Induction of synaptic protein degradation enhances memory destabilization
upon retrieval
Mohammad Shehata1,2, Kareem Abdou1,2, Qi Zhao1,2, Reiko, Hirofumi Nishizono2,3, Mina Matsuo3, Kaoru Inokuchi1,2
1 Department of Biochemistry, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan
2 Japan Science and Technology Agency, CREST, Kawaguchi, Japan
3 Division of Animal Experimental Laboratory, Life Science Research Center, University of Toyama, Toyama, Japan.

Introduction

Abstract
Memories, when retrieved, enter in destabilization step which require protein
synthesis for re-stabilization. It has been reported that inhibition of synaptic protein
degradation prevents memory destabilization; however, whether the reverse
relationship is true, is still unknown.
This study demonstrates that induction of autophagic protein degradation enhances
synaptic destabilization in a long-term potentiation (LTP)-reconsolidation model infreely moving rats, and enhances fear memory destabilization in a contextual fearreconsolidation paradigm in mice. Furthermore, induction of autophagy overcomes aboundary condition hindering auditory fear memory reconsolidation. The autophagy
induction effects are dependent on AMPA receptor endocytosis, and correlate with its
degradation in ensemble neurons.
Our results complement the evidence for a causal relationship between protein
degradation and memory destabilization, give more insight into the mechanisms
controlling memory destabilization and boundary conditions, and suggest autophagy
inducers as a useful tool for the treatment of memory-related psychological diseases,
such as post-traumatic stress disorder (PTSD).

①

Memory state is dependent on protein
synthesis and/or degradation

Autophagic process regulates synapticfunction and plasticity.
Retrieval

Question: Whether Autophagy induction can enhance memory destabilization,
therefore more fear memory erasure will be observed.

Autophagy induction enhances synaptic destabilization of LTP in
freely moving rats
Ani+tBC returns LTP to basal level after LFS reactivationaThe Ani+tBC effect was blocked by IFN

dcb

Two-way ANOVA;
Holm-Sidak multiple comparison;* p < 0.05; ** p < 0.01; *** p < 0.001;**** p < 0.0001▪ Electrophysiological stimulation: Tetanus = High frequency stimulation (500 pulses; 10 trains with 1 min intertrain interval. Each train consists of 5 bursts; each one is 10 pulses at 400 Hz, delivered at 1 s interburst interval).
Reactivation = Low frequency stimulation (128 pulses at 8 Hz).

②Autophagy induction combined with protein synthesis inhibition erases context details fromthe hippocampus after context fear conditioning (CFC) retrieval

Autophagy induction by triflouperazine (TFP) or
tat-beclin peptide (tBC) in the hippocampus

cbdaTwo-way ANOVA
Multiple comparisons tests:
Bonferroni's (within group);
Tukey's (Between groups);* P < 0.05; ** P < 0.01, *** p < 0.001)③

Autophagy induction combined with protein synthesis
inhibition erases fear memory from the amygdalaaInduction of autophagy enhances passing of the boundary
conditions for tone fear memory destabilization④

Basolateral amygdala(BLA)b

Two-way ANOVA
Multiple comparisons tests:
Holm-Sidak’s (within group);
Newman-Keuls (Between groups);* P < 0.05; ** P < 0.01, *** p < 0.001)➢ TFC: Tone Fear Conditioning

Lateral amygdala (LA)acb

Two-way ANOVA Multiple comparisons tests:
Bonferroni's (within group); Tukey's (Between groups);* P < 0.05; ** P < 0.01, *** p < 0.001)⑤

Two-way ANOVA
Multiple comparisons tests:
Bonferroni's (within group);
Tukey's (Between groups);* P < 0.05; ** P < 0.01, *** p < 0.001)

One-way ANOVA ;Tukey's Multiple comparisons test
* P < 0.05; ** P < 0.01, *** p < 0.001)

The Autophagy destabilization effect is mediated by AMPA receptor endocytosis inspines of engram neuronsdabcefc

Two-way ANOVAMultiple comparisons tests:
Bonferroni's (within group);
Tukey's (Between groups);* P < 0.05; ** P < 0.01, *** p < 0.001)

Two-way ANOVA ; Bonferroni's Multiple comparison* P < 0.05; ** P < 0.01,Conclusion- Autophagy induction can enhance both synaptic and memory destabilization and it is useful to pass the boundary conditions for memory reconsolidation through thedegradation of the endocytosed AMPAR.
- The behavioral outcome of the combined protein degradation induction and synthesis inhibition differs according to the brain area targeted.

aa) Proposed molecular mechanism for the effect ofautophagy induction on synaptic and memory strengthcbb) The behavior outcome differ according to the brain area targeted