基因修饰骨髓源性神经元样干细胞治疗帕金森大鼠的研究

目的 观察大鼠酪氨酸羟化酶(tyrosinehydroxylase,TH)修饰的骨髓基质源性神经元样干细胞(neuronoid stem cells derived from bone marrow stem cells,NdSCs-D-BMSCs)在脑室移植途径下对帕金森病(Parkinson disease,PD)大鼠的治疗作用.方法 将酶切鉴定后的新构建质粒pEGFP-C2-TH经电穿孔法转染培养第8天NdSCs-D-BMSCs,注射到PD大鼠模型右侧脑室,观察大鼠行为学变化,移植细胞在大鼠脑组织内的迁移,以及高效液相方法检测脑内DA含量.结果 质粒pEGFP-C2-TH转染NdSCs-D-BMSCs移植后10周,PD大鼠症状显著改善,DA恢复至正常水平33.0%,移植细胞可以在PD大鼠脑内存活,并出现远处迁移.结论 TH修饰的大鼠NdSCs-D-BMSCs经脑室移植对PD大鼠具有明显的治疗作用,为临床中腰椎穿刺干细胞移植的应用提供实验依据.     

Cocaine differentially alters behavior and neurochemistry in periadolescent versus adult rats

The expansion and differentiation of neural progenitor cells in vitro provides an approach to study the development and differentiation of neurons. The ventral mesencephalic area of the brain is an important source of neural progenitor cells and the differentiated neural progenitor cell has paramount potential for use in transplant therapies such as those used in the treatment of neurodegenerative diseases. Here, the controlled conversion of human foetal progenitor cells derived from ventral mesencephalon into dopaminergic neurons is reported. The immunoreactivity to tyrosine hydroxylase (TH) and levels of dopamine (DA) and its metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC), secreted into culture medium, were used to assess dopaminergic neuronal phenotype. Expansion of the neural progenitor cells for 3 weeks in the presence of basic fibroblast growth factor (2 ng/ml) followed by its withdrawal resulted in approximately 60% of cells staining positive for TH, when challenged in concert with brain-derived neurotrophic factor (50 ng/ml), DA (10 microM) and forskolin (10 microM) for a further 3 weeks. A corresponding 41-fold increase in DA and DOPAC was measured in the incubation medium by HPLC. Therefore, the successful conversion of human foetal progenitor cells in vitro resulting in the desired dopaminergic neuronal phenotype, could provide a solution to the problem of limited availability of human foetuses for clinical surgical transplantation therapies, which are currently in progress for the treatment of neurodegenerative diseases such as Parkinson's disease.     

Human neural progenitor cell transplants into the subthalamic nucleus lead to functional recovery in a rat model of Parkinson's disease

Despite the success of foetal nigral transplantation for the treatment of Parkinson's disease, supply limitations of tissue means that alternative sources must be found. Transplantation of human neural progenitor cells (HNPCs) may offer a solution, however few studies have shown functional recovery in animal models of PD without cell modification. Here we show that unmodified HNPC grafted into the subthalamic nucleus (STN) show excellent survival of up to 5 months and induce significant functional recovery following amphetamine-induced rotations within 4 weeks. For the first time we also show that HNPCs, which remain in an immature nestin-positive state, produce VEGF in vivo allowing further modification of the host brain. This suggests that even in the absence of cell replacement strategies utilising immature progenitor cells could be of real therapeutic value.     

Neural-Targeted Gene Therapy for Rodent and Primate Hemiparkinsonism

Expression of the rate-limiting enzyme for catecholamine biosynthesis, tyrosine hydroxylase (TH), via retrovital and plasmid expression vectors improved the efficacy of conditionally immortalized nigral neural cells in ameliorating rodent and nonhuman primate models of Parkinson's disease through neural transplantation. No improvement in rotational behavior occurred when sham transplants or nondopaminergic transplants were performed. Transplantation of the temperature-sensitive immortalized parental nigral neural line with a TH expression vector resulted in improvement for at least 2 months. Improvement was accompanied by HPLC evidence of increased -DOPA production and immunocytochemical evidence of TH in the transfected cells increased over that of the parental line. No tumor formation was detected. These results suggest that: (1) temperature-sensitive immortalized neural cells may be genetically engineered successfully to improve their efficacy for the treatment of parkinsonism; and (2) a change in -DOPA production, as opposed to growth factor production or other factors, is likely to account for the observed improvement, since the parental and derived lines differ by a single gene.     

Age-related changes of DNA repair and mitochondrial DNA synthesis in the mouse brain

Using quantitative autoradiography, both nuclear DNA repair – measured as nuclear unscheduled DNA synthesis (UDS) – and mitochondrial (mt) DNA synthesis were evaluated in situ for several types of cells in the brains of untreated mice of various age. It was found that distinct types of neuronal cells showed a decline of both UDS and mtDNA synthesis with age, whereas – except for glial cells of the cerebral cortex – no glial or endothelial cells showed age-related alterations of UDS. Together with various data reported in the literature, these patterns of a cell type-specific decrease of UDS and mtDNA synthesis with age in the mouse brain lead to an improved understanding of the complex interrelationships between the molecular events associated with the phenomenon of aging as well as to a new idea regarding the cause of the specific distribution pattern of those cells in the human brain that are affected by the formation of paired helical filaments in Alzheimer’s disease. Received: 12 May 1998 / Revised, accepted: 16 Juli 1998     

Tetrahydrobiopterin-dependent functional recovery in 6-hydroxydopamine-treated rats by intracerebral grafting of fibroblasts transfected with tyrosine hydroxylase cDNA.

Fibroblasts (NRK-49F) were transfected with human type 2 tyrosine hydroxylase (TH; EC 1.14.16.29) cDNA, to clarify the mechanism involved in amelioration of parkinsonism by intracerebral grafting of catecholaminergic neurons and to investigate its possible use as a donor material. These genetically manipulated fibroblasts did not develop into a mass of tissue, and survived well in the host striatum. Expression of the TH minigene in the cells was successful even when they were transplanted into the host brain. Intracerebral microdialysis revealed that a measurable amount of L-3,4-dihydroxyphenylalanine (L-DOPA) was not spontaneously released from the implanted cells into the host striatum. However, release of a large amount of L-DOPA from the cells was observed when (6R)-L-erythro-5,6,7,8-tetrahydrobiopterin (BH4) was perfused through a dialysis probe. Finally, we investigated whether these BH4-dependent L-DOPA-secreting fibroblasts are able to ameliorate the abnormal behavior of 6-hydroxydopamine-treated rats. Apomorphine-induced rotating behavior was not reversed by the grafting alone, whereas a marked reduction in drug-induced circling was observed temporarily after BH4 was perfused around the implanted cells. These findings indicate that TH cDNA-transfected non-neuronal cells might be able to be used as donor material for intracerebral grafting and ameliorate the abnormal behavior of rats with experimental Parkinson's disease.     

Effect of amyloid peptides on the increase in TrkA receptor expression induced by nicotine in vitro and in vivo

The ability of nicotine to induce a cytoprotective or neuroprotective action occurs through several down-stream mechanisms. One possibility is that the drug increases the expression of tyrosine kinase A (TrkA) nerve growth factor (NGF) receptors. Certain β-amyloid peptides (e.g., Aβ1–42) have been shown to bind with high affinity to α7 nicotinic receptors and thus interfere with a potentially neurotrophic influence. Treatment of differentiated PC-12 cells with nicotine produced a concentration-dependent increase in cell-surface TrkA receptors that occurred concomitantly with cytoprotection. The effect of nicotine was blocked by either of the α7 receptor antagonists α-bungarotoxin (α-BTX) or methyllycaconatine. The cytoprotective action of nicotine also was inhibited by pretreatment with 10–100 nM Aβ1–42. Nicotine also was administered (four injections of 30 μg, spaced evenly over 24 h) to rats by direct injection into a lateral cerebral ventricle. Brain TrkA expression was increased significantly in hippocampus and entorhinal cortex (up to 32% above control), with no changes found in cerebral cortex or hypothalamus. The nicotine-induced increases in TrKA expression in hippocampus and entorhinal cortex were significantly inhibited by 10 μg α-BTX or by 10 nmol Aβ1–42. Therefore, physiologically relevant concentrations of Aβ1–42 can prevent nicotine-induced TrkA receptor expression in brain regions containing cholinergic neurons susceptible to the neurotoxicity associated with Alzheimer’s disease.     

Intrastriatal and intranigral grafting of hNT neurons in the 6-OHDA rat model of Parkinson's disease

The clinical findings on neural transplantation for Parkinson's disease (PD) reported thus far are promising but many issues must be addressed before neural transplantation can be considered a routine therapeutic option for PD. The future of neural transplantation for the treatment of neurological disorders may rest in the discovery of a suitable alternative cell type for fetal tissue. One such alternative may be neurons derived from a human teratocarcinoma (hNT). hNT neurons have been shown to survive and integrate within the host brain following transplantation and provide functional recovery in animal models of stroke and Huntington's disease. In this study, we describe the transplantation of hNT neurons in the substantia nigra (SN) and striatum of the rat model for PD. Twenty-seven rats were grafted with one of three hNT neuronal products; hNT neurons, hNT-DA neurons, or lithium chloride (LiCl) pretreated hNT-DA neurons. Robust hNT grafts could be seen with anti-neural cell adhesion molecule and anti-neuron-specific enolase immunostaining. Immunostaining for tyrosine hydroxylase (TH) expression revealed no TH-immunoreactive (THir) neurons in any animals with hNT neuronal grafts. THir cells were observed in 43% of animals with hNT-DA neuronal grafts and all animals with LiCl pretreated hNT-DA neuronal grafts (100%). The number of THir neurons in these animals was low and not sufficient to produce significant functional recovery. In summary, this study has demonstrated that hNT neurons survive transplantation and express TH in the striatum and SN. Although hNT neurons are promising as an alternative to fetal tissue and may have potential clinical applications in the future, further improvements in enhancing TH expression are needed.     

外源EGFP和hTH基因在恒河猴骨髓源神经干细胞内的稳定表达

目的构建携带人酪氨酸羟化酶(hTH)的荧光真核表达质粒-pEGFP-C2-hTH,转染骨髓基质细胞源神经干细胞(BMSCs-D-NSCs),观察外源EGFP和hTH基因在BMSCs-D-NSCs中的表达情况。方法应用基因重组技术,将pWAV2-TH中的TH目的基因亚克隆到荧光真核表达载体 pEGFP-C2,以酶切和测序鉴定重组质粒pEGFP-C2-hTH的正确性:pEGFP-C2-hTH经NucleofectorTM 核转染仪转染培养的恒河猴BMSCs-D-NSCs,24 h后观察绿色荧光蛋白的瞬时表达情况,10 d后行 TH单克隆抗体的免疫组化和TH基因的RT-PCR。结果 (1)酶切、PCR和DNA序列鉴定均证实插入片段的正确性;(2)细胞转染24 h后,荧光显微镜下可观察到绿色荧光蛋白(GFP)的表达,观察到 80％的转染细胞发出绿色荧光;转染10 d后细胞的RT-PCR检测到hTH基因的表达,TH单克隆抗体免疫组化结果显示转染细胞呈阳性染色,同时在荧光显微镜下观察到绿色荧光。结论构建的 hTH荧光真核表达重组质粒pEGFP-C2-hTH,经电转染方法转染至BMSCs-D-NSCs内,成功表达hTH 和EGFP,为BMSCs-D-NSCs基因治疗提供了实验基础。     

Functional correlates of pallidal stimulation for Parkinson's disease

We measured regional cerebral blood flow with H2 15O and positron emission tomography (PET) scanning at rest and during a motor task to study the mechanism of motor improvement induced by deep brain stimulation of the internal globus pallidus in Parkinson's disease. Six right-handed patients with Parkinson's disease were scanned while performing a predictable paced sequence of reaching movements and while observing the same screen displays and tones. PET studies were performed ON and OFF stimulation in a medication-free state. Internal globus pallidus deep brain stimulation improved off-state United Parkinson's Disease Rating Scale motor ratings (37%, p < 0.002) and reduced timing errors (movement onset time, 55%, p < 0.01) as well as spatial errors (10%, p < 0.02). Concurrent regional cerebral blood flow recordings revealed a significant enhancement of motor activation responses in the left sensorimotor cortex (Brodmann area [BA] 4), bilaterally in the supplementary motor area (BA 6), and in the right anterior cingulate cortex (BA 24/32). Significant correlations were evident between the improvement in motor performance and the regional cerebral blood flow changes mediated by stimulation. With internal globus pallidus deep brain stimulation, improved movement initiation correlated with regional cerebral blood flow increases in the left sensorimotor cortex and ventrolateral thalamus and in the contralateral cerebellum. By contrast, improved spatial accuracy correlated with regional cerebral blood flow increases in both cerebellar hemispheres and in the left sensorimotor cortex. These results suggest that internal globus pallidus deep brain stimulation may selectively improve different aspects of motor performance. Multiple, overlapping neural pathways may be modulated by this intervention.     

Pig xenografts to the immunocompetent rat brain: Survival rates using distinct neurotoxic lesions in the nigrostriatal pathway and two rat strains

Porcine foetal neurons for xenotransplantation in Parkinson's disease (PD) is an alternative source to human fetuses. One of the obstacles facing brain xenotransplantation is the existence of an immune response, which prevents long-term graft survival. Experimental results concerning the survival time of porcine foetal neurons implanted into the brain of immunocompetent rats have been quite different from one study to another, suggesting an effect on graft survival of uncontrolled experimental parameters. To identify such parameters, we have first analyzed the survival of porcine foetal nigral neurons at 5 and 10 weeks after implantation into the striatum of immunocompetent rats having different types of brain lesion affecting cells (quinolinic acid) or projections to the striatum (MPP+, 6-OHDA). In a second experiment, graft survival was analyzed in two strains of recipient rats (female Sprague-Dawley and male Lewis rats) in conditions of ipsilateral dopaminergic denervation using 6-OHDA. The characteristics of surviving grafts were assessed by measuring the graft volume, the number of TH+ neurons, the size of TH+ neurons soma, and CD5+ cell infiltration. Long-term survival (> or = 10 weeks) of porcine neurons could be observed in all experimental models. However, there was no significant difference in graft survival rates and characteristics of the surviving grafts between the lesioned groups, or between Sprague-Dawley and Lewis rats. Altogether, results were highly variable within groups of grafts exposed to similar experimental procedures at both 5 and 10 weeks post-grafting. We conclude that the distinct neurotoxins and host rat strains used in our experimental design are not major factors influencing the rejection time-course of primary neural xenografts.     

Induction of dopaminergic neurons from growth factor expanded neural stem/progenitor cell cultures derived from human first trimester forebrain

Multipotent stem/progenitor cells derived from human first trimester forebrain can be expanded as free-floating aggregates, so called neurospheres. These cells can differentiate into neurons, astrocytes and oligodendrocytes. In vitro differentiation protocols normally yield γ-aminobutyric acid-immunoreactive neurons, whereas only few tyrosine hydroxylase (TH) expressing neurons are found. The present report describes conditions under which 4–10% of the cells in the culture become TH immunoreactive (ir) neurons within 24 h. Factors including acidic fibroblast growth factor (aFGF) in combination with agents that increase intracellular cyclic AMP and activate protein kinase C, in addition to a substrate that promotes neuronal differentiation appear critical for efficient TH induction. The cells remain THir after trypsinization and replating, even when their subsequent culturing takes place in the absence of inducing factors. Consistent with a dopaminergic phenotype, mRNAs encoding aromatic acid decarboxylase, but not dopamine-β-hydroxylase were detected by quantitative real time RT-PCR. Ten weeks after the cells had been grafted into the striatum of adult rats with unilateral nigrostriatal lesions, only very few of the surviving human neurons expressed TH. Our data suggest that a significant proportion of expandable human neural progenitors can differentiate into TH-expressing cells in vitro and that they could be useful for drug and gene discovery. Additional experiments, however, are required to improve the survival and phenotypic stability of these cells before they can be considered useful for cell replacement therapy in Parkinson's disease.     

Preliminary study of the behavioral effects of LBS-neuron implantation on seizure susceptibility following middle cerebral artery occlusion in the rat

Neural transplantation is a promising treatment strategy that can restore the motor, sensory and cognitive functions in the rat middle cerebral artery occlusion (MCAO) model of stroke. In particular, neuronal cells derived from a human teratocarcinoma cell line, called hNT neurons or LBS neurons (clinical grade preparation), are effective in improving behavioral recovery after stroke. In the elderly, epilepsy is a common sequelae of stroke, especially if the infarction involves cerebral cortex. However, the effect of implanting neural cells on seizure susceptibility in the MCAO model has not yet been determined. The purpose of this study was to determine the susceptibility to pentylenetetrazol (PTZ)-induced seizures in normal, MCAO-lesioned and MCAO-lesioned rats in which the LBS neurons were injected. Adult, male Sprague-Dawley rats were subjected to 60 min of MCAO using the intraluminal filament technique followed 3–4 weeks later by transplantation of 80,000 LBS-neurons into the ipsilateral cortex. Susceptibility to PTZ-induced seizures was tested 4–6 weeks post-transplant at doses of 35, 50 and 70 mg/kg, administered subcutaneously. Latency to the first ictal response, latency to first generalized seizure, duration of the first generalized seizure, and the number of generalized seizures in an hour post-PTZ treatment observation period was determined. Even though there was a tendency for groups that underwent MCAO to be more susceptible to seizures, there were no statistically significant differences between the groups and no differences between MCAO alone and MCAO animals in which cells had been implanted. While grafted cells were identified in all but one injected animal, the results suggest that the grafts may not have been healthy either from immunological rejection or PTZ-induced injury. These results suggest that while placing cells within the cortex does not reduce seizure susceptibility, it also does not increase the incidence of seizures. Further investigations are warranted.     

Rapid differentiation of NT2 cells in Sertoli-NT2 cell tissue constructs grown in the rotating wall bioreactor

Cell replacement therapy is of great interest as a long-term treatment of neurodegenerative diseases such as Parkinson's disease (PD). We have previously shown that Sertoli cells (SC) provide neurotrophic support to transplants of dopaminergic fetal neurons and NT2N neurons, derived from the human clonal precursors cell line NTera2/D1 (NT2), which differentiate into dopaminergic NT2N neurons when exposed to retinoic acid. We have created SC-NT2 cell tissue constructs cultured in the high aspect ratio vessel (HARV) rotating wall bioreactor. Sertoli cells, NT2, and SC plus NT2 cells combined in starting ratios of 1:1, 1:2, 1:4 and 1:8 were cultured in the HARV in DMEM with 10% fetal bovine serum and 1% growth factor reduced Matrigel for 3 days, without retinoic acid. Conventional, non-HARV, cultures grown in the same culture medium were used as controls. The presence of tyrosine hydroxylase (TH) was assessed in all culture conditions. Sertoli-neuron-aggregated-cell (SNAC) tissue constructs grown at starting ratios of 1:1 to 1:4 contained a significant amount of TH after 3 days of culture in the HARV. No TH was detected in SC HARV cultures, or SC, NT2 or SC-NT2 conventional co-cultures. Quantitative stereology of immunolabled 1:4 SNAC revealed that approximately 9% of NT2 cells differentiate into TH-positive (TH+) NT2N neurons after 3 days of culture in the HARV, without retinoic acid. SNAC tissue constructs also released dopamine (DA) when stimulated with KCl, suggesting that TH-positive NT2N neurons in the SNAC adopted a functional dopaminergic phenotype. SNAC tissue constructs may be an important source of dopaminergic neurons for neuronal transplantation.     

Cellular localization of tyrosine hydroxylase mRNA and its regulation in the rat adrenal medulla and brain by in situ hybridization with an oligodeoxyribonucleotide probe

Tyrosine hydroxylase (TH) is the rate-limiting enzyme in the synthesis of catecholamines in neural tissues and adrenal medulla. To study the expression of the TH gene and its regulation in adult and developing neural tissues, we have synthesized an oligodeoxyribonucleotide probe (oligomer) that is specific for TH mRNA. Using Northern blot hybridization of polyadenylated RNAs from adrenal gland, brain stem, liver, and cerebral cortex with the 32P-labeled oligomer, a single TH mRNA of 1.9 kb was detected in adrenal gland and brain stem but not in liver and cerebral cortex. Using this TH-specific oligomer, TH mRNAs were localized to the chromaffin cells in the adrenal medulla and to catecholaminergic neurons in locus coeruleus and substantia nigra by in situ hybridization histochemistry. After reserpine administration, the intensity of hybridization signal was increased to threefold that of normal in sections of adrenal medulla and twofold that of normal in locus ceruleus. No difference in hybridization signal intensity was observed in the substantia nigra of normal and reserpine-treated animals. Use of this specific TH probe in in situ hybridization procedures represents a powerful approach to the study of regulation of TH gene expression at the cellular level.     

A muscle-derived factor(s) induces expression of a catecholamine phenotype in neurons of cultured rat cerebral cortex

We sought to determine the source of the signal(s) that promotes expression of the catecholamine (CA) enzyme tyrosine hydroxylase (TH) in cultured neurons of embryonic rat cerebral cortex, a tissue which is not thought to contain CA cells in vivo. Cortical neurons were cultured with their non-neuronal constituents and 48 hr later immunostained for TH. Fibroblasts or glia had no effects, however, blood vessels increased the numbers of TH neurons nearly 4-fold. Coculture with either perinatal aorta, skeletal or cardiac muscle, clonal muscle cell lines 1440 (smooth) and L6 (skeletal), conditioned media from L6 cells, or a soluble extract of L6 cells increased the number of TH neurons up to 20-fold. The induction of TH by muscle extract was (1) dose dependent; (2) paralleled by a proportional increase in the steady-state levels of TH mRNA; (3) greatly reduced by the RNA synthesis inhibitor alpha-amanitin or the protein synthesis inhibitor cycloheximide; and (4) unassociated with change in the survival of neurons in culture. The response was not replicated by treatment with other established neurotrophic substances, including NGF, EGF, FGF, PDGF, neuroleukin, insulin, pyruvate, KCI, adenosine, or inosine. We conclude that muscle contains a potentially novel substance, muscle-derived differentiation factor (MDF) that promotes differentiation but not survival of neurons of cerebral cortex by de novo synthesis of TH mRNA and TH protein. Thus, neurons of the CNS, as in periphery, may undergo phenotypic interconversion in response to biologically derived molecules in their environment.     

Intracerebral grafting of cell line or patient-derived neural stem cells for the treatment of neurological disorders]

Due to the development of molecular biology techniques, several types of neurotransmitter or neurotrophic factor secreting cell line can be established. These cell lines were grafted into the brain of animal models of Parkinson's disease and cerebral ischemia after encapsulating into the hollow fiber consisted of semipermeable membrane. Immunological reaction and tumor formation were prevented and functional effects were observed histologically, chemically and behaviorally. Current issues regarding encapsulated cell grafting are: delivery of neurotransmitter and neurotrophic factor simultaneously from one capsule, usage of human-derived cell lines and control of secretion from outside. There are two possible approaches regarding the usage of patient's own neural stem cells for regenerative therapy. Neural stem cells are collected from the subventricular zone of the lateral ventricle and these cells are differentiated into dopaminergic neurons using tyrosine hydroxylase induction cocktail (TH cocktail). Then, these neurons are grafted into the striatum of the patient. Another method is to inject TH cocktail into the patient's striatum in order to induce differentiation of dopaminergic neurons from the neural stem cells in vivo.     

Leukocyte Recruitment and Ischemic Brain Injury

Leukocytes are recruited into the cerebral microcirculation following an ischemic insult. The leukocyte–endothelial cell adhesion manifested within a few hours after ischemia (followed by reperfusion, I/R) largely reflects an infiltration of neutrophils, while other leukocyte populations appear to dominate the adhesive interactions with the vessel wall at 24 h of reperfusion. The influx of rolling and adherent leukocytes is accompanied by the recruitment of adherent platelets, which likely enhances the cytotoxic potential of the leukocytes to which they are attached. The recruitment of leukocytes and platelets in the postischemic brain is mediated by specific adhesion glycoproteins expressed by the activated blood cells and on cerebral microvascular endothelial cells. This process is also modulated by different signaling pathways (e.g., CD40/CD40L, Notch) and cytokines (e.g., RANTES) that are activated/released following I/R. Some of the known risk factors for cardiovascular disease, including hypercholesterolemia and obesity appear to exacerbate the leukocyte and platelet recruitment elicited by brain I/R. Although lymphocyte–endothelial cell and –platelet interactions in the postischemic cerebral microcirculation have not been evaluated to date, recent evidence in experimental animals implicate both CD4+ and CD8+ T-lymphocytes in the cerebral microvascular dysfunction, inflammation, and tissue injury associated with brain I/R. Evidence implicating regulatory T-cells as cerebroprotective modulators of the inflammatory and tissue injury responses to brain I/R support a continued focus on leukocytes as a target for therapeutic intervention in ischemic stroke.