Sphingolipid metabolites in neural signalling and function

Sphingolipid metabolites, such as ceramide, sphingosine, sphingosine-1-phosphate (S1P) and complex sphingolipids (gangliosides), are recognized as molecules capable of regulating a variety of cellular processes. The role of sphingolipid metabolites has been studied mainly in non-neuronal tissues. These studies have underscored their importance as signals transducers, involved in control of proliferation, survival, differentiation and apoptosis. In this review, we will focus on studies performed over the last years in the nervous system, discussing the recent developments and the current perspectives in sphingolipid metabolism and functions.     

鞘脂激活蛋白C抑制LNCaP细胞雄激素受体降解的研究

目的:探讨Saposin C对LNCaP细胞雄激素受体(AR)蛋白降解的影响。方法:通过转染实验,将Saposin C、TAT-Saposin C真核表达载体转染至LNCaP细胞,MTS检测Saposin C对LNCaP细胞增殖的影响,Western blot检测Saposin C对AR蛋白水平的影响及其在细胞中降解的调节作用。结果:Saposin C抑制LNCaP细胞AR蛋白的降解,上调胞内AR蛋白水平,促进LNCaP细胞增殖。结论:Saposin C增强AR蛋白的稳定性抑制其在细胞中的降解。     

Differential effects of ceramide species on exocytosis in rat PC12 cells

Increases in several ceramide species have been shown by non-targeted lipid profiling (lipidomics) of the rat hippocampus after kainate lesions (Guan et al. FASEB J 20:1152–1161, 2006). This study was carried out to examine possible effects of ceramide species on exocytosis. Significant increase in membrane capacitance in voltage-clamped rat pheochromocytoma (PC12) cells, an indication of exocytosis, was detected immediately after external application of C2, C6, and C18 ceramide. In contrast, no increase in capacitance was found after addition of C16 and C20 ceramide, or DMSO vehicle. The effect of ceramide on exocytosis was dependent on the integrity of lipid rafts. Treatment of cells with the cholesterol binding agent/disruptor of lipid rafts, methyl β cyclodextrin, prior to addition of C18 ceramide suppressed the increase in capacitance induced by this lipid species. The ability of C2, C6 and C18 ceramide to trigger exocytosis was confirmed using total internal reflection fluorescence microscopy (TIRFM) experiments. External application of these species caused an exponential decrease in the number of subplasmalemmal neuropeptide Y (NPY)-enhanced green fluorescence protein (EGFP) labeled vesicles, indicating exocytosis. Interestingly, C18 is also the ceramide species that showed the greatest increase in the rat hippocampus after kainate excitotoxicity. It is postulated that C18 ceramide might facilitate exocytosis of glutamate from damaged neurons, thus propagating neuronal injury.     

Die pigmentierte Form der orthochromatischen Leukodystrophie

Zusammenfassung Die pigmentierte Form der orthochromatischen Leukodystrophie (M. van Bogaert-Nyssen) ist eine wenig bekannte neurologische Erkrankung, die in der Regel erst im Erwachsenenalter auftritt, in vivo kaum zu diagnostizieren ist und innerhalb weniger Jahre zum Tode führen kann. Neuropathologisch ist sie hauptsächlich durch den Nachweis einer nichtentzündlichen Demyelinisierung und von zum Teil eisenpositiven pigmentierten Makrophagen und Astrozyten gekennzeichnet. Klinisch stehen ein demenzielles Syndrom, psychiatrische Auffälligkeiten, epileptische Anfälle, spastische Paresen und gelegentlich extrapyramidal-motorische Störungen im Vordergrund der Symptomatik. Die vorliegende Arbeit illustriert zum einen die diagnostischen Überlegungen und gibt eine Übersicht über die Literatur. Zum anderen konnte in unserem Fall immunhistochemisch Galaktozerebrosid in noch vorhandenen Makrophagen und Astrozyten nachgewiesen werden. Möglicherweise liegt hier ein Hinweis auf die zugrunde liegende biochemische Störung vor. Vielleicht bestehen Beziehungen zur genetischen definierten Globoidzellleukodystrophie (M. Krabbe). Der heterogene Pool der orthochromatischen Leukodystrophien könnte in diesem Fall durch Ausgliederung dieser Form weiter eingeengt werden.     

The Trypanosoma brucei sphingolipid synthase, an essential enzyme and drug target

Sphingolipids are important components of eukaryotic membranes, particularly the plasma membrane, and are involved in a diverse array of signal transduction processes. In the Eukaryota the biosynthetic pathway for the formation of these lipid species is largely conserved. However, in contrast to mammals which produce sphingomyelin (SM), several pathogenic fungi and protozoa synthesize inositol phosphorylceramide (IPC) as the primary phosphosphingolipid. This process is catalyzed by the enzyme IPC synthase, a recognized target for anti-fungals encoded by the AUR1 gene in yeast. Recently, functional orthologues of the AUR1p have been identified in a group of insect vector-borne pathogenic protozoa, the Kinetoplastida, which are responsible for a range of so-called neglected diseases. Of these the Trypanosoma brucei species are the causative agents of human African trypanosomiasis in many of the most under-developed regions of Africa. The available treatments for these diseases are limited, of decreasing efficacy, and often demonstrate severe side-effects. Against this background the T. brucei sphingolipid synthase, an orthologue of the yeast AUR1p, may represent a promising target for novel anti-protozoals. Our studies identify an isoform of this protein as a novel bi-functional enzyme capable of catalyzing the synthesis of both IPC and SM, both known to be present in the parasite. Furthermore, the synthase is essential for parasite growth and can be inhibited by a known anti-fungal at low nanomolar levels in vitro. Most notably this drug demonstrates trypanocidal activity against cultured bloodstream form parasites. Thus, the T. brucei sphingolipid synthase represents a valid and promising drug target.     

Regulation and functional roles of sphingosine kinases

Sphingosine kinases (SphKs) catalyze the phosphorylation of sphingosine to sphingosine-1-phosphate (S1P). Together with other sphingolipid metabolizing enzymes, SphKs regulate the balance of the lipid mediators, ceramide, sphingosine, and S1P. The ubiquitous mediator S1P regulates cellular functions such as proliferation and survival, cytoskeleton architecture and Ca²⁺ homoeostasis, migration, and adhesion by activating specific high-affinity G-protein-coupled receptors or by acting intracellularly. In mammals, two isoforms of SphK have been identified. They are activated by G-protein-coupled receptors, receptor tyrosine kinases, immunoglobulin receptors, cytokines, and other stimuli. The molecular mechanisms by which SphK1 and SphK2 are specifically regulated are complex and only partially understood. Although SphK1 and SphK2 appear to have opposing roles, promoting cell growth and apoptosis, respectively, they can obviously also substitute for each other, as mice deficient in either SphK1 or SphK2 had no obvious abnormalities, whereas double-knockout animals were embryonic lethal. In this review, our understanding of structure, regulation, and functional roles of SphKs is updated and discussed with regard to their implication in pathophysiological and disease states. This review is dedicated to Prof. Dr. Karl H. Jakobs, who has guided the sphingolipid research at the Institut für Pharmakologie with his invaluable advice.     

Inhibition of atherosclerosis by the serine palmitoyl transferase inhibitor myriocin is associated with reduced plasma glycosphingolipid concentration

Glycosphingolipids (GSL) have been implicated as potential atherogenic lipids. Inhibition of hepatic serine palmitoyl transferase (SPT) reduces plasma sphingomyelin (SM) levels in the absence of changes in cholesterol or triglyceride (TG) concentration and this leads to a reduction of atherosclerosis in apolipoprotein-E gene knockout (apoE(-/-)) mice. The possibility that the reduced atherosclerosis resulting from SPT inhibition is associated with decreases in plasma GSL concentration has not been examined and was the primary aim of this investigation. We show that intraperitoneal delivery of the SPT inhibitor myriocin for 9 weeks inhibits atherosclerosis in apoE(-/-) mice fed a high fat diet. Lesion inhibition was most pronounced at the aortic arch and distal sites of the thoracic and abdominal aorta. There was also a trend towards a reduction in lesion area at the aortic root. Myriocin treatment resulted in significant reductions in both plasma SM and GSL concentration of 42% and 25%, as assessed by enzymatic and HPLC methods, respectively. Moreover, SM and GSL concentrations were significantly correlated, indicating that SPT inhibition suppresses the synthesis of both these sphingolipids concomitantly. The inhibition of atherosclerosis induced by myriocin was not associated with changes in plasma cholesterol or TG concentrations or lipoprotein profiles as determined by FPLC. These data indicate that therapeutic reduction of plasma SM and/or GSL concentrations may offer a novel treatment for atherosclerosis.     

Bioactive Sphingolipids as Major Regulators of Coronary Artery Disease

Atherosclerosis is the deposition of plaque in the main arteries. It is an inflammatory condition involving the accumulation of macrophages and various lipids (low-density lipoprotein [LDL] cholesterol, ceramide, S1P). Moreover, endothelial cells, macrophages, leukocytes, and smooth muscle cells are the major players in the atherogenic process. Sphingolipids are now emerging as important regulators in various pathophysiological processes, including the atherogenic process. Various sphingolipids exist, such as the ceramides, ceramide-1-phosphate, sphingosine, sphinganine, sphingosine-1-phosphate (S1P), sphingomyelin, and hundreds of glycosphingolipids. Among these, ceramides, glycosphingolipids, and S1P play important roles in the atherogenic processes. The atherosclerotic plaque consists of higher amounts of ceramide, glycosphingolipids, and sphingomyelin. The inhibition of the de novo ceramide biosynthesis reduces the development of atherosclerosis. S1P regulates atherogenesis via binding to the S1P receptor (S1PR). Among the five S1PRs (S1PR1-5), S1PR1 and S1PR3 mainly exert anti-atherosclerotic properties. This review mainly focuses on the effects of ceramide and S1P via the S1PR in the development of atherosclerosis. Moreover, it discusses the recent findings and potential therapeutic implications in atherosclerosis.     

Stereoselective synthesis of L-threo-sphingosine, L-threo-sphinganine, D-threo-sphingosine, and D-threo-sphinganine via oxazoline formation and olefin cross-metathesis; potent protein kinase C inhibitor analogues

In this study, we explored a convenient and concise route for synthesis of L-threo-sphingosine, D-threo-sphingosine, L-threo-sphinganine and D-threo-sphinganine from commercially available L- or D-serine. The key steps are the simple preparation of trans-oxazoline and intermolecular olefin cross metathesis.