Differential regulation of ciliary neurotrophic factor (CNTF) and CNTF receptor alpha (CNTFR alpha) expression following focal cerebral ischemia

Cerebrolysin enhances spinal cord conduction and reduces blood-spinal cord barrier breakdown, edema formation, immediate early gene expression and cord pathology after injury

Spinal cord evoked potentials (SCEP) are good indicators of spinal cord function in health and disease. Disturbances in SCEP amplitudes and latencies during spinal cord monitoring predict spinal cord pathology following trauma. Treatment with neuroprotective agents preserves SCEP and reduces cord pathology after injury. The possibility that cerebrolysin, a balanced composition of neurotrophic factors improves spinal cord conduction, attenuates blood-spinal cord barrier (BSCB) disruption, edema formation, and cord pathology was examined in spinal cord injury (SCI). SCEP is recorded from epidural space over rat spinal cord T9 and T12 segments after peripheral nerves stimulation. SCEP consists of a small positive peak (MPP), followed by a prominent negative peak (MNP) that is stable before SCI. A longitudinal incision (2mm deep and 5mm long) into the right dorsal horn (T10 and T11 segments) resulted in an immediate long-lasting depression of the rostral MNP with an increase in the latencies. Pretreatment with either cerebrolysin (CBL 5mL/kg, i.v. 30min before) alone or TiO₂ nanowired delivery of cerebrolysin (NWCBL 2.5mL/kg, i.v.) prevented the loss of MNP amplitude and even enhanced further from the pre-injury level after SCI without affecting latencies. At 5h, SCI induced edema, BSCB breakdown, and cell injuries were significantly reduced by CBL and NWCBL pretreatment. Interestingly this effect on SCEP and cord pathology was still prominent when the NWCBL was delivered 2min after SCI. Moreover, expressions of c-fos and c-jun genes that are prominent at 5h in untreated SCI are also considerably reduced by CBL and NWCBL treatment. These results are the first to show that CBL and NWCBL enhanced SCEP activity and thwarted the development of cord pathology after SCI. Furthermore, NWCBL in low doses has superior neuroprotective effects on SCEP and cord pathology, not reported earlier. The functional significance and future clinical potential of CBL and NWCBL in SCI are discussed.

Effects of Neurotrophic Factors in Glial Cells in the Central Nervous System: Expression and Properties in Neurodegeneration and Injury

Astrocytes, oligodendrocytes, and microglia are abundant cell types found in the central nervous system and have been shown to play crucial roles in regulating both normal and disease states. An increasing amount of evidence points to the critical importance of glia in mediating neurodegeneration in Alzheimer’s and Parkinson’s diseases (AD, PD), and in ischemic stroke, where microglia are involved in initial tissue clearance, and astrocytes in the subsequent formation of a glial scar. The importance of these cells for neuronal survival has previously been studied in co-culture experiments and the search for neurotrophic factors (NTFs) initiated after finding that the addition of conditioned media from astrocyte cultures could support the survival of primary neurons in vitro. This led to the discovery of the potent dopamine neurotrophic factor, glial cell line-derived neurotrophic factor (GDNF). In this review, we focus on the relationship between glia and NTFs including neurotrophins, GDNF-family ligands, CNTF family, and CDNF/MANF-family proteins. We describe their expression in astrocytes, oligodendrocytes and their precursors (NG2-positive cells, OPCs), and microglia during development and in the adult brain. Furthermore, we review existing data on the glial phenotypes of NTF knockout mice and follow NTF expression patterns and their effects on glia in disease models such as AD, PD, stroke, and retinal degeneration.

Sigma-1 receptor in brain ischemia/reperfusion: Possible role in the NR2A-induced pathway to regulate brain-derived neurotrophic factor

Sigma-1 receptor (σ1r) activation could attenuate the learning and memory deficits in the AD model, ischemia model and others. In our previous study, the activation of σ1r increased the expression of brain-derived neurotrophic factor (BDNF), possibly through the NR2A-induced pathway, and σ1r agonists might function as neuroprotectant agents in vascular dementia. Here, we used σ1r knockout mice to confirm the role of σ1r. Furthermore, an antagonist of NR2A was first used to investigate whether the NR2A-induced pathway is the necessary link between σ1r and BDNF. The operation of brain ischemia/reperfusion was induced by bilateral common carotid artery occlusion for 20min in C57BL/6 and σ1r knockout mice as the ischemic group. A σ1r agonist, PRE084 (1mg/kg, i.p.), and NR2A antagonist, PEAQX (10mg/kg, i.p.), were administered once daily throughout the experiment. Behavioral tests were performed starting on day 8. On day 22 after brain ischemia/reperfusion, mice were sacrificed and brains were immediately collected and the injured and the hippocampus was isolated and stored at -80°C for western blot analysis. After ischemic operation, contrast with the σ1r knockout mice, PRE084 significantly ameliorated learning and memory impairments in the behavioral evaluation, and prevented the protein decline of BDNF, NR2A, CaMKIV and TORC1 expression in wild-type mice. However, the effects of PRE084 on CaMKIV-TORC1-CREB and BDNF, even for learning and memory impairment, were antagonized by the co-administration of PEAQX, an antagonist of NR2A. The activation of σ1r improves the impairment of learning and memory in the ischemia/reperfusion model, and the expression of BDNF, which may have been achieved through the NR2A-CaMKIV-TORC1 pathway.

Leukemia Inhibitory Factor Haplodeficiency Desynchronizes Glial Reactivity and Exacerbates Damage and Functional Deficits after a Concussive Brain Injury

Reactions of both astrocytes and microglia to central nervous system injury can be beneficial or detrimental to recovery. To gain insights into the functional importance of gliosis, we developed a new model of adolescent closed-head injury (CHI) and interrogated the behavioral, physiological, and cellular outcomes after a concussive CHI in leukemia inhibitory factor (LIF) haplodeficient mice. These mice were chosen because LIF is important for astrocyte and microglial activation. Behaviorally, the LIF haplodeficient animals were equally impaired 4 h after the injury, but in the subsequent 2 weeks, the LIF haplodeficient mice acquired more severe motor and sensory deficits, compared with wild type mice. The prolonged accumulation of neurological impairment was accompanied by desynchronization of the gliotic response, increased cell death, axonal degeneration, diminished callosal compound action potential, and hypomyelination. Our results clearly show that LIF is an essential injury-induced cytokine that is required to prevent the propagation of secondary neurodegeneration.

Altering 5-hydroxymethylcytosine modification impacts ischemic brain injury

Epigenetic modifications such as cytosine methylation and histone modification are linked to the pathology of ischemic brain injury. Recent research has implicated 5-hydroxymethylcytosine (5hmC), a DNA base derived from 5-methylcytosine (5mC) via oxidation by ten-eleven translocation (Tet) enzymes, in DNA methylation-related plasticity. Here we show that 5hmC abundance was increased after ischemic injury, and Tet2 was responsible for this increase; furthermore, inhibiting Tet2 expression abolished the increase of 5hmC caused by ischemic injury. The decrease in 5hmC modifications from inhibiting Tet2 activity was accompanied by increased infarct volume after ischemic injury. Genome-wide profiling of 5hmC revealed differentially hydroxymethylated regions (DhMRs) associated with ischemic injury, and DhMRs were enriched among the genes involved in cell junction, neuronal morphogenesis and neurodevelopment. In particular, we found that 5hmC modifications at the promoter region of brain-derived neurotrophic factor (BDNF) increased, which was accompanied by increased BDNF mRNA, whereas the inhibition of Tet2 reduced BDNF mRNA and protein expression. Finally, we show that the abundance of 5hmC in blood samples from patients with acute ischemic stroke was also significantly increased. Together, these data suggest that 5hmC modification could serve as both a potential biomarker and a therapeutic target for the treatment of ischemic stroke.

Vascular Signal Transducer and Activator of Transcription-3 Promotes Angiogenesis and Neuroplasticity Long-Term After Stroke

Background—

Poststroke angiogenesis contributes to long-term recovery after stroke. Signal transducer and activator of transcription-3 (Stat3) is a key regulator for various inflammatory signals and angiogenesis. It was the aim of this study to determine its function in poststroke outcome.

Methods and Results—

We generated a tamoxifen-inducible and endothelial-specific Stat3 knockout mouse model by crossbreeding Stat3 floxed/KO and Tie2-Cre ERT2 mice. Cerebral ischemia was induced by 30 minutes of middle cerebral artery occlusion. We demonstrated that endothelial Stat3 ablation did not alter lesion size 2 days after ischemia but did worsen functional outcome at 14 days and increase lesion size at 28 days. At this late time point vascular Stat3 expression and phosphorylation were still increased in wild-type mice. Gene array analysis of a CD31-enriched cell population of the neurovascular niche showed that endothelial Stat3 ablation led to a shift toward an antiangiogenic and axon growth-inhibiting micromilieu after stroke, with an increased expression of Adamts9. Remodeling and glycosylation of the extracellular matrix and microglia proliferation were increased, whereas angiogenesis was reduced.

Conclusions—

Endothelial Stat3 regulates angiogenesis, axon growth, and extracellular matrix remodeling and is essential for long-term recovery after stroke. It might serve as a potent target for stroke treatment after the acute phase by fostering angiogenesis and neuroregeneration.

Activation of CNTF/CNTFRα signaling pathway by hRheb(S16H) transduction of dopaminergic neurons in vivo

Ciliary neurotrophic factor (CNTF) is one of representative neurotrophic factors for the survival of dopaminergic neurons. Its effects are primarily mediated via CNTF receptor α (CNTFRα). It is still unclear whether the levels of CNTFRα change in the substantia nigra of Parkinson's disease (PD) patients, but CNTF expression shows the remarkable decrease in dopaminergic neurons in the substantia nigra pars compacta (SNpc), suggesting that the support of CNTF/CNTFRα signaling pathway may be a useful neuroprotective strategy for the nigrostriatal dopaminergic projection in the adult brain. Here, we report that transduction of rat SNpc dopaminergic neurons by adeno-associated virus with a gene encoding human ras homolog enriched in brain (hRheb), with an S16H mutation [hRheb(S16H)], significantly upregulated the levels of both CNTF and CNTFRα in dopaminergic neurons. Moreover, the hRheb(S16H)-activated CNTF/CNTFRα signaling pathway was protective against 1-methyl-4-phenylpyridinium-induced neurotoxicity in the nigrostriatal dopaminergic projections. These results suggest that activation of CNTF/CNTFRα signaling pathway by specific gene delivery such as hRheb(S16H) may have therapeutic potential in the treatment of PD.

The effect of hemorrhage on the development of the postnatal mouse cerebellum

Recent studies have shown that hemorrhagic injury in the preterm cerebellum leads to long-term neurological sequelae, such as motor, affective, and cognitive dysfunction. How cerebellar hemorrhage (CBH) affects the development and function of the cerebellum is largely unknown. Our study focuses on developing a mouse model of CBH to determine the anatomical, behavioral, and molecular phenotypes resulting from a hemorrhagic insult to the developing cerebellum. To induce CBH in the postnatal mouse cerebellum, we injected bacterial collagenase, which breaks down surrounding blood vessel walls, into the fourth ventricle at postnatal day two. We found a reduction in cerebellar size during postnatal growth, a decrease in granule cells, and persistent neurobehavioural abnormalities similar to abnormalities reported in preterm infants with CBH. We further investigated the molecular pathways that may be perturbed due to postnatal CBH and found a significant upregulation of genes in the inflammatory and sonic hedgehog pathway. These results point to an activation of endogenous mechanisms of injury and neuroprotection in response to postnatal CBH. Our study provides a preclinical model of CBH that may be used to understand the pathophysiology of preterm CBH and for potential development of preventive therapies and treatments.

Loss of neuron-astroglial interaction rapidly induces protective CNTF expression after stroke in mice

Ciliary neurotrophic factor (CNTF) is a potent neural cytokine with very low expression in the CNS, predominantly by astrocytes. CNTF increases rapidly and greatly following traumatic or ischemic injury. Understanding the underlying mechanisms would help to design pharmacological treatments to increase endogenous CNTF levels for neuroprotection. Here, we show that astroglial CNTF expression in the adult mouse striatum is increased twofold within 1 h and increases up to >30-fold over 2 weeks following a focal stroke caused by a transient middle cerebral artery occlusion (MCAO). Selective neuronal loss caused by intrastriatal injection of quinolinic acid resulted in a comparable increase. Cocultured neurons reduced CNTF expression in astrocytes, which was prevented by light trypsinization. RGD (arginine-glycine-aspartic acid) blocking peptides induced CNTF expression, which was dependent on transcription. Astroglial CNTF expression was not affected by diffusible neuronal molecules or by neurotransmitters. The transient ischemia does not seem to directly increase CNTF, as intrastriatal injection of an ischemic solution or exposure of naive mice or cultured cells to severe hypoxia had minimal effects. Inflammatory mechanisms were probably also not involved, as intrastriatal injection of proinflammatory cytokines (IFNγ, IL6) in naive mice had no or small effects, and anti-inflammatory treatments did not diminish the increase in CNTF after MCAO. CNTF-/- mice had more extensive tissue loss and similar astrocyte activation after MCAO than their wild-type littermates. These data suggest that contact-mediated integrin signaling between neurons and astrocytes normally represses CNTF expression and that neuronal dysfunction causes a rapid protective response by the CNS.

Endogenous CNTF mediates stroke-induced adult CNS neurogenesis in mice

Focal brain ischemia in adult rats rapidly and robustly induces neurogenesis in the subventricular zone (SVZ) but there are few and inconsistent reports in mice, presenting a hurdle to genetically investigate the endogenous neurogenic regulators such as ciliary neurotrophic factor (CNTF). Here, we first provide a platform for further studies by showing that middle cerebral artery occlusion in adult male C57BL/6 mice robustly enhances neurogenesis in the SVZ only under very specific conditions, i.e., 14days after a 30min occlusion. CNTF expression paralleled changes in the number of proliferated, BrdU-positive, SVZ cells. Stroke-induced proliferation was absent in CNTF-/- mice, suggesting that it is mediated by CNTF. MCAO-increased CNTF appears to act on C cell proliferation and by inducing FGF2 expression but not via EGF expression or Notch1 signaling of neural stem cells in the SVZ. CNTF is unique, as expression of other gp130 ligands, IL-6 and LIF, did not predict SVZ proliferation or showed no or only small compensatory increases in CNTF-/- mice. Expression of tumor necrosis factor-α, which can inhibit neurogenesis, and the presence of leukocytes in the SVZ were inversely correlated with neurogenesis, but pro-inflammatory cytokines did not affect CNTF expression in cultured astrocytes. These results suggest that slowly up-regulated CNTF in the SVZ mediates stroke-induced neurogenesis and is counteracted by inflammation. Further pharmacological stimulation of endogenous CNTF might be a good therapeutic strategy for cell replacement after stroke as CNTF regulates normal patterns of neurogenesis and is expressed almost exclusively in the nervous system.

Axotomy induces axonogenesis in hippocampal neurons through STAT3

After axotomy of embryonic hippocampal neurons in vitro, some of the axotomized axons lose their identity, and new axons arise and grow. This axotomy-induced axonogenesis requires importin, suggesting that some injury-induced signals are transported via axons to elicit axonogenesis after axotomy. In this study, we show that STAT3 is activated in response to axotomy. Because STAT3 was co-immunoprecipitated with importin β in the axotomized neurons, we suggest that STAT3 is retrogradely transported as molecular cargo of importin α/β heterodimers. Indeed, inhibition of importin α binding with STAT3 resulted in the attenuation of axonogenesis. Silencing STAT3 blocked the axonogenesis, demonstrating that STAT3 is necessary for axotomy-induced axonogenesis. Furthermore, the overexpression of STAT3 enhanced axotomy-induced axonogenesis. Taken together, these results demonstrate that activation and retrograde transport of STAT3 in injured axons have key roles in the axotomy-induced axonogenesis of hippocampal neurons.

Role of signal transducer and activator of transcription 3 in neuronal survival and regeneration

Signal Transducers and Activators of Transcription (STATs) comprise a family of transcription factors that mediate a wide variety of biological functions in the central and peripheral nervous systems. Injury to neural tissue induces STAT activation, and STATs are increasingly recognized for their role in neuronal survival. In this review, we discuss the role of STAT3 during neural development and following ischemic and traumatic injury in brain, spinal cord and peripheral nerves. We focus on STAT3 because of the expanding body of literature that investigates protective and regenerative effects of growth factors, hormones and cytokines that use STAT3 to mediate their effect, in part through transcriptional upregulation of neuroprotective and neurotrophic genes. Defining the endogenous molecular mechanisms that lead to neuroprotection by STAT3 after injury might identify novel therapeutic targets against acute neural tissue damage as well as chronic neurodegenerative disorders.

Ambivalent aspects of interleukin-6 in cerebral ischemia: inflammatory versus neurotrophic aspects

Interleukin-6 (IL-6) is pleiotropic cytokine involved in many central nervous system disorders including stroke, and elevated serum IL-6 has been found in acute stroke patients. IL-6 is implicated in the inflammation, which contributes to both injury and repair process after cerebral ischemia. However, IL-6 is one of the neurotrophic cytokines sharing a common receptor subunit, gp130, with other neurotrophic cytokines, such as leukemia inhibitory factor (LIF) and ciliary neurotrophic factor. The expression of IL-6 is most prominently identified in neurons in the peri-ischemic regions, and LIF expression shows a similar pattern. The direct injection of these cytokines into the brain after ischemia can reduce ischemic brain injury. The cytokine receptors are localized on the neuron surface, suggesting that neurons are the cytokine target. The major IL-6 downstream signaling pathway is JAK-STAT, and Stat3 activation occurs mainly in neurons during postischemic reperfusion. Further investigation is necessary to clarify the exact role of Stat3 signaling in neuroprotection. Taken together, the information suggests that IL-6 plays a double role in cerebral ischemia, as an inflammatory mediator during the acute phase and as a neurotrophic mediator between the subacute and prolonged phases.

CNTF protects oligodendrocytes from ammonia toxicity: intracellular signaling pathways involved

In pediatric patients, hyperammonemia can provoke irreversible damages to developing CNS like cortical atrophy, ventricular enlargement, demyelination or gray and white matter hypodensities which are concordant with alterations of neurons and oligodendrocytes. Cerebral injury triggers endogenous protective mechanisms that can prevent or limit brain damage. Understanding these mechanisms may lead to new therapeutic strategies. We investigated whether ciliary neurotrophic factor (CNTF), a cytokine-like protein expressed by astrocytes and described as an injury-associated survival factor, was up-regulated by ammonia in developing reaggregated 3D brain cell cultures. We showed that CNTF is up-regulated by ammonia exposure, through mediation of p38 MAPK activation in astrocytes. We also observed that SAPK/JNK and Erk1/2 activations in oligodendrocytes and neurons, respectively, also play indirect roles in CNTF synthesis by astrocytes. Co-treatment with exogenous CNTF demonstrated strong protective effects on oligodendrocytes, but not on neurons, against ammonia toxicity. These protective effects involved JAK/STAT, SAPK/JNK and c-jun proteins.

Human umbilical cord blood-derived CD34+ cells cause attenuation of multiorgan dysfunction during experimental heatstroke

Multiorgan dysfunction ensuing from severe heatstroke includes hypotension, hepatic and renal failure, hypercoagulable state, activated inflammation, and cerebral ischemia and injury. We attempted to assess whether human umbilical cord blood-derived CD34+ cell therapy improves survival during experimental heatstroke by attenuating multiorgan dysfunction. Anesthetized rats, immediately after the onset of heatstroke, were divided into 2 major groups and given CD34- or CD34+ cells (1 x 10(5)-5 x 10(5)/mL/kg body weight) i.v. They were exposed to ambient temperature of 43 degrees C to induce heatstroke. Another group of rats were exposed to room temperature (26 degrees C) and used as normothermic controls. Hypotension, hepatic and renal failure (evidenced by increased serum urea nitrogen, creatinine, aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase levels in plasma), hypercoagulable state (evidenced by increased prothrombin time, activated partial thromboplastin time, and D-dimer, and decreased platelet count and protein C in plasma), activated inflammation (evidence by increased TNF-alpha levels in serum), and cerebral dysfunction (evidenced by intracranial hypertension, cerebral hypoperfusion and hypoxia, and cerebral ischemia and injury) were monitored. When the CD34- cell-treated or untreated rats underwent heat stress, their survival time values were found to be 19 to 23 min. Resuscitation with CD34+ cells significantly improved survival time (duration, 63-291 min). As compared with normothermic controls, all CD34- cell-treated heatstroke animals displayed hypotension, hepatic and renal failure, hypercoagulable state, activated inflammation, and cerebral ischemia and injury. However, CD34+ cell therapy significantly caused attenuation of all the above-mentioned heatstroke reactions. In addition, the levels of IL-10 in plasma and glial cell line-derived neurotrophic factors in brain were all significantly increased after CD34+ cell therapy during heatstroke. Our data indicate that CD34+ cell therapy may resuscitate persons who had a heatstroke by reducing multiorgan dysfunction or failure.

Human umbilical cord blood cells or estrogen may be beneficial in treating heatstroke

This current review summarized animal models of heatstroke experimentation that promote our current knowledge of therapeutic effects on cerebrovascular dysfunction, coagulopathy, and/or systemic inflammation with human umbilical cord blood cells (HUCBCs) or estrogen in the setting of heatstroke. Accumulating evidences have demonstrated that HUCBCs provide a promising new therapeutic method against neurodegenerative diseases, such as stroke, traumatic brain injury, and spinal cord injury as well as blood disease. More recently, we have also demonstrated that post- or pretreatment by HUCBCs may resuscitate heatstroke rats with by reducing circulatory shock, and cerebral nitric oxide overload and ischemic injury. Moreover, CD34+ cells sorted from HUCBCs may improve survival by attenuating inflammatory, coagulopathy, and multiorgan dysfunction during experimental heatstroke. Many researchers indicated pro- (e.g. tumor necrosis factor-alpha [TNF-alpha]) and anti-inflammatory (e.g. interleukin-10 [IL-10]) cytokines in the peripheral blood stream correlate with severity of circulatory shock, cerebral ischemia and hypoxia, and neuronal damage occurring in heatstroke. It has been shown that intravenous administration of CD34+ cells can secrete therapeutic molecules, such as neurotrophic factors, and attenuate systemic inflammatory reactions by decreasing serum TNF-alpha but increasing IL-10 during heatstroke. Another line of evidence has suggested that estrogen influences the severity of injury associated with cerebrovascular shock. Recently, we also successfully demonstrated estrogen resuscitated heatstroke rats by ameliorating systemic inflammation. Conclusively, HUCBCs or estrogen may be employed as a beneficial therapeutic strategy in prevention and repair of cerebrovascular dysfunction, coagulopathy, and/or systemic inflammation during heatstroke.

Activation of cytokine signaling through leukemia inhibitory factor receptor (LIFR)/gp130 attenuates ischemic brain injury in rats

Cytokine signaling through leukemia inhibitory factor receptor (LIFR)/gp130 is known to exert a neurotrophic action in the central nervous system, although the role of this signaling in cerebral ischemia remains unknown. We examined the effect of intracerebral injection of LIF after focal cerebral ischemia in rats. The animals underwent a sham operation (sham group) or middle cerebral artery occlusion (MCAO) followed by direct injection of either vehicle (phosphate-buffered saline, the PBS group) or recombinant LIF (10 ng in the low-LIF group and 100 ng in the high-LIF group) into the cerebral cortex adjacent to the inner boundary zone of the infarct area, and neurologic and histologic evaluations were conducted 24 h later. Expression of LIFR, gp130, and phosphorylated Stat3, Akt, and ERK1/2 was investigated by Western blot analysis and immunohistochemistry. The neurologic deficits and ischemic damage were significantly less severe in the high-LIF group than in the PBS group and the low-LIF group. Leukemia inhibitory factor receptor and gp130 were expressed in neurons, and the ischemic damage of these proteins was rescued in the high-LIF group. Early induction of phosphorylated Stat3 was significantly detected on the ischemic side in the high-LIF group after LIF injection. Exogenous LIF attenuates ischemic brain injury by activating cytokine signaling through LIFR/gp130.

Neurotrophic Factor Expression after Focal Brain Ischemia Preceded by Different Preconditioning Strategies

BACKGROUND

Both prolonged brain ischemia and preconditioning (PC) induce expression of neurotrophic factors. However, the influence of PC on their expression after a long-term ischemia remains vague. Previously, we have found various effects of PC on mRNA levels of different cytokines after focal brain ischemia. Thus, we investigated mRNA expression of nerve growth factor, brain-derived neurotrophic factor (BDNF) and ciliary neurotrophic factor after 90-min middle cerebral artery occlusion (MCAo) preceded by ischemic or chemical PC.

METHODS

MCAo was induced in rats using the suture method. PC had been carried out 3 days earlier. There were 4 experimental groups: MCAo alone; ischemic PC and MCAo; chemical PC and MCAo, and sham-operated rats. Expression of mRNAs in the ipsi- and contralateral cortex was studied by semiquantitative RT-PCR at 12 and 24 h after MCAo.

RESULTS

Despite clearly neuroprotective effects of both PC strategies, mRNA levels of neurotrophic factors were similar in tolerant and nontolerant rats. Only BDNF mRNA expression, 12 h after reperfusion, was lower when ischemic PC was applied prior to long-term ischemia.

CONCLUSIONS

These results suggest that PC generally does not change the expression of neurotrophic factor expression after a long-term focal brain ischemia compared to the nontolerant state.

Mesenchymal stem cells that produce neurotrophic factors reduce ischemic damage in the rat middle cerebral artery occlusion model

Mesenchymal stem cells (MSC) were reported to ameliorate functional deficits after stroke in rats, with some of this improvement possibly resulting from the action of cytokines secreted by these cells. To enhance such cytokine effects, we previously transfected the telomerized human MSC with the BDNF gene using a fiber-mutant adenovirus vector and reported that such treatment contributed to improved ischemic recovery in a rat transient middle cerebral artery occlusion (MCAO) model. In the present study, we investigated whether other cytokines in addition to BDNF, i.e., GDNF, CNTF, or NT3, might have a similar or greater effect in this model. Rats that received MSC-BDNF (P < 0.05) or MSC-GDNF (P < 0.05) showed significantly more functional recovery as demonstrated by improved behavioral test results and reduced ischemic damage on MRI than did control rats 7 and 14 days following MCAO. On the other hand, rats that received MSC-CNTF or MSC-NT3 showed neither functional recovery nor ischemic damage reduction compared to control rats. Thus, MSC transfected with the BDNF or GDNF gene resulted in improved function and reduced ischemic damage in a rat model of MCAO. These data suggest that gene-modified cell therapy may be a useful approach for the treatment of stroke.

Neuregulin-1 reduces ischemia-induced brain damage in rats

Neuregulin-1 (NRG-1) is expressed throughout the immature and adult central nervous system and it has been demonstrated to influence the migration of a variety of cell types in developing brain. Elevated levels of NRG-1 transcript are found in the adult brain after injury, leading to the suggestion that NRG-1 is involved in the physiological response to neuronal injury. Here, we report our findings that rats pre-treated with NRG-1 protein, undergoing cerebral ischemia 30 min later, had increased motor performance and less cerebral infarction than untreated rats. In the cortex of NRG-1 treated rats, ischemia induced a decrease in caspase-3 immunoreactivity and a reduction in the density of cells positive for terminal deoxynucleotidyl transferase-mediated dUTP-biotin in situ nick end-labeling. Improvement in behavioral assays was also found in animals treated with NRG-1. Pre-treatment with NRG-1 did not alter cerebral blood flow or other physiological parameters. NRG-1 reduced ischemia/reperfusion injury, indicating that it may act as an endogenous neuroprotective factor against stroke. Therefore, NRG-1 may represent a target for the development of new treatments for stroke.

Characterization of the rat A2A adenosine receptor gene: a 4.8-kb promoter-proximal DNA fragment confers selective expression in the central nervous system

We isolated and characterized a 4.8-kb 5' flanking region of the rat A2A adenosine receptor (A2A-R) gene in the present study. Promoter activity was observed with this DNA fragment in PC12 cells and C6 cells which contain endogenous A2A-Rs. A fusion fragment consisting of the 4.8-kb promoter-proximal DNA fragment of the A2A-R gene, and the coding region of lacZ was utilized to produce mice harbouring the fusion gene. In three independent founder lines, proteins and transcripts of the transgene were found in many areas of the central nervous system (CNS), but not in three peripheral tissues examined. Double immunohistochemical analyses revealed that the transgene was coexpressed with endogenous A2A-R and proper neuronal markers in the brain. Specifically, the transgene in the striatum was found in the enkephalin-containing GABAergic neurons and in the cholinergic neurons as was found for the endogenous A2A-R. However, a selectively enriched striatal expression of the transgene was not found as was observed for the endogenous A2A-R. Collectively, the 4.8-kb promoter-proximal DNA fragment of the rat A2A-R gene contains important element(s) to direct its expression in the CNS where functional A2A-R are found, but were not sufficient to confer the highly concentrated expression of the striatal A2A-R. Furthermore, expressions of A2A-R and the transgene were found in both neurons and astrocytes, suggesting that adenosine might mediate its function through A2A-R in both cell types.

Gene expression profiling of ciliary neurotrophic factor-overexpressing rat striatal progenitor cells (ST14A) indicates improved stress response during the early stage of differentiation

Neuronal progenitor cells delivering neurotrophic factors are a promising therapeutic tool for treatment of neurodegenerative diseases. Although several promising results have come from studies in different animal models, detailed knowledge of the action of neurotrophic factors in the CNS is still lacking. A clonally derived, immortalized rat striatal cell line (ST14A) expressing ciliary neurotrophic factor (CNTF) offers a stable and controlled background with which to analyze CNTF actions on the transcriptional level in CNS progenitor cells. To identify early transcriptional changes induced by CNTF expression, we transfected the CNTF gene into ST14A cells, which differentiate at the nonpermissive temperature of 39 degrees C via suppression of the immortalizing SV40 large T antigen. This shows a CNTF-dependent hypoxic/ischemic stress response during the earliest stage of differentiation, with expression of specific transcripts and evidence of translational repression leading to decreased protein synthesis in the transfected cells. This process is mediated by the Ras/MAP kinase pathway and is accompanied by impaired proliferation and metabolism as well as signs of neuronal differentiation. The stress-like response in the early stage of differentiation improves the ability of the transfected cells to respond to and cope with a stressful environment in vivo. The present data indicate higher viability, longer life, and greater differentiation capacity of CNTF-ST14A cells if they are used for transplantation. We conclude that the stress-like response during the early stage of differentiation improves the ability of the CNTF-ST14A cells to respond and adapt to a stressful environment, which renders them useful candidate cells for in vivo trials of treatment for neurodegenerative diseases in animal models, e.g., of Huntington's disease.

Astrocytes and stroke: networking for survival?

Astrocytes are now known to be involved in the most integrated functions of the central nervous system. These functions are not only necessary for the normally working brain but are also critically involved in many pathological conditions, including stroke. Astrocytes may contribute to damage by propagating spreading depression or by sending proapoptotic signals to otherwise healthy tissue via gap junction channels. Astrocytes may also inhibit regeneration by participating in formation of the glial scar. On the other hand, astrocytes are important in neuronal antioxidant defense and secrete growth factors, which probably provide neuroprotection in the acute phase, as well as promoting neurogenesis and regeneration in the chronic phase after injury. A detailed understanding of the astrocytic response, as well as the timing and location of the changes, is necessary to develop effective treatment strategies for stroke patients.

Gene therapy for treatment of cerebral ischemia using defective recombinant adeno-associated virus vectors

In this review we present our results and experiences in performing gene therapy of cerebral stroke using recombinant adeno-associated virus (rAAV) vectors in a rat model. The methodologies involving the production of AAV vectors, gene transfer to the brain, and a trivessel ligation model of focal ischemic cerebral stroke in rats are described. Furthermore, a brief description of other viral vectors and candidates of therapeutic transgenes used for gene therapy of cerebral stroke are presented. The potential advantages and limitations of stroke gene therapy are also discussed with the intention of outlining the design of more appropriate experiments.

Ciliary neurotrophic factor activates spinal cord astrocytes, stimulating their production and release of fibroblast growth factor-2, to increase motor neuron survival

At focal CNS injury sites, several cytokines accumulate, including ciliary neurotrophic factor (CNTF) and interleukin-1beta (IL-1beta). Additionally, the CNTF alpha receptor is induced on astrocytes, establishing an autocrine/paracrine loop. How astrocyte function is altered as a result of CNTF stimulation remains incompletely characterized. Here, we demonstrate that direct injection of CNTF into the spinal cord increases GFAP expression and astroglial size and that primary cultures of spinal cord astrocytes treated with CNTF, IL-1beta, or leukemia inhibitory factor exhibit nuclear hypertrophy comparable to that observed in vivo. Using a coculture bioassay, we further demonstrate that CNTF treatment of astrocytes increases their ability to support ChAT(+) ventral spinal cord neurons (presumably motor neurons) more than twofold compared with untreated astrocytes. Also, the complexity of neurites was significantly increased in neurons cultured with CNTF-treated astrocytes compared with untreated astrocytes. RT-PCR analysis demonstrated that CNTF increased levels of FGF-2 and nerve growth factor (NGF) mRNA and that IL-1beta increased NGF and hepatocyte growth factor mRNA levels. Furthermore, both CNTF and IL-1beta stimulated the release of FGF-2 from cultured spinal cord astrocytes. These findings demonstrate that cytokine-activated astrocytes better support CNS neuron survival via the production of neurotrophic molecules. We also show that CNTF synergizes with FGF-2, but not epidermal growth factor, to promote DNA synthesis in spinal cord astrocyte cultures. The significance of these findings is discussed by presenting a new model depicting the sequential activation of astrocytes by cytokines and growth factors in the context of CNS injury and repair.

Adenovirus-mediated GDNF and CNTF pretreatment protects against striatal injury following transient middle cerebral artery occlusion in mice

During the last few years, adenoviral gene transfer techniques have achieved increasing interest in the treatment of neurodegenerative diseases. However, gene therapy requires that delivered genes are translated into proteins. This may pose a problem in focal ischemia where protein synthesis is compromized. The present study was conducted to find out the feasibility of adenoviral GDNF and CNTF delivery in transient focal ischemia, as induced by 30 min of intraluminar middle cerebral artery (MCA) occlusion in mice. Injections of vehicle, of an adenoviral vector deleted in the E1 region (Ad-dE1) and of vectors expressing the GDNF (Ad-GDNF), CNTF (Ad-CNTF), or GFP (Ad-EGFP) gene from a CMV promoter were stereotactically placed in the dorsolateral striatum, i.e., the core of the MCA territory, and focal ischemia was induced seven days later. Thread occlusion resulted in disseminated injury of the striatum, but not the overlying cortex. The number of viable neurons was significantly increased after 1 and 3 days of reperfusion both in Ad-GDNF and Ad-CNTF as compared with vehicle or Ad-dE1-treated animals, whereas the number of injured cells was significantly reduced, as shown by cresyl violet staining, terminal transferase biotinylated-dUTP nick end-labeling (TUNEL), and immunocytochemistry for activated caspase-3. Interestingly, the protective effects of Ad-GDNF were similarly strong in areas of the striatum adjacent and remote of the adenoviral infusion site, while Ad-CNTF showed pronounced rescue effects in the surrounding, but rather little effects distant to the infusion. The present study demonstrates that adenoviral delivery of neurotrophic factors may be a useful tool for the treatment of focal ischemia.

Phosphorylation of signal transducer and activator of transcription-3 (Stat3) after focal cerebral ischemia in rats

JAK-STAT is the major downstream signal pathway of interleukin-6 (IL-6) cytokine family and is regulated by Tyr705 phosphorylation of Stat3. The present study examined the extent and the localization of phosphorylated Stat3 protein in brain tissue after focal ischemia in rats. The localizations of unphosphorylated and phosphorylated Stat3 were immunohistochemically examined in rats after 0.5 to 168 h of reperfusion following 1.5 h of middle cerebral artery occlusion (MCAO), induced by the intraluminal suture method. Absolute phosphorylated Stat3 immunoreactive cell counts were made in the cerebral cortex (ischemic core, peri-ischemia region, and contralareral cortex) and lateral striatal regions on both the ischemic and the contralateral sides. Stat3 protein was localized diffusely in cortical and striatal neurons in the sham-operated animals. Although weak Stat3 staining was detected in damaged neurons in the ischemic region, activated microglia, astrocytes, and endothelial cells clearly expressed Stat3 in this region. On the other hand, the sham group showed no phosphorylated Stat3 immunoreactivity. Phosphorylated Stat3 immunoreactivity was first detected in neurons after 3.5 h of reperfusion in each cortical and striatal region. Thereafter, Stat3 phosphorylation was marked in neurons in the peri-infarct region, peaked at 24 h, and then gradually declined throughout the reperfusion period. Endothelial cells expressed phosphorylated Stat3 in the ischemic core at 48 h of reperfusion. To identify the cellular source of phosphorylated Stat3, lectin histochemical study and immunohistochemical study with anti-microtubule-associated proten-2 and anti-glial fibrillary acidic protein antibodies were carried out. Double-staining immunohistochemistry with these cellular makers revealed phosphorylated Stat3 to be present in neurons, but in neither astrocytes nor microglia/macrophages. These results were also confirmed be western blot analysis. The present results indicate that Stat3 activation occurs in neurons and endothelial cells only during post-ischemic reperfusion despite widespread expression of IL-6 cytokines.

Increased susceptibility to ischemia-induced brain damage in transgenic mice overexpressing a dominant negative form of SHP2

Cell culture studies have established SH2 domain-containing protein tyrosine phosphatase-2 (SHP2) as an important factor in growth factor and cytokine-activated signaling pathways. However, the significance of SHP2 in the mammalian central nervous system (CNS) is not known since early embryonic lethality occurs in shp2 null mice. To bypass this embryonic lethality, transgenic animals containing a catalytically inactive mutant of SHP2 (SHP2-CS) under the control of a nestin intron II/thymidine kinase minimal promoter were generated. In the developing CNS of these animals, although high-level transgene expression was detected in the neuroepithelium, there was no obvious abnormality in progenitor cell proliferation or migration. In the adult brain, high-level transgene expression was detected in the subventricular zone, rostral migratory stream, dentate gyrus of hippocampus, and cerebellum. Because SHP2 function is likely important in cell survival pathways, we used a focal cerebral ischemia model to examined whether SHP2 is important during CNS injury. Ischemia-induced damage and neuronal death was found to be significantly greater in nestin-SHP2-CS mice than in wild-type littermates. These findings indicate that SHP2 is a required factor in signaling pathway(s) important for neuronal survival.

Multiple molecular penumbras after focal cerebral ischemia

Though the ischemic penumbra has been classically described on the basis of blood flow and physiologic parameters, a variety of ischemic penumbras can be described in molecular terms. Apoptosis-related genes induced after focal ischemia may contribute to cell death in the core and the selective cell death adjacent to an infarct. The HSP70 heat shock protein is induced in glia at the edges of an infarct and in neurons often at some distance from the infarct. HSP70 proteins are induced in cells in response to denatured proteins that occur as a result of temporary energy failure. Hypoxia-inducible factor (HIF) is also induced after focal ischemia in regions that can extend beyond the HSP70 induction. The region of HIF induction is proposed to represent the areas of decreased cerebral blood flow and decreased oxygen delivery. Immediate early genes are induced in cortex, hippocampus, thalamus, and other brain regions. These distant changes in gene expression occur because of ischemia-induced spreading depression or depolarization and could contribute to plastic changes in brain after stroke.

Activation of the JAK/STAT pathway following transient focal cerebral ischemia: signaling through Jak1 and Stat3 in astrocytes

JAK/STAT is one of the pathways bearing signals from the cell membrane to the nucleus in response to extracellular growth factors and cytokines. In the present study, we examined the cellular distribution of Jak1 and Stat3, and activation of the JAK/STAT pathway following transient focal cerebral ischemia in the rat. Jak1 was mainly seen in white matter astrocytes and in certain neurons. Notably, large pyramidal neurons of cortical layer V showed the highest neuronal Jak1 expression within cerebral cortex and, in addition, expressed Stat3 indicating that the JAK/STAT pathway is involved in signaling in the corticofugal projection system. Shortly following ischemia, Jak1 immunoreactive astrocytes located in the ipsilateral neighbouring white matter and ischemic cortex and striatum showed nuclear translocation of Stat3. These features were maintained in large reactive astrocytes that surrounded the infarct from 3 to 7 days. At these later times, the abundant reactive microglia/macrophages were strongly immunoreactive to Stat3 and, to a lesser extent, Jak1. Two main protein complexes showing DNA binding activity at the sis-inducible element site were found under basal conditions, followed by changes in this pattern following ischemia concomitant with neuronal cell loss and activation of glia. This study showed basal cerebral activity of JAK/STAT signaling pathway, involving Jak1 and Stat3 proteins, and selective activation following ischemia. It is suggested that the kinase activity of Jak1 mediates nuclear translocation of Stat3 in astrocytes, and that this signaling pathway is involved in the astroglial response to focal cerebral ischemia.

Differential regulation of ciliary neurotrophic factor and its receptor in the rat hippocampus following transient global ischemia

To investigate a potential role of ciliary neurotrophic factor (CNTF) in transient global ischemia, we have studied the postischemic regulatory changes in the expression of CNTF and its receptor, the ligand-binding alpha-subunit (CNTFRalpha). Immunoblot analysis demonstrated CNTF levels were slightly upregulated already during the first day after ischemia and then increased markedly by more than 10-fold until 2 weeks postischemia. Immunoreactivity for CNTF became detectable 1 day after ischemia and was localized in reactive astrocytes. The intensity of the immunolabeling was maximal in CA1 during the phase of neuronal cell death (days 3-7 postischemia) and in the deafferented inner molecular layer of the dentate gyrus. Upregulation of CNTF expression was less pronounced in CA3 and absent in the stratum lacunosum moleculare and the outer molecular layer of the dentate gyrus and thus did not simply correlate with astroliosis as represented by upregulation of glial fibrillary acidic protein (GFAP). As shown by in situ hybridization, expression of CNTFRalpha mRNA was restricted to neurons of the pyramidal cell and granule cell layers in control animals. Following ischemia, reactive astrocytes, identified by double labeling with antibodies to GFAP, transiently expressed CNTFRalpha mRNA with a maximum around postischemic day 3. This astrocytic response was most pronounced in CA1 and in the hilar part of CA3. These results show that CNTF and its receptor are differentially regulated in activated astrocytes of the postischemic hippocampus, indicating that they are involved in the regulation of astrocytic responses and the neuronal reorganizations occurring after an ischemic insult.

Induction of angiopoietin and Tie receptor mRNA expression after cerebral ischemia-reperfusion

The angiopoietin/Tie receptor system may contribute to angiogenesis and vascular remodeling by mediating interactions of endothelial cells with smooth muscle cells and pericytes. The temporal expression of angiopoietin-1 (Angpo-1), angiopoietin-2 (Angpo-2), Tie-1, and Tie-2 mRNA was studied in a focal cerebral ischemia model in rats. The cDNA fragments obtained from reverse transcription polymerase chain reaction amplification were cloned and used as a probe to detect individual genes. Northern blot analysis showed a delayed increase of a 4.4-kb Angpo-1 transcript for up to 2 weeks after ischemia, eightfold higher than the values of the sham-operated controls. A biphasic expression of a 2.4-kb Angpo-2 transcript was noted, peaking at 24 hours (6.4-fold) and 2 weeks (4.6-fold) after ischemia. The expression of Tie-2 mRNA (4.3 kb), a receptor for Angpo-1, and Tie-1 mRNA (4.3 kb) also increased starting 24 hours after reperfusion and remained elevated for up to 2 weeks after ischemia. The temporal profiles of the expression of these genes were different from those of other angiogenic genes such as basic fibrobast growth factor/fibroblast growth factor receptor and vascular endothelial growth factor/vascular endothelial growth factor receptor and proteolytic enzymes (tissue-type plasminogen activator and urokinase plasminogen activator) and their inhibitors (plasminogen activator inhibitor-1). The expression patterns of these genes could be related to progressive tissue liquefaction and neovascularization after ischemia in this stroke model. Differential expression of these angiogenesis genes suggests the involvement of complex regulatory mechanisms that remain to be characterized.

Enhanced neuronal expression of the oxidoreductase--biliverdin reductase--after permanent focal cerebral ischemia

This is the first report on increased neuronal levels of biliverdin reductase (BVR) in response to ischemic brain injury. BVR is an oxidoreductase, and is unique among all enzymes characterized to date in having dual pH/dual cofactor requirements--NADH and NADPH at 6.7 and 8.7, respectively. BVR catalyses the final step in the heme metabolic pathway and reduces the heme degradation product, biliverdin, to bilirubin. Bilirubin can be both a neurotoxicant and an antioxidant depending on its ratio to protein and concentration. Bilirubin also has immunomodulatory activity. Other biologically active heme degradation products are iron and CO. This study assessed time-dependent changes in the level of BVR, following permanent middle cerebral artery occlusion (MCAo). It also examined correlation of the change in BVR expression with display of indices of ischemic tissue injury. Under halothane anesthesia and normothermic conditions, 72 DNX inbred mice were subjected to MCAo. A time-dependent enlargement of an ischemic lesion over the course of 24 h was observed and measured 55 +/- 5 mm3 at 6 h, 63 +/- 6.7 mm3 at 12 h, and 73 +/- 5 mm3 at 24 h. Six hours after MCAo, increased immunoreactivity for BVR was noted in neurons in the peri-ischemic areas, intraischemic cortical layers 3 and 5, as well as in neurons in regions distant from the borders of vascular distribution of the MCA, such as those in substantia nigra, in the Purkinje layer of the cerebellum and in the central nucleus of inferior colliculus. Twenty-four hours after MCAo, immunoreactivity for BVR remained increased in the peri-ischemia areas. At all time points staining for BVR was decreased in the ischemic core. At the 24 h time point there was an increase in Fe staining in the perimeter of the lesion and an increase in Schiff's staining for lipid peroxidation at the rim of the lesion. In situ hybridization analysis demonstrated a time dependent increase in BVR mRNA labeling in neurons of the peri-ischemic area. In the ischemic hemisphere, when compared with the contralateral hemisphere, neither measurable decreases in BVR mRNA or total protein levels nor a decrease in NADH-dependent BVR activity at pH 6.7 were observed. As judged by Northern and Western blots and activity analysis, despite the apparent loss of BVR from the ischemic core, and its increase in the peri-ischemic region, when compared with the contralateral hemisphere, the overall capacity of the ischemic hemisphere to catalyze the reduction of biliverdin was unchanged throughout the experiment. Should, in the case of ischemia, the conditions favor the antioxidant activity of bilirubin, then we suggest that increase in BVR expression in ischemic penumbra may present a cellular defense mechanism against free radical-mediated neuronal damage. Furthermore, we interpret the apparent tightly regulated expression of BVR in the ischemic hemisphere as an important factor in protection against bilirubin neurotoxicity. Data suggest that pharmacological modulation of BVR expression is a possible new direction for protecting neurons against ischemic injury and oxidative stress.

Topical application of neurotrophin-3 attenuates ischemic brain injury after transient middle cerebral artery occlusion in rats

In order to examine the effect of neurotrophin-3 (NT-3) on ischemic brain injury, NT-3 was topically applied to brain surface just after 90 min of middle cerebral artery occlusion (MCAO) in rats. NT-3 significantly reduced the infarct size at 24 h of reperfusion. Terminal deoxynucleotidyl transferase-mediated dUTP-biotin in situ nick labeling (TUNEL) staining and immunohistochemical study for caspase-3 and heat shock protein 72 (HSP72) showed that NT-3 treatment decreased the number of cells with DNA fragmentation and caspase-3 and HSP72 expressions. These data suggest that NT-3 protects neuronal cells from ischemic injury, and it is possibly associated with inhibition of DNA fragmentation.

Expression of CNTF in Müller cells of the rat retina after pressure-induced ischemia

We have investigated the expression and cellular localization of ciliary neurotrophic factor (CNTF) in the rat retina following ischemia induced by transiently increasing the intraocular pressure. In the normal retina, CNTF immunoreactivity was restricted to profiles in the ganglion cell layer. Following ischemia and reperfusion, immunoreactivity appeared in Müller cell somata and processes and its intensity increased between 1 day and 2 weeks post-lesion. Quantitative evaluation by immunoblotting confirmed that CNTF expression continuously increased up to 2 weeks after ischemic injury (to 600% of control levels), but had declined again to 250% of controls at 4 weeks post-lesion. Our findings suggest that CNTF supplied by Müller cells has a protective function for lesioned neurons following transient ischemia.