A ratiometric two-photon fluorescent probe reveals reduction in mitochondrial H2S production in Parkinson's disease gene knockout astrocytes

Article abstract of DOI:10.1021/ja404004v

Hydrogen sulfide (H₂S) is a multifunctional signaling molecule that exerts neuroprotective effects in oxidative stress. In this article, we report a mitochondria-localized two-photon probe, SHS-M2, that can be excited by 750 nm femtosecond puls

Full text of DOI:10.1021/ja404004v

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Article
A Ratiometric Two-Photon Fluorescent Probe Reveals
Reduction in Mitochondrial H2S Production in a
Parkinson’s Disease Gene Knockout Astrocytes
Sung Keun Bae, Cheol Ho Heo, Dong Joo Choi, Debabrata
Sen, Eun-Hye Joe, Bong Rae Cho, and Hwan Myung Kim
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/ja404004v • Publication Date (Web): 07 Jun 2013
Downloaded from http://pubs.acs.org on June 16, 2013
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A Ratiometric Two-Photon Fluorescent Probe Reveals
Reduction in Mitochondrial H2S Production in a
Parkinson’s Disease Gene Knockout Astrocytes
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Sung Keun Bae,‡a Cheol Ho Heo,‡a Dong Joo Choi,‡b Debabrata Sen,a Eun-Hye Joe,*b Bong Rae Cho,*c and
Hwan Myung Kim*a
aDivision of Energy Systems Research, Ajou University, Suwon 443-749, Korea
bDepartment of Pharmacology/Neuroscience Graduate Program, Ajou University School of Medicine,
Suwon 443-721, Korea
cDepartment of Chemistry, Korea University, Seoul 136-701, Korea
RECEIVED DATE (to be automatically inserted after your manuscript is accepted if required
according to the journal that you are submitting your paper to)
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ABSTRACT
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Hydrogen sulfide (H2S) is a multifunctional signaling molecule that exerts neuroprotective effects in
oxidative stress. In this article, we report a mitochondria-localized two-photon probe (SHS-M2) that can
be excited by 750 nm femtosecond pulses and ratiometrically detect H2S in live astrocytes and living
brain slices using two-photon microscopy (TPM). SHS-M2 showed a bright two-photon excited
fluorescence and a marked blue-to-yellow emission color change in response to H2S, low cytotoxicity
with easy loading and minimum interference from other biologically relevant species including reactive
sulfur, oxygen and nitrogen species, thereby allowing quantitative analysis of H2S level. Molecular
TPM imaging with SHS-M2 in astrocytes reveals that there is a correlation between the ratiometric
analysis and expression levels of cystathionine β-synthase (CBS), the major enzyme that catalyzes H2S
production. In comparison to wild-type controls, the attenuated H2S production was observed in DJ-1 (a
Parkinson’s disease gene) knockout astrocytes and brain slices where CBS expression is decreased.
These findings demonstrate that reduced H2S levels in astrocytes may contribute to the development of
Parkinson’s disease (PD), and SHS-M2 may be useful as a marker to detect a risk of neurodegenerative
diseases including PD.
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KEYWORDS. Hydrogen sulfide · fluorescent probe · mitochondria · Parkinson’s disease · two-photon
microscopy.
Introduction
Hydrogen sulfide (H2S) is an endogenous signalling molecule produced by enzymes such as
cystathionine β-synthase (CBS), cystathionine γ-lyase (CSE) and 3-mercaptopyruvate sulfurtransferase
(3MST).1 H2S has diverse functions in several pathophysiological processes such as neurotransmittion,
modulation of redox status, neuroprotection from oxidative stress, and anti-inflammation.2-4
Mitochondrial H2S has been recognized to exert protective effects in oxidative stress leading to the
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dysfunction and cell death.5-7 In the brain, there is relatively high concentration of H2S while CBS has
been identified as the major H2S producing enzyme, which is mainly expressed in astrocytes.8-11 Defects
in H2S production in the brain could be related to neurodegenerative diseases. Moreover, H2S treatment
protects neurons in Parkinson’s disease (PD) animal models.10,12
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In order to understand its biological and pathological roles, it is crucial to monitor mitochondrial H2S
in live cells and tissues in normal and abnormal systems. To detect H2S in cells, a number of fluorescent
probes derived from azide,13 azamacrocyclic copper(II) ion complex,14 and H2S-specific Michael
acceptors15 have been reported. However, most of them have limitations imposed by fluorescent turn-on
responses at single detection window and/or their short excitation wavelength encountered by most
conventional probe. The turn-on response can vary depending on the experimental conditions such as
incident laser power and/or probe distribution, thereby a quantitative measurement of H2S was not
possible. More recently, a mitochondrial-targeted ratiometric fluorescent probe for H2S has been also
reported.16 However, the short excitation wavelength limits their application in live tissue imaging due
to the shallow penetration depth.
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An attractive approach to the detection of H2S in live cells and tissues is ratiometric imaging with
two-photon microscopy (TPM). TPM, which employs two near-infrared photons as the excitation
source, offers a number of advantages including greater penetration depth (> 500 µm), localization of
excitation, and longer observation times.17-19 Therefore, there is a strong need to develop a ratiometric
TP probe for mitochondrial H2S.
In this work, we developed ratiometric TP probes (SHS-M1 and SHS-M2, Scheme 1) for
mitochondrial H2S, derived from 6-(benzo[d]thiazol-2'-yl)-2-(N,N-dimethylamino)naphthalene as the
fluorophore, 4-azidobenzyl carbamate as the H2S response site,13a and triphenylphosphonium salt (TPP)
as the mitochondrial targeting moiety (Scheme 1).20 We anticipated that thiolate-triggered reaction with
azide would cleave the carbamate linkage and liberate the amino group, thereby shifting the emission
maxima and increasing the TP cross section.21
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Scheme 1. Structures of SHS-M1, SHS-M2, 1 and 2.
Results and Discussion
Spectroscopic properties of SHS-M1 and SHS-M2
The preparation of SHS-M1 and SHS-M2 is described in the Supporting Information. The solubilities
of SHS-M1 and SHS-M2 in HEPES buffer (30 mM HEPES, 100 mM KCl, pH 7.4) are approximately
3−5 µM, which is sufficient to stain the cells (Figure S1, SI). Under this condition, SHS-M1 and 1
exhibit absorption maxima (λabs) at 340 nm (ε = 1.90 × 104 M-1cm-1) and 365 nm (ε = 1.80 × 104 M-1cm-
1), with emission maxima (λfl) at 420 nm (Φ = 0.23) and 500 nm (Φ = 0.50), respectively (Table 1). The
λabs of SHS-M1 and SHS-M2 are nearly the same, while that of 2 is red-shifted from 1 by 18 nm (Figure
1 and Table 1), presumably because of the stronger electron-withdrawing group. The larger Stokes shifts
observed for SHS-M2 and 2 compared to SHS-M1 and 1 can also be attributed to the greater
stabilization of the charge-transfer excited state in the former that contains a stronger electron-
withdrawing group. Consistently, the emission spectra of 1 and 2 showed larger red-shifts with the
solvent polarity than those of SHS-M1 and SHS-M2 (Δλfl = 16−45 vs 56−72 nm, Figure S2 and Table
S1, SI). Further, the two-photon excited fluorescence (TPEF) spectra of 1 and 2 measured in HeLa cells
were similar to those measured in EtOH (Figure S2b,d), indicating that EtOH can adequately represent
the polarity of the cellular environments.
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with 100 µM Na2S in the HEPES buffer (30 mM HEPES, 100 mM KCl, pH 7.4). Spectra were acquired
at 0 to 60 min after addition of Na2S. The λex = 340 nm (A) and 373 nm (B).
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The reaction between SHS-M1 (or SHS-M2) and Na2S (a commonly employed H2S donor)14,15,22
produced 1 (or 2) as the only major product as monitered by fluorescent emission (Figure 1) and LC-MS
analysis (Figure S3, SI). The emission spectra of a 1 µM solution of SHS-M1 treated with 100 µM Na2S
in HEPES buffer increased gradually at 500 nm with a concomitant decrease at 420 nm (Figure 1a). A
similar result was observed for SHS-M2, except that both λfl were significantly red-shifted (Figure 1b).
These processes followed pseudo 1st-order kinetics with kobs = 1.4 × 10-3 s-1 and 9.1 × 10-4 s-1 for SHS-
M1 and SHS-M2, respectively (Figure S4). Moreover, the plots of kobs versus [Na2S] are straight lines
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passing through the origin (Figure S4, SI), indicating that the reactions are overall 2nd order with k2 = 5.8
M-1s-1 and k2 = 7.0 M-1s-1 for SHS-M1 and SHS-M2, respectively. These results can be attributed to the
rate-limiting attack of the thiolate ion at azide group followed by the cleavage of the carbamate moeity
to afford 1 or 2, as reported.21 Further, the in vitro detection limits of H2S with SHS-M1 and SHS-M2
are 0.2 and 0.4 µM (Figure S5), respectively.
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SHS-M1 and SHS-M2 showed good selectivity for Na2S over other biologically relevant reactive
sulfur (RSS), oxygen (ROS) and nitrogen species (RNS) (Figure 2). Both probes displayed ∼5−8-fold
greater response for H2S over 10 mM glutathione (GSH, 100-fold larger amount than H2S tested), 1 mM
cysteine (Cys), and 1 mM 2-mercaptoethanol (2-ME). Moreover, these probes displayed strong response
upon addition of 100 µM Na2S in the presence of GSH (10 mM) or Cys (1 mM) (Figure 2), thereby
conforming the high selectivity for H2S over GSH and Cys. Other biologically relevant RSS (lipoic acid,
SO32-, S2O32-, SCN-), RNS (NO2-, NO), ROS (H2O2, O2-, t-BuOOH, HOCl), amino acids without thiol
groups (ala, glu), and metal ions (Ca2+, K+, Na+, Fe3+, Zn2+, Mg2+) showed negligible responses (Figure
2). Further, SHS-M1 and SHS-M2 were pH insensitive at a biologically relevant pH range (Figure S6,
SI). Therefore, these probes can detect the intracellular sulphide with minimum interference from other
biologically relevant analytes and pH.
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Figure 2. Fluorescence responses of 1 µM (A) SHS-M1 and (B) SHS-M2 toward 100 µM Na2S, and
other reactive sulfur, nitrogen, and oxygen species, as well as amino acids and metal ions. Bars
represent the ratio of the emission intensities at λfl at 0, 30, 60 and 90 min after addition of RSS, RNS,
ROS, amino acids, or metal ions. Data were acquired in HEPES buffer (pH 7.4). The λex = 340 nm (A)
and 373 nm (B).
The TP action cross sections (Φδmax) were determined by investigating the TPEF spectra with
rhodamine-6G as the reference (SI).23 The Φδmax values of SHS-M1, 1, SHS-M2, and 2 are 14, 63, 17,
and 55 GM, respectively (Table 1 and Figure S7, SI). The larger values of 1 and 2 than those of SHS-
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M1 and SHS-M2 can be attributed to the enhanced donor or acceptor abilities, respectively24 (Table 1).
In EtOH, which is a good model for the cellular environment (vide supra), the Φδmax of SHS-M2 and 2
is 1.9−2.3-fold larger than those of SHS-M1 and 1. Indeed, the TPM images of the cells labeled with
SHS-M2 are much brighter than those labeled with SHS-M1, while both probes show high
photostability (Figure S8, SI). Moreover, the emission spectra of SHS-M2 in EtOH increased gradually
at 510 nm with a concomitant decrease at 445 nm in the presence of excess Na2S with k2 = 4.6 M-1s-1, a
result similar to that observed in HEPES buffer (Figure S9, SI). The relative emission intensity ratios
(Fyellow/Fblue) at 425-470 nm (Fblue) and 525-575 nm (Fyellow) showed a 9-fold increase, establishing that
SHS-M2 can serve as a ratiometric fluorescent probe for H2S in cells. Therefore, we have used SHS-M2
in the imaging experiments.
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Table 1. Photophysical data for SHS-M1, SHS-M2, 1, and 2.
Cpda
c
(!)
!"#
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λabs (10-4 ε)b lλfl
Φd
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365 (1.8)
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14 (32)
63 (76)
17 (60)
55 (177)
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SHS-M2
2
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0.24 (1.00)
0.12 (1.00)
aAll measurements were performed in HEPES buffer (30 mM HEPES, 100 mM KCl, pH 7.4) unless
b
otherwise noted. λmax of the one-photon absorption spectra in nm. The numbers in parentheses are
d
molar extinction coefficients in M-1cm-1. cλmax of the one-photon emission spectra in nm. Fluorescence
e
quantum yield, ± 15 %. The numbers in parentheses are measured in EtOH. λmax of the two-photon
f
excitation spectra in nm. The peak two-photon action cross section in 10-50 cm4s/photon (GM), ± 15%.
The numbers in parentheses are measured in EtOH.
Detection of mitochondrial H2S with SHS-M2 in live cell and tissue
We then tested the utility of SHS-M2 to detect H2S in the cellular environment. The TPM image of
the HeLa cells labeled with SHS-M2 was bright, presumably because of the easy loading, convenient
rate of H2S-induced reduction, and large Φδmax value of the reaction product (Figures 3A-D).
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To confirm whether the probes can specifically stain the mitochondria, HeLa cells were stained with
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SHS-M2 and MitoTracker Red (MTR),25 a well-known one-photon fluorescent marker for
mitochondria. The TPM image of SHS-M2 merged well with the OPM image of MTR (Figure S10).
The Pearson’s colocalization coefficient (A),26 calculated by using Autoquant X2 software, of SHS-M2
and MTR was 0.85, indicating that this probe exists predominantly in mitochondria. Experiment in
astrocytes gave similar result with A value of 0.82 (Figure 4). Further, SHS-M2 show low cytotoxicity
as determined by using a CCK-8 kit (Figure S11, SI).
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Figure 3. (A-D) Pseudocolored ratiometric TPM images (Fyellow/Fblue) of HeLa cells incubated with 2
μM (A) SHS-M2 and (D) 2. HeLa cells pretreated with (B) GSH (100 μM) for 30 min and (C) cysteine
(100 μM) for 30 min before labeling with SHS-M2. (E) Average Fyellow/Fblue intensity ratios in (A-D).
Images were acquired using 750 nm excitation and emission windows of 425-470 nm (blue) and 525-
575 nm (yellow). Cells shown are representative images from replicate experiments (n = 5). (F-I)
Images of a rat hippocampal slice stained with 20 μM (G) SHS-M2 and (I) 2 for 1 h. (F) Bright-field
images of the CA1 and CA3 regions. Ratiometric TPM images of a fresh rat hippocampal slices that
were (G) not treated and (H) pretreated with 1 mM cysteine for 1 h before labeling with SHS-M2. TPM
images were acquired at a depth of 120 μm with 40x magnification. (J) Average Fyellow/Fblue intensity
ratios in (G-I). The TP fluorescence emission was collected in two channels (blue = 425-470 nm and
yellow = 525-575 nm) upon excitation at 750 nm with a fs-pulses. Scale bars: (D) 20 μm, (F) 300 μm,
and (I) 75 μm.
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Figure 4. (A) TPM and (B) OPM images of astrocytes colabeled with (A) SHS-M2 and (B)
MitoTracker Red FM. (C) Merged image. The wavelengths for TP and OP excitation were 750 and 514
nm, respectively, and the corresponding emissions were collected at 425-575 nm (SHS-M2) and 600-
700 nm (Mitotracker Red FM). Scale bar, 30 μm. Cells shown are representative images from replicate
experiments (n = 3).
Next, we tested whether SHS-M2 can monitor the changes in mitochondrial H2S levels in live cells
and tissues. Upon TP excitation at 750 nm, the average emission ratios (Fyellow/Fblue) of HeLa cells
labeled with SHS-M2 and 2 were 0.49 and 1.00, respectively (Figures 3A,D,E, and S12, SI). The ratio
increased from 0.49 to 0.76 or 0.81, respectively, after addition of GSH or Cys, which are the precursors
to H2S.5b,27,28 Further, we investigated the utility of SHS-M2 in a fresh rat hippocampal slice. We
accumulated 10 TPM images at depths of 90−180 µm to visualize the overall H2S distribution. They
revealed that H2S are more or less evenly distributed in both the CA1 and CA3 regions (Figure S13 and
S14, SI) as well as at different depths. Moreover, the image at a higher magnification clearly shows the
H2S distribution in the individal cells in the CA1 region with an average emission ratio of 0.51 at a
depth of 120 µm (Figure 3G,J). The Fyellow/Fblue ratio increased to 0.80 when the tissue was treated with 1
mM cystein for 50 min (Figure 3H,J). These results confirm that SHS-M2 is clearly capable of
monitoring the endogenous H2S levels in live cells and at > 100 µm depth in living tissues using TPM.
Measurement of H2S levels in cultured astrocytes with SHS-M2
We next investigated whether SHS-M2 can measure H2S levels produced by different levels of
cystathionine β-synthase (CBS), the major enzyme that catalyzes H2S production, in astrocytes. It is
well established that astrocytes express CBS and produce H2S in the brain.2,11,12 We knocked out CBS
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from astrocytes using CBS siRNA (5’-CCC AAA AUU UUA CCA GAU AUU CUU U-3’). Astrocytes
pretreated with CBS siRNA for 5 days showed significantly reduced CBS mRNA and CBS protein
levels as compared to the cells pretreated with non-targeted (NT) siRNA (5’-CCU CGU GCC GUU
CCA UCA GGU AGU U-3’) (Fig. 5A, B). Moreover, the Fyellow/Fblue ratio of SHS-M2-labeled astrocytes
decreased from 0.66 to 0.56 when pretreated with NT-siRNA and CBS siRNA, respectively, indicating
a parallel decrease in the H2S levels (Fig. 5C, D). This result demonstrates the capability of SHS-M2 to
delineate the relationship between the expression levels of CBS and H2S levels in astrocytes by TPM.
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Measurement of endogenous H2S levels in DJ-1 deficient astrocytes and brain slices
We then utilized SHS-M2 to measure the endogenous H2S levels in DJ-1 deficient astrocytes and
mouse brain slices. DJ-1 is a PD-related gene that has multiple functions. It was reported that DJ-1
exerts anti-inflammatory and anti-oxidant effect in astrocytes.29-32 Since H2S also has anti-inflammatory
and antioxidant effects,4,10,11 it was interesting to find out whether DJ-1 regulates H2S production. Using
SHS-M2 as the probe, we found that the Fyellow/Fblue ratio in DJ-1 knockout (KO) astrocytes decreased to
0.46 from 0.71 measured in wild-type (WT) astrocytes (Fig. 6A, B). This outcome indicates a parallel
decrease in the endogenous H2S levels. Moreover, the CBS mRNA and CBS protein levels were
significantly reduced in DJ-1 KO astrocytes compared to WT astrocytes (Fig. 6C, D). Here again, a
parallel decrease in the CBS expression levels and endogenous H2S level is clearly indicated.
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(A)
(B)
1.2
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NT
CBS siRNA 0.57 ± 0.037
NT
C B S s iR NA
Figure 5. SHS-M2 showed correlation between CBS expression levels and amount of H2S production.
(A, B) Astrocytes prepared from neonate mice brain were treated with CBS-specific siRNA (20 nM) or
non-targeted siRNA (NT) for 5 days. CBS mRNA levels (A), and protein levels (B) were analyzed with
Q-PCR and Western blot, respectively, and quantified (B). (C) Astrocytes treated with CBS-specific or
NT siRNA were stained with 2 μM SHS-M2 for 1 h. Images were acquired using 750 nm excitation and
emission windows of 425-470 nm (blue) and 525-575 nm (yellow). (D) Average intensity ratios
(Fyellow/Fblue) in TPM images were calculated as described above. Values in A and B are mean ± SEM of
3 samples, and values in D are mean ± SD of 3 samples. Cells shown in C are representative images
from replicate experiments (n = 3). Scale bar in (C), 20 μm.
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**
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WT KO
Figure 6. Attenuated H2S production and expression of CBS in DJ-1 KO astrocytes. (A, B) Astrocytes
cultured from WT and DJ-1 KO mice brain were stained with 20 μM SHS-M2 for 1 h. Ratiometric TPM
images of astrocytes revealed decreased H2S production in KO astrocytes compared to WT cells (A).
Average Fyellow/Fblue intensity ratios in TPM images were calculated as described above (B). (C, D) CBS
mRNA (C) and protein levels (D) in WR and KO astrocytes were determined with Q-PCR and Western
blot, respectively. Values in B are mean ± SD of 3 samples, and values in C and D are mean ± SEM of 3
samples. Scale bar in A, 20 μm.
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We further investigated the relationship between CBS expression and H2S production in WT and DJ-1
KO brain slices. Slices were freshly prepared from WT and KO brain hippocampus, and double-stained
with antibodies specific for GFAP (an astrocyte marker) and CBS, respectively. As expected, CBS was
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detected in GFAP-positive astrocytes, and its expression was dramatically reduced in DJ-1 KO
astrocytes (Fig. 7A). H2S was also detected in cells having astrocyte-morphology (Fig. 7B), and was
significantly reduced in DJ-1 KO slices compared to WT slices (Fig. 7B, C). We then analyzed H2S
production in cortical slices 7 d after slicing to stabilize tissues from slicing stress.33 The ratiometric
images of SHS-M2-labeled tissues showed reduced H2S levels in DJ-1 KO cortical slices (Fig. 7D, E),
as observed in cultured astrocyte (Fig. 6) and freshly prepared slice (Fig. 7B, C). These results indicate
that the TPM ratiometric imaging using SHS-M2 as the probe is an effective tool to measure different
H2S levels produced by different CBS expression levels. To the best of our knowledge, this is the first
report showing that genetically mutated PD genes can affect H2S production in PD patients’ brain,
partially in astrocytes.
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(A)
GFAP
CBS
Merged
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(B)
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Ratio
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0.2
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K O
Figure 7. Attenuated CBS expression and H2S production in astrocytes in DJ-1 KO brain. Brain slices
were prepared from WT and DJ-1 KO mice. (A, B, C) Hippocampal slices were acutely prepared and
used for GFAP and CBS staining as described in Experimental section (A) or H2S analysis as above (B,
C). Right panels in (B) are higher magnification of boxed areas in left panels in (B). (D, E) Cortical
slices were cultured for 7 d after slicing to stabilize tissues from slicing stress, H2S production was
measured. Values in C and E are mean ± SD of 3 samples. Scale bars: 30 μm for A and right panel in B,
and 75 μm for left panel in B and D.
Concluding Remarks
In this study, we have developed a new mitochondrial specific and emission ratiometric TP probe for
H2S (SHS-M2), which shows a significant TP cross section, a marked blue-to-yellow emission color
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change in response to H2S, high mitochondrial H2S selectivity, high photostability, low cytotoxicity, and
well-working in biologically relevant pH range. This probe can ratiometrically detect mitochondrial H2S
in the live cells and living tissues for a long period of time by TPM with minimum interference from
other biologically relevant species.
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In addition, the TPM ratiometric imaging using SHS-M2 is an effective tool to measure different H2S
levels produced by different expression levels of CBS in WT and DJ-1 KO astrocytes and brain slices.
These findings demonstrate that H2S levels decrease in a genetic model of PD. Furthermore, SHS-M2
may find useful applications in biomedical research including PD through the use of TPM.
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EXPERIMENTAL SECTION
Spectroscopic measurements. Absorption spectra were recorded on a S-3100 UV-Vis
spectrophotometer and fluorescence spectra were obtained with FluoroMate FS-2 fluorescence
spectrophotometer with a 1 cm standard quartz cell. The fluorescence quantum yield was determined by
using coumarin 307 (Φ = 0.95 in MeOH) as the reference by the literature method.34
Measurement of Two-Photon Cross Section. The two-photon cross section (δ) was determined by
using femto second (fs) fluorescence measurement technique as described.35 Dye (1.0 × 10-6 M) was
dissolved in 30 mM HEPES buffer (pH = 7.4) and the two-photon induced fluorescence intensity was
measured at 720−880 nm by using rhodamine 6G as the reference, whose two-photon property has been
well characterized in the literature.36 The intensities of the two-photon induced fluorescence spectra of
the reference and sample emitted at the same excitation wavelength were determined. The TPA cross
section was calculated by using δ = δr(SsФrφrcr)/(SrФsφscs): where the subscripts s and r stand for the
sample and reference molecules. The intensity of the signal collected by a CCD detector was denoted as
S. Φ is the fluorescence quantum yield. φ is the overall fluorescence collection efficiency of the
experimental apparatus. The number density of the molecules in solution was denoted as c. δr is the TPA
cross section of the reference molecule.
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Animals. DJ-1 Knock out (KO) mice used in this study were a gift from UJ Kang in Chicago
University. DJ-1 KO mice were previously generated by deleting 9.3-kb genomic DNA including the
first 5 exons and part of the promoter region of DJ-1 gene (Chen et al., 2005).37
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Cell Culture. HeLa human cervical carcinoma cells (ATCC, Manassas, VA, USA) were cultured in
DMEM (WelGene Inc, Seoul, Korea) supplemented with 10 % FBS (WelGene), penicillin (100
units/ml), and streptomycin (100 µg/mL). Two days before imaging, the cells were passed and plated on
glass-bottomed dishes (NEST). All the cells were maintained in a humidified atmosphere of 5/95 (v/v)
of CO2/air at RT. For labeling, the growth medium was removed and replaced with DMEM without
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FBS. The cells were treated and incubated with 2 µM SHS-M1, 1, SHS-M2, and 2 at 37 C under 5 %
CO2 for 30 min. The cells were washed three times with phosphate buffered saline (PBS; Gibco) and
then imaged after further incubation in colorless serum-free media for 30 min.
Primary astrocytes were cultured from the cortex of DJ-1 KO, or WT mice brains. In brief, cortexes
were removed and triturated in DMEM (Invitrogen, Carlsbad, CA, USA) containing 10% FBS
(HyClone, Logan, UT, USA), plated in 75 cm2 T-flasks (0.5 hemisphere/flask), and incubated for 2~3
weeks. Microglia were detached from flasks by mild shaking, filtered through a nylon mesh to remove
cell clumps, and cultured in DMEM containing 10% FBS.38 Astrocytes remaining in the flask were
harvested with 0.1% trypsin and cultured in DMEM containing 10% FBS. BV2 murine microglia were
cultured in DMEM containing 5% FBS as previously described (Min et al., 2003).39 For activation of
glial cells, cells were treated with 5 ng/ml recombinant murine IFN-(PeproTech, Rocky Hill, NJ, USA).
Preparation and Staining of fresh rat Hippocampal slices. Rat Hippocampal slices were prepared
from the hippocampi of 2-weeks-old rat (SD) according to an approved institutional review board
protocol. Coronal slices were cut into 400 µm-thick using a vibrating-blade microtome in artificial
cerebrospinal fluid (ACSF; 124 mM NaCl, 3 mM KCl, 26 mM NaHCO3, 1.25 mM NaH2PO4, 10 mM
D-glucose, 2.4 mM CaCl2, and 1.3 mM MgSO4). Slices were incubated with 20 µM SHS-M2 in ACSF
bubbled with 95% O2 and 5% CO2 for 1 hr 30 min at 37 °C. Slices were then washed three times with
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ACSF and transferred to glass-bottomed dishes (NEST) and observed in a spectral confocal multiphoton
microscope.
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Oragnotypic cortical slice cultures (OCSCs). Cortical slices were prepared according to a
previously described protocol with modification.40 Slices were obtained from postnatal day 7 mice.
Briefly, brains were rapidly removed and cortices separated by thin forceps in culture medium. Coronal
cortical slices (400 µm thick) were prepared using a McIlwain tissue chopper (Mickle Laboratory
Engineering, Goose Green, UK). Slices were placed on membranes (0.4 mm pore size) of inserts
(Millipore, cork, Ireland). Each well was filled with slice culture medium (MEM containing 25% [v/v]
Hanks’ balanced salt solution, 25% [v/v] heat-inactivated horse serum [HyClone], 6.5 mg/mL glucose, 1
mM L-glutamine, 10 U/mL penicillin-G, and 10 mg/mL streptomycin). For stabilization, slices were
incubated for 7 days with changing media at day 3 and 5. At day 7, slices were used for experiments.
siRNA transfection. The CBS protein expression in astrocytes was knocked down using CBS-specific
siRNA (Genolution Phamaceuticals, Seoul, Korea). CBS specific siRNA sequence was 5’-CCC AAA
AUU UUA CCA GAU AUU CUU U-3’, and non-targeted siRAN sequence was 5’-CCU CGU GCC
GUU CCA UCA GGU AGU U-3’. For siRNA transfection, astrocytes were placed in Opti-MEM
(Invitrogen , Carlsbad, CA, USA), and treated with 20 nM siRNA and RNAiMAX transfection reagent.
Four hours later, astrocytes were placed in 10% FBS-containg DMEM, and incubated for 5 days.
Reduced CBS expression was confirmed using qPCR and Western blot.
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Quantitative real-time PCR. CBS mRNA expression was analyzed using Quantitative real-time
PCR(qPCR). In brief, total RNA was isolated using RNAzol B (iNtRON, Sungnam, Korea), and cDNA
was prepared using Avian Myeloblastosis Virus reverse transcriptase (Promega, Madison, WI, USA)
according to the manufacturer’s protocol. qPCR was done using 2x KAPA SYBR Fast Master Mix
(Kapa Biosystem, Cape Town, South Africa) and RG-6000 real-time amplification instrument (Corbett
Research, Sydney, Australia). qPCR primer sets specific for CBS were 5’-CCA TGG CTG TGG CTG
TGA A-3’(sense) and 5’-CCA TTT GTC ACT CAG GAA CTT GGA-3’(antisense); For actin, 5’- GCT
CTG GCT CCT AGC ACC AT-3’(sense), 5’-GCC ACC GAT CCA CAC AGA GT-3’(antisense). Actin
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was used as a reference gene. The threshold cycle values of each of the genes were presented as relative
fold induction.
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Western blot. Astrocytes were washed with cold PBS and lysed with RIPAa buffer (1% NP-40, 150
mL NaCl, 10 mM Na2HPO4, pH 7.2, 0.5% sodium deoxycholate) containing protease inhibitors (2 mM
PMSF, 10 µg/L leupeptin, 10 µg/L pepstatin and 0.5 mM NaVO3). Proteins were separated by 10%
sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and transferred to
nitrocellulose membrane. Membranes were incubated with 5% non-fat milk non-specific antibody
binding was blocked with solution, and antibodies specific for CBS (1:1000; Santa Cruz Biotechnology,
Santa Cruz, CA, USA), DJ-1 (1:1000; Cell Signaling Technology, Beverly, MA, USA), and b-actin
(1:1000; Santa Cruz Biotechnology, Santa Cruz, CA, USA). Membranes were washed, incubated with
peroxidase-conjugated secondary antibodies (1:10000; Zymed, San Fransico, CA), visualized by
Enhanced ChemiLuminescence (ECL) system (BioNote, Gyeonggi, Korea).
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Immunohistochemistry For immunofluorescence staining, slices and/or brain sections were obtained,
washed three times in PBS containing 0.2% Triton X-100 (PBST). Non-specific antibody binding was
blocked with 1% BSA in PBST. Slices and/or sections were incubated with specific antibodies for
GFAP (1:50; Signaling Technology, Beverly, MA, USA) or CBS (1:50; Santa Cruz Biotechnology,
Santa Cruz, CA, USA). After washing, slices and/or sections were incubated with secondary antibodies
conjugated with Alexa Fluor488- or Alexa Fluor555 (1600 dilution; Invitrogen, Eugene, OR, USA).
DAPI (Vector Laboratories, Burlingame, CA) was used to detect nuclei. All samples were analyzed
under a confocal microscope (Carl Zeiss, Germany) with 63× oil immersion objectives.
Two-Photon Fluorescence Microscopy. Two-photon fluorescence microscopy images of SHS-M1,
1, SHS-M2, and 2-labeled cells and tissues were obtained with spectral confocal and multiphoton
microscopes (Leica TCS SP8 MP) with ×10 dry, ×40 oil, ×63 oil, and ×100 oil objectives, numerical
aperture (NA) = 0.30, 0.30, 1.40, and 1.30, respectively. The two-photon fluorescence microscopy
images were obtained with a DMI6000B Microscope (Leica) by exciting the probes with a mode-locked
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titanium-sapphire laser source (MaiTai spectra physics, 80 MHz, 100 fs) set at wavelength 750 nm and
output power 2710 mW, which corresponded to approximately 10 mW average power in the focal
plane. To obtain images at 425~575 nm range, internal PMTs were used to collect the signals in an 8 bit
unsigned 512 × 512 and 1024 × 1024 pixels at 400 and 200 Hz scan speed, respectively. Ratiometric
image processing and analysis was carried out using MetaMorph software.
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ASSOCIATED CONTENT
Supporting Information. Synthesis, additional methods, figures (Figure S1-S20) and table S1. This
material is available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Authors
kimhm@ajou.ac.kr; chobr@korea.ac.kr; ehjoe@ajou.ac.kr
Author Contributions
‡These authors contributed equally.
ACKNOWLEDGMENT
National Research Foundation (NRF) grants funded by the Korean Government (No. 20120008780 and
2012007850), Priority Research Centers Program through the NRF (20120006687 and 20120005860),
and NRF through the Chronic Inflammatory Disease Research Center (CIDRC) at Ajou University
(NRF-2012R1A5A2051429).
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H2 S2
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