Inducible gene expression plays a central role in neuronal plasticity, learning, and memory. Dysregulation of these processes can lead to severe neuronal disorders and cognitive impairment. In addition to coding transcripts (mRNAs), non-coding microRNA (miRNAs) appear to play a regulatory role in the neuronal plasticity. miRNAs are small, evolutionarily-conserved signaling molecules that act as silencing regulators of mRNA targets. Disruption of miRNA expression and signaling is associated with severe cognitive impairment. Thus, the functional role of miRNAs in nervous system physiology and cognition merits close examination. This proposal focuses on the CREB-regulated miRNA132 (miR132), which has been shown to be expressed in an activity-dependant manner in vitro and in vivo. Altered miR132 is associated with several psychiatric (schizophrenia) and degenerative (Huntington's disease) disorders of the nervous system. Recently, my published work using a miR132 transgenic mouse strain revealed that miR132 significantly regulates hippocampal dendrite spinogenesis in vivo, as well as recognition memory. However, the details of miR132's molecular regulation and its behavioral consequences remain unclear. I hypothesize that miR132 is expressed in mature and developing neurons throughout the hippocampus, and its inducible expression is required for normal memory formation. As an extension of this idea, I further propose that miR132 levels (both basal and inducible) must be tightly controlled, and that deviation from this range will result in cognitive deficits. Here, I propose a strategy to assess the hippocampal expression of miR132, to explore its behavioral/cognitive consequences and to profile a subset of its putative molecular (mRNA) targets. To this end, Aim 1 will utilize in situ hybridization and immunolabeling techniques to examine basal miR132 expression patterns within the hippocampus, as well as profile its inducible expression following environmental enrichment and learning paradigms.
In Aim 2, I will employ the noted tetracycline-regulated transgenic mouse strain (tTA:miR132) that expresses miR132 in forebrain neurons to explore the contribution of miR132 to learning and memory. To this end, I will initially profile cognitive consequences of tonic transgenic miR132 expression. I will then examine whether the miR132 learning phenotype is plastic in nature, or whether it is fixed (i.e. a permanent cognitive deficit) by taking advantage of the tetracycline-controlled promoter to shut down transcription of the transgenic miR132. Finally, although I have shown that tonically high levels of transgenic miR132 impair learning, I hypothesize that there exists an optimized level of miR132 expression that facilitates cognitive performance. This idea will be tested in experiments which will titer transgenic miR132 (using doxycycline) to parallel the level observed following environmental enrichment, in an attempt to phenocopy cognitive enhancement resulting environmental enrichment. Finally, Aim 3 proposes to use the Solexa Deep Sequencing technique to profile downstream targets of miR132 in the tTA:miR132 mouse strain. Further, a small subset of these targets (5 in total) will be validated using molecular and histological approaches. In sum, a more complete understanding of miR132's role in neuronal signaling and cognition should further our efforts to develop novel therapeutic strategies for the treatment of a variety of mental disorders.
miR132 is a molecular regulator of neuronal signaling that is readily expressed in the hippocampus, but the details of its effect on learning and memory remain poorly understood. My research will examine the behavioral consequences of miR132, its regulation of putative downstream targets, and its role within specific cell populations within the hippocampus.
|Hansen, Katelin F; Sakamoto, Kensuke; Pelz, Carl et al. (2014) Profiling status epilepticus-induced changes in hippocampal RNA expression using high-throughput RNA sequencing. Sci Rep 4:6930|
|Hansen, Katelin F; Karelina, Kate; Sakamoto, Kensuke et al. (2013) miRNA-132: a dynamic regulator of cognitive capacity. Brain Struct Funct 218:817-31|