Study On The Effect Of β-arrestin On Memory Consolidtion And Memory Reconsolidation

Theβ-arrestins are expressing ubiquitously in mammals, includingβ-arrestin 1 andβ-arrestin 2 respectively, which were originally described as molecules that desensitize the seven transmembrane spanning receptors (7TMR) in conjunction with G protein coupled receptor kinases.β-arrestins bind with the receptor, which blocks their interaction with heterotrimeric G proteins. In this way, the G protein dependent signal pathways activation by the activation of 7TMR is terminated. For example, deletion ofβ-arrestin 2 can enhance morphine-induced analgesia and reward in mice by desensitizingμopioid receptor. Recently some research have establisded the new roles ofβ-arrestin by serving as multifunctional adaptors/scaffolding proteins to promote 7TMR trafficking and signaling. By scaffolding the kinases,β-arrestins bring the activited kinases to the target subcellular localization under the control of the receptor. With scaffolds compartmentalized signalling cascades,β-arrestins regulate the biological effects of the kinases by bringing them into close proximity with their ultimate targets. For example, with the activation of opioid receptor,β-arrestin translocates to nuclear and recruits p300 to p27 and c-fos promoter regions. Under the activation ofβ-adrenergic receptors in the plasma membrane,β-arrestin recruited PDEs to limit activation of membrane associated cAMP-activated protein kinase through receptor desensitization and increasing the rate of its degradation at the membrane. Meanwhile, through recruiting the kinases and changing their activity,β-arrestin transfer the signals from receptors to the target molecues. For example, with the activation ofβ-adrenergic receptor,β-arrestin also function as mitogen activated protein kinase (MAPK) scaffolds, bringing together three components of MAPK signaling modules and inducingβ-arrestin dependently sustained ERK activation. However most studies are still limited to the in vitro results and the physiological function ofβ-arrestin dependent signal pathways are unclear.β-arrestin is abundant in the central nerves system, such as cortex, hippocampus, extended amygdala and hypothalamus, while the central functions have not been extensively studied. Based on the recent investigation aboutβ-arrestin, this study tries to explore the physiological and patholoical role ofβ-arrestins in central nerves system. Combined with molecular biological methods, the behaviors of learning and memory were performed in theβ-arrestin wild type and knockout mice to reveal the potential role ofβ-arrestin in learning and memory. Our results showed that:1)β-arrestin 2 deletion impaires consolidation of conditioned fear memory in mice. With one pair of a tone and a foot shock, theβ-arrestin 2 KO mice was impaired in conditioned fear memory retention one hour or one day after training. What's more, with 5 pairs intense training, the KO mice showed the decrease learning ability and impaired fear conditioned memory retention one day after training. The above results indicated thatβ-arrestin 2 is involved in consolidation of fear conditioning.2) PKA activity change isβ-arrestin 2 dependent in amygdala during the consolidation of fear conditioning. One pair training increased the PKA activity in membrane of WT mice amygdala, but had no effect on that ofβ-arrestin 2 KO mice. Mean while, the PDE4 selective inhibitor could decrease the PKA activity in WT mice amygdala but not inβ-arrestin 2 KO mice. AC activator forskolin could enhance the PKA activity in amygdala of WT mice but could not increase PKA activity further after paired training. The results suggest thatβ-arrestin 2 dependent regulation of PKA activity takes part in the formation of fear conditioned memory.3)β-arrestin 2 expressing in lateral amygdala (LA) restored fear conditioned memory. With microinjection the adenovirus expressingβ-arrestin 2 was delivered into the bilateral amygdala, which restored the impaired fear conditioned memory and the regulation of PKA activity. The results indicated that theβ-arrestin 2 in LA is necessary of the consolidation of fear conditioning.1)β-arrestin 2 is required for memory reconsolidation of object recognition. With the extensive training of two object recognition, theβ-arrestin 2 KO mice did not show the deficiency in memory consolidation. While one day after the re-exposure of orignal two object, the long-term memory was impaired inβ-arrestin 2 KO mice, while the short-term memory was intact after retrieval in the KO mice. At the same time,β-arrestin 2 KO mice also showed the impaired reconsolidation of spatial memory with Morris water maze test. The results show that deficiency ofβ-arrestin 2 leads to the failure the reconsolidation of object recognition.2)β-arrestin 1 is not necessary for memory reconsolidation of object recogniton. Theβ-arrestin 1 KO mice showed intact memory reconsolidation in object recognition.3)β-adrenergic receptor (β-AR) activation participates in memory reconsolidation of object recognition. To testify the effect ofβ-adrenergic receptor, the upstream signals of P-arrestin 2, on reconsolidation of recognition retention, propranolol, theβ-adrenergic receptor antagonist, was introduced in our study. With administration right after retrieval,β-AR, especiallyβ1-AR inhition disrupted reconsolidation expression of WT mice.4)β-AR activation andβ-arrestin 2 are crucial for ERK activation in entorhinal cortex post retrieval. ERK inhibition with U0126 impaired the reconsolidation of object recognition. Meanwhile, the level of ERK phosphorylation greatly increased after retrieval, which could be inhibited by the performation ofβ-AR antagonist andβ-arrestin 2 deficiency. Additionally, the activation of ERK could not be induced byβ-AR agonist inβ-arrestin 2 KO mice.5) Local Expression ofβ-arrestin 2 in ECM restores the impaired reconsolidation in KO mice. The adenovirus expressing green fluorescent protein (GFP) andβ-arrestin 2 were introduced in ECM via a microcannula. The percentages of ECM neurons expressing GFP in KO mice were 23.15±5.7%. The memory retention test showed that KO mice with the expression ofβ-arrestin 2 restored memory reconsolidation, which could be suppressed byβ-AR antagonist.Taken together, the different roles and mechanisms ofβ-arrestin in learning and memory were systematically studied in this research. In the present study, we explored the novel function ofβ-arrestin in memory consolidation and reconsolidation. Firstly, we find thatβ-arrestin 2 is crucially involved in consolidation of fear conditioning through the regulation of PKA activity; Secondly, we show thatβ-arrestin 2/β-adrenergic receptors dependent activation of ERK signal especially in the medial entorhinal cortex is critical for the reconsolidation of object recognition. Ultimately, the understanding of molecular and anatomical mechanisms of memory consolidation and reconsolidation will contribute to the theoretical discussion in ongoing memory maintenance and its relation to other memory processes.