| Volume 3, Number
2, April 2001
Pages 159-168
Helen Lasn, Bengt Winblad, Nenad Bogdanovic
The number of neurons in the inferior olivary nucleus in
Alzheimer’s disease and normal aging: a stereological study using
the optical fractionator
Abstract: The nuclei of the olivary complex are involved in
regulating motor movements and in motor learning. Aging is
characterized by a progressive accumulation of lipofuscin while the
number of olivary neurons is unchanged. It is not known whether
neuronal loss occurs in the olivary nucleus during Alzheimer’s
disease (AD). The aim of this study was to estimate the total number
of neurons in the principal olivary nucleus (PO) in AD and control
brains using an optimized design for sampling and an unbiased
stereological method called the optical fractionator. This study was
based on 13 control (mean age = 57y, range 17-95 y) and 16 AD brains
(mean age = 86 y, range 67-93 y). Using paraffin-embedded, Nissl
stained-sections for quantification, we found a significant
difference between the mean values (mean±SD) of the AD group vs.
aged-matched controls (4.3 x105±1.1 vs. 6.53x105±1.39 p<0,003).
There was no significant difference between younger controls vs.
older controls (7.1 x105±1.5 vs. 6.5 x105±1.4 p=0.76). While there
was no neuronal loss in normal aging, while in AD the PO is
characterized by a significant neuronal loss up to 34%. The results
suggest that neuronal loss in AD can occur in regions devoid of
neurofibrillary changes.
Pages 169-180
Yi Jing, Yaping Gu, Anil Kumar, Yogesh Sharma, Hisashi Fujioka, and
Neena Singh
Isolation of human neuronal cells resistant to toxicity by the
prion protein peptide 106-126
Abstract: Prion diseases or transmissible spongiform
encephalopathies, are neurodegenerative disorders that are genetic,
sporadic, or infectious. The pathogenetic event common to all prion
disorders is the conformational transformation of the cellular prion
protein (PrPC) to the scrapie form (PrPSc), that deposits in the
brain parenchyma and induces neuronal death. Infectious prion
disorders are caused by exogenously introduced PrPSc that acts as a
template in the conversion of endogenous PrPC to nascent PrPSc, and
subsequently the process becomes autocatalytic. To understand the
process of cellular uptake of PrPSc and its mechanism of cellular
toxicity, previous studies have used a PrP fragment spanning
residues 106-126 (PrPTx) that is toxic to primary neurons in
culture, and mimics PrPSc in its biophysical properties [9, 11, 14].
Several possible mechanisms of cell death by PrPTx have been
proposed [2, 3, 10, 11, 18], but the existing data are unclear. To
identify the biochemical pathways of neurotoxicity by this fragment,
we have isolated mutant neuroblastoma and NT-2 cells that are
resistant to toxicity by PrPTx. We show that these cells bind and
internalize PrPTx in a temperature dependent fashion, and the
peptide accumulates in intracellular compartments, probably
lysosomes, where it has an unusually long half-life. The PrPTx-resistant
phenotype of the cells reported in this study could result from
aberrant binding or internalization of the peptide, or due to an
abnormality in the downstream pathway(s) of neuronal toxicity. The
PrPTx-resistant cells are therefore a useful tool for evaluating the
cellular and biochemical pathways that lead to cell death by this
peptide, and will provide insight into the mechanism(s) of
neurotoxicity by PrPSc.
Pages 181-190
Luca Pellegrini, Brent J. Passer, Matilde Canelles, Ilyia Lefterov,
J. Kelly Ganjei, B.J. Fowlkes, Eugene V. Koonin, and Luciano
D’Adamio
PAMP and PARL, two novel putative metalloproteases interacting
with the COOH-terminus of Presenilin-1 and –2
Abstract: The familial Alzheimer's disease gene products,
presenilin-1 and presenilin-2 (PS1 and PS2), are involved in amyloid
ß-protein precursor processing (AßPP), Notch receptor signaling, and
programmed cell death. However, the molecular mechanisms by which
presenilins regulate these processes remain unknown. Clues about the
function of a protein can be obtained by seeing whether it interacts
with another protein of known function. Using the yeast two-hybrid
system, we identified two proteins that interact and colocalize with
the presenilins. One of these newly detected presenilin-interacting
proteins belongs to the FtsH family of ATP-dependent proteases, and
the other one belongs to Rhomboid superfamily of membrane proteins
that are highly conserved in eukaryotes, archaea and bacteria. Based
on the pattern of amino acid residues conservation in the Rhomboid
superfamily, we hypothesize that these proteins possess a
metal-dependent enzymatic, possibly protease activity. The two
putative proteases interacting with presenilins could mediate
specific proteolysis of membrane proteins and contribute to the
network of interactions in which presenilins are involved.
Commentary on the Pellegrini et
al. manuscript:
Pages 191-194
Benjamin Wolozin
Peering into proteolysis with presenilins
Pages 195-208
Andrei Tomashevski, Jacob Husseman, Lee-Way Jin, David Nochlin, and
Inez Vincent (communicated by Robert Bowser)
Constitutive Wee1 activity in adult brain neurons with M
phase-type alterations in Alzheimer neurodegeneration
Abstract: The cdc2/cyclin B1 kinase is absent from neurons
that are terminally differentiated. However, unscheduled activation
of Cdc2/cyclin B and accumulation of mitotic phosphoepitopes have
been described in degenerating neurons of Alzheimer’s disease (AD),
and their appearance precedes hallmark lesion formation. In cycling
cells the timing of cdc2 activation and onset of mitosis are
determined by the Wee1 tyrosine kinase. We therefore investigated
the Wee1 kinase in human brain. Surprisingly, we have found that the
enzyme is constitutively active in neurons of normal brain.
Consistent with its behavior in M phase, Wee1 in AD has decreased
activity, becomes MPM-2 immunoreactive, and is redistributed from
its normally nuclear domain to the cytoplasm of affected neurons.
These data suggest that Wee1 functions in normal postmitotic
neurons, but is altered in AD so as to promote activation of Cdc2/cyclin
B1. Thus, Wee1 is yet another mitotic regulator that participates in
the AD neurodegenerative process.
Pages 209-220
Justin Fonte, Judith Miklossy, Craig Atwood, and Ralph Martins
The severity of cortical Alzheimer’s type changes is positively
correlated with increased amyloid-ß levels: resolubilization of
amyloid-ß with transition metal ion chelators
Abstract: The most consistent diagnostic neuropathological
lesion in Alzheimer’s disease (AD) is the senile plaque of which the
4 kD amyloid-ß (Aß) peptide is the major proteinaceous component.
In this study cortical Aß levels were immunochemically measured in
70 post-mortem human brains and compared against their
neuropathological grading as determined by the densities of amyloid
plaques and neurofibrillary tangles. The mean concentration of
cortical Aß/mg protein increased with the severity of the cortical
degenerative changes (AD0<AD1<AD2<AD3). Brains with the severe
degenerative changes (AD3), corresponded to definite AD cases and
exhibited significantly increased concentrations of Aß (11.1 ±
3.08ng/mg total protein, n=17) when compared with control brains
without any degenerative changes (AD0; 0.06 ± 0.06ng/mg total
protein, n=14, P=0.003). The extraction of Aß from the cortex of
AD3 brains was significantly enhanced in a dose dependent manner by
the presence of the metal ion chelator
N,N,N’,N’-tetrakis(2-pyridylmethyl) ethylenediamine (5mM TPEN, P <
0.0001). The chelator/antioxidant 1,2-dithiolane-3-pentanoic acid
(lipoic acid), also resolubilized Aß in a dose-dependant manner.
Both chelators also enhanced the extraction of Aß from the frontal
cortex of AßPP-transgenic mice suggesting this animal model of
amyloidosis may be useful for evaluating the biochemical and
therapeutic effects of chelators/antioxidants on Aß deposition. In
summary our results indicate that increased Aß load is correlated
with the severity of the cortical AD-type changes and that
chelators/antioxidants may be useful in reducing neuronal amyloid
burden.
Pages 221-230
Joseph D. Buxbaum, Neil S. M. Geoghagen, and Lawrence T. Friedhoff
Cholesterol depletion with physiological concentrations of a
statin decreases the formation of the Alzheimer amyloid Aß peptide
Abstract: Epidemiological studies have demonstrated that
hypercholsterolemia is a significant risk factor for Alzheimer’s
disease (AD). The mechanism by which increased cholesterol may
contribute to AD is unknown. However, as the generation and
accumulation of the amyloid Aß peptide in the brain appears to be
significant for the initiation and progression of AD, it is possible
that cholesterol levels can regulate Aß formation and/or clearance.
To test the effects of altering cholesterol on Aß formation, we
incubated cells in the presence of lipid depleted serum, with or
without the active metabolite of the HMG-CoA reductase inhibitor
lovastatin. After confirming that cholesterol was depleted in the
cells, we then measured the fraction of Aß formed from its precursor
AßPP under each condition. We observed that cholesterol depletion
led to a profound decrease in the levels of Aß released from the
cells. This effect of lovastatin acid was observed at concentrations
of 0.05-5 µM, ranges where this compound is effective at inhibiting
HMG-CoA reductase, thereby inhibiting cholesterol synthesis. In
contrast, the release of an additional AßPP fragment, AßPPs, was
only modestly reduced by cholesterol treatment. In further studies,
we determined that the decreased release of Aß was not due to its
accumulation in the cell, but rather due to decreased formation of
Aß. Finally, we were able to exclude decreased maturation (glycosylation
and sulfation) of newly synthesized AßPP as a cause for the effects
of lovastatin acid on AßPP processing and Aß formation. Our results
demonstrate that reducing cellular cholesterol by the use of an
HMG-CoA reductase inhibitor regulates Aß formation. This effect may
involve alterations in the trafficking of AßPP and/or alterations in
the activity of the proteases that cleave AßPP. The results suggest
a mechanism by which hypercholesterolemia may increase risk for AD
and indicate that reduction in cholesterol may delay the onset
and/or slow the progression of AD.
Pages 231-240
DH Chui, E Dobo, T Makifuchi, H Akiyama, S Kawakatsu, A Petit, F
Checler, W Araki, K Takahashi and T Tabira
Apoptotic Neurons In Alzheimer’s Disease Frequently Show
Intracellular Ab42 Labeling
Abstract: It is widely accepted that Aß plays a pivotal role
in the pathogenesis of Alzheimer’s disease (AD). Attention has been
focused mainly on how extracellular Aß exerts its effects on
neuronal cells. However, neuronal degeneration from an accumulation
of intracellular Aßx-42 (iAß42) occurs in presenilin 1 (PS1) mutant
mice without extracellular Aß deposits. In the present study,
intracellular deposits of iAß42 are correlated with apoptotic cell
death in AD and PS-1 familial AD (PS1 FAD) brains by means of triple
staining with antibodies to Aß, TUNEL, and staining with Hoechst
33342. Neurons simultaneously positive for iAß42 and the TUNEL assay
were significantly more abundant in AD brains than in controls. The
number of apoptotic neurons with intracellular neurofibrillary
tangles (iNFTs) was insignificant. Our results indicate that
intraneuronal deposition of a neurotoxic form of Aß seems to be an
early event in the neurodegeneration of AD.
Pages 241-248
Tina L. Tekirian (communicated by James Geddes)
Aß N- Terminal Isoforms: Critical Contributors in The Course of
AD Pathophysiology
Abstract: The assessment of protein or amino acid variations
across evolution allows one to glean divergent features of
disease-specific pathology. Within the Alzheimer's disease (AD)
literature, extensive differences in Aß processing across cell lines
and evolution have clearly been observed. In the recent past,
increased levels of Aß1-42 have been heralded to be what
distinguishes whether one is prone to the development of AD.
However, observations in naturally occurring, non-transgenic animals
which display a great deal of parenchymal Aß1-42 (Aß found within
extracellular plaque deposits) and a complete lack of Aß1-40 within
these same Aß1-42 plaques raise the issue of whether Aßx-42 (Aß that
is truncated or modified at the N- terminus), rather than Aß1-42, is
instead the critical mediator of Aß production and pathogenesis.
Distinct ratios of Aß N-terminal variants (i.e. Aß1-x, Aß3-x,
Aß11-x, Aß17-x) have been assessed in human amyloid plaques.
Moreover, ratios of specific Aß N-terminal variants separate
naturally occurring, non-transgenic animals which develop abundant
levels of Aßx-42 and not Aßx-40 from human AD participants who
harbor plaques that contain both the Aßx-42 and Aßx-40 variants.
Next, Teller and colleagues have demonstrated the presence of
N-terminal truncated soluble 3kD (likely Aß17-x) and 3.7kD peptides
(in addition to 4kD Aß) well before the appearance of amyloid
plaques in Down Syndrome brain, indicating an early contribution of
the Aß N-terminus to the formation of amyloid pathology. Additional
critical facts concerning the major contribution of the Aß
N-terminus in AD pathogenesis include observations which support
that Aß generated by rodent neurons is predominantly truncated at
Aß11-x, the major form of APP C-terminal fragments in mice lacking
functional PS1 is AßPP11-98, Aß11-x expression is increased as a
function of BACE expression, and an interrelationship between
presenilin-1 mutations and increased levels of N-terminally
truncated Aß (40). This commentary highlights current understanding
and potential biochemical, pathological, and cell biological
contributions of Aß N-terminal variants implicated during the course
of AD pathogenesis.
Pages 249-252
John Q. Trojanowski
Alzheimer’s Disease Centers and the Dementias of Aging Program of
the National Institute on Aging: a Brief Overview
Abstract: The National Institute on Aging (NIA) of the
National Institutes of Health (NIH) has stimulated many recent
landmark advances in the understanding and treatment of Alzheimer’s
disease (AD) and related dementing disorders. This progress is due
in part to an extramural network of AD Centers (ADCs) that was
established 15 years ago as a component of the NIA Dementias of
Aging Program. The ADCs provide a unique infrastructure to support
and augment studies on the pathobiology of AD and related disorders
as well as to educate scientists and the public about these
neurodegenerative dementias. The mission and structure of the ADC
network are summarized to illustrate how the ADCs play important
roles in accelerating development of effective therapies for AD and
related disorders.
Pages 253-254
Book Review: S. Gauthier, J.L. Cummings; Alzheimer’s Disease
and Related Disorders Annual, Martin Dunitz Ltd, 2000, London, UK,
225 pp. Reviewed by Catherine Bergeron
Page 255
Dorothy G. Flood
In Memoriam: Ann Marie Schwartz Kazee
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