The effects of insulin-like growth factor (IGF)-1, IGF-2, and des-IGF-1 on neuronal loss after hypoxic-ischemic brain injury in adult rats: evidence for a role for IGF binding proteins

Insulin-like growth factor binding protein-2 in at-risk adults and autopsy-confirmed Alzheimer brains

Insulin, insulin-like growth factors (IGF) and their receptors are highly expressed in the adult hippocampus. Thus, disturbances in the insulin-IGF signalling pathway may account for the selective vulnerability of the hippocampus to nascent Alzheimer's disease (AD) pathology. In the present study, we examined the predominant IGF-binding protein in the CSF, IGFBP2. CSF was collected from 109 asymptomatic members of the parental history-positive PREVENT-AD cohort. CSF levels of IGFBP2, core AD and synaptic biomarkers were measured using proximity extension assay, ELISA and mass spectrometry. Cortical amyloid-beta (Aβ) and tau deposition were examined using 18F-NAV4694 and flortaucipir. Cognitive assessments were performed during up to 8 years of follow-up, using the Repeatable Battery for the Assessment of Neuropsychological Status. T1-weighted structural MRI scans were acquired, and neuroimaging analyses were performed on pre-specified temporal and parietal brain regions. Next, in an independent cohort, we allocated 241 dementia-free ADNI-1 participants into four stages of AD progression based on the biomarkers CSF Aβ42 and total-tau (t-tau). In this analysis, differences in CSF and plasma IGFBP2 levels were examined across the pathological stages. Finally, IGFBP2 mRNA and protein levels were examined in the frontal cortex of 55 autopsy-confirmed AD and 31 control brains from the Quebec Founder Population (QFP) cohort, a unique population isolated from Eastern Canada. CSF IGFBP2 progressively increased over 5 years in asymptomatic PREVENT-AD participants. Baseline CSF IGFBP2 was positively correlated with CSF AD biomarkers and synaptic biomarkers, and negatively correlated with longitudinal changes in delayed memory (P = 0.024) and visuospatial abilities (P = 0.019). CSF IGFBP2 was negatively correlated at a trend-level with entorhinal cortex volume (P = 0.082) and cortical thickness in the piriform (P = 0.039), inferior temporal (P = 0.008), middle temporal (P = 0.014) and precuneus (P = 0.033) regions. In ADNI-1, CSF (P = 0.009) and plasma (P = 0.001) IGFBP2 were significantly elevated in Stage 2 [CSF Aβ(+)/t-tau(+)]. In survival analyses in ADNI-1, elevated plasma IGFBP2 was associated with a greater rate of AD conversion (hazard ratio = 1.62, P = 0.021). In the QFP cohort, IGFBP2 mRNA was reduced (P = 0.049); however, IGFBP2 protein levels did not differ in the frontal cortex of autopsy-confirmed AD brains (P = 0.462). Nascent AD pathology may induce an upregulation in IGFBP2 in asymptomatic individuals. CSF and plasma IGFBP2 may be valuable markers for identifying CSF Aβ(+)/t-tau(+) individuals and those with a greater risk of AD conversion.

IGF2 in memory, neurodevelopmental disorders, and neurodegenerative diseases

Insulin-like growth factor 2 (IGF2) emerged as a critical mechanism of synaptic plasticity and learning and memory. Deficits in IGF2 in the brain, serum, or cerebrospinal fluid (CSF) are associated with brain diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), and amyotrophic lateral sclerosis (ALS). Increasing IGF2 levels enhances memory in healthy animals and reverses numerous symptoms in laboratory models of aging, neurodevelopmental disorders, and neurodegenerative diseases. These effects occur via the IGF2 receptor (IGF2R) - a receptor that is highly expressed in neurons and regulates protein trafficking, synthesis, and degradation. Here, I summarize the current knowledge regarding IGF2 expression and functions in the brain, particularly in memory, and propose a novel conceptual model for IGF2/IGF2R mechanisms of action in brain health and diseases.

Insulin-like Growth Factor-1 Prevents Hypoxia/Reoxygenation-Induced White Matter Injury in Sickle Cell Mice

Occlusion of cerebral blood vessels causes acute cerebral hypoxia—an important trigger of ischemic white matter injury and stroke in sickle cell disease (SCD). While chronic hypoxia triggers compensatory neuroprotection via insulin-like growth factor-1 (IGF-1) and hypoxia inducible factor-1α (HIF-1α), severe bouts of acute hypoxia and subsequent restoration of blood flow (hypoxia/reoxygenation, H/R) overwhelm compensatory mechanisms and cause neuroaxonal damage–identified as white matter lesions–in the brain. The neuroprotective role of IGF-1 in the pathogenesis of white matter injury in SCD has not been investigated; however, it is known that systemic IGF-1 is reduced in individuals with SCD. We hypothesized that IGF-1 supplementation may prevent H/R-induced white matter injury in SCD. Transgenic sickle mice homozygous for human hemoglobin S and exposed to H/R developed white matter injury identified by elevated expression of non-phosphorylated neurofilament H (SMI32) with a concomitant decrease in myelin basic protein (MBP) resulting in an increased SMI32/MBP ratio. H/R-challenge also lowered plasma and brain IGF-1 expression. Human recombinant IGF-1 prophylaxis significantly induced HIF-1α and averted H/R-induced white matter injury in the sickle mice compared to vehicle-treated mice. The expression of the IGF-1 binding proteins IGFBP-1 and IGFBP-3 was elevated in the IGF-1-treated brain tissue indicating their potential role in mediating neuroprotective HIF-1α signaling. This study provides proof-of-concept for IGF-1-mediated neuroprotection in SCD.

Association of serum biomarkers with early neurologic improvement after intravenous thrombolysis in ischemic stroke

BACKGROUND

Early neurologic improvement (ENI) after intravenous thrombolysis is associated with favorable outcome, but associated serum biomarkers were not fully determined. We aimed to investigate the issue based on a prospective cohort.

METHODS

In INTRECIS study, five centers were designed to consecutively collect blood sample from enrolled patients. The patients with ENI and without ENI were matched by propensity score matching with a ratio of 1:1. Preset 49 biomarkers were measured through microarray analysis. Enrichment of gene ontology and pathway, and protein-protein interaction network were analyzed in the identified biomarkers.

RESULTS

Of 358 patients, 19 patients with ENI were assigned to ENI group, while 19 matched patients without ENI were assigned to Non ENI group. A total of nine biomarkers were found different between two groups, in which serum levels of chemokine (C-C motif) ligand (CCL)-23, chemokine (C-X-C motif) ligand (CXCL)-12, insulin-like growth factor binding protein (IGFBP)-6, interleukin (IL)-5, lymphatic vessel endothelial hyaluronan receptor (LYVE)-1, plasminogen activator inhibitor (PAI)-1, platelet-derived growth factor (PDGF)-AA, suppression of tumorigenicity (ST)-2, and tumor necrosis factor (TNF)-α were higher in the ENI group, compared with those in the Non ENI group.

CONCLUSIONS

We found that serum levels of CCL-23, CXCL-12, IGFBP-6, IL-5, LYVE-1, PAI-1, PDGF-AA, ST-2, and TNF-α at admission were associated with post-thrombolytic ENI in stroke. The role of biomarkers warrants further investigation.

TRIAL REGISTRATION

Clinical Trial Registration: https://www.clinicaltrials.gov; identifier: NCT02854592.

Association of Serum Biomarkers With Post-Thrombolytic Symptomatic Intracranial Hemorrhage in Stroke: A Comprehensive Protein Microarray Analysis From INTRECIS Study

Background

Symptomatic intracranial hemorrhage (sICH) after intravenous thrombolysis is closely related to the poor outcome of stroke.

Aims

To determine the serum biomarkers associated with sICH based on the INTRECIS study.

Methods

Enrolled patients with sICH and without any ICH were matched by propensity score matching with the ratio of 1:1. Preset 49 biomarkers were measured by protein microarray analysis. Gene Ontology and Pathway Enrichment Analysis and protein-protein interaction network (PPI) were analyzed in the identified biomarkers.

Results

Of the consecutive 358 patients, eight patients occurred with sICH, which was assigned as an sICH group, while eight matched patients without any ICH were assigned as a Non-sICH group. A total of nine biomarkers were found significantly different between groups, among which the levels of interferon (IFN)-γ and interleukin (IL)-4 were higher, while the levels of C-reactive protein (CRP), glial cell line-derived neurotrophic factor (GDNF), insulin-like growth factor-binding protein (IGFBP)-6, lymphatic vessel endothelial hyaluronan receptor (LYVE)-1, matrix metalloprotein (MMP)-2, plasminogen activator inhibitor (PAI)-1, and platelet-derived growth factor (PDGF)-AA were lower in the sICH group compared with those in the Non-sICH group.

Conclusions

Our finding indicated that baseline serum CRP, GDNF, IFN-γ, IGFBP-6, IL-4, LYVE-1, MMP-2, PAI-1, and PDGF-AA levels were associated with post-thrombolytic sICH in stroke.

Insulin-Like Growth Factor 2 As a Possible Neuroprotective Agent and Memory Enhancer-Its Comparative Expression, Processing and Signaling in Mammalian CNS

A number of studies performed on rodents suggest that insulin-like growth factor 2 (IGF-2) or its analogs may possibly be used for treating some conditions like Alzheimer’s disease, Huntington’s disease, autistic spectrum disorders or aging-related cognitive impairment. Still, for translational research a comparative knowledge about the function of IGF-2 and related molecules in model organisms (rats and mice) and humans is necessary. There is a number of important differences in IGF-2 signaling between species. In the present review we emphasize species-specific patterns of IGF-2 expression in rodents, humans and some other mammals, using, among other sources, publicly available transcriptomic data. We provide a detailed description of Igf2 mRNA expression regulation and pre-pro-IGF-2 protein processing in different species. We also summarize the function of IGF-binding proteins. We describe three different receptors able to bind IGF-2 and discuss the role of IGF-2 signaling in learning and memory, as well as in neuroprotection. We hope that comprehensive understanding of similarities and differences in IGF-2 signaling between model organisms and humans will be useful for development of more effective medicines targeting IGF-2 receptors.

Evidence for altered energy metabolism, increased lactate, and decreased pH in schizophrenia brain: A focused review and meta-analysis of human postmortem and magnetic resonance spectroscopy studies

Though the pathophysiology of schizophrenia remains poorly understood, altered brain energy metabolism is increasingly implicated. Here, we conduct meta-analyses of the available human studies measuring lactate or pH in schizophrenia brain and discuss the accumulating evidence for increased lactate and decreased pH in schizophrenia brain and evidence linking these to negative and cognitive symptom severity. Meta-analysis of six postmortem studies revealed a significant increase in lactate in schizophrenia brain while meta-analysis of 14 magnetic resonance spectroscopy studies did not reveal a significant change in brain pH in schizophrenia. However, only five of these studies were likely sufficiently powered to detect differences in brain pH, and meta-analysis of these five studies found a nonsignificant decrease in pH in schizophrenia brain. Next, we discuss evidence for altered brain energy metabolism in schizophrenia and how this may underlie a buildup of lactate and decreased pH. This alteration, similar to the Warburg effect extensively described in cancer biology, involves diminished tricarboxylic acid cycle and oxidative phosphorylation along with a shift toward increased reliance on glycolysis for energy production. We then explore the role that mitochondrial dysfunction, oxidative stress, and hypoxia-related changes in gene expression likely play in this shift in brain energy metabolism and address the functional consequences of lowered brain pH in schizophrenia including alterations in neurotransmitter regulation, mRNA stability, and overall patterns of gene expression. Finally, we discuss how altered energy metabolism in schizophrenia brain may serve as an effective target in the treatment of this illness.

Cyclic glycine-proline administration normalizes high-fat diet-induced synaptophysin expression in obese rats

Childhood metabolic disorders are associated with insulin-like growth factor (IGF)-1 deficiency, which can adversely affect brain development and function. As a neuropeptide, cyclic glycine-proline (cGP) improves IGF-1 function in brain and regulates IGF-1 bioavailability in plasma. Whether such a regulatory process mediates the neurotrophic effects of cGP remains unknown. This study examined the effects cGP treatment on synaptic expression and their association with IGF-1, IGF binding protein (IGFBP)-2 and cGP concentrations in the brain of rats with high fat diet (HFD)-induced obesity. Male rats received either a HFD or a standard chow diet (STD) from weaning and were then treated with either saline or cGP from 11 to 15 weeks of age. The concentrations of cGP, IGF-1 and IGFBP-2 were measured in the brain tissues using ELISA and HPLC-MS. The expressions of synaptic markers were evaluated in the hippocampus, hypothalamus and striatum using immunohistochemical staining. Compared to the STD group, IGF-1 and IGFBP-2, but not cGP concentrations, were lower in the HFD groups. The expression of hippocampal synaptophysin, glutamate receptor-1, GFAP and striatal tyrosine-hydroxylase were also reduced in the HFD groups. While treatment did not alter tissue IGF-1, cGP administration that increased the concentration of cGP in brain tissues, normalized the expression of synaptophysin, GFAP and tyrosine-hydroxylase, but not glutamate receptor-1. IGF-1 concentration in brain tissues correlated with the expression of all synaptic markers. HFD feeding reduced synaptic expression and tissue IGF-1 in brains which were closely associated, thus suggesting IGF-1 in the brain is largely bioavailable. Without increasing IGF-1 in the brain, administration of cGP normalized synaptic expression, possibly be mediated through increasing bioavailable IGF-1, but further studies are required to confirm this.

Glia-Like Cells from Late-Passage Human MSCs Protect Against Ischemic Stroke Through IGFBP-4

Stem cell therapy is considered to be a promising future treatment for intractable neurological diseases, although all the clinical trials using stem cells have not yet shown any good results. Early passage mesenchymal stem cells (MSCs) have been used in most clinical trials because of the issues on safety and efficacy. However, it is not easy to get plenty of cells enough for the treatment and it costs too much. Lots of late passage MSCs can be obtained at lower cost but their efficacy would be a big hurdle for clinical trials. If late passage MSCs with better efficacy could be used in clinical trials, it could be a new and revolutionary solution to reduce cost and enhance easier clinical trials. In the present study, it was investigated whether late passage MSCs could be induced into glia-like cells (ghMSCs); ghMSCs had better efficacy and they protected neurons and the brain from ischemia, and insulin-like growth factor binding protein-4 (IGFBP-4) played a critical role in beneficial effect of ghMSCs. ghMSCs were induced from MSCs and treated in in vitro and in vivo models of ischemia. They effectively protected neurons from ischemia and restored the brain damaged by cerebral infarction. These beneficial effects were significantly blocked by IGFBP-4 antibody. The current study demontsrated that late passage hMSCs can be efficiently induced into ghMSCs with better neuroprotective effect on ischemic stroke. Moreover, the results indicate that IGFBP-4 released from ghMSCs may serve as one of the key neuronal survival factors secreted from ghMSCs.

The Role of Insulin-Like Growth Factors and Insulin-Like Growth Factor-Binding Proteins in the Nervous System

The insulin-like growth factors (IGF-I and IGF-II) and their receptors are widely expressed in nervous tissue from early embryonic life. They also cross the blood brain barriers by active transport, and their regulation as endocrine factors therefore differs from other tissues. In brain, IGFs have paracrine and autocrine actions that are modulated by IGF-binding proteins and interact with other growth factor signalling pathways. The IGF system has roles in nervous system development and maintenance. There is substantial evidence for a specific role for this system in some neurodegenerative diseases, and neuroprotective actions make this system an attractive target for new therapeutic approaches. In developing new therapies, interaction with IGF-binding proteins and other growth factor signalling pathways should be considered. This evidence is reviewed, gaps in knowledge are highlighted, and recommendations are made for future research.

Deficient neurotrophic factors of CSPG4-type neural cell exosomes in Alzheimer disease

Exosomes derived from chondroitin sulfate proteoglycan (CSPG) 4 type neural precursor cells (CSPG4Es) were purified from human plasma by sequential immunoabsorption with anti-CSPG4 and anti-platelet growth factor receptor α mAb to characterize the potential in vivo roles of CSPG4 cells in neuronal repair. Hepatocyte growth factor, fibroblast growth factors (FGFs)-2 and -13, and type 1 insulin-like growth factor (IGF-1), which enhance neuronal survival and functions, were quantified in CSPG4E extracts. For CSPG4Es of 24 healthy control subjects, mean levels of hepatocyte growth factor, FGF-13, and IGF-1, but not FGF-2, were significantly higher by up to 7-fold than in their neuronal-derived exosomes, and mean levels of all 4 growth factors were significantly higher by up to 8-fold than in their astrocyte-derived exosomes. Mean CSPG4E levels of all growth factors were significantly lower in patients with mild Alzheimer disease (AD) ( n = 24) than in age- and sex-matched cognitively normal control subjects ( n = 24). Mean CSPG4E levels of all growth factors were also significantly lower in 15 patients at the stage of moderate dementia from AD (AD₂) and at their preclinical stage 3 to 8 yr earlier (AD₁), with no differences between values at stages AD₁ and AD₂. Current findings suggest that CSPG4 cells export in exosomes higher levels of neurotrophic factors than neurons or astrocytes and that CSPG4E neurotrophic factors are diminished early in AD, with no significant progression of decreases later in the course.-Goetzl, E. J., Nogueras-Ortiz, C., Mustapic, M., Mullins, R. J., Abner, E. L., Schwartz, J. B., Kapogiannis, D. Deficient neurotrophic factors of CSPG4-type neural cell exosomes in Alzheimer disease.

Insulin-like growth factor binding protein-6 released from human mesenchymal stem cells confers neuronal protection through IGF-1R-mediated signaling

Human bone marrow-derived mesenchymal stem cells (hMSCs) are a desirable cell source for cell-based therapy to treat nervous system injuries due to their ability to differentiate into specific cell types. In addition to their multi-potency, hMSCs render the tissue microenvironment more favorable for tissue repair by secreting various growth factors. Our previous study demonstrated that hMSCs secrete several growth factors, including several insulin-like growth factor binding proteins (IGFBPs). Among these, IGFBP-6 binds with high affinity and inhibits insulin growth factor-2 (IGF-2) to inhibit the growth of IGF-2-dependent tumors. However, the function of IGFBP-6 in the nervous system remains to be fully elucidated. The present study investigated the protective effects of IGFBP-6 secreted by hMSCs on H₂O₂-injured primary cortical neuron cultures and lysolecithin-injured organotypic spinal cord slice cultures. Treatment of the H₂O₂-injured cortical neurons with conditioned media from hMSCs (hMSC-CM) increased the phosphorylation of Akt, reduced cell death and mitochondrial translocation of Bax, and regulated extracellular levels of IGF-1 and IGF-2. MTT assay, western blot analysis and ELISA were used to detect the cell viability and protein expression levels, respectively. An inhibitory antibody against IGFBP-6 eliminated this hMSC-CM-mediated neuroprotective effect in the injured cortical neuron cultures and spinal cord slice cultures. In addition, treatment with cyclolignan picropodophyllin, an inhibitor of IGF-1 receptor (IGF-1R), significantly inhibited neuronal protection by hMSC-CM. These findings demonstrated that hMSC-CM-mediated neuroprotection was attributed to IGF-1R-mediated signaling, potentiated via the inhibition of IGF-2 by IGFBP-6. The results of the present study provide insight into the mechanism by which hMSC administration may promote recovery from nerve injury.

Insulin-Like Growth Factor Binding Protein-3 Deficiency Leads to Behavior Impairment with Monoaminergic and Synaptic Dysfunction

Insulin-like growth factor binding protein (IGFBP)-3 regulates IGF bioactivity, induces apoptosis, and inhibits cell growth independent of IGFs, but the functional role of IGFBP3 in the brain is not clear. In the present study, we revealed the effect of IGFBP3 on the brain by characterizing the phenotype of Igfbp3-null mice. Compared with wild-type mice, Igfbp3-null mice had significantly decreased IGF-1 content in the brain but no change in weights of brain and body. In Igfbp3-null mice, the number of dendritic spines was significantly reduced, and the dendritic diameter was thickening. In addition, in Igfbp3-null mice, a decrease in phosphorylated Akt and ERK1/2 significantly reduced PSD-95 expression, and GAD65/67 expression was significantly decreased. These results indicate that IGFBP3 deficiency impairs neuronal structure and signaling. In behavioral studies, Igfbp3-null mice were hyperactive, and a Y-maze alternation test revealed impaired spatial working memory but no anxiety-like behavior. Monoaminergic analysis using high-performance liquid chromatography indicated that Igfbp3-null mice had lower levels of dopamine and serotonin compared with wild-type mice, suggesting an abnormal monoaminergic neurotransmission. In conclusion, our studies found that the deletion of IGFBP3 results in behavioral impairments that are associated with abnormal synaptic function and monoaminergic neurotransmission, which helps to characterize the critical role of IGFBP3 in the brain.

Estimated Prestroke Peak VO2 Is Related to Circulating IGF-1 Levels During Acute Stroke

Background Insulin-like growth factor-1 (IGF-1) is neuroprotective after stroke and is regulated by insulin-like binding protein-3 (IGFBP-3). In healthy individuals, exercise and improved aerobic fitness (peak oxygen uptake; peak VO₂) increases IGF-1 in circulation. Understanding the relationship between estimated prestroke aerobic fitness and IGF-1 and IGFBP-3 after stroke may provide insight into the benefits of exercise and aerobic fitness on stroke recovery. Objective The purpose of this study was to determine the relationship of IGF-1 and IGFBP-3 to estimated prestroke peak VO₂ in individuals with acute stroke. We hypothesized that (1) estimated prestroke peak VO₂ would be related to IGF-1 and IGFBP-3 and (2) individuals with higher than median IGF-1 levels will have higher estimated prestroke peak VO₂ compared to those with lower than median levels. Methods Fifteen individuals with acute stroke had blood sampled within 72 hours of hospital admission. Prestroke peak VO₂ was estimated using a nonexercise prediction equation. IGF-1 and IGFBP-3 levels were quantified using enzyme-linked immunoassay. Results Estimated prestroke peak VO₂ was significantly related to circulating IGF-1 levels (r = .60; P = .02) but not IGFBP-3. Individuals with higher than median IGF-1 (117.9 ng/mL) had significantly better estimated aerobic fitness (32.4 ± 6.9 mL kg^-1 min^-1) than those with lower than median IGF-1 (20.7 ± 7.8 mL kg^-1 min^-1; P = .03). Conclusions Improving aerobic fitness prior to stroke may be beneficial by increasing baseline IGF-1 levels. These results set the groundwork for future clinical trials to determine whether high IGF-1 and aerobic fitness are beneficial to stroke recovery by providing neuroprotection and improving function.

The Effect of Layer-by-Layer Assembly Coating on the Proliferation and Differentiation of Neural Stem Cells

Nanocoating of a single-cell with biocompatible materials creates a defined microenvironment for cell differentiation and proliferation, as well as a model for studies in cell biology. In addition, the acidic environment in the tissue of stroke victims necessitates drug release upon pH stimuli. Here, we report the encapsulation of single neural stem cells (NSCs) using a layer-by-layer (LbL) self-assembly technique with polyelectrolytes gelatin and alginate. Analysis of the NSCs showed that the LbL encapsulation would not affect the viability, proliferation, or differentiation of the cells. When insulin-like growth factor-1 (IGF-1) was loaded on the coating material alginate, its release from alginate into the medium presented in a time-dependent and pH-dependent way. IGF-1 significantly enhanced the proliferation of the encapsulated NSCs, demonstrating a drug-carrier function of the LbL single-cell nanocoating. It provided a potential treatment strategy for nervous system disorders such as stroke.

Neurotrophic and neuroprotective potential of human limbus-derived mesenchymal stromal cells

BACKGROUND AIMS

The purpose of this study was to examine neurotrophic and neuroprotective effects of limbus stroma-derived mesenchymal stromal cells (L-MSCs) on cortical neurons in vitro and in vivo.

METHODS

Cultured L-MSCs were characterized by flow cytometry and immunofluorescence through the use of specific MSC marker antibodies. Conditioned media were collected from normoxia- and hypoxia-treated L-MSCs to assess neurotrophic effects. Neuroprotective potentials were evaluated through the use of in vitro hypoxic cortical neuron culture and in vivo rat focal cerebral ischemia models. Neuronal morphology was confirmed by immunofluorescence with the use of anti-MAP2 antibody. Post-ischemic infarct volume and motor behavior were assayed by means of triphenyltetrazolium chloride staining and open-field testing, respectively. Human growth antibody arrays and enzyme-linked immunoassays were used to analyze trophic/growth factors contained in conditioned media.

RESULTS

Isolated human L-MSCs highly expressed CD29, CD90 and CD105 but not CD34 and CD45. Mesenchymal lineage cell surface expression pattern and differentiation capacity were identical to MSCs derived form human bone marrow and adipose tissue. The L-MSC normoxic and hypoxic conditioned media both promoted neurite outgrowth in cultured cortical neurons. Hypoxic conditioned medium showed superior neurotrophic function and neuroprotective potential with reduced ischemic brain injury and improved functional recovery in rat focal cerebral ischemia models. Human growth factor arrays and enzyme-linked immunoassays measurements showed neuroprotective and growth-associated cytokines (vascular endothelial growth factor [VEGF], VEGFR3, brain-derived neurotrophic factor, insulin-like growth factor -2 and hepatocyte growth factor) contained in conditioned media. Hypoxic exposure caused VEGF and brain-derived neurotrophic factor upregulation, possibly contributing to neurotrophic and neuroprotective effects.

CONCLUSIONS

L-MSCs can secrete various neurotrophic factors stimulating neurite outgrowth and protecting neurons against brain ischemic injury through paracrine mechanism.

Spatial distribution of insulin-like growth factor binding protein-2 following hypoxic-ischemic injury

BACKGROUND

Insulin-like growth factor binding protein-2 (IGFBP-2) regulates the bioavailability, transportation, and localization of insulin-like growth factor-I (IGF-I), an effective neuroprotectant in animal stroke models especially when administered intranasally. Therefore, determining IGFBP-2's endogenous distribution in the normal and ischemic brain is essential in maximizing the neuroprotective potential of the intranasal IGF-I treatment approach. However, current data on IGFBP-2 is limited to mRNA and in situ hybridization studies. The purpose of this study was to determine if there are any changes in IGFBP-2 protein levels and distribution in ischemic brain and also to determine if IGFBPs play a role in the transportation of intranasally administered IGF-I into the brain.

RESULTS

Using an in vitro approach, we show that ischemia causes changes in the distribution of IGFBP-2 in primary cortical neurons and astrocytes. In addition, we show using the transient middle cerebral artery occlusion (MCAO) model in mice that there is a significant increase in IGFBP-2 levels in the stroke penumbra and core after 72 h. This correlated with an overall increase in IGF-I after stroke, with the highest levels of IGF-I in the stroke core after 72 h. Brain sections from stroke mice indicate that neurons and astrocytes located in the penumbra both have increased expression of IGFBP-2, however, IGFBP-2 was not detected in microglia. We used binding competition studies to show that intranasally administered exogenous IGF-I uptake into the brain is not receptor mediated and is likely facilitated by IGFBPs.

CONCLUSIONS

The change in protein levels indicates that IGFBP-2 plays an IGF-I-dependent and -independent role in the brain's acute (neuroprotection) and chronic (tissue remodeling) response to hypoxic-ischemic injury. Competition studies indicate that IGFBPs may have a role in rapid transportation of exogenous IGF-I from the nasal tissue to the site of injury.

Window of opportunity for neuroprotection with an antioxidant, allene oxide synthase, after hypoxia-ischemia in adult male rats

AIMS

Oxidative stress is an early event in the cascade leading in neuronal damage after hypoxic-ischemic (HI) brain injury. In the present study, we examined the dose response and window of opportunity for neuroprotection after HI injury with Allene Oxide Synthase (AOS), an anti-oxidative enzyme of the member of cytochrome P450 family.

METHODS

Adult male rats received intra-cerebro-ventricular infusions of either saline (vehicle) or AOS (1 μg or 10 μg or 100 μg per rat, intracerebroventricular n = 16 all groups) either 45 min or 3 h after unilateral HI brain injury. Brains were collected 5 days later. The extent of brain damage, neuronal survival, apoptosis, and glial reactions were assessed in the striatum, hippocampus, and cortex.

RESULTS

Allene Oxide Synthase was associated with reduced neuronal damage scores when given 45 min, but not 3 h, after HI injury (P < 0.0001) in all brain regions. AOS treatment (10 μg) improved neuronal survival in the striatum, cortex, and hippocampus (P < 0.05, P < 0.001) and reduced the microglia reaction (P < 0.05) and numbers of caspase-3-positive cells in the hippocampus (P < 0.01).

CONCLUSIONS

Early blockade of oxidative stress after HI injury reduces inflammatory response, neuronal necrosis, and apoptosis. The neuroprotective effects of AOS were time of administration-dependent suggesting a relatively restricted window of opportunity for acute brain injury.

Neurodevelopmental effects of insulin-like growth factor signaling

Insulin-like growth factor (IGF) signaling greatly impacts the development and growth of the central nervous system (CNS). IGF-I and IGF-II, two ligands of the IGF system, exert a wide variety of actions both during development and in adulthood, promoting the survival and proliferation of neural cells. The IGFs also influence the growth and maturation of neural cells, augmenting dendritic growth and spine formation, axon outgrowth, synaptogenesis, and myelination. Specific IGF actions, however, likely depend on cell type, developmental stage, and local microenvironmental milieu within the brain. Emerging research also indicates that alterations in IGF signaling likely contribute to the pathogenesis of some neurological disorders. This review summarizes experimental studies and shed light on the critical roles of IGF signaling, as well as its mechanisms, during CNS development.

Growth factors in ischemic stroke

Data from pre-clinical and clinical studies provide evidence that colony-stimulating factors (CSFs) and other growth factors (GFs) can improve stroke outcome by reducing stroke damage through their anti-apoptotic and anti-inflammatory effects, and by promoting angiogenesis and neurogenesis. This review provides a critical and up-to-date literature review on CSF use in stroke. We searched for experimental and clinical studies on haemopoietic GFs such as granulocyte CSF, erythropoietin, granulocyte-macrophage colony-stimulating factor, stem cell factor (SCF), vascular endothelial GF, stromal cell-derived factor-1α and SCF in ischemic stroke. We also considered studies on insulin-like growth factor-1 and neurotrophins. Despite promising results from animal models, the lack of data in human beings hampers efficacy assessments of GFs on stroke outcome. We provide a comprehensive and critical view of the present knowledge about GFs and stroke, and an overview of ongoing and future prospects.

Insulin-like growth factor binding protein-6 delays replicative senescence of human fibroblasts

Cellular senescence can be induced by a variety of mechanisms, and recent data suggest a key role for cytokine networks to maintain the senescent state. Here, we have used a proteomic LC-MS/MS approach to identify new extracellular regulators of senescence in human fibroblasts. We identified 26 extracellular proteins with significantly different abundance in conditioned media from young and senescent fibroblasts. Among these was insulin-like growth factor binding protein-6 (IGFBP-6), which was chosen for further analysis. When IGFBP-6 gene expression was downregulated, cell proliferation was inhibited and apoptotic cell death was increased. Furthermore, downregulation of IGFBP-6 led to premature entry into cellular senescence. Since IGFBP-6 overexpression increased cellular lifespan, the data suggest that IGFBP-6, in contrast to other IGF binding proteins, is a negative regulator of cellular senescence in human fibroblasts.

Blunting type 1 insulin-like growth factor receptor expression exacerbates neuronal apoptosis following hypoxic/ischemic injury

Background

Abundant experimental data have implicated an important role for insulin-like growth factor (IGF) in protecting neuronal cells from injury, including hypoxia/ischemia (H/I) injury, a major cause of neuron death. While the specific interaction of IGFs with neuronal or glial type 1 IGF receptors (IGF1R) has been shown to be essential to IGF actions during development, the same has not been directly demonstrated following H/I injury. To directly examine the role of neuronal IGF1R following H/I injury, we utilized conditional mutant nes-igf1r^-/Wt mice and determined the impact of IGF1R haplodeficiency specifically in nestin-expressing neuronal precursors and their progeny on H/I-induced neuronal damage and apoptosis in hippocampus.

Results

H/I induced significant damage to the cerebral hemisphere and hippocampus ipsilateral to the ligated right common carotid artery both in control and nes-igf1r^-/Wt mice at postnatal day 10. Blunting IGF1R expression, however, markedly exacerbated H/I-induced damage and appeared to increase mortality. In the ipsilateral hemisphere and hippocampus, nes-igf1r^-/Wt mice had infarct areas double the size of those in controls. The size of the ipsilateral hemisphere and hippocampus in nes-igf1r^-/Wt mice were 15% to 17% larger than those in controls, reflecting more severe edema. Consistent with its effects on infarct area, IGF1R haplodeficiency causes a greater decrease in neurons in the ipsilateral hippocampus of nes-igf1r^-/Wt mice. The reduction in neurons was largely due to increases in neuronal apoptosis. Judged by pyknotic nuclei, TUNEL and caspase-3 labeling, nes-igf1r^-/Wt mice had significantly more apoptotic cells than that in controls after injury. To determine possible mechanisms of IGF1R actions, the mRNA expression of the pro-survival proteins IAP-1 and XIAP was determined. Compared to controls, the abundance of cIAP-1 and XIAP mRNA was markedly suppressed in mice with blunted IGF1R or IGF-I expression, while was increased in the brain of IGF-I overexpressing transgenic mice.

Conclusion

IGF1R in neuronal cells is critically important for their survival following H/I injury, and IGF-upregulated expression of neuronal cIAP-1 and XIAP likely in part contributes to IGF-IGF1R protection against neuronal apoptosis following H/I injury.

Leu27 insulin-like growth factor-II, an insulin-like growth factor-II analog, attenuates depolarization-evoked GABA release from adult rat hippocampal and cortical slices

Accumulated evidence suggests that the single transmembrane domain insulin-like growth factor-II/mannose 6-phosphate receptor (IGF-II/M6P or IGF-II receptor) plays an important role in the intracellular trafficking of lysosomal enzymes and endocytosis-mediated degradation of insulin like growth factor (IGF-II). However, the role of this receptor in signal transduction following IGF-II binding remains controversial. In the present study, we revealed that Leu(27)IGF-II, an analog which binds preferentially to the IGF-II receptor, can attenuate K(+)-as well as veratridine-evoked GABA release from the adult rat hippocampal formation. Tetrodotoxin failed to alter the effects of Leu(27)IGF-II on GABA release, thus suggesting the lack of involvement of voltage-dependent Na(+) channels. Interestingly, the effect is found to be sensitive to pertussis toxin (PTX), indicating the possible involvement of a Gi/o protein-dependent pathway in mediating the release of GABA from the hippocampal slices. Additionally, Leu(27)IGF-II was found to attenuate GABA release from frontal cortex but not from striatum. These results, together with the evidence that IGF-II receptors are localized on GABAergic neurons, raised the possibility that this receptor, apart from mediating intracellular trafficking, may also be involved in the regulation of endogenous GABA release by acting directly on GABAergic terminals.

Insulin-like growth factor -1 (IGF-1) derived neuropeptides, a novel strategy for the development of pharmaceuticals for managing ischemic brain injury

Insulin-Like Growth Factor-1 (IGF-1) is neuroprotective and improves long-term function after brain injury. However, its clinical application to neurological disorders is limited by its large molecular size, poor central uptake, and mitogenic potential. Glycine-proline-glutamate (GPE) is naturally cleaved from the IGF-1 N-terminal and is also neuroprotective after ischemic injury, thus providing a potential novel strategy of drug discovery for management of neurological disorders. GPE is not enzymatically stable, thus intravenous infusion of GPE becomes necessary for stable and potent neuroprotection. The broad effective dose range and treatment window of 3-7 h after the lesion suggest its potential for treating acute brain injuries. The neuroprotective action of GPE is not age selective, is not dependent on cerebral reperfusion, plasma glucose concentrations, and core body temperature. G-2mPE, a GPE analogue designed to be more resistant to enzymatic activity, has a prolonged plasma half-life and is more potent in neuroprotection. Neuroprotection by GPE and its analogue may be involved in modulation of inflammation, promotion of astrocytosis, inhibition of apoptosis, and in vascular remodeling. Small neuropeptides have advantages over growth factors in the treatment of brain injury, and modified neuropeptides, designed to overcome the limitations of their endogenous counterparts, represent a novel strategy of pharmaceutical discovery for neurological disorders.

IGF-1 and pAKT signaling promote hippocampal CA1 neuronal survival following injury to dentate granule cells

Insulin-like growth factor-1 (IGF-1) protects neurons from apoptosis and in vivo offers neuroprotective support to hippocampal CA1 pyramidal neurons following ischemia or seizure. IGF-1 signals through IGF-1 receptors activating phosphytidylinositol 3-kinase (PI3K)/Akt or pMAPK pathways. IGF-1 can be induced with injury and microglia and astrocytes may serve as a source of this neurotrophic factor to promote neuronal survival. An acute systemic injection of trimethyltin (TMT; 2 mg/kg, ip) to mice induces apoptosis of dentate granule neurons within 24 h and a differential response of microglia with ramified microglia present in the CA-1 region. Using this model, we studied the role of IGF-1 in the survival of CA-1 pyramidal neurons under conditions of altered synaptic input due to changes in the dentate gyrus. Within 24 h of injection, IGF-1 mRNA levels were elevated in the hippocampus and IGF-1 protein detected in both astrocytes and microglia. IGF-1 was redistributed within the CA-1 neurons corresponding with an increase in cytoplasmic pAkt, elevated PKBalpha/Akt protein levels, and a decrease in the antagonist, Rho. pMAPK was not detected in CA-1 neurons and ERK2 showed a transient decrease followed by a significant increase, suggesting a lack of recruitment of the pMAPK signaling pathway for neuronal survival. In mice deficient for IGF-1, a similar level of apoptosis was observed in dentate granule neurons as compared to wildtype; however, TMT induced a significant level CA-1 neuronal death, further supporting a role for IGF-1 in the survival of CA-1 neurons.

IGF-1 derived small neuropeptides and analogues: a novel strategy for the development of pharmaceuticals for neurological conditions

Insulin-like growth factor-1 (IGF-1) is neuroprotective and improves long-term function after brain injury. However, its clinical application to neurological disorders is limited by its large molecular size, poor central uptake and mitogenic potential. Glycine-proline-glutamate (GPE) is naturally cleaved from the IGF-1 N-terminal and it is also neuroprotective after ischemic injury, which provided a novel strategy of drug discovery for neurological disorders. GPE is not enzymatically stable, thus intravenous infusion of GPE becomes necessary for stable and potent neuroprotection. The broad effective dose range and treatment window of 3-7 h after the lesion suggest its potential for treating acute brain injuries. G-2meth-PE, a GPE analogue designed to be more enzymatic resistant, has a prolonged plasma half-life and is more potent in neuroprotection. Neuroprotection by GPE and its analogue may involve modulation of inflammation, promotion of astrocytosis, inhibition of apoptosis and vascular remodelling. Acute administration of GPE also prevents 6-OHDA-induced nigrostrial dopamine depletion. Delayed treatment with GPE does not prevent dopamine loss, but improves long-term function. Cyclo-glycyl-proline (cyclic Gly-Pro) is an endogenous DKP that may be derived from GPE. Cyclic Gly-Pro and its analogue cyclo-L-glycyl-L-2-allylproline (NNZ 2591) are both neuroprotective after ischaemic injury. NNZ2591 is highly enzymatic resistant and centrally accessible. Its peripheral administration improves somatosensory-motor function and long-term histological outcome after brain injury. Our research suggests that small neuropeptides have advantages over growth factors in the treatment of brain injury, and that modified neuropeptides designed to overcome the limitations of their endogenous counterparts represent a novel strategy of pharmaceutical discovery for neurological disorders.

Intranasal administration of IGF-1 attenuates hypoxic-ischemic brain injury in neonatal rats

To determine whether intranasal administration (iN) of recombinant human insulin-like growth factor-1 (rhIGF-1) provides neuroprotection to the neonatal rat brain following cerebral hypoxia-ischemia (HI), two doses of rhIGF-1 (50 microg at a 1 h interval) were infused into the right naris of postnatal day 7 (P7) rat pups with or without a prior HI insult (right common carotid artery ligation, followed by an exposure to 8% oxygen for 2 h). Our result showed that rhIGF-1 administered via iN was successfully delivered into the brain 30 min after the second dose. In the following studies rhIGF-1 was administered to P7 rat pups at 0, 1 or 2 h after HI at the dose described above. Pups in the control group received cerebral HI and vehicle treatment. Pups that underwent sham operation and vehicle treatment served as the sham group. Brain pathological changes were evaluated 2 and 15 days after HI. Our results showed that rhIGF-1 treatment up to 1 h after cerebral HI effectively reduced brain injury as compared to that in the vehicle-treated rats. Moreover, rhIGF-1 treatment improved neurobehavioral performance (tested on P5-P21) in juvenile rats subjected to HI. Our results further showed that rhIGF-1 inhibited apoptotic cell death, possibly through activating the Akt signal transduction pathway. rhIGF-1 enhanced proliferation of neuronal and oligodendroglial progenitors after cerebral HI as well. These data suggest that iN administration of IGF-1 has the potential to be used for clinical treatment.

Insulin-like growth factor I: a potential neuroprotective compound for the treatment of acute ischemic stroke?

BACKGROUND AND PURPOSE

Insulin-like growth factor I (IGF-I) exerts neuroprotective effects in both white and gray matter under different detrimental conditions. The purpose of this review is to collect the evidence whether IGF-I is a candidate neuroprotective drug in patients with acute ischemic stroke.

RESULTS

IGF-I was found to be neuroprotective in animal models of focal brain ischemia when given >or=2 hours after the insult. Different routes of administration (eg, cerebroventricular, intravenous, and intranasal) were found to be effective. In addition to inhibition of apoptosis and reduction of the infarct volume, IGF-I also improved neurological outcome. Furthermore, there are strong indications that IGF-I can also stimulate the regeneration of neural tissue.

CONCLUSIONS

Additional studies are required to reveal the neuroprotective mechanisms of IGF-I in detail and to elucidate the role of IGF-binding proteins. Preclinical studies in relevant animal models for studying stroke (ie, hypertensive, diabetic, or aged animals) should be done testing different doses and routes of IGF-I administration and different combinations of IGF-I and IGF-binding proteins.

Loss of responsiveness to IGF-I in cells with reduced cathepsin L expression levels

The lysosomal cysteine proteinase cathepsin L is involved in proteolytic processing of internalized proteins. In transformed cells, where it is frequently overexpressed, its intracellular localization and functions can be altered. Previously, we reported that treatment of highly metastatic, murine carcinoma H-59 cells with small molecule cysteine proteinase inhibitors altered the responsiveness of the type I insulin-like growth factor (IGF-I) receptor and consequently reduced cell invasion and metastasis. To assess more specifically the role of cathepsin L in IGF-I-induced signaling and tumorigenicity, we generated H-59 subclones with reduced cathepsin L expression levels. These clonal lines showed an altered responsiveness to IGF-I in vitro, as evidenced by (i) loss of IGF-I-induced receptor phosphorylation and Shc recruitment, (ii) reduced IGF-I (but not IGF-II)-induced cellular proliferation and migration, (iii) decreased anchorage-independent growth and (iv) reduced plasma membrane levels of IGF-IR. These changes resulted in increased apoptosis in vivo and an impaired ability of the cells to form liver metastases. The results demonstrate that cathepsin L expression levels regulate cell responsiveness to IGF-I and thereby identify a novel function for cathepsin L in the control of the tumorigenic/metastatic phenotype.

Serum insulin-like growth factor I and ischemic brain injury

Serum insulin-like growth factor I (IGF-I), which is mostly produced by the liver, has recently been shown to have the unexpected ability to modulate normal brain function as well as brain response to injury. Moreover, serum IGF-I levels are modified in many brain diseases, including stroke. However, whether these modifications are related to the disease process remains uncertain. We now examined a potential relationship between serum IGF-I and ischemic brain injury after middle cerebral artery occlusion (MCAo) and reperfusion in mice with either high or low serum IGF-I levels prior to insult. Surprisingly, we found that chronic high serum IGF-I correlates with increased brain infarct size following MCAo, while low levels correlate with reduced lesion size. Immunocytochemistry and immunoblot analyses revealed that levels of phosphorylated (i.e., activated) MAPK, known to be associated with the severity of ischemic brain injury, were increased in IGF-I treated mice. No overall effect of IGF-I treatment on IGF family mRNA expression in the brain was observed. Altogether, these results indicate that serum IGF-I levels negatively correlate with stroke outcome. Therefore, lowering serum IGF-I levels in aging mammals, including humans, may be beneficial against the increased risk of stroke associated to old age.

Delayed peripheral administration of a GPE analogue induces astrogliosis and angiogenesis and reduces inflammation and brain injury following hypoxia-ischemia in the neonatal rat

Glycine 2-methyl proline glutamate (G-2mPE) is a proline-modified analogue to the naturally existing N-terminal tripeptide glycine-proline-glutamate that is a cleaved product from insulin-like growth factor-1. G-2mPE is designed to be more enzymatically resistant than glycine-proline-glutamate and to increase its bioavailability. The current study has investigated the protective effects of G-2mPE following hypoxic-ischemic brain injury in the neonatal brain. On postnatal day 7, Wistar rats were exposed to hypoxia-ischemia (HI). HI was induced by unilateral ligation of the left carotid artery followed by hypoxia (7.7% O2, 36 degrees C) for 60 min. The drug treatment started 2 h after the insult, and the pups were given either 1.2 mg/kg (bolus), 1.2 mg/ml once a day for 7 days, or vehicle. The degree of brain damage was determined histochemically by thionin/acid fuchsin staining. G-2mPE's anti-inflammatory properties were investigated by IL-1beta, IL-6, and IL-18 ELISA, and effects on apoptosis by caspase 3 activity. Vascularization was determined immunohistochemically by the total length of isolectin-positive blood vessels. Effect on astrocytosis was also determined in the hippocampus. Animals treated with multiple doses of G-2mPE demonstrated reduced overall brain injury 7 days after HI, particularly in the hippocampus and thalamus compared to vehicle-treated rats. The expression of IL-6 was decreased in G-2mPE-treated animals compared to vehicle-treated pups, and both the capillary length and astrogliosis were increased in the drug-treated animals. There was no effect on caspase 3 activity. This study indicates that peripheral administration of G-2mPE, starting 2 h after a hypoxic-ischemic insult, reduces the degree of brain injury in the immature rat brain. The normalization of IL-6 levels and the promotion of both neovascularization and reactive astrocytosis may be potential mechanisms that underlie its protective effects.

IGF2 knockout mice are resistant to kainic acid-induced seizures and neurodegeneration

Insulin-like growth factor 2 (Igf2), a member of the insulin gene family, is important for brain development and has known neurotrophic properties. Though Igf2, its receptors, and binding proteins, are expressed in the adult CNS, their role in the adult brain is less well-understood. Here we studied how Igf2 deficiency affects brains of adult Igf2 knockout (Igf2(-/-)) mice following neurotoxic insult produced by the glutamate analog kainic acid (KA). Igf2(-/-) mice exhibited attenuated epileptiform activity in response to KA and were less susceptible to hippocampal neurodegeneration compared with Igf2(+/+) mice. Other brain areas protected by the lack of Igf2 included the amygdala complex, septal nuclei, and thalamic region. Apoptosis, as determined by TUNEL and Hoechst 33342 staining, was accordingly less for Igf2(-/-) mice. Hippocampal slices from Igf2(-/-) mice also were protected against the effects epileptogenic effects of KA compared to Igf2(+/+) mice suggesting that neuroprotection afforded by a lack of Igf2 may be developmental in origin and experiments demonstrating enhanced synaptic inhibition in slices taken from Igf2(-/-) mice support this hypothesis. Taken together, these results suggest that Igf2 may be important for mechanisms and circuits that contribute to neurodegeneration and epilepsy.

Effect of kainic acid treatment on insulin-like growth factor-2 receptors in the IGF2-deficient adult mouse brain

Insulin-like growth factor-2 (IGF2) is a member of the insulin gene family with known neurotrophic properties. The actions of IGF2 are mediated via the IGF type 1 and type 2 receptors as well as through the insulin receptors, all of which are widely expressed throughout the brain. Since IGF2 is up-regulated in the brain after injury, we wanted to determine whether the absence of IGF2 can lead to any alteration on brain morphology and/or in the response of its receptor binding sites following a neurotoxic insult. No morphological differences were observed between the brains of IGF2 knockout (IGF2(-/-)) and wild-type control (IGF2(+/+)) mice. However, our in vitro receptor autoradiography results indicate that IGF2(-/-) mice had lower endogenous levels of [(125)I]IGF1 and [(125)I]insulin receptor binding sites in the hippocampus and cerebellum as compared to IGF2(+/+) mice, while endogenous [(125)I]IGF2 receptor binding showed a decrease only in the cerebellum. Seven days after kainic acid administration, the [(125)I]insulin receptor binding sites were significantly decreased in all brain regions of the IGF2(+/+) mice, while the levels of [(125)I]IGF1 and [(125)I]IGF2 binding sites were decreased only in select brain areas. The IGF2(-/-) mice, on the other hand, showed increased [(125)I]IGF1 and [(125)I]IGF2 and [(125)I]insulin receptor binding sites in selected regions such as the hippocampus and cerebellum. These results, taken together, suggest that deletion of IGF2 gene does not affect gross morphology of the brain but does selectively alter endogenous [(125)I]IGF1, [(125)I]IGF2 and [(125)I]insulin receptor binding sites and their response to neurotoxicity.

The insulin-like growth factor system and its pleiotropic functions in brain

In recent years, much interest has been devoted to defining the role of the IGF system in the nervous system. The ubiquitous IGFs, their cell membrane receptors, and their carrier binding proteins, the IGFBPs, are expressed early in the development of the nervous system and are therefore considered to play a key role in these processes. In vitro studies have demonstrated that the IGF system promotes differentiation and proliferation and sustains survival, preventing apoptosis of neuronal and brain derived cells. Furthermore, studies of transgenic mice overexpressing components of the IGF system or mice with disruptions of the same genes have clearly shown that the IGF system plays a key role in vivo.

Stem/progenitor cell proliferation factors FGF-2, IGF-1, and VEGF exhibit early decline during the course of aging in the hippocampus: role of astrocytes

Dentate neurogenesis, important for learning and memory, declines dramatically by middle age. Although studies have shown that this age-related decrease can be reversed to some extent by exogenous applications of mitogenic factors, it is unclear whether one or more of these factors exhibits decline by middle age. We hypothesize that multiple stem/progenitor cell proliferation factors exhibit early decline during the course of aging in the hippocampus, and some of these declines are linked to age-related alterations in hippocampal astrocytes. We measured the concentrations of fibroblast growth factor-2 (FGF-2), insulin-like growth factor-1 (IGF-1), and vascular endothelial growth factor (VEGF) in the hippocampus of young, middle-aged, and aged F344 rats, using enzyme-linked immunosorbent assay (ELISA). In addition, we quantified the total number of FGF-2 immunopositive (FGF-2+) and glial fibrillary acidic protein immunopositive (GFAP+) cells in the dentate gyrus and the entire hippocampus. Our results provide new evidence that the concentrations of FGF-2, IGF-1, and VEGF decline considerably by middle age but remain steady between middle age and old age. Further, decreased concentrations of FGF-2 during aging are associated with decreased numbers of FGF-2+ astrocytes. Quantification of GFAP+ cells, and GFAP and FGF-2 dual immunostaining analyses, reveal that aging does not decrease the total number of astrocytes but fractions of astrocytes that express FGF-2 decline considerably by middle age. Thus, dramatically decreased dentate neurogenesis by middle age is likely linked to reduced concentrations of FGF-2, IGF-1, and VEGF in the hippocampus, as each of these factors can individually influence the proliferation of stem/progenitor cells in the dentate gyrus. Additionally, the results demonstrate that decreased FGF-2 concentration during aging is a consequence of age-related impairment in FGF-2 synthesis by astrocytes.

In normal rat, intraventricularly administered insulin-like growth factor-1 is rapidly cleared from CSF with limited distribution into brain

Background

Putatively active drugs are often intraventricularly administered to gain direct access to brain and circumvent the blood-brain barrier. A few studies on the normal central nervous system (CNS) have shown, however, that the distribution of materials after intraventricular injections is much more limited than presumed and their exit from cerebrospinal fluid (CSF) is more rapid than generally believed. In this study, we report the intracranial distribution and the clearance from CSF and adjacent CNS tissue of radiolabeled insulin-like growth factor-1 after injection into one lateral ventricle of the normal rat brain.

Methods

Under barbiturate anesthesia, ¹²⁵I-labeled insulin-like growth factor-1 (IGF-1) was injected into one lateral ventricle of normal Sprague-Dawley rats. The subsequent distribution of IGF-1 through the cerebrospinal fluid (CSF) system and into brain, cerebral blood vessels, and systemic blood was measured over time by gamma counting and quantitative autoradiography (QAR).

Results

Within 5 min of infusion, IGF-1 had spread from the infused lateral ventricle into and through the third and fourth ventricles. At this time, 25% of the infused IGF-1 had disappeared from the CSF-brain-meningeal system; the half time of this loss was 12 min. The plasma concentration of cleared IGF-1 was, however, very low from 2 to 9 min and only began to rise markedly after 20 min. This delay between loss and gain plus the lack of radiotracer in the cortical subarachnoid space suggested that much of the IGF-1 was cleared into blood via the cranial and/or spinal nerve roots and their associated lymphatic systems rather than periventricular tissue and arachnoid villi. Less than 10% of the injected radioactivity remained in the CSF-brain system after 180 min. The CSF and arteries and arterioles within the subarachnoid cisterns were labeled with IGF-1 within 10 min. Between 60 and 180 min, most of the radioactivity within the cranium was retained within and around these blood vessels and by periaqueductal gray matter. Tissue profiles at two sites next to ventricular CSF showed that IGF-1 penetrated less than 1.25 mm into brain tissue and appreciable ¹²⁵I-activity remained at the tissue-ventricular CSF interface after 180 min.

Conclusion

Our findings suggest that entry of IGF-1 into normal brain parenchyma after lateral ventricle administration is limited by rapid clearance from CSF and brain and slow movement, apparently by diffusion, into the periventricular tissue. Various growth factors and other neuroactive agents have been reported to be neuroprotective within the injured brain after intraventricular administration. It is postulated that the delivery of such factors to neurons and glia in the injured brain may be facilitated by abnormal CSF flow. These several observations suggest that the flow of CSF and entrained solutes may differ considerably between normal and abnormal brain and even among various neuropathologies.

Insulin-like growth factor 1 as a predictor of ischemic stroke outcome in the elderly

PURPOSE

To examine whether serum insulin-like growth factor 1 (IGF-1) and IGF binding protein 3 (IGFBP-3) concentrations, determined early after the onset of stroke, are predictive of clinical outcome in elderly patients.

METHODS

The sample comprised 85 patients (mean [+/- SD] age, 83 +/- 7.4 years; range, 67 to 99 years; 34% male) who were admitted with acute stroke to a geriatric ward between January 1998 and June 2000, and 88 control patients who were similar in age and sex. Clinical and laboratory assessments, computed tomographic scan of the head, carotid ultrasonography, and electrocardiography were employed to define the clinical and etiologic stroke subtype. Fasting blood samples were collected within 24 hours of admission for IGF-I and IGFBP-3 measurement. Univariate and multiple logistic regression analyses, with adjustment for other related clinical covariates, were used to assess the relation of IGF-I and IGFBP-3 to poor outcome, defined as severe disability (Barthel index <60/100) or death, at 1 month (or at discharge), 3 months, and 6 months.

RESULTS

Mean (+/- SD) IGF-1 levels were lower in patients with stroke than in controls (69 +/- 45 ng/mL vs. 102 +/- 67 ng/mL, P adjusted for age = 0.001). The mean IGF-1/IGFBP-3 molar ratio was also lower in stroke patients (0.12 +/- 0.07 vs. 0.19 +/- 0.09, P adjusted for age <0.0001). However, there was no relation of hormone levels to either the clinical subtype of stroke or the extent of neurologic impairment. IGF-1 levels were inversely related to poor outcome (mainly death) at 3 and 6 months, independent of other clinical covariates that were highly predictive of outcome, such as age and stroke scale score on admission (hazard ratio for death at 6 months for each 20-ng/mL increase = 0.7; 95% confidence interval: 0.5 to 0.9). An independent association of the molar ratio with death at 3 and 6 months was also found.

CONCLUSION

Low levels of circulating IGF-1 may predict the clinical outcome of stroke in elderly patients.

Mitochondrial dysfunction in schizophrenia: evidence for compromised brain metabolism and oxidative stress

The etiology and pathophysiology of schizophrenia remain unknown. A parallel transcriptomics, proteomics and metabolomics approach was employed on human brain tissue to explore the molecular disease signatures. Almost half the altered proteins identified by proteomics were associated with mitochondrial function and oxidative stress responses. This was mirrored by transcriptional and metabolite perturbations. Cluster analysis of transcriptional alterations showed that genes related to energy metabolism and oxidative stress differentiated almost 90% of schizophrenia patients from controls, while confounding drug effects could be ruled out. We propose that oxidative stress and the ensuing cellular adaptations are linked to the schizophrenia disease process and hope that this new disease concept may advance the approach to treatment, diagnosis and disease prevention of schizophrenia and related syndromes.

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.

Estrogen interacts with the IGF-1 system to protect nigrostriatal dopamine and maintain motoric behavior after 6-hydroxdopamine lesions

The most prominent neurochemical hallmark of Parkinson's disease (PD) is the loss of nigrostriatal dopamine (DA). Animal models of PD have concentrated on depleting DA and therapies have focused on maintaining or restoring DA. Within this context estrogen protects against 6-hydroxdopamine (6-OHDA) and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) lesions of the nigrostriatal DA pathway. Present studies tested the hypothesis that neuroprotective estrogen actions involve activation of the insulin-like growth factor-1 (IGF-1) system. Ovariectomized rats were treated with either a single subcutaneous injection of 17beta-estradiol benzoate or centrally or peripherally IGF-1. All rats were infused unilaterally with 6-OHDA into the medial forebrain bundle (MFB) to lesion the nigrostriatal DA pathway. Tyrosine hydroxylase (TH) immunocytochemistry confirmed that rats injected with 6-OHDA had a massive loss of TH immunoreactivity in both the ipsilateral substantia nigra compacta (60% loss) and the striatum (>95% loss) compared to the contralateral side. Loss of TH immunoreactivity was correlated with loss of asymmetric forelimb movements, a behavioral assay for motor deficits. Pretreatment with estrogen or IGF-1 significantly prevented 6-OHDA-induced loss of substantia nigra compacta neurons (20% loss) and TH immunoreactivity in DA fibers in the striatum (<20% loss) and prevented the loss of asymmetric forelimb use. Blockage of IGF-1 receptors by intracerebroventricular JB-1, an IGF-1 receptor antagonist, attenuated both estrogen and IGF-1 neuroprotection of nigrostriatal DA neurons and motor behavior. These findings suggest that IGF-1 and estrogen acting through the IGF-1 system may be critical for neuroprotective effects of estrogen on nigrostriatal DA neurons in this model of PD.

Neuroprotective effects of insulin-like growth factor-binding protein ligand inhibitors in vitro and in vivo

The role of brain insulin-like growth factors (IGFs) and IGF binding proteins (IGFBPs) in neuroprotection was further investigated using in vitro and in vivo models of cerebral ischemia by assessing the effects of IGF-I, IGF-II, and high affinity IGFBP ligand inhibitors (the peptide [Leu24, 59, 60, Ala31]hIGF-I (IGFBP-LI) and the small molecule NBI-31772 (1-(3,4-dihydroxybenzoyl)-3-hydroxycarbonyl-6, 7-dihydroxyisoquinoline), which pharmacologically displace and elevate endogenous, bioactive IGFs from IGFBPs. Treatment with IGF-I, IGF-II, or IGFBP-LI (2 microg/mL) significantly (P < 0.05) reduced CA1 damage in organotypic hippocampal cultures resulting from 35 minutes of oxygen and glucose deprivation by 71%, 60%, and 40%, respectively. In the subtemporal middle cerebral artery occlusion (MCAO) model of focal ischemia, intracerebroventricular (icv) administration of IGF-I and IGF-II at the time of artery occlusion reduced ischemic brain damage in a dose-dependent manner, with maximum reductions in total infarct size of 37% (P < 0.01) and 38% (P < 0.01), respectively. In this model of MCAO, i.c.v. administration of NBI-31772 at the time of ischemia onset also dose-dependently reduced infarct size, and the highest dose (100 microg) significantly reduced both total (by 40%, P < 0.01) and cortical (by 43%, P < 0.05) infarct volume. In the intraluminal suture MCAO model, administration of NBI-31772 (50 microg i.c.v.) at the time of artery occlusion reduced both cortical infarct volume (by 40%, P < 0.01) and brain swelling (by 24%, P < 0.05), and it was still effective when treatment was delayed up to 3 hours after the induction of ischemia. These results further define the neuroprotective properties of IGFs and IGFBP ligand inhibitors in experimental models of cerebral ischemia.

Insulin-like growth factor (IGF)-1 suppresses oligodendrocyte caspase-3 activation and increases glial proliferation after ischemia in near-term fetal sheep

Insulin-like growth factor (IGF-1) markedly increases myelination and glial numbers in white matter after ischemia in near-term fetal sheep; however, it is unclear whether this is due to reduced cell loss or increased secondary proliferation. Brain injury was induced in near-term fetal sheep by 30 minutes of bilateral carotid artery occlusion. Ninety minutes after the occlusion, fetuses were given, intracerebroventricularly, either a single dose of IGF-1 (either 3 or 30 micro g), or 3 micro g followed by 3 micro g over 24 hours (3 + 3 micro g). White matter was assessed 4 days after reperfusion. Three micrograms, but not 30 micro g of IGF-1 prevented loss of oligodendrocytes and myelin basic protein density (P < 0.001) compared to the vehicle-treated ischemia controls. No additional effect was observed in the 3 + 3 micro g group. IGF-1 treatment was associated with reduced caspase-3 activation and increased glial proliferation in a similar dose-dependent manner. Caspase-3 was only expressed in oligodendrocytes that showed apoptotic morphology. Proliferating cell nuclear antigen co-localized with both oligodendrocytes and astrocytes and microglia. Thus, increased oligodendrocyte numbers after IGF-1 treatment is partly due to suppression of apoptosis, and partly to increased proliferation. In contrast, the increase in reactive glia was related only to proliferation. Speculatively, reactive glia may partly mediate IGF-1 white matter protection.

IGF-I and microglia/macrophage proliferation in the ischemic mouse brain

We have used a model of hypoxic-ischemic brain injury in adult male C57BL/6 mice to study insulin-like growth factor-I (IGF-I) and IGF-binding protein (IGFBP) expression in response to cerebral hypoxia-ischemia (H/I) in the adult mouse. A period of 20 min of H/I that resulted in histopathology in cortex, striatum, and thalamus was correlated with induction of mRNA for IGF-I, IGFBP-2, IGFBP-3, IGFBP-5, and glial fibrillary acidic protein (GFAP) by 4 days of recovery. Increased IGF-I mRNA was located within damaged regions and was surrounded by IGFBP-2 mRNA expression. The results of combined immunostaining/in situ hybridzation showed that the cells expressing IGFBP-2 mRNA were also GFAP-positive and comprised a subset of activated astrocytes immediately surrounding areas of damage. In contrast, staining within damaged regions showed high numbers of cells immunopositive for F4/80 and lectin B(4) indicative of microglia and macrophages but no cells immunopositive for the astrocytic proteins GFAP or S-100beta. Microglia/macrophages within the damaged areas expressed IGF-I mRNA and were also immunopositive for the proliferating cell nuclear antigen. To determine whether expression of IGF-I could contribute to proliferation of microglia, we treated purified cultures of adult brain microglia with IGF-I in the presence of (3)H-thymidine. IGF-I stimulated a twofold increase in DNA synthesis in cultures of adult brain microglia. Taken together with previous data demonstrating that IGF-I promotes proliferation of peripheral macrophages, these data support the hypothesis that IGF-I is an autocrine/paracrine mitogen for microglia/macrophages after H/I.

Neuroprotective effects of the N-terminal tripeptide of IGF-1, glycine-proline-glutamate, in the immature rat brain after hypoxic-ischemic injury

Insulin growth factor 1 (IGF-1) has an important role in brain development and is strongly expressed during recovery after a hypoxic-ischemic injury. Some of its central actions could be mediated through the N-terminal tripeptide fragment of IGF-1: Gly-Pro-Glu (GPE). The neuroprotective properties of GPE given after a moderate injury in the developing rat brain were evaluated and the binding sites of [(3)H]GPE characterised by autoradiography. After right unilateral injury, GPE or vehicle (V) was injected in the right lateral ventricle (i.c.v.) or in the peritoneal cavity (i.p.) of 21-day-old rats. The percentage of surviving neurons in CA1-2 of the hippocampus was higher in the animals treated with 30 microg of GPE i.c.v. (V: 7.7+/-4.9%, GPE: 26.4+/-7.5%, P=0.02) and 300 microg i.p. (V: 30.2+/-9.1%, GPE: 68.8+/-10.6%, P=0.02) than in animals receiving vehicle. I.p. injection of 300 microg of GPE (V: 78.4+/-7.5%, GPE: 88.4+/-3.2%, P=0.04) was also neuroprotective in the lateral cortex. I.c.v. injection of [(3)H]GPE suggested binding to glial cells in the white matter tracts, the cortex and striatum as opposed to neurons. Although the precise mode of action of GPE is unknown, this study suggests that local administration of GPE is neuroprotective after brain HI injury via glial cells. In addition, systemic administration of GPE showed a more widespread neuroprotective effect. GPE may represent a complementary pathway for central and systemic IGF-1's antiapoptotic effects.

Depolarization induces insulin-like growth factor binding protein-2 expression in vivo via NMDA receptor stimulation

The effect of depolarization and N-methyl-D-aspartate (NMDA) receptor blockade on insulin-like growth factor-I (IGF-I), IGF binding protein-2 (IGFBP-2) and IGFBP-4 expression was analysed in vivo. Depolarization was induced in adult rat brains by applying 3 M KCl to the exposed cortex for 10 min. A subgroup of animals also received daily injections of MK-801. Four days after KCl exposure, the brains were analysed by in situ hybridization, immunohistochemistry and TUNEL. A significant upregulation of IGFBP-2 mRNA and protein was detected in astrocytes after KCl exposure This upregulation was reduced by MK-801 treatment. No alterations in IGF-I or IGFBP-4 mRNA levels were noted. We did not detect TUNEL positive cells, morphological signs of necrosis or apoptosis, or neuronal loss in the depolarized zone. Taken together, these findings indicate that upregulation of IGFBP-2 by depolarization is mediated by NMDA receptors, and, as no neuronal damage was detected, astrocytic NMDA receptors may be responsible for this upregulation.

Neuroprotective effect of sodium orthovanadate on delayed neuronal death after transient forebrain ischemia in gerbil hippocampus

In transient forebrain ischemia, sodium orthovanadate as well as insulinlike growth factor-1 (IGF-1) rescued cells from delayed neuronal death in the hippocampal CA1 region. Adult Mongolian gerbils were subjected to 5-minute forebrain ischemia. Immunoblotting analysis with anti-phospho-Akt/PKB (Akt) antibody showed that phosphorylation of Akt at serine-473 (Akt-Ser-473) in the CA1 region decreased immediately after reperfusion, and in turn transiently increased 6 hours after reperfusion. The decreased phosphorylation of Akt-Ser-473 was not observed in the CA3 region. The authors then tested effects of intraventricular injection of orthovanadate and IGF-1, which are known to activate Akt. Treatment with orthovanadate or IGF-1 30 minutes before ischemia blocked delayed neuronal death in the CA1 region. The neuroprotective effects of orthovanadate and IGF-1 were associated with preventing decreased Akt-Ser-473 phosphorylation in the CA1 region observed immediately after reperfusion. Immunohistochemical studies with the anti-phospho-Akt-Ser-473 antibody also demonstrated that Akt was predominantly in the nucleus and was moderately activated in the cell bodies and dendrites of pyramidal neurons after orthovanadate treatment. The orthovanadate treatment also prevented the decrease in phosphorylation of mitogen-activated protein kinase (MAPK). Pretreatment with combined blockade of phosphatidylinositol 3-kinase and MAPK pathways totally abolished the orthovanadate-induced neuroprotective effect. These results suggest that the activation of both Akt and MAPK activities underlie the neuroprotective effects of orthovanadate on the delayed neuronal death in the CA1 region after transient forebrain ischemia.

Delayed neuroprotective effect of insulin-like growth factor-i after experimental transient focal cerebral ischemia monitored with mri

BACKGROUND AND PURPOSE

Insulin-like growth factor (IGF) treatment has been shown to have trophic and neuroprotective effects in vitro and in vivo in different lesion models. IGF-I has potent neuroprotective effects after hypoxic-ischemic injury and global ischemia. The role of IGF-I in focal cerebral ischemia is only partially understood. Therefore, in the present study, we evaluated, by applying MRI monitoring, whether a clinically relevant systemic administration of IGF-I can achieve a long-lasting neuroprotective effect.

METHODS

Male Wistar rats underwent transient occlusion of the right middle cerebral artery for 1 hour by using the suture occlusion model. Animals then were intraventricularly treated with 33.33 microg IGF-I/d for 3 days (group A, the IGF-I group [n=13]; group B, the placebo group [n=14]) or subcutaneously treated with 200 microg IGF-I/d for 7 days (group D, the IGF-I group [n=10]; group E, the placebo group [n=10]). Groups C and F served as sham-operated controls (n=5 and n=3, respectively). Treatment was begun 30 minutes after occlusion of the middle cerebral artery. Subcutaneously treated animals underwent MRI studies (diffusion-weighted imaging, perfusion imaging, and T2-weighted imaging) beginning 60 minutes after vessel occlusion at 6 hours and at days 1, 2, 5, and 7 after ischemia. The animals were weighed and neurologically assessed daily (rating scale ranged from 0, indicating no deficit, to 5, indicating death). On the third day (intraventricular trial) and on the seventh day (subcutaneous trial), animals were euthanized, and brain sections were stained with triphenyltetrazolium chloride.

RESULTS

The mean infarct volume was 52.9+/-25.2 mm(3) in intraventricularly treated animals versus 146.4+/-62.2 mm(3) in control animals (P<0.01) and 42.2+/-17.9 mm(3) in subcutaneously IGF-I-treated animals versus 73.1+/-38.1 mm(3) in control animals (P<0.05). Apparent diffusion coefficient-derived lesion volume at 60 minutes after occlusion was 40.4+/-23.7 mm(3) versus 38.3+/-19.3 mm(3) (P=NS), increased to 168.3+/-49.55 mm(3) versus 105.5+/-33.8 mm(3) (P<0.05) at 24 hours, and then decreased to 55.8+/-30.3 mm(3) versus 23.3+/-20.2 mm(3) (P<0.05) for control and IGF-I-treated animals, respectively. The T2-weighted-derived ischemic lesion volume at 24 hours after occlusion was 236+/-49.2 mm(3) versus 115.9+/-56.8 mm(3) (P<0.05) and decreased to 115.9+/-26.2 mm(3) versus 75.7+/-35.8 mm(3) (P<0.05) at day 7 for control and IGF-I-treated animals, respectively. The relative regional cerebral blood volume was reduced to 50% before reperfusion in all regions of interest except for region of interest 1 (vessel territory of anterior cerebral artery), recovered during reperfusion, but was not different between the control and the growth factor-treated group at any imaging time point. There was no significant difference in weight loss. There was less neurological deficit after ischemia in intraventricularly and subcutaneously IGF-I-treated animals compared with control animals (P<0.05).

CONCLUSIONS

Continuous treatment with intraventricularly and subcutaneously administered IGF-I achieved a long-lasting neuroprotective effect as early as 24 hours after ischemia as measured by MRI. Therefore, IGF-I may represent a new approach to the treatment of focal cerebral ischemia.