Interactions between bcl-2 and the IGF system control apoptosis in the developing mouse brain

Diverse transcriptional regulation and functional effects revealed by CRISPR/Cas9-directed epigenetic editing

DNA methylation is an epigenetic process that controls DNA accessibility and serves as a transcriptomic switch when deposited at regulatory regions. The adequate functioning of this process is indispensable for tissue homeostasis and cell fate determination. Conversely, altered DNA methylation patterns result in abnormal gene transcription profiles that contribute to tumor initiation and progression. However, whether the consequence of DNA methylation on gene expression and cell fate is uniform regardless of the cell type or state could so far not been tested due to the lack of technologies to target DNA methylation in-situ. Here, we have taken advantage of CRISPR/dCas9 technology adapted for epigenetic editing through site-specific targeting of DNA methylation to characterize the transcriptional changes of the candidate gene and the functional effects on cell fate in different tumor settings. As a proof-of-concept, we were able to induce de-novo site-specific methylation of the gene promoter of IGFBP2 up to 90% with long-term and bona-fide inheritance by daughter cells. Strikingly, this modification led to opposing expression profiles of the target gene in different cancer cell models and affected the expression of mesenchymal genes CDH1, VIM1, TGFB1 and apoptotic marker BCL2. Moreover, methylation-induced changes in expression profiles was also accompanied by a phenotypic switch in cell migration and cell morphology. We conclude that in different cell types the consequence of DNA methylation on gene expression and cell fate can be completely different.

Serum insulin-like growth factor-binding protein 2 levels as an indicator for disease severity in enterohemorrhagic Escherichia coli induced hemolytic uremic syndrome

Background

Insulin-like growth factor-binding protein (IGFBP) 2 plays an important role in the regulation of cell adhesion, migration, growth, and apoptosis. This study aimed to investigate the clinical significance of serum IGFBP2 as a biomarker for disease activity and severity in hemolytic uremic syndrome (HUS) induced by enterohemorrhagic Escherichia coli (EHEC).

Methods

IGFBP2 production by human renal glomerular endothelial cells (RGECs) after exposure to Shiga toxin 2 (Stx-2) was investigated in vitro. Serum IGFBP2 levels in blood samples obtained from 22 patients with HUS and 10 healthy controls (HCs) were quantified using an enzyme-linked immunosorbent assay. The results were compared to the clinical features of HUS and serum tau and cytokine levels.

Results

Stx-2 induced the production of IGFBP2 in RGECs in a dose-dependent manner. Serum IGFBP2 levels were significantly higher in patients with HUS than in HCs and correlated with disease severity. Additionally, serum IGFBP2 levels were significantly higher in patients with encephalopathy than in those without encephalopathy. A serum IGFBP2 level above 3585 pg/mL was associated with a high risk of encephalopathy. Furthermore, serum IGFBP2 levels significantly correlated with serum levels of tau and inflammatory cytokines associated with the development of HUS.

Conclusions

Correlation of serum IGFBP2 level with disease activity in patients with HUS suggests that IGFBP2 may be considered as a possible indicator for disease activity and severity in HUS. Larger studies and additional experiments using various cells in central nervous system should elucidate the true value of IGFBP2 as a clinical diagnostic marker.

Abbreviations

IGFBP: insulin-like growth factor-binding protein; HUS: hemolytic uremic syndrome; EHEC: enterohemorrhagic Escherichia coli; RGECs: renal glomerular endothelial cells; STx-2: Shiga toxin 2; HCs: healthy controls; LPS: lipopolysaccharide; ROC: receiver operating characteristic; sTNFR: soluble tumor necrosis factor receptor.

Insulin-like growth factor-1 overexpression increases long-term survival of posttrauma-born hippocampal neurons while inhibiting ectopic migration following traumatic brain injury

Cellular damage associated with traumatic brain injury (TBI) manifests in motor and cognitive dysfunction following injury. Experimental models of TBI reveal cell death in the granule cell layer (GCL) of the hippocampal dentate gyrus acutely after injury. Adult-born neurons residing in the neurogenic niche of the GCL, the subgranular zone, are particularly vulnerable. Injury-induced proliferation of neural progenitors in the subgranular zone supports recovery of the immature neuron population, but their development and localization may be altered, potentially affecting long-term survival. Here we show that increasing hippocampal levels of insulin-like growth factor-1 (IGF1) is sufficient to promote end-stage maturity of posttrauma-born neurons and improve cognition following TBI. Mice with conditional overexpression of astrocyte-specific IGF1 and wild-type mice received controlled cortical impact or sham injury and bromo-2'-deoxyuridine injections for 7d after injury to label proliferating cells. IGF1 overexpression increased the number of GCL neurons born acutely after trauma that survived 6 weeks to maturity (NeuN+BrdU+), and enhanced their outward migration into the GCL while significantly reducing the proportion localized ectopically to the hilus and molecular layer. IGF1 selectively affected neurons, without increasing the persistence of posttrauma-proliferated glia in the dentate gyrus. IGF1 overexpressing animals performed better during radial arm water maze reversal testing, a neurogenesis-dependent cognitive test. These findings demonstrate the ability of IGF1 to promote the long-term survival and appropriate localization of granule neurons born acutely after a TBI, and suggest these new neurons contribute to improved cognitive function.

IGFBP-2 Signaling in the Brain: From Brain Development to Higher Order Brain Functions

Insulin-like growth factor-binding protein-2 (IGFBP-2) is a pleiotropic polypeptide that functions as autocrine and/or paracrine growth factors. IGFBP-2 is the most abundant of the IGFBPs in the cerebrospinal fluid (CSF), and developing brain showed the highest expression of IGFBP-2. IGFBP-2 expressed in the hippocampus, cortex, olfactory lobes, cerebellum, and amygdala. IGFBP-2 mRNA expression is seen in meninges, blood vessels, and in small cell-body neurons (interneurons) and astrocytes. The expression pattern of IGFBP-2 is often developmentally regulated and cell-specific. Biological activities of IGFBP-2 which are independent of their abilities to bind to insulin-like growth factors (IGFs) are mediated by the heparin binding domain (HBD). To execute IGF-independent functions, some IGFBPs have shown to bind with their putative receptors or to translocate inside the cells. Thus, IGFBP-2 functions can be mediated both via insulin-like growth factor receptor-1 (IGF-IR) and independent of IGF-Rs. In this review, I suggest that IGFBP-2 is not only involved in the growth, development of the brain but also with the regulation of neuronal plasticity to modulate high-level cognitive operations such as spatial learning and memory and information processing. Hence, IGFBP-2 serves as a neurotrophic factor which acts via metaplastic signaling from embryonic to adult stages.

Quantification of growth factors in different platelet concentrates

Concentrated growth factor (CGF), a new generation of platelet concentrate product, appears to have more abundant growth factors because of its special centrifugation process. However, there are few studies supporting this. This study was designed to evaluate the contents of major growth factors in CGF and compare them with those found in PRP (platelet-rich plasma) and PRF (platelet-rich fibrin). PRP, PRF, and CGF were obtained from the same samples of peripheral blood. Concentrations of five representative growth factors in platelets were measured with enzyme-linked immunosorbent assay (ELISA): platelet-derived growth factor-BB (PDGF-BB), transforming growth factor β-1 (TGF-β1), insulin-like growth factor-1 (IGF-1), vascular endothelial growth factor (VEGF), and basic fibroblast growth factor (bFGF). The results showed that the bFGF levels in CGF and PRF were significantly higher than that in activated PRP. For other growth factors, such as PDGF-BB, TGF-β1, IGF-1, and VEGF, the levels did not differ significantly among activated PRP, PRF, and CGF. Our findings extended the currently available data on the release and measurement of growth factors in CGF and other platelet gels. In future studies, we need more data to find the proper therapeutic doses for platelet concentrates suitable for different clinical applications.

Maternal immune activation produces cerebellar hyperplasia and alterations in motor and social behaviors in male and female mice

There have been suggestions that maternal immune activation is associated with alterations in motor behavior in offspring. To explore this further, we treated pregnant mice with polyinosinic:polycytidylic acid (poly(I:C)), a viral mimetic that activates the innate immune system, or saline on embryonic days 13-15. At postnatal day (P) 18, offspring cerebella were collected from perfused brains and immunostained as whole-mounts for zebrin II. Measurements of zebrin II+/- stripes in both sexes indicated that prenatal poly(I:C)-exposed offspring had significantly wider stripes; this difference was also seen in similarly treated offspring in adulthood (~P120). When sagittal sections of the cerebellum were immunostained for calbindin and Purkinje cell numbers were counted, we observed greater numbers of Purkinje cells in poly(I:C) offspring at both P18 and ~ P120. In adolescence (~P40), both male and female prenatal poly(I:C)-exposed offspring exhibited poorer performance on the rotarod and ladder rung tests; deficits in performance on the latter test persisted into adulthood. Offspring of both sexes from poly(I:C) dams also exhibited impaired social interaction in adolescence, but this difference was no longer apparent in adulthood. Our results suggest that maternal immune exposure at a critical time of cerebellum development can enhance neuronal survival or impair normal programmed cell death of Purkinje cells, with lasting consequences on cerebellar morphology and a variety of motor and non-motor behaviors.

IGF binding protein-3 mediates stress-induced apoptosis in non-transformed mammary epithelial cells

Mammary epithelial cell (MEC) number is an important determinant of milk production in lactating dairy cows. IGF-I increases IGF binding protein-3 (IGFBP-3) production in these cells, which plays a role in its ability to enhance proliferation. In the present study, we show that the apoptotic factor anisomycin (ANS) also increases IGFBP-3 mRNA and protein in a dose- and concentration-dependent manner that mirrors activation of caspase-3 and -7, with significant increases in both IGFBP-3 protein and caspase activation observed by 3 h. Knock-down of IGFBP-3 with small interfering (si) RNA attenuated the ability of ANS to induce apoptosis, while knock-down of IGFBP-2, the other major IGFBP made by bovine MEC, had no effect. Reducing IGFBP-3 also decreased the ability of ANS to induce mitochondrial cytochrome c release, indicating its involvement in the intrinsic apoptotic pathway. In contrast, transfection with IGFBP-3 in the absence of ANS failed to induce apoptosis. Since both the mitogen IGF-I and the apoptotic inducer ANS increase IGFBP-3 production in MEC, we proposed that cellular localization might determine IGFBP-3 action. While both IGF-I and ANS stimulated the release of IGFBP-3 into conditioned media, only ANS induced nuclear localization of IGFBP-3. A pan-caspase inhibitor had no effect on ANS-induced nuclear localization of IGFBP-3, indicating that nuclear entry of IGFBP-3 precedes caspase activation. Treatment with IGF-I had no effect on ANS-induced nuclear localization, but did block ANS-induced apoptosis. In summary, our data indicate that IGFBP-3 plays a role in stress-induced apoptosis that may require nuclear localization in non-transformed MEC.

Combination of platelet rich fibrin, hydroxyapatite and PRF membrane in the management of large inflammatory periapical lesion

Periapical inflammatory lesion is the local response of bone around the apex of tooth that develops after the necrosis of the pulp tissue or extensive periodontal disease. The final outcome of the nature of wound healing after endodontic surgery can be repair or regeneration depending on the nature of the wound; the availability of progenitor cells; signaling molecules; and micro-environmental cues such as adhesion molecules, extracellular matrix, and associated non-collagenous protein molecules. The purpose of this case report is to add knowledge to the existing literature about the combined use of graft material [platelet rich fibrin (PRF) and hydroxyapatite (HA)] and barrier membrane in the treatment of large periapical lesion. A periapical endodontic surgery was performed on a 45 year old male patient with a swelling in the upper front teeth region and a large bony defect radiologically. The surgical defect was filled with a combination of PRF and HA bone graft crystals. The defect was covered by PRF membrane and sutured. Clinical examination revealed uneventful wound healing. Radiologically the HA crystals have been completely replaced by new bone at the end of 2 years. On the basis of the results obtained in our case report, we hypothesize that the use of PRF in conjunction with HA crystals might have accelerated the resorption of the graft crystals and would have induced the rapid rate of bone formation.

Neuro-protective effects of growth hormone (GH) after hypoxia-ischemia injury in embryonic chicken cerebellum

Neuroprotection is a mechanism within the central nervous system (CNS) that protects neurons from damage as a result of a severe insult. It is known that growth hormone (GH) is involved in cell survival and may inhibit apoptosis in several cell types, including those of the CNS. Both GH and GH-receptor (GHR) genes are expressed in the cerebellum. Thus, we investigated the possible neuroprotective role of GH in this organ, which is very sensitive to hypoxic/ischemic conditions. Endogenous GH levels increased in the brain and cerebellum (30% and 74%, respectively) of 15-day-old chicken embryos exposed to hypoxia during 24h compared to normoxia. In primary embryonic cerebellar neuron cultures treated under hypoxia (0.5% O(2)) and low glucose (1g/L) conditions (HLG) for 1h, GH levels increased 1.16-fold compared to the control. The addition of 1nM recombinant chicken GH (rcGH) to cultures during HLG increased cell viability (1.7-fold) and the expression of Bcl-2 (1.67-fold); in contrast the caspase-3 activity and the proportion of apoptotic cells decreased (37% and 54.2%, respectively) compared to HLG. rcGH activated the PI3K/Akt pathway both under normoxic and HLG conditions, increasing the proportion of phosphorylated Akt (1.7- and 1.4-fold, respectively). These effects were abolished by wortmannin and by immunoneutralization, indicating that GH acts through this signaling pathway. Furthermore, the 15-kDa GH variant (10nM) significantly increased cell viability and decreased caspase-3 activity during HLG condition. Thus GH may act as a paracrine/autocrine neuroprotective factor that preserves cellular viability and inhibits apoptotic cell death.

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.

Transcriptional profiling in the lumbar spinal cord of a mouse model of amyotrophic lateral sclerosis: a role for wild-type superoxide dismutase 1 in sporadic disease?

Mice bearing mutations of copper-zinc-superoxide dismutase recapitulate spinal cord motor neuron degeneration and disease progression occurring in human amyotrophic lateral sclerosis. We have investigated the relationship between disease progression and altered gene expression by comparing the transcriptional profiles in lumbar spinal cord, fronto-parietal cortex and hippocampus of mutant G93A-SOD1, wild-type SOD1 transgenic and non-transgenic mice. Gene expression was evaluated at 55 and 110 days of age, representing pre-symptomatic and advanced disease stages of G93A mice, respectively. Whereas no significant variations were detectable in cortical and hippocampal areas, several mutation-related changes were detected in the lumbar spinal cord at the symptomatic stage, consistent with a condition of neuronal distress. Also, at both ages, we found a number of transgene-related changes, i.e. variations occurring in both transgenic groups independently of the G93A mutation, with wild-type SOD1- and G93A-SOD1-overexpressing mice displaying global transcriptional similarity at 110 days of age. Some of the changes in common between the two transgenic groups involve genes implicated in oxidative stress, inflammation, spinocerebellar degeneration and other neurodegenerative disorders. The finding that gene expressional alterations potentially associated to cellular distress are shared by wild-type and mutant human SOD1-overexpressing mice raises the possibility that mutated (in familial ALS) or otherwise dysregulated (in sporadic ALS) SOD1 expression is a common pathogenetic substrate of the disease.

Insulin-like growth factor binding protein 2: gene expression microarrays and the hypothesis-generation paradigm

A major goal of modern medicine is to identify key genes and their products that are altered in the diseased state and to elucidate the molecular mechanisms underlying disease development, progression, and resistance to therapy. This is a daunting task given the exceptionally high complexity of the human genome. The paradigm for research has historically been hypothesis-driven despite the fact that the hypotheses under scrutiny often rest on tenuous subjective grounds or are derived from and dependent on chance observation. The imminent deciphering of the complete human genome, coupled with recent advances in high-throughput bioanalytical technology, has made possible a new paradigm in which data-based hypothesis-generation is the initial step in the investigative process, followed by hypothesis-testing. Genomics technologies are the primary source of the new hypothesis-generating capabilities that are now empowering biomedical researchers. The synergistic interaction between contemporary genomics technologies and the hypothesis-generation paradigm is well-illustrated by the discovery and subsequent ongoing study of the role of insulin-like growth factor binding protein 2 (IGFBP2) in human glioma biology. Using gene expression microarray technology, the IGFBP2 gene was recently found to be highly and differentially overexpressed in the most advanced grade of human glioma, glioblastoma. Based on this discovery, subsequent functional studies were initiated that suggest that IGFBP2 overexpression may contribute to the invasive nature of glioblastoma, and that IGFBP2 may exert its function via a newly identified novel binding protein. The IGFBP2 story is but one example of the power and potential of the new molecular methodologies that are transforming modern diagnostic and investigative neuropathology.

Insulin-like growth factor-I accelerates the cell cycle by decreasing G1 phase length and increases cell cycle reentry in the embryonic cerebral cortex

Neurogenesis in the developing cerebral cortex of mice occurs in the dorsal telencephalon between embryonic day 11 (E11) and E17, during which time the majority of cortical projection neurons and some glia are produced from proliferating neuroepithelial cells in the ventricular zone. The number of cells produced by this process is governed by several factors, including cell cycle kinetics and the proportion of daughter cells exiting the cell cycle after a given round of cell division. The in vivo effects of IGF-I on cell cycle kinetics were investigated in nestin/IGF-I transgenic (Tg) embryos, in which IGF-I is overexpressed in the cerebral cortex and dorsal telencephalon. These Tg mice have been shown to exhibit increased cell number in the cortical plate by E16 and increased numbers of neurons and glia in the cerebral cortex during postnatal development. Cumulative S phase labeling with 5-bromo-2'-deoxyuridine revealed a decrease in total cell cycle length (TC) in Tg embryos on E14. This decrease in TC was found to result entirely from a reduction in the length of the G1 phase of the cell cycle from 10.66 to 8.81 hr, with no significant changes in the lengths of the S, G2, and M phases. Additionally, the proportion of daughter cells reentering the cell cycle was significantly increased by 15% in Tg embryos on E14-E15 compared with littermate controls. These data demonstrate that IGF-I regulates progenitor cell division in the ventricular zone by reducing G1 phase length and decreasing TC but increases cell cycle reentry.

Increased expression of insulin-like growth factor-I (IGF-I) during embryonic development produces neocortical overgrowth with differentially greater effects on specific cytoarchitectonic areas and cortical layers

The in vivo actions of insulin-like growth factor-I (IGF-I) on the growth and development of the cerebral cortex were investigated in transgenic (Tg) mice that overexpress IGF-I in the brain, beginning as early as embryonic day (E) 13. Compared to non-Tg littermate controls, Tg mice at postnatal day (P) 12 exhibited significant increases in total cortical volume (31%) and in total neuron number (27%). The numerical density of neurons did not differ significantly between Tg and control mice, except in layer I. Comparing cytoarchitectonic areas in Tg mice, significantly greater increases in cortical volume were found for the motor cortex (42%), compared to somatosensory cortex (35%). Similarly, greater increases in total neuron number were found for motor cortex (44%) compared to somatosensory cortex (28%). Comparing individual cortical layers in Tg mice, the greatest increase in neuron number was found in layer I for both motor (93%) and somatosensory (76%) regions, followed by layer V (36-53%)>II/III (26-47%)>VI (26-37%)>IV (22-34%). Our results demonstrate that increased expression of IGF-I in vivo during embryonic and early postnatal development produces substantial overgrowth of the neocortex. IGF-I-mediated growth and development exhibits differential effects in some cytoarchitectonic areas and in lamina-specific neuron populations, most notably the neurons of layer I.

Treatment of Periapical Inflammatory Lesion with the Combination of Platelet-Rich Plasma and Tricalcium Phosphate: A Case Report

Periapical surgery is an important treatment alternative in the presence of a periapical inflammatory lesion. To achieve optimal healing and regeneration of the bone, different bone substitutes or barrier membranes can be used after degranulation of the lesion. Tricalcium phosphate (TCP) graft material is one of these substitutes. Platelet Rich Plasma (PRP) preparation is a new biotechnology and can be used in many different surgical procedures. It consists of thrombocyte concentrates and high amounts of growth factors (GFs), especially platelet derived growth factor (PDGF), insulin-like growth factor (IGF-I) and transforming growth factor (TGF-beta), which are important in wound healing and regeneration. In this case report, use of platelet gel in conjunction with TCP in the treatment of periapical inflammatory lesion and the results of 12 months has been reported.

Generation of transgenic mice expressing insulin-like growth factor-1 under the control of the myelin basic protein promoter: increased myelination and potential for studies on the effects of increased IGF-1 on experimentally and genetically induced demyelination

In order to investigate a role for insulin-like growth factor-1 (IGF-1) in ameliorating the effects of demyelinating events and potentiating remyelination, we have generated transgenic (tg) mice expressing IGF-1 under the control of the myelin basic protein promoter. Heterozygous tg mice expressed the highest levels of IGF-1 in brain during the most active periods of myelination as determined by Western and Northern blotting. A high level of expression was found throughout the lives of the tg mice. There was no increased expression of IGF-1 in other organs. The brains of heterozygous mice were larger than those of normal mice by 2 weeks of age, and they continued to increase in size for several months. Light and electron microscopy showed extensive myelination of axons. Behavioral studies of the older heterozygous mice documented difficulty with balance. This new tg mouse model can be bred to mice that are heterozygous for genetic leukodystrophies to produce eventually mice that are affected with a given leukodystrophy but overexpress IGF-1 during myelination and remyelination. It will be interesting to see if overexpression of IGF-1 can modulate the pathological and clinical features of the inherited leukodystrophies with or without supplemental therapies.

Fibroblast growth factor-2 over-rides insulin-like growth factor-I induced proliferation and cell survival in human neuroblastoma cells

The insulin-like growth factor (IGF) system is a key regulator of cell growth, survival and differentiation, and these functions are co-modulated by other growth factors including fibroblast growth factor-2 (FGF-2). To investigate IGF/FGF interactions in neuronal cells, we employed neuroblastoma cells (SK-N-MC). In serum free conditions proliferation of the SK-N-MC cells was promoted by IGF-I (25 ng/ml), but blunted by FGF-2 (50 ng/ml). IGF-I-induced proliferation was abolished in the presence of FGF-2 even when IGF-I was used at 100 ng/ml. In addition to our previously described FGF-2 induced proteolytic cleavage of IGFBP-2, we found that FGF-2 increased IGFBP-6 levels in conditioned medium (CM) without affecting IGFBP-6 mRNA abundance. Modulation of IGFBP-2 and -6 levels were not significant mechanisms involved in the blockade of IGF-I action since the potent IGF-I analogues [QAYL]IGF-I and des(1-3)IGF-I (minimal IGFBP affinity) were unable to overcome FGF-2 inhibition of cell proliferation. FGF-2 treated cells showed morphological differentiation expressing the TUJ1 neuronal marker while cells treated with IGF-I alone showed no morphological change. When IGF-I was combined with FGF-2, however, cell morphology was indistinguishable from that seen with FGF-2 alone. FGF-2 inhibited proliferation and enhanced differentiation was also associated with a 70% increase in cell death. Although IGF-I alone was potently anti-apoptotic (60% decreased), IGF-I was unable to prevent apoptosis when administrated in combination with FGF-2. Gene-array analysis confirmed FGF-2 activation of the intrinsic and extrinsic apoptotic pathways and blockade of IGF anti-apoptotic signaling. FGF-2, directly and indirectly, overcomes the proliferative and anti-apoptotic activity of IGF-I by complex mechanisms, including enhancement of differentiation and apoptotic pathways, and inhibition of IGF-I induced anti-apoptotic signalling. Modulation of IGF binding protein abundance by FGF-2 does not play a significant role in inhibition of IGF-I induced mitogenesis.

Neuronal protection from glucose deprivation via modulation of glucose transport and inhibition of apoptosis: a role for the insulin-like growth factor system

Glucose is the brain's major energy source; therefore, loss of neuronal cells is a potential consequence of hypoglycaemia. Since apoptosis is a major mechanism of neuronal loss following a range of insults, we explored potent anti-apoptotic systems (IGF-I and bcl-2) as means of enhancing neuronal survival in the face of glucose deprivation. Human neuroblastoma cells (SH-SY5Y, SHEP and SHEP-bcl-2) were exposed to low glucose as a model of glucopenia-induced neuronal damage. Administration of IGF-I and/or over-expression of the survival gene bcl-2 were exploited to attempt to limit neuronal loss. Neuronal survival mechanisms and interactions between these systems were investigated. Low glucose (0.25-2.5 mM) adversely affected cell growth and survival; however, IGF-I ameliorated these outcomes. Over-expression of bcl-2 blunted low glucose-induced apoptosis and up-regulated IGF-I receptor, with the effect of IGF-I addition being negligible on apoptosis, while significantly enhancing mitochondrial activity. In SH-SY5Y cells, IGF-I significantly changed >two-fold mRNA levels of the apoptosis-related genes gadd45, fas, iNOS, NFkB, TRAIL, without further affecting bcl-2 expression. In low glucose, IGF-I acutely enhanced glucose transport and translocation of GLUT1 protein to the cell membrane. GLUT1 mRNA expression was up-regulated by both IGF-I and bcl-2. The potent anti-apoptotic systems IGF-I and bcl-2 are both thus able to enhance cell survival in a glucose-deprived human neuronal model. Although we clearly show evidence of positive cross-talk via bcl-2 modulation of IGF-I receptor, IGF-I also has enhancing effects on mitochondrial function outside the bcl-2 pathway. The common effect of both systems on enhancement of GLUT-1 expression suggests that this is a key mechanism for enhanced survival. These studies also point to the potential use of IGF-I therapy in prevention or amelioration of hypoglycaemic brain injury.

Insulin-like growth factor binding protein-2 modulates podocyte mitogenesis

To study the role of insulin-like growth factors (IGF) in podocyte maturation, we isolated and characterized fetal visceral glomerular epithelial cells from human kidneys obtained at 8-18 weeks gestation. Cells were identified as podocyte lineage by their cobblestone morphology and immunoreactivity with synaptopodin, Wilms tumor-1 suppressor gene product (WT-1), complement receptor CR1, and cytoskeletal proteins smooth muscle actin and vimentin. Stimulation of the podocyte cell monolayers with IGF-II resulted in a slight increase in mitogenesis, an effect that was concentration and time dependent and abrogated by co-incubation with exogenous IGF binding protein 2 (IGFBP-2). Western blot analysis of conditioned media revealed that cultured podocytes expressed endogenous IGFBP-2 exclusively. IGF-II stimulation enhanced IGFBP-2 production in a dose- and time-dependent fashion and was associated with an increase in IGFBP-2 mRNA production. These data demonstrate that IGF-II-stimulated IGFBP-2 production appears to inhibit the mitogenic effect of IGF-II, and may have an autocrine effect on the maturation, differentiation, and survival of fetal podocytes.

Prenatal exposure of rats to Ginkgo biloba extract (EGb 761) increases neuronal survival/growth and alters gene expression in the developing fetal hippocampus

Hippocampal neuron survival/growth and gene expression have been examined after prenatal (in utero) exposure of rats to EGb 761, a leaf extract of Ginkgo biloba. Oral administration of EGb 761 (100 or 300 mg/kg/day) to pregnant dams for 5 days increased the number of hippocampal neurons (maintained in culture) of their fetuses, indicating a neurotrophic effect of the extract. Using large-scale oligonucleotide microarrays containing over 8000 combined rat genes and expressed sequence tag clusters, it was shown that treatment of pregnant dams with EGb 761 (25, 50 or 100 mg/kg/day for 5 days) altered the expression of 187 genes in the hippocampi of male fetuses and 160 genes in those of female fetuses. Using gene-cluster analysis, these genes were grouped into 18 distinct clusters for males and 17 distinct clusters for females. Among these clusters, 35 genes shared a common expression pattern in male and female hippocampal development. Of these genes, the changes observed in insulin growth factor II, insulin growth factor binding protein 2, testosterone repressed prostate message-2, glutathione-dependent dehydroascorbate reductase, lipoprotein lipase, guanylate cyclase and DNA binding protein Brn-2 were confirmed by real-time quantitative polymerase chain reaction. These findings, which have provided the first genetic profile of the effects of EGb 761 on the developing rat hippocampus, increase our understanding of the molecular and genetic programs that are activated by the extract. These effects of EGb 761 may underlie its neuroprotective properties.

Insulin-like growth factor-1 and post-ischemic brain injury

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

Spatiotemporal distribution of the insulin-like growth factor receptor in the rat olfactory bulb

Insulin-like growth factor I (IGF-I) and its receptor (IGF-IR) are involved in growth of neurons. In the rat olfactory epithelium, we previously showed IGF-IR immunostaining in subsets of olfactory receptor neurons. We now report that IGF-IR staining was heaviest in the olfactory nerve layer of the rat olfactory bulb at embryonic days 18, and 19 and postnatal day 1, with labeling of protoglomeruli. In the adult, only a few glomeruli were IGF-IR-positive, some of which were unusually small and strongly labeled. Some IGF-IR-positive fibers penetrated deeper into the external plexiform layer, even in adults. In developing tissues, IGF-IR staining co-localized with that for olfactory marker protein and growth associated protein GAP-43, but to a lesser extent with synaptophysin. In the adult, IGF-IR-positive fibers were compartmentalized within glomeruli. IGF-I may play a role in glomerular synaptogenesis and/or plasticity, possibly contributing to development of coding patterns for odor detection or identification.

Growth hormone (GH) and GH-releasing peptide-6 increase brain insulin-like growth factor-I expression and activate intracellular signaling pathways involved in neuroprotection

Beneficial effects of GH on memory, mental alertness, and motivation have been documented. Many actions of GH are mediated through IGF-I; hence, we investigated whether systemic administration of GH or GH-releasing peptide (GHRP)-6 modulates the brain IGF system. Treatment of adult male rats with GHRP-6 or GH for 1 wk significantly increased IGF-I mRNA levels in the hypothalamus, cerebellum, and hippocampus, with no effect in cerebral cortex. Expression of the IGF receptor and IGF-binding protein (IGFBP)-2 were not affected. Phosphorylation of Akt and Bad was stimulated in areas where IGF-I was increased, with no change in MAPK or glycogen synthase kinase-3beta. This suggests that GH and GHRP-6 activate phosphatidylinositol kinase intracellular pathways involved in cell survival in response to growth factors. Indeed, the antiapoptotic protein Bcl-2 was augmented in these same areas, with no change in the proapoptotic protein Bax. IGFBP-5, also reported to be involved in neuron survival processes, was increased mainly in the hypothalamus, suggesting a possible neuroendocrine role. In conclusion, GH and GHRP-6 modulate IGF-I expression in the central nervous system in an anatomically specific manner. This is coincident with activation of intracellular signaling pathways used by IGF-I and increased expression of proteins involved in cell survival or neuroprotection.

Bone growth factors in maxillofacial skeletal reconstruction

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

Suppression of death receptor signaling in cerebellar Purkinje neurons protects neighboring granule neurons from apoptosis via an insulin-like growth factor I-dependent mechanism

Neuronal apoptosis contributes to the progression of neurodegenerative disease. Primary cerebellar granule neurons are an established in vitro model for investigating neuronal death. After removal of serum and depolarizing potassium, granule neurons undergo apoptosis via a mechanism that requires intrinsic (mitochondrial) death signals; however, the role of extrinsic (death receptor-mediated) signals is presently unclear. Here, we investigate involvement of death receptor signaling in granule neuron apoptosis by expressing adenoviral, AU1-tagged, dominant-negative Fas-associated death domain (Ad-AU1-deltaFADD). Ad-AU1-deltaFADD decreased apoptosis of granule neurons from 65 +/- 5 to 27 +/- 2% (n = 7, p < 0.01). Unexpectedly, immunocytochemical staining for AU1 revealed that <5% of granule neurons expressed deltaFADD. In contrast, deltaFADD was expressed in >95% of calbindin-positive Purkinje neurons ( approximately 2% of the cerebellar culture). Granule neurons in proximity to deltaFADD-expressing Purkinje cells demonstrated markedly increased survival. Both granule and Purkinje neurons expressed insulin-like growth factor-I (IGF-I) receptors, and deltaFADD-mediated survival of granule neurons was inhibited by an IGF-I receptor blocking antibody. These results demonstrate that the selective suppression of death receptor signaling in Purkinje neurons is sufficient to rescue neighboring granule neurons that depend on Purkinje cell-derived IGF-I. Thus, the extrinsic death pathway has a profound but indirect effect on the survival of cerebellar granule neurons.

Insulin-like growth factor I partly prevents axon elimination in the neonate rat optic nerve

Developmental neuronal death ensues after access of innervating neurons to target-derived neurotrophic factors is restricted. Recent evidence suggests, however, that growth factors such as those of the insulin family modulate neuronal death through autocrine/paracrine mechanisms. In rats, retinal ganglion neurons (RGNs) undergo massive death during early postnatal life. During this same period, the expression of various members of the insulin-like growth factor I (IGF-I) protein family is down regulated. To evaluate whether ocular IGF-I might modulate RGN death, we administered IGF-I in the posterior chamber of the eye of newborn rats. Optic nerve fiber number was estimated in control and IGF-I treated animals at postnatal day 5 when RGN death peaks. Intraocular IGF-I treatment at birth partly prevented optic nerve fiber elimination. Because the axon number in the optic nerve correlates to some extent with the RGN number, these results suggest that IGF-I may modulate RGN death in vivo through local interactions.

Mutant mouse models of insulin-like growth factor actions in the central nervous system

Insulin-like growth factor-I (IGF-I) and its cognate receptor, the type 1 IGF receptor (IGF1R), as well as high-affinity IGF binding proteins (IGFBP) that modulate IGF-I actions, are expressed throughout the course of brain development. These observations, taken together with studies in cultured neural cells demonstrating a variety of IGF-I growth-promoting activities, provide a strong argument for IGF-I having a central role in the growth and development of the CNS. This report reviews studies of brain development in mutant mice with alterations of IGF-I expression or action. Transgenic (Tg) mice overexpressing IGF-I postnatally exhibit brain overgrowth characterized by increased neuron and oligodendrocyte number, as well as marked increases in myelination. Mutant mice with ablated IGF-I and IGF1R expression, as well as those with overexpression of IGFBPs capable of inhibiting IGF actions, exhibit brain growth retardation with a variety of growth deficits. These studies confirm a role for IGF-I in neural development, and indicate that IGF-I stimulates neurogenesis and synaptogenesis, facilitates oligodendrocyte development, promotes neuron and oligodendrocyte survival, and stimulates myelination. Evidence from experiments in these mouse models also indicates that IGF-I has a role in recovery from neural injury.

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

In studies of transgenic (Tg) mice that overexpress insulin-like growth factor-I (IGF-I) exclusively in the CNS, we demonstrated a dramatic increase in cerebellar granule cell number that appeared to be attributable predominantly to enhanced survival. IGF-I anti-apoptotic actions are well established in cultured neurons, but comparable studies in vivo are few. Using the same Tg mice, therefore, we set out to document IGF-I anti-apoptotic effects during cerebellar development and to probe IGF-I signaling mechanisms. Compared with cerebella (CBs) of non-Tg littermates, those of Tg mice had fewer apoptotic cells at postnatal day 7 (P7) and showed a similar tendency at P14 and P21. At each age studied, procaspase-3 and caspase-3 were decreased in CBs of Tg mice. The caspase-3 decline was accompanied by decreases in the 85 kDa fragment of Poly(ADP-ribose) polymerase, a known product of caspase cleavage, suggesting decreased caspase activity. At P7 decreased apoptosis in Tg mice was associated with increased expression of the anti-apoptotic Bcl genes, Bcl-x(L) and Bcl-2. The mRNA expression of the proapoptotic Bcl genes, Bax and Bad, also was increased, but no changes were observed in the abundance of their proteins. At P14 Bcl-xL and Bcl-2 expression were similar in normal and Tg mice; Bax mRNA was unchanged in Tg mice, but its protein abundance was decreased, and both Bad mRNA and protein abundance were decreased. At P21 Bcl-xL and Bcl-2 expression were unchanged, but Bax and Bad expression were decreased. Our data show that IGF-I exerts anti-apoptotic actions during cerebellar development, and thereby alters the magnitude of naturally occurring apoptosis. IGF-I appears to affect multiple steps in the apoptotic pathway in a developmentally specific manner. IGF-I decreases caspase-3 availability and activity, increases the expression of anti-apoptotic Bcl-x(L) and Bcl-2 during early postnatal development, and decreases proapoptotic Bax and Bad expression at later developmental stages.

Uteroplacental insufficiency lowers the threshold towards hypoxia-induced cerebral apoptosis in growth-retarded fetal rats

Infants suffering uteroplacental insufficiency and hypoxic ischemic injury often demonstrate cerebral apoptosis. Our objective was to determine the global effects of uteroplacental insufficiency upon cerebral gene expression of the apoptosis related proteins Bcl-2 and Bax and their role in increasing vulnerability to hypoxia-induced cerebral apoptosis. We therefore caused uteroplacental insufficiency and growth retardation by performing bilateral uterine artery ligation upon pregnant rats 2 days prior to term delivery and elicited further perinatal fetal hypoxia by placing maternal rats in 14% FiO(2) 3 h prior to delivery. We quantified cerebral levels of Bcl-2 and Bax mRNA, lipid peroxidation, caspase-3 activity, and cAMP in control and growth retarded term rat pups that experienced either normoxia or hypoxia. Uteroplacental insufficiency alone caused a significant decrease in cerebral Bcl-2 mRNA levels without altering cerebral Bax mRNA levels, malondialdehyde levels, or caspase-3 activity. In contrast, uteroplacental insufficiency and subsequent fetal hypoxia significantly increased cerebral Bax mRNA levels, lipid peroxidation and caspase-3 activity; Bcl-2 mRNA levels continued to be decreased. Hypoxia alone increased cerebral cAMP levels, whereas uteroplacental insufficiency and subsequent hypoxia decreased cerebral cAMP levels. We speculate that the decrease in Bcl-2 gene expression increases the vulnerability towards cerebral apoptosis in fetal rats exposed initially to uteroplacental insufficiency and subsequent hypoxic stress.

Apoptosis contributes to amphotericin B-induced nephrotoxicity

The aim of this study was to investigate whether apoptosis contributes to nephrotoxicity caused by amphotericin B (AmB). By detecting apoptosis-specific DNA fragmentation, it is demonstrated that proximal tubular cells (LLC-PK(1)) and medullary interstitial cells (RMIC) respond with programmed cell death when treated with therapeutic doses of AmB. Concomitant application of AmB and recombinant human insulin-like growth factor-1 (rhIGF-1), a known antiapoptotic agent, abrogated apoptosis in vitro. To validate that the observed apoptotic effects on renal tissue culture cells are applicable to an in vivo setting, an animal model was used for verification. Therefore, Sprague-Dawley rats were treated with AmB. The drug caused hypokalemia, decreased weight gain, loss of renal concentrating ability, and dehydration in a dose-dependent fashion. Microscopic examination of renal tissue sections revealed apoptotic alterations predominantly in proximal and distal tubular epithelial cells. To verify that the observed clinical side effects were linked to apoptosis, rhIGF-1 was applied concomitantly with AmB. In all animals, rhIGF-1 prevented the above-mentioned clinical side effects. Moreover, significantly reduced apoptosis was observed in renal tissue sections of these animals, indicating the relevance of apoptosis in nephrotoxicity. This is the first report to demonstrate that AmB induces apoptosis in the rat kidney in a dose-dependent fashion. The incidence of apoptosis correlates with renal toxicity and can be abrogated by concomitant treatment with rhIGF-1.