AKT/GSK-3 β / β -CATENIN SIGNALLING WITHIN HIPPOCAMPUS

ANDAMYGDALA REFLECTS GENETICALLY

DETERMINED DIFFERENCESIN POSTTRAUMATIC STRESS DISORDER LIKE SYMPTOMS

Presented by Justin P. Smith

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

PTSD Review

Evidence for genetic & environmental factors β-catenin required in amygdala for normal

consolidation, but not acquisition of fear memories* Suggesting β-catenin modulates synaptic

remodeling and stabilization of long-term memory*

*Maguschak & Ressler Nat Neurosci 2008

Background

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 β-catenin plays a similarly important role in consolidation of fear memories at the level of the basolateral amygdala

Background cont.

GSK-3 β (glycogen synthase kinase -3 β) controls β-catenin

“Normal” conditions: GSK-3 β phosphorylates (℗) β-catenin to decrease activity

AKT ℗ inactivates GSK-3 β ℗ which stabilizes β-catenin Stabilized levels of β-catenin then mediates

gene transcription

Mechanism

Wada 2009

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 β / β -catenin-cascades within the dorsal hippocampus and basolateral amygdala (BLA) in the long-term aftermath of exposure to an inescapable foot shock

Why-What

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)

Animals

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!)

Experiments

Box plot

Minimum

Upper quartile (75th percentile)

Lower quartile (25th percentile)

Median

Maximum

Dr. John Tukey

Fig 1. B6N mice purchased from commercial breeders. Western blot, shock/no shock. Relative to mean levels of non-shock controls.

Amygdala

PTSD-like symptoms coincide with changesin kinase and transcription factor activities at remote time points

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)

Tone (Afternoon)

Embryo transfers-within-strain (N/N, J/J)-between-strain (N/J, J/N)-N- PTSD mice-J- Resilient mice

Maternal effect

Maternal effect

Maternal effect

Fig 3 Fig 4

Embryo

Mother

DonorEffect

Fig 5 Fig 6

RecipientEffect

Fig. 7. Changes in signaling cascades within the hippocampus.

Fig. 8. Changes in signaling cascades within the amygdala.

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?)

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???

Discussion cont.

Fig 2C- _/J had higher sensitized fear than _/N Not statistically secured were separately

analyzed (Fig 5C & 6C) AKT/GSK-3 β /β -catenin pathway

decreased rather than increased GSK-3 β 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

Discussion cont.

Take home Identifies lasting changes in AKT/GSK-3 β / β -

catenin-cascades in the amygdala and hippocampus

B6N’s showed long-term contextual & sensitized fear dHippocampus: increased phosphorylated AKT In BLA:

higher levels of phosphorylated AKT and GSK-3 β Increased β -catenin levels

Embryo transfer did not alter effect (mother’s genotype had no effect) Shocked B6N levels of phosphorylated GSK-3 β

and β -catenin levels were decreased in dHippocampus but increased in BLA compared to shocked B6JOIa

Thank you