title: The Timing of Raf/ERK and AKT Activation in Protecting PC12 Cells against Oxidative Stress.
abstract: Acute brain injuries such as ischemic stroke or traumatic brain injury often cause massive neural death and irreversible brain damage with grave consequences. Previous studies have established that a key participant in the events leading to neural death is the excessive production of reactive oxygen species. Protecting neuronal cells by activating their endogenous defense mechanisms is an attractive treatment strategy for acute brain injuries. In this work, we investigate how the precise timing of the Raf/ERK and the AKT pathway activation affects their protective effects against oxidative stress. For this purpose, we employed optogenetic systems that use light to precisely and reversibly activate either the Raf/ERK or the AKT pathway. We find that preconditioning activation of the Raf/ERK or the AKT pathway immediately before oxidant exposure provides significant protection to cells. Notably, a 15-minute transient activation of the Raf/ERK pathway is able to protect PC12 cells against oxidant strike that is applied 12 hours later, while the transient activation of the AKT pathway fails to protect PC12 cells in such a scenario. On the other hand, if the pathways are activated after the oxidative insult, i.e. postconditioning, the AKT pathway conveys greater protective effect than the Raf/ERK pathway. We find that postconditioning AKT activation has an optimal delay period of 2 hours. When the AKT pathway is activated 30min after the oxidative insult, it exhibits very little protective effect. Therefore, the precise timing of the pathway activation is crucial in determining its protective effect against oxidative injury. The optogenetic platform, with its precise temporal control and its ability to activate specific pathways, is ideal for the mechanistic dissection of intracellular pathways in protection against oxidative stress.
authors.affiliation: Department of Chemistry, Stanford University, Stanford, California, 94305, United States of America.
authors.forename: Qunxiang
authors.initials: Q
authors.lastname: Ong
authors.affiliation: Department of Chemistry, Stanford University, Stanford, California, 94305, United States of America.
authors.forename: Shunling
authors.initials: S
authors.lastname: Guo
authors.affiliation: Department of Chemistry, Stanford University, Stanford, California, 94305, United States of America.
authors.forename: Liting
authors.initials: L
authors.lastname: Duan
authors.affiliation: Department of Biochemistry, School of Molecular and Cellular Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois, 61801, United States of America.
authors.forename: Kai
authors.initials: K
authors.lastname: Zhang
authors.affiliation: Department of Chemistry, Stanford University, Stanford, California, 94305, United States of America.
authors.forename: Eleanor Ann
authors.initials: EA
authors.lastname: Collier
authors.affiliation: Department of Chemistry, Stanford University, Stanford, California, 94305, United States of America.
authors.forename: Bianxiao
authors.initials: B
authors.lastname: Cui
mesh_terms: D000818:Animals; D019610:Cytoprotection / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D006861:Hydrogen Peroxide / Q000494:pharmacology; D020935:MAP Kinase Signaling System / Q000187:drug effects; D051379:Mice; D041681:NIH 3T3 Cells; D018384:Oxidative Stress / Q000187:drug effects / Q000502:physiology*; D016716:PC12 Cells; D051381:Rats; D013997:Time Factors; D048490:raf Kinases / Q000378:metabolism*
chemical_list: D006861:Hydrogen Peroxide; D048490:raf Kinases; D048049:Extracellular Signal-Regulated MAP Kinases