Insulin-like growth factor I protects oligodendrocytes from tumor necrosis factor-alpha-induced injury

In utero ethanol exposure induces mitochondrial DNA damage and inhibits mtDNA repair in developing brain

Introduction

Mitochondrial dysfunction is postulated to be a central event in fetal alcohol spectrum disorders (FASD). People with the most severe form of FASD, fetal alcohol syndrome (FAS) are estimated to live only 34 years (95% confidence interval, 31 to 37 years), and adults who were born with any form of FASD often develop early aging. Mitochondrial dysfunction and mitochondrial DNA (mtDNA) damage, hallmarks of aging, are postulated central events in FASD. Ethanol (EtOH) can cause mtDNA damage, consequent increased oxidative stress, and changes in the mtDNA repair protein 8-oxoguanine DNA glycosylase-1 (OGG1). Studies of molecular mechanisms are limited by the absence of suitable human models and non-invasive tools.

Methods

We compared human and rat EtOH-exposed fetal brain tissues and neuronal cultures, and fetal brain-derived exosomes (FB-Es) from maternal blood. Rat FASD was induced by administering a 6.7% alcohol liquid diet to pregnant dams. Human fetal (11-21 weeks) brain tissue was collected and characterized by maternal self-reported EtOH use. mtDNA was amplified by qPCR. OGG1 and Insulin-like growth factor 1 (IGF-1) mRNAs were assayed by qRT-PCR. Exosomal OGG1 was measured by ddPCR.

Results

Maternal EtOH exposure increased mtDNA damage in fetal brain tissue and FB-Es. The damaged mtDNA in FB-Es correlated highly with small eye diameter, an anatomical hallmark of FASD. OGG1-mediated mtDNA repair was inhibited in EtOH-exposed fetal brain tissues. IGF-1 rescued neurons from EtOH-mediated mtDNA damage and OGG1 inhibition.

Conclusion

The correlation between mtDNA damage and small eye size suggests that the amount of damaged mtDNA in FB-E may serve as a marker to predict which at risk fetuses will be born with FASD. Moreover, IGF-1 might reduce EtOH-caused mtDNA damage and neuronal apoptosis.

Dysregulation of IGF-1/GLP-1 signaling in the progression of ALS: potential target activators and influences on neurological dysfunctions

The prominent causes for motor neuron diseases like ALS are demyelination, immune dysregulation, and neuroinflammation. Numerous research studies indicate that the downregulation of IGF-1 and GLP-1 signaling pathways plays a significant role in the progression of ALS pathogenesis and other neurological disorders. In the current review, we discussed the dysregulation of IGF-1/GLP-1 signaling in neurodegenerative manifestations of ALS like a genetic anomaly, oligodendrocyte degradation, demyelination, glial overactivation, immune deregulation, and neuroexcitation. In addition, the current review reveals the IGF-1 and GLP-1 activators based on the premise that the restoration of abnormal IGF-1/GLP-1 signaling could result in neuroprotection and neurotrophic effects for the clinical-pathological presentation of ALS and other brain diseases. Thus, the potential benefits of IGF-1/GLP-1 signal upregulation in the development of disease-modifying therapeutic strategies may prevent ALS and associated neurocomplications.

Hormonal Regulation of Oligodendrogenesis II: Implications for Myelin Repair

Alterations in myelin, the protective and insulating sheath surrounding axons, affect brain function, as is evident in demyelinating diseases where the loss of myelin leads to cognitive and motor dysfunction. Recent evidence suggests that changes in myelination, including both hyper- and hypo-myelination, may also play a role in numerous neurological and psychiatric diseases. Protecting myelin and promoting remyelination is thus crucial for a wide range of disorders. Oligodendrocytes (OLs) are the cells that generate myelin, and oligodendrogenesis, the creation of new OLs, continues throughout life and is necessary for myelin plasticity and remyelination. Understanding the regulation of oligodendrogenesis and myelin plasticity within disease contexts is, therefore, critical for the development of novel therapeutic targets. In our companion manuscript, we review literature demonstrating that multiple hormone classes are involved in the regulation of oligodendrogenesis under physiological conditions. The majority of hormones enhance oligodendrogenesis, increasing oligodendrocyte precursor cell differentiation and inducing maturation and myelin production in OLs. Thus, hormonal treatments present a promising route to promote remyelination. Here, we review the literature on hormonal regulation of oligodendrogenesis within the context of disorders. We focus on steroid hormones, including glucocorticoids and sex hormones, peptide hormones such as insulin-like growth factor 1, and thyroid hormones. For each hormone, we describe whether they aid in OL survival, differentiation, or remyelination, and we discuss their mechanisms of action, if known. Several of these hormones have yielded promising results in both animal models and in human conditions; however, a better understanding of hormonal effects, interactions, and their mechanisms will ultimately lead to more targeted therapeutics for myelin repair.

Hormonal Regulation of Oligodendrogenesis I: Effects across the Lifespan

The brain’s capacity to respond to changing environments via hormonal signaling is critical to fine-tuned function. An emerging body of literature highlights a role for myelin plasticity as a prominent type of experience-dependent plasticity in the adult brain. Myelin plasticity is driven by oligodendrocytes (OLs) and their precursor cells (OPCs). OPC differentiation regulates the trajectory of myelin production throughout development, and importantly, OPCs maintain the ability to proliferate and generate new OLs throughout adulthood. The process of oligodendrogenesis, the creation of new OLs, can be dramatically influenced during early development and in adulthood by internal and environmental conditions such as hormones. Here, we review the current literature describing hormonal regulation of oligodendrogenesis within physiological conditions, focusing on several classes of hormones: steroid, peptide, and thyroid hormones. We discuss hormonal regulation at each stage of oligodendrogenesis and describe mechanisms of action, where known. Overall, the majority of hormones enhance oligodendrogenesis, increasing OPC differentiation and inducing maturation and myelin production in OLs. The mechanisms underlying these processes vary for each hormone but may ultimately converge upon common signaling pathways, mediated by specific receptors expressed across the OL lineage. However, not all of the mechanisms have been fully elucidated, and here, we note the remaining gaps in the literature, including the complex interactions between hormonal systems and with the immune system. In the companion manuscript in this issue, we discuss the implications of hormonal regulation of oligodendrogenesis for neurological and psychiatric disorders characterized by white matter loss. Ultimately, a better understanding of the fundamental mechanisms of hormonal regulation of oligodendrogenesis across the entire lifespan, especially in vivo, will progress both basic and translational research.

The impact of trophic and immunomodulatory factors on oligodendrocyte maturation: Potential treatments for encephalopathy of prematurity

Encephalopathy of prematurity (EoP) is a major cause of morbidity in preterm neonates, causing neurodevelopmental adversities that can lead to lifelong impairments. Preterm birth-related insults, such as cerebral oxygen fluctuations and perinatal inflammation, are believed to negatively impact brain development, leading to a range of brain abnormalities. Diffuse white matter injury is a major hallmark of EoP and characterized by widespread hypomyelination, the result of disturbances in oligodendrocyte lineage development. At present, there are no treatment options available, despite the enormous burden of EoP on patients, their families, and society. Over the years, research in the field of neonatal brain injury and other white matter pathologies has led to the identification of several promising trophic factors and cytokines that contribute to the survival and maturation of oligodendrocytes, and/or dampening neuroinflammation. In this review, we discuss the current literature on selected factors and their therapeutic potential to combat EoP, covering a wide range of in vitro, preclinical and clinical studies. Furthermore, we offer a future perspective on the translatability of these factors into clinical practice.

Biology of Microglia in the Developing Brain

Microglia exist in different morphological forms in the developing brain. They show a small cell body with scanty cytoplasm with many branching processes in the grey matter of the developing brain. However, in the white matter such as the corpus callosum where the unmyelinated axons are loosely organized, they appear in an amoeboid form having a round cell body endowed with copious cytoplasm rich in organelles. The amoeboid cells eventually transform into ramified microglia in the second postnatal week when the tissue becomes more compact with the onset of myelination. Microglia serve as immunocompetent macrophages that act as neuropathology sensors to detect and respond swiftly to subtle changes in the brain tissues in pathological conditions. Microglial functions are broadly considered as protective in the normal brain development as they phagocytose dead cells and sculpt neuronal connections by pruning excess axons and synapses. They also secrete a number of trophic factors such as insulin-like growth factor-1 and transforming growth factor-β among many others that are involved in neuronal and oligodendrocyte survival. On the other hand, microglial cells when activated produce a plethora of molecules such as proinflammatory cytokines, chemokines, reactive oxygen species, and nitric oxide that are implicated in the pathogenesis of many pathological conditions such as epilepsy, cerebral palsy, autism, and perinatal hypoxic-ischemic brain injury. Although many studies have investigated the origin and functions of the microglia in the developing brain, in-depth in vivo studies along with analysis of their transcriptome and epigenetic changes need to be undertaken to elucidate their full potential be it protective or neurotoxic. This would lead to a better understanding of their roles in the healthy and diseased developing brain and advancement of therapeutic strategies to target microglia-mediated neurotoxicity.

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.

Protandim Protects Oligodendrocytes against an Oxidative Insult

Oligodendrocyte damage and loss are key features of multiple sclerosis (MS) pathology. Oligodendrocytes appear to be particularly vulnerable to reactive oxygen species (ROS) and cytokines, such as tumor necrosis factor-α (TNF), which induce cell death and prevent the differentiation of oligodendrocyte progenitor cells (OPCs). Here, we investigated the efficacy of sulforaphane (SFN), monomethyl fumarate (MMF) and Protandim to induce Nrf2-regulated antioxidant enzyme expression, and protect oligodendrocytes against ROS-induced cell death and ROS-and TNF-mediated inhibition of OPC differentiation. OLN-93 cells and primary rat oligodendrocytes were treated with SFN, MMF or Protandim resulting in significant induction of Nrf2-driven (antioxidant) proteins heme oygenase-1, nicotinamide adenine dinucleotide phosphate (NADPH): quinone oxidoreductase-1 and p62/SQSTM1, as analysed by Western blotting. After incubation with the compounds, oligodendrocytes were exposed to hydrogen peroxide. Protandim most potently promoted oligodendrocyte cell survival as measured by live/death viability assay. Moreover, OPCs were treated with Protandim or vehicle control prior to exposing them to TNF or hydrogen peroxide for five days, which inhibited OPC differentiation. Protandim significantly promoted OPC differentiation under influence of ROS, but not TNF. Protandim, a combination of five herbal ingredients, potently induces antioxidants in oligodendrocytes and is able to protect oligodendrocytes against oxidative stress by preventing ROS-induced cell death and promoting OPC differentiation.

Effects of Interferon-γ and Tumor Necrosis Factor-α on Survival and Differentiation of Oligodendrocyte Progenitors

OBJECTIVE

There is strong evidence from recent clinical studies that ascending intrauterine infection is associated with an increased incidence of periventricular leukomalacia in very premature fetuses. Periventricular leukomalacia is characterized by disrupted myelination from a loss of oligodendrocyte progenitors. We investigated the effects of proinflammatory cytokines on the survival and differentiation of this cell type.

METHODS

Cultures of more than 90% A2B5-positive progenitors were prepared from neonatal rats and kept for 3 days in medium supplemented with factors that stimulate cell proliferation. After 1 day in proliferation medium, cells were treated with interferon-gamma (100 U/mL) and tumor necrosis factor-alpha (100 ng/mL) for 48 hours triggering an increase in apoptotic A2B5 progenitor cells from 3.2 +/- 2.3% to 11.0 +/- 2.6%. After cytokine treatment cultures were transferred to medium containing factors to promote differentiation of progenitors into the myelinating phenotype.

RESULTS

In cytokine pretreated cultures, only 2.6 +/- 1.1% of total cells survived after a total of 9 days in vitro, whereas in untreated cultures most cells differentiated as shown by expression of myelin basic protein, myelin-associated glycoprotein, 2,3-cyclic nucleotide 3-phosphodiesterase, and myelin oligodendrocyte-specific protein. Using ten-fold reduced concentrations of combined interferon-gamma (10 U/mL) and tumor necrosis factor-alpha (10 ng/mL) pretreatment resulted in a survival to 11.2 +/- 4.9% of total cells with 36.3 +/- 11.6% A2B5-positive cells at day 9. This indicates a major enrichment of undifferentiated cells compared with untreated controls which harbored only 1.0 +/- 0.3% A2B5-positive cells.

CONCLUSION

Inflammatory cytokines not only induced apoptotic cell death but also prevented the differentiation of immature A2B5 oligodendrocyte progenitors into the myelinating phenotype.

Impaired oligodendrocyte maturation in preterm infants: Potential therapeutic targets

Preterm birth is an evolving challenge in neonatal health care. Despite declining mortality rates among extremely premature neonates, morbidity rates remain very high. Currently, perinatal diffuse white matter injury (WMI) is the most commonly observed type of brain injury in preterm infants and has become an important research area. Diffuse WMI is associated with impaired cognitive, sensory and psychological functioning and is increasingly being recognized as a risk factor for autism-spectrum disorders, ADHD, and other psychological disturbances. No treatment options are currently available for diffuse WMI and the underlying pathophysiological mechanisms are far from being completely understood. Preterm birth is associated with maternal inflammation, perinatal infections and disrupted oxygen supply which can affect the cerebral microenvironment by causing activation of microglia, astrogliosis, excitotoxicity, and oxidative stress. This intricate interplay of events negatively influences oligodendrocyte development, causing arrested oligodendrocyte maturation or oligodendrocyte cell death, which ultimately results in myelination failure in the developing white matter. This review discusses the current state in perinatal WMI research, ranging from a clinical perspective to basic molecular pathophysiology. The complex regulation of oligodendrocyte development in healthy and pathological conditions is described, with a specific focus on signaling cascades that may play a role in WMI. Furthermore, emerging concepts in the field of WMI and issues regarding currently available animal models are put forward. Novel insights into the molecular mechanisms underlying impeded oligodendrocyte maturation in diffuse WMI may aid the development of novel treatment options which are desperately needed to improve the quality-of-life of preterm neonates.

Pathophysiology and neuroprotection of global and focal perinatal brain injury: lessons from animal models

BACKGROUND

Arterial ischemic stroke occurs more frequently in term newborns than in the elderly, and brain immaturity affects mechanisms of ischemic injury and recovery. The susceptibility to injury of the brain was assumed to be lower in the perinatal period as compared with childhood. This concept was recently challenged by clinical studies showing marked motor disabilities after stroke in neonates, with the severity of motor and cortical sensory deficits similar in both perinatal and childhood ischemic stroke. Our understanding of the triggers and the pathophysiological mechanisms of perinatal stroke has greatly improved in recent years, but many factors remain incompletely understood.

METHODS

In this review, we focus on the pathophysiology of perinatal stroke and on therapeutic strategies that can protect the immature brain from the consequences of stroke by targeting inflammation and brain microenvironment.

RESULTS

Studies in neonatal rodent models of cerebral ischemia have suggested a potential role for soluble inflammatory molecules as important modulators of injury and recovery. A great effort is underway to investigate neuroprotective molecules based on our increasing understanding of the pathophysiology.

CONCLUSION

In this review, we provide a comprehensive summary of new insights concerning pathophysiology of focal and global perinatal brain injury and their implications for new therapeutic approaches.

Glial development: the crossroads of regeneration and repair in the CNS

Given the complexities of the mammalian CNS, its regeneration is viewed as the holy grail of regenerative medicine. Extraordinary efforts have been made to understand developmental neurogenesis, with the hopes of clinically applying this knowledge. CNS regeneration also involves glia, which comprises at least 50% of the cellular constituency of the brain and is involved in all forms of injury and disease response, recovery, and regeneration. Recent developmental studies have given us unprecedented insight into the processes that regulate the generation of CNS glia. Because restorative processes often parallel those found in development, we will peer through the lens of developmental gliogenesis to gain a clearer understanding of the processes that underlie glial regeneration under pathological conditions. Specifically, this review will focus on key signaling pathways that regulate astrocyte and oligodendrocyte development and describe how these mechanisms are reutilized in these populations during regeneration and repair after CNS injury.

ERK1/2 pathway-mediated differentiation of IGF-1-transfected spinal cord-derived neural stem cells into oligodendrocytes

Spinal cord injury (SCI) is a devastating event that causes substantial morbidity and mortality, for which no fully restorative treatments are available. Stem cells transplantation offers some promise in the restoration of neurological function but with limitations. Insulin-like growth factor 1 (IGF-1) is a well-appreciated neuroprotective factor that is involved with various aspects of neural cells. Herein, the IGF-1 gene was introduced into spinal cord-derived neural stem cells (NSCs) and expressed steadily. The IGF-1-transfected NSCs exhibited higher viability and were promoted to differentiate into oligodendrocytes. Moreover, the most possible underlying mechanism, through which IGF-1 exerted its neuroprotective effects, was investigated. The result revealed that the differentiation was mediated by the IGF-1 activated extracellular signal-regulated kinases 1 and 2 (ERK1/2) and its downstream pathway. These findings provide the evidence for revealing the therapeutic merits of IGF-1-modified NSCs for SCI.

Olanzapine ameliorates neuropathological changes and increases IGF-1 expression in frontal cortex of C57BL/6 mice exposed to cuprizone

Cuprizone (CPZ) induced demyelinating mouse has been used as an animal model to examine the assumed roles of altered oligodendrocytes in the pathophysiology and treatment of schizophrenia. The objectives of this study were to examine the effect of olanzapine, an atypical antipsychotic, on cuprizone-induced neuropathological changes in the frontal cortex of C57BL/6 mice, and to explore the underlying mechanism for the possible protective effects. The effects of six-week olanzapine (10 mg/kg/day) treatments on neuropathological changes were examined by immunohistochemistry and Western-blot analyses. Olanzapine treatment for six weeks effectively decreased the breakdown of myelin and oligodendrocytes loss of cuprizone-fed mice. Reactive cellular changes, including astrocyte gliosis, microglia accumulation and increased activation of oligodendrocyte progenitor cells, were also attenuated by olanzapine. However, the cortical expression level of insulin-like growth factor 1 (IGF-1) was significantly increased by olanzapine treatment in cuprizone-fed mice as measured by the quantitative real-time polymerase chain reaction (PCR) method. Olanzapine treatment in control mice consuming normal food had no effect on all above measures. These results provide the first in vivo evidence for the protective effects of olanzapine on cuprizone-induced neuropathological changes and suggest that up-regulated insulin-like growth factor 1 may contribute to the protective effects of this antipsychotic.

From precursors to myelinating oligodendrocytes: contribution of intrinsic and extrinsic factors to white matter plasticity in the adult brain

Oligodendrocyte precursor cells (OPC) are glial cells that metamorphose into myelinating oligodendrocytes during embryogenesis and early stages of post-natal life. OPCs continue to divide throughout adulthood and some eventually differentiate into oligodendrocytes in response to demyelinating lesions. There is growing evidence that OPCs are also involved in activity-driven de novo myelination of previously unmyelinated axons and myelin remodeling in adulthood. In this review, we summarize the interwoven factors and cascades that promote the activation, recruitment and differentiation of OPCs into myelinating oligodendrocytes in the adult brain based mostly on results found in the study of demyelinating diseases. The goal of the review was to draw a complete picture of the transformation of OPCs into mature oligodendrocytes to facilitate the study of this transformation in both the normal and diseased adult brain.

Glial response during cuprizone-induced de- and remyelination in the CNS: lessons learned

Although astrogliosis and microglia activation are characteristic features of multiple sclerosis (MS) and other central nervous system (CNS) lesions the exact functions of these events are not fully understood. Animal models help to understand the complex interplay between the different cell types of the CNS and uncover general mechanisms of damage and repair of myelin sheaths. The so called cuprizone model is a toxic model of demyelination in the CNS white and gray matter, which lacks an autoimmune component. Cuprizone induces apoptosis of mature oligodendrocytes that leads to a robust demyelination and profound activation of both astrocytes and microglia with regional heterogeneity between different white and gray matter regions. Although not suitable to study autoimmune mediated demyelination, this model is extremely helpful to elucidate basic cellular and molecular mechanisms during de- and particularly remyelination independently of interactions with peripheral immune cells. Phagocytosis and removal of damaged myelin seems to be one of the major roles of microglia in this model and it is well known that removal of myelin debris is a prerequisite of successful remyelination. Furthermore, microglia provide several signals that support remyelination. The role of astrocytes during de- and remyelination is not well defined. Both supportive and destructive functions have been suggested. Using the cuprizone model we could demonstrate that there is an important crosstalk between astrocytes and microglia. In this review we focus on the role of glial reactions and interaction in the cuprizone model. Advantages and limitations of as well as its potential therapeutic relevance for the human disease MS are critically discussed in comparison to other animal models.

Immunopathogenesis and immunotherapeutic approaches in multiple sclerosis

Multiple sclerosis is an organ-specific autoimmune disease, characterized pathologically by cell-mediated inflammation, demyelination and variable degrees of axonal loss. Although inflammation is considered central to the pathogenesis of multiple sclerosis, to date, the only licensed and hence widely used multiple sclerosis immunotherapies are interferon-beta, glatiramer acetate and mitoxantrone. This review discusses the immunopathogenesis of multiple sclerosis, focusing on a number of emerging immunotherapies. A number of new approaches likely to manipulate the immunopathogenesis of multiple sclerosis and which may ultimately allow for the development of more effective immunotherapy are also highlighted.

Molecular mechanisms of cognitive impairment in iron deficiency: alterations in brain-derived neurotrophic factor and insulin-like growth factor expression and function in the central nervous system

OBJECTIVE

The present review examines the relationship between iron deficiency and central nervous system (CNS) development and cognitive impairment, focusing on the cellular and molecular mechanisms related to the expression and function of growth factors, particularly the insulin-like growth factors I and II (IGF-I/II) and brain-derived neurotrophic factor (BDNF), in the CNS.

METHODS

Nutritional deficiencies are important determinants in human cognitive impairment. Among these, iron deficiency has the highest prevalence worldwide. Although this ailment is known to induce psychomotor deficits during development, the precise molecular and cellular mechanisms underlying these alterations have not been properly elucidated. This review summarizes the available information on the effect of iron deficiency on the expression and function of growth factors in the CNS, with an emphasis on IGF-I/II and BDNF.

RESULTS AND DISCUSSION

Recent studies have shown that specific growth factors, such as IGF-I/II and BDNF, have an essential role in cognition, particularly in processes involving learning and memory, by the activation of intracellular-signaling pathways involved in cell proliferation, differentiation, and survival. It is known that nutritional deficiencies promote reductions in systemic and CNS concentrations of growth factors, and that altered expression of these molecules and their receptors in the CNS leads to psychomotor and developmental deficits. Iron deficiency may induce these deficits by decreasing the expression and function of IGF-I/II and BDNF in specific areas of the brain.

Mesenchymal stromal-cell transplants induce oligodendrocyte progenitor migration and remyelination in a chronic demyelination model

Demyelinating disorders such as leukodystrophies and multiple sclerosis are neurodegenerative diseases characterized by the progressive loss of myelin that may lead toward a chronic demyelination of the brain's white matter, impairing normal axonal conduction velocity and ultimately causing neurodegeneration. Current treatments modifying the pathological mechanisms are capable of ameliorating the disease; however, frequently, these therapies are not sufficient to repress the progressive demyelination into a chronic condition and permanent loss of function. To this end, we analyzed the effect that bone marrow-derived mesenchymal stromal cell (BM-MSC) grafts exert in a chronically demyelinated mouse brain. As a result, oligodendrocyte progenitors were recruited surrounding the graft due to the expression of various trophic signals by the grafted MSCs. Although there was no significant reaction in the non-grafted side, in the grafted regions oligodendrocyte progenitors were detected. These progenitors were derived from the nearby tissue as well as from the neurogenic niches, including the subependymal zone and dentate gyrus. Once near the graft site, the cells matured to myelinating oligodendrocytes. Finally, electrophysiological studies demonstrated that axonal conduction velocity was significantly increased in the grafted side of the fimbria. In conclusion, we demonstrate here that in chronic demyelinated white matter, BM-MSC transplantation activates oligodendrocyte progenitors and induces remyelination in the tissue surrounding the stem cell graft.

Insulin-like growth factor-1 in CNS and cerebrovascular aging

Insulin-like growth factor-1 (IGF-1) is an important anabolic hormone that decreases with age. In the past two decades, extensive research has determined that the reduction in IGF-1 is an important component of the age-related decline in cognitive function in multiple species including humans. Deficiency in circulating IGF-1 results in impairment in processing speed and deficiencies in both spatial and working memory. Replacement of IGF-1 or factors that increase IGF-1 to old animals and humans reverses many of these cognitive deficits. Despite the overwhelming evidence for IGF-1 as an important neurotrophic agent, the specific mechanisms through which IGF-1 acts have remained elusive. Recent evidence indicates that IGF-1 is both produced by and has important actions on the cerebrovasculature as well as neurons and glia. Nevertheless, the specific regulation and actions of brain- and vascular-derived IGF-1 is poorly understood. The diverse effects of IGF-1 discovered thus far reveal a complex endocrine and paracrine system essential for integrating many of the functions necessary for brain health. Identification of the mechanisms of IGF-1 actions will undoubtedly provide critical insight into regulation of brain function in general and the causes of cognitive decline with age.

White matter injury following fetal inflammatory response syndrome induced by chorioamnionitis and fetal sepsis: lessons from experimental ovine models

Chorioamnionitis and fetal sepsis can induce a fetal inflammatory response syndrome (FIRS) which is closely related to the development of white matter injury in the fetal brain. Large epidemiological studies support the link between FIRS and fetal brain injury with a clear association between the presence of in utero inflammation and neurodevelopmental complications such as cerebral palsy, autism and cognitive impairments later in life. Translational animal models of chorioamnionitis and fetal sepsis are essential in understanding the underlying pathophysiological mechanisms of fetal brain injury after exposure to intra-uterine inflammation. Concerning this aspect, ovine models have high translational value since neurodevelopment in sheep closely resembles the human situation. In this article, we will review clinical and experimental evidence for the link between FIRS and white matter injury in the fetal brain. With respect to experimental findings, we will particularly focus on the lessons learned from ovine models of chorioamnionitis and fetal sepsis. We also highlight two key players implied in the pathophysiology of white matter injury after in utero exposure to inflammation.

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.

Pathophysiology of hypopituitarism in the setting of brain injury

The complex pathophysiology of traumatic brain injury (TBI) involves not only the primary mechanical event but also secondary insults such as hypotension, hypoxia, raised intracranial pressure and changes in cerebral blood flow and metabolism. It is increasingly evident that these initial insults as well as transient events and treatments during the early injury phase can impact hypothalamic-pituitary function both acutely and chronically after injury. In turn, untreated pituitary hormonal dysfunction itself can further hinder recovery from brain injury. Secondary adrenal insufficiency, although typically reversible, occurs in up to 50% of intubated TBI victims and is associated with lower systemic blood pressure. Chronic anterior hypopituitarism, although reversible in some patients, persists in 25-40% of moderate and severe TBI survivors and likely contributes to long-term neurobehavioral and quality of life impairment. While the rates and risk factors of acute and chronic pituitary dysfunction have been documented for moderate and severe TBI victims in numerous recent studies, the pathophysiology remains ill-defined. Herein we discuss the hypotheses and available data concerning hypothalamic-pituitary vulnerability in the setting of head injury. Four possible pathophysiological mechanisms are considered: (1) the primary brain injury event, (2) secondary brain insults, (3) the stress of critical illness and (4) medication effects. Although each of these factors appears to be important in determining which hormonal axes are affected, the severity of dysfunction, their time course and possible reversibility, this process remains incompletely understood.

Acute gonadotroph and somatotroph hormonal suppression after traumatic brain injury

Hormonal dysfunction is a known consequence of moderate and severe traumatic brain injury (TBI). In this study we determined the incidence, time course, and clinical correlates of acute post-TBI gonadotroph and somatotroph dysfunction. Patients had daily measurement of serum luteinizing hormone (LH), follicle-stimulating hormone (FSH), testosterone, estradiol, growth hormone, and insulin-like growth factor-1 (IGF-1) for up to 10 days post-injury. Values below the fifth percentile of a healthy cohort were considered abnormal, as were non-measurable growth hormone (GH) values. Outcome measures were frequency and time course of hormonal suppression, injury characteristics, and Glasgow Outcome Scale (GOS) score. The cohort consisted of 101 patients (82% males; mean age 35 years; Glasgow Coma Scale [GCS] score <or=8 in 87%). In men, 100% had at least one low testosterone value, and 93% of all values were low; in premenopausal women, 43% had at least one low estradiol value, and 39% of all values were low. Non-measurable GH levels occurred in 38% of patients, while low IGF-1 levels were observed in 77% of patients, but tended to normalize within 10 days. Multivariate analysis revealed associations of younger age with low FSH and low IGF-1, acute anemia with low IGF-1, and older age and higher body mass index (BMI) with low GH. Hormonal suppression was not predictive of GOS score. These results indicate that within 10 days of complicated mild, moderate, and severe TBI, testosterone suppression occurs in all men and estrogen suppression occurs in over 40% of women. Transient somatotroph suppression occurs in over 75% of patients. Although this acute neuroendocrine dysfunction may not be TBI-specific, low gonadal steroids, IGF-1, and GH may be important given their putative neuroprotective functions.

Involvement of Src-suppressed C kinase substrate in experimental autoimmune encephalomyelitis: a link between release of astrocyte proinflammatory factor and oligodendrocyte apoptosis

Src-suppressed C kinase substrate (SSeCKS) is involved in inflammation in the central nervous system (CNS), and plays a role in control of cell signaling and cytoskeletal arrangement. However, the expression and function of SSeCKS and its function in multiple sclerosis (MS) and its common animal model, experimental autoimmune encephalomyelitis (EAE) remained to be elucidated. In the present study, we first reported that SSeCKS was remarkably increased in astrocytes of EAE rats in vivo. TNF-alpha and NO were significantly induced in astrocytes stimulated with LPS/IFN-gamma in vitro, which was blocked in astrocytes transfected with SSeCKS siRNA. These results indicated that SSeCKS played a role in the production of TNF-alpha and NO in astrocytes with inflammatory stimulation. As excessive release of TNF-alpha and NO were major mediators in autoimmune diseases and correlated with oligodendrocyte cell death, we further investigated whether SSeCKS participated in oligodendrocyte apoptosis. Conditioned media (CM) from astrocytes treated with LPS/IFN-gamma decreased oligodendrocyte cell viability, while siRNA targeted to SSeCKS in astrocytes inhibited oligodendrocyte cell death. The results from antibody neutralization and NO inhibition suggested that the oligodendrocyte apoptosis may be due to the production of astrocyte-derived proinflammatory factors (TNF-alpha and NO). These findings revealed that there was a pathogenic interaction between SSeCKS expression in astrocytes and oligodendrocyte apoptosis. Understanding the mechanism of SSeCKS in the pathogenesis of EAE may contribute to the development of new therapeutic strategies against EAE and MS.

17beta-estradiol protects male mice from cuprizone-induced demyelination and oligodendrocyte loss

In addition to regulating reproductive functions in the brain and periphery, estrogen has tropic and neuroprotective functions in the central nervous system (CNS). Estrogen administration has been demonstrated to provide protection in several animal models of CNS disorders, including stroke, brain injury, epilepsy, Parkinson's disease, Alzheimer's disease, age-related cognitive decline and multiple sclerosis. Here, we use a model of toxin-induced oligodendrocyte death which results in demyelination, reactive gliosis, recruitment of oligodendrocyte precursor cells and subsequent remyelination to study the potential benefit of 17beta-estradiol (E2) administration in male mice. The results indicate that E2 partially ameliorates loss of oligodendrocytes and demyelination in the corpus callosum. This protection is accompanied by a delay in microglia accumulation as well as reduced mRNA expression of the pro-inflammatory cytokine, tumor necrosis factor alpha (TNFalpha), and insulin-like growth factor-1 (IGF-1). E2 did not significantly alter the accumulation of astrocytes or oligodendrocyte precursor cells, or remyelination. These data obtained from a toxin-induced, T cell-independent model using male mice provide an expanded view of the beneficial effects of estrogen on oligodendrocyte and myelin preservation.

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.

Importance of oligodendrocyte protection, BBB breakdown and inflammation for remyelination

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of the CNS. A better understanding of why remyelination fails in MS is necessary to improve remyelination strategies. Remyelination is mediated by oligodendrocyte precursor cells (OPCs), which are widely distributed throughout the adult CNS. However, it is still unclear whether OPCs detectable in MS lesions survive the inflammatory response but are unable to myelinate or whether OPC and oligodendrocyte death is primarily responsible for remyelination failure and detectable OPCs enter demyelinated areas from adjacent tissue as the lesion evolves. Remyelination strategies should, therefore, focus on stimulation of differentiation or prevention of apoptosis, as well as establishment of a supportive environment for OPC-mediated remyelination, which may be especially important in chronically demyelinated lesions.

Interaction of NG2(+) glial progenitors and microglia/macrophages from the injured spinal cord

Spinal cord contusion produces a central lesion surrounded by a peripheral rim of residual white matter. Despite stimulation of NG2(+) progenitor cell proliferation, the lesion remains devoid of normal glia chronically after spinal cord injury (SCI). To investigate potential cell-cell interactions of the predominant cells in the lesion at 3 days after injury, we used magnetic activated cell sorting to purify NG2(+) progenitors and OX42(+) microglia/macrophages from contused rat spinal cord. Purified NG2(+) cells from the injured cord grew into spherical masses when cultured in defined medium with FGF2 plus GGF2. The purified OX42(+) cells did not form spheroids and significantly reduced sphere growth by NG2(+) cells in co-cultures. Conditioned medium from these OX42(+) cells, unlike that from normal peritoneal macrophages or astrocytes also inhibited growth of NG2(+) cells, suggesting inhibition by secreted factors. Expression analysis of freshly purified OX42(+) cells for a panel of six genes for secreted factors showed expression of several that could contribute to inhibition of NG2(+) cells. Further, the pattern of expression of four of these, TNFalpha, TSP1, TIMP1, MMP9, in sequential coronal tissue segments from a 2 cm length of cord centered on the injury epicenter correlated with the expression of Iba1, a marker gene for OX42(+) cells, strongly suggesting a potential regional influence by activated microglia/macrophages on NG2(+) cells in vivo after SCI. Thus, the nonreplacement of lost glial cells in the central lesion zone may involve, at least in part, inhibitory factors produced by microglia/macrophages that are concentrated within the lesion.

Oligovascular signaling in white matter stroke

Stroke is one of the leading causes of death and disability in developed countries. Since protecting neurons alone is not sufficient for stroke therapy, research has shifted to the rescue of multiple cell types in the brain. In particular, attention has focused on the study of how cerebral blood vessels and brain cells communicate with each other. Recent findings suggest that cerebral endothelial cells may secrete trophic factors that nourish neighboring cells. Although data are strongest in terms of supporting endothelial-neuronal interactions, it is likely that similar interactions occur in white matter as well. In this mini-review, we summarize recent advances in the dissection of cell-cell interactions in white matter. We examine two key concepts. First, trophic interactions between vessels and oligodendrocytes (OLGs) and oligodendrocyte precursor cells (OPCs) play critical roles in white matter homeostasis. Second, cell-cell trophic coupling is disturbed under diseased conditions that incur oxidative stress. White matter pathophysiology is very important in stroke. A deeper understanding of the mechanisms of oligovascular signaling in normal and pathologic conditions may lead us to new therapeutic targets for stroke and other neurodegenerative diseases.

Role of PPARs in Radiation-Induced Brain Injury

Whole-brain irradiation (WBI) represents the primary mode of treatment for brain metastases; about 200 000 patients receive WBI each year in the USA. Up to 50% of adult and 100% of pediatric brain cancer patients who survive >6 months post-WBI will suffer from a progressive, cognitive impairment. At present, there are no proven long-term treatments or preventive strategies for this significant radiation-induced late effect. Recent studies suggest that the pathogenesis of radiation-induced brain injury involves WBI-mediated increases in oxidative stress and/or inflammatory responses in the brain. Therefore, anti-inflammatory strategies can be employed to modulate radiation-induced brain injury. Peroxisomal proliferator-activated receptors (PPARs) are ligand-activated transcription factors that belong to the steroid/thyroid hormone nuclear receptor superfamily. Although traditionally known to play a role in metabolism, increasing evidence suggests a role for PPARs in regulating the response to inflammation and oxidative injury. PPAR agonists have been shown to cross the blood-brain barrier and confer neuroprotection in animal models of CNS disorders such as stroke, multiple sclerosis and Parkinson's disease. However, the role of PPARs in radiation-induced brain injury is unclear. In this manuscript, we review the current knowledge and the emerging insights about the role of PPARs in modulating radiation-induced brain injury.

Adult-onset deficiency in growth hormone and insulin-like growth factor-I alters oligodendrocyte turnover in the corpus callosum

Growth hormone (GH) and insulin-like growth factor-I (IGF-I) provide trophic support during development and also appear to influence cell structure, function and replacement in the adult brain. Recent studies demonstrated effects of the GH/IGF-I axis on adult neurogenesis, but it is unclear whether the GH/IGF-I axis influences glial turnover in the normal adult brain. In the current study, we used a selective model of adult-onset GH and IGF-I deficiency to evaluate the role of GH and IGF-I in regulating glial proliferation and survival in the adult corpus callosum. GH/IGF-I-deficient dwarf rats of the Lewis strain were made GH/IGF-I replete via twice daily injections of GH starting at postnatal day 28 (P28), approximately the age at which GH pulse amplitude increases in developing rodents. GH/IGF-I deficiency was initiated in adulthood by removing animals from GH treatment. Quantitative analyses revealed that adult-onset GH/IGF-I deficiency decreased cell proliferation in the white matter and decreased the survival of newborn oligodendrocytes. These findings are consistent with the hypothesis that aging-related changes in the GH/IGF-I axis produce deficits in ongoing turnover of oligodendrocytes, which may contribute to aging-related cognitive changes and deficits in remyelination after injury.

PPARalpha ligands inhibit radiation-induced microglial inflammatory responses by negatively regulating NF-kappaB and AP-1 pathways

Whole-brain irradiation (WBI) can lead to cognitive impairment several months to years after irradiation. Studies on rodents have shown a rapid and sustained increase in activated microglia (brain macrophages) following brain irradiation, contributing to a chronic inflammatory response and a corresponding decrease in hippocampal neurogenesis. Thus, alleviating microglial activation following radiation represents a key strategy to minimize WBI-induced morbidity. We hypothesized that pretreatment with peroxisomal proliferator-activated receptor (PPAR)alpha agonists would ameliorate the proinflammatory responses seen in the microglia following in vitro radiation. Irradiating BV-2 cells (a murine microglial cell line) with single doses (2-10 Gy) of (137)Cs gamma-rays led to increases in (1) the gene expression of IL-1beta and TNFalpha, (2) Cox-2 protein levels, and (3) intracellular ROS generation. In addition, an increase in the DNA-binding activity of redox-regulated proinflammatory transcription factors AP-1 and NF-kappaB was observed. Pretreating BV-2 cells with the PPARalpha agonists GW7647 and Fenofibrate significantly inhibited the radiation-induced microglial proinflammatory response, in part, via decreasing (i) the nuclear translocation of the NF-kappaB p65 subunit and (ii) phosphorylation of the c-jun subunit of AP-1 in the nucleus. Taken together, these data support the hypothesis that activation of PPARalpha can modulate the radiation-induced microglial proinflammatory response.

Lysosomal disorders: from storage to cellular damage

Lysosomal storage diseases represent a group of about 50 genetic disorders caused by deficiencies of lysosomal and non-lysosomal proteins. Patients accumulate compounds which are normally degraded in the lysosome. In many diseases this accumulation affects various organs leading to severe symptoms and premature death. The revelation of the mechanism by which stored compounds affect cellular function is the basis for understanding pathophysiology underlying lysosomal storage diseases. In the past years it has become clear that storage compounds interfere with various processes on the cellular level. The spectrum covers e.g. receptor activation by non-physiologic ligands, modulation of receptor response and intracellular effectors of signal transduction cascades, impairment of autophagy, and others. Importantly, many of these processes are associated with accumulation of storage material in non-lysosomal compartments. Here we summarize current knowledge on the effects that storage material can elicit on the cellular level.

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.

Exercise and brain health--implications for multiple sclerosis: Part 1--neuronal growth factors

The benefits of regular exercise to promote general health and reduce the risk of hypokinetic diseases associated with sedentary lifestyles are well recognized. Recent studies suggest that exercise may enhance neurobiological processes that promote brain health in aging and disease. A current frontier in the neurodegenerative disorder multiple sclerosis (MS) concerns the role of physical activity for promoting brain health through protective, regenerative and adaptive neural processes. Research on neuromodulation, raises the possibility that regular physical activity may mediate favourable changes in disease factors and symptoms associated with MS, in part through changes in neuroactive proteins. Insulin-like growth factor-I appears to act as a neuroprotective agent and studies indicate that exercise could promote this factor in MS. Neurotrophins, brain-derived neurotrophic factor (BDNF) and nerve growth factor likely play roles in neuronal survival and activity-dependent plasticity. Physical activity has also been shown to up-regulate hippocampal BDNF, which may play a role in mood states, learning and memory to lessen the decline in cognitive function associated with MS. In addition, exercise may promote anti-oxidant defences and neurotrophic support that could attenuate CNS vulnerability to neuronal degeneration. Exercise exposure (preconditioning) may serve as a mechanism to enhance stress resistance and thereby may support neuronal survival under heightened stress conditions. Considering that axonal loss and cerebral atrophy occur early in the disease, exercise prescription in the acute stage could promote neuroprotection, neuroregeneration and neuroplasticity and reduce long-term disability. This review concludes with a proposed conceptual model to connect these promising links between exercise and brain health.

CB2 cannabinoid receptors as an emerging target for demyelinating diseases: from neuroimmune interactions to cell replacement strategies

Amongst the various demyelinating diseases that affect the central nervous system, those induced by an inflammatory response stand out because of their epidemiological relevance. The best known inflammatory-induced demyelinating disease is multiple sclerosis, but the immune response is a common pathogenic mechanism in many other less common pathologies (e.g., acute disseminated encephalomyelitis and acute necrotizing haemorrhagic encephalomyelitis). In all such cases, modulation of the immune response seems to be a logical therapeutic approach. Cannabinoids are well known immunomodulatory molecules that act through CB1 and CB2 receptors. While activation of CB1 receptors has a psychotropic effect, activation of CB2 receptors alone does not. Therefore, to bypass the ethical problems that could result from the treatment of inflammation with psychotropic molecules, considerable effort is being made to study the potential therapeutic value of activating CB2 receptors. In this review we examine the current knowledge and understanding of the utility of cannabinoids as therapeutic molecules for inflammatory-mediated demyelinating pathologies. Moreover, we discuss how CB2 receptor activation is related to the modulation of immunopathogenic states.

Delayed IGF-1 administration rescues oligodendrocyte progenitors from glutamate-induced cell death and hypoxic-ischemic brain damage

We previously demonstrated that IGF-1 blocks glutamate-mediated death of late oligodendrocyte progenitors (OPs) by preventing Bax translocation, mitochondrial cytochrome c release and cleavage of caspases 9 and 3. Here, we demonstrate that IGF-1 prevents caspase 3 activation in late OPs when administered up to 16 h following exposure to glutamate. Moreover, late addition of IGF-1 to OPs previously exposed to toxic levels of glutamate promotes oligodendrocyte maturation as measured by myelin basic protein expression. We also demonstrate that intraventricularly administered IGF-1 retains OPs in the perinatal white matter after hypoxia-ischemia when given after insult. These results suggest that delayed administration of IGF-1 will rescue OPs in the immature white matter and promote myelination following hypoxia-ischemia.

Synergistic induction of cyclin D1 in oligodendrocyte progenitor cells by IGF-I and FGF-2 requires differential stimulation of multiple signaling pathways

D-type cyclins are direct targets of extracellular signals and critical regulators of G(1) progression. Our previous data demonstrated that IGF-I and FGF-2 synergize to enhance cyclin D1 expression, cyclin E/cdk2 complex activation, and S-phase entry in OP cells. Here, we provide a mechanistic explanation for how two growth factor signaling pathways converge on a major cell cycle regulator. IGF-I and FGF-2 differentially activate signaling pathways to coordinately promote cyclin D1 expression. We show that the p44/p42 MAPK signaling pathway is essential for FGF-2 induction of cyclin D1 mRNA. In contrast, blocking the PI3-Kinase pathway results in loss of IGF-I/FGF-2 synergistic induction of cyclin D1 protein levels. Moreover, the presence of IGF-I significantly enhances nuclear localization of cyclin D1, which also requires PI3K signaling. GSK-3beta, a downstream target of the PI3K/Akt pathway, is phosphorylated in the presence of IGF-I in OPs. Consistent with a known role for GSK-3beta in cyclin D1 degradation, we show that proteasome inhibition in OPs exposed to FGF-2 increased cyclin D1 levels, equivalent to levels seen in IGF-I/FGF-2 treated cells. Thus, we provide a model for cyclin D1 coordinate regulation where FGF-2 stimulation of the MAPK pathway promotes cyclin D1 mRNA expression while IGF-I activation of the PI3K pathway inhibits proteasome degradation of cyclin D1 and enhances nuclear localization of cyclin D1.

Inflammation at birth and the insulin-like growth factor system in very preterm infants

BACKGROUND

Foetal inflammation is associated with an increased risk of brain damage in preterm infants whereas IGF-I is essential for cerebral development and exhibits anti-apoptotic properties.

AIM

To assess levels of IGF-I and IGF binding proteins at very preterm birth and to evaluate their relationship with foetal pro-inflammation and cerebral damage.

METHODS

Levels of IGF-I, IGF binding protein 3 (IGFBP-3), high- (hp) and low-phosphorylated (lp) IGFBP-1 in cord blood and neonatal blood at 72 h after delivery were analysed in relation to levels of cytokines and cerebral damage as detected by ultrasound in 74 inborn infants [mean gestational age (GA) 27.1 weeks]. Evaluation was performed separately according to birth weight for GA.

RESULTS

In cord blood of infants appropriate for gestational age (AGA) higher levels of IL-6 and IL-8 were associated with lower IGF-I (r =-0.38, p = 0.008 and r =-0.36, p = 0.014). Higher levels of IL-6, IL-8 and TNF-alpha were associated with both higher levels of lpIGFBP-1 (r = 0.54, p < 0.001, r = 0.50, p < 0.001 and r = 0.13, p = 0.012, respectively) and hpIGFBP-1 (r = 0.55, p < 0.001, r = 0.45, p = 0.002 and r = 0.32, p = 0.026, respectively). Infants with intraventricular haemorrhage grade III (n = 5) had higher levels of lp/hpIGFBP-1 in cord blood (p = 0.001 and 0.002, respectively).

CONCLUSION

Pro-inflammation at birth is associated with changes in the IGF-system. This may be of importance for development of brain damage in preterm infants.

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.

Insulin-like growth factor-I (IGF-I) inhibits neuronal apoptosis in the developing cerebral cortex in vivo

Increased expression of insulin-like growth factor-I (IGF-I) in embryonic neural progenitors in vivo has been shown to accelerate neuron proliferation in the neocortex. In the present study, the in vivo actions of (IGF-I) on naturally occurring neuron death in the cerebral cortex were investigated during embryonic and early postnatal development in a line of transgenic (Tg) mice that overexpress IGF-I in the brain, directed by nestin genomic regulatory elements, beginning at least as early as embryonic day (E) 13. The areal density of apoptotic cells (N(A), cells/mm2) at E16 in the telencephalic wall of Tg and littermate control embryos was determined by immunostaining with an antibody specific for activated caspase-3. Stereological analyses were conducted to measure the numerical density (N(V), cells/mm3) and total number of immunoreactive apoptotic cells in the cerebral cortex of nestin/IGF-I Tg and control mice at postnatal days (P) 0 and 5. The volume of cerebral cortex and both the N(V) and total number of all cortical neurons also were determined in both cerebral hemispheres at P0, P5 and P270. Apoptotic cells were rare in the embryonic telencephalic wall at E16. However, the overall N(A) of apoptotic cells was found to be significantly less by 46% in Tg embryos. The volume of the cerebral cortex was significantly greater in Tg mice at P0 (30%), P5 (13%) and P270 (26%). The total number of cortical neurons in Tg mice was significantly increased at P0 (29%), P5 (29%) and P270 (31%), although the N(V) of cortical neurons did not differ significantly between Tg and control mice at any age. Transgenic mice at P0 and P5 exhibited significant decreases in the N(V) of apoptotic cells in the cerebral cortex (31% and 39%, respectively). The vast majority of these apoptotic cells (> 90%) were judged to be neurons by their morphological appearance. Increased expression of IGF-I inhibits naturally occurring (i.e. apoptotic) neuron death during early postnatal development of the cerebral cortex to a degree that sustains a persistent increase in total neuron number even in the adult animal.

Insulin-like growth factor type 1 receptor signaling in the cells of oligodendrocyte lineage is required for normal in vivo oligodendrocyte development and myelination

Insulin-like growth factor-I (IGF-I) has been shown to be a potent agent in promoting the growth and differentiation of oligodendrocyte precursors, and in stimulating myelination during development and following injury. To definitively determine whether IGF-I acts directly on the cells of oligodendrocyte lineage, we generated lines of mice in which the type 1 IGF receptor gene (igf1r) was conditionally ablated either in Olig1 or proteolipid protein expressing cells (termed IGF1R(pre-oligo-ko) and IGF1R(oligo-ko) mice, respectively). Compared with wild type mice, IGF1R(pre-oligo-ko) mice had a decreased volume (by 35-55%) and cell number (by 54-70%) in the corpus callosum (CC) and anterior commissure at 2 and 6 weeks of age, respectively. IGF1R(oligo-ko) mice by 25 weeks of age also showed reductions, albeit less marked, in CC volume and cell number. Unlike astrocytes, the percentage of NG2(+) oligodendrocyte precursors was decreased by approximately 13% in 2-week-old IGF1R(pre-oligo-ko) mice, while the percentage of CC1(+) mature oligodendrocytes was decreased by approximately 24% in 6-week-old IGF1R(pre-oligo-ko) mice and approximately 25% in 25-week-old IGF1R(oligo-ko) mice. The reduction in these cells is apparently a result of decreased proliferation and increased apoptosis. These results indicate that IGF-I directly affects oligodendrocytes and myelination in vivo via IGF1R, and that IGF1R signaling in the cells of oligodendrocyte lineage is required for normal oligodendrocyte development and myelination. These data also provide a fundamental basis for developing strategies with the potential to target IGF-IGF1R signaling pathways in oligodendrocyte lineage cells for the treatment of demyelinating disorders.

A non-transformed oligodendrocyte precursor cell line, OL-1, facilitates studies of insulin-like growth factor-I signaling during oligodendrocyte development

The process by which oligodendrocyte progenitors differentiate into mature oligodendrocytes is complex and incompletely understood in part because of the paucity of oligodendrocyte precursors cell lines that can be studied in culture. We have developed a non-immortalized rat oligodendrocyte precursor line, called OL-1, which behaves in a fashion consistent with developing oligodendrocytes in vivo. This OL-1 line provides a model for the study of oligodendrocyte development and offers an alternative to the CG-4 cell line. When OL-1 cells are propagated in conditioned growth media, they have morphology consistent with immature oligodendrocytes and exhibit A2B5 antigen positive and myelin basic protein-negative immunoreactivity. Withdrawal of conditioned growth media and culture in serum-free medium results in OL-1 cell maturation, manifested by a shift to myelin basic protein-positive immunoreactivity, A2B5 antigen-negative immunoreactivity, decreased NG2 mRNA expression, increased expression of proteolipid protein mRNA, and increased expression of CNP protein. In addition, the expression of proteolipid protein and its splicing variant DM-20 exhibit a pattern that is similar to brain proteolipid protein expression during development. When OL-1 cells are exposed to Insulin-like growth factor-I, there are significant increases in proteolipid protein mRNA expression (p<0.05), the number of cell processes (p<0.05), and cell number (p<0.05). Treatment with the caspase inhibitors Z-DEVD-FMK and Z-VAD-FMK (inhibitors of caspases 3, 6, 7, 8, 10 and 1, 3, 4, respectively), Insulin-like growth factor-I, or both, results in a similar increase in cell number. Because Insulin-like growth factor-I does not substantially increase the BrdU labeling of OL-1 cells, these data collectively indicate that Insulin-like growth factor-I increases OL-1 cell number predominately by promoting survival, rather than stimulating proliferation. This non-immortalized oligodendrocyte precursor cell line, therefore, exhibits behavior consistent with the in vivo development of oligodendrocytes and provides an excellent model for the study of developing oligodendrocytes.

IGF-1 protects oligodendrocyte progenitors against TNFα-induced damage by activation of PI3K/Akt and interruption of the mitochondrial apoptotic pathway

Proinflammatory cytokine-mediated injury to oligodendrocyte progenitor cells (OPCs) has been proposed as a cause of periventricular leukomalacia (PVL), the most common brain injury found in preterm infants. Preventing death of OPCs is a potential strategy to prevent or treat PVL. In the current study, we utilized an in vitro cell culture system to investigate the effect of insulin-like growth factor-1 (IGF-1) on tumor necrosis factor-alpha (TNFalpha)-induced OPC injury and the possible mechanisms involved. OPCs were isolated from neonatal rat optic nerves and cultured in chemically defined medium (CDM) supplemented with platelet-derived growth factor and basic fibroblast growth factor. Exposure to TNFalpha resulted in death of OPCs. IGF-1 protected OPCs from TNFalpha cytotoxicity in a dose-dependent manner as measured by the XTT and TUNEL assays. IGF-1 activates both the PI3K/Akt and the extracellular signal-regulated kinase (ERK) pathway. However, IGF-1-enhanced cell survival signals were mediated by the PI3K/Akt, but not by the ERK pathway, as evidenced by the observation that IGF-1-enhanced cell survival was partially abrogated by Akti, the Akt inhibitor, or wortmannin, the PI3K inhibitor, but not by PD98,059, the MAPK kinase/ERK kinase inhibitor. The downstream events of IGF-1-triggered survival signals included phosphorylation of BAD, blockade of TNFalpha-induced translocation of Bax from the cytosol to the mitochondrial membrane, and suppression of caspase-9 and caspase-3 activation. These observations indicate that the protection of OPCs by IGF-1 is mediated, at least partially, by interruption of the mitochondrial apoptotic pathway via activation of PI3K/Akt.

Combination of growth factors enhances remyelination in a cuprizone-induced demyelination mouse model

Loss of oligodendrocytes (OLs) is often associated with demyelination. PDGF-AA, bFGF, NT3 and IGF-1 are known to regulate OL proliferation, survival and/or differentiation. Following cuprizone-induced demyelination in mice a combination of above four growth factors (GF) was intracranially injected to stimulate remyelination in vivo. Activation of cell signaling and transcription factors involved in cell proliferation, survival and differentiation was observed in response to GF. Increased cell proliferation and migration occurred in corpus callosum, lateral ventricles, rostral migratory stream and cerebri at 2-5 days post injection (dpi) of GF cocktail. The fate of these newly formed nestin or bromodeoxyuridine (BrdU) positive progenitors was traced to proteoglycan NG2 and glutathione transferase (GST) pi positive cells, early and mature OL lineage markers, respectively. Immunostaining for myelin showed the presence of more myelinated fibers in GF-injected brains at 21 dpi. Remyelination in response to GF was confirmed by electron microscopy. In conclusion, this combination of GF is a promising tool to consider for remyelination strategies.

Increased citrullination of histone H3 in multiple sclerosis brain and animal models of demyelination: a role for tumor necrosis factor-induced peptidylarginine deiminase 4 translocation

Modification of arginine residues by citrullination is catalyzed by peptidylarginine deiminases (PADs), of which five are known, generating irreversible protein structural modifications. We have shown previously that enhanced citrullination of myelin basic protein contributed to destabilization of the myelin membrane in the CNS of multiple sclerosis (MS) patients. We now report increased citrullination of nucleosomal histones by PAD4 in normal-appearing white matter (NAWM) of MS patients and in animal models of demyelination. Histone citrullination was attributable to increased levels and activity of nuclear PAD4. PAD4 translocation into the nucleus was attributable to elevated tumor necrosis factor-alpha (TNF-alpha) protein. The elevated TNF-alpha in MS NAWM was not associated with CD3+ or CD8+ lymphocytes, nor was it associated with CD68+ microglia/macrophages. GFAP, a measure of astrocytosis, was the only cytological marker that was consistently elevated in the MS NAWM, suggesting that TNF-alpha may have been derived from astrocytes. In cell cultures of mouse and human oligodendroglial cell lines, PAD4 was predominantly cytosolic but TNF-alpha treatment induced its nuclear translocation. To address the involvement of TNF-alpha in targeting PAD4 to the nucleus, we found that transgenic mice overexpressing TNF-alpha also had increased levels of citrullinated histones and elevated nuclear PAD4 before demyelination. In conclusion, high citrullination of histones consequent to PAD4 nuclear translocation is part of the process that leads to irreversible changes in oligodendrocytes and may contribute to apoptosis of oligodendrocytes in MS.

Deleterious role of IFNgamma in a toxic model of central nervous system demyelination

Interferon-gamma (IFNgamma) is a pleiotropic cytokine that plays an important role in many inflammatory processes, including autoimmune diseases such as multiple sclerosis (MS). Demyelination is a hallmark of MS and a prominent pathological feature of several other inflammatory diseases of the central nervous system, including experimental autoimmune encephalomyelitis, an animal model of MS. Accordingly, in this study we followed the effect of IFNgamma in the demyelination and remyelination process by using an experimental autoimmune encephalomyelitis model of demyelination/remyelination after exposure of mice to the neurotoxic agent cuprizone. We show that demyelination in response to cuprizone is delayed in mice lacking the binding chain of IFNgamma receptor. In addition, IFNgammaR(-/-) mice exhibited an accelerated remyelination process after cuprizone was removed from the diet. Our results also indicate that the levels of IFNgamma were able to modulate the microglia/macrophage recruitment to the demyelinating areas. Moreover, the accelerated regenerative response showed by the IFNgammaR(-/-) mice was associated with a more efficient recruitment of oligodendrocyte precursor cells in the demyelinated areas. In conclusion, this study suggests that IFNgamma regulates the development and resolution of the demyelinating syndrome and may be associated with toxic effects on both mature oligodendrocytes and oligodendrocyte precursor cells.