Insulin-like growth factor-I (IGF-I) immunoreactivity in the Alzheimer's disease temporal cortex and hippocampus

Impact of Prenatal Alcohol Exposure on the Development and Myocardium of Adult Mice: Morphometric Changes, Transcriptional Modulation of Genes Related to Cardiac Dysfunction, and Antioxidant Cardioprotection

The impact of prenatal alcohol exposure (PAE) varies considerably between individuals, leading to morphological and genetic changes. However, minor changes usually go undetected in PAE children. We investigated PAE's effects on gene transcription of genes related to cardiac dysfunction signaling in mouse myocardium and morphological changes. C57Bl/6 mice were subjected to a 10% PAE protocol. In postnatal days 2 and 60 (PN2 and PN60), morphometric measurements in the offspring were performed. Ventricular samples of the heart were collected in PN60 from male offspring for quantification of mRNA expression of 47 genes of nine myocardial signal transduction pathways related to cardiovascular dysfunction. Animals from the PAE group presented low birth weight than the Control group, but the differences were abolished in adult mice. In contrast, the mice's size was similar in PN2; however, PAE mice were oversized at PN60 compared with the Control group. Cardiac and ventricular indexes were increased in PAE mice. PAE modulated the mRNA expression of 43 genes, especially increasing the expressions of genes essential for maladaptive tissue remodeling. PAE animals presented increased antioxidant enzyme activities in the myocardium. In summary, PAE animals presented morphometric changes, transcription of cardiac dysfunction-related genes, and increased antioxidant protection in the myocardium.

Distinct characteristics of microglia from neurogenic and non-neurogenic regions of the human brain in patients with Mesial Temporal Lobe Epilepsy

The study of microglia isolated from adult human brain tissue provides unique insight into the physiology of these brain immune cells and their role in adult human brain disorders. Reports of microglia in post-mortem adult human brain tissue show regional differences in microglial populations, however, these differences have not been fully explored in living microglia. In this study biopsy tissue was obtained from epileptic patients undergoing surgery and consisted of both cortical areas and neurogenic ventricular and hippocampal (Hp) areas. Microglia were concurrently isolated from both regions and compared by immunochemistry. Our initial observation was that a greater number of microglia resulted from isolation and culture of ventricular/Hp tissue than cortical tissue. This was found to be due to a greater proliferative capacity of microglia from ventricular/Hp regions compared to the cortex. Additionally, ventricular/Hp microglia had a greater proliferative response to the microglial mitogen Macrophage Colony-Stimulating Factor (M-CSF). This enhanced response was found to be associated with higher M-CSF receptor expression and higher expression of proteins involved in M-CSF signalling DAP12 and C/EBPβ. Microglia from the ventricular/Hp region also displayed higher expression of the receptor for Insulin-like Growth Factor-1, a molecule with some functional similarity to M-CSF. Compared to microglia isolated from the cortex, ventricular/Hp microglia showed increased HLA-DP, DQ, DR antigen presentation protein expression and a rounded morphology. These findings show that microglia from adult human brain neurogenic regions are more proliferative than cortical microglia and have a distinct protein expression profile. The data present a case for differential microglial phenotype and function in different regions of the adult human brain and suggest that microglia in adult neurogenic regions are "primed" to an activated state by their unique tissue environment.

Morphological classification and changes in dementia (Review)

The progressive functional decline that involves both cognitive and neuropsychiatric symptoms characteristic to dementia is one of the leading research topics. The risk for dementia is an intertwined mix between aging, genetic risk factors, and environmental influences. APOEε4, which is one of the apolipoprotein E (APOE) alleles, is the major genetic risk factor for late-onset of the most common form of dementia, Alzheimer's. Advances in machine learning have led to the development of artificial intelligence (AI) algorithms to help diagnose dementia by magnetic resonance imaging (MRI) in order to detect it in the preclinical stage. The basis of the determinations starts from the morphometry of cerebral atrophies. The present review focused on MRI techniques which are a leading tool in identifying cortical atrophy, white matter dysfunctionalities, cerebral vessel quality (as a factor for cognitive impairment) and metabolic asymmetries. In addition, a brief overview of Alzheimer's disease was presented and recent neuroimaging in the field of dementia with an emphasis on structural MR imaging and more powerful methods such as diffusion tensor imaging, quantitative susceptibility mapping, and magnetic transfer imaging were explored in order to propose a simple systematic approach for the diagnosis and treatment of dementia.

Systematic review of human post-mortem immunohistochemical studies and bioinformatics analyses unveil the complexity of astrocyte reaction in Alzheimer's disease

AIMS

Reactive astrocytes in Alzheimer's disease (AD) have traditionally been demonstrated by increased glial fibrillary acidic protein (GFAP) immunoreactivity; however, astrocyte reaction is a complex and heterogeneous phenomenon involving multiple astrocyte functions beyond cytoskeletal remodelling. To better understand astrocyte reaction in AD, we conducted a systematic review of astrocyte immunohistochemical studies in post-mortem AD brains followed by bioinformatics analyses on the extracted reactive astrocyte markers.

METHODS

NCBI PubMed, APA PsycInfo and WoS-SCIE databases were interrogated for original English research articles with the search terms 'Alzheimer's disease' AND 'astrocytes.' Bioinformatics analyses included protein-protein interaction network analysis, pathway enrichment, and transcription factor enrichment, as well as comparison with public human -omics datasets.

RESULTS

A total of 306 articles meeting eligibility criteria rendered 196 proteins, most of which were reported to be upregulated in AD vs control brains. Besides cytoskeletal remodelling (e.g., GFAP), bioinformatics analyses revealed a wide range of functional alterations including neuroinflammation (e.g., IL6, MAPK1/3/8 and TNF), oxidative stress and antioxidant defence (e.g., MT1A/2A, NFE2L2, NOS1/2/3, PRDX6 and SOD1/2), lipid metabolism (e.g., APOE, CLU and LRP1), proteostasis (e.g., cathepsins, CRYAB and HSPB1/2/6/8), extracellular matrix organisation (e.g., CD44, MMP1/3 and SERPINA3), and neurotransmission (e.g., CHRNA7, GABA, GLUL, GRM5, MAOB and SLC1A2), among others. CTCF and ESR1 emerged as potential transcription factors driving these changes. Comparison with published -omics datasets validated our results, demonstrating a significant overlap with reported transcriptomic and proteomic changes in AD brains and/or CSF.

CONCLUSIONS

Our systematic review of the neuropathological literature reveals the complexity of AD reactive astrogliosis. We have shared these findings as an online resource available at www.astrocyteatlas.org.

The Involvement of Insulin-Like Growth Factor 1 and Nerve Growth Factor in Alzheimer's Disease-Like Pathology and Survival Role of the Mix of Embryonic Proteoglycans: Electrophysiological Fingerprint, Structural Changes and Regulatory Effects on Neurotrophins

Alzheimer’s disease (AD)-associated neurodegeneration is triggered by different fragments of amyloid beta (Aβ). Among them, Aβ (25–35) fragment plays a critical role in the development of neurodegeneration—it reduces synaptic integrity by disruption of excitatory/inhibitory ratio across networks and alters the growth factors synthesis. Thus, in this study, we aimed to identify the involvement of neurotrophic factors—the insulin-like growth factor 1 (IGF-1) and nerve growth factor (NGF)—of AD-like neurodegeneration induced by Aβ (25–35). Taking into account our previous findings on the neuroprotective effects of the mix of proteoglycans of embryonic genesis (PEG), it was suggested to test its regulatory effect on IGF-1 and NGF levels. To evaluate the progress of neurodegeneration, in vivo electrophysiological investigation of synaptic activity disruption of the entorhinal cortex–hippocampus circuit at AD was performed and the potential recovery effects of PEG with relative structural changes were provided. To reveal the direct effects of PEG on brain functional activity, the electrophysiological pattern of the single cells from nucleus supraopticus, sensomotor cortex and hippocampus after acute injection of PEG was examined. Our results demonstrated that after i.c.v. injection of Aβ (25–35), the level of NGF decreased in cerebral cortex and hypothalamus, and, in contrast, increased in hippocampus, prompting its multidirectional role in case of brain damage. The concentration of IGF-1 significantly increased in all investigated brain structures. The administration of PEG balanced the growth factor levels accompanied by substantial restoration of neural tissue architecture and synaptic activity. Acute injection of PEG activated the hypothalamic nucleus supraopticus and hippocampal neurons. IGF-1 and NGF levels were found to be elevated in animals receiving PEG in an absence of amyloid exposure. We suggest that IGF-1 and NGF play a critical role in the development of AD. At the same time, it becomes clear that the neuroprotective effects of PEG are likely mediated via the regulation of neurotrophins.

More Than Mortar: Glia as Architects of Nervous System Development and Disease

Glial cells are an essential component of the nervous system of vertebrates and invertebrates. In the human brain, glia are as numerous as neurons, yet the importance of glia to nearly every aspect of nervous system development has only been expounded over the last several decades. Glia are now known to regulate neural specification, synaptogenesis, synapse function, and even broad circuit function. Given their ubiquity, it is not surprising that the contribution of glia to neuronal disease pathogenesis is a growing area of research. In this review, we will summarize the accumulated evidence of glial participation in several distinct phases of nervous system development and organization-neural specification, circuit wiring, and circuit function. Finally, we will highlight how these early developmental roles of glia contribute to nervous system dysfunction in neurodevelopmental and neurodegenerative disorders.

Altered Insulin/Insulin-Like Growth Factor Signaling in a Comorbid Rat model of Ischemia and β-Amyloid Toxicity

Ischemic stroke and diabetes are vascular risk factors for the development of impaired memory such as dementia and/or Alzheimer's disease. Clinical studies have demonstrated that minor striatal ischemic lesions in combination with β-amyloid (Aβ) load are critical in generating cognitive deficits. These cognitive deficits are likely to be associated with impaired insulin signaling. In this study, we examined the histological presence of insulin-like growth factor-I (IGF-1) and insulin receptor substrate (IRS-1) in anatomically distinct brain circuits compared with morphological brain damage in a co-morbid rat model of striatal ischemia (ET1) and Aβ toxicity. The results demonstrated a rapid increase in the presence of IGF-1 and IRS-1 immunoreactive cells in Aβ + ET1 rats, mainly in the ipsilateral striatum and distant regions with synaptic links to the striatal lesion. These regions included subcortical white matter, motor cortex, thalamus, dentate gyrus, septohippocampal nucleus, periventricular region and horizontal diagonal band of Broca in the basal forebrain. The alteration in IGF-1 and IRS-1 presence induced by ET1 or Aβ rats alone was not severe enough to affect the entire brain circuit. Understanding the causal or etiologic interaction between insulin and IGF signaling and co-morbidity after ischemia and Aβ toxicity will help design more effective therapeutics.

H2O2 attenuates IGF-1R tyrosine phosphorylation and its survival signaling properties in neuronal cells via NR2B containing NMDA receptor

Impairment of insulin-like growth factor I (IGF-I) signaling plays an important role in the development of neurodegeneration. In the present study, we investigated the effect of H₂O₂ on the survival signaling of IGF-1 and its underlying mechanisms in human neuronal cells SH-SY5Y. Our results showed that IGF-1 promoted cell survival and stimulated phosphorylation of IGF-1R as well as its downstream targets like AKT and ERK1/2 in these cells. Meanwhile, these effects of IGF-1 were abolished by H₂O₂ at 200μM concentration which did not cause any significant toxicity to cells itself in our experiments. Moreover, studies using various glutamate receptor subtype antagonists displayed that N-methyl-D -aspartate (NMDA) receptor antagonist dizocilpine maleate (MK-801) blocked the effects of H₂O₂, whereas other glutamate receptor subtype antagonists, such as non-NMDA receptor antagonist 6,7-dinitroquinoxaline-2,3-dione (DNQX), metabolic glutamate receptor antagonists LY341495 and CPCCOEt, had no effect. Further studies revealed that NR2B-containing NMDARs are responsible for these effects as its effects were blocked by pharmacological inhibitor Ro25-698 or specific siRNA for NR2B, but not NR2A. Finally, our data also showed that Ca²⁺ influx contributes to the effects of H₂O₂. Similar results were obtained in primary cultured cortical neurons. Taken together, the results from the present study suggested that H₂O₂ attenuated IGF-1R tyrosine phosphorylation and its survival signaling properties via NR2B containing NMDA receptors and Ca²⁺ influx in SH-SY5Y cells. Therefore, NMDAR antagonists, especially NR2B-selective ones, combined with IGF-1 may serve as an alternative therapeutic agent for oxidative stress related neurodegenerative disease.

miRNAs: Key Players in Neurodegenerative Disorders and Epilepsy

MicroRNAs (miRNAs) are endogenous, ∼22 nucleotide, non-coding RNA molecules that function as post-transcriptional regulators of gene expression. miRNA dysregulation has been observed in cancer and in neurodegenerative disorders such as Alzheimer's, Parkinson's, and Huntington's diseases, amyotrophic lateral sclerosis, and the neurological disorder, epilepsy. Neuronal degradation and death are important hallmarks of neurodegenerative disorders. Additionally, abnormalities in metabolism, synapsis and axonal transport have been associated with Alzheimer's disease, Parkinson's disease, and frontotemporal dementia. A number of recently published studies have demonstrated the importance of miRNAs in the nervous system and have contributed to the growing body of evidence on miRNA dysregulation in neurological disorders. Knowledge of the expressions and activities of such miRNAs may aid in the development of novel therapeutics. In this review, we discuss the significance of miRNA dysregulation in the development of neurodegenerative disorders and the use of miRNAs as targets for therapeutic intervention.

Hydrogen peroxide attenuates the prosurvival signaling of insulin-like growth factor-1 through two pathways

Although it has been well established that oxidative stress triggering a variety of signaling pathways leads to cell death, little attention has been paid to how these pathways affect prosurvival factors such as insulin-like growth factor-1 (IGF-1). In this study, we found that the prosurvival signaling of IGF-1 was attenuated by H₂O₂. To study the mechanism underlying this phenomenon, cells pretreated with Trolox or various glutamate receptor antagonists [i.e. N-methyl-D-aspartate (NMDA) receptor antagonist dizocilpine maleate (MK-801), non-NMDA receptor antagonist 6,7-dinitroquinoxaline-2,3-dione (DNQX), metabolic glutamate receptor antagonists LY341495 and CPCCOEt] were exposed to H₂O₂, and then stimulated by IGF-1. The phosphorylation statuses of IGF-1 receptors, Akt and ERK, were determined by western blotting, and cell viability was analyzed by an MTT assay. IGF-1 exerted a potent neuroprotective effect against B27 deprivation, and this effect was abolished by 100 μM H₂O₂. Meanwhile, the phosphorylation of IGF-1 receptors, Akt and ERK, was attenuated. Moreover, the phosphorylation of Akt was more susceptible to H₂O₂ insult than IGF-1 receptors. MK-801 increased the phosphorylation of IGF-1 receptors and its downstream target Akt, and thereby promoted cell survival, whereas the other glutamate receptor antagonists exerted no effect. Antioxidant Trolox did not restore IGF-1 signaling, but it increased Akt phosphorylation and also increased cell viability. These results showed that H₂O₂ impaired IGF-1 prosurvival signaling through two pathways. One pathway disrupted the autophosphorylation of IGF-1 receptors through NMDA receptors and the other directly dephosphorylated Akt.

Treating age-related changes in somatotrophic hormones, sleep, and cognition

Many of the body's systems that function to maintain optimal health and well-being decline with advancing age. Aerobic capacity, muscle mass, and strength all progressively decline. Significant sleep disturbances are associated with increases in morbidity and mortality. Cognition declines, impacting an older individual's ability to function independently. Interventions that could at least stabilize or possibly improve functional capacity, sleep quality, and cognitive function have the theoretical potential to prolong an older individual's ability to live independently, and interest in their possible utility is growing rapidly. One such intervention may be stimulation of the “somatotrophic” axis via growth hormone-releasing hormone (GHRH). Here we review the evidence for such somatotrophic interventions. We also report preliminary findings on the effects of chronic GHRH treatment on the somatotrophic hormones, body composition, functional status, sleep, and cognitive function of healthy older men and women from two major GHRH intervention studies, one recently completed and the other ongoing.

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.

Reciprocal induction between α-synuclein and β-amyloid in adult rat neurons

In spite of definite roles for β-amyloid (Aβ) in familial Alzheimer's disease (AD), the cause of sporadic AD remains unknown. Amyloid senile plaques and Lewy body pathology frequently coexist in neocortical and hippocampal regions of AD and Parkinson's diseases. However, the relationship between Aβ and α-synuclein (α-Syn), the principle components in the pathological structures, in neuronal toxicity and the mechanisms of their interaction are not well studied. As Aβ and α-Syn accumulate in aging patients, the biological functions and toxicity of these polypeptides in the aging brain may be different from those in young brain. We examined the neurotoxicity influences of Aβ1-42 or α-Syn on mature neurons and the effects of Aβ1-42 or α-Syn on the production of endogenous α-Syn or Aβ1-40 reciprocally using a model of culture enriched with primary neurons from the hippocampus of adult rats. Treatment of neurons with high concentrations of Aβ1-42 or α-Syn caused significant apoptosis of neurons. Following Aβ1-42 treatment at sub apoptotic concentrations, both intra- and extra-cellular α-Syn levels were significantly increased. Reciprocally, the non-toxic levels of α-Syn treatment also increased intra- and extra-cellular Aβ1-40 levels. The phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002, suppressed α-Syn-induced Aβ1-40 elevation, as well as Aβ1-42-induced α-Syn elevation. Thus, high concentrations of Aβ1-42 and α-Syn exert toxic effects on mature neurons; however, non-toxic concentration treatment of these polypeptides induced the production of each other reciprocally with possible involvement of PI3K pathway.

Activation of amyloid precursor protein processing by growth factors is dependent on Ras GTPase activity

The β-amyloid peptide is generated by the proteolysis of the amyloid precursor protein (APP) by the action of β- and γ-secretase. The mechanisms underlying this process are poorly understood. Using a cell-based reporter gene assay we analysed the possible signals and pathways that could be involved in APP cleavage. We used the stable cell line HeLa AG that expresses the human APP(695) fused with the yeast transcription factor Gal4. This fusion protein is normally translocated into the plasma membrane and after APP-Gal4 cleavage, the AICD-Gal4 fragment released can activate the transcription of a luciferase reporter gene. Through this reporter system, we demonstrated that Ras GTPase, but not Ral and Rap, could promote APP-Gal4 cleavage. In addition HeLa AG cells stimulated with EGF or PDGF or overexpressing EGFR exhibit increased APP proteolysis in a Ras-dependent way. This process is also dependent on γ-secretase activity, being abolished by the γ-secretase inhibitor DAPT.

Alcohol exposure during late gestation adversely affects myocardial development with implications for postnatal cardiac function

Prenatal exposure to high levels of ethanol is associated with cardiac malformations, but the effects of lower levels of exposure on the heart are unclear. Our aim was to investigate the effects of daily exposure to ethanol during late gestation, when cardiomyocytes are undergoing maturation, on the developing myocardium. Pregnant ewes were infused with either ethanol (0.75 g/kg) or saline for 1 h each day from gestational days 95 to 133 (term ∼145 days); tissues were collected at 134 days. In sheep, cardiomyocytes mature during late gestation as in humans. Within the left ventricle (LV), cardiomyocyte number was determined using unbiased stereology and cardiomyocyte size and nuclearity determined using confocal microscopy. Collagen deposition was quantified using image analysis. Genes relating to cardiomyocyte proliferation and apoptosis were examined using quantitative real-time PCR. Fetal plasma ethanol concentration reached 0.11 g/dL after EtOH infusions. Ethanol exposure induced significant increases in relative heart weight, relative LV wall volume, and cardiomyocyte cross-sectional area. Ethanol exposure advanced LV maturation in that the proportion of binucleated cardiomyocytes increased by 12%, and the number of mononucleated cardiomyocytes was decreased by a similar amount. Apoptotic gene expression increased in the ethanol-exposed hearts, although there were no significant differences between groups in total cardiomyocyte number or interstitial collagen. Daily exposure to a moderate dose of ethanol in late gestation accelerates the maturation of cardiomyocytes and increases cardiomyocyte and LV tissue volume in the fetal heart. These effects on cardiomyocyte growth may program for long-term cardiac vulnerability.

Defects in IGF-1 receptor, insulin receptor and IRS-1/2 in Alzheimer's disease indicate possible resistance to IGF-1 and insulin signalling

Insulin like growth factor-1 receptor (IGF-1R) and insulin receptor (IR) signalling control vital growth, survival and metabolic functions in the brain. Here we describe specific and significant alterations in IGF-1R, IR, and their key substrate adaptor proteins IRS-1 and IRS-2 in Alzheimer's disease (AD). Western immunoblot analysis detected increased IGF-1R levels, and decreased levels of IGF-1-binding protein-2 (IGFBP-2), a major IGF-1-binding protein, in AD temporal cortex. Increased IGF-1R was observed surrounding and within amyloid-beta (Abeta)-containing plaques, also evident in an animal model of AD, and in astrocytes in AD. However, despite the overall increase in IGF-1R levels, a significantly lower number of neurons expressed IGF-1R in AD, and IGF-1R was aberrantly distributed in AD neurons especially evident in those with neurofibrillary tangles (NFTs). IR protein levels were similar in AD and control cases, however, the IR was concentrated intracellularly in AD neurons, unlike its distribution throughout the neuronal cell soma and in dendrites in control brain. Significant decreases in IRS-1 and IRS-2 levels were identified in AD neurons, in association with increased levels of inactivated phospho(Ser312)IRS-1 and phospho(Ser616)IRS-1, where increased levels of these phosphoserine epitopes colocalised strongly with NFTs. Our results show that IGF-1R and IR signalling is compromised in AD neurons and suggest that neurons that degenerate in AD may be resistant to IGF-1R/IR signalling.

Tumor necrosis factor-alpha and insulin-like growth factor-1 levels in patients with relapsing-remitting multiple sclerosis receiving interferon-beta1a

To examine the effect of high-dose interferon (IFN)-beta1a [44 microg administered subcutaneously (sc) 3 times weekly (tiw)] on tumor necrosis factor-alpha (TNF-alpha) and insulin-like growth factor-1 (IGF-1) levels in patients with relapsing-remitting multiple sclerosis (RRMS), and any correlation with clinical and magnetic resonance imaging (MRI) data. Previously treatment-naive patients with RRMS and an Expanded Disability Status Scale score < or = 3.5 were enrolled. At baseline, monthly for the first 5 months, and then after 12 months of treatment with 44 microg sc tiw of IFN-beta1a, all patients underwent clinical examination, assessment of serum TNF-alpha and IGF-1 levels and baseline, 5th, and 12th months to MRI scanning. Mean TNF-alpha values decreased significantly from months 0 to 12 of the study (P = 0.003), but mean IGF-1 values showed a nonsignificant reduction (P = 0.265). Serum levels of TNF-alpha and IGF-1 were sometimes correlated throughout the study, but no significant interactions were observed between serum TNF-alpha or IGF-1 and clinical or MRI findings. A borderline significant trend toward higher basal TNF-alpha levels was found in patients who developed new T1 lesions at 12 months compared with those who did not (P = 0.057). Interferon-beta1a therapy may reduce serum TNF-alpha levels in patients with RRMS, without a clear correlation with disease activity.

The insulin-like growth factor system and its pleiotropic functions in brain

In recent years, much interest has been devoted to defining the role of the IGF system in the nervous system. The ubiquitous IGFs, their cell membrane receptors, and their carrier binding proteins, the IGFBPs, are expressed early in the development of the nervous system and are therefore considered to play a key role in these processes. In vitro studies have demonstrated that the IGF system promotes differentiation and proliferation and sustains survival, preventing apoptosis of neuronal and brain derived cells. Furthermore, studies of transgenic mice overexpressing components of the IGF system or mice with disruptions of the same genes have clearly shown that the IGF system plays a key role in vivo.

Therapeutic potential of neurotrophic factors in neurodegenerative diseases

There is a vast amount of evidence indicating that neurotrophic factors play a major role in the development, maintenance, and survival of neurons and neuron-supporting cells such as glia and oligodendrocytes. In addition, it is well known that alterations in levels of neurotrophic factors or their receptors can lead to neuronal death and contribute to the pathogenesis of neurodegenerative diseases such as Parkinson disease, Alzheimer disease, Huntington disease, amyotrophic lateral sclerosis, and also aging. Although various treatments alleviate the symptoms of neurodegenerative diseases, none of them prevent or halt the neurodegenerative process. The high potency of neurotrophic factors, as shown by many experimental studies, makes them a rational candidate co-therapeutic agent in neurodegenerative disease. However, in practice, their clinical use is limited because of difficulties in protein delivery and pharmacokinetics in the central nervous system. To overcome these disadvantages and to facilitate the development of drugs with improved pharmacotherapeutic profiles, research is underway on neurotrophic factors and their receptors, and the molecular mechanisms by which they work, together with the development of new technologies for their delivery into the brain.

Alzheimer's disease: the two-hit hypothesis

There are many lines of evidence showing that oxidative stress and aberrant mitogenic changes have important roles in the pathogenesis of Alzheimer's disease (AD). However, although both oxidative stress and cell cycle-related abnormalities are early events, occurring before any cytopathology, the relation between these two events, and their role in pathophysiology was, until recently, unclear. However, on the basis of studies of mitogenic and oxidative stress signalling pathways in AD, we proposed a "two-hit hypothesis" which states that although either oxidative stress or abnormalities in mitotic signalling can independently serve as initiators, both processes are necessary to propagate disease pathogenesis. In this paper, we summarise evidence for oxidative stress and abnormal mitotic alterations in AD and explain the two-hit hypothesis by describing how both mechanisms are necessary and invariant features of disease.

Small dense low-density lipoprotein and carotid atherosclerosis in relation to vascular dementia

Vascular dementia (VaD) and Alzheimer's disease (AD) are the most common causes of dementia in the elderly. The aim of this study was to investigate carotid atherosclerosis, serum lipid profiles, and atherogenic hormone levels in nondiabetic Japanese men with VaD or AD. Carotid artery intima-media thickness (IMT) and plaque, serum lipid and lipoprotein profiles, including low-density lipoprotein (LDL) particle size, as well as insulin-like growth factor-I (IGF-I, somatomedin C) and testosterone levels, were determined in 34 patients with AD, 37 patients with VaD, and 63 healthy male controls. Age, body mass index, systolic and diastolic blood pressure, and fasting plasma glucose, hemoglobin A(1c) (HbA(1c)), triglyceride, high-density lipoprotein (HDL)-cholesterol, and apolipoproteins (apo) A-I, B, and E levels did not differ significantly among the 3 groups. However, the mean value of carotid IMT, the frequency of atherosclerotic plaque deposition, the serum levels of LDL-cholesterol, lipoprotein(a), and lipid peroxides, and the incidence of small dense LDL (particle diameter </= 25.5 nm) were increased significantly in VaD patients compared with AD patients or controls. VaD patients had a close reverse correlation between carotid IMT and LDL particle diameter, which were statistically proven independent risk factors for VaD. In contrast, AD patients had significantly lower serum levels of IGF-I and testosterone than either VaD patients or controls. Our results indicate that VaD is associated with atherogenic dyslipidemia, in particular, small dense LDL and carotid atherosclerosis, whereas AD is associated with hyposomatomedinemia and hypogonadism rather than atherosclerosis.

Activation of mitogen-activated protein kinase cascade and phosphorylation of cytoskeletal proteins after neurone-specific activation of p21ras. I. Mitogen-activated protein kinase cascade

Alterations in the phosphorylation state of the microtubule-associated protein tau have been associated with the pathogenesis of neurofibrillary degeneration as well as with a neuroprotective action against apoptotic cell death. Mitogen-activated protein kinases (MAPK) phosphorylate tau protein in vitro but the pathophysiological significance of this tau phosphorylation and its effects on neuronal viability is far from clear. Moreover, an in vivo model of activation of MAPK, a key candidate for in vivo tau phosphorylation, is still lacking. The aim of the present study and the accompanying paper was to establish an animal model of stimulated MAPK and to analyse the consequences on tau phosphorylation and the neuronal cytoskeleton. We took advantage of transgenic mice with neurone-specific expression of activated ras protein (p21H-ras(Val12)). The expression of the transgene in these animals is forced to a subset of neurones by the use of the synapsin I promoter. Activity of B-raf was elevated by 37%, while activity of MAPK (ERK1/ERK2) was increased by 25% associated with a subcellular redistribution from the cytoplasmic to the nuclear compartment. Kinases downstream of MAPK such as p90rsk and glycogen synthase kinase 3beta were only marginally affected. Activity of p70S6 kinase was unaltered. The present model might be useful to study the effects of activation of the MAPK cascade on tau phosphorylation and its cell biological sequelae.

Tumor necrosis factor(alpha) and insulin-like growth factor-I in the brain: is the whole greater than the sum of its parts?

The cytokine tumor necrosis factor(alpha) (TNFalpha) and the hormone insulin-like growth factor-I (IGF-I) have both been shown to regulate inflammatory events in the central nervous system (CNS). This review summarizes the seemingly independent roles of TNFalpha and IGF-I in promoting and inhibiting neurodegenerative diseases. We then offer evidence that the combined effects of IGF-I and TNFalpha on neuronal survival can be vastly different when both receptors are stimulated simultaneously, as is likely to occur in vivo. We propose the framework of a molecular model of hormone-cytokine receptor cross talk in which disparate cell surface receptors share intracellular substrates that regulate neuronal survival.

Disturbance of neuronal plasticity is a critical pathogenetic event in Alzheimer's disease

Brain areas affected by AD pathology are primarily those structures that are invovled in the regulation of "higher brain functions". The functions these areas subserve such as learning, memory, perception, self-awareness, and consciousness require a life-long re-fittng of synaptic contacts that allows for the acquistion of new epigenetic information, a process based on a particularly high degree of structural plasticity. Here, we outline a hypothesis that it is the "labile state fo differentiation" of a subset of neurons in the adult brain that allows for ongoing neuroplastic processes after development is completed but at the same time renders these neurons particularly vulnerable. Mechanisms of molecular and cellular control of neuronal differentiation and proliferation might, thus, not only play a role during development but critically involved in the pathogenesis of neurodegeneration.

Alzheimer's disease as a disorder of mechanisms underlying structural brain self-organization

Mental function has as its cerebral basis a specific dynamic structure. In particular, cortical and limbic areas involved in "higher brain functions" such as learning, memory, perception, self-awareness and consciousness continuously need to be self-adjusted even after development is completed. By this lifelong self-optimization process, the cognitive, behavioural and emotional reactivity of an individual is stepwise remodelled to meet the environmental demands. While the presence of rigid synaptic connections ensures the stability of the principal characteristics of function, the variable configuration of the flexible synaptic connections determines the unique, non-repeatable character of an experienced mental act. With the increasing need during evolution to organize brain structures of increasing complexity, this process of selective dynamic stabilization and destabilization of synaptic connections becomes more and more important. These mechanisms of structural stabilization and labilization underlying a lifelong synaptic remodelling according to experience, are accompanied, however, by increasing inherent possibilities of failure and may, thus, not only allow for the evolutionary acquisition of "higher brain function" but at the same time provide the basis for a variety of neuropsychiatric disorders. It is the objective of the present paper to outline the hypothesis that it might be the disturbance of structural brain self-organization which, based on both genetic and epigenetic information, constantly "creates" and "re-creates" the brain throughout life, that is the defect that underlies Alzheimer's disease (AD). This hypothesis is, in particular, based on the following lines of evidence. (1) AD is a synaptic disorder. (2) AD is associated with aberrant sprouting at both the presynaptic (axonal) and postsynaptic (dendritic) site. (3) The spatial and temporal distribution of AD pathology follows the pattern of structural neuroplasticity in adulthood, which is a developmental pattern. (4) AD pathology preferentially involves molecules critical for the regulation of modifications of synaptic connections, i.e. "morphoregulatory" molecules that are developmentally controlled, such as growth-inducing and growth-associated molecules, synaptic molecules, adhesion molecules, molecules involved in membrane turnover, cytoskeletal proteins, etc. (5) Life events that place an additional burden on the plastic capacity of the brain or that require a particularly high plastic capacity of the brain might trigger the onset of the disease or might stimulate a more rapid progression of the disease. In other words, they might increase the risk for AD in the sense that they determine when, not whether, one gets AD. (6) AD is associated with a reactivation of developmental programmes that are incompatible with a differentiated cellular background and, therefore, lead to neuronal death. From this hypothesis, it can be predicted that a therapeutic intervention into these pathogenetic mechanisms is a particular challenge as it potentially interferes with those mechanisms that at the same time provide the basis for "higher brain function".

Insulin-like growth factor-I and its receptor in the frontal cortex, hippocampus, and cerebellum of normal human and alzheimer disease brains

Assimilated evidence indicates that the neurotoxic potential of amyloid beta (Abeta) peptide and an alteration in the level of growth factor(s) may possibly be involved in the loss of neurons observed in the brain of patients suffering from Alzheimer disease (AD), the prevalent cause of dementia in the elderly. In the present study, using receptor binding assays and immunocytochemistry, we evaluated the pharmacological profile of insulin-like growth factor-I (IGF-I) receptors and the distribution of IGF-I immunoreactivity in the frontal cortex, hippocampus, and cerebellum of AD and age-matched control brains. In control brains, [(125)I]IGF-I binding was inhibited more potently by IGF-I than by Des(1-3)IGF-I, IGF-II or insulin. The IC(50) values for IGF-I in the frontal cortex, hippocampus, and cerebellum of the normal brain did not differ significantly from the corresponding regions of the AD brain. Additionally, neither K(D) nor B(max) values were found to differ in the hippocampus of AD brains from the controls. At the regional levels, [(125)I]IGF-I binding sites in the AD brain also remained unaltered compared to the controls. As for the peptide itself, IGF-I immunoreactivity, in normal control brains, was evident primarily in a subpopulation of astrocytes in the frontal cortex and hippocampus, and in certain Purkinje cells of the cerebellum. In AD brains, a subset of Abeta-containing neuritic plaques, apart from astrocytes, exhibit IGF-I immunoreactivity. These results, taken together, suggest a role for IGF-I in compensatory plasticity and/or survival of the susceptible neurons in AD brains.

Neurotrophic factors in Alzheimer's and Parkinson's disease brain

The biomedical literature on the subject of neurotrophic growth factors has expanded prodigiously. This essay reviews neurotrophic factors (NTF) and their receptors in Alzheimer's disease (AD) and Parkinson's disease (PD) brain and recent updates on receptor signaling. The hypotheses for specific NTF involvement in neurodegenerative diseases in human and as potential therapy are based mainly on experimental animal and in vitro models. There are wide gaps in information on regional synthesis and cell contents of NTFs and their receptors in human brain. Observations on AD brain indicate increases in NGF and decreases in BDNF in surviving neurons of hippocampus and certain neocortical regions and decreases in TrkA in cortex and nucleus basalis. In PD brain, the few data available indicate decreases in neuronal content of GDNF and bFGF in surviving substantia nigra dopaminergic neurons. There are very few data regarding age-dependent effects on NTFs and on their receptors in human brain. Since NTFs in neurons are subject to retrograde and, in at least some cases, to anterograde transport from and to target neurons, their effects may be related to synthesis in local or remote sites or to changes in axoplasmic transport. Also, certain NTFs and their receptors are found to be expressed in activated glia. Thus, comparative in situ data for transcription levels and protein contents for NTFs and their receptors in both sites of neuronal origin and termination in human brain are needed to understand their potential roles in treating human diseases.

Reduced expression of insulin-like growth factor 1 messenger RNA in the hippocampus of aged rats

Adult neurones remain dependent on neurotrophic factors such as insulin-like growth factor 1 (IGF-1) to sustain neuronal viability by maintaining cell phenotype, supporting synaptic plasticity and providing neuroprotective and neuroregenerative mechanisms. A decline in the cellular expression of neurotrophic factors has been speculated to contribute to the age-related changes that occur in the brain, where the hippocampus appears particularly susceptible. Using in situ hybridisation, we have made a detailed comparison of the expression of IGF-1 mRNA in the hippocampal formation between young (6 months) and aged (23 months) rats. IGF-1 mRNA expression was measured from cell populations containing only high density radioactive labelling (>20 grains/cell) to avoid ambiguity of signal. The amount of IGF-1 mRNA signal was significantly lower in cells of the alveus (P<0.05) and stratum lacunosum moleculare (P<0.01) of aged compared to young rats. These findings challenge reports that IGF-1 mRNA is unaltered in the ageing hippocampus and provide further evidence that changes in the IGF-1 system is a significant factor in the progressive age-related deterioration of normal neuronal function.

Growth hormone, insulin-like growth factor I and cognitive function in adults

This review focuses on the possible contribution of the growth hormone (GH)-insulin-like growth factor I (IGF-I) axis to cognitive function. Binding sites for GH and IGF-I are found in various areas of the brain. Their distribution suggests that GH and IGF-I contribute to the function of the hippocampus, a brain structure important for the maintenance of cognitive functions such as learning and memory. Evidence for cognitive deficits in GH-deficient individuals has been found in various studies, some of which have shown that these deficits can be reversed by GH substitution therapy. In addition to examining conditions of GH deficiency, this article reviews studies evaluating the correlation between the cognitive deficits associated with ageing and age-related decreases in GH or IGF-I secretion. Based on the available data, one might hypothesize that relative GH or IGF-I deficiency could contribute to the deterioration of cognitive functions observed in the elderly.

Dexamethasone effects on cortisol secretion in Alzheimer's disease: some clinical and hormonal features in suppressor and nonsuppressor patients

Alterations in the hypothalamic-pituitary-adrenal axis (HPAA) and failure of dexamethasone (DXT) to suppress cortisol secretion occur in Alzheimer's disease (AD). This study was aimed to settle possible differences in some clinical (age, body weight, body mass index, dementia severity) and hormonal parameters in AD patients non-responders to overnight 1 mg-DXT suppression test compared with the responder subjects. ACTH, cortisol and dehydroepiandrosterone sulphate (DHEAS) day-time levels were assessed in 25 AD patients and in 12 age-matched healthy controls before DXT administration. In view of their neuroprotective effects, plasma levels of Insulin-like Growth Factor-I (IGF-I) and of IGF-Binding Proteins (IGFBPs) were also determined. After DXT, 8 AD subjects (32%) showed cortisol levels above the conventional cut-off of 140 nmol/L. No significant differences were found in clinical parameters in suppressor vs nonsuppressor patients. AD subjects showed higher cortisol, cortisol/DHEAS ratios, and lower DHEAS levels in comparison with controls. Both ACTH and cortisol levels were not different in suppressor and nonsuppressor patients, but DHEAS levels were significantly lower in nonsuppressor cases, who also exhibited ACTH and cortisol periodicities more altered than in suppressor and in control subjects. IGF-I and IGFBP-3 levels were lower and those of IGFBP-1 higher in nonsuppressor than in suppressor cases and in healthy controls. IGF-I/IGFBPs system data were correlated with cognitive impairment and adrenal steroid levels in AD patients.

Actions and interactions of the IGF system in Alzheimer's disease: review and hypotheses

Insulin-like growth factors (IGF) are pleiotrophic polypeptides affecting all aspects of growth and development. The IGF system, including ligands, receptors, binding proteins and proteases is also involved in pathophysiological conditions, such as cancer and degenerative conditions. In this review, the actions and interactions of the IGF system as it relates to Alzheimer's disease will be investigated.

Aberrant expression of nNOS in pyramidal neurons in Alzheimer's disease is highly co-localized with p21ras and p16INK4a

Aberrancies of growth and proliferation-regulating mechanisms might be critically involved in the processes of neurodegeneration in Alzheimer's disease (AD). Expression of p21ras and further downstream signalling elements involved in regulation of proliferation and differentiation as, for example, MEK, ERK1/2, cyclins, cyclin-dependent kinases and their inhibitors such as those of the p16INK4a family, are elevated early during the course of neurodegeneration. Activation of p21ras can also directly be triggered by nitric oxide (NO), synthesized in the brain by various isoforms of nitric oxide synthase (NOS) that might be differentially involved into the pathomechanism of AD. To study the potential link of NO and critical regulators of cellular proliferation and differentiation in the process of neurofibrillary degeneration, we analyzed the expression pattern of NOS-isoforms, p21ras and p16INK4a compared to neurofibrillary degeneration in AD. Additionally to its expression in a subtype of cortical interneurons that contain the nNOS-isoform also in normal brain, nNOS was detected in pyramidal neurons containing neurofibrillary tangles or were even unaffected by neurofibrillary degeneration. Expression of nNOS in these neurons was highly co-localized with p21ras and p16INK4a. Because endogenous NO can activate p21ras in the same cell which in turn leads to cellular activation and stimulation of NOS expression [H.M. Lander, J.S. Ogiste, S.F.A. Pearce, R. Levi, A. Novogrodsky, Nitric oxide-stimulated guanine nucleotide exchange on p21 ras, J. Biol. Chem. 270 (1995) 7017-7020], the high level of co-expression of NOS and p21ras in neurons vulnerable to neurofibrillary degeneration early in the course of AD thus provides the basis for an autocrine feedback mechanism that might exacerbate the progression of neurodegeneration in a self-propagating manner.

Growth factor-mediated stabilization of amyloid precursor protein mRNA is mediated by a conserved 29-nucleotide sequence in the 3'-untranslated region

Using a cell-free translation system, we previously demonstrated that the turnover and translation of amyloid precursor protein (APP) mRNA was regulated by a 29-nucleotide instability element, located 200 nucleotides downstream from the stop codon. Here we have examined the regulatory role of this element in primary human capillary endothelial cells under different nutritional conditions. Optimal proliferation required a growth medium (endothelial cell growth medium) supplemented with epidermal, basic fibroblast, insulin-like, and vascular endothelial growth factors. In vitro transcribed mRNAs with the 5'-untranslated region (UTR) and coding region of beta-globin and the entire 3'-UTR of APP 751 were transfected into cells cultured in endothelial cell growth medium. Wild-type globin-APP mRNA containing an intact APP 3'-UTR and mutant globin-APP mRNA containing a mutated 29-nucleotide element decayed with identical half-lives (t 1/2 = 60 min). Removal of all supplemental growth factors from the culture medium significantly accelerated the decay of transfected wild-type mRNA (t 1/2 = 10 min), but caused only a moderate decrease in the half-life of transfected mutant mRNA (t 1/2 = 40 min). We therefore conclude that the 29-nucleotide 3'-UTR element is an mRNA destabilizer whose function can be inhibited by inclusion of the aforementioned mixture of growth factors in the culture medium.

A new mechanism of neurodegeneration: a proinflammatory cytokine inhibits receptor signaling by a survival peptide

Heightened expression of both a proinflammatory cytokine, tumor necrosis factor alpha (TNF-alpha), and a survival peptide, insulin-like growth factor I (IGF-I), occurs in diverse diseases of the central nervous system, including Alzheimer's disease, multiple sclerosis, the AIDS-dementia complex, and cerebral ischemia. Conventional roles for these two proteins are neuroprotection by IGF-I and neurotoxicity by TNF-alpha. Although the mechanisms of action for IGF-I and TNF-alpha in the central nervous system originally were established as disparate and unrelated, we hypothesized that the signaling pathways of these two cytokines may interact during neurodegeneration. Here we show that concentrations of TNF-alpha as low as 10 pg/ml markedly reduce the capacity of IGF-I to promote survival of primary murine cerebellar granule neurons. TNF-alpha suppresses IGF-I-induced tyrosine phosphorylation of insulin receptor substrate 2 (IRS-2) and inhibits IRS-2-precipitable phosphatidylinositol 3'-kinase activity. These experiments indicate that TNF-alpha promotes IGF-I receptor resistance in neurons and inhibits the ability of the IGF-I receptor to tyrosine-phosphorylate the IRS-2 docking molecule and to subsequently activate the critical downstream enzyme phosphatidylinositol 3'-kinase. This intracellular crosstalk between discrete cytokine receptors reveals a novel pathway that leads to neuronal degeneration whereby a proinflammatory cytokine inhibits receptor signaling by a survival peptide.

Elevated expression of p21ras is an early event in Alzheimer's disease and precedes neurofibrillary degeneration

Alzheimer's disease is a chronic degenerative disorder characterized by the intracellular accumulation of "paired helical filaments" consisting of highly phosphorylated tau and by extracellular deposits of aggregated Abeta-peptide. Furthermore, neurodegeneration in Alzheimer's disease is associated with the appearance of neuritic growth profiles that are aberrant with respect to their localization, morphological appearance, and composition of cytoskeletal elements. During early stages of Alzheimer's disease, a variety of growth factors and mitogenic compounds are elevated. Most of these factors mediate their cellular effects through activation of the p21ras-dependent mitogen-activated protein kinase cascade, a pathway that is also involved in the regulation of expression and post-translational modification of the amyloid precursor protein and tau protein. We previously reported on the elevated expression of p21ras associated with paired helical filament formation and Abeta-deposits. However, the question arises as to whether induction of p21ras and the downstream mitogen-activated protein kinase cascade is an early event with rather primary importance in the pathogenetic chain or simply occurs as a cellular response to neurodegeneration. The present study shows that expression of p21ras is clearly elevated in very early stages of the disease, preceding both neurofibrillary pathology and formation of Abeta.

The role of neuronal growth factors in neurodegenerative disorders of the human brain

Recent evidence suggests that neurotrophic factors that promote the survival or differentiation of developing neurons may also protect mature neurons from neuronal atrophy in the degenerating human brain. Furthermore, it has been proposed that the pathogenesis of human neurodegenerative disorders may be due to an alteration in neurotrophic factor and/or trk receptor levels. The use of neurotrophic factors as therapeutic agents is a novel approach aimed at restoring and maintaining neuronal function in the central nervous system (CNS). Research is currently being undertaken to determine potential mechanisms to deliver neurotrophic factors to selectively vulnerable regions of the CNS. However, while there is widespread interest in the use of neurotrophic factors to prevent and/or reduce the neuronal cell loss and atrophy observed in neurodegenerative disorders, little research has been performed examining the expression and functional role of these factors in the normal and diseased human brain. This review will discuss recent studies and examine the role members of the nerve growth factor family (NGF, BDNF and NT-3) and trk receptors as well as additional growth factors (GDNF, TGF-alpha and IGF-I) may play in neurodegenerative disorders of the human brain.

Apoptosis, neurotrophic factors and neurodegeneration

Apoptosis is an active process of cell death characterized by distinct morphological features, and is often the end result of a genetic programme of events, i.e. programmed cell death (PCD). There is growing evidence supporting a role for apoptosis in some neurodegenerative diseases. This conclusion is based on DNA fragmentation studies and findings of increased levels of pro-apoptotic genes in human brain and in in vivo and in vitro model systems. Additionally, there is some evidence for a loss of neurotrophin support in neurodegenerative diseases. In Alzheimer's disease, in particular, there is strong evidence from human brain studies, transgenic models and in vitro models to suggest that the mode of nerve cell death is apoptotic. In this review we describe the evidence implicating apoptosis in neurodegenerative diseases with a particular emphasis on Alzheimer's disease.