Abstract
Coordinated regulation of gene expression is essential for consolidation of the memory mechanism, long-term potentiation (LTP). Triggering of LTP by N-methyl-D-aspartate receptor (NMDAR) activation rapidly activates constitutive and inducible transcription factors, which promote expression of genes responsible for LTP maintenance. As microRNA (miRNA) coordinate expression of genes related through seed sites, we hypothesize that miRNA contribute to the regulation of the LTP-induced gene response. MiRNA function primarily as negative regulators of gene expression. As LTP induction promotes a generalized rapid up-regulation of gene expression, we predicted a complementary rapid down-regulation of miRNA levels. Accordingly, we carried out global miRNA expression profiling in the rat dentate gyrus 20 min post-LTP induction in vivo. Consistent with our hypothesis, we found a large number of differentially expressed miRNA, the majority down-regulated. Detailed analysis of miR-34a-5p and miR-132-3p revealed this down-regulation was transient and NMDAR-dependent, whereby block of NMDARs released an activity-associated inhibitory mechanism. Furthermore, down-regulation of mature miR-34a-5p and miR-132-3p occurred solely by post-transcriptional mechanisms, occurring despite an associated up-regulation of the pri-miR-132 transcript. To understand how down-regulation of miR-34a-5p and miR-132-3p intersects with the molecular events occurring following LTP, we used bioinformatics to identify potential targets. Previously validated targets included the key LTP-regulated genes Arc and glutamate receptor subunits. Predicted targets included the LTP-linked kinase, Mapk1, and neuropil-associated transcripts Hn1 and Klhl11, which were validated using luciferase reporter assays. Furthermore, we found that the level of p42-Mapk1, the protein encoded by the Mapk1 transcript, was up-regulated following LTP. Together, these data support the interpretation that miRNA, in particular miR-34a-5p and miR-132-3p, make a surprisingly rapid contribution to synaptic plasticity via dis-inhibition of translation of key plasticity-related molecules.
Highlights
Long-term potentiation (LTP) exhibits many properties key to a mnemonic device
While induction of LTP is dependent largely on activation and trafficking of 2-amino-3(3-hydroxy-5-methyl-isoxazol-4-yl) propanoic acid (AMPA) and N -methyl-D-aspartate (NMDA)-subtypes of glutamate receptors, its persistence is dependent on regulated protein synthesis at synapses and activation of both constitutive and inducible transcription factors (Abraham and Williams, 2003)
DBS resulted in significant increases in the field excitatory postsynaptic potential and population spike (PS; Figures 1A,B) measured 15–20 min post-DBS (n = 10), as well as a dramatic up-regulation of activity-related cytoskeletal protein (Arc) mRNA, a canonical LTP-associated gene (RT-qPCR: tetanised/control: p = 0.02, n = 10; one-sample t-test; Figure 1C)
Summary
Long-term potentiation (LTP) exhibits many properties key to a mnemonic device. Paramount among these is its remarkable persistence (Abraham et al, 2002). Our bioinformatics analysis showed that these regulated genes form highly significant networks, comprising groups of co-regulated genes and “hub” molecules that are likely to act as central controllers of the LTP-related gene response. Consistent with the dogma of the field, the networks engaged 20 min post-LTP induction featured transcription factors as central hubs and predicted that these rapidly responding gene networks contribute to the regulation of protein kinase activity and calcium dynamics. The analysis predicted important roles for microRNA (miRNA) in the control of LTP-related gene expression, even at this early time-point
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