Two distinct ubiquitin immunoreactive senile plaques in Alzheimer's disease: relationship with the intellectual status in 29 cases

A History of Senile Plaques: From Alzheimer to Amyloid Imaging

Senile plaques have been studied in postmortem brains for more than 120 years and the resultant knowledge has not only helped us understand the etiology and pathogenesis of Alzheimer disease (AD), but has also pointed to possible modes of prevention and treatment. Within the last 15 years, it has become possible to image plaques in living subjects. This is arguably the single greatest advance in AD research since the identification of the Aβ peptide as the major plaque constituent. The limitations and potentialities of amyloid imaging are still not completely clear but are perhaps best glimpsed through the perspective gained from the accumulated postmortem histological studies. The basic morphological classification of plaques into neuritic, cored and diffuse has been supplemented by sophisticated immunohistochemical and biochemical analyses and increasingly detailed mapping of plaque brain distribution. Changes in plaque classification and staging have in turn contributed to changes in the definition and diagnostic criteria for AD. All of this information continues to be tested by clinicopathological correlations and it is through the insights thereby gained that we will best be able to employ the powerful tool of amyloid imaging.

The levels of water-soluble and triton-soluble Aβ are increased in Alzheimer's disease brain

Although plaques composed of the amyloid β-protein (Aβ) are considered a defining feature of Alzheimer's disease (AD), they are also found in cognitively normal individuals and extensive evidence suggests that non-plaque, water-soluble forms of Aβ may play a role in AD pathogenesis. However, the relationship between the levels of water-soluble Aβ and the clinical severity of disease has never been investigated. Here, we present results of a pilot study designed to examine the levels of water-soluble forms of Aβ in brains of individuals who died at clinically distinct stages of AD. Using a serial extraction method, we also investigated the levels of triton-soluble and formic acid-soluble Aβ. We found that water-soluble and detergent-soluble Aβ monomer and SDS-stable dimer were elevated in AD and that the levels of water soluble Aβ did not increase with plaque pathology. These results support the notion that both water- and detergent-soluble Aβ are important in AD and are not simply released from plaques by mechanical disruption. Moreover, the fact that the levels of water- and triton-soluble Aβ were similar in very mild/mild AD and moderate/severe AD suggests that once a certain level of these species is attained, further accumulation is not necessary for the disease to progress. Consequently, therapeutic targeting of water-soluble Aβ should best benefit individuals in earliest phases of the disease process.

Classification and basic pathology of Alzheimer disease

The lesions of Alzheimer disease include accumulation of proteins, losses of neurons and synapses, and alterations related to reactive processes. Extracellular Abeta accumulation occurs in the parenchyma as diffuse, focal or stellate deposits. It may involve the vessel walls of arteries, veins and capillaries. The cases in which the capillary vessel walls are affected have a higher probability of having one or two apoepsilon 4 alleles. Parenchymal as well as vascular Abeta deposition follows a stepwise progression. Tau accumulation, probably the best histopathological correlate of the clinical symptoms, takes three aspects: in the cell body of the neuron as neurofibrillary tangle, in the dendrites as neuropil threads, and in the axons forming the senile plaque neuritic corona. The progression of tau pathology is stepwise and stereotyped from the entorhinal cortex, through the hippocampus, to the isocortex. The neuronal loss is heterogeneous and area-specific. Its mechanism is still discussed. The timing of the synaptic loss, probably linked to Abeta peptide itself, maybe as oligomers, is also controversial. Various clinico-pathological types of Alzheimer disease have been described, according to the type of the lesions (plaque only and tangle predominant), the type of onset (focal onset), the cause (genetic or sporadic) and the associated lesions (Lewy bodies, vascular lesions, hippocampal sclerosis, TDP-43 inclusions and argyrophilic grain disease).

Application of Ubiquitin Immunohistochemistry to the Diagnosis of Disease

Ubiquitin immunohistochemistry has changed understanding of the pathophysiology of many diseases, particularly chronic neurodegenerative diseases. Protein aggregates (inclusions) containing ubiquitinated proteins occur in neurones and other cell types in the central nervous system in afflicted cells. The inclusions are present in all the neurological illnesses, including Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, polyglutamine diseases, and rarer forms of neurodegenerative disease. A new cause of cognitive decline in the elderly, "dementia with Lewy bodies," accounting for some 15-30% of cases, was initially discovered and characterized by ubiquitin immunocytochemistry. The optimal methods for carrying out immunohistochemical analyses of paraffin-embedded tissues are described, and examples of all the types of intracellular inclusions detected by ubiquitin immunohistochemistry in the diseases are illustrated. The role of the ubiquitin proteasome system (UPS) in disease progression is being actively researched globally and increasingly, because it is now realized that the UPS controls most pathways in cellular homeostasis. Many of these regulatory mechanisms will be dysfunctional in diseased cells. The goal is to understand fully the role of the UPS in the disorders and then therapeutically intervene in the ubiquitin pathway to treat these incurable diseases.

A grading system of Alzheimer disease lesions in neocortical areas

Progression of neuritic and Abeta pathology in the cerebral cortex during aging and Alzheimer disease is well known, but the chronology of the various types of lesions (Abeta deposition, amyloid formation, inflammation, ubiquitination, tangle formation) within a given area has not been fully elucidated. We examined these lesions in the primary visual cortex (Brodmann area 17), correlating them with the severity of the disease (as evaluated by the cognitive status and the number of cortical samples that contained neurofibrillary tangles). Four 'grades' were identified. At grade 1, only deposits of Abeta peptide were noticed. At grade 2, Congo red positive deposits, and processes containing ubiquitin and cathepsin D immunoreactivity around plaque cores could also be found. At grade 3, neuritic plaques and neuropil threads were present, and at grade 4, neurofibrillary tangles. The density of all the lesions dramatically increased at grade 4. The sequence of isocortical lesions from grade 1 to grade 4 is compatible with a cascade of events beginning with deposition of Abeta peptide and ending with neurofibrillary tangle.

Immunohistochemical study of neuronal intranuclear and cytoplasmic inclusions in Machado-Joseph disease

Machado-Joseph disease (MJD) is a dominantly inherited spinocerebellar disorder, and expansions of trinucleotide (CAG) at chromosome 14 have been shown to be the locus of this disorder. Polyglutamine CAG stretches in the neuronal cytoplasms and nuclei were studied with immunolabeling using 1C2, a monoclonal antibody recognizing polyglutamine stretches, and polyclonal antiubiquitin antibody in six genetically verified cases of MJD. 1C2 clearly labeled two types of neuronal intranuclear inclusions (NII) and neuronal cytoplasmic inclusions (NCI) in the substantia nigra, pontine nucleus, dentate nucleus and spinal anterior horn where NII and NCI were also positive for ubiquitin, as were extracellular dot-like structures and oligodendroglial inclusions. 1C2-positive NII and NCI had a lesion-specific distribution. While the spinal motoneurons contained only 1C2-positive NCI and lacked 1C2-positive NII, the ventral pontine nucleus neurons had many 1C2-positive NII and few 1C2-positive NCI. Semi-quantitative examination of NII and NCI positive for 1C2 or ubiquitin demonstrated that there were more 1C2-positive NII and NCI than ubiquitin-positive ones. It is noteworthy that the nuclei of the spinal motoneurons lacked 1C2-positive immunoreactivity, so that ubiquitination of 1C2-positive structures is presumed to occur late in the course of the disease.

Ubiquitin and the molecular pathology of neurodegenerative diseases

Ubiquitin plays a central role in normal cellular function as well as in disease. It is possible to group ubiquitin-immunostained structures into several main groups, the most distinctive being the ubiquitin/intermediate filament/alphaB crystallin family of inclusions that seem to represent a general cellular response to abnormal proteins recently termed the aggresomal response. While ubiquitin immunohistochemistry is a very useful technique for detecting pathological changes and inclusion bodies in the nervous system this alone is not enough to classify inclusions, and a panel of antibodies is recommended to clarify any findings made by screening tissues with anti-ubiquitin. Several mechanistic possibilities now exist to explain the accumulation of ubiquitinated proteins in cells of the nervous system, understanding of which should lead to new therapeutic advances in the group of chronic neurodegenerative diseases.

Microglia, amyloid and dementia in alzheimer disease. A correlative study

To elucidate the role of microglia in Alzheimer's disease, a clinicopathological study was performed involving 26 cases, the mental status of which had been studied pre mortem by the Blessed test score (BTS). We measured the volume density of CD 68 immunoreactive (IR) microglia, congophilic plaques and Abeta deposits, and the numerical density of neurofibrillary tangles (NFT) in a sample of Area 9 (middle frontal gyrus). Dementia was significantly correlated only with the volume density of Abeta deposits and the numerical density of NFT. The volume densities of microglia and congophilic plaques were strongly correlated. With the intellectual status used as a time scale, IR microglia and amyloid deposits appeared almost simultaneously at an early stage in the pathological cascade and decreased, whereas Abeta and NFT were still accumulating. The intellectual deficit seemed to be more significantly related to the latter two lesions than to the microglia-amyloid complex, that was visible at an earlier stage (around BTS = 15).

Structural and kinetic features of amyloid beta-protein fibrillogenesis

Alzheimer's disease (AD) is an archetype of a class of diseases characterized by abnormal protein deposition. In each case, deposition manifests itself in the form of amyloid deposits composed of fibrils of otherwise normal, soluble proteins or peptides. An ever-increasing body of genetic, physiologic, and biochemical data supports the hypothesis that fibrillogenesis of the amyloid beta-protein is a seminal event in Alzheimer's disease. Inhibiting A beta fibrillogenesis is thus an important strategy for AD therapy. However, before this strategy can be implemented, a mechanistic understanding of the fibrillogenesis process must be achieved and appropriate steps selected as therapeutic targets. Following a brief introduction to AD, I review here the current state of knowledge of A beta fibrillogenesis. Special emphasis is placed on the morphologic, structural, and kinetic aspects of this complex process.

An immunohistochemical study of amyloid P component, apolipoprotein E and ubiquitin in human and murine amyloidoses

Amyloid P component (AP) and apolipoprotein E (Apo E), which are known to be minor constituents of amyloid deposits, commonly are associated with almost all types of amyloid deposits. In this study, the distribution of AP-, Apo E- and ubiquitin (Ub)-immunoreactivity (IR) in amyloid deposits in the liver and spleen of human systemic amyloidosis (34 autopsy cases: 17 immunoglobulin light chain derived, 17 amyloid A protein derived) and experimental murine amyloidosis is examined using an immuno-histochemical technique. In human cases, all of the amyloid deposits examined showed colocalization of AP- and Apo E-IR with individual amyloid proteins. In experimental amyloidosis, AP-IR of amyloid deposits in the liver and spleen and Apo E-IR in the liver were seen uniformly throughout this experiment. In contrast, Apo E-IR in the spleen was not uniform at the phase of amyloid deposition. At 4 weeks and at 16 weeks after casein injection, Apo E-IR was unevenly distributed in amyloid deposits in the perifollicular area; however, from 6 to 12 weeks it was seen to be uniform. Ubiquitin-IR of amyloid deposits in human cases was seen in 22 of 34 livers and in 22 of 33 spleens. In experimental amyloidosis, Ub-IR of amyloid deposits was demonstrated in the space of Disse in all mice examined, and there appeared to be a gradual increase in intensity with the amount of amyloid deposition. However, in the spleen, amyloid deposits did not react with anti-Ub antibody in any phase of amyloid induction. These results suggest that Apo E and Ub are not always associated with the process of amyloid deposition and may appear in a deposit after the deposition.

Cholinergic immunolesions by 192IgG-saporin--useful tool to simulate pathogenic aspects of Alzheimer's disease

Alzheimer's disease, the most common cause of senile dementia, is characterized by intracellular formation of neurofibrillary tangles, extracellular deposits of beta amyloid as well as cerebrovascular amyloid accumulation and a profound loss of cholinergic neurons within the nucleus basalis Meynert with alterations in cortical neurotransmitter receptor densities. The use of the cholinergic immunotoxin 192IgG-saporin allows for the first time study of the impact of cortical cholinergic deafferentation on cortical neurotransmission, learning, and memory without direct effects on other neuronal systems. This model also allows the elucidation of contributions of cholinergic mechanisms to the establishment of other pathological features of Alzheimer's disease. The findings discussed here demonstrate that cholinergic immunolesions by 192IgG-saporin induce highly specific, permanent cortical cholinergic hypoactivity and alterations in cortical neurotransmitter densities comparable to those described for Alzheimer's disease. The induced cortical cholinergic deficit also leads to cortical/hippocampal neurotrophin accumulation and reduced amyloid precursor protein (APP) secretion, possibly reflecting the lack of stimulation of postsynaptic M1/M3 muscarinic receptors coupled to protein kinase C. This immunolesion model should prove useful to test therapeutic strategies based on stimulation of cortical cholinergic neurotransmission or amelioration of pathogenic aspects of cholinergic degeneration in the basal forebrain. Application of the model to animal species that can develop beta-amyloid plaques could provide information about the contribution of cholinergic function to amyloidogenic APP processing.

Diagnosis and staging of Alzheimer disease

Rather than determining lesions "threshold" between "normal" cases and patients, we prefer to use clinicopathological correlations, assigning a given intellectual deficit to a given amount of lesions with a chosen level of probability. Because large amounts of A beta diffuse deposits may be found in the absence of dementia, we think advisable not to take them into account for the diagnosis. The diffusion of the neurofibrillary tangles in the paralimbic, limbic and isocortical areas (described by braak and Braak stages or by the number of areas containing tangles) and the density of isocortical senile plaques (A beta focal deposits) as assessed by the CERAD protocol are both correlated with the intellectual status but give complementary information. They should thus be jointly used. We analyzed the variability of the lesions counts, their coefficients of error, and their causes, as a first step toward standardization. We have shown, however, that semiquantitative estimates are presently more reproducible than quantitative measures.

Neuropathological diagnosis of Alzheimer's disease: a perspective from longitudinal clinicopathological studies

Alzheimer's disease (AD) is the most common cause of primary progressive dementia. It is defined by its pathological features, because the clinical syndrome of dementia lacks specificity. Although the brain in AD has many structural alterations, the two cardinal pathological features and sine qua non of AD are senile plaques and neurofibrillary degeneration. The latter takes the form of neurofibrillary tangles composed of paired helical filaments, as well as degenerating neurites within the neuropil ("neuropil threads") and within a diagnostically significant subset of SP, referred to as "neuritic plaques." All SP contain amyloid, but not all have pair helical filament-type neurites. The presence of even a small number of plaques with paired helical filament-type neurites in the neocortex is associated with cognitive impairment, and this lesion may be the most specific histopathological feature of AD. Although these observations suggest that the major difference between SP in aging and AD relate to differences in neuritic degeneration, more recent studies have also indicated that amyloid deposits are biochemically heterogenous and that amyloid deposits in aging may be different from those in AD. As more specific markers become available for recognizing AD-specific structural lesions, refined neuropathological diagnostic criteria will evolve. In the meantime, a practical neuropathological approach to the diagnosis of AD requires both widespread neocortical SP and an advanced stage of neurofibrillary degeneration. Using these criteria, it is very unlikely that AD will be diagnosed in an individual who was not demented in life. The rationale for adopting this conservative approach is that our knowledge is incomplete with respect to fundamental differences between the lesions in aging and AD.

Beta-amyloid deposition and other measures of neuropathology predict cognitive status in Alzheimer's disease

The relationship between progressive cognitive decline and underlying neuropathology associated with Alzheimer s disease (AD) is a key issue in defining the mechanisms responsible for functional loss. This has been a subject of much controversy, with separate studies comparing various clinical and neuropathological indices in AD. Further, it is difficult to compare studies with differences in histochemical staining protocols, brain regions examined, and data quantification criteria. There are many difficulties in designing a clinical-pathological correlative study involving AD patients. It is necessary to control for several key parameters. For example, a broad range of cognitively impaired subjects is needed, as well as short postmortem delays, brief intervals between cognitive testing and death, and the most sensitive detection and quantification techniques. In this study, we carefully controlled for each of these parameters to determine if there is a relationship between global cognitive dysfunction and multiple neuropathological indices. We selected 20 individuals representing a broad range of cognitive ability from normal to severely impaired based on the MMSE, Blessed IMC, and CDR. We counted plaque number, NFT number, dystrophic neurite number, and the relative extent of thioflavine positive plaques and neuritic involvement within plaques. We also quantified cortical area occupied by beta-amyloid immunoreactivity (A beta Load) and PHF-1 positive neuropil threads and tangles (PHF Load) using computer-based image analysis. Interestingly, we found that most pathologic measures correlated highly with the severity of dementia. However, the strongest predictor of premortem cognitive dysfunction on all three cognitive measures was the relative area of entorhinal cortex occupied by beta-amyloid deposition. In conclusion, our data show that in a carefully controlled correlative study, a variety of neuropathological variables are strongly correlated with cognitive impairment. Plaque related variables may be as strongly related to cognitive dysfunction as other established measures, including synapse loss, cell death and tau hyperphosphorylation, although no correlative study can demonstrate causality.

Image analysis of beta-amyloid load in Alzheimer's disease and relation to dementia severity

The protein beta-amyloid is said to be central to the disease process of Alzheimer's disease (AD). Several groups have developed transgenic models that overexpress the amyloid precursor protein or beta-amyloid and then develop AD-like neuropathology. Another report suggests that beta-amyloid accumulation in old dogs correlates with cognitive impairment. However, many other researchers argue that beta-amyloid deposition in senile plaques is a secondary event because plaque numbers in man do not correlate well with cognition. We set out to analyse this conumdrum in man. We selected 16 mild to severely demented AD cases on the basis of mini-mental state exam scores (MMSE; n = 16). We also included 4 controls who represented the upper range of cognitive ability. We used a computer-based image analysis of cross-sectional area of the brain occupied by beta-amyloid immunopositive deposition. We used this technique in preference to conventional methods of manual plaque counts and found a strong relation between beta-amyloid load in entorhinal cortex and cognition measured on various scales (r = -0.93 versus the Blessed IMC). Our study suggests that the size of cortical area affected by beta-amyloid deposition is an important factor in the clinical manifestation of dementia, and lends support to the possibility that beta-amyloid is central to the aetiology of AD.

Immunoreactivity patterns in neurofibrillary tangles of the inferior temporal cortex in Alzheimer disease

The distributions of various immunohistochemical markers of neurofibrillary tangles (NFT) were compared to that of a normal nerve cell cytoskeletal marker, SMI32, in the inferior temporal cortex of Alzheimer brains and normal aged controls. NFT markers included antibodies to the microtubule-associated proteins tau, ubiquitin, or amyloid P component (AP). The results showed that, in our group of patients, the decrease of SMI32 immunoreactivity in the Alzheimer temporal cortex is paralleled by an increase in AP immunoreactivity in neurons and neurofibrillary tangles. This suggests that AP may play an important role in NFT formation or evolution in Alzheimer disease.