Autophagosome-lysosome fusion is independent of V-ATPase-mediated acidification

Fibroinase plays a vital role in silk gland degeneration by regulating autophagy and apoptosis in the silkworm, Bombyx mori

The silkworm is an incredibly valuable insect that produces silk through its silk gland. Within this organ, Fibroinase has been identified and named due to its ability to fibroin degradation. The expression of Fibroinase in the silk gland significantly increases during the larval-pupal stage, which might be associated with the degeneration of the silk gland. In this study, Fibroinase was overexpressed and knocked down specifically both in the middle and posterior silk glands, respectively, using transgenic technology. The investigation of silk gland development in these transgenic silkworms showed that Fibroinase plays a direct role in accelerating silk gland degeneration. The staining analyses performed in the silk glands of transgenic silkworms suggest that Fibroinase is involved in the processes of autophagy and apoptosis during silk gland degeneration. Further experiments demonstrated that Fibroinase, acting as a lysosomal regulator, negatively regulates autophagy via the mTOR (mechanistic target of rapamycin) pathway. Moreover, during apoptosis, Fibroinase could activate Caspase3 by increasing the activity of BmCaspase1, ultimately accelerating the apoptosis process. These findings enhance our understanding of the physiological role of Fibroinase in promoting silk gland degeneration, which plays a role in breaking down proteins in the silk gland and coordinating the regulation of autophagy and apoptosis.

Nuclear Chloride Ion-Selective Fluorescent Probe and Its Biological Applications

Owing to the biological significance of Cl- in cells, several chemical fluorescent probes and biosensors have been constructed to monitor this anion in the cytosol and subcellular organelles. However, a fluorescent probe for the selective detection of nuclear Cl- has not been described thus far. In the current study, we developed the first nuclear Cl--selective biosensor, Cl-YFP-NLS, whose fluorescence was effectively quenched by this anion, and demonstrated that it is an efficient and powerful tool for determining the levels of nuclear Cl-. The results of cell studies using Cl-YFP-NLS as the probe suggested that the level of Cl- in the nucleus is lower than that in the cytosol. In addition, Cl-YFP-NLS along with lysosomal (Lyso-MQAE) and mitochondrial Cl--selective fluorescent probes (Mito-MQAE) were utilized to determine the effects of various substances on the levels of Cl- in subcellular organelles. The results showed that lysosomotropic agents decrease the lysosomal Cl- concentration and increase the levels of mitochondrial and nuclear Cl-. Also, observations suggested that substances capable of inducing mitochondrial outer membrane permeabilization without inducing lysosomal membrane permeabilization increase mitochondrial and nuclear Cl- concentrations but they do not affect the level of lysosomal Cl-. Moreover, a substance directly disrupting nuclear pore complexes increased the level of nuclear Cl- and did not change the levels of lysosomal and mitochondrial Cl-. Finally, nucleus-affecting substances that cause deoxyribonucleic acid damage and activate p53 and Bax increased the levels of mitochondrial and nuclear Cl- without influencing the level of lysosomal Cl-.

No energy, no autophagy-Mechanisms and therapeutic implications of autophagic response energy requirements

Autophagy is a lysosome-mediated self-degradation process of central importance for cellular quality control. It also provides macromolecule building blocks and substrates for energy metabolism during nutrient or energy deficiency, which are the main stimuli for autophagy induction. However, like most biological processes, autophagy itself requires ATP, and there is an energy threshold for its initiation and execution. We here present the first comprehensive review of this often-overlooked aspect of autophagy research. The studies in which ATP deficiency suppressed autophagy in vitro and in vivo were classified according to the energy pathway involved (oxidative phosphorylation or glycolysis). A mechanistic insight was provided by pinpointing the critical ATP-consuming autophagic events, including transcription/translation/interaction of autophagy-related molecules, autophagosome formation/elongation, autophagosome fusion with the lysosome, and lysosome acidification. The significance of energy-dependent fine-tuning of autophagic response for preserving the cell homeostasis, and potential implications for the therapy of cancer, autoimmunity, metabolic disorders, and neurodegeneration are discussed.

The ion channels of endomembranes

The endomembrane system consists of organellar membranes in the biosynthetic pathway [endoplasmic reticulum (ER), Golgi apparatus, and secretory vesicles] as well as those in the degradative pathway (early endosomes, macropinosomes, phagosomes, autophagosomes, late endosomes, and lysosomes). These endomembrane organelles/vesicles work together to synthesize, modify, package, transport, and degrade proteins, carbohydrates, and lipids, regulating the balance between cellular anabolism and catabolism. Large ion concentration gradients exist across endomembranes: Ca2+ gradients for most endomembrane organelles and H+ gradients for the acidic compartments. Ion (Na+, K+, H+, Ca2+, and Cl-) channels on the organellar membranes control ion flux in response to cellular cues, allowing rapid informational exchange between the cytosol and organelle lumen. Recent advances in organelle proteomics, organellar electrophysiology, and luminal and juxtaorganellar ion imaging have led to molecular identification and functional characterization of about two dozen endomembrane ion channels. For example, whereas IP3R1-3 channels mediate Ca2+ release from the ER in response to neurotransmitter and hormone stimulation, TRPML1-3 and TMEM175 channels mediate lysosomal Ca2+ and H+ release, respectively, in response to nutritional and trafficking cues. This review aims to summarize the current understanding of these endomembrane channels, with a focus on their subcellular localizations, ion permeation properties, gating mechanisms, cell biological functions, and disease relevance.

Risk factors of using late-autophagy inhibitors: Aspects to consider when combined with anticancer therapies

Cancer resistance to therapy is still an unsolved scientific and clinical problem. In 2022, the hallmarks of cancer have been expanded to include four new features, including cellular senescence. Therapy-induced senescence (TIS) is a stressor-based response to conventional treatment methods, e.g. chemo- and radiotherapy, but also to non-conventional targeted therapies. Since TIS reinforces resistance in cancers, new strategies for sensitizing cancer cells to therapy are being adopted. These include macroautophagy as a potential target for inhibition due to its potential cytoprotective role in many cancers. The mechanism of late-stage autophagy inhibitors is based on blockage of autophagolysosome formation or an increase in lysosomal pH, resulting in disrupted cargo degradation. Such inhibitors are relevant candidates for increasing anticancer therapy effectiveness. In particular, 4-aminoquoline derivatives: chloroquine/hydroxychloroquine (CQ/HCQ) have been tested in multiple clinical trials in combination with senescence-inducing anti-cancer drugs. In this review, we summarize the properties of selected late-autophagy inhibitors and their role in the regulation of autophagy and senescent cell phenotype in vitro and in vivo models of cancer as well as treatment response in clinical trials on oncological patients. Additionally, we point out that, although these compounds increase the effectiveness of treatment in some cases, their practical usage might be hindered due to systemic toxicity, hypoxic environment, dose- ant time-dependent inhibitory effects, as well as a possible contribution to escaping from TIS.

Systemic administration of a novel Beclin 1-derived peptide significantly upregulates autophagy in the spinal motor neurons of autophagy reporter mice

Autophagy, an intracellular degradation system, plays a vital role in protecting cells by clearing damaged organelles, pathogens, and protein aggregates. Autophagy upregulation through pharmacological interventions has gained significant attention as a potential therapeutic avenue for proteinopathies. Here, we report the development of an autophagy-inducing peptide (BCN4) derived from the Beclin 1 protein, the master regulator of autophagy. To deliver the BCN4 into cells and the central nervous system (CNS), it was conjugated to our previously developed cell and blood-brain barrier-penetrating peptide (CPP). CPP-BCN4 significantly upregulated autophagy and reduced protein aggregates in motor neuron (MN)-like cells. Moreover, its systemic administration in a reporter mouse model of autophagy resulted in a significant increase in autophagy activity in the spinal MNs. Therefore, this novel autophagy-inducing peptide with a demonstrated ability to upregulate autophagy in the CNS has significant potential for the treatment of various neurodegenerative diseases with protein aggregates as a characteristic feature.

The different roles of V-ATPase a subunits in phagocytosis/endocytosis and autophagy

Microglia are specialized macrophages responsible for the clearance of dead neurons and pathogens by phagocytosis and degradation. The degradation requires phagosome maturation and acidification provided by the vesicular- or vacuolar-type H+-translocating adenosine triphosphatase (V-ATPase), which is composed of the cytoplasmic V1 domain and the membrane-embedded Vo domain. The V-ATPase a subunit, an integral part of the Vo domain, has four isoforms in mammals. The functions of different isoforms on phagosome maturation in different cells/species remain controversial. Here we show that mutations of both the V-ATPase Atp6v0a1 and Tcirg1b/Atp6v0a3 subunits lead to the accumulation of phagosomes in zebrafish microglia. However, their mechanisms are different. The V-ATPase Atp6v0a1 subunit is mainly distributed in early and late phagosomes. Defects of this subunit lead to a defective transition from early phagosomes to late phagosomes. In contrast, The V-ATPase Tcirg1b/Atp6v0a3 subunit is primarily located on lysosomes and regulates late phagosome-lysosomal fusion. Defective Tcirg1b/Atp6v0a3, but not Atp6v0a1 subunit leads to reduced acidification and impaired macroautophagy/autophagy in microglia. We further showed that ATP6V0A1/a1 and TCIRG1/a3 subunits in mouse macrophages preferentially located in endosomes and lysosomes, respectively. Blocking these subunits disrupted early-to-late endosome transition and endosome-to-lysosome fusion, respectively. Taken together, our results highlight the essential and conserved roles played by different V-ATPase subunits in multiple steps of phagocytosis and endocytosis across various species.Abbrevations: Apoe: apolipoprotein E; ANXA5/annexin V: annexin A5; ATP6V0A1/a1: ATPase H+-transporting V0 subunit a1; ATP6V0A2/a2: ATPase H+-transporting V0 subunit a2; ATP6V0A4/a4: ATPase H+-transporting V0 subunit a4; dpf: days post-fertilization; EEA1: early endosome antigen 1; HOPS: homotypic fusion and protein sorting; LAMP1: lysosomal associated membrane protein 1; Lcp1: lymphocyte cytosolic protein 1 (L-plastin); Map1lc3/Lc3: microtubule-associated protein 1 light chain 3; NR: neutral red; PBS: phosphate-buffered saline; PtdIns: phosphatidylinositol; PtdIns3P: phosphatidylinositol-3-phosphate; PtdIns(3,5)P2: phosphatidylinositol (3,5)-bisphosphate; RAB4: RAB4, member RAS oncogene family; RAB5: RAB5, member RAS oncogene family; RAB7: RAB7, member RAS oncogene family; TCIRG1/Atp6v0a3/a3: T cell immune regulator 1, ATPase H+-transporting V0 subunit a3; V-ATPase: vacuolar-type H+-translocating adenosine triphosphatase; Xla.Tubb2b/NBT: tubulin beta 2B class IIb.

Alpha-Hederin induces incomplete autophagic injury in non-small cell lung cancer by interfering with the lysosomal acidification

Lung cancer is the most common oncological disease worldwide, with non-small cell lung cancer accounting for approximately 85% of lung cancer cases. α-Hederin is a monodesmosidic triterpenoid saponin isolated from the leaves of Hedera helix L. or Nigella sativa and has been extensively studied for its antitumor activity against a variety of tumor cells. It has been suggested that α-Hederin is a potential regulator of autophagy and has high promise for application. However, the specific mechanism and characteristics of α-Hederin in regulating autophagy are not well understood. In this study, we confirmed the potential of α-Hederin application in lung cancer treatment and comprehensively explored the mechanism and characteristics of α-Hederin in regulating autophagy in lung cancer cells. Our results suggest that α-Hederin is an incomplete autophagy inducer that targets mTOR to activate the classical autophagic pathway, inhibits lysosomal acidification without significantly affecting the processes of autophagosome transport, lysosome biogenesis, autophagosome and lysosome fusion, and finally leads to impaired autophagic flux and triggers autophagic damage in NSCLC.

Neurotropic virus infection and neurodegenerative diseases: Potential roles of autophagy pathway

Neurodegenerative diseases (NDs) constitute a group of disorders characterized by the progressive deterioration of nervous system functionality. Currently, the precise etiological factors responsible for NDs remain incompletely elucidated, although it is probable that a combination of aging, genetic predisposition, and environmental stressors participate in this process. Accumulating evidence indicates that viral infections, especially neurotropic viruses, can contribute to the onset and progression of NDs. In this review, emerging evidence supporting the association between viral infection and NDs is summarized, and how the autophagy pathway mediated by viral infection can cause pathological aggregation of cellular proteins associated with various NDs is discussed. Furthermore, autophagy-related genes (ARGs) involved in Herpes simplex virus (HSV-1) infection and NDs are analyzed, and whether these genes could link HSV-1 infection to NDs is discussed. Elucidating the mechanisms underlying NDs is critical for developing targeted therapeutic approaches that prevent the onset and slow the progression of NDs.

Increased V-ATPase activity can lead to chemo-resistance in oral squamous cell carcinoma via autophagy induction: new insights

Oral squamous cell carcinoma (OSCC) is a cancer type with a high rate of recurrence and a poor prognosis. Tumor chemo-resistance remains an issue for OSCC patients despite the availability of multimodal therapy options, which causes an increase in tumor invasiveness. Vacuolar ATPase (V-ATPase), appears to be one of the most significant molecules implicated in MDR in tumors like OSCC. It is primarily responsible for controlling the acidity in the solid tumors' microenvironment, which interferes with the absorption of chemotherapeutic medications. However, the exact cellular and molecular mechanisms V-ATPase plays in OSCC chemo-resistance have not been understood. Uncovering these mechanisms can contribute to combating OSCC chemo-resistance and poor prognosis. Hence, in this review, we suggest that one of these underlying mechanisms is autophagy induced by V-ATPase which can potentially contribute to OSCC chemo-resistance. Finally, specialized autophagy and V-ATPase inhibitors may be beneficial as an approach to reduce drug resistance to anticancer therapies in addition to serving as coadjuvants in antitumor treatments. Also, V-ATPase could be a prognostic factor for OSCC patients. However, in the future, more investigations are required to demonstrate these suggestions and hypotheses.

Restoring cellular copper homeostasis in Alzheimer disease: a novel peptide shuttle is internalized by an ATP-dependent endocytosis pathway involving Rab5- and Rab14-endosomes

CPPs, or Cell-Penetrating Peptides, offer invaluable utility in disease treatment due to their ability to transport various therapeutic molecules across cellular membranes. Their unique characteristics, such as biocompatibility and low immunogenicity, make them ideal candidates for delivering drugs, genes, or imaging agents directly into cells. This targeted delivery enhances treatment efficacy while minimizing systemic side effects. CPPs exhibit versatility, crossing biological barriers and reaching intracellular targets that conventional drugs struggle to access. This capability holds promise in treating a wide array of diseases, including cancer, neurodegenerative disorders, and infectious diseases, offering a potent avenue for innovative and targeted therapies, yet their precise mechanism of cell entry is far from being fully understood. In order to correct Cu dysregulation found in various pathologies such as Alzheimer disease, we have recently conceived a peptide Cu(II) shuttle, based on the αR5W4 CPP, which, when bound to Cu(II), is able to readily enter a neurosecretory cell model, and release bioavailable Cu in cells. Furthermore, this shuttle has the capacity to protect cells in culture against oxidative stress-induced damage which occurs when Cu binds to the Aβ peptide. The aim of this study was therefore to characterize the cell entry route used by this shuttle and determine in which compartment Cu is released. Pharmacological treatments, siRNA silencing and colocalization experiments with GFP-Rab fusion proteins, indicate that the shuttle is internalized by an ATP-dependent endocytosis pathway involving both Rab5 and Rab14 endosomes route and suggest an early release of Cu from the shuttle.

PIKFYVE inhibitors trigger interleukin-24-dependent cell death of autophagy-dependent melanoma

Inhibitors specifically targeting the 1-phosphatidylinositol 3-phosphate 5-kinase (PIKFYVE) disrupt lysosome homeostasis, thereby selectively terminating autophagy-dependent human cancer cells in vivo as well as in vitro without harming the viability of nonmalignant cells. To elucidate the mechanism by which PIKFYVE inhibition induces cell death, autophagy-dependent melanoma cells were compared with normal foreskin fibroblasts. RNA sequence profiling suggested that PIKFYVE inhibitors upregulated an endoplasmic reticulum (ER) stress response involving interleukin-24 (IL24; also known as MDA7) selectively in melanoma cells. Subsequent biochemical and genetic analyses confirmed these results and extended them to tumor xenografts in which tumor formation and expansion were inhibited. IL24 expression was upregulated by the DDIT3/CHOP/CEBPz transcription factor, a component of the PERK-dependent ER-stress response. Ectopic expression of IL24-induced cell death in melanoma cells, but not in foreskin fibroblasts, whereas ablation of the IL24 gene in melanoma cells prevented death. IL24 upregulation was triggered specifically by PIKFYVE inhibition. Thus, unlike thapsigargin and tunicamycin, which induce ER-stress indiscriminately, PIKFYVE inhibitors selectively terminated PIKFYVE-sensitive melanoma by inducing IL24-dependent ER-stress. Moreover, induction of cell death by a PIKFYVE inhibitor together with ectopic expression of IL24 protein was cumulative, thereby confirming the therapeutic potential of PIKFYVE inhibitors in the treatment of melanoma.

Sucrose Treatment Enhances the Electrotransfer of DNA by Activating Phospholipase A2

Our previous study discovered that sucrose and other non-reducing sugars (e.g., trehalose and raffinose) could be used to improve the electrotransfer (ET) of molecular cargo, including DNA, mRNA, and ribonucleoprotein in various cell lines and primary human cells in vitro and in vivo. To understand the molecular mechanisms of this improvement, we used RNA sequencing technology to analyze changes in the cell transcriptome after sucrose treatment. The results from our analysis demonstrated that the sucrose treatment upregulated phospholipase A2 and V-ATPase gene families, which could potentially influence the acidity of intracellular vesicles through augmenting vesicle fusion and the influx of proton, respectively. To determine how this upregulation affects ET efficiency, we treated cells with pharmaceutical inhibitors of phospholipase A2 and V-ATPase. The data demonstrated that the treatment with the phospholipase A2 inhibitor could reverse the ET improvement elicited by the sucrose treatment. The V-ATPase inhibitor treatment either had little influence or further enhanced the effect of the sucrose treatment on the ET efficiency. These observations provide a molecular explanation for our previous findings, demonstrating that the sucrose treatment primarily enhanced the ET efficiency by promoting vesicle trafficking and fusion through the activation of phospholipase A2.

HTRA1-driven detachment of type I collagen from endoplasmic reticulum contributes to myocardial fibrosis in dilated cardiomyopathy

BACKGROUND

The aberrant secretion and excessive deposition of type I collagen (Col1) are important factors in the pathogenesis of myocardial fibrosis in dilated cardiomyopathy (DCM). However, the precise molecular mechanisms underlying the synthesis and secretion of Col1 remain unclear.

METHODS AND RESULTS

RNA-sequencing analysis revealed an increased HtrA serine peptidase 1 (HTRA1) expression in patients with DCM, which is strongly correlated with myocardial fibrosis. Consistent findings were observed in both human and mouse tissues by immunoblotting, quantitative reverse transcription polymerase chain reaction (qRT-PCR), immunohistochemistry, and immunofluorescence analyses. Pearson's analysis showed a markedly positive correlation between HTRA1 level and myocardial fibrosis indicators, including extracellular volume fraction (ECV), native T1, and late gadolinium enhancement (LGE), in patients with DCM. In vitro experiments showed that the suppression of HTRA1 inhibited the conversion of cardiac fibroblasts into myofibroblasts and decreased Col1 secretion. Further investigations identified the role of HTRA1 in promoting the formation of endoplasmic reticulum (ER) exit sites, which facilitated the transportation of Col1 from the ER to the Golgi apparatus, thereby increasing its secretion. Conversely, HTRA1 knockdown impeded the retention of Col1 in the ER, triggering ER stress and subsequent induction of ER autophagy to degrade misfolded Col1 and maintain ER homeostasis. In vivo experiments using adeno-associated virus-serotype 9-shHTRA1-green fluorescent protein (AAV9-shHTRA1-GFP) showed that HTRA1 knockdown effectively suppressed myocardial fibrosis and improved left ventricular function in mice with DCM.

CONCLUSIONS

The findings of this study provide valuable insights regarding the treatment of DCM-associated myocardial fibrosis and highlight the therapeutic potential of targeting HTRA1-mediated collagen secretion.

Drosophila TMEM63 and mouse TMEM63A are lysosomal mechanosensory ion channels

Cells sense physical forces and convert them into electrical or chemical signals, a process known as mechanotransduction. Whereas extensive studies focus on mechanotransduction at the plasma membrane, little is known about whether and how intracellular organelles sense mechanical force and the physiological functions of organellar mechanosensing. Here we identify the Drosophila TMEM63 (DmTMEM63) ion channel as an intrinsic mechanosensor of the lysosome, a major degradative organelle. Endogenous DmTMEM63 proteins localize to lysosomes, mediate lysosomal mechanosensitivity and modulate lysosomal morphology and function. Tmem63 mutant flies exhibit impaired lysosomal degradation, synaptic loss, progressive motor deficits and early death, with some of these mutant phenotypes recapitulating symptoms of TMEM63-associated human diseases. Importantly, mouse TMEM63A mediates lysosomal mechanosensitivity in Neuro-2a cells, indicative of functional conservation in mammals. Our findings reveal DmTMEM63 channel function in lysosomes and its physiological roles in vivo and provide a molecular basis to explore the mechanosensitive process in subcellular organelles.

Cascade Catalytic Nanoparticles Selectively Alkalize Cancerous Lysosomes to Suppress Cancer Progression and Metastasis

Lysosomes are critical in modulating the progression and metastasis for various cancers. There is currently an unmet need for lysosomal alkalizers that can selectively and safely alter the pH and inhibit the function of cancer lysosomes. Here an effective, selective, and safe lysosomal alkalizer is reported that can inhibit autophagy and suppress tumors in mice. The lysosomal alkalizer consists of an iron oxide core that generates hydroxyl radicals (•OH) in the presence of excessive H+ and hydrogen peroxide inside cancer lysosomes and cerium oxide satellites that capture and convert •OH into hydroxide ions. Alkalized lysosomes, which display impaired enzyme activity and autophagy, lead to cancer cell apoptosis. It is shown that the alkalizer effectively inhibits both local and systemic tumor growth and metastasis in mice. This work demonstrates that the intrinsic properties of nanoparticles can be harnessed to build effective lysosomal alkalizers that are both selective and safe.

Migrasomal autophagosomes relieve endoplasmic reticulum stress in glioblastoma cells

BACKGROUND

Glioblastoma (GBM) is more difficult to treat than other intractable adult tumors. The main reason that GBM is so difficult to treat is that it is highly infiltrative. Migrasomes are newly discovered membrane structures observed in migrating cells. Thus, they can be generated from GBM cells that have the ability to migrate along the brain parenchyma. However, the function of migrasomes has not yet been elucidated in GBM cells.

RESULTS

Here, we describe the composition and function of migrasomes generated along with GBM cell migration. Proteomic analysis revealed that LC3B-positive autophagosomes were abundant in the migrasomes of GBM cells. An increased number of migrasomes was observed following treatment with chloroquine (CQ) or inhibition of the expression of STX17 and SNAP29, which are involved in autophagosome/lysosome fusion. Furthermore, depletion of ITGA5 or TSPAN4 did not relieve endoplasmic reticulum (ER) stress in cells, resulting in cell death.

CONCLUSIONS

Taken together, our study suggests that increasing the number of autophagosomes, through inhibition of autophagosome/lysosome fusion, generates migrasomes that have the capacity to alleviate cellular stress.

Studying Autophagy in Microglia: Overcoming the Obstacles

In this chapter, we provide an overview of the main techniques and experimental approaches that can be used to analyze autophagy flux in microglia, the brain-resident macrophages. For this purpose, we first briefly introduce the main peculiarities of microglial biology, describe the basic mechanisms and functions of autophagy, and summarize the evidence accumulated so far on the role of autophagy in the regulation of microglial survival and functions, mainly phagocytosis and inflammation. Then, we highlight conceptual and technical aspects of autophagic recycling and microglial physiology that need to be taken into account for the accurate evaluation of autophagy flux in microglia. Finally, we describe the main assays that can be used to analyze the complete sequence of autophagosome formation and degradation or autophagy flux, mainly in cultured microglia and in vivo. The main approaches include indirect tracking of autophagosomes by autophagic enzymes such as LC3 by western blot and fluorescence-based confocal microscopy, as well as direct analysis of autophagic vesicles by electron microscopy. We also discuss the advantages and disadvantages of using these methods in specific experimental contexts and highlight the need to complement LC3 and/or electron microscopy data with analysis of other autophagic effectors and lysosomal proteins that participate in the initiation and completion of autophagy flux, respectively. In summary, we provide an experimental guide for the analysis of autophagosome turnover in microglia, emphasizing the need to combine as many markers and complementary approaches as possible to fully characterize the status of autophagy flux in microglia.

Molecular mechanism of autophagy and apoptosis in endometriosis: Current understanding and future research directions

Background

Endometriosis is a common gynecological condition, with symptoms including pain and infertility. Regurgitated endometrial cells into the peritoneal cavity encounter hypoxia and nutrient starvation. Endometriotic cells have evolved various adaptive mechanisms to survive in this inevitable condition. These adaptations include escape from apoptosis. Autophagy, a self-degradation system, controls apoptosis during stress conditions. However, to date, the mechanisms regulating the interplay between autophagy and apoptosis are still poorly understood. In this review, we summarize the current understanding of the molecular characteristics of autophagy in endometriosis and discuss future therapeutic challenges.

Methods

A search of PubMed and Google Scholar databases were used to identify relevant studies for this narrative literature review.

Results

Autophagy may be dynamically regulated through various intrinsic (e.g., PI3K/AKT/mTOR signal transduction network) and extrinsic (e.g., hypoxia and iron-mediated oxidative stress) pathways, contributing to the development and progression of endometriosis. Upregulation of mTOR expression suppresses apoptosis via inhibiting the autophagy pathway, whereas hypoxia or excess iron often inhibits apoptosis via promoting autophagy.

Conclusion

Endometriotic cells may have acquired antiapoptotic mechanisms through unique intrinsic and extrinsic autophagy pathways to survive in changing environments.

Zinc attenuates sulfamethoxazole-induced lipotoxicity by reversing sulfamethoxazole-induced mitochondrial dysfunction and lysosome impairment in a freshwater teleost

Sulfamethoxazole (SMZ) and zinc (Zn) are widespread harmful materials in aquatic ecosystems and cause toxic effects to aquatic animals under their individual exposure. Although they often co-exist in aquatic environments, little is known about their joint effects and mechanism influencing aquatic animals. Herein, SMZ induced mitochondrial and lysosomal dysfunction, inhibited autophagy flux, and induced lipotoxicity. However, SMZ-induced changes of these physiological and metabolic processes above were reversed by Zn exposure, indicating the antagonism between Zn and SMZ. SOD1-knockdown abrogated the reversing effects of Zn on mitochondria dysfunction and autophagy flux blockage induced by SMZ, suggesting that SOD1 was essential for Zn to reverse SMZ-induced mitochondria dysfunction and autophagy impairment. Our further investigation found that Zn regulated STAT3 translocation to lysosomes and mitochondria to attenuate SMZ-induced lipotoxicity, and SOD1 was required for these processes. Mechanistically, STAT3 was associated with ATP6V1 A in a coiled-coil domain-dependent manner, and pS710-STAT3-and pY753-STAT3-independent manners. Moreover, SMZ suppressed autophagic degradation of damaged mitochondria via inhibiting interaction between STAT3 and ATP6V1 A and increasing pS710-STAT3 level; SMZ impaired mitochondrial β-oxidation via decreasing pY753-STAT3 level and STAT3 mitochondrial localization. Zn reversed these SMZ-induced effects to alleviate SMZ-induced lipotoxicity. Taken together, our data showed that SMZ impaired mitochondrial β-oxidation and lysosomal acidification via the downregulation of SOD1, leading to lipotoxicity, and that Zn reversed SMZ-induced changes of these important biological processes and attenuated SMZ-induced lipotoxicity. Thus, our study identified previously unidentified mechanisms for the antagonistic mechanisms of Zn and SMZ on aquatic animals, which provided novel insights into the environmental risk assessments of the joint exposure between heavy metals and antibiotics in the aquatic organisms.

Integrative analysis reveals a conserved role for the amyloid precursor protein in proteostasis during aging

Aβ peptides derived from the amyloid precursor protein (APP) have been strongly implicated in the pathogenesis of Alzheimer's disease. However, the normal function of APP and the importance of that role in neurodegenerative disease is less clear. We recover the Drosophila ortholog of APP, Appl, in an unbiased forward genetic screen for neurodegeneration mutants. We perform comprehensive single cell transcriptional and proteomic studies of Appl mutant flies to investigate Appl function in the aging brain. We find an unexpected role for Appl in control of multiple cellular pathways, including translation, mitochondrial function, nucleic acid and lipid metabolism, cellular signaling and proteostasis. We mechanistically define a role for Appl in regulating autophagy through TGFβ signaling and document the broader relevance of our findings using mouse genetic, human iPSC and in vivo tauopathy models. Our results demonstrate a conserved role for APP in controlling age-dependent proteostasis with plausible relevance to Alzheimer's disease.

Dysregulation of the progranulin-driven autophagy-lysosomal pathway mediates secretion of the nuclear protein TDP-43

The cytoplasmic accumulation of the nuclear protein transactive response DNA-binding protein 43 kDa (TDP-43) has been linked to the progression of amyotrophic lateral sclerosis and frontotemporal lobar degeneration. TDP-43 secreted into the extracellular space has been suggested to contribute to the cell-to-cell spread of the cytoplasmic accumulation of TDP-43 throughout the brain; however, the underlying mechanisms remain unknown. We herein demonstrated that the secretion of TDP-43 was stimulated by the inhibition of the autophagy-lysosomal pathway driven by progranulin (PGRN), a causal protein of frontotemporal lobar degeneration. Among modulators of autophagy, only vacuolar-ATPase inhibitors, such as bafilomycin A1 (Baf), increased the levels of the full-length and cleaved forms of TDP-43 and the autophagosome marker LC3-II (microtubule-associated proteins 1A/1B light chain 3B) in extracellular vesicle fractions prepared from the culture media of HeLa, SH-SY5Y, or NSC-34 cells, whereas vacuolin-1, MG132, chloroquine, rapamycin, and serum starvation did not. The C-terminal fragment of TDP-43 was required for Baf-induced TDP-43 secretion. The Baf treatment induced the translocation of the aggregate-prone GFP-tagged C-terminal fragment of TDP-43 and mCherry-tagged LC3 to the plasma membrane. The Baf-induced secretion of TDP-43 was attenuated in autophagy-deficient ATG16L1 knockout HeLa cells. The knockdown of PGRN induced the secretion of cleaved TDP-43 in an autophagy-dependent manner in HeLa cells. The KO of PGRN in mouse embryonic fibroblasts increased the secretion of the cleaved forms of TDP-43 and LC3-II. The treatment inducing TDP-43 secretion increased the nuclear translocation of GFP-tagged transcription factor EB, a master regulator of the autophagy-lysosomal pathway in SH-SY5Y cells. These results suggest that the secretion of TDP-43 is promoted by dysregulation of the PGRN-driven autophagy-lysosomal pathway.

The Molecular Mechanism and Therapeutic Application of Autophagy for Urological Disease

Autophagy is a lysosomal degradation process known as autophagic flux, involving the engulfment of damaged proteins and organelles by double-membrane autophagosomes. It comprises microautophagy, chaperone-mediated autophagy (CMA), and macroautophagy. Macroautophagy consists of three stages: induction, autophagosome formation, and autolysosome formation. Atg8-family proteins are valuable for tracking autophagic structures and have been widely utilized for monitoring autophagy. The conversion of LC3 to its lipidated form, LC3-II, served as an indicator of autophagy. Autophagy is implicated in human pathophysiology, such as neurodegeneration, cancer, and immune disorders. Moreover, autophagy impacts urological diseases, such as interstitial cystitis /bladder pain syndrome (IC/BPS), ketamine-induced ulcerative cystitis (KIC), chemotherapy-induced cystitis (CIC), radiation cystitis (RC), erectile dysfunction (ED), bladder outlet obstruction (BOO), prostate cancer, bladder cancer, renal cancer, testicular cancer, and penile cancer. Autophagy plays a dual role in the management of urologic diseases, and the identification of potential biomarkers associated with autophagy is a crucial step towards a deeper understanding of its role in these diseases. Methods for monitoring autophagy include TEM, Western blot, immunofluorescence, flow cytometry, and genetic tools. Autophagosome and autolysosome structures are discerned via TEM. Western blot, immunofluorescence, northern blot, and RT-PCR assess protein/mRNA levels. Luciferase assay tracks flux; GFP-LC3 transgenic mice aid study. Knockdown methods (miRNA and RNAi) offer insights. This article extensively examines autophagy's molecular mechanism, pharmacological regulation, and therapeutic application involvement in urological diseases.

Autophagy in Heart Failure: Insights into Mechanisms and Therapeutic Implications

Autophagy, a dynamic and complex process responsible for the clearance of damaged cellular components, plays a crucial role in maintaining myocardial homeostasis. In the context of heart failure, autophagy has been recognized as a response mechanism aimed at counteracting pathogenic processes and promoting cellular health. Its relevance has been underscored not only in various animal models, but also in the human heart. Extensive research efforts have been dedicated to understanding the significance of autophagy and unravelling its complex molecular mechanisms. This review aims to consolidate the current knowledge of the involvement of autophagy during the progression of heart failure. Specifically, we provide a comprehensive overview of published data on the impact of autophagy deregulation achieved by genetic modifications or by pharmacological interventions in ischemic and non-ischemic models of heart failure. Furthermore, we delve into the intricate molecular mechanisms through which autophagy regulates crucial cellular processes within the three predominant cell populations of the heart: cardiomyocytes, cardiac fibroblasts, and endothelial cells. Finally, we emphasize the need for future research to unravel the therapeutic potential associated with targeting autophagy in the management of heart failure.

Drosophila as a Robust Model System for Assessing Autophagy: A Review

Autophagy is the process through which a body breaks down and recycles its own cellular components, primarily inside lysosomes. It is a cellular response to starvation and stress, which plays decisive roles in various biological processes such as senescence, apoptosis, carcinoma, and immune response. Autophagy, which was first discovered as a survival mechanism during starvation in yeast, is now known to serve a wide range of functions in more advanced organisms. It plays a vital role in how cells respond to stress, starvation, and infection. While research on yeast has led to the identification of many key components of the autophagy process, more research into autophagy in more complex systems is still warranted. This review article focuses on the use of the fruit fly Drosophila melanogaster as a robust testing model in further research on autophagy. Drosophila provides an ideal environment for exploring autophagy in a living organism during its development. Additionally, Drosophila is a well-suited compact tool for genetic analysis in that it serves as an intermediate between yeast and mammals because evolution conserved the molecular machinery required for autophagy in this species. Experimental tractability of host-pathogen interactions in Drosophila also affords great convenience in modeling human diseases on analogous structures and tissues.

A conserved STRIPAK complex is required for autophagy in muscle tissue

Autophagy is important for cellular homeostasis and to prevent the abnormal accumulation of proteins. While many proteins that comprise the canonical autophagy pathway have been characterized, the identification of new regulators may help understand tissue and/or stress-specific responses. Using an in-silico approach, we identified Striatin interacting protein (Strip), MOB kinase activator 4, and fibroblast growth factor receptor 1 oncogene partner 2 as conserved mediators of muscle tissue maintenance. We performed affinity purification-mass spectrometry (AP-MS) experiments with Drosophila melanogaster Strip as a bait protein and copurified additional Striatin-interacting phosphatase and kinase (STRIPAK) complex members from larval muscle tissue. NUAK family kinase 1 (NUAK) and Starvin (Stv) also emerged as Strip-binding proteins and these physical interactions were verified in vivo using proximity ligation assays. To understand the functional significance of the STRIPAK-NUAK-Stv complex, we employed a sensitized genetic assay combined with RNA interference (RNAi) to demonstrate that both NUAK and stv function in the same biological process with genes that encode for STRIPAK complex proteins. RNAi-directed knockdown of Strip in muscle tissue led to the accumulation of ubiquitinated cargo, p62, and Autophagy-related 8a, consistent with a block in autophagy. Indeed, autophagic flux was decreased in Strip RNAi muscles, while lysosome biogenesis and activity were unaffected. Our results support a model whereby the STRIPAK-NUAK-Stv complex coordinately regulates autophagy in muscle tissue.

The ATP6V1B2 DDOD/DOORS-Associated p.Arg506* Variant Causes Hyperactivity and Seizures in Mice

The vacuolar H+-ATPase is a multisubunit enzyme which plays an essential role in the acidification and functions of lysosomes, endosomes, and synaptic vesicles. Many genes encoding subunits of V-ATPases, namely ATP6V0C, ATP6V1A, ATP6V0A1, and ATP6V1B2, have been associated with neurodevelopmental disorders and epilepsy. The autosomal dominant ATP6V1B2 p.Arg506* variant can cause both congenital deafness with onychodystrophy, autosomal dominant (DDOD) and deafness, onychodystrophy, osteodystrophy, mental retardation, and seizures syndromes (DOORS). Some but not all individuals with this truncating variant have intellectual disability and/or epilepsy, suggesting incomplete penetrance and/or variable expressivity. To further explore the impact of the p.Arg506* variant in neurodevelopment and epilepsy, we generated Atp6v1b2emR506* mutant mice and performed standardized phenotyping using the International Mouse Phenotyping Consortium (IMPC) pipeline. In addition, we assessed the EEG profile and seizure susceptibility of Atp6v1b2emR506* mice. Behavioral tests revealed that the mice present locomotor hyperactivity and show less anxiety-associated behaviors. Moreover, EEG analyses indicate that Atp6v1b2emR506* mutant mice have interictal epileptic activity and that both heterozygous (like patients) and homozygous mice have reduced seizure thresholds to pentylenetetrazol. Our results confirm that variants in ATP6V1B2 can cause seizures and that the Atp6v1b2emR506* heterozygous mouse model is a valuable tool to further explore the pathophysiology and potential treatments for vacuolar ATPases-associated epilepsy and disorders.

Lysosomal LAMP proteins regulate lysosomal pH by direct inhibition of the TMEM175 channel

Maintaining a highly acidic lysosomal pH is central to cellular physiology. Here, we use functional proteomics, single-particle cryo-EM, electrophysiology, and in vivo imaging to unravel a key biological function of human lysosome-associated membrane proteins (LAMP-1 and LAMP-2) in regulating lysosomal pH homeostasis. Despite being widely used as a lysosomal marker, the physiological functions of the LAMP proteins have long been overlooked. We show that LAMP-1 and LAMP-2 directly interact with and inhibit the activity of the lysosomal cation channel TMEM175, a key player in lysosomal pH homeostasis implicated in Parkinson's disease. This LAMP inhibition mitigates the proton conduction of TMEM175 and facilitates lysosomal acidification to a lower pH environment crucial for optimal hydrolase activity. Disrupting the LAMP-TMEM175 interaction alkalinizes the lysosomal pH and compromises the lysosomal hydrolytic function. In light of the ever-increasing importance of lysosomes to cellular physiology and diseases, our data have widespread implications for lysosomal biology.

Cyclin-G-associated kinase GAK/dAux regulates autophagy initiation via ULK1/Atg1 in glia

Autophagy is a major means for the elimination of protein inclusions in neurons in neurodegenerative diseases such as Parkinson's disease (PD). Yet, the mechanism of autophagy in the other brain cell type, glia, is less well characterized and remains largely unknown. Here, we present evidence that the PD risk factor, Cyclin-G-associated kinase (GAK)/Drosophila homolog Auxilin (dAux), is a component in glial autophagy. The lack of GAK/dAux increases the autophagosome number and size in adult fly glia and mouse microglia, and generally up-regulates levels of components in the initiation and PI3K class III complexes. GAK/dAux interacts with the master initiation regulator UNC-51like autophagy activating kinase 1/Atg1 via its uncoating domain and regulates the trafficking of Atg1 and Atg9 to autophagosomes, hence controlling the onset of glial autophagy. On the other hand, lack of GAK/dAux impairs the autophagic flux and blocks substrate degradation, suggesting that GAK/dAux might play additional roles. Importantly, dAux contributes to PD-like symptoms including dopaminergic neurodegeneration and locomotor function in flies. Our findings identify an autophagy factor in glia; considering the pivotal role of glia under pathological conditions, targeting glial autophagy is potentially a therapeutic strategy for PD.

Phosphorylation of EIF2S1 (eukaryotic translation initiation factor 2 subunit alpha) is indispensable for nuclear translocation of TFEB and TFE3 during ER stress

There are diverse links between macroautophagy/autophagy pathways and unfolded protein response (UPR) pathways under endoplasmic reticulum (ER) stress conditions to restore ER homeostasis. Phosphorylation of EIF2S1/eIF2α is an important mechanism that can regulate all three UPR pathways through transcriptional and translational reprogramming to maintain cellular homeostasis and overcome cellular stresses. In this study, to investigate the roles of EIF2S1 phosphorylation in regulation of autophagy during ER stress, we used EIF2S1 phosphorylation-deficient (A/A) cells in which residue 51 was mutated from serine to alanine. A/A cells exhibited defects in several steps of autophagic processes (such as autophagosome and autolysosome formation) that are regulated by the transcriptional activities of the autophagy master transcription factors TFEB and TFE3 under ER stress conditions. EIF2S1 phosphorylation was required for nuclear translocation of TFEB and TFE3 during ER stress. In addition, EIF2AK3/PERK, PPP3/calcineurin-mediated dephosphorylation of TFEB and TFE3, and YWHA/14-3-3 dissociation were required for their nuclear translocation, but were insufficient to induce their nuclear retention during ER stress. Overexpression of the activated ATF6/ATF6α form, XBP1s, and ATF4 differentially rescued defects of TFEB and TFE3 nuclear translocation in A/A cells during ER stress. Consequently, overexpression of the activated ATF6 or TFEB form more efficiently rescued autophagic defects, although XBP1s and ATF4 also displayed an ability to restore autophagy in A/A cells during ER stress. Our results suggest that EIF2S1 phosphorylation is important for autophagy and UPR pathways, to restore ER homeostasis and reveal how EIF2S1 phosphorylation connects UPR pathways to autophagy.Abbreviations: A/A: EIF2S1 phosphorylation-deficient; ACTB: actin beta; Ad-: adenovirus-; ATF6: activating transcription factor 6; ATZ: SERPINA1/α1-antitrypsin with an E342K (Z) mutation; Baf A1: bafilomycin A1; BSA: bovine serum albumin; CDK4: cyclin dependent kinase 4; CDK6: cyclin dependent kinase 6; CHX: cycloheximide; CLEAR: coordinated lysosomal expression and regulation; Co-IP: coimmunoprecipitation; CTSB: cathepsin B; CTSD: cathepsin D; CTSL: cathepsin L; DAPI: 4',6-diamidino-2-phenylindole dihydrochloride; DMEM: Dulbecco's modified Eagle's medium; DMSO: dimethyl sulfoxide; DTT: dithiothreitol; EBSS: Earle's Balanced Salt Solution; EGFP: enhanced green fluorescent protein; EIF2S1/eIF2α: eukaryotic translation initiation factor 2 subunit alpha; EIF2AK3/PERK: eukaryotic translation initiation factor 2 alpha kinase 3; ER: endoplasmic reticulum; ERAD: endoplasmic reticulum-associated degradation; ERN1/IRE1α: endoplasmic reticulum to nucleus signaling 1; FBS: fetal bovine serum; gRNA: guide RNA; GSK3B/GSK3β: glycogen synthase kinase 3 beta; HA: hemagglutinin; Hep: immortalized hepatocyte; IF: immunofluorescence; IRES: internal ribosome entry site; KO: knockout; LAMP1: lysosomal associated membrane protein 1; LMB: leptomycin B; LPS: lipopolysaccharide; MAP1LC3A/B/LC3A/B: microtubule associated protein 1 light chain 3 alpha/beta; MAP1LC3B/LC3B: microtubule associated protein 1 light chain 3 beta; MEFs: mouse embryonic fibroblasts; MFI: mean fluorescence intensity; MTORC1: mechanistic target of rapamycin kinase complex 1; NES: nuclear export signal; NFE2L2/NRF2: NFE2 like bZIP transcription factor 2; OE: overexpression; PBS: phosphate-buffered saline; PLA: proximity ligation assay; PPP3/calcineurin: protein phosphatase 3; PTM: post-translational modification; SDS: sodium dodecyl sulfate; SDS-PAGE: sodium dodecyl sulfate-polyacrylamide gel electrophoresis; SEM: standard error of the mean; TEM: transmission electron microscopy; TFE3: transcription factor E3; TFEB: transcription factor EB; TFs: transcription factors; Tg: thapsigargin; Tm: tunicamycin; UPR: unfolded protein response; WB: western blot; WT: wild-type; Xbp1s: spliced Xbp1; XPO1/CRM1: exportin 1.

The RagA GTPase protects young egg chambers in Drosophila

The preservation of female fertility under unfavorable conditions is essential for animal reproduction. Inhibition of the target of rapamycin complex 1 (TORC1) is indispensable for Drosophila young egg chamber maintenance under nutrient starvation. Here, we show that knockdown of RagA results in young egg chamber death independent of TORC1 hyperactivity. RagA RNAi ovaries have autolysosomal acidification and degradation defects, which make the young egg chambers sensitive to autophagosome augmentation. Meanwhile, RagA RNAi ovaries have nuclear-localized Mitf, which promotes autophagic degradation and protects young egg chambers under stress. Interestingly, GDP-bound RagA rescues autolysosome defects, while GTP-bound RagA rescues Mitf nuclear localization in RagA RNAi young egg chambers. Moreover, Rag GTPase activity, rather than TORC1 activity, controls Mitf cellular localization in the Drosophila germ line. Our work suggests that RagA separately controls autolysosomal acidification and Mitf activity in the Drosophila young egg chambers.

Identification of Fangjihuangqi Decoction as a late-stage autophagy inhibitor with an adjuvant anti-tumor effect against non-small cell lung cancer

BACKGROUND

Clinically, although chemotherapy is one of the most commonly used methods of treating tumors, chemotherapeutic drugs can induce autophagic flux and increase tumor cell resistance, leading to drug tolerance. Therefore, theoretically, inhibiting autophagy may improve the efficacy of chemotherapy. The discovery of autophagy regulators and their potential application as adjuvant anti-cancer drugs is of substantial importance. In this study, we clarified that Fangjihuangqi Decoction (FJHQ, traditional Chinese medicine) is an autophagy inhibitor, which can synergistically enhance the effect of cisplatin and paclitaxel on non-small cell lung cancer (NSCLC) cells.

METHODS

We observed the changes of autophagy level in NSCLC cells under the effect of FJHQ, and verified the level of the autophagy marker protein and cathepsin. Apoptosis was detected after the combination of FJHQ with cisplatin or paclitaxel, and NAC (ROS scavenger) was further used to verify the activation of ROS-MAPK pathway by FJHQ.

RESULTS

We observed that FJHQ induced autophagosomes in NSCLC cells and increased the levels of P62 and LC3-II protein expression in a concentration- and time-gradient-dependent manner, indicating that autophagic flux was inhibited. Co-localization experiments further showed that while FJHQ did not inhibit autophagosome and lysosome fusion, it affected the maturation of cathepsin and thus inhibited the autophagic pathway. Finally, we found that the combination of FJHQ with cisplatin or paclitaxel increased the apoptosis rate of NSCLC cells, due to increased ROS accumulation and further activation of the ROS-MAPK pathway. This synergistic effect could be reversed by NAC.

CONCLUSION

Collectively, these results demonstrate that FJHQ is a novel late-stage autophagy inhibitor that can amplify the anti-tumor effect of cisplatin and paclitaxel against NSCLC cells.

Title: The C-terminal amphipathic helix of Carboxypeptidase E mediates export from the ER and secretion via lysosomes

Carboxypeptidase E (CPE), an essential enzyme in the biosynthetic production line of most peptide hormones and neuropeptides, is predominantly expressed in endocrine tissues and in the nervous system. CPE is active in acidic environments where it cleaves the C'-terminal basic residues of peptide precursors to generate their bioactive form. Consequently, this highly conserved enzyme regulates numerous fundamental biological processes. Here, we combined live-cell microscopy and molecular analysis to examine the intracellular distribution and secretion dynamics of fluorescently tagged CPE. We show that, in non-endocrine cells, tagged-CPE is a soluble luminal protein that is efficiently exported from the ER via the Golgi apparatus to lysosomes. The C'-terminal conserved amphipathic helix serves as a lysosomal and secretory granule targeting and a secretion motif. Following secretion, CPE may be reinternalized into the lysosomes of neighboring cells.

Reversible binding of divalent cations to Ductin protein assemblies-A putative new regulatory mechanism of membrane traffic processes

Ductins are a family of homologous and structurally similar membrane proteins with 2 or 4 trans-membrane alpha-helices. The active forms of the Ductins are membranous ring- or star-shaped oligomeric assemblies and they provide various pore, channel, gap-junction functions, assist in membrane fusion processes and also serve as the rotor c-ring domain of V-and F-ATPases. All functions of the Ductins have been reported to be sensitive to the presence of certain divalent metal cations (Me2+), most frequently Cu2+ or Ca2+ ions, for most of the better known members of the family, and the mechanism of this effect is not yet known. Given that we have earlier found a prominent Me2+ binding site in a well-characterised Ductin protein, we hypothesise that certain divalent cations can structurally modulate the various functions of Ductin assemblies via affecting their stability by reversible non-covalent binding to them. A fine control of the stability of the assembly ranging from separated monomers through a loosely/weakly to tightly/strongly assembled ring might render precise regulation of Ductin functions possible. The putative role of direct binding of Me2+ to the c-ring subunit of active ATP hydrolase in autophagy and the mechanism of Ca2+-dependent formation of the mitochondrial permeability transition pore are also discussed.

Inhibition of STX17-SNAP29-VAMP8 complex formation by costunolide sensitizes ovarian cancer cells to cisplatin via the AMPK/mTOR signaling pathway

Ovarian cancer (OC) is the most common gynecological malignancy. Chemotherapy failure is a major challenge in OC treatment. Targeting autophagy is a promising strategy to enhance the cytotoxicity of chemotherapeutic agents. In this study, we found that costunolide (CTD) inhibits autophagic flux and exhibits high therapeutic efficacy for OC treatment in an in vitro model. Mechanistically, CTD inactivates AMPK/mTOR signaling to inhibit autophagy initiation at the early stage and blocks mTORC1-dependent autophagosome-lysosome fusion at the late stage during autophagy by disrupting SNARE complex (STX17-SNAP29-VAMP8) formation, resulting in lethal autophagy arrest in OC cells. Furthermore, CTD sensitizes OC cells to cisplatin (CDDP) by blocking CDDP-induced autophagy both in vitro and in vivo. Together, our data provide novel mechanistic insights into CTD-induced autophagy arrest and suggest a new autophagy inhibitor for effective treatment of OC.

HTT (huntingtin) and RAB7 co-migrate retrogradely on a signaling LAMP1-containing late endosome during axonal injury

ABBREVIATIONS

Atg5: Autophagy-related 5; Atg8a: Autophagy-related 8a; AL: autolysosome; AP: autophagosome; BAF1: bafilomycin A1; BDNF: brain derived neurotrophic factor; BMP: bone morphogenetic protein; Cyt-c-p: Cytochrome c proximal; CQ: chloroquine; DCTN1: dynactin 1; Dhc: dynein heavy chain; EE: early endosome; DYNC1I1: dynein cytoplasmic 1 intermediate chain 1; HD: Huntington disease; HIP1/Hip1: huntingtin interacting protein 1; HTT/htt: huntingtin; iNeuron: iPSC-derived human neurons; IP: immunoprecipitation; Khc: kinesin heavy chain; KIF5C: kinesin family member 5C; LAMP1/Lamp1: lysosomal associated membrane protein 1; LE: late endosome; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MAP3K12/DLK: mitogen-activated protein kinase kinase kinase 12; MAPK8/JNK/bsk: mitogen-activated protein kinase 8/basket; MAPK8IP3/JIP3: mitogen-activated protein kinase 8 interacting protein 3; NGF: nerve growth factor; NMJ: neuromuscular junction; NTRK1/TRKA: neurotrophic receptor tyrosine kinase 1; NRTK2/TRKB: neurotrophic receptor tyrosine kinase 2; nuf: nuclear fallout; PG: phagophore; PtdIns3P: phosphatidylinositol-3-phosphate; puc: puckered; ref(2)P: refractory to sigma P; Rilpl: Rab interacting lysosomal protein like; Rip11: Rab11 interacting protein; RTN1: reticulon 1; syd: sunday driver; SYP: synaptophysin; SYT1/Syt1: synaptotagmin 1; STX17/Syx17: syntaxin 17; tkv: thickveins; VF: vesicle fraction; wit: wishful thinking; wnd: wallenda.

Azithromycin, a potent autophagy inhibitor for cancer therapy, perturbs cytoskeletal protein dynamics

BACKGROUND

Autophagy plays an important role in tumour cell growth and survival and also promotes resistance to chemotherapy. Hence, autophagy has been targeted for cancer therapy. We previously reported that macrolide antibiotics including azithromycin (AZM) inhibit autophagy in various types of cancer cells in vitro. However, the underlying molecular mechanism for autophagy inhibition remains unclear. Here, we aimed to identify the molecular target of AZM for inhibiting autophagy.

METHODS

We identified the AZM-binding proteins using AZM-conjugated magnetic nanobeads for high-throughput affinity purification. Autophagy inhibitory mechanism of AZM was analysed by confocal microscopic and transmission electron microscopic observation. The anti-tumour effect with autophagy inhibition by oral AZM administration was assessed in the xenografted mice model.

RESULTS

We elucidated that keratin-18 (KRT18) and α/β-tubulin specifically bind to AZM. Treatment of the cells with AZM disrupts intracellular KRT18 dynamics, and KRT18 knockdown resulted in autophagy inhibition. Additionally, AZM treatment suppresses intracellular lysosomal trafficking along the microtubules for blocking autophagic flux. Oral AZM administration suppressed tumour growth while inhibiting autophagy in tumour tissue.

CONCLUSIONS

As drug-repurposing, our results indicate that AZM is a potent autophagy inhibitor for cancer treatment, which acts by directly interacting with cytoskeletal proteins and perturbing their dynamics.

An affinity-directed phosphatase, AdPhosphatase, system for targeted protein dephosphorylation

Reversible protein phosphorylation, catalyzed by protein kinases and phosphatases, is a fundamental process that controls protein function and intracellular signaling. Failure of phospho-control accounts for many human diseases. While a kinase phosphorylates multiple substrates, a substrate is often phosphorylated by multiple kinases. This renders phospho-control at the substrate level challenging, as it requires inhibition of multiple kinases, which would thus affect other kinase substrates. Here, we describe the development and application of the affinity-directed phosphatase (AdPhosphatase) system for targeted dephosphorylation of specific phospho-substrates. By deploying the Protein Phosphatase 1 or 2A catalytic subunits conjugated to an antigen-stabilized anti-GFP nanobody, we can promote the dephosphorylation of two independent phospho-proteins, FAM83D or ULK1, knocked in with GFP-tags using CRISPR-Cas9, with exquisite specificity. By redirecting protein phosphatases to neo-substrates through nanobody-mediated proximity, AdPhosphatase can alter the phospho-status and function of target proteins and thus, offers a new modality for potential drug discovery approaches.

Nucleic acid uptake occurs independent of lysosomal acidification but dependent on ATP consumption during RNautophagy/DNautophagy

RNautophagy/DNautophagy (RDA) is an autophagic process that refers to the direct uptake of nucleic acids by lysosomes for degradation. Autophagy relies on lysosomes and lysosomal acidification is crucial for the degradation of intracellular components. However, whether lysosomal acidification interferes with nucleic acid uptake during RDA is unclear. In this study, we focused on vacuolar H⁺-ATPase (V-ATPase), the major proton pump responsible for maintaining an acidic pH in lysosomes. Our results show that lysosomes take up nucleic acids independently of the intralysosomal acidic pH during RDA. Isolated lysosomes treated with bafilomycin A1, a potent V-ATPase inhibitor, did not degrade, but took up RNA at similar levels as the control lysosomes. Similarly, the knockdown of Atp6v1a, the gene that encodes V-ATPase catalytic subunit A, did not affect the RNA uptake ability of isolated lysosomes. In addition, we demonstrated that nucleic acid uptake by isolated lysosomes necessitates ATP consumption, although V-ATPase is not required for the uptake process. These results broaden our understanding of the mechanisms underlying nucleic acid degradation via autophagy.

ULK1-mediated phosphorylation regulates the conserved role of YKT6 in autophagy

Autophagy is a catabolic process during which cytosolic material is enwrapped in a newly formed double-membrane structure called the autophagosome, and subsequently targeted for degradation in the lytic compartment of the cell. The fusion of autophagosomes with the lytic compartment is a tightly regulated step and involves membrane-bound SNARE proteins. These play a crucial role as they promote lipid mixing and fusion of the opposing membranes. Among the SNARE proteins implicated in autophagy, the essential SNARE protein YKT6 is the only SNARE protein that is evolutionarily conserved from yeast to humans. Here, we show that alterations in YKT6 function, in both mammalian cells and nematodes, produce early and late autophagy defects that result in reduced survival. Moreover, mammalian autophagosomal YKT6 is phospho-regulated by the ULK1 kinase, preventing premature bundling with the lysosomal SNARE proteins and thereby inhibiting autophagosome-lysosome fusion. Together, our findings reveal that timely regulation of the YKT6 phosphorylation status is crucial throughout autophagy progression and cell survival.

Cellular Uptake and Transport Mechanism of 6-Mercaptopurine Nanomedicines for Enhanced Oral Bioavailability

Background

Nanomedicines have significant advantages in enhancing the oral bioavailability of drugs, but a deeper understanding of the underlying mechanisms remains to be interpreted. Hence, the present study aims to explain the uptake and trafficking mechanism for 6-MP nanomedicines we previously constructed.

Methods

6-MP loaded poly(lactide-co-glycolide) (PLGA) nanomedicines (6-MPNs) were prepared by the multiple emulsion method. The transcytosis mechanism of 6-MPNs was investigated in Caco-2 cells, Caco-2 monolayers, follicle associated epithelium (FAE) monolayers and rats, including transmembrane pathway, intracellular trafficking, paracellular transport and the involvement of transporter.

Results

Pharmacokinetics in rats showed that the area under the curve (AUC) of 6-MP in the 6-MPNs group (147.3 ± 42.89 μg/L·h) was significantly higher than that in the 6-MP suspensions (6-MPCs) group (70.31 ± 18.24 μg/L·h). The uptake of 6-MPNs in Caco-2 cells was time-, concentration- and energy-dependent. The endocytosis of intact 6-MPNs was mediated mainly through caveolae/lipid raft, caveolin and micropinocytosis. The intracellular trafficking of 6-MPNs was affected by endoplasmic reticulum (ER)-Golgi complexes, late endosome-lysosome and microtubules. The multidrug resistance associated protein 4 (MRP4) transporter-mediated transport of free 6-MP played a vital role on the transmembrane of 6-MPNs. The trafficking of 6-MPNs from the apical (AP) side to the basolateral (BL) side in Caco-2 monolayers was obviously improved. Besides, 6-MPNs affected the distribution and expression of zona occludens-1 (ZO-1). The transport of 6-MPNs in FAE monolayers was concentration- and energy-dependent, while reaching saturation over time. 6-MPNs improved the absorption of the intestinal Peyer's patches (PPs) in rats.

Conclusion

6-MPNs improve the oral bioavailability through multiple pathways, including active transport, paracellular transport, lymphatic delivery and MRP4 transporter. The findings of current study may shed light on the cellular uptake and transcellular trafficking mechanism of oral nanomedicines.

Celastrol directly binds with VAMP7 and RAB7 to inhibit autophagy and induce apoptosis in preadipocytes

Obesity is one of the most prevalent chronic metabolic diseases, and induction of apoptosis in preadipocytes and adipocytes is a potential strategy to treat obesity. Celastrol represents one of the most robust anti-obesity phytochemicals so far, yet its direct binding target remains elusive. Here, we determined that celastrol could induce apoptosis in preadipocytes via mitochondrial mediated pathway. Further study clarified that celastrol inhibited the fusion of autophagosome and lysosome to prohibit autophagy, leading to cell apoptosis. By conducting virtual screening and genetic manipulation, we verified that overexpression of VAMP7 and RAB7 could block the effects of celastrol on inhibiting autophagy and inducing apoptosis. The Surface Plasmon Resonance study confirmed the direct binding of celastrol with VAMP7 and RAB7. The functional study illustrated the inhibition of RAB7 GTPase activity after celastrol treatment. Moreover, celastrol induced comparable apoptosis in murine epididymal adipose tissue, human preadipocytes and adipocytes, but not in human hepatocytes. An inhibitory effect on differentiation of human primary visceral preadipocytes was also observed. In conclusion, celastrol exhibited inhibitory effect of autophagy via direct binding with VAMP7 and RAB7, leading to an increase in preadipocytes apoptosis. These results advance our understanding in the potential application of celastrol in treating obesity.

Ursolic Acid Impairs Cellular Lipid Homeostasis and Lysosomal Membrane Integrity in Breast Carcinoma Cells

Cancer is one of the leading causes of death worldwide, thus the search for new cancer therapies is of utmost importance. Ursolic acid is a naturally occurring pentacyclic triterpene with a wide range of pharmacological activities including anti-inflammatory and anti-neoplastic effects. The latter has been assigned to its ability to promote apoptosis and inhibit cancer cell proliferation by poorly defined mechanisms. In this report, we identify lysosomes as the essential targets of the anti-cancer activity of ursolic acid. The treatment of MCF7 breast cancer cells with ursolic acid elevates lysosomal pH, alters the cellular lipid profile, and causes lysosomal membrane permeabilization and leakage of lysosomal enzymes into the cytosol. Lysosomal membrane permeabilization precedes the essential hallmarks of apoptosis placing it as an initial event in the cascade of effects induced by ursolic acid. The disruption of the lysosomal function impairs the autophagic pathway and likely partakes in the mechanism by which ursolic acid kills cancer cells. Furthermore, we find that combining treatment with ursolic acid and cationic amphiphilic drugs can significantly enhance the degree of lysosomal membrane permeabilization and cell death in breast cancer cells.

Intracellular cholesterol transport inhibition Impairs autophagy flux by decreasing autophagosome-lysosome fusion

BACKGROUND

Autophagy is an intracellular degradation process crucial for homeostasis. During autophagy, a double-membrane autophagosome fuses with lysosome through SNARE machinery STX17 to form autolysosome for degradation of damaged organelle. Whereas defective autophagy enhances cholesterol accumulation in the lysosome and impaired autophagic flux that results Niemann-Pick type C1 (NPC1) disease. However, exact interconnection between NPC1 and autophagic flux remain obscure due to the existence of controversial reports.

RESULTS

This study aimed at a comparison of the effects of three autophagic inhibitor drugs, including chloroquine, U18666A, and bafilomycin A1, on the intracellular cholesterol transport and autophagy flux. Chloroquine, an autophagic flux inhibitor; U1866A, a NPC1 inhibitor, and bafilomycin A, a lysosomotropic agent are well known to inhibit autophagy by different mechanism. Here we showed that treatment with U1866A and bafilomycin A induces lysosomal cholesterol accumulation that prevented autophagic flux by decreasing autophagosome-lysosome fusion. We also demonstrated that accumulation of cholesterol within the lysosome did not affect lysosomal pH. Although the clearance of accumulated cholesterol by cyclodextrin restored the defective autophagosome-lysosome fusion, the autophagy flux restoration was possible only when lysosomal acidification was not altered. In addition, a failure of STX17 trafficking to autophagosomes plays a key role in prevention of autophagy flux caused by intracellular cholesterol transport inhibitors.

CONCLUSIONS

Our data provide a new insight that the impaired autophagy flux does not necessarily result in lysosomal cholesterol accumulation even though it prevents autophagosome-lysosome fusion. Video abstract.

YAP promotes cell-autonomous immune responses to tackle intracellular Staphylococcus aureus in vitro

Transcriptional cofactors YAP/TAZ have recently been found to support autophagy and inflammation, which are part of cell-autonomous immunity and are critical in antibacterial defense. Here, we studied the role of YAP against Staphylococcus aureus using CRISPR/Cas9-mutated HEK293 cells and a primary cell-based organoid model. We found that S. aureus infection increases YAP transcriptional activity, which is required to reduce intracellular S. aureus replication. A 770-gene targeted transcriptomic analysis revealed that YAP upregulates genes involved in autophagy/lysosome and inflammation pathways in both infected and uninfected conditions. The YAP-TEAD transcriptional activity promotes autophagic flux and lysosomal acidification, which are then important for defense against intracellular S. aureus. Furthermore, the staphylococcal toxin C3 exoenzyme EDIN-B was found effective in preventing YAP-mediated cell-autonomous immune response. This study provides key insights on the anti-S. aureus activity of YAP, which could be conserved for defense against other intracellular bacteria.

Convergence of secretory, endosomal, and autophagic routes in trans-Golgi-associated lysosomes

At the trans-Golgi, complex traffic connections exist to the endolysosomal system additional to the main Golgi-to-plasma membrane secretory route. Here, we investigated three hits in a Drosophila screen displaying secretory cargo accumulation in autophagic vesicles: ESCRT-III component Vps20, SNARE-binding Rop, and lysosomal pump subunit VhaPPA1-1. We found that Vps20, Rop, and lysosomal markers localize near the trans-Golgi. Furthermore, we document that the vicinity of the trans-Golgi is the main cellular location for lysosomes and that early, late, and recycling endosomes associate as well with a trans-Golgi-associated degradative compartment where basal microautophagy of secretory cargo and other materials occurs. Disruption of this compartment causes cargo accumulation in our hits, including Munc18 homolog Rop, required with Syx1 and Syx4 for Rab11-mediated endosomal recycling. Finally, besides basal microautophagy, we show that the trans-Golgi-associated degradative compartment contributes to the growth of autophagic vesicles in developmental and starvation-induced macroautophagy. Our results argue that the fly trans-Golgi is the gravitational center of the whole endomembrane system.

Resolving subcellular pH with a quantitative fluorescent lifetime biosensor

Changes in sub-cellular pH play a key role in metabolism, membrane transport, and triggering cargo release from therapeutic delivery systems. Most methods to measure pH rely on intensity changes of pH sensitive fluorophores, however, these measurements are hampered by high uncertainty in the inferred pH and the need for multiple fluorophores. To address this, here we combine pH dependant fluorescent lifetime imaging microscopy (pHLIM) with deep learning to accurately quantify sub-cellular pH in individual vesicles. We engineer the pH sensitive protein mApple to localise in the cytosol, endosomes, and lysosomes, and demonstrate that pHLIM can rapidly detect pH changes induced by drugs such as bafilomycin A1 and chloroquine. We also demonstrate that polyethylenimine (a common transfection reagent) does not exhibit a proton sponge effect and had no measurable impact on the pH of endocytic vesicles. pHLIM is a simple and quantitative method that will help to understand drug action and disease progression.

Measuring sub-cellular pH with high accuracy and spatiotemporal resolution remains challenging. Here, Johnston and co-workers develop a pH biosensor that combines the pH dependant fluorescent lifetime of mApple with deep learning to accurately determine sub-cellular pH in individual vesicles.

Autophagy in health and disease: From molecular mechanisms to therapeutic target

Macroautophagy/autophagy is an evolutionally conserved catabolic process in which cytosolic contents, such as aggregated proteins, dysfunctional organelle, or invading pathogens, are sequestered by the double‐membrane structure termed autophagosome and delivered to lysosome for degradation. Over the past two decades, autophagy has been extensively studied, from the molecular mechanisms, biological functions, implications in various human diseases, to development of autophagy‐related therapeutics. This review will focus on the latest development of autophagy research, covering molecular mechanisms in control of autophagosome biogenesis and autophagosome–lysosome fusion, and the upstream regulatory pathways including the AMPK and MTORC1 pathways. We will also provide a systematic discussion on the implication of autophagy in various human diseases, including cancer, neurodegenerative disorders (Alzheimer disease, Parkinson disease, Huntington's disease, and Amyotrophic lateral sclerosis), metabolic diseases (obesity and diabetes), viral infection especially SARS‐Cov‐2 and COVID‐19, cardiovascular diseases (cardiac ischemia/reperfusion and cardiomyopathy), and aging. Finally, we will also summarize the development of pharmacological agents that have therapeutic potential for clinical applications via targeting the autophagy pathway. It is believed that decades of hard work on autophagy research is eventually to bring real and tangible benefits for improvement of human health and control of human diseases.