The role of sphingolipids in meibomian gland dysfunction and ocular surface inflammation

Inflammation occurs in response to tissue injury and invasion of microorganisms and is carried out by the innate and adaptive immune systems, which are regulated by numerous chemokines, cytokines, and lipid mediators. There are four major families of bioactive lipid mediators that play an integral role in inflammation – eicosanoids, sphingolipids (SPL), specialized pro-resolving mediators (SPM), and endocannabinoids. SPL have been historically recognized as important structural components of cellular membranes; their roles as bioactive lipids and inflammatory mediators are recent additions. Major SPL metabolites, including sphingomyelin, ceramide, ceramide 1-phosphate (C1P), sphingosine, sphingosine 1-phosphate (S1P), and their respective enzymes have been studied extensively, primarily in cell-culture and animal models, for their roles in cellular signaling and regulating inflammation and apoptosis. Less focus has been given to the involvement of SPL in eye diseases. As such, the aim of this review was to examine relationships between the SPL family and ocular surface diseases, focusing on their role in disease pathophysiology and discussing the potential of therapeutics that disrupt SPL pathways.     

Engineering in vivo gradients of sphingosine-1-phosphate receptor ligands for localized microvascular remodeling and inflammatory cell positioning

Biomaterial-mediated controlled release of soluble signaling molecules is a tissue engineering approach to spatially control processes of inflammation, microvascular remodeling and host cell recruitment, and to generate biochemical gradients in vivo. Lipid mediators, such as sphingosine 1-phosphate (S1P), are recognized for their essential roles in spatial guidance, signaling and highly regulated endogenous gradients. S1P and pharmacological analogs such as FTY720 are therapeutically attractive targets for their critical roles in the trafficking of cells between blood and tissue spaces, both physiologically and pathophysiologically. However, the interaction of locally delivered sphingolipids with the complex metabolic networks controlling the flux of lipid species in inflamed tissue has yet to be elucidated. In this study, complementary in vitro and in vivo approaches are investigated to identify relationships between polymer composition, drug release kinetics, S1P metabolic activity, signaling gradients and spatial positioning of circulating cells around poly(lactic-co-glycolic acid) biomaterials. Results demonstrate that biomaterial-based gradients of S1P are short-lived in the tissue due to degradation by S1P lyase, an enzyme that irreversibly degrades intracellular S1P. On the other hand, in vivo gradients of the more stable compound, FTY720, enhance microvascular remodeling by selectively recruiting an anti-inflammatory subset of monocytes (S1P₃^high) to the biomaterial. Results highlight the need to better understand the endogenous balance of lipid import/export machinery and lipid kinase/phosphatase activity in order to design biomaterial products that spatially control the innate immune environment to maximize regenerative potential.     

Effects of long term exposure to the mycotoxin fumonisin B1 in p53 heterozygous and p53 homozygous transgenic mice

The fungal toxin fumonisin B₁ (FB₁) is a potential human carcinogen based on evidence of renal carcinogenicity in rats and hepatocarcinogenicity in mice. The toxicity and carcinogenicity of FB₁ is linked to ceramide synthase inhibition. Based on this mechanism of action and on lack of evidence of genotoxicity, FB₁ is considered a non-genotoxic carcinogen. The p53 heterozygous (p53+/−) mouse is a cancer-prone model used for carcinogenesis. The effects of chronic dietary FB₁ exposure were characterized in p53+/− mice to confirm non-genotoxicity using a model which is more sensitive to genotoxic than non-genotoxic carcinogens and to clarify the relationship between p53 expression, altered sphingolipid metabolism, and FB₁-induced carcinogenesis. Responses to FB₁ were similar in p53+/− and p53+/+ mice after 26 weeks exposure to 0, 5, 50 or 150 mg FB₁/kg diet, supporting a non-genotoxic mechanism of action. Hepatic adenomas and cholangiomas were observed in mice exposed to 150 mg/kg FB₁. For a 10% increase in hepatic megalocytosis, the estimated 95% lower confidence limit of the benchmark dose (BMDL₁₀) ranged from 0.15 and 1.11 mg FB₁/kg bw/day. Based on similar responses in p53+/− and p53+/+ mice, p53 and related pathways play a secondary role in responses to FB₁ toxicity and carcinogenesis.     

1-磷酸神经鞘氨醇与肥胖相关性炎症的研究进展

背景 肥胖是一种病理状态,系能量代谢失衡导致脂肪组织在体内过度或异常的积聚所致.脂肪组织可以合成并分泌炎性介质,趋化炎性细胞的浸润,促进机体的炎症反应,参与代谢性疾病的发生发展.近年来的研究发现,肥胖相关性炎症将导致l磷酸神经鞘氨醇(sphingosine-1-phosphate,S1P)代谢紊乱,增加代谢性疾病,如动脉粥样硬化、2型糖尿病、非酒精性脂肪肝病(non-alcoholic fatty liver disease,NAFLD)的发生风险.目的 探讨肥胖相关性炎症与S1P代谢的相互作用.内容 肥胖相关性炎症的病理过程、S1P代谢的调控以及S1P在代谢性疾病中的作用.趋向 S1P在肥胖相关性炎症中作用机制的阐述将为代谢性疾病及其后续并发症的防治提供分子靶标.     

Neuronopathic juvenile glucosylceramidosis due to sap-C deficiency: clinical course, neuropathology and brain lipid composition in this Gaucher disease variant

Glucosylceramide lipidosis results from a defective lysosomal degradation of this glycolipid. Lipid degradation is controlled by two components, the enzyme β-glucocerebrosidase and a sphingolipid activator protein. While most Gaucher cases are due to mutations within the gene that codes for the lysosomal enzyme, only two patients have been described with normal enzyme levels and mutations in the gene for the sphingolipid activator protein C (sap-C). Here we present the detailed neurological manifestations, neuropathological findings and brain lipid composition in one sap-C-deficient patient. The patient was an 8-year-old boy who presented with transient losses of consciousness, myoclonic jerks and generalized seizures resistant to all antiepileptic drugs. He developed progressive horizontal ophthalmoplegia, pyramidal and cerebellar signs, and died at the age of 15.5 years. Neuropathological studies demonstrated neuronal cell loss and neuronophagia, massive intraneuronal lipid storage and lack of perivascular Gaucher cells. Electron microscopy examination showed different types of storage including lipofuscin granules as well as the cytosomes with parallel arrays of bilayers that are assumed to be formed by stored lipids. General brain lipid composition did not show a remarkable increase or loss of any of the major lipid fractions but the glucosylceramide concentration in the cortex of several anatomical regions showed a striking increase. Fatty acid composition of the ceramide moiety clearly suggests that gangliosides are the main precursors in the cerebral cortex, while it implies an additional and distinct source in the cerebellum. Studying the phenotypic consequences of mutant sphingolipid activator proteins is critical to a better understanding of the physiological significance of these proteins. Received: 28 July 1997 / Revised: 22 June 1998 / Revised, accepted: 10 July 1998     

Sphingosine-1-phosphate-induced ERK activation protects human melanocytes from UVB-induced apoptosis

Ultraviolet B (UVB) is known to induce apoptosis in human melanocytes. Here we show the cytoprotective effect of sphingosine-1-phosphate (S1P) against UVB-induced apoptosis. We also show that UVB-induced apoptosis of melanocytes is mediated by caspase-3 activation and poly(ADP-ribose) polymerase (PARP) cleavage, and that S1P prevents apoptosis by inhibiting this apoptotic pathway. We further investigated three major mitogen-activated protein (MAP) kinases after UVB irradiation. UVB gradually activated c-Jun N-terminal kinase (JNK) and p38 MAP kinase, while extracellular signal-regulated protein kinase (ERK) was inactivated transiently. Blocking of the p38 MAP kinase pathway using SB203580 promoted cell survival and inhibited the activation of caspase-3 and PARP cleavage. These results suggest that p38 MAP kinase activation may play an important role in the UVB-induced apoptosis of human melanocytes. To explain this cytoprotective effect, we next examined whether S1P could inhibit UVB-induced JNK and p38 MAP kinase activation. However, S1P was not found to have any influence on UVB-induced JNK or p38 MAP kinase activation. In contrast, S1P clearly stimulated the phosphorylation of ERK, and the specific inhibition of the ERK pathway using PD98059 abolished the cytoprotective effect of S1P. Based on these results, we conclude that the activation of p38 MAP kinase plays an important role in UVB-induced apoptosis, and that S1P may show its cytoprotective effect through ERK activation in human melanocytes.     

A computational approach to the inference of sphingolipid pathways from the genome of Aspergillus fumigatus

A growing body of evidence suggests that sphingolipids are important bioactive molecules, in addition to being critical structural components of cellular membranes. These molecules have been implicated in regulating cell growth, differentiation, angiogenesis, apoptosis, and senescence. Many of the enzymes involved in sphingolipid biosynthesis are the targets of fungal toxins, thus underscoring the importance of this pathway. An international consortium has made considerable progress in sequencing the genome of Aspergillus fumigatus, one of the most common mold pathogens of humans; however, most genes have not yet been annotated. Here, we have identified genes involved in the sphingolipid pathway of A. fumigatus by comparative analysis with four other fungal species and the gene prediction program GlimmerM. Our results shows that A. fumigatus has most of the sphingolipid pathway genes found in other fungi, except for the CSG2 and IPT1 genes; the former is involved in the mannosylation of inositol phosphorylceramide (IPC) to mannose-inositol-phosphorylceramide and the latter involved in the synthesis of mannose-(inositol-P)₂-ceramide from mannose-inositol-phosphorylceramide.     

Neutral lipid and sphingolipid composition of the brain of a patient with membranous lipodystrophy

Summary Lipids were extracted from brains of a patient with membranous lipodystrophy (ML) and three normal patients and the neutral lipid and sphingolipid constituents were investigated. The storage of a large amount of free fatty acid was observed in the ML brain, but no cholesterol ester was found. Total lipid, cholesterol and cerebroside contents were slightly decreased in the white matter of the ML brain. The compositions of free and sphingolipid fatty acids did not differ between ML and normal brains.

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Zusammenfassung Im Gehirn einer sogenannten Membranolipodystrophie (ML) und in drei normalen Gehirnen wurden Neutrallipide und Sphingolipide vergleichend analysiert. Eine große Menge Frei-Fettsäure wurde beobachtet, aber Cholesterolester fand sich weder in der grauen noch in der weißen Substanz des ML-Gehirns. In der weißen Substanz des ML-Gehirns wurde eine geringe Abnahme des Cholesterins, der Cerebroside und auch Totallipide im Vergleich mit den normalen Gehirnen beobachtet. Es gab nicht eine bedeutsame Differenz zwischen ML und den normalen in der Komposition der Frei-und Sphingolipide-Fettsäure.

     

A systematic comparison of all mutations in hereditary sensory neuropathy type I (HSAN I) reveals that the G387A mutation is not disease associated

Hereditary sensory neuropathy type 1 (HSAN I) is an autosomal dominant inherited neurodegenerative disorder of the peripheral nervous system associated with mutations in the SPTLC1 subunit of the serine palmitoyltransferase (SPT). Four missense mutations (C133W, C133Y, V144D and G387A) in SPTLC1 were reported to cause HSAN I. SPT catalyses the condensation of Serine and Palmitoyl-CoA, which is the first and rate-limiting step in the de novo synthesis of ceramides. Earlier studies showed that C133W and C133Y mutants have a reduced activity, whereas the impact of the V144D and G387A mutations on the human enzyme was not tested yet. In this paper, we show that none of the HSAN I mutations interferes with SPT complex formation. We demonstrate that also V144D has a reduced SPT activity, however to a lower extent than C133W and C133Y. In contrast, the G387A mutation showed no influence on SPT activity. Furthermore, the growth phenotype of LY-B cells—a SPTLC1 deficient CHO cell line—could be reversed by expressing either the wild-type SPTLC1 or the G387A mutant, but not the C133W mutant. This indicates that the G387A mutation is most likely not directly associated with HSAN I. These findings were genetically confirmed by the identification of a nuclear HSAN family which showed segregation of the G387A variant as a non-synonymous SNP.     

A sphingolipid and tyrosinase inhibitors from the fruiting body of<Emphasis Type="Italic">phellinus linteus</Emphasis>

This paper for the first time reports the isolation of 5 compounds from Phellinus linteus. A sphingolipid (1) and two tyrosinase inhibitory compounds (2, 3) along with two carboxylic acids (4, 5), were isolated from the fruiting body of Phellinus linteus (Berk & Curt) Aoshima. The structure of compound 1 was identified as 1-omicron-beta-D-glucopyranosyl-(2S, 3R, 4E, 8E)-2-[(2R)-2-hydroxyhexadecanoylamino]-9-methyl-4,8-octadecadiene-1,3-diol, known as cerebroside B, based on spectroscopic methods such as 1 D and 2D NMR as well as by acid hydrolysis. Compounds 2 -5 were identified as protocatechualdehyde (2), 5-hydroxymethyl-2-furaldehyde (HMF) (3), succinic acid (4), and fumaric acid (5) based on the spectroscopic evidence. Compounds 2 and 3 inhibited the oxidation of L-tyrosine catalyzed by mushroom tyrosinase with an IC50 of 0.40 and 90.8 microg/mL, respectively. The inhibitory kinetics, which were analyzed by the Lineweaver-Burk plots, were found to be competitive and noncompetitive inhibitors with a Ki of 1.1 microM and 1.4 mM, respectively.