bims-lysosi Biomed News
on Lysosomes and signaling
Issue of 2020‒10‒04
33 papers selected by
Stephanie Fernandes
Max Planck Institute for Biology of Ageing

  1. Nat Cell Biol. 2020 Oct;22(10): 1252-1263
      Sensing and clearance of dysfunctional lysosomes is critical for cellular homeostasis. Here we show that transcription factor EB (TFEB)-a master transcriptional regulator of lysosomal biogenesis and autophagy-is activated during the lysosomal damage response, and its activation is dependent on the function of the ATG conjugation system, which mediates LC3 lipidation. In addition, lysosomal damage triggers LC3 recruitment on lysosomes, where lipidated LC3 interacts with the lysosomal calcium channel TRPML1, facilitating calcium efflux essential for TFEB activation. Furthermore, we demonstrate the presence and importance of this TFEB activation mechanism in kidneys in a mouse model of oxalate nephropathy accompanying lysosomal damage. A proximal tubule-specific TFEB-knockout mouse exhibited progression of kidney injury induced by oxalate crystals. Together, our results reveal unexpected mechanisms of TFEB activation by LC3 lipidation and their physiological relevance during the lysosomal damage response.
  2. J Biol Regul Homeost Agents. 2020 Jul-Aug;34(4 Suppl. 2):34(4 Suppl. 2): 107-119
      Lysosomal storage diseases (LSDs) include a heterogeneous group of rare, inborn, metabolic diseases characterized by deficiency of lysosomal enzymes or of other proteins involved in lysosomal function, leading to multi organ system substrates accumulation, with consequent multi systemic clinical presentation. Cardiac disease is particularly important in some group of LSDs as glycogen storage diseases (Pompe), mucopolysaccharidoses and in glycosphingolipidoses (Anderson-Fabry disease and less frequently Gaucher disease). Various cardiac manifestations may be observed including hypertrophic and dilated cardiomyopathy, coronary artery disease and valvular disease. The availability of enzyme replacement therapy (ERT) has changed the natural history of some LSDs such as Pompe disease, thanks to the significant effects on cardiological involvement. In other LSDs such as MPSs or Fabry disease, ERT has been shown to stabilize or slow the progression of heart damage. This imposes the need for a timely diagnosis that allows a rapid onset of ERT.
    Keywords:  Anderson-Fabry disease (AFD); Enzyme replacement therapy (ERT); Gaucher disease; Heart; Lysosomal storage diseases (LSDs); Mucopolysaccharidoses (MPSs); Pompe disease (PD); cardiomyopathy; valvular disease
  3. Biochem Biophys Res Commun. 2020 Sep 29. pii: S0006-291X(20)31840-4. [Epub ahead of print]
      Cell-penetrating peptides (CPPs) can deliver payloads into cells by forming complexes with bioactive molecules via either covalent or non-covalent bonds. Previously, we reported polyhistidine (H16 peptide: HHHHHHHHHHHHHHHH-NH2) as a new CPP. This peptide is anticipated to be a valuable new carrier for drug delivery to intracellular lysosomes; the peptide can transport macromolecules into these organelles. In the present study, we examined the application of the H16 peptide as a drug delivery system (DDS) to reverse to lysosomal storage disease (LSD) in cells in vitro. LSDs are metabolic disorders caused by the loss of specific lysosomal enzymes. The majority of lysosomal enzymes are acidic proteins and we utilized this common feature for our DDS. We synthesized a polylysine-polyhistidine fusion peptide (K10H16 peptide: KKKKKKKKKKGHHHHHHHHHHHHHHHH-NH2) and developed a simple method for transporting acidic proteins into intracellular lysosomes via formation of complexes of enzymes with the K10H16 peptide by electrostatic interaction. First, we demonstrated our strategy using maltose-binding protein-fused green fluorescent protein (MBP-GFP) to model an acidic protein. The K10H16 peptide bound to MBP-GFP and transported it into intracellular lysosomes. Further, alpha-galactosidase A (GLA), one of the lysosomal enzymes associated with LSD, was also delivered to intracellular lysosomes by the peptide. The complex between K10H16 peptide and GLA restored typical proliferation to LSD cells, which otherwise grew more slowly than normal cells. These results suggest that K10H16 peptide replenished lysosomal enzyme deficiency in LSD cells. The K10H16 peptide may be useful as a DDS for LSD therapy.
    Keywords:  Acidic protein; Cell-penetrating peptide; Drug delivery system; Lysosomal enzyme; Lysosomal storage disease; Lysosome
  4. Cell Death Dis. 2020 Sep 30. 11(9): 817
      In eukaryotic cells, lysosomes are digestive centers where biological macromolecules are degraded by phagocytosis and autophagy, thereby maintaining cellular self-renewal capacity and energy supply. Lysosomes also serve as signaling hubs to monitor the intracellular levels of nutrients and energy by acting as platforms for the assembly of multiple signaling pathways, such as mammalian target of rapamycin complex 1 (mTORC1) and adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK). The structural integrity and functional balance of lysosomes are essential for cell function and viability. In fact, lysosomal damage not only disrupts intracellular clearance but also results in the leakage of multiple contents, which pose great threats to the cell by triggering cell death pathways, including apoptosis, necroptosis, pyroptosis, and ferroptosis. The collapse of lysosomal homeostasis is reportedly critical for the pathogenesis and development of various diseases, such as tumors, neurodegenerative diseases, cardiovascular diseases, and inflammatory diseases. Lysosomal quality control (LQC), comprising lysosomal repair, lysophagy, and lysosomal regeneration, is rapidly initiated in response to lysosomal damage to maintain lysosomal structural integrity and functional homeostasis. LQC may be a novel but pivotal target for disease treatment because of its indispensable role in maintaining intracellular homeostasis and cell fate.
  5. Nat Cell Biol. 2020 Oct;22(10): 1170-1179
      SIRT1 (Sir2) is an NAD+-dependent deacetylase that plays critical roles in a broad range of biological events, including metabolism, the immune response and ageing1-5. Although there is strong interest in stimulating SIRT1 catalytic activity, the homeostasis of SIRT1 at the protein level is poorly understood. Here we report that macroautophagy (hereafter referred to as autophagy), a catabolic membrane trafficking pathway that degrades cellular components through autophagosomes and lysosomes, mediates the downregulation of mammalian SIRT1 protein during senescence and in vivo ageing. In senescence, nuclear SIRT1 is recognized as an autophagy substrate and is subjected to cytoplasmic autophagosome-lysosome degradation, via the autophagy protein LC3. Importantly, the autophagy-lysosome pathway contributes to the loss of SIRT1 during ageing of several tissues related to the immune and haematopoietic system in mice, including the spleen, thymus, and haematopoietic stem and progenitor cells, as well as in CD8+CD28- T cells from aged human donors. Our study reveals a mechanism in the regulation of the protein homeostasis of SIRT1 and suggests a potential strategy to stabilize SIRT1 to promote productive ageing.
  6. Mov Disord. 2020 Sep 28.
    Keywords:  Gaucher disease; lysosomal storage disorders; nonmotor symptoms; Parkinson's disease
  7. J Biol Regul Homeost Agents. 2020 Jul-Aug;34(4 Suppl. 2):34(4 Suppl. 2): 71-77
      Mucolipidosis II and III are lysosomal storage diseases caused by pathogenetic mutations in GNPTAB and GNPTG genes which cause an impaired activity of the lysosomal hydrolase N-acetylglucosamine- 1-phosphotransferase, a key enzyme in the synthesis of the mannose-6-phosphate targeting signals on lysosomal enzymes. Patients with MLII alpha/beta present coarse facial features, cessation of statural growth, important skeletal manifestations, impaired neuromotor development and cardiorespiratory involvement. All children appear to have cardiac involvement, but severe dilated cardiomyopathy is uncommon. In this report we describe the case of an 11-month-old girl who is affected by a MLII. Analysis of the GNPTAB gene identified at a heterozygous level the previously described gene variants c. 2693delA p(Lys898Serfs*13) and c. 2956C>T p(Arg986Cys). Her main clinical features were coarse face with gingival hypertrophy, dysostosis multiplex, recurrent respiratory infection and an early onset of dilated cardiomyopathy, an uncommon feature for MLII. To our knowledge, dilated cardiomyopathy has been previously described in literature in only two cases of MLII and in one patient affected by MLIII.
    Keywords:  GNPTAB gene; GNPTG gene; dilated cardiomyopathy; mucolipidosis
  8. Cell Death Dis. 2020 Sep 26. 11(9): 810
      Autophagy is a highly conserved lysosome-dependent degradation system in eukaryotic cells. This process removes long-lived intracellular proteins, damaged organelles, and recycles biological material to maintain cellular homeostasis. Dysfunction of autophagy triggers a wide spectrum of human diseases, including cancer and neurodegenerative diseases. In the present study, we show that RNF115, an E3 ubiquitin ligase, regulates autophagosome-lysosome fusion and autophagic degradation under both nutrient-enriched and stress conditions. Depletion of the RNF115 gene caused the accumulation of autophagosomes by impairing fusion with lysosomes, which results in an accumulation of autophagic substrates. Further investigation suggests that RNF115 interacts with STX17 and enhances its stability, which is essential for autophagosome maturation. Importantly, we provide in vitro and in vivo evidence that RNF115 inactivation inhibits the tumorigenesis and metastasis of BGC823 gastric cancer cells. We additionally show that high expression levels of RNF115 mRNA correlate with poor prognosis in gastric cancer patients. These findings indicate that RNF115 may play an evolutionarily conserved role in the autophagy pathway, and may act to maintain protein homeostasis under physiological conditions. These data demonstrate the need to further evaluate the potential therapeutic implications of RNF115 in gastric cancer.
  9. Adv Carbohydr Chem Biochem. 2020 ;pii: S0065-2318(19)30027-7. [Epub ahead of print]77 71-117
      Mucopolysaccharidosis type II (MPS II, Hunter syndrome) is a rare X-linked lysosomal storage disease caused by mutations of the gene encoding the lysosomal enzyme iduronate-2-sulfatase (IDS), the role of which is to hydrolytically remove O-linked sulfates from the two glycosaminoglycans (GAGs) heparan sulfate (HS) and dermatan sulfate (DS). HS and DS are linear, heterogeneous polysaccharides composed of repeating disaccharide subunits of l-iduronic acid (IdoA) or d-glucuronic acid, (1→4)-linked to d-glucosamine (for HS), or (1→3)-linked to 2-acetamido-2-deoxy-d-galactose (N-acetyl-d-galactosamine) (for DS). In healthy cells, IDS cleaves the sulfo group found at the C-2 position of terminal non-reducing end IdoA residues in HS and DS. The loss of IDS enzyme activity leads to progressive lysosomal storage of HS and DS in tissues and organs such as the brain, liver, spleen, heart, bone, joints and airways. Consequently, this leads to the phenotypic features characteristic of the disease. This review provides an overview of the disease profile and clinical manifestation, with a particular focus on the biochemical basis of the disease and chemical approaches to the development of new diagnostics, as well as discussing current treatment options and emerging new therapies.
    Keywords:  Dermatan sulfate; Glycosaminoglycans; Heparan sulfate; Hunter syndrome; Iduronate-2-sulfatase; Mucopolysaccharidosis type II
  10. Physiol Int. 2020 Sep 29.
      Purpose: Acid-base transport in renal proximal tubules (PTs) is mainly sodium-dependent and conducted in coordination by the apical Na+/H+ exchanger (NHE3), vacuolar H+-adenosine triphosphatase (V-ATPase), and the basolateral Na+/HCO3- cotransporter. V-ATPase on PTs is well-known to play an important role in proton excretion. Recently we reported a stimulatory effect of insulin on these transporters. However, it is unclear whether insulin is involved in acid-base balance in PTs. Thus, we assessed the role of insulin in acid-base balance in PTs.Methods: V-ATPase activity was evaluated using freshly isolated PTs obtained from mice, and specific inhibitors were then used to assess the signaling pathways involved in the observed effects.
    Results: V-ATPase activity in PTs was markedly enhanced by insulin, and its activation was completely inhibited by bafilomycin (a V-ATPase-specific inhibitor), Akt inhibitor VIII, and PP242 (an mTORC1/2 inhibitor), but not by rapamycin (an mTORC1 inhibitor). V-ATPase activity was stimulated by 1 nm insulin by approximately 20% above baseline, which was completely suppressed by Akt1/2 inhibitor VIII. PP242 completely suppressed the insulin-mediated V-ATPase stimulation in mouse PTs, whereas rapamycin failed to influence the effect of insulin. Insulin-induced Akt phosphorylation in the mouse renal cortex was completely suppressed by Akt1/2 inhibitor VIII and PP242, but not by rapamycin.
    Conclusion: Our results indicate that stimulation of V-ATPase activity by insulin in PTs is mediated via the Akt2/mTORC2 pathway. These results reveal the mechanism underlying the complex signaling in PT acid-base balance, providing treatment targets for renal disease.
    Keywords:  V-ATPase; insulin; mTOR; mTORC2; proximal tubules
  11. . 2020 Sep 29.
      Chediak-Higashi disease is a rare disease caused by bi-allelic mutations in the lysosomal trafficking regulator gene, LYST. Individuals typically present in early childhood with partial oculocutaneous albinism, a bleeding diathesis, recurrent infections secondary to immune dysfunction, and risk of developing hemophagocytic lymphohistiocytosis (HLH). Without intervention, mortality is high in the first decade of life. However, some individuals with milder phenotypes have attenuated hematologic and immunologic presentations, and lower risk of HLH. Both classic and milder phenotypes develop progressive neurodegeneration in early adulthood. Here we present a remarkable patient diagnosed with Chediak-Higashi disease at age 67, many decades after the diagnosis is usually established. Diagnosis was suspected by observing the pathognomonic granules within leukocytes, and confirmed by identification of bi-allelic mutations in LYST, reduced LYST mRNA expression, enlarged lysosomes within fibroblasts, and decreased NK cell lytic activity. This case further expands the phenotype of Chediak-Higashi disease and highlights the need for increased awareness. Individuals with milder phenotypes may escape early diagnosis, but identification is important for close monitoring of potential complications, and to further our understanding of the function of LYST.
    Keywords:  lysosomal disorders; next generation sequencing; rare disorders
  12. Microcirculation. 2020 Sep 26. e12660
      OBJECTIVES: FLI1 and ERG, important regulators of endothelial cell homeostasis, are reduced in microvascular endothelial cells (MVEC) in scleroderma patients and their deficiency has been implicated in disease pathogenesis. The goal of this study was to identify the mechanisms involved in the protein turnover of FLI1 and ERG in MVECs.METHODS: The effects of lysosome and proteosome inhibitors on FLI1 and ERG levels was assessed by western blotting and capillary morphogenesis. The effect of scleroderma and control sera on the levels of FLI1 and ERG was examined.
    RESULTS: The reduction of the protein levels of FLI1 and ERG in response to IFNα or Poly:(IC) was reversed by blocking either lysosomal (leupeptin and Cathepsin B inhibitor) or proteosomal degradation (MG132). MG132, leupeptin or CTSB-(i) also counteracted the anti-angiogenic effects of Poly:(IC) or IFNα. Scleroderma sera reduced protein levels of FLI1 and ERG in comparison to control sera. Treatment with CTSB(i) increased the levels of FLI1 and ERG in a majority of serum-treated samples.
    CONCLUSIONS: Inhibition of cathepsin B was effective in reversing the reduction of FLI1 and ERG protein levels after treatment with IFNα or SSc sera, suggesting that targeting cathepsin B may have a beneficial effect in SSc vascular disease.
  13. Pediatr Nephrol. 2020 Oct 01.
      Tuberous sclerosis complex (TSC) is a multisystem hereditary disorder characterized by the growth of benign tumors (hamartomas) in multiple organs, including the kidneys. Renal angiomyolipomas (AML) are a major diagnostic feature of TSC and are present in the majority of patients by adulthood. However, AML are usually asymptomatic during childhood when neurological and developmental manifestations are the main source of morbidity. Kidney manifestations of TSC have historically been the main cause of morbidity and mortality of adults with TSC. The recognition that the complications of TSC are caused by dysregulation of the mammalian target of rapamycin (mTOR) pathway has led to an enormous progress in the management of patients with TSC in the last two decades, the establishment of diagnostic guidelines, and trials which have shown the therapeutic benefit of mTOR inhibitors. Kidney surveillance of children with TSC now provides the opportunity for timely interventions to reduce the impact of TSC in adulthood. In this review, we discuss the current management of kidney tumors associated with TSC, including the diagnosis, surveillance, and treatment options for these lesions. We also present outcome data from international registries demonstrating the effectiveness of the current management strategies. With clear management guidelines and efficient treatment of kidney tumors, we envisage that the long-term outcomes of patients with TSC will further improve in the future.
    Keywords:  Renal angiomyolipoma; Renal cell carcinoma; Tuberous sclerosis complex; mTOR inhibitor
  14. FASEB J. 2020 Sep;34(9): 12932-12945
      We previously demonstrated that Tetraticopeptide 4 (TTC4) inhibited apoptosis in vascular endothelial cells (VEC) deprived of serum and fibroblast growth factor 2 (FGF-2). In this study, we aimed to resolve the mechanism of TTC4 inhibiting VEC apoptosis. TTC4, predicted as a HSP70 co-chaperone protein, may regulate the fate of cells by affecting the activity of HSP70, however, there is no experimental evidence showing the interaction of TTC4 and HSP70. Using Co-immunoprecipitation (Co-IP), we demonstrated that TTC4 interacted with HSP70. If HSP70 was knockdown, TTC4 no longer suppressed apoptosis. Furthermore, we found ABO, an inhibitor of annexin A7 (ANXA7) GTPase, could promote the interaction of TTC4 and HSP70 and the translocation of ANXA7 to lysosome. At the same time, ABO inhibited the interaction of HSP70 and ANXA7. Moreover, Akt, as a downstream effector of HSP70 was upregulated, and ANXA7 translocating to lysosome protected the stability of lysosomal membrane. Here, we discovered a special mechanism by which TTC4 inhibited apoptosis via HSP70 in VECs. On the one hand, increasing TTC4 and HSP70 interaction upregulated Akt that inhibited apoptosis. On the other hand, decreasing HSP70 and ANXA7 interaction promoted the translocation of ANXA7 to lysosome, which inhibited apoptosis through protecting the lysosomal membrane stability.
    Keywords:  Akt; Ca2+ homeostasis; GTPase; chemical small molecules; lysosomal membrane permeabilization
  15. Int J Mol Sci. 2020 Sep 29. pii: E7213. [Epub ahead of print]21(19):
      Fabry disease (FD) is an X-linked lysosomal disorder caused by mutations in GLA gene resulting in lack of or faulty α-galactosidase A (α-GalA) enzyme. Enzyme replacement therapy (ERT) with recombinant human α-GalA enzyme (agalsidase) is the standard treatment option for FD. Infusion-related reactions (IRRs), with symptoms ranging from rigors, to fever, pain, vomiting, angioedema and diarrhea, are often seen due to immune response against the exogenous enzyme. To elucidate the mechanisms causing the IRRs in FD, eight patients who developed IRRs were investigated. All, except one, tested negative for agalsidase-specific IgE and had normal tryptase levels. Circulating dendritic cells were drastically reduced during IRRs, suggesting possible sequestration to the sites of inflammation. An increase in NK cells and a decrease in T cells were also observed. Cytokines IL-4, IL-8 and TNF-α showed a significant increase, indicating nonspecific degranulation of mast cells. All IRRs were managed successfully using a combination of standard premedications and mast cell stabilizers without any interruption of therapy. Taken together, the results indicate crosstalk between immune cells resulting in IgE-independent mast-cell-specific allergic inflammation. Mast cell stabilizers could be used to control IRRs and for safe reintroduction of agalsidase in patients previously treated with ERT.
    Keywords:  Fabry disease; agalsidase; enzyme replacement therapy; infusion-related reactions
  16. J Immunol. 2020 Sep 28. pii: ji2000244. [Epub ahead of print]
      Mutations in MEFV, the gene encoding pyrin in humans, are associated with the autoinflammatory disorder familial Mediterranean fever. Pyrin is an innate sensor that assembles into an inflammasome complex in response to Rho-modifying toxins, including Clostridium difficile toxins A and B. Cell death pathways have been shown to intersect with and modulate inflammasome activation, thereby affecting host defense. Using bone marrow-derived macrophages and a murine model of peritonitis, we show in this study that receptor-interacting protein kinase (RIPK) 3 impacts pyrin inflammasome activation independent of its role in necroptosis. RIPK3 was instead required for transcriptional upregulation of Mefv through negative control of the mechanistic target of rapamycin (mTOR) pathway and independent of alterations in MAPK and NF-κB signaling. RIPK3 did not affect pyrin dephosphorylation associated with inflammasome activation. We further demonstrate that inhibition of mTOR was sufficient to promote Mefv expression and pyrin inflammasome activation, highlighting the cross-talk between the mTOR pathway and regulation of the pyrin inflammasome. Our study reveals a novel interaction between molecules involved in cell death and the mTOR pathway to regulate the pyrin inflammasome, which can be harnessed for therapeutic interventions.
  17. Biochem Biophys Res Commun. 2020 Sep 29. pii: S0006-291X(20)31853-2. [Epub ahead of print]
      Mechanistic target of rapamycincomplex 1 (mTORC1) integrates various environmental signals to regulate cell growth and metabolism. mTORC1 activity is sensitive to changes in amino acid levels. Here, we investigated the effect of lysine on mTORC1 activity in non-small cell lung cancer (NSCLC) cells. Lysine deprivation suppressed mTORC1 activity and lysine replenishment restored the decreased mTORC1 activity in lysine-deprived cells. Supplementing growth factors, such as insulin growth factor-1 or insulin restored the decreased mTORC1 activity in serum-deprived cells. However, in serum/lysine-deprived cells, supplementing growth factors was not sufficient to restore mTORC1 activity, suggesting thatgrowth factors could not activate mTORC1 efficiently in the absence of lysine. General control nonderepressible 2 and AMP-activated protein kinase were involved in lysine deprivation-mediated inhibition of mTORC1. Taken together, these results suggest that lysine might play role in the regulation of mTORC1 activation in NSCLC cells.
    Keywords:  AMP-Activated protein kinase; Amino acid; General control nonderepressible 2; Lysine; Mechanistic target of rapamycin complex 1
  18. Genet Med. 2020 Sep 30.
      PURPOSE: To assess the utility of globotriaosylsphingosine (lyso-Gb3) for clinical monitoring of treatment response in patients with Fabry disease receiving migalastat.METHODS: A post hoc analysis evaluated data from 97 treatment-naive and enzyme replacement therapy (ERT)-experienced patients with migalastat-amenable GLA variants from FACETS (NCT00925301) and ATTRACT (NCT01218659) and subsequent open-label extension studies. The relationship between plasma lyso-Gb3 and measures of Fabry disease progression (left ventricular mass index [LVMi], estimated glomerular filtration rate [eGFR], and pain) and the relationship between lyso-Gb3 and incidence of Fabry-associated clinical events (FACEs) were assessed in both groups. The relationship between changes in lyso-Gb3 and kidney interstitial capillary (KIC) globotriaosylceramide (Gb3) inclusions was assessed in treatment-naive patients.
    RESULTS: No significant correlations were identified between changes in lyso-Gb3 and changes in LVMi, eGFR, or pain. Neither baseline lyso-Gb3 levels nor the rate of change in lyso-Gb3 levels during treatment predicted FACE occurrences in all patients or those receiving migalastat for ≥24 months. Changes in lyso-Gb3 correlated with changes in KIC Gb3 inclusions in treatment-naive patients.
    CONCLUSIONS: Although used as a pharmacodynamic biomarker in research and clinical studies, plasma lyso-Gb3 may not be a suitable biomarker for monitoring treatment response in migalastat-treated patients.
    Keywords:  Fabry disease; biomarker; clinical monitoring; lyso-Gb3; migalastat
  19. J Cell Sci. 2020 Sep 28. pii: jcs.248310. [Epub ahead of print]
      Translation arrest is a part of the cellular stress response that decreases energy consumption and enables rapid reprioritisation of gene expression. Often translation arrest leads to condensation of untranslated messenger ribonucleoproteins (mRNPs) into stress granules (SGs). Studies into mechanisms of SG formation and functions are complicated because various types of stress cause formation of SGs with different properties and composition. In this work we focused on the mechanism of SG formation triggered by UV damage. We demonstrate that UV-induced inhibition of translation does not involve inhibition of the mechanistic target of rapamycin (mTOR) signaling or dissociation of the 48S preinitiation complexes. The general control non-derepressible 2 (GCN2) kinase contributes to UV-induced SG formation, which is independent of the phosphorylation of the eukaryotic translation initiation factor 2α. Like many other types of SGs, condensation of UV-induced granules requires the Ras-GTPase-Activating Protein SH3-Domain-Binding Protein 1 (G3BP1). Our work reveals that in UV-treated cells the mechanisms of translation arrest and SG formation may be unlinked, resulting in SGs that do not contain the major type of polysome-free preinitiation complexes that accumulate in the cytoplasm.
    Keywords:  G3BP1; GCN2; MTOR; Stress granule; UVC
  20. Front Mol Biosci. 2020 ;7 177
      The brain is the physical organ of the mind but efforts to understand mental illness within a neurobiological context have hitherto been unavailing. Mental disorders (anxiety, depression, bipolar disorder, and schizophrenia) affect about one fifth of the population and present an almost endless societal challenge at the frontier of human sciences. Prodigious technological advances in functional neuroimaging and large-scale genetics have not yet delivered the prospect of refined molecular understanding of mental illness beyond early anatomical descriptions of brain metabolism. However, intensive clinical phenotyping and quantitative metabolic studies using sophisticated radio-ligands in positron-emission tomography, persistently favor the neurobiological approach. This Perspective pursues a familiar maxim in Medicine, aptly summarized in the words of Arthur Koestler: "Nature is generous in her senseless experiments on mankind." Hitherto, studies in neuropsychiatry have largely ignored rare genetic disorders but derangements of specific components within the cerebral laboratory offer rich opportunities for mechanistic exploration. Aberrant psychic behavior is characteristic of many inborn errors of metabolism and although each disorder represents a universe of its own, we are at a threshold for understanding, since contemporary genetics and cell biology furnish abundant materials to take on the perturbing enigma of mental derangement. A further development relates to orphan drugs with actions on defined molecular targets: these represent new ways to study the pathogenesis of psychiatric phenomena associated with rare diseases and in a manner not formerly possible. Here we introduce the frontier of schizophrenia and its strong association with late-onset Tay-Sachs disease as a paradigm to explore.
    Keywords:  GM2 gangliosidoses; Thudichum; late-onset Tay-Sachs disease; lysosomal diseases; psychiatric manifestations; schizophrenia; sphingolipids; substrate-reduction therapy
  21. Front Mol Neurosci. 2020 ;13 162
      The neuromuscular junction (NMJ) is the chemical synapse connecting motor neurons and skeletal muscle fibers. NMJs allow all voluntary movements, and ensure vital functions like breathing. Changes in the structure and function of NMJs are hallmarks of numerous pathological conditions that affect muscle function including sarcopenia, the age-related loss of muscle mass and function. However, the molecular mechanisms leading to the morphological and functional perturbations in the pre- and post-synaptic compartments of the NMJ remain poorly understood. Here, we discuss the role of the metabolic pathway associated to the kinase TOR (Target of Rapamycin) in the development, maintenance and alterations of the NMJ. This is of particular interest as the TOR pathway has been implicated in aging, but its role at the NMJ is still ill-defined. We highlight the respective functions of the two TOR-associated complexes, TORC1 and TORC2, and discuss the role of localized protein synthesis and autophagy regulation in motor neuron terminals and sub-synaptic regions of muscle fibers and their possible effects on NMJ maintenance.
    Keywords:  ALS; NMJ; TOR; aging; autophagy; mTORC1; mTORC2; sarcopenia
  22. Rev Endocr Metab Disord. 2020 Oct 01.
      Growth hormone (GH) actions impact growth, metabolism, and body composition and have been associated with aging and longevity. Lack of GH results in slower growth, delayed maturation, and reduced body size and can lead to delayed aging, increased healthspan, and a remarkable extension of longevity. Adult body size, which is a GH-dependent trait, has a negative association with longevity in several mammalian species. Mechanistic links between GH and aging include evolutionarily conserved insulin/insulin-like growth factors and mechanistic target of rapamycin signaling pathways in accordance with long-suspected trade-offs between anabolic/growth processes and longevity. Height and the rate and regulation of GH secretion have been related to human aging, but longevity is not extended in humans with syndromes of GH deficiency or resistance. However, the risk of age-related chronic disease is reduced in individuals affected by these syndromes and various indices of increased healthspan have been reported.
    Keywords:  GH excess; GH resistance; Growth hormone; Healthspan; Human aging; Lifespan; Mice
  23. . 2020 Sep 28. e51668
      Mutations in GRN, which encodes progranulin, are a common cause of familial frontotemporal dementia (FTD). FTD is a devastating disease characterised by neuronal loss in the frontal and temporal lobes that leads to changes in personality, behaviour and language. There are no effective treatments for this complex condition. TMEM106B is a well-recognised risk factor for FTD caused by GRN mutation. While the specific relationship between progranulin and TMEM106B is unclear, it is well established that they are both required for correct lysosome function and trafficking. Elegant experiments have suggested that increased risk for FTD is due to elevated levels of TMEM106B (Nicholson et al, 2013; Gallagher et al, 2017). Therefore, recent work has explored the therapeutic potential of reducing TMEM106B levels, with initial results looking encouraging, as crossing a Grn-deficient mouse to a Tmem106b knockout showed a rescue in FTD-related behavioural defects and specific aspects of lysosome dysfunction (Klein et al, 2017). However, three independent studies in this issue report that completely removing Tmem106b from Grn knockout mice leads to clear exacerbation of phenotypes, causing severe motor deficits, neurodegeneration and enhanced lysosome abnormalities and gliosis. Remarkably, the double knockout mice also develop TDP-43 pathology-a hallmark of FTD patients with GRN mutations that have not been consistently observed in either of the single knockouts. These concurrent publications that all reach the same surprising but definitive conclusion are a cautionary tale in the control of TMEM106B levels as a potential therapeutic for FTD. They also re-ignite the debate as to whether loss or gain of TMEM106B function is critical for altering FTD risk.
  24. Molecules. 2020 Sep 30. pii: E4493. [Epub ahead of print]25(19):
      Increasing evidence indicates that native mu and delta opioid receptors can associate to form heteromers in discrete brain neuronal circuits. However, little is known about their signaling and trafficking. Using double-fluorescent knock-in mice, we investigated the impact of neuronal co-expression on the internalization profile of mu and delta opioid receptors in primary hippocampal cultures. We established ligand selective mu-delta co-internalization upon activation by 1-[[4-(acetylamino)phenyl]methyl]-4-(2-phenylethyl)-4-piperidinecarboxylic acid, ethyl ester (CYM51010), [d-Ala2, NMe-Phe4, Gly-ol5]enkephalin (DAMGO), and deltorphin II, but not (+)-4-[(αR)-α-((2S,5R)-4-Allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]-N,N-diethylbenzamide (SNC80), morphine, or methadone. Co-internalization was driven by the delta opioid receptor, required an active conformation of both receptors, and led to sorting to the lysosomal compartment. Altogether, our data indicate that mu-delta co-expression, likely through heteromerization, alters the intracellular fate of the mu opioid receptor, which provides a way to fine-tune mu opioid receptor signaling. It also represents an interesting emerging concept for the development of novel therapeutic drugs and strategies.
    Keywords:  delta opioid receptor; heteromer; internalization; lysosomes; mu opioid receptor; primary hippocampal culture
  25. Dev Neurobiol. 2020 Sep 29.
      Newly-synthesized proteins support the development of functional neural circuits and previous work has suggested that dysregulated translation mediates certain forms of autism spectrum disorder (ASD). Here we investigated the role of Target of Rapamycin Complex 1 (TORC1) in synaptic and dendritic development in vivo in the retinotectal system of Xenopus laevis tadpoles. We found that TORC1 signaling regulates dendritic growth and branching and that acute over-activation of TORC1 by Rheb overexpression drove enhanced maturation of excitatory synapses by recruiting AMPA receptors. Interestingly, TORC1 over-activation did not affect inhibitory transmission, resulting in a significant imbalance in the excitatory-to-inhibitory ratio. Rheb overexpression also enlarged excitatory visual input fields in tectal neurons, consistent with dysregulation of retinotopic input refinement and integration of the cell into the circuit. Contrary to other reports that mainly found impairments in synaptic inhibition using broad systemic deletion or mutation of TORC1 regulatory proteins, our findings from acute, local manipulation of TORC1 reveal its critical role in selectively regulating the number and maturity of excitatory, but not inhibitory, synapses in the developing brain.
    Keywords:  Xenopus laevis; development; electroporation; mTOR; receptive field; retinotectal
  26. J Virol. 2020 Sep 30. pii: JVI.01001-20. [Epub ahead of print]
      Marek's disease virus (MDV) transforms CD4+ T cells and causes a deadly neoplastic disease which is associated with metabolic dysregulation leading to atherosclerosis in chickens. While MDV-infected chickens have normal serum concentrations of cholesterol, their aortic tissues were found to have elevated concentrations of free and esterified cholesterol. Here, we demonstrate that infection of chicken embryonated fibroblasts (CEFs) with the highly pathogenic MDV-RB1B increases cellular cholesterol content and upregulates the genes involved in cholesterol synthesis and cellular cholesterol homeostasis using comprehensive two-dimensional gas chromatography mass spectrometry and real-time PCR (RT-PCR), respectively. Using small pharmacological inhibitors and gene silencing, we established an association between MDV-RB1B replication and mevalonic acid, sterol and cholesterol biosynthesis and trafficking/redistribution. We propose that MDV trafficking is mediated by lysosomal associated membrane protein 1+ (LAMP-1) vesicles based on short hairpin RNA (shRNA) gene silencing and colocalization of LAMP-1, glycoprotein B (gB) of MDV and cholesterol (Filipin III) fluorescent signal intensity peaks. In conclusion, our results demonstrate that MDV hijacks cellular cholesterol biosynthesis and cholesterol trafficking to facilitate cell-to-cell spread in a LAMP-1 dependent mechanism.IMPORTANCE MDV disrupts lipid metabolism and causes atherosclerosis in the MDV-infected chickens, however the role of cholesterol metabolism in replication and spread of MDV is unknown. The MDV-infected cells do not produce infectious cell free virus in vitro, raising the question about the mechanism involved in cell-to-cell spread of MDV. In this report, we provide evidence that MDV replication depends on de novo cholesterol biosynthesis and uptake. Interruption of cholesterol trafficking within multivesicular bodies (MVBs) by chemical inhibitors or gene silencing reduced MDV titre and cell-to-cell spread. Lastly, we demonstrated that MDV gB colocalizes with cholesterol and LAMP-1 suggesting that the viral protein trafficking is mediated through LAMP-1 positive vesicles in association with cholesterol. These results provide new insights into the cholesterol dependence of MDV replication.
  27. Cell Rep. 2020 Sep 29. pii: S2211-1247(20)31185-2. [Epub ahead of print]32(13): 108196
      Loss of PTEN, the negative regulator of PI3K activity, is frequent in glioblastomas (GBMs). However, the role of the two major PI3K isoforms, p110α and p110β, in PTEN-deficient gliomagenesis remains unknown. We show that PTEN-deficient GBM largely depends on p110α for proliferation and p110β for migration. Genetic ablation of either isoform delays tumor progression in mice, but only ablating both isoforms completely blocks GBM driven by the concurrent ablation of Pten and p53. BKM120 (buparlisib) treatment only modestly prolongs survival in mice bearing intracranial Pten/p53 null tumors due to partial pathway inhibition. BKM120 extends the survival of mice bearing intracranial tumors in which p110β, but not p110α, has been genetically ablated in the Pten/p53 null glioma, indicating that BKM120 fails to inhibit p110β effectively. Our study suggests that the failure of PI3K inhibitors in GBM may be due to insufficient inhibition of p110β and indicates a need to develop brain-penetrant p110α/β inhibitors.
    Keywords:  BKM120; BYL719; GEMM; PDX; PI3K isoform; PTEN; PTEN-deficient; glioblastoma; isoform-selective inhibitor; migration
  28. Cell Death Discov. 2020 ;6 85
      Macular corneal dystrophy (MCD) is ascribed to mutations in the carbohydrate sulfotransferase (CHST6) gene affecting keratan sulfate (KS) hydrophilicity and causing non-sulfated KS to precipitate in keratocytes and the corneal stroma. We investigated roles for inflammatory responses in MCD pathogenesis by examining the lysosomal-autophagy pathway and activation of pyroptosis in MCD keratocytes. Normal and lesioned keratocytes were obtained from MCD patients undergoing corneal transplantation. The keratocytes were subjected to gene sequencing, RT-PCR, western blotting, transmission electron microscopy, histological staining, induction and inhibition assays of autophagy and pyroptosis, CCK-8 and LysoTracker Green DND-26 labeling, and flow cytometry. A novel homozygous MCD mutation was identified in a family from Northeast China; the mutation was distinguished by cytoplasmic vacuolation, cell membrane disruption, electron dense deposits, and deposition of a band of Periodic acid-Schiff and Alcian blue-positive material in the keratocytes and stroma layer. KS protein levels were decreased, expression of p62 and LC3-II proteins was enhanced, cathepsin D expression was declined and the LysoTracker Green DND-26 signal was dramatically reduced in MCD keratocytes. Bafilomycin-A1 treatment significantly increased caspase-1 and Pro-IL-1β expression in normal and MCD keratocytes. Nod-like receptors pyrins-3 (NLRP3), caspase-1, Pro-IL-1β, and IL-1β levels were pronouncedly elevated in cells exposed to H2O2. Ac-YVAD-CMK treatment reversed this expression in normal and MCD keratocytes. Suppression of the autophagic degradation of non-sulfated KS by impaired autophagic flux in MCD keratocytes triggers pyroptosis. Amelioration of impaired autophagy and restraint of pyroptosis may, therefore, have therapeutic efficacy in the treatment of MCD.
    Keywords:  Disease genetics; Gene expression; Inflammasome; Metabolic disorders
  29. Mol Cell. 2020 Sep 17. pii: S1097-2765(20)30612-2. [Epub ahead of print]
      Necroptosis induction in vitro often requires caspase-8 (Casp8) inhibition by zVAD because pro-Casp8 cleaves RIP1 to disintegrate the necrosome. It has been unclear how the Casp8 blockade of necroptosis is eliminated naturally. Here, we show that pro-Casp8 within the necrosome can be inactivated by phosphorylation at Thr265 (pC8T265). pC8T265 occurs in vitro in various necroptotic cells and in the cecum of TNF-treated mice. p90 RSK is the kinase of pro-Casp8. It is activated by a mechanism that does not need ERK but PDK1, which is recruited to the RIP1-RIP3-MLKL-containing necrosome. Phosphorylation of pro-Casp8 at Thr265 can substitute for zVAD to permit necroptosis in vitro. pC8T265 mimic T265E knockin mice are embryonic lethal due to unconstrained necroptosis, and the pharmaceutical inhibition of RSK-mediated pC8T265 diminishes TNF-induced cecum damage and lethality in mice by halting necroptosis. Thus, phosphorylation of pro-Casp8 at Thr265 by RSK is an intrinsic mechanism for passing the Casp8 checkpoint of necroptosis.
    Keywords:  PDK1; TNF; caspase-8; necroptosis; necrosome; p90 RSK; phosphorylation; zVAD
  30. Cancers (Basel). 2020 Sep 29. pii: E2795. [Epub ahead of print]12(10):
      The multifunctional protein Y-box binding protein-1 (YB-1) regulates all the so far described cancer hallmarks including cell proliferation and survival. The MAPK/ERK and PI3K/Akt pathways are also the major pathways involved in cell growth, proliferation, and survival, and are the frequently hyperactivated pathways in human cancers. A gain of function mutation in KRAS mainly leads to the constitutive activation of the MAPK pathway, while the activation of the PI3K/Akt pathway occurs either through the loss of PTEN or a gain of function mutation of the catalytic subunit alpha of PI3K (PIK3CA). In this study, we investigated the underlying signaling pathway involved in YB-1 phosphorylation at serine 102 (S102) in KRAS(G13D)-mutated triple-negative breast cancer (TNBC) MDA-MB-231 cells versus PIK3CA(H1047R)/PTEN(E307K) mutated TNBC MDA-MB-453 cells. Our data demonstrate that S102 phosphorylation of YB-1 in KRAS-mutated cells is mainly dependent on the MAPK/ERK pathway, while in PIK3CA/PTEN-mutated cells, YB-1 S102 phosphorylation is entirely dependent on the PI3K/Akt pathway. Independent of the individual dominant pathway regulating YB-1 phosphorylation, dual targeting of MEK and PI3K efficiently inhibited YB-1 phosphorylation and blocked cell proliferation. This represents functional crosstalk between the two pathways. Our data obtained from the experiments, applying pharmacological inhibitors and genetic approaches, shows that YB-1 is a key player in cell proliferation, clonogenic activity, and tumor growth of TNBC cells through the MAPK and PI3K pathways. Therefore, dual inhibition of these two pathways or single targeting of YB-1 may be an effective strategy to treat TNBC.
    Keywords:  KRAS; MAPK/ERK; PI3K/Akt; PIK3CA; PTEN; YB-1; triple negative breast cancer cells
  31. Int J Mol Sci. 2020 Sep 28. pii: E7159. [Epub ahead of print]21(19):
      The challenges in the diagnosis, prognosis, and monitoring of Gaucher disease (GD), an autosomal recessive inborn error of glycosphingolipid metabolism, can negatively impact clinical outcomes. This systematic literature review evaluated the value of glucosylsphingosine (lyso-Gb1), as the most reliable biomarker currently available for the diagnosis, prognosis, and disease/treatment monitoring of patients with GD. Literature searches were conducted using MEDLINE, Embase, PubMed, ScienceOpen,, Biological Abstracts, and Sci-Hub to identify original research articles relevant to lyso-Gb1 and GD published before March 2019. Seventy-four articles met the inclusion criteria, encompassing 56 related to pathology and 21 related to clinical biomarkers. Evidence for lyso-Gb1 as a pathogenic mediator of GD was unequivocal, although its precise role requires further elucidation. Lyso-Gb1 was deemed a statistically reliable diagnostic and pharmacodynamic biomarker in GD. Evidence supports lyso-Gb1 as a disease-monitoring biomarker for GD, and some evidence supports lyso-Gb1 as a prognostic biomarker, but further study is required. Lyso-Gb1 meets the criteria for a biomarker as it is easily accessible and reliably quantifiable in plasma and dried blood spots, enables the elucidation of GD molecular pathogenesis, is diagnostically valuable, and reflects therapeutic responses. Evidentiary standards appropriate for verifying inter-laboratory lyso-Gb1 concentrations in plasma and in other anatomical sites are needed.
    Keywords:  Gaucher disease; biomarker; glucosylsphingosine; lyso-Gb1; lysosomal storage disorder; systematic literature review
  32. Biochem Pharmacol. 2020 Sep 23. pii: S0006-2952(20)30466-4. [Epub ahead of print] 114230
      L-asparaginase (ASNase) from Escherichia coli (EcAII) is used in the treatment of acute lymphoblastic leukaemia (ALL). EcAII activity in vivo has been described to be influenced by the human lysosomal proteases asparaginyl endopeptidase (AEP) and cathepsin B (CTSB); these hydrolases cleave and could expose epitopes associated with the immune response against EcAII. In this work, we show that ASNase resistance to CTSB and/or AEP influences the formation of anti-ASNase antibodies, one of the main causes of hypersensitivity reactions in patients. Error-prone polymerase chain reaction was used to produce variants of EcAII more resistant to proteolytic cleavage by AEP and CTSB. The variants with enzymatic activity and cytotoxicity levels equivalent to or better than EcAII WT were submitted to in vivo assays. Only one of the mutants presented increased serum half-life, so resistance to these proteases is not the only feature involved in EcAII stability in vivo. Our results showed alteration of the phenotypic profile of B cells isolated after animal treatment with different protease-resistant proteoforms. Furthermore, mice that were exposed to the protease-resistant proteoforms presented lower anti-asparaginase antibodies production in vivo. Our data suggest that modulating resistance to lysosomal proteases can result in less immunogenic protein drugs.
    Keywords:  Acute lymphoblastic leukaemia; Biopharmaceutical; Error-prone polymerase chain reaction; Human proteases; L-asparaginase; Protein stability
  33. Proc Natl Acad Sci U S A. 2020 Sep 28. pii: 201912772. [Epub ahead of print]
      Deregulated global mRNA translation is an emerging feature of cancer cells. Oncogenic transformation in colorectal cancer (CRC) is driven by mutations in APC, KRAS, SMAD4, and TP53, known as the adenoma-carcinoma sequence (ACS). Here we introduce each of these driver mutations into intestinal organoids to show that they are modulators of global translational capacity in intestinal epithelial cells. Increased global translation resulting from loss of Apc expression was potentiated by the presence of oncogenic Kras G12D Knockdown of Smad4 further enhanced global translation efficiency and was associated with a lower 4E-BP1-to-eIF4E ratio. Quadruple mutant cells with additional P53 loss displayed the highest global translational capacity, paralleled by high proliferation and growth rates, indicating that the proteome is heavily geared toward cell division. Transcriptional reprogramming facilitating global translation included elevated ribogenesis and activation of mTORC1 signaling. Accordingly, interfering with the mTORC1/4E-BP/eIF4E axis inhibited the growth potential endowed by accumulation of multiple drivers. In conclusion, the ACS is characterized by a strongly altered global translational landscape in epithelial cells, exposing a therapeutic potential for direct targeting of the translational apparatus.
    Keywords:  colorectal cancer; driver mutations; global translation; protein synthesis