Monocyte apoptotic bodies are vehicles for influenza A virus propagation

Tailoring of apoptotic bodies for diagnostic and therapeutic applications:advances, challenges, and prospects

Apoptotic bodies (ABs) are extracellular vesicles released during apoptosis and possess diverse biological activities. Initially, ABs were regarded as garbage bags with the main function of apoptotic cell clearance. Recent research has found that ABs carry and deliver various biological agents and are taken by surrounding and distant cells, affecting cell functions and behavior. ABs-mediated intercellular communications are involved in various physiological processes including anti-inflammation and tissue regeneration as well as the pathogenesis of a variety of diseases including cancer, cardiovascular diseases, neurodegeneration, and inflammatory diseases. ABs in biological fluids can be used as a window of altered cellular and tissue states which can be applied in the diagnosis and prognosis of various diseases. The structural and constituent versatility of ABs provides flexibility for tailoring ABs according to disease diagnostic and therapeutic needs. An in-depth understanding of ABs' constituents and biological functions is mandatory for the effective tailoring of ABs including modification of bio membrane and cargo constituents. ABs' tailoring approaches including physical, chemical, biological, and genetic have been proposed for bench-to-bed translation in disease diagnosis, prognosis, and therapy. This review summarizes the updates on ABs tailoring approaches, discusses the existing challenges, and speculates the prospects for effective diagnostic and therapeutic applications.

Bergamottin Inhibits Bovine Viral Diarrhea Virus Replication by Suppressing ROS-Mediated Endoplasmic Reticulum Stress and Apoptosis

Bovine viral diarrhea virus (BVDV) is one of the most important etiological agents that causes serious economic losses to the global livestock industry. Vaccines usually provide limited efficacy against BVDV due to the emergence of mutant strains. Therefore, developing novel strategies to combat BVDV infection is urgently needed. Bergamottin (Berg), a natural furanocoumarin compound, possesses various pharmaceutical bioactivities, but its effect on BVDV infection remains unknown. The present study aimed to investigate the antiviral effect and underlying mechanism of Berg against BVDV infection. The results showed that Berg exhibited an inhibitory effect on BVDV replication in MDBK cells by disrupting the viral replication and release, rather than directly inactivating virus particles. Mechanistically, Berg inhibits BVDV replication by suppressing endoplasmic reticulum (ER) stress-mediated apoptosis via reducing reactive oxygen species (ROS) generation. Studies in vivo demonstrated that oral gavage of Berg at doses of 50 mg/kg and 75 mg/kg significantly reduced the viral load within the intestines and spleen in BVDV-challenged mice. Furthermore, histopathological damage and oxidative stress caused by BVDV were also mitigated with Berg treatment. Our data indicated that Berg suppressed BVDV propagation both in vitro and in vivo, suggesting it as a promising antiviral option against BVDV.

Diversity of Intercellular Communication Modes: A Cancer Biology Perspective

From the moment a cell is on the path to malignant transformation, its interaction with other cells from the microenvironment becomes altered. The flow of molecular information is at the heart of the cellular and systemic fate in tumors, and various processes participate in conveying key molecular information from or to certain cancer cells. For instance, the loss of tight junction molecules is part of the signal sent to cancer cells so that they are no longer bound to the primary tumors and are thus free to travel and metastasize. Upon the targeting of a single cell by a therapeutic drug, gap junctions are able to communicate death information to by-standing cells. The discovery of the importance of novel modes of cell-cell communication such as different types of extracellular vesicles or tunneling nanotubes is changing the way scientists look at these processes. However, are they all actively involved in different contexts at the same time or are they recruited to fulfill specific tasks? What does the multiplicity of modes mean for the overall progression of the disease? Here, we extend an open invitation to think about the overall significance of these questions, rather than engage in an elusive attempt at a systematic repertory of the mechanisms at play.

Riding apoptotic bodies for cell-cell transmission by African swine fever virus

African swine fever virus (ASFV), a devastating pathogen to the worldwide swine industry, mainly targets macrophage/monocyte lineage, but how the virus enters host cells has remained unclear. Here, we report that ASFV utilizes apoptotic bodies (ApoBDs) for infection and cell-cell transmission. We show that ASFV induces cell apoptosis of primary porcine alveolar macrophages (PAMs) at the late stage of infection to productively shed ApoBDs that are subsequently swallowed by neighboring PAMs to initiate a secondary infection as evidenced by electron microscopy and live-cell imaging. Interestingly, the virions loaded within ApoBDs are exclusively single-enveloped particles that are devoid of the outer layer of membrane and represent a predominant form produced during late infection. The in vitro purified ApoBD vesicles are capable of mediating virus infection of naive PAMs, but the transmission can be significantly inhibited by blocking the "eat-me" signal phosphatidyserine on the surface of ApoBDs via Annexin V or the efferocytosis receptor TIM4 on the recipient PAMs via anti-TIM4 antibody, whereas overexpression of TIM4 enhances virus infection. The same treatment however did not affect the infection by intracellular viruses. Importantly, the swine sera to ASFV exert no effect on the ApoBD-mediated transmission but can partially act on the virions lacking the outer layer of membrane. Thus, ASFV has evolved to hijack a normal cellular pathway for cell-cell spread to evade host responses.

Apoptotic Vesicles of MSCs: The Natural Therapeutic Agents and Bio-Vehicles for Targeting Drug Delivery

Mesenchymal stem cell (MSC)-based therapies are increasingly recognized as promising cellular therapeutics and show the ability to treat various diseases. However, the underlying mechanism is not fully elucidated. Some recent studies have shown an unexpected result whereby MSCs undergo rapid apoptosis following administration but still exert therapeutic effects in some disease treatments. Such a therapeutic mechanism is believed to associate with the released apoptotic vesicles from apoptotic MSCs (MSC-ApoVs). This finding inspires a novel therapeutic strategy for using MSC-ApoVs for disease treatment. The present review aims to summarize the biogenesis, physiological functions, therapeutic potentials, and related mechanisms of apoptotic vesicles in MSC-based therapy. In addition, the potential applications of MSC-ApoVs as natural therapeutic agents and natural drug delivery vehicles are proposed and highlighted. The present review is hoped to provide a general understanding of MSC-ApoVs in disease treatment and inspire potential applications in targeted drug delivery.

Advances in biological functions and applications of apoptotic vesicles

BACKGROUND

Apoptotic vesicles are extracellular vesicles generated by apoptotic cells that were previously regarded as containing waste or harmful substances but are now thought to play an important role in signal transduction and homeostasis regulation.

METHODS

In the present review, we reviewed many articles published over the past decades on the subtypes and formation of apoptotic vesicles and the existing applications of these vesicles.

RESULTS

Apoptotic bodies were once regarded as vesicles released by apoptotic cells, however, apoptotic vesicles are now regarded to include apoptotic bodies, apoptotic microvesicles and apoptotic exosomes, which exhibit variation in terms of biogenesis, sizes and properties. Applications of apoptotic vesicles were first reported long ago, but such reports have been rarer than those of other extracellular vesicles. At present, apoptotic vesicles have been utilized mainly in four aspects, including in direct therapeutic applications, in their engineering as carriers, in their construction as vaccines and in their utilization in diagnosis.

CONCLUSION

Building on a deeper understanding of their composition and characteristics, some studies have utilized apoptotic vesicles to treat diseases in more novel ways. However, their limitations for clinical translation, such as heterogeneity, have also emerged. In general, apoptotic vesicles have great application potential, but there are still many barriers to overcome in their investigation. Video Abstract.

Apoptotic bodies: bioactive treasure left behind by the dying cells with robust diagnostic and therapeutic application potentials

Apoptosis, a form of programmed cell death, is essential for growth and tissue homeostasis. Apoptotic bodies (ApoBDs) are a form of extracellular vesicles (EVs) released by dying cells in the last stage of apoptosis and were previously regarded as debris of dead cells. Recent studies unraveled that ApoBDs are not cell debris but the bioactive treasure left behind by the dying cells with an important role in intercellular communications related to human health and various diseases. Defective clearance of ApoBDs and infected-cells-derived ApoBDs are possible etiology of some diseases. Therefore, it is necessary to explore the function and mechanism of the action of ApoBDs in different physiological and pathological conditions. Recent advances in ApoBDs have elucidated the immunomodulatory, virus removal, vascular protection, tissue regenerative, and disease diagnostic potential of ApoBDs. Moreover, ApoBDs can be used as drug carriers enhancing drug stability, cellular uptake, and targeted therapy efficacy. These reports from the literature indicate that ApoBDs hold promising potential for diagnosis, prognosis, and treatment of various diseases, including cancer, systemic inflammatory diseases, cardiovascular diseases, and tissue regeneration. This review summarizes the recent advances in ApoBDs-related research and discusses the role of ApoBDs in health and diseases as well as the challenges and prospects of ApoBDs-based diagnostic and therapeutic applications.

The Immunosuppressive Roles of PD-L1 during Influenza A Virus Infection

The clinical benefits of targeting programmed death-ligand 1 (PD-L1) in various cancers represent a strategy for the treatment of immunosuppressive diseases. Here, it was demonstrated that the expression levels of PD-L1 in cells were greatly upregulated in response to H1N1 influenza A virus (IAV) infection. Overexpression of PD-L1 promoted viral replication and downregulated type-I and type-III interferons and interferon-stimulated genes. Moreover, the association between PD-L1 and Src homology region-2, containing protein tyrosine phosphatase (SHP2), during IAV/H1N1 infection was analyzed by employing the SHP2 inhibitor (SHP099), siSHP2, and pNL-SHP2. The results showed that the expressions of PD-L1 mRNA and protein were decreased under SHP099 or siSHP2 treatment, whereas the cells overexpressing SHP2 exhibited the opposite effects. Additionally, the effects of PD-L1 on the expression of p-ERK and p-SHP2 were investigated in PD-L1-overexpressed cells following WSN or PR8 infection, determining that the PD-L1 overexpression led to the decreased expression of p-SHP2 and p-ERK induced by WSN or PR8 infection. Taken together, these data reveal that PD-L1 could play an important role in immunosuppression during IAV/H1N1 infection; thus, it may serve as a promising therapeutic target for development of novel anti-IAV drugs.

Exploring the Metabolic Differences between Cisplatin- and UV Light-Induced Apoptotic Bodies in HK-2 Cells by an Untargeted Metabolomics Approach

Among the extracellular vesicles, apoptotic bodies (ABs) are only formed during the apoptosis and perform a relevant role in the pathogenesis of different diseases. Recently, it has been demonstrated that ABs from human renal proximal tubular HK-2 cells, either induced by cisplatin or by UV light, can lead to further apoptotic death in naïve HK-2 cells. Thus, the aim of this work was to carry out a non-targeted metabolomic approach to study if the apoptotic stimulus (cisplatin or UV light) affects in a different way the metabolites involved in the propagation of apoptosis. Both ABs and their extracellular fluid were analyzed using a reverse-phase liquid chromatography-mass spectrometry setup. Principal components analysis showed a tight clustering of each experimental group and partial least square discriminant analysis was used to assess the metabolic differences existing between these groups. Considering the variable importance in the projection values, molecular features were selected and some of them could be identified either unequivocally or tentatively. The resulting pathways indicated that there are significant, stimulus-specific differences in metabolites abundancies that may propagate apoptosis to healthy proximal tubular cells; thus, we hypothesize that the share in apoptosis of these metabolites might vary depending on the apoptotic stimulus.

You are what you eat and how you digest it! A discussion on inflammatory efferocytosis

Efferocytosis is a process by which phagocytes remove dead or dying cells. It is considered anti-inflammatory, as the removal process reduces potential inflammatory molecules originating from dead cells and results in the reprogramming of macrophages to an anti-inflammatory state. However, engulfment of infected dead cells, deregulated phagocytosis and perturbed digestion of apoptotic bodies induce inflammatory signalling pathways during efferocytosis. The affected inflammatory signalling molecules and the mechanism of activation are largely unknown. I discuss how the choice of dead cell cargo, the type of ingestion, and the digestion efficiency can influence phagocyte programming in the context of disease. I also present the latest findings, highlight knowledge gaps, and propose selected experimental approaches to fill them.

Monocyte distribution width as a pragmatic screen for SARS-CoV-2 or influenza infection

Monocyte distribution width (MDW) is a novel marker of monocyte activation, which is known to occur in the immune response to viral pathogens. Our objective was to determine the performance of MDW and other leukocyte parameters as screening tests for SARS-CoV-2 and influenza infection. This was a prospective cohort analysis of adult patients who underwent complete blood count (CBC) and SARS-CoV-2 or influenza testing in an Emergency Department (ED) between January 2020 and July 2021. The primary outcome was SARS-CoV-2 or influenza infection. Secondary outcomes were measures of severity of illness including inpatient hospitalization, critical care admission, hospital lengths of stay and mortality. Descriptive statistics and test performance measures were evaluated for monocyte percentage, MDW, white blood cell (WBC) count, and neutrophil to lymphocyte ratio (NLR). 3,425 ED patient visits were included. SARS-CoV-2 testing was performed during 1,922 visits with a positivity rate of 5.4%; influenza testing was performed during 2,090 with a positivity rate of 2.3%. MDW was elevated in patients with SARS-Cov-2 (median 23.0U; IQR 20.5-25.1) or influenza (median 24.1U; IQR 22.0-26.9) infection, as compared to those without (18.9U; IQR 17.4-20.7 and 19.1U; 17.4-21, respectively, P < 0.001). Monocyte percentage, WBC and NLR values were within normal range in patients testing positive for either virus. MDW identified SARS-CoV-2 and influenza positive patients with an area under the curve (AUC) of 0.83 (95% CI 0.79-0.86) and 0.83 (95% CI 0.77-0.88), respectively. At the accepted cut-off value of 20U for MDW, sensitivities were 83.7% (95% CI 76.5-90.8%) for SARS-CoV-2 and 89.6% (95% CI 80.9-98.2%) for influenza, compared to sensitivities below 45% for monocyte percentage, WBC and NLR. MDW negative predictive values were 98.6% (95% CI 98.0-99.3%) and 99.6% (95% CI 99.3-100.0%) respectively for SARS-CoV-2 and influenza. Monocyte Distribution Width (MDW), available as part of a routine complete blood count (CBC) with differential, may be a useful indicator of SARS-CoV-2 or influenza infection.

Apoptotic bodies for advanced drug delivery and therapy

Extracellular vesicles (EVs) have emerged as promising candidates for multiple biomedical applications. Major types of EVs include exosomes, microvesicles, and apoptotic bodies (ABs). ABs are conferred most properties from parent cells in the final stages of apoptosis. A wide variety of sources and stable morphological features are endowed to ABs by the rigorous apoptotic program. ABs accommodate more functional biomolecules by relying on the larger volume and maintaining their naturalness in circulation. The predominant body surface ratio of ABs facilitates their recognition by recipient cells and is advantageous for interactions with microenvironments. ABs can modulate and alleviate symptoms of numerous diseases for their origins, circulation, and high biocompatibility. In addition, ABs have been emerging in disease diagnosis, immunotherapy, regenerative therapy, and drug delivery. Here, we aim to present a thorough discussion on current knowledge about ABs. Of particular interest, we will summarize the application of AB-based strategies for diagnosis and disease therapy. Perspectives for the development of ABs in biomedical applications are highlighted.

Translating extracellular vesicle packaging into therapeutic applications

Extracellular vesicles (EVs) are membrane-bound particles released by cells in various (patho)physiological conditions. EVs can transfer effector molecules and elicit potent responses in recipient cells, making them attractive therapeutic agents and drug delivery platforms. In contrast to their tremendous potential, only a few EV-based therapies and drug delivery have been approved for clinical use, which is largely attributed to limited therapeutic loading technologies and efficiency. As EV cargo has major influence on their functionality, understanding and translating the biology underlying the packaging and transferring of biomolecule cargos (e.g. miRNAs, pathogen antigens, small molecule drugs) into EVs is key in harnessing their therapeutic potential. In this review, through recent insights into EVs’ content packaging, we discuss different mechanisms utilized by EVs during cargo packaging, and how one might therapeutically exploit this process. Apart from the well-characterized EVs like exosomes and microvesicles, we also cover the less-studied and other EV subtypes like apoptotic bodies, large oncosomes, bacterial outer membrane vesicles, and migrasomes to highlight therapeutically-diverse opportunities of EV armoury.

Extracellular Vesicles and Acute Kidney Injury: Potential Therapeutic Avenue for Renal Repair and Regeneration

Acute kidney injury (AKI) is a sudden decline of renal function and represents a global clinical problem due to an elevated morbidity and mortality. Despite many efforts, currently there are no treatments to halt this devastating condition. Extracellular vesicles (EVs) are nanoparticles secreted by various cell types in both physiological and pathological conditions. EVs can arise from distinct parts of the kidney and can mediate intercellular communication between various cell types along the nephron. Besides their potential as diagnostic tools, EVs have been proposed as powerful new tools for regenerative medicine and have been broadly studied as therapeutic mediators in different models of experimental AKI. In this review, we present an overview of the basic features and biological relevance of EVs, with an emphasis on their functional role in cell-to-cell communication in the kidney. We explore versatile roles of EVs in crucial pathophysiological mechanisms contributing to AKI and give a detailed description of the renoprotective effects of EVs from different origins in AKI. Finally, we explain known mechanisms of action of EVs in AKI and provide an outlook on the potential clinical translation of EVs in the setting of AKI.

Immunopeptidomic analysis of influenza A virus infected human tissues identifies internal proteins as a rich source of HLA ligands

CD8+ and CD4+ T cells provide cell-mediated cross-protection against multiple influenza strains by recognising epitopes bound as peptides to human leukocyte antigen (HLA) class I and -II molecules respectively. Two challenges in identifying the immunodominant epitopes needed to generate a universal T cell influenza vaccine are: A lack of cell models susceptible to influenza infection which present population-prevalent HLA allotypes, and an absence of a reliable in-vitro method of identifying class II HLA peptides. Here we present a mass spectrometry-based proteomics strategy for identifying viral peptides derived from the A/H3N2/X31 and A/H3N2/Wisconsin/67/2005 strains of influenza. We compared the HLA-I and -II immunopeptidomes presented by ex-vivo influenza challenged human lung tissues. We then compared these with directly infected immortalised macrophage-like cell line (THP1) and primary dendritic cells fed apoptotic influenza-infected respiratory epithelial cells. In each of the three experimental conditions we identified novel influenza class I and II HLA peptides with motifs specific for the host allotype. Ex-vivo infected lung tissues yielded few class-II HLA peptides despite significant numbers of alveolar macrophages, including directly infected ones, present within the tissues. THP1 cells presented HLA-I viral peptides derived predominantly from internal proteins. Primary dendritic cells presented predominantly viral envelope-derived HLA class II peptides following phagocytosis of apoptotic infected cells. The most frequent viral source protein for HLA-I and -II was matrix 1 protein (M1). This work confirms that internal influenza proteins, particularly M1, are a rich source of CD4+ and CD8+ T cell epitopes. Moreover, we demonstrate the utility of two ex-vivo fully human infection models which enable direct HLA-I and -II immunopeptide identification without significant viral tropism limitations. Application of this epitope discovery strategy in a clinical setting will provide more certainty in rational vaccine design against influenza and other emergent viruses.

Gift bags from the sentinel cells of the immune system: The diverse role of dendritic cell-derived extracellular vesicles

Dendritic cells (DCs) are professional APCs of the immune system that continuously sample their environment and function to stimulate an adaptive immune response by initiating Ag-specific immunity or tolerance. Extracellular vesicles (EVs), small membrane-bound structures, are released from DCs and have been discovered to harbor functional peptide-MHC complexes, T cell costimulatory molecules, and other molecules essential for Ag presentation, immune cell regulation, and stimulating immune responses. As such, DC-derived EVs are being explored as potential immunotherapeutic agents. DC-derived EVs have also been implicated to function as a trafficking mechanism of infectious particles aiding viral propagation. This review will explore the unique features that enable DC-derived EVs to regulate immune responses and interact with recipient cells, their roles within Ag-presentation and disease settings, as well as speculating on a potential immunological role of apoptotic DC-derived EVs.

Pattern Recognition Proteins: First Line of Defense Against Coronaviruses

The rapid outbreak of COVID-19 caused by the novel coronavirus SARS-CoV-2 in Wuhan, China, has become a worldwide pandemic affecting almost 204 million people and causing more than 4.3 million deaths as of August 11 2021. This pandemic has placed a substantial burden on the global healthcare system and the global economy. Availability of novel prophylactic and therapeutic approaches are crucially needed to prevent development of severe disease leading to major complications both acutely and chronically. The success in fighting this virus results from three main achievements: (a) Direct killing of the SARS-CoV-2 virus; (b) Development of a specific vaccine, and (c) Enhancement of the host's immune system. A fundamental necessity to win the battle against the virus involves a better understanding of the host's innate and adaptive immune response to the virus. Although the role of the adaptive immune response is directly involved in the generation of a vaccine, the role of innate immunity on RNA viruses in general, and coronaviruses in particular, is mostly unknown. In this review, we will consider the structure of RNA viruses, mainly coronaviruses, and their capacity to affect the lungs and the cardiovascular system. We will also consider the effects of the pattern recognition protein (PRP) trident composed by (a) Surfactant proteins A and D, mannose-binding lectin (MBL) and complement component 1q (C1q), (b) C-reactive protein, and (c) Innate and adaptive IgM antibodies, upon clearance of viral particles and apoptotic cells in lungs and atherosclerotic lesions. We emphasize on the role of pattern recognition protein immune therapies as a combination treatment to prevent development of severe respiratory syndrome and to reduce pulmonary and cardiovascular complications in patients with SARS-CoV-2 and summarize the need of a combined therapeutic approach that takes into account all aspects of immunity against SARS-CoV-2 virus and COVID-19 disease to allow mankind to beat this pandemic killer.

Unleashing the therapeutic potential of apoptotic bodies

Extracellular vesicles (EVs), membrane-bound vesicles that are naturally released by cells, have emerged as new therapeutic opportunities. EVs, particularly exosomes and microvesicles, can transfer effector molecules and elicit potent responses in recipient cells, making them attractive therapeutic targets and drug delivery platforms. Furthermore, containing predictive biomarkers and often being dysregulated in various disease settings, these EVs are being exploited for diagnostic purposes. In contrast, the therapeutic application of apoptotic bodies (ApoBDs), a distinct type of EVs released by cells undergoing a form of programmed cell death called apoptosis, has been largely unexplored. Recent studies have shed light on ApoBD biogenesis and functions, promisingly implicating their therapeutic potential. In this review, we discuss many strategies to develop ApoBD-based therapies as well as highlight their advantages and challenges, thereby positioning ApoBD for potential EV-based therapy.

Apoptotic Bodies: Mechanism of Formation, Isolation and Functional Relevance

In the final stages of apoptosis, apoptotic cells can generate a variety of membrane-bound vesicles known as apoptotic extracellular vesicles (ApoEVs). Apoptotic bodies (ApoBDs), a major subset of ApoEVs, are formed through a process termed apoptotic cell disassembly characterised by a series of tightly regulated morphological steps including plasma membrane blebbing, apoptotic membrane protrusion formation and fragmentation into ApoBDs. To better characterise the properties of ApoBDs and elucidate their function, a number of methods including differential centrifugation, filtration and fluorescence-activated cell sorting were developed to isolate ApoBDs. Furthermore, it has become increasingly clear that ApoBD formation can contribute to various biological processes such as apoptotic cell clearance and intercellular communication. Together, recent literature demonstrates that apoptotic cell disassembly and thus, ApoBD formation, is an important process downstream of apoptotic cell death. In this chapter, we discuss the current understandings of the molecular mechanisms involved in regulating apoptotic cell disassembly, techniques for ApoBD isolation, and the functional roles of ApoBDs in physiological and pathological settings.

Stoking the Fire: How Dying Cells Propagate Inflammatory Signalling through Extracellular Vesicle Trafficking

Communication between dying cells and their environment is a critical process that promotes tissue homeostasis during normal cellular turnover, whilst during disease settings, it can contribute to inflammation through the release of intracellular factors. Extracellular vesicles (EVs) are a heterogeneous class of membrane-bound cell-derived structures that can engage in intercellular communication via the trafficking of bioactive molecules between cells and tissues. In addition to the well-described functions of EVs derived from living cells, the ability of dying cells to release EVs capable of mediating functions on target cells or tissues is also of significant interest. In particular, during inflammatory settings such as acute tissue injury, infection and autoimmunity, the EV-mediated transfer of proinflammatory cargo from dying cells is an important process that can elicit profound proinflammatory effects in recipient cells and tissues. Furthermore, the biogenesis of EVs via unique cell-death-associated pathways has also been recently described, highlighting an emerging niche in EV biology. This review outlines the mechanisms and functions of dying-cell-derived EVs and their ability to drive inflammation during various modes of cell death, whilst reflecting on the challenges and knowledge gaps in investigating this subgenre of extracellular vesicles research.