Phospholipids in Autophagosome Formation and Fusion

Getting Grip on Phosphorus: Potential of Microalgae as a Vehicle for Sustainable Usage of This Macronutrient

Phosphorus (P) is an important and irreplaceable macronutrient. It is central to energy and information storage and exchange in living cells. P is an element with a "broken geochemical cycle" since it lacks abundant volatile compounds capable of closing the P cycle. P fertilizers are critical for global food security, but the reserves of minable P are scarce and non-evenly distributed between countries of the world. Accordingly, the risks of global crisis due to limited access to P reserves are expected to be graver than those entailed by competition for fossil hydrocarbons. Paradoxically, despite the scarcity and value of P reserves, its usage is extremely inefficient: the current waste rate reaches 80% giving rise to a plethora of unwanted consequences such as eutrophication leading to harmful algal blooms. Microalgal biotechnology is a promising solution to tackle this challenge. The proposed review briefly presents the relevant aspects of microalgal P metabolism such as cell P reserve composition and turnover, and the regulation of P uptake kinetics for maximization of P uptake efficiency with a focus on novel knowledge. The multifaceted role of polyPhosphates, the largest cell depot for P, is discussed with emphasis on the P toxicity mediated by short-chain polyPhosphates. Opportunities and hurdles of P bioremoval via P uptake from waste streams with microalgal cultures, either suspended or immobilized, are discussed. Possible avenues of P-rich microalgal biomass such as biofertilizer production or extraction of valuable polyPhosphates and other bioproducts are considered. The review concludes with a comprehensive assessment of the current potential of microalgal biotechnology for ensuring the sustainable usage of phosphorus.

Abemaciclib and Vacuolin-1 decrease aggregate-prone TDP-43 accumulation by accelerating autophagic flux

(Macro)autophagy is a cellular degradation system for unnecessary materials, such as aggregate-prone TDP-43, a central molecule in neurodegenerative diseases including amyotrophic lateral sclerosis and frontotemporal lobar degeneration. Abemaciclib (Abe) and vacuolin-1 (Vac) treatments are known to induce vacuoles characterized by an autophagosome and a lysosome component, suggesting that they facilitate autophagosome-lysosome fusion. However, it remains unknown whether Abe and Vac suppress the accumulation of aggregate-prone TDP-43 by accelerating autophagic flux. In the present study, the Abe and Vac treatment dose-dependently reduced the GFP/RFP ratio in SH-SY5Y neuroblastoma cells stably expressing the autophagic flux marker GFP-LC3-RFP-LC3ΔG. Abe and Vac also increased the omegasome marker GFP-ATG13 signal and the autophagosome marker mCherry-LC3 localized to the lysosome marker LAMP1-GFP. The Abe and Vac treatment decreased the intracellular level of the lysosome marker LAMP1-GFP in SH-SY5Y cells stably expressing LAMP1-GFP, but did not increase the levels of LAMP1-GFP, the autophagosome marker LC3-II, or the multivesicular body marker TSG101 in the extracellular vesicle-enriched fraction. Moreover, Abe and Vac treatment autophagy-dependently inhibited GFP-tagged aggregate-prone TDP-43 accumulation. The results of a PI(3)P reporter assay using the fluorescent protein tagged-2 × FYVE and LAMP1-GFP indicated that Abe and Vac increased the intensity of the PI(3)P signal on lysosomes. A treatment with the VPS34 inhibitor wortmannin (WM) suppressed Abe-/Vac-facilitated autophagic flux and the degradation of GFP-tagged aggregate-prone TDP-43. Collectively, these results suggest that Abe and Vac degrade aggregate-prone TDP-43 by accelerating autophagosome formation and autophagosome-lysosome fusion through the formation of PI(3)P.

Targeting autophagy drug discovery: Targets, indications and development trends

Autophagy plays a vital role in sustaining cellular homeostasis and its alterations have been implicated in the etiology of many diseases. Drugs development targeting autophagy began decades ago and hundreds of agents were developed, some of which are licensed for the clinical usage. However, no existing intervention specifically aimed at modulating autophagy is available. The obstacles that prevent drug developments come from the complexity of the actual impact of autophagy regulators in disease scenarios. With the development and application of new technologies, several promising categories of compounds for autophagy-based therapy have emerged in recent years. In this paper, the autophagy-targeted drugs based on their targets at various hierarchical sites of the autophagic signaling network, e.g., the upstream and downstream of the autophagosome and the autophagic components with enzyme activities are reviewed and analyzed respectively, with special attention paid to those at preclinical or clinical trials. The drugs tailored to specific autophagy alone and combination with drugs/adjuvant therapies widely used in clinical for various diseases treatments are also emphasized. The emerging drug design and development targeting selective autophagy receptors (SARs) and their related proteins, which would be expected to arrest or reverse the progression of disease in various cancers, inflammation, neurodegeneration, and metabolic disorders, are critically reviewed. And the challenges and perspective in clinically developing autophagy-targeted drugs and possible combinations with other medicine are considered in the review.

GRAF1 Acts as a Downstream Mediator of Parkin to Regulate Mitophagy in Cardiomyocytes

Cardiomyocytes rely on proper mitochondrial homeostasis to maintain contractility and achieve optimal cardiac performance. Mitochondrial homeostasis is controlled by mitochondrial fission, fusion, and mitochondrial autophagy (mitophagy). Mitophagy plays a particularly important role in promoting the degradation of dysfunctional mitochondria in terminally differentiated cells. However, the precise mechanisms by which this is achieved in cardiomyocytes remain opaque. Our study identifies GRAF1 as an important mediator in PINK1-Parkin pathway-dependent mitophagy. Depletion of GRAF1 (Arhgap26) in cardiomyocytes results in actin remodeling defects, suboptimal mitochondria clustering, and clearance. Mechanistically, GRAF1 promotes Parkin-LC3 complex formation and directs autophagosomes to damaged mitochondria. Herein, we found that these functions are regulated, at least in part, by the direct binding of GRAF1 to phosphoinositides (PI(3)P, PI(4)P, and PI(5)P) on autophagosomes. In addition, PINK1-dependent phosphorylation of Parkin promotes Parkin-GRAF1-LC3 complex formation, and PINK1-dependent phosphorylation of GRAF1 (on S668 and S671) facilitates the clustering and clearance of mitochondria. Herein, we developed new phosphor-specific antibodies to these sites and showed that these post-translational modifications are differentially modified in human hypertrophic cardiomyopathy and dilated cardiomyopathy. Furthermore, our metabolic studies using serum collected from isoproterenol-treated WT and GRAF1CKO mice revealed defects in mitophagy-dependent cardiomyocyte fuel flexibility that have widespread impacts on systemic metabolism. In summary, our study reveals that GRAF1 co-regulates actin and membrane dynamics to promote cardiomyocyte mitophagy and that dysregulation of GRAF1 post-translational modifications may underlie cardiac disease pathogenesis.

Tolerability and Effects of 2-Aminoethyl Dihydrogen Phosphate in Dogs With Mast Cell Tumors

Canine mast cell tumor is a malignant neoplasm, and a gold standard treatment remains to be determined despite the proposed chemotherapies or other therapies in dogs. This study aimed to determine therapeutic, adverse effects and toxicity, tumor-free, and overall survival times of 10 dogs with surgically excised mast cell tumors evaluated by histopathological/immunohistochemistry and treated with four weekly intravenous administrations of 2-Aminoethyl Dihydrogen Phosphate (70 mg/kg) as adjuvant therapy. No adverse events were noted. Laboratory changes were limited (p < 0.05) in red blood cell, hemoglobin, and platelet counts. Mean tumor-free and overall survival were 599.1 ± 469 and 755.5 ± 423.5 days, respectively. In conclusion, 2-Aminoethyl Dihydrogen Phosphate administration was safe in dogs. However, 2-Aminoethyl Dihydrogen Phosphate was not sufficiently effective to prevent a recurrence, new tumor, or metastasis of canine mast cell tumors with poor immunohistochemical prognostic factors.

Adipocytes Promote Breast Cancer Cell Survival and Migration through Autophagy Activation

Simple Summary

Breast tumours are in direct contact with the adipose tissue of the mammary gland. Although the interactions between breast cancer cells and adipocytes that secrete tumour-promoting factors are well known, the molecular mechanisms remain under investigation. The aim of our study was to understand whether and how adipocytes regulate a cell-recycling pathway in breast cancer cells—autophagy. We show that adipocytes promote autophagy in breast cancer cells through the acidification of lysosomes, leading to cancer cell survival in nutrient-deprived conditions and to cancer cell migration. In this study, we have identified a new mechanism, which can link adipose tissue with breast cancer progression.

Abstract

White adipose tissue interacts closely with breast cancers through the secretion of soluble factors such as cytokines, growth factors or fatty acids. However, the molecular mechanisms of these interactions and their roles in cancer progression remain poorly understood. In this study, we investigated the role of fatty acids in the cooperation between adipocytes and breast cancer cells using a co-culture model. We report that adipocytes increase autophagy in breast cancer cells through the acidification of lysosomes, leading to cancer cell survival in nutrient-deprived conditions and to cancer cell migration. Mechanistically, the disturbance of membrane phospholipid composition with a decrease in arachidonic acid content is responsible for autophagy activation in breast cancer cells induced by adipocytes. Therefore, autophagy might be a central cellular mechanism of white adipose tissue interactions with cancer cells and thus participate in cancer progression.

Targeting autophagy in disease: established and new strategies

Macroautophagy/autophagy is an evolutionarily conserved pathway responsible for clearing cytosolic aggregated proteins, damaged organelles or invading microorganisms. Dysfunctional autophagy leads to pathological accumulation of the cargo, which has been linked to a range of human diseases, including neurodegenerative diseases, infectious and autoimmune diseases and various forms of cancer. Cumulative work in animal models, application of genetic tools and pharmacologically active compounds, has suggested the potential therapeutic value of autophagy modulation in disease, as diverse as Huntington, Salmonella infection, or pancreatic cancer. Autophagy activation versus inhibition strategies are being explored, while the role of autophagy in pathophysiology is being studied in parallel. However, the progress of preclinical and clinical development of autophagy modulators has been greatly hampered by the paucity of selective pharmacological agents and biomarkers to dissect their precise impact on various forms of autophagy and cellular responses. Here, we summarize established and new strategies in autophagy-related drug discovery and indicate a path toward establishing a more efficient discovery of autophagy-selective pharmacological agents. With this knowledge at hand, modern concepts for therapeutic exploitation of autophagy might become more plausible.

Abbreviations: ALS: amyotrophic lateral sclerosis; AMPK: AMP-activated protein kinase; ATG: autophagy-related gene; AUTAC: autophagy-targeting chimera; CNS: central nervous system; CQ: chloroquine; GABARAP: gamma-aminobutyric acid type A receptor-associated protein; HCQ: hydroxychloroquine; LYTAC: lysosome targeting chimera; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MTOR: mechanistic target of rapamycin kinase; NDD: neurodegenerative disease; PDAC: pancreatic ductal adenocarcinoma; PE: phosphatidylethanolamine; PIK3C3/VPS34: phosphatidylinositol 3-kinase catalytic subunit type 3; PtdIns3K: class III phosphatidylinositol 3-kinase; PtdIns3P: phosphatidylinositol 3-phosphate; PROTAC: proteolysis-targeting chimera; SARS-CoV-2: severe acute respiratory syndrome coronavirus 2; SQSTM1/p62: sequestosome 1; ULK1: unc-51 like autophagy activating kinase 1.

Lipophagy and prostate cancer: association with disease aggressiveness and proximity to periprostatic adipose tissue

The prostate gland is surrounded by periprostatic adipose tissue (PPAT), which is believed to play a role in prostate cancer (PCa) progression. Cancer cells can take up lipids from the microenvironment and store them in lipid droplets (LDs). Fatty acids released from LDs are used by PCa cells as preferential metabolic fuels to provide energy and promote cancer progression. Recently, fatty acids have been associated with autophagy, a cellular recycling pathway. Lipophagy is a selective form of autophagy involved in LD degradation, the role of which in PCa progression remains unknown. Here, we explored markers of autophagy and lipophagy in human PCa tissues in correlation with factors of aggressiveness, and we evaluated the influence of PPAT adipocytes on autophagy and lipophagy. We analyzed markers of autophagy (p62, LC3), lipid droplets (PLIN and Oil Red O), androgen receptor (AR), proliferation (Ki67), and epithelial-mesenchymal transition (Zeb1) on 465 PCa samples. Co-cultures of PCa cell lines PC3 and 22RV1 with adipocytes isolated from patients' PPAT were used to analyze the influence of PPAT on autophagy and lipophagy in vitro. In human PCa tissues, we observed a correlation between markers of LD and those of autophagy, which are associated with clinical and biological factors of disease aggressiveness. In addition, PLIN staining was associated with AR expression. In locally advanced PCa, p62, LC3, and PLIN were increased in extraprostatic areas where cancer cells are in contact with PPAT. Co-culture of PCa cell lines with adipocytes decreased autophagy activity and increased LD flux in PC3 cells. These results suggest an active process of lipophagy in PCa, linked to disease aggressiveness, to the proximity of PPAT, and induced in vitro in co-culture with adipocytes. Lipophagy is therefore likely to be a crucial player in PCa progression. © 2021 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Condition-dependent functional shift of two Drosophila Mtmr lipid phosphatases in autophagy control

Myotubularin (MTM) and myotubularin-related (MTMR) lipid phosphatases catalyze the removal of a phosphate group from certain phosphatidylinositol derivatives. Because some of these substrates are required for macroautophagy/autophagy, during which unwanted cytoplasmic constituents are delivered into lysosomes for degradation, MTM and MTMRs function as important regulators of the autophagic process. Despite its physiological and medical significance, the specific role of individual MTMR paralogs in autophagy control remains largely unexplored. Here we examined two Drosophila MTMRs, EDTP and Mtmr6, the fly orthologs of mammalian MTMR14 and MTMR6 to MTMR8, respectively, and found that these enzymes affect the autophagic process in a complex, condition-dependent way. EDTP inhibited basal autophagy, but did not influence stress-induced autophagy. In contrast, Mtmr6 promoted the process under nutrient-rich settings, but effectively blocked its hyperactivation in response to stress. Thus, Mtmr6 is the first identified MTMR phosphatase with dual, antagonistic roles in the regulation of autophagy, and shows conditional antagonism/synergism with EDTP in modulating autophagic breakdown. These results provide a deeper insight into the adjustment of autophagy.

Abbreviations: Atg, autophagy-related; BDSC, Bloomington Drosophila Stock Center; DGRC, Drosophila Genetic Resource Center; EDTP, Egg-derived tyrosine phosphatase; FYVE, zinc finger domain from Fab1 (yeast ortholog of PIKfyve), YOTB, Vac1 (vesicle transport protein) and EEA1 cysteine-rich proteins; LTR, LysoTracker Red; MTM, myotubularin; MTMR, myotubularin-related; PI, phosphatidylinositol; Pi3K59F, Phosphotidylinositol 3 kinase 59F; PtdIns3P, phosphatidylinositol-3-phosphate; PtdIns(3,5)P₂, phosphatidylinositol-3,5-bisphosphate; PtdIns5P, phosphatidylinositol-5-phosphate; ref(2)P, refractory to sigma P; Syx17, Syntaxin 17; TEM, transmission electron microscopy; UAS, upstream activating sequence; Uvrag, UV-resistance associated gene; VDRC, Vienna Drosophila RNAi Center; Vps34, Vacuolar protein sorting 34.

Mechanobiology of Autophagy: The Unexplored Side of Cancer

Proper execution of cellular function, maintenance of cellular homeostasis and cell survival depend on functional integration of cellular processes and correct orchestration of cellular responses to stresses. Cancer transformation is a common negative consequence of mismanagement of coordinated response by the cell. In this scenario, by maintaining the balance among synthesis, degradation, and recycling of cytosolic components including proteins, lipids, and organelles the process of autophagy plays a central role. Several environmental stresses activate autophagy, among those hypoxia, DNA damage, inflammation, and metabolic challenges such as starvation. In addition to these chemical challenges, there is a requirement for cells to cope with mechanical stresses stemming from their microenvironment. Cells accomplish this task by activating an intrinsic mechanical response mediated by cytoskeleton active processes and through mechanosensitive protein complexes which interface the cells with their mechano-environment. Despite autophagy and cell mechanics being known to play crucial transforming roles during oncogenesis and malignant progression their interplay is largely overlooked. In this review, we highlight the role of physical forces in autophagy regulation and their potential implications in both physiological as well as pathological conditions. By taking a mechanical perspective, we wish to stimulate novel questions to further the investigation of the mechanical requirements of autophagy and appreciate the extent to which mechanical signals affect this process.

The relationship between endoplasmic reticulum stress and autophagy in apoptosis of BEAS-2B cells induced by cigarette smoke condensate

Cigarette smoke (CS) is one of the severe risk factors for the development of the pulmonary disease. However, the underlying mechanisms, especially the CS-induced the human bronchial epithelial cells (BEAS-2B) apoptosis related to endoplasmic reticulum stress (ERS) and autophagy, remains to be studied. This study aims to investigate the relationship between ERS and autophagy in apoptosis induced by CS condensate (CSC). BEAS-2B cells were stimulated with 0.02, 0.04 and 0.08 mg/ml CSC for 24 h to detect the ERS, autophagy and apoptosis. Then, ERS and autophagy of BEAS-2B cells were inhibited, respectively, by using 4-PBA and 3-MA, and followed by CSC treatment. The results showed that CSC decreased cell viability, increased cell apoptosis, elevated cleaved-caspase 3/pro-caspase 3 ratio and Bax expressions, but decreased Bcl-2 expressions. The GRP78 and CHOP expressions and LC3-II/LC3-I ratio were dose-dependently increased. The structure of the endoplasmic reticulum was abnormal and the number of autolysosomes was increased in BEAS-2B cells after CSC stimulation. The LC3-II/LC3-I ratio was decreased after ERS inhibition with 4-PBA, but GRP78 and CHOP expressions were enhanced after autophagy inhibition with 3-MA. CSC-induced apoptosis was further increased, Bax expressions and cleaved-caspase 3/pro-caspase 3 ratio were improved, but Bcl-2 expressions were decreased after 3-MA or 4-PBA treatment. In conclusion, the study indicates that ERS may repress apoptosis of BEAS-2B cells induced by CSC via activating autophagy, but autophagy relieves ERS in a negative feedback. This study provides better understanding and experimental support on the underlying mechanisms of pulmonary disease stimulated by CS.

Pancreas-specific SNAP23 depletion prevents pancreatitis by attenuating pathological basolateral exocytosis and formation of trypsin-activating autolysosomes

Intrapancreatic trypsin activation by dysregulated macroautophagy/autophagy and pathological exocytosis of zymogen granules (ZGs), along with activation of inhibitor of NFKB/NF-κB kinase (IKK) are necessary early cellular events in pancreatitis. How these three pancreatitis events are linked is unclear. We investigated how SNAP23 orchestrates these events leading to pancreatic acinar injury. SNAP23 depletion was by knockdown (SNAP23-KD) effected by adenovirus-shRNA (Ad-SNAP23-shRNA/mCherry) treatment of rodent and human pancreatic slices and in vivo by infusion into rat pancreatic duct. In vitro pancreatitis induction by supraphysiological cholecystokinin (CCK) or ethanol plus low-dose CCK were used to assess SNAP23-KD effects on exocytosis and autophagy. Pancreatitis stimuli resulted in SNAP23 translocation from its native location at the plasma membrane to autophagosomes, where SNAP23 would bind and regulate STX17 (syntaxin17) SNARE complex-mediated autophagosome-lysosome fusion. This SNAP23 relocation was attributed to IKBKB/IKKβ-mediated SNAP23 phosphorylation at Ser95 Ser120 in rat and Ser120 in human, which was blocked by IKBKB/IKKβ inhibitors, and confirmed by the inability of IKBKB/IKKβ phosphorylation-disabled SNAP23 mutant (Ser95A Ser120A) to bind STX17 SNARE complex. SNAP23-KD impaired the assembly of STX4-driven basolateral exocytotic SNARE complex and STX17-driven SNARE complex, causing respective reduction of basolateral exocytosis of ZGs and autolysosome formation, with consequent reduction in trypsinogen activation in both compartments. Consequently, pancreatic SNAP23-KD rats were protected from caerulein and alcoholic pancreatitis. This study revealed the roles of SNAP23 in mediating pathological basolateral exocytosis and IKBKB/IKKβ's involvement in autolysosome formation, both where trypsinogen activation would occur to cause pancreatitis. SNAP23 is a strong candidate to target for pancreatitis therapy.

AGXT2L1 is downregulated in carcinomas of the digestive system

Alanine-glyoxylate aminotransferase 2-like 1 (AGXT2L1) is a modulator of phospholipid metabolism, and its role in tumor biology is obscure. Previously, significant downregulation of AGXT2L1 has been observed in hepatocellular carcinoma. The aim of the present study was to investigate AGXT2L1 expression and its association with the clinical characteristics of common carcinomas of the digestive system. In the present study, the expression levels of AGXT2L1 were detected by immunohistochemical staining in colorectal cancer (CRC), gastric cancer and pancreatic cancer tissues. The associations between AGXT2L1 expression and clinicopathological features were analyzed using public gene expression datasets. Small interfering RNA was transfected into SW480 and HCT116 cells to explore the role of AGXT2L1 in CRC cells. AGXT2L1 expression was significantly decreased in cancerous tissues compared with in normal tissues, and low AGXT2L1 expression was associated with an unfavorable prognosis in patients. Furthermore, it was revealed that AGXT2L1 may regulate phosphatidylinositol and phosphatidylserine metabolism in cancerous tissues, and that decreased AGXT2L1 expression could induce autophagy in CRC cells. Overall, the present study provides a basis for further understanding of the role of AGXT2L1 and its association with autophagy in cancer.

Autophagy in Neurodegenerative Diseases: A Hunter for Aggregates

Cells have developed elaborate quality-control mechanisms for proteins and organelles to maintain cellular homeostasis. Such quality-control mechanisms are maintained by conformational folding via molecular chaperones and by degradation through the ubiquitin-proteasome or autophagy-lysosome system. Accumulating evidence suggests that impaired autophagy contributes to the accumulation of intracellular inclusion bodies consisting of misfolded proteins, which is a hallmark of most neurodegenerative diseases. In addition, genetic mutations in core autophagy-related genes have been reported to be linked to neurodegenerative diseases, such as Alzheimer’s disease, Parkinson’s disease, and Huntington’s disease. Conversely, the pathogenic proteins, such as amyloid β and α-synuclein, are detrimental to the autophagy pathway. Here, we review the recent advances in understanding the relationship between autophagic defects and the pathogenesis of neurodegenerative diseases and suggest autophagy induction as a promising strategy for the treatment of these conditions.

Mechanisms governing autophagosome biogenesis

Autophagosomes are double-membrane vesicles newly formed during autophagy to engulf a wide range of intracellular material and transport this autophagic cargo to lysosomes (or vacuoles in yeasts and plants) for subsequent degradation. Autophagosome biogenesis responds to a plethora of signals and involves unique and dynamic membrane processes. Autophagy is an important cellular mechanism allowing the cell to meet various demands, and its disruption compromises homeostasis and leads to various diseases, including metabolic disorders, neurodegeneration and cancer. Thus, not surprisingly, the elucidation of the molecular mechanisms governing autophagosome biogenesis has attracted considerable interest. Key molecules and organelles involved in autophagosome biogenesis, including autophagy-related (ATG) proteins and the endoplasmic reticulum, have been discovered, and their roles and relationships have been investigated intensely. However, several fundamental questions, such as what supplies membranes/lipids to build the autophagosome and how the membrane nucleates, expands, bends into a spherical shape and finally closes, have proven difficult to address. Nonetheless, owing to recent studies with new approaches and technologies, we have begun to unveil the mechanisms underlying these processes on a molecular level. We now know that autophagosome biogenesis is a highly complex process, in which multiple proteins and lipids from various membrane sources, supported by the formation of membrane contact sites, cooperate with biophysical phenomena, including membrane shaping and liquid-liquid phase separation, to ensure seamless segregation of the autophagic cargo. Together, these studies pave the way to obtaining a holistic view of autophagosome biogenesis.

The Fusarium mycotoxin, 2-Amino-14,16-dimethyloctadecan-3-ol (AOD) induces vacuolization in HepG2 cells

The mycotoxin 2-Amino-14,16-dimethyloctadecan-3-ol (AOD) has been isolated from cultures of the fungus Fusarium avenaceum, one of the most prevalent Fusarium species. AOD is an analogue of sphinganine and 1-deoxysphinganine, important intermediates in the de novo biosynthesis of cellular sphingolipids. Here we studied cellular effects of AOD using the human liver cell line HepG2 as a model system. AOD (10 μM) induced a transient accumulation of vacuoles in the cells. The effect was observed at non-cytotoxic concentrations and was not linked to cell death processes. Proteomic analyses indicated that protein degradation and/or vesicular transport may be a target for AOD. Further studies revealed that AOD had only minor effects on the initiation rate of macropinocytosis and autophagy. However, the AOD-induced vacuoles were lysosomal-associated membrane protein-1 (LAMP-1) positive, suggesting that they most likely originate from lysosomes or late endosomes. Accordingly, both endosomal and autophagic protein degradation were inhibited. Further studies revealed that treatment with concanamycin A or chloroquine completely blocked the AOD-induced vacuolization, suggesting that the vacuolization is dependent of acidic lysosomes. Overall, the results strongly suggest that the increased vacuolization is due to an accumulation of AOD in lysosomes or late endosomes thereby disturbing the later stages of the endolysosomal process.

The Nootropic Drug Α-Glyceryl-Phosphoryl-Ethanolamine Exerts Neuroprotective Effects in Human Hippocampal Cells

Brain aging involves changes in the lipid membrane composition that lead to a decrease in membrane excitability and neurotransmitter release. These membrane modifications have been identified as contributing factors in age-related memory decline. In this sense, precursors of phospholipids (PLs) can restore the physiological composition of cellular membranes and produce valuable therapeutic effects in brain aging. Among promising drugs, alpha-glycerylphosphorylethanolamine (GPE) has demonstrated protective effects in amyloid-injured astrocytes and in an aging model of human neural stem cells. However, the compound properties on mature neuronal cells remain unexplored. Herein, GPE was tested in human hippocampal neurons, which are involved in learning and memory, and characterized by a functional cholinergic transmission, thus representing a valuable cellular model to explore the beneficial properties of GPE. GPE induced the release of the main membrane phospholipids and of the acetylcholine neurotransmitter. Moreover, the compound reduced lipid peroxidation and enhanced membrane fluidity of human brain cells. GPE counteracted the DNA damage and viability decrease observed in in vitro aged neurons. Among GPE treatment effects, the autophagy was found positively upregulated. Overall, these results confirm the beneficial effects of GPE treatment and suggest the compound as a promising drug to preserve hippocampal neurons and virtually memory performances.

Lipids and Lipid-Binding Proteins in Selective Autophagy

Eukaryotic cells have the capacity to degrade intracellular components through a lysosomal degradation pathway called macroautophagy (henceforth referred to as autophagy) in which superfluous or damaged cytosolic entities are engulfed and separated from the rest of the cell constituents into double membraned vesicles known as autophagosomes. Autophagosomes then fuse with endosomes and lysosomes, where cargo is broken down into basic building blocks that are released to the cytoplasm for the cell to reuse. Autophagic degradation can target either cytoplasmic material in bulk (non-selective autophagy) or particular cargo in what is called selective autophagy. Proper autophagic turnover requires the orchestrated participation of several players that need to be tightly and temporally coordinated. Whereas a large number of autophagy-related (ATG) proteins have been identified and their functions and regulation are starting to be understood, there is substantially less knowledge regarding the specific lipids constituting the autophagic membranes as well as their role in initiating, enabling or regulating the autophagic process. This review focuses on lipids and their corresponding binding proteins that are crucial in the process of selective autophagy.

Neuroprotective Autophagic Flux Induced by Hyperbaric Oxygen Preconditioning is Mediated by Cystatin C

We have previously reported that Cystatin C (CysC) is a pivotal mediator in the neuroprotection induced by hyperbaric oxygen (HBO) preconditioning; however, the underlying mechanism and how CysC changes after stroke are not clear. In the present study, we demonstrated that CysC expression was elevated as early as 3 h after reperfusion, and this was further enhanced by HBO preconditioning. Concurrently, LC3-II and Beclin-1, two positive-markers for autophagy induction, exhibited increases similar to CysC, while knockdown of CysC blocked these elevations. As a marker of autophagy inhibition, p62 was downregulated by HBO preconditioning and this was blocked by CysC knockdown. Besides, the beneficial effects of preserving lysosomal membrane integrity and enhancing autolysosome formation induced by HBO preconditioning were abolished in CysC^−/− rats. Furthermore, we demonstrated that exogenous CysC reduced the neurological deficits and infarct volume after brain ischemic injury, while 3-methyladenine partially reversed this neuroprotection. In the present study, we showed that CysC is biochemically and morphologically essential for promoting autophagic flux, and highlighted the translational potential of HBO preconditioning and CysC for stroke treatment.

Promoting the clearance of neurotoxic proteins in neurodegenerative disorders of ageing

Neurodegenerative disorders of ageing (NDAs) such as Alzheimer disease, Parkinson disease, frontotemporal dementia, Huntington disease and amyotrophic lateral sclerosis represent a major socio-economic challenge in view of their high prevalence yet poor treatment. They are often called 'proteinopathies' owing to the presence of misfolded and aggregated proteins that lose their physiological roles and acquire neurotoxic properties. One reason underlying the accumulation and spread of oligomeric forms of neurotoxic proteins is insufficient clearance by the autophagic-lysosomal network. Several other clearance pathways are also compromised in NDAs: chaperone-mediated autophagy, the ubiquitin-proteasome system, extracellular clearance by proteases and extrusion into the circulation via the blood-brain barrier and glymphatic system. This article focuses on emerging mechanisms for promoting the clearance of neurotoxic proteins, a strategy that may curtail the onset and slow the progression of NDAs.

Dydrogesterone Causes Male Bias and Accelerates Sperm Maturation in Zebrafish ( Danio rerio)

Synthetic progestins are widely used in human and veterinary medicine. They can enter aquatic environments mainly via wastewater discharge and agricultural runoff, thus affecting fish populations in receiving waters. Here, we investigated the chronic effects of dydrogesterone (DDG) on zebrafish from 21 to 140 days post-fertilization (dpf) at 3.39, 33.1, and 329 ng L^-1. The results showed that the male ratio increased with the exposure concentration, and after 120 days of exposure to 329 ng L^-1, 98% of the fish were males. The DDG exposure during sex differentiation significantly increased the transcription of dmrt1 (1.83-fold) and apoptosis-related genes but suppressed the transcription of cyp19a1a (3.16-fold). Histological analysis showed that the exposure to DDG at 329 ng L^-1 caused 61.5% of mature spermatocytes in males, while the exposure to DDG at 33.1 ng L^-1 resulted in 14.7% of atretic follicles in females. Microarray analysis identified spermatogenesis-related gene ontology (endothelial barrier and immune response) in the testes at all concentrations. Genes from phagosome, lysosome, and sphingolipid metabolism pathways were enriched and could be responsible for sperm maturation. The findings from this study demonstrate that DDG in the aquatic environment can cause male bias and accelerate sperm maturation in zebrafish, resulting in potential high ecological risks to fish populations.

The Lysosome and Intracellular Signalling

In addition to being the terminal degradative compartment of the cell's endocytic and autophagic pathways, the lysosome is a multifunctional signalling hub integrating the cell's response to nutrient status and growth factor/hormone signalling. The cytosolic surface of the limiting membrane of the lysosome is the site of activation of the multiprotein complex mammalian target of rapamycin complex 1 (mTORC1), which phosphorylates numerous cell growth-related substrates, including transcription factor EB (TFEB). Under conditions in which mTORC1 is inhibited including starvation, TFEB becomes dephosphorylated and translocates to the nucleus where it functions as a master regulator of lysosome biogenesis. The signalling role of lysosomes is not limited to this pathway. They act as an intracellular Ca²⁺ store, which can release Ca²⁺ into the cytosol for both local effects on membrane fusion and pleiotropic effects within the cell. The relationship and crosstalk between the lysosomal and endoplasmic reticulum (ER) Ca²⁺ stores play a role in shaping intracellular Ca²⁺ signalling. Lysosomes also perform other signalling functions, which are discussed. Current views of the lysosomal compartment recognize its dynamic nature. It includes endolysosomes, autolysosome and storage lysosomes that are constantly engaged in fusion/fission events and lysosome regeneration. How signalling is affected by individual lysosomal organelles being at different stages of these processes and/or at different sites within the cell is poorly understood, but is discussed.

Scaffolding the cup-shaped double membrane in autophagy

Autophagy is a physiological process for the recycling and degradation of cellular materials. Forming the autophagosome from the phagophore, a cup-shaped double-membrane vesicle, is a critical step in autophagy. The origin of the cup shape of the phagophore is poorly understood. In yeast, fusion of a small number of Atg9-containing vesicles is considered a key step in autophagosome biogenesis, aided by Atg1 complexes (ULK1 in mammals) localized at the preautophagosomal structure (PAS). In particular, the S-shaped Atg17-Atg31-Atg29 subcomplex of Atg1 is critical for phagophore nucleation at the PAS. To study this process, we simulated membrane remodeling processes in the presence and absence of membrane associated Atg17. We show that at least three vesicles need to fuse to induce the phagophore shape, consistent with experimental observations. However, fusion alone is not sufficient. Interactions with 34-nm long, S-shaped Atg17 complexes are required to overcome a substantial kinetic barrier in the transition to the cup-shaped phagophore. Our finding rationalizes the recruitment of Atg17 complexes to the yeast PAS, and their unusual shape. In control simulations without Atg17, with weakly binding Atg17, or with straight instead of S-shaped Atg17, the membrane shape transition did not occur. We confirm the critical role of Atg17-membrane interactions experimentally by showing that mutations of putative membrane interaction sites result in reduction or loss of autophagic activity in yeast. Fusion of a small number of vesicles followed by Atg17-guided membrane shape-remodeling thus emerges as a viable route to phagophore formation.

Phospholipase C δ1 negatively regulates autophagy in colorectal cancer cells

Colorectal cancer (CRC) is one of the leading causes of cancer-related death worldwide. Kirsten rat sarcoma viral oncogene homolog (KRAS) is frequently mutated in CRC, and KRAS mutations promote cell motility, growth, and survival. We previously revealed that the expression of phospholipase C (PLC) δ1, one of the most basal PLCs, is down-regulated in colon adenocarcinoma, and that the KRAS signaling pathway suppresses PLCδ1 expression. Although recent studies revealed that KRAS mutations activate autophagy in cancer cells, a relation between PLCδ1 and autophagy remains unclear. Here, we found that PLCδ1 overexpression suppresses the formation of autophagosomes, which are key structures of autophagy, whereas endogenous PLCδ1 knockdown increases autophagosome formation in CRC cells. We also showed that PLCδ1 overexpression promotes cell death under nutrient deprivation. Furthermore, PLCδ1 overexpression suppresses the autophagy induced by the anti-cancer drug oxaliplatin and promotes cell death under oxaliplatin treatment. These data suggest that PLCδ1 negatively regulates autophagy, and PLCδ1 suppression contributes to the tolerance of CRC cells harboring KRAS mutations to nutrient deprivation and anti-cancer drug treatment.