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Chronic psychosocial stress enhances
long-term depression in a subthreshold
amyloid-beta rat model of Alzheimer's
disease
Tran, Trinh, Srivareerat,et al.
Khalil Khlifi
Pharm D. Candidate 2012
University of Georgia, College of Pharmacy
Alzheimer's Disease
• Progressive, irreversible brain disorder that gradually destroys
memory and cognitive abilities
• Clinically, patient's are seen to have marked memory loss and
impairment of social and occupational functions
• Pathologically, it is characterized by the accumulation of amyloidbeta peptides and tau protein
o Accumulation is caused by abnormally folded amyloid-beta
and tau proteins
o The plaques are made up of small peptides 39-43 amino acids
in length and deposit outside neurons
o Tau is used to stabilize the microtubules and a chemical change
causes it to be hyperphosphorylated and thereby creates
neurofibrillary tangles and disintegrates the neuronal transport
system
Stress and AD
• Genetic factors have a very definitive role on the progression of
the disease but what does the effect of non-genetic factors have on
progression of these patients?
o Exposure to severe and/or prolonged stress challenges
homeostasis mechanisms and may cause over-activation and
dysregulation of stress-activated systems
o These may lead to subsequent negative changes in the brain
• The hippocampus is particularly susceptible to stress functions and
is one of the first regions to be affected by AD
o The hippocampus is involved in learning and memory
processes
Methods and Materials
• Adult male Wistar rats weighing 200-225g at the beginning of the
experiment
• Housed in groups of 6 with free access to food and water in
a temperature and light controlled environment
• 4 Treatment groups were designated in this study
o Control
o Stress
o Sub-amyloid-beta (SAB)
o Stress and sub-amyloid-beta (SSAB)
• The SAB and SSAB groups were infused with subpathogenic
doses of AB1-42
• The Control and Stress groups were infused with an inactive
reverse peptide AB42-1
Methods and Materials
• Both SAB and SSAB were subjected to chronic psychosocial
stress using a form of "intruder" stress
o Rats were kept in the same cages for 1 week then 2 rats were
swapped in each cage daily for 6 weeks total
 Stress was measured by marked increases in corticosterone
levels
• Hippocampal Dissection
o Animals were killed under urethane anaesthesia and the right
hippocampi was removed and the dorsal and vental sides of
area CA1 were separated and placed in microcentrifuge tubes
and stored at -80C until processed
Method and Materials
• Immunoblotting
o Hippocampal tissue was placed in an isotonic buffered cocktail
containing protease and phosphatase inhibitors
o Following antibodies were used in the study
 Amyloid precursor protein (APP)
 Beta-site amyloid precursor protein cleaving enzyme
(BACE)
 p-CaMKII
 CaMKII
 Calcineurin
 Brain-derived neutrotrophic fator
 GAPDH antibody
Statistics
• Carried out with a two-way analysis of variance (ANOVA)
followed by Tukey's post hoc test
• Minimum significance of p<0.05
ANOVA
• Provides statistical test of whether or not the means of several
groups are all equal and therefore generalizes t-test to more than
two groups
o Doing multiple t-tests between 2 groups would result in an
increased chance of committing a type I error (rejects a true
null hypothesis)
Results
• Effects on chronic stress on long term depression (LTD) in subAB
rats
o Magnitude of LTD was similar in both control and subAB rats
however it was significantly enhanced in the stress compared
with the control and subAB rats as shown as a decline in fEPSP
(field exictatory post-synaptic potential) slope
 Control 78.38 +/- 1.97%
 Stress 62.93 +/- 4.35%
 SubAB 75.98 +/- 3.41%
o The slope of fEPSP was significantly (<0.001) lower in SSAB
than those in control, stress, and SAB groups
Results
• Levels of calcineurin during expression of LTD
o The levels of calcineurin were markedly increased by 30 +/- 6%
in stimulated stress group and 26 +/- 3% in SSAB compared to
unstimulated control group
• Levels of p-CaMkII and total CaMKII during expression of LTD
o Levels of p-CaMKII were significantly increased by 116+/31% in SAB and 125+/-47% in SSAB rats as compared to
unstimulated control group
o Significant increases in levels of CaMKII in all the stimulated
groups as compared to the unstimulated groups
• Basal levels of APP
o There was no significant change in the APP levels across all
groups
Discussion
• Human studies have never revealed an association between the
number of stressful or negative life events and the effects on
cognitive decline
• However, studies involving those with AD have shown that
increased cortisol levels with one APOE-4 allele showed poorer
coginitive decline
o The researchers agree with the above statement based on the
data in this study that points towards accelerated cognitive
impairment in chronic stress situations
• Chronic stress compounded with amyloid-beta causes an enhanced
LTD shown in the SSAB group
• Total CaMKII was increased in all groups whereas p-CaMKII was
only increased in the stress groups and the normal brain both work
to reverse LTD but in the SAB and SSAB group it potentiated
LTD
Discussion
• As the great majority of the cases of AD are of the late onset
sporadic type, it is presumed that it may be triggered or
accelerated by non-genetic risk factors, such as chronic stress
• Exposure to stress lead to an increase in LTD but was enhanced
with the addition of amyloid-beta
• The exact mechanism of acceleration is still to be explained but
there are currently 2 ideas
o Excessive secretion or prolonged exposure to glucocorticoids
increases neuronal vulnerability to age-related disease
o Alter the processing and production of various AD-related
proteins resulting in negative alterations in cognition and
synaptic plasticity
Author's Conclusions
Resources
1. "Analysis of Variance." Wikipedia, the Free Encyclopedia.
Web. 08 Feb. 2012. <http://en.wikipedia.org/wiki/ANOVA>.
2. Alzheimer, Alois. "Alzheimer's Disease." Wikipedia, the Free
Encyclopedia. Web. 08 Feb. 2012.
<http://en.wikipedia.org/wiki/Alzheimer>.