In vivo depletion of myeloid cells in Mafia mice results in HSPC mobilization and collapse of endosteal niches. Effect of a 5-day systemic treatment with AP20187 ligand (filled columns) or vehicle (empty columns) in Mafia and wild-type mice on femoral content in CD11b⁺GFP⁺ myeloid cells (A) and CD11b⁺Ly6-G⁺ granulocytes (B) and number of CFCs mobilized into blood (C) and spleen (D). CD11b⁺GFP⁺ myeloid cells were not determined (ND) in wild-type mice, as they do not express the GFP transgene. Data are mean ± SD of 4-6 mice per group. ***P < .001, **P < .01, and *P < .05 between vehicle- and AP20187-treated mice. (E) Effect of a 5-day systemic treatment with AP20187 ligand (filled symbols) or vehicle (empty columns) in Mafia and wild-type mice on osteocalcin, Ang-1, and KL in endosteal cells measured by qRT-PCR. Each symbol represents an individual mouse; bars are means. (F) Immunohistochemical staining of tibial sections from Mafia and C57BL/6 mice treated for 5 days with AP20187 or vehicle. Brown positive staining for F4/80 (left panels) or osteocalcin (right panels) is shown in near serial section of metaphyseal and diaphyseal endocortical regions. F4/80⁺ osteomacs can be seen directly on bone surfaces or immediately adjacent to cubiodal osteocalcin⁺ osteoblasts in control groups, and osteomac canopy structure is clearly evident on endocortical bone. Dramatic depletion of F4/80⁺ cells and subsequent loss of osteocalcin⁺ osteoblasts is clearly evident in ligand-treated Mafia mice. Original magnifications ×20 and ×40. All sections were counterstained with hematoxylin.