Increased apolipoprotein E expression correlates with the onset of neuronal degeneration in the spinal cord of G93A-SOD1 mice

Cross interactions between Apolipoprotein E and amyloid proteins in neurodegenerative diseases

Three common Apolipoprotein E isoforms, ApoE2, ApoE3, and ApoE4, are key regulators of lipid homeostasis, among other functions. Apolipoprotein E can interact with amyloid proteins. The isoforms differ by one or two residues at positions 112 and 158, and possess distinct structural conformations and functions, leading to isoform-specific roles in amyloid-based neurodegenerative diseases. Over 30 different amyloid proteins have been found to share similar characteristics of structure and toxicity, suggesting a common interactome. The molecular and genetic interactions of ApoE with amyloid proteins have been extensively studied in neurodegenerative diseases, but have not yet been well connected and clarified. Here we summarize essential features of the interactions between ApoE and different amyloid proteins, identify gaps in the understanding of the interactome and propose the general interaction mechanism between ApoE isoforms and amyloid proteins. Perhaps more importantly, this review outlines what we can learn from the interactome of ApoE and amyloid proteins; that is the need to see both ApoE and amyloid proteins as a basis to understand neurodegenerative diseases.

Blood Transcriptome Response to Environmental Metal Exposure Reveals Potential Biological Processes Related to Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disease which is manifested by a progressive and irreversible decline of cognition, memory loss, a shortened attention span, and changes in personality. Aging and genetic pre-dispositions, particularly the presence of a specific form of apolipoprotein E (APOE), are main risk factors of sporadic AD; however, a large body of evidence has shown that multiple environmental factors, including exposure to toxic metals, increase the risk for late onset AD. Lead (Pb) and cadmium (Cd) are ubiquitous toxic metals with a wide range of applications resulting in global distribution in the environment and exposure of all living organisms on earth. In addition to being classified as carcinogenic (Cd) and possibly carcinogenic (Pb) to humans by the International Agency for Research on Cancer, both compounds disrupt metal homeostasis and can cause toxic responses at the cellular and organismal levels. Pb toxicity targets the central nervous system and evidence for that has emerged also for Cd. Recent epidemiological studies show that both metals possibly are etiological factors of multiple neurodegenerative diseases, including Alzheimer's disease (AD). To further explore the association between metal exposure and AD risk we applied whole transcriptome gene expression analysis in peripheral blood leukocytes (PBLs) from 632 subjects of the general population, taken from the EnviroGenomarkers project. We used linear mixed effect models to associate metal exposure to gene expression after adjustment for gender, age, BMI, smoking, and alcohol consumption. For Pb exposure only few associations were identified, including a downregulation of the human eukaryotic translation initiation factor 5 (eIF5). In contrast, Cd exposure, particularly in males, revealed a much stronger transcriptomic response, featuring multiple pathways related to pathomolecular mechanisms of AD, such as endocytosis, neutrophil degranulation, and Interleukin−7 signaling. A gender stratified analysis revealed that the Cd responses were male-specific and included a downregulation of the APOE gene in men. This exploratory study revealed novel hypothetical findings which might contribute to the understanding of the neurotoxic effects of chronic Pb and Cd exposure and possibly improve our knowledge on the molecular mechanisms linking metal exposure to AD risk.

Elucidating the Role of Apolipoprotein E Isoforms in Spinal Cord Injury-Associated Neuropathology

Spinal cord injury (SCI) is a devastating, life-altering, neurological event that affects ∼300,000 individuals in the United States. Currently, there are no effective treatments to reverse the neurological impairments caused by the lesion. Until a cure is available, there is an urgent need for strategies that can either spare injured neurons or promote neuroplasticity and functional recovery. Genetic links to outcomes after SCI may provide insights into the pathological mechanisms, and possible new avenues for drug development. In the present review, we discuss the current knowledge linking apolipoprotein E genotypes with better or worse functional outcomes after an SCI, and the possible molecular mechanisms that may contribute to this association.

hnRNP R and its main interactor, the noncoding RNA 7SK, coregulate the axonal transcriptome of motoneurons

Neurons are highly polarized cells. RNA-binding proteins contribute to this polarization by generating diverse subcellular transcriptomes. The RNA-binding protein hnRNP R is essential for axon growth in motoneurons. This study reports the RNA interactome for hnRNP R. The main interacting RNA of hnRNP R was the noncoding RNA 7SK. Depletion of 7SK from primary motoneurons disturbed axon growth. This effect was dependent on the interaction of 7SK with hnRNP R. Both hnRNP R and 7SK localize to axons. Loss of 7SK led to a similar depletion of axonal transcripts as loss of hnRNP R. Our data suggest that 7SK, in addition to its role in transcriptional regulation, acts in concert with hnRNP R to sort specific transcripts into axons.

Disturbed RNA processing and subcellular transport contribute to the pathomechanisms of motoneuron diseases such as amyotrophic lateral sclerosis and spinal muscular atrophy. RNA-binding proteins are involved in these processes, but the mechanisms by which they regulate the subcellular diversity of transcriptomes, particularly in axons, are not understood. Heterogeneous nuclear ribonucleoprotein R (hnRNP R) interacts with several proteins involved in motoneuron diseases. It is located in axons of developing motoneurons, and its depletion causes defects in axon growth. Here, we used individual nucleotide-resolution cross-linking and immunoprecipitation (iCLIP) to determine the RNA interactome of hnRNP R in motoneurons. We identified ∼3,500 RNA targets, predominantly with functions in synaptic transmission and axon guidance. Among the RNA targets identified by iCLIP, the noncoding RNA 7SK was the top interactor of hnRNP R. We detected 7SK in the nucleus and also in the cytosol of motoneurons. In axons, 7SK localized in close proximity to hnRNP R, and depletion of hnRNP R reduced axonal 7SK. Furthermore, suppression of 7SK led to defective axon growth that was accompanied by axonal transcriptome alterations similar to those caused by hnRNP R depletion. Using a series of 7SK-deletion mutants, we show that the function of 7SK in axon elongation depends on its interaction with hnRNP R but not with the PTEF-B complex involved in transcriptional regulation. These results propose a role for 7SK as an essential interactor of hnRNP R to regulate its function in axon maintenance.

Caveats in Transneuronal Tracing with Unmodified Rabies Virus: An Evaluation of Aberrant Results Using a Nearly Perfect Tracing Technique

Apart from the genetically engineered, modified, strains of rabies virus (RABV), unmodified ‘fixed’ virus strains of RABV, such as the ‘French’ subtype of CVS11, are used to examine synaptically connected networks in the brain. This technique has been shown to have all the prerequisite characteristics for ideal tracing as it does not metabolically affect infected neurons within the time span of the experiment, it is transferred transneuronally in one direction only and to all types of neurons presynaptic to the infected neuron, number of transneuronal steps can be precisely controlled by survival time and it is easily detectable with a sensitive technique. Here, using the ‘French’ CVS 11 subtype of RABV in Wistar rats, we show that some of these characteristics may not be as perfect as previously indicated. Using injection of RABV in hind limb muscles, we show that RABV-infected spinal motoneurons may already show lysis 1 or 2 days after infection. Using longer survival times we were able to establish that Purkinje cells may succumb approximately 3 days after infection. In addition, some neurons seem to resist infection, as we noted that the number of RABV-infected inferior olivary neurons did not progress in the same rate as other infected neurons. Furthermore, in our hands, we noted that infection of Purkinje cells did not result in expected transneuronal labeling of cell types that are presynaptic to Purkinje cells such as molecular layer interneurons and granule cells. However, these cell types were readily infected when RABV was injected directly in the cerebellar cortex. Conversely, neurons in the cerebellar nuclei that project to the inferior olive did not take up RABV when this was injected in the inferior olive, whereas these cells could be infected with RABV via a transneuronal route. These results suggest that viral entry from the extracellular space depends on other factors or mechanisms than those used for retrograde transneuronal transfer. We conclude that transneuronal tracing with RABV may result in unexpected results, as not all properties of RABV seem to be ubiquitously valid.

Dysregulated expression of death, stress and mitochondrion related genes in the sciatic nerve of presymptomatic SOD1(G93A) mouse model of Amyotrophic Lateral Sclerosis

Schwann cells are the main source of paracrine support to motor neurons. Oxidative stress and mitochondrial dysfunction have been correlated to motor neuron death in Amyotrophic Lateral Sclerosis (ALS). Despite the involvement of Schwann cells in early neuromuscular disruption in ALS, detailed molecular events of a dying-back triggering are unknown. Sciatic nerves of presymptomatic (60-day-old) SOD1(G93A) mice were submitted to a high-density oligonucleotide microarray analysis. DAVID demonstrated the deregulated genes related to death, stress and mitochondrion, which allowed the identification of Cell cycle, ErbB signaling, Tryptophan metabolism and Rig-I-like receptor signaling as the most representative KEGG pathways. The protein-protein interaction networks based upon deregulated genes have identified the top hubs (TRAF2, H2AFX, E2F1, FOXO3, MSH2, NGFR, TGFBR1) and bottlenecks (TRAF2, E2F1, CDKN1B, TWIST1, FOXO3). Schwann cells were enriched from the sciatic nerve of presymptomatic mice using flow cytometry cell sorting. qPCR showed the up regulated (Ngfr, Cdnkn1b, E2f1, Traf2 and Erbb3, H2afx, Cdkn1a, Hspa1, Prdx, Mapk10) and down-regulated (Foxo3, Mtor) genes in the enriched Schwann cells. In conclusion, molecular analyses in the presymptomatic sciatic nerve demonstrated the involvement of death, oxidative stress, and mitochondrial pathways in the Schwann cell non-autonomous mechanisms in the early stages of ALS.

Lack of association between APOE gene polymorphisms and amyotrophic lateral sclerosis: a comprehensive meta-analysis

Several studies have evaluated the association between APOE gene polymorphisms and the risk for amyotrophic lateral sclerosis (ALS), with inconclusive results. The aim of our study was to further define the risk associated with carriage of the APOE alleles and development and clinical characteristics of ALS. We performed a comprehensive meta-analysis of all existing studies investigating the association between the APOE gene and ALS published up to September 2013, comprising a total of 4249 ALS patients and 10,397 controls. Pooled odds ratios (OR) were estimated using the random effect (RE) model. Results showed that the carriage of different APOE alleles had no effect on disease risk. In particular, the ϵ4 allele was not associated with a significantly increased disease risk (ϵ4 carriers vs. non-ϵ4 carriers: RE OR 1.18; 95% CI 0.91-1.53). In conclusion, our study suggests that the APOE gene does not have a significant effect in ALS aetiopathogenesis.

Proteome analysis of post-transplantation recovery mechanisms of an EAE model of multiple sclerosis treated with embryonic stem cell-derived neural precursors

Multiple sclerosis (MS) is a chronic inflammatory and progressive disorder of the central nervous system (CNS), which ultimately causes demyelination and subsequent axonal injury. Experimental autoimmune encephalomyelitis (EAE) is a well-characterized animal model to study the etiology and pathogenesis of MS. This model can also be used to investigate various therapeutic approaches for MS. Herein; we have treated a score 3 EAE mouse model with an embryonic stem cell-derived neural precursor. Clinical analysis showed recovery of the EAE model of MS following transplantation. We analyzed the proteome of spinal cords of healthy and EAE samples before and after transplantation. Proteome analysis revealed that expressions of 86 spinal cord protein spots changed in the EAE or transplanted mouse compared to controls. Mass spectrometry resulted in identification of 72 proteins. Of these, the amounts of 27 differentially expressed proteins in EAE samples returned to sham levels after transplantation, suggesting a possible correlation between changes at the proteome level and clinical signs of EAE in transplanted mice. The recovered proteins belonged to various functional groups that included disturbances in ionic and neurotransmitter release, apoptosis, iron hemostasis, and signal transduction. Our results provided a proteomic view of the molecular mechanisms of EAE recovery after stem cell transplantation.

BIOLOGICAL SIGNIFICANCE

In this study, we applied proteomics to analyze the changes in proteome pattern of EAE mouse model after embryonic stem cell-derived neural precursor transplantation. Our proteome results clearly showed that the expression levels of several differentially expressed proteins in EAE samples returned to sham levels after transplantation, which suggested a possible correlation between changes at the proteome level and decreased clinical signs of EAE in transplanted mice. These results will serve as a basis to address new questions and design new experiments to elucidate the biology of EAE and recovery after transplantation. A thorough understanding of stem cell-mediated therapeutic mechanisms might result in the development of more efficacious therapies for MS than are currently available.

Low frequency stimulation of the perforant pathway generates anesthesia-specific variations in neural activity and BOLD responses in the rat dentate gyrus

To study how various anesthetics affect the relationship between stimulus frequency and generated functional magnetic resonance imaging (fMRI) signals in the rat dentate gyrus, the perforant pathway was electrically stimulated with repetitive low frequency (i.e., 0.625, 1.25, 2.5, 5, and 10 Hz) stimulation trains under isoflurane/N(2)O, isoflurane, medetomidine, and α-chloralose. During stimulation, the blood oxygen level-dependent signal intensity (BOLD response) and local field potentials in the dentate gyrus were simultaneously recorded to prove whether the present anesthetic controls the generation of a BOLD response via targeting general hemodynamic parameters, by affecting mechanisms of neurovascular coupling, or by disrupting local signal processing. Using this combined electrophysiological/fMRI approach, we found that the threshold frequency (i.e., the minimal frequency required to trigger significant BOLD responses), the optimal frequency (i.e., the frequency that elicit the strongest BOLD response), and the spatial distribution of generated BOLD responses are specific for each anesthetic used. Concurrent with anesthetic-dependent characteristics of the BOLD response, we found the pattern of stimulus-induced neuronal activity in the dentate gyrus is also specific for each anesthetic. Consequently, the anesthetic-specific influence on local signaling processes is the underlying cause for the observation that an identical stimulus elicits different BOLD responses under various anesthetics.

AP-2β regulates amyloid beta-protein stimulation of apolipoprotein E transcription in astrocytes

Two key players involved in Alzheimer's disease (AD) are amyloid beta protein (Aβ) and apolipoprotein E (apoE). Aβ increases apoE protein levels in astrocytes which is associated with cholesterol trafficking, neuroinflammatory responses and Aβ clearance. The mechanism for the increase in apoE protein abundance is not understood. Based on different lines of evidence, we propose that the beta-adrenergic receptor (βAR), cAMP and the transcription factor activator protein-2 (AP-2) are contributors to the Aβ-induced increase in apoE abundance. This hypothesis was tested in mouse primary astrocytes and in cells transfected with an apoE promoter fragment with binding sites for AP-2. Aβ(42) induced a time-dependent increase in apoE mRNA and protein levels which were significantly inhibited by βAR antagonists. A novel finding was that Aβ incubation significantly reduced AP-2α levels and significantly increased AP-2β levels in the nuclear fraction. The impact of Aβ-induced translocation of AP-2 into the nucleus was demonstrated in cells expressing AP-2 and incubated with Aβ(42). AP-2 expressing cells had enhanced activation of the apoE promoter region containing AP-2 binding sites in contrast to AP-2 deficient cells. The transcriptional upregulation of apoE expression by Aβ(42) may be a neuroprotective response to Aβ-induced cytotoxicity, consistent with apoE's role in cytoprotection.

Cholesterol metabolism in neurons and astrocytes

Cells in the mammalian body must accurately maintain their content of cholesterol, which is an essential membrane component and precursor for vital signalling molecules. Outside the brain, cholesterol homeostasis is guaranteed by a lipoprotein shuttle between the liver, intestine and other organs via the blood circulation. Cells inside the brain are cut off from this circuit by the blood-brain barrier and must regulate their cholesterol content in a different manner. Here, we review how this is accomplished by neurons and astrocytes, two cell types of the central nervous system, whose cooperation is essential for normal brain development and function. The key observation is a remarkable cell-specific distribution of proteins that mediate different steps of cholesterol metabolism. This form of metabolic compartmentalization identifies astrocytes as net producers of cholesterol and neurons as consumers with unique means to prevent cholesterol overload. The idea that cholesterol turnover in neurons depends on close cooperation with astrocytes raises new questions that need to be addressed by new experimental approaches to monitor and manipulate cholesterol homeostasis in a cell-specific manner. We conclude that an understanding of cholesterol metabolism in the brain and its role in disease requires a close look at individual cell types.

Association of ALS with head injury, cigarette smoking and APOE genotypes

OBJECTIVE

An increased risk of ALS has been reported for US veterans, but the cause is unknown. Since head injury and cigarette smoking are two previously implicated environmental risk factors that are more common in military than civilian study populations, we tested their association with ALS in a US veteran study population.

METHODS

We used logistic regression to examine the association of ALS with head injury and cigarette smoking in 241 incident cases and 597 controls. Since APOE is a plausible ALS candidate gene, we also tested its main effect and its statistical interaction with these environmental exposures.

RESULTS

Cigarette smoking was not associated with ALS in this predominantly male and Caucasian population. Veterans who had experienced head injuries during the last 15years before the reference date had an adjusted odds ratio of 2.33 (95% confidence interval 1.18-4.61), relative to veterans without any head injuries. This association was strongest in APOE-4 carriers.

CONCLUSIONS

Our results add to the body of evidence suggesting that head injuries may be a risk factor for multiple neurodegenerative diseases, including ALS. We hypothesize that the strength of association between head injuries and ALS may depend upon APOE genotype.

Full-length apolipoprotein E protects against the neurotoxicity of an apoE-related peptide

Apolipoprotein E was found to protect against the neurotoxic effects of a dimeric peptide derived from the receptor-binding region of this protein (residues 141-149). Both apoE3 and apoE4 conferred protection but the major N-terminal fragment of each isoform did not. Nor was significant protection provided by bovine serum albumin or apoA-I. Full-length apoE3 and apoE4 also inhibited the uptake of a fluorescent-labeled derivative of the peptide, suggesting that the mechanism of inhibition might involve competition for cell surface receptors/proteoglycans that mediate endocytosis and/or signaling pathways. These results might bear on the question of the role of apoE in neuronal degeneration, such as occurs in Alzheimer's disease where apoE4 confers a significantly greater risk of pathology.

Genetic studies of amyotrophic lateral sclerosis: controversies and perspectives

The genetic causes of amyotrophic lateral sclerosis (ALS) are slowly being dissected out with the help of recent advances in genetic technology. Linkage studies and association studies examining candidate genes, candidate pathways, and genome-wide association have been used, based on direct sequencing and correlations between genetic variations. Copy number and microsatellite variants have also been examined, although the ideal methods for analysis are still being developed. In this review we examine the evidence for a genetic basis to ALS, discuss the challenges and difficulties faced and summarize the support for the reported genetic causes of ALS.

Spinal cord mRNA profile in patients with ALS: comparison with transgenic mice expressing the human SOD-1 mutant

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease characterized by loss of motor neurons in the cerebral cortex, brain stem, and spinal cord. Most cases (90%) are classified as sporadic ALS (sALS). The remainder 10% are inherited and referred to as familial ALS, and 2% of instances are due to mutations in Cu/Zn superoxide dismutase (SOD1). Using cDNA microarray on postmortem spinal cord specimens of four sALS patients compared to four age-matched nonneurological controls, we found major changes in the expression of mRNA in 60 genes including increase of cathepsin B and cathepsin D (by the factors 2 and 2.3, respectively), apolipoprotein E (Apo E; factor 4.2), epidermal growth factor receptor (factor 10), ferritin (factor 2), and lysosomal trafficking regulator (factor 10). The increase in the expression of these genes was verified by quantitative reverse transcriptase polymerase chain reaction. Further analysis of these genes in hSOD1-G93A transgenic mice revealed increase in the expression in parallel with the deterioration of motor functions quantified by means of rotorod performance. The comparability of the findings in sALS patients and in the hSOD1-G93A transgenic mouse model suggests that the examined genes may play a specific role in the pathogenesis of ALS.

Selective impairment of the cerebellar C1 module involved in rat hind limb control reduces step-dependent modulation of cutaneous reflexes

The cerebellum is divided into multiple parasagittally organized modules, which are thought to represent functional entities. How individual modules participate in cerebellar control of complex movements such as locomotion remains largely unknown. To a large extent, this is caused by the inability to study the contribution of individual modules during locomotion. Because of the architecture of modules, based on narrow, elongated cortical strips that may be discontinuous in the rostrocaudal direction, lesion of a complete module, without affecting neighboring modules, has not been possible. Here, we report on a new method for inducing a selective dysfunction of spatially separated parts of a single module using a small cortical injection of a retrogradely transported neurotoxin, cholera toxin b-subunit-saporin. We show that such a local injection into the C1 module results in climbing fiber and partial mossy fiber deafferentation of functionally related areas of this module, thereby resulting in a severe impairment of the whole module without affecting neighboring modules. A subsequent functional analysis indicates that such an impairment of the hindlimb part of the C1 module did not have a significant impact on skilled walking or overall stepping pattern. However, the modulation of cutaneously induced reflexes during stepping was severely diminished. We propose that the C1 module is specifically involved in the adaptive control of reflexes.

Apolipoprotein E gene polymorphism and the risk of cervical myelopathy in patients with chronic spinal cord compression

STUDY DESIGN

Prospective evaluation of apolipoprotein E (APOE) genotypes in 106 consecutive patients with stenosis of the cervical spinal canal.

OBJECTIVE

To determine the association between cervical spondylotic myelopathy (CSM) in patients with chronic spinal cord compression and the APOE genotype.

SUMMARY OF BACKGROUND DATA

The APOE allele epsilon 4 is a risk factor for the occurrence, progression, and poor outcome in several neurologic diseases. Information of the association between APOE genotype and CSM in the literature are lacking so far.

METHODS

One hundred six consecutive patients with chronic cervical spinal cord compression due to stenosis of the spinal canal were evaluated prospectively. APOE genotypes were determined by polymerase chain reaction followed by restriction enzyme digestion and sodiumdodecylsulfate poyacrylamide gel electrophoresis (SDS PAGE) of digested fragments. Clinical and radiologic variables evaluated were age, occurrence of CSM, duration of symptoms, number of affected segments, and diameter of spinal canal of most affected segment. Univariate association between variables was tested. A backward stepwise method was used to construct multivariate logistic regression models in relation to the occurrence of CSM as dependent variable.

RESULTS

The following distribution of APOE genotypes was found: epsilon 2 epsilon 2 3 patients (2.8%), epsilon 2 epsilon 3 9 patients (8.5%), epsilon 2 epsilon 4 1 patient (0.9), epsilon 3 epsilon 3 67 patients (63.2%), epsilon 3 epsilon 4 24 patients (22.6%), epsilon 4 epsilon 4 2 patients (1.9%). Univariate analysis showed that patients with chronic spinal cord compression and homo- or heterozygous allele epsilon 4 are more likely to develop CSM than patients without allele epsilon 4 (65.0% vs. 35.0%, P < 0008; OR 3.5; 95% CI 1.3-9.8). This effect remained significant in a binary logistic regression model adjusted to other known risk factors for CSM. Inclusion of the variable homo- or heterozygous epsilon 4 allele led to an increased goodness of fit of the model compared with the model without epsilon 4. CONCLUSION.: This study supports the hypothesis that the APOE epsilon 4 allele increases the risk of CSM in patients with chronic cervical spinal cord compression; however, a larger prospective population-based study is needed to answer this question definitively.

WITHDRAWN: Association between polymorphisms in genes of inflammatory response and axonal repair with spinal cord injury

Ahead of Print article withdrawn by publisher. Please see re-submitted article 'DNA polymorphisms as tools for spinal cord injury research' Spinal Cord advance online publication, 20 May 2008; doi:10.1038/sc.2008.67.

Mechanism for FGF-1 to regulate biogenesis of apoE-HDL in astrocytes

Fibroblast growth factor-1 (FGF-1) is secreted by astrocytes and stimulates apolipoprotein E (apoE)-HDL biogenesis by an autocrine mechanism to help in recovery from brain injury. In apoE-deficient mouse astrocytes, FGF-1 stimulated cholesterol biosynthesis without enhancing its release, indicating a signaling pathway independent of apoE biosynthesis upregulation. SU5402, an inhibitor of FGF receptor, inhibited FGF-1-induced phosphorylation of MEK, ERK, and Akt, as well as all the apoE-HDL biogenesis-related events in rat astrocytes. LY294002, an inhibitor of phosphatidylinositide 3-OH kinase (PI3K) and of Akt phosphorylation, inhibited apoE-HDL secretion but not cholesterol biosynthesis, whereas U0126, an inhibitor of MEK and of ERK phosphorylation, inhibited cholesterol biosynthesis but not apoE-HDL secretion. Increase of apoE-mRNA by FGF-1 was not influenced by either inhibitor. When rat apoE/pcDNA3.his was transfected to transformed rat astrocyte GA-1 cells that otherwise do not synthesize apoE (GA-1/25), FGF-1 did not influence apoE-mRNA, but did increase the apoE secretion and Akt phosphorylation that were suppressed by LY294002. Lipid biosynthesis was increased by FGF-1 in GA-1/25 cells and suppressed by U0126. FGF-1 upregulates apoE-HDL biogenesis by three independent signaling pathways. The PI3K/Akt pathway upregulates secretion of apoE/apoE-HDL, the MEK/ERK pathway stimulates cholesterol biosynthesis, and an unknown pathway enhances apoE transcription.

Deletion of FMR1 in Purkinje Cells Enhances Parallel Fiber LTD, Enlarges Spines, and Attenuates Cerebellar Eyelid Conditioning in Fragile X Syndrome

Absence of functional FMRP causes Fragile X syndrome. Abnormalities in synaptic processes in the cerebral cortex and hippocampus contribute to cognitive deficits in Fragile X patients. So far, the potential roles of cerebellar deficits have not been investigated. Here, we demonstrate that both global and Purkinje cell-specific knockouts of Fmr1 show deficits in classical delay eye-blink conditioning in that the percentage of conditioned responses as well as their peak amplitude and peak velocity are reduced. Purkinje cells of these mice show elongated spines and enhanced LTD induction at the parallel fiber synapses that innervate these spines. Moreover, Fragile X patients display the same cerebellar deficits in eye-blink conditioning as the mutant mice. These data indicate that a lack of FMRP leads to cerebellar deficits at both the cellular and behavioral levels and raise the possibility that cerebellar dysfunctions can contribute to motor learning deficits in Fragile X patients.

Astrocytes produce and secrete FGF-1, which promotes the production of apoE-HDL in a manner of autocrine action

The astrocytes prepared by 1 week secondary culture after 1 month primary culture of rat brain cells (M/W cells) synthesized and secreted apolipoprotein E (apoE) and cholesterol more than the astrocytes prepared by conventional 1 week primary and 1 week secondary culture (W/W cells) (Ueno, S., J. Ito, Y. Nagayasu, T. Furukawa, and S. Yokoyama. 2002. An acidic fibroblast growth factor-like factor secreted into the brain cell culture medium upregulates apoE synthesis, HDL secretion and cholesterol metabolism in rat astrocytes. Biochim. Biophys. Acta. 1589: 261-272). M/W cells also highly expressed fibroblast growth factor-1 (FGF-1) mRNA. FGF-1 was identified in the cell lysate of both cell types, but M/W cells released more of it into the medium. Immunostaining of FGF-1 and apoE revealed that both localized in the cells that produce glial fibrillary acidic protein. The conditioned media of M/W cells and FGF-1 stimulated W/W cells to release apoE and cholesterol to generate more HDL. Pretreatment with a goat anti-FGF-1 antibody or heparin depleted the stimulatory activity of M/W cell-conditioned medium. The presence of the anti-FGF-1 antibody in the medium suppressed apoE secretion by M/W cells. Differential inhibition of signaling pathways suggested that FGF-1 stimulates apoE synthesis via the phosphoinositide 3-OH kinase for PI3K/Akt pathway. Thus, astrocytes release FGF-1, which promotes apoE-HDL production by an autocrine mechanism. These results are consistent with our in vivo observation that astrocytes produce FGF-1 before the increase of apoE in the postinjury lesion of the mouse brain (Tada, T., J. Ito, M. Asai, and S. Yokoyama. 2004. Fibroblast growth factor 1 is produced prior to apolipoprotein E in the astrocytes after cryo-injury of mouse brain. Neurochem. Int. 45: 23-30).

Dysregulation of stathmin, a microtubule-destabilizing protein, and up-regulation of Hsp25, Hsp27, and the antioxidant peroxiredoxin 6 in a mouse model of familial amyotrophic lateral sclerosis

Gain-of-function mutations of the Cu/Zn superoxide dismutase (SOD1) gene cause dominantly inherited familial amyotrophic lateral sclerosis. The identification of differentially regulated proteins in spinal cords of paralyzed mice expressing SOD1(G93A) may contribute to understanding mechanisms of toxicity by mutant SOD1. Protein profiling showed dysregulation of Stathmin with a marked decrease of its most acidic and phosphorylated isoform, and up-regulation of heat shock proteins 25 and 27, peroxiredoxin 6, phosphatidylinositol transfer protein-alpha, apolipoprotein E, and ferritin heavy chain. Stathmin accumulated in the cytoplasm of 30% of spinal cord motor neurons with fragmented Golgi apparatus. Overexpression of Stathmin in HeLa cells was associated with collapse of microtubule networks and Golgi fragmentation. These results, together with the decrease of one Stathmin isoform, suggest a role of the protein in Golgi fragmentation. Mutant SOD1 co-precipitated and co-localized with Hsp25 in neurons and astrocytes. Mutant SOD1 may thus deprive cells of the anti-apoptotic and other protective activities of Hsp25. Astrocytes contained peroxiredoxin 6, a unique nonredundant antioxidant. The up-regulation of peroxiredoxin 6 probably constitutes a defense to oxidative stress induced by SOD1(G93A). Direct effects of SOD1(G93A) or sequential reactions triggered by the mutant may cause the protein changes.

Amyloidogenesis: historical and modern observations point to heparan sulfate proteoglycans as a major culprit

Amyloids are complex tissue deposits and each type is identified by one of 22 different proteins or peptides which become re-folded into non-native conformational intermediates and then assemble into fibrils of a highly regular structure. All amyloid deposits also contain apolipoprotein E (apoE) as well as the basement membrane (BM) components, serum amyloid P and heparan sulfate proteoglycans (HSPG), perlecan or agrin. These BM components likely contribute to the overall organization of amyloid fibrils and HSPG has been further implicated in the genesis of amyloid. A growing body of evidence, summarized in this review, suggests that heparan sulfate (HS) promotes fibrillogenesis by associating with the amyloid precursors and inducing the conformational change required for their assembly into fibrils. HS also remains associated with the nascent fibrils contributing to its stability. These activities of HS are likely mediated through specific binding sites on the precursor proteins which appear to have sequence characteristics that are unique to amyloid.