5--amino-5--deoxyadenosine and 2--deoxyadenosine-triphosphate

Thymocyte development past the CD4(-)CD8(-) stage is markedly inhibited in adenosine deaminase-deficient (ADA-deficient) murine fetal thymic organ cultures (FTOCs) due to the accumulation of ADA substrates derived from thymocytes failing developmental checkpoints. Such cultures can be rescued by overexpression of Bcl-2, suggesting that apoptosis is an important component of the mechanism by which ADA deficiency impairs thymocyte development. Consistent with this conclusion, ADA-deficient FTOCs were partially rescued by a rearranged T cell receptor beta transgene that permits virtually all thymocytes to pass the beta-selection checkpoint. ADA-deficient cultures were also rescued by the adenosine kinase inhibitor 5'-amino-5'-deoxyadenosine (5'A5'dAdo), indicating that the metabolite responsible for the inhibition of thymocyte development is not adenosine or deoxyadenosine, but a phosphorylated derivative of an ADA substrate. Correction of ADA-deficient FTOCs by 5'A5'dAdo correlated with reduced accumulation of dATP, implicating this compound as the toxic metabolite. In ADA-inhibited FTOCs rescued with a Bcl-2 transgene, however, dATP levels were superelevated, suggesting that cells failing positive and negative selection continued to contribute to the accumulation of ADA substrates. Our data are consistent with dATP-induced mitochondrial cytochrome c release followed by apoptosis as the mechanism by which ADA deficiency leads to reduced thymic T cell production.

Topics: Adenosine Deaminase; Adenosine Kinase; Adenosylhomocysteinase; Animals; CD4-Positive T-Lymphocytes; CD8-Positive T-Lymphocytes; Cell Differentiation; Cell Survival; Deoxyadenine Nucleotides; Deoxyadenosines; Hydrolases; Mice; Mice, Inbred C57BL; Mice, Knockout; Mice, Transgenic; Proto-Oncogene Proteins c-bcl-2; Purinergic P1 Receptor Agonists; Purinergic P1 Receptor Antagonists; Receptor, Adenosine A2A; Receptor, Adenosine A2B; Receptor, Adenosine A3; Receptors, Antigen, T-Cell, alpha-beta; Receptors, Purinergic P1; Thymus Gland