229 research outputs found
The X-ray structure of human acid-beta-glucosidase : Implications for second-generation enzyme replacement therapy
No full textDistinct Roles for Ceramide and Glucosylceramide at Different Stages of Neuronal Growth
No full textSphingolipids (SLs) are important structural and regulatory components of neuronal plasma membranes. Previous studies using fumonisin B1, an inhibitor of the synthesis of ceramide, the precursor of all SLs, demonstrated that ceramide synthesis is required to sustain axonal growth in hippocampal neurons (Harel and Futerman, 1993; Schwarz et al., 1995) and dendritic growth in cerebellar Purkinje cells (Furuya et al., 1995). We now show that ceramide plays distinct roles at different stages of neuronal development. (1) During axon growth, ceramide must be metabolized to glucosylceramide (GlcCer) to sustain growth. Thus, whereasd-erythro-ceramide, which is metabolized to GlcCer, is able to antagonize the disruptive effects of fumonisin B1on axon growth,l-threo-ceramide, which is not metabolized to GlcCer, is ineffective. (2) The formation of minor processes from lamellipodia can be stimulated by incubation with short-acyl chain analogs of ceramide that are active in ceramide-mediated signaling pathways, or by generation of endogenous ceramide by incubation with sphingomyelinase. However, GlcCer synthesis is not required for this initial stage of neuronal development. (3) During minor process formation and during axon growth, incubation with high concentrations of ceramide or sphingomyelinase, but not dihydroceramide, induces apoptosis. Together, these observations are consistent with the possibility that minor process formation and apoptosis can be regulated by ceramide-dependent signaling pathways and that the decision whether to enter these diametrically opposed pathways depends on intracellular ceramide concentrations. In contrast, axonal growth requires the synthesis of GlcCer from ceramide, perhaps to support an intracellular transport pathway.</jats:p
Lyso-glycosphingolipids mobilize calcium from brain microsomes via multiple mechanisms
No full textRecently, we demonstrated that the GSL (glycosphingolipid), GlcCer (glucosylceramide), modulates Ca2+ release from intracellular stores and from microsomes by sensitizing the RyaR (ryanodine receptor), a major Ca2+-release channel of the endoplasmic reticulum, whereas the lyso derivative of GlcCer, namely GlcSph (glucosylsphingosine), induced Ca2+ release via a mechanism independent of the RyaR [Lloyd-Evans, Pelled, Riebeling, Bodennec, de-Morgan, Waller, Schiffmann and Futerman (2003) J. Biol. Chem. 278, 23594–23599]. We now systematically examine the mechanism by which GlcSph and other lyso-GSLs modulate Ca2+ mobilization from rat brain cortical and cerebellar microsomes. GlcSph, lactosylsphingosine and galactosylsphingosine all mobilized Ca2+, but at significantly higher concentrations than those required for GlcCer-mediated sensitization of the RyaR. GlcSph-induced Ca2+ mobilization was partially blocked by heparin, an inhibitor of the Ins(1,4,5)P3 receptor, and also partially blocked by thapsigargin or ADP, inhibitors of SERCA (sarcoplasmic/endoplasmic reticulum Ca2+-ATPase), but completely blocked when both acted together. In contrast, neither lactosylsphingosine nor galactosylsphingosine had any effect on Ca2+ release via either the Ins(1,4,5)P3 receptor or SERCA, but acted as agonists of the RyaR. Finally, and surprisingly, all three lyso-GSLs reversed inhibition of SERCA by thapsigargin. We conclude that different lyso-GSLs modulate Ca2+ mobilization via different mechanisms, and discuss the relevance of these findings to the GSL storage diseases in which lyso-GSLs accumulate
Self-segregation of myelin membrane lipids in model membranes
No full textRapid conduction of nerve impulses requires coating of axons by myelin sheaths, which are multilamellar, lipid-rich membranes produced by oligodendrocytes in the central nervous system. To act as an insulator, myelin has to form a stable and firm membrane structure. In this study, we have analyzed the biophysical properties of myelin membranes prepared from wild-type mice and from mouse mutants that are unable to form stable myelin. Using C-Laurdan and fluorescence correlation spectroscopy, we find that lipids are tightly organized and highly ordered in myelin isolated from wild-type mice, but not from shiverer and ceramide synthase 2 null mice. Furthermore, only myelin lipids from wild-type mice laterally segregate into physically distinct lipid phases in giant unilamellar vesicles in a process that requires very long chain glycosphingolipids. Taken together, our findings suggest that oligodendrocytes exploit the potential of lipids to self-segregate to generate a highly ordered membrane for electrical insulation of axons
Distinct roles for sphingolipids and glycosphingolipids at different stages of neuronal development
No full textCeramide turnover in GtoPdb v.2023.1
No full textCeramides are a family of sphingophospholipids synthesized in the endoplasmic reticulum, which mediate cell stress responses, including apoptosis, autophagy and senescence, Serine palmitoyltransferase generates 3-ketosphinganine, which is reduced to dihydrosphingosine. N-Acylation allows the formation of dihydroceramides, which are subsequently reduced to form ceramides. Once synthesized, ceramides are trafficked from the ER to the Golgi bound to the ceramide transfer protein, CERT (COL4A3BP, Q9Y5P4). Ceramide can be metabolized via multiple routes, ensuring tight regulation of its cellular levels. Addition of phosphocholine generates sphingomyelin while carbohydrate is added to form glucosyl- or galactosylceramides. Ceramidase re-forms sphingosine or sphinganine from ceramide or dihydroceramide. Phosphorylation of ceramide generates ceramide phosphate. The determination of accurate kinetic parameters for many of the enzymes in the sphingolipid metabolic pathway is complicated by the lipophilic nature of the substrates
Exploring the biophysical properties of biological membranes: from ceramide domains to lipid droplets
No full textActualmente é reconhecido que a organização da membrana e as suas propriedades são reguladores de funções celulares. As alterações na organização membranar e a formação de domínios ordenados estão implicados em diversos processos biológicos, tais como na sinalização celular. As ceramidas constituem as cadeias estruturais de todos os esfingolípidos complexos, e são considerados lípidos bioactivos capazes de modular vários processos celulares e implicados no desenvolvimento de várias doenças. O mecanismo molecular subjacente ao modo de acção das ceramidas parece estar relacionado com o modo como estes lípidos alteram as propriedades biofísicas das membranas, nomeadamente através da formação de domínios enriquecidos em ceramida. No entanto, o efeito da ceramida nas propriedades das membranas são complexos e dependem tanto da composição lipídica da membrana como da estrutura da ceramida, e estão pouco caracterizados em situações que mimetizem comportamentos biológicos. Por isso, este estudo tem como objectivo investigar o impacto biofísico das ceramidas em membranas biológicas e em condições fisiologicamente relevantes, e identificar as consequências biológicas associadas a estas alterações. Vários estudos foram feitos tendo como objectivo i) melhorar a caracterização das ceramidas em membranas artificiais e ii) desenvolver e implementar metodologias biofísicas para caracterizar as propriedades de membranas e organelos em células e em condições fisiológicas. Os resultados obtidos neste estudo confirmam a complexidade associadas às alterações promovidas pela ceramida nas propriedades biofísicas das membranas, que passam pela formação de fases gel metaestáveis interdigitadas. Para além disso, também é mostrado que a formação de ceramida induzida por factores de stress promove alterações na fluidez da membrana plasmática, nos lisossomas e na célula em geral. A capacidade da ceramida promover um aumento da ordem da membrana, causado pela formação dos domínios gel de ceramida, está coordenado com o aumento da internalização de sondas lipofílicas, e é acompanhado por um aumento na internalização de vesiculas enriquecidas em ceramida, as quais são transportadas através da via endo/lisossomal. Além disso, este estudo mostra que a formação de ceramida e as alterações biofísicas estão associadas ao metabolismo e propriedades das gotículas lipídicas (“lipid droplets”). Resumindo, este estudo demostra que as acções biológicas da ceramida poderão estar associadas às alterações biofísicas induzidas nas membranas. O efeito das ceramidas nas propriedades das membranas propaga-se para além do local onde são formadas, e envolvem alterações em vários organelos. Estas evidências sugerem que activação de alvos intracelulares relacionados com as ceramidas possa ser mediada pelas vesiculas enriquecidas em ceramida com propriedades biofísicas únicas.It is nowadays recognized that membrane organization and properties are key regulators of cell function. Changes in lateral organization of the membranes and formation of ordered membrane domains have been implicated in many biological processes, including cell signaling. Ceramides, the backbone of all complex sphingolipids, are bioactive lipids involved in many cellular processes and implicated in several diseases. It is hypothesized that the biological actions of this highly hydrophobic lipid occur at the membrane level, through modulation of membrane biophysical properties, including the formation of ceramide-enriched domains. However, the effects of ceramides on membrane properties are complex and depend both on membrane lipid composition and ceramide structure and are poorly characterized in biological relevant settings. Therefore, this study aimed to investigate the biophysical impact of ceramides in biological membranes under physiological relevant conditions and identify biological consequences associated to these changes. To that end, multiple studies were performed that i) enabled a better characterization of the biophysical properties of ceramides in artificial membranes and ii) the development and implementation of biophysical methodologies to characterize the properties of membranes and organelles in live cells under physiological relevant conditions. The results obtained in this study further confirmed the complexity of ceramides associated changes on membrane biophysical properties, which encompass the formation of metastable interdigitated gel phases. Moreover, it is shown that stress-induced ceramide generation causes alterations in the fluidity of the plasma membrane, but also of the lysosomes and whole cells. Membrane ordering caused by ceramide-gel domains formation is coordinated with increased internalization of lipophilic probes and accompanied by increased internalization of ceramide-enriched vesicles that traffic via the endo-lysosomal pathway. Moreover, this study further shows that ceramide-generation and membrane biophysical alterations are linked to lipid droplet metabolism and properties. In summary, this study demonstrates that ceramide biological actions might be linked to the alterations induced by these lipids in the membranes. The effects of ceramides extend beyond the site where they are formed, reaching multiple intracellular sites. This evidence further suggests that ceramides might reach and activate their intracellular targets via formation of ceramide-enriched vesicles with distinct biophysical properties
Exploring the biophysical properties of biological membranes: from ceramide domains to lipid droplets
No full textActualmente é reconhecido que a organização da membrana e as suas propriedades são reguladores de funções celulares. As alterações na organização membranar e a formação de domínios ordenados estão implicados em diversos processos biológicos, tais como na sinalização celular. As ceramidas constituem as cadeias estruturais de todos os esfingolípidos complexos, e são considerados lípidos bioactivos capazes de modular vários processos celulares e implicados no desenvolvimento de várias doenças. O mecanismo molecular subjacente ao modo de acção das ceramidas parece estar relacionado com o modo como estes lípidos alteram as propriedades biofísicas das membranas, nomeadamente através da formação de domínios enriquecidos em ceramida. No entanto, o efeito da ceramida nas propriedades das membranas são complexos e dependem tanto da composição lipídica da membrana como da estrutura da ceramida, e estão pouco caracterizados em situações que mimetizem comportamentos biológicos. Por isso, este estudo tem como objectivo investigar o impacto biofísico das ceramidas em membranas biológicas e em condições fisiologicamente relevantes, e identificar as consequências biológicas associadas a estas alterações. Vários estudos foram feitos tendo como objectivo i) melhorar a caracterização das ceramidas em membranas artificiais e ii) desenvolver e implementar metodologias biofísicas para caracterizar as propriedades de membranas e organelos em células e em condições fisiológicas. Os resultados obtidos neste estudo confirmam a complexidade associadas às alterações promovidas pela ceramida nas propriedades biofísicas das membranas, que passam pela formação de fases gel metaestáveis interdigitadas. Para além disso, também é mostrado que a formação de ceramida induzida por factores de stress promove alterações na fluidez da membrana plasmática, nos lisossomas e na célula em geral. A capacidade da ceramida promover um aumento da ordem da membrana, causado pela formação dos domínios gel de ceramida, está coordenado com o aumento da internalização de sondas lipofílicas, e é acompanhado por um aumento na internalização de vesiculas enriquecidas em ceramida, as quais são transportadas através da via endo/lisossomal. Além disso, este estudo mostra que a formação de ceramida e as alterações biofísicas estão associadas ao metabolismo e propriedades das gotículas lipídicas (“lipid droplets”). Resumindo, este estudo demostra que as acções biológicas da ceramida poderão estar associadas às alterações biofísicas induzidas nas membranas. O efeito das ceramidas nas propriedades das membranas propaga-se para além do local onde são formadas, e envolvem alterações em vários organelos. Estas evidências sugerem que activação de alvos intracelulares relacionados com as ceramidas possa ser mediada pelas vesiculas enriquecidas em ceramida com propriedades biofísicas únicas.It is nowadays recognized that membrane organization and properties are key regulators of cell function. Changes in lateral organization of the membranes and formation of ordered membrane domains have been implicated in many biological processes, including cell signaling. Ceramides, the backbone of all complex sphingolipids, are bioactive lipids involved in many cellular processes and implicated in several diseases. It is hypothesized that the biological actions of this highly hydrophobic lipid occur at the membrane level, through modulation of membrane biophysical properties, including the formation of ceramide-enriched domains. However, the effects of ceramides on membrane properties are complex and depend both on membrane lipid composition and ceramide structure and are poorly characterized in biological relevant settings. Therefore, this study aimed to investigate the biophysical impact of ceramides in biological membranes under physiological relevant conditions and identify biological consequences associated to these changes. To that end, multiple studies were performed that i) enabled a better characterization of the biophysical properties of ceramides in artificial membranes and ii) the development and implementation of biophysical methodologies to characterize the properties of membranes and organelles in live cells under physiological relevant conditions. The results obtained in this study further confirmed the complexity of ceramides associated changes on membrane biophysical properties, which encompass the formation of metastable interdigitated gel phases. Moreover, it is shown that stress-induced ceramide generation causes alterations in the fluidity of the plasma membrane, but also of the lysosomes and whole cells. Membrane ordering caused by ceramide-gel domains formation is coordinated with increased internalization of lipophilic probes and accompanied by increased internalization of ceramide-enriched vesicles that traffic via the endo-lysosomal pathway. Moreover, this study further shows that ceramide-generation and membrane biophysical alterations are linked to lipid droplet metabolism and properties. In summary, this study demonstrates that ceramide biological actions might be linked to the alterations induced by these lipids in the membranes. The effects of ceramides extend beyond the site where they are formed, reaching multiple intracellular sites. This evidence further suggests that ceramides might reach and activate their intracellular targets via formation of ceramide-enriched vesicles with distinct biophysical properties
Do longevity assurance genes containing Hox domains regulate cell development via ceramide synthesis?
No full textAbstractA gene family containing a longevity assurance gene (Lag1p) motif is described. Database searches revealed >40 members of this family of transmembrane proteins, two of which have recently been shown to regulate the synthesis of ceramide, a lipid second messenger involved in a variety of cellular processes. We speculate that other family members, some of which contain a Hox domain, may also be involved in the synthesis of specific ceramide pools, perhaps explaining the role of longevity assurance genes in regulating development
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