Ceramides (SP02)

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LIPID MAPS Subclasses


Ceramide forms the backbone for all Sphingolipids (SP). It is an important second messenger in various stress responses and growth mechanisms, and formation of ceramide by the hydrolysis of sphingomyelin or de novo synthesis occurs in response to many inducers of stress.



Natural sources



Biophysical properties

Biochemical pathways

Biochemical synthesis

De novo synthesis

Figure 32.  De novo synthesis of ceramide
Figure 32. De novo synthesis of ceramide
The biosynthesis of ceramide (which occurs in the endoplasmic reticulum) is initiated by the condensation of serine and palmitoyl-CoA, a reaction, which is catalyzed by serine-palmitoyl CoA transferase (SPT). Mammalian SPT is a heterodimer of 35-kDa LCB1/SPT1 and 63-kDa LCB2/SPT2 subunits bound to the endoplasmic reticulum (Dickson et al. 2000, Hanada et al. 2003) and building the enzyme in a 1:1 ratio (Hanada et al. 2000). The long-chain base gene 1 (LCB1) was isolated primarily from a yeast mutant strain lacking SPT activity and requiring exogenous long-chain base for growth (Wells and Lester 1983). The protein encoded by this gene showed similarity at the amino acid level to the enzyme catalysing the serine-palmitoyl CoA transfer. Further experiments revealed that LCB1 and the homolog LCB2 are subunits of the SPT enzyme complex (Buede et al. 1991, Pinto et al. 1992). One of the more direct factors that affect SPT activity is the availability of both serine- and palmitoyl-CoA, and because SPT is highly selective for fatty acyl-CoA with 16 +/- 1 carbon atoms, other fatty acids can be inhibitory in vivo, possibly by competing for the CoA pool (Merrill et al. 1988). SPT is the first and rate-limiting enzyme in the de novo pathway (Perry et al. 2000). The newly formed 3-ketosphinganine is subsequently reduced by NADPH-dependent ketosphinganine reductase to dihydrosphingosine. The amide linkage of fatty acyl groups to dihydrosphingosine forms dihydroceramide. This reaction is catalyzed by dihydroceramide synthase, an enzyme, which acylates various long chain bases and utilizes a wide spectrum of fatty acyl-CoAs. Since there are four kinds of fatty acids in sphingolipids, there are not yet confirmed suspections of existence of more than one dihydroceramide synthase (Fig. 33). Untill now reasonable molecular and biochemical evidences are missing. However, It has been only very recently proven, that LASS5 (LAG1 longevity assurance homolog 5), is a bona fide (dihydro) ceramide synthase (Lahiri, Futerman, 2005).

Ceramide is formed from dihydroceramide by the introduction of the trans-4, 5-double bond. The reaction is catalyzed by dihydroceramide desaturase originating from the cytosolic side of the endoplasmic reticulum. At the state of cellular homeostasis, once formed, ceramide is not accumulated but translocated to the Golgi where it serves as a starting point and metabolic precursor for all other sphingolipids such as sphingomyelin, glycosphingolipids of the lacto-, globo- and ganglioside series, and sulfatides. There are at least two pathways by which ceramide is transported to the Golgi: an ATP- and cytosol-dependent major pathway and an ATP- or cytosol-independent minor pathway (Hanada et al. 1998, Fukasawa et al. 1999, Yasuda et al. 2001).

Figure 33. The relationship between LAG1 longevity assurance homolog (LASS) genes as candidates for ceramide synthases
Figure 33. The relationship between LAG1 longevity assurance homolog (LASS) genes as candidates for ceramide synthases

Recently, a gene called ceramide transfer protein (CERT) has been identified (Hanada et al. 2003). This gene is a splice variant of the Goodpasture antigen-binding protein (GPBP-delta26) and codes for a cytoplasmic protein with a lipid-transfer catalysing START domain, a phosphoinositde-binding pleckstrin homology (PH) domain and two phenylalanines (FF) in an acidic tract (FFAT) motif. The FFAT motif is found on diverse human lipid binding proteins and its combination with a PH domain which binds to the Golgi apparatus seems to predict the role of CERT (Loewen et al. 2003). It has been suggested that CERT acts as ceramide carrier that shuttles between ER and Golgi in a non-vesicular manner. CERT specifically extracts ceramide from phospholipid bilayer showing very little affinity to other related sphingolipids. As it has been observed, CERT is involved in transport of ceramide for sphingomyelin synthesis and not for glycosylceramide synthesis (Futerman, Riezman, 2005).

Once delivered to the Golgi membrane, ceramide needs to translocate to the Gogi lumen for sphingomyelin synthesis, what occurs via “flip-flop” as a spontaneous transbilayer movement (Contreras et al 2005). ceramide de novo synthesis is influenced by factors regulating the activity of serine palmitoyltransferase and it has been documented that LCB mRNA expression and SPT activity increase in response to various inflammatory and stress stimuli. Interleukin-1β (Memon et al. 1998), UVB radiation (Farrell et al. 1998), Fatty acids and cholesterol (Shimabukuro et al. 1998) stimulate the activity of SPT resulting in the cytotoxic accumulation of palmitate accompanied by the elevation of intracellular ceramide and induction of apoptosis.

Ceramide is also generated at various subcellular locations by sphingomyelin hydrolysis (van Meer et al. 2000). This process of ceramide formation is a receptor-operated pathway (Hannun and Bell, 1989), which remained evolutionary, unchanged and is induced by different environmental and physiological stimuli. At the plasma membrane, ceramide is generated from sphingomyelin hydrolysis by acidic and/or neutral sphingomyelinases activated by diverse cytokines, death receptor ligands, differentiation factors or drugs (Levade and Jaffrezou, 1999). Stimulation of cells with 1,25-dihydroxy-vitamin D3, TNF-alpha and CD40 ligand activates a neutral sphingomyelinase at the plasma membrane of cells, generating at the cytosolic side intracellular ceramide and phosphocholine (Geilen et al. 1996, Kolesnick and Kronke, 19984). ceramide can also be formed through the action of an acidic sphingomyelinase that is activated by 1,2-diacylglycerol. Up till now, several sphingomyelinases have been characterized in mammalian tissues and they differ from each other by their location, Mg+2 and Zn+2 dependence and pH optimum (Levade and Jaffrezou, 1999, Hofmann et al. 2000). Ceramide catabolism starts with a ceramidase catalysing the cleavage of ceramide at the amide bond resulting in sphingosine and a free fatty acid. Three types of ceramidases have been described to date and classified according to pH optima as acid, neutral, or alkaline (Pettus et al. 2002). The deficiency of acidic ceramidase, which is located in lysosomes, provides the genetic background for Farber’s disease (Sugita et al. 1972). Sphingosine released due to the action of ceramidase can be reacylated to ceramide or phosphorylated by sphingosine kinase to sphingosine-1-phosphate.


Ceramide can be reutilized for the synthesis of sphingomyelin from phosphatidylcholine via choline phosphotransferase or may be phosphorylated to form ceramide-1-phosphate. The third pathway leads to glycosphingolipid synthesis. The sequential transfer of sugar residues from nucleotide sugars to ceramide results in the synthesis of glucosylceramide (GlcCer) at the cytosolic side of the Golgi, and in specialized cells, e.g. epithelial cells, ceramide serves for synthesis of galactosylceramide (GalCer) in the lumen of the ER (20). It has been proposed that GlcCer synthase in the cis-Golgi receives ceramide via the vesicular pathway whereas GlcCer synthase in the trans-Golgi receives ceramide from the ER via membrane contacts (Sadeghlar et al. 2000). The activity of galactosyltransferase 2 (GalT-2), which catalyses the synthesis of lactosylceramide, another glycosphingolipid, has been found increased in familial hypercholesterolemia and atherosclerosis (Chatterjee et al. 1982, Chatterjee et al. 1997). The increased levels of other glycosphingolipids in atherosclerotic lesions have been also reported (Mukhin et al. 1995).

Ceramide-1-phosphate, an interconvertable metabolite of ceramide, is emerging as an important biological mediator. It is generated in the reaction of ceramide phosphorylation catalysed by ceramide kinase (CERK). As a bioactive lipid, ceramide-1-phosphate was demonstrated to play a role in mediation of inflammatory responses (Pettus et al, 2004).


Biological processes associated

Link to Lipids as constituents of biological processes

Similarities with lipid A moiety of lipopolysaccharide

Ceramide shares some structural and functional similarities with the lipid A moiety of lipopolysaccharide (LPS), a lipid from the outer membrane of Gram-negative bacteria. The cellular responses to LPS include changes in shape, metabolism, and gene expression but also induction of a variety of biological effects that are involved in systemic inflammation and sepsis (Sweet et al. 1996). The initiation of these effects is due to the activation of monocyte/macrophages, leading to the secretion of proinflammatory cytokines such as TNF-alpha, IL-1ß, IL-6 and IL-8. It has been suggested that LPS and ceramide recognize the same intracellular molecules (Wright and Kolesnick, 1995) and LPS was shown to mimick some ceramide properties. Ceramide-activated protein kinase (CAPK) appears to be a common target and its activation by both agonists leads to the activation of MAP kinase and the translocation of activated NF-kappa-B. Recent data emphasize that although LPS and ceramide may share many signalling components, the signalling pathways are not identical (Wright and Kolesnick, 1995, MacKichan and DeFranco, 1999, Pfau et al. 1998)


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Analysis methods

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