GENETIC REGULATION OF HEMATOPOIETIC STEM CELL AGING

It is well documented that both quantitative and qualitative changes in the murine hematopoietic stem cell (HSC) population occur with age. In mice, the effect of aging on stem cells is highly strain-specific, thus suggesting genetic regulation plays a role in HSC aging. In C57BL/6 (B6) mice, the HSC population steadily increases with age, whereas in DBA/2 (D2) mice, this population declines. Our lab has previously mapped a quantitative trait locus (QTL) to murine chromosome 2 that is associated with the variation in frequency of HSCs between aged B6 and D2 mice. In these dissertation studies, I first aim to characterize the congenic mouse model which was generated by introgressing D2 alleles in the QTL onto a B6 background. Using a surrogate assay to mimic aging, I analyzed the cell cycle, apoptotic and self-renewal capabilities of congenic and B6 HSCs and show that D2 alleles in the QTL affect the apoptotic and selfrenewal capabilities of HSCs. In the second aim of these studies, I used oligonucleotide arrays to compare the differential expression of B6 and congenic cells using a population enriched for primitive stem and progenitor cells. Extensive analysis of the expression arrays pointed to two strong candidates, the genes encoding Retinoblastoma like protein 1 (p107) and Sorting nexin 5 (Snx5). B6 alleles were associated with increased p107 and Snx5 expression in old HSCs therefore both genes were hypothesized to be positive regulators of stem cell number in aged mice. Finally, in the third aim of these studies, I show that the individual overexpression of p107 and Snx5 in congeic HSCs increases day35 cobblestone area forming cell (CAFC) numbers, therefore confirming their roles as positive regulators of HSC number in vitro. These studies uncover novel roles for p107 and Snx5 in the regulation of HSC numbers and provide additional clues in the complex regulation of HSC aging