Aged hematopoietic stem cells, p53 mutants

Age-related defects in stem cells can limit proper tissue maintenance and hence contribute to a shortened life-span. Using highly purified hematopoietic stem cells from mice aged 2 to 21 months, we demonstrate a deficit in function yet an increase in stem cell number with advancing age. Expression analysis of more than 14,000 genes identified 1500 that were age-induced and 1600 that were age-repressed. Genes associated with the stress response, inflammation, and protein aggregation dominated the upregulated expression profile, while the downregulated profile was marked by genes involved in the preservation of genomic integrity and chromatin remodeling. Many chromosomal regions showed coordinate loss of transcriptional regulation, and an overall increase in transcriptional activity with aged, and inappropriate expression genes normally regulated by epigenetic mechanisms was observed. Hematopoietic stem cells from early-aging mice expressing a mutant p53 allele reveal that aging of stem cells can be uncoupled from aging at an organismal level. These studies show that HSC are not protected from aging. Instead, loss of epigenetic regulation at the chromatin level may drive both functional attenuation of cells, as well as other manifestations of aging, including the increased propensity for neoplastic transformation. Keywords: Aging time course