title: Microparticles induce cell cycle arrest through redox-sensitive processes in endothelial cells: implications in vascular senescence.
abstract: BACKGROUND
  Chronic disease accelerates endothelial dysfunction in aging, a process associated with cell senescence. However, the mechanisms underlying this process are unclear. We examined whether endothelial cell (EC)-derived microparticles (MPs) facilitate EC senescence and questioned the role of reactive oxygen species in this process.
  
  
  RESULTS
  Senescence was induced by sequential passaging of primary mouse ECs. Cells retained phenotypic characteristics of ECs from passage 4 through passage 21. Passage 21 ECs exhibited features of senescence, including increased staining of senescence-associated β-galactosidase (SA-βgal), a greater percentage of cells in G(1)/G(0) phase of the cell cycle, and increased phosphorylation of p66(Shc) (P<0.05). Microparticle formation from passage 21 ECs was increased versus passage 4 ECs (∼2.2-fold increase versus passage 4, P<0.05), and the Rho kinase inhibitor fasudil blocked this increase. Exposure of passage 4 ECs to MPs shifted cells from a proliferating to a nonproliferating phenotype, as indicated by cell cycle analysis and increased senescence-associated β-galactosidase staining. MPs increased EC generation of O(2) (•-) (∼2.7-fold) and H(2)O(2) (∼2.6-fold), effects blocked by apocynin (nicotinamide adenine dinucleotide phosphate oxidase inhibitor) and rotenone (mitochondrial oxidase inhibitor) but not by allopurinol (xanthine oxidase inhibitor). MPs increased expression of cell cycle proteins p 21 cip1 and p16ink4a and stimulated phosphorylation of p66(Shc) in ECs (P<0.05 versus untreated ECs). Pretreatment with the reactive oxygen species scavenger sodium 4,5-dihydroxybenzene-1,3-disulfonate (tiron) abrogated the prosenescent effects of MPs.
  
  
  CONCLUSIONS
  MPs promote EC senescence through nicotinamide adenine dinucleotide phosphate oxidase- and mitochondrial-derived reactive oxygen species. Such redox-sensitive processes may be important in vascular dysfunction in aging. (J Am Heart Assoc. 2012;1:e001842 doi: 10.1161/JAHA.112.001842.).
authors.affiliation: Kidney Research Centre, Ottawa Hospital Research Institute, University of Ottawa,  Ottawa, Ontario, Canada (D.B., D.G.K., A.C.M., N.C.R., C.R.J.K., R.M.T.).
authors.forename: Dylan
authors.initials: D
authors.lastname: Burger
authors.forename: Dylan G
authors.initials: DG
authors.lastname: Kwart
authors.forename: Augusto C
authors.initials: AC
authors.lastname: Montezano
authors.forename: Naomi C
authors.initials: NC
authors.lastname: Read
authors.forename: Christopher R J
authors.initials: CR
authors.lastname: Kennedy
authors.forename: Charlie S
authors.initials: CS
authors.lastname: Thompson
authors.forename: Rhian M
authors.initials: RM
authors.lastname: Touyz
keywords: cell cycle; endothelium; microparticles; oxidative stress; senescence