The many functions of ESCRTs

Nuclear and degradative functions of the ESCRT-III pathway: implications for neurodegenerative disease

The ESCRT machinery plays a pivotal role in membrane-remodeling events across multiple cellular processes including nuclear envelope repair and reformation, nuclear pore complex surveillance, endolysosomal trafficking, and neuronal pruning. Alterations in ESCRT-III functionality have been associated with neurodegenerative diseases including Frontotemporal Dementia (FTD), Amyotrophic Lateral Sclerosis (ALS), and Alzheimer's Disease (AD). In addition, mutations in specific ESCRT-III proteins have been identified in FTD/ALS. Thus, understanding how disruptions in the fundamental functions of this pathway and its individual protein components in the human central nervous system (CNS) may offer valuable insights into mechanisms underlying neurodegenerative disease pathogenesis and identification of potential therapeutic targets. In this review, we discuss ESCRT components, dynamics, and functions, with a focus on the ESCRT-III pathway. In addition, we explore the implications of altered ESCRT-III function for neurodegeneration with a primary emphasis on nuclear surveillance and endolysosomal trafficking within the CNS.

Intervention strategies targeting virus and host factors against porcine reproductive and respiratory syndrome virus: A systematic review

Porcine reproductive and respiratory syndrome (PRRS) caused by porcine reproductive and respiratory syndrome virus (PRRSV) causes considerable economic losses to the global swine industry every year and seriously hinders the healthy development of this industry. Although tremendous efforts have been made over the past 30 years toward the development of prevention and control strategies against PRRSV infection, to date, treatments with proven efficacy have yet to be available due to our incomplete understanding of the molecular basis and complexity of the infection machinery. This review systematically discusses recent advances in the research and development of anti-PRRSV therapies targeting different stages of the viral life cycle. Furthermore, this review puts forward novel intervention targets and research approaches based on our in-depth exploration of virus-host interactions and the latest biological technologies, which have the potential to complement or transform current anti-PRRSV strategies and become breakthrough points for the control of PRRS in the future.

ESCRT disruption provides evidence against trans-synaptic signaling via extracellular vesicles

Extracellular vesicles (EVs) are released by many cell types, including neurons, carrying cargoes involved in signaling and disease. It is unclear whether EVs promote intercellular signaling or serve primarily to dispose of unwanted materials. We show that loss of multivesicular endosome-generating endosomal sorting complex required for transport (ESCRT) machinery disrupts release of EV cargoes from Drosophila motor neurons. Surprisingly, ESCRT depletion does not affect the signaling activities of the EV cargo Synaptotagmin-4 (Syt4) and disrupts only some signaling activities of the EV cargo evenness interrupted (Evi). Thus, these cargoes may not require intercellular transfer via EVs, and instead may be conventionally secreted or function cell-autonomously in the neuron. We find that EVs are phagocytosed by glia and muscles, and that ESCRT disruption causes compensatory autophagy in presynaptic neurons, suggesting that EVs are one of several redundant mechanisms to remove cargoes from synapses. Our results suggest that synaptic EV release serves primarily as a proteostatic mechanism for certain cargoes.

Mechanism and therapeutic targets of the involvement of a novel lysosomal proton channel TMEM175 in Parkinson's disease

Parkinson's disease (PD), recognized as the second most prevalent neurodegenerative disease in the aging population, presents a significant challenge due to the current lack of effective treatment methods to mitigate its progression. Many pathogenesis of PD are related to lysosomal dysfunction. Moreover, extensive genetic studies have shown a significant correlation between the lysosomal membrane protein TMEM175 and the risk of developing PD. Building on this discovery, TMEM175 has been identified as a novel potassium ion channel. Intriguingly, further investigations have found that potassium ion channels gradually close and transform into hydrion "excretion" channels in the microenvironment of lysosomes. This finding was further substantiated by studies on TMEM175 knockout mice, which exhibited pronounced motor dysfunction in pole climbing and suspension tests, alongside a notable reduction in dopamine neurons within the substantia nigra compacta. Despite these advancements, the current research landscape is not without its controversies. In light of this, the present review endeavors to methodically examine and consolidate a vast array of recent literature on TMEM175. This comprehensive analysis spans from the foundational research on the structure and function of TMEM175 to expansive population genetics studies and mechanism research utilizing cellular and animal models.A thorough understanding of the structure and function of TMEM175, coupled with insights into the intricate mechanisms underpinning lysosomal dysfunction in PD dopaminergic neurons, is imperative. Such knowledge is crucial for pinpointing precise intervention targets, thereby paving the way for novel therapeutic strategies that could potentially alter the neurodegenerative trajectory of PD.

Membrane remodeling and trafficking piloted by SARS-CoV-2

The molecular mechanisms underlying SARS-CoV-2 host cell invasion and life cycle have been studied extensively in recent years, with a primary focus on viral entry and internalization with the aim of identifying antiviral therapies. By contrast, our understanding of the molecular mechanisms involved in the later steps of the coronavirus life cycle is relatively limited. In this review, we describe what is known about the host factors and viral proteins involved in the replication, assembly, and egress phases of SARS-CoV-2, which induce significant host membrane rearrangements. We also discuss the limits of the current approaches and the knowledge gaps still to be addressed.

The potential of exosomes as a new therapeutic strategy for glioblastoma

Glioblastoma (GBM) stands for the most common and aggressive type of brain tumour in adults. It is highly invasive, which explains its short rate of survival. Little is known about its risk factors, and current therapy is still ineffective. Hence, efforts are underway to develop novel and effective treatment approaches against this type of cancer. Exosomes are being explored as a promising strategy for conveying and delivering therapeutic cargo to GBM cells. They can fuse with the GBM cell membrane and, consequently, serve as delivery systems in this context. Due to their nanoscale size, exosomes can cross the blood-brain barrier (BBB), which constitutes a significant hurdle to most chemotherapeutic drugs used against GBM. They can subsequently inhibit oncogenes, activate tumour suppressor genes, induce immune responses, and control cell growth. However, despite representing a promising tool for the treatment of GBM, further research and clinical studies regarding exosome biology, engineering, and clinical applications still need to be completed. Here, we sought to review the application of exosomes in the treatment of GBM through an in-depth analysis of the scientific and clinical studies on the entire process, from the isolation and purification of exosomes to their design and transformation into anti-oncogenic drug delivery systems. Surface modification of exosomes to enhance BBB penetration and GBM-cell targeting is also a topic of discussion.

Rab27a GTPase and its effector Myosin Va are host factors required for efficient Oropouche virus cell egress

Oropouche fever, a debilitating illness common in South America, is caused by Oropouche virus (OROV), an arbovirus. OROV belongs to the Peribunyaviridae family, a large group of RNA viruses. Little is known about the biology of Peribunyaviridae in host cells, especially assembly and egress processes. Our research reveals that the small GTPase Rab27a mediates intracellular transport of OROV induced compartments and viral release from infected cells. We show that Rab27a interacts with OROV glycoproteins and colocalizes with OROV during late phases of the infection cycle. Moreover, Rab27a activity is required for OROV trafficking to the cell periphery and efficient release of infectious particles. Consistently, depleting Rab27a's downstream effector, Myosin Va, or inhibiting actin polymerization also hinders OROV compartments targeting to the cell periphery and infectious viral particle egress. These data indicate that OROV hijacks Rab27a activity for intracellular transport and cell externalization. Understanding these crucial mechanisms of OROV's replication cycle may offer potential targets for therapeutic interventions and aid in controlling the spread of Oropouche fever.

Aberrant regulation of serine metabolism drives extracellular vesicle release and cancer progression

Cancer cells secrete extracellular vesicles (EVs) to regulate cells in the tumor microenvironment to benefit their own growth and survive in the patient's body. Although emerging evidence has demonstrated the molecular mechanisms of EV release, regulating cancer-specific EV secretion remains challenging. In this study, we applied a microRNA library to reveal the universal mechanisms of EV secretion from cancer cells. Here, we identified miR-891b and its direct target gene, phosphoserine aminotransferase 1 (PSAT1), which promotes EV secretion through the serine-ceramide synthesis pathway. Inhibition of PSAT1 affected EV secretion in multiple types of cancer, suggesting that the miR-891b/PSAT1 axis shares a common mechanism of EV secretion from cancer cells. Interestingly, aberrant PSAT1 expression also regulated cancer metastasis via EV secretion. Our data link the PSAT1-controlled EV secretion mechanism and cancer metastasis and show the potential of this mechanism as a therapeutic target in multiple types of cancer.

Functions of the UL51 protein during the herpesvirus life cycle

The herpesvirus UL51 protein is a multifunctional tegument protein involved in the regulation of multiple aspects of the viral life cycle. This article reviews the biological characteristics of the UL51 protein and its functions in herpesviruses, including participating in the maintenance of the viral assembly complex (cVAC) during viral assembly, affecting the production of mature viral particles and promoting primary and secondary envelopment, as well as its positive impact on viral cell-to-cell spread (CCS) through interactions with multiple viral proteins and its key role in the proliferation and pathogenicity of the virus in the later stage of infection. This paper discusses how the UL51 protein participates in the life cycle of herpesviruses and provides new ideas for further research on UL51 protein function.

USP8 PROMOTES INTRACELLULAR INFECTION by ENHANCING ESCRT-MEDIATED MEMBRANE REPAIR, LIMITING XENOPHAGY, and REDUCING OXIDATIVE STRESS

The host ESCRT-machinery repairs damaged endolysosomal membranes. If damage persists, selective macroautophagy/autophagy clears the damaged compartment. Mycobacterium tuberculosis (Mtb) is an intracellular pathogen that damages the phagosomal membrane and targets ESCRT-mediated repair as part of its virulence program. The E3 ubiquitin ligases PRKN and SMURF1 promote autophagic capture of damaged, Mtb-containing phagosomes. Because ubiquitination is a reversible process, we anticipated that host deubiquitinases (DUBs) would also be involved. Here, we screened all predicted mouse DUBs for their role in ubiquitin targeting and control of intracellular Mtb. We show that USP8 (ubiquitin specific peptidase 8) colocalizes with intracellular Mtb, recognizes phagosomal membrane damage, and is required for ESCRT-dependent membrane repair. Furthermore, we show that USP8 regulates the NFE2L2/NRF2-dependent antioxidant signature. Taken together, our study demonstrates a central role of USP8 in promoting Mtb intracellular growth by promoting phagosomal membrane repair, limiting ubiquitin-driven selective autophagy, and reducing oxidative stress.

Molecular Mechanisms of Autophagy Decline during Aging

Macroautophagy (hereafter autophagy) is a cellular recycling process that degrades cytoplasmic components, such as protein aggregates and mitochondria, and is associated with longevity and health in multiple organisms. While mounting evidence supports that autophagy declines with age, the underlying molecular mechanisms remain unclear. Since autophagy is a complex, multistep process, orchestrated by more than 40 autophagy-related proteins with tissue-specific expression patterns and context-dependent regulation, it is challenging to determine how autophagy fails with age. In this review, we describe the individual steps of the autophagy process and summarize the age-dependent molecular changes reported to occur in specific steps of the pathway that could impact autophagy. Moreover, we describe how genetic manipulations of autophagy-related genes can affect lifespan and healthspan through studies in model organisms and age-related disease models. Understanding the age-related changes in each step of the autophagy process may prove useful in developing approaches to prevent autophagy decline and help combat a number of age-related diseases with dysregulated autophagy.

Capsaicin alleviates acute alcohol-induced pyroptosis by activating ESCRT-III-dependent cell membrane repair in hepatocytes

Capsaicin (CAP), the active ingredient in hot chilli peppers, has anti-inflammatory and hepatoprotection effects. Acute alcoholic liver injury (AALI) is liver damage caused by acute alcohol abuse, which can lead to severe liver lesions and even be life-threatening. Pyroptosis is inflammation-related programmed cell death characterized by membrane rupture and plays a key role in AALI. The endosomal sorting complexes required for transport (ESCRT) proteins can gather at damaged areas of the membrane to facilitate the process of sealing the membrane. In this study, we found that CAP could relieve acute alcohol-induced pyroptosis of hepatocytes in vitro and in vivo. Mechanically, we found that CAP could alleviate acute alcohol-induced pyroptosis by activating the ESCRT-III-dependent membrane repair machinery. Furthermore, the data showed that CAP induced ESCRT-III protein expression by activating transient receptor potential vanilloid member 1 (TRPV1) on the cell membrane and Ca2+ influx. TRPV1 inhibitor capsazepine (CPZ) inhibited the relief effect of CAP on acute alcohol-induced pyroptosis. Overall, these results showed that CAP might activate ESCRT-III-dependent membrane repair machinery through Ca2+ influx, which is regulated by TRPV1 calcium channels, therefore mitigating acute alcohol-induced pyroptosis. Our research provides a new perspective on a naturally active food product to promote cell repair and relieve AALI.

Preserving Genome Integrity: Unveiling the Roles of ESCRT Machinery

The endosomal sorting complex required for transport (ESCRT) machinery is composed of an articulated architecture of proteins that assemble at multiple cellular sites. The ESCRT machinery is involved in pathways that are pivotal for the physiology of the cell, including vesicle transport, cell division, and membrane repair. The subunits of the ESCRT I complex are mainly responsible for anchoring the machinery to the action site. The ESCRT II subunits function to bridge and recruit the ESCRT III subunits. The latter are responsible for finalizing operations that, independently of the action site, involve the repair and fusion of membrane edges. In this review, we report on the data related to the activity of the ESCRT machinery at two sites: the nuclear membrane and the midbody and the bridge linking cells in the final stages of cytokinesis. In these contexts, the machinery plays a significant role for the protection of genome integrity by contributing to the control of the abscission checkpoint and to nuclear envelope reorganization and correlated resilience. Consistently, several studies show how the dysfunction of the ESCRT machinery causes genome damage and is a codriver of pathologies, such as laminopathies and cancer.

Subcellular localization of viral proteins after porcine epidemic diarrhea virus infection and their roles in the viral life cycle

Porcine epidemic diarrhea virus (PEDV) is one of the most devastating diseases affecting the pig industry globally. Due to the emergence of novel strains, no effective vaccines are available for prevention and control. Investigating the pathogenic mechanisms of PEDV may provide insights for creating clinical interventions. This study constructed and expressed eukaryotic expression vectors containing PEDV proteins (except NSP11) with a 3' HA tag in Vero cells. The subcellular localization of PEDV proteins was examined using endogenous protein antibodies to investigate their involvement in the viral life cycle, including endocytosis, intracellular trafficking, genome replication, energy metabolism, budding, and release. We systematically analyzed the potential roles of all PEDV viral proteins in the virus life cycle. We found that the endosome sorting complex required for transport (ESCRT) machinery may be involved in the replication and budding processes of PEDV. Our study provides insight into the molecular mechanisms underlying PEDV infection. IMPORTANCE: The global swine industry has suffered immense losses due to the spread of PEDV. Currently, there are no effective vaccines available for clinical protection. Exploring the pathogenic mechanisms of PEDV may provide valuable insights for clinical interventions. This study investigated the involvement of viral proteins in various stages of the PEDV lifecycle in the state of viral infection and identified several previously unreported interactions between viral and host proteins. These findings contribute to a better understanding of the pathogenic mechanisms underlying PEDV infection and may serve as a basis for further research and development of therapeutic strategies.

Aloperine Suppresses Cancer Progression by Interacting with VPS4A to Inhibit Autophagosome-lysosome Fusion in NSCLC

Aloperine (ALO), a quinolizidine-type alkaloid isolated from a natural Chinese herb, has shown promising antitumor effects. Nevertheless, its common mechanism of action and specific target remain elusive. Here, it is demonstrated that ALO inhibits the proliferation and migration of non-small cell lung cancer cell lines in vitro and the tumor development in several mouse tumor models in vivo. Mechanistically, ALO inhibits the fusion of autophagosomes with lysosomes and the autophagic flux, leading to the accumulation of sequestosome-1 (SQSTM1) and production of reactive oxygen species (ROS), thereby inducing tumor cell apoptosis and preventing tumor growth. Knockdown of SQSTM1 in cells inhibits ROS production and reverses ALO-induced cell apoptosis. Furthermore, VPS4A is identified as a direct target of ALO, and the amino acids F153 and D263 of VPS4A are confirmed as the binding sites for ALO. Knockout of VPS4A in H1299 cells demonstrates a similar biological effect as ALO treatment. Additionally, ALO enhances the efficacy of the anti-PD-L1/TGF-β bispecific antibody in inhibiting LLC-derived subcutaneous tumor models. Thus, ALO is first identified as a novel late-stage autophagy inhibitor that triggers tumor cell death by targeting VPS4A.

New advances in innate immune endosomal trafficking

The exocytic and endocytic intracellular trafficking pathways in innate immune cells are known for mediating the secretion of key inflammatory mediators or the internalization of growth factors, nutrients, antigens, cell debris, pathogens and even therapeutics, respectively. Inside cells, these pathways are intertwined as an elaborate network that supports the regulation of immune functions. Endosomal membranes host dynamic platforms for molecular complexes that control signaling and inflammatory responses. High content screens, coupled with elegant microscopy across the scale of resolving molecular complexes to tracking live cellular organelles, have been employed to generate the studies highlighted here. With a focus on deactivation of STING, scaffolding by SLC15A4/TASL complexes and macropinosome shrinkage via the chloride channel protein TMEM206, new studies are identifying molecules, molecular interactions and mechanisms for immune regulation throughout endosomal pathways.

Lysosomes drive the piecemeal removal of mitochondrial inner membrane

Mitochondrial membranes define distinct structural and functional compartments. Cristae of the inner mitochondrial membrane (IMM) function as independent bioenergetic units that undergo rapid and transient remodelling, but the significance of this compartmentalized organization is unknown1. Using super-resolution microscopy, here we show that cytosolic IMM vesicles, devoid of outer mitochondrial membrane or mitochondrial matrix, are formed during resting state. These vesicles derived from the IMM (VDIMs) are formed by IMM herniation through pores formed by voltage-dependent anion channel 1 in the outer mitochondrial membrane. Live-cell imaging showed that lysosomes in proximity to mitochondria engulfed the herniating IMM and, aided by the endosomal sorting complex required for transport machinery, led to the formation of VDIMs in a microautophagy-like process, sparing the remainder of the organelle. VDIM formation was enhanced in mitochondria undergoing oxidative stress, suggesting their potential role in maintenance of mitochondrial function. Furthermore, the formation of VDIMs required calcium release by the reactive oxygen species-activated, lysosomal calcium channel, transient receptor potential mucolipin 1, showing an interorganelle communication pathway for maintenance of mitochondrial homeostasis. Thus, IMM compartmentalization could allow for the selective removal of damaged IMM sections via VDIMs, which should protect mitochondria from localized injury. Our findings show a new pathway of intramitochondrial quality control.

Phage display identification of high-affinity ligands for human TSG101-UEV: A structural and thermodynamic study of PTAP recognition

The ubiquitin E2 variant domain of TSG101 (TSG101-UEV) plays a pivotal role in protein sorting and virus budding by recognizing PTAP motifs within ubiquitinated proteins. Disrupting TSG101-UEV/PTAP interactions has emerged as a promising strategy for the development of novel host-oriented antivirals with a broad spectrum of action. Nonetheless, finding inhibitors with good properties as therapeutic agents remains a challenge since the key determinants of binding affinity and specificity are still poorly understood. Here we present a detailed thermodynamic, structural, and dynamic characterization viral PTAP Late domain recognition by TSG101-UEV, combining isothermal titration calorimetry, X-ray diffraction structural studies, molecular dynamics simulations, and computational analysis of intramolecular communication pathways. Our analysis highlights key contributions from conserved hydrophobic contacts and water-mediated hydrogen bonds at the PTAP binding interface. We have identified additional electrostatic hotspots adjacent to the core motif that modulate affinity. Using competitive phage display screening we have improved affinity by 1-2 orders of magnitude, producing novel peptides with low micromolar affinities that combine critical elements found in the best natural binders. Molecular dynamics simulations revealed that optimized peptides engage new pockets on the UEV domain surface. This study provides a comprehensive view of the molecular forces directing TSG101-UEV recognition of PTAP motifs, revealing that binding is governed by conserved structural elements yet tuneable through targeted optimization. These insights open new venues to design inhibitors targeting TSG101-dependent pathways with potential application as novel broad-spectrum antivirals.

The cyanobacterial protein VIPP1 forms ESCRT-III-like structures on lipid bilayers

The biogenesis and maintenance of thylakoid membranes require vesicle-inducing protein in plastids 1 (VIPP1). VIPP1 is a member of the endosomal sorting complex required for transport-III (ESCRT-III) superfamily, whose members form diverse filament-based supramolecular structures that facilitate membrane deformation and fission. VIPP1 cryo-electron microscopy (EM) structures in solution revealed helical rods and baskets of stacked rings, with amphipathic membrane-binding domains in the lumen. However, how VIPP1 interacts with membranes remains largely unknown. Here, using high-speed atomic force microscopy (HS-AFM), we show that VIPP1 assembles into right-handed chiral spirals and regular polygons on supported lipid bilayers via ESCRT-III-like filament assembly and dynamics. VIPP1 filaments grow clockwise into spirals through polymerization at a ring-shaped central polymerization hub, and into polygons through clockwise polymerization at the sector peripheries. Interestingly, VIPP1 initially forms Archimedean spirals, which upon maturation transform into logarithmic spirals through lateral annealing of strands to the outermore low-curvature spiral turns.

ESCRT-III: a versatile membrane remodeling machinery and its implications in cellular processes and diseases

The endosomal sorting complexes required for transport (ESCRT) machinery is an evolutionarily conserved cytosolic protein complex that plays a crucial role in membrane remodeling and scission events across eukaryotes. Initially discovered for its function in multivesicular body (MVB) formation, the ESCRT complex has since been implicated in a wide range of membrane-associated processes, including endocytosis, exocytosis, cytokinesis, and autophagy. Recent advances have elucidated the ESCRT assembly pathway and highlighted the distinct functions of the various ESCRT complexes and their associated partners. Among the ESCRT complexes, ESCRT-III stands out as a critical player in membrane remodeling, with its subunits assembled into higher-order multimers capable of bending and severing membranes. This review focuses on the ESCRT-III complex, exploring its diverse functions in cellular processes beyond MVB biogenesis. We delve into the molecular mechanisms underlying ESCRT-III-mediated membrane remodeling and highlight its emerging roles in processes such as viral budding, autophagosome closure, and cytokinetic abscission. We also discuss the implications of ESCRT-III dysregulation in neurodegenerative diseases. The versatile membrane remodeling capabilities of ESCRT-III across diverse cellular processes underscore its importance in maintaining proper cellular function. Furthermore, we highlight the promising potential of ESCRT-III as a therapeutic target for neurodegenerative diseases, offering insights into the treatments of the diseases and the technical applications in related research fields.

Therapeutic potential of microglia-derived extracellular vesicles in ischemic stroke

Ischemic stroke (IS) is a debilitating neurological disorder with limited treatment options. Extracellular vesicles (EVs) have emerged as crucial lipid bilayer particles derived from various cell types that facilitate intercellular communication and enable the exchange of proteins, lipids, and genetic material. Microglia are resident brain cells that play a crucial role in brain development, maintenance of neuronal networks, and injury repair. They secrete numerous extracellular vesicles in different states. Recent evidence indicates that microglia-derived extracellular vesicles (M-EVs) actively participate in mediating various biological processes, such as neuroprotection and neurorepair, in stroke, making them an excellent therapeutic approach for treating this condition. This review comprehensively summarizes the latest research on M-EVs in stroke and explores their potential as novel therapeutic targets for this disorder. Additionally, it provides an overview of the effects and functions of M-EVs on stroke recovery to facilitate the development of clinically relevant therapies for IS.

The Conserved YPX3L Motif in the BK Polyomavirus VP1 Protein Is Important for Viral Particle Assembly but Not for Its Secretion into Extracellular Vesicles

The BK polyomavirus (BKPyV) is a small DNA non-enveloped virus whose infection is asymptomatic in most of the world's adult population. However, in cases of immunosuppression, the reactivation of the virus can cause various complications, and in particular, nephropathies in kidney transplant recipients or hemorrhagic cystitis in bone marrow transplant recipients. Recently, it was demonstrated that BKPyV virions can use extracellular vesicles to collectively traffic in and out of cells, thus exiting producing cells without cell lysis and entering target cells by diversified entry routes. By a comparison to other naked viruses, we investigated the possibility that BKPyV virions recruit the Endosomal-Sorting Complexes Required for Transport (ESCRT) machinery through late domains in order to hijack extracellular vesicles. We identified a single potential late domain in the BKPyV structural proteins, a YPX3L motif in the VP1 protein, and used pseudovirions to study the effect of point mutations found in a BKPyV clinical isolate or known to ablate the interaction of such a domain with the ESCRT machinery. Our results suggest that this domain is not involved in BKPyV association with extracellular vesicles but is crucial for capsomere interaction and thus viral particle assembly.

Extracellular vesicles as carriers for mitochondria: Biological functions and clinical applications

In recent years, research has increasingly focused on the biogenesis of extracellular vesicles (EVs) and the sorting mechanisms for their contents. Mitochondria can be selectively loaded into EVs, serving as a way to maintain cellular mitochondrial homeostasis. EV-mediated mitochondrial transfer has also been shown to greatly impact the function of target cells. Based on the mechanism of EV-mediated mitochondrial transfer, therapies can be developed to treat human diseases. This review summarizes the recent advances in the biogenesis and molecular composition of EVs. It also highlights the sorting and trafficking mechanisms of mitochondrial components into EVs. Furthermore, it explores the current role of EV-mediated mitochondrial transfer in the development of human diseases, as well as its diagnostic and therapeutic applications.

Unveiling the role of ferroptosis in the progression from NAFLD to NASH: recent advances in mechanistic understanding

Non-alcoholic fatty liver disease (NAFLD) is a prevalent and significant global public health issue. Nonalcoholic steatohepatitis (NASH) represents an advanced stage of NAFLD in terms of pathology. However, the intricate mechanisms underlying the progression from NAFLD to NASH remain elusive. Ferroptosis, characterized by iron-dependent cell death and distinguished from other forms of cell death based on morphological, biochemical, and genetic criteria, has emerged as a potential participant with a pivotal role in driving NAFLD progression. Nevertheless, its precise mechanism remains poorly elucidated. In this review article, we comprehensively summarize the pathogenesis of NAFLD/NASH and ferroptosis while highlighting recent advances in understanding the mechanistic involvement of ferroptosis in NAFLD/NASH.

Exosomes based strategies for cardiovascular diseases: Opportunities and challenges

Exosomes, as nanoscale extracellular vesicles (EVs), are secreted by all types of cells to facilitate intercellular communication in living organisms. After being taken up by neighboring or distant cells, exosomes can alter the expression levels of target genes in recipient cells and thereby affect their pathophysiological outcomes depending on payloads encapsulated therein. The functions and mechanisms of exosomes in cardiovascular diseases have attracted much attention in recent years and are thought to have cardioprotective and regenerative potential. This review summarizes the biogenesis and molecular contents of exosomes and details the roles played by exosomes released from various cells in the progression and recovery of cardiovascular disease. The review also discusses the current status of traditional exosomes in cardiovascular tissue engineering and regenerative medicine, pointing out several limitations in their application. It emphasizes that some of the existing emerging industrial or bioengineering technologies are promising to compensate for these shortcomings, and the combined application of exosomes and biomaterials provides an opportunity for mutual enhancement of their performance. The integration of exosome-based cell-free diagnostic and therapeutic options will contribute to the further development of cardiovascular regenerative medicine.

Most recent advances and applications of extracellular vesicles in tackling neurological challenges

Over the past few decades, there has been a notable increase in the global burden of central nervous system (CNS) diseases. Despite advances in technology and therapeutic options, neurological and neurodegenerative disorders persist as significant challenges in treatment and cure. Recently, there has been a remarkable surge of interest in extracellular vesicles (EVs) as pivotal mediators of intercellular communication. As carriers of molecular cargo, EVs demonstrate the ability to traverse the blood-brain barrier, enabling bidirectional communication. As a result, they have garnered attention as potential biomarkers and therapeutic agents, whether in their natural form or after being engineered for use in the CNS. This review article aims to provide a comprehensive introduction to EVs, encompassing various aspects such as their diverse isolation methods, characterization, handling, storage, and different routes for EV administration. Additionally, it underscores the recent advances in their potential applications in neurodegenerative disorder therapeutics. By exploring their unique capabilities, this study sheds light on the promising future of EVs in clinical research. It considers the inherent challenges and limitations of these emerging applications while incorporating the most recent updates in the field.

Neurons dispose of hyperactive kinesin into glial cells for clearance

Microtubule-based kinesin motor proteins are crucial for intracellular transport, but their hyperactivation can be detrimental for cellular functions. This study investigated the impact of a constitutively active ciliary kinesin mutant, OSM-3CA, on sensory cilia in C. elegans. Surprisingly, we found that OSM-3CA was absent from cilia but underwent disposal through membrane abscission at the tips of aberrant neurites. Neighboring glial cells engulf and eliminate the released OSM-3CA, a process that depends on the engulfment receptor CED-1. Through genetic suppressor screens, we identified intragenic mutations in the OSM-3CA motor domain and mutations inhibiting the ciliary kinase DYF-5, both of which restored normal cilia in OSM-3CA-expressing animals. We showed that conformational changes in OSM-3CA prevent its entry into cilia, and OSM-3CA disposal requires its hyperactivity. Finally, we provide evidence that neurons also dispose of hyperactive kinesin-1 resulting from a clinic variant associated with amyotrophic lateral sclerosis, suggesting a widespread mechanism for regulating hyperactive kinesins.

Lysosomal microautophagy: an emerging dimension in mammalian autophagy

Autophagy is a self-catabolic process through which cellular components are delivered to lysosomes for degradation. There are three types of autophagy, i.e., macroautophagy, chaperone-mediated autophagy (CMA), and microautophagy. In macroautophagy, a portion of the cytoplasm is wrapped by the autophagosome, which then fuses with lysosomes and delivers the engulfed cytoplasm for degradation. In CMA, the translocation of cytosolic substrates to the lysosomal lumen is directly across the limiting membrane of lysosomes. In microautophagy, lytic organelles, including endosomes or lysosomes, take up a portion of the cytoplasm directly. Although macroautophagy has been investigated extensively, microautophagy has received much less attention. Nonetheless, it has become evident that microautophagy plays a variety of cellular roles from yeast to mammals. Here we review the very recent updates of microautophagy. In particular, we focus on the feature of the degradative substrates and the molecular machinery that mediates microautophagy.

RNA binding protein RALY facilitates colorectal cancer metastasis via enhancing exosome biogenesis in m6A dependent manner

Tumor metastasis is the leading cause of cancer-related death in patients with colorectal cancer (CRC). Heterogeneous nuclear ribonucleoproteins (hnRNPs) are RNA-binding proteins, involved in the tumorigenesis and metastasis of various cancers. However, the molecular mechanisms of hnRNPs in CRC metastasis remain unclear. This study aims to uncover the pivotal roles and molecular mechanisms of hnRNPs in CRC metastasis. Clinical database analysis suggested that the expression of hnRNP-Associated with Lethal Yellow (RALY, an important member of hnRNPs) was strongly correlated with the aggressiveness and survival of CRC patients. Gain- and loss-of-function studies demonstrated that RALY promotes the production of exosomes by increasing the formation of multivesicular bodies (MVBs) and enhancing the fusion of MVBs with the plasma membrane. Notably, RALY directly interacts with phospholipase D2 (PLD2) to enable exosome biogenesis, and cooperates with RBM15b to control PLD2 mRNA stability in an m6A-dependent manner. RALY-mediated exosome secretion activates pro-tumor macrophages and further facilitates CRC metastasis, while rescue experiments in vivo further confirmed that RALY-mediated exosome biogenesis facilitates CRC metastasis. Collectively, our findings demonstrate that RALY promotes exosome biogenesis and facilitates colorectal cancer metastasis by upregulating PLD2 and enhancing exosome production in an m6A-dependent manner, suggesting potential therapeutic strategies for combating CRC metastasis.

Engineering Approaches for Exosome Cargo Loading and Targeted Delivery: Biological versus Chemical Perspectives

Exosomes are nanoscale membrane bound vesicles secreted by almost all types of cells. Their unique attributes, such as minimal immunogenicity and compatibility with biological systems, make them novel carriers for drug delivery. These native exosomes harbor proteins, nucleic acids, small molecule compounds, and fluorogenic agents. Moreover, through a combination of chemical and bioengineering methodologies, exosomes are tailored to transport precise therapeutic payloads to designated cells or tissues. In this review, we summarize the strategies for exosome modification and drug loading modalities in engineered exosomes. In addition, we provide an overview of the advances in the use of engineered exosomes for targeted drug delivery. Lastly, we discuss the merits and limitations of chemically engineered versus bioengineered exosome-mediated target therapies. These insights offer additional options for refining engineered exosomes in pharmaceutical development and hold promise for expediting the successful translation of engineered exosomes from the bench to the bedside.

The role of exosomal molecular cargo in exosome biogenesis and disease diagnosis

Exosomes represent a type of extracellular vesicles derived from the endosomal pathway that transport diverse molecular cargoes such as proteins, lipids, and nucleic acids. These cargoes have emerged as crucial elements impacting disease diagnosis, treatment, and prognosis, and are integral to the process of exosome formation. This review delves into the essential molecular cargoes implicated in the phases of exosome production and release. Emphasis is placed on their significance as cancer biomarkers and potential therapeutic targets, accompanied by an exploration of the obstacles and feasible applications linked to these developments.

Arabidopsis CaLB1 undergoes phase separation with the ESCRT protein ALIX and modulates autophagosome maturation

Autophagy is relevant for diverse processes in eukaryotic cells, making its regulation of fundamental importance. The formation and maturation of autophagosomes require a complex choreography of numerous factors. The endosomal sorting complex required for transport (ESCRT) is implicated in the final step of autophagosomal maturation by sealing of the phagophore membrane. ESCRT-III components were shown to mediate membrane scission by forming filaments that interact with cellular membranes. However, the molecular mechanisms underlying the recruitment of ESCRTs to non-endosomal membranes remain largely unknown. Here we focus on the ESCRT-associated protein ALG2-interacting protein X (ALIX) and identify Ca2+-dependent lipid binding protein 1 (CaLB1) as its interactor. Our findings demonstrate that CaLB1 interacts with AUTOPHAGY8 (ATG8) and PI(3)P, a phospholipid found in autophagosomal membranes. Moreover, CaLB1 and ALIX localize with ATG8 on autophagosomes upon salt treatment and assemble together into condensates. The depletion of CaLB1 impacts the maturation of salt-induced autophagosomes and leads to reduced delivery of autophagosomes to the vacuole. Here, we propose a crucial role of CaLB1 in augmenting phase separation of ALIX, facilitating the recruitment of ESCRT-III to the site of phagophore closure thereby ensuring efficient maturation of autophagosomes.

Hepatitis E Virus: What More Do We Need to Know?

Hepatitis E virus (HEV) infection is typically a self-limiting, acute illness that spreads through the gastrointestinal tract but replicates in the liver. However, chronic infections are possible in immunocompromised individuals. The HEV virion has two shapes: exosome-like membrane-associated quasi-enveloped virions (eHEV) found in circulating blood or in the supernatant of infected cell cultures and non-enveloped virions ("naked") found in infected hosts' feces and bile to mediate inter-host transmission. Although HEV is mainly spread via enteric routes, it is unclear how it penetrates the gut wall to reach the portal bloodstream. Both virion types are infectious, but they infect cells in different ways. To develop personalized treatment/prevention strategies and reduce HEV impact on public health, it is necessary to decipher the entry mechanism for both virion types using robust cell culture and animal models. The contemporary knowledge of the cell entry mechanism for these two HEV virions as possible therapeutic target candidates is summarized in this narrative review.

The Endosomal Sorting Complex, ESCRT, has diverse roles in blood progenitor maintenance, lineage choice and immune response

Most hematological malignancies are associated with reduced expression of one or more components of the Endosomal Sorting Complex Required for Transport (ESCRT). However, the roles of ESCRT in stem cell and progenitor maintenance are not resolved. Parsing signaling pathways in relation to the canonical role of ESCRT poses a challenge. The Drosophila hematopoietic organ, the larval lymph gland, provides a path to dissect the roles of cellular trafficking pathways such as ESCRT in blood development and maintenance. Drosophila has 13 core ESCRT components. Knockdown of individual ESCRTs showed that only Vps28 and Vp36 were required in all lymph gland progenitors. Using the well-conserved ESCRT-II complex as an example of the range of phenotypes seen upon ESCRT depletion, we show that ESCRTs have cell-autonomous as well as non-autonomous roles in progenitor maintenance and differentiation. ESCRT depletion also sensitized posterior lobe progenitors to respond to immunogenic wasp infestation. We also identify key heterotypic roles for ESCRT in position-dependent control of Notch activation to suppress crystal cell differentiation. Our study shows that the cargo sorting machinery determines the identity of progenitors and their adaptability to the dynamic microenvironment. These mechanisms for control of cell fate may tailor developmental diversity in multiple contexts.

Extracellular Vesicular miRNA in Pancreatic Cancer: From Lab to Therapy

Pancreatic cancer is a prevalent lethal gastrointestinal cancer that generally does not show any symptoms until it reaches advanced stages, resulting in a high mortality rate. People at high risk, such as those with a family history or chronic pancreatitis, do not have a universally accepted screening protocol. Chemotherapy and radiotherapy demonstrate limited effectiveness in the management of pancreatic cancer, emphasizing the urgent need for innovative therapeutic strategies. Recent studies indicated that the complex interaction among pancreatic cancer cells within the dynamic microenvironment, comprising the extracellular matrix, cancer-associated cells, and diverse immune cells, intricately regulates the biological characteristics of the disease. Additionally, mounting evidence suggests that EVs play a crucial role as mediators in intercellular communication by the transportation of different biomolecules, such as miRNA, proteins, DNA, mRNA, and lipids, between heterogeneous cell subpopulations. This communication mediated by EVs significantly impacts multiple aspects of pancreatic cancer pathogenesis, including proliferation, angiogenesis, metastasis, and resistance to therapy. In this review, we delve into the pivotal role of EV-associated miRNAs in the progression, metastasis, and development of drug resistance in pancreatic cancer as well as their therapeutic potential as biomarkers and drug-delivery mechanisms for the management of pancreatic cancer.

Lysosome damage triggers acute formation of ER to lysosomes membrane tethers mediated by the bridge-like lipid transport protein VPS13C

Based on genetic studies, lysosome dysfunction is thought to play a pathogenetic role in Parkinson's disease (PD). Here we show that VPS13C, a bridge-like lipid transport protein and a PD gene, is a sensor of lysosome stress/damage. Upon lysosome membrane perturbation, VPS13C rapidly relocates from the cytosol to the surface of lysosomes where it tethers their membranes to the ER. This recruitment depends on Rab7 and requires release of a brake, most likely an intramolecular interaction within VPS13C, which hinders access of its VAB domain to lysosome-bound Rab7. While another PD protein, LRRK2, is also recruited to stressed/damaged lysosomes, its recruitment occurs at much later stages and by different mechanisms. Given the putative role of VPS13 proteins in bulk lipid transport, these findings suggest lipid delivery to lysosomes by VPS13C is part of an early response to lysosome damage.

Intrinsic Disorder in the Host Proteins Entrapped in Rabies Virus Particles

A proteomics analysis of purified rabies virus (RABV) revealed 47 entrapped host proteins within the viral particles. Out of these, 11 proteins were highly disordered. Our study was particularly focused on five of the RABV-entrapped mouse proteins with the highest levels of disorder: Neuromodulin, Chmp4b, DnaJB6, Vps37B, and Wasl. We extensively utilized bioinformatics tools, such as FuzDrop, D2P2, UniProt, RIDAO, STRING, AlphaFold, and ELM, for a comprehensive analysis of the intrinsic disorder propensity of these proteins. Our analysis suggested that these disordered host proteins might play a significant role in facilitating the rabies virus pathogenicity, immune system evasion, and the development of antiviral drug resistance. Our study highlighted the complex interaction of the virus with its host, with a focus on how the intrinsic disorder can play a crucial role in virus pathogenic processes, and suggested that these intrinsically disordered proteins (IDPs) and disorder-related host interactions can also be a potential target for therapeutic strategies.

The GTPase activating protein Gyp7 regulates Rab7/Ypt7 activity on late endosomes

Organelles of the endomembrane system contain Rab GTPases as identity markers. Their localization is determined by guanine nucleotide exchange factors (GEFs) and GTPase activating proteins (GAPs). It remains largely unclear how these regulators are specifically targeted to organelles and how their activity is regulated. Here, we focus on the GAP Gyp7, which acts on the Rab7-like Ypt7 protein in yeast, and surprisingly observe the protein exclusively in puncta proximal to the vacuole. Mistargeting of Gyp7 to the vacuole strongly affects vacuole morphology, suggesting that endosomal localization is needed for function. In agreement, efficient endolysosomal transport requires Gyp7. In vitro assays reveal that Gyp7 requires a distinct lipid environment for membrane binding and activity. Overexpression of Gyp7 concentrates Ypt7 in late endosomes and results in resistance to rapamycin, an inhibitor of the target of rapamycin complex 1 (TORC1), suggesting that these late endosomes are signaling endosomes. We postulate that Gyp7 is part of regulatory machinery involved in late endosome function.

Stress-induced Rab11a-exosomes induce amphiregulin-mediated cetuximab resistance in colorectal cancer

Exosomes are secreted vesicles made intracellularly in the endosomal system. We have previously shown that exosomes are not only made in late endosomes, but also in recycling endosomes marked by the monomeric G-protein Rab11a. These vesicles, termed Rab11a-exosomes, are preferentially secreted under nutrient stress from several cancer cell types, including HCT116 colorectal cancer (CRC) cells. HCT116 Rab11a-exosomes have particularly potent signalling activities, some mediated by the epidermal growth factor receptor (EGFR) ligand, amphiregulin (AREG). Mutant activating forms of KRAS, a downstream target of EGFR, are often found in advanced CRC. When absent, monoclonal antibodies, such as cetuximab, which target the EGFR and block the effects of EGFR ligands, such as AREG, can be administered. Patients, however, inevitably develop resistance to cetuximab, either by acquiring KRAS mutations or via non-genetic microenvironmental changes. Here we show that nutrient stress in several CRC cell lines causes the release of AREG-carrying Rab11a-exosomes. We demonstrate that while soluble AREG has no effect, much lower levels of AREG bound to Rab11a-exosomes from cetuximab-resistant KRAS-mutant HCT116 cells, can suppress the effects of cetuximab on KRAS-wild type Caco-2 CRC cells. Using neutralising anti-AREG antibodies and an intracellular EGFR kinase inhibitor, we show that this effect is mediated via AREG activation of EGFR, and not transfer of activated KRAS. Therefore, presentation of AREG on Rab11a-exosomes affects its ability to compete with cetuximab. We propose that this Rab11a-exosome-mediated mechanism contributes to the establishment of resistance in cetuximab-sensitive cells and may explain why in cetuximab-resistant tumours only some cells carry mutant KRAS.

LTN1 promotes RLR degradation to inhibit immune response to RNA virus through the ESCRT pathway

The excessive activation of immune responses will trigger autoimmune diseases or inflammatory injury. The endosomal sorting complexes required for transport (ESCRT) system can capture and mediate ubiquitinated protein degradation, which timely terminates signaling pathway hyperactivation. However, whether the ESCRT system participates in regulating RIGI-like receptor (RLR)-mediated antiviral responses remains unknown. In this study, we show that LTN1/listerin, a major component of RQC, can recruit E3 ubiquitin ligase TRIM27 to trigger K63-linked polyubiquitination of RIGI and IFIH1/MDA5. This K63-linked polyubiquitination facilitates the sorting and degradation of RIGI and IFIH1 proteins through the ESCRT-dependent pathway. Concordantly, LTN1 deficiency enhances the innate antiviral response to infection with RNA viruses. Thus, our work uncovers a new mechanism for RIGI and IFIH1 degradation and identifies the role of LTN1 in negatively regulating RLR-mediated antiviral innate immunity, which may provide new targets for the intervention of viral infection.Abbreviation: 5'-pppRNA: 5' triphosphate double stranded RNA; ATG5: autophagy related 5; ATG7: autophagy related 7; BafA1: bafilomycin A1; ESCRT: endosomal sorting complexes required for transport; CHX: cycloheximide; IFIH1/MDA5: interferon induced with helicase C domain 1; IFN: interferon; PIK3C3/VPS34: phosphatidylinositol 3-kinase catalytic subunit type 3; RIGI: RNA sensor RIG-I; RLR: RIGI-like receptors; RQC: ribosome-associated protein quality control; SeV: Sendai virus; TRIM27: tripartite motif-containing 27; VSV: vesicular stomatitis virus; VPS4: vacuolar protein sorting 4.

A T-Cell Inspired Sonoporation System Enhances Low-Dose X-Ray-Mediated Pyroptosis and Radioimmunotherapy Efficacy by Restoring Gasdermin-E Expression

Genome editing has the potential to improve the unsatisfactory therapeutic effect of antitumor immunotherapy. However, the cell plasma membrane prevents the entry of almost all free genome-manipulation agents. Therefore, a system can be spatiotemporally controlled and can instantly open the cellular membrane to allow the entry of genome-editing agents into target cells is needed. Here, inspired by the ability of T cells to deliver cytotoxins to cancer cells by perforation, an ultrasound (US)-controlled perforation system (UPS) is established to enhance the delivery of free genome-manipulating agents. The UPS can perforate the tumor cell membrane while maintaining cell viability via a controllable lipid peroxidation reaction. In vitro, transmembrane-incapable plasmids can enter cells and perform genome editing with the assistance of UPS, achieving an efficiency of up to 90%. In vivo, the UPS is biodegradable, nonimmunogenic, and tumor-targeting, enabling the puncturing of tumor cells under US. With the application of UPS-assisted genome editing, gasdermin-E expression in 4T1 tumor-bearing mice is successfully restored, which leads to pyroptosis-mediated antitumor immunotherapy via low-dose X-ray irradiation. This study provides new insights for designing a sonoporation system for genome editing. Moreover, the results demonstrate that restoring gasdermin expression by genome editing significantly improves the efficacy of radioimmunotherapy.

Pyroptosis Signature Gene CHMP4B Regulates Microglia Pyroptosis by Inhibiting GSDMD in Alzheimer's Disease

In this study, we aimed to work through the key genes involved in the process of pyroptosis in Alzheimer's disease (AD) to identify potential biomarkers using bioinformatics technology and further explore the underlying molecular mechanisms. The transcriptome data of brain tissue in AD patients were screened from the GEO database, and pyroptosis-related genes were analyzed. The functions of differential genes were analyzed by enrichment analysis and protein-protein interaction. The diagnostic model was established using LASSO and logistic regression analysis, and the correlation of clinical data was analyzed. Based on single-cell analysis of brain tissues of patients with AD, immunofluorescence and western blotting were used to explore the key cells affected by the hub gene. After GSEA, qRT-PCR, western blotting, LDH, ROS, and JC-1 were used to investigate the potential mechanism of the hub gene on pyroptosis. A total of 15 pyroptosis differentially expressed genes were identified. A prediction model consisting of six genes was established by LASSO and logistic regression analysis, and the area under the curve was up to 0.81. As a hub gene, CHMP4B was negatively correlated with the severity of AD. CHMP4B expression was decreased in the hippocampal tissue of patients with AD and mice. Single-cell analysis showed that CHMP4B was downregulated in AD microglia. Overexpression of CHMP4B reduced the release of LDH and ROS and restored mitochondrial membrane potential, thereby alleviating the inflammatory response during microglial pyroptosis. In summary, CHMP4B as a hub gene provides a new strategy for the diagnosis and treatment of AD.

Applications of Stem Cell-Derived Extracellular Vesicles in Nerve Regeneration

Extracellular vesicles (EVs), including exosomes, microvesicles, and other lipid vesicles derived from cells, play a pivotal role in intercellular communication by transferring information between cells. EVs secreted by progenitor and stem cells have been associated with the therapeutic effects observed in cell-based therapies, and they also contribute to tissue regeneration following injury, such as in orthopaedic surgery cases. This review explores the involvement of EVs in nerve regeneration, their potential as drug carriers, and their significance in stem cell research and cell-free therapies. It underscores the importance of bioengineers comprehending and manipulating EV activity to optimize the efficacy of tissue engineering and regenerative therapies.

Tau fibrils induce nanoscale membrane damage and nucleate cytosolic tau at lysosomes

The prion-like spread of protein aggregates is a leading hypothesis for the propagation of neurofibrillary lesions in the brain, including the spread of tau inclusions associated with Alzheimer's disease. The mechanisms of cellular uptake of tau seeds and subsequent nucleated polymerization of cytosolic tau are major questions in the field, and the potential for coupling between the entry and nucleation mechanisms has been little explored. We found that in primary astrocytes and neurons, endocytosis of tau seeds leads to their accumulation in lysosomes. This in turn leads to lysosomal swelling, deacidification, and recruitment of ESCRT proteins, but not Galectin-3, to the lysosomal membrane. These observations are consistent with nanoscale damage of the lysosomal membrane. Live cell imaging and STORM superresolution microscopy further show that the nucleation of cytosolic tau occurs primarily at the lysosome membrane under these conditions. These data suggest that tau seeds escape from lysosomes via nanoscale damage rather than wholesale rupture and that nucleation of cytosolic tau commences as soon as tau fibril ends emerge from the lysosomal membrane.

Methylation of ESCRT-III components regulates the timing of cytokinetic abscission

Abscission is the final stage of cytokinesis, which cleaves the intercellular bridge (ICB) connecting two daughter cells. Abscission requires tight control of the recruitment and polymerization of the Endosomal Protein Complex Required for Transport-III (ESCRT-III) components. We explore the role of post-translational modifications in regulating ESCRT dynamics. We discover that SMYD2 methylates the lysine 6 residue of human CHMP2B, a key ESCRT-III component, at the ICB, impacting the dynamic relocation of CHMP2B to sites of abscission. SMYD2 loss-of-function (genetically or pharmacologically) causes CHMP2B hypomethylation, delayed CHMP2B polymerization and delayed abscission. This is phenocopied by CHMP2B lysine 6 mutants that cannot be methylated. Conversely, SMYD2 gain-of-function causes CHMP2B hypermethylation and accelerated abscission, specifically in cells undergoing cytokinetic challenges, thereby bypassing the abscission checkpoint. Additional experiments highlight the importance of CHMP2B methylation beyond cytokinesis, namely during ESCRT-III-mediated HIV-1 budding. We propose that lysine methylation signaling fine-tunes the ESCRT-III machinery to regulate the timing of cytokinetic abscission and other ESCRT-III dependent functions.

LS, Saftics A, Shodubi O, Raghunandan S, Xu J, Tsai SJ, Dong Y, Li R, Jovanovic-Talisman T, Gould SJ. Endocytosis blocks the vesicular secretion of exosome marker proteins

Exosomes are secreted vesicles of ~30 to 150 nm diameter that play important roles in human health and disease. To better understand how cells release these vesicles, we examined the biogenesis of the most highly enriched human exosome marker proteins, the exosomal tetraspanins CD81, CD9, and CD63. We show here that endocytosis inhibits their vesicular secretion and, in the case of CD9 and CD81, triggers their destruction. Furthermore, we show that syntenin, a previously described exosome biogenesis factor, drives the vesicular secretion of CD63 by blocking CD63 endocytosis and that other endocytosis inhibitors also induce the plasma membrane accumulation and vesicular secretion of CD63. Finally, we show that CD63 is an expression-dependent inhibitor of endocytosis that triggers the vesicular secretion of lysosomal proteins and the clathrin adaptor AP-2 mu2. These results suggest that the vesicular secretion of exosome marker proteins in exosome-sized vesicles occurs primarily by an endocytosis-independent pathway.

ESCRT disruption provides evidence against transsynaptic signaling functions for extracellular vesicles

Extracellular vesicles (EVs) are released by many cell types including neurons, carrying cargoes involved in signaling and disease. It is unclear whether EVs promote intercellular signaling or serve primarily to dispose of unwanted materials. We show that loss of multivesicular endosome-generating ESCRT (endosomal sorting complex required for transport) machinery disrupts release of EV cargoes from Drosophila motor neurons. Surprisingly, ESCRT depletion does not affect the signaling activities of the EV cargo Synaptotagmin-4 (Syt4) and disrupts only some signaling activities of the EV cargo Evenness Interrupted (Evi). Thus, these cargoes may not require intercellular transfer via EVs, and instead may be conventionally secreted or function cell autonomously in the neuron. We find that EVs are phagocytosed by glia and muscles, and that ESCRT disruption causes compensatory autophagy in presynaptic neurons, suggesting that EVs are one of several redundant mechanisms to remove cargoes from synapses. Our results suggest that synaptic EV release serves primarily as a proteostatic mechanism for certain cargoes.

Human ESCRT-I and ALIX function as scaffolding helical filaments in vivo

The Endosomal Sorting Complex Required for Transport (ESCRT) is an evolutionarily conserved machinery that performs reverse-topology membrane scission in cells universally required from cytokinesis to budding of enveloped viruses. Upstream acting ESCRT-I and ALIX control these events and link recruitment of viral and cellular partners to late-acting ESCRT-III CHMP4 through incompletely understood mechanisms. Using structure-function analyses combined with super-resolution imaging, we show that ESCRT-I and ALIX function as distinct helical filaments in vivo . Together, they are essential for optimal structural scaffolding of HIV-1 nascent virions, the retention of viral and human genomes through defined functional interfaces, and recruitment of CHMP4 that itself assembles into corkscrew-like filaments intertwined with ESCRT-I or ALIX helices. Disruption of filament assembly or their conformationally clustered RNA binding interfaces in human cells impaired membrane abscission, resulted in major structural instability and leaked nucleic acid from nascent virions and nuclear envelopes. Thus, ESCRT-I and ALIX function as helical filaments in vivo and serve as both nucleic acid-dependent structural scaffolds as well as ESCRT-III assembly templates.

Significance statement

When cellular membranes are dissolved or breached, ESCRT is rapidly deployed to repair membranes to restore the integrity of intracellular compartments. Membrane sealing is ensured by ESCRT-III filaments assembled on the inner face of membrane; a mechanism termed inverse topology membrane scission. This mechanism, initiated by ESCRT-I and ALIX, is universally necessary for cytokinesis, wound repair, budding of enveloped viruses, and more. We show ESCRT-I and ALIX individually oligomerize into helical filaments that cluster newly discovered nucleic acid-binding interfaces and scaffold-in genomes within nascent virions and nuclear envelopes. These oligomers additionally appear to serve as ideal templates for ESCRT-III polymerization, as helical filaments of CHMP4B were found intertwined ESCRT-I or ALIX filaments in vivo . Similarly, corkscrew-like filaments of ALIX are also interwoven with ESCRT-I, supporting a model of inverse topology membrane scission that is synergistically reinforced by inward double filament scaffolding.

Treating cancer through modulating exosomal protein loading and function: The prospects of natural products and traditional Chinese medicine

Exosomes, small yet vital extracellular vesicles, play an integral role in intercellular communication. They transport critical components, such as proteins, lipid bilayers, DNA, RNA, and glycans, to target cells. These vesicles are crucial in modulating the extracellular matrix and orchestrating signal transduction processes. In oncology, exosomes are pivotal in tumor growth, metastasis, drug resistance, and immune modulation within the tumor microenvironment. Exosomal proteins, noted for their stability and specificity, have garnered widespread attention. This review delves into the mechanisms of exosomal protein loading and their impact on tumor development, with a focus on the regulatory effects of natural products and traditional Chinese medicine on exosomal protein loading and function. These insights not only offer new strategies and methodologies for cancer treatment but also provide scientific bases and directions for future clinical applications.