Insulin-like growth factor-I overexpression attenuates cerebellar apoptosis by altering the expression of Bcl family proteins in a developmentally specific manner

NMDA receptor-mediated Ca2+ signaling: Impact on cell cycle regulation and the development of neurodegenerative diseases and cancer

NMDA receptors are Ca2+-permeable ligand-gated ion channels that mediate fast excitatory transmission in the central nervous system. NMDA receptors regulate the proliferation and differentiation of neural progenitor cells and also play critical roles in neural plasticity, memory, and learning. In addition to their physiological role, NMDA receptors are also involved in glutamate-mediated excitotoxicity, which results from excessive glutamate stimulation, leading to Ca2+ overload, and ultimately to neuronal death. Thus, NMDA receptor-mediated excitotoxicity has been linked to several neurodegenerative diseases such as Alzheimer's, Parkinson's, Huntington's, dementia, and stroke. Interestingly, in addition to its effects on cell death, aberrant expression or activation of NMDA receptors is also involved in pathological cellular proliferation, and is implicated in the invasion and proliferation of various types of cancer. These disorders are thought to be related to the contribution of NMDA receptors to cell proliferation and cell death through cell cycle modulation. This review aims to discuss the evidence implicating NMDA receptor activity in cell cycle regulation and the link between aberrant NMDA receptor activity and the development of neurodegenerative diseases and cancer due to cell cycle dysregulation. The information presented here will provide insights into the signaling pathways and the contribution of NMDA receptors to these diseases, and suggests that NMDA receptors are promising targets for the prevention and treatment of these diseases, which are leading causes of death and disability worldwide.

Anti-Gene IGF-I Vaccines in Cancer Gene Therapy: A Review of a Case of Glioblastoma

OBJECTIVE

Vaccines for the deadliest brain tumor - glioblastoma (GBM) - are generally based on targeting growth factors or their receptors, often using antibodies. The vaccines described in the review were prepared to suppress the principal cancer growth factor - IGF-I, using anti-gene approaches either of antisense (AS) or of triple helix (TH) type. Our objective was to increase the median survival of patients treated with AS and TH cell vaccines.

METHODOLOGY

The cells were transfected in vitro by both constructed IGF-I AS and IGF-I TH expression episomal vectors; part of these cells was co-cultured with plant phytochemicals, modulating IGF-I expression. Both AS and TH approaches completely suppressed IGF-I expression and induced MHC-1 / B7 immunogenicity related to the IGF-I receptor signal.

RESULTS

This immunogenicity proved to be stronger in IGF-I TH than in IGF-I AS-prepared cell vaccines, especially in TH / phytochemical cells. The AS and TH vaccines generated an important TCD8+ and TCD8+CD11b- immune response in treated GBM patients and increased the median survival of patients up to 17-18 months, particularly using TH vaccines; in some cases, 2- and 3-year survival was reported. These clinical results were compared with those obtained in therapies targeting other growth factors.

CONCLUSION

The anti-gene IGF-I vaccines continue to be applied in current GBM personalized medicine. Technical improvements in the preparation of AS and TH vaccines to increase MHC-1 and B7 immunogenicity have, in parallel, allowed to increase in the median survival of patients.

IGF-1 as a Potential Therapy for Spinocerebellar Ataxia Type 3

Although the effects of growth hormone (GH) therapy on spinocerebellar ataxia type 3 (SCA3) have been examined in transgenic SCA3 mice, it still poses a nonnegligible risk of cancer when used for a long term. This study investigated the efficacy of IGF-1, a downstream mediator of GH, in vivo for SCA3 treatment. IGF-1 (50 mg/kg) or saline, once a week, was intraperitoneally injected to SCA3 84Q transgenic mice harboring a human ATXN3 gene with a pathogenic expanded 84 cytosine–adenine–guanine (CAG) repeat motif at 9 months of age. Compared with the control mice harboring a 15 CAG repeat motif, the SCA3 84Q mice treated with IGF-1 for 9 months exhibited the improvement only in locomotor function and minimized degeneration of the cerebellar cortex as indicated by the survival of more Purkinje cells with a more favorable mitochondrial function along with a decrease in oxidative stress caused by DNA damage. These findings could be attributable to the inhibition of mitochondrial fission, resulting in mitochondrial fusion, and decreased immunofluorescence staining in aggresome formation and ataxin-3 mutant protein levels, possibly through the enhancement of autophagy. The findings of this study show the therapeutic potential effect of IGF-1 injection for SCA3 to prevent the exacerbation of disease progress.

Associations between IGF1, IGFBP2 and TGFß3 Genes Polymorphisms and Growth Performance of Broiler Chicken Lines

Marker-assisted selection based on fast and accurate molecular analysis of individual genes is considered an acceptable tool in the speed-up of the genetic improvement of production performance in chickens. The objective of this study was to detect the single nucleotide polymorphisms (SNPs) in the IGF1, IGFBP2 and TGFß3 genes, and to investigate their associations with growth performance (body weight (BW) and average daily gain (ADG) at 14, 21, 28, 35 and 42 days of age) and carcass traits in broilers. Performance (carcass) data (weight before slaughter; weights of the trunk, giblets, abdominal fat, breast muscle and thigh muscle; slaughter value and slaughter percentage), as well as blood samples for DNA extraction and SNP analysis, were obtained from 97 chickens belonging to two different lines (Hubbard F15 and Cobb E) equally divided between the two sexes. The genotypes were detected using polymerase chain reaction- restriction fragment length polymorphism (PCR-RFLP) methods with specific primers and restrictase for each gene. The statistical analysis discovered significant associations (p < 0.05) between the TGFβ3 SNP and the following parameters: BW at 21, 28 and 35 days, trunk weight and slaughter value. Association analysis of BWs (at 21, 28 and 35 days) and SNPs was always significant for codominant, dominant and overdominant genetic models, showing a possible path for genomic selection in these chicken lines. Slaughter value was significant for codominant, recessive and overdominant patterns, whereas other carcass traits were not influenced by SNPs. Based on the results of this study, we suggested that the TGFβ3 gene could be used as a candidate gene marker for chicken growth traits in the Hubbard F15 and Cobb E population selection programs, whereas for carcass traits further investigation is needed.

Jdp2-deficient granule cell progenitors in the cerebellum are resistant to ROS-mediated apoptosis through xCT/Slc7a11 activation

The Jun dimerization protein 2 (Jdp2) is expressed predominantly in granule cell progenitors (GCPs) in the cerebellum, as was shown in Jdp2-promoter-Cre transgenic mice. Cerebellum of Jdp2-knockout (KO) mice contains lower number of Atoh-1 positive GCPs than WT. Primary cultures of GCPs from Jdp2-KO mice at postnatal day 5 were more resistant to apoptosis than GCPs from wild-type mice. In Jdp2-KO GCPs, the levels of both the glutamate‒cystine exchanger Sc7a11 and glutathione were increased; by contrast, the activity of reactive oxygen species (ROS) was decreased; these changes confer resistance to ROS-mediated apoptosis. In the absence of Jdp2, a complex of the cyclin-dependent kinase inhibitor 1 (p21^Cip1) and Nrf2 bound to antioxidant response elements of the Slc7a11 promoter and provide redox control to block ROS-mediated apoptosis. These findings suggest that an interplay between Jdp2, Nrf2, and p21^Cip1 regulates the GCP apoptosis, which is one of critical events for normal development of the cerebellum.

Anti-Apoptotic Effects of Diosgenin in D-Galactose-Induced Aging Brain

The purpose of this study was to evaluate the effects of diosgenin on the D-galactose-induced cerebral cortical widely dispersed apoptosis. Male 12-week-old Wistar rats were divided into four groups: Control (1mg/kg/day of saline, i.p.), DD0 (150mg/kg/day of D-galactose, i.p.), DD10, and DD50 (D-galactose+10 or 50mg/kg/day of diosgenin orally). After eight weeks, histopathological analysis, positive TUNEL and Western blotting assays were performed on the excised cerebral cortex from all four groups. The TUNEL-positive apoptotic cells, the components of Fas pathway (Fas, FADD, active caspase-8 and active caspase-3), and mitochondria pathway (t-Bid, Bax, cytochrome c, active caspase-9 and active caspase-3) were increased in the DD0 group compared with the control group, whereas they were decreased in the DD50 group. The components of survival pathway (p-Bad, Bcl-2, Bcl-xL, IGF-1, p-PI3K and p-AKT) were increased in the DD50 group compared to the control group, whereas the levels of Bcl-xL, p-PI3K, and p-AKT were also compensatorily increased in the DD0 group compared to the control group. Taken together, diosgenin suppressed D-galactose-induced neuronal Fas-dependent and mitochondria-dependent apoptotic pathways and enhanced the Bcl-2 family associated pro-survival and IGF-1-PI3K-AKT survival pathways, which might provide neuroprotective effects of diosgenin for prevention of the D-galactose-induced aging brain.

Artemin and an Artemin-Derived Peptide, Artefin, Induce Neuronal Survival, and Differentiation Through Ret and NCAM

Artemin (ARTN) is a neurotrophic factor from the GDNF family ligands (GFLs) that is involved in development of the nervous system and neuronal differentiation and survival. ARTN signals through a complex receptor system consisting of the RET receptor tyrosine kinase and a glycosylphosphatidylinositol-anchored co-receptor GFL receptor α, GFRα3. We found that ARTN binds directly to neural cell adhesion molecule (NCAM) and that ARTN-induced neuritogenesis requires NCAM expression and activation of NCAM-associated signaling partners, thus corroborating that NCAM is an alternative receptor for ARTN. We designed a small peptide, artefin, that could interact with GFRα3 and demonstrated that this peptide agonist induces RET phosphorylation and mimics the biological functions of ARTN – neuroprotection and neurite outgrowth. Moreover, artefin mimicked the binding of ARTN to NCAM and required NCAM expression and activation for its neurite elongation effect, thereby suggesting that artefin represents a binding site for NCAM within ARTN. We showed that biological effects of ARTN and artefin can be inhibited by abrogation of both NCAM and RET, suggesting a more complex signaling mechanism that previously thought. As NCAM plays a significant role in neurodevelopment, regeneration, and synaptic plasticity we suggest that ARTN and its mimetics are promising candidates for treatment of neurological disorders and warrant further investigations.

The insulin-like growth factor system in multiple myeloma: diagnostic and therapeutic potential

Multiple myeloma (MM) is a highly heterogeneous plasma cell malignancy. The MM cells reside in the bone marrow (BM), where reciprocal interactions with the BM niche foster MM cell survival, proliferation, and drug resistance. As in most cancers, the insulin-like growth factor (IGF) system has been demonstrated to play a key role in the pathogenesis of MM. The IGF system consists of IGF ligands, IGF receptors, IGF binding proteins (IGFBPs), and IGFBP proteases and contributes not only to the survival, proliferation, and homing of MM cells, but also MM-associated angiogenesis and osteolysis. Furthermore, increased IGF-I receptor (IGF-IR) expression on MM cells correlates with a poor prognosis in MM patients. Despite the prominent role of the IGF system in MM, strategies targeting the IGF-IR using blocking antibodies or small molecule inhibitors have failed to translate into the clinic. However, increasing preclinical evidence indicates that IGF-I is also involved in the development of drug resistance against current standard-of-care agents against MM, including proteasome inhibitors, immunomodulatory agents, and corticoids. IGF-IR targeting has been able to overcome or revert this drug resistance in animal models, enhancing the efficacy of standard-of-care agents. This finding has generated renewed interest in the therapeutic potential of IGF-I targeting in MM. The present review provides an update of the impact of the different IGF system components in MM and discusses the diagnostic and therapeutic potentials.

Neuronal survival in the brain: neuron type-specific mechanisms

Neurogenic regions of mammalian brain produce many more neurons that will eventually survive and reach a mature stage. Developmental cell death affects both embryonically produced immature neurons and those immature neurons that are generated in regions of adult neurogenesis. Removal of substantial numbers of neurons that are not yet completely integrated into the local circuits helps to ensure that maturation and homeostatic function of neuronal networks in the brain proceed correctly. External signals from brain microenvironment together with intrinsic signaling pathways determine whether a particular neuron will die. To accommodate this signaling, immature neurons in the brain express a number of transmembrane factors as well as intracellular signaling molecules that will regulate the cell survival/death decision, and many of these factors cease being expressed upon neuronal maturation. Furthermore, pro-survival factors and intracellular responses depend on the type of neuron and region of the brain. Thus, in addition to some common neuronal pro-survival signaling, different types of neurons possess a variety of 'neuron type-specific' pro-survival constituents that might help them to adapt for survival in a certain brain region. This review focuses on how immature neurons survive during normal and impaired brain development, both in the embryonic/neonatal brain and in brain regions associated with adult neurogenesis, and emphasizes neuron type-specific mechanisms that help to survive for various types of immature neurons. Importantly, we mainly focus on in vivo data to describe neuronal survival specifically in the brain, without extrapolating data obtained in the PNS or spinal cord, and thus emphasize the influence of the complex brain environment on neuronal survival during development.

Insulin-Like Growth Factor 1: At the Crossroads of Brain Development and Aging

Insulin-like growth factor 1 (IGF1) is a polypeptide hormone structurally similar to insulin. It is central to the somatotropic axis, acting downstream of growth hormone (GH). It activates both the mitogen-activated protein (MAP) kinase and PI3K signaling pathways, acting in almost every tissue in the body to promote tissue growth and maturation through upregulation of anabolic processes. Overall GH and IGF1 signaling falls with age, suggesting that it is this reduced IGF1 activity that leads to age-related changes in organisms. However, mutations that reduce IGF1-signaling activity can dramatically extend the lifespan of organisms. Therefore, the role of IGF1 in the overall aging process is unclear. This review article will focus on the role of IGF1 in brain development and aging. The evidence points towards a role for IGF1 in neurodevelopment both prenatally and in the early post-natal period, and in plasticity and remodeling throughout life. This review article will then discuss the hallmarks of aging and cognitive decline associated with falls in IGF1 levels towards the end of life. Finally, the role of IGF1 will be discussed within the context of both neuropsychiatric disorders caused by impaired development of the nervous system, and neurodegenerative disorders associated with aging. IGF1 and its derivatives are shown to improve the symptoms of certain neuropsychiatric disorders caused by deranged neurodevelopment and these effects have been correlated with changes in the underlying biology in both in vitro and in vivo studies. On the other hand, studies looking at IGF1 in neurodegenerative diseases have been conflicting, supporting both a role for increased and decreased IGF1 signaling in the underlying pathogenesis of these diseases.

Delineating the factors and cellular mechanisms involved in the survival of cerebellar granule neurons

Cerebellar granule neurons (CGNs) constitute the most abundant neuronal population in the mammalian brain. Their postnatal generation and the feasibility to induce their apoptotic death in vitro make them an excellent model to study the effect of several neurotransmitters and neurotrophins. Here, we first review which factors are involved in the generation and proliferation of CGNs in the external granule layer (EGL) and in the regulation of their differentiation and migration to internal granule layer (IGL). Special attention was given to the role of several neurotrophins and the NMDA subtype of glutamate receptor. Then, using the paradigm of potassium deprivation in cultured CGNs, we address several extracellular factors that promote the survival of CGNs, with particular emphasis on the cellular mechanisms. The role of specific protein kinases leading to the regulation of transcription factors and recent data involving the small G protein family is also discussed. Finally, the participation of some members of Bcl-2 family and the inhibition of mitochondria-related apoptotic pathway is also considered. Altogether, these studies evidence that CGNs are a key model to understand the development and the survival of neuronal populations.

The role of selenium in insulin-like growth factor I receptor (IGF-IR) expression and regulation of apoptosis in mouse osteoblasts

Selenium (Se) is an essential component for animals and human beings. The chemoprotective role of Se, via the regulation of the cell cycle, stimulation of apoptosis and activation of some cytokines among others, is well known; however, the comprehensive effects of Se on the expression of IGF-IR and its regulation of apoptosis have not been investigated. Thus the aim of this study was to report on the effects that different concentrations of Se extert on body weight, blood serum IGF-IR levels and histopathology in mice; and on IGF-IR expression, proliferation and apoptosis in mouse osteoblasts. In vivo experiments showed a significant decrease in body weight, serum levels of IGF-IR and prominent toxicant effects on the liver, kidney, heart and spleen following the administration of defined concentrations of Se for 30 d. However, moderate levels (0.1 mg/kg) of Se gradually improved weight and serum IGF-IR. In vitro osteoblast experiments revealed that at concentrations of 5 × 10(-6) and 10(-5) mol/L Se, MTT activity decreased in comparison with control cells. Cell cycle, TEM and caspase-3 activity supported these observations including an increase in the sub-G1 phase and notable apoptosis in osteoblasts, along with a decrease in the expression of mRNA and protein levels of IGF-IR. Moreover, the MTT activity, mRNA and protein levels of IGF-IR in osteoblasts were decreased and caspase-3 activity was increased in siRNA groups as compared with non-siRNA groups. These data suggest that Se significantly affects IGF-IR expression, and that it contributes to the proliferation and regulation of apoptosis in osteoblasts.

Estrogen Receptor-β Up-Regulates IGF1R Expression and Activity to Inhibit Apoptosis and Increase Growth of Medulloblastoma

Medulloblastoma (Med) is the most common malignant brain tumor in children. The role of ESR2 [estrogen receptor (ER)-β] in promoting Med growth was comprehensively examined in three in vivo models and human cell lines. In a novel Med ERβ-null knockout model developed by crossing Esr2(-/-) mice with cerebellar granule cell precursor specific Ptch1 conditional knockout mice, the tumor growth rate was significantly decreased in males and females. The absence of Esr2 resulted in increased apoptosis, decreased B-cell lymphoma 2 (BCL2), and IGF-1 receptor (IGF1R) expression, and decreased levels of active MAPKs (ERK1/2) and protein kinase B (AKT). Treatment of Med in Ptch1(+/-) Trp53(-/-) mice with the antiestrogen chemotherapeutic drug Faslodex significantly increased symptom-free survival, which was associated with increased apoptosis and decreased BCL2 and IGF1R expression and signaling. Similar effects were also observed in nude mice bearing D283Med xenografts. In vitro studies in human D283Med cells metabolically stressed by glutamine withdrawal found that 17β-estradiol and the ERβ selective agonist 2,3-bis(4-hydroxyphenyl)-propionitrile dose dependently protected Med cells from caspase-3-dependent cell death. Those effects were associated with increased phosphorylation of IGF1R, long-term increases in ERK1/2 and AKT signaling, and increased expression of IGF-1, IGF1R, and BCL2. Results of pharmacological experiments revealed that the cytoprotective actions of estradiol were dependent on ERβ and IGF1R receptor tyrosine kinase activity and independent of ERα and G protein-coupled estrogen receptor 1 (G protein coupled receptor 30). The presented results demonstrate that estrogen promotes Med growth through ERβ-mediated increases in IGF1R expression and activity, which induce cytoprotective mechanisms that decrease apoptosis.

Effects of Microglia on Neurogenesis

This review summarizes and organizes the literature concerning the effects of microglia on neurogenesis, particularly focusing on the subgranular zone (SGZ) of the hippocampus and subventricular zone (SVZ) of the lateral ventricles, in which the neurogenic potential is progressively restricted during the life of the organism. A comparison of microglial roles in neurogenesis in these two regions indicates that microglia regulate neurogenesis in a temporally and spatially specific manner. Microglia may also sense signals from the surrounding environment and have regulatory effects on neurogenesis. We speculate microglia function as a hub for the information obtained from the inner and outer brain regions for regulating neurogenesis.

Insulin-like growth factor system in cancer: novel targeted therapies

Insulin-like growth factors (IGFs) are essential for growth and survival that suppress apoptosis and promote cell cycle progression, angiogenesis, and metastatic activities in various cancers. The IGFs actions are mediated through the IGF-1 receptor that is involved in cell transformation induced by tumour. These effects depend on the bioavailability of IGFs, which is regulated by IGF binding proteins (IGFBPs). We describe here the role of the IGF system in cancer, proposing new strategies targeting this system. We have attempted to expand the general viewpoint on IGF-1R, its inhibitors, potential limitations of IGF-1R, antibodies and tyrosine kinase inhibitors, and IGFBP actions. This review discusses the emerging view that blocking IGF via IGFBP is a better option than blocking IGF receptors. This can lead to the development of novel cancer therapies.

The (Na(+)/K (+))-ATPase activity in the developing rat retina: the role of insulin-like growth factor-I (IGF-I)

In this work, the (Na(+)/K(+))-ATPase activity was evaluated during the early stages of the postnatal development of rat retina and showed an almost three-time increase from P0 to P14. Expression of the three catalytic subunit isoforms (α1, α2, and α3) of the (Na(+)/K(+))-ATPase was also evaluated by immunoblot in the same period, but no correlation to the catalytic activity increment was observed. On the other hand, immunolocalization of these three α-catalytic isoforms in the developing retina showed an age-related pattern. Involvement of IGF-I in the stimulation of the (Na(+)/K(+))-ATPase was investigated. Our results demonstrate that the exogenous IGF-I (10 ng/mL) stimulates enzyme activity at the age of P7 only. Incubation of retinas with 10 μM I-OMe-AG 538 (inhibitor of the IGF-I receptor) indicates that the basal (Na(+)/K(+))-ATPase activity is sustained by endogenous IGF-I in P7 animals. These data were corroborated by an age-dependent decrease in the immunodetection of endogenous IGF-I as well as in the phosphorylation level of its cognate receptor in rat retina homogenates. The signaling pathway involved in IGF-I-induced modulation of the (Na(+)/K(+))-ATPase was also investigated. Our data show that the inhibitory effects induced by I-OMe-AG 538 and the PI 3-kinase inhibitor Ly 294002 on the basal (Na(+)/K(+))-ATPase activity were non-cumulative. Furthermore, IGF-I induced phosphorylation of PKB in a Ly 294002-sensitive manner. Together, these data demonstrate that the PI 3-kinase/PKB signaling pathway is involved in the IGF-I-sustained basal (Na(+)/K(+))-ATPase activity during the first 7 days of the postnatal development of rat retina.

The effect of hemorrhage on the development of the postnatal mouse cerebellum

Recent studies have shown that hemorrhagic injury in the preterm cerebellum leads to long-term neurological sequelae, such as motor, affective, and cognitive dysfunction. How cerebellar hemorrhage (CBH) affects the development and function of the cerebellum is largely unknown. Our study focuses on developing a mouse model of CBH to determine the anatomical, behavioral, and molecular phenotypes resulting from a hemorrhagic insult to the developing cerebellum. To induce CBH in the postnatal mouse cerebellum, we injected bacterial collagenase, which breaks down surrounding blood vessel walls, into the fourth ventricle at postnatal day two. We found a reduction in cerebellar size during postnatal growth, a decrease in granule cells, and persistent neurobehavioural abnormalities similar to abnormalities reported in preterm infants with CBH. We further investigated the molecular pathways that may be perturbed due to postnatal CBH and found a significant upregulation of genes in the inflammatory and sonic hedgehog pathway. These results point to an activation of endogenous mechanisms of injury and neuroprotection in response to postnatal CBH. Our study provides a preclinical model of CBH that may be used to understand the pathophysiology of preterm CBH and for potential development of preventive therapies and treatments.

The frontal cortex IGF system is down regulated in the term, intrauterine growth restricted fetal baboon

OBJECTIVE

The IGF system exerts systemic and local actions during development. We previously demonstrated that fetal cerebral cortical IGF1 is reduced at 0.5 gestation in our IUGR baboon nonhuman primate model. We hypothesized that by term protein expression of several key IGF system stimulatory peptide pathway components and downstream nutrient signaling effectors of IGF, mammalian target of rapamycin (mTOR) and S6, would decrease, indicating reduced cellular nutrient uptake and protein synthesis.

DESIGN

We fed 7 control baboons ad libitum while 6 baboons ate a globally reduced diet (70% of feed eaten by controls) from 0.16 gestation through pregnancy that produces IUGR. Fetuses were removed at Cesarean section at 0.9 gestation. Frontal cortex sections were stained for IGFI, IGFII, IGFRI, IGFR2, IGFBP2, 3, 5 and 6, and mTOR and ribosomal protein S6 and double stained with NeuN a neuron-specific nuclear antigen.

RESULTS

All proteins stained neuronal cytoplasm except IGFRI which showed only glial cell cytoplasmic and blood vessel staining. IUGR fetuses showed decreased frontal cortical immunoreactive IGFI, IGFII, IGFRI, IGFBP2, 5 and 6, and mTOR and S6 (p < 0.05). IGFBP3 increased (p < 0.05) and IGFR2 was unchanged (p > 0.05). There were no differences between male and female fetal brains.

CONCLUSIONS

When fetal nutrient availability is decreased, IUGR down regulates the IGF system and its mTOR signaling pathway in the fetal frontal cortex coincident with slowed growth. These findings emphasize the importance of the local tissue IGF system in fetal primate brain development.

The effects of induced type-I diabetes on developmental regulation of insulin & insulin like growth factor-1 (IGF-1) receptors in the cerebellum of rat neonates

Diabetes during pregnancy impairs brain development in offspring, leading to behavioral problems, motor dysfunction and learning deficits. Insulin and insulin-like growth factor-1 (IGF-1) are important regulators of developmental and cognitive functions in the central nervous system. Aim of the present study was to examine the effects of maternal diabetes on insulin receptor (InsR) and IGF-1 receptor (IGF-1R) expression in the developing rat cerebellum. Wistar female rats were maintained diabetic from a week before pregnancy through parturition and male offspring was killed at P0, P7, and P14, an active neurogenesis period in brain development equivalent to the third trimester in human. The expression of InsR and IGF-1R in cerebelli was evaluated using real-time PCR and western blot analysis. We found a significant upregulation of both IGF-1R and InsR transcripts in cerebellum of pups born to diabetic mothers at P0, compared to controls. However, at the same time point, the results of western blot analysis revealed only a slight change in their protein levels. In contrast to InsR, which does not show any difference, there was a markedly reduction in cerebellar expression of IGF-1R mRNA and protein level in the diabetic group of newborns at P7. Moreover, 2 weeks after birth, mRNA expression and protein levels of both InsR and IGF-1R in cerebellum of the diabetic group was significantly downregulated. Compared to controls, we did not find any difference in cerebellar InsR or IGF-1R mRNA and protein levels in the insulin treated group. The present study revealed that diabetes during pregnancy strongly influences the regulation of both InsR and IGF-1R in the developing cerebellum. Furthermore, optimal maternal glycaemia control by insulin administration normalized these effects.

Sexual dimorphism in expression of insulin and insulin-like growth factor-I receptors in developing rat cerebellum

The insulin and insulin-like growth factor-1 (IGF-1) are considered to play important roles in brain development; and their cognate receptors -InsR and IGF-1R- localized within distinct brain regions including cerebellum. Using Real-Time PCR and western blot analysis, we compared the expression of InsR and IGF-1R in male and female developing rat cerebellum at P0, P7, and P14. At all time points studied, the cerebellar expression of IGF-1R, both at mRNA and protein levels was higher than that of InsR. The lowest InsR and IGF-1R mRNA and protein levels were measured in the neonate cerebellum, independent of gender. In males, the highest InsR and IGF-1R mRNA and protein expression were found at P7. InsR and IGF-1R expression increased significantly between P0 and P7, followed by a marked downregulation at P14. In contrast, in females, mRNA and protein levels of InsR and IGF-1R remain unchanged between P0 and P7, and are upregulated at P14. Therefore, peaked InsR and IGF-1R expression in female cerebelli occurred at P14. Interestingly, changes in mRNA expression and in protein levels followed the same developmental pattern, indicating that InsR and IGF-1R transcription is not subject to modulatory effects during the first 2 weeks of development. These findings indicate that there are prominent sexual differences in InsR and IGF-1R expression in the developing rat cerebellum, suggesting a probable mechanism for the control of gender differences in development and function of the cerebellum.

miR-296-3p, miR-298-5p and their downstream networks are causally involved in the higher resistance of mammalian pancreatic α cells to cytokine-induced apoptosis as compared to β cells

Background

The molecular bases of mammalian pancreatic α cells higher resistance than β to proinflammatory cytokines are very poorly defined. MicroRNAs are master regulators of cell networks, but only scanty data are available on their transcriptome in these cells and its alterations in diabetes mellitus.

Results

Through high-throughput real-time PCR, we analyzed the steady state microRNA transcriptome of murine pancreatic α (αTC1-6) and β (βTC1) cells: their comparison demonstrated significant differences. We also characterized the alterations of αTC1-6 cells microRNA transcriptome after treatment with proinflammatory cytokines. We focused our study on two microRNAs, miR-296-3p and miR-298-5p, which were: (1) specifically expressed at steady state in αTC1-6, but not in βTC1 or INS-1 cells; (2) significantly downregulated in αTC1-6 cells after treatment with cytokines in comparison to untreated controls. These microRNAs share more targets than expected by chance and were co-expressed in αTC1-6 during a 6–48 h time course treatment with cytokines. The genes encoding them are physically clustered in the murine and human genome. By exploiting specific microRNA mimics, we demonstrated that experimental upregulation of miR-296-3p and miR-298-5p raised the propensity to apoptosis of transfected and cytokine-treated αTC1-6 cells with respect to αTC1-6 cells, treated with cytokines after transfection with scramble molecules. Both microRNAs control the expression of IGF1Rβ, its downstream targets phospho-IRS-1 and phospho-ERK, and TNFα. Our computational analysis suggests that MAFB (a transcription factor exclusively expressed in pancreatic α cells within adult rodent islets of Langerhans) controls the expression of miR-296-3p and miR-298-5p.

Conclusions

Altogether, high-throughput microRNA profiling, functional analysis with synthetic mimics and molecular characterization of modulated pathways strongly suggest that specific downregulation of miR-296-3p and miR-298-5p, coupled to upregulation of their targets as IGF1Rβ and TNFα, is a major determinant of mammalian pancreatic α cells resistance to apoptosis induction by cytokines.

Human conditions of insulin-like growth factor-I (IGF-I) deficiency

Insulin-like growth factor I (IGF-I) is a polypeptide hormone produced mainly by the liver in response to the endocrine GH stimulus, but it is also secreted by multiple tissues for autocrine/paracrine purposes. IGF-I is partly responsible for systemic GH activities although it possesses a wide number of own properties (anabolic, antioxidant, anti-inflammatory and cytoprotective actions). IGF-I is a closely regulated hormone. Consequently, its logical therapeutical applications seems to be limited to restore physiological circulating levels in order to recover the clinical consequences of IGF-I deficiency, conditions where, despite continuous discrepancies, IGF-I treatment has never been related to oncogenesis. Currently the best characterized conditions of IGF-I deficiency are Laron Syndrome, in children; liver cirrhosis, in adults; aging including age-related-cardiovascular and neurological diseases; and more recently, intrauterine growth restriction. The aim of this review is to summarize the increasing list of roles of IGF-I, both in physiological and pathological conditions, underlying that its potential therapeutical options seem to be limited to those proven states of local or systemic IGF-I deficiency as a replacement treatment, rather than increasing its level upper the normal range.

Neurodevelopmental effects of insulin-like growth factor signaling

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

Signalling through the type 1 insulin-like growth factor receptor (IGF1R) interacts with canonical Wnt signalling to promote neural proliferation in developing brain

Signalling through the IGF1R [type 1 IGF (insulin-like growth factor) receptor] and canonical Wnt signalling are two signalling pathways that play critical roles in regulating neural cell generation and growth. To determine whether the signalling through the IGF1R can interact with the canonical Wnt signalling pathway in neural cells in vivo, we studied mutant mice with altered IGF signalling. We found that in mice with blunted IGF1R expression specifically in nestin-expressing neural cells (IGF1R^Nestin−KO mice) the abundance of neural β-catenin was significantly reduced. Blunting IGF1R expression also markedly decreased: (i) the activity of a LacZ (β-galactosidase) reporter transgene that responds to Wnt nuclear signalling (LacZ^TCF reporter transgene) and (ii) the number of proliferating neural precursors. In contrast, overexpressing IGF-I (insulin-like growth factor I) in brain markedly increased the activity of the LacZ^TCF reporter transgene. Consistently, IGF-I treatment also markedly increased the activity of the LacZ^TCF reporter transgene in embryonic neuron cultures that are derived from LacZ^TCF Tg (transgenic) mice. Importantly, increasing the abundance of β-catenin in IGF1R^Nestin−KO embryonic brains by suppressing the activity of GSK3β (glycogen synthase kinase-3β) significantly alleviated the phenotypic changes induced by IGF1R deficiency. These phenotypic changes includes: (i) retarded brain growth, (ii) reduced precursor proliferation and (iii) decreased neuronal number. Our current data, consistent with our previous study of cultured oligodendrocytes, strongly support the concept that IGF signalling interacts with canonical Wnt signalling in the developing brain to promote neural proliferation. The interaction of IGF and canonical Wnt signalling plays an important role in normal brain development by promoting neural precursor proliferation.

Sodium fluoride affects proliferation and apoptosis through insulin-like growth factor I receptor in primary cultured mouse osteoblasts

Insulin-like growth factor-I receptor (IGF-IR) is important for maintaining proliferation and apoptosis in osteoblasts. However, the details about the effect of sodium fluoride supplementation on primary osteoblast cultures on mediating IGF-IR expression are still not well-known. In this study, we used mouse osteoblasts to examine the impact of sodium fluoride on the proliferation and apoptosis; the cells were treated with IGF-IR small interfering RNA (or left untreated) and subsequently divided into a control group and six experimental groups, which were exposed to different concentrations of NaF (10(-6), 10(-5), 10(-4), 10(-3), 5 × 10(-3), and 10(-2) mol/L) for analysis at 48 h. In particular, we examined cell proliferation, apoptosis, IGF-IR messenger RNA, and protein expression levels of the various cell groups. In summary, our findings suggest that the administration of NaF affects the expression of IGF-IR in mouse osteoblasts, contributing to the proliferation and apoptosis induced by fluoride.

Gene expression profiling of preovulatory follicle in the buffalo cow: effects of increased IGF-I concentration on periovulatory events

The preovulatory follicle in response to gonadotropin surge undergoes dramatic biochemical, and morphological changes orchestrated by expression changes in hundreds of genes. Employing well characterized bovine preovulatory follicle model, granulosa cells (GCs) and follicle wall were collected from the preovulatory follicle before, 1, 10 and 22 h post peak LH surge. Microarray analysis performed on GCs revealed that 450 and 111 genes were differentially expressed at 1 and 22 h post peak LH surge, respectively. For validation, qPCR and immunocytochemistry analyses were carried out for some of the differentially expressed genes. Expression analysis of many of these genes showed distinct expression patterns in GCs and the follicle wall. To study molecular functions and genetic networks, microarray data was analyzed using Ingenuity Pathway Analysis which revealed majority of the differentially expressed genes to cluster within processes like steroidogenesis, cell survival and cell differentiation. In the ovarian follicle, IGF-I is established to be an important regulator of the above mentioned molecular functions. Thus, further experiments were conducted to verify the effects of increased intrafollicular IGF-I levels on the expression of genes associated with the above mentioned processes. For this purpose, buffalo cows were administered with exogenous bGH to transiently increase circulating and intrafollicular concentrations of IGF-I. The results indicated that increased intrafollicular concentrations of IGF-I caused changes in expression of genes associated with steroidogenesis (StAR, SRF) and apoptosis (BCL-2, FKHR, PAWR). These results taken together suggest that onset of gonadotropin surge triggers activation of various biological pathways and that the effects of growth factors and peptides on gonadotropin actions could be examined during preovulatory follicle development.

Postnatal decrease in circulating insulin-like growth factor-I and low brain volumes in very preterm infants

CONTEXT

IGF-I and IGF binding protein-3 (IGFBP-3) are essential for growth and maturation of the developing brain.

OBJECTIVE

The aim of this study was to evaluate the association between postnatal serum concentrations of IGF-I and IGFBP-3 and brain volumes at term in very preterm infants.

DESIGN

Fifty-one infants with a mean (sd) gestational age (GA) of 26.4 (1.9) wk and birth weight (BW) of 888 (288) g were studied, with weekly blood sampling of IGF-I and IGFBP-3 from birth until 35 gestational weeks (GW) and daily calculation of protein and caloric intake. Magnetic resonance images obtained at 40 GW were segmented into total brain, cerebellar, cerebrospinal fluid, gray matter, and unmyelinated white matter volumes.

MAIN OUTCOME MEASURES

We evaluated brain growth by measuring brain volumes using magnetic resonance imaging.

RESULTS

Mean IGF-I concentrations from birth to 35 GW correlated with total brain volume, unmyelinated white matter volume, gray matter volume, and cerebellar volume [r = 0.55 (P < 0.001); r = 0.55 (P < 0.001); r = 0.44 (P = 0.002); and r = 0.58 (P < 0.001), respectively]. Similar correlations were observed for IGFBP-3 concentrations. Correlations remained after adjustment for GA, mean protein and caloric intakes, gender, severe brain damage, and steroid treatment. Protein and caloric intakes were not related to brain volumes. Infants with BW small for GA had lower mean concentrations of IGF-I (P = 0.006) and smaller brain volumes (P = 0.001-0.013) than infants with BW appropriate for GA.

CONCLUSION

Postnatal IGF-I and IGFBP-3 concentrations are positively associated with brain volumes at 40 GW in very preterm infants. Normalization of the IGF-I axis, directly or indirectly, may support normal brain development in very preterm infants.

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.

beta-catenin mediates insulin-like growth factor-I actions to promote cyclin D1 mRNA expression, cell proliferation and survival in oligodendroglial cultures

By promoting cell proliferation, survival and maturation insulin-like growth factor (IGF)-I is essential to the normal growth and development of the central nervous system. It is clear that IGF-I actions are primarily mediated by the type I IGF receptor (IGF1R), and that phosphoinositide 3 (PI3)-Akt kinases and MAP kinases signal many of IGF-I-IGF1R actions in neural cells, including oligodendrocyte lineage cells. The precise downstream targets of these signaling pathways, however, remain to be defined. We studied oligodendroglial cells to determine whether beta-catenin, a molecule that is a downstream target of glycogen synthase kinase-3beta (GSK3beta) and plays a key role in the Wnt canonical signaling pathway, mediates IGF-I actions. We found that IGF-I increases beta-catenin protein abundance within an hour after IGF-I-induced phosphorylation of Akt and GSK3beta. Inhibiting the PI3-Akt pathway suppressed IGF-I-induced increases in beta-catenin and cyclin D1 mRNA, while suppression of GSK3beta activity simulated IGF-I actions. Knocking-down beta-catenin mRNA by RNA interference suppressed IGF-I-stimulated increases in the abundance of cyclin D1 mRNA, cell proliferation, and cell survival. Our data suggest that beta-catenin is an important downstream molecule in the PI3-Akt-GSK3beta pathway, and as such it mediates IGF-I upregulation of cyclin D1 mRNA and promotion of cell proliferation and survival in oligodendroglial cells.

Insulin-like growth factor-I-stimulated Akt phosphorylation and oligodendrocyte progenitor cell survival require cholesterol-enriched membranes

Previously we showed that insulin-like growth factor-I (IGF-I) promotes sustained phosphorylation of Akt in oligodendrocyte progenitor cells (OPCs) and that Akt phosphorylation is required for survival of these cells. The direct mechanisms, however, by which IGF-I promotes Akt phosphorylation are currently undefined. Recently, cholesterol-enriched membranes (CEMs) have been implicated in regulation of growth factor-mediated activation of the PI3K/Akt pathway and survival of mature oligodendrocytes; however, less is know about their role in OPC survival. In the present study, we investigate the role of CEMs in IGF-I-mediated Akt phosphorylation and OPC survival. We report that acute disruption of membrane cholesterol with methyl-beta-cyclodextrin results in altered OPC morphology and inhibition of IGF-I-mediated Akt phosphorylation. We also report that long-term inhibition of cholesterol biosynthesis with 25-hydroxycholesterol blocks IGF-I stimulated Akt phosphorylation and cell survival. Moreover, we show that the PI3K regulatory subunit, p85, Akt, and the IGF-IR are sequestered within cholesterol-enriched fractions in steady-state stimulation of the IGF-IR and that phosphorylated Akt and IGF-IR are present in cholesterol-enriched fractions with IGF-I stimulation. Together, the results of these studies support a role for CEMs or "lipid rafts" in IGF-I-mediated Akt phosphorylation and provide a better understanding of the mechanisms by which IGF-I promotes OPC survival.

Type 1 insulin-like growth factor receptor signaling is essential for the development of the hippocampal formation and dentate gyrus

Type 1 insulin-like growth factor receptor (IGF1R) signaling in neuronal development was studied in mutant mice with blunted igf1r gene expression in nestin-expressing neuronal precursors. At birth [postnatal (P) day 0] brain weights were reduced to 37% and 56% of controls in mice homozygous (nes-igf1r(-/-)) and heterozygous (nes-igf1r(-/Wt)) for the null mutation, respectively, and this brain growth retardation persisted postnatally. Stereological analysis demonstrated that the volumes of the hippocampal formation, CA fields 1-3, dentate gyrus (DG), and DG granule cell layer (GCL) were decreased by 44-54% at P0 and further by 65-69% at P90 in nes-igf1r(-/Wt) mice. In nes-igf1r(-/-) mice, volumes were 29-31% of controls at P0 and, in the two mice that survived to P90, 6-19% of controls, although the hilus could not be identified. Neuron density did not differ among the mice at any age studied; therefore, decreased volumes were due to reduced cell number. In postnatal nes-igf1r(-/Wt) mice, the percentage of apoptotic cells, as judged by activated caspase-3 immunostaining, was increased by 3.5-5.3-fold. The total number of proliferating DG progenitors (labeled by BrdU incorporation and Ki67 staining) was reduced by approximately 50%, but the percentage of these cells was similar to the percentages in littermate controls. These findings suggest that 1) the postnatal reduction in DG size is due predominantly to cell death, pointing to the importance of the IGF1R in regulating postnatal apoptosis, 2) surviving DG progenitors remain capable of proliferation despite reduced IGF1R expression, and 3) IGF1R signaling is necessary for normal embryonic brain development.

Growth factor-dependent trafficking of cerebellar NMDA receptors via protein kinase B/Akt phosphorylation of NR2C

NMDA receptor subunit composition varies throughout the brain, providing molecular diversity in NMDA receptor function. The NR2 subunits (NR2A-D) in large part dictate the distinct functional properties of NMDA receptors and differentially regulate receptor trafficking. Although the NR2C subunit is highly enriched in cerebellar granule cells and plays a unique role in cerebellar function, little is known about NR2C-specific regulation of NMDA receptors. Here, we demonstrate that PKB/Akt directly phosphorylates NR2C on serine 1096 (S1096). In addition, we identify 14-3-3epsilon as an NR2C interactor, whose binding is dependent on S1096 phosphorylation. Both growth factor stimulation and NMDA receptor activity lead to a robust increase in both phosphorylation of NR2C on S1096 and surface expression of cerebellar NMDA receptors. Finally, we find that NR2C expression, unlike NR2A and NR2B, supports neuronal survival. Thus, our data provide a direct mechanistic link between growth factor stimulation and regulation of cerebellar NMDA receptors.

Insulin/IGF-like signalling, the central nervous system and aging

Enormous strides in understanding aging have come from the discovery that mutations in single genes can extend healthy life-span in laboratory model organisms such as the yeast Saccharomyces, the fruit fly Drosophila melanogaster, the nematode worm Caenorhabditis elegans and the mouse. IIS [insulin/IGF (insulin-like growth factor)-like signalling] stands out as an important, evolutionarily conserved pathway involved in the determination of lifespan. The pathway has diverse functions in multicellular organisms, and mutations in IIS can affect growth, development, metabolic homoeostasis, fecundity and stress resistance, as well as lifespan. The pleiotropic nature of the pathway and the often negative effects of its disruption mean that the extent, tissue and timing of IIS manipulations are determinants of a positive effect on lifespan. One tissue of particular importance for lifespan extension in diverse organisms is the CNS (central nervous system). Although lowered IIS in the CNS can extend lifespan, IIS is also widely recognized as being neuroprotective and important for growth and survival of neurons. In the present review, we discuss our current understanding of the role of the nervous system in extension of lifespan by altered IIS, and the role of IIS in determination of neuronal function during aging. The nervous system can play both endocrine and cell-autonomous roles in extension of lifespan by IIS, and the effects of IIS on lifespan and neuronal function can be uncoupled to some extent. Tissue-specific manipulation of IIS and the cellular defence mechanisms that it regulates will better define the ways in which IIS affects neuronal and whole-organism function during aging.

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.

Insulin-like growth factor-I mitigates motor coordination deficits associated with neonatal alcohol exposure in rats

Prenatal alcohol exposure can affect brain development, leading to behavioral problems, including overactivity, motor dysfunction and learning deficits. Despite warnings about the effects of drinking during pregnancy, rates of fetal alcohol syndrome remain unchanged and thus, there is an urgent need to identify interventions that reduce the severity of alcohol's teratogenic effects. Insulin-like growth factor-I (IGF-I) is neuroprotective against ethanol-related toxicity and promotes white matter production following a number of insults. Given that prenatal alcohol leads to cell death and white matter deficits, the present study examined whether IGF-I could reduce the severity of behavioral deficits associated with developmental alcohol exposure. Sprague-Dawley rat pups received ethanol intubations (5.25 g/kg/day) or sham intubations on postnatal days (PD) 4-9, a period of brain development equivalent to the third trimester. On PD 10-13, subjects from each treatment received 0 or 10 microg IGF-I intranasally each day. Subjects were then tested on a series of behavioral tasks including open field activity (PD 18-21), parallel bar motor coordination (PD 30-32) and Morris maze spatial learning (PD 45-52). Ethanol exposure produced overactivity, motor coordination impairments, and spatial learning deficits. IGF-I treatment significantly mitigated ethanol's effects on motor coordination, but not on the other two behavioral tasks. These data indicate that IGF-I may be a potential treatment for some of ethanol's damaging effects, a finding that has important implications for children of women who drink alcohol during pregnancy.

Role of IGF signaling in olfactory sensory map formation and axon guidance

Olfactory neurons project their axons to spatially invariant glomeruli in the olfactory bulb, forming an ordered pattern of innervation comprising the olfactory sensory map. A mirror symmetry exists within this map, such that neurons expressing a given receptor typically project to one glomerulus on the medial face and one glomerulus on the lateral face of the bulb. The mechanisms underlying an olfactory neuron's choice to project medially versus laterally remain largely unknown, however. Here we demonstrate that insulin-like growth factor (IGF) signaling is required for sensory innervation of the lateral olfactory bulb. Mutations that eliminate IGF signaling cause axons destined for targets in the lateral bulb to shift to ectopic sites on the ventral-medial surface. Using primary cultures of olfactory and cerebellar neurons, we further show that IGF is a chemoattractant for axon growth cones. Together these observations reveal a role of IGF signaling in sensory map formation and axon guidance.

Bile salts regulate proliferation and apoptosis of liver cells by modulating the IGF1 system

BACKGROUND

In different cell types, the insulin-like growth factor 1 and its receptor modulate growth, apoptosis and damage repair in cooperation with estrogen receptors.

AIM

To evaluate the involvement of the insulin-like growth factor 1 system and estrogen receptors in bile salts modulation of apoptosis/proliferation of hepatocytes and cholangiocytes. Primary cultures of rat hepatocytes and cholangiocytes were exposed to glycochenodeoxycholate or tauro-CDC in the presence or absence of insulin-like growth factor 1 receptor blocking antibody (alphaIR3), small interfering RNA for insulin-like growth factor 1, 17beta-estradiol or estrogen receptor antagonist (ICI 182,780). Proliferation was evaluated by proliferating cell nuclear antigen Western blot and apoptosis by measuring caspase-3 activity or annexin-V.

RESULTS

In hepatocytes, the insulin-like growth factor 1 receptor blocker enhanced glycochenodeoxycholate-induced apoptosis and caused tauro-CDC to promote apoptosis. 17Beta-estradiol or the estrogen receptor antagonist (ICI 182,780) did not influence the apoptotic effect of glycochenodeoxycholate. In cholangiocytes, both glycochenodeoxycholate and tauro-CDC induced proliferation at 100microM, while they induced apoptosis at 1mM with a more pronounced effect of glycochenodeoxycholate. Apoptosis induced by 1mM glycochenodeoxycholate or tauro-CDC in cholangiocytes was enhanced by blocking insulin-like growth factor 1 receptor or by silencing insulin-like growth factor 1. 17Beta-estradiol counteracts glycochenodeoxycholate-induced cholangiocyte apoptosis by enhancing insulin-like growth factor 1 secretion and activating the insulin-like growth factor 1 system.

CONCLUSIONS

Modulation of the IGF1 system could represent a potential strategy for the management of bile salts-induced liver injury.

The insulin-like growth factor system and the fetal brain: effects of poor maternal nutrition

The insulin-like growth factor (IGF) signaling system plays indispensable roles in pre- and post-natal brain growth and development. A large body of studies using both in vivo null mutant and transgenic mice and in vitro neuronal culture techniques indicate that IGF-I acts directly on the brain while IGF-II effects are mediated to a large extent by IGF-II control of placental growth. It appears that all of the mechanisms, except migration, that are involved in normal brain development, e.g., proliferation, apoptosis, maturation and differentiation, are influenced by IGF-I. While IGF system members are produced in the brain, recent reports in post-natal animals indicate that normal brain health and function are dependent upon transfer of circulating IGF-I from the liver and its transfer across the blood brain barrier. Data showing that this phenomenon applies to pre-natal brain growth and development would make an important contribution to fetal physiology. A number of kinase pathways are able to participate in IGF signaling in brain with respect to nutrient restriction; among the most important are the PI3K/AKT, Ras-Raf-MEK-ERK and mTOR-nutrient sensing pathways. Both maternal and fetal IGF-I peripheral plasma concentrations are greatly reduced in nutrient restriction while IGF-II does not appear to be affected. Nutrient restriction also affects IGF binding protein concentrations while effects on the IGF-I receptor appear to vary with the paradigm. Studies on the effects of nutrient restriction on the fetal primate brain in relation to activity of the IGF system are needed to determine the applicability of rodent studies to humans.

Insulin-like growth factor-I ameliorates demyelination induced by tumor necrosis factor-alpha in transgenic mice

Our groups have reported that tumor necrosis factor-alpha (TNF-alpha) causes myelin damage and apoptosis of oligodendrocytes and their precursors in vitro and in vivo. We also have reported that insulin-like growth factor-I (IGF-I) can protect cultured oligodendrocytes and their precursors from TNF-alpha-induced damage. In this study, we investigated whether IGF-I can protect oligodendrocytes and myelination from TNF-alpha-induced damage in vivo by cross-breeding TNF-alpha transgenic (Tg) mice with IGF-I Tg mice that overexpress IGF-I exclusively in brain. At 8 weeks of age, compared with those of wild-type (WT) mice, the brain weights of TNF-alpha Tg mice were decreased by approximately 20%, and those of IGF-I Tg mice were increased by approximately 20%. The brain weights of mice that carry both TNF-alpha and IGF-I transgenes (TNF-alpha/IGF-I Tg mice) did not differ from those of WT mice. As judged by histochemical staining and immunostaining, myelin content in the cerebellum of TNF-alpha/IGF-I Tg mice was similar to that in WT mice and much more than that in TNF-alpha Tg mice. Consistently, Western immunoblot analysis showed that myelin basic protein (MBP) abundance in the cerebellum of TNF-alpha/IGF-I Tg mice was double that in TNF-alpha Tg mice. In comparison with WT mice, the number of oligodendrocytes was decreased by approximately 36% in TNF-alpha Tg mice, whereas it was increased in IGF-I Tg mice by approximately 40%. Oligodendrocyte number in TNF-alpha/IGF-I Tg mice was almost twice that in TNF-alpha Tg mice. Furthermore, IGF-I overexpression significantly reduced TNF-alpha-induced increases in apoptotic cell number, active caspase-3 abundance, and degradaion of MBP. Our results indicate that IGF-I is capable of protecting myelin and oligodendrocytes from TNF-alpha-induced damage in vivo.