LRP1 is critical for the surface distribution and internalization of the NR2B NMDA receptor subtype

Abstract

BackgroundThe N-methyl-D-aspartate receptors are key mediators of excitatory transmission and are implicated in many forms of synaptic plasticity. These receptors are heterotetrameres consisting of two obligatory NR1 and two regulatory subunits, usually NR2A or NR2B. The NR2B subunits are abundant in the early postnatal brain, while the NR2A/NR2B ratio increases during early postnatal development. This shift is driven by NMDA receptor activity. A functional interplay of the Low Density Lipoprotein Receptor Related Protein 1 (LRP1) NMDA receptor has already been reported. Such abilities as interaction of LRP1 with NMDA receptor subunits or its important role in tPa-mediated NMDA receptor signaling were already demonstrated. Moreover, mice harboring a conditional neuronal knock-out mutation of the entire Lrp1 gene display NMDA-associated behavioral changes. However, the exact role of LRP1 on NMDA receptor function remains still elusive.ResultsTo provide a mechanistic explanation for such effects we investigated whether an inactivating knock-in mutation into the NPxY2 motif of LRP1 might influence the cell surface expression of LRP1 and NMDA receptors in primary cortical neurons. Here we demonstrate that a knock-in into the NPxY2 motif of LRP1 results in an increased surface expression of LRP1 and NR2B NMDA receptor subunit due to reduced endocytosis rates of LRP1 and the NR2B subunit in primary neurons derived from LRP1ΔNPxY2 animals. Furthermore, we demonstrate an altered phosphorylation pattern of S1480 and Y1472 in the NR2B subunit at the surface of LRP1ΔNPxY2 neurons, while the respective kinases Fyn and casein kinase II are not differently regulated compared with wild type controls. Performing co-immunoprecipitation experiments we demonstrate that binding of LRP1 to NR2B might be linked by PSD95, is phosphorylation dependent and this regulation mechanism is impaired in LRP1ΔNPxY2 neurons. Finally, we demonstrate hyperactivity and changes in spatial and reversal learning in LRP1ΔNPxY2 mice, confirming the mechanistic interaction in a physiological readout.ConclusionsIn summary, our data demonstrate that LRP1 plays a critical role in the regulation of NR2B expression at the cell surface and may provide a mechanistic explanation for the behavioral abnormalities detected in neuronal LRP1 knock-out animals reported earlier.

Neuronal low-density lipoprotein receptor-related protein 1 (LRP1) enhances the anti-apoptotic effect of intravenous immunoglobulin (IVIg) in ischemic stroke

“…However, recent studies have shown that LRP1 may exert biological functions beyond cellular uptake and cargo transport (May et al, 2007). LRP1 is abundantly expressed in neurons (May et al, 2004;Liu et al, 2011;Ruzali et al, 2012;Maier et al, 2013), and it has been shown to trans-activate Trk receptors through Src family kinase (SFK) activation and signaling, leading to the activation of Akt and to neurite outgrowth (Shi et al, 2009). By showing that knocking down endogenous LRP1 leads to caspase-3 activation and increased neuronal apoptosis, Fuentealba et al (2009) demonstrated that LRP1 plays a pivotal role in the survival of primary neurons under different stress conditions such as trophic withdrawal, the presence of apoptosis inducers, or amyloid-beta-induced neurotoxicity.…”

ApoE, ApoE Receptors, and the Synapse in Alzheimer's Disease

“…For example, Lrp1 interacts with the N-methyl-D-aspartate receptor (NMDAR), promoting the endocytosis of NMDAR from the cell surface [19]. Additionally, loss of Lrp1 hinders some elements of NMDAR signaling, such as internalization of GluA1 and degradation of PSD-95 [20].…”

Low‐density lipoprotein receptor‐related protein 1 is a novel modulator of radial glia stem cell proliferation, survival, and differentiation

“…Also, the expression of LRP1 in radial glia of the adult spinal cord and the involvement of LRP1 in neuroblast migration along the rostral-migratory stream has recently been reported (Petit et al 2011; Rabiej et al 2016). Furthermore, LRP1 is responsible for amyloid precursor protein (APP)-transport and post-synaptic receptor trafficking, which underlines its essential function in the adult brain (Jaeger and Pietrzik 2008; Maier et al 2013). …”