Lysosomes, as waste disposal systems of cells, have many important interactions with the plasma membrane, especially in the repair of cracked plasma membrane. Unfortunately, a way to study the relationship between them synchronously is still lacking. Therefore, in this work, we constructed a dual-targeting probe (Mem-Lyso) to simultaneously visualize the plasma membrane and lysosomes for the first time. Taking advantage of dual-targeting, the probe Mem-Lyso could successfully track and analyze the dynamic changes of the plasma membrane and lysosomes in different bioprocesses. The experimental results demonstrated that, compared to the normal status, there was obvious fusion between the plasma membrane and lysosomes in the apoptosis process. Furthermore, because of the sensitivity to polarity, Mem-Lyso could label the plasma membrane and lysosomes with red and yellow colors in cells, respectively. Moreover, the skeleton and gastrointestinal wall of zebrafish were visualized by dual-color imaging, respectively. More importantly, the dual-targeting property endowed Mem-Lyso with the ability to spatially distinguish the cholesterol (CL) content in the plasma membrane, which provided a potential detection tool for biological research and diagnosis of related diseases.

Radiotherapy transiently reduces the sensitivity of cancer cells to lymphocyte cytotoxicity

The impact of radiotherapy on the interaction between immune cells and cancer cells is important not least because radiotherapy can be used alongside immunotherapy as a cancer treatment. Unexpectedly, we found that X-ray irradiation of cancer cells induced significant resistance to natural killer (NK) cell killing. This was true across a wide variety of cancer-cell types as well as for antibody-dependent cellular cytotoxicity. Resistance appeared 72 h postirradiation and persisted for 2 wk. Resistance could also occur independently of radiotherapy through pharmacologically induced cell-cycle arrest. Crucially, multiple steps in NK-cell engagement, synapse assembly, and activation were unaffected by target cell irradiation. Instead, radiotherapy caused profound resistance to perforin-induced calcium flux and lysis. Resistance also occurred to a structurally similar bacterial toxin, streptolysin O. Radiotherapy did not affect the binding of pore-forming proteins at the cell surface or membrane repair. Rather, irradiation instigated a defect in functional pore formation, consistent with phosphatidylserine-mediated perforin inhibition. In vivo, radiotherapy also led to a significant reduction in NK cell-mediated clearance of cancer cells. Radiotherapy-induced resistance to perforin also constrained chimeric antigen receptor T-cell cytotoxicity. Together, these data establish a treatment-induced resistance to lymphocyte cytotoxicity that is important to consider in the design of radiotherapy-immunotherapy protocols.