Lactosylceramide recruits PKCalpha/epsilon and phospholipase A2 to stimulate PECAM-1 expression in human monocytes and adhesion to endothelial cells

SPTLC3 Is Essential for Complex I Activity and Contributes to Ischemic Cardiomyopathy

BACKGROUND

Dysregulated metabolism of bioactive sphingolipids, including ceramides and sphingosine-1-phosphate, has been implicated in cardiovascular disease, although the specific species, disease contexts, and cellular roles are not completely understood. Sphingolipids are produced by the serine palmitoyltransferase enzyme, canonically composed of 2 subunits, SPTLC1 (serine palmitoyltransferase long chain base subunit 1) and SPTLC2 (serine palmitoyltransferase long chain base subunit 2). Noncanonical sphingolipids are produced by a more recently described subunit, SPTLC3 (serine palmitoyltransferase long chain base subunit 3).

METHODS

The noncanonical (d16) and canonical (d18) sphingolipidome profiles in cardiac tissues of patients with end-stage ischemic cardiomyopathy and in mice with ischemic cardiomyopathy were analyzed by targeted lipidomics. Regulation of SPTLC3 by HIF1α under ischemic conditions was determined with chromatin immunoprecipitation. Transcriptomics, lipidomics, metabolomics, echocardiography, mitochondrial electron transport chain, mitochondrial membrane fluidity, and mitochondrial membrane potential were assessed in the cSPTLC3KO transgenic mice we generated. Furthermore, morphological and functional studies were performed on cSPTLC3KO mice subjected to permanent nonreperfused myocardial infarction.

RESULTS

Herein, we report that SPTLC3 is induced in both human and mouse models of ischemic cardiomyopathy and leads to production of atypical sphingolipids bearing 16-carbon sphingoid bases, resulting in broad changes in cell sphingolipid composition. This induction is in part attributable to transcriptional regulation by HIF1α under ischemic conditions. Furthermore, cardiomyocyte-specific depletion of SPTLC3 in mice attenuates oxidative stress, fibrosis, and hypertrophy in chronic ischemia, and mice demonstrate improved cardiac function and increased survival along with increased ketone and glucose substrate metabolism utilization. Depletion of SPTLC3 mechanistically alters the membrane environment and subunit composition of mitochondrial complex I of the electron transport chain, decreasing its activity.

CONCLUSIONS

Our findings suggest a novel essential role for SPTLC3 in electron transport chain function and a contribution to ischemic injury by regulating complex I activity.

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.

Sphingolipid Profiling: A Promising Tool for Stratifying the Metabolic Syndrome-Associated Risk

Metabolic syndrome (MetS) is a multicomponent risk condition that reflects the clustering of individual cardiometabolic risk factors related to abdominal obesity and insulin resistance. MetS increases the risk for cardiovascular diseases (CVD) and type 2 diabetes mellitus (T2DM). However, there still is not total clinical consensus about the definition of MetS, and its pathophysiology seems to be heterogeneous. Moreover, it remains unclear whether MetS is a single syndrome or a set of diverse clinical conditions conferring different metabolic and cardiovascular risks. Indeed, traditional biomarkers alone do not explain well such heterogeneity or the risk of associated diseases. There is thus a need to identify additional biomarkers that may contribute to a better understanding of MetS, along with more accurate prognosis of its various chronic disease risks. To fulfill this need, omics technologies may offer new insights into associations between sphingolipids and cardiometabolic diseases. Particularly, ceramides –the most widely studied sphingolipid class– have been shown to play a causative role in both T2DM and CVD. However, the involvement of simple glycosphingolipids remains controversial. This review focuses on the current understanding of MetS heterogeneity and discuss recent findings to address how sphingolipid profiling can be applied to better characterize MetS-associated risks.

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.

Glycosphingolipid-associated β-1,4 galactosyltransferase is elevated in patients with systemic lupus erythematosus

OBJECTIVE

β-1,4 galactosyltransferase-V (β-1,4 GalT-V) is an enzyme that synthesises a glycosphingolipid known as lactosylceramide, which has been implicated in general inflammation and atherosclerosis. We asked if β-1,4 GalT-V was present at elevated levels in patients with SLE, a disease which is associated with increased risk of atherosclerosis.

METHODS

In this case-control observational study, serum samples were obtained from patients with SLE who are part of the Johns Hopkins Lupus Cohort. Control serum samples were obtained from healthy adult community members recruited from the Baltimore area. All serum samples (n=50 in the SLE group and n=50 in the healthy control group) were analysed with enzyme-linked immunoassays. These assays used antibodies raised against antigens that enabled us to measure the absorbance of oxidised phosphocholines per apolipoprotein B-100 (ox-PC/apoB) and the concentration of lipoprotein(a) (Lp(a)) and β-1,4 GalT-V.

RESULTS

Absorbance of ox-PC/apoB and concentrations of Lp(a) and β-1,4 GalT-V were significantly higher in the SLE serum samples as compared with the control serum (p<0.0001).

CONCLUSIONS

We conclude that patients with SLE have elevated levels of β-1,4 GalT-V and ox-PC, which have previously been recognised as risk factors 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.

Lysosome (Dys)function in Atherosclerosis-A Big Weight on the Shoulders of a Small Organelle

Atherosclerosis is a progressive insidious chronic disease that underlies most of the cardiovascular pathologies, including myocardial infarction and ischemic stroke. The malfunctioning of the lysosomal compartment has a central role in the etiology and pathogenesis of atherosclerosis. Lysosomes are the degradative organelles of mammalian cells and process endogenous and exogenous substrates in a very efficient manner. Dysfunction of these organelles and consequent inefficient degradation of modified low-density lipoproteins (LDL) and apoptotic cells in atherosclerotic lesions have, therefore, numerous deleterious consequences for cellular homeostasis and disease progression. Lysosome dysfunction has been mostly studied in the context of the inherited lysosomal storage disorders (LSDs). However, over the last years it has become increasingly evident that the consequences of this phenomenon are more far-reaching, also influencing the progression of multiple acquired human pathologies, such as neurodegenerative diseases, cancer, and cardiovascular diseases (CVDs). During the formation of atherosclerotic plaques, the lysosomal compartment of the various cells constituting the arterial wall is under severe stress, due to the tremendous amounts of lipoproteins being processed by these cells. The uncontrolled uptake of modified lipoproteins by arterial phagocytic cells, namely macrophages and vascular smooth muscle cells (VSMCs), is the initial step that triggers the pathogenic cascade culminating in the formation of atheroma. These cells become pathogenic "foam cells," which are characterized by dysfunctional lipid-laden lysosomes. Here, we summarize the current knowledge regarding the origin and impact of the malfunctioning of the lysosomal compartment in plaque cells. We further analyze how the field of LSD research may contribute with some insights to the study of CVDs, particularly how therapeutic approaches that target the lysosomes in LSDs could be applied to hamper atherosclerosis progression and associated mortality.

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.

Aortic Gene Expression Profiles Show How ApoA-I Levels Modulate Inflammation, Lysosomal Activity, and Sphingolipid Metabolism in Murine Atherosclerosis

OBJECTIVE

HDL (high-density lipoprotein) particles are known to possess several antiatherogenic properties that include the removal of excess cholesterol from peripheral tissues, the maintenance of endothelial integrity, antioxidant, and anti-inflammatory activities. ApoA-I overexpression in apoE-deficient (EKO) mice has been shown to increase HDL levels and to strongly reduce atherosclerosis development. The aim of the study was to investigate gene expression patterns associated with atherosclerosis development in the aorta of EKO mice and how HDL plasma levels relate to gene expression patterns at different stages of atherosclerosis development and with different dietary treatments. Approach and Results: Eight-week-old EKO mice, EKO mice overexpressing human apoA-I, and wild-type mice as controls were fed either normal laboratory or Western diet for 6 or 22 weeks. Cholesterol distribution among lipoproteins was evaluated, and atherosclerosis of the aorta was quantified. High-throughput sequencing technologies were used to analyze the transcriptome of the aorta of the 3 genotypes in each experimental condition. In addition to the well-known activation of inflammation and immune response, the impairment of sphingolipid metabolism, phagosome-lysosome system, and osteoclast differentiation emerged as relevant players in atherosclerosis development. The reduced atherosclerotic burden in the aorta of EKO mice expressing high levels of apoA-I was accompanied by a reduced activation of immune system markers, as well as reduced perturbation of lysosomal activity and a better regulation of the sphingolipid synthesis pathway.

CONCLUSIONS

ApoA-I modulates atherosclerosis development in the aorta of EKO mice affecting the expression of pathways additional to those associated with inflammation and immune response.

Indomethacin reduces rates of aortic dissection and rupture of the abdominal aorta by inhibiting monocyte/macrophage accumulation in a murine model

Aortic dissection is a life-threatening condition, which is characterised by separation of the constituent layers of the aortic wall. We have recently shown that monocyte/macrophage infiltration into the aortic wall is a pathogenic mechanism of the condition. In the present study, we investigated whether the anti-inflammatory agent, indomethacin, could inhibit monocyte/macrophage accumulation in the aortic wall and ensuing dissection. Indomethacin was administered (from 3 days prior with daily oral administration) to mice in which aortic dissection was induced using beta-aminopropionitrile (BAPN) and angiotensin II (Ang II) infusion (2 weeks). Indomethacin prevented death from abdominal aortic dissection and decreased incidence of aortic dissection by as high as 40%. Histological and flow cytometry analyses showed that indomethacin administration resulted in inhibition of monocyte transendothelial migration and monocyte/macrophage accumulation in the aortic wall. These results indicate that indomethacin administration reduces rate of onset of aortic dissection in a murine model of the condition.

Potential therapeutic targets for atherosclerosis in sphingolipid metabolism

Sphingolipids, such as sphingomyelins, ceramides, glycosphingolipids, and sphingosine-1-phosphates (S1P) are a large group of structurally and functionally diverse molecules. Some specific species are found associated with atherogenesis and provide novel therapeutic targets. Herein, we briefly review how sphingolipids are implicated in the progression of atherosclerosis and related diseases, and then we discuss the potential therapy options by targetting several key enzymes in sphingolipid metabolism.

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.

Inhibition of glycosphingolipid synthesis reverses skin inflammation and hair loss in ApoE-/- mice fed western diet

Sphingolipids have been accorded numerous biological functions however, the effects of feeding a western diet (diet rich in cholesterol and fat) on skin phenotypes, and color is not known. Here, we observed that chronic high-fat and high-cholesterol diet intake in a mouse model of atherosclerosis (ApoE-/-) decreases the level of ceramides and glucosylceramide. At the expense of increased levels of lactosylceramide due to an increase in the expression of lactosylceramide synthase (GalT-V). This is accompanied with neutrophil infiltration into dermis, and enrichment of tumor necrosis factor-stimulated gene-6 (TSG-6) protein. This causes skin inflammation, hair discoloration and loss, in ApoE-/- mice. Conversely, inhibition of glycosphingolipid synthesis, by D-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (D-PDMP), unbound or encapsulated in a biodegradable polymer (BPD) reversed these phenotypes. Thus, inhibition of glycosphingolipid synthesis represents a unique therapeutic approach relevant to human skin and hair Biology.

Protein kinase C and cardiac dysfunction: a review

Heart failure (HF) is a physiological state in which cardiac output is insufficient to meet the needs of the body. It is a clinical syndrome characterized by impaired ability of the left ventricle to either fill or eject blood efficiently. HF is a disease of multiple aetiologies leading to progressive cardiac dysfunction and it is the leading cause of deaths in both developed and developing countries. HF is responsible for about 73,000 deaths in the UK each year. In the USA, HF affects 5.8 million people and 550,000 new cases are diagnosed annually. Cardiac remodelling (CD), which plays an important role in pathogenesis of HF, is viewed as stress response to an index event such as myocardial ischaemia or imposition of mechanical load leading to a series of structural and functional changes in the viable myocardium. Protein kinase C (PKC) isozymes are a family of serine/threonine kinases. PKC is a central enzyme in the regulation of growth, hypertrophy, and mediators of signal transduction pathways. In response to circulating hormones, activation of PKC triggers a multitude of intracellular events influencing multiple physiological processes in the heart, including heart rate, contraction, and relaxation. Recent research implicates PKC activation in the pathophysiology of a number of cardiovascular disease states. Few reports are available that examine PKC in normal and diseased human hearts. This review describes the structure, functions, and distribution of PKCs in the healthy and diseased heart with emphasis on the human heart and, also importantly, their regulation in heart failure.

Optimal bone fracture repair requires 24R,25-dihydroxyvitamin D3 and its effector molecule FAM57B2

The biological activity of 24R,25-dihydroxyvitamin D3 [24R,25(OH)2D3] remains controversial, but it has been suggested that it contributes to fracture healing. Cyp24a1-/- mice, synthesizing no 24R,25(OH)2D3, show suboptimal endochondral ossification during fracture repair, with smaller callus and reduced stiffness. These defects were corrected by 24R,25(OH)2D3 treatment, but not by 1,25-dihydroxyvitamin D3. Microarrays with Cyp24a1-/- callus mRNA identified FAM57B2 as a mediator of the 24R,25(OH)2D3 effect. FAM57B2 produced lactosylceramide (LacCer) upon specific binding of 24R,25(OH)2D3. Fam57b inactivation in chondrocytes (Col2-Cre Fam57bfl/fl) phenocopied the callus formation defect of Cyp24a1-/- mice. LacCer or 24R,25(OH)2D3 injections restored callus volume, stiffness, and mineralized cartilage area in Cyp24a1-null mice, but only LacCer rescued Col2-Cre Fam57bfl/fl mice. Gene expression in callus tissue suggested that the 24R,25(OH)2D3/FAM57B2 cascade affects cartilage maturation. We describe a previously unrecognized pathway influencing endochondral ossification during bone repair through LacCer production upon binding of 24R,25(OH)2D3 to FAM57B2. Our results identify potential new approaches to ameliorate fracture healing.

A key role for transketolase-like 1 in tumor metabolic reprogramming

Metabolic reprogramming, a crucial cancer hallmark, shifts metabolic pathways such as glycolysis, tricarboxylic acid cycle or lipogenesis, to enable the growth characteristics of cancer cells. Here, we provide evidence that transketolase-like 1 (TKTL1) orchestrates aerobic glycolysis, fatty acid and nucleic acid synthesis, glutamine metabolism, protection against oxidative stress and cell proliferation. Furthermore, silencing of TKTL1 reduced the levels of sphingolipids such as lactosylceramide (a sphingolipid regulating cell survival, proliferation and angiogenesis) and phosphatidylinositol (which activates PI3K/Akt/mTOR signaling). Thus, in addition to its well-known roles in glucose and amino acid metabolism, TKTL1 also regulates lipid metabolism. In conclusion, our study provides unprecedented evidence that TKTL1 plays central roles in major metabolic processes subject to reprogramming in cancer cells and thus identifies TKTL1 as a promising target for new anti-cancer therapies.

Lactosylceramide-Induced Phosphorylation Signaling to Group IVA Phospholipase A2 via Reactive Oxygen Species in Tumor Necrosis Factor-α-Treated Cells

The activity of α-type cytosolic phospholipase A₂ (cPLA₂ α, group IVA PLA₂ ), which releases arachidonic acid (AA), is mainly regulated by the Ca²⁺ -induced intracellular translocation/attachment of the enzyme to substrate membranes and its phosphorylation. We previously reported that tumor necrosis factor-α (TNFα) stimulated the formation of lactosylceramide (LacCer) in L929 fibroblast cells, and this lipid directly bound with and activated cPLA₂ α [Nakamura et al. [2013] J. Biol. Chem. 288:23264-23272]. We herein investigated the role of phosphorylation signaling in the TNFα/LacCer-induced activation of cPLA₂ α in cells. TNFα-treated L929 cells released AA via the phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2) and cPLA₂ α, while a treatment with LacCer alone released AA in a similar manner. The TNFα-induced responses including release of AA were decreased by the inhibition of LacCer synthesis. The treatment with TNFα and LacCer increased the levels of reactive oxygen species (ROS), and the reduction/scavenging of ROS decreased the phosphorylation cascade and release of AA in TNFα/LacCer-treated L929 cells. In the cell line CHO, the treatment with LacCer stimulated the phosphorylation cascade and release of AA via the formation of ROS. Treatments with the anti-LacCer antibody and 4β-phorbol 12-myristate 13-acetate stimulated the phosphorylation cascade, but did not release AA by itself. When combined with the Ca²⁺ ionophore A23187, treatments with the anti-LacCer antibody and 4β-phorbol 12-myristate 13-acetate released AA. These results, including our previous findings, showed that LacCer alone simultaneously stimulates two processes to activate cPLA₂ α: a phosphorylation signal and attachment of the enzyme to substrate membranes. J. Cell. Biochem. 118: 4370-4382, 2017. © 2017 Wiley Periodicals, Inc.

Sphingolipids and glycerophospholipids - The "ying and yang" of lipotoxicity in metabolic diseases

Sphingolipids in general and ceramides in particular, contribute to pathophysiological mechanisms by modifying signalling and metabolic pathways. Here, we present the available evidence for a bidirectional homeostatic crosstalk between sphingolipids and glycerophospholipids, whose dysregulation contributes to lipotoxicity induced metabolic stress. The initial evidence for this crosstalk originates from simulated models designed to investigate the biophysical properties of sphingolipids in plasma membrane representations. In this review, we reinterpret some of the original findings and conceptualise them as a sort of "ying/yang" interaction model of opposed/complementary forces, which is consistent with the current knowledge of lipid homeostasis and pathophysiology. We also propose that the dysregulation of the balance between sphingolipids and glycerophospholipids results in a lipotoxic insult relevant in the pathophysiology of common metabolic diseases, typically characterised by their increased ceramide/sphingosine pools.

Sphingolipids in High Fat Diet and Obesity-Related Diseases

Nutrient oversupply associated with a high fat diet (HFD) significantly alters cellular metabolism, and specifically including sphingolipid metabolism. Sphingolipids are emerging as bioactive lipids that play key roles in regulating functions, in addition to their traditional roles as membrane structure. HFD enhances de novo sphingolipid synthesis and turnover of sphingolipids via the salvage pathway, resulting in the generation of ceramide, and more specifically long chain ceramide species. Additionally, HFD elevates sphingomyelin and sphingosine-1 phosphate (S1P) levels in several tissues including liver, skeletal muscle, adipose tissue, and cardiovascular tissues. HFD-stimulated sphingolipid generation contributes to systemic insulin resistance, dysregulated lipid accumulation, and cytokine expression and secretion from skeletal muscle and adipose tissues, exacerbating obesity-related conditions. Furthermore, altered sphingolipid levels, particularly ceramide and sphingomyelin, are involved in obesity-induced endothelial dysfunction and atherosclerosis. In this review, HFD-mediated sphingolipid metabolism and its impact on HFD-induced biology and pathobiology will be discussed.

Interictal, circulating sphingolipids in women with episodic migraine: A case-control study

OBJECTIVE

To evaluate interictal, circulating sphingolipids in women migraineurs.

METHODS

In the fasting state, serum samples were obtained pain-free from 88 women with episodic migraine (EM; n=52) and from controls (n=36). Sphingolipids were detected and quantified by high-performance liquid chromatography coupled with tandem mass spectrometry using multiple reaction monitoring. Multivariate logistic regression was used to examine the association between serum sphingolipids and EM odds. A recursive partitioning decision tree based on the serum concentrations of 10 sphingolipids was used to determine the presence or absence of EM in a subset of participants.

RESULTS

Total ceramide (EM 6,502.9 ng/mL vs controls 10,518.5 ng/mL; p<0.0001) and dihydroceramide (EM 39.3 ng/mL vs controls 63.1 ng/mL; p<0.0001) levels were decreased in those with EM as compared with controls. Using multivariate logistic regression, each SD increase in total ceramide (odds ratio [OR] 0.07; 95% confidence interval [CI]: 0.02, 0.22; p<0.001) and total dihydroceramide (OR 0.05; 95% CI: 0.01, 0.21; p<0.001) levels was associated with more than 92% reduced odds of migraine. Although crude sphingomyelin levels were not different in EM compared with controls, after adjustments, every SD increase in the sphingomyelin species C18:0 (OR 4.28; 95% CI: 1.87, 9.81; p=0.001) and C18:1 (OR 2.93; 95% CI: 1.55, 5.54; p=0.001) was associated with an increased odds of migraine. Recursive portioning models correctly classified 14 of 14 randomly selected participants as EM or control.

CONCLUSION

These results suggest that sphingolipid metabolism is altered in women with EM and that serum sphingolipid panels may have potential to differentiate EM presence or absence.

CLASSIFICATION OF EVIDENCE

This study provides Class III evidence that serum sphingolipid panels accurately distinguish women with migraine from women without migraine.

Specific miRNA and its target in neutrophils after traumatic injury

Traumatic injury is a leading cause of mortality and morbidity. MicroRNAs (miRNAs) regulate the cellular responses when traumatic injury occurs. Previously, we reported that miR-3945, miR-125a-5p, miR-363-3p, and miR-150-5p were significantly altered in neutrophils of patients who suffered traumatic injury. In the present study, by comparing neutrophils of patients suffering from major trauma with neutrophils of patients with a inflammatory disease, we found that the variation trend of miR-150-5p was relatively different in the process of these two diseases. Gene Ontology and pathway analysis of miR-150-5p revealed that it may activate the mitogen-activated protein kinase and Toll-like receptor signaling pathways and cell adhesion molecules when the traumatic injury occurs. In addition, protein kinase C alpha (PRKCA) was also identified as a direct target of miR-150-5p by establishing a miRNA-mRNA network, and this target was validated via dual-luciferase reporter and western blot analysis. Our results suggested that the expression of miR-150-5p was down-regulated in neutrophils after a major traumatic injury. miR-150-5p and its identified target PRKCA play important roles in the development of traumatic process.

Endothelial LSP1 Modulates Extravascular Neutrophil Chemotaxis by Regulating Nonhematopoietic Vascular PECAM-1 Expression

During inflammation, leukocyte-endothelial cell interactions generate molecular signals that regulate cell functions. The Ca(2+)- and F-actin-binding leukocyte-specific protein 1 (LSP1) expressed in leukocytes and nonhematopoietic endothelial cells is pivotal in regulating microvascular permeability and leukocyte recruitment. However, cell-specific function of LSP1 during leukocyte recruitment remains elusive. Using intravital microscopy of cremasteric microvasculature of chimeric LSP1-deficient mice, we show that not neutrophil but endothelial LSP1 regulates neutrophil transendothelial migration and extravascular directionality without affecting the speed of neutrophil migration in tissue in response to CXCL2 chemokine gradient. The expression of PECAM-1-sensitive α6β1 integrins on the surface of transmigrated neutrophils was blunted in mice deficient in endothelial LSP1. Functional blocking studies in vivo and in vitro elucidated that α6β1 integrins orchestrated extravascular directionality but not the speed of neutrophil migration. In LSP1-deficient mice, PECAM-1 expression was reduced in endothelial cells, but not in neutrophils. Similarly, LSP1-targeted small interfering RNA silencing in murine endothelial cells mitigated mRNA and protein expression of PECAM-1, but not ICAM-1 or VCAM-1. Overexpression of LSP1 in endothelial cells upregulated PECAM-1 expression. Furthermore, the expression of transcription factor GATA-2 that regulates endothelial PECAM-1 expression was blunted in LSP1-deficient or LSP1-silenced endothelial cells. The present study unravels endothelial LSP1 as a novel cell-specific regulator of integrin α6β1-dependent neutrophil extravascular chemotactic function in vivo, effective through GATA-2-dependent transcriptional regulation of endothelial PECAM-1 expression.

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.

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.

Regulation of astrocyte activation by glycolipids drives chronic CNS inflammation

Astrocytes have complex roles in health and disease, thus it is important to study the pathways that regulate their function. Here we report that lactosylceramide (LacCer) synthesized by β-1,4-galactosyltransferase 6 (B4GALT6) is upregulated in the central nervous system (CNS) of mice during chronic experimental autoimmune encephalomyelitis (EAE), a model of multiple sclerosis (MS). LacCer acts in an autocrine manner to control astrocyte transcriptional programs that promote neurodegeneration. In addition, LacCer in astrocytes controls the recruitment and activation of microglia and CNS-infiltrating monocytes in a non-cell autonomous manner by regulating production of the chemokine CCL2 and granulocyte-macrophage colony-stimulating factor (GM-CSF), respectively. We also detected high B4GALT6 gene expression and LacCer concentrations in CNS MS lesions. Inhibition of LacCer synthesis in mice suppressed local CNS innate immunity and neurodegeneration in EAE and interfered with the activation of human astrocytes in vitro. Thus, B4GALT6 regulates astrocyte activation and is a potential therapeutic target for MS and other neuroinflammatory disorders.

Renal PKC-ε deficiency attenuates acute kidney injury and ischemic allograft injury via TNF-α-dependent inhibition of apoptosis and inflammation

Acute kidney injury (AKI) increases the risk of morbidity and mortality after major surgery and transplantation. We investigated the effect of PKC-ε deficiency on AKI and ischemic allograft damage after kidney transplantation. PKC-ε-deficient and wild type (WT) control mice were subjected to 35 min of renal pedicle clamping to induce AKI. PKC-ε deficiency was associated with a marked improvement in survival and an attenuated loss of kidney function. Furthermore, functional MRI experiments revealed better renal perfusion in PKC-ε-deficient mice than in WT mice one day after IRI. Acute tubular necrosis and neutrophil infiltration were markedly reduced in PKC-ε-deficient mice. To determine whether this resistance to ischemia-reperfusion injury resulted from changes in local renal cells or infiltrating leukocytes, we studied a life-supporting renal transplant model of ischemic graft injury. We transplanted kidneys from H2b PKC-ε-deficient mice (129/SV) and their corresponding WT littermates into major histocompatibility complex-incompatible H2d recipients (BALB/c) and induced ischemic graft injury by prolonged cold ischemia time. Recipients of WT allografts developed severe renal failure and died within 10 days of transplantation. Recipients of PKC-ε-deficient allografts had better renal function and survival; they had less generation of ROS and upregulation of proinflammatory proteins (i.e., ICAM-1, inducible nitric oxide synthase, and TNF-α) and showed less tubular epithelial cell apoptosis and inflammation in their allografts. These data suggest that local renal PKC-ε expression mediates proapoptotic and proinflammatory signaling and that an inhibitor of PKC-ε signaling could be used to prevent hypoxia-induced AKI.

Inhibition of glycosphingolipid synthesis ameliorates atherosclerosis and arterial stiffness in apolipoprotein E-/- mice and rabbits fed a high-fat and -cholesterol diet

BACKGROUND

Glycosphingolipids, integral components of the cell membrane, have been shown to serve as messengers, transducing growth factor-initiated phenotypes. Here, we have examined whether inhibition of glycosphingolipid synthesis could ameliorate atherosclerosis and arterial stiffness in transgenic mice and rabbits.

METHODS AND RESULTS

Apolipoprotein E(-/-) mice (12 weeks of age; n=6) were fed regular chow or a Western diet (1.25% cholesterol, 2% fat). Mice were fed 5 or 10 mg/kg of an inhibitor of glycosphingolipid synthesis, D-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (D-PDMP), solubilized in vehicle (5% Tween-80 in PBS); the placebo group received vehicle only. At 20 and 36 weeks of age, serial echocardiography was performed to measure aortic intima-media thickening. Aortic pulse-wave velocity measured vascular stiffness. Feeding mice a Western diet markedly increased aortic pulse-wave velocity, intima-media thickening, oxidized low-density lipoprotein, Ca(2+) deposits, and glucosylceramide and lactosylceramide synthase activity. These were dose-dependently decreased by feeding D-PDMP. In liver, D-PDMP decreased cholesterol and triglyceride levels by raising the expression of SREBP2, low-density lipoprotein receptor, HMGCo-A reductase, and the cholesterol efflux genes (eg, ABCG5, ABCG8). D-PDMP affected very-low-density lipoprotein catabolism by increasing the gene expression for lipoprotein lipase and very-low-density lipoprotein receptor. Rabbits fed a Western diet for 90 days had extensive atherosclerosis accompanied by a 17.5-fold increase in total cholesterol levels and a 3-fold increase in lactosylceramide levels. This was completely prevented by feeding D-PDMP.

CONCLUSIONS

Inhibition of glycosphingolipid synthesis ameliorates atherosclerosis and arterial stiffness in apolipoprotein E(-/-) mice and rabbits. Thus, inhibition of glycosphingolipid synthesis may be a novel approach to ameliorate atherosclerosis and arterial stiffness.

Lactosylceramide promotes hypertrophy through ROS generation and activation of ERK1/2 in cardiomyocytes

Hypertrophy is central to several heart diseases; however, not much is known about the role of glycosphingolipids (GSLs) in this phenotype. Since GSLs have been accorded several physiological functions, we sought to determine whether these compounds affect cardiac hypertrophy. By using a rat cardiomyoblast cell line, H9c2 cells and cultured primary neonatal rat cardiomyocytes, we have determined the effects of GSLs on hypertrophy. Our study comprises (a) measurement of [(3)H]-leucine incorporation into protein, (b) measurement of cell size and morphology by immunofluorescence microscopy and (c) real-time quantitative mRNA expression assay for atrial natriuretic peptide and brain natriuretic peptide. Phenylephrine (PE), a well-established agonist of cardiac hypertrophy, served as a positive control in these studies. Subsequently, mechanistic studies were performed to explore the involvement of various signaling transduction pathways that may contribute to hypertrophy in these cardiomyocytes. We observed that lactosylceramide specifically exerted a concentration- (50-100 µM) and time (48 h)-dependent increase in hypertrophy in cardiomyocytes but not a library of other structurally related GSLs. Further, in cardiomyocytes, LacCer generated reactive oxygen species, stimulated the phosphorylation of p44 mitogen activated protein kinase and protein kinase-C, and enhanced c-jun and c-fos expression, ultimately leading to hypertrophy. In summary, we report here that LacCer specifically induces hypertrophy in cardiomyocytes via an "oxygen-sensitive signal transduction pathway."

Lactosylceramide interacts with and activates cytosolic phospholipase A2α

Lactosylceramide (LacCer) is a member of the glycosphingolipid family and is known to be a bioactive lipid in various cell physiological processes. However, the direct targets of LacCer and cellular events mediated by LacCer are largely unknown. In this study, we examined the effect of LacCer on the release of arachidonic acid (AA) and the activity of cytosolic phospholipase A2α (cPLA2α). In CHO-W11A cells, treatment with 1-phenyl-2-palmitoylamino-3-morpholino-1-propanol (PPMP), an inhibitor of glucosylceramide synthase, reduced the glycosphingolipid level, and the release of AA induced by A23187 or platelet-activating factor was inhibited. The addition of LacCer reversed the PPMP effect on the stimulus-induced AA release. Exogenous LacCer stimulated the release of AA, which was decreased by treatment with an inhibitor of cPLA2α or silencing of the enzyme. Treatment of CHO-W11A cells with LacCer induced the translocation of full-length cPLA2α and its C2 domain from the cytosol to the Golgi apparatus. LacCer also induced the translocation of the D43N mutant of cPLA2α. Treatment of L929 cells with TNF-α induced LacCer generation and mediated the translocation of cPLA2α and AA release, which was attenuated by treatment with PPMP. In vitro studies were then conducted to test whether LacCer interacts directly with cPLA2α. Phosphatidylcholine vesicles containing LacCer increased cPLA2α activity. LacCer bound to cPLA2α and its C2 domain in a Ca(2+)-independent manner. Thus, we propose that LacCer is a direct activator of cPLA2α.

Protein kinase C ε expression in platelets from patients with acute myocardial infarction

Objective

Platelets play crucial roles in the pathophysiology of thrombosis and myocardial infarction. Protein kinase C ε (PKCε) is virtually absent in human platelets and its expression is precisely regulated during human megakaryocytic differentiation. On the basis of what is known on the role of platelet PKCε in other species, we hypothesized that platelets from myocardial infarction patients might ectopically express PKCε with a pathophysiological role in the disease.

Methods and Results

We therefore studied platelet PKCε expression from 24 patients with myocardial infarction, 24 patients with stable coronary artery disease and 24 healthy subjects. Indeed, platelets from myocardial infarction patients expressed PKCε with a significant frequency as compared to both stable coronary artery disease and healthy subjects. PKCε returned negative during patient follow-up. The forced expression of PKCε in normal donor platelets significantly increased their response to adenosine diphosphate-induced activation and adhesion to subendothelial collagen.

Conclusions

Our data suggest that platelet generations produced before the acute event retain PKCε-mRNA that is not down-regulated during terminal megakaryocyte differentiation. Results are discussed in the perspective of peri-infarctual megakaryocytopoiesis as a critical component of myocardial infarction pathophysiology.

Hypertension is associated with marked alterations in sphingolipid biology: a potential role for ceramide

Background

Hypertension is, amongst others, characterized by endothelial dysfunction and vascular remodeling. As sphingolipids have been implicated in both the regulation of vascular contractility and growth, we investigated whether sphingolipid biology is altered in hypertension and whether this is reflected in altered vascular function.

Methods and Findings

In isolated carotid arteries from spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats, shifting the ceramide/S1P ratio towards ceramide dominance by administration of a sphingosine kinase inhibitor (dimethylsphingosine) or exogenous application of sphingomyelinase, induced marked endothelium-dependent contractions in SHR vessels (DMS: 1.4±0.4 and SMase: 2.1±0.1 mN/mm; n = 10), that were virtually absent in WKY vessels (DMS: 0.0±0.0 and SMase: 0.6±0.1 mN/mm; n = 9, p<0.05). Imaging mass spectrometry and immunohistochemistry indicated that these contractions were most likely mediated by ceramide and dependent on iPLA₂, cyclooxygenase-1 and thromboxane synthase. Expression levels of these enzymes were higher in SHR vessels. In concurrence, infusion of dimethylsphingosine caused a marked rise in blood pressure in anesthetized SHR (42±4%; n = 7), but not in WKY (−12±10%; n = 6). Lipidomics analysis by mass spectrometry, revealed elevated levels of ceramide in arterial tissue of SHR compared to WKY (691±42 vs. 419±27 pmol, n = 3–5 respectively, p<0.05). These pronounced alterations in SHR sphingolipid biology are also reflected in increased plasma ceramide levels (513±19 pmol WKY vs. 645±25 pmol SHR, n = 6–12, p<0.05). Interestingly, we observed similar increases in ceramide levels (correlating with hypertension grade) in plasma from humans with essential hypertension (185±8 pmol vs. 252±23 pmol; n = 18 normotensive vs. n = 19 hypertensive patients, p<0.05).

Conclusions

Hypertension is associated with marked alterations in vascular sphingolipid biology such as elevated ceramide levels and signaling, that contribute to increased vascular tone.

Myriocin-mediated up-regulation of hepatocyte apoA-I synthesis is associated with ERK inhibition

Sphingolipids including sphingomyelin have been implicated as potential atherogenic lipids. Studies in apoE (apolipoprotein E)-null mice have revealed that the serine palmitoyltransferase inhibitor myriocin reduces plasma levels of sphingomyelin, ceramide, sphingosine-1-phosphate and glycosphingolipids and that this is associated with potent inhibition of atherosclerosis. Interestingly, hepatic apoA-I (apolipoprotein A-I) synthesis and plasma HDL (high-density lipoprotein)-cholesterol levels were also increased in apoE-null mice treated with myriocin. Since myriocin is a known inhibitor of ERK (extracellular-signal-related kinase) phosphorylation, we assessed the possibility that myriocin may be acting to increase hepatic apoA-I production via this pathway. To address this, HepG2 cells and primary mouse hepatocytes were treated with 200 muM myriocin for up to 48 h. Myriocin increased apoA-I mRNA and protein levels by approx. 3- and 2-fold respectively. Myriocin also increased apoA-I secretion up to 3.5-fold and decreased ERK phosphorylation by approx. 70%. Similar findings were obtained when primary hepatocytes were isolated from apoE-null mice that were treated with myriocin (intraperitoneal injection at a dose of 0.3 mg/kg body weight). Further experiments revealed that the MEK (mitogen-activated protein kinase/ERK kinase) inhibitor PD98059 potently inhibited ERK phosphorylation, as expected, and increased primary hepatocyte apoA-I production by 3-fold. These results indicate that ERK phosphorylation plays a role in regulating hepatic apoA-I expression and suggest that the anti-atherogenic mechanism of action for myriocin may be linked to this pathway.

Inhibition of glycosphingolipid synthesis induces a profound reduction of plasma cholesterol and inhibits atherosclerosis development in APOE*3 Leiden and low-density lipoprotein receptor-/- mice

OBJECTIVE

The iminosugar N-(5'-adamantane-1'-yl-methoxy)-pentyl-1-deoxynoijirimycin (AMP-DNM), an inhibitor of the enzyme glucosylceramide synthase catalyzing glycosphingolipid (GSL) biosynthesis, ameliorates diabetes and reduces liver steatosis in ob/ob mice. Because an accumulation of sphingolipids, including sphingomyelin and GSLs, has been reported in atherosclerotic lesions in animal models and in humans, the objective of this study was to determine whether AMP-DNM also exerts beneficial effects on the development of atherosclerosis.

METHODS AND RESULTS

APOE*3 Leiden mice, maintained on a high-cholesterol diet, were treated for up to 18 weeks with AMP-DNM. The iminosugar prevented hyperlipidemia, generated a less atherogenic lipid profile, and induced a dramatic reduction in the development of atherosclerotic lesions. At the highest dose, no lesions were detectable. The effect of AMP-DNM was associated with a decrease in liver cholesterol, an increase in bile secretion, and enhanced excretion of cholesterol in the feces. Similar effects of AMP-DNM were observed in mice deficient for the low-density lipoprotein receptor.

CONCLUSION

By lowering plasma cholesterol, the iminosugar AMP-DNM dramatically reduces the development of atherosclerosis in APOE*3 Leiden and low-density lipoprotein receptor -/- mice. Thus, targeting GSL synthesis may be a new treatment modality to prevent cardiovascular disease.

Protein kinase Calpha: disease regulator and therapeutic target

Protein kinase Cα (PKCα) is a member of the AGC (which includes PKD, PKG and PKC) family of serine/threonine protein kinases that is widely expressed in mammalian tissues. It is closely related in structure, function and regulation to other members of the protein kinase C family, but has specific functions within the tissues in which it is expressed. There is substantial recent evidence, from gene knockout studies in particular, that PKCα activity regulates cardiac contractility, atherogenesis, cancer and arterial thrombosis. Selective targeting of PKCα therefore has potential therapeutic value in a wide variety of disease states, although will be technically complicated by the ubiquitous expression and multiple functions of the molecule.

Lactosylceramide promotes cell migration and proliferation through activation of ERK1/2 in human aortic smooth muscle cells

Increased plasma levels of lactosylceramide (LacCer) have been associated with cardiovascular disease. However, it is largely unknown whether LacCer directly contributes to dysfunction of smooth muscle cells (SMCs), a key event in vascular lesion formation. In the present study, we determined the effects and potential mechanisms of LacCer on cell migration and proliferation in human aortic SMCs (AoSMCs). Cell migration and proliferation were determined by a modified Boyden chamber assay and nonradioactive colorimetric (MTS) assay, respectively. We found that LacCer significantly induced AoSMC migration and proliferation in a concentration- and time-dependent manner. In addition, LacCer significantly upregulated the expression of PDGFR-B, integrins (alpha(v) and beta(3)), and matrix metalloproteinases (matrix metalloproteinase-1 and -2) at both mRNA and protein levels, as determined by real-time PCR and Western blot analyses, respectively. Furthermore, LacCer increased superoxide anion production and the transient phosphorylation of ERK1/2 in AoSMCs, as determined by dihydroethidium staining and immunoassay, respectively. Accordingly, LacCer-induced cell migration and proliferation were effectively blocked by antioxidants (seleno-l-methionine and Mn tetrakis porphyrin) and by a specific ERK1/2 inhibitor. Thus, LacCer promotes cell migration and proliferation through oxidative stress and activation of ERK1/2 in AoSMCs. These findings demonstrate the functional role of LacCer in the vascular disease pathogenesis.

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.

Reduction of plasma glycosphingolipid levels has no impact on atherosclerosis in apolipoprotein E-null mice

Glycosphingolipids (GSLs) have been implicated as potential atherogenic lipids. Studies in apolipoprotein E-null (apoE(-/-)) mice indicate that exacerbated tissue GSL accumulation resulting from alpha-galactosidase deficiency promotes atherosclerosis, whereas the serine palmitoyl transferase inhibitor myriocin (which reduces plasma and tissue levels of several sphingolipids, including sphingomyelin, ceramide, sphingosine-1-phosphate, and GSLs) inhibits atherosclerosis. It is not clear whether GSL synthesis inhibition per se has an impact on atherosclerosis. To address this issue, apoE(-/-) mice maintained on a high-fat diet were treated with a potent glucosylceramide synthesis inhibitor, d-threo-1-ethylendioxyphenyl-2-palmitoylamino-3-pyrrolidino-propanol (EtDO-P4), 10 mg/kg/day for 94 days, and lesion development was compared in mice that were treated with vehicle only. EtDO-P4 reduced plasma GSL concentration by approximately 50% but did not affect cholesterol or triglyceride levels. Assessment of atherosclerotic lesions at four different sites indicated that EtDO-P4 had no significant impact on lesion area. Thus, despite the previously observed positive correlations between plasma and aortic GSL concentrations and the development of atherosclerosis, and the in vitro evidence implying that GSLs may be pro-atherogenic, our current data indicate that inhibition of GSL synthesis does not inhibit atherosclerosis in vivo.

Higher order structure of (1,3)-beta-D-glucans and its influence on their biological activities and complexation abilities

(1,3)-beta-D-Glucans form a group of biologically active biopolymers that exist in different structural organizations depending on the environmental conditions. The biological effect of (1,3)-beta-D-glucans is a core issue stimulating large research efforts of the molecular properties and their consequences for action as biological response modifiers. The fascination for these molecules increased further following the finding of their ability to form complexes of defined geometry with a number of structures, ranging from linear architectures as polymers or carbon nanotubes, to globular structures as gold particles or dye molecules. The fascinating information concerning the relationship between sample treatment history and molecular organization has not yet reached out to all the contributors within the field, resulting in unnecessary apparent inconsistencies in the literature. In addition to environmental conditions, the sample history is known to influence on the precise structural organization of these molecules. The present knowledge related to the structure of native as well as denatured, renatured and annealed (1,3)-beta-D-glucans is reviewed. The influence of their structural organization on the biological activity and complexation abilities is discussed, and some factors hindering progress in the understanding of their biological effects or complexation abilities are pointed out.

PKC isozymes in chronic cardiac disease: possible therapeutic targets?

Cardiovascular disease is the leading cause of death in the United States. Therefore, identifying therapeutic targets is a major focus of current research. Protein kinase C (PKC), a family of serine/threonine kinases, has been identified as playing a role in many of the pathologies of heart disease. However, the lack of specific PKC regulators and the ubiquitous expression and normal physiological functions of the 11 PKC isozymes has made drug development a challenge. Here we discuss the validity of therapeutically targeting PKC, an intracellular signaling enzyme. We describe PKC structure, function, and distribution in the healthy and diseased heart, as well as the development of rationally designed isozyme-selective regulators of PKC functions. The review focuses on the roles of specific PKC isozymes in atherosclerosis, fibrosis, and cardiac hypertrophy, and examines principles of pharmacology as they pertain to regulators of signaling cascades associated with these diseases.

Involvement of very long fatty acid-containing lactosylceramide in lactosylceramide-mediated superoxide generation and migration in neutrophils

The neutral glycosphingolipid lactosylceramide (LacCer) forms lipid rafts (membrane microdomains) coupled with the Src family kinase Lyn on the plasma membranes of human neutrophils; ligand binding to LacCer activates Lyn, resulting in neutrophil functions, such as superoxide generation and migration (Iwabuchi and Nagaoka, Lactosylceramide-enriched glycosphingolipid signaling domain mediates superoxide generation from human neutrophils, Blood 100, 1454-1464, 2002 and Sato et al. Induction of human neutrophil chemotaxis by Candida albicans-derived beta-1,6-long glycoside side-chain-branched beta glycan, J. Leukoc. Biol. 84, 204-211, 2006). Neutrophilic differentiated HL-60 cells (D-HL-60 cells) express almost the same amount of LacCer as neutrophils. However, D-HL-60 cells do not have Lyn-associated LacCer-enriched lipid rafts and lack LacCer-mediated superoxide-generating and migrating abilities. Here, we examined the roles of LacCer molecular species of different fatty acid compositions in these processes. Liquid chromatography-mass spectrometry analyses revealed that the very long fatty acid C24:0 and C24:1 chains were the main components of LacCer (31.6% on the total fatty acid content) in the detergent-resistant membrane fraction (DRM) from neutrophil plasma membranes. In contrast, plasma membrane DRM of D-HL-60 cells included over 70% C16:0-LacCer, but only 13.6% C24-LacCer species. D-HL-60 cells loaded with C24:0 or C24:1-LacCer acquired LacCer-mediated migrating and superoxide-generating abilities, and allowed Lyn coimmunoprecipitation by anti-LacCer antibody. Lyn knockdown by siRNA completely abolished the effect of C24:1-LacCer loading on LacCer-mediated migration of D-HL-60 cells. Immunoelectron microscopy revealed that LacCer clusters were closely associated with Lyn molecules in neutrophils and C24:1-LacCer-loaded D-HL-60 cells, but not in D-HL-60 cells or C16:0-LacCer-loaded cells. Taken together, these observations suggest that LacCer species with very long fatty acids are specifically necessary for Lyn-coupled LacCer-enriched lipid raft-mediated neutrophil superoxide generation and migration.

Effects of TNF-alpha on leukocyte adhesion molecule expressions in cultured human lymphatic endothelium

TNF-alpha alters leukocyte adhesion molecule expression of cultured endothelial cells like human umbilical vein endothelial cells (HUVEC). This study was designed to investigate the changes in vascular cell adhesion molecule-1 (VCAM-1), intercellular adhesion molecule-1 (ICAM-1), and platelet endothelial cell adhesion molecule-1 (PECAM-1) expression with TNF-alpha stimulation in cultured human neonatal dermal lymphatic endothelial cells (HNDLEC). The real-time quantitative PCR analysis on HNDLEC showed that TNF-alpha treatment leads to increases of VCAM-1 and ICAM-1 mRNAs to the 10.8- and 48.2-fold levels of untreated cells and leads to a reduction of PECAM-1 mRNA to the 0.42-fold level of untreated cells. Western blot and immunohistochemical analysis showed that TNF-alpha leads to VCAM-1 and ICAM-1 expressions that were inhibited by antiserum to human TNF receptor or by AP-1 inhibitor nobiletin. In flow cytometry analysis, the number of VCAM-1- and ICAM-1-positive cells increased, and PECAM-1-positive cells decreased with TNF-alpha treatment. Regarding protein amounts produced in cells and amounts expressed on the cell surface, VCAM-1 and ICAM-1 increased in HNDLEC and HUVEC, and PECAM-1 decreased in HNDLEC in a TNF-alpha concentration-dependent manner. VCAM-1, ICAM-1, and PECAM-1 protein amounts in TNF-alpha-stimulated cells were lower in HNDLEC than in HUVEC. This suggests that the lymphatic endothelium has the TNF-alpha-induced signaling pathway, resulting in increased VCAM-1 and ICAM-1 expression to a weaker extent than blood endothelium and PECAM-1 reduction to a stronger extent than blood endothelium.