bims-auttor 2021-10-10 papers

bims-auttor

Biomed News

on Autophagy and mTOR

Issue of 2021–10–10
34 papers selected by
Viktor Korolchuk, Newcastle University

The deubiquitinase USP11 is a versatile and conserved regulator of autophagy.
Autophagy deficiency activates rDNA transcription.
LGALS3 (galectin 3) mediates an unconventional secretion of SNCA/α-synuclein in response to lysosomal membrane damage by the autophagic-lysosomal pathway in human midbrain dopamine neurons.
The PINK1 repertoire: Not just a one trick pony.
New insights into the role of autophagy in retinal and eye diseases.
Rab9 mediates pancreatic autophagy switch from canonical to noncanonical, aggravating experimental pancreatitis.
TFG: a novel regulator of ULK1-dependent autophagy.
Overexpressed Smurf1 is degraded in glioblastoma cells through autophagy in a p62-dependent manner.
Autophagy-dependent glutaminolysis drives superior IL21 production in HIV-1-specific CD4 T cells.
Monomethyl branched-chain fatty acid mediates amino acid sensing upstream of mTORC1.
Mapping of mTOR drug targets: Featured platforms for anti-cancer drug discovery.
An Overview of the Molecular Mechanisms and Functions of Autophagic Pathways in Plants.
Labeling and Measuring Stressed Mitochondria Using a PINK1-Based Ratiometric Fluorescent Sensor.
Neurons die with heightened but functional macro- and chaperone mediated autophagy upon increased amyloid-ß induced toxicity with region-specific protection in prolonged intermittent fasting.
Humanin-induced autophagy plays important roles in skeletal muscle function and lifespan extension.
Autophagy is involved in neurofibromatosis type I gene-modulated osteogenic differentiation in human bone mesenchymal stem cells.
Managing risky assets - mitophagy in vivo.
Primary cells derived from Tuberous Sclerosis Complex patients show autophagy alteration in the haploinsufficiency state.
Serum- and glucocorticoid-induced kinase drives hepatic insulin resistance by directly inhibiting AMP-activated protein kinase.
Cadmium attenuates testosterone synthesis by promoting ferroptosis and blocking autophagosome-lysosome fusion.
VPS35 Downregulation Alters Degradation Pathways in Neuronal Cells.
Rheb-regulated mitochondrial pyruvate metabolism of Schwann cells linked to axon stability.
Role of autophagy in muscle disease.
Overexpression of ATG8/LC3 enhances wound-induced somatic reprogramming in Physcomitrium patens.
Mitophagy in the basolateral amygdala mediates increased anxiety induced by aversive social experience.
BNIP3 in melanoma: isn't it IRONic?
SIRT3 protects kidneys from ischemia-reperfusion injury by modulating the DRP1 pathway to induce mitochondrial autophagy.
Axitinib and HDAC Inhibitors Interact to Kill Sarcoma Cells.
An interplay between UCP2 and ROS protects cells from high-salt-induced injury through autophagy stimulation.
Sulforaphane downregulated fatty acid synthase and inhibited microtubule-mediated mitophagy leading to apoptosis.
mTOR-Activating Mutations in RRAGD are Causative for Kidney Tubulopathy and Cardiomyopathy.
Regulation of autophagy protects against liver injury in liver surgery-induced ischaemia/reperfusion.
Atractyloside Protect Mice Against Liver Steatosis by Activation of Autophagy via ANT-AMPK-mTORC1 Signaling Pathway.
Microglia regulate brain Progranulin levels through the endocytosis-lysosomal pathway.

J Biol Chem. 2021 Sep 30. pii: S0021-9258(21)01066-8. [Epub ahead of print] 101263

The deubiquitinase USP11 is a versatile and conserved regulator of autophagy.

Mila Basic, Alexandra Hertel, Justyna Bajdzienko, Florian Bonn, Mariana Tellechea, Alexandra Stolz, Andreas Kern, Christian Behl, Anja Bremm.

  Autophagy is a major cellular quality control system responsible for degradation of proteins and organelles in response to stress and damage in order to maintain homeostasis. Ubiquitination of autophagy-related proteins or regulatory components is important for the precise control of autophagy pathways. Here, we show that the deubiquitinase USP11 restricts autophagy and that knockout (KO) of USP11 in mammalian cells results in elevated autophagic flux. We also demonstrate that depletion of the USP11 homolog H34C03.2 in Caenorhabditis elegans triggers hyperactivation of autophagy and protects the animals against human β-amyloid peptide 42 aggregation-induced paralysis. USP11 co-precipitated with the autophagy-specific class III phosphatidylinositol 3-kinase complex I (PI3KC3-C1) and limited its interaction with nuclear receptor-binding factor 2 (NRBF2), thus decreasing lipid kinase activity of the PI3KC3-C1 and subsequent recruitment of effectors like WIPI proteins to the autophagosomal membrane. Accordingly, more WIPI2-puncta accumulated in USP11 KO cells. In addition, USP11 interacts with and stabilizes the serine/threonine kinase mTOR, thereby further contributing to the regulation of autophagy induction. Taken together, our data suggested that USP11 impinges on the autophagy pathway at multiple sites and that inhibiting USP11 alleviates symptoms of proteotoxicity, which is a major hallmark of neurodegenerative diseases.

Keywords:  Autophagy; PI3KC3-C1; deubiquitinase (DUB); mTORC1; proteostasis; ubiquitin

DOI:  https://doi.org/10.1016/j.jbc.2021.101263
Autophagy. 2021 Oct 06. 1-12

Autophagy deficiency activates rDNA transcription.

Yinfeng Xu, Yaosen Wu, Lei Wang, Zhuo Ren, Lijiang Song, Hui Zhang, Chuying Qian, Qian Wang, Zhengfu He, Wei Wan.

  Macroautophagy/autophagy, a highly conserved lysosome-dependent degradation pathway, has been intensively studied in regulating cell metabolism by degradation of intracellular components. In this study, we link autophagy to RNA metabolism by uncovering a regulatory role of autophagy in ribosomal RNA (rRNA) synthesis. Autophagy-deficient cells exhibit much higher 47S precursor rRNA level, which is caused by the accumulation of SQSTM1/p62 (sequestosome 1) but not other autophagy receptors. Mechanistically, SQSTM1 accumulation potentiates the activation of MTOR (mechanistic target of rapamycin kinase) complex 1 (MTORC1) signaling and promotes the assembly of RNA polymerase I pre-initiation complex at ribosomal DNA (rDNA) promoters, which leads to an increase of 47S rRNA transcribed from rDNA. Functionally, autophagy deficiency promotes protein synthesis, cell growth and cell proliferation, both of which are dependent on SQSTM1 accumulation. Taken together, our findings suggest that autophagy deficiency is involved in RNA metabolism by activating rDNA transcription and provide novel mechanisms for the reprogramming of cell metabolism in autophagy-related diseases including multiple types of cancers.Abbreviations: 5-FUrd: 5-fluorouridine; AMPK: AMP-activated protein kinase; ATG: autophagy related; CALCOCO2/NDP52: calcium binding and coiled-coil domain 2; ChIP: chromatin immunoprecipitation; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MAPK/ERK: mitogen-activated protein kinase; MTOR: mechanistic target of rapamycin kinase; NBR1: NBR1 autophagy cargo receptor; NFKB/NF-κB: nuclear factor kappa B; NFE2L2/NRF2: nuclear factor, erythroid 2 like 2; OPTN: optineurin; PIC: pre-initiation complex; POLR1: RNA polymerase I; POLR1A/RPA194: RNA polymerase I subunit A; POLR2A: RNA polymerase II subunit A; rDNA: ribosomal DNA; RPS6KB1/S6K1: ribosomal protein S6 kinase B1; rRNA: ribosomal RNA; RUBCN/Rubicon: rubicon autophagy regulator; SQSTM1/p62: sequestosome 1; STX17: syntaxin 17; SUnSET: surface sensing of translation; TAX1BP1: Tax1 binding protein 1; UBTF/UBF1: upstream binding transcription factor; WIPI2: WD repeat domain, phosphoinositide interacting 2; WT: wild-type.

Keywords:  Autophagy; MTORC1; SQSTM1/p62; rDNA; rRNA

DOI:  https://doi.org/10.1080/15548627.2021.1974178
Autophagy. 2021 Oct 06. 1-29

LGALS3 (galectin 3) mediates an unconventional secretion of SNCA/α-synuclein in response to lysosomal membrane damage by the autophagic-lysosomal pathway in human midbrain dopamine neurons.

Kevin Burbidge, David J Rademacher, Jessica Mattick, Stephanie Zack, Andrea Grillini, Luc Bousset, Ochan Kwon, Konrad Kubicki, Alexander Simon, Ronald Melki, Edward M Campbell.

  Numerous lines of evidence support the premise that the misfolding and subsequent accumulation of SNCA/α-synuclein (synuclein alpha) is responsible for the underlying neuronal pathology observed in Parkinson disease (PD) and other synucleinopathies. Moreover, the cell-to-cell transfer of these misfolded SNCA species is thought to be responsible for disease progression and the spread of cellular pathology throughout the brain. Previous work has shown that when exogenous, misfolded SNCA fibrils enter cells through endocytosis, they can damage and rupture the membranes of their endocytotic vesicles in which they are trafficked. Rupture of these vesicular membranes exposes intralumenal glycans leading to galectin protein binding, subsequent autophagic protein recruitment, and, ultimately, their introduction into the autophagic-lysosomal pathway. Increasing evidence indicates that both pathological and non-pathological SNCA species undergo autophagy-dependent unconventional secretion. While other proteins have also been shown to be secreted from cells by autophagy, what triggers this release process and how these specific proteins are recruited to a secretory autophagic pathway is largely unknown. Here, we use a human midbrain dopamine (mDA) neuronal culture model to provide evidence in support of a cellular mechanism that explains the cell-to-cell transfer of pathological forms of SNCA that are observed in PD. We demonstrate that LGALS3 (galectin 3) mediates the release of SNCA following vesicular damage. SNCA release is also dependent on TRIM16 (tripartite motif containing 16) and ATG16L1 (autophagy related 16 like 1), providing evidence that secretion of SNCA is mediated by an autophagic secretory pathway.

Keywords:  Autophagy; Parkinson disease; alpha-synuclein (synuclein alpha); extracellular vesicles; galectins; induced pluripotent stem cells; lysosomes; tripartite motif proteins; unconventional secretion

DOI:  https://doi.org/10.1080/15548627.2021.1967615
Bioessays. 2021 Oct 07. e2100168

The PINK1 repertoire: Not just a one trick pony.

Liam Pollock, Jane Jardine, Sylvie Urbé, Michael J Clague.

  PTEN-induced kinase 1 (PINK1) is a Parkinson's disease gene that acts as a sensor for mitochondrial damage. Its best understood role involves phosphorylating ubiquitin and the E3 ligase Parkin (PRKN) to trigger a ubiquitylation cascade that results in selective clearance of damaged mitochondria through mitophagy. Here we focus on other physiological roles of PINK1. Some of these also lie upstream of Parkin but others represent autonomous functions, for which alternative substrates have been identified. We argue that PINK1 orchestrates a multi-arm response to mitochondrial damage that impacts on mitochondrial architecture and biogenesis, calcium handling, transcription and translation. We further discuss a role for PINK1 in immune signalling co-ordinated at mitochondria and consider the significance of a freely diffusible cleavage product, that is constitutively generated and degraded under basal conditions.

Keywords:  ISR; PINK1; Parkin; Parkinson's disease; mitochondria; mitochondrial quality control; mitophagy; stress response

DOI:  https://doi.org/10.1002/bies.202100168
Mol Aspects Med. 2021 Oct 04. pii: S0098-2997(21)00098-4. [Epub ahead of print] 101038

New insights into the role of autophagy in retinal and eye diseases.

Beatriz Villarejo-Zori, Juan Ignacio Jiménez-Loygorri, Juan Zapata-Muñoz, Katharina Bell, Patricia Boya.

  Autophagy is a fundamental homeostatic pathway that mediates the degradation and recycling of intracellular components. It serves as a key quality control mechanism, especially in non-dividing cells such as neurons. Proteins, lipids, and even whole organelles are engulfed in autophagosomes and delivered to the lysosome for elimination. The retina is a light-sensitive tissue located in the back of the eye that detects and processes visual images. Vision is a highly demanding process, making the eye one of the most metabolically active tissues in the body and photoreceptors display glycolytic metabolism, even in the presence of oxygen. The retina and eye are also exposed to other stressors that can impair their function, including genetic mutations and age-associated changes. Autophagy, among other pathways, is therefore a key process for the preservation of retinal homeostasis. Here, we review the roles of both canonical and non-canonical autophagy in normal retinal function. We discuss the most recent studies investigating the participation of autophagy in eye diseases such as age-related macular degeneration, glaucoma, and diabetic retinopathy and its role protecting photoreceptors in several forms of retinal degeneration. Finally, we consider the therapeutic potential of strategies that target autophagy pathways to treat prevalent retinal and eye diseases.

Keywords:  Autophagy; Glaucoma; Macular degeneration; Retina; Retinal dystrophies

DOI:  https://doi.org/10.1016/j.mam.2021.101038
Cell Mol Gastroenterol Hepatol. 2021 Oct 02. pii: S2352-345X(21)00207-1. [Epub ahead of print]

Rab9 mediates pancreatic autophagy switch from canonical to noncanonical, aggravating experimental pancreatitis.

Olga A Mareninova, Dustin L Dillon, Carli J M Wightman, Iskandar Yakubov, Toshimasa Takahashi, Herbert Y Gaisano, Keith Munson, Masaki Ohmuraya, David Dawson, Ilya Gukovsky, Anna S Gukovskaya.

   BACKGROUND: Autophagosome, the central organelle in autophagy process, can assemble via canonical pathway mediated by LC3-II, the lipidated form of autophagy-related protein LC3/ATG8, or noncanonical pathway mediated by the small GTPase Rab9. Canonical autophagy is essential for exocrine pancreas homeostasis, and its disordering initiates and drives pancreatitis. The involvement of noncanonical autophagy has not been explored. We examine the role of Rab9 in pancreatic autophagy and pancreatitis severity.
METHODS: We measured the effect of Rab9 on parameters of autophagy and pancreatitis responses using transgenic mice overexpressing Rab9 (Rab9TG) and adenoviral transduction of acinar cells. Effect of canonical autophagy on Rab9 was assessed in ATG5-deficient acinar cells.
RESULTS: Pancreatic levels of Rab9 and its membrane-bound (active) form decreased in rodent pancreatitis models and in human disease. Rab9 overexpression stimulated noncanonical and inhibited canonical/LC3-mediated autophagosome formation in acinar cells through upregulation of ATG4B, the cysteine protease that delipidates LC3-II. Conversely, ATG5 deficiency caused Rab9 increase in acinar cells. Inhibition of canonical autophagy in Rab9TG pancreas was associated with accumulation of Rab9-positive vacuoles containing markers of mitochondria, protein aggregates and trans-Golgi. The shift to the noncanonical pathway caused pancreatitis-like damage in acinar cells and aggravated experimental pancreatitis.
CONCLUSIONS: The results show that Rab9 regulates pancreatic autophagy and indicate a mutually antagonistic relationship between the canonical/LC3-mediated and noncanonical/Rab9-mediated autophagy pathways in pancreatitis. Noncanonical autophagy fails to substitute for its canonical counterpart in protecting against pancreatitis. Thus, Rab9 decrease in experimental and human pancreatitis is a protective response to sustain canonical autophagy and alleviate disease severity.

Keywords:  Rab GTPase; RabGDI; alternative autophagy; autophagosome

DOI:  https://doi.org/10.1016/j.jcmgh.2021.09.017
Mol Cell Oncol. 2021 ;8(4): 1945895

TFG: a novel regulator of ULK1-dependent autophagy.

Francesco Cecconi, Francesca Nazio.

  TRK-fused gene (TFG) is a protein implicated in multiple neurodegenerative diseases and oncogenesis. We have recently shown that, under starvation conditions, TFG contributes to spatial control of autophagy by facilitating Unc-51 like autophagy activating kinase 1 (ULK1)-microtubule-associated protein 1 light chain 3 gamma (MAP1LC3C) interaction to modulate omegasome and autophagosome formation. Defective TFG-mediated autophagy could thus be postulated as a possible contributor to ontogenesis or progression of TFG-related diseases.

Keywords:  ERGIC; TFG; ULK1; neurological disorders; omegasome

DOI:  https://doi.org/10.1080/23723556.2021.1945895
FEBS Open Bio. 2021 Oct 06.

Overexpressed Smurf1 is degraded in glioblastoma cells through autophagy in a p62-dependent manner.

Han Da, Shengzhen Li, Qin Xia, Xinyi Meng, Lei Dong.

  HECT-type E3 ubiquitin ligase Smurf1 was originally identified to ubiquitinate Smad protein in the TGF-β/BMP signaling pathway. Recently, Smurf1 has been reported to promote tumorigenesis by regulating multiple biological processes. High expression of Smurf1 plays a vital role in brain tumor progression by mediating aberrant cell signaling pathways. Previous reports have shown that Smurf1 is degraded mainly through the ubiquitin proteasome system, but it remains unclear whether Smurf1 is degraded by autophagy in tumor cells. In this study, we show that autophagy activators promote Smurf1 degradation in glioblastoma cells. The autophagy receptor p62 co-localizes with ubiquitinated substrates to promote sequestration of cytoplasm cargo into the autophagosome. We report that autophagic degradation of Smurf1 is dependent on p62. Moreover, the autophagic degradation of Smurf1 is prevented in the absence of the HECT domain or E3 ubiquitin ligase activity. We further proved that activation of autophagy leads to a decrease of Smurf1 and the inhibition of the PI3K/Akt signaling pathway in glioblastoma cells. Our results suggest that enhancement of autophagic degradation of Smurf1 may be a potential approach to treating glioblastoma.

Keywords:  E3 ubiquitin ligase activity; PI3K/Akt signaling; Smurf1; autophagy; degradation; p62

DOI:  https://doi.org/10.1002/2211-5463.13310
Autophagy. 2021 Oct 06. 1-18

Autophagy-dependent glutaminolysis drives superior IL21 production in HIV-1-specific CD4 T cells.

Hamza Loucif, Xavier Dagenais-Lussier, Daina Avizonis, Luc Choinière, Cherifa Beji, Léna Cassin, Jean-Pierre Routy, Jörg H Fritz, David Olagnier, Julien van Grevenynghe.

  The maintenance of a strong IL21 production in memory CD4 T cells, especially in HIV-1-specific cells, represents a major correlate of natural immune protection against the virus. However, the molecular mechanisms underlying IL21 production during HIV-1 infection, which is only elevated among the naturally protected elite controllers (EC), are still unknown. We recently found out that lipophagy is a critical immune mediator that control an antiviral metabolic state following CD8A T cell receptor engagement, playing an important role in the natural control of HIV-1 infection. This led us to investigate whether the beneficial role of a strong macroautophagy/autophagy, could also be used to ensure effective IL21 production as well. Herein, we confirm that after both polyclonal and HIV-1-specific activation, memory CD4 T cells (Mem) from EC display enhanced activity of the autophagy-mediated proteolysis compared to ART. Our results indicate that the enhanced autophagy activity in EC was controlled by the energy-sensing PRKAA1 (protein kinase AMP-activated catalytic subunit alpha 1). We further confirmed the critical role of the autophagy-mediated proteolysis in the strong IL21 production in EC by using BECN1 gene silencing as well as protease, PRKAA1, and lysosomal inhibitors. Finally, we established that high autophagy-mediated proteolysis in EC fuels their cellular rates of mitochondrial respiration due to glutaminolysis. Our data confirm the critical role of autophagy in dictating the metabolic input, which is required not only to ensure protective cytotoxic CD8A T cell responses, but also to provide strong IL21 production among antiviral CD4 T cells.Abbreviations: AKG: alpha-ketoglutarate; ART: patients under antiretroviral therapy; ATG7: autophagy related 7; BaF: bafilomycin A1; BECN1: beclin 1; Chloro.: chloroquine; EC: elite controllers; EIF4EBP1: eukaryotic translation initiation factor 4E binding protein 1; FOXO3: forkhead box O3; GLS: glutaminase; GLUD1: glutamate dehydrogenase 1; HIVneg: HIV-1-uninfected control donors; IFNG/IFN-γ: interferon gamma; IL21: interleukin 21; MTOR: mechanistic target of rapamycin kinase; PBMC: peripheral blood mononuclear cells; PRKAA1: protein kinase AMP-activated catalytic subunit alpha 1; SQSTM1: sequestosome 1; TCA: tricarboxylic acid cycle; ULK1: unc-51 like autophagy activating kinase.

Keywords:  Antiretroviral therapy; HIV-1; IL21; PRKAA1; autophagy-mediated proteolysis; elite controllers; glutaminolysis

DOI:  https://doi.org/10.1080/15548627.2021.1972403
Dev Cell. 2021 Oct 01. pii: S1534-5807(21)00728-0. [Epub ahead of print]

Monomethyl branched-chain fatty acid mediates amino acid sensing upstream of mTORC1.

Mengnan Zhu, Fukang Teng, Na Li, Li Zhang, Shuxian Zhang, Fan Xu, Jing Shao, Haipeng Sun, Huanhu Zhu.

  Animals have developed various nutrient-sensing mechanisms for survival under fluctuating environmental conditions. Although extensive cell-culture-based analyses have identified diverse mediators of amino acid sensing upstream of mTOR, studies using animal models to examine intestine-initiated amino acid sensing mechanisms under specific physiological conditions are lacking. Here, we developed a Caenorhabditis elegans model to examine the impact of amino acid deficiency on development. We discovered a leucine-derived monomethyl branched-chain fatty acid and its downstream metabolite, glycosphingolipid, which critically mediates the overall amino acid sensing by intestinal and neuronal mTORC1, which in turn regulates postembryonic development at least partly by controlling protein translation and ribosomal biogenesis. Additional data suggest that a similar mechanism may operate in mammals. This study uncovers an amino-acid-sensing mechanism mediated by a lipid biosynthesis pathway.

Keywords:  C. elegans; amino acid sensing; developmental arrest; developmental control; glucosylceramide; mTOR; mTORC1; mmBCFA; nutrient sensing; sphingolipid

DOI:  https://doi.org/10.1016/j.devcel.2021.09.010
Pharmacol Ther. 2021 Oct 05. pii: S0163-7258(21)00214-X. [Epub ahead of print] 108012

Mapping of mTOR drug targets: Featured platforms for anti-cancer drug discovery.

Raef Shams, Yoshihiro Ito, Hideyuki Miyatake.

  The mammalian/mechanistic target of rapamycin (mTOR) is a regulatory protein kinase involved in cell growth and proliferation. mTOR is usually assembled in two different complexes with different regulatory mechanisms, mTOR complex 1 (mTORC1) and mTORC2, which are involved in different functions such as cell proliferation and cytoskeleton assembly, respectively. In cancer cells, mTOR is hyperactivated in response to metabolic alterations and/or oncogenic signals to overcome the stressful microenvironments. Therefore, recent research progress for mTOR inhibition involves a variety of compounds that have been developed to disturb the metabolic processes of cancer cells through mTOR inhibition. In addition to competitive or allosteric inhibition, a new inhibition strategy that emerged mTOR complexes destabilization has recently been a concern. Here, we review the history of mTOR and its inhibition, along with the timeline of the mTOR inhibitors. We also introduce prospective drug targets to inhibit mTOR by disrupting the complexation of the components with peptides and small molecules.

Keywords:  Cancer therapy; Drug target; mTOR; mTOR inhibitors generations; mTORC1/2 destabilizers

DOI:  https://doi.org/10.1016/j.pharmthera.2021.108012
Plant Signal Behav. 2021 Oct 07. 1977527

An Overview of the Molecular Mechanisms and Functions of Autophagic Pathways in Plants.

Yang Yang, Yun Xiang, Yue Niu.

  Autophagy is an evolutionarily conserved pathway for the degradation of damaged or toxic components. Under normal conditions, autophagy maintains cellular homeostasis. It can be triggered by senescence and various stresses. In the process of autophagy, autophagy-related (ATG) proteins not only function as central signal regulators but also participate in the development of complex survival mechanisms when plants suffer from adverse environments. Therefore, ATGs play significant roles in metabolism, development and stress tolerance. In the past decade, both the molecular mechanisms of autophagy and a large number of components involved in the assembly of autophagic vesicles have been identified. In recent studies, an increasing number of components, mechanisms, and receptors have appeared in the autophagy pathway. In this paper, we mainly review the recent progress of research on the molecular mechanisms of plant autophagy, as well as its function under biotic stress and abiotic stress.

Keywords:  ATGs; abiotic stress; arabidopsis; autophagosome; autophagy

DOI:  https://doi.org/10.1080/15592324.2021.1977527
J Biol Chem. 2021 Oct 05. pii: S0021-9258(21)01082-6. [Epub ahead of print] 101279

Labeling and Measuring Stressed Mitochondria Using a PINK1-Based Ratiometric Fluorescent Sensor.

Rie Uesugi, Shunsuke Ishii, Akira Matsuura, Eisuke Itakura.

  Mitochondria are essential organelles that carry out a number of pivotal metabolic processes and maintain cellular homeostasis. Mitochondrial dysfunction caused by various stresses is associated with many diseases such as type 2 diabetes, obesity, cancer, heart failure, neurodegenerative disorders, and aging. Therefore, it is important to understand the stimuli that induce mitochondrial stress. However, broad analysis of mitochondrial stress has not been carried out to date. Here, we present a set of fluorescent tools, called mito-Pain (mitochondrial PINK1 accumulation index), which enables the labeling of stressed mitochondria. Mito-Pain utilizes PINK1 stabilization on mitochondria and quantifies mitochondrial stress levels by comparison with PINK1-GFP, which is stabilized under mitochondrial stress, and RFP-Omp25, which is constitutively localized on mitochondria. To identify compounds that induce mitochondrial stress, we screened a library of 3374 compounds using mito-Pain and identified 57 compounds as mitochondrial stress inducers. Furthermore, we classified each compound into several categories based on mitochondrial response: depolarization, mitochondrial morphology, or Parkin recruitment. Parkin recruitment to mitochondria was often associated with mitochondrial depolarization and aggregation, suggesting that Parkin is recruited to heavily damaged mitochondria. In addition, many of the compounds led to various mitochondrial morphological changes, including fragmentation, aggregation, elongation, and swelling, with or without Parkin recruitment or mitochondrial depolarization. We also found that several compounds induced an ectopic response of Parkin, leading to the formation of cytosolic puncta dependent on PINK1. Thus, mito-Pain enables the detection of stressed mitochondria under a wide variety of conditions and provide insights into mitochondrial quality control systems.

Keywords:  PTEN‐induced putative kinase 1 (PINK1); Parkin; mitochondria; mitochondrial membrane potential; mitochondrial sensor; mitochondrial stress

DOI:  https://doi.org/10.1016/j.jbc.2021.101279
Exp Cell Res. 2021 Oct 05. pii: S0014-4827(21)00394-3. [Epub ahead of print] 112840

Neurons die with heightened but functional macro- and chaperone mediated autophagy upon increased amyloid-ß induced toxicity with region-specific protection in prolonged intermittent fasting.

Claudia Matlakala Ntsapi, Ben Loos.

  Alzheimer's disease (AD) is a devastating neurodegenerative condition with significant socio-economic impact that is exacerbated by the rapid increase in population aging, particularly impacting already burdened health care systems of poorly resourced countries. Accumulation of the amyloid-β (Aβ) peptide, generated through amyloid precursor protein (APP) processing, manifesting in senile plaques, is a well-established neuropathological feature. Aβ plays a key role in driving synaptic dysfunction, neuronal cell loss, glial cell activation and oxidative stress associated with the pathogenesis of AD. Thus, the enhanced clearance of Aβ peptide though modulation of the mechanisms that regulate intracellular Aβ metabolism and clearance during AD progression have received major attention. Autophagy, a lysosome-based major proteolytic pathway, plays a crucial role in intracellular protein quality control and has been shown to contribute to the clearance of Aβ peptide. However, to what extent autophagy activity remains upregulated and functional in the process of increasing Aβ neurotoxicity is largely unclear. Here, we investigated the extent of neuronal toxicity in vitro by characterising autophagic flux, the expression profile of key amyloidogenic proteins, and proteins associated with prominent subtypes of the autophagy pathway to dissect the interplay between the engagement of proteolytic pathways and cell death onset in the context of APP overexpression. Moreover, we assessed the neuroprotective effects of a caloric restriction regime in vivo on the modulation of autophagy in specific brain regions. Our results reveal that autophagy is upregulated in the presence of high levels of APP and Aβ and remains heightened and functional despite concomitant apoptosis induction, suggestive of a mismatch between autophagy cargo generation and clearance capacity. These findings were confirmed when implementing a prolonged intermittent fasting (IF) intervention in a model of paraquat-induced neuronal toxicity, where markers of autophagic activity were increased, while apoptosis onset and lipid peroxidation were robustly decreased in brain regions associated with neurodegeneration. This work highlights that especially caloric restriction mimetics and controlled prolonged IF may indeed be a highly promising therapeutic strategy at all stages of AD-associated pathology progression, for a cell-inherent and cell specific augmentation of Aβ clearance through the powerful engagement of autophagy and thereby robustly contributing to neuronal protection.

Keywords:  Autophagy; amyloid beta peptide; caloric restriction; chaperone-mediated autophagy; macroautophagy

DOI:  https://doi.org/10.1016/j.yexcr.2021.112840
Biochim Biophys Acta Gen Subj. 2021 Oct 05. pii: S0304-4165(21)00176-8. [Epub ahead of print] 130017

Humanin-induced autophagy plays important roles in skeletal muscle function and lifespan extension.

Su-Jeong Kim, Anjali Devgan, Brendan Miller, Sam Mool Lee, Hiroshi Kumagai, Kenneth A Wilson, Gabriella Wassef, Richard Wong, Hemal H Mehta, Pinchas Cohen, Kelvin Yen.

   BACKGROUND: Autophagy, a highly conserved homeostatic mechanism, is essential for cell survival. The decline of autophagy function has been implicated in various diseases as well as aging. Although mitochondria play a key role in the autophagy process, whether mitochondrial-derived peptides are involved in this process has not been explored.
METHODS: We developed a high through put screening method to identify potential autophagy inducers among mitochondrial-derived peptides. We used three different cell lines, mice, c.elegans, and a human cohort to validate the observation.
RESULTS: Humanin, a mitochondrial-derived peptide, increases autophagy and maintains autophagy flux in several cell types. Humanin administration increases the expression of autophagy-related genes and lowers accumulation of harmful misfolded proteins in mice skeletal muscle, suggesting that humanin-induced autophagy potentially contributes to the improved skeletal function. Moreover, autophagy is a critical role in humanin-induced lifespan extension in C. elegans.
CONCLUSIONS: Humanin is an autophagy inducer.
GENERAL SIGNIFICANCE: This paper presents a significant, novel discovery regarding the role of the mitochondrial derived peptide humanin in autophagy regulation and as a possible therapeutic target for autophagy in various age-related diseases.

Keywords:  Autophagy; Humanin; Lifespan; Mitochondrial-derived peptides

DOI:  https://doi.org/10.1016/j.bbagen.2021.130017
Exp Ther Med. 2021 Nov;22(5): 1262

Autophagy is involved in neurofibromatosis type I gene-modulated osteogenic differentiation in human bone mesenchymal stem cells.

Yiqiang Li, Mingwei Zhu, Xuemei Lin, Jingchun Li, Zhe Yuan, Yanhan Liu, Hongwen Xu.

  Neurofibromatosis type I (NF1) is an autosomal dominant genetic disease that is caused by mutations in the NF1 gene. Various studies have previously demonstrated that the mTOR complex 1 signaling pathway is essential for the NF1-modulated osteogenic differentiation of bone mesenchymal stem cells (BMSCs). Additionally, the mTOR signaling pathway plays a notable role in autophagy. The present study hypothesized that NF1 could modulate the osteogenic differentiation of BMSCs by regulating the autophagic activities of BMSCs. In the present study, human BMSCs were cultured in an osteogenic induction medium. The expression of the NF1 gene was either knocked down or overexpressed by transfection with a specific small interfering RNA (siRNA) targeting NF1 or the pcDNA3.0 NF1-overexpression plasmid, respectively. Autophagic activities of BMSCs (Beclin-1, P62, LC3B I, and LC3B II) were determined using western blotting, electron microscopy, acridine orange (AO) staining and autophagic flux/lysosomal detection by fluorescence microscopy. In addition, the autophagy activator rapamycin (RAPA) and inhibitor 3-methyladenine (3-MA) were used to investigate the effects of autophagy on NF1-modulated osteogenic differentiation in BMSCs. Inhibiting NF1 with siRNA significantly decreased the expression levels of autophagy markers Beclin-1 and LC3B-II, in addition to osteogenic differentiation markers osterix, runt-related transcription factor 2 and alkaline phosphatase. By contrast, overexpressing NF1 with pcDNA3.0 significantly increased their levels. Transmission electron microscopy, AO staining and autophagic flux/lysosomal detection assays revealed that the extent of autophagosome formation was significantly decreased in the NF1-siRNA group but significantly increased in the NF1-pcDNA3.0 group when compared with the NC-siRNA and pcDNA3.0 groups, respectively. In addition, the activity of the PI3K/AKT/mTOR pathway [phosphorylated (p)-PI3K, p-AKT, p-mTOR and p-p70S6 kinase] was significantly upregulated in the NF1-siRNA group compared with the NC-siRNA group, and significantly inhibited in the NF1-pcDNA3.0 group, compared with the pcDNA3.0 group. The knockdown effects of NF1-siRNA on the autophagy and osteogenic differentiation of BMSCs were reversed by the autophagy activator RAPA, while the overexpression effects of NF1-pcDNA3.0 on the autophagy and osteogenic differentiation of BMSCs were reversed by the autophagy inhibitor 3-MA. In conclusion, results from the present study suggest at the involvement of autophagy in the NF1-modulated osteogenic differentiation of BMSCs. Furthermore, NF1 may partially regulate the autophagic activity of BMSCs through the PI3K/AKT/mTOR signaling pathway.

Keywords:  PI3K/AKT/mTOR pathway; autophagy; bone marrow stem cells; neurofibromatosis type I; osteogenic differentiation

DOI:  https://doi.org/10.3892/etm.2021.10697
J Cell Sci. 2021 Oct 01. pii: jcs240465. [Epub ahead of print]134(19):

Managing risky assets - mitophagy in vivo.

Derek P Narendra.

  Mitochondria, which resemble their α-proteobacteria ancestors, are a major cellular asset, producing energy 'on the cheap' through oxidative phosphorylation. They are also a liability. Increased oxidative phosphorylation means increased oxidative stress, and damaged mitochondria incite inflammation through release of their bacteria-like macromolecules. Mitophagy (the selective macroautophagy of mitochondria) controls mitochondria quality and number to manage these risky assets. Parkin, BNIP3 and NIX were identified as being part of the first mitophagy pathways identified in mammals over a decade ago, with additional pathways, including that mediated by FUNDC1 reported more recently. Loss of Parkin or PINK1 function causes Parkinson's disease, highlighting the importance of mitophagy as a quality control mechanism in the brain. Additionally, mitophagy is induced in idiopathic Parkinson's disease and Alzheimer's disease, protects the heart and other organs against energy stress and lipotoxicity, regulates metabolism by controlling mitochondrial number in brown and beige fat, and clears mitochondria during terminal differentiation of glycolytic cells, such as red blood cells and neurons. Despite its importance in disease, mitophagy is likely dispensable under physiological conditions. This Review explores the in vivo roles of mitophagy in mammalian systems, focusing on the best studied examples - mitophagy in neurodegeneration, cardiomyopathy, metabolism, and red blood cell development - to draw out common themes.

Keywords:  Mitochondria quality control; Neurodegeneration; PRKN; Park2; Park6

DOI:  https://doi.org/10.1242/jcs.240465
Genet Mol Biol. 2021 ;pii: S1415-47572021000600701. [Epub ahead of print]44(4): e20200475

Primary cells derived from Tuberous Sclerosis Complex patients show autophagy alteration in the haploinsufficiency state.

Clévia Rosset, Mariane da Cunha Jaeger, Eduardo Filippi-Chiela, Larissa Brussa Reis, Ivaine Taís Sauthier Sartor, Cristina Brinckmann Oliveira Netto, Caroline Brunetto de Farias, Rafael Roesler, Patricia Ashton-Prolla.

Tuberous sclerosis complex (TSC) is an autosomal dominant cancer predisposition disorder caused by heterozygous mutations in TSC1 or TSC2 genes and characterized by mTORC1 hyperactivation. TSC-associated tumors develop after loss of heterozygosity mutations and their treatment involves the use of mTORC1 inhibitors. We aimed to evaluate cellular processes regulated by mTORC1 in TSC cells with different mutations before tumor development. Flow cytometry analyses were performed to evaluate cell viability, cell cycle and autophagy in non-tumor primary TSC cells with different heterozygous mutations and in control cells without TSC mutations, before and after treatment with rapamycin (mTORC1 inhibitor). We did not observe differences in cell viability and cell cycle between the cell groups. However, autophagy was reduced in mutated cells. After rapamycin treatment, mutated cells showed a significant increase in the autophagy process (p=0.039). We did not observe differences between cells with distinct TSC mutations. Our main finding is the alteration of autophagy in non-tumor TSC cells. Previous studies in literature found autophagy alterations in tumor TSC cells or knock-out animal models. We showed that autophagy could be an important mechanism that leads to TSC tumor formation in the haploinsufficiency state. This result could guide future studies in this field.

DOI: https://doi.org/10.1590/1678-4685-GMB-2020-0475
Cell Rep. 2021 Oct 05. pii: S2211-1247(21)01244-4. [Epub ahead of print]37(1): 109785

Serum- and glucocorticoid-induced kinase drives hepatic insulin resistance by directly inhibiting AMP-activated protein kinase.

Ben Zhou, Yuyao Zhang, Sainan Li, Lianfeng Wu, Geza Fejes-Toth, Aniko Naray-Fejes-Toth, Alexander A Soukas.

  A hallmark of type 2 diabetes (T2D) is hepatic resistance to insulin's glucose-lowering effects. The serum- and glucocorticoid-regulated family of protein kinases (SGK) is activated downstream of mechanistic target of rapamycin complex 2 (mTORC2) in response to insulin in parallel to AKT. Surprisingly, despite an identical substrate recognition motif to AKT, which drives insulin sensitivity, pathological accumulation of SGK1 drives insulin resistance. Liver-specific Sgk1-knockout (Sgk1Lko) mice display improved glucose tolerance and insulin sensitivity and are protected from hepatic steatosis when fed a high-fat diet. Sgk1 promotes insulin resistance by inactivating AMP-activated protein kinase (AMPK) via phosphorylation on inhibitory site AMPKαSer485/491. We demonstrate that SGK1 is dominant among SGK family kinases in regulation of insulin sensitivity, as Sgk1, Sgk2, and Sgk3 triple-knockout mice have similar increases in hepatic insulin sensitivity. In aggregate, these data suggest that targeting hepatic SGK1 may have therapeutic potential in T2D.

Keywords:  AMPK; SGK; glucose homeostasis; hepatic insulin resistance; lipid homeostasis; mTORC1; mTORC2; obesity; type 2 diabetes

DOI:  https://doi.org/10.1016/j.celrep.2021.109785
Free Radic Biol Med. 2021 Oct 02. pii: S0891-5849(21)00748-6. [Epub ahead of print]176 176-188

Cadmium attenuates testosterone synthesis by promoting ferroptosis and blocking autophagosome-lysosome fusion.

Ling Zeng, Jinzhao Zhou, Xiaofei Wang, Yanwei Zhang, Mei Wang, Ping Su.

  Ferroptosis is a newly defined programmed cell death pathway characterized by iron overload and lipid peroxidation. Increasing studies show that autophagy regulates testosterone synthesis and promotes ferroptosis. Testosterone is essential for sexual development and the maintenance of male characteristics. The deficiency of testosterone induced by cadmium (Cd) can severely affect male fertility. However, the underlying mechanism of testosterone reduction after Cd exposure remains blurry. In this study, we found that Cd affected iron homeostasis and elicited ferroptosis, ultimately reducing testosterone production. Mechanically, our findings revealed that Cd-induced ferroptosis depended upon the excessive activation of Heme oxygenase 1 (HMOX1) and the release of free iron from heme. Additionally, Cd exposure promoted autophagosome formation but blocked autophagosome-lysosome fusion, which attenuated the absorption of total cholesterol and triglycerides, further aggravating testosterone synthesis disorder. Collectively, Cd induced ferroptosis by iron homeostasis dysregulation, mediated by excessive activation of HMOX-1. The disruption of autophagy flow contributed to Cd-induced testicular dysfunction and attenuated testosterone synthesis.

Keywords:  Autophagy; Cadmium; Ferroptosis; Iron homeostasis; Testosterone synthesis

DOI:  https://doi.org/10.1016/j.freeradbiomed.2021.09.028
J Alzheimers Dis. 2021 Oct 01.

VPS35 Downregulation Alters Degradation Pathways in Neuronal Cells.

Alessia Filippone, Jian-Guo Li, Domenico Praticò.

   BACKGROUND: The vacuolar protein sorting 35 (VPS35) is the main component of the retromer recognition core complex system which regulates intracellular cargo protein sorting and trafficking. Downregulation of VPS35 has been linked to the pathogenesis of neurodegenerative disorders such Alzheimer's and Parkinson's diseases via endosome dysregulation.
OBJECTIVE: Here we show that the genetic manipulation of VPS35 affects intracellular degradation pathways.
METHODS: A neuronal cell line expressing human APP Swedish mutant was used. VPS35 silencing was performed treating cells with VPS35 siRNA or Ctr siRNA for 72 h.
RESULTS: Downregulation of VPS35 was associated with alteration of autophagy flux and intracellular accumulation of acidic and ubiquitinated aggregates suggesting that dysfunction of the retromer recognition core leads to a significant alteration in both pathways.
CONCLUSION: Taken together, our data demonstrate that besides cargo sorting and trafficking, VPS35 by supporting the integral function of the retromer complex system plays an important role also as a critical regulator of intracellular degradation pathways.

Keywords:  Alzheimer’s disease; autophagy pathway; endosomal system; proteosome pathway; retromer complex

DOI:  https://doi.org/10.3233/JAD-210701
Dev Cell. 2021 Sep 29. pii: S1534-5807(21)00731-0. [Epub ahead of print]

Rheb-regulated mitochondrial pyruvate metabolism of Schwann cells linked to axon stability.

Lanlan Jia, Maoxing Liao, Aidi Mou, Quanzhen Zheng, Wanchun Yang, Zongyan Yu, Yiyuan Cui, Xiaoqiang Xia, Yue Qin, Mina Chen, Bo Xiao.

  The metabolic coupling of Schwann cells (SCs) and peripheral axons is poorly understood. Few molecules in SCs are known to regulate axon stability. Using SC-specific Rheb knockout mice, we demonstrate that Rheb-regulated mitochondrial pyruvate metabolism is critical for SC-mediated non-cell-autonomous regulation of peripheral axon stability. Rheb knockout suppresses pyruvate dehydrogenase (PDH) activity (independently of mTORC1) and shifts pyruvate metabolism toward lactate production in SCs. The increased lactate causes age-dependent peripheral axon degeneration, affecting peripheral nerve function. Lactate, as an energy substrate and a potential signaling molecule, enhanced neuronal mitochondrial metabolism and energy production of peripheral nerves. Albeit beneficial to injured peripheral axons in the short term, we show that persistently increased lactate metabolism of neurons enhances ROS production, eventually damaging mitochondria, neuroenergetics, and axon stability. This study highlights the complex roles of lactate metabolism to peripheral axons and the importance of lactate homeostasis in preserving peripheral nerves.

Keywords:  ROS; Rheb; Schwann cells; axon degeneration; lactate shuttle; mTORC1; metabolic coupling; oxidative stress; peripheral axons; pyruvate metabolism

DOI:  https://doi.org/10.1016/j.devcel.2021.09.013
Mol Aspects Med. 2021 Oct 05. pii: S0098-2997(21)00101-1. [Epub ahead of print] 101041

Role of autophagy in muscle disease.

Anais Franco-Romero, Marco Sandri.

  Beside inherited muscle diseases many catabolic conditions such as insulin resistance, malnutrition, cancer growth, aging, infections, chronic inflammatory status, inactivity, obesity are characterized by loss of muscle mass, strength and function. The decrease of muscle quality and quantity increases morbidity, mortality and has a major impact on the quality of life. One of the pathogenetic mechanisms of muscle wasting is the dysregulation of the main protein and organelles quality control system of the cell: the autophagy-lysosome. This review will focus on the role of the autophagy-lysosome system in the different conditions of muscle loss. We will also dissect the signalling pathways that are involved in excessive or defective autophagy regulation. Finally, the state of the art of autophagy modulators that have been used in preclinical or clinical studies to ameliorate muscle mass will be also described.

Keywords:  Atrophy; Autophagy; Disuse; Muscle wasting; Proteostasis; Skeletal muscle

DOI:  https://doi.org/10.1016/j.mam.2021.101041
Autophagy. 2021 Oct 06. 1-4

Overexpression of ATG8/LC3 enhances wound-induced somatic reprogramming in Physcomitrium patens.

Jakob V Kanne, Masaki Ishikawa, Simon Bressendorff, Jeppe Ansbøl, Mitsuyasu Hasebe, Eleazar Rodriguez, Morten Petersen.

  Animal and plant somatic cells have the capacity to switch states or reprogram into stem cells to adapt during stress and injury. This ability to deal with stochastic changes or reprogramming of somatic cells also needs macroautophagy/autophagy. Here, we expand on this notion and provide a primary example of how overexpression of ATG8/LC3 in the moss Physcomitrium patens enhances the ability to reprogram somatic cells into stem cells when subjected to severe wounding. This observation suggests that autophagy is not only required for cells to dedifferentiate but also makes cells more competent to do so.ABBREVIATION: ATG: autophagy related; atg5: AUTOPHAGY 5; ATG8/LC3: AUTOPHAGY 8/microtubule associated protein 1 light chain 3; GFP: green fluorescent protein.

Keywords:  Autophagy; differentiation; pluripotency; reprogramming; stem cell

DOI:  https://doi.org/10.1080/15548627.2021.1975913
Neuron. 2021 Sep 27. pii: S0896-6273(21)00680-2. [Epub ahead of print]

Mitophagy in the basolateral amygdala mediates increased anxiety induced by aversive social experience.

Kaizheng Duan, Qinhua Gu, Ronald S Petralia, Ya-Xian Wang, Debabrata Panja, Xing Liu, Michael L Lehmann, Huiwen Zhu, Jun Zhu, Zheng Li.

Psychosocial stress is a common risk factor for anxiety disorders. The cellular mechanism for the anxiogenic effect of psychosocial stress is largely unclear. Here, we show that chronic social defeat (CSD) stress in mice causes mitochondrial impairment, which triggers the PINK1-Parkin mitophagy pathway selectively in the amygdala. This mitophagy elevation causes excessive mitochondrial elimination and consequent mitochondrial deficiency. Mitochondrial deficiency in the basolateral amygdalae (BLA) causes weakening of synaptic transmission in the BLA-BNST (bed nucleus of the stria terminalis) anxiolytic pathway and increased anxiety. The CSD-induced increase in anxiety-like behaviors is abolished in Pink1-/- and Park2-/- mice and alleviated by optogenetic activation of the BLA-BNST synapse. This study identifies an unsuspected role of mitophagy in psychogenetic-stress-induced anxiety elevation and reveals that mitochondrial deficiency is sufficient to increase anxiety and underlies the psychosocial-stress-induced anxiety increase. Mitochondria and mitophagy, therefore, can be potentially targeted to ameliorate anxiety.

DOI: https://doi.org/10.1016/j.neuron.2021.09.008
Mol Cell Oncol. 2021 ;8(4): 1947169

BNIP3 in melanoma: isn't it IRONic?

Mónica Vara-Pérez, Patrizia Agostinis.

  Melanoma cells exploit mitophagy and hypoxia signaling to promote their growth. In a recent study, we found that loss of B-cell lymphoma 2 (BCL-2)/adenovirus E1B 19kDa protein-interacting protein 3 (BNIP3) curbed Hypoxia Inducible Factor 1 alpha (HIF-1α) levels and melanoma growth in vivo. Insufficient levels of BNIP3 boost iron-driven prolyl hydroxylase 2 (Phd2)-mediated degradation of HIF-1α by exacerbating nuclear receptor activator 4 (Ncoa4)-mediated ferritinophagy. Thus, BNIP3 promotes melanoma growth by controlling iron metabolism.

Keywords:  BNIP3; HIF-1α; autophagy; ferritinophagy; iron; melanoma; metabolism

DOI:  https://doi.org/10.1080/23723556.2021.1947169
Life Sci. 2021 Oct 01. pii: S0024-3205(21)00992-9. [Epub ahead of print] 120005

SIRT3 protects kidneys from ischemia-reperfusion injury by modulating the DRP1 pathway to induce mitochondrial autophagy.

Wenyu Zhao, Mingxing Sui, Rui Chen, Hanlan Lu, Youhua Zhu, Lei Zhang, Li Zeng.

  Renal ischemia-reperfusion injury (IRI) is a leading cause of acute kidney injury (AKI) and may influence renal graft survival. In this study, we investigate the involvement of SIRT3 and DRP1 in mitochondrial autophagy and AKI in a mouse model of IRI. Autophagy was detected in the absence of SIRT3, and hypoxic reoxygenation (H/R) experiments using renal tubular epithelial cells NRK52E were performed in vitro to validate these results. We found that autophagosomes increased following IRI and that the expression of autophagy-related genes was up-regulated. The inhibition of autophagy with 3-methyladenine exacerbated IRI, whereas the DRP1 inhibitor Mdivi-1 reversed this inhibition. Mdivi-1 did not reverse the inhibition of autophagy in the absence of SIRT3. During IRI, Mdivi-1 reduced autophagy and DRP1 expression, whereas SIRT3 overexpression attenuated this condition. Rescue experiment showed that autophagy was increased when both SIRT3 or DRP1 were over- or under-expressed or just DRP1 was under-expressed but expression was reduced when just SIRT3 was under-expressed. However, the expression of DRP1-related molecules was reduced when SIRT3 was overexpressed and when DRP1 was under-expressed. Taken together, these findings indicate that SIRT3 protects against kidney damage from IRI by modulating the DRP1 pathway to induce mitochondrial autophagy.

Keywords:  Acute kidney injury; Ischemia-reperfusion injury; Mitophagy; SIRT3, DRP1

DOI:  https://doi.org/10.1016/j.lfs.2021.120005
Front Oncol. 2021 ;11 723966

Axitinib and HDAC Inhibitors Interact to Kill Sarcoma Cells.

Jane L Roberts, Laurence Booth, Andrew Poklepovic, Paul Dent.

  We have extended our analyses of HDAC inhibitor biology in sarcoma. The multi-kinase inhibitor axitinib interacted with multiple HDAC inhibitors to kill sarcoma cells. Axitinib and HDAC inhibitors interacted in a greater than additive fashion to inactivate AKT, mTORC1 and mTORC2, and to increase Raptor S722/S792 phosphorylation. Individually, all drugs increased phosphorylation of ATM S1981, AMPKα T172, ULK1 S317 and ATG13 S318 and reduced ULK1 S757 phosphorylation; this correlated with enhanced autophagic flux. Increased phosphorylation of ULK1 S317 and of Raptor S722/S792 required ATM-AMPK signaling. ULK1 S757 is a recognized site for mTORC1 and knock down of either ATM or AMPKα reduced the drug-induced dephosphorylation of this site. Combined exposure of cells to axitinib and an HDAC inhibitor significantly reduced the expression of HDAC1, HDAC2, HDAC3, HDAC4, HDAC6 and HDAC7. No response was observed for HDACs 10 and 11. Knock down of ULK1, Beclin1 or ATG5 prevented the decline in HDAC expression, as did expression of a constitutively active mTOR protein. Axitinib combined with HDAC inhibitors enhanced expression of Class I MHCA and reduced expression of PD-L1 which was recapitulated via knock down studies, particularly of HDACs 1 and 3. In vivo, axitinib and the HDAC inhibitor entinostat interacted to significantly reduce tumor growth. Collectively our findings support the exploration of axitinib and HDAC inhibitors being developed as a novel sarcoma therapy.

Keywords:  HDACi; MHCA; PD-L1; autophagy; axitinib; sarcoma

DOI:  https://doi.org/10.3389/fonc.2021.723966
Cell Death Dis. 2021 Oct 08. 12(10): 919

An interplay between UCP2 and ROS protects cells from high-salt-induced injury through autophagy stimulation.

Maurizio Forte, Franca Bianchi, Maria Cotugno, Simona Marchitti, Rosita Stanzione, Vittorio Maglione, Sebastiano Sciarretta, Valentina Valenti, Roberto Carnevale, Francesco Versaci, Giacomo Frati, Massimo Volpe, Speranza Rubattu.

The mitochondrial uncoupling protein 2 (UCP2) plays a protective function in the vascular disease of both animal models and humans. UCP2 downregulation upon high-salt feeding favors vascular dysfunction in knock-out mice, and accelerates cerebrovascular and renal damage in the stroke-prone spontaneously hypertensive rat. Overexpression of UCP2 counteracts the negative effects of high-salt feeding in both animal models. We tested in vitro the ability of UCP2 to stimulate autophagy and mitophagy as a mechanism mediating its protective effects upon high-salt exposure in endothelial and renal tubular cells. UCP2 silencing reduced autophagy and mitophagy, whereas the opposite was true upon UCP2 overexpression. High-salt exposure increased level of reactive oxygen species (ROS), UCP2, autophagy and autophagic flux in both endothelial and renal tubular cells. In contrast, high-salt was unable to induce autophagy and autophagic flux in UCP2-silenced cells, concomitantly with excessive ROS accumulation. The addition of an autophagy inducer, Tat-Beclin 1, rescued the viability of UCP2-silenced cells even when exposed to high-salt. In summary, UCP2 mediated the interaction between high-salt-induced oxidative stress and autophagy to preserve viability of both endothelial and renal tubular cells. In the presence of excessive ROS accumulation (achieved upon UCP2 silencing and high-salt exposure of silenced cells) autophagy was turned off. In this condition, an exogenous autophagy inducer rescued the cellular damage induced by excess ROS level. Our data confirm the protective role of UCP2 toward high-salt-induced vascular and renal injury, and they underscore the role of autophagy/mitophagy as a mechanism counteracting the high-salt-induced oxidative stress damage.

DOI: https://doi.org/10.1038/s41419-021-04188-4
Cell Death Dis. 2021 Oct 07. 12(10): 917

Sulforaphane downregulated fatty acid synthase and inhibited microtubule-mediated mitophagy leading to apoptosis.

Yuting Yan, Yan Zhou, Juntao Li, Zhongnan Zheng, Yabin Hu, Lei Li, Wei Wu.

We previously demonstrated that sulforaphane (SFN) inhibited autophagy leading to apoptosis in human non-small cell lung cancer (NSCLC) cells, but the underlying subcellular mechanisms were unknown. Hereby, high-performance liquid chromatography-tandem mass spectrometry uncovered that SFN regulated the production of lipoproteins, and microtubule- and autophagy-associated proteins. Further, highly expressed fatty acid synthase (FASN) contributed to cancer malignancy and poor prognosis. Results showed that SFN depolymerized microtubules, downregulated FASN, and decreased its binding to α-tubulin; SFN downregulated FASN, acetyl CoA carboxylase (ACACA), and ATP citrate lyase (ACLY) via activating proteasomes and downregulating transcriptional factor SREBP1; SFN inhibited the interactions among α-tubulin and FASN, ACACA, and ACLY; SFN decreased the amount of intracellular fatty acid (FA) and mitochondrial phospholipids; and knockdown of FASN decreased mitochondrial membrane potential (ΔΨm) and increased reactive oxygen species, mitochondrial abnormality, and apoptosis. Further, SFN downregulated mitophagy-associated proteins Bnip3 and NIX, and upregulated mitochondrial LC3 II/I. Transmission electron microscopy showed mitochondrial abnormality and accumulation of mitophagosomes in response to SFN. Combined with mitophagy inducer CCCP or autophagosome-lysosome fusion inhibitor Bafilomycin A1, we found that SFN inhibited mitophagosome-lysosome fusion leading to mitophagosome accumulation. SFN reduced the interaction between NIX and LC3 II/I, and reversed CCCP-caused FA increase. Furthermore, knockdown of α-tubulin downregulated NIX and BNIP3 production, and upregulated LC3 II/I. Besides, SFN reduced the interaction and colocalization between α-tubulin and NIX. Thus, SFN might cause apoptosis via inhibiting microtubule-mediated mitophagy. These results might give us a new insight into the mechanisms of SFN-caused apoptosis in the subcellular level.

DOI: https://doi.org/10.1038/s41419-021-04198-2
J Am Soc Nephrol. 2021 Oct 04. pii: ASN.2021030333. [Epub ahead of print]

mTOR-Activating Mutations in RRAGD are Causative for Kidney Tubulopathy and Cardiomyopathy.

Karl-Peter Schlingmann, François Jouret, Kuang Shen, Anukrati Nigam, Francisco Arjona, Claudia Dafinger, Pascal Houillier, Deborah Jones, Felix Kleinerüschkamp, Jun Oh, Nathalie Godefroid, Mehmet Eltan, Tülay Güran, Stéphane Burtey, Marie-Christine Parotte, Jens König, Alina Braun, Caro Bos, Maria Ibars Serra, Holger Rehmann, Fried Zwartkruis, Kirsten Renkema, Karin Klingel, Eric Schulze-Bahr, Bernhard Schermer, Carsten Bergmann, Janine Altmüller, Holger Thiele, Bodo Beck, Karin Dahan, David Sabatini, Max Liebau, Rosa Vargas-Poussou, Nine Knoers, Martin Konrad, Jeroen de Baaij.

Background Over the last decade, advances in genetic techniques have resulted in the identification of rare hereditary disorders of renal magnesium and salt handling. Nevertheless, approximately 20% of all tubulopathy patients lack a genetic diagnosis. Methods We performed whole-exome and genome sequencings of a patient cohort with a novel inherited salt-losing tubulopathy, hypomagnesemia, and dilated cardiomyopathy. We also conducted subsequent functional analyses in vitro of identified variants of RRAGD, a gene that encodes a small Rag guanosine triphosphatase (GTPase). Results In eight children from unrelated families with a tubulopathy characterized by hypomagnesemia, hypokalemia, salt wasting, and nephrocalcinosis, we identified heterozygous missense variants in RRAGD that mostly occurred de novo Six of these patients also had dilated cardiomyopathy and three underwent heart transplantation. We identified a heterozygous variant in RRAGD that segregated with the phenotype in eight members of a large family with similar kidney manifestations. The GTPase RagD encoded by RRAGD plays a role in mediating amino acid signaling to the mechanistic target of rapamycin complex 1 (mTORC1). RagD expression along the mammalian nephron included the thick ascending limb and the distal convoluted tubule. The identified RRAGD variants were shown to induce a constitutive activation of mTOR signaling in vitro Conclusions Our findings establish a novel disease, which we call autosomal dominant kidney hypomagnesemia (ADKH-RRAGD), that combines an electrolyte-losing tubulopathy and dilated cardiomyopathy. The condition is caused by variants in the RRAGD gene, which encodes Rag GTPase D; these variants lead to an activation of mTOR signaling, suggesting a critical role of Rag GTPase D for renal electrolyte handling and cardiac function.

DOI: https://doi.org/10.1681/ASN.2021030333
J Cell Mol Med. 2021 Oct 08.

Regulation of autophagy protects against liver injury in liver surgery-induced ischaemia/reperfusion.

Chenxia Hu, Lingfei Zhao, Fen Zhang, Lanjuan Li.

  Transient ischaemia and reperfusion in liver tissue induce hepatic ischaemia/reperfusion (I/R) tissue injury and a profound inflammatory response in vivo. Hepatic I/R can be classified into warm I/R and cold I/R and is characterized by three main types of cell death, apoptosis, necrosis and autophagy, in rodents or patients following I/R. Warm I/R is observed in patients or animal models undergoing liver resection, haemorrhagic shock, trauma, cardiac arrest or hepatic sinusoidal obstruction syndrome when vascular occlusion inhibits normal blood perfusion in liver tissue. Cold I/R is a condition that affects only patients who have undergone liver transplantation (LT) and is caused by donated liver graft preservation in a hypothermic environment prior to entering a warm reperfusion phase. Under stress conditions, autophagy plays a critical role in promoting cell survival and maintaining liver homeostasis by generating new adenosine triphosphate (ATP) and organelle components after the degradation of macromolecules and organelles in liver tissue. This role of autophagy may contribute to the protection of hepatic I/R-induced liver injury; however, a considerable amount of evidence has shown that autophagy inhibition also protects against hepatic I/R injury by inhibiting autophagic cell death under specific circumstances. In this review, we comprehensively discuss current strategies and underlying mechanisms of autophagy regulation that alleviates I/R injury after liver resection and LT. Directed autophagy regulation can maintain liver homeostasis and improve liver function in individuals undergoing warm or cold I/R. In this way, autophagy regulation can contribute to improving the prognosis of patients undergoing liver resection or LT.

Keywords:  autophagy; cell death; ischaemia/reperfusion; liver resection; liver transplantation

DOI:  https://doi.org/10.1111/jcmm.16943
Front Pharmacol. 2021 ;12 736655

Atractyloside Protect Mice Against Liver Steatosis by Activation of Autophagy via ANT-AMPK-mTORC1 Signaling Pathway.

Pengfei Zhang, Xinyu Cheng, Huimin Sun, Yajing Li, Wuxuan Mei, Changchun Zeng.

  Objective: Adenine nucleotide translocase (ANT) can transport ADP from cytoplasm to mitochondrial matrix and provide raw materials for ATP synthesis by oxidative phosphorylation. Dysfunction of ANT leads to limitation of ADP transport and decrease of ATP production. Atractyloside (ATR) is considered as a cytotoxic competitive inhibitor binding to ANT, making ANT vulnerable to transport ADP, and reduces ATP synthesis. Moreover, the blockage of ANT by ATR may increase ADP/ATP ratio, activate AMPK-mTORC1-autophagy signaling pathway, and promote lipid degradation in steatosis hepatocytes. The present study was conducted to investigate the mechanism of ATR, regulate ANT-AMPK-mTORC1 signaling pathway to activate autophagy, and promote the degradation of lipid droplets in high-fat diet (HFD) induced liver steatosis. Methods: ICR mice were fed with HFD for 8 weeks to induce liver steatosis, and ATR solution was given by intraperitoneal injection. Intracellular triglyceride level and oil red O staining-lipid droplets (LDs) were assessed, the expression of proteins related to ANT-AMPK-mTORC1 signaling pathway and autophagy were determined, and the colocalization of LC3B and Perilipin 2 was performed. Results: ATR treatment decreased the serum AST level, relative weight of liver and epididymal fat, and body weight of HFD mice. The LDs in HFD mice livers were reduced in the presence of ATR, and the TG level in serum and liver of HFD mice was significantly reduced by ATR. In addition, ATR inhibited ANT2 expression, promoted the activation of AMPK, then increased Raptor expression, and finally decreased the mTOR activity. Furthermore, ATR increased the protein level of LC3A/B and ATG7, and a strong colocalization of LC3B and PLIN2 was observed. Conclusion: ATR treatment blocks ANT2 expression, promotes the activation of AMPK, then decreases the mTOR activity, and finally promotes autophagosomes formation, thus accelerating the degradation of HFD-induced accumulated lipids in the liver. This will provide new therapeutic ideas and experimental data for clinical prevention and treatment of non-alcoholic fatty liver disease.

Keywords:  adenine nucleotide translocase; atractyloside; autophagy; lipid degradation; nonalcoholic fatty liver disease

DOI:  https://doi.org/10.3389/fphar.2021.736655
JCI Insight. 2021 Oct 07. pii: e136147. [Epub ahead of print]

Microglia regulate brain Progranulin levels through the endocytosis-lysosomal pathway.

Tingting Dong, Leon Tejwani, Youngseob Jung, Hiroshi Kokubu, Kimberly Luttik, Terri M Driessen, Janghoo Lim.

  Genetic variants in Granulin (GRN), which encodes the secreted glycoprotein Progranulin (PGRN), are associated with several neurodegenerative diseases including frontotemporal lobar degeneration, neuronal ceroid lipofuscinosis, and Alzheimer's disease. These genetic alterations manifest in pathological changes due to a reduction of PGRN expression; therefore, identifying factors that can modulate PGRN levels in vivo would enhance our understanding of PGRN in neurodegeneration, and could reveal novel potential therapeutic targets. Here, we report that modulation of the endocytosis-lysosomal pathway via reduction of Nemo-like kinase (Nlk) in microglia, and not neurons, can alter total brain Pgrn levels in mice. We demonstrate that Nlk reduction promotes Pgrn degradation by enhancing its trafficking through endocytosis-lysosomal pathway, specifically in microglia. Furthermore, genetic interaction studies in mice showed that Nlk heterozygosity in Grn haploinsufficient mice further reduces Pgrn levels and induces neuropathological phenotypes associated with PGRN deficiency. Our results reveal a new mechanism for Pgrn level regulation in the brain through the active catabolism by microglia and provide insights into the pathophysiology of PGRN-associated diseases.

Keywords:  Dementia; Mouse models; Neurodegeneration; Neuroscience

DOI:  https://doi.org/10.1172/jci.insight.136147