Tehran University of Medical Sciences International Journal of Hematology-Oncology and Stem Cell Research 2008-2207 5 3 2011 09 15 1 10 Abdolkhaleg Deezagi Department of Biochemistry, National Institute of Genetic Engineering and Biotechnology, Tehran-Iran Neda Vaseli-hagh Department of Biochemistry, National Institute of Genetic Engineering and Biotechnology, Tehran-Iran Masoumeh Nouri Department of Biochemistry, National Institute of Genetic Engineering and Biotechnology, Tehran-Iran 2015 10 01 Introduction: Accumulating evidences indicated that during increasing of the animals' age, the number and the functional properties of hematopoietic stem cells (HSCs) become altered because of a gradual decrease in replication potential.  The efficient factors in this process are DNA damaging, reduced telomerase activity, shortening of telomeres and oxidative stresses. For overcoming these factors, using of the anti-oxidants and activating of telomerase would be effective. The aim of this research was to study the effect of Nitric Oxide (NO) as an anti-oxidant on the cell proliferation, cell viability and telomerase activity of HSCs in vitro. Methods: HSCs were isolated from human cord bloods.  Cells were treated by L-Arginine and Sodium Nitro-Pruscide (as NO donors) in a dose dependent manner. The cell viability and proliferation were assayed by trypan blue, MTT and BrdU methods. The profile of aging was assayed by senescence sensitive β-Galactosidase staining and telomerase activity was assayed by TRAP-PCR E ISA method. Finally, Nitric Oxide Synthatase mRNA expression level was analyzed by RT-PCR. Result: HSCs those treated with SNP exhibited an increase 3-7 fold (400-1000 µmol) in NO production in comparison to untreated control cells (140µmol).Treatment of cells by L-Arg resulted lower release of NO (Up to 200 µmol) in comparison to SNP. Increasing NO production resulted to the inducing of cells growth potential and proliferation parameters up to 40% which accompanied  by the increasing of telomerase activity up to 25% in the presence of 100 µM of SNP or  1.0 mM of L-Arg in comparison to untreated control cells. Discussion: The present work demonstrates that NO affect telomerase activity and cellular replicative capacity in human hematopoietic stem cells. A significant behavior was observed on the telomerase activity and cell proliferation after treatment of cells. Induction of cell proliferation  was accompanied by a slight inhibition of HSCs senescence. Finally the telomerase induction and reduction in cell enescence were accompanied by increasing  of the cell proliferation parameters. https://ijhoscr.tums.ac.ir/index.php/ijhoscr/article/view/280 https://ijhoscr.tums.ac.ir/index.php/ijhoscr/article/download/280/273