Inhibition of autophagy with bafilomycin and chloroquine decreases mitochondrial quality and bioenergetic function in primary neurons

Monitoring stress-induced autophagic engulfment and degradation of the 26S proteasome in mammalian cells

Almost 70 years after the discovery of the lysosome, and about four decades following the unraveling of ubiquitin as a specific "mark of death," the field of protein turnover-the numerous processes it regulates, the pathologies resulting from its dysregulation, and the drugs that have been developed to target them-is still growing exponentially. Accordingly, the need for new technologies and methods is ever growing. One interesting question in the field is the mechanism(s) by which the "predators become prey". We have reported recently that the 26S proteasome, the catalytic arm of the ubiquitin system, is degraded by the autophagy-lysosome machinery, in a process requiring specific ubiquitination of the proteasome, and subsequent recognition by the shuttle protein p62/SQSTM1. Studying the modification(s), recognition sites, engulfment, and breakdown of the 26S proteasome via such "proteaphagy" has required the use of microscopy, subcellular fractionation, 'classical biochemistry', and proteomics. In this chapter, we present the essentials of these protocols, with emphasis on the refinements we have introduced in order for them to better suit the particular study of proteaphagy.

Toxicant-mediated redox control of proteostasis in neurodegeneration

Disruption in redox signaling and control of cellular processes has emerged as a key player in many pathologies including neurodegeneration. As protein aggregations are a common hallmark of several neuronal pathologies, a firm understanding of the interplay between redox signaling, oxidative and free radical stress, and proteinopathies is required to sort out the complex mechanisms in these diseases. Fortunately, models of toxicant-induced neurodegeneration can be utilized to evaluate and report mechanistic alterations in the proteostasis network (PN). The epidemiological links between environmental toxicants and neurological disease gives further credence into characterizing the toxicant-mediated PN disruptions observed in these conditions. Reviewed here are examples of mechanistic interaction between oxidative or free radical stress and PN alterations. Additionally, investigations into toxicant-mediated PN disruptions, specifically focusing on environmental metals and pesticides, are discussed. Finally, we emphasize the need to distinguish whether the presence of protein aggregations are contributory to phenotypes related to neurodegeneration, or if they are a byproduct of PN deficiencies.

The Complex Nature of Tupanviruses

The discovery of giant viruses revealed a new level of complexity in the virosphere, raising important questions about the diversity, ecology, and evolution of these viruses. The family Mimiviridae was the first group of amoebal giant viruses to be discovered (by Bernard La Scola and Didier Raoult team), containing viruses with structural and genetic features that challenged many concepts of classic virology. The tupanviruses are among the newest members of this family and exhibit structural, biological, and genetic features never previously observed in other giant viruses. The complexity of these viruses has put us one step forward toward the comprehension of giant virus biology and evolution, but also has raised important questions that still need to be addressed. In this chapter, we tell the history behind the discovery of one of the most complex viruses isolated to date, highlighting the unique features exhibited by tupanviruses, and discuss how these giant viruses have contributed to redefining limits for the virosphere.

Autophagy: A Lysosome-Dependent Process with Implications in Cellular Redox Homeostasis and Human Disease

SIGNIFICANCE

Autophagy, a lysosome-dependent homeostatic process inherent to cells and tissues, has emerging significance in the pathogenesis of human disease. This process enables the degradation and turnover of cytoplasmic substrates via membrane-dependent sequestration in autophagic vesicles (autophagosomes) and subsequent lysosomal delivery of cargo. Recent Advances: Selective forms of autophagy can target specific substrates (e.g., organelles, protein aggregates, and lipids) for processing. Autophagy is highly regulated by oxidative stress, including exposure to altered oxygen tension, by direct and indirect mechanisms, and contributes to inducible defenses against oxidative stress. Mitochondrial autophagy (mitophagy) plays a critical role in the oxidative stress response, through maintenance of mitochondrial integrity.

CRITICAL ISSUES

Autophagy can impact a number of vital cellular processes including inflammation and adaptive immunity, host defense, lipid metabolism and storage, mitochondrial homeostasis, and clearance of aggregated proteins, all which may be of significance in human disease. Autophagy can exert both maladaptive and adaptive roles in disease pathogenesis, which may also be influenced by autophagy impairment. This review highlights the essential roles of autophagy in human diseases, with a focus on diseases in which oxidative stress or inflammation play key roles, including human lung, liver, kidney and heart diseases, metabolic diseases, and diseases of the cardiovascular and neural systems.

FUTURE DIRECTIONS

Investigations that further elucidate the complex role of autophagy in the pathogenesis of disease will facilitate targeting this pathway for therapies in specific diseases.

Lidocaine induces protective autophagy in rat C6 glioma cell line

Malignant glioma is the most common type of brain cancer with poor prognosis. Surgical resection, chemotherapy and radiotherapy are the main therapeutic options; however, in addition to their insufficient efficacy, they are associated with the pain experienced by patients. To relieve pain, local anesthetics, such as lidocaine can be used. In the present study, the effects of lidocaine on the C6 rat glioma cell line were investigated. An MTT assay and Annexin V/propidium iodide analysis indicated the increase in the percentage of apoptotic and necrotic cells in response to lidocaine. Furthermore, light microscopy analysis on the ultrastructural level presented the occurrence of vacuole-like structures associated with autophagy, which was supported by the analysis of autophagy markers (microtubule-associated protein 1A/1B-light chain 3, acridine orange and Beclin-1). Additionally, reorganization of the cytoskeleton was observed following treatment with lidocaine, which serves an important role in the course of autophagy. To determine the nature of autophagy, an inhibitor, bafilomycin A1 was applied. This compound suppressed the fusion of autophagosomes with lysosomes and increased the percentage of apoptotic cells. These results demonstrated that lidocaine may induce cytoprotective autophagy and that manipulation of this process could be an alternative therapeutic strategy in the treatment of cancer.

The Roles of Autophagy in Cancer

Autophagy is an intracellular degradative process that occurs under several stressful conditions, including organelle damage, the presence of abnormal proteins, and nutrient deprivation. The mechanism of autophagy initiates the formation of autophagosomes that capture degraded components and then fuse with lysosomes to recycle these components. The modulation of autophagy plays dual roles in tumor suppression and promotion in many cancers. In addition, autophagy regulates the properties of cancer stem-cells by contributing to the maintenance of stemness, the induction of recurrence, and the development of resistance to anticancer reagents. Although some autophagy modulators, such as rapamycin and chloroquine, are used to regulate autophagy in anticancer therapy, since this process also plays roles in both tumor suppression and promotion, the precise mechanism of autophagy in cancer requires further study. In this review, we will summarize the mechanism of autophagy under stressful conditions and its roles in tumor suppression and promotion in cancer and in cancer stem-cells. Furthermore, we discuss how autophagy is a promising potential therapeutic target in cancer treatment.

Altered nuclear envelope structure and proteasome function of micronuclei

Micronuclei are extra-nuclear bodies containing whole chromosomes that were not incorporated into the nucleus after cell division or damaged chromosome fragments. Even though the link between micronuclei and DNA damage is described for a long time, little is known about the functional organization of micronuclei and their contribution to tumorigenesis. We showed fusions between micronuclear membranes and lysosomes by electron microscopy and linked lysosome function to DNA damage levels in micronuclei. In addition, micronuclei drastically differ from primary nuclei in nuclear envelope composition, with a significant increase in the relative amount of nuclear envelope proteins LBR and emerin and a decrease in nuclear pore proteins. Strikingly, micronuclei lack active proteasomes, as the processing subunits and other factors of the ubiquitin proteasome system. Moreover, micronuclear chromatin shows a higher degree of compaction as compared to primary nuclei. The specific aberrations identified in micronuclei and the potential functional consequences of these defects may contribute to the role of micronuclei in catastrophic genomic rearrangements.

Contribution of Mitophagy to Cell-Mediated Mineralization: Revisiting a 50-Year-Old Conundrum

Biomineralization in vertebrates is initiated via amorphous calcium phosphate (ACP) precursors. These precursors infiltrate the extracellular collagen matrix where they undergo phase transformation into intrafibrillar carbonated apatite. Although it is well established that ACP precursors are released from intracellular vesicles through exocytosis, an unsolved enigma in this cell-mediated mineralization process is how ACP precursors, initially produced in the mitochondria, are translocated to the intracellular vesicles. The present study proposes that mitophagy provides the mechanism for transfer of ACP precursors from the dysfunctioned mitochondria to autophagosomes, which, upon fusion with lysosomes, become autolysosomes where the mitochondrial ACP precursors coalesce to form larger intravesicular granules, prior to their release into the extracellular matrix. Apart from endowing the mitochondria with the function of ACP delivery through mitophagy, the present results indicate that mitophagy, triggered upon intramitochondrial ACP accumulation in osteogenic lineage-committed mesenchymal stem cells, participates in the biomineralization process through the BMP/Smad signaling pathway.

Autophagy-independent induction of LC3B through oxidative stress reveals its non-canonical role in anoikis of ovarian cancer cells

Cancer cells display abnormal redox metabolism. Autophagy, anoikis and reactive oxygen species (ROS) play a regulatory role during metastasis. LC3 is a well-known essential molecule for autophagy. Therefore, we wanted to explore the molecular interplay between autophagy, anoikis, and ROS in relation to LC3B. We observed enhanced LC3B level along with increased expression of p62 and modulation of other autophagy-related molecules (Atg 3, 5, 7, 12, 16L1 and Beclin1) by inducing oxidative-stress in ovarian cancer cells using a ROS-producing pro-oxidant molecule. Surprisingly, enhanced LC3B was unable to induce autophagosome formation rather promoted anoikis. ROS-induced inhibition of autophagosome-formation is possibly due to the instability of autophagy initiator, ULK1 complex. Moreover, such upregulation of LC3B via ROS enhanced several apoptotic molecules. Silencing LC3B reduced these apoptotic molecules and increased when overexpressed, suggesting its role in apoptosis. Furthermore, LC3B-dependent apoptosis was decreased by inhibiting ROS, indicating a possible link between ROS, LC3B, and apoptosis. Additionally, ROS-induced enhanced LC3B promoted detachment-induced cell death (anoikis). This was further reflected by reduced cell adhesion molecules (integrin-β3 and focal adhesion kinase) and mesenchymal markers (snail and slug). Our in vitro experimental data was further confirmed in primary tumors developed in syngeneic mice, which also showed ROS-mediated LC3B enhancement along with reduced autophagosomes, integrin-β3 and focal adhesion kinase ultimately leading to the decreased tumor mass. Additionally, primary cells from high-grade serous carcinoma patient's ascites exhibited LC3B enhancement and autophagy inhibition through ROS which provided a clinical relevance of our study. Taken together, this is the first evidence for a non-canonical role of LC3B in promoting anoikis in contrast to autophagy and may, therefore, consider as a potential therapeutic target molecule in ovarian cancer. Taken together, autophagy-inhibition may be an alternative approach to induce apoptosis/anoikis in cancer.

Autophagy Is Indispensable for the Self-Renewal and Quiescence of Ovarian Cancer Spheroid Cells with Stem Cell-Like Properties

Epithelial ovarian cancer has the highest mortality rate of all gynecologic cancers. Cancer stem cells are considered to be the initiating cells of tumors. It is known that spheroid culture promotes ovarian cancer cells to acquire stem cell characteristics and to become stem cell-like. But the mechanisms remain largely unclear. Our data show that autophagy is sustainably activated in ovarian cancer spheroid cells. Inhibition of autophagy by knockdown of ATG5 abolishes the self-renewal ability of ovarian cancer spheroid cells. Knockdown of ATG5 prevents ovarian cancer spheroid cells to enter quiescent state. Autophagy is critical for quiescent ovarian cancer spheroid cells to reenter the cell cycle because rapamycin can promote quiescent ovarian cancer spheroid cells to form colonies on soft agar and knockdown of ATG5 can arrest ovarian cancer cells in G0/G1. Autophagy and NRF2 form a positive feedback regulation loop to regulate reactive oxygen species (ROS) levels in ovarian cancer spheroid cells. The optimal ROS level, neither too high nor too low, facilitates the self-renewal marker, NOTCH1, to reach to the highest level. Bafilomycin A1 can impair the self-renewal of ovarian cancer spheroid cells by disturbing ROS levels.

Pseudomonas aeruginosa utilizes host polyunsaturated phosphatidylethanolamines to trigger theft-ferroptosis in bronchial epithelium

Ferroptosis is a death program executed via selective oxidation of arachidonic acid-phosphatidylethanolamines (AA-PE) by 15-lipoxygenases. In mammalian cells and tissues, ferroptosis has been pathogenically associated with brain, kidney, and liver injury/diseases. We discovered that a prokaryotic bacterium, Pseudomonas aeruginosa, that does not contain AA-PE can express lipoxygenase (pLoxA), oxidize host AA-PE to 15-hydroperoxy-AA-PE (15-HOO-AA-PE), and trigger ferroptosis in human bronchial epithelial cells. Induction of ferroptosis by clinical P. aeruginosa isolates from patients with persistent lower respiratory tract infections was dependent on the level and enzymatic activity of pLoxA. Redox phospholipidomics revealed elevated levels of oxidized AA-PE in airway tissues from patients with cystic fibrosis (CF) but not with emphysema or CF without P. aeruginosa. We believe that the evolutionarily conserved mechanism of pLoxA-driven ferroptosis may represent a potential therapeutic target against P. aeruginosa-associated diseases such as CF and persistent lower respiratory tract infections.

Bafilomycin A1 alleviates depression‑like symptoms in chronic unpredictable mild stress rats

Major depression is a multifactorial disease. Emerging evidence has suggested that autophagy is involved in the pathological process of depressive disorders. Bafilomycin A1 (Baf A1), is an inhibitor of vacuolar H+‑ATPase that is frequently used at high concentrations to block late‑phase autophagy. However, whether Baf A1 has antidepressant effects remains to be elucidated. The current study aimed to evaluate the antidepressant effects of Baf A1 in rats with chronic unpredictable mild stress (CUMS) and its potential mechanism. The CUMS animal model was established. The sucrose preference test, open‑field test (OFT) and forced swim test (FST) were applied to evaluate the depressive behavior. Synaptic plasticity‑associated proteins synaptophysin and postsynaptic density protein 95 were measured by western blotting and immunofluorescence. Apoptosis‑ and autophagy‑associated proteins in addition to pro‑inflammatory cytokines, including interleukin‑1β and tumor necrosis factor‑α, were detected by western blotting, reverse transcription‑quantitative polymerase chain reaction or ELISA. A 4‑week treatment period with Baf A1 markedly ameliorated CUMS‑induced behavioral abnormalities, including increasing sucrose intake, improving locomotor activity in the OFT, and decreasing immobility time in the FST. In addition, treatment with Baf A1 restored the dysregulation of synaptic plasticity and inhibited neuroinflammation in rats exposed to CUMS. Furthermore, Baf A1 decreased the levels of apoptosis‑ and autophagy‑associated proteins induced by CUMS. The present study demonstrated that Bafilomycin A1 resulted in antidepressant effects in rats, which may be mediated by the reversal of apoptosis, autophagy and neuroinflammation in the hippocampus.

What We Learned From Big Data for Autophagy Research

Autophagy is the process by which cytoplasmic components are engulfed in double-membraned vesicles before being delivered to the lysosome to be degraded. Defective autophagy has been linked to a vast array of human pathologies. The molecular mechanism of the autophagic machinery is well-described and has been extensively investigated. However, understanding the global organization of the autophagy system and its integration with other cellular processes remains a challenge. To this end, various bioinformatics and network biology approaches have been developed by researchers in the last few years. Recently, large-scale multi-omics approaches (like genomics, transcriptomics, proteomics, lipidomics, and metabolomics) have been developed and carried out specifically focusing on autophagy, and generating multi-scale data on the related components. In this review, we outline recent applications of in silico investigations and big data analyses of the autophagy process in various biological systems.

Investigating the autophagy pathway in silver@gold core-shell nanoparticles-treated cells using surface-enhanced Raman scattering

Previous studies have shown that nanoparticles can induce autophagy, and the main approach for investigating autophagy induced by nanoparticles is via traditional methods such as TEM and biochemical assay. These methods measurements suffer from the disadvantages of complicated experimental processes, cell destruction, as well as lack of characterization of individual stages of the autophagy pathway. Surface-enhanced Raman scattering (SERS) has been extensively used in biological applications. With the combination of SERS and chemometric methods, such as principal component analysis-linear discriminant analysis (PCA-LDA), identification and distribution mapping of endosomes and lysosomes in the endocytosis of Au nanoparticles has been achieved by segregating the spectra from complex SERS data sets in the previous study. In this study, silver@gold core-shell nanoparticles (Ag@Au NPs) were synthesized by reduction of gold ions on the surface of the silver nanoparticles, and the autophagy induced by Ag@Au NPs was studied with Ag@Au NPs serving both as an autophagy inducer and as a high-performance SERS substrate. Pro-survival autophagy induced by Ag@Au NPs was proved by the western blot assay, flow cytometry and fluorescent staining. Furthermore, the autophagy pathway in Ag@Au NPs-treated cells was first elucidated by SERS combined with a modified reference-based PCA-LDA methodology. This study provides a feasible way of using SERS to elucidate the autophagy pathway induced by nanoparticles.

Chloroquine plays a cell-dependent role in the response to treatment of pancreatic adenocarcinoma

In this study, our aim is to assess the role played by autophagy and its inhibition in the different PDAC cellular compartments, and its involvement in chemo-resistance using primary human pancreatic cancer-derived cells (PCC) and Cancer Associated Fibroblasts (CAF). Autophagy flux, as measured by LC3-I and -II in the presence of Chloroquine, showed a variable level in PCC and CAFs. We found no correlation between autophagy level and degree of tumor differentiation. Association of Chloroquine with gemcitabine, 5FU, oxaliplatin, irinotecan and docetaxel revealed that its effect on survival is cell- and drug-dependent in vitro and in vivo. In addition, we demonstrated that autophagy in CAFs can play an important role in sensitizing PDAC to anticancer treatments since its inhibition increased the resistance of PCCs to gemcitabine. In conclusion, this work clearly shows a heterogeneity in the effect of Chloroquine and highlights a role of CAFs autophagy in sensitizing tumors to treatments. It also reveals that the role of autophagy is more complex than expected in PDAC as well as its sensitivity to treatments.

Methods for assessing mitochondrial quality control mechanisms and cellular consequences in cell culture

Mitochondrial quality is under surveillance by autophagy, the cell recycling process which degrades and removes damaged mitochondria. Inadequate autophagy results in deterioration in mitochondrial quality, bioenergetic dysfunction, and metabolic stress. Here we describe in an integrated work-flow to assess parameters of mitochondrial morphology, function, mtDNA and protein damage, metabolism and autophagy regulation to provide the framework for a practical assessment of mitochondrial quality. This protocol has been tested with cell cultures, is highly reproducible, and is adaptable to studies when cell numbers are limited, and thus will be of interest to researchers studying diverse physiological and pathological phenomena in which decreased mitochondrial quality is a contributory factor.

Chloroquine and nanoparticle drug delivery: A promising combination

Clinically approved cancer therapies include small molecules, antibodies, and nanoparticles. There has been major progress in the treatment of several cancer types over recent decades. However, many challenges remain for optimal use of conventional and nanoparticle-based therapies in oncology including poor drug delivery, rapid clearance, and drug resistance. The antimalarial agent chloroquine has been found to mitigate some of these challenges by modulating cancer cells and the tissue microenvironment. Particularly, chloroquine was recently found to reduce immunological clearance of nanoparticles by resident macrophages in the liver, leading to increased tumor accumulation of nanodrugs. Additionally, chloroquine has been shown to improve drug delivery and efficacy through normalization of tumor vasculature and suppression of several oncogenic and stress-tolerance pathways, such as autophagy, that protect cancer cells from cytotoxic agents. This review will discuss the use of chloroquine as combination therapy to improve cancer treatment.

Autophagy in cancer: a complex relationship

Macroautophagy is the process by which cells package and degrade cytosolic components, and recycle the breakdown products for future use. Since its initial description by Christian de Duve in the 1960s, significant progress has been made in understanding the mechanisms that underlie this vital cellular process and its specificity. Furthermore, macroautophagy is linked to pathologic conditions such as cancer and is being studied as a therapeutic target. In this review, we will explore the connections between autophagy and cancer, which are tumor- and context-dependent and include the tumor microenvironment. We will highlight the importance of tumor compartment-specific autophagy in both cancer aggressiveness and treatment.

Neuronal Rho GTPase Rac1 elimination confers neuroprotection in a mouse model of permanent ischemic stroke

The Rho GTPase Rac1 is a multifunctional protein involved in distinct pathways ranging from development to pathology. The aim of the present study was to unravel the contribution of neuronal Rac1 in regulating the response to brain injury induced by permanent focal cerebral ischemia (pMCAO). Our results show that pMCAO significantly increased total Rac1 levels in wild type mice, mainly through rising nuclear Rac1, while a reduction in Rac1 activation was observed. Such changes preceded cell death induced by excitotoxic stress. Pharmacological inhibition of Rac1 in primary neuronal cortical cells prevented the increase in oxidative stress induced after overactivation of glutamate receptors. However, this was not sufficient to prevent the associated neuronal cell death. In contrast, RNAi-mediated knock down of Rac1 in primary cortical neurons prevented cell death elicited by glutamate excitotoxicity and decreased the activity of NADPH oxidase. To test whether in vivo down regulation of neuronal Rac1 was neuroprotective after pMCAO, we used tamoxifen-inducible neuron-specific conditional Rac1-knockout mice. We observed a significant 50% decrease in brain infarct volume of knockout mice and a concomitant increase in HIF-1α expression compared to littermate control mice, demonstrating that ablation of Rac1 in neurons is neuroprotective. Transmission electron microscopy performed in the ischemic brain showed that lysosomes in the infarct of Rac1- knockout mice were preserved at similar levels to those of non-infarcted tissue, while littermate mice displayed a decrease in the number of lysosomes, further corroborating the notion that Rac1 ablation in neurons is neuroprotective. Our results demonstrate that Rac1 plays important roles in the ischemic pathological cascade and that modulation of its levels is of therapeutic interest.

Chloroquine sensitizes hepatocellular carcinoma cells to chemotherapy via blocking autophagy and promoting mitochondrial dysfunction

Cisplatin/cisplatin-based combination chemotherapy is the main therapy strategy against hepatocellular carcinoma. However, the cisplatin efficiency is dimmed by the development of drug resistance. Numerous clinical trials are now revealing the promising role of chloroquine, an autophagy inhibitor, as a novel antitumor drug. In the present study, we investigated the regulation by chloroquine on the autophagy and on the sensitivity of hepatocellular carcinoma cells in vitro. Reverse transcription quantitative-polymerase chain reaction (RT-qPCR), western blotting assay, confocal microscopy and flow cytometry (FCM) were used to analyze the autophagy induction by cisplatin in hepatocellular carcinoma HepG2 cells, to examine the chloroquine-mediated autophagy inhibition on the cisplatin-induced apoptosis in HepG2 cells, and to explore the possible involvement of mitochondrial dysfunction in such process. Our results found the autophagy induction by cisplatin in HepG2 cells, basing on such results as increased induction of autophagic vesicles and upregulated conversion of A subunit (LC3-A) to B (LC3-B) subunit of microtubule-associated protein 1 light chain 3. Flow cytometry analysis results demonstrated that the cisplatin-induced apoptosis was aggravated by chloroquine. In addition, the mitochondrial function was downregulated by cisplatin and was deteriorated by chloroquine in HepG2 cells; the mitochondrial membrane potential (MMP) downregulation, the accumulation of reactive oxygen species (ROS) and the mitochondrial superoxide were markedly higher in the chloroquine/cisplatin-treated HepG2 cells than in the cisplatin-treated cells. In conclusion, we concluded that chloroquine sensitized the chemotherapy efficiency of cisplatin against hepatocellular carcinoma HepG2 cells, probably via blocking autophagy and via deteriorating the mitochondrial dysfunction. Chloroquine might be a potential adjuvant agent for overcoming chemotherapy resistance in hepatocellular carcinoma.

O-GlcNAc regulation of autophagy and α-synuclein homeostasis; implications for Parkinson's disease

Post-translational modification on protein Ser/Thr residues by O-linked attachment of ß-N-acetyl-glucosamine (O-GlcNAcylation) is a key mechanism integrating redox signaling, metabolism and stress responses. One of the most common neurodegenerative diseases that exhibit aberrant redox signaling, metabolism and stress response is Parkinson’s disease, suggesting a potential role for O-GlcNAcylation in its pathology. To determine whether abnormal O-GlcNAcylation occurs in Parkinson’s disease, we analyzed lysates from the postmortem temporal cortex of Parkinson’s disease patients and compared them to age matched controls and found increased protein O-GlcNAcylation levels. To determine whether increased O-GlcNAcylation affects neuronal function and survival, we exposed rat primary cortical neurons to thiamet G, a highly selective inhibitor of the enzyme which removes the O-GlcNAc modification from target proteins, O-GlcNAcase (OGA). We found that inhibition of OGA by thiamet G at nanomolar concentrations significantly increased protein O-GlcNAcylation, activated MTOR, decreased autophagic flux, and increased α-synuclein accumulation, while sparing proteasomal activities. Inhibition of MTOR by rapamycin decreased basal levels of protein O-GlcNAcylation, decreased AKT activation and partially reversed the effect of thiamet G on α-synuclein monomer accumulation. Taken together we have provided evidence that excessive O-GlcNAcylation is detrimental to neurons by inhibition of autophagy and by increasing α-synuclein accumulation.

Integrative metabolomics as emerging tool to study autophagy regulation

Recent technological developments in metabolomics research have enabled in-depth characterization of complex metabolite mixtures in a wide range of biological, biomedical, environmental, agricultural, and nutritional research fields. Nuclear magnetic resonance spectroscopy and mass spectrometry are the two main platforms for performing metabolomics studies. Given their broad applicability and the systemic insight into metabolism that can be obtained it is not surprising that metabolomics becomes increasingly popular in basic biological research. In this review, we provide an overview on key metabolites, recent studies, and future opportunities for metabolomics in studying autophagy regulation. Metabolites play a pivotal role in autophagy regulation and are therefore key targets for autophagy research. Given the recent success of metabolomics, it can be expected that metabolomics approaches will contribute significantly to deciphering the complex regulatory mechanisms involved in autophagy in the near future and promote understanding of autophagy and autophagy-related diseases in living cells and organisms.