Synaptic Glutamate Receptor Trafficking

Investigator: Roger Nicoll, MD
Sponsor: NIH National Institute of Mental Health

Location(s): United States


Persistent, activity dependent changes in synaptic strength underlie learning and memory. Thus identifying the cellular and molecular underpinnings of such dynamic behavior is of critical importance for understanding this most important of brain functions. We have found that the trafficking of glutamate receptors is central to this process and auxiliary proteins, which bind to the receptors and assist in the trafficking. We are defining the various ways that the auxiliary proteins work with the goal of establishing therapeutic targets for treating diseases involving cognitive decline.

 The overall goal of my research program is to elucidate the underlying molecular principles that govern the assembly of the postsynaptic component of a synapse. There are three main questions we wish to address. First, what are the sequences of events that occur during synapse formation? Second, how does a synapse maintain a stable anatomical identity? Finally, what is the mechanism whereby activity can induce a change in synapse function? Central to the understanding of synaptic transmission are the glutamate receptors embedded in the postsynaptic density (PSD). To tackle these ambitious goals we use a combination of a number of techniques. The most central to our studies is electrophysiology, since this is the most critical way to measure the functional consequences of our molecular manipulations. This grant is focused on a variety of proteins that act as glutamate receptor auxiliary subunits. While voltage gated ion channels have long been know to be decorated with auxiliary subunits, which control all aspects of trafficking and function, the notio that ligand gated ion channels also associate with auxiliary subunits is quite new. The most studied family of auxiliary subunits is the TARPs, which selectively control the trafficking and function of the AMPAR subtype of glutamate receptor. However, recent studies indicate that other structurally unrelated proteins, such as CNIH2, CKAMP44, and SynDIG1 also serve as AMPAR auxiliary subunits. In addition, NETO-1/2 has been shown to serve a similar role for kainate receptors. In this renewal we will characterize the role of CNIH2 in the brain with the use of conditional knockout mice. Initial results suggest widespread effects of deleting CNIH2. We will also determine the physiological role of TARP ¿-7, an unusual TARP, which sets it apart from the other well characterize TARPs. Understanding the role of SynDIG1 forms the third Aim of this grant. Both overexpression and RNAi in slice culture will be used for these experiments. Finally we will use the CA1 synapse, which normally lacks kainate receptors, as a null to determine the role of NETO-1/2 in trafficking and gating of kainate receptors. It is hoped that these studies will uncover novel roles for glutamate auxiliary proteins in the nervous system. Given the critical role that receptor trafficking plays in synaptic plasticity it is anticipated tht findings from these studies will have direct clinical impact. Indeed, clinically promising AMPAkines exert their effect, in part, by controlling the kinetics of AMPAR gating similar to TARPs.