Kelly Del Tredici

Correlation of Alzheimer Disease Neuropathologic Changes With Cognitive Status: A Review of the Literature

Abstract Clinicopathologic correlation studies are critically important for the field of Alzheimer disease (AD) research. Studies on human subjects with autopsy confirmation entail numerous potential biases that affect both their general applicability and the validity of the correlations. Many sources of data variability can weaken the apparent correlation between cognitive status and AD neuropathologic changes. Indeed, most persons in advanced old age have significant non-AD brain lesions that may alter cognition independently of AD. Worldwide research efforts have evaluated thousands of human subjects to assess the causes of cognitive impairment in the elderly, and these studies have been interpreted in different ways. We review the literature focusing on the correlation of AD neuropathologic changes (i.e. &bgr;-amyloid plaques and neurofibrillary tangles) with cognitive impairment. We discuss the various patterns of brain changes that have been observed in elderly individuals to provide a perspective forunderstanding AD clinicopathologic correlation and conclude that evidence from many independent research centers strongly supports the existence of a specific disease, as defined by the presence of A&bgr; plaques and neurofibrillary tangles. Although A&bgr; plaques may play a key role in AD pathogenesis, the severity of cognitive impairment correlates best with the burden of neocortical neurofibrillary tangles.

Stages of the Pathologic Process in Alzheimer Disease: Age Categories From 1 to 100 Years

Two thousand three hundred and thirty two nonselected brains from 1- to 100-year-old individuals were examined using immunocytochemistry (AT8) and Gallyas silver staining for abnormal tau; immunocytochemistry (4G8) and Campbell-Switzer staining were used for the detection of&bgr;-amyloid. A total of 342 cases was negative in the Gallyas stain but when restaged for AT8 only 10 were immunonegative. Fifty-eight cases had subcortical tau predominantly in the locus coeruleus, but there was no abnormal cortical tau (subcortical Stages a-c). Cortical involvement (abnormal tau in neurites) was identified first in the transentorhinal region (Stage 1a, 38 cases). Transentorhinal pyramidal cells displayed pretangle material (Stage 1b, 236 cases). Pretangles gradually became argyrophilic neurofibrillary tangles (NFTs) that progressed in parallel with NFT Stages I to VI. Pretangles restricted to subcortical sites were seen chiefly at younger ages. Of the total cases, 1,031 (44.2%) had &bgr;-amyloid plaques. The first plaques occurred in the neocortex after the onset of tauopathy in the brainstem. Plaques generally developed in the 40s in 4% of all cases, culminating in their tenth decade (75%). &bgr;-amyloid plaques and NFTs were significantly correlated (p < 0.0001). These data suggest that tauopathy associated with sporadic Alzheimer disease may begin earlier than previously thought and possibly in the lower brainstem rather than in the transentorhinal region.

The pathological process underlying Alzheimer’s disease in individuals under thirty

Brains of 42 individuals between the ages of 4 and 29 were examined with antibodies (AT8, 4G8) and silver stains for the presence of intraneuronal and extracellular protein aggregates associated with Alzheimer’s disease. Thirty-eight of 42 (38/42) cases displayed abnormally phosphorylated tau protein (pretangle material) in nerve cells or in portions of their cellular processes, and 41/42 individuals showed no extracellular amyloid-β protein deposition or neuritic plaques—an individual with Down syndrome was the only exception. In 16/42 cases abnormal tau was found in the transentorhinal region, and in 3/42 cases this site was Gallyas-positive for isolated NFTs (NFT stage I). Of 26 cases that lacked abnormal tau in the transentorhinal region, 4 did not show pretangle material at subcortical sites. The remaining 22 of these same 26 cases, however, had subcortical lesions confined to non-thalamic nuclei with diffuse projections to the cerebral cortex, and, remarkably, in 19/22 individuals the pretangle material was confined to the noradrenergic coeruleus/subcoeruleus complex. Assuming the pretangle alterations are not transient and do not regress, these findings may indicate that the Alzheimer’s disease-related pathological process leading to neurofibrillary tangle formation does not begin in the cerebral cortex but, rather, in select subcortical nuclei, and it may start quite early, i.e., before puberty or in early young adulthood.

100 years of Lewy pathology

In 1817, James Parkinson described the symptoms of the shaking palsy, a disease that was subsequently defined in greater detail, and named after Parkinson, by Jean-Martin Charcot. Parkinson expected that the publication of his monograph would lead to a rapid elucidation of the anatomical substrate of the shaking palsy; in the event, this process took almost a century. In 1912, Fritz Heinrich Lewy identified the protein aggregates that define Parkinson disease (PD) in some brain regions outside the substantia nigra. In 1919, Konstantin Nikolaevich Tretiakoff found similar aggregates in the substantia nigra and named them after Lewy. In the 1990s, α-synuclein was identified as the main constituent of the Lewy pathology, and its aggregation was shown to be central to PD, dementia with Lewy bodies, and multiple system atrophy. In 2003, a staging scheme for idiopathic PD was introduced, according to which α-synuclein pathology originates in the dorsal motor nucleus of the vagal nerve and progresses from there to other brain regions, including the substantia nigra. In this article, we review the relevance of Lewys discovery 100 years ago for the current understanding of PD and related disorders.

Invited Article: Nervous system pathology in sporadic Parkinson disease

Sporadic Parkinson disease (PD) is, after Alzheimer disease (AD), the second most frequent neurodegenerative disorder.1 The pathologic process in PD is progressive and takes years to reach its full extent. It does not affect nonhuman vertebrates or organ systems other than the nervous system, and, apparently, it does not go into remission. Unlike AD, however, the pathology is distributed throughout the entire nervous system—that is, not only the central but also the peripheral and the enteric nervous systems (CNS, PNS, ENS). As a result, PD has come to be acknowledged as more than a monosystemic disorder with preferential obliteration of nigral dopaminergic neurons.2–8,e1-e3 In the clinically recognizable, i.e., motor, phase of sporadic PD, most patients display signs of motor dysfunction (hypo- or bradykinesia, cogwheel rigidity, postural instability, resting tremor),9,e4,e5 but these symptoms also occur in other disorders associated with dopamine loss in the nigrostriatal system.e6,e7 Familial forms of parkinsonism exist,3,e8,e9 and the syndrome may also develop as a sequel to intoxication, trauma, vascular alterations, metabolic disease, or infection.e3,e10-e14 In addition, parkinsonism can develop in tauopathies, including corticobasal degeneration and progressive supranuclear palsy,e15-e17 or in synucleinopathies, such as multiple system atrophy and Lewy body disease.10,11,e18-e20 Lewy body disease has been subdivided further into pure autonomic failure, dementia with Lewy bodies, and sporadic PD.11,12 The latter two entities are nearly indistinguishable at neuropathologic examination, and there is a growing consensus that, clinically, they are closely related, if not identical.13–17 Here, we refer only to the Lewy body pathology associated with the synucleinopathy sporadic (or idiopathic) PD, the most widespread form of parkinsonism.1,8,e25 In PD, typical α-synuclein immunoreactive inclusions (Lewy neurites [LNs], Lewy bodies [LBs]) develop within specific types of projection neurons in all portions of the …

Neuropathological assessment of Parkinson's disease: refining the diagnostic criteria

To date, there have been few systematic attempts to provide a standard operating procedure for the neuropathological diagnosis of Parkinsons disease (PD). Pathological examination cannot classify the clinical syndrome with certainty; therefore, the neuropathological diagnosis is, at best, a probability statement. The neuropathological diagnosis of parkinsonism has become increasingly based on fundamental molecular underpinnings, with recognition that the genetics of parkinsonism is heterogeneous and includes disorders that are associated with and without Lewy bodies. The advent of alpha-synuclein immunohistochemistry has substantially improved the ability to identify Lewy pathology, particularly cortical Lewy bodies and smaller aggregates within processes and the neuropil. In this Review we discuss the diagnostic criteria for the neuropathological assessment of PD. These criteria are provisional and need to be validated through an iterative process that could help with their refinement. Additionally, we suggest future directions for neuropathology research on PD.

Stages of pTDP-43 pathology in amyotrophic lateral sclerosis

To see whether the distribution patterns of phosphorylated 43kDa TAR DNA‐binding protein (pTDP‐43) intraneuronal inclusions in amyotrophic lateral sclerosis (ALS) permit recognition of neuropathological stages.

Spreading of pathology in neurodegenerative diseases: a focus on human studies

The progression of many neurodegenerative diseases is thought to be driven by the template-directed misfolding, seeded aggregation and cell–cell transmission of characteristic disease-related proteins, leading to the sequential dissemination of pathological protein aggregates. Recent evidence strongly suggests that the anatomical connections made by neurons — in addition to the intrinsic characteristics of neurons, such as morphology and gene expression profile — determine whether they are vulnerable to degeneration in these disorders. Notably, this common pathogenic principle opens up opportunities for pursuing novel targets for therapeutic interventions for these neurodegenerative disorders. We review recent evidence that supports the notion of neuron–neuron protein propagation, with a focus on neuropathological and positron emission tomography imaging studies in humans.

Alzheimer’s pathogenesis: is there neuron-to-neuron propagation?

There is increasing interest in the early phase of Alzheimer’s disease before severe neuronal dysfunction occurs, but it is still not known when or where in the central nervous system the underlying pathological process begins. In this review, we discuss the idea of possible disease progression from the locus coeruleus to the transentorhinal region of the cerebral cortex via neuron-to-neuron transmission and transsynaptic transport of tau protein aggregates, and we speculate that such a mechanism together with the very long prodromal period that characterizes Alzheimer’s disease may be indicative of a prion-like pathogenesis for this tauopathy. The fact that AT8-immunoreactive abnormal tau aggregates (pretangles) develop within proximal axons of noradrenergic coeruleus projection neurons in the absence of both tau lesions (pretangles, NFTs/NTs) in the transentorhinal region as well as cortical amyloid-β pathology means that currently used neuropathological stages for Alzheimer’s disease will have to be reclassified.

Amyotrophic lateral sclerosis—a model of corticofugal axonal spread

The pathological process underlying amyotrophic lateral sclerosis (ALS) is associated with the formation of cytoplasmic inclusions consisting mainly of phosphorylated 43-kDa transactive response DNA-binding protein (pTDP-43), which plays an essential part in the pathogenesis of ALS. Preliminary evidence indicates that neuronal involvement progresses at different rates, but in a similar sequence, in different patients with ALS. This observation supports the emerging concept of prion-like propagation of abnormal proteins in noninfectious neurodegenerative diseases. Although the distance between involved regions is often considerable, the affected neurons are connected by axonal projections, indicating that physical contacts between nerve cells along axons are important for dissemination of ALS pathology. This article posits that the trajectory of the spreading pattern is consistent with the induction and dissemination of pTDP-43 pathology chiefly from cortical neuronal projections, via axonal transport, through synaptic contacts to the spinal cord and other regions of the brain.