Developmental expression of insulin-like growth factor-II receptor immunoreactivity in the rat central nervous system

Translational studies of intravenous and intracerebroventricular routes of administration for CNS cellular biodistribution for BMN 250, an enzyme replacement therapy for the treatment of Sanfilippo type B

BMN 250 is being developed as enzyme replacement therapy for Sanfilippo type B, a primarily neurological rare disease, in which patients have deficient lysosomal alpha-N-acetylglucosaminidase (NAGLU) enzyme activity. BMN 250 is taken up in target cells by the cation-independent mannose 6-phosphate receptor (CI-MPR, insulin-like growth factor 2 receptor), which then facilitates transit to the lysosome. BMN 250 is dosed directly into the central nervous system via the intracerebroventricular (ICV) route, and the objective of this work was to compare systemic intravenous (IV) and ICV delivery of BMN 250 to confirm the value of ICV dosing. We first assess the ability of enzyme to cross a potentially compromised blood-brain barrier in the Naglu-/- mouse model and then assess the potential for CI-MPR to be employed for receptor-mediated transport across the blood-brain barrier. In wild-type and Naglu-/- mice, CI-MPR expression in brain vasculature is high during the neonatal period but virtually absent by adolescence. In contrast, CI-MPR remains expressed through adolescence in non-affected non-human primate and human brain vasculature. Combined results from IV administration of BMN 250 in Naglu-/- mice and IV and ICV administration in healthy juvenile non-human primates suggest a limitation to therapeutic benefit from IV administration because enzyme distribution is restricted to brain vascular endothelial cells: enzyme does not reach target neuronal cells following IV administration, and pharmacological response following IV administration is likely restricted to clearance of substrate in endothelial cells. In contrast, ICV administration enables central nervous system enzyme replacement with biodistribution to target cells.

Insulin growth factor 2 (IGF2) as an emergent target in psychiatric and neurological disorders. Review

Insulin-like growth factor 2 (IGF2) is abundantly expressed in the central nervous system (CNS). Recent evidence highlights the role of IGF2 in the brain, sustained by data showing its alterations as a common feature across a variety of psychiatric and neurological disorders. Previous studies emphasize the potential role of IGF2 in psychiatric and neurological conditions as well as in memory impairments, targeting IGF2 as a pro-cognitive agent. New research on animal models supports that upcoming investigations should explore IGF2's strong promising role as a memory enhancer. The lack of effective treatments for cognitive disturbances as a result of psychiatric diseases lead to further explore IGF2 as a promising target for the development of new pharmacology for the treatment of memory dysfunctions. In this review, we aim at gathering all recent relevant studies and findings on the role of IGF2 in the development of psychiatric diseases that occur with cognitive problems.

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.

Generating new neurons to circumvent your fears: the role of IGF signaling

Extinction of fear memory is a particular form of cognitive function that is of special interest because of its involvement in the treatment of anxiety and mood disorders. Based on recent literature and our previous findings (EMBO J 30(19):4071-4083, 2011), we propose a new hypothesis that implies a tight relationship among IGF signaling, adult hippocampal neurogenesis and fear extinction. Our proposed model suggests that fear extinction-induced IGF2/IGFBP7 signaling promotes the survival of neurons at 2-4 weeks old that would participate in the discrimination between the original fear memory trace and the new safety memory generated during fear extinction. This is also called "pattern separation", or the ability to distinguish similar but different cues (e.g., context). To understand the molecular mechanisms underlying fear extinction is therefore of great clinical importance.

The many faces of insulin-like peptide signalling in the brain

Central and peripheral insulin-like peptides (ILPs), which include insulin, insulin-like growth factor 1 (IGF1) and IGF2, exert many effects in the brain. Through their actions on brain growth and differentiation, ILPs contribute to building circuitries that subserve metabolic and behavioural adaptation to internal and external cues of energy availability. In the adult brain each ILP has distinct effects, but together their actions ultimately regulate energy homeostasis - they affect nutrient sensing and regulate neuronal plasticity to modulate adaptive behaviours involved in food seeking, including high-level cognitive operations such as spatial memory. In essence, the multifaceted activity of ILPs in the brain may be viewed as a system organization involved in the control of energy allocation.

The cerebrospinal fluid: regulator of neurogenesis, behavior, and beyond

The cerebrospinal fluid (CSF) has attracted renewed interest as an active signaling milieu that regulates brain development, homeostasis, and disease. Advances in proteomics research have enabled an improved characterization of the CSF from development through adulthood, and key neurogenic signaling pathways that are transmitted via the CSF are now being elucidated. Due to its immediate contact with neural stem cells in the developing and adult brain, the CSF's ability to swiftly distribute signals across vast distances in the central nervous system is opening avenues to novel and exciting therapeutic approaches. In this review, we will discuss the development of the choroid plexus-CSF system, and review the current literature on how the CSF actively regulates mammalian brain development, behavior, and responses to traumatic brain injury.

The distribution of mannose-6-phosphate receptors changes from newborns to adults in rat liver

The co-existence of two types of mannose-6-phosphate receptors (CD-MPR and CI-MPR) in most cell types is still not well explained. Some evidence suggests that the CI-MPR could be actively involved in the regulation of growth factors in the early stages of mammalian organ development. In this study, it was demonstrated that both receptors are distributed in a non-overlapping fashion in rat liver, and that the distribution of CI-MPR changes over a percoll gradient between newborn and adult animals. By using marker proteins it was observed that in newborns the CI-MPR is located both in intracellular fractions and in fractions that coincide with a plasma membrane marker, whereas in adults it is only detected in intracellular fractions. It was also noted that N-acetyl-β-D-glucosaminidase distribution is closer to CI-MPR than to CD-MPR and that acid phosphatase did not match with any receptor. This evidence may also suggest that both receptors have different functions, mainly at early stages in the development of organs.

Proinsulin/insulin is synthesized locally and prevents caspase- and cathepsin-mediated cell death in the embryonic mouse retina

Programmed cell death is an essential, highly regulated process in neural development. Although the role of insulin-like growth factor I in supporting the survival of neural cells has been well characterized, studies on proinsulin/insulin are scarce. Here, we characterize proinsulin/insulin effects on cell death in embryonic day 15.5 mouse retina. Both proinsulin mRNA and proinsulin/insulin immunoreactivity were found in the developing retina. Organotypic embryonic day 15.5 retinas cultured under growth factor deprivation showed an increase in cell death that was reversed by proinsulin, insulin and insulin-like growth factor I, with similar median effective concentration values via phosphatidylinositol-3-kinase activation. Although insulin and insulin-like growth factor I provoked a sustained Akt phosphorylation, proinsulin-induced phosphorylation of Akt was not found. Analysis of the growth factor deprivation-induced cell death mechanisms, using caspase and cathepsin inhibitors, demonstrated that both protease families were required for the effective execution of cell death. The insulin survival effect, which decreased the extent and distribution of cell death to levels similar to those found in vivo, was not enhanced by simultaneous treatment with caspase and cathepsin inhibitors, suggesting that insulin interferes with these protease pathways in the embryonic mouse retina. The mechanisms characterized in this study provide new details on early neural cell death and its genuine regulation by insulin/proinsulin.

Changes in phosphomannosyl ligands correlate with cation-dependent mannose-6-phosphate receptors in rat liver during perinatal development

The co-existence of two mannose-6-phosphate receptors (CD-MPR and CI-MPR) in most cell types is still a dilemma to be resolved. In this study, some parameters were measured to explore lysosomal apparatus evolution in rat liver during perinatal development, and establish a possible involvement of CD- and/or CI-MPR in lysosome maturation. Activity of four acid hydrolases was measured in the whole organ at different ages and it was found that N-acetyl-beta-D-glucosaminidase (NAG), beta-galactosidase, and beta-glucuronidase change during development, reaching a peak at the 10th day after birth. These results correlated with the expression and binding properties of CD-MPR previously reported. We also used a method that recognizes phosphomannosylated ligands by using purified biotinylated CI-MPR as a probe, and found that the highest concentrations of ligands also appear around the 10th day. Binding assays were also carried out, incubating endogenous NAG from 10-day-old and adult rats with membranes from their respective ages, and the results indicated that cation-dependent mannose-6-phosphate receptor (CD-MPR) has more impact on trafficking of the enzyme at the 10th day after birth. We concluded that lysosome maturation in the rat liver occurs around the 10th day after birth, and that the CD-MPR may participate in that event.

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.

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.

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).

Insulin-like growth factor-II/mannose-6-phosphate receptor: widespread distribution in neurons of the central nervous system including those expressing cholinergic phenotype

The insulin-like growth factor-II/mannose-6-phosphate (IGF-II/M6P) receptor is single transmembrane glycoprotein that plays a critical role in the trafficking of lysosomal enzymes and the internalization of circulating IGF-II. At present, there is little information regarding the cellular distribution of the IGF-II/M6P receptor within the adult rat brain. With the use of immunoblotting and immunocytochemical methods, we found that the IGF-II/M6P receptor is widely but selectively expressed in all major brain areas, including the olfactory bulb, striatum, cortex, hippocampus, thalamus, hypothalamus, cerebellum, brainstem, and spinal cord. Intense IGF-II/M6P receptor immunoreactivity was apparent on neuronal cell bodies within the striatum, deeper layers (layers IV and V) of the cortex, pyramidal and granule cell layers of the hippocampal formation, selected thalamic nuclei, Purkinje cells of the cerebellum, pontine nucleus and motoneurons of the brainstem as well as in the spinal cord. Moderate neuronal labeling was evident in the olfactory bulb, basal forebrain areas, hypothalamus, superior colliculus, midbrain areas, granule cells of the cerebellum and in the intermediate regions of the spinal gray matter. We also observed dense neuropil labeling in many regions, suggesting that this receptor is localized in dendrites and/or axon terminals. Double-labeling studies further indicated that a subset of IGF-II/M6P receptor colocalizes with cholinergic cell bodies and fibers in the septum, striatum, diagonal band complex, nucleus basalis, cortex, hippocampus, and motoneurons of the brainstem and spinal cord. The observed widespread distribution and colocalization of IGF-II/M6P receptor in the adult rat brain provide an anatomic basis to suggest a multifunctional role for the receptor in a wide-spectrum of central nervous system neurons, including those expressing a cholinergic phenotype.

Insulin-like growth factor-II/Mannose-6-phosphate receptor in the spinal cord and dorsal root ganglia of the adult rat

The insulin-like growth factor-II/mannose-6-phosphate (IGF-II/M6P) receptor is a multifunctional transmembrane glycoprotein, which interacts with a number of molecules, including IGF-II and M6P-containing lysosomal enzymes. The receptor is widely distributed throughout the brain and is known to be involved in lysosomal enzyme trafficking, cell growth, internalization and degradation of IGF-II. In the present study, using autoradiographic, Western blotting and immunocytochemical methods, we provide the first report that IGF-II/M6P receptors are discretely distributed at all major segmental levels of the spinal cord and dorsal root ganglia of the adult rat. In the spinal cord, a high density of [(125)I]IGF-II binding sites was evident in the ventral horn (lamina IX) and in areas around the central canal (lamina X), whereas intermediate grey matter and dorsal horn were associated with moderate receptor levels. The dorsal root ganglia exhibited rather high density of [(125)I]IGF-II binding sites. Interestingly, meninges present around the spinal cord displayed highest density of [(125)I]IGF-II binding compared to any given region of the spinal grey matter or the dorsal root ganglia. Western blot results indicated the presence of the IGF-II/M6P receptor at all major levels of spinal cord and dorsal root ganglia, with little segmental variation. At the cellular level, spinal motorneurons demonstrated the most intense IGF-II/M6P receptor immunoreactivity, followed by interneurons in the intermediate region and deeper dorsal horn. Some scattered IGF-II/M6P immunoreactive fibers were found in the superficial laminae of the dorsal horn and dorsolateral funiculus. The meninges of the spinal cord also seemed to express IGF-II receptor immunoreactivity. In the dorsal root ganglia, receptor immunoreactivity was evident primarily in a subset of neurons of all diameters. These results, taken together, provide anatomical evidence of a role for the IGF-II/M6P receptor in general cellular functions such as transport of lysosomal enzymes and/or internalization followed by clearance of IGF-II in the spinal cord and dorsal root ganglia.

Different distribution patterns of the two mannose 6-phosphate receptors in rat liver

Two mannose 6-phosphate receptors, cation-dependent and -independent receptors (CDMPR and CIMPR), play an important role in the intracellular transport of lysosomal enzymes. To investigate functional differences between the two in vivo, their distribution was examined in the rat liver using immunohistochemical techniques. Positive signals corresponding to CIMPR were detected intensely in hepatocytes and weakly in sinusoidal Kupffer cells and interstitial cells in Glisson's capsule. In the liver acinus, hepatocytes in the perivenous region showed a more intense immunoreactivity than those in the periportal region. On the other hand, positive staining of CDMPR was detected at a high level in Kupffer cells, epithelial cells of interlobular bile ducts, and fibroblast-like cells, but the corresponding signal was rather weak in hepatocytes. In situ hybridization analysis also revealed a high level of expression of CIMPR mRNAs in hepatocytes and of CDMPR mRNA in Kupffer cells. By double immunostaining, OX6-positive antigen-presenting cells in Glisson's capsule were co-labeled with the CDMPR signal but were only faintly stained with anti-CIMPR. These different distribution patterns of the two MPRs suggest distinct functional properties of each receptor in liver tissue.

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.

Beta-adrenergic receptors mediate a stress-induced decrease in IGF-II mRNA in the rat cerebellum

1. Exposure to a combined forced swimming-confinement stress resulted in a decrease in insulin-like growth factor II (IGF-II) mRNA levels in the whole brain (without the cerebellum) and in the isolated brain areas of the cerebral cortex, the hippocampus, and the cerebellum. 2. In an effort to elucidate the neurotransmitter systems involved in this stress-induced decrease, animals were injected prior to exposure to the stress, with either propranolol, diazepam, or MK-801. 3. Administration of diazepam or MK-801 did not affect the stress-induced decrease in IGF-II mRNA in any of the three brain areas examined. 4. Administration of propranolol prior to the exposure to the stress inhibited the stress-induced decrease in IGF-II mRNA in the cerebellum. Propranolol had no such effect in the cerebral cortex or the hippocampus. 5. Our results suggest that in the cerebellum, the stress-induced decrease in IGF-II mRNA is mediated by beta 2-adrenergic receptors.

Insulin-like growth factor-1 is a radial cell-associated neurotrophin that promotes neuronal recruitment from the adult songbird edpendyma/subependyma

In the adult songbird forebrain, neurons continue to be produced from precursor cells in the forebrain ependymal/subependymal zone (SZ), from which they migrate upon radial guide fibers. The new neurons and their radial cell partners may coderive from a common SZ progenitor, which may be the radial cell itself. On this basis, we asked whether radial cells might provide trophic support for the migration or survival of newly generated neurons. We focused upon the insulin-like growth factors (IGFs) IGF-1 and IGF-2, which have previously been shown to support the survival and differentiation of neural progenitor cells. We found that IGF-1 immunoreactivity was expressed heavily by adult zebra finch radial cells and their fibers, with little expression otherwise. IGF-2, in contrast, was expressed by parenchymal astrocytes and exhibited little radial cell expression. Despite their distinct distributions, IGF-1 and IGF-2 exerted similar trophic effects on finch SZ cells in vitro; both greatly increased the number of neurons migrating from explants of the adult finch SZ, relative to explants raised in low-insulin, IGF-1-deficient media. However, neither factor extended neuronal survival. These results suggest that in neurogenic regions of the adult avian forebrain, IGF-1 acts as a radial cell-associated neuronal differentiation and/or departure factor, which may serve to regulate neuronal recruitment into the adult brain.

Decreased skin sensory innervation in transgenic mice overexpressing insulin-like growth factor-II

Cutaneous sensory innervation was studied in transgenic mice overexpressing insulin-like growth factor II using a keratin promoter. The skin area of these animals is enlarged providing increased target for sensory neurons. L4 dorsal root ganglion cell counts revealed that the total number of sensory neurons was the same in transgenics as control animals. Levels of nerve growth factor per unit weight of skin were also unchanged. The cutaneous nerves of the hindlimb were immunostained with the pan-neuronal marker PGP 9.5 in transgenic and control mice at postnatal day 0 and 21. The innervation in transgenic mice was markedly reduced, particularly in superficial dermis and epidermis and in some areas innervation was completely absent. The effect was greatest in distal skin regions and increased with age. Since insulin-like growth factor II has been reported to be a sensory neurotrophic factor, its effect on neurite outgrowth was tested on embryonic day 14 and 18 mouse lumbar dorsal root ganglion explants in culture. Under these conditions insulin-like growth factor II (5-100 ng/ml) did not have strong growth promoting activity and at embryonic day 18, in the presence of 5-10 ng/ml nerve growth factor, neurite outgrowth was suppressed by insulin-like growth factor II. The results show that increased skin target and availability of nerve growth factor per se do not alter the number of innervating sensory neurons. However, reduced sensory terminal arborization and skin hypoinnervation does occur in the presence of excess insulin-like growth factor-II. It is possible that insulin-like growth factor-II inhibits terminal axon growth directly via receptors on sensory neurons or peripheral glia.

The early intracellular signaling pathway for the insulin/insulin-like growth factor receptor family in the mammalian central nervous system

Several studies support the idea that the polypeptides belonging to the family of insulin and insulin-like growth factors (IGFs) play an important role in brain development and continue to be produced in discrete areas of the adult brain. In numerous neuronal populations within the olfactory bulb, the cerebral and cerebellar cortex, the hippocampus, some diencephalic and brainstem nuclei, the spinal cord and the retina, specific insulin and IGF receptors, as well as crucial components of the intracellular receptor signaling pathway have been demonstrated. Thus, mature neurons are endowed with the cellular machinery to respond to insulin and IGF stimulation. Studies in vitro and in vivo, using normal and transgenic animals, have led to the hypothesis that, in the adult brain, IGF-I not only acts as a trophic factor, but also as a neuromodulator of some higher brain functions, such as long-term potentiation and depression. Furthermore, a trophic effect on certain neuronal populations becomes clearly evident in the ischemic brain or neurodegenerative disorders. Thus, the analysis of the early intracellular signaling pathway for the insulin/IGF receptor family in the brain is providing us with new intriguing findings on the way the mammalian brain is sculpted and operates.

Insulin-like growth factors and IGF binding proteins in cyst fluid from patients with craniopharyngioma prior to intracavitary irradiation with Yttrium and thereafter

Aim-To examine a series of cyst fluid samples from patients with craniopharyngioma at various stages of treatment in order to evaluate the use of insulin-like growth factors (IGFs) and IGF binding proteins as tumour markers or indicators of successful treatment, or both.Methods-Cyst fluid samples were obtained by stereotactic puncture prior to the intracavitary application of (90)Yttrium and at subsequent occasions. Analysis was performed by gel chromatography, radio-immunoassays, binding studies, and sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) with subsequent western blotting.Results-IGF-I, -II and IGF binding protein-1 concentrations were measured in three craniopharyngioma cyst fluid samples. Immunoreactive IGF-I and IGF binding protein-1 concentrations in these three samples were between 6 and 29 ng/ml, and 17 and 48 ng/ml, respectively. In contrast, the IGF-II concentrations measured in 19 cyst fluid samples from seven patients with craniopharyngioma at various stages of treatment were much higher at 25-671 ng/ml. SDS-PAGE and subsequent western blotting using [(125)I]IGF-II as the ligand gave bands with estimated molecular weights of 330, 220, 135, 96, 46, 43, 34, 29, and 13.5 kDa in one adult, and identical bands at 220, 41.5, 37.5, 32, and 19 kDa in three cyst fluid samples from three children with craniopharyngioma.Conclusions-These results suggest that IGFs and IGF binding proteins are secreted by craniopharyngiomas and that they may alter the growth characteristics of these tumours. Furthermore, the distinct pattern of IGF binding protein sizes might be used as a tool for the differential diagnosis of tumours of the central nervous system.

Increase in insulin-like growth factor II receptor within ischemic neurons following focal cerebral infarction

The mechanisms underlying the response of the brain to ischemia are not fully understood. Biochemical and morphological changes following neocortical infarction can be investigated in rats using a model of focal cerebral ischemia induced by unilateral occlusion of the middle cerebral artery (MCA). Evaluation of ischemic damage often employs conventional histologic stains. Immunocytochemistry can be used as a valuable tool in this model to define changes in specific proteins of interest. In this study, an antiserum raised against insulin-like growth factor II (IGF-II) receptor was used to evaluate changes of IGF-II receptor immunoreactivity in the cerebral cortex of rats 4 and 7 days following permanent MCA occlusion. IGF-II receptor immunoreactivity was found to be associated with neocortical pyramidal neurons within the core of the ischemic infarct itself. The staining intensity was markedly elevated above that observed in nonischemic neurons. Immunopositive neurons exhibited a punctate staining pattern. These neurons appeared to correspond to argentophilic neurons, as defined by modified Bielschowsky silver staining. Evaluation of other neuronal markers revealed the absence of immunoreactivity for neuron-specific enolase and for tyrosine hydroxylase within the ischemic area. These observations show an increase in a specific growth factor receptor within neurons in the ischemic core of a focal infarct several days following permanent focal infarction, a time when neurons are presumed to be dead. The significance and the potential role of IGF-II receptor in lesion-induced plasticity are discussed.

Regional distribution of messenger RNA encoding the insulin-like growth factor type 2 receptor in the rat lower brainstem

Distribution of messenger RNA (mRNA) encoding the insulin-like growth factor (IGF) type 2 receptor (IGF2R) is investigated in the rat lower brainstem by in situ hybridization histochemistry. Cells with IGF2R mRNA are distributed widely in a region-specific manner. It is expressed in: (1) motor nuclei such as the oculomotor nucleus, trochlear nucleus, motor trigeminal nucleus, abducens nucleus, facial nucleus, ambiguus nucleus, dorsal motor nucleus of vagus and hypoglossal nucleus; (2) several sensory-related nuclei like the mesencephalic trigeminal nucleus, ventral nucleus of the lateral lemniscus, lateral and spinal vestibular nuclei, ventral and dorsal cochlear nuclei and nucleus of the trapezoid body; and (3) other regions such as the red nucleus, dorsal raphe nucleus, pontine nuclei, three cerebellar nuclei (medial, interposed and lateral), Purkinje cells, cells in the granular layer of the cerebellum, locus coeruleus, several areas of the reticular nucleus and area postrema.

The developing CNS: a scenario for the action of proinsulin, insulin and insulin-like growth factors

The multifunctional cytokines of the family of insulin and insulin-like growth factors (IGFs) have not yet gained general recognition as essential cell signals for the development of the vertebrate nervous system. This is, in part, a consequence of previous constraints in our thinking, focused for many years on the endocrine roles of these factors in late mammalian development and postnatal stages. The cellular distribution of the components of the insulin and IGFs signalling system in the developing mammalian and avian CNS is remarkably conserved. While receptors are widespread, the much less abundant factors and modulatory proteins are highly regulated in time and space. Progression of neural development through the steps of cell proliferation, differentiation, maturation and survival is stimulated, at least in culture, by proinsulin and insulin and the IGFs. Thus, these factors might be important autocrine and paracrine signals during development of the CNS.

Brain growth retardation due to the expression of human insulin like growth factor binding protein-1 in transgenic mice: an in vivo model for the analysis of igf function in the brain

Three lines of transgenic (Tg) mice carrying a fusion gene linking the mouse metallothionein-I promoter to a cDNA encoding human insulin-like growth factor binding protein-1 (hIGFBP-1) were found to express the transgene in brain. As judged by comparing Tg brain weights to those of non-transgenic littermates, adult hemizygotic Tg mice of each line exhibited brain growth retardation (16.2%, 14.4% and 8.1% reductions in weight, respectively in each line). In two lines, total brain DNA and protein content were decreased. Further analysis indicated that the brain growth retardation was manifested in the second week of postnatal life. Given that the insulin-like growth factors (IGFs) stimulate cell proliferation and/or survival in neural cultures and that hIGFBP-1, when present in a molar excess, inhibits IGF interactions with their cell surface receptors, the brain growth retardation in hIGFBP-1 Tg mice likely results from hIGFBP-1 inhibition of IGF-stimulated growth-promoting actions. These hIGFBP-1 Tg mice should prove useful in defining IGF actions during postnatal brain maturation.

Role of insulin-like growth factors in peripheral nerve regeneration

Prolonged denervation results in atrophy of target organs and increased risk of permanent paralysis. A better understanding of the mechanism responsible for nerve regeneration may one day lead to improved rates of nerve regeneration and diminished risk of loss of function. Neurobiologists have known for decades that soluble neurotrophic activity is present in nerves and nerve targets. Until recently, the soluble molecules that regulate the rate of nerve regeneration have eluded identification. Insulin-like growth factor (IGF) gene expression is correlated with synapse formation during development and regeneration. IGFs are now identified as the first soluble nerve- and muscle-derived neurotrophic factors found to regulate the rate of peripheral nerve regeneration. The roles of IGFs and other neurotrophic factors in peripheral nerve regeneration, motor nerve terminal sprouting and synapse formation are reviewed.

Bioactive peptides in anterior pituitary cells

The anterior pituitary (AP) has been shown to contain a wide variety of bioactive peptides: brain-gut peptides, growth factors, hypothalamic releasing factors, posterior lobe peptides, opioids, and various other peptides. The localization of most of these peptides was first established by immunocytochemical methods and some of the peptides were localized in identified cell types. Although intracellular localization of a peptide may be the consequence of internalization from the plasma compartment, there is evidence for local synthesis of most of these peptides in the AP based on the identification of their messenger-RNA (mRNA). In several cases the release of the peptide from the AP cell has been shown and regulation of synthesis, storage and release have also been described. Because the amount of most of the AP peptides is very low (except for POMC peptides and galanin), endocrine functions are not expected. There is more evidence for paracrine, autocrine, or intracrine roles in growth, differentiation, and regeneration, or in the control of hormone release. To demonstrate such functions, in vitro AP experiments have been designed to avoid the interference of hypothalamic or peripheral hormones. The strategy is first to show a direct effect of the peptide after adding it to the in vitro system and, secondly, to explore if the endogenous AP peptide has a similar action by using blockers of peptide receptors or antisera immunoneutralizing the peptide.

Transient expression of calbindin-D28k immunoreactivity in layer V pyramidal neurons during postnatal development of kitten cortical areas

Calbindin-D28k is a 28 kDa calcium binding protein that has been shown to colocalize with a specific subpopulation of gamma-aminobutyric acid inhibitory interneurons in mammalian neocortex. We have examined the ontogeny of calbindin in neonatal kitten cortex in areas 17,18,19,7, medial and lateral suprasylvian visual areas, splenial visual area and cingulate cortex from the day of birth (P0) through maturation of the brain (P101). Transient staining of immature layer V pyramidal cells was seen in kittens six weeks old and younger. This transient staining of pyramidal cells was most intense and the stained neurons were most numerous in cingulate cortex. Apical dendrites of pyramidal cells in cingulate cortex were prominently stained and could be followed to layer I, where they were seen to branch extensively. There were very few calbindin immunoreactive pyramidal cells in primary cortical areas postnatally. Transient staining in extrastriate visual cortical areas disappeared first from the lateral suprasylvian areas, and persisted longest in area 7. Pyramidal neurons in the cingulate gyrus expressed calbindin longest, but calbindin expression by pyramidal neurons ceased by the sixth postnatal week in all areas of the brain.

Quantitative autoradiographic localization of [125I]insulin-like growth factor I, [125I]insulin-like growth factor II, and [125I]insulin receptor binding sites in developing and adult rat brain

Insulin-like growth factors I and II (IGF I and IGF II) and insulin itself, which are structurally related polypeptides, play an important role in regulating brain growth and development as well as in the maintenance of its normal functions during adulthood. In order to provide a substrate for the better understanding of the roles of these growth factors, we have investigated the anatomical distribution as well as the variation in the density of [125I]IGF I, [125I]IGF II, and [125I]insulin receptor binding sites in developing and adult rat brain by in vitro quantitative autoradiography. The distributional profile of [125I]IGF I, [125I]IGF II, and [125I]insulin receptor binding sites showed a widespread but selective regional localization throughout the brain at all stages of development. The neuroanatomic regions which exhibited relatively high density of binding sites with each of these radioligands include the olfactory bulb, cortex, hippocampus, choroid plexus, and cerebellum. However, in any given region, receptor binding sites for IGF I, IGF II, or insulin are concentrated in anatomically distinct areas. In the cerebellum, for example, [125I]IGF II receptor binding sites are concentrated in the granular cell layer, [125I]insulin binding sites are localized primarily in the molecular layer, whereas [125I]IGF I receptor binding sites are noted in relatively high amounts in granular as well as molecular cell layers. The apparent density of sites recognized by each radioligand also undergoes remarkable variation in most brain nuclei, being relatively high either during late embryonic (i.e., IGF I and IGF II) or early postnatal (i.e., insulin) stages and then declining gradually to adult levels around the third week of postnatal development. These results, taken together, suggest that each receptor-ligand system is regulated differently during development and thus may have different roles in the process of cellular growth, differentiation, and maintenance of the nervous system. Furthermore, the localization of [125I]IGF I, [125I]IGF II, and [125I]insulin receptor binding sites over a wide variety of physiologically distinct brain regions suggests possible involvement of these growth factors in a variety of functions associated with specific neuronal pathways.

Entorhinal cortex lesion induces differential responses in [125I]insulin-like growth factor I, [125I]insulin-like growth factor II and [125I]insulin receptor binding sites in the rat hippocampal formation

The hippocampus can be induced by deafferentation to selectively reorganize its neuronal input. Entorhinal cortex lesion, which causes degeneration of the perforant pathway, evokes sprouting of septal afferents as well as glutamatergic commissural/associational fibers in the deafferentated zone of the molecular layer of the dentate gyrus. Although the process of reactive synaptogenesis that follows deafferentation has been extensively studied, at present little is known about its molecular basis and the mechanism of initiation. In this study, following unilateral lesion of the entorhinal cortex, the time-course of possible alterations of insulin-like growth factors I and II, and insulin binding sites were evaluated by in vitro quantitative receptor autoradiography. [125I]Insulin-like growth factor I receptor binding sites did not exhibit any significant variation between the contralateral and ipsilateral hippocampal formation at any time periods following lesion except in the molecular layer of the dentate gyrus (P < 0.05) at day 8. However, when compared with the unlesioned animals, a differential time-dependent response of [125I]insulin-like growth factor I binding sites was noted in selective layers of the hippocampus. [125I]Insulin-like growth factor II receptor binding sites showed a significant decrease (P < 0.05) in the ipsilateral granular cell layer of the dentate gyrus only at day 14 post lesion. Interestingly, compared to controls, a dramatic bilateral increase (P < 0.05) in [125I]insulin-like growth factor II binding was evident between days 1 and 8 in most layers of the hippocampal formation. A lesion-induced bilateral increase (P < 0.05) in [125I]insulin binding sites was evident in all layers of the hippocampus between two to eight days and at 30 days post lesion. In selective layers, however, a significant increase (P < 0.05) in [125I]insulin binding sites was also observed at days 1 and 14 after lesion. These results, which are compatible with the process of degeneration and/or sprouting of the terminal fibers, suggest possible involvement of insulin-like growth factors and insulin in the sequence of molecular events that occur to facilitate neuronal repair and to promote neuronal survival following entorhinal cortex lesion.

Aging-related changes in IGF-II and c-fos gene expression in the rat brain

The protein products of growth factor genes such as IGF-II and cellular oncogenes such as c-fos are believed to be necessary for the support of normal neuronal function. Steady-state levels of c-fos and IGF-II mRNA were determined in the brain of young and old rats, using Northern analysis. Both RNAs were found to be decreased in the brain of aged rats. Age-related decrease was detected in the hippocampus, hypothalamus, striatum, cerebral cortex and cerebellum, for IGF-II mRNA, and in the cerebral cortex and cerebellum for c-fos mRNA. Furthermore, changes in the degree and pattern of DNA methylation were noted at both gene loci, in the aged rat brain. Our results could reflect changes at the genomic level possibly related to the process of aging and the accompanying decline in brain function.

Localization of Insulin-Like Growth Factor-II Receptors in Rat Brain by in vitro Autoradiography and Immunohistochemistry

Insulin-like growth factor-ll (IGF-II) and its receptor, which is homologous with the mannose-6-phosphate (M6P) receptor, are found in high levels in adult rat and human brain, though their role remains unclear. In order to point to possible regional functions, we have mapped and quantified IGF-II/M6P receptors in sagittal sections of adult rat brain by in vitro autoradiography/computerized densitometry and immunohistochemistry. While in vitro autoradiography allowed mapping and quantitation, immunohistochemistry both confirmed mapping and allowed more detailed determination of cellular distribution of receptors. The two methods were generally in agreement with few areas of mismatching. By in vitro autoradiography, a discrete and characteristic distribution of IGF-II receptor binding was demonstrated, with specific binding representing 85% of total binding. Displacement and specificity competition curves in arcuate nucleus and choroid plexus were typical for authentic IGF-II receptors with half maximal displacement at 1 nM cold IGF-II. IGF-II receptor density, estimated by in vitro autoradiography, was very high in circumventricular organs, especially the median eminence, which had the highest binding in the brain. In the remainder of the brain there was concordance between the distribution of receptors identified by the two techniques, with greatest densities in the olfactory bulb and olfactory pathways, the hippocampus and discrete regions of the cerebral cortex, cerebellum, hypothalamus, thalamus and brainstem. There were however, some notable mismatches. Autoradiographic binding was high to very high in the median eminence, arcuate nucleus, suprachiasmatic nucleus and anterodorsal thalamic nucleus, whereas these areas were only poorly immunostained. Conversely, the septum showed moderate autoradiographic binding, but very prominent immunostaining of neurons in its dorsolat-eral aspect. Using the immunohistochemical technique IGF-II receptors were localized to specific neuronal groups such as the mitral cells of the olfactory bulb, Purkinje cells of the cerebellum and neurons in the red nucleus. Fibre pathways were not labelled by either technique. We conclude that IGF-II/M6P receptors are widespread throughout rat brain, specifically in neurons and blood vessels, with a similar, but distinct distribution to IGF-I and insulin receptors. Many of these regions have in common high rates of metabolic and synthetic activity, which may be mediated by IGF-II/M6P and their receptors.

Insulin-like growth factors (IGFs): implications for aging

The insulin-like growth factors (IGF)-I and IGF-II are peptides with structural homology to insulin and potent mitogenic and anabolic actions in vitro and in vivo. IGF-I levels are growth hormone (GH)-dependent and vary strikingly with age. IGF-I levels are typically low in infancy and childhood, increase dramatically during puberty, and then gradually decline with advancing age. Whether age-associated changes in GH production or sex steroid secretion, or other unknown factors, cause diminished IGF production in the elderly remains to be determined. In the brain, IGF-II appears to be the most prevalent IGF, but a truncated form of IGF-I also has been recognized. IGF actions are mediated by binding to a family of receptors, which includes the insulin receptor, the structurally homologous type I IGF receptor, and the IGF-II/M-6P receptor, all of which are found in the central nervous system. Additionally, the IGFs bind with high affinity to a family of IGF-binding proteins (IGFBPs). Of the six known IGFBPs, IGFBP-2 appears to be the major one in the mammalian brain and is a major component of CSF. Immunoreactive IGFBP-2 has been identified in astrocytes, and its mRNA has been identified in fetal and adult brain and choroid plexus. The IGFBPs transport the IGFs in serum and other body fluids and appear to regulate IGF access to receptors. In vivo regulation of IGFBPs includes tissue-specific proteases, which cleave specific IGFBPs, altering their affinities for IGF peptides.(ABSTRACT TRUNCATED AT 250 WORDS)

The molecular and cellular biology of insulin-like growth factor II

Insulin-like growth factor II (IGF-II) is a 67 amino acid polypeptide that belongs to the family of insulin-like peptides. The IGF-II gene is coupled to the insulin gene and paternally imprinted. Multiple IGF-II mRNAs with identical coding regions and 3' untranslated regions (UTRs) but different 5' UTRs are generated from 3 promoters. The transcripts are translationally discriminated and inactivated by a specific endonucleolytic cleavage in their 3' UTR. These features may be important in the control of IGF-II production. IGF-II functions in an auto- and paracrine manner and binds to two types of receptors. The IGF-I receptor that is a tyrosine kinase and closely related with the insulin receptor and the IGF-II/mannose 6-phosphate (IGF-II/Man 6-P) receptor that is identical with the cation-independent mannose 6-phosphate receptor. The mitogenic and metabolic actions of IGF-II are propagated by the IGF-I receptor. In contrast, the IGF-II/Man 6-P receptor, that target lysosomal enzymes from the Golgi apparatus or the plasma membrane to the lysosomes, mediates the rapid internalization and degradation of IGF-II. IGF-II is expressed at high levels during foetal life and it is a major growth factor for the foetus in rodents. The developmental profiles and tissue distribution of the IGF-I and the maternally imprinted IGF-II/Man 6-P receptors both parallel that of IGF-II. In this scenario IGF-II promotes the growth of the embryo through the IGF-I receptor, whereas the IGF-II/Man 6-P receptor balance the activity by controlling the extracellular level of IGF-II.

Distribution of insulin-like growth factor 1 (IGF-1) and 2 (IGF-2) receptors in the hippocampal formation of rats and mice

This study demonstrated species differences in IGF-1 and IGF-2 receptor binding and localization in the hippocampus of the rat and mouse. Competition binding studies indicated that there were no differences in the relative binding affinities for the type 1 or type 2 receptors between the brains of these animals. These results suggested that the observed species differences were not attributable to alterations in IGF receptor kinetics. Receptor autoradiographic analyses demonstrated that IGF-1 binding differed in both the localization and overall receptor densities observed, with the rat demonstrating more specific localization and greater receptor density in the hippocampus than the mouse. The rat also exhibited a greater density of IGF-2 receptors in the hippocampus than the mouse. Despite differences in IGF receptor populations, both species exhibit similar hippocampal structure and lamination. Therefore, these results demonstrate a disparity in the localization of IGF receptor binding in the rat and mouse, suggesting that IGFs in these species are differentially regulated, with distinct neuromodulatory, neurotrophic, and/or developmental roles in this region of the brain. Previous comparative anatomical studies of the hippocampal formation of rats and mice fail to offer an explanation for the absence or reduction of binding of IGF-1 in the mouse. Although the mouse has a greater cell density in the s. granulosum than the rat, and both species exhibit similar glia and synaptic contact densities in the s. moleculare of the dentate gyrus, the mouse exhibits a complete absence of IGF-1 binding in this region. The lack of anatomical differences in the hippocampal formation of these species suggests that the patterns observed in IGF binding result from alterations in either neurochemical modulation of these neurons or specific neurotrophic requirements of the cells in this region. Differences have been reported on the concentrations and binding of various neurotransmitters in the hippocampus of these species, however these differences do not easily account for the variations observed in IGF binding in this study. IGFs are known to influence acetylcholine neurotransmission in the hippocampus as well as other brain areas in the rat. Recently, a truncated form of IGF-1, in which a tripeptide is cleaved from the N-terminus of the peptide, has been reported in brain. The cleaved tripeptide has been shown to activate glutamate receptors, which may dramatically influence excitatory neurotransmission in this region. Therefore, in addition to the possible neurotrophic actions of the peptide itself, subsequent processing of IGF-1 may be an important aspect of IGF-1 activity in the brain.(ABSTRACT TRUNCATED AT 400 WORDS)