Peripheral infusion of insulin-like growth factor-I increases the number of newborn oligodendrocytes in the cerebral cortex of adult hypophysectomized rats

The Impact of Prenatal Alcohol Exposure on Longitudinal Growth, Nutritional Status, and Insulin-Like Growth Factor 1 in Early Childhood in Leyte, the Philippines

OBJECTIVE

To assess the impact and potential mechanistic pathways of prenatal alcohol exposure (PAE) on longitudinal growth and nutritional status in early childhood.

STUDY DESIGN

A cohort of 296 mother-infant dyads (32% with PAE vs 68% unexposed) were recruited in Leyte, the Philippines, and followed from early gestation through 24 months of age. PAE was assessed using serum phosphatidylethanol (PEth) captured twice prenatally and in cord blood and supplemented with self-reported alcohol consumption. Linear mixed models were used to examine longitudinal effects of PAE on growth from birth through 2 years including key potential mediating factors (placental histopathology, and infant serum leptin and Insulin-like Growth Factor 1 [IGF-1]).

RESULTS

After adjusting for potential confounders, we found that PAE was significantly associated with a delayed blunting of linear growth trajectories (height-for-age z-score, body length) and weight (weight-for-age z-score, body weight) that manifested between 4 and 6 months and continued through 12-24 months. PAE was also associated with a decreased rate of mid-upper-arm circumference growth from birth to 12 months, and a lower mean IGF-1 levels at birth and 6 months.

CONCLUSION

This study demonstrates a delayed impact of PAE on growth that manifested around 6 months of age, underscoring the importance of routine clinical monitoring in early childhood. Furthermore, the findings supported prior animal model findings that suggest a mechanistic role for IGF-1 in PAE-induced growth delay.

Consequences of oxygen deprivation on myelination and sex-dependent alterations

Oxygen deprivation is one of the main causes of morbidity and mortality in newborns, occurring with a higher prevalence in preterm infants, reaching 20 % to 50 % mortality in newborns in the perinatal period. When they survive, 25 % exhibit neuropsychological pathologies, such as learning difficulties, epilepsy, and cerebral palsy. White matter injury is one of the main features found in oxygen deprivation injury, which can lead to long-term functional impairments, including cognitive delay and motor deficits. The myelin sheath accounts for much of the white matter in the brain by surrounding axons and enabling the efficient conduction of action potentials. Mature oligodendrocytes, which synthesize and maintain myelination, also comprise a significant proportion of the brain's white matter. In recent years, oligodendrocytes and the myelination process have become potential therapeutic targets to minimize the effects of oxygen deprivation on the central nervous system. Moreover, evidence indicate that neuroinflammation and apoptotic pathways activated during oxygen deprivation may be influenced by sexual dimorphism. To summarize the most recent research about the impact of sexual dimorphism on the neuroinflammatory state and white matter injury after oxygen deprivation, this review presents an overview of the oligodendrocyte lineage development and myelination, the impact of oxygen deprivation and neuroinflammation on oligodendrocytes in neurodevelopmental disorders, and recent reports about sexual dimorphism regarding the neuroinflammation and white matter injury after neonatal oxygen deprivation.

Hydrogen Ion Dynamics as the Fundamental Link between Neurodegenerative Diseases and Cancer: Its Application to the Therapeutics of Neurodegenerative Diseases with Special Emphasis on Multiple Sclerosis

The pH-related metabolic paradigm has rapidly grown in cancer research and treatment. In this contribution, this recent oncological perspective has been laterally assessed for the first time in order to integrate neurodegeneration within the energetics of the cancer acid-base conceptual frame. At all levels of study (molecular, biochemical, metabolic, and clinical), the intimate nature of both processes appears to consist of opposite mechanisms occurring at the far ends of a physiopathological intracellular pH/extracellular pH (pHi/pHe) spectrum. This wide-ranging original approach now permits an increase in our understanding of these opposite processes, cancer and neurodegeneration, and, as a consequence, allows us to propose new avenues of treatment based upon the intracellular and microenvironmental hydrogen ion dynamics regulating and deregulating the biochemistry and metabolism of both cancer and neural cells. Under the same perspective, the etiopathogenesis and special characteristics of multiple sclerosis (MS) is an excellent model for the study of neurodegenerative diseases and, utilizing this pioneering approach, we find that MS appears to be a metabolic disease even before an autoimmune one. Furthermore, within this paradigm, several important aspects of MS, from mitochondrial failure to microbiota functional abnormalities, are analyzed in depth. Finally, and for the first time, a new and integrated model of treatment for MS can now be advanced.

Oligodendrocyte Response to Pathophysiological Conditions Triggered by Episode of Perinatal Hypoxia-Ischemia: Role of IGF-1 Secretion by Glial Cells

Differentiation of oligodendrocyte progenitors towards myelinating cells is influenced by a plethora of exogenous instructive signals. Insulin-like growth factor 1 (IGF-1) is one of the major factors regulating cell survival, proliferation, and maturation. Recently, there is an ever growing recognition concerning the role of autocrine/paracrine IGF-1 signaling in brain development and metabolism. Since oligodendrocyte functioning is altered after the neonatal hypoxic-ischemic (HI) insult, a question arises if the injury exerts any influence on the IGF-1 secreted by neural cells and how possibly the change in IGF-1 concentration affects oligodendrocyte growth. To quantify the secretory activity of neonatal glial cells, the step-wise approach by sequentially using the in vivo, ex vivo, and in vitro models of perinatal asphyxia was applied. A comparison of the results of in vivo and ex vivo studies allowed evaluating the role of autocrine/paracrine IGF-1 signaling. Accordingly, astroglia were indicated to be the main local source of IGF-1 in the developing brain, and the factor secretion was shown to be significantly upregulated during the first 24 h after the hypoxic-ischemic insult. And conversely, the IGF-1 amounts released by oligodendrocytes and microglia significantly decreased. A morphometric examination of oligodendrocyte differentiation by means of the Sholl analysis showed that the treatment with low IGF-1 doses markedly improved the branching of oligodendroglial cell processes and, in this way, promoted their differentiation. The changes in the IGF-1 amounts in the nervous tissue after HI might contribute to the resulting white matter disorders, observed in newborn children who experienced perinatal asphyxia. Pharmacological modulation of IGF-1 secretion by neural cells could be reasonable solution in studies aimed at searching for therapies alleviating the consequences of perinatal asphyxia.

Insulin-like growth factor 1 signaling in motor neuron and polyglutamine diseases: From molecular pathogenesis to therapeutic perspectives

The pleiotropic peptide insulin-like growth factor 1 (IGF-I) regulates human body homeostasis and cell growth. IGF-I activates two major signaling pathways, namely phosphoinositide-3-kinase (PI3K)/protein kinase B (PKB/Akt) and Ras/extracellular signal-regulated kinase (ERK), which contribute to brain development, metabolism and function as well as to neuronal maintenance and survival. In this review, we discuss the general and tissue-specific effects of the IGF-I pathways. In addition, we present a comprehensive overview examining the role of IGF-I in neurodegenerative diseases, such as spinal and muscular atrophy, amyotrophic lateral sclerosis, and polyglutamine diseases. In each disease, we analyze the disturbances of the IGF-I pathway, the modification of the disease protein by IGF-I signaling, and the therapeutic strategies based on the use of IGF-I developed to date. Lastly, we highlight present and future considerations in the use of IGF-I for the treatment of these disorders.

Exercise in Adulthood after Irradiation of the Juvenile Brain Ameliorates Long-Term Depletion of Oligodendroglial Cells

Cranial radiation severely affects brain health and function, including glial cell production and myelination. Recent studies indicate that voluntary exercise has beneficial effects on oligodendrogenesis and myelination. Here, we hypothesized that voluntary running would increase oligodendrocyte numbers in the corpus callosum after irradiation of the juvenile mouse brain. The brains of C57Bl/6J male mice were 6 Gy irradiated on postnatal day 9 during the main gliogenic developmental phase, resulting in a loss of oligodendrocyte precursor cells. Upon adulthood, the mice were injected with bromodeoxyuridine and allowed to exercise on a running wheel for four weeks. Cell proliferation and survival, Ascl1⁺ oligodendrocyte precursor and Olig2⁺ oligodendrocyte cell numbers as well as CC1⁺ mature oligodendrocytes were quantified using immunohistology. Radiation induced a reduction in the number of Olig2⁺ oligodendrocytes by nearly 50% without affecting production or survival of new Olig2⁺ cells. Ascl1⁺ cells earlier in the oligodendroglial cell lineage were also profoundly affected, with numbers reduced by half. By three weeks of age, Olig2⁺ cell numbers had not recovered, and this was paralleled by a volumetric loss in the corpus callosum. The deficiency of Olig2⁺ oligodendrocytes persisted into adulthood. Additionally, the depletion of Ascl1⁺ progenitor cells was irreversible, and was even more pronounced at 12 weeks postirradiation compared to day 2 postirradiation. Furthermore, the overall number of CC1⁺ mature oligodendrocytes decreased by 28%. The depletion of Olig2⁺ cells in irradiated animals was reversed by 4 weeks of voluntary exercise. Moreover, voluntary exercise also increased the number of Ascl1⁺ progenitor cells in irradiated animals. Taken together, these results demonstrate that exercise in adulthood significantly ameliorates the profound and long-lasting effects of moderate exposure to immature oligodendrocytes during postnatal development.

Mode of GH administration and gene expression in the female rat brain

The endogenous secretion of growth hormone (GH) is sexually dimorphic in rats with females having a more even and males a more pulsatile secretion and low trough levels. The mode of GH administration, mimicking the sexually dimorphic secretion, has different systemic effects. In the brains of male rats, we have previously found that the mode of GH administration differently affects neuron-haemoglobin beta (Hbb) expression whereas effects on other transcripts were moderate. The different modes of GH administration could have different effects on brain transcripts in female rats. Hypophysectomised female rats were given GH either as injections twice daily or as continuous infusion and GH-responsive transcripts were assessed by quantitative reverse transcription polymerase chain reaction in the hippocampus and parietal cortex (cortex). The different modes of GH-administration markedly increased Hbb and 5'-aminolevulinate synthase 2 (Alas2) in both brain regions. As other effects were relatively moderate, a mixed model analysis (MMA) was used to investigate general effects of the treatments. In the hippocampus, MMA showed that GH-infusion suppressed glia- and neuron-related transcript expression levels, whereas GH-injections increased expression levels. In the cortex, GH-infusion instead increased neuron-related transcripts, whereas GH-injections had no significant effect. Interestingly, this contrasts to previous results obtained from male rat cortex where GH-infusion generally decreased expression levels. In conclusion, the results indicate that there is a small but significant difference in response to mode of GH administration in the hippocampus as compared to the cortex. For both modes of GH administration, there was a robust effect on Hbb and Alas2.

IGF-1 as a Drug for Preterm Infants: A Step-Wise Clinical Development

BACKGROUND

Insulin-like growth factor 1 (IGF-1) is a mitogenic hormone involved in many processes such as growth, metabolism, angiogenesis and differentiation. After very preterm birth, energy demands increase while maternal supplies of nutrients and other factors are lost and the infant may become dependent on parenteral nutrition for weeks. Low postnatal IGF-1 concentrations in preterm infants are associated with poor weight gain, retinopathy of prematurity (ROP) and other morbidities. We will describe the process by which we aim to develop supplementation with recombinant human (rh) IGF-1 and its binding protein rhIGFBP-3 as a possible therapy to promote growth and maturation and reduce morbidities in extremely preterm infants.

METHODS

In order to calculate a dose of IGF-1 tolerated by neonates, a pharmacokinetic study of transfusion with fresh frozen plasma was performed, which provided a relatively low dose of IGF-1, (on average 1.4 µg/kg), that increased serum IGF-1 to levels close to those observed in fetuses and preterm infants of similar GAs. Thereafter, a Phase I 3 hours IV infusion of rhIGF-1/rhIGFBP-3 was conducted in 5 infants, followed by a Phase II study with four sections (A-D). In the Phase II, sections A-D studies, time on infusion increased and younger gestational ages were included.

RESULTS

IV infusion increased IGF-1 but with short half-life (0.5h) implying a need for continuous infusion. In order to obtain in utero levels of IGF-I, the dose was increased from 100 to 250 µg/kg/24 h and the infusion was prolonged from 3 weeks postnatal age until a postmenstrual age of 29 weeks and 6 days.

CONCLUSION

The purpose has been to ensure high-quality research into the development of a new drug for preterm infants. We hope that our work will help to establish a new standard for the testing of medications for preterm infants.

Multiple Effects of Growth Hormone in the Body: Is it Really the Hormone for Growth?

In this review, we analyze the effects of growth hormone on a number of tissues and organs and its putative role in the longitudinal growth of an organism. We conclude that the hormone plays a very important role in maintaining the homogeneity of tissues and organs during the normal development of the human body or after an injury. Its effects on growth do not seem to take place during the fetal period or during the early infancy and are mediated by insulin-like growth factor I (IGF-I) during childhood and puberty. In turn, IGF-I transcription is dependent on an adequate GH secretion, and in many tissues, it occurs independent of GH. We propose that GH may be a prohormone, rather than a hormone, since in many tissues and organs, it is proteolytically cleaved in a tissue-specific manner giving origin to shorter GH forms whose activity is still unknown.

Different modes of GH administration influence gene expression in the male rat brain

The endogenous secretion pattern in males of GH is episodic in rats and in humans, whereas GH administration is usually even. Different types of GH administration have different effects on body mass, longitudinal bone growth, and liver metabolism in rodents, whereas possible effects on brain plasticity have not been investigated. In this study, GH was administered as a continuous infusion or as two daily injections in hypophysectomized male rats. Thirteen transcripts previously known to respond to GH in the hippocampus and parietal cortex (cortex) were assessed by RT-PCR. To investigate the effects of type of GH administration on several transcripts with different variations, and categories of transcripts (neuron-, glia-, and GH-related), a mixed model analysis was applied. Accordingly, GH injections increased overall transcript abundance more than GH infusions (21% in the hippocampus, P<0.001 and 10% in the cortex, P=0.09). Specifically, GH infusions and injections robustly increased neuronal hemoglobin beta (Hbb) expression significantly (1.8- to 3.6-fold), and GH injections were more effective than GH infusions in increasing Hbb in the cortex (41%, P=0.02), whereas a 23% difference in the hippocampus was not significant. Also cortical connexin 43 was higher in the group with GH injections than in those with GH infusions (26%, P<0.007). Also, there were differences between GH injections and infusions in GH-related transcripts of the cortex (23%, P=0.04) and glia-related transcripts of the hippocampus (15%, P=0.02). Thus, with the exception of Hbb there is a moderate difference in responsiveness to different modes of GH administration.

GH/IGF1 axis disturbances in the fibromyalgia syndrome: is there a rationale for GH treatment?

Fibromyalgia Syndrome (FMS) is a frequent idiopathic condition in which patients experience intense pain in specific tender points, profound fatigue and sleep disturbances. Although pain had not account so far in growth hormone deficiency syndrome (GHD) description, symptoms of FMS are very similar; and there is strong evidence of decreased GH secretion at least in a subset of FMS patients. Is there an overlap of the two diseases? A systematic Medline/Embase search for preliminary proof-of-concept trials, but also larger placebo-controlled studies, have shown that GH replacement in low-IGF1 patients can significantly improve some symptoms of FMS and quality of life, suggesting a direct causal effect of GH deficiency. Despite the use of relatively high doses of GH in these patients, treatment seems to be well tolerated. Several mechanisms of action for GH in FMS relief have been suggested, including both central modulation of pain and peripheral musculo-tendinous effects, as already described in classic GHD.

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.

Systemic effects of fractionated, whole-brain irradiation in young adult and aging rats

Cranial irradiation is a critical and effective treatment for primary brain tumors and metastases. Unfortunately, most patients who are treated and survive for more than a few months develop neural and cognitive problems as the result of radiation-induced normal tissue injury. The neurobiological mechanisms underlying these cognitive deficits remain largely unknown and there are no validated treatments to prevent or ameliorate them; thus, there is a significant and continuing need for preclinical studies in animal models. Investigations from several laboratories have demonstrated neurobiological changes after cranial irradiation in rodents. To date, however, experimental studies in animal models have included little assessment of the systemic effects of cranial irradiation, despite evidence from the clinic that cranial irradiation results in changes throughout the body and recognition that systemic responses may influence the development of neural and cognitive deficits. This study evaluated systemic effects of clinically relevant, fractionated whole-brain irradiation in adult rats and demonstrates effects on the growth hormone/insulin-like growth factor-I axis, which may contribute to the development of neural changes. These and other systemic responses are important to consider in ongoing efforts to understand the mechanisms of radiation-induced normal tissue injury.

Role of growth hormone (GH) in the treatment on neural diseases: from neuroprotection to neural repair

Growth hormone (GH) is a pleiotropic hormone that exerts important functions in the control of brain development as well as in the regulation neuronal differentiation and function, together with several behavioral and psychological effects that have been linked to its modulatory actions on brain neurotransmitters. In addition, the possibility that GH may play a role on brain repair after injury has been also envisaged, and a number of reports have shown that GH administration following injury confers neuroprotection and accelerates the recovery of some neural functions. In this review we have analyzed the state of the art of GH administration in several neural diseases. Though more studies are still necessary in order to completely understand the importance of GH in these processes, the promising results obtained so far, together with the absence of untoward effects during GH therapy, encourages the development of clinical assays in order to further support the use GH treatment in neural diseases in which neuroprotection and/or neuroregeneration are involved.

Early growth hormone (GH) treatment promotes relevant motor functional improvement after severe frontal cortex lesion in adult rats

A number of studies, in animals and humans, describe the positive effects of the growth hormone (GH) treatment combined with rehabilitation on brain reparation after brain injury. We examined the effect of GH treatment and rehabilitation in adult rats with severe frontal motor cortex ablation. Thirty-five male rats were trained in the paw-reaching-for-food task and the preferred forelimb was recorded. Under anesthesia, the motor cortex contralateral to the preferred forelimb was aspirated or sham-operated. Animals were then treated with GH (0.15 mg/kg/day, s.c) or vehicle during 5 days, commencing immediately or 6 days post-lesion. Rehabilitation was applied at short- and long-term after GH treatment. Behavioral data were analized by ANOVA following Bonferroni post hoc test. After sacrifice, immunohistochemical detection of glial fibrillary acid protein (GFAP) and nestin were undertaken in the brain of all groups. Animal group treated with GH immediately after the lesion, but not any other group, showed a significant improvement of the motor impairment induced by the motor lesion, and their performances in the motor test were no different from sham-operated controls. GFAP immunolabeling and nestin immunoreactivity were observed in the perilesional area in all injured animals; nestin immunoreactivity was higher in GH-treated injured rats (mainly in animals GH-treated 6 days post-lesion). GFAP immunoreactivity was similar among injured rats. Interestingly, nestin re-expression was detected in the contralateral undamaged motor cortex only in GH-treated injured rats, being higher in animals GH-treated immediately after the lesion than in animals GH-treated 6 days post-lesion. Early GH treatment induces significant recovery of the motor impairment produced by frontal cortical ablation. GH effects include increased neurogenesis for reparation (perilesional area) and for increased brain plasticity (contralateral motor area).

Growth hormone (GH) and brain trauma

Growth hormone (GH) is a pleiotropic hormone with known neurotrophic effects. We aimed to study whether GH administration might be useful together with rehabilitation in the recovery of TBI patients. 13 TBI patients (8 M, 5 F; age: 6-53 years old) were studied. Time after TBI: 2.5 months to 11 years; 5 patients showed acquired GH-deficiency (GHD). Disabilities observed: cognitive disorders; motor plegias; neurogenic dysphagia (n=5), vegetative coma (n=2) and amaurosis (n=1). All but one TBI patient followed intense rehabilitation for years. Treatment consisted of GH administration (maximal dose 1 mg/day, 5 days/week, resting 15-days every 2-months, until a maximum of 8 months) and clinical rehabilitation according to the individual needs (3-4 h/day, 5 days/week, during 6-12 months). Informed consent was obtained before commencing GH administration. GH significantly increased plasma IGF-1 values (ng.mL(-1)) in both GHD and no GHD patients, being then similar between both groups (GHD: 275.6±35.6 [p<0.01 vs. baseline], no GHD: 270.2±64 [p<0.05 vs. baseline]). In all the cases clear significant improvements were observed during and at the end of the combined treatment. Cognitive improvements appeared earlier and were more important than motor improvements. Swallowing improved significantly in all TBI patients with neurogenic dysphagia (2 of them in a vegetative state). Visual performance was ameliorated in the patient with amaurosis. No undesirable side-effects were observed. Our data indicate that GH can be combined with rehabilitation for improving disabilities in TBI patients, regardless of whether or not they are GHD.

Local overexpression of GH and GH/IGF1 effects in the adult mouse hippocampus

GH therapy improves hippocampal functions mainly via circulating IGF1. However, the roles of local GH and IGF1 expression are not well understood. We investigated whether transgenic (TG) overexpression in the adult brain of bovine GH (bGH) under the control of the glial fibrillary acidic protein (GFAP) promoter affected cellular proliferation and the expression of transcripts known to be induced by systemic GH in the hippocampus. Cellular proliferation was examined by 5-bromo-2'-deoxyuridine immunohistochemistry. Quantitative PCR and western blots were performed. Although robustly expressed, bGH-Tg did not increase either cell proliferation or survival. However, bGH-Tg modestly increased Igf1 and Gfap mRNAs, whereas other GH-associated transcripts were unaffected, i.e. the GH receptor (Ghr), IGF1 receptor (Igf1r), 2',3'-cyclic nucleotide 3'-phosphodiesterase (Cnp), ionotropic glutamate receptor 2a (Nr2a (Grin2a)), opioid receptor delta (Dor), synapse-associated protein 90/postsynaptic density-95-associated protein (Sapap2 (Dlgap2)), haemoglobin beta (Hbb) and glutamine synthetase (Gs (Glul)). However, IGF1R was correlated with the expression of Dor, Nr2a, Sapap2, Gs and Gfap. In summary, although local bGH expression was robust, it activated local IGF1 very modestly, which is probably the reason for the low response of previous GH-associated response parameters. This would, in turn, indicate that hippocampal GH is less important than endocrine GH. However, as most transcripts were correlated with the expression of IGF1R, there is still a possibility for endogenous circulating or local GH to act via IGF1R signalling. Possible reasons for the relative bio-inactivity of bGH include the bell-shaped dose-response curve and cell-specific expression of bGH.

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.

Neuroglialpharmacology: myelination as a shared mechanism of action of psychotropic treatments

Current psychiatric diagnostic schema segregate symptom clusters into discrete entities, however, large proportions of patients suffer from comorbid conditions that fit neither diagnostic nor therapeutic schema. Similarly, psychotropic treatments ranging from lithium and antipsychotics to serotonin reuptake inhibitors (SSRIs) and acetylcholinesterase inhibitors have been shown to be efficacious in a wide spectrum of psychiatric disorders ranging from autism, schizophrenia (SZ), depression, and bipolar disorder (BD) to Alzheimer's disease (AD). This apparent lack of specificity suggests that psychiatric symptoms as well as treatments may share aspects of pathophysiology and mechanisms of action that defy current symptom-based diagnostic and neuron-based therapeutic schema. A myelin-centered model of human brain function can help integrate these incongruities and provide novel insights into disease etiologies and treatment mechanisms. Available data are integrated herein to suggest that widely used psychotropic treatments ranging from antipsychotics and antidepressants to lithium and electroconvulsive therapy share complex signaling pathways such as Akt and glycogen synthase kinase-3 (GSK3) that affect myelination, its plasticity, and repair. These signaling pathways respond to neurotransmitters, neurotrophins, hormones, and nutrition, underlie intricate neuroglial communications, and may substantially contribute to the mechanisms of action and wide spectra of efficacy of current therapeutics by promoting myelination. Imaging and genetic technologies make it possible to safely and non-invasively test these hypotheses directly in humans and can help guide clinical trial efforts designed to correct myelination abnormalities. Such efforts may provide insights into novel avenues for treatment and prevention of some of the most prevalent and devastating human diseases.

Reprint of: 'Brain insulin signaling: A key component of cognitive processes and a potential basis for cognitive impairment in type 2 diabetes'

Understanding of the role of insulin in the brain has gradually expanded, from initial conceptions of the brain as insulin-insensitive through identification of a role in regulation of feeding, to recent demonstration of insulin as a key component of hippocampal memory processes. Conversely, systemic insulin resistance such as that seen in type 2 diabetes is associated with a range of cognitive and neural deficits. Here we review the evidence for insulin as a cognitive and neural modulator, including potential effector mechanisms, and examine the impact that type 2 diabetes has on these mechanisms in order to identify likely bases for the cognitive impairments seen in type 2 diabetic patients.

Brain insulin signaling: a key component of cognitive processes and a potential basis for cognitive impairment in type 2 diabetes

Understanding of the role of insulin in the brain has gradually expanded, from initial conceptions of the brain as insulin-insensitive through identification of a role in regulation of feeding, to recent demonstration of insulin as a key component of hippocampal memory processes. Conversely, systemic insulin resistance such as that seen in type 2 diabetes is associated with a range of cognitive and neural deficits. Here we review the evidence for insulin as a cognitive and neural modulator, including potential effector mechanisms, and examine the impact that type 2 diabetes has on these mechanisms in order to identify likely bases for the cognitive impairments seen in type 2 diabetic patients.

Nucleotides affect neurogenesis and dopaminergic differentiation of mouse fetal midbrain-derived neural precursor cells

The fetal midbrain is a preferred source for isolating and producing dopaminergic neurons for subsequent grafting and replacement of damaged or lost dopaminergic midbrain neurons. We analysed the potential of a variety of nucleotides and of adenosine to support dopaminergic neuron formation from primary mouse fetal midbrain-derived cells, harvested at E10.5 and at E13.5 and subjected to adherent cell culture. In contrast to cells derived at E13.5, cells derived at E10.5 have the potential to produce dopaminergic neurons in culture. These neurons express tyrosine hydroxylase and the dopamine transporter. The fetal ventral midbrain contained mRNA encoding almost all P2X and P2Y receptors, all adenosine receptors as well as the ectonucleotidases nucleoside triphosphate diphosphohydrolase 2 and tissue nonspecific alkaline phosphatase. Essentially, all components of the purinergic signalling pathway were also expressed by the cultured cells. ATP, ADPβS, 2MeSATP, 2ClATP and adenosine increased neuron formation. There was, however, no preference for the formation of dopaminergic neurons-with the exception of 2ClATP that increased the relative contribution of tyrosine hydroxylase-positive neurons. In cells isolated at E13.5 UTP promoted neuron survival but ADPβS and ATPγS essentially eliminated neurons. These data showed that the outcome of nucleotide application was different even though cells isolated at E10.5 and E13.5 expressed very similar receptor mRNA profiles. They suggest that purinergic agonists carry potential for stimulating neurogenesis and enriching the contribution of dopaminergic neurons in vitro. Nucleotide receptor agonists may be of value for contributing to the formation and survival of dopaminergic neurons in vivo.

Peripheral growth hormone induces cell proliferation in the intact adult rat brain

Growth hormone (GH) and insulin-like growth factor I (IGF-I) increase cell genesis in several regions of the brains of GH-IGF-I-deficient hypophysectomized rats. However, it is not known to what degree GH treatment stimulates adult cell genesis in pituitary-intact rodents. We investigated the effect of peripheral administration of bovine growth hormone (bGH) on cellular proliferation in various regions of the brains of normal adult female rats. To monitor cell division, bromodeoxyuridine (BrdU) was administered daily for 5 days. We studied the two areas of ongoing neurogenesis, the subventricular zone (SVZ) and the dentate gyrus (DG) of the hippocampus, as well as the corpus callosum, striatum, and the parietal and piriform cortices. After bGH treatment, the numbers of BrdU-positive cells increased 2.0- to 2.5-fold in all the brain regions, with the exception of the SVZ, in which there was no increase in the numbers of BrdU-positive cells. The present study shows for the first time that peripheral bGH administration increases the generation of new brain cells in normal adult female rats. Thus, bGH may stimulate cellular proliferation not only under GH-deficiency, but also under physiologic conditions. These findings have important implications for GH treatment strategies for patients who have normal or near-normal circulating levels of GH or IGF-I.

Alzheimer's disease as homeostatic responses to age-related myelin breakdown

The amyloid hypothesis (AH) of Alzheimer's disease (AD) posits that the fundamental cause of AD is the accumulation of the peptide amyloid beta (Aβ) in the brain. This hypothesis has been supported by observations that genetic defects in amyloid precursor protein (APP) and presenilin increase Aβ production and cause familial AD (FAD). The AH is widely accepted but does not account for important phenomena including recent failures of clinical trials to impact dementia in humans even after successfully reducing Aβ deposits. Herein, the AH is viewed from the broader overarching perspective of the myelin model of the human brain that focuses on functioning brain circuits and encompasses white matter and myelin in addition to neurons and synapses. The model proposes that the recently evolved and extensive myelination of the human brain underlies both our unique abilities and susceptibility to highly prevalent age-related neuropsychiatric disorders such as late onset AD (LOAD). It regards oligodendrocytes and the myelin they produce as being both critical for circuit function and uniquely vulnerable to damage. This perspective reframes key observations such as axonal transport disruptions, formation of axonal swellings/sphenoids and neuritic plaques, and proteinaceous deposits such as Aβ and tau as by-products of homeostatic myelin repair processes. It delineates empirically testable mechanisms of action for genes underlying FAD and LOAD and provides "upstream" treatment targets. Such interventions could potentially treat multiple degenerative brain disorders by mitigating the effects of aging and associated changes in iron, cholesterol, and free radicals on oligodendrocytes and their myelin.

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.

17beta-estradiol and progesterone prevent cuprizone provoked demyelination of corpus callosum in male mice

Sex hormones, for example, estrogen and progesterone, are thought to affect and delay progression of multiple sclerosis (MS) in pregnant women. Although both steroid hormones are neuroprotective in the brain and elevated during pregnancy, only estrogen was tested in clinical trials. To evaluate the role of 17beta-estradiol (E) and progesterone (P) in prevention demyelination, young adult male mice were fed with cuprizone for a defined time interval and simultaneously treated with steroids by repeated injections into the neck region. The status of myelination was analyzed by magnetic resonance imaging and conventional histological staining. The individual application of E and P resulted only in a moderate prevention of demyelination in the corpus callosum (CC). The combined treatment with both steroid hormones counteracted the process of demyelination. Expression of the mature (PLP and MBP) and premature (PDGF-alpha-R) oligodendrocyte markers were significantly increased after hormone application in the affected CC. In addition, both hormones stimulated astrogliosis and the expression of IGF-1. Microglial invasion in demyelinated CC was pronounced and additionally localized in the midline of CC after hormone treatment. These data show that sex steroids can protect the brain from demyelination and stimulate remyelination. It appears that only the administration of both hormones is fully effective. The beneficial steroid effect requires interactions with oligodendrocytes possibly by preventing their degeneration or recruitment from precursor cells which are stimulated to remyelinated fibers. The positive hormonal influence on myelination in the CNS may be a future therapeutically strategy for the treatment of MS.

Efficient serum-free derivation of oligodendrocyte precursors from neural stem cell-enriched cultures

Oligodendrocytes derived in the laboratory from stem cells have been proposed as a treatment for acute and chronic injury to the central nervous system. Platelet-derived growth factor (PDGF) receptor alpha (PDGFRalpha) signaling is known to regulate oligodendrocyte precursor cell numbers both during development and adulthood. Here, we analyze the effects of PDGFRalpha signaling on central nervous system (CNS) stem cell-enriched cultures. We find that AC133 selection for CNS progenitors acutely isolated from the fetal cortex enriches for PDGF-AA-responsive cells. PDGF-AA treatment of fibroblast growth factor 2-expanded CNS stem cell-enriched cultures increases nestin(+) cell number, viability, proliferation, and glycolytic rate. We show that a brief exposure to PDGF-AA rapidly and efficiently permits the derivation of O4(+) oligodendrocyte-lineage cells from CNS stem cell-enriched cultures. The derivation of oligodendrocyte-lineage cells demonstrated here may support the effective use of stem cells in understanding fate choice mechanisms and the development of new therapies targeting this cell type.

Mechanisms mediating brain plasticity: IGF1 and adult hippocampal neurogenesis

This review addresses the role of serum insulin-like growth factor 1 (IGF1) as one mechanism of adult neural plasticity, specifically, its regulation of hippocampal neurogenesis among other plasticity-related processes. It is suggested that IGF has been reused advantageously both for the control of energy expenditure as a function of the organism's activity and to protect, repair, and plastically modulate the brain. Moreover, because as the main source of IGF1 in the adult organism is outside the brain and its presence in this organ is a function of the activity, IGF1 becomes an ideal factor to induce plastic/neuroprotective functions as a function of the organism's activity. The link for this point of view comes from the original function of IGF1 during ontogeny/phylogeny, the promotion of cell survival and control of neural cell numbers, whereas one of the IGF1 functions in the adult brain is the control of hippocampal neurogenesis. The investigation of the IGF1 role as mediator of exercise effects suggests that many but not all the effects of physical activity are mediated by IGF1. These investigations have contributed to delimit the role of IGF1 as mediator of exercise actions, but at the same time are unveiling new roles for serum IGF1 inside the brain.

Delayed IGF-1 treatment reduced long-term hypoxia-ischemia-induced brain damage and improved behavior recovery of immature rats

Cerebral hypoxia-ischemia during the perinatal period is the single most important cause of acute newborn mortality and chronic disability. Despite our increasing understanding of the mechanisms of neuronal injury, an effective clinical therapy has yet to be established to mitigate brain damage and improve the prognosis and well-being of these newborn patients. Insulin-like growth factor 1 (IGF-1) is a well-known neurotrophic factor, essential for the survival and functional maturation of immature neurons. This study demonstrated that subcutaneous administration of IGF-1 at 24 and 48 hours of recovery significantly reduced hypoxia-ischemia-induced injury to immature rat brains and improved long-term memory and cognitive behavior. IGF-1's therapeutic effects likely involve its ability to prevent delayed apoptosis, as we demonstrated in primary cortical neuronal cultures under oxygen and glucose deprivation. IGF-1's neuroprotective effects parallel the activities of phosphatidylinositol-3/Akt and its down-stream signaling pathway, suggesting a potential mechanistic link. Overall, evidence from this investigation strongly supports IGF-1's potential therapeutic use in the treatment of hypoxic-ischemic encephalopathy in newborn patients.

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.