Preamyloid deposits, amyloid deposits, and senile plaques in Alzheimer's disease, Down syndrome, and aging

Neuritic Plaques - Gateways to Understanding Alzheimer's Disease

Extracellular deposits of amyloid-β (Aβ) in the form of plaques are one of the main pathological hallmarks of Alzheimer's disease (AD). Over the years, many different Aβ plaque morphologies such as neuritic plaques, dense cored plaques, cotton wool plaques, coarse-grain plaques, and diffuse plaques have been described in AD postmortem brain tissues, but correlation of a given plaque type with AD progression or AD symptoms is not clear. Furthermore, the exact trigger causing the development of one Aβ plaque morphological subtype over the other is still unknown. Here, we review the current knowledge about neuritic plaques, a subset of Aβ plaques surrounded by swollen or dystrophic neurites, which represent the most detrimental and consequential Aβ plaque morphology. Neuritic plaques have been associated with local immune activation, neuronal network dysfunction, and cognitive decline. Given that neuritic plaques are at the interface of Aβ deposition, tau aggregation, and local immune activation, we argue that understanding the exact mechanism of neuritic plaque formation is crucial to develop targeted therapies for AD.

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.

One or more β-amyloid(s)? New insights into the prion-like nature of Alzheimer's disease

Misfolding and aggregation of proteins play a central role in the pathogenesis of several neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's and Lewy Body diseases, Frontotemporal Lobar Degeneration and prion diseases. Increasing evidence supports the view that Aβ and tau, which are the two main molecular players in AD, share with the prion protein several "prion-like" features that can be relevant for disease pathogenesis. These features essentially include structural/conformational/biochemical variations, resistance to degradation by endogenous proteases, seeding ability, attitude to form neurotoxic assemblies, spreading and propagation of toxic aggregates, transmissibility of tau- and Aβ-related pathology to animal models. Following this view, part of the recent scientific literature has generated a new reading frame for AD pathophysiology, based on the application of the prion paradigm to the amyloid cascade hypothesis in an attempt to definitely explain the key events causing the disease and inducing its occurrence under different clinical phenotypes.

Senile myoclonic epilepsy: delineation of a common condition associated with Alzheimer's disease in Down syndrome

In Down syndrome (DS), epilepsy is frequent in all age classes and is recognized as a significant cause of additional handicap and morbidity. Longer life expectancy has led to the recognition of the high incidence of both Alzheimer's disease and seizures in elderly persons with DS. Neuropathological markers of AD are found in all DS brains and clinical symptoms of AD become apparent by the age of 60 years and above in over 50% of DS subjects. Following preliminary description of myoclonic seizures and/or myoclonic epilepsy in isolated cases or small series, we wish to report the diagnostic criteria, treatment and prognosis of a specific and recognizable form of epilepsy associated with AD in a larger group of middle-aged to elderly DS patients. This markedly under-recognized entity may indeed concern an already large and steadily increasing number of patients. We reviewed all medical records of patients with DS referred to our centers (Centre Saint Paul-Gastaut, Marseille; Epilepsy Unit, Montpellier University Hospital; Department of Neurology, Hospital General de Asturias, Oviedo) since 1995. DS had been diagnosed in all at birth, and all presented with the typical morphological changes associated with DS. We selected all cases (18) referred as adults with new onset of myoclonic jerks (MJ) and/or behavioral or cognitive deterioration (CD).

Glycation and microglial reaction in lesions of Alzheimer's disease

Single, double, and triple immunostaining of cryostat sections of elderly normal and Alzheimer disease (AD) brain was performed with monoclonal and polyclonal antibodies to advanced glycation end products (AGE). The sections were counterstained with thioflavin-S or with immunocytochemistry for A beta and also stained with markers for microglia. AGE-immunoreactivity was detected in senile plaques and neurofibrillary tangles (NFT). AGE immunoreactivity was most intense in dense or reticular amyloid deposits and extracellular NFT, while intracellular NFT and diffuse amyloid had less AGE immunoreactivity. This pattern of immunoreactivity was similar to that noted in previous studies with antibodies to apolipoprotein-E (apo-E). Therefore, double labeling with antibodies to apo-E and AGE was performed. AGE immunoreactivity colocalized to a very high degree with apo-E immunoreactivity, except that relatively more intense apo-E immunoreactivity was detected in amyloid deposits and more intense AGE immunoreactivity in NFT. The lesions that were immunostained with antibodies to AGE and apo-E were often, but not always, associated with a local microglial reaction. The results raise the possibility that apo-E or a fragment of apo-E may be glycated. Biochemical studies are needed to determine the extent of possible apo-E glycation in AD. The present results raise the possibility that glycation may serve as one of the signals for activation of microglia associated with amyloid deposits and extracellular NFT.