Synaptic pathology in Alzheimer's disease: immunological data for markers of synaptic and large dense-core vesicles

Structure, function, and pathology of Neurexin-3

Neurexin-3 is primarily localized in the presynaptic membrane and forms complexes with various ligands located in the postsynaptic membrane. Neurexin-3 has important roles in synapse development and synapse functions. Neurexin-3 mediates excitatory presynaptic differentiation by interacting with leucine-rich-repeat transmembrane neuronal proteins. Meanwhile, neurexin-3 modulates the expression of presynaptic α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors and γ-aminobutyric acid A receptors by interacting with neuroligins at excitatory and inhibitory synapses. Numerous studies have documented the potential contribution of neurexin-3 to neurodegenerative and neuropsychiatric disorders, such as Alzheimer's disease, addiction behaviors, and other diseases, which raises hopes that understanding the mechanisms of neurexin-3 may hold the key to developing new strategies for related illnesses. This review comprehensively covers the literature to provide current knowledge of the structure, function, and clinical role of neurexin-3.

Damaged mitochondria coincide with presynaptic vesicle loss and abnormalities in alzheimer's disease brain

Loss of synapses is the most robust pathological correlate of Alzheimer's disease (AD)-associated cognitive deficits, although the underlying mechanism remains incompletely understood. Synaptic terminals have abundant mitochondria which play an indispensable role in synaptic function through ATP provision and calcium buffering. Mitochondrial dysfunction is an early and prominent feature in AD which could contribute to synaptic deficits. Here, using electron microscopy, we examined synapses with a focus on mitochondrial deficits in presynaptic axonal terminals and dendritic spines in cortical biopsy samples from clinically diagnosed AD and age-matched non-AD control patients. Synaptic vesicle density within the presynaptic axon terminals was significantly decreased in AD cases which appeared largely due to significantly decreased reserve pool, but there were significantly more presynaptic axons containing enlarged synaptic vesicles or dense core vesicles in AD. Importantly, there was reduced number of mitochondria along with significantly increased damaged mitochondria in the presynapse of AD which correlated with changes in SV density. Mitochondria in the post-synaptic dendritic spines were also enlarged and damaged in the AD biopsy samples. This study provided evidence of presynaptic vesicle loss as synaptic deficits in AD and suggested that mitochondrial dysfunction in both pre- and post-synaptic compartments contribute to synaptic deficits in AD.

Beyond monoamines: I. Novel targets and radiotracers for Positron emission tomography imaging in psychiatric disorders

With the emergence of positron emission tomography (PET) in the late 1970s, psychiatry had access to a tool capable of non-invasive assessment of human brain function. Early applications in psychiatry focused on identifying characteristic brain blood flow and metabolic derangements using radiotracers such as [¹⁵ O]H₂ O and [¹⁸ F]FDG. Despite the success of these techniques, it became apparent that more specific probes were needed to understand the neurochemical bases of psychiatric disorders. The first neurochemical PET imaging probes targeted sites of action of neuroleptic (dopamine D₂ receptors) and psychoactive (serotonin receptors) drugs. Based on the centrality of monoamine dysfunction in psychiatric disorders and the measured success of monoamine-enhancing drugs in treating them, the next 30 years witnessed the development of an armamentarium of PET radiopharmaceuticals and imaging methodologies for studying monoamines. Continued development of monoamine-enhancing drugs over this time however was less successful, realizing only modest gains in efficacy and tolerability. As patent protection for many widely prescribed and profitable psychiatric drugs lapsed, drug development pipelines shifted away from monoamines in search of novel targets with the promises of improved efficacy, or abandoned altogether. Over this period, PET radiopharmaceutical development activities closely paralleled drug development priorities resulting in the development of new PET imaging agents for non-monoamine targets. Part one of this review will briefly survey novel PET imaging targets with relevance to the field of psychiatry, which include the metabotropic glutamate receptor type 5 (mGluR5), purinergic P₂ X₇ receptor, type 1 cannabinoid receptor (CB₁ ), phosphodiesterase 10A (PDE10A), and describe radiotracers developed for these and other targets that have matured to human subject investigations. Current limitations of the targets and techniques will also be discussed.

Large-scale deep multi-layer analysis of Alzheimer's disease brain reveals strong proteomic disease-related changes not observed at the RNA level

The biological processes that are disrupted in the Alzheimer's disease (AD) brain remain incompletely understood. In this study, we analyzed the proteomes of more than 1,000 brain tissues to reveal new AD-related protein co-expression modules that were highly preserved across cohorts and brain regions. Nearly half of the protein co-expression modules, including modules significantly altered in AD, were not observed in RNA networks from the same cohorts and brain regions, highlighting the proteopathic nature of AD. Two such AD-associated modules unique to the proteomic network included a module related to MAPK signaling and metabolism and a module related to the matrisome. The matrisome module was influenced by the APOE ε4 allele but was not related to the rate of cognitive decline after adjustment for neuropathology. By contrast, the MAPK/metabolism module was strongly associated with the rate of cognitive decline. Disease-associated modules unique to the proteome are sources of promising therapeutic targets and biomarkers for AD.

Serum chromogranin A correlated with albuminuria in diabetic patients and is associated with early diabetic nephropathy

BACKGROUND

The kidney is the main site for the removal of chromogranin A (CgA). Previous studies have found that patients with renal impairment displayed elevated concentrations of CgA in plasma and that CgA concentrations reflect a deterioration of renal function. In this study, we aimed to estimate serum CgA levels and to evaluate the role of serum CgA in the early diagnosis of diabetic nephropathy (DN).

METHODS

A total of 219 patients with type 2 diabetes mellitus (T2DM) were included in this cross-sectional study. These patients were classified into normoalbuminuria (n = 121), microalbuminuria (n = 73), or macroalbuminuria (n = 25) groups based on their urine albumin to creatinine ratios (UACRs). The degree of DN is reflected by UACR. A control group consisted of 45 healthy subjects. The serum CgA levels were measured by ELISA, and other key parameters were assayed.

RESULTS

Serum CgA levels were higher in patients with T2DM than in control subjects, and a statistically significant difference among the studied subgroups regarding CgA was found (P < 0.05). The levels of serum CgA increased gradually with the degree of DN (P < 0.001). Serum CgA levels showed a moderate-intensity positive correlation with UACRs (P < 0.001). A cutoff level of 3.46 ng/ml CgA showed 69.86% sensitivity and 66.12% specificity to detect DN in the early stage.

CONCLUSION

The levels of serum CgA increased gradually with the degree of DN and can be used as a biomarker in the early detection of DN.

A comprehensive review on medicinal herbs and novel formulations for the prevention of Alzheimer's disease

Alzheimer's disease (AD) is one of the most prevalent neurodegenerative diseases reported in the aging population across the globe. About 46.8 million people are reported to have dementia, and AD is mainly responsible for dementia in aged people. Alzheimer's disease (AD) is thought to occur due to the accumulation of β-amyloid (Aβ) in the neocortex portion of the brain, nitric oxide mediated dysfunctioning of blood-brain barrier, reduced activity of serine racemase enzyme, cell cycle disturbances, damage of N-methyl-D-aspartate (NMDA) receptors and glutamatergic neurotransmission. Modern treatment methods target the pathways responsible for the disease. To date, solely symptomatic treatments exist for this disease, all making an attempt to counterbalance the neurotransmitter disturbance. Treatments able to prevent or at least effectively modifying the course of AD, referred to as 'disease-modifying' drugs, are still under extensive research. Effective treatments entail a better indulgence of the herbal bioactives by novel drug delivery systems. The herbal bioactive administered by novel drug delivery systems have proved beneficial in treating this disease. This review provides detailed information about the role of medicinal plants and their formulations in treating Alzheimer disease which will be highly beneficial for the researchers working in this area.

Alzheimer's disease; a review of the pathophysiological basis and therapeutic interventions

Alzheimer's disease (AD) is a neurodegenerative disorder and is identified as the most common cause for dementia. Despite huge global economic burden and the impact on the close family of the patients, there is no definitive cure and thus, improved treatment methods are of need. While memory and cognition are severely affected in AD, exact etiology is yet unknown. The β-Amyloid plaque formation and aggregation hypothesis is among the well-known hypotheses used to explain disease pathogenesis. Currently there are five Food and Drug Administration (FDA) approved drugs as treatment options. All these drugs are used for symptomatic treatment of AD. Thus, disease modifying therapies which can directly address the pathological changes in AD, are needed. Such therapies could be designed based on inhibiting key steps of pathogenesis. Currently there are novel AD drug candidates with various therapeutic mechanisms, undergoing different stages of drug development. Extensive research is being done globally to broaden understanding of the exact mechanisms involved in AD and to develop therapeutic agents that can successfully hinder the occurrence and progression of the disease. In this review, a comprehensive approach to understanding AD and suggestions to be considered in the development of therapeutics for it are presented.

BAMBI and CHGA in Prion Diseases: Neuropathological Assessment and Potential Role as Disease Biomarkers

Prion diseases affect both animals and humans. Research in the natural animal model of the disease could help in the understanding of neuropathological mechanisms and in the development of biomarkers for human pathologies. For this purpose, we studied the expression of 10 genes involved in prion propagation in vitro in the central nervous system of scrapie-infected sheep. Dysregulated genes (BAMBI and CHGA) were further analysed in a transgenic murine model (Tg338) of scrapie, and their protein distribution was determined using immunohistochemistry and Western blot. Their potential as biomarkers was finally assessed using enzyme-linked immunosorbent assay (ELISA) in cerebrospinal fluid (CSF) of scrapie sheep and Creutzfeldt-Jakob disease (CJD) patients. Protein BAMBI was upregulated in highly affected brain areas and CHGA was overexpressed along the brain in both models. Moreover, BAMBI and CHGA immunostaining scores strongly correlated with spongiosis and microgliosis in mice. Finally, levels of BAMBI were significantly higher in the CSF of clinical sheep and CJD patients. In addition to their potential as biomarkers, our work confirms the role of BAMBI and CHGA in prion neuropathology in vivo, but besides prion replication, they seem to be involved in the characteristic neuroinflammatory response associated to prion infection.

Chromogranin A in the early steps of the neurosecretory pathway

Chromogranin A (CgA) is a soluble glycoprotein stored with hormones and neuropeptides in secretory granules (SG) of most (neuro)endocrine cells and neurons. Since its discovery in 1967, many studies have reported its structural characteristics, biological roles, and mechanisms of action. Indeed, CgA is both a precursor of various biologically active peptides and a granulogenic protein regulating the storage and secretion of hormones and neuropeptides. This review emphasizes the findings and theoretical concepts around the CgA-linked molecular machinery controlling hormone/neuropeptide aggregation and the interaction of CgA-hormone/neuropeptide aggregates with the trans-Golgi membrane to allow hormone/neuropeptide targeting and SG biogenesis. We will also discuss the intriguing alteration of CgA expression and secretion in various neurological disorders, which could provide insights to elucidate the molecular mechanisms underlying these pathophysiological conditions.

Persistent Infection with Herpes Simplex Virus 1 and Alzheimer's Disease-A Call to Study How Variability in Both Virus and Host may Impact Disease

Increasing attention has focused on the contributions of persistent microbial infections with the manifestation of disease later in life, including neurodegenerative conditions such as Alzheimer’s disease (AD). Current data has shown the presence of herpes simplex virus 1 (HSV-1) in regions of the brain that are impacted by AD in elderly individuals. Additionally, neuronal infection with HSV-1 triggers the accumulation of amyloid beta deposits and hyperphosphorylated tau, and results in oxidative stress and synaptic dysfunction. All of these factors are implicated in the development of AD. These data highlight the fact that persistent viral infection is likely a contributing factor, rather than a sole cause of disease. Details of the correlations between HSV-1 infection and AD development are still just beginning to emerge. Future research should investigate the relative impacts of virus strain- and host-specific factors on the induction of neurodegenerative processes over time, using models such as infected neurons in vitro, and animal models in vivo, to begin to understand their relationship with cognitive dysfunction.

Amyloid beta peptides, locus coeruleus-norepinephrine system and dense core vesicles

The evolution of peptidergic signaling systems in the central nervous system serves a distinct and crucial role in brain processes and function. The diversity of physiological peptides and the complexity of their regulation and secretion from the dense core vesicles (DCV) throughout the brain is a topic greatly in need of investigation, though recent years have shed light on cellular and molecular mechanisms that are summarized in this review. Here, we focus on the convergence of peptidergic systems onto the Locus Coeruleus (LC), the sole provider of norepinephrine (NE) to the cortex and hippocampus, via large DCV. As the LC-NE system is one of the first regions of the brain to undergo degeneration in Alzheimer's Disease (AD), and markers of DCV have consistently been demonstrated to have biomarker potential for AD progression, here we summarize the current literature linking the LC-NE system with DCV dysregulation and Aβ peptides. We also include neuroanatomical data suggesting that the building blocks of senile plaques, Aβ monomers, may be localized to DCV of the LC and noradrenergic axon terminals of the prefrontal cortex. Finally, we explore the putative consequences of chronic stress on Aβ production and the role that DCV may play in LC degeneration. Clinical data of immunological markers of DCV in AD patients are discussed.

Molecular Mechanisms for Herpes Simplex Virus Type 1 Pathogenesis in Alzheimer's Disease

This review focuses on research in the areas of epidemiology, neuropathology, molecular biology and genetics that implicates herpes simplex virus type 1 (HSV-1) as a causative agent in the pathogenesis of sporadic Alzheimer’s disease (AD). Molecular mechanisms whereby HSV-1 induces AD-related pathophysiology and pathology, including neuronal production and accumulation of amyloid beta (Aβ), hyperphosphorylation of tau proteins, dysregulation of calcium homeostasis, and impaired autophagy, are discussed. HSV-1 causes additional AD pathologies through mechanisms that promote neuroinflammation, oxidative stress, mitochondrial damage, synaptic dysfunction, and neuronal apoptosis. The AD susceptibility genes apolipoprotein E (APOE), phosphatidylinositol binding clathrin assembly protein (PICALM), complement receptor 1 (CR1) and clusterin (CLU) are involved in the HSV lifecycle. Polymorphisms in these genes may affect brain susceptibility to HSV-1 infection. APOE, for example, influences susceptibility to certain viral infections, HSV-1 viral load in the brain, and the innate immune response. The AD susceptibility gene cholesterol 25-hydroxylase (CH25H) is upregulated in the AD brain and is involved in the antiviral immune response. HSV-1 interacts with additional genes to affect cognition-related pathways and key enzymes involved in Aβ production, Aβ clearance, and hyperphosphorylation of tau proteins. Aβ itself functions as an antimicrobial peptide (AMP) against various pathogens including HSV-1. Evidence is presented supporting the hypothesis that Aβ is produced as an AMP in response to HSV-1 and other brain infections, leading to Aβ deposition and plaque formation in AD. Epidemiologic studies associating HSV-1 infection with AD and cognitive impairment are discussed. Studies are reviewed supporting subclinical chronic reactivation of latent HSV-1 in the brain as significant in the pathogenesis of AD. Finally, the rationale for and importance of clinical trials treating HSV-1-infected MCI and AD patients with antiviral medication is discussed.

Mitochondrial Dysfunction and Synaptic Transmission Failure in Alzheimer's Disease

Alzheimer's disease (AD) is a chronic neurodegenerative disorder, in which multiple risk factors converge. Despite the complexity of the etiology of the disease, synaptic failure is the pathological basis of cognitive impairment, the cardinal sign of AD. Decreased synaptic density, compromised synaptic transmission, and defected synaptic plasticity are hallmark synaptic pathologies accompanying AD. However, the mechanisms by which synapses are injured in AD-related conditions have not been fully elucidated. Mitochondria are a critical organelle in neurons. The pivotal role of mitochondria in supporting synaptic function and the concomitant occurrence of mitochondrial dysfunction with synaptic stress in postmortem AD brains as well as AD animal models seem to lend the credibility to the hypothesis that mitochondrial defects underlie synaptic failure in AD. This concept is further strengthened by the protective effect of mitochondrial medicine on synaptic function against the toxicity of amyloid-β, a key player in the pathogenesis of AD. In this review, we focus on the association between mitochondrial dysfunction and synaptic transmission deficits in AD. Impaired mitochondrial energy production, deregulated mitochondrial calcium handling, excess mitochondrial reactive oxygen species generation and release play a crucial role in mediating synaptic transmission deregulation in AD. The understanding of the role of mitochondrial dysfunction in synaptic stress may lead to novel therapeutic strategies for the treatment of AD through the protection of synaptic transmission by targeting to mitochondrial deficits.

Amyloid Accumulation Drives Proteome-wide Alterations in Mouse Models of Alzheimer's Disease-like Pathology

Amyloid beta (Aβ) peptides impair multiple cellular pathways and play a causative role in Alzheimer's disease (AD) pathology, but how the brain proteome is remodeled by this process is unknown. To identify protein networks associated with AD-like pathology, we performed global quantitative proteomic analysis in three mouse models at young and old ages. Our analysis revealed a robust increase in Apolipoprotein E (ApoE) levels in nearly all brain regions with increased Aβ levels. Taken together with prior findings on ApoE driving Aβ accumulation, this analysis points to a pathological dysregulation of the ApoE-Aβ axis. We also found dysregulation of protein networks involved in excitatory synaptic transmission. Analysis of the AMPA receptor (AMPAR) complex revealed specific loss of TARPγ-2, a key AMPAR-trafficking protein. Expression of TARPγ-2 in hAPP transgenic mice restored AMPA currents. This proteomic database represents a resource for the identification of protein alterations responsible for AD.

Dynamic presenilin 1 and synaptotagmin 1 interaction modulates exocytosis and amyloid β production

Background

Alzheimer’s disease (AD)-linked protein, presenilin 1 (PS1), is present at the synapse, and the knock-out of presenilin in mice leads to synaptic dysfunction. On the other hand, synaptic activity was shown to influence PS1-dependent generation of distinct amyloid β (Aβ) species. However, the precise nature of these regulations remains unclear. The current study reveals novel role of PS1 at the synapse, and deciphers how PS1 and synaptic vesicle-associated protein, synaptotagmin 1 (Syt1) modulate each other functions in neurons via direct activity-triggered interaction. Additionally, the therapeutic potential of fostering PS1-Syt1 binding is investigated as a synapse-specific strategy for AD prevention.

Methods

PS1-based cell-permeable peptide targeting PS1-Syt1 binding site was designed to inhibit PS1-Syt1 interaction in neurons. PS1 conformation, synaptic vesicle exocytosis and trafficking were assayed by fluorescence lifetime imaging microscopy (FLIM), glutamate release/synaptopHluorin assay, and fluorescence recovery after photobleaching, respectively. Syt1 level and interaction with PS1 in control and sporadic AD brains were determined by immunohistochemistry and FLIM. AAV-mediated delivery of Syt1 into mouse hippocampi was used to investigate the therapeutic potential of strengthening PS1-Syt1 binding in vivo. Statistical significance was determined using two-tailed unpaired Student’s t-test, Mann-Whitney’s U-test or two-way ANOVA followed by a Bonferroni’s post-test.

Results

We demonstrate that targeted inhibition of the PS1-Syt1 binding in neurons, without changing the proteins’ expression level, triggers “pathogenic” conformational shift of PS1, and consequent increase in the Aβ42/40 ratio. Moreover, our data indicate that PS1, by binding directly to Syt1, regulates synaptic vesicle trafficking and facilitates exocytosis and neurotransmitter release. Analysis of human brain tissue revealed that not only Syt1 levels but also interactions between remaining Syt1 and PS1 are diminished in sporadic AD. On the other hand, overexpression of Syt1 in mouse hippocampi was found to potentiate PS1-Syt1 binding and promote “protective” PS1 conformation.

Conclusions

The study reports novel functions of PS1 and Syt1 at the synapse, and demonstrates the importance of PS1-Syt1 binding for exocytosis and safeguarding PS1 conformation. It suggests that reduction in the Syt1 level and PS1-Syt1 interactions in AD brain may present molecular underpinning of the pathogenic PS1 conformation, increased Aβ42/40 ratio, and impaired exocytosis.

Electronic supplementary material

The online version of this article (doi:10.1186/s13024-017-0159-y) contains supplementary material, which is available to authorized users.

The role of neuropathological markers in the interpretation of neuropsychiatric disorders: Focus on fetal and perinatal programming

The study of neuropathological markers in patients affected by mental/psychiatric disorders is relevant for the comprehension of the pathogenesis and the correlation with the clinical symptomatology. The neuropathology of Alzheimer's disease (AD) recognizes intraneuronal and extracellular neurofibrillary formation responsible for neuronal degeneration. Immunohistochemical studies discovered many interesting results for a better interpretation of the AD pathogenesis, while the "metal hypothesis" supports that metal ions might differentially influence the formation of amyloid aggregates. The most relevant pathological findings reported in schizophrenia originate from computer assisted tomography (CT), Magnetic Resonance Imaging (MRI) studies and Diffusion Tensor Imaging (DTI), suggesting the brain abnormalities involved in the pathophysiology of schizophrenia. The theory of fetal programming illustrates the epigenetic factors that may act during the intrauterine life on brain development, with relevant consequences on the susceptibility to develop AD or schizophrenia later in life. The neuropathological interpretation of AD and schizophrenia shows that the presence of severe neuropathological changes is not always associated with severe cognitive impairment. A better dialogue between psychiatrics and pathologists might help to halt insurgence and progression of neurodegenerative diseases.

Elevated Expression of the Cerebrospinal Fluid Disease Markers Chromogranin A and Clusterin in Astrocytes of Multiple Sclerosis White Matter Lesions

Using proteomics, we previously identified chromogranin A (CgA) and clusterin (CLU) as disease-related proteins in the cerebrospinal fluid (CSF) of patients with multiple sclerosis (MS). CgA and CLU are involved in cell survival and are implicated in neurodegenerative disorders and may also have roles in MS pathophysiology. We investigated CgA and CLU expression in lesions and nonlesional regions in postmortem brains of MS patients and controls and in the brains of marmosets with experimental autoimmune encephalomyelitis. By quantitative PCR, mRNA levels of CgA and CLU were elevated in white matter but not in grey matter of MS patients. In situ analyses showed greater expression of CgA and CLU in white matter lesions than in normal-appearing regions in MS patients and in the marmosets, primarily in or adjacent to perivascular spaces and inflammatory infiltrates. Both proteins were expressed by glial fibrillary acidic protein-positive astrocytes. CgA was more localized in astrocytic processes and endfeet surrounding blood vessels and was abundant in the superficial glia limitans and ependyma, 2 CSF-brain borders. Increased expression of CgA and CLU in reactive astrocytes in MS white matter lesions supports a role for these molecules as neuro-inflammatory mediators and their potential as CSF markers of active pathological processes in MS patients.

Meta-analysis of synaptic pathology in Alzheimer's disease reveals selective molecular vesicular machinery vulnerability

INTRODUCTION

Loss of synapses best correlates to cognitive deficits in Alzheimer's disease (AD) in which oligomeric neurotoxic species of amyloid-β appears to contribute synaptic pathology. Although a number of clinical pathologic studies have been performed with limited sample size, there are no systematic studies encompassing large samples. Therefore, we performed a meta-analysis study.

METHODS

We identified 417 publications reporting postmortem synapse and synaptic marker loss from AD patients. Two meta-analyses were performed using a single database of subselected publications and calculating the standard mean differences.

RESULTS

Meta-analysis confirmed synaptic loss in selected brain regions is an early event in AD pathogenesis. The second meta-analysis of 57 synaptic markers revealed that presynaptic makers were affected more than postsynaptic markers.

DISCUSSION

The present meta-analysis study showed a consistent synaptic loss across brain regions and that molecular machinery including endosomal pathways, vesicular assembly mechanisms, glutamate receptors, and axonal transport are often affected.

Loss of Munc18-1 long splice variant in GABAergic terminals is associated with cognitive decline and increased risk of dementia in a community sample

BACKGROUND

Presynaptic terminals contribute to cognitive reserve, balancing the effects of age-related pathologies on cognitive function in the elderly. The presynaptic protein Munc18-1, alternatively spliced into long (M18L) or short (M18S) isoforms, is a critical modulator of neurotransmission. While subtle alterations in Munc18-1 have been shown to cause severe neuropsychiatric disorders with cognitive impairment, little information is known regarding the specific roles of Munc18-1 splice variants. We first investigated functional and anatomical features evidencing the divergent roles of M18L and M18S, and then evaluated their contribution to the full range of age-related cognitive impairment in the dorsolateral prefrontal cortex of a large sample of participants from a community-based aging study, including subjects with no-(NCI, n = 90), or mild-(MCI, n = 86) cognitive impairment, or with clinical dementia (n = 132). Finally, we used APP23 mutant mice to study the association between M18L/S and the time-dependent accumulation of common Alzheimer's disease pathology.

RESULTS

Using isoform-specific antibodies, M18L was localized to the synaptosomal fraction, with a distribution matching lipid raft microdomains. M18S was found widely across cytosolic and synaptosomal compartments. Immunocytochemical studies identified M18L in perisomatic, GABAergic terminals, while M18S was broadly distributed in GABAergic and glutamatergic terminals. Using regression models taking into account multiple age-related pathologies, age, education and sex, global cognitive function was associated with the level of M18L (p = 0.006) but not M18S (p = 0.88). Mean M18L in dementia cases was 51 % lower than in NCI cases (p < 0.001), and each unit of M18L was associated with a lower likelihood of dementia (odds ratio = 0.68, 95 % confidence interval = 0.50-0.90, p = 0.008). In contrast, M18S balanced across clinical and pathologically diagnosed groups. M18L loss may not be caused by age-related amyloid pathology, since APP23 mice (12- and 22-months of age) had unchanged cortical levels of M18L/S compared with wild-type animals.

CONCLUSIONS

M18L was localized to presynaptic inhibitory terminals, and was associated with cognitive function and protection from dementia in an elderly, community-based cohort. Lower M18L in inhibitory presynaptic terminals may be an early, independent contributor to cognitive decline.

Tau-mediated synaptic damage in Alzheimer's disease

Synapses are the principal sites for chemical communication between neurons and are essential for performing the dynamic functions of the brain. In Alzheimer’s disease and related tauopathies, synapses are exposed to disease modified protein tau, which may cause the loss of synaptic contacts that culminate in dementia. In recent decades, structural, transcriptomic and proteomic studies suggest that Alzheimer’s disease represents a synaptic disorder. Tau neurofibrillary pathology and synaptic loss correlate well with cognitive impairment in these disorders. Moreover, regional distribution and the load of neurofibrillary lesions parallel the distribution of the synaptic loss. Several transgenic models of tauopathy expressing various forms of tau protein exhibit structural synaptic deficits. The pathological tau proteins cause the dysregulation of synaptic proteome and lead to the functional abnormalities of synaptic transmission. A large body of evidence suggests that tau protein plays a key role in the synaptic impairment of human tauopathies.

GDF-15 secreted from human umbilical cord blood mesenchymal stem cells delivered through the cerebrospinal fluid promotes hippocampal neurogenesis and synaptic activity in an Alzheimer's disease model

Our previous studies demonstrated that transplantation of human umbilical cord blood-derived mesenchymal stem cells (hUCB-MSCs) into the hippocampus of a transgenic mouse model of Alzheimer's disease (AD) reduced amyloid-β (Aβ) plaques and enhanced cognitive function through paracrine action. Due to the limited life span of hUCB-MSCs after their transplantation, the extension of hUCB-MSC efficacy was essential for AD treatment. In this study, we show that repeated cisterna magna injections of hUCB-MSCs activated endogenous hippocampal neurogenesis and significantly reduced Aβ42 levels. To identify the paracrine factors released from the hUCB-MSCs that stimulated endogenous hippocampal neurogenesis in the dentate gyrus, we cocultured adult mouse neural stem cells (NSCs) with hUCB-MSCs and analyzed the cocultured media with cytokine arrays. Growth differentiation factor-15 (GDF-15) levels were significantly increased in the media. GDF-15 suppression in hUCB-MSCs with GDF-15 small interfering RNA reduced the proliferation of NSCs in cocultures. Conversely, recombinant GDF-15 treatment in both in vitro and in vivo enhanced hippocampal NSC proliferation and neuronal differentiation. Repeated administration of hUBC-MSCs markedly promoted the expression of synaptic vesicle markers, including synaptophysin, which are downregulated in patients with AD. In addition, in vitro synaptic activity through GDF-15 was promoted. Taken together, these results indicated that repeated cisterna magna administration of hUCB-MSCs enhanced endogenous adult hippocampal neurogenesis and synaptic activity through a paracrine factor of GDF-15, suggesting a possible role of hUCB-MSCs in future treatment strategies for AD.

Locus Coeruleus, norepinephrine and Aβ peptides in Alzheimer's disease

Monoaminergic brainstem systems have widespread projections that participate in many central processes and, when dysregulated, contribute to a plethora of neuropsychiatric and neurodegenerative disorders. Synapses are the foundation of these neuronal circuits, and their local dysfunction results in global aberrations leading to pathophysiological disease states. This review focuses on the locus coeruleus (LC) norepinephrine (NE) brainstem system and its underappreciated role in Alzheimer's disease (AD). Amyloid beta (Aβ), a peptide that accumulates aberrantly in AD has recently been implicated as a modulator of neuronal excitability at the synapse. Evidence is presented showing that disruption of the LC-NE system at a synaptic and circuit level during early stages of AD, due to conditions such as chronic stress, can potentially lead to amyloid accumulation and contribute to the progression of this neurodegenerative disorder. Additional factors that impact neurodegeneration include neuroinflammation, and network de-synchronization. Consequently, targeting the LC-NE system may have significant therapeutic potential for AD, as it may facilitate modulation of Aβ production, curtail neuroinflammation, and prevent sleep and behavioral disturbances that often lead to negative patient outcomes.

Brain neuroplastic changes accompany anxiety and memory deficits in a model of complex regional pain syndrome

BACKGROUND

Complex regional pain syndrome (CRPS) is a painful condition with approximately 50,000 annual new cases in the United States. It is a major cause of work-related disability, chronic pain after limb fractures, and persistent pain after extremity surgery. Additionally, CRPS patients often experience cognitive changes, anxiety, and depression. The supraspinal mechanisms linked to these CRPS-related comorbidities remain poorly understood.

METHODS

The authors used a previously characterized mouse model of tibia fracture/cast immobilization showing the principal stigmata of CRPS (n = 8 to 20 per group) observed in humans. The central hypothesis was that fracture/cast mice manifest changes in measures of thigmotaxis (indicative of anxiety) and working memory reflected in neuroplastic changes in amygdala, perirhinal cortex, and hippocampus.

RESULTS

The authors demonstrate that nociceptive sensitization in these mice is accompanied by altered thigmotactic behaviors in the zero maze but not open field assay, and working memory dysfunction in novel object recognition and social memory but not in novel location recognition. Furthermore, the authors found evidence of structural changes and synaptic plasticity including changes in dendritic architecture and decreased levels of synaptophysin and brain-derived neurotrophic factor in specific brain regions.

CONCLUSIONS

The study findings provide novel observations regarding behavioral changes and brain plasticity in a mouse model of CRPS. In addition to elucidating some of the supraspinal correlates of the syndrome, this work supports the potential use of therapeutic interventions that not only directly target sensory input and other peripheral mechanisms, but also attempt to ameliorate the broader pain experience by modifying its associated cognitive and emotional comorbidities.

Selective distribution and dynamic modulation of miRNAs in the synapse and its possible role in Alzheimer's Disease

MicroRNAs (miRNAs) are small non-coding RNAs that control a wide range of functions in the cell. They act as post-transcriptional gene regulators throughout in development and in adulthood, although recent evidence suggests their potential role in the onset and development of various diseases and neuropathologies. In neurons miRNAs seem to play a key role as regulators of synaptic function. Synapses are vulnerable structures in neurodegenerative diseases. In particular, synaptic loss has been described as an early event in the pathogenesis of Alzheimer's Disease (AD). MicroRNA-mediated gene silencing represents a candidate event for the repression of specific mRNAs and protein synthesis that could account for synaptic dysfunction. In this work, we review the participation of miRNAs in synaptic function and consider their possible role in synaptic alterations in AD. First we review the biogenesis of miRNAs and their role as post-transcriptional regulators. Then we discuss recently published data on the distribution of miRNAs in the brain as well as their role in dynamic regulation at the synapse. In the second part, we briefly introduce the reader to AD, focusing on synaptic alterations in the progression of the pathology. Then we discuss possible implications of miRNAs in the associated synaptic dysfunction.

Role for the neurexin-neuroligin complex in Alzheimer's disease

Synaptic damage is a critical hallmark of Alzheimer's disease, and the best correlate with cognitive impairment ante mortem. Synapses, the loci of communication between neurons, are characterized by signature protein combinations arrayed at tightly apposed pre- and post-synaptic sites. The most widely studied trans-synaptic junctional complexes, which direct synaptogenesis and foster the maintenance and stability of the mature terminal, are conjunctions of presynaptic neurexins and postsynaptic neuroligins. Fluctuations in the levels of neuroligins and neurexins can sway the balance between excitatory and inhibitory neurotransmission in the brain, and could lead to damage of synapses and dendrites. This review summarizes current understanding of the roles of neurexins and neuroligins proteolytic processing in synaptic plasticity in the human brain, and outlines their possible roles in β-amyloid metabolism and function, which are central pathogenic events in Alzheimer's disease progression.

Amyloid plaque formation precedes dendritic spine loss

Amyloid-beta plaque deposition represents a major neuropathological hallmark of Alzheimer's disease. While numerous studies have described dendritic spine loss in proximity to plaques, much less is known about the kinetics of these processes. In particular, the question as to whether synapse loss precedes or follows plaque formation remains unanswered. To address this question, and to learn more about the underlying kinetics, we simultaneously imaged amyloid plaque deposition and dendritic spine loss by applying two-photon in vivo microscopy through a cranial window in double transgenic APPPS1 mice. As a result, we first observed that the rate of dendritic spine loss in proximity to plaques is the same in both young and aged animals. However, plaque size only increased significantly in the young cohort, indicating that spine loss persists even many months after initial plaque appearance. Tracking the fate of individual spines revealed that net spine loss is caused by increased spine elimination, with the rate of spine formation remaining constant. Imaging of dendritic spines before and during plaque formation demonstrated that spine loss around plaques commences at least 4 weeks after initial plaque formation. In conclusion, spine loss occurs, shortly but with a significant time delay, after the birth of new plaques, and persists in the vicinity of amyloid plaques over many months. These findings hence give further hope to the possibility that there is a therapeutic window between initial amyloid plaque deposition and the onset of structural damage at spines.

Oxidative insults to neurons and synapse are prevented by aged garlic extract and S-allyl-L-cysteine treatment in the neuronal culture and APP-Tg mouse model

Alzheimer's disease (AD) is one of the most common forms of dementia in the elderly. In AD patients, β-amyloid peptide (Aβ) plaques and neurofibrillary tangles are common features observed in the CNS. Aβ deposition results in the production of reactive oxygen species (ROS) leading to the hyperphosphorylation of tau that are associated with neuronal damage. Cholinesterase inhibitors and a partial NMDA receptor antagonist (memantine) have been identified as potential treatment options for AD. However, clinical studies have found that these drugs fail to prevent the disease progression. From ancient times, garlic (Allium sativum) has been used to treat several diseases. By 'aging' of garlic, some adverse reactions of garlic can be eliminated. Recent findings suggest that 'aged garlic extract' (AGE) may be a therapeutic agent for AD because of its antioxidant and Aβ lowering properties. To date, the molecular properties of AGE have been sparsely studied in vitro or in vivo. The present study tested specific biochemical and molecular effects of AGE in neuronal and AD rodent models. Furthermore, we identified S-allyl-L-cysteine (SAC) as one of the most active chemicals responsible for the AGE-mediated effect(s). We observed significant neuroprotective and neurorescue properties of AGE and one of its ingredients, SAC, from ROS (H(2)O(2))-mediated insults to neuronal cells. Treatment of AGE and SAC were found to protect neuronal cells when they were independently co-treated with ROS. Furthermore, a novel neuropreservation effect of AGE was detected in that pre-treatment with AGE alone protected ∼ 80% neuronal cells from ROS-mediated damage. AGE was also found to preserve pre-synaptic protein synaptosomal associated protein of 25 kDa (SNAP25) from ROS-mediated insult. For example, treatment with 2% AGE containing diet and SAC (20 mg/kg of diet) independently increased (∼70%) levels of SNAP25 and synaptophysin in Alzheimer's amyloid precursor protein-transgenic mice, of which the latter was significantly decreased in AD. Taken together, the neuroprotective, including preservation of pre-synaptic proteins by AGE and SAC can be utilized in future drug development in AD.

Chromogranin peptides in brain diseases

Synaptic disturbances may play a key role in the pathophysiology of neuropsychiatric diseases. In this article, we review immunohistological findings of chromogranin peptides in neurodegenerative and neurodevelopmental disorders, with particular emphasis on Alzheimer's disease, the disorder chromogranins have been studied most extensively. Data was collected from existing and new experimental data and medline research. This review focuses on synaptic changes elicited by chromogranin peptides immunoreactivity in Alzheimer's disease, as well in schizophrenia and amyotrophic lateral sclerosis (ALS). An imbalanced availability of chromogranin peptides may be responsible for impaired neurotransmission and a reduced functioning of dense core vesicles. Since chromogranin A was postulated as a potent proinflammatory agent, we focused on chromogranin A in neuroinflammation in Alzheimer's disease and ALS. Further understanding of role and function of chromogranin peptides in neuropathological conditions is still required.

Identification and validation of novel cerebrospinal fluid biomarkers for staging early Alzheimer's disease

BACKGROUND

Ideally, disease modifying therapies for Alzheimer disease (AD) will be applied during the 'preclinical' stage (pathology present with cognition intact) before severe neuronal damage occurs, or upon recognizing very mild cognitive impairment. Developing and judiciously administering such therapies will require biomarker panels to identify early AD pathology, classify disease stage, monitor pathological progression, and predict cognitive decline. To discover such biomarkers, we measured AD-associated changes in the cerebrospinal fluid (CSF) proteome.

METHODS AND FINDINGS

CSF samples from individuals with mild AD (Clinical Dementia Rating [CDR] 1) (n = 24) and cognitively normal controls (CDR 0) (n = 24) were subjected to two-dimensional difference-in-gel electrophoresis. Within 119 differentially-abundant gel features, mass spectrometry (LC-MS/MS) identified 47 proteins. For validation, eleven proteins were re-evaluated by enzyme-linked immunosorbent assays (ELISA). Six of these assays (NrCAM, YKL-40, chromogranin A, carnosinase I, transthyretin, cystatin C) distinguished CDR 1 and CDR 0 groups and were subsequently applied (with tau, p-tau181 and Aβ42 ELISAs) to a larger independent cohort (n = 292) that included individuals with very mild dementia (CDR 0.5). Receiver-operating characteristic curve analyses using stepwise logistic regression yielded optimal biomarker combinations to distinguish CDR 0 from CDR>0 (tau, YKL-40, NrCAM) and CDR 1 from CDR<1 (tau, chromogranin A, carnosinase I) with areas under the curve of 0.90 (0.85-0.94 95% confidence interval [CI]) and 0.88 (0.81-0.94 CI), respectively.

CONCLUSIONS

Four novel CSF biomarkers for AD (NrCAM, YKL-40, chromogranin A, carnosinase I) can improve the diagnostic accuracy of Aβ42 and tau. Together, these six markers describe six clinicopathological stages from cognitive normalcy to mild dementia, including stages defined by increased risk of cognitive decline. Such a panel might improve clinical trial efficiency by guiding subject enrollment and monitoring disease progression. Further studies will be required to validate this panel and evaluate its potential for distinguishing AD from other dementing conditions.

Chromogranin A detection in saliva of type 2 diabetes patients

Chromogranin A is present in secretion granules of nerve, endocrine and immune cells and is a precursor of several peptides with antibacterial and antifungal properties at micromolar concentrations.Our aim in this prospective, double blind study, was to determine the expression of chromogranin A and its peptides at protein level in saliva of type 2 diabetic patients and thereby to obtain a new non-invasive diagnostic means for the future.Saliva was taken from 30 type 2 diabetic patients and 30 healthy individuals at the same time interval in the morning without any oral stimuli. Circadianic periodics in protein productions have been avoided. The presence of chromogranin A and its derived peptides was determined in whole saliva, after centrifugation at 40C for 12 min at 14 000 rpm, by SDS-PAGE electrophoresis and Immunoblotting (Western Blot). To ensure same protein concentrations Bradford protein quantification assay has been performed before.For the first time, we have determined an overexpression of chromogranin A in saliva of diabetic patients in 100% of the individuals. Chromogranin A, a circulating biomarker for epithelial tumours, is also overexpressed in saliva of type 2 diabetic patients. To confirm our results, more studies with a large amount of patients is necessary.

Synaptic degeneration in Alzheimer's disease

Synaptic loss is the major neurobiological substrate of cognitive dysfunction in Alzheimer's disease (AD). Synaptic failure is an early event in the pathogenesis that is clearly detectable already in patients with mild cognitive impairment (MCI), a prodromal state of AD. It progresses during the course of AD and in most early stages involves mechanisms of compensation before reaching a stage of decompensated function. This dynamic process from an initially reversible functionally responsive stage of down-regulation of synaptic function to stages irreversibly associated with degeneration might be related to a disturbance of structural brain self-organization and involves morpho-regulatory molecules such as the amyloid precursor protein. Further, recent evidence suggests a role for diffusible oligomers of amyloid beta in synaptic dysfunction. To form synaptic connections and to continuously re-shape them in a process of ongoing structural adaptation, neurons must permanently withdraw from the cell cycle. Previously, we formulated the hypothesis that differentiated neurons after having withdrawn from the cell cycle are able to use molecular mechanisms primarily developed to control proliferation alternatively to control synaptic plasticity. The existence of these alternative effector pathways within neurons might put them at risk of erroneously converting signals derived from plastic synaptic changes into the program of cell cycle activation, which subsequently leads to cell death. The molecular mechanisms involved in cell cycle activation might, thus, link aberrant synaptic changes to cell death.

Alzheimer's disease is type 3 diabetes-evidence reviewed

Alzheimer's disease (AD) has characteristic histopathological, molecular, and biochemical abnormalities, including cell loss; abundant neurofibrillary tangles; dystrophic neurites; amyloid precursor protein, amyloid-beta (APP-Abeta) deposits; increased activation of prodeath genes and signaling pathways; impaired energy metabolism; mitochondrial dysfunction; chronic oxidative stress; and DNA damage. Gaining a better understanding of AD pathogenesis will require a framework that mechanistically interlinks all these phenomena. Currently, there is a rapid growth in the literature pointing toward insulin deficiency and insulin resistance as mediators of AD-type neurodegeneration, but this surge of new information is riddled with conflicting and unresolved concepts regarding the potential contributions of type 2 diabetes mellitus (T2DM), metabolic syndrome, and obesity to AD pathogenesis. Herein, we review the evidence that (1) T2DM causes brain insulin resistance, oxidative stress, and cognitive impairment, but its aggregate effects fall far short of mimicking AD; (2) extensive disturbances in brain insulin and insulin-like growth factor (IGF) signaling mechanisms represent early and progressive abnormalities and could account for the majority of molecular, biochemical, and histopathological lesions in AD; (3) experimental brain diabetes produced by intracerebral administration of streptozotocin shares many features with AD, including cognitive impairment and disturbances in acetylcholine homeostasis; and (4) experimental brain diabetes is treatable with insulin sensitizer agents, i.e., drugs currently used to treat T2DM. We conclude that the term "type 3 diabetes" accurately reflects the fact that AD represents a form of diabetes that selectively involves the brain and has molecular and biochemical features that overlap with both type 1 diabetes mellitus and T2DM.

Postsynaptic density protein PSD-95 expression in Alzheimer's disease and okadaic acid induced neuritic retraction

In order to understand how plasticity is related to neurodegeneration, we studied synaptic proteins with quantitative immunohistochemistry in the entorhinal cortex from Alzheimer patients and age-matched controls. We observed a significant decrease in presynaptic synaptophysin and an increase in postsynaptic density protein PSD-95, positively correlated with beta amyloid and phosphorylated Tau proteins in Alzheimer cases. Furthermore, Alzheimer-like neuritic retraction was generated in okadaic acid (OA) treated SH-SY5Y neuroblastoma cells with no decrease in PSD-95 expression. However, in a SH-SY5Y clone with decreased expression of transcription regulator LMO4 (as observed in Alzheimer's disease) and increased neuritic length, PSD-95 expression was enhanced but did not change with OA treatment. Therefore, increased PSD-95 immunoreactivity in the entorhinal cortex might result from compensatory mechanisms, as in the SH-SY5Y clone, whereas increased Alzheimer-like Tau phosphorylation is not related to PSD-95 expression, as suggested by the OA-treated cell models.

A novel panel of cerebrospinal fluid biomarkers for the differential diagnosis of Alzheimer's disease versus normal aging and frontotemporal dementia

BACKGROUND

An early and accurate diagnosis of Alzheimer's disease (AD) is important in order to initiate symptomatic treatment with currently approved drugs and will be of even greater importance with the advent of disease-modifying compounds.

METHODS

Protein profiles of human cerebrospinal fluid samples from patients with AD (n = 85), frontotemporal dementia (n = 20), and healthy controls (n = 32) were analyzed by surface-enhanced laser desorption/ionization time-of-flight mass spectrometry to verify previously discovered biomarkers.

RESULTS

We verified 15 protein biomarkers that were able to differentiate between AD and controls, and 7 of these 15 markers also differentiated AD from FTD.

CONCLUSION

A panel of cerebrospinal fluid protein markers was verified by a proteomics technology which may potentially improve the accuracy of the AD diagnosis.

Synaptic proteins, neuropathology and cognitive status in the oldest-old

An increasing number of individuals in our population are surviving to over 90 years and a subset is at risk for developing dementia. However, senile plaque and neurofibrillary tangle pathology do not consistently differentiate individuals with and without dementia. Synaptic protein loss is a feature of aging and dementia and may dissociate 90+ individuals with and without dementia. Synaptophysin (SYN), postsynaptic density 95 (PSD-95) and growth-associated protein 43 (GAP-43) were studied in the frontal cortex of an autopsy series of 32 prospectively followed individuals (92-105 years) with a range of cognitive function. SYN protein levels were decreased in individuals with dementia and increased in those with clinical signs of cognitive impairment insufficient for a diagnosis of dementia. SYN but neither PSD-95 nor GAP-43 protein levels were significantly correlated with mini-mental status examination (MMSE) scores. Frontal cortex SYN protein levels may protect neuronal function in oldest-old individuals and reflect compensatory responses that may be involved with maintaining cognition.

Selective loss of synaptic proteins in Alzheimer's disease: evidence for an increased severity with APOE varepsilon4

A pathological feature of Alzheimer's disease (AD) is an area-specific neuronal loss that may be caused by excitotoxicity-related synaptic dysfunction. Relative expression levels of synaptophysin, dynamin I, complexins I and II, N-cadherin, and alphaCaMKII were analysed in human brain tissue from AD cases and controls in hippocampus, and inferior temporal and occipital cortices. Synaptophysin and dynamin I are presynaptic terminal proteins not specific to any neurotransmitter system whereas complexin II, N-cadherin, and alphaCaMKII are specific for excitatory synapses. Complexin I is a presynaptic protein localised to inhibitory synapses. There were no significant differences in synaptophysin, dynamin I, N-cadherin, or alphaCaMKII protein levels between AD cases and controls. The complexin proteins were both markedly lower in AD cases than in controls (P < 0.01). Cases were also categorised by APOE genotype. Averaged across areas there was a 36% lowering of presynaptic proteins in AD cases carrying at least one epsilon4 allele compared with in AD cases lacking the epsilon4 allele. We infer that synaptic protein level is not indicative of neuronal loss, but the synaptic dysfunction may result from the marked relative loss of the complexins in AD, and lower levels of presynaptic proteins in AD cases with the APOE epsilon4 allele.

Differential expression of synaptic proteins in the frontal and temporal cortex of elderly subjects with mild cognitive impairment

Alterations in synaptic protein stoichiometry may contribute to neocortical synaptic dysfunction in Alzheimer disease (AD). Whether perturbations in synaptic protein expression occur during the earliest stages of cognitive decline remain unclear. We examined protein levels of synaptophysin (SYP), synaptotagmin (SYT), and drebrin (DRB) in 5 neocortical regions (anterior cingulate, superior frontal, superior temporal, inferior parietal, and visual) of people clinically diagnosed with no cognitive impairment (NCI), mild cognitive impairment (MCI), mild/moderate AD, or severe AD. Normalized SYP levels were decreased approximately 35% in the superior temporal and inferior parietal cortex in severe AD compared with NCI. SYT levels were unchanged across clinical diagnosis in the cortical regions. Levels of DRB, a dendritic spine plasticity marker, were reduced approximately 40% to 60% in all cortical regions in AD compared with NCI. DRB protein was also reduced approximately 35% in the superior temporal cortex of MCI subjects, and DRB and SYP levels in the superior temporal cortex correlated with Mini-Mental State Examination and Braak scores. In contrast, DRB levels in the superior frontal cortex increased approximately 30% in MCI subjects. The differential changes in DRB expression in the frontal and temporal cortex in MCI suggest a disparity of dendritic plasticity within these regions that may contribute to the early impairment of temporal cortical functions subserving memory and language compared with the relative preservation of frontal cortical executive function during the initial stages of cognitive decline.

Neuropathology of Alzheimer's disease

In 1907, Alois Alzheimer described the presence of plaques and neurofibrillary tangles in a demented patient. Currently, Alzheimer's disease is known to be the most common cause of dementia in elderly patients. In this article, we summarize the most important neuropathologic features of Alzheimer's disease, including amyloid plaques, neurofibrillary tangles, neuronal loss, synaptic depletion, cerebral amyloid angiopathy, Hirano bodies, and granulovacuolar degeneration. We also review the history and application of Alzheimer's disease diagnostic criteria.

Cellular responses to protein accumulation involve autophagy and lysosomal enzyme activation

Protein oligomerization and aggregation are key events in age-related neurodegenerative disorders, causing neuronal disturbances including microtubule destabilization, transport failure and loss of synaptic integrity that precede cell death. The abnormal buildup of proteins can overload digestive systems and this, in turn, activates lysosomes in different disease states and stimulates the inducible class of lysosomal protein degradation, macroautophagy. These responses were studied in a hippocampal slice model well known for amyloidogenic species, tau aggregates, and ubiquitinated proteins in response to chloroquine-mediated disruption of degradative processes. Chloroquine was found to cause a pronounced appearance of prelysosomal autophagic vacuoles in pyramidal neurons. The vacuoles and dense bodies were concentrated in the basal pole of neurons and in dystrophic neurites. In hippocampal slice cultures treated with Abeta(142), ultrastructural changes were also induced. Autophagic responses may be an attempt to compensate for protein accumulation, however, they were not sufficient to prevent axonopathy indicated by swellings, transport deficits, and reduced expression of synaptic components. Additional chloroquine effects included activation of cathepsin D and other lysosomal hydrolases. Abeta(142) produced similar lysosomal activation, and the effects of Abeta(142) and chloroquine were not additive, suggesting a common mechanism. Activated levels of cathepsin D were enhanced with the lysosomal modulator Z-Phe-Ala-diazomethylketone (PADK). PADK-mediated lysosomal enhancement corresponded with the restoration of synaptic markers, in association with stabilization of microtubules and transport capability. To show that PADK can modulate the lysosomal system in vivo, IP injections were administered over a 5-day period, resulting in a dose-dependent increase in lysosomal hydrolases. The findings indicate that degradative responses can be modulated to promote synaptic maintenance.

Inhibition of microglia multinucleated giant cell formation and induction of differentiation by GM-CSF using a porcine in vitro model

Multinucleated giant cell (MNGC) formation is an important histopathologic feature of AIDS dementia complex and tuberculous meningitis. We investigated the effect of several cytokines (GM-CSF, IFN-gamma, TNF-alpha, IL-3) and other stimuli (vaso-I, LPS, PMA) on MNGC formation in vitro by microglia from porcine neonatal brain. GM-CSF dose-dependently inhibited giant cell formation at physiological conditions (10 ng/ml) up till 4 days in culture. When confronted with a high concentration (1 microg/ml) they were 5.5 times less likely to form MNGC and 3.3 times more likely to develop a ramified morphology. In contrast, interferon-gamma (6 ng/ml) doubled the formation of MNGC. GM-CSF primed (4 days) microglia also produced significantly higher amounts of superoxide after PMA-stimulation. We conclude that GM-CSF leads microglia to a specific activation other than MNGC formation. Comparison of the present results with earlier reports on rodents reveals important inter-species differences.

Neuronal structure is altered by amyloid plaques

During the course of Alzheimer's disease (AD), neurons undergo extensive remodeling, contributing to the loss of function observed in the disease. Many brain regions in patients with AD show changes in axonal and dendritic fields, dystrophic neurites, synapse loss, and neuron loss. Accumulation of amyloid-beta protein, a pathological hallmark of the disease, contributes to many of these alterations of neuronal structure. Areas of the brain displaying a high degree of plasticity are particularly vulnerable to degeneration in Alzheimer's disease. This article describes neuronal changes that occur in AD, reviews evidence that amyloid-beta contributes to these changes, and finally discusses the recovery of amyloid-induced changes in the brains of transgenic mice, lending hope to the idea that therapeutic strategies which reduce amyloid-beta production will lead to functional recovery in patients with AD.

The expression of calcium/calmodulin-dependent protein kinase II-α in the hippocampus of patients with Alzheimer's disease and its links with AD-related pathology

Alzheimer's disease (AD) is characterized pathologically by selective neuronal loss and by the formation of neurofibrillary tangles (NFTs) and senile plaques (SPs). Since calcium/calmodulin-dependent protein kinase II-alpha (CaMKII-alpha), one of the most abundant kinases in the brain, is involved in the phosphorylation of tau and amyloid precursor protein (APP), we examined the expression of CaMKII-alpha and its relationships with the neuropathology in the hippocampus of AD patients using immunohistochemistry and double-labeling immunofluorescence methods. The results showed that CaMKII-alpha containing neurons were selectively lost in the CA1 subfield of AD hippocampus and accompanied with enhanced immunoreactivity in the remaining neurons. About 33% hyperphosphorylated tau-containing neurons labeled by monoclonal antibody AT-8 were also immunoreactive for CaMKII-alpha. Moreover, we found for the first time that the immunoreactivity of CaMKII-alpha was largely deposited in the SPs of the AD hippocampus. The pattern of the co-localization of CaMKII-alpha with beta amyloid depended on the type of SPs. Since the co-localization of CaMKII-alpha with hyperphosphorylated tau is relatively rare, we concluded that CaMKII-alpha may be related with beta-amyloid more closely than being involved in tau hyperphosphorylation.

Amyloid-β-stimulated plasminogen activation by tissue-type plasminogen activator results in processing of neuroendocrine factors

Alzheimer's disease brain is characterized by the abundant presence of amyloid deposits. Accumulation of the major constituent of these deposits, amyloid-beta (Abeta), has been associated with decreased neurotransmission, increased neuronal cell death, and with cognitive decline. The mechanisms underlying these phenomena have not yet been fully elucidated. We have previously shown that amyloid peptides like Abeta bind tissue-type plasminogen activator (tPA) and cause enhanced plasmin production. Here we describe the identification of five major neuronal cell-produced Abeta-associated proteins and how Abeta-stimulated plasmin formation affects their processing. These five proteins are all neuroendocrine factors (NEFs): chromogranins A, B and C; truncated chromogranin B; and VGF. Plasminogen caused processing of Abeta-bound (but not soluble) tPA, chromogranin B and VGF and the degradation products were released from Abeta. Processing of the neuroendocrine factors was dependent on tPA as it was largely abrogated in tPA-/- cells or in the presence of a specific tPA-inhibitor. If plasmin indeed produces NEF-derived peptides in vivo, some of these peptides may have biological activity, for instance in regulating neurotransmitter release that may affect the pathology of Alzheimer's disease.

Alzheimer's disease as a disorder of dynamic brain self-organization

Mental function is based on the dynamic organization of neuronal networks. In particular, phylogenetically young brain areas (e.g., cortical associative circuits), involved in the realization of "higher brain functions" such as learning, memory, perception, self-awareness, and consciousness, are continuously re-adjusted even after development is completed. By this life-long self-optimization process, epigenetic information remodels the cognitive, behavioral and emotional reactivity of an individual to meet the environmental demands. To organize brain structures of increasing complexity during evolution, the process of selective dynamic stabilization and destabilization of synaptic connections becomes more and more important. The mechanisms of structural stabilization and labilization underlying a lifelong synaptic remodeling according to experience, are accompanied, however, by an increasing inherent potential of failure and may, thus, not only allow for the evolutionary acquisition of "higher brain function" but at the same time may provide the basis for selective neuronal vulnerability. The mechanisms of synaptic plasticity, i.e., of modifiable interneuronal connectivity, are largely based on external morphoregulatory cues and internal signaling pathways that nonneuronal cells have phylogenetically acquired to sense their relationship to the local neighborhood and to control proliferation and differentiation in the process of tissue repair and regeneration after development is completed. Differentiated neurons that have withdrawn from the cell cycle use these molecular machinery alternatively to control synaptic plasticity. The existence of these alternative effector pathways within a neuron puts it on the risk to erroneously convert signals derived from plastic synaptic changes into positional cues that will activate the cell cycle. This cell cycle activation potentially links synaptic plasticity to cell death. Preventing cell cycle activation by locking neurons in a differentiated but still highly plastic phenotype will, thus, be crucial to prevent neurodegeneration.

Chromogranin peptides in Alzheimer's disease

Synaptic disturbances may play a key role in the pathophysiology of Alzheimer's disease. To characterize differential synaptic alterations in the brains of Alzheimer patients, chromogranin A, chromogranin B and secretoneurin were applied as soluble constituents for large dense core vesicles, synaptophysin as a vesicle membrane marker and calbindin as a cytosolic protein. In controls, chromogranin B and secretogranin are largely co-contained in interneurons, whereas chromogranin A is mostly found in pyramidal neurons. In Alzheimer's disease, about 30% of beta-amyloid plaques co-labelled with chromogranin A, 20% with secretoneurin and 15% with chromogranin B. Less than 5% of beta-amyloid plaques contained synaptophysin or calbindin, respectively. Semiquantitative immunohistochemistry revealed a significant loss for chromogranin B- and secretoneurin-like immunoreactivity in the dorsolateral, the entorhinal, and orbitofrontal cortex. Chromogranin A displayed more complex changes. It was the only chromogranin peptide to be expressed in glial fibrillary acidic protein containing cells. About 40% of chromogranin A immunopositive plaques and extracellular deposits were surrounded and pervaded by activated microglia. The present study demonstrates a loss of presynaptic proteins involved in distinct steps of exocytosis. An imbalanced availability of chromogranins may be responsible for impaired neurotransmission and a reduced functioning of dense core vesicles. Chromogranin A is likely to be a mediator between neuronal, glial and inflammatory mechanisms found in Alzheimer disease.

Selective PrP-like protein, doppel immunoreactivity in dystrophic neurites of senile plaques in Alzheimer's disease

Doppel (Dpl) is a prion-like protein encoded by the gene PRND, which has been found downstream of the prion gene PRNP in several species. The present study examines by immunohistochemistry Dpl expression in brain samples from 10 patients with Alzheimer's disease (AD), three patients with Pick's disease, four patients with Parkinson's disease, eight patients with diffuse Lewy body disease (DLBD), six patients with sporadic Creutzfeldt-Jakob disease (CJD) methionine/methionine at the codon 129, two patients with sporadic CJD methionine/valine at the codon 129 and numerous kuru plaques in the cerebellum, one patient with fatal familial insomnia (FFI), and 10 age-matched controls. In the adult human brain, Dpl immunoreactivity was restricted to scattered granule cells of the cerebellum and scattered small granules in the cerebral cortex. Dpl immunoreactivity was seen around betaA4 amyloid deposits in neuritic plaques, but not in diffuse plaques, AD and the common form of DLBD. Neurofibrillary tangles, Pick bodies and Lewy bodies were not stained with anti-Dpl antibodies. No modifications in Dpl immunoreactivity were observed in CJD excepting those associated with accompanying senile plaques. No Dpl-positive deposits were seen in FFI. Whether Dpl in neuritic plaques may attenuate amyloid-induced oxidative stress and participate in the glial response around amyloid cores is discussed in light of the few available data on Dpl functions.

Cycles of aberrant synaptic sprouting and neurodegeneration in Alzheimer's and dementia with Lewy bodies

Alzheimer's disease (AD) and dementia with Lewy bodies (DLB) are the most common neurodegenerative disorders affecting the elderly. The cognitive and motor deficits in these diseases are associated with the disruption of neuritic substructure, loss of synaptic contacts in selectively vulnerable circuitries, and aberrant sprouting. Where as in AD, accumulation of misfolded forms of Abeta triggers neurodegeneration, in DLB accumulation of alpha-synuclein might play a central role. The mechanisms by which oligomeric forms of these proteins might lead to cycles of synapse loss and aberrant sprouting are currently under investigation. Several possibilities are being considered, including mitochondrial damage, caspase activation, lysosomal leakage, fragmentation of the Golgi apparatus, interference with synaptic vesicle transport and function, and interference with gene transcription and signaling. Among them, recent lines of research support the possibility that alterations in signaling pathways such extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK) and p38 relevant to synaptic plasticity and cell survival might play a pivotal role. A wide range of cellular functions are affected by the accumulation of misfolded Abeta and alpha-synuclein; thus it is possible that a more fundamental cellular alteration may underlie the mechanisms of synaptic pathology in these disorders. Among them, one possibility is that scaffold proteins, such as caveolin and JNK-interacting protein (JIP), which are necessary to integrate signaling pathways, are affected, leading to cycles of synapse loss and aberrant sprouting. This is significant because both caveolar dysfunction and altered axonal plasticity might be universally important in the pathogenesis of various neurodegenerative disorders, and therefore these signaling pathways might be common therapeutic targets for these devastating diseases.

The impact of Aβ-plaques on cortical cholinergic and non-cholinergic presynaptic boutons in alzheimer's disease-like transgenic mice

A previous study in our laboratory, involving early stage, amyloid pathology in 8-month-old transgenic mice, demonstrated a selective loss of cholinergic terminals in the cerebral and hippocampal cortices of doubly transgenic (APP(K670N,M671L)+PSl(M146L)) mice, an up-regulation in the single mutant APP(K670N,M671L) mice and no detectable change in the PSl(M146L) transgenics [J Neurosci 19 (1999) 2706]. The present study investigates the impact of amyloid plaques on synaptophysin and vesicular acetylcholine transporter (VAChT) immunoreactive bouton numbers in the frontal cortex of the three transgenic mouse models previously described. When compared as a whole, the frontal cortices of transgenic and control mice show no observable differences in the densities of synaptophysin-immunoreactive boutons. An individual comparison of layer V of the frontal cortex, however, shows a significant increase in density in transgenic models. Analysis of the cholinergic system alone shows significant alterations in the VAChT-immunoreactive bouton densities as evidenced by an increased density in the single (APP(K670N,M671L)) transgenics and a decreased density in the doubly transgenics (APP(K670N,M671L)+PSl(M146L)). In investigating the impact of plaque proximity on bouton density at early stages of the amyloid pathology in our doubly (APP(K670N,M671L)+PSl(M146L)) transgenic mouse line, we observed that plaque proximity reduced cholinergic pre-synaptic bouton density by 40%, and yet increased synaptophysin-immunoreactive pre-synaptic bouton density by 9.5%. Distance from plaques (up to 60 microm) seemed to have no effect on bouton density; however a significant inverse relationship was visible between plaque size and cholinergic pre-synaptic bouton density. Finally, the number of cholinergic dystrophic neurites surrounding the truly amyloid, Thioflavin-S(+) plaque core, was disproportionately large with respect to the incidence of cholinergic boutons within the total pre-synaptic bouton population. Confocal and electron microscopic observations confirmed the preferential infiltration of dystrophic cholinergic boutons into fibrillar amyloid aggregates. We therefore hypothesize that extracellular Abeta aggregation preferentially affects cholinergic terminations prior to progression onto other neurotransmitter systems. This is supported by the observable presence of non-cholinergic sprouting, which may be representative of impending neuritic degeneration.

Different chromogranin immunoreactivity between prion and a-beta amyloid plaque

Brain lesions in Creutzfeldt-Jakob disease (CJD) include spongiform change, neuronal loss, amyloid plaques, astrogliosis and microglial activation. Microglia are thought to play a key role in prion-induced neurodegeneration. However, the intermediate molecules supporting relationships between neurons and microglia are still unknown. Chromogranins (Cg) are soluble glycophosphoproteins that can activate microglial cells leading to a neurotoxic phenotype. The immunoreactive patterns of CgA and CgB were investigated in CJD and compared to those observed in Alzheimer's disease. We found that CgB, but not CgA, immunoreactivity was selectively associated with prion protein deposits, whereas CgA was only seen in Abeta plaques. This suggests a specific influence of the constitutive amyloid protein on chromogranin secretion and a role of CgB in the CJD neurodegenerative process.