Alterations in neurofilament protein immunoreactivity in human hippocampal neurons related to normal aging and Alzheimer's disease

Molecular and functional alterations in the cerebral microvasculature in an optimized mouse model of sepsis-associated cognitive dysfunction

Systemic inflammation has been implicated in the development and progression of neurodegenerative conditions such as cognitive impairment and dementia. Recent clinical studies indicate an association between sepsis, endothelial dysfunction, and cognitive decline. However, the investigations of the role and therapeutic potential of the cerebral microvasculature in systemic inflammation-induced cognitive dysfunction have been limited by the lack of standardized experimental models for evaluating the alterations in the cerebral microvasculature and cognition induced by the systemic inflammatory response. Herein, we validated a mouse model of endotoxemia that recapitulates key pathophysiology related to sepsis-induced cognitive dysfunction, including the induction of an acute systemic hyperinflammatory response, blood-brain barrier (BBB) leakage, neurovascular inflammation, and memory impairment after recovery from the systemic inflammatory response. In the acute phase, we identified novel molecular (e.g. upregulation of plasmalemma vesicle associated protein, a driver of endothelial permeability, and the pro-coagulant plasminogen activator inhibitor-1, PAI-1) and functional perturbations (i.e., albumin and small molecule BBB leakage) in the cerebral microvasculature along with neuroinflammation. Remarkably, small molecule BBB permeability, elevated levels of PAI-1, intra/perivascular fibrin/fibrinogen deposition and microglial activation persisted 1 month after recovery from sepsis. We also highlight molecular neuronal alterations of potential clinical relevance following systemic inflammation including changes in neurofilament phosphorylation and decreases in postsynaptic density protein 95 and brain-derived neurotrophic factor suggesting diffuse axonal injury, synapse degeneration and impaired neurotrophism. Our study serves as a standardized model to support future mechanistic studies of sepsis-associated cognitive dysfunction and to identify novel endothelial therapeutic targets for this devastating condition.

SIGNIFICANCE

The limited knowledge of how systemic inflammation contributes to cognitive decline is a major obstacle to the development of novel therapies for dementia and other neurodegenerative diseases. Clinical evidence supports a role for the cerebral microvasculature in sepsis-induced neurocognitive dysfunction, but the investigation of the underlying mechanisms has been limited by the lack of standardized experimental models. Herein, we optimized a mouse model that recapitulates important pathophysiological aspects of systemic inflammation-induced cognitive decline and identified key alterations in the cerebral microvasculature associated with cognitive dysfunction. Our study provides a reliable experimental model for mechanistic studies and therapeutic discovery of the impact of systemic inflammation on cerebral microvascular function and the development and progression of cognitive impairment.

Phytochemical Extract from Carica papaya Leaves and Punica granatum Seeds as Therapy Against Cognitive Impairment in a Murine Model

Mild cognitive impairment (MCI) is defined as inter-stage between normal cognitive aging and major neurocognitive disorder (MND). This state of decay is a crucial factor in treatment to prevent the progression to MND. In this study, our group developed a virtual screening process to evaluate 2568 phytochemical compounds against 5 key proteins associated with MCI and MND. As a result, two potential candidates were identified: carpaine, found in Carica papaya leaves, and punicalagin, present in Punica granatum. A model of cognitive impairment (CI) was developed in 10-month-old male Sprague Dawley rats by administering aluminum chloride (AlCl3) at a dose of 100 mg/kg/day for 30 days. After AlCl3 administration period, one of the groups received carpaine and punicalagin in a phytochemical extract (PE) by oral gavage for 30 days. Novel object recognition test (NOR) was assessed at three different time points (T1 - before CI, T2 - after CI, and T3 - after PE treatment). Glial fibrillary acidic protein (GFAP) and neurofilament light chain (NfL) were identified in the hippocampus of rats at the end of the study period. After administration of AlCl3, a reduction in discrimination index vs control rats (CI = 0.012 ± 0.08 vs Control = 0.076 ± 0.03), was observed. After phytochemical extract treatment, a significant increase in discrimination index values was observed in the PE group 0.4643 ± 0.13 vs CI group 0.012 ± 0.08. Additionally, the evaluation of immunohistochemistry showed an increase in GFAP positivity in the hippocampus of the CI groups, while a slight decrease was observed in the PE group. This work addressed a comprehensive methodology that utilized in silico tools to identify phytochemical compounds (carpaine and punicalagin) as potential candidates for affecting key proteins in CI. The phytochemical extract containing carpaine and punicalagin resulted in a trend in the decrease of GFAP expression in the hippocampus and improved recognition memory in rats with CI induced by age and AlCl3 administration.

Cerebral organoids derived from patients with Alzheimer's disease with PSEN1/2 mutations have defective tissue patterning and altered development

During the past two decades, induced pluripotent stem cells (iPSCs) have been widely used to study human neural development and disease. Especially in the field of Alzheimer's disease (AD), remarkable effort has been put into investigating molecular mechanisms behind this disease. Then, with the advent of 3D neuronal cultures and cerebral organoids (COs), several studies have demonstrated that this model can adequately mimic familial and sporadic AD. Therefore, we created an AD-CO model using iPSCs derived from patients with familial AD forms and explored early events and the progression of AD pathogenesis. Our study demonstrated that COs derived from three AD-iPSC lines with PSEN1(A246E) or PSEN2(N141I) mutations developed the AD-specific markers in vitro, yet they also uncover tissue patterning defects and altered development. These findings are complemented by single-cell sequencing data confirming this observation and uncovering that neurons in AD-COs likely differentiate prematurely.

Pan-retinal ganglion cell markers in mice, rats, and rhesus macaques

Univocal identification of retinal ganglion cells (RGCs) is an essential prerequisite for studying their degeneration and neuroprotection. Before the advent of phenotypic markers, RGCs were normally identified using retrograde tracing of retinorecipient areas. This is an invasive technique, and its use is precluded in higher mammals such as monkeys. In the past decade, several RGC markers have been described. Here, we reviewed and analyzed the specificity of nine markers used to identify all or most RGCs, i.e., pan-RGC markers, in rats, mice, and macaques. The best markers in the three species in terms of specificity, proportion of RGCs labeled, and indicators of viability were BRN3A, expressed by vision-forming RGCs, and RBPMS, expressed by vision- and non-vision-forming RGCs. NEUN, often used to identify RGCs, was expressed by non-RGCs in the ganglion cell layer, and therefore was not RGC-specific. γ-SYN, TUJ1, and NF-L labeled the RGC axons, which impaired the detection of their somas in the central retina but would be good for studying RGC morphology. In rats, TUJ1 and NF-L were also expressed by non-RGCs. BM88, ERRβ, and PGP9.5 are rarely used as markers, but they identified most RGCs in the rats and macaques and ERRβ in mice. However, PGP9.5 was also expressed by non-RGCs in rats and macaques and BM88 and ERRβ were not suitable markers of viability.

Cerebellar Calcium-Binding Protein and Neurotrophin Receptor Defects in Down Syndrome and Alzheimer's Disease

Cerebellar hypoplasia is a major characteristic of the Down syndrome (DS) brain. However, the consequences of trisomy upon cerebellar Purkinje cells (PC) and interneurons in DS are unclear. The present study performed a quantitative and qualitative analysis of cerebellar neurons immunostained with antibodies against calbindin D-28k (Calb), parvalbumin (Parv), and calretinin (Calr), phosphorylated and non-phosphorylated intermediate neurofilaments (SMI-34 and SMI-32), and high (TrkA) and low (p75NTR) affinity nerve growth factor (NGF) receptors as well as tau and amyloid in DS (n = 12), Alzheimer's disease (AD) (n = 10), and healthy non-dementia control (HC) (n = 8) cases. Our findings revealed higher Aβ42 plaque load in DS compared to AD and HC but no differences in APP/Aβ plaque load between HC, AD, and DS. The cerebellar cortex neither displayed Aβ40 containing plaques nor pathologic phosphorylated tau in any of the cases examined. The number and optical density (OD) measurements of Calb immunoreactive (-ir) PC soma and dendrites were similar between groups, while the number of PCs positive for Parv and SMI-32 were significantly reduced in AD and DS compared to HC. By contrast, the number of SMI-34-ir PC dystrophic axonal swellings, termed torpedoes, was significantly greater in AD compared to DS. No differences in SMI-32- and Parv-ir PC OD measurements were observed between groups. Conversely, total number of Parv- (stellate/basket) and Calr (Lugaro, brush, and Golgi)-positive interneurons were significantly reduced in DS compared to AD and HC. A strong negative correlation was found between counts for Parv-ir interneurons, Calr-ir Golgi and brush cells, and Aβ42 plaque load. Number of TrkA and p75NTR positive PCs were reduced in AD compared to HC. These findings suggest that disturbances in calcium binding proteins play a critical role in cerebellar neuronal dysfunction in adults with DS.

Phosphorylated tau interactome in the human Alzheimer's disease brain

Accumulation of phosphorylated tau is a key pathological feature of Alzheimer's disease. Phosphorylated tau accumulation causes synaptic impairment, neuronal dysfunction and formation of neurofibrillary tangles. The pathological actions of phosphorylated tau are mediated by surrounding neuronal proteins; however, a comprehensive understanding of the proteins that phosphorylated tau interacts with in Alzheimer's disease is surprisingly limited. Therefore, the aim of this study was to determine the phosphorylated tau interactome. To this end, we used two complementary proteomics approaches: (i) quantitative proteomics was performed on neurofibrillary tangles microdissected from patients with advanced Alzheimer's disease; and (ii) affinity purification-mass spectrometry was used to identify which of these proteins specifically bound to phosphorylated tau. We identified 542 proteins in neurofibrillary tangles. This included the abundant detection of many proteins known to be present in neurofibrillary tangles such as tau, ubiquitin, neurofilament proteins and apolipoprotein E. Affinity purification-mass spectrometry confirmed that 75 proteins present in neurofibrillary tangles interacted with PHF1-immunoreactive phosphorylated tau. Twenty-nine of these proteins have been previously associated with phosphorylated tau, therefore validating our proteomic approach. More importantly, 34 proteins had previously been associated with total tau, but not yet linked directly to phosphorylated tau (e.g. synaptic protein VAMP2, vacuolar-ATPase subunit ATP6V0D1); therefore, we provide new evidence that they directly interact with phosphorylated tau in Alzheimer's disease. In addition, we also identified 12 novel proteins, not previously known to be physiologically or pathologically associated with tau (e.g. RNA binding protein HNRNPA1). Network analysis showed that the phosphorylated tau interactome was enriched in proteins involved in the protein ubiquitination pathway and phagosome maturation. Importantly, we were able to pinpoint specific proteins that phosphorylated tau interacts with in these pathways for the first time, therefore providing novel potential pathogenic mechanisms that can be explored in future studies. Combined, our results reveal new potential drug targets for the treatment of tauopathies and provide insight into how phosphorylated tau mediates its toxicity in Alzheimer's disease.

2,3,7,8-Tetrachlorodibenzo-p-dioxin and up-regulation of neurofilament expression in neuronal cells: Evaluation of AhR and MAPK pathways

Dioxin exposure is reported to affect nervous system development and increase the risk of neurodegenerative diseases. Generally, dioxin exerts its neurotoxicity via aryl hydrocarbon receptor (AhR). Neurofilament (NF) light (NFL) protein is a biomarker for both neuronal differentiation and neurodegeneration and its expression is controlled by the mitogen-activated protein kinase (MAPK) pathway. However, the effects of dioxin on NFL expression and involved mechanisms are incompletely understood. We aimed to investigate the effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on NFL expression and elucidate the underlining signaling pathways and their potential crosstalk, specifically between MAPK and AhR pathway. We employed primary cultured rat cortical neurons to evaluate the effect of TCDD exposure on NFL expression. We also used nerve growth factor (NGF)-treated PC12 cells with specific inhibitors to investigate the involvement of and potential crosstalk between the MAPK pathway and the AhR pathway in mediating the effects of TCDD on NFL expression. After TCDD exposure, NFL mRNA and protein levels were upregulated in cultured neurons. NFL protein was preferentially found in the cell body compared with neurites of the cultured neurons. In PC12 cells, TCDD enhanced both NGF-induced NFL expression and phosphorylation of ERK1/2 and p38. The addition of MAPK-pathway inhibitors (PD98059 and SB230580) partially blocked the TCDD-induced NFL upregulation. CH223191, an AhR antagonist, reversed the upregulation of NFL and phosphorylation of ERK1/2 and p38 induced by TCDD. This study demonstrated TCDD-induced upregulation of NFL in cultured neurons, with protein retained in the cell body. TCDD action was dependent on activation of AhR and MAPK, while crosstalk was found between these two signaling pathways.

Current state of Alzheimer's fluid biomarkers

Alzheimer’s disease (AD) is a progressive neurodegenerative disease with a complex and heterogeneous pathophysiology. The number of people living with AD is predicted to increase; however, there are no disease-modifying therapies currently available and none have been successful in late-stage clinical trials. Fluid biomarkers measured in cerebrospinal fluid (CSF) or blood hold promise for enabling more effective drug development and establishing a more personalized medicine approach for AD diagnosis and treatment. Biomarkers used in drug development programmes should be qualified for a specific context of use (COU). These COUs include, but are not limited to, subject/patient selection, assessment of disease state and/or prognosis, assessment of mechanism of action, dose optimization, drug response monitoring, efficacy maximization, and toxicity/adverse reactions identification and minimization. The core AD CSF biomarkers Aβ42, t-tau, and p-tau are recognized by research guidelines for their diagnostic utility and are being considered for qualification for subject selection in clinical trials. However, there is a need to better understand their potential for other COUs, as well as identify additional fluid biomarkers reflecting other aspects of AD pathophysiology. Several novel fluid biomarkers have been proposed, but their role in AD pathology and their use as AD biomarkers have yet to be validated. In this review, we summarize some of the pathological mechanisms implicated in the sporadic AD and highlight the data for several established and novel fluid biomarkers (including BACE1, TREM2, YKL-40, IP-10, neurogranin, SNAP-25, synaptotagmin, α-synuclein, TDP-43, ferritin, VILIP-1, and NF-L) associated with each mechanism. We discuss the potential COUs for each biomarker.

Loss of calretinin and parvalbumin positive interneurones in the hippocampal CA1 of aged Alzheimer's disease mice

Neuronal degeneration associated with Alzheimer's disease (AD), is linked to impaired calcium homeostasis and to changes in calcium-binding proteins (CBPs). The AD-related modification of neuronal CBPs remains controversial. Here we analysed the presence and expression of calretinin (CR) and parvalbumin (PV) in the hippocampal CA1 neurones of 18 months old 3xTg-AD mice compared to non-Tg animals. We found a layer specific decrease in number of interneurones expressing CR and PV (by 33.7% and 52%, respectively). Expression of PV decreased (by 13.8%) in PV-positive neurones, whereas expression of CR did not change in CR positive cells. The loss of specific subpopulations of Ca²⁺-binding proteins expressing interneurones (CR and PV) together with the decrease of PV in the surviving cells may be linked to their vulnerability to AD pathology. Specific loss of inhibitory interneurones with age could contribute to overall increase in the network excitability associated with AD.

Antioxidants reduce neurodegeneration and accumulation of pathologic Tau proteins in the auditory system after blast exposure

Cochlear neurodegeneration commonly accompanies hair cell loss resulting from aging, ototoxicity, or exposures to intense noise or blast overpressures. However, the precise pathophysiological mechanisms that drive this degenerative response have not been fully elucidated. Our laboratory previously demonstrated that non-transgenic rats exposed to blast overpressures exhibited marked somatic accumulation of neurotoxic variants of the microtubule-associated protein, Tau, in the hippocampus. In the present study, we extended these analyses to examine neurodegeneration and pathologic Tau accumulation in the auditory system in response to blast exposure and evaluated the potential therapeutic efficacy of antioxidants on short-circuiting this pathological process. Blast injury induced ribbon synapse loss and retrograde neurodegeneration in the cochlea in untreated animals. An accompanying perikaryal accumulation of neurofilament light chain and pathologic Tau oligomers were observed in neurons from both the peripheral and central auditory system, spanning from the spiral ganglion to the auditory cortex. Due to its coincident accumulation pattern and well-documented neurotoxicity, our results suggest that the accumulation of pathologic Tau oligomers may actively contribute to blast-induced cochlear neurodegeneration. Therapeutic intervention with a combinatorial regimen of 2,4-disulfonyl α-phenyl tertiary butyl nitrone (HPN-07) and N-acetylcysteine (NAC) significantly reduced both pathologic Tau accumulation and indications of ongoing neurodegeneration in the cochlea and the auditory cortex. These results demonstrate that a combination of HPN-07 and NAC administrated shortly after a blast exposure can serve as a potential therapeutic strategy for preserving auditory function among military personnel or civilians with blast-induced traumatic brain injuries.

DNA methylation alterations in Alzheimer's disease

The observation that Alzheimer's disease (AD) patients with similar and even identical genetic backgrounds often present with heterogeneous pathologies has prompted the hypothesis that epigenetics may contribute to AD. While the study of epigenetics encompasses a variety of modifications including histone modifications and non-coding RNAs, much of the research on how epigenetics might impact AD pathology has been focused on DNA methylation. To this end, several studies have characterized DNA methylation alterations in various brain regions of individuals with AD, with conflicting results. This review examines the results of studies analyzing both global and gene-specific DNA methylation changes in AD and also assesses the results of studies analyzing DNA hydroxymethylation in patients with AD.

Combination treatment with leptin and pioglitazone in a mouse model of Alzheimer's disease

INTRODUCTION

Combination therapy approaches may be necessary to address the many facets of pathologic change in the brain in Alzheimer's disease (AD). The drugs leptin and pioglitazone have previously been shown individually to have neuroprotective and anti-inflammatory actions, respectively, in animal models.

METHODS

We studied the impact of combined leptin and pioglitazone treatment in 6-month-old APP/PS1 (APPswe/PSEN1dE9) transgenic AD mouse model.

RESULTS

We report that an acute 2-week treatment with combined leptin and pioglitazone resulted in a reduction of spatial memory deficits (Y maze) and brain β-amyloid levels (soluble β-amyloid and amyloid plaque burden) relative to vehicle-treated animals. Combination treatment was also associated with amelioration in plaque-associated neuritic pathology and synapse loss, and also a significantly reduced neocortical glial response.

DISCUSSION

Combination therapy with leptin and pioglitazone ameliorates pathologic changes in APP/PS1 mice and may represent a potential treatment approach for AD.

Defining the earliest pathological changes of Alzheimer's disease

The prospects for effectively treating well-established dementia, such as Alzheimer's disease (AD), are slim, due to the destruction of key brain pathways that underlie higher cognitive function. There has been a substantial shift in the field towards detecting conditions such as AD in their earliest stages, which would allow preventative or therapeutic approaches to substantially reduce risk and/or slow the progression of disease. AD is characterized by hallmark pathological changes such as extracellular Aβ plaques and intracellular neurofibrillary pathology, which selectively affect specific subclasses of neurons and brain circuits. Current evidence indicates that Aβ plaques begin to form many years before overt dementia, a gradual and progressive pathology which offers a potential target for early intervention. Early Aβ changes in the brain result in localized damage to dendrites, axonal processes and synapses, to which excitatory synapses and the processes of projection neurons are highly vulnerable. Aβ pathology is replicated in a range of transgenic models overexpressing mutant human familial AD genes (e.g. APP and presenilin 1). Studying the development of aberrant regenerative and degenerative changes in neuritic processes associated with Aβ plaques may represent the best opportunity to understand the relationship between the pathological hallmarks of AD and neuronal damage, and to develop early interventions to prevent, slow down or mitigate against Aβ pathology and/or the neuronal alterations that leads to cognitive impairment.

CSF neurofilament light levels predict hippocampal atrophy in cognitively healthy older adults

Cerebrospinal fluid (CSF) neurofilament light (NFL) is a marker of axonal degeneration. We tested whether CSF NFL levels predict hippocampal atrophy rate in cognitively healthy older adults independently of the established CSF Alzheimer's disease (AD) biomarkers, β-amyloid 1-42, and phosphorylated tau (P-tau). We included 144 participants in a 2-year longitudinal study with baseline CSF measures and 2 magnetic resonance images. Eighty-eight participants had full data available. A subgroup of 36 participants with very low AD risk was also studied. NFL predicted hippocampal atrophy rate independently of age, β-amyloid 1-42, and P-tau. Including NFL, P-tau, and age in the same model, higher NFL and lower P-tau predicted higher hippocampal atrophy (R² = 0.20, NFL: β = -0.34; p = 0.003; P-tau: β = 0.27; p = 0.009). The results were upheld in the participants with very low AD risk. NFL predicted neurodegeneration in older adults with very low AD probability. We suggest that factors previously shown to be important for brain degeneration in mild cognitive impairment may also impact changes in normal aging, demonstrating that NFL is likely to indicate AD-independent, age-expected neurodegeneration.

Specialized roles of neurofilament proteins in synapses: Relevance to neuropsychiatric disorders

Neurofilaments are uniquely complex among classes of intermediate filaments in being composed of four subunits (NFL, NFM, NFH and alpha-internexin in the CNS) that differ in structure, regulation, and function. Although neurofilaments have been traditionally viewed as axonal structural components, recent evidence has revealed that distinctive assemblies of neurofilament subunits are integral components of synapses, especially at postsynaptic sites. Within the synaptic compartment, the individual subunits differentially modulate neurotransmission and behavior through interactions with specific neurotransmitter receptors. These newly uncovered functions suggest that alterations of neurofilament proteins not only underlie axonopathy in various neurological disorders but also may play vital roles in cognition and neuropsychiatric diseases. Here, we review evidence that synaptic neurofilament proteins are a sizable population in the CNS and we advance the concept that changes in the levels or post-translational modification of individual NF subunits contribute to synaptic and behavioral dysfunction in certain neuropsychiatric conditions.

The reaction of cerebral cortex to a nearby lesion: damage, survival, self-protection

A needlestick injury to cerebral cortex causes immediate damage along the track of the needle (haemorrhage, cell death) and sequelae (the formation of amyloid-positive plaques, extracellular deposits of hyperphosphorylated tau protein, microglial proliferation, astrogliosis) that are long lasting, and mimic the neuropathology associated with Alzheimer's disease. We report here that the same injury also elicits a distinctive response in the cortex flanking (up to 1mm from) the direct injury. Needlestick injury was made in the neo- and hippocampal cortex of young (3 months) healthy Sprague-Dawley rats. After survival times of up to 7d, the response of the cortex was assessed with histology, immunohistochemistry and stereology. Uptake of FluoroJade B at 1d survival and labelling for 4-hydroxynonenal (4-HNE) gave measures of membrane damage; labelling for 8-hydroxy-2'-deoxyguanosine (8-OHDG) gave a measure of DNA damage, and labelling with the AT8 antibody gave a measure of the hyperphosphorylation of tau. Two probes, for neuroglobin and basic fibroblast growth factor (FGF-2), gave measures of a self-protective response in the tissue. Results indicate that neurones in the flanking region are damaged by the nearby lesion, and within 1d upregulate self-protective mechanisms. Over the next 6d survival, evidence of neuronal damage reduces markedly. In summary, cells in the region flanking a lesion are stressed by the lesion, and react to the stress with a self-protective response, which prevents their death. This response may be an important, previously unrecognised feature of brain tissue close to a focus of stress, such as a microhaemorrhage.

Purkinje Cell Pathology and Loss in Multiple Sclerosis Cerebellum

Cerebellar ataxia commonly occurs in multiple sclerosis, particularly in chronic progressive disease. Previous reports have highlighted both white matter and grey matter pathological changes within the cerebellum; and demyelination and inflammatory cell infiltrates appear commonly. As Purkinje cell axons are the sole output of the cerebellar cortex, understanding pathologic processes within these cells is crucial to develop strategies to prevent their loss and thus reduce ataxia. We studied pathologic changes occurring within Purkinje cells of the cerebellum. Using immunohistochemic techniques, we found changes in neurofilament phosphorylation states within Purkinje cells, including loss of dephosphorylated neurofilament and increased phosphorylated and hyperphosphorylated neurofilament. We also found Purkinje axonal spheroids and Purkinje cell loss, both of which occurred predominantly within areas of leucocortical demyelination within the cerebellar cortex. These changes have important implications for the study of cerebellar involvement in multiple sclerosis and may help design therapies to reduce the burden of ataxia in the condition.

Up-regulation of Synaptotagmin IV within amyloid plaque-associated dystrophic neurons in Tg2576 mouse model of Alzheimer's disease

AIM

To investigate the involvement of the vesicular membrane trafficking regulator Synaptotagmin IV (Syt IV) in Alzheimer's disease pathogenesis and to define the cell types containing increased levels of Syt IV in the β-amyloid plaque vicinity.

METHODS

Syt IV protein levels in wild type (WT) and Tg2576 mice cortex were determined by Western blot analysis and immunohistochemistry. Co-localization studies using double immunofluorescence staining for Syt IV and markers for astrocytes (glial fibrillary acidic protein), microglia (major histocompatibility complex class II), neurons (neuronal specific nuclear protein), and neurites (neurofilaments) were performed in WT and Tg2576 mouse cerebral cortex.

RESULTS

Western blot analysis showed higher Syt IV levels in Tg2576 mice cortex than in WT cortex. Syt IV was found only in neurons. In plaque vicinity, Syt IV was up-regulated in dystrophic neurons. The Syt IV signal was not up-regulated in the neurons of Tg2576 mice cortex without plaques (resembling the pre-symptomatic conditions).

CONCLUSIONS

Syt IV up-regulation within dystrophic neurons probably reflects disrupted vesicular transport or/and impaired protein degradation occurring in Alzheimer's disease and is probably a consequence but not the cause of neuronal degeneration. Hence, Syt IV up-regulation and/or its accumulation in dystrophic neurons may have adverse effects on the survival of the affected neuron.

BDNF and COMT polymorphisms have a limited association with episodic memory performance or engagement in complex cognitive activity in healthy older adults

Cognitive decline is a major factor in lowering the quality of life in older populations, and contributes substantially to social, economic, and health costs. As humans age, cognitive function decreases differentially, and individual differences in cognitive ageing are likely attributed to a range of causes, including environmental and genetic influences. The current study included 360 participants (240 females and 120 males) aged between 50 and 79years from the Tasmanian Healthy Brain Project. The brain-derived neurotrophic factor (BDNF) Val66Met and Catechol-O-Methyltransferase (COMT) Val158Met polymorphisms were examined for their association with visual and auditory episodic memory performance. The polymorphisms were also investigated for their association with reported life-long engagement in complex cognitive activity using a retrospective questionnaire. Relative to the demographic variables, the gene variations were found to have no association with episodic memory performance, with the exception of the COMT polymorphism on a single measure of auditory memory (RAVLT). Several other studies also demonstrated that these polymorphisms have no, small, or inconsistent effects on memory function. The BDNF Val66Met and COMT Val158Met polymorphisms were also found to be of little significance to active engagement in complex cognitive activity throughout most of the lifespan. An association was detected between BDNF Val66Met and engagement in cognitive activity in early life (p=.04, d=.23), however this did not reach significance when adjusted for multiple comparisons. The biological mechanisms that underlie engagement in cognitive activity are elusive, thus the potential relationship between BDNF Val66Met genotype and early life cognitive engagement warrants further investigation.

Alzheimer's disease pathology in the neocortex and hippocampus of the western lowland gorilla (Gorilla gorilla gorilla)

The two major histopathologic hallmarks of Alzheimer's disease (AD) are amyloid beta protein (Aβ) plaques and neurofibrillary tangles (NFT). Aβ pathology is a common feature in the aged nonhuman primate brain, whereas NFT are found almost exclusively in humans. Few studies have examined AD-related pathology in great apes, which are the closest phylogenetic relatives of humans. In the present study, we examined Aβ and tau-like lesions in the neocortex and hippocampus of aged male and female western lowland gorillas using immunohistochemistry and histochemistry. Analysis revealed an age-related increase in Aβ-immunoreactive plaques and vasculature in the gorilla brain. Aβ plaques were more abundant in the neocortex and hippocampus of females, whereas Aβ-positive blood vessels were more widespread in male gorillas. Plaques were also Aβ40-, Aβ42-, and Aβ oligomer-immunoreactive, but only weakly thioflavine S- or 6-CN-PiB-positive in both sexes, indicative of the less fibrillar (diffuse) nature of Aβ plaques in gorillas. Although phosphorylated neurofilament immunostaining revealed a few dystrophic neurites and neurons, choline acetyltransferase-immunoreactive fibers were not dystrophic. Neurons stained for the tau marker Alz50 were found in the neocortex and hippocampus of gorillas at all ages. Occasional Alz50-, MC1-, and AT8-immunoreactive astrocyte and oligodendrocyte coiled bodies and neuritic clusters were seen in the neocortex and hippocampus of the oldest gorillas. This study demonstrates the spontaneous presence of both Aβ plaques and tau-like lesions in the neocortex and hippocampus in old male and female western lowland gorillas, placing this species at relevance in the context of AD research.

Morphologic and immunohistochemical organization of the human habenular complex

The habenular complex (HbCpx) is a phylogenetically conserved brain structure located in the epithalamus of vertebrates. Despite its fundamental role in decision-making processes and the proposed link between habenular dysfunction and neuropsychiatric conditions, little is known about the structural and functional organization of the HbCpx in humans. The goal of this study was thus to provide a first systematic morphologic and immunohistochemical analysis of the human HbCpx to begin dissecting its nuclear and subnuclear organization. Our results confirmed that the human HbCpx is subdivided into medial (MHb) and lateral (LHb) nuclei, each showing a large degree of intranuclear morphologic heterogeneity. Analysis of serially stained sections using a combination of morphologic and immunohistochemical criteria allowed the distinction of five subnuclei in both the MHb and LHb. Overall, the observed subnuclear organization of the MHb in humans resembles the organization of subnuclei in the MHb of rats. The shape, relative size, and intranuclear organization of the LHb, however, show significant differences. The contribution of the LHb to the entire HbCpx is about five times larger in humans than in rats. Noteworthy, a dorsal domain of the LHb that contains afferent myelinated fibers from the stria medullaris and shows GABA-(B) -R(1) immunoreactive cells, appears substantially enlarged in humans when compared to rats. This feature seems to account for a large part of the relative growth in size of the LHb in humans and opens the intriguing possibility of an increased influence of limbic and striatal afferents into the LHb of humans.

Response of ERβ and aromatase expression in the monkey hippocampal formation to ovariectomy and menopause

Changes in the expression of estrogen-related substances in monkeys' brains at the menopausal transition, when estrogen deficit starts to occur, have not yet been examined thoroughly. In the present study, we immunohistochemically investigated the expression levels of estrogen receptor beta (ERβ) and aromatase (local estrogen synthesizing enzyme) in the hippocampal formation of premenopausal, menopausal, and ovariectomized premenopausal monkeys. In all monkeys tested, ERβ immunoreactivity was observed in interneurons located in the subiculum and the Ammon's horn, and most of these ERβ-immunoreactive neurons coexpressed a GABAergic neuron marker, parvalbumin. In the menopausal monkeys who exhibited a decline in estrogen concentration, hippocampal ERβ was highly upregulated, while aromatase expression was not markedly changed. By contrast, aromatase in the ovariectomized monkeys was significantly upregulated, while ERβ expression was not changed. In the brains of ovariectomized and menopausal monkeys, depletion of ovary-derived estrogen brought about different reactions which may be attributed to the senescence of brain aging.

Staging of Alzheimer's pathology in triple transgenic mice: a light and electron microscopic analysis

The age-related pathological cascade underlying intraneuronal tau formation in 3xTg-AD mice, which harbor the human APP_Swe, PS1_M126V , and Tau_P301L gene mutations, remains unclear. At 3 weeks of age, AT180, Alz50, MC1, AT8, and PHF-1 intraneuronal immunoreactivity appeared in the amygdala and hippocampus and at later ages in the cortex of 3xTg-AD mice. AT8 and PHF-1 staining was fixation dependent in young mutant mice. 6E10 staining was seen at all ages. Fluorescent immunomicroscopy revealed CA1 neurons dual stained for 6E10 and Alz50 and single Alz50 immunoreactive neurons in the subiculum at 3 weeks and continuing to 20 months. Although electron microscopy confirmed intraneuronal cytoplasmic Alz50, AT8, and 6E10 reaction product in younger 3xTg-AD mice, straight filaments appeared at 23 months of age in female mice. The present data suggest that other age-related biochemical mechanisms in addition to early intraneuronal accumulation of 6E10 and tau underlie the formation of tau filaments in 3xTg-AD mice.

Loss of nonphosphorylated neurofilament immunoreactivity in temporal cortical areas in Alzheimer's disease

The distribution of immunoreactive neurons with nonphosphorylated neurofilament protein (SMI32) was studied in temporal cortical areas in normal subjects and in patients with Alzheimer's disease (AD). SMI32 immunopositive neurons were localized mainly in cortical layers II, III, V and VI, and were medium to large-sized pyramidal neurons. Patients with AD had prominent degeneration of SMI32 positive neurons in layers III and V of Brodmann areas 38, 36, 35 and 20; in layers II and IV of the entorhinal cortex (Brodmann area 28); and hippocampal neurons. Neurofibrillary tangles (NFTs) were stained with Thioflavin-S and with an antibody (AT8) against hyperphosphorylated tau. The NFT distribution was compared to that of the neuronal cytoskeletal marker SMI32 in these temporal cortical regions. The results showed that the loss of SMI32 immunoreactivity in temporal cortical regions of AD brain is paralleled by an increase in NFTs and AT8 immunoreactivity in neurons. The SMI32 immunoreactivity was drastically reduced in the cortical layers where tangle-bearing neurons are localized. A strong SMI32 immunoreactivity was observed in numerous neurons containing NFTs by double-immunolabeling with SMI32 and AT8. However, few neurons were labeled by AT8 and SMI32. These results suggest that the development of NFTs in some neurons results from some alteration in SMI32 expression, but does not account for all, particularly, early NFT-related changes. Also, there is a clear correlation of NFTs with selective population of pyramidal neurons in the temporal cortical areas and these pyramidal cells are specifically prone to formation of paired helical filaments. Furthermore, these pyramidal neurons might represent a significant portion of the neurons of origin of long corticocortical connection, and consequently contribute to the destruction of memory-related input to the hippocampal formation.

Postmortem changes in the neuroanatomical characteristics of the primate brain: hippocampal formation

Comparative studies of the structural organization of the brain are fundamental to our understanding of human brain function. However, whereas brains of experimental animals are fixed by perfusion of a fixative through the vasculature, human or ape brains are fixed by immersion after varying postmortem intervals. Although differential treatments might affect the fundamental characteristics of the tissue, this question has not been evaluated empirically in primate brains. Monkey brains were either perfused or acquired after varying postmortem intervals before immersion-fixation in 4% paraformaldehyde. We found that the fixation method affected the neuroanatomical characteristics of the monkey hippocampal formation. Soma size was smaller in Nissl-stained, immersion-fixed tissue, although overall brain volume was larger as compared to perfusion-fixed tissue. Nonphosphorylated high-molecular-weight neurofilament immunoreactivity was lower in CA3 pyramidal neurons, dentate mossy cells, and the entorhinal cortex, whereas it was higher in the mossy fiber pathway in immersion-fixed tissue. Serotonin-immunoreactive fibers were well stained in perfused tissue but were undetectable in immersion-fixed tissue. Although regional immunoreactivity patterns for calcium-binding proteins were not affected, intracellular staining degraded with increasing postmortem intervals. Somatostatin-immunoreactive clusters of large axonal varicosities, previously reported only in humans, were observed in immersion-fixed monkey tissue. In addition, calretinin-immunoreactive multipolar neurons, previously observed only in rodents, were found in the rostral dentate gyrus in both perfused and immersion-fixed brains. In conclusion, comparative studies of the brain must evaluate the effects of fixation on the staining pattern of each marker in every structure of interest before drawing conclusions about species differences.

Cytoskeletal alterations differentiate presenilin-1 and sporadic Alzheimer's disease

Most cases of Alzheimer's disease (AD) are sporadic in nature, although rarer familial AD (FAD) cases have provided important insights into major pathological disease mechanisms. Mutations in the presenilin 1 gene (PS1) are responsible for the majority of FAD cases, causing an earlier age of onset and more rapid progression to end-stage disease than seen in sporadic AD. We have investigated the cytoskeletal alterations in neuritic AD pathology in a cohort of FAD cases in comparison to sporadic AD and pathologically aged cases. Tau-immunoreactive neurofibrillary tangle (NFT) loads were similar between PS1 FAD and sporadic AD cases. Similarly, plaque loads, both beta-amyloid (Abeta) and thioflavine S, in PS1 FAD and sporadic AD cases were not significantly different; however, in pathologically aged cases, they were significantly lower than those in PS1 cases, but were not different from sporadic AD cases. The 'cotton wool' plaque characteristic of PS1 cases did not demonstrate a high density of dystrophic neurites compared to other Abeta plaque types, but did demonstrate a localised mass effect on the neuropil. Despite minimal differences in plaque and NFT loads, immunolabelling demonstrated clear phenotypic differences in the NFTs and dystrophic neurites in PS1 FAD cases. Presenilin-1 cases exhibited significantly (P < 0.05) more tau-positive NFTs that were immunolabelled by the antibody SMI312 (anti-phosphorylated NF protein and phosphorylated tau) than sporadic AD cases. Presenilin-1 cases also exhibited numerous ring-like NF-positive and elongated tau-labelled dystrophic neurites, whereas these dystrophic neurite types were only abundant at the very early (pathologically aged cases) or very late stages of sporadic AD progression, respectively. These differences in cytoskeletal pathology in PS1 cases suggest an accelerated rate of neuritic pathology development, potentially due to mutant PS1 influencing multiple pathogenic pathways.

Changes in the structural complexity of the aged brain

Structural changes of neurons in the brain during aging are complex and not well understood. Neurons have significant homeostatic control of essential brain functions, including synaptic excitability, gene expression, and metabolic regulation. Any deviations from the norm can have severe consequences as seen in aging and injury. In this review, we present some of the structural adaptations that neurons undergo throughout normal and pathological aging and discuss their effects on electrophysiological properties and cognition. During aging, it is evident that neurons undergo morphological changes such as a reduction in the complexity of dendrite arborization and dendritic length. Spine numbers are also decreased, and because spines are the major sites for excitatory synapses, changes in their numbers could reflect a change in synaptic densities. This idea has been supported by studies that demonstrate a decrease in the overall frequency of spontaneous glutamate receptor-mediated excitatory responses, as well as a decrease in the levels of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid and N-methyl-d-aspartate receptor expression. Other properties such as gamma-aminobutyric acid A receptor-mediated inhibitory responses and action potential firing rates are both significantly increased with age. These findings suggest that age-related neuronal dysfunction, which must underlie observed decline in cognitive function, probably involves a host of other subtle changes within the cortex that could include alterations in receptors, loss of dendrites, and spines and myelin dystrophy, as well as the alterations in synaptic transmission. Together these multiple alterations in the brain may constitute the substrate for age-related loss of cognitive function.

Life and death of neurons in the aging cerebral cortex

The transition from age-associated memory impairment (AAMI) to the dramatic loss of cognitive abilities accompanying Alzheimer's disease (AD) requires progressive development of neocortical pathology that results in neuron death. The selective vulnerability of this neuron death is reflected in the characteristics of cortical pyramidal neurons that are prone to form neurofibrillary tangles. Loss of the neurons that form long corticocortical projections in the association neocortex emerges as the pathological outcome most directly related to the dementia observed in AD. AAMI likely involves alterations of neuronal spines and synapses without neuron death. Interestingly, the same circuits that are vulnerable to degeneration in AD are vulnerable to synaptic alterations short of neuron death. These synaptic alterations likely impact cognitive function in normal aging in a manner consistent with the more modest cognitive decline typically seen in aging. Estrogen levels affect spine density on pyramidal neurons in the prefrontal cortex; these neurons may provide many of the same circuits implicated in AAMI. This association demonstrates an important interface between reproductive and neural senescence and suggests that the synaptic alterations prevalent in normal aging may be responsive to therapy.

Estrogen receptor alpha and its splice variants in the hippocampus in aging and Alzheimer's disease

Clinical and experimental studies show that estrogens can have beneficial effects on hippocampus-dependent cognitive functions that may be mediated by estrogen receptor (ER)alpha. We investigated whether menopause and Alzheimer's disease (AD) cause changes in this ER subtype. Immunocytochemical staining of ERalpha, aromatase and Golgi complex (GC) was performed on paraffin embedded hippocampal tissue from women of the pre-, peri- and postmenopausal age. Canonical ERalpha mRNA amplicons, ERalpha splice variants (del.2, del.4, del.7, MB1) and aromatase transcripts were measured by Q-PCR in frozen hippocampal samples of AD and matched control cases. Nuclear ERalpha, aromatase and the GC enhanced during aging in women indicating availability of locally synthesized estrogens that may up-regulate ERalpha by which neuronal metabolism can be augmented in the hippocampus after the menopause. In AD cases canonical and alternatively spliced ERalpha mRNA, and aromatase gene expression were down-regulated suggesting a deficit in local estrogen levels and diminished signalling through ERalpha. The major ERalpha splice variants in the hippocampus were found to be MB1 and del.4. A novel ERalpha isoform TADDI was isolated and sequenced from two female patients. It lacks 31 bp at the junction between exons 3 and 4 with an insertion of 13 nucleotides from the middle of the exon 2.

Aluminum in hippocampal neurons from humans with Alzheimer's disease

Using a staining technique developed in 2004, we examined hippocampal tissue from autopsy-confirmed cases of Alzheimer's disease (AD) and controls. The stain disclosed aluminum in cells and subcellular structure. All pyramidal neurons in these aged specimens appeared to exhibit at least some degree of aluminum staining. Many displayed visible aluminum only in their nucleolus. At the other extreme were neurons that stained for aluminum throughout their nucleus and cytoplasm. The remainder exhibited intermediate degrees of staining. On the basis of their aluminum staining patterns, all pyramidal neurons could be classified into stages that indicated two distinct neuropathological processes, either (1) progressive increase of nuclear aluminum (often accompanied by granulovacuolar degeneration with granules that stain for aluminum) or (2) formation of neurofibrillary tangles (NFTs) in regions of aluminum-rich cytoplasm, especially in AD brain tissue. In the latter process, intraneuronal NFTs appeared to displace nuclei and then enucleate the affected neurons during the course of their transformation into extracellular NFTs. Given that the NFTs we observed in human neurons always developed in conjunction with cytoplasmic aluminum, we hypothesize that aluminum plays an important role in their formation and should therefore be reconsidered as a causative factor for AD.

No difference in expression of apoptosis-related proteins and apoptotic morphology in control, pathologically aged and Alzheimer's disease cases

Apoptotic-like changes in the neocortex of control, pathologically aged and Alzheimer's disease (AD) cases were investigated. There was no increase in labeling or change in localization of labeling that distinguished between these cases for active caspase-3, -8, -9, Bax, Bcl-2 or TRADD. Bax, Bcl-2 and TRADD mRNA levels also differed little between case types, although there were small but significant decreases in Bax mRNA levels in AD compared to control cases and Bcl-2 mRNA in AD cases compared to pathologically aged and control cases. There was no difference in the percentage of apoptotic-like nuclei between these cases, except for a small but significant decrease in the inferior temporal gyrus of AD cases relative to controls. Nuclei observed within or adjacent to beta-amyloid plaques were rarely abnormal, and neurons bearing neurofibrillary tangles (NFTs) did not have abnormal nuclei. Apoptosis may not play a major role in the pathogenesis of neuronal degeneration of AD.

Mitochondrial microheteroplasmy and a theory of aging and age-related disease

We implicate a recently described form of mitochondrial mutation, mitochondrial microheteroplasmy, as a candidate for the principal component of aging. Microheteroplasmy is the presence of hundreds of independent mutations in one organism, with each mutation usually found in 1-2% of all mitochondrial genomes. Despite the low abundance of single mutations, the vast majority of mitochondrial genomes in all adults are mutated. This mutational burden includes inherited mutations, de novo germline mutations, as well as somatic mutations acquired either during early embryonic development or later in adult life. We postulate that microheteroplasmy is sufficient to explain the pathomechanism of several age-associated diseases, especially in conditions with known mitochondrial involvement, such as diabetes (DM), cardiovascular disease, Parkinson's disease (PD), and Alzheimer's disease (AD) and cancer. The genetic properties of microheteroplasmy reconcile the results of disease models (cybrids, hypermutable PolG variants and mitochondrial toxins), with the relatively low levels of maternal inheritance in the aforementioned diseases, and provide an explanation of their delayed, progressive course.

Effect of hypothermia on postmortem alterations in MAP2 immunostaining in the human hippocampus

Ischemic neuronal injury induce degradation of microtubule-associated protein 2 (MAP2). In addition to ischemia, postmortem brains show alterations in MAP2 immunoreactivity in the hippocampus, suggesting that the factors inducing cytoskeletal disruption in postmortem brain are similar to those in ischemic brains. Hypothermia reduces the severity of ischemic injury including disruption of MAP2 in the hippocampus. However, whether hypothermia reduces postmortem changes of MAP2 was not clear. In this study, we evaluated the effect of hypothermia on postmortem degradation of MAP2 in the human hippocampus at various postmortem intervals using immunohistochemistry. In postmortem brains without hypothermia (the normothermic group), the locus of MAP2 immunoreactivity moved from the dendrites to the cell bodies prior to becoming undetectable with increasing postmortem interval, particularly in the CA1-subiculum region. On the other hand, the change in MAP2 immunoreactivity was remarkably attenuated in brains of death from cold (the hypothermic group). The present study demonstrated that MAP2 disruption is remarkable in the CA1-subiculum region of autopsied brains and that hypothermia reduces the postmortem change of MAP2, as observed in ischemic brain. Therefore, immunostaining of MAP2 in the hippocampus could be used to diagnose hypothermia.

Nonphosphorylated high-molecular-weight neurofilament expression suggests early maturation of the monkey subiculum

We analyzed the distribution of nonphosphorylated high-molecular-weight neurofilaments (NF-H) in the hippocampal formation of infant (3-week-old and 3-month-old) and adult (9-17-year-old) macaque monkeys in order to obtain neuroanatomical evidence of the maturity of these structures shortly after birth. We employed the monoclonal antibody SMI-32, a well-characterized antibody raised against nonphosphorylated NF-H, the expression of which is believed to reflect the maturation of certain neuronal populations. Patterns of SMI-32 immunoreactivity differed dramatically between infant and adult monkeys. In adults, nonphosphorylated NF-H expression was prominent in the CA3 and CA2 fields of the hippocampus, in the subiculum and in the entorhinal cortex. In infants, only the subiculum stained heavily for nonphosphorylated NF-H. These findings suggest that different subregions of the primate hippocampal formation mature at different times during development. The subiculum, the major source of efferent projections from the hippocampal formation toward subcortical structures, matures early during development. In contrast, the entorhinal cortex, the main interface of the hippocampal formation with the neocortex, matures relatively later. These findings have direct implications for the type of information processing that might be subserved by the primate hippocampal formation shortly after birth, as well as for the emergence of particular behavioral and memory processes during postnatal development.

Effect of hypothermia on postmortem alterations in MAP2 immunostaining in the human hippocampus

Ischemic neuronal injury induce degradation of microtubule-associated protein 2 (MAP2). In addition to ischemia, postmortem brains show alterations in MAP2 immunoreactivity in the hippocampus, suggesting that the factors inducing cytoskeletal disruption in postmortem brain are similar to those in ischemic brains. Hypothermia reduces the severity of ischemic injury including disruption of MAP2 in the hippocampus. However, whether hypothermia reduces postmortem changes of MAP2 was not clear. In this study, we evaluated the effect of hypothermia on postmortem degradation of MAP2 in the human hippocampus at various postmortem intervals using immunohistochemistry. In postmortem brains without hypothermia (the normothermic group), the locus of MAP2 immunoreactivity moved from the dendrites to the cell bodies prior to becoming undetectable with increasing postmortem interval, particularly in the CA1-subiculum region. On the other hand, the change in MAP2 immunoreactivity was remarkably attenuated in brains of death from cold (the hypothermic group). The present study demonstrated that MAP2 disruption is remarkable in the CA1-subiculum region of autopsied brains and that hypothermia reduces the postmortem change of MAP2, as observed in ischemic brain. Therefore, immunostaining of MAP2 in the hippocampus could be used to diagnose hypothermia.

The nature and effects of cortical microvascular pathology in aging and Alzheimer's disease

Age-related and amyloid-induced pathology of the cerebral microvasculature have been implicated as potential contributing factors to the pathogenesis of Alzheimer's disease (AD). The microvasculature plays a crucial role in maintaining brain homeostasis and deterioration of its integrity may have deleterious effects on brain function in AD, possibly leading to neurofibrillary degeneration, plaque formation, and cell loss. Brain vessels possess peculiar anatomical and physiological properties owing to their role in the exchange processes of various substances between blood and brain, which are highly regulated for the maintenance of ionic homeostasis of the neuronal environment. Here we review neuropathological aspects of cortical microvessels in aging and AD in relationship to known cardiovascular risk factors and their possible impact on the cognitive decline seen in late-onset dementia.

Increased tau Phosphorylation in Apolipoprotein E4 Transgenic Mice Is Associated with Activation of Extracellular Signal-regulated Kinase

Although apolipoprotein (apo) E4 is present in amyloid plaques and neurofibrillary tangles, its pathogenic role in Alzheimer's disease (AD) is unclear. Neuronal expression of apoE4 or apoE4 fragments in transgenic mice increases tau phosphorylation. To identify the kinase responsible for the increase, we studied transgenic mice expressing human apoE3 or apoE4 in neurons under the control of the neuron-specific enolase promoter. Brain levels of phosphorylated tau (p-tau) and phosphorylated (active) extracellular signal-regulated kinase (p-Erk) increased with age in both groups but were considerably higher in the apoE4 mice. Other candidate kinases, including glycogen synthase kinase 3beta and cyclin-dependent kinase-5 and its activators p25 and p35, were not significantly altered. The increases in p-Erk and p-tau were highest in the hippocampus, intermediate in the cortex, and lowest in the cerebellum. In the hippocampus, p-Erk and p-tau accumulated in the hilus and CA3 region of the dentate gyrus, where high levels of zinc are found along mossy fibers. In Neuro-2a cells stably expressing apoE3 or apoE4, treatment with ZnCl2 generated 2-fold more p-Erk and 3-fold more p-tau in the apoE4-expressing cells. Phosphorylation of Erk and tau was reduced by preincubation with the Erk pathway inhibitor U0126. Thus, increased tau phosphorylation in apoE4 transgenic mice was associated with Erk activation and could be modified by zinc, suggesting that apoE4 and zinc act in concert to contribute to the pathogenesis of AD.

Calpain mediates calcium-induced activation of the erk1,2 MAPK pathway and cytoskeletal phosphorylation in neurons: relevance to Alzheimer's disease

Aberrant phosphorylation of the neuronal cytoskeleton is an early pathological event in Alzheimer's disease (AD), but the underlying mechanisms are unclear. Here, we demonstrate in the brains of AD patients that neurofilament hyperphosphorylation in neocortical pyramidal neurons is accompanied by activation of both Erk1,2 and calpain. Using immunochemistry, Western blot analysis, and kinase activity measurements, we show in primary hippocampal and cerebellar granule (CG) neurons that calcium influx activates calpain and Erk1,2 and increases neurofilament phosphorylation on carboxy terminal polypeptide sites known to be modulated by Erk1,2 and to be altered in AD. Blocking Erk1,2 activity either with antisense oligonucleotides to Erk1,2 mRNA sequences or by specifically inhibiting its upstream activating kinase MEK1,2 markedly reduced neurofilament phosphorylation. Calpeptin, a cell-permeable calpain inhibitor, blocked both Erk1,2 activation and neurofilament hyperphosphorylation at concentrations that inhibit calpain-mediated cleavage of brain spectrin. By contrast, inhibiting Erk1,2 with U-0126, a specific inhibitor of Mek1,2, had no appreciable effect on ionomycin-induced calpain activation. These findings demonstrate that, under conditions of calcium injury in neurons, calpains are upstream activators of Erk1,2 signaling and are likely to mediate in part the hyperphosphorylation of neurofilaments and tau seen at early stages of AD as well as the neuron survival-related functions of the MAP kinase pathway.

Carboxyl-terminal-truncated apolipoprotein E4 causes Alzheimer's disease-like neurodegeneration and behavioral deficits in transgenic mice

Apolipoprotein (apo) E4 increases the risk and accelerates the onset of Alzheimer's disease (AD). However, the underlying mechanisms remain to be determined. We previously found that apoE undergoes proteolytic cleavage in AD brains and in cultured neuronal cells, resulting in the accumulation of carboxyl-terminal-truncated fragments of apoE that are neurotoxic. Here we show that this fragmentation is caused by proteolysis of apoE by a chymotrypsin-like serine protease that cleaves apoE4 more efficiently than apoE3. Transgenic mice expressing the carboxyl-terminal-cleaved product, apoE4(Delta272-299), at high levels in the brain died at 2-4 months of age. The cortex and hippocampus of these mice displayed AD-like neurodegenerative alterations, including abnormally phosphorylated tau (p-tau) and Gallyas silver-positive neurons that contained cytosolic straight filaments with diameters of 15-20 nm, resembling preneurofibrillary tangles. Transgenic mice expressing lower levels of the truncated apoE4 survived longer but showed impaired learning and memory at 6-7 months of age. Thus, carboxyl-terminal-truncated fragments of apoE4, which occur in AD brains, are sufficient to elicit AD-like neurodegeneration and behavioral deficits in vivo. Inhibiting their formation might inhibit apoE4-associated neuronal deficits.

Progressive degeneration of nonphosphorylated neurofilament protein-enriched pyramidal neurons predicts cognitive impairment in Alzheimer's disease: stereologic analysis of prefrontal cortex area 9

We performed a stereologic analysis of a subset of pyramidal neurons known to be vulnerable in Alzheimer's disease (AD) and characterized by particularly high somatodendritic levels of nonphosphorylated neurofilament protein. In the neocortex, these large pyramidal neurons reside in the deep part of layer III (layer IIIc) and the superficial part of layer V (layer Va). We focused on prefrontal cortex area 9 in elderly control cases in comparison to cases with different degrees of cognitive dysfunction. The results confirmed that these neurons are preferentially vulnerable in AD, as their numbers decrease dramatically in cases with definite dementia, correlating strongly with the severity of the disease, to a nearly complete loss (>90%) in the endstages of AD. Furthermore, a triple-labeling experimental paradigm revealed that these particular neurons are far more likely to develop neurofibrillary tangles (NFT) and do so at a faster rate than other pyramidal cells. Nonphosphorylated neurofilament protein-rich neurons also shrink considerably during formation of NFT and the largest among them are preferentially affected. Laminar differences in the severity of these effects were observed, layer Va being more severely affected, possibly correlating with the involvement of specific cortical projections. These data reveal that different populations of neurons prone to NFT formation are lost at different rates in AD, and that nonphosphorylated neurofilament protein-enriched neurons emerge as a strikingly vulnerable subpopulation of neurons. Their preferential involvement suggests that neurons providing specific corticocortical connections between association areas are at high risk for degeneration in AD.