title: Protein phosphatase role in adenosine A1 receptor-induced AMPA receptor trafficking and rat hippocampal neuronal damage in hypoxia/reperfusion injury.
abstract: Adenosine signaling via A1 receptor (A1R) and A2A receptor (A2AR) has shown promise in revealing potential targets for neuroprotection in cerebral ischemia. We recently showed a novel mechanism by which A1R activation with N(6)-cyclopentyl adenosine (CPA) induced GluA1 and GluA2 AMPA receptor (AMPAR) endocytosis and adenosine-induced persistent synaptic depression (APSD) in rat hippocampus. This study further investigates the mechanism of A1R-mediated AMPAR internalization and hippocampal slice neuronal damage through activation of protein phosphatase 1 (PP1), 2A (PP2A), and 2B (PP2B) using electrophysiological, biochemical and imaging techniques. Following prolonged A1R activation, GluA2 internalization was selectively blocked by PP2A inhibitors (okadaic acid and fostriecin), whereas inhibitors of PP2A, PP1 (tautomycetin), and PP2B (FK506) all prevented GluA1 internalization. Additionally, GluA1 phosphorylation at Ser831 and Ser845 was reduced after prolonged A1R activation in hippocampal slices. PP2A inhibitors nullified A1R-mediated downregulation of pSer845-GluA1, while PP1 and PP2B inhibitors prevented pSer831-GluA1 downregulation. Each protein phosphatase inhibitor also blunted CPA-induced synaptic depression and APSD. We then tested whether A1R-mediated changes in AMPAR trafficking and APSD contribute to hypoxia-induced neuronal injury. Hypoxia (20 min) induced A1R-mediated internalization of both AMPAR subunits, and subsequent normoxic reperfusion (45 min) increased GluA1 but persistently reduced GluA2 surface expression. Neuronal damage after hypoxia-reperfusion injury was significantly blunted by pre-incubation with the above protein phosphatase inhibitors. Together, these data suggest that A1R-mediated protein phosphatase activation causes persistent synaptic depression by downregulating GluA2-containing AMPARs; this previously undefined role of A1R stimulation in hippocampal neuronal damage represents a novel therapeutic target in cerebral ischemic damage.
authors.affiliation: Department of Surgery, Neuroscience Research Group, University of Saskatchewan, Saskatoon, Saskatchewan, Canada. Electronic address: jas157@mail.usask.ca.
authors.forename: Jocelyn
authors.initials: J
authors.lastname: Stockwell
authors.affiliation: Department of Surgery, Neuroscience Research Group, University of Saskatchewan, Saskatoon, Saskatchewan, Canada. Electronic address: zhicheng.chen@gmail.com.
authors.forename: Zhicheng
authors.initials: Z
authors.lastname: Chen
authors.affiliation: Department of Surgery, Neuroscience Research Group, University of Saskatchewan, Saskatoon, Saskatchewan, Canada. Electronic address: minaniazi1@gmail.com.
authors.forename: Mina
authors.initials: M
authors.lastname: Niazi
authors.affiliation: Department of Surgery, Neuroscience Research Group, University of Saskatchewan, Saskatoon, Saskatchewan, Canada. Electronic address: sasnosib@gmail.com.
authors.forename: Siddarth
authors.initials: S
authors.lastname: Nosib
authors.affiliation: Department of Surgery, Neuroscience Research Group, University of Saskatchewan, Saskatoon, Saskatchewan, Canada. Electronic address: frank.cayabyab@usask.ca.
authors.forename: Francisco S
authors.initials: FS
authors.lastname: Cayabyab
mesh_terms: D000818:Animals; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects; D005663:Furans / Q000494:pharmacology; D006624:Hippocampus / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D008055:Lipids / Q000494:pharmacology; D008297:Male; D009474:Neurons / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D019319:Okadaic Acid / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011090:Polyenes / Q000494:pharmacology; D021381:Protein Transport / Q000502:physiology; D011753:Pyrones / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D043682:Receptor, Adenosine A1 / Q000378:metabolism*; D018091:Receptors, AMPA / Q000378:metabolism*; D015427:Reperfusion Injury / Q000378:metabolism* / Q000473:pathology; D009435:Synaptic Transmission / Q000187:drug effects; D016559:Tacrolimus / Q000494:pharmacology
chemical_list: D005663:Furans; D008055:Lipids; D011090:Polyenes; D011753:Pyrones; D043682:Receptor, Adenosine A1; D018091:Receptors, AMPA; C058744:tautomycetin; D019319:Okadaic Acid; D010749:Phosphoprotein Phosphatases; D016559:Tacrolimus; C040313:fostriecin
keywords: 8-cyclopentyl-1,3-dipropylxanthine or DPCPX (PubChem CID: 1329); AMPAR trafficking; Adenosine A1 receptor; Adenosine-induced persistent synaptic depression; Cerebral ischemia; FK506 (PubChem CID: 445643); Hippocampal neurotoxicity; N(6)-cyclopentyl adenosine or CPA (PubChem CID: 104968); Serine/threonine protein phosphatase; fostriecin (PubChem CID: 6436285); okadaic acid (PubChem CID: 446512); tautomycetin (PubChem CID: 6439037)