Induction of glial cell line-derived neurotrophic factor receptor proteins in cerebral cortex and striatum after permanent middle cerebral artery occlusion in rats

Glial Cell Line-Derived Neurotrophic Factor and Focal Ischemic Stroke

Focal ischemic stroke (FIS) is a leading cause of human debilitation and death. Following the onset of a FIS, the brain experiences a series of spatiotemporal changes which are exemplified in different pathological processes. One prominent feature of FIS is the development of reactive astrogliosis and glial scar formation in the peri-infarct region (PIR). During the subacute phase, astrocytes in PIR are activated, referred to as reactive astrocytes (RAs), exhibit changes in morphology (hypotrophy), show an increased proliferation capacity, and altered gene expression profile, a phenomenon known as reactive astrogliosis. Subsequently, the morphology of RAs remains stable, and proliferation starts to decline together with the formation of glial scars. Reactive astrogliosis and glial scar formation eventually cause substantial tissue remodeling and changes in permanent structure around the PIR. Glial cell line-derived neurotrophic factor (GDNF) was originally isolated from a rat glioma cell-line and regarded as a potent survival neurotrophic factor. Under normal conditions, GDNF is expressed in neurons but is upregulated in RAs after FIS. This review briefly describes properties of GDNF, its receptor-mediated signaling pathways, as well as recent studies regarding the role of RAs-derived GDNF in neuronal protection and brain recovery. These results provide evidence suggesting an important role of RA-derived GDNF in intrinsic brain repair and recovery after FIS, and thus targeting GDNF in RAs may be effective for stroke therapy.

Recurrent non-severe hypoglycemia aggravates cognitive decline in diabetes and induces mitochondrial dysfunction in cultured astrocytes

The present study aimed to determine the relationship between astrocytes and recurrent non-severe hypoglycemia (RH)2 -associated cognitive decline in diabetes. RH induced cognitive impairment and neuronal cell death in the cerebral cortex of diabetic mice, accompanied by excessive activation of astrocytes. Levels of the neurotrophins BDNF and GDNF, together with BDNF and GDNF- related signaling, were downregulated by RH. In vitro, recurrent low glucose (RLG)3 impaired cell viability and induced apoptosis of high-glucose cultured astrocytes. Accumulating mitochondrial ROS and dysregulated mitochondrial functions, including abnormal morphology, decreased membrane potential, downregulated ATP levels, and disrupted bioenergetic status, were observed in these cells. SS-31 mediated protection of mitochondrial functions reversed RLG-induced cell viability defects and neurotrophin production. These findings demonstrate that RH induced astrocyte overactivation and mitochondrial dysfunction, leading to astrocyte-derived neurotrophin disturbance, which might contribute to diabetic cognitive decline. Targeting astrocyte mitochondria might represent a neuroprotective therapy for hypoglycemia-associated neurodegeneration in diabetes.

Potential role of exosome in post-stroke reorganization and/or neurodegeneration

Currently, stroke is a common and devastating condition, which is sometimes associated with permanent cerebral damages. Although in early time after stroke, the related treatments are mainly focused on the restoration of cerebral blood flow (CBF), at the same time, some changes are commencing that continue for a long time and need to be specially noticed. Previous studies have proposed several molecular mechanisms in these post-stroke events. Exosomes are a type of vesicle, which are formed and secreted by most cells as a mean to transfer cellular constituents such as proteins, DNA and/or RNA to distant cells. Therefore, they are considered as a novel mechanism of cellular communication. Herein, we reviewed the current knowledge on cascades, which are activated after stroke and consequently lead to the reorganization and/or continuance of tissue damage and development of other disorders such as Neurodegenerative diseases (ND). Thereafter, we summarized the latest proofs about the possible participation of exosomes in transferring some components such as proteins and micro-RNAs (miRs), from the affected areas to other parts of the brain and eventually cause the above-mentioned post-stroke events.

GLAST-CreERT2 mediated deletion of GDNF increases brain damage and exacerbates long-term stroke outcomes after focal ischemic stroke in mouse model

Focal ischemic stroke (FIS) is a leading cause of human death. Glial scar formation largely caused by reactive astrogliosis in peri-infarct region (PIR) is the hallmark of FIS. Glial cell-derived neurotrophic factor (GDNF) was originally isolated from a rat glioma cell-line supernatant and is a potent survival neurotrophic factor. Here, using CreER^T2 -LoxP recombination technology, we generated inducible and astrocyte-specific GDNF conditional knockout (cKO), that is, GLAST-GDNF^-/- cKO mice to investigate the effect of reactive astrocytes (RAs)-derived GDNF on neuronal death, brain damage, oxidative stress and motor function recovery after photothrombosis (PT)-induced FIS. Under non-ischemic conditions, we found that adult GLAST-GDNF^-/- cKO mice exhibited significant lower numbers of Brdu+, Ki67+ cells, and DCX+ cells in the dentate gyrus (DG) in hippocampus than GDNF floxed (GDNF^f/f ) control (Ctrl) mice, indicating endogenous astrocytic GDNF can promote adult neurogenesis. Under ischemic conditions, GLAST-GDNF^-/- cKO mice had a significant increase in infarct volume, hippocampal damage and FJB+ degenerating neurons after PT as compared with the Ctrl mice. GLAST-GDNF^-/- cKO mice also had lower densities of Brdu+ and Ki67+ cells in the PIR and exhibited larger behavioral deficits than the Ctrl mice. Mechanistically, GDNF deficiency in astrocytes increased oxidative stress through the downregulation of glucose-6-phosphate dehydrogenase (G6PD) in RAs. In summary, our study indicates that RAs-derived endogenous GDNF plays important roles in reducing brain damage and promoting brain recovery after FIS through neural regeneration and suggests that promoting anti-oxidant mechanism in RAs is a potential strategy in stroke therapy.

Systemic Factors Trigger Vasculature Cells to Drive Notch Signaling and Neurogenesis in Neural Stem Cells in the Adult Brain

It is well documented that adult neural stem cells (NSCs) residing in the subventricular zone (SVZ) and the subgranular zone (SGZ) are induced to proliferate and differentiate into new neurons after injury such as stroke and hypoxia. However, the role of injury‐related cues in driving this process and the means by which they communicate with NSCs remains largely unknown. Recently, the coupling of neurogenesis and angiogenesis and the extensive close contact between vascular cells and other niche cells, known as the neurovascular unit (NVU), has attracted interest. Further facilitating communication between blood and NSCs is a permeable blood‐brain‐barrier (BBB) present in most niches, making vascular cells a potential conduit between systemic signals, such as vascular endothelial growth factor (VEGF), and NSCs in the niche, which could play an important role in regulating neurogenesis. We show that the leaky BBB in stem cell niches of the intact and stroke brain can respond to circulating VEGF₁₆₅ to drive induction of the Notch ligand DLL4 (one of the most important cues in angiogenesis) in endothelial cells (ECs), pericytes, and further induce significant proliferation and neurogenesis of stem cells. Stem Cells2019;37:395–406

Targeting Adult Neurogenesis for Poststroke Therapy

Adult neurogenesis mainly occurs at the subventricular zone (SVZ) on the walls of the lateral ventricle and the subgranular zone (SGZ) of the dentate gyrus (DG). However, the majority of newborn neurons undergo programmed cell death (PCD) during the period of proliferation, migration, and integration. Stroke activates neural stem cells (NSCs) in both SVZ and SGZ. This process is regulated by a wide variety of signaling pathways. However, the newborn neurons derived from adult neurogenesis are insufficient for tissue repair and function recovery. Thus, enhancing the endogenous neurogenesis driven by ischemia and promoting the survival of newborn neurons can be promising therapeutic interventions for stroke. Here, we present an overview of the process of adult neurogenesis and the potential of stroke-induced neurogenesis on brain repair.

T155g-Immortalized Kidney Cells Produce Growth Factors and Reduce Sequelae of Cerebral Ischemia

Fetal rat kidney cells produce high levels of glial-derived neurotrophic factor (GDNF) and exert neuroprotective effects when transplanted into the brain in animal models of Parkinson's disease and stroke. The purpose of the present experiment was to produce kidney cell lines that secrete GDNF. Genes encoding two truncated N-terminal fragments of SV40 large T antigen, T155g and T155c, which does not code for small t antigen, were used. T155g was transduced into E17 cultured fetal Sprague-Dawley rat kidney cortex cells using a plasmid vector, and T155c was transduced with a plasmid and a retroviral vector. Sixteen clones were isolated from cultures transfected with the T155g-expressing plasmid. No cell lines were obtained with T155c. Four clones produced GDNF at physiological concentrations ranging from 55 to 93 pg/ml of medium. These four clones were transplanted into the ischemic core or penumbra of rats that had undergone middle cerebral artery occlusion (MCAO). Three of the four clones reduced the volume of infarction and the behavioral abnormalities normally resulting from MCAO. Blocking experiments with antibodies to GDNF and platelet-derived growth factor (PDGF) suggested that these growth factors contributed only minimally to the reduction in infarct volume and behavioral abnormality. These cell lines may be useful for intracerebral transplantation in animal models of brain injury, stroke, or Parkinson's disease.

Brain ischemia downregulates the neuroprotective GDNF-Ret signaling by a calpain-dependent mechanism in cultured hippocampal neurons

The glial cell line-derived neurotrophic factor (GDNF) has an important role in neuronal survival through binding to the GFRα1 (GDNF family receptor alpha-1) receptor and activation of the receptor tyrosine kinase Ret. Transient brain ischemia alters the expression of the GDNF signaling machinery but whether the GDNF receptor proteins are also affected, and the functional consequences, have not been investigated. We found that excitotoxic stimulation of cultured hippocampal neurons leads to a calpain-dependent downregulation of the long isoform of Ret (Ret51), but no changes were observed for Ret9 or GFRα1 under the same conditions. Cleavage of Ret51 by calpains was selectively mediated by activation of the extrasynaptic pool of N-methyl-d-aspartate receptors and leads to the formation of a stable cleavage product. Calpain-mediated cleavage of Ret51 was also observed in hippocampal neurons subjected to transient oxygen and glucose deprivation (OGD), a model of global brain ischemia, as well as in the ischemic region in the cerebral cortex of mice exposed to transient middle cerebral artery occlusion. Although the reduction of Ret51 protein levels decreased the total GDNF-induced receptor activity (as determined by assessing total phospho-Ret51 protein levels) and their downstream signaling activity, the remaining receptors still showed an increase in phosphorylation after incubation of hippocampal neurons with GDNF. Furthermore, GDNF protected hippocampal neurons when present before, during or after OGD, and the effects under the latter conditions were more significant in neurons transfected with human Ret51. These results indicate that the loss of Ret51 in brain ischemia partially impairs the neuroprotective effects of GDNF.

Astrocyte reactivity and reactive astrogliosis: costs and benefits

Astrocytes are the most abundant cells in the central nervous system (CNS) that provide nutrients, recycle neurotransmitters, as well as fulfill a wide range of other homeostasis maintaining functions. During the past two decades, astrocytes emerged also as increasingly important regulators of neuronal functions including the generation of new nerve cells and structural as well as functional synapse remodeling. Reactive gliosis or reactive astrogliosis is a term coined for the morphological and functional changes seen in astroglial cells/astrocytes responding to CNS injury and other neurological diseases. Whereas this defensive reaction of astrocytes is conceivably aimed at handling the acute stress, limiting tissue damage, and restoring homeostasis, it may also inhibit adaptive neural plasticity mechanisms underlying recovery of function. Understanding the multifaceted roles of astrocytes in the healthy and diseased CNS will undoubtedly contribute to the development of treatment strategies that will, in a context-dependent manner and at appropriate time points, modulate reactive astrogliosis to promote brain repair and reduce the neurological impairment.

Neural precursor cells in the ischemic brain - integration, cellular crosstalk, and consequences for stroke recovery

After an ischemic stroke, neural precursor cells (NPCs) proliferate within major germinal niches of the brain. Endogenous NPCs subsequently migrate toward the ischemic lesion where they promote tissue remodeling and neural repair. Unfortunately, this restorative process is generally insufficient and thus unable to support a full recovery of lost neurological functions. Supported by solid experimental and preclinical data, the transplantation of exogenous NPCs has emerged as a potential tool for stroke treatment. Transplanted NPCs are thought to act mainly via trophic and immune modulatory effects, thereby complementing the restorative responses initially executed by the endogenous NPC population. Recent studies have attempted to elucidate how the therapeutic properties of transplanted NPCs vary depending on the route of transplantation. Systemic NPC delivery leads to potent immune modulatory actions, which prevent secondary neuronal degeneration, reduces glial scar formation, diminishes oxidative stress and stabilizes blood–brain barrier integrity. On the contrary, local stem cell delivery allows for the accumulation of large numbers of transplanted NPCs in the brain, thus achieving high levels of locally available tissue trophic factors, which may better induce a strong endogenous NPC proliferative response. Herein we describe the diverse capabilities of exogenous (systemically vs. locally transplanted) NPCs in enhancing the endogenous neurogenic response after stroke, and how the route of transplantation may affect migration, survival, bystander effects and integration of the cellular graft. It is the authors’ claim that understanding these aspects will be of pivotal importance in discerning how transplanted NPCs exert their therapeutic effects in stroke.

Neuroprotection by GDNF in the ischemic brain

The glial cell line-derived neurotrophic factor (GDNF) was first identified as a survival factor for midbrain dopaminergic neurons, but additional studies provided evidences for a role as a trophic factor for other neurons of the central and peripheral nervous systems. GDNF regulates cellular activity through interaction with glycosyl-phosphatidylinositol-anchored cell surface receptors, GDNF family receptor-α1, which might signal through the transmembrane Ret tyrosine receptors or the neural cell adhesion molecule, to promote cell survival, neurite outgrowth, and synaptogenesis. The neuroprotective effect of exogenous GDNF has been shown in different experimental models of focal and global brain ischemia, by local administration of the trophic factor, using viral vectors carrying the GDNF gene and by transplantation of GDNF-expressing cells. These different strategies and the mechanisms contributing to neuroprotection by GDNF are discussed in this review. Importantly, neuroprotection by GDNF was observed even when administered after the ischemic injury.

Astrocytic endogenous glial cell derived neurotrophic factor production is enhanced by bone marrow stromal cell transplantation in the ischemic boundary zone after stroke in adult rats

Bone marrow stromal cells (BMSCs) facilitate functional recovery in rats after focal ischemic attack. Growing evidence suggests that the secretion of various bioactive factors underlies BMSCs' beneficial effects. This study investigates the expression of glial cell derived neurotrophic factor (GDNF) in the ischemic hemisphere with or without BMSC administration. Adult male Wistar rats were subjected to 2 h of middle cerebral artery occlusion followed by an injection of 3 x 10(6) BMSCs (n = 11) or phosphate-buffered saline (n = 10) into the tail vein 24 h later. Animals were sacrificed seven days later. Single and double immunohistochemical staining was performed to measure GDNF, Ki67, doublecortin, and glial fibrillary acidic protein expression as well as the number of apoptotic cells along the ischemic boundary zone (IBZ) and/or in the subventricular zone (SVZ). BMSC treatment significantly increased GDNF expression and decreased the number of apoptotic cells in the IBZ (P < 0.05). GDNF expression was colocalized with GFAP. Meanwhile, BMSCs increased the number of Ki-67 positive cells and the density of DCX positive migrating neuroblasts (P < 0.05). GDNF expression was significantly increased in single astrocytes collected from animals treated with BMSCs, and in astrocytes cocultured with BMSCs after OGD (P < 0.05). Our data suggest that BMSCs increase GDNF levels in the ischemic hemisphere; the major source of GDNF protein is reactive astrocytes. We propose that the increase of GDNF in response to BMSC administration creates a hospitable environment for local cellular repair as well as for migrating neuroblasts from the SVZ, and thus contributes to the functional improvement.

Adenosine induces expression of glial cell line-derived neurotrophic factor (GDNF) in primary rat astrocytes

Adenosine, which accumulates rapidly during ischemia due to the breakdown of ATP, has beneficial effects in many tissues. We examined whether adenosine induces the production of glial cell line-derived neurotrophic factor (GDNF) in cultured astrocytes. We evaluated GDNF mRNA expression and GDNF production in astrocytes cultured with adenosine and the adenosine selective receptor agonists 5-(N-ethylcarboxamido) adenosine (NECA), N(6)-cyclopentyladenosine (CPA) and 2-p-(2-carboxyethyl) phenethylamino-5'-N-ethylcarboxamindo-adenosine hydrochloride (CGS 21680). Moreover, we examined the possibility that the expression of GDNF is regulated differently in cultured astrocytes from the stroke-prone spontaneously hypertensive rat (SHRSP) than in those from Wistar Kyoto rats (WKY). In this study, we confirmed that adenosine and the selective A(2B) adenosine receptor agonist NECA induced the expression of GDNF in cultured astrocytes. The A(2B) receptor antagonist alloxazine was able to inhibit the increase in extracellular GDNF produced by adenosine. Furthermore, the amounts of GDNF produced were significantly reduced in astrocytes of the adenosine-treated SHRSP compared with those of WKY. These results indicate that adenosine induces the expression of GDNF, and adenosine A(2B) receptors participate in the regulation of GDNF levels in astrocytes. This expression was attenuated in astrocytes of SHRSP compared with those of WKY.

Regulators of adult neurogenesis in the healthy and diseased brain

1. In recent decades evidence has accumulated demonstrating the birth and functional integration of new neurons in specific regions of the adult mammalian brain, including the dentate gyrus of the hippocampus and the subventricular zone. 2. Studies in a variety of models have revealed genetic, environmental and pharmacological factors that regulate adult neurogenesis. The present review examines some of the molecular and cellular mechanisms that could be mediating these regulatory effects in both the normal and dysfunctional brain. 3. The dysregulation of adult neurogenesis may contribute to the pathogenesis of neurodegenerative disorders, such as Huntington's, Alzheimer's and Parkinson's disease, as well as psychiatric disorders such as depression. Recent evidence supports this idea and, furthermore, also indicates that factors promoting neurogenesis can modify the onset and progression of specific brain disorders, including Huntington's disease and depression.

Tissue distribution of Ret, GFRalpha-1, GFRalpha-2 and GFRalpha-3 receptors in the human brainstem at fetal, neonatal and adult age

Occurrence and localization of receptor components of the glial cell line-derived neurotrophic factor (GDNF) family ligands, the Ret receptor tyrosine kinase and the GDNF family receptor (GFR) alpha-1 to -3, were examined by immunohistochemistry in the normal human brainstem at fetal, neonatal, and adult age. Immunoreactive elements were detectable at all examined ages with uneven distribution and consistent pattern for each receptor. As a rule, the GFRalpha-1 and GFRalpha-2 antisera produced the most abundant and diffuse tissue labelling. Immunoreactive perikarya were observed within sensory and motor nuclei of cranial nerves, dorsal column nuclei, olivary nuclear complex, reticular formation, pontine nuclei, locus caeruleus, raphe nuclei, substantia nigra, and quadrigeminal plate. Nerve fibers occurred within gracile and cuneate fasciculi, trigeminal spinal tract and nucleus, facial, trigeminal, vestibular and oculomotor nerves, solitary tract, medial longitudinal fasciculus, medial lemniscus, and inferior and superior cerebellar peduncles. Occasionally, glial cells were stained. Age changes were appreciable in the distribution pattern of each receptor. On the whole, in the grey matter, labelled perikarya were more frequently observed in pre- and perinatal than in adult specimens; on the other hand, in discrete regions, nerve fibers and terminals were abundant and showed a plexiform arrangement only in adult tissue; finally, distinct fiber systems in the white matter were immunolabelled only at pre- and perinatal ages. The results obtained suggest the involvement of Ret and GFRalpha receptors signalling in processes subserving both the organization of discrete brainstem neuronal systems during development and their functional activity and maintenance in adult life.

Gene Transfer of Hepatocyte Growth Factor Gene Improves Learning and Memory in the Chronic Stage of Cerebral Infarction

There is no specific treatment to improve the functional recovery in the chronic stage of ischemic stroke. To provide the new therapeutic options, we examined the effect of overexpression of hepatocyte growth factor (HGF) in the chronic stage of cerebral infarction by transferring the HGF gene into the brain using hemagglutinating virus of Japan envelope vector. Sixty rats were exposed to permanent middle cerebral artery occlusion (day 1). Based on the sensorimotor deficits at day 7, the rats were divided equally into control vector or HGF-treated rats. At day 56, rats transfected with the HGF gene showed a significant recovery of learning and memory in Morris water maze tests (control vector 50±4 s; HGF 33±5 s; P <0.05) and passive avoidance task (control vector 132.4±37.5 s; HGF 214.8±26.5 s; P <0.05). Although the total volume of cerebral infarction was not related to the outcome, immunohistochemical analysis for Cdc42 and synaptophysin in the peri-infarct region revealed that HGF enhanced the neurite extension and increased synapses. Immunohistochemistry for glial fibriary acidic protein revealed that the formation of glial scar was also prevented by HGF gene treatment. Additionally, the number of the arteries was increased in the HGF group at day 56. These data demonstrated that HGF has a pivotal role for the functional recovery after cerebral infarction through neuritogenesis, improved microcirculation, and the prevention of gliosis. Our results also provide evidence for the feasibility of gene therapy in the chronic stage of cerebral infarction.

Adult neurogenesis and the ischemic forebrain

The recent identification of endogenous neural stem cells and persistent neuronal production in the adult brain suggests a previously unrecognized capacity for self-repair after brain injury. Neurogenesis not only continues in discrete regions of the adult mammalian brain, but new evidence also suggests that neural progenitors form new neurons that integrate into existing circuitry after certain forms of brain injury in the adult. Experimental stroke in adult rodents and primates increases neurogenesis in the persistent forebrain subventricular and hippocampal dentate gyrus germinative zones. Of greater relevance for regenerative potential, ischemic insults stimulate endogenous neural progenitors to migrate to areas of damage and form neurons in otherwise dormant forebrain regions, such as the neostriatum and hippocampal pyramidal cell layer, of the mature brain. This review summarizes the current understanding of adult neurogenesis and its regulation in vivo, and describes evidence for stroke-induced neurogenesis and neuronal replacement in the adult. Current strategies used to modify endogenous neurogenesis after ischemic brain injury also will be discussed, as well as future research directions with potential for achieving regeneration after stroke and other brain insults.

Ret, GFRalpha‐1, GFRalpha‐2 and GFRalpha‐3 receptors in the human hippocampus and fascia dentata

The immunohistochemical occurrence and localization of the receptor components of the glial cell line-derived neurotrophic factor (GDNF) family ligands, the Ret receptor tyrosine kinase and GDNF family receptor (GFR) alpha-1 to -3, is described in the human post-mortem hippocampal formation at pre- and full-term newborn, and adult age. Two different antibodies for each of the four-receptor molecules were used. Western blot analysis indicates that the availability of GFRalpha receptor proteins may vary with age and post-mortem delay. The immunohistochemical detectability of GFRalpha-1, GFRalpha-2, GFRalpha-3 and Ret receptor molecules is shown in the rat up to 72 h post-mortem. In the human specimens, labelled neuronal perikarya were detectable for each receptor protein at all examined ages, with prevalent localization in the pyramidal layer of the Ammon's horn and hilus and granular layer of the fascia dentata. In the adult subjects, abundant punctate-like structures were also present. Labelled glial elements were identifiable. Comparison of the pattern of immunoreactive elements among young and adult subjects suggests that the intracellular distribution of the GDNF family ligands may vary between pre- and perinatal life and adult age. The results obtained suggest the involvement of the Ret and GFRalpha receptors signalling in processes subserving both the organization of this cortical region during development and the functional activity and maintenance of the mature hippocampal neurons.

Neuroprotective role of astrocytes in cerebral ischemia: focus on ischemic preconditioning

Following focal cerebral ischemia ("stroke") a complex and dynamic interaction of vascular cells, glial cells, and neurons determines the extent of the ensuing lesion. Traditionally, the focus has been on mechanisms of damage, while recently it has become clear that endogenous mechanisms of protection are equally important for the final outcome. Glial cells, in particular astrocytes, have always been viewed as supporters of neuronal function. Only recently a very active role for glial cells has been emerging in physiology and pathophysiology. Not surprisingly, then, specific protective pathways have been identified by which these cells can protect or even help to regenerate brain tissue after acute insults. However, as exemplified by the existence of the glial scar, which forms around lesioned brain tissue, is composed mainly of astrocytes and plays a key role in regeneration failure, it is an oversimplification to assign merely protective functions to astrocytes. The present review will discuss the role of astrocytes in ischemic brain injury with a focus on neuroprotection in general. In this context we will consider particularly the phenomenon of "ischemic tolerance," which is an experimental paradigm helpful in discriminating destructive from protective mechanisms after cerebral ischemia.

Neuregulin-1 is neuroprotective and attenuates inflammatory responses induced by ischemic stroke

Recent work from our laboratory demonstrated that the expression neuregulin-1 in neurons was induced in the ischemic penumbra by focal stroke in the rat. Here, we show that a single intravascular injection of neuregulin-1beta (approximately 2.5 ng/kg) reduced cortical infarct volume by >98% when given immediately before middle cereral artery occlusion. Subcortical infarct volume was reduced by approximately 40%. Analysis of DNA fragmentation in brain tissues indicated that neuregulin-1 blocked apoptosis in cortical neurons in the penumbra. Neuregulin-1 prevented macrophage/microglial infiltration and astrocytic activation following focal ischemia. The neuroprotective effect of neuregulin-1 was also associated with a suppression of interleukin-1beta mRNA levels. These data suggest that neuregulin-1 protects neurons from delayed, ischemia-induced apoptotic cell death in the cortex by inhibiting pro-inflammatory responses. Neuregulins represent a novel, potent neuroprotective strategy that has potential therapeutic value in treating individuals after acute ischemic stroke.

Glial cell line-derived neurotrophic factor receptor GFRα1 is expressed in the rat striatum during postnatal development

Dopamine neurons of the substantia nigra (SN) undergo a natural cell death event which is biphasic, with peaks at postnatal days (PNDs) 2 and 14. There is growing evidence that GDNF functions as a striatal target-derived neurotrophic factor to regulate the first phase. It has been unknown whether the GDNF receptor, GFRalpha1, may play a role in regulating either phase. To evaluate a possible role for GFRalpha1 we have examined its expression throughout postnatal development in the SN and particularly in the striatum, where its expression has been uncertain. GFRalpha1 mRNA is highly expressed in SN, as previously shown, with highest levels at PND14-28. We find that it is also expressed in striatum with a similar time course, but with a more discrete period of maximal expression between PND10 and PND14. The cellular basis of this maximum of expression is an increased number of GFRalpha1 mRNA-positive medium-sized neurons evenly distributed within the striatum. Immunostaining reveals GFRalpha1 protein-positive neurons with a similar morphology and distribution. We conclude that GFRalpha1 is expressed in striatum maximally late in postnatal development. In this location it may act in trans to influence the viability and development of nigral dopamine neurons.

Elevated GDNF levels following viral vector-mediated gene transfer can increase neuronal death after stroke in rats

Previous studies have indicated that administration of glial cell line-derived neurotrophic factor (GDNF) counteracts neuronal death after stroke. However, in these studies damage was evaluated at most a few days after the insult. Here, we have explored the long-term consequences of two routes of GDNF delivery to the rat striatum prior to stroke induced by 30 min of middle cerebral artery occlusion (MCAO): striatal transduction with a recombinant lentiviral vector or transduction of the substantia nigra with a recombinant adeno-associated viral vector and subsequent anterograde transport of GDNF to striatum. Despite high GDNF levels, stereological quantification of striatal neuron numbers revealed no protection at 5 or 8 weeks after MCAO. In fact, anterograde GDNF delivery exacerbated neuronal loss. Moreover, supply of GDNF did not alleviate the striatum-related behavioral deficits. Thus, we demonstrate that the actions of GDNF after stroke are more complex than previously believed and that high levels of this factor, which are neuroprotective in models of Parkinson's disease, can increase ischemic damage. Our findings also underscore the need for quantitative assessment of long-term neuronal survival and behavioral changes to evaluate the therapeutic potential of factors such as GDNF.

Effect of 6-hydroxydopamine on striatal GDNF and nigral GFRα1 and RET mRNAs in the adult rat

Exogenous GDNF as well as vectors containing the gene for this trophic factor has been shown to be neuroprotective in animal models of Parkinson's disease. We therefore investigated whether changes in striatal GDNF protein and nigral mRNA levels of its co-receptors GFRalpha1 and RET occur in response to lesions of dopamine (DA) neurons and examined the temporal profile of these changes as they relate to the loss of dopaminergic markers. Rats were lesioned with 6-hydroxydopamine and sacrificed 3 h to 60 days post-infusion. DA tissue levels in the striatum and tyrosine hydroxylase immunoreactivity in the substantia nigra (SN) and ventral tegmental area (VTA) were used to determine the size of the lesions. GDNF protein was measured in the striatum using radioimmunocytochemistry. In situ hybridization was used to determine alterations in the mRNAs of RET and GFRalpha1 in the SN and VTA. We observed no persistent changes in GDNF protein in the striatum in response to 6-hydroxydopamine over the 60-day observation period, suggesting that compensatory changes in this trophic factor do not occur in response to injury. Dramatic decreases in RET and GFRalpha1 were observed in both SN and VTA that were generally correlated with the loss of TH protein and striatal DA content, strongly suggesting that these receptors are located on DA neurons and that the protective effect of GDNF reflects a direct action of the trophic factor on these neurons.

Functional improvement by electro-acupuncture after transient middle cerebral artery occlusion in rats

Functional recovery by the application of electro-acupuncture (EA) on different acupoints was investigated using a transient middle cerebral artery occlusion (MCAO) model in rat. Acupoints were Baihui (D20) plus Renzhong (D26) (MCAO + D group), and Hanyan (G4), Xuanlu (G5), Xuanli (G6), plus Qubin (G7) (MCAP + G group). Animals with EA treatment showed significant functional improvements from 12 days after the reperfusion against those without EA treatment. Among EA treated groups, MCAO + G showed a more significant recovery than MCAO + D. Infarct volume revealed the significant reduction in the EA treated groups especially in MCAO + G at 30 days. Immunohistochemical study showed a remarkable induction of vascular endothelial growth factor (VEGF) in astrocytes of the peri-infarct area at 30 days, more in EA treated groups than in groups treated with MCAO alone. These results suggest that the acupoints applied in this study are effective for the functional recovery, and an enhanced expression of VEGF may play a certain role in recovery process after stroke.

GDNF elicits distinct immediate-early gene responses in cultured cortical and mesencephalic neurons

Glial cell line-derived neurotrophic factor (GDNF) has been recognized as a survival-promoting molecule for several neuronal populations in the central nervous system (CNS), including midbrain dopaminergic neurons and cortical neurons. Whereas it is well established that GDNF affects dopaminergic cell survival through a receptor complex composed of the tyrosine kinase, Ret, and the glycosylphosphatidylinositol (GPI)-anchored protein, GFRalpha-1, c-Ret is basically undetectable in cortical neurons. In the present study, we have compared GDNF signaling in cortical and mesencephalic neurons by using GDNF-induced expression of the immediate-early genes, c-fos and mgif, as a readout. We found that stimulation of embryonic day (E)17 cortical cultures for 3 hr with GDNF at concentrations ranging from 10 to 80 ng/ml did not result in detectable c-fos expression. In contrast, c-fos expression occurred in E14 mesencephalic cultures exposed to both low and high GDNF concentrations. Vice versa, cortical neurons responded to high GDNF concentrations (80 ng/ml) with an increase in mRNA encoding mGIF, while a similar mGIF response was absent in mesencephalic cultures. Cleavage of GFRalpha receptor subunits from their GPI anchors by phosphatidylinositol-specific phospholipase C (PIPLC) abolished GDNF-induced c-fos expression in mesencephalic cultures, but did not interfere with the effects of GDNF on cortical mgif expression. Together, these findings point to distinct differences in the GDNF recognition and/or signal transduction machinery of cortical and mesencephalic neurons.

Potentiation of Akt and suppression of caspase-9 activations by electroacupuncture after transient middle cerebral artery occlusion in rats

Electroacupuncture (EA) is an effective curative method for diseases including cerebral ischemia. In the current study, we investigated the effects of EA treatment on the activations of survival Akt and proapoptotic caspase-9 after 90 min of transient middle cerebral artery occlusion (tMCAO) in rat. Immunoreactivity of phospho-Akt (p-Akt) increased in the ipsilateral hemisphere after tMCAO with a peak at 8 h, and EA enhanced the Akt expression both in the number and the staining strength mainly in the ischemic penumbra (IP) at 8 and 24 h. Cleaved caspase-9 was strongly induced at 8 h in IP, which was suppressed with EA. The number of terminal deoxynucleotidyl transferase-mediated uridine 5' triphosphate-biotin nick end labelling positive cells reduced at 24 h in the cerebral cortex. These results suggest that EA potentiated the Akt and suppressed the caspase-9 activations, and may have a potential to reduce the number of neuronal cells undergoing apoptotic cell death.

Stroke induces widespread changes of gene expression for glial cell line-derived neurotrophic factor family receptors in the adult rat brain

Gene expression for glial cell line-derived neurotrophic factor (GDNF) family ligands and receptors was analyzed with in situ hybridization after two focal ischemic insults of different severities. Focal ischemia was induced in rats by either 30 min or 2 h of middle cerebral artery occlusion (MCAO), causing damage to the striatum only, or involving also the parietal cortex, respectively. We found modest, transient elevation of GDNF mRNA in the dentate granule cell layer. In addition, the number of GDNF mRNA-expressing cells increased in the cortex and striatum after 2 h or 30 min of MCAO, respectively. No changes of neurturin or persephin mRNA expression were detected. Both c-Ret and GFRalpha1 mRNA levels were markedly increased in the ipsilateral cortex outside the ischemic lesion at 6-24 h after the 2-h insult, whereas GFRalpha2 expression was decreased in cortical areas both within and outside the lesion. Similar increases of c-Ret and GFRalpha1 mRNA levels were detected in the striatum, and to a lesser extent, in the cortex following 30 min of MCAO. The 2-h insult also gave rise to transient increases of c-Ret and GFRalpha1 mRNA in hippocampal subregions. Thirty minutes and 2 h of MCAO lead to elevated c-Ret, and GFRalpha1 or GFRalpha2 mRNA expression, respectively, in the ipsilateral ventroposterolateral thalamic nucleus. Both insults induced increased levels of GFRalpha1 mRNA in the subventricular zone of the lateral ventricle. Our data indicate major changes of GDNF family signaling in the forebrain, regulated mainly through altered receptor levels, in the post-ischemic phase. These changes could enhance neuroprotective and neuroregenerative responses both to endogenous and exogenous GDNF ligands.

Differential regulation of glial cell line-derived neurotrophic factor (GDNF) mRNA expression during hypoxia and reoxygenation in astrocytes isolated from stroke-prone spontaneously hypertensive rats

Glial cell line-derived neurotrophic factor (GDNF) plays several important roles in the survival and recovery of mature neurons during ischemia. We examined the possibility that the expression of GDNF mRNA and the release of GDNF protein are regulated differentially in cultured astrocytes from the stroke-prone spontaneously hypertensive rat (SHRSP) compared with those from Wistar Kyoto rats (WKY) during hypoxia and reoxygenation (H/R) and after exposure to glutamate and hydrogen peroxide (H(2)O(2)). The mRNA expression was quantitated by reverse transcription-polymerase chain reaction (RT-PCR) based on the fluorescent TaqMan methodology. A new instrument capable of measuring fluorescence in real-time was used to quantify gene amplification in astrocytes. GDNF protein was investigated by enzyme-linked immunosorbent assay (ELISA). GDNF mRNA expression and GDNF protein release at normoxia were greater in SHRSP than in WKY astrocytes. During H/R, however, the mRNA expression and protein release tended to be reduced in SHRSP compared with WKY. Glutamate and H(2)O(2) induced the expression of GDNF mRNA and the release of GDNF protein in both WKY and SHRSP in a dose-dependent manner. Levels of GDNF mRNA and protein in SHRSP were significantly lower than in WKY. These findings indicate that GDNF production in SHRSP astrocytes was low in response to H/R, glutamate, and H(2)O(2), compared with that observed in WKY. We conclude that the attenuated production of GDNF in astrocytes is involved in neuronal vulnerability in SHRSP during H/R, as GDNF production, which is stimulated by glutamate and H(2)O(2), is closely related to the protective effect against H/R-mediated neurotoxicity.

Expression of glial cell line-derived neurotrophic factor (GDNF) in the developing human fetal brain

GDNF expression was examined immunocytochemically in developing human fetal brains obtained from aborted fetuses ranging from 7 to 39 weeks in gestational age. At 7-8 weeks, strong immunoreactivity was noted within radial glial processes, glia limitans and choroid plexus of the telencephalic vesicle. By 10 weeks, ependymal cells, primitive matrix cells and early developing cortical plate neurons showed positive staining. By 15-16 weeks, migrating neurons in the subventricular and intermediate zones and in the cortical plate were strongly positive for GDNF. The glia limitans of the cerebral cortex and subependymal astrocytes remained positive at this time. As fetal age increased, GDNF expression shifted to neurons and glial cells in the deeper structures of the brain. The most prominent GDNF staining was observed in the cytoplasm and dendrites of Purkinje cells of the cerebellum by 25 weeks and thereafter. Pyramidal neurons of the CA1 region and granule cells of the dentate fascia of the hippocampus, neurons of the entorhinal cortex, and scattered neurons within the brain stem, medulla and spinal cord all showed strong GDNF staining by 25-35 weeks. Widespread GDNF expression in neuronal and non-neuronal cells with distinct developmental shifts suggests that GDNF may play a critical role in the survival, differentiation and maintenance of neurons at different stages of development in the developing human fetal brain.

Impaired water maze learning performance without altered dopaminergic function in mice heterozygous for the GDNF mutation

Exogenous glial cell line-derived neurotrophic factor (GDNF) exhibits potent survival-promoting effects on dopaminergic neurons of the nigrostriatal pathway that is implicated in Parkinson's disease and also protects neurons in forebrain ischemia of animal models. However, a role for endogenous GDNF in brain function has not been established. Although mice homozygous for a targeted deletion of the GDNF gene have been generated, these mice die within hours of birth because of deficits in kidney morphogenesis, and, thus, the effect of the absence of GDNF on brain function could not be studied. Herein, we sought to determine whether adult mice, heterozygous for a GDNF mutation on two different genetic backgrounds, demonstrate alterations in the nigrostriatal dopaminergic system or in cognitive function. While both neurochemical and behavioural measures suggested that reduction of GDNF gene expression in the mutant mice does not alter the nigrostriatal dopaminergic system, it led to a significant and selective impairment of performance in the spatial version of the Morris water maze. A standard panel of blood chemistry tests and basic pathological analyses did not reveal alterations in the mutants that could account for the observed performance deficit. These results suggest that endogenous GDNF may not be critical for the development and functioning of the nigrostriatal dopaminergic system but it plays an important role in cognitive abilities.

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.

Trophic factor secreting kidney cell lines: in vitro characterization and functional effects following transplantation in ischemic rats

Several kidney cell lines were investigated for their ability to produce glial cell line-derived neurotrophic factor (GDNF). Cell line-conditioned medium was analyzed using ELISA and two cell lines were identified which produce GDNF in physiologically active concentrations. ELISA analyses revealed that conditioned medium from these two cell lines also contained PDGF, bFGF, TGFbeta1 and TGFbeta2. Both of these cell lines were then transplanted into the striatal penumbra of rats, 1 h following middle cerebral artery occlusion. Behavioral testing revealed that both cell lines reduced the deficit associated with cerebral ischemia and reduced the infarct volume relative to controls. Reduction of infarct volume was likely achieved by the action of GDNF and/or other growth factors produced by the cells.

Differential expression of GDNF, BDNF, and NT-3 in the aging nigrostriatal system following a neurotoxic lesion

Protein levels for brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and glial cell line-derived neurotrophic factor (GDNF) were measured in the striatum and ventral midbrain of young and aged Brown Norway/F344 F1 (F344BNF(1)) hybrid rats following a unilateral 6-hydroxydopamine (6-OHDA) lesion of the nigrostriatal pathway. At 2 weeks post-lesion, protein levels of BDNF and GDNF were higher in the denervated striatum when compared to the intact striatum for young (4-5 months old) but not old (31-33 months old) rats. Interestingly, in old rats BDNF protein in the denervated striatum was significantly lower than that measured in the intact striatum. At the same time point BDNF protein levels in the ventral midbrain were higher on the lesioned versus intact side for both young and old rats while no significant side differences were detected for GDNF protein in the ventral midbrain of young or old rats. No significant differences in NT-3 protein levels were detected between the lesioned and intact sides for striatal or ventral midbrain regions in either young or old brain. While no significant age effects were detected for BDNF or NT-3 protein, young rats showed higher GDNF protein levels in both the striatum (lesioned or intact) and ventral midbrain (lesioned or intact) than old rats. These data show that two endogenous neurotrophic factors, BDNF and GDNF, are differentially affected by a 6-OHDA lesion in the aging nigrostriatal system with young brain showing a significant compensatory increase of these two factors in the denervated striatum while no compensatory increase is observed in aged brain.