Neuritic involvement within bFGF immunopositive plaques of Alzheimer's disease

Association between plasma cytokine levels and multiple neuroimaging modalities in mild cognitive impairment

BACKGROUND

The relationship between peripheral cytokines and neuroimaging biomarkers for Alzheimer's disease (AD) is not yet well established.

OBJECTIVE

To determine the association of cytokine plasma levels with brain amyloid deposition, cortical glucose metabolism, hippocampal volume, and white matter lesions (WMLs) in older adults with mild cognitive impairment (MCI).

METHODS

We recruited 50 older individuals with amnestic MCI (25 men and 25 women; median age, 75 years) and performed plasma analysis, 11C-Pittsburgh compound-B positron-emission tomography (PiB-PET), 18F-fluorodeoxyglucose positron-emission tomography, and magnetic resonance imaging. Global PiB and fluorodeoxyglucose (FDG) uptake were assessed by the ratio of the voxel number-weighted average of the mean uptake in the frontal, temporoparietal, and posterior cingulate, in reference to the cerebellum. The Fazekas scale was used to evaluate WMLs. Plasma levels of 48 cytokines were simultaneously measured with bead-based multiplex assays.

RESULTS

The plasma levels of IL-2Ra, IL-3, IL-5, IL-7, IL-9, IL-16, IL-18, fibroblast growth factor (FGF-basic), granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage colony-stimulating factor (GM-CSF), macrophage inflammatory protein-1α (MIP-1α), regulated on activation, normal T-cell expressed and secreted (RANTES), tumor necrosis factor-α (TNF-α), cutaneous T-cell attracting chemokine (CTACK), growth-regulated oncogene α (GROα), hepatocyte growth factor (HGF), interferon-α2 (IFN-α2), leukemia inhibitory factor (LIF), monocyte chemoattractant protein-3 (MCP-3), β-nerve growth factor (β-NGF), stem cell factor (SCF), stem cell growth factor-β (SCGF-β), and TNF-related apoptosis-inducing ligand (TRAIL) were significantly associated with global PiB uptake, whereas those of IL-7 and GROα were significantly associated with hippocampal volume after covariate adjustment and false discovery rate correction.

CONCLUSIONS

Plasma cytokines are associated with brain amyloid deposition rather than brain dysfunction or hippocampal atrophy. Moreover, cytokines may play important roles in early-stage AD pathophysiology.

Concordant and Discordant Cerebrospinal Fluid and Plasma Cytokine and Chemokine Responses in Mild Cognitive Impairment and Early-Stage Alzheimer's Disease

Neuroinflammation may be a pathogenic mediator and biomarker of neurodegeneration at the boundary between mild cognitive impairment (MCI) and early-stage Alzheimer's disease (AD). Whether neuroinflammatory processes are endogenous to the central nervous system (CNS) or originate from systemic (peripheral blood) sources could impact strategies for therapeutic intervention. To address this issue, we measured cytokine and chemokine immunoreactivities in simultaneously obtained lumbar puncture cerebrospinal fluid (CSF) and serum samples from 39 patients including 18 with MCI or early AD and 21 normal controls using a 27-plex XMAP bead-based enzyme-linked immunosorbent assay (ELISA). The MCI/AD combined group had significant (p < 0.05 or better) or statistically trend-wise (0.05 ≤ p ≤ 0.10) concordant increases in CSF and serum IL-4, IL-5, IL-9, IL-13, and TNF-α and reductions in GM-CSF, b-FGF, IL-6, IP-10, and MCP-1; CSF-only increases in IFN-y and IL-7 and reductions in VEGF and IL-12p70; serum-only increases in IL-1β, MIP-1α, and eotaxin and reductions in G-CSF, IL-2, IL-8 and IL-15; and discordant CSF-serum responses with reduced CSF and increased serum PDGF-bb, IL-17a, and RANTES. The results demonstrate simultaneously parallel mixed but modestly greater pro-inflammatory compared to anti-inflammatory or neuroprotective responses in CSF and serum. In addition, the findings show evidence that several cytokines and chemokines are selectively altered in MCI/AD CSF, likely corresponding to distinct neuroinflammatory responses unrelated to systemic pathologies. The aggregate results suggest that early management of MCI/AD neuroinflammation should include both anti-inflammatory and pro-neuroprotective strategies to help prevent disease progression.

The fibroblast growth factor system in cognitive disorders and dementia

Cognitive impairment is the core precursor to dementia and other cognitive disorders. Current hypotheses suggest that they share a common pathological basis, such as inflammation, restricted neurogenesis, neuroendocrine disorders, and the destruction of neurovascular units. Fibroblast growth factors (FGFs) are cell growth factors that play essential roles in various pathophysiological processes via paracrine or autocrine pathways. This system consists of FGFs and their receptors (FGFRs), which may hold tremendous potential to become a new biological marker in the diagnosis of dementia and other cognitive disorders, and serve as a potential target for drug development against dementia and cognitive function impairment. Here, we review the available evidence detailing the relevant pathways mediated by multiple FGFs and FGFRs, and recent studies examining their role in the pathogenesis and treatment of cognitive disorders and dementia.

Molecular and Clinical Significance of Fibroblast Growth Factor 2 in Development and Regeneration of the Auditory System

The fibroblast growth factor 2 (FGF2) is a member of the FGF family which is involved in key biological processes including development, cellular proliferation, wound healing, and angiogenesis. Although the utility of the FGF family as therapeutic agents has attracted attention, and FGF2 has been studied in several clinical contexts, there remains an incomplete understanding of the molecular and clinical function of FGF2 in the auditory system. In this review, we highlight the role of FGF2 in inner ear development and hearing protection and present relevant clinical studies for tympanic membrane (TM) repair. We conclude by discussing the future implications of FGF2 as a potential therapeutic agent.

Normal aging, motor neurone disease, and Alzheimer's disease are characterized by cortical changes in inflammatory cytokines

The role of increased brain inflammation in the development of neurodegenerative diseases is unclear. Here, we have compared cytokine changes in normal aging, motor neurone disease (MND), and Alzheimer's disease (AD). After an initial analysis, six candidate cytokines, interleukin (IL)- 4, 5, 6, 10, macrophage inhibitory protein (MIP)-1α, and fibroblast growth factor (FGF)-2, showing greatest changes were assayed in postmortem frozen human superior frontal gyri (n = 12) of AD patients, aging and young adult controls along with the precentral gyrus (n = 12) of MND patients. Healthy aging was associated with decreased anti-inflammatory IL-10 and FGF-2 levels. AD prefrontal cortex was associated with increased levels of IL-4, IL-5, and FGF-2, with the largest increase seen for FGF-2. Notwithstanding differences in the specific frontal lobe gyrus sampled, MND patients' primary motor cortex (precentral gyrus) was associated with increased levels of IL-5, IL-6, IL-10, and FGF-2 compared to the aging prefrontal cortex (superior frontal gyrus). Immunocytochemistry showed that FGF-2 is expressed in neurons, astrocytes, and microglia in normal aging prefrontal cortex, AD prefrontal cortex, and MND motor cortex. We report that healthy aging and age-related neurodegenerative diseases have different cortical inflammatory signatures that are characterized by increased levels of anti-inflammatory cytokines and call into question the view that increased inflammation underlies the development of age-related neurodegenerative diseases.

Neuronal excitation/inhibition imbalance: core element of a translational perspective on Alzheimer pathophysiology

Our incomplete understanding of the link between Alzheimer's Disease pathology and symptomatology is a crucial obstacle for therapeutic success. Recently, translational studies have begun to connect the dots between protein alterations and deposition, brain network dysfunction and cognitive deficits. Disturbance of neuronal activity, and in particular an imbalance in underlying excitation/inhibition (E/I), appears early in AD, and can be regarded as forming a central link between structural brain pathology and cognitive dysfunction. While there are emerging (non-)pharmacological options to influence this imbalance, the complexity of human brain dynamics has hindered identification of an optimal approach. We suggest that focusing on the integration of neurophysiological aspects of AD at the micro-, meso- and macroscale, with the support of computational network modeling, can unite fundamental and clinical knowledge, provide a general framework, and suggest rational therapeutic targets.

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.

Physical Exercise-Induced Myokines in Neurodegenerative Diseases

Neurodegenerative diseases (NDs), such as Alzheimer’s disease (AD), Parkinson’s disease (PD), Huntington’s disease (HD), and amyotrophic lateral sclerosis (ALS), are disorders characterized by progressive degeneration of the nervous system. Currently, there is no disease-modifying treatments for most NDs. Meanwhile, numerous studies conducted on human and animal models over the past decades have showed that exercises had beneficial effects on NDs. Inter-tissue communication by myokine, a peptide produced and secreted by skeletal muscles during exercise, is thought to be an important underlying mechanism for the advantages. Here, we reviewed studies about the effects of myokines regulated by exercise on NDs and their mechanisms. Myokines could exert beneficial effects on NDs through a variety of regulatory mechanisms, including cell survival, neurogenesis, neuroinflammation, proteostasis, oxidative stress, and protein modification. Studies on exercise-induced myokines are expected to provide a novel strategy for treating NDs, for which there are no adequate treatments nowadays. To date, only a few myokines have been investigated for their effects on NDs and studies on mechanisms involved in them are in their infancy. Therefore, future studies are needed to discover more myokines and test their effects on NDs.

Growth Factors and Alcohol Use Disorder

Neurotrophic growth factors were originally characterized for their support in neuronal differentiation, outgrowth, and survival during development. However, it has been acknowledged that they also play a vital role in the adult brain. Abnormalities in growth factors have been implicated in a variety of neurological and psychiatric disorders, including alcohol use disorder (AUD). This work focuses on the interaction between alcohol and growth factors. We review literature suggesting that several growth factors play a unique role in the regulation of alcohol consumption, and that breakdown in these growth factor systems is linked to the development of AUD. Specifically, we focus on the brain-derived neurotrophic factor (BDNF), glial cell line-derived neurotrophic factor (GDNF), fibroblast growth factor 2 (FGF2), and insulin growth factor 1 (IGF-1). We also review the literature on the potential role of midkine (MDK) and pleiotrophin (PTN) and their receptor, anaplastic lymphoma kinase (ALK), in AUD. We show that alcohol alters the expression of these growth factors or their receptors in brain regions previously implicated in addiction, and that manipulations on these growth factors and their downstream signaling can affect alcohol-drinking behaviors in animal models. We conclude that there is a need for translational and clinical research to assess the therapeutic potential of new pharmacotherapies targeting these systems.

Identifying the molecular systems that influence cognitive resilience to Alzheimer's disease in genetically diverse mice

Individual differences in cognitive decline during normal aging and Alzheimer's disease (AD) are common, but the molecular mechanisms underlying these distinct outcomes are not fully understood. We utilized a combination of genetic, molecular, and behavioral data from a mouse population designed to model human variation in cognitive outcomes to search for the molecular mechanisms behind this population-wide variation. Specifically, we used a systems genetics approach to relate gene expression to cognitive outcomes during AD and normal aging. Statistical causal-inference Bayesian modeling was used to model systematic genetic perturbations matched with cognitive data that identified astrocyte and microglia molecular networks as drivers of cognitive resilience to AD. Using genetic mapping, we identified Fgf2 as a potential regulator of the astrocyte network associated with individual differences in short-term memory. We also identified several immune genes as regulators of a microglia network associated with individual differences in long-term memory, which was partly mediated by amyloid burden. Finally, significant overlap between mouse and two different human coexpression networks provided strong evidence of translational relevance for the genetically diverse AD-BXD panel as a model of late-onset AD. Together, this work identified two candidate molecular pathways enriched for microglia and astrocyte genes that serve as causal AD cognitive biomarkers, and provided a greater understanding of processes that modulate individual and population-wide differences in cognitive outcomes during AD.

Neuroregeneration: Regulation in Neurodegenerative Diseases and Aging

It had been commonly believed for a long time, that once established, degeneration of the central nervous system (CNS) is irreparable, and that adult person merely cannot restore dead or injured neurons. The existence of stem cells (SCs) in the mature brain, an organ with minimal regenerative ability, had been ignored for many years. Currently accepted that specific structures of the adult brain contain neural SCs (NSCs) that can self-renew and generate terminally differentiated brain cells, including neurons and glia. However, their contribution to the regulation of brain activity and brain regeneration in natural aging and pathology is still a subject of ongoing studies. Since the 1970s, when Fuad Lechin suggested the existence of repair mechanisms in the brain, new exhilarating data from scientists around the world have expanded our knowledge on the mechanisms implicated in the generation of various cell phenotypes supporting the brain, regulation of brain activity by these newly generated cells, and participation of SCs in brain homeostasis and regeneration. The prospects of the SC research are truthfully infinite and hitherto challenging to forecast. Once researchers resolve the issues regarding SC expansion and maintenance, the implementation of the SC-based platform could help to treat tissues and organs impaired or damaged in many devastating human diseases. Over the past 10 years, the number of studies on SCs has increased exponentially, and we have already become witnesses of crucial discoveries in SC biology. Comprehension of the mechanisms of neurogenesis regulation is essential for the development of new therapeutic approaches for currently incurable neurodegenerative diseases and neuroblastomas. In this review, we present the latest achievements in this fast-moving field and discuss essential aspects of NSC biology, including SC regulation by hormones, neurotransmitters, and transcription factors, along with the achievements of genetic and chemical reprogramming for the safe use of SCs in vitro and in vivo.

Levels of glial cell line-derived neurotrophic factor are decreased, but fibroblast growth factor 2 and cerebral dopamine neurotrophic factor are increased in the hippocampus in Parkinson's disease

Growth factors can facilitate hippocampus-based learning and memory and are potential targets for treatment of cognitive dysfunction via their neuroprotective and neurorestorative effects. Dementia is common in Parkinson's disease (PD), but treatment options are limited. We aimed to determine if levels of growth factors are altered in the hippocampus of patients with PD, and if such alterations are associated with PD pathology. Enzyme-linked immunosorbent assays were used to quantify seven growth factors in fresh frozen hippocampus from 10 PD and nine age-matched control brains. Western blotting and immunohistochemistry were used to explore cellular and inflammatory changes that may be associated with growth factor alterations. In the PD hippocampus, protein levels of glial cell line-derived neurotrophic factor were significantly decreased, despite no evidence of neuronal loss. In contrast, protein levels of fibroblast growth factor 2 and cerebral dopamine neurotrophic factor were significantly increased in PD compared to controls. Levels of the growth factors epidermal growth factor, heparin-binding epidermal growth factor, brain-derived neurotrophic factor and mesencephalic astrocyte-derived neurotrophic factor did not differ between groups. Our data demonstrate changes in specific growth factors in the hippocampus of the PD brain, which potentially represent targets for modification to help attenuate cognitive decline in PD. These data also suggest that multiple growth factors and direction of change needs to be considered when approaching growth factors as a potential treatment for cognitive decline.

The Full Spectrum of Alzheimer's Disease Is Rooted in Metabolic Derangements That Drive Type 3 Diabetes

The standard practice in neuropathology is to diagnose Alzheimer's disease (AD) based on the distribution and abundance of neurofibrillary tangles and Aβ deposits. However, other significant abnormalities including neuroinflammation, gliosis, white matter degeneration, non-Aβ microvascular disease, and insulin-related metabolic dysfunction require further study to understand how they could be targeted to more effectively remediate AD. This review addresses non-Aβ and non-pTau AD-associated pathologies, highlighting their major features, roles in neurodegeneration, and etiopathic links to deficits in brain insulin and insulin-like growth factor signaling and cognitive impairment. The discussion delineates why AD with its most characteristic clinical and pathological phenotypic profiles should be regarded as a brain form of diabetes, i.e., type 3 diabetes, and entertains the hypothesis that type 3 diabetes is just one of the categories of insulin resistance diseases that can occur independently or overlap with one or more of the others, including type 2 diabetes, metabolic syndrome, and nonalcoholic fatty liver disease.

The role of fibroblast growth factor 2 in drug addiction

Fibroblast growth factor 2 (FGF2) is a member of the FGF-family, which consists of 22 members, with four known FGF receptors (five in humans). Over the last 30 years, FGF2 has been extensively studied for its role in cell proliferation, differentiation, growth, survival and angiogenesis during development, as well as for its role in adult neurogenesis and regenerative plasticity. Over the past decade, FGF2 has been implicated in learning and memory, as well as in several neuropsychiatric disorders, including anxiety, stress, depression and drug addiction. In this review, we present accumulating evidence indicating the involvement of FGF2 in neuroadaptations caused by drugs of abuse, namely, amphetamine, cocaine, nicotine and alcohol. Moreover, evidence suggests that FGF2 is a positive regulator of alcohol and drug-related behaviors. Thus, although additional studies are yet required, we suggest that reducing FGF2 activity may provide a novel therapeutic approach for substance use disorders.

An acute bout of aerobic or strength exercise specifically modifies circulating exerkine levels and neurocognitive functions in elderly individuals with mild cognitive impairment

Although exercise is an effective way to decrease the risk of developing Alzheimer's disease, the biological basis for such benefits from the different exercise modes remains elusive. The present study thus aimed (i) to investigate the effects of acute aerobic or resistance exercise on neurocognitive performances and molecular markers when performing a cognitive task involving executive functioning in older adults with amnestic mild cognitive impairment (aMCI), and (ii) to explore relationships of acute exercise-induced neurocognitive changes with changes in circulating levels of neuroprotective growth factors (e.g., BDNF, IGF-1, VEGF, and FGF-2, collectively termed 'exerkines'), elicited by different acute exercise modes. Sixty-six older adults with aMCI were recruited and randomly assigned to an aerobic exercise (AE) group, a resistance exercise (RE) group, or a non-exercise-intervention (control) group. The behavioral [i.e., accuracy rate (AR) and reaction time (RT)] and electrophysiological [i.e., event-related potential (ERP) P3 latency and amplitude collected from the Fz, Cz, and Pz electrodes] indices were simultaneously measured when participants performed a Flanker task at baseline and after either an acute bout of 30 min of moderate-intensity AE, RE or a control period. Blood samples were taken at three time points, one at baseline (T1) and two after an acute exercise intervention (T2 and T3: before and after cognitive task test, respectively). The results showed that the acute AE and RE not only improved behavioral (i.e., RTs) performance but also increased the ERP P3 amplitudes in the older adults with aMCI. Serum FGF-2 levels did not change with acute aerobic or resistance exercise. However, an acute bout of aerobic exercise significantly increased serum levels of BDNF and IGF-1 and tended to increase serum levels of VEGF in elderly aMCI individuals. Acute resistance exercise increased only serum IGF-1 levels. However, the exercise-induced elevated levels of these molecular markers returned almost to baseline levels in T3 (about 20 min after acute exercise). In addition, changes in the levels of neurotrophic and angiogenic factors were not correlated with changes in RTs and P3 amplitudes. The present findings of changes in neuroprotective growth factors and neurocognitive performances through acute AE or RE suggest that molecular and neural prerequisites for exercise-dependent plasticity are preserved in elderly aMCI individuals. However, the distinct pattern of changes in circulating molecular biomarkers induced by two different exercise modes in aMCI elderly individuals and the potentially interactive mechanisms of the effects of BDNF, IGF-1, and VEGF on amyloid-β provide a basis for future long-term exercise intervention to investigate whether AE relative to RE might be more effective in prevention/treatment of an early stage neurodegenerative disease.

Friends Turned Foes: Angiogenic Growth Factors beyond Angiogenesis

Angiogenesis, the formation of new blood vessels from pre-existing ones is a biological process that ensures an adequate blood flow is maintained to provide the cells with a sufficient supply of nutrients and oxygen within the body. Numerous soluble growth factors and inhibitors, cytokines, proteases as well as extracellular matrix proteins and adhesion molecules stringently regulate the multi-factorial process of angiogenesis. The properties and interactions of key angiogenic molecules such as vascular endothelial growth factors (VEGFs), fibroblast growth factors (FGFs) and angiopoietins have been investigated in great detail with respect to their molecular impact on angiogenesis. Since the discovery of angiogenic growth factors, much research has been focused on their biological actions and their potential use as therapeutic targets for angiogenic or anti-angiogenic strategies in a context-dependent manner depending on the pathologies. It is generally accepted that these factors play an indispensable role in angiogenesis. However, it is becoming increasingly evident that this is not their only role and it is likely that the angiogenic factors have important functions in a wider range of biological and pathological processes. The additional roles played by these molecules in numerous pathologies and biological processes beyond angiogenesis are discussed in this review.

Changes in the Golgi Apparatus of Neocortical and Hippocampal Neurons in the Hibernating Hamster

Hibernating animals have been used as models to study several aspects of the plastic changes that occur in the metabolism and physiology of neurons. These models are also of interest in the study of Alzheimer's disease because the microtubule-associated protein tau is hyperphosphorylated during the hibernation state known as torpor, similar to the pretangle stage of Alzheimer's disease. Hibernating animals undergo torpor periods with drops in body temperature and metabolic rate, and a virtual cessation of neural activity. These processes are accompanied by morphological and neurochemical changes in neurons, which reverse a few hours after coming out of the torpor state. Since tau has been implicated in the structural regulation of the neuronal Golgi apparatus (GA) we have used Western Blot and immunocytochemistry to analyze whether the GA is modified in cortical neurons of the Syrian hamster at different hibernation stages. The results show that, during the hibernation cycle, the GA undergo important structural changes along with differential modifications in expression levels and distribution patterns of Golgi structural proteins. These changes were accompanied by significant transitory reductions in the volume and surface area of the GA elements during torpor and arousal stages as compared with euthermic animals.

Systemic administration of fibroblast growth factor-2 (FGF2) reduces BACE1 expression and amyloid pathology in APP23 mice

There is an emerging evidence that growth factors may have a potential beneficial use in the treatment of Alzheimer's disease (AD) because of their neuroprotective properties and effects on neuronal proliferation. Basic fibroblast growth factor or fibroblast growth factor-2 (FGF2) is an anti-inflammatory, angiogenic, and neurotrophic factor that is expressed in many cell types, including neurons and glial cells. Here, we explored whether subcutaneous administration of FGF2 could have therapeutic effects in the APP 23 transgenic mouse, a model of amyloid pathology. FGF2 treatment attenuated spatial memory deficits, reduced amyloid-β (Aβ) and tau pathologies, decreased inducible nitric oxide synthase expression, and increased the number of astrocytes in the dentate gyrus in APP 23 mice compared with the vehicle-treated controls. The decrease in Aβ deposition was associated with a reduction in the expression of BACE1, the main enzyme responsible for Aβ generation. These results were confirmed in a neuroblastoma cell line, which demonstrated that incubation with FGF2 regulates BACE1 transcription. In addition, and in contrast with what has been previously published, the levels of FGF2 were reduced in postmortem brains from AD patients compared with controls. These data, therefore, suggest that systemic administration of FGF2 could have a potential therapeutic application in AD.

Neuroprotective role of γ-enolase in microglia in a mouse model of Alzheimer's disease is regulated by cathepsin X

γ-Enolase is a neurotrophic-like factor promoting growth, differentiation, survival and regeneration of neurons. Its neurotrophic activity is regulated by cysteine protease cathepsin X which cleaves the C-terminal end of the molecule. We have investigated the expression and colocalization of γ-enolase and cathepsin X in brains of Tg2576 mice overexpressing amyloid precursor protein. In situ hybridization of γ-enolase and cathepsin X revealed that mRNAs for both enzymes were expressed abundantly around amyloid plaques. Immunostaining demonstrated that the C-terminally cleaved form of γ-enolase was present in the immediate plaque vicinity, whereas the intact form, exhibiting neurotrophic activity, was observed in microglia cells in close proximity to senile plaque. The upregulation of γ-enolase in microglial cells in response to amyloid-β peptide (Aβ) was confirmed in mouse microglial cell line EOC 13.31 and primary microglia and medium enriched with γ-enolase proved to be neuroprotective against Aβ toxicity; however, the effect was reversed by cathepsin X proteolytic activity. These results demonstrate an upregulation of γ-enolase in microglia cells surrounding amyloid plaques in Tg2576 transgenic mice and demonstrate its neuroprotective role in amyloid-β-related neurodegeneration.

Fibroblast growth factor-2 counteracts the effect of ciliary neurotrophic factor on spontaneous differentiation in adult hippocampal progenitor cells

Neural stem/progenitor cells (NSCs) can spontaneously differentiate into neurons and glial cells in the absence of mitogen fibroblast growth factor-2 (FGF-2) or epidermal growth factor (EGF) in medium and the spontaneous differentiation of NSCs is mediated partially by endogenous ciliary neurotrophic factor (CNTF). This study examined the relationship of FGF-2 and CNTF in the spontaneous differentiation of adult hippocampal progenitor cells (AHPs). AHPs were cultured in the medium containing different concentration of FGF-2 (1-100 ng/mL). Western blotting and immunofluorescence staining were applied to detect the expression of the astrocytic marker GFAP, the neuronal marker Tuj1, the oligodendrocytic marker CNPase and, Nestin, the marker of AHPs. The expression of endogenous CNTF in AHPs at early (passage 4) and late stage (passage 22) was also measured by Western blotting. The results showed that FGF-2 increased the expression of Nestin, dramatically inhibited the expression of GFAP and Tuj1 and slightly suppressed the expression of CNPase. FGF-2 down-regulated the expression of endogenous CNTF in AHPs at both early (passage 4) and late stage (passage 22). These results suggested that FGF-2 could inhibit the spontaneous differentiation of cultured AHPs by negatively regulating the expression of endogenous CNTF in AHPs.

FGF2 gene transfer restores hippocampal functions in mouse models of Alzheimer's disease and has therapeutic implications for neurocognitive disorders

The adult hippocampus plays a central role in memory formation, synaptic plasticity, and neurogenesis. The subgranular zone of the dentate gyrus contains neural progenitor cells with self-renewal and multilineage potency. Transgene expression of familial Alzheimer's disease-linked mutants of β-amyloid precursor protein (APP) and presenilin-1 leads to a significant inhibition of neurogenesis, which is potentially linked to age-dependent memory loss. To investigate the effect of neurogenesis on cognitive function in a relevant disease model, FGF2 gene is delivered bilaterally to the hippocampi of APP+presenilin-1 bigenic mice via an adenoassociated virus serotype 2/1 hybrid (AAV2/1-FGF2). Animals injected with AAV2/1-FGF2 at a pre- or postsymptomatic stage show significantly improved spatial learning in the radial arm water maze test. A neuropathological investigation demonstrates that AAV2/1-FGF2 injection enhances the number of doublecortin, BrdU/NeuN, and c-fos-positive cells in the dentate gyrus, and the clearance of fibrillar amyloid-β peptide (Aβ) in the hippocampus. AAV2/1-FGF2 injection also enhances long-term potentiation in another APP mouse model (J20) compared with control AAV2/1-GFP-injected littermates. An in vitro study confirmed the enhanced neurogenesis of mouse neural stem cells by direct AAV2/1-FGF2 infection in an Aβ oligomer-sensitive manner. Further, FGF2 enhances Aβ phagocytosis in primary cultured microglia, and reduces Aβ production from primary cultured neurons after AAV2/1-FGF2 infection. Thus, our data indicate that virus-mediated FGF2 gene delivery has potential as an alternative therapy of Alzheimer's disease and possibly other neurocognitive disorders.

Behavior of neural stem cells in the Alzheimer brain

Alzheimer's disease (AD) is characterized by the deposition of beta-amyloid peptides (Abeta) and a progressive loss of neurons leading to dementia. Because hippocampal neurogenesis is linked to functions such as learning, memory and mood, there has been great interest in examining the effects of AD on hippocampal neurogenesis. This article reviews the pertinent studies and tries to unite them in one possible disease model. Early in the disease, oligomeric Abeta may transiently promote the generation of immature neurons from neural stem cells (NSCs). However, reduced concentrations of multiple neurotrophic factors and higher levels of fibroblast growth factor-2 seem to induce a developmental arrest of newly generated neurons. Furthermore, fibrillary Abeta and down-regulation of oligodendrocyte-lineage transcription factor-2 (OLIG2) may cause the death of these nonfunctional neurons. Therefore, altering the brain microenvironment for fostering apt maturation of graft-derived neurons may be critical for improving the efficacy of NSC transplantation therapy for AD.

Neurotrophic factors in Alzheimer's disease: role of axonal transport

Neurotrophic factors (NTF) are small, versatile proteins that maintain survival and function to specific neuronal populations. In general, the axonal transport of NTF is important as not all of them are synthesized at the site of its action. Nerve growth factor (NGF), for instance, is produced in the neocortex and the hippocampus and then retrogradely transported to the cholinergic neurons of the basal forebrain. Neurodegenerative dementias like Alzheimer’s disease (AD) are linked to deficits in axonal transport. Furthermore, they are also associated with imbalanced distribution and dysregulation of NTF. In particular, brain-derived neurotrophic factor (BDNF) plays a crucial role in cognition, learning and memory formation by modulating synaptic plasticity and is, therefore, a critical molecule in dementia and neurodegenerative diseases. Here, we review the changes of NTF expression and distribution (NGF, BDNF, neurotrophin-3, neurotrophin-4/5 and fibroblast growth factor-2) and their receptors [tropomyosin-related kinase (Trk)A, TrkB, TrkC and p75^NTR] in AD and AD models. In addition, we focus on the interaction with neuropathological hallmarks Tau/neurofibrillary tangle and amyloid-β (Abeta)/amyloid plaque pathology and their influence on axonal transport processes in order to unify AD-specific cholinergic degeneration and Tau and Abeta misfolding through NTF pathophysiology.

Current insights into molecular mechanisms of Alzheimer disease and their implications for therapeutic approaches

During the last 10 years, a lot of progress has been made in unraveling the pathogenic cascade leading to Alzheimer disease (AD). According to the most widely accepted hypothesis, production and aggregation of the amyloid beta (Abeta) peptide plays a key role in AD, and thus therapeutic interference with these processes is the subject of intense research. However, some important aspects of the disease mechanism are not yet fully understood. There is no consensus as yet on whether the disease acts through a loss- (LOF) or a gain-of-function (GOF) mechanism. While for many years, an increased production of Abeta42 was considered to be the prime culprit for the initiation of the disease process, and accordingly Abeta42 is elevated by AD-related presenilin(PS) mutations, recent data strongly suggest that PS mutations also lead to a LOF of PS towards a plethora of its substrates including amyloid precursor protein. How this PS LOF, especially decreased Abeta40 secretion due to mutant PS, impacts on the disease pathogenesis is yet to be elucidated. Secondly, vascular abnormalities--frequently observed to co-occur with AD--might also play a critical role in the initiation and aggravation of AD pathology given that the elimination of Abeta through a vascular route is an important brain Abeta clearance mechanism and its failure leads to formation of vascular amyloidosis and dense-core plaques. In this review, we will first focus on the important issue of a LOF versus a GOF mechanism for AD due to mutant PS, as well as on the possible role of vascular damage and reduced perfusion in AD. Special emphasis will be given to some of the AD mouse models that have helped to gain insights into the disease mechanism. Secondly, considering these mechanistic insights, we will discuss some therapeutic strategies which are currently in clinical or preclinical trials for AD.

Neprilysin Inhibits Angiogenesis via Proteolysis of Fibroblast Growth Factor-2

Neprilysin is a cell surface peptidase that catalytically inactivates neuropeptide substrates and functions as a tumor suppressor via its enzymatic function and multiple protein-protein interactions. We investigated whether neutral endopeptidase could inhibit angiogenesis in vivo utilizing a murine corneal pocket angiogenesis model and found that it reduced fibroblast growth factor-2-induced angiogenesis by 85% (p < 0.01) but had no effect on that of vascular endothelial growth factor. Treatment with recombinant neprilysin, but not enzymatically inactive neprilysin, resulted in a slight increase in basic fibroblast growth factor electrophoretic mobility from proteolytic cleavage between amino acids Leu-135 and Gly-136, which was inhibited by the neutral endopeptidase inhibitor CGS24592 and heparin. Cleavage kinetics were rapid, comparable with that of other known neprilysin substrates. Functional studies involving neprilysin-expressing vascular endothelial cells demonstrated that neutral endopeptidase inhibition significantly enhanced fibroblast growth factor-mediated endothelial cell growth, capillary array formation, and signaling, whereas exogenous recombinant neprilysin inhibited signaling. Recombinant constructs confirmed that cleavage products neither promoted capillary array formation nor induced signaling. Moreover, mutation of the cleavage site resulted in concomitant loss of cleavage and increased the potency of fibroblast growth factor-2 to induce capillary array formation. These data indicate that neprilysin proteolytically inactivates fibroblast growth factor-2, resulting in negative regulation of angiogenesis.

Hyperforin prevents beta-amyloid neurotoxicity and spatial memory impairments by disaggregation of Alzheimer's amyloid-beta-deposits

The major protein constituent of amyloid deposits in Alzheimer's disease (AD) is the amyloid beta-peptide (Abeta). In the present work, we have determined the effect of hyperforin an acylphloroglucinol compound isolated from Hypericum perforatum (St John's Wort), on Abeta-induced spatial memory impairments and on Abeta neurotoxicity. We report here that hyperforin: (1) decreases amyloid deposit formation in rats injected with amyloid fibrils in the hippocampus; (2) decreases the neuropathological changes and behavioral impairments in a rat model of amyloidosis; (3) prevents Abeta-induced neurotoxicity in hippocampal neurons both from amyloid fibrils and Abeta oligomers, avoiding the increase in reactive oxidative species associated with amyloid toxicity. Both effects could be explained by the capacity of hyperforin to disaggregate amyloid deposits in a dose and time-dependent manner and to decrease Abeta aggregation and amyloid formation. Altogether these evidences suggest that hyperforin may be useful to decrease amyloid burden and toxicity in AD patients, and may be a putative therapeutic agent to fight the disease.

Trophic factors counteract elevated FGF-2-induced inhibition of adult neurogenesis

The dentate gyrus of adult mammalian brain contains neural progenitor cells with self-renewal and multi-lineage potential. The lineage and maturation of the neural progenitors are determined by the composition and levels of the trophic factors in their microenvironment. In Alzheimer disease (AD) brain, especially the hippocampus, the level of basic fibroblast growth factor (FGF-2) is markedly elevated. Here we show that elevated FGF-2 enhances the division and nestin levels of cultured adult rat hippocampal progenitors but impairs neuronal lineage determination and maturation of these cells in culture. The trophic factors ciliary neurotrophic factor (CNTF), glial-derived neurotrophic factor (GDNF), and insulin-like growth factors-1 and -2 (IGF-1, IGF-2) as well as an Alzheimer peptidergic drug, Cerebrolysin((R)) (CL), in which we found these neurotrophic activities, counteract the effect of FGF-2 in inducing neuronal lineage (early neurogenesis). Whereas CNTF is the most active of the neurotrophic factors studied in promoting neurogenesis, CL, probably because of a combined effect of these factors, induces similar changes but without inhibiting cell proliferation. These findings suggest that CNTF, GDNF, IGF-1, and IGF-2 are promising therapeutic targets for AD and other diseases in which neurogenesis is probably inhibited.

Evidence for increased lysyl oxidase, the extracellular matrix-forming enzyme, in Alzheimer's disease brain

The study is based on the premise that the enzyme lysyl oxidase (LO), which catalyzes the crosslinking of extracellular matrix (ECM) proteins, participates in ECM modulation and senile plaque formation in Alzheimer's disease (AD). Experiments on hippocampal samples indicate that LO activity is increased (about 30%) in AD, but also in non-Alzheimer's dementia, as compared to controls with unrelated diseases. Immunohistochemistry with specific LO antibody indicates localization in blood vessel walls and in plaque-like structures. The number of LO-positive plaque-like structures in AD was over two-fold higher as compared to both non-Alzheimer's dementia and control groups. The findings lead us to suggest that active LO molecules in the ECM may be associated with plaque formation.

Pathways towards and away from Alzheimer's disease

Slowly but surely, Alzheimer's disease (AD) patients lose their memory and their cognitive abilities, and even their personalities may change dramatically. These changes are due to the progressive dysfunction and death of nerve cells that are responsible for the storage and processing of information. Although drugs can temporarily improve memory, at present there are no treatments that can stop or reverse the inexorable neurodegenerative process. But rapid progress towards understanding the cellular and molecular alterations that are responsible for the neuron's demise may soon help in developing effective preventative and therapeutic strategies.

Role of tau phosphorylation by glycogen synthase kinase-3beta in the regulation of organelle transport

Anterograde organelle transport is known to be inhibited by overexpression of the microtubule-associated protein tau in cultured cells. However, the molecular mechanism regulating this function of tau protein has not previously been understood. We found that in PC12 cells treated with NGF or fibroblast growth factor-2, glycogen synthase kinase-3beta and tau were upregulated simultaneously from around day 2 of differentiation, with increasing glycogen synthase kinase-3-mediated tau phosphorylation. This phosphorylation did not alter tau's ability to bind to microtubules but appeared to be required for the maintenance of the anterograde organelle transport in differentiated cells. Lithium, alsterpaullone or valproate, three independent glycogen synthase kinase-3 inhibitors, but not butyrolactone 1, an inhibitor of cyclin-dependent protein kinases, induced mitochondrial clustering in association with tau dephosphorylation. In CHO cells transfected with human tau(441), mitochondrial clustering was found in cells in which tau was unphosphorylated. These findings raise the possibility that the phosphorylation of tau by glycogen synthase kinase-3 might be involved in the regulation of organelle transport.

Acetylcholinesterase induces neuronal cell loss, astrocyte hypertrophy and behavioral deficits in mammalian hippocampus

Previous studies have demonstrated that acetylcholinesterase (AChE) promotes the assembly of amyloid-beta-peptides into neurotoxic amyloid fibrils and is toxic for chick retina neuronal cultures and neuroblastoma cells. Moreover, AChE is present in senile plaques in Alzheimer's disease (AD) brains. Here we have studied the effect of AChE on astrocytes and hippocampal neurons in vivo. Morphological as well as behavioral disturbances were analyzed after intrahippocampal injection of AChE. Rats were trained in the Morris water maze and assayed for behavioral parameters. Neuronal cell loss was found in the upper leaf of the dentate gyrus in rats injected with AChE in comparison with control animals. Glial fibrillary acidic protein immunoreactivity showed astrocytic hypertrophy and the magnitude of the response was associated with neuronal cell loss. Behavioral results show that injection of AChE produces cognitive impairment demonstrated by an altered water maze performance including (i) a higher escape latency score, (ii) a decreased spatial acuity and (iii) a shorter time of swimming in the platform quadrant. These findings indicate that a local increment in neuronal AChE concentration at the mammalian hippocampus, such as those present in amyloid deposits, may play a role in triggering neuropathological and behavioral changes such as those observed in AD brains.

Identification of a novel domain of fibroblast growth factor 2 controlling its angiogenic properties

Fibroblast growth factor 2 (FGF-2) is a potent factor modulating the activity of many cell types. Its dimerization and binding to high affinity receptors are considered to be necessary steps to induce FGF receptor phosphorylation and signaling activation. A structural analysis was carried out and a region encompassing residues 48-58 of human FGF-2 was identified, as potentially involved in FGF-2 dimerization. A peptide (FREG-48-58) derived from this region strongly and specifically inhibited FGF-2 induced proliferation and migration of primary bovine aorta endothelial cells (BAEC) in vitro, and markedly reduced FGF-2-dependent angiogenesis in two distinct in vivo assays. To further investigate the role of region 48-58, a polyclonal antibody raised against FREG-(48-58) was tested and was found to block FGF-2 action in vitro. Human FGF-2 has three histidine residues, one falling within the region 48-58. Chemical modification of histidine residues blocked FGF-2 activity and FREG-(48-58) inhibitory effect in vitro, indicating that histidine residues, in particular the one within FREG-(48-58) region, play a crucial role in the observed activity. Additional experiments showed that FREG-(48-58) specifically interacted with FGF-2, impaired FGF-2-interaction with itself, with heparin and with FGF receptor 1, and inhibited FGF-2-induced receptor phosphorylation and FGF-2 internalization. These data indicate for the first time that region 48-58 of FGF-2 is a functional domain controlling FGF-2 activity.

Heparan sulfate proteoglycans are ligands for receptor protein tyrosine phosphatase sigma

RPTPsigma is a cell adhesion molecule-like receptor protein tyrosine phosphatase involved in nervous system development. Its avian orthologue, known as cPTPsigma or CRYPalpha, promotes intraretinal axon growth and controls the morphology of growth cones. The molecular mechanisms underlying the functions of cPTPsigma are still to be determined, since neither its physiological ligand(s) nor its substrates have been described. Nevertheless, a major class of ligand(s) is present in the retinal basal lamina and glial endfeet, the potent native growth substrate for retinal axons. We demonstrate here that cPTPsigma is a heparin-binding protein and that its basal lamina ligands include the heparan sulfate proteoglycans (HSPGs) agrin and collagen XVIII. These molecules interact with high affinity with cPTPsigma in vitro, and this binding is totally dependent upon their heparan sulfate chains. Using molecular modelling and site-directed mutagenesis, a binding site for heparin and heparan sulfate was identified in the first immunoglobulin-like domain of cPTPsigma. HSPGs are therefore a novel class of heterotypic ligand for cPTPsigma, suggesting that cPTPsigma signaling in axons and growth cones is directly responsive to matrix-associated cues.

Intracellular mechanisms of amyloid accumulation and pathogenesis in Alzheimer's disease

Cell-culture studies have revealed some of the fundamental features of the interaction of amyloid Abeta with cells and the mechanism of amyloid accumulation and pathogenesis in vitro. A(beta)1-42, the longer isoform of amyloid that is preferentially concentrated in senile plaque (SP) amyloid deposits in Alzheimer's disease (AD), is resistant to degradation and accumulates as insoluble aggregates in late endosomes or lysosomes. Once these aggregates have nucleated inside the cell, they grow by the addition of aberrantly folded APP and amyloidgenic fragments of APP, that would otherwise be degraded, onto the amyloid lattice in a fashion analogous to prion replication. This accumulation of heterogeneous aggregated APP fragments and Abeta appears to mimic the pathophysiologyof dystrophic neurites, where the same spectrum of components has been identified by immunohistochemistry. In the brain, this residue appears to be released into the extracellular space, possibly by a partially apoptotic mechanism that is restricted to the distal compartments of the neuron. Ultimately, this insoluble residue may be further digested to the protease-resistant A(beta)n-42 core, perhaps by microglia, where it accumulates as senile plaques. Thus, the dystrophic neurites are likely to be the source of the immediate precursors of amyloid in the senile plaques. This is the opposite of the commonly held view that extracellular accumulation of amyloid induces dystrophic neurites. Many of the key pathological events of AD may also be directly related to the intracellular accumulation of this insoluble amyloid. The aggregated, intracellular amyloid induces the production of reactive oxygen species (ROS) and lipid peroxidation products and ultimately results in the leakage of the lysosomal membrane. The breakdown of the lysosomal membrane may be a key pathogenic event, leading to the release of heparan sulfate and lysosomal hydrolases into the cytosol. Together, these observations provide the novel view that amyloid deposits and some of the early events of amyloid pathogenesis initiate randomly within single cells in AD. This pathogenic mechanism can explain some of the more enigmatic features of Alzheimer's pathogenesis, like the focal nature of amyloid plaques, the relationship between amyloid, dystrophic neurites and neurofibrillary-tangle pathology, and the miscompartmentalization of extracellular and cytosolic components observed in AD brain.

Beta-catenin expression in human neural cell lines following exposure to cytokines and growth factors

Beta-catenin acts as a key mediator of the Wnt/Wingless signaling pathway involved in cell proliferation, differentiation and survival. Recent studies have shown that an unstable interaction between beta-catenin and the mutant presenilin-1 induces neuronal apoptosis, and that beta-catenin levels are decreased in the brains of patients with Alzheimer's disease (AD). Since activated microglia and astrocytes play a role in the process of neuronal degeneration in AD, the cytokine/growth factor-regulated expression of beta-catenin in human neural cell lines, including NTera2 teratocarcinoma-derived differentiated neurons (NTera2-N), IMR-32 neuroblastoma, SKN-SH neuroblastoma and U-373MG astrocytoma, was studied quantitatively following exposure to epidermal growth factor (EGF), basic fibroblast growth factor (bFGF), brain-derived neurotrophic factor (BDNF), tumor necrosis factor-alpha (TNF-alpha), interleukin (IL)-1beta, IL-6, interferon (IFN)-gamma, transforming growth factor (TGF)-beta1, dibutyryl cyclic adenosine 3',5'-cyclic monophosphate (cAMP) (dbcAMP) or phorbol 12-myristate 13-acetate (PMA). Beta-catenin mRNA expressed constitutively in all of these cell lines was unaffected by treatment with any factors examined. In contrast, beta-catenin protein levels were reduced markedly in NTera2-N cells by exposure to dbcAMP, EGF or bFGF, and in U-373MG cells by treatment with dbcAMP or PMA, but were unaffected in any cell lines by BDNF, TNF-alpha, IL-1beta, IL-6, IFN-gamma or TGF-beta1. These results indicate that beta-catenin is expressed constitutively in human neural cells and downregulated at a protein level by a set of growth factors in a cell type-specific manner.

Agrin binds to beta-amyloid (Abeta), accelerates abeta fibril formation, and is localized to Abeta deposits in Alzheimer's disease brain

Agrin is an extracellular matrix heparan sulfate proteoglycan (HSPG) well known for its role in modulation of the neuromuscular junction during development. Although agrin is one of the major HSPGs of the brain, its function there remains elusive. Here we provide evidence suggesting a possible function for agrin in Alzheimer's disease brain. Agrin protein binds the amyloidogenic peptide Abeta (1-40) in its fibrillar state via a mechanism that involves the heparan sulfate glycosaminoglycan chains of agrin. Furthermore, agrin is able to accelerate Abeta fibril formation and protect Abeta (1-40) from proteolysis, in vitro. Supporting a biological significance for these in vitro data, immunocytochemical studies demonstrate agrin's presence within senile plaques and cerebrovascular amyloid deposits, and agrin immunostained capillaries exhibit pathological alterations in AD brain. These data therefore suggest that agrin may be an important factor in the progression of Abeta peptide aggregation and/or its persistence in Alzheimer's disease brain.

Dynamic regulation of expression and phosphorylation of tau by fibroblast growth factor-2 in neural progenitor cells from adult rat hippocampus

The nature of the extracellular signals that regulate the expression and the phosphorylation of the microtubule-associated protein tau, which is aberrantly hyperphosphorylated in Alzheimer disease and other adult-onset neurodegenerative diseases, is not known. We have found that neural progenitor cells from adult rat hippocampus express adult isoforms of tau and that the expression and the phosphorylation of tau are regulated by fibroblast growth factor-2 (FGF-2). Astrocytes that are differentiated from these cells by stimulation with ciliary neurotrophic factor express phosphorylated tau similarly when cultured in the presence of FGF-2. In fetal progenitor cells that express only the fetal tau isoform, expression, but not the phosphorylation, of this protein is regulated by FGF-2 in cultures of higher passages. The FGF-2-mediated tau hyperphosphorylation is inhibited by lithium, an inhibitor of glycogen synthase kinase-3 (GSK-3), but not by inhibitors of mitogen-activated protein kinase or the cyclin-dependent kinases. Furthermore, both GSK-3 activity and the phosphorylation of tau increase when the concentration of FGF-2 is increased up to 40 ng/ml. These results demonstrate that proliferating adult rat hippocampal progenitor cells express adult isoforms of tau stably and that FGF-2 upregulates the expression and, by upregulating GSK-3 activity, the phosphorylation of tau.

Identification of beta-amyloid-responsive genes by RNA differential display: early induction of a DNA damage-inducible gene, gadd45

Alzheimer's disease is a neurodegenerative disorder characterized by the extracellular deposition in the brain of amyloid beta-peptide (A beta), presumed to play a pathogenic role. However, the precise molecular mechanisms of its neurotoxicity are not fully understood. Recent studies have suggested that it may exert its toxic effect via activation of transcription factors. We investigated A beta-responsive genes in human preneuron NT2 cells, at early stages of A beta (25-35) exposure, by RNA differential display. A beta induced the expression of (i) the growth arrest and DNA damage-inducible gene (gadd45) implicated in the DNA excision-repair process; (ii) a stress-signaling kinase gene encoding the mitogen-activated protein kinase/Erk kinase kinase-1 (MEKK1); (iii) a new growth factor-inducible immediate-early gene, CYR61, the product of which functions as an extracellular matrix signaling molecule; (iv) other immediate-early genes, such as c-jun and c-fos; (v) the gene encoding the basic fibroblast growth factor (bFGF); (vi) a gene encoding a constituent of the mitochondrial pyruvate dehydrogenase complex, the dihydrolipoamide dehydrogenase-binding protein (E3-BP); and (vii) an unidentified human gene (KIAA0099). A beta not only activates but also respresses genes: (i) the gene encoding "hinge" protein, a subunit of the mitochondrial cytochrome-c reductase and (ii) the SRp55 gene encoding a splicing factor involved in constitutive pre-mRNA splicing and alternative splice site selection. Our results underscored A beta-responsive genes that play key roles in the response (damage/recovery) of neuron cells to A beta exposure. In particular, the strong upregulation of gadd45, indicating DNA damage, was detected early in A beta cytotoxicity. This suggests that DNA strand breaks occurred rapidly in cells exposed to A beta, which may be a critical event in A beta neurotoxicity.

Fibroblast growth factor receptor-1 expression in the cortex and hippocampus in Alzheimer's disease

Localization of fibroblast growth receptor (FGFR)-1 immunoreactivity was investigated immunochemically in postmortem brain tissue of Alzheimer's disease (AD) and age-matched control cases using a rabbit polyclonal antibody and a mouse monoclonal antibody specific for FGFR-1. In control cases, FGFR-1 immunoreactivity was identified in astrocytes in white matter and in hippocampal pyramidal neurons. In AD cases, the immunoreactivity in reactive astrocytes surrounding senile plaques was increased. The pattern of FGFR-1 immunoreactivity was confirmed in selected cases by in situ hybridization for FGFR-1 mRNA. Immunoreactivity using a monoclonal antibody demonstrated a similar distribution pattern. The localization of FGFR-1 is consistent with previous reports on the involvement of FGF-1 and FGF-2 in AD.

Beta-amyloid plaques: stages in life history or independent origin?

Several types of discrete beta-amyloid (Abeta) deposit or senile plaque have been identified in the brains of individuals with Alzheimer's disease and Down's syndrome. The majority of these plaques can be classified into four morphological types: diffuse, primitive, classic and compact. Two hypotheses have been proposed to account for these plaques. Firstly, that the diffuse, primitive, classic and compact plaques develop in sequence and represent stages in the life history of a single plaque type. Secondly, that the different Abeta plaques develop independently and therefore, unique factors are involved in the formation of each type. To attempt to distinguish between these hypotheses, the morphology, ultrastructure, composition, and spatial distribution in the brain of the four types of plaque were compared. Although some primitive plaques may develop from diffuse plaques, the evidence suggests that a unique combination of factors is involved in the pathogenesis of each plaque type and, therefore, supports the hypothesis that the major types of Abeta plaque develop independently.

The progression of beta-amyloid deposition in the frontal cortex of the aged canine

Brains from 41 aged canines (> or = 10 years of age) were examined immunohistochemically to characterize the laminar distribution and age-related progression of beta-amyloid (A beta) in frontal cortex. We classified the A beta patterns into four distinct types. Type I was characterized by small, faint deposits of A beta in deep cortical layers. Type II consisted of diffuse deposits of A beta mainly in layers V and VI. Type III had both dense plaques in superficial layers, and diffuse deposits in deep layers. Finally, Type IV had solely dense plaques throughout all layers of cortex. We compared the A beta distribution pattern between the Old canines (10-15 years, n = 22) and the Very Old canines (> 15 years, n = 19). The Old group primarily had negative staining, or Type I and Type II patterns of amyloid deposition (73%). Conversely, the Very Old group had predominantly Types II, III and IV deposits (89.5%), a difference that was significant (P < 0.05). We suggest that A beta deposition in canine frontal cortex is a progressive age-related process beginning with diffuse deposits in the deep cortical layers followed by the development of deposits in outer layers. In support of this hypothesis, the deeper layer diffuse plaques in the Very Old group of dogs also contain the largest proportion of beta-amyloid with an isomerized aspartic acid residue at position 7, indicating that these deposits had been present for some time. We also observed fiber-like A beta immunoreactivity within regions of diffuse A beta deposits. These fibers appeared to be degenerating neurites, which were negative for hyperphosphorylated tau. Therefore, these fibers may represent a very early form of neuritic change that precede tau hyperphosphorylation or develop by an alternative pathway.

Basic FGF attenuates amyloid beta-peptide-induced oxidative stress, mitochondrial dysfunction, and impairment of Na+/K+-ATPase activity in hippocampal neurons

Basic fibroblast growth factor (bFGF) exhibits trophic activity for many populations of neurons in the brain, and can protect those neurons against excitotoxic, metabolic and oxidative insults. In Alzheimer's disease (AD), amyloid beta-peptide (A beta) fibrils accumulate in plaques which are associated with degenerating neurons. A beta can be neurotoxic by a mechanism that appears to involve induction of oxidative stress and disruption of calcium homeostasis. Plaques in AD brain contain high levels of bFGF suggesting a possible modulatory role for bFGF in the neurodegenerative process. We now report that bFGF can protect cultured hippocampal neurons against A beta25-35 toxicity by a mechanism that involves suppression of reactive oxygen species (ROS) accumulation and maintenance of Na+/K+-ATPase activity. A beta25-35 induced lipid peroxidation, accumulation of H2O2, mitochondrial ROS accumulation, and a decrease in mitochondrial transmembrane potential; each of these effects of A beta25-35 was abrogated in cultures pre-treated with bFGF. Na+/K+-ATPase activity was significantly reduced following exposure to A beta25-35 in control cultures, but not in cultures pre-treated with bFGF. bFGF did not protect neurons from death induced by ouabain (a specific inhibitor of the Na+/K+-ATPase) or 4-hydroxynonenal (an aldehydic product of lipid peroxidation) consistent with a site of action of bFGF prior to induction of oxidative stress and impairment of ion-motive ATPases. By suppressing accumulation of oxyradicals, bFGF may slow A beta-induced neurodegenerative cascades.

Constructional apraxia in Alzheimer's disease correlates with neuritic neuropathology in occipital cortex

A variety of measures of neuropathology in Alzheimer's disease (AD) correlate with dementia severity. However, the role of beta-amyloid protein and abnormally phosphorylated tau protein in the decline of specific cognitive abilities is unknown. "Constructional praxis' (e.g., copying, constructing) is believed to require integrity of the parietal-occipital lobes. Unlike most other cognitive tasks, some AD patients are able to perform some constructional tasks even late in the disease course. Thus, it may be an ideal task to evaluate the relationship between various measures of AD neuropathology and cognitive performance. Fixed brain tissue was obtained from 16 AD patients who were cognitively assessed shortly before death. Parietal, frontal, entorhinal, and occipital cortices were examined by immunocytochemistry for beta-amyloid protein and abnormally phosphorylated tau protein at both early and later stages of neuropil thread and tangle formation. Constructional praxis in AD was strongly related to early-stage tau hyperphosphorylation in occipital cortex. Praxis ability was specific in that it was not significantly related to pathology in other areas and non-constructive tasks were not associated with occipital cortex pathology. In contrast, global dementia severity was related to beta-amyloid deposition in entorhinal, parietal, and frontal regions. These findings suggest that occipital cortex is critical for some constructional praxis tasks and that some regionally localizable tasks may be good indices of underlying pathology in corresponding brain regions.