Current Neurovascular Research

ISSN: 1567-2026

Current Neurovascular Research
Volume 3, Number 3, August 2006

Contents

Editorial Pp. 169-170
Medicine's “Da Vinci Code”: Deciphering the Intricate Origins of Clinical Neurovascular Pathology
K. Maiese


ORIGINAL ARTICLES


Morphine Stimulates Vascular Endothelial Growth Factor-Like Signaling in Mouse Retinal Endothelial Cells Pp. 171-180
C. Chen, M. Farooqui and K. Gupta
[Abstract]


Aging is Neuroprotective During Global Ischemia but Leads to Increased Caspase-3 and Apoptotic Activity in Hippocampal Neurons Pp. 181-186
Z. He, J.F. Meschia, T.G. Brott, D.W. Dickson and M. Mckinney
[Abstract]


Microglial Integrity is Maintained by Erythropoietin Through Integration of Akt and Its Substrates of Glycogen Synthase Kinase-3β, β-Catenin, and Nuclear Factor-κB Pp. 187-201
F. Li, Z.Z. Chong and K. Maiese
[Abstract]


Delayed Treatment with Nicotinamide Inhibits Brain Energy Depletion, Improves Cerebral Microperfusion, Reduces Brain Infarct Volume, but does not Alter Neurobehavioral Outcome Following Permanent Focal Cerebral Ischemia in Sprague Dawley Rats Pp. 203-213
E-J. Lee, T.-S. Wu, G.-L. Chang, C.-Y. Li, T.-Y. Chen, M.-Y. Lee, H.-Y. Chen and K.I. Maynard
[Abstract]


REVIEW ARTICLES


Implications of Prion Protein Biology Pp. 215-223
V.P. Perez and A.S. Coitinho
[Abstract]


Role of Taurine in Spinal Cord Injury Pp. 225-235
R.C. Gupta, Y. Seki and J. Yosida
[Abstract]


Growth, Vascular Malformations, and Moyamoya Pp. 237-245
M. Lim, S. Cheshier and G.K. Steinberg
[Abstract]




Abstracts

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Editorial
K. Maiese

Medicine's “Da Vinci Code”: Deciphering the Intricate Origins of Clinical Neurovascular Pathology

One of the initial descriptions of dialysis dementia as a fatal and severe complication of chronic hemodialysis appeared in the year 1972 by Albert C. Alfrey. Alfrey described five chronically dialyzed patients who developed intermittent speech abnormalities followed by a distinct encephalopathy. Subsequent reports in the literature followed and emphasized the progressive, frequently fatal neurological manifestations of chronic hemodialysis. The clinical presentation of dialysis dementia is a progressive neurological impairment consisting of dysarthria, mutism, and facial grimacing. Other findings include multifocal myoclonus, seizures, depression, paranoia, psychosis, and dementia. In the early stages, symptoms are usually intermittent and can be worse during dialysis. Over time, the symptoms become more persistent in nature with the most frequent clinical manifestations involving disturbances in speech, cognition, and movement. In most cases, consciousness is retained despite severe personality and mood changes, but the disease can progress to death within six months of onset. Interestingly, the development of encephalopathy represents only a single manifestation of the dialysis syndrome with one of the most debilitating complications also involving hypochromic microcytic anemia.

Although the precise mechanisms that lead to impaired cognition during dialysis dementia are not known, several lines of evidence have linked the detrimental effects of this disorder to a diverse set of pathways that involve elevated levels of aluminum in dialysate water, reactive oxygen species, and the induction of neurodegenerative processes. For example, aluminum decreases the levels of thiols, glutathione reductase, and adenosine triphosphatase, which can lead to oxidative stress. Additional work suggests that aluminum may impair cytochrome c oxidase and contributes to cell injury through the release of free radicals. Senile plaques and neurofibrillary tangles similar to Alzheimer's disease also have been found in the brains of patients with dialysis dementia to suggest a progressive neurodegenerative process. In some of these cases, the plaques are as extensive as in Alzheimer's disease and it is notable that aluminum can be a component of senile plaques and neurofibrillary tangles. Spongiform encephalopathies also have been proposed as an etiologic factor linked to dialysis dementia, since the clinical manifestations of dialysis dementia may resemble those of Kuru or Creutzfeldt-Jakob disease. Taken together, these observations suggest that dialysis dementia may share some of the same cellular mechanisms that can precipitate oxidative stress cell injury and progressive neurodegeneration.

In many respects, the clinical presentation of dialysis dementia is ultimately dependent upon a host of cellular pathways that involve a complex interplay between neuronal and vascular systems. On initial observation, these pathways may take on the appearance of author Dan Brown's mystery novel "The Da Vinci Code" and the progressive thwarted attempts of its character Dr. Robert Langdon to uncover the San gréal and the secret origins of this bloodline. Fortunately with this issue of Current Neurovascular Research, we embark on more concrete footing with both original work and review papers to elucidate the fine interplay between the brain and the body's systems that can precipitate clinical pathology such as occurs in dialysis dementia. In fact, our initial original article by Chen et al. brings to light novel mechanisms that surprisingly link analgesic pathways to new vessel formation and pro-survival signaling pathways. They show that morphine, an agonist of mu opioid receptors, leads to mouse retinal endothelial cell proliferation similar to vascular endothelial growth factor and activates common survival pathways that involve mitogen-activated protein kinase/extracellular signal-regulated kinase, protein kinase B, and signal transducer and activator of transcription signaling. The authors also illustrate an additive effect by morphine and vascular endothelial growth factor on the induction of angiogenesis and suggest that during retinopathy the secretion of endogenous mu opioid receptor agonists, such as β-endorphins, may represent a new therapeutic strategy for angiogenesis-based therapies to treat retinopathy.

Yet, vascular mediated pathways do not appear to reveal all of the "hidden messages" in the picture that can explain ultimate pathology in the nervous system. For example, He et al. show that following ischemic induced neurodegeneration in the rat, young animals had significantly higher number of hippocampal neurons with apoptotic DNA degradation and a reduced number of neurons with caspase 3 immunoreactivity than in aged animals, suggesting that aging in itself may impart a tolerance to acute brain injury and result in an enhanced "living cell ratio". Studies that can further dissect the mechanisms that can impart cell tolerance to injury would be highly desirable. In the original work by Li et al., the role of inflammatory cells during the administration of the trophic factor erythropoietin are also brought to light. Erythropoietin has a high clinical relevance especially for conditions such as dialysis dementia since it is approved by the Food and Drug Administration for the treatment of anemia and it is also under consideration for the treatment of a variety of disorders that include ischemic brain injury, Alzheimer's disease, and chronic congestive heart failure. The authors show that the strong cytoprotective capacity of erythropoietin that has been demonstrated for both neuronal and vascular cell populations is also preserved for microglial cells of the brain that are subjected to oxidative stress injury. This protection by erythropoietin for microglia during oxidative stress not only requires the "pro-survival" and "pro-angiogenic" pathways of protein kinase B that may be relevant during mu opioid receptor activation discussed previously, but also the complementary regulation of glycogen synthase kinase-3β and the intra-cellular trafficking of nuclear factor-κB. The work brings new insight into the strong cytoprotective capacity of erythropoietin and highlights the close relationship among neurons, vascular cells, and microglia that may be required to foster a significant level of protection against neurodegenerative disorders.

Our review papers in this issue of Current Neurovascular Research further expand upon the vital role of trophic and other factors in the nervous system that impact upon vascular cell integrity and survival. Lim et al. describe the ability of vascular endothelial growth factor, fibroblast growth factor, angiopoietins, platelet derived growth factor, and integrins to influence a wide range of disorders that can involve tumor cell growth, arteriovenous malformations, and Moyamoya disease. Interestingly, Gupta et al. bring potential treatment for traumatic nervous system injury in the spinal cord to the level of amino acids with the discussion of taurine, a sulfur amino acid endogenously present in humans. The authors outline the potential role of taurine to function as a cellular protectant during spinal cord injury and its control of reactive oxygen species and cytokine release. Yet, our article by Perez and Coitinho appear to fittingly integrate several disorders in the nervous system with their fascinating description of prion protein biology. Cellular prion protein is anchored by a glycosyl-phosphatidylinositol residue on many cells and functions during several physiological processes that involve oxidative stress protection, cell adhesion, stress inducible protein generation, memory, and immune system maintenance. However, the authors also provide a dark side of prion protein biology that discusses the role of prion protein isoforms and the generation of spongiform encephalopathies that include Creuzfeldt-Jakob disease, Gerstmann-Straussler-Scheinker syndrome, and fatal familial insomnia.

Brown's novel "The Da Vinci Code" compels the reader to closely follow a plot that interweaves a murder with a conspiracy theory. These elements usually do not form the most essential components for basic and clinical investigative studies, but the work presented in this issue of Current Neurovascular Research compels one to understand the multiplicity of cellular pathways that can influence both disease regression as well as functional recovery. Furthermore, similar to a detective thriller, scientific investigation fosters excitement with its own plot of surprises to reveal pathways that may appear to function independently, but actually compliment one another during both cell function and cell injury. Such lessons serve to keep us on the edge of our seats as we seek to develop new avenues of therapy for disorders affecting both neuronal and vascular origins.

Kenneth Maiese
Editor-in-Chief


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Morphine Stimulates Vascular Endothelial Growth Factor-Like Signaling in Mouse Retinal Endothelial Cells
C. Chen, M. Farooqui and K. Gupta

Go/Gi coupled G-protein receptor mediated transactivation is critical in the activation of receptor tyrosine kinases (RTK). Here we show that mu opioid receptor (MOR) transactivates Flk1 and platelet-derived growth factor-β (PDGF-β) receptors and its agonist morphine stimulates pro-angiogenic and survival-promoting signaling in mouse retinal endothelial cells (mREC). Morphine stimulates mREC proliferation in a dose dependent fashion and promotes survival to the same extent as vascular endothelial growth factor₁₆₄ (VEGF₁₆₄). Morphine stimulates mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) and Akt phosphorylation in a time dependent manner like VEGF in mREC. Moreover, analogous to VEGF, morphine stimulates oncogenic signal transducer and activator of transcription 3 (STAT3) signaling. Morphine as well as VEGF-induced phospho-STAT3 and phospho-Flk1 immunoprecipitated with MOR-associated proteins. In addition morphine also stimulated MOR associated PDGF-β receptor phosphorylation. Consistent with the relationship between VEGF and MOR we found that VEGF upregulates MOR protein and RNA expression in mREC. These data suggest that MOR associates and transactivates RTKs for Flk1 and PDGF-β , which may have a compounding effect on angiogenic signaling in endothelium. Therefore, G-Protein coupled receptors including MOR provide novel targets to develop anti-angiogenic agents.


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Aging is Neuroprotective During Global Ischemia but Leads to Increased Caspase-3 and Apoptotic Activity in Hippocampal Neurons
Z. He, J.F. Meschia, T.G. Brott, D.W. Dickson and M. Mckinney

Previously, we found a significantly greater number of surviving CA1 neurons to global ischemia in the aged (24-month-old) F344 rats than in young (4-month-old) rats. The present study tests the hypothesis that aging retards neuronal death in the hippocampal CA1 region following cerebral ischemia. The CA1 “living cell ratio” was significantly greater in aged than in young rats at three days (62±8% vs. 30±8%) and at eight days (36±6% vs. 17±5%), but not at 14 days (15±12% vs. 18±12%) following ischemia. The number of the CA1 cells exhibiting co-localized TdT-mediated X-dUTP nick end labeling reaction and caspase-3 active peptide (C3AP) immunoreactivity was greater in aged than young animals at three and eight days following ischemia (36±8/mm vs. 3±1/mm and 36±14 vs. 0±0, p<0.05 respectively). Also, the total number of C3AP-positive cells in the CA1 region in the aged group was significantly greater than in the young group at three and eight days post-ischemia (p<0.05). Aging appears to delay caspase-3-dependent apoptotic cell death induced by global ischemia in the CA1 region of the hippocampus, consistent with an age-induced neuroprotective process.


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Microglial Integrity is Maintained by Erythropoietin Through Integration of Akt and Its Substrates of Glycogen Synthase Kinase-3β, β-Catenin, and Nuclear Factor-κB
F. Li, Z.Z. Chong and K. Maiese

Recognized as a robust cytoprotectant for multiple tissues of the hematopoietic, vascular, cardiac, and nervous systems, erythropoietin (EPO) also is considered to be an attractive therapeutic candidate to modulate inflammatory cell function and survival during neurodegenerative disorders. To this end, microglia of the central nervous system serve a complex function not only to dispense of foreign organisms and injured cells of the brain, but also to foster tissue repair and reorganization during neuronal and vascular cell insults. We therefore examined the ability of EPO to modulate microglial cell survival and the underlying signal transduction pathways that govern microglial integrity during oxygen-glucose deprivation (OGD) - induced oxidative stress. We demonstrate in the microglial cell line EOC 2 that EPO provides direct microglial protection against early and late apoptotic programs of membrane phosphatidylserine exposure and genomic DNA degradation. Furthermore, expression and activation of Akt1 is vital to the cytoprotective capacity of EPO, since pharmacological inhibition of the PI 3-K pathway or gene silencing of Akt1 expression eliminates the ability of EPO to protect microglial cells. Through Akt1 dependent mechanisms that can be abrogated through the gene silencing of Akt1, maintenance of microglial cell integrity during OGD by EPO is closely integrated with the phosphorylation and inhibition of glycogen synthase kinase-3β activity as well as the intracellular trafficking of β -catenin and nuclear factor-κB. Further work that continues to elucidate the ability of EPO to target the intricate pathways that determine inflammatory cell function and integrity may lay the ground work for new therapeutic avenues for neurodegenerative disease.


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Delayed Treatment with Nicotinamide Inhibits Brain Energy Depletion, Improves Cerebral Microperfusion, Reduces Brain Infarct Volume, but does not Alter Neurobehavioral Outcome Following Permanent Focal Cerebral Ischemia in Sprague Dawley Rats
E-J. Lee, T.-S. Wu, G.-L. Chang, C.-Y. Li, T.-Y. Chen, M.-Y. Lee, H.-Y. Chen and K.I. Maynard

Delayed treatment with nicotinamide (NAm) reduces infarction induced by middle cerebral artery occlusion (MCAO) in rats. This study explored some potential mechanisms by which delayed NAm treatment may confer protection in the brain of Sprague-Dawley rats following permanent MCAO (pMCAO). NAm (500 mg/kg) or vehicle was given 2 h after the onset of pMCAO. Cortical microperfusion, brain and rectal temperature were serially measured. Neurobehavioral examinations were performed at 24 h post-ischemia followed by sacrifice for histologic assessment. Some rats were also sacrificed at 4 h post-ischemia for analyses of ATP, ADP, AMP, and adenosine. Permanent MCAO induced spontaneous hyperthermia and a sharp decrease in cortical microperfusion, ATP concentration, and the sum of adenine nucleotides (p < 0.05). At 4 h post-ischemia, NAm improved ATP recovery, the sum of adenine nucleotides (p < 0.05) and attenuated the ischemia-induced systemic hyperthermia (p < 0.05) without affecting brain temperature or cortical microperfusion. At 24 h, NAm improved cortical microperfusion in the ischemic hemisphere and reduced total infarct volume (p < 0.05), but did not affect behavioral scores. The data suggest that NAm attenuated brain damage following pMCAo initially by improving cerebral bioenergetic metabolism during the sub-acute phase of ischemia, followed by a delayed improvement in microvascular perfusion.


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Implications of Prion Protein Biology
V.P. Perez and A.S. Coitinho

The cellular prion protein (PrP^c) is a protein found on the cell surface of many cell subtypes, especially neurons, anchored by a glycosyl-phosphatidylinositol residue. The physiological role of PrP^c is still not understood. However, it is known that participates in copper uptake, protection against oxidative stress, cell adhesion, differentiation, signalling and cell survival. Moreover, it is also involved in memory formation. Despite the numerous functions given to PrP^c, its discovery did not occur due to its altered isoform involvement (PrP^sc) as an infectious agent of spongiform encephalopathies These diseases are unique because they can be hereditary, sporadic or have an acquired etiology. Much has been done concerning this intriguing protein, but there is still the need for more studies to truly understand PrP^c functions and PrP^sc pathogenesis mechanisms. In this way, new and more effective therapeutichal approaches can be developed, and more information on other amyloid diseases can be gathered.


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Role of Taurine in Spinal Cord Injury
R.C. Gupta, Y. Seki and J. Yosida

Taurine is a sulfur amino acid. It is found endogenously in human and several others tissues. It is significantly in high concentration in mammals. Human body contains about 0.1% of body weight as taurine. It has a number of physiological and pharmacological actions. It is also used in the therapy of important organs dysfunctions. In spinal cord it has inhibitory effects; like antiepileptic and anti-nociceptive. Taurine also inhibits substance p induced biting and scratching behavior. In spinal cord injury elevated level of taurine has been observed. Higher level of taurine has been also recorded in SCI therapy using, known clinical agent methyl prednisolone (MP). The increased taurine concentration seems to be involved in protection and regeneration of tissues following injury. In SCI along with physical injury secondary activities also takes place which are complex in nature. Secondary activity includes vascular events and activation of neutrophils, resulting endothelial damage. Activated neutrophils; release a variety of inflammatory mediators such as myeloperoxidase (MPO), reactive oxygen species (ROS), and some others. It is believed that taurine exert its protective action through scavenging of ROS and down regulating several other inflammatory mediators like tumor necrosis factors (TNFα). The inside of mechanism reveals toxic substance HOCl is produced by MPO is converted to less toxic substances through scavenging action of taurine. Amino acid therapy has its own limitations and to over come such situation there is a need to develop small, simple lipophelic analogs of taurine. Use of taurine analogs has provided better results; for example, N- chloro taurine (NCT) which is a taurine derivative has exhibited therapeutic advances over taurine. Taurine and its analogs with sound experimental and clinical support may constitute a new class of therapeutic agents for SCI., and perhaps this review may provide enough material to think of this.


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Growth, Vascular Malformations, and Moyamoya
M. Lim, S. Cheshier and G.K. Steinberg

In the normal adult brain, blood vessel formation is tightly down-regulated. However, pathologic processes such as brain tumors can increase the proportion of endothelial cells involved in angiogenesis. When this process is initiated, a complex series of timed events result in new vessel formation. In this review, we will describe the process of angiogenesis in the central nervous system. We will discuss the roles of Vascular Endothelial Growth Factor (VEGF), Fibroblast Growth Factor (FGF), Angiopoietins, Platelet Derived Growth Factor (PDGF), and integrins in angiogenesis. We will also look into their significance in disease processes such as neoplasms, arteriovenous malformations (AVM), and Moyamoya disease.