IGF-I protects cortical neurons against ceramide-induced apoptosis via activation of the PI-3K/Akt and ERK pathways; is this protection independent of CREB and Bcl-2?

Geniposide ameliorates chronic unpredictable mild stress induced depression-like behavior through inhibition of ceramide-PP2A signaling via the PI3K/Akt/GSK3β axis

BACKGROUND

Depression is a severe mental disorder. Unfortunately, more than half of patients with major depression disorder cannot achieve remission after initial treatment with an antidepressant. Geniposide, a bioactive iridoid glycoside isolated from Gardenia jasminoides Ellis, can ameliorate depressive-like behaviors in mice. However, the underlying mechanism is still not very clear.

METHODS

The pharmacological methods including ELISA, immunofluorescence, and Western blot were used to investigate the role of geniposide on chronic unpredictable mild stress (CUMS)-induced depression mice.

RESULTS

In this study, we found that geniposide could inhibit CUMS-induced depressive-like behaviors in mice. Geniposide is able to reduce the levels of ceramide and lower the activity of acid sphingomyelinase (ASM) in hippocampus; besides, ASM inhibitor (amitriptyline) can decrease the concentration of ceramide and ameliorate depressive-like behaviors of mice. Moreover, geniposide can also alleviate CUMS-induced hippocampal neuronal apoptosis and increase the phosphorylated form of PI3K, Akt, and GSK3β. Additionally, PI3K inhibitor (LY294002) can also abolish the neuroprotective effect of geniposide on hippocampal neurons in vitro.

CONCLUSIONS

These results indicate that geniposide exert a potential antidepressant-like effect on CUMS mice, and its effect might be associated with activated PI3K/Akt/GSK3β signaling, reduced the level of ceramide and hippocampal neuron apoptosis.

The Protective Effect of Insulin on Rat Cortical Neurons in Oxidative Stress and Its Dependence on the Modulation of Akt, GSK-3beta, ERK1/2, and AMPK Activities

Insulin is a promising drug for the treatment of diseases associated with brain damage. However, the mechanism of its neuroprotective action is far from being understood. Our aim was to study the insulin-induced protection of cortical neurons in oxidative stress and its mechanism. Immunoblotting, flow cytometry, colorimetric, and fluorometric techniques were used. The insulin neuroprotection was shown to depend on insulin concentration in the nanomolar range. Insulin decreased the reactive oxygen species formation in neurons. The insulin-induced modulation of various protein kinase activities was studied at eight time-points after neuronal exposure to prooxidant (hydrogen peroxide). In prooxidant-exposed neurons, insulin increased the phosphorylation of GSK-3beta at Ser⁹ (thus inactivating it), which resulted from Akt activation. Insulin activated ERK1/2 in neurons 5–30 min after cell exposure to prooxidant. Hydrogen peroxide markedly activated AMPK, while it was for the first time shown that insulin inhibited it in neurons at periods of the most pronounced activation by prooxidant. Insulin normalized Bax/Bcl-2 ratio and mitochondrial membrane potential in neurons in oxidative stress. The inhibitors of the PI3K/Akt and MEK1/2/ERK1/2 signaling pathways and the AMPK activator reduced the neuroprotective effect of insulin. Thus, the protective action of insulin on cortical neurons in oxidative stress appear to be realized to a large extent through activation of Akt and ERK1/2, GSK-3beta inactivation, and inhibition of AMPK activity increased by neuronal exposure to prooxidant.

LPS-induced modules of co-expressed genes in equine peripheral blood mononuclear cells

BACKGROUND

Lipopolysaccharide (endotoxin, LPS) is a strong inducer of the innate immune response. It is widespread in our environment, e.g. in house dust and contributes to asthma. Compared to humans, horses are even more sensitive to LPS. However, data on LPS effects on the equine transcriptome are very limited. Using RNA-seq we analysed LPS-induced differences in the gene expression in equine peripheral blood mononuclear cells at the gene and gene-network level in two half-sib families and one group of unrelated horses.

RESULTS

24 h-LPS challenge of equine immune cells resulted in substantial changes in the transcriptomic profile (1,265 differentially expressed genes) showing partial overlap with human data. One of the half-sib families showed a specific response different from the other two groups of horses. We also identified co-expressed gene modules that clearly differentiated 24 h-LPS- from non-stimulated samples. These modules consisted of 934 highly interconnected genes and included genes involved in the immune response (e.g. IL6, CCL22, CXCL6, CXCL2), however, none of the top ten hub genes of the modules have been annotated as responsive to LPS in gene ontology.

CONCLUSIONS

Using weighted gene co-expression network analysis we identified ten co-expressed gene modules significantly regulated by in vitro stimulation with LPS. Apart from 47 genes (5%) all other genes highly interconnected within the most up- and down-regulated modules were also significantly differentially expressed (FDR < 0.05). The LPS-regulated module hub genes have not yet been described as having a role in the immune response to LPS (e.g. VAT1 and TTC25).

Insulin-like growth factor 1 rescues R28 retinal neurons from apoptotic death through ERK-mediated BimEL phosphorylation independent of Akt

Insulin-like growth factor 1 (IGF-1) can provide long-term neurotrophic support by activation of Akt, inhibition of FoxO nuclear localization and suppression of Bim gene transcription in multiple neuronal systems. However, MEK/ERK activation can also promote neuron survival through phosphorylation of BimEL. We explored the contribution of the PI3K/Akt/FoxO and MEK/ERK/BimEL pathways in IGF-1 stimulated survival after serum deprivation (SD) of R28 cells differentiated to model retinal neurons. IGF-1 caused rapid activation of Akt leading to FoxO1/3-T32/T24 phosphorylation, and prevented FoxO1/3 nuclear translocation and Bim mRNA upregulation in response to SD. IGF-1 also caused MAPK/MEK pathway activation as indicated by ERK1/2-T202/Y204 and Bim-S65 phosphorylation. Overexpression of FoxO1 increased Bim mRNA expression and amplified the apoptotic response to SD without shifting the serum response curve. Inhibition of Akt activation with LY294002 or by Rictor knockdown did not block the protective effect of IGF-1, while inhibition of MEK activity with PD98059 prevented Bim phosphorylation and blocked IGF-1 protection. In addition, knockdown of Bim expression was protective during SD, while co-silencing of FoxO1 and Fox03 expression had little effect. Thus, the PI3K/Akt/FoxO pathway was not essential for protection from SD-induced apoptosis by IGF-1 in R28 cells. Instead, IGF-1 protection was dependent on activation of the MEK/ERK pathway leading to BimEL phosphorylation, which is known to prevent Bax/Bak oligomerization and activation of the intrinsic mitochondrial apoptosis pathway. These studies demonstrate the requirement of the MEK/ERK pathway in a model of retinal neuron cell survival and highlight the cell specificity for IGF-1 signaling in this response.

IGF-1 protects dopamine neurons against oxidative stress: association with changes in phosphokinases

Insulin-like growth factor-1 (IGF-1) is an endogenous peptide transported across the blood brain barrier that is protective in several brain injury models, including an acute animal model of Parkinson's disease (PD). Motor deficits in PD are due largely to the progressive loss of nigrostriatal dopaminergic neurons. Thus, we examined the neuroprotective potential of IGF-1 in a progressive model of dopamine deficiency in which 6-hydroxydopamine (6-OHDA) is infused into the striatum. Rats received intrastriatal IGF-1 (5 or 50 µg) 6 h prior to infusion of 4 µg 6-OHDA into the same site and were euthanized 1 or 4 weeks later. Both concentrations of IGF-1 protected tyrosine hydroxylase (TH) immunoreactive terminals in striatum at 4 weeks but not at 1 week, indicating that IGF-induced restoration of the dopaminergic phenotype occurred over several weeks. TH-immunoreactive cell loss was only attenuated with 50 µg IGF-1. We then examined the effect of striatal IGF-1 on the Ras/ERK1/2 and PI3K/Akt pathways to ascertain whether their activation correlated with IGF-1-induced protection. Striatal and nigral levels of phospho-ERK1/2 were maximal 6 h after IGF-1 infusion and, with the exception of an increase in nigral pERK2 at 48 h, returned to basal levels by 7 days. Phospho-Akt (Ser473) was elevated 6-24 h post-IGF-1 infusion in both striatum and substantia nigra concomitant with inhibition of pro-death GSK-3β, a downstream target of Akt. These results suggest that IGF-1 can protect the nigrostriatal pathway in a progressive PD model and that this protection is preceded by activation of key pro-survival signaling cascades.

Silencing of PINK1 inhibits insulin-like growth factor-1-mediated receptor activation and neuronal survival

The etiology of Parkinson's disease remains unknown. Mutations in PINK1 have provided an understanding of the molecular mechanisms of this pathology. PINK1 and Parkin are important in the dismissal of dysfunctional mitochondria. However, the role of PINK1 in the control of neuronal survival pathways is not clear. To determine the role of PINK1 in the control of the phosphatidyl inositol 3-kinase (PI3K)/Akt pathway mediated by insulin-like grow factor type 1 (IGF-1), we use a model of mesencephalic neurons (CAD cells), which were transfected with lentiviral PINK1 shRNA or control shRNA constructs. Silencing of PINK1 was determined by RT-PCR and immunoblotting; cell viability was analyzed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and lactate dehydrogenase (LDH) assays; proteins of the PI3K/Akt signaling pathway were tested by immunoblotting and IGF-1 receptor, and mitochondria were examined using fluorescence microscopy. PINK1 shRNA-transfected cells showed a reduction in cell survival compared to control shRNA cells. Exposure to IGF-1 induced a rapid and high increase in the phosphorylation level of IGF-1 receptor in control shRNA-transfected cells; however, silencing of PINK1 decreases phosphorylation level of IGF-1 receptor and downstream target proteins such as Akt, GSK3-beta, IRS-1, and hexokinase. Our results further suggest that PINK1 may be regulating the PI3K/Akt neuronal survival pathway through tyrosine kinase receptors such as IGF-1 receptor.

IPLEX administration improves motor neuron survival and ameliorates motor functions in a severe mouse model of spinal muscular atrophy

Spinal muscular atrophy (SMA) is an inherited neurodegenerative disorder and the first genetic cause of death in childhood. SMA is caused by low levels of survival motor neuron (SMN) protein that induce selective loss of α-motor neurons (MNs) in the spinal cord, resulting in progressive muscle atrophy and consequent respiratory failure. To date, no effective treatment is available to counteract the course of the disease. Among the different therapeutic strategies with potential clinical applications, the evaluation of trophic and/or protective agents able to antagonize MNs degeneration represents an attractive opportunity to develop valid therapies. Here we investigated the effects of IPLEX (recombinant human insulinlike growth factor 1 [rhIGF-1] complexed with recombinant human IGF-1 binding protein 3 [rhIGFBP-3]) on a severe mouse model of SMA. Interestingly, molecular and biochemical analyses of IGF-1 carried out in SMA mice before drug administration revealed marked reductions of IGF-1 circulating levels and hepatic mRNA expression. In this study, we found that perinatal administration of IPLEX, even if does not influence survival and body weight of mice, results in reduced degeneration of MNs, increased muscle fiber size and in amelioration of motor functions in SMA mice. Additionally, we show that phenotypic changes observed are not SMN-dependent, since no significant SMN modification was addressed in treated mice. Collectively, our data indicate IPLEX as a good therapeutic candidate to hinder the progression of the neurodegenerative process in SMA.

Hyperinsulinemia induces insulin resistance in dorsal root ganglion neurons

Insulin resistance (IR) is the major feature of metabolic syndrome, including type 2 diabetes. IR studies are mainly focused on peripheral tissues, such as muscle and liver. There is, however, little knowledge about IR in neurons. In this study, we examined whether neurons develop IR in response to hyperinsulinemia. We first examined insulin signaling using adult dorsal root ganglion neurons as a model system. Acute insulin treatment resulted in time- and concentration-dependent activation of the signaling cascade, including phosphorylation of the insulin receptor, Akt, p70S6K, and glycogen synthase kinase-3β. To mimic hyperinsulinemia, cells were pretreated with 20 nM insulin for 24 h and then stimulated with 20 nM insulin for 15 min. Chronic insulin treatment resulted in increased basal Akt phosphorylation. More importantly, acute insulin stimulation after chronic insulin treatment resulted in blunted phosphorylation of Akt, p70S6K, and glycogen synthase kinase-3β. Interestingly, when the cells were treated with phosphatidylinositol 3-kinase pathway inhibitor, but not MAPK pathway inhibitor, chronic insulin treatment did not block acute insulin treatment-induced Akt phosphorylation. Insulin-induced Akt phosphorylation was lower in dorsal root ganglion neurons from BKS-db/db compared with control BKS-db+ mice. This effect was age dependent. Our results suggest that hyperinsulinemia cause IR by disrupting the Akt-mediated pathway. We also demonstrate that hyperinsulinemia increases the mitochondrial fission protein dynamin-related protein 1. Our results suggest a new theory for the etiology of diabetic neuropathy, i.e. that, similar to insulin dependent tissues, neurons develop IR and, in turn, cannot respond to the neurotrophic properties of insulin, resulting in neuronal injury and the development of neuropathy.

Asperosaponin VI protects cardiac myocytes from hypoxia-induced apoptosis via activation of the PI3K/Akt and CREB pathways

Cardiomyocyte apoptosis plays a critical role in the progress of heart diseases. Asperosaponin VI (ASA VI), a triterpene saponin isolated from Dipsacus asper Wall, has shown cardioprotective effects in vivo. However, whether ASA VI has a protective effect against cardiomyocyte apoptosis is poorly understood. The present study was aimed to investigate the cardioprotective role of ASA VI and the underlying mechanisms in hypoxia-induced cardiomyocyte apoptosis. Cardiomyocytes were exposed to hypoxic condition for 6 h and then cell viability markedly decreased, lactate dehydrogenase (LDH) and creatine phosphokinase (CK) activities in the culture supernatant significantly increased. Hypoxia-activated apoptosis were confirmed by Hoechst 33258 nuclear staining and Annexin V-FITC staining. These changes were associated with the decrease of the Bcl-2/Bax ratio, active caspase-3 expression, phosphorylations of Akt and cAMP response element-binding protein (CREB). Moreover, ASA VI significantly attenuated increased LDH and CK activities, and increased cell viability in hypoxia treated myocytes in a dose-dependent fashion. Hoechst 33258 nuclear staining and Annexin V-FITC staining observations demonstrated the same protective effects. ASA VI treatment inhibited apoptosis in hypoxia-induced cardiomyocyte by increasing the Bcl-2/Bax ratio and decreasing active caspase-3 expression, as well as enhancing of p-Akt and p-CREB. Furthermore, the protective effects of ASA VI were prevented by phosphatidylinositol-3-kinase (PI3K) inhibitor LY294002 treatment. In consequence, we demonstrated that ASA VI had protective effect against hypoxia-induced cardiomyocytes apoptosis probably by activating the PI3K/Akt and CREB pathways.

Blueberry treatment antagonizes C-2 ceramide-induced stress signaling in muscarinic receptor-transfected COS-7 cells

Previous research has shown that muscarinic receptors (MAChRs) show loss of sensitivity in aging and AD and are selectively sensitive to oxidative stress (OS). Thus, COS-7 cells transfected (tn) with MAChR subtype M1 show > OS sensitivity [as reflected in the ability of the cell to extrude or sequester Ca(2+) following depolarization (recovery) by oxotremorine (oxo) and exposure to dopamine (DA) or amyloid beta (Abeta)] than M3-transfected COS-7 cells. Blueberry (BB) extract pretreatment prevented these deficits. Research has also indicated that C2 ceramide (Cer) has several age-related negative cellular effects (e.g., OS). When these cells were treated with Cer, the significant decrements in the ability of both types of tn cells to initially respond to oxo were antagonized by BB treatment. Present experiments assessed signaling mechanisms involved in BB protection in the presence or absence of DA, Abeta, and/or Cer in this model. Thus, control or BB-treated M1 and M3 tn COS-7 cells were exposed to DA or Abeta(42) in the presence or absence of Cer. Primarily, results showed that the effects of DA or Abeta(42) were to increase stress (e.g., PKCgamma, p38MAPK) and protective signals (e.g., pMAPK). Cer also appeared to raise several of the stress and protective signals in the absence of the other stressors, including PKCgamma, pJNK, pNfkappaB, p53, and p38MAPK, while not significantly altering MAPK, or Akt. pArc was, however, increased by Cer in both types of transfected cells. The protective effects of BB when combined with Cer generally showed greater protection when BB extract was applied prior to Cer, except for one protective signal (pArc) where a greater effect was seen in the M3 cells exposed to Abeta(42.) In the absence of the Abeta(42) or DA, for several of the stress signals (e.g., pNfkappaB, p53), BB lowered their Cer-induced increases in M1- and M3-transfected cells. We are exploring these interactions further, but it is clear that increases in ceramide, to the same levels as are seen in aging, can have profound effects on calcium clearance and signaling during oxidative stress.

Maturation-dependent alcohol resistance in the developing mouse: cerebellar neuronal loss and gene expression during alcohol-vulnerable and -resistant periods

BACKGROUND

Alcohol abuse during pregnancy injures the fetal brain. One of alcohol's most important neuroteratogenic effects is neuronal loss. Rat models have shown that the cerebellum becomes less vulnerable to alcohol-induced neuronal death as it matures. We determined if maturation-dependent alcohol resistance occurs in mice and compared patterns of gene expression during the alcohol resistant and sensitive periods.

METHODS

Neonatal mice received alcohol daily over postnatal day (PD) 2 to 4 or PD8 to 10. Purkinje cells and granule cells were quantified on PD25. The temporal expression patterns of 4 neuro-developmental genes and 3 neuro-protective genes in the cerebellum were determined daily over PD0 to 15 to determine how gene expression changes as the cerebellum transitions from alcohol-vulnerable to alcohol-resistant. The effect of alcohol on expression of these genes was determined when the cerebellum is alcohol sensitive (PD4) and resistant (PD10).

RESULTS

Purkinje and granule cells were vulnerable to alcohol-induced death at PD2 to 4, but not at PD8 to 10. Acquisition of maturation-dependent alcohol resistance coincided with changes in the expression of neurodevelopmental genes. The vulnerability of cerebellar neurons to alcohol toxicity declined in parallel with decreasing levels of Math1 and Cyclin D2, markers of immature granule cells. Likewise, the rising resistance to alcohol toxicity paralleled increasing levels of GABA alpha-6 and Wnt-7a, markers of mature granule neurons. Expression of growth factors and genes with survival promoting function (IGF-1, BDNF, and cyclic AMP response element binding protein) did not rise as the cerebellum transitioned from alcohol-vulnerable to alcohol-resistant. All 3 were expressed at substantial levels during the vulnerable period and were not expressed at higher levels later. Acute alcohol exposure altered the expression of neurodevelopmental genes and growth factor genes when administered either during the alcohol vulnerable period or resistant period. However, the patterns in which gene expression changed varied among the genes and depended on timing of alcohol administration.

CONCLUSIONS

Mice have a temporal window of vulnerability in the first week of life, during which cerebellar neurons are more sensitive to alcohol toxicity than during the second week. Expression of genes governing neuronal maturation changes in synchrony with the acquisition of alcohol resistance. Growth factors do not rise as the cerebellum transitions from alcohol-vulnerable to alcohol-resistant. Thus, a process intrinsic to neuronal maturation, rather than rising levels of growth factors, likely underlies maturation-dependent alcohol resistance.

Interactions of PACAP and ceramides in the control of granule cell apoptosis during cerebellar development

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide that belongs to the secretin/glucagon/vasoactive intestinal polypeptide superfamily. The PACAPergic system is actively expressed in the developing cerebellum of mammals. In particular, PACAP receptors are expressed by granule cell precursors suggesting a role of the peptide in neurogenesis of this cell type. Consistent with this hypothesis, several studies reported antiapoptotic effects of PACAP in the developing cerebellum. On the other hand, the sphingomyelin metabolites ceramides are recognized as important signaling molecules that play pivotal roles during neuronal development. Ceramides, which production can be induced by death factors such as FasL or TNFalpha, are involved in the control of cell survival during brain development through activation of caspase-dependent mechanisms. The present review focuses on the interactions between PACAP and ceramides in the control of granule cell survival and on the transduction mechanisms associated with the anti- and proapoptotic effects of PACAP and ceramides, respectively.

TLQP-21, a neuroendocrine VGF-derived peptide, prevents cerebellar granule cells death induced by serum and potassium deprivation

Different VGF peptides derived from Vgf, originally identified as a nerve growth factor responsive gene, have been detected in neurons within the central and peripheral nervous system and in various endocrine cells. In the current study, we have evaluated the ability of TLQP-21, a VGF-derived peptide, to protect, in a dose- and time-dependent manner, primary cultures of rat cerebellar granule cells (CGCs) from serum and potassium deprivation-induced cell death. We demonstrated that TLQP-21 increased survival of CGCs by decreasing the degree of apoptosis as assessed by cell viability and DNA fragmentation. Moreover, TLQP-21 significantly activated extracellular signal-regulated kinase 1/2, serine/threonine protein kinase, and c-jun N-terminal kinase phosphorylation, while decreased the extent of protein kinase C phosphorylation, as demonstrated by western blot analysis. In addition, TLQP-21 induced significant increase in intracellular calcium (as measured by fura-2AM) in about 60% of the recorded neurons. Taken together, the present results demonstrate that TLQP-21 promotes the survival of CGCs via pathways involving, within few minutes, modulation of kinases associated with CGCs survival, and by increasing intracellular calcium which can contribute to the neuroprotective effect of the peptide.

In vivo and in vitro characterization of a novel neuroprotective strategy for stroke: ischemic postconditioning

As clinical trials of pharmacological neuroprotective strategies in stroke have been disappointing, attention has turned to the brain's own endogenous strategies for neuroprotection. Recently, a hypothesis has been offered that modified reperfusion subsequent to a prolonged ischemic episode may also confer ischemic neuroprotection, a phenomenon termed 'postconditioning'. Here we characterize both in vivo and in vitro models of postconditioning in the brain and offer data suggesting a biological mechanism for protection. Postconditioning treatment reduced infarct volume by up to 50% in vivo and by approximately 30% in vitro. A duration of 10 mins of postconditioning ischemia after 10 mins of reperfusion produced the most effective postconditioning condition both in vivo and in vitro. The degree of neuroprotection after postconditioning was equivalent to that observed in models of ischemic preconditioning. However, subjecting the brain to both preconditioning as well as postconditioning did not cause greater protection than each treatment alone. The prosurvival protein kinases extracellular signal-regulated kinase (ERK), p38 mitogen-activated protein kinase (MAPK), and Akt show prolonged phosphorylation in the cortex of postconditioned rats. Neuroprotection after postconditioning was inhibited only in the presence of LY294002, which blocks Akt activation, but not U0126 or SB203580, which block ERK and P38 MAP kinase activity. In contrast, preconditioning-induced protection was blocked by LY294002, U0126, and SB203580. Our data suggest that postconditioning may represent a novel neuroprotective approach for focal ischemia/reperfusion, and one that is mediated, at least in part, by the activation of the protein kinase Akt.

Differential, age-dependent MEK-ERK and PI3K-Akt activation by insulin acting as a survival factor during embryonic retinal development

Programmed cell death is a genuine developmental process of the nervous system, affecting not only projecting neurons but also proliferative neuroepithelial cells and young neuroblasts. The embryonic chick retina has been employed to correlate in vivo and in vitro studies on cell death regulation. We characterize here the role of two major signaling pathways, PI3K-Akt and MEK-ERK, in controlled retinal organotypic cultures from embryonic day 5 (E5) and E9, when cell death preferentially affects proliferating neuroepithelial cells and ganglion cell neurons, respectively. The relative density of programmed cell death in vivo was much higher in the proliferative and early neurogenic stages of retinal development (E3-E5) than during neuronal maturation and synaptogenesis (E8-E19). In organotypic cultures from E5 and E9 retinas, insulin, as the only growth factor added, was able to completely prevent cell death induced by growth factor deprivation. Insulin activated both the PI3K-Akt and the MEK-ERK pathways. Insulin survival effect, however, was differentially blocked at the two stages. At E5, the effect was blocked by MEK inhibitors, whereas at E9 it was blocked by PI3K inhibitors. The cells which were found to be dependent on insulin activation of the MEK-ERK pathway at E5 were mostly proliferative neuroepithelial cells. These observations support a remarkable specificity in the regulation of early neural cell death.

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.

Evidence of Abeta- and transgene-dependent defects in ERK-CREB signaling in Alzheimer's models

Extracellular-signal regulated kinase (ERK) signaling is critical for memory and tightly regulated by acute environmental stimuli. In Alzheimer disease transgenic models, active ERK is shown to first be increased, then later reduced, but whether these baseline changes reflect disruptions in ERK signaling is less clear. We investigated the influence of the familial Alzheimer's disease transgene APPsw and beta-amyloid peptide (Abeta) immunoneutralization on cannulation injury-associated (i.c.v. infusion) ERK activation. At both 12 and 22 months of age, the trauma-associated activation of ERK observed in Tg(-) mice was dramatically attenuated in Tg(+). In cortices of 22-month-old non-infused mice, a reduction in ERK activation was observed in Tg(+), relative to Tg(-) mice. Intracerebroventricular (i.c.v.) anti-Abeta infusion significantly increased phosphorylated ERK, its substrate cAMP-response element-binding protein (CREB) and a downstream target, the NMDA receptor subunit. We also demonstrated that Abeta oligomer decreased active ERK and subsequently active CREB in human neuroblastoma cells, which could be prevented by oligomer immunoneutralization. Abeta oligomers also inhibited active ERK and CREB in primary neurons, in addition to reducing the downstream post-synaptic protein NMDA receptor subunit. These effects were reversed by anti-oligomer. Our data strongly support the existence of an APPsw transgene-dependent and Abeta oligomer-mediated defect in regulation of ERK activation.

Characterizing the neuroprotective effects of alkaline extract of Lycium barbarum on β-amyloid peptide neurotoxicity

Lycium barbarum is an oriental medicinal herb that has long been used for its anti-aging and cell-protective properties. Previous studies have shown that aqueous extracts from L. barbarum exhibit neuroprotection via inhibiting pro-apoptotic signaling pathways. Other active components can also be accomplished by novel alkaline extraction method, which may give different profiles of water-soluble components. We hypothesize that another active component obtained by alkaline extraction method exerts different biological mechanisms to protect neurons. In this study, we aim to examine the neuroprotective effects from the alkaline extract of L. barbarum, namely LBB, to attenuate beta-amyloid (Abeta) peptide neurotoxicity. Primary cortical neurons were exposed to Abeta-peptides inducing apoptosis and neuronal cell death. Pretreatment of LBB significantly reduced the level of lactate dehydrogenase (LDH) release and the activity of caspase-3 triggered by Abeta. "Wash-out" procedures did not reduce its neuroprotective effects, suggesting that LBB may not bind directly to Abeta. We have further isolated three subfractions from LBB, namely LBB-0, LBB-I and LBB-II. LBB-I and LBB-II showed differential neuroprotective effects. Western blot analysis demonstrated that LBB-I and LBB-II markedly enhanced the phosphorylation of Akt. Taken together, our results suggested that the glycoconjugate isolated from novel alkaline extraction method can open up a new avenue for drug discovery in neurodegenerative diseases.

Interleukin-1 beta impairs brain derived neurotrophic factor-induced signal transduction

The expression of IL-1 is elevated in the CNS in diverse neurodegenerative disorders, including Alzheimer's disease. The hypothesis was tested that IL-1 beta renders neurons vulnerable to degeneration by interfering with BDNF-induced neuroprotection. In trophic support-deprived neurons, IL-1 beta compromised the PI3-K/Akt pathway-mediated protection by BDNF and suppressed Akt activation. The effect was specific as in addition to Akt, the activation of MAPK/ERK, but not PLC gamma, was decreased. Activation of CREB, a target of these signaling pathways, was severely depressed by IL-1 beta. As the cytokine did not influence TrkB receptor and PLC gamma activation, IL-1 beta might have interfered with BDNF signaling at the docking step conveying activation to the PI3-K/Akt and Ras/MAPK pathways. Indeed, IL-1 beta suppressed the activation of the respective scaffolding proteins IRS-1 and Shc; this effect might involve ceramide generation. IL-1-induced interference with BDNF neuroprotection and signal transduction was corrected, in part, by ceramide production inhibitors and mimicked by the cell-permeable C2-ceramide. These results suggest that IL-1 beta places neurons at risk by interfering with BDNF signaling involving a ceramide-associated mechanism.

Running exercise- and antidepressant-induced increases in growth and survival-associated signaling molecules are IGF-dependent

It is known that physical exercise increases hippocampal brain-derived neurotrophic factor (BDNF) mRNA and protein, as well as the expression of several pro-survival signaling proteins and that many of these effects depend on the uptake of peripheral insulin-like growth factor-1 (IGF-1) into the CNS. Because treatment with antidepressants has similar effects upon neurotrophin expression, we investigated whether antidepressant-induced BDNF changes also depend on IGF-1 uptake, as well as whether IGF-1 plays a role in the exercise/antidepressant-induced expression of molecules associated with plasticity/growth (GAP-43, SCG-10) and the intracellular activation of molecules associated with neuronal survival (Akt, ERK1/2). We evaluated the effects of a well known monoamine oxidase inhibitor, tranylcypromine, on BDNF mRNA and protein levels and phospho-Akt and phospho-ERK1/2 immunoreactivity, both with and without systemic blockade of IGF-1 uptake through the use of an antiserum raised against IGF-1. Anti-IGF-1 reversed the increase in BDNF mRNA and protein elicited by exercise as well as tranylcypromine. Exercise also significantly enhanced transcription of axon growth protein, GAP-43, an effect that was also evidenced to be IGF-1-dependent. The combination of exercise-plus-tranylcypromine also increased several cell survival signaling measures, but the BDNF changes associated with the combination treatment appeared to be independent of IGF-1 uptake. Together, these results indicate that the uptake of peripheral IGF-1 in the CNS is essential for antidepressant- as well as exercise-induced enhancement in hippocampal BDNF expression and thus, enhanced hippocampal neuronal survival and plasticity.

Involvement of the ERK/MAP kinase signalling pathway in milli-calpain activation and myogenic cell migration

Recent research carried out in our laboratory has shown that IGF-1, TGF-beta1, and insulin were able to strongly stimulate myoblast migration by increasing milli-calpain expression and activity. However, the signalling pathways involved in these phenomena remain unknown. The aim of this study was to identify the signalling pathway(s) responsible for the effects of IGF-1, TGF-beta1, and insulin on myoblast migration and on milli-calpain expression and activity. For this purpose, wound healing assays were carried out in the presence of growth factors with or without specific inhibitors of ERK/MAP kinase and PI3K/Akt pathways. The results clearly showed that the inhibition of the ERK/MAP kinase pathway prevents the effects of growth factors on myoblast migration. Secondly, the expression and the activity of milli-calpain were studied in cells treated with growth factor, alone or with ERK/MAP kinase inhibitor. The results demonstrated that the up-regulation of milli-calpain expression and activity was mediated by the ERK/MAP kinase pathway. Finally, the possible implication of MyoD and myogenin, myogenic regulatory factors able to regulate milli-calpain expression, was studied. Taken together our results clearly showed that the ERK/MAP kinase signalling pathway is responsible for the effects of the three growth factors on myoblast migration and on milli-calpain expression and activity. On the opposite, the PI3K/Akt signalling pathway, MyoD and myogenin seem to be not implicated in these phenomena.

Sphingolipids in apoptosis, survival and regeneration in the nervous system

Simple sphingolipids such as ceramide, sphingosine and sphingosine 1-phosphate are key regulators of diverse cellular functions. Their roles in the nervous system are supported by extensive evidence derived primarily from studies in cultured cells. More recently animal studies and studies with human samples have revealed the importance of ceramide and its metabolites in the development and progression of neurodegenerative disorders. The roles of sphingolipids in neurons and glial cells are complex, cell dependent, and many times contradictory. In this review I will summarize the effects elicited by ceramide and ceramide metabolites in cells of the nervous system, in particular those effects related to cell survival and death, emphasizing the molecular mechanisms involved. I also discuss recent evidence for the implication of sphingolipids in the development and progression of certain dementias.

The neuroprotective effects of a locally acting IGF-1 isoform

In the last decade, dramatic progress has been made in elucidating the molecular defects underlying a number of neuromuscular diseases. With the characterization of mutations responsible for muscle and nerve dysfunction in several inherited pathologies, and the identification of novel signaling pathways, in which subtle alterations can lead to significant defects in tissue metabolism, the field is poised to devise successful strategies for treatment of this debilitating and often fatal group of human ailments. Yet progress in therapeutic application has been slow despite our newly gained knowledge of basic biology. Hence, where direct therapeutic approaches to address the primary diseases are still sub-optimal, it may be more effective to focus on strategies for improving neuromuscular function. Among potential candidates, insulin-like growth factor (IGF-1) has been involved in several anabolic pathways in both skeletal muscle and the nervous system and it is a promising candidate to attenuate neuromuscular diseases. In this review, we will discuss the role of IGF-1 isoforms in neuromuscular diseases and the contribution of muscle-produced IGF-1 (mIGF-1) to motor neuron survival and activity.