title: Green tea polyphenols precondition against cell death induced by oxygen-glucose deprivation via stimulation of laminin receptor, generation of reactive oxygen species, and activation of protein kinase Cε.
abstract: As the development of synthetic drugs for the prevention of stroke has proven challenging, utilization of natural products capable of preconditioning neuronal cells against ischemia-induced cell death would be a highly useful complementary approach. In this study using an oxygen-glucose deprivation and reoxygenation (OGD/R) model in PC12 cells, we show that 2-day pretreatment with green tea polyphenols (GTPP) and their active ingredient, epigallocatechin-3-gallate (EGCG), protects cells from subsequent OGD/R-induced cell death. A synergistic interaction was observed between GTPP constituents, with unfractionated GTPP more potently preconditioning cells than EGCG. GTPP-induced preconditioning required the 67-kDa laminin receptor (67LR), to which EGCG binds with high affinity. 67LR also mediated the generation of reactive oxygen species (ROS) via activation of NADPH oxidase. An exogenous ROS-generating system bypassed 67LR to induce preconditioning, suggesting that sublethal levels of ROS are indeed an important mediator in GTPP-induced preconditioning. This role for ROS was further supported by the fact that antioxidants blocked GTPP-induced preconditioning. Additionally, ROS induced an activation and translocation of protein kinase C (PKC), particularly PKCε from the cytosol to the membrane/mitochondria, which was also blocked by antioxidants. The crucial role of PKC in GTPP-induced preconditioning was supported by use of its specific inhibitors. Preconditioning was increased by conditional overexpression of PKCε and decreased by its knock-out with siRNA. Collectively, these results suggest that GTPP stimulates 67LR and thereby induces NADPH oxidase-dependent generation of ROS, which in turn induces activation of PKC, particularly prosurvival isoenzyme PKCε, resulting in preconditioning against cell death induced by OGD/R.
authors.affiliation: Department of Cell and Neurobiology, Keck School of Medicine, University of Southern California, Los Angeles, California 90089, USA.
authors.forename: Usha
authors.initials: U
authors.lastname: Gundimeda
authors.forename: Thomas H
authors.initials: TH
authors.lastname: McNeill
authors.forename: Albert A
authors.initials: AA
authors.lastname: Elhiani
authors.forename: Jason E
authors.initials: JE
authors.lastname: Schiffman
authors.forename: David R
authors.initials: DR
authors.lastname: Hinton
authors.forename: Rayudu
authors.initials: R
authors.lastname: Gopalakrishna
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000737:chemistry / Q000494:pharmacology*; D002392:Catechin / Q000031:analogs & derivatives* / Q000737:chemistry / Q000493:pharmacokinetics / Q000494:pharmacology; D016923:Cell Death; D002462:Cell Membrane / Q000201:enzymology*; D003600:Cytosol / Q000201:enzymology*; D004789:Enzyme Activation / Q000187:drug effects; D005947:Glucose; D010100:Oxygen; D016716:PC12 Cells; D059808:Polyphenols / Q000737:chemistry / Q000494:pharmacology*; D011485:Protein Binding / Q000187:drug effects; D051744:Protein Kinase C-epsilon / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport / Q000187:drug effects; D051381:Rats; D017382:Reactive Oxygen Species / Q000378:metabolism*; D017474:Receptors, Laminin / Q000235:genetics / Q000378:metabolism*; D013662:Tea / Q000737:chemistry*
chemical_list: D000975:Antioxidants; D059808:Polyphenols; D017382:Reactive Oxygen Species; D017474:Receptors, Laminin; D013662:Tea; D002392:Catechin; C045651:epigallocatechin gallate; C497257:Prkce protein, rat; D051744:Protein Kinase C-epsilon; D005947:Glucose; D010100:Oxygen