Glucosylceramide and glucosylsphingosine modulate calcium mobilization from brain microsomes via different mechanisms

Examining the Role of a Functional Deficiency of Iron in Lysosomal Storage Disorders with Translational Relevance to Alzheimer's Disease

The recently presented Azalea Hypothesis for Alzheimer's disease asserts that iron becomes sequestered, leading to a functional iron deficiency that contributes to neurodegeneration. Iron sequestration can occur by iron being bound to protein aggregates, such as amyloid β and tau, iron-rich structures not undergoing recycling (e.g., due to disrupted ferritinophagy and impaired mitophagy), and diminished delivery of iron from the lysosome to the cytosol. Reduced iron availability for biochemical reactions causes cells to respond to acquire additional iron, resulting in an elevation in the total iron level within affected brain regions. As the amount of unavailable iron increases, the level of available iron decreases until eventually it is unable to meet cellular demands, which leads to a functional iron deficiency. Normally, the lysosome plays an integral role in cellular iron homeostasis by facilitating both the delivery of iron to the cytosol (e.g., after endocytosis of the iron-transferrin-transferrin receptor complex) and the cellular recycling of iron. During a lysosomal storage disorder, an enzyme deficiency causes undigested substrates to accumulate, causing a sequelae of pathogenic events that may include cellular iron dyshomeostasis. Thus, a functional deficiency of iron may be a pathogenic mechanism occurring within several lysosomal storage diseases and Alzheimer's disease.

Glycosphingolipids are linked to elevated neurotransmission and neurodegeneration in a Drosophila model of Niemann Pick type C

The lipid storage disease Niemann Pick type C (NPC) causes neurodegeneration owing primarily to loss of NPC1. Here, we employed a Drosophila model to test links between glycosphingolipids, neurotransmission and neurodegeneration. We found that Npc1a nulls had elevated neurotransmission at the glutamatergic neuromuscular junction (NMJ), which was phenocopied in brainiac (brn) mutants, impairing mannosyl glucosylceramide (MacCer) glycosylation. Npc1a; brn double mutants had the same elevated synaptic transmission, suggesting that Npc1a and brn function within the same pathway. Glucosylceramide (GlcCer) synthase inhibition with miglustat prevented elevated neurotransmission in Npc1a and brn mutants, further suggesting epistasis. Synaptic MacCer did not accumulate in the NPC model, but GlcCer levels were increased, suggesting that GlcCer is responsible for the elevated synaptic transmission. Null Npc1a mutants had heightened neurodegeneration, but no significant motor neuron or glial cell death, indicating that dying cells are interneurons and that elevated neurotransmission precedes neurodegeneration. Glycosphingolipid synthesis mutants also had greatly heightened neurodegeneration, with similar neurodegeneration in Npc1a; brn double mutants, again suggesting that Npc1a and brn function in the same pathway. These findings indicate causal links between glycosphingolipid-dependent neurotransmission and neurodegeneration in this NPC disease model.

Novel Therapeutic Approaches in Inherited Neuropathies: A Systematic Review

The management of inherited neuropathies relies mostly on the treatment of symptoms. In recent years, a better understanding of the pathogenic mechanisms that underlie neuropathies has allowed for the development of disease-modifying therapies. Here, we systematically review the therapies that have emerged in this field over the last five years. An updated list of diseases with peripheral neuropathy as a clinical feature was created based on panels of genes used clinically to diagnose inherited neuropathy. This list was extended by an analysis of published data by the authors and verified by two experts. A comprehensive search for studies of human patients suffering from one of the diseases in our list yielded 28 studies that assessed neuropathy as a primary or secondary outcome. Although the use of various scales and scoring systems made comparisons difficult, this analysis identified diseases associated with neuropathy for which approved therapies exist. An important finding is that the symptoms and/or biomarkers of neuropathies were assessed only in a minority of cases. Therefore, further investigation of treatment efficacy on neuropathies in future trials must employ objective, consistent methods such as wearable technologies, motor unit indexes, MRI or sonography imaging, or the use of blood biomarkers associated with consistent nerve conduction studies.

Sphingoid Bases Regulate the Sigma-1 Receptor-Sphingosine and N,N'-Dimethylsphingosine Are Endogenous Agonists

Both bioactive sphingolipids and Sigma-1 receptor (S1R) chaperones occur ubiquitously in mammalian cell membranes. Endogenous compounds that regulate the S1R are important for controlling S1R responses to cellular stress. Herein, we interrogated the S1R in intact Retinal Pigment Epithelial cells (ARPE-19) with the bioactive sphingoid base, sphingosine (SPH), or the pain-provoking dimethylated SPH derivative, N,N'-dimethylsphingosine (DMS). As informed by a modified native gel approach, the basal and antagonist (BD-1047)-stabilized S1R oligomers dissociated to protomeric forms in the presence of SPH or DMS (PRE-084 as control). We, thus, posited that SPH and DMS are endogenous S1R agonists. Consistently, in silico docking of SPH and DMS to the S1R protomer showed strong associations with Asp126 and Glu172 in the cupin beta barrel and extensive van der Waals interactions of the C18 alkyl chains with the binding site including residues in helices 4 and 5. Mean docking free energies were 8.73-8.93 kcal/mol for SPH and 8.56-8.15 kcal/mol for DMS, and calculated binding constants were ~40 nM for SPH and ~120 nM for DMS. We hypothesize that SPH, DMS, and similar sphingoid bases access the S1R beta barrel via a membrane bilayer pathway. We further propose that the enzymatic control of ceramide concentrations in intracellular membranes as the primary sources of SPH dictates availability of endogenous SPH and DMS to the S1R and the subsequent control of S1R activity within the same cell and/or in cellular environments.

Type 2 diabetes disrupts circadian orchestration of lipid metabolism and membrane fluidity in human pancreatic islets

Recent evidence suggests that circadian clocks ensure temporal orchestration of lipid homeostasis and play a role in pathophysiology of metabolic diseases in humans, including type 2 diabetes (T2D). Nevertheless, circadian regulation of lipid metabolism in human pancreatic islets has not been explored. Employing lipidomic analyses, we conducted temporal profiling in human pancreatic islets derived from 10 nondiabetic (ND) and 6 T2D donors. Among 329 detected lipid species across 8 major lipid classes, 5% exhibited circadian rhythmicity in ND human islets synchronized in vitro. Two-time point-based lipidomic analyses in T2D human islets revealed global and temporal alterations in phospho- and sphingolipids. Key enzymes regulating turnover of sphingolipids were rhythmically expressed in ND islets and exhibited altered levels in ND islets bearing disrupted clocks and in T2D islets. Strikingly, cellular membrane fluidity, measured by a Nile Red derivative NR12S, was reduced in plasma membrane of T2D diabetic human islets, in ND donors’ islets with disrupted circadian clockwork, or treated with sphingolipid pathway modulators. Moreover, inhibiting the glycosphingolipid biosynthesis led to strong reduction of insulin secretion triggered by glucose or KCl, whereas inhibiting earlier steps of de novo ceramide synthesis resulted in milder inhibitory effect on insulin secretion by ND islets. Our data suggest that circadian clocks operative in human pancreatic islets are required for temporal orchestration of lipid homeostasis, and that perturbation of temporal regulation of the islet lipid metabolism upon T2D leads to altered insulin secretion and membrane fluidity. These phenotypes were recapitulated in ND islets bearing disrupted clocks.

Sphingolipids and their role in health and disease in the central nervous system

Sphingolipids (SLs) are lipids derived from sphingosine, and their metabolism involves a broad and complex network of reactions. Although SLs are widely distributed in the body, it is well known that they are present in high concentrations within the central nervous system (CNS). Under physiological conditions, their abundance and distribution in the CNS depend on brain development and cell type. Consequently, SLs metabolism impairment may have a significant impact on the normal CNS function, and has been associated with several disorders, including sphingolipidoses, Parkinson's, and Alzheimer's. This review summarizes the main SLs characteristics and current knowledge about synthesis, catabolism, regulatory pathways, and their role in physiological and pathological scenarios in the CNS.

Restoration of Sarco/Endoplasmic Reticulum Ca2+-ATPase Activity Functions as a Pivotal Therapeutic Target of Anti-Glutamate-Induced Excitotoxicity to Attenuate Endoplasmic Reticulum Ca2+ Depletion

Glutamate-induced excitotoxicity is a pathological basis of many acute/chronic neurodegenerative diseases. Sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA2b) is a membrane-embedded P-type ATPase pump that manages the translocation of calcium ions (Ca²⁺) from cytosol into the lumen of the endoplasmic reticulum (ER) calcium stores. It participates in a wide range of biological functions in the central nervous system (CNS). However, the role of SERCA2b in glutamate-induced excitotoxicity and its mechanism must be elucidated. Herein, we demonstrate that SERCA2b mutants exacerbate the excitotoxicity of hypo-glutamate stimulation on HT22 cells. In this study, SERCA2b mutants accelerated Ca²⁺ depletion through loss-of-function (reduced pumping capacity) or gain-of-function (acquired leakage), resulting in ER stress. In addition, the occurrence of ER Ca²⁺ depletion increased mitochondria-associated membrane formation, which led to mitochondrial Ca²⁺ overload and dysfunction. Moreover, the enhancement of SERCA2b pumping capacity or inhibition of Ca²⁺ leakage attenuated Ca²⁺ depletion and impeded excitotoxicity in response to hypo-glutamate stimulation. In conclusion, SERCA2b mutants exacerbate ER Ca²⁺-depletion-mediated excitotoxicity in glutamate-sensitive HT22 cells. The mechanism of disruption is mainly related to the heterogeneity of SERCA2b mutation sites. Stabilization of SRECA2b function is a critical therapeutic approach against glutamate-induced excitotoxicity. These data will expand understanding of organelle regulatory networks and facilitate the discovery and creation of drugs against excitatory/inhibitory imbalance in the CNS.

Neurodegeneration in Niemann-Pick Type C Disease: An Updated Review on Pharmacological and Non-Pharmacological Approaches to Counteract Brain and Cognitive Impairment

Niemann–Pick type C (NPC) disease is an autosomal recessive storage disorder, characterized by abnormal sequestration of unesterified cholesterol in the late endo-lysosomal system of cells. Progressive neurological deterioration and the onset of symptoms, such as ataxia, seizures, cognitive decline, and severe dementia, are pathognomonic features of the disease. In addition, different pathological similarities, including degeneration of hippocampal and cortical neurons, hyperphosphorylated tau, and neurofibrillary tangle formation, have been identified between NPC disease and other neurodegenerative pathologies. However, the underlying pathophysiological mechanisms are not yet well understood, and even a real cure to counteract neurodegeneration has not been identified. Therefore, the combination of current pharmacological therapies, represented by miglustat and cyclodextrin, and non-pharmacological approaches, such as physical exercise and appropriate diet, could represent a strategy to improve the quality of life of NPC patients. Based on this evidence, in our review we focused on the neurodegenerative aspects of NPC disease, summarizing the current knowledge on the molecular and biochemical mechanisms responsible for cognitive impairment, and suggesting physical exercise and nutritional treatments as additional non-pharmacologic approaches to reduce the progression and neurodegenerative course of NPC disease.

An overview of therapeutic potential of N-alkylated 1-deoxynojirimycin congeners

Polyhydroxylated alkaloids display a wide range of biological activities, suggesting their use in the treatment of various diseases. Their most famous representative, 1-deoxynojirimycin (DNJ), is a natural product that shows α- and β-glucosidase inhibition. This molecule has been since converted into two clinically approved drugs i.e., Zavesca® and Glyset®, targeting type I Gaucher's disease and type II diabetes mellitus, respectively. This review examines the therapeutic potential of important DNJ congeners reported in last decade and presents concise mechanism of glycosidase inhibition. A brief overview of substituents conjugation's impact on DNJ scaffold (including N-alkylated DNJ derivatives, mono-valent, di-valent and multivalent DNJ congeners, N-[5-(adamantan-1-yl-methoxy)-pentyl]-1-deoxynojirimycin (AMP-DNM) look alike DNJ based lipophilic derivatives, AMP-DNM based neoglycoconjugates, DNJ click derivatives with varying carboxylic acids and aromatic moieties, conjugates of DNJ and glucose, and N-bridged DNJ analogues) towards various enzymes such as α/β glucosidase, porcine trehalase, as F508del-CFTR correctors, α-mannosidase, human placental β-glucocerebrosidase, N370S β-GCase, α-amylase and insect trehalase as potent and selective inhibitors have been discussed with potential bioactivities, which can provide inspiration for future studies.

Sphingolipid lysosomal storage diseases: from bench to bedside

Johann Ludwig Wilhelm Thudicum described sphingolipids (SLs) in the late nineteenth century, but it was only in the past fifty years that SL research surged in importance and applicability. Currently, sphingolipids and their metabolism are hotly debated topics in various biochemical fields. Similar to other macromolecular reactions, SL metabolism has important implications in health and disease in most cells. A plethora of SL-related genetic ailments has been described. Defects in SL catabolism can cause the accumulation of SLs, leading to many types of lysosomal storage diseases (LSDs) collectively called sphingolipidoses. These diseases mainly impact the neuronal and immune systems, but other systems can be affected as well. This review aims to present a comprehensive, up-to-date picture of the rapidly growing field of sphingolipid LSDs, their etiology, pathology, and potential therapeutic strategies. We first describe LSDs biochemically and briefly discuss their catabolism, followed by general aspects of the major diseases such as Gaucher, Krabbe, Fabry, and Farber among others. We conclude with an overview of the available and potential future therapies for many of the diseases. We strive to present the most important and recent findings from basic research and clinical applications, and to provide a valuable source for understanding these disorders.

Gender-Specific Effects of Two Treatment Strategies in a Mouse Model of Niemann-Pick Disease Type C1

In a mouse model of Niemann-Pick disease type C1 (NPC1), a combination therapy (COMBI) of miglustat (MIGLU), the neurosteroid allopregnanolone (ALLO) and the cyclic oligosaccharide 2-hydroxypropyl-β-cyclodextrin (HPßCD) has previously resulted in, among other things, significantly improved motor function. The present study was designed to compare the therapeutic effects of the COMBI therapy with that of MIGLU or HPßCD alone on body and brain weight and the behavior of NPC1^−/− mice in a larger cohort, with special reference to gender differences. A total of 117 NPC1^−/− and 123 NPC1^+/+ mice underwent either COMBI, MIGLU only, HPßCD only, or vehicle treatment (Sham), or received no treatment at all (None). In male and female NPC1^−/− mice, all treatments led to decreased loss of body weight and, partly, brain weight. Concerning motor coordination, as revealed by the accelerod test, male NPC1^−/− mice benefited from COMBI treatment, whereas female mice benefited from COMBI, MIGLU, and HPßCD treatment. As seen in the open field test, the reduced locomotor activity of male and female NPC1^−/− mice was not significantly ameliorated in either treatment group. Our results suggest that in NPC1^−/− mice, each drug treatment scheme had a beneficial effect on at least some of the parameters evaluated compared with Sham-treated mice. Only in COMBI-treated male and female NPC^+/+ mice were drug effects seen in reduced body and brain weights. Upon COMBI treatment, the increased dosage of drugs necessary for anesthesia in Sham-treated male and female NPC1^−/− mice was almost completely reduced only in the female groups.

How Is the Fidelity of Proteins Ensured in Terms of Both Quality and Quantity at the Endoplasmic Reticulum? Mechanistic Insights into E3 Ubiquitin Ligases

The endoplasmic reticulum (ER) is an interconnected organelle that plays fundamental roles in the biosynthesis, folding, stabilization, maturation, and trafficking of secretory and transmembrane proteins. It is the largest organelle and critically modulates nearly all aspects of life. Therefore, in the endoplasmic reticulum, an enormous investment of resources, including chaperones and protein folding facilitators, is dedicated to adequate protein maturation and delivery to final destinations. Unfortunately, the folding and assembly of proteins can be quite error-prone, which leads to the generation of misfolded proteins. Notably, protein homeostasis, referred to as proteostasis, is constantly exposed to danger by flows of misfolded proteins and subsequent protein aggregates. To maintain proteostasis, the ER triages and eliminates terminally misfolded proteins by delivering substrates to the ubiquitin–proteasome system (UPS) or to the lysosome, which is termed ER-associated degradation (ERAD) or ER-phagy, respectively. ERAD not only eliminates misfolded or unassembled proteins via protein quality control but also fine-tunes correctly folded proteins via protein quantity control. Intriguingly, the diversity and distinctive nature of E3 ubiquitin ligases determine efficiency, complexity, and specificity of ubiquitination during ERAD. ER-phagy utilizes the core autophagy machinery and eliminates ERAD-resistant misfolded proteins. Here, we conceptually outline not only ubiquitination machinery but also catalytic mechanisms of E3 ubiquitin ligases. Further, we discuss the mechanistic insights into E3 ubiquitin ligases involved in the two guardian pathways in the ER, ERAD and ER-phagy. Finally, we provide the molecular mechanisms by which ERAD and ER-phagy conduct not only protein quality control but also protein quantity control to ensure proteostasis and subsequent organismal homeostasis.

Lyso-Gb3 Increases αvβ3 Integrin Gene Expression in Cultured Human Podocytes in Fabry Nephropathy

Background: Podocyturia in Fabry nephropathy leads to glomerulosclerosis and kidney disease progression. Integrins are involved in podocyte attachment to the glomerular basement membrane. We hypothesized that in Fabry nephropathy, lyso-Gb3 could modulate αvβ3 expression in podocytes. Together with UPAR, the αvβ3 integrin is a key mechanism involved in podocyte detachment and podocyturia. Methods: In cultured human podocytes stimulated with lyso-Gb3, the mRNA expression of the ITGAV and ITGB3 genes encoding integrins αv and β3, respectively, was analyzed by RT-qPCR. Results: In cultured human podocytes, lyso-Gb3 at concentrations encountered in the serum of Fabry patients increased ITGAV and ITGB3 mRNA levels within 3 to 6 h. This pattern of gene expression is similar to that previously observed for PLAUR (UPAR) gene expression but is in contrast to the delayed (24 h) upregulation of other markers of podocyte stress and mediators of injury, such as CD80, TGFβ1, CD74, Notch1, and HES. Conclusions: Human podocyte stress in response to glycolipid overload in Fabry nephropathy, exemplified by lyso-Gb3, is characterized by an early increase in the expression of components of the αvβ3/UPAR system, which contrasts with the delayed rise in the expression of other mediators of podocyte injury. This suggests that the αvβ3/UPAR system may be a therapeutic target in Fabry nephropathy.

Glycosphingolipids and neuroinflammation in Parkinson's disease

Parkinson's disease is a progressive neurodegenerative disease characterized by the loss of dopaminergic neurons of the nigrostriatal pathway and the formation of neuronal inclusions known as Lewy bodies. Chronic neuroinflammation, another hallmark of the disease, is thought to play an important role in the neurodegenerative process. Glycosphingolipids are a well-defined subclass of lipids that regulate crucial aspects of the brain function and recently emerged as potent regulators of the inflammatory process. Deregulation in glycosphingolipid metabolism has been reported in Parkinson's disease. However, the interrelationship between glycosphingolipids and neuroinflammation in Parkinson's disease is not well known. This review provides a thorough overview of the links between glycosphingolipid metabolism and immune-mediated mechanisms involved in neuroinflammation in Parkinson's disease. After a brief presentation of the metabolism and function of glycosphingolipids in the brain, it summarizes the evidences supporting that glycosphingolipids (i.e. glucosylceramides or specific gangliosides) are deregulated in Parkinson's disease. Then, the implications of these deregulations for neuroinflammation, based on data from human inherited lysosomal glycosphingolipid storage disorders and gene-engineered animal studies are outlined. Finally, the key molecular mechanisms by which glycosphingolipids could control neuroinflammation in Parkinson's disease are highlighted. These include inflammasome activation and secretion of pro-inflammatory cytokines, altered calcium homeostasis, changes in the blood-brain barrier permeability, recruitment of peripheral immune cells or production of autoantibodies.

The Resurrection of Phenotypic Drug Discovery

Prior to genetic mapping, the majority of drug discovery efforts involved phenotypic screening, wherein compounds were screened in either in vitro or in vivo models thought to mimic the disease state of interest. While never completely abandoning phenotypic approaches, the labor intensive nature of such tests encouraged the pharmaceutical industry to move away from them in favor of target-based drug discovery, which facilitated throughput and allowed for the efficient screening of large numbers of compounds. However, a consequence of reliance on target-based screening was an increased number of failures in clinical trials due to poor correlation between novel mechanistic targets and the actual disease state. As a result, the field has seen a recent resurrection in phenotypic drug discovery approaches. In this work, we highlight some recent phenotypic projects from our industrial past and in our current academic drug discovery environment that have provided encouraging results.

Value of Glucosylsphingosine (Lyso-Gb1) as a Biomarker in Gaucher Disease: A Systematic Literature Review

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, Science.gov, 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.

Lyso-glycosphingolipids: presence and consequences

Lyso-glycosphingolipids are generated in excess in glycosphingolipid storage disorders. In the course of these pathologies glycosylated sphingolipid species accumulate within lysosomes due to flaws in the respective lipid degrading machinery. Deacylation of accumulating glycosphingolipids drives the formation of lyso-glycosphingolipids. In lysosomal storage diseases such as Gaucher Disease, Fabry Disease, Krabbe disease, GM1 -and GM2 gangliosidosis, Niemann Pick type C and Metachromatic leukodystrophy massive intra-lysosomal glycosphingolipid accumulation occurs. The lysosomal enzyme acid ceramidase generates the deacylated lyso-glycosphingolipid species. This review discusses how the various lyso-glycosphingolipids are synthesized, how they may contribute to abnormal immunity in glycosphingolipid storing lysosomal diseases and what therapeutic opportunities exist.

Chemical inhibition of β-glucocerebrosidase does not affect phagocytosis and early containment of Leishmania by murine macrophages

Gaucher disease is a lysosomal storage disease in which a genetic deficiency in β-glucocerebrosidase leads to the accumulation of glycosphingolipids in lysosomes. Macrophages are amongst the cells most severely affected in Gaucher disease patients. One phenotype associated with Gaucher macrophages is the impaired capacity to fight bacterial infections. Here, we investigate whether inhibition of β-glucocerebrosidase activity affects the capacity of macrophages to phagocytose and act on the early containment of human pathogens of the genus Leishmania. Towards our aim, we performed in vitro infection assays on macrophages derived from the bone marrow of C57BL/6 mice. To mimic Gaucher disease, macrophages were incubated with the β-glucocerebrosidase inhibitor, conduritol B epoxide (CBE), prior to contact with Leishmania. This treatment guaranteed that β-glucocerebrosidase was fully inhibited during the contact of macrophages with Leishmania, its enzymatic activity being progressively recovered along the 48 h that followed removal of the inhibitor. Infections were performed with L. amazonensis, L. infantum, or L. major, so as to explore potential species-specific responses in the context of β-glucocerebrosidase inactivation. Parameters of infection, recorded immediately after phagocytosis, as well as 24 and 48 h later, revealed no noticeable differences in the infection parameters of CBE-treated macrophages relative to non-treated controls. We conclude that blocking β-glucocerebrosidase activity during contact with Leishmania does not interfere with the phagocytic capacity of macrophages and the early onset of leishmanicidal responses.

Lysosomal Biology and Function: Modern View of Cellular Debris Bin

Lysosomes are the main proteolytic compartments of mammalian cells comprising of a battery of hydrolases. Lysosomes dispose and recycle extracellular or intracellular macromolecules by fusing with endosomes or autophagosomes through specific waste clearance processes such as chaperone-mediated autophagy or microautophagy. The proteolytic end product is transported out of lysosomes via transporters or vesicular membrane trafficking. Recent studies have demonstrated lysosomes as a signaling node which sense, adapt and respond to changes in substrate metabolism to maintain cellular function. Lysosomal dysfunction not only influence pathways mediating membrane trafficking that culminate in the lysosome but also govern metabolic and signaling processes regulating protein sorting and targeting. In this review, we describe the current knowledge of lysosome in influencing sorting and nutrient signaling. We further present a mechanistic overview of intra-lysosomal processes, along with extra-lysosomal processes, governing lysosomal fusion and fission, exocytosis, positioning and membrane contact site formation. This review compiles existing knowledge in the field of lysosomal biology by describing various lysosomal events necessary to maintain cellular homeostasis facilitating development of therapies maintaining lysosomal function.

Dynamics of sphingolipids and the serine palmitoyltransferase complex in rat oligodendrocytes during myelination

Myelin is a unique lipid-rich membrane structure that accelerates neurotransmission and supports neuronal function. Sphingolipids are critical myelin components. Yet sphingolipid content and synthesis have not been well characterized in oligodendrocytes, the myelin-producing cells of the CNS. Here, using quantitative real-time PCR, LC-MS/MS-based lipid analysis, and biochemical assays, we examined sphingolipid synthesis during the peak period of myelination in the postnatal rat brain. Importantly, we characterized sphingolipid production in isolated oligodendrocytes. We analyzed sphingolipid distribution and levels of critical enzymes and regulators in the sphingolipid biosynthetic pathway, with focus on the serine palmitoyltransferase (SPT) complex, the rate-limiting step in this pathway. During myelination, levels of the major SPT subunits increased and oligodendrocyte maturation was accompanied by extensive alterations in the composition of the SPT complex. These included changes in the relative levels of two alternative catalytic subunits, SPTLC2 and -3, in the relative levels of isoforms of the small subunits, ssSPTa and -b, and in the isoform distribution of the SPT regulators, the ORMDLs. Myelination progression was accompanied by distinct changes in both the nature of the sphingoid backbone and the N-acyl chains incorporated into sphingolipids. We conclude that the distribution of these changes among sphingolipid family members is indicative of a selective channeling of the ceramide backbone toward specific downstream metabolic pathways during myelination. Our findings provide insights into myelin production in oligodendrocytes and suggest how dysregulation of the biosynthesis of this highly specialized membrane could contribute to demyelinating diseases.

Species-Specific Differences in the Susceptibility of Fungi to the Antifungal Protein AFP Depend on C-3 Saturation of Glycosylceramides

Our data suggest a fundamental role of glycosylceramides in the susceptibility of fungi to AFP. We discovered that only a minor structural difference in these molecules—namely, the saturation level of their fatty acid chain, controlled by a 2-hydroxy fatty N-acyl-Δ3(E)-desaturase—represents a key to understanding the inhibitory activity of AFP. As glycosylceramides are important components of fungal plasma membranes, we propose a model which links AFP-mediated inhibition of chitin synthesis in fungi with its potential to disturb plasma membrane integrity.

AFP is an antimicrobial peptide (AMP) produced by the filamentous fungus Aspergillus giganteus and is a very potent inhibitor of fungal growth that does not affect the viability of bacteria, plant, or mammalian cells. It targets chitin synthesis and causes plasma membrane permeabilization in many human- and plant-pathogenic fungi, but its exact mode of action is not known. After adoption of the “damage-response framework of microbial pathogenesis” regarding the analysis of interactions between AMPs and microorganisms, we have recently proposed that the cytotoxic capacity of a given AMP depends not only on the presence/absence of its target(s) in the host and the AMP concentration applied but also on other variables, such as microbial survival strategies. We show here using the examples of three filamentous fungi (Aspergillus niger, Aspergillus fumigatus, and Fusarium graminearum) and two yeasts (Saccharomyces cerevisiae and Pichia pastoris) that the important parameters defining the AFP susceptibilities of these fungi are (i) the presence/absence of glycosylceramides, (ii) the presence/absence of Δ3(E) desaturation of the fatty acid chain therein, and (iii) the (dis)ability of these fungi to respond to AFP inhibitory effects with the fortification of their cell walls via increased chitin and β-(1,3)-glucan synthesis. These observations support the idea of the adoption of the damage-response framework to holistically understand the outcome of AFP inhibitory effects.

IMPORTANCE Our data suggest a fundamental role of glycosylceramides in the susceptibility of fungi to AFP. We discovered that only a minor structural difference in these molecules—namely, the saturation level of their fatty acid chain, controlled by a 2-hydroxy fatty N-acyl-Δ3(E)-desaturase—represents a key to understanding the inhibitory activity of AFP. As glycosylceramides are important components of fungal plasma membranes, we propose a model which links AFP-mediated inhibition of chitin synthesis in fungi with its potential to disturb plasma membrane integrity.

Mixing brain cerebrosides with brain ceramides, cholesterol and phospholipids

The properties of bilayers composed of pure brain cerebroside (bCrb) or of binary mixtures of bCrb with brain ceramide, cholesterol, egg phosphatidylcholine or brain sphingomyelin have been studied using a combination of physical techniques. Pure bCrb exhibits a rather narrow gel-fluid transition centred at ≈65 °C, with a half-width at half-height T1/2 ≈ 3 °C. bCrb mixes well with both fluid and gel phospholipids and ceramide, and it rigidifies bilayers of egg phosphatidylcholine or brain sphingomyelin when the latter are in the fluid state. Cholesterol markedly widens the bCrb gel-fluid transition, while decreasing the associated transition enthalpy, in the manner of cholesterol mixtures with saturated phosphatidylcholines, or sphingomyelins. Laurdan and DPH fluorescence indicate the formation of fluid ordered phases in the bCrb:cholesterol mixtures. Macroscopic phase separation of more and less fluid domains is observed in giant unilamellar vesicles consisting of bCrb:egg phosphatidylcholine or bCrb:sphingomyelin. Crb capacity to induce bilayer permeabilization or transbilayer (flip-flop) lipid motion is much lower than those of ceramides. The mixtures explored here contained mostly bCrb concentrations >50 mol%, mimicking the situation of cell membranes in Gaucher's disease, or of the Crb-enriched microdomains proposed to exist in healthy cell plasma membranes.

The intersection of lysosomal and endoplasmic reticulum calcium with autophagy defects in lysosomal diseases

The lysosomal storage disorders (LSDs) encompass a group of more than 50 inherited diseases characterized by the accumulation of lysosomal substrates. Two-thirds of patients experience significant neurological symptoms, but the mechanisms of neurodegeneration are not well understood. Interestingly, a wide range of LSDs show defects in both autophagy and Ca2+ homeostasis, which is notable as Ca2+ is a key regulator of autophagy. The crosstalk between these pathways in the context of LSD pathogenesis is not well characterized, but further understanding of this relationship could open up promising therapeutic targets. This review discusses the role of endoplasmic reticulum and lysosomal Ca2+ in autophagy regulation and highlights what is known about defects in autophagy and Ca2+ homeostasis in two LSDs, Niemann-Pick type C disease and Gaucher disease.

Miglustat in Niemann-Pick disease type C patients: a review

OBJECTIVE

Niemann-Pick disease type C (NP-C) is a rare, autosomal recessive, neurodegenerative disease associated with a wide variety of progressive neurological manifestations. Miglustat is indicated for the treatment of progressive neurological manifestations in both adults and children. Since approval in 2009 there has been a vast growth in clinical experience with miglustat. The effectiveness of miglustat has been assessed using a range of measures.

METHODS

Comprehensive review of published data from studies of cellular neuropathological markers and structural neurological indices in the brain, clinical impairment/disability, specific clinical neurological manifestations, and patient survival.

RESULTS

Cranial diffusion tensor imaging and magnetic resonance spectroscopy studies have shown reduced levels of choline (a neurodegeneration marker), and choline/N-acetyl aspartate ratio (indicating increased neuronal viability) in the brain during up to 5 years of miglustat therapy, as well as a slowing of reductions in fractional anisotropy (an axonal/myelin integrity marker). A 2-year immunoassay study showed significant reductions in CSF-calbindin during treatment, indicating reduced cerebellar Purkinje cell loss. Magnetic resonance imaging studies have demonstrated a protective effect of miglustat on cerebellar and subcortical structure that correlated with clinical symptom severity. Numerous cohort studies assessing core neurological manifestations (impaired ambulation, manipulation, speech, swallowing, other) using NP-C disability scales indicate neurological stabilization over 2-8 years, with a trend for greater benefits in patients with older (non-infantile) age at neurological onset. A randomized controlled trial and several cohort studies have reported improvements or stabilization of saccadic eye movements during 1-5 years of therapy. Swallowing was also shown to improve/remain stable during the randomized trial (up to 2 years), as well as in long-term observational cohorts (up to 6 years). A meta-analysis of dysphagia - a potent risk factor for aspiration pneumonia and premature death in NP-C - demonstrated a survival benefit with miglustat due to improved/stabilized swallowing function.

CONCLUSIONS

The effects of miglustat on neurological NP-C manifestations has been assessed using a range of approaches, with benefits ranging from cellular changes in the brain through to visible clinical improvements and improved survival.

Chronic pain in Gaucher disease: skeletal or neuropathic origin?

Backgound

Pain is one of the most disabling symptoms of Gaucher disease. It is referred by the majority of Gaucher patients and often persists despite long-term enzyme replacement treatment. It has been mainly considered as nociceptive pain secondary to skeletal involvement but it is described even in the absence of bone disease without a clear explanation. In the last years an increasing number of reports have described the presence of neurological manifestation in Gaucher type 1 patients, including subclinical large fibre neuropathy. In our Gaucher clinic we have observed the recurrence of painful symptoms in a group of type 1 Gaucher patients even after a long-term enzyme replacement therapy.

Methods

A cross-sectional study was designed to investigate the pathophysiology of pain in a cohort of 25 Gaucher patients (13 females, 12 males). Twenty-two patients received enzyme replacement therapy for a period of time ranging from 10 to >20 years, while three were new diagnosis. Pain was classified as bone or neurologic related on the basis of anamnestic data, clinical and electrophysilogical examinations. Intensity and quality of pain were recorded by Douleur Neuropathique en 4 questionnaire and Neuropathic Pain Symptom Inventory. Neuroalgological evaluation, quantitative sensory testing, nerve conduction studies and evaluation of epidermal nerve fibres density were performed. Comorbidities for peripheral neuropathy were excluded.

Results

Thirteen patients complained of pain suggestive of neuropathic origin with proximal patchy distribution, six manifested severe pain paroxysmal, nine pinprick hypoesthesia and 17 thermal hypoesthesia. At quantitative sensory testing, all of them showed high cold thresholds with errata sensation (burning instead of cold), paradoxical heat sensation and mechanic hypoesthesia; three patients showed pressure pain hyperalgesia. Epidermal denervation was present in 19 patients, 12 of them with non-length dependent pattern.

Conclusions

These results confirm the role of peripheral neuropathy in Gaucher pain and demonstrate that skin denervation is as a constitutive feature of the disorder. In addition, they further confirm the existence of a continuum Gaucher phenotype, and provide a new interpretation of pain origin that should be considered for an appropriate disease management and to avoid unnecessary dose escalations of enzyme therapy.

Sphingomyelin-induced inhibition of the plasma membrane calcium ATPase causes neurodegeneration in type A Niemann-Pick disease

Niemann-Pick disease type A (NPA) is a rare lysosomal storage disorder characterized by severe neurological alterations that leads to death in childhood. Loss-of-function mutations in the acid sphingomyelinase (ASM) gene cause NPA, and result in the accumulation of sphingomyelin (SM) in lysosomes and plasma membrane of neurons. Using ASM knockout (ASMko) mice as a NPA disease model, we investigated how high SM levels contribute to neural pathology in NPA. We found high levels of oxidative stress both in neurons from these mice and a NPA patient. Impaired activity of the plasma membrane calcium ATPase (PMCA) increases intracellular calcium. SM induces PMCA decreased activity, which causes oxidative stress. Incubating ASMko-cultured neurons in the histone deacetylase inhibitor, SAHA, restores PMCA activity and calcium homeostasis and, consequently, reduces the increased levels of oxidative stress. No recovery occurs when PMCA activity is pharmacologically impaired or genetically inhibited in vitro. Oral administration of SAHA prevents oxidative stress and neurodegeneration, and improves behavioral performance in ASMko mice. These results demonstrate a critical role for plasma membrane SM in neuronal calcium regulation. Thus, we identify changes in PMCA-triggered calcium homeostasis as an upstream mediator for NPA pathology. These findings can stimulate new approaches for pharmacological remediation in a disease with no current clinical treatments.

Expression of uPAR in Urinary Podocytes of Patients with Fabry Disease

Background. Despite enzyme replacement therapy, Fabry nephropathy still progresses. Podocyturia is an irreversible event that antedates proteinuria and leads to chronic renal failure. We evaluated a potential mechanism of podocyte detachment via the expression of the urokinase-type Plasminogen Activator Receptor (uPAR) in urinary podocytes of Fabry patients. Methods. This is a cross-sectional study that included controls (n = 20) and Fabry patients (n = 44) either untreated (n = 23) or treated with agalsidase-β (n = 21). Variables. Variables are estimated glomerular filtration rate (eGFR), urinary protein : creatinine ratio, and urinary uPAR+ podocyte : creatinine ratio. uPAR mRNA expression in response to lyso-Gb3, a bioactive glycolipid accumulated in Fabry disease, was studied in cultured human podocytes. Results. Controls and Fabry patients had similar age, gender, and renal function. Urinary uPAR+ podocytes were higher in patients than in controls. Untreated patients were significantly younger; had more females, and presented lower urinary protein : creatinine ratios and significantly higher urinary uPAR+ podocytes than treated subjects. In treated patients, urinary uPAR+ podocytes correlated with urinary protein : creatinine ratio (ρ = 0.5; p = 0.02). Lyso-Gb3 at concentrations found in the circulation of Fabry patients increased uPAR expression in cultured podocytes. Conclusions. Urinary podocytes expressing uPAR are increased in Fabry patients, especially in untreated patients. The potential contribution of uPAR expression to podocyte detachment merits further studies.

Lysosomal Re-acidification Prevents Lysosphingolipid-Induced Lysosomal Impairment and Cellular Toxicity

Neurodegenerative lysosomal storage disorders (LSDs) are severe and untreatable, and mechanisms underlying cellular dysfunction are poorly understood. We found that toxic lipids relevant to three different LSDs disrupt multiple lysosomal and other cellular functions. Unbiased drug discovery revealed several structurally distinct protective compounds, approved for other uses, that prevent lysosomal and cellular toxicities of these lipids. Toxic lipids and protective agents show unexpected convergence on control of lysosomal pH and re-acidification as a critical component of toxicity and protection. In twitcher mice (a model of Krabbe disease [KD]), a central nervous system (CNS)-penetrant protective agent rescued myelin and oligodendrocyte (OL) progenitors, improved motor behavior, and extended lifespan. Our studies reveal shared principles relevant to several LSDs, in which diverse cellular and biochemical disruptions appear to be secondary to disruption of lysosomal pH regulation by specific lipids. These studies also provide novel protective strategies that confer therapeutic benefits in a mouse model of a severe LSD.

The lysosomal storage disease continuum with ageing-related neurodegenerative disease

Lysosomal storage diseases and diseases of ageing share many features both at the physiological level and with respect to the mechanisms that underlie disease pathogenesis. Although the exact pathophysiology is not exactly the same, it is astounding how many similar pathways are altered in all of these diseases. The aim of this review is to provide a summary of the shared disease mechanisms, outlining the similarities and differences and how genetics, insight into rare diseases and functional research has changed our perspective on the causes underlying common diseases of ageing. The lysosome should no longer be considered as just the stomach of the cell or as a suicide bag, it has an emerging role in cellular signalling, nutrient sensing and recycling. The lysosome is of fundamental importance in the pathophysiology of diseases of ageing and by comparing against the LSDs we not only identify common pathways but also therapeutic targets so that ultimately more effective treatments can be developed for all neurodegenerative diseases.

A saposin deficiency model in Drosophila: Lysosomal storage, progressive neurodegeneration and sensory physiological decline

Saposin deficiency is a childhood neurodegenerative lysosomal storage disorder (LSD) that can cause premature death within three months of life. Saposins are activator proteins that promote the function of lysosomal hydrolases that mediate the degradation of sphingolipids. There are four saposin proteins in humans, which are encoded by the prosaposin gene. Mutations causing an absence or impaired function of individual saposins or the whole prosaposin gene lead to distinct LSDs due to the storage of different classes of sphingolipids. The pathological events leading to neuronal dysfunction induced by lysosomal storage of sphingolipids are as yet poorly defined. We have generated and characterised a Drosophila model of saposin deficiency that shows striking similarities to the human diseases. Drosophila saposin-related (dSap-r) mutants show a reduced longevity, progressive neurodegeneration, lysosomal storage, dramatic swelling of neuronal soma, perturbations in sphingolipid catabolism, and sensory physiological deterioration. Our data suggests a genetic interaction with a calcium exchanger (Calx) pointing to a possible calcium homeostasis deficit in dSap-r mutants. Together these findings support the use of dSap-r mutants in advancing our understanding of the cellular pathology implicated in saposin deficiency and related LSDs.

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Drosophila model of PSD recapitulates neurodegenerative phenotype of human PSD.

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Preferential degeneration of sensory regions correlates with loss of sensory function.

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Sphingosine levels rise with age with an imbalance in sphingosine/ceramide ratios.

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Genetic interaction with the Na +/Ca + exchanger points to a calcium regulation deficit.

Increased urinary CD80 excretion and podocyturia in Fabry disease

BACKGROUND

Certain glomerulopathies are associated with increased levels of CD80 (B7-1). We measured the urinary excretion of CD80, podocyturia and proteinuria in controls and in subjects with Fabry disease either untreated or on enzyme replacement therapy (ERT).

METHODS

Cross-sectional study including 65 individuals: controls (n = 20) and Fabry patients (n = 45, 23 of them not on ERT and 22 on ERT). Variables included age, gender, urinary protein/creatinine ratio (UPCR), estimated glomerular filtration rate (eGFR), urinary uCD80/creatinine ratio (uCD80) and podocyturia. CD80 mRNA expression in response to lyso-Gb3, a bioactive glycolipid accumulated in Fabry disease, was studied in cultured human podocytes.

RESULTS

Controls and Fabry patients did not differ in age, eGFR and gender. However, UPCR, uCD80 and podocyturia were significantly higher in Fabry patients than in controls. As expected, Fabry patients not on ERT were younger and a higher percentage were females. Non-ERT Fabry patients had less advanced kidney disease than ERT Fabry patients: UPCR was lower and eGFR higher, but uCD80 and podocyturia did not differ between non-ERT or ERT Fabry patients. There was a significant correlation between uCD80 and UPCR in the whole population (r 0.44, p 0.0005) and in Fabry patients (r 0.42, p 0.0046). Lyso-Gb3 at concentrations found in the circulation of Fabry patients increased uCD80 expression in cultured podocytes.

CONCLUSIONS

Fabry disease is characterized by early occurrence of increased uCD80 excretion that appears to be a consequence of glycolipid accumulation. The potential for uCD80 excretion to reflect early, subclinical renal Fabry involvement should be further studied.

Progression of Behavioral and CNS Deficits in a Viable Murine Model of Chronic Neuronopathic Gaucher Disease

To study the neuronal deficits in neuronopathic Gaucher Disease (nGD), the chronological behavioral profiles and the age of onset of brain abnormalities were characterized in a chronic nGD mouse model (9V/null). Progressive accumulation of glucosylceramide (GC) and glucosylsphingosine (GS) in the brain of 9V/null mice were observed at as early as 6 and 3 months of age for GC and GS, respectively. Abnormal accumulation of α-synuclein was present in the 9V/null brain as detected by immunofluorescence and Western blot analysis. In a repeated open-field test, the 9V/null mice (9 months and older) displayed significantly less environmental habituation and spent more time exploring the open-field than age-matched WT group, indicating the onset of short-term spatial memory deficits. In the marble burying test, the 9V/null group had a shorter latency to initiate burying activity at 3 months of age, whereas the latency increased significantly at ≥12 months of age; 9V/null females buried significantly more marbles to completion than the WT group, suggesting an abnormal response to the instinctive behavior and an abnormal activity in non-associative anxiety-like behavior. In the conditional fear test, only the 9V/null males exhibited a significant decrease in response to contextual fear, but both genders showed less response to auditory-cued fear compared to age- and gender-matched WT at 12 months of age. These results indicate hippocampus-related emotional memory defects. Abnormal gait emerged in 9V/null mice with wider front-paw and hind-paw widths, as well as longer stride in a gender-dependent manner with different ages of onset. Significantly higher liver- and spleen-to-body weight ratios were detected in 9V/null mice with different ages of onsets. These data provide temporal evaluation of neurobehavioral dysfunctions and brain pathology in 9V/null mice that can be used for experimental designs to evaluate novel therapies for nGD.

Acidic Ca2+ stores in neurodegeneration

Lysosomes have emerged in the last decade as an immensely important intracellular site of Ca²⁺ storage and signalling. More recently there has been an increase in the number of new ion channels found to be functional on lysosomes and the potential roles that these signalling pathways might play in fundamental cellular processes are being uncovered. Defects in lysosomal function have been shown to result in changes in lysosomal Ca²⁺ homeostasis and ultimately can result in cell death. Several neurodegenerative diseases, from rare lysosomal storage diseases through to more common diseases of ageing, have recently been identified as having alterations in lysosomal Ca²⁺ homeostasis that may play an important role in neuronal excitotoxicity and ultimately cell death. This review will critically summarise these recent findings.

Connecting Ca2+ and lysosomes to Parkinson disease

The neurodegenerative movement disorder Parkinson disease (PD) is prevalent in the aged population. However, the underlying mechanisms that trigger disease are unclear. Increasing work implicates both impaired Ca²⁺ signalling and lysosomal dysfunction in neuronal demise. Here I aim to connect these distinct processes by exploring the evidence that lysosomal Ca²⁺ signalling is disrupted in PD. In particular, I highlight defects in lysosomal Ca²⁺ content and signalling through NAADP-regulated two-pore channels in patient fibroblasts harbouring mutations in the PD-linked genes, GBA1 and LRRK2. As an emerging contributor to PD pathogenesis, the lysosomal Ca²⁺ signalling apparatus could represent a novel therapeutic target.

A new glucocerebrosidase-deficient neuronal cell model provides a tool to probe pathophysiology and therapeutics for Gaucher disease

Glucocerebrosidase is a lysosomal hydrolase involved in the breakdown of glucosylceramide. Gaucher disease, a recessive lysosomal storage disorder, is caused by mutations in the gene GBA1. Dysfunctional glucocerebrosidase leads to accumulation of glucosylceramide and glycosylsphingosine in various cell types and organs. Mutations in GBA1 are also a common genetic risk factor for Parkinson disease and related synucleinopathies. In recent years, research on the pathophysiology of Gaucher disease, the molecular link between Gaucher and Parkinson disease, and novel therapeutics, have accelerated the need for relevant cell models with GBA1 mutations. Although induced pluripotent stem cells, primary rodent neurons, and transfected neuroblastoma cell lines have been used to study the effect of glucocerebrosidase deficiency on neuronal function, these models have limitations because of challenges in culturing and propagating the cells, low yield, and the introduction of exogenous mutant GBA1. To address some of these difficulties, we established a high yield, easy-to-culture mouse neuronal cell model with nearly complete glucocerebrosidase deficiency representative of Gaucher disease. We successfully immortalized cortical neurons from embryonic null allele gba^−/− mice and the control littermate (gba^+/+) by infecting differentiated primary cortical neurons in culture with an EF1α-SV40T lentivirus. Immortalized gba^−/− neurons lack glucocerebrosidase protein and enzyme activity, and exhibit a dramatic increase in glucosylceramide and glucosylsphingosine accumulation, enlarged lysosomes, and an impaired ATP-dependent calcium-influx response; these phenotypical characteristics were absent in gba^+/+ neurons. This null allele gba^−/− mouse neuronal model provides a much-needed tool to study the pathophysiology of Gaucher disease and to evaluate new therapies.

Summary: This work describes the generation of a novel immortalized glucocerebrosidase-deficient neuronal cell model with utility for pathophysiology research and therapeutic development in Gaucher disease.

Psychosine-triggered endomitosis is modulated by membrane sphingolipids through regulation of phosphoinositide 4,5-bisphosphate production at the cleavage furrow

Endomitosis is a special type of mitosis in which only cytokinesis-the final step of the cell division cycle-is defective, resulting in polyploid cells. Although endomitosis is biologically important, its regulatory aspects remain elusive. Psychosine, a lysogalactosylceramide, prevents proper cytokinesis when supplemented to proliferating cells. Cytokinetic inhibition by psychosine does not inhibit genome duplication. Consequently cells undergo multiple rounds of endomitotic cell cycles, resulting in the formation of giant multiploid cells. Here we successfully quantified psychosine-triggered multiploid cell formation, showing that membrane sphingolipids ratios modulate psychosine-triggered polyploidy in Namalwa cells. Among enzymes that experimentally remodel cellular sphingolipids, overexpression of glucosylceramide synthase to biosynthesize glycosylsphingolipids (GSLs) and neutral sphingomyelinase 2 to hydrolyze sphingomyelin (SM) additively enhanced psychosine-triggered multiploidy; almost all of the cells became polyploid. In the presence of psychosine, Namalwa cells showed attenuated cell surface SM clustering and suppression of phosphatidylinositol 4,5-bisphosphate production at the cleavage furrow, both important processes for cytokinesis. Depending on the sphingolipid balance between GSLs and SM, Namalwa cells could be effectively converted to viable multiploid cells with psychosine.

Parkinson's disease: acid-glucocerebrosidase activity and alpha-synuclein clearance

The role of mutations in the gene GBA1 encoding the lysosomal hydrolase β-glucocerebrosidase for the development of synucleinopathies, such as Parkinson's disease and dementia with Lewy bodies, was only very recently uncovered. The knowledge obtained from the study of carriers or patients suffering from Gaucher disease (a common lysosomal storage disorder because of GBA1 mutations) is of particular importance for understanding the role of the enzyme and its catabolic pathway in the development of synucleinopathies. Decreased activity of β-glucocerebrosidase leads to lysosomal dysfunction and the accumulation of its substrate glucosylceramide and related lipid derivatives. Glucosylceramide is suggested to stabilize toxic oligomeric forms of α-synuclein that negatively influence the activity of β-glucocerebrosidase and to partially block export of newly synthesized β-glucocerebrosidase from the endoplasmic reticulum to late endocytic compartments, amplifying the pathological effects of α-synuclein and ultimately resulting in neuronal cell death. This pathogenic molecular feedback loop and most likely other factors (such as impaired endoplasmic reticulum-associated degradation, activation of the unfolded protein response and dysregulation of calcium homeostasis induced by misfolded GC mutants) are involved in shifting the cellular homeostasis from monomeric α-synuclein towards oligomeric neurotoxic and aggregated forms, which contribute to Parkinson's disease progression. From a therapeutic point of view, strategies aiming to increase either the expression, stability or delivery of the β-glucocerebrosidase to lysosomes are likely to decrease the α-synuclein burden and may be useful for an in depth evaluation at the organismal level. Lysosomes are critical for protein and lipid homeostasis. Recent research revealed that dysfunction of this organelle contributes to the development of neurodegenerative diseases such as Parkinson's disease (PD). Mutations in the lysosomal hydrolase β-glucocerebrosidase (GBA1) are a major risk factor for the development of PD and the molecular events linked to the reduced activity of GBA1 and the pathological accumulation of lipids and α-synuclein are just at the beginning to be understood. New therapeutic concepts in regards to how to increase the expression, stability, or delivery of β-glucocerebrosidase to lysosomes are currently developed. This article is part of a special issue on Parkinson disease.

Glucosylceramide Reorganizes Cholesterol-Containing Domains in a Fluid Phospholipid Membrane

Glucosylceramide (GlcCer), one of the simplest glycosphingolipids, plays key roles in physiology and pathophysiology. It has been suggested that GlcCer modulates cellular events by forming specialized domains. In this study, we investigated the interplay between GlcCer and cholesterol (Chol), an important lipid involved in the formation of liquid-ordered (lo) phases. Using fluorescence microscopy and spectroscopy, and dynamic and electrophoretic light scattering, we characterized the interaction between these lipids in different pH environments. A quantitative description of the phase behavior of the ternary unsaturated phospholipid/Chol/GlcCer mixture is presented. The results demonstrate coexistence between lo and liquid-disordered (ld) phases. However, the extent of lo/ld phase separation is sparse, mainly due to the ability of GlcCer to segregate into tightly packed gel domains. As a result, the phase diagram of these mixtures is characterized by an extensive three-phase coexistence region of fluid (ld-phospholipid enriched)/lo (Chol enriched)/gel (GlcCer enriched). Moreover, the results show that upon acidification, GlcCer solubility in the lo phase is increased, leading to a larger lo/ld coexistence region. Quantitative analyses allowed us to determine the differences in the composition of the phases at neutral and acidic pH. These results predict the impact of GlcCer on domain formation and membrane organization in complex biological membranes, and provide a background for unraveling the relationship between the biophysical properties of GlcCer and its biological action.

Glycosphingolipids and cell death: one aim, many ways

Glycosphingolipids (GSLs) are a family of bioactive lipids that in addition to their role in the regulation of structural properties of membrane bilayers have emerged as crucial players in many biological processes and signal transduction pathways. Rather than being uniformly distributed within membrane bilayers, GSLs are localized in selective domains called lipid rafts where many signaling platforms operate. One of the most important functions of GSLs, particularly ceramide, is their ability to regulate cell death pathways and hence cell fate. This complex role is accomplished by the ability of GSLs to act in distinct subcellular strategic centers, such as mitochondria, endoplasmic reticulum (ER) or lysosomes to mediate apoptosis, ER stress, autophagy, lysosomal membrane permeabilization and necroptosis. Hence better understanding the role of GSLs in cell death may be of relevance for a number of pathological processes and diseases, including neurodegeneration, metabolic liver diseases and cancer.

Gaucher Disease: Clinical, Biological and Therapeutic Aspects

We present a brief review of Gaucher disease (GD), the most common lysosomal storage disease. GD is a rare autosomal recessive disorder characterized by the defective function of the catabolic enzyme β-glucocerebrosidase (GBA), leading to an accumulation of its substrate, glucocerebroside. Clinical signs and symptoms include neurological dysfunctions, bone infarcts and malformations, hepatosplenomegaly and hypersplenism leading to anemia, neutropenia and thrombocytopenia. Enzyme replacement therapy with recombinant GBA is the mainstay of treatment for GD, which became the first successfully managed lipid storage disease. Future treatments may include oral enzyme replacement and/or gene therapy interventions.

Mitochondrial dysfunction associated with glucocerebrosidase deficiency

The lysosomal hydrolase glucocerebrosidase (GCase) is encoded for by the GBA gene. Homozygous GBA mutations cause Gaucher disease (GD), a lysosomal storage disorder. Furthermore, homozygous and heterozygous GBA mutations are numerically the greatest genetic risk factor for developing Parkinson's disease (PD), the second most common neurodegenerative disorder. The loss of GCase activity results in impairment of the autophagy‐lysosome pathway (ALP), which is required for the degradation of macromolecules and damaged organelles. Aberrant protein handling of α-synuclein by the ALP occurs in both GD and PD. α-synuclein is the principle component of Lewy bodies, a defining hallmark of PD. Mitochondrial dysfunction is also observed in both GD and PD. In this review we will describe how mitochondria are affected following loss of GCase activity. The pathogenic mechanisms leading to mitochondria dysfunction will also be discussed, focusing on the likely inhibition of the degradation of mitochondria by the ALP, also termed mitophagy. Other pathogenic cellular processes associated with GBA mutations that might contribute, such as the unfolding of GCase in the endoplasmic reticulum, calcium dysregulation and neuroinflammation will also be described. Impairment of the ALP and mitochondria dysfunction are common pathogenic themes between GD and PD and probably explain why GBA mutations increase the risk of developing PD that is very similar to sporadic forms of the disease.

ERdj3 is an endoplasmic reticulum degradation factor for mutant glucocerebrosidase variants linked to Gaucher's disease

Gaucher's disease (GD) is caused by mutations that compromise β-glucocerebrosidase (GCase) folding in the endoplasmic reticulum (ER), leading to excessive degradation instead of trafficking, which results in insufficient lysosomal function. We hypothesized that ER GCase interacting proteins play critical roles in making quality control decisions, i.e., facilitating ER-associated degradation (ERAD) instead of folding and trafficking. Utilizing GCase immunoprecipitation followed by mass-spectrometry-based proteomics, we identified endogenous HeLa cell GCase protein interactors, including ERdj3, an ER resident Hsp40 not previously established to interact with GCase. Depleting ERdj3 reduced the rate of mutant GCase degradation in patient-derived fibroblasts, while increasing folding, trafficking, and function by directing GCase to the profolding ER calnexin pathway. Inhibiting ERdj3-mediated mutant GCase degradation while simultaneously enhancing calnexin-associated folding, by way of a diltiazem-mediated increase in ER Ca(2+) levels, yields a synergistic rescue of L444P GCase lysosomal function. Our findings suggest a combination therapeutic strategy for ameliorating GD.

Unbiased Cell-based Screening in a Neuronal Cell Model of Batten Disease Highlights an Interaction between Ca2+ Homeostasis, Autophagy, and CLN3 Protein Function

Abnormal accumulation of undigested macromolecules, often disease-specific, is a major feature of lysosomal and neurodegenerative disease and is frequently attributed to defective autophagy. The mechanistic underpinnings of the autophagy defects are the subject of intense research, which is aided by genetic disease models. To gain an improved understanding of the pathways regulating defective autophagy specifically in juvenile neuronal ceroid lipofuscinosis (JNCL or Batten disease), a neurodegenerative disease of childhood, we developed and piloted a GFP-microtubule-associated protein 1 light chain 3 (GFP-LC3) screening assay to identify, in an unbiased fashion, genotype-sensitive small molecule autophagy modifiers, employing a JNCL neuronal cell model bearing the most common disease mutation in CLN3. Thapsigargin, a sarco/endoplasmic reticulum Ca(2+)-ATPase (SERCA) Ca(2+) pump inhibitor, reproducibly displayed significantly more activity in the mouse JNCL cells, an effect that was also observed in human-induced pluripotent stem cell-derived JNCL neural progenitor cells. The mechanism of thapsigargin sensitivity was Ca(2+)-mediated, and autophagosome accumulation in JNCL cells could be reversed by Ca(2+) chelation. Interrogation of intracellular Ca(2+) handling highlighted alterations in endoplasmic reticulum, mitochondrial, and lysosomal Ca(2+) pools and in store-operated Ca(2+) uptake in JNCL cells. These results further support an important role for the CLN3 protein in intracellular Ca(2+) handling and in autophagic pathway flux and establish a powerful new platform for therapeutic screening.

Monogenic neurological disorders of sphingolipid metabolism

Sphingolipids comprise a wide variety of molecules containing a sphingoid long-chain base that can be N-acylated. These lipids are particularly abundant in the central nervous system, being membrane components of neurons as well as non-neuronal cells. Direct evidence that these brain lipids play critical functions in brain physiology is illustrated by the dramatic consequences of genetic disturbances of their metabolism. Inherited defects of both synthesis and catabolism of sphingolipids are now identified in humans. These monogenic disorders are due to mutations in the genes encoding for the enzymes that catalyze either the formation or degradation of simple sphingolipids such as ceramides, or complex sphingolipids like glycolipids. They cause varying degrees of central nervous system dysfunction, quite similarly to the neurological disorders induced in mice by gene disruption of the corresponding enzymes. Herein, the enzyme deficiencies and metabolic alterations that underlie these diseases are reviewed. Their possible pathophysiological mechanisms and the functions played by sphingolipids one can deduce from these conditions are discussed. This article is part of a Special Issue entitled Brain Lipids.

Role of extracellular calcium and mitochondrial oxygen species in psychosine-induced oligodendrocyte cell death

Globoid cell leukodystrophy (GLD) is a metabolic disease caused by mutations in the galactocerebrosidase (GALC) gene. GALC is a lysosomal enzyme whose function is to degrade galacto-lipids, including galactosyl-ceramide and galactosyl-sphingosine (psychosine, PSY). GALC loss of function causes progressive intracellular accumulation of PSY. It is widely held that PSY is the main trigger for the degeneration of myelinating cells and progressive white-matter loss. However, still little is known about the molecular mechanisms by which PSY imparts toxicity. Here, we address the role of calcium dynamics during PSY-induced cell death. Using the human oligodendrocyte cell line MO3.13, we report that cell death by PSY is accompanied by robust cytosolic and mitochondrial calcium (Ca(2+)) elevations, and by mitochondrial reactive oxygen species (ROS) production. Importantly, we demonstrate that the reduction of extracellular calcium content by the chelating agent ethylenediaminetetraacetic acid can decrease intra-mitochondrial ROS production and enhance cell viability. Antioxidant administration also reduces mitochondrial ROS production and cell loss, but this treatment does not synergize with Ca(2+) chelation. Our results disclose novel intracellular pathways involved in PSY-induced death that may be exploited for therapeutic purposes to delay GLD onset and/or slow down its progression.