15-deoxy-delta12,14-prostaglandin J2 attenuates endothelial-monocyte interaction: implication for inflammatory diseases
Journal of Inflammation
15-deoxy-delta12,14-prostaglandin J2 attenuates endothelial-monocyte interaction: implication for inflammatory diseases
Ratna Prasad 1
Shailendra Giri 1
Avtar K Singh 0
Inderjit Singh 1
0 Department of Pathology and Laboratory Medicine, Ralph Johnson Veterans Affairs Medical Center , Charleston, SC, 29425 , USA
1 Department of Pediatrics, Medical University of South Carolina , Charleston, SC, 29425 , USA
Background: The Infiltration of leukocytes across the brain endothelium is a hallmark of various neuroinflammatory disorders. Under inflammatory conditions, there is increased expression of specific cell adhesion molecules (CAMs) on activated vascular endothelial cells which increases the adhesion and infiltration of leukocytes. TNF is one of the major proinflammatory cytokines that causes endothelial dysfunction by various mechanisms including activation of transcription factor NF-B, a key transcription factor that regulates expression of CAMs. Peroxisome proliferatoractivated receptor gamma (PPAR) is a member of the nuclear hormone superfamily of ligandactivated transcriptional factors. 15-deoxy- 12, 14-prostaglandin J2 (15d-PGJ2) is a well recognized natural ligand of PPAR and possesses anti-inflammatory properties both in vitro and in vivo. This study aims to elucidate the mechanism of 15-PGJ2 on the adhesion of mononuclear cells to activated endothelial cells. Methods: To delineate the signaling pathway of 15d-PGJ2 mediated effects, we employed an in vitro adhesion assay model of endothelial-monocyte interaction. Expression of CAMs was examined using flow cytometry and real time PCR techniques. To define the mechanism of 15d-PGJ2, we explored the role of NF-B by EMSA (Electrophoretic Mobility Shift Assay) gels, NF-B reporter and p65-transcriptional activities by transient transfection in the brain-derived endothelial cell line (bEND.3). Results: Using an in vitro adhesion assay model, we demonstrate that 15d-PGJ2 inhibits TNF induced monocyte adhesion to endothelial cells, which is mediated by downregulation of endothelial cell adhesion molecules in a PPAR independent manner. 15d-PGJ2 modulated the adhesion process by inhibiting the TNF induced IKK-NF-B pathway as evident from EMSA, NFB reporter and p65 mediated transcriptional activity results in bEND.3 cells. Conclusion: These findings suggest that 15d-PGJ2 inhibits inflammation at multiple steps and thus is a potential therapeutic target for various inflammatory diseases.
Inflammatory mechanisms are pivotal in many disease
states, including atherosclerosis, autoimmune disorders
and ischemia/reperfusion injury [1-4]. Under
inflammatory conditions there is activation of vascular endothelial
cells that involves various morphological and metabolic
changes . There is induction of specific cell adhesion
molecules, such as, intercellular adhesion molecule-1
(ICAM-1), vascular cell adhesion molecule-1 (VCAM-1)
and E-selectin. These interact with their corresponding
ligands on leukocytes namely, lymphocyte
function-associated antigen-1 (LFA-1), very late antigen-4 (VLA-4) and
carbohydrate moieties respectively [2,6]. The process of
infiltration involves sequential capture, rolling, firm
adhesion and transmigration across the endothelial
barrier . Blockade of CAMs that mediate the accumulation
of mononuclear cells under inflammation is now
considered as an effective treatment strategy in clinical
TNF is one of the major proinflammatory cytokines that
is dysregulated in inflammatory diseases mentioned
earlier and has been shown to contribute to endothelial
dysfunction . TNF causes endothelial dysfunction by
various mechanisms that includes activation of
transcription factor NF-B . Transcriptional regulation of many
pro-inflammatory genes, including CAMs, is under the
control of different transcriptional factors including
NFB [10,11]. NF-B is a redox sensitive transcription factor
that most commonly exists as a p50/p65 heterodimer.
This heterodimer remains sequestered in the cytoplasm
when associated with inhibitor of kappa B (IB) proteins.
Upon stimulation (e.g. by TNF) IB proteins get
phosphorylated by upstream IB kinases (IKKs) followed by
degradation, releasing the active dimer to translocate into
the nucleus to transcribe its target genes [12,13].
Peroxisome proliferator-activated receptors (PPARs) are
members of the nuclear hormone superfamily of
ligandactivated transcriptional factors. PPARs heterodimerize
with retinoid receptor (RXR) and bind to peroxisome
proliferator-response elements in target genes . The
subtype PPAR is a regulator of adipogenesis . A
number of studies have demonstrated that PPAR may
play a role in regulating inflammatory responses [16,17].
15-deoxy-d 12, 14-prostaglandin J2, the ultimate
metabolite of prostaglandin (PG) D2, is a natural ligand of PPAR.
15d-PGJ2 has been shown to inhibit expression of iNOS
and TNF in several cell types that are dependent on
PPAR [18,19]. However, there are also anti-inflammatory
responses of 15d-PGJ2 that are PPAR independent
[20,21]. There are studies that report protective effects
mediated by 15d-PGJ2 via inhibition of infiltration of
immune cells in various models of inflammation e.g.
endotoxic shock , lung injury ,
ischemia/reperfusion injury  and experimental autoimmune
encephalomyelitis (EAE) [25,26]. Thus, based on these studies,
we hypothesized that 15d-PGJ2 inhibits the adhesion of
mononuclear cells to the endothelial cells and thereby
attenuates their transmigration. We observed that
15dPGJ2 inhibited the adhesion of monocytes to bEND.3
endothelial cell line, activated by TNF, by
downregulation of endothelial CAMs via inhibition of IKK-NF-B
Reagents and Antibodies
DMEM (4.5 g/L glucose), minimum essential medium
alpha (MEM alpha) with ribonucleotides and
deoxyribonucleotides, RPMI-1640 medium and FBS were purchased
from Gibco BRL (Carlsbad, CA, USA). Granulocyte
macrophage colony stimulating factor (GMCSF) and
recombinant mouse TNF were from R & D Systems
(Minneapolis, MN, USA). Vybrant Cell adhesion kit
containing Calcein AM fluorescent dye was from Molecular
Probes (Eugene, OR, USA). ECL detection kit was from GE
healthcare (Piscataway, NJ, USA). Antibodies for p65,
p50, IB, VCAM-1 were purchased from Santa Cruz
Biotechnologies (Santa Cruz, CA, USA). Texas red conjugated
rabbit IgG antibody was from Vector Lab. Inc.
(Burlington, CA, USA). Trizol reagent and Lipofectamine Plus
were from Invitrogen (Carlsbad, CA, USA).
FluoromountG was from Electron Microscopy Sciences (Hartfield, PA,
USA). Antibodies against VCAM-1 (FITC labeled),
ICAM1 and E-selectin (PE labeled) were from BD Pharmingen
(Franklin Lakes, NJ). Luciferase assay system was
purchased from Promega (Madison, WI).
The bEND.3 mouse brain endothelial cells were from
ATCC (American Type Culture Collection, Manassas, VA,
USA) and were cultured in Dulbecco's modified Eagle's
medium (high glucose) supplemented with 10% Fetal
Bovine serum (FBS) and antibiotics. Cells were grown to
confluence, made serum free for further treatments, and
stimulation with TNF (50 ng/ml) for all the experiments.
JAWS II, a mouse monocyte cell line (ATCC) was
maintained in MEM Alpha medium with 10% heat inactivated
FBS, 0.5% gentamycin and granulocyte-macrophage
colony-stimulating factor (GMCSF) (1 ng/mL; R & D
Plasmids and Transfection
NF-B-luciferase was kindly provided by Dr. George
Rewadi (Institut Pasteur, Laboratoire des Mycoplasmes,
Paris, France), flag-IKK was a gift from Dr. Zheng-Gang
Liu (National Institute of Health, Bathesda, MD) and
FLAG-tagged wild-type (wt) PPAR and FLAG-tagged
L468A/E471A PPAR were provided by Dr. V. Chatterjee
(University of Cambridge, Cambridge, U.K.). The
peroxisome proliferator-response element (PPRE)-containing
reporter plasmid (J6-thymidine kinase (TK)-Luc) was
provided by B. Staels (Institut Pasteur de Lille, Lille, France).
PTL-luciferase, Gal-p65 and Gal-DBD (DNA binding
domain) were purchased from Panomics (Fremont, CA).
The endothelial cell line was transfected with the
indicated plasmid (0.5 g/well) using Lipofectamine Plus
Reagent under serum free conditions as described before
. pcDNA3.1 was used to normalize the total content
of DNA in all transfection experiments.
In vitro Adhesion assay model
As described earlier, bEND.3 cells were grown as
monolayers in double chamber slides (Nalge Nunc, Naperville,
IL, USA) . Cells were pre-treated with 15d-PGJ2 for 30
min followed by TNF for 6 h. Dye labeled monocytes at
the concentration of 2 106 cells/ml were added per
chamber on the bEND.3 cells and allowed to interact for
30 min with gentle shaking at 37C. Adherent fluorescent
cells were observed using a fluorescence microscope
(Olympus, BX60) and images were captured in Adobe
Photoshop 7.0 at 100. Adherent fluorescent cells were
counted using Image Pro-Plus 4.0 software. Mean and SD
were calculated for independent experiments. Results
were plotted as fold change compared to the control
values for all the experiments.
BEND.3 cells were grown in chamber slides and treated
with 15d-PGJ2 and stimulated with TNF for 20 min.
Cells were fixed with paraformaldehyde (4%) followed by
blocking in blocking reagent. Cells were then incubated in
anti-p65 antibody followed by incubation in secondary
antibody and mounting with Flouromount-G. The
stained sections were analyzed by immunofluorescence
microscopy (Olympus BX-60 from Opelco, Dulles, VA,
USA) with images captured using an Olympus digital
camera (Optronics, Goleta, CA, USA) at 400
magnification. Captured images were processed using Adobe
Photoshop 7.0 and were adjusted using brightness and
contrast tools. Three independent experiments were done
and 5 fields for each treatment were taken. Representative
images are shown.
Real-time or quantitative (q) PCR
Cells were harvested in Trizol reagent and RNA was
isolated per the manufacturer's protocol. cDNA synthesis was
done using iScript CDNA synthesis kit (BIO-RAD
Laboratories, Hercules, CA, USA) per the manufacturer's
protocol. qPCR was performed using SYBR GREEN PCR master
mix (Applied Biosciences, Foster city, CA, USA) and
BIORAD laboratories iCycler iQ PCR using primers as
described before . primers of CAMs and 18S are as
follows, ICAM-1 FP 5'-gca gag tgt aca gcc tct tt-3' RP 5'-ctg gta
tcc cat cac ttg-3', VCAM-1 FP 5'-gca gag tgt aca gcc tct tt-3',
RP 5'-ctg gta tcc cat cac tcg ag-3'; E-selectin FP 5'-act tca gtg
tgg tcc aag ag-3' RP 5'-gca cat gag gac ttg tag gt-3'; 18S FP
5'-gaa aac att ctt ggc aaa tgc ttt-3' RP5'-gccgct aga ggt gaa att
ctt-3'. The normalized mRNA expression was computed
with that of 18s expression. Values are expressed as fold
change from the control values and plotted.
Preparation of cytosolic and nuclear extracts
Cytosolic and nuclear extracts from bEND.3 cells were
prepared using the method of Digman et al  with
slight modification . Cells were harvested, washed
twice with ice-cold PBS, and lysed in 400 l of buffer A (10
mM HEPES, pH 7.9, 10 mM KCl, 2 mM MgCl2, 1 mM
PMSF, 5 g/ml aprotinin, 5 g/ml pepstatin A, and 5 g/
ml leupeptin) containing 0.1% Nonidet P-40 for 15 min
on ice, vortexed vigorously for 15 s, and centrifuged at
14,000 rpm for 30 s. The pelleted nuclei were resuspended
in 40 l of buffer B [20 mM HEPES, pH 7.9, 25% (v/v)
glycerol, 0.42 M NaCl, 1.5 mM MgCl2, 0.2 mM EDTA, 1
mM PMSF, 5 g/ml aprotinin, 5 g/ml pepstatin A, and 5
g/ml leupeptin]. After 30 min on ice, lysates were
centrifuged at 14,000 rpm for 10 min. Supernatants containing
the nuclear proteins were diluted with 20 l of modified
buffer C [20 mM HEPES, pH 7.9, 20% (v/v) glycerol, 0.05
M KCl, 0.2 mM EDTA and 0.5 mM PMSF] and stored at
70C until use. Cytosolic fraction (50 g) was used for
western blot analysis for the detection of IB and IKK
using their specific antibodies as described before .
Cell extracts were prepared as previously described with
lysis buffer (50 mM Tris-HCl, pH 7.4, containing 50 mM
NaCl, 1 mM EDTA, 0.5 mM EGTA, 1% Triton X-100, 10%
glycerol, and protease inhibitor mixture) [27,29]. Protein
(50 g) was loaded with appropriate marker (Bio-Rad
Laboratories, Hercules, CA, USA) on 8% sodium dodecyl
sulfate-polyacrylamide gel (SDS_.PAGE), followed by
transfer to nitrocellulose membrane. The membrane was
blocked with 5% milk or 3% BSA in Tris buffered
salinetween (TBST). Primary anti-p65, -IB, -pIKK was
added. Blots were washed, followed by incubation in
secondary antibody and then detection by
Electrophoretic mobility shift assay (EMSA)
Nuclear extracts from treated and untreated cells were
prepared and EMSA was performed as described previously
[29,30] using NF-B consensus sequence that was
endlabeled with [-32P] ATP. Nuclear extracts were
normalized on the basis of protein concentration and equal
amounts of protein (5 g) were loaded. The gels were
dried and then autoradiographed at -70C using x-ray
15-PGJ2 treated and untreated bEND.3 cells in the
presence or absence of TNF (50 ng/ml) were harvested and
processed as described earlier . Cells were blocked
with anti-CD16/CD32 and incubated with FITC- or
PElabeled antibodies against ICAM-1, VCAM-1 and
E-selectin. The cells were acquired by FACS and analyzed by
CellQuest (BD PharMingen, Franklin Lakes, NJ).
15d-PGJ2 inhibits monocyte adhesion to a brain-derived
endothelial cell line
Activated bEND.3 endothelial cells under
pro-inflammatory environment allows increased adherence of
leukocytes to its surface to facilitate their migration . In our
in vitro system, bEND.3 cells were activated with TNF
that caused a significant increase in the adhesion of
monocytes (~9 fold) compared to untreated cells.
However, treatment with15d-PGJ2 (110 M) 30 min prior to
the addition of TNF significantly inhibited the adhesion
of monocytes (Fig. 1a, b). Prostaglandin production
begins with the liberation of arachidonic acid which
under cyclooxygenase enzymes 1 and 2 gets converted to
PGH2. Specific prostaglandin synthase convert PGH2 into
a series of prostaglandins including PGI2, PGF2, PGD2
and PGE2 . We also treated the bEND.3 cells with
different prostaglandins (PGA1, PGB2, PGD2, PGE1, PGE2,
PGF1, 15d-PGJ2, PGJ2), arachidonic acid, leukotriene
(LTB4) and thromboxane (TXB4) and observed that PGA1
and PGD2 treatment showed a significant decrease in
TNF induced adhesion of monocytes, as these are
precursors of 15d-PGJ2 (Fig. 1c). These results suggest the
specificity of 15d-PGJ2 in mediating the inhibition of the
adhesion process of monocytes on activated bEND.3 cells.
15d-PGJ2 did not cause any cell death (assessed by MTT
and LDH release assays) at the concentrations used (data
15d-PGJ2 inhibits expression of endothelial CAMs
Extravasation of mononuclear cells the recruitment
cascade are orchestrated by cell adhesion molecules on both
endothelial and immune cells . Accordingly, we
examined the effect of 15d-PGJ2 on TNF induced expression
of CAMs (VCAM-1, ICAM-1 and E-selectin). For this,
bEND.3 cells were pretreated with15d-PGJ2 (510 M)
followed by TNF (50 ng/ml) treatment. After 2 h of
incubation, bEND.3 cells were processed for RNA isolation
and quantitative analysis of CAMs using real time PCR
(qPCR). Treatment with TNF significantly increased the
mRNA expression of VCAM-1, ICAM-1 and E-selectin as
compared to control cells. 15d-PGJ2 markedly
downregulated their expression with a most pronounced effect
5Fdig-PuGr eJ21inhibits monocyte adhesion to endothelial cells
5d-PGJ2 inhibits monocyte adhesion to endothelial
cells. bEND.3 cells were incubated with different
concentrations of 15d-PGJ2 (120 M) (A) or mentioned
prostaglandins (5 M), arachidonic acid (5 M), Leukotriene 4 (LTB 4, 5
M) and Thromboxanes 4 (TXB 4, 5 M) (C) for 30 min
followed by TNF (50 ng/ml) stimulation for 6 h. Fluorescently
labeled monocytes were allowed to interact with activated
bEND.3 cells. Adhered monocytes were counted as
mentioned in 'Material and Methods'. Data calculated as mean
SD of 21 fields from 3 different experiments. *** p < 0.001
compared to untreated control cells and !!! p < 0.001
compared to TNF treated cells. (B) is the pictorial
representation of adhesion under TNF (50 ng/ml) and 15d-PGJ2 (10
observed on expression of VCAM-1 as compared to
Eselectin or ICAM-1 (Fig. 2a, b and 2c). These observations
are in agreement with flow cytometry analysis which also
showed that 15d-PGJ2 treatment significantly reduced the
expression of endothelial CAMs with maximum affect on
VCAM-1 expression (Fig. 2d).
15d-PGJ2 inhibits VCAM-1 expression in a PPAR
To determine whether 15d-PGJ2 mediates its inhibitory
effect through PPAR, we employed GW9662, an
irreversible PPAR antagonist. GW9662 (10 M) did not reverse
15d-PGJ2 mediated inhibition of TNF induced
expression of VCAM-1 in the endothelial cell line (Fig. 3A).
Another activator of PPAR, troglitazone, was used to
examine if PPAR plays any role in expression of VCAM-1
l1Fia5ilgdCu-PrAGeMJ2s inhibits mRNA and protein expression of
endothe15d-PGJ2 inhibits mRNA and protein expression of
endothelial CAMs. bEND.3 cells were pretreated with
15d-PGJ2 (520 M) for 30 min followed by stimulation with
TNF (50 ng/ml) for 2 h. Cells were harvested in Trizol
reagent for RNA isolation and cDNA synthesis. RT-PCR analysis
was done for ICAM-1 (A), VCAM-1 (B) and E-selectin (C).
Results were calculated as mean SD for 3 independent
experiments. Samples were examined in triplicates. &&& p <
0.001 compared with control (untreated and unstimulated
cells) and !!! p < 0.001 as compared to TNF treatment. For
the quantitation of expression of surface CAMs, bEND.3
cells were treated with TNF (50 ng/ml) in the presence or
absence of 15d-PGJ2 (520 M) for 6 h followed by flow
cytometry analysis (D) (n = 2).
in bEND.3 cells. Troglitazone treatment, similar to
15dPGJ2 treatment, inhibited the expression of VCAM-1,
which could not be reversed by GW9662 (Fig. 3a). To
examine the ability of GW9662 on 15d-PGJ2 and
troglitazone mediated induction of PPAR transcription, we used
a chimeric receptor system in which the putative
ligandbinding domain of the PPAR is fused to the DNA binding
domain of the yeast transcription factor
galactose-responsive gene 4 (GAL4). The 15d-PGJ2 and troglitazone
potently activated the PPAR-dependent chloramphenicol
acetyltransferase (CAT) reporter activity, which was
completely blocked by GW9662 treatment (Fig. 3b). To
confirm this observation, bEND.3 cells were transfected with
PPAR wild type (Wt) and dominant-negative (DN)
expression vectors and determined the effects on
VCAM1mRNA expression. 15d-PGJ2 was able to inhibit the
TNF induced expression of VCAM-1 in both control and
PPAR Wt transfected cells. However, transfection with
PPAR DN was not able to attenuate the 15-dPGJ2
mediated inhibition of VCAM-1 mRNA expression indicating
1F5igdu-PrGeJ32 inhibits VCAM-1 in PPAR independent manner
15d-PGJ2 inhibits VCAM-1 in PPAR independent
manner. bEND.3 cells were treated with GW9662 (10 M)
30 min prior to treatment with 15d-PGJ2 (10 M) or
troglitazone (10 M) followed by TNF treatment (50 ng/ml).
bEND.3 cells were lysed and processed for immunoblot
analysis for VCAM-1 and actin expression (A). Endothelial cell
line was cotransfected with PPAR-GAL4 chimeras and the
reporter plasmid (upstream activating sequences)5-TK-CAT.
After 48 h, cells were treated with 15d-PGJ2 or trogliatzone
in the presence or absence of GW9662 (10 M) for 24 h.
Cell extracts were subsequently assayed for CAT activity by
ELISA (Roche) (B). pCMV-GAL4-binding domain (without
insert) and (upstream activating sequences)5-TK-CAT were
transfected as a control to detect the basal levels of CAT
activity (first lane). Data are mean of three values SD. *** p
< 0.001 as compared with untreated cells; !!! p < 0.001 as
compared with 15d-PGJ2 treated cells. (C) Cells were
transfected with PPAR wild type (Wt) and dominant negative
(DN) constructs followed by treatment with 15-dPGJ2 (5
and 10 M; 30 min) and TNF (50 ng/ml, 2 h) and processed
for qPCR for detection of VCAM1 mRNA expression as
described in 'Material and Methods' (C). Results were
calculated as mean SD for 3 independent experiments. Samples
were run in triplicates. &&& p < 0.001 compared with
control (untreated and unstimulated cells) and !!! p < 0.001 as
compared to TNF treatment. Cells were co-transfected
with PPAR wild type (Wt) and dominant negative (DN) (0.5
g/well) constructs along with PPRE-luc reporter (0.5 g/
well) and pRL-TK (0.5 g/well) followed by treatment with
15-dPGJ2 (10 M) after 24 h. After 24 h incubation,
luciferase activity was performed, as described before
pcDNA3.1 was added to normalize the total content of DNA
for transfection. Data are mean SD of three different
values. ***, p < 0.001 as compared with untreated cells; !!!, p <
0.001 as compared with 15d-PGJ2-treated PPAR wt
that the inhibitory effect of 15d-PGJ2 is independent of
PPAR (Fig. 3c). Treatment with 15d-PGJ2 induced the
PPRE-luciferase activity in transiently transfected PPAR
Wt expression vector, whereas, it had no effect in PPAR
DN transfected cells (Fig. 3d) suggesting that 15d-PGJ2
has the ability to activate PPAR but its effect on VCAM-1
expression in the bEND.3 endothelial cell line is
independent of PPAR.
15d-PGJ2 inhibits NF-B function in brain-derived
endothelial cell line
To further understand the mechanism of inhibitory action
of 15d-PGJ2 on endothelial CAMs and the process of
adhesion we examined the effect of 15d-PGJ2 on NF-B
pathway, which is a pleiotropic regulator of many genes
involved in inflammation including CAMs . Using
EMSA, we observed that 15d-PGJ2 inhibited the TNF
induced binding of the NF-B complex, in a time and
dose-dependent manner (Fig. 4a). To further define the
inhibitory effect of 15d-PGJ2 on TNF mediated
activation of the NF-B pathway, the bEND.3 cells were
transfected with the p65/p50 complex along with the NF-B
luciferase reporter construct. Cells transfected with p65/
p50 exhibited increased reporter activity, which was
markedly reduced in a dose-dependent manner with 15d-PGJ2
treatment (Fig. 4b). These observations obtained from
EMSA and transfection studies were further confirmed by
immunostaining for p65 nuclear translocation. Under
TNF stimulation, p65 translocated to the nucleus and
was markedly attenuated by 15d-PGJ2 treatment (Fig. 4c).
Correspondingly, we also observed that 15d-PGJ2
inhibited the TNF induced nuclear translocation of p65 and
degradation of IB protein in a time and dose-depended
manner (Fig. 4d).
To support the 15d-PGJ2 mediated inhibition on NF-B
pathway, we examined the effect of 15d-PGJ2 on
p65DNA binding domain-gal4 transcriptional activity. The
p65-DNA binding domain-gal4 (p65-DNA-gal4) is a
chimeric-transactivator, which consists of transcriptional
activation domain of NF-B p65 protein fused to the
DNA-binding domain of GAL4 protein from yeast. As
evident from figure 5, treatment with TNF induced the
transcriptional activity of p65-DBD-gal4 which was
completely blocked by 15d-PGJ2 treatment.
Inhibition of IKK activity by 15d-PGJ2
Based on preceeding results, we examined the effect of
15d-PGJ2 on the activity of IKK, the upstream kinase of
the NF-B pathway. Cells were treated with 15d-PGJ2
followed by TNF for 15 min and phosphorylation of IKK
was detected using a specific antibody. As shown in figure
6a, TNF treatment induced phosphorylation of IKK in
bEND.3 cells which was completely blocked by 15d-PGJ2
treatment. bEND.3 cells were further cotransiently
transfected with IKK and NF-B luciferase reporter constructs
and after 24 h, cells were treated with TNF with or
without 15d-PGJ2. TNF induced the IKK mediated
NF-Breporter activity, which was a significantly downregulated
by 15d-PGJ2 treatment (Fig. 6b). This observation was
further supported when bEND.3 cells were transiently
l1Fia5ilgdcu-ePrlGelsJ42 inhibits TNF induced NF-B function in
endothe15d-PGJ2 inhibits TNF induced NF-B function in
endothelial cells. bEND.3 cells were treated with
15dPGJ2 (110 M) and TNF (50 ng/ml) for various time
periods (540 min) and processed for EMSA as described in
'Material and Methods' (A). bEND.3 cells were transiently
transfected with p65, p50 expression vectors along with
NFB luciferase reporter construct (0.5 g/well) and
pCMV-galactosidase (0.5 g/well) followed by treatment with
15dPGJ2 (520 M) for 4 h and processed for luciferase and
galactosidase activities. Luciferase activity was normalized
with respect to -gal activity (B). Results were calculated as
mean SD for 3 independent experiments. Samples were
run in triplicates. &&& p < 0.001 compared with control and
!!! p < 0.001 compared with TNF treatment (50 ng/ml).
Cells were treated with 15d-PGJ2(10 M) for 30 min
followed by TNF for 20 min and stained with anti-p65
antibody as described in 'Material and Methods' (C). Images
taken at 200 magnification are representative of 6 fields
from each treatment and 3 independent experiments.
Treated and untreated cells were processed for immunoblot
analysis for p65 and IB levels (D). Representative blot
from two independent experiments are shown.
cotransfected with p65-DBD-gal4 and IKK expression
vectors. Transient transfection with IKK significantly
induced p65 transcriptional activity which was
completely blocked by 15d-PGJ2 treatment (Fig. 6c)
suggesting that 15d-PGJ2 inhibits NF-B function by inhibiting
IKK activity in bEND.3 cells.
Post treatment of 15d-PGJ2 inhibits adhesion of
monocytes on activated brain-derived endothelial cell line
Our results suggested that 15d-PGJ2 inhibits the adhesion
of mononuclear cells on activated endothelial cells by
inhibiting the CAMs expression via downregulation of
NF-B pathway when pretreated before stimulation with
c1Fe5igldlsu-PrGeJ52 inhibits p65 transcriptional activity in endothelial
15d-PGJ2 inhibits p65 transcriptional activity in
endothelial cells. bEND.3 cells were transfected with
Galp65 or Gal-DBD along with PTL-luciferase and PRL-TK
reporter constructs as described in Material and Method.
bEND.3 cells were pretreated with 15d-PGJ2 (10 M) for 30
min followed by TNF treatment (50 ng/ml). After 6 h of
TNF treatment, cells were processed for luciferase assay
and results were normalized with PRL-TK luciferase activity
in each sample. Results were calculated as mean SD for 3
independent experiments. *** and !!! p < 0.001 compared
with control, @@@ p < 0.001 compared with TNF
TNF. We wanted to examine if post treatment with
15dPGJ2 could inhibit the adhesion of mononuclear cells on
TNF-stimulated cells. For this, bEND.3 cells were
stimulated with TNF for 6 h followed by addition of various
concentrations (520 M) of15d-PGJ2. After 30 min of
treatment with 15d-PGJ2, cells were washed and labeled
monocytes were added for adhesion assay. Interestingly,
post treatment with 15d-PGJ2 inhibited adhesion of
mononuclear cells on activated bEND.3 cells (Fig. 7)
suggesting that 15d-PGJ2 probably inhibits multiple
pathways including NF-B-CAMs expression and other
signaling pathway required for monocyte-endothelial cell
PGs are small lipid molecules that regulate numerous
processes in the body and their biological effects is an area
of concentrated research . The J series of PGs have
been demonstrated to regulate processes like
adipogenesis, inflammation and tumorigenesis . 15d-PGJ2 is a
metabolite of PGD2 and is produced by mast cells, T cells,
platelets and alveolar macrophages . 15d-PGJ2 is
emerging as a key anti-inflammatory mediator.
Consistent with this we have previously shown that 15d-PGJ2 has
an anti-inflammatory role in primary astrocytes . This
study reports for the first time that 15d-PGJ2 inhibits
r1Fe5ipgdou-PrrtGeeJr62aicnthi vibitiyts TNF induced IKK mediated NF-B
15d-PGJ2 inhibits TNF induced IKK mediated
NFB reporter activity. bEND.3 cells were treated with
TNF (50 ng/ml) in the presence or absence of 15d-PGJ2 (10
M) followed by detection of pIKK using its specific
antibody (Cell Signaling) (A). actin was used as a control for
equal content of protein loaded. bEND.3 cells were
transfected with IKK, NF-B luciferase and
pCMV--galactosidase constructs and treated with 15d-PGJ2 (520 M) and
TNF (50 ng/ml). After 4 h of TNF treatment, cells were
processed for luciferase assay as described in 'Material and
Methods' (B). Results were calculated as mean SD for 3
independent experiments. &&& p < 0.001 compared with
control, !!! p < 0.001 compared with TNF treatment and
### p > 0.001 compared with IKK. bEND.3 cells were
transfected with Gal-p65 or Gal-DBD in the presence or
absence of flag-IKK along with PTL-luciferase and PRL-TK
reporter constructs as described in Material and Method.
bEND.3 cells were pretreated with 15d-PGJ2 (10 M) for 30
min followed by TNF treatment. After 6 h of TNF
treatment (50 ng/ml), cells were processed for luciferase assay
and results were normalized with PRL-TK luciferase activity
in each sample (C). Total DNA content was normalized with
pcDNA3. Results were calculated as mean SD for 3
adhesion of monocytes to TNF activated bEND.3
endothelial cells by downregulating endothelial CAMs via
inhibition of IKK-NF-B pathway but in a PPAR
Infiltration of leukocytes is a crucial response in
inflammatory reactions in numerous disorders where these
leukocytes are intended to induce inflammation in CNS
aPFcoitgsivutarttreeeda7temnednotthoefli1a5ldc-ePllGsJ2 inhibits monocyte adhesion to
Post treatment of 15d-PGJ2 inhibits monocyte
adhesion to activated endothelial cells. bEND.3 cells were
treated with TNF (50 ng/ml) for 6 h, followed by addition of
different concentrations of 15d-PGJ2 (520 M). After 30
min of incubation with 15-PGJ2, fluorescently labeled
monocytes were allowed to interact with activated bEND.3 cells.
Adhered monocytes were counted as mentioned in 'Material
and Methods'. Data calculated as mean SD of 21 fields from
3 different experiments. *** p < 0.001 compared to
untreated control cells and @ p < 0.001 compared to TNF
when BBB is compromised. However, when misdirected,
they destroy healthy cells and matrix components causing
tissue damage . Therefore, in recent years efforts have
been directed to limit the infiltration of mononuclear
cells so as to minimize the tissue injury during the disease
process. In earlier studies in different disease models, it
was reported that 15d-PGJ2 inhibits infiltration of
leuckocytes to site of inflammation [29,35]. Since adhesion of
infiltrating cells to endothelium, is a prerequisite for
infiltration, we investigated the effect of PPAR activator
15dPGJ2 on the adhesion process. 15d-PGJ2 was observed to
inhibit the adhesion of monocytes to activated bEND.3
endothelial cells in a dose-dependent manner. These
Results were consistent with previous studies where
15dPGJ2 inhibited the adhesion of mononuclear cells to
PMA, IFN or IL-1 activated endothelial cells [36,37].
The inhibition of the adhesion process by15d-PGJ2 was
mediated by down regulation of TNF induced
endothelial CAMs expression, namely, VCAM-1, E-selectin and
ICAM-1. Further, this effect was found to be PPAR
independent. Our Results were consistent with other reports in
which 15d-PGJ2 and other PPAR activators negatively
modulate endothelial CAMs in vitro [37-39]. Treatment of
bEND.3 cells with 15d-PGJ2 showed effects by
attenuating signaling taking place during adhesion process as well
as downregulating endothelial CAMs expression, thereby
giving a significant additive effect on inhibition on
adhesion of monocytes. To further understand the mechanism
of inhibition mediated by15d-PGJ2, we determined its
effect on the NF-B transcription factor which is known to
be activated by TNF . 15d-PGJ2 was observed to
inhibit DNA binding of the NF-B complex in a gel shift
assay. Interestingly, this inhibition was through
modulation of upstream targets of the NF-B pathway. There was
inhibition of TNF induced degradation of IkB protein
thereby preventing p65 nuclear translocation. Our study
is supported by other reports of inhibition of NF-B by
15d-PGJ2, though in different cell types [29,35,40,41].
Thus, our data showed that 15d-PGJ2 inhibits TNF
induced NF-B activity and consequently the expression
of endothelial CAMs under our experimental model.
Moreover, we have previously suggested IKK as a target of
15d-PGJ2 in modulating NF-B pathway in brain glial
cells [29,35], which is consistent in endothelial cells too.
We can conclude from our in vitro data that 15d-PGJ2
inhibits endothelial-monocyte interactions via
IKK-NFB-CAMs pathway in endothelial cells. PI3 kinase and Akt
are also known to play an important role in the adhesion
process . The activation of IKK is also regulated via
phosphorylation by Akt . 15d-PGJ2 has been
demonstrated to inhibit the PI3 kinase/Akt pathway in brain glial
cells . PI3 kinase and Akt pathway play important role
in adhesion as we have documented before that
inhibition of PI3Kinase and Akt is able to inhibit the adhesion
of monocytes .
Thus, 15d-PGJ2 might be modulating PI3
kinase-Akt-IKKNF-B-CAMs pathway. Interestingly, post treatment with
15d-PGJ2 was also able to inhibit monocyte adhesion on
activated bEND.3 cells, suggesting the possibility
that15dPGJ2 may also inhibit other signaling pathway/s
important for firm and sustained adhesion of monocyte on
15d-PGJ2 is a natural ligand of PPAR and has numerous
effects which are PPAR dependent. Moreover, it has been
shown to has therapeutic potential in various human
autoimmune diseases as well as animal models of
autoimmunity, including arthritis [44-46], ischemia-reperfusion
injury [47,48], Alzheimer's disease [49-51], lupus
nephritis [52,53] and EAE [26,54,55]. More recent evidences
have shown that there are effects of 15d-PGJ2 that are
independent of PPAR activation , while, the exact
mechanism of action of 15d-PGJ2 in different systems is
unknown. There are various propositions such as presence
of another cytoplasmic PG receptor , recruitment of
p300 by NF-B , inhibition of NF-B DNA binding by
alkylation of cysteine residue of p65 , or ROR
dependent mechanism .
All together, the present data shows that 15d-PGJ2
regulates inflammatory responses by inhibiting the infiltration
of leukocytes across the endothelial barrier, which it does
so by inhibiting monocyte adhesion to activated
endothelial cells via downregulation of IKK-NF-B-CAMs pathway
in endothelial cells, independent of PPAR.
15d-PGJ 2: 15-deoxy-Delta (12, 14)-prostaglandin J;
CAM: cell adhesion molecule; ICAM: Intercellular cell
adhesion molecule-1; VCAM-1: Vascular cell adhesion
molecule-1; NF-B: Nuclear factor kappa B; IB:
Inhibitory kappa B; IKK: Inhibitory kappa B kinase.
The authors declare that they have no competing interests.
This study is based on an original idea of SG and IS. RP
and SG wrote the manuscript. SG directed and RP
performed the in vitro experiments. AKS helped in finalizing
manuscript. All authors read and approved the final
RP and SG are equal contributors for this work. We would like to thank
Drs. Anne G. Gilg and Ramandeep Rattan for editing manuscript and Ms
Joyce Bryan for procurement of chemicals used in this study. These studies
were supported by grants (NS-40144, NS-22576, NS-34741, NS-37766,
and NS-40810) from the NIH and (SCIRF 0406 and SCIRF 0506) from State
of South Carolina Spinal Cord Injury Research Fund Board. This work was
supported by the NIH (NS-22576, NS-34741, NS-37766 and NS-40810)
and from the Extramural Research Facilities Program of the National
Center for Research Resources (Grants C06 RR018823 and No C06
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