Secreted Amyloid Precursor Protein-Alpha Promotes Arc Protein Synthesis in Hippocampal Neurons

Abstract

Secreted amyloid precursor protein-α (sAPPα) is a neuroprotective and memory-enhancing molecule, however, the mechanisms through which sAPPα promotes these effects are not well understood. Recently, we have shown that sAPPα enhances cell-surface expression of glutamate receptors. Activity-related cytoskeletal-associated protein Arc (Arg3.1) is an immediate early gene capable of modulating long-term potentiation, long-term depression and homeostatic plasticity through regulation of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor localization. Accordingly, we hypothesized that sAPPα may enhance synaptic plasticity, in part, by the de novo synthesis of Arc. Using primary cortical and hippocampal neuronal cultures we found that sAPPα (1 nM, 2 h) enhances levels of Arc mRNA and protein. Arc protein levels were increased in both the neuronal somata and dendrites in a Ca 2+ /calmodulin-dependent protein kinase II-dependent manner. Additionally, dendritic Arc expression was dependent upon activation of mitogen-activated protein kinase and protein kinase G. The enhancement of dendritic Arc protein was significantly reduced by antagonism of N -methyl- D -aspartate (NMDA) and nicotinic acetylcholine (α7nACh) receptors, and fully eliminated by dual application of these antagonists. This effect was further corroborated in area CA1 of acute hippocampal slices. These data suggest sAPPα-regulated plasticity within hippocampal neurons is mediated by cooperation of NMDA and α7nACh receptors to engage a cascade of signal transduction molecules to enhance the transcription and translation of Arc.

Secreted Amyloid Precursor Protein-Alpha Enhances LTP Through the Synthesis and Trafficking of Ca2+-Permeable AMPA Receptors

“…Treatment of primary hippocampal cultures with an siRNA (1 μM, pre-treatment: 60 min, treatment: 2 h) targeting Arc mRNA or a non-targeting (NT) siRNA with no known homology to rat or human genes had no significant effect on basal Arc protein expression in either the soma (Arc siRNA: 0.78 ± 0.06, p ≥ 0.99; NT siRNA: 1.11 ± 0.09, p = 0.0509; Figure 4A ) or the dendrites (Arc siRNA: 1.26 ± 0.12, p = 0.8774; NT siRNA: 1.28 ± 0.08, p = 0.7561; Figure 4B ). As previously shown ( Livingstone et al, 2019 ), sAPPα treatment (1 nM, 2 h) enhanced both somatic (2.05 ± SEM, p = 0.0306; Figure 4A ) and dendritic (2.33 ± 0.29, p = 0.0010; Figure 4B ) Arc protein expression. Co-treatment with sAPPα and the NT siRNA (1 μM, pre-treatment: 60 min, co-treatment: 2 h) also enhanced Arc expression (soma: 1.59 ± 0.23, p = 0.0198; dendrites: 1.98 ± 0.18, p = 0.0022), and no significant difference was detected between sAPPα-treated and sAPPα + NT siRNA in either the soma or dendrites ( p ≥ 0.99).…”

“…Prolonged treatment of sAPPα (1 nM, 2 h) enhances the de novo transcription and translation of the immediate early gene Arc, a protein intrinsically linked to glutamate receptor expression at the cell surface ( Livingstone et al, 2019 ). Treatment of primary hippocampal cultures with an siRNA (1 μM, pre-treatment: 60 min, treatment: 2 h) targeting Arc mRNA or a non-targeting (NT) siRNA with no known homology to rat or human genes had no significant effect on basal Arc protein expression in either the soma (Arc siRNA: 0.78 ± 0.06, p ≥ 0.99; NT siRNA: 1.11 ± 0.09, p = 0.0509; Figure 4A ) or the dendrites (Arc siRNA: 1.26 ± 0.12, p = 0.8774; NT siRNA: 1.28 ± 0.08, p = 0.7561; Figure 4B ).…”

“…Furthermore, the NO-cGMP-PKG and MAPK pathways have been found to be involved in de-clustering of GluA2/3-containing AMPARs ( Endo and Launey, 2003 ), an event which is typically associated with subsequent internalization of receptors ( Matsuda et al, 2000 ). As synaptic protein synthesis, expression of Arc protein, and GluA1 trafficking are dependent on the activity of PKG and MAPK ( Claasen et al, 2009 ; Livingstone et al, 2019 ; Mockett et al, 2019 ), sAPPα’s induction of these pathways may also contribute to GluA2/3 receptor internalization. Further, rapid downregulation of GluA2-containing calcium impermeable AMPARs (CI-AMPARs) may facilitate GluA1 cell-surface expression via increasing the available “slots” within the PSD ( MacDougall and Fine, 2013 ) to be filled by CP-AMPARs ( Bellone and Lüscher, 2005 , 2006 ; Hong et al, 2013 ).…”

“…Of note, sAPPα has been previously shown to enhance LTP and plasticity-related protein synthesis via a mechanism involving α7nAChRs ( Richter et al, 2018 ; Livingstone et al, 2019 ) in that antagonism of α7nAChRs during the priming phase, but not during the induction of LTP, impairs the expression of sAPPα-enhanced LTP ( Richter et al, 2018 ). Our current work suggests that this occurs by promoting the synthesis and trafficking of CP-AMPARs.…”

“…sAPPα, as well as peptide derivatives, enhances hippocampal LTP ( Ishida et al, 1997 ; Richter et al, 2018 ), and rescues memory impairments ( Meziane et al, 1998 ; Mileusnic et al, 2004 ; Fol et al, 2016 ; Xiong et al, 2017 ; Tan et al, 2018 ). We have shown that sAPPα not only promotes synaptodendritic protein synthesis ( Claasen et al, 2009 ) and new gene transcription ( Ryan et al, 2013 ), but brings about a protein synthesis-dependent trafficking of GluA1-AMPARs to the cell surface ( Mockett et al, 2019 ) and enhances Arc protein expression ( Livingstone et al, 2019 ), yet how these changes contribute to the documented sAPPα-driven enhancement of synaptic plasticity in the hippocampus is unresolved. Here, we show that sAPPα rapidly and specifically induces the synthesis of CP-AMPARs which are transported to the cell surface.…”