Novel role of lactosylceramide in vascular endothelial growth factor-mediated angiogenesis in human endothelial cells

Role of UDP-glucose ceramide glucosyltransferase in venous malformation

Venous malformation (VM) results from the abnormal growth of the vasculature; however, the detailed molecular mechanism remains unclear. As a glycosyltransferase, UDP-glucose ceramide glucosyltransferase (UGCG) is localized to the Golgi body and is a key enzyme in the first step of glycosphingolipid synthesis. Here, we aimed to explore the relationship between UGCG and the development of VM. First, investigations using RT-qPCR and Western blotting on the diseased vasculature of VM patients and normal vascular tissues revealed that UGCG expression was markedly elevated in the diseased vessels. Subsequently, immunofluorescence assay showed that UGCG was co-localized with CD31, an endothelial cell marker, in tissues from patients with VM and healthy subjects. Then, we established TIE2-L914F-mutant human umbilical vein endothelial cells (HUVECs) by lentivirus transfection. Next, Western blotting revealed that UGCG expression was considerably higher in HUVECs^TIE2-L914F. In addition, we established a UGCG-overexpressing HUVECs line by plasmid transfection. With the CCK8 cell proliferation experiment, wound healing assay, and tube formation assay, we found that UGCG could promote the proliferation, migration, and tube formation activity of HUVECs, whereas the inhibition of UGCG could inhibit the proliferation, migration, and tube formation activity of HUVECs^TIE2-L914F. Finally, Western blotting revealed that UGCG regulates the AKT/mTOR pathway in HUVECs. These data demonstrated that UGCG can affect the activity of vascular endothelial cells and regulate the AKT/mTOR signaling pathway; this is a potential mechanism underlying VM pathogenesis.

A Comprehensive Profiling of Cellular Sphingolipids in Mammalian Endothelial and Microglial Cells Cultured in Normal and High-Glucose Conditions

Sphingolipids (SPLs) play a diverse role in maintaining cellular homeostasis. Dysregulated SPL metabolism is associated with pathological changes in stressed and diseased cells. This study investigates differences in SPL metabolism between cultured human primary retinal endothelial (HREC) and murine microglial cells (BV2) in normal conditions (normal glucose, NG, 5 mM) and under high-glucose (HG, 25 mM)-induced stress by sphingolipidomics, immunohistochemistry, biochemical, and molecular assays. Measurable differences were observed in SPL profiles between HREC and BV2 cells. High-glucose treatment caused a >2.5-fold increase in the levels of Lactosyl-ceramide (LacCer) in HREC, but in BV2 cells, it induced Hexosyl-Ceramides (HexCer) by threefold and a significant increase in Sphingosine-1-phosphate (S1P) compared to NG. Altered SPL profiles coincided with changes in transcript levels of inflammatory and vascular permeability mediators in HREC and inflammatory mediators in BV2 cells. Differences in SPL profiles and differential responses to HG stress between endothelial and microglial cells suggest that SPL metabolism and signaling differ in mammalian cell types and, therefore, their pathological association with those cell types.

Involvement of Ceramide Metabolism in Cerebral Ischemia

Ischemic stroke, caused by the interruption of blood flow to the brain and subsequent neuronal death, represents one of the main causes of disability in worldwide. Although reperfusion therapies have shown efficacy in a limited number of patients with acute ischemic stroke, neuroprotective drugs and recovery strategies have been widely assessed, but none of them have been successful in clinical practice. Therefore, the search for new therapeutic approaches is still necessary. Sphingolipids consist of a family of lipidic molecules with both structural and cell signaling functions. Regulation of sphingolipid metabolism is crucial for cell fate and homeostasis in the body. Different works have emphasized the implication of its metabolism in different pathologies, such as diabetes, cancer, neurodegeneration, or atherosclerosis. Other studies have shown its implication in the risk of suffering a stroke and its progression. This review will highlight the implications of sphingolipid metabolism enzymes in acute ischemic stroke.

Metabolomic analysis reveals potential biomarkers and serum metabolomic profiling in spontaneous intracerebral hemorrhage patients using UPLC/quadrupole time-of-flight MS

Spontaneous intracerebral hemorrhage (ICH) accounts for 10-20% of all strokes and contributes to higher mortalities and severe disabilities. The aims of this study were, therefore, to characterize novel biomarkers, metabolic disruptions, and mechanisms involving ICH. A total 30 ICH patients and 30 controls were enrolled in the study, and their clinical characteristics were analyzed. Nontargeted metabolomic analysis was conducted using ultra-performance liquid chromatography quadrupole time-of-flight tandem mass spectrometry (UPLC/Q-TOF). Multivariate statistical analysis and receiver operating characteristic curve analysis were used for screening and evaluating the predictive ability of biomarkers. ICH patients showed significantly higher systolic blood pressure, diastolic blood pressure, blood glucose levels, white blood cell counts, neutrophil count, percentage of neutrophils and globulin and a lower albumin/globin ratio when compared with controls. In sum, 11 important metabolites were identified, which were associated with disruption of fatty acid oxidation and sphingolipid and phospholipid metabolism, as well as increased inflammation, oxidative stress, and vascular pathologies. Further multiple logistic regression analyses of these metabolites showed that l-carnitine and phosphatidylcholine (20:3/22:6) have potential as biomarkers of ICH, and the area under the curve, sensitivity, specificity were 0.974, 90%, and 93%, respectively. These findings provide insights into the pathogenesis, early prevention, and diagnosis of ICH.

Lipidomics analysis of monocytes from patients with acute myocardial infarction reveals lactosylceramide as a new player in monocyte migration

Monocyte recruitment after vascular injury and their migration through the vessel wall represent crucial events in the initiation, progression, and destabilization of atherosclerotic plaque. Circulating monocytes are exposed to stimuli that alter their physiological state, and among them, lipids play a key role. Several studies investigated the mechanisms by which lipids affect monocyte functions promoting coronary atherosclerotic plaque initiation, but information on the relationship between lipid composition and function of monocyte is scant. We aimed at studying the migration of circulating monocytes isolated from patients with acute myocardial infarction (AMI) at hospital presentation and investigating its correlation with cellular lipid profile. The migration of monocytes was tested using both fetal bovine serum (FBS) and autologous serum as chemoattractant stimuli. Monocyte lipid profile was evaluated through an untargeted lipidomics approach, using a liquid chromatography/time-of-flight mass spectrometry platform. We observed that AMI patients' monocytes showed a significant increase in FBS and autologous serum-mediated migration compared to controls. Moreover, a different monocyte lipidomic profile between the two study groups was detected. In particular, AMI patients' monocytes showed an altered composition in ceramides, with an increase in lactosylceramide and in phospholipids (ie, phosphatidylethanolamine and lisophosphatidylethanolamine). Of note, a positive correlation between lactosylceramide levels and monocyte migration was observed. Furthermore, the lactosylceramide synthase inhibition significantly reduced FBS-induced monocyte migration. Our results highlight the influence of lactosylceramide on the monocyte migration capacity, pointing out a new possible mechanism of lipids in the onset of atherothrombosis and, hence, in AMI.

Convergence: Lactosylceramide-Centric Signaling Pathways Induce Inflammation, Oxidative Stress, and Other Phenotypic Outcomes

Lactosylceramide (LacCer), also known as CD17/CDw17, is a member of a large family of small molecular weight compounds known as glycosphingolipids. It plays a pivotal role in the biosynthesis of glycosphingolipids, primarily by way of serving as a precursor to the majority of its higher homolog sub-families such as gangliosides, sulfatides, fucosylated-glycosphingolipids and complex neutral glycosphingolipids—some of which confer “second-messenger” and receptor functions. LacCer is an integral component of the “lipid rafts,” serving as a conduit to transduce external stimuli into multiple phenotypes, which may contribute to mortality and morbidity in man and in mouse models of human disease. LacCer is synthesized by the action of LacCer synthase (β-1,4 galactosyltransferase), which transfers galactose from uridine diphosphate galactose (UDP-galactose) to glucosylceramide (GlcCer). The convergence of multiple physiologically relevant external stimuli/agonists—platelet-derived growth factor (PDGF), vascular endothelial growth factor (VEGF), stress, cigarette smoke/nicotine, tumor necrosis factor-α (TNF-α), and in particular, oxidized low-density lipoprotein (ox-LDL)—on β-1,4 galactosyltransferase results in its phosphorylation or activation, via a “turn-key” reaction, generating LacCer. This newly synthesized LacCer activates NADPH (nicotinamide adenine dihydrogen phosphate) oxidase to generate reactive oxygen species (ROS) and a highly “oxidative stress” environment, which trigger a cascade of signaling molecules and pathways and initiate diverse phenotypes like inflammation and atherosclerosis. For instance, LacCer activates an enzyme, cytosolic phospholipase A2 (cPLA2), which cleaves arachidonic acid from phosphatidylcholine. In turn, arachidonic acid serves as a precursor to eicosanoids and prostaglandin, which transduce a cascade of reactions leading to inflammation—a major phenotype underscoring the initiation and progression of several debilitating diseases such as atherosclerosis and cancer. Our aim here is to present an updated account of studies made in the field of LacCer metabolism and signaling using multiple animal models of human disease, human tissue, and cell-based studies. These advancements have led us to propose that previously unrelated phenotypes converge in a LacCer-centric manner. This LacCer synthase/LacCer-induced “oxidative stress” environment contributes to inflammation, atherosclerosis, skin conditions, hair greying, cardiovascular disease, and diabetes due to mitochondrial dysfunction. Thus, targeting LacCer synthase may well be the answer to remedy these pathologies.

Alteration of Sphingolipids in Biofluids: Implications for Neurodegenerative Diseases

Sphingolipids (SL) modulate several cellular processes including cell death, proliferation and autophagy. The conversion of sphingomyelin (SM) to ceramide and the balance between ceramide and sphingosine-1-phosphate (S1P), also known as the SL rheostat, have been associated with oxidative stress and neurodegeneration. Research in the last decade has focused on the possibility of targeting the SL metabolism as a therapeutic option; and SL levels in biofluids, including serum, plasma, and cerebrospinal fluid (CSF), have been measured in several neurodegenerative diseases with the aim of finding a diagnostic or prognostic marker. Previous reviews focused on results from diseases such as Alzheimer's Disease (AD), evaluated total SL or species levels in human biofluids, post-mortem tissues and/or animal models. However, a comprehensive review of SL alterations comparing results from several neurodegenerative diseases is lacking. The present work compiles data from circulating sphingolipidomic studies and attempts to elucidate a possible connection between certain SL species and neurodegeneration processes. Furthermore, the effects of ceramide species according to their acyl-chain length in cellular pathways such as apoptosis and proliferation are discussed in order to understand the impact of the level alteration in specific species. Finally, enzymatic regulations and the possible influence of insulin resistance in the level alteration of SL are evaluated.

Role of Bioactive Sphingolipids in Inflammation and Eye Diseases

Inflammation is a common underlying factor in a diversity of ocular diseases, ranging from macular degeneration, autoimmune uveitis, glaucoma, diabetic retinopathy and microbial infection. In addition to the variety of known cellular mediators of inflammation, such as cytokines, chemokines and lipid mediators, there is now considerable evidence that sphingolipid metabolites also play a central role in the regulation of inflammatory pathways. Various sphingolipid metabolites, such as ceramide (Cer), ceramide-1-phosphate (C1P), sphingosine-1-phosphate (S1P), and lactosylceramide (LacCer) can contribute to ocular inflammatory diseases through multiple pathways. For example, inflammation generates Cer from sphingomyelins (SM) in the plasma membrane, which induces death receptor ligand formation and leads to apoptosis of retinal pigment epithelial (RPE) and photoreceptor cells. Inflammatory stress by reactive oxygen species leads to LacCer accumulation and S1P secretion and induces proliferation of retinal endothelial cells and eventual formation of new vessels. In sphingolipid/lysosomal storage disorders, sphingolipid metabolites accumulate in lysosomes and can cause ocular disorders that have an inflammatory etiology. Sphingolipid metabolites activate complement factors in the immune-response mediated pathogenesis of macular degeneration. These examples highlight the integral association between sphingolipids and inflammation in ocular diseases.

Decrease in VEGF-Induced Pericardial Adhesion Formation Using Bevacizumab After Surgery

Objectives. Some degrees of postoperative cardiac adhesions occur in response to the first cardiac surgery in patients that may limit surgeons for subsequent operations and increase the risk of heart injury. In this article, we established a model of postoperative pericardial adhesions, and because vascular endothelial growth factor (VEGF) seems to initiate adhesion formation through inflammatory responses, we used an anti-VEGF antibody, that is, bevacizumab, to examine its effects on postoperative adhesion formation. Methods. Twenty Wistar rats were divided in 2 groups: control and bevacizumab. After chest opening, pericardial sac was opened and the heart was fully exposed. In the bevacizumab group, bevacizumab (2.5 mg/kg) was applied locally on the heart and then the chest was closed. The control group received saline solution as placebo. After 42 days, high-sensitivity C-reactive protein in peripheral blood was measured, and re-sternotomy was performed to measure severity of pericardial adhesions. Then, the hearts were collected from all rats to evaluate percentage of CD-31-positive cells (as a marker of angiogenesis) using immunohistochemical staining. Results. When the bevacizumab group was compared with the control group, we found that the mean score of adhesion (0.89 ± 0.38 vs 2.56 ± 0.41) and CD-31 expression (27.45 ± 3.75% vs 56.26 ± 1.98%) was decreased significantly after bevacizumab administration. However, we did not find any difference in high-sensitivity C-reactive protein levels of control and bevacizumab animals. Conclusion. In the current study, bevacizumab administration could effectively reduce adhesion formation after first sternotomy by preventing VEGF-induced angiogenesis through CD-31 downregulation.

Colocalization of receptors for Shiga toxins with lipid rafts in primary human renal glomerular endothelial cells and influence of D-PDMP on synthesis and distribution of glycosphingolipid receptors

Damage of human renal glomerular endothelial cells (HRGECs) of the kidney represents the linchpin in the pathogenesis of the hemolytic uremic syndrome caused by Shiga toxins of enterohemorrhagic Escherichia coli (EHEC). We performed a comprehensive structural analysis of the Stx-receptor glycosphingolipids (GSLs) globotriaosylceramide (Gb3Cer, Galα4Galβ4Glcβ1Cer) and globotetraosylceramide (Gb4Cer, GalNAcβ3Galα4Galβ4Glcβ1Cer) and their distribution in lipid raft analog detergent-resistant membranes (DRMs) and nonDRMs prepared from primary HRGECs. Predominant receptor lipoforms were Gb3Cer and Gb4Cer with Cer (d18:1, C16:0), Cer (d18:1, C22:0) and Cer (d18:1, C24:1/C24:0). Stx-receptor GSLs co-distribute with sphingomyelin (SM) and cholesterol as well as flotillin-2 in DRMs, representing the liquid-ordered membrane phase and indicating lipid raft association. Lyso-phosphatidylcholine (lyso-PC) was identified as a nonDRM marker phospholipid of the liquid-disordered membrane phase. Exposure of primary HRGECs to the ceramide analogon d-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (D-PDMP) reduced total Gb3Cer and Gb4Cer content, roughly calculated from two biological replicates, down to half and quarter of its primordial content, respectively, but strengthened their prevalence and cholesterol preponderance in DRMs. At the same time, the distribution of PC, SM and lyso-PC to subcellular membrane fractions remained unaffected by D-PDMP treatment. Defining the GSL composition and precise microdomain structures of primary HRGECs may help to develop novel therapeutic options to combat life-threatening EHEC infections.

Glycosylation as a Main Regulator of Growth and Death Factor Receptors Signaling

Glycosylation is a very frequent and functionally important post-translational protein modification that undergoes profound changes in cancer. Growth and death factor receptors and plasma membrane glycoproteins, which upon activation by extracellular ligands trigger a signal transduction cascade, are targets of several molecular anti-cancer drugs. In this review, we provide a thorough picture of the mechanisms bywhich glycosylation affects the activity of growth and death factor receptors in normal and pathological conditions. Glycosylation affects receptor activity through three non-mutually exclusive basic mechanisms: (1) by directly regulating intracellular transport, ligand binding, oligomerization and signaling of receptors; (2) through the binding of receptor carbohydrate structures to galectins, forming a lattice thatregulates receptor turnover on the plasma membrane; and (3) by receptor interaction with gangliosides inside membrane microdomains. Some carbohydrate chains, for example core fucose and β1,6-branching, exert a stimulatory effect on all receptors, while other structures exert opposite effects on different receptors or in different cellular contexts. In light of the crucial role played by glycosylation in the regulation of receptor activity, the development of next-generation drugs targeting glyco-epitopes of growth factor receptors should be considered a therapeutically interesting goal.

Enriching plausible new hypothesis generation in PubMed

Background

Most of earlier studies in the field of literature-based discovery have adopted Swanson's ABC model that links pieces of knowledge entailed in disjoint literatures. However, the issue concerning their practicability remains to be solved since most of them did not deal with the context surrounding the discovered associations and usually not accompanied with clinical confirmation. In this study, we aim to propose a method that expands and elaborates the existing hypothesis by advanced text mining techniques for capturing contexts. We extend ABC model to allow for multiple B terms with various biological types.

Results

We were able to concretize a specific, metabolite-related hypothesis with abundant contextual information by using the proposed method. Starting from explaining the relationship between lactosylceramide and arterial stiffness, the hypothesis was extended to suggest a potential pathway consisting of lactosylceramide, nitric oxide, malondialdehyde, and arterial stiffness. The experiment by domain experts showed that it is clinically valid.

Conclusions

The proposed method is designed to provide plausible candidates of the concretized hypothesis, which are based on extracted heterogeneous entities and detailed relation information, along with a reliable ranking criterion. Statistical tests collaboratively conducted with biomedical experts provide the validity and practical usefulness of the method unlike previous studies. Applying the proposed method to other cases, it would be helpful for biologists to support the existing hypothesis and easily expect the logical process within it.

Associations between metabolomic-identified changes of biomarkers and arterial stiffness in subjects progressing to impaired fasting glucose

OBJECTIVE

We investigated correlations between age-related changes in circulating metabolites and arterial stiffness in impaired fasting glucose (IFG).

DESIGN, SUBJECTS, MEASUREMENT

This prospective cohort study included 602 healthy, normal fasting glucose (NFG) subjects (30-65 years old) who underwent triennial medical evaluation. After 3 years, 9·3% of subjects developed IFG (n = 56). Age, gender, BMI and fasting glucose were used to match the remaining NFG subjects (n = 546) that were included for the control group (NFG group, n = 80).

RESULTS

After 3 years, levels of fasting glucose, insulin and malondialdehyde, and brachial-ankle pulse wave velocity (baPWV) were significantly greater in the IFG group than in the NFG group after adjusting for baseline values. The IFG group had a greater increase in lactosylceramide (P = 0·001, q < 0·05) and a greater reduction in phosphatidylcholine (PC) (18:0/20:4) than the NFG group. Multiple linear regression analysis showed that the change in baPWV was independently and positively associated with changes in fasting glucose and lactosylceramide. In all subjects, lactosylceramide levels positively correlated with changes in baPWV and fasting glucose, while premenopausal women were not shown, and negatively correlated with changes in PC and LDL particle size.

CONCLUSIONS

This study indicates that age-related increase in circulating lactosylceramide is an independent predictor of increased arterial stiffness in subjects with impaired fasting glucose.

Glycosphingolipids are modulators of disease pathogenesis in amyotrophic lateral sclerosis

Recent genetic evidence suggests that aberrant glycosphingolipid metabolism plays an important role in several neuromuscular diseases including hereditary spastic paraplegia, hereditary sensory neuropathy type 1, and non-5q spinal muscular atrophy. Here, we investigated whether altered glycosphingolipid metabolism is a modulator of disease course in amyotrophic lateral sclerosis (ALS). Levels of ceramide, glucosylceramide, galactocerebroside, lactosylceramide, globotriaosylceramide, and the gangliosides GM3 and GM1 were significantly elevated in spinal cords of ALS patients. Moreover, enzyme activities (glucocerebrosidase-1, glucocerebrosidase-2, hexosaminidase, galactosylceramidase, α-galactosidase, and β-galactosidase) mediating glycosphingolipid hydrolysis were also elevated up to threefold. Increased ceramide, glucosylceramide, GM3, and hexosaminidase activity were also found in SOD1(G93A) mice, a familial model of ALS. Inhibition of glucosylceramide synthesis accelerated disease course in SOD1(G93A) mice, whereas infusion of exogenous GM3 significantly slowed the onset of paralysis and increased survival. Our results suggest that glycosphingolipids are likely important participants in pathogenesis of ALS and merit further analysis as potential drug targets.

Improved intervention of atherosclerosis and cardiac hypertrophy through biodegradable polymer-encapsulated delivery of glycosphingolipid inhibitor

D-Threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (D-PDMP), a glycosphingolipid synthesis inhibitor, holds promise for the treatment of atherosclerosis and cardiac hypertrophy but rapid in vivo clearance has severely hindered translation to the clinic. To overcome this impediment, we used a materials-based delivery strategy wherein D-PDMP was encapsulated within a biodegradable polymer composed of poly ethylene glycol (PEG) and sebacic acid (SA). PEG-SA was formulated into nanoparticles that were doped with (125)I-labeled PEG to allow in vivo bio-distribution and release kinetics of D-PDMP to be determined by using γ-scintigraphy and subsequently, by mass spectrometry. Polymer-encapsulation increased the residence time of D-PDMP in the body of a treated mouse from less than one hour to at least four hours (and up to 48 h or longer). This substantially increased in vivo longevity provided by polymer encapsulation resulted in an order of magnitude gain in efficacy for interfering with atherosclerosis and cardiac hypertrophy in apoE-/- mice fed a high fat and high cholesterol (HFHC) diet. These results establish that D-PDMP encapsulated in a biodegradable polymer provides a superior mode of delivery compared to unconjugated D-PDMP by way of increased gastrointestinal absorption and increased residence time thus providing this otherwise rapidly cleared compound with therapeutic relevance in interfering with atherosclerosis, cardiac hypertrophy, and probably other diseases associated with the deleterious effects of abnormally high glycosphingolipid biosynthesis or deficient catabolism.

Association between arterial stiffness and serum L-octanoylcarnitine and lactosylceramide in overweight middle-aged subjects: 3-year follow-up study

Existing data on the association between being overweight and cardiovascular morbidity and mortality risk in adults are inconsistent. We prospectively and longitudinally investigated the effects of weight on arterial stiffness and plasma metabolites in middle-aged subjects (aged 40–55 years). A group of 59 individuals who remained within the range of overweight during repeated measurements over a 3-year period was compared with a control group of 59 normal weight subjects who were matched for age and gender. Changes in metabolites by UPLC-LTQ-Orbitrap mass spectrometry and changes in brachial-ankle pulse wave velocity (ba-PWV) were examined. At baseline, the overweight group showed higher BMI, waist circumference, triglyceride, free fatty acid (FFA), glucose, insulin, and hs-CRP, and lower HDL-cholesterol than controls. After 3 years, the changes in waist circumference, diastolic and systolic blood pressure (DBP and SBP), triglyceride, FFA, glucose, insulin, hs-CRP, and ba-PWV observed in the overweight group were significantly different from those in the control group after adjusting for baseline levels. Furthermore, the overweight group showed greater increases in L-octanoylcarnitine (q=0.006) and decanoylcarnitine (q=0.007), and higher peak intensities of L-leucine, L-octanoylcarnitine, and decanoylcarnitine. Multiple linear regression analysis showed that the change in ba-PWV was independently and positively associated with changes in L-octanoylcarnitine, lactosylceramide, and SBP, and with baseline BMI. Our results indicate that the duration of overweight is an important aggravating factor for arterial stiffness, especially during middle age. Additionally, an age-related increase in plasma L-octanoylcarnitine, lactosylceramide, SBP, and baseline BMI are independent predictors of increased arterial stiffness in middle-aged individuals.

Inhibition of tumor angiogenesis by globotriaosylceramide immunotargeting

Current antiangiogenic immunotherapeutic strategies mainly focus on the blockade of circulating cytokines or receptors that are overexpressed by endothelial cells. We proposed globotriaosylceramide (Gb3) as a viable alternative target for antiangiogenic therapies. In this setting, we developed an anti-Gb3 antibody and validated its therapeutic efficacy in metastatic tumor models.

Glycoconjugates and related molecules in human vascular endothelial cells

Vascular endothelial cells (ECs) form the inner lining of blood vessels. They are critically involved in many physiological functions, including control of vasomotor tone, blood cell trafficking, hemostatic balance, permeability, proliferation, survival, and immunity. It is considered that impairment of EC functions leads to the development of vascular diseases. The carbohydrate antigens carried by glycoconjugates (e.g., glycoproteins, glycosphingolipids, and proteoglycans) mainly present on the cell surface serve not only as marker molecules but also as functional molecules. Recent studies have revealed that the carbohydrate composition of the EC surface is critical for these cells to perform their physiological functions. In this paper, we consider the expression and functional roles of endogenous glycoconjugates and related molecules (galectins and glycan-degrading enzymes) in human ECs.

Highly angiogenic CXCR4(+)CD31(+) monocyte subset derived from 3D culture of human peripheral blood

Ex vivo expansion of human circulating angiogenic cells is a major challenge in autologous cell therapy for ischemic diseases. Here, we demonstrate that hematosphere-derived CXCR4(+)CD31(+) myeloid cells using peripheral blood possess robust proangiogenic capacity such as formation of vessel-like structures and tip cell-like morphology in Matrigel. We also found that CD31 positive myeloid cells are principal cellular component of hematospheres by magnetic cell sorting. Flow cytometry analysis showed that fresh peripheral blood contained 40.3 ± 15.2% of CXCR4(+)CD31(+) myeloid cells, but at day 5 of hematosphere culture, most of myeloid cells were CXCR4(+)CD31(+) by 86.9 ± 5.4%. Hematosphere culture significantly increased the production of angiogenic niche-supporting cytokines. Moreover, CD31-homophilic interaction and VEGF-VEGF receptor loop signaling were essential for sphere formation and acquisition of angiogenic capacity in hematospheres. Matrigel plug and ischemic hindlimb model provide in vivo evidence that hematosphere-derived myeloid cells have highly vasculogenic capacities, participate in new and mature vessel formation, and exert therapeutic effects on ischemic hindlimb. In conclusion, our strategy for ex vivo expansion of human CXCR4(+)CD31(+) angiogenic cells using hematospheres provides an autologous therapeutic cell source for ischemic diseases and a new model for investigating the microenvironment of angiogenesis.

Use of a glycolipid inhibitor to ameliorate renal cancer in a mouse model

In a xenograft model wherein, live renal cancer cells were implanted under the kidney capsule in mice, revealed a 30-fold increase in tumor volume over a period of 26 days and this was accompanied with a 32-fold increase in the level of lactosylceramide (LacCer). Mice fed D- threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (D-PDMP), an inhibitor of glucosylceramide synthase and lactosylceramide synthase (LCS: β-1,4-GalT-V), showed marked reduction in tumor volume. This was accompanied by a decrease in the mass of lactosylceramide and an increase in glucosylceramide (GlcCer) level. Mechanistic studies revealed that D-PDMP inhibited cell proliferation and angiogenesis by inhibiting p44MAPK, p-AKT-1 pathway and mammalian target for rapamycin (mTOR). By linking glycosphingolipid synthesis with tumor growth, renal cancer progression and regression can be evaluated. Thus inhibiting glycosphingolipid synthesis can be a bonafide target to prevent the progression of other types of cancer.

Inhibition of de novo ceramide biosynthesis by FTY720 protects rat retina from light-induced degeneration

Light-induced retinal degeneration (LIRD) in albino rats causes apoptotic photoreceptor cell death. Ceramide is a second messenger for apoptosis. We tested whether increases in ceramide mediate photoreceptor apoptosis in LIRD and if inhibition of ceramide synthesis protects the retina. Sprague-Dawley rats were exposed to 2,700 lux white light for 6 h, and the retinal levels of ceramide and its intermediary metabolites were measured by GC-MS or electrospray ionization tandem mass spectrometry. Enzymes of the de novo biosynthetic and sphingomyelinase pathways of ceramide generation were assayed, and gene expression was measured. The dosage and temporal effect of the ceramide synthase inhibitor FTY720 on the LIRD retina were measured by histological and functional analyses. Retinal ceramide levels increased coincident with the increase of dihydroceramide at various time points after light stress. Light stress in retina induces ceramide generation predominantly through the de novo pathway, which was prevented by systemic administration of FTY720 (10 mg/kg) leading to the protection of retinal structure and function. The neuroprotection of FTY720 was independent of its immunosuppressive action. We conclude that ceramide increase by de novo biosynthesis mediates photoreceptor apoptosis in the LIRD model and that inhibition of ceramide production protects the retina against light stress.

The role of immunoglobulin superfamily cell adhesion molecules in cancer metastasis

Metastasis is a major clinical problem and results in a poor prognosis for most cancers. The metastatic pathway describes the process by which cancer cells give rise to a metastatic lesion in a new tissue or organ. It consists of interconnecting steps all of which must be successfully completed to result in a metastasis. Cell-cell adhesion is a key aspect of many of these steps. Adhesion molecules belonging to the immunoglobulin superfamily (Ig-SF) commonly play a central role in cell-cell adhesion, and a number of these molecules have been associated with cancer progression and a metastatic phenotype. Surprisingly, the contribution of Ig-SF members to metastasis has not received the attention afforded other cell adhesion molecules (CAMs) such as the integrins. Here we examine the steps in the metastatic pathway focusing on how the Ig-SF members, melanoma cell adhesion molecule (MCAM), L1CAM, neural CAM (NCAM), leukocyte CAM (ALCAM), intercellular CAM-1 (ICAM-1) and platelet endothelial CAM-1 (PECAM-1) could play a role. Although much remains to be understood, this review aims to raise the profile of Ig-SF members in metastasis formation and prompt further research that could lead to useful clinical outcomes.

Effects of erythropoietin on ICAM-1 and PECAM-1 expressions on human umbilical vein endothelial cells subjected to oxidative stress

The protective effect of erythropoietin (Epo) is based on its ability to reduce oxidation and to stabilize the cells. The aim of the study was to evaluate the influence of Epo on malonyl dialdehyde (MDA), intercellular adhesion molecule-1 (ICAM-1) (CD54) and platelet-endothelial cell adhesion molecule-1 (PECAM-1) (CD31) levels on human umbilical vein endothelial cells (HUVECs) stimulated by tumour necrosis factor-α (TNF-α). HUVECs were incubated with Epo (10-40 IU ml⁻¹) or TNF-α (10-40 ng ml⁻¹) alone or preincubated with Epo (20 IU ml⁻¹) and subsequently stimulated with TNF-α (10-40 ng ml⁻¹). MDA concentrations were measured using the high-performance liquid chromatography, whereas ICAM-1 and PECAM-1 expressions were evaluated by flow cytometry. Incubation with Epo resulted in a decrease in MDA and the increased expressions of ICAM-1 and PECAM-1. Exposure to TNF-α reflected an increase in MDA, ICAM-1 and PECAM-1 levels. These changes were inhibited by preincubation with Epo. The cytoprotective activity proven in this study points to new applications and therapeutic possibilities for Epo.

Elastin peptides signaling relies on neuraminidase-1-dependent lactosylceramide generation

The sialidase activity of neuraminidase-1 (Neu-1) is responsible for ERK 1/2 pathway activation following binding of elastin peptide on the elastin receptor complex. In this work, we demonstrate that the receptor and lipid rafts colocalize at the plasma membrane. We also show that the disruption of these microdomains as well as their depletion in glycolipids blocks the receptor signaling. Following elastin peptide treatment, the cellular GM₃ level decreases while lactosylceramide (LacCer) content increases consistently with a GM₃/LacCer conversion. The use of lactose or Neu-1 siRNA blocks this process suggesting that the elastin receptor complex is responsible for this lipid conversion. Flow cytometry analysis confirms this elastin peptide-driven LacCer generation. Further, the use of a monoclonal anti-GM₃ blocking antibody shows that GM₃ is required for signaling. In conclusion, our data strongly suggest that Neu-1-dependent GM₃/LacCer conversion is the key event leading to signaling by the elastin receptor complex. As a consequence, we propose that LacCer is an early messenger for this receptor.

Transmembrane BAX inhibitor motif containing (TMBIM) family proteins perturbs a trans-Golgi network enzyme, Gb3 synthase, and reduces Gb3 biosynthesis

Globotriaosylceramide (Gb3) is a well known receptor for Shiga toxin (Stx), produced by enterohemorrhagic Escherichia coli and Shigella dysenteriae. The expression of Gb3 also affects several diseases, including cancer metastasis and Fabry disease, which prompted us to look for factors involved in its metabolism. In the present study, we isolated two cDNAs that conferred resistance to Stx-induced cell death in HeLa cells by expression cloning: ganglioside GM3 synthase and the COOH terminus region of glutamate receptor, ionotropic, N-methyl-D-asparate-associated protein 1 (GRINA), a member of the transmembrane BAX inhibitor motif containing (TMBIM) family. Overexpression of the truncated form, named GRINA-C, and some members of the full-length TMBIM family, including FAS inhibitory molecule 2 (FAIM2), reduced Gb3, and lactosylceramide was accumulated instead. The change of glycolipid composition was restored by overexpression of Gb3 synthase, suggesting that the synthase is affected by GRINA-C and FAIM2. Interestingly, the mRNA level of Gb3 synthase was unchanged. Rather, localization of the synthase as well as TGN46, a trans-Golgi network marker, was perturbed to form punctate structures, and degradation of the synthase in lysosomes was enhanced. Furthermore, GRINA-C was associated with Gb3 synthase. These observations may demonstrate a new type of posttranscriptional regulation of glycosyltransferases.

Beta4-galactosyltransferase-5 is a lactosylceramide synthase essential for mouse extra-embryonic development

Glycosphingolipids (GSLs) are important for various biological functions in the nervous system, the immune system, embryogenesis and in other tissues and processes. Lactosylceramide (LacCer), which is synthesized from glucosylceramide (GlcCer) by LacCer synthase, is a core structure of GSLs, including gangliosides. LacCer synthase was reported to be synthesized by the beta4-galactosyltransferase-6 (beta4GalT-6) gene in the rat brain. However, the existence of another LacCer synthase gene was shown in cultured cells lacking beta4GalT-6. Here, we report that LacCer synthase is mainly synthesized by the beta4GalT-5 gene during early mouse embryogenesis, and its disruption is embryonic lethal. beta4GalT-5-deficient embryos showed developmental retardation from E7.5 and died by E10.5 as reported previously. LacCer synthase activity was significantly reduced in beta4GalT-5-deficient embryos and extra-embryonic endoderm (XEN) cells derived from blastocysts, and it was recovered when beta4GalT-5 cDNA was introduced into beta4GalT-5-deficient XEN cells. The amounts of LacCer and GM3 ganglioside were drastically reduced, while GlcCer accumulated in the beta4GalT-5-deficient XEN cells. Hematoma and ectopically accumulated trophoblast giant cells were observed in the anti-mesometrial pole of the extra-embryonic tissues, although all three embryonic layers formed. beta4GalT-5-deficient embryos developed until E12.5 as chimeras with wild-type tetraploid cells, which formed the extra-embryonic membranes, indicating that extra-embryonic defects caused the early embryonic lethality. Our results suggest that beta4GalT-5 is essential for extra-embryonic development during early mouse embryogenesis.

Specific saposin C deficiency: CNS impairment and acid beta-glucosidase effects in the mouse

Saposins A, B, C and D are derived from a common precursor, prosaposin (psap). The few patients with saposin C deficiency develop a Gaucher disease-like central nervous system (CNS) phenotype attributed to diminished glucosylceramide (GC) cleavage activity by acid β-glucosidase (GCase). The in vivo effects of saposin C were examined by creating mice with selective absence of saposin C (C−/−) using a knock-in point mutation (cysteine-to-proline) in exon 11 of the psap gene. In C−/− mice, prosaposin and saposins A, B and D proteins were present at near wild-type levels, but the saposin C protein was absent. By 1 year, the C−/− mice exhibited weakness of the hind limbs and progressive ataxia. Decreased neuromotor activity and impaired hippocampal long-term potentiation were evident. Foamy storage cells were observed in dorsal root ganglion and there was progressive loss of cerebellar Purkinje cells and atrophy of cerebellar granule cells. Ultrastructural analyses revealed inclusions in axonal processes in the spinal cord, sciatic nerve and brain, but no excess of multivesicular bodies. Activated microglial cells and astrocytes were present in thalamus, brain stem, cerebellum and spinal cord, indicating regional pro-inflammatory responses. No storage cells were found in visceral organs of these mice. The absence of saposin C led to moderate increases in GC and lactosylceramide (LacCer) and their deacylated analogues. These results support the view that saposin C has multiple roles in glycosphingolipid (GSL) catabolism as well as a prominent function in CNS and axonal integrity independent of its role as an optimizer/stabilizer of GCase.

VEGF recruits lactosylceramide to induce endothelial cell adhesion molecule expression and angiogenesis in vitro and in vivo

Angiogenesis is largely driven by vascular endothelial growth factor (VEGF). However, the role of lipid second messengers such as lactosylceramide (LacCer) and LacCer synthase in angiogenesis is not well understood. We have determined the distribution of various LacCer synthase mRNA transcripts using sequential analysis of gene expression (SAGE). Endothelial cells from colon cancer tissues had a 4.5-fold increase in a LacCer synthase transcript (beta1,4GalT-V) as compared to normal colon tissue endothelial cells. Consequently, our focus turned to understanding the role of this enzyme in regulating VEGF-induced angiogenesis in vitro and in vivo. Herein, we show that in human endothelial cells, VEGF-induced angiogenesis is mitigated by dimethylsphingosine and suramin; inhibitors of sphingosine kinase 1(SphK-1) and sphingosine1-phosphate receptor 1(S1P (1)), respectively, and this were bypassed by LacCer but not by S1P. VEGF and basic fibroblast growth factor-induced angiogenesis was mitigated by PDMP; an inhibitor of glucosylceramide synthase and LacCer synthase in human umbilical vein endothelial cells (HUVEC) and human aortic endothelial cells (HAEC). Likewise, GalT-V gene ablation using corresponding siRNA also mitigated VEGF-induced angiogenesis. In Matrigel plug angiogenesis assay in nude mice, angiogenesis was markedly inhibited by D-PDMP with concordantly diminished LacCer synthase activity. Mechanistic studies revealed that the use of LY294002, a PI3 kinase inhibitor, mitigated VEGF-induced expression of platelet-endothelial cell adhesion molecule (PECAM-1/CD31); the trans-endothelial migration of a monocyte cell line (U-937) and angiogenesis in HAEC cells. Since this enzyme is a target for VEGF action and LacCer serves as a lipid second messenger in inducing angiogenesis in vitro and in vivo, novel therapeutic approaches may be developed using our findings to mitigate colon cancer.

C(6)-Ceramide-Coated Catheters Promote Re-Endothelialization of Stretch-Injured Arteries

OBJECTIVE: Drug eluting stents have recently been associated with the increased risk of adverse thrombogenic events and/or late luminal loss, which is highly associated with incomplete re-endothelialization. The increased risks behoove the design of alternative delivery modalities and/or drugs that do not compromise the re-endotheliaization process. The objective of the present study is to elucidate the biological mechanism(s) by which non-stent-based delivery modalities for the anti-proliferative lipid metabolite, C(6)-ceramide, could lead to a reduction in arterial injury after angioplasty. RESULTS: Immunohistochemical studies in rabbit and porcine models suggest that C(6)-ceramide-coated balloon catheters limit arterial stenosis without inhibiting endothelial wound healing responses. Specifically, C(6)-ceramide-coated balloon catheters reduce internal elastica injury with a corresponding reduction in medial fracture length in a 28-day porcine coronary artery stretch model. In addition, C(6)-ceramide decreases the formation of the fibrin matrix to possibly augment the subsequent wound healing response. We hypothesized that differential metabolism of exogenous ceramide by coronary endothelial and smooth muscle cells could explain the apparent discrepancy between the anti-proliferative actions of ceramide and the pro-wound healing responses of ceramide. Human coronary artery endothelial cells (HCAEC), in contrast to human coronary artery smooth muscle cells (HCASMC), preferentially express ceramide kinase and form ceramide-1-phosphate, which promotes endothelial cell survival. CONCLUSION: Differential metabolism of ceramide between HCASMC and HCAEC offers a mechanism by which ceramide preferentially limits smooth muscle cell growth, in the presence of active wound healing. The combinatorial ability of ceramide to limit vascular smooth muscle proliferation and promote re-endothelialization, offers the potential for C(6)-ceramide-coated catheters to serve as adjuncts to stent-based modalities or as a stand-alone treatment.

Aminopeptidase O contains a functional nucleolar localization signal and is implicated in vascular biology

We have identified a gene trap integration into Aminopeptidase O, the gene encoding a member of the M1 family of metalloproteases. Using the betagal reporter of the gene trap vector, we have revealed that at least some ApO isoforms are expressed predominantly in embryonic and adult blood vessels leading us to propose that ApO plays a role in vascular cell biology. The protein produced from an engineered Gfp-ApO fusion cDNA localises to the nucleolus in transfected COS7 cells. We confirm that indeed the APO protein contains a functional nucleolar localisation domain by demonstrating that GFP-APO fusion proteins that lack the predicted nucleolar localisation signal are retained in the cytoplasm. We report the existence of multiple alternatively spliced Apo isoforms that differ with respect to the presence of exons encoding important functional domains. Alternative splicing predictably produces protein products with or without the catalytic domain and/or a nucleolar localisation signal and therefore likely represents an important mechanism in regulating the biological activity of APO that has been reported to cleave one of the peptides of the renin angiotensin pathway.

Lipid second messengers and cell signaling in vascular wall

Agonists of cellular receptors, such as receptor tyrosine kinases, G protein-coupled receptors, cytokine receptors, etc., activate phospholipases (C(gamma), C(beta), A(2), D), sphingomyelinase, and phosphatidylinositol-3-kinase. This produces active lipid metabolites, some of which are second messengers: inositol trisphosphate, diacylglycerides, ceramide, and phosphatidylinositol 3,4,5-trisphosphate. These universal mechanisms are involved in signal transduction to maintain blood vessel functions: regulation of vasodilation and vasoconstriction, mechanical stress resistance, and anticoagulant properties of the vessel lumen surface. Different signaling pathways realized through lipid second messengers interact to one another and modulate intracellular events. In early stages of atherogenesis, namely, accumulation of low density lipoproteins in the vascular wall, cascades of pro-atherogenic signal transduction are triggered through lipid second messengers. This leads to atherosclerosis, the general immuno-inflammatory disease of the vascular system.

Poly(ADP-ribose)polymerase inhibition decreases angiogenesis

Inhibitors of poly(ADP-ribose)polymerase (PARP), a nuclear enzyme involved in regulating cell death and cellular responses to DNA repair, show considerable promise in the treatment of cancer both in monotherapy as well as in combination with chemotherapeutic agents and radiation. We have recently demonstrated that PARP inhibition with 3-aminobenzamide or PJ-34 reduced vascular endothelial growth factor (VEGF)-induced proliferation, migration, and tube formation of human umbilical vein endothelial cells (HUVECs) in vitro. Here, we show dose-dependent reduction of VEGF- and basic fibroblast growth factor (bFGF)-induced proliferation, migration, and tube formation of HUVECs in vitro by two potent PARP inhibitors 5-aminoisoquinolinone-hydrochloride (5-AIQ) and 1,5-isoquinolinediol (IQD). Moreover, PARP inhibitors prevented the sprouting of rat aortic ring explants in an ex vivo assay of angiogenesis. These results establish the novel concept that PARP inhibitors have antiangiogenic effects, which may have tremendous clinical implications for the treatment of various cancers, tumor metastases, and certain retinopathies.

Pharmacological inhibition of poly(ADP-ribose) polymerase inhibits angiogenesis

Poly(ADP-ribose) polymerase (PARP) is a nuclear enzyme which plays an important role in regulating cell death and cellular responses to DNA repair. Pharmacological inhibitors of PARP are being considered as treatment for cancer both in monotherapy as well as in combination with chemotherapeutic agents and radiation, and were also reported to be protective against untoward effects exerted by certain anticancer drugs. Here we show that pharmacological inhibition of PARP with 3-aminobenzamide or PJ-34 dose-dependently reduces VEGF-induced proliferation, migration, and tube formation of human umbilical vein endothelial cells in vitro. These results suggest that treatment with PARP inhibitors may exert additional benefits in various cancers and retinopathies by decreasing angiogenesis.