Biology Reference
In-Depth Information
120
110
100
90
80
70
60
50
40
30
20
10
0
Thr 1U/ml
Fsk (0.1
m
M)
Fig. 4 Effects of PDE inhibitors on forskolin-inhibited thrombin-induced permeability. HUVEC
were stimulated with vehicle, 1 U/ml thrombin (Thr), 1 U/ml thrombin and 0.1
m
M forskolin (Fsk),
or thrombin, forskolin, and PDE inhibitors. Bay 60-7550 (PDE2) was used at 100 nM. Trequinsin
(PDE3) was used at 30 nM. Rolipram (PDE4) was used at 10
m
M. Sildenafil (PDE5) was
used at 100 nM. IBMX (nonspecific) was used at 100
m
M. All inhibitors were added 15 min
prior to thrombin + forskolin stimulation. Permeability was analyzed as described previously
(Surapisitchat et al.
2007
). Data represent means (mean
SEM) from three independent experi-
ments using HUVEC isolated from three different umbilical cords
combinations of PDEs, cyclases, effector molecules, and pools are possible. Until
more sensitive techniques with increased resolution become available, an accurate
description of cyclic nucleotide signaling pools in time and space will have to wait.
The findings that the inflammatory cytokine, TNF-
a
, can increase PDE2 and
decrease PDE3A expression demonstrates that endothelial cells can be altered by
various stimuli to respond to cGMP signaling under different conditions. The
alteration in PDE expression in response to various stimuli is a common mechanism
that many cells and tissues use to alter cyclic nucleotide signaling. For example,
nitroglycerine (NTG) is used in the treatment of hypertension for its vasorelaxing
effects, but its therapeutic use is limited due to the development of nitrate tolerance.
In rats treated with NTG, PDE1A expression and activity is upregulated (Kim et al.
2001
). Inhibition of PDE1A leads to partial restoration of smooth muscle respon-
siveness to nitrates. PDE1C is found to be upregulated in proliferating smooth
muscle, suggesting a potential target in the treatment of atherosclerosis or restenosis
after angioplasty (Rybalkin et al.
1997
). PDE7 upregulation is required for T-cell
activation by CD3 and CD28 (Li et al.
1999
). Other examples of PDE upregulation
include the upregulation of PDE1B in monocyte to macrophage differentiation and
PDE5 in vascular smooth muscle in response to angiotensin II stimulation (Bender
et al.
2005
; Kim et al.
2005
). Few examples of downregulation of PDEs have been
reported to our knowledge. PDE3A expression and activity has been found to be
decreased in patients with heart failure (Ding et al.
2005
). In 3T3-L1 adipocytes,
TNF-
a
decreased PDE3B expression, implicating a mechanism by which TNF-
a
regulates lipolysis (Rahn Landstrom et al.
2000
). The findings that TNF-
a
can also
decrease PDE3A in addition to increasing PDE2 to alter endothelial response to
