Cognition, learning, and memory all rely on precise neurotransmission and plasticity at glutamatergic
synapses in the brain. These processes require glutamate-responsive AMPA receptors (AMPARs), which
mediate fast synaptic transmission in the central nervous system. During many forms of plasticity, including
Long-Term Potentiation (LTP), synaptic AMPAR levels are altered to modulate synaptic strength and regulate
neural circuit function. However, recent studies have shown that synaptic strength is not determined simply by
the number of AMPARs at the synapse, but also by their nanoorganization within it. AMPARs are enriched
subsynaptically in high-density nanoclusters that are often aligned with presynaptic neurotransmitter release
sites, and this molecular architecture impacts both basal synaptic transmission and plasticity. Despite long
acknowledgement that AMPAR trafficking is critical for synaptic strength and plasticity, the mechanisms
controlling their positioning and even their retention at synapses remain unclear. The overarching goal of this
proposal is to investigate mechanisms by which AMPARs are regulated at both synaptic and subsynaptic scales.
Leucine-Rich Repeat Transmembrane protein 2 (LRRTM2) has emerged as potential candidate for these
functions, with essential roles in multiple synaptic processes including AMPAR-mediated transmission and LTP.
Critically, by using an acute method rather than knockout to disrupt LRRTM2, our lab recently found that LRRTM2
regulates both the abundance and nanopositioning of AMPARs after long and short-term manipulations,
respectively. As a transmembrane protein located in the postsynaptic density, LRRTM2 forms multiple protein
interactions, including with PSD-95, presynaptic Neurexins, and directly with AMPARs. These interactions
suggest fascinating hypotheses about how LRRTM2 might retain AMPARs and position them specifically within
the synapse, both basally and during AMPAR recruitment post-LTP stimulation.
To visualize and control endogenous LRRTM2, I have successfully adapted a new CRISPR-based tool
to genetically replace the LRRTM2 protein with a tagged, acutely cleavable, and/or mutated version. I will use
this approach to perform the first evaluation of LRRTM2 distribution and plasticity-dependent enrichment in
neurons. With this tool, I will then determine the mechanisms of LRRTM2-driven AMPAR alignment, stability,
and enrichment. I will engineer selective mutations of the genomic sequence and use super resolution
microscopy and single-molecule tracking to delineate how LRRTM2 interactions with its partners specifically
contribute to AMPAR trafficking. Finally, I will examine how LRRTM2 supports LTP. Our surprising preliminary
data suggests an unexpected role for LRRTM2 in LTP-dependent spine growth not explained by current models
of LRRTM2 function. I will investigate these mechanisms using a combination of live cell imaging and
electrophysiology. These tools and approaches establish new paradigms for understanding the roles of cell
adhesion molecules at mature synapses, and will provide a firm foundation for my independent career.