APLP1/APLP2 and NMDA Receptors

What is amyloid precursor protein?

Amyloid precursor protein (APP) is a ubiquitously expressed type I transmembrane protein. It is implicated in pathogenic mechanisms leading to Alzheimer's disease (AD) because of its known proteolytic processing via the amyloidogenic pathway to generate the neurotoxic amyloid-β peptides. These amyloid-β peptides form the extracellular amyloid plaques, key pathological traits of AD. The function of APP itself is unclear, although evidence does support a role as a trophic factor promoting neurite outgrowth, neuronal migration and repair via interaction with extracellular matrix proteins. We recently proposed a new role for APP as a regulator of cell surface N-methyl-d-aspartate (NMDA) receptor homoeostasis. This is because it was found that APP co-associated with the two major NMDA receptors expressed in adult brain, i.e. GluN1/GluN2A and GluN1/GluN2B, and indeed also GluN1/GluN2A/neuropilin tolloid-like 1 and GluN1/GluN2B/neuropilin tolloid-like 1 complexes. Over-expression of APP resulted in an enhanced cell surface NMDA receptor expression.

APLP1/ APLP2 associate with NMDA receptors

APLP1 and APLP2 associate with GluN1/GluN2 NMDA receptors via association with GluN1 subunits. To gain insight into the functional significance of APP/NMDA receptor association, the potential interaction of NMDA receptors with these other family members was investigated initially in a model heterologous expression system. In the first instance, the co-immunoprecipitation of APLP1 and APLP2 with GluN1, GluN2A and GluN2B single subunits was investigated. The results showns that similarly to APP695FLAG, both APLP1c-Myc and APLP2c-Myc co-immunoprecipitate with GluN1 single subunits but not with GluN2A nor GluN2B single subunits. Since when expressed alone, GluN1 is retained in the endoplasmic reticulum, this suggests that similarly to APP, APLP1 and APLP2 associate with GluN1 in this subcellular compartment. The results shows that indeed this is the case. Immunoprecipitation with anti-GluN2A antibodies results in the detection of GluN1 and APLP1c-Myc or APLP2c-Myc in the respective immune pellets. Similarly, immunoprecipitation with anti-GluN2A/2B antibodies to precipitate GluN2B subunits, results in the detection of GluN1 and APLP1c-Myc or APLP2C-Myc in the respective immune pellets.

View NMDA Receptors - GRIN1/ NMDA1/ NMDAR1
View NMDA Receptors - GRIN2A/GluN2A/NMDAR2A
View NMDA Receptors - GRIN2B/GluN2B/NMDAR2B
View NMDA Receptors - GRIN2C/GluN2C/NMDAR2C
View NMDA Receptors - GRIN2D/GluN2D/NMDAR2D

APLP1 and APLP2 associate with NMDA receptors in native brain tissues. The co-association of APLP1 and APLP2 with native NMDA receptors was also investigated. Firstly, APP695FLAG, APLP1c-Myc and APLP2c-Myc were each expressed alone in HEK293 cells, and the resultant transfected solubilized lysates probed with anti-APP (679–695), anti-APLP1 (200–300) and anti-APLP2 (262-491) antibodies. The results show that the primary band size recognized by anti-APLP1 antibody and APLP2 antibody is consistent with the predicted size. Immunoprecipitations from detergent extracts of adult rat brain were carried out using anti-GluN1 C2 antibodies and immune pellets were analysed for GluN1 immunoreactivity to prove that the immunoprecipitation was successful; for GluN2A and GluN2B immunoreactivities to demonstrate the pelleting of an assembled GluN1/GluN2 NMDA receptor and, anti-APP, anti-APLP1 and anti-APLP2 antibodies to determine possible co-immunoprecipitation with APP family members. It was found that GluN1 was always immunoprecipitated as was GluN2A and GluN2B. Furthermore, APP, APLP1 and APLP2 were also all co-immunoprecipitated by anti-GluN1 C2 antibodies. The immunoreactive bands were strongest for APP and APLP1. It was difficult to detect APLP2 in detergent extracts reflecting a low level of APLP2 expression in adult brain. Nevertheless, a clear immunoreactive species was found in anti-GluN1 C2 immunoprecipitates. As always, control non-immune Ig was used as a negative control and no APP, APLP1 nor APLP2 immunoreactivities were found in these samples.

View NMDA Receptors - GRIN3A/GluN3A/NMDAR3A
View NMDA Receptors - GRIN3B/GluN3B/NMDAR3B
View NMDA Receptors - GRINA/GluNA

APLP1 and APLP2 enhance GluN1/GluN2A and GluN1/GluN2B NMDA receptor cell surface expression with no concomitant change in receptor subunits. In addition to interacting with NMDA receptors, others showed that APP enhanced the cell surface expression of NMDA receptors. To determine if this was the case for APLP1 and APLP2, GluN1/GluN2A and GluN1/GluN2B NMDA receptors were co-expressed in parallel with either APLP1, APLP2 and with APP as a positive control and cell surface NMDA receptor expression was measured by ELISA 24 h post-transfection. Similarly to APP, APLP1 and APLP2 both enhanced GluN1/GluN2A and GluN1/GluN2B cell surface receptor expression. There was no significant difference in the fold enhancement when APP was compared to that elicited by APLP1 and APLP2 i.e. for each, an appro ximate twofold increase in cell surface expression was observed. Again, similarly to APP the increase in cell surface expression was not accompanied by any observed change in the total expression of GluN1, GluN2A or GluN2B subunits.

In summary, both APLP1 and APLP2 behaved similarly to APP in that they both co-immunoprecipitated with the two major NMDA receptor subtypes, GluN1/GluN2A and GluN1/GluN2B, via interaction with the obligatory GluN1 subunit. Furthermore, APLP1 and APLP2 both enhanced GluN1/GluN2A and GluN1/GluN2B cell surface expression to fold-increases that are similar to those induced by APP.

Amyloid Precursor Protein (APP) Antibodies

Amyloid Precursor Protein (APP) Antigens

Amyloid Precursor Protein (APP) ELISA Kits

APLP1 Antibodies and APLP2 Antibodies

APLP1 ELISA Kits and APLP2 ELISA Kits