Gangliosides as apoptotic signals in ER stress response

Gene therapy approaches for GM1 gangliosidosis: Focus on animal and cellular studies

One of the most important inherited metabolic disorders is GM1 gangliosidosis, which is a progressive neurological disorder. The main cause of this disease is a genetic defect in the enzyme β-galactosidase due to a mutation in the glb1 gene. Lack of this enzyme in cells (especially neurons) leads to the accumulation of ganglioside substrate in nerve tissues, followed by three clinical forms of GM1 disease (neonatal, juvenile, and adult variants). Genetically, many mutations occur in the exons of the glb1 gene, such as exons 2, 6, 15, and 16, so the most common ones reported in scientific studies include missense/nonsense mutations. Therefore, many studies have examined the genotype-phenotype relationships of this disease and subsequently using gene therapy techniques have been able to reduce the complications of the disease and alleviate the signs and symptoms of the disease. In this regard, the present article reviews the general features of GM1 gangliosidosis and its mutations, as well as gene therapy studies and animal and human models of the disease.

Longitudinal spatial mapping of lipid metabolites reveals pre-symptomatic changes in the hippocampi of Huntington's disease transgenic mice

In Huntington's disease (HD), a key pathological feature includes the development of inclusion-bodies of fragments of the mutant huntingtin protein in the neurons of the striatum and hippocampus. To examine the molecular changes associated with inclusion-body formation, we applied MALDI-mass spectrometry imaging and deuterium pulse labelling to determine lipid levels and synthesis rates in the hippocampus of a transgenic mouse model of HD (R6/1 line). The R6/1 HD mice lacked inclusions in the hippocampus at 6 weeks of age (pre-symptomatic), whereas inclusions were pervasive by 16 weeks of age (symptomatic). Hippocampal subfields (CA1, CA3 and DG), which formed the highest density of inclusion formation in the mouse brain showed a reduction in the relative abundance of neuron-enriched lipids that have roles in neurotransmission, synaptic plasticity, neurogenesis, and ER-stress protection. Lipids involved in the adaptive response to ER stress (phosphatidylinositol, phosphatidic acid, and ganglioside classes) displayed increased rates of synthesis in HD mice relative to WT mice at all the ages examined, including prior to the formation of the inclusion bodies. Our findings, therefore, support a role for ER stress occurring pre-symptomatically and potentially contributing to pathological mechanisms underlying HD.

Aberrant autophagy in lysosomal storage disorders marked by a lysosomal SNARE protein shortage due to suppression of endocytosis

Lysosomal storage disorders (LSDs) are inherited metabolic diseases caused by genetic defects in lysosomal enzymes or related factors. LSDs are associated with excessive accumulation of natural substrates in lysosomes leading to central nervous system and peripheral tissue damage. Abnormal autophagy is also involved in pathogenesis, although the underlying mechanisms remain unclear. We demonstrated that impairment of lysosome-autophagosome fusion is due to suppressed endocytosis in LSDs. The fusion was reduced in several LSD cells and the brains of LSD model mice, suggesting that the completion of autophagy is suppressed by the accumulation of substrates. In this brain, the expression of the soluble N-ethylmaleimide sensitive factor attachment protein receptor (SNARE) proteins, VAMP8 and Syntaxin7, was decreased on the lysosomal surface but not intracellular. This aberrant autophagy preceded the development of pathological phenotypes in LSD-model mice. Furthermore, the enzyme deficiency leading to the substrate accumulation could suppress endocytosis, and the inhibited endocytosis decreased SNARE proteins localized on lysosomes. These findings suggest that the shortage of SNARE proteins on lysosomes is one of the reasons for the impairment of lysosome-autophagosome fusion in LSD cells. Defects in lysosomal enzyme activity suppress endocytosis and decrease the supply of intracellular SNARE proteins recruited to lysosomes. This shortage of lysosomal SNARE proteins impairs lysosome-autophagosome fusion in lysosomal storage disorders.

Pathogenic Roles of Heparan Sulfate and Its Use as a Biomarker in Mucopolysaccharidoses

Heparan sulfate (HS) is an essential glycosaminoglycan (GAG) as a component of proteoglycans, which are present on the cell surface and in the extracellular matrix. HS-containing proteoglycans not only function as structural constituents of the basal lamina but also play versatile roles in various physiological processes, including cell signaling and organ development. Thus, inherited mutations of genes associated with the biosynthesis or degradation of HS can cause various diseases, particularly those involving the bones and central nervous system (CNS). Mucopolysaccharidoses (MPSs) are a group of lysosomal storage disorders involving GAG accumulation throughout the body caused by a deficiency of GAG-degrading enzymes. GAGs are stored differently in different types of MPSs. Particularly, HS deposition is observed in patients with MPS types I, II, III, and VII, all which involve progressive neuropathy with multiple CNS system symptoms. While therapies are available for certain symptoms in some types of MPSs, significant unmet medical needs remain, such as neurocognitive impairment. This review presents recent knowledge on the pathophysiological roles of HS focusing on the pathogenesis of MPSs. We also discuss the possible use and significance of HS as a biomarker for disease severity and therapeutic response in MPSs.

Harnessing Antibody Polyspecificity for Cancer Immunotherapy

Targeting the diverse glycan repertoire expressed on tumor cells is considered a viable therapeutic strategy to deal with tumor cell heterogeneity. Inherently polyspecific, natural, glycan-reactive antibodies are purported to be protective in thwarting infections and in cancer immunotherapy. Tumor-associated carbohydrate antigens (TACAs) are related to pathogen glycans, to which nascent or natural antibodies exist and IgM responses are elicited. To capture the polyspecific nature of anticarbohydrate responses, we have focused on the rational design of carbohydrate mimetic peptides (CMPs) cross-reactive with TACA reactive antibodies. In particular, we have focused on the development of CMPs that display reactivity to GD2 and Lewis Y (LeY) reactive monoclonal antibodies. They would serve as templates for pan-immunogens inducing biosimilar polyreactive antibodies. In the design, we relied on structural analyses of CMP's enhanced binding to the templates using molecular modeling. Glycan reactivity patterns of affinity CMP-purified human antibodies further refined specificity profiles in comparison with the immune response to the CMP in clinical trials. In this study, we further define the molecular characteristics for this mimicry by considering the polyspecificity of LeY and GD2 reactive antibodies binding to the lacto-ceramide core Galβ(1,4)Glcβ(1-1')Cer. Binding to this minimum building block can be capitalized on for cancer therapy and diagnostics and illustrates a new approach in designing cancer vaccines taking advantage of the latent polyspecificity of antibodies and the relevance of natural antibodies in antigen discovery and design.

Vitamin B12 enhances the antitumor activity of 1,25-dihydroxyvitamin D3 via activation of caspases and targeting actin cytoskeleton

BACKGROUND

1,25-dihydroxyvitamin D3 (1,25(OH)2D3) is an effective anticancer agent, and when combined with other agents it shows superior activities. Vitamin B12 has been shown to contribute to increasing the effectiveness of anticancer drugs when used in combination. Thus, the current study aimed at investigating the anticancer potential of the combination of 1,25(OH)2D3 and vitamin B12.

METHODS

MTT assay was used to determine the cytotoxic activity of combining 1,25(OH)2D3 and vitamin B12 against six different cancer cell lines and one normal cell line. The surviving fraction after clonogenic assay was measured, and the effects of 1,25(OH)2D3/B12 combination on the activity of different caspases, cell adhesion, actin cytoskeleton, cell morphology, and percentage of polarized cells were evaluated.

RESULTS

Vitamin B12 did not cause cytotoxicity, however, it enhanced the cytotoxicity of 1,25(OH)2D3 against cancer cells. The cytotoxic effects of 1,25(OH)2D3 and its combination with vitamin B12 was not evident in the normal mammary MCF10A cell line indicating cancer cell-specificity. The cytotoxic effects of 1,25(OH)2D3/B12 combination occurred in a dose-dependent manner and was attributed to apoptosis induction which was mediated by caspase 4 and 8. Moreover, 1,25(OH)2D3/B12-treated cells showed enhanced inhibition of clonogenic tumor growth, reduced cell adhesion, reduced cell area, reduced percentage of cell polarization, and disorganized actin cytoskeleton resulting in reduced migratory phenotype when compared to cells treated with 1,25(OH)2D3 alone.

CONCLUSION

1,25(OH)2D3 and vitamin B12 exhibited synergistic anticancer effects against different cancer cell lines. The combination therapy of 1,25(OH)2D3 and vitamin B12 may provide a potential adjunctive treatment option for some cancer types.

A novel derivative of picolinic acid induces endoplasmic reticulum stress-mediated apoptosis in human non-small cell lung cancer cells: synthesis, docking study, and anticancer activity

Thirteen new derivatives of picolinic acid (4–7) were designed and synthesized from the starting parent molecule, picolinic acid. The new compounds were characterized by ATR-FTIR, 1HNMR, and CHNS analysis. A molecular docking study was performed to evaluate the binding affinity of the synthesized compounds toward EGFR kinase domain that indicated occupation of the critical site of EGFR kinase pocket and excellent positioning of the compounds in the pocket. The cytotoxic activity of the compounds against two human cancer cell lines (A549 and MCF-7), the non-tumorigenic MCF10A cell line, and white blood cells (WBC) was evaluated using the MTT assay. Compound 5 showed anticancer activity against A549 lung cancer cells (IC50 = 99.93 µM) but not against MCF-7 breast cancer cells or normal cells. Compound 5 mediated cytotoxicity in A549 lung cancer cells by inducing apoptotic cell death, as suggested by fragmented nuclei after DAPI staining, and agarose gel electrophoresis. Moreover, compound 5 triggered the activation of caspases 3, 4 and 9. However, compound 5 treatment did not affect the release of cytochrome c from the mitochondria to the cytosol, as compared to the vehicle-treated control cells. Nevertheless, compound 5-treated cells reported greater release of smac/DIABLO to the cytosol. In the same context, both compound 5 and thapsigargin (specific inhibitor of sarco/endoplasmic reticulum Ca2+-ATPase (SERCA)) enhanced eIF2 phosphorylation, reflecting the activation of the atypical ER stress pathway and the potential applicability of compound 5 in lung cancer treatment.

Ganglioside GD3 is up-regulated in microglia and regulates phagocytosis following global cerebral ischemia

Gangliosides, the major sialic-acid containing glycosphingolipids in the mammalian brain, play important roles in brain development and neural functions. Here, we show that the b-series ganglioside GD3 and its biosynthetic enzyme, GD3-synthase (GD3S), were up-regulated predominantly in the microglia of mouse hippocampus from 2 to 7 days following global cerebral ischemia (GCI). Interestingly, GD3S knockout (GD3S-KO) mice exhibited decreased hippocampal neuronal loss following GCI, as compared to wild-type (WT) mice. While comparable levels of astrogliosis and microglial proliferation were observed between WT and GD3S-KO mice, the phagocytic capacity of the GD3S-KO microglia was significantly compromised after GCI. At 2 and 4 days following GCI, the GD3S-KO microglia demonstrated decreased amoebic morphology, reduced neuronal material engulfment, and lower expression of the phagolysosome marker CD68, as compared to the WT microglia. Finally, by using a microglia-primary neuron co-culture model, we demonstrated that the GD3S-KO microglia isolated from mouse brains at 2 days after GCI are less neurotoxic to co-cultured hippocampal neurons than the WT-GCI microglia. Moreover, the percentage of microglia with engulfed neuronal elements in the co-cultured wells was also significantly decreased in the GD3S-KO mice after GCI. Interestingly, the impaired phagocytic capacity of GD3S-KO microglia could be partially restored by pre-treatment with exogenous ganglioside GD3. Altogether, this study provides functional evidence that ganglioside GD3 regulates phagocytosis by microglia in an ischemic stroke model. Our data also suggest that the GD3-linked microglial phagocytosis may contribute to the mechanism of delayed neuronal death following ischemic brain injury.

Pathogenic Genome Signatures That Damage Motor Neurons in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is the most frequent motor neuron disease and a neurodegenerative disorder, affecting the upper and/or lower motor neurons. Notably, it invariably leads to death within a few years of onset. Although most ALS cases are sporadic, familial amyotrophic lateral sclerosis (fALS) forms 10% of the cases. In 1993, the first causative gene (SOD1) of fALS was identified. With rapid advances in genetics, over fifty potentially causative or disease-modifying genes have been found in ALS so far. Accordingly, routine diagnostic tests should encompass the oldest and most frequently mutated ALS genes as well as several new important genetic variants in ALS. Herein, we discuss current literatures on the four newly identified ALS-associated genes (CYLD, S1R, GLT8D1, and KIF5A) and the previously well-known ALS genes including SOD1, TARDBP, FUS, and C9orf72. Moreover, we review the pathogenic implications and disease mechanisms of these genes. Elucidation of the cellular and molecular functions of the mutated genes will bring substantial insights for the development of therapeutic approaches to treat ALS.

Tumor hypoxia regulates ganglioside GM3 synthase, which contributes to oxidative stress resistance in malignant melanoma

BACKGROUND

Tumor hypoxia drastically changes cancer phenotypes, including angiogenesis, invasion, and cell death. Gangliosides are sialic acid-containing glycosphingolipids that are ubiquitously distributed on plasma membranes and are involved in many biological processes, such as the endoplasmic reticulum stress response and apoptosis. In this study, we investigated the regulation and function of glycosphingolipids, which associate with lipid raft on mammalian plasma membranes under hypoxic condition.

METHODS

B16F10 melanoma cells were subjected to chemical hypoxia and low pO2 condition, and the effect of hypoxia on expression of GM3 synthase were analyzed. Cellular resistance to oxidative stress was analyzed in GM3S-KO B16F10 cells.

RESULTS

Hypoxia treatment decreased the expression of ganglioside GM3 synthase (GM3S; ST3GAL5), which synthesizes the common substrate of ganglioside biosynthesis. RNA interference of hypoxia inducible factor 1 subunit alpha (HIF-1α) inhibited hypoxia-induced GM3S suppression. Additionally, GM3S deficiency increased cellular resistance to oxidative stress and radiation therapy via upregulation of ERK.

CONCLUSIONS

Altered synthesis of glycosphingolipids downstream of HIF-1α signaling increased the resistance of melanoma cells to oxidative stress. Furthermore, GM3 has important role on cellular adaptive response to hypoxia.

GENERAL SIGNIFICANCE

This study indicates that tumor hypoxia regulates therapy-resistance via modulation of ganglioside synthesis.

Metabolism of Glycosphingolipids and Their Role in the Pathophysiology of Lysosomal Storage Disorders

Glycosphingolipids (GSLs) are a specialized class of membrane lipids composed of a ceramide backbone and a carbohydrate-rich head group. GSLs populate lipid rafts of the cell membrane of eukaryotic cells, and serve important cellular functions including control of cell-cell signaling, signal transduction and cell recognition. Of the hundreds of unique GSL structures, anionic gangliosides are the most heavily implicated in the pathogenesis of lysosomal storage diseases (LSDs) such as Tay-Sachs and Sandhoff disease. Each LSD is characterized by the accumulation of GSLs in the lysosomes of neurons, which negatively interact with other intracellular molecules to culminate in cell death. In this review, we summarize the biosynthesis and degradation pathways of GSLs, discuss how aberrant GSL metabolism contributes to key features of LSD pathophysiology, draw parallels between LSDs and neurodegenerative proteinopathies such as Alzheimer's and Parkinson's disease and lastly, discuss possible therapies for patients.

The role of sphingolipids in endoplasmic reticulum stress

The endoplasmic reticulum (ER) is an important intracellular compartment in eukaryotic cells and has diverse functions, including protein synthesis, protein folding, lipid metabolism and calcium homeostasis. ER functions are disrupted by various intracellular and extracellular stimuli that cause ER stress, including the inhibition of glycosylation, disulphide bond reduction, ER calcium store depletion, impaired protein transport to the Golgi, excessive ER protein synthesis, impairment of ER-associated protein degradation and mutated ER protein expression. Distinct ER stress signalling pathways, which are known as the unfolded protein response, are deployed to maintain ER homeostasis, and a failure to reverse ER stress triggers cell death. Sphingolipids are lipids that are structurally characterized by long-chain bases, including sphingosine or dihydrosphingosine (also known as sphinganine). Sphingolipids are bioactive molecules long known to regulate various cellular processes, including cell proliferation, migration, apoptosis and cell-cell interaction. Recent studies have uncovered that specific sphingolipids are involved in ER stress. This review summarizes the roles of sphingolipids in ER stress and human diseases in the context of pathogenic events.

Axonopathy and Reduction of Membrane Resistance: Key Features in a New Murine Model of Human GM1-Gangliosidosis

G_M1-gangliosidosis is caused by a reduced activity of β-galactosidase (Glb1), resulting in intralysosomal accumulations of G_M1. The aim of this study was to reveal the pathogenic mechanisms of G_M1-gangliosidosis in a new Glb1 knockout mouse model. Glb1^−/− mice were analyzed clinically, histologically, immunohistochemically, electrophysiologically and biochemically. Morphological lesions in the central nervous system were already observed in two-month-old mice, whereas functional deficits, including ataxia and tremor, did not start before 3.5-months of age. This was most likely due to a reduced membrane resistance as a compensatory mechanism. Swollen neurons exhibited intralysosomal storage of lipids extending into axons and amyloid precursor protein positive spheroids. Additionally, axons showed a higher kinesin and lower dynein immunoreactivity compared to wildtype controls. Glb1^−/− mice also demonstrated loss of phosphorylated neurofilament positive axons and a mild increase in non-phosphorylated neurofilament positive axons. Moreover, marked astrogliosis and microgliosis were found, but no demyelination. In addition to the main storage material G_M1, G_A1, sphingomyelin, phosphatidylcholine and phosphatidylserine were elevated in the brain. In summary, the current Glb1^−/− mice exhibit a so far undescribed axonopathy and a reduced membrane resistance to compensate the functional effects of structural changes. They can be used for detailed examinations of axon–glial interactions and therapy trials of lysosomal storage diseases.

Autophagy in the Central Nervous System and Effects of Chloroquine in Mucopolysaccharidosis Type II Mice

Mucopolysaccharidosis type II (MPS II) is a rare lysosomal storage disease (LSD) involving a genetic error in iduronic acid-2-sulfatase (IDS) metabolism that leads to accumulation of glycosaminoglycans within intracellular lysosomes. The primary treatment for MPS II, enzyme replacement therapy, is not effective for central nervous system (CNS) symptoms, such as intellectual disability, because the drugs do not cross the blood-brain barrier. Recently, autophagy has been associated with LSDs. In this study, we examined the morphologic relationship between neuronal damage and autophagy in IDS knockout mice using antibodies against subunit c of mitochondrial adenosine triphosphate (ATP) synthetase and p62. Immunohistological changes suggesting autophagy, such as vacuolation, were observed in neurons, microglia, and pericytes throughout the CNS, and the numbers increased over postnatal development. Oral administration of chloroquine, which inhibits autophagy, did not suppress damage to microglia and pericytes, but greatly reduced neuronal vacuolation and eliminated neuronal cells with abnormal inclusions. Thus, decreasing autophagy appears to prevent neuronal degeneration. These results suggest that an autophagy modulator could be used in addition to conventional enzyme replacement therapy to preserve the CNS in patients with MPS II.

Effect of Transmembrane Electric Field on GM1 Containing DMPC-Cholesterol Monolayer: A Computational Study

Transmembrane electric potentials and membrane curvature have always provided pathways to mediate different cellular processes. We present results of molecular dynamics (MD) simulations of lipid monolayer composed of 1, 2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and cholesterol (CHOL) under a transverse electric field to monitor the effect of electric field on membrane containing ganglioside monosialo 1 (GM1). Four systems were studied with membrane monolayer in the presence and absence of GM1 with and without applying electric field along the normal of the monolayer. The applied transmembrane electric field was 0.4 mV/Å which corresponds to the action potential of animal cell. Our results indicate that the electric field induces a considerable lateral stress on the monolayer in the presence of GM1, which is evident from the lateral pressure profiles. It was found that due to the application of electric field major perturbation was caused to the system containing GM1, manifested by the bending of the monolayer. We believe this study provides correlation between electric field and spontaneous membrane bending, specially based on the membrane composition. The consequences of these MD simulations provide considerable insights to different biological phenomenon and lipid membrane models.

Pathobiology of Christianson syndrome: Linking disrupted endosomal-lysosomal function with intellectual disability and sensory impairments

Christianson syndrome (CS) is a recently described rare neurogenetic disorder presenting early in life with a broad range of neurological symptoms, including severe intellectual disability with nonverbal status, hyperactivity, epilepsy, and progressive ataxia due to cerebellar atrophy. CS is due to loss-of-function mutations in SLC9A6, encoding NHE6, a sodium-hydrogen exchanger involved in the regulation of early endosomal pH. Here we review what is currently known about the neuropathogenesis of CS, based on insights from experimental models, which to date have focused on mechanisms that affect the CNS, specifically the brain. In addition, parental reports of sensory disturbances in their children with CS, including an apparent insensitivity to pain, led us to explore sensory function and related neuropathology in Slc9a6 KO mice. We present new data showing sensory deficits in Slc9a6 KO mice, which had reduced behavioral responses to noxious thermal and mechanical stimuli (Hargreaves and Von Frey assays, respectively) compared to wild type (WT) littermates. Immunohistochemical and ultrastructural analysis of the spinal cord and peripheral nervous system revealed intracellular accumulation of the glycosphingolipid GM2 ganglioside in KO but not WT mice. This cellular storage phenotype was most abundant in neurons of lamina I-II of the dorsal horn, a major relay site in the processing of painful stimuli. Spinal cords of KO mice also exhibited changes in astroglial and microglial populations throughout the gray matter suggestive of a neuroinflammatory process. Our findings establish the Slc9a6 KO mouse as a relevant tool for studying the sensory deficits in CS, and highlight selective vulnerabilities in relevant cell populations that may contribute to this phenotype. How NHE6 loss of function leads to such a multifaceted neurological syndrome is still undefined, and it is likely that NHE6 is involved with many cellular processes critical to normal nervous system development and function. In addition, the sensory issues exhibited by Slc9a6 KO mice, in combination with our neuropathological findings, are consistent with NHE6 loss of function impacting the entire nervous system. Sensory dysfunction in intellectually disabled individuals is challenging to assess and may impair patient safety and quality of life. Further mechanistic studies of the neurological impairments underlying CS and other genetic intellectual disability disorders must also take into account mechanisms affecting broader nervous system function in order to understand the full range of associated disabilities.

Intracerebroventricular enzyme replacement therapy with β-galactosidase reverses brain pathologies due to GM1 gangliosidosis in mice

Autosomal recessive mutations in the galactosidase β1 (GLB1) gene cause lysosomal β-gal deficiency, resulting in accumulation of galactose-containing substrates and onset of the progressive and fatal neurodegenerative lysosomal storage disease, GM1 gangliosidosis. Here, an enzyme replacement therapy (ERT) approach in fibroblasts from GM1 gangliosidosis patients with recombinant human β-gal (rhβ-gal) produced in Chinese hamster ovary cells enabled direct and precise rhβ-gal delivery to acidified lysosomes. A single, low dose (3 nm) of rhβ-gal was sufficient for normalizing β-gal activity and mediating substrate clearance for several weeks. We found that rhβ-gal uptake by the fibroblasts is dose-dependent and saturable and can be competitively inhibited by mannose 6-phosphate, suggesting cation-independent, mannose 6-phosphate receptor–mediated endocytosis from the cell surface. A single intracerebroventricularly (ICV) administered dose of rhβ-gal (100 μg) resulted in broad bilateral biodistribution of rhβ-gal to critical regions of pathology in a mouse model of GM1 gangliosidosis. Weekly ICV dosing of rhβ-gal for 8 weeks substantially reduced brain levels of ganglioside and oligosaccharide substrates and reversed well-established secondary neuropathology. Of note, unlike with the ERT approach, chronic lentivirus-mediated GLB1 overexpression in the GM1 gangliosidosis patient fibroblasts caused accumulation of a prelysosomal pool of β-gal, resulting in activation of the unfolded protein response and endoplasmic reticulum stress. This outcome was unsurprising in light of our in vitro biophysical findings for rhβ-gal, which include pH-dependent and concentration-dependent stability and dynamic self-association. Collectively, our results highlight that ICV-ERT is an effective therapeutic intervention for managing GM1 gangliosidosis potentially more safely than with gene therapy approaches.

The transcriptome of the marine calanoid copepod Temora longicornis under heat stress and recovery

Understanding the impacts of global change in zooplankton communities is crucial, as alterations in the zooplankton communities can affect entire marine ecosystems. Despite the economic and ecological importance of the calanoid copepod Temora longicornis in the Belgian part of the North Sea, molecular data is still very limited for this species. Using HiSeq Illumina sequencing, we sequenced the whole transcriptome of T. longicornis, after being exposed to realistic temperatures of 14 and 17 °C. After both an acute (1 day) and a more sustained (5 days) thermal exposure to 17 °C, we investigated gene expression differences with animals exposed to 14 °C, which may be critical for the thermal acclimation and resilience of this copepod species. We also studied the possibility of a short term stress recovery of a heat shock. A total of 179,569 transcripts were yielded, of which 44,985 putative ORF transcripts were identified. These transcripts were subsequently annotated into roughly 22,000 genes based on known sequences using Gene Ontology (GO) and KEGG databases. Temora only showed a mild response to both the temperature and the duration of the exposure. We found that the expression of 27 transcripts varied significantly with an increase in temperature of 3 °C, of which eight transcripts were differentially expressed after acute exposure only. Gene set enrichment analysis revealed that, overall, T. longicornis was more impacted by a sustained thermal exposure, rather than an immediate (acute) exposure, with two times as many enriched GO terms in the sustained treatment. We also identified several general stress responses independent of exposure time, such as modified protein synthesis, energy mobilisation, cuticle and chaperone proteins. Finally, we highlighted candidate genes of a possible recovery from heat exposure, identifying similar terms as those enriched in the heat treatments, i.e. related to for example energy metabolism, cuticle genes and extracellular matrix. The data presented in this study provides the first transcriptome available for T. longicornis which can be used for future genomic studies.

Neurite atrophy and apoptosis mediated by PERK signaling after accumulation of GM2-ganglioside

GM2-gangliosidosis, a subgroup of lysosomal storage disorders, is caused by deficiency of hexosaminidase activity, and comprises the closely related Tay-Sachs and Sandhoff diseases. The enzyme deficiency prevents normal metabolization of ganglioside GM2, usually resulting in progressive neurodegenerative disease. The molecular mechanisms whereby GM2 accumulation in neurons triggers neurodegeneration remain unclear. In vitro experiments, using microsomes from Sandhoff mouse model brain, showed that increase of GM2 content negatively modulates sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA) (Pelled et al., 2003). Furthermore, Ca²⁺ depletion in endoplasmic reticulum (ER) triggers Unfolded Protein Response (UPR), which tends to restore homeostasis in the ER; however, if cellular damage persists, an apoptotic response is initiated. We found that ER GM2 accumulation in cultured neurons induces luminal Ca²⁺ depletion, which in turn activates PERK (protein kinase RNA [PKR]-like ER kinase), one of three UPR sensors. PERK signaling displayed biphasic activation; i.e., early upregulation of cytoprotective calcineurin (CN) and, under prolonged ER stress, enhanced expression of pro-apoptotic transcription factor C/EBP homologous protein (CHOP). Moreover, GM2 accumulation in neuronal cells induced neurite atrophy and apoptosis. Both processes were effectively modulated by treatment with the selective PERK inhibitor GSK2606414, by CN knockdown, and by CHOP knockdown. Overall, our findings demonstrate the essential role of PERK signaling pathway contributing to neurodegeneration in a model of GM2-gangliosidosis.

Lysosomal storage diseases

Lysosomal storage diseases (LSDs) are a group of over 70 diseases that are characterized by lysosomal dysfunction, most of which are inherited as autosomal recessive traits. These disorders are individually rare but collectively affect 1 in 5,000 live births. LSDs typically present in infancy and childhood, although adult-onset forms also occur. Most LSDs have a progressive neurodegenerative clinical course, although symptoms in other organ systems are frequent. LSD-associated genes encode different lysosomal proteins, including lysosomal enzymes and lysosomal membrane proteins. The lysosome is the key cellular hub for macromolecule catabolism, recycling and signalling, and defects that impair any of these functions cause the accumulation of undigested or partially digested macromolecules in lysosomes (that is, 'storage') or impair the transport of molecules, which can result in cellular damage. Consequently, the cellular pathogenesis of these diseases is complex and is currently incompletely understood. Several LSDs can be treated with approved, disease-specific therapies that are mostly based on enzyme replacement. However, small-molecule therapies, including substrate reduction and chaperone therapies, have also been developed and are approved for some LSDs, whereas gene therapy and genome editing are at advanced preclinical stages and, for a few disorders, have already progressed to the clinic.

Phase Behavior of GM1-Containing DMPC-Cholesterol Monolayer: Experimental and Theoretical Study

Organization and distribution of lipids in cellular membranes play an important role in a diverse range of biological processes, such as membrane trafficking and signaling. Here, we present the combined experimental and simulated results to elucidate the phase behavioral features of ganglioside monosialo 1 (GM1)-containing mixed monolayer of the lipids 1,2-dimyristoyl- sn-glycero-3-phosphocholine (DMPC) and cholesterol (CHOL). Two monolayers having compositions DMPC-CHOL and GM1-DMPC-CHOL are investigated at air-water and air-solid interfaces using Langmuir-Blodgett experiments and scanning electron microscopy (SEM), respectively, to ascertain the phase behavior change of the monolayers. Surface pressure isotherms and SEM imaging of domain formation indicate that addition of GM1 to the monolayer at low surface pressure causes a fluidization of the system but once the system attains the surface pressure corresponding to its liquid-condensed phase, the monolayer becomes more ordered than the system devoid of GM1 and interacts among each other more cooperatively. Besides, the condensing effect of cholesterol on the DMPC monolayer was also verified by our experiments. Apart from these, the effects induced by GM1 on the phase behavior of the binary mixture of DMPC-CHOL were studied with and without applying liquid-expanded (L_E)-liquid-condensed (L_C) equilibrium surface pressure using molecular dynamics (MD) simulation. Our molecular dynamics (MD) simulation results give an atomistic-level explanation of our experimental findings and furnish a similar conclusion.

An LC-MS-based lipidomics pre-processing framework underpins rapid hypothesis generation towards CHO systems biotechnology

INTRODUCTION

Given a raw LC-MS dataset, it is often required to rapidly generate initial hypotheses, in conjunction with other 'omics' datasets, without time-consuming lipid verifications. Furthermore, for meta-analysis of many datasets, it may be impractical to conduct exhaustive confirmatory analyses. In other cases, samples for validation may be difficult to obtain, replicate or maintain. Thus, it is critical that the computational identification of lipids is of appropriate accuracy, coverage, and unbiased by a researcher's experience and prior knowledge.

OBJECTIVES

We aim to prescribe a systematic framework for lipid identifications, without usage of their characteristic retention-time by fully exploiting their underlying mass features.

RESULTS

Initially, a hybrid technique, for deducing both common and distinctive daughter ions, is used to infer parent lipids from deconvoluted spectra. This is followed by parent confirmation using basic knowledge of their preferred product ions. Using the framework, we could achieve an accuracy of ~ 80% by correctly identified 101 species from 18 classes in Chinese hamster ovary (CHO) cells. The resulting inferences could explain the recombinant-producing capability of CHO-SH87 cells, compared to non-producing CHO-K1 cells. For comparison, a XCMS-based study of the same dataset, guided by a user's ad-hoc knowledge, identified less than 60 species of 12 classes from thousands of possibilities.

CONCLUSION

We describe a systematic LC-MS-based framework that identifies lipids for rapid hypothesis generation.

Mitochondria-associated ER membranes (MAMs) and lysosomal storage diseases

Lysosomal storage diseases (LSDs) comprise a large group of disorders of catabolism, mostly due to deficiency of a single glycan-cleaving hydrolase. The consequent endo-lysosomal accumulation of undigested or partially digested substrates in cells of virtually all organs, including the nervous system, is diagnostic of these diseases and underlies pathogenesis. A subgroup of LSDs, the glycosphingolipidoses, are caused by deficiency of glycosidases that process/degrade sphingolipids and glycosphingolipids (GSLs). GSLs are among the lipid constituents of mammalian membranes, where they orderly distribute and, together with a plethora of membrane proteins, contribute to the formation of discrete membrane microdomains or lipid rafts. The composition of intracellular membranes enclosing organelles reflects that at the plasma membrane (PM). Organelles have the tendencies to tether to one another and to the PM at specific membrane contact sites that, owing to their lipid and protein content, resemble PM lipid rafts. The focus of this review is on the MAMs, mitochondria associated ER membranes, sites of juxtaposition between ER and mitochondria that function as biological hubs for the exchange of molecules and ions, and control the functional status of the reciprocal organelles. We will focus on the lipid components of the MAMs, and highlight how failure to digest or process the sialylated GSL, GM1 ganglioside, in lysosomes alters the lipid conformation and functional properties of the MAMs and leads to neuronal cell death and neurodegeneration.

Gangliosides of the Nervous System

This review begins by attempting to recount some of the pioneering discoveries that first identified the presence of gangliosides in the nervous system, their structures and topography. This is presented as prelude to the current emphasis on physiological function, about which much has been learned but still remains to be elucidated. These areas include ganglioside roles in nervous system development including stem cell biology, membranes and organelles within neurons and glia, ion transport mechanisms, receptor modulation including neurotrophic factor receptors, and importantly the pathophysiological role of ganglioside aberrations in neurodegenerative disorders. This relates to their potential as therapeutic agents, especially in those conditions characterized by deficiency of one or more specific gangliosides. Finally we attempt to speculate on future directions ganglioside research is likely to take so as to capitalize on the impressive progress to date.

Leukodystrophies: a proposed classification system based on pathological changes and pathogenetic mechanisms

Leukodystrophies are genetically determined disorders characterized by the selective involvement of the central nervous system white matter. Onset may be at any age, from prenatal life to senescence. Many leukodystrophies are degenerative in nature, but some only impair white matter function. The clinical course is mostly progressive, but may also be static or even improving with time. Progressive leukodystrophies are often fatal, and no curative treatment is known. The last decade has witnessed a tremendous increase in the number of defined leukodystrophies also owing to a diagnostic approach combining magnetic resonance imaging pattern recognition and next generation sequencing. Knowledge on white matter physiology and pathology has also dramatically built up. This led to the recognition that only few leukodystrophies are due to mutations in myelin- or oligodendrocyte-specific genes, and many are rather caused by defects in other white matter structural components, including astrocytes, microglia, axons and blood vessels. We here propose a novel classification of leukodystrophies that takes into account the primary involvement of any white matter component. Categories in this classification are the myelin disorders due to a primary defect in oligodendrocytes or myelin (hypomyelinating and demyelinating leukodystrophies, leukodystrophies with myelin vacuolization); astrocytopathies; leuko-axonopathies; microgliopathies; and leuko-vasculopathies. Following this classification, we illustrate the neuropathology and disease mechanisms of some leukodystrophies taken as example for each category. Some leukodystrophies fall into more than one category. Given the complex molecular and cellular interplay underlying white matter pathology, recognition of the cellular pathology behind a disease becomes crucial in addressing possible treatment strategies.

Detailed Structural Characterization of Sphingolipids via 193 nm Ultraviolet Photodissociation and Ultra High Resolution Tandem Mass Spectrometry

Sphingolipids serve not only as components of cellular membranes but also as bioactive mediators of numerous cellular functions. As the biological activities of these lipids are dependent on their structures, and due to the limitations of conventional ion activation methods employed during tandem mass spectrometry (MS/MS), there is a recognized need for the development of improved structure-specific methods for their comprehensive identification and characterization. Here, positive-ionization mode 193 nm ultraviolet photodissociation (UVPD)-MS/MS has been implemented for the detailed structural characterization of lipid species from a range of sphingolipid classes introduced to the mass spectrometer via electrospray ionization as their lithiated or protonated adducts. These include sphingosine d18:1(4E), dihydrosphingosine (sphinganine) d18:0, sphingadiene d18:2(4E,11Z), the isomeric sphingolipids ceramide d18:1(4E)/18:0 and dihydroceramide d18:0/18:1(9Z), ceramide-1-phosphate d18:1(4Z)/16:0, sphingomyelin d18:1(4E)/18:1(9Z) the glycosphingolipids galactosyl ceramide d18:1(4E)/24:1(15Z) and lactosyl ceramide d18:1(4E)/24:0, and several endogenous lipids present within a porcine brain total lipid extract. In addition to the product ions formed by higher energy collision dissociation (HCD), UVPD is shown to yield a series of novel structurally diagnostic product ions resulting from cleavage of both sphingosine carbon-carbon and acyl chain carbon-carbon double bonds for direct localization of site(s) of unsaturation, as well as via diagnostic cleavages of the sphingosine backbone and N-C amide bond linkages. With activation timescales and dissociation efficiencies similar to those found in conventional MS/MS strategies, this approach is therefore a promising new tool in the arsenal of ion activation techniques toward providing complete structural elucidation in automated, high-throughput lipid analysis workflows. Graphical Abstract ᅟ.

Protective effects of monosialotetrahexosylganglioside sodium on H2O2-induced human vascular endothelial cells

Monosialotetrahexosylganglioside sodium (GM1) is widely used in the treatment of central and peripheral neurological injuries. In addition to its neuroprotective activity, GM1 exerts protective effects on brain microvascular endothelial cells, although the mechanisms underlying these effects remain unclear. The aim of the present study was to clarify the protective effects and underlying mechanisms of GM1 on human umbilical vein endothelial cells (HUVECs). In this study, hydrogen peroxide (H₂O₂) was applied to induce the HUVEC injury. HUVECs in a logarithmic growth phase were divided into five groups, namely the control, H₂O₂-treated, 10-mg/l GM1, 5-mg/l GM1 and 1-mg/l GM1 groups. In all the groups, cell proliferation was detected using a Cell Counting Kit-8 assay, a flow cytometric method was applied to analyze the cell cycle and nuclear factor (NF)-κB expression was evaluated using immunofluorescence analysis. In addition, the protein expression levels of NF-κB, phosphatidylinositol 3-kinase (PI3K) and glycogen synthase kinase (GSK)-3 were detected via western blot analysis. The results indicated that GM1 exerted significant protective effects on H₂O₂-injured cells by increasing the ratio of cells in the S/G₂ phase. Furthermore, western blot analysis revealed that PI3K expression levels were markedly increased after 24 h, as a result of the GM1 treatment, while the expression of both GSK-3 markedly decreased. In addition, the ratio of nuclear-to-cytoplasmic NF-κB expression increased in the GM1-treated cells. In summary, GM1 exhibited marked protective effects on the HUVECs, possibly due to the ability of GM1 in maintaining the integrity of the endothelium and increasing the proportion of cells undergoing mitosis, a process in which the PI3K/GSK-3 and NF-κB pathways are crucially involved.

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.

Universal artificial antigen presenting cells to selectively propagate T cells expressing chimeric antigen receptor independent of specificity

T cells genetically modified to stably express immunoreceptors are being assessed for therapeutic potential in clinical trials. T cells expressing a chimeric antigen receptor (CAR) are endowed with a new specificity to target tumor-associated antigen (TAA) independent of major histocompatibility complex. Our approach to nonviral gene transfer in T cells uses ex vivo numeric expansion of CAR T cells on irradiated artificial antigen presenting cells (aAPC) bearing the targeted TAA. The requirement for aAPC to express a desired TAA limits the human application of CARs with multiple specificities when selective expansion through coculture with feeder cells is sought. As an alternative to expressing individual TAAs on aAPC, we expressed 1 ligand that could activate CAR T cells for sustained proliferation independent of specificity. We expressed a CAR ligand (designated CARL) that binds the conserved IgG4 extracellular domain of CAR and demonstrated that CARL aAPC propagate CAR T cells of multiple specificities. CARL avoids technical issues and costs associated with deploying clinical-grade aAPC for each TAA targeted by a given CAR. Using CARL enables 1 aAPC to numerically expand all CAR T cells containing the IgG4 domain, and simplifies expansion, testing, and clinical translation of CAR T cells of any specificity.

The ganglioside GM3 is associated with cisplatin-induced apoptosis in human colon cancer cells

Cisplatin (cis-diamminedichloroplatinum, CDDP) is a well-known chemotherapeutic agent for the treatment of several cancers. However, the precise mechanism underlying apoptosis of cancer cells induced by CDDP remains unclear. In this study, we show mechanistically that CDDP induces GM3-mediated apoptosis of HCT116 cells by inhibiting cell proliferation, and increasing DNA fragmentation and mitochondria-dependent apoptosis signals. CDDP induced apoptosis within cells through the generation of reactive oxygen species (ROS), regulated the ROS-mediated expression of Bax, Bcl-2, and p53, and induced the degradation of the poly (ADP-ribosyl) polymerase (PARP). We also checked expression levels of different gangliosides in HCT116 cells in the presence or absence of CDDP. Interestingly, among the gangliosides, CDDP augmented the expression of only GM3 synthase and its product GM3. Reduction of the GM3 synthase level through ectopic expression of GM3 small interfering RNA (siRNA) rescued HCT116 cells from CDDP-induced apoptosis. This was evidenced by inhibition of apoptotic signals by reducing ROS production through the regulation of 12-lipoxigenase activity. Furthermore, the apoptotic sensitivity to CDDP was remarkably increased in GM3 synthase-transfected HCT116 cells compared to that in controls. In addition, GM3 synthase-transfected cells treated with CDDP exhibited an increased accumulation of intracellular ROS. These results suggest the CDDP-induced oxidative apoptosis of HCT116 cells is mediated by GM3.

Current and potential therapeutic strategies for mucopolysaccharidoses

WHAT IS KNOWN AND OBJECTIVE

Mucopolysaccharidoses (MPSs) are a group of rare inherited metabolic diseases caused by genetic defects in the production of lysosomal enzymes. MPSs are clinically heterogeneous and are characterized by progressive deterioration in visceral, skeletal and neurological functions. This article aims to review the classification and pathophysiology of MPSs and discuss current therapies and new targeted agents under development.

METHODS

A Medline search through PubMed was performed for relevant articles and treatment guidelines on MPSs published in English for years 1970 to September of 2013 inclusive. The references listed in the identified articles, prescribing information of the drugs approved for the treatment of MPSs, as well as recent clinical trial information posted on Clinicaltrials.gov website, were reviewed.

RESULTS AND DISCUSSION

Until recently, supportive care was the only option available for the management of MPSs. In the early 2000s, enzyme replacement therapy (ERT) was approved by the United States Food and Drug Administration (FDA) for the treatment of MPS I, II and VI. Clinical trials of ERT showed substantial improvements in patients' somatic symptoms; however, no benefit was found in the neurological symptoms because the enzymes do not readily cross the blood-brain barrier (BBB). Haematopoietic stem cell transplantation (HSCT), another potentially curative treatment, is not routinely advocated in clinical practice due to its high risk profile and lack of evidence for efficacy, except in preserving cognition and prolonging survival in young patients with severe MPS I. In recent years, substrate reduction therapy (SRT) and gene therapy have been rapidly gaining greater recognition as potential therapeutic avenues.

WHAT IS NEW AND CONCLUSION

Enzyme replacement therapy (ERT) is effective for the treatment of many somatic symptoms, particularly walking ability and respiratory function, and remains the mainstay of MPS treatment. The usefulness of HSCT has not been established adequately for most MPSs. Although still under investigation, SRT and gene therapy are promising MPS treatments that may prevent the neurodegeneration not affected by ERT.

Interorganellar membrane microdomains: dynamic platforms in the control of calcium signaling and apoptosis

The dynamic interplay among intracellular organelles occurs at specific membrane tethering sites, where two organellar membranes come in close apposition but do not fuse. Such membrane microdomains allow for rapid and efficient interorganelle communication that contributes to the maintenance of cell physiology. Pathological conditions that interfere with the proper composition, number, and physical vicinity of the apposing membranes initiate a cascade of events resulting in cell death. Membrane contact sites have now been identified that tether the extensive network of the endoplasmic reticulum (ER) membranes with the mitochondria, the plasma membrane (PM), the Golgi and the endosomes/lysosomes. Thus far, the most extensively studied are the MAMs, or mitochondria associated ER membranes, and the ER-PM junctions that share functional properties and crosstalk to one another. Specific molecular components that define these microdomains have been shown to promote the interaction in trans between these intracellular compartments and the transfer or exchange of Ca²⁺ ions, lipids, and metabolic signaling molecules that determine the fate of the cell.

Mitochondria-associated ER membranes (MAMs) and glycosphingolipid enriched microdomains (GEMs): isolation from mouse brain

Intracellular organelles are highly dynamic structures with varying shape and composition, which are subjected to cell-specific intrinsic and extrinsic cues. Their membranes are often juxtaposed at defined contact sites, which become hubs for the exchange of signaling molecules and membrane components(1,2,3,4). The inter-organellar membrane microdomains that are formed between the endoplasmic reticulum (ER) and the mitochondria at the opening of the IP3-sensitive Ca(2+) channel are known as the mitochondria associated-ER membranes or MAMs(4,5,6). The protein/lipid composition and biochemical properties of these membrane contact sites have been extensively studied particularly in relation to their role in regulating intracellular Ca(2+) (4,5,6). The ER serves as the primary store of intracellular Ca(2+), and in this capacity regulates a myriad of cellular processes downstream of Ca(2+) signaling, including post-translational protein folding and protein maturation (7). Mitochondria, on the other hand, maintain Ca(2+) homeostasis, by buffering cytosolic Ca(2+) concentration thereby preventing the initiation of apoptotic pathways downstream of Ca(2+) unbalance(4,8). The dynamic nature of the MAMs makes them ideal sites to dissect basic cellular mechanisms, including Ca(2+) signaling and regulation of mitochondrial Ca(2+) concentration, lipid biosynthesis and transport, energy metabolism and cell survival (4,9,10,11,12). Several protocols have been described for the purification of these microdomains from liver tissue and cultured cells(13,14). Taking previously published methods into account, we have adapted a protocol for the isolation of mitochondria and MAMs from the adult mouse brain. To this procedure we have added an extra purification step, namely a Triton X100 extraction, which enables the isolation of the glycosphingolipid enriched microdomain (GEM) fraction of the MAMs. These GEM preparations share several protein components with caveolae and lipid rafts, derived from the plasma membrane or other intracellular membranes, and are proposed to function as gathering points for the clustering of receptor proteins and for protein-protein interactions(4,15).

Expression profiling and biochemical analysis suggest stress response as a potential mechanism inhibiting proliferation of polyamine-depleted cells

Polyamines are small organic polycations that are absolutely required for cell growth and proliferation; yet the basis for this requirement is mostly unknown. Here, we combined a genome-wide expression profiling with biochemical analysis to reveal the molecular basis for inhibited proliferation of polyamine-depleted cells. Transcriptional responses accompanying growth arrest establishment in polyamine-depleted cells or growth resumption following polyamine replenishment were monitored and compared. Changes in the expression of genes related to various fundamental cellular processes were established. Analysis of mirror-symmetric expression patterns around the G(1)-arrest point identified a set of genes representing a stress-response signature. Indeed, complementary biochemical analysis demonstrated activation of the PKR-like endoplasmic reticulum kinase arm of the unfolded protein response and of the stress-induced p38 MAPK. These changes were accompanied by induction of key growth-inhibitory factors such as p21 and Gadd45a and reduced expression of various cyclins, most profoundly cyclin D1, setting the basis for the halted proliferation. However, although the induced stress response could arrest growth, polyamine depletion also inhibited proliferation of PKR-like endoplasmic reticulum kinase and p38α-deficient cells and of cells harboring a nonphosphorylatable mutant eIF2α (S51A), suggesting that additional yet unidentified mechanisms might inhibit proliferation of polyamine-depleted cells. Despite lengthy persistence of the stress and activation of apoptotic signaling, polyamine-depleted cells remained viable, apparently due to induced expression of protective genes and development of autophagy.

Filipin recognizes both GM1 and cholesterol in GM1 gangliosidosis mouse brain

Filipin is an antibiotic polyene widely used as a histochemical marker for cholesterol. We previously reported cholesterol/filipin-positive staining in brain of β-galactosidase (β-gal) knockout ((-/-)) mice (GM1 gangliosidosis). The content and distribution of cholesterol and gangliosides was analyzed in plasma membrane (PM) and microsomal (MS) fractions from whole-brain tissue of 15 week-old control (β-gal(+/-)) and GM1 gangliosidosis (β-gal(-/-)) mice. Total ganglioside content (μg sialic acid/mg protein) was 3-fold and 7-fold greater in the PM and MS fractions, respectively, in βgal(-/-) mice than in βgal(+/-) mice. GM1 content was 30-fold and 50-fold greater in the PM and MS fractions, respectively. In contrast, unesterified cholesterol content (μg/mg protein) was similar in the PM and the MS fractions of the βgal(-/-) and βgal(+/-) mice. Filipin is known to bind to various sterol derivatives and phospholipids on thin-layer chromatograms. Biochemical evidence is presented showing that filipin also binds to GM1 with an affinity similar to that for cholesterol, with a corresponding fluorescent reaction. Our data suggest that the GM1 storage seen in the β-gal(-/-) mouse contributes to the filipin ultraviolet fluorescence observed in GM1 gangliosidosis brain. The data indicate that in addition to cholesterol, filipin can also be useful for detecting GM1.

Quantitative proteome analysis of detergent-resistant membranes identifies the differential regulation of protein kinase C isoforms in apoptotic T cells

Several lines of evidence suggest that detergent-resistant membranes (DRMs) (also known as lipid rafts and glycosphingolipid-enriched microdomains) may have a role in signaling pathways of apoptosis. Here, we developed a method that combines DRMs isolation and methanol/chloroform extraction with stable isotope labeling with amino acids in cell culture-based quantitative proteome analysis of DRMs from control and cisplatin-induced apoptotic Jurkat T cells. This approach enabled us to enrich proteins with a pivotal role in cell signaling of which several were found with increased or decreased amounts in DRMs upon induction of apoptosis. Specifically, we show that three isoforms of protein kinase C (PKC) are regulated differently upon apoptosis. Although PKC alpha which belongs to the group of conventional PKCs is highly up-regulated in DRMs, the levels of two novel PKCs, PKC eta and PKC theta, are significantly reduced. These alterations/differences in PKC regulation are verified by immunoblotting and confocal microscopy. In addition, a specific enrichment of PKC alpha in apoptotic blebs and buds is shown. Furthermore, we observe an increased expression of ecto-PKC alpha as a result of exposure to cisplatin using flow cytometry. Our results demonstrate that in-depth proteomic analysis of DRMs provides a tool to study differential localization and regulation of signaling molecules important in health and disease.

Pathophysiology of neuropathic lysosomal storage disorders

Although neurodegenerative diseases are most prevalent in the elderly, in rare cases, they can also affect children. Lysosomal storage diseases (LSDs) are a group of inherited metabolic neurodegenerative disorders due to deficiency of a specific protein integral to lysosomal function, such as enzymes or lysosomal components, or to errors in enzyme trafficking/targeting and defective function of nonenzymatic lysosomal proteins, all preventing the complete degradation and recycling of macromolecules. This primary metabolic event determines a cascade of secondary events, inducing LSD's pathology. The accumulation of intermediate degradation affects the function of lysosomes and other cellular organelles. Accumulation begins in infancy and progressively worsens, often affecting several organs, including the central nervous system (CNS). Affected neurons may die through apoptosis or necrosis, although neuronal loss usually does not occur before advanced stages of the disease. CNS pathology causes mental retardation, progressive neurodegeneration, and premature death. Many of these features are also found in adult neurodegenerative disorders, such as Alzheimer's, Parkinson's, and Huntington's diseases. However, the nature of the secondary events and their exact contribution to mental retardation and dementia remains largely unknown. Recently, lysosomal involvement in the pathogenesis of these disorders has been described. Improved knowledge of secondary events may have impact on diagnosis, staging, and follow-up of affected children. Importantly, new insights may provide indications about possible disease reversal upon treatment. A discussion about the CNS pathophysiology involvement in LSDs is the aim of this review. The lysosomal involvement in adult neurodegenerative diseases will also be briefly described.

Multi-system disorders of glycosphingolipid and ganglioside metabolism

Glycosphingolipids (GSLs) and gangliosides are a group of bioactive glycolipids that include cerebrosides, globosides, and gangliosides. These lipids play major roles in signal transduction, cell adhesion, modulating growth factor/hormone receptor, antigen recognition, and protein trafficking. Specific genetic defects in lysosomal hydrolases disrupt normal GSL and ganglioside metabolism leading to their excess accumulation in cellular compartments, particularly in the lysosome, i.e., lysosomal storage diseases (LSDs). The storage diseases of GSLs and gangliosides affect all organ systems, but the central nervous system (CNS) is primarily involved in many. Current treatments can attenuate the visceral disease, but the management of CNS involvement remains an unmet medical need. Early interventions that alter the CNS disease have shown promise in delaying neurologic involvement in several CNS LSDs. Consequently, effective treatment for such devastating inherited diseases requires an understanding of the early developmental and pathological mechanisms of GSL and ganglioside flux (synthesis and degradation) that underlie the CNS diseases. These are the focus of this review.

GM1-ganglioside accumulation at the mitochondria-associated ER membranes links ER stress to Ca(2+)-dependent mitochondrial apoptosis

Mitochondria-associated ER membranes, or MAMs, define the sites of endoplasmic reticulum/mitochondria juxtaposition that control Ca(2+) flux between these organelles. We found that in a mouse model of the human lysosomal storage disease GM1-gangliosidosis, GM1-ganglioside accumulates in the glycosphingolipid-enriched microdomain (GEM) fractions of MAMs, where it interacts with the phosphorylated form of IP3 receptor-1, influencing the activity of this channel. Ca(2+) depleted from the ER is then taken up by the mitochondria, leading to Ca(2+) overload in this organelle. The latter induces mitochondrial membrane permeabilization (MMP), opening of the permeability transition pore, and activation of the mitochondrial apoptotic pathway. This study identifies the GEMs as the sites of Ca(2+) diffusion between the ER and the mitochondria. We propose a new mechanism of Ca(2+)-mediated apoptotic signaling whereby GM1 accumulation at the GEMs alters Ca(2+) dynamics and acts as a molecular effector of both ER stress-induced and mitochondria-mediated apoptosis of neuronal cells.

Polar lipid remodeling and increased sulfatide expression are associated with the glioma therapeutic candidates, wild type p53 elevation and the topoisomerase-1 inhibitor, irinotecan

We report changes in gene and polar lipid expression induced by adenovirus-delivered wild-type (wt) p53 gene and chemotherapy of U87 MG glioblastoma cells, a treatment known to trigger apoptosis and cell cycle arrest. Sulfatides (sulfonated glycolipids) were most highly modulated by wild-type p53 treatment; however, no changes were observed in expression levels of mRNA for genes involved in sulfatide metabolism, indicating post-transcriptional control of sulfatide synthesis. Modulation of the aglycones of GD1 and GM1b was observed in wild-type p53-treated cells. The treatment also leads to an increase in phospholipids such as phosphatidyl inositols, phosphatidyl serines, phosphatidyl glycerols, and phosphatidyl ethanolamines, especially hydroxylated phospholipids. These dramatic changes in the composition of cellular glycolipids in response to p53 gene expression and cytotoxic chemotherapy treatment indicate the large role that they play in cell signaling. The use of the human glioma cell line U87 appears to be an excellent model system both in tissue culture and in intracranial murine xenograft models to further characterize the role of sulfatides in modulating glioma responsivity to therapeutic agents.

Secondary lipid accumulation in lysosomal disease

Lysosomal diseases are inherited metabolic disorders caused by defects in a wide spectrum of lysosomal and a few non-lysosomal proteins. In most cases a single type of primary storage material is identified, which has been used to name and classify the disorders: hence the terms sphingolipidoses, gangliosidoses, mucopolysaccharidoses, glycoproteinoses, and so forth. In addition to this primary storage, however, a host of secondary storage products can also be identified, more often than not having no direct link to the primary protein defect. Lipids - glycosphingolipids and phospholipids, as well as cholesterol - are the most ubiquitous and best studied of these secondary storage materials. While in the past typically considered nonspecific and nonconsequential features of these diseases, newer studies suggest direct links between secondary storage and disease pathogenesis and support the view that understanding all aspects of this sequestration process will provide important insights into the cell biology and treatment of lysosomal disease.

Pathogenic cascades in lysosomal disease-Why so complex?

Lysosomal disease represents a large group of more than 50 clinically recognized conditions resulting from inborn errors of metabolism affecting the organelle known as the lysosome. The lysosome is an integral part of the larger endosomal/lysosomal system, and is closely allied with the ubiquitin-proteosomal and autophagosomal systems, which together comprise essential cell machinery for substrate degradation and recycling, homeostatic control, and signalling. More than two-thirds of lysosomal diseases affect the brain, with neurons appearing particularly vulnerable to lysosomal compromise and showing diverse consequences ranging from specific axonal and dendritic abnormalities to neuron death. While failure of lysosomal function characteristically leads to lysosomal storage, new studies argue that lysosomal diseases may also be appropriately viewed as 'states of deficiency' rather than simply overabundance (storage). Interference with signalling events and salvage processing normally controlled by the endosomal/lysosomal system may represent key mechanisms accounting for the inherent complexity of lysosomal disorders. Analysis of lysosomal disease pathogenesis provides a unique window through which to observe the importance of the greater lysosomal system for normal cell health.

Saturated with fat: new perspectives on lipotoxicity

PURPOSE OF REVIEW

To present current perspectives on the mediators and mechanisms of cyto-lipotoxic events and their relevance to human health.

RECENT FINDINGS

The relatively recent isolation of lipid acyltransferase genes from yeast to mice and humans has resulted in a paradigm shift that now establishes all fatty acids as toxic, albeit in tissue specific patterns and by different mechanisms. Furthermore, the dysregulation of glucose homeostasis in combination with excess fatty acids provides a synergistic effect leading to glucolipotoxicity and cell death. These findings are relevant to the development of disease states associated with the pathogenesis of the metabolic syndrome.

SUMMARY

In an era when an astounding number of people are diagnosed with metabolic disorders, it is imperative that we understand the consequences of a chronic metabolic surplus. Excessive fat, saturated or otherwise, has to be accommodated. Multiple aspects of this homeostasis are emerging, some of which are described here.

Lysosomal disorders: from storage to cellular damage

Lysosomal storage diseases represent a group of about 50 genetic disorders caused by deficiencies of lysosomal and non-lysosomal proteins. Patients accumulate compounds which are normally degraded in the lysosome. In many diseases this accumulation affects various organs leading to severe symptoms and premature death. The revelation of the mechanism by which stored compounds affect cellular function is the basis for understanding pathophysiology underlying lysosomal storage diseases. In the past years it has become clear that storage compounds interfere with various processes on the cellular level. The spectrum covers e.g. receptor activation by non-physiologic ligands, modulation of receptor response and intracellular effectors of signal transduction cascades, impairment of autophagy, and others. Importantly, many of these processes are associated with accumulation of storage material in non-lysosomal compartments. Here we summarize current knowledge on the effects that storage material can elicit on the cellular level.