Age Dependent Alternations In Hematopoietic Stem Cell Niches

Abstract 2395

Age associated decline in hematopoietic system is a well-documented process which encompasses a substantial expansion of the hematopoietic stem cell (HSC) pool and a decline of their competitive repopulating ability on a per cell basis. Expansion occurs predominantly in the myeloid biased HSC subset, subsequently leading to a global skewing of lineage differentiation from lymphopoiesis toward myelopoiesis. These age-related effects are known to partially result from cell-intrinsic alterations of HSC, which include DNA damage accumulation, oxidative stress and activation of tumor suppressor pathways. HSCs exist in specialized microanatomical locations within the bone marrow (BM), where they receive critical regulatory cues that control HSC homeostasis. While the cell-autonomous effects of HSC aging have been extensively studied, little is known on how aging of the surrounding microenvironment may contribute to the age-associated alterations of HSC function, and thus the focus of our study.

Here, we have employed novel imaging approaches to analyze age-related changes of the BM microenvironment, and how these affect the global spatial distribution of HSPC-enriched subsets in the BM parenchyma. Our preliminary studies suggest during aging leads to a profound disruption of the BM microvascular compartment. By using imaging cytometry of two-dimensional (2D) sections, as well as confocal microscopy of 3D-BM slices, we demonstrate that the characteristic sinusoidal network found in young mice, degenerated with aging into a highly disorganized and expanded vascular bed, in which expression of the arterial marker Sca-1 was strongly upregulated. Flow cytometry analysis further revealed a 3–4 fold increase of CD45-Ter119-CD31+ Sca-1+cells in 22–24 month old mice. We next investigated how the changes in vasculature network impact HSC distribution. We employed imaging cytometry to track the presence in BM sections of a population of Lineage-Cd48-kit+ cells, 60% of which are long term HSC. Our preliminary results indicate that, in aged mice, HSPC-accumulation in endosteal zones (<100μm from endosteal surfaces) remains unchanged. Of note, consistent with the increase in vascularization, HSPCs display a significantly increased tendency to directly associate to BM microvessels in 22–24month old mice. We are currently investigating at the molecular level how altered vasculature influence HSC aging which would enable us to enhance the regenerative properties of the aged stem cells.