Neuroprotective Mitochondrial Remodeling By PKA/AKAP121 Protect HT22 Cell From Glutamate-induced Oxidative Stress

Protein Kinase A(PKA)is a ser/thr kinase that is critical for maintaining essential neuronal functions including mitochondrial homeostasis,bioenergetics,neuronal development,and neurotransmission.The endogenous pool of PKA is targeted to the mitochondrion by forming a complex with the mitochondrial scaffold A-kinase anchoring protein 121(AKAP121).Enhanced PKA signaling via AKAP121 leads to PKA-mediated phosphorylation of the fission modulator Drp1,leading to increase mitochondrial networks and blocks apoptosis against different toxic insults,and in a genetic model of Parkinson’s disease.Here,we show for the first time that AKAP121/PKA confers neuroprotection in an in vitro model of glutamate excitotoxicity.In brief,treating mouse hippocampal progenitor neuronal HT22 cells with anacute dose or chronicexposureof glutamate robustly elevates PKA signaling as evident by a time-dependent increase in cyclic AMP level,phosphorylation of CREB,and level of AKAP121,and phosphorylated Drp1.This data suggest that glutamate excitotoxicity leads to compensatory,beneficial PKA signaling.Secondly,transient expression of exogenous AKAP121,of mitochondrially targeted PKA(OMM-PKA),or of an isoform of AKAP121 that lacks the KH and tudor domains(AKAP84)are sufficient to significantly to block cell death induced by glutamate excitotoxicity while having no effect against hypoxic conditions.Furthermore,we show that AKAP121 protectsagainst glutamate excitotoxicity by phosphorylating Drp1 as transiently expressing a phosphomimetic mutant of Drp1 phenocopies the cytoprotectiveability of AKAP121.Mechanistically,AKAP121 promotes neuroprotection by elevating ATP levels and inducing an increase in antioxidants GSH and superoxide dismutase 2 leading to a reduction in oxidative stress.Overall,our data supports D-AKAP121/PKA as a new molecular target that confers neuroprotection against glutamate excitotoxicity to stabilize mitochondrial networks by phosphorylating Drp1,thereby reducing oxidative stress,maintaining mitochondrial function and enhancing antioxidant responses.