Inhibition of apoptosis-inducing factor translocation is involved in protective effects of hepatocyte growth factor against excitotoxic cell death in cultured hippocampal neurons

Fosgonimeton, a Novel Positive Modulator of the HGF/MET System, Promotes Neurotrophic and Procognitive Effects in Models of Dementia

All types of dementia, including Alzheimer's disease, are debilitating neurodegenerative conditions marked by compromised cognitive function for which there are few effective treatments. Positive modulation of hepatocyte growth factor (HGF)/MET, a critical neurotrophic signaling system, may promote neuronal health and function, thereby addressing neurodegeneration in dementia. Here, we evaluate a series of novel small molecules for their ability to (1) positively modulate HGF/MET activity, (2) induce neurotrophic changes and protect against neurotoxic insults in primary neuron culture, (3) promote anti-inflammatory effects in vitro and in vivo, and (4) reverse cognitive deficits in animal models of dementia. Through screening studies, the compound now known as fosgonimeton-active metabolite (fosgo-AM) was identified by use of immunocytochemistry to be the most potent positive modulator of HGF/MET and was selected for further testing. Primary hippocampal neurons treated with fosgo-AM showed enhanced synaptogenesis and neurite outgrowth, supporting the neurotrophic effects of positive modulators of HGF/MET. Additionally, fosgo-AM protected against neurotoxic insults in primary cortical neuron cultures. In vivo, treatment with fosgo-AM rescued cognitive deficits in the rat scopolamine amnesia model of dementia. Although fosgo-AM demonstrated several procognitive effects in vitro and in vivo, a prodrug strategy was used to enhance the pharmacological properties of fosgo-AM, resulting in the development of fosgonimeton (ATH-1017). The effect of fosgonimeton on cognition was confirmed in a lipopolysaccharide (LPS)-induced neuroinflammatory mouse model of dementia. Together, the results of these studies support the potential of positive modulators of HGF/MET to be used as novel therapeutics and suggest the drug candidate fosgonimeton might protect against neurodegeneration and be therapeutic in the management of Alzheimer's disease and other types of dementia.

HGF and MET: From Brain Development to Neurological Disorders

Hepatocyte growth factor (HGF) and its tyrosine kinase receptor, encoded by the MET cellular proto-oncogene, are expressed in the nervous system from pre-natal development to adult life, where they are involved in neuronal growth and survival. In this review, we highlight, beyond the neurotrophic action, novel roles of HGF-MET in synaptogenesis during post-natal brain development and the connection between deregulation of MET expression and developmental disorders such as autism spectrum disorder (ASD). On the pharmacology side, HGF-induced MET activation exerts beneficial neuroprotective effects also in adulthood, specifically in neurodegenerative disease, and in preclinical models of cerebral ischemia, spinal cord injuries, and neurological pathologies, such as Alzheimer’s disease (AD), amyotrophic lateral sclerosis (ALS), and multiple sclerosis (MS). HGF is a key factor preventing neuronal death and promoting survival through pro-angiogenic, anti-inflammatory, and immune-modulatory mechanisms. Recent evidence suggests that HGF acts on neural stem cells to enhance neuroregeneration. The possible therapeutic application of HGF and HGF mimetics for the treatment of neurological disorders is discussed.

Mitochondrial AIF loss causes metabolic reprogramming, caspase-independent cell death blockade, embryonic lethality, and perinatal hydrocephalus

OBJECTIVES

Apoptosis-Inducing Factor (AIF) is a protein involved in mitochondrial electron transport chain assembly/stability and programmed cell death. The relevant role of this protein is underlined because mutations altering mitochondrial AIF properties result in acute pediatric mitochondriopathies and tumor metastasis. By generating an original AIF-deficient mouse strain, this study attempted to analyze, in a single paradigm, the cellular and developmental metabolic consequences of AIF loss and the subsequent oxidative phosphorylation (OXPHOS) dysfunction.

METHODS

We developed a novel AIF-deficient mouse strain and assessed, using molecular and cell biology approaches, the cellular, embryonic, and adult mice phenotypic alterations. Additionally, we conducted ex vivo assays with primary and immortalized AIF knockout mouse embryonic fibroblasts (MEFs) to establish the cell death characteristics and the metabolic adaptive responses provoked by the mitochondrial electron transport chain (ETC) breakdown.

RESULTS

AIF deficiency destabilized mitochondrial ETC and provoked supercomplex disorganization, mitochondrial transmembrane potential loss, and high generation of mitochondrial reactive oxygen species (ROS). AIF-/Y MEFs counterbalanced these OXPHOS alterations by mitochondrial network reorganization and a metabolic reprogramming toward anaerobic glycolysis illustrated by the AMPK phosphorylation at Thr172, the overexpression of the glucose transporter GLUT-4, the subsequent enhancement of glucose uptake, and the anaerobic lactate generation. A late phenotype was characterized by the activation of P53/P21-mediated senescence. Notably, approximately 2% of AIF-/Y MEFs diminished both mitochondrial mass and ROS levels and spontaneously proliferated. These cycling AIF-/Y MEFs were resistant to caspase-independent cell death inducers. The AIF-deficient mouse strain was embryonic lethal between E11.5 and E13.5 with energy loss, proliferation arrest, and increased apoptotic levels. Contrary to AIF-/Y MEFs, the AIF KO embryos were unable to reprogram their metabolism toward anaerobic glycolysis. Heterozygous AIF+/- females displayed progressive bone marrow, thymus, and spleen cellular loss. In addition, approximately 10% of AIF+/- females developed perinatal hydrocephaly characterized by brain development impairment, meningeal fibrosis, and medullar hemorrhages; those mice died 5 weeks after birth. AIF+/- with hydrocephaly exhibited loss of ciliated epithelium in the ependymal layer. This phenotype was triggered by the ROS excess. Accordingly, it was possible to diminish the occurrence of hydrocephalus AIF+/- females by supplying dams and newborns with an antioxidant in drinking water.

CONCLUSIONS

In a single knockout model and at 3 different levels (cell, embryo, and adult mice) we demonstrated that by controlling the mitochondrial OXPHOS/metabolism, AIF is a key factor regulating cell differentiation and fate. Additionally, by providing new insights into the pathological consequences of mitochondrial OXPHOS dysfunction, our new findings pave the way for novel pharmacological strategies.

Exploring the potential of natural and synthetic neuroprotective steroids against neurodegenerative disorders: A literature review

Neurodegeneration is a complex process, which leads to progressive brain damage due to loss of neurons. Despite exhaustive research, the cause of neuronal loss in various degenerative disorders is not entirely understood. Neuroprotective steroids constitute an important line of attack, which could play a major role against the common mechanisms associated with various neurodegenerative disorders like Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis. Natural endogenous steroids induce the neuroprotection by protecting the nerve cells from neuronal injury through multiple mechanisms, therefore the structural modifications of the endogenous steroids could be helpful in the generation of new therapeutically useful neuroprotective agents. The review article will keep the readers apprised of the detailed description of natural as well as synthetic neuroprotective steroids from the medicinal chemistry point of view, which would be helpful in drug discovery efforts aimed toward neurodegenerative diseases.

Open label study to assess the safety of VM202 in subjects with amyotrophic lateral sclerosis

OBJECTIVE

To assess safety and define efficacy measures of hepatocyte growth factor (HGF) DNA plasmid, VM202, administered by intramuscular injections in patients with amyotrophic lateral sclerosis (ALS).

METHODS

Eighteen participants were treated with VM202 administered in divided doses by injections alternating between the upper and lower limbs on d 0, 7, 14, and 21. Subjects were followed for nine months to evaluate possible adverse events. Functional outcome was assessed using the ALS Functional Rating Scale-Revised (ALSFRS-R) as well as by serially measuring muscle strength, muscle circumference, and forced vital capacity.

RESULTS

Seventeen of 18 participants completed the study. All participants tolerated 64 mg of VM202 well with no serious adverse events (SAE) related to the drug. Twelve participants reported 26 mild or moderate injection site reactions. Three participants experienced five SAEs unrelated to VM202. One subject died from respiratory insufficiency secondary to ALS progression.

CONCLUSIONS

Multiple intramuscular injection of VM202 into the limbs appears safe in ALS subjects. Future trials with retreatment after three months will determine whether VM202 treatment alters the long-term course of ALS.

Endogenous Neuroprotective Molecules and Their Mechanisms in the Central Nervous System

Functions of the central nervous system (CNS) are based on a complex neural network. It is believed that the CNS has several neuroprotective mechanisms operated by neurons, glia and other types of cells against various types of neuronal damage. Since mature, differentiated neurons are not able to divide, it is important to protect neurons from damage prior to death. The neuroprotective effects of a number of pharmaceutical agents and natural products against necrosis and apoptosis of the CNS neurons have been reported, thus this review will mainly discuss several endogenous neuroprotectants and their mechanisms.

Role of HGF/MET axis in resistance of lung cancer to contemporary management

Lung cancer is the number one cause of cancer related mortality with over 1 million cancer deaths worldwide. Numerous therapies have been developed for the treatment of lung cancer including radiation, cytotoxic chemotherapy and targeted therapies. Histology, stage of presentation and molecular aberrations are main determinants of prognosis and treatment strategy. Despite the advances that have been made, overall prognosis for lung cancer patients remains dismal. Chemotherapy and/or targeted therapy yield objective response rates of about 35% to 60% in advanced stage non-small cell lung cancer (NSCLC). Even with good initial responses, median overall survival of is limited to about 12 months. This reflects that current therapies are not universally effective and resistance develops quickly. Multiple mechanisms of resistance have been proposed and the MET/HGF axis is a potential key contributor. The proto-oncogene MET (mesenchymal-epithelial transition factor gene) and its ligand hepatocyte growth factor (HGF) interact and activate downstream signaling via the mitogen-activated protein kinase (ERK/MAPK) pathway and the phosphatidylinositol 3-kinase (PI3K/AKT) pathways that regulate gene expression that promotes carcinogenesis. Aberrant MET/HGF signaling promotes emergence of an oncogenic phenotype by promoting cellular proliferation, survival, migration, invasion and angiogenesis. The MET/HGF axis has been implicated in various tumor types including lung cancers and is associated with adverse clinicopathological profile and poor outcomes. The MET/HGF axis plays a major role in development of radioresistance and chemoresistance to platinums, taxanes, camtothecins and anthracyclines by inhibiting apoptosis via activation of PI3K-AKT pathway. DNA damage from these agents induces MET and/or HGF expression. Another resistance mechanism is inhibition of chemoradiation induced translocation of apoptosis-inducing factor (AIF) thereby preventing apoptosis. Furthermore, this MET/HGF axis interacts with other oncogenic signaling pathways such as the epidermal growth factor receptor (EGFR) pathway and the vascular endothelial growth factor receptor (VEGFR) pathway. This functional cross-talk forms the basis for the role of MET/HGF axis in resistance against anti-EGFR and anti-VEGF targeted therapies. MET and/or HGF overexpression from gene amplification and activation are mechanisms of resistance to cetuximab and EGFR-TKIs. VEGF inhibition promotes hypoxia induced transcriptional activation of MET proto-oncogene that promotes angiogenesis and confers resistance to anti-angiogenic therapy. An extensive understanding of these resistance mechanisms is essential to design combinations with enhanced cytotoxic effects. Lung cancer treatment is challenging. Current therapies have limited efficacy due to primary and acquired resistance. The MET/HGF axis plays a key role in development of this resistance. Combining MET/HGF inhibitors with chemotherapy, radiotherapy and targeted therapy holds promise for improving outcomes.

Hepatocyte growth factor overexpression in the nervous system enhances learning and memory performance in mice

Hepatocyte growth factor (HGF) and its receptor, c-Met, play pivotal roles in the nervous system during development and in disease states. However, the physiological roles of HGF in the adult brain are not well understood. In the present study, to assess its role in learning and memory function, we used transgenic mice that overexpress HGF in a neuron-specific manner (HGF-Tg) to deliver HGF into the brain without injury. HGF-Tg mice displayed increased alternation rates in the Y-maze test compared with age-matched wild-type (WT) controls. In the Morris water maze (MWM) test, HGF-Tg mice took less time to find the platform on the first day, whereas the latency to escape to the hidden platform was decreased over training days compared with WT mice. A transfer test revealed that the incidence of arrival at the exact location of the platform was higher for HGF-Tg mice compared with WT mice. These results demonstrate that overexpression of HGF leads to an enhancement of both short- and long-term memory. Western blot analyses revealed that the levels of N-methyl-D-aspartate (NMDA) receptor subunits NR2A and NR2B, but not NR1, were increased in the hippocampus of HGF-Tg mice compared with WT controls, suggesting that an upregulation of NR2A and NR2B could represent one mechanism by which HGF enhances learning and memory performance. These results demonstrate that modulation of learning and memory performance is an important physiological function of HGF that contributes to normal CNS plasticity, and we propose HGF as a novel regulator of higher brain functions.

Neuronal expression, cytosolic localization, and developmental regulation of the organic solute carrier partner 1 in the mouse brain

Organic solute carrier partner 1 (OSCP1) is a mammalian, transporter-related protein that is able to facilitate the uptake of structurally diverse organic compounds into the cell when expressed in Xenopus laevis oocytes. This protein has been implicated in testicular handling of organic solutes because its mRNA expression is almost exclusive in the testis. However, in this study, we demonstrated significant expression of OSCP1 protein in mouse brain, the level of which was rather higher than that in the testis, although the corresponding mRNA expression was one-tenth of the testicular level. Immunohistochemistry revealed that OSCP1 was broadly distributed throughout the brain, and various neuronal cells were immunostained, including pyramidal cells in the cerebral cortex and hippocampus. However, there was no evidence of OSCP1 expression in glia. In primary cultures of cerebral cortical neurons, double-labeling immunofluorescence localized OSCP1 to the cytosol throughout the cell body and neurites including peri-synaptic regions. This was consistent with the subcellular fractionation of brain homogenates, in which OSCP1 was mainly recovered after centrifugation both in the cytosolic fraction and the particulate fraction containing synaptosomes. Immunoelectron microscopy of brain sections also demonstrated OSCP1 in the cytosol near synapses. In addition, it was revealed that changes in the expression level of OSCP1 correlated with neuronal maturation during postnatal development of mouse brain. These results indicate that OSCP1 may have a role in the brain indirectly mediating substrate uptake into the neurons in adult animals.

Adipose-derived mesenchymal stem cells protect PC12 cells from glutamate excitotoxicity-induced apoptosis by upregulation of XIAP through PI3-K/Akt activation

Glutamate excitotoxicity has been implicated as one of the factors contributing to neuronal apoptosis and is involved in many neurodegenerative diseases. Previous studies suggest that mesenchymal stem cells have the ability to protect cultured neurons from excitotoxicity-induced apoptosis, although the underlying mechanisms are not clear. In this study, we evaluated whether adipose mesenchymal stem cells (AMSCs) could protect against glutamate-induced injury in PC12 cells by secreting neurotrophic factors. We found that AMSCs secreted neurotrophic factors including vascular endothelial growth factor (VEGF), hepatocyte growth factor (HGF), brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) under both normoxic and hypoxic conditions. AMSC - conditioned medium (AMSC-CM) had a protective effect on excitotoxicity-injured PC12 cells, as indicated by increased cell viability, decreased number of TUNEL-staining positive nuclei and lowered caspase-3 activity. By using neutralizing monoclonal antibodies and specific inhibitors, VEGF, HGF and BDNF were identified as the mediators of AMSC effects and PI3-K/Akt and MAPK pathways were involved. Western blot analysis showed that AMSC-CM can increase the level of p-Akt, up-regulate XIAP and reduce the level of cleaved-caspase-3 in PC12 cells. These results suggest that AMSCs can effectively protect PC12 cells from glutamate excitotoxicity-induced apoptosis and support the hypothesis that AMSCs may be a useful treatment for stroke or neurodegenerative diseases which often involve excitotoxicity.

Hepatocyte growth factor protects human embryonic stem cell derived-neural progenitors from hydrogen peroxide-induced apoptosis

Promoting human embryonic stem cell (hESC)-derived-neural progenitor survival in the pro-apoptotic niche is pivotal for stem cell replacement therapy. The present study was designed to investigate the protective effect of hepatocyte growth factor (HGF) on hESC-derived neural progenitor injured by hydrogen peroxide (H(2)O(2)) exposure. Treatment of hESC-derived neural progenitor cells with HGF prior to H(2)O(2) exposure conferred protective effect against oxidative stress-induced apoptosis. HGF treatment increased both phosphoinositide 3-kinase (PI3K)/Akt and extracellular signal-regulated kinase1/2 (ERK1/2) phosphorylation. However, selective inhibition of each pathway supported that the activation of PI3K/AKT, but not ERK1/2, provides survival advantage to the neural progenitor cells. Further investigation indicated that HGF pretreatment could attenuate the decrease of the expression of Bcl-2 protein induced by H(2)O(2), whereas the level of Bax was not affected. Additionally, we observed that H(2)O(2)-induced decrease of mitochondrial transmembrane potential, release of cytochrome c and increase of caspase-3 activation were alleviated by HGF pretreatment. These effects of HGF could be reversed by inhibition of the PI3K/Akt and ERKs pathways, indicating PI3K/Akt and ERKs signaling might be involved in HGF-mediated regulation of mitochondrial apoptotic pathway mediated by H(2)O(2). The neuroprotective effect of HGF might potentially be useful in stem cell-based therapies for neurodegenerative disorders.

AIF promotes chromatinolysis and caspase-independent programmed necrosis by interacting with histone H2AX

Programmed necrosis induced by DNA alkylating agents, such as MNNG, is a caspase-independent mode of cell death mediated by apoptosis-inducing factor (AIF). After poly(ADP-ribose) polymerase 1, calpain, and Bax activation, AIF moves from the mitochondria to the nucleus where it induces chromatinolysis and cell death. The mechanisms underlying the nuclear action of AIF are, however, largely unknown. We show here that, through its C-terminal proline-rich binding domain (PBD, residues 543-559), AIF associates in the nucleus with histone H2AX. This interaction regulates chromatinolysis and programmed necrosis by generating an active DNA-degrading complex with cyclophilin A (CypA). Deletion or directed mutagenesis in the AIF C-terminal PBD abolishes AIF/H2AX interaction and AIF-mediated chromatinolysis. H2AX genetic ablation or CypA downregulation confers resistance to programmed necrosis. AIF fails to induce chromatinolysis in H2AX or CypA-deficient nuclei. We also establish that H2AX is phosphorylated at Ser139 after MNNG treatment and that this phosphorylation is critical for caspase-independent programmed necrosis. Overall, our data shed new light in the mechanisms regulating programmed necrosis, elucidate a key nuclear partner of AIF, and uncover an AIF apoptogenic motif.

Salidroside attenuates glutamate-induced apoptotic cell death in primary cultured hippocampal neurons of rats

Salidroside, a compound of natural origin, has displayed a broad spectrum of pharmacological properties. This study aimed to evaluate the inhibitory effects of salidroside on glutamate-induced cell death in a primary culture of rat hippocampal neurons as compared to brain-derived neurotrophic factor (BDNF), a usual positive control. MTT and LDH assays, together with Hoechst 33342 staining, terminal deoxynucleotidyl transferase dUTP-mediated nicked end labeling (TUNEL) assay and flow cytometric analysis using annexin-V and propidium (PI) label, indicated that salidroside pretreatment attenuated glutamate-induced apoptotic cell death in primary cultured hippocampal neurons, showing a dose-dependent pattern. Furthermore, caspase-3 activity assay and calcium measurements with Fluo 4-AM, respectively, revealed that salidroside pretreatment antagonized activation of caspase-3 and elevation of intracellular calcium level, both of which were induced by glutamate stimulation, thus adding to the understanding of how salidroside offered neuroprotection against glutamate excitotoxicity.

HGF increases cisplatin resistance via down-regulation of AIF in lung cancer cells

Our previous study had shown that advanced stages of lung adenocarcinomas (ADC) was frequently associated with overexpression of hepatocyte growth factor (HGF), which has multipotent and anti-apoptotic activities. In this study, we examined the effect of HGF on gene expression of apoptosis-inducing factor (AIF) and cisplatin sensitivity in lung ADC cells. Expression of AIF was determined by immunocytochemistry and confocal immunofluorescence microscopy. Our data show that addition of HGF suppressed AIF expression and increased cisplatin resistance. The effect could be through HGF receptor and its downstream effector, focal adhesion kinase (FAK). Interestingly, knockout of FAK gene increased AIF expression and drug sensitivity. Re-introduction of FAK gene, on the other hand, restored drug resistance. These results suggested that HGF might induce cisplatin resistance via c-Met to activate FAK and down-regulate AIF expression.

Hepatocyte growth factor improves synaptic localization of the NMDA receptor and intracellular signaling after excitotoxic injury in cultured hippocampal neurons

To examine the effects of HGF on synaptic densities under excitotoxic conditions, we investigated changes in the number of puncta detected by double immunostaining with NMDA receptor subunits and presynaptic markers in cultured hippocampal neurons. Exposure of hippocampal neurons to excitotoxic NMDA (100 muM) decreased the synaptic localization of NMDA receptor subunit NR2B, whereas synaptic NR1 and NR2A clusters were not altered. Colocalization of PSD-95, a scaffolding protein of the receptor, with the presynaptic protein synapsin I was also decreased after excitotoxicity. Treatment with HGF attenuated these decreases in number. The decrease in the levels of surface NR2B subunits following the addition of the excitotoxic NMDA was also attenuated by the HGF treatment. The decrease in CREB phosphorylation in response to depolarization-evoked NMDA receptor activation was prevented by the HGF treatment. These results suggest that HGF not only prevented neuronal cell death but also attenuated the decrease in synaptic localization of NMDA receptor subunits and prevented intracellular signaling through the NMDA receptor.

HGF protects cultured cortical neurons against hypoxia/reoxygenation induced cell injury via ERK1/2 and PI-3K/Akt pathways

Hepatocyte growth factor (HGF) has been revealed to exert multipotent activities on a variety of cells. In this study, we investigated whether HGF had a direct neuroprotection on cultured cerebral cortical neurons subjected to hypoxia/reoxygenation (H/R) and explored the intracellular signalings mediated the effects. The decrease in cell viability and increase in number of apoptotic cells resulting from H/R were significantly prevented by HGF pre-treatment. HGF stimulated both ERK1/2 and Akt activities in cortical neurons. Inhibition of ERK activation completely abolished the protective effects of HGF, and inhibition of Akt activation reduced, but did not completely eliminate the HGF mediated neuroprotection. It is suggested that the neuroprotection of HGF depend on ERK1/2 pathway, and, to a lesser extent, PI-3K/Akt pathway. In addition, we found that pre-treatment with HGF remarkably attenuated the decrease in expression of Bcl-2 and Bcl-xL induced by H/R, but failed to affect the amount of Bax. It is likely that Bcl-2 and Bcl-xL contribute to the protective effects of HGF.

Hepatocyte growth factor promotes the number of PSD-95 clusters in young hippocampal neurons

Hepatocyte growth factor (HGF) and its receptor are expressed in various regions of the brain and have protective effects against excitotoxic injuries. However, their effects on synapse formation remain to be elucidated. To determine whether HGF has the ability to alter synaptic function during development, we investigated changes in the number of synapse detected by double immunostaining for NMDA receptor subunits and a presynaptic marker in cultured young hippocampal neurons. Whereas application of HGF increased the number of cluster of synapsin, a presynaptic protein, the clusters of NMDA receptor subunits NR1 and NR2B were not altered. Interestingly, colocalization of PSD-95, a scaffolding protein of the receptor, with synapsin was increased by HGF treatment without a change in the total amount of it. In addition, we investigated the expression of surface NMDA receptor, neuroligin, and neurexin, which were assessed by use of a cell-surface biotinylation assay. The application of HGF did not change the surface expression of these proteins. Furthermore, we determined the release of glutamate in response to depolarization. Treatment with HGF promoted depolarization-evoked release of glutamate. These results suggest that HGF modulates the expression of the scaffolding protein of the NMDA receptor at the synapse and promotes maturation of excitatory synapses in young hippocampal neurons.

Effect of NMDA receptor antagonist on proliferation of neurospheres from embryonic brain

The N-methyl-D-aspartate (NMDA) receptor, a subtype of ionotropic glutamate receptors, plays an important role in the regulation of neuronal development, learning and memory, and neurodegenerative diseases. NMDA receptor blockade enhances neurogenesis in the hippocampal dentate gyrus in vivo. The effect of NMDA receptor antagonist on proliferation of neural progenitor cells, however, remains to be determined. We investigated changes in the diameter and number of neurospheres derived from the embryonic rat brain after NMDA receptor blockade. Cortical progenitor cells were isolated from gestational day 18 fetal rats according to the Percoll density gradient method. Cultured spheres expressed neural progenitor markers, musashi-1 and nestin. Immunohistochemical analysis demonstrated that cells in Dulbecco's modified Eagle medium/F12 containing 1% fetal bovine serum on day 8 differentiated to MAP-2-positive neurons and GFAP-positive astrocytes. The expression of NR1 and NR2B subunits of the NMDA receptor in neurospheres was detected. Neither brief nor sustained exposure to NMDA altered the diameter and number of neurospheres. Brief exposure to 30 microM MK-801, an NMDA receptor antagonist, decreased the diameter of neurospheres. Sustained exposure to 30 microM MK-801 decreased the diameter and number of neurospheres. Our results provide evidence that MK-801 directly decreased proliferation of neural progenitor cells.

Hepatocyte growth factor (HGF) promotes oligodendrocyte progenitor cell proliferation and inhibits its differentiation during postnatal development in the rat

Hepatocyte growth factor (HGF) was initially cloned as a mitogen for hepatocytes and has been identified as a neurotrophic factor for a variety of neurons. However, few attempts have assessed the role of HGF in cells of oligodendrocyte lineage. The purpose of this study was to elucidate the role of HGF in such cells during development. Double immunostaining for either c-Met/HGF receptor or phospho-c-Met with either NG2 or RIP in rat striatum at postnatal day 3 (P3), P7, and P14 revealed that c-Met was phosphorylated on tyrosine residues and thereby activated in NG2(+) oligodendrocyte progenitor cells (OPCs) at P3-P14 and in RIP(+) oligodendrocytes at P14. Intrastriatal injections of recombinant human HGF at both P7 and P10 revealed that the relative ratio of BrdU(+)/NG2(+) cells per total number of NG2(+) cells increased, while BrdU(+)/MBP(+) oligodendrocyte numbers decreased. Western blot analysis showed a down-regulation of myelin basic protein (MBP) after HGF injection. Electron microscopy revealed that the numbers of myelinated nerve fibers decreased after HGF treatment. Furthermore, administration of anti-HGF IgG into the striatum increased the number of BrdU(+)/MBP(+) oligodendrocytes. These findings demonstrated that HGF increases proliferation of OPCs and attenuates their differentiation into myelinating oligodendrocytes, presumably by favoring neurite outgrowth that may be inhibited by the myelin inhibitory molecules on oligodendrocytes. Down-regulation of HGF mRNA in the striatum from P7 to P14, as revealed by quantitative real-time RT-PCR, may be favorable for OPC differentiation into myelinating oligodendrocytes. Our findings suggest that c-Met signaling, together with HGF regulation, plays an important role in developmental oligodendrogenesis.

Prevention of apoptosis-inducing factor translocation is a possible mechanism for protective effects of hepatocyte growth factor against neuronal cell death in the hippocampus after transient forebrain ischemia

Hepatocyte growth factor (HGF) is one of the prospective agents for therapy against a variety of neurologic and neurodegenerative disorders, although the precise mechanisms for the effect of HGF remain to be elucidated. We showed that treatment with HGF protected hippocampal cornu ammonis (CA) subregion 1 neurons from apoptotic cell death after transient forebrain ischemia. Accumulating evidence indicates that ischemia-induced neuronal damage occurs via caspase-independent pathways. In the present study, we focused on the localization of apoptosis-inducing factor (AIF), which is an important protein in the signal-transduction system through caspase-independent pathways, to investigate the possible mechanism for the protective effect of HGF after transient forebrain ischemia. Hepatocyte growth factor attenuated the increase in the expression of AIF protein in the nucleus after transient forebrain ischemia. We further explored the upstream components of AIF translocation. Primary DNA damage induced by Ca(2+) influx and subsequent NO formation are thought to be the initial events for AIF translocation, which results in the subsequent DNA damage by AIF. Hepatocyte growth factor prevented the primary oxidative DNA damage, as was estimated by using anti-8-OHdG (8-hydroxy-2'-deoxyguanosine) antibody. Oxidative DNA damage after ischemia is known to lead to the activation of poly(ADP-ribose) polymerase (PARP) and p53, resulting in AIF translocation. Marked increases in the PAR polymer formation and the expression of p53 protein after ischemia were effectively prevented by HGF treatment. In the present study, we first showed that HGF was capable of preventing neuronal cell death by inhibiting the primary oxidative DNA damage and then preventing the activation of the PARP/p53/AIF pathway.