Longevity Promoting Interventions Inhibit Molecular and Functional Changes In Aging Hematopoietic Stem Cells

Recent studies strongly suggest that aging results in the decreased regenerative capacity of adult somatic stem cells, but this process is poorly understood. Hematopoietic stem cell (HSC) aging is associated with myeloid-biased differentiation, reduced capacity for self-renewal, and reduced production of lymphoid and red blood cells. These functional changes lead to alterations in peripheral blood cell counts and reduction in adaptive immunity, as well as an increased incidence of myeloid malignancies. Previous studies have demonstrated that cell-intrinsic changes underlie HSC aging and persist through transplantation. MicroRNAs (miRNAs) are small non-coding RNAs that regulate HSC self-renewal and lineage specificity by suppressing the expression of hundreds of genes. Since rapamycin treatment has previously been shown to inhibit age-associated phenotypes in old HSCs, we hypothesized that investigating the expression and function of miRNAs in HSCs purified from mouse models of longevity may yield significant insights into the molecular mechanisms that underlie the phenotypic changes observed in the aging hematopoietic system.

Thus, we have characterized the cellular and functional alterations in aged HSCs after anti-aging interventions [rapamycin treatment and calorie restriction (CR)] in old mice versus age-matched non-treated controls. We found that anti-aging interventions significantly reduce the expansion of HSC numbers, restore erythroid and B-lymphocyte numbers, reverse age-related thrombocytosis in C57BL/6 mice, and reduce reactive oxygen species (ROS) levels specifically in the HSC compartment. Moreover, the diminished function of aged HSCs in vivo was restored by anti-aging interventions. To identify the transcriptional regulatory networks involved in age-associated functional HSC alterations, we performed miRNA expression profiling studies using highly purified HSCs from young, age-matched non-treated, and treated old mice (12 weeks old or 27 months old, n=5 per group). Analysis of age-associated miRNA expression changes revealed differential expression (p<0.05 compared with internal controls) of 30 in 768 (3.9%) mouse miRNAs tested. Compellingly, one third of these age-associated miRNA expression changes were inhibited by CR and rapamycin treatment. Thus, our findings provide evidence that anti-aging interventions also inhibit HSC aging, and that these effects are evident at the level of miRNA expression. Overall, these data provide a molecular view of HSC aging and identify numerous candidate genes that may regulate HSC aging.