Extended Data Figure 6. CLPs and peri-arteriolar Osteolectin⁺ cells are depleted during aging but most other hematopoietic stem and progenitor cell populations are not.

The differences among treatments in cell frequencies were also evident in absolute numbers. (a-d) Oln^mT/+ mice received daily subcutaneous injections with PBS or 40 μg/kg human PTH for 28 days. PTH treated mice exhibited significantly thicker cortical bone (a, b) and significant reductions in the frequencies of Osteolectin⁺ cells (c) and CLPs (d; 8 mice per treatment analyzed in 4 independent experiments). Micro CT images (b, scale bar = 800μm) of cortical bone are representative of 8 independent experiments. (e, f) The frequency of LepR⁺ cells (e) and the percentage of LepR⁺ cells that were Oln-mTomato⁺ (f) in Oln^mT/+ bone marrow at 2 to 18 months of age (8 mice per time point analyzed in 4 independent experiments). (g) Femur bone marrow from an 18-month-old Oln^mT/+ mouse showing an arteriole surrounded by Oln-mTomato⁺ cells (arrowhead) and an arteriole lacking Oln-mTomato⁺ cells (arrow) in the diaphysis (image is representative of 4 independent experiments; scale bar = 100μm). (h) The frequency of CLPs in Oln^mT/+ mice at 2 to 18 months of age. (i-m) During aging, the frequencies of HSCs (i) and MPPs (j) in the bone marrow increased while the frequencies of GMPs (k), CMPs (l), and MEPs (m) did not significantly change (8 mice per time point analyzed in 4 independent experiments). (n) Localization of IL7Rα⁺Lineage⁻ cells in the bone marrow of 2- and 18-month old mice (7 mice per time point analyzed in 3 independent experiments). (o) Aging significantly depleted Osteolectin⁺ cells associated with arterioles in both endosteal and non-endosteal regions of diaphysis bone marrow (8 mice per time point analyzed in 4 independent experiments). (p) Number of IL7Rα⁺Lineage⁻ cells per 100 μm of Osteolectin⁺ or Osteolectin⁻ arteriole at 2 and 18 months of age (7 mice per time point analyzed in 3 independent experiments). All data represent mean ± SD. Statistical significance was assessed using paired t-tests (a, c, d, o, p), one-way ANOVA followed by Dunnett’s multiple comparisons test (e), matched samples two-way ANOVAs followed by Dunnett’s multiple comparisons tests (f, h-m), Cochran-Mantel-Haenszel test (n), or Mann–Whitney tests followed by Holm-Sidak’s multiple comparisons adjustments (o).