| Current
Neurovascular Research
ISSN: 1567-2026
Current Neurovascular Research
Volume 3, Number 1, February 2006
Contents
A Path to Development or Demise? Pp. 1-2
K. Maiese
[Abstract]
ORIGINAL ARTICLE
Accelerated Delimitation of the Infarct Zone by Capillary-Derived
Nestin-Positive Cells in Aged Rats Pp. 3-13
A. Popa-Wagner, I. Dinca, S. Yalikun, L. Walker,
H. Kroemer and C. Kessler
[Abstract]
Cerebral Angiogenesis and Expression of
Angiogenic Factors in Aging Rats after Exercise Pp.
15-23
Y.-H. Ding, J. Li, Y. Zhou, J.A. Rafols, J.C.
Clark and Y. Ding
[Abstract]
Attempted Cell Cycle Induction in Post-Mitotic Neurons
Occurs in Early and Late Apoptotic Programs Through Rb, E2F1,
and Caspase 3 Pp. 25-39
Z.Z. Chong, F. Li and K. Maiese
[Abstract]
Lovastatin Reduces Apoptosis and Downregulates the
CD40 Expression Induced by TNF-α
in Cerebral Vascular Endothelial Cells Pp.
41-47
R. Lin, J. Liu, N. Peng, W. Gan, W. Wang, C. Han and C. Ding
[Abstract]
High Glucose-Mediated Imbalance of Nitric Oxide Synthase
and Dimethylarginine Dimethylamino-hydrolase Expression in
Endothelial Cells Pp. 49-54
V. Sorrenti, F. Mazza, A. Campisi, L. Vanella, G.L. Volti
and C. Di Giacomo
[Abstract]
Structure and Function of Myelinated Nerve Fibers
in the Rabbit Eye Following Ischemia/Reperfusion Injury Pp.
55-65
W. Guo, S.J. Cringle, E.-N. Su, P.K. Yu, X.-B.
Yu, X. Sun, W. Morgan and D.-Y. Yu
[Abstract]
REVIEW ARTICLES
Stroke-Induced Neurogenesis: Physiopathology and Mechanisms
Pp. 67-72
P. Taupin
[Abstract]
Role of Advanced Glycation End Products (AGEs) in
Thrombogenic Abnormalities in Diabetes Pp. 73-77
K. Takenaka, S.-i. Yamagishi, T. Matsui, K.
Nakamura and T. Imaizumi
[Abstract]
Abstracts
[Back to top]
A Path to Development or Demise ?
Early reports in the lay literature describe individuals
that suffer severe brain injury, but later are able to resume
either previously lost cognitive function or motor function
of paralyzed limbs. For example, in The Count of Monte-Cristo,
the character Monsieur Noirtier de Villefort was reported
to have suffered an incomplete injury to the brain, but subsequently
was able to communicate by blinking with vertical eye movements.
Reports of partial recovery from incomplete lesions to the
brain later began to surface in the medical literature. In
1947, the first published case described a patient with an
infarction in the territory of the vertebral-basilar artery
system who became tetraplegic, was without speech, but regained
consciousness. Reports such as this are consistent with a
"de-efferented" lesion occurring in the brainstem,
usually at the level of the pons that allows cortical function
to remain unimpaired, but leads to quadriplegia. In the purest
sense, individuals with these presentations are considered
to suffer from a "locked-in" syndrome. Yet, other
reports that include the present literature describe patients
with a variety of nervous system disabilities that may be
exclusive of the brainstem, but these patients achieve partial
or full recovery from their brain insults raising the question
whether the brain is able to repair itself.
As a result, it becomes essential to understand the underlying
pathology that may determine an individual patient's prognosis.
The etiology of the initial insult will more often than not
determine the overall prognosis of the patient. For example,
transient ischemic insults in the vertebral-basilar artery
distribution have been reported to lead to a complete resolution
of all deficits within twenty-four hours after the initial
onset of vascular occlusion. In contrast, aggressive disease
processes, such as malignant neoplasms that involve the posterior
fossa and the pons, ultimately may lead to the demise of the
patient.
Yet, evaluation of a patient's ability to recover from a
nervous system injury should also be considered at the cellular
level. If one examines cells that are able to regenerate and
proliferate, they must be able to enter and execute a normal
cell cycle. However, as we acquire further knowledge of each
cell's ability to enter the cell cycle during different times
in its development or maturation, it becomes evident that
not all cells, at least in the final stages of development,
should attempt cellular pathways leading to cell cycle induction.
Aberrant cell cycle induction, such as with post-mitotic neurons,
can ultimately lead to the death of the cell. In this issue
of Current Neurovascular Research, we present several
investigations that provide insight into common cellular pathways
that can serve to foster opposing outcomes in a cell during
either normal physiological processes or during acute toxic
insults. In particular, some of the studies address the necessary
role of new cell growth and cell cycle induction for tissue
repair while other studies provide an alternative perspective
on cell cycle induction describing cellular pathways that
utilize a "dysfunctional" cell cycle to lead to
apoptotic cell destruction.
In their original article, Popa-Wagner et al. employed
experimental focal cerebral ischemia models in both young
and aged rats and assessed cell cycle induction, cell growth,
and proliferation in the brains of these animals. They report
that aged rats have nestin-positive cells in the region of
the brain infarct as well as an early incorporation of nestin-positive
cells into the glial scar region. Moreover, the capillaries
of the corpus callosum were the principal source of proliferating
nestin-positive cells, but surprisingly, these cells did not
significantly contribute to new neuronal cell formation in
the infracted cortex of the aged rats. They hypothesize that
blocked migration of these cells may produce the limited neurogenesis
response, but postulate that further understanding of the
active capillary proliferation response in these aged animals
may be applicable to neurodegenerative diseases in the elderly.
Interestingly in our next article, Ding et al. note
a significant vascular response also in aged rats with new
cell proliferation in the brain, but with a novel twist. Angiogenesis
in the cerebral cortex was documented during a monitored exercise
protocol with a significant upregulation of vascular endothelial
growth factor protein, providing evidence that vascular cell
proliferation in the elderly brain may not only be necessary
for tissue repair during acute insults, but also for daily
physiological function of the nervous system.
Chong et al. offer a different perspective on the
potential role of attempted cell cycle induction in post-mitotic
neurons, cells which are under most circumstances believed
to lack the cellular machinery to fully execute a cell cycle
program. They show that attempted cell cycle induction in
neurons during oxidative stress with nitric oxide leads to
an early phase of apoptotic injury closely tied to cellular
inflammation and is regulated by specific cellular pathways
that involve the retinoblastoma protein, the transcription
factor E2F1, and caspase 3. Interestingly, these studies not
only highlight critical pathways that control aberrant cell
cycle induction during committed steps of apoptosis with nuclear
DNA degradation, but also point to a broader scenario that
impacts upon cellular inflammation and activation of phagocytic
cells with the modulation of early apoptotic pathways involving
phosphatidylserine externalization and calreticulin expression.
Our following series of original articles provide additional
insight into several of the cellular pathways that may control
apoptotic injury in vascular cells, during elevated glucose,
and during ischemic insults to myelinated nerve fibers. Lin
et al. show that the CD40-CD40L signaling pathway
in vascular cells can have a pro-inflammatory effect, but
surprisingly the administration of the cholesterol lowering
agent lovastatin may block the detrimental effects of the
CD40-CD40L system through mechanisms that involve tumor necrosis
factor and the free radical nitric oxide. These observations
provide an interesting format for the work by Sorrenti et
al., which shows that high glucose-induced oxidative
stress, such as during diabetes, may also be the result of
the nitric oxide pathway with dysregulation of the inducible
and endothelial nitric oxide synthase isoforms. Guo et
al. extend these cellular injury models by focusing on
ocular myelinated nerve fibers during ischemia/reperfusion.
Interestingly, they illustrate that although electroretinography
following such an injury may not reveal any loss of retinal
function, other parameters that involve cellular examination
and visual evoked responses can detect suppression in nerve
fiber transmission that is eventually accompanied by demyelination
and a strong cellular inflammatory response.
Our two review articles serve as "bookends" for
this issue of Current Neurovascular Research to provide
a broader overview of the cellular pathways described in several
of the original articles by focusing on cell development,
cell proliferation, and cell death. In the article by Taupin,
the brain's ability to form new neuronal precursors and neurons
following stroke are discussed. The article provides an interesting
perspective concerning the nervous system's reparative capacity
following acute injury and describes many of the intricate
pathways involved with induction of neurogenesis in the hippocampus
and the subventricular zone. At the opposite end of the spectrum,
Takenaka et al. focuses upon the processes responsible for
diabetic oxidative stress in relation to the formation and
accumulation of advanced glycation end products and how these
agents may yield a "hyperglycemic memory" to mediate
thrombogenic abnormalities in diabetes.
Despite our advances in neuroscience, we continue to be humbled
by new investigations that point to the enormous complexity
of the nervous system and its capacity to use common cellular
pathways, such as those that mediate the cell cycle, to achieve
conceivably opposite outcomes dependent upon a variety of
variables. With this present issue of Current Neurovascular
Research, we are taking new steps forward to understand
these variables of the cellular machinery that can lead to
either "development or demise" and widely alter
the function of a cell as well as the clinical outcome of
a patient. Possibly, someday we may even attain the capacity
to accurately grasp the nervous system disability and recovery
of individuals portrayed by characters such as Monsieur Noirtier
de Villefort.
Kenneth Maiese
Editor-in-Chief
[Back to top]
Accelerated Delimitation of the Infarct Zone by Capillary-Derived
Nestin-Positive Cells in Aged Rats
A. Popa-Wagner, I. Dinca, S. Yalikun, L. Walker,
H. Kroemer and C. Kessler
An important cellular event associated with reduced structural
and functional recovery after stroke in aged animals is the
early formation of a scar in the infarcted region that impairs
neural recovery and repair. Despite the detrimental impact
of infarct scar formation, the brain regions and cell types
that supply the components of the scar are not well characterized.
We hypothesized that premature cerebral scar formation in
aged animals is associated with an altered cellular response
to cerebral ischemia. Focal cerebral ischemia was produced
by reversible occlusion of the right middle cerebral artery
in 3 month- and 20 month-old male Sprague Dawley
rats. After 3, 7, 14, and 28 days, brain tissue was subjected
to real-time reverse-transcriptase-PCR (RT-PCR) and immunostaining
for 1) a cellular proliferation marker (BrdU); 2) a neuroepithelial
marker (nestin); 3) an astrocytic marker (glial fibrillary
acidic protein [GFAP]); 4) a neuronal marker, doublecortin;
and 5) a basal lamina marker (laminin), and analyzed using
3D-reconstruction of confocal images. In this model the infarct
was localized primarily in the parietal cortex. By RT-PCR
there was a robust increase in nestin mRNA transcripts shortly
after stroke, and this increase was particularly intense in
aged rats. Accord-antly, we found in aged rats a rapid delimitation
of the infarct area by nestin-positive cells and an early
incorporation of these cells into the glial scar. The capillaries
of the corpus callosum were the major source of proliferating,
nestin-positive cells, many of which were also immunoreactive
for doublecortin, although a smaller population of nestin
cells were associated with the ventricular walls. Despite
the proliferation of nestin cells, they did not make a significant
contribution to neurogenesis in the infarcted cortex, possibly
because the corpus callosum impedes the migration of subven-tricular
zone-derived nestin-positive cells into the lesioned area.
We conclude that: (i) the aged brain has the capability to
mount a cytoproliferative response to injury, but the timing
of the cellular and genetic reaction to cerebral insult is
accelerated in aged animals; (ii) the proliferating cells
contribute to the formation of the glial scar, but few of
the cells ap-pear to become neurons; and (iii) the vasculature
plays a hitherto unrecognized role as a source of proliferating
cells after stroke. Because capillary-derived cells help to
form the glial scar, elucidating the molecular basis of this
phenome-non and its acceleration in the aging brain could
yield novel approaches to enhancing neurorestoration in the
elderly.
[Back to top]
Cerebral Angiogenesis and Expression of Angiogenic
Factors in Aging Rats after Exercise
Y.-H. Ding, J. Li, Y. Zhou, J.A. Rafols, J.C.
Clark and Y. Ding
The effect that exercise has on angiogenesis in the aging
rat is unknown. We initiated this study with the intent to
determine if exercise could induce angiogenesis in aging rats,
as well as in adult rats reported previously. The markers
we used to determine our endpoint were vascular endothelial
growth factor (VEGF) and angiopoietin 1 and 2, as well as
vascular density. Aged (22 month old) female Fisher 344 rats
(n=16) were exercised on a treadmill 30 minutes each day for
3 weeks, or housed as non-exercised controls for the same
duration. At the end of the exercise protocol, a significant
(p<0.01) increase in the density of microvessels was found
within the cerebral vasculature of the rats. Exercise was
also associated with a significantly (p<0.01) increased
mRNA expression of angiopoietin 1 and 2 in the aged cohort
of rats. A mild but significant (p<0.01) increase in the
four isoforms of VEGF mRNA (120, 144, 164, 188) were observed,
with VEGF120 and VEGF144 being more
markedly up-regulated than the other two. VEGF protein expression
was also significantly (p<0.01) increased. This study demonstrates
that angiogenesis can be induced in aging rats via
exercise. The induced angiogenesis was associated with overexpression
of angiogenic factors. These results support the hypothesis
that an angiogenic response to chronic physical exercise is
maintained with aging.
[Back to top]
Attempted Cell Cycle Induction in Post-Mitotic Neurons
Occurs in Early and Late Apoptotic Programs Through Rb, E2F1,
and Caspase 3
Z.Z. Chong, F. Li and K. Maiese
Either the absence or dysfunction of a number of critical
pathways, such as those that involve the nuclear retinoblastoma
protein (Rb) and the transcription factor E2F1, may account
for the aberrant induction of the cell cycle in post-mitotic
neurons that can be responsible for oxidative stress-induced
apoptotic cellular destruction. Yet, it is unclear whether
early programs of apoptotic injury that involve membrane phosphatidylserine
(PS) exposure and calreticulin expression as well as later
phases of apoptotic injury with nuclear DNA injury require
the critical modulation of Rb and E2F1. We demonstrate that
both the post-translational of phosphorylation of Rb to prevent
E2F1 transcription as well as the protein integrity of Rb
are closely aligned with the modulation of cell cycle induction
in post mitotic neurons during oxidative stress. More importantly,
we illustrate that both the initial onset of apoptosis with
either membrane PS expo-sure or calreticulin analysis as well
as the more terminal phases of apoptosis that involve nuclear
DNA degradation pro-ceed concurrently in the same neuronal
cells with cell cycle induction. Progression of attempted
cell cycle induction is closely associated with the phosphorylation
of Rb, its inability to bind to E2F1, and the degradation
of the Rb protein. Inhibition of Rb phosphorylation using
cyclin dependent kinase inhibitors maintains the integrity
of the E2F1/Rb complex and is neuroprotective during free
radical exposure. Furthermore, maintenance of the integrity
of the Rb protein is specifically dependent upon caspase 3-like
activity, since caspase 3 can cleave Rb during free radical
activity and this degradation of Rb can be blocked during
the inhibition of caspase 3 activity. Our studies not only
highlight the critical role of attempted cell cycle induction
during oxidative stress-induced neuronal apoptotic injury,
but also bring to light the significant impact of the Rb and
E2F1 pathways upon early apoptotic programs that can directly
influence both intrinsic cell survival as well as extrinsic
inflammatory cell activation.
[Back to top]
Lovastatin Reduces Apoptosis and Downregulates the
CD40 Expression Induced by TNF-α
in Cerebral Vascular Endothelial Cells
R. Lin, J. Liu, N. Peng, W. Gan, W. Wang, C. Han and C. Ding
Inflammation may be one of the independent risk factors
contributing to many neurological diseases. Moreover, there
is an emerging body of data indicating that statins may have
neuroprotective action. Recent studies suggest that CD40-CD40
ligand (CD40L) system is proven to be an important mediator
of several auto-immune and chronic inflammation diseases.
To address whether lovastatin produces neuroprotection as
a potential novel anti-inflammatory pathway through the inhibition
of CD40 expression, we examined the possible effects of lovastatin
on expression of CD40, apoptosis, level of nitric oxide (NO)
and nitric oxide synthase (NOS) activity induced by tumor
necrosis factor α
(TNF-α)
in the cerebral vascular endothelial cells (CVECs) involved
in cerebrovascular diseases. Preincubation with lovastatin
(10-7, 10-6 and 10-5 mol/l)
for 24 hours (h) protected CVECs from TNF-α-induced
decrease of cellular viability. Further, lovastatin inhibited
the TNF-α-induced
increases of NO level, NOS activity, apoptotic cells and CD40
expression in a dose-dependent manner, and anti-CD40 antibody
also inhibited the cellular apoptosis induced by TNF-α.
In conclusion, our data provide evidence to support a direct
pro-inflammatory effect of CD40-CD40L signaling pathway in
CVECs, and lovastatin possesses an anti-inflammatory effect
independent of its lipid-lowering action involved in the cerebrovascular
diseases.
[Back to top]
High Glucose-Mediated Imbalance of Nitric Oxide Synthase
and Dimethylarginine Dimethylamino-hydrolase Expression in
Endothelial Cells
V. Sorrenti, F. Mazza, A. Campisi, L. Vanella, G.L. Volti
and C. Di Giacomo
The mechanisms involved in endothelial dysfunction are multifactorial.
A correlation between oxidative stress and derangements of
nitric oxide synthase (NOS) pathways in altered endothelial
homeostasis has been most studied and demonstrated in different
pathophysiological conditions. NOS activities are regulated
by endogenous inhibitors such as asymmetric dimethyl-L-arginine
(ADMA) that is metabolized by dimethylarginine dimethylaminohydrolase
(DDAH). Since recent data demonstrated that some endothelial
dysfunction may be related to reduced expression and/or activity
of DDAH, the aim of the present research was to investigate
the expression of DDAH-2 and NOS isoforms in high glucose-mediated
oxidative stress. Endothelial cells were incubated with normal
(7 mM) and high concentrations (33 mM) of D-glucose for 5
days; mannose (26 mM) plus D-glucose (7 mM) was used as osmotic
control. Data obtained in the present study show that the
exposure for 5 days to high glucose increases oxidative stress,
reduces DDAH-2 and eNOS expression and increases iNOS expression.
These results indicate that DDAH-2 and iNOS/eNOS dysregulation
may play a key role in high glucose-mediated oxidative stress,
suggesting that selective modulation of DDAH isoforms may
result in selective inhibition/activation of NOS isoforms,
thereby providing a novel strategy of approach in vascular
complications of several pathologies.
[Back to top]
Structure and Function of Myelinated Nerve Fibers
in the Rabbit Eye Following Ischemia/Reperfusion Injury
W. Guo, S.J. Cringle, E.-N. Su, P.K. Yu, X.-B.
Yu, X. Sun, W. Morgan and D.-Y. Yu
The rabbit eye presents a valuable model to study the effects
of vascular occlusion on the function and structure of myelinated
nerve fibers. The rabbit eye has a band of myelinated nerve
fibers within the intraocular compartment that are supplied
by a narrow band of retinal vasculature. These vessels were
transiently occluded (~8 hours) using laser photocoagulation
and the transmission of electrical signals along the nerve
fibers was assessed by recording the visual evoked response
(VER). Morphological damage was assessed by histological techniques.
The ischemic insult produced no permanent change in retinal
function as assessed by electroretinography, but the VER was
suppressed, indicating failure of nerve fiber transmission.
Histologically, the visible damage to the region supported
by the retinal vasculature worsened following reperfusion,
showing evidence of demyelination and necrosis followed by
macrophage responses and gliosis. This rabbit model of ischemia/reperfusion
of the retinal vasculature offers a rare opportunity to reliably
study the response of myelinated nerve fibers to ischemia/reperfusion
insults and has demonstrated the susceptibility of myelinated
nerve fibers to such insults.
[Back to top]
Stroke-Induced Neurogenesis: Physiopathology and Mechanisms
P. Taupin
Long-term disabilities are the main outcome of cerebral
strokes, though some of the deficits show receding signs in
the weeks and months following the “brain attack”.
Studies show that neurogenesis is induced in the hippocampus
and subventricular zone (SVZ) in animal models of ischemia,
and that new neurons are generated at the sites of de-generation,
where they replace some of the lost nerve cells. The enhanced
neurogenesis suggests the involvement of the hippocampus and
SVZ in the physiopathology of cerebral strokes, and the generation
of new neuronal cells at the sites of degeneration suggests
that the central nervous system (CNS) may attempt to repair
itself. In this manuscript, we will review the studies on
adult neurogenesis in cerebral strokes, discuss the contribution
of adult neurogenesis to the physiopathology of strokes, and
its underlying mechanisms.
[Back to top]
Role of Advanced Glycation End Products (AGEs) in
Thrombogenic Abnormalities in Diabetes
K. Takenaka, S.-i. Yamagishi, T. Matsui, K.
Nakamura and T. Imaizumi
Accelerated atherosclerosis and microvascular complications
are perhaps the leading cause of coronary heart disease, blindness
and renal failure, which could account for disabilities and
high mortality rates in patients with diabetes. Several thrombogenic
abnormalities have been shown to play a central role in the
pathogenesis of these devastating complications. However,
the molecular mechanism for thrombogenic diathesis in diabetes
is not fully elucidated. A recent clinical study, the Diabetes
Control and Complications Trial-Epidemiology of Diabetes Interventions
and Complications (DCCT-EDIC) Research, has revealed that
the reduction in the risk of progressive retinopathy and nephropathy
resulting from intensive therapy in patients with type 1 diabetes
persist for at least several years, despite increasing hyperglycemia.
Further, intensive therapy during the DCCT resulted in decreased
progression of carotid intima-media thick-ness six years after
the end of the trial as well. These clinical studies strongly
suggest that so-called ‘hyperglycemic memory’
causes chronic abnormalities in diabetic vessels that are
not easily reversed, even by subsequent, relatively good control
of blood glucose. Among various biochemical pathways activated
under diabetes, the process of formation and accumulation
of advanced glycation end products (AGEs) and their mode of
action are most compatible with the theory ‘hyperglycemic
memory’. In this review, we discuss the role of AGEs
in thrombogenic abnormalities in diabetes.
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