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Emerging clinical data show that three ceramide molecules, Cer d18:1/16:0, Cer d18:1/24:1, and Cer d18:1/24:0, are biomarkers of a fatal outcome in patients with cardiovascular disease. This finding raises basic questions about their metabolic origin, their contribution to disease pathogenesis, and the utility of targeting the underlying enzymatic machinery for treatment of cardiometabolic disorders. Here, we outline the development of a potent N-acetylgalactosamine-conjugated antisense oligonucleotide engineered to silence ceramide synthase 2 specifically in hepatocytes in vivo. We demonstrate that this compound reduces the ceramide synthase 2 mRNA level and that this translates into efficient lowering of protein expression and activity as well as Cer d18:1/24:1 and Cer d18:1/24:0 levels in liver. Intriguingly, we discover that the hepatocyte-specific antisense oligonucleotide also triggers a parallel modulation of blood plasma ceramides, revealing that the biomarkers predictive of cardiovascular death are governed by ceramide biosynthesis in hepatocytes. Our work showcases a generic therapeutic framework for targeting components of the ceramide enzymatic machinery to disentangle their roles in disease causality and to explore their utility for treatment of cardiometabolic disorders. ispartof: MOLECULAR THERAPY vol:30 issue:4 pages:1661-1674 ispartof: location:United States status: published

Entamoeba invadens is the protozoan which causes multiple damages in reptiles and is considered a prototype for the study of the Entamoeba encystment/excystment in vitro. Here we report that EinCerS2 knockdown promoted decrease in sphingomyelin (SM) subspecies with long-chain fatty acids (24:0) down to 50% but increase sphingolipids with short-chain fatty acids (16:0) up to three times in both trophozoites and cysts of E. invadens. EinCerS2 silencing also resulted in decreased trophozoites’ movement, proliferation, cysts formation, and trophozoites hatched after excystment. By immunofluorescence assays, a polyclonal antibody against EinCerS2 detected the enzyme in the cytoplasm of E. invadens trophozoites, colocalizing with Endoplasmic Reticulum-resident cognate EiSERCA. Interestingly, EinCerS2 was redistributed close to the plasma membrane during encystation, suggesting that the generation of diacylglycerol (DAG) via synthesis of sphingolipids and the activation protein kinase C might participate in the encystment process of E. invadens.

Background Increased plasma free fatty acids (FFAs) impair insulin sensitivity in dairy cows via unknown mechanisms. In nonruminants, saturated FFAs upregulate the hepatic synthesis and secretion of ceramide, which inhibits insulin action. Objective We aimed to determine whether an increase in plasma FFAs promotes hepatic and plasma ceramide accumulation in dairy cows. Methods Six nonpregnant, nonlactating Holstein cows were used in a study with a crossover design and treatments consisting of intravenous infusion of either saline (control) or triacylglycerol emulsion (TG; 20 g/h) for 16 h. The feeding level was set at 120% of energy requirements. Blood was collected at regular intervals and liver was biopsied at 16 h. Ceramides, monohexosylceramides (Glc/Gal-Cer), lactosylceramides (LacCer), and sphingomyelins (SMs) in plasma and liver were profiled. Hepatic expression of ceramide synthases was determined. Data were analyzed with the use of mixed models, regressions, and Spearman rank correlations. Results After 16 h of infusion, plasma FFA concentrations were >5-fold and liver triacylglycerol concentrations were 4-fold greater in TG cows, relative to control. Plasma total and very long-chain ceramide (e.g., C24:0-ceramide) concentrations increased ∼4-fold in TG over control by hour 16 of infusion, while C16:0-ceramide were not modified by TG. Infusion of TG increased plasma Glc/Gal-Cer (e.g., C16:0-Glc/Gal-Cer, 4-fold by hour 16) relative to control, but did not alter LacCer or SM concentrations. Hepatic ceramide concentrations increased with TG relative to control (e.g., C24:0-ceramide by 1.7-fold). Hepatic expression of ceramide synthase 2 was 60% greater after TG infusion compared with the control. Circulating ceramides were related to circulating FFA and hepatic triacylglycerol concentrations (e.g., C24:0-ceramide, ρ = 0.73 and 0.80, respectively; P Conclusion Hepatic ceramide synthesis is associated with elevations in circulating FFAs and hepatic triacylglycerol during the induction of hyperlipidemia in dairy cows. This work supports the emerging evidence for the role of ceramide during hepatic steatosis and insulin antagonism in cows.

The replacement of two consecutive histidine residues by alanine residues in the catalytic center of ceramide synthase 2 in a new transgenic mouse mutant (CerS2 H/A) leads to inactivation of catalytic activity and reduces protein level to 60% of the WT level. We show here by qRT-PCR and transcriptome analyses that several transcripts of genes involved in lipid metabolism and cell division are differentially regulated in livers of CerS2 H/A mice. Thus, very long chain ceramides produced by CerS2 are required for transcriptional regulation of target genes. The hepatocellular carcinomata previously described in old CerS2 KO mice were already present in 8-week-old CerS2 H/A animals and thus are caused by the loss of CerS2 catalytic activity already during early life.

Chinese Hamster Ovary (CHO) cells are the most commonly used host for the production of biopharmaceuticals. Although transcription and translation engineering strategies have been employed to generate high-producer cell clones, the secretory pathway still remains a bottleneck in cellular productivity. In this study we show that ectopic expression of a human mitochondrial genome-encoded small RNA (mitosRNA-1978) in an IgG expressing CHO cell line strongly improved specific productivity by functioning in a microRNA-like fashion. By next generation sequencing we identified two endoplasmic reticulum (ER)-localized proteins, Ceramide Synthase 2 (CerS2) and the Rab1 GAP Tbc domain family member 20 (Tbc1D20), as target genes of mitosRNA-1978. Combined transient siRNA-mediated knockdown of CerS2 and Tbc1D20 resulted in increased specific productivity of CHO-IgG cells, thus recapitulating the mitosRNA-1978 phenotype. In support of a function in vesicular trafficking at the level of the ER, we provide evidence for altered cellular ceramide composition upon CerS2 knockdown and increased activity of Rab1 in CHO-IgG cells depleted of Tbc1D20. Importantly, in a fed-batch process, the combined stable knockdown of CerS2 and Tbc1D20 in CHO-IgG cells resulted in dramatically increased antibody production which was accompanied by enhanced cell growth. Thus, by identifying mitosRNA-1978 target genes in combination with an informed shRNA-mediated co-engineering approach we successfully optimized the secretory capacity of CHO producer cells used for the manufacturing of therapeutic proteins.

In a recent study, we showed that in response to high fat feeding C57BL/6, 129X1, DBA/2 and FVB/N mice all developed glucose intolerance, while BALB/c mice displayed minimal deterioration in glucose tolerance and insulin action. Lipidomic analysis of livers across these five strains has revealed marked strain-specific differences in ceramide (Cer) and sphingomyelin (SM) species with high-fat feeding; with increases in C16-C22 (long-chain) and reductions in C>22 (very long-chain) Cer and SM species observed in the four strains that developed HFD-induced glucose intolerance. Intriguingly, the opposite pattern was observed in sphingolipid species in BALB/c mice. These strain-specific changes in sphingolipid acylation closely correlated with ceramide synthase 2 (CerS2) protein content and activity, with reduced CerS2 levels/activity observed in glucose intolerant strains and increased content in BALB/c mice. Overexpression of CerS2 in primary mouse hepatocytes induced a specific elevation in very long-chain Cer, but despite the overall increase in ceramide abundance, there was a substantial improvement in insulin signal transduction, as well as decreased ER stress and gluconeogenic markers. Overall our findings suggest that very long-chain sphingolipid species exhibit a protective role against the development of glucose intolerance and hepatic insulin resistance.

Ceramide synthases (CerS) synthesise ceramides of defined acyl chain lengths, which are thought to mediate cellular processes in a chain length-dependent manner. In experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS), we observed a significant elevation of CerS2 and its products, C24-ceramides, in CD11b(+) cells (monocytes and neutrophils) isolated from blood. This result correlates with the clinical finding that CerS2 mRNA expression and C24-ceramide levels were significantly increased by 2.2- and 1.5-fold, respectively, in white blood cells of MS patients. The increased CerS2 mRNA/C24-ceramide expression in neutrophils/monocytes seems to mediate pro-inflammatory effects, since a specific genetic deletion of CerS2 in blood cells or a total genetic deletion of CerS2 significantly delayed the onset of clinical symptoms, due to a reduced infiltration of immune cells, in particular neutrophils, into the central nervous system. CXCR2 chemokine receptors, expressed on neutrophils, promote the migration of neutrophils into the central nervous system, which is a prerequisite for the recruitment of further immune cells and the inflammatory process that leads to the development of MS. Interestingly, neutrophils isolated from CerS2 null EAE mice, as opposed to WT EAE mice, were characterised by significantly lower CXCR2 receptor mRNA expression resulting in their reduced migratory capacity towards CXCL2. Most importantly, G-CSF-induced CXCR2 expression was significantly reduced in CerS2 null neutrophils and their migratory capacity was significantly impaired. In conclusion, our data strongly indicate that G-CSF-induced CXCR2 expression is regulated in a CerS2-dependent manner and that CerS2 thereby promotes the migration of neutrophils, thus, contributing to inflammation and the development of EAE and MS.

Ceramide synthase 2 (CerS2) null mice cannot synthesize very-long acyl chain (C22-C24) ceramides resulting in significant alterations in the acyl chain composition of sphingolipids. We now demonstrate that hepatic triacylglycerol (TG) levels are reduced in the liver but not in the adipose tissue or skeletal muscle of the CerS2 null mouse, both before and after feeding with a high fat diet (HFD), where no weight gain was observed and large hepatic nodules appeared. Uptake of both BODIPY-palmitate and [VH]-palmitate was also abrogated in the hepa- tocytes and liver. The role of a number of key proteins involved in fatty acid uptake was examined, including FATP5, CD36/FAT, FABPpm and cytoplasmic FABP1. Levels of FATP5 and FABP1 were decreased in the CerS2 null mouse liver, whereas CD36/FAT levels were significantly elevated and CD36/FAT was also mislocalized upon insulin treatment. Moreover, treatment of hepatocytes with C22-C24-ceramides down-regulated CD36/FAT levels. Infection of CerS2 null mice with recombinant adeno-associated virus (rAAV)-CerS2 restored normal TG levels and corrected the mislocalization of CD36/FAT, but had no effect on the intracellular localization or levels of FATP5 or FABP1. Together, these results demonstrate that hepatic fatty acid uptake via CD36/FAT can be regulated by altering the acyl chain composition of sphingolipids.

Mammalian kidneys are rich in sulfatides. Papillary sulfatides, especially, contribute to renal adaptation to chronic metabolic acidosis. Due to differences in their cer-amide (Cer) anchors, the structural diversity of renal sulfatides is large. However, the underling biological function of this complexity is not understood. As a compound's function and its tissue location are intimately connected, we analyzed individual renal sulfatide distributions of control and Cer synthase 2 (CerS)2-deficient mice by imaging MS (IMS) and by LC-MS(2) (in controls for the cortex, medulla, and papillae separately). To explain locally different structures, we compared our lipid data with regional mRNA levels of corresponding anabolic enzymes. The combination of IMS and in source decay-LC-MS(2) analyses revealed exclusive expression of C20-sphingosine-containing sulfatides within the renal papillae, whereas conventional C18-sphingosine-containing compounds were predominant in the medulla, and sulfatides with a C18-phytosphingosine were restricted to special cortical structures. CerS2 deletion resulted in bulk loss of sulfatides with C23/C24-acyl chains, but did not lead to decreased urinary pH, as previously observed in sulfatide-depleted kidneys. The reasons may be the almost unchanged C22-sulfatide levels and constant total renal sulfatide levels due to compensation with C16- to C20-acyl chain-containing compounds. Intriguingly, CerS2-deficient kidneys were completely depleted of phytosphingosine-containing cortical sulfatides without any compensation.

Summary Inhibition of ceramide synthesis prevents diabetes, steatosis, and cardiovascular disease in rodents. Six different ceramide synthases (CerS) that differ in tissue distribution and substrate specificity account for the diversity in acyl-chain composition of distinct ceramide species. Haploinsufficiency for ceramide synthase 2 (CerS2), the dominant isoform in the liver that preferentially makes very-long-chain (C22/C24/C24:1) ceramides, led to compensatory increases in long-chain C16-ceramides and conferred susceptibility to diet-induced steatohepatitis and insulin resistance. Mechanistic studies revealed that these metabolic effects were likely due to impaired β-oxidation resulting from inactivation of electron transport chain components. Inhibiting global ceramide synthesis negated the effects of CerS2 haploinsufficiency in vivo, and increasing C16-ceramides by overexpressing CerS6 recapitulated the phenotype in isolated, primary hepatocytes. Collectively, these studies reveal that altering sphingolipid acylation patterns impacts hepatic steatosis and insulin sensitivity and identify CerS6 as a possible therapeutic target for treating metabolic diseases associated with obesity.

Very long chain (C22-C24) ceramides are synthesized by ceramide synthase 2 (CerS2). A CerS2 null mouse displays hepatopathy because of depletion of C22-C24 ceramides, elevation of C16-ceramide, and/or elevation of sphinganine. Unexpectedly, CerS2 null mice were resistant to acetaminophen-induced hepatotoxicity. Although there were a number of biochemical changes in the liver, such as increased levels of glutathione and multiple drug-resistant protein 4, these effects are unlikely to account for the lack of acetaminophen toxicity. A number of other hepatotoxic agents, such as d-galactosamine, CCl4, and thioacetamide, were also ineffective in inducing liver damage. All of these drugs and chemicals require connexin (Cx) 32, a key gap junction protein, to induce hepatotoxicity. Cx32 was mislocalized to an intracellular location in hepatocytes from CerS2 null mice, which resulted in accelerated rates of its lysosomal degradation. This mislocalization resulted from the altered membrane properties of the CerS2 null mice, which was exemplified by the disruption of detergent-resistant membranes. The lack of acetaminophen toxicity and Cx32 mislocalization were reversed upon infection with recombinant adeno-associated virus expressing CerS2. We establish that Gap junction function is compromised upon altering the sphingolipid acyl chain length composition, which is of relevance for understanding the regulation of drug-induced liver injury.

Ceramides are known to be key players in intracellular signaling and are involved in apoptosis, cell senescence, proliferation, cell growth and differentiation. They are synthesized by ceramide synthases (CerS). So far, six different mammalian CerS (CerS1-6) have been described. Recently, we demonstrated that human breast cancer tissue displays increased activity of CerS2, 4, and 6, together with enhanced generation of their products, ceramides C(16:0), C(24:0), and C(24:1). Moreover, these increases were significantly associated with tumor dignity. To clarify the impact of this observation, we manipulated cellular ceramide levels by overexpressing ceramide synthases 2, 4 or 6 in MCF-7 (breast cancer) and HCT-116 (colon cancer) cells, respectively. Overexpression of ceramide synthases 4 and 6 elevated generation of short chain ceramides C(16:0), C(18:0) and C(20:0), while overexpression of ceramide synthase 2 had no effect on ceramide production in vivo, presumably due to limited substrate availability, because external addition of very long chain acyl-CoAs resulted in a significant upregulation of very long chain ceramides. We also demonstrated that upregulation of CerS4 and 6 led to the inhibition of cell proliferation and induction of apoptosis, whereas upregulation of CerS2 increased cell proliferation. On the basis of our data, we propose that a disequilibrium between ceramides of various chain length is crucial for cancer progression, while normal cells require an equilibrium between very long and long chain ceramides for normal physiology.

Ceramide is an important lipid signaling molecule that plays critical roles in regulating cell behavior. Ceramide synthesis is surprisingly complex and is orchestrated by six mammalian ceramide synthases, each of which produces ceramides with restricted acyl chain lengths. We have generated a CerS2 null mouse and characterized the changes in the long chain base and sphingolipid composition of livers from these mice. Ceramide and downstream sphingolipids were devoid of very long (C22–C24) acyl chains, consistent with the substrate specificity of CerS2 toward acyl-CoAs. Unexpectedly, C16-ceramide levels were elevated, and as a result, total ceramide levels were unaltered; however, C16-ceramide synthesis in vitro was not increased. Levels of sphinganine were also significantly elevated, by up to 50-fold, reminiscent of the effect of the ceramide synthase inhibitor, fumonisin B1. With the exceptions of glucosylceramide synthase and neutral sphingomyelinase 2, none of the other enzymes tested in either the sphingolipid biosynthetic or degradative pathways were significantly changed. Total glycerophospholipid and cholesterol levels were unaltered, although there was a marked elevation in C18:1 and C18:2 fatty acids in phosphatidylethanolamine, concomitant with a reduction in C18:0 and C20:4 fatty acids. Finally, differences were observed in the biophysical properties of lipid extracts isolated from liver microsomes, with membranes from CerS2 null mice displaying higher membrane fluidity and showing morphological changes. Together, these results demonstrate novel modes of cross-talk and regulation between the various branches of lipid metabolic pathways upon inhibition of very long acyl chain ceramide synthesis.

We have generated a mouse that cannot synthesize very long acyl chain (C22–C24) ceramides (Pewzner-Jung, Y., Park, H., Laviad, E. L., Silva, L. C., Lahiri, S., Stiban, J., Erez-Roman, R., Brugger, B., Sachsenheimer, T., Wieland, F. T., Prieto, M., Merrill, A. H., and Futerman, A. H. (2010) J. Biol. Chem. 285, 10902–10910) due to ablation of ceramide synthase 2 (CerS2). As a result, significant changes were observed in the sphingolipid profile of livers from these mice, including elevated C16-ceramide and sphinganine levels. We now examine the functional consequences of these changes. CerS2 null mice develop severe nonzonal hepatopathy from about 30 days of age, the age at which CerS2 expression peaks in wild type mice, and display increased rates of hepatocyte apoptosis and proliferation. In older mice there is extensive and pronounced hepatocellular anisocytosis with widespread formation of nodules of regenerative hepatocellular hyperplasia. Progressive hepatomegaly and noninvasive hepatocellular carcinoma are also seen from ∼10 months of age. Even though CerS2 is found at equally high mRNA levels in kidney and liver, there are no changes in renal function and no pathological changes in the kidney. High throughput analysis of RNA expression in liver revealed up-regulation of genes associated with cell cycle regulation, protein transport, cell-cell interactions and apoptosis, and down-regulation of genes associated with intermediary metabolism, such as lipid and steroid metabolism, adipocyte signaling, and amino acid metabolism. In addition, levels of the cell cycle regulator, the cyclin dependent-kinase inhibitor p21WAF1/CIP1, were highly elevated, which occurs by at least two mechanisms, one of which may involve p53. We propose a functional rationale for the synthesis of sphingolipids with very long acyl chains in liver homeostasis and in cell physiology.

Ceramide is an important lipid signaling molecule and a key intermediate in sphingolipid biosynthesis. Recent studies have implied a previously unappreciated role for the ceramide N-acyl chain length, inasmuch as ceramides containing specific fatty acids appear to play defined roles in cell physiology. The discovery of a family of mammalian ceramide synthases (CerS), each of which utilizes a restricted subset of acyl-CoAs for ceramide synthesis, strengthens this notion. We now report the characterization of mammalian CerS2. qPCR analysis reveals that CerS2 mRNA is found at the highest level of all CerS and has the broadest tissue distribution. CerS2 has a remarkable acyl-CoA specificity, showing no activity using C16:0-CoA and very low activity using C18:0, rather utilizing longer acyl-chain CoAs (C20–C26) for ceramide synthesis. There is a good correlation between CerS2 mRNA levels and levels of ceramide and sphingomyelin containing long acyl chains, at least in tissues where CerS2 mRNA is expressed at high levels. Interestingly, the activity of CerS2 can be regulated by another bioactive sphingolipid, sphingosine 1-phosphate (S1P), via interaction of S1P with two residues that are part of an S1P receptor-like motif found only in CerS2. These findings provide insight into the biochemical basis for the ceramide N-acyl chain composition of cells, and also reveal a novel and potentially important interplay between two bioactive sphingolipids that could be relevant to the regulation of sphingolipid metabolism and the opposing functions that these lipids play in signaling pathways.

Ceramide is thekey intermediate in thepathwayof sphingolipid (SL)2 biosynthesis (1) and an important intracellular signaling molecule (2, 3). Ceramide consists of a sphingoid long chain base to which a fatty acid is attached via an amide bond (Fig. 1). When the chemical composition of SLswas first determined in the 1940s (4), stearic acid (C18:0) was identified as the major fatty acid attached to the sphingoid base. Later, with the development of more sensitive techniques (5, 6), it became clear that mammalian SLs contain a wide variety of fatty acids, ranging in length from C14 to C32, that are predominantly saturated and can contain !or "-hydroxyl groups (7, 8). Within the past few years, there has been renewed interest in the functional significance of this fatty acid variability, and thisminireviewwill focus on current advances in our understanding of how the fatty acid composition of ceramide is regulated. In particular, we will discuss a recently discovered family of mammalian ceramide synthase (CerS) genes and emerging evidence that specific ceramides containing distinct fatty acids play important roles in cell growth and apoptosis.