The Origin of Deoxynucleosides in Brain: Implications for the Study of Neurogenesis and Stem Cell Therapy
- 117 Downloads
Detection of DNA synthesis in brain employing (3H)thymidine ((3H)dT) or bromo deoxyuridine (BrdU) is widely used as a measure of the “birth” of cells in brain development, adult neurogenesis and neuronal stem cell replacement strategies. However, recent studies have raised serious questions about whether this methodology adequately measures the “birth” of cells in brain either quantitatively or in an interpretable way in comparative studies, or in stem cell investigations. To place these questions in perspective, we review deoxynucleoside synthesis and pharmacokinetics focusing on the barriers interfacing the blood-brain (cerebral capillaries) and blood-cerebrospinal fluid (choroid plexus), and the mechanisms, molecular biology and location of the deoxynucleoside transport systems in the central nervous system. Brain interstitial fluid and CSF nucleoside homeostasis depend upon the activity of concentrative nucleoside transporters (CNT) on the ‘central side’ of the barrier cells and equilibrative nucleoside transporters (ENT) on their ‘plasma side.’ With this information about nucleoside transporters, blood/CSF concentrations and metabolic pathways, we discuss the assumptions and weaknesses of using (3H)dT or BrdU methodologies alone for studying DNA synthesis in brain in the context of neurogenesis and potential stem cell therapy. We conclude that the use of (3H)dT and/or BrdU methodologies can be useful if their limitations are recognized and they are used in conjunction with independent methods.
Key wordsbrain DNA repair brain ribonucleosides and deoxyribonucleosides cerebral microvessels cerebrospinal fluid homeostasis choroid plexus epithelium CNT2 CNT3 ENT1 ENT2 nucleoside pharmacokinetics thymidine kinase thymidylate synthetase
The authors thank Michiko Spector for her aid in the preparation of the manuscript and Julie Johanson for assistance with graphics.
- 1.G. Kempermann. Adult Neurogenesis. Oxford, New York, 2006.Google Scholar
- 9.A. Kornberg and T. A. Baker. DNA Replication, 2nd ed. Freeman, New York, 1992.Google Scholar
- 22.Z. B. Redzic. Homeostasis of nucleosides and nucleobases in the brain: the role of flux between the CSF and the brain ISF, transport across the choroid plexus and the blood-brain barrier, and cellular uptake. In W. Zheng and A. Chodobski (eds)., The Blood-Cerebrospinal Fluid Barrier, CRC, Boca Raton, 2005, pp. 175–208.Google Scholar
- 30.R. Spector and S. Huntoon. Deoxycytidine transport metabolism in the central nervous system. Neurochemistry 40:1474–1480 (1983).Google Scholar
- 36.M. W. L. Ritzel, A. M. L. Ng, S. Y. M. Yao, et al. Molecular identification and characterization of novel human and mouse concentrative Na+-nucleoside cotransporter proteins (hCNT3 and mCNT3) broadly selective for purine and pyrimidine nucleosides (system cib). J. Biol. Chem. 276:2914–2927 (2001).PubMedCrossRefGoogle Scholar
- 44.B. Tavazzi, G. Lazzarino, P. Leone, et al. Simultaneous high performance liquid chromatographic separation of purines, pyrimidines, N-acetylated amino acids, and dicarboxylic acids for the chemical diagnosis of inborn errors of metabolism. Clin. Biochem. 38:997–1008 (2005).PubMedCrossRefGoogle Scholar