A role for fucose α(1-2) galactose carbohydrates in neuronal growth

Article abstract of DOI:10.1021/ja044631v

We report a fucose α(1-2) galactose-mediated pathway for the modulation of neuronal growth and morphology. Our studies provide strong evidence for the presence of Fucα(1-2)Gal glycoproteins and lectin receptors in hippocampal neurons. Additionally, we sho

Full text of DOI:10.1021/ja044631v

-Supporting Information-
A Role for Fucose α(1-2) Galactose Carbohydrates in Neuronal Growth
Stacey A. Kalovidouris, Cristal I. Gama, Linda C. Hsieh-Wilson
Division of Chemistry and Chemical Engineering, California Institute of Technology,
Pasadena, California 91125
General Methods:
Chemicals were purchased from commercial suppliers and used as received.
Lectins were purchased from Vector Labs (Burlingame, California), polymers from
GlycoTech (Gaithersburg, Maryland), and tissue culture reagents from Gibco (Carlsbad,
California). Unless stated otherwise, reactions were performed in flame-dried glassware
under an argon environment, using freshly distilled solvents. Thin-layer chromatography
(TLC) was carried out on glass sheets coated with Kieselgel 60 F254 Fertigplatten (Merck,
Darmstadt, Germany). The plates were inspected by UV light and developed by
treatment with a cerium ammonium molybdate stain followed by heating. Column
chromatography was carried out using silica gel 60 (ICN Silitech 32-63 D, 60 Å). High-
resolution fast atom bombardment mass spectra (FAB-MS) were obtained on a Jeol JMS-
600H spectometer, and low-resolution electrospray mass spectra (ES-MS) were acquired
on a PE Sciex API 365 LC/MS/MS Triple Quadrupole mass spectrometer with a proton
1
13
nanospray source. H and C NMR spectra were recorded using a Varian Mercury 300
1
spectrometer with the residual solvent or TMS as the internal standard. Data for H are
reported as follows: chemical shift (δ ppm), multiplicity (s = singlet, d = doublet, t =
triplet, q = quartet, m = multiplet), coupling constant in Hz, and integration.
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Experimental Details:
Scheme 1a Synthesis of Probe 1.
O
RO
RO
OR
OAc
O
AcO
AcO
OAc
O
O
AcO
O
a
b
NHR'
SPh
O
O
O
O
O
O
O
OR
OAc
OAc
OR
OR
OAc
OAc
OAc
OAc
R = Ac R' = COCF3
2
3
4
c
R = R' = H
5
OH
O
HO
HO
d
O
H
O
N
O
O
5
NH
O
HN
O
OH
S
OH
OH
1
aConditions: (a) i.TMSSPh, ZnI2 (76%) ii. Ac2O, DMAP, C5H6N (quant.); (b) NIS-AgOTf, 2-(2-
trifluoroacetamido ethoxy)ethanol, CH2Cl2 (68%); (c) K2CO3, MeOH (100%); (d) Et3N, DMF, NHS-
Biotin (60%).
Phenyl 3,4,5-tri-O-(2,3,4-tri-O-acetyl-α-L-fucopyranosyl)-1-thio-β-D-galactopyrano-
side (3): The following thioglycoside formation procedure was adapted from a method
reported by Motawia and coworkers.1 Known compound 22 (1.80 g, 3.40 mmol),
(phenylthio)trimethylsilane (2.0 mL, 10.4 mmol) and zinc iodide (3.30 g, 10.4 mmol) in
CH2Cl2 (20.0 mL) were stirred at rt for 21 h. The mixture was diluted with EtOAc (120
mL) and washed successively with saturated aqueous NaHCO3 (150 mL), water (3 x 50
mL) and brine (20 mL). The organic layer was then dried over sodium sulfate, filtered
and concentrated in vacuo. The residue was dissolved in dry THF (15.0 mL) and 1M
tetrabutylammonium fluoride in THF (6.0 mL) was added. After this reaction mixture
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stirred for an additional 20 min at rt, the solvent was evaporated. Thereafter, the residue
was redissolved in EtOAc (60 mL), washed with water (3 x 30 mL), saturated aqueous
NaHCO3 (30 mL) and brine (30 mL), dried over Na2SO4, then filtered and concentrated
to afford the β−thioglycoside (1.6 g, 76%). To a solution of the β− thioglycoside (310
mg, 0.50 mmol) in dry pyridine (6.0 mL) was added acetic anhydride (3.0 mL). The
reaction was allowed to stir at rt overnight. The solvent was evaporated and residual
pyridine was azeotroped with toluene. Column chromatography (SiO2, Hexane/EtOAc,
1
3:1) afforded 3 (330 mg, quant.). H NMR (300 MHz, CDCl3): δ = 1.12 (d, 3H, J = 6.5
Hz, H-6'), 1.51 (s, 3H, OAc), 1.66 (2s, 6H, OAc), 1.76 (s, 3H, OAc), 1.87 (s, 3H, OAc),
1.93 (s, 3H, OAc), 3.41 (ddd, 1H, J = 0.8 Hz, 7.0 Hz, 7.3 Hz, H-5), 3.83 (dd, 1H, J = 7.7
Hz, H-1), 4.06 (dd, 1H, J = 7.3 Hz, 10.2 Hz, H-6b), 4.12 (dd, 1H, J = 7.7 Hz, J = 10 Hz,
H-2), 4.13 (dd, 1H, J = 7.0 Hz, 10.2 Hz, H-6a), 4.62 (dq, 1H, J = 1.1 Hz, 6.5 Hz, H-5'),
5.19 (dd, 1H, J = 3.5 Hz, 10 Hz, H-3), 5.42 (dd, 1H, J = 0.8 Hz, 3.5 Hz, H-4), 5.44 (dd,
1H, J = 3.8 Hz, 11.0 Hz, H-2'), 5.60 (dd, 1H, J = 1.1Hz, 3.4 Hz, H-4'), 5.74 (d, 1H, J =
13
3.8, H-1'), 5.83 (dd, 1H, J = 3.4 Hz, 11.0 Hz, H-3'), 7.20-7.59 (m, 5H, Ph); C NMR (75
MHz, CDCl3): δ = 15.9, 20.7 (3C), 20.8 (3C), 61.8, 65.8, 67.3, 67.9, 68.1, 70.1, 71.0,
73.1 (3C), 87.8, 98.2, 100.2, 127.7, 129.3, 131.7, 133.2, 169.9, 170.0, 170.2, 170.5,
170.6, 170.6. HRMS m/z Calculated for C30H38O15NaS [M+Na]+ 693.1253. Found
693.1271.
2-(2-Trifluoroacetamido ethoxy)ethyl-3,4,5-tri-O-(2,3,4-tri-O-acetyl-α-L-fucopyran-
osyl)-1-β-D-galactopyranoside (4): The following is a modified procedure from Kanie
et. al.3 Compound 3 (330 mg, 0.50 mmol) was azeotroped with toluene and then
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dissolved in CH2Cl2 (5.0 mL) and 2-(2-trifluoroacetamido ethoxy) ethanol (67 mg, 0.30
mmol) containing molecular sieves (4Å). After stirring for 10 min, the mixture was
cooled to 20 °C. N-Iodosuccinimide (107 mg, 0.40 mmol), followed by silver triflate
(108 mg, 0.40 mmol), was added. The reaction was allowed to warm to rt and proceeded
for 2 h after addition of the silver triflate. After the reaction was complete, it was diluted
with CH2Cl2 and filtered. The filtrate was washed with saturated aqueous Na2SO4,
filtered and concentrated. Column chromatography (SiO2, Hexane/EtOAc, 3:1) afforded
1
4 (210 mg, 68%, α:β = 1:3): only β was used. H-NMR (300 MHz, CDCl3): δ 1.10 (d,
3H, J = 6.5 Hz, H-6'), 1.99 (s, 3H, OAc), 2.00 (s, 3H, OAc), 2.01 (s, 3H, OAc), 2.04 (s,
3H, OAc), 2.13 (s, 3H, OAc), 2.15 (s, 3H, OAc), 3.40 (ddd, 3H, J = 0.8 Hz, 7.0 Hz, 7.3
Hz, H-5, OCH2), 3.55-3.78 (m, 6H,OCH2), 3.88 (dd, 1H, J = 7.8 Hz, H-1), 3.97 (dd, 1H, J
= 7.8 Hz, 10.2 Hz, H-6b), 4.02 (dd, 1H, J = 7.8, 10.0 Hz, H-2), 4.14 (dd, 1H, J = 7.8 Hz,
10.2 Hz, H-6a), 4.28 (m, 1H, H-3'), 4.50 (dq, 1H, J = 1.1 Hz, 6.5 Hz, H-5'), 5.00 (dd, 1H,
J = 3.6 Hz, 10.0 Hz, H-3), 5.32 (dd, 1H, J = 0.5 Hz, 3.3 Hz, H-4), 5.31-5.42 (m, 3H, H-2',
H-4', H-1'), 7.49 (bs, 1H, N-H); 13C NMR (75 MHz, CDCl3): δ = 16.3, 21.0 (2C), 28.7,
29.7, 45.5, 61.8, 65.0, 66.2, 67.9, 68.2 (2C), 69.4, 69.7, 70.3, 70.6, 71.0, 71.4, 97.9, 98.5,
128.6 (2C), 129.5 (2C), 130.1(2C), 132.4, 170.1, 170.2, 170.4. HRMS m/z Calculated for
C30H42F3NO18 [M+H]+ 762.2465. Found 762.2470.
(N - [6-([Biotinoyl]amino) ethoxy) ethyl - O-(α-L-fucopyranosyl)-(1-2)-β-D-
galactopyranoside (1): The procedure for the preparation of 5 was adapted from
Newman et al.4 Compound 4 (0.50 g, 0.70 mmol) was dissolved in a 7% solution of
K2CO3 in aqueous MeOH (2:5, v:v), and the reaction mixture was stirred for 12 h at rt.
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The solution was neutralized with 1N HCl, and the organic layer was extracted with
MeOH and concentrated to afford 5 (270 mg, quant.) as a white foam. Amine 5 (70 mg,
0.17 mmol) was dissolved in DMF (2.0 mL), and the pH was adjusted to 9 using TEA.
N-Hydroxysuccinimido biotin (70 mg, 0.20 mmol) was added and the reaction stirred for
12 h at rt. The reaction mixture was concentrated to afford an off-white syrup.
Preparative reversed-phase chromatography using a gradient of 0% to 50% aqueous 0.1
% TFA in CH3CN over 60 min followed by a gradient of 50% to 100% CH3CN over 60
min (retention time 40 min; flow rate 21 mL/min) afforded pure 1 (60 mg) in 60% yield.
1H NMR (300 MHz, D2O): δ 1.05 (d, 3H, J = 6.6 Hz, H-6'), 1.23-1.31 (m, 2H, CH2),
1.41-1.60 (m, 4H, CH2), 2.12 (t, 2H, J = 7.0 Hz, CH2), 2.62 (d, 2H, J = 13.2 Hz, SCH2),
2.84 (dd, 2H, J = 4.8 Hz, 12.6 Hz, CH2), 3.17 (m, 4H, CH2), 3.23 (dd, 2H, J = 4.8 Hz, J =
8.7 Hz, CH2), 3.42-4.10 (m, 12H, H-2, H-3, H-4, H-5, H-6a, H-6b, H-2', H-3', H-4', H-5',
CH), 4.45 (d, 1H, J = 7.8 Hz, H-1), 4.46 (m, 1H, CH), 5.08 (d, 1H, J = 2.2 Hz, H-1'); 13C
NMR (75 MHz, D2O): δ = 15.6, 25.1, 27.7 (2C), 27.9, 35.4 (2C), 39.0, 39.7, 55.4, 60.2,
61.1, 62.1, 66.8, 67.2, 68.3, 68.8, 69.3, 69.4, 70.8, 71.7, 77.9, 98.2, 101.6, 165.3, 176.9.
HRMS m/z Calculated for C26H45N3O13S [M+H]+ 640.2751. Found 640.2725.
Treatment of Hippocampal Neurons with PAA Polymers and Lectins:
Hippocampal neurons were cultured using a procedure modified from Goslin and
Banker.5 Briefly, the hippocampi of embryonic day 18 (E18) rats were dissected and
transferred to 4.5 mL of ice-cold Calcium and Magnesium Free-Hank's Balanced Salt
Solution (CMF-HBSS). Trypsin (2.5%, no EDTA) was added to 5 mL, and the tissue
was incubated for 15 min at 37 °C. The trypsin solution was removed and the tissue
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sample washed three times with 5 mL of CMF-HBSS. Cells were then dissociated from
the tissue in 1 mL of CMF-HBSS by passing through a P1000 pipet tip twenty times.
The cells were counted, diluted into Minimal Eagle's Medium (MEM) plus 10% fetal
bovine serum, and seeded on poly-DL-ornithine-coated glass coverslips (Carolina
Biological) at a density of 75 cells/mm2 (100 µL/coverslip) for 30 min. After this time,
500 µL of supplemented Neurobasal medium (47.5 mL Neurobasal medium without L-
glutamine; 0.5 mL L-glutamine (200 mM); 0.5 mL penicillin/streptomycin (10,000
U/mL); 0.5 mL antibiotic-antimycotic (100X stock), 1.0 mL B-27 serum-free supplement
(50X stock); 50 µL of 0.5 M kynurenic acid in 1 N NaOH) was added to each coverslip.
The use of kynurenic acid to block glutamate receptor ion channels and enhance neuronal
health and survival is standard protocol for neuronal cultures.5 The cultures were
incubated in 5% CO2 at 37 °C for 20 h. The media was then removed, and a 50 µL
solution of carbohydrate-PAA conjugate (1.3 µM, 13 µM, or 130 µM) in PBS or a 50 µL
solution of lectin (3.7 µM) in HEPES was added to supplemented Neurobasal medium
(450 µL) on each coverslip. For the competition experiments, a 50 µL solution of the
lectin (3.7 µM) and probe 1 (1.5 mM) in HEPES was preincubated at 4 °C for 12 h and
was then added to supplemented Neurobasal medium (450 µL) on each coverslip. The
cultures were incubated for 24 h in 5% CO2 at 37 °C and analyzed as described below.
Immunocytochemistry of Hippocampal Neuronal Cultures:
The hippocampal neurons on the coverslips were rinsed one time with PBS, fixed in 4%
paraformaldehyde for 20 min at rt, washed twice with PBS, permeabilized in 0.3% Triton
X-100 for 5 min at rt, and washed twice with PBS. Non-specific binding was blocked by
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incubating with 3% BSA for 1 h at rt and then rinsing once with PBS. Cells were then
incubated with anti-tau antibodies (rabbit polyclonal, 1:600; Sigma) in 3% BSA for 2 h at
rt. Excess antibody was rinsed away 5 times with PBS. The secondary antibody, anti-
rabbit IgG AlexaFluor 488 (1:600; Molecular Probes), was added for 1 h at 37 °C in 3%
BSA. Excess secondary antibody was washed off 5 times with PBS. The coverslips
were mounted onto glass slides using Vectashield mounting medium (Vector Labs) and
sealed with clear nail polish. Cells were imaged using a Zeiss Axiovert 100M inverted
laser microscope (Biological Imaging Center in the Beckman Institute at Caltech).
Images were captured with LSM Pascal software using a 40X plan-neofluar oil objective
and an excitation wavelength of 488 nm or 568nm.
Morphometric Analysis:
All experiments were performed in duplicate. For each experiment, 50 randomly selected
cells were analyzed per coverslip using similar quantitative analysis techniques reported
by Schmid et al. 6 Briefly, only neurites longer than ~10 µm and not in contact with other
cells were measured using NIH Image 1.62 software. The mean neurite lengths were
compared among the different conditions by the ANOVA test using the statistical
analysis program StatView (SAS Institute Inc., Cary, NC).
Staining of Hippocampal Neurons with Probe 1 and Fluorescein-Conjugated UEA-I
Lectin:
Hippocampal neuronal cultures were prepared as described above and maintained at 37
°C, 5% CO2 in supplemented Neurobasal medium. After 23 days in culture, the medium
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was replaced, and neurons were treated with the endocytosis inhibitor phenylarsine
oxide7 (PAO; 4 µL in DMSO, final concentration 10 µM) and either probe 1 (24 µL in
PBS, final concentration 3 mM), biotin (24 µL in PBS, final concentration 3 mM), or
fluorescein-conjugated UEA I lectin (4 µL, 1:100 final dilution) in supplemented
Neurobasal medium (400 µL final volume) for 1 h at 37 °C, 5% CO2. After 1 h, neurons
were rinsed 2 times with PBS, fixed in 4% paraformaldehyde for 20 min at rt, washed 2
times with PBS, permeabilized in 0.3% Triton X-100 for 5 min at rt, and washed 2 times
with PBS. Non-specific binding was blocked with 3% BSA for 1 h at rt and then rinsed
one time with PBS. Anti-tau antibody (rabbit polyclonal, 1:600; Sigma) was added in 3%
BSA for 2 h at rt and the excess antibody rinsed off 5 times with PBS. Probe 1 was
detected with streptavidin conjugated to AlexaFluor 488 (1:200; Molecular Probes), and
anti-tau was detected with a secondary antibody conjugated to AlexaFluor 568 (goat anti-
rabbit IgG, 1:600; Molecular Probes). Both dye-conjugated streptavidin and secondary
antibodies were added in 3% BSA for 1 h at 37 °C and the excess reagent washed off 5
times with PBS. Coverslips were then mounted onto slides with Vectashield, sealed, and
imaged using confocal laser microscopy.
De-lipidation of Neurons with MeOH/CHCl3 Prior to Treatment with Probe 1 and
Fluorescein-Conjugated UEA-I Lectin:
To confirm that probe 1 was binding specifically to proteins rather than interacting with
the membrane lipids, neurons were delipidated following the protocol of Yavin and
Yavin.8 Briefly, after 23 days in culture, cells were rinsed once with PBS then exposed to
MeOH/CHCl3 (1/2 by vol) for 15 min at –80 °C. This procedure fixes the cells to the
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coverslip and extracts cellular lipids. After removing the MeOH/CHCl3 mixture,
coverslips were dried at rt then incubated with 3% BSA for 1 hr at rt. After one rinse
with PBS, neurons were treated with the endocytosis inhibitor phenylarsine oxide7 (PAO;
4 µL in DMSO, final concentration 10 µM) and either probe 1 (24 µL in PBS, final
concentration 3 mM), biotin (24 µL in PBS, final concentration 3 mM), or fluorescein-
conjugated UEA I lectin (4 µL, 1:100 final dilution) in supplemented Neurobasal medium
(400 µL final volume) for 1 h at 37 °C, 5% CO2. Excess reagents were rinsed off 5 times
with PBS before incubating with anti-tau antibody (1:600) for 2 h at rt. Cells were
washed 5 times with PBS and then treated with streptavidin conjugated to AlexaFluor
488 (1:200) and secondary antibody conjugated to AlexaFluor 568 (goat anti-rabbit IgG,
1:600) in 3% BSA for 1 h at 37 °C. Cells were then rinsed 5 times with PBS before
mounted onto slides and analyzed by confocal laser microscopy. De-lipidation did not
alter the staining of either 1 or UEA I lectin (Figures S1 and S2).
Treatment of Neuronal Cultures with 2-Deoxy-D-Galactose, 3-Deoxy-D-Galactose and D-
Galactose:
Hippocampal neurons were plated on poly-DL-ornithine-coated glass coverslips as
described above. After one day in culture, the medium was replaced with fresh medium,
and the small molecules were added. A dose-response experiment was initially
performed to determine the minimum concentration of 2-dGal needed to elicit an effect.
Neurons were treated with varying concentrations of 2-dGal (1, 5, 10, 15, or 30 mM in 25
µL PBS with 475 µL of supplemented Neurobasal medium) for 2 days before
immunostaining with anti-tau antibodies as described above (Figure S3). Importantly, no
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cellular toxicity was observed at concentrations up to 30 mM 2-dGal, as demonstrated by
trypan blue staining, adherence of the cells to the coverslip, and healthy cellular
morphology. A concentration of 15 mM was used in subsequent experiments as it
produced a strong effect on neurite outgrowth. Cells were treated as above under 4
different conditions: (1) incubation with 15 mM 2-dGal for 2 days, (2) incubation with 15
mM 3-deoxy-D-galactose for 2 days, (3) incubation with 15 mM 2-dGal for 2 days
followed by incubation with 75 mM D-galactose for 2 days, or (4) no treatment for 2
days. After adding the small molecules, cultures were incubated at 37 °C, 5% CO2, then
washed once with PBS, and immunostained with the anti-tau antibody as described
above.
Analysis of the Fucα(1-2)Gal Epitope on Neuronal Proteins Following Treatment with 2-
Deoxy-D-Galactose:
In addition to cells plated on coverslips, hippocampal neurons were grown in 30 mm
dishes and treated with or without 30 mM 2-dGal (25 µL in PBS with 475 µL
supplemented Neurobasal medium). After 4 days, cells were harvested with 2.5%
trypsin, lysed with 1% boiling SDS with protease inhibitors, and cell lysates probed by
Western blotting using the anti-Fucα(1-2)Gal antibody A46-B/B10.9 Protein
concentrations of the neuronal lysates were determined using the BCA Protein Assay
(Pierce). Equal amounts of total protein were resolved by 10% SDS-PAGE, and proteins
were transferred to PVDF membrane (Millipore) in 20 mM Tris-Cl pH 8.6/ 120 mM
glycine/ 20% methanol. Western blots were blocked for 1 h with 3% periodated BSA10
and rinsed with TBST (50 mM Tris-Cl pH 7.4/ 150 mM NaCl/ 0.1% Tween-20). Blots
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were incubated with anti-Fucα(1-2)Gal antibody A46-B/B109 (0.5 µg/mL; gift from Dr.
U. Karsten, Max-Delbruck Centre for Molecular Medicine, Berlin-Buch, Germany) in
TBST overnight at 4 °C with constant rocking, then rinsed and washed twice for 10 min
with TBST. Immunoreactivity was visualized by incubation with a horseradish
peroxidase conjugated goat anti-mouse antibody (1:2500; Pierce) in TBST for 1 h
followed by a rinse and four washes of 20 min with TBST. Blots were visualized by
chemiluminescence using ECL reagents (Amersham) on X-Omat R film (Kodak).
Treated neurons exhibited significantly reduced levels of the Fucα(1-2)Gal epitope on
several glycoproteins (Figure S4).
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Figure S1. Lipid extraction of neurons does not alter the labeling with probe 1. E18
hippocampal neurons (23 days in vitro) were de-lipidated with MeOH/CHCl3 prior to
labeling with 3 mM of (A) 1 or (B) biotin in the presence of 10 µM PAO. Scale bars
represent 45 µm.
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Figure S2. Co-staining of E18 hippocampal neurons (23 days in vitro) with UEA I
lectin (1:100; green) and anti-tau antibody (1:600; red) in the presence of 10 µM PAO
following lipid extraction. An overlay of both images is shown in yellow. Scale bars
represent 45 µm.
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Figure S3. Treatment of E18 hippocampal neurons with varying concentrations of 2-
dGal. After 1 day in culture, neurons were treated with the specified concentrations of 2-
dGal for 2 days, followed by immunostaining with anti-tau antibodies. Scale bar
represents 40 µm.
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Figure S4. Treatment of E18 hippocampal neuronal cultures with 2-dGal diminishes
expression of the Fucα(1-2)Gal epitope on glycoproteins. After a 4-day incubation with
or without 30 mM 2-dGal, protein lysates were analyzed by Western blotting using an
anti-Fucα(1-2)Gal antibody. Lane 1: Untreated neurons (75 µg total protein). Lane 2:
Neurons treated with 30 mM 2-dGal (75 µg total protein).
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