title: The NADPH oxidase Nox4 restricts the replicative lifespan of human endothelial cells.
abstract: The free radical theory of aging proposes that ROS (reactive oxygen species) are major driving forces of aging, and are also critically involved in cellular senescence. Besides the mitochondrial respiratory chain, alternative sources of ROS have been described that might contribute to cellular senescence. Noxs (NADPH oxidases) are well-known sources of superoxide, which contribute to the antimicrobial capabilities of macrophages, a process involving the prototypical member of the family referred to as Nox2. However, in recent years non-phagocytic homologues of Nox2 have been identified that are involved in processes other than the host defence. Superoxide anions produced by these enzymes are believed to play a major role in signalling by MAPKs (mitogen-activated protein kinases) and stress-activated kinases, but could also contribute to cellular senescence, which is known to involve oxygen radicals. In HUVECs (human umbilical vein endothelial cells), Nox4 is predominantly expressed, but its role in replicative senescence of HUVECs remains to be elucidated. Using shRNA (small-hairpin RNA)-mediated knockdown of Nox4, implicating lentiviral vectors, we addressed the question of whether lifelong depletion of Nox4 in HUVECs would influence the senescent phenotype. We found a significant extension of the replicative lifespan of HUVECs upon knockdown of Nox4. Surprisingly, mean telomere length was significantly reduced in Nox4-depleted cells. Nox4 depletion had no discernable influence on the activity of MAPKs and stress-activated kinases, but reduced the degree of oxidative DNA damage. These results suggest that Nox4 activity increases oxidative damage in HUVECs, leading to loss of replicative potential, which is at least partly independent of telomere attrition.
authors.affiliation: Institute for Biomedical Aging Research, Austrian Academy of Sciences, Rennweg 10, A-6020 Innsbruck, Austria.
authors.forename: Barbara
authors.initials: B
authors.lastname: Lener
authors.forename: Rafał
authors.initials: R
authors.lastname: Kozieł
authors.forename: Haymo
authors.initials: H
authors.lastname: Pircher
authors.forename: Eveline
authors.initials: E
authors.lastname: Hütter
authors.forename: Ruth
authors.initials: R
authors.lastname: Greussing
authors.forename: Dietmar
authors.initials: D
authors.lastname: Herndler-Brandstetter
authors.forename: Martin
authors.initials: M
authors.lastname: Hermann
authors.forename: Hermann
authors.initials: H
authors.lastname: Unterluggauer
authors.forename: Pidder
authors.initials: P
authors.lastname: Jansen-Dürr
mesh_terms: D002478:Cells, Cultured; D016922:Cellular Senescence; D004249:DNA Damage; D042783:Endothelial Cells / Q000201:enzymology*; D055785:Gene Knockdown Techniques; D006801:Humans; D020935:MAP Kinase Signaling System; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism; D000074662:NADPH Oxidase 2; D000074663:NADPH Oxidase 4; D019255:NADPH Oxidases / Q000235:genetics / Q000378:metabolism*; D010084:Oxidation-Reduction; D013481:Superoxides / Q000378:metabolism; D016615:Telomere / Q000235:genetics / Q000378:metabolism*
chemical_list: D008562:Membrane Glycoproteins; D013481:Superoxides; C056558:CYBB protein, human; D000074662:NADPH Oxidase 2; D000074663:NADPH Oxidase 4; D019255:NADPH Oxidases; C498910:NOX4 protein, human
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