Figure 1. Irradiation disrupted sinusoids and depleted HSCs, endothelial cells, and LepR⁺ stromal cells while dramatically increasing adipocytes in the bone marrow.

One million bone marrow cells from wild-type mice were transplanted into irradiated wild-type (a–e and m–p) or Lepr^cre; R26^tdTomato (f–l) mice. Statistical significance was assessed using repeated measures one-way ANOVAs with Geisser-Greenhouse sphericity corrections along with Tukey’s multiple comparisons tests (a–e, i–m). * indicates statistical significance relative to control (Con) while # indicates statistical significance of differences between 2 and 4 weeks after irradiation (* or # P<0.05, ** or ## P<0.01, *** or ### P<0.001). All data represent mean±SD.

(a–e) Flow cytometric analysis of mechanically dissociated bone marrow cells revealed significant reductions in bone marrow cellularity (a) and the numbers of Lineage⁻Sca-1⁺c-kit⁺ (LSK) cells (b), CD150⁺CD48⁻Lineage⁻Sca-1⁺c-kit⁺ HSCs (c), Mac1⁺Gr-1⁺ myeloid cells (d) and Ter119⁺ erythroid cells (e) at 2 and/or 4 weeks after irradiation as compared to non-irradiated control mice. Cell numbers reflect two femurs and two tibias per mouse (n=5 mice/treatment from 5 independent experiments).

(f–h) Confocal imaging of thin femur sections from non-irradiated Lepr^cre; R26^tdTomato mice (control, f) or at 2 weeks (g) or 4 weeks (h) after irradiation and bone marrow transplantation. Arrows indicate sinusoidal blood vessels and arrowheads indicate arterioles.

(i, j) The densities of VE-cadhern^brightlaminin^dim sinusoids (i) and VE-cadherin^dimlaminin^bright arterioles (j) were quantified in sections (n=5 mice/condition from 3 independent experiments).

(k, l) Flow cytometric analysis of enzymatically dissociated bone marrow cells from Lepr^cre; R26^tdTomato mice revealed significant reductions in the numbers of VE-cadherin⁺ endothelial cells (k) and Tomato⁺ stromal cells (l) after irradiation (n=4 mice/condition from 4 independent experiments).

(m) Adipocyte numbers in thick femur sections from non-irradiated mice (Con) or mice at 2 or 4 weeks after irradiation (n=6 mice/condition from 3 independent experiments).

(n–p) Whole-mount imaging of thick femur sections (50-μm) from non-irradiated mice (Control, n) or mice 2 (o) or 4 (p) weeks after irradiation and bone marrow transplantation. Adipocytes were identified based on anti-perilipin staining (n=6 mice/condition from 3 independent experiments).