ETD

• IEGs

Memory formation and learning are complex processes initiated by neuronal activation. This activation induces activity-dependent transcriptional and epigenetic changes, with Immediate Early Genes (IEGs) playing a central role in converting transient synaptic activity into long-lasting molecular programs. These enduring neuronal and synaptic modifications underlie brain plasticity and ultimately enable the incorporation of neurons into a memory trace.
Among IEGs, the transcriptional complex Activator Protein-1 (AP-1), resulting from the heterodimerization of FOS and JUN family members, is considered a master regulator of synaptic gene expression. FOS, in particular, is a well-established marker of neuronal activity and it has been widely used to tag, track and ultimately modulate activated neurons. Nevertheless, the specific role of AP-1 in memory and plasticity has remained unresolved, largely due to the functional redundancy of FOS (Fos, Fosb, Fosl1, Fosl2) and JUN (Jun, Junb, Jund) gene families, which has jeopardized classical loss-of-function approaches targeting individual AP-1 subunits.
To overcome this limitation, we propose two different approaches to target specifically the DNA-binding activity of AP-1. The first approach is aimed to buffer the DNA-binding capacity of AP-1 by the usage of double-stranded oligonucleotides containing the AP-1 binding-site consensus sequence (Decoy oligos). The second approach relies on a small molecule which interacts and inhibits AP-1 DNA-binding.
The efficiency of these strategies was evaluated in neuronal primary culture, using KCl excitation as a paradigm to induce AP-1 activity. Through molecular biology techniques, including RT-qPCR, immunocytochemistry (ICC) and luciferase reporter assay, we were able to assess the effects of our two inhibitory approaches on AP-1-dependent gene expression.

While the cell toxicity and death caused by the decoy approach prevented a fine assessment of its specific impact in transcription, we were able to demonstrate the efficacy of the AP-1 inhibitor to partially block the induction ofon multiple known AP-1 targets. These results endorse further experiments in vivo, to determine how AP-1 inhibition in the hippocampus might affect memory processes at the molecular, synaptic and behavioural levels.
These results underscore the potential of targeting AP-1 or its downstream effectors for therapeutic purposes, for example to counteract cognitive decline during aging or to support cognitive enhancement in brain disease.