Role of AMPA receptors in homocysteine‐NMDA receptor‐induced crosstalk between ERK and p38 MAPK

Abstract

Homocysteine, a metabolite of the methionine cycle has been reported to play a role in neurotoxicity through activation of NMDAR-mediated signaling pathway. The proposed mechanisms associated with homocysteine-NMDAR induced neurotoxicity involve a unique signaling pathway that triggers a crosstalk between ERK and p38 MAPKs, where activation of p38 MAPK is downstream of and dependent on ERK MAPK. However, the molecular basis of the ERK MAPK mediated p38 MAPK activation is not understood. The current study investigates whether AMPARs play a role in facilitating the ERK MAPK mediated p38 MAPK activation. Using surface biotinylation and immunoblotting approaches we show that treatment with homocysteine leads to a decrease in surface expression of GluA2-AMPAR subunit in neurons, but has no effect on the surface expression of GluA1-AMPAR subunit. Inhibition of NMDAR activation with D-AP5 or ERK MAPK phosphorylation with PD98059 attenuates homocysteine-induced decrease in surface expression of GluA2-AMPAR subunit. The decrease in surface expression of GluA2-AMPAR subunit is associated with p38 MAPK phosphorylation, which is inhibited by NASPM, a selective antagonist of GluA2-lacking Ca2+-permeable AMPARs. These results suggest that homocysteine-NMDAR mediated ERK MAPK phosphorylation leads to a decrease in surface expression of GluA2-AMPAR subunit resulting in Ca2+ influx through the GluA2-lacking Ca2+-permeable AMPARs and p38 MAPK phosphorylation. Cell death assays further show that inhibition of AMPAR activity with NBQX/CNQX or GluA2-lacking Ca2+-permeable AMPAR activity with NASPM attenuates homocysteine-induced neurotoxicity. We have identified an important mechanism involved in homocysteine-induced neurotoxicity that highlights the intermediary role of GluA2-lacking Ca2+-permeable AMPARs in the crosstalk between ERK and p38 MAPKs.

Transcriptional modulation of calcium‐permeable AMPA receptor subunits in glioblastoma by MEK–ERK1/2 inhibitors and their role in invasion

“…Glioma stem cells are remarkably sensitive to calcium, and an increase in intracellular calcium is mediated through AMPA type of glutamate receptors (Wee et al, 2014); this fact underscores the significance of AMPAR-mediated calcium permeability in the pathobiology of glioma. Downregulation of GluA2 mRNA synthesis and switch toward calcium-permeable AMPARs phenotype that lacks GluA2 has been demonstrated in primary cortical neuron culture (Poddar et al, 2017).…”

“…According to Song et al (), ERK activity facilitates the insertion of AMPA‐type glutamate receptors in the membrane of primary striatal neurons. Further, in cortical neurons, ERK–MAPK phosphorylation decreases the surface expression of the GluA2–AMPAR subunit with a resultant increase in calcium influx (Poddar et al, ). On the other hand, overexpression of GluA1 is associated with perivascular invasion of glioma via β1 integrin‐dependent adhesion to the extracellular matrix (Piao et al, ).…”

“…Further, it has also been reported that the surface expression of GluA2 subunit is accompanied with phosphorylation of serine880 residue, which enables the internalization of GluA2 as well as the recycling of GluA2 (Matsuda et al, ; Chung et al, ; Lin and Huganir, ). Inhibition of ERK with PD98059 was reported to block the phosphorylation of serine880 in GluA2 subunit (Poddar et al, ). Our experimental results in GBM revealed that inhibition of MEK‐ERK by PD98059 remarkably enhanced the mRNA expression of GluA2 subunit of AMPARs, subsequently leading to enhanced surface expression of GluA2‐containing AMPAR with consequential calcium‐impermeability.…”

Role of GluN2A NMDA receptor in homocysteine‐induced prostaglandin E2 release from neurons

“…We also observed sustained activation of the stress‐activated p38 MAPK, which is downstream of and dependent on ERK MAPK activation (Poddar and Paul ; Poddar and Paul ). This unique crosstalk involves ERK MAPK‐dependent internalization of the Ca 2+ ‐impermeable GluA2‐subunit of α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid receptor (AMPAR) resulting in increased Ca 2+ influx through the GluA2‐lacking AMPAR, which leads to p38 MAPK activation (Poddar et al ). The increased p38 MAPK activation subsequently leads to caspase‐3–dependent neuronal cell death (Poddar and Paul ).…”

“…It is evident from earlier studies that homocysteine is an agonist of N-methyl-D-aspartate (NMDA) subtype of glutamate receptors, and prolonged exposure of neurons to high levels of homocysteine leads to NMDAR-mediated cell death (Lipton et al 1997;Kruman et al 2000;Kruman et al 2002;Mattson and Shea 2003;Jara-Prado et al 2003;Poddar and Paul 2009;Poddar and Paul 2013;Poddar et al 2017). The tetrameric NMDAR channel is comprised of two essential GluN1 subunits and two regulatory GluN2 subunits (GluN2A/B/C/D).…”