Memory Enhancement by a Genetic Increase in cAMP Signals

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DESCRIPTION (provided by applicant): Consolidation of hippocampus-dependent memory depends on de novo transcription and translation. One of the transcriptional pathways required for consolidation of hippocampus-dependent memory is CRE-,mediated transcription. Calmodulin (CaM)-stimulated adenylyl cyclases, and Erk/MAP kinase (MAPK) plays a major role in calcium activation of CRE-mediated transcription during formation of memory. This proposal focuses on the role of CaM-stimulated adenylyl cyclases in memory and the mechanism for enhanced memory exhibited by mice over-expressing AC1 in the forebrain (AC1+ mice). It is based upon several observations made by this lab including the discovery that CaM-stimulated adenylyl cyclases are required for consolidation of hippocampus-dependent memory, as well as the persistence of remote contextual memory. We also discovered that the nuclear translocation and activation of MAPK during contextual memory formation depends upon CaM-stimulated adenylyl cyclases. We found that the persistence of contextual memory may be maintained by the circadian oscillation of the cAMP/MAPK/MSK1/CREB transcriptional pathway in the hippocampus, an oscillation which depends upon CaM-stimulated adenylyl cyclases. Therefore, we made a transgenic mouse strain over-expressing AC1 in the forebrain, AC1+ mice. Young AC1+ mice have superior memory for novel objects and social recognition and more persistent remote contextual memory. However, the spatial memory of old AC1+ mice is inferior to old wild-type littermates, yet unaffected in young AC1+ mice. We propose that CaM-stimulated adenylyl cyclase activity is required for memory consolidation and memory persistence because it supports the activation and nuclear translocation of MAPK during memory formation and the circadian oscillation of MAPK activity in the hippocampus required to maintain memory. We propose that the stronger memory exhibited by young AC1+ mice may be due to enhanced signaling through the cAMP/MAPK/ MSK-1/CREB signaling pathway as well as amplification of the circadian oscillation of this pathway. We propose that the circadian oscillation of MAPK in the hippocampus may be due to circadian oscillation of CaM-stimulated adenylyl cyclases in the hippocampus. PUBLIC HEALTH RELEVANCE: The brain has the remarkable ability to process and store enormous amounts of information. Consequently, there is intense interest in molecular mechanisms underlying the formation and persistence of memory. Memory loss associated with aging and neurodegenerative diseases including Alzheimer's disease is devastating, not only to the patient but also the patient's family. This grant focuses on the molecular mechanisms for memory formation and the persistence of long-term memory. In the last grant period, we identified a potential molecular target for memory improvement, a calcium-sensitive adenylyl cyclase, AC1. This enzyme generates signals at the synapses in the brain, which leads to memory trace. We made a transgenic mouse over-expressing AC1 in mouse brain. This mouse strain has superior memory. The objectives of this grant are to understand why AC1 is required for memory and why AC1 over-expressing mice have superior memory.