Apolipoprotein E Receptor 2 Interactions with the N-Methyl-D-aspartate Receptor

Abstract

In our previous studies we showed that apoE treatment of neurons activated ERK 1/2 signaling, and activation was blocked by treatment with inhibitors of the low density lipoprotein receptor family, the N-methyl-D-aspartate (NMDA) receptor antagonist MK 801, and calcium channel blockers. We hypothesized an interaction between the low density lipoprotein receptor family members and the NMDA receptor. In the present study, we confirmed through co-immunoprecipitation experiments an interaction between the apoE receptor, ApoEr2, and NMDAR1 through their extracellular domains. We also found that the PDZ1 domain of PSD95, a postsynaptic scaffolding protein, interacted with the C terminus of ApoEr2 via an alternatively spliced, intracellular exon. This interaction between ApoEr2 and PSD95 in neurons was modulated by NMDA receptor activation and an ApoEr2 ligand. We also found that the PDZ2 domain of PSD95 interacted with the NR2A and NR2B subunits of NMDA receptors. Full-length PSD95 increased cell surface levels of ApoEr2 and its cleavage, resulting in increases in secreted ApoEr2 and C-terminal fragments of ApoEr2. These studies suggest that ApoEr2 can form a multiprotein complex with NMDA receptor subunits and PSD95. Apolipoprotein E (apoE)2 allows lipoproteins to introduce a variety of lipophilic molecules to cells (1). Cholesterol and lipids are essential in remodeling neuronal membranes and developing new growth terminals. These processes mediate synaptic plasticity and responses to neurodegeneration. ApoE-containing lipoproteins are endocytosed into cells via apoE receptors, including the low density lipoprotein receptor, low density lipoprotein receptor-related protein (LRP1), very low density lipoprotein receptor, apoE receptor type 2 (ApoEr2), and the LR11 receptor (2). Ligand activation of these receptors has also been implicated in a variety of neuronal signaling processes. These receptors play roles in neuronal migration during development (3), calcium influx through the NMDA channel (4, 5), and neurite outgrowth (6). Our previous work showed that apoE and an apoE-derived peptide also activated the extracellular signal-regulated kinase 1/2 (ERK 1/2) (7). The activation of ERK 1/2 by apoE was blocked by an inhibitor to the low density lipoprotein receptor family, the NMDA receptor antagonist MK 801, and calcium channel blockers. We also found that apoE promoted extracellular and intramembranous cleavages of these receptors, affecting metabolism of their C-terminal fragments (8).Several in vivo and in vitro studies have supported roles for apoE and apoE receptors in signaling processes involving NMDA channels. ApoE targeted replacement mice revealed that long term potentiation (LTP) was significantly greater in animals expressing mouse apoE or human apoE3 than in apoE knock-out (9), apoE2, or apoE4 mice (10). Mice deficient in the very low density lipoprotein receptor and ApoEr2 also have moderate defects in LTP (11). Biochemical and immunohistochemical studies showed that the LRP1 interacts with NMDA recepto...

Differential Reelin-Induced Enhancement of NMDA and AMPA Receptor Activity in the Adult Hippocampus

“…Indeed, one of the reelin receptors, apoER2, may be well suited to modulate glutamatergic responses, for several reasons. First, apoER2 and NMDAR are physically associated, coimmunoprecipitate in heterologous expression cell lines, and colocalize in CA1 postsynaptic densities Hoe et al, 2006). These observations were further confirmed in CA1 tissues by this study.…”

“…It has been shown previously that reelin signaling components, including apoER2 and NMDA receptor subunits, are physically associated with PSD-95 protein in transfected cell lines as well as hippocampal tissues Hoe et al, 2006). These results were reproducible in our slice preparations using only CA1 tissues (Fig.…”

Apolipoprotein E and Apolipoprotein E Receptors: Normal Biology and Roles in Alzheimer Disease

“…However, they harbor a variety of short conserved sequence stretches, such as the tetra-amino acid NPxY motif, which serve as docking sites for a wide array of cytoplasmic adaptor and scaffolding proteins (Trommsdorff et al 1998;Gotthardt et al 2000;Beffert et al 2005;Hoe et al 2006a;Hoe et al 2006b). The receptors can also interact as coreceptors through their extracellular domains with other types of signaling proteins and modules, and thereby modulate their intrinsic activity (Boucher et al 2002;Loukinova et al 2002;Huang et al 2003;Lillis et al 2008;Zurhove et al 2008), including that of the N-methyl-D-aspartate (NMDA) receptor Beffert et al 2005;Hoe et al 2006b). …”

“…ApoE4 sequesters Apoer2 in intracellular compartments along with glutamate receptors (NMDAR and GluR), thereby reducing the ability of the postsynaptic neuron to recycle these proteins with normal kinetics, whereas ApoE2 or ApoE3 efficiently recycle back to the cell surface and thus deplete surface Apoer2 and glutamate receptor levels to a lesser extent (illustrated on the left for ApoE3). Ab oligomers interfere with NMDAR tyrosine phosphorylation by activating tyrosine phosphatases (Snyder et al 2005) insert, which functionally couples Apoer2 to NMDA receptors, presumably through a PSD95-mediated interaction Hoe et al 2006b), but also serves to recruit a c-jun amino-terminal kinase (JNK) signaling complex to the cytoplasmic tail of Apoer2 Stockinger et al 2000). Intriguingly, JNK3 knockout mice and Apoer2 mutants lacking the alternatively spliced insert are resistant to lesion-induced neuronal death, suggesting that JNK recruitment to the Apoer2 cytoplasmic domain can promote both, neuronal loss or survival, depending on context (Beffert et al 2006b).…”

N-methyl-d-aspartate receptor inhibition by an apolipoprotein E-derived peptide relies on low-density lipoprotein receptor-associated protein

“…Also, in the case of apoER2, evidence has emerged suggesting its participation in a multiprotein complex that includes NMDAR subunits (Hoe, et al, 2006). Unlike LRP, neither apoER2 nor VLDLR are present in CHO cells (Tacken et al, 2000).…”