bims-lysosi Biomed News
on Lysosomes and signaling
Issue of 2020‒08‒02
forty papers selected by
Stephanie Fernandes
Max Planck Institute for Biology of Ageing


  1. Nature. 2020 Jul 29.
    Banik SM, Pedram K, Wisnovsky S, Ahn G, Riley NM, Bertozzi CR.
      The majority of therapies that target individual proteins rely on specific activity-modulating interactions with the target protein-for example, enzyme inhibition or ligand blocking. However, several major classes of therapeutically relevant proteins have unknown or inaccessible activity profiles and so cannot be targeted by such strategies. Protein-degradation platforms such as proteolysis-targeting chimaeras (PROTACs)1,2 and others (for example, dTAGs3, Trim-Away4, chaperone-mediated autophagy targeting5 and SNIPERs6) have been developed for proteins that are typically difficult to target; however, these methods involve the manipulation of intracellular protein degradation machinery and are therefore fundamentally limited to proteins that contain cytosolic domains to which ligands can bind and recruit the requisite cellular components. Extracellular and membrane-associated proteins-the products of 40% of all protein-encoding genes7-are key agents in cancer, ageing-related diseases and autoimmune disorders8, and so a general strategy to selectively degrade these proteins has the potential to improve human health. Here we establish the targeted degradation of extracellular and membrane-associated proteins using conjugates that bind both a cell-surface lysosome-shuttling receptor and the extracellular domain of a target protein. These initial lysosome-targeting chimaeras, which we term LYTACs, consist of a small molecule or antibody fused to chemically synthesized glycopeptide ligands that are agonists of the cation-independent mannose-6-phosphate receptor (CI-M6PR). We use LYTACs to develop a CRISPR interference screen that reveals the biochemical pathway for CI-M6PR-mediated cargo internalization in cell lines, and uncover the exocyst complex as a previously unidentified-but essential-component of this pathway. We demonstrate the scope of this platform through the degradation of therapeutically relevant proteins, including apolipoprotein E4, epidermal growth factor receptor, CD71 and programmed death-ligand 1. Our results establish a modular strategy for directing secreted and membrane proteins for lysosomal degradation, with broad implications for biochemical research and for therapeutics.
    DOI:  https://doi.org/10.1038/s41586-020-2545-9
  2. EMBO J. 2020 Jul 27. e105696
    Cinque L, De Leonibus C, Iavazzo M, Krahmer N, Intartaglia D, Salierno FG, De Cegli R, Di Malta C, Svelto M, Lanzara C, Maddaluno M, Wanderlingh LG, Huebner AK, Cesana M, Bonn F, Polishchuk E, Hübner CA, Conte I, Dikic I, Mann M, Ballabio A, Sacco F, Grumati P, Settembre C.
      Lysosomal degradation of the endoplasmic reticulum (ER) via autophagy (ER-phagy) is emerging as a critical regulator of cell homeostasis and function. The recent identification of ER-phagy receptors has shed light on the molecular mechanisms underlining this process. However, the signaling pathways regulating ER-phagy in response to cellular needs are still largely unknown. We found that the nutrient responsive transcription factors TFEB and TFE3-master regulators of lysosomal biogenesis and autophagy-control ER-phagy by inducing the expression of the ER-phagy receptor FAM134B. The TFEB/TFE3-FAM134B axis promotes ER-phagy activation upon prolonged starvation. In addition, this pathway is activated in chondrocytes by FGF signaling, a critical regulator of skeletal growth. FGF signaling induces JNK-dependent proteasomal degradation of the insulin receptor substrate 1 (IRS1), which in turn inhibits the PI3K-PKB/Akt-mTORC1 pathway and promotes TFEB/TFE3 nuclear translocation and enhances FAM134B transcription. Notably, FAM134B is required for protein secretion in chondrocytes, and cartilage growth and bone mineralization in medaka fish. This study identifies a new signaling pathway that allows ER-phagy to respond to both metabolic and developmental cues.
    Keywords:   TFEB ; ER-phagy; FGF signaling; Fam134B; IRS1/PI3K signaling
    DOI:  https://doi.org/10.15252/embj.2020105696
  3. Cell Rep. 2020 Jul 28. pii: S2211-1247(20)30954-2. [Epub ahead of print]32(4): 107973
    Albrecht LV, Tejeda-Muñoz N, Bui MH, Cicchetto AC, Di Biagio D, Colozza G, Schmid E, Piccolo S, Christofk HR, De Robertis EM.
      Canonical Wnt signaling is emerging as a major regulator of endocytosis. Here, we report that Wnt-induced macropinocytosis is regulated through glycogen synthase kinase 3 (GSK3) and the β-catenin destruction complex. We find that mutation of Axin1, a tumor suppressor and component of the destruction complex, results in the activation of macropinocytosis. Surprisingly, inhibition of GSK3 by lithium chloride (LiCl), CHIR99021, or dominant-negative GSK3 triggers macropinocytosis. GSK3 inhibition causes a rapid increase in acidic endolysosomes that is independent of new protein synthesis. GSK3 inhibition or Axin1 mutation increases lysosomal activity, which can be followed with tracers of active cathepsin D, β-glucosidase, and ovalbumin degradation. Microinjection of LiCl into the blastula cavity of Xenopus embryos causes a striking increase in dextran macropinocytosis. The effects of GSK3 inhibition on protein degradation in endolysosomes are blocked by the macropinocytosis inhibitors EIPA or IPA-3, suggesting that increases in membrane trafficking drive lysosomal activity.
    Keywords:  Axin1; Pak1; cathepsin D; colorectal carcinoma; hepatocellular carcinoma; lysosome; membrane trafficking; multivesicular bodies; nutrient acquisition; β-glucosidase
    DOI:  https://doi.org/10.1016/j.celrep.2020.107973
  4. Proc Natl Acad Sci U S A. 2020 Jul 31. pii: 202008021. [Epub ahead of print]
    Wei W, Ruvkun G.
      Mitochondrial fission and fusion are highly regulated by energy demand and physiological conditions to control the production, activity, and movement of these organelles. Mitochondria are arrayed in a periodic pattern in Caenorhabditis elegans muscle, but this pattern is disrupted by mutations in the mitochondrial fission component dynamin DRP-1. Here we show that the dramatically disorganized mitochondria caused by a mitochondrial fission-defective dynamin mutation is strongly suppressed to a more periodic pattern by a second mutation in lysosomal biogenesis or acidification. Vitamin B12 is normally imported from the bacterial diet via lysosomal degradation of B12-binding proteins and transport of vitamin B12 to the mitochondrion and cytoplasm. We show that the lysosomal dysfunction induced by gene inactivations of lysosomal biogenesis or acidification factors causes vitamin B12 deficiency. Growth of the C. elegans dynamin mutant on an Escherichia coli strain with low vitamin B12 also strongly suppressed the mitochondrial fission defect. Of the two C. elegans enzymes that require B12, gene inactivation of methionine synthase suppressed the mitochondrial fission defect of a dynamin mutation. We show that lysosomal dysfunction induced mitochondrial biogenesis, which is mediated by vitamin B12 deficiency and methionine restriction. S-adenosylmethionine, the methyl donor of many methylation reactions, including histones, is synthesized from methionine by S-adenosylmethionine synthase; inactivation of the sams-1 S-adenosylmethionine synthase also suppresses the drp-1 fission defect, suggesting that vitamin B12 regulates mitochondrial biogenesis and then affects mitochondrial fission via chromatin pathways.
    Keywords:  interorganelle communication; methionine restriction; mitochondrial dynamics; vacuolar V-ATPase; vitamin B12
    DOI:  https://doi.org/10.1073/pnas.2008021117
  5. FASEB J. 2020 Jul 27.
    Nam TS, Park DR, Rah SY, Woo TG, Chung HT, Brenner C, Kim UH.
      Nicotinic acid adenine dinucleotide phosphate (NAADP) is the most potent Ca2+ mobilizing second messenger whose formation has remained elusive. In vitro, CD38-mediated NAADP synthesis requires an acidic pH and a nonphysiological concentration of nicotinic acid (NA). We discovered that CD38 catalyzes synthesis of NAADP by exchanging the nicotinamide moiety of nicotinamide adenine dinucleotide phosphate (NADP+ ) for the NA group of nicotinic acid adenine dinucleotide (NAAD) inside endolysosomes of interleukin 8 (IL8)-treated lymphokine-activated killer (LAK) cells. Upon IL8 stimulation, cytosolic NADP+ is transported to acidified endolysosomes via connexin 43 (Cx43) and gated by cAMP-EPAC-RAP1-PP2A signaling. CD38 then performs a base-exchange reaction with the donor NA group deriving from NAAD, produced by newly described endolysosomal activities of NA phosphoribosyltransferase (NAPRT) and NMN adenyltransferase (NMNAT) 3. Thus, the membrane organization of endolysosomal CD38, a signal-mediated transport system for NADP+ and luminal NAD+ biosynthetic enzymes integrate signals from a chemokine and cAMP to specify the spatiotemporal mobilization of Ca2+ to drive cell migration.
    Keywords:  calcium; cell migration; nicotinamide adenine dinucleotide; signal transduction
    DOI:  https://doi.org/10.1096/fj.202001249R
  6. Cell Cycle. 2020 Jul 29. 1-11
    Jacobs KA, Maghe C, Gavard J.
      Lysosomes are acidic, dynamic organelles that supervise catabolism, integrate signaling cascades, and tune cellular trafficking. Moreover, the loss of their integrity may jeopardize cell viability. In cancer cells, lysosomes are qualitatively and quantitatively modified for the tumor's own benefit. For all these reasons, these organelles emerge as appealing intracellular targets to manipulate non-oncogene addiction. This is of particular interest for brain diseases, including neurodegenerative disorders and cancer, in which stem cells are exhausted and transformed, respectively. Recent publications had demonstrated that stem cells displayed disarmed lysosomes in terms of number and functions during aging and oncogenic progression. Likewise, our laboratory identified that the arginine protease MALT1, normally dedicated to the assembly of proper NF-kB activation and processing a number of substrates, arbitrates lysosome biogenesis and mTOR signaling in glioblastoma stem-like cells. Indeed, blocking either the expression or the activity of this enzyme leads to an aberrant increase of lysosomes, alongside of the down-regulation of the mTOR signaling. This surge of lysosomes eradicates glioblastoma stem-like cells. Targeting lysosomes might thus inspire the design of new strategies to face this devastating human cancer. Here, we provide an overview of the functions of the lysosome as well as its role as a cell death initiator, to highlight the potential of lysosomal drugs for glioblastoma therapy.
    Keywords:  Lysosome; MALT1; glioma; mTOR; membrane permeabilization; stem cells
    DOI:  https://doi.org/10.1080/15384101.2020.1796016
  7. Am J Physiol Cell Physiol. 2020 Jul 29.
    Abou Sawan S, Mazzulla M, Moore DR, Hodson N.
      Skeletal muscle is a highly plastic tissue capable of remodeling in response to a range of physiological stimuli including nutrients and exercise. Historically, the lysosome has been considered an essentially catabolic organelle contributing to autophagy, phagocytosis, and exo/endocytosis in skeletal muscle. However, recent evidence has emerged of several anabolic roles for the lysosome including the requirement for autophagy in skeletal muscle mass maintenance, the discovery of the lysosome as an intracellular signaling hub for mTORC1 activation, and the importance of TFEB/lysosomal biogenesis-related signaling in the regulation of mTORC1-mediated protein synthesis. We therefore propose that the lysosome is an understudied organelle with the potential to underpin the skeletal muscle adaptive response to anabolic stimuli. Within this review we describe the molecular regulation of lysosome biogenesis and detail the emerging anabolic roles of the lysosome in skeletal muscle with particular emphasis on how these roles may mediate adaptations to chronic resistance exercise. Furthermore, given the well-established role of amino acids to support muscle protein remodeling, we describe how dietary proteins 'labeled' with stable isotopes could provide a complimentary research tool to better understand how lysosomal biogenesis, autophagy regulation, and/or mTORC1-lysosomal repositioning can mediate the intracellular usage of dietary amino acids in response anabolic stimuli. Finally, we provide avenues for future research with the aim of elucidating how the regulation of this important organelle could mediate skeletal muscle anabolism.
    Keywords:  Lysosomal Biogenesis; Lysosome; Resistance Exercise; TFEB; mTORC1
    DOI:  https://doi.org/10.1152/ajpcell.00241.2020
  8. Front Cell Dev Biol. 2020 ;8 539
    Hurst LR, Fratti RA.
      The Saccharomyces cerevisiae lysosome-like vacuole is a useful model for studying membrane fusion events and organelle maturation processes utilized by all eukaryotes. The vacuolar membrane is capable of forming micrometer and nanometer scale domains that can be visualized using microscopic techniques and segregate into regions with surprisingly distinct lipid and protein compositions. These lipid raft domains are liquid-ordered (L o ) like regions that are rich in sphingolipids, phospholipids with saturated acyl chains, and ergosterol. Recent studies have shown that these lipid rafts contain an enrichment of many different proteins that function in essential activities such as nutrient transport, organelle contact, membrane trafficking, and homotypic fusion, suggesting that they are biologically relevant regions within the vacuole membrane. Here, we discuss recent developments and the current understanding of sphingolipid and ergosterol function at the vacuole, the composition and function of lipid rafts at this organelle and how the distinct lipid and protein composition of these regions facilitates the biological processes outlined above.
    Keywords:  lipid rafts; membrane fusion; membrane trafficking; sphingolipids; vacuole
    DOI:  https://doi.org/10.3389/fcell.2020.00539
  9. Front Oncol. 2020 ;10 1156
    Geisslinger F, Müller M, Vollmar AM, Bartel K.
      To date, cancer remains a worldwide leading cause of death, with a still rising incidence. This is essentially caused by the fact, that despite the abundance of therapeutic targets and treatment strategies, insufficient response and multidrug resistance frequently occur. Underlying mechanisms are multifaceted and extensively studied. In recent research, it became evident, that the lysosome is of importance in drug resistance phenotypes. While it has long been considered just as cellular waste bag, it is now widely known that lysosomes play an important role in important cellular signaling processes and are in the focus of cancer research. In that regard lysosomes are now considered as so-called "drug safe-houses" in which chemotherapeutics are trapped passively by diffusion or actively by lysosomal P-glycoprotein activity, which prevents them from reaching their intracellular targets. Furthermore, alterations in lysosome to nucleus signaling by the transcription factor EB (TFEB)-mTORC1 axis are implicated in development of chemoresistance. The identification of lysosomes as essential players in drug resistance has introduced novel strategies to overcome chemoresistance and led to innovate therapeutic approaches. This mini review gives an overview of the current state of research on the role of lysosomes in chemoresistance, summarizing underlying mechanisms and treatment strategies and critically discussing open questions and drawbacks.
    Keywords:  TFEB; cancer; chemoresistance; cytostatics; lysosome
    DOI:  https://doi.org/10.3389/fonc.2020.01156
  10. J Biol Chem. 2020 Jul 28. pii: jbc.RA119.010794. [Epub ahead of print]
    Luu AR, Wong H, Agrawal V, Wise N, Handyside B, Lo MJ, Pacheco G, Felix JB, Giaramita A, d'Azzo A, Vincelette J, Bullens S, Bunting S, Christianson TM, Hague C, Lebowitz JH, Yogalingam G.
      Mutations in the galactosidase β 1 (GLB1) gene cause lysosomal β-galactosidase (β-Gal) deficiency and clinical onset of the neurodegenerative lysosomal storage disease, GM1 gangliosidosis. β-Gal and neuraminidase 1 (NEU1) form a multi-enzyme complex in lysosomes along with the molecular chaperone, protective protein cathepsin A (PPCA). NEU1 is deficient in the neurodegenerative lysosomal storage disease sialidosis, and its targeting to and stability in lysosomes strictly depend on PPCA. In contrast, β-Gal only partially depends on PPCA, prompting us to investigate the role that β-Gal plays in the multienzyme complex. Here, we demonstrate that β-Gal negatively regulates NEU1 levels in lysosomes by competitively displacing this labile sialidase from PPCA. Chronic cellular uptake of purified recombinant human β-Gal (rhβ-Gal) or chronic lentiviral-mediated GLB1 over-expression in GM1 gangliosidosis patient fibroblasts coincides with profound secondary NEU1 deficiency. A regimen of intermittent enzyme replacement therapy (ERT) dosing with rhβ-Gal, followed by enzyme withdrawal, is sufficient to augment β-Gal activity levels in GM1 gangliosidosis patient fibroblasts without promoting NEU1 deficiency. In the absence of β-Gal, NEU1 levels are elevated in the GM1 gangliosidosis mouse brain, which are restored to normal levels following weekly intracerebroventricular (ICV) dosing with rhβ-Gal.  Collectively, our results highlight the need to carefully titrate the dose and dosing frequency of β-Gal augmentation therapy for GM1 gangliosidosis. They further suggest that intermittent ICV-ERT dosing with rhβ-Gal is a tunable approach that can safely augment β-Gal levels while maintaining NEU1 at physiological levels in the GM1 gangliosidosis brain.
    Keywords:  Beta-Galactosidase; Enzyme replacement therapy; GM1 gangliosidosis; Neuraminidase; PPCA; complex; gene therapy; genetic disease; neuraminidase; sialidase
    DOI:  https://doi.org/10.1074/jbc.RA119.010794
  11. Nat Med. 2020 Jul 27.
    Centa JL, Jodelka FM, Hinrich AJ, Johnson TB, Ochaba J, Jackson M, Duelli DM, Weimer JM, Rigo F, Hastings ML.
      CLN3 Batten disease is an autosomal recessive, neurodegenerative, lysosomal storage disease caused by mutations in CLN3, which encodes a lysosomal membrane protein1-3. There are no disease-modifying treatments for this disease that affects up to 1 in 25,000 births, has an onset of symptoms in early childhood and typically is fatal by 20-30 years of life4-7. Most patients with CLN3 Batten have a deletion encompassing exons 7 and 8 (CLN3∆ex7/8), creating a reading frameshift7,8. Here we demonstrate that mice with this deletion can be effectively treated using an antisense oligonucleotide (ASO) that induces exon skipping to restore the open reading frame. A single treatment of neonatal mice with an exon 5-targeted ASO-induced robust exon skipping for more than a year, improved motor coordination, reduced histopathology in Cln3∆ex7/8 mice and increased survival in a new mouse model of the disease. ASOs also induced exon skipping in cell lines derived from patients with CLN3 Batten disease. Our findings demonstrate the utility of ASO-based reading-frame correction as an approach to treat CLN3 Batten disease and broaden the therapeutic landscape for ASOs in the treatment of other diseases using a similar strategy.
    DOI:  https://doi.org/10.1038/s41591-020-0986-1
  12. Biomolecules. 2020 Jul 26. pii: E1110. [Epub ahead of print]10(8):
    Pinto E Vairo F, Rojas Málaga D, Kubaski F, Fischinger Moura de Souza C, de Oliveira Poswar F, Baldo G, Giugliani R.
      Precision medicine (PM) is an emerging approach for disease treatment and prevention that accounts for the individual variability in the genes, environment, and lifestyle of each person. Lysosomal diseases (LDs) are a group of genetic metabolic disorders that include approximately 70 monogenic conditions caused by a defect in lysosomal function. LDs may result from primary lysosomal enzyme deficiencies or impairments in membrane-associated proteins, lysosomal enzyme activators, or modifiers that affect lysosomal function. LDs are heterogeneous disorders, and the phenotype of the affected individual depends on the type of substrate and where it accumulates, which may be impacted by the type of genetic change and residual enzymatic activity. LDs are individually rare, with a combined incidence of approximately 1:4000 individuals. Specific therapies are already available for several LDs, and many more are in development. Early identification may enable disease course prediction and a specific intervention, which is very important for clinical outcome. Driven by advances in omics technology, PM aims to provide the most appropriate management for each patient based on the disease susceptibility or treatment response predictions for specific subgroups. In this review, we focused on the emerging diagnostic technologies that may help to optimize the management of each LD patient and the therapeutic options available, as well as in clinical developments that enable customized approaches to be selected for each subject, according to the principles of PM.
    Keywords:  enzyme replacement therapy; gene therapy.; lysosomal diseases; pharmacological chaperones; precision medicine
    DOI:  https://doi.org/10.3390/biom10081110
  13. Front Cell Dev Biol. 2020 ;8 591
    Julian LM, Stanford WL.
      Regulation of stem cell fate is best understood at the level of gene and protein regulatory networks, though it is now clear that multiple cellular organelles also have critical impacts. A growing appreciation for the functional interconnectedness of organelles suggests that an orchestration of integrated biological networks functions to drive stem cell fate decisions and regulate metabolism. Metabolic signaling itself has emerged as an integral regulator of cell fate including the determination of identity, activation state, survival, and differentiation potential of many developmental, adult, disease, and cancer-associated stem cell populations and their progeny. As the primary adenosine triphosphate-generating organelles, mitochondria are well-known regulators of stem cell fate decisions, yet it is now becoming apparent that additional organelles such as the lysosome are important players in mediating these dynamic decisions. In this review, we will focus on the emerging role of organelles, in particular lysosomes, in the reprogramming of both metabolic networks and stem cell fate decisions, especially those that impact the determination of cell identity. We will discuss the inter-organelle interactions, cell signaling pathways, and transcriptional regulatory mechanisms with which lysosomes engage and how these activities impact metabolic signaling. We will further review recent data that position lysosomes as critical regulators of cell identity determination programs and discuss the known or putative biological mechanisms. Finally, we will briefly highlight the potential impact of elucidating mechanisms by which lysosomes regulate stem cell identity on our understanding of disease pathogenesis, as well as the development of refined regenerative medicine, biomarker, and therapeutic strategies.
    Keywords:  cancer stem cell (CSC); lysosomes; metabolism; neural crest (NC); neural stem cell (NSC); pluripotent stem cell (PSC); stem cell identity and fate
    DOI:  https://doi.org/10.3389/fcell.2020.00591
  14. Cell Calcium. 2020 Jul 17. pii: S0143-4160(20)30091-9. [Epub ahead of print]91 102249
    Pihán P, Hetz C.
      The endoplasmic reticulum (ER) is the source of lysosomal calcium. The finding that the protein TMBIM6 -a putative ER calcium channel and cell death regulator -promotes calcium transfer from the ER to lysosomes to induce autophagy uncovers a missing piece in the puzzle of inter-organelle communication.
    Keywords:  Autophagy; Calcium; ER stress; Lysosome; Protein misfolding; UPR
    DOI:  https://doi.org/10.1016/j.ceca.2020.102249
  15. Curr Opin Cell Biol. 2020 Jul 27. pii: S0955-0674(20)30085-5. [Epub ahead of print]65 122-130
    Bohannon KP, Hanson PI.
      The ESCRT (endosomal complex required for transport) machinery remodels membranes to bud vesicles away from the cytoplasm. In addition to this classic role, ESCRTs are now understood to repair damage in the plasma membrane, nuclear envelope, and throughout the endolysosomal network. Wounds in endolysosomal membranes are caused by pathogens, particulates, and other chemical or metabolic stresses. Nanoscale damage in these membranes promotes activation and engagement of ESCRT proteins. A full understanding of damage signals, molecular sensing, and the mechanism of membrane repair is yet to be developed. Nevertheless, a triggering role for calcium and ESCRT-I in recruiting ESCRT-III machinery for membrane remodeling is a repeated theme in functional studies of this response. In our current understanding of the continuum of cellular responses to lipid bilayer damage, the ESCRT machinery is fast, sensitive, and deployed independently of other systems.
    DOI:  https://doi.org/10.1016/j.ceb.2020.06.002
  16. Brain Dev. 2020 Jul 28. pii: S0387-7604(20)30179-0. [Epub ahead of print]
    Suzuki Y.
      In lysosomal diseases, enzyme deficiency is caused by misfolding of mutant enzyme protein with abnormal steric structure that is expressed by gene mutation. Chaperone therapy is a new molecular therapeutic approach primarily for lysosomal diseases. The misfolded mutant enzyme is digested rapidly or aggregated to induce endoplasmic reticulum stress. As a result, the catalytic activity is lost. The following sequence of events are follows the chaperone therapy to achieve correction of molecular pathology. An orally administered low molecular competitive inhibitor (chaperone) is absorbed into the bloodstream and reaches the target cells and tissues. The mutant enzyme is stabilized by the chaperone and subjected to normal enzyme proteinfolding (proteostasis). The first chaperone drug was developed for Fabry disease and is currently available in medical practice. At present three types of chaperones are available: competitive chaperone with enzyme inhibitory bioactivity (exogenous), non-competitive (or allosteric) chaperone without inhibitory bioactivity (exogenous), and molecular chaperone (heat shock protein; endogenous). The third endogenous chaperone would be directed to overexpression or activated by an exogenous low-molecular inducer. This new molecular therapeutic approach, utilizing the three types of chaperone, is expected to apply to a variety of diseases, genetic or non-genetic, and neurological or non-neurological, in addition to lysosomal diseases.
    Keywords:  Chaperone therapy; Endoplasmic reticulum stress; Fabry disease; G(M1)-gangliosidosis; Gaucher disease; Heat shock protein; Lysosomal disease; Protein misfolding; Proteostasis
    DOI:  https://doi.org/10.1016/j.braindev.2020.06.015
  17. Oxid Med Cell Longev. 2020 ;2020 8735249
    Wu J, Yu X, Xue K, Wu J, Wang R, Xie X, Li K, Yang Z, Yue J.
      Background and Purpose. Alterations in cholesterol homeostasis have been reported in cell and animal models of Parkinson's disease (PD), although there are inconsistent data about the association between serum cholesterol levels and risk of PD. Here, we investigated the effects of miR-873 on lysosomal cholesterol homeostasis and progressive dopaminergic neuron damage in a lipopolysaccharide-(LPS) induced model of PD. Experimental Approach. To evaluate the therapeutic benefit of the miR-873 sponge, rats were injected with a LV-miR-873 sponge or the control vector 3 days before the right-unilateral injection of LPS into the substantia nigra (SN) pars compacta, or 8 and 16 days after LPS injection. Normal SH-SY5Y cells or SH-SY5Y cells overexpressing α-synuclein were used to evaluate the distribution of α-synuclein and cholesterol in lysosomes and to assess the autophagic flux after miR-873 transfection or ABCA1 silencing. The inhibition of miR-873 significantly ameliorated the LPS-induced accumulation of α-synuclein and loss of dopaminergic neurons in the SN at the early stage. miR-873 mediated the inhibition of ABCA1 by LPS. miR-873 transfection or ABCA1 silencing increased the lysosomal cholesterol and α-synuclein levels, and decreased the autophagic flux. The knockdown of ABCA1 or A20, which are the downstream target genes of miR-873, exacerbated the damage to LPS-induced dopaminergic neurons. Conclusion and Implications. The results suggest that the inhibition of miR-873 may play a dual protective role by improving intracellular cholesterol homeostasis and neuroinflammation in PD. The therapeutic effects of the miR-873 sponge in PD may be due to the upregulation of ABCA1 and A20.
    DOI:  https://doi.org/10.1155/2020/8735249
  18. Med Res Arch. 2020 Feb 01. 8(2):
    Pearse Y, Iacovino M.
      Mucopolysaccharidoses III (MPS III, Sanfilippo syndrome) is a subtype of the Mucopolysaccharidoses (MPS), a group of inherited lysosomal disorders caused by a deficiency of lysosomal enzymes responsible for catabolizing glycosaminoglycans (GAGs). Although MPS III is rare, MPS diseases as a group are relatively frequent with an overall incidence of approximately 1 in 20,000 - 25,000 births. MPS III are paediatric diseases, which cause learning difficulties, behavioural disorders and dementia, as well as skeletal deformities and ultimately result in premature death. There are currently no approved treatments for MPS III, but a number of therapeutic approaches are under development. In the past 30 years, research using cellular and animal models have led to clinical trials involving enzyme replacement therapy (ERT), substrate reduction therapy (SRT) and gene therapy, while stem cells approaches remain at the pre-clinical stage. Although safety and clinical efficacy in animal models have shown promise, the results of clinical trials have proved costly and shown limited therapeutic effects. In this review, we describe the most recent results from clinical trials. While ERT and gene therapy are the most developed therapies for MPS III, we highlight the work that needs to be done to bring us closer to a real treatment for these devastating diseases.
    Keywords:  Mucopolysaccharidoses III; Sanfilippo syndrome; clinical trial; enzyme replacement therapy; gene therapy; lysosomal storage disease; neurodegeneration; stem cell therapy; substrate reduction therapy
    DOI:  https://doi.org/10.18103/mra.v8i2.2045
  19. Ther Adv Chronic Dis. 2020 ;11 2040622320942042
    Bestion E, Jilkova ZM, Mège JL, Novello M, Kurma K, Pour STA, Lalmanach G, Vanderlynden L, Fizanne L, Bassissi F, Rachid M, Tracz J, Boursier J, Courcambeck J, Serdjebi C, Ansaldi C, Decaens T, Halfon P, Brun S.
      Background: Hepatic fibrosis is the result of chronic liver injury that can progress to cirrhosis and lead to liver failure. Nevertheless, there are no anti-fibrotic drugs licensed for human use. Here, we investigated the anti-fibrotic activity of GNS561, a new lysosomotropic molecule with high liver tropism.Methods: The anti-fibrotic effect of GNS561 was determined in vitro using LX-2 hepatic stellate cells (HSCs) and primary human HSCs by studying cell viability, activity of caspases 3/7, autophagic flux, cathepsin maturation and activity, HSC activation and transforming growth factor-β1 (TGF-β1) maturation and signaling. The contribution of GNS561 lysosomotropism to its anti-fibrotic activity was assessed by increasing lysosomal pH. The potency of GNS561 on fibrosis was evaluated in vivo in a rat model of diethylnitrosamine-induced liver fibrosis.
    Results: GNS561 significantly decreased cell viability and promoted apoptosis. Disrupting the lysosomal pH gradient impaired its pharmacological effects, suggesting that GNS561 lysosomotropism mediated cell death. GNS561 impaired cathepsin activity, leading to defective TGF-β1 maturation and autophagic processes. Moreover, GNS561 decreased HSC activation and extracellular matrix deposition by downregulating TGF-β1/Smad and mitogen-activated proteine kinase signaling and inducing fibrolysis. Finally, oral administration of GNS561 (15 mg/kg per day) was well tolerated and attenuated diethylnitrosamine-induced liver fibrosis in this rat model (decrease of collagen deposition and of pro-fibrotic markers and increase of fibrolysis).
    Conclusion: GNS561 is a new potent lysosomotropic compound that could represent a valid medicinal option for hepatic fibrosis treatment through both its anti-fibrotic and its pro-fibrolytic effects. In addition, this study provides a rationale for targeting lysosomes as a promising therapeutic strategy in liver fibrosis.
    Keywords:  GNS561; TGF-β1; autophagy; cathepsin; liver fibrosis; lysosomotropism
    DOI:  https://doi.org/10.1177/2040622320942042
  20. Neuropathol Appl Neurobiol. 2020 Jul 27.
    Wang Y, Wu Q, Anand BG, Karthivashan G, Phukan G, Yang J, Thinakaran G, Westaway D, Kar S.
      BACKGROUND: Evidence suggests that amyloid β (Aβ) peptides play an important role in the degeneration of neurons during the development of Alzheimer's disease (AD), the prevalent cause of dementia affecting the elderly. The endosomal-lysosomal system, which acts as a major site for Aβ metabolism, has been shown to exhibit abnormalities in vulnerable neurons of the AD brain, reflected by enhanced levels/expression of lysosomal enzymes including cathepsin D (CatD). At present, the implication of CatD in selective neuronal vulnerability in AD pathology remains unclear.METHODS: We evaluated the role of CatD in the degeneration of neurons in Aβ-treated cultures, transgenic AD mouse model (i.e., 5xFAD) and post-mortem AD brain samples.
    RESULTS: Our results showed that Aβ1-42 -induced toxicity in cortical cultured neurons is associated with impaired lysosomal integrity, enhanced levels of carbonylated proteins and tau phosphorylation. The cellular and cytosolic levels/activity of CatD are also elevated in cultured neurons following exposure to Aβ peptide. Additionally, we observed that CatD cellular and subcellular levels/activity are increased in the affected cortex, but not in the unaffected cerebellum, of 5xFAD mice and post-mortem AD brains. Interestingly, treatment of cultured neurons with nanoparticles PLGA, which targets lysosomal system, attenuated Aβ toxicity by reducing the levels of carbonylated proteins, tau phosphorylation and the level/distribution/activity of CatD.
    CONCLUSION: Our study reveals that increased cytosolic level/activity of CatD play an important role in determining neuronal vulnerability in AD. Additionally, native PLGA can protect neurons against Aβ toxicity by restoring lysosomal membrane integrity, thus signifying its implication in attenuating AD.
    Keywords:  Alzheimer’s disease; Cathepsin D; Cell signalling; Lysosomes; Neuroprotection; PLGA nanoparticles; β-amyloid
    DOI:  https://doi.org/10.1111/nan.12647
  21. Mol Genet Metab Rep. 2020 Sep;24 100626
    Thurberg BL.
      Acid sphingomyelinase deficiency (ASMD; also known as Niemann-Pick Disease [NPD] A and B) is a rare lysosomal storage disease characterized by the pathological accumulation of sphingomyelin within multiple cell types throughout the body. The infantile neurovisceral (ASMD type A, also known as Niemann-Pick Disease type A) form of the disease is characterized by markedly low or absent enzyme levels resulting in both visceral and severe neurodegenerative involvement with death in early childhood. We report here the clinical course and autopsy findings in the case of a 3 year old male patient with infantile neurovisceral ASMD. A comprehensive examination of the autopsy tissue was conducted, including routine paraffin processing and staining, high resolution light microscopy and staining for sphingomyelin, and ultrastructural examination by electron microscopy. Profound sphingomyelin accumulation was present in virtually every organ and cell type. We report the clinicopathologic correlations of these findings and discuss the relevance of these results to the clinical practice of physicians following all patients with ASMD. This case represents one of the most extensive and detailed examinations of ASMD type A to date.
    Keywords:  Acid sphingomyelinase deficiency; Niemann-Pick Disease type A; Sphingomyelin
    DOI:  https://doi.org/10.1016/j.ymgmr.2020.100626
  22. Cell Metab. 2020 Jul 19. pii: S1550-4131(20)30358-2. [Epub ahead of print]
    Tomita I, Kume S, Sugahara S, Osawa N, Yamahara K, Yasuda-Yamahara M, Takeda N, Chin-Kanasaki M, Kaneko T, Mayoux E, Mark M, Yanagita M, Ogita H, Araki SI, Maegawa H.
      SGLT2 inhibitors offer strong renoprotection in subjects with diabetic kidney disease (DKD). But the mechanism for such protection is not clear. Here, we report that in damaged proximal tubules of high-fat diet-fed ApoE-knockout mice, a model of non-proteinuric DKD, ATP production shifted from lipolysis to ketolysis dependent due to hyperactivation of the mechanistic target of rapamycin complex 1 (mTORC1). We further found that empagliflozin raised endogenous ketone body (KB) levels, and thus its use or treatment with 1,3-butanediol, a KB precursor, prevented decreases in renal ATP levels and organ damage in the mice. The renoprotective effect of empagliflozin was abolished by gene deletion of Hmgcs2, a rate-limiting enzyme of ketogenesis. Furthermore, KBs attenuated mTORC1-associated podocyte damage and proteinuria in diabetic db/db mice. Our findings show that SGLT2 inhibition-associated renoprotection is mediated by an elevation of KBs that in turn corrects mTORC1 hyperactivation that occurs in non-proteinuric and proteinuric DKD.
    Keywords:  SGLT2 inhibitor; atherosclerosis; diabetic kidney disease; ketolysis; ketone body; lipolysis; mTORC1; nutrient-sensing signal; renal energy metabolism
    DOI:  https://doi.org/10.1016/j.cmet.2020.06.020
  23. J Neurol. 2020 Jul 27.
    Simoncini C, Torri S, Montano V, Chico L, Gruosso F, Tuttolomondo A, Pinto A, Simonetta I, Cianci V, Salviati A, Vicenzi V, Marchi G, Girelli D, Concolino D, Sestito S, Zedde M, Siciliano G, Mancuso M.
      BACKGROUND: Fabry disease (FD) is an X-linked lysosomal storage disorder, caused by deficient activity of the alpha-galactosidase A enzyme leading to progressive and multisystemic accumulation of globotriaosylceramide. Recent data point toward oxidative stress signalling which could play an important role in both pathophysiology and disease progression.METHODS: We have examined oxidative stress biomarkers [Advanced Oxidation Protein Products (AOPP), Ferric Reducing Antioxidant Power (FRAP), thiolic groups] in blood samples from 60 patients and 77 healthy controls.
    RESULTS: AOPP levels were higher in patients than in controls (p < 0.00001) and patients presented decreased levels of antioxidant defences (FRAP and thiols) with respect to controls (p < 0.00001). In a small group of eight treatment-naïve subjects with FD-related mutations, we found altered levels of oxidative stress parameters and incipient signs of organ damage despite normal lyso-Gb3 levels.
    CONCLUSIONS: Oxidative stress occurs in FD in both treated and naïve patients, highlighting the need of further research in oxidative stress-targeted therapies. Furthermore, we found that oxidative stress biomarkers may represent early markers of disease in treatment-naïve patients with a potential role in helping interpretation of FD-related mutations and time to treatment decision.
    Keywords:  Biomarkers; Fabry disease; Oxidative stress; lysoGb3
    DOI:  https://doi.org/10.1007/s00415-020-10044-w
  24. Int J Mol Sci. 2020 Jul 28. pii: E5368. [Epub ahead of print]21(15):
    Cougnoux A, Yerger JC, Fellmeth M, Serra-Vinardell J, Martin K, Navid F, Iben J, Wassif CA, Cawley NX, Porter FD.
      Niemann-Pick disease, type C1 (NPC1) is a lysosomal disease characterized by endolysosomal storage of unesterified cholesterol and decreased cellular cholesterol bioavailability. A cardinal symptom of NPC1 is cerebellar ataxia due to Purkinje neuron loss. To gain an understanding of the cerebellar neuropathology we obtained single cell transcriptome data from control (Npc1+/+) and both three-week-old presymptomatic and seven-week-old symptomatic mutant (Npc1-/-) mice. In seven-week-old Npc1-/- mice, differential expression data was obtained for neuronal, glial, vascular, and myeloid cells. As anticipated, we observed microglial activation and increased expression of innate immunity genes. We also observed increased expression of innate immunity genes by other cerebellar cell types, including Purkinje neurons. Whereas neuroinflammation mediated by microglia may have both neuroprotective and neurotoxic components, the contribution of increased expression of these genes by non-immune cells to NPC1 pathology is not known. It is possible that dysregulated expression of innate immunity genes by non-immune cells is neurotoxic. We did not anticipate a general lack of transcriptomic changes in cells other than microglia from presymptomatic three-week-old Npc1-/- mice. This observation suggests that microglia activation precedes neuronal dysfunction. The data presented in this paper will be useful for generating testable hypotheses related to disease progression and Purkinje neurons loss as well as providing insight into potential novel therapeutic interventions.
    Keywords:  NPC1; Niemann–Pick disease; cerebellar ataxia; cerebellum; single cell RNA sequencing; transcriptome; type C1
    DOI:  https://doi.org/10.3390/ijms21155368
  25. Am J Med Sci. 2020 Jul 10. pii: S0002-9629(20)30305-0. [Epub ahead of print]
    Michaud M, Mauhin W, Belmatoug N, Garnotel R, Bedreddine N, Catros F, Ancellin S, Lidove O, Gaches F.
      Fabry disease is a frequent lysosomal storage disorder secondary to the deficiency of alpha-galactosidase A enzyme. This X-linked genetic disease realizes progressive and systemic manifestations that affect both male and female. Fabry disease may present as "classical", as "late-onset" or "non-classical" forms. Symptoms and organ involvements of classical Fabry disease are acral pain crisis, cornea verticillata, hypertrophic cardiomyopathy, stroke and chronic kidney disease with proteinuria. Other common symptoms are often poorly recognized, such as gastrointestinal or ear involvements. In classical Fabry disease, symptoms first appear during childhood or during teenage years in males, but later in females. Patients with non-classical or late-onset Fabry disease have delayed manifestations or a single-organ involvement. Diagnosis is therefore difficult when classical organ involvements are missing, in paucisymptomatic patients or in late-onset forms. Recognition of Fabry disease is important because effective treatments are available. They have to be prescribed early. In male, diagnosis is made with alpha-galactosidase A enzyme activity dosage in leukocyte, that is very low or null in classical forms and under 30 percent in late-onset forms. Diagnosis is more challenging in females who may express normal residual enzyme activity. Other plasmatic biomarkers, such as lyso-globotriaosylceramide are interesting, especially in females. In this review, we aimed to summarize main clinical manifestations of Fabry disease to know when to evoke Fabry disease and propose a practical diagnosis algorithm to know how to diagnose.
    Keywords:  Alpha galactosidase a; Fabry disease; Gla; Globotriaosylceramide.; Hypertrophic cardiomyopathy
    DOI:  https://doi.org/10.1016/j.amjms.2020.07.011
  26. Muscle Nerve. 2020 Aug 01.
    Sadjadi R, Sullivan S, Grant N, Thomas SE, Doyle M, Hammond C, Corre C, Mello N, David WS, Eichler F.
      INTRODUCTION: Nephropathic cystinosis is a lysosomal storage disorder with late-onset systemic complications, such as myopathy and dysphagia. Currently employed outcome measures lack sensitivity and responsiveness for dysphagia and myopathy, a limitation to clinical trial readiness.METHODS: We evaluated 20 patients with nephropathic cystinosis in two visits over the course of a year to identify outcomes sensitive to detect changes over time. Patients also underwent an expiratory muscle strength training program to assess any effects on aspiration and dysphagia.
    RESULTS: There were significant differences in the Timed Up and Go Test (TUG) and Timed 25-Foot Walk (25-FW) between baseline and one-year follow-up (p < 0.05). Maximum Expiratory Pressure (MEP) and Peak Cough Flow (PCF) significantly improved following respiratory training (p < 0.05).
    DISCUSSION: Improved respiratory outcomes may enhance patients' ability to expel aspirated material from the airway, stave off pulmonary sequelae associated with chronic aspiration, and yield an overall improvement in physical health and well-being.
    Keywords:  Distal myopathy; Dysphagia; EMST150; Nephropathic Cystinosis; Videofluoroscopy; respiratory therapy
    DOI:  https://doi.org/10.1002/mus.27039
  27. Leuk Res. 2020 Jul 17. pii: S0145-2126(20)30128-4. [Epub ahead of print]96 106423
    Chanas-Larue A, Villalpando-Rodriguez GE, Henson ES, Johnston JB, Gibson SB.
      Lysosomes in chronic lymphocytic leukemia (CLL) cells have previously been identified as a promising target for therapeutic intervention in combination with targeted therapies. Recent studies have shown that antihistamines can induce lysosomal membrane permeabilization (LMP) in a variety of cell lines. Furthermore, our previous data indicates that lysosomotropic agents can cause synergistic cell death in vitro when combined with some tyrosine kinase inhibitors (TKI). In the current study, we have shown that three over-the-counter antihistamines, clemastine, desloratadine, and loratadine, preferentially induce cell death via LMP in CLL cells, as compared to normal lymphocytes. We treated primary CLL cells with antihistamines and found clemastine was the most effective at inducing LMP and cell death. More importantly, the antihistamines induced synergistic cytotoxicity when combined with the tyrosine kinase inhibitor, ibrutinib, but not with chemotherapy. Moreover, the synergy between clemastine and ibrutinib was associated with the induction of reactive oxygen species (ROS), loss of mitochondrial membrane potential and decreased Mcl-1 expression leading to apoptosis. This study proposes a potential novel treatment strategy for CLL, repurposing FDA-approved allergy medications in combination with the targeted therapy ibrutinib to enhance drug efficacy.
    Keywords:  Cell death; Chronic lymphocytic leukemia; Lysosome
    DOI:  https://doi.org/10.1016/j.leukres.2020.106423
  28. Nat Metab. 2020 Jul 27.
    Orozco JM, Krawczyk PA, Scaria SM, Cangelosi AL, Chan SH, Kunchok T, Lewis CA, Sabatini DM.
      The mechanistic target of rapamycin complex 1 (mTORC1) kinase regulates cell growth by setting the balance between anabolic and catabolic processes. To be active, mTORC1 requires the environmental presence of amino acids and glucose. While a mechanistic understanding of amino acid sensing by mTORC1 is emerging, how glucose activates mTORC1 remains mysterious. Here, we used metabolically engineered human cells lacking the canonical energy sensor AMP-activated protein kinase to identify glucose-derived metabolites required to activate mTORC1 independent of energetic stress. We show that mTORC1 senses a metabolite downstream of the aldolase and upstream of the GAPDH-catalysed steps of glycolysis and pinpoint dihydroxyacetone phosphate (DHAP) as the key molecule. In cells expressing a triose kinase, the synthesis of DHAP from DHA is sufficient to activate mTORC1 even in the absence of glucose. DHAP is a precursor for lipid synthesis, a process under the control of mTORC1, which provides a potential rationale for the sensing of DHAP by mTORC1.
    DOI:  https://doi.org/10.1038/s42255-020-0250-5
  29. FASEB J. 2020 Jul 28.
    Go YM, Zhang J, Fernandes J, Litwin C, Chen R, Wensel TG, Jones DP, Cai J, Chen Y.
      The retinal pigment epithelium (RPE) is a particularly vulnerable tissue to age-dependent degeneration. Over the life span, the RPE develops an expanded endo-lysosomal compartment to maintain the high efficiency of phagocytosis and degradation of photoreceptor outer segments (POS) necessary for photoreceptor survival. As the assembly and activation of the mechanistic target of rapamycin complex 1 (mTORC1) occur on the lysosome surface, increased lysosome mass with aging leads to higher mTORC1 activity. The functional consequences of hyperactive mTORC1 in the RPE are unclear. In the current study, we used integrated high-resolution metabolomic and genomic approaches to examine mice with RPE-specific deletion of the tuberous sclerosis 1 (Tsc1) gene which encodes an upstream suppressor of mTORC1. Our data show that RPE cells with constitutively high mTORC1 activity were reprogramed to be hyperactive in glucose and lipid metabolism. Lipolysis was suppressed, mitochondrial carnitine shuttle was inhibited, while genes involved in fatty acid (FA) biosynthesis were upregulated. The metabolic changes occurred prior to structural changes of RPE and retinal degeneration. These findings have revealed cellular events and intrinsic mechanisms that contribute to lipid accumulation in the RPE cells during aging and age-related degeneration.
    Keywords:  AMD; Mtor; aging; lipid; metabolism
    DOI:  https://doi.org/10.1096/fj.202000612R
  30. Int J Mol Sci. 2020 Jul 26. pii: E5301. [Epub ahead of print]21(15):
    Rios-Fuller TJ, Mahe M, Walters B, Abbadi D, Pérez-Baos S, Gadi A, Andrews JJ, Katsara O, Vincent CT, Schneider RJ.
      Non-communicable diseases (NCDs) are medical conditions that, by definition, are non-infectious and non-transmissible among people. Much of current NCDs are generally due to genetic, behavioral, and metabolic risk factors that often include excessive alcohol consumption, smoking, obesity, and untreated elevated blood pressure, and share many common signal transduction pathways. Alterations in cell and physiological signaling and transcriptional control pathways have been well studied in several human NCDs, but these same pathways also regulate expression and function of the protein synthetic machinery and mRNA translation which have been less well investigated. Alterations in expression of specific translation factors, and disruption of canonical mRNA translational regulation, both contribute to the pathology of many NCDs. The two most common pathological alterations that contribute to NCDs discussed in this review will be the regulation of eukaryotic initiation factor 2 (eIF2) by the integrated stress response (ISR) and the mammalian target of rapamycin complex 1 (mTORC1) pathways. Both pathways integrally connect mRNA translation activity to external and internal physiological stimuli. Here, we review the role of ISR control of eIF2 activity and mTORC1 control of cap-mediated mRNA translation in some common NCDs, including Alzheimer's disease, Parkinson's disease, stroke, diabetes mellitus, liver cirrhosis, chronic obstructive pulmonary disease (COPD), and cardiac diseases. Our goal is to provide insights that further the understanding as to the important role of translational regulation in the pathogenesis of these diseases.
    Keywords:  eIF2 stress; mTOR signaling; non-communicable diseases; translation
    DOI:  https://doi.org/10.3390/ijms21155301
  31. Cell Rep. 2020 Jul 28. pii: S2211-1247(20)30935-9. [Epub ahead of print]32(4): 107954
    Kogot-Levin A, Hinden L, Riahi Y, Israeli T, Tirosh B, Cerasi E, Mizrachi EB, Tam J, Mosenzon O, Leibowitz G.
      Diabetic kidney disease (DKD) increases the risk for mortality and is the leading cause of end-stage renal disease. Treatment with sodium-glucose cotransporter 2 inhibitors (SGLT2i) attenuates the progression of DKD, especially in patients with advanced kidney disease. Herein, we show that in diabetes, mTORC1 activity is increased in renal proximal tubule cells (RPTCs) along with enhanced tubule-interstitial fibrosis; this is prevented by SGLT2i. Constitutive activation of mTORC1 in RPTCs induces renal fibrosis and failure and abolishes the renal-protective effects of SGLT2i in diabetes. On the contrary, partial inhibition of mTORC1 in RPTCs prevents fibrosis and the decline in renal function. Stimulation of mTORC1 in RPTCs turns on a pro-fibrotic program in the renal cortex, whereas its inhibition in diabetes reverses the alterations in gene expression. We suggest that RPTC mTORC1 is a critical node that mediates kidney dysfunction in diabetes and the protective effects of SGLT2i by regulating fibrogenesis.
    Keywords:  SGLT2 inhibitors; complications; diabetes; diabetic kidney disease; fibrosis; mTOR; signal transduction
    DOI:  https://doi.org/10.1016/j.celrep.2020.107954
  32. J Biol Chem. 2020 Jul 30. pii: jbc.RA120.014994. [Epub ahead of print]
    Maity S, Das F, Kasinath BS, Ghosh-Choudhury N, Ghosh Choudhury G.
      Interaction of TGFβ-induced canonical signaling with the noncanonical kinase cascades regulates glomerular hypertrophy and matrix protein deposition, which are early features of glomerulosclerosis. However, the specific target downstream of TGFβ receptor involved in the noncanonical signaling is unknown. Here, we show that TGFβ increased the catalytic loop phosphorylation of platelet-derived growth factor receptor beta (PDGFRβ), a receptor tyrosine kinase expressed abundantly in glomerular mesangial cells. TGFβ increased phosphorylation of the PI 3 kinase-interacting Tyr-751 residue of PDGFRβ, thus activating Akt. Inhibition of PDGFRβ using a pharmacological inhibitor and siRNAs blocked TGFβ-stimulated phosphorylation of PRAS40, an intrinsic inhibitory component of mTORC1, and prevented activation of mTORC1 in the absence of any effect on Smad 2/3 phosphorylation. Expression of constitutively active Myr-Akt reversed the siPDGFRβ-mediated inhibition of mTORC1 activity; however, co-expression of phospho-deficient mutant of PRAS40 inhibited the effect of Myr-Akt, suggesting a definitive role of PRAS40 phosphorylation in mTORC1 activation downstream of PDGFRβ in mesangial cells. Additionally, we demonstrate that PDGFRβ-initiated phosphorylation of PRAS40 is required for TGFβ-induced mesangial cell hypertrophy and, fibronectin and collagen I (α2) production. Increased activating phosphorylation of PDGFRβ is also associated with enhanced TGFβ expression and mTORC1 activation in the kidney cortex and glomeruli of diabetic mice and rat, respectively. Thus, pursuing the TGFβ noncanonical signaling, we identified how TGFβ receptor I achieves mTORC1 activation through PDGFRβ-mediated Akt/PRAS40 phosphorylation to spur mesangial cell hypertrophy and matrix protein accumulation. These findings provide support for targeting PDGFRβ in TGFβ-driven renal fibrosis.
    Keywords:  Akt PKB; PDGFRb; diabetic nephropathy; kidney; mTOR complex (mTORC); transforming growth factor beta (TGF-B)
    DOI:  https://doi.org/10.1074/jbc.RA120.014994
  33. EMBO J. 2020 Jul 28. e103009
    Fan SJ, Kroeger B, Marie PP, Bridges EM, Mason JD, McCormick K, Zois CE, Sheldon H, Khalid Alham N, Johnson E, Ellis M, Stefana MI, Mendes CC, Wainwright SM, Cunningham C, Hamdy FC, Morris JF, Harris AL, Wilson C, Goberdhan DC.
      Exosomes are secreted extracellular vesicles carrying diverse molecular cargos, which can modulate recipient cell behaviour. They are thought to derive from intraluminal vesicles formed in late endosomal multivesicular bodies (MVBs). An alternate exosome formation mechanism, which is conserved from fly to human, is described here, with exosomes carrying unique cargos, including the GTPase Rab11, generated in Rab11-positive recycling endosomal MVBs. Release of Rab11-positive exosomes from cancer cells is increased relative to late endosomal exosomes by reducing growth regulatory Akt/mechanistic Target of Rapamycin Complex 1 (mTORC1) signalling or depleting the key metabolic substrate glutamine, which diverts membrane flux through recycling endosomes. Vesicles produced under these conditions promote tumour cell proliferation and turnover and modulate blood vessel networks in xenograft mouse models in vivo. Their growth-promoting activity, which is also observed in vitro, is Rab11a-dependent, involves ERK-MAPK-signalling and is inhibited by antibodies against amphiregulin, an EGFR ligand concentrated on these vesicles. Therefore, glutamine depletion or mTORC1 inhibition stimulates release from Rab11a compartments of exosomes with pro-tumorigenic functions, which we propose promote stress-induced tumour adaptation.
    Keywords:  Rab11(a); exosome; extracellular vesicle; mechanistic Target of Rapamycin; multivesicular body
    DOI:  https://doi.org/10.15252/embj.2019103009
  34. J Biol Chem. 2020 Jul 28. pii: jbc.RA120.014907. [Epub ahead of print]
    Krycer JR, Quek LE, Francis D, Zadoorian A, Weiss FC, Cooke KC, Nelson ME, Diaz-Vegas A, Humphrey SJ, Scalzo R, Hirayama A, Ikeda S, Shoji F, Suzuki K, Huynh K, Giles C, Varney B, Nagarajan SR, Hoy AJ, Soga T, Meikle PJ, Cooney GJ, Fazakerley DJ, James DE.
      Adipose tissue is essential for metabolic homeostasis, balancing lipid storage and mobilisation based on nutritional status. This is coordinated by insulin, which triggers kinase signalling cascades to modulate numerous metabolic proteins, leading to increased glucose uptake and anabolic processes like lipogenesis. Given recent evidence that glucose is dispensable for adipocyte respiration, we sought to test whether glucose is necessary for insulin-stimulated anabolism. Examining lipogenesis in cultured adipocytes, glucose was essential for insulin to stimulate the synthesis of fatty acids and glyceride-glycerol. Importantly, glucose was dispensable for lipogenesis in the absence of insulin, suggesting distinct carbon sources are used with or without insulin. Metabolic tracing studies revealed glucose was required for insulin to stimulate pathways providing carbon substrate, NADPH, and glycerol 3'-phosphate for lipid synthesis and storage. Glucose also displaced leucine as a lipogenic substrate and was necessary to suppress fatty acid oxidation. Together, glucose provided substrates and metabolic control for insulin to promote lipogenesis in adipocytes. This contrasted with the suppression of lipolysis by insulin signalling, which occurred independently of glucose. Given previous observations that signal transduction acts primarily before glucose uptake in adipocytes, these data are consistent with a model whereby insulin initially utilises protein phosphorylation to stimulate lipid anabolism, which is sustained by subsequent glucose metabolism. Consequently, lipid abundance was sensitive to glucose availability, both during adipogenesis and in Drosophila flies in vivo. Together, these data highlight the importance of glucose metabolism to support insulin action, providing a complementary regulatory mechanism to signal transduction to stimulate adipose anabolism.
    Keywords:  Drosophila; adipocyte; cell metabolism; fat tissue; fatty acid; glucose; insulin; kinase signaling; lipid; metabolic regulation
    DOI:  https://doi.org/10.1074/jbc.RA120.014907
  35. Aging Cell. 2020 Jul 30. e13189
    De Risi M, Torromino G, Tufano M, Moriceau S, Pignataro A, Rivagorda M, Carrano N, Middei S, Settembre C, Ammassari-Teule M, Gardoni F, Mele A, Oury F, De Leonibus E.
      Autophagy agonists have been proposed to slow down neurodegeneration. Spermidine, a polyamine that acts as an autophagy agonist, is currently under clinical trial for the treatment of age-related memory decline. How Spermidine and other autophagy agonists regulate memory and synaptic plasticity is under investigation. We set up a novel mouse model of mild cognitive impairment (MCI), in which middle-aged (12-month-old) mice exhibit impaired memory capacity, lysosomes engulfed with amyloid fibrils (β-amyloid and α-synuclein) and impaired task-induced GluA1 hippocampal post-translation modifications. Subchronic treatment with Spermidine as well as the autophagy agonist TAT-Beclin 1 rescued memory capacity and GluA1 post-translational modifications by favouring the autophagy/lysosomal-mediated degradation of amyloid fibrils. These findings provide new mechanistic evidence on the therapeutic relevance of autophagy enhancers which, by improving the degradation of misfolded proteins, slow down age-related memory decline.
    Keywords:  GluA1; Spermidine; ageing; alpha-synuclein; amyloid fibrils; autophagy; mild cognitive impairment
    DOI:  https://doi.org/10.1111/acel.13189
  36. Nat Metab. 2020 Jul 27.
    Zhang ZD, Milman S, Lin JR, Wierbowski S, Yu H, Barzilai N, Gorbunova V, Ladiges WC, Niedernhofer LJ, Suh Y, Robbins PD, Vijg J.
      Ageing is the greatest risk factor for most common chronic human diseases, and it therefore is a logical target for developing interventions to prevent, mitigate or reverse multiple age-related morbidities. Over the past two decades, genetic and pharmacologic interventions targeting conserved pathways of growth and metabolism have consistently led to substantial extension of the lifespan and healthspan in model organisms as diverse as nematodes, flies and mice. Recent genetic analysis of long-lived individuals is revealing common and rare variants enriched in these same conserved pathways that significantly correlate with longevity. In this Perspective, we summarize recent insights into the genetics of extreme human longevity and propose the use of this rare phenotype to identify genetic variants as molecular targets for gaining insight into the physiology of healthy ageing and the development of new therapies to extend the human healthspan.
    DOI:  https://doi.org/10.1038/s42255-020-0247-0
  37. Dev Cell. 2020 Jul 12. pii: S1534-5807(20)30541-4. [Epub ahead of print]
    Zhao YG, Zhang H.
      In eukaryotic cells, various membrane-bound organelles compartmentalize diverse cellular activities in a spatially and temporally controlled manner. Numerous membraneless organelles assembled via liquid-liquid phase separation (LLPS), known as condensates, also facilitate compartmentalization of cellular functions. Emerging evidence shows that these two organelle types interact in many biological processes. Membranes modulate the biogenesis and dynamics of phase-separated condensates by serving as assembly platforms or by forming direct contacts. Phase separation of membrane-associated proteins participates in various trafficking events, such as clustering of vesicles for temporally controlled fusion and storage, and transport of membraneless condensates on membrane-bound organelles. Phase separation also acts in cargo trafficking pathways by sorting and docking cargos for translocon-mediated transport across membranes, by shuttling cargos through the nuclear pore complex, and by triggering the formation of surrounding autophagosomes for delivery to lysosomes. The coordinated actions of membrane-bound and membraneless organelles ensure spatiotemporal control of various cellular functions.
    Keywords:  autophagy; condensates; membrane-bound organelles; phase separation; vesicle trafficking
    DOI:  https://doi.org/10.1016/j.devcel.2020.06.033
  38. Elife. 2020 Jul 28. pii: e56177. [Epub ahead of print]9
    Arriola Apelo SI, Lin A, Brinkman JA, Meyer E, Morrison M, Tomasiewicz JL, Pumper CP, Baar EL, Richardson NE, Alotaibi M, Lamming DW.
      Inhibition of mTOR (mechanistic Target Of Rapamycin) signaling by rapamycin promotes healthspan and longevity more strongly in females than males, perhaps because inhibition of hepatic mTORC2 (mTOR Complex 2) specifically reduces the lifespan of males. Here, we demonstrate using gonadectomy that the sex-specific impact of reduced hepatic mTORC2 is not reversed by depletion of sex hormones. Intriguingly, we find that ovariectomy uncouples lifespan from metabolic health, with ovariectomized females having improved survival despite paradoxically having increased adiposity and decreased control of blood glucose levels. Further, ovariectomy unexpectedly promotes midlife survival of female mice lacking hepatic mTORC2, significantly increasing the survival of those mice that do not develop cancer. In addition to identifying a sex hormone-dependent role for hepatic mTORC2 in female longevity, our results demonstrate that metabolic health is not inextricably linked to lifespan in mammals, and highlight the importance of evaluating healthspan in mammalian longevity studies.
    Keywords:  aging; genetics; genomics; healthspan; human biology; mTOR; mTORC2; medicine; mouse; ovariectomy; sex
    DOI:  https://doi.org/10.7554/eLife.56177
  39. Biochim Biophys Acta Mol Cell Res. 2020 Jul 23. pii: S0167-4889(20)30158-0. [Epub ahead of print] 118800
    Silva BSC, DiGiovanni L, Kumar R, Carmichael RE, Kim PK, Schrader M.
      Membrane-bound organelles in eukaryotic cells form an interactive network to coordinate and facilitate cellular functions. The formation of close contacts, termed "membrane contact sites" (MCSs), represents an intriguing strategy for organelle interaction and coordinated interplay. Emerging research is rapidly revealing new details of MCSs. They represent ubiquitous and diverse structures, which are important for many aspects of cell physiology and homeostasis. Here, we provide a comprehensive overview of the physiological relevance of organelle contacts. We focus on mitochondria, peroxisomes, the Golgi complex and the plasma membrane, and discuss the most recent findings on their interactions with other subcellular organelles and their multiple functions, including membrane contacts with the ER, lipid droplets and the endosomal/lysosomal compartment.
    Keywords:  Acyl-CoA binding domain containing protein; FFAT motif; lipid metabolism; membrane contact sites; mitochondria; peroxisomes
    DOI:  https://doi.org/10.1016/j.bbamcr.2020.118800
  40. Front Cell Dev Biol. 2020 ;8 512
    Chen C, Li J, Qin X, Wang W.
      Peroxisomes participate in essential cellular metabolic processes, such as oxidation of fatty acids (FAs) and maintenance of reactive oxygen species (ROS) homeostasis. Peroxisomes must communicate with surrounding organelles to exchange information and metabolites. The formation of membrane contact sites (MCSs), where protein-protein or protein-lipid complexes tether the opposing membranes of two organelles, represents an essential means of organelle crosstalk. Peroxisomal MCS (PO-MCS) studies are emerging but are still in the early stages. In this review, we summarize the identified PO-MCSs with the ER, mitochondria, lipid droplets, and lysosomes in mammalian cells and discuss their tethering mechanisms and physiological roles. We also highlight several features of PO-MCSs that may help future studies.
    Keywords:  membrane contact sites; metabolism; organelle crosstalk; peroxisomes; tethering complexes
    DOI:  https://doi.org/10.3389/fcell.2020.00512