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

Identification of the molecular mechanism of insulin-like growth factor-1 (IGF-1): a promising therapeutic target for neurodegenerative diseases associated with metabolic syndrome

Neurodegenerative disorders are accompanied by neuronal degeneration and glial dysfunction, resulting in cognitive, psychomotor, and behavioral impairment. Multiple factors including genetic, environmental, metabolic, and oxidant overload contribute to disease progression. Recent evidences suggest that metabolic syndrome is linked to various neurodegenerative diseases. Metabolic syndrome (MetS) is known to be accompanied by symptoms such as hyperglycemia, abdominal obesity, hypertriglyceridemia, and hypertension. Despite advances in knowledge about the pathogenesis of neurodegenerative disorders, effective treatments to combat neurodegenerative disorders caused by MetS have not been developed to date. Insulin growth factor-1 (IGF-1) deficiency has been associated with MetS-related pathologies both in-vivo and in-vitro. IGF-1 is essential for embryonic and adult neurogenesis, neuronal plasticity, neurotropism, angiogenesis, metabolic function, and protein clearance in the brain. Here, we review the evidence for the potential therapeutic effects of IGF-1 in the neurodegeneration related to metabolic syndrome. We elucidate how IGF-1 may be involved in molecular signaling defects that occurs in MetS-related neurodegenerative disorders and highlight the importance of IGF-1 as a potential therapeutic target in MetS-related neurological diseases.

Immunomodulatory effects of polysaccharides enzymatic hydrolysis from Hericium erinaceus on the MODE-K/DCs co-culture model

The aim of this study was to explore the indirect immunomodulatory activities and its mechanism of enzymatic hydrolysis of Hericium erinaceus polysaccharides (EHEP) in the MODE-K/DCs co-culture model. According to the TEER value, transmission of phenol red and AKP activity of MODE-K cells, single model was established in order to evaluate the eligibility of MODE-K cells monolayer. Then the MODE-K/DCs co-culture model was set up and HEP and EHEP were added into the apical chamber, DCs were obtained for the expression of key surface markers, the ability of phagocytosis, the morphology, the secretion of cytokines and the production of target proteins. We found that after 21 d of culture, the MODE-K cells monolayer became intact and dense, which can be used for the MODE-K/DCs co-culture model. Under the treatment of HEP and EHEP, immature DCs become into mature DCs with the high expression of CD86 and MHCII, the low antigens up-taking, the typical morphology, the more content of IL-12 and TNF-α and the high level of TLR4, MyD88 and NF-κB proteins. However, compared with HEP, EHEP showed the better immunomodulatory activities. These findings indicated that EHEP could indirectly affect the immune function of DCs in the MODE-K/DCs co-culture model.

Single-cell transcriptomes reveal molecular specializations of neuronal cell types in the developing cerebellum

The cerebellum is critical for controlling motor and non-motor functions via cerebellar circuit that is composed of defined cell types, which approximately account for more than half of neurons in mammals. The molecular mechanisms controlling developmental progression and maturation processes of various cerebellar cell types need systematic investigation. Here, we analyzed transcriptome profiles of 21119 single cells of the postnatal mouse cerebellum and identified eight main cell clusters. Functional annotation of differentially expressed genes revealed trajectory hierarchies of granule cells (GCs) at various states and implied roles of mitochondrion and ATPases in the maturation of Purkinje cells (PCs), the sole output cells of the cerebellar cortex. Furthermore, we analyzed gene expression patterns and co-expression networks of 28 ataxia risk genes, and found that most of them are related with biological process of mitochondrion and around half of them are enriched in PCs. Our results also suggested core transcription factors that are correlated with interneuron differentiation and characteristics for the expression of secretory proteins in glia cells, which may participate in neuronal modulation. Thus, this study presents a systematic landscape of cerebellar gene expression in defined cell types and a general gene expression framework for cerebellar development and dysfunction.

IGF-1 receptor regulates dynamic changes in neuronal polarity during cerebral cortical migration

During cortical development, neurons undergo polarization, oriented migration and layer-type differentiation. The biological and biochemical mechanisms underlying these processes are not completely understood. In neurons in culture we showed that IGF-1 receptor activation is important for growth cone assembly and axonal formation. However, the possible roles of the insulin like growth factor-1 receptor (IGF-1R) on neuronal differentiation and polarization in vivo in mammals have not yet been studied. Using in utero electroporation, we show here that the IGF-1R is essential for neocortical development. Neurons electroporated with a shRNA targeting IGF-1 receptor failed to migrate to the upper cortical layers and accumulated at the ventricular/subventricular zones. Co-electroporation with a constitutively active form of PI3K rescued migration. The change of the morphology from multipolar to bipolar cells was also attenuated. Cells lacking the IGF-1 receptor remain arrested as multipolar forming a highly disorganized tissue. The typical orientation of the migrating neurons with the Golgi complex oriented toward the cortical upper layers was also affected by electroporation with shRNA targeting IGF-1 receptor. Finally, cells electroporated with the shRNA targeting IGF-1 receptor were unable to form an axon and, therefore, neuron polarity was absent.

Differentiation of human induced pluripotent stem cells to mature functional Purkinje neurons

It remains a challenge to differentiate human induced pluripotent stem cells (iPSCs) or embryonic stem (ES) cells to Purkinje cells. In this study, we derived iPSCs from human fibroblasts and directed the specification of iPSCs first to Purkinje progenitors, by adding Fgf2 and insulin to the embryoid bodies (EBs) in a time-sensitive manner, which activates the endogenous production of Wnt1 and Fgf8 from EBs that further patterned the cells towards a midbrain-hindbrain-boundary tissue identity. Neph3-positive human Purkinje progenitors were sorted out by using flow cytometry and cultured either alone or with granule cell precursors, in a 2-dimensional or 3-dimensional environment. However, Purkinje progenitors failed to mature further under above conditions. By co-culturing human Purkinje progenitors with rat cerebellar slices, we observed mature Purkinje-like cells with right morphology and marker expression patterns, which yet showed no appropriate membrane properties. Co-culture with human fetal cerebellar slices drove the progenitors to not only morphologically correct but also electrophysiologically functional Purkinje neurons. Neph3-posotive human cells could also survive transplantation into the cerebellum of newborn immunodeficient mice and differentiate to L7- and Calbindin-positive neurons. Obtaining mature human Purkinje cells in vitro has significant implications in studying the mechanisms of spinocerebellar ataxias and other cerebellar diseases.

Klf9 is necessary and sufficient for Purkinje cell survival in organotypic culture

During their phase of developmental programmed cell death (PCD), neurons depend on target-released trophic factors for survival. After this period, however, they critically change as their survival becomes target-independent. The molecular mechanisms underlying this major transition remain poorly understood. Here, we investigated, which transcription factors (TFs) might be responsible for the closure of PCD. We used Purkinje cells as a model since their PCD is restricted to the first postnatal week in the mouse cerebellum. Transcriptome analysis of Purkinje cells during or after PCD allowed the identification of Krüppel like factor 9 (Klf9) as a candidate for PCD closure, given its high increase of expression at the end of the 1st postnatal week. Klf9 function was tested in organotypic cultures, through lentiviral vector-mediated manipulation of Klf9 expression. In absence of trophic factors, the Purkinje cell survival rate is of 40%. Overexpression of Klf9 during PCD dramatically increases the Purkinje cell survival rate from 40% to 88%, whereas its down-regulation decreases it to 14%. Accordingly, in organotypic cultures of Klf9 knockout animals, Purkinje cell survival rate is reduced by half as compared to wild-type mice. Furthermore, the absence of Klf9 could be rescued by Purkinje cell trophic factors, Insulin growth factor-1 and Neurotrophin3. Altogether, our results ascribe a clear role of Klf9 in Purkinje cell survival. Thus, we propose that Klf9 might be a key molecule involved in turning off the phase of Purkinje PCD.

Immunofluorescent spectral analysis reveals the intrathecal cannabinoid agonist, AM1241, produces spinal anti-inflammatory cytokine responses in neuropathic rats exhibiting relief from allodynia

During pathological pain, the actions of the endocannabinoid system, including the cannabinoid 2 receptor (CB(2)R), leads to effective anti-allodynia and modifies a variety of spinal microglial and astrocyte responses. Here, following spinal administration of the CB(2)R compound, AM1241, we examined immunoreactive alterations in markers for activated p38 mitogen-activated protein kinase, interleukin-1β (IL-1β), the anti-inflammatory cytokine, interleukin-10 (IL-10) as well as degradative endocannabinoid enzymes, and markers for altered glial responses in neuropathic rats. In these studies, the dorsal horn of the spinal cord and dorsal root ganglia were examined. AM1241 produced profound anti-allodynia with corresponding immunoreactive levels of p38 mitogen-activated kinase, IL-1β, IL-10, the endocannabinoid enzyme monoacylglycerol lipase, and astrocyte activation markers that were similar to nonneuropathic controls. In contrast, spinal AM1241 did not suppress the increased microglial responses observed in neuropathic rats. The differences in fluorescent markers were determined within discrete anatomical regions by applying spectral analysis methods, which virtually eliminated nonspecific signal during the quantification of specific immunofluorescent intensity. These data reveal expression profiles that support the actions of intrathecal AM1241 control pathological pain through anti-inflammatory mechanisms by modulating critical glial factors, and additionally decrease expression levels of endocannabinoid degradative enzymes.

Insulin-like growth factor signaling regulates the timing of sensory cell differentiation in the mouse cochlea

The mammalian auditory sensory epithelium, the organ of Corti, is a highly ordered cellular structure that comprises two types of auditory hair cells and several types of nonsensory supporting cells. During embryogenesis, a stereotyped sequence of cellular and molecular events is required for its development. These processes are assumed to be regulated by multiple growth and transcription factors. However, the majority of these factors have not been identified. One potential regulator of cochlear development is the insulin-like growth factor (IGF) signaling family. To examine the roles of the IGF pathway in inner ear formation, cochleae from Igf1r mutant mice were analyzed. Deletion of Igf1r leads to several changes in inner ear development including a shortened cochlear duct, a decrease in the total number of cochlear hair cells, and defects in the formation of the semicircular canals. In addition, maturation of the cochlear sensory epithelium was delayed at the transition point between cellular proliferation and differentiation. To determine the molecular basis for these defects, inhibition of IGF signaling was replicated pharmacologically in vitro. Results indicated that IGF signaling regulates cochlear length and hair cell number as well as Atoh1 expression through the phosphatidylinositol 3-kinase/Akt signaling pathway. These results demonstrate novel roles for IGF signaling in inner ear development including regulation of vestibular formation, length of the cochlear duct, and the number of cochlear hair cells. The results also provide new insights regarding the pathological processes that underlie auditory defects in the absence of IGF signaling in both humans and mice.

Age-related Purkinje cell death is steroid dependent: RORα haplo-insufficiency impairs plasma and cerebellar steroids and Purkinje cell survival

A major problem of ageing is progressive impairment of neuronal function and ultimately cell death. Since sex steroids are neuroprotective, their decrease with age may underlie age-related neuronal degeneration. To test this, we examined Purkinje cell numbers, plasma sex steroids and cerebellar neurosteroid concentrations during normal ageing (wild-type mice, WT), in our model of precocious ageing (Rora(+/sg), heterozygous staggerer mice in which expression of the neuroprotective factor RORα is disrupted) and after long-term hormone insufficiency (WT post-gonadectomy). During normal ageing (WT), circulating sex steroids declined prior to or in parallel with Purkinje cell loss, which began at 18 months of age. Although Purkinje cell death was advanced in WT long-term steroid deficiency, this premature neuronal loss did not begin until 9 months, indicating that vulnerability to sex steroid deficiency is a phenomenon of ageing Purkinje neurons. In precocious ageing (Rora(+/sg)), circulating sex steroids decreased prematurely, in conjunction with marked Purkinje cell death from 9 months. Although Rora(+/sg) Purkinje cells are vulnerable through their RORα haplo-insufficiency, it is only as they age (after 9 months) that sex steroid failure becomes critical. Finally, cerebellar neurosteroids did not decrease with age in either genotype or gender; but were profoundly reduced by 3 months in male Rora(+/sg) cerebella, which may contribute to the fragility of their Purkinje neurons. These data suggest that ageing Purkinje cells are maintained by circulating sex steroids, rather than local neurosteroids, and that in Rora(+/sg) their age-related death is advanced by premature sex steroid loss induced by RORα haplo-insufficiency.

Local insulin-like growth factor I expression is essential for Purkinje neuron survival at birth

IGF1, an anabolic and neuroprotective factor, promotes neuronal survival by blocking apoptosis. It is released into the bloodstream by the liver, or synthesized locally by muscles and neural cells, acting in an autocrine or paracrine fashion. Intriguingly, genetic studies conducted in invertebrate and murine models also suggest that an excess of IGF1 signaling may trigger neurodegeneration. This emphasizes the importance of gaining a better understanding of the mechanisms controlling IGF1 regulation and gene transcription. In the cerebellum, Igf1 expression is activated just before birth in a subset of Purkinje cells (PCs). Mice carrying a null mutation for HLH transcription factor EBF2 feature PC apoptosis at birth. We show that Igf1 is sharply downregulated in Ebf2 null PCs starting before the onset of PC death. In vitro, EBF2 binds a conserved distal Igf1 promoter region. The pro-survival PI3K signaling pathway is strongly inhibited in mutant cerebella. Finally, Ebf2 null organotypic cultures respond to IGF1 treatment by inhibiting PC apoptosis. Consistently, wild type slices treated with an IGF1 competitor feature a sharp increase in PC death. Our findings reveal that IGF1 is required for PC survival in the neonatal cerebellum, and identify a new mechanism regulating its local production in the CNS.

AF4 is a critical regulator of the IGF-1 signaling pathway during Purkinje cell development

Deregulation of the insulin-like growth factor 1 (IGF-1) signaling pathway is a recurrent finding in mouse models and human patients with cerebellar ataxia and thus represents a common pathological cascade in neuronal cell death that may be targeted for therapy. We have previously identified a point mutation in AF4, a transcription cofactor of RNA polymerase II elongation and chromatin remodeling, that causes progressive and highly specific Purkinje cell (PC) death in the ataxic mouse mutant robotic, leading to the accumulation of AF4 in PCs. Here we confirm that the spatiotemporal pattern of PC degeneration in the robotic cerebellum correlates with the specific profile of AF4 upregulation. To identify the underlying molecular pathways, we performed microarray gene expression analysis of PCs obtained by laser capture microdissection (LCM) at the onset of degeneration. Igf-1 was significantly downregulated in robotic PCs compared with wild-type controls before and throughout the degenerative process. Consistently, we observed a decrease in the activation of downstream signaling molecules including type 1 IGF receptor (IGF-1R) and the extracellular signal-regulated kinase (ERK) 1 and ERK2. Chromatin immunoprecipitation confirmed that Igf-1 is a direct and the first validated target of the AF4 transcriptional regulatory complex, and treatment of presymptomatic robotic mice with IGF-1 indeed markedly delayed the progression of PC death. This study demonstrates that small changes in the levels of a single transcriptional cofactor can deleteriously affect normal cerebellum function and opens new avenues of research for the manipulation of the IGF-1 pathway in the treatment of cerebellar ataxia in humans.

C-terminal mechano growth factor protects dopamine neurons: a novel peptide that induces heme oxygenase-1

To assess potential efficacy of mechano growth factor (MGF) for chronic neurodegenerative disorders, we studied whether MGF protects dopamine (DA) neurons subjected to neurotoxic stress. We show that a short 24-amino acid C-terminal peptide of MGF (MGF24) upregulates heme oxygenase-1 (HO-1) expression and protects SH-SY5Y cells against apoptosis and cell loss induced by three DA cell-specific neurotoxins: 6-hydroxydopamine (6-OHDA), 1-methyl-4-phenylpyridinium (MPP(+)), and rotenone. MGF24 maintains the mitochondrial membrane potential and blocks the release of mitochondrial apoptotic-inducing factor into the cytoplasm induced by 6-OHDA, MPP(+), and rotenone. Chemical inhibition of HO-1 with zinc protoporphyrin-IX prevents neuroprotection by MGF24 against the three neurotoxins. MGF24 does not activate Akt signaling nor does Akt inhibition block MGF24 protection of SH-SY5Y cells. In 6-OHDA-lesioned rats, central or peripheral MGF24 administration protects against the development of contralateral forelimb under-utilization, reduces ipsilateral nigral DA cell body loss, and attenuates tyrosine hydroxylase fiber loss in the ipsilateral striatum, independent of IGF-1 receptor activation. Peripheral MGF24 administration upregulates HO-1 expression in striatal and midbrain tissue. This report is the first to demonstrate that a small peptide, MGF24, upregulates HO-1, an important cell defense mediator, and protects DA cells, suggesting new strategies for neuroprotection in Parkinson's disease.

Expanding the mind: insulin-like growth factor I and brain development

Signaling through the type 1 IGF receptor (IGF1R) after interaction with IGF-I is crucial to the normal brain development. Manipulations of the mouse genome leading to changes in the expression of IGF-I or IGF1R significantly alters brain growth, such that IGF-I overexpression leads to brain overgrowth, whereas null mutations in either IGF-I or the IGF1R result in brain growth retardation. IGF-I signaling stimulates the proliferation, survival, and differentiation of each of the major neural lineages, neurons, oligodendrocytes, and astrocytes, as well as possibly influencing neural stem cells. During embryonic life, IGF-I stimulates neuron progenitor proliferation, whereas later it promotes neuron survival, neuritic outgrowth, and synaptogenesis. IGF-I also stimulates oligodendrocyte progenitor proliferation although inhibiting apoptosis in oligodendrocyte lineage cells and stimulating myelin production. These pleiotropic IGF-I activities indicate that other factors provide instructive signals for specific cellular events and that IGF-I acts to facilitate them. Studies of the few humans with IGF-I and/or IGF1R gene mutations indicate that IGF-I serves a similar role in man.

Chicken Ovalbumin Upstream Promoter-Transcription Factor II (COUP-TFII) regulates growth and patterning of the postnatal mouse cerebellum

COUP-TFII (also known as Nr2f2), a member of the nuclear orphan receptor superfamily, is expressed in several regions of the central nervous system (CNS), including the ventral thalamus, hypothalamus, midbrain, pons, and spinal cord. To address the function of COUP-TFII in the CNS, we generated conditional COUP-TFII knockout mice using a tissue-specific NSE-Cre recombinase. Ablation of COUP-TFII in the brain resulted in malformation of the lobule VI in the cerebellum and a decrease in differentiation of cerebellar neurons and cerebellar growth. The decrease in cerebellar growth in NSE(Cre/+)/CII(F/F) mice is due to reduced proliferation and increased apoptosis in granule cell precursors (GCPs). Additional studies demonstrated that insulin like growth factor 1 (IGF-1) expression was reduced in the cerebellum of NSE(Cre/+)/CII(F/F) mice, thereby leading to decreased Akt1 and GSK-3beta activities, and the reduced expression of mTOR. Using ChIP assays, we demonstrated that COUP-TFII was recruited to the promoter region of IGF-1 in a Sp1-dependent manner. In addition, dendritic branching of Purkinje cells was decreased in the mutant mice. Thus, our results indicate that COUP-TFII regulates growth and maturation of the mouse postnatal cerebellum through modulation of IGF-1 expression.

SGP-1 increases dendritic and synaptic development dependent on synaptic activity

Neurotrophic factors are a group of secreted proteins which generally regulate neurite outgrowth and synaptic development. SGP-1 has been reported as a neurotrophic factor, though little is known of its effect on neurite outgrowth, and it is unknown whether SGP-1 affects synaptic development. We report here that SGP-1 is distributed in vesicle-like puncta in somas and dendrites of primary neurons in culture, and that SGP-1 is secreted in culture and is taken up by endocytosis in dendrites. Endogenous extracellular activity of SGP-1 promotes dendritic, but not axonal outgrowth. Furthermore, endogenous activity of SGP-1 increases synaptogenesis in hippocampal neurons as determined by measuring the density and size of synaptophysin puncta and by determining the density of dendritic spines, their surface expression of GluR2 and their immunoreactivity for GluR1. The effect of SGP-1 on the amount of postsynaptic receptors in dendritic spines depends on synaptic activity and apparently on activation of MAPK, as inhibition of either of these abolished the affect. Hence, SGP-1 has neurotrophic effects, increasing dendritic growth and promoting synaptic development in an activity-dependent fashion.

Postnatal head growth deficit among premature infants parallels retinopathy of prematurity and insulin-like growth factor-1 deficit

BACKGROUND

We hypothesized that in premature infants, retinal vascular growth retardation between birth and postmenstrual age of approximately 30 to 32 weeks that initiates retinopathy of prematurity is paralleled by brain growth retardation.

METHODS

In a prospective longitudinal study, we measured postnatal head growth, retinopathy of prematurity stage, protein and energy intake, severity of illness and serum insulin-like growth factor-1 levels in 58 preterm infants (mean gestational age at birth: 27.6 weeks) from birth until postmenstrual age of approximately 40 weeks.

RESULTS

Premature infant head growth decelerates dramatically after birth until postmenstrual age of approximately 30 weeks. Head growth retardation coincides with retinal vascular growth suppression. Accelerated growth follows between post menstrual ages of approximately 30 to 32 weeks and approximately 40 weeks. The degree of head growth retardation up to postmenstrual age of 31 weeks corresponds to the degree of retinopathy of prematurity and to the degree of suppression of serum levels of insulin-like growth factor-1. At postmenstrual age of 31 weeks, if a child's head circumference SD is below -2.5, then the probability of also developing at least stage 3 retinopathy of prematurity increases fivefold compared with head circumference above -2.5 SD (32% vs 6%) suggesting parallel processes in brain and retina. Serum insulin-like growth factor-1 levels correlate positively with head circumference SD score and with the degree of retinopathy of prematurity.

CONCLUSIONS

The correlation between head and retinal growth is consistent with insulin growth factor-1 being one of the postnatal growth factors involved in this multifactorial process and also suggests that factors that contribute to retinopathy of prematurity during this critical period may also affect neurological dysfunction. Additional studies are required to establish this connection.

Intranasal administration of IGF-I improves behavior and Purkinje cell pathology in SCA1 mice

Spinocerebellar ataxia type 1 (SCA1) is a neurodegenerative disease caused by the expansion of polyglutamine repeat within ataxin-1 protein. Cerebellar Purkinje cells are the primary targets of SCA1 pathology. These cells synthesize insulin-like growth factor-I (IGF-I) and express its receptors during their entire life. The aim of present study was to determine if intranasally administered IGF-I to SCA1 transgenic mice suppresses toxic effects of ataxin-1. Two-week old SCA1 heterozygous animals were randomly divided into two treatment groups of IGF-I (30 and 60 microg IGF-I/animal) and a vehicle-treated control group. The wildtype animals served as normal controls. IGF-I or vehicle was administered at 48 h intervals for the total of 10 doses. Animals were then subjected to rotarod test, sacrificed, brains removed and processed for immunohistochemical and Western blot analysis. Radiolabeled IGF-I and bioactive TAT peptide accumulated in the brains of SCA1 mice following intranasal administration validating the use of intranasal route. SCA1 mice showed SCA1 pathology with impaired motor function and downregulation of calcium binding proteins as compared to wildtype mice. However, 30 and 60 microg IGF-I-treated animals showed improved performance on the rotarod as compared to vehicle-treated SCA1 mice with significant improvement (p < 0.05) on day 3 in 60 microg IGF-I group. The immunohistochemical data further showed partial recovery in the expression of calbindin D28k and protein kinase C-gamma in Purkinje cells in IGF-I-treated SCA1 animals. Our results indicate that suppression of ataxin-1-mediated adverse effects by intranasal IGF-I treatment may be of a therapeutic value to treat SCA1.

Afferent-target interactions during olivocerebellar development: transcommissural reinnervation indicates interdependence of Purkinje cell maturation and climbing fibre synapse elimination

We have used a model of postlesional reinnervation to observe the interactions between synaptic partners during neosynaptogenesis to determine how the developmental states of the pre- and postsynaptic cells influence circuit maturation. After unilateral transection of the neonatal rat olivocerebellar pathway (pedunculotomy), axons from the remaining ipsilateral inferior olive grow into the denervated hemicerebellum and develop climbing fibre (CF) terminal arbors on Purkinje cells (PCs) at a later stage of development than normal. However, the significance of delayed CF-PC interactions on subsequent circuit maturation remains poorly defined. To examine this question, we recorded CF-induced currents in PCs and analysed PC morphology during the first two postnatal weeks in control animals and following left unilateral inferior cerebellar pedunculotomy on postnatal day (P)3. Our results show that transcommissural olivary axons multiply-reinnervate PCs in the denervated hemisphere over 4 days following pedunculotomy. Each PC received fewer CFs than did age-matched controls and the maximal multi-reinnervation was reached on P7, 2 days later than in controls. Consequently, the onset of CF synapse elimination in reinnervated PCs was delayed, but then proceeded in parallel with controls so that all PCs were monoinnervated by P15. Furthermore, reinnervated PCs had delayed dendritic maturation and subsequent dendritic abnormalities consistent with the role of CF innervation in PC dendritic growth. Thus, within the olivocerebellar system, our data suggest that target neurons depend upon sufficient afferent investment arriving at the correct time for their normal development, and maturation of the target neuron regulates afferent selection and therefore circuit maturation.

Regulation of adult olfactory neurogenesis by insulin-like growth factor-I

Insulin-like growth factor-I (IGF-I) has multiple effects within the developing nervous system but its role in neurogenesis in the adult nervous system is less clear. The adult olfactory mucosa is a site of continuing neurogenesis that expresses IGF-I, its receptor and its binding proteins. The aim of the present study was to investigate the roles of IGF-I in regulating proliferation and differentiation in the olfactory mucosa. The action of IGF-I was assayed in serum-free culture combined with bromodeoxyuridine-labelling of proliferating cells and immunochemistry for specific cell types. IGF-I and its receptor were expressed by globose basal cells (the neuronal precursor) and by olfactory neurons. IGF-I reduced the numbers of proliferating neuronal precursors, induced their differentiation into neurons and promoted morphological differentiation of neurons. The evidence suggests that IGF-I is an autocrine and/or paracrine signal that induces neuronal precursors to differentiate into olfactory sensory neurons. These effects appear to be similar to the cellular effects of IGF-I in the developing nervous system.

A strong neuroprotective effect of the autonomous C‐terminal peptide of IGF‐1 Ec (MGF) in brain ischemia

The ischemic stroke is the third leading cause of death in developed countries. The C-terminal peptide of mechano-growth factor (MGF), an alternatively spliced variant of insulin-like growth factor 1 (IGF-1), was found to function independently from the rest of the molecule and showed a neuroprotective effect in vivo and in vitro. In vivo, in a gerbil model of transient brain ischemia, treatment with the synthetic MGF C-terminal peptide provided very significant protection to the vulnerable neurons. In the same model, ischemia evoked increased expression of endogenous MGF in the ischemia-resistant hippocampal neurons, suggesting that the endogenous MGF might have an important neuroprotective function. In an in vitro organotypic hippocampal culture model of neurodegeneration, the synthetic peptide was as potent as the full-length IGF-1 while its effect lasted significantly longer than that of recombinant IGF-1. While two peptides showed an additive effect, the neuroprotective action of the C-terminal MGF was independent from the IGF-1 receptor, indicating a new mode of action for this molecule. Although MGF is known for its regenerative capability in skeletal muscle, our findings demonstrate for the first time a neuroprotective role against ischemia for this specific IGF-1 isoform. Therefore, the C-terminal MGF peptide has a potential to be developed into a therapeutic modality for the prevention of neuronal damage.

Expression of insulin-like growth factor 1 and receptor in ischemic rats treated with human marrow stromal cells

Human bone marrow stromal cells (hMSCs) enhance neurological recovery after stroke in rodents, possibly via induction of growth factors. We therefore elected to test the effects of hMSC treatment on insulin-like growth factor 1 (IGF-1), which plays an important role in growth, development, neuroprotection and repair in the adult. Rats (n=57) were subjected to permanent middle cerebral artery occlusion (MCAo) and injected intravenously with 3 x 10(6) hMSCs or phosphate-buffered saline (PBS) at 1 day after MCAo. Functional outcome was measured after MCAo using a modified Neurological Severity Score (mNSS). Gene expression of IGF-1 and IGF-1 receptor (IGF-1R) in the ischemic brain tissue were measured at 2 and 7 days after MCAo using reverse transcription-polymerase chain reaction (RT-PCR). Immunohistochemistry was performed to measure the expression of bromodeoxyuridine (BrdU), doublecortin (DCX), IGF-1 and IGF-1R at 7, 14 and 30 days after MCAo. Treatment of MCAo with hMSCs significantly improved functional recovery from 14 to 30 days. MAB1281-labeled hMSCs entered the ischemic brain and increased time-dependently. hMSC treatment significantly increased IGF-1 mRNA and BrdU(+), DCX(+), IGF-1(+) and IGF-1R(+) cells compared to PBS-treated rats (p<0.05). The percentage of BrdU(+) or DCX(+) cells colocalized with IGF-1 increased in the hMSC-treated rats compared to the PBS-treated rats (p<0.05). IGF-1 and IGF-1R may contribute to improved functional recovery and increased neurogenesis after treatment of stroke with hMSCs.

Neurotrophin expression in the hippocampus and cerebellum is affected by chronic placental insufficiency in the late gestational ovine fetus

Our aim was to determine the effects of chronic placental insufficiency (CPI) during late gestation on the expression of neurotrophic factors and their receptors in the hippocampus and cerebellum in the near-term fetus. Structural alterations were also assessed in these brain regions. CPI was induced in eight fetal sheep by umbilicoplacental embolization (UPE) from 120 to 140 days of gestation (term approximately 147d) such that fetal arterial O2 saturation (SaO2) was maintained at approximately 50% of pre-UPE values. Five non-UPE fetuses served as controls. UPE resulted in fetal hypoxemia, hypoglycaemia, and growth restriction. In hippocampi from UPE fetuses, there were reductions in the optical density (OD) of the immunoreactivity (IR) of brain-derived neurotrophic factor (BDNF) protein within the mossy fibre collaterals of the polymorphic layer and in stratum lucidum (p<0.05); there was no consistent effect on tyrosine-related kinase (Trk) B receptor or neurotrophin-3 (NT-3) expression. Within the cerebellum, there was an increase in BDNF-IR (p<0.05) in the molecular layer; however, Trk B-IR and NT-3-IR were unaltered. There were no significant alterations to the structural parameters measured in the hippocampus. We conclude that CPI in late gestation affects the expression of BDNF in the fetal hippocampus and cerebellum, but these changes do not have a well-defined relationship to structural outcome.

Cellular and molecular control of dendritic growth and development of cerebellar Purkinje cells

Purkinje cells are the principal neurons of the cerebellar cortex and are characterized by a large and highly branched dendritic tree. For this reason, they have for a long time been an attractive model system to study the regulation of dendritic growth and differentiation. In this article, I will first review studies on different aspects of Purkinje cell dendritic development and then go on to present studies which have aimed at experimentally altering Purkinje cell dendritic development. Some of the cellular and molecular mechanisms which have been shown by these studies to be important determinants of Purkinje cell dendritic development will be discussed, in particular the role of the parallel fiber input, of hormones, and of neuronal growth factors. The organotypic slice culture method will be introduced as an important experimental tool to study Purkinje cell dendritic development under controlled conditions. Using cerebellar slice cultures, protein kinase C (PKC) has been identified as a major determinant of Purkinje cell dendritic development and the contribution of specific isoforms of PKC will be discussed. Finally, it will be shown that Purkinje cell dendritic development in slice cultures does not depend on the activation of glutamate receptors and appears to be independent of the presence of the neurotrophin BDNF. These studies indicate that the initial outgrowth of the Purkinje cell dendritic tree can occur in the absence of signals derived from afferent fibers, but is under control of PKC signaling.

Microglia in Culture: What Genes Do They Express?

The cell culture model utilized in this study represents one of the most widely used paradigms of microglia in vitro. After 14 days, microglia harvested from the neonatal rat brain are considered 'mature'. However, it is clear that this represents a somewhat arbitrary definition. In this paper, we provide a transcriptome definition of such microglial cells. More than 7,000 known genes and 1,000 expressed sequence tag clusters were analysed. 'Microglia genes' were defined as sequences consistently expressed in all microglia samples tested. Accordingly, 388 genes were identified as microglia genes. Another 1,440 sequences were detected in a subset of the cultures. Genes consistently expressed by microglia included genes known to be involved in the cellular immune response, brain tissue surveillance, microglial migration as well as proliferation. The expression profile reported here provides a baseline against which changes of microglia in vitro can be examined. Importantly, expression profiling of normal microglia will help to provide the presently purely operational definition of 'microglial activation' with a molecular biological correlate. Furthermore, the data reported here add to our understanding of microglia biology and allow projections as to what functions microglia may exert in vivo, as well as in vitro.

Corticotropin-releasing factor and urocortin differentially modulate rat Purkinje cell dendritic outgrowth and differentiation in vitro

The precise outgrowth and arborization of dendrites is crucial for their function as integrators of signals relayed from axons and, hence, the functioning of the brain. Proper dendritic differentiation is particularly resonant for Purkinje cells as the intrinsic activity of this cell-type is governed by functionally distinct regions of its dendritic tree. Activity-dependent mechanisms, driven by electrical signaling and trophic factors, account for the most active period of dendritogenesis. An as yet unexplored trophic modulator of Purkinje cell dendritic development is corticotropin-releasing factor (CRF) and family member, urocortin, both of which are localized in climbing fibers. Here, we use rat organotypic cerebellar slice cultures to investigate the roles of CRF and urocortin on Purkinje cell dendritic development. Intermittent exposure (12 h per day for 10 days in vitro) of CRF and urocortin induced significantly more dendritic outgrowth (45% and 70%, respectively) and elongation (25% and 15%, respectively) compared with untreated cells. Conversely, constant exposure to CRF and urocortin significantly inhibited dendritic outgrowth. The trophic effects of CRF and urocortin are mediated by the protein kinase A and mitogen-activating protein kinase pathways. The study shows unequivocally that CRF and urocortin are potent regulators of dendritic development. However, their stimulatory or inhibitory effects are dependent upon the degree of expression of these peptides. Furthermore, the effects of CRF and urocortin on neuronal differentiation and re-modeling may provide a cellular basis for pathologies such as major depression, which show perturbations in the expression of these stress peptides.