Platelet-derived growth factor B-chain-like immunoreactivity in the developing and adult rat brain

Cellular Localization and Distribution of TGF-β1, GDNF and PDGF-BB in the Adult Primate Central Nervous System

The available data on the localization of transforming growth factor beta1 (TGF-β1), glial cell line-derived neurotrophic factor (GDNF), and platelet-derived growth factor-BB (PDGF-BB) in the adult primate and human central nervous system (CNS) are limited and lack comprehensive and systematic information. This study aimed to investigate the cellular localization and distribution of TGF-β1, GDNF, and PDGF-BB in the CNS of adult rhesus macaque (Macaca mulatta). Seven adult rhesus macaques were included in the study. The protein levels of TGF-β1, PDGF-BB, and GDNF in the cerebral cortex, cerebellum, hippocampus, and spinal cord were analyzed by western blotting. The expression and location of TGF-β1, PDGF-BB, and GDNF in the brain and spinal cord was examined by immunohistochemistry and immunofluorescence staining, respectively. The mRNA expression of TGF-β1, PDGF-BB, and GDNF was detected by in situ hybridization. The molecular weight of TGF-β1, PDGF-BB, and GDNF in the homogenate of spinal cord was 25 KDa, 30 KDa, and 34 KDa, respectively. Immunolabeling revealed GDNF was ubiquitously distributed in the cerebral cortex, hippocampal formation, basal nuclei, thalamus, hypothalamus, brainstem, cerebellum, and spinal cord. TGF-β1 was least distributed and found only in the medulla oblongata and spinal cord, and PDGF-BB expression was also limited and present only in the brainstem and spinal cord. Besides, TGF-β1, PDGF-BB, and GDNF were localized in the astrocytes and microglia of spinal cord and hippocampus, and their expression was mainly found in the cytoplasm and primary dendrites. The mRNA of TGF-β1, PDGF-BB, and GDNF was localized to neuronal subpopulations in the spinal cord and cerebellum. These findings suggest that TGF-β1, GDNF and PDGF-BB may be associated with neuronal survival, neural regeneration and functional recovery in the CNS of adult rhesus macaques, providing the potential insights into the development or refinement of therapies based on these factors.

NG2 Glia: Novel Roles beyond Re-/Myelination

Neuron-glia antigen 2-expressing glial cells (NG2 glia) serve as oligodendrocyte progenitors during development and adulthood. However, recent studies have shown that these cells represent not only a transitional stage along the oligodendroglial lineage, but also constitute a specific cell type endowed with typical properties and functions. Namely, NG2 glia (or subsets of NG2 glia) establish physical and functional interactions with neurons and other central nervous system (CNS) cell types, that allow them to constantly monitor the surrounding neuropil. In addition to operating as sensors, NG2 glia have features that are expected for active modulators of neuronal activity, including the expression and release of a battery of neuromodulatory and neuroprotective factors. Consistently, cell ablation strategies targeting NG2 glia demonstrate that, beyond their role in myelination, these cells contribute to CNS homeostasis and development. In this review, we summarize and discuss the advancements achieved over recent years toward the understanding of such functions, and propose novel approaches for further investigations aimed at elucidating the multifaceted roles of NG2 glia.

Oligomer-prone E57K-mutant alpha-synuclein exacerbates integration deficit of adult hippocampal newborn neurons in transgenic mice

In the adult mammalian hippocampus, new neurons are constantly added to the dentate gyrus. Adult neurogenesis is impaired in several neurodegenerative mouse models including α-synuclein (a-syn) transgenic mice. Among different a-syn species, a-syn oligomers were reported to be the most toxic species for neurons. Here, we studied the impact of wild-type vs. oligomer-prone a-syn on neurogenesis. We compared the wild-type a-syn transgenic mouse model (Thy1-WTS) to its equivalent transgenic for oligomer-prone E57K-mutant a-syn (Thy1-E57K). Transgenic a-syn was highly expressed within the hippocampus of both models, but was not present within adult neural stem cells and neuroblasts. Proliferation and survival of newly generated neurons were unchanged in both transgenic models. Thy1-WTS showed a minor integration deficit regarding mushroom spine density of newborn neurons, whereas Thy1-E57K exhibited a severe reduction of all spines. We conclude that cell-extrinsic a-syn impairs mushroom spine formation of adult newborn neurons and that oligomer-prone a-syn exacerbates this integration deficit. Moreover, our data suggest that a-syn reduces the survival of newborn neurons by a cell-intrinsic mechanism during the early neuroblast development. The finding of increased spine pathology in Thy1-E57K is a new pathogenic function of oligomeric a-syn and precedes overt neurodegeneration. Thus, it may constitute a readout for therapeutic approaches.

Neural Stem Cells, Neural Progenitors, and Neurotrophic Factors

Neural stem cells (NSCs) have been proposed as a promising cellular source for the treatment of diseases in nervous systems. NSCs can self-renew and generate major cell types of the mammalian central nervous system throughout adulthood. NSCs exist not only in the embryo, but also in the adult brain neurogenic region: the subventricular zone (SVZ) of the lateral ventricle. Embryonic stem (ES) cells acquire NSC identity with a default mechanism. Under the regulations of leukemia inhibitory factor (LIF) and fibroblast growth factors, the NSCs then become neural progenitors. Neurotrophic and differentiation factors that regulate gene expression for controlling neural cell fate and function determine the differentiation of neural progenitors in the developing mammalian brain. For clinical application of NSCs in neurodegenerative disorders and damaged neurons, there are several critical problems that remain to be resolved: 1) how to obtain enough NSCs from reliable sources for autologous transplantation; 2) how to regulate neural plasticity of different adult stem cells; 3) how to control differentiation of NSCs in the adult nervous system. In order to understand the mechanisms that control NSC differentiation and behavior, we review the ontogeny of NSCs and other stem cell plasticity of neuronal differentiation. The role of NSCs and their regulation by neurotrophic factors in CNS development are also reviewed.

A review of platelet derived growth factor playing pivotal role in bone regeneration

This article is focused on the literature review and study of recent advances in the field of bone grafting, which involves platelet-derived growth factor (PDGF) as one of the facilitating factors in bone regeneration. This article includes a description of the mechanism of PDGF for use in surgeries where bone grafting is required, which promotes future application of PDGF for faster bone regeneration or inhibition of bone growth if required as in osteosarcoma. The important specific activities of PDGF include mitogenesis (increase in the cell populations of healing cells), angiogenesis (endothelial mitoses into functioning capillaries), and macrophage activation (debridement of the wound site and a second phase source of growth factors for continued repair and bone regeneration). Thus PDGF can be utilized in wound with bone defect to conceal the wound with repair of bony defect.

Platelet-derived growth factor receptor-β antagonism restores morphine analgesic potency against neuropathic pain

Background

Chronic, intractable pain is a problem of pandemic proportions. Pain caused by nerve injuries (neuropathic pain) is extremely difficult to treat. For centuries, opiates such as morphine have been the first-line treatment for severe chronic pain. However, opiates are often ineffective against neuropathic pain, leaving few options for suffering patients. We previously demonstrated that platelet-derived growth factor- β (PDGFR-β) inhibition completely eliminated morphine tolerance. In these studies, we determined whether PDGFR-β inhibition could improve the effectiveness of morphine for neuropathic pain treatment.

Results and Findings

Spinal nerve ligation was performed in male Sprague-Dawley rats. The clinically used PDGFR antagonist imatinib did not relieve mechanical pain in a nerve injury model as determined by Von Frey assay. Surprisingly, combining imatinib with a previously ineffective dose of morphine led to complete pain relief. Scavenging released PDGF-B also markedly augmented the analgesic effect of morphine.

Conclusions

These findings suggest the novel hypothesis that PDGF-B released by injured nerves renders animals resistant to morphine, implying that PDGFR-β inhibition could potentially eliminate the tremendous suffering caused by neuropathic pain.

Changes in Otx2 and parvalbumin immunoreactivity in the superior colliculus in the platelet-derived growth factor receptor-β knockout mice

The superior colliculus (SC), a relay nucleus in the subcortical visual pathways, is implicated in socioemotional behaviors. Homeoprotein Otx2 and β subunit of receptors of platelet-derived growth factor (PDGFR-β) have been suggested to play an important role in development of the visual system and development and maturation of GABAergic neurons. Although PDGFR-β-knockout (KO) mice displayed socio-emotional deficits associated with parvalbumin (PV-)immunoreactive (IR) neurons, their anatomical bases in the SC were unknown. In the present study, Otx2 and PV-immunolabeling in the adult mouse SC were investigated in the PDGFR-β KO mice. Although there were no differences in distribution patterns of Otx2 and PV-IR cells between the wild type and PDGFR-β KO mice, the mean numbers of both of the Otx2- and PV-IR cells were significantly reduced in the PDGFR-β KO mice. Furthermore, average diameters of Otx2- and PV-IR cells were significantly reduced in the PDGFR-β KO mice. These findings suggest that PDGFR-β plays a critical role in the functional development of the SC through its effects on Otx2- and PV-IR cells, provided specific roles of Otx2 protein and PV-IR cells in the development of SC neurons and visual information processing, respectively.

The roles of PDGF in development and during neurogenesis in the normal and diseased nervous system

The four platelet-derived growth factor (PDGF) ligands and PDGF receptors (PDGFRs), α and β (PDGFRA, PDGFRB), are essential proteins that are expressed during embryonic and mature nervous systems, i.e., in neural progenitors, neurons, astrocytes, oligodendrocytes, and vascular cells. PDGF exerts essential roles from the gastrulation period to adult neuronal maintenance by contributing to the regulation of development of preplacodal progenitors, placodal ectoderm, and neural crest cells to adult neural progenitors, in coordinating with other factors. In adulthood, PDGF plays critical roles for maintenance of many specific cell types in the nervous system together with vascular cells through controlling the blood brain barrier homeostasis. At injury or various stresses, PDGF modulates neuronal excitability through adjusting various ion channels, and affecting synaptic plasticity and function. Furthermore, PDGF stimulates survival signals, majorly PI3-K/Akt pathway but also other ways, rescuing cells from apoptosis. Studies imply an involvement of PDGF in dendrite spine morphology, being critical for memory in the developing brain. Recent studies suggest association of PDGF genes with neuropsychiatric disorders. In this review, we will describe the roles of PDGF in the nervous system, from the discovery to recent findings, in order to understand the broad spectrum of PDGF in the nervous system. Recent development of pharmacological and replacement therapies targeting the PDGF system is discussed.

Time course and progression of wild type α-synuclein accumulation in a transgenic mouse model

Background

Progressive accumulation of α-synuclein (α-Syn) protein in different brain regions is a hallmark of synucleinopathic diseases, such as Parkinson’s disease, dementia with Lewy bodies and multiple system atrophy. α-Syn transgenic mouse models have been developed to investigate the effects of α-Syn accumulation on behavioral deficits and neuropathology. However, the onset and progression of pathology in α-Syn transgenic mice have not been fully characterized. For this purpose we investigated the time course of behavioral deficits and neuropathology in PDGF-β human wild type α-Syn transgenic mice (D-Line) between 3 and 12 months of age.

Results

These mice showed progressive impairment of motor coordination of the limbs that resulted in significant differences compared to non-transgenic littermates at 9 and 12 months of age. Biochemical and immunohistological analyses revealed constantly increasing levels of human α-Syn in different brain areas. Human α-Syn was expressed particularly in somata and neurites of a subset of neocortical and limbic system neurons. Most of these neurons showed immunoreactivity for phosphorylated human α-Syn confined to nuclei and perinuclear cytoplasm. Analyses of the phenotype of α-Syn expressing cells revealed strong expression in dopaminergic olfactory bulb neurons, subsets of GABAergic interneurons and glutamatergic principal cells throughout the telencephalon. We also found human α-Syn expression in immature neurons of both the ventricular zone and the rostral migratory stream, but not in the dentate gyrus.

Conclusion

The present study demonstrates that the PDGF-β α-Syn transgenic mouse model presents with early and progressive accumulation of human α-Syn that is accompanied by motor deficits. This information is essential for the design of therapeutical studies of synucleinopathies.

Platelet-derived growth factor-BB restores human immunodeficiency virus Tat-cocaine-mediated impairment of neurogenesis: role of TRPC1 channels

Platelet-derived growth factor-BB (PDGF-BB) has been reported to provide tropic support for neurons in the CNS. However, whether PDGF-BB regulates neurogenesis, especially in the context of HIV-associated neurological disorder and drug abuse, remains essentially unknown. In this study, we demonstrate that pretreatment of rat hippocampal neuronal progenitor cells (NPCs) with PDGF-BB restored proliferation that had been impaired by HIV Tat-cocaine via the cognate receptors. We identify the essential role of transient receptor potential canonical (TRPC) channels in PDGF-BB-mediated proliferation. Parallel but distinct ERK/CREB, phosphatidylinositol 3-kinase/Akt signaling pathways with downstream activation of mammalian target of rapamycin (mTOR)/eukaryotic translation initiation factor 4E-binding protein (4E-BP)-p70S6K and nuclear factor-κB were critical for proliferation. Blocking TRPC1 channel suppressed PDGF-mediated proliferation as well as PDGF-BB-induced ERK/CREB and mTOR/4E-BP-p70S6K activation, thereby underscoring its role in this process. In vivo relevance of these findings was further corroborated in Tat transgenic mice wherein hippocampal injection of recombinant AAV2-PDGF-B restored impaired NPC proliferation that was induced by Tat-cocaine. Together, these data underpin the role of TRPC1 channel as a novel target that regulates cell proliferation mediated by PDGF-BB with implications for therapeutic intervention for reversal of impaired neurogenesis inflicted by Tat and cocaine.

Fluoxetine rescues impaired hippocampal neurogenesis in a transgenic A53T synuclein mouse model

The accumulation of alpha-synuclein in Lewy bodies and Lewy neurites of different neuronal populations is one of the neuropathological hallmarks in Parkinson disease (PD). Overexpression of human wildtype or mutant alpha-synuclein affects the generation of new neurons in the adult dentate gyrus (DG) of the hippocampus in models of PD. Hippocampal dysfunction with reduced neurogenesis plays an important role in the pathogenesis of depression, an important non-motor symptom in PD. Moreover, effective antidepressant treatment is still an unmet need in PD. The present study explored if impaired hippocampal neurogenesis in the A53T transgenic animal model of PD may be restored by chronic oral application of the selective serotonin reuptake inhibitor (SSRI) fluoxetine. First, we determined the expression pattern of transgenic mutant A53T synuclein in developing DG neurons and showed early expression of the transgene linked to a severely impaired neurogenesis. After chronic fluoxetine treatment we observed an increased adult neurogenesis in the hippocampus of more than threefold in treated A53T mice compared with controls. The pro-neurogenic effect of chronic fluoxetine application is predominantly related to an increased proliferation of neural precursor cells in the DG, and to a lesser extent by induction of differentiation into mature neurons. Analysis of the underlying mechanisms revealed an induction of brain-derived and glial cell-derived neurotrophic factor levels as a result of fluoxetine treatment. This study underlines the large potential of SSRI-dependent mechanisms to stimulate adult hippocampal neurogenesis in alpha-synuclein models and may lead to novel means to improve neuropsychiatric symptoms in PD.

Cognitive and socio-emotional deficits in platelet-derived growth factor receptor-β gene knockout mice

Platelet-derived growth factor (PDGF) is a potent mitogen. Extensive in vivo studies of PDGF and its receptor (PDGFR) genes have reported that PDGF plays an important role in embryogenesis and development of the central nervous system (CNS). Furthermore, PDGF and the β subunit of the PDGF receptor (PDGFR-β) have been reported to be associated with schizophrenia and autism. However, no study has reported on the effects of PDGF deletion on mice behavior. Here we generated novel mutant mice (PDGFR-β KO) in which PDGFR-β was conditionally deleted in CNS neurons using the Cre/loxP system. Mice without the Cre transgene but with floxed PDGFR-β were used as controls. Both groups of mice reached adulthood without any apparent anatomical defects. These mice were further examined by conducting several behavioral tests for spatial memory, social interaction, conditioning, prepulse inhibition, and forced swimming. The test results indicated that the PDGFR-β KO mice show deficits in all of these areas. Furthermore, an immunohistochemical study of the PDGFR-β KO mice brain indicated that the number of parvalbumin (calcium-binding protein)-positive (i.e., putatively γ-aminobutyric acid-ergic) neurons was low in the amygdala, hippocampus, and medial prefrontal cortex. Neurophysiological studies indicated that sensory-evoked gamma oscillation was low in the PDGFR-β KO mice, consistent with the observed reduction in the number of parvalbumin-positive neurons. These results suggest that PDGFR-β plays an important role in cognitive and socioemotional functions, and that deficits in this receptor may partly underlie the cognitive and socioemotional deficits observed in schizophrenic and autistic patients.

Platelet-derived growth factor-mediated induction of the synaptic plasticity gene Arc/Arg3.1

Platelet-derived growth factor (PDGF) is a pleiotropic protein with critical roles in both developmental as well as pathogenic processes. In the central nervous system specifically, PDGF is critical for neuronal proliferation and differentiation and has also been implicated as a neuroprotective agent. Whether PDGF also plays a role in synaptic plasticity, however, remains poorly understood. In the present study we demonstrated that in the rat hippocampal neurons PDGF regulated the expression of Arc/Arg3.1 gene that has been implicated in both synapse plasticity and long term potentiation. Relevance of these findings was further confirmed in vivo by injecting mice with intracerebral inoculations of PDGF, which resulted in a rapid induction of Arc in the hippocampus of the injected mice. PDGF induced long term potentiation in rat hippocampal slices, which was abolished by PDGF receptor-tyrosine kinase inhibitor STI-571. We also present evidence that PDGF-mediated induction of Arc/Arg3.1 involved activation of the MAPK/ERK (MEK) pathway. Additionally, induction of Arc/Arg3.1 also involved the upstream release of intracellular calcium stores, an effect that could be blocked by thapsigargin but not by EGTA. Pharmacological approach using inhibitors specific for either MAPK/ERK phosphorylation or calcium release demonstrated that the two pathways converged downstream at a common point involving activation of the immediate early gene Egr-1. Chromatin immunoprecipitation assays demonstrated the binding of Egr-1, but not Egr-3, to the Arc promoter. These findings for the first time, thus, suggest an additional role of PDGF, that of induction of Arc.

Endothelin-1 regulates oligodendrocyte development

In the postnatal brain, oligodendrocyte progenitor cells (OPCs) arise from the subventricular zone (SVZ) and migrate into the developing white matter, where they differentiate into oligodendrocytes and myelinate axons. The mechanisms regulating OPC migration and differentiation are not fully defined. The present study demonstrates that endothelin-1 (ET-1) is an astrocyte-derived signal that regulates OPC migration and differentiation. OPCs in vivo and in culture express functional ET(A) and ET(B) receptors, which mediate ET-1-induced ERK (extracellular signal-regulated kinase) and CREB (cAMP response element-binding protein) phosphorylation. ET-1 exerts both chemotactic and chemokinetic effects on OPCs to enhance cell migration; it also prevents lineage progression from the O4(+) to the O1(+) stage without affecting cell proliferation. Astrocyte-conditioned medium stimulates OPC migration in culture through ET receptor activation, whereas multiphoton time-lapse imaging shows that selective ET receptor antagonists or anti-ET-1 antibodies inhibit OPC migration from the SVZ. Inhibition of ET receptor activity also derepresses OPC differentiation in the corpus callosum in slice cultures. Our findings indicate that ET-1 is a soluble astrocyte-derived signal that regulates OPC migration and differentiation during development.

Longitudinal changes of defensive and offensive factors in focal cerebral ischemia-reperfusion in rats

The cerebral ischemia-reperfusion injury remains a major medical problem due to the lack of effective treatment. The mechanism of brain injury is still unknown. The defensive and offensive factors, such as platelet-derived growth factor-BB (PDGF-BB), 5-lipoxygenase (5-LO), aquaporin-4 (AQP-4) and insulin-like growth factor-1 (IGF-1) may play important roles. So far, only individual factors were reported. What are the relationships among them in brain ischemia-reperfusion injury remains obscure. The present study is to investigate simultaneously the expression of PDGF-BB, 5-LO, AQP-4 and IGF-1 in middle cerebral artery occlusion/reperfusion (MCAO/R) in rats. We found that 5-LO and IGF-1 reached the peak level at 24h after reperfusion, AQP-4 at 72 h and PDGF-BB at 7 days. With these results we inferred that both defensive factors, such as PDGF-BB, AQP-4 and IGF-1, and offensive factor, like 5-LO, play some roles in the ischemia-reperfusion injury.

Changes in PDGF expression in spared dorsal root ganglia and associated spinal dorsal horns in cats subjected to partial dorsal root ganglionectomy

Changes in the platelet derived growth factor (PDGF) in the spared dorsal root ganglia (DRG) and associated spinal dorsal horns were evaluated in cats subjected to unilateral removal of L1-L5 and L7-S2 DRG, sparing the L6 DRG. The number of PDGF immunopositive neurons and protein expression decreased significantly in the spared DRG and associated dorsal horns of the L3 and L6 cord segments at 3 days post-operation (dpo). It bottomed to the lowest level at 7 dpo in the DRG, then returned to the control level at 14 dpo; while in the L6 dorsal horn, it rapidly increased at 7 dpo and exceeded the control level at 14 dpo. This showed a significant upregulation in the spared DRG and associated spinal dorsal horns, especially in the L6 cord segment following a transient decrease. Meanwhile, a significant upregulation of PDGF mRNA was also seen in L6 DRG and L3 and L6 dorsal horns at 3 dpo. The upregulation of the endogenous PDGF in the said structures indicated a potential role of this factor in spinal cord plasticity after partial dorsal root ganglia removal in cats.

Effects of Electro-acupuncture on PDGF Expression in Spared Dorsal Root Ganglion and Associated Dorsal Horn Subjected to Partial Dorsal Root Ganglionectomy in Cats

The effects of electro-acupuncture (EA) on the expression of platelet derived growth factor (PDGF) in spared dorsal root ganglion (DRG) and associated dorsal horns were evaluated in cats subjected to bilateral removal of L1-L5 and L7-S2 DRG, while sparing L6 DRG and were demonstrated using Immunohistochemistry, Western blot and RT-PCR techniques. On the acupunctured side, there was a significant increase in the total number of PDGF positive neurons. Large neurons of the L6 DRG at 7 days post operation (dpo), and small to medium-sized neurons at 14 dpo, as well as in the lamina II of the L6 spinal cord at 14 dpo was observed. The expression of PDGF protein increased significantly in the L6 DRG at 7 and 14 dpo and in the dorsal horn of the L6 spinal cord at 14 dpo while the upregulation of PDGF mRNA was seen at 3 dpo in the L6 DRG and the dorsal horn of the L3 and L6 spinal cord. These findings demonstrate that intrinsic PDGF has been upregulated in cats subjected to partial dorsal root ganglionectomy following EA, indicating endogenous PDGF is involved in promoting spinal plasticity following EA.

Mouse brains deficient in neuronal PDGF receptor-beta develop normally but are vulnerable to injury

Platelet-derived growth factors (PDGFs) and PDGF receptors (PDGFRs) are widely expressed in the mammalian CNS, though their functional significance remains unclear. The corresponding null-knockout mutations are lethal. Here, we developed novel mutant mice in which the gene encoding the beta subunit of PDGFR (PDGFR-beta) was genetically deleted in CNS neurons to elucidate the role of PDGFR-beta, particularly in the post-natal stage. Our mutant mice reached adulthood without apparent anatomical defects. In the mutant brain, immunohistochemical analyses showed that PDGFR-beta detected in neurons and in the cells in the subventricular zone of the lateral ventricle in wild-type mice was depleted, but PDGFR-beta detected in blood vessels remained unaffected. The cerebral damage after cryogenic injury was severely exacerbated in the mutants compared with controls. Furthermore, TdT-mediated dUTP-biotin nick end labeling (TUNEL)-positive neuronal cell death and lesion formation in the cerebral hemisphere were extensively exacerbated in our mutant mice after direct injection of NMDA without altered NMDA receptor expression. Our results clearly demonstrate that PDGFR-beta expressed in neurons protects them from cryogenic injury and NMDA-induced excitotoxicity.

Autocrine/Paracrine Platelet-Derived Growth Factor Regulates Proliferation of Neural Progenitor Cells

Growth factors play an important role in regulating neural stem cell proliferation and differentiation. This study shows that platelet-derived growth factor (PDGF) induces a partial differentiation of neural stem/progenitor cells (NSPCs) in the absence of other mitogens in vitro. NSPCs thus acquire an immature morphology and display markers for both neurons and glia. In addition, these cells do not readily mature in the absence of further stimuli. When NSPC cultures treated with PDGF were exposed to additional differentiation factors, however, the differentiation proceeded into neurons, astrocytes, and oligodendrocytes. We find that NSPC cultures are endowed with an endogenous PDGF-BB production. The PDGF-BB expression peaks during early differentiation and is present both in cell lysates and in conditioned medium, allowing for autocrine as well as paracrine signaling. When the NSPC-derived PDGF was inhibited, progenitor cell numbers decreased, showing that PDGF is involved in NSPC expansion. Addition of a PDGF receptor (PDGFR) inhibitor resulted in a more rapid differentiation. Neurons and oligodendrocytes appeared earlier and had more elaborate processes than in control cultures where endogenous PDGFR signaling was not blocked. Our observations point to PDGF as an inducer of partial differentiation of NSPC that also sustains progenitor cell division. Such an intermediate stage in stem cell differentiation is of relevance for the understanding of brain tumor development because autocrine PDGF stimulation is believed to drive malignant conversion of central nervous system progenitor cells.

Platelet-derived growth factor (PDGF-BB) and brain-derived neurotrophic factor (BDNF) induce striatal neurogenesis in adult rats with 6-hydroxydopamine lesions

The effects of i.c.v. infused platelet-derived growth factor and brain-derived neurotrophic factor on cell genesis, as assessed with bromodeoxyuridine (BrdU) incorporation, were studied in adult rats with unilateral 6-hydroxydopamine lesions. Both growth factors increased the numbers of newly formed cells in the striatum and substantia nigra to an equal extent following 10 days of treatment. At 3 weeks after termination of growth factor treatment, immunostaining of BrdU-labeled cells with the neuronal marker NeuN revealed a significant increase in newly generated neurons in the striatum. In correspondence, many doublecortin-labeled neuroblasts were also observed in the denervated striatum following growth factor treatment. Further evaluation suggested that a subset of these new neurons expresses the early marker for striatal neurons Pbx. However, no BrdU-positive cells were co-labeled with DARPP-32, a protein expressed by mature striatal projection neurons. Both in the striatum and in the substantia nigra there were no indications of any newly born cells differentiating into dopaminergic neurons following growth factor treatment, such that BrdU-labeled cells never co-expressed tyrosine hydroxylase, the rate-limiting enzyme in dopamine synthesis. In conclusion, our results suggest that administration of these growth factors is capable of recruiting new neurons into the striatum of hemiparkinsonian rats.

An aberrant autocrine activation of the platelet-derived growth factor alpha-receptor in follicular and papillary thyroid carcinoma cell lines

Platelet-derived growth factor receptor (PDGFR) can bind to its ligand and consequently possess a kinase activity, and which is associated with the carcinogenesis of different cell types, including astrocytomas, oligodendrogliomas, and glioblastoma. In a cDNA microarray analysis, we observe the over-expressed mRNA of both PDGF-A and PDGF-alpha receptor in thyroid carcinoma cells. And the elevated protein expressions of PDGF-A and PDGF-alpha receptor in thyroid carcinoma cells were also confirmed by a Western blot analysis. The phosphorylation of PDGF-alpha receptor evaluated by an antibody against Tyr 720-phosphate was found in thyroid carcinoma cells. The tyrosine kinase activity of PDGF-alpha receptor was inhibited by tyrphostin AG1295 and showed a dose-dependent inhibition for the proliferation of thyroid carcinoma cells. These findings imply that autocrine activation of PDGF-alpha receptor plays a crucial role in the carcinogenesis of thyroid cells.

Platelet-derived growth factor-BB pretreatment attenuates excitotoxic death in cultured hippocampal neurons

Neuronal excitotoxic death results from excess stimulation by elevated levels of extracellular glutamate acting on N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors. While excitotoxicity is typically attenuated by using glutamate receptor antagonists, we report here that neuronal deaths induced directly by brief exposures to glutamate or NMDA were both attenuated by preincubation with platelet-derived growth factor-BB (PDGF-BB). The neuroprotection was concentration and time dependent; preincubation for at least 24 h with a minimum of 10 ng/mL of PDGF-BB was required for maximal neuroprotective effect. The NMDA receptor antagonist MK-801 also afforded partial protection, and when MK-801 was used with PDGF-BB, neuronal survival was comparable to that of untreated controls. When protection of inhibitory and excitatory neurons by PDGF treatment was compared, the excitatory neurons appeared to be selectively protected. The present results demonstrate that PDGF pretreatment can protect neurons from direct glutamate-induced excitotoxicity in vitro and suggests that PDGF might possibly function as a neuroprotective agent in potential therapeutic applications.

Endothelium-specific ablation of PDGFB leads to pericyte loss and glomerular, cardiac and placental abnormalities

Platelet-derived growth factor-B (PDGFB) is necessary for normal cardiovascular development, but the relative importance of different cellular sources of PDGFB has not been established. Using Cre-lox techniques, we show here that genetic ablation of Pdgfb in endothelial cells leads to impaired recruitment of pericytes to blood vessels. The endothelium-restricted Pdgfb knockout mutants also developed organ defects including cardiac, placental and renal abnormalities. These defects were similar to those observed in Pdgfb null mice. However, in marked contrast to the embryonic lethality of Pdgfb null mutants, the endothelium-specific mutants survived into adulthood with persistent pathological changes, including brain microhemorrhages, focal astrogliosis, and kidney glomerulus abnormalities. This spectrum of pathological changes is reminiscent of diabetic microangiopathy, suggesting that the endothelium-restricted Pdgfb knockouts may serve as models for some of the pathogenic events of vascular complications to diabetes.

Biology of platelet-derived growth factors in development

Platelet-derived growth factor (PDGF) was one of the first growth factors to be characterized, and the PDGF family of ligand and receptors has remained an archetype system for studies of the mechanisms of action of growth factors and receptor tyrosine kinases for more than two decades. The small size of the family has also facilitated genetic studies and, in particular, manipulations of the mouse PDGF and PDGF receptor genes have given important insights into the role of this family during mammalian development. These studies have shown that discrete populations of mesenchymal and neuroectodermal progenitor cells depend on PDGF signaling for their growth and distribution within developing organs. Other studies suggest that the same, or similar, cells may be targeted by exaggerated PDGF signaling in a number of pathological processes, including different types of cancer. The present review summarizes current views on the roles of PDGFs in developmental processes, and discusses the critical importance of the amount, spatial distribution, and bioavailability of the PDGF proteins for acquisition of the correct number and location of target cells.

The PDGF B-chain is involved in the ontogenic susceptibility of the developing rat brain to NMDA toxicity

Hypoxic-ischemic (H-I) injury to neonatal brains can cause a life-long neuronal deficit because of increased susceptibility in the neonatal period. Excitotoxicity due to overstimulation of the N-methyl-d-aspartate receptor (NMDAR) is assumed to be the basis of the injury. However, the ontogenic profile of the susceptibility does not directly correlate with the levels of NMDAR expression. Platelet-derived growth factor B-chain (PDGF-B) has been reported to protect neurons by suppressing the NMDA-evoked current and translocating the glutamate transporter to the cell membrane. Thus, we assessed the relationship between the susceptibility to H-I injury and the expression of PDGF-B in neonatal rat brain. PDGF-B infusion before and after an intrastriatal NMDA injection significantly reduced the size of the lesions in 7-day-old rats, when they are most susceptible and the neuronal expression of PDGF-B is low. Fourteen-day-old neonatal rats were found to be resistant to NMDA injury, even though NMDARs are expressed at high levels in the brain at this age. Inhibition of PDGF-B protein synthesis by antisense oligodeoxynucleotides increased the size of the NMDA-induced lesions up to 6-fold at postnatal day 14, when PDGF-B is expressed at high levels in neurons. These data suggest that PDGF-B is an important physiological modulator of NMDAR excitability in the developing brain, and that the balance between the expression of NMDAR and PDGF-B partly determines the ontogenic susceptibility to brain injury. Enhancement of the PDGF-B/receptor signal pathway might rescue neonatal brains at risk of H-I injury.

Ciliary neurotrophic factor in the olfactory bulb of rats and mice

Ciliary neurotrophic factor (CNTF) is primarily regarded as an astrocytic lesion factor, promoting neuronal survival and influencing plasticity processes in deafferented areas of the CNS. Postnatal loss of neurons in CNTF-deficient mice indicates a function of the factor also under physiological conditions. In the olfactory bulb, where neurogenesis, axo- and synaptogenesis continue throughout life, CNTF content is constitutively high. The cellular localization of CNTF in the rat olfactory bulb is not fully resolved, and species differences between mouse and rat are not yet characterized. In the present study, four different CNTF antibodies and double immunolabeling with specific markers for glial and neuronal cells were used to study the cellular localization of CNTF in rat and mouse olfactory bulb. Specificity of the detection was checked with tissue from CNTF-deficient mice, and investigations were complemented by immunolocalization of reporter protein in mice synthesizing beta-galactosidase under control of the CNTF promoter (CNTF lacZ-knock-in mice). In both species, CNTF localized to ensheathing cell nuclei, cell bodies and axon-enveloping processes. Additionally, individual axons of olfactory neurons were CNTF immunoreactive. Both CNTF protein content and immunoreaction intensity were lower in mice than in rats. Scattered lightly CNTF-reactive cells were found in the granular and external plexiform layers in rats. Some CNTF-positive cells were associated with immunoreactivity for the polysialylated form of the neural cell adhesion molecule, which is expressed by maturing interneurons derived from the rostral migratory stream. In CNTF lacZ-knock-in mice, beta-galactosidase reactivity was found in ensheathing cells of the olfactory nerve layer, and in cells of the glomerular, external plexiform and granular layers. The study proves that CNTF is localized in glial and neuronal structures in the rodent olfactory bulb. Results in mice provide a basis for investigations concerning the effects of a lack of the factor in CNTF-deficient mice.

Angiogenic factors in the central nervous system

The past decade has seen considerable advances in the understanding of angiogenesis. Blood vessel development and growth in the central nervous system are tightly controlled processes that are regulated by angiogenic factors. Angiogenic factors have been implicated in the pathogenesis of a wide variety of disorders, including primary and metastatic brain tumors, aneurysms, arteriovenous malformations, and cavernous malformations. The potential clinical applications of angiogenesis research include inhibition of angiogenesis to control brain tumors and therapeutic angiogenesis to promote collateral blood vessel formation among patients at risk of ischemia. This article summarizes the processes of blood vessel formation in the brain, examines the angiogenic factors that are prominent in the central nervous system, reviews the clinical use of angiogenesis inhibitors, and identifies areas for future investigation.

Neuron-specific ablation of PDGF-B is compatible with normal central nervous system development and astroglial response to injury

Members of the PDGF family have multiple roles during embryogenesis and in a variety of pathological situations in the adult. One of the major sites of PDGF-B expression in adult mammals are postmitotic CNS neurons. Combined with reported neurotrophic and neuroprotective effects of exogenously administered PDGFs, this has led to the speculation that PDGF-B may have a role in CNS development, in maintenance, or in response to CNS injury. To test these hypotheses, we developed mice in which PDGF-B was ablated genetically in postmitotic neurons at sites where PDGF-B is normally expressed. We found that these mice develop to adulthood without apparent defects. We demonstrate PDGF-B expression in the postnatal mouse hippocampus and forebrain cortex. We show that neuron-specific knockout of PDGF-B does not influence the astroglial and angiogenic responses to injury in the hippocampus or forebrain cortex. We conclude that the role of neuron-derived PDGF-B remains obscure. A role for neuron-derived PDGF-B, if existing, might be redundant with other CNS growth factors. Alternatively, other and more specific analyses of CNS functions in the normal and injured states will be required to demonstrate such a role.

Platelet-derived growth factor-B and -C and active alpha-receptors in medulloblastoma cells

The malignant childhood brain tumor medulloblastoma belongs to the group of primitive neuroectodermal tumours (PNETs). Medulloblastomas are thought to arise from remnants of the transient external germinal layer in the cerebellum. Proliferation, differentiation, and motility of cells in the central nervous system are regulated by growth factors, e.g., platelet-derived growth factor (PDGF). Recently, it was shown that higher level of PDGF alpha-receptor expression is characteristic of metastatic medulloblastomas. We have investigated five medulloblastoma/PNET cell lines and found that the PDGF alpha-receptor is actively signalling in most of them, an activity most likely driven by endogenously produced PDGF-C. PDGF-C is normally present in cells of the developing external germinal layer and our results are consistent with the idea that medulloblastomas are derived from such cells undergoing early neuronal differentiation. Moreover, the expression of PDGF and its receptors was associated with neuronal characteristics, but not with high levels of c-myc expression in the medullablastoma cells.

Platelet-derived growth factor-b expression induced after rat peripheral nerve injuries

Schwann cells are crucially important for peripheral nerve regeneration. These cells synthesize several factors that are supposed to enhance axonal regeneration when injured. Platelet-derived growth factor (PDGF) B-chain and its beta-receptor are expressed in Schwann cells in both normal peripheral nerves and culture. To elucidate the role of PDGF-B in peripheral nerve regeneration, we investigated its expression in cut or crush-injured rat sciatic nerves for up to 28 days. Northern blotting identified substantial increase of PDGF B-chain transcripts in injured nerves. Immunohistochemistry demonstrated that protein products of the transcripts were augmented at the distal tip of swollen axons in proximal nerve segments and in regenerating axons. Soon after both types of injury, considerable amounts of PDGF-B accumulated in numerous Schwann cells in distal segments of both models. With restoration of the axon-Schwann cell relationship in the crush model, levels of PDGF-B tended to decrease, eventually returning to normal. In the cut model in which the relationship cannot be restored, the PDGF-B was depleted to a very low level. The spatiotemporal correlation between PDGF-B and cell proliferation was very close throughout the study. These results differed strikingly from those of our previous study of rat optic nerve transection, in which PDGF-B was expressed only in a few recruited macrophages and glial cells. Augmented PDGF-B expression after sciatic nerve injury might contribute to peripheral nerve regeneration because PDGF-B is a mitogen and survival factor for Schwann cells and because it has trophic activity on neurons.

A single intracerebral microinjection of platelet-derived growth factor (PDGF) accelerates the rate of remyelination in vivo

We had demonstrated that platelet-derived growth factor (PDGF) enhanced the reconstruction of myelin-like membranes after their disruption by lysophosphatidylcholine (LPC) in vitro. To investigate its role in vivo, a demyelinating lesion of the corpus callosum was induced in adult Wistar rats by a stereotaxic microinjection of 1 microl LPC, then 63 pairs of rats received either 1 microg PDGF, or its vehicle buffer which were injected above LPC. The effects of PDGF were significant after 2 weeks: the number of oligodendrocytes (OL) expressing 2',3'-cyclic nucleotide 3'-phosphodiesterase in the lesion increased by 49%, mature OL labelled by in situ hybridization for myelin basic protein-mRNA increased by 27% (P<10(-2)), and the total volume of demyelination decreased by 60% compared to controls. The proliferation of cells of the OL lineage was also enhanced up to 67% by PDGF compared to LPC controls (P<2.5 x 10(-2)). Ultrastructural studies confirmed this dramatic improvement, and the ratio of remyelinated to demyelinated axons, determined at the maximal demyelination site, in the centre of the lesion, increased by 10-fold (P<2.5 x 10(-3)) in animals treated with PDGF. Remyelination was complete after 3 months for both treatments. Neither exacerbation of gliosis nor glial tumoural transformation were observed. Mechanisms through which PDGF improves remyelination could involve proliferation of OL progenitors, and/or of already differentiated surviving OLs, and a chemotactic effect, which had been identified in vitro.

Immature neurons from CNS stem cells proliferate in response to platelet-derived growth factor

Identifying external signals involved in the regulation of neural stem cell proliferation and differentiation is fundamental to the understanding of CNS development. In this study we show that platelet-derived growth factor (PDGF) can act as a mitogen for neural precursor cells. Multipotent stem cells from developing CNS can be maintained in a proliferative state under serum-free conditions in the presence of fibroblast growth factor-2 (FGF2) and induced to differentiate into neurons, astrocytes, and oligodendrocytes on withdrawal of the mitogen. PDGF has been suggested to play a role during the differentiation into neurons. We have investigated the effect of PDGF on cultured stem cells from embryonic rat cortex. The PDGF alpha-receptor is constantly expressed during differentiation of neural stem cells but is phosphorylated only after PDGF-AA treatment. In contrast, the PDGF beta-receptor is hardly detectable in uncommitted cells, but its expression increases during differentiation. We show that PDGF stimulation leads to c-fos induction, 5'-bromo-2'deoxyuridine incorporation, and an increase in the number of immature cells stained with antibodies to neuronal markers. Our findings suggest that PDGF acts as a mitogen in the early phase of stem cell differentiation to expand the pool of immature neurons.

Platelet-derived growth factor receptor-alpha in ventricular zone cells and in developing neurons

Cells in the early neuroepithelium differentiate and give rise to all cells in the central nervous system (CNS). The ways from a multipotent CNS stem cell to specialized neurons and glia are not fully understood. Using immunohistochemistry we found that neuroepithelial cells express the platelet-derived growth factor receptor-alpha (PDGFR-alpha) in the neural plate at embryonic day 8.5 and onwards in the neural tube. The protein was polarized to ventricular endfeet. Furthermore, PDGFR-alpha expression was localized to cells undergoing early neuronal development. We also found PDGFR-alpha expression in developing granule cells in the postnatal cerebellum, in Purkinje cells in the adult cerebellum and on processes of developing dorsal root ganglion cells. Previous reports mainly describe PDGFR-alpha expression in oligodendrocyte precursors and glial cells. We believe, in line with a few previous reports, that the PDGFR-alpha in addition marks a pool of undifferentiated cells, which are able to differentiate into neurons.

Neurotrophic factors in the primary olfactory pathway

The number of identified growth factors continues to increase rapidly with many being implicated in the development of the nervous system, although for most of them the autocrine and paracrine pathways of cellular regulation still remain to be elucidated. The primary olfactory pathway, consisting of the olfactory epithelium and olfactory bulb, is presented here as a very useful model for the analysis of growth factor function. Review of the available literature suggests that a large proportion of neuroactive growth factors and their receptors are present in the olfactory epithelium or olfactory bulb. Furthermore, the primary olfactory pathway is one of the most plastic in the nervous system with neurogenesis continuing to contribute new sensory neurones in the olfactory epithelium and new interneurones in the olfactory bulb throughout adult life. The rich diversity of growth factors and their receptors in the olfactory system indicates that it will be useful in elucidating how these molecules regulate the formation of the nervous system. The olfactory epithelium in particular is proving useful as a model for the actions of growth factors in directing the neuronal lineage from stem cell to mature neurone.

Infarct tolerance induced by intra-cerebral infusion of recombinant brain-derived neurotrophic factor

Neuronal expression of brain-derived neurotrophic factor (BDNF) has been implicated in the mechanism of infarct tolerance (resistance to stroke) (H. Yanamoto et al., Infarct tolerance accompanied enhanced BDNF-like immunoreactivity in neuronal nuclei, submitted to Brain Res.), a process that takes more than 7 days following a preconditioning of repetitive cortical spreading depression (CSD). To investigate whether an elevated level of BDNF protein in the brain solely protects neurons against temporary focal ischemia, recombinant (r)BDNF was infused into the rat neocortex. Recombinant BDNF (or vehicle: saline) was administered into the left neocortex via an implanted osmotic minipump for 2.5, 7, 10 or 14 days pre-ischemia, during ischemia and for 2 days post-ischemia (8 microgram in total) in male Sprague-Dawley rats (n=6 each). Temporary focal ischemia was induced in the left middle cerebral artery (MCA) territory by three-vessel occlusion of bilateral common carotid arteries (CCAs) and MCA for 2 h, and the cerebral infarct volume was analyzed 2 days after ischemia using TTC staining. Regional cerebral blood flow (rCBF) of the left neocortex was monitored after 14 days of intracerebral administration of BDNF or vehicle (n=10 each). The distribution of BDNF following different periods of rBDNF or vehicle-infusion was analyzed using immunohistochemical techniques (n=5 each). In the groups treated with 8 microgram of rhBDNF for 7, 10, or 14 days pre-ischemia, there were significant reductions of neocortical infarct volume compared to in the control or vehicle-treated groups (p<0.05). In the rCBF study, there was no significant change after the infusion of 8 microgram rhBDNF for 14 days. In the histological study, a wide distribution of BDNF-like immunoreactivity in the neuronal nuclei in the ipsilateral neocortex was demonstrated after the infusion of 8 microgram rhBDNF for 14 days. The BDNF-like immunoreactivity in the neuronal nuclei was enhanced at the time that the resistance to stroke was achieved by direct intra-cerebral infusion of exogenous rBDNF. Elucidating the function of the BDNF-like protein located in the neuronal nuclei should reveal a new strategy for neuroprotection against ischemic brain attack in humans.

Bipotent cortical progenitor cells process conflicting cues for neurons and glia in a hierarchical manner

Neurons and glia of the cerebral cortex are thought to arise from a common, multipotent progenitor cell that is instructed toward alternate fates by extracellular cues. How do these cells behave when confronted with conflicting cues? We show here that nestin-positive neuroepithelial (NE) cells from embryonic day 14 rat cortex coexpress surface receptor proteins for ciliary neurotrophic factor (CNTF) and platelet-derived growth factor (PDGF). Both sets of these receptor proteins are functional in NE cells, as shown by ligand-dependent activation of downstream signal-generating proteins. Transient (30') exposure to CNTF instructs NE cells toward an astrocyte fate. Brief exposure to PDGF initiates neuronal differentiation. However, when challenged with conflicting cues, PDGF is dominant to CNTF. Moreover, CNTF-treated NE cells can be "redirected" by a subsequent exposure to PDGF to form neurons instead of astrocytes, whereas the converse is not true. The asymmetric relationship between CNTF and PDGF indicates that these two growth factors act on a common progenitor cell that has, at a minimum, two fates available to it rather than separate populations of precommitted neuroblasts and astroblasts. This bipotent progenitor cell processes conflicting cues for neurons and glia in a hierarchical manner.

Mechanism of action and in vivo role of platelet-derived growth factor

Platelet-derived growth factor (PDGF) is a major mitogen for connective tissue cells and certain other cell types. It is a dimeric molecule consisting of disulfide-bonded, structurally similar A- and B-polypeptide chains, which combine to homo- and heterodimers. The PDGF isoforms exert their cellular effects by binding to and activating two structurally related protein tyrosine kinase receptors, denoted the alpha-receptor and the beta-receptor. Activation of PDGF receptors leads to stimulation of cell growth, but also to changes in cell shape and motility; PDGF induces reorganization of the actin filament system and stimulates chemotaxis, i.e., a directed cell movement toward a gradient of PDGF. In vivo, PDGF has important roles during the embryonic development as well as during wound healing. Moreover, overactivity of PDGF has been implicated in several pathological conditions. The sis oncogene of simian sarcoma virus (SSV) is related to the B-chain of PDGF, and SSV transformation involves autocrine stimulation by a PDGF-like molecule. Similarly, overproduction of PDGF may be involved in autocrine and paracrine growth stimulation of human tumors. Overactivity of PDGF has, in addition, been implicated in nonmalignant conditions characterized by an increased cell proliferation, such as atherosclerosis and fibrotic conditions. This review discusses structural and functional properties of PDGF and PDGF receptors, the mechanism whereby PDGF exerts its cellular effects, and the role of PDGF in normal and diseased tissues.

From neural stem cells to myelinating oligodendrocytes

The potential to generate oligodendrocytes progenitors (OP) from neural stem cells (NSCs) exists throughout the developing CNS. Yet, in the embryonic spinal cord, the oligodendrocyte phenotype is induced by sonic hedgehog in a restricted anterior region. In addition, neuregulins are emerging as potent regulators of early and late OP development. The ability to isolate and grow NSCs as well as glial-restricted progenitors has revealed that FGF2 and thyroid hormone favor an oligodendrocyte fate. Analysis of genetically modified mice showed that PDGF controls the migration and production of oligodendrocytes in vivo. Interplay between mitogens, thyroid hormone, and neurotransmitters may maintain the undifferentiated stage or result in OP growth arrest. Notch signaling by axons inhibits oligodendrocyte differentiation until neuronal signals--linked to electrical activity-trigger initiation of myelination. To repair myelin in adult CNS, multipotential neural precursors, rather than slowly cycling OP, appear the cells of choice to rapidly generate myelin-forming cells.

Expression of platelet-derived growth factor B-chain and beta-receptor in hypoxic/ischemic encephalopathy of neonatal rats

Expression of platelet-derived growth factor B-chain and of its specific receptor (beta-receptor) was investigated in immature brains with hypoxic/ischemic injury. After the left common carotid arteries of seven-day-old rats were ligated and pups were placed in a hypoxic chamber, the protein and messenger RNA of both B-chain and beta-receptor were assessed using immunocytochemistry and northern analysis, respectively. Transcripts for B-chain were localized by in situ hybridization. Faint but definite expression of B-chain and beta-receptor was seen in the brains of untreated neonatal controls. Three to 48 h after hypoxia B-chain protein was generally increased above control levels, but focally decreased expression was seen in infarcted areas. Enhanced induction of messenger RNA of B-chain was seen in the both sides of cerebral cortices and hippocampi at 3 h. Strongly increased positivity for B-chain protein and mRNA occurred in the neurons surrounding the infarct. In situ hybridization still showed this up-regulation seven days after hypoxia. Beta-receptor protein expression was enhanced in some neurons immediately surrounding the infarct at 3 h of hypoxia, and marked up-regulation was seen at 16 h. Beta-receptor messenger RNA remained at control levels. Immunocytochemistry showed strong immunoreactivity for the beta-receptor on the neurons surrounding the infarct at 72 h. These results indicate that a neonatal hypoxic/ischemic insult induces neuronal up-regulation of the platelet-derived growth factor B-chain as well as beta-receptor immediately after hypoxia. While this up-regulation is relatively transient in most neurons, sublethal damage to neurons immediately surrounding an infarct induces sustained up-regulation. Through autocrine and paracrine mechanisms, platelet-derived growth factor B-chain molecules may act as a neuroprotective factor in immature brain experiencing with hypoxic/ischemic injury.

Platelet-derived growth factor B-chain expression in the rat retina and optic nerve: distribution and changes after transection of the optic nerve

To test the possible involvement of platelet-derived growth factor B-chain (PDGF-B) in anterograde and retrograde degenerations of the CNS neurons, we studied the changes of PDGF-B localization and its mRNA expression in the rat retina and optic nerve (ON) after unilateral ON transection, using immunohistochemistry and in situ hybridization. In the control retinas immunoreactivity for PDGF-B and its mRNA expression were localized in the retinal ganglion cells (RGCs) and the nerve fiber layer. After ON transection PDGF-B immunoreactivity in the nerve fiber layer started to decrease on post-injury day 3 or 4. Atrophic changes in the RGCs started on day 5 just after the decrease of PDGF expression, and thereafter the RGC number decreased. In the longitudinal section of the ON rostral to the transected site, swollen axons showed intense PDGF-B immunoreactivity and macrophages, and some glial cells revealed a significant increase in both immunoreactivity and hybridization signals. Based on these findings, we hypothesized that the decrease in PDGF-B in RGCs after axotomy causes the loss of RGCs, and that increased PDGF-B expression in the ON plays a role in the cascade of tissue reactions following ON transection.

Cellular localization of PDGF mRNAs in developing human forebrain

Platelet-derived growth factor (PDGF) has been implicated in the processes regulating gliogenesis in the CNS. Conflicting in vivo data in rodents have variously implicated either glia or neurons as being the primary source of PDGF. We have used in situ hybridization and immunocytochemical analysis to study the in vivo expression and cellular localization of PDGF-A, sis/PDGF-B, together with the two PDGF receptors alpha and beta, in developing human forebrain. In this study we demonstrate the strong expression of mRNA and protein of both PDGF chains, A and B, and their receptors, alpha and beta, in human embryonic glial cells. The neurons, in contrast to glial cells, expressed lower levels of PDGF and PDGF-receptor mRNAs and protein. Identification of the cell types expressing the PDGF and PDGF-receptor mRNAs was achieved by counterstaining with antibodies specific for glial cells (GFAP) and neurons (NF). The predominant glial-specific expression of both PDGF-A and PDGF-B, together with the coexpression of their receptors alpha and beta, suggests an important role for the PDGF isoforms in the development of human embryonic glial cells and neurons in vivo.

Neuronal and glial expression of heparin-binding EGF-like growth factor in central nervous system of prenatal and early-postnatal rat

We investigated heparin-binding epidermal growth factor-like growth factor (HB-EGF) gene and protein expression in the central nervous system of prenatal and early postnatal rats. Assay by northern blot analysis showed that the HB-EGF mRNA was markedly expressed in the brain. In situ hybridization and immunohistochemical techniques showed that concordant expression of HB-EGF mRNA and protein was widely observed in the neurons and interfascicular oligodendrocytes, especially in the cerebellum, the hippocampus, the cerebral cortex, the subventricular area, and the brain stem nuclei. The intense expression of the HB-EGF mRNA was related anatomically and temporally to the proliferating neuroblasts in the external granular layer of the cerebellum and the subventricular layer of the cerebrum. These findings suggest that HB-EGF acts as a mitogen for the neuroblasts. Moreover, HB-EGF expression was observed in the post-mitogenic cells, such as in the cells of the molecular layer, the white matter, the IGL, or the Purkinje cells of the cerebellum. Since EGF receptors are abundantly expressed in the post-mitogenic period, the HB-EGF mRNA expression observed in the post-mitogenic period in our study suggests that HB-EGF also has a non-mitogenic function. These results suggest that HB-EGF significantly contributes to the development of the brain.

Induction of infarct tolerance by platelet-derived growth factor against reversible focal ischemia

Nerve growth factor, brain-derived neurotrophic factor, and other neurotrophic factors have been reported to have neuroprotective effects against global ischemia. To investigate whether the homodimer of platelet-derived growth factor B-chain (PDGF-BB) can protect neurons against focal temporary ischemia, PDGF-BB was administered to the rat brain for a prolonged period prior to, during, and after ischemia, since PDGF-BB protected rat neurons from global ischemia in our previous study. A total of 82 male Sprague-Dawley rats were used. Recombinant PDGF-BB, or saline was administered into the left neocortex via an implanted osmotic pump for 3 days (1.2 microg in total), 7 days (2 microgram or 4 microgram in total), or 14 days (4 microgram in total) pre-ischemia and 2 days post-ischemia. In an additional group, PDGF-BB (4 microgram in total) was administered for 14 days by osmotic pump and focal ischemia was induced after an additional 7-day interval following removal of the pump. Focal temporary ischemia was induced in the left MCA territory by bilateral CCA and MCA occlusion for 2 h. All rats were sacrificed 2 days after ischemia and the volume of cerebral infarct was analyzed using TTC staining. In a separate set of animals, regional cerebral blood flow (rCBF) was monitored by the hydrogen clearance method and laser Doppler flowmetry (LDF) of the neocortex after 14 days of intracerebral administration of PDGF-BB or saline. In the group receiving PDGF-BB (4 microgram in total) for 7 or 14 days pre-ischemia, there was a significant reduction of neocortical infarction compared to that in the control or saline-infused group. The size of cerebral infarct was smallest in the group that received PDGF-BB for 14 days, when ischemia was induced 7 days after removal of the pump. Regarding rCBF measurement, there were no significant differences in groups receiving PDGF-BB or saline infusion for 14 days. The potent neuroprotective effect of PDGF-BB on global ischemia was also demonstrated in the focal ischemia model. However, prolonged intracerebral infusion for 7 to 14 days was necessary to achieve a significant reduction of infarct volume. Neuroprotection was not due to increased collateral flow during ischemia.

Platelet-derived growth factor prevents ischemia-induced neuronal injuries in vivo

Platelet-derived growth factor (PDGF) has been considered to be a neuroprotective factor candidate on the basis of several in vitro studies. However, the in vivo effect of PDGF on ischemic neurons has not been determined. In the present study, the effect of PDGF-BB on the ischemia-induced disability of passive avoidance task and hippocampal CA1 neuron death in normothermic gerbils, whose the brain temperature was kept at 37.0 +/- 0.2 degrees C during 3-min occlusion of the common carotid arteries was investigated. When PDGF-BB was continuously infused for 7 days into the cerebral ventricles of gerbils with transient forebrain ischemia, response latency time in a passive avoidance task was significantly prolonged. Subsequent histological examinations showed that PDGF-BB effectively increased the number of viable pyramidal neurons in the hippocampal CA1 region as well as synapses within the strata moleculare, radiatum and oriens of the region in comparison with the numbers of neurons and synapses in vehicle-treated ischemic gerbils. In situ detection of DNA fragmentation (TUNEL staining) revealed that TUNEL-positive neurons in the hippocampal CA1 field of vehicle-treated ischemic gerbils were much more numerous than those in the field of PDGF-BB-treated ischemic animals after 7 days ischemia. These findings suggest that the present ischemic animal model exhibits a more delayed neuronal degeneration of the hippocampal CA1 field than the conventional 5-min ischemic model and that the 7-day infusion of PDGF-BB, starting 2 h before ischemic insult, not only prevents delayed neuronal death in the hippocampal CA1 field at 7 days after forebrain ischemia but also inhibits a slowly progressive neuronal degeneration occurring thereafter.

Platelet-derived growth factor-BB, but not -AA, prevents delayed neuronal death after forebrain ischemia in rats

Our previous studies demonstrated coordinate expression of platelet-derived growth factor (PDGF) -B chain and beta-receptor in neurons at risk in the rat brain with focal ischemia. To clarify a role of the -B chain in the brain further, we examined whether PDGF-A or -B chain protects CA1 pyramidal neurons from delayed neuronal death after forebrain ischemia in rats. Pretreatment with PDGF-BB, but not -AA, at 120 ng/d for 2 days until forebrain ischemia was performed markedly ameliorated delayed neuronal death in CA1 pyramidal neurons on day 7 after ischemia. This neuroprotective effect of PDGF-BB was dose-dependent, and pretreatment with PDGF-BB at 240 ng/d showed almost complete inhibition of delayed neuronal death. In contrast, posttreatment with PDGF-BB at 120 ng/d starting 20 minutes after ischemia demonstrated no significant neuroprotective effect. The current study established marked neuroprotective actions of PDGF-BB in ischemic neuronal damage.

Increased expression of extracellular signal regulated kinase 1 after axotomy in the dorsal motor nucleus of the vagus nerve and the hypoglossal nucleus

The extracellular signal regulated kinases (Erks) cascade is a major signalling system by which cells transduce extracellular signals into intracellular responses. To obtain information about the role of Erks in retrograde neuronal reaction, we investigated the changes of Erk 1 and Erk 2 with in situ hybridization and immunohistochemical study in the dorsal motor nucleus of vagus nerve, which shows degenerative changes, and the hypoglossal nucleus, which shows regenerative changes, of adult rats after axotomy. The expression of mRNA and protein of Erk 1 increased between 7 and 28 days after axotomy both in the vagal and hypoglossal nuclei, however, there was no remarkable change in those of Erk 2. The increased expression of Erk 1 is common to both regenerative hypoglossal and degenerative vagal neurons. These findings indicate that Erk 1 is closely related with the retrograde neuronal reaction but whether neurons are destined to survive or die depends on some other factors.