Nitric oxide has contrasting age-dependent effects on the functionality of murine hematopoietic stem cells

The success of hematopoietic stem cell (HSC) transplantation is dependent on the quality of the donor HSCs. Some sources of HSCs display reduced engraftment efficiency either because of inadequate number (e.g., fetal liver and cord blood), or age-related dysfunction (e.g. in older individuals). Therefore, use of pharmacological compounds to improve functionality of HSCs is a forefront research area in hematology.

Lineage negative (Lin^-) cells isolated from murine bone marrow or sort-purified Lin^-Sca-1⁺c-Kit⁺CD34^- (LSK-CD34^-) were treated with a nitric oxide donor, sodium nitroprusside (SNP). The cells were subjected to various phenotypic and functional assays.

We found that SNP treatment of Lin^- cells leads to an increase in the numbers of LSK-CD34⁺ cells in them. Using sort-purified LSK CD34^- HSCs, we show that this is related to acquisition of CD34 expression by LSK-CD34^- cells, rather than proliferation of LSK-CD34⁺ cells. Most importantly, this upregulated expression of CD34 had age-dependent contrasting effects on HSC functionality. Increased CD34 expression significantly improved the engraftment of juvenile HSCs (6-8 weeks); in sharp contrast, it reduced the engraftment of adult HSCs (10-12 weeks). The molecular mechanism behind this phenomenon involved nitric oxide (NO)-mediated differential induction of various transcription factors involved in commitment with regard to self-renewal in adult and juvenile HSCs, respectively. Preliminary experiments performed on cord blood-derived and mobilized peripheral blood-derived cells revealed that NO exerts age-dependent contrasting effects on human HSCs as well.

This study demonstrates novel age-dependent contrasting effects of NO on HSC functionality and suggests that HSC age may be an important parameter in screening of various compounds for their use in manipulation of HSCs.