title: Global ischemia induces lysosomal-mediated degradation of mTOR and activation of autophagy in hippocampal neurons destined to die.
abstract: The mammalian target of rapamycin (mTOR) is a key regulator of cell growth, autophagy, translation, and survival. Dysregulation of mTOR signaling is associated with cancer, diabetes, and autism. However, a role for mTOR signaling in neuronal death is not well delineated. Here we show that global ischemia triggers a transient increase in mTOR phosphorylation at S2448, whereas decreasing p-mTOR and functional activity in selectively vulnerable hippocampal CA1 neurons. The decrease in mTOR coincides with an increase in biochemical markers of autophagy, pS317-ULK-1, pS14-Beclin-1, and LC3-II, a decrease in the cargo adaptor p62, and an increase in autophagic flux, a functional readout of autophagy. This is significant in that autophagy, a catabolic process downstream of mTORC1, promotes the formation of autophagosomes that capture and target cytoplasmic components to lysosomes. Inhibitors of the lysosomal (but not proteasomal) pathway rescued the ischemia-induced decrease in mTOR, consistent with degradation of mTOR via the autophagy/lysosomal pathway. Administration of the mTORC1 inhibitor rapamycin or acute knockdown of mTOR promotes autophagy and attenuates ischemia-induced neuronal death, indicating an inverse causal relation between mTOR, autophagy, and neuronal death. Our findings identify a novel and previously unappreciated mechanism by which mTOR self-regulates its own levels in hippocampal neurons in a clinically relevant model of ischemic stroke.
authors.affiliation: Dominick P Purpura Department of Neuroscience, Rose F Kennedy Center, Albert Einstein College of Medicine, New York, NY 10461, USA.
authors.forename: Jee-Yeon
authors.initials: JY
authors.lastname: Hwang
authors.affiliation: Dominick P Purpura Department of Neuroscience, Rose F Kennedy Center, Albert Einstein College of Medicine, New York, NY 10461, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Gertner
authors.affiliation: Dominick P Purpura Department of Neuroscience, Rose F Kennedy Center, Albert Einstein College of Medicine, New York, NY 10461, USA.
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Pontarelli
authors.affiliation: Dominick P Purpura Department of Neuroscience, Rose F Kennedy Center, Albert Einstein College of Medicine, New York, NY 10461, USA.
authors.forename: Brenda
authors.initials: B
authors.lastname: Court-Vazquez
authors.affiliation: Dominick P Purpura Department of Neuroscience, Rose F Kennedy Center, Albert Einstein College of Medicine, New York, NY 10461, USA.
authors.forename: Michael Vander Laan
authors.initials: MV
authors.lastname: Bennett
authors.affiliation: Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA.
authors.forename: Dimitry
authors.initials: D
authors.lastname: Ofengeim
authors.affiliation: Dominick P Purpura Department of Neuroscience, Rose F Kennedy Center, Albert Einstein College of Medicine, New York, NY 10461, USA.
authors.forename: Ruth Suzanne
authors.initials: RS
authors.lastname: Zukin
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000378:metabolism; D000111:Acetylcysteine / Q000031:analogs & derivatives / Q000494:pharmacology; D000225:Adenine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001343:Autophagy / Q000187:drug effects; D000071189:Autophagy-Related Protein-1 Homolog / Q000378:metabolism; D000071186:Beclin-1 / Q000378:metabolism; D002478:Cells, Cultured; D006624:Hippocampus / Q000166:cytology; D007511:Ischemia / Q000378:metabolism / Q000473:pathology; D007976:Leupeptins / Q000494:pharmacology; D008247:Lysosomes / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D034622:RNA Interference; D051381:Rats; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*
chemical_list: D000071186:Beclin-1; D007976:Leupeptins; D008869:Microtubule-Associated Proteins; C067713:lactacystin; C025946:3-methyladenine; D000071189:Autophagy-Related Protein-1 Homolog; D058570:TOR Serine-Threonine Kinases; D055372:AMP-Activated Protein Kinases; C032854:leupeptin; D000225:Adenine; D020123:Sirolimus; D000111:Acetylcysteine