Insulin-like growth factor-I-mediated neurite outgrowth in vitro requires mitogen-activated protein kinase activation

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.

Unphosphorylated MARCKS is involved in neurite initiation induced by insulin-like growth factor-I in SH-SY5Y cells

Myristoylated alanine-rich C kinase substrate (MARCKS) has been suggested to be involved in various aspects of neuronal cell differentiation, including neurite outgrowth. However, the precise mechanisms by which MARCKS phosphorylation is regulated, and how MARCKS contributes to neurite outgrowth, are poorly understood. Here, we found that treatment of SH-SY5Y cells with insulin-like growth factor-I (IGF-I) induced a rapid and transient decrease in the level of phosphorylated MARCKS (P-MARCKS) to below the basal level. The decrease in P-MARCKS induced by IGF-I was blocked by pretreatment of cells with phosphoinositide 3-kinase (PI3K) inhibitors, LY294002 and wortmannin. A decrease in P-MARCKS was also observed in cells treated with a Rho-dependent kinase (ROCK) inhibitor, Y27632. Furthermore, IGF-I induced transient inactivation of RhoA, an upstream effector of ROCK. We showed that MARCKS was translocated to the membrane and colocalized with F-actin at the lamellipodia and the tips of neurites in the cells stimulated with IGF-I. Finally, overexpression of wild-type MARCKS or an unphosphorylatable mutant of MARCKS enhanced the number of neurite-bearing cells relative to vector-transfected cells. Taken together, these findings suggest that unphosphorylated MARCKS is involved in neurite initiation, and highlight the important role played by MARCKS in organization of the actin cytoskeleton.

The insulin-like growth factor system in multiple sclerosis

Multiple sclerosis (MS) is a chronic disorder of the central nervous system characterized by inflammation, demyelination, and axonal degeneration. Present therapeutic strategies for MS reduce inflammation and its destructive consequences, but are not effective in the progressive phase of the disease. There is a need for neuroprotective and restorative therapies in MS. Insulin-like growth factor-1 (IGF-1) is of considerable interest because it is not only a potent neuroprotective trophic factor but also a survival factor for cells of the oligodendrocyte lineage and possesses a potent myelinogenic capacity. However, the IGF system is complex and includes not only IGF-1 and IGF-2 and their receptors but also modulating IGF-binding proteins (IGFBPs), of which six have been identified. This chapter provides an overview of the role of the IGF system in the pathophysiology of MS, relevant findings in preclinical models, and discusses the possible use of IGF-1 as a therapeutic agent for MS.

Anti-Thy-1 antibody-induced neurite outgrowth in cultured dorsal root ganglionic neurons is mediated by the c-Src-MEK signaling pathway

Our previous study has shown that anti-Thy-1 antibody promotes neurite outgrowth of cultured dorsal root ganglion (DRG) neurons in a protein kinase A (PKA)-dependent manner. The present study provided another intracellular signaling pathway for the neurotrophic effect of anti-Thy-1 antibody. In DMSO-treated control cells, Thy-1 was enriched in microdomain-like structures on cell membranes by immunofluorescence observation. Treatment of DRG neurons with anti-Thy-1 antibody not only stimulated neurite outgrowth, but also increased the branching complexity of the neurites in both small and large neurons. We have previously shown that anti-Thy-1 antibody causes a time-dependent activation of mitogen-activated protein kinase (MEK) and of cyclic AMP response-element binding protein (CREB). Here, anti-Thy-1 antibody elicited a transient activation of c-Src kinase, and the activation of c-Src kinase appeared occurring upstream of the activation of MEK and CREB, since pretreatment with the Src kinase inhibitor, PP2, effectively abolished the anti-Thy-1 antibody-induced neurite outgrowth and the phosphorylation of MEK and CREB. CREB phosphorylation might result in upregulation of certain neurite outgrowth-related proteins. We therefore conclude that anti-Thy-1 antibody activates the c-Src kinase-MEK-CREB cascade and overcomes the inhibitory effect of Thy-1 on neurite outgrowth in DRG neurons.

Insulin and insulin-like growth factor type-I up-regulate the vanilloid receptor-1 (TRPV1) in stably TRPV1-expressing SH-SY5Y neuroblastoma cells

The capsaicin receptor, transient receptor potential, vanilloid type 1 (TRPV1), is a Ca(2+)-permeable ion channel activated by noxious stimuli eliciting pain. Several reports have shown modulation of TRPV1 activity and expression by neuronal growth factors. Here, we study the long-term effects on TRPV1 expression mediated by insulin-like growth factor type-I (IGF-I) and insulin in a stably TRPV1-expressing SH-SY5Y neuroblastoma cell line. We show that, after 72 hr of 10 nM IGF-I or insulin exposure, the TRPV1 protein level was up-regulated 2.5- and 2-fold, respectively. By blocking phosphatidylinositol-3-kinase [PI(3)K] or mitogen-activated protein kinase (MAPK) signaling, we concluded that the increase in total TRPV1 protein content induced by IGF-I was controlled by PI(3)K signaling, whereas insulin seemed to regulate TRPV1 protein expression via both PI(3)K and MAPK pathways. Inhibiting protein kinase C (PKC) blocked the effects of both IGF-I and insulin. Furthermore, the concentrations causing a 50% Ca(2+) increase (EC(50)) after insulin and IGF-I treatments were significantly lowered compared with untreated cells. We conclude that IGF-I and insulin enhance TRPV1 protein expression and activity, and impaired pain sensation might result from distorted TRPV1 regulation in the peripheral nervous system.

Association of Polymorphisms ofIGF1Rand Genes in the Transforming Growth Factor–β/Bone Morphogenetic Protein Pathway with Bacteremia in Sickle Cell Anemia

Infection and bacteremia are common in sickle cell disease. We hypothesized that, consistent with evidence for the genetic modulation of other disease complications, the risk of developing bacteremia might also be genetically modulated. Accordingly, we studied the association of single nucleotide polymorphisms (SNPs) in candidate genes with the risk of bacteremia in sickle cell anemia. We found significant associations with SNPs in IGF1R and genes of the TGF-beta /BMP pathway (BMP6, TGFBR3, BMPR1A, SMAD6 and SMAD3). We suggest that both IGF1R and the TGF-beta /BMP pathway could play important roles in immune function in sickle cell anemia and their polymorphisms may help identify a "bacteremia-prone" phenotype.

The opening effect of pregabalin on ATP-sensitive potassium channels in differentiated hippocampal neuron-derived H19-7 cells

PURPOSE

Adenosine triphosphate (ATP)-sensitive K+ (KATP) channels can couple an intracellular metabolic state to an electrical activity, which is important in the control of neuronal excitability and seizure propagation. We investigated whether the newer antiepileptic drug, pregabalin (PGB), could exert effects on KATP channels in differentiated hippocampal neuron-derived H19-7 cells.

METHODS

The inside-out configuration of the patch-clamp technique was used to investigate KATP channel activities in H19-7 cells in the presence of PGB. Effects of various compounds known to alter KATP channel activities were compared.

RESULTS

The activity of KATP channels in these cells was characterized. The single-channel conductance from a linear current-voltage relation was 78 +/- 2 pS (n = 8) with a reversal potential of 63 +/- 2 mV (n = 8), similar to that of KATP channels reported in pancreatic beta cells. 2,4-Dinitrophenol activated channel activity, but the further addition of glucose (20 mM) or glibenclamide (30 microM) could offset these increments. PGB significantly opened these KATP channel activities in a concentration-dependent fashion with a median effective concentration (EC50) value of 18 microM. A significant increase was noted in the mean open lifetime of KATP channels in the presence of PGB (1.71 +/- 0.04 to 5.62 +/- 0.04 ms).

CONCLUSIONS

This study suggests that in differentiated hippocampal neuron-derived H19-7 cells, the opening effect on KATP channels could be one of the underlying mechanisms of PGB in the reduction of neuronal excitability.

Adenoviral GDNF gene transfer enhances neurofunctional recovery after recurrent laryngeal nerve injury

To assess the possibility of gene therapy for recurrent laryngeal nerve (RLN) injury, we examined functional and histological recovery after glial cell line-derived neurotrophic factor (GDNF) gene transfer in a rat RLN crush model. Adenoviral vector encoding beta-galactosidase gene (AxCALacZ) or human GDNF gene (AxCAhGDNF) was injected into the crush site of the RLN. Neurons in the nucleus ambiguus on the crushed side were labeled with X-gal or GDNF immnohistochemistry after AxCALacZ or AxCAhGDNF injection. Reverse transcription-polymerase chain reaction analysis revealed expression of human GDNF mRNA transcripts in brainstem tissue containing the nucleus ambiguus on the crushed side after AxCAhGDNF injection. Animals injected with AxCAhGDNF displayed significantly improved motor nerve conduction velocity of the RLN and recovery rate of vocal fold movement at 2 and 4 weeks after treatment as compared to controls. AxCAhGDNF-injected animals showed a significantly larger axonal diameter and improved remyelination in crushed RLN as compared to controls. Adenoviral GDNF gene transfer may thus promote laryngeal function recovery after RLN injury. Inoculation of adenoviral vector containing the GDNF gene at the site of damage soon after nerve injury may assist patients with laryngeal paralysis caused by nerve injury during head and neck surgery.

Retinoic acid receptors and tissue-transglutaminase mediate short-term effect of retinoic acid on migration and invasion of neuroblastoma SH-SY5Y cells

Long-term treatment with all trans-retinoic acid (RA) induces neuronal differentiation and apoptosis. However, the effect of short-term RA treatment on cell proliferation, migration and invasion of neuroblastoma cell lines (SH-SY5Y and IMR-32) remains unclear. RA induces expression of tissue-transglutaminase (TGase) and promotes migration and invasion after 24 h of treatment in SH-SY5Y cells, but not in IMR-32 cells. RA receptor (RAR) agonist (4-(E-2-[5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthalenyl]-1-propenyl) benzoic acid) and RAR/retinoid X receptor (RXR) agonist (9-cis-RA) promote expression of TGase, migration and invasion of SH-SY5Y cells, while RXR agonist has no significant effect. RAR antagonist blocks RA effect on migration and invasion, indicating that RAR receptors are required. Retinoid receptors are expressed and activated by RA in both cell lines. However, only transient activation of RAR is observed in IMR-32 cells. These findings suggest that different responses observed in SH-SY5Y and IMR-32 cells could be due to differential activation of retinoid receptors. Overexpression of TGase has no effect on migration or invasion, while overexpression of antisense TGase blocks RA-induced migration and invasion, indicating that other molecules along with TGase mediate RA effects. In addition to the long-term effects of RA that are coupled with cell differentiation, short-term effects involve migration and invasion of neuroblastoma SH-SY5Y cells.

Neurofibromin binds to caveolin-1 and regulates ras, FAK, and Akt

Neurofibromin (Nf1) is an approximately 280 kDa protein having tumor suppressor function, presumably by virtue of its GTPase activating domain, but little is known regarding molecular aspects of its effector pathways. Caveolin-1 (Cav-1) regulates diverse signaling molecules and has itself been implicated as a tumor suppressor. Here we demonstrate that Nf1 binds to Cav-1's scaffolding domain and co-immunoprecipitates with Cav-1. Analysis of Nf1's primary structure reveals four potential caveolin binding domains, and interestingly, in individuals with neurofibromatosis I, missense mutations occur with high frequency in 3 of the 4 putative domains. We show that Nf1 modulates ras, Akt, and focal adhesion kinase pathways, thereby affecting cytoskeletal organization; moreover, Nf1's effects on signaling are altered when lipid rafts and caveolae are disrupted by cholesterol depletion. These novel findings provide insight into possible signaling mechanisms of Nf1 and suggest that together Nf1 and Cav-1 may coordinately regulate cell growth and differentiation.

Dendritic stability in a model of adult-onset IGF-I deficiency

OBJECTIVE

A significant decrease in plasma levels of insulin-like growth factor-I (IGF-I) is one of the most robust hallmarks of aging and may contribute to functional changes associated with senescence. This study examined the role of IGF-I in the maintenance of adult dendritic morphology.

DESIGN

We utilized a model of the aging-related decrease in plasma IGF-I to examine whether such a decrease, in itself, leads to dendritic changes in the cerebral cortex. The dw/dw rat, originally of the Lewis strain, suffers from a spontaneous mutation in which growth hormone (GH) production is severely decreased. Since GH is responsible for the production of circulating IGF-I by the liver, these animals are deficient in plasma IGF-I. Homozygous dw/dw rats were administered porcine GH to sustain IGF-I levels during development and then GH injections were stopped as adults in order to examine the effects of adult-onset GH and IGF-I deficiency. Animals sacrificed after two or eight weeks of GH and IGF-I deficiency were compared to age-matched dw/dw animals that received GH both developmentally and throughout adulthood (GH/IGF-I replete). The dendritic arbors of pyramidal neurons in cingulate cortex were labeled by intracellular injection and reconstructed in three dimensions.

RESULTS

Comparing GH/IGF-I replete and deficient dw/dw rats, we found no differences in the apical or basal arbors of either layer two or layer five pyramidal neurons.

CONCLUSIONS

These findings indicate that a decrease in plasma levels of IGF-I is not sufficient in itself to produce dendritic changes like those seen in aging animals.

IGF-1 and BDNF promote chick bulbospinal neurite outgrowth in vitro

Injured neurons in the CNS do not experience significant functional regeneration and so spinal cord insult often results in permanently compromised locomotor ability. The capability of a severed axon to re-grow is thought to depend on numerous factors, one of which is the decreased availability of neurotrophic factors. Application of trophic factors to axotomized neurons has been shown to enhance survival and neurite outgrowth. Although brainstem-spinal connections play a pivotal role in motor dysfunction after spinal cord injury, relatively little is known about the trophic sensitivity of these populations. This study explores the response of bulbospinal populations to various trophic factors. Several growth factors were initially examined for potential trophic effects on the projection neurons of the brainstem. Brain derived neurotrophic factor (BDNF) and insulin-like growth factor (IGF-1) significantly enhance mean process length in both the vestibulospinal neurons and spinal projection neurons from the raphe nuclei. Nerve growth factor (NGF), neurotrophin-4 (NT-4) and glial derived neurotrophic factor (GDNF) did not effect process outgrowth in vestibulospinal neurons. At the developmental stages used in this study, it was determined that receptors for BDNF and IGF-1 were present both on bulbospinal neurons and on surrounding cells with a non-neuronal morphology.

A novel neurotrophic agent, T-817MA [1-{3-[2-(1-benzothiophen-5-yl) ethoxy] propyl}-3-azetidinol maleate], attenuates amyloid-beta-induced neurotoxicity and promotes neurite outgrowth in rat cultured central nervous system neurons

Progressive neuronal loss in Alzheimer's disease (AD) is considered to be a consequence of the neurotoxic properties of amyloid-beta peptides (A beta). T-817MA (1-{3-[2-(1-benzothiophen-5-yl) ethoxy] propyl}-3-azetidinol maleate) was screened as a candidate therapeutic agent for the treatment of AD based on its neuroprotective potency against A beta-induced neurotoxicity and its effect of enhancing axonal regeneration in the sciatic nerve axotomy model. The neuroprotective effect of T-817MA against A beta(1-42) or oxidative stress-induced neurotoxicity was assessed using a coculture of rat cortical neurons with glia. T-817MA (0.1 and 1 microM) was strongly protective against A beta(1-42)-induced (10 microM for 48 h) or H2O2-induced (100 microM for 24 h) neuronal death. T-817MA suppressed the decrease of GSH levels induced by H2O2 exposure (30 microM for 4 h) in cortical neuron culture; therefore, T-817MA was likely to alleviate oxidative stress. Besides the neuroprotective effect, T-817MA (0.1 and 1 microM) promoted neurite outgrowth in hippocampal slice cultures and reaggregation culture of rat cortical neurons. T-817MA also increased the growth-associated protein 43 content in the reaggregation culture of cortical neurons. These findings suggest that T-817MA exerts neuroprotective effect and promotes neurite outgrowth in rat primary cultured neurons. Based on these neurotrophic features, T-817MA may have a potential for disease modification and be useful for patients with neurodegenerative diseases, such as AD.

The metabotropic P2Y4 receptor participates in the commitment to differentiation and cell death of human neuroblastoma SH-SY5Y cells

Extracellular nucleotides exert a variety of biological actions through different subtypes of P2 receptors. Here we characterized in the human neuroblastoma SH-SY5Y cells the simultaneous presence of various P2 receptors, belonging to the P2X ionotropic and P2Y metabotropic families. Western blot analysis detected the P2X1,2,4,5,6,7 and P2Y1,2,4,6, but not the P2X3 and P2Y12 receptors. We then investigated which biological effects were mediated by the P2Y4 subtype and its physiological pyrimidine agonist UTP. We found that neuronal differentiation of the SH-SY5Y cells with dibutiryl-cAMP increased the expression of the P2Y4 protein and that UTP itself was able to positively interfere with neuritogenesis. Moreover, transient transfection and activation of P2Y4 also facilitated neuritogenesis in SH-SY5Y cells, as detected by morphological phase contrast analysis and confocal examination of neurofilament proteins NFL. This was concurrent with increased transcription of immediate-early genes linked to differentiation such as cdk-5 and NeuroD6, and activity of AP-1 transcription family members such as c-fos, fos-B, and jun-D. Nevertheless, a prolonged activation of the P2Y4 receptor by UTP also induced cell death, both in naive, differentiated, and P2Y4-transfected SH-SY5Y cells, as measured by direct count of intact nuclei and cytofluorimetric analysis of damaged DNA. Taken together, our data indicate that the high expression and activation of the P2Y4 receptor participates in the neuronal differentiation and commitment to death of SH-SY5Y cells.

Developmental regulation of activated ERK expression in the spinal cord and dorsal root ganglion of the chick embryo

Mitogen-activated protein kinases (MAPKs) are involved in the intracellular pathways that respond to various extracellular signals. Extracellular signal-regulated kinase (ERK) is a member of MAPKs and has various functions in neural development. However, the in vivo distribution of the activated form of ERK (p-ERK) in the developing nervous system is not well understood. Here, we investigated the expression of p-ERK in the spinal cord and dorsal root ganglion (DRG) of chick embryos. In the spinal cord, p-ERK-positive cells appeared in the ventral ventricular zone on embryonic day 4 (E4). From E6 onward, they appeared in the gray matter and in the white matter, suggesting migration from the ventricular zone. A double labeling method revealed that these p-ERK-positive cells included oligodendrocyte precursors. In the dorsal horn, p-ERK-positive small cells appeared on E6. Subsequently, the positive cells in the dorsal horn increased transiently in number and then decreased markedly by E10. Motoneurons also expressed p-ERK transiently on E7. In the DRG, weak p-ERK immunoreaction appeared in the ventrolateral region on E5. From E6, the immunoreactivity became stronger and by E9 intense p-ERK-positive cells were observed throughout the DRG. These data provide a neuroanatomical framework to begin to examine the in vivo role of ERK in neural development.

Expression of the repressor element-1 silencing transcription factor (REST) is influenced by insulin-like growth factor-I in differentiating human neuroblastoma cells

The repressor element-1 (RE-1) silencing transcription factor (REST) interacts with an RE-1 cis element and represses the transcription of neuron-specific genes in neuronal progenitors but is down-regulated in post-mitotic neurons. We report that REST expression is modified, in a time-dependent manner, in SH-SY5Y neuroblastoma cells exposed to insulin-like growth factor I (IGF-I), a polypeptide hormone affecting various aspects of neuronal induction and maturation. REST is increased in cells treated with IGF-I for 2 days and then declines in 5-day-treated cells concomitant with a progressive neurite extension. To investigate any role played by REST in neurodifferentiation by IGF-I, we employed an antisense oligonucleotide (AS-ODN) complementary to REST mRNA. In AS-ODN-treated cells, the effects elicited by IGF-I on cell proliferation are not influenced whereas a marked decrease of REST significantly increases neurite elongation without any gross perturbation of neurogenesis. Synapsin I and betaIII-tubulin gene promoters contain an RE-1 motif and their transcription is repressed by REST; both of them are increased in cells exposed to IGF-I for 5 days and further elevated by AS-ODN treatment. A parallel increase of growth cone-associated protein 43, a protein chosen as a neuronal marker not directly regulated by REST, is also observed. Therefore, REST is elevated during early steps of neural induction by IGF-I and could contribute to down-regulate genes not yet required by the differentiation program while it declines later for the acquisition of neural phenotypes. These results suggest a model in which differentiating neuroblastoma cells determine their extent of neurite outgrowth on the basis of REST disappearance.

INGAP peptide improves nerve function and enhances regeneration in streptozotocin-induced diabetic C57BL/6 mice

INGAP peptide comprises the core active sequence of Islet Neogenesis Associated Protein (INGAP), a pancreatic cytokine that can induce new islet formation and restore euglycemia in diabetic rodents. The ability of INGAP peptide in vitro to enhance nerve growth from sensory ganglia suggests its potential utility in peripheral nerve disorders. In this study, INGAP peptide was administered alone or in combination with insulin to streptozotocin-induced diabetic mice exhibiting signs of peripheral neuropathy. Following a 2-wk treatment period, thermal hypoalgesia in diabetic mice was significantly improved in groups that received INGAP peptide, without development of hyperalgesia. Explanted dorsal root ganglia (DRG) from these groups showed enhanced nerve outgrowth and evidence of increased mitochondrial activity. Western blotting experiments revealed attenuation of neurofilament hyperphosphorylation, up-regulation of beta-tubulin and actin, and increased phosphorylation of the transcription factor STAT3 in DRG. These findings suggest that INGAP peptide can activate some of the signaling pathways implicated in nerve regeneration in sensory ganglia, thereby providing a means of improvement of nociceptive dysfunction in the peripheral nervous system.

Phosphatidylinositol 3-kinase and Akt effectors mediate insulin-like growth factor-I neuroprotection in dorsal root ganglia neurons

Insulin-like growth factor-I (IGF-I) protects neurons of the peripheral nervous system from apoptosis, but the underlying signaling pathways are not well understood. We studied IGF-I mediated signaling in embryonic dorsal root ganglia (DRG) neurons. DRG neurons express IGF-I receptors (IGF-IR), and IGF-I activates the phosphatidylinositol 3-kinase (PI3K)/Akt pathway. High glucose exposure induces apoptosis, which is inhibited by IGF-I through the PI3K/Akt pathway. IGF-I stimulation of the PI3K/Akt pathway phosphorylates three known Akt effectors: the survival transcription factor cyclic AMP response element binding protein (CREB) and the pro-apoptotic effector proteins glycogen synthase kinase-3beta (GSK-3beta) and forkhead (FKHR). IGF-I regulates survival at the nuclear level through accumulation of phospho-Akt in DRG neuronal nuclei, increased CREB-mediated transcription, and nuclear exclusion of FKHR. High glucose increases expression of the pro-apoptotic Bcl protein Bim (a transcriptional target of FKHR). However, IGF-I does not regulate Bim or anti-apoptotic Bcl-xL protein expression levels, which suggests that IGF-I neuroprotection is not through regulation of their expression. High glucose also induces loss of the initiator caspase-9 and increases caspase-3 cleavage, effects blocked by IGF-I. These data suggest that IGF-I prevents apoptosis in DRG neurons by regulating PI3K/Akt pathway effectors, including GSK-3beta, CREB, and FKHR, and by blocking caspase activation.

Degradation and dephosphorylation of focal adhesion kinase during okadaic acid-induced apoptosis in human neuroblastoma cells

Focal adhesion kinase (FAK) prevents apoptosis in many cell types. We have reported that tyrosine residues in FAK are dephosphorylated and FAK is degraded during mannitol-induced apoptosis in human neuroblastoma cells. Several studies suggest that FAK dephosphorylation and degradation are separate events. The current study defines the relationship between FAK dephosphorylation and degradation in neuroblastoma cells using okadaic acid (OA). OA, a serine phosphatase inhibitor, promotes serine/threonine phosphorylation, which in turn blocks tyrosine phosphorylation. OA induced focal adhesion loss, actin cytoskeleton disorganization, and cellular detachment, which corresponded to a loss of FAK Tyr397 phosphorylation. These changes preceded caspase-3 activation, Akt and MAP kinase activity loss, protein ubiquitination, and cellular apoptosis. Insulin-like growth factor-I prevented mannitol-induced, but not OA-induced, substrate detachment and FAK Tyr397 dephosphorylation, and the effects of OA on FAK Tyr397 phosphorylation were irreversible. The proteolytic degradation of FAK is temporally distinct from its tyrosine dephosphorylation, occurring when apoptotic pathways are already initiated and during a generalized destruction of signaling proteins. Therefore, agents resulting in the dephosphorylation of FAK may be beneficial for therapeutic treatment, irrespective of FAK protein levels, as this may result in apoptosis, which cannot be prevented by growth factor signaling.

IGF-I increases IGFBP-5 and collagen alpha1(I) mRNAs by the MAPK pathway in rat intestinal smooth muscle cells

IGF-I is a potent fibrogenic growth factor that stimulates proliferation of intestinal smooth muscle cells and increases synthesis of collagen and IGF-I-binding proteins by the cells. These processes contribute to intestinal fibrosis that develops in patients with Crohn's disease and in Lewis-strain rats with experimental Crohn's disease. The aim of this study was to determine which early docking proteins are associated with IGF-I receptor signal transduction and which transduction pathway is involved in IGF-I-mediated gene regulation in intestinal smooth muscle cells. Primary cultures of smooth muscle cells isolated from the muscularis externa of the distal colon of Lewis rats were treated with IGF-I (100 ng/ml). Immunoprecipitation studies demonstrated that IGF-I stimulation resulted in tyrosine phosphorylation of IRS-1, IRS-2, and Shc. Coimmunoprecipitation demonstrated a close association between the IGF-I receptor and these three early docking proteins. Concurrent treatment with the MAPK inhibitor PD98059 (10 microM) resulted in an inhibition of the IGF-I-mediated increase in IGFBP-5 and collagen alpha(1)(I) mRNAs, while concurrent treatment with the phosphatidylinositol 3-kinase (PI3-K) inhibitor wortmannin (100 nM) had no effect. In additional experiments, cells were transiently transfected with adenoviral vectors dominantly expressing inactive mutant Akt or constitutively expressing wild-type Akt. In both cases, the IGF-I-mediated increase in collagen I protein did not differ from that observed in control cultures that had been transfected with an adenoviral vector carrying the LacZ reporter gene. These results suggest that the MAPK pathway is key to IGF-I-mediated gene regulation in intestinal smooth muscle cells, whereas data do not suggest a role for the Akt-dependent pathway in our system.

Neuronal protection from glucose deprivation via modulation of glucose transport and inhibition of apoptosis: a role for the insulin-like growth factor system

Glucose is the brain's major energy source; therefore, loss of neuronal cells is a potential consequence of hypoglycaemia. Since apoptosis is a major mechanism of neuronal loss following a range of insults, we explored potent anti-apoptotic systems (IGF-I and bcl-2) as means of enhancing neuronal survival in the face of glucose deprivation. Human neuroblastoma cells (SH-SY5Y, SHEP and SHEP-bcl-2) were exposed to low glucose as a model of glucopenia-induced neuronal damage. Administration of IGF-I and/or over-expression of the survival gene bcl-2 were exploited to attempt to limit neuronal loss. Neuronal survival mechanisms and interactions between these systems were investigated. Low glucose (0.25-2.5 mM) adversely affected cell growth and survival; however, IGF-I ameliorated these outcomes. Over-expression of bcl-2 blunted low glucose-induced apoptosis and up-regulated IGF-I receptor, with the effect of IGF-I addition being negligible on apoptosis, while significantly enhancing mitochondrial activity. In SH-SY5Y cells, IGF-I significantly changed >two-fold mRNA levels of the apoptosis-related genes gadd45, fas, iNOS, NFkB, TRAIL, without further affecting bcl-2 expression. In low glucose, IGF-I acutely enhanced glucose transport and translocation of GLUT1 protein to the cell membrane. GLUT1 mRNA expression was up-regulated by both IGF-I and bcl-2. The potent anti-apoptotic systems IGF-I and bcl-2 are both thus able to enhance cell survival in a glucose-deprived human neuronal model. Although we clearly show evidence of positive cross-talk via bcl-2 modulation of IGF-I receptor, IGF-I also has enhancing effects on mitochondrial function outside the bcl-2 pathway. The common effect of both systems on enhancement of GLUT-1 expression suggests that this is a key mechanism for enhanced survival. These studies also point to the potential use of IGF-I therapy in prevention or amelioration of hypoglycaemic brain injury.

Neurotoxicity of platinum compounds: comparison of the effects of cisplatin and oxaliplatin on the human neuroblastoma cell line SH-SY5Y

The main dose-limiting side effect of cancer treatment with platinum compounds is peripheral neurotoxicity. To investigate the intracellular mechanisms of platinum drugs neurotoxicity we have studied the effects of cisplatin and oxaliplatin on the human neuroblastoma cell line SH-SY5Y. Both platinum compounds are toxic causing cellular death by inducing apoptosis but oxaliplatin is less neurotoxic than cisplatin. The study of the proteins involved in the intracellular transduction pathways that may cause apoptotic death, revealed a very similar pattern of changes after exposure to cisplatin or oxaliplatin. In particular, as demonstrated by densitometric analysis, after exposure to both platinum compounds the total amount of the anti-apoptotic protein Bcl-2 was significantly reduced. Conversely, the amount of the pro-apoptotic protein p53 significantly increased. Caspases 3 and 7 were activated, but their activation was a late event, indicating a secondary role in the apoptotic process. Among the mitogen activated protein kinases, only the p38 protein was activated (phosphorylated) early enough to have a possible role in inducing apoptosis, possibly through p53 stabilization. The results of the present study and the data of the literature demonstrate that the ways in which cisplatin and oxaliplatin are neurotoxic are very similar and include not only DNA damage, but also the modulation of specific molecules involved in regulating the cellular equilibrium between apoptotic death and the cell cycle.

Impaired Shc, Ras, and MAPK activation but normal Akt activation in FL5.12 cells expressing an insulin-like growth factor I receptor mutated at tyrosines 1250 and 1251

The Y1250F/Y1251F mutant of the insulin-like growth factor I receptor (IGF-IR) has tyrosines 1250 and 1251 mutated to phenylalanines and is deficient in IGF-I-mediated suppression of apoptosis in FL5.12 lymphocytic cells. To address the mechanism of loss of function in this mutant we investigated signaling responses in FL5.12 cells overexpressing either a wild-type (WT) or Y1250F/Y1251F (mutant) IGF-IR. Cells expressing the mutant receptor were deficient in IGF-I-induced phosphorylation of the JNK pathway and had decreased ERK and p38 phosphorylation. IGF-I induced phosphorylation of Akt was comparable in WT and mutant expressing cells. The decreased activation of the mitogen-activated protein kinase (MAPK) pathways was accompanied by greatly decreased Ras activation in response to IGF-I. Although phosphorylation of Gab2 was similar in WT and mutant cell lines, phosphorylation of Shc on Tyr(313) in response to IGF-I was decreased in cells expressing the mutant receptor, as was recruitment of Grb2 and Ship to Shc. However, phosphorylation of Shc on Tyr(239), the Src phosphorylation site, was normal. A role for JNK in the survival of FL5.12 cells was supported by the observation that the JNK inhibitor SP600125 suppressed IGF-I-mediated protection from apoptosis. Altogether these data demonstrate that phosphorylation of Shc, and assembly of the Shc complex necessary for activation of Ras and the MAPK pathways are deficient in cells expressing the Y1250F/Y1251F mutant IGF-IR. This would explain the loss of IGF-I-mediated survival in FL5.12 cells expressing this mutant and may also explain why this mutant IGF-IR is deficient in functions associated with cellular transformation and cell migration in fibroblasts and epithelial tumor cells.

Systemic complications of acromegaly: epidemiology, pathogenesis, and management

This review focuses on the systemic complications of acromegaly. Mortality in this disease is increased mostly because of cardiovascular and respiratory diseases, although currently neoplastic complications have been questioned as a relevant cause of increased risk of death. Biventricular hypertrophy, occurring independently of hypertension and metabolic complications, is the most frequent cardiac complication. Diastolic and systolic dysfunction develops along with disease duration; and other cardiac disorders, such as arrhythmias, valve disease, hypertension, atherosclerosis, and endothelial dysfunction, are also common in acromegaly. Control of acromegaly by surgery or pharmacotherapy, especially somatostatin analogs, improves cardiovascular morbidity. Respiratory disorders, sleep apnea, and ventilatory dysfunction are also important contributors in increasing mortality and are advantageously benefitted by controlling GH and IGF-I hypersecretion. An increased risk of colonic polyps, which more frequently recur in patients not controlled after treatment, has been reported by several independent investigations, although malignancies in other organs have also been described, but less convincingly than at the gastrointestinal level. Finally, the most important cause of morbidity and functional disability of the disease is arthropathy, which can be reversed at an initial stage, but not if the disease is left untreated for several years.

Retinoic acid-induced neuritogenesis of human neuroblastoma SH-SY5Y cells is ERK independent and PKC dependent

Retinoic acid (RA), an active metabolite of vitamin A, is a natural morphogen involved in development and differentiation of the nervous system. To elucidate signaling mechanisms involved in RA-induced neuritogenesis, we used human neuroblastoma SH-SY5Y cells, an established in vitro model for studying RA action, to examine the role of extracellular signal-regulated kinase (ERK) 1 and 2 in RA-induced neuritogenesis and cell survival. From immunoblotting experiments, we observed that RA induced delayed but persistent ERK1 and ERK2 phosphorylation (until 96 hr) that was reduced significantly by the specific mitogen-activated protein kinase (MAPK)/ERK kinase (MEK) inhibitor U0126. For the subsequent studies we chose 24 hr as the reference time. Inhibition of ERK activation did not affect RA-induced neuritogenesis (percentage of neurite-bearing cells and neurite length) but significantly reduced cell survival. In addition, we analyzed the signaling pathway that mediates ERK activation. Our results suggest that RA-induced ERK phosphorylation does not follow the classic Raf kinase-dependent pathway. Protein kinase C (PKC) and phosphatidylinositol 3-kinase (PI 3-K) are possible alternative kinases involved in the ERK signaling pathway. In fact, in the presence of the specific PKC inhibitor GF 109203X, or the specific PI 3-K inhibitor wortmannin, we observed a significant dose-dependent reduction in ERK phosphorylation. RA-induced neuritogenesis and cell survival were reduced by GF 109203X in a concentration-dependent manner. These results suggest that rather than ERK1 and ERK2, it is PKC that plays an important role during early phases of RA-induced neuritogenesis.

Insulin-like growth factor-I signaling in human neuroblastoma cells

Neuroblastoma is a heterogeneous tumor consisting of N (neuronal) and S (stromal) cells. We report that more tumorigenic and motile N cells express higher levels of IGF-I receptor (IGF-IR) than less tumorigenic, more adherent S cells. Shc, one of the two major docking partners of IGF-IR, is equally expressed in N and S cell lines. IGF-I treatment phosphorylates Shc in N cells, but only weakly activates Shc in S cells. Expression of the second partner, insulin receptor substrate (IRS), is cell type specific. S cells exclusively express IRS-1 that undergoes sustained phosphorylation by IGF-I. In contrast, N cells express IRS-2 that is transiently phosphorylated by IGF-I. Downstream of IRS-2 and Shc, IGF-I treatment results in strong activation of Akt and MAPK in N cells and activation of both pathways is required for IGF-I-mediated differentiation. Only IGF-IR activation of phosphatidylinositol-3 kinase is required for tumor edge ruffling in N and S cells, with stimulation of focal adhesion kinase (FAK) and paxillin. This detailed understanding of the 'biochemical signature' of N and S cells provides the background needed to target and disrupt specific IGF signaling pathways in an attempt to develop more effective therapies.

Signalling pathways for insulin-like growth factor type 1-mediated expression of uncoupling protein 3

Uncoupling protein 3 (UCP3) is a mitochondrial protein with antioxidant properties and its regulation by factors promoting cell-survival may be important for protection of, for instance, neurons in states of oxidative stress. In the present study, we investigated regulatory pathways for UCP3 expression mediated by the neuroprotective hormone insulin-like growth factor type 1 (IGF-1) in human neuroblastoma SH-SY5Y cells. Northern blot analysis and RT-PCR showed that treatment with 10 nm IGF-1 increased the UCP3 mRNA levels 2.5-fold after 5 h. Co-incubation with the phosphatidylinositol 3 (PI3)-kinase inhibitor LY294002 prohibited IGF-1-mediated induction of both UCP3 mRNA and protein in a concentration-dependent manner, with a complete blockage at 1 microm, as shown by RT-PCR and western blot analyses. The mitogen-activated protein (MAP) kinase kinase 1 (MKK1 or MEK) inhibitor PD98059 also decreased the UCP3 mRNA expression at 10 microm, however, this concentration only partly inhibited the protein expression. We conclude that IGF-1 enhanced UCP3 expression at transcriptional level, primarily through the PI3-kinase-dependent pathway and partly through the MAP kinase pathway.

Parallel phosphatidylinositol-3 kinase and p42/44 mitogen-activated protein kinase signaling pathways subserve the mitogenic and antiapoptotic actions of insulin-like growth factor I in osteoblastic cells

IGF-I is an endocrine and paracrine regulator of skeletal homeostasis, principally by virtue of its anabolic effects on osteoblastic cells. In the current study, we examined the intracellular signaling pathways by which IGF-I promotes proliferation and survival in SaOS-2 human osteoblastic cells. Inhibition of each of the phosphatidylinositol-3 kinase (PI-3 kinase), p42/44 MAPK, and p70s6 kinase pathways partially inhibited the ability of IGF-I to stimulate osteoblast proliferation and survival. Because activation of p70s6 kinase is downstream of both PI-3 kinase and p42/44 MAPK activation in osteoblasts treated with IGF-I, this ribosomal kinase represents a convergence point for IGF-I-induced PI-3 kinase and p42/44 MAPK signaling in osteoblastic cells. In addition, abrogation of PI-3 kinase-dependent Akt signaling, which does not inhibit IGF-I-induced p70s6 kinase phosphorylation, also inhibited the antiapoptotic effects of IGF-I in osteoblasts. Finally, interruption of G beta gamma signaling partially abrogated the ability of IGF-I to promote osteoblast survival, without inhibiting signaling through PI-3 kinase/Akt, p42/44 MAPKs, or p70s6 kinase. These data suggest that IGF-I signals osteoblast mitogenesis and survival through parallel, partly overlapping intracellular pathways involving PI-3 kinase, p42/44 MAPKs, and G beta gamma subunits.

Potentiation of quantal secretion by insulin-like growth factor-1 at developing motoneurons in Xenopus cell culture

Although evidence suggests that insulin-like growth factor (IGF) plays an important role in the development and growth of the nervous system, the effect of IGF-1 in the regulation of neurotransmitter release in the peripheral nervous system remains unknown. Here we show that acute application of IGF-1, a factor widely expressed in developing myocytes, dose-dependently enhances the spontaneous acetylcholine (ACh) secretion at developing neuromuscular synapses in Xenopus cell culture using whole-cell patch clamp recording. We studied the role of endogenously released IGF-1 by examining the effect of IGF-1 antibody on the frequency of spontaneous synaptic currents (SSCs) at high-activity synapses, and found SSC frequency was markedly reduced at these high-activity synapses. The IGF-1-induced synaptic potentiation was not abolished when Ca2+ was eliminated from the culture medium or there was bath-application of the pharmacological Ca2+ channel inhibitor Cd2+, indicating that Ca2+ influxes through voltage-activated Ca2+ channels are not required. Application of membrane-permeable inhibitors of inositol 1,4,5-trisphosphate (IP3) or ryanodine receptors effectively occluded the increase of SSC frequency elicited by IGF-I. Treating cells with the phosphoinositide-3 kinase (PI3-K) inhibitors wortmannin or LY294002, and with phospholipase Cgamma (PLCgamma) inhibitor U73122, but not the inhibitor of mitogen-activated protein (MAP) kinase PD98059, abolished IGF-1-induced synaptic potentiation. Taken collectively, these results suggest that endogenously released IGF-1 from myocytes elicits Ca2+ release from IP3- and/or ryanodine-sensitive intracellular Ca2+ stores of the presynaptic nerve terminal. This is done via PI3-K and PLCgamma signalling cascades, leading to an enhancement of spontaneous transmitter release.

The chemotactic and mitogenic responses of vascular smooth muscle cells to insulin-like growth factor-I require the activation of ERK1/2

Insulin-like growth factors (IGFs) play an important role in regulating vascular smooth muscle cell (VSMC) proliferation and directed migration. IGFs exert these biological actions through the activation of the IGF-I receptor and its downstream signaling network. While the involvement of the IRS-PI3 kinase-Akt pathway in mediating the chemotactic and mitogenic actions of IGFs is clear, the role of the mitogen-activated protein kinase (MAPK) signaling pathway is still under debate. In this study, the role of ERK1 and 2 in mediating the chemotactic and mitogenic actions of IGF-I in cultured porcine VSMCs was investigated. IGF-I treatment caused a significant increase in the phosphorylation state, as well as the kinase activity, of ERK1 and 2. Compared to the strong and sustained MAPK activation induced by platelet-derived growth factor-BB, the IGF-I-induced MAPK activation was weaker and more transient. Specific inhibition of the MAPK activation by PD98059 or U0126, two selective MEK inhibitors, significantly inhibited IGF-I-stimulated cell proliferation, and reduced the number of cells that migrated towards IGF-I. The p38 MAPK inhibitor SB203580 had no such effect. Likewise, depletion of ERK1/2 using antisense oligonucleotides abolished the IGF-I-induced VSMC migration and proliferation. These results suggest that the chemotactic and mitogenic responses of VSMCs to IGF-I require the activation of ERK1 and 2.

Insulin-like growth factor 1 is essential for normal dendritic growth

This study evaluated somatic and dendritic growth of neurons in the frontoparietal cortex of Igf1-/- brains. Pyramidal neuron density was increased by approximately 25% (P =.005) and soma size reduced by approximately 10% (P <.001). Golgi staining revealed that cortical layer II-III neurons exhibited a significant reduction in dendritic length and complexity in Igf1 null mice. Dendritic spine density and presumably synaptic contacts were reduced by 16% (P =.002). Similar findings were obtained for cortical layer V and piriform cortex pyramids. Supporting a reduction in synapses, synaptotagmin levels were reduced by 30% (P <.02) in the Igf1 null brain. Investigation of factors critically involved in dendritic growth and synaptogenesis showed an approximately 50% reduction in cortical CDC42 protein expression (P <.001) and an approximately 10% reduction in brain cholesterol levels (P <.01) in Igf1 null mice. Evidence is presented that Igf1 deletion causes disruptions in lipid and microtubule metabolism, leading to impaired neuronal somatic and dendritic growth. Published 2003 Wiley-Liss, Inc.

Delivery of an adenoviral vector to the crushed recurrent laryngeal nerve

OBJECTIVES

Objectives were to create a model of recurrent laryngeal nerve injury for testing the efficacy of potential therapeutic viral gene therapy vectors and to demonstrate that remote injection of a viral vector does not cause significant additional neuronal injury.

STUDY DESIGN

Animal model.

METHODS

Rats were randomly assigned to three groups of 10 animals each. In group I, the recurrent laryngeal nerve was crushed. In group II, the nerve was crushed and then injected with an adenoviral vector containing no transgene. In group III, the nerve was identified but was not crushed. Rats were killed at 1 week, and their larynges and brainstems were cryosectioned in 15-microm sections. Laryngeal cryosections were processed for acetylcholine histochemical analysis (motor endplates) followed by neurofilament immunoperoxidase (nerve fibers). Percentage of nerve-endplate contact was determined and compared between groups. Fluorescent in situ hybridization was performed on brainstem sections from rats in group II to confirm the presence of virus.

RESULTS

No significant difference in percentage of nerve-endplate contact exists between the two crushed-nerve groups (groups I and II) (P =.88). The difference between both crushed-nerve groups and the group with noncrushed nerves (group III) was highly significant (P <.0001). The presence of virus was confirmed in group II rats.

CONCLUSIONS

Crush provides a significant measurable injury to the recurrent laryngeal nerve and may be used as a model to explore therapeutic interventions for nerve injury. The remote injection of viral vector did not cause significant additional neuronal injury. Remote delivery of viral vectors to the central nervous system holds promise in the treatment of recurrent laryngeal nerve injury and central nervous system diseases.

Insulin-like growth factor-I as a promoting factor for cerebellar Purkinje cell development

In the mammalian CNS, the peptide hormone insulin-like growth factor-I (IGF-I) is synthesized in a certain subset of neurons and, it has been suggested, serves as a local neurotrophic factor. A postnatal increase in the expression of IGF-I and the type-1 IGF receptors (IGFR1) in the cerebellar cortex and its related brain regions indicates that developing cerebellar Purkinje cells (PC) may be an important target of IGF-I. However, little is known about how IGF-I influences PC development. Here we addressed this question, using a reduced environment of cerebellar neuron culture derived from perinatal mice. IGF-I exogenously applied at a physiological concentration (10 nm) greatly promoted the dendritic growth and survival of the PCs. By contrast, IGF-I only slightly promoted the somatic growth and little affected the maturation of the electrophysiological excitability of the PCs. The closely related hormone insulin had weaker promoting effects than did IGF-I. IGF-I appeared to at least bind to IGFR1 and to up-regulate the signalling pathways involving the phosphoinositide 3-kinase (PI3-K), mitogen-activated protein kinase (MAPK), p38 kinase (p38K), and an unknown signalling molecule(s). These signalling pathways may be coupled to the individual aspects of PC development in different manners and this may explain the difference in effects of IGF-I among these aspects. These findings suggest that IGF-I serves as a promoting factor for PC development, particularly postnatal survival and dendritic growth.

N-Myc overexpression leads to decreased beta1 integrin expression and increased apoptosis in human neuroblastoma cells

Neuroblastoma is a childhood tumor thought to arise through improper differentiation of neural crest cells. Increased N-Myc expression in neuroblastoma indicates highly malignant disease and poor patient prognosis. N-myc enhances cell growth, insulin-like growth factor type I receptor (IGF-IR) expression, and tumorigenicity in combination with Bcl-2. Despite these effects, N-Myc overexpression in SHEP neuroblastoma cells (SHEP/N-Myc cells) increases serum-withdrawal and mannitol-induced apoptosis. Although we have previously shown a protective effect of IGF-I in SHEP cells, in SHEP/N-Myc cells IGF-I rescue from mannitol-induced apoptosis is prevented. N-Myc overexpression has little effect on IGF-IR signaling pathways, but results in increased Akt phosphorylation when Bcl-2 is coexpressed. A loss of integrin-mediated adhesion promotes apoptosis in many systems. SHEP/N-Myc cells have dramatically less beta1 integrin expression than control cells, consistent with previous reports. beta1 integrin expression is decreased in more tumorigenic neuroblastoma cells lines, including IMR32 and SH-SY5Y cells. Reintroduction of beta1 integrin into the N-Myc-overexpressing cells prevents mannitol-mediated apoptosis. We speculate that N-Myc repression of beta1 integrin expression leads to a less differentiated phenotype, resulting in increased growth and tumorigenesis if properly supported or apoptosis if deprived of growth sustaining molecules.

Effect of trans-resveratrol on signal transduction pathways involved in paclitaxel-induced apoptosis in human neuroblastoma SH-SY5Y cells

trans-Resveratrol (3,4',5-trihydroxystilbene) is able to significantly reduce paclitaxel-induced apoptosis in the human neuroblastoma (HN) SH-SY5Y cell line, acting on several cellular signaling pathways that are involved in paclitaxel-induced apoptosis. trans-Resveratrol reverses phosphorylation of Bcl-2 induced by paclitaxel and concomitantly blocks Raf-1 phosphorylation, also observed after paclitaxel exposure, thus suggesting that Bcl-2 inactivation may be dependent on the activation of the Raf/Ras cascade. trans-Resveratrol also reverses the sustained phosphorylation of JNK/SAPK, which specifically occurs after paclitaxel exposure.Overall, our observations demonstrate that (a) the toxic action of paclitaxel on neuronal-like cells is not only related to the effect of the drug on tubulin, but also to its capacity to activate several intracellular pathways leading to inactivation of Bcl-2, thus causing cells to die by apoptosis, (b) trans-resveratrol significantly reduces paclitaxel-induced apoptosis by modulating the cellular signaling pathways which commit the cell to apoptosis.

L- and D-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP) inhibit neurite outgrowth from SH-SY5Y cells

Gangliosides and extracellular matrix molecules influence neurite outgrowth, but the combinatorial effects of these endogenous agents on outgrowth are unclear. Exogenous gangliosides inhibit neurite outgrowth from SH-SY5Y cells stimulated with platelet-derived growth factor-BB, and different isoforms of the ceramide analog threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP) stimulate (L-PDMP) or inhibit (D-PDMP) glycosphingolipid biosynthesis. In this study, we determined whether altering the endogenous ganglioside levels with PDMP in SH-SY5Y cells regulates neurite outgrowth on the outgrowth-supporting extracellular matrix molecule, laminin. In cells stimulated with 20 ng/ml platelet-derived growth factor-BB to promote outgrowth, we used image analysis to evaluate neurite outgrowth from SH-SY5Y cells grown on endogenous matrix or laminin and exposed to L- or D-PDMP. Both L- and D-PDMP decreased neurite initiation (the number of neurites/cell, the percent of neurite-bearing cells), elongation (the length of the longest neurite/cell, the total neurite length/cell), and branching (the number of branch points/neurite) from SH-SY5Y cells on endogenous matrix or laminin in a dose-dependent manner in serum-free or serum-containing medium. The inhibitory effects of each PDMP isoform were reversible. Inhibition of neurite outgrowth by L-PDMP could be mimicked by addition of exogenous gangliosides or C2-ceramide. Our analyses of neurite outgrowth in SH-SY5Y cells, a model of developing or regenerating noradrenergic neurons, demonstrate that increasing or decreasing endogenous ganglioside levels decreases neurite outgrowth. These results may indicate that SH-SY5Y cells undergo tight regulation by gangliosides, possibly through modulation of growth/trophic factor- and/or extracellular matrix-activated signaling cascades.

Interactions of estrogen and insulin-like growth factor-I in the brain: molecular mechanisms and functional implications

In the brain, as in other tissues, estradiol interacts with growth factors. One of the growth factors that is involved in the neural actions of estradiol is insulin-like growth factor-I (IGF-I). Estradiol and IGF-I cooperate in the central nervous system to regulate neuronal development, neural plasticity, neuroendocrine events and the response of neural tissue to injury. The precise molecular mechanisms involved in these interactions are still not well understood. In the central nervous system there is abundant co-expression of estrogen receptors (ERs) and IGF-I receptors (IGF-IRs) in the same cells. Furthermore, the expression of estrogen receptors and IGF-I receptors in the brain is cross-regulated. In addition, using specific antibodies for the phosphorylated forms of extracellular-signal regulated kinase (ERK) 1 and ERK2 and Akt/protein kinase B (Akt/PKB) it has been shown that estradiol affects IGF-I signaling pathways in the brain. Estradiol treatment results in a dose-dependent increase in the phosphorylation of ERK and Akt/PKB in the brain of adult ovariectomized rats. In addition, estradiol and IGF-I have a synergistic effects on the activation of Akt/PKB in the adult rat brain. These findings suggest that estrogen effects in the brain may be mediated in part by the activation of the signaling pathways of the IGF-I receptor.

Synergistic interaction of estradiol and insulin-like growth factor-I in the activation of PI3K/Akt signaling in the adult rat hypothalamus

Estradiol and insulin-like growth factor-I (IGF-I) interact in the hypothalamus to regulate neuronal function, synaptic plasticity and neuroendocrine events. However, the molecular mechanisms involved in these interactions are still unknown. In the present study, the effect of estradiol on the signaling pathways of IGF-I receptor has been assessed in the hypothalamus of young adult ovariectomized rats, using specific antibodies for the phosphorylated forms of extracellular-signal regulated kinase (ERK) 1 and ERK2 and Akt/protein kinase B (Akt/PKB). Estradiol treatment resulted, between 6 and 24 h after systemic administration, in dose-dependent effects on the phosphorylation of ERK and Akt/PKB. Estradiol did not modify the level of ERK phosphorylation induced by intracerebroventricular administration of IGF-I. However, both hormones had a synergistic effect on the phosphorylation of Akt/PKB. These findings suggest that estrogen effects in the hypothalamus may be mediated in part by the activation of the signaling pathways of the IGF-I receptor.

Anti-tumor mechanisms of valproate: a novel role for an old drug

Valproic acid (VPA, 2-propylpentanoic acid) is an established drug in the long-term therapy of epilepsy. During the past years, it has become evident that VPA is also associated with anti-cancer activity. VPA not only suppresses tumor growth and metastasis, but also induces tumor differentiation in vitro and in vivo. Several modes of action might be relevant for the biological activity of VPA: (1) VPA increases the DNA binding of activating protein-1 (AP-1) transcription factor, and the expression of genes regulated by the extracellular-regulated kinase (ERK)-AP-1 pathway; (2) VPA downregulates protein kinase C (PKC) activity; (3) VPA inhibits glycogen synthase kinase-3beta (GSK-3beta), a negative regulator of the Wnt signaling pathway; (4) VPA activates the peroxisome proliferator-activated receptors PPARgamma and delta; (5) VPA blocks HDAC (histone deacetylase), causing hyperacetylation. The findings elucidate an important role of VPA for cancer therapy. VPA might also be useful as low toxicity agent given over long time periods for chemoprevention and/or for control of residual minimal disease.

Insulin-like growth factor I prevents mannitol-induced degradation of focal adhesion kinase and Akt

In our laboratory, we are interested in hyperosmolarity-induced apoptosis in neuronal cells. We have shown that high concentrations of glucose or mannitol induce apoptotic cell death in dorsal root ganglia in culture and in SH-SY5Y and SH-EP human neuroblastoma cells. Focal adhesion kinase (FAK) is a cytoplasmic tyrosine kinase that has a critical role for transmitting integrin-mediated-signals. In this study, we report that hyperosmolar treatment mediates FAK dephosphorylation and cleavage, which is prevented by insulin-like growth factor I (IGF-I) treatment. Mannitol treatment of SH-EP cells transfected with vector (SH-EP/pSFFV) results in concentration- and time-dependent dephosphorylation and degradation of FAK. Dephosphorylation and degradation of FAK are tightly correlated with apoptotic morphological changes, including the disruption of actin stress fibers, the loss of focal adhesion sites, membrane blebbing, and cell detachment. Treatment of SH-EP/pSFFV cells with IGF-I or transfection of IGF-I receptor prevents these changes. Treatment of cells with pharmacologic inhibitors of the mitogen-activated protein kinase or phosphatidylinositol 3-kinase pathways does not affect mannitol-induced FAK dephosphorylation and degradation. However, phosphatidylinositol 3-kinase is necessary for IGF-I-mediated protection against FAK alteration. Mannitol treatment also results in the degradation of Akt. Mannitol induces the activation of caspases-3 and -9 in a time course similar to the dephosphorylation and degradation of FAK. Treatment of the cells with ZVAD, a general caspase inhibitor, blocks the mannitol-induced FAK and Akt degradation as well as cell detachment and apoptosis. These results suggest that one of the pathways of mannitol-mediated apoptosis is through the degradation of FAK and Akt and that IGF-I protects the cells from apoptosis by blocking the activation of caspases, which may be responsible for the loss of FAK and Akt.

Phosphatidylinositol-3-kinase-Akt kinase and p42/p44 mitogen-activated protein kinases mediate neurotrophic and excitoprotective actions of a secreted form of amyloid precursor protein

The alpha-secretase-derived form of the amyloid precursor protein (sAPPalpha), which is released from neurons in an activity-dependent manner, has been shown to promote long-term survival of hippocampal and cortical neurons in culture and can protect those neurons against excitotoxic and ischemic injury in culture and in vivo. The signal transduction pathway(s) activated by sAPPalpha has not been established. We now report that sAPPalpha activates the phosphatidylinositol-3-kinase (PI(3)K)-Akt kinase signaling pathway in cultured hippocampal neurons. sAPPalpha also stimulates phosphorylation of p42 (ERK1) and p44 (ERK2) mitogen-activated protein (MAP) kinases by a PI(3)K-independent pathway. Treatment of neurons with sAPPalpha protects them against death induced by trophic factor deprivation and exposure to glutamate, and these survival-promoting effects of sAPPalpha are abolished or attenuated when either PI(3)K or p42/p44 MAP kinases are selectively blocked. Exposure of neurons to sAPPalpha resulted in a decrease in the level of IkappaBbeta and an increase in NF-kappaB DNA binding activity, both of which were blocked by wortmannin, suggesting that the transcription factor NF-kappaB may be a downstream target of the PI(3)K-Akt pathway that may play a role in the cell survival-promoting action of sAPPalpha. These findings suggest that the PI(3)K-Akt pathway and p42/p44 MAP kinases mediate responses of neurons to sAPPalpha in physiological and pathological settings, with implications for synaptic plasticity and the pathogenesis of Alzheimer's disease.

Direct interaction of insulin-like growth factor-1 receptor with leukemia-associated RhoGEF

Insulin-like growth factor (IGF)-1 plays crucial roles in growth control and rearrangements of the cytoskeleton. IGF-1 binds to the IGF-1 receptor and thereby induces the autophosphorylation of this receptor at its tyrosine residues. The phosphorylation of the IGF-1 receptor is thought to initiate a cascade of events. Although various signaling molecules have been identified, they appear to interact with the tyrosine-phosphorylated IGF-1 receptor. Here, we identified leukemia-associated Rho guanine nucleotide exchange factor (GEF) (LARG), which contains the PSD-95/Dlg/ZO-1 (PDZ), regulator of G protein signaling (RGS), Dbl homology, and pleckstrin homology domains, as a nonphosphorylated IGF-1 receptor-interacting molecule. LARG formed a complex with the IGF-1 receptor in vivo, and the PDZ domain of LARG interacted directly with the COOH-terminal domain of IGF-1 receptor in vitro. LARG had an exchange activity for Rho in vitro and induced the formation of stress fibers in NIH 3T3 fibroblasts. When MDCKII epithelial cells were treated with IGF-1, Rho and its effector Rho-associated kinase (Rho-kinase) were activated and actin stress fibers were enhanced. Furthermore, the IGF-1-induced Rho-kinase activation and the enhancement of stress fibers were inhibited by ectopic expression of the PDZ and RGS domains of LARG. Taken together, these results indicate that IGF-1 activates the Rho/Rho-kinase pathway via a LARG/IGF-1 receptor complex and thereby regulates cytoskeletal rearrangements.

Insulin-like growth factor I stimulates motility in human neuroblastoma cells

Motility is an important process that contributes to cancer cell spread. Growth factors are key regulators of motility in many cell types. Insulin-like growth factor I (IGF-I) causes SH-SY5Y human neuroblastoma cells to undergo dynamic morphological changes, leading to the extension of lamellipodia. IGF-I stimulated lamellipodia extension requires signaling through both phosphatidylinositol 3-kinase (PI3-K) and MAP kinase pathways. IGF-I, over a period of hours, stimulates SH-SY5Y and SHEP neuroblastoma cells to become more motile. While SH-SY5Y and SHEP cells use different insulin receptor substrate (IRS) isoforms to transduce signals from the IGF-I receptor, IGF-I has the same relative effect on the motility of both cell lines. Blocking the PI3-K and MAP kinase pathways attenuates the ability of IGF-I to increase motility. Overexpression of PTEN also attenuates IGF-I mediated motility. These results delineate some of the proximal events in the signaling mechanism utilized by IGF-I to stimulate cell motility.

Remote delivery of rAAV-GFP to the rat brainstem through the recurrent laryngeal nerve

OBJECTIVE

To demonstrate that a recombinant adeno-associated viral vector (rAAV) carrying the gene for green fluorescent protein (GFP) could be delivered to the rat brainstem by remote injection into the recurrent laryngeal nerve.

STUDY DESIGN/METHODS

rAAV-GFP is a serotype 2 adeno-associated vector containing the cDNA of GFP and woodchuck hepatitis virus posttranscriptional regulatory element (WPRE) under the control of the CAG promoter (obtained from Matthew During, PhD, Thomas Jefferson Medical College). Five microliters or 10 microL of 1.4 x 109 particles/microL of rAAV-GFP were injected into the right recurrent laryngeal nerve of adult Sprague-Dawley rats. Rats were killed and perfused at 3 (n = 3) and 11 weeks (n = 3). Brainstems were removed and cryosectioned. Fluorescent in-situ hybridization (FISH) was performed on cryosections from animals killed at 3 weeks using a cDNA probe for woodchuck polyribosomal enzyme within the rAAV vector. In a third group (n = 2), Fluoro-Gold (Fluorochrome, Inc., Denver, CO) was injected into the right thyroarytenoid muscle for comparison of neuronal uptake distribution. These rats were killed and perfused at 3 weeks.

RESULTS

The presence of GFP was noted in neurons throughout the medulla of all rat brainstems after unilateral rAAV-GFP injection at both 3 and 11 weeks. In contrast to the Fluoro-Gold, GFP was noted bilaterally and outside of the nucleus ambiguus. FISH confirmed the presence of virus within neurons expressing GFP at 3 weeks.

CONCLUSIONS

Remote delivery of rAAV-GFP to the rat brainstem is possible through injection into the recurrent laryngeal nerve. This has important therapeutic implications for the future treatment of recurrent laryngeal nerve injury and neurodegenerative diseases.

Insulin-like growth factor type 1 upregulates uncoupling protein 3

In this study the expression of uncoupling protein 3 (UCP3) and its regulation by insulin-like growth factor 1 (IGF-I) and insulin in human neuroblastoma SH-SY5Y cells were characterized. Reverse transcriptase-PCR, Western blot, and immunofluorescence analysis showed that SH-SY5Y cells express UCP3 natively. IGF-I induced a time- and concentration-dependent induction of UCP3 protein reaching a twofold expression after 72 h with 10 nM IGF-I. Extremely high insulin concentrations (860 nM) and 10 nM trIGF-I, a truncated form of IGF-I with the same affinity for the IGF-I receptor as the full-length IGF-I, but with lower activity on the insulin receptor, also upregulated UCP3. We conclude that SH-SY5Y cells express UCP3 natively and that the expression is regulated by IGF-I via the IGF-I receptor.

Does a vegan diet reduce risk for Parkinson's disease?

Three recent case-control studies conclude that diets high in animal fat or cholesterol are associated with a substantial increase in risk for Parkinson's disease (PD); in contrast, fat of plant origin does not appear to increase risk. Whereas reported age-adjusted prevalence rates of PD tend to be relatively uniform throughout Europe and the Americas, sub-Saharan black Africans, rural Chinese, and Japanese, groups whose diets tend to be vegan or quasi-vegan, appear to enjoy substantially lower rates. Since current PD prevalence in African-Americans is little different from that in whites, environmental factors are likely to be responsible for the low PD risk in black Africans. In aggregate, these findings suggest that vegan diets may be notably protective with respect to PD. However, they offer no insight into whether saturated fat, compounds associated with animal fat, animal protein, or the integrated impact of the components of animal products mediates the risk associated with animal fat consumption. Caloric restriction has recently been shown to protect the central dopaminergic neurons of mice from neurotoxins, at least in part by induction of heat-shock proteins; conceivably, the protection afforded by vegan diets reflects a similar mechanism. The possibility that vegan diets could be therapeutically beneficial in PD, by slowing the loss of surviving dopaminergic neurons, thus retarding progression of the syndrome, may merit examination. Vegan diets could also be helpful to PD patients by promoting vascular health and aiding blood-brain barrier transport of L-dopa.

The mood stabilizer valproic acid activates mitogen-activated protein kinases and promotes neurite growth

The mood-stabilizing agents lithium and valproic acid (VPA) increase DNA binding activity and transactivation activity of AP-1 transcription factors, as well as the expression of genes regulated by AP-1, in cultured cells and brain regions involved in mood regulation. In the present study, we found that VPA activated extracellular signal-regulated kinase (ERK), a kinase known to regulate AP-1 function and utilized by neurotrophins to mediate their diverse effects, including neuronal differentiation, neuronal survival, long term neuroplasticity, and potentially learning and memory. VPA-induced activation of ERK was blocked by the mitogen-activated protein kinase/ERK kinase inhibitor PD098059 and dominant-negative Ras and Raf mutants but not by dominant-negative stress-activated protein kinase/ERK kinase and mitogen-activated protein kinase kinase 6 mutants. VPA also increased the expression of genes regulated by the ERK pathway, including growth cone-associated protein 43 and Bcl-2, promoted neurite growth and cell survival, and enhanced norepinephrine uptake and release. These data demonstrate that VPA is an ERK pathway activator and produces neurotrophic effects.

The role of the insulin receptor substrate-1 in the differentiation of rat hippocampal neuronal cells

H19-7/IGF-IR cells are rat hippocampal cells expressing a human IGF-I receptor, which differentiate to a neuronal phenotype when stimulated by IGF-I at 39 degrees C. H19-7/IGF-IR cells have low levels of expression of insulin receptor substrate-l (IRS-1), a major substrate of the IGF-IR. IGF-I induces serine-phosphorylation and down-regulation of the endogenous IRS-1 upon differentiation of H19-7/IGF-IR cells. The profound influence of IRS-1 on differentiation of H19-7/IGF-IR cells was confirmed by transfecting these cells with a plasmid expressing mouse IRS-1. Over-expression of wild type IRS-1 in H19-7/IGF-IR cells abolishes IGF-I-induced differentiation at 39 degrees C. A mutant of IRS-1 lacking the PTB domain loses the ability to inhibit the differentiation program. H19-7/IGF-IR/IRS-1 cells at 39 degrees C show a stronger and prolonged activation of Akt, when compared to H19-7/IGF-IR cells. The role of Akt in the inhibition of the differentiation program was confirmed by using the inhibitor of Class I PI3 kinases LY29400, which restores IGF-I-induced differentiation of H19-7/IGF-IR/IRS-1 cells. H19-7/IGF-IR/IRS-1 cells show a strong reduction in MAP kinases signaling, which is related to the superactivation of Akt. This was confirmed by expressing in H19-7/IGF-IR cells a constitutively active Akt, which inhibited MAP kinases activation in these cells. These experiments confirm the importance of MAPK in the mechanism of IGF-I-mediated differentiation of H19-7/IGF-IR cells

DNA synthesis and mitotic clonal expansion is not a required step for 3T3-L1 preadipocyte differentiation into adipocytes

Upon differentiation induction of 3T3-L1 preadipocytes by a hormone mixture containing 1-isobutyl-3-methylxanthine, dexamethasone, and insulin, the preadipocytes undergo approximately 2 rounds of mitotic clonal expansion, which just precedes the adipogenic gene expression program and has been thought to be an essential early step for differentiation initiation. By inducing 3T3-L1 preadipocytes with each individual hormone, it was determined that the mitotic clonal expansion was induced only by insulin and not by 1-isobutyl-3-methylxanthine or dexamethasone. Cell number counting and fluorescence-activated cell-sorting analysis indicated that a significant fraction of 3T3-L1 preadipocytes differentiated into adipocytes without mitotic clonal expansion when induced with the combination of 1-isobutyl-3-methylxanthine and dexamethasone. Furthermore, when normally induced 3T3-L1 preadipocytes were treated with PD98059 (an inhibitor of mitogen-activated protein kinase/extracellular signal-regulated kinase kinase 1) to block the activation of extracellular signal-regulated kinase (Erk) 1 and Erk2, the mitotic clonal expansion was blocked, but adipocyte differentiation was not affected. These observations were confirmed by bromodeoxyuridine labeling. The differentiated adipocytes induced with 1-isobutyl-3-methylxanthine and dexamethasone or standard hormone mixture plus PD98059 were not labeled by bromodeoxyuridine. Thus, it is evident that 3T3-L1 preadipocytes could differentiate into adipocytes without DNA synthesis and mitotic clonal expansion. Our results also suggested that activation of Erk1 and Erk2 is essential to but not sufficient for induction of mitotic clonal expansion.

Calcium regulates the expression of insulin-like growth factor binding protein-3 by the human keratinocyte cell line HaCaT

The insulin-like growth factor (IGF) system is essential for epidermal homeostasis. Insulin-like growth factor binding protein 3 (IGFBP-3), a modulator of IGF action that also exhibits IGF-independent activity, is localized to selected keratinocytes in the basal epidermal layer and may thus contribute to keratinocyte differentiation. We have utilized the human keratinocyte cell line, HaCaT, to examine the effect of calcium on the regulation of components of the IGF system. Western ligand and northern blot analyses revealed secreted IGFBP-3 and IGFBP-3 mRNA were reduced by an elevation in calcium levels in the culture medium. At 1.0 and 1.2 mM CaCl2 culture conditions IGFBP-3 abundance was reduced to 36% +/- 1.6% and 26% +/- 7.1%, respectively, of that from cells grown at 0.03 mM CaCl2. IGFBP-3 mRNA levels in 0.7 mM and 1.2 mM CaCl2 were reduced to 46% +/- 17.4% and 24% +/- 4.6%, respectively, compared with IGFBP-3 mRNA levels at 0.03 mM CaCl2. The observed reduction of IGFBP-3 was not associated with IGFBP-3 proteolysis. In contrast IGF-I receptor protein and mRNA levels remained unchanged. The IGF-I stimulated proliferative response of HaCaT keratinocytes showed that under low (0.03 mM) and high (1.2 mM) CaCl2 conditions IGF-I at 100 and 1000 ng per ml similarly increased cell number 2.4- and 2.7-fold, respectively, with similar dose-response curves. HaCaT keratinocytes grown under medium (0.7 mM) and high (1.2 mM), but not low (0.03 mM), CaCl2 conditions for 21 d revealed an induction of profilaggrin mRNA, a marker of keratinocyte differentiation. These studies indicate that the exposure of HaCaT keratinocytes to elevated calcium levels is associated with a decline in IGFBP-3 but not IGF-I receptor levels. These findings suggest a potential mechanism for the distribution of IGFBP-3 in the epidermis, which may be involved in the process of keratinocyte differentiation.