AKT/GSK-3/-CATENIN SIGNALLING WITHIN HIPPOCAMPUS AND AMYGDALA REFLECTS GENETICALLY DETERMINED DIFFERENCES IN POSTTRAUMATIC STRESS DISORDER LIKE SYMPTOMS

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AKT/GSK-3 ß / ß -CATENIN SIGNALLING WITHIN
HIPPOCAMPUS ANDAMYGDALA REFLECTS GENETICALLY
DETERMINED DIFFERENCESIN POSTTRAUMATIC STRESS
DISORDER LIKE SYMPTOMS

• Presented by Justin P. Smith

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PTSD Review

• Traumatic Event
• Persistent exaggerated fear responses, avoidance
  behavior, hyper-arousal, and emotional numbing
• .33 of PTSD patients have symptoms for 10 years
  despite therapeutic interventions

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Background

• Evidence for genetic environmental factors
• ß-catenin required in amygdala for normal
  consolidation, but not acquisition of fear
  memories
• Suggesting ß-catenin modulates synaptic
  remodeling and stabilization of long-term memory
• Maguschak Ressler Nat
  Neurosci 2008

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Background cont.

• Inescapable foot shock- their model of PTSD
• Maternal inexperience as potential risk factor
• B6N PTSD susceptible, increased contextual and
  sensitized fear response
• B6JOIa PTSD resilient
• Maguschak and Ressler paper suggests that the
  transcription factor ß-catenin plays a similarly
  important role in consolidation of fear memories
  at the level of the basolateral amygdala

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Mechanism

• GSK-3 ß (glycogen synthase kinase -3 ß) controls
  ß-catenin
• Normal conditions GSK-3 ß phosphorylates (?)
  ß-catenin to decrease activity
• AKT ? inactivates GSK-3 ß ? which stabilizes
  ß-catenin
• Stabilized levels of ß-catenin then mediates gene
  transcription

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Wada 2009
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Why-What

• Evidence for role of kinases and transcription
  factors, little info about activity changes that
  last more than a couple of hours (exempli gratia
  PTSD)
• This study looks at AKT/GSK-3 ß / ß
  -catenin-cascades within the dorsal hippocampus
  and basolateral amygdala (BLA) in the long-term
  aftermath of exposure to an inescapable foot shock

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Animals

• Male B6N (N) B6JOIa (J) mice
• Embryo-transfers
• (Donor/Recipients)
• (Embryo/Mom)
• B6N donors and B6N recipients (N/N), B6N donors
  and B6JOla recipients (N/J), B6JOla donors and
  B6JOla recipients (J/J), B6JOla donors and B6N
  recipients (J/N)

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Experiments

• Experiment 1. Male B6N
• Groups foot shock, unshocked (cage control).
• tested for sensitized and contextual fear (28
  days after shock) before brain removal (42 days
  after shock)
• Experiment 2. Male B6N and B6JOla
• Within-strain (N/N, J/J) and between-strain (N/J,
  J/N) embryo transfers
• Shocked, tested for sensitized and contextual
  fear (28 days after shock), Western blot analysis
  hippocampus and amygdala
• Limited yield of the transfers did not allow
  inclusion of unshocked controls (no cage
  controls!)

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Box plot
Dr. John Tukey
Maximum
Upper quartile (75th percentile)
Median
Lower quartile (25th percentile)
Minimum
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Fig 1. B6N mice purchased from commercial
breeders. Western blot, shock/no shock.
Relative to mean levels of non-shock controls.
PTSD-like symptoms coincide with changes in
kinase and transcription factor activities at
remote time points
Amygdala
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Fig.2 Fear behavior in mice originating from
commercial breeders or within-strain and
between-strain embryo transfers. 28 days after
shock.
Back in box (Morning)
Embryo transfers -within-strain (N/N,
J/J) -between-strain (N/J, J/N) -N- PTSD mice -J-
Resilient mice
Maternal effect
Tone (Afternoon)
Maternal effect
Maternal effect
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Fig 3
Fig 4
Embryo
Mother
Donor Effect
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Fig 5
Fig 6
Recipient Effect
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Fig. 7. Changes in signaling cascades within the
hippocampus.
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Fig. 8. Changes in signaling cascades within the
amygdala.
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Discussion

• Behavior influenced by both genetic and maternal
  factors
• Molecular level results influenced by embryo
  genotype, not maternal genotype
• Unclear as to when after foot shock changes occur
  (different waves of kinase activity?)

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Discussion cont.

• It is tempting to speculate that the changes in
  kinase activity observed in the present study
  contribute to this phenotype, similarly to the
  role of PKA/adenylate cyclase 1, NMDA receptor
  NR1 subunits and CaMKII in development and/or
  maintenance of remote contextual fear memory.
• Are they speculating???

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Discussion cont.

• Fig 2C- _/J had higher sensitized fear than _/N
• Not statistically secured were separately
  analyzed (Fig 5C 6C)
• AKT/GSK-3 ß /ß -catenin pathway
• decreased rather than increased GSK-3 ß activity
  within the amygdala coincides with sustained
  PTSD-like symptoms
• the same pathway appears to be regulated in the
  opposite manner in the amygdala and hippocampus

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Take home

• Identifies lasting changes in AKT/GSK-3 ß / ß
  -catenin-cascades in the amygdala and hippocampus
• B6Ns showed long-term contextual sensitized
  fear
• dHippocampus increased phosphorylated AKT
• In BLA
• higher levels of phosphorylated AKT and GSK-3 ß
• Increased ß -catenin levels
• Embryo transfer did not alter effect (mothers
  genotype had no effect)
• Shocked B6N levels of phosphorylated GSK-3 ß and
  ß -catenin levels were decreased in dHippocampus
  but increased in BLA compared to shocked B6JOIa

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Thank you