title: Effects of purine nucleoside phosphorylase deficiency on thymocyte development.
abstract: BACKGROUND
  Inherited or acquired defects in purine nucleoside phosphorylase (PNP) impair purine metabolism, as well as the survival and function of T lymphocytes. However, the effects of PNP deficiency on thymocyte development are not well known.
  
  
  OBJECTIVE
  We sought to study thymocyte development in PNP-deficient (PNP-KO) mice.
  
  
  METHODS
  Maturation, proliferation, and apoptosis were determined in thymocytes from PNP-KO mice and hematopoietic stem cells from these mice grown ex vivo into thymocyte-like cells.
  
  
  RESULTS
  Reduced percentages of CD4(+)CD8(+) double-positive (DP) thymocytes with normal percentages of CD4(-)CD8(+) and CD4(+)CD8(-) single-positive thymocytes were found in the thymi of PNP-KO mice. Similarly, reduced DP-like thymocytes grew ex vivo from hematopoietic stem cells of PNP-KO mice. Thymi of PNP-KO mice contained increased apoptotic DP thymocytes. Increased apoptosis of PNP-deficient DP thymocytes occurred after exposure to deoxyguanosine (dGuo), although not after Fas ligation, and could be prevented by restoring PNP activity within the cells. In DP thymocytes from PNP-KO mice, dGuo caused mitochondrial membrane potential dissipation and induced release of cytochrome c from the mitochondria followed by nuclear DNA fragmentation. Inhibition of the caspase pathway prevented dGuo-induced nuclear DNA fragmentation but not mitochondrial membrane potential dissipation, indicating that PNP deficiency induces apoptosis that is initiated in the mitochondria of DP thymocytes. 5-Bromo-2-deoxyuridine incorporation demonstrated that PNP deficiency does not interfere with DP or single-positive thymocyte proliferation.
  
  
  CONCLUSIONS
  PNP is important for the survival of DP thymocytes. Accumulation of dGuo in cases of PNP deficiency leads to mitochondria-initiated apoptosis of DP thymocytes, which can be prevented by restoring PNP activity in the cells.
authors.affiliation: Developmental and Stem Cell Biology Program, Research Institute, Hospital for Sick Children, Toronto, Ontario, Canada.
authors.forename: Taniya
authors.initials: T
authors.lastname: Papinazath
authors.forename: Wexian
authors.initials: W
authors.lastname: Min
authors.forename: Suntharalingam
authors.initials: S
authors.lastname: Sujiththa
authors.forename: Amos
authors.initials: A
authors.lastname: Cohen
authors.forename: Cameron
authors.initials: C
authors.lastname: Ackerley
authors.forename: Chaim M
authors.initials: CM
authors.lastname: Roifman
authors.forename: Eyal
authors.initials: E
authors.lastname: Grunebaum
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000276:immunology*; D002460:Cell Line; D049109:Cell Proliferation; D002470:Cell Survival; D053938:DNA Fragmentation; D003849:Deoxyguanosine / Q000276:immunology; D006412:Hematopoietic Stem Cells / Q000201:enzymology / Q000276:immunology; D053078:Membrane Potential, Mitochondrial / Q000235:genetics / Q000276:immunology; D051379:Mice; D018345:Mice, Knockout; D011683:Purine-Nucleoside Phosphorylase / Q000235:genetics / Q000276:immunology*; D013601:T-Lymphocytes / Q000201:enzymology / Q000276:immunology*; D013950:Thymus Gland / Q000201:enzymology / Q000276:immunology*; D019014:fas Receptor / Q000276:immunology / Q000378:metabolism
chemical_list: C491899:Fas protein, mouse; D019014:fas Receptor; D011683:Purine-Nucleoside Phosphorylase; D003849:Deoxyguanosine