Calpains orchestrate secretion of annexin-containing microvesicles during membrane repair

Microvesicles (MVs) are membrane-enclosed, plasma membrane-derived particles released by cells from all branches of life. MVs have utility as disease biomarkers and may participate in intercellular communication; however, physiological processes that induce their secretion are not known. Here, we isolate and characterize annexin-containing MVs and show that these vesicles are secreted in response to the calcium influx caused by membrane damage. The annexins in these vesicles are cleaved by calpains. After plasma membrane injury, cytoplasmic calcium-bound annexins are rapidly recruited to the plasma membrane and form a scab-like structure at the lesion. In a second phase, recruited annexins are cleaved by calpains-1/2, disabling membrane scabbing. Cleavage promotes annexin secretion within MVs. Our data support a new model of plasma membrane repair, where calpains relax annexin-membrane aggregates in the lesion repair scab, allowing secretion of damaged membrane and annexins as MVs. We anticipate that cells experiencing plasma membrane damage, including muscle and metastatic cancer cells, secrete these MVs at elevated levels.

Advances in Exosome Research: Multifaceted Roles in Myeloid Leukemia Progression and Therapy

Recent advancements in exosome research have revealed their crucial role in myeloid leukemia, encompassing chronic myeloid leukemia (CML) and acute myeloid leukemia (AML). Exosomes, small extracellular vesicles released by various cells, play a significant role in intercellular communication and impact key cellular processes such as growth, proliferation, angiogenesis, survival, and apoptosis. In leukemia, exosomes contribute to disease progression and therapeutic resistance by facilitating immune evasion, enhancing tumor cell proliferation, and promoting angiogenesis. For instance, exosomes derived from CML cells can transfer drug resistance to sensitive cells, and some exosomes derived from AML patients contain cytokines like TGF-β1 that inhibit immune cell activity. Exosomes also influence tumor organotropism by interacting with extracellular matrix molecules and modifying the tumor microenvironment. Despite their high potential, clinical applications of exosomes are limited. Their natural nanoparticle properties-such as adaptability, biodegradability, low toxicity, and the ability to cross biological barriers-make them promising candidates for targeted drug delivery and personalized medicine. Further research is necessary to scale up exosome production and harness their full therapeutic potential. By integrating advancements in exosome biology with innovative therapeutic strategies, there is significant potential for improved management and treatment of leukemia.

Cry11Aa toxin of Bacillus thuringiensis interactions with intracellular organelles in insect gut implicating actin depolymerization, massive endocytosis, and vesicle secretion

Proteins with insecticidal activity from Bacillus thuringiensis are key factors in the process of bacterial pathogenesis. We examined the response of mosquito-larval midgut cells to Cry11Aa toxin. After Cry11Aa binding to specific membrane receptors, located in the brush border microvilli, pore formation activity of the toxin induced actin depolymerization and extensive endocytosis, followed by the secretion of large membrane vesicles into the lumen. These vesicles are segmented by endoplasmic reticulum membranes and actin, and contained damaged organelles (endosomes, lysosomes, mitochondria) but lacked DNA. The Cry11Aa toxin was also found in these vesicles, suggesting that vesicle secretion may be participating in a detoxification mechanism. Transmission electron microscopy confirmed the presence of these vesicles in the midgut lumen. Finally, Cry11Aa also invaded the cytoplasm of some midgut cells. Comparison with the non-toxic Cry11E97A mutant, defective in oligomerization and membrane insertion, confirmed the role of pore formation activity of Cry11Aa for triggering these processes. Here, we provide high-resolution images by using a novel image analysis strategy named Mean Shift Super Resolution (MSSR) microscopy, showing the cellular responses to this pore forming toxin, revealing conserved mechanisms across organisms and expanding our understanding of host interactions of this insecticidal protein during its mechanism of action.

Autophagy-independent role of ATG9A vesicles as carriers for galectin-9 secretion

Galectins play vital roles in cellular processes such as adhesion, communication, and survival, yet the mechanisms underlying their unconventional secretion remain poorly understood. This study identifies ATG9A, a core autophagy protein, as a key regulator of galectin-9 secretion via a mechanism independent of classical autophagy, secretory autophagy, or the LC3-dependent extracellular vesicle loading and secretion pathway. ATG9A vesicles function as specialized carriers, with the N-terminus of ATG9A and both carbohydrate recognition domains of galectin-9 being critical for the process. TMED10 mediates the incorporation of galectin-9 into ATG9A vesicles, which then fuse with the plasma membrane via the STX13-SNAP23-VAMP3 SNARE complex. Furthermore, ATG9A regulates the secretion of other proteins, including galectin-4, galectin-8, and annexin A6, but not IL-1β, galectin-3, or FGF2. This mechanism is potentially conserved across other cell types, including monocytic cells, which underscores its broader significance in unconventional protein secretion.

Proteostasis and lysosomal repair deficits in transdifferentiated neurons of Alzheimer's disease

Ageing is the most prominent risk factor for Alzheimer's disease (AD). However, the cellular mechanisms linking neuronal proteostasis decline to the characteristic aberrant protein deposits in the brains of patients with AD remain elusive. Here we develop transdifferentiated neurons (tNeurons) from human dermal fibroblasts as a neuronal model that retains ageing hallmarks and exhibits AD-linked vulnerabilities. Remarkably, AD tNeurons accumulate proteotoxic deposits, including phospho-tau and amyloid β, resembling those in APP mouse brains and the brains of patients with AD. Quantitative tNeuron proteomics identify ageing- and AD-linked deficits in proteostasis and organelle homeostasis, most notably in endosome-lysosomal components. Lysosomal deficits in aged tNeurons, including constitutive lysosomal damage and ESCRT-mediated lysosomal repair defects, are exacerbated in AD tNeurons and linked to inflammatory cytokine secretion and cell death. Providing support for the centrality of lysosomal deficits in AD, compounds ameliorating lysosomal function reduce amyloid β deposits and cytokine secretion. Thus, the tNeuron model system reveals impaired lysosomal homeostasis as an early event of ageing and AD.

Organelle homeostasis requires ESCRTs

The endosomal sorting complexes required for transport (ESCRT) catalyze membrane shape transformations throughout the cell. Canonical functions of the ESCRTs include endosomal multivesicular body biogenesis, enveloped virus budding, and abscission of daughter cell plasma membranes. The ESCRT machinery is also required for membranous organelle homeostasis generally, including by facilitating lipid transport at membrane contact sites, repairing membrane damage, driving lysosomal catabolism, and maintaining nuclear envelope integrity, among other roles. Here, we review a subset of recent discoveries and highlight opportunities to better understand how ESCRT activities support cell health.

Atrial cardiomyocyte-restricted cleavage of gasdermin D promotes atrial arrhythmogenesis

BACKGROUND AND AIMS

Enhanced inflammatory signalling causally contributes to atrial fibrillation (AF) development. Gasdermin D (GSDMD) is an important downstream effector of several inflammasome pathways. However, the role of GSDMD, particularly the cleaved N-terminal (NT)-GSDMD, in non-immune cells remains elusive. This study aimed to elucidate the function of NT-GSDMD in atrial cardiomyocytes (ACMs) and determine its contribution to atrial arrhythmogenesis.

METHODS

Human atrial appendages were used to assess the protein levels and localization. A modified adeno-associated virus 9 was employed to establish ACM-restricted overexpression of NT-GSDMD in mice.

RESULTS

The cleavage of GSDMD was enhanced in ACMs of AF patients. Atrial cardiomyocyte-restricted overexpression of NT-GSDMD in mice increased susceptibility to pacing-induced AF. The NT-GSDMD pore formation facilitated interleukin-1β secretion from ACMs, promoting macrophage infiltration, while up-regulating 'endosomal sorting complexes required for transport'-mediated membrane-repair mechanisms, which prevented inflammatory cell death (pyroptosis) in ACMs. Up-regulated NT-GSDMD directly targeted mitochondria, increasing mitochondrial reactive oxygen species (ROS) generation, which triggered proarrhythmic calcium-release events. The NT-GSDMD-induced arrhythmogenesis was mitigated by the mitochondrial-specific antioxidant MitoTEMPO. A mutant NT-GSDMD lacking pore-formation capability failed to cause mitochondrial dysfunction or induce atrial arrhythmia. Genetic ablation of Gsdmd prevented spontaneous AF development in a mouse model.

CONCLUSIONS

These findings establish a unique pyroptosis-independent role of NT-GSDMD in ACMs and arrhythmogenesis, which involves ROS-driven mitochondrial dysfunction. Mitochondrial-targeted therapy, either by reducing ROS production or inhibition of GSDMD, prevents AF inducibility, positioning GSDMD as a novel therapeutic target for AF prevention.

Mechanistic insights into gasdermin-mediated pyroptosis

Pyroptosis, a novel mode of inflammatory cell death, is executed by membrane pore-forming gasdermin (GSDM) family members in response to extracellular or intracellular injury cues and is characterized by a ballooning cell morphology, plasma membrane rupture and the release of inflammatory mediators such as interleukin-1β (IL-1β), IL-18 and high mobility group protein B1 (HMGB1). It is a key effector mechanism for host immune defence and surveillance against invading pathogens and aberrant cancerous cells, and contributes to the onset and pathogenesis of inflammatory and autoimmune diseases. Manipulating the pore-forming activity of GSDMs and pyroptosis could lead to novel therapeutic strategies. In this Review, we discuss the current knowledge regarding how GSDM-mediated pyroptosis is initiated, executed and regulated, its roles in physiological and pathological processes, and the crosstalk between different modes of programmed cell death. We also highlight the development of drugs that target pyroptotic pathways for disease treatment.

Versatility of gasdermin D beyond pyroptosis

Gasdermin D (GSDMD) has garnered significant attention primarily for the pore-forming role of its p30 N-terminal fragment (NT-p30) generated during pyroptosis, a proinflammatory form of cell death. However, emerging evidence suggests that the formation of GSDMD-NT pores is reversible, and the activation of GSDMD does not necessarily lead to pyroptosis. Instead, this process may take part either in other forms of cell death, or in various state changes of living cells, including (i) inflammation regulation, (ii) endolysosomal pathway rewiring, (iii) granule exocytosis, (iv) type II immunity, (v) food tolerance maintenance, and (vi) temporary permeability alteration. This review explores the latest insights into the involvement of GSDMD in cell death and homeostasis maintenance, aiming to underscore the pleiotropic nature of GSDMD.

The spectrum of lysosomal stress and damage responses: from mechanosensing to inflammation

Cells and tissues turn over their aged and damaged components in order to adapt to a changing environment and maintain homeostasis. These functions rely on lysosomes, dynamic and heterogeneous organelles that play essential roles in nutrient redistribution, metabolism, signaling, gene regulation, plasma membrane repair, and immunity. Because of metabolic fluctuations and pathogenic threats, lysosomes must adapt in the short and long term to maintain functionality. In response to such challenges, lysosomes deploy a variety of mechanisms that prevent the breaching of their membrane and escape of their contents, including pathogen-associated molecules and hydrolases. While transient permeabilization of the lysosomal membrane can have acute beneficial effects, supporting inflammation and antigen cross-presentation, sustained or repeated lysosomal perforations have adverse metabolic and transcriptional consequences and can lead to cell death. This review outlines factors contributing to lysosomal stress and damage perception, as well as remedial processes aimed at addressing lysosomal disruptions. We conclude that lysosomal stress plays widespread roles in human physiology and pathology, the understanding and manipulation of which can open the door to novel therapeutic strategies.

STING-induced noncanonical autophagy regulates endolysosomal homeostasis

The cGAS-STING pathway mediates innate immune responses to cytosolic DNA. In addition to its well-established role in inducing inflammatory cytokines, activation of the cGAS-STING pathway also induces noncanonical autophagy, a process involving the conjugation of the ATG8 family of ubiquitin-like proteins to membranes of the endolysosomal system. The mechanisms and functions of STING-induced autophagy remain poorly understood. In this study, we demonstrated that STING activation induced formation of pH-elevated Golgi-derived vesicles that led to ATG16L1 and V-ATPase-dependent noncanonical autophagy. We showed that STING-induced noncanonical autophagy resulted in activation of the MiT/TFE family of transcription factors (TFEB, TFE3, and MITF), which regulate lysosome biogenesis. We found that lipidation of the ATG8 proteins, particularly GABARAPs, inhibited phosphorylation of MiT/TFE transcription factors by mTORC1. The lipidated GABARAPs bound to the Folliculin-interacting proteins (FNIPs), thereby sequestering the FNIP-folliculin protein complexes from activating mTORC1, resulting in dephosphorylation and nuclear translocation of MiT/TFE transcription factors. Furthermore, we found that STING-induced autophagy activated Leucine-rich repeat kinase 2 (LRRK2), a protein implicated in Parkinson's disease, through GABARAPs lipidation. We further showed that STING-induced autophagy induced ALIX-mediated ESCRT machinery recruitment to mitigate endolysosomal perturbation. These results reveal the multifaceted functions of STING-induced noncanonical autophagy in regulating endolysosomal homeostasis.

Genomic Insight into Primary Adaptation of Mycobacterium tuberculosis to Aroylhydrazones and Nitrofuroylamides In Vitro

Background/Objectives: New anti-tuberculosis compounds are needed to treat patients infected with multi- or extensively drug-resistant Mycobacterium tuberculosis strains. Studies based on spontaneous in vitro mutagenesis can provide insights into the possible modes of action and resistance mechanisms of such new compounds. We evaluated the primary response of M. tuberculosis in vitro to the action of new aroylhydrazones and nitrofuroylamides. Methods: The reference strain H37Rv was cultured on solid media with compounds at increased concentrations relative to MIC. Resistant clones were investigated using whole-genome sequencing and bioinformatics tools to assess the role and potential impact of identified mutations. Results: Some of the mutations are significant (based on in silico analysis), located in essential genes, and therefore of particular interest. Frameshift mutations were observed in (i) Rv2702/ppgK, which is associated with starvation-induced drug tolerance and persistence in mice, and (ii) Rv3696c/glpK, which has been described as a switch on/off mutation associated with drug tolerance. Nonsynonymous substitutions were found in Rv0506/mmpS2, which belongs to the Mmp protein family involved in transport and drug efflux, and in infB, encoding the translation initiation factor IF-2. Conclusions: The primary adaptation of M. tuberculosis to the selective pressure of the tested compounds is complex and multifaceted. It involves multiple unrelated genes and pathways linked to non-specific drug tolerance, efflux systems, or mechanisms counteracting oxidative stress.

Asgard archaea reveal the conserved principles of ESCRT-III membrane remodeling

ESCRT-III proteins assemble into composite polymers that undergo stepwise changes in composition and structure to deform membranes across the tree of life. Here, using a phylogenetic analysis, we demonstrate that the two endosomal sorting complex required for transport III (ESCRT-III) proteins present in eukaryote's closest Asgard archaeal relatives are evolutionarily related to the B- and A-type eukaryotic paralogs that initiate and execute membrane remodeling, respectively. We show that Asgard ESCRT-IIIB assembles into parallel arrays on planar membranes to initiate membrane deformation, from where it recruits ESCRT-IIIA to generate composite polymers. Last, we show that Asgard ESCRT-IIIA is able to remodel membranes into tubes as a likely prelude to scission. Together, these data reveal a set of conserved principles governing ESCRT-III-dependent membrane remodeling that first emerged in a two-component ESCRT-III system in archaea.

VPS18 contributes to phagosome membrane integrity in Mycobacterium tuberculosis-infected macrophages

Mycobacterium tuberculosis (Mtb) has evolved to be exquisitely adapted to survive within host macrophages. The capacity to damage the phagosomal membrane has emerged as central to Mtb virulence. While Mtb factors driving membrane damage have been described, host factors that maintain phagosomal integrity or repair Mtb-induced damage to contain the pathogen remain largely unknown. We used a genome-wide CRISPR screen to identify host factors required to repair Mtb-damaged phagosomal membranes. Vacuolar protein sorting-associated protein 18 (VPS18), a member of the HOPS and CORVET trafficking complexes, was among the top hits. VPS18 colocalized with Mtb in macrophages beginning shortly after infection, and VPS18-knockout macrophages demonstrated increased damage of Mtb-containing phagosomes without impaired autophagy. Mtb grew more robustly in VPS18-knockout cells, and the first-line antituberculosis antibiotic pyrazinamide was less effective. Our results identify VPS18 as required for phagosomal membrane integrity in Mtb-infected cells and suggest that modulating phagosome integrity may hold promise for improving the efficacy of antibiotic treatment for TB.

Vps4a Mediates a Unified Membrane Repair Machinery to Attenuate Ischemia/Reperfusion Injury

BACKGROUND

Cardiac ischemia/reperfusion disrupts plasma membrane integrity and induces various types of programmed cell death. The ESCRT (endosomal sorting complex required for transport) proteins, particularly AAA-ATPase Vps4a (vacuolar protein sorting 4a), play an essential role in the surveillance of membrane integrity. However, the role of ESCRT proteins in the context of cardiac injury remains unclear.

METHODS

We simultaneously visualized the formation of membrane blebs and the subcellular translocation of Vps4a during a variety of cell death programs in primary cardiomyocytes. Vps4a cardiomyocyte-specific knockout and overexpression mice were generated and characterized. In vivo and ex vivo surgeries were performed to determine the effects of altered Vps4a expression levels on plasma membrane repair and cell survival. Given the role of Ripk3 (receptor-interacting kinase 3)-mediated pore formation in regulating cell membrane integrity, hearts from Ripk3 and Vps4a double-knockout mice were examined. The sequential recruitment of upstream ESCRT components that promote the translocation of Vps4a to injured sites was also assessed using genetic gain- and loss-of-function approaches. Finally, we overexpressed a mutated form of Vps4a with defective ATPase activity and investigated its function during cardiomyocyte membrane repair.

RESULTS

Ischemia/reperfusion stimulation or forced induction of apoptosis, necroptosis, and pyroptosis in primary cardiomyocytes leads to membrane blebbing and the exposure of phosphatidylserine to the extracellular space. In response to injury, Vps4a promptly translocates to injured sites to reseal damaged membranes. Vps4a gain- and loss-of-function in the postnatal stage minimally affects cardiac structure formation and function. However, in the context of ischemia/reperfusion stimulation, overexpression of Vps4a protects cardiomyocytes against injury, whereas Vps4a-deficient hearts are more susceptible to cell damage. Additionally, Ripk3 deletion abrogates the detrimental effects of Vps4a deficiency during ischemia/reperfusion injury, and the Ca2+-Alix-Ist1 axis plays an essential role in recruiting Vps4a to the injured site. Mechanistically, Vps4a promotes the shedding of plasma membrane blebs to restrict permeability to the extracellular environment, and the surveillance of membrane integrity requires the ATPase activity of Vps4a.

CONCLUSIONS

These results demonstrate that Vps4a-mediated plasma membrane repair is an intrinsic cell protection machinery that antagonizes cardiac ischemia/reperfusion injury, and our findings may contribute to the development of therapeutic strategies towards attenuating cardiac injury.

Proteostasis and lysosomal repair deficits in transdifferentiated neurons of Alzheimer's disease

Aging is the most prominent risk factor for Alzheimer's disease (AD). However, the cellular mechanisms linking neuronal proteostasis decline to the characteristic aberrant protein deposits in AD brains remain elusive. Here, we develop transdifferentiated neurons (tNeurons) from human dermal fibroblasts as a neuronal model that retains aging hallmarks and exhibits AD-linked vulnerabilities. Remarkably, AD tNeurons accumulate proteotoxic deposits, including phospho-Tau and Aβ, resembling those in AD patient and APP mouse brains. Quantitative tNeuron proteomics identify aging and AD-linked deficits in proteostasis and organelle homeostasis, most notably in endosome-lysosomal components. Lysosomal deficits in aged tNeurons, including constitutive lysosomal damage and ESCRT-mediated lysosomal repair defects, are exacerbated in AD tNeurons and linked to inflammatory cytokine secretion and cell death. Supporting lysosomal deficits' centrality in AD, compounds ameliorating lysosomal function reduce Aβ deposits and cytokine secretion. Thus, the tNeuron model system reveals impaired lysosomal homeostasis as an early event of aging and AD.

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.

Extracellular vesicles as emerging players in glaucoma: Mechanisms, biomarkers, and therapeutic targets

In recent years, extracellular vesicles (EVs) have attracted significant scientific interest due to their widespread distribution, their potential as disease biomarkers, and their promising applications in therapy. Encapsulated by lipid bilayers these nanovesicles include small extracellular vesicles (sEV) (30-150 nm), microvesicles (100-1000 nm), and apoptotic bodies (100-5000 nm) and are essential for cellular communication, immune responses, biomolecular transport, and physiological regulation. As they reflect the condition and functionality of their originating cells, EVs play critical roles in numerous physiological processes and diseases. Therefore, EVs offer valuable opportunities for uncovering disease mechanisms, enhancing drug delivery systems, and identifying novel biomarkers. In the context of glaucoma, a leading cause of irreversible blindness, the specific roles of EVs are still largely unexplored. This review examines the emerging role of EVs in the pathogenesis of glaucoma, with a focus on their potential as diagnostic biomarkers and therapeutic agents. Through a thorough analysis of current literature, we summarize key advancements in EV research and identify areas where further investigation is needed to fully understand their function in glaucoma.

Inflammasome-mediated pyroptosis in defense against pathogenic bacteria

Macrophages, neutrophils, and epithelial cells are pivotal components of the host's immune response against bacterial infections. These cells employ inflammasomes to detect various microbial stimuli during infection, triggering an inflammatory response aimed at eradicating the pathogens. Among these inflammatory responses, pyroptosis, a lytic form of cell death, plays a crucial role in eliminating replicating bacteria and recruiting immune cells to combat the invading pathogen. The immunological function of pyroptosis varies across macrophages, neutrophils, and epithelial cells, aligning with their specific roles within the innate immune system. This review centers on elucidating the role of pyroptosis in resisting gram-negative bacterial infections, with a particular focus on the mechanisms at play in macrophages, neutrophils, and intestinal epithelial cells. Additionally, we underscore the cell type-specific roles of pyroptosis in vivo in these contexts during defense.

Epsilon Toxin from Clostridium perfringens Induces the Generation of Extracellular Vesicles in HeLa Cells Overexpressing Myelin and Lymphocyte Protein

Epsilon toxin (ETX) from Clostridium perfringens is a pore-forming toxin (PFT) that crosses the blood-brain barrier and binds to myelin structures. In in vitro assays, ETX causes oligodendrocyte impairment, subsequently leading to demyelination. In fact, ETX has been associated with triggering multiple sclerosis. Myelin and lymphocyte protein (MAL) is widely considered to be the receptor for ETX as its presence is crucial for the effects of ETX on the plasma membrane of host cells that involve pore formation, resulting in cell death. To overcome the pores formed by PFTs, some host cells produce extracellular vesicles (EVs) to reduce the amount of pores inserted into the plasma membrane. The formation of EVs has not been studied for ETX in host cells. Here, we generated a highly sensitive clone from HeLa cells overexpressing the MAL-GFP protein in the plasma membrane. We observed that ETX induces the formation of EVs. Moreover, the MAL protein and ETX oligomers are found in these EVs, which are a very useful tool to decipher and study the mode of action of ETX and characterize the mechanisms involved in the binding of ETX to its receptor.

Unanticipated specificity in effector-triggered immunity

Effector-triggered immunity (ETI) enables hosts to react to pathogens by monitoring few key cellular processes. ETI responses are assumed to be similar toward related pathogen effectors. However, recent evidence from the invertebrate model Caenorhabditis elegans and pore-forming toxins indicates a much more complex and specific ETI than previously anticipated.

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.

Membrane Tension Regulation is Required for Wound Repair

Disruptions of the eukaryotic plasma membrane due to chemical and mechanical challenges are frequent and detrimental and thus need to be repaired to maintain proper cell function and avoid cell death. However, the cellular mechanisms involved in wound resealing and restoration of homeostasis are diverse and contended. Here, it is shown that clathrin-mediated endocytosis is induced at later stages of plasma membrane wound repair following the actual resealing of the wound. This compensatory endocytosis occurs near the wound, predominantly at sites of previous early endosome exocytosis which is required in the initial stage of membrane resealing, suggesting a spatio-temporal co-ordination of exo- and endocytosis during wound repair. Using cytoskeletal alterations and modulations of membrane tension and membrane area, membrane tension is identified as a major regulator of the wounding-associated exo- and endocytic events that mediate efficient wound repair. Thus, membrane tension changes are a universal trigger for plasma membrane wound repair modulating the exocytosis of early endosomes required for resealing and subsequent clathrin-mediated endocytosis acting at later stages to restore cell homeostasis and function.

The invasion pore induced by Toxoplasma gondii

Obligate intracellular parasites invade host cells to survive. Following host cell contact, the apicomplexan Toxoplasma gondii injects proteins required for invasion into the host cell. Here, electrophysiological recordings of host cells acquired at sub-200 ms resolution allowed detection and analysis of a transient increase in host membrane conductance following exposure to Toxoplasma gondii. Transients always preceded invasion but parasites depleted of the moving junction protein RON2 generated transients without invading, ruling out a direct structural role for RON2 in generating the conductance pathway or restricting the diffusion of its components. Time-series analysis developed for transients and applied to the entire transient dataset (910,000 data points) revealed multiple quantal conductance changes in the parasite-induced transient, consistent with a rapid insertion, then slower removal, blocking, or inactivation of pore-like conductance steps. Quantal steps for RH had a principal mode with Gaussian mean of 0.26 nS, similar in step size to the apicomplexan protein translocon EXP2. Without RON2 the quantal mean was significantly different (0.19 nS). Because no invasion occurs without poration, the term 'invasion pore' is proposed.

Ca2+-dependent vesicular and non-vesicular lipid transfer controls hypoosmotic plasma membrane expansion

Robust coordination of surface and volume changes is critical for cell integrity. Few studies have elucidated the plasma membrane (PM) remodeling events during cell surface and volume alteration, especially regarding PM sensing and its subsequent rearrangements. Here, using fission yeast protoplasts, we reveal a Ca2+-dependent mechanism for membrane addition that ensures PM integrity and allows its expansion during acute hypoosmotic cell swelling. We show that MscS-like mechanosensitive channels activated by PM tension control extracellular Ca2+ influx, which triggers direct lipid transfer at endoplasmic reticulum (ER)-PM contact sites by conserved extended-synaptotagmins and accelerates exocytosis, enabling PM expansion necessary for osmotic equilibrium. Defects in any of these key events result in rapid protoplast rupture upon severe hypotonic shock. Our numerical simulations of hypoosmotic expansion further propose a cellular strategy that combines instantaneous non-vesicular lipid transfer with bulk exocytic membrane delivery to maintain PM integrity for dramatic cell surface/volume adaptation.

Cell death: Revisiting the roads to ruin

A paradigm shift in the study of cell death is currently occurring: whereas previously we had always considered that there were "points of no return" in any cell death pathway, we now realize that in many types of active, regulated cell death, this is not the case. We are also learning that cells that "almost die," but nevertheless survive, can transiently take on an altered state, with potential implications for understanding cancer therapies and relapse. In this perspective, we parse the many forms of cell death by analogy to suicide, sabotage, and murder, and consider how cells that might be "instructed" to engage a cell death pathway might nevertheless survive.

Quantitative assessment of the nanoanatomy of the contractile vacuole complex in Trypanosoma cruzi

Trypanosoma cruzi uses various mechanisms to cope with osmotic fluctuations during infection, including the remodeling of organelles such as the contractile vacuole complex (CVC). Little is known about the morphological changes of the CVC during pulsation cycles occurring upon osmotic stress. Here, we investigated the structure-function relationship between the CVC and the flagellar pocket domain where fluid discharge takes place-the adhesion plaque-during the CVC pulsation cycle. Using TcrPDEC2 and TcVps34 overexpressing mutants, known to have low and high efficiency for osmotic responses, we described a structural phenotype for the CVC that matches their corresponding physiological responses. Quantitative tomography provided data on the volume of the CVC and spongiome connections. Changes in the adhesion plaque during the pulsation cycle were also quantified and a dense filamentous network was observed. Together, the results suggest that the adhesion plaque mediates fluid discharge from the central vacuole, revealing new aspects of the osmoregulatory system in T. cruzi.

CORM‑2 reduces cisplatin accumulation in the mouse inner ear and protects against cisplatin-induced ototoxicity

INTRODUCTION

Cisplatin is a life-saving anticancer compound used to treat multiple solid malignant tumors, while it causes permanent hearing loss. There is no known cure, and the FDA has not approved any preventative treatment for cisplatin-based ototoxicity.

OBJECTIVES

This study investigated whether the carbon monoxide (CO)-releasing tricarbonyldichlororuthenium (II) dimer, CORM-2, reverses cisplatin-induced hearing impairment and reduces cisplatin accumulation in the mouse inner ear.

METHODS

Male 6-week-old BALB/c mice were randomly assigned to one of the following groups: control (saline-treated, i.p.), CORM-2 only (30 mg/kg, i.p., four doses), cisplatin only (20 mg/kg, i.p., one dose), and CORM-2 + cisplatin, to determine whether cisplatin-based hearing impairment was alleviated by CORM-2 treatment.

RESULTS

Our results revealed CORM-2 significantly attenuated cisplatin-induced hearing loss in young adult mice. CORM-2 co-treatment significantly decreased platinum accumulation in the inner ear and activated the plasma membrane repair system of the stria vascularis. Moreover, CORM-2 co-treatment significantly decreased cisplatin-induced inflammation, apoptosis, and cochlear necroptosis. Because the stria vascularis is the likely cochlear entry point of cisplatin, we next focused on the microvasculature. Cisplatin induced increased extravasation of a chromatic tracer (fluorescein isothiocyanate [FITC]-dextran, MW 75 kDa) around the cochlear microvessels at 4 days post-treatment; this extravasation was completely inhibited by CORM-2 co-therapy. CORM-2 co-treatment effectively maintained the integrity of stria vascularis components including endothelial cells, pericytes, and perivascular-resident macrophage-type melanocytes.

CONCLUSION

CORM-2 co-therapy substantially protects against cisplatin-induced ototoxicity by reducing platinum accumulation and toxic cellular stress responses. These data indicate that CORM-2 co-treatment may be translated into clinical strategy to reduce cisplatin-induced hearing loss.

Pyroptosis: Induction and inhibition strategies for immunotherapy of diseases

Cell death is a central process for organismal health. Pyroptosis, namely pyroptotic cell death, is recognized as a critical type that disrupts membrane and triggers pro-inflammatory cytokine secretion via gasdermins, providing a robust form of cytolysis. Meanwhile, along with the thorough research, a great deal of evidence has demonstrated the dual effects of pyroptosis in host defense and inflammatory diseases. More importantly, the recent identification of abundant gasdermin-like proteins in bacteria and fungi suggests an ancient origin of pyroptosis-based regulated cell death in the life evolution. In this review, we bring a general overview of pyroptosis pathways focusing on gasdermin structural biology, regulatory mechanisms, and recent progress in induction and inhibition strategies for disease treatment. We look forward to providing an insightful perspective for readers to comprehend the frame and challenges of the pyroptosis field, and to accelerating its clinical application.

Tissue-specific knockout in the Drosophila neuromuscular system reveals ESCRT's role in formation of synapse-derived extracellular vesicles

Tissue-specific gene knockout by CRISPR/Cas9 is a powerful approach for characterizing gene functions during development. However, this approach has not been successfully applied to most Drosophila tissues, including the Drosophila neuromuscular junction (NMJ). To expand tissue-specific CRISPR to this powerful model system, here we present a CRISPR-mediated tissue-restricted mutagenesis (CRISPR-TRiM) toolkit for knocking out genes in motoneurons, muscles, and glial cells. We validated the efficacy of CRISPR-TRiM by knocking out multiple genes in each tissue, demonstrated its orthogonal use with the Gal4/UAS binary expression system, and showed simultaneous knockout of multiple redundant genes. We used CRISPR-TRiM to discover an essential role for SNARE components in NMJ maintenance. Furthermore, we demonstrate that the canonical ESCRT pathway suppresses NMJ bouton growth by downregulating retrograde Gbb signaling. Lastly, we found that axon termini of motoneurons rely on ESCRT-mediated intra-axonal membrane trafficking to release extracellular vesicles at the NMJ. Thus, we have successfully developed an NMJ CRISPR mutagenesis approach which we used to reveal genes important for NMJ structural plasticity.

TMEM16F Expressed in Kupffer Cells Regulates Liver Inflammation and Metabolism to Protect Against Listeria Monocytogenes

Infection by bacteria leads to tissue damage and inflammation, which need to be tightly controlled by host mechanisms to avoid deleterious consequences. It is previously reported that TMEM16F, a calcium-activated lipid scramblase expressed in various immune cell types including T cells and neutrophils, is critical for the control of infection by bacterium Listeria monocytogenes (Lm) in vivo. This function correlated with the capacity of TMEM16F to repair the plasma membrane (PM) damage induced in T cells in vitro, by the Lm toxin listeriolysin O (LLO). However, whether the protective effect of TMEM16F on Lm infection in vivo is mediated by an impact in T cells, or in other cell types, is not determined. Herein, the immune cell types and mechanisms implicated in the protective effect of TMEM16F against Lm in vivo are elucidated. Cellular protective effects of TMEM16F correlated with its capacity of lipid scrambling and augment PM fluidity. Using cell type-specific TMEM16F-deficient mice, the indication is obtained that TMEM16F expressed in liver Kupffer cells (KCs), but not in T cells or B cells, is key for protection against Listeria in vivo. In the absence of TMEM16F, Listeria induced PM rupture and fragmentation of KCs in vivo. KC death associated with greater liver damage, inflammatory changes, and dysregulated liver metabolism. Overall, the results uncovered that TMEM16F expressed in Kupffer cells is crucial to protect the host against Listeria infection. This influence is associated with the capacity of Kupffer cell-expressed TMEM16F to prevent excessive inflammation and abnormal liver metabolism.

Ferroptosis: Regulatory mechanisms and potential targets for bone metabolism: A review

Bone homeostasis is a homeostasis process constructed by osteoblast bone formation and osteoclast bone resorption. Bone homeostasis imbalance and dysfunction are the basis for the development of various orthopedic diseases such as osteoporosis, osteoarthritis, and steroid-induced avascular necrosis of femoral head. Previous studies have demonstrated that ferroptosis can induce lipid peroxidation through the generation of reactive oxygen species, activate a number of signaling pathways, and participate in the regulation of osteoblast bone formation and osteoclast bone resorption, resulting in bone homeostasis imbalance, which is an important factor in the pathogenesis of many orthopedic diseases, but the mechanism of ferroptosis is still unknown. In recent years, it has been found that, in addition to iron metabolism and intracellular antioxidant system imbalance, organelle dysfunction is also a key factor affecting ferroptosis. This paper takes this as the starting point, reviews the latest literature reports at home and abroad, elaborates the pathogenesis and regulatory pathways of ferroptosis and the relationship between ferroptosis and various organelles, and summarizes the mechanism by which ferroptosis mediates bone homeostasis imbalance, with the aim of providing new directions for the research related to ferroptosis and new ideas for the prevention and treatment of bone and joint diseases.

HRS Facilitates Newcastle Disease Virus Replication in Tumor Cells by Promoting Viral Budding

Newcastle disease virus (NDV) is a highly pathogenic avian infectious disease agent and also a promising oncolytic virus with broad application prospects. The Endosomal Sorting Complex Required for Transport (ESCRT) machinery has been increasingly recognized for its crucial role in the life cycles of enveloped viruses, influencing processes such as viral entry, replication, and budding. In this study, we employed an RNA interference screening approach to identify key ESCRT components that regulate NDV replication in tumor cells. qPCR, immunofluorescence, and Western blot assays demonstrated that knockdown of HRS, CHMP4A, CHMP4B, and CHMP4C significantly impaired NDV replication in HeLa cells, with HRS exhibiting the most pronounced inhibitory effect. Additionally, HRS knockout significantly inhibited viral budding and suppressed NDV-induced cell death in HeLa cells. Notably, NDV infection was shown to significantly upregulate HRS gene and protein expression in a time-dependent manner. In conclusion, this study systematically identifies critical ESCRT components involved in NDV replication within tumor cells, with a particular focus on the role of HRS in promoting NDV's replication by promoting viral budding, offering new insights for the development of NDV-based oncolytic therapies.

Calpains Orchestrate Secretion of Annexin-containing Microvesicles during Membrane Repair

Microvesicles (MVs) are membrane-enclosed, plasma membrane-derived particles released by cells from all branches of life. MVs have utility as disease biomarkers and may participate in intercellular communication; however, physiological processes that induce their secretion are not known. Here, we isolate and characterize annexin-containing MVs and show that these vesicles are secreted in response to the calcium influx caused by membrane damage. The annexins in these vesicles are cleaved by calpains. After plasma membrane injury, cytoplasmic calcium-bound annexins are rapidly recruited to the plasma membrane and form a scab-like structure at the lesion. In a second phase, recruited annexins are cleaved by calpains-1/2, disabling membrane scabbing. Cleavage promotes annexin secretion within MVs. Our data supports a new model of plasma membrane repair, where calpains relax annexin-membrane aggregates in the lesion repair scab, allowing secretion of damaged membrane and annexins as MVs. We anticipate that cells experiencing plasma membrane damage, including muscle and metastatic cancer cells, secrete these MVs at elevated levels.

The V-ATPase complex component RNAseK is required for lysosomal hydrolase delivery and autophagosome degradation

Autophagy is a finely orchestrated process required for the lysosomal degradation of cytosolic components. The final degradation step is essential for clearing autophagic cargo and recycling macromolecules. Using a CRISPR/Cas9-based screen, we identify RNAseK, a highly conserved transmembrane protein, as a regulator of autophagosome degradation. Analyses of RNAseK knockout cells reveal that, while autophagosome maturation is intact, cargo degradation is severely disrupted. Importantly, lysosomal protease activity and acidification remain intact in the absence of RNAseK suggesting a specificity to autolysosome degradation. Analyses of lysosome fractions show reduced levels of a subset of hydrolases in the absence of RNAseK. Of these, the knockdown of PLD3 leads to a defect in autophagosome clearance. Furthermore, the lysosomal fraction of RNAseK-depleted cells exhibits an accumulation of the ESCRT-III complex component, VPS4a, which is required for the lysosomal targeting of PLD3. Altogether, here we identify a lysosomal hydrolase delivery pathway required for efficient autolysosome degradation.

The septin cytoskeleton is required for plasma membrane repair

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

Engineering Cells for Cancer Therapy

Cells, particularly living cells, serve as natural carriers of bioactive substances. Their inherent low immunogenicity and multifunctionality have garnered significant attention in the realm of disease treatment applications, specifically within the domains of cancer immunotherapy and regenerative tissue repair. Nevertheless, several prominent challenges impede their swift translation into clinical applications, including obstacles related to large-scale production feasibility and high utilization costs. To address these issues comprehensively, researchers have proposed the notion of bionic cells that are synthetically generated through chemical or biosynthetic means to emulate cellular functions and behaviors. However, artificial cell strategies encounter difficulties in fully replicating the intricate functionalities exhibited by living cells while also grappling with the complexities associated with design implementation for clinical translation purposes. The convergence of disciplines has facilitated the reform of living cells through a range of approaches, including chemical-, biological-, genetic-, and materials-based methods. These techniques can be employed to impart specific functions to cells or enhance the efficacy of therapy. For example, cells are engineered through gene transduction, surface modifications, endocytosis of drugs as delivery systems, and membrane fusion. The concept of engineered cells presents a promising avenue for enhancing control over living cells, thereby enhancing therapeutic efficacy while concurrently mitigating toxic side effects and ultimately facilitating the realization of precision medicine.In this Account, we present a comprehensive overview of our recent research advancements in the field of engineered cells. Our work involves the application of biological or chemical engineering techniques to manipulate endogenous cells for therapeutics or drug delivery purposes. For instance, to avoid the laborious process of isolating, modifying, and expanding engineered cells in vitro, we proposed the concept of in situ engineered cells. By applying a hydrogel loaded with nanoparticles carrying edited chimeric antigen receptor (CAR) plasmids within the postoperative cavity of glioma, we successfully targeted tumor-associated macrophages for gene editing, leading to effective tumor recurrence inhibition. Furthermore, leveraging platelet's ability to release microparticles upon activation at injury sites, we modified antiprogrammed death 1 (PD-1) antibodies on their surface to suppress postoperative tumor recurrence and provide immunotherapy for inoperable tumors. Similarly, by exploiting bacteria's active tropism toward sites of inflammation and hypoxia, we delivered protein drugs by engineered bacteria to induce cancer cell death through pyroptosis initiation and immunotherapy strategies. In the final section, we summarize our aforementioned research progress while providing an outlook on cancer therapy and the hurdles for clinical translation with potential solutions or future directions based on the concept of engineered cells.

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

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

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.

FSP1-mediated ferroptosis in cancer: from mechanisms to therapeutic applications

Ferroptosis is a new discovered regulated cell death triggered by the ferrous ion (Fe2+)-dependent accumulation of lipid peroxides associated with cancer and many other diseases. The mechanism of ferroptosis includes oxidation systems (such as enzymatic oxidation and free radical oxidation) and antioxidant systems (such as GSH/GPX4, CoQ10/FSP1, BH4/GCH1 and VKORC1L1/VK). Among them, ferroptosis suppressor protein 1 (FSP1), as a crucial regulatory factor in the antioxidant system, has shown a crucial role in ferroptosis. FSP1 has been well validated to ferroptosis in three ways, and a variety of intracellular factors and drug molecules can alleviate ferroptosis via FSP1, which has been demonstrated to alter the sensitivity and effectiveness of cancer therapies, including chemotherapy, radiotherapy, targeted therapy and immunotherapy. This review aims to provide important frameworks that, bring the regulation of FSP1 mediated ferroptosis into cancer therapies on the basis of existing studies.

An explanation of the role of pyroptosis playing in epilepsy

Epilepsy is a severe central nervous system disorder characterized by an imbalance between neuronal excitation and inhibition, resulting in heightened neuronal excitability, particularly within the hippocampus. About one-third of individuals with epilepsy experience difficult-to-manage seizures, known as refractory epilepsy. Epilepsy is closely linked to inflammatory immune response, with elevated levels of inflammatory mediators observed in individuals with this condition. This inflammation of the brain can lead to seizures of various types and is further exacerbated by the release of inflammatory factors, which heighten the excitability of peripheral neurons and worsen the progression of epilepsy. Pyroptosis is an inflammatory programmed cell death which has been shown to be involved in the pathological process of epilepsy. Inflammatory factors released during pyroptosis increase neuronal excitability and promote abnormal discharge in epilepsy, increasing susceptibility to epilepsy. This article provides an overview of the current knowledge on cell pyroptosis and its potential mechanisms, including both canonical and noncanonical pathways. Additionally, we discuss the potential mechanisms of pyroptosis occurrence in epilepsy and the potential therapeutic drugs targeting pyroptosis as a treatment strategy. In summary, this review highlights the promising potential of pyroptosis as a target for developing innovative therapies for epilepsy.

The multifunction Coxiella effector Vice stimulates macropinocytosis and interferes with the ESCRT machinery

Intracellular bacterial pathogens divert multiple cellular pathways to establish their niche and persist inside their host. Coxiella burnetii, the causative agent of Q fever, secretes bacterial effector proteins via its Type 4 secretion system to generate a Coxiella-containing vacuole (CCV). Manipulation of lipid and protein trafficking by these effectors is essential for bacterial replication and virulence. Here, we have characterized the lipid composition of CCVs and found that the effector Vice interacts with phosphoinositides and membranes enriched in phosphatidylserine and lysobisphosphatidic acid. Remarkably, eukaryotic cells ectopically expressing Vice present compartments that resemble early CCVs in both morphology and composition. We found that the biogenesis of these compartments relies on the double function of Vice. The effector protein initially localizes at the plasma membrane of eukaryotic cells where it triggers the internalization of large vacuoles by macropinocytosis. Then, Vice stabilizes these compartments by perturbing the ESCRT machinery. Collectively, our results reveal that Vice is an essential C. burnetii effector protein capable of hijacking two major cellular pathways to shape the bacterial replicative niche.

Phosphatidylserine regulates plasma membrane repair through tetraspanin-enriched macrodomains

The integrity of the plasma membrane is critical to cell function and survival. Cells have developed multiple mechanisms to repair damaged plasma membranes. A key process during plasma membrane repair is to limit the size of the damage, which is facilitated by the presence of tetraspanin-enriched rings surrounding damage sites. Here, we identify phosphatidylserine-enriched rings surrounding damaged sites of the plasma membrane, resembling tetraspanin-enriched rings. Importantly, the formation of both the phosphatidylserine- and tetraspanin-enriched rings requires phosphatidylserine and its transfer proteins ORP5 and ORP9. Interestingly, ORP9, but not ORP5, is recruited to the damage sites, suggesting cells acquire phosphatidylserine from multiple sources upon plasma membrane damage. We further demonstrate that ORP9 contributes to efficient plasma membrane repair. Our results thus unveil a role for phosphatidylserine and its transfer proteins in facilitating the formation of tetraspanin-enriched macrodomains and plasma membrane repair.

Adaptations of membrane trafficking in cancer and tumorigenesis

Membrane trafficking, a fundamental cellular process encompassing the transport of molecules to specific organelles, endocytosis at the plasma membrane and protein secretion, is crucial for cellular homeostasis and signalling. Cancer cells adapt membrane trafficking to enhance their survival and metabolism, and understanding these adaptations is vital for improving patient responses to therapy and identifying therapeutic targets. In this Review, we provide a concise overview of major membrane trafficking pathways and detail adaptations in these pathways, including COPII-dependent endoplasmic reticulum (ER)-to-Golgi vesicle trafficking, COPI-dependent retrograde Golgi-to-ER trafficking and endocytosis, that have been found in cancer. We explore how these adaptations confer growth advantages or resistance to cell death and conclude by discussing the potential for utilising this knowledge in developing new treatment strategies and overcoming drug resistance for cancer patients.

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.

Essential role of Alix in regulating cardiomyocyte exosome biogenesis under physiological and stress conditions

BACKGROUND

Exosomes released by cardiomyocytes are essential mediators of intercellular communications within the heart, and various exosomal proteins and miRNAs are associated with cardiovascular diseases. However, whether the endosomal sorting complex required for transport (ESCRT) and its key component Alix is required for exosome biogenesis within cardiomyocyte remains poorly understood.

METHODS

Super-resolution imaging was performed to investigate the subcellular location of Alix and multivesicular body (MVB) in primary cardiomyocytes. Cardiomyocyte-specific Alix-knockout mice were generated using AAV9/CRISPR/Cas9-mediated in vivo gene editing. A stable Alix-knockdown H9c2 cardiomyocyte line was constructed through lentiviral-mediated delivery of short hairpin RNA. In order to determine the role of Alix in controlling exosome biogenesis, exosomes from cardiomyocyte-specific Alix-knockout mice plasma and Alix-knockdown H9c2 culture medium were isolated and examined by western blot, NTA analysis and transmission electron microscopy. Biochemical and immunofluorescence analysis were performed to determine the role of ESCRT machinery in regulating MVB formation. Lastly, transverse aortic constriction (TAC)-induced cardiac pressure overload model was established to further explore the role of Alix-mediated exosome biogenesis under stress conditions.

RESULTS

A significant proportion of Alix localized to the MVB membrane within cardiomyocytes. Genetic deletion of Alix in murine heart resulted in a reduction of plasma exosome content without affecting cardiac structure or contractile function. Consistently, the downregulation of Alix in H9c2 cardiomyocyte line also suppressed the biogenesis of exosomes. We found the defective ESCRT machinery and suppressed MVB formation upon Alix depletion caused compromised exosome biogenesis. Remarkably, TAC-induced cardiac pressure overload led to increased Alix, MVB levels, and elevated plasma exosome content, which could be totally abolished by Alix deletion.

CONCLUSION

These results establish Alix as an essential and stress-sensitive regulator of cardiac exosome biogenesis and the findings may yield valuable therapeutic implications.

A chemical inhibitor of IST1-CHMP1B interaction impairs endosomal recycling and induces noncanonical LC3 lipidation

The endosomal sorting complex required for transport (ESCRT) machinery constitutes multisubunit protein complexes that play an essential role in membrane remodeling and trafficking. ESCRTs regulate a wide array of cellular processes, including cytokinetic abscission, cargo sorting into multivesicular bodies (MVBs), membrane repair, and autophagy. Given the versatile functionality of ESCRTs, and the intricate organizational structure of the ESCRT machinery, the targeted modulation of distinct ESCRT complexes is considerably challenging. This study presents a pseudonatural product targeting IST1-CHMP1B within the ESCRT-III complexes. The compound specifically disrupts the interaction between IST1 and CHMP1B, thereby inhibiting the formation of IST1-CHMP1B copolymers essential for normal-topology membrane scission events. While the compound has no impact on cytokinesis, MVB sorting, or biogenesis of extracellular vesicles, it rapidly inhibits transferrin receptor recycling in cells, resulting in the accumulation of transferrin in stalled sorting endosomes. Stalled endosomes become decorated by lipidated LC3, suggesting a link between noncanonical LC3 lipidation and inhibition of the IST1-CHMP1B complex.

Lipid Nanoparticle-Associated Inflammation is Triggered by Sensing of Endosomal Damage: Engineering Endosomal Escape Without Side Effects

Lipid nanoparticles (LNPs) have emerged as the dominant platform for RNA delivery, based on their success in the COVID-19 vaccines and late-stage clinical studies in other indications. However, we and others have shown that LNPs induce severe inflammation, and massively aggravate pre-existing inflammation. Here, using structure-function screening of lipids and analyses of signaling pathways, we elucidate the mechanisms of LNP-associated inflammation and demonstrate solutions. We show that LNPs' hallmark feature, endosomal escape, which is necessary for RNA expression, also directly triggers inflammation by causing endosomal membrane damage. Large, irreparable, endosomal holes are recognized by cytosolic proteins called galectins, which bind to sugars on the inner endosomal membrane and then regulate downstream inflammation. We find that inhibition of galectins abrogates LNP-associated inflammation, both in vitro and in vivo . We show that rapidly biodegradable ionizable lipids can preferentially create endosomal holes that are smaller in size and reparable by the endosomal sorting complex required for transport (ESCRT) pathway. Ionizable lipids producing such ESCRT-recruiting endosomal holes can produce high expression from cargo mRNA with minimal inflammation. Finally, we show that both routes to non-inflammatory LNPs, either galectin inhibition or ESCRT-recruiting ionizable lipids, are compatible with therapeutic mRNAs that ameliorate inflammation in disease models. LNPs without galectin inhibition or biodegradable ionizable lipids lead to severe exacerbation of inflammation in these models. In summary, endosomal escape induces endosomal membrane damage that can lead to inflammation. However, the inflammation can be controlled by inhibiting galectins (large hole detectors) or by using biodegradable lipids, which create smaller holes that are reparable by the ESCRT pathway. These strategies should lead to generally safer LNPs that can be used to treat inflammatory diseases.

Wheat ESCRT-III protein TaSAL1 regulates male gametophyte transmission and controls tillering and heading date

Charged multivesicular protein 1 (CHMP1) is a member of the endosomal sorting complex required for transport-III (ESCRT-III) complex that targets membrane localized signaling receptors to intralumenal vesicles in the multivesicular body of the endosome and eventually to the lysosome for degradation. Although CHMP1 plays roles in various plant growth and development processes, little is known about its function in wheat. In this study, we systematically analysed the members of the ESCRT-III complex in wheat (Triticum aestivum) and found that their orthologs were highly conserved in eukaryotic evolution. We identified CHMP1 homologous genes, TaSAL1s, and found that they were constitutively expressed in wheat tissues and essential for plant reproduction. Subcellular localization assays showed these proteins aggregated with and closely associated with the endoplasmic reticulum when ectopically expressed in tobacco leaves. We also found these proteins were toxic and caused leaf death. A genetic and reciprocal cross analysis revealed that TaSAL1 leads to defects in male gametophyte biogenesis. Moreover, phenotypic and metabolomic analysis showed that TaSAL1 may regulate tillering and heading date through phytohormone pathways. Overall, our results highlight the role of CHMP1 in wheat, particularly in male gametophyte biogenesis, with implications for improving plant growth and developing new strategies for plant breeding and genetic engineering.

Fluorogenic Chemical Probes for Wash-free Imaging of Cell Membrane Damage in Ferroptosis, Necrosis, and Axon Injury

Selectively labeling cells with damaged membranes is needed not only for identifying dead cells in culture, but also for imaging membrane barrier dysfunction in pathologies in vivo. Most membrane permeability stains are permanently colored or fluorescent dyes that need washing to remove their non-uptaken extracellular background and reach good image contrast. Others are DNA-binding environment-dependent fluorophores, which lack design modularity, have potential toxicity, and can only detect permeabilization of cell volumes containing a nucleus (i.e., cannot delineate damaged volumes in vivo nor image non-nucleated cell types or compartments). Here, we develop modular fluorogenic probes that reveal the whole cytosolic volume of damaged cells, with near-zero background fluorescence so that no washing is needed. We identify a specific disulfonated fluorogenic probe type that only enters cells with damaged membranes, then is enzymatically activated and marks them. The esterase probe MDG1 is a reliable tool to reveal live cells that have been permeabilized by biological, biochemical, or physical membrane damage, and it can be used in multicolor microscopy. We confirm the modularity of this approach by also adapting it for improved hydrolytic stability, as the redox probe MDG2. We conclude by showing the unique performance of MDG probes in revealing axonal membrane damage (which DNA fluorogens cannot achieve) and in discriminating damage on a cell-by-cell basis in embryos in vivo. The MDG design thus provides powerful modular tools for wash-free in vivo imaging of membrane damage, and indicates how designs may be adapted for selective delivery of drug cargoes to these damaged cells: offering an outlook from selective diagnosis toward therapy of membrane-compromised cells in disease.