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Published in final edited form as:
Pain. 2009 November ; 146(1-2): 130–140. doi:10.1016/j.pain.2009.07.011.
Role of SIP30 in the development and maintenance of peripheral
nerve injury-induced neuropathic pain
Yu-Qiu Zhang1,2,*,¶, Ning Guo1,5,*, Guangdun Peng3,*, Mei Han2, Jeremy Raincrow5, Chihua Chiu5, Lique M. Coolen1, Robert J. Wenthold4, Zhi-Qi Zhao2,¶, Naihe Jing3,¶, and Lei
Yu1,5,¶
1 Department of Cell Biology, Neurobiology and Anatomy, University of Cincinnati College of
Medicine, Cincinnati, Ohio, USA
2
Institute of Neurobiology, Institutes of Brain Science and State Key Laboratory of Medical
Neurobiology, Fudan University, Shanghai, China
3
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Laboratory of Molecular Cell Biology and Key Laboratory of Stem Cell Biology, Institute of
Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of
Sciences, Shanghai, China
4
Laboratory of Neurochemistry, NIDCD, National Institutes of Health, Bethesda, Maryland, USA
5
Department of Genetics and Center of Alcohol Studies, Rutgers University, Piscataway, New
Jersey, USA
Abstract
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Using the chronic constriction injury (CCI) model of neuropathic pain, we profiled gene expression
in the rat spinal cord, and identified SIP30 as a gene whose expression was elevated after CCI. SIP30
was previously shown to interact with SNAP25, but whose function was otherwise unknown. We
now show that in the spinal cord, SIP30 was present in dorsal horn laminae where peripheral
nociceptive inputs first synapse, colocalizing with nociception-related neuropeptides CGRP and
substance P. With the onset of neuropathic pain after CCI surgery, SIP30 mRNA and protein levels
increased in the ipsilateral side of the spinal cord, suggesting a potential association between SIP30
and neuropathic pain. When CCI-upregulated SIP30 was inhibited by intrathecal antisense
oligonucleotide administration, neuropathic pain was attenuated. This neuropathic pain-reducing
effect was observed both during neuropathic pain onset following CCI, and after neuropathic pain
was fully established, implicating SIP30 involvement in the development and maintenance phases
of neuropathic pain. Using a secretion assay in PC12 cells, anti-SIP30 siRNA decreased the total
pool of synaptic vesicles available for exocytosis, pointing to a potential function for SIP30. These
results suggest a role of SIP30 in the development and maintenance of peripheral nerve injuryinduced neuropathic pain.
Send proofs to: Lei Yu, Department of Genetics and Center of Alcohol Studies, Rutgers University, 607 Allison Road, Piscataway, New
Jersey 08854, USA; tel: 732-445-0794, fax: 732-445-3500, lei.yu@rutgers.edu.
*Equal contribution
¶Co-corresponding authors
Red font denotes the changes that have been made to the text of the original submission
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Zhang et al.
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Keywords
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SIP30; neuropathic pain; chronic constriction injury; spinal cord; intrathecal; dorsal horn
1. Introduction
Neuropathic pain is a chronic and persistent painful condition, originating from nerve damage
or dysfunction. Different from somatic pain that tends to subside after the injury heals,
neuropathic pain often continues long after the initial injury has healed, and may persist in the
absence of observable tissue damage. Effective alleviation of neuropathic pain remains
clinically challenging, since neuropathic pain is refractory to the available therapeutic means
in many patients [1,4,5,12]. Indeed, a recent survey of treatment options for neuropathic pain
noted that “existing pharmacologic treatments for neuropathic pain are limited, with no more
than 40–60% of patients obtaining partial relieve of their pain” [14]. To develop more effective
therapeutic approaches, it is crucial to understand the mechanistic basis for neuropathic pain,
and to identify molecules involved in the development and maintenance of neuropathic pain.
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SIP30 is a SNAP25 (synaptosome-associated proteins of 25 kDa) interacting protein of 30 kDa
[23]. This novel protein of 266 amino acids, like all SNAREs (soluble N-ethylmaleimidesensitive factor attachment protein receptors), has a coiled-coil domain that forms a key
component in protein-protein interactions [11,23,31]. SNAREs, including t-SNAREs
(localized to the target membrane, grouped into the synaptosome-associated proteins of 25
kDa, and syntaxin families) and v-SNAREs (localized to the membrane of the trafficking
vesicle, comprised by vesicle-associated membrane proteins, VAMP) are essential for
regulated exocytosis of synaptic vesicles during neurotransmission [7,8,15,32,35]. SIP30 has
been detected in various brain areas [23,26]. However, molecular and cellular functions for
SIP30 remain unknown so far. In this study, we present evidence for a functional role of SIP30
in the development and maintenance of neuropathic pain, using the chronic constriction injury
(CCI) model.
2. Methods
2.1. Animals
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Adult male Sprague-Dawley rats, weighing 200–280 g, were housed in climate-controlled
rooms with a 12:12 hr light/dark cycle, with food and water available ad libitum. All
experimental protocols and animal handling procedures were approved by the Institutional
Animal Care and Use Committee (IACUC) at the University of Cincinnati and the Animal
Care and Facilities Committee at the Rutgers University, adhered to the guidelines of the
Committee for Research and Ethical Issues of IASP, and were consistent with the National
Institutes of Health Guide for the Care and Use of Laboratory Animals.
2.2. Intrathecal cannula implantation
Under sodium pentobarbital (45 mg/kg, i.p.) anesthesia, an intrathecal catheter (PE-10 tubing)
was inserted through the space between the L4 and L5 vertebrae and extended to the
subarachnoid space of the lumbar enlargement (L4 and L5 segments) of the rat spinal cord.
The catheter was filled with sterile saline (approximately 4 μl), and the external end was closed.
Cannulated rats were allowed to recover for 4 days and were housed individually. Rats that
showed any neurological deficits resulting from the surgical procedure were excluded from
the experiments.
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2.3. Chronic constriction injury (CCI) of the sciatic nerve
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Rats were anesthetized with pentobarbital sodium (45 mg/kg i.p.), and the right sciatic nerve
was exposed at the mid-thigh level by blunt dissection of the biceps femoris. For CCI, four
ligatures with chromic gut (4-0) were tied loosely around the nerve at approximately 1 mm
apart, proximal to its trifurcation, as previously described [6,30,40]. For sham surgery, the
sciatic nerve was isolated but not ligated. After CCI or sham surgery, the overlying muscles
and skin were closed in layers with 4-0 silk sutures.
2.4. Antisense oligonucleotides and delivery
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Oligonucleotides, including an antisense sequence (AS, 5′-TTT CTC CGC GTC CGC CAT
GGT –3′) complementary to nucleotides 11–31 of the coding region of the rat SNAP25
interacting protein 30 (SIP30, GenBank accession number BC063144), and a corresponding
missense sequence (MM, 5′-TTT CCT CGC GTC CCG CAT GGT- 3′), were obtained from
Integrated DNA Technologies, Inc. (Coralville, IA). All of the oligonucleotide sequences were
examined against the GenBank database using the BLAST algorithm to exclude non-specific
match with any unintended nucleotide sequences. The oligonucleotides were reconstituted in
0.9 % normal saline (NS) before administration. Rats received intrathecal administration of
normal saline (10 μl), antisense oligonucleotide (50 μg/10 μl), or missense oligonucleotide (50
μg/10 μl), respectively, followed by 5 μl of normal saline for flushing, every 24 hrs for 4 days
(delivering protocol I: from day 0 (6 hrs before CCI surgery) to day 3 post-CCI surgery;
delivering protocol II: from day 4 to day 7 post-CCI surgery).
2.5. Antibodies
Antibodies were made to amino acids 65–266 and 140–233 of SIP30 in rabbits as previously
described [23]. In addition, A GST-tagged SIP30 full-length sequence was inserted in-frame
into the pGEX-4T-1 vector (GE Health Life Science) at the BamHI and EcoRI cloning sites.
The resulted plasmid clone expressed a ~60kd protein which was identified as GST-SIP30 by
anti-GST. The GST-SIP30 was purified with glutathione Sepharose 4B (Amersham Pharmacia
Biotech, Piscataway, NJ) and was used as the antigen to raise antisera from 2 rabbits. The
specificity of antisera was determined by Western blotting and immunohistochemical staining
with proteins from SIP30-transfected 293-T cells, using the pre-immune serum as the control.
2.6. Immunohistochemical staining
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Immunohistochemical staining was performed as previously described [16]. Briefly, rats were
deeply anesthetized with sodium pentobarbital (120 mg/kg, i.p.) and transcardially perfused
with 50–100 ml of warm saline with heparin sodium, followed by 400 ml of 4%
paraformaldehyde. The L5 DRGs and the L4 and L5 segments of the spinal lumbar enlargement
were removed, post-fixed in the same fixative for 90 min, and then placed in 30% sucrose
solution at 4°C overnight. Tissues were embedded with Leica OCT Cryocompound (Leica
Microsystems, Nussloch, Germany), cut coronally in a cryostat at 15 μm thickness, and
mounted onto gelatin-coated slides. Immunohistochemical staining was performed using the
following antibodies: Primary antibodies against SIP30 or CGRP (1:2000, monoclonal, SigmaAldrich), Substance P (1:1000 Guinea pig, a gift from Dr. JiSong Guan), NF200 (1:100, SigmaAldrich) and FITC-IB4 (1:400, Sigma-Aldrich); FITC-, Cy3- and Cy5-conjugated secondary
antibodies were obtained from Jackson ImmunoResearch Laboratories (West Grove, PA).
Normal mouse and rabbit IgG (Zymed, South San Francisco, CA) were used as the negative
control. Digital images were captured with a confocal microscope (TCS SP2, Leica,
Heidelberg, Germany).
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2.7. RNA isolation from spinal cord tissue and DRG
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Rats were sacrificed on the 3rd or 7th day after CCI or sham surgery. In order to assess the
development of neuropathic pain and effects of antisense oligonucleotide, rats were tested for
both mechanical allodynia and thermal hyperalgesia as described before being sacrificed. The
spinal cord from naïve, sham, or CCI rats was dissected and cut along the midsagital plane into
two halves, one ipsilateral and one contralateral to the CCI surgery side. The DRG tissues (L4–
L6) from the same animals were also dissected. After dissection, all tissues were rapidly frozen
in dry ice and stored at −80 °C until further processing. Frozen spinal cord tissues were directly
homogenized in 1 ml TRIZOL reagent (Invitrogen, Carlsbad, CA). Total RNA was extracted
following manufacturer’s protocol with minor modifications. Briefly, following chloroform
extraction, RNA was precipitated with isopropanol and the pellet washed two times in 70%
ethanol. After air drying, RNA was resuspended in DNase/RNase-free water. Both the quality
and quantity of the total RNA were examined by gel electrophoresis and by UV absorption
measurements (Agilent 2001 Bioanalyzer, Palo Alto, CA). Extracted RNA was treated with
DNase I (DNA-free, Ambion) to remove genomic DNA. cDNA was synthesized with random
decamers using the Ambion RETROscript reverse transcription kit according to the
manufacturer’s instructions. Negative control reactions were run without RNA template to test
for contamination of reagents.
2.8. Real-time PCR
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Real-time PCR analysis was performed on a Cepheid Smart Cycler. Threshold cycles (Ct) were
calculated using the Smart Cycler Data Analysis Software 2.0 (Cepheid). PCR reaction was
performed in a final volume of 20 μl using LightCycler DNA Master SYBR Green I kit
containing: 12.6 μl of PCR grade water, 2.4 μl of MgCl2 (25 mM), 2 μl of 10X LightCycler
DNA Master SYBR Green I (Taq DNA polymerase, reaction buffer dNTP mix with dUTP
instead of dTTP, SYBR Green I dye, and 10 mM MgCl2), 2 μl of cDNA template, 0.5 μl of
forward and reverse primer (100 ng/μl) respectively. The amplification protocol included 150
sec at 95 °C to activate the Taq DNA polymerase, then 40 cycles of 10 sec denaturation at 95
°C, 15 sec annealing at 58 °C, and 20 sec extension at 72 °C. Each sample was run in triplicates
and Ct values were averaged. For controls, no-template reactions were run in which water
replaced the cDNA template. In this study, β-actin was used as the reference gene to normalize
expression levels. The relative gene expression level was computed from the target and β-actin
using the following formula [3,24,27]: mRNA relative expression =
2 − (Ct of target − Ct of β-actin). Primers were designed with Invitrogen Custom Primer Designer.
The primer sequences are listed in Supplemental Table 1.
2.9. Protein extraction
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Frozen spinal cord tissues were directly homogenized in 500 μl of lysis buffer containing 50
mM Tris-HCl, pH 7.5, 150 mM NaCl, 5 mM EDTA, 1% Triton, 1% SDS, 1 mM
phenylmethylsulfonyl fluoride, 2 μg/ml aprotintin, 2 μg/ml leupeptin, and 2 μg/ml pepstain.
Protein concentrations were determined by the Bradford method.
2.10. Western blotting
Twenty micrograms of total protein for each sample were separated by 10% SDS-PAGE, and
were transferred onto polyvinylidene difluoride membranes. The membranes were blocked in
3% nonfat dry milk, and incubated overnight at 4 °C with an anti-SIP30 primary antibody
(1:2000) against amino acids 65–266 of SIP30 [23]. Western blots were incubated for 1 hr at
room temperature with a horseradish peroxidase (HRP)-conjugate secondary antibody (1:5000;
Santa Cruz Biotechnology). Visualization of signals was aided with enhanced
chemiluminescence (ECL, Amersham Biosciences), and the Western blots were exposed to Xray films. The blots were then stripped in stripping buffer (67.5 mM Tris, pH 6.8, 2% SDS,
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and 0.7% β-mercaptoethanol) for 30 min at 50 °C and reprobed with an antibody against βactin (1:3000; Santa Cruz, Biotechnology) as the loading control. All Western blot analyses
were performed at least three times, and similar results were obtained. Bands on Western blots
were scanned and quantified using the Metamorph program.
2.11. Von Frey filament test of mechanical sensitivity
The hindpaw withdrawal threshold was determined using a series of von Frey filaments
(Stoelting, IL) with calibrated bending force ranging from 0.6 to 18 g. Animals were placed
individually in wire mesh-bottom cages, and allowed to acclimate for 30 min. Von Frey
filaments were applied to the central region of the plantar surface of a hindpaw in ascending
order of force (0.6, 0.9, 1.3, 2.2, 4.8, 6, 7.2, 9, 13, and 18 g). Testing was performed only when
the rat was stationary and standing on all four paws. A withdrawal response was considered
valid only if the hindpaw was completely lifted from the mesh-bottom. When a withdrawal
response was established for a given animal, a von Frey filament with the next lower force was
used to retest, until no response occurred. A trial consisted of applying a von Frey filament
five times at 15 s intervals to each hindpaw. The hindpaw withdrawal threshold was defined
as the lowest force that caused at least three withdrawals out of five consecutive applications.
Once the threshold was determined for the left hindpaw, the same testing procedure was
repeated on the right hindpaw of the same rat after 5 min.
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2.12. Hargreaves test for thermal sensitivity
Thermal hyperalgesia was assessed by measuring the latency of paw withdrawal in response
to a radiant heat source. Rats were placed individually into Plexiglas chambers on an elevated
glass platform, and were allowed to acclimate to the test chamber. A radiant heat source (model
336 combination unit, IITC/life Science Instruments, Woodland Hill, CA) was applied from
underneath the platform to the glabrous surface of the paw through the glass plate. When the
rat lifted the hindpaw, the heat source was turned off, and the elapsed time was recorded; this
was the hindpaw withdrawal latency. Throughout the testing, the heat intensity was maintained
at a constant level, giving a consistent withdrawal latency of approximately 8–10 s in the
absence of CCI. A 20 s cut-off was used to prevent tissue damage in the absence of a response.
Rats were tested individually in groups of four, such that the stimulation was delivered once
to the left hindpaw (control side) of each rat and then to the right hindpaw (CCI side) with a 5
min interval. This process was repeated two more times, and the values from the three trials
for each hindpaw were averaged.
2.13. Motor activity testing
Locomotor activity was measured as previously described [33,39,41].
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2.14. PC12 cell transfection and synaptic vesicle exocytosis assay
PC12 cells (ATCC) were seeded in poly-D-lysine coated 60-mm diameter Petri dish at a density
of 3 × 106 cells/dish, with DMEM high glucose culture medium (Sigma-Aldrich) supplemented
with 6.5% FBS (Lifeblood Medical Inc.), and 6.5% horse serum (Hyclone). siGENOME
SMARTpool siRNA for both SIP30 and universal control were from Dharmacon. One day
after seeding, cells were transfected with pHGH-CMV5 plasmid, which expresses human
growth hormone [9,37], plus either the universal control siRNA or the SIP30 siRNA. One day
after transfection, PC12 cells were harvested, and were reseeded into 6 wells of a 12-well plate.
Two days after reseeding, PC12 cells were subject to secretion assay. Of the 6 wells of cells
for each sample, cells from 3 wells were used for measuring baseline growth hormone secretion,
and those from the other 3 wells were used to measure stimulated secretion.
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Secretion assay to determine synaptic vesicle exocytosis was carried out as previously
described [9,37] with some modifications. Briefly, culture medium was removed by aspiration,
and PC12 cells were washed with pre-warmed PBS. For measuring baseline secretion, 500 μl
of low K+ PSS buffer (5.6 mM KCl, 145 mM NaCl, 2.2 mM CaCl2. 0.5 mM MgCl2, 5.6 mM
Glucose, 15 mM HEPES, pH 7.4) was added to each well. For measuring stimulated secretion,
500 μl of high K+ PSS buffer (56 mM KCl, 95 mM NaCl, 2.2 mM CaCl2. 0.5 mM MgCl2, 5.6
mM Glucose, 15 mM HEPES, pH 7.4) was added to each well. Cells were incubated at 37°C
in a CO2 incubator for 15 min. The plate was then placed on ice, and the buffer was transferred
to a 1.5 ml microcentrifuge tube. The microcentrifuge tubes were centrifuged for 5 min at 300
× g to pellet any dislodged cells, and the supernatant was transferred to a fresh microcentrifuge
tube for assay of secreted hormone. To the cells remaining in the well, an aliquot of 200 μl
CelLyticM reagent (Sigma-Aldrich) was added to each well, and the plate was placed on ice
on an orbital shaker for 10 min to lyse the cells. Cell lysate was transferred to the
correspondence microcentrifuge tube with the pelleted cells. One milliliter PBS was added to
each well to wash, and the solution was pooled with the correspondence cell lysate. The cell
lysate was centrifuged at 14,000 rpm for 10 min to pellet cell debris, and the supernatant was
transferred to a fresh microcentrifuge tube for assay of retained hormone in PC12 cells. The
content of human growth hormone (hGH) was measured using the Roche hGH ELISA kit
following the manufacturer’s instructions. The percentage of hGH being secreted was
calculated with the function hGHsecreted/(hGHsecreted+hGHretained) × 100% as an index of
synaptic vesicle exocytosis.
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2.15. Statistical analysis
Data were expressed as mean ± S.E.M. Data were analyzed for statistical significance by two
way repeated measures analysis of variance [Two-way RM ANOVA (treatment × time)] with
a pair-wise multiple comparison assessed with Turkey’s test. P<0.05 was considered
statistically significant.
3. Results
3.1. Identification of SIP30 as a candidate molecule involved in neuropathic pain in a rodent
model
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In an effort to uncover novel molecular components that are involved in modulating
neuropathic pain, we used chronic constriction injury (CCI) as a rodent model of neuropathic
pain [6,30,40], so as to look for differentially expressed genes in the spinal cord of the CCI
rats. To identify genes that are involved in the early phase of the neuropathic pain, time course
of neuropathic pain development after CCI surgery was determined in rats that had received
unilateral CCI surgery (Supplemental Fig. 1). At 2-day post-CCI surgery, for the CCI hindpaw
compared with the control hindpaw (i.e., no surgery), both thermal and tactile nociceptive
thresholds were greatly decreased, to approaching almost maximum. These results are
consistent with the previous studies that mechanical allodynia and thermal hyperalgesia
developed within a few days following CCI [21]. Based on this time course information, we
chose post-CCI day 3 as the time point, and isolated RNA from the lumbar enlargement portion
of the control and CCI-surgery animals. Gene expression profiles were analyzed using a
custom-constructed cDNA library as previously described [18,20,38]. We focused on those
genes whose expression was elevated after CCI, of which a cDNA clone coding for SIP30 was
identified in this process. SIP30 has been shown to be present in the rat brain and interact with
SNAP25 [23], but its molecular function was unknown so far. Because our preliminary analysis
showed increased expression of SIP30 with the onset of neuropathic pain in the CCI animals
(data not shown), we chose SIP30 to further examine its potential role as a candidate molecule
involved in neuropathic pain.
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3.2. SIP30 mainly colocalizes with markers for small-diameter neurons
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To evaluate SIP30 expression pattern in various CNS and peripheral tissues, Northern blot
analysis was carried out, showing that SIP30 was mainly expressed in the CNS (Fig. 1A). These
results corroborate with an earlier report [23].
Next, we examined the expression of SIP30 in the DRG. Small-diameter DRG neurons are
primarily nociceptors. They can be divided neurochemically into two populations: isolectinB4
(IB4)-positive nonpeptidergic neurons, and IB4-negative peptidergic neurons. IB4 negative
neurons express TrkA receptors for nerve growth factor (NGF), depend on NGF for survival,
and contain neuropeptides such as calcitonin gene-related peptide and substance P. IB4 positive
neurons express receptors for glial-derived neurotrophic factor (GDNF), neurturin, or artemin.
IB4-positive and -negative nociceptors are functionally distinct [36]. It has been hypothesized
that IB4-negative neurons contribute to inflammatory pain, whereas IB4-positive neurons
contribute to neuropathic pain [10,25,34].
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SIP30 expression was examined together with IB4 and CGRP in normal adult rats DRG (L4–
L5). SIP30 is expressed almost entirely across small- to medium-diameter DRG neurons (Fig.
1B). SIP30 displayed an overlapping pattern with IB4 and CGRP in some neurons but mainly
co-expressed with CGRP (Fig. 1B, panel d,e), suggesting a peptidergic nature. We also used
large-diameter neuron marker NF200 in DRG staining (Fig. 1C, panel g,h), and found that
SIP30 colocalized with very few large-diameter neurons (Fig. 1C, panel i).
SIP30 immunoreactivity was examined in the lumbar spinal cord, where it was found to be
expressed in all lumbar levels and throughout all laminae. SIP30 immunoreactivity was
particularly concentrated in the superficial dorsal horn lamina I and II (Fig. 1D, panel a), and
showed a strong co-expression pattern with nociception-related neuropeptides CGRP and
substance P (Fig. 1D, panels d,e,f). In addition, SIP30 immunohistochemical staining was
present in cell bodies in laminae IV-VII as well as in motor neurons in the ventral horn.
3.3. Upregulation of SIP30 in the spinal cord following CCI
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SIP30 mRNA was measured by quantitative real-time PCR, in both the spinal cord and DRG
of either CCI or sham-operated rats. The expression levels of two other genes were used as
reference points to normalize the amount of total RNA amount in each sample. We first
examined the expression of β-actin and glyceraldehydes-3-phosphate dehydrogenase
(GAPDH) among the normal and CCI rats’ spinal cord and DRG using quantitative real-time
PCR analysis. The β-actin and GAPDH gene expression levels of the CCI rats were normalized
to those of the normal rats. We observed that β-actin expression was more consistent than
GAPDH expression in the spinal cord and DRG (data not shown). Thus, β-actin was chosen
as the reference in the present study. Both on day 3 and 7 post-CCI, a statistically significant
(p<0.05) increase of SIP30 mRNA in the ipsilateral, but not contralateral spinal cord was
observed in CCI rats compared to sham-operated or normal rats (Fig. 2A, upper panel).
However, in the DRG, SIP30 mRNA expression was not significantly changed by CCI; there
was no difference between the ipsilateral and contralateral DRG in either sham or CCI rats
(Fig. 2A, lower panel).
The upregulation of SIP30 protein was also demonstrated by Western blot analysis. Increased
levels of SIP30 were observed in ipsilateral lumbar spinal cord compared with the contralateral
side of CCI rats and both sides of sham-operated animals (Fig. 2B). Similar to the expression
of SIP30 mRNA in the DRG from CCI and sham-operated rats, no significant changes in SIP30
protein were found in DRG following CCI (Fig. 2C).
Spinal cord immunohistochemical staining indicated that SIP30 protein level was elevated in
the ipsilateral side of the spinal cord dorsal horn 3 and 7 days after CCI (Fig. 2D). Quantification
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of SIP30 expression level by the number of SIP30-IR cells (Fig. 2D, panel c) indicated a
significant increase both in the superficial layers (laminae I–II) and deep layers (laminae IV–
V) in the ipsilateral side of the dorsal horn. At high magnification, SIP30 immunoreactivity
was observed in the cytoplasm, but not in the nucleus (Fig. 2D, panel d).
SIP30 localization in CCI spinal cord was examined, showing colocalization with NeuN, a
neuronal marker, in the spinal dorsal horn, 3 days after CCI (Fig. 2E, panel a). SIP30 did not
show overlap staining with either the microglial marker OX-42 (Fig. 2E, panel b) or the
astrocytic marker GFAP (Fig. 2E, panel c).
These results indicated that during CCI, SIP30 levels were upregulated in the ipsilateral side
of the spinal cord, suggesting a potential functional association between elevated SIP30 levels
and neuropathic pain.
3.4. SIP30 is involved in the development and maintenance of neuropathic pain
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Intrathecal administration of SIP30 antisense oligonucleotide (50 μg/10 μl, once a day for 4
days) starting on day 0 (6 hrs before CCI), produced a partial attenuation in the development
of mechanical allodynia and thermal hyperalgesia by day 4 of SIP30 antisense oligonucleotide
administration (Fig. 3). Two-way ANOVA showed a statistically significant difference
between the antisense group and normal saline group (p<0.05). The antisense oligonucleotideinduced attenuation was reversible: two days after the cessation of antisense oligonucleotide
administration (post-CCI day 5), mechanical allodynia was similar in the antisense
oligonucleotide group and the normal saline group (Fig. 3A); on post-CCI day 7, thermal
hyperalgesia appeared with similar paw withdrawal latencies to that of the normal saline group
(Fig. 3B). Administration of missense oligonucleotide had no effect on the development of
mechanical allodynia and thermal hyperalgesia. Contralateral paw withdrawal thresholds and
latencies were not affected by antisense oligonucleotide, missense oligonucleotide, or normal
saline treatment (Fig. 3C,D). Using another SIP30 antisense oligonucleotide (against
nucleotides 143-162 of the coding region of the SIP30 gene) also showed similar attenuating
effect on CCI-induced neuropathic pain (Supplemental Fig. 2).
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By 3 d after CCI, animals developed both mechanical allodynia and thermal hyperalgesia. After
this point of established neuropathic pain, 4 d of treatment with SIP30 antisense oligonucleotide
resulted in an attenuation of neuropathic pain (Fig. 4). Two-way ANOVA showed a statistically
significant difference between the antisense oligonucleotide group and the normal saline or
missense oligonucleotide group on day 7 and 9 post-CCI (p<0.05, Fig. 4A,B). Four days after
antisense oligonucleotide withdrawal, mechanical allodynia and thermal hyperalgesia
reappeared. Neither missense oligonucleotide nor normal saline altered paw withdrawal
responses to mechanical and thermal stimuli in CCI rats. There was no effect of normal saline,
antisense oligonucleotide and missense oligonucleotide treatment on contralateral hindpaw
during and post treatment period (Fig. 4C,D).
Treatment with SIP30 antisense oligonucleotide (50 μg/10 μl, once a day for 4 days) had no
detectable effect on the responses of naïve rats to von Frey and thermal stimuli in both hindpaws
(p>0.05, Fig. 5). Additionally, to rule out the possibility that intrathecal SIP30 antisense
oligonucleotide may produce non-specific motor deficiencies, locomotor activities were
measured in naïve rats receiving SIP30 antisense oligonucleotide, and no abnormal behavior
or motor deficiencies were observed during treatment with SIP30 antisense oligonucleotide
(data not shown).
Taken together, these findings showed that inhibition of upregulated SIP30 levels in the spinal
cord resulted in attenuation of neuropathic pain behaviors both during the development process
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and the maintenance phase of neuropathic pain, suggesting a cause-effect relation between
SIP30 upregulation and the phenomenon of neuropathic pain.
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3.5. SIP30 antisense oligonucleotide knock-down inhibits both SIP30 and SNAP25
expression in the spinal cord
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Because SIP30 levels in the DRG did not change after CCI at either mRNA or protein level,
in the subsequent experiments we focused only on the spinal cord. In order to verify whether
intrathecal administration of SIP30 antisense oligonucleotide indeed resulted in knockdown
of SIP30 over-expression, the effect of SIP30 antisense oligonucleotide on SIP30 mRNA and
protein expression was assessed. SIP30 antisense oligonucleotide (50 μg/10 μl) and missense
oligonucleotide (50 μg/10 μl) were administered intrathecally. The lumbar enlargement
segments of the spinal cord were harvested at 6 hrs after the last injection. Quantitative realtime PCR showed that SIP30 antisense oligonucleotide significantly decreased the overexpression of SIP30 mRNA in the ipsilateral spinal cord compared with that by SIP30 missense
oligonucleotide administration, for both day 0–3 and day 4–7 treatment procedures (Fig. 6A).
Moreover, Western blot analysis showed that the SIP30 antisense oligonucleotide, but not the
missense oligonucleotide, markedly suppressed the over-expression of SIP30 protein levels in
the ipsilateral spinal cord for day 0–3 intrathecal administration procedure (Fig. 6B), further
substantiating the antisense oligonucleotide-mediated “knockdown” of the over-expression of
SIP30 protein. Antisense oligonucleotide only suppressed the CCI-induced over-expression of
SIP30 on the ipsilateral side, and did not reduce the baseline levels of SIP30 mRNA or protein
expression on the contralateral side (Fig. 6A,B), consistent with the observation that antisense
oligonucleotide did not affect nociceptive behavior in normal animals (Fig. 5). This lack of
adverse effect by antisense oligonucleotide on normal levels of gene expression has been
reported for a sodium channel in a neuropathic pain study [17].
To assess whether SIP30 antisense oligonucleotide affects other protein factors that may
interact with SIP30, we also examined two related synaptic proteins that are expressed in the
spinal cord, synaptosome-associated proteins of 25 kDa (SNAP25), and postsynaptic density
protein-95 (PSD95). As shown in Fig. 6C, PSD95 mRNA exhibited a significant upregulation
in the ipsilateral spinal cord on day 7 post-CCI, and this upregulation of PSD95 mRNA was
not blocked by SIP30 antisense oligonucleotide. On the other hand, SNAP25 mRNA in the
ipsilateral spinal cord also showed a significant upregulation on both day 3 and 7 post-CCI,
and this CCI-induced upregulation of SNAP25 mRNA was suppressed by SIP30 antisense
oligonucleotide (Fig. 6D). As a cytological basis of interaction between SIP30 and SNAP25,
double immunofluorescence staining indicated that SIP30 co-localized with SNAP25 in
terminals of spinal dorsal horn neurons (Fig. 7).
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3.6. SIP30 inhibition resulted in reduced synaptic vesicle exocytosis in PC12 cells
In an effort to identify cellular functions that SIP30 may be involved in, we considered its
molecular interaction with SNAP25 as a potential lead. Several other SNAP25 interacting
proteins have been identified with yeast two-hybrid screening by various investigators.
SNAP25 contains coiled-coil domains known to mediate protein-protein interaction [11,29].
Some of these SNAP25 interacting proteins, such as SNIP, Snapin and Hrs (hepatocyte growth
factor-regulated tyrosine kinase substrate), also contain coiled-coil domains, and their
interactions with SNAP25 are mediated by the coiled-coil domains of both proteins [13,19,
22]. Since a major function of SNAP25 is the regulation of synaptic vesicle docking during
exocytosis [2,28], we sought to examine SIP30 involvement in synaptic vesicle exocytosis.
Using a growth hormone secretion assay in PC12 cells [9,37], we first examined the effect of
over-expression of SIP30. PC12 cells were either transfected with pHGH-CMV5 and pcDNA3
empty vector as the negative control, or with pHGH-CMV5 and pcDNA3-SIP30. Thirty-six
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hrs after transfection, both baseline and stimulated secretion of hGH were assayed by
incubating the cells in a low or high K+ buffer, respectively. Our results indicated that vesicular
exocytosis was not affected by over-expression of SIP30 (data not shown), even though a
positive control plasmid over-expressing synaptogyrin1, a protein that was previous reported
to inhibit stimulated secretion when over-expressed [37], did result in reduced vesicular
exocytosis (data not shown). This may be due to the fact that PC12 cells already express
relatively high levels of endogenous SIP30.
We next examined the effect of SIP30 inhibition, using an siRNA approach. PC12 cells were
cotransfected either with the hGH plasmid and a control siRNA, or with the hGH plasmid and
the SIP30 siRNA. As shown in Fig. 8, total vesicular hormone levels were significantly
decreased by SIP30 siRNA treatment compared to the control (p < 0.05), and the baseline
secreted hormone was also reduced (p < 0.05). These results indicated that the total pool of
hormone-containing synaptic vesicles available for exocytosis was diminished by a reduced
level of SIP30.
4. Discussion
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The results of the present study pointed to SIP30 involvement in CCI-induced neuropathic
pain. After CCI surgery, SIP30 levels were up-regulated in the spinal cord at both mRNA and
protein levels (Fig. 2). It is noteworthy that CCI-induced up-regulation of SIP30 is restricted
to the ipsilateral side of the spinal cord, not the contralateral side, suggesting specificity of the
molecular change in correlation with CCI-induced neuropathic pain.
In addition to expression-level correlation with neuropathic pain, SIP30 also displayed a causal
relationship with both the development and maintenance of neuropathic pain induced by CCI.
With intrathecal SIP30 antisense oligonucleotide administration starting from the day of CCI
surgery (days 0 of CCI surgery till day 4 post surgery), CCI-induced mechanical allodynia and
thermal hyperalgesia were attenuated (Fig. 3; also Fig. 7), together with concomitant decrease
of SIP30 mRNA and protein in the ipsilateral side of the CCI spinal cord (Fig. 6A,B). These
data showed that inhibition of SIP30 over-expression at the time of nerve injury resulted in
attenuated neuropathic pain, suggesting a causal relationship between SIP30 over-expression
and the development of neuropathic pain. Furthermore, once neuropathic pain has established,
intrathecal SIP30 antisense oligonucleotide administration also reduced mechanical allodynia
and thermal hyperalgesia (Fig. 4), suggesting that the sustained elevation of SIP30 was also
critical for the continued maintenance of neuropathic pain. Together, antisense knock-down
experiments suggest that SIP30 is involved in both the development and maintenance of
neuropathic pain in CCI rats.
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One clue to a potential SIP30 function came from the synaptic vesicle exocytosis experiments.
Inhibition of SIP30 by siRNA in PC12 cells resulted in much reduced neurotransmitter pool
available for synaptic vesicle exocytosis (Fig. 8), suggesting that SIP30 may participate in
modulating the steady-state neurotransmitter level in packed synaptic vesicles available for
exocytosis in the presynaptic terminals. Previously, it has been shown that SIP30 is one of the
molecules that are associated with SNAP25 [23]. Both SNAP25 and other SNAP25-associated
SNAREs have been shown to be involved in synaptic vesicle exocytosis [2,13,19,22,28]. In
this regard, the involvement of SIP30 in modulating synaptic neurotransmitter vesicle pool is
suggestive of SIP30 being involved in the overall process of synaptic vesicle regulation.
Additionally, it is noteworthy that SNAP25 mRNA over-expression was also reduced in the
ipsilateral side of the spinal cord in the antisense knock-down experiments (Fig. 6D), even
though the antisense oligonucleotide was against the SIP30 sequence. SNAP25 downregulation appeared to be specific, since another synaptic density molecule, PSD95, was not
affected by the SIP30 antisense oligonucleotide (Fig. 6C). To what extent such a co-regulation
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of SIP30 and SNAP25 mRNA in the CCI spinal cord relates to their interaction and involvement
in mediating neuropathic pain remains to be seen.
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In conclusion, we identified a SNAP25-associated protein, SIP30, to be a molecule involved
in both the development and maintenance of neuropathic pain in the CCI model. Intrathecal
infusion of SIP30 antisense oligonucleotides significantly attenuated mechanical allodynia and
thermal hyperalgesia during both the development and maintenance phase of chronic
neuropathic pain, by knocking-down the levels of spinal SIP30, but not in DRG. These results
suggest that SIP30 may be involved in the central mechanisms mediating chronic neuropathic
pain, and that elevated levels of SIP30 may be necessary for the development and maintenance
of allodynia and hyperalgesia induced by peripheral nerve injury.
Supplementary Material
Refer to Web version on PubMed Central for supplementary material.
Acknowledgments
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We thank Dr. Thomas Sudhof and Dr. Mary Bittner for generously providing human growth hormone plasmids. This
work was supported in part by grants from the National Institutes of Health of the United States (DA013471 and
DA020555), the Life Science Special Fund of the Chinese Academy of Sciences for Human Genome Research
(KJ95T-06 and KSCX1-Y02), the National Natural Science Foundation of China (30821002, 30870338, 30623003,
30721065, 30830034), the National Key Basic Research and Development Program of China (2007CB512303,
2007CB512502, 2006CB500807, 2005CB522704, 2006CB943902, 2007CB947101, 2008KR0695 and
2009CB941100), the Shanghai Key Project of Basic Science Research (06DJ14001, 06DZ22032 and 08DJ1400501),
and the Council of the Shanghai Municipal for Science and Technology (088014199). The authors have no conflict
of interest regarding this manuscript.
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Fig. 1.
Expression pattern of SIP30 in normal rats. Scale bars, 50 μm. A, Northern blot analysis of
SIP30 expression in various rat tissues. The 2 kb mRNA band of SIP30 was shown in the upper
panel, and 18S ribosomal RNA (lower panel) was used as an internal control for sample loading.
Source of tissue for RNA was indicated across the top for each lane. B, SIP30 levels in smalldiameter neurons in the DRG. Immunological staining using antibodies against SIP30 (a), IB4
(b), and CGRP (c). Pair-wise superimposed composite images are shown as follows: SIP30
with IB4 (d), SIP30 with CGRP (e), and IB4 with CGRP (f). White arrowheads mark the cells
with double staining. C, SIP30 levels in large-diameter neurons in the DRG. Immunological
staining using antibodies against SIP30 (g) and NF200 (h). As seen in the merged image (i),
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only a few large-diameter neurons showed colocalization with SIP30 (white arrowheads mark
the cells with double staining). D, SIP30 levels in the spinal cord. Immunological staining
using antibodies against SIP30 (a), substance P (b), and CGRP (c). Superimposed composite
images are shown as follows: SIP30 with substance P (d), SIP30 with CGRP (e), and triple
composite of SIP30 with substance P and CGRP (f).
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Fig. 2. SIP30 was up-regulated during CCI
A, SIP30 mRNA levels in the spinal cord (upper panel) and DRG (lower panel). Real-time
PCR amplification results for SIP30 mRNA are shown relative to the mean levels in normal
animals. Spinal cord tissues from rats receiving no surgery (normal), sham-CCI surgery (sham),
or CCI surgery (3 days and 7 days post surgery, respectively) were collected, and RNA was
isolated from the ipsilateral and contralateral side of the sham or CCI surgery for real-time
PCR analysis. *, significant difference (p < 0.05 vs. normal or sham group) in the ipsilateral
but not contralateral spinal cord for both day 3 and day 7 after CCI surgery. No significant
difference was observed in DRG.
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B, Western blot analysis of SIP30 protein levels in the spinal cord. Spinal cord tissues from
rats receiving sham or CCI surgery (3 days post surgery) were collected, and protein was
isolated from the ipsilateral and contralateral side of the sham or CCI surgery for Western blot
analysis. Upper panel, representative Western blots of SIP30 protein. β-Actin was used as the
internal control. Lower panel, quantitative results of SIP30 protein. *, significant difference (p
< 0.05 vs. sham group) for the ipsilateral side of the spinal cord.
C. Western blot analysis of SIP30 protein levels in DRG. DRG tissues from rats receiving sham
or CCI surgery (3 days post surgery) were collected, and protein was isolated from the
ipsilateral and contralateral side of the sham or CCI surgery for Western blot analysis. Upper
panel, representative Western blots of SIP30 protein. β-Actin was used as the internal control.
Lower panel, quantitative results of SIP30 protein. No significant difference was observed on
either ipsilateral or contralateral side of DRG.
D, SIP30 protein level was elevated in the ipsilateral side of spinal cord dorsal horn after CCI.
(a) Immunofluorescence shows basal expression of SIP30-IR cells in naïve rats; (b)
Immunofluorescence indicates an increase in SIP30-IR cells in the dorsal horn on the ipsilateral
side; (c) quantification of SIP30 expression level, as indicated by the number of SIP30-IR cells
(per 30 μm section) in the superficial (laminae I–II) and deeper (laminae IV–V) dorsal horn;
(d) A high magnification image showing SIP30 immunoreactivity in the cytoplasm but not
nucleus. Scale bars, 50 μm.
E, Double immunofluorescence reveals that SIP30 (red) co-localized with NeuN (neuronal
marker, green) (a), but dose not co-localize with OX-42 (microglial marker, green) (b) or GFAP
(astrocytic marker, green) (c), in the dorsal horn of the spinal cord. Scale bar, 50 μm.
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Fig. 3.
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SIP30 participates in the development of peripheral nerve injury-induced neuropathic pain.
Antisense oligonucleotide treatment was initiated on the day of CCI surgery, before the
development of neuropathic pain. Shaded area (marked “i.t.”) indicates the duration of
intrathecal injection. Upward arrow marked “CCI” indicates the day of CCI surgery. PWT,
paw withdrawal threshold; PTL, paw withdrawal latency. Following the intrathecal injection
of SIP30 antisense oligonucleotide (CCI+ASI) for 4 days (from day 0 to day 3 post-CCI), the
development of mechanical allodynia (A) and thermal hyperalgesia (B) was attenuated in the
CCI ipsilateral paw (“Ipsi.”), whereas normal saline (CCI+NS) and missense oligonucleotide
(CCI+MS) had no effect. *p<0.05 for the SIP30 antisense oligonucleotide group vs. either
normal saline or missense oligonucleotide group. (C, D) No significant change was seen in the
CCI contralateral paw (“Cont.”) after the same treatments.
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Fig. 4.
SIP30 participates in the maintenance of peripheral nerve injury-induced neuropathic pain.
After mechanical allodynia and thermal hyperalgesia were already developed post CCI surgery,
antisense oligonucleotide treatment was initiated. Shaded area (marked “i.t.”) indicates
intrathecal injection. Upward arrow marked “CCI” indicates the day of CCI surgery. PWT,
paw withdrawal threshold; PTL, paw withdrawal latency. Intrathecal injection of SIP30
antisense oligonucleotide (CCI+ASI) for 4 days (from day 3 to day 7 post-CCI) attenuated
both mechanical allodynia (a) and thermal hyperalgesia (b) in the CCI ipsilateral paw (“Ipsi.”),
but normal saline (CCI+NS) and missense oligonucleotide (CCI+MS) had no effect. *p<0.05
for the SIP30 antisense oligonucleotide group vs. either normal saline or missense
oligonucleotide group. (c, d) No significant change was seen in the CCI contralateral paw after
the same treatments.
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Fig. 5.
Treatment of SIP30 antisense oligonucleotide does not affect basal nociceptive response in
control animals. In surgery-naïve rats, intrathecal injection of SIP30 antisense oligonucleotide
for 4 days did not affect the basal responses to either von Frey (a) or thermal stimuli (b) in
either paw. Shaded area (marked “i.t.”) indicates intrathecal injection. PWT, paw withdrawal
threshold; PTL, paw withdrawal latency.
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Fig. 6.
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SIP30 antisense oligonucleotide knock down of SIP30 and SNAP25 levels. Abbreviations: NS,
normal saline; AS, antisense oligonucleotide; MS, missense oligonucleotide. (0–3 d) indicates
that rats received daily intrathecal injection from day 0 (6 hrs before CCI surgery) to day 3
post-CCI; (4–7 d) indicates that rats received daily intrathecal injection from day 4 to day 7
post-CCI.
A, SIP30 mRNA was increased after CCI, and the increase was reduced by antisense
oligonucleotide. After four times of intrathecal administration of SIP30 antisense (AS) or
missense (MS) oligonucleotide, rats were sacrificed and the lumbar spinal cords were dissected
at six hours after the last injection. Real-time PCR amplification for SIP30 mRNA showed a
significant decrease in the ipsilateral spinal cord in CCI rats receiving SIP30 antisense
oligonucleotide compared with animals receiving missense oligonucleotide. *, significant
difference (p < 0.05).
B, Western blot for SIP30 protein indicated a significant decrease in ipsilateral spinal cord in
CCI rats receiving SIP30 antisense oligonucleotide compared with animals receiving missense
oligonucleotide or normal saline. Upper panel, representative Western blots of SIP30 protein.
β-Actin was used as the internal control. Lower panel, quantitative results of SIP30 protein. *,
significant difference (p < 0.05).
C, Real-time PCR amplification for PSD95 mRNA showed a significant increase in ipsilateral
spinal cord after CCI surgery. Intrathecal injection of SIP30 antisense oligonucleotide every
24 hours for 4 times did not appreciably affect PSD95 mRNA levels. *, significant difference
(p < 0.05).
D, Real-time PCR amplification for SNAP25 mRNA showed a significant increase in
ipsilateral spinal cord after CCI surgery. Intrathecal injection of SIP30 antisense
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oligonucleotide every 24 hours for 4 times caused a trend to decrease in SNAP25 mRNA in
ipsilateral spinal cord of CCI rats, although that did not reach statistical significance. *,
significant difference (p < 0.05).
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Fig. 7.
Double immunofluorescence staining shows that SIP30 (green) co-localized with SNAP-25
(red) in the dorsal horn of the spinal cord. Left panel: SIP30 immunoreactivity was present in
both soma and terminals of spinal dorsal horn neurons. Middle panel: SNAP-25
immunoreactivity was present in presynaptic terminals of spinal dorsal horn neurons. Right
panel: SIP30 (green) co-localized with SNAP-25 (red) in terminals of spinal dorsal horn
neurons. Arrowheads indicate double-labeled terminals.
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Fig. 8.
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SIP30 siRNA inhibition of synaptic vesicle exocytosis in PC12 cells. Using human growth
hormone (hGH) secretion in PC12 cells as an assay for synaptic vesicle exocytosis, cells were
co-transfected with a hGH-coding plasmid plus either the control or anti-SIP30 siRNA
oligonucleotides, and baseline secreted (grey bars) vs. total secretable hGH (filled bars) were
measured. *, significant difference (p < 0.05, unpaired t test).
NIH-PA Author Manuscript
Pain. Author manuscript; available in PMC 2010 November 1.