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

Homocysteine, a metabolite of the methionine cycle has been reported to play a role in neurotoxicity through activation of N‐methyl‐d‐aspartate receptors (NMDAR)‐mediated signaling pathway. The proposed mechanisms associated with homocysteine‐NMDAR‐induced neurotoxicity involve a unique signaling pathway that triggers a crosstalk between extracellular signal‐regulated kinase (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. This study investigates whether α‐Amino‐3‐hydroxy‐5‐methyl‐4‐isoxazolepropionic acid receptors (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 have 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 1‐napthyl acetyl spermine trihydrochloride (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 2,3‐dioxo‐6‐nitro‐1,2,3,4,tetrahydrobenzoquinoxaline‐7‐sulfonamide (NBQX)/6‐cyano‐7‐nitroquinoxaline‐2,3, ‐dione (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. Homocysteine‐induced neurotoxicity involves NMDAR‐mediated activation of a unique crosstalk between ERK and p38 MAPKs. We report here that ERK MAPK activation leads to decrease in GluA2‐AMPAR surface expression causing increased Ca2+ influx through GluA2‐lacking Ca2+‐permeable AMPARs resulting in p38 MAPK phosphorylation. The findings reveal an impor