title: Increase in double-stranded DNA break-related foci in early-stage thymocytes of aged mice.
abstract: Cellular and molecular mechanisms involved in aging are notoriously complex. Aging-related immune decline of T lymphocyte function is partly caused by attrition of thymic T cell development, which involves programmed creation and repair of DNA breaks for generating T cell receptors. Aging also leads to significant alterations in the cellular DNA repair ability. We show that higher levels of gamma-phosphorylated H2AX (pH2AX), which marks DNA double-stranded breaks (DSBs), were detectable in early thymocyte subsets of aged as compared to young mice. Also, while only 1-2 foci of nuclear accumulation of pH2AX were detectable in these early thymocytes from young mice, cells from aged mice showed higher numbers of pH2AX foci. In CD4-CD8- double-negative (DN) thymocytes of aged mice, which showed the highest levels of DSBs, there was a modest increase in levels of the DNA repair protein MRE11, but not of either Ku70, another DNA repair protein, or the cell cycle checkpoint protein p53. Thus, immature thymocytes in aged mice show a marked increase in DNA DSBs with only a modest enhancement of repair processes, and the resultant cell cycle block could contribute to aging-related defects of T cell development.
authors: Department of Biological Sciences, University of Arkansas, Fayetteville, 72701, USA.
authors: J E
authors: JE
authors: Hesse
authors: Matthew F
authors: MF
authors: Faulkner
authors: Jeannine M
authors: JM
authors: Durdik
mesh_terms: D000375:Aging / Q000235:genetics / Q000276:immunology*; D000818:Animals; D000945:Antigens, Differentiation, T-Lymphocyte / Q000096:biosynthesis*; D002469:Cell Separation; D053903:DNA Breaks, Double-Stranded; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D007376:Interleukin-2 / Q000235:genetics / Q000276:immunology*; D008213:Lymphocyte Activation / Q000235:genetics / Q000276:immunology*; D051379:Mice; D008810:Mice, Inbred C57BL; D013601:T-Lymphocytes / Q000378:metabolism*
chemical_list: D000945:Antigens, Differentiation, T-Lymphocyte; D004268:DNA-Binding Proteins; D007376:Interleukin-2