title: The PI3K/Akt/mTOR pathway mediates retinal progenitor cell survival under hypoxic and superoxide stress.
abstract: Oxygen (O₂) tension has emerged as a major regulator of stem cell (SC) biology. Low O₂ concentrations that are toxic to mature cells can confer advantage to stem and early progenitors, while superoxide stress remains a constant threat in aerobic biology and may be partially avoided through sequestration of SCs in the relatively hypoxic stem or regenerative niche. Using primary retina-derived retinal progenitor cells (RPCs) and the R28 progenitor cell line in vitro, we show that RPCs are sensitive to hydrogen peroxide (H₂O₂) induced damage and resistant to moderate levels of low oxygen stress (1% O₂). Under hypoxic conditions, multipotent RPCs upregulate Epo receptors, and Epo, along with insulin, protects against both superoxide- and severe hypoxia- (0.25% O₂) induced apoptosis through activation of the canonical PI3K/Akt/mTOR pathway. This survival advantage is sensitive to inhibitors of PI3K and mTOR. We further demonstrate phosphorylation of the p70S6 ribosomal kinase, a downstream mediator of PI3K/Akt/mTOR and translational activator. Overall, these data confirm that RPCs are sensitive to superoxide stress and resistant to hypoxia and that this resistance is mediated in part by Epo. They further suggest that manipulation of RPCs ex vivo prior to ocular delivery, or the in vivo delivery of exogenous survival factors at the time of cell implantation, could enhance the success of regenerative therapies aimed to restore sight.
authors.affiliation: Department of Ophthalmology and Vision Sciences, University of Toronto, Toronto, Ontario, Canada.
authors.forename: Karan P
authors.initials: KP
authors.lastname: Sanghera
authors.forename: Nurit
authors.initials: N
authors.lastname: Mathalone
authors.forename: Ramteen
authors.initials: R
authors.lastname: Baigi
authors.forename: Elan
authors.initials: E
authors.lastname: Panov
authors.forename: Dan
authors.initials: D
authors.lastname: Wang
authors.forename: Xu
authors.initials: X
authors.lastname: Zhao
authors.forename: Howard
authors.initials: H
authors.lastname: Hsu
authors.forename: Hai
authors.initials: H
authors.lastname: Wang
authors.forename: Vincent
authors.initials: V
authors.lastname: Tropepe
authors.forename: Michael
authors.initials: M
authors.lastname: Ward
authors.forename: Shelley R
authors.initials: SR
authors.lastname: Boyd
mesh_terms: D000818:Animals; D015687:Cell Hypoxia / Q000502:physiology*; D002470:Cell Survival / Q000502:physiology*; D002478:Cells, Cultured; D004921:Erythropoietin / Q000378:metabolism / Q000494:pharmacology; D006861:Hydrogen Peroxide / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism; D051379:Mice; D016877:Oxidants / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D012160:Retina / Q000166:cytology*; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D013234:Stem Cells / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D013312:Stress, Physiological; D013481:Superoxides / Q000378:metabolism*; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism*
chemical_list: D004921:Erythropoietin; D006861:Hydrogen Peroxide; D007328:Insulin; D016877:Oxidants; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D013481:Superoxides; D058570:TOR Serine-Threonine Kinases; C546842:MTOR protein, human