Disruption of the plasma membrane stimulates rearrangement of microtubules and lipid traffic toward the wound site

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.

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.

Dynamics of Actin Cytoskeleton and Their Signaling Pathways during Cellular Wound Repair

The repair of wounded cell membranes is essential for cell survival. Upon wounding, actin transiently accumulates at the wound site. The loss of actin accumulation leads to cell death. The mechanism by which actin accumulates at the wound site, the types of actin-related proteins participating in the actin remodeling, and their signaling pathways are unclear. We firstly examined how actin accumulates at a wound site in Dictyostelium cells. Actin assembled de novo at the wound site, independent of cortical flow. Next, we searched for actin- and signal-related proteins targeting the wound site. Fourteen of the examined proteins transiently accumulated at different times. Thirdly, we performed functional analyses using gene knockout mutants or specific inhibitors. Rac, WASP, formin, the Arp2/3 complex, profilin, and coronin contribute to the actin dynamics. Finally, we found that multiple signaling pathways related to TORC2, the Elmo/Doc complex, PIP2-derived products, PLA2, and calmodulin are involved in the actin dynamics for wound repair.

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.

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.

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.

Opening doors with ultrasound and microbubbles: Beating biological barriers to promote drug delivery

Apart from its clinical use in imaging, ultrasound has been thoroughly investigated as a tool to enhance drug delivery in a wide variety of applications. Therapeutic ultrasound, as such or combined with cavitating nuclei or microbubbles, has been explored to cross or permeabilize different biological barriers. This ability to access otherwise impermeable tissues in the body makes the combination of ultrasound and therapeutics very appealing to enhance drug delivery in situ. This review gives an overview of the most important biological barriers that can be tackled using ultrasound and aims to provide insight on how ultrasound has shown to improve accessibility as well as the biggest hurdles. In addition, we discuss the clinical applicability of therapeutic ultrasound with respect to the main challenges that must be addressed to enable the further progression of therapeutic ultrasound towards an effective, safe and easy-to-use treatment tailored for drug delivery in patients.

Plasma membrane wound repair is characterized by extensive membrane lipid and protein rearrangements in vascular endothelial cells

Vascular endothelial cells are subject to mechanical stress resulting from blood flow and interactions with leukocytes. Stress occurs at the apical, vessel-facing cell surface and leads to membrane ruptures that have to be resealed to ensure cell survival. To mimic this process, we developed a laser ablation protocol selectively inducing wounds in the apical plasma membrane of endothelial cells. We show that Ca²⁺-dependent membrane resealing is initiated following this wounding protocol and that the process is accompanied by substantial membrane lipid dynamics at the wound site. Specifically, phosphatidylinositol (4,5)-bisphosphate, phosphatidylserine and phosphatidic acid rapidly accumulate at membrane wounds forming potential interaction platforms for Ca²⁺/phospholipid binding proteins of the annexin (Anx) family that are also recruited within seconds after wounding. Depletion of one annexin, AnxA2, and its putative binding partner S100A11 interferes with membrane resealing suggesting that Ca²⁺-dependent annexin-phospholipid interactions are required for efficient membrane wound repair in endothelial cells.

Ca2+-Calmodulin Dependent Wound Repair in Dictyostelium Cell Membrane

Wound repair of cell membrane is a vital physiological phenomenon. We examined wound repair in Dictyostelium cells by using a laserporation, which we recently invented. We examined the influx of fluorescent dyes from the external medium and monitored the cytosolic Ca²⁺ after wounding. The influx of Ca²⁺ through the wound pore was essential for wound repair. Annexin and ESCRT components accumulated at the wound site upon wounding as previously described in animal cells, but these were not essential for wound repair in Dictyostelium cells. We discovered that calmodulin accumulated at the wound site upon wounding, which was essential for wound repair. The membrane accumulated at the wound site to plug the wound pore by two-steps, depending on Ca²⁺ influx and calmodulin. From several lines of evidence, the membrane plug was derived from de novo generated vesicles at the wound site. Actin filaments also accumulated at the wound site, depending on Ca²⁺ influx and calmodulin. Actin accumulation was essential for wound repair, but microtubules were not essential. A molecular mechanism of wound repair will be discussed.

A novel study on curcumin metal complexes: solubility improvement, bioactivity, and trial burn wound treatment in rats

This paper describes a new technique to enhance the solubility of metal curcumin complexes.

Actin dynamics and myosin contractility during plasma membrane repair and restoration: Does one ring really heal them all?

In order to survive daily insults, cells have evolved various mechanisms that detect, stabilize and repair damages done to their plasma membrane and cytoskeletal structures. Damage to the PM endangers wounded cells by exposing them to uncontrolled exchanges with the extracellular milieu. The processes and molecular machinery enabling PM repair are therefore at the center of the bulk of the investigations into single-cell repair program. Wounds are repaired by dynamically remodeling the composition and shape of the injured area through exocytosis-mediated release of intracellular membrane components to the wounded area, endocytosis-mediated removal of the injured area, or the shedding of the injury. The wound healing program of Xenopus oocytes and early Drosophila embryos is by contrast, mostly characterized by the rapid formation of a large membrane patch over the wound that eventually fuse with the plasma membrane which restores plasma membrane continuity and lead to the shedding of patch material into the extracellular space. Formation and contraction of actomyosin ring restores normal plasma membrane composition and organizes cytoskeletal repairs. The extend of the contributions of the cytoskeleton to the wound healing program of somatic cells have comparatively received little attention. This review offers a survey of the current knowledge on how actin dynamics, myosin-based contraction and other cytoskeletal structures affects PM and cortical cytoskeleton repair of somatic cells.

Signaling pathways involved in adaptive responses to cell membrane disruption

Plasma membrane disruption occurs frequently in many animal tissues. Cell membrane disruption induces not only a rapid and massive influx of Ca²⁺ into the cytosol but also an efflux or release of various signaling molecules, such as ATP, from the cytosol; in turn, these signaling molecules stimulate a variety of pathways in both wounded and non-wounded neighboring cells. These signals first trigger cell membrane repair responses in the wounded cell but then induce an adaptive response, which results in faster membrane repair in the event of future wounds in both wounded and non-wounded neighboring cells. In addition, signaling pathways stimulated by membrane disruption induce other adaptive responses, including cell survival, regeneration, migration, and proliferation. This chapter summarizes the role of intra- and intercellular signaling pathways in adaptive responses triggered by cell membrane disruption.

Dynamics of actin polymerisation during the mammalian single-cell wound healing response

OBJECTIVE

The contribution of actomyosin contractile rings in the wound healing program of somatic cells as never been directly assessed. This contrast with the events characterising the wound healing response of in wounded Xenopus oocytes, in which formation and contraction of an actomyosin ring provides a platform for cytoskeletal repair and drives the restoration of proper plasma membrane composition at the site of injury. As such, we aimed to characterize, using high-resolution live-cell confocal microscopy, the cytoskeletal repair dynamics of HeLa cells.

RESULTS

We confirm here that the F-actin enrichment that characterizes the late repair program of laser-wounded cells is mostly uniform and is not associated with co-enrichment of myosin-II or the formation of concentric zones of RhoA and Cdc42 activity.

Mechanisms protecting host cells against bacterial pore-forming toxins

Pore-forming toxins (PFTs) are key virulence determinants produced and secreted by a variety of human bacterial pathogens. They disrupt the plasma membrane (PM) by generating stable protein pores, which allow uncontrolled exchanges between the extracellular and intracellular milieus, dramatically disturbing cellular homeostasis. In recent years, many advances were made regarding the characterization of conserved repair mechanisms that allow eukaryotic cells to recover from mechanical disruption of the PM membrane. However, the specificities of the cell recovery pathways that protect host cells against PFT-induced damage remain remarkably elusive. During bacterial infections, the coordinated action of such cell recovery processes defines the outcome of infected cells and is, thus, critical for our understanding of bacterial pathogenesis. Here, we review the cellular pathways reported to be involved in the response to bacterial PFTs and discuss their impact in single-cell recovery and infection.

Autocrine purinergic signaling stimulated by cell membrane disruption is involved in both cell membrane repair and adaptive response in MDCK cells

Disruption and repair of plasma membranes is normally observed in many animal tissues. Recent studies demonstrated that wounding of Madin-Darby canine kidney cells potentiates membrane repair in cells adjacent to wounded cells via paracrine purinergic signaling. The present study demonstrated that cyclic adenosine monophosphate signaling in a wounded cell was induced by autocrine purinergic signaling, and protein kinase A potentiates membrane resealing for repeated wounds in those cells. Furthermore, the present study revealed that an increase in the intracellular free Ca²⁺ concentration upon cell membrane disruption was not only due to Ca²⁺ influx through the wound site, but also because of autocrine purinergic signaling. Although the influx of extracellular Ca²⁺ is essential for membrane resealing, the present study suggested that an increase in the intracellular free Ca²⁺ concentration induced by autocrine signaling accelerates membrane resealing of the initial cell membrane disruption.

Cellular mechanisms and signals that coordinate plasma membrane repair

Plasma membrane forms the barrier between the cytoplasm and the environment. Cells constantly and selectively transport molecules across their plasma membrane without disrupting it. Any disruption in the plasma membrane compromises its selective permeability and is lethal, if not rapidly repaired. There is a growing understanding of the organelles, proteins, lipids, and small molecules that help cells signal and efficiently coordinate plasma membrane repair. This review aims to summarize how these subcellular responses are coordinated and how cellular signals generated due to plasma membrane injury interact with each other to spatially and temporally coordinate repair. With the involvement of calcium and redox signaling in single cell and tissue repair, we will discuss how these and other related signals extend from single cell repair to tissue level repair. These signals link repair processes that are activated immediately after plasma membrane injury with longer term processes regulating repair and regeneration of the damaged tissue. We propose that investigating cell and tissue repair as part of a continuum of wound repair mechanisms would be of value in treating degenerative diseases.

Intracellular Delivery by Membrane Disruption: Mechanisms, Strategies, and Concepts

Intracellular delivery is a key step in biological research and has enabled decades of biomedical discoveries. It is also becoming increasingly important in industrial and medical applications ranging from biomanufacture to cell-based therapies. Here, we review techniques for membrane disruption-based intracellular delivery from 1911 until the present. These methods achieve rapid, direct, and universal delivery of almost any cargo molecule or material that can be dispersed in solution. We start by covering the motivations for intracellular delivery and the challenges associated with the different cargo types-small molecules, proteins/peptides, nucleic acids, synthetic nanomaterials, and large cargo. The review then presents a broad comparison of delivery strategies followed by an analysis of membrane disruption mechanisms and the biology of the cell response. We cover mechanical, electrical, thermal, optical, and chemical strategies of membrane disruption with a particular emphasis on their applications and challenges to implementation. Throughout, we highlight specific mechanisms of membrane disruption and suggest areas in need of further experimentation. We hope the concepts discussed in our review inspire scientists and engineers with further ideas to improve intracellular delivery.

Muscle Cells Fix Breaches by Orchestrating a Membrane Repair Ballet

Skeletal muscle undergoes many micro-membrane lesions at physiological state. Based on their sizes and magnitude these lesions are repaired via different complexes on a specific spatio-temporal manner. One of the major repair complex is a dysferlin-dependent mechanism. Accordingly, mutations in the DYSF gene encoding dysferlin results in the development of several muscle pathologies called dysferlinopathies, where abnormalities of the membrane repair process have been characterized in patients and animal models. Recent efforts have been deployed to decipher the function of dysferlin, they shed light on its direct implication in sarcolemma resealing after injuries. These discoveries served as a strong ground to design therapeutic approaches for dysferlin-deficient patients. This review detailed the different partners and function of dysferlin and positions the sarcolemma repair in normal and pathological conditions.

Intracellular cAMP Sensor EPAC: Physiology, Pathophysiology, and Therapeutics Development

This review focuses on one family of the known cAMP receptors, the exchange proteins directly activated by cAMP (EPACs), also known as the cAMP-regulated guanine nucleotide exchange factors (cAMP-GEFs). Although EPAC proteins are fairly new additions to the growing list of cAMP effectors, and relatively "young" in the cAMP discovery timeline, the significance of an EPAC presence in different cell systems is extraordinary. The study of EPACs has considerably expanded the diversity and adaptive nature of cAMP signaling associated with numerous physiological and pathophysiological responses. This review comprehensively covers EPAC protein functions at the molecular, cellular, physiological, and pathophysiological levels; and in turn, the applications of employing EPAC-based biosensors as detection tools for dissecting cAMP signaling and the implications for targeting EPAC proteins for therapeutic development are also discussed.

Cell membrane disruption stimulates cAMP and Ca2+ signaling to potentiate cell membrane resealing in neighboring cells

Disruption of cellular plasma membranes is a common event in many animal tissues, and the membranes are usually rapidly resealed. Moreover, repeated membrane disruptions within a single cell reseal faster than the initial wound in a protein kinase A (PKA)- and protein kinase C (PKC)-dependent manner. In addition to wounded cells, recent studies have demonstrated that wounding of Madin-Darby canine kidney (MDCK) cells potentiates membrane resealing in neighboring cells in the short-term by purinergic signaling, and in the long-term by nitric oxide/protein kinase G signaling. In the present study, real-time imaging showed that cell membrane disruption stimulated cAMP synthesis and Ca²⁺ mobilization from intracellular stores by purinergic signaling in neighboring MDCK cells. Furthermore, inhibition of PKA and PKC suppressed the ATP-mediated short-term potentiation of membrane resealing in neighboring cells. These results suggest that cell membrane disruption stimulates PKA and PKC via purinergic signaling to potentiate cell membrane resealing in neighboring MDCK cells.

Control of cytoskeletal dynamics during cellular responses to pore forming toxins

Following damage by pore forming toxins (PFTs) host cells engage repair processes and display profound cytoskeletal remodeling and concomitant plasma membrane (PM) blebbing. We have recently demonstrated that host cells utilize similar mechanisms to control cytoskeletal dynamics in response to PFTs and during cell migration. This involves assembly of cortical actomyosin bundles, reorganisation of the endoplasmic reticulum (ER) network, and the interaction between the ER chaperone Gp96 and the molecular motor Non-muscle Myosin Heavy Chain IIA (NMHCIIA). Consequently, Gp96 regulates actomyosin activity, PM blebbing and cell migration, and protects PM integrity against PFTs. In addition, we observed that PFTs increase association of Gp96 and ER vacuoles with the cell surface or within PM blebs loosely attached to the cell body. Similarly, gut epithelial cells damaged by PFTs in vivo were shown to release microvilli structures or directly purge cytoplasmic content. Cytoplasmic purging involves profound cytoskeletal remodeling and ER vacuolation, suggesting that our observations recapitulate recovery processes in vivo. Here, we discuss our findings in light of the current understanding of PM repair mechanisms and in vivo recovery responses to PFTs.

Cell repair: Revisiting the patch hypothesis

Plasma membrane damage elicits a complex and dynamic cellular response. A vital component of this response, membrane resealing, is thought to arise from fusion of intracellular membranous compartments to form a temporary, impermeant patch at the site of damage; however, this hypothesis has been difficult to confirm visually. By utilizing advanced microscopy technologies with high spatiotemporal resolution in wounded Xenopus laevis oocytes, we provide the first direct visualization of the membrane fusion events predicted by the patch hypothesis; we show the barrier formed by patching is capable of abating exchange of material across the plasma membrane within seconds. Profound changes also occur to the plasma membrane surrounding wounds; lipid remodeling is accompanied by membrane fusion events, both conventional (e.g., exocytosis) and novel (e.g., “explodosis”). Further, we reveal additional complexity in wound-induced subcellular patterning, supporting existing evidence that extensive interactions between lipid, protein, and ionic signaling pathways shape the cellular wound response.

Characterizing the malignancy and drug resistance of cancer cells from their membrane resealing response

In this report, we showed that two tumor cell characteristics, namely the malignancy and drug-resistance status can be evaluated by their membrane resealing response. Specifically, membrane pores in a number of pairs of cancer and normal cell lines originated from nasopharynx, lung and intestine were introduced by nano-mechanical puncturing. Interestingly, such nanometer-sized holes in tumor cells can reseal ~2-3 times faster than those in the corresponding normal cells. Furthermore, the membrane resealing time in cancer cell lines exhibiting resistance to several leading chemotherapeutic drugs was also found to be substantially shorter than that in their drug-sensitive counterparts, demonstrating the potential of using this quantity as a novel marker for future cancer diagnosis and drug resistance detection. Finally, a simple model was proposed to explain the observed resealing dynamics of cells which suggested that the distinct response exhibited by normal, tumor and drug resistant cells is likely due to the different tension levels in their lipid membranes, a conclusion that is also supported by direct cortical tension measurement.

Mechanics of epithelial tissues during gap closure

The closure of gaps is crucial to maintaining epithelium integrity during developmental and repair processes such as dorsal closure and wound healing. Depending on biochemical as well as physical properties of the microenvironment, gap closure occurs through assembly of multicellular actin-based contractile cables and/or protrusive activity of cells lining the gap. This review discusses the relative contributions of 'purse-string' and cell crawling mechanisms regulated by cell-substrate and cell-cell interactions, cellular mechanics and physical constraints from the environment.

Co-option of Membrane Wounding Enables Virus Penetration into Cells

During cell entry, non-enveloped viruses undergo partial uncoating to expose membrane lytic proteins for gaining access to the cytoplasm. We report that adenovirus uses membrane piercing to induce and hijack cellular wound removal processes that facilitate further membrane disruption and infection. Incoming adenovirus stimulates calcium influx and lysosomal exocytosis, a membrane repair mechanism resulting in release of acid sphingomyelinase (ASMase) and degradation of sphingomyelin to ceramide lipids in the plasma membrane. Lysosomal exocytosis is triggered by small plasma membrane lesions induced by the viral membrane lytic protein-VI, which is exposed upon mechanical cues from virus receptors, followed by virus endocytosis into leaky endosomes. Chemical inhibition or RNA interference of ASMase slows virus endocytosis, inhibits virus escape to the cytosol, and reduces infection. Ceramide enhances binding of protein-VI to lipid membranes and protein-VI-induced membrane rupture. Thus, adenovirus uses a positive feedback loop between virus uncoating and lipid signaling for efficient membrane penetration.

Cell healing: Calcium, repair and regeneration

Cell repair is attracting increasing attention due to its conservation, its importance to health, and its utility as a model for cell signaling and cell polarization. However, some of the most fundamental questions concerning cell repair have yet to be answered. Here we consider three such questions: (1) How are wound holes stopped? (2) How is cell regeneration achieved after wounding? (3) How is calcium inrush linked to wound stoppage and cell regeneration?

Short-term potentiation of membrane resealing in neighboring cells is mediated by purinergic signaling

Resealing of a disrupted plasma membrane in the micron-size range requires Ca(2+)-regulated exocytosis. When cells are wounded twice, the second membrane disruption reseals more quickly than the initial wound. This response is protein kinase C (PKC)-dependent and protein kinase A dependent in the early stages. In the long term (24 h), potentiation of membrane resealing in a wounded cell depends on gene expression mediated by a transcription factor, cyclic adenosine monophosphate response element binding protein(CREB), which is activated by a PKC-dependent and p38 mitogen-activated protein kinase-dependent pathway. In addition,a recent study demonstrated that wounding of Madin–Darby canine kidney (MDCK) cells potentiates membrane resealing in neighboring cells by activating CREB-dependent gene expression through nitric oxide (NO) signaling. The present study demonstrated that wounding of MDCK cells induces short-term potentiation of membrane resealing in neighboring cells in addition to a long-term response. Inhibition of purinergic signaling suppressed short-term potentiation of membrane resealing in neighboring cells, but not long-term potentiation. By contrast, inhibition of NO signaling did not suppress the short-term response in neighboring cells. These results suggest that cell membrane disruption stimulates at least two intercellular signaling pathways, NO and purinergic signaling, to potentiate cell membrane resealing in neighboring cells.

Imaging cell membrane injury and subcellular processes involved in repair

The ability of injured cells to heal is a fundamental cellular process, but cellular and molecular mechanisms involved in healing injured cells are poorly understood. Here assays are described to monitor the ability and kinetics of healing of cultured cells following localized injury. The first protocol describes an end point based approach to simultaneously assess cell membrane repair ability of hundreds of cells. The second protocol describes a real time imaging approach to monitor the kinetics of cell membrane repair in individual cells following localized injury with a pulsed laser. As healing injured cells involves trafficking of specific proteins and subcellular compartments to the site of injury, the third protocol describes the use of above end point based approach to assess one such trafficking event (lysosomal exocytosis) in hundreds of cells injured simultaneously and the last protocol describes the use of pulsed laser injury together with TIRF microscopy to monitor the dynamics of individual subcellular compartments in injured cells at high spatial and temporal resolution. While the protocols here describe the use of these approaches to study the link between cell membrane repair and lysosomal exocytosis in cultured muscle cells, they can be applied as such for any other adherent cultured cell and subcellular compartment of choice.

Membrane damage-induced vesicle-vesicle fusion of dysferlin-containing vesicles in muscle cells requires microtubules and kinesin

Mutations in the dysferlin gene resulting in dysferlin-deficiency lead to limb-girdle muscular dystrophy 2B and Myoshi myopathy in humans. Dysferlin has been proposed as a critical regulator of vesicle-mediated membrane resealing in muscle fibers, and localizes to muscle fiber wounds following sarcolemma damage. Studies in fibroblasts and urchin eggs suggest that trafficking and fusion of intracellular vesicles with the plasma membrane during resealing requires the intracellular cytoskeleton. However, the contribution of dysferlin-containing vesicles to resealing in muscle and the role of the cytoskeleton in regulating dysferlin-containing vesicle biology is unclear. Here, we use live-cell imaging to examine the behavior of dysferlin-containing vesicles following cellular wounding in muscle cells and examine the role of microtubules and kinesin in dysferlin-containing vesicle behavior following wounding. Our data indicate that dysferlin-containing vesicles move along microtubules via the kinesin motor KIF5B in muscle cells. Membrane wounding induces dysferlin-containing vesicle-vesicle fusion and the formation of extremely large cytoplasmic vesicles, and this response depends on both microtubules and functional KIF5B. In non-muscle cell types, lysosomes are critical mediators of membrane resealing, and our data indicate that dysferlin-containing vesicles are capable of fusing with lysosomes following wounding which may contribute to formation of large wound sealing vesicles in muscle cells. Overall, our data provide mechanistic evidence that microtubule-based transport of dysferlin-containing vesicles may be critical for resealing, and highlight a critical role for dysferlin-containing vesicle-vesicle and vesicle-organelle fusion in response to wounding in muscle cells.

Measurement of tension release during laser induced axon lesion to evaluate axonal adhesion to the substrate at piconewton and millisecond resolution

The formation of functional connections in a developing neuronal network is influenced by extrinsic cues. The neurite growth of developing neurons is subject to chemical and mechanical signals, and the mechanisms by which it senses and responds to mechanical signals are poorly understood. Elucidating the role of forces in cell maturation will enable the design of scaffolds that can promote cell adhesion and cytoskeletal coupling to the substrate, and therefore improve the capacity of different neuronal types to regenerate after injury. Here, we describe a method to apply simultaneous force spectroscopy measurements during laser induced cell lesion. We measure tension release in the partially lesioned axon by simultaneous interferometric tracking of an optically trapped probe adhered to the membrane of the axon. Our experimental protocol detects the tension release with piconewton sensitivity, and the dynamic of the tension release at millisecond time resolution. Therefore, it offers a high-resolution method to study how the mechanical coupling between cells and substrates can be modulated by pharmacological treatment and/or by distinct mechanical properties of the substrate.

Dysferlin-deficient muscular dystrophy and innate immune activation

Cells encounter many physical, chemical and biological stresses that perturb plasma membrane integrity, warranting an immediate membrane repair response to regain cell homeostasis. Failure to respond properly to such perturbation leads to individual cell death, which may also produce systemic influence by triggering sterile immunological responses. In this review, we discuss recent progress on understanding the mechanisms underlying muscle cell membrane repair and the potential mediators of innate immune activation when the membrane repair system is defective, specifically focusing on pathology associated with dysferlin deficiency.

Tissue damage in organic rainbow trout muscle investigated by proteomics and bioinformatics

The response to tissue damage is a complex process, which involves the coordinated regulation of multiple proteins to ensure tissue repair. In order to investigate the effect of tissue damage in a lower vertebrate, samples were taken from rainbow trout (Oncorhynchus mykiss) at day 7 after damage and proteins were separated using 2DE. The experimental design included two groups of rainbow trout, which were fed organic feed either with or without astaxanthin. In total, 96 proteins were found to be affected by tissue damage, clearly demonstrating in this lower vertebrate the complexity and magnitude of the cellular response, in the context of a regenerative process. Using a bioinformatics approach, the main biological function of these proteins were assigned, showing the regulation of proteins involved in processes such as apoptosis, iron homeostasis, and regulation of muscular structure. Interestingly, it was established that exclusively within the astaxanthin feed group, three members of the annexin protein family (annexin IV, V, and VI) were regulated in response to tissue damage.

Cell membrane disruption stimulates NO/PKG signaling and potentiates cell membrane repair in neighboring cells

Resealing of a disrupted plasma membrane at the micron-diameter range requires Ca²⁺-regulated exocytosis. Repeated membrane disruptions reseal more quickly than the initial wound, and this potentiation of membrane resealing persists for at least 24 hours after the initial wound. Long-term potentiation of membrane resealing requires CREB-dependent gene expression, which is activated by the PKC- and p38 MAPK-dependent pathway in a wounded cell. The present study demonstrates that membrane resealing is potentiated in both wounded and neighboring cells in MDCK cells. Wounding of cells expressing CREB133, a mutant variant of CREB, does not show the potentiated response of cell membrane resealing in either wounded or neighboring cells. Furthermore, wounding of cells induces CREB phosphorylation, not only in wounded cells, but also in neighboring cells. Inhibition of the nitric oxide/PKG signaling pathway suppresses CREB phosphorylation in neighboring cells, but not in wounded cells. The potentiation of membrane resealing in neighboring cells is suppressed if the nitric oxide/PKG pathway is inhibited during the initial wound. Together, these results suggest that the nitric oxide/PKG pathway stimulates CREB phosphorylation in neighboring cells so that subsequent cell membrane disruptions of the neighboring cells reseal more quickly.

Cytoskeleton responses in wound repair

Wound repair on the cellular and multicellular levels is essential to the survival of complex organisms. In order to avoid further damage, prevent infection, and restore normal function, cells and tissues must rapidly seal and remodel the wounded area. The cytoskeleton is an important component of wound repair in that it is needed for actomyosin contraction, recruitment of repair machineries, and cell migration. Recent use of model systems and high-resolution microscopy has provided new insight into molecular aspects of the cytoskeletal response during wound repair. Here we discuss the role of the cytoskeleton in single-cell, embryonic, and adult repair, as well as the striking resemblance of these processes to normal developmental events and many diseases.

The formation of actin waves during regeneration after axonal lesion is enhanced by BDNF

During development, axons of neurons in the mammalian central nervous system lose their ability to regenerate. To study the regeneration process, axons of mouse hippocampal neurons were partially damaged by an UVA laser dissector system. The possibility to deliver very low average power to the sample reduced the collateral thermal damage and allowed studying axonal regeneration of mouse neurons during early days in vitro. Force spectroscopy measurements were performed during and after axon ablation with a bead attached to the axonal membrane and held in an optical trap. With this approach, we quantified the adhesion of the axon to the substrate and the viscoelastic properties of the membrane during regeneration. The reorganization and regeneration of the axon was documented by long-term live imaging. Here we demonstrate that BDNF regulates neuronal adhesion and favors the formation of actin waves during regeneration after axonal lesion.

The role of electrically stimulated endocytosis in gene electrotransfer

Gene electrotransfer is an established method for transfer of genes into cells, however, the mechanism of transfer of DNA across the cell membrane is still not known. Some studies suggest that DNA is translocated through membrane pores while others propose that DNA enters the cell via electro-endocytosis, but no direct observation was performed. In this paper we investigated the second hypothesis. Cells were stained with membrane dye FM 1-43FX, which is used for observation of endocytosis, and then exposed to electric pulses. We analyzed if endocytosis was stimulated by applying electric pulses with intensities below and above the threshold value for gene electrotransfer. No increase in endocytosis from 20 min or even up to 2h after the pulse delivery was observed, regardless of the electric field strength. These observations do not correlate with electrotransfer efficiency, which increases with field strength and is observed only above the threshold value. Our results suggest that electro-endocytosis is not a crucial mechanism for gene electrotransfer and that the hypothesis of DNA entry by translocation through permeabilized membrane is more plausible. The presented results are important for better understanding of the mechanisms of gene electrotransfer and for its optimization for clinical applications.

Wound repair: toward understanding and integration of single-cell and multicellular wound responses

The importance of wound healing to medicine and biology has long been evident, and consequently, wound healing has been the subject of intense investigation for many years. However, several relatively recent developments have added new impetus to wound repair research: the increasing application of model systems; the growing recognition that single cells have a robust, complex, and medically relevant wound healing response; and the emerging recognition that different modes of wound repair bear an uncanny resemblance to other basic biological processes such as morphogenesis and cytokinesis. In this review, each of these developments is described, and their significance for wound healing research is considered. In addition, overlapping mechanisms of single-cell and multicellular wound healing are highlighted, and it is argued that they are more similar than is often recognized. Based on this and other information, a simple model to explain the evolutionary relationships of cytokinesis, single-cell wound repair, multicellular wound repair, and developmental morphogenesis is proposed. Finally, a series of important, but as yet unanswered, questions is posed.

Plasma membrane damage sensing and repairing. Role of heterotrimeric G-proteins and the cytoskeleton

Different toxic agents, derived from bacteria, viruses or cells of the immune system, as well as mechanical forces generated during cell locomotion are able to open pores in the cell plasma membrane. Most of these biological agents operate through specific receptors. We studied the formation and resealing of the "non-specific" plasma membrane pores generated by the mild non-ionic detergent Triton X-100. In HL-60-derived granulocytic cells plasma membrane pore opening after a 1-h treatment with Triton X-100 is documented by entry into the cell of the membrane impermeant dye ethidium bromide. As a consequence of the opening of pores the intracellular K(+) concentration falls dramatically, the cytosolic pH diminishes and the cell membrane is depolarized. Furthermore the cells acquire a polarized morphology, demonstrating the involvement of the actin cytoskeleton. At the Triton concentration used the membrane lesions are progressively repaired and by 8h the impermeability to ethidium bromide is restored and the intracellular K(+) concentration is virtually normal. Following treatments with Triton+Pertussis toxin, Triton+Cytochalasin, or Triton+Pertussis toxin+Cytochalasin the progress of membrane repair is dramatically slowed and is no longer completed by 8h. It is concluded that the membrane damage activates pertussis-sensitive G-proteins which likely act as sensors of the damage, while both G-proteins and the actin cytoskeleton are involved in the membrane repair mechanism.

Spatiotemporal dynamics of actin remodeling and endomembrane trafficking in alveolar epithelial type I cell wound healing

Alveolar epithelial type I cell (ATI) wounding is prevalent in ventilator-injured lungs and likely contributes to pathogenesis of "barotrauma" and "biotrauma." In experimental models most wounded alveolar cells repair plasma membrane (PM) defects and survive insults. Considering the force balance between edge energy at the PM wound margins and adhesive interactions of the lipid bilayer with the underlying cytoskeleton (CSK), we tested the hypothesis that subcortical actin depolymerization is a key facilitator of PM repair. Using real-time fluorescence imaging of primary rat ATI transfected with a live cell actin-green fluorescent protein construct (Lifeact-GFP) and loaded with N-rhodamine phosphatidylethanolamine (PE), we examined the spatial and temporal coordination between cytoskeletal remodeling and PM repair following micropuncture. Membrane integrity was inferred from the fluorescence intensity profiles of the cytosolic label calcein AM. Wounding led to rapid depolymerization of the actin CSK near the wound site, concurrent with accumulation of endomembrane-derived N-rhodamine PE. Both responses were sustained until PM integrity was reestablished, which typically occurs between ∼10 and 40 s after micropuncture. Only thereafter did the actin CSK near the wound begin to repolymerize, while the rate of endomembrane lipid accumulation decreased. Between 60 and 90 s after successful PM repair, after translocation of the actin nucleation factor cortactin, a dense actin fiber network formed. In cells that did not survive micropuncture injury, actin remodeling did not occur. These novel results highlight the importance of actin remodeling in ATI cell repair and suggest molecular targets for modulating the repair process.

Dysferlin interacts with tubulin and microtubules in mouse skeletal muscle

Dysferlin is a type II transmembrane protein implicated in surface membrane repair in muscle. Mutations in dysferlin lead to limb girdle muscular dystrophy 2B, Miyoshi Myopathy and distal anterior compartment myopathy. Dysferlin's mode of action is not well understood and only a few protein binding partners have thus far been identified. Using affinity purification followed by liquid chromatography/mass spectrometry, we identified alpha-tubulin as a novel binding partner for dysferlin. The association between dysferlin and alpha-tubulin, as well as between dysferlin and microtubules, was confirmed in vitro by glutathione S-transferase pulldown and microtubule binding assays. These interactions were confirmed in vivo by co-immunoprecipitation. Confocal microscopy revealed that dysferlin and alpha-tubulin co-localized in the perinuclear region and in vesicular structures in myoblasts, and along thin longitudinal structures reminiscent of microtubules in myotubes. We mapped dysferlin's alpha-tubulin-binding region to its C2A and C2B domains. Modulation of calcium levels did not affect dysferlin binding to alpha-tubulin, suggesting that this interaction is calcium-independent. Our studies identified a new binding partner for dysferlin and suggest a role for microtubules in dysferlin trafficking to the sarcolemma.

SOCIC: the store-operated calcium influx complex

Depletion of intracellular calcium stores via activation of G-protein-coupled receptors associated to the inositol trisphosphate cascade, or by the blockade of the endoplasmic reticulum calcium APTase (SERCA) results in the activation of calcium influx via the so-called store-operated channels (SOCs). The recent identification of STIM1 as the putative sensing molecule responsible for communicating the depleted state of intracellular calcium stores to the plasma membrane channel highlights the relevance of protein complexes in calcium signaling. Further developments in this area identify Orai as part of the store-operated channel complex. Upon depletion of intracellular calcium stores, STIM1 (at the ER) and Orai (at the plasma membrane) aggregate into macromolecular complexes. This molecular aggregation appears to be necessary to induce activation of calcium influx. Several studies have identified novel members from what I would like to define here as the store-operated calcium influx complex (SOCIC), such as the TRPC1 channel, SERCA and the microtubule end tracking protein, EB1. An orchestrated series of events involving the association and dissociation of several protein complexes culminate with the activation of calcium influx upon depletion of the ER. There are other likely players in this sophisticated signaling mechanism, waiting to be uncovered. The SOCIC assembly does not appear to occur in random areas of the plasma membrane, but rather in highly specialized areas known as lipid raft domains. These results strongly suggest that not only proteins but lipids also may be part or active players in the modulation of the store-operated calcium entry (SOCE). In this review we will analyze the evidence supporting macromolecular complex assembly as a prerequisite for SOC activation. We will highlight the evidence showing novel members from SOCIC and speculate about possible yet undiscovered members and players in this highly regulated calcium signaling mechanism. Finally we will discuss about the role of lipid raft domains in controlling store- and agonist-activated calcium influx.

Ca(2+) regulates the subcellular localization of adenomatous polyposis coli tumor suppressor protein

Microtubule (MT) plus-end tracking proteins (+TIPs) are involved in the regulation of MT plus-end dynamics and stabilization. It was reported previously that an increase in intracellular Ca(2+) concentration ([Ca(2+)](i)) induced by disruption of the plasma membrane stimulates rearrangement of MTs [T. Togo, Disruption of the plasma membrane stimulates rearrangement of microtubules and lipid traffic toward the wound site, J. Cell Sci. 119 (2006) 2780-2786], suggesting that some +TIPs are regulated by Ca(2+). In the present study, the behavior of adenomatous polyposis coli (APC) following an increase in [Ca(2+)](i) was observed using Xenopus A6 epithelial cell expressing GFP-tagged APC. An increase in [Ca(2+)](i) by cell membrane disruption or by ionomycin treatment induced dissociation of APC without depolymerizing MTs. Inhibition of a tyrosine kinase and GSK-3beta suppressed APC dissociation upon an increase in [Ca(2+)](i). Western blotting analysis showed that Ca(2+) transients activated GSK-3beta through a tyrosine kinase. These results suggest that Ca(2+) stimulates redistribution of APC through a tyrosine kinase- and GSK-3beta-dependent pathway.

Effects of extracellular calcium on cell membrane resealing in sonoporation

Sonoporation has been exploited as a promising strategy for intracellular drug and gene delivery. The technique uses ultrasound to generate pores on the cell membrane to allow entry of extracellular agents into the cell. Resealing of these non-specific pores is a key factor determining both the uptake and post-ultrasound cell survival. This study examined the effects of extracellular Ca(2+) on membrane resealing in sonoporation, using Xenopus oocytes as a model system. The cells were exposed to tone burst ultrasound (1.06 MHz, duration 0.2 s, acoustic pressure 0.3 MPa) in the presence of 0.1% Definity at various extracellular [Ca(2+)] (0-3 mM). Sonoporation inception and resealing in a single cell were monitored in real time via the transmembrane current of the cell under voltage clamp. The time-resolved measurements of transmembrane current revealed the involvement of two or more Ca(2+) related processes with different rate constants and characteristics. Rapid resealing occurred immediately after ultrasound application followed by a much slower resealing process. Complete resealing required [Ca(2+)] above 0.54 mM. The cells resealed in 6-26 s at 1.8 mM Ca(2+), but took longer at lower concentrations, up to 58-170 s at 0.54 mM Ca(2+).

Multiple roles of the furrow deepening Ca2+ transient during cytokinesis in zebrafish embryos

The generation of a required series of localized Ca(2+) transients during cytokinesis in zebrafish embryos suggests that Ca(2+) plays a necessary role in regulating this process. Here, we report that cortical actin remodeling, characterized by the reorganization of the contractile band and the formation during furrow deepening of pericleavage F-actin enrichments (PAEs), requires a localized increase in intracellular Ca(2+), which is released from IP(3)-sensitive stores. We demonstrate that VAMP-2 vesicle fusion at the deepening furrow also requires Ca(2+) released via IP(3) receptors, as well as the presence of PAEs and the action of calpains. Finally, by expressing a dominant-negative form of the kinesin-like protein, kif23, we demonstrate that its recruitment to the furrow region is required for VAMP-2 vesicle transport; and via FRAP analysis, that kif23 localization is also Ca(2+)-dependent. Collectively, our data demonstrate that a localized increase in intracellular Ca(2+) is involved in regulating several key events during furrow deepening and subsequent apposition.

Rehabilitation and the single cell

Cellular damage triggers rapid resealing of the plasma membrane and repair of the cortical cytoskeleton. Plasma membrane resealing results from calcium-dependent fusion of membranous organelles and the plasma membrane at the site of the damage. Cortical cytoskeletal repair results from local assembly of actin filaments (F-actin), myosin-2 and microtubules into an array that closes around the original wound site. Control of the cytoskeletal response is exerted by local activation of the small GTPases, Rho and Cdc42. Recent work has given insight into both the membrane fusion and cytoskeletal responses to plasma membrane damage and we propose that Rho GTPase activation results at least in part from the events that drive membrane repair.