title: Induction of autophagy contributes to the neuroprotection of nicotinamide phosphoribosyltransferase in cerebral ischemia.
abstract: Recent reports indicate that autophagy serves as a stress response and may participate in pathophysiology of cerebral ischemia. Nicotinamide phosphoribosyltransferase (Nampt, also known as visfatin), the rate-limiting enzyme in mammalian NAD (+)  biosynthesis, protects against ischemic stroke through inhibiting neuronal apoptosis and necrosis. This study was taken to determine the involvement of autophagy in neuroprotection of Nampt in cerebral ischemia. Middle cerebral artery occlusion (MCAO) in rats and oxygen-glucose deprivation (OGD) in cultured cortical neurons were performed. Nampt was overexpressed or knocked-down using lentivirus-mediated gene transfer in vivo and in vitro. Immunochemistry (LC3-II), electron microscope and immunoblotting assays (LC3-II, beclin-1, mammalian target of rapamycin [mTOR], S6K1 and tuberous sclerosis complex-2 [TSC2]) were performed to assess autophagy. We found that overexpression of Nampt increased autophagy (LC3 puncta immunochemistry staining, LC3-II/beclin-1 expression and autophagosomes number) both in vivo and in vitro at 2 hours after MCAO. At the early stage of OGD, autophagy inducer rapamycin protected against neuronal injury induced by Nampt knockdown, whereas autophagy inhibitor 3-methyladenine abolished the neuroprotective effect of Nampt partly. Overexpression or knockdown of Nampt regulated the phosphorylation of mTOR and S6K1 signaling pathway upon OGD stress through enhancing phosphorylation of TSC2 at Ser1387 but not Thr1462 site. Furthermore, in cultured SIRT1-knockout neurons, the regulation of Nampt on autophagic proteins LC3-II and beclin-1 was abolished. Our results demonstrate that Nampt promotes neuronal survival through inducing autophagy via regulating TSC2-mTOR-S6K1 signaling pathway in a SIRT1-dependent manner during cerebral ischemia.
authors: Department of Pharmacology, Second Military Medical University, Shanghai, China.
authors: Pei
authors: P
authors: Wang
authors: Yun-Feng
authors: YF
authors: Guan
authors: Hui
authors: H
authors: Du
authors: Qi-Wei
authors: QW
authors: Zhai
authors: Ding-Feng
authors: DF
authors: Su
authors: Chao-Yu
authors: CY
authors: Miao
mesh_terms: D000225:Adenine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001343:Autophagy / Q000187:drug effects; D002545:Brain Ischemia / Q000150:complications / Q000201:enzymology* / Q000517:prevention & control*; D002478:Cells, Cultured; D004195:Disease Models, Animal; D005947:Glucose / Q000172:deficiency; D020244:Infarction, Middle Cerebral Artery / Q000201:enzymology / Q000473:pathology; D051379:Mice; D009474:Neurons / Q000187:drug effects / Q000201:enzymology / Q000473:pathology; D018696:Neuroprotective Agents / Q000378:metabolism*; D054409:Nicotinamide Phosphoribosyltransferase / Q000378:metabolism*; D010100:Oxygen; D010588:Phagosomes / Q000648:ultrastructure; D010766:Phosphorylation / Q000187:drug effects; D010768:Phosphoserine / Q000378:metabolism; D010769:Phosphothreonine; D051381:Rats; D017207:Rats, Sprague-Dawley; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D056564:Sirtuin 1 / Q000378:metabolism; D013312:Stress, Physiological / Q000187:drug effects; D020521:Stroke / Q000150:complications / Q000201:enzymology / Q000473:pathology; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins / Q000378:metabolism
chemical_list: D018696:Neuroprotective Agents; C000624654:Tsc2 protein, mouse; C000624655:Tsc2 protein, rat; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins; D010769:Phosphothreonine; D010768:Phosphoserine; C025946:3-methyladenine; D054409:Nicotinamide Phosphoribosyltransferase; D019893:Ribosomal Protein S6 Kinases; D058570:TOR Serine-Threonine Kinases; C470545:Sirt1 protein, mouse; D056564:Sirtuin 1; D005947:Glucose; D000225:Adenine; D010100:Oxygen