Transcription factor Egr-1 is required for long-term fear memory and anxiety

Shanelle W. Ko^1,**, AO Hu-Shan^1,**, Amelia Gallitano-Mendel², QIU Chang-Shen¹, WEI Feng¹, Jeffrey Milbrandt², ZHUO Min^1,*

¹Department of Physiology, University of Toronto, Faculty of Medicine, University of Toronto Centre for the Study of Pain, Medical Science Building, 1 King's College Circle, Toronto, Ontario, M5S 1A8, Canada; ²Washington University School of Medicine, Departments of Pathology and Psychiatry, St. Louis, MO 63110, USA

Abstract: The zinc finger transcription factor Egr-1 is critical for coupling extracellular signals to changes in cellular gene expression. In the hippocampus and amygdala, two major central regions for memory formation and storage, Egr-1 is up-regulated by long-term potentiation (LTP) and learning paradigms. Using Egr-1 knockout mice, we showed that Egr-1 was selectively required for late auditory fear memory while short term, trace and contextual memory were not affected. Additionally, synaptic potentiation induced by theta burst stimulation in the amygdala and auditory cortex was significantly reduced or blocked in Egr-1 knockout mice. Our study suggests that the transcription factor Egr-1 plays a selective role in late auditory fear memory.

Key words: Egr-1; long-term potentiation; fear memory; amygdala; auditory cortex

转录因子Egr-1参与长期性恐惧记忆和焦虑

Shanelle W. Ko^1,**，敖虎山^1,**，Amelia Gallitano-Mendel²，邱长申¹，魏 峰¹，Jeffrey Milbrandt²，卓 敏^1,*

¹多伦多大学医学院生理系，多伦多大学痛觉研究中心，多伦多，安大略省 M5S1A8，加拿大；²华盛顿大学医学院病理和精神病系，圣路易丝，密苏里州 63110，美国

摘 要：锌指转录因子Egr-1在将细胞外信号和胞内基因表达的变化相耦联过程中发挥重要的作用。海马和杏仁体是记忆形成 和储存的两个主要的脑区。在海马和杏仁体中，Egr-1 可被长时程增强(long-term potentiation, LTP)和学习过程上调。在Egr-1敲除小鼠上观察到晚时相声音恐惧记忆受损，而短时的痕迹和场景记忆却不受影响；另外，在 Egr-1敲除小鼠上，用theta burst刺激杏仁体和听觉皮层所引起的突触增强被明显减弱或完全阻断。因此，我们的研究表明，转录因子 Egr-1选择性地在晚时相听觉恐惧记忆中发挥作用。

关键词：Egr-1；长时程增强；恐惧记忆；杏仁体；听觉皮层

中图分类号：Q426; Q427; R338.64

Received 2005-03-03 Accepted 2005-05-09
This work was supported by the EJLB-CIHR Michael Smith Chair in Neurosciences and Mental Health, Canadian Research Chair, and NIH NINDS NS42722.
^*Corresponding author. Tel: +1-416-9784018; E-mail: min.zhuo@utoronto.ca
^**Contributed equally to this work.

Emotional learning and its expression in mammals depends on activity-dependent plasticity in higher brain structures including the amygdala, hippocampus and related cortical areas^[1-5]. Long-term changes in synaptic transmission, also called long-term potentiation (LTP), have been predominantly studied in brain slice preparations and are thought to be required for the establishment and consolidation of fear memory^[3,6]. Two different temporal phases of synaptic LTP have been reported in the hippocampus and amygdala: short-term potentiation requires rapid signaling in synapses^[7-9] while late phases of LTP require gene activation and new protein synthesis^[10,11]. Supporting the role of the late phase of LTP in long-term memory, inhibition of protein synthesis has been shown to affect long-term memory^[12-15].

The cyclic AMP-response element binding protein (CREB) is a major transcription factor associated with long-term memory^[16-21]. CREB in hippocampal neurons can be activated by physiological learning and artificial high-frequency tetanic stimulation^[16]. Activation of NMDA receptors and/or L-type voltage-gated calcium channels (VDCCs) leads to activation of CREB in hippocampal neurons^[10,22]. Numerous studies elucidate CREB's role in memory. Inhibition of CREB activity by blockade of its upstream signaling pathways, inactivation by antisense oligonucleotides, or genetic deletion, reduces or blocks late-phase LTP and produces deficits in long term memory^{[16,20,21,23]}. Other studies show that CREB expression is important for memory of fear associations and taste aversion^[17,18]. Similarly, the overexpression of CREB was reported to facilitate long-term fear memory^[24,25]. Recent studies show that a signaling pathway consisting of mitogen activated protein kinase (MAPK), CREB, and the transcription factor Egr-1 may be important for long term memory and associated synaptic plasticity^[20].

The zinc finger transcription factor Egr-1 (also called NGFI-A, Krox24, or zif/268) is critical for coupling extracellular signals to changes in cellular gene expression^[26-28]. EGR-1 mRNA and protein are expressed in the neocortex, hippocampus, entorhinal cortex, amygdala, striatum and cerebellum^[29-31]. The upstream promoter region of Egr-1 contains binding sites for cyclic AMP-response elements (CRE), suggesting that Egr-1 may act downstream from the CREB pathway^[20,32]. In the hippocampus, Egr-1 is up-regulated by tetanic stimulation^[33-36] and during learning or memory retrieval^[19,37-40]. Deletion of Egr-1 leads to a reduction or blockade of hippocampal LTP in the CA1 region and dendate gyrus^[41,42], as well as an impairment in long term spatial memory^[42]. A role for Egr-1 in the amygdala has been reported in the acquisition^[43] or recall^[19,44] of contextual fear memory. Long-term fear memory induced by fear conditioning triggered the NMDA receptor-dependent activation of Egr-1 in neurons found in the amygdala^[43,45,46]. Two recent reports highlight the importance of Egr-1 in remote memory and the reconsolidation fear memory^[44,47]. An impairment in the reconsolidation of contextual fear memory was reported when antisense oligodeoxynucle otides for Egr-1 were infused into the hippocampus of rats^[47]. In another study, Egr-1 expression was increased in the anterior cingulate cortex of mice upon re-exposure to the chamber where they had received footshocks 36 d prior^[44]. While both studies reinforce the idea the Egr-1 is an important player in the retention of contextual fear memory, the role of Egr-1 in auditory fear memory has not been investigated. In addition, no study has reported the role of Egr-1 in contextual and auditory fear memory using Egr-1 knockout mice. (责任编辑：泉水)