The morphologic and neurochemical basis of dementia: aging, hierarchical patterns of lesion distribution and vulnerable neuronal phenotype

The Role of Extracellular Matrix in Human Neurodegenerative Diseases

The dense neuropil of the central nervous system leaves only limited space for extracellular substances free. The advent of immunohistochemistry, soon followed by advanced diagnostic tools, enabled us to explore the biochemical heterogeneity and compartmentalization of the brain extracellular matrix in exploratory and clinical research alike. The composition of the extracellular matrix is critical to shape neuronal function; changes in its assembly trigger or reflect brain/spinal cord malfunction. In this study, we focus on extracellular matrix changes in neurodegenerative disorders. We summarize its phenotypic appearance and biochemical characteristics, as well as the major enzymes which regulate and remodel matrix establishment in disease. The specifically built basement membrane of the central nervous system, perineuronal nets and perisynaptic axonal coats can protect neurons from toxic agents, and biochemical analysis revealed how the individual glycosaminoglycan and proteoglycan components interact with these molecules. Depending on the site, type and progress of the disease, select matrix components can either proactively trigger the formation of disease-specific harmful products, or reactively accumulate, likely to reduce tissue breakdown and neuronal loss. We review the diagnostic use and the increasing importance of medical screening of extracellular matrix components, especially enzymes, which informs us about disease status and, better yet, allows us to forecast illness.

Gami-Chunghyuldan ameliorates memory impairment and neurodegeneration induced by intrahippocampal Aβ 1-42 oligomer injection

Soluble oligomeric forms of amyloid beta (AβO) are regarded as a main cause of synaptic and cognitive dysfunction in Alzheimer's disease (AD) and have been a primary target in the development of drug treatments for AD. The present study utilized a mouse model of AD induced by intrahippocampal injection of AβO (10 μM) to investigate the effects of Gami-Chunghyuldan (GCD), a standardized multi-herbal medicinal formula, on the presentation of memory deficits and neurohistological pathogenesis. GCD (10 and 50mg/kg/day, 5 days, p.o.) improved AβO-induced memory impairment as well as reduced neuronal cell death, astrogliosis, and microgliosis in the hippocampus. In addition, GCD prevented AβO-triggered synaptic disruption and cholinergic fiber loss. These results suggest that GCD may be useful in the prevention and treatment of AD.

The Geneva brain collection

The University of Geneva brain collection was founded at the beginning of the 20th century. Today, it consists of 10,154 formaldehyde- or buffered formaldehyde-fixed brains obtained from the autopsies of the Department of Psychiatry and, since 1971, from the Department of Geriatrics. More than 100,000 paraffin-embedded blocks and 200,000 histological slides have also been collected since 1901. From the time of its creation, this collection has served as an important resource for pathological studies and clinicopathological correlations, primarily in the field of dementing illnesses and brain aging research. These materials have permitted a number of original neuropathological observations, such as the classification of Pick's disease by Constantinidis, or the description of dyshoric angiopathy and laminar sclerosis by Morel. The large number of cases, including some very rare conditions, provides a unique resource and an opportunity for worldwide collaborations.

Pericellular innervation of neurons expressing abnormally hyperphosphorylated tau in the hippocampal formation of Alzheimer's disease patients

Neurofibrillary tangles (NFT) represent one of the main neuropathological features in the cerebral cortex associated with Alzheimer's disease (AD). This neurofibrillary lesion involves the accumulation of abnormally hyperphosphorylated or abnormally phosphorylated microtubule-associated protein tau into paired helical filaments (PHF-tau) within neurons. We have used immunocytochemical techniques and confocal microscopy reconstructions to examine the distribution of PHF-tau-immunoreactive (ir) cells, and their perisomatic GABAergic and glutamatergic innervations in the hippocampal formation and adjacent cortex of AD patients. Furthermore, correlative light and electron microscopy was employed to examine these neurons and the perisomatic synapses. We observed two patterns of staining in PHF-tau-ir neurons, pattern I (without NFT) and pattern II (with NFT), the distribution of which varies according to the cortical layer and area. Furthermore, the distribution of both GABAergic and glutamatergic terminals around the soma and proximal processes of PHF-tau-ir neurons does not seem to be altered as it is indistinguishable from both control cases and from adjacent neurons that did not contain PHF-tau. At the electron microscope level, a normal looking neuropil with typical symmetric and asymmetric synapses was observed around PHF-tau-ir neurons. These observations suggest that the synaptic connectivity around the perisomatic region of these PHF-tau-ir neurons was apparently unaltered.

The seed extract of Cassia obtusifolia offers neuroprotection to mouse hippocampal cultures

The precise causative factors in neurodegenerative diseases such as Alzheimer's (AD) and Parkinson's disease remain elusive, but mechanisms implicated comprise excitotoxicity, mitochondrial dysfunction, and in the case of AD, the amyloid beta peptide (Abeta). Current therapeutic strategies for such disorders are very limited; thus, traditional herbal medicines currently receive increased attention. The seeds of Cassia obtisufolia have long been used in traditional eastern medicine and more recently the ethanolic fraction of the seeds (COE) has been shown to attenuate memory impairments in mice. In this study, we set out to determine the effect of COE (range: 0.1 - 10 microg/ml) on calcium dysregulation and cell death models in mouse primary hippocampal cultures implicated in general neurodegenerative processes and in the pathogenesis of AD: excitotoxicity, mitochondrial dysfunction, and Abeta toxicity. It was found that treatment with COE attenuated secondary Ca2+ dysregulation induced by NMDA (700 microM), while a pre-application of COE also reduced NMDA-induced cell death. Furthermore, COE was neuroprotective against the mitochondrial toxin 3-NP (1 mM), while having no significant effect on cell death induced by incubation with naturally-secreted oligomers of Abeta (8.2 pg/ml). Collectively, these results are important for the therapeutic use of COE in the treatment of neurodegenerative disorders.

Susceptibility of hippocampal neurons to Abeta peptide toxicity is associated with perturbation of Ca2+ homeostasis

Neuritic dystrophy, loss of synapses and neuronal death in the cerebral cortex and hippocampus are hallmarks of Alzheimer's disease. The aim of the present study was to investigate the differential susceptibility of cortical and hippocampal neurons to amyloid-beta (Abeta)-induced toxicity. For that, we have used primary neuronal cultures prepared from rat brain cortex and hippocampus which were treated with the synthetic peptides Abeta25-35 or Abeta1-40. Abeta-induced apoptotic cell death was analyzed by determining caspase-3-like activity. Neuritic dystrophy was evaluated by cobalt staining and MAP2 immunoreactivity. Perturbation of Ca(2+) homeostasis caused by exposure to Abeta was evaluated by determining basal cytosolic calcium levels in the whole neuronal population and by single cell calcium imaging under basal and KCl-depolarization conditions. Finally, levels of GluR2 subunit of glutamate AMPA (alpha-amino-3-hydroxy-5-methylisoxazole-4-proprionate) receptors were quantified by western blotting. Our results demonstrated that hippocampal neurons in culture are more susceptible than cortical neurons to Abeta-induced apoptosis and also that this mechanism involves the perturbation of Ca(2+) homeostasis. Accordingly, the exposure of hippocampal neurons to Abeta peptides decreases the protein levels of the GluR2 subunit of glutamate AMPA receptors that may be associated with a significant rise of cytosolic Ca(2+) concentration, leading to dendritic dystrophy and activation of apoptotic neuronal death.

Neuronal gene expression profiling: uncovering the molecular biology of neurodegenerative disease

The development of gene array techniques to quantify expression levels of dozens to thousands of genes simultaneously within selected tissue samples from control and diseased brain has enabled researchers to generate expression profiles of vulnerable neuronal populations in several neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, schizophrenia, multiple sclerosis, and Creutzfeld-Jakob disease. Intriguingly, gene expression analysis reveals that vulnerable brain regions in many of these diseases share putative pathogenetic alterations in common classes of genes, including decrements in synaptic transcript levels and increments in immune response transcripts. Thus, gene expression profiles of diseased neuronal populations may reveal mechanistic clues to the molecular pathogenesis underlying various neurological diseases and aid in identifying potential therapeutic targets. This chapter will review how regional and single cell gene array technologies have advanced our understanding of the genetics of human neurological disease.

The novel cytosolic RING finger protein dactylidin is up-regulated in brains of patients with Alzheimer's disease

Alzheimer's disease (AD) is characterized by a progressive degeneration of neurons along with deposition of amyloid plaques and the formation of neurofibrillary tangles. Neurodegeneration in AD follows both a spatial pattern of selective vulnerability and temporal staging of affected neurons. In order to address transcriptional changes associated with this selective vulnerability, we used subtractive hybridization of transcripts derived from human frontal cortex, which degenerates in late stages of AD, against transcripts of the inferior temporal cortex, which is affected both heavily and early in the course of AD. Moreover, we compared these to brain sections obtained from age-matched control subjects. We isolated a differentially expressed novel gene encoding a polypeptide that contained an amino-terminal C3HC4 RING finger domain, called dactylidin. It is ubiquitously expressed in all tissues examined and in situ hybridization of mouse brain sections revealed specific expression in neurons. Further, heterologous expression studies revealed a cytoplasmic localization of dactylidin and as all known cytoplasmic RING finger proteins function as ubiquitin protein ligases, an E3-like ligase function of dactylidin is probable. However, the up-regulation of dactylidin in highly vulnerable brain tissues of AD patients was confirmed by a quantitative PCR approach, suggesting that dactylidin may function early in the progression of neurodegenerative diseases.

Perineuronal nets potentially protect against oxidative stress

A specialized form of extracellular matrix (ECM) termed perineuronal nets (PNs) consisting of large aggregating chondroitin sulfate proteoglycans (CSPGs), with hyaluronan and tenascin as main components, surrounds subpopulations of neurons. The glycosaminoglycan components of perineuronal nets form highly charged structures in the direct microenvironment of neurons and thus might be involved in local ion homeostasis. The polyanionic character suggests that perineuronal nets also potentially contribute to reduce the local oxidative potential in the neuronal microenvironment by scavenging and binding redox-active iron, thus providing some neuroprotection to net-associated neurons. Here, we show that neurons ensheathed by a perineuronal net in the human cerebral cortex are less frequently affected by lipofuscin accumulation than neurons without a net both in normal-aged brain and Alzheimer's disease (AD). As lipofuscin is an intralysosomal pigment composed of cross-linked proteins and lipids generated by iron-catalyzed oxidative processes, the present results suggest a neuroprotective function of perineuronal nets against oxidative stress, potentially involved in neurodegeneration.

Interleukin-1beta up-regulates expression of neurofilament light in human neuronal cells

Elevated expression of interleukin-1 (IL-1beta), a pro-inflammatory cytokine secreted by activated microglia, is a pathogenic marker of numerous neurodegenerative processes including Alzheimer's disease (AD). We have characterized a link between IL-1beta and the 68-kDa neurofilament light (NF-L) protein, which is a major component of the neuronal cytoskeleton. Using human brain aggregate cultures, we found that IL-1beta treatment significantly increased NF-L expression in primary neurons. Analysis of mRNA levels demonstrated elevated NF-L expression within 72 h while imaging of neurons by immunofluorescent staining for NF-L confirmed IL-1beta-induced NF-L protein expression. These observations suggest a potential inflammatory-induced mechanism for deregulation of an important cytoskeletal protein, NF-L, possibly leading to neuronal dysfunction.

Altered apolipoprotein D expression in the brain of patients with Alzheimer disease

The etiology of late-onset Alzheimer disease is poorly understood. Predisposing factors such as the apolipoprotein E4 allele, as well as protective factors (e.g., antioxidants) have been proposed to play a role in the disease's process. A search for predisposing factors contributing to sporadic late-onset Alzheimer disease was initiated using the differential display technique. RNA expression profiles of the entorhinal cortex and the cerebellum of Alzheimer-diseased and normal patients were compared. The entorhinal cortex is the first brain region to accumulate neurofibrillary tangles during disease progression, whereas the cerebellum is spared. In the Alzheimer cases of this study, one signal showing preferential expression in the entorhinal cortex corresponded to the apolipoprotein D gene. This preferential expression might be genuine at the RNA level as suggested by the in situ hybridization method used. In addition, immunohistochemical experiments showed higher percentages of Apolipoprotein D reactive pyramidal neurons in the entorhinal cortex and region 1 of Ammon's horn in diseased patients. This increase correlated with the number of neurofibrillary tangles in Alzheimer as well as in normal patients. Colocalization of Apolipoprotein D proteins and neurofibrillary tangles in the same neuron was rare. Thus, these results suggest that in Alzheimer disease and aging, apolipoprotein D gene expression is increased in stressed cortical neurons before they possibly accumulate neurofibrillary tangles.

Motor cortex inhibition is not impaired in patients with Alzheimer's disease: evidence from paired transcranial magnetic stimulation

Motor cortex excitability was studied by transcranial magnetic stimulation (TMS) in 17 patients with Alzheimer's disease (AD). Resting and active thresholds for TMS were significantly reduced in AD patients compared to young and aged healthy subjects. The maximum amplitude of the motor response evoked by TMS was also significantly increased in AD patients. We have tested if these changes are related to a modification of the short-lasting intracortical inhibition of the motor cortex by paired conditioning-test TMS. We found no significant differences between AD patients and aged healthy subjects even if there is a slight but significant difference between aged and young normal subjects. We conclude that the modification of excitability of the motor cortex does not result from an impaired intracortical inhibition.

Cortical areas abundant in extracellular matrix chondroitin sulphate proteoglycans are less affected by cytoskeletal changes in Alzheimer's disease

In the human brain, the distribution of perineuronal nets occurring as lattice-like neuronal coatings of extracellular matrix proteoglycans ensheathing several types of non-pyramidal neurons and subpopulations of pyramidal cells in the cerebral cortex is largely unknown. Since proteoglycans are presumably involved in the pathogenesis of Alzheimer's disease, we analysed the distribution pattern of extracellular chondroitin sulphate proteoglycans in cortical areas, including primary motor, primary auditory and several prefrontal and temporal association areas, in normal human brains and in those showing neuropathological criteria of Alzheimer's disease. In both groups, neurons with perineuronal nets were most numerous in the primary motor cortex (approximately 10% in Brodmann's area 4) and in the primary auditory cortex as a representative of the primary sensory areas. Their number was lower in secondary and higher order association areas. Net-associated pyramidal cells occurred predominantly in layers III and V in motor areas, as well as throughout lower parts of layer III in the primary auditory cortex and neocortical association areas. In the entorhinal cortex, net-associated pyramidal cells were extremely rare. In brains showing hallmarks of Alzheimer's disease, the characteristic patterns of hyperphosphorylated tau protein, stained with the AT8 antibody, largely excluded the zones abundant in perineuronal nets and neuropil-associated chondroitin sulphate proteoglycans. As shown in double-stained sections, pyramidal and non-pyramidal neurons ensheathed by perineuronal nets were virtually unaffected by the formation of neurofibrillary tangles even in severely damaged regions. The distribution patterns of amyloid B deposits overlapped but showed no congruence with that of the extracellular chondroitin sulphate proteoglycans. It can be concluded that low susceptibility of neurons and cortical areas to neurofibrillary changes corresponds with high proportions of aggregating chondroitin sulphate proteoglycans in the neuronal microenvironment.

Cerebral cortex pathology in aging and Alzheimer's disease: a quantitative survey of large hospital-based geriatric and psychiatric cohorts

In order to explore the relationships between the involvement of specific neuronal populations and cognitive deterioration, and to compare the hierarchical patterns of cortical involvement in normal brain aging and Alzheimer's disease, over 1200 brains from elderly subjects without cognitive deficits, as well as from patients with age-associated memory impairment and Alzheimer's disease, were examined. Our results suggest that the neuropathological changes associated with normal brain aging and Alzheimer's disease affect select cortical circuits at different points in time. Extensive hippocampal alterations are correlated with age-associated memory impairment, whereas substantial neurofibrillary tangle formation in neocortical association areas of the temporal lobe is a prerequisite for the development of Alzheimer's disease. Despite several lines of evidence involving amyloid deposit in the pathogenesis of Alzheimer's disease and Down's syndrome, our observations indicate that there is no correlation between senile plaque densities and degree of dementia in both disorders. In contrast to younger elderly cases, in the ninth and tenth decades of life, there is a differential cortical involvement in that parietal and cingulate areas are early affected in the course of Alzheimer's disease, and neocortical senile plaques densities are strongly correlated with the severity of dementia. Moreover, Alzheimer's disease symptomatology is characterized in these very old patients by high neurofibrillary tangle densities in the anterior CA1 field, but not in the entorhinal cortex and inferior temporal cortex. These observations are discussed in the light of the hypothesis of global corticocortical disconnection and with respect to the notion of selective neuronal vulnerability in Alzheimer's disease.