Insulin-like growth factor II is induced during wound repair following hypoxic-ischemic injury in the developing rat brain

How do we reach the goal of personalized medicine for neuroprotection in neonatal hypoxic-ischemic encephalopathy?

Therapeutic hypothermia is now standard of care for neonates with hypoxic-ischemic encephalopathy (HIE) in high income countries (HIC). Conversely, compelling trial evidence suggests that hypothermia is ineffective, and may be deleterious, in low- and middle-income countries (LMIC), likely reflecting the lower proportion of infants who had sentinel events at birth, suggesting that injury had advanced to a stage when hypothermia is no longer effective. Although hypothermia significantly reduced the risk of death and disability in HICs, many infants survived with disability and in principle may benefit from targeted add-on neuroprotective or neurorestorative therapies. The present review will assess biomarkers that could be used to personalize treatment for babies with HIE - to determine first whether an individual infant is likely to respond to hypothermia, and second, whether additional treatments may be beneficial.

Insulin-like growth factor 1 and its prognostic value in the course of acute ischemic cerebrovascular events

Introduction

The aim of the study was to evaluate insulin-like growth factor 1 (IGF-1) as a predictor of the course of an acute cerebral ischemic event (AICE). This polypeptide, by activating receptors that are present in most tissues, including the brain, mediates the anabolic activity of growth hormone (GH) and its impact on growth and maturation processes, as well as organisms' survival time. AICE can occur in the form of a transient ischemic attack (TIA) or an ischemic stroke (IS).

Material and methods

The study included 86 participants. The correlation between serum IGF-1 concentration and the clinical status of 56 patients on days 1 and 9 of AICE, as well as risk factors and the course of the disease, were prospectively analyzed. The control group consisted of 30 healthy volunteers.

Results

Patients with a minor baseline neurological syndrome had higher serum IGF-1 concentrations than patients with severe baseline neurological dysfunctions. Multidimensional analyses showed that high IGF-1 values independently determined the worse course of the disease, especially in patients with a severe neurological deficit present on the first day of AICE.

Conclusions

Our results indicate that the high level of circulating IGF-1 on the first day of AICE is an independent factor determining the unfavorable course of the stroke, and this relationship is proportional to the severity of the baseline neurological deficit. The study also revealed a positive correlation between the decreased plasma IGF-1 concentration on the first day of AICE and the severity of neurological symptoms.

Stereological Evidence of Non-Selective Hippocampal Neurodegeneration, IGF-1 Depletion, and Behavioral Deficit following Short Term Bilateral Adrenalectomy in Wistar Rats

The development of animal models to study cell death in the brain is a delicate task. One of the models, that was discovered in the late eighties, is the induction of neurodegeneration through glucocorticoid withdrawal by adrenalectomy in albino rats. Such a model is one of the few noninvasive models for studying neurodegeneration. In the present study, using stereological technique and ultrastructural examination, we aimed to investigate the impact of short-term adrenalectomy (2 weeks) on different hippocampal neuronal populations in Wistar rats. In addition, the underlying mechanism(s) of degeneration in these neurons were investigated by measuring the levels of insulin-like growth factor-1 (IGF-1) and β-nerve growth factor (β-NGF). Moreover, we examined whether the biochemical and histological changes in the hippocampus, after short-term adrenalectomy, have an impact on the cognitive behavior of Wistar rats. Stereological counting in the hippocampus revealed significant neuronal deaths in the dentate gyrus and CA4/CA3, but not in the CA2 and CA1 areas, 7 and 14 days post adrenalectomy. The ultrastructural examinations revealed degenerated and degenerating neurons in the dentate, as well as CA4, and CA3 areas, over the course of 3, 7 and 14 days. The levels of IGF-1 were significantly decreased in the hippocampus of ADX rats 24 h post adrenalectomy, and lasted over the course of two weeks. However, β-NGF was not affected in rats. Using a passive avoidance task, we found a cognitive deficit in the ADX compared to the SHAM operated rats over time (3, 7, and 14 days). In conclusion, both granule and pyramidal cells were degenerated in the hippocampus following short-term adrenalectomy. The early depletion of IGF-1 might play a role in hippocampal neuronal degeneration. Consequently, the loss of the hippocampal neurons after adrenalectomy leads to cognitive deficits.

Insulin-Like Growth Factor-II and Ischemic Stroke-A Prospective Observational Study

Insulin-like growth factor-II (IGF-II) regulates prenatal brain development, but the role in adult brain function and injury is unclear. Here, we determined whether serum levels of IGF-II (s-IGF-II) are associated with mortality and functional outcome after ischemic stroke (IS). The study population comprised ischemic stroke cases (n = 492) and controls (n = 514) from the Sahlgrenska Academy Study on Ischemic Stroke (SAHLSIS). Functional outcome was evaluated after 3 months and 2 years using the modified Rankin Scale (mRS), and additionally, survival was followed at a minimum of 7 years or until death. S-IGF-II levels were higher in IS cases both in the acute phase and at 3-month follow-up compared to controls (p < 0.05 and p < 0.01, respectively). The lowest quintile of acute s-IGF-II was, compared to the four higher quintiles, associated with an increased risk of post-stroke mortality (median follow-up 10.6 years, crude hazard ratio (HR) 2.34, 95% confidence interval (CI) 1.56–3.49, and fully adjusted HR 1.64, 95% CI 1.02–2.61). In contrast, crude associations with poor functional outcome (mRS 3–6) lost significance after full adjustment for covariates. In conclusion, s-IGF-II was higher in IS cases than in controls, and low acute s-IGF-II was an independent risk marker of increased mortality.

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.

Insulin-Like Growth Factor-II/Cation-Independent Mannose 6-Phosphate Receptor in Neurodegenerative Diseases

The insulin-like growth factor II/mannose 6-phosphate (IGF-II/M6P) receptor is a multifunctional single transmembrane glycoprotein. Recent studies have advanced our understanding of the structure, ligand-binding properties, and trafficking of the IGF-II/M6P receptor. This receptor has been implicated in a variety of important cellular processes including growth and development, clearance of IGF-II, proteolytic activation of enzymes, and growth factor precursors, in addition to its well-known role in the delivery of lysosomal enzymes. The IGF-II/M6P receptor, distributed widely in the central nervous system, has additional roles in mediating neurotransmitter release and memory enhancement/consolidation, possibly through activating IGF-II-related intracellular signaling pathways. Recent studies suggest that overexpression of the IGF-II/M6P receptor may have an important role in regulating the levels of transcripts and proteins involved in the development of Alzheimer's disease (AD)-the prevalent cause of dementia affecting the elderly population in our society. It is reported that IGF-II/M6P receptor overexpression can increase the levels/processing of amyloid precursor protein leading to the generation of β-amyloid peptide, which is associated with degeneration of neurons and subsequent development of AD pathology. Given the significance of the receptor in mediating the transport and functioning of the lysosomal enzymes, it is being considered for therapeutic delivery of enzymes to the lysosomes to treat lysosomal storage disorders. Notwithstanding these results, additional studies are required to validate and fully characterize the function of the IGF-II/M6P receptor in the normal brain and its involvement in various neurodegenerative disorders including AD. It is also critical to understand the interaction between the IGF-II/M6P receptor and lysosomal enzymes in neurodegenerative processes, which may shed some light on developing approaches to detect and prevent neurodegeneration through the dysfunction of the receptor and the endosomal-lysosomal system.

The role for IGF-1-derived small neuropeptides as a therapeutic target for neurological disorders

INTRODUCTION

Exogenous IGF-1 protects the brain from ischemic injury and improves function. However, its clinical application to neurological disorders is limited by its large molecular size, poor central uptake and mitogenic potential.

AREAS COVERED

In this review, the authors have discussed the efficacy, pharmacokinetics and mechanisms of IGF-1 derivatives on protecting acute brain injury, preventing memory impairment and improving recovery from neurological degenerative conditions evaluated in various animal models. We have included natural metabolites of IGF-1, glycine-proline-glutamate (GPE), cleaved from N-terminal IGF-1 and cyclic glycine-proline (cGP) as well as the structural analogues of GPE and cGP, glycine-2-methyl-proline-glutamate and cyclo-l-glycyl-l-2-allylproline, respectively. In addition, the regulatory role for cGP in bioavailability of IGF-1 has also been discussed.

EXPERT OPINION

These small neuropeptides provide effective neuroprotection by offering an improved pharmacokinetic profile and more practical route of administration compared with IGF-1 administration. Developing modified neuropeptides to overcome the limitations of their endogenous counterparts represents a novel strategy of pharmaceutical discovery for neurological disorders. The mechanism of action may involve a regulation of IGF-1 bioavailability.

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.

Growth hormone receptor immunoreactivity is increased in the subventricular zone of juvenile rat brain after focal ischemia: a potential role for growth hormone in injury-induced neurogenesis

BACKGROUND

During recovery from an ischemic brain injury, a cerebral growth hormone (GH) axis is activated. Whilst GH has been demonstrated to be neuroprotective both in vitro and in vivo, a role for GH in neuro-restorative processes after brain injury has yet to be studied.

OBJECTIVE

To explore a role for GH in injury-induced neurogenesis by examining GH receptor (GH-R) immunoreactivity within the subventricular zone (SVZ) of juvenile rats after brain injury and by testing the proliferative capacity of GH on embryonic mouse neural stem cells.

DESIGN

Twenty-one day old rats were subjected to unilateral hypoxic-ischemia of the brain and sacrificed 1-15days later. Coronal brain sections from these animals and age-matched naïve controls were immunostained for GH-R and cell markers of neurogenesis. The level of GH-R immunoreactivity in the ipsilateral and contralateral SVZ of each animal was semi-quantified both by independent blinded scoring by two examiners and blinded image analysis. To examine the effect of GH on proliferation of embryonic mouse neural stem cells, cells were treated with increasing concentrations of rat pituitary GH for 48h in the presence of 5'-bromo-2'-deoxyuridine.

RESULTS

The level of GH-R immunoreactivity in the ipsilateral SVZ was significantly increased 5days after injury vs. the contralateral SVZ, coinciding both spatially and temporally with injury-induced neurogenesis. The population of GH-R immunopositive cells in the ipsilateral SVZ at this time was found to include proliferating cells (Ki67 immunopositive), neural progenitor cells (nestin immunopositive) and post-proliferative migratory neuroblasts (doublecortin immunopositive). Stimulation of embryonic mouse NSCs with physiological concentrations of rat pituitary GH elicited a dose-dependent proliferative response.

CONCLUSION

These results indicate a novel role for GH and its receptor in injury-induced neurogenesis, and suggest that GH treatment may potentiate endogenous neuro-restorative processes after brain injury.

Identification and characterization of demethylase JMJD1A as a gene upregulated in the human cellular response to hypoxia

Hypoxia is commonly found in human solid cancers and serves as a selective environment for the survival of aggressive cancer cells and as protection from anti-cancer therapies. In addition to a shift to anaerobic metabolism, the cellular response to hypoxia includes cessation of cell division and/or cell death. These mechanisms have still not been defined. Identification of the members of hypoxia-induced growth arrest pathways remain incomplete. We have undertaken an expression microarray analysis of the cellular response to hypoxia in diverse cell lines. An identified cohort of genes is reliably upregulated in various cells in response to hypoxia, as validated by reverse-transcriptase polymerase chain reaction (RT-PCR). One of the upregulated targets corresponds to an expressed sequence tag encoded by JMJD1A (a gene also known as JHDM2A), which has been identified as a histone demethylase that regulates the transcription of androgen receptor targets. We confirm, by RT-PCR, the upregulation of JMJD1A after hypoxia and desferroxamine treatment in multiple cell lines. We also show that JMJD1A is predominantly, but not exclusively, a nuclear protein. Immunofluorescent staining of HeLa cells shows a shift of cytoplasmic JMJD1A into the nucleus on hypoxia treatment. Immunohistochemical staining has revealed that JMJD1A is widely expressed in tissues, even in cells that are not known to express the androgen receptor, and is significantly increased in smooth muscle cells upon hypoxia treatment.

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.

Transcriptome analysis of the response to chronic constant hypoxia in zebrafish hearts

Insufficient blood supply during acute infarction and chronic ischemia leads to tissue hypoxia which can significantly alter gene expression patterns in the heart. In contrast to most mammals, some teleost fishes are able to adapt to extremely low oxygen levels. We describe here that chronic constant hypoxia (CCH) leads to a smaller ventricular outflow tract, reduced lacunae within the central ventricular cavity and around the trabeculae and an increase in the number of cardiac myocyte nuclei per area in the hearts of two teleost species, zebrafish (Danio rerio) and cichlids (Haplochromis piceatus). In order to identify the molecular basis for the adaptations to CCH, we profiled the gene expression changes in the hearts of adult zebrafish. We have analyzed over 15,000 different transcripts and found 376 differentially regulated genes, of which 260 genes showed increased and 116 genes decreased expression levels. Two notch receptors (notch-2 and notch-3) as well as regulatory genes linked to cell proliferation were transcriptionally upregulated in hypoxic hearts. We observed a simultaneous increase in expression of IGF-2 and IGFbp1 and upregulation of several genes important for the protection against reactive oxygen species (ROS). We have identified here many novel genes involved in the response to CCH in the heart, which may have potential clinical implications in the future.

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.

Mucosal tolerance to E-selectin and response to systemic inflammation

Mucosal tolerance to E-selectin has been shown to prevent stroke and reduce brain infarcts in experimental stroke models. However, the effective E-selectin dose range required to achieve mucosal tolerance and the precise mechanisms of neuroprotection remain unclear. We sought to examine the mechanisms of cytoprotection using gene expression profiling of tissues in the setting of mucosal tolerance and inflammatory challenge. Using spontaneously hypertensive rats (SHRs), we achieved immune tolerance with 0.1 to 5 microg E-selectin per nasal instillation and observed a dose-related anti-E-selectin immunoglobulin G antibody production. We also show the distinct patterns of gene expression changes in the brain and spleen with the different tolerizing doses and lipopolysaccharide (LPS) exposure. Prominent differences were seen with such genes as insulin-like growth factors in the brain and downregulation of those encoding the major histocompatibility complex class I molecules in the spleen. In all, mucosal tolerance to E-selectin and subsequent exposure to LPS resulted in significant tissue changes. These changes, while giving an insight to the underlying mechanisms, serve as possible targets for future studies to facilitate translation to human clinical trials.

Oxidative metabolism, apoptosis and perinatal brain injury

Perinatal hypoxic-ischaemic injury (HII) is a significant cause of neurodevelopmental impairment and disability. Studies employing 31P magnetic resonance spectroscopy to measure phosphorus metabolites in situ in the brains of newborn infants and animals have demonstrated that transient hypoxia-ischaemia leads to a delayed disruption in cerebral energy metabolism, the magnitude of which correlates with the subsequent neurodevelopmental impairment. Prominent among the biochemical features of HII is the loss of cellular ATP, resulting in increased intracellular Na+ and Ca2+, and decreased intracellular K+. These ionic imbalances, together with a breakdown in cellular defence systems following HII, can contribute to oxidative stress with a net increase in reactive oxygen species. Subsequent damage to lipids, proteins, and DNA and inactivation of key cellular enzymes leads ultimately to cell death. Although the precise mechanisms of neuronal loss are unclear, it is now clear both apoptosis and necrosis are the significant components of cell death following HII. A number of different factors influence whether a cell will undergo apoptosis or necrosis, including the stage of development, cell type, severity of mitochondrial injury and the availability of ATP for apoptotic execution. This review will focus on some pathological mechanisms of cell death in which there is a disruption to oxidative metabolism. The first sections will discuss the process of damage to oxidative metabolism, covering the data collected both from human infants and from animal models. Following sections will deal with the molecular mechanisms that may underlie cerebral energy failure and cell death in this form of brain injury, with a particular emphasis on the role of apoptosis and mitochondria.

Temporal transcriptome of mouse ATDC5 chondroprogenitors differentiating under hypoxic conditions

The formation of cartilage takes place in vivo in an environment of reduced oxygen tension. To study the effect of hypoxia on the process of chondrogenesis, ATDC5 mouse chondroprogenitor cells were induced to differentiate by the addition of insulin and cultured under ambient and hypoxic conditions corresponding to 21% and 1% O2 in the gas phase, respectively. The production of extracellular proteoglycans as well as the transcriptional profile of 104 selected genes was determined by real-time RT-PCR. Hypoxia alone induced early chondrogenesis as evidenced by the synthesis of glycosaminoglycans and expression of aggrecan and collagen type II genes. Surprisingly, however, hypoxic incubation of insulin-treated cells delayed and suppressed the insulin-mediated early chondrogenesis and almost completely blocked hypertrophic differentiation. Analysis of the gene expression yielded several clues as to the mechanisms involved. In addition, a group of genes was identified that have not previously been associated with hypoxia, including Ak4, Akt3, Col X, Fmod, Ier3, IGFbp4, MafF, Mxi1, Rcor2, Rras, Sox6, Tnni2, Wnt5a, and Zfp313.

Insulin-like growth factor I and II expression and modulation in amoeboid microglial cells by lipopolysaccharide and retinoic acid

Insulin-like growth factors I and II are known to regulate the development of the CNS. We examined the developmental changes in insulin-like growth factor I and insulin-like growth factor II expression in the postnatal rat corpus callosum. Insulin-like growth factor I and insulin-like growth factor II mRNA expression increased at 3 days as compared with 1 day whereas the protein expression increased up to 7 days. Insulin-like growth factor I and insulin-like growth factor II immunoexpression was specifically localized in round cells confirmed by double immunofluorescence with OX-42 to be the amoeboid microglial cells. Insulin-like growth factor I expression was observed up to 7 days in amoeboid microglial cells while insulin-like growth factor II expression was detected in 1-3 day old rats. Exposure of primary rat microglial cell cultures to lipopolysaccharide increased insulin-like growth factor I and insulin-like growth factor II mRNA and protein expression significantly along with their immunoexpression in microglial cells. The lipopolysaccharide-induced increase in insulin-like growth factor I and insulin-like growth factor II mRNA and protein expression was significantly decreased with all-trans-retinoic acid. We conclude that insulin-like growth factor I and insulin-like growth factor II expression in amoeboid microglial cells in the developing brain is related to their activation. Once the activation is inhibited, either by transformation of the amoeboid microglial cells into ramified microglia regarded as resting cells or as shown by the effect of all-trans-retinoic acid administration, insulin-like growth factor I and insulin-like growth factor II mRNA and protein expression is downregulated.

Birth insults involving hypoxia produce long-term increases in hippocampal [125I]insulin-like growth factor-I and -II receptor binding in the rat

Insulin-like growth factors-I and -II and insulin are structurally related mitogenic growth factors with multiple actions in the developing nervous system and adult CNS. Previous studies have demonstrated acute induction of insulin-like growth factors and their receptors, over a time course of several days, in response to hypoxic/ischemic insult to developing or adult brain. The current study tested whether birth insults involving hypoxia may produce long term changes in brain insulin-like growth factor or insulin receptor levels, lasting into adulthood. For this, rats were born vaginally (controls), by cesarean section, or by cesarean section with 15 min of added global anoxia (cesarean section+anoxia), and brain [125I]insulin-like growth factor-I, [125I]insulin-like growth factor-II and [125I]insulin receptor binding sites were assessed autoradiographically at adulthood. [125I]Insulin-like growth factor-I receptor binding sites were increased in all hippocampal subfields (CA1-CA3, dentate gyrus) in rats born either by cesarean section or by cesarean section+anoxia, compared with vaginal birth. [125I]Insulin-like growth factor-II binding was increased in all hippocampal subfields only in rats born by cesarean section+anoxia compared with either vaginal birth or cesarean section groups. [125I]Insulin-like growth factor-I and [125I]insulin-like growth factor-II binding in frontal cortex, striatum and cerebellum were unaffected by birth group, except for increased [125I]insulin-like growth factor-I binding in the cerebellar molecular layer of cesarean-sectioned animals. Birth group had no significant effect on [125I]insulin binding in any brain region. Affinity cross-linking experiments performed with hippocampal membranes from the three birth groups showed that i) [125I]insulin-like growth factor-I and [125I]insulin-like growth factor-II recognized bands of molecular weights characteristic of insulin-like growth factor-I and insulin-like growth factor-II receptors, respectively, and ii) [125I]insulin-like growth factor-I and [125I]insulin-like growth factor-II were displaced more potently by their respective unlabeled ligands than by related molecules. It is concluded that birth insults involving hypoxia can induce lasting increases in insulin-like growth factor-I and -II receptors in the CNS. There is specificity with respect to the subtype of insulin-like growth factor receptor affected by the particular birth insult and the brain region affected. It is suggested that enduring increases in levels of insulin-like growth factor receptors consequent to hypoxic birth insult may help to maintain hippocampal function at adulthood, and could modulate responsiveness to insulin-like growth factor administration.

Developmental differences between cation-independent and cation-dependent mannose-6-phosphate receptors in rat brain at perinatal stages

Mannose-6-phosphate receptors (MPRs) play a role in the selective transport of macromolecules bearing mannose-6-phosphate residue to lysosomes. To date, two types of MPRs have been described in most of cells and tissues: the cation-dependent (CD-MPR) and cation-independent mannose-6-phosphate receptor (CI-MPR). In order to elucidate their possible role in the central nervous system, the expression and binding properties of both MPRs were studied in rat brain along perinatal development. It was observed that the expression of CI-MPR decreases progressively from fetuses to adults, while the CD-MPR increases around the 10th day of birth, and maintains these values up to adulthood. Binding assays showed differences in the Bmax and KD values between the ages studied, and they did not correlate with the expression levels of both MPRs. Variations in lysosomal enzyme activities and expression of phosphomannosylated ligands during development correlated more with CD-MPR than with CI-MPR expression. These results suggest that both receptors play a different role in rat brain during perinatal development, being CD-MPR mostly involved in lysosome maturation.

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.

Differential patterns of insulin-like growth factor-I and -II mRNA expression in medulloblastoma

Insulin-like growth factors (IGFs) play an important role in tumour growth and development. We hypothesized that this is also the case for medulloblastomas, which are highly malignant cerebellar brain tumours usually occurring in children. In these tumours the expression patterns of IGF-I and -II mRNA were studied. Tumour specimens obtained from 12 children and two adults at diagnosis were hybridized in situ with digoxigenin-labelled cRNA probes for hIGF-I and hIGF-II mRNAs. In all cases, tumour cells showed abundant expression of IGF-I mRNA. Nine of the 14 tumours showed variable but significant IGF-II expression. In these tumours, the hybridization signal almost exclusively colocalized with a subpopulation of Ki-M1P positive cells that were identified as ramified microglia (RM) cells. In the five tumours without IGF-II expression, microglia/brain macrophages with a more rounded amoeboid-like morphology predominated. RM cells in normal cerebellar tissues, residing abundantly in areas of the white and, to a less extent, in the grey matter, were IGF-II mRNA-negative. These RM cells showed a thinner and more extensively branched appearance and were more evenly distributed than those encountered in medulloblastoma. Probably, during the transformation from the resting ramified towards the amoeboid morphology (or vice versa) IGF-II mRNA expression is only temporarily induced. The physiological meaning of the induction of IGF-II mRNA expression by these cells in medulloblastoma remains unclear but any IGF-II peptide synthesized could exert unfavourable mitogenic and antiapoptotic effects on adjacent tumour cells. However, in this relatively small number of cases we could not find any indications for a relationship between clinical characteristics of the various cases and the extent of IGF-II mRNA expression.

The insulin-like growth factor-II/mannose-6-phosphate receptor: structure, distribution and function in the central nervous system

The insulin-like growth factor-II/mannose-6-phosphate (IGF-II/M6P) receptor is a multifunctional single transmembrane glycoprotein which, along with the cation-dependent M6P (CD-M6P) receptor, mediates the trafficking of M6P-containing lysosomal enzymes from the trans-Golgi network (TGN) to lysosomes. Cell surface IGF-II/M6P receptors also function in the degradation of the non-glycosylated IGF-II polypeptide hormone, as well as in the capture and activation/degradation of extracellular M6P-bearing ligands. In recent years, the multifaceted role of the receptor has become apparent, as several lines of evidence have indicated that in addition to its role in lysosomal enzyme trafficking, clearance and/or activation of a variety of growth factors and endocytosis-mediated degradation of IGF-II, the IGF-II/M6P receptor may also mediate transmembrane signal transduction in response to IGF-II binding under certain conditions. However, very little is known about the physiological significance of the receptor in the function of the central nervous system (CNS). This review aims to delineate what is currently known about IGF-II/M6P receptor structure, its ligand binding properties and role in lysosomal enzyme transport. It also summarizes the recent data regarding the role of the receptor in the CNS, including its distribution, possible importance for normal and activity-dependent functioning as well as its implications in neurodegenerative disorders such as Alzheimer's disease (AD).

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-1 and post-ischemic brain injury

Insulin-like growth factor-1 (IGF-1) is a naturally occurring neurotrophic factor that plays an important role in promoting cell proliferation and differentiation during normal brain development and maturation. The present review examines recent evidence that endogenous IGF-1 also plays a significant role in recovery from insults such as hypoxia-ischemia and that giving additional exogenous IGF-1 can actively ameliorate damage. It is now well established that neurons and other cell types die many hours or even days after initial injury due to activation of programmed cell death pathways. IGF-1 and its binding proteins and receptors are intensely induced within damaged brain regions following brain injury, suggesting a possible a role for IGF-1 in brain recovery. Exogenous administration of IGF-1 within a few hours after brain injury is now known to be protective in both gray and white matter and leads to improved somatic function. In contrast, pre-treatment is ineffective, likely reflecting limited intracerebral penetration of IGF-1 into the uninjured brain. The neuroprotective effects of IGF-1 are mediated by IGF-1 receptors and its binding proteins and are specific to particular cellular phenotypes and brain regions. The window of opportunity for treatment with IGF-1 is limited to a few hours after normothermic brain injury, reflecting its specific actions on early, intracellular events in the apoptotic cascade. However, injury-associated mild post-hypoxic hypothermia, which delays the development of cell death, can shift and dramatically extend the window of opportunity for delayed treatment with IGF-1. Such a combined approach is likely to be essential for any clinical treatment.

Bone growth factors in maxillofacial skeletal reconstruction

A literature review was performed to survey the available information on the potential of bone growth factors in skeletal reconstruction in the maxillofacial area. The aim of this review was to characterize the biological and developmental nature of the growth factors considered, their molecular level of activity and their osteogenic potential in craniofacial bone repair and reconstruction. A total of 231 references were selected for evaluation by the content of the abstracts. All growth factors considered have a fundamental role in growth and development. In postnatal skeletal regeneration, PDGF plays an important role in inducing proliferation of undifferentiated mesenchymal cells. It is an important mediator for bone healing and remodelling during trauma and infection. It can enhance bone regeneration in conjunction with other growth factors but is unlikely to provide entirely osteogenic properties itself. IGFs have an important role in general growth and maintenance of the body skeleton. The effect of local application of IGFs alone in craniofacial skeletal defects has not yet shown a clear potential for enhancement of bone regeneration in the reported dosages. The combination of IGF-I with PDGF has been effective in promoting bone regeneration in dentoalveolar defects around implants or after periodontal bone loss. TGFbeta alone in skeletal reconstruction appears to be associated with uncertain results. The presence of committed cells is required for enhancement of bone formation by TGFbeta. It has a biphasic effect, which suppresses proliferation and osteoblastic differentiation at high concentrations. BMPs, BMP2, BMP4 and BMP7 in particular, appear to be the most effective growth factors in terms of osteogenesis and osseous defect repair. Efficacy of BMPs for defect repair is strongly dependent on the type of carrier and has been subject to unknown factors in clinical feasibility trials resulting in ambiguous results. The current lack of clinical data may prolong the period until this factor is introduced into routine clinical application. PRP is supposed to increase proliferation of undifferentiated mesenchymal cells and to enhance angiogenesis. There is little scientific evidence about the benefit of PRP in skeletal reconstructive and preprosthetic surgery yet and it is unlikely that peri-implant bone healing or regeneration of local bone into alloplastic material by the application of PRP alone will be significantly enhanced.

Microglia-derived IGF-2 prevents TNFalpha induced death of mature oligodendrocytes in vitro

Insulin-like growth factor-2 (IGF-2) present in media conditioned by non-activated and interferon gamma (IFN gamma)-treated microglia reduces galactocerebroside(+) (GalC) oligodendrocyte apoptosis in cultures derived both from the CG4 cell line and primary rat cortices. Microglia-derived IGF-2 also acts in each culture system to block GalC(+) oligodendrocyte toxicity resulting from soluble microglial-derived tumour necrosis factor alpha (TNF alpha). IGF-2 inhibits TNF alpha-induced c-Jun kinase (JNK) activation of the CG4 cell line. Microglial activation results in the release of soluble factors that are potentially toxic to oligodendrocytes but this may be offset by the production of soluble factors that protect these vulnerable cells. Allowing for extrapolation of these in vitro findings to intact tissue, our observations suggest one mechanism for limiting bystander damage in the context of inflammatory brain disease.

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.

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.

Insulin-like growth factor-1 (IGF-1): a neuroprotective trophic factor acting via the Akt kinase pathway

Insulin-like growth factor-I (IGF-I) is a pleiotropic polypeptide with a wide range of actions in both central and peripheral nervous sytems. Over the past few years, we studied the trophic as well as neuromodulatory roles of IGF-I in the brain. Accumulated evidence indicates that IGF-I, apart from regulating growth and development, protects neurons against cell death induced by amyloidogenic derivatives, glucose or serum deprivation via the activation of intracellular pathways implicating phosphatidylinositide 3/Akt kinase, winged-helix family of transcription factor FKHRL1 phosphorylation or production of free radicals. The effects of IGF-I on neuroprotection, glucose metabolism and activity-dependent plasticity suggest the potential usefulness of this growth factor or related mimetics in the treatment of Alzheimer's disease and other neurodegenerative disorders.

Gene expression in neurotrauma

It has been established that following injury to the central nervous system two types of damage take place, the initial insult and the secondary response to injury. This review will focus on the secondary molecular aspects of neurotrauma. These responses may be either deleterious or have protective effects upon the injured cell population. Molecular responses include the regulation of genes which change cellular architecture, up-regulate of growth factors, induce reparative stress responses, influence apoptosis and regulate the transcriptional process. The purpose of this study is to provide the reader with a brief overview of some of the molecular mechanisms which are activated following a neurological insult.

NMDA receptor mediated changes in IGF-II gene expression in the rat brain after injury and the possible role of nitric oxide

This study was undertaken in order to investigate the role of insulin-like growth factor (IGF)-II, c-fos, N-methyl-D-aspartate (NMDA) receptors, and nNOS in the cellular processes following a penetrating brain injury. IGF-II mRNA levels, as determined by Northern analysis, were decreased at 4, 8, and 24 h after brain injury, in the lesioned, compared to the contralateral intact hemisphere. Forty-eight and 72 h after the injury, there was no difference between the lesioned and the contralateral intact hemisphere in IGF-II mRNA levels. c-fos mRNA levels followed a parallel, but opposite course: They were increased at 4, 8 and 24 h after the injury, while at 48 and 72 h c-fos mRNA levels in the lesioned hemisphere did not differ from those in the intact. Administration of MK-801 reversed the injury-induced decrease in IGF-II mRNA levels. Administration of MK-801 resulted in an increase in IGF-II mRNA in both the intact and the lesioned hemispheres. Brain injury resulted in an increase in nNOS immunopositive cells in the hippocampal formation, which was detectable at 4 and 12, but not 48 h after the injury. These results suggest that IGF-II, c-fos, NMDA receptors and nNOS are involved in the cellular responses to brain injury.

Rediscovering good old friend IGF-I in the new millenium: possible usefulness in Alzheimer's disease and stroke

Much research has been done over the past two decades on the role of insulin-like growth factors I and II (IGF) in the maintenance of normal body homeostasis, especially in regard to various endocrine functions, growth and aging. For example, IGF-I is a well established promoter of tissue growth and has been used in the clinics for the treatment of growth related disorders, even being abused by athletes to enhance performance in competitions. In contrast, comparatively limited attention has been given to the potential significance of the IGFs in the central nervous system. Over the past few years, we have studied the trophic as well as neuromodulatory roles of the IGFs in the brain. IGF-I and IGF-II are potent modulators of acetylcholine release, IGF-I inhibiting release while IGF-II is a potent stimulant. Moreover, only the internalization of the IGF-I receptor complex was blocked by an inhibitor of phosphotyrosylation. This is in accordance with the differential nature of the IGF-I and IGF-II receptors, the former being a tyrosine kinase receptor while the later is a single transmembrane domain protein bearing binding sites for 6-mannose phosphate containing residues. The activation of IGF-I receptors protected neurons against cell death induced by amyloidogenic derivatives likely by an intracellular mechanism distinct from those involved in the regulation of acetylcholine release and neuronal growth. The stimulation of IGF-I receptors can activate intracellular pathways implicating a PI3/Akt kinase and CREB phosphorylation or modulate the production of free radicals. The effects, particularly those of IGF-I on key markers of the Alzheimer's (AD) brains namely cholinergic dysfunction, neuronal amyloid toxicity, tau phosphorylation and glucose metabolism suggest the potential usefulness of this growth factor in the treatment of neurodegenerative diseases. However, the poor bioavailability, enzymatic stability and brain penetration of IGF-I hamper progress in this regard. The recent development of a small, non-peptidyl mimetic of insulin able to directly activate the insulin receptor [Zhang, B., Salituro, G., Szalkowski, D., Li, Z., Zhang, Y., Royo, I., Vilella, D., Diez, M.T., Pelaez, F., Ruby, C., Kendall, R.L., Mao, X., Griffin, P., Calaycay, J., Zierath, J.R., Heck, J. V., Smith, R.G., Moller, D.E., 1999. Science, 284, 974-977] suggests that a similar strategy could be used for IGF-I and the IGF-I receptor leading to the characterization of IGF-I mimics of potential clinical usefulness.

Impact of neonatal kainate treatment on hippocampal insulin-like growth factor receptors

The insulin-like growth factors-I and -II have neurotrophic properties and act through specific membrane receptors. High levels of binding sites for these growth factors are distributed discretely throughout the brain, being concentrated in the hippocampal formation. Functionally, the insulin-like growth factors, in addition to their growth-promoting actions, are considered to play important roles in normal cell functions, as well as in response to pharmacological or surgical manipulations. In adult rats, we have previously shown that systemic injection of kainate produces an overall decrease, in a time-dependent manner, in insulin-like growth factor-I and -II receptor binding sites in the hippocampus [Kar S. et al. (1997) Neuroscience 80, 1041-1055]. Given the evidence that insulin-like growth factors play a critical role during the early stages of brain development, the present study is a logical extension of this earlier report and established the effect of neonatal kainate injection on the developmental profile of insulin-like growth factor receptors. We have evaluated the time-course alteration of these receptors following systemic injection of kainate to newborn rats. After injection of a sublethal dose of kainate (5 mg/kg, i.p.) to postnatal one-day-old pups, [125I]insulin-like growth factor-I, [125I]insulin-like growth factor-II and [125I]insulin binding sites were studied at different postnatal days (7, 14, 21, 28 and 35) using receptor autoradiography. In the developing hippocampus, insulin-like growth factor-I and insulin binding sites are concentrated primarily in the dentate gyrus and the CA2/CA3 subfields, whereas insulin-like growth factor-II binding is discretely localized to the pyramidal layer and the granular layer of the dentate gyrus. Following kainate injection, we observed a slight increase in insulin-like growth factor-I binding sites in given hippocampal subfields starting at postnatal day 14, being significant at day 21. At later days, a progressive decrease was noted. This transient increase may represent an attempt for neuronal plasticity by up-regulating receptor levels. In contrast, insulin-like growth factor-II and insulin receptor binding sites are found to be decreased in various regions of the hippocampus in kainate-treated pups. Taken together, these results provide further evidence for the existence and differential alterations of insulin-like growth factor-I, insulin-like growth factor-II and insulin receptors in the developing rat hippocampus following kainate-induced lesion, suggesting possible involvement of these growth factors in brain plasticity.

Mitochondrial physiology and pathology; concepts of programmed death of organelles, cells and organisms

The review summarizes the present state of our knowledge concerning alternative functions of mitochondria, namely energy conservation in forms of protonic potential and ATP, thermoregulatory energy dissipation as heat, production of useful substances, decomposition of harmful substances, control of cellular processes. The recent progress in understanding of some mitochondrion-linked pathologies is described. The role of reactive oxygen species in these processes is stressed. Possible mechanisms of programmed death of mitochondrion (mitoptosis), cell (apoptosis) and organism (phenoptosis) are considered. A concept is put forward assuming that mitoptosis is involved in some types of apoptosis whereas apoptosis can be a part of a phenoptotic cascade. It is hypothesized that septic shock, as well as the stress-induced brain and heart ischemic diseases and cancer, exemplify mechanisms of phenoptosis purifying population, community of organisms or kin from dangerous or useless individuals.

Insulin-like growth factors and binding proteins in multiple sclerosis plaques

Insulin-like growth factors (IGFs) play an important role in development and myelination in the central nervous system (CNS) as well as in the proliferation and differentiation of cells of the immune system. To assess the influence of this growth factor family on demyelination and repair in multiple sclerosis (MS), the expression of IGF-I, IGF-II, insulin, IGF binding proteins (IGFBP) 1-3 and IGF-I receptor (IGF-IR) in CNS tissue from MS and normal control cases was studied by immunocytochemistry. In active MS lesions, the expression of IGF-I, insulin and IGFBP1 was detected in hypertrophic astrocytes while that of IGF-II and IGFBP2 and 3 was confined to foamy macrophages within lesions and activated microglia in adjacent white matter. IGF-IR, the major IGF receptor, was immunolocalized in macrophages and an astrocyte subpopulation in plaques. Oligodendrocytes in normal-appearing white matter expressed only IGFBP1, not IGFs or IGF-IR. As the remyelinating capacity of oligodendrocytes could be impaired owing to the absence of IGF-IR, the prevailing role of IGFs in inflammatory demyelination may be to promote phagocytosis of myelin and astrogliosis.

Alterations in the neural growth hormone axis following hypoxic-ischemic brain injury

Recently, there has been considerable interest in determining the role of the growth hormone receptor (GHR) in the central nervous system (CNS). The aim of this study was to investigate the role of circulating growth hormone (GH) and the neural GHR after hypoxic-ischemic (HI) brain injury in the 21-day old rat. We observed growth hormone receptor/binding protein (GHR/BP) immunoreactivity to be rapidly upregulated following a severe unilateral HI injury. There was a biphasic increase with an initial rise occurring in blood vessels within a few hours after injury followed by a secondary rise evident by 3 days post-hypoxia in microglia/macrophages, some of which are destined to express insulin-like growth factor-I (IGF-I). There was also an increased immunoreactivity in reactive astrocytes, some of which were in the process of dividing. Subsequently, we attempted to activate the endothelial GHR/BP which was found to be increased after injury by treating with 15 microgram g-1 day-1 s.c. bGH for 7 days. Circulating concentrations of IGF-I fell after injury and were restored with GH treatment (P=0.001), whereas treatment of normal animals had no effect on serum IGF-I. Peripheral GH treatment increased the cerebrospinal fluid (CSF) concentration of immunoreactive IGF-I in the injured rats (P=0.017). GH treatment also reversed the systemic catabolism caused by the injury but had no significant neuroprotective effects. These results indicate that GH therapy can be used to reverse the systemic catabolism that occurs after CNS injury. In addition, these data suggest a role for the neural GHR during the recovery from brain injury, both in terms of the induction of IGF-I and in terms of glial proliferation.

Activity and injury-dependent expression of inducible transcription factors, growth factors and apoptosis-related genes within the central nervous system

This review primarily discusses work that has been performed in our laboratories and that of our direct collaborators and therefore does not represent an exhaustive review of the current literature. Our aim is to further discuss the role that gene expression plays in neuronal plasticity and pathology. In the first part of this review we examine activity-dependent changes in the expression of inducible transcription factors (ITFs) and neurotrophins with long-term potentiation (LTP) and kindling. This work has identified particular ITFs (Krox-20 and Krox-24) and neurotrophin systems (particularly the brain-derived neurotrophic factor (BDNF)/tyrosine receptor kinase-B, Trk-B system) that may be involved in stabilizing long-lasting LTP (i.e. LTP3). We also show that changes in the expression of other ITFs (Fos, Jun-D and Krox-20) and the BDNF/trkB neurotrophin system may play a central role in the development of hippocampal kindling, an animal model of human temporal lobe epilepsy. In the next part of this review we examine changes in gene expression after neuronal injuries (ischemia, prolonged seizure activity and focal brain injury) and after nerve transection (axotomy). We identify apoptosis-related genes (p53, c-Jun, Bax) whose delayed expression selectively increases in degenerating neurons, further suggesting that some forms of neuronal death may involve apoptosis. Moreover, since overexpression of the tumour-suppressor gene p53 induces apoptosis in a wide variety of dividing cell types we speculate that it may perform the same function in post-mitotic neurons following brain injuries. Additionally, we show that neuronal injury is associated with rapid, transient, activity-dependent expression of neurotrophins (BDNF and activinA) in neurons, contrasting with a delayed and more persistent injury-induced expression of certain growth factors (IGF-1 and TGFbeta) in glia. In this section we also describe results linking ITFs and neurotrophic factor expression. Firstly, we show that while BDNF and trkB are induced as immediate-early genes following injury, the injury-induced expression of activinA and trkC may be regulated by ITFs. We also discuss whether loss of retrograde transport of neurotrophic factors such as nerve growth factor following nerve transection triggers the selective and prolonged expression of c-Jun in axotomized neurons and whether c-Jun is responsible for regeneration or degeneration of these axotomized neurons. In the last section we further examine the role that gene expression may play in memory formation, epileptogenesis and neuronal degeneration, lastly speculating whether the expression of various growth factors after brain injury represents an endogenous neuroprotective response of the brain to injury. Here we discuss our results which show that pharmacological enhancement of this response with exogenous application of IGF-1 or TGF-beta reduces neuronal loss after brain injury.

Co-ordinated and cellular specific induction of the components of the IGF/IGFBP axis in the rat brain following hypoxic-ischemic injury

Insulin-like growth factor 1 (IGF-1) is induced after hypoxic-ischemic (HI) brain injury, and therapeutic studies suggest that IGF-1 may restrict delayed neuronal and glial cell loss. We have used a well-characterised rat model of HI injury to extend our understanding of the modes of action of the IGF system after injury. The induction of the IGF system by injury was examined by in situ hybridization, immunohistochemistry, Northern blot analysis, RNase protection assay and reverse transcriptase-polymerase chain reaction (RT-PCR). IGF-1 accumulated in blood vessels of the damaged hemisphere within 5 h after a severe injury. By 3 days, IGF-1 mRNA was expressed by reactive microglia in regions of delayed neuronal death, and immunoreactive IGF-1 was associated with these microglia and reactive astrocytes juxtaposed to surviving neurones surrounding the infarct. Total IGF-1 receptor mRNA was unchanged by the injury. IGFBP-2 mRNA was strongly induced in reactive astrocytes throughout the injured hemisphere, and IGFBP-3 and IGFBP-5 mRNA were moderately induced in reactive microglia and neurones of the injured hippocampus, respectively. IGFBP-6 mRNA was induced in the damaged hemisphere by 3 days and increased protein was seen on the choroid plexus, ependyma and reactive glia. In contrast, insulin II was not induced. These results indicate cell type-specific expression for IGF-1, IGFBP-2,3,5 and 6 after injury. Our findings suggest that the IGF-1 produced by microglia after injury is transferred to perineuronal reactive astrocytes expressing IGFBP-2. Thus, modulation of IGF-1 action by IGFBP-2 might represent a key mechanism that restricts neuronal cell loss following HI brain injury.

Asphyxial brain injury--the role of the IGF system

Transient neural injuries, such as asphyxia, can trigger considerable delayed neuronal death. Inappropriate induction of apoptosis is thought to play an important role in this process. Our studies have shown marked changes in the IGF system in the brain in response to these injuries with an induction of insulin growth factor (IGF)-1 and insulin growth factor binding protein (IGFBP)-2 and IGFBP-3 in glial cells in the region of injury. This suggests that the IGF-1 system may be an endogenous neuroprotective system. Earlier administration of IGF-1 - 2 h after injury reduced the phase of secondary neuronal loss suggesting that IGF-1 may well have therapeutic potential as a neuronal rescue agent. The action of IGF-1 appears to involve binding proteins, transport to the site of injury and the IGF-1 receptor and inhibition of apoptosis, but might also involve generation of GPE which itself appears to be neuroprotective. Together these results indicate considerable potential of these agents to treat stroke, perinatal asphyxia and other forms of acute brain injury.

Displacement of insulin-like growth factors from their binding proteins as a potential treatment for stroke

Insulin-like growth factors I and II (IGF-I and IGF-II) play an important role in normal growth and brain development and protect brain cells from several forms of injury. The effects of IGFs are mediated by type-I and type-II receptors and modulated by potentially six specific binding proteins that form high-affinity complexes with IGFs in blood and cerebrospinal fluid (CSF) and under most circumstances inactivate them. Because brain injury is commonly associated with increases in IGFs and their associated binding proteins, we hypothesized that displacement of this large "pool" of endogenous IGF from the binding proteins would elevate "free" IGF levels to elicit neuroprotective effects comparable to those produced by administration of exogenous IGF. A human IGF-I analog [(Leu24, 59, 60, Ala31)hIGF-I] with high affinity to IGF-binding proteins (Ki = 0.3-3.9 nM) and no biological activity at the IGF receptors (Ki = >10,000 nM) increased the levels of "free, bioavailable" IGF-I in the CSF. Intracerebroventricular administration of this analog up to 1h after an ischemic insult to the rat brain had a potent neuroprotective action comparable to IGF-I. This novel strategy for increasing "free" IGF levels in the brain may be useful for the treatment of stroke and other neurodegenerative diseases.

Insulin-like growth factors-I and -II differentially regulate endogenous acetylcholine release from the rat hippocampal formation

Insulin-like growth factors-I and -II (IGF-I and -II) are structurally related mitogenic polypeptides with potent growth promoting effects. These peptides and their corresponding IGF-I and -II receptors are selectively localized in the brain. To date, most of the effects of IGFs are believed to be mediated by IGF-I receptors whereas the significance of IGF-II receptor in mediating biological responses remains unclear. In the present study, we characterized the distribution of IGF-I and IGF-II receptor sites and investigated the effects of both factors on endogenous acetylcholine (ACh) release in adult rat hippocampus. [125I]IGF-I receptor binding sites are recognized by IGF-I> IGF-II> insulin, whereas [125I]IGF-II binding was competed potently by IGF-II> IGF-I but not by insulin. At the cellular level, IGF-I receptor sites were primarily noted in the molecular layer of the dentate gyrus and the CA2-CA3 subfields of the Ammon's horn whereas IGF-II sites were localized predominantly in the pyramidal cell layer of the CA1-CA3 subfields and in the granular cell layer of the dentate gyrus. IGF-I (10(-14)-10(-8) M) and des(1-3) IGF-I (10(-10)-10(-8) M) were found to inhibit whereas IGF-II (10(-14)-10(-8) M) potentiated K+-evoked ACh release from hippocampal slices. Tetrodotoxin altered the effects of IGF-I but not those of IGF-II suggesting that IGF-I acts indirectly via the release of other modulators whereas IGF-II acts directly on or in close proximity to the cholinergic terminals. The inhibitory effects of IGF-I were also observed in the frontal cortex but not in the striatum. In contrast, the stimulatory effects of IGF-II were evident both in the frontal cortex and striatum. Taken together, these results reveal the differential localization of IGF-I and IGF-II receptor sites in the hippocampal formation and the opposite role for these growth factors in the acute regulation of ACh release likely via two distinct mechanisms. Additionally, these data provide the first evidence for a direct role for IGF-II and its receptors in the regulation of transmitter release in the central nervous system.

Systemic administration of kainic acid induces selective time dependent decrease in [125I]insulin-like growth factor I, [125I]insulin-like growth factor II and [125I]insulin receptor binding sites in adult rat hippocampal formation

Administration of kainic acid evokes acute seizure in hippocampal pathways that results in a complex sequence of functional and structural alterations resembling human temporal lobe epilepsy. The structural alterations induced by kainic acid include selective loss of neurones in CA1-CA3 subfields and the hilar region of the dentate gyrus followed by sprouting and permanent reorganization of the synaptic connections of the mossy fibre pathways. Although the neuronal degeneration and process of reactive synaptogenesis have been extensively studied, at present little is known about means to prevent pathological conditions leading to kainate-induced cell death. In the present study, to address the role of insulin-like growth factors I and II, and insulin in neuronal survival as well as synaptic reorganization following kainate-induced seizure, the time course alterations of the corresponding receptors were evaluated. Additionally, using histological preparations, the temporal profile of neuronal degeneration and hypertrophy of resident astroglial cells were also studied. [125I]Insulin-like growth factor I binding was found to be decreased transiently in almost all regions of the hippocampal formation at 12 h following treatment with kainic acid. The dentate hilar region however, exhibited protracted decreases in [125I]insulin-like growth factor I receptor sites throughout (i.e. 30 days) the study. [125I]Insulin-like growth factor II receptor binding sites in the hippocampal formation were found to be differentially altered following systemic administration of kainic acid. A significant decrease in [125I]insulin-like growth factor II receptor sites was observed in CA1 subfield and the pyramidal cell layer of the Ammon's horn at all time points studied whereas the hilar region and the stratum radiatum did not exhibit alteration at any time. A kainate-induced decrease in [125I]insulin receptor binding was noted at all time points in the molecular layer of the dentate gyrus whereas binding in CA1-CA3 subfields and discrete layers of the Ammon's horn was found to be affected only after 12 h of treatment. These results, when analysed with reference to the observed histological changes and established neurotrophic/protective roles of insulin-like growth factors and insulin, suggest possible involvement of these growth factors in the cascade of neurotrophic events that is associated with the reorganization of the hippocampal formation observed following kainate-induced seizures.

Insulin-like growth factor I protects and rescues hippocampal neurons against beta-amyloid- and human amylin-induced toxicity

Insulin-like growth factors (IGF-I and IGF-II) are well known trophic factors and their specific receptors are uniquely distributed throughout the brain, being especially concentrated in the hippocampal formation. IGFs possess neurotrophic activities in the hippocampus, an area severely affected in Alzheimer disease. These data, together with the evidence that beta-amyloid (Abeta)-derived peptides likely play an important role in the neurodegenerative process observed in Alzheimer disease, led us to investigate if IGFs could be neuroprotective to hippocampal neurons against toxicity induced by amyloidogenic derivatives. Exposure of rat primary hippocampal neurons to different concentrations of Abeta25-35, Abeta1-40, Abeta1-42, and human amylin produced marked toxicity, while similar concentrations of two control Abeta peptides-reverse (Abeta40-1) and scrambled sequence (Abeta25-35)-and rat amylin failed to exhibit any significant effect on neuronal survival. IGF-I (10-100 nM) significantly protected hippocampal neurons against neurotoxicity induced by Abeta derivatives and human amylin. The homolog IGF-II was also effective although less potent than IGF-I suggesting the involvement of a typical IGF-I receptor in the observed neuroprotective effect. Most interestingly, IGF-I (10-100 nM) was even able to rescue neurons pre-exposed (up to 4 days) to amyloidogenic peptides. Other neurotrophic factors are reported to lack such rescuing abilities. These results suggest that IGF-I may have unique properties as a potent neuroprotective and neurorescuing agent against amyloid-related neurotoxicity.