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

Role of MAPK and PI3K-Akt signaling pathways in cuprizone-induced demyelination and cognitive impairment in mice

This study aimed to find the genes and signaling pathways underlying cuprizone-induced demyelination and cognitive impairments in mice. We used the cuprizone-exposed mice as an animal model of schizophrenia and assessed cognitive function in mice. Total RNA was extracted from mouse brain tissues for RNA sequencing. The DESeq2 R package was utilized to analyze the differentially expressed genes (DEGs). Functional and pathway enrichment analyses were performed simultaneously. We also constructed a protein-protein interaction (PPI) network to screen potential hub genes, and quantitative real-time polymerase chain reaction (qRT-PCR) was employed to validate the screened genes. After 6 weeks of cuprizone treatment, the cognitive function of mice was impaired. Compared to the controls, the cuprizone-exposed mice contained 351 DEGs, including 167 upregulated and 184 downregulated genes. Enrichment analysis showed that the DEGs were enriched in some biological processes involved in demyelination, including the MAPK pathway. Functional pathway analysis revealed that the DEGs were significantly enriched in the PI3K-Akt signaling pathway, which may be associated with cognitive impairments. MBP, IGF1, GFAP, PTPRC, CD14, CD68, ITGB2, LYN, TLR2, TLR4, VAV1, and PLEK were considered as potential hub genes. Except for MBP, all genes were upregulated in the cuprizone models, as verified by qRT-PCR. We suggest that the MAPK and PI3K-Akt signaling pathways may be associated with demyelination and cognitive impairments, respectively. GFAP and IGF-1 expression levels increased in cuprizone-exposed mice, suggesting that astrocytes may play a role in protecting the myelin sheath following treatment with cuprizone.

Degenerative Cervical Myelopathy: Insights into Its Pathobiology and Molecular Mechanisms

Degenerative cervical myelopathy (DCM), earlier referred to as cervical spondylotic myelopathy (CSM), is the most common and serious neurological disorder in the elderly population caused by chronic progressive compression or irritation of the spinal cord in the neck. The clinical features of DCM include localised neck pain and functional impairment of motor function in the arms, fingers and hands. If left untreated, this can lead to significant and permanent nerve damage including paralysis and death. Despite recent advancements in understanding the DCM pathology, prognosis remains poor and little is known about the molecular mechanisms underlying its pathogenesis. Moreover, there is scant evidence for the best treatment suitable for DCM patients. Decompressive surgery remains the most effective long-term treatment for this pathology, although the decision of when to perform such a procedure remains challenging. Given the fact that the aged population in the world is continuously increasing, DCM is posing a formidable challenge that needs urgent attention. Here, in this comprehensive review, we discuss the current knowledge of DCM pathology, including epidemiology, diagnosis, natural history, pathophysiology, risk factors, molecular features and treatment options. In addition to describing different scoring and classification systems used by clinicians in diagnosing DCM, we also highlight how advanced imaging techniques are being used to study the disease process. Last but not the least, we discuss several molecular underpinnings of DCM aetiology, including the cells involved and the pathways and molecules that are hallmarks of this disease.

Neuronal insulin signaling and brain structure in nondemented older adults: the Atherosclerosis Risk in Communities Study

We used plasma neuronal extracellular vesicles to examine how neuronal insulin signaling proteins relate cross-sectionally to brain structure in nondemented older adults with varying levels of cortical amyloid. Extracellular vesicles enriched for neuronal origin by anti-L1CAM immunoabsorption were isolated from plasma of Atherosclerosis Risk in Communities-Positron Emission Tomography study participants (n = 88; mean age: 77 years [standard deviation: 6]). Neuronal extracellular vesicle levels of phosphorylated insulin signaling cascade proteins were quantified. Brain volume and white matter hyperintensity (WMH) volume were assessed using 3T magnetic resonance imaging. After adjusting for demographic variables and extracellular vesicle marker Alix, higher levels of a neuronal insulin signaling composite measure were associated with lower WMH and greater temporal lobe volume. Secondary analyses found the levels of downstream protein kinases involved in cell survival (p70S6K) and tau phosphorylation/neuroinflammation (GSK-3β) to be most strongly associated with WMH and temporal lobe volume, respectively. Associations between neuronal insulin signaling and lower WMH volume were attenuated in participants with elevated cortical amyloid. These results suggest that enhanced neuronal proximal insulin signaling is associated with preserved brain structure in nondemented older adults.

Origin and dynamics of oligodendrocytes in the developing brain: Implications for perinatal white matter injury

Infants born prematurely are at high risk to develop white matter injury (WMI), due to exposure to hypoxic and/or inflammatory insults. Such perinatal insults negatively impact the maturation of oligodendrocytes (OLs), thereby causing deficits in myelination. To elucidate the precise pathophysiology underlying perinatal WMI, it is essential to fully understand the cellular mechanisms contributing to healthy/normal white matter development. OLs are responsible for myelination of axons. During brain development, OLs are generally derived from neuroepithelial zones, where neural stem cells committed to the OL lineage differentiate into OL precursor cells (OPCs). OPCs, in turn, develop into premyelinating OLs and finally mature into myelinating OLs. Recent studies revealed that OPCs develop in multiple waves and form potentially heterogeneous populations. Furthermore, it has been shown that myelination is a dynamic and plastic process with an excess of OPCs being generated and then abolished if not integrated into neural circuits. Myelination patterns between rodents and humans show high spatial and temporal similarity. Therefore, experimental studies on OL biology may provide novel insights into the pathophysiology of WMI in the preterm infant and offers new perspectives on potential treatments for these patients.

Blocked, delayed, or obstructed: What causes poor white matter development in intrauterine growth restricted infants?

Poor white matter development in intrauterine growth restricted (IUGR) babies remains a major, untreated problem in neonatology. New therapies, guided by an understanding of the mechanisms that underlie normal and abnormal oligodendrocyte development and myelin formation, are required. Much of our knowledge of the mechanisms that underlie impaired myelination come from studies in adult demyelinating disease, preterm brain injury, or experimental models of hypoxia-ischemia. However, relatively less is known for IUGR which is surprising because IUGR is a leading cause of perinatal mortality and morbidity, second only to premature birth. IUGR is also a significant risk factor for the later development of cerebral palsy, and is a greater risk compared to some of the more traditionally researched antecedents - asphyxia and inflammation. Recent evidence suggests that the white matter injury and reduced myelination in the brains of some preterm babies is due to impaired maturation of oligodendrocytes thereby resulting in the reduced capacity to synthesize myelin. Therefore, it is not surprising that the hypomyelination observable in the central nervous system of IUGR infants has similarly lead to investigations identifying a delay or blockade in the progress of maturation of oligodendrocytes in these infants. This review will discuss current ideas thought to account for the poor myelination often present in the neonate's brain following IUGR, and discuss novel interventions that are promising as treatments that promote oligodendrocyte maturation, and thereby repair the myelination deficits that otherwise persist into infancy and childhood and lead to neurodevelopmental abnormalities.

Electroacupuncture Promotes Remyelination after Cuprizone Treatment by Enhancing Myelin Debris Clearance

Promoting remyelination is crucial for patients with demyelinating diseases including multiple sclerosis. However, it is still a circuitous conundrum finding a practical remyelinating therapy. Electroacupuncture (EA), originating from traditional Chinese medicine (TCM), has been widely used to treat CNS diseases all over the world, but the role of EA in demyelinating diseases is barely known. In this study, we examined the remyelinating properties and mechanisms of EA in cuprizone-induced demyelinating model, a CNS demyelinating murine model of multiple sclerosis. By feeding C57BL/6 mice with chow containing 0.2% cuprizone for 5 weeks, we successfully induce demyelination as proved by weight change, beam test, pole test, histomorphology, and Western Blot. EA treatment significantly improves the neurobehavioral performance at week 7 (2 weeks after withdrawing cuprizone chow). RNA-seq and RT-PCR results reveal up-regulated expression of myelin-related genes, and the expression of myelin associated protein (MBP, CNPase, and O4) are also increased after EA treatment, indicating therapeutic effect of EA on cuprizone model. It is widely acknowledged that microglia exert phagocytic effect on degraded myelin debris and clear these detrimental debris, which is a necessary process for subsequent remyelination. We found the remyelinating effect of EA is associated with enhanced clearance of degraded myelin debris as detected by dMBP staining and red oil O staining. Our further studies suggest that more microglia assemble in demyelinating area (corpus callosum) during the process of EA treatment, and cells inside corpus callosum are mostly in a plump, ameboid, and phagocytic shape, quite different from the ramified cells outside corpus callosum. RNA-seq result also unravels that most genes relating to positive regulation of phagocytosis (GO:0050766) are up-regulated, indicating enhanced phagocytic process after EA treatment. During the process of myelin debris clearance, microglia tend to change their phenotype toward M2 phenotype. Thus, we also probed into the phenotype of microglia in our study. Immuno-staining results show increased expression of CD206 and Arg1, and the ratio of CD206/CD16/32 are also higher in EA group. In conclusion, these results demonstrate for the first time that EA enhances myelin debris removal from activated microglia after demyelination, and promotes remyelination.

Differential Sphingolipid and Phospholipid Profiles in Alcohol and Nicotine-Derived Nitrosamine Ketone-Associated White Matter Degeneration

BACKGROUND

Alcohol-mediated neurodegeneration is associated with white matter (WM) atrophy due to targeting of myelin and oligodendrocytes. However, variability in disease severity suggests cofactors contribute to WM degeneration. We examined the potential cofactor role of the tobacco-specific nitrosamine, nicotine-derived nitrosamine ketone (NNK), because smoking causes WM atrophy and most heavy drinkers consume tobacco products.

METHODS

This 8-week study of Long Evans rats had 4 treatment groups: control; NNK-2 mg/kg, 3×/wk in weeks 3 to 8; ethanol (EtOH) (chronic-26% caloric + binge-2 g/kg, 3×/wk in weeks 7 to 8); and EtOH + NNK. Exposure effects on WM lipid biochemical profiles and in situ distributions were examined using matrix-assisted laser desorption/ionization imaging mass spectrometry and tandem mass spectrometry.

RESULTS

NNK mainly caused WM fiber degeneration and fiber loss, EtOH caused demyelination, and dual exposures had additive effects. EtOH and EtOH + NNK decreased WM (including corpus callosum) and/or gray matter (hypothalamus, cortex, medial temporal) levels of several phosphatidylserine, phosphatidylinositol, and sphingolipid (sulfatide [ST]) species, while NNK increased or had minimal effect on these lipids. EtOH + NNK had broader and larger inhibitory effects on phospholipids and ST than EtOH or NNK alone. Principal component analysis clustered control with NNK, and EtOH with EtOH + NNK groups, highlighting the independent EtOH- rather than NNK-driven responses.

CONCLUSIONS

Chronic EtOH exposures decreased several phospholipid and sphingolipid species in brain, while concomitant NNK exposures exacerbated these effects. These findings support our hypothesis that tobacco smoking is a pathogenic cofactor in alcohol-mediated WM degeneration.

Extracellular cues influencing oligodendrocyte differentiation and (re)myelination

There is an increasing number of neurologic disorders found to be associated with loss and/or dysfunction of the CNS myelin sheath, ranging from the classic demyelinating disease, multiple sclerosis, through CNS injury, to neuropsychiatric diseases. The disabling burden of these diseases has sparked a growing interest in gaining a better understanding of the molecular mechanisms regulating the differentiation of the myelinating cells of the CNS, oligodendrocytes (OLGs), and the process of (re)myelination. In this context, the importance of the extracellular milieu is becoming increasingly recognized. Under pathological conditions, changes in inhibitory as well as permissive/promotional cues are thought to lead to an overall extracellular environment that is obstructive for the regeneration of the myelin sheath. Given the general view that remyelination is, even though limited in human, a natural response to demyelination, targeting pathologically 'dysregulated' extracellular cues and their downstream pathways is regarded as a promising approach toward the enhancement of remyelination by endogenous (or if necessary transplanted) OLG progenitor cells. In this review, we will introduce the extracellular cues that have been implicated in the modulation of (re)myelination. These cues can be soluble, part of the extracellular matrix (ECM) or mediators of cell-cell interactions. Their inhibitory and permissive/promotional roles with regard to remyelination as well as their potential for therapeutic intervention will be discussed.

Potential Contributions of the Tobacco Nicotine-Derived Nitrosamine Ketone to White Matter Molecular Pathology in Fetal Alcohol Spectrum Disorder

Background

Fetal alcohol spectrum disorder (FASD) is associated with long-term deficits in cognitive and motor functions. Previous studies linked neurodevelopmental abnormalities to increased oxidative stress and white matter hypotrophy. However, similar effects occur with low-dose nitrosamine exposures, alcohol abuse correlates with cigarette smoking, and tobacco smoke contains tobacco-specific nitrosamines, including NNK.

Hypothesis

Tobacco smoke exposure is a co-factor in FASD.

Design

Long Evans rat pups were i.p. administered ethanol (2 g/kg) on postnatal days (P) 2, 4, 6 and/or NNK (2 mg/kg) on P3, P5, and P7 to simulate third trimester human exposures. Oligodendroglial myelin-associated, neuroglial, and relevant transcription factor mRNA transcripts were measured using targeted PCR arrays.

Results

Ethanol and NNK differentially altered the expression of immature and mature oligodendroglial, neuronal and astrocytic structural and plasticity-associated, and various transcription factor genes. NNK’s effects were broader and more pronounced than ethanol’s, and additive or synergistic effects of dual exposures impacted expression of all four categories of genes investigated.

Conclusion

Developmental exposures to alcohol and NNK (via tobacco smoke) contribute to sustained abnormalities in brain white matter structure and function via distinct but overlapping alterations in the expression of genes that regulate oligodendrocyte survival, maturation and function, neuroglial structural integrity, and synaptic plasticity. The results support the hypothesis that smoking may contribute to brain abnormalities associated with FASD.

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.

Involvement of IRS-1 interaction with ADAM10 in the regulation of neurite extension

The insulin-like growth factor-1 (IGF-1) signaling pathway plays an important role in neuronal cell differentiation. Recent studies have shown that IGF-1 has the capacity to counteract the retraction of neuronal processes in response to inflammatory cytokines such as TNF-α, which is a known factor for neuronal injury in the central nervous system. This event is thought to be mediated via interference of TNF-α-induced interaction of β1-integrin with insulin receptor substrate-1 (IRS-1). Here, we demonstrate the interaction of IRS-1 with disintegrin and metalloproteinase ADAM10 through the N-terminal domain of IRS-1 and that this is involved in the regulation of neurite extension and retraction by IGF-1 and TNF-α, respectively. PC12 cells expressing the N-terminal domain show enhanced neurite extension after IGF-1 treatment and reduced neurite depletion relative to control cells after TNF-α treatment. The level of ADAM10 was found to be increased in immunohistochemical studies of HIV encephalitis clinical samples and is present with TNF-α and TNFR1 in both astrocytes and neurons. Altogether, these observations suggest a role for ADAM10 in the mechanism for IGF1/IRS-1 signaling pathway in sustaining the stability of neuronal processes.

Signaling mechanisms regulating myelination in the central nervous system

The precise and coordinated production of myelin is essential for proper development and function of the nervous system. Diseases that disrupt myelin, including multiple sclerosis, cause significant functional disability. Current treatment aims to reduce the inflammatory component of the disease, thereby preventing damage resulting from demyelination. However, therapies are not yet available to improve natural repair processes after damage has already occurred. A thorough understanding of the signaling mechanisms that regulate myelin generation will improve our ability to enhance repair. in this review, we summarize the positive and negative regulators of myelination, focusing primarily on central nervous system myelination. Axon-derived signals, extracellular signals from both diffusible factors and the extracellular matrix, and intracellular signaling pathways within myelinating oligodendrocytes are discussed. Much is known about the positive regulators that drive myelination, while less is known about the negative regulators that shift active myelination to myelin maintenance at the appropriate time. Therefore, we also provide new data on potential negative regulators of CNS myelination.

Motor Function Deficits Following Chronic Prenatal Ethanol Exposure are Linked to Impairments in Insulin/IGF, Notch and Wnt Signaling in the Cerebellum

BACKGROUND

Fetal alcohol spectrum disorder (FASD) is associated with deficits in cerebellar function that can persist through adolescence. Previous studies demonstrated striking inhibition of insulin and insulin-like growth factor (IGF) signaling in ethanol-exposed cerebella.

OBJECTIVES

We sought to determine if FASD-induced impairments in motor function were associated with deficits in insulin/IGF signaling in juvenile cerebella. Given the growing evidence that insulin/IGF pathways cross-talk with Notch and Wnt to promote brain development and maturation; we also examined the integrity of canonical Wnt and Notch signaling networks in the brain following chronic prenatal ethanol exposure.

METHODS

Pregnant Long Evans rats were fed isocaloric liquid diets containing 0% or 24% ethanol by caloric content from gestation day 6 through delivery. Pups were subjected to rotarod testing on postnatal days (P) 15-16 and sacrificed on P30. Cerebella were used for molecular and biochemical analysis of insulin/IGF-1, canonical Wnt, and Notch signaling mechanisms.

RESULTS

Prenatal ethanol exposures impaired rotarod performance, inhibited signaling through insulin and IGF-1 receptors, IRS-1, and Akt, increased activation of GSK-3β, and broadly suppressed genes mediating the canonical Wnt and Notch networks.

CONCLUSIONS

Abnormalities in cerebellar function following chronic prenatal ethanol exposure are associated with inhibition of insulin/IGF, canonical Wnt, and Notch networks that cross-talk via GSK-3β. Effective therapeutic measures for FASD may require multi-pronged support of interrelated signaling networks that regulate brain development.

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.

Sustained Impairments in Brain Insulin/IGF Signaling in Adolescent Rats Subjected to Binge Alcohol Exposures during Development

Background

Chronic or binge ethanol exposures during development can cause fetal alcohol spectrum disorder (FASD) which consists of an array of neurobehavioral deficits, together with structural, molecular, biochemical, and neurotransmitter abnormalities in the brain. Previous studies showed that perinatal neurodevelopmental defects in FASD are associated with inhibition of brain insulin and insulin-like growth factor (IGF) signaling. However, it is not known whether sustained abnormalities in adolescent brain structure and function are mediated by the same phenomena.

Aims

Using an early postnatal (3^rd trimester equivalent) binge ethanol exposure model, we assessed neurobehavioral function, structure, and the integrity of insulin/IGF signaling in young adolescent cerebella.

Methods

Long Evans male rats were treated with 50 µl of saline (vehicle) or 2 mg/kg of ethanol by i.p. injection on postnatal days (P) 2, 4, 6, and 8. On P19–20, rats were subjected to rotarod testing of motor function, and on P30, they were sacrificed to harvest cerebella for histological, molecular, and biochemical studies.

Results

Binge ethanol exposures impaired motor function, caused sustained cerebellar hypocellularity, and reduced neuronal and oligodendrocyte gene expression. These effects were associated with significant deficits in insulin and IGF signaling, including impaired receptor binding, reduced Akt, and increased GSK-3β activation.

Conclusions

FASD-associated neurobehavioral, structural, and functional abnormalities in young adolescent brains may be mediated by sustained inhibition of insulin/IGF-1 signaling needed for cell survival, neuronal plasticity, and myelin maintenance.

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

CONTEXT

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

OBJECTIVE

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

DESIGN

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

MAIN OUTCOME MEASURES

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

RESULTS

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

CONCLUSION

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

si-RNA inhibition of brain insulin or insulin-like growth factor receptors causes developmental cerebellar abnormalities: relevance to fetal alcohol spectrum disorder

BACKGROUND

In experimental models of fetal alcohol spectrum disorder (FASD), cerebellar hypoplasia and hypofoliation are associated with insulin and insulin-like growth factor (IGF) resistance with impaired signaling through pathways that mediate growth, survival, plasticity, metabolism, and neurotransmitter function. To more directly assess the roles of impaired insulin and IGF signaling during brain development, we administered intracerebroventricular (ICV) injections of si-RNA targeting the insulin receptor, (InR), IGF-1 receptor (IGF-1R), or IGF-2R into postnatal day 2 (P2) Long Evans rat pups and examined the sustained effects on cerebellar function, structure, and neurotransmitter-related gene expression (P20).

RESULTS

Rotarod tests on P20 demonstrated significant impairments in motor function, and histological studies revealed pronounced cerebellar hypotrophy, hypoplasia, and hypofoliation in si-InR, si-IGF-1R, and si-IGF-2R treated rats. Quantitative RT-PCR analysis showed that si-InR, and to a lesser extent si-IGF-2R, broadly inhibited expression of insulin and IGF-2 polypeptides, and insulin, IGF-1, and IGF-2 receptors in the brain. ELISA studies showed that si-InR increased cerebellar levels of tau, phospho-tau and β-actin, and inhibited GAPDH. In addition, si-InR, si-IGF-1R, and si-IGF-2R inhibited expression of choline acetyltransferase, which mediates motor function. Although the ICV si-RNA treatments generally spared the neurotrophin and neurotrophin receptor expression, si-InR and si-IGF-1R inhibited NT3, while si-IGF-1R suppressed BDNF.

CONCLUSIONS

early postnatal inhibition of brain InR expression, and to lesser extents, IGF-R, causes structural and functional abnormalities that resemble effects of FASD. The findings suggest that major abnormalities in brains with FASD are mediated by impairments in insulin/IGF signaling. Potential therapeutic strategies to reduce the long-term impact of prenatal alcohol exposure may include treatment with agents that restore brain insulin and IGF responsiveness.

ADAM12 is expressed by astrocytes during experimental demyelination

A disintegrin and metalloproteinase (ADAM) 12 represents a member of a large family of similarly structured multi-domain proteins. In the central nervous system (CNS), ADAM12 has been suggested to play a role in brain development, glioblastoma cell proliferation, and in experimental autoimmune encephalomyelitis. Furthermore, ADAM12 was reported to be almost exclusively expressed by oligodendrocytes and could, therefore, be considered as suitable marker for this cell type. In the present study, we investigated ADAM12 expression in the healthy and pathologically altered murine CNS. As pathological paradigm, we used the cuprizone demyelination model in which myelin loss during multiple sclerosis is imitated. Besides APC(+) oligodendrocytes, SMI311(+) neurons and GFAP(+) astrocytes express ADAM12 in the adult mouse brain. ADAM12 expression was further analyzed in vitro. After the induction of demyelination, we observed that activated astrocytes are the main source of ADAM12 in brain regions affected by oligodendrocyte loss. Exposure of astrocytes in vitro to either lipopolysaccharides (LPS), tumor necrosis factor alpha (TNFalpha), glutamate, or hydrogen peroxide revealed a highly stimulus-specific regulation of ADAM12 expression which was not seen in microglial BV2 cells. It appears that LPS- and TNFalpha-induced ADAM12 expression is mediated via the classic NFkappaB pathway. In summary, we demonstrated that ADAM12 is not a suitable marker for oligodendrocytes. Our results further suggest that ADAM12 might be implicated in the course of distinct CNS diseases such as demyelinating disorders.

Activation and deactivation of periventricular white matter phagocytes during postnatal mouse development

Brain microglia are related to peripheral macrophages but undergo a highly specific process of regional maturation and differentiation inside the brain. Here, we examined this deactivation and morphological differentiation in cerebral cortex and periventricular subcortical white matter, the main "fountain of microglia" site, during postnatal mouse development, 0-28 days after birth (P0-P28). Only macrophages in subcortical white matter but not cortical microglia exhibited strong expression of typical activation markers alpha5, alpha6, alphaM, alphaX, and beta2 integrin subunits and B7.2 at any postnatal time point studied. White matter phagocyte activation was maximal at P0, decreased linearly over P3 and P7 and disappeared at P10. P7 white matter phagocytes also expressed high levels of IGF1 and MCSF, but not TNFalpha mRNA; this expression disappeared at P14. This process of deactivation followed the presence of ingested phagocytic material but correlated only moderately with ramification, and not with the extent of TUNEL+ death in neighboring cells, their ingestion or microglial proliferation. Intravenous fluosphere labeling revealed postnatal recruitment and transformation of circulating leukocytes into meningeal and perivascular macrophages as well as into ramified cortical microglia, but bypassing the white matter areas. In conclusion, this study describes strong and selective activation of postnatally resident phagocytes in the P0-P7 subcortical white matter, roughly equivalent to mid 3rd trimester human fetal development. This presence of highly active and IGF1- and MCSF-expressing phagocytes in the neighborhood of vulnerable white matter could play an important role in the genesis of or protection against axonal damage in the fetus and premature neonate.

Insulin resistance and neurodegeneration: roles of obesity, type 2 diabetes mellitus and non-alcoholic steatohepatitis

Recent studies have linked obesity, type 2 diabetes mellitus (T2DM) or non-alcoholic steatohepatitis (NASH) to insulin resistance in the brain, cognitive impairment and neurodegeneration. Insulin resistance compromises cell survival, metabolism and neuronal plasticity, and increases oxidative stress, cytokine activation and apoptosis. T2DM/NASH has been demonstrated to be associated with increased ceramide generation, suggesting a mechanistic link between peripheral insulin resistance and neurodegeneration because ceramides mediate insulin resistance and can cross the blood-brain barrier (BBB). Peripheral insulin resistance diseases may potentially cause brain insulin resistance via a liver-brain axis of neurodegeneration as a result of the trafficking of ceramides across the BBB. Therapy that includes insulin-sensitizing agents may help prevent brain insulin resistance-mediated cognitive impairment.

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.

The liver-brain axis of alcohol-mediated neurodegeneration: role of toxic lipids

Alcohol abuse causes progressive toxicity and degeneration in liver and brain due to insulin resistance, which exacerbates oxidative stress and pro-inflammatory cytokine activation. Alcohol-induced steatohepatitis promotes synthesis and accumulation of ceramides and other toxic lipids that cause insulin resistance. Ceramides can readily cross the blood-brain barrier, and ceramide exposure causes neurodegeneration with insulin resistance and oxidative stress, similar to the effects of alcohol. Therefore, in addition to its direct neurotoxic effects, alcohol misuse establishes a liver-brain axis of neurodegeneration mediated by toxic lipid trafficking across the blood-brain barrier, leading to progressive white matter degeneration and cognitive impairment.

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.

IGF-1 signaling reduces neuro-inflammatory response and sensitivity of neurons to MPTP

Reduced expression of IGF-1R increases lifespan and resistance to oxidative stress in the mouse, raising the possibility that this also confers relative protection against the pro-parkinsonian neurotoxin MPTP, known to involve an oxidative stress component. We used heterozygous IGF-1R(+/-) mice and challenged them with MPTP. Interestingly, MPTP induced more severe lesions of dopaminergic neurons of the substantia nigra, in IGF-1R(+/-) mice than in wild-type animals. Using electron spin resonance, we found that free radicals were decreased in IGF-1R(+/-) mice in comparison with controls, both before and after MPTP exposure, suggesting that the increased vulnerability of dopamine neurons is not caused by oxidative stress. Importantly, we showed that IGF-1R(+/-) mice display a dramatically increased neuro-inflammatory response to MPTP that may ground the observed increase in neuronal death. Microarray analysis revealed that oxidative stress-associated genes, but also several anti-inflammatory signaling pathways were downregulated under control conditions in IGF-1R(+/-) mice compared to WT. Collectively, these data indicate that IGF signaling can reduce neuro-inflammation dependent sensitivity of neurons to MPTP.

Insulin-like growth factor system regulates oligodendroglial cell behavior: therapeutic potential in CNS

Amongst the many soluble extracellular factors stimulating intracellular signal transduction pathways and driving cellular processes such as proliferation, differentiation and survival, insulin-like growth factors (IGFs) stand out as indispensable factors for proper oligodendrocyte differentiation and accompanying myelin production. Owing to its potent myelinogenic capacity and its neuroprotective properties, IGFs hold therapeutic potential in demyelinating and neurodengenerative diseases. However, the IGF system is comprised of a complex molecular network involving regulatory binding proteins, proteases, cell surface and extracellular matrix components which orchestrate IGF-specific functions. Thus, the complexity by which these factors are tightly regulated makes a simplistic therapeutic approach towards treating demyelinating conditions unfeasible. In the present review, we address these issues and consider current therapeutic prospects of oligodendrocyte-targeted IGF-based therapies.