RESUMO
Sphingolipidoses are inherited metabolic disorders associated with glycosphingolipids accumulation, neurodegeneration, and neuroinflammation leading to severe neurological symptoms. Lysoglycosphingolipids (lysoGSLs), also known to accumulate in the tissues of sphingolipidosis patients, exhibit cytotoxicity. LysoGSLs are the possible pathogenic cause, but the mechanisms are still unknown in detail. Here, we first show that lysoGSLs are potential inhibitors of phosphoinositide 3-kinase (PI3K) to reduce cell survival signaling. We found that phosphorylated Akt was commonly reduced in fibroblasts from patients with sphingolipidoses, including GM1/GM2 gangliosidoses and Gaucher's disease, suggesting the contribution of lysoGSLs to the pathogenesis. LysoGSLs caused cell death and decreased the level of phosphorylated Akt as in the patient fibroblasts. Extracellularly administered lysoGM1 permeated the cell membrane to diffusely distribute in the cytoplasm. LysoGM1 and lysoGM2 also inhibited the production of phosphatidylinositol-(3,4,5)-triphosphate and the translocation of Akt from the cytoplasm to the plasma membrane. We also predicted that lysoGSLs could directly bind to the catalytic domain of PI3K by in silico docking study, suggesting that lysoGSLs could inhibit PI3K by directly interacting with PI3K in the cytoplasm. Furthermore, we revealed that the increment of lysoGSLs amounts in the brain of sphingolipidosis model mice correlated with the neurodegenerative progression. Our findings suggest that the down-regulation of PI3K/Akt signaling by direct interaction of lysoGSLs with PI3K in the brains is a neurodegenerative mechanism in sphingolipidoses. Moreover, we could propose the intracellular PI3K activation or inhibition of lysoGSLs biosynthesis as novel therapeutic approaches for sphingolipidoses because lysoGSLs should be cell death mediators by directly inhibiting PI3K, especially in neurons.
Assuntos
Fosfatidilinositol 3-Quinases , Esfingolipidoses , Humanos , Camundongos , Animais , Fosfatidilinositol 3-Quinases/metabolismo , Fosfatidilinositol 3-Quinase , Proteínas Proto-Oncogênicas c-akt/metabolismo , Esfingolipidoses/metabolismo , Morte CelularRESUMO
Lysosomal storage diseases are inborn errors of metabolism that arise due to loss of function mutations in genes encoding lysosomal enzymes, protein co-factors or lysosomal membrane proteins. As a consequence of the genetic defect, lysosomal function is impaired and substrates build up in the lysosome leading to 'storage'. A sub group of these disorders are the sphingolipidoses in which sphingolipids accumulate in the lysosome. In this review, I will discuss how the study of these rare lysosomal disorders reveals unanticipated links to other rare and common human diseases using Niemann-Pick disease type C as an example.
Assuntos
Doenças por Armazenamento dos Lisossomos , Doença de Niemann-Pick Tipo C , Esfingolipidoses , Humanos , Doença de Niemann-Pick Tipo C/genética , Doença de Niemann-Pick Tipo C/metabolismo , Esfingolipídeos/metabolismo , Doenças por Armazenamento dos Lisossomos/genética , Doenças por Armazenamento dos Lisossomos/metabolismo , Esfingolipidoses/genética , Esfingolipidoses/metabolismo , Lisossomos/metabolismoRESUMO
Sphingolipidoses are a group of metabolic diseases in which lysosomal hydrolases dysfunction disrupt normal sphingolipids' metabolism, leading to excess accumulation in cellular compartments and excretion in urine. These pathologies represent a significant burden among Moroccan population, for which an easy access to enzymatic assays and genetic tests is not guaranteed. Parallel analytical methods thus have to be developed for preliminary screening. In this study, 107 patients were addressed to the metabolic platform of the Marrakesh Faculty of Medicine for diagnosis confirmation. Thin-Layer Chromatography was used as a first step to perform chemical profiling of the patients' urinary lipids, allowing 36% of the patients to be efficiently oriented towards the adequate enzymatic assay. UPLC-MS/MS analyses of urinary sulfatides excreted in urines patient had been used to control the reliability of TLC analysis and to obtain more accurate information related to the sulfatides isoforms. This analytical process combining TLC with UPLC-MS/MS has enabled rapid and appropriate patient management in a reduced time and with reduced resources.
Assuntos
Esfingolipidoses , Sulfoglicoesfingolipídeos , Humanos , Cromatografia Líquida/métodos , Marrocos , Reprodutibilidade dos Testes , Espectrometria de Massas em Tandem/métodos , Esfingolipidoses/diagnósticoRESUMO
Sphingolipidoses are a subcategory of lysosomal storage diseases (LSDs) caused by mutations in enzymes of the sphingolipid catabolic pathway. Like many LSDs, neurological involvement in sphingolipidoses leads to early mortality with limited treatment options. Given the role of myelin loss as a major contributor toward LSD-associated neurodegeneration, we investigated the pathways contributing to demyelination in a CRISPR-Cas9-generated zebrafish model of combined saposin (psap) deficiency. psap knockout (KO) zebrafish recapitulated major LSD pathologies, including reduced lifespan, reduced lipid storage, impaired locomotion and severe myelin loss; loss of myelin basic protein a (mbpa) mRNA was progressive, with no changes in additional markers of oligodendrocyte differentiation. Brain transcriptomics revealed dysregulated mTORC1 signaling and elevated neuroinflammation, where increased proinflammatory cytokine expression preceded and mTORC1 signaling changes followed mbpa loss. We examined pharmacological and genetic rescue strategies via water tank administration of the multiple sclerosis drug monomethylfumarate (MMF), and crossing the psap KO line into an acid sphingomyelinase (smpd1) deficiency model. smpd1 mutagenesis, but not MMF treatment, prolonged lifespan in psap KO zebrafish, highlighting the modulation of acid sphingomyelinase activity as a potential path toward sphingolipidosis treatment.
Assuntos
Doenças por Armazenamento dos Lisossomos , Esfingolipidoses , Animais , Esfingomielina Fosfodiesterase/genética , Peixe-Zebra/metabolismo , Saposinas/genética , Alvo Mecanístico do Complexo 1 de RapamicinaRESUMO
Sphingolipidoses are inborn errors of metabolism due to the pathogenic mutation of genes that encode for lysosomal enzymes, transporters, or enzyme cofactors that participate in the sphingolipid catabolism. They represent a subgroup of lysosomal storage diseases characterized by the gradual lysosomal accumulation of the substrate(s) of the defective proteins. The clinical presentation of patients affected by sphingolipid storage disorders ranges from a mild progression for some juvenile- or adult-onset forms to severe/fatal infantile forms. Despite significant therapeutic achievements, novel strategies are required at basic, clinical, and translational levels to improve patient outcomes. On these bases, the development of in vivo models is crucial for a better understanding of the pathogenesis of sphingolipidoses and for the development of efficacious therapeutic strategies. The teleost zebrafish (Danio rerio) has emerged as a useful platform to model several human genetic diseases owing to the high grade of genome conservation between human and zebrafish, combined with precise genome editing and the ease of manipulation. In addition, lipidomic studies have allowed the identification in zebrafish of all of the main classes of lipids present in mammals, supporting the possibility to model diseases of the lipidic metabolism in this animal species with the advantage of using mammalian lipid databases for data processing. This review highlights the use of zebrafish as an innovative model system to gain novel insights into the pathogenesis of sphingolipidoses, with possible implications for the identification of more efficacious therapeutic approaches.
Assuntos
Doenças por Armazenamento dos Lisossomos , Esfingolipidoses , Animais , Humanos , Peixe-Zebra/metabolismo , Esfingolipídeos/metabolismo , Esfingolipidoses/genética , Modelos Biológicos , Mamíferos/metabolismoRESUMO
Sphingolipidoses are defined as a group of rare hereditary diseases resulting from mutations in the genes encoding lysosomal enzymes. This group of lysosomal storage diseases includes more than 10 genetic disorders, including GM1-gangliosidosis, Tay-Sachs disease, Sandhoff disease, the AB variant of GM2-gangliosidosis, Fabry disease, Gaucher disease, metachromatic leukodystrophy, Krabbe disease, Niemann-Pick disease, Farber disease, etc. Enzyme deficiency results in accumulation of sphingolipids in various cell types, and the nervous system is also usually affected. There are currently no known effective methods for the treatment of sphingolipidoses; however, gene therapy seems to be a promising therapeutic variant for this group of diseases. In this review, we discuss gene therapy approaches for sphingolipidoses that are currently being investigated in clinical trials, among which adeno-associated viral vector-based approaches and transplantation of hematopoietic stem cells genetically modified with lentiviral vectors seem to be the most effective.
Assuntos
Doença de Gaucher , Esfingolipidoses , Doença de Tay-Sachs , Humanos , Esfingolipídeos/metabolismo , Esfingolipidoses/genética , Terapia GenéticaRESUMO
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.
Assuntos
Esfingolipidoses , Esfingolipídeos , Sistema Nervoso Central/metabolismo , Humanos , Metabolismo dos Lipídeos , Esfingolipidoses/metabolismo , Esfingolipídeos/metabolismoRESUMO
Sphingolipidoses is a cluster of genetic rare disorders regarding glycosphingolipid metabolism, classified as lysosomal storage disorders (LSD). Here, we focus on eight inheritable diseases, including GM1 gangliosidosis, GM2 gangliosidosis, Fabry disease, Gaucher's disease, metachromatic leukodystrophy, Krabbe disease, Niemann-Pick disease A and B, and Farber disease. Mostly, pathogenic mutations in the key enzyme are loss-function, resulting in accumulation of substrates and deficiency of products. Thus, cellular overload of substrates causes lipotoxicity, which is deleterious to cellular and organ function. In the terms of clinical manifestations in sphingolipidoses, multiple systems and organs, especially central nervous system (CNS) are usually affected. As for diagnosis strategy, enzymatic activity assay and genetic sequencing are helpful. Up till now, limited treatment approaches have approved for treating sphingolipidoses, with some potential strategies for further evaluation. In general, enzyme replacement therapy (ERT), substrate reduction therapy (SRT), and molecular chaperones are feasible choices for enzyme deficiency disorders, but these therapies are limited to relieve CNS lesions and symptoms due to prevention from blood-brain barrier. Other possible treatments such as gene therapy, bone marrow transplantation (BMT), and hematopoietic stem cell transplantation (HSCT) need further evaluation.
Assuntos
Doença de Fabry , Doenças por Armazenamento dos Lisossomos , Esfingolipidoses , Glicoesfingolipídeos , Humanos , Doenças por Armazenamento dos Lisossomos/metabolismo , Doenças Raras/diagnóstico , Doenças Raras/genética , Doenças Raras/terapia , Esfingolipidoses/diagnóstico , Esfingolipidoses/genética , Esfingolipidoses/metabolismoRESUMO
Sphingolipids, which function as plasma membrane lipids and signaling molecules, are highly enriched in neuronal and myelin membranes in the nervous system. They are degraded in lysosomes by a defined sequence of enzymatic steps. In the related group of disorders, the sphingolipidoses, mutations in the genes that encode the individual degradative enzymes cause lysosomal accumulation of sphingolipids and often result in severe neurodegenerative disease. Here we review the information indicating that microglia, which actively clear sphingolipid-rich membranes in the brain during development and homeostasis, are directly affected by these mutations and promote neurodegeneration in the sphingolipidoses. We also identify parallels between the sphingolipidoses and more common forms of neurodegeneration, which both exhibit evidence of defective sphingolipid clearance in the nervous system.
Assuntos
Microglia/metabolismo , Mutação , Doenças Neurodegenerativas , Transdução de Sinais , Esfingolipidoses , Esfingolipídeos , Animais , Humanos , Doenças Neurodegenerativas/genética , Doenças Neurodegenerativas/metabolismo , Esfingolipidoses/genética , Esfingolipidoses/metabolismo , Esfingolipídeos/genética , Esfingolipídeos/metabolismoRESUMO
Sphingolipidoses are diseases caused by mutations in genes responsible for sphingolipid degradation and thereby lead to sphingolipid accumulation. Most sphingolipidoses have a neurodegenerative manifestation characterized by innate immune activation in the brain. However, the role of the immune response in disease progression is ill-understood. In contrast to infectious diseases, immune activation is unable to eliminate the offending agent in sphingolipidoses resulting in ineffective, chronic inflammation. This paradox begs two fundamental questions: Why has this immune response evolved in sphingolipidoses? What role does it play in disease progression? Here, starting from the observation that sphingolipids (SLs) are elevated also in infectious diseases, I discuss the possibility that the activation of the brain immune response by SLs has evolved as a part of the immune response against pathogens and plays no major role in sphingolipidoses.
Assuntos
Encéfalo/imunologia , Esfingolipidoses/imunologia , Esfingolipídeos/metabolismo , Encéfalo/patologia , Progressão da Doença , Humanos , Imunidade Inata , Esfingolipidoses/patologia , Esfingolipídeos/efeitos adversosRESUMO
Aim: Our objective was to develop and qualify a bioanalytical method for the estimation of di-18:1-bis(monoacylglycero)phosphate (di-18:1 BMP) as a urinary biomarker for the assessment of drug-induced phospholipidosis and demonstrate its application in a preclinical study. Methodology/results: di-18:1 BMP was extracted by liquid-liquid extraction using n-butanol and analyzed by LC-MS/MS. The qualified method was selective, precise, robust and accurate across the linearity range (0.2-250 ng/ml). Qualified method was then used to assess chloroquine-induced phospholipidosis in rats dosed at 120 mg/kg for 5 days. A fivefold increase in di-18:1 BMP was observed on Day 5 compared with predose. Conclusion: Di-18:1 BMP can be used as a noninvasive biomarker to assess/screen compounds that could cause drug-induced phospholipidosis in rats.
Assuntos
Biomarcadores/urina , Cromatografia Líquida/métodos , Lisofosfolipídeos/urina , Doenças por Armazenamento dos Lisossomos/induzido quimicamente , Monoglicerídeos/urina , Fosfolipídeos/metabolismo , Esfingolipidoses/induzido quimicamente , Espectrometria de Massas em Tandem/métodos , Animais , Humanos , Doenças por Armazenamento dos Lisossomos/urina , Masculino , Ratos , Ratos Sprague-Dawley , Esfingolipidoses/urinaRESUMO
Multiple sulfatase deficiency (MSD, MIM #272200) is an ultra-rare disease comprising pathophysiology and clinical features of mucopolysaccharidosis, sphingolipidosis and other sulfatase deficiencies. MSD is caused by impaired posttranslational activation of sulfatases through the formylglycine generating enzyme (FGE) encoded by the sulfatase modifying factor 1 (SUMF1) gene, which is mutated in MSD. FGE is a highly conserved, non-redundant ER protein that activates all cellular sulfatases by oxidizing a conserved cysteine in the active site of sulfatases that is necessary for full catalytic activity. SUMF1 mutations result in unstable, degradation-prone FGE that demonstrates reduced or absent catalytic activity, leading to decreased activity of all sulfatases. As the majority of sulfatases are localized to the lysosome, loss of sulfatase activity induces lysosomal storage of glycosaminoglycans and sulfatides and subsequent cellular pathology. MSD patients combine clinical features of all single sulfatase deficiencies in a systemic disease. Disease severity classifications distinguish cases based on age of onset and disease progression. A genotype- phenotype correlation has been proposed, biomarkers like excreted storage material and residual sulfatase activities do not correlate well with disease severity. The diagnosis of MSD is based on reduced sulfatase activities and detection of mutations in SUMF1. No therapy exists for MSD yet. This review summarizes the unique FGE/ sulfatase physiology, pathophysiology and clinical aspects in patients and their care and outlines future perspectives in MSD.
Assuntos
Mucopolissacaridoses/genética , Doença da Deficiência de Múltiplas Sulfatases/genética , Oxirredutases atuantes sobre Doadores de Grupo Enxofre/genética , Esfingolipidoses/genética , Glicina/análogos & derivados , Glicina/genética , Glicina/metabolismo , Humanos , Mucopolissacaridoses/patologia , Doença da Deficiência de Múltiplas Sulfatases/patologia , Mutação/genética , Processamento de Proteína Pós-Traducional/genética , Esfingolipidoses/patologia , Sulfatases/deficiência , Sulfatases/genéticaRESUMO
Sphingolipidoses are inherited genetic diseases characterized by the accumulation of glycosphingolipids. Sphingolipidoses (SP), which usually involve the loss of sphingolipid hydrolase function, are of lysosomal origin, and represent an important group of rare diseases among lysosomal storage disorders. Initial treatments consisted of enzyme replacement therapy, but, in recent decades, various therapeutic approaches have been developed. However, these commonly used treatments for SP fail to be fully effective and do not penetrate the blood-brain barrier. New approaches, such as genome editing, have great potential for both the treatment and study of sphingolipidoses. Here, we review the most recent advances in the treatment and modelling of SP through the application of CRISPR-Cas9 genome editing. CRISPR-Cas9 is currently the most widely used method for genome editing. This technique is versatile; it can be used for altering the regulation of genes involved in sphingolipid degradation and synthesis pathways, interrogating gene function, generating knock out models, or knocking in mutations. CRISPR-Cas9 genome editing is being used as an approach to disease treatment, but more frequently it is utilized to create models of disease. New CRISPR-Cas9-based tools of gene editing with diminished off-targeting effects are evolving and seem to be more promising for the correction of individual mutations. Emerging Prime results and CRISPR-Cas9 difficulties are also discussed.
Assuntos
Sistemas CRISPR-Cas/genética , Edição de Genes/métodos , Esfingolipidoses/terapia , Animais , Modelos Animais de Doenças , Terapia de Reposição de Enzimas , Doença de Gaucher/genética , Doença de Gaucher/terapia , Humanos , Esfingolipidoses/genética , beta-Glucosidase/genéticaRESUMO
Drug-induced phospholipidosis is a lysosomal storage disorder characterized by excessive accumulation of phospholipids. Its cellular mechanism is still not well understood, but it is known that cationic amphiphilic drugs can induce it. These drugs have a hydrophilic amine head group that can be protonated in the endolysosomal compartment. As cationic amphiphiles, they are trapped in lysosomes, where they interfere with negatively charged intralysosomal vesicles, the major platforms of cellular sphingolipid degradation. Metabolic principles observed in sphingolipid and phospholipid catabolism and inherited sphingolipidoses are of great importance for lysosomal function and physiological lipid turnover at large. Therefore, we also propose intralysosomal vesicles as major platforms for degradation of lipids and phospholipids reaching them by intracellular pathways like autophagy and endocytosis. Phospholipids are catabolized as components of vesicle surfaces by protonated, positively charged phospholipases, electrostatically attracted to the negatively charged vesicles. Model experiments suggest that progressively accumulating cationic amphiphilic drugs inserting into the vesicle membrane with their hydrophobic molecular moieties disturb and attenuate the main mechanism of lipid degradation as discussed here. By compensating the negative surface charge, cationic enzymes are released from the surface of vesicles and proteolytically degraded, triggering a progressive lipid storage and the formation of inactive lamellar bodies.
Assuntos
Metabolismo dos Lipídeos/genética , Doenças por Armazenamento dos Lisossomos/genética , Fosfolipídeos/metabolismo , Esfingolipidoses/genética , Humanos , Interações Hidrofóbicas e Hidrofílicas , Lipídeos/química , Lipídeos/genética , Doenças por Armazenamento dos Lisossomos/induzido quimicamente , Doenças por Armazenamento dos Lisossomos/metabolismo , Doenças por Armazenamento dos Lisossomos/patologia , Lisossomos/genética , Lisossomos/metabolismo , Organelas/metabolismo , Fosfolipídeos/genética , Esfingolipidoses/induzido quimicamente , Esfingolipidoses/metabolismo , Esfingolipidoses/patologiaRESUMO
Sphingolipidoses are severe, mostly infantile lysosomal storage disorders (LSDs) caused by defective glycosphingolipid degradation. Two of these sphingolipidoses, Tay Sachs and Sandhoff diseases, are caused by ß-Hexosaminidase (HEXB) enzyme deficiency, resulting in ganglioside (GM2) accumulation and neuronal loss. The precise sequence of cellular events preceding, and leading to, neuropathology remains unclear, but likely involves inflammation and lysosomal accumulation of GM2 in multiple cell types. We aimed to determine the consequences of Hexb activity loss for different brain cell types using zebrafish. Hexb deficient zebrafish (hexb-/- ) showed lysosomal abnormalities already early in development both in radial glia, which are the neuronal and glial progenitors, and in microglia. Additionally, at 5 days postfertilization, hexb-/- zebrafish showed reduced locomotor activity. Although specific oligosaccharides accumulate in the adult brain, hexb-/- ) zebrafish are viable and apparently resistant to Hexb deficiency. In all, we identified cellular consequences of loss of Hexb enzyme activity during embryonic brain development, showing early effects on glia, which possibly underlie the behavioral aberrations. Hereby, we identified clues into the contribution of non-neuronal lysosomal abnormalities in LSDs affecting the brain and provide a tool to further study what underlies the relative resistance to Hexb deficiency in vivo.
Assuntos
Encéfalo/enzimologia , Encéfalo/crescimento & desenvolvimento , Lisossomos/enzimologia , Neuroglia/enzimologia , Cadeia beta da beta-Hexosaminidase/genética , Animais , Animais Geneticamente Modificados , Apoptose/fisiologia , Encéfalo/patologia , Modelos Animais de Doenças , Lisossomos/patologia , Atividade Motora/fisiologia , Neuroglia/patologia , Esfingolipidoses/enzimologia , Peixe-ZebraRESUMO
Background Lysosphingolipids, the N-deacylated forms of sphingolipids, have been identified as potential biomarkers of several sphingolipidoses, such as Gaucher, Fabry, Krabbe and Niemann-Pick diseases and in GM1 and GM2 gangliosidoses. To date, different methods have been developed to measure various lysosphingolipids (LysoSLs) in plasma. Here, we present a novel liquid chromatography tandem mass spectrometry (LC-MS/MS) assay for a simultaneous quantification of LysoSLs (HexSph, LysoGb3, LysoGM1, LysoGM2, LysoSM and LysoSM509) in dried blood spot (DBS). This LC-MS/MS method was used to compare the levels of LysoSLs in DBS and plasma in both affected patients and healthy controls. Methods Lysosphingolipids were extracted from a 3.2 mm diameter DBS with a mixture of methanol:acetonitrile:water (80:15:5, v/v) containing internal stable isotope standards. Chromatographic separation was performed using a C18 column with a gradient of water and acetonitrile both with 0.1% formic acid in a total run time of 4 min. The compounds were detected in the positive ion mode electrospray ionization (ESI)-MS/MS by multiple reaction monitoring (MRM). Results The method was validated on DBS to demonstrate specificity, linearity, lowest limit of quantification, accuracy and precision. The reference ranges were determined in pediatric and adult populations. The elevated levels of LysoSLs were identified in Gaucher disease (HexSph), Fabry disease (LysoGb3), prosaposin deficiency (HexSph and LysoGb3) and Niemann-Pick disease types A/B and C (LysoSM and LysoSM509). The correlation in the levels between DBS and plasma was excellent for LysoGb3 and HexSph but poor for LysoSM and LysoSM509. Conclusions Despite the fact that plasma LysoSLs determination remains the gold standard, our LC-MS/MS method allows a rapid and reliable quantification of lysosphingolipids in DBS. The method is a useful tool for the diagnosis of different sphingolipidoses except for Niemann-Pick type C.
Assuntos
Teste em Amostras de Sangue Seco/métodos , Esfingolipidoses/diagnóstico , Esfingolipídeos/análise , Adolescente , Adulto , Idoso , Biomarcadores/sangue , Criança , Pré-Escolar , Cromatografia Líquida/métodos , Feminino , Humanos , Lactente , Recém-Nascido , Doenças por Armazenamento dos Lisossomos/sangue , Doenças por Armazenamento dos Lisossomos/diagnóstico , Masculino , Pessoa de Meia-Idade , Plasma/química , Valores de Referência , Reprodutibilidade dos Testes , Sensibilidade e Especificidade , Esfingolipidoses/sangue , Esfingolipídeos/sangue , Espectrometria de Massas em Tandem/métodosRESUMO
Glycosphingolipid (GSL) accumulation is implicated in the neuropathology of several lysosomal conditions, such as Krabbe disease, and may also contribute to neuronal and glial dysfunction in adult-onset conditions such as Parkinson's disease, Alzheimer's disease and multiple sclerosis. GSLs accumulate in cellular membranes and disrupt their structure; however, how membrane disruption leads to cellular dysfunction remains unknown. Using authentic cellular and animal models for Krabbe disease, we provide a mechanism explaining the inactivation of lipid raft (LR)-associated IGF-1-PI3K-Akt-mTORC2, a pathway of crucial importance for neuronal function and survival. We show that psychosine, the GSL that accumulates in Krabbe disease, leads to a dose-dependent LR-mediated inhibition of this pathway by uncoupling IGF-1 receptor phosphorylation from downstream Akt activation. This occurs by interfering with the recruitment of PI3K and mTORC2 to LRs. Akt inhibition can be reversed by sustained IGF-1 stimulation, but only during a time window before psychosine accumulation reaches a threshold level. Our study shows a previously unknown connection between LR-dependent regulation of mTORC2 activity at the cell surface and a genetic neurodegenerative disease. Our results show that LR disruption by psychosine desensitizes cells to extracellular growth factors by inhibiting signal transmission from the plasma membrane to intracellular compartments. This mechanism serves also as a mechanistic model to understand how alterations of the membrane architecture by the progressive accumulation of lipids undermines cell function, with potential implications in other genetic sphingolipidoses and adult neurodegenerative conditions. This article has an associated First Person interview with the first author of the paper.
Assuntos
Fator de Crescimento Insulin-Like I/metabolismo , Lisossomos/metabolismo , Alvo Mecanístico do Complexo 2 de Rapamicina/metabolismo , Microdomínios da Membrana/metabolismo , Neurônios/patologia , Fosfatidilinositol 3-Quinases/metabolismo , Proteínas Proto-Oncogênicas c-akt/metabolismo , Esfingolipidoses/genética , Animais , Encéfalo/metabolismo , Sobrevivência Celular/efeitos dos fármacos , Citosol/efeitos dos fármacos , Citosol/metabolismo , Regulação para Baixo/efeitos dos fármacos , Ativação Enzimática/efeitos dos fármacos , Peptídeos e Proteínas de Sinalização Intercelular/farmacologia , Lisossomos/efeitos dos fármacos , Microdomínios da Membrana/efeitos dos fármacos , Camundongos Endogâmicos C57BL , Modelos Biológicos , Neurônios/efeitos dos fármacos , Fosforilação/efeitos dos fármacos , Psicosina/farmacologia , Receptor IGF Tipo 1/metabolismo , Proteínas Quinases S6 Ribossômicas 70-kDa/metabolismo , Transdução de Sinais/efeitos dos fármacos , Esfingolipidoses/metabolismoRESUMO
Ceramide, sphingomyelin, and glycosphingolipids (both neutral and acidic) are characterized by the presence in the lipid moiety of an aliphatic base known as sphingosine. Altogether, they are called sphingolipids and are particularly abundant in neuronal plasma membranes, where, via interactions with the other membrane lipids and membrane proteins, they play a specific role in modulating the cell signaling processes. The metabolic pathways determining the plasma membrane sphingolipid composition are thus the key point for functional changes of the cell properties. Unnatural changes of the neuronal properties are observed in sphingolipidoses, lysosomal storage diseases occurring when a lysosomal sphingolipid hydrolase is not working, leading to the accumulation of the substrate and to its distribution to all the cell membranes interacting with lysosomes. Moreover, secondary accumulation of sphingolipids is a common trait of other lysosomal storage diseases. This article is part of the Special Issue "Lysosomal Storage Disorders".
Assuntos
Doenças por Armazenamento dos Lisossomos/metabolismo , Degeneração Neural/metabolismo , Esfingolipidoses/metabolismo , Esfingolipídeos/metabolismo , Animais , Humanos , Doenças por Armazenamento dos Lisossomos/patologia , Lisossomos/metabolismo , Lisossomos/patologia , Degeneração Neural/patologia , Esfingolipidoses/patologiaRESUMO
In order to delineate a better approach to functional studies, we have selected 23 missense mutations distributed in different domains of two lysosomal enzymes, to be studied by in silico analysis. In silico analysis of mutations relies on computational modeling to predict their effects. Various computational platforms are currently available to check the probable causality of mutations encountered in patients at the protein and at the RNA levels. In this work we used four different platforms freely available online (Protein Variation Effect Analyzer- PROVEAN, PolyPhen-2, Swiss-model Expert Protein Analysis System-ExPASy, and SNAP2) to check amino acid substitutions and their effect at the protein level. The existence of functional studies, regarding the amino acid substitutions, led to the selection of the distinct protein mutants. Functional data were used to compare the results obtained with different bioinformatics tools. With the advent of next-generation sequencing, it is not feasible to carry out functional tests in all the variants detected. In silico analysis seems to be useful for the delineation of which mutants are worth studying through functional studies. Therefore, prediction of the mutation impact at the protein level, applying computational analysis, confers the means to rapidly provide a prognosis value to genotyping results, making it potentially valuable for patient care as well as research purposes. The present work points to the need to carry out functional studies in mutations that might look neutral. Moreover, it should be noted that single nucleotide polymorphisms (SNPs), occurring in coding and non-coding regions, may lead to RNA alterations and should be systematically verified. Functional studies can gain from a preliminary multi-step approach, such as the one proposed here.
Assuntos
Simulação por Computador , Glucosilceramidase , Modelos Biológicos , Mutação de Sentido Incorreto , Esfingolipidoses , alfa-Galactosidase , Glucosilceramidase/genética , Glucosilceramidase/metabolismo , Humanos , Esfingolipidoses/enzimologia , Esfingolipidoses/genética , alfa-Galactosidase/genética , alfa-Galactosidase/metabolismoRESUMO
Niemann-Pick type C (NPC) disease is a lysosomal storage disorder resulting from mutations in either the NPC1 (95%) or NPC2 (5%) genes. NPC typically presents in childhood with visceral lipid accumulation and complex progressive neurodegeneration characterized by cerebellar ataxia, dysphagia, and dementia, resulting in a shortened lifespan. While cholesterol is widely acknowledged as the principal storage lipid in NPC, multiple species of sphingolipids accumulate as well. This accumulation of sphingolipids led to the initial assumption that NPC disease was caused by a deficiency in a sphingolipid catabolism enzyme, similar to sphingomyelinase deficiencies with which it shares a family name. It took about half a century to determine that NPC was in fact caused by a cholesterol trafficking defect, and still as we approach a century after the initial identification of the disease, the mechanisms by which sphingolipids accumulate remain poorly understood. Here we focus on the defects of sphingolipid catabolism in the endolysosomal compartment and how they contribute to the biology and pathology observed in NPC disease. This review highlights the need for further work on understanding and possibly developing treatments to correct the accumulation of sphingolipids in addition to cholesterol in this currently untreatable disease.