The Role Of Steroid Receptor Coactivator-1 In The Consolidation And Reconsolidation Of Contextual Fear Memory

Posttraumatic stress disorder(PTSD)is a psychiatric disorder that develops following exposure to a traumatic event.PTSD was found to be associated with deficits in interpersonal relationships and social functions,or comorbid with anxiety,depression,substance abuse,etc.,which means the low quality of life.However,the neurobiological mechanism of PTSD is not fully understood,and the current mainstream psychotherapy and drug treatment have limited efficacy.Therefore,it is of great significance to study the pathogenesis of PTSD and find new targets for its prevention or intervention.The exposure of trauma-related clues trigger flashbacks of fear memory in PTSD patients,which in turn leads to avoidance behavior,excessive alertness,and negative cognition and emotions which are important characteristics of PTSD,indicating that fear memory is closely related to the occurrence,development,and prognosis of PTSD.The study of the mechanisms underlying fear memory may bring new opportunities for the prevention and treatment of PTSD.Studies have shown that memory is a dynamic process,which usually includes several processes such as the acquisition,consolidation,reactivation,reconsolidation,and extinction.It is an important experimental paradigm to study the mechanism of PTSD-related fear memory in the laboratory by establishing a connection between conditional stimulus(context)and non-conditioned sensory stimulus(shock)that cause fear through paired training.The conditioned memory is transformed into a conditional response to fear through a process of consolidation.Recently acquired memories are fragile and progressively stabilize into stable long-term memory(LTM)through a protracted protein synthesis process referred to as consolidation,which is sustained in the next many hours or days after memory acquisition.When reexposure to memory-related conditional cues,fear memory will be reactivated and returned to the labile state.The reactivated memory must undergo a similar protein synthesis-dependent stabilization phase named reconsolidation for re-stabilization.Memory consolidation and reconsolidation depend on the context,and the hippocampus is a crucial area for contextual information processing as well as a target of stress-related memory impairment,because this area is vulnerable to stress-induced neuroendocrine responses.Previous studies have demonstrated that hippocampal-dependent memory is profoundly affected by steroids such as sex steroids and stress steroids.However,the mechanisms underlying the role of steroids in the regulation of memory processes are far from clear.Steroid receptor coactivator-1(SRC-1),a member of the p160 coactivator family,has been shown to enhance the transcriptional activity of steroid receptors,such as androgen receptor(AR),estrogen receptors(ER)and thyroid receptor(TR)in a ligand-dependent manner.Accumulating studies have shown that SRC-1 appears to be closely related not only to hormone-dependent structures and reproductive behaviors but also to cognition,motor control,and neuroendocrine regulation.It is worth noting that SRC-1 is strongly involved in hippocampal structure and function.High levels of SRC-1 immunoreactivity are observed predominantly in the hippocampus,and changes in SRC-1 levels in the hippocampus are highly correlated with the expression of synaptic proteins,such as GluR1,PSD-95,and spinophilin.Our recent study showed that downregulated SRC-1 in the hippocampus induced a decrease in CA1 synapse density as well as postsynaptic density(PSD)thickness,and long-term potentiation(LTP)and spatial memory were significantly impaired at the same time.However,the effect of hippocampal SRC-1 on memory processes,such as consolidation and reconsolidation,remains unknown.In the present study,we used western blot,immunofluorescent staining,high plus maze and open field test for the examination.First,the contextual fear conditioning paradigm was constructed in adult male C57BL/6 mice to test whether SRC-1 is involved in the consolidation and reconsolidation of contextual fear memory.Then,adeno-associated virus(AAV)delivery short hairpin RNA(shSRC-1 and GFP control)was infused into the hippocampus to block hippocampal SRC-1 level.Immunofluorescent staining and western blot were used to detect the efficiency of transfection.Afterward,elevated cross and open field experiments were used to observe the effects of virus injection and inhibition of hippocampal SRC-1 on anxiety and locomotor activity of mice,subsequently,test the effect of SRC-1 knockdown on the consolidation of contextual fear memory.At last,we measured the effects of SRC-1 knockdown on the reconsolidation of contextual fear memory,and the possible mechanism of hippocampal SRC-1 in the regulation of contextual fear memory.Main results:1.After contextual fear memory acquisition,the expression of SRC-1 was significantly increased at 90 minutes.The increased expression of SRC-1 during contextual fear memory acquisition was specific to the association of the context with the shock rather than the context or shock alone.After contextual fear memory recall,the expression of SRC-1 was significantly increased at 30 minutes.2.The adeno-associated virus carried short hairpin RNA can be successfully transfected and expressed in the CA1 pyramidal cells on both sides of the hippocampus.Additionally,western blot analyses showed that injection with shSRC-1 induced a significant decrease in SRC-1 expression in the hippocampus compared with the GFP control group.3.Both the shSRC-1 group and GFP control group were presented to the same behaviour paradigm.For the elevated plus maze,there was no significant difference between the two groups in the distance traveled,time spent in the open arm and the number of entries in the open arms.The open field test presented similar results: the distance traveled,time spent in the center and distance traveled in the center of mice injected with shSRC-1 were not lower than those of the control group.4.For the fear acquisition,both the SRC-1 knockdown group and the control group showed intact post-shock freezing.However,animals injected with shSRC-1 exhibited less freezing time than GFP control animals in the test session 24 h later,indicating that the impaired consolidation of contextual fear memory.Contextual fear memory acquisition leads to an increased expression of synaptic plasticity protein PSD-95 and GluR1,while SRC-1 knockdown revised the expression.5.No significant difference was found between the R-Con,NR-shSRC-1 and R-shSRC-1 groups in fear memory acquisition.Tests were conducted 24 h after fear memory retrieval,and the results showed a significant interaction between treatment and session.The R-shSRC-1 group showed the lowest freezing time compared with the R-Con and NR-shSRC-1 groups.Furthermore,the levels of GluR1 and PSD-95 were significantly increased following memory retrieval.However,this increase was reversed by SRC-1 knockdown.main conclusions:1.The expression of SRC-1 in the hippocampus increased during the consolidation of episodic fear memory,and inhibition of SRC-1 expression during consolidation could damage the fear memory of mice;suggesting that SRC-1 participates in the regulation of episodic fear memory consolidation.2.Reactivation of episodic fear memory up-regulates the expression of SRC-1 in the hippocampus,and inhibition of SRC-1 expression during reconsolidation can damage the fear memory of mice;suggesting that SRC-1 regulates the consolidation of episodic fear memory.3.The establishment and activation of contextual fear memory led to increased expression of synaptic plasticity-related proteins,PSD-95 and GluR1,while inhibition of hippocampal SRC-1 expression suppresses the expression of synaptic proteins,suggesting that the change of synaptic protein expression may be the foundation of SRC-1 affects the consolidation and reconsolidation fear memory.