Role of CK2 in NMDAR trafficking during development and in Alzheimer's disease

N-methyl-D-aspartate receptors (NMDARs) control critical brain functions such as learning and memory, and their altered function and/or trafficking is a share hallmark for several neurological disorders. Many functional properties of NMDARs rely on their GluN2 subunit composition, which, for example, determines decay kinetics, calcium permeability and protein-protein interactions with the receptor. Accordingly, GluN2 subunits are strongly regulated by a plethora of different mechanisms. Interestingly, GluN2A and GluN2B (the major GluN2 subunits expressed in cortex and hippocampus) are controlled in a differential, sometimes opposite, manner. This is particularly evident during development when a switch in the predominant GluN2 subunit expressed at synapses (from GluN2B to GluN2A) occurs. Similarly, many neurological disorders impair NMDAR function by affecting differentially GluN2A- or GluN2B-containing NMDARs. The general goal of the R00 phase of this award is to define the precise mechanisms that control the developmental GluN2B/A switch and analyze these same mechanisms during the pathogenesis of Alzheimer’s disease (AD), in which a reduction of NMDAR synaptic expression has been observed. The central hypothesis, based upon preliminary data obtained during the K99 phase, is that the phosphorylation of the PDZ ligand of GluN2B by casein kinase 2 (CK2) is a critical determinant for controlling synaptic NMDAR content during development and that Abeta-mediated CK2 overactivation contributes to the aberrant NMDAR trafficking observed in AD. In Specific Aim 1, we will use molecular genetic approaches to define the mechanisms controlling the switch of synaptic GluN2 subunits. We propose the switch is a process with two sequential and coupled steps, in which the synaptic removal of GluN2B via the phosphorylation of its PDZ ligand by CK2 is required to allow synaptic incorporation of GluN2A. We will test this hypothesis by analyzing a newly generated knock-in mouse line expressing a point-mutated form of GluN2B non-phosphorylatable by CK2 (GluN2B E1479Q). In Specific Aim 2, we will test an unexplored mechanism underlying the reduced GluN2B synaptic expression observed in AD: the aberrant increase in GluN2B S1480 phosphorylation by CK2. Understanding the precise molecular mechanisms governing NMDAR trafficking is an important goal for both basic and translational investigation. The successful completion of this phase of the award will identify CK2 as a key player in synaptic maturation and as a potential pharmacological target for AD treatment.