Macrophages engulf apoptotic and primary necrotic thymocytes through similar phosphatidylserine-dependent mechanisms

Loss of periostin function impairs ligament fibroblast activity and facilitates ROS-mediated cellular senescence

Anterior cruciate ligament (ACL) injuries pose a significant challenge due to their limited healing potential, often resulting in premature arthritis. The factors and mechanisms contributing to this inadequate healing process remain elusive. During the acute phase of injury, ACL tissues express elevated periostin levels that decline over time. The functional significance of periostin in ligament biology remains understudied. In this study, we investigated the functional and mechanistic implications of periostin deficiency in ACL biology, utilizing ligament fibroblasts derived from patients and a murine model of ACL rupture. Our investigations unveiled that periostin knockdown compromised fibroblast growth characteristics, hindered the egress of progenitor cells from explants, and arrested cell-cycle progression, resulting in the accumulation of cells in the G0/G1 phase and moderate apoptosis. Concurrently, a significant reduction in the expression of cell-cycle and matrix-related genes was observed. Moreover, periostin deficiency triggered apoptosis through STAT3Y705/p38MAPK signaling and induced cellular senescence through increased production of reactive oxygen species (ROS). Mechanistically, inhibition of ROS production mitigated cell senescence in these cells. Notably, in vivo data revealed that ACL in Postn-/- mice exhibited a higher tearing frequency than wild-type mice under equivalent loading conditions. Furthermore, injured ACL with silenced periostin expression, achieved through nanoparticle-siRNA complex delivery, displayed an elevated propensity for apoptosis and senescence compared to intact ACL in C57BL/6 mice. Together, our findings underscore the pivotal role of periostin in ACL health, injury, and potential for healing.

All-trans retinoic acid and dexamethasone regulate phagocytosis-related gene expression and enhance dead cell uptake in C2C12 myoblast cells

Extensive mechanical stress frequently causes micro-traumas in skeletal muscle, followed by a regeneration period. The effective removal of dead myofibers is a prerequisite for proper regeneration, and several cell types, including professional phagocytes, were reported to be active in this process. Myoblasts express several molecules of the phagocytic machinery, such as BAI1, stabilin-2, and TAM (Tyro3, Axl, Mertk) tyrosine kinase receptors, but these molecules were reported to serve primarily cell fusion and survival, and their role in the phagocytosis was not investigated. Therefore, we aimed to investigate the in vitro phagocytic capacity of the C2C12 mouse myoblast cell line. RNA sequencing data were analyzed to determine the level and changes of phagocytosis-related gene expression during the differentiation process of C2C12 cells. To study the phagocytic capacity of myoblasts and the effect of dexamethasone, all-trans retinoic acid, hemin, and TAM kinase inhibitor treatments on phagocytosis, C2C12 cells were fed dead thymocytes, and their phagocytic capacity was determined by flow cytometry. The effect of dexamethasone and all-trans retinoic acid on phagocytosis-related gene expression was determined by quantitative PCR. Both undifferentiated and differentiated cells engulfed dead cells being the undifferentiated cells more effective. In line with this, we observed that the expression of several phagocytosis-related genes was downregulated during the differentiation process. The phagocytosis could be increased by dexamethasone and all-trans retinoic acid and decreased by hemin and TAM kinase inhibitor treatments. Our results indicate that myoblasts not only express phagocytic machinery genes but are capable of efficient dead cell clearance as well, and this is regulated similarly, as reported in professional phagocytes.

Comparison of immunotherapy mediated by apoptotic bodies, microvesicles and exosomes: apoptotic bodies' unique anti-inflammatory potential

Immunotherapy, including immunostimulation and immunosuppression, has seen significant development in the last 10 years. Immunostimulation has been verified as effective in anti-cancer treatment, while immunosuppression is used in the treatment of autoimmune disease and inflammation. Currently, with the update of newly-invented simplified isolation methods and the findings of potent triggered immune responses, extracellular vesicle-based immunotherapy is very eye-catching. However, the research on three main types of extracellular vesicles, exosomes, microvesicles and apoptotic bodies, needs to be more balanced. These three subtypes share a certain level of similarity, and at the same time, they have their own properties caused by the different methods of biogensis. Herein, we summarized respectively the status of immunotherapy based on each kind of vesicle and discuss the possible involved mechanisms. In conclusion, we highlighted that the effect of the apoptotic body is clear and strong. Apoptotic bodies have an excellent potential in immunosuppressive and anti-inflammatory therapies .

How do necrotic cells expose phosphatidylserine to attract their predators—What’s unique and what’s in common with apoptotic cells

Phosphatidylserine (PS) is a lipid component of the plasma membrane. It is asymmetrically distributed to the inner leaflet in live cells. In cells undergoing apoptosis, phosphatidylserine is exposed to the outer surfaces. The exposed phosphatidylserine acts as an evolutionarily conserved “eat-me” signal that attracts neighboring engulfing cells in metazoan organisms, including the nematode Caenorhabditis elegans, the fruit fly Drosophila melanogaster, and mammals. During apoptosis, the exposure of phosphatidylserine to the outer surface of a cell is driven by the membrane scramblases and flippases, the activities of which are regulated by caspases. Cells undergoing necrosis, a kind of cell death frequently associated with cellular injuries and morphologically distinct from apoptosis, were initially believed to allow passive exposure of phosphatidylserine through membrane rupture. Later studies revealed that necrotic cells actively expose phosphatidylserine before any rupture occurs. A recent study in C. elegans further reported that the calcium ion (Ca2+) plays an essential role in promoting the exposure of phosphatidylserine on the surfaces of necrotic cells. These findings indicate that necrotic and apoptotic cells, which die through different molecular mechanisms, use common and unique mechanisms for promoting the exposure of the same “eat me” signal. This article will review the mechanisms regulating the exposure of phosphatidylserine on the surfaces of necrotic and apoptotic cells and highlight their similarities and differences.

Tissue Transglutaminase Knock-Out Preadipocytes and Beige Cells of Epididymal Fat Origin Possess Decreased Mitochondrial Functions Required for Thermogenesis

Beige adipocytes with thermogenic function are activated during cold exposure in white adipose tissue through the process of browning. These cells, similar to brown adipocytes, dissipate stored chemical energy in the form of heat with the help of uncoupling protein 1 (UCP1). Recently, we have shown that tissue transglutaminase (TG2) knock-out mice have decreased cold tolerance in parallel with lower utilization of their epididymal adipose tissue and reduced browning. To learn more about the thermogenic function of this fat depot, we isolated preadipocytes from the epididymal adipose tissue of wild-type and TG2 knock-out mice and differentiated them in the beige direction. Although differentiation of TG2 knock-out preadipocytes is phenotypically similar to the wild-type cells, the mitochondria of the knock-out beige cells have multiple impairments including an altered electron transport system generating lower electrochemical potential difference, reduced oxygen consumption, lower UCP1 protein content, and a higher portion of fragmented mitochondria. Most of these differences are present in preadipocytes as well, and the differentiation process cannot overcome the functional disadvantages completely. TG2 knock-out beige adipocytes produce more iodothyronine deiodinase 3 (DIO3) which may inactivate thyroid hormones required for the establishment of optimal mitochondrial function. The TG2 knock-out preadipocytes and beige cells are both hypometabolic as compared with the wild-type controls which may also be explained by the lower expression of solute carrier proteins SLC25A45, SLC25A47, and SLC25A42 which transport acylcarnitine, Co-A, and amino acids into the mitochondrial matrix. As a consequence, the mitochondria in TG2 knock-out beige adipocytes probably cannot reach the energy-producing threshold required for normal thermogenic functions, which may contribute to the decreased cold tolerance of TG2 knock-out mice.

Regenerating Skeletal Muscle Compensates for the Impaired Macrophage Functions Leading to Normal Muscle Repair in Retinol Saturase Null Mice

Skeletal muscle repair is initiated by local inflammation and involves the engulfment of dead cells (efferocytosis) by infiltrating macrophages at the injury site. Macrophages orchestrate the whole repair program, and efferocytosis is a key event not only for cell clearance but also for triggering the timed polarization of the inflammatory phenotype of macrophages into the healing one. While pro-inflammatory cytokines produced by the inflammatory macrophages induce satellite cell proliferation and differentiation into myoblasts, healing macrophages initiate the resolution of inflammation, angiogenesis, and extracellular matrix formation and drive myoblast fusion and myotube growth. Therefore, improper efferocytosis results in impaired muscle repair. Retinol saturase (RetSat) initiates the formation of various dihydroretinoids, a group of vitamin A derivatives that regulate transcription by activating retinoid receptors. Previous studies from our laboratory have shown that RetSat-null macrophages produce less milk fat globule-epidermal growth factor-factor-8 (MFG-E8), lack neuropeptide Y expression, and are characterized by impaired efferocytosis. Here, we investigated skeletal muscle repair in the tibialis anterior muscle of RetSat-null mice following cardiotoxin injury. Our data presented here demonstrate that, unexpectedly, several cell types participating in skeletal muscle regeneration compensate for the impaired macrophage functions, resulting in normal muscle repair in the RetSat-null mice.

Impaired Skeletal Muscle Development and Regeneration in Transglutaminase 2 Knockout Mice

Skeletal muscle regeneration is triggered by local inflammation and is accompanied by phagocytosis of dead cells at the injury site. Efferocytosis regulates the inflammatory program in macrophages by initiating the conversion of their inflammatory phenotype into the healing one. While pro-inflammatory cytokines induce satellite cell proliferation and differentiation into myoblasts, growth factors, such as GDF3, released by healing macrophages drive myoblast fusion and myotube growth. Therefore, improper efferocytosis may lead to impaired muscle regeneration. Transglutaminase 2 (TG2) is a versatile enzyme participating in efferocytosis. Here, we show that TG2 ablation did not alter the skeletal muscle weights or sizes but led to the generation of small size myofibers and to decreased grip force in TG2 null mice. Following cardiotoxin-induced injury, the size of regenerating fibers was smaller, and the myoblast fusion was delayed in the tibialis anterior muscle of TG2 null mice. Loss of TG2 did not affect the efferocytic capacity of muscle macrophages but delayed their conversion to Ly6C-CD206+, GDF3 expressing cells. Finally, TG2 promoted myoblast fusion in differentiating C2C12 myoblasts. These results indicate that TG2 expressed by both macrophages and myoblasts contributes to proper myoblast fusion, and its ablation leads to impaired muscle development and regeneration in mice.

Neutrophil and remnant clearance in immunity and inflammation

Neutrophil-centred inflammation and flawed clearance of neutrophils cause and exuberate multiple pathological conditions. These most abundant leukocytes exhibit very high daily turnover in steady-state and stress conditions. Various armours including oxidative burst, NETs and proteases function against pathogens, but also dispose neutrophils to spawn pro-inflammatory responses. Neutrophils undergo death through different pathways upon ageing, infection, executing the intruder's elimination. These include non-lytic apoptosis and other lytic deaths including NETosis, necroptosis and pyroptosis with distinct disintegration of the cellular membrane. This causes release and presence of different intracellular cytotoxic, and tissue-damaging content as cell remnants in the extracellular environment. The apoptotic cells and apoptotic bodies get cleared with non-inflammatory outcomes, while lytic deaths associated remnants including histones and cell-free DNA cause pro-inflammatory responses. Indeed, the enhanced frequencies of neutrophil-associated proteases, cell-free DNA and autoantibodies in diverse pathologies including sepsis, asthma, lupus and rheumatoid arthritis, imply disturbed neutrophil resolution programmes in inflammatory and autoimmune diseases. Thus, the clearance mechanisms of neutrophils and associated remnants are vital for therapeutics. Though studies focused on clearance mechanisms of senescent or apoptotic neutrophils so far generated a good understanding of the same, clearance of neutrophils undergoing distinct lytic deaths, including NETs, are being the subjects of intense investigations. Here, in this review, we are providing the current updates in the clearance mechanisms of apoptotic neutrophils and focusing on not so well-defined recognition, uptake and degradation of neutrophils undergoing lytic death and associated remnants that may provide new therapeutic approaches in inflammation and autoimmunity.

Cellular Uptake Pathways of Nanoparticles: Process of Endocytosis and Factors Affecting Their Fate

BACKGROUND

Efficient and controlled internalization of NPs into the cells depends on their physicochemical properties and dynamics of the plasma membrane. NPs-cell interaction is a complex process that decides the fate of NPs internalization through different endocytosis pathways.

OBJECTIVE

The aim of this review is to highlight the physicochemical properties of synthesized nanoparticles (NPs) and their interaction with the cellular-dynamics and pathways like phagocytosis, pinocytosis, macropinocytosis, clathrin, and caveolae-mediated endocytosis and the involvement of effector proteins domain such as clathrin, AP2, caveolin, Arf6, Cdc42, dynamin and cell surface receptors during the endocytosis process of NPs.

METHOD

An electronic search was performed to explore the focused reviews and research articles on types of endocytosis and physicochemical properties of nanoparticles and their impact on cellular internalizations. The search was limited to peer-reviewed journals in the PubMed database.

RESULTS

This article discusses in detail how different types of NPs and their physicochemical properties such as size, shape, aspect ratio, surface charge, hydrophobicity, elasticity, stiffness, corona formation, surface functionalization changes the pattern of endocytosis in the presence of different pharmacological blockers. Some external forces like a magnetic field, electric field, and ultrasound exploit the cell membrane dynamics to permeabilize them for efficient internalization with respect to fundamental principles of membrane bending and pore formation.

CONCLUSION

This review will be useful to attract and guide the audience to understand the endocytosis mechanism and their pattern with respect to physicochemical properties of NPs to improve their efficacy and targeting to achieve the impactful outcome in drug-delivery and theranostics applications.

TAM kinase signaling is indispensable for proper skeletal muscle regeneration in mice

Skeletal muscle regeneration following injury results from the proliferation and differentiation of myogenic stem cells, called satellite cells, located beneath the basal lamina of the muscle fibers. Infiltrating macrophages play an essential role in the process partly by clearing the necrotic cell debris, partly by producing cytokines that guide myogenesis. Infiltrating macrophages are at the beginning pro-inflammatory, but phagocytosis of dead cells induces a phenotypic change to become healing macrophages that regulate inflammation, myoblast fusion and growth, fibrosis, vascularization and return to homeostasis. The TAM receptor kinases Mer and Axl are known efferocytosis receptors in macrophages functioning in tolerogenic or inflammatory conditions, respectively. Here we investigated their involvement in the muscle regeneration process by studying the muscle repair following cardiotoxin-induced injury in Mer^-/- mice. We found that Axl was the only TAM kinase receptor expressed on the protein level by skeletal muscle and C2C12 myoblast cells, while Mer was the dominant TAM kinase receptor in the CD45⁺ cells, and its expression significantly increased during repair. Mer ablation did not affect the skeletal muscle weight or structure, but following injury it resulted in a delay in the clearance of necrotic muscle cell debris, in the healing phenotype conversion of macrophages and consequently in a significant delay in the full muscle regeneration. Administration of the TAM kinase inhibitor BMS-777607 to wild type mice mimicked the effect of Mer ablation on the muscle regeneration process, but in addition, it resulted in a long-persisting necrotic area. Finally, in vitro inhibition of TAM kinase signaling in C2C12 myoblasts resulted in decreased viability and in impaired myotube growth. Our work identifies Axl as a survival and growth receptor in the mouse myoblasts, and reveals the contribution of TAM kinase-mediated signaling to the skeletal muscle regeneration both in macrophages and in myoblasts.

Biochanin A Regulates Key Steps of Inflammation Resolution in a Model of Antigen-Induced Arthritis via GPR30/PKA-Dependent Mechanism

Biochanin A (BCA) is a natural organic compound of the class of phytochemicals known as flavonoids and isoflavone subclass predominantly found in red clover (Trifolium pratense). It has anti-inflammatory activity and some pro-resolving actions, such as neutrophil apoptosis. However, the effect of BCA in the resolution of inflammation is still poorly understood. In this study, we investigated the effects of BCA on the neutrophilic inflammatory response and its resolution in a model of antigen-induced arthritis. Male wild-type BALB/c mice were treated with BCA at the peak of the inflammatory process (12 h). BCA decreased the accumulation of migrated neutrophils, and this effect was associated with reduction of myeloperoxidase activity, IL-1β and CXCL1 levels, and the histological score in periarticular tissues. Joint dysfunction, as seen by mechanical hypernociception, was improved by treatment with BCA. The resolution interval (Ri) was also quantified, defining profiles of acute inflammatory parameters that include the amplitude and duration of the inflammatory response monitored by the neutrophil infiltration. BCA treatment shortened Ri from ∼23 h observed in vehicle-treated mice to ∼5.5 h, associated with an increase in apoptotic events and efferocytosis, both key steps for the resolution of inflammation. These effects of BCA were prevented by H89, an inhibitor of protein kinase A (PKA) and G15, a selective G protein–coupled receptor 30 (GPR30) antagonist. In line with the in vivo data, BCA also increased the efferocytic ability of murine bone marrow–derived macrophages. Collectively, these data indicate for the first time that BCA resolves neutrophilic inflammation acting in key steps of the resolution of inflammation, requiring activation of GPR30 and via stimulation of cAMP-dependent signaling.

Phagocytic clearance of apoptotic, necrotic, necroptotic and pyroptotic cells

Although millions of cells in the human body will undergo programmed cell death each day, dying cells are rarely detected under homeostatic settings in vivo. The swift removal of dying cells is due to the rapid recruitment of phagocytes to the site of cell death which then recognise and engulf the dying cell. Apoptotic cell clearance - the engulfment of apoptotic cells by phagocytes - is a well-defined process governed by a series of molecular factors including 'find-me', 'eat-me', 'don't eat-me' and 'good-bye' signals. However, in recent years with the rapid expansion of the cell death field, the removal of other necrotic-like cell types has drawn much attention. Depending on the type of death, dying cells employ different mechanisms to facilitate engulfment and elicit varying functional impacts on the phagocyte, from wound healing responses to inflammatory cytokine secretion. Nevertheless, despite the mechanism of death, the clearance of dying cells is a fundamental process required to prevent the uncontrolled release of pro-inflammatory mediators and inflammatory disease. This mini-review summarises the current understandings of: (i) apoptotic, necrotic, necroptotic and pyroptotic cell clearance; (ii) the functional consequences of dying cell engulfment and; (iii) the outstanding questions in the field.

Research and application of hydrostatic high pressure in tumor vaccines (Review)

It is well known that hydrostatic pressure (HP) is a physical parameter that is now regarded as an important variable for life. High hydrostatic pressure (HHP) technology has influenced biological systems for more than 100 years. Food and bioscience researchers have shown great interest in HHP technology over the past few decades. The development of knowledge related to this area can better facilitate the application of HHP in the life sciences. Furthermore, new applications for HHP may come from these current studies, particularly in tumor vaccines. Currently, cancer recurrence and metastasis continue to pose a serious threat to human health. The limited efficacy of conventional treatments has led to the need for breakthroughs in immunotherapy and other related areas. Research into tumor vaccines is providing new insights for cancer treatment. The purpose of this review is to present the main findings reported thus far in the relevant scientific literature, focusing on knowledge related to HHP technology and tumor vaccines, and to demonstrate the potential of applying HHP technology to tumor vaccine development.

From Cell Death to Regeneration: Rebuilding After Injury

The ability to regrow lost or damaged tissues is widespread, but highly variable among animals. Understanding this variation remains a challenge in regeneration biology. Numerous studies from Hydra to mouse have shown that apoptosis acts as a potent and necessary mechanism in regeneration. Much is known about the involvement of apoptosis during normal development in regulating the number and type of cells in the body. In the context of regeneration, apoptosis also regulates cell number and proliferation in tissue remodeling. Apoptosis acts both early in the process to stimulate regeneration and later to regulate regenerative patterning. Multiple studies indicate that apoptosis acts as a signal to stimulate proliferation within the regenerative tissues, producing the cells needed for full regeneration. The conservation of apoptosis as a regenerative mechanism demonstrated across species highlights its importance and motivates the continued investigation of this important facet of programmed cell death. This review summarizes what is known about the roles of apoptosis during regeneration, and compares regenerative apoptosis with the mechanisms and function of apoptosis in development. Defining the complexity of regenerative apoptosis will contribute to new knowledge and perspectives for understanding mechanisms of apoptosis induction and regulation.

C-type lectin Mincle mediates cell death-triggered inflammation in acute kidney injury

Accumulating evidence indicates that cell death triggers sterile inflammation and that impaired clearance of dead cells causes nonresolving inflammation; however, the underlying mechanisms are still unclear. Here, we show that macrophage-inducible C-type lectin (Mincle) senses renal tubular cell death to induce sustained inflammation after acute kidney injury in mice. Mincle-deficient mice were protected against tissue damage and subsequent atrophy of the kidney after ischemia–reperfusion injury. Using lipophilic extract from the injured kidney, we identified β-glucosylceramide as an endogenous Mincle ligand. Notably, free cholesterol markedly enhanced the agonistic effect of β-glucosylceramide on Mincle. Moreover, β-glucosylceramide and free cholesterol accumulated in dead renal tubules in proximity to Mincle-expressing macrophages, where Mincle was supposed to inhibit clearance of dead cells and increase proinflammatory cytokine production. This study demonstrates that β-glucosylceramide in combination with free cholesterol acts on Mincle as an endogenous ligand to induce cell death–triggered, sustained inflammation after acute kidney injury.

Key differences between olfactory ensheathing cells and Schwann cells regarding phagocytosis of necrotic cells: implications for transplantation therapies

Transplantation of peripheral nervous system glia is being explored for treating neural injuries, in particular central nervous system injuries. These glia, olfactory ensheathing cells (OECs) and Schwann cells (SCs), are thought to aid regeneration by clearing necrotic cells, (necrotic bodies, NBs), as well as myelin debris. The mechanism by which the glia phagocytose and traffic NBs are not understood. Here, we show that OECs and SCs recognize phosphatidylserine on NBs, followed by engulfment and trafficking to endosomes and lysosomes. We also showed that both glia can phagocytose and process myelin debris. We compared the time-course of glial phagocytosis (of both NBs and myelin) to that of macrophages. Internalization and trafficking were considerably slower in glia than in macrophages, and OECs were more efficient phagocytes than SCs. The two glial types also differed regarding their cytokine responses after NB challenge. SCs produced low amounts of the pro-inflammatory cytokine TNF-α while OECs did not produce detectable TNF-α. Thus, OECs have a higher capacity than SCs for phagocytosis and trafficking, whilst producing lower amounts of pro-inflammatory cytokines. These findings suggest that OEC transplantation into the injured nervous system may lead to better outcomes than SC transplantation.

Vascular Endothelial Growth Factor Inhibits Phagocytosis of Apoptotic Cells by Airway Epithelial Cells

Professional phagocytes such as dendritic cells and macrophages can ingest particles larger than 0.5 μm in diameter. Epithelial cells are nonprofessional phagocytes that cannot ingest pathogenic microorganisms, but they can ingest apoptotic cells. Inhibition of the engulfment of apoptotic cells by the airway epithelium can cause severe airway inflammation. Vascular endothelial growth factor (VEGF) is an angiogenesis-promoting factor that can mediate allergic airway inflammation and can promote airway epithelial cells (AECs) proliferation, but it is not clear whether it affects the engulfment of apoptotic cells by AECs. In the present study, VEGF inhibited engulfment of apoptotic cells by AECs via binding to VEGF receptor(R)2. This inhibitory effect of VEGF was not influenced by masking of phosphatidylserine (PS) on the surface of apoptotic cells and was partially mediated by the PI3K-Akt signaling pathway. VEGF inhibition of phagocytosis involved polymerization of actin and downregulation of the expression of the phagocytic-associated protein Beclin-1 in AECs. Since engulfment of apoptotic cells by AECs is an important mechanism for airway inflammation regression, VEGF inhibition of the engulfment of apoptotic cells by airway epithelial cells may be important for mediating allergic airway inflammation.

Isolation and Quantification of Blood Apoptotic Bodies, a Non-invasive Tool to Evaluate Apoptosis in Patients with Ischemic Stroke and Neurodegenerative Diseases

Background

Improper regulation of apoptosis has been postulated as one of the main factors that contributes to the etiology and/or progression of several prevalent diseases, including ischemic stroke and neurodegenerative pathologies. Consequently, in the last few years, there has been an ever-growing interest in the in vivo study of apoptosis. The clinical application of the tissue sampling and imaging approaches to analyze apoptosis in neurological diseases is, however, limited. Since apoptotic bodies are membrane vesicles that are released from fragmented apoptotic cells, it follows that the presence of these vesicles in the bloodstream is likely due to the apoptotic death of cells in tissues. We therefore propose to use circulating apoptotic bodies as biomarkers for measuring apoptotic death in patients with ischemic stroke and neurodegenerative diseases.

Results

Since there is no scientific literature establishing the most appropriate method for collecting and enumerating apoptotic bodies from human blood samples. Authors, here, describe a reproducible centrifugation-based method combined with flow cytometry analysis to isolate and quantify plasma apoptotic bodies of patients with ischemic stroke, multiple sclerosis, Parkinson’s disease and also in healthy controls. Electron microscopy, dynamic light scattering and proteomic characterization in combination with flow cytometry studies revealed that our isolation method achieves notable recovery rates of highly-purified intact apoptotic bodies.

Conclusions

This easy, minimally time consuming and effective procedure for isolating and quantifying plasma apoptotic bodies could help physicians to implement the use of such vesicles as a non-invasive tool to monitor apoptosis in patients with cerebrovascular and neurodegenerative diseases for prognostic purposes and for monitoring disease activity.

Uptake of osteoblast-derived extracellular vesicles promotes the differentiation of osteoclasts in the zebrafish scale

Differentiation of osteoclasts (OCs) from hematopoietic cells requires cellular interaction with osteoblasts (OBs). Due to the difficulty of live-imaging in the bone, however, the cellular and molecular mechanisms underlying intercellular communication involved in OC differentiation are still elusive. Here, we develop a fracture healing model using the scale of trap:GFP; osterix:mCherry transgenic zebrafish to visualize the interaction between OCs and OBs. Transplantation assays followed by flow cytometric analysis reveal that most trap:GFPhigh OCs in the fractured scale are detected in the osterix:mCherry+ fraction because of uptake of OB-derived extracellular vesicles (EVs). In vivo live-imaging shows that immature OCs actively interact with osterix:mCherry+ OBs and engulf EVs prior to convergence at the fracture site. In vitro cell culture assays show that OB-derived EVs promote OC differentiation via Rankl signaling. Collectively, these data suggest that EV-mediated intercellular communication with OBs plays an important role in the differentiation of OCs in bone tissue.

Flipping the dogma - phosphatidylserine in non-apoptotic cell death

The exposure of phosphatidylserine (PS) on the outer plasma membrane has long been considered a unique feature of apoptotic cells. Together with other "eat me" signals, it enables the recognition and phagocytosis of dying cells (efferocytosis), helping to explain the immunologically-silent nature of apoptosis. Recently, however, PS exposure has also been reported in non-apoptotic forms of regulated inflammatory cell death, such as necroptosis, challenging previous dogma. In this review, we outline the evidence for PS exposure in non-apoptotic cells and extracellular vesicles (EVs), and discuss possible mechanisms based on our knowledge of apoptotic-PS exposure. In addition, we examine the outcomes of non-apoptotic PS exposure, including the reversibility of cell death, efferocytosis, and consequent inflammation. By examining PS biology, we challenge the established approach of distinguishing apoptosis from other cell death pathways by AnnexinV staining of PS externalization. Finally, we re-evaluate how PS exposure is thought to define apoptosis as an immunologically silent process distinct from other non-apoptotic and inflammatory cell death pathways. Ultimately, we suggest that a complete understanding of how regulated cell death processes affect the immune system is far from being fully elucidated.