Transcript Slide 1

LIPID MAPS Lipid Metabolomics Tutorial
Sphingolipids
Professor Edward A. Dennis
Department of Chemistry and Biochemistry
Department of Pharmacology, School of Medicine
University of California, San Diego
Copyright/attribution notice: You are free to copy, distribute, adapt and transmit this tutorial or
individual slides (without alteration) for academic, non-profit and non-commercial purposes.
Attribution: Edward A. Dennis (2010) “LIPID MAPS Lipid Metabolomics Tutorial” www.lipidmaps.org
E.A. DENNIS 2010 ©
Sphingolipid definitions
Sphingosine: a family of compounds, with the most common found in mammals being
this 18-carbon amino alcohol with a trans double bond; the starting point for ceramides.
Ceramide: a sphingosine molecule connected to a fatty acid by an amide bond.
Ceramides are the starting point for sphingomyelin, cerebrosides and gangliosides.
Sphingomyelin: a ceramide that has a phosphorylcholine head group in place
of its hydroxyl. Present in most mammalian cells, and rich in myelin sheaths
around nerves.
E.A. DENNIS 2010 ©
Palmitoyl CoA + Serine = Sphingosine
Serine
Palmitoyl-CoA
1. Serine donates 2 carbons
and an amino group
2. Reduction of the carbonyl to
a hydroxyl
3. Acyl group added to convert
to a dihydroceramide
4. Then, oxidation to add a
double bond
Look familiar?
Resembles both b-oxidation
and D4 desaturation
N-acyl-Sphingosine (Ceramide)
E.A. DENNIS 2010 ©
Sphingosine-1-phosphate
+H N
3
Sphingosine
kinase
Sphingosine
phosphatase
• Sphingosine can be phosphorylated by
sphingosine kinases, ubiquitous
enzymes in the cytosol, ER and nucleus
to make sphingosine-1-phosphate
(S1P).
• Sphingosine-1-phosphate, a
lysophospholipid, acts as a potent
messenger molecule that operates both
intra- and inter-cellularly.
• Within the cell, it promotes mitosis and
inhibits apoptosis. It also regulates
calcium mobilization and cell growth in
response to a variety of extracellular
stimuli.
+H N
3
•
•
Outside the cell, S1P exerts many of its
effects through interaction with five specific
G protein-coupled receptors on cell
surfaces. Different cells have different
receptor profiles.
S1P is vital to the function of several
immune cells. It is a major regulator of T
cell development, B and T cell
recirculation, tissue homing patterns, and
chemotactic responses to chemokines.
E.A. DENNIS 2010 ©
Sphingosine + Fatty Acid = Ceramide
Sphingosine
Fatty acyl-CoA
R = (CH2)n-CH3
Simple acyl transfer,
but to an amide
bond instead of the
typical ester
Ceramide
E.A. DENNIS 2010 ©
Ceramide + Choline = Sphingomyelin
Phosphocholine head
group gives sphingomyelin
a hydrophilic end
Choline carries a positive
charge the whole molecule
becomes more amphoteric
The phosphocholine
headgroup is transferred
to ceramide from PC
Choline
E.A. DENNIS 2010 ©
Comparison of Sphingomyelin and PC
At least one fatty acid of PC is usually unsaturated or polyunsaturated,
whereas, SM is usually saturated or mono-unsaturated; therefore,
SM rich membranes are less “fluid” than typical PC-rich membranes.
E.A. DENNIS 2010 ©
Comparison of S-1-P and LPA
Sphingosine-1-phosphate
(neutral zwitterion; net charge 0)
+H N
3
Lysophosphatidic acid
(Example: 1-myristoyl-sn-glycerophosphate)
(net negative charge)
E.A. DENNIS 2010 ©
More Definitions
Galactose (polar head)
Ceramide (non-polar tail)
Glycosidic
bond
Cerebrosides: a ceramide
that has a sugar added to the
head group. Most commonly,
the sugar is glucose (Glu) or
galactose (Gal).
Sialic acid
Gangliosides: a ceramide
that has multiple sugars
including at least 1 sialic
acid residue added to the
head group. Increased
variety and complexity.
E.A. DENNIS 2010 ©
Ceramide + Sugar = Cerebroside
Ceramide
UDP-Glucose
Sugar is activated
by UDP
UDP
Addition of sugar
occurs at the C1
OH group of
ceramide
Cerebroside
(Example:glucosyl-ceramide)
E.A. DENNIS 2010 ©
Ceramide + (Many Sugars) = Gangliosides
GM1
GM2
GM3
Sugars are activated
by UDP
(sialic acid by CMP)
Each sugar is added
individually
Gangliosides can
have varied,
complex structures
They often function
as antigens and
surface markers
Stearic acid (C18) N-acyl chain
Trivia: Do you know your blood type? Is it A+? B-? O? The letters refer to the
specific multi-sugar structures are attached to gangliosides and proteins on the
surface of your red blood cells.
E.A. DENNIS 2010 ©
Degradation of Sphingolipids
• The amide bond of sphingolipids does not break down easily
– which is why they make good membrane components
• Enzymatic degradation is used for turnover
– LOTS of degradation enzymes exist
• it’s a long, complicated bunch of pathways
• Genetic defects in these enzymes cause a long list of
diseases
–
–
–
–
all involve unhealthy accumulation of some sphingolipid
most are rare, but more common in specific ethnicities
key diseases: Gaucher’s, Tay-Sachs’, Fabry’s and Niemann-Pick
Resources: (Online Mendelian Inheritance in Man)
• OMIM Web site: www.ncbi.nih.gov/OMIM/searchomim.html
E.A. DENNIS 2010 ©
Degradation of Sphingolipids
GM1
Sulfatide
Globoside
GM1 b -galactosidase
Hexosaminidase A/B
GM1 Gangliosidosis
Gal
GM2
GM3
Metachromatic leukodystrophy
GalNAc
Trihexosylceramide
GalNAc
Fabry’s disease
Lactosylceramide
Ganglioside neuraminidase
Galactocerebrosidase
Krabbe’s disease
Gal
Glucocerebroside
b -galactosidase
NANA
Sphingomyelin
SO42-
Galactocerebroside
a -galactosidase A
Hexosaminidase A
Tay-Sachs disease
Sandhoff’s disease
Arylsulfatase A
Gal
Gal
Ceramide
Glucocerebrosidase
Gaucher’s disease
Glc
Sphingomyelinase
Phosphocholine
Fatty acid
+
Niemann-Pick disease
Sphingosine
Ceramidase
Farber’s disease
E.A. DENNIS 2010 ©
Tay-Sachs’ Disease
• Incidence: Like Gaucher’s but rarer
– ~1:30 Ashkenazi Jews are carriers
– ~1:500 carriers in general population
• Symptoms:Neurodegenerative
– mental retardation and seizures
– listlessness, fixed gaze, hypotonia
– cherry-red spot on retina (see picture)
• Mechanism: Genetic
– Lack of GM2 hexosaminidase A
Cherry-red spot on a patient’s retina, a
common finding in patients with TaySachs’ disease.
• Auto recessive, OMIM #272800
– Ganglioside GM2
• Builds up in CNS
• Treatments: No good therapy yet
Trivia: Injections of recombinant hexosaminidase A do not
help Tay-Sachs’ patients because it cannot cross the
blood-brain barrier.
– Supportive and symptomatic
– Patients die by age 5
– Gene therapy target (future)
E.A. DENNIS 2010 ©
Gaucher’s Disease
• Incidence: Uncommon in most groups
– ~1:13 Ashkenazi Jews are carriers
• Symptoms:
– enlarged liver and spleen (see picture)
– easy bruising and bone fractures
– hyperpigmentation of skin
– sometimes: anemia
• Mechanism: Genetic
– Lack of working b-glucosidase
• Auto recessive, OMIM #230800
– Glucosyl acylsphingosine
• Builds up in liver, spleen & bone
Magic marker outlines of the enlarged
liver and spleen in a school-aged boy with
Gaucher’s disease. Note also the
hyperpigmented skin.
• Treatments:
– Recombinant acid b-glucosidase
– Symptomatic support
– Gene therapy target (future)
E.A. DENNIS 2010 ©
Niemann-Pick Disease Type A
• Incidence: Type A is the most severe of
the 5 subtypes of Niemann-Pick Disease
– ~1:90 Ashkenazi Jews are carriers
• Symptoms: Neurodegenerative
– Large abdomen within 3-6 mos. and jaundice
– Progressive loss of early motor skills,
progressive spasticity, developmental delay
– Cherry red spot in the eye
– (Generally) a very rapid decline leading to
death by two to three years of age.
• Mechanism: Genetic
– Lack of Sphingomyelinase
• Auto recessive, OMIM #257200
– Sphingomyelin
Patient with Niemann Pick Disease
• builds up in CNS, liver and lungs
• Treatments:
– Supportive and symptomatic
– Patients die by age 3
– No effective therapy to date
E.A. DENNIS 2010 ©
Summary of Today’s Sphingolipids
Molecule(s)
Synthesis Scheme
Significance
Sphingosine
Palmitoyl CoA + Serine
Brings in the amine group
Important signaling molecule
Ceramides
Sphingosine + Fatty Acid
Amide bond, hydrophobicity
Important signaling molecule
Sphingomyelins
Ceramide + PhosphoCholine
Amphoteric & charged, diseases
Membrane component
Cerebrosides
Ceramide + (Mono)saccharides
Amphoteric & neutral, diseases
Rich in brain
Gangliosides
Ceramide + Polysaccharides
+ Sialic acid
Complexity, diseases
Rich in brain
E.A. DENNIS 2010 ©
Acknowledgement
This tutorial is based on an evolving subset of lectures and
accompanying slides presented to medical students in the Cell
Biology and Biochemistry course at the School of Medicine of the
University of California, San Diego.
I wish to thank Dr. Bridget Quinn and Dr. Keith Cross for aid in
developing many of the original slides, Dr. Eoin Fahy for advice in
applying the LIPID MAPS nomenclature and structural drawing
conventions [Fahy et al (2005) J Lipid Res, 46, 839-61; Fahy et al
(2009) J Lipid Res, 50, S9-14] and Masada Disenhouse for help in
adopting to the tutorial format.
Edward A. Dennis
September, 2010
La Jolla, California
E.A. DENNIS 2010 ©